Metal Oxide-Based Electrode Compositions
20210218075 ยท 2021-07-15
Inventors
Cpc classification
H01M4/131
ELECTRICITY
H01M4/485
ELECTRICITY
Y02E60/10
GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
H01M4/1391
ELECTRICITY
H01M2004/021
ELECTRICITY
H01M10/0525
ELECTRICITY
International classification
H01M10/0525
ELECTRICITY
Abstract
The invention provides a method of charging and/or discharging an electrochemical cell at a high rate, wherein the electrochemical cell has a working electrode comprising a niobium tungsten oxide and/or a niobium molybdenum oxide. The invention also provides an electrode comprising a niobium tungsten oxide wherein, the ratio of Nb.sub.2O.sub.5 to WO.sub.3 is from 8:5 to 11:20, and an electrode comprising niobium molybdenum oxide, wherein the ratio of Nb.sub.2O.sub.5 to MoO.sub.3 is from 6:1 to 1:3.
Claims
1. A method of charging and/or discharging an electrochemical cell at a C-rate of at least 5C, wherein the electrochemical cell has a working electrode comprising a niobium tungsten oxide and/or niobium molybdenum oxide.
2. The method of claim 1, wherein the method is a method of charging and/or discharging an electrochemical cell at a C-rate of at least 10C, 15C, 20C, 25C, 30C, 35C, 40C, 50C, 60C or 80C.
3. The method of claim 1, wherein the method is a method of charging and/or discharging an electrochemical cell at a current density of at least 750 mA.Math.g.sup.1, preferably at least 800 mA.Math.g.sup.1, 850 mA.Math.g.sup.1, 900 mA.Math.g.sup.1, 950 mA.Math.g.sup.1, 1000 mA.Math.g.sup.1, 1050 mA.Math.g.sup.1, 1100 mA.Math.g.sup.1, 1200 mA.Math.g.sup.1 or 1300 mA.Math.g.sup.1.
4. The method of claim 1, wherein the electrochemical cell has a working electrode comprising a niobium tungsten oxide.
5. The method of claim 4, wherein the ratio of Nb.sub.2O.sub.5 to WO.sub.3 in the working electrode is from 6:1 to 1:15, preferably from 8:5 to 11:20.
6. The method of claim 4, wherein the working electrode comprises a niobium tungsten oxide selected from Nb.sub.12WO.sub.33, Nb.sub.26W.sub.4O.sub.77, Nb.sub.14W.sub.3O.sub.44, Nb.sub.16W.sub.5O.sub.55, Nb.sub.18W.sub.8O.sub.69, Nb.sub.2WO.sub.8, Nb.sub.18W.sub.16O.sub.93, Nb.sub.22W.sub.20O.sub.115, Nb.sub.8W.sub.9O.sub.47, Nb.sub.54W.sub.82O.sub.381, Nb.sub.20W.sub.31O.sub.143, Nb.sub.4W.sub.7O.sub.31, or Nb.sub.2W.sub.15O.sub.50, or combinations thereof.
7. The method of claim 4, wherein the working electrode comprises a mixture of a niobium tungsten oxide and an additional active material, preferably wherein the additional active material is Li.sub.4Ti.sub.5O.sub.12.
8. The method of claim 1, wherein the electrochemical cell has a working electrode comprising a niobium molybdenum oxide, preferably wherein: i) the ratio of Nb.sub.2O.sub.5 to MoO.sub.3 in the electrode is from 6:1 to 1:3, and/or ii) the niobium molybdenum oxide is selected from Nb.sub.2Mo.sub.3O.sub.14, Nb.sub.14Mo.sub.3O.sub.44 or Nb.sub.12MoO.sub.44.
9.-10. (canceled)
11. The method of claim 1, wherein the method comprises a cycle of charging and discharging, or discharging and charging the electrochemical cell.
12. The method of claim 11, wherein the method comprises 2 cycles or more, 5 cycles or more, 10 cycles or more, 50 cycles or more, 100 cycles or more, 500 cycles or more, 1,000 cycles or more, or 2,000 cycles or more.
13. An electrochemical cell comprising an electrode, wherein the electrode comprises niobium tungsten oxide, wherein the ratio of Nb.sub.2O.sub.5 to WO.sub.3 in the electrode is from 8:5 to 11:20.
14. The electrochemical cell of claim 13, wherein the electrode comprises Nb.sub.16W.sub.5O.sub.55, Nb.sub.18W.sub.8O.sub.69, Nb.sub.2WO.sub.8, Nb.sub.18W.sub.16O.sub.93, or Nb.sub.22W.sub.20O.sub.115, or combinations thereof.
15. The electrochemical cell of claim 13, wherein the electrode comprises Nb.sub.16W.sub.5O.sub.55 or Nb.sub.18W.sub.16O.sub.93.
16. The electrochemical cell of claim 13, wherein the electrode comprises a mixture of a niobium tungsten oxide and an additional active material, preferably wherein the additional active material is Li.sub.4Ti.sub.5O.sub.12.
17. An electrochemical cell comprising an electrode, wherein the electrode comprises niobium molybdenum oxide, wherein the ratio of Nb.sub.2O.sub.5 to MoO.sub.3 in the electrode is from 6:1 to 1:3.
18. The electrochemical cell of claim 17, wherein the electrode comprises Nb.sub.2Mo.sub.3O.sub.14, Nb.sub.14Mo.sub.3O.sub.44 or Nb.sub.12MoO.sub.44, preferably Nb.sub.2Mo.sub.3O.sub.14.
19. (canceled)
20. The electrochemical cell of claim 13, wherein the electrode does not have a porous nor hierarchical structure, preferably wherein the electrode has a specific surface area of less than 100 m.sup.2.Math.g.sup.1.
21. The electrochemical cell of claim 13, wherein the electrode comprises a niobium tungsten oxide in particulate form, preferably wherein the niobium tungsten oxide particles have an average primary particle size of at least 1 m.
22. (canceled)
23. The electrochemical cell of claim 13, in a lithium ion battery.
24. The electrochemical cell of claim 13, in a vehicle.
25. (canceled)
Description
SUMMARY OF THE FIGURES
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DETAILED DESCRIPTION OF THE INVENTION
[0065] The invention generally provides an electrode comprising a niobium tungsten oxide, an electrochemical cell comprising the electrode, and the use of the cell, for example, in a lithium ion battery, at high C-rates of 5C during charging and/or discharging.
[0066] The preparation of Nb.sub.16W.sub.5O.sub.55 has previously been described by, amongst others, Roth and Wadsley. The preparation of Nb.sub.18W.sub.16O.sub.93 has previously been described by, amongst others, Stephensen. However, the electrochemical properties of Nb.sub.16W.sub.5O.sub.55 and Nb.sub.18W.sub.16O.sub.93 are not described in these documents.
[0067] Electrodes comprising Nb.sub.8W.sub.9O.sub.47 (Montemayor et al.); Nb.sub.26W.sub.4O.sub.77 (Fuentes et al.); Nb.sub.14W.sub.3O.sub.44 (Fuentes et al.); and Nb.sub.xW.sub.1-xO.sub.3-x/2, wherein 0x0.25 (Yamada et el.), have been previously described. However, the capacity of the materials against the C-rate was not measured.
[0068] Electrodes comprising Nb.sub.8-xW.sub.9-xO.sub.47, wherein 1x6, have been described by Cruz et el. However, the electrochemical cell comprising the electrodes is used under limited conditions, and there is no disclosure of the cell operating under high-rate conditions. Moreover, the authors report that irreversible structural transformations in the matrix-host result in loss of capacity after the first cycle.
[0069] Electrodes comprising Nb.sub.12WO.sub.33 have been described by Saritha et al. and Yan et al. Yan et al. test an electrochemical cell comprising a electrospun Nb.sub.12WO.sub.33 electrode at a maximum current density of 700 mA.Math.g.sup.1 (corresponding to a C-rate of 3.6C). Saritha et al. test an electrochemical cell comprising Nb.sub.12WO.sub.33 at a reported C-rate of no more than 20C.
