Electrode composition

Abstract

To provide an electrode having a niobium-containing metal oxide surface, an electrochemical cell including the electrode, and use of the cell at elevated or reduced temperatures, for example, in a lithium-ion battery.SOLUTION: The present invention provides an electrode having a surface layer of a niobium-containing metal oxide disposed on a secondary electrode active material. The niobium-containing metal oxide can be the Nb2O5 polymorph, NbO2, or Nb2O3, or can be a mixed metal oxide such as niobium tungsten oxide, titanium niobium oxide, or niobium molybdenum oxide. There is also provided an electrochemical cell containing the electrode and the use of the cell at high or low temperature, for example, in a lithium-ion battery.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This case relates to and claims the benefit of GB1914983.0, filed on October 16, 2019, the contents of which are incorporated herein by reference in their entirety.

[0002] FIELD OF THE INVENTION The present invention provides electrodes and electrochemical cells, such as lithium ion batteries, that include the electrodes, as well as methods of using the electrodes in electrochemical cells. [Background technology]

[0003] Lithium-ion batteries are widely designed to operate optimally at temperatures between 15°C and 40°C. The main limitations to this operation stem from the materials used in the positive and negative electrodes and the lithium-ion-containing electrolyte. Under these optimal conditions, characteristics associated with battery performance, such as specific energy, specific power, cycle life, shelf life, and safety, are maximized.

[0004] Variations in the operating temperature of lithium-ion batteries beyond this typical range limit their energy, power, cycle life, and safety performance. This variation typically occurs due to external factors such as seasons and weather conditions. However, temperature variations also occur from the use of batteries intended for portable electronic device applications such as cell phones, laptops, and power tools, as well as for use in electric vehicles (EVs).

[0005] When such battery-powered devices are used in high power regimes, such as fast charging in EVs or fast charging of cell phone batteries (fully charging a battery within an hour or partially charging to more than 80% of the battery capacity within 30 minutes), heat generation (ohmic losses) from the high currents causes the temperature to rise sharply, limiting the battery's ability to provide sustained power or allow more charge.

[0006] Overheating of batteries is understood to cause catastrophic failure due to thermal runaway, fire, and explosion. Battery management systems, which control the charging and discharging of lithium-ion batteries, shut down the device to prevent sudden temperature changes (Shuai Ma, et al.).

[0007] To overcome this limitation, large thermal management systems are used to keep the battery within optimal operating temperatures. The weight of these systems typically reduces the range of an EV by 40 to 50 percent.

[0008] A similar reduction in EV range occurs in cold environments, such as below 10°C. In particular, using an EV in an open-circuit state can significantly reduce range (American Automobile Association, February 2019). At low temperatures, chemical reactions within the battery proceed more slowly, and at freezing temperatures, plating of metallic lithium can occur on the graphite anode (negative electrode) surface.

[0009] Furthermore, at temperatures above 45°C, the interfacial layer between the electrode material and the electrolyte, known as the solid electrolyte interface (SEI), deteriorates, shortening the cell's cycle life. This SEI layer, which is normally formed on the surface of the anode material, is responsible for the stable operation of lithium-ion batteries, and at high temperatures the SEI layer decomposes, significantly reducing the cell's capacity, which is why the upper limit of 45°C exists.

[0010] In light of the above challenges, there is a need to provide novel electrode materials and surfaces for lithium-ion batteries that can operate at high rates and high temperatures to extend the range of EVs and enable optimal battery function over a wide temperature range in portable battery-powered devices.

[0011] In light of the above challenges, there is a need to provide new electrode materials for lithium-ion batteries that can operate at high or low temperatures. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] US Patent Application Publication No. 2016 / 0351973 [Patent Document 2] US Patent Application Publication No. 2013 / 0266858 [Patent Document 3] European Patent Application Publication No. 3522268 [Patent Document 4] US Patent Application Publication No. 2019 / 0097226 [Patent Document 5] US Patent Application Publication No. 2015 / 0221933 [Patent Document 6] US Patent Application Publication No. 2017 / 0141386 [Non-patent literature]

[0013] [Non-Patent Document 1] Shuai Ma et al., Temperature effect and thermal impact in lithium-ion batteries: A Review, Progress in Natural Science: Materials International, December 2018). [Non-patent document 2] Electric Vehicle Range Testing: AAA proprietary research into the effect of ambient temperature and HVAC use on driving range and MPGe, American Automobile Association, February 2019 [Non-patent document 3] Griffith et al., Niobium tungsten oxides for high-rate lithium-ion energy storage, Nature, Vol559, pp. 556-559 Summary of the Invention [Means for solving the problem]

[0014] The present invention generally provides electrodes having niobium-containing metal oxide surfaces, electrochemical cells including the electrodes, and the use of the cells at elevated or reduced temperatures, for example, in lithium-ion batteries.

[0015] The inventors have established that high energy density can be achieved by using electrode materials having a niobium-containing metal oxide surface in lithium-ion cells, even when the cells are cycled at high or low temperatures. The cells exhibit excellent capacity retention when repeatedly cycled at high or low temperatures. Furthermore, the cells can be charged and discharged at high C rates at both high and low temperatures. Thus, lithium-ion cells containing electrodes having a niobium-containing metal oxide surface have a wider operating temperature range and exhibit improved cycling stability at high or low temperatures compared to typical lithium-ion cells containing graphite electrodes.

[0016] The working electrode having a niobium-containing metal oxide surface and bulk has favorable lithium diffusion properties and therefore exhibits excellent rate characteristics. + Above / Li, the formation of SEI is minimized, which means that lithium is not lost to side reactions with the electrolyte.

[0017] A typical lithium-ion cell containing graphite electrodes has a voltage of 1V vs. Li + 1 / Li and require an initial formation cycle before the cell can be sealed. Typically, this formation cycle is performed at a high temperature, e.g., 60 °C, to rapidly form the SEI and allow outgassing to occur in one cycle. This adds significant time and cost to the cell manufacturing process.

