SHUTTLING-FREE BATTERIES AND PREPARATION METHOD THEREOF PRIORITY DOCUMENT [0001] The present application claims priority from Australian Provisional Patent Application No. 2022902644 titled “SHUTTLING-FREE BATTERIES AND PREPARATION METHOD THEREOF” and filed on 13 September 2022, the content of which is hereby incorporated by reference in its entirety. TECHNICAL FIELD [0002] The present disclosure relates generally to electrochemical devices and methods for their preparation. In particular, the present disclosure relates to shuttling-free electrochemical devices wherein the shuttle effect caused by polyiodide or polybromide is suppressed and methods for their preparation. BACKGROUND [0003] Energy storage will dramatically transform the way the world uses energy. Although organic electrolyte-based batteries show high energy densities which are, in principle, suitable for large scale energy storage, they suffer from inherent instability and safety issues caused by the use of expensive yet highly volatile and flammable organic solvents (for example dimethyl carbonate and diethyl carbonate) and of chemically unstable and toxic salts (for example lithium hexafluorophosphate (LiPF ₆ )). The leakage hazard of organic solvents is also a concern for large scale energy storage. Aqueous batteries are promising to resolve these issues and have shown enormous potential for large scale energy storage given their cost effectiveness, high ionic conductivity and much improved safety. [0004] Furthermore, the abundance of iodine (about 50 µg L ⁻¹ ) and bromine (about 65 mg L ^-1 ) in seawater as well as highly reversible redox chemistry of iodine or bromine make iodine-based or bromine-based batteries a promising cheap energy storage system. Accordingly, increasing attention has been drawn to iodine-based batteries and bromine-based batteries, for example, metal-iodine or metal- bromine batteries, such as aqueous zinc-iodine (Zn-I2) batteries, aqueous zinc-bromine (Zn-Br2) batteries, aqueous lithium-iodine (Li-I2) batteries, non-aqueous Li-I2 batteries, aqueous sodium-iodine (Na-I2) batteries, non-aqueous magnesium-bromine (Mg-Br2) batteries, aqueous aluminum-iodine (Al-I2) batteries, and non-aqueous Al-I2 batteries. [0005] Aqueous zinc-based batteries with high safety and low cost provide a new candidate for large scale energy storage. [1] Among zinc-based batteries, rechargeable Zn-I2 batteries are appealing because of the abundant reserves of iodine in seawater (55 ^g L ^‒1 )[2], high specific capacity (211 mAh giodine ^‒1 )[3] and high discharge potential plateau (1.38 V vs. Zn/Zn ²⁺ )[4]. Besides, the liquid phase conversion mechanism of I ^‒ /I2 at the cathode endows a Zn-I2 system with excellent rate capability.[5] In addition, rechargeable aqueous Zn-Br2 batteries can present a higher theoretical specific capacity (355 mAh g ^-1 ) and higher theoretical voltage plateau (1.85 V vs. Zn/Zn ²⁺ ) compared with rechargeable aqueous Zn-I2 batteries. [0006] However, the existing rechargeable aqueous and non-aqueous metal-iodine or metal-bromine batteries are still far from satisfactory due to the challenges of intermediate dissolution as well as metal anode corrosion.[2] Particularly, weak interaction between the conductive support of the cathode and iodine/bromine species leads to the dissolution of intermediate polyiodide or polybromide anions or molecules in the aqueous or non-aqueous electrolyte and the subsequent migration of polyiodide or polybromide through the separator towards the metal anode, i.e. the shuttle effect. The polyiodide or polybromide shuttle effect typically occurs in five steps: (i) formation of long-chain polyhalogen anions, (ii) detachment of polyhalogen anions from the halogen source, (iii) dissolution of polyhalogen anions into the electrolyte solution, (iv) migration of polyhalogen anions toward the anode side, and (v) reaction between polyhalogen anions and the anode metal. The shuttle effect can result in irreversible loss of iodine or bromine, corrosion of the anode metal, rapid capacity fading and poor Coulombic efficiency of the batteries. In aqueous electrolytes, Zn-I ₂ batteries present a reversible I ^‒ /I ₂ redox reaction, in which polyiodide species form as highly-soluble intermediates such as I ₅ - and I ₃ - that cause the shuttle effect and lead to irreversible loss of active mass.[5] Therefore, it is important to suppress the shuttle effect and stabilise the iodine or bromine cathode and alleviate the corrosion of anode metal, which in turn expands the life span of iodine or bromine based batteries. [0007] The shuttle effect is known as one of the crucial issues that hinder the development of a high- performance metal-iodine or metal-bromine battery with long cycling life. Taking polyiodide as an example, the confinement of polyiodide species in porous host materials, including functionalized porous carbon[6], graphene[6], and Mxenes[7] has been attempted to surpress the shuttle effect. However, these host materials still suffer from weak interaction with various iodine species through physical adsorption, which is still far from satisfactory to effectively address the shuttle effect, especially for long-time cycles. These polyiodide species will gradually dissolve into the electrolyte from the host materials, which results in the failure in the construction of shuttling-free Zn-I ₂ batteries. CN107068989 discloses a strategy for solving the polyidode shuttle effect, which uses a composite of a specific polymer such as polyvinylpyrrolidone (PVP) and an active iodine substance as the positive electrode. The specific polymer is capable of interacting with iodine and effectively confining polyiodides around the positive electrode, so as to inhibit their diffusion towards the negative electrode and suppress the shuttle effect. However, availability of the composite is limited, and the costs associated with the materials and the cathode preparation are relatively high. In addition, replacing liquid electrolytes with solid/quasi-solid electrolytes has been claimed to be effective to retard the shuttling of polyiodide,[8] however, the Zn ²⁺ diffusion is also mitigated. Building anode functionalized films also has been proposed to inhibit the parasitic reaction between shuttling polyiodide and Zn anodes, but it cannot fundamentally address the dissolution of polyiodide from the cathode.[2] Therefore, developing an efficient and cost effective strategy beyond the traditional physical adsorption is still highly desirable to suppress the polyiodide or polybromide shuttling towards high-reversibility batteries. [0008] Accordingly, there remains a need for shuttling-free electrochemical devices which solve or alleviate one or more of the above problems and may be of practical use in large scale energy storage. SUMMARY [0009] In a first aspect, provided herein is a solid positive electrode for a shuttling-free electrochemical device, the solid positive electrode comprising a functional carbohydrate capable of confining polyiodide and/or polybromide species to the positive electrode during operation of the device. [0010] In a second aspect, provided herein is a shuttling-free electrochemical device comprising a negative electrode, a solid positive electrode, and an electrolyte solution, the solid positive electrode comprising a functional carbohydrate capable of confining polyiodide and/or polybromide species to the positive electrode during operation of the device. [0011] Optionally, the electrochemical device of the second aspect comprises a source of iodine and/or bromine as a positive electrode active material. The source of iodine and/or bromine as a positive electrode active material may be contained within the solid positive electrode and/or within an electrolyte solution in contact with the solid positive electrode. [0012] In a third aspect, provided herein is a method of fabricating a shuttling-free electrochemical device comprising a negative electrode, a solid positive electrode, and an electrolyte solution, the method comprising introducing into the solid positive electrode a functional carbohydrate capable of confining polyiodide and/or polybromide species to the positive electrode during operation of the device. [0013] Optionally, the method of the third aspect further comprises introducing a source of iodine and/or bromine as a positive electrode active material. The source of iodine and/or bromine may be contained within the solid positive electrode and/or within an electrolyte solution in contact with the solid positive electrode. [0014] In a fourth aspect, provided herein is use of a functional carbohydrate in a shuttling-free electrochemical device comprising a negative electrode, a solid positive electrode, and an electrolyte solution, wherein the functional carbohydrate is introduced into the solid positive electrode to confine polyiodide and/or polybromide species to the positive electrode during operation of the device. [0015] In certain embodiments of the first, second, third or fourth aspect, the positive electrode further comprises a source of iodine and/or bromine as a positive electrode active material. In some embodiments, the source of iodine and/or bromine as a positive electrode active material is contained within the solid positive electrode and/or within an electrolyte solution in contact with the solid positive electrode. In some embodiments, the source of iodine and/or bromine as a positive electrode active material is selected from elemental iodine (I2), LiI, NaI, KI, ZnI2, NH4I, quaternary ammonium iodides such as trimethylammonium iodide, quaternary ammonium bromides such as trimethylammonium bromide, triiodomethane (CH3I), poly(vinylpyrrolidone)-Iodine (PVP-I), elemental bromine (Br2), LiBr, and combinations thereof. [0016] In certain embodiments of the second, third or fourth aspect, the negative electrode has a source of zinc, lithium, sodium, aluminium or magnesium as a negative electrode active material. [0017] In certain embodiments of the first, second, third or fourth aspect, the shuttling-free electrochemical device is an aqueous battery. In some embodiments, the aqueous battery is selected from an aqueous metal-iodine battery and an aqueous metal-bromine battery. In some further embodiments, the aqueous battery is an aqueous zinc-iodine battery or an aqueous zinc-bromine battery. In even further embodiments, the aqueous battery is an aqueous zinc-iodine battery wherein metallic zinc (Zn) is used as the negative electrode active material and elemental iodine (I ₂ ) is used as the positive electrode active material. [0018] In certain embodiments of the first, second, third or fourth aspect, the solid positive electrode is loaded with the source of iodine (for example, I ₂ and LiI) in the range of about 0.01 to about 20 mg·cm ^-2 or the solid positive electrode is loaded with the source of bromine (for example, Br ₂ and LiBr) in the range of about 0.01 to about 20 mg·cm ^-2 . [0019] In certain embodiments of the first, second, third or fourth aspect, the functional carbohydrate is selected from polysaccharides, oligosaccharides and combinations thereof. In some embodiments, the functional carbohydrate is selected from helical polysaccharides, cyclic polysaccharides, cyclic oligosaccharides, and combinations thereof. In some embodiments, the helical polysaccharides are selected from amylose, amylopectin, agarose, carrageenans, ß-1,3 glucans, and combinations