Lithium-ion cells using high-rate electrolytes for cells using silicon oxide active materials to achieve high power discharge and long cycle life

Abstract

Electrolytes comprising a blend of lithium salts and a compatible non-aqueous solvent are described that provide high rate performance, charge and discharge for lithium-ion cells using silicon-based active materials such as silicon suboxide composites, e.g., silicon oxide / silicon / carbon composites. The lithium salts were typically blends of LiPF6 and LiFSI or LiTFSI. The solvents typically included fluoroethylene carbonate and dimethyl carbonate with optional co-solvents and / or other additives.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to co-pending U.S. Provisional Patent Application No. 63 / 242,732 to Hays et al., entitled “Lithium Ion Cells With High Rate Electrolyte for Cells With Silicon Oxide Active Materials Achieving Long Cycle Life,” filed September 10, 2021, which is incorporated herein by reference.

[0002] The present invention relates to lithium ion cells containing silicon oxide active materials that have very high power capabilities with high energy density combined with good cycling. The present invention also relates to electrolytes that facilitate achieving these performance features. [Background technology]

[0003] Lithium batteries are widely used in consumer electronics due to their relatively high energy density. For some current commercially available batteries, the anode material can be graphite and the cathode material can be lithium cobalt oxide (LiCoO 2 ), lithium manganese oxide (LiMn 2 O 4 ), lithium iron phosphate (LiFePO 4 ), lithium nickel oxide (LiNiO 2 ), lithium nickel cobalt oxide (LiNiCoO 2 ), lithium nickel cobalt manganese oxide (LiNiMnCoO 2 ), lithium nickel cobalt aluminum oxide (LiNiCoAlO 2) and the like. For the negative electrode, lithium titanate is a graphite substitute with good cycling properties, but with a lower energy density. Other substitutes for graphite, such as tin oxide and silicon, have the potential to provide increased energy density. However, some high capacity negative electrode materials, especially for silicon, have proven commercially unsuitable due to high irreversible capacity losses and poor discharge and charge cycles associated with the structural changes and very large volume expansion associated with the intercalation / alloying of lithium, particularly for silicon. The structural changes and large volume changes can compromise the structural integrity of the electrode, thereby reducing cycling efficiency. Summary of the Invention

[0004] In a first aspect, the present invention provides a high rate capable electrolyte for a lithium-based cell comprising: Approximately 0.05M to 0.8M LiPF 6 about 1.3 M to about 2.5 M lithium salts consisting of about 0.8 M to about 2.1 M lithium bis(fluorosulfonyl)imide (LiFSI) or lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and up to about 5 mole percent of optional other lithium salts; about 5 weight percent (wt%) to about 25 wt% fluoroethylene carbonate; from about 65% to about 95% by weight of a co-solvent consisting of at least about 30% by weight dimethyl carbonate, 0 to about 50% by weight diethyl carbonate, 0 to about 50% by weight hydrofluoroether, from about 0 to about 50% by weight fluorinated linear carbonate, from about 0 to about 20% by weight propylene carbonate, from about 0 to about 20% by weight alkyl acetate, and mixtures thereof, the weight percentages of fluoroethylene carbonate and co-solvent adding up to 100% by weight; about 10 weight percent or less of optional additives based on the total electrolyte weight; The present invention relates to a high rate compatible electrolyte comprising:

[0005] In a further aspect, the present invention relates to a lithium-ion cell comprising a negative electrode, a positive electrode, a separator between the negative electrode and the positive electrode, an electrolyte, and a container enclosing the negative electrode, the positive electrode, the separator, and the electrolyte. The negative electrode may comprise about 75% to about 96% by weight of active material, about 0.1% to about 7% by weight of nanoscale conductive particles, and about 4% to about 20% by weight of a polymer binder, and the active material comprises about 45% to about 100% by weight of a silicon-based active material and 0% to about 55% by weight of graphitic carbon. The positive electrode may comprise lithium metal oxide, conductive particles, and a polymer binder. The electrolyte can include about 1.1M to about 2.2M of a lithium salt and a non-aqueous solvent, the lithium salt includes about 60 mole percent to about 100 mole percent of LiFSI, LiTFSI, or mixtures thereof, and the non-aqueous solvent includes about 5% to about 25% by weight of fluoroethylene carbonate, 35% to 90% by weight of dimethyl carbonate, and 0 to about 50% by weight of diethyl carbonate, hydrofluoroether, fluoroalkyl carbonate, propylene carbonate, ethyl acetate, methyl acetate, propyl acetate, or mixtures thereof, the weight percentage values ​​being relative to the solvent. The cell can exhibit a discharge specific capacity at a rate of 2.5V to 4C at a selected charge voltage of at least about 120 mAh / g based on the weight of the cathode active material, and an impedance of about 10 mOhms or less at the 600th cycle at a 30% state of charge.

[0006] In another aspect, the present invention relates to a lithium-ion cell comprising a negative electrode, a positive electrode, a separator between the negative electrode and the positive electrode, an electrolyte, and a container enclosing the negative electrode, the positive electrode, the separator, and the electrolyte. The negative electrode may comprise about 75% to about 96% by weight of active material, about 0.1% to about 7% by weight of nanoscale conductive carbon, and about 4% to about 20% by weight of a polymer binder, and the active material comprises about 45% to about 100% by weight of a silicon-based active material and 0 to about 55% by weight of graphitic carbon. The positive electrode may comprise lithium metal oxide, conductive carbon, and a polymer binder. The electrolyte may comprise about 1.1M to about 2.2M of a lithium salt and a non-aqueous solvent, the lithium salt comprising about 60 mole percent to about 100 mole percent of LiFSI, LiTFSI, or mixtures thereof, and the non-aqueous solvent comprising about 5% to about 25% by weight of fluoroethylene carbonate, 35% to 90% by weight of dimethyl carbonate, and 0 to about 50% by weight of diethyl carbonate, hydrofluoroether, fluoroalkyl carbonate, propylene carbonate, ethyl acetate, methyl acetate, propyl acetate, or mixtures thereof, the weight percentage values ​​being relative to the solvent. The cell may exhibit a discharge capacity at a 5C discharge from a specified charge voltage to 2.5V of at least about 90 mAh / g based on the weight of the cathode active material, and a pulse power density at a rate of 5C for a 30 second pulse at a 30% state of charge of at least about 2.0 kW / kg. [Brief description of the drawings]