[0018] According to the present invention, the niobium-based metal oxide surface minimizes or eliminates SEI formation that is typically observed on graphite surfaces during the initial formation steps of lithium-ion batteries during the first charge cycle.

[0019] Furthermore, in full cells for example for LiFePO4, LiN(CF3SO2)2 (LiTFSI) can be used to replace the more toxic LiPF6 electrolyte salt commonly used in standard commercial electrolytes. Furthermore, the LiAl alloying potential (≤0.3 V vs Li + Aluminum can be used as the current collector instead of the more expensive copper, while avoiding the need for copper (Li).

[0020] Generally, the present invention provides methods of charging and / or discharging an electrochemical cell, wherein the electrochemical cell includes a working electrode having a niobium-containing metal oxide surface, and the temperature of the electrochemical cell is 45°C or higher, e.g., 50°C or higher, 55°C or higher, or 60°C or higher.

[0021] In general, the present invention also provides a method of charging and / or discharging an electrochemical cell, wherein the electrochemical cell comprises a working electrode having a niobium-containing metal oxide surface, and the temperature of the electrochemical cell is 10°C or less, e.g., 5°C or less, or 0°C or less.

[0022] In a first aspect of the present invention, there is provided a method of charging and / or discharging an electrochemical cell, wherein the electrochemical cell comprises a working electrode having a surface layer of a niobium-containing metal oxide disposed on a secondary electrode active material, and the temperature of the electrochemical cell is 45°C or greater, e.g., 50°C or greater, 55°C or greater, or 60°C or greater.

[0023] In a second aspect of the present invention, there is provided a method of charging and / or discharging an electrochemical cell, wherein the electrochemical cell comprises a working electrode having a surface layer of a niobium-containing metal oxide disposed on a secondary electrode active material, and wherein the temperature of the electrochemical cell is 10°C or less, such as 5°C or less or 0°C or less.

[0024] The electrochemical cell may include a counter electrode and an electrolyte, and optionally the electrodes are connectable to or connected to a power source.

[0025] The method of any embodiment may include charging and / or discharging the electrochemical cell at a C-rate of at least 5C, e.g., at least 10C, at least 20C, at least 30C, at least 40C, at least 50C, or at least 60C.

[0026] The method may involve cycling the electrochemical cell through charging and discharging, or discharging and charging, and the method may involve 2 or more cycles, 5 or more cycles, 10 or more cycles, 50 or more cycles, 100 or more cycles, 500 or more cycles, 1000 or more cycles, or 2000 or more cycles.

[0027] The layer of niobium-containing metal oxide may have a maximum thickness of 4.5 nm or less.

[0028] The layer of niobium-containing metal oxide can be disposed on particles of the secondary electrode active material, or alternatively, the layer of niobium-containing metal oxide can be disposed on a film of the secondary electrode active material.

[0029] The niobium-containing metal oxide may be selected from different polymorphs of Nb2O5, NbO2, Nb2O3, or combinations thereof.

[0030] The niobium-containing metal oxides may be doped with additional elements such as phosphorus, aluminum, copper, chromium, zirconium, vanadium, and lithium.

[0031] The niobium-containing metal oxide can be selected from niobium tungsten oxide, titanium niobium oxide, niobium molybdenum oxide, or a combination thereof. Niobium vanadium oxide can also be used as the niobium-containing metal oxide.

[0032] The secondary electrode active material can be selected from carbon, silicon, or metal oxides. Lithium and silver can also be used as secondary electrode active materials.

[0033] The secondary electrode active material may be selected from graphite, reduced graphite oxide, or hard carbon.

[0034] The secondary electrode active material can be selected from lithium titanate, titanium tantalum oxide, or tantalum molybdenum oxide. Lithium vanadium oxide, lithium titanium silicate, and lithium vanadium oxide phases can also be used as secondary electrode active materials.

[0035] In a third aspect of the present invention, there is provided an electrode, which may be referred to as a working electrode, having a niobium-containing metal oxide surface, the working electrode being suitable for use as an electrode in a lithium-ion battery.

[0036] The working electrode includes a surface layer of a niobium-containing metal oxide disposed on the secondary electrode active material.

[0037] The layer of niobium-containing metal oxide can be disposed on particles of the secondary electrode active material, or alternatively, the layer of niobium-containing metal oxide can be disposed on a film of the secondary electrode active material.

[0038] The niobium-containing metal oxide may be selected from the Nb2O5 polymorph, NbO2, Nb2O3, or a combination thereof.

[0039] The niobium-containing metal oxides may be doped with additional elements such as phosphorus, aluminum, copper, chromium, zirconium, vanadium, and lithium.

[0040] The niobium-containing metal oxide can be selected from niobium tungsten oxide, titanium niobium oxide, niobium molybdenum oxide, or a combination thereof. Niobium vanadium oxide can also be used as the niobium-containing metal oxide.

[0041] The secondary electrode active material can be selected from carbon, silicon, or metal oxides. Lithium and silver can also be used as secondary electrode active materials.

[0042] The secondary electrode active material may be selected from graphite, reduced graphite oxide, or hard carbon.

[0043] The secondary electrode active material can be selected from lithium titanate, titanium tantalum oxide, and tantalum molybdenum oxide. Lithium vanadium oxide, lithium titanium silicate, and lithium vanadium oxide phases can also be used as secondary electrode active materials.

[0044] In a fourth aspect of the present invention, there is provided an electrochemical cell comprising a working electrode of the present invention.

[0045] In a fifth aspect of the present invention, there is provided a lithium ion battery comprising one or more electrochemical cells of the present invention, where multiple cells are present, these may be provided in series or in parallel.

[0046] In a sixth aspect of the present invention, there is provided the use of a working electrode having a surface layer of a niobium-containing metal oxide disposed on a secondary electrode active material in an electrochemical cell, wherein the temperature of the electrochemical cell during charging or discharging is 45°C or higher, for example 50°C or higher, 55°C or higher, or 60°C or higher.

