SULFUR CATHODE

FIELD OF THE DISCLOSURE

[0001] The present disclosure relates to double-shell encapsulated sulfur composites suitable for use as cathodes in lithium-sulfur batteries.

BACKGROUND OF THE DISCLOSURE

[0002] Increasing energy demands and environmental considerations have led to a search for more environmentally friendly energy storage systems that are safe, low cost, and that have high energy densities. Lithium-sulfur batteries are among the more promising energy storage devices and have attracted attention in recent years due to: (1) a high theoretical capacity of up to 1672 milliamp hour per gram (mAh/g), which is over 5 times that of currently used transition metal oxide cathode materials; (2) a relative low cost due to abundant resources of sulfur; and (3) the nonhazardous and environmentally benign nature of the components. The practical application of Li-S cells is still limited by several drawbacks, however, including: (1) the poor electrical conductivity of sulfur (5 10 ⁰ siemens per centimeter (S/cm)) limits the utilization efficiency of the active material and the rate capability; (2) the high solubility of polysulfide intermediates in the electrolyte results in a shuttling effect in the charge-discharge process; and (3) a large volumetric expansion (-80%) during charge and discharge results in rapid capacity decay and low Coulombic efficiency.

[0003] The high capacity and cycling ability of sulfur arises from the electrochemical cleavage and re-formation of sulfur-sulfur bonds in the cathode, which is believed to proceed in two steps. First, the reduction of sulfur to lithium higher poly sulfides (LriSn, 4 < n < 8) is followed by further reduction to lithium lower polysulfides (LriSn, 1 < n < 3). The higher polysulfides are easily dissolved into the organic liquid electrolyte, enabling them to penetrate through the polymer separator and react with the lithium metal anode, leading to the loss of sulfur active materials. Even if some of the dissolved poly sulfides could diffuse back to the cathode during the recharge process, the sulfur particles formed on the surface of the cathode are electrochemically inactive owing to the poor conductivity. Such a degradation path leads to poor capacity retention, especially during long cycling (i.e., more than 100 cycles). [0004] In order to improve the capacity and improve the conductivity and prevent the polysulfide dissolution and shuttling, several different approaches have been developed during the past few decades. One strategy that has had success is the encapsulation of sulfur to prevent the leakage of active materials and suppress the shuttle effect of high order LriSn (Li ₂ S n, 4 < n < 8). A yolk-shell concept was proposed and demonstrated by Wei Seh el al. via sulfur@Ti02 yolk-shell nanoparticles which were proven as a superior cathode for Li-S batteries with excellent cycling stability. Wei Seh, Z. et al. , Sulphur-Ti02 yolk-shell nanoarchitecture with internal void space for long-cycle lithium-sulphur batteries, Nature Communications, 4, 1331 (2013). This group also developed an alternative approach to confine sulfur with voids in the form of hollow sulfur nanoparticles coated with a thin layer of polyvinylpyrrolidone that appeared promising. The sulfur-based yolk-shell nanostructure was further developed using a conducting polymer shell, polyaniline, and the cycling stability was demonstrated in Li-S batteries. Sulfur-carbon yolk-shell particles have also been synthesized with sulfur fully confined inside the conductive carbon shells, with the filling content of sulfur controlled and fine-tuned.

[0005] A second approach is the controllable deposition of the discharge product

L12S, which is an ionic and electronic insulator. Metal oxides have been used to trap polysulfides to enhance cyclability of the Li-S battery via chemical adsorption. It has been reported that the composite cathode materials based on MgO/C, La203/C and CeCh/C nanoflakes showed higher capacity and better cycling performance.

[0006] A third approach is to use L12S as a starting cathode material, which undergoes volumetric contraction instead of the expansion in the case of sulfur.

[0007] Each of these approaches, while demonstrating potential for incorporation into

Li-S batteries, has not fully overcome the drawbacks discussed herein.

These and other shortcomings are addressed by aspects of the present disclosure.

SUMMARY

[0008] Aspects of the disclosure relate to methods of preparing a double-shell encapsulated sulfur composite, the composite including a hollow sulfur core, an inner shell including manganese dioxide and an outer shell including a polymeric material, the method including either:

(a) applying the inner shell including manganese dioxide to the hollow sulfur core and applying the outer shell including the polymeric material to the inner shell; or (b) applying the outer shell including the polymeric material to the hollow sulfur core and impregnating manganese dioxide through the outer shell so that it forms the inner shell between the hollow sulfur core and the outer shell.

The hollow sulfur core includes a single particle of sulfur having a hollow interior core.

[0009] In further aspects the disclosure relates to methods of preparing a double-shell encapsulated sulfur composite, the composite including a single yolk-core including sulfur, an inner shell including manganese dioxide and an outer shell including a polymeric material, the method including:

(a) either

(i) applying the inner shell including manganese dioxide to a solid sulfur core and applying the outer shell including the polymeric material to the inner shell, or

(ii) applying the outer shell including the polymeric material to the solid sulfur core and impregnating manganese dioxide through the outer shell so that it forms the inner shell between the solid sulfur core and the outer shell; and

(b) causing the solid sulfur core to form the single yolk-core.

