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Title:
POTASSIUM ION ELECTRIC ENERGY STORAGE DEVICES
Document Type and Number:
WIPO Patent Application WO/2016/168496
Kind Code:
A1
Abstract:
Certain disclosed embodiments of the present invention concern anodes for use in an electric energy storage device, such as electric current producing cells, rechargeable batteries, capacitors, etc., containing potassium ions as the charge compensating ions in the electrodes and/or electrolyte. Certain disclosed embodiments concern carbon electrodes comprising an electroactive carbon, an electrically conductive carbon filler and a non-electroactive binder component. The invention particularly pertains to potassium ion rechargeable batteries (KIBs) comprising carbon electrodes.

Inventors:
JI, Xiulei (14526 SE Lyon Court, Happy Valley, OR, 97086, US)
JIAN, Zelang (953 NW Oak Avenue, Corvallis, OR, 97330, US)
Application Number:
US2016/027586
Publication Date:
October 20, 2016
Filing Date:
April 14, 2016
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
OREGON STATE UNIVERSITY (312 Kerr Administration Building, Corvallis, OR, 97331, US)
International Classes:
H01M4/133; H01M4/1393; H01M4/38; H01M4/583; H01M4/587; H01M10/36
Domestic Patent References:
WO2014116814A22014-07-31
Foreign References:
US6087043A2000-07-11
US20110117448A12011-05-19
US20070287068A12007-12-13
US6350544B12002-02-26
CN103708437A2014-04-09
CN103000884A2013-03-27
US7405020B22008-07-29
US5069764A1991-12-03
Other References:
LIU, Y ET AL.: "In situ transmission electron microscopy study of electrochemical sodiation and potassiation of carbon nanofibers.", NANO LETTERS., vol. 14, no. 6, 11 June 2014 (2014-06-11), pages 3445 - 3452, XP055321453
MASQUELIER, C ET AL.: "Hydrated Iron Phosphates FeP04.nH20 and Fe4(P207)3.n H20 as 3 V Positive Electrodes in Rechargeable Lithium Batteries.", JOURNAL OF THE ELECTROCHEMICAL SOCIETY, vol. 149, no. 8, 2002
Attorney, Agent or Firm:
BURGESS, Steven, J. (Klarquist Sparkman, LLPOne World Trade Center, Suite 1600,121 SW Salmon Stree, Portland OR, 97204, US)
Download PDF:
Claims:
We claim:

1. A potassiated, carbon-material-based anode.

2. The anode according to claim 1 wherein the carbon material is graphite having a long-range crystalline order.

3. The anode according to claim 1 wherein the carbon material is selected from highly oriented pyrolytic graphite, natural graphite, carbon nanotubes, fullerene and graphene- related structures.

4. The anode according to claim 1 comprising carbon material selected from soft carbon or hard carbon, wherein the carbon material comprises intercalated potassium ions.

5. The anode according to claim 4 wherein the carbon material is hard carbon having a short-range crystalline order.

6. The anode according to claim 1 comprising graphite having a density of from about 2 g/cm3 to about 2.3 g/ cm3. 7. The anode according to claim 1 comprising graphite having a density of from about 2.09 g/ cm3to about 2.26 g/ cm3.

8. The anode according to claim 1 comprising soft carbon having a density of from about 1.5 g/ cm3 to about 2 g/ cm3.

9. The anode according to claim 1 comprising soft carbon having a density of from about 1.6 to 1.8 g/ cm3.

10. The anode according to claim 1 comprising hard carbon having a density of from about 1.5 g/ cm3to about 1.7 g/ cm3.

11. The anode according to claim 1 comprising a doped carbon material.

12. The anode according to claim 1 comprising carbon material doped with phosphorous, nitrogen, sulfur or combinations thereof.

13. The anode according to claim 1 where the carbon-material-based anode comprises an electroactive carbon, an electrically conductive carbon filler, a non-electroactive binder component, and combinations thereof.

14. The anode according to claim 13 where the electroactive carbon material is selected from graphite, soft carbon, hard carbon, multiwall carbon nanotubes, single-wall carbon nanotubes, fullerene, graphene, glassy carbon, phosphorus -doped hard carbon, boron-doped hard carbon, sulfur-doped hard carbon, N-doped hard carbon, phosphorus-doped soft carbon, boron- doped soft carbon, sulfur-doped soft carbon, N-doped soft carbon, and combinations thereof.

15. The anode according to claim 13 where the electrically conductive carbon filler is selected from carbon black, carbon nanospheres, carbon nanofibers, carbon nanotubes, and combinations thereof.

16. The anode according to claim 13 where the non-electroactive binder component is selected from polyvinylidene fluoride or polyvinylidene difluoride (PVDF),

polytetrafluoroethylene, (PTFE), carboxymethyl cellulose (CMC), and combinations thereof.

17. The anode according to claim 1 comprising carbon material produced by biomass pyrolysis.

18. The anode according to claim 1 comprising an electrochemically potassiated anode.

19. An energy storage device, comprising at least one electrode and an aprotic electrolyte comprising a potassium ion.

20. The energy storage device according to claim 19 wherein the electrode is an anode.

21. The energy storage device according to claim 19 wherein the anode comprises a carbon-based material.

22. The energy storage device according to claim 19 wherein a cathode or electrolyte comprises potassium ions.

23. The energy storage device according to claim 19 wherein the electrolyte comprises a potassium salt. 24. The energy storage device according to claim 19 comprising aprotic liquid electrolytes.