[0047] In a seventh aspect of the present invention, there is provided the use of a working electrode having a surface layer of a niobium-containing metal oxide disposed on a secondary electrode active material in an electrochemical cell, wherein the temperature of the electrochemical cell during charging or discharging is 10°C or less, for example 5°C or less, or 0°C or less.

[0048] These and other aspects and embodiments of the invention are described in more detail below. [Brief explanation of the drawings]

[0049] [Figure 1] 1 shows working electrode particles having a niobium-containing metal oxide surface layer with (top) and without (bottom) an intermediate metal oxide layer. [Figure 2]Figure 2a shows the rate characteristics of the NWO (Nb16W5O55) / NMC (LiNi0.6Co0.2Mn0.2O2) cell at cell operating temperatures of 60°C (top), 25°C (middle), and 10°C (bottom). Figure 2b shows the long-term cycling characteristics of the NWO / NMC cell at 60°C and a 10°C rate. Figure 2c shows the long-term cycling characteristics of the NWO / NMC cell at 25°C (top) and 10°C (bottom) under a 5°C rate. Figure 2d shows a comparison of the rate characteristics of the NWO / LFP cell at temperatures of 60°C (top), 25°C (middle), and 10°C (bottom). Figure 2e shows the long-term cycling characteristics of the NWO / LFP cell at 10°C, 25°C, and 60°C under a 5°C rate. [Figure 3] Figure 3a shows the rate characteristics of a cell containing an anode with a niobium-containing metal oxide surface layer disposed on a graphite secondary active material at 65°C (top) and the rate characteristics of a cell containing an anode in which the niobium-containing surface layer dissolves (bottom) at 65°C. Figure 3b shows the long-term cycling characteristics of the niobium-coated cell (top) and the uncoated cell (bottom) at 65°C. Figure 3c shows the rate characteristics of the niobium-coated cell at 65°C (top) and 25°C (bottom). Figure 3d shows the long-term cycling characteristics of the niobium-coated cell at 65°C (bottom) and 25°C (top). [Figure 4] Figure 4a is a scanning electron micrograph of primary particles of a niobium-based metal oxide used to prepare an anode according to an embodiment of the present invention; Figure 4b is a scanning electron micrograph of a niobium-containing metal oxide coated on irregular graphite particles; Figure 4c is a scanning electron micrograph of a niobium-containing metal oxide coated on irregular graphite particles; and Figure 4d is a scanning electron micrograph of a niobium-containing metal oxide coated on regular graphite particles. [Figure 5] Figure 5a shows a pouch cell according to an embodiment of the present invention. Figure 5b shows a cylindrical cell according to an embodiment of the present invention. Figure 5c shows an anode electrode according to an embodiment of the present invention coated onto a current collector. Figure 5d shows a jelly roll anode and cathode electrodes with a separator (left) placed inside a metal can (right) with an electrolyte to create an electrochemical cell according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0050] The present invention generally provides electrodes having niobium-containing metal oxide surfaces, electrochemical cells including the electrodes, and the use of the cells at elevated or reduced temperatures, for example, in lithium-ion batteries.

[0051] Electrodes containing niobium tungsten oxide have been described, for example, by Griffiths et al. However, the electrochemical properties of niobium tungsten oxide were tested in a temperature-controlled chamber at 293 ± 2 K using lithium metal as the counter electrode. The electrochemical properties were not tested at higher or lower temperatures.

[0052] Electrodes consisting of atomically thin coatings containing aluminum oxide (Al2O3) or titanium oxide (TiO2) on the secondary electrode active material have also been reported (Lee Se-Hee et al., US 9,196,901 B2). However, the electrochemical properties of the coated electrodes have not been tested at high or low temperatures.

[0053] The present inventors have developed electrochemical cells including electrodes having niobium-containing metal oxide surfaces that have favorable lithium ion diffusion properties, high volumetric energy density, and high capacity, even when cycled at high or low temperatures.

[0054] The voltage values ​​given herein are, as is common in the art, Li + / Li is used as the standard.

[0055] The C-rate is a measure of the rate at which a battery is discharged relative to its maximum capacity. The C-rate can be defined as the reciprocal of the number of hours required to reach a defined maximum capacity; for example, 10 C corresponds to a 6-minute discharge or charge time. The maximum capacity can be the theoretical maximum capacity or an empirically determined maximum capacity. For example, the theoretical maximum capacity can be defined relative to one electron transfer per transition metal atom in the electrode active material.

[0056] High charge and discharge rates can also be explained in terms of (gravimetric) current density relative to the weight of electrode active material.

[0057] US2017 / 0141386 describes the preparation of a negative electrode comprising a layer of LiNbO3 coated on a conductive material (carbon black) rather than on a secondary electrode active material, which teaches against coating the secondary electrode active material with a niobium-containing metal oxide.

[0058] US2019 / 0097226 describes the preparation of a niobium-containing positive electrode active material. The material is a single component and is not disposed on a secondary electrode active material. This teaches against layered construction and against the use of niobium in negative electrodes.

[0059] EP 3522268 describes a positive electrode comprising a layer of lithium niobate on an NMC active material, which teaches against the use of niobium in the negative electrode.

[0060] US2015 / 0221933 describes a positive electrode containing an NMC active material having a niobium oxide compound sintered on a portion of its surface.

[0061] [Working electrode] The present invention provides a working electrode having a niobium-containing metal oxide surface, which is electrically conductive and can be electrically connected to a counter electrode, for example, in an electrochemical cell.

[0062] The working electrode can be the anode (negative electrode) or the cathode (positive electrode) during the discharging step, for example in a lithium-ion battery. Usually, the working electrode is the anode during the discharging step.