thereof. In some further embodiments, the cyclic polysaccharides are cyclic glucans, for example cyclic ß-glucans. In even further embodiments, the cyclic oligosaccharides are cyclodextrins and cyclosophorans. In even further embodiments, the functional carbohydrate is selected from amylose, amylopectin, α-cyclodextrin (α-CD), β-cyclodextrin (β-CD), ^-cyclodextrin ( ^-CD), and combinations thereof. [0020] In certain embodiments of the first, second, third or fourth aspect, the functional carbohydrate is combined with a conductive substrate. In some embodiments, the conductive substrate is a conductive carbonaceous substrate. In some further embodiments, the conductive carbonaceous substrate is selected from carbon black, Ketjen Black (KB), graphene, graphene oxide, carbon nanotubes (CNT), carbon nanofiber (CNF), carbon cloth, carbon felt, carbon paper, carbon fibre, carbon pellet, carbon powder, hollow carbon spheres, metal-organic frameworks (MOF), carbonised MOF, active carbon cloth/polyvinylpyrrolidone (ACC/PVPI) composite, and combinations thereof. In some further embodiments, a cyclodextrin selected from α-cyclodextrin (α-CD), β-cyclodextrin (β-CD), ^-cyclodextrin ( ^-CD) and combinations thereof is combined with carbon nanotubes (CNT) to form cyclodextrin modified carbon nanotubes (CNT). [0021] In certain embodiments of the first, second, third or fourth aspect, when the shuttling-free electrochemical device is an aqueous battery, the electrolyte is selected from ZnSO4, ZnI2, ZnBr2, ZnCl2, ZnNO ₃ , zinc acetate, zinc bis(trifluoromethylsulfonyl)imide (Zn(TFSI) ₂ ), zinc trifluoromethanesulfonate (Zn(OTf) ₂ ), Zn(ClO ₄ ) ₂ , a mixture of KI and ZnBr ₂ , a mixture of ZnSO ₄ and ZnI ₂ , a mixture of ZnSO ₄ and Li2SO4, a mixture of ZnCl2 and KCl, a mixture of ZnCl2, LiCl and acetonitrile. In some embodiments, when the shuttling-free electrochemical device is an aqueous battery, the electrolyte is selected from ZnSO4, ZnCl2, ZnNO3, and a mixture of ZnSO4 and Li2SO4. In other embodiments, when the shuttling- free electrochemical device is an aqueous zinc-iodine battery, an electrolyte for the solid positive electrode (i.e. catholyte) is a mixture of LiI and I2, an electrolyte for the negative electrode (i.e. anolyte) is a mixture of ZnSO4 and Li2SO4. [0022] In certain embodiments of the first, second, third or fourth aspect, the shuttling-free electrochemical device comprises a separator which is selected from glass fibre separators, ceramic separators, polyolefin separators, nonwoven separators, and porous polymer separators. [0023] In certain embodiments of the first, second, third or fourth aspect, the shuttling-free electrochemical device further comprises a conductive agent in the solid positive electrode and/or a negative electrode. In some embodiments, the conductive agent is selected from carbon black, Ketjen black, graphene, conductive nano carbon fiber (VGCF), carbon nanotubes (CNTs), multi-walled carbon nanotubes (MWCNTs) and combinations thereof. [0024] In certain embodiments of the first, second, third or fourth aspect, the electrochemical device delivers a specific capacity of 182.5 mAh g ^‒1 at 0.2 A g ^‒1 and a Coulombic efficiency of ~100%. In some embodiments, the electrochemical device remains a value of 167.8 mAh g ^‒1 after 100 cycles. In some embodiments, the electrochemical device exhibits a cycle lifespan of 10,000 cycles at 4 A g ^‒1 and of 50,000 cycles at 10 A g ^‒1 . BRIEF DESCRIPTION OF THE FIGURES [0025] Non-limiting embodiments of the present disclosure will be discussed with reference to the accompanying figures wherein: [0026] Figure 1 shows (a) the structure of starch polymer chains, (b) a schematic diagram of the double-helix structure of starch, (c) a schematic diagram of a starch/polyiodide complex, (d) photographs revealing the polyiodide capture processes by starch, (e) scanning electron microscope (SEM) images of pristine starch, (f) SEM images of starch/polyiodide clathrate (the inset in (f) is the corresponding I element mapping analysis), and (g) Raman spectra of starch and starch/polyiodide clathrate. [0027] Figure 2 shows a schematic diagram of the starch structure showing the intramolecular hydrogen bonds in the starch polymer chain. [0028] Figure 3 shows photographs of I2/H2O solution (a) before and (b) after iodine species have been captured by starch. [0029] Figure 4 shows the Raman spectrum of starch after is it immersed in I ₂ solution. [0030] Figure 5 shows polyiodide capture capacity. (a) The UV-vis spectra of iodide/H2O, triiodide/H ₂ O, and I ₂ /ethanol solutions before (full line) and after (dash line) iodine species have been captured in the starch. (b) Corresponding iodine species capture capacity of starch. (c) The focused ion beam scanning electron microscopy (FIB-SEM) image of starch/polyiodide complex and corresponding element energy dispersive spectroscopy (EDS) mapping: (d) C and (e) I. (f) I 3d X-ray photoelectron spectroscopy (XPS) depth profiles of the starch/polyiodide complex and (g) corresponding calculated ratios of triiodide species (left columns) and pentaiodide (right columns) species in starch/polyiodide complex. (h) The evolution of bonding energy of starch towards iodine species: from starch unit (left columns), ring (middle columns) to double helix (right columns). The optimized structure models of (i) triiodides and (j) pentaiodide ion interacted with starch unit, ring, and double helix. [0031] Figure 6 shows (a) The UV-vis spectra of iodide solutions with different concentrations (from top line to bottom line: 0.24 mM I-, 0.18 mM I-, 0.12 mM I-, 0.06 mM I-). (b) The corresponding working plots revealing the relationship between concentration and absorbance. [0032] Figure 7 shows (a) The UV-vis spectra of triiodide solutions with different concentrations (from top line to bottom line: 0.4 mM I ₃ -, 0.3 mM I ₃ -, 0.2 mM I ₃ -, 0.1 mM I ₃ -). (b) The corresponding working plots revealing the relationship between concentration and absorbance. [0033] Figure 8 shows (a) The UV-vis spectra of iodine/ethanol solutions with different concentrations (from top line to bottom line: 2.16 mM I2, 1.80 mM I2, 1.44 mM I2, 1.08 mM I2, 0.72 mM I2). (b) The corresponding working plots revealing the relationship between concentration and absorbance. [0034] Figure 9 shows X-ray diffraction (XRD) patterns of starch (upper line) and starch/polyiodide (lower line). [0035] Figure 10 shows Fourier-transform infrared spectroscopy (FTIR) spectra of starch (lower line) and starch/polyiodide complex (upper line). [0036] Figure 11 shows N2 adsorption/desorption isotherms of KB (upper line) and KB/polyiodide complex (lower line). [0037] Figure 12 shows UV-vis spectra of triiodide solution before (upper line) and after (lower line) iodine species have been captured by KB. [0038] Figure 13 shows I 3d XPS spectrum of KB/polyiodide complex. [0039] Figure 14 shows N ₂ adsorption/desorption isotherms of starch. [0040] Figure 15 shows (a) Photograph of a mixture of KB/polyiodide and electrolyte after one-week resting, and corresponding (b) UV-vis spectra of electrolyte before (lower line) and after resting (upper line). [0041] Figure 16 shows (a) Photograph of a mixture of starch/polyiodide and electrolyte after one- week resting. (b) The corresponding UV-vis spectra of electrolyte before (lower line) and after resting (upper line). [0042] Figure 17 shows the optimized structure and bonding energies of iodine species bonded on the graphene: (a) I ₂ , (b) I ₃ ^‒ , and (c) I ₅ ^‒ . [0043] Figure 18 shows the electrochemical performance of Zn-I ₂ batteries. (a) The cycling stability and Coulombic efficiency of Zn-I ₂ batteries at 0.2 A g ^‒1 with KB (lower lines) and starch (upper lines) cathodes, (b) corresponding charging-discharging curves with KB (lower lines) and starch (upper lines) cathodes. (c) Rate performance of Zn-I ₂ batteries with KB (lower lines) and starch (upper lines) cathodes. (d) The cycling stability of Zn-I ₂ batteries at 2 A g ^‒1 with starch (longer lines) and KB (shorter lines) cathodes, and (e) corresponding charge-discharge curves with left lines for 10000 ^th cycle and right lines for 5 ^th cycle. (f) The long-term cycling stability of Zn-I ₂ batteries with starch cathodes under a high current density of 10 A g ^‒1 . (g) Literature survey of rechargeable Zn batteries: Zn _0.25 V ₂ O ₅ ∙nH ₂ O//Zn[19], K1.28Ni[Fe(CN)6]0.821∙2.64H2O//Zn[20], LiMn2O4//Zn [21], MnO2//Zn[22], I2-NPC//Zn[23], I2- ACC//Zn[6a], I2-C-50//Zn, H2O/I2//Zn-BTC@Zn[2a], H2O/I2//Zn@ZIF-8[24], I2-Nb2CTix//Zn[7]. [0044] Figure 19 shows photographs of separator in (a) KB-based and (b) starch-based Zn-I2 batteries after the batteries being charged to 1.3 V at 0.2 A g ^-1 . [0045] Figure 20 shows CV curves of Zn-I2 batteries with (a) KB (shortest loop line for 1 ^st cycle, shorter loop line for 2 ^nd cycle, longest loop line for 3 ^rd cycle) and (b) starch cathode (shortest loop line for 1 ^st cycle, shorter loop line for 2 ^nd cycle, longest loop line for 3 ^rd cycle) at a sweeping rate of 0.2 mV s ^-1 . [0046] Figure 21 shows Nyquist plots of KB-based (left line) and starch-based (right line) Zn-I2 batteries after one cycle. [0047] Figure 22 shows the charge-discharge curves of Zn-I ₂ batteries with KB cathodes at 4 A g ^-1 (from left to right, 2000 ^th cycle, 1800 ^th cycle, 1000 ^th cycle, 5 ^th cycle). [0048] Figure 23 shows the shuttle effect in Zn-I ₂ batteries. (a) The schematic diagram revealing the estimation of shuttle effect on cathode, electrolyte, and anode components by in-situ Raman spectra, in- situ UV-vis, and XPS depth profiles, respectively. (b) In-situ Raman spectra, showing the electrochemical process of I ^‒ /I2 conversion in starch-based Zn-I2 batteries. In-situ UV-vis spectra for the electrolyte during the charging process with (c) KB and (d) starch cathodes. (e) The evolution of polyiodide concentration in electrolytes with KB (right columns) and starch (left columns) cathodes. SEM images with the I mapping of starch cathodes at different electrochemical states: (f) charge to 1.3 V, (g) charge to 1.6 V, (h) discharge to 1.3 V, and (i) discharge to 0.5 V. [0049] Figure 24 shows I 3d XPS spectra of starch cathodes in Zn-I ₂ batteries after (a) charge to 1.3 V and (b) discharge to 1.3 V. [0050] Figure 25 shows digital images of (a) commercial quartz cell and (b) home-made quartz cell for in-situ UV-vis measurement. [0051] Figure 26 shows SEM images and corresponding I mapping (inset) of KB electrodes at different electrochemical states: (a) charge to 1.3 V, (b) charge to 1.6 V, (c) discharge to 1.3 V, and (d) discharge to 0.5 V. [0052] Figure 27 shows the linear polarization curves of Zn foils in electrolytes with (line with a peak on the left)/without (line with a peak on the right) 10 mM triiodide. [0053] Figure 28 shows the Zn Coulombic efficiency of Cu/Zn cells in electrolytes with (lower lines) /without (upper lines) 10 mM triiodide. [0054] Figure 29 shows the cycling stability of Zn/Zn symmetric cells in the (a) triiodide-containing electrolyte and (b) bare electrolyte. [0055] Figure 30 shows photographs of Zn foils immersed in the electrolyte with/without triiodide (a) before and (b) after three-day resting. [0056] Figure 31 shows UV-vis spectra of the triiodide-containing electrolyte before (top line with two sharp peaks) and after reacting with Zn foils (middle line with two flat peaks for after one-day resting, bottom smooth line for after