[0007] [Figure 1A] FIG. 1 is an exploded view of a pouch battery having a battery core separated from a two-part pouch case. [Figure 1B] FIG. 1B is a perspective bottom view of the assembled pouch battery of FIG. 1A. [Figure 1C] FIG. 1C is a bottom view of the pouch battery of FIG. [Figure 1D] 1 illustrates an embodiment of a battery core including an electrode stack. [Diagram 2]1 is a plot of the specific capacity as a function of cycles at various charge / discharge rates for coin cells made with electrolytes E1, E13, and E19. The electrode active materials were NMC622 for the positive electrode active material and silicon oxide composite SOC for the negative electrode active material. [Diagram 3] 1 shows combined plots of conductivity and viscosity as a function of increasing concentration of LiFSI (left to right), with LiPF6 held constant, for electrolytes E4-E8. [Figure 4] 1 is a plot of specific capacity as a function of cycles at various discharge rates for coin cells made with electrolytes E5-E7 and E17. The electrode active materials were NMC622 for the positive electrode active material and silicon oxide composite SOC for the negative electrode active material. [Diagram 5] 1 is a plot of the specific capacity at various charge rates for coin cells made with electrolytes E5-E7 and E17. The electrode active materials were NMC622 for the positive electrode active material and silicon oxide composite SOC for the negative electrode active material. [Figure 6A] 1 is a plot of the specific capacity as a function of cycle number for coin cells made with electrolyte E5. The coin cells were cycled at a 4C charge / 1C discharge rate. The electrode active materials were NMC622 for the positive electrode active material and silicon oxide composite SOC for the negative electrode active material. [Figure 6B] 1 is a plot of the specific capacity as a function of cycle number for coin cells made with electrolyte E6. The coin cells were cycled at a 4C charge / 1C discharge rate. The electrode active materials were NMC622 for the positive electrode active material and silicon oxide composite SOC for the negative electrode active material. [Figure 6C] 1 is a plot of the specific capacity as a function of cycle number for coin cells made with electrolyte E7. The coin cells were cycled at a 4C charge / 1C discharge rate. The electrode active materials were NMC622 for the positive electrode active material and silicon oxide composite SOC for the negative electrode active material. [Figure 6D]1 is a plot of the specific capacity as a function of cycle number for coin cells made with electrolyte E17. The coin cells were cycled at a 4C charge / 1C discharge rate. The electrode active materials were NMC622 for the positive electrode active material and silicon oxide composite SOC for the negative electrode active material. [Figure 7] 1 is a plot of the specific capacity as a function of cycles at various charge / discharge rates for coin cells made with electrolytes E2, E3, E7, E9, E17 and E18. The electrode active materials were NMC811 for the positive electrode active material and silicon oxide composite SOC for the negative electrode active material. [Figure 8] Figure 1 is a plot of specific capacity as a function of cycle number for coin cells made with electrolytes E9, E14-16, and E20-E22. The coin cells were cycled at various charge / discharge rates. The electrode active materials were NMC811 for the positive electrode active material and silicon oxide composite SOC for the negative electrode active material. [Figure 9A] 1 is a plot of the specific capacity as a function of cycle number for coin cells made with electrolyte E7. The coin cells were cycled at 1C charge / 1C discharge rate. The electrode active materials were NMC811 for the positive electrode active material and silicon oxide composite SOC for the negative electrode active material. [Figure 9B] 1 is a plot of the specific capacity as a function of cycle number for coin cells made with electrolyte E9. The coin cells were cycled at 1C charge / 1C discharge rate. The electrode active materials were NMC811 for the positive electrode active material and silicon oxide composite SOC for the negative electrode active material. [Figure 9C] 1 is a plot of the specific capacity as a function of cycle number for coin cells made with electrolyte E14. The coin cells were cycled at 1C charge / 1C discharge rate. The electrode active materials were NMC811 for the positive electrode active material and silicon oxide composite SOC for the negative electrode active material. [Figure 9D]1 is a plot of specific capacity as a function of cycle number for coin cells made with electrolyte E15. The coin cells were cycled at 1C charge / 1C discharge rate. The electrode active materials were NMC811 for the positive electrode active material and silicon oxide composite SOC for the negative electrode active material. [Figure 9E] 1 is a plot of the specific capacity as a function of cycle number for coin cells made with electrolyte E20. The coin cells were cycled at 1C charge / 1C discharge rate. The electrode active materials were NMC811 for the positive electrode active material and silicon oxide composite SOC for the negative electrode active material. [Figure 9F] 1 is a plot of the specific capacity as a function of cycle number for coin cells made with electrolyte E21. The coin cells were cycled at a 1C charge / 1C discharge rate. The electrode active materials were NMC811 for the positive electrode active material and silicon oxide composite SOC for the negative electrode active material. [Figure 9G] 1 is a plot of the specific capacity as a function of cycle number for coin cells made with electrolyte E22. The coin cells were cycled at 1C charge / 1C discharge rate. The electrode active materials were NMC811 for the positive electrode active material and silicon oxide composite SOC for the negative electrode active material. [Figure 10] 1 is a plot of power output as a function of state of charge, plotted as cell voltage, for large format pouch cells made with electrolytes E7, E9-E12, and E17. The pouch cells were designed to have a total capacity of approximately 12 Ah. The cells were discharged at a rate of 1 C at 30° C. After every 10% discharge, the cells were pulsed at 5 C for 30 seconds and the power output was measured. The electrode active materials were NMC811 for the positive electrode active material and silicon oxide composite SOC for the negative electrode active material. [Figure 11A]1 is a plot of normalized specific capacity as a function of cycle number for large format pouch cells made with electrolyte E7. The pouch cells were designed to have a total capacity of about 12 Ah at 1C charge / discharge rate at 30° C. The pouch cells were cycled at 1C charge / 1C discharge and the data was normalized to the specific capacity obtained at a C / 3 charge rate. The electrode active materials were NMC811 for the positive electrode active material and silicon oxide composite SOC for the negative electrode active material. [Figure 11B] 1 is a plot of normalized specific capacity as a function of cycle number for large format pouch cells made with electrolyte E9. The pouch cells were designed to have a total capacity of about 12 Ah at 1C charge / discharge rate at 30° C. The pouch cells were cycled at 1C charge / 1C discharge and the data was normalized to the specific capacity obtained at a C / 3 charge rate. The electrode active materials were NMC811 for the positive electrode active material and silicon oxide composite SOC for the negative electrode active material. [Figure 11C] 1 is a plot of normalized specific capacity as a function of cycle number for large format pouch cells made with electrolyte E10. The pouch cells were designed to have a total capacity of about 12 Ah at 1C charge / discharge rate at 30° C. The pouch cells were cycled at 1C charge / 1C discharge and the data was normalized to the specific capacity obtained at a C / 3 charge rate. The electrode active materials were NMC811 for the positive electrode active material and silicon oxide composite SOC for the negative electrode active material. [Figure 11D] 1 is a plot of normalized specific capacity as a function of cycle number for large format pouch cells made with electrolyte E11. The pouch cells were designed to have a total capacity of about 12 Ah at 1C charge / discharge rate at 30° C. The pouch cells were cycled at 1C charge / 1C discharge and the data was normalized to the specific capacity obtained at a C / 3 charge rate. The electrode active materials were NMC811 for the positive electrode active material and silicon oxide composite SOC for the negative electrode active material. [Figure 11E]1 is a plot of normalized specific capacity as a function of cycle number for large format pouch cells made with electrolyte E12. The pouch cells were designed to have a total capacity of about 12 Ah at 1C charge / discharge rate at 30° C. The pouch cells were cycled at 1C charge / 1C discharge and the data was normalized to the specific capacity obtained at a C / 3 charge rate. The electrode active materials were NMC811 for the positive electrode active material and silicon oxide composite SOC for the negative electrode active material. [Figure 11F] FIG. 11B is a plot of normalized specific capacity as a function of cycle number for the large format pouch cell described for FIG. 11A, except that the pouch cell was cycled at a 3C charge (20 min constant current + constant voltage charge) / 1C discharge rate with a cap check at C / 3 rate every 48 cycles. [Figure 11G] FIG. 11C is a plot of normalized specific capacity as a function of cycle number for the large format pouch cell described for FIG. 11B, except that the pouch cell was cycled at a 3C charge (20 min constant current + constant voltage charge) / 1C discharge rate with a cap check at C / 3 rate every 48 cycles. [Figure 11H] FIG. 11C is a plot of normalized specific capacity as a function of cycle number for the large format pouch cell described for FIG. 11C, except that the pouch cell was cycled at a 3C charge (20 min constant current + constant voltage charge) / 1C discharge rate with a cap check at C / 3 rate every 48 cycles. [Figure 11I] FIG. 11D is a plot of normalized specific capacity as a function of cycle number for the large format pouch cell described for FIG. 11D, except that the pouch cell was cycled at a 3C charge (20 min constant current + constant voltage charge) / 1C discharge rate with a cap check at C / 3 rate every 48 cycles. [Figure 11J] FIG. 11C is a plot of normalized specific capacity as a function of cycle number for the large format pouch cell described for FIG. 11E, except that the pouch cell was cycled at a 3C charge (20 min constant current + constant voltage charge) / 1C discharge rate with a cap check at C / 3 rate every 48 cycles. [Figure 12A]1 is a plot of capacity as a function of cycle number for large format pouch cells made with electrolyte E9. The pouch cells were designed to have a total capacity of about 12 Ah at 1C charge / discharge rate at 30° C. The pouch cells were cycled at 1C charge / 1C discharge. The electrode active materials were NMC811 for the positive electrode active material and silicon oxide composite SOC for the negative electrode active material. [Figure 12B] 1 is a plot of capacity as a function of cycle number for large format pouch cells made with electrolyte E9. The pouch cells were designed to have a total capacity of about 12 Ah at 1C charge / discharge rate at 30° C. The pouch cells were cycled at 1C charge / 1C discharge. The electrode active materials were NMC811 for the positive electrode active material and silicon oxide composite SOC for the negative electrode active material. [Figure 13A] 1 is a plot of normalized specific capacity as a function of cycle number for coin cells made with electrolytes E7 and E7. The coin cells were cycled at 1C charge / 1C discharge rate. The electrode active materials were NMC811 for the positive electrode active material and silicon oxide composite SOC for the negative electrode active material. [Figure 13B] FIG. 13B is a plot of coulombic efficiency as a function of cycle number for the coin cells described for FIG. 13A. [Figure 14A] 1 is a plot of normalized capacity as a function of cycle number for large format pouch cells made with electrolyte E7. The pouch cells were designed to have a total capacity of about 32 Ah at a discharge rate of C / 3 at 30° C. The pouch cells were cycled at 1 C charge / 1 C discharge at 30° C. The electrode active materials were NMC811 for the positive electrode active material and silicon oxide composite SOC for the negative electrode active material. [Figure 14B] 14B is a plot of resistance as a function of percent SOC at various cycles ranging from cycle 0 to cycle 900 for the pouch cell described for FIG. 14A. The pouch cell was cycled at a 1C charge / 1C discharge rate with a 1C Hybrid Pulsed Power Characterization (HPPC) pulse every 100 cycles. [Figure 15A]Figure 1 is a plot of voltage as a function of capacity for a large format pouch cell made with electrolyte E7. The pouch cell was designed to have a total capacity of about 32 Ah at a discharge rate of C / 3 at 30°C. The pouch cell was cycled at C / 3 charge and C / 10-12C discharge at 30°C. The electrode active materials were NMC811 for the positive electrode active material and silicon oxide composite SOC for the negative electrode active material. [Figure 15B] 15B is a plot of voltage as a function of capacity for the pouch cell described for FIG. 15A. The pouch cell was cycled at various charge rates ranging from 1C to 6C. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] The lithium-ion cells described herein have a particular ability to produce high power (fast discharge rate) and fast charging, while also exhibiting high energy and long cycle life. The lithium-ion cells were developed with a novel electrolyte formulation that provides improved cycle life, fast charging, and high power capabilities. The electrolyte combines a blend of lithium salts with selected organic solvents, a combination that has been found to provide particularly good rate and cycling characteristics. The described lithium-ion cells generally use electrodes that include a nickel-rich cathode paired with an electrode that includes a SiOx-graphite composite. In prior patent applications, various SiOx anode formulations have been described to achieve long cycle life while maintaining high energy. In this work, lithium-ion cells were developed with electrolyte formulations that improve cycle life, fast charging cycling, and high power capabilities. In some applications, it is desirable for the cell to perform over a wide state-of-charge range. For example, in cell-powered flying vehicles, high power is used during landing to provide a safe and comfortable landing experience. The availability of high power during the later stages of cell discharge provides significant potential for range within safety parameters.