[0063] The working electrode has a niobium-containing metal oxide surface. That is, the surface of the working electrode is terminated with a metal oxide containing niobium (Nb). The niobium-containing metal oxide surface is the active electrode surface of the electrochemical cell. That is, the niobium-containing metal oxide surface is the surface that contacts the electrolyte in a typical electrochemical cell.

[0064] The working electrode can include a layer of a niobium-containing metal oxide disposed on the secondary electrode active material. The layer of niobium-containing metal oxide can be a coating on the secondary electrode active material.

[0065] The thickness of the niobium-containing metal oxide layer is known or can be determined using standard techniques such as SEM.

[0066] In one embodiment, the layer of niobium-containing metal oxide can have a maximum thickness of 10 μm or less, eg, 5 μm or less, 4 μm or less, 3 μm or less, or 2 μm or less.

[0067] Preferably, the layer of niobium-containing metal oxide has a maximum thickness of 5 nm or less, eg, 4.5 nm or less, 4.0 nm or less, 3 nm or less, or 2 nm or less.

[0068] The layer of niobium-containing metal oxide can have a minimum thickness of 0.1 nm or more, eg, 0.2 nm or more, 0.3 nm or more, 0.4 nm or more, or 0.5 nm or more.

[0069] The niobium-containing metal oxide may have a thickness within a range selected from the above maximum and minimum amounts. The inventors have found that thinner coatings of the niobium-containing metal oxide are preferred because they provide reduced impedance compared to thicker layers while maintaining the temperature stability of the electrode and mitigating SEI formation.

[0070] The layer of niobium-containing metal oxide may be disposed directly on the secondary electrode active material, or there may be an intermediate layer of active material.

[0071] A layer of niobium oxide can be disposed on particles of secondary electrode active material.

[0072] The size of the particles of the secondary electrode active material is known or can be determined using standard techniques such as SEM.

[0073] Particles of the secondary electrode active material can have a maximum primary particle size of 100 μm or less, eg, 50 μm or less, 40 μm or less, 30 μm or less, or 20 μm or less.

[0074] The particles of the secondary electrode active material can have a primary particle size of 5 nm or more, eg, 10 nm or more, 15 nm or more, 20 nm or more, or 25 nm or more.

[0075] The particles of the secondary electrode active material can have a primary particle size within a range selected from the maximum and minimum amounts noted above. The particles may be regular or irregular in shape.

[0076] Alternatively, a layer of niobium-containing metal oxide can be disposed on a film of secondary electrode active material. The thickness of the film of the secondary electrode active material is not particularly limited.

[0077] Methods for coating films or particles with metal oxides are known and include chemical solution deposition, spin coating, dip coating, chemical vapor deposition, atomic layer deposition, molecular layer deposition, sputtering, and physical vapor deposition.

[0078] Alternatively, the niobium-containing metal oxide surface may exist as a concentration gradient in a single material that includes a niobium-rich surface layer and a niobium-poor interior.

[0079] The niobium-containing metal oxide may be selected from the Nb2O5 polymorph, NbO2, Nb2O3, or a combination thereof.

[0080] Niobium-containing metal oxides can be doped with additional elements such as phosphorus (P), aluminum (Al), copper (Cu), chromium (Cr), zirconium (Zr), vanadium (V) and lithium (Li).

[0081] The niobium-containing metal oxide can be a lithium conductor such as lithium niobate (LiNbO3), Li3NbO4LiNbVO LiNbLaZrO (garnets), LiNbSPO (LISICONs), LiNbAlTiP / LiNbAlGeP (NASICONs).

[0082] The niobium-containing metal oxide may be a mixture (e.g., an amorphous mixture) of niobium oxide with an additional metal oxide. Suitable additional metal oxides include titanium oxide, hafnium oxide, tantalum oxide, or aluminum oxide. Vanadium oxide is also a suitable metal oxide.

[0083] The niobium-containing metal oxide may be a compound (e.g., having a crystalline structure) of niobium oxide and an additional metal oxide. Suitable niobium-containing metal oxides include niobium tungsten oxide (e.g., Nb 16 W5O 55 or Nb 18 W 16 O 93 ), titanium niobium oxide (e.g., TiNb2O7), niobium molybdenum oxide (e.g., Nb2Mo3O 14 ), or combinations thereof. Niobium vanadium oxide may also be used.

[0084] Suitable niobium tungsten oxides include Nb 12 WO 33 , Nb 26 W4O 77 , Nb 14 W3O 44 , Nb 16 W5O 55 , Nb 18 W8O 69 , Nb2WO8, Nb 18 W 16 O 93 , Nb 22W 20 O 115 , Nb8W9O 47 , Nb 54 W 82 O 381 , Nb 20 W 31 O 143 , Nb4W7O 31 , or NbW 15 O 50 , or a combination thereof.

[0085] The secondary electrode active material is lithium ion (Li + ) is a reversibly intercalable material. The secondary electrode active material can be selected from carbon, silicon, or metal oxides. Lithium and silver can also be used as secondary electrode active materials.

[0086] The secondary electrode active material may be selected from graphite, reduced graphite oxide, or hard carbon.

[0087] The secondary electrode active material is lithium titanate (LTO; Li4Ti5O 12 ), titanium tantalum oxide (e.g., TiTa2O7), or tantalum molybdenum oxide (e.g., Ta8W9O 47 Lithium vanadium oxide (e.g., LiV3O8), lithium titanium silicate, and lithium vanadium oxide phases can also be used as secondary electrode active materials.

[0088] The working electrode may contain a conductive carbon material to improve conductivity. The conductive carbon material may be carbon black, graphite, nanoparticle carbon powder, carbon fiber, and / or carbon nanotubes. The conductive carbon material may be Ketjenblack, Super P carbon, or hard or soft amorphous carbon.

[0089] The working electrode may contain a binder to improve adhesion of the active material to the current collecting surface. Typical examples of binders include PVDF, PTFE, CMC, PAA, PMMA, PEO, SBR, and copolymers thereof.