three-day resting). [0057] Figure 32 shows XRD patterns of Zn foils after one-week immersion in electrolytes with/without triiodide (from top to bottom, 15 mM I3-, 10 mM I3-, 5 mM I3-, without I3-). [0058] Figure 33 shows SEM images of Zn foils after three-day immersion into (a) bare electrolyte and (b) 10 mM triiodide-containing electrolyte. [0059] Figure 34 shows I 3d XPS depth profiles of Zn after immersed in triiodide-containing electrolyte for three days. [0060] Figure 35 shows photographs of Zn foils after 50 cycles in (a) KB-based Zn-I ₂ battery and (b) starch-based Zn-I ₂ battery at 0.2 A g ^-1 . [0061] Figure 36 shows polyiodide corrosion of Zn anodes. The (a, e) Zn LMM Auger depth profiles and (b, f) corresponding intensity evolution (in b, steeply rising line corresponds to metallic Zn, gently declining line corresponds to Zn ₄ (SO ₄ ) ₄ (OH) ₆ ) (in f, top line corresponds to Zn ₄ (SO ₄ ) ₄ (OH) ₆ , bottom line corresponds to metallic Zn) of by-products and metallic Zn components of Zn anodes after 50 cycles in (a, b) starch-based Zn-I ₂ and (e, f) KB-based Zn-I ₂ battery. The (c, g) Zn 2p3/2 and (d, h) S 2p XPS depth profiles of Zn anodes after 50 cycles in (c, d) starch-based Zn-I ₂ and (g, h) KB-based Zn-I ₂ battery. SEM images of Zn anodes after 50 cycles in (i) starch-based Zn-I ₂ and (j) KB-based Zn-I ₂ battery. (k) XRD patterns of cycled Zn electrodes in both cells (top line corresponds to the starch-based cell, bottom line corresponds to the KB-based cell). [0062] Figure 37 shows (a) XRD pattern and (b) Zn LMM spectrum of Zn ₄ SO ₄ (OH) ₆ powder. [0063] Figure 38 shows the Zn LMM spectrum (a) before and (b) after differential analysis. [0064] Figure 39 shows the differential Zn LMM AES depth profiles of Zn anodes after cycled in (a) starch-based Zn-I2 battery and (b) KB-based Zn-I2 battery. [0065] Figure 40 shows a schematic diagram for preparation of β-cyclodextrin (β-CD) modified carbon nanotubes (CNT). [0066] Figure 41 shows the cycling performance of Zn-I2 batteries using β-CD/CNTs at 4 A g ^-1 . [0067] Figure 42 shows the cycling performance of Zn-I2 batteries using β -CD/CNTs at 6 A g ^-1 . [0068] Figure 43 shows the charge-discharge curves of Zn-I2 batteries using β-CD/CNTs at 6 A g ^-1 . [0069] Figure 44 shows the cycling performance of Zn-I ₂ batteries using ^-CD/CNTs at 10 A g ^-1 . [0070] Figure 45 shows the cycling performance of Zn-I2 batteries using ^-CD/CNTs at 20 A g ^-1 . [0071] Figure 46 shows the cycling performance of Zn-Br2 batteries using ^-CD/CNTs at 4 A g ^-1 . [0072] Figure 47 shows the charge-discharge curves of Zn-Br ₂ batteries using ^-CD/CNTs at 4 A g ^-1 . DESCRIPTION OF EMBODIMENTS [0073] The term “electrochemical device” used herein refers to a device that can convert chemical energy into electrical energy through an electrochemical reaction. Examples of the electrochemical device include a battery and a cell such as a coin cell. [0074] The phrase “shuttling-free” used herein means that the shuttling of polyiodide and/or polybromide species to the negative electrode of the electrochemical device is effectively suppressed without adversely affecting the performance of the electrochemical device. [0075] The term “aqueous electrolyte” used herein generally refers to a water-based electrolyte solution. However, this does not exclude the possibility of presence of other constituents like ionic liquids. [0076] The term “negative electrode active material” used herein refers to an active material for the negative electrode of the electrochemical device. The term “positive electrode active material” used herein refers to an active material for the positive electrode of the electrochemical device. The active materials may be combined with other materials such as a conductive agent and a component to form a composite comprising the active material in order to prepare the desirable electrodes. [0077] The term “polyiodide” used herein refers to a class of polyhalogen anions composed entirely of iodine atoms. Examples of polyiodides commonly involved in the shuttle effect of an electrochemical device include I3 ⁻ and I5 ⁻ . [0078] The term “polybromide” used herein refers to a class of polyhalogen anions composed entirely of bromine atoms. Examples of polybromides commonly involved in the shuttle effect of an electrochemical device include Br3 ⁻ , Br5 ⁻ and Br7 ⁻ . [0079] The term “helical polysaccharide” used herein refers to a polysaccharide whose molecule or molecule part tends to form a helical secondary structure. Non-limiting examples include amylose, amylopectin, agarose, carrageenans, and ß-1,3 glucans, such as lentinan, curdlan, and schizophyllan. [0080] The disclosure arises from the inventors’ research into the shuttle effect that occurs with iodine based batteries and bromine based batteries. It has been surprisingly found that a functional carbohydrate (for example, starch and cyclodextrins) can be used in the solid positive electrode to serve as a “host” to effectively trap guest species like polyiodide and the interaction between the functional carbohydrate and the “guest” species is strong enough to substantially prevent or minimise dissolution of polyiodide in a electrolyte solution and thereby suppress the shuttle effect and alleviate the corrosion of anode metal (see, for example, Figure 35). Without being bound by any theory, it is suggested that the conformation or the molecular shape as well as hydroxyl active sites of the functional carbohydrate contribute to a strong interaction between the polyiodide/polybromide species and the functional carbohydrate, thereby allowing a more effective confinement than that provided through physical adsorption of porous carbonaceous materials. [0081] Accordingly, disclosed herein are a solid positive electrode for a shuttling-free electrochemical device and a shuttling-free electrochemical device. The shuttling-free electrochemical device comprises a negative electrode, a solid positive electrode, and an electrolyte solution. A source of iodine and/or bromine as a positive electrode active material is contained within the solid positive electrode and/or within an electrolyte solution for the solid positive electrode. A functional carbohydrate capable of confining polyiodide and/or polybromide species to the positive electrode during operation of the device is contained within the solid positive electrode. [0082] The shuttling-free electrochemical device disclosed herein may be in the form of a battery or a cell. The solid positive electrode for the present disclosure or an electrolyte solution for the solid positive electrode may comprise a source of iodine and/or bromine as a positive electrode active material. In some circumstances, the source of iodine and/or bromine as a positive electrode active material is selected from elemental iodine (I ₂ ), LiI, NaI, KI, NH ₄ I, ZnI ₂ , quaternary ammonium iodides such as trimethylammonium iodide, quaternary ammonium bromides such as trimethylammonium bromide, triiodomethane (CH3I), poly(vinylpyrrolidone)-Iodine (PVP-I), elemental bromine (Br2), LiBr and combinations thereof. The negative electrode of the shuttle-free electrochemical device may have a source of zinc, lithium, sodium, aluminium or magnesium as a negative electrode active material, for example zinc foil. If needed, the batteries known in the art may be adapted to the present disclosure through incorporating the functional carbohydrate as detailed below. [0083] The negative electrode and the positive electrode are connected to each other by an electrolyte solution. In some circumstances, the electrolyte (i.e. anolyte) used for the negative electrode is different from the electrolyte (i.e. catholyte) used for the positive electrode. At least the following factors may be considered when choosing an electrolyte solution for the aqueous electrolyte: (i) chemical inertness; (ii) wide liquid range and thermal stability; (iii) balanced viscosity; (iv) high ionic and no electronic conductivity; (v) interphase properties and control of by-products during the redox process; and (vi) availability. It may be desirable for the electrolyte solution to be modified by introducing corrosion inhibitors or complexing agents in order to make the electrolyte solution less corrosive. It is also possible to introduce an additive into the aqueous electrolyte to optimise electrochemical performance in the electrochemical device. Factors such as balanced viscosity, ionic conductivity, and control of by products during the redox process may play a role in selecting the electrolyte. It is possible for the shuttling-free electrochemical device disclosed herein to have an aqueous electrolyte or a non-aqueous electrolyte such as an organic electrolyte. Iodine is soluble in organic solvents because of its small dielectric constant but exhibits low solubility in aqueous solution due to the formation of halogen bonds. For embodiments where iodine is utilised as the positive electrode active material, organic solvents particularly with low dielectric properties, e.g. carbon disulphide, diethyl ether and hexane, may be suitable non-aqueous electrolytes. For an aqueous electrolyte, potassium iodide (KI) or other iodide aqueous solutions may be added to increase the solubility of iodine. [0084] High abundance (1.5 wt% in earth crust and 0.13 wt% in sea water), high volumetric energy density (3,833 mAh cm ⁻³ ), very negative reduction potential (-2.37 V versus Standard Hydrogen Electrode) and, most importantly, highly reversible dendrite-free deposition, have made magnesium (Mg) metal a competent candidate for the negative electrode active material. In this regard, reference may be made to Mg-I ₂ batteries wherein metallic magnesium is used as the negative electrode active material and a composite of active carbon cloth (ACC) and I ₂ is used to prepare the positive electrode, and the electrolyte solution can be synthesised by reacting magnesium bis(trimethylsilyl)amide ((HMDS) ₂ Mg) with aluminum chloride (AlCl3) and magnesium chloride (MgCl2) in tetraglyme (TEGDME) in situ. [0085] Aluminum-iodine batteries that suffer from the polyiodide shuttle effect due to dissolution of polyiodide in an ionic liquid electrolyte may also be considered. For the purpose of illustration, the aluminum-iodine batteries may comprise Al foil as the negative electrode active material and I2 as the positive electrode active material, and the ionic liquid electrolyte may be a mixture of 1-ethyl-3- methylimidazolium chloride (EMIC) and AlCl3, for example in a ratio of 1:1.3. [0086] In some preferable embodiments, the shuttling-free electrochemical device is an aqueous battery. The aqueous battery may include an aqueous metal-iodine battery and an aqueous metal-bromine battery. A particular example of the metal mentioned here is zinc. Accordingly, consideration may be given to aqueous zinc-iodine (Zn-I2) batteries and aqueous zinc-bromine (Zn-Br2) batteries. Aqueous Zn- I2 batteries may be advantageous owing to the abundance of iodine in seawater, the high theoretical specific capacity of 211 mAh g ^-1 and high discharge plateau (1.38 V vs. Zn/Zn ²⁺ ). Furthermore, iodine has high chemical stability in the majority of commonly available solvents, even water. Aqueous Zn-Br2 batteries may have advantages in their higher theoretical specific capacity of 355 mAh g ^-1 and higher theoretical voltage plateau (1.85 V vs. Zn/Zn ²⁺ ) compared with Zn-I2 batteries. [0087] When