[0070] However, Saritha et al. apparently define the C-rate as reaction (i.e. removal or insertion) of one lithium ion in one hour. This corresponds to one electron transfer per formula unit. Thus, the 20C rate for Nb.sub.12WO.sub.33 reported by Saritha et al. corresponds to 1.54C using the convention defined in this work (equivalent to 294 mA.Math.g.sup.1).
[0071] The present inventors have developed electrodes comprising a niobium tungsten oxide that has favorable lithium ion diffusion properties, and thus exhibit superior performance even with micron sizes particles. The electrodes exhibit extremely high volumetric energy densities and high capacities at high rates of charging and discharging.
[0072] The voltage values described herein are made with reference to Li.sup.+/Li, as is common in the art.
[0073] The C-rate is a measure of the rate at which a battery is discharged relative to its maximum capacity. The C-rate may be defined as the inverse of the number of hours to reach a defined theoretical capacity e.g., 10C corresponds to a 6 min discharge or charge time. In this work, C-rate is defined relative to one electron transfer per transition metal, e.g., for Nb.sub.16W.sub.5O.sub.55, 1C=171.3 mA.Math.h.Math.g.sup.1, 20C=3426 mA.Math.h.Math.g.sup.1. The theoretical capacity is calculated by:
[0074] where n is the number of electrons transferred per formula unit, F is Faraday's constant, 3.6 is a conversion factor between Coulombs and the conventional mA.Math.h.Math.g.sup.1, and m is the mass per formula unit. Thus, a 1C rate corresponds to the reaction (i.e. insertion or removal) of 21 lithium ions per formula unit of Nb.sub.16W.sub.5O.sub.55 in one hour, as this material contains 21 transition metals per formula unit.
[0075] The high-rate application may also be described by reference to (gravimetric) current density, for example where the current density is at least 800 mA.Math.g.sup.1 or 1000 mA.Math.g.sup.1. Current density is related to C-rate by:
[0076] Thus, for Nb.sub.16W.sub.5O.sub.55 a current density of 800 mA.Math.g.sup.1 corresponds to a C-rate of 4.67C and for Nb.sub.18W.sub.16O.sub.93 a current density of 800 mA.Math.g.sup.1 corresponds to a C-rate of 5.36C using the convention defined in this work.
[0077] All (gravimetric) capacities are quoted based on the mass of the active electrode material.
Working Electrode
[0078] The invention provides a working electrode comprising a niobium tungsten oxide. The working electrode is electrically conductive, and is electrically connectable to a counter electrode, for example within an electrochemical cell.
[0079] The working electrode may be an anode or cathode during a discharge step, for example in a lithium ion battery. Typically, the working electrode is the anode during a discharge step.
[0080] Typically, the working electrode for use in the method comprises a molar ratio of Nb.sub.2O.sub.5 to WO.sub.3 from 6:1 to 1:15. Preferably, the molar ratio of Nb.sub.2O.sub.5 to WO.sub.3 in the working electrode is from 8:5 to 11:20.
[0081] Typically, the working electrode for use in the method comprises a niobium tungsten oxide selected from Nb.sub.12WO.sub.33, Nb.sub.26W.sub.4O.sub.77, Nb.sub.14W.sub.3O.sub.44, Nb.sub.16W.sub.5O.sub.55, Nb.sub.18W.sub.8O.sub.69, Nb.sub.2WO.sub.8, Nb.sub.18W.sub.16O.sub.93, Nb.sub.22W.sub.20O.sub.115, Nb.sub.8W.sub.9O.sub.47, Nb.sub.54W.sub.82O.sub.381, Nb.sub.20W.sub.31O.sub.143, Nb.sub.4W.sub.7O.sub.31, or Nb.sub.2W.sub.15O.sub.50 or combinations thereof. Preferably, the working electrode comprises Nb.sub.16W.sub.5O.sub.55, Nb.sub.18W.sub.8O.sub.69, Nb.sub.2WO.sub.8, Nb.sub.18W.sub.16O.sub.93 or Nb.sub.22W.sub.20O.sub.115 or combinations thereof.
[0082] Typically, the molar ratio of Nb.sub.2O.sub.5 to WO.sub.3 in the working electrode is from 8:5 to 11:20. Preferably, the molar ratio of Nb.sub.2O.sub.5 to WO.sub.3 in the working electrode is 8:5 or 9:16.
[0083] Typically, the working electrode comprises Nb.sub.16W.sub.5O.sub.55, Nb.sub.18W.sub.8O.sub.69, Nb.sub.2WO.sub.8, Nb.sub.18W.sub.16O.sub.93, or Nb.sub.22W.sub.20O.sub.115, or combinations thereof. Preferably the working electrode comprises Nb.sub.16W.sub.5O.sub.55 or Nb.sub.18W.sub.16O.sub.93, or combinations thereof.
[0084] Optionally, the working electrode comprises a mixture of niobium tungsten oxide and an additional active material. The additional active material may be an additional metal oxide. For example, the working electrode may comprise a mixture of niobium tungsten oxide and an additional active material selected from lithium titanate (LTO; Li.sub.4Ti.sub.5O.sub.12), titanium niobium oxides (for example TiNb.sub.2O.sub.7), titanium tantalum oxides (for example TiTa.sub.2O.sub.7), tantalum molybdenum oxides (for example Ta.sub.8W.sub.9O.sub.47) and niobium molybdenum oxides (for example Nb.sub.2Mo.sub.3O.sub.14).
[0085] Graphite may also be used as an additional active material. A working electrode comprising a mixture of niobium tungsten oxide and graphite is cheaper to produce while maintaining the beneficial properties outlined above.
[0086] Preferably, the working electrode comprises a mixture of niobium tungsten oxide and LTO. The ratio of niobium tungsten oxide to LTO may be from 95:5 to 5:95 by weight. For example, the ratio may be from 90:10 to 10:90 by weight, from 80:20 to 20:80 by weight, from 70:30 to 30:70 by weight, from 60:40 to 40:60 by weight or the ratio of niobium tungsten oxide to LTO may be 1:1 by weight.
[0087] Preferably, the working electrode consists essentially of niobium tungsten oxide and an additional active material. For example, the working electrode consists essential of a mixture of niobium tungsten oxide and LTO.
[0088] Typically, the working electrode does not have a porous nor hierarchical structure. For example, the electrode material may have a specific surface area of less than 20 m.sup.2.Math.g.sup.1, less than 10 m.sup.2.Math.g.sup.1, less than 5 m.sup.2.Math.g.sup.1, less than 3 m.sup.2.Math.g.sup.1, less than 2 m.sup.2.Math.g.sup.1 or less than 1 m.sup.2.Math.g.sup.1.
[0089] The specific surface area of the electrode material may be known, or it may be determined using standard techniques such as N2 adsorption isotherm analysis and Brunauer-Emmett Teller (BET) theory.
[0090] Alternatively, the working electrode may have a porous structure. For example, the working electrode may have a specific surface area of at least 50 m.sup.2.Math.g.sup.1, at least 60 m.sup.2.Math.g.sup.1, 70 m.sup.2.Math.g.sup.1, 80 m.sup.2.Math.g.sup.1, 90 m.sup.2.Math.g.sup.1, 100 m.sup.2.Math.g.sup.1, 150 m.sup.2.Math.g.sup.1, 200 m.sup.2.Math.g.sup.1, 300 m.sup.2.Math.g.sup.1, g or 400 m.sup.2 g.sup.1.