[0090] The working electrode is usually fixed to a current collector, such as a copper or aluminum current collector, which may be in the form of a plate.

[0091] In 2032-type coin cells using 1.0 M LiPF6 in ethylene carbonate / dimethyl carbonate as the electrolyte, we used an electrode configuration of 9:0.5:0.5 active material / carbon / binder with an NMC or LiFePO4 counter electrode, and the amount of active material was 8–10 mg cm -2 and the electrode area is 1.27 cm 2 A working electrode containing a niobium tungsten oxide (NWO) surface was evaluated.

[0092] We found that cycling a NWO / NMC cell at 60°C (10C rate) for 300 cycles resulted in a loss of 30.8% of the discharge capacity, whereas cycling the cell at 10°C (5C rate) showed a capacity loss of 15.5%. Cycling a NWO / LFP cell at 60°C (5C rate) for 1000 cycles showed a capacity loss of 18.1%, and cycling at 10°C (5C rate) showed a capacity loss of 6.9%.

[0093] [Electrochemical Cell] The present invention also provides an electrochemical cell comprising a working electrode of the present invention. The working electrode can be the anode or the cathode during the discharging step, for example, in a lithium-ion battery. Typically, the working electrode can be the anode during the discharging step.

[0094] Electrochemical cells typically include a counter electrode and an electrolyte. Electrochemical cells may include current collecting plates. Electrochemical cells may be electrically connected to a power source. Electrochemical cells may be electrically connected to a measuring device, such as an ammeter or voltmeter.

[0095] The electrochemical cell may be a lithium-ion cell. The counter electrode can be the anode or the cathode during the discharging step, for example in a lithium ion battery. The counter electrode is usually the cathode during the discharging step.

[0096] Suitable cathode materials include lithium-containing or lithium-insertion materials, such as lithium metal oxides, where the metal is typically a transition metal such as Co, Fe, Ni, V, or Mn, or a combination thereof. Some examples of positive electrode materials include lithium cobalt oxide (LiCoO), lithium nickel manganese cobalt oxide (NMC, LiNiMnCoO, e.g., LiNi 0.6 Co 0.2 Mn 0.2 O2), lithium vanadium fluorophosphate (LiVPO4F), lithium nickel cobalt aluminum oxide (NCA, LiNiCoAlO2), lithium iron phosphate (LFP, LiFePO4), and manganese-based spinels (e.g., LiMn2O4).

[0097] The counter electrode may contain a conductive carbon material to improve electrical conductivity. The conductive carbon material may be carbon black, graphite, nanoparticle carbon powder, carbon fiber, and / or carbon nanotubes. The conductive carbon material may be Ketjenblack, Super P carbon, or hard or soft amorphous carbon.

[0098] The counter electrode may contain a binder to improve adhesion of the active material to the current collecting surface. Typical examples of binders include PVDF, PTFE, CMC, PAA, PMMA, PEO, SBR, and copolymers thereof.

[0099] The counter electrode is usually fixed to a current collector, such as a copper or aluminum current collector, which may be in the form of a plate.

[0100] Typically, the electrolyte of the electrochemical cell is suitable for solubilizing lithium ions. Typically, the electrolyte in a charged and discharged cell contains lithium ions.

[0101] Typically, the electrolyte comprises a lithium salt such as LiTFSI (lithium salt of bis(trifluoromethane)sulfonimide, LiPF, LiBF, LiClO, LiTF (lithium triflate), or lithium bis(oxalato)borate (LiBOB).

[0102] The electrolyte may be a liquid electrolyte, such as a liquid at ambient temperature, for example 25° C. Preferred electrolytes are stable at high and low temperatures.

[0103] The electrolyte can be a non-aqueous electrolyte. The electrolyte can include a polar aprotic solvent. The electrolyte can include an organic solvent. Solvents for dissolving lithium ions are well known in the art.

[0104] Suitable solvents include carbonate solvents, such as propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), chloroethylene carbonate, fluorocarbonate solvents (e.g., fluoroethylene carbonate and trifluoromethylpropylene carbonate), and dialkyl carbonate 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).

[0105] Suitable solvents also include sulfone solvents, such as 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), diphenyl sulfone (phenyl sulfone), dibenzyl sulfone (benzyl sulfone), vinylene sulfone, butadiene sulfone, 4-methoxyphenyl methyl sulfone, 4-chlorophenyl methyl sulfone, 2 ... 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, sultones (e.g., 1,3-propane sultone), and sulfone solvents containing ether groups (e.g., 2-methoxyethyl(methyl) sulfone and 2-methoxyethoxyethyl(ethyl) sulfone).

[0106] Suitable solvents also include silicon-containing solvents such as siloxanes or silanes. For example, hexamethyldisiloxane (HMDS), 1,3-divinyltetramethyldisiloxane, polysiloxanes, and polysiloxane-polyoxyalkylene derivatives. Some examples of silane solvents include methoxytrimethylsilane, ethoxytrimethylsilane, dimethoxydimethylsilane, methyltrimethoxysilane, and 2-(ethoxy)ethoxytrimethylsilane.

[0107] Typically, electrolytes contain additives to improve performance, such as vinylene carbonate (VC), vinyl ethylene carbonate, allyl ethyl carbonate, t-butylene carbonate, vinyl acetate, divinyl adipate, acrylic nitrile, 2-vinylpyridine, maleic anhydride, methyl cinnamate, ethylene carbonate, halogenated ethylene carbonates, α-bromo-γ-butyrolactone, methyl chloroformate, 1,3-propane sultone, ethylene sulfite (ES), propylene sulfite (PS), vinyl ethylene sulfite (VES), fluoroethylene sulfite (FES), 12-crown-4 ether, carbon dioxide (CO2), sulfur dioxide (SO2), and sulfur trioxide (SO3).