the negative electrode active material is made from metallic zinc, the latter may be in the form of a zinc foil. In the case that a source of iodine and/or bromine (for example, LiI and I ₂ ) as a positive electrode active material is contained within the solid positive electrode, the active mass loading of the source of iodine (for example, LiI and I ₂ ) for the positive electrode may be in the range of about 0.01 to 20 mg·cm ^-2 , and the active mass loading of the source of bromine (for example, KrBr and Br ₂ ) for the positive electrode may be in the range of about 0.01 to 20 mg·cm ^-2 . Non-limiting examples of the electrolyte that can be used for the aqueous Zn-I2 or Zn-Br2 batteries include ZnSO4, ZnI2, ZnBr2, KCl, ZnCl ₂ , ZnNO ₃ , zinc acetate, zinc bis(trifluoromethylsulfonyl)imide (Zn(TFSI) ₂ ), zinc trifluoromethanesulfonate (Zn(OTf) ₂ ), Zn(ClO ₄ ) ₂ , a mixture of KI and ZnBr ₂ , a mixture of ZnSO ₄ and ZnI ₂ , a mixture of ZnSO ₄ and Li ₂ SO ₄ , a mixture of ZnCl ₂ and KCl, a mixture of ZnCl ₂ , LiCl and acetonitrile. ZnSO ₄ , ZnCl ₂ , ZnNO ₃ , and a mixture of ZnSO ₄ and Li ₂ SO ₄ may be preferred in some circumstances. In circumstances that the shuttling-free electrochemical device is an aqueous battery, an electrolyte solution for the solid positive electrode (i.e. catholyte solution) comprises a mixture of LiI and I ₂ , an electrolyte solution for the negative electrode (i.e. anolyte solution) comprises a mixture of ZnSO ₄ and Li ₂ SO ₄ . Li ₂ SO ₄ may be used to improve reversibility of an anode, for example a metal Zn anode. A neutral, acidic or alkalescent aqueous electrolyte of the aqueous Zn-I ₂ batteries may be recommended as strong alkalinity could result in direct reaction with I ₂ or Br ₂ . [0088] To form the positive electrode, a conductive substrate may be used to support the positive electrode active material and enhance the conductivity of the positive electrode. Furthermore, a porous conductive substrate may further facilitate reversible interfacial reaction at the positive electrode and assist in accommodating the guest species like polyiodide through physical adsorption. In some embodiments, a conductive substrate may be used to be carry the functional carbohydrate, for example, a cyclodextrin selected from α-cyclodextrin (α-CD), β-cyclodextrin (β-CD) and ^-cyclodextrin ( ^-CD) is combined with carbon nanotubes (CNT) to form a cyclodextrin modified carbon nanotubes (CNT). Factors such as wettability and electronic conductivity, and fixation and promotion of the redox reaction (for example, in relation to elemental iodine, bromine and sulfur) might be considered in selecting components of the positive electrode. In some circumstances, a substrate with large surface area and pore volume may be desirable. The conductive substrate used herein may be a conductive carbonaceous substrate and examples thereof include carbon black, Ketjen Black (KB), graphene, graphene oxide, carbon nanotubes (CNT), carbon nanofiber (CNF), carbon cloth, carbon felt, carbon paper, carbon fibre, carbon pellets, carbon powder, hollow carbon spheres, metal-organic frameworks (MOF), carbonised MOF, active carbon cloth/polyvinylpyrrolidone (ACC/PVPI) composite, and combinations thereof. The conductive substrate may be commercially available or prepared through a method known in the art. For instance, carbon nanotubes (CNT) are commercially available, for example, from Sigma-Aldrich, or grown by chemical vapor deposition (CVD) techniques. For the purpose of the present disclosure, the positive electrode active material such as I2 may be dissolved in solutions and then continuously adsorbed on the conductive substrate such as carbon cloth which incorporates the functional carbohydrate, so as to allow uniform distribution of the positive electrode active material within the conductive substrate. Alternatively, a mixture of I ₂ and active carbon cloth which incorporates the functional carbohydrate are sealed into an argon-filled container, and then heated to about 60 °C to 150  °C for a period of time so that the fluid I ₂ will be infiltrated into the pores of the ACC through the capillarity effect. The ball milling may also be employed. For instance, the positive electrode active material such as I ₂ and/or KI and host materials which may include the conductive substrate described herein, starch, and a binder are mixed through ball milling for a period of time, for example for about 5 to 48 hours at a rotation speed of 100 to 800 rpm. Then the iodine or metal iodide@host may be mixed with a conductive agent and a binder, and the mixture may then be coated onto a current collector. [0089] It is acknowledged that carbon, being non-polar in nature, is not able to adsorb polar species such as I- and Br-. In order to significantly suppress the shuttle effect, it is suggested by the present inventors that a functional carbohydrate be introduced into the positive electrode as a host to effectively trap the guest species such as polyiodide or polybromide and limit the exposure of the guest species to the electrolyte solution. [0090] Functional carbohydrates that may be used for this purpose include, but not limited to, polysaccharides, oligosaccharides, and combinations thereof. A functional carbohydrate of natural origin may be chosen to lower the cost of the electrochemical device. Polysaccharides and oligosaccharides are rich in functional groups, particularly hydroxyl groups the acetal groups. It is believed that some of those functional groups may serve as active sites for interaction with the polyiodide or polybromide species formed during the operation of the electrochemical device. It may be preferable to utilise a polysaccharide selected from helical polysaccharides and cyclic polysaccharides given their conformation or molecular shape. Similarly, cyclic oligosaccharides may be a preferred option from oligosaccharides. [0091] An illustrative example of helical polysaccharides that may be useful for the present disclosure is starch, which comprises amylose and amylopectin. Starch can be obtained from a great variety of botanical species, among which corn, wheat, potato and rice are the most common sources. Taking corn starch as an example, it may comprise about 20-50wt% amylose and about 80-50wt% amylopectin, for example a corn starch with about 35% amylose and about 65% amylopectin. Both amylose and amylopectin contain a unique double-helix structure. It is shown herein that starch can strongly confine the various iodine species inside the helical chains through bonding effects and form a starch/polyiodide complex (see Figure 1). This prevents dissolution of the iodine species into an electrolyte solution. It is also shown herein that I5 ^‒ is the predominant species in the starch/polyiodide complex, and it has a stronger interaction with double-helix structure of starch compared to I3 ^‒ . Other examples of helical polysaccharides include agarose, carrageenans, and ß-1,3 glucans. [0092] In some embodiments, the cyclic polysaccharides are cyclic glucans, for example cyclic ß- glucans. Cyclic β-1,2-D-glucans (CβG) are natural bionanopolymers, and their molecules are ring-shaped and their building blocks are exclusively D-glucose linked by β-glycosidic bonds. [0093] Illustrative examples of the cyclic oligosaccharides are cyclodextrins and cyclosophorans. Cyclodextrins are cyclic oligosaccharides composed of six or more α-1,4-linked glucose units and can be obtained through the enzymatic degradation of starch. All cyclodextrins have a height of about 8.0 Å and an outer diameter of 15~18 Å. They could be able to encapsulate the guest polyiodide or polybromide species in their toroidal cavity. The most abundant natural cyclodextrins are α-cyclodextrin (α-CD), β- cyclodextrin (β-CD), and γ-cyclodextrin (γ-CD), which contain six, seven, and eight glucopyranose units respectively. The diameter of the cavity is 4.7~5.2 Å for α-cyclodextrin (α-CD), 6.0~6.4 Å for β- cyclodextrin (β-CD), and 7.5~8.3 Å for γ-cyclodextrin (γ-CD). They may be used independently or in combination. In some embodiments, β-CD is preferable owing to its complexing abilities and low cost. [0094] Introducing the functional carbohydrate into the positive electrode may be achieved through modifying the conductive substrate with the functional carbohydrate. For example, the conductive substrate may be modified with the functional carbohydrate by physical mixing and/or chemically reacting the components. In this regard, a known method can be used to prepare β-cyclodextrin (β-CD) modified carbon nanotubes (CNTs) and β-CD functionalized graphene oxide. Figure 40 schematically illustrates the preparation of β-cyclodextrin (β-CD) modified carbon nanotubes. As shown by Figure 40, carbon nanotubes (CNTs) are subject to a hydrophilic treatment using a concentrated nitric acid, which increases the amounts of COOH groups to their wall. Then the treated CNTs are dispersed into a NaOH solution and cyclodextrin (β-CD) is dissolved into another NaOH solution. The two solutions may be mixed and reacted at about 60 °C to form a cyclodextrin linkage onto the CNTs. Another example is to graft starch onto the surfaces of carboxylated multi-wall carbon nanotubes. It is also possible to prepare nanocomposites comprising starch and graphene oxide (GO). [0095] In fabricating the electrochemical device, other components such as a separator, a binder, a conductive agent, and a current collector may be employed. A separator serves to provide a barrier with no electrical conductivity between the negative electrode (anode) and the positive electrode (cathode) while allowing ion transport from one electrode to the other electrode. The separator is expected to retain chemical stability in the electrolyte while also having a high affinity for the electrolyte. It is also desirable for the separator to have good mechanical stability. Non-limiting examples of the separator include glass fibre separators, ceramic separators, polyolefin separators (e.g. polyolefin porous membrane), nonwoven separators, and porous polymer separators. [0096] When powdered materials are used for the electrodes, a binder may be added to the electrodes to bring various components together and provide consistent mixing of electrode components so as to allow the electrodes to conduct the requisite amount of electrons and guarantee electronic contact during cycling of the electrochemical device. Non-limiting examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and carboxymethyl cellulose (CMC). [0097] The primary role of a conductive agent is to enhance conductivity of the electrodes. In some circumstances, the conductive agent used can be identical to the conductive substrate used for the functional carbohydrate, such as cyclodextrins. Non-limiting examples of the conductive agent include carbon black, Ketjen black, graphene, conductive nano carbon fiber (VGCF), carbon nanotubes (CNTs), and multi-walled carbon nanotubes (MWCNTs). In some embodiments, a conductive agent may be introduced into the solid positive electrode in addition to the conductive substrate combined with the functional carbohydrate. [0098] A current collector is a bridging component that collects electrical current generated at the electrodes and connects with external circuits. It can have influence on the capacity, rate capability and long-term stability of the electrochemical device. Non-limiting examples of the current collector