25. The energy storage device according to claim 24 wherein the electrolyte comprises an aliphatic carbonate.

26. The energy storage device according to claim 24 comprising an aprotic electrolyte selected from propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethoxycthane (DME), dimethyl carbonate (DMC), dimethyl sulfoxide (DMSO), acrylonitrile (ACN), dimethyl formamide (DMF), 1,3-dioxolane (DIOX), dimethyl sulfite (DMSU), Tetraethylene glycol dimethyl ether (TEGDME), Triethylene glycol dimethyl ether, Diglyme, dimethoxy, ethylene glycol (DME), 1 -Ethyl- 1 -methyl piperidinium

bis(trifluoromethanesulfonyl)imide, acetonitrile (AN), ethyl methyl sulfone (EMS),

tetramethylene sulfone (TMS), ethyl-iso-propyl sulfone (EiPS), ethyl-iso-butyl sulfone (EiBS), adiponitrile (ADN), glutaronitrile (GLN), sebaconitrile (SEN), (2,2,2- trifluoro)ethoxypropionitrile, 2-trifluoromethyl-3-methoxyperfluoropentane (TMMP), 2- (trifluoro-2-fluoro-3-difluoroproxy)-3-difluoro-4-fluoro-5-trifluoropentane (TPTP),

fluoroethylene carbonate (FEC), or combinations thereof.

27. The energy storage device according to claim 19 comprising a potassium salt selected from KPF6, KAsF6, KSbF6, KBF4, KOH, KBH4, KC104, KC1, KBr, HCOOK, KI,

KNO3, KCIO3, K2Cr04, KHS04, K2S04, KBr03, KNO2, KCH3COCT, KIO3, KI04, KH2P04, K2HP04, K3P04, KSCN, K2SO3, KSO3F, KCH3COS, KC4B08, K(CF3S02)2N, K(C2F5S02)2N, KCF3SO3, K3Fe(CN)6, [(CH3)3Si]2NK, C6H5COOK, (CH3)3SiOK, K2Se03, KF, K2W04, C6H5BF3K, K2Sx, KNb03, K2SiF6, K2TiF6, K2NbF7, or combinations thereof.

28. The energy storage device according to claim 19 comprising a cathode material selected from KMn204, KxCo02 (0<x<l), KxNi02 (0<x<l), KxFe02 (0<x<l), KxCrO2 (0<x<l), KxFeMn02 (0<x<l), KxMn02 (0<x<l), Ko.6Cr0.6Tio.402, KxTio.5Coo.502 (0<x<l),

KxCoi/3Nii/ Mni/3O2 (0<x<l), Kx(Nio.8Co0.i5Alo.o5)02 (0<x<l), KxFePO4 (0<x<l), K2FeP04F, KxV2O5 (0<x<2), KxVP04F (0<x<l), KxMnPO4 (0<x<l), FeP04, K3V2(P04) , K3V2(P04)2F3, V2O5, Ki.5VOP04Fo.5, K2Fe2(S04)3, KNio.5Mno.5O2, K2/3Nii/3Mn2/302, K045Nio.22Coo.11Mno.66O2, K0.44MnO2, K4Fe3(P04)2P207, KxFeFe(CN)6 (0<x<l), KxCuFe(CN)6 (0<x<l), KxNiFe(CN)6 (0<x<l), or combinations thereof.

29. The energy storage device according to claim 19 comprising a secondary battery.

30. A potassium ion secondary battery, comprising:

an anode comprising a carbon-based material;

a cathode comprising a cathode material selected from KMm04, KxCoO2 (0<x<l), KxNiO2 (0<x<l), KxFe02 (0<x<l), KxCrO2 (0<x<l), KxFeMnO2 (0<x<l), KxMn02 (0<x<l), Ko.6Cro.6Tio.402, KxTio.5Coo.5O2 (0<x<l), KxCoi/3Nii/ Mm/3O2 (0<x<l), Kx(Nio.8Co0.i5Al0.o5)02 (0<x<l), KxFeP04 (0<x<l), K2FeP04F, KxV205 (0<x<2), KxVP04F (0<x<l), KxMnP04 (0<x<l), FeP04, K3V2(P04) , K3V2(P04)2F3, V2O5, Ki.5VOPO4F0.5, K2Fe2(S04) ,

KNio.5Mno.5O2, K2/3Nii/3Mn2/302, K045Nio.22Coo.11Mno.60O2, Ko.44Mn02, K4Fe3(P04)2P207, KxFeFe(CN)6 (0<x<l), KxCuFe(CN)6 (0<x<l), KxNiFe(CN)6 (0<x<l), or combinations thereof; and

an aprotic electrolyte selected from propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethoxycthane (DME), dimethyl carbonate (DMC), dimethyl sulfoxide (DMSO), acrylonitrile (ACN), dimethyl formamide (DMF), 1,3-dioxolane (DIOX), dimethyl sulfite (DMSU), tetraethylene glycol dimethyl ether (TEGDME), Methylene glycol dimethyl ether, diglyme, dimethoxy, ethylene glycol (DME), 1 -Ethyl- 1 -methyl piperidinium bis(trifluoromethanesulfonyl)imide, acetonitrile (AN), ethyl methyl sulfone (EMS),

tetramethylene sulfone (TMS), ethyl-iso-propyl sulfone (EiPS), ethyl-iso-butyl sulfone (EiBS), adiponitrile (ADN), glutaronitrile (GLN), sebaconitrile (SEN), (2,2,2- trifluoro)ethoxypropionitrile, 2-trifluoromethyl-3-methoxyperfluoropentane (TMMP), 2- (trifluoro-2-fluoro-3-difluoroproxy)-3-difluoro-4-fluoro-5-trifluoropentane (TPTP), fluoroethylene carbonate (FEC), or combinations thereof, the electrolyte comprising a potassium salt selected from KPF6, KAsF6, KSbF6, KBF4, KOH, KBH4, KC104, KCl, KBr, HCOOK, KI, KNO3, KCIO3, K2Cr04, KHS04, K2S04, KBr03, KNO2, KCH3COO, KIO3, KI04, KH2P04, K2HP04, K3P04, KSCN, K2SO3, KSO3F, KCH3COS, KC4B08, K(CF3S02)2N, K(C2F5S02)2N, KCF3SO3, K3Fe(CN)6, [(CH3)3Si]2NK, C6H5COOK, (CH3)3SiOK, K2Se03, KF, K2W04, C6H5BF3K, K2Sx, KNb03, K2SiF6, K2TiF6, K2NbF7, or combinations thereof.