[0009] The preferred electrolyte generally contains a higher amount of lithium bis(fluorosulfonyl)imide (LiFSI, LiN(SO 2 F) 2 ), lithium bis(trifluoromethane)-sulfonimide (LiTFSL, LiN(SO 2 CF 3 ) 2 ) or mixtures thereof in combination with smaller amounts of lithium hexafluorophosphate (LiPF 6 ) are based on a mixture of salts including . For anode chemistries based on silicon suboxide composites and their salts, useful organic solvents may include blends of fluoroethylene carbonate (FEC) and dimethyl carbonate (DMC), which may optionally further include linear fluoroalkyl carbonates, hydrofluoroethers, propylene carbonate (PC), alkyl acetates, or mixtures thereof. For a particular organic solvent, DMC is generally present at least 35 percent (wt%). The weight percentage values ​​of the solvent components are based on the total weight of the solvent. The electrolyte formulations may also use various types of additives in smaller amounts to improve certain performance characteristics. Based on these high-rate electrolytes, extremely high rates of discharge and charge can be achieved while maintaining good cycling performance. Throughout this application and claims, unless otherwise noted, all electrochemical results are at room temperature.

[0010] The electrolyte described herein is designed to provide the key properties necessary to use a relatively large percentage of silicon-based negative electrode active material in commercial cells. Applicant has been able to achieve cycling of silicon-based negative electrodes suitable for vehicle applications of secondary lithium-ion cells. The improved electrolyte allows for fast charging and high discharge rates with significantly reduced gassing while maintaining good cycling of cells using relatively large amounts of silicon-based active material. The cell also exhibits a relatively constant impedance over a significant depth of discharge, allowing high power pulses to be delivered at a relatively low state of charge. Such high power pulse capability is important for certain applications such as landing of flying vehicles where high power pulses are required during landing after significant cell discharge has occurred.

[0011] In some embodiments, the improved electrolyte is LiTFSI and LiPF 6 Or LiFSI and LiPF 6 It contains a mixture of lithium salts containing LiTFSI or LiFSI, with LiFSI and LiPF 6 Blends with LiPF4, LiPF5, LiPF6, LiPF7, LiPF8, LiPF9, LiPF10, LiPF11, LiPF12, LiPF13, LiPF14, LiPF15, LiPF16, LiPF17, LiPF18, LiPF19, LiPF20, LiPF21, LiPF30, LiPF41, LiPF50, LiPF61, LiPF70, LiPF81, LiPF90, LiPF11, LiPF12, LiPF15, LiPF16, LiPF17, LiPF18, LiPF19, LiPF21, LiPF19, LiPF22, LiPF30, LiPF41, LiPF50, LiPF61, LiPF16, LiPF17, LiPF18, LiPF19, LiPF21, LiPF30, LiPF41, LiPF50, LiPF61, LiPF19, LiPF22, LiPF15, LiPF16, LiPF17, LiPF21, LiPF30, LiPF41, LiPF50, LiPF61, LiPF19, LiPF21, LiPF30, LiPF41, LiPF50, LiPF61, LiPF70, LiPF81, LiPF90, LiPF10, LiPF11, LiPF12, LiPF13, LiPF14, LiPF15, LiPF16, LiPF17, LiPF18, LiPF19, LiPF21, LiPF19, LiPF22, LiPF30, LiPF41, LiPF50, LiPF61, LiPF19, LiPF15, LiPF16, LiPF17, LiPF21, LiPF18, LiPF19, LiPF21, LiPF30, LiPF41, LiPF50, LiPF61, LiPF19, LiPF15, LiPF21, LiPF19, LiPF22, LiPF30, LiPF41 4and LiTFSI blends, with optional additives. See U.S. patent application Ser. No. 17 / 831,180 to Dong et al., entitled "Lithium Ion Cells With High Performance Electrolytes and Silicon Oxide Active Materials Achieving Long Cycle Life, Fast Charge and High Thermal Stability" (hereinafter the '180 application), which is incorporated herein by reference.

[0012] The properties of various lithium salts are shown in Table 1. The properties of LiFSI are described in Han et al. Journal of Power Sources, 2011, 196, 3623. LiFSI is thermally stable up to 200°C, and when used in battery structures containing aluminum, aluminum was found to be stable in the high potential region (3.0-5.0 V vs. Li+ / Li). LiFSI has the highest ionic conductivity (LiFSI>LiPF) when measuring solutions containing lithium salts in ethylene carbonate (EC) and EMC at 30 / 70 volume %. 6 >LiTFSI>LiClO 4 >LiBF 4 ). Lithium tetrafluoroborate (LiBF 4 ) and lithium perchlorate (LiClO 4 ) properties are also included in Table 1.

[0013] [Table 1]

[0014] In some desirable embodiments, the electrolyte comprises a lithium salt in a non-aqueous solvent at a concentration of about 1.1 M to about 2.5 M, in further embodiments about 1.2 M to about 2.2 M, and in other embodiments about 1.3 M to about 2.1 M or about 1.7 M to about 2.5 M. The lithium salt is generally (LiTFSI or LiFSI) and LiPF 6in a molar ratio of about 40:1 to about 1.5:1, in further embodiments from about 25:1 to about 2:1, or in some embodiments from about 20:1 to about 3:1. The amounts of each of the lithium salts can be expressed as separate molar concentration ranges as well. Thus, LiPF 6 LiPF may have a concentration of about 0.05M to about 0.8M, in further embodiments about 0.1M to about 0.5M, and in further embodiments about 0.15M to about 0.4M. LiFSI and / or LiTFSI may have a concentration of about 0.8M to about 2.4M, in further embodiments about 0.9M to about 2.2M, in further embodiments about 1.0M to about 2.1M, and in some embodiments about 1.05M to about 2.0M. The electrolyte may optionally include an additional lithium salt in an amount of less than about 10 mole percent, in further embodiments about 6 mole percent or less, and in further embodiments about 5 mole percent or less of the total lithium salt, and in some embodiments is absent. Examples of suitable lithium salt additives are set forth below within a more comprehensive list of additives. Additional ranges of salt concentrations and concentration ratios within the above explicit ranges are contemplated and will be understood by one of ordinary skill in the art to be within the scope of the present invention, including, but not limited to, LiPF 6 It will be appreciated that ranges with interchangeable upper and lower limits, such as 0.1M to 0.4M, are within the scope of this disclosure.