include aluminium (Al) foil, copper (Cu) foil, carbon-coated aluminium, carbon-coated titanium (Ti) foil, and carbonaceous materials. [0099] The shuttling-free electrochemical device disclosed herein may be advantageous in many aspects and it may especially achieve significant improvement in electrochemical performance and stability. It has been surprisingly found by the present inventors that the electrochemical device disclosed herein may deliver a specific capacity of 182.5 mAh g ^‒1 at 0.2 A g ^‒1 and a Coulombic efficiency of ~100%. The electrochemical device disclosed herein may remain at a value of 167.8 mAh g ^‒1 after 100 cycles, which provides a remarkable cycling performance. Furthermore, the electrochemical device may achieve a cycle lifespan of 10,000 cycles at 4 A g ^‒1 and of 50,000 cycles at 10 A g ^‒1 . [0100] On this basis, a method of fabricating a shuttling-free electrochemical device comprising a negative electrode, a solid positive electrode, and an electrolyte solution has been developed. The method includes introducing into the solid positive electrode a functional carbohydrate capable of confining polyiodide and/or polybromide species to the positive electrode during operation of the device. Optionally, the method further comprises introducing a source of iodine and/or bromine as a positive electrode active material. The source of iodine and/or bromine may be contained within the solid positive electrode and/or within an electrolyte solution in contact with the solid positive electrode. Methods of fabricating an electrochemical device such as a battery are known in the art and can be adapted to the present disclosure. The functional carbohydrate that is used to trap polyiodide and/or polybromide species can be selected and incorporated into the positive electrode with reference to the detailed description herein and the Examples. [0101] Also disclosed herein is use of a functional carbohydrate in a shuttling-free electrochemical device comprising a negative electrode, a solid positive electrode, and an electrolyte solution, wherein the functional carbohydrate is introduced into the solid positive electrode to confine polyiodide and/or polybromide species to the positive electrode during operation of the device. Optionally, the electrochemical device comprises a source of iodine and/or bromine as a positive electrode active material. The source of iodine and/or bromine as a positive electrode active material may be contained within the solid positive electrode and/or within an electrolyte solution in contact with the solid positive electrode. It has been found by the inventors that inclusion of the functional carbohydrate may provide significant bonding interaction(s) with the guest species and facilitate effective confinement of the guest species to the positive electrode. On this basis, the shuttle effect caused by polyiodide and/or polybromide can be inhibited and a highly reversible electrochemical device can be achieved. [0102] EXAMPLES [0103] Zn-I ₂ batteries with starch cathodes [0104] Chemical reagents [0105] Starch powder (A.R.) was purchased from Sinopharm Chemical Reagent Co., Ltd. Anhydrous LiI (>99.0%), I ₂ (>99.9%), ZnSO ₄ ·7H ₂ O (A.R.), and anhydrous Li ₂ SO ₄ (A.R.) were purchased from Shanghai International Aladdin Regent Inc. The Zn foil (15 μm in thickness), polytetrafluoroethylene aqueous dispersion (PTFE, 40 wt.% solid content), Ketjen black (KB), and glass fibers were provided by Canrd New Energy Technology Co., Ltd. The carbon cloth (W1S1010) was provided by CeTech Co., Ltd. [0106] Preparation of electrodes and electrolytes [0107] For the starch electrodes preparation, starch (corn starch with about 35 wt% amylose), and conductive agent (KB) were mixed with PTFE binder in a mass ratio of 8:1:1, and then the mixture was compressed on carbon cloth. As a comparison, the KB electrode was fabricated using a similar method, in which KB was mixed with the PTFE binder in a mass ratio of 9:1. The mass loading was all controlled at around 3 mg·cm ^‒2 . Two types of electrolyte solutions were used, which can be divided into a catholyte solution and an anolyte solution. The catholyte solution was prepared by dissolving 0.1 M I2 and 1 M LiI into H2O, and the anolyte solution was an aqueous solution containing 0.5 M ZnSO4 and 0.5 M Li2SO4. [0108] Electrochemical measurements [0109] The electrochemical performance of Zn-I2 batteries was tested using CR-2016 coin-type cells (Canrd Corp.), which were assembled in the ambient environment. In Zn-I2 batteries, starch electrodes or KB electrodes were matched with Zn foils (15 μm), where the glass fibre was used as a separator. During the assembling, 30 μL of the catholyte solution was firstly dropped in starch electrodes or KB electrodes. And then an appropriate volume of the anolyte solution was dropped to wet the glass fibre. Galvanostatic discharge/charge measurements were conducted at a potential range of 0.5-1.6 V using the battery test system (CT-4008T, Neware, Shenzhen, China) under the ambient environment. The cyclic voltammetry (CV) technique was used to investigate the redox couple of I ^‒ /I ₃ ^‒ at the voltage range of 0.5-1.6 V with a scan rate of 0.2 mV s ^‒1 . All current densities were calculated based on the mass of iodine in the catholyte solution. [0110] Materials characterisation [0111] Powder X-ray diffraction (XRD) analysis was carried out on Rigaku Ultima IV with the Cu Kα radiation source. The samples were scanned at a 2θ range of 5° to 80° with scan speed of 5° min ^‒1 . A field emission scanning electron microscope (FESEM, Hitachi S-4800) with energy dispersive X-ray spectroscopy (EDS) was used to observe the morphology and element distribution. The focused ion beam (FIB) (ZEISS Crossbeam 540) was used to split the particle and the transection was further analysed by the SEM. X-ray photoelectron spectroscopy (XPS) was collected by Escalab 250Xi instrument (Thermo Fisher Scientific, USA) and an Al Kα monochromatized radiation was employed as an X-ray source. The sputtering was carried out by an inset Argon ion gun, the sputter rate was normalized by the SiO ₂ (25 nm min ^‒1 ) with a sputter area of 1 mm × 1 mm. The binding energies reported herein were corrected regarding C‒C signal at 284.8 eV, and the fitting analysis was conducted in XPS Peak software. The UV laser Raman spectroscopy was collected by LabRAM HR800 confocal Raman microscope (Horiba Jobin Yvon) with a laser of 633 nm. The in-situ Raman spectroscopy was collected by using a two-electrode battery testing the Raman cell (Gaoss Union, B002-RM). During the test, galvanostatic charge-discharge tests of Zn-I2 batteries were performed on the electrochemical workstation (CHI660E, Chenhua, Shanghai), and Raman spectra were in-situ collected by the Raman microscope from the quartz window of Raman cell. UV-vis spectra were collected on a UV3600 instrument (Shimadzu, Japan). In-situ UV-vis spectra were acquired by attached cathode and Zn anode on the two sides of quartz cell, and the electrolyte was fulfilled into the quartz cell. Galvanostatic charge-discharge curves of Zn-I2 batteries were collected on the electrochemical workstation (CHI660E, Chenhua, Shanghai), and UV-vis spectra were used to in-situ monitor the polyiodide dissolution. [0112] Calculation methods [0113] All calculations presented herein were carried out based on the density functional theory (DFT) as implemented in the VASP code. The electronic exchange-correlation energy was modelled using the Perdew-Burke-Ernzerhof (PBE) functional within the generalized gradient approximation (GGA). The projector augmented wave (PAW) method was used to describe the ionic cores. For the plane-wave expansion, a 450-eV kinetic energy cut-off was used after testing a series of different cut-off energies. The convergence criterion for the electronic structure iteration was set to be 10 ^‒4 eV, and that for geometry optimizations was set to be 0.02 eV Å ^‒1 on the force. A Gaussian smearing of 0.1 eV was applied during the geometry optimization and for the total energy computations. The molecule structure of starch unit with the hexatomic ring was obtained from the ChemSpider website. The double-helix structure of starch was acquired from PolySacDb website (http://polysac3db.cermav.cnrs.fr). [0114] Results and Discussion [0115] Identification of the interaction between starch and polyiodide [0116] It is widely known that the starch turns bluish-violet colour when it encounters iodine. This phenomenon originates from the formation of starch/iodine complex that gives rise to the intense optical absorption ( ^ _max ≈ 600 nm).[9] Figure 1a shows the molecule structure of starch, which is constituted of linked α-D-glucopyranosyl units by α-1, 4-glucosidic linkage.[10] In the starch, helical polymer chains are formed via the intramolecular hydrogen bonds, which are generated between the hydroxyl group at C– 3 site of one α-D-glucopyranosyl unit and another hydroxyl group at C–2 site of adjacent α-D- glucopyranosyl unit (Figure1 and Figure 2).[10a] In the starch, two anti-parallel helical polymer chains intertwine together to form a typical double-helix structure (Figure 1b).[11] Benefiting the unique structure, the starch can form a strong bond with polyiodide anions, which effectively captures the polyiodide anions inside the starch (Figure 1c).[12] Figure 1d presents the formation of starch/polyiodide complex. A bluish-violet mixture generates immediately when starch encounters polyiodide solution (0.1 M LiI and 0.05 M I ₂ in H ₂ O). After one-day resting and filtration, a colorless supernatant is obtained, indicating that the polyiodide can be fully adsorbed by starch. The generation of bluish-violet precipitate confirms the formation of starch/polyiodide complex. The similar color change phenomenon also can be observed when starch was mixed with I2/H2O solution. As shown in Figure 3, the orange I2 solution turns colorless after mixing with starch, indicating that starch also has a specific adsorption ability for elementary iodine and iodine species. [0117] The scanning electron microscope (SEM) was further used to verify the iodine species captured by starch. Pristine starch shows the morphology of spherical or polyhedral shape with a diameter of ~10 μm (Figure 1e). After polyiodide adsorption, the spherical morphology of starch is slightly distorted. Importantly, the smooth surface without any crystal of iodine species can be observed after polyiodide adsorption, indicating the polyiodide anions are captured in the main body of starch due to the bond formation. (Figure 1f). Corresponding elemental mapping analysis by energy dispersive spectrometer (EDS) displays a uniform distribution of iodine element in starch particle (inset in Figure 1f). As-acquired starch/polyiodide complex is further confirmed by Raman spectra (Figure 1g). Raman peaks at 440, 478, and 576 cm ^‒1 can be ascribed to the skeletal vibrations of the pyranose rings in α-D-glucose units of starch.[13] This vibration of pyranose rings is suppressed after the polyiodide capture, demonstrating the significant bonding interaction between polyiodide and molecule structure of starch. Two new Raman peaks located at 110 cm ^‒1 and 160 cm ^‒1 can be ascribed to the triiodide ion (I ₃ ^‒ ) and pentaiodide ion (I ₅ ^‒ ), respectively.[12] An intense I ₅ ^‒ signal along with a weak I ₃ ^‒ signal highlights that the I ₅ ^‒ is a preponderant polyiodide adsorbed in starch, which well coincides to the pioneering study reported before.