[0091] The working electrode may have a pore volume of of at least 0.1 cm.sup.3.Math.g.sup.1, at least 0.2 cm.sup.3.Math.g.sup.1, at least 0.4 cm.sup.3.Math.g.sup.1, at least 0.5 cm.sup.3.Math.g.sup.1, at least 0.7 cm.sup.3.Math.g.sup.1, at least 0.8 cm.sup.3.Math.g.sup.1, at least 0.9 cm.sup.3.Math.g.sup.1, at least 1.0 cm.sup.3.Math.g.sup.1, at least 1.5 cm.sup.3.Math.g.sup.1 or at least 2.0 cm.sup.3.Math.g.sup.1.
[0092] The pore volume of the electrode material may be known, or it may be determined using standard techniques such as N2 adsorption isotherm analysis and Barrett-Joyner-Halenda (BJH) theory.
[0093] The porous working electrode may have an average pore size (largest cross section) of at least 1 nm, at least 5 nm, at least, 10 nm, at least 20 nm, at least 30 nm, at least 40 nm, at least 50 nm or at least 100 nm.
[0094] The porous working electrode may have macroporous structure. Thus, the porous working electrode may contain pores having pores having a largest cross section of at least 200 nm, at least 500 nm, at least 1 m, or at least 5 m.
[0095] The pore size of the electrode material may be known, or it may be determined using standard techniques such as scanning electron microscopy (SEM).
[0096] The working electrode may additionally comprise porous carbon, such as porous reduced graphene oxide.
[0097] Electrodes comprising porous carbon are generally light and conductive, and can provide large pore volumes, which can allow rapid transport of lithium ions and electrons to the active materials. They may also increase the electrochemical capacity of the working device.
[0098] The working electrode may additionally comprise reduced graphene oxide, Ketjen black or Super P carbon.
[0099] Alternatively, the working electrode may have a hierarchical structure. For example, the working electrode may additionally comprise hierarchical reduced graphene oxide (rGO).
[0100] Typically, the working electrode comprise a niobium tungsten oxide in particulate form. The size of the niobium tungsten oxide particles of the working electrode may be known, or it may be determined using standard techniques such as SEM.
[0101] Typically, the niobium tungsten oxide particles of the working electrode have primary particle size of at least 1 m. The primary particle size is the size of the individual crystallite. It is the smallest identifiable subdivision in a particulate system. For example, the niobium tungsten oxide particles have a primary particle size of at least 2 m, 3 m, 4 m, 5 m or 10 m.
[0102] The individual niobium tungsten oxide particles may agglomerate to form secondary particles. Typically, the niobium tungsten oxide particles have an agglomerate (secondary) particle size of at least 5 m. More preferably, the niobium tungsten oxides have an agglomerate particle size of at least 10 m, 15 m, 20 m, 25 m or 30 m.
[0103] Where present, the additional active material may be in particulate form. The size of the additional active material particles may be known, or it may be determined using standard techniques such as SEM.
[0104] Preferably, the additional active material particles have a primary particle size of 1 m or less. For example, the additional active material particles have a primary particle size of 800 nm or less, 750 nm or less, 700 nm or less, 600 nm or less, 500 nm or less, 400 nm or less, 300 nm or less, 200 nm or less or 150 nm or less. Particulate lithium titanate typically has a particle size within this range.
[0105] Electrodes comprising a mixture of niobium tungsten oxide and an additional active material having partial sizes within the ranges described above can be charged and discharged at very high C-rates and at very high charge densities.
[0106] To improve conductivity at the working electrode, a conductive carbon material (e.g., carbon black, graphite, nanoparticulate carbon powder, carbon fiber and/or carbon nanotubes) is typically admixed with the working electrode material. Alternatively, the conductive carbon material may be coated onto the working electrode material. In one embodiment, the working electrode comprises porous carbon, such as porous reduced graphene oxide, which may wrap the larger niobium oxides particles.
[0107] Typically, the working electrode contains 1-5% by weight of binders.
[0108] The electrode may consist essentially of niobium tungsten oxide.
[0109] Alternatively, the working electrode is admixed with a binder or adhesive. Some examples of binders or adhesives include PVDF, PTFE, CMC, PAA, PMMA, PEO, SBR and co-polymers thereof.
[0110] The working electrode is typically fixed to a current collector, such as a copper or aluminum collector, which may be in the form of a plate.
[0111] The inventors have assessed a working electrode comprising a particulate niobium tungsten oxide using a standard electrode configuration of 8:1:1 active material/carbon/binder with a 2-3 mg.Math.cm.sup.2 loading of active material and a 1.27 cm.sup.2 electrode area against a lithium counter electrode in a 2032-type coin cell geometry and using 1.0 M LiPF.sub.6 in ethylene carbonate/dimethyl carbonate as electrolyte.
[0112] Under these conditions, the inventors have found that a working electrode comprising a niobium tungsten oxide can maintain a capacity of up to 150 mA.Math.h.Math.g.sup.1 at 100 for 1000 cycles, and a capacity of up to 125 mA.Math.h.Math.g.sup.1 at 20C for 750 cycles.
[0113] In addition, the inventors have found that a working electrode comprising a niobium tungsten oxide has a sloping, rather than flat, voltage profile.
[0114] The inventors have assessed solid-state lithium diffusion within niobium tungsten oxides using both pulsed field gradient NMR (PFG NMR) and the galvanostatic intermittent titration technique (GITT). The inventors have found that the niobium tungsten oxides have a solid-state lithium diffusion coefficient (D.sub.Li) of 10.sup.13 to 10.sup.12 m.sup.2.Math.s.sup.1 at 298 K. This corresponds to a characteristic diffusion length of ca. 10 m for a 1 minute discharge.
[0115] The invention also provides a working electrode comprising a niobium molybdenum oxide. The working electrode is electrically conductive, and is electrically connectable to a counter electrode, for example within an electrochemical cell.
[0116] The working electrode may be an anode or cathode during a discharge step, for example in a lithium ion battery. Typically, the working electrode is the anode during a discharge step.
[0117] Typically, the working electrode for use in the method comprises a molar ratio of Nb.sub.2O.sub.5 to MoO.sub.3 of from 6:1 to 1:3. Preferably, the molar ratio of Nb.sub.2O.sub.5 to MoO.sub.3 in the working electrode is 1:3.
[0118] Typically, the working electrode for use in the method comprises a niobium molybdenum oxide selected from Nb.sub.2Mo.sub.3O.sub.14, Nb.sub.14Mo.sub.3O.sub.44 or Nb.sub.12MoO.sub.44. Preferably, the working electrode comprises Nb.sub.2Mo.sub.3O.sub.14.
[0119] Typically, the working electrode does not have a porous nor hierarchical structure. The working electrode may have a specific surface area, pore volume and average pore size as described above.
[0120] Typically, the working electrode comprise a niobium molybdenum oxide in particulate form. The niobium molybdenum oxide particles of the working electrode may have a primary or agglomerate particle size as described above.
[0121] The working electrode may contain binders and adhesives as described above.
Electrochemical Cell
[0122] The present invention also provides an electrochemical cell comprising a working electrode of the invention. The working electrode may be an anode or cathode during a discharge step, for example in a lithium ion battery. Typically, the working electrode is the anode during a discharge step.
[0123] The electrochemical cell typically comprises a counter electrode and an electrolyte. The electrochemical cell may comprise a current collecting plate. The electrochemical cell may be in electrical connection with a power supply. The electrochemical cell may be in electrical connection with a measurement device, for example an ammeter or voltmeter.
[0124] The counter electrode may be an anode or cathode during a discharge step, for example in a lithium ion battery. The counter electrode is typically the cathode during a discharge step.
[0125] Suitable cathode materials include lithium-containing or lithium-intercalated material, such as a lithium metal oxide, wherein the metal is typically a transition metal such as Co, Fe, Ni, V or Mn, or combination thereof. Some examples of positive electrode materials include lithium cobalt oxide (LiCoO.sub.2), lithium nickel manganese cobalt oxide (NMC, LiNiMnCoO.sub.2, e.g. LiNi.sub.0.6Coo.sub.2Mn.sub.0.2O.sub.2), lithium vanadium fluorophosphate (LiVPO.sub.4F), lithium nickel cobalt aluminum oxide (NCA, LiNiCoAlO.sub.2), lithium iron phosphate (LFP, LiFePO.sub.4) and manganese-based spinels (e.g. LiMn.sub.2O.sub.4).