[0108] The electrochemical cell may also include a solid porous membrane disposed between the negative electrode and the positive electrode. 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 copolymers thereof), or an inorganic material such as a transition metal oxide (e.g., titania, zirconia, yttria, hafnia, or niobia), or a main group metal oxide such as silicon oxide, which may be in the form of glass fiber.

[0109] The solid non-porous membrane can include lithium ion conductors such as LLZO (garnets), LSPO (LISICONs), LGPS (thio-LISICONs), LATP / LAGP (NASICONs), LLTO (perovskites), and phosphide / sulfide glass ceramics.

[0110] 〔method〕 The present invention provides a method for charging and / or discharging an electrochemical cell at high or low temperatures. The electrochemical cell includes a working electrode, a niobium-containing metal oxide surface, and typically includes a counter electrode and an electrolyte.

[0111] Preferably, the method is a method of charging and / or discharging an electrochemical cell at an elevated temperature (above ambient temperature; about 20° C.). For example, the method may be carried out at 30° C. or higher, e.g., 40° C. or higher, 45° C. or higher, 50° C. or higher, 55° C. or higher, or 60° C. or higher.

[0112] The inventors have found that a working electrode having a niobium-containing metal oxide surface can be stable up to 600°C. Therefore, the maximum temperature for charging and / or discharging an electrochemical cell at high temperatures is determined by the selection of electrolyte and counter electrode materials. For example, an electrochemical cell containing a working electrode having a niobium-containing metal oxide surface, a solid ceramic electrolyte, and an LPF counter electrode is expected to be cycled at 300°C.

[0113] Alternatively, the method is a method of charging and / or discharging an electrochemical cell at low temperatures (ambient temperature; below about 20° C.). For example, the method can be carried out at 18° C. or below, e.g., 15° C. or below, 10° C. or below, 5° C. or below, or 0° C. or below.

[0114] The inventors believe that the minimum temperature for the method of charging and / or discharging an electrochemical cell at low temperatures is defined by the selection of the electrolyte. By appropriately selecting the electrolyte, the method of charging and / or discharging an electrochemical cell at low temperatures can be carried out at a minimum temperature of at least -70°C.

[0115] The method requires at least 750 mA·g -1 , e.g., at least 800mA·g -1 Preferably, the method comprises charging and / or discharging an electrochemical cell at a current density of at least 800 mA g -1 , 850mA·g -1 , 900mA·g -1 , 950mA·g -1 , 1000mA·g -1 , 1050mA·g -1 , 1100mA·g -1 , 1200mA·g -1 , or 1300mA·g -1A method for charging and / or discharging an electrochemical cell at a current density of

[0116] The method can include cycling the electrochemical cell through charging and discharging, or discharging and charging. The cycle can be repeated multiple times. Thus, the method can include 2 or more cycles, 5 or more cycles, 10 or more cycles, 50 or more cycles, 100 or more cycles, 500 or more cycles, 1000 or more cycles, or 2000 or more cycles.

[0117] 〔battery〕 The present invention also provides a battery comprising one or more electrochemical cells of the present invention. The battery may be a lithium-ion battery. If there are multiple cells, these may be provided in series or in parallel.

[0118] The battery of the present invention can be provided in road vehicles such as automobiles, mopeds, or trucks. Alternatively, the battery of the present invention can be provided in rail vehicles such as trains or trams. The battery of the present invention can also be provided in electric bicycles (e-bikes), drones, electric aircraft, and electric or hybrid boats. Similarly, the battery of the present invention can be provided in power tools such as electric drills or saws, garden tools such as lawn mowers or grass trimmers, or household appliances such as toothbrushes or hair dryers.

[0119] The battery of the present invention may be provided in a regenerative braking system. The battery of the present invention may be provided in a portable electronic device such as a mobile phone, laptop, or tablet. The battery of the present invention may be provided in a power grid management system.

[0120] 〔use〕 The present invention generally provides for the use of a working electrode having a niobium-containing metal oxide surface in an electrochemical cell, such as the electrochemical cell described herein. Typically, the temperature of the electrochemical cell during charging or discharging is 45°C or higher, e.g., 50°C or higher, 55°C or higher, or 60°C or higher. Alternatively, the temperature of the electrochemical cell during charging or discharging is 10°C or lower, e.g., 5°C or lower, or 0°C or lower. The working electrode can be used in the methods described herein.

[0121] [Other options] All compatible combinations of the above embodiments are expressly disclosed herein as if each and every combination were individually and expressly set forth. Various further aspects and embodiments of the present invention will be apparent to those skilled in the art in view of the present disclosure.

[0122] As used herein, "and / or" should be interpreted as a specific disclosure of each of the two specified features or components, with or without the other. For example, "A and / or B" should be interpreted as a specific disclosure of (i) A, (ii) B, and (iii) each of A and B, as if each were individually set forth herein.

[0123] Unless the context dictates otherwise, the above feature descriptions and definitions are not limited to any particular aspect or embodiment of the invention, but apply equally to all aspects and embodiments described. Certain aspects and embodiments of the present invention will now be described, by way of example, with reference to the above-mentioned drawings.

[0124] 〔experiment〕 The following examples are provided to illustrate the present invention and are not intended to limit the scope of the invention. Example 1 [Nb 16 W5O 55 Synthesis of NbO2 (Alfa Aesar, 99+%) or white Nb2O5 (Sigma, 99.9985%) was co-thermally oxidized with WO2 (Alfa Aesar, 99.9%) in batches of approximately 1 to 5 grams. 16 W5O 55 (NWO) was synthesized. The partially reduced oxides were combined in a 16:5 molar ratio to within 0.001 g, manually crushed using an agate mortar and pestle, pressed into pellets at 10 MPa, and heated at 10 K min in a platinum crucible. -1 The NWO powder was heated to 1473 K at a rate of 1000 K and then allowed to cool naturally in the furnace for approximately 2 hours. The NWO powder was confirmed to be phase pure by X-ray diffraction.