31. A method for making a K ion energy storage device, comprising:

providing a carbon-material-based anode material;

providing a potassium-ion based aprotic electrolyte;

forming a K ion energy storage device comprising the carbon-material-based anode material and the potassium-ion electrolyte.

Description:
POTASSIUM ION ELECTRIC ENERGY STORAGE DEVICES

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of the earlier filing date of U.S. provisional patent application Nos. 62/149,179 and 62/149,208, both filed on April 17, 2015, which are

incorporated herein by reference in their entirety.

FIELD

The present invention concerns energy storage devices, such as rechargeable batteries, capacitors and more specifically potassium ion batteries and hybrid capacitors.

BACKGROUND

Clean and renewable energy plays an important role in energy consumption. Renewable energy sources, such as solar and wind power, are intermittent, and energy produced using the methods must be stored for load leveling. Lithium ion batteries (LIBs) have been explored as power sources for various types of important applications, such as portable electric devices and electrical vehicles. However, lithium resources are too rare to meet the increasing global demand market for LIBs. LIBs cannot address long-term sustainability because lithium resources are scarce, and are concomitantly expensive. Accordingly, new types of batteries are required.

Na ion batteries are currently considered the best substitution for LIBs. Na ion batteries (NIBs) were investigated beginning in the 1980s, but NIB development was suspended until around 2010. The fate of different battery technologies is cyclical, depending primarily on societal needs. NIBs recently reemerged because NIBs fit better than LIBs in stationary electric energy storage. Moreover, sodium resources are essentially unlimited and ubiquitous.

Unfortunately, the abundant accumulation of LIB knowledge cannot be simply 'copied' and 'pasted' to make batteries based on other materials, such as NIBs, work. This is particularly true when considering anodes. Graphite is the most successful anode material used to make LIBs. But graphite does not accept meaningful quantities of Na ions - only by forming a NaC 7 o versus LiC 6 in LIBs - which has spurred persons of ordinary skill in the battery art to search for carbon anodes for NIBs. To date, only hard carbon demonstrates electrochemical reversibility in terms of sodium ion storage. However, hard carbon presents a long plateau near 0 V versus Na + /Na, causing a serious, detrimental formation of sodium metal dendrites on the hard carbon surface when a high current rate is used. Furthermore, hard carbon is expensive to prepare due to the low production yield from biomass pyrolysis. Based on the rich knowledge of LIBs and well- established industry for graphite anodes, it is critical to use graphite for newly developed energy storage devices.

As presently understood, potassium insertion into graphite is solely restricted to solid- state reactions, where potassium is vaporized and potassium atoms are inserted into the crystal structure of graphite. Again as presently understood, the only reference teaching using carbon to store potassium ions is Wang et al. Nano letters 2014, 14 (6), 3445). Wang et al. studied in situ Transmission Electron Microscopy of electrochemical potassiation of nanofibers comprising 25% crystalline carbon and 75% disordered carbon. Wang et al. did not cover crystalline graphitic carbon for potassium ion storage

Other devices using potassium in batteries are K-0 2 batteries where potassium metal is used as the anode (US Patent Application 2014/012730, JACS 2013, 135, 2923-2926, Inorg. Chem. 2014, 53, 9000-9005). However, potassium metal is violently reactive. It is therefore desirable to have electrodes store K ions, which can be used to produce rechargeable energy storage devices.

SUMMARY

This invention concerns K-ion batteries (KIBs) and K-ion hybrid capacitors that utilize a carbon anode for K-ion storage. This invention demonstrates, for the first time, the

electrochemical reversibility of K ion insertion into, and deinsertion out of, graphite, and amorphous or non-graphitic carbon, including amorphous/non-graphitic carbon, including soft carbon and hard carbon.

Certain embodiments of the present invention concern an anode for a potassium ion electric energy storage device, particularly an electrochemically potassiated, carbon-material- based anode. The anode may comprise, for example, graphite having a long-range crystalline order, such as highly oriented pyrolytic graphite, natural graphite, carbon nanotubes, fullerene and graphene-related structures. The anode may also comprise a carbon-based material selected from amorphous/non-graphitic carbon, including soft carbon or hard carbon as well as polynanocrystalline graphite. The anode also may comprise a doped carbon-based material, such as a carbon-based-material doped with phosphorous, nitrogen, boron and sulfur. Disclosed anode embodiments may also comprise an electroactive carbon, an electrically conductive carbon filler, a non-electroactive binder component, and combinations thereof. Certain disclosed embodiments concern a potassium ion energy storage device, such as batteries, particularly secondary batteries, and capacitors, such as a hybrid capacitor. For a hybrid capacitor, the anode can be K ion intercalated carbon, graphite, soft carbon, or hard carbon, while the cathode is a capacitive electrode.