[0126] To improve conductivity at the counter electrode, a conductive carbon material (e.g., carbon black, graphite, nanoparticulate carbon powder or carbon nanotubes) is typically admixed with the counter electrode material. In one embodiment, the counter electrode comprises porous carbon, such as porous reduced graphene oxide.
[0127] In one embodiment, the counter electrode is substantially free of binders.
[0128] In an alternative embodiment, the counter electrode is admixed with a binder or adhesive. Some examples of binders or adhesives include PVDF, PTFE, CMC, PAA, PMMA, PEO, SBR and co-polymers thereof.
[0129] The counter electrode is typically fixed to a current collecting substrate, such as an aluminum plate.
[0130] Typically, the electrolyte in the electrochemical cell is suitable for solubilising lithium ions.
[0131] Typically, the electrolyte in a charged and discharged cell contains lithium ions.
[0132] Typically, the electrolyte comprises lithium salts, such as LiTFSI, (bis(trifluoromethane)sulfonimide lithium salt, LiPF.sub.6, LiBF.sub.4, LiClO.sub.4, LiTF (lithium triflate) or lithium bis(oxalato) borate (LiBOB).
[0133] The electrolyte may be a liquid electrolyte, such as a liquid at ambient temperature, for example at 25 C.
[0134] The electrolyte may be a non-aqueous electrolyte. The electrolyte may comprise a polar aprotic solvent. The electrolyte may comprise an organic solvent. Solvents for dissolving lithium ions are well known in the art.
[0135] Suitable solvents include carbonate solvents. For example propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), chloroethylene carbonate, fluorocarbonate solvents (e.g., fluoroethylene carbonate and trifluoromethyl propylene carbonate), as well as the dialkylcarbonate solvents, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC).
[0136] Suitable solvents also include sulfone solvents. For example methyl sulfone, ethyl methyl sulfone, methyl phenyl sulfone, methyl isopropyl sulfone (MiPS), propyl sulfone, butyl sulfone, tetramethylene sulfone (sulfolane), phenyl vinyl sulfone, allyl methyl sulfone, methyl vinyl sulfone, divinyl sulfone (vinyl sulfone), di phenyl sulfone (phenyl sulfone), dibenzyl sulfone (benzyl sulfone), vinylene sulfone, butadiene sulfone, 4-methoxyphenyl methyl sulfone, 4-chlorophenyl methyl sulfone, 2-chlorophenyl methyl sulfone, 3,4-dichlorophenyl methyl sulfone, 4-(methylsulfonyl)toluene, 2-(methylsulfonyl) ethanol, 4-bromophenyl methyl sulfone, 2-bromophenyl methyl sulfone, 4-fluorophenyl methyl sulfone, 2-fluorophenyl methyl sulfone, 4-aminophenyl methyl sulfone, a sultone (e.g., 1,3-propanesultone), and sulfone solvents containing ether groups (e.g., 2-methoxyethyl(methyl)sulfone and 2-methoxyethoxyethyl(ethyl)sulfone).
[0137] Suitable solvents also include silicon-containing solvents such as a siloxane or silane. For example hexamethyldisiloxane (HMDS), 1,3-divinyltetramethyldisiloxane, the polysiloxanes, and polysiloxane-polyoxyalkylene derivatives. Some examples of silane solvents include methoxytrimethy Isilane, ethoxytrimethy Isilane, dimethoxydimethylsilane, methyltrimethoxysilane, and 2-(ethoxy)ethoxytrimethylsilane.
[0138] Typically, an additive may be included in the electrolyte to improve performance. For example vinylene carbonate (VC), vinyl ethylene carbonate, allyl ethyl carbonate, t-butylene carbonate, vinyl acetate, divinyl adipate, acrylic acid nitrile, 2-vinyl pyridine, maleic anhydride, methyl cinnamate, ethylene carbonate, halogenated ethylene carbonate, -bromo--butyrolactone, methyl chloroformate, 1,3-propanesultone, ethylene sulfite (ES), propylene sulfite (PS), vinyl ethylene sulfite (VES), fluoroethylene sulfite (FES), 12-crown-4 ether, carbon dioxide (CO.sub.2), sulfur dioxide (SO.sub.2), and sulfur trioxide (SO.sub.3).
[0139] The electrochemical cell may also include a solid porous membrane positioned between the negative and positive electrodes. The solid porous membrane may partially or completely replace the liquid electrolyte. The solid porous membrane may comprise a polymer (e.g., polyethylene, polypropylene, or copolymer thereof) or an inorganic material, such as a transition metal oxide (e.g., titania, zirconia, yttria, hafnia, or niobia) or main group metal oxide, such as silicon oxide, which can be in the form of glass fiber.
[0140] The solid non-porous membrane may comprises a lithium-ion conductor. For example, LLZO (garnet family), LSPO (LISICON family), LGPS (thio-LISICON family), LATP/LAGP (NASICON family), LLTO (perovskite family) and phosphide/sulfide glass ceramics
[0141] The electrochemical cell may be charged or discharged at a C-rate of at least 5C, such as the electrochemical cell may be charged or discharged at a C-rate of at least 5C with respect to one electron transfer per transition metal per formula unit of working electrode material. Preferably, the electrochemical cell may be charged or discharged at a C-rate of at least 100, 15C, 20C, 25C, 30C, 35C, 40C, 50C, 60C or 80C.
[0142] The electrochemical cell may be charged or discharged at a current density of at least 750 mA.Math.g.sup.1. Preferably, the electrochemical cell may be charged or discharged at a current density of at least 800 mA.Math.g.sup.1, 850 mA.Math.g.sup.1, 900 mA.Math.g.sup.1, 950 mA.Math.g.sup.1, 1000 mA.Math.g.sup.1, 1050 mA.Math.g.sup.1, 1100 mA.Math.g.sup.1, 1200 mA.Math.g.sup.1 or 1300 mA.Math.g.sup.1.
[0143] The electrochemical cell may have a volumetric charge density of at least 200, 300, 400, 500, 600 or 700 A.Math.h.Math.L.sup.1 at 1C. Typically, the electrochemical cell has a volumetric charge density of up to 100, 200, 300 or 400 A.Math.h.Math.L.sup.1 at 20C.
[0144] The electrochemical cell may have a capacity retention of at least 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, or 100% at 20C maintained over at least 50, 100, 150, 200, 250, 300, 400, 500, 600, 700, 800, 900, 1,000, 1,200, 1,500, 1,800, or 2,000 cycles.
[0145] The electrochemical cell may be regarded as fully charged when the voltage passes a threshold value. For example, an electrochemical cell comprising a lithium metal anode and a niobium tungsten oxide cathode may be regarded as fully charged when the voltage rises above a practicable level, such as where the voltage rises above 2.0 V against Li/Li.sup.+, such as above 2.25 V or above 2.5 V.
[0146] The electrochemical cell may be regarded as fully discharged when the voltage passes a threshold value. For example, an electrochemical cell comprising a lithium metal anode and a niobium tungsten oxide cathode may be regarded as fully discharged when the voltage drops below a practicable level, such as where the voltage drops below 1.5 V against Li/Li.sup.+, such as below 1.25 V or below 1.0 V.
[0147] The electrochemical cell may be a lithium ion cell.
Methods
[0148] The invention provides a method of charging and/or discharging an electrochemical cell at a C-rate of at least 5C, such as the electrochemical cell may be charged or discharged at a C-rate of at least 5C with respect to one electron transfer per transition metal per formula unit of working electrode material. The electrochemical cell comprises a working electrode comprising a niobium tungsten oxide and/or niobium molybdenum oxide. Preferably the electrochemical cell contains a counter electrode and an electrolyte.