[12] It was reported that there is an equilibrium between I ₃ ^‒ to I ₅ ^‒ (I ₃ ^‒ + I ₂ → I ₅ ^‒ ).[14] The high content of I ₅ ^‒ species in starch originates from the polyiodide transformation from I3 ^‒ to I5 ^‒ , which demonstrates that I5 ^‒ is the more stable polyiodide species in starch than I3 ^‒ . The high stability of I5 ^‒ in starch also can be proved by the Raman spectrum of starch/I2 complex, which is obtained by immersing starch into I2 aqueous solution. As shown in Figure 4, the I5 ^‒ species is the main polyiodide in starch/I2 complex. According to the literature, the I2 in solution has an equilibrium (I2 + H2O → I ^‒ + H ⁺ + HIO)[15], and as-generated I ^‒ can interact with I ₂ to from I ₃ ^‒ in solution. The much higher ratio of I ₅ ^‒ in starch/I ₂ complex than that of I ₃ ^‒ also proves that I ₅ ^‒ is the more stable polyiodide specie in starch. [0118] High polyiodide capture capacity of starch [0119] The adsorption capacity of starch toward various iodine species (I ^‒ , I3 ^‒ , and I2) was measured via ultraviolet-visible (UV-vis) spectra. As shown in Figure 5a, the strong peak with maximum absorption wavelength of 210 nm can be identified as I ^‒ , the maximum absorption wavelength located at ~288 and 350 nm can be ascribed to the I3 ^‒ ,[4a,16] and the significant adsorption wavelength at ~450 nm can be assigned to the I2 adsorption. [18] The linearity between UV-vis absorbance and iodine species concentration suggests that UV-vis spectra can be applied for the quantification of iodine species. Figures 6 to 8 provide the working plots revealing the relationship between absorbance and concentration of iodine species. As shown in Figure 5a, an obvious decline in adsorption peaks of iodine species (I ^‒ , I3 ^‒ , I2) after mixing with starch manifests the specific adsorption of starch towards different iodine species. According to the concentration declination, the specific capture capacity of starch can be calculated as 0.38 g g ^‒1 for I ^‒ , 0.82 g g ^‒1 for I3 ^‒ , and 0.72 g g ^‒1 for I2 (Figure 5b), respectively. [0120] To intuitively observe the iodine element distribution in the whole particle of starch, the focused ion beam (FIB) technology was applied to cut the starch/polyiodide particle to expose the cross section of the particle (Figure 5c), and inset EDS mapping analysis was employed to study the element distribution inside starch/polyiodide particles (Figures 5d and e). Results indicate the uniform distribution of C and I elements on the cross section of the particle, which strongly underlines the massive adsorption of polyiodide in the starch. To study the specific type of adsorbed polyiodide, XPS depth profiles were further analysed. As shown in Figure 5f, main iodine species in starch/polyiodide complex can be identified as two species: I3 ^‒ (618.2 eV/629.8 eV) and I5 ^‒ (619.8 eV/631.3 eV).[17] Significantly, an enhanced intensity of iodine species after sputtering demonstrates the strong adsorption capacity of starch. On the surface of starch/polyiodide complex, the I ₃ ^‒ species presents a dominant role, while the preponderant species changes to I ₅ ^‒ along with the XPS etching. The precise percentage of I ₃ ^‒ and I ₅ ^‒ in starch/polyiodide complex was calculated, as shown in Figure 5g. The intensity of polyiodide on the surface is much lower than that in the bulk, proving the stronger adsorption in the bulk of starch. On the surface, the content of I ₅ ^‒ is only 21%, while this value increases to ~85% in the bulk, confirming the preponderant specie in starch/polyiodide is I ₅ ^‒ . Almost the same percentage of I ₅ ^‒ under different etching depths also demonstrates the uniform polyiodide adsorption in starch. The powder X-ray diffraction (XRD) patterns and Fourier transform infrared spectroscopy (FT-IR) were further adopted to explore the bonding interaction between starch and polyiodide. As revealed in Figure 9, strong reflections at approximately 15°, 23°, 17°, and 18° indicate the typical A-type starch structure, in which double helixes are packed in monoclinic unit cells.[18] After polyiodide interacted with starch, the diffraction peaks at ~17° and 18° are significantly suppressed, which evidences that polyiodide anions are trapped inside the double-helix structure of starch. The FT-IR confirms the significant intensity decline of ‒OH vibration (~3400 cm ^‒1 ) Figure 10, indicating that hydroxy groups in α-D-glucose units act as the active sites for polyiodide interaction. These results highlight that the iodine species are trapped inside the starch via the helical structure confinement. [0121] To understand the unique structure confinement mechanism of starch, a common-used physical adsorbent, Ketjen black (KB), was used for comparison. Benefiting from its high specific surface area (1122.9 cm ² g ^‒1 ) (Figure 11), KB performs a high polyiodide capture capacity of 2.35 g g ^‒1 (Figure 12). The surface area of KB declines to only 222.9 cm ² g ^‒1 after polyiodide adsorption, testifying the polyiodide is physically adsorbed in the pores of KB. Besides, the XPS spectrum of KB/polyiodide complex shows that the main polyiodide specie adsorbed in KB is I3 ^‒ , which further confirms the physical adsorption of KB (Figure 13). Different from KB, starch has almost no pore as demonstrated by the N2 adsorption/desorption isotherms (Figure 14), which further confirms the bonding interaction of polyiodide in starch is mainly contributed to the unique structure of starch. To suppress the polyiodide shuttling, it not only requires large polyiodide capture capacity, but also needs high bonding strength to prevent the re-dissolution of polyiodide species. To compare the bonding strength of KB and starch to polyiodide, the KB/polyiodide and starch/polyiodide complexes were respectively immersed into the electrolyte (0.5 M ZnSO4/0.5 M Li2SO4 in H2O). As shown in Figure 15a, the electrolyte turns light-yellow when mixed with KB/polyiodide complex after one-week resting, indicating the re-dissolution of polyiodide. The UV- vis spectra of electrolytes after mixing display an obvious triiodide signal (Figure 15b), which further confirms the release of polyiodide from KB/polyiodide complex. Whereas the starch can avoid the re- dissolution of polyiodide because of its higher bonding strength with polyiodide than KB (Figure 16), which would benefit the shuttling suppression in Zn-I2 batteries. [0122] To in-depth understand the structure confinement of iodine species in the starch, the density functional theory (DFT) computations were conducted to compare the bonding energy of starch with iodine species and estimated the impacts of double-helix structure of starch on polyiodide confinement. To explore the impacts of starch structure on enhancing iodine species interaction, the bonding energies between iodine species and starch unit (α-D-glucose unit), hexatomic ring (constituted by six α-D-glucose units), and double helix were compared. As shown in Figure 5h, α-D-glucose units exhibit a high bonding energy with iodine species (-0.45 eV for I ₂ , -0.32 eV for I ₃ ^‒ , and -0.79 eV for I ₅ ^‒ ). When α-D-glucose units form hexatomic ring, the bonding energy reduces to -0.54 eV, -0.88 eV, and -1.01 eV for I ₂ , I ₃ ^‒ , and I ₅ ^‒ , respectively. This result indicates the ring structure could reinforce the interaction between starch and iodine species. A formed double-helix structure could further strengthen the polyiodide confinement, which is evidenced by the lower bonding energy between double-helix structure and polyiodide (-1.18 eV for I ₃ ^‒ , and -1.61 eV for I ₅ ^‒ ). This result reveals that the double-helix structure could reinforce the polyiodide confinement. Figures 5i and j further present the optimized structures of I ₃ ^‒ and I ₅ ^‒ interacted starch. The I ₃ ^‒ and I ₅ ^‒ show weak interaction with α-D-glucose units. And I ₃ ^‒ and I ₅ ^‒ trend to be trapped inside the ring structure, which is constituted by six α-D-glucose units, accompanied with bonding strength enhancement. When interacted with double-helix structure, the optimized structures reveal that I ₃ ^‒ and I ₅ ^‒ are preferred to be anchored at the inside of the helical structure, showing a higher bonding strength than ring structure. These results further prove that the unique structure of double helix could reinforce the interaction between starch and polyiodide. Specifically, the interaction between double-helix structure and I ₅ ^‒ (-1.61 eV) is much stronger than that with I ₃ ^‒ (-1.18 eV), and I ₅ ^‒ is also demonstrated as the predominant iodine species in starch/polyiodide complex (Figure 5g). This confinement of double- helix structure also performs a stronger interaction of starch with iodine species compared with carbon- based materials, demonstrated by the relatively higher bonding energy between graphene structure and iodine species (-0.56 eV for I3 ^‒ , and -1.01 eV for I5 ^‒ ) (Figure 17). Strong structure confinement of starch benefits to suppress the shuttle effect, which provides a feasible approach to shuttling-free Zn-I2 configurations. [0123] High-cyclability Zn-I2 batteries with starch cathodes [0124] The electrochemical performance was collected to estimate the effects of starch on the enhancing cycling performance of Zn-I2 coin-cells. All the specific capacities and current densities are normalized on the mass of iodide in cells. As shown in Figure 18a, an initial specific capacity of 152.1 mAh g ^‒1 is delivered by the KB-based Zn-I2 battery, corresponding to a low iodide utilization of 72.1% (vs. theoretical capacity of 211 mAh g ^‒1 ). Nonetheless, the discharge capacity decays to 126.8 mAh g ^‒1 after 100 cycles, corresponding to low-capacity retention of 83.4%. In striking contrast, the starch-based Zn-I2 battery shows a higher initial capacity of 182.5 mAh g ^‒1 and remains a value of 167.8 mAh g ^‒1 after 100 cycles, which manifests a remarkable cycling enhancement. As is well known, the CE is a crucial parameter for estimating the reversibility of Zn-I2 batteries, which can directly reflect the polyiodide shuttle effect. ^[4a] The KB-based Zn-I2 battery delivers a low-level average CE of 77.6% for 100 cycles, implying the serious polyiodide shuttle effect (upper figure in Figure 18a). In comparison, the CE of starch-based Zn-I ₂ battery can reach 99.5% after several cycles’ activation, and maintain at nearly 100% in the following cycles, exhibiting desirable shuttling suppression. Charge-discharge curves further confirm the reversibility enhancement by using starch with similar charge and discharge capacities (Figure 18b). However, the KB-based Zn-I ₂ battery delivers a high charge capacity (230.1 mAh g ^‒1 ) but a low discharge capacity (158.2 mAh g ^‒1 ), indicating its poor reversibility. The shuttle effect can be vividly observed from the colour change of glass fibre separator. When charged to 1.3 V, the conspicuous brown can be observed on the surface of glass fibre separator in the KB-based Zn-I ₂ battery, indicating KB cathode cannot avoid the dissolution of polyiodide (Figure 19a). Almost white colour can be maintained on the surface of separator in the starch-based Zn-I ₂ battery (Figure 19b), indicating the distinct suppression of shuttle effect by using starch. Cyclic voltammetry (CV) curves of Zn-I ₂ battery with starch and KB cathodes present paired reduction and oxidation