[0015] The non-aqueous solvent generally comprises a blend of solvents. The solvent blend may comprise fluoroethylene carbonate (C 3 O 3 H 3The electrolyte consists essentially of FEC, cyclic carbonate, dimethyl carbonate (DMC), optional co-solvents, and optional additives. The total amount of FEC, DMC, and co-solvents is evaluated as a weight percent value with the total being 100% by volume, and the optional additives are referenced as a weight percent value with respect to the total electrolyte weight. The optional additives may or may not be liquid. The organic solvent may include about 5% to about 25% by weight of FEC, in further embodiments about 7% to about 20% by weight of FEC, in further embodiments about 8% to about 18% by weight, and in some embodiments about 9% to about 16% by weight of FEC. The organic solvent generally includes about 35% to about 95% by weight of DMC, in further embodiments about 38% to about 92% by weight, and in further embodiments about 40% to about 90% by weight of DMC. If additional co-solvents are present, a lower amount of DMC is used, while if additional co-solvents are not present, a higher amount of DMC is used. Optional co-solvents include diethyl carbonate, linear fluorocarbonates, hydrofluoroethers, propylene carbonate (cyclic carbonate, 4-methyl-1,3-dioxolan-2-one), alkyl acetates (methyl acetate, ethyl acetate, propyl acetate or mixtures thereof) or mixtures thereof. Acyclic (dialkyl) fluorocarbonates include, for example, methyl 2,2,2-trifluoroethyl carbonate (FEMC, CF 3 CH 2 O(CO)OCH 3). Hydrofluoroethers are generally partially fluorinated ethers, and representative compounds include, for example, IH,IH,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, or 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, or mixtures thereof. Suitable hydrofluoroethers for electrolytes are further described in U.S. Patent Application Publication No. 2022 / 0216518 to Li et al., entitled "Electrolyte for Lithium Ion Battery, Lithium Ion Battery, Battery Module, Battery Pack and Apparatus," which is incorporated herein by reference. The co-solvent can be present in an amount of about 5% to about 60% by weight, in further embodiments about 7% to about 58% by weight, in other embodiments about 8% to about 55% by weight, in further embodiments about 9% to about 50% by weight, and in some embodiments about 10% to about 45% by weight, of the individual compounds or blends thereof. In some embodiments, the solvent can comprise about 35% to about 55% by weight of a fluorodialkyl carbonate, a hydrofluoroether, or a mixture thereof. In some embodiments, the solvent can comprise about 9% to about 35% by weight of a propylene carbonate, an alkyl acetate, or a mixture thereof. A person of ordinary skill in the art will recognize that additional ranges of solvent component concentrations within the explicit ranges above are contemplated and are within the scope of the present disclosure, including ranges with the corresponding upper and lower limits interchanged with each other.

[0016] With respect to electrolyte terminology, many embodiments have a base composition with optional additives for salt and other non-salt additives. To the extent that the electrolyte composition consists of a specific composition, tunable additives allow for variation around the base composition to provide tuning of properties. In this specification, when a composition is indicated as consisting essentially of a specific composition, it is intended to mean that any additives do not significantly change the electrochemical properties, but other properties such as gassing, thermal stability, fire resistance, etc. may be different.

[0017] The electrolyte additives can provide anti-gassing effects, reduced flammability, and / or other safety effects. Any additive should be selected to help maintain the desired cycling stability. Suitable additives of interest include, for example, anti-flammability additives (e.g., triethyl phosphite (TEP), trimethyl phosphite (TMP), triphenyl phosphite (TPP), pentafluoro(phenoxy)cyclotriphosphazene (PFPCTP), ethoxy(pentafluoro)cyclotriphosphazene (EPFCTP, C 2 H 5 F 5 N 3 OP 3 ) or hexaphenoxycyclotriphosphazene (HPCTP); gassing inhibitors (e.g., vinylene carbonate (VC); 4-vinyl-1,3-dioxolan-2-one (VEC); 1,3-propane sultone (PS, C 3 H 6 SO 3); prop-1-ene-1,3-sultone (PES); 1,3,2-dioxathiolane 2,2-dioxide (DTD); lithium difluorophosphate (LiDFP, TEP, TMP or TPP); HF scavenger (e.g., fluorobenzene (FB); succinonitrile (SN) or lithium 4,5-dicyano-2-(trifluoromethyl)imidazole (LiTDI)); solid electrolyte interphase (SEI) modifiers on the anode active material surface (e.g., VC; VEC; lithium bis(oxalato)borate (LiBOB); lithium difluoro(oxalato)borate (LiDFOB); trimethylborate (TMB); LPTB (lithium 4-pyridyltrimethylborate)) or mixtures thereof. Some additives can affect the formation of the cathode electrolyte interface (CEI) (such as LiDFP, LiBOB or LiDFOB). Some additives can have multiple effects on performance. Any additive having lithium ions can be considered a lithium salt additive with the concentration limits specified for lithium salt additives, and other additives are considered to be within the general groupings of additives and corresponding limits for such additives provided herein. A person of ordinary skill in the art will recognize that additional ranges of electrolyte components within the explicit ranges above are contemplated and are within the scope of the present disclosure.

[0018] Applicants have achieved very good cycle performance of silicon-based electrodes using previously developed electrolytes described in U.S. Patent Application Publication No. 2020 / 0411901 to Dong et al., entitled "Lithium Ion Cells with High Performance Electrolyte and Silicon Oxide Active Materials Achieving Very Long Cycle Life Performance" (hereinafter the '901 Application), which is incorporated herein by reference. While the '901 Application achieved significant breakthroughs in cycle life performance of silicon-based cells, the results herein are directed to achieving high discharge power and high rate charge while maintaining high energy and good cycling performance. The reference electrolyte used in the examples is similar to that in the '901 Application and is referred to as E17, although the nomenclature is not intended to be construed as limiting the scope of the invention. Applicants have also described a similar electrolyte in the '180 Application cited above. The electrolytes described herein are particularly effective for very high power performance for the described active materials while achieving long cycle life.

[0019] In some embodiments, the electrolyte formulation described in this work comprises LiPF in FEC and DMC solvents. 6 The electrolyte formulations show better rate performance than reference electrolyte formulations consisting of salts, while showing comparable or better cycle life. As exemplified herein, the electrolyte family consists of LiPF in a solvent consisting of FEC and (DMC or fluorinated EMC (FEMC) or a blend of DEC and HFE (highly fluorinated ethylene)), optional PC, and optional MA [or EA]. 6 and (LiTFSI or LiFSI) salt blend formulations. These exemplified electrolytes suggest other variations within these explicit ranges taught.

[0020] As exemplified herein, some specific embodiments include a method for preparing lithium salts, LiTFSI and LiPF in a solvent comprising FEC and one or more additional solvents selected from the group consisting of DMC, fluorinated ethers, fluorinated carbonates, PC, alkyl acetates, and mixtures thereof. 6 Or LiFSI and LiPF 6 The electrolyte family includes a formulation with a blend of DEC. Higher concentrations of DEC generally result in a significant decrease in high-rate performance. The one or more additional solvents may consist essentially of DMC. The one or more additional solvents may consist essentially of DMC, PC and alkyl acetates. The one or more additional solvents may include a hydrofluoroether (HFE) or consist essentially of one or more HFEs. The one or more additional solvents may consist essentially of a fluorinated ether, a fluorinated dialkyl carbonate or a mixture thereof. The one or more additional solvents may consist essentially of a fluorinated ether, such as 1H,1H,5H-octafluoropentyl 1,1,2,2-tetrafluoroethyl ether (OTE). Other fluorinated ethers include 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE); bis(2,2,2-trifluoroethyl) ether (BTFE) and ethyl 1,1,2,2-tetrafluoroethyl ether (ETE). The one or more additional solvents may consist essentially of DMC and OTE.