Certain disclosed potassium ion energy storage devices comprise at least an anode, a cathode and an aprotic electrolyte comprising a potassium ion. In certain embodiments, the solvents in the aprotic electrolyte may be selected from propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethoxyethane (DME), dimethyl carbonate (DMC), dimethyl sulfoxide (DMSO), acrylonitrile (ACN), dimethyl formamide (DMF), 1,3-dioxolane (DIOX), dimethyl sulfite (DMSU), tetraethylene glycol dimethyl ether (TEGDME), triethylene glycol dimethyl ether, diglyme, dimethoxy, ethylene glycol (DME), 1 -Ethyl- 1 -methyl piperidinium bis(trifluoromethanesulfonyl)imide, acetonitrile (AN), ethyl methyl sulfone (EMS), tetramethylene sulfone (TMS), ethyl-iso-propyl sulfone (EiPS), ethyl-iso-butyl sulfone (EiBS), adiponitrile (ADN), glutaronitrile (GLN), sebaconitrile (SEN), (2,2,2- trifluoro)ethoxypropionitrile, 2-trifluoromethyl-3-methoxyperfluoropentane (TMMP), 2- (trifluoro-2-fluoro-3-difluoroproxy)-3-difluoro-4-fluoro-5-t rifluoropentane (TPTP),

fluoroethylene carbonate (FEC), and combinations thereof. The potassium salt in the electrolyte may be selected from KPF 6 , KAsF 6 , KSbF 6 , KBF 4 , KOH, KBH 4 , KC10 4 , KC1, KBr, HCOOK, KI, KNO3, KCIO3, K 2 Cr0 4 , KHS0 4 , K 2 S0 4 , KBrOs, KNO2, KCH 3 COO " , KI0 , KI0 4 , KH 2 P0 4 , K 2 HP0 4 , K 3 P0 4 , KSCN, K 2 S0 , KS0 F, KCH 3 COS, KC 4 B0 8 , K(CF 3 S0 2 )2N, K(C 2 F 5 S0 2 )2N, KCF 3 S0 , K 3 Fe(CN) 6 , [(CH3) Si] 2 NK, C 6 H 5 COOK, (CH3) SiOK, K 2 Se0 , KF, K 2 W0 4 , C 6 H5BF 3 K, K2SX, KNb0 3 , K2S1F6, K2T1F6, K2NbF 7 , and combinations thereof. And, the energy storage device may comprise a cathode material selected from KMm0 4 , KxCoC (0<x<l), K x NiO 2 (0<x<l), K x Fe0 2 (0<x<l), K x CrO 2 (0<x<l), K x FeMnO 2 (0<x<l), K x Mn0 2 (0<x<l), Ko.6Cro. 6 Tio. 4 02, KxTio.5Coo.5O2 (0<x<l), K x Coi/ 3 Nii/ Mni/ 3 02 (0<x<l), K x (Nio. 8 Co 0 .i5Alo.o5)02 (0<x<l), K x FeP0 4 (0<x<l), K 2 FeP0 4 F, K x V 2 0 5 (0<x<2), K x VP0 4 F (0<x<l), K x MnP0 4

(0<x<l), FeP0 4 , K 3 V 2 (P0 4 ) , K 3 V 2 (P0 4 ) 2 F 3 , V2O5, Ki. 5 VOPO 4 F 0 .5, K 2 Fe 2 (S0 4 ) ,

KNio.5Mno.5O2, K2/ 3 Nii/ 3 Mn2/ 3 02, K045Nio.22Coo.11Mno.60O2, Ko. 44 Mn02, K 4 Fe 3 (P0 4 )2P20 7 , KxFeFe(CN) 6 (0<x<l), K x CuFe(CN) 6 (0<x<l), K x NiFe(CN) 6 (0<x<l), and combinations thereof. For particular embodiments, the energy storage device comprises a secondary potassium ion battery. The foregoing and other objects, features, and advantages of the invention will become more apparent from the following detailed description, which proceeds with reference to the accompanying figures. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows typical potassiation/depotassiation potential profiles of graphite in K ion batteries at a current density of 50 mA/g.

FIG. 2 shows initial cycling performance at a current of 250 mA/g of graphite in K ion batteries.

FIG. 3 shows the molecular structure of PTCDA.

FIG. 4 shows typical potassiation/depotassiation potential profiles of soft carbon in K ion batteries at a current density of 50 mA/g.

FIG. 5 shows the initial cycling performance at a current density of 250 mA/g of soft carbon in K ion batteries.

FIG. 6 shows typical potassiation/depotassiation potential profiles of hard carbon in K ion batteries at a current density of 50 mA/g.

FIG. 7 shows initial cycling performance at a current of 250 mA/g of hard carbon in K ion batteries.

FIG. 8 is a schematic of one embodiment of an energy storage device according to the present invention.

FIG. 9 is a schematic of one embodiment of an energy storage device according to the present invention.

FIG. 10 is a graph of intensity versus angle showing X-ray diffraction (XRD) data of graphite, with an inset of a transmission electron microscopy (TEM) image.

FIG. 11 is a graph of potential versus specific capacity illustrating the discharge/charge profiles of graphite for the initial two cycles between 0.01 and 1.5 volts at C/40.

FIG. 12 is a graph of voltage versus specific capacity illustrating the galvanostatic intermittent titration technique (GITT) profiles of graphite at C/10 in a second cycle.

FIG. 13 is a graph of dQ/dV versus voltage showing the dQ/dV profiles corresponding to discharge/charge profiles of graphite for the initial two cycles between 0.01 and 1.5 V at C/40.

FIG. 14 is a graph of capacity versus cycle number illustrating the rate performance of an exemplary graphite electrode at C/2 in a K ion battery. FIG. 15 is a graph of capacity and efficiency versus cycle number illustrating the cycling performance of the exemplary graphite electrode from FIG. 14.

FIG. 16 is a graph of voltage versus specific capacity showing the first-cycle

discharge/charge potential profiles of a graphite electrode at C/10.

FIG. 17 is a graph of intensity versus angle showing the XRD patterns of electrodes corresponding to the marked states of charge in FIG. 16.