peaks located at 1.28 and 1.47 V (vs. Zn ²⁺ /Zn) at a scan rate of 0.2 mV s ^‒1 , respectively (Figure 20). The higher peak current with well-overlapped curves in starch-based Zn-I ₂ battery than that of KB-based Zn-I ₂ battery demonstrates the better iodine utilization and cycling reversibility. [0125] The rate performance of Zn-I ₂ battery with KB and starch cathodes under current densities range from 0.2 to 10 A g ^‒1 was compared (Figure 18c). With KB cathodes, the Zn-I ₂ battery delivers a low capacity of 146.5 mAh g ^‒1 at 0.2 A g ^‒1 , and fast decays to only 24.5 mAh g ^‒1 when the current density increases to 10 A g ^‒1 . Significantly, the starch-based Zn-I ₂ battery can perform a much higher specific capacity of 180.5 mAh g ^‒1 at 0.2 A g ^‒1 , and still maintain ~75 mAh g ^‒1 at 10 A g ^‒1 , showing an outstanding rate performance. Nyquist plots of the Zn-I ₂ batteries using KB and starch as cathodes are also provided (Figure 21). The KB cathode with good electronic conductivity enables Zn-I ₂ batteries with small charge-transfer resistance (Rct) of only 13.5 ^. while the Rct only slightly increases to 24.3 ^ when replacing KB cathode by starch, indicating that starch with poor electronic conductivity would not affect severely on reaction dynamic of I ^‒ /I ₂ conversion. [0126] Then the long-term stability of Zn-I2 battery under a high current density of 2 A g ^‒1 is performed. The KB-based Zn-I2 battery delivers an initial capacity of 73.8 mAh g ^‒1 , which is much lower than that of starch-based Zn-I2 battery (90.2 mAh g ^‒1 ) (Figure 18d). The capacity of KB-based battery gradually increases in the following cycles, but suffers a sharp degradation after 1,700 cycles. For the starch-based Zn-I2 battery, ultra-stable cycling performance over 10,000 cycles with negligible capacity fading are achieved (Figure 18d), delivering a five-time longer lifespan than KB-based Zn-I2 battery. Corresponding charge-discharge curves of Zn-I2 battery with the starch cathodes indicate almost no polarization increase and negligible capacity loss after 10,000 cycles (Figure 18e). However, the capacity fading with enlarged polarization occurs in the cell with KB cathodes after 2,000 cycles (Figure 22). Distinguished cycling stability is also achieved at a higher current density of 10 A g ^‒1 . As shown in Figure 18f, the starch-based Zn-I2 battery delivers an initial specific capacity of 75 mAh g ^‒1 at 10 A g ^‒1 , and ultra-long cycling performance of over 50,000 cycles is achieved with a capacity retention of 90.5%. By comparing with some representative literatures, starch-based Zn-I2 battery delivers an outstanding cycling life and competitive power density (Figure 18g). Overall, profiting from the strong structure confinement of polyiodide in starch materials, a high-reversible, shuttling-free, and long-life Zn-I ₂ battery is realised. [0127] Suppression of polyiodide shuttling by using starch [0128] Figure 23a shows the shuttle effect during the cycling of Zn-I ₂ batteries. The oxidation of I ^‒ to I ₂ would generate I ₃ ^‒ as an intermediate. Highly soluble I ₃ ^‒ would be easily dissolved into the electrolyte solution and migrate to Zn anode, leading to serious Zn corrosion. Reduced I ₃ ^‒ by metallic Zn would lead to the regeneration of I ^‒ , which migrates back to the cathode for re-oxidation. This undesirable polyiodide shuttling accelerates the consumption of active Zn, leading to the rapid declination of cycling life. Herein, different components of Zn-I ₂ batteries (cathode, electrolyte, and Zn anode) were systematically investigated to understand the impacts of shuttle effect (Figure 23a). In detail, in-situ Raman spectra were used to reveal the electrochemical process of I ^‒ /I ₂ conversion reaction, in-situ UV-vis spectra were analysed to detect the polyiodide dissolution during cycling, and XPS depth profiles together with XRD, SEM etc. were performed to investigate the impacts of shuttle effect on Zn anodes. [0129] Figure 23b illustrates in-situ Raman spectra during the whole charge-discharge process of Zn-I ₂ batteries with the starch cathode. Raman peaks located at 110 cm ^‒1 and 160 cm ^‒1 can be associated with the I ₃ ^‒ and I ₅ ^‒ , respectively. The Zn-I ₂ battery endows an I ^‒ /I ₂ conversion with I ₃ ^‒ and I ₅ ^‒ as intermediates. As shown in Figure 23b, the intensity of I ₃ ^‒ and I ₅ ^‒ gradually increases at the initial charging period, then decreases in the later charging period. Raman peaks of I ₃ ^‒ and I ₅ ^‒ disappear when the battery is charged to the upper voltage, indicating that as-generated polyiodide can be fully converted to I2. During the discharge process, the similar evolution tendency of I3 ^‒ and I5 ^‒ with intensity increasing at the initial discharge process and intensity decreasing in the following discharge process can also be confirmed. Specifically, Raman peaks of I3 ^‒ and I5 ^‒ disappear at the end of discharge, emphasising the complete I ^‒ /I2 conversion. This conversion mechanism was further confirmed by XPS spectra. Starch cathode exhibits three pairs of split peaks associated with I3 ^‒ , I5 ^‒ , and I2 when charged to 1.3 V and discharged to 1.3 V, which further demonstrates intermediate products of I3 ^‒ and I5 ^‒ (Figure 24). More importantly, I5 ^‒ is demonstrated as the dominated polyiodide intermediate for I ^‒ /I2 conversion in starch-based Zn-I2 batteries, which is evidenced by the significantly strong intensity of I5 ^‒ signal compared to that of I3 ^‒ (Figure 23b). The I5 ^‒ has been already proved as the predominant specie in starch/polyiodide complex with a much stronger bonding with double-helix structure. Thus, an I5 ^‒ -dominated conversion mechanism could benefit to a shuttling-free Zn-I2 battery. [0130] The low CE and limited cycling life of Zn-I ₂ batteries can be ascribed to the dissolution of polyiodide in the electrolyte. And the dissolved polyiodide anions migrate to Zn anodes, leading to the aggravated corrosion of Zn anodes. Thus, the in-situ UV-vis spectra were further applied to monitor the dissolution of polyiodide during the cycle. A home-made quartz cell was designed for in-situ UV-vis experiments (Figure 25). Commercial quartz cell has two rough sides for handhold, and two smooth sides for light penetration. The cathode and metallic Zn anode were attached on each rough side, respectively. The electrolyte was fully filled into the quartz cell. During the cycling, the UV-vis light can pass through the smooth side of quartz cell to identify and quantify the dissolved polyiodide species. As shown in Figure 23c, with the KB cathode, the cell shows an increased absorbance of I ₃ ^‒ signal during the charging process, indicating the significant dissolution of I ₃ ^‒ . However, when replacing the cathode by starch, the absorbance of I ₃ ^‒ can maintain at a low level in the whole charging process (Figure 23d). The concentration of dissolved I ₃ ^‒ in the electrolyte solution is calculated and shown in Figure 23e. With the starch cathode, the concentration of I ₃ ^‒ in the electrolyte solution maintains at around 0.07 mM in the whole charging process. With the KB cathode, however, a much higher concentration of I ₃ ^‒ (0.13 mM) is obtained at initial charge state, and it increases to 0.15 mM at the end of charge process, which is over 2- time higher than that with starch cathode. The high I ₃ ^‒ dissolution in KB-based Zn-I ₂ batteries reveals the poor bonding strength between I ₃ ^‒ and KB, which well accords to the serious shuttle effect, low CE, and limited cycling life of KB-based Zn-I ₂ batteries. Benefiting from the comprehensive structure confinement of starch toward iodine species (I ^‒ , I ₃ ^‒ , I ₂ ), polyiodide anions can be tightly anchored at the cathode sides during the cycling, resulting in the suppressed shuttle effect. To further study the structure confinement of starch during the battery cycling, SEM images with corresponding EDS mapping of starch cathodes were collected at different charge/discharge states. Starch cathode maintains the similar morphology upon cycling. When charged to 1.3 V, the mapping result shows that iodine element uniformly distributes in the starch particles (Figure 23f). The generated I2 also can be well preserved by the starch as charged to 1.6 V (Figure 23g). Similar polyiodide and iodide anchoring in starch at the state of discharge to 1.3 V (Figure 23h) and 0.5 V (Figure 23i) also can be found in the I mapping images. The stronger I signal on the starch particles than surroundings indicates the significant capacity of iodine species gathering by starch. As a comparison, KB cathodes at different electrochemical states were also studied. As shown in Figure 26, the weak I signal can be observed at different electrochemical states, testifying the poor iodine species anchoring capacity of KB. These results highlight that the starch has a strong bonding interaction with iodine species during the battery operation, which leads to shuttle-free and high-reversible I ^‒ /I2 conversion. [0131] The impact of polyiodide on Zn anodes [0132] The relationship between shuttling polyiodide and the corrosion of Zn anodes in Zn-I2 batteries was studied. Linear polarization curves reveal a more negative corrosion potential and larger corrosion current density in triiodide-containing electrolyte compared to the electrolyte without triiodide, which indicates that shuttling polyiodide would deteriorate the Zn corrosion (Figure 27). As a result, a low CE (~98%) (Figure 28) and poor Zn plating/stripping stability (Figure 29) were obtained in triiodide- containing electrolyte. Except that, Zn foils were directly immersed into electrolytes with triiodide to investigate the impacts of triiodide on the Zn corrosion. As shown in Figure 30, the brown triiodide- containing electrolyte gradually turns into colorless after three-day resting. Corresponding UV-vis spectra reveal the triiodide absorbance signal disappears after resting (Figure 31), suggesting the directly chemical reaction between Zn and triiodide. XRD patterns and SEM images of Zn foils after immersion also show that the triiodide corrosion on Zn foils greatly accelerates the formation of by-products (Zn ₄ SO ₄ (OH) ₆ ∙xH ₂ O) (Figure 32-33). As a result, the direct reaction between polyiodide and Zn anodes would corrode the Zn anodes, which consumes the active Zn to form electrochemically inert by-products, shortening the cycling life of Zn-I ₂ battery. The I 3d XPS depth profiles of Zn foil after triiodide corrosion show no any iodine species from its surface to the bulk (Figure 34), indicating the polyiodide corrosion would consume the active Zn but not affect the ingredient of by-product. [0133] The polyiodide-induced Zn corrosion can aggravate the by-product generation, which consumes the active Zn and shortens the cycling life of Zn-I ₂ batteries. Thus, the investigation of the anode is critical for understanding the degradation of Zn-I ₂ battery. The structure confinement effect of starch endows a suppressive polyiodide shuttling, which retards the polyiodide-induced Zn corrosion. Digital images of cycled Zn anode in KB-based Zn-I ₂ battery also show obvious holes on its surface due to the shuttling polyiodide corrosion, which confirms the serious polyiodide shuttling when using KB cathodes (Figure 35). In contrast, the Zn electrode still shows a clean and unbroken surface after cycling in starch- based Zn-I ₂ battery. To further understand