[0021] Alkyl acetates for use in any of the electrolytes described herein include methyl acetate, ethyl acetate, propyl acetate, and mixtures thereof.

[0022] Batteries of particular interest today exhibit both rapid charging and high power capabilities, which are related concepts of charging versus discharging. Examples include charging at rates up to 5C and discharging at rates up to 12C. Specifically, high power is achieved by high-rate discharge with adequate energy, while rapid charging is the corresponding high-rate operation of the charging reaction. Charge capacity is rate dependent, and it is desirable for the cell to have good rate capability at rapid charging to exhibit good high-rate performance. Charging can be done at constant current, followed by a relatively short constant voltage charging step to terminate. The constant voltage charging can be stopped when the current falls below an appropriate value, e.g., C / 20 or C / 50, which provides a value close to the target voltage. As with the discharge step, the capacity during charging is generally rate dependent. Therefore, after constant current charging, the open circuit voltage may be slightly short of the target voltage when the constant current charging step is completed. The voltage drop depends on the charge rate and charging capability of the cell, with cells with lower rate capabilities exhibiting larger voltage drops. The open circuit voltage can be increased to a desired value with a relatively short low current charging step. For testing purposes, the discharge rate can be selected to a desired high value to represent a high power discharge corresponding to a high current discharge. In the examples, some results are shown for a 3C constant current charge followed by a 10 minute constant voltage charge with a total charge time of 30 minutes, although other high rate charges are also illustrated.

[0023] Since charge capacity is rate or current dependent, the use of electrolytes described herein that improve rate capability facilitates rapid charging. When materials without rate capability are forced to charge at high rates, cycling performance may be compromised and / or the target charge voltage may not be achieved within the allotted time. During constant current charging, increasing the rate shortens the time to reach the selected voltage at that rate, but if the rate capability is low, it may take longer to complete the constant voltage portion of the charge. If the rate capability is high, a faster charge rate may be effective while preventing the constant voltage charge interval from becoming too long. An example is shown of a 20 minute 3C constant current charge and a 10 minute constant voltage charge. In some embodiments, a 15 minute charge can be achieved with a constant voltage charge period of about 6 minutes or less, in further embodiments about 5.5 minutes or less, and in further embodiments about 5 minutes or less. A person of ordinary skill in the art will recognize that additional ranges of constant voltage times within the above explicit ranges are contemplated and are within the scope of the present disclosure.

[0024] In practical use, the power output generally varies according to the power requirements of the application. Thus, high power discharges may be used during acceleration and deceleration, such as takeoff and landing of a flight vehicle, while cruise may be at low power operation. Especially during landing, there may be very high power discharges (e.g., >10C) for a short period of time to achieve a soft landing. Of course, landing is at the end of the discharge cycle, so there must be enough capacity remaining to accommodate large pulse discharges. Therefore, it is highly desirable to exhibit both high power and high capacity at a reasonable state of charge (SOC), such as >50% discharge. Having high power capability allows the range to be safely extended without serious concerns about insufficient capacity remaining for landing. The electrolytes and corresponding cells described herein are designed to accommodate both rapid charging and high power discharge. In an exemplary embodiment, the cells are formed using a first cycle (and optionally two or several cycles) of charge and discharge at a C / 10 rate to form a stable passivation layer on the active material and form the cell for cycling in subsequent cycles. One or more subsequent cycles can be performed at C / 3 to complete a stable formation process.

[0025] In addition to the high rate charge and discharge during cycling, additional high rate pulse tests were performed. To perform the pulse tests, the cell is first fully charged. Next, a 5C (fully discharged in 12 minutes) discharge is performed with a 30 second pulse. The cell is then discharged to 90% state of charge (SOC) and again a 5C, 30 second discharge pulse is applied. This pulse is repeated stepping down every 10% SOC. For each 5C pulse, the cell power output and resistance are calculated. Plots of these pulse tests are shown in the Examples. A desirable 5C pulse power output at 50% SOC is at least 3 kW / kg. More generally, for pouch cells having a capacity of at least 1 A, the 5C pulse power output at 50% SOC is at least 2.0 kW / kg, in further embodiments at least about 2.5 kW / kg, in other embodiments at least about 2.75 kW / kg, and in further embodiments between about 3.0 kW / kg and 4.25 kW / kg. This high power capability may be achieved simultaneously with a high energy density at a discharge rate of C / 3 of at least about 200 Wh / kg, and in further embodiments, from about 250 Wh / kg to about 375 Wh / kg. A person of ordinary skill in the art will recognize that additional ranges of power and energy density within the explicit ranges above are contemplated and are within the present disclosure.

[0026] Electronic vehicles have received significant commercial attention for lithium-ion cells. Suitable vehicles include, for example, automobiles, trucks, vans, sport utility vehicles, crossover styles, commercial trucks, construction equipment, utility vehicles such as forklifts, ambulatory vehicles such as personal air vehicles, unmanned ground vehicles such as tractors, people movers, unmanned aerial vehicles such as drones, and similar vehicles. High-power cells are useful in all high-performance vehicles, as well as power tools, some medical equipment, and other high-power applications.

[0027] In such applications, it is desirable to use pouch-type cells with flexible housing. In flexible housings, it may be desirable to incorporate the cells into a battery pack that holds the cells within a predetermined volume. Such volume constraint effects are similarly exhibited for cells assembled in metal containers, such as the coin cell embodiment used in the examples and conventional cylindrical cells. Positioning the cells in the pack may correspond to clamping the cells to control disassembly of the electrode stack, which may impair cycling. In the following examples, cell expansion is tested for unclamped pouch cells to test the impact of gassing. In the constrained configuration, the cell cannot expand, but gassing is manifested through an increase in pressure. The increase in pressure may be exacerbated by an increase in temperature. For these reasons, cycling performance at 45° C. may reflect the ability to control gassing.

[0028] General battery characteristics The negative and positive electrode structures can be assembled into a suitable cell. As further described below, the electrodes are generally formed in association with current collectors to form an electrode structure. A separator is placed between the positive and negative electrodes to form a cell. The separator is electrically insulating while providing at least a selected ionic conductivity between the two electrodes. A variety of materials can be used as the separator. Some commercially available separator materials can be formed from polymers such as polyethylene and / or polypropylene, which are porous sheets that provide ionic conductivity. Commercially available polymer separators include, for example, the Celgard® line of separator materials from Celgard, LLC, a subsidiary of Asahi Kasei (Japan). Ceramic and polymer composite materials have also been developed for separators. These ceramic composite separators can be stable at higher temperatures, and the composite materials can reduce fire risks. Polymer ceramic composites for lithium ion battery separators are sold by Celgard®, and by Evonik Industries, Germany under the trademark Separion®, and by Tiejin Lielsort Korea Co., Ltd. under the trademark Lielsort®. A porous polymer sheet coated with a gel-forming polymer can also be used to form the separator. Such separator designs are further described in U.S. Pat. No. 7,794,511 B2 to Wensley et al., entitled "Battery Separator for Lithium Polymer Battery," which is incorporated herein by reference. Suitable gel-forming polymers include, for example, polyvinylidene fluoride (PVDF), polyurethane, polyethylene oxide (PEO), polypropylene oxide (PPO), polyacylonitrile, gelatin, polyacrylamide, polymethyl acrylate, polymethyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, polytetraethylene glycol diacrylate, copolymers thereof, and mixtures thereof.

[0029] The electrolyte provides ion transport between the anode and cathode of the battery during the charging and discharging processes. Electrolytes for lithium-ion batteries incorporate a non-aqueous solvent and a lithium salt. Improved electrolytes for silicon-based electrodes are described in detail below. The electrolyte is generally permeated into the cell before sealing the case.