FIG. 18 is a schematic structure diagram illustrating side and top views of different potassium-graphite intercalation compounds (K-GICs) showing possible potassium intercalation into graphite.

FIG. 19 is a graph of intensity versus angle comparing the XRD data from soft carbon to that of graphite.

FIG. 20 is a TEM image of soft carbon, with a selected area electron diffraction (SAED) image shown in the inset.

FIG. 21 is a graph of potential versus specific capacity for an exemplary soft carbon electrode in a K ion battery.

FIG. 22 is a graph of capacity versus cycle number illustrating the rate performance of a soft carbon electrode in a K ion battery and comparing it to a graphite electrode.

FIG. 23 is a graph of specific capacity and efficiency versus cycle number showing the cycling performance of a soft carbon electrode at 2C.

FIG. 24 is a scanning electron microscopy (SEM) image of hard carbon spheres (HCSs), with the scale bar representing 50 μιη.

FIG. 25 is a high resolution TEM image of a HCS, with the scale bar representing 50 nm.

FIG. 26 is a graph of intensity versus angle illustrating the XRD pattern of HCSs.

FIG. 27 is a graph of voltage versus specific capacity illustrating the discharge/charge profiles at C/10 in a second cycle of an HCS/K cell.

FIG. 28 is a graph of dQ/dV versus voltage showing the dQ/dV profiles from the cell of FIG. 27.

FIG. 29 is a graph of capacity versus cycle number comparing the rate performances of HCS/K and HCS/Na cells.

FIG. 30 is a graph of capacity versus rate showing the retention at increasing rates, for HCS/K and HCS/Na cells.

FIG. 31 is a graph of capacity and efficiency versus cycle number illustrating the cycling performance of a HCS/K cell. FIG. 32 is a graph of diffusion coefficient D versus over potential illustrating the insertion diffusion coefficients calculated from GITT potential profiles for HCS/K and HCS/Na cells as a function of state of charge during a second cycle.

FIG. 33 is a graph of diffusion coefficient D versus over potential illustrating the extraction diffusion coefficients calculated from GITT potential profiles for HCS/K and HCS/Na cells as a function of state of charge during a second cycle.

FIG. 34 is a graph of voltage versus specific capacity showing the discharge/charge curves of an HCS/Na cell at different C-rates.

FIG. 35 is a graph of voltage versus specific capacity showing the discharge/charge curves of an HCS/K cell at different C-rates.

DETAILED DESCRIPTION

I. Introduction

It has been long assumed that K ions cannot be electrochemically intercalated into graphite or other carbon materials due to the large ionic radii, 136 pm, versus 76 pm for Li ions and 106 pm for Na ions. Considering that Na ions are already "too large" to be inserted into graphite, this assumption seemed reasonable. It is known, however, that KCs, the first ever known graphite intercalation compound (GIC), can be formed by soaking graphite in a potassium vapor {Journal of Chemical Physics 1980, 72, 3840-3841).

Potassium ion batteries would provide several advantages. A first advantage is source material sustainability. Potassium is a rock-forming element, occupying 1.5% by weight of the Earth's crust, compared to 2.3% Na and 0.0017% Li. Potassium also is substantially equally distributed throughout the Earth.

Another advantage is that large potassium ions normally exhibit better electrolyte conductivity {Journal of solution chemistry, 1999, 28, 223-235) and may provide better rate capability than LIBs and NIBs. With the same trend, in fact, NIBs recently demonstrated good power performance compared to LIBs. {Nano letters, 2014, 14, 2175-2180).

Persons of ordinary skill in the art have, to date, assumed that potassium ions cannot be electrochemically intercalated into carbon materials, other than hard carbon materials. The present invention demonstrates, for the first time, the electrochemical reversibility of K ion insertion into and deinsertion out of graphite, soft carbon and hard carbon. The electrochemical performance of different carbon-based materials comprising intercalated potassium ions for use as potassium ion batteries is shown in FIGS. 1, 2, and 4-7. II. Carbon-Based Anode Materials

Certain disclosed embodiments use carbon-based materials to produce anodes suitable for K ion intercalation. Certain exemplary carbon-based materials are discussed in more detail below.

A. Graphite Classifications

Graphitic carbon can be classified as graphite, soft carbon and hard carbon. Graphite exhibits a long-range order in a highly crystalline structure formed by stacked graphene sheets that exhibit few defects (FIG. 10). "Long-range order" refers to an arrangement of particles or atoms in a crystalline lattice that is substantially repeated throughout the material. Thus the symmetry and regularity of the arrangement of the particles or atoms is substantially repeated at any distance from a given particle or atom.

Soft carbon is generally classified as a disordered or amorphous carbon. Soft carbon typically has an intermediate-range or short-range order with turbostratic graphitic domains aligned in a fashion of waves. "Short-range order" refers to an arrangement of particles or atoms in a material where the orderliness is typically comparable over interatomic distances and nanometric distances, but the symmetry and regularity of the arrangement is not repeated throughout the crystalline lattice. Thus, the nearest few neighboring atoms, such as the nearest two neighboring atoms, are still at positions that correspond to a crystalline lattice, but with some bond angle and/or length variations, such as from 0% to 20% from the corresponding crystalline lattice structure. However, at greater distances from a given atom, the variations from the corresponding crystalline lattice increase such that the regularity of the arrangement is not repeated.

Hard carbon is yet another type of disordered or short-range order carbon having a structure comprising turbostratic nanodomains and nanovoids between these turbostratic nanodomains. Soft carbon and hard carbon are normally referred to as amorphous carbon, although soft carbon and hard carbon are polycrystalline graphitic carbon comprising nanosized graphitic domains.