[0149] Preferably the method is a method of charging and/or discharging an electrochemical cell at a C-rate of at least 10C, 15C, 20C, 25C, 30C, 35C, 40C, 50C, 60C or 80C.
[0150] The method may be a method of charging and/or discharging an electrochemical cell at a current density of at least 750 mA.Math.g.sup.1 such as at least 800 mA.Math.g.sup.1. Preferably the method is a method of charging and/or discharging an electrochemical cell at a current density of at least 800 mA.Math.g.sup.1, 850 mA.Math.g.sup.1, 900 mA.Math.g.sup.1, 950 mA.Math.g.sup.1, 1000 mA.Math.g.sup.1, 1050 mA.Math.g.sup.1, 1100 mA.Math.g.sup.1, 1200 mA.Math.g.sup.1 or 1300 mA.Math.g.sup.1.
[0151] The method may involve a cycle of charging and discharging or discharging and charging the electrochemical cell. The cycle may be repeated more than once. Thus, the method comprises 2 cycles or more, 5 cycles or more, 10 cycles or more, 50 cycles or more, 100 cycles or more, 500 cycles or more, 1,000 cycles or more, or 2,000 cycles or more.
Battery
[0152] The present invention also provides a battery comprising one or more electrochemical cells of the invention. The battery may be a lithium ion battery.
[0153] Where there are a plurality of cells, these may be provided in series or parallel.
[0154] A battery of the invention may be provided in a road vehicle, such as an automobile, moped or truck. Alternatively, a battery of the invention may be provided in a rail vehicle, such as a train or a tram. A battery of the invention may also be provided in an electric bicycle (e-bike).
[0155] A battery of the invention may be provided in a regenerative braking system.
[0156] A battery of the invention may be provided in a portable electronic device, such as a mobile phone, laptop or tablet.
[0157] A battery of the invention may be provided in a power grid management system.
Uses
[0158] The invention generally provides the use of a working electrode comprising a niobium tungsten oxide in a high-rate electrochemical cell, such as an electrochemical cell as described herein. Typically, the electrochemical cell may be charged or discharged at a C-rate of at least 5C, such as the electrochemical cell may be charged or discharged at a C-rate of at least 5C with respect to one electron transfer per transition metal per formula unit of working electrode material. Preferably, the electrochemical cell may be charged or discharged at a C-rate of at least 10C, 15C, 20C, 25C, 30C, 35C, 40C, 50C, 60C or 80C.
[0159] The electrochemical cell may be charged or discharged at a current density of at least 750 mA.Math.g.sup.1. Preferably, the electrochemical cell may be charged or discharged at a current density of at least 800 mA.Math.g.sup.1, 850 mA.Math.g.sup.1, 900 mA.Math.g.sup.1, 950 mA.Math.g.sup.1, 1000 mA.Math.g.sup.1, 1050 mA.Math.g.sup.1, 1100 mA.Math.g.sup.1, 1200 mA.Math.g.sup.1 or 1300 mA.Math.g.sup.1.
[0160] The working electrode may find use in the methods described herein.
Other Preferences
[0161] Each and every compatible combination of the embodiments described above is explicitly disclosed herein, as if each and every combination was individually and explicitly recited.
[0162] Various further aspects and embodiments of the present invention will be apparent to those skilled in the art in view of the present disclosure.
[0163] and/or where used herein is to be taken as specific disclosure of each of the two specified features or components with or without the other. For example A and/or B is to be taken as specific disclosure of each of (i) A, (ii) B and (iii) A and B, just as if each is set out individually herein.
[0164] Unless context dictates otherwise, the descriptions and definitions of the features set out above are not limited to any particular aspect or embodiment of the invention and apply equally to all aspects and embodiments which are described.
[0165] Certain aspects and embodiments of the invention will now be illustrated by way of example and with reference to the figures described above.
Experimental
[0166] The following examples are provided solely to illustrate the present invention and are not intended to limit the scope of the invention, as described herein.
Synthesis of Nb.sub.16W.sub.5O.sub.55 and Nb.sub.18W.sub.16O.sub.93
[0167] Nb.sub.16W.sub.5O.sub.55 and Nb.sub.18W.sub.16O.sub.93 were synthesized by co-thermal oxidation of dark blue NbO.sub.2 (Alfa Aesar, 99+%) and brown WO.sub.2 (Alfa Aesar, 99.9%) in approximately one to five gram batches. The partially reduced oxides were massed to within 0.001 g of the 16:5 or 18:16 molar ratios, ground together by hand with an agate mortar and pestle, pressed into a pellet at 10 MPa, and heated in a platinum crucible at a rate of 10 K.Math.min.sup.1 to 1473 K, and naturally cooled in the furnace over ca. 2 h.
Synthesis of Nb.sub.8W.sub.9O.sub.47 and Nb.sub.12WO.sub.33
[0168] Nb.sub.8W.sub.9O.sub.47 and Nb.sub.12WO.sub.33 were synthesized by co-thermal oxidation of dark blue NbO.sub.2 (Alfa Aesar, 99+%) and brown WO.sub.2 (Alfa Aesar, 99.9%) in approximately one to five gram batches. The partially reduced oxides were massed to within 0.001 g of the 8:9 or 12:1 molar ratios, ground together by hand with an agate mortar and pestle, pressed into a pellet at 10 MPa, and heated in a platinum crucible at a rate of 10 K.Math.min.sup.1 to 1473 K, and naturally cooled in the furnace over ca. 2 h.
Synthesis of Nb.sub.2Mo.sub.3O.sub.14
[0169] Nb.sub.2Mo.sub.3014 synthesized by co-thermal oxidation of dark blue NbO.sub.2 (Alfa Aesar, 99+%) and dark brown MoO.sub.2 (Sigma, 99%), or co-thermal oxidation of white Nb.sub.2O.sub.5 (Sigma, 99.9985%) and off-white MoO.sub.3 (Sigma, 99.5%), in approximately one to five gram batches. The partially reduced oxides were massed to within 0.001 g of the 2:3 or 1:3 molar ratio, ground together by hand with an agate mortar and pestle, pressed into a pellet at 10 MPa, and heated in a platinum or alumina crucible at a rate of 10 K.Math.min.sup.1 to 873 K, 923 K or 973 K, and quenched in air outside the furnace on a metal plate.
Microscopic Characterisation
[0170] Scanning electron microscopy (SEM) images were taken with a Zigma VP instrument (Zeiss) at 3.0 kV and a MIRA3 instrument (TESCAN) at 5.0 kV with secondary electron detection. Tap density was recorded on an AutoTap (Quantachrome Instruments) instrument operating at 257 taps.Math.min.sup.1. Tap densities were measured according to ASTM international standard B527-15 modified to accommodate a 5 to 10 cm.sup.3 graduated cylinder.
[0171] Both Nb.sub.16W.sub.5O.sub.55 and Nb.sub.18W.sub.16O.sub.93 formed subhedral particles with ca. 3 to 10 m primary particles that appeared in the electron microscope to be intergrown/cemented into larger secondary particles of ca. 10 to 30 m (
[0172] Nb.sub.16W.sub.5O.sub.55 has a monoclinic structure comprised of subunits of corner-shared octahedra arranged into ReO.sub.3-like blocks, four octahedra wide by five octahedra long, and infinite in the third dimension (
[0173] Nb.sub.18W.sub.16O.sub.93 is orthorhombic, a 131 superstructure of the classic tetragonal tungsten bronze (TTB) (
Electrochemical Characterization of Nb.sub.16W.sub.5O.sub.55 and Nb.sub.18W.sub.16O.sub.93
[0174] Electrochemical characterisation was conducted using a stainless steel 2032-coin cell (Cambridge Energy Solutions) with a conical spring, two 0.5 mm stainless steel spacer disks, a plastic gasket, and a glass microfiber separator (Whatman). To form the niobium tungsten oxide electrode, the niobium tungsten oxide and conductive carbon (Super P, TIMCAL) were ground by hand in an agate mortar and pestle in an 8:1 mass ratio. This powder was ground in a 9:1 mass ratio with poly(vinylidene difluoride) (PVDF, Kynar) dispersed in N-methyl pyrrolidone (NMP, Sigma-Aldrich, anhydrous, 99.5%). The slurry was coated onto aluminium or copper foil with a doctor blade (bar coater). The NMP was removed by heating in an oven at 60 C. for 24 hours. Though standard, Super P carbon is a nanoparticulate powder and NMP is a hazardous organic solvent so appropriate nanoparticle cabinets/fume hoods should be used.