[0010] In yet further aspects the disclosure relates to a double-shell encapsulated sulfur composite, including: a sulfur core; an inner shell including manganese dioxide; and an outer shell including a polymeric material. The sulfur core includes either (1) a single particle of sulfur having a hollow interior core or (2) a single yolk-core.

[0011] The double-shell encapsulated sulfur composite may be suitable for use as a cathode material for lithium-sulfur electrodes. The hollow sulfur core or yolk-core provides a void to accommodate the volume expansion of sulfur during lithiation (S/LriS, -80% of volume increase). The manganese dioxide (MnCh) shell functions as a polysulfide absorbent. The polymeric (e.g., polyaniline) shell functions to block the open pores of MnCh. thereby minimizing the opportunity for polysulfides to leach into the electrolytes of the Li-S battery.

BRIEF DESCRIPTION OF THE FIGURES

[0012] In the drawings, which are not necessarily drawn to scale, like numerals may describe similar components in different views. Like numerals having different letter suffixes may represent different instances of similar components. The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments discussed in the present document.

[0013] FIG. 1 is a block diagram illustrating methods for preparing a double-shell encapsulated sulfur composite according to an aspect of the disclosure.

[0014] FIGS. 2A and 2B are process flow diagrams illustrating methods for preparing a double-shell encapsulated sulfur composite according to aspects of the disclosure.

[0015] FIG. 3 provides chemical structures for exemplary conductive polymers that may be used in methods according to aspects of the disclosure.

[0016] FIG. 4 is a block diagram illustrating methods for preparing a double-shell encapsulated sulfur composite according to an aspect of the disclosure.

[0017] FIGS. 5A-5C are process flow diagrams illustrating methods for preparing a double-shell encapsulated sulfur composite according to aspects of the disclosure.

[0018] FIGS. 6A-6D are images and data relating to sulfur particles formed according to aspects of the disclosure.

[0019] FIGS. 7A-7D are images and data relating to MnCh-coated sulfur particles formed according to aspects of the disclosure.

[0020] FIGS. 8A-8D are images and data relating to sulfur-MnCh-poly dopamine core-shell and yolk-shell particles formed according to aspects of the disclosure.

[0021] FIG. 9 shows the thermogravimetric analysis (TGA) of core-shell and yolk- shell sulfur-MnCh-poly dopamine particles formed according to aspects of the disclosure.

DETAILED DESCRIPTION

[0022] The present disclosure can be understood more readily by reference to the following detailed description of the disclosure and the Examples included therein. In various aspects, the present disclosure pertains to methods of preparing a double-shell encapsulated sulfur composite, the composite including either a hollow sulfur core or a yolk- core, an inner shell including manganese dioxide and an outer shell including a polymeric material. One method in which the composite includes a hollow sulfur core includes either:

(a) applying the inner shell including manganese dioxide to the hollow sulfur core and applying the outer shell including the polymeric material to the inner shell; or

(b) applying the outer shell including the polymeric material to the hollow sulfur core and impregnating manganese dioxide through the outer shell so that it forms the inner shell between the hollow sulfur core and the outer shell, wherein the hollow sulfur core includes a single particle of sulfur having a hollow interior core.

[0023] Another method in which the composite includes a yolk-core includes:

(a) either

(i) applying the inner shell including manganese dioxide to a solid sulfur core and applying the outer shell including the polymeric material to the inner shell, or

(ii) applying the outer shell including the polymeric material to the solid sulfur core and impregnating manganese dioxide through the outer shell so that it forms the inner shell between the solid sulfur core and the outer shell; and

(b) causing the solid sulfur core to form the single yolk-core.

[0024] Before the present compounds, compositions, articles, systems, devices, and/or methods are disclosed and described, it is to be understood that they are not limited to specific synthetic methods unless otherwise specified, or to particular reagents unless otherwise specified, as such can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting.

[0025] Various combinations of elements of this disclosure are encompassed by this disclosure, e.g., combinations of elements from dependent claims that depend upon the same independent claim.

[0026] Moreover, it is to be understood that unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not actually recite an order to be followed by its steps or it is not otherwise specifically stated in the claims or descriptions that the steps are to be limited to a specific order, it is no way intended that an order be inferred, in any respect. This holds for any possible non-express basis for interpretation, including: matters of logic with respect to arrangement of steps or operational flow; plain meaning derived from grammatical organization or punctuation; and the number or type of embodiments described in the specification.

[0027] All publications mentioned herein are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited. Definitions

[0028] It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting. As used in the specification and in the claims, the term“comprising” can include the embodiments “consisting of’ and“consisting essentially of.” Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. In this specification and in the claims which follow, reference will be made to a number of terms which shall be defined herein.

[0029] As used in the specification and the appended claims, the singular forms“a,”

“an” and“the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to“a polymeric material” includes mixtures of two or more polymeric materials.

[0030] As used herein, the term“combination” is inclusive of blends, mixtures, alloys, reaction products, and the like.