All graphite, soft carbon and hard carbon materials demonstrate good performance for Li ion storage. To date, only hard carbon demonstrates desirable electrochemical reversibility in terms of Na ion storage with a specific capacity close to 300 mAh/g. However, hard carbon presents a long plateau near 0 V versus Na + /Na, causing a serious safety concern associated with sodium metal dendrite formation on the surface of hard carbon. Furthermore, hard carbon is, indeed, expensive to prepare due to the low yields of hard carbon based on biomass pyrolysis. For potassium ion storage in carbon, no one has demonstrated the capacity of graphitic carbon materials, including graphite and soft carbon.

B. Graphite Classification Based on Density

Carbon-based anode materials, such as graphite, soft carbon and hard carbon, also can be classified based on density. Graphite typically has a density of from about 2 g/cm 3 to about 2.3 g/ cm 3 , more typically from about 2.1 g/ cm 3 to about 2.3 g/ cm 3 . Soft carbon has a density of from about 1.5 g/ cm 3 to about 2 g/ cm 3 , more typically about 1.6 to 1.8 g/ cm 3 . And hard carbon has a density of from about 1.5 g/ cm 3 to about 1.7 g/ cm 3 .

C. Doping

Anode materials, such as carbon-based materials, also can be doped to improve or modify properties for end use applications. For example, carbon-based materials according to the present invention can be doped with phosphorous.

III. Anodes

Anodes based on carbon materials can include additional materials. For example, certain embodiments of disclosed carbon-material-based electrodes comprise an electroactive carbon, an electrically conductive carbon filler, a non-electroactive binder component, and combinations thereof. Examples of electroactive carbon materials include graphite, soft carbon, hard carbon, multiwall carbon nanotubes, single-wall carbon nanotubes, fullerene, graphene, glassy carbon, phosphorus-doped hard carbon, boron-doped hard carbon, sulfur-doped hard carbon, nitrogen- doped hard carbon, phosphorus-doped soft carbon, boron-doped soft carbon, sulfur-doped soft carbon, and nitrogen-doped soft carbon. Examples of electrically conductive carbon fillers include carbon black, carbon nanospheres, carbon nanofibers, and carbon nanotubes. And examples of non-electroactive binder components include polyvinylidene fluoride or polyvinylidene difluoride (PVDF), polytetrafluoroethylene, (PTFE), and carboxymethyl cellulose (CMC).

IV. Aprotic Electrolyte Compositions Certain disclosed embodiments of the present invention utilize aprotic liquid electrolytes. For example, the solvents in the electrolyte can comprise an aliphatic carbonate, wherein aliphatic refers to "a substantially hydrocarbon-based group or moiety, including alkyl, alkenyl, alkynyl groups, cyclic versions thereof, such as cycloalkyl, cycloalkenyl or cycloalkynyl, and further including straight- and branched-chain arrangements. Unless expressly stated otherwise, an aliphatic group suitable for the present embodiments comprises from one to about twenty-five carbon atoms; for example, from one to fifteen, from one to ten, from one to six, or from one to four carbon atoms. Particular embodiments use lower aliphatic carbonate electrolytes containing from one to ten carbon atoms. An aliphatic group also may be substituted or unsubstituted.

Exemplary species of aprotic solvents for use with disclosed embodiments include, by way of example and without limitation, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethoxyethane (DME), dimethyl carbonate (DMC), dimethyl sulfoxide (DMSO), acrylonitrile (ACN), dimethyl formamide (DMF), 1,3-dioxolane (DIOX), dimethyl sulfite (DMSU), tetraethylene glycol dimethyl ether (TEGDME), triethylene glycol dimethyl ether, diglyme, dimethoxy, ethylene glycol (DME), 1 -ethyl- 1 -methyl piperidinium bis(trifluoromethanesulfonyl)imide, acetonitrile (AN), ethyl methyl sulfone (EMS),

tetramethylene sulfone (TMS), ethyl-iso-propyl sulfone (EiPS), ethyl-iso-butyl sulfone (EiBS), adiponitrile (ADN), glutaronitrile (GLN), sebaconitrile (SEN), (2,2,2- trifluoro)ethoxypropionitrile, 2-trifluoromethyl-3-methoxyperfluoropentane (TMMP), 2- (trifluoro-2-fluoro-3-difluoroproxy)-3-difluoro-4-fluoro-5-t rifluoropentane (TPTP), and fluoroethylene carbonate (FEC).

Certain exemplary reduced to practice embodiments used ethylene carbonate, diethyl carbonate, and mixtures thereof.

V. Potassium Ion Electrolyte Salts

Potassium ions are used to make energy storage devices, such as secondary batteries, according to the present invention. Any suitable potassium salt, now known or hereafter developed or discovered, that is suitable for potassium ion batteries is within the scope of the present invention.

Exemplary potassium salts for the electrolyte include by way of example, and without limitation, KPF 6 , KAsF 6 , KSbF 6 , KBF 4 , KOH, KBH 4 , KC10 4 , KC1, KBr, HCOOK, KI, KN0 3 , KCIO3, K 2 Cr0 4 , KHS0 4 , K 2 S0 4 , KBrOs, KN0 2 , KCH 3 COO, KI0 , KI0 4 , KH 2 P04, K 2 HP0 4 , K 3 P0 4 , KSCN, K 2 S0 , KS0 F, KCH 3 COS, KC 4 B0 8 , K(CF 3 S0 2 ) 2 N, K(C 2 F 5 S0 2 ) 2 N, KCF 3 S0 , K 3 Fe(CN) 6 , [(CH 3 ) 3 Si] 2 NK, C 6 H 5 COOK, (CH 3 ) 3 SiOK, K 2 Se0 , KF, K 2 W0 4 , C 6 H 5 BF 3 K, K 2 Sx, KNb0 3 , K 2 SiF 6 , K 2 TiF 6 , K 2 NbF 7 , and mixtures thereof. VI. Cathode Materials