[0030] The electrodes described herein can be assembled into various commercially available cell / battery designs, such as prismatic batteries, wound cylindrical cells, coin cells, or other suitable cell / battery designs. A cell can include a pair of electrodes (optionally wound or folded) or multiple pairs of electrodes assembled in parallel and / or series electrical connection. The electrode stack can have additional electrodes such that the stack ends with the same polarity as the other end of the stack for convenient placement in a container. Although the electrode structures described herein can be used in batteries for primary or single charging, the resulting batteries generally have the desired cycling characteristics for secondary battery applications upon multiple cycling of the battery.

[0031] In some embodiments, the positive and negative electrodes can be stacked with a separator between them, and the resulting stack structure can be rolled into a cylindrical or prismatic configuration to form a cell structure. Appropriate conductive tabs can be welded to the current collectors, etc., and the resulting jellyroll structure can be placed in a metal canister or polymer package with the negative and positive tabs welded to appropriate external contacts. Electrolyte is added to the canister, and the canister is sealed, optionally completing the cell after formation cycling. Some currently used rechargeable commercially available cells include, for example, cylindrical 18650 cells (diameter 18 mm and length 65 mm), 26700 cells (diameter 26 mm and length 70 mm), although other cell / battery sizes as well as selected size prismatic cells and foil pouch cells / batteries can be used.

[0032] Pouch batteries can be particularly desirable for a variety of applications, including certain vehicle applications, due to their stacking convenience and relatively low container weight. Pouch battery designs for vehicle batteries incorporating high capacity cathode active materials are further described in U.S. Patent No. 8,187,752 to Buckley et al., entitled "High Energy Lithium Ion Secondary Batteries," and U.S. Patent No. 9,083,062 B2 to Kumar et al., entitled "Battery Packs for Vehicles and High Capacity Pouch Secondary Batteries for Incorporation into Compact Battery Packs," both of which are incorporated herein by reference. Although the pouch battery design is particularly convenient for use in certain battery pack designs, pouch batteries can also be effectively used in other situations.

[0033] 1A-1D show a representative embodiment of a pouch battery. In this embodiment, the pouch battery 100 includes a pouch enclosure 102, an electrode core 104, and a pouch cover 106. The electrode core is further described below. The pouch enclosure 102 includes a cavity 110 and an edge 112 surrounding the cavity. The cavity 110 has dimensions such that the electrode core 104 can fit within the cavity 110. As shown in FIGS. 1B and 1C, the pouch cover 106 can be sealed around the edge 112 to seal the electrode core 104 within the sealed battery. End tabs 114, 116 extend outwardly from the sealed pouch for electrical contact with the electrode core 104. FIG. 1C is a schematic cross-sectional view of the battery of FIG. 1B as viewed along line 3-3. With various configurations of edges and seals, many additional embodiments of the pouch battery are possible.

[0034] FIG. 1D illustrates an embodiment of an electrode core 104 that generally includes an electrode stack. In this embodiment, the electrode stack 130 includes anode structures 132, 134, 136, cathode structures 138, 140, and separators 150, 152, 154, 156 disposed between adjacent cathodes and anodes. The separators may be provided as a single folded sheet with the electrode structures disposed within the pleats of the separator. The anode structures 132, 134, 136 include anodes 160, 162, anodes 164, 166, and anodes 168, 170 disposed on either side of current collectors 172, 174, 176, respectively. The cathode structures 138, 140 include cathodes 180, 182, anodes 184, 186, respectively disposed on opposite sides of current collectors 188, 190, respectively. Tabs 192, 194, 196, 198, 200 are connected to current collectors 172, 188, 174, 190, 176, respectively, to facilitate connection of the individual electrodes in series or parallel. For vehicle applications, the tabs are typically connected in parallel, with tabs 192, 196, 200 electrically connected to electrical contacts accessible from outside the container, and tabs 194, 198 electrically connected to electrical contacts as opposite poles accessible from outside the container.

[0035] The electrode stack may have an additional negative electrode such that both outer electrodes adjacent the container are negative. Typically, a battery with stacked electrodes of the dimensions described herein will have 5 to 40 negative electrode elements (current collectors coated on both sides with active material), and in further embodiments, 7 to 35 negative electrode elements. The corresponding number of positive electrode elements will generally be one less than the negative electrode elements. A person of ordinary skill in the art will recognize that additional ranges of electrode numbers within the explicit ranges above are contemplated and are within the present disclosure.

[0036] As mentioned above, the wound electrodes can be used for either cylindrical batteries or generally prismatic batteries. Wound cells for cylindrical lithium ion batteries are further described in U.S. Patent No. 8,277,969 to Kobayashi et al., entitled "Lithium Ion Secondary Battery," which is incorporated herein by reference. Prismatic batteries with wound electrodes are described in U.S. Patent No. 7,700,221 to Yeo, entitled "Electrode Assembly and Lithium Ion Secondary Battery Using the Same," which is incorporated herein by reference. Kobayashi's '969 patent and Yeo's '221 patent do not describe how to achieve adequate cycling or high energy density with silicon-based active materials. Designs for prismatic batteries using wound electrodes are further described, for example, in the '221 patent. The specific design of either the stacked combination of electrodes or the wound cell can also be influenced by the target size and target capacity of the battery.

[0037] The improved anode can be used for various applications and cell / battery designs. For electrode stacks, the area of ​​the electrodes can be appropriately selected based on the volume and design constraints for a particular application. The following discussion focuses on large cells that are typically designed for vehicle applications such as drones, cars, trucks, or other vehicles. However, the improved anode described herein can be effectively used for consumer electronics applications that may be based on smaller cell configurations. It should be noted that automobiles may also use smaller consumer electronics cells, and Tesla cars are currently known to use thousands of small consumer electronics cells in their battery packs. In general, within certain ranges, larger cells / batteries can achieve greater energy density. It may be desirable to select a positive electrode active material based on a particular application to balance various considerations such as energy density.

[0038] Selection of electrode parameters allows the design of a high gravimetric energy density cell to incorporate a balance of factors such as electrode area, number of electrode structures, and battery capacity. Electrode area refers to the spatial extent of one electrode along one side of a current collector. Figure A shows the length "L" of the electrode, and Figure C shows the width "W". As shown in the figures, the area of ​​the electrode can be defined as L x W. In some embodiments, the area of ​​each electrode can be similar such that the dimensions of a battery including an electrode stack can have a length and width similar to the length and width of each electrode in the stack. In some embodiments, the separator can be in the form of a sheet with an area slightly larger than the area of ​​the electrodes, and in some embodiments, the separator can be folded, pleated, or formed with pockets, with the electrodes placed in the pleats or pockets of the separator.

[0039] Electrode structure The electrodes of the cell include active materials along with binders and conductive additives. The electrodes are formed into sheets, dried, and pressed to achieve the desired density and porosity. Typically, the electrode sheets are formed directly on a metal current collector, such as a metal foil or a thin metal grid. In many cell structures, electrode layers are formed on both sides of the current collector to provide the desired performance in the assembled cell or battery. The electrode layers on both sides of the current collector are at the same potential in the cell and can be considered elements of the same electrode structure, but the current collector itself, although part of the electrode structure, is generally not considered part of the electrode because it is electrochemically inactive. Thus, references to the physical aspects of the electrode generally refer to the electrode composition of one layer within the electrode structure. The conductive current collector can facilitate the flow of electrons between the electrode and an external circuit.

[0040] In some embodiments, when the positive or negative electrode uses a high loading level, the density of the electrode can be reduced to provide good cycling stability of the electrode. The density of the electrode is a function of the pressing pressure within a suitable range. In general, the density of the electrode cannot be arbitrarily increased without sacrificing performance with respect to loading level while achieving the desired cycling performance and capacity at higher discharge rates. The following sections describe the characteristics of certain negative and positive electrode layers.

[0041] In some embodiments, the current collector can be formed from nickel, aluminum, stainless steel, copper, and the like. The electrode material can be cast onto the current collector as a thin film. The electrode material together with the current collector can then be dried, for example in an oven, to remove the solvent from the electrode. In some embodiments, the dried electrode material can be subjected to a pressure of about 2 to about 10 kg / cm2 while in contact with a current collector foil or other structure. 2 (kilograms per square centimeter) pressure. The current collector used in the positive electrode can have a thickness of about 5 microns to about 30 microns, in other embodiments about 10 microns to about 25 microns, and in further embodiments about 14 microns to about 20 microns. In one embodiment, the positive electrode uses an aluminum foil current collector. The current collector used in the negative electrode can have a thickness of about 2 microns to about 20 microns, in other embodiments about 4 microns to about 14 microns, and in further embodiments about 6 microns to about 10 microns. In one embodiment, the negative electrode uses a copper foil or nickel foil as a current collector. A person of ordinary skill in the art will recognize that additional ranges of current collector thickness within the explicit ranges above are contemplated and are within the present disclosure.