[0125] [Adjusting the electrodes] NMC-662 was obtained from Targray USA. Super P (TIMCAL) and polyvinylidene fluoride (PVdF; Kynar) dispersed in N-methyl-2-pyrrolidone were used as the conductive material and binder, respectively. All slurries consisted of 90% active material, 5% Super P, and 5% PVdF binder, and mixing was performed using a Thinky Mixer 250. NMC and LFP electrodes were dried in a drying chamber at 80 °C for 2 hours, while NWO electrodes were dried in an oven at 60 °C overnight under ambient atmosphere. All electrodes were calendered at room temperature, and electrode loadings ranged from 8.0 to 8.3 mg / cm. 2 (NMC), 8.4–8.7 mg / cm 2 (LFP), and 8.8–9.4 mg / cm 2 (NWO).

[0126] [Electrochemical Characterization] All electrochemical measurements were performed using 2032-type stainless steel coin cells. The prepared cathode and anode electrodes were dried under vacuum at 100 °C for 3 h and then transferred to an argon-filled glove box (MBraun) without exposure to air. Half and full cells were assembled in the glove box using LP30 electrolyte (Sigma-Aldrich) containing 1.0 M lithium hexafluorophosphate (LiPF6) in ethylene carbonate (EC):dimethyl carbonate (DMC) (1:1 v / v). After drying under vacuum at 40 °C for 2 h, polyethylene separators (Toray) were used. For electrolyte analysis, glass fiber filters (Whatman, GE) were used as separators. The filters were also dried under vacuum at 150 °C in a drying oven (Buchi). Galvanostatic electrochemical tests were performed at various current densities using a galvanostat / potentiostat (BioLogic) in a temperature-controlled oven at 10, 25, and 60 °C. The negative-to-positive capacity ratios for all test cells were 1.1–1.2, calculated based on the actual capacity of the active materials: 171.3 mAh / g for NWO, 175 mAh / g for NMC, and 165 mAh / g for LFP. The full-cell capacity for this test was calculated based on the mass of the cathode active material. For the symmetric cell test, two full cells with the same charge capacity were operated at 0.2 C, and the impedance was measured at 2.0 V during the charge step. Scanning was performed with a 10 mV amplitude at frequencies ranging from 1 MHz to 100 mHz. The cells were then disassembled in a glovebox, and two symmetric cells were reassembled using new LP30 electrolyte. The electrochemical impedance was measured again for the symmetric cells under the same conditions.

[0127] [Electrode characteristic evaluation] For characterization, the cells were disassembled, rinsed with DMC, and then thoroughly dried in a pre-chamber under vacuum. X-ray diffraction patterns of the pristine and used electrodes were acquired in transmission mode from an X-ray diffractometer (Empyrean, Panalytical) at ambient temperature using a CuKα source. The lattice constants, phases, and purity of the materials were determined by Rietveld refinement using Fullprof software.

[0128] [Thermal stability] The thermal performance stability of NWO / NMC and NWO / LFP cells was tested at 10, 25, and 60 °C (Figure 2). For both cells, the discharge capacity of cells tested at different C rates at 60 °C (10 C) was relatively higher (lower) than that at 25 °C. These phenomena are likely related to the kinetics of charge transfer and diffusion reactions within the cells. The long-term cycling characteristics of the NWO / NMC cells were evaluated for 300 cycles under three different conditions: 60 °C at 10 C (Figure 2b), and 10 °C and 25 °C at 5 C (Figure 2c). Cell cycling at 60 °C (10 C) resulted in a 30.8% loss of discharge capacity, while cycling at 25 °C (5 C) and 10 °C (5 C) showed capacity losses of 9.2% and 15.5%. Variable temperature cycling of the NWO / LFP cells was performed at a 5 C rate for 1,000 cycles. At temperatures of 10, 25, and 60 °C (Figure 2 e), capacity losses of 6.9%, 7.9%, and 18.1%, respectively, were observed over 1000 cycles, suggesting that the NWO / LFP combination has better cycling stability and operating temperature range than the NWO / NMC with the electrolyte used here.

[0129] Example 2 Several cells were constructed with different capacities ranging from 0.1 Ah to 5 Ah. The anode contained platelet-like graphite-like platelets with a lithium niobium oxide surface layer. A slurry of 92% active material, 3% conductive material, and 5% binder (PVDF or SBR / CMC) was prepared, mixed, and deposited as a coating on a current collector such as aluminum or copper. This was paired with a cathode containing lithium metal oxide such as NMC622 or N811 and wound with a polypropylene or polyethylene separator to obtain a jelly roll (see Figure 5).

[0130] The jelly roll is placed inside a metal can or pouch (Figure 5), filled with an electrolyte containing a lithium salt such as LiPF6, and sealed. The sealed cell is charged in constant current, constant voltage mode using an external power source to charge the cell to a desired voltage such as 3 V or 4.2 V, and then discharged by constant current to 1 V or 0 V.

[0131] For a 1Ah cell, 1C equals a charge or discharge current of 1A, fully charging / discharging the cell in 1 hour. At 2C, the same cell will charge / discharge in 0.5 hours, and at 0.5C it will charge / discharge in 2 hours. Cycle data is generated by varying the C rate or current input to the cell during charging or taken from the cell during discharge.

[0132] [Thermal stability] Figure 3 shows the thermal performance stability of a cell with a capacity of 0.16 Ah. The cell was tested at 65 °C against a cell without a lithium niobium oxide surface layer. The discharge rate was 0.5 C (155 mhA), and the charge rate was varied between 0.5 C and 10 C (Figure 3a). The cell containing the uncoated anode exhibited a capacity loss of nearly 50% at 10 C charging, while the cell containing the anode with the surface niobium-containing metal oxide layer exhibited a capacity loss of less than 15% at 10 C. The long-term cycling characteristics of the coated cell were evaluated over 500 cycles under a 12 C charge and 0.5 C discharge regime (Figure 3b). The uncoated cell exhibited a capacity loss of nearly 50% over 500 cycles at 65 °C. In contrast, the cell containing the coated anode exhibited little capacity loss (less than 5%) over 500 cycles at 65 °C.