A person of ordinary skill in the art will appreciate that the presently disclosed embodiments can utilize any cathode materials now known or hereafter developed that are suitable for use with a potassium ion energy storage device. Exemplary cathode materials include, but are not limited to, KMn 2 0 4 , K x Co0 2 (0<x<l), K x Ni0 2 (0<x<l), K x Fe0 2 (0<x<l), KxCr0 2 (0<x<l), K x FeMn0 2 (0<x<l), K x Mn0 2 (0<x<l), Ko. 6 Cro.6Ti 0 . 4 0 2 , KxTio. 5 Co 0 .50 2 (0<x<l), K x Coi/ 3 Nii/ Mni/ 3 O 2 (0<x<l), K x (Ni 0 . 8 Co 0 .i5Alo.o5)0 2 (0<x<l), K x FeP0 4 (0<x<l), K 2 FeP0 4 F, KxV 2 0 5 (0<x<2), K x VP0 4 F (0<x<l), K x MnP0 4 (0<x<l), FeP0 4 , K 3 V 2 (P0 4 ) , K 3 V 2 (P0 4 ) 2 F 3 , V 2 0 5 , Ki. 5 VOP0 4 Fo.5, K 2 Fe 2 (S0 4 ) , KNio.5Mno.5O2, K 2/3 Nii/ Mn 2/3 0 2 ,

Ko. 4 5Nio. 22 Coo.nMno.660 2 , K 0 . 44 MnO 2 , K 4 Fe 3 (P0 4 ) 2 P 2 0 7 , K x FeFe(CN) 6 (0<x<l), K x CuFe(CN) 6 (0<x<l), K x NiFe(CN)6 (0<x<l), and combinations thereof.

VII. Electric Energy Storage Devices

The present invention is particularly directed to electric energy storage devices that utilize potassium, particularly potassium ion-containing anodes. Most typically, the energy storage device is a secondary battery.

FIG. 8 is a schematic drawing of one embodiment of an electric storage device 10, such as a secondary battery, according to the present invention. Device 10 includes an anode current collector 10 positioned functionally adjacent to an anode 14. Device 10 further comprises a non-aqueous electrolyte 16. Device 10 further comprises a cathode 18, positioned functionally adjacent to a cathode current collector 20, and a separator 22.

FIG. 9 is a schematic drawing of another embodiment of an electric storage device 30, such as a capacitor, according to the present invention. Device 30 includes a negative electrode current collector 32 positioned functionally adjacent to a carbon negative electrode 34. Device 30 further comprises a non-aqueous electrolyte 36. Device 32 further comprises a porous carbon electrode 38, positioned functionally adjacent to a positive electrode current collector 40, and a separator 42.

VIII. Examples The following examples are provided to illustrate certain features of particular embodiments. A person of ordinary skill in the art will appreciate that the scope of the invention is not limited to the particular features of these examples. Example 1

K-ion storage was tested in graphite, both in highly oriented pyrolytic graphite (HOPG) and well-known microcarbon microbeads (MCMB), using a potassium metal foil as the counter/reference electrode and 1.0 M KPF 6 solvated in ethylene carbonate (EC) and diethyl carbonate (DEC) as the electrolyte. The graphite electrode with particle sizes of about 10 μιη delivered a specific capacity of 260 mAh/g in the depotassiation process at a current density of 50 mA/g. The capacity is reduced slightly when the current density is switched to 250 mA/g. With reference to FIG. 1, both potassiation (grey) and depotassiation (black) curves showed one primary plateau, corresponding to intercalation and de-intercalation of potassium ions, respectively. The depotassiation plateau is located at 0.33 V. FIG. 2 established that the K ion- intercalated graphite electrode exhibited stable cycling performance.

Potassium ion radii are much larger than that of sodium ions. However, sodium ions cannot be inserted into graphite with a meaningful capacity, i.e. 32 mAh/g. The present invention therefore indicates that the limitation of Na + -ion intercalation in graphite is not solely regulated by ionic radii.

Example 2

K-ion storage performance in a soft carbon was tested as well using the cell setup described in Example 1. The soft carbon used in this example was produced by annealing Perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) under Argon at 900 °C for 6 hours. FIG. 3 provides the molecular structure of PTCDA.

FIG. 4 shows the typical potassiation and depotassiation potential profiles of soft carbon for K-ion batteries at a current density of 50 mA/g. The reversible depotassiation capacity is 266 mAh/g. The potassiation and depotassiation curves present a single sloping region with an average depotassiation voltage of about 0.7 V.

FIG. 5 illustrates soft carbon's good cycling performance, where capacity maintained at

207 mAh/g at a current rate of 250 mA/g, indicating an excellent rate capability. The

Coulombic efficiency exceeded 99% after several initial cycles. Example 3

Hard carbon also was tested as an anode material for K-ion batteries using the cell setup described for Example 1. Hard carbon was prepared by pyrolysis of sucrose at 1100 °C for 6 hours. As FIG. 6 shows, at a current rate of 50 mA/g, the hard carbon provided a reversible depotassiation capacity of 204 mAh/g. Both potassiation and depotassiation potential curves showed two characteristic sections: a sloping area and a plateau region, presumably

corresponding to different K ion storage mechanisms. The average charge plateau was about 0.7 V. Its cycling performance is shown in FIG. 7. Over 50 cycles, its capacity faded from 191 mAh/g to 126 mAh/g.

Example 4

Carbon-material-based electrodes, such as anodes, according to the present invention can be doped. This example describes one exemplary process for doping hard carbon with phosphorous.

A composition was made comprising H 3 P0 4 with sucrose as a carbon precursor in the presence of graphene oxide. After drying, dehydration and pyrolysis, a P-doped hard carbon was obtained. This hard carbon exhibited a lower density of 1.5 g/cm 3 compared with other un- doped hard carbons, and had a surface area of less than 20 m 2 /g.