[0042] negative electrode The basic electrode design includes one or a blend of active composition, polymer binder, and conductive diluent. As mentioned above, in some embodiments, the improved electrode design may include a blend of polymer binder, and optionally a blend of active composition, and nanoscale conductive carbon additive. While the active material can be only silicon-based material or composite, the active material blend may in some embodiments include a majority of silicon-based active material, such as silicon oxide composite, and at least 2.5 weight percent of unique graphite, or in some embodiments, at least about 4 weight percent graphite. A general description of high capacity silicon-based active materials can be found in U.S. Pat. No. 9,190,694 to Lopez et al., entitled "High Capacity Anode Materials for Lithium Ion Batteries," which is incorporated herein by reference.

[0043] It has also been discovered that stabilization of electrode cycling with silicon-based active materials can be obtained with solvent-based or water-based binders. Although either graphite can provide electrical conductivity to the electrode, it has nevertheless been discovered that in some embodiments, a certain amount of unique nanoscale conductive carbon can be significant with respect to the ability to fabricate long cycling negative electrodes. Generally, nanoscale conductive carbon is thought to be not electrochemically active, but graphite can be electrochemically active. These improved design aspects are further incorporated into the electrode with previously discovered improvements in silicon-based electrodes.

[0044] There has been significant attention given to silicon-based high capacity anode active materials. Silicon-based active materials have generally not achieved cycling stability suitable for automotive applications of batteries containing significant amounts of silicon. With silicon-based active materials, applicants have demonstrated successful cycling suitable for consumer electronics applications and the like, with cycling up to about 200-300 cycles at values ​​of at least 80% of initial capacity. See U.S. Patent Application Publication No. 2015 / 0050535 to Amiruddin et al., entitled "Lithium Ion Batteries With High Capacity Anode Active Materials for Consumer Electronics," which is incorporated herein by reference. Applicants have been particularly successful with materials based primarily on silicon oxide composites in terms of cycling stability. With conventional electrolyte formulations, applicants have used effective electrode designs (see the '901 application cited above) that can be cycled over a large voltage range at reasonable rates and succeed in over 800 cycles without experiencing less than 80% capacity loss. Therefore, the present work is directed towards providing very high rate capability while maintaining cycling stability up to the region suitable for vehicular use.

[0045] As described herein, good cycling results are obtained using a blended active material composition of silicon-based active material and graphitic carbon. In general, the total capacity of the negative electrode blended active material can be at least about 750 mAh / g, in further embodiments at least about 900 mAh / g, in further embodiments at least about 1000 mAh / g, and in other embodiments at least about 1100 mAh / g, when cycled against lithium metal at a rate of C / 3 at 5 millivolts (mV) to 1.5 V. Although a silicon-based active material such as a SiO / Si / C composite can be used as the only anode active material, the blended active material can include at least about 40% by weight of silicon-based active material, in further embodiments at least about 50% by weight of silicon-based active material, in other embodiments from about 55% by weight to about 99% by weight of silicon-based active material, and in further embodiments from about 60% by weight to about 95% by weight of silicon-based active material. Correspondingly, the blended active material may include from about 1 wt.% graphite to about 65 wt.% graphite, in further embodiments from about 2 wt.% graphite to about 60 wt.% graphite, in further embodiments from about 3 wt.% graphite to about 55 wt.% graphite, and in other embodiments from about 5 wt.% graphite to about 50 wt.% graphite. Desirable graphite is described below. A person of ordinary skill in the art will recognize that additional ranges of specific discharge capacity and concentrations of silicon-based active material within the explicit ranges above are contemplated and are within the present disclosure.

[0046] As described above and in detail below, suitable silicon-based active materials may include composites with carbon components. The following section will provide a detailed description of silicon-based active materials. Composites refer to particulate materials with components intimately combined in a monolithic material with effective uniformity on a suitable scale, as opposed to blends, which include mixtures held together by polymer binders. Composite components may include, for example, silicon, oxygen, carbon, and the like. Without wishing to be limited by theory, the carbon components of composites with silicon are generally not considered to be electrochemically active and are generally not graphite-based. However, activity is an abstract concept given the intimate combinations in the composite and crystal structure can be very complex and difficult to evaluate. In any case, the carbon components of the composite are readily understood by those skilled in the art as being distinguishable from the separate graphite that is not present in the composite in the active material blend. The following examples are based on commercially available composite compositions that are believed to contain primarily silicon suboxide and some amount of elemental silicon crystals and elemental carbon in the combined composite particulate materials.

[0047] Graphite is commercially available in natural and synthetic forms, and suitable graphites include natural or synthetic graphite. Graphite is a crystalline form of carbon, containing carbon covalently bonded in sheets. As used herein, graphite refers to graphitic carbon without requiring perfect crystallinity, and some natural graphitic materials may contain some crystalline impurities. However, graphite generally refers to materials dominated by the graphitic structure as recognized in the art. Graphite is conductive along the plane of the covalently bonded carbon sheets stacked in the crystal. Graphitic crystalline carbon is an established electrochemically active material for lithium-ion batteries, as it can intercalate lithium, but the morphology of the graphite particles can affect the efficacy of graphite's lithium intercalation.

[0048] The graphite particles may have an average particle size of about 1 micron to about 30 microns, in further embodiments about 1.5 microns to about 25 microns, and in other embodiments about 2 microns to about 20 microns. In general, it is believed desirable for the graphite to not contain particles larger than the thickness of the electrode to avoid an uneven electrode surface, and graphite particles having a size significantly smaller than 1 micron may have reduced crystallinity. In some embodiments, the graphitic carbon may have a D50 (mass median diameter) of about 5 microns to about 50 microns, in further embodiments about 7 microns to about 40 microns, and in additional embodiments about 10 microns to about 8 microns to about 30 microns. In some embodiments, the BET surface area of ​​the graphitic carbon active material (assessable according to ISO 4652) is about 1 m 2 / g~about 50m 2 / g, and in a further embodiment about 1.5m 2 / g ~ approx. 35m 2 / g and in a further embodiment, about 2m 2 / g ~ approx. 25m 2 / g. A person of ordinary skill in the art will recognize that additional ranges of particle size and surface area for graphitic carbon active materials are contemplated and are within the present disclosure. In contrast, conductive carbon blacks and the like (called quasicrystalline) generally have particle sizes of about 40 m 2 / g~1000m 2 / g or more.

[0049] With respect to the polymer binder, applicants have obtained suitable cycling of silicon-based cells using high tensile strength binders, such as polyimide binders. See U.S. Pat. No. 9,601,228 to Deng et al., entitled "Silicon Oxide Based High Capacity Anode Materials for Lithium Ion Batteries," (hereinafter the '228 patent), which is incorporated herein by reference. In some embodiments to obtain longer cycling stability, it has surprisingly been found that polymer binder blends further stabilize cycling. In particular, a second polymer or combination of polymers providing a lower modulus of elasticity (corresponding to higher elasticity) can be blended with the high tensile strength polyimide. The binder blend generally comprises at least about 50% by weight polyimide, in further embodiments at least about 55% by weight polyimide, and in other embodiments from about 60% to about 95% by weight polyimide. Similarly, the binder blend generally comprises at least about 5% by weight of a polymer having a low modulus of elasticity, in further embodiments at least about 10% by weight, and in other embodiments from about 12% to about 40% by weight of a polymer having a low modulus of elasticity, as further defined below. A person of ordinary skill in the art will recognize that additional ranges of amounts of polymer within the above explicit ranges are contemplated and are within the present disclosure. The polymers of the blend may be selected to be soluble in the same solvent. Polymer blends useful for achieving good cycling of silicon-based anodes are summarized below and are further described in U.S. Pat. No. 11,094,925 to Venkatachalam et al. (hereinafter the '925 patent), entitled "Electrodes with Silicon Oxide Active Materials for Lithium Ion Cells Achieving High Capacity, High Energy Density and Long Cycle Life Performance," which is incorporated herein by reference.