[0175] This 80/10/10 metal oxide/carbon/polymer electrode served as the cathode against a Li metal disk (LTS Research, 99.95%) anode in a half-cell geometry. In the electrochemical tests, the electrolyte was 1 M LiPF.sub.6 dissolved in 1:1 v/v ethylene carbonate/dimethyl carbonate (EC/DMC; Sigma-Aldrich, battery grade; also known as LP30). No additives were used. Electrochemistry was performed in a temperature-controlled room at 293 K. A Biologic galvanostat/potentiostat with EC-Lab software was used to perform the electrochemical measurements.
[0176] Dense electrodes of large particles with 2 to 3 mg.Math.cm.sup.2 active mass loading were tested at current densities corresponding to discharge times of several hours to tens of seconds. Nb.sub.16W.sub.5O.sub.55 was charged with a 1 h constant voltage step at the top of charge to ensure a comparable starting point on discharge; Nb.sub.19W.sub.16O.sub.93 was cycled without this step and stored over 100 mA.Math.h.Math.g.sup.1 at 60C (i.e., in <60 s). High-rate cycling for 1000 cycles was performed on both oxides at 100/200 constant current without any potentiostatic step.
[0177] Reaction of Nb.sub.16W.sub.5O.sub.55 with lithium (
[0178] The average voltage of Nb.sub.18W.sub.16O.sub.93 is 1.67 V (
Comparison of Cu Foil to Carbon-Coated Al Foil Current Collector
[0179]
[0180] For Nb.sub.16W.sub.5O.sub.55 cycled for 1000 cycles under constant current discharge and charge at 10C/20C, Cu foil current collector displayed moderately higher capacity than carbon-coated Al (C@Al) foil (
Longer Term Cycling as a Function of Minimum Cutoff Voltage
[0181]
[0182] Constant current constant voltage charging is a common method to maximize capacity without overcharging, as in (
Overpotential in a LiLi Symmetric Cell as a Function of Current Density
[0183] As a control, LiLi symmetric cells were cycled at current densities corresponding to those in
[0184] The overpotentials in the symmetric cell (
.SUP.7.Li Pulsed Field Gradient NMR Spectroscopy
[0185] .sup.7Li NMR diffusion spectra were recorded on a Bruker Avance III 300 MHz spectrometer using a Diff50 probehead equipped with an extended variable temperature capabilities. Spectra were recorded with the stimulated echo pulsed field gradient (PFG) sequence shown in
[0186] During this sequence, the gradient strength, g, was varied from 0.87 to 1800 or 2300 G.Math.cm.sup.1, and 16 gradient steps were acquired using opt shaped pulses with 1024-4096 transients. The opt shape is a composite pulse that starts with a quarter of a sine wave, followed by a constant gradient, and ends with a ramp down (
[0187] Spectra were analysed in phase-sensitive mode and the response of the NMR signal intensity, I, to variation in g, is described by the Stejskal-Tanner equation:
[0188] where I.sub.0 is the intensity in the absence of gradients, is the gyromagnetic ratio (.sub.7Li=103.96210.sup.6.Math.s.sup.1.Math.T.sup.1), is the effective gradient pulse duration, and D is the diffusion coefficient. Here, NMR signal intensity and integral gave similar .sup.7Li diffusivities, but NMR signal intensities gave more reliable data, as evaluated by the standard deviation of the fit. Typical values ranged from 0.8 ms to 1.5 ms and 0.6 values ranged from 50-100 ms for the bronze and the block phase samples, respectively.
[0189] Diffusion spectra were recorded at elevated temperatures (333-453 K) due to the increase in T.sub.2 observed at high temperature (e.g. T.sub.2 for Li.sub.34Nb.sub.18W.sub.16O.sub.93 is approximately 700 s at room temperature vs. 1.9 ms at 453 K). (N.b. No attempt was made to calibrate the temperature for this experimental setup because a single-tuned .sup.7Li coil was used and no reliable .sup.7Li reference is routinely used for temperature calibration. The Bruker manual states that for static measurements, the temperature calibration should be within 7 degrees of the set value.) The increase in T.sub.2 allowed the use of longer gradient pulses, , that were necessary to measure diffusion coefficients in the solid oxides.
[0190] Representative .sup.7Li diffusion decay curves are shown in
[0191] Li.sub.6.3Nb.sub.16W.sub.5O.sub.55 shows two-component behavior with lithium transport as rapid as 4.310.sup.12 m.sup.2.Math.s.sup.1 at 333 K (
[0192] Li.sub.xNb.sub.18W.sub.16O.sub.93 (x=3.4, 6.8, 10.2) exhibited similar diffusion and activation energies, with room temperature diffusion coefficients of 1.110.sup.13 m.sup.2.Math.s.sup.1 and E.sub.a in the range of 0.27 to 0.30 eV.
TABLE-US-00001 TABLE 1 D.sub.Li and E.sub.a measurements for selected niobium tungsten oxide materials D.sub.Li (m.sup.2 .Math. s.sup.1) D.sub.Li (m.sup.2 .Math. s.sup.1) E.sub.a Compound at 298K at 413K (eV) Li.sub.6.3Nb.sub.16W.sub.5O.sub.55-a (15%) 2.1 10.sup.12 2.7 10.sup.11 0.23 0.04 Li.sub.6.3Nb.sub.16W.sub.5O.sub.55-b (85%) 1.7 10.sup.13 5.2 10.sup.13 0.10 0.04 Li.sub.8.4Nb.sub.16W.sub.5O.sub.55 1.6 10.sup.13 6.5 10.sup.13 0.13 0.01 (403K) Li.sub.3.4Nb.sub.18W.sub.16O.sub.93 1.1 10.sup.13 2.0 10.sup.12 0.27 0.03 Li.sub.6.8Nb.sub.18W.sub.16O.sub.93 1.1 10.sup.13 1.8 10.sup.12 0.30 0.01 Li.sub.10.2Nb.sub.18W.sub.16O.sub.93 1.1 10.sup.13 2.7 10.sup.12 0.29 0.01
[0193] Lithium diffusion in both niobium tungsten oxide structures is markedly faster than that of Li.sub.4+xTi.sub.5O.sub.12 or Li.sub.xTiO.sub.2 at ca. 10.sup.16-10.sup.15 m.sup.2.Math.s.sup.1 and is close to the best known lithium solid electrolytes (Table 2).