Example 5

In another test using the cell setup described for Example 1, a graphite electrode exhibited surprisingly high capacities of 475 and 273 mAh/g in potassiation and depotassiation in the first cycle, respectively (FIGS. 11 and 12). The initial Coulombic efficiency (CE) of 57.4% was low, and increased in the subsequent cycles. The primary potassiation and depotassiation plateaus were located at 0.17 V and 0.27 V, respectively. Galvanostatic intermittent titration technique (GITT) results indicated that the quasi-equilibrium potentials for both potassiation and depotassiation were close to 0.24 V (FIG. 12), much higher than that of Li insertion in graphite, which is typically about 0.1 V for Li+/Li.

The higher potassiation potential was advantageous as it relieved the risk of the dendrite formation on the graphite surface. Besides the primary plateau, located at 0.27 V and 0.17 V of Ol/Rl redox couple, there existed other minor plateaus in discharge/charge profiles, which were more evident in the dQ/dV profiles, i.e., 02/R2 and 03/R3 peaks (FIG. 13). The graphite exhibited a large capacity at low rates of discharge, but its capacity dropped as the rates increased. Capacities of 263, 234, 172, and 80 niAh/g were obtained at C/10, C/5, C/2, and 1C, respectively (FIG. 14). Unfortunately, over 50 cycles at C/2, the capacity of graphite faded from 197 to 100 mAh/g (FIG. 15). In cycling, the CE promptly increased to 93.5% in the second cycle and eventually stabilized at about 99%. This phenomenon of rising CE values indicated the formation of a solid electrolyte interface (SEI) during initial cycling.

Ex situ XRD results showed the staging -behavior of potassium- graphite intercalation compound (K-GICs) in a K/graphite cell. KC 3 6, KC24 and KCs sequentially formed upon potassiation while depotassiation recovered the graphite through phase transformations in an opposite sequence (FIGS. 16-18).

Example 6

Soft carbon was obtained from pyrolyzed PTCDA, and tested using the cell setup described for Example 1. Compared to graphite, the (002) XRD peak of soft carbon was much broadened, revealing a larger average d-spacing of 0.355 nm (FIG. 19), which was confirmed by

TEM (FIG. 20). Soft carbon also exhibited a high depotassiation capacity of 273 mAh/g at

C/40, and presented a slope not plateau. The initial CE was 56.4 and eventually stabilized at about 99% (FIG. 21).

At 1C and 2C, soft carbon exhibited very high capacities of 210 and 185 mAh/g, respectively, compared with 264 mAh/g at C/10. Even at 5C (1395 mA/g), the soft carbon still retained a capacity of 140 mA/g, which was much higher than that of the graphite anode (FIG.

22). The soft carbon also exhibited much improved cyclability with a capacity retention of

81.4% after 50 cycles at 2C (FIG. 23). Example 7

Hard carbon spheres (HCSs) were obtained by a hydrothermal reaction of dissolved sucrose, followed by pyrolysis. The HCSs comprised carbon microspheres with diameters of around 5-10 μιη (FIG. 24), and had a porous surface texture (FIG. 25). The HCSs exhibited an average inter-layer distance of about 0.4 nm, as indicated by the position of the (002) peak (FIG. 26).

In a test using the cell setup described for Example 1, the HCS/K cell demonstrated a reversible capacity of 262 mAh/g, with a capacity contribution of 210 mAh/g, 80% of the total capacity in HCS/K cells, above 0.1 V (FIG. 27). The dQ/dV profiles exhibited potassiation and depotassiation peaks at 0.2 and 0.33 V, respectively (FIG. 28). Additionally, the long plateau close to 0V in the dQ/dV profiles suggested that K + ions inserted into HCSs might be safer than Na + ions inserted into HCSs.

The rate capability of HCS electrodes were compared in K-ion batteries and Na-ion batteries. FIG. 29 shows that, at low rates of C/10 and C/5, the specific ion-extraction capacities of HCS/K cells were smaller than those of HCS/Na cells. Nevertheless, at higher rates equal to and above C/2, the capacities of HCS/K cells overtook those of HCS/Na cells. The HCS/K cells exhibited 229, 205, 190 and 136 mAh/g at C/2, 1C, 2C and 5C, respectively, while HCS/Na cells showed capacities of 190, 127, 97 and 73 mAh/g at the same rates. Impressively, at 2C and 5C, HCS/K cells retained 73% and 52% of their capacity at C/10, respectively, while such retention ratios were only 30% and 23% for HCS/Na cells (FIG. 30). The HCS/K cell also exhibited good cycling performance, with about 83% capacity retention and maintaining at 216 mAh/g over 100 cycles at C/10 (FIG. 31).

The insertion and extraction diffusion coefficients, calculated from the GITT potential profiles, were higher for K + ions in the HCS/K cells than for Na + ions in the HCS/Na cells

(FIGS. 32 and 33). Also, the sodiation plateau of the HCS/Na cell disappeared when the C-rate was increased to 1C, whereas the counterpart plateau in the HCS/K cell remained even at 5C, demonstrating the difference in the absolute values of cutoff potentials for HCS/K and HCS/Na cells (FIGS. 34 and 35). Without being bound to a particular theory, the higher rate performance of K + ions in the HCSs compared to the performance of Na + ions in HCSs might be due, at least in part, to these differences.

In view of the many possible embodiments to which the principles of the disclosed invention may be applied, it will be recognized that the illustrated embodiments are only preferred examples of the invention and should not be taken as limiting the scope of the invention. Rather, the scope of the invention is defined by the following claims. We therefore claim as our invention all that comes within the scope and spirit of these claims.