[0133] Figures 3c and 3d show a comparison of cycling at 60 °C and 25 °C for a cell containing a lithium niobium-coated anode. Cycling the cell at the tested C-rates resulted in only a 20% loss of capacity (Figure 3c), and the capacity was largely retained over 400 cycles (Figure 3d). This demonstrates that the niobium-containing metal oxide-coated anode cell has superior cycling stability at high temperatures compared to the uncoated anode cell.

[0134] Additional Examples Additional cells were constructed in which the negative electrode composition included platelet graphite with a niobium tungsten oxide surface, and the cells also showed excellent cycling stability at high temperatures.

Claims

1. 1. A method for charging and / or discharging an electrochemical cell, the electrochemical cell comprising a working electrode having a surface layer of a niobium-containing metal oxide disposed on a secondary electrode active material, and the temperature of the electrochemical cell is 45° C. or higher, e.g., 50° C. or higher, 55° C. or higher, or 60° C. or higher.

2. 1. A method for charging and / or discharging an electrochemical cell, the electrochemical cell comprising a working electrode having a surface layer of a niobium-containing metal oxide disposed on a secondary electrode active material, and wherein the temperature of the electrochemical cell is 10° C. or less, e.g., 5° C. or less, or 0° C. or less.

3. The method of claim 1 or 2, wherein the working electrode is an anode.

4. 4. The method of claim 1, wherein the layer of niobium-containing metal oxide has a maximum thickness of 4.5 nm or less.

5. The niobium-containing metal oxide is Nb ２ O ５ Polymorph, NbO ２ , Nb ２ O ３ or a combination thereof.

6. 6. The method of any one of claims 1 to 5, wherein the niobium-containing metal oxide is doped with an element selected from phosphorus, aluminum, copper, chromium, zirconium, vanadium, and lithium.

7. 5. The method of any one of claims 1 to 4, wherein the niobium-containing metal oxide is selected from niobium tungsten oxide, titanium niobium oxide, niobium molybdenum oxide, niobium vanadium oxide, or a combination thereof.

8. 8. The method of claim 1, wherein the layer of niobium-containing metal oxide is disposed on particles of the secondary electrode active material.

9. 8. The method of claim 1, wherein the layer of niobium-containing metal oxide is disposed on the film of secondary electrode active material.

10. 10. The method of claim 1, wherein the secondary electrode active material is selected from carbon, silicon, or a metal oxide.

11. The method of claim 10 , wherein the secondary electrode active material is selected from graphite, reduced graphite oxide, or hard carbon.

12. 11. The method of claim 10, wherein the secondary electrode active material is selected from lithium titanate, titanium tantalum oxide, tantalum molybdenum oxide, and lithium vanadium oxide.

13. 13. The method of any one of claims 1 to 12, wherein the method is a method of charging and / or discharging an electrochemical cell at a C-rate of at least 5C, such as at least 10C, at least 20C, at least 30C, at least 40C, at least 50C, or at least 60C.

14. 14. The method of any one of claims 1 to 13, comprising cycling the electrochemical cell between charging and discharging or discharging and charging.

15. 15. The method of claim 14, comprising 2 or more cycles, 5 or more cycles, 10 or more cycles, 50 or more cycles, 100 or more cycles, 500 or more cycles, 1000 or more cycles, or 2000 or more cycles.

16. An electrode comprising a surface layer of a niobium-containing metal oxide disposed on a secondary electrode active material.

17. 17. The electrode of claim 16, wherein the electrode is an anode.

18. 18. The electrode of claim 16 or 17, wherein the layer of niobium-containing metal oxide has a maximum thickness of 45 nm or less.

19. The niobium-containing metal oxide is Nb ２ O ５ Polymorph, NbO ２ , Nb ２ O ３ 19. The electrode of claim 16, wherein the electrode is selected from:

20. 20. The electrode of any one of claims 16 to 19, wherein the niobium-containing metal oxide is doped with an element selected from phosphorus, aluminum, copper, chromium, zirconium, vanadium, and lithium.

21. 20. The electrode of any one of claims 16 to 19, wherein the niobium-containing metal oxide is selected from niobium tungsten oxide, titanium niobium oxide, niobium molybdenum oxide, niobium vanadium oxide, or combinations thereof.

22. 22. The electrode of any one of claims 16 to 21, wherein the layer of niobium-containing metal oxide is disposed on a film of secondary electrode active material.

23. 22. The electrode of any one of claims 16 to 21, wherein the layer of niobium-containing metal oxide is disposed on particles of secondary electrode active material.

24. 24. The electrode of any one of claims 16 to 23, wherein the secondary electrode active material is selected from carbon, silicon, or a metal oxide.

25. 25. The electrode of claim 24, wherein the secondary electrode active material is selected from graphite, reduced graphite oxide, or hard carbon.

26. 25. The electrode of claim 24, wherein the secondary electrode active material is selected from lithium titanate, titanium tantalum oxide, tantalum molybdenum oxide, and lithium vanadium oxide.

27. 27. An electrochemical cell comprising an electrode according to any one of claims 16 to 26.

28. 27. An all-solid-state battery comprising the electrode according to any one of claims 16 to 26.

29. Use of a working electrode having a surface layer of a niobium-containing metal oxide disposed on a secondary electrode active material in an electrochemical cell, wherein the temperature of the electrochemical cell during charging or discharging is 45°C or higher, e.g., 50°C or higher, 55°C or higher, or 60°C or higher.

30. Use of a working electrode having a surface layer of a niobium-containing metal oxide disposed on a secondary electrode active material of an electrochemical cell, wherein the temperature of the electrochemical cell during charging or discharging is 10°C or less, for example 5°C or less or 0°C or less.

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