the impacts of Zn corrosion resulting from polyiodide shuttling, the XPS and AES depth profiles together with XRD and SEM technologies were conducted. As shown in Figure 36a, there are two main AES peaks located at 992.5 eV and 987.8 eV in Zn LMM spectra, which can be ascribed to the metallic Zn and Zn-O interaction, respectively. [25] The Zn-O AES peak is mainly ascribed to the by-product of Zn4SO4(OH)6, which can be evidenced by the same AES peak position compared with the Zn4SO4(OH)6 powder (Figure 37). The Zn anode cycled in starch-based Zn-I2 battery displays a gradually increased intensity for metallic Zn and decreased intensity for Zn4SO4(OH)6 with the etching depth increasing (Figure 36a). To quantify the amount of by-products generation, the differential spectra derived from Zn LMM spectra were analyzed. After differential analysis, the peaks in Zn LMM AES spectra can be split into couples of centrosymmetric peaks (Figure 38). And the bottom peak-to-background value shows linearity versus the species contents, [26] which can be used to calculate the intensity evolution of species on the Zn surface. The differential of Zn LMM spectra of Zn foils after cycled in KB-based and starch-based Zn-I2 batteries are shown in Figure 39. When coupling with starch cathodes, the intensity of metallic Zn peak after cycles gradually increases along with the further etching, while Zn4SO4(OH)6 peak intensity decreases (Figure 36b). These results can be further demonstrated by Zn 2p3/2 and S 2p spectra, as shown in Figure 36c. Zn anodes cycled in starch-based Zn-I2 battery exhibit only Zn compound (Zn ²⁺ ) on the surface. With the etching depth increasing, the binding energy shifts to a lower energy level, indicating the metallic Zn (Zn ⁰ ) domination.[27] Moreover, S 2p spectra also reveal the declined intensity of SO4 ^2‒ with the etching depth increasing,[28] which further confirms the thin Zn4SO4(OH)6-based passivated film generation in starch- based Zn-I ₂ battery (Figure 36d). The thin passivated film on Zn anode cycled in starch-based Zn-I ₂ battery is attributed to the suppressed polyiodide corrosion, which contributes to long-term stability when using starch. [0134] For the Zn anodes cycled in KB-based Zn-I ₂ battery, almost no metallic Zn peaks can be observed during the whole etching process, indicating that a thick by-products passivation film generates on Zn anode (Figure 36e). Calculated intensity evolution also shows negligible intensity change with the etching depth increasing, and no metallic Zn intensity can be observed, which is due to the serious Zn corrosion induced by the shuttling polyiodide in such battery (Figure 36f). Except that, there are almost no binding energy shifts in Zn 2p3/2 (Figure 36g) and intensity changes in SO ₄ ^2‒ peak with KB cathode (Figure 36h), which indicates a thick passivated film generation. The accumulation of by-product leads to the anode passivation and active Zn loss, which triggers the fast degradation of the Zn-I ₂ batteries. [0135] Zn anodes cycled in KB/starch-based Zn-I ₂ batteries were further characterized by SEM and XRD. The Zn foil cycled in starch-based Zn-I ₂ battery (Figure 36i) endows a much flatter surface with less by-product generation compared to the one cycled in KB-based Zn-I ₂ battery (Figure 36j). The XRD patterns further reveal the by-product generation on Zn anodes cycled in KB/starch-based Zn-I ₂ batteries (Figure 36k). The diffraction peak located at ~8.5° can be identified as the generation of Zn ₄ SO ₄ (OH) ₆ ∙4H ₂ O (JCPDS No.44-0673).[29] The Zn anode generates Zn ₄ SO ₄ (OH) ₆ ∙4H ₂ O by-product when cycled in the ZnSO4-based electrolytes.[3b] Compared to the Zn anode cycled in KB-based Zn-I2 battery, the one cycled in starch-based Zn-I ₂ battery shows a much lower diffraction peak intensity at ~8.5°, demonstrating the suppressed side reaction in starch-based Zn-I ₂ battery. Based on these results, introducing starch as polyiodide trapping material can significantly suppress the shuttle effect and inhibit the polyiodide corrosion and parasitic reactions on Zn anodes, which enables an ultra-stable, long-life, and shuttle-free Zn-I2 battery [0136] Zn-I2 batteries with ^-cyclodextrin modified carbon nanotubes ( ^-CD/CNTs) cathodes [0137] Chemical reagents [0138] Carbon nanotubes (CNTs) were purchased from Sinopharm Chemical Reagent Co., Ltd. Anhydrous LiI (>99.0%), I2 (>99.9%), ZnSO4·7H2O (A.R.), and anhydrous Li2SO4 (A.R.) were purchased from Shanghai International Aladdin Regent Inc. The Zn foil (15 μm in thickness), polytetrafluoroethylene aqueous dispersion (PTFE, 40 wt.% solid content), Ketjen black (KB), and glass fibers were provided by Canrd New Energy Technology Co., Ltd. The carbon cloth (W1S1010) was provided by CeTech Co., Ltd. ^−cyclodextrin and NaOH were purchased from sigma Aldrich. [0139] Preparation of ^-cyclodextrin modified carbon nanotubes ( ^-CD/CNTs) [0140] CNTs was treated by concentrated nitric acid under reflux at 100 °C for 1 hour. The treated CNTs was collected by filtration. Then treated CNTs was dispersed into a 6M NaOH solution, and CDs was dissolved into another 6 M NaOH solution. Then two as-obtained CNTs and CDs solutions were mixed and reacted at 60 °C for 6 hours to obtain ^-cyclodextrin modified CNTs (see Figure 40). [0141] Preparation of electrodes and electrolytes [0142] To prepare the ^-CD/CNTs positive electrode, ^-CD/CNTs was mixed with I ₂ or metal iodide and heated at 80 °C for about 10 hours to obtain I ₂ or metal iodide@host. The iodine content in ^- CD/CNTs was range from 30 wt% to 90 wt%. Then, the ^-CD/CNTs@I2 or ^-CD/CNTs@metal iodide (80wt%) prepared was mixed with a conductive agent (10 wt%) and PTFE or PVDF binder (10wt%) and then pressed onto carbon cloth. The electrolyte solution used was an aqueous solution containing a certain concentration of zinc salts. The electrolyte contains zinc salts (ZnSO ₄ , ZnCl2, ZnSO ₂ CF ₃ , Zn(TFSI) ₂ , Zn(ClO4)2, etc.) and water solvent. Li2SO4 can be included to improve the Zn anode reversibility. [0143] High-cyclability Zn-I2 batteries with ^-cyclodextrin modified carbon nanotubes ( ^-CD/CNTs) cathodes [0144] As shown in Figure 41, ^-cyclodextrin modified CNTs@I2 can deliver a capacity of 140.2 mAh g ^-1 at a current density of 4.0 A g ^-1 . A stable cycling can well preserve for over 20000 cycles with an only slight capacity fading (Figure 41). Besides, excellent rate capability and cycling stability also can be observed at a current density of 6 A g-1. A high specific capacity of 110 mAh g ^-1 was performed by using ^-cyclodextrin modified CNTs@I2, and still maintained at 100 mAh g ^-1 for over 30000 cycles (Figure 42). The corresponding charge-discharge curves reveal that there is almost no battery polarization increase after 30000 cycles, and the capacity fading is controlled within 10 mAh g ^-1 (Figure 43). A stable cycling for over 50000 cycles at a current density of 10 A g ^-1 also can be achieved with ^-CD/CNTs@I ₂ cathodes (Figure 44). An outstanding cycling lifespan of over 100000 cycles can be achieved at 20 A g ^-1 , demonstrating excellent polyiodide confinement of ^-CD/CNTs host (Figure 45). [0145] Zn-Br2 batteries with ^-cyclodextrin modified carbon nanotubes ( ^-CD/CNTs) cathodes [0146] Chemical reagents [0147] Carbon nanotubes (CNTs) were purchased from Sinopharm Chemical Reagent Co., Ltd. Anhydrous LiBr (>99.0%), Br ₂ (>99.9%), ZnSO ₄ ·7H ₂ O (A.R.), and anhydrous Li ₂ SO ₄ (A.R.) were purchased from Shanghai International Aladdin Regent Inc. The Zn foil (15 μm in thickness), polytetrafluoroethylene aqueous dispersion (PTFE, 40 wt.% solid content), Ketjen black (KB), and glass fibers were provided by Canrd New Energy Technology Co., Ltd. The carbon cloth (W1S1010) was provided by CeTech Co., Ltd. ^-cyclodextrin and NaOH were purchased from sigma Aldrich. ^- cyclodextrin modified carbon nanotubes ( ^-CD/CNTs) were prepared as above (see Figure 40). [0148] Preparation of electrodes and electrolytes [0149] To prepare the ^-CD/CNTs positive electrode, ^-CD/CNTs was mixed with Br2 or metal bromide and heated at 80 °C for about 10 hours to obtain I2 or metal bromide@host. The bromide content in ^-CD/CNTs was range from 30 wt% to 90 wt%. Then, the ^-CD/CNTs@Br2 or ^-CD/CNTs@metal bromide prepared was mixed with a conductive agent (10 wt%) and PTFE or PVDF binder (10wt%) and then pressed onto carbon cloth. The electrolyte solution used was an aqueous solution containing a certain concentration of zinc salts. The electrolyte contains zinc salts (ZnSO4, ZnCl2, ZnSO2CF3, Zn(TFSI)2, Zn(ClO ₄ ) ₂ , etc.) and water solvent. Li ₂ SO ₄ can be included to improve the Zn anode reversibility. [0150] High-cyclability Zn-Br2 batteries with ^-cyclodextrin modified carbon nanotubes ( ^-CD/CNTs) cathodes [0151] Zn-Br ₂ battery suffers from similar shuttle effect compared with Zn-I ₂ batteries. Cyclodextrin also presents significant functions on suppressing the shuttle effect of polybromide. As shown in Figure 46, ^-CD/CNTs@LiBr cathode can deliver a reversible capacity of 245 mAh g ^-1 at 5 A g ^-1 , and a stable cycling of 5000 cycles was achieved. Charge-discharge curves shown that Zn-Br ₂ battery can allow an over 1.6 V output potential with a 245 mAh g ^-1 capacity. [0152] In summary, it is demonstrated that use of a functional carbohydrate in the positive electrode can strongly anchor polyiodide and polybromide species. This structure confinement strategy allows a highly reversible conversion reaction with a high Coulombic Efficiency and a high specific capacity and enables long-life and shuttling free batteries. [0153] The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that such prior art forms part of the common general knowledge. [0154] It will be understood that the terms “comprise” and “include” and any of their derivatives (e.g. comprises, comprising, includes, including) as used in this specification, and the claims that follow, is to be taken to be inclusive of features to which the term refers, and is not meant to exclude the presence of any additional features unless otherwise stated or implied. [0155] In some cases, a single embodiment may, for succinctness and/or to assist in understanding the scope of the disclosure, combine multiple features. It is to be understood that in such a case, these multiple features may be provided separately (in separate embodiments), or in any other suitable combination. Alternatively, where separate features are described in separate embodiments, these separate features may be combined into a single embodiment unless otherwise stated or implied. This also applies to the claims which can be recombined in any combination. That is a claim may be amended to include a feature defined in any other claim. Further a phrase referring to “at least one of” a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover: a, b, c, a-b, a-c, b-c, and a-b-c. [0156] It will be appreciated by those skilled in the art that the disclosure is not restricted in its use to the particular application or applications described. Neither is the present disclosure restricted in its preferred embodiment with regard to the particular elements and/or features described or depicted herein. It will be appreciated that the disclosure is not limited to the embodiment or embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the scope as set forth and defined by the following claims.

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