[0031] Ranges can be expressed herein as from one value (first value) to another value (second value). When such a range is expressed, the range includes in some aspects one or both of the first value and the second value. Similarly, when values are expressed as approximations, by use of the antecedent‘about,’ it will be understood that the particular value forms another aspect. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. It is also understood that there are a number of values disclosed herein, and that each value is also herein disclosed as“about” that particular value in addition to the value itself. For example, if the value“10” is disclosed, then“about 10” is also disclosed. It is also understood that each unit between two particular units are also disclosed. For example, if 10 and 15 are disclosed, then 11, 12, 13, and 14 are also disclosed.

[0032] As used herein, the terms“about” and“at or about” mean that the amount or value in question can be the designated value, approximately the designated value, or about the same as the designated value. It is generally understood, as used herein, that it is the nominal value indicated ±10% variation unless otherwise indicated or inferred. The term is intended to convey that similar values promote equivalent results or effects recited in the claims. That is, it is understood that amounts, sizes, formulations, parameters, and other quantities and characteristics are not and need not be exact, but can be approximate and/or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like, and other factors known to those of skill in the art. In general, an amount, size, formulation, parameter or other quantity or characteristic is“about” or“approximate” whether or not expressly stated to be such. It is understood that where “about” is used before a quantitative value, the parameter also includes the specific quantitative value itself, unless specifically stated otherwise.

[0033] Disclosed are the components to be used to prepare the compositions of the disclosure as well as the compositions themselves to be used within the methods disclosed herein. These and other materials are disclosed herein, and it is understood that when combinations, subsets, interactions, groups, etc. of these materials are disclosed that while specific reference of each various individual and collective combinations and permutation of these compounds cannot be explicitly disclosed, each is specifically contemplated and described herein. For example, if a particular compound is disclosed and discussed and a number of modifications that can be made to a number of molecules including the compounds are discussed, specifically contemplated is each and every combination and permutation of the compound and the modifications that are possible unless specifically indicated to the contrary. Thus, if a class of molecules A, B, and C are disclosed as well as a class of molecules D, E, and F and an example of a combination molecule, A-D is disclosed, then even if each is not individually recited each is individually and collectively

contemplated meaning combinations, A-E, A-F, B-D, B-E, B-F, C-D, C-E, and C-F are considered disclosed. Likewise, any subset or combination of these is also disclosed. Thus, for example, the sub-group of A-E, B-F, and C-E would be considered disclosed. This concept applies to all aspects of this application including, but not limited to, steps in methods of making and using the compositions of the disclosure. Thus, if there are a variety of additional steps that can be performed it is understood that each of these additional steps can be performed with any specific aspect or combination of aspects of the methods of the disclosure.

[0034] As used herein the terms“weight percent,”“wt%,” and“wt. %,” which can be used interchangeably, indicate the percent by weight of a given component based on the total weight of the composition, unless otherwise specified. That is, unless otherwise specified, all wt% values are based on the total weight of the composition. It should be understood that the sum of wt% values for all components in a disclosed composition or formulation are equal to 100

[0035] Unless otherwise stated to the contrary herein, all test standards are the most recent standard in effect at the time of filing this application. [0036] Each of the materials disclosed herein are either commercially available and/or the methods for the production thereof are known to those of skill in the art.

[0037] It is understood that the compositions disclosed herein have certain functions.

Disclosed herein are certain structural requirements for performing the disclosed functions and it is understood that there are a variety of structures that can perform the same function that are related to the disclosed structures, and that these structures will typically achieve the same result.

Methods of preparing double-shell encapsulated sulfur composite

[0038] Double-shell encapsulated sulfur composite with a hollow sulfur core

[0039] With reference to FIGS. 1, 2A and 2B, aspects of the disclosure relate to methods 100 for preparing a double-shell encapsulated sulfur composite 200. The composite 200 includes a hollow sulfur core 210, an inner shell 220 including manganese dioxide and an outer shell 230 including a polymeric material. The hollow sulfur core 210 includes a single particle of sulfur having a hollow interior core.

[0040] The method 100 for preparing the double-shell encapsulated sulfur composite

200 begins with the hollow sulfur core 210. The hollow sulfur core 210 may be formed according to conventional methods, such as by dissolving sodium thiosulfate (Na2S2Ch) and polyvinylpyrrolidone (PVP) in water and then stirring the solution with hydrochloric acid.

[0041] In one aspect, at step 110, the inner shell 220 including manganese dioxide is applied to the hollow sulfur core 210, and at step 120 the outer shell 230 including the polymeric material is applied to the inner shell 220.

[0042] In another aspect, at step 130, the outer shell 230 including the polymeric material is applied to the hollow sulfur core 210, and at step 140 manganese dioxide is impregnated through the outer shell 230 so that it forms the inner shell 220 between the hollow sulfur core 210 and the outer shell 230.