[0050] Polyimides are polymers based on repeating units of imide monomer structures. Polyimide polymer chains can be aliphatic, but for high tensile strength applications, the polymer backbone is generally aromatic, with the polymer backbone extending along the N atoms of the polyimide structure. For silicon-based anodes that exhibit significant morphological changes during cycling, it has been found that thermosetting polyimide polymers are desirable for high capacity anodes. This may be due to their high mechanical strength. Table 2 shows the sources of high tensile strength polyimide polymers and the corresponding polyimide polymer names.

[0051] [Table 2]

[0052] The polyimide polymer may have a tensile strength of at least about 60 MPa, in further embodiments at least about 100 MPa, and in other embodiments at least about 125 MPa. Some commercially available polyimides with high tensile strength may also have relatively high elongation values. Elongation value is the amount of elongation that a polymer will withstand before tearing. In some embodiments, the polyimide may have an elongation of at least about 40%, in further embodiments at least about 50%, and in other embodiments at least about 55%. Tensile strength and elongation values ​​may be measured according to the procedures of ASTM D638-10 Standard Test Method for Tensile Properties of Plastics or ASTM D882-91 Standard Test Method for Tensile Properties of Thin Plastic Sheets, both of which are incorporated herein by reference. Based on values ​​reported by commercial suppliers, the results from these alternative ASTM protocols appear to be similar to one another for polyimides. A person of ordinary skill in the art will recognize that additional ranges of polymer properties within the explicit ranges above are contemplated and are within the present disclosure.

[0053] A suitable more flexible polymer component can be selected that is inert to the electrochemistry of the cell and compatible with processing with polyimide. Particularly suitable more flexible polymer components include, for example, PVDF, carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), lithiated polyacrylic acid (LiPAA) or mixtures thereof. Regarding polymer properties, some significant properties for high capacity anode applications are summarized in Table 3.

[0054] [Table 3]

[0055] PVDF, CMC, SBR are commercially available from a number of sources. LiPAA can be made from LiOH and commercially available polyacrylic acid (PAA). For example, a stoichiometric amount of LiOH can be added to a solution of PAA, with one mole of LiOH per monomer unit of PAA. The formation and use of LiPAA is further described in Li et al., “Lithium polyacrylate as a binder for tin-cobalt-carbon negative electrodes in lithium-ion batteries”, Electrochemica Acta 55 (2010) 2991-2995, which is incorporated herein by reference.

[0056] By elongation is meant the percentage of elongation before the polymer is torn. In general, to accommodate silicon-based materials, an elongation of at least about 30%, in some embodiments at least about 50%, and in further embodiments at least about 70% is desired. For polymer binder blends, it may be desirable for the more elastic polymer binder component to have an elastic modulus (alternatively referred to as Young's modulus or tensile modulus) of about 2.4 GPa or less, in further embodiments at most about 2.25 GPa, in other embodiments at most about 2 GPa, and in additional embodiments at most about 1.8 GPa. A person skilled in the art will recognize that additional ranges of properties of the more elastic polymer component within the above explicit ranges are contemplated and are within the present disclosure.

[0057] To form the electrode, the powder can be blended with the polymer in a suitable liquid, such as a solvent for dissolving the polymer. Polyimides and PVdF can generally be processed in N-methylpyrrolidone (NMP), although other suitable organic solvents can be used. Aqueous processable polyimides are commercially available and are suitable for blending with a wide range of other polymers. The particulate components of the electrode, i.e., the active material and nanoscale conductive carbon, can be blended with the polymer binder blend in a solvent before forming a paste. The resulting paste can be pressed into an electrode structure.

[0058] Although the above-mentioned polymer binders have helped achieve good cycling stability of silicon-based negative electrodes, water-based polymer binders have been developed that can achieve similar or better cycling performance. In some embodiments, the water-processable polymer binder is a copolymer of acrylate monomers (S-PAA) and acrylamide monomers, where the cation (S) can be a metal cation. It has been found that desirable polymer binders have both good adhesion to the current collector and good cohesion between particles. The S-PAA monomer can contribute to good cohesion, and the acrylamide comonomer can contribute to good adhesion. Binders based on S-PAA and acrylamide copolymers can be provided with the appropriate ratio of monomers that results in good cycling with silicon-based negative electrode active materials. Water-based polymer blends that are effective in achieving excellent cycling of silicon-based anodes are summarized below and are further described in U.S. Patent Application Publication No. 2022 / 0006090 to Hays et al., entitled "Lithium Ion Cells With Silicon Based Active Materials and Negative Electrodes with Water-Based Binders Having Good Adhesion and Cohesion" (hereinafter the '047 Application), which is incorporated herein by reference.

[0059] Achieving good adhesion and good cohesion simultaneously has been found to be important to achieve improved cycling. The monomer units of the copolymer binder are acrylamide and the salt of polyacrylic acid (S-PAA). The salt cation can be a metal cation such as lithium (LiPAA) or sodium (NaPAA) or potassium (KPAA), although other metals may be used or ammonium NH 4 +Non-metallic cations such as , , and , can also be used. Mixtures of counterions can be used if desired. S-PAA polymers have been found to impart strong cohesive strength to corresponding electrodes. Cohesive strength can be evaluated for electrode structures on current collectors by bending them around a mandrel of a specific diameter. Forces are applied in a controlled manner to evaluate the force required to peel the electrode from the current collector, and adhesion is evaluated using commercially available testing equipment. The ratio of monomer units can be selected to achieve the desired balance of adhesive and cohesive stability.

[0060] The copolymer can be synthesized according to published methods. Specifically, acrylate groups can be formed from nucleophilic substitution of amide groups with carboxylate groups, and the extent of the reaction controls the degree of acrylamide groups in the final polymer. Alternatively, the copolymer can be formed directly by a polymerization reaction. In the direct synthesis, the relative amounts of carboxylate and acrylamide groups can be controlled. The molecular weight of the polymer can also be appropriately controlled or selected.

[0061] The molar ratio of acrylamide moieties to S-PAA moieties can range from about 5:95 to about 95:5, in further embodiments from about 10:90 to about 90:10, in further embodiments from about 20:80 to about 80:20, in other embodiments from about 25:75 to about 75:25, and in some embodiments from about 30:70 to about 70:30. In terms of average molecular weight, the copolymers can have an average molecular weight of about 50,000 Daltons to about 5,000,000 Daltons in some embodiments, from about 75,000 Daltons to about 2,000,000 Daltons in further embodiments, and from about 100,000 Daltons to about 1,000,000 Daltons in other embodiments. A person of ordinary skill in the art will recognize that additional ranges of moiety ratios and average molecular weights within the explicit ranges above are contemplated and are within the present disclosure.

[0062] While desirable cycling results have been obtained with the copolymer alone as an electrode binder, applicants have had success using polymer blends to improve binder performance. The copolymers described herein may also be useful in polymer blends. Suitable polymer blends will generally include at least 25 weight percent, in further embodiments at least about 35 weight percent, and in other embodiments about 40 weight percent to about 90 weight percent poly(acrylamide-co-M-PAA). One of ordinary skill in the art will recognize that additional ranges of polymer blend ratios within the explicit ranges above are contemplated and are within the scope of the present disclosure. A commercially available aqueous electrode binder is sold by Sumitomo Seika Chemicals Co., Ltd. under the trademark Aquacharge®.

[0063] The active material loading of the binder may be high. In some embodiments, the negative electrode has from about 75 to about 94 weight percent negative electrode active material, in other embodiments from about 77 to about 93 weight percent negative electrode active material, and in further embodiments from about 80 to about 92 weight percent negative electrode active material. In some embodiments, the negative electrode has from about 4 to about 20 weight percent polymer binder, in other embodiments from about 5 to 19 weight percent polymer binder, and in further embodiments from about 6 to 18 weight percent polymer binder. In some embodiments, the negative electrode also includes from about 1 to about 7 weight percent nanoscale conductive carbon, in further embodiments from about 1.5 to about 6.5 weight percent, and in additional embodiments from about 2 to about 6 weight percent nanoscale conductive carbon. A person of ordinary skill in the art will recognize that additional ranges of polymer loadings within the explicit ranges above are contemplated and are within the present