[0194] PFG NMR (
TABLE-US-00002 TABLE 2 D.sub.Li measurements for known materials D.sub.Li Compound Structure Type (m.sup.2 .Math. s.sup.1) T (K) Technique Reference Li.sub.10GeP.sub.2S.sub.12 Thio-LISICON .sup.2 10.sup.12 298 PFG NMR Kuhn, et al. (2013) Li.sub.10GeP.sub.2S.sub.12 Thio-LISICON .sup.4 10.sup.11 453 PFG NMR Kuhn, et al. (2013) Li.sub.7GePS.sub.8 Thio-LISICON .sup.2 10.sup.12 298 PFG NMR Kuhn, et al. (2013) Li.sub.7GePS.sub.8 Thio-LISICON .sup.4 10.sup.11 453 PFG NMR Kuhn, et al. (2013) Li.sub.10SnP.sub.2S.sub.12 Thio-LISICON 1.4 10.sup.12 298 PFG NMR Kuhn, et al. (2014) Li.sub.10SnP.sub.2S.sub.12 Thio-LISICON .sup.4 10.sup.11 453 PFG NMR Kuhn, et al. (2014) Li.sub.11Si.sub.2PS.sub.12 Thio-LISICON 3.5 10.sup.12 298 PFG NMR Kuhn, et al. (2014) Li.sub.11Si.sub.2PS.sub.12 Thio-LISICON .sup.4 10.sup.11 453 PFG NMR Kuhn, et al. (2014) Li.sub.7P.sub.3S.sub.11 Thio-LISICON 1-5 10.sup.12 303 PFG NMR Hayamizu, et al. (2013) Li.sub.7P.sub.3S.sub.11 Thio-LISICON 2-11 10.sup.12 353 PFG NMR Hayamizu, et al. (2013) -Li.sub.3PS.sub.4 Thio-LISICON 5.4 10.sup.13 373 PFG NMR Gobet, et al. amorphous-Li.sub.3PS.sub.4 Amorphous 6.5 10.sup.13 303 PFG NMR Hayamizu, et al. (2016) (Thio-LISICON) amorphous-Li.sub.3PS.sub.4 Amorphous 1.6-3.4 10.sup.12 353 PFG NMR Hayamizu, et al. (2016) (Thio-LISICON) Li.sub.0.6[Li.sub.0.2Sn.sub.0.8S.sub.2] Layered (O1) 2-20 10.sup.12 298 PFG NMR Holzmann, et al. Li.sub.0.6[Li.sub.0.2Sn.sub.0.8S.sub.2] Layered (O1) 2.6 10.sup.10 407 PFG NMR Holzmann, et al. Li.sub.3.4V.sub.0.6Si.sub.0.4O.sub.4 LISICON .sup.5 10.sup.15 333 tracer Ishiyama, et al. Li.sub.1.5Al.sub.0.5Ge.sub.1.5(PO.sub.4).sub.3 NASICON 2.9 10.sup.13 311 PFG NMR Hayamizu et al. (2017) Li.sub.1.2AI.sub.0.2Ti.sub.1.8 (PO.sub.4).sub.3 NASICON 1.5 10.sup.12 250 NMR relaxometry Arbi, et al. PFG NMR Li.sub.6.6La.sub.3Zr.sub.1.6Ta.sub.0.4O.sub.12 Garnet 3.5 10.sup.13 353 PFG NMR Hayamizu et al. (2015) Li.sub.7La.sub.3Zr.sub.2O.sub.12 Garnet 1.8 10.sup.18 298 NMR relaxometry Kuhn, et al. (2011) Li.sub.7La.sub.3Zr.sub.2O.sub.12 Garnet 1.3 10.sup.17 325 NMR relaxometry Kuhn, et al. (2011) Li.sub.7La.sub.3Zr.sub.2O.sub.12 Garnet 3.3 10.sup.14 530 NMR relaxometry Kuhn, et al. (2011) Graphite (Stage I) Graphite 1-2 10.sup.15 298 NMR relaxometry Langer, et al. Li metal bcc .sup.5 10.sup.15 298 PFG NMR (extrapolated) Mali, et al. Li metal bcc .sup.1 10.sup.12 400 PFG NMR Mali, et al. Li.sub.4Ti.sub.5O.sub.12 Spinel 3.2 10.sup.15 298 .sup.+-SR Sugiyama, et al. Li.sub.5.7Ti.sub.5O.sub.12 Spinel 2.7 10.sup.16 298 NMR relaxometry Wilkening, et al. LiTi.sub.2O.sub.4 Spinel 3.6 10.sup.15 298 .sup.+-SR Sugiyama, et al. -Li.sub.2TiO.sub.3 Li.sub.2SnO.sub.3 .sup.2 10.sup.17 433 NMR relaxometry Ruprecht, et al. Li.sub.0.12TiO.sub.2 micro Anatase component 4.7 10.sup.16 293 NMR relaxometry Wagemaker, et al. (2001) Li.sub.0.12TiO.sub.2 micro Li-titanate component 1.3 10.sup.15 293 NMR relaxometry Wagemaker, et al.(2001) Li.sub.0.06TiO.sub.2 nano Anatase component 1.9 10.sup.16 293 NMR relaxometry Wagemaker, et al. (2007) Li.sub.0.06TiO.sub.2 nano Li-titanate component 5.7 10.sup.16 293 NMR relaxometry Wagemaker, et al. (2007) Li.sub.0.12TiO.sub.2 nano Anatase component 1.1 10.sup.16 293 NMR relaxometry Wagemaker, et al. (2007) Li.sub.0.12TiO.sub.2 nano Li-titanate component 1.8 10.sup.16 293 NMR relaxometry Wagemaker, et al. (2007) Li.sub.0.12TiO.sub.2 nano Li-titanate component 4.9 10.sup.16 413 NMR relaxometry Wagemaker, et al. (2007) Li.sub.0.55TiO.sub.2 nano Li-titanate 1.7 10.sup.16 293 NMR relaxometry Wagemaker, et al. (2007) Li.sub.0.55TiO.sub.2 nano Li-titanate 4.6 10.sup.16 413 NMR relaxometry Wagemaker, et al. (2007) LiMn.sub.2O.sub.4 Spinel .sup.1 10.sup.20 350 NMR relaxometry Verhoevenm et al. LiMn.sub.2O.sub.4 Spinel 1.8 10.sup.16 623 Tracer Ishiyama, et al. (2016) LiNbO.sub.3 LiNbO.sub.3 7.5 10.sup.15 890 NMR relaxometry Bork and Heitjans Li.sub.3NbO.sub.4 Li.sub.3NbO.sub.4 .sup.4 10.sup.21 353 NMR relaxometry Ruprecht and Heitjans Li.sub.3NbO.sub.4 Li.sub.3NbO.sub.4 .sup.1 10.sup.16 553 NMR relaxometry Ruprecht and Heitjans Abbreviations: bcc = body-centered cubic, .sup.+-SR = muon spin resonance
Galvanostatic Intermittent Titration Technique (GITT)
[0195] Information on electrode thermodynamics, including phase transitions, and lithium kinetics can in principle be extracted from GITT measurements by tracking the voltage evolution after a brief current pulse as lithium diffuses and the chemical potential equilibrates within the electrode/particles. Reliable quantitative diffusion coefficients, D.sub.Li, are, however, difficult to extract from GITT alone. In order to determine a diffusion coefficient from GITT measurements, a diffusion length (L) must be defined but a battery electrode is a heterogeneous system. First, it is a composite of active material (here, metal oxide), porous carbon, and polymeric binder. Within this composite, there will be a distribution of particle sizes (unless single crystals or well-defined particles are employed; even then the diffusion varies with lattice direction). Furthermore, different regimes of diffusion must exist as there are solid/liquid interfaces and porous electrode structure. Nevertheless, in an electrode that does not undergo severe pulverization (e.g. an intercalation electrode), L is a fixed quantity throughout the experiment. Variation in L a parameter required to relate the rate of relaxation to the diffusion causes values of D.sub.Li to vary significantly between reports even for the same material. Thus, while a physically meaningful diffusion coefficient may not be extracted, a relative measure of diffusion is readily obtained. For this reason, we use an extracted proxy for lithium diffusion (D.sub.Li.Math.L.sup.2,
[0196] As shown in
Anode Material Ragone Plot
[0197] Anode material Ragone plot: the energy density of a cathode material is the product of capacity (Q) and voltage (V); however, this product does not work when comparing anode materials, where energy and voltage have an inverse relationship. In the calculation of the anode material Ragone plot in
[0198] When compared strictly on the basis of theoretical 1.0 Li.sup.+/TM reaction and crystallographic density of the active material, titania, niobia, and graphite all display theoretical charge densities of greater than 800 A.Math.h.Math.L.sup.1 (
Commercial MaterialsHalf-Cell Tests
[0199] Additionally, in order to test the suitability of the niobium tungsten oxides as high-rate anode materials, the commercially-available high-rate cathode materials NMC622 (LiNi.sub.0.6Mn.sub.0.2Co.sub.0.2O.sub.2; Targray), lithium iron phosphate (LiFePO.sub.4; Johnson Matthey) and LiMn.sub.2O.sub.4 (MTI Corp) were purchased. These commercial materials were first characterised in half-cell geometry against Li metal. Electrochemical measurements were conducted using a stainless steel 2032-coin cell and glass microfiber separator in the same manner as for Nb.sub.16W.sub.5O.sub.55 and Nb.sub.18W.sub.16O.sub.93 described above. The commercial cathode material, conductive carbon (Li-250 carbon; Deka Chemicals) and PVDF were ground together in the same manner as described above to prepare an 80/10/10 electrode (comprising 80 wt % active material, 10 wt % carbon and 10 wt % polymer) which served as the cathode against a Li metal disk anode in half-cell geometry. The electrolyte was 150 L LP30. No additives were used.