[0043] The step of applying the inner shell 220 including manganese dioxide to the hollow sulfur core 210 at step 110 includes in some aspects combining the hollow sulfur core 210 with a solution including potassium permanganate and heating the solution. In further aspects the solution further includes manganese sulfate. The reaction to form the

manganese(IV) oxide (MnCh) shell can proceed in accordance with one or both of the following equations:

3 MnSOr + 2 KMnOr + 2 H2O = 5 MnCh + K2SO4 + 2 H2SO4 (1)

2 KMnCri + S = K2SO4 + 2 MnCh (2) [0044] The step of applying the outer shell 230 including the polymeric material at either step 120 or step 130 includes polymerizing the polymeric material into the outer shell. Polymerization may be performed according to known methods by mixing the particles (hollow sulfur cores 210 with or without an inner shell 220 applied thereon) with the polymer precursor and a polymerization initiator (e.g., ammonium persulfate).

[0045] In some aspects the polymeric material is conductive. Exemplary conductive polymeric materials include, but are not limited to, polyaniline, polyparaphenylene vinylene, polyisothianaphthalene, polypyrrole, polythiophene, polyparaphenylene sulfide,

polyparaphenylene, polyacetylene, polycarbazole, polyindole, polyfluorene,

polyparaphenylene, ethynylene, and combinations thereof. Chemical structures for these materials are shown in FIG. 3.

[0046] In further aspects the polymeric material is non-conductive. Exemplary non- conductive polymeric materials include, but are not limited to, poly dopamine,

polyacrylonitrile, polyalkylene, polystyrene, polyacrylate, polyhalide, polyester,

polycarbonate, polyimide, phenol formaldehyde resin, epoxy, polyalkylene glycol, polysaccharide, polyethylene, polypropylene, polymethylmethacrylate, polyvinyl chloride, polyethylene terephthalate, polyethylene glycol, polypropylene glycol, starch, glycogen, cellulose, chitin, one or more polymers polymerized from poly(ethylene glycol) diacrylate (PEGDA), poly(ethylene glycol) dimethacrylate (PEGDMA), poly(ethylene glycol) methyl ether acrylate (PEGMEA), poly(ethylene glycol) methyl ether methacrylate (PEGMEMA), mono-acrylate and vinylene carbonate, and combinations thereof.

[0047] In some aspects the step of impregnating manganese dioxide through the outer shell 230 so that it forms the inner shell 220 between the hollow sulfur core 210 and the outer shell 230 (step 140) includes combining the hollow sulfur core 2l0/outer shell 230 with a solution including potassium permanganate and heating the combination. Manganese dioxide forms according to one or both of the reactions (1) and (2) described above and diffuses through the polymeric material in the outer shell 230 and forms the inner shell 220 between the hollow sulfur core 210 and the outer shell 230.

[0048] In some aspects the double-shell encapsulated sulfur composite 200 may further include a metal oxide. The metal oxide may function to trap poly sulfides, such as when the double-shell encapsulated sulfur composite 200 is used in a cathode of a lithium- sulfur battery. The metal oxide may be included in the double-shell encapsulated sulfur composite 200 in any suitable manner. In one aspect the metal oxide is added with the sulfur (such as by grinding) to form a metal oxide/sulfur composite. The metal oxide/sulfur composite may then be reacted with KMnCri to encapsulate it. In further aspects the metal oxide may be absorbed on the surface of the MnCh shell. Exemplary metal oxides suitable for use in aspects of the disclosure include, but are not limited to, MnCh. MnO, M Ch, C03O4, C02O3, CoO, NiO, RuCh, AI2O3, TiCh, Fe203, FeO, Fe30 ₄ , V2O5, MgO, CaO, Ce02, La203, SnCh, ZnO, CuO, Cr203, W2O3, CdO, SC2O3, TriCh, or any combination thereof.

[0049] In some aspects the double-shell encapsulated sulfur composite formed according to the method 100 has a particle size of from 5 nanometers (nm) to 50 micrometers (pm).

[0050] Double-shell encapsulated sulfur composite with a yolk-core

[0051] With reference to FIGS. 4, 5A, 5B and 5C aspects of the disclosure further relate to methods 400 for preparing a double-shell encapsulated sulfur composite 500. The composite 500 includes a single yolk-core 510 including sulfur, an inner shell 520 including manganese dioxide and an outer shell 530 including a polymeric material.

[0052] The method 400 for preparing the double-shell encapsulated sulfur composite

500 begins with the solid sulfur core 540.

[0053] In one aspect, at step 410, the inner shell 520 including manganese dioxide is applied to the solid sulfur core 540, and at step 420 the outer shell 530 including the polymeric material is applied to the inner shell 520.

[0054] In another aspect, at step 430, the outer shell 530 including the polymeric material is applied to the solid sulfur core 540, and at step 440 manganese dioxide is impregnated through the outer shell 530 so that it forms the inner shell 520 between the solid sulfur core 540 and the outer shell 530.

[0055] In some aspects, following formation of the double-shell encapsulated sulfur composite 500 including the solid sulfur core 540, the inner shell 520 including manganese dioxide and the outer shell 530 including a polymeric material - via either steps 410/420 or steps 430/440 - the single yolk-core 510 is formed from the solid sulfur core 540 at step 450.

[0056] In other aspects, as illustrated in FIG. 5C and the right column of FIG. 4, the single yolk-core 510 is formed from the solid sulfur core 540 at step 450 after the outer shell 530 including the polymeric material is applied to the solid sulfur core 540 at step 430, and then manganese dioxide is impregnated through the outer shell 530 so that it forms the inner shell 520 between the single yolk-core 510 and the outer shell 530. In such aspects, the inner shell 520 may form around the single yolk-core 510 as illustrated in FIG. 5C.

[0057] The step of applying the inner shell 520 including manganese dioxide to the solid sulfur core 540 at step 410 includes in some aspects combining the solid sulfur core 540 with a solution including potassium permanganate and heating the solution. In further aspects the solution further includes manganese sulfate. The reaction to form the

manganese(IV) oxide (MnC ) shell can proceed in accordance with one or both of equations (1) and (2) described above.

[0058] The step of applying the outer shell 530 including the polymeric material at either step 420 or step 430 includes polymerizing the polymeric material into the outer shell. Polymerization may be performed according to known methods by mixing the particles (solid sulfur cores 540 with or without an inner shell 520 applied thereon) with the polymer precursor and a polymerization initiator (e.g., ammonium persulfate).

[0059] In some aspects the polymeric material is conductive. Exemplary conductive polymeric materials include, but are not limited to, the conductive polymeric materials described above.

[0060] In further aspects the polymeric material is non-conductive. Exemplary non- conductive polymeric materials include, but are not limited to, the non-conductive polymeric materials described above.

[0061] In some aspects the step of impregnating manganese dioxide through the outer shell 530 so that it forms the inner shell 520 between the solid sulfur core 540 and the outer shell 530 (step 440) includes combining the solid sulfur core 540/outer shell 530 with a solution including potassium permanganate and heating the combination. Manganese dioxide forms according to one or both of the reactions (1) and (2) described above and diffuses through the polymeric material in the outer shell 530 and forms the inner shell 520 between the solid sulfur core 540 and the outer shell 530.

[0062] The step of causing the solid sulfur core 540 to form the single yolk-core 510 includes applying a vacuum to the double-shell encapsulated sulfur composite 500. The vacuum causes the solid sulfur core 540 to contract/shrink, resulting in formation of the yolk- core 510 and a void within the core of the double-shell encapsulated sulfur composite 500.

[0063] In some aspects the double-shell encapsulated sulfur composite 500 may further include a metal oxide. The metal oxide may function to trap poly sulfides, such as when the double-shell encapsulated sulfur composite 500 is used in a cathode of a lithium- sulfur battery. The metal oxide may be included in the double-shell encapsulated sulfur composite 500 in any suitable manner. In one aspect the metal oxide is added with the sulfur (such as by grinding) to form a metal oxide/sulfur composite. The metal oxide/sulfur composite may then be reacted with KMnCri to encapsulate it. In further aspects the metal oxide may be absorbed on the surface of the MnCh shell. Exemplary metal oxides suitable for use in aspects of the disclosure include, but are not limited to, MnCh. MnO, MmCb, C03O4, C02O3, CoO, NiO, RU0 ₂ , AI2O3, T1O2, Fe ₂ 03, FeO, Fe304, V2O5, MgO, CaO, CeCh, La ₂ 03, SnC , ZnO, CuO, CnCb, W2O3, CdO, SC2O3, T14O7, or any combination thereof.

[0064] In some aspects the double-shell encapsulated sulfur composite formed according to the method 400 has a particle size of from 5 nm to 50 pm.

Double-shell encapsulated sulfur composites

[0065] Aspects of the disclosure further relate to a double-shell encapsulated sulfur composite 200/500, including: a sulfur core; an inner shell 220/520 including manganese dioxide; an outer shell 230/530 including a polymeric material. The sulfur core includes either (1) a single particle of sulfur having a hollow interior core (a hollow sulfur core 210) or (2) a single yolk-core (510). The polymeric material may include, but is not limited to, the conductive or non-conductive materials described above.

Lithium-Sulfur Battery

[0066] Aspects of the disclosure further relate to a lithium-sulfur battery including a plurality of the double-shell encapsulated sulfur composites 200/500 described herein. The double-shell encapsulated sulfur composites 200/500 can individually include any of the features described herein and can be formed according to any of the methods described herein.

[0067] The lithium-sulfur battery includes in some aspects a cathode, an anode and an electrolyte. The cathode includes a plurality of the double-shell encapsulated sulfur composites 200/500.

[0068] The resulting double-shell encapsulated sulfur composite provides the following advantages:

the hollow sulfur core/single yolk-core, which includes a void in the core of the composite, accommodates for volume expansion of sulfur during lithiation (S/L12S, -80% of volume increase);

the MnCh particles in the MOC shell provide a good absorbent to absorb poly sulfide, which can decrease the amount of poly sulfide diffusing into the electrolytes;

the polymer shell can prevent polysulfide from leaching into the electrolyte in the lithium-sulfur battery; and

if a conductive (e.g., poly aniline) shell is used, it contributes to the conductivity of the cathode material in the battery. [0069] Various combinations of elements of this disclosure are encompassed by this disclosure, e.g., combinations of elements from dependent claims that depend upon the same independent claim.