[0200] NMC622 showed an average voltage of 3.8 V and a practical capacity of 175 mA.Math.h.Math.g.sup.1 under these conditions (
Electrode OptimisationNb.sub.16W.sub.5O.sub.55
[0201] In order to optimise the performance of the Nb.sub.16W.sub.5O.sub.55 electrode, a series of electrodes were made to the specifications set out in Table 3, below. Electrochemical characterisation was conducting using a stainless steel 2032 coin cell and glass microfiber separator as described above. A Li metal disk was used as anode in half-cell geometry. The electrolyte was 150 L LP30. No additives were used.
TABLE-US-00003 TABLE 3 Electrode Optimisation Entry Active Separator Carbon Binder Calendaring Ref 80% Glass 10% 10% No Nb.sub.16W.sub.5O.sub.55 microfiber Super P PVDF 1 80% Polypropylene.sup.1 10% 10% No Nb.sub.16W.sub.5O.sub.55 Super P PVDF 2 80% Glass 10% 4% No Nb.sub.16W.sub.5O.sub.55 microfiber Super P SRB.sup.2 1% CMC.sup.3 3 80% Glass 15% 5% No Nb.sub.16W.sub.5O.sub.55 microfiber Super P PVDF 4 80% Glass 8% 10% No Nb.sub.16W.sub.5O.sub.55 microfiber Super P PVDF 2% CNT.sup.4 5 80% Glass 10% 10% Yes Nb.sub.16W.sub.5O.sub.55 microfiber Super P PVDF .sup.1Celgard; .sup.2Styrene-butadiene rubber (Zeon); .sup.3Carboxymethyl cellulose (Sigma Aldrich); .sup.4Carbon nanotubes (Sigma Aldrich)
[0202] Bulk rate performance was shown to be improved where 5 wt % PVDF or 4 wt % SRB and 1 w % CMC as binder (
Full Cell Operation with Commercial Electrode Materials
[0203] To test the suitability of the niobium tungsten oxides as high-rate anode materials, full cells were produced using the commercially-available high-rate cathode materials NMC622, LiFePO.sub.4 and LiMn.sub.2O.sub.4. Electrochemical measurements were conducted using a stainless steel 2032-coin cell and glass microfiber separator in the same manner as for Nb.sub.16W.sub.5O.sub.55 and Nb.sub.18W.sub.16O.sub.93 described above. The commercial cathode material, Li-250 carbon and PVDF were ground together as described above to prepare an 80/10/10 electrode (comprising 80 wt % active material, 10 wt % carbon and 10 wt % polymer) which served as cathode. The Nb.sub.16W.sub.5O.sub.55, Li-250 carbon and PVDF were ground together to prepare an 80/10/10 electrode (comprising 80 wt % active material, 10 wt % carbon and 10 wt % polymer) which served as anode. When the cathode comprised NMC622, the anode comprised Nb.sub.16W.sub.5O.sub.55, Li-250 carbon and PVDF in a 80/15/5 ratio. The electrolyte in all cases was 150 L LP30. No additives were used. The capacity ratio of the anode and cathode was 1:1. For full cell balancing, the theoretical capacity of NMC622 was taken to be 175 mA.Math.h.Math.g.sup.1.
[0204] The full cells were evaluated between 1.0 and 3.0 V. The initial change/discharge curves of the full cells with LiFePO.sub.4 and LiMn.sub.2O.sub.4 cathodes are shown in
[0205] The rate performance of the NMC622 full cell was evaluated in a range of current densities from C/5 to 20C. The NMC622 full cell maintained a capacity of 125 mA.Math.h.Math.g.sup.1 at 20C, greater than 75% capacity retention relative to the capacity at C/5 (
Investigation of Electrode Degradation
[0206] In order to investigate the cause of capacity loss, a full cell using a Nb.sub.16W.sub.5O.sub.55 anode and NMC622 cathode as described above was cycled for 500 cycles at 10 change and 10 discharge. A 71.1% capacity retention was observed (
Mixtures of Nb.sub.16W.sub.5O.sub.55 and LTO as Anode
[0207] Additional experiments were carried out to test the use of a mixture of Nb.sub.16W.sub.5O.sub.55 and LTO as electrode material. Electrodes comprising three different ratios of Nb.sub.16W.sub.5O.sub.55 to LTO were produced and measured against an Li metal anode in the same manner as for Nb.sub.16W.sub.5O.sub.55 and Nb.sub.18W.sub.16O.sub.93 described above. The galvanostatic charge-discharge curves are shown in
[0208] A full cell comprising a 3:7 (Nb.sub.16W.sub.5O.sub.55:LTO) anode and an NMC622 cathode was prepared in a stainless steel 2032-coin cell with glass microfiber separator in the same manner as for Nb.sub.16W.sub.5O.sub.55 and Nb.sub.18W.sub.16O.sub.93 described above. The Nb.sub.16W.sub.5O.sub.55, LTO, Super P carbon and PVDF were ground together to prepare an 80/15/5 active material/carbon/polymer anode. The NMC622, Li.sub.250 carbon and PVD were ground together as described above to prepare an 80/10/10 active material/carbon/polymer electrode which served as cathode. The electrolyte was 150 L LP30. No additives were used
[0209] The full cell was evaluated between 1.0 and 3.25 V, as shown in
Electrochemical Characterisation of Nb.sub.2Mo.sub.3O.sub.14
[0210] Electrochemical characterisation of Nb.sub.2Mo.sub.3O.sub.14 was conducted in the same manner as for Nb.sub.16W.sub.5O.sub.55 and Nb.sub.18W.sub.16O.sub.93 described above, using a stainless steel 2032-coin cell (Cambridge Energy Solutions) with a conical spring, two 0.5 mm stainless steel spacer disks, a plastic gasket, and a glass microfiber separator (Whatman). The metal oxide and conductive carbon (Super P, TIMCAL) were ground by hand in an agate mortar and pestle in an 8:1 mass ratio. This powder was ground in a 9:1 mass ratio with poly(vinylidene difluoride) (PVDF, Kynar) dispersed in N-methyl pyrrolidone (NMP, Sigma-Aldrich, anhydrous, 99.5%). This metal oxide/carbon/polymer electrode served as the cathode against a Li metal disk (LTS Research, 99.95%) anode in half-cell geometry. The electrolyte was 1 M LiPF.sub.6 dissolved in 1:1 v/v ethylene carbonate/dimethyl carbonate (EC/DMC, Sigma-Aldrich, battery grade). No additives were used. Electrochemistry was performed in a temperature-controlled room at 293 K. A Biologic galvanostat/potentiostat with EC-Lab software was used to perform the electrochemical measurements.
[0211] At C/20 it is possible to maintain a gravimetric capacity of ca. 200 mA.Math.h.Math.g.sup.1 (
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