Aspects of the Disclosure

[0070] In various aspects, the present disclosure pertains to and includes at least the following aspects.

[0071] Aspect 1: A method of preparing a double-shell encapsulated sulfur composite, the composite comprising a hollow sulfur core, an inner shell comprising manganese dioxide and an outer shell comprising a polymeric material, the method comprising either:

(a) applying the inner shell comprising manganese dioxide to the hollow sulfur core and applying the outer shell comprising the polymeric material to the inner shell; or

(b) applying the outer shell comprising the polymeric material to the hollow sulfur core and impregnating manganese dioxide through the outer shell so that it forms the inner shell between the hollow sulfur core and the outer shell,

wherein the hollow sulfur core comprises a single particle of sulfur having a hollow interior core.

[0072] Aspect 2: The method according to Aspect 1, wherein applying the inner shell comprising manganese dioxide to the hollow sulfur core in step (a) comprises combining the hollow sulfur core with a solution comprising potassium permanganate and optionally manganese sulfate and heating the combination.

[0073] Aspect 3: The method according to Aspect 1 or 2, wherein applying the outer shell comprising the polymeric material in either step (a) or step (b) comprises polymerizing the polymeric material into the outer shell.

[0074] Aspect 4: The method according to any of Aspects 1 to 3, wherein the polymeric material is conductive and comprises polyaniline, polyparaphenylene vinylene, polyisothianaphthalene, polypyrrole, polythiophene, polyparaphenylene sulfide,

polyparaphenylene, polyacetylene, polycarbazole, polyindole, polyfluorene,

polyparaphenylene, ethynylene, or combinations thereof.

[0075] Aspect 5: The method according to any of Aspects 1 to 3, wherein the polymeric material is non-conductive and comprises polydopamine, polyacrylonitrile, polyalkylene, polystyrene, polyacrylate, polyhalide, polyester, polycarbonate, polyimide, phenol formaldehyde resin, epoxy, polyalkylene glycol, polysaccharide, polyethylene, polypropylene, polymethylmethacrylate, polyvinyl chloride, polyethylene terephthalate, polyethylene glycol, polypropylene glycol, starch, glycogen, cellulose, chitin, one or more polymers polymerized from poly(ethylene glycol) diacrylate (PEGDA), poly(ethylene glycol) dimethacrylate (PEGDMA), poly(ethylene glycol) methyl ether acrylate (PEGMEA), poly(ethylene glycol) methyl ether methacrylate (PEGMEMA), mono-acrylate and vinylene carbonate, or combinations thereof.

[0076] Aspect 6: The method according to any of Aspects 1 to 5, wherein impregnating manganese dioxide through the outer shell so that it forms the inner shell between the hollow sulfur core and the outer shell in step (b) comprises:

combining the hollow sulfur core comprising the outer shell comprising the polymeric material with a solution comprising potassium permanganate; and

heating the combination.

[0077] Aspect 7: The method according to any of Aspects 1 to 6, wherein the double shell encapsulated sulfur composite has a particle size of from 5 nanometers (nm) to 50 micrometers (pm).

[0078] Aspect 8: A method of preparing a double-shell encapsulated sulfur composite, the composite comprising a single yolk-core comprising sulfur, an inner shell comprising manganese dioxide and an outer shell comprising a polymeric material, the method comprising:

(a) either

(i) applying the inner shell comprising manganese dioxide to a solid sulfur core and applying the outer shell comprising the polymeric material to the inner shell, or

(ii) applying the outer shell comprising the polymeric material to the solid sulfur core and impregnating manganese dioxide through the outer shell so that it forms the inner shell between the solid sulfur core and the outer shell; and

(b) causing the solid sulfur core to form the single yolk-core.

[0079] Aspect 9: The method according to Aspect 8, wherein applying the inner shell comprising manganese dioxide to the solid sulfur core in step (a) comprises combining the solid sulfur core with a solution comprising potassium permanganate and optionally manganese sulfate and heating the combination.

[0080] Aspect 10: The method according to Aspect 8 or 9, wherein applying the outer shell comprising the polymeric material in either step (a)(i) or step (a)(ii) comprises polymerizing the polymeric material into the outer shell. [0081] Aspect 11 : The method according to any of Aspects 8 to 10, wherein the polymeric material is conductive and comprises polyaniline, polyparaphenylene vinylene, polyisothianaphthalene, polypyrrole, polythiophene, polyparaphenylene sulfide,

polyparaphenylene, polyacetylene, polycarbazole, polyindole, polyfluorene,

polyparaphenylene, ethynylene, or combinations thereof.

[0082] Aspect 12: The method according to any of Aspects 8 to 10, wherein the polymeric material is non-conductive and comprises polydopamine, polyacrylonitrile, polyalkylene, polystyrene, polyacrylate, polyhalide, polyester, polycarbonate, polyimide, phenol formaldehyde resin, epoxy, polyalkylene glycol, polysaccharide, polyethylene, polypropylene, polymethylmethacrylate, polyvinyl chloride, polyethylene terephthalate, polyethylene glycol, polypropylene glycol, starch, glycogen, cellulose, chitin, one or more polymers polymerized from poly(ethylene glycol) diacrylate (PEGDA), poly(ethylene glycol) dimethacrylate (PEGDMA), poly(ethylene glycol) methyl ether acrylate (PEGMEA), poly(ethylene glycol) methyl ether methacrylate (PEGMEMA), mono-acrylate and vinylene carbonate, or combinations thereof.

[0083] Aspect 13: The method according to any of Aspects 9 to 12, wherein impregnating manganese dioxide through the outer shell so that it forms the inner shell between the hollow sulfur core and the outer shell in step (a)(ii) comprises:

combining the hollow sulfur core comprising the outer shell comprising the polymeric material with a solution comprising potassium permanganate; and

heating the combination.

[0084] Aspect 14: The method according to any of Aspects 8 to 13, wherein the double-shell encapsulated sulfur composite has a particle size of from 5 nm to 50 pm.

[0085] Aspect 15: The method according to any of Aspects 8 to 14, wherein causing the solid sulfur core to form the single yolk-core comprises applying a vacuum to the double shell encapsulated sulfur composite.

[0086] Aspect 16: The method according to any of Aspects 8 to 15, wherein the step of causing the solid sulfur core to form the single yolk-core is performed prior to

impregnating manganese dioxide through the outer shell in step (a)(ii).

[0087] Aspect 17: A double-shell encapsulated sulfur composite, comprising:

a sulfur core;

an inner shell comprising manganese dioxide; and

an outer shell comprising a polymeric material, wherein the sulfur core comprises either (1) a single particle of sulfur having a hollow interior core or (2) a single yolk-core.

[0088] Aspect 18: The double-shell encapsulated sulfur composite according to

Aspect 17, wherein the polymeric material is conductive and comprises poly aniline, polyparaphenylene vinylene, polyisothianaphthalene, polypyrrole, polythiophene, polyparaphenylene sulfide, polyparaphenylene, polyacetylene, polycarbazole, polyindole, polyfluorene, polyparaphenylene, ethynylene, or combinations thereof.

[0089] Aspect 19: The double-shell encapsulated sulfur composite according to

Aspect 17, wherein the polymeric material is non-conductive and comprises poly dopamine, polyacrylonitrile, polyalkylene, polystyrene, polyacrylate, polyhalide, polyester,

polycarbonate, polyimide, phenol formaldehyde resin, epoxy, polyalkylene glycol, polysaccharide, polyethylene, polypropylene, polymethylmethacrylate, polyvinyl chloride, polyethylene terephthalate, polyethylene glycol, polypropylene glycol, starch, glycogen, cellulose, chitin, one or more polymers polymerized from poly(ethylene glycol) diacrylate (PEGDA), poly(ethylene glycol) dimethacrylate (PEGDMA), poly(ethylene glycol) methyl ether acrylate (PEGMEA), poly(ethylene glycol) methyl ether methacrylate (PEGMEMA), mono-acrylate and vinylene carbonate, or combinations thereof.

[0090] Aspect 20: The double-shell encapsulated sulfur composite according to any of Aspects 17 to 19, wherein the double-shell encapsulated sulfur composite has a particle size of from 5 nm to 50 pm.

[0091] Aspect 21 : A lithium-sulfur battery comprising a cathode, an anode and an electrolyte, wherein the cathode includes a plurality of the double-shell encapsulated sulfur composites according to any of Aspects 1 to 20.

EXAMPLES

[0092] The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how the compounds, compositions, articles, devices and/or methods claimed herein are made and evaluated, and are intended to be purely exemplary and are not intended to limit the disclosure. Efforts have been made to ensure accuracy with respect to numbers (e.g., amounts, temperature, etc.), but some errors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight, temperature is in °C or is at ambient temperature, and pressure is at or near atmospheric. Unless indicated otherwise, percentages referring to composition are in terms of wt%.

[0093] There are numerous variations and combinations of reaction conditions, e.g., component concentrations, desired solvents, solvent mixtures, temperatures, pressures and other reaction ranges and conditions that can be used to optimize the product purity and yield obtained from the described process. Only reasonable and routine experimentation will be required to optimize such process conditions.

Materials and characterization

[0094] Potassium permanganate, sodium thiosulfate, polyvinylpyrrolidone

(PVP, Mw -40,000), dopamine hydrochloride, tris(hydroxymethyl)aminomethane and sulfuric acid were acquired from Sigma- Aldrich.

[0095] Scanning electron microscopic (SEM) images were taken by a Nova

NanoSEM™ (FEI). Transmission electron microscope (TEM) pictures were obtained by a Tecnai™ Twin TEM (FEI) operating at 120 kilovolt (kV). Energy dispersive x-ray spectroscopy (EDX) was obtained using a Nova NanoSEM™ (FEI) operated at 10-15 kV. X- ray diffraction (XRD) patterns were recorded at room temperature on a powder PANalytical Empyrean diffractometer using CuKa radiation (l = 1.54059 A) at 40 kV and 40 milliamp (mA). Thermogravimetric analysis (TGA) was obtained using a TGA Q500 (TA instrument) from 25-800 °C with a heat ramp of 10 °C/minute (min) under a nitrogen atmosphere.

Synthesis of sulfur particles

[0096] Na2S ₂ 03 (15.81 gram (g), 0.1 mol) in 250 milliliter (mL) of water was slowly added into a dilute FESCM solution (500 mL, 0.04 M) containing 1 g of polyvinylpyrrolidone (Mw - 40,000). After stirring for 2 hours at room temperature, the sulfur nanoparticles were collected by centrifugation.

[0097] FIG. 6A shows the SEM image of the sulfur particles as-synthesized, having a diameter of from 0.6-1.1 micron (pm). FIG. 6B shows the TEM image of the sulfur particles. A spherical shape can be observed. The powder XRD patterns of the sulfur as-synthesized and from Sigma are shown in FIG. 6C. The two patterns matched very well. FIG. 6D shows the TGA of sulfur as-synthesized and from Sigma.

Synthesis of sulfur/MnC core-shell (S@MnC )

[0098] The synthesized sulfur particles were dispersed in 600 mL of deionized (DI) water with the assistance of ultra-sonication, followed by mixing with a potassium

permanganate solution (1 g in 200 mL DI water), and then maintained at 76 °C for a given duration. After filtration and washing several times with DI water and isopropanol, the resulting powders were dried at 50 °C overnight under vacuum, thus obtaining the MnCh- coated sulfur (S@MnCh).

[0099] FIG. 7A shows the SEM image and EDX of the S@MnCh particles. The EDX analysis indicates the components of the particles are S, Mn and O. FIG. 7B shows the TEM image of the S@MnCh particles. Only hollow Mn0 ₂ shell can be observed because sulfur was melted and evaporated away under the TEM beam. FIG. 7C shows the XRD patterns of sulfur, S@Mn0 ₂ and hollow Mn0 ₂ . The peaks with an asterisk (*) are from 5-Mn0 ₂ , which matched very well with the literature (Liang, X.; Nazar, L. F., In Situ Reactive Assembly of Scalable Core-Shell Sulfur-Mn02 Composite Cathodes. ACS Nano 2016, 10 (4), 4192- 4198). The two patterns matched very well. FIG. 7D shows the TGA of sulfur and

S@Mn0 ₂ . It indicates the weight ratio of Mn0 ₂ is around 12%.

Synthesis of sulfur@Mn0 ₂ @polydopamine yolk-shell (S@Mn0 ₂ @PDA)

[00100] The synthesized S@Mn0 ₂ particles were dispersed in 300 ml of FhO and then 1 g of PVP (Mw=40,000) was added and dissolved by stirring. Then 1.8 g of

tris(hydroxymethyl)aminomethane (12 mmol) was added into the above mixture and stirred for about 30 minutes. Finally, 1.2 g of dopamine hydrochloride (16.9 mmol) was added under stirring. The reaction mixture became black immediately; stirring was continued for 2 days and then the mixture was centrifuged and washed with water and ethanol (120 ml twice). A black powder (sulfur@Mn0 ₂ @poly dopamine core-shell) was obtained and dried at 55 °C under vacuum overnight. To prepare the sulfur@Mn0 ₂ @polydopamine yolk-shell, an amount of the sulfur@Mn0 ₂ @poly dopamine core-shell was loaded into a sublimator and heated at 120 °C under a vacuum.

[00101] FIG. 8A shows the SEM image of the S@Mn0 ₂ @PDA core-shell particles. The TEM image (FIG. 8B) shows a clear core-shell structure. FIG. 8C shows the EDX of the S@Mn0 ₂ @PDA core-shell particles. The components are C, N, O, S and Mn. The nitrogen and carbon elements are from poly dopamine. FIG. 8D is the TEM image of the

S@Mn0 ₂ @PDA yolk-shell particles. A void between the core and shell can be seen.

[00102] FIG. 9 shows the TGA of the core-shell and yolk-shell of the S@Mn0 ₂ @PDA particles. It can be seen that the sulfur loading of the yolk-shell particles is less than that of the core-shell particles.

[00103] The above description is intended to be illustrative, and not restrictive. For example, the above-described examples (or one or more aspects thereof) may be used in combination with each other. Other embodiments can be used, such as by one of ordinary skill in the art upon reviewing the above description. The Abstract is provided to comply with 37 C.F.R. §1.72(b), to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Also, in the above Detailed Description, various features may be grouped together to streamline the disclosure. This should not be interpreted as intending that an unclaimed disclosed feature is essential to any claim. Rather, inventive subject matter may he in less than all features of a particular disclosed embodiment. Thus, the following claims are hereby incorporated into the Detailed Description as examples or embodiments, with each claim standing on its own as a separate embodiment, and it is contemplated that such embodiments can be combined with each other in various combinations or permutations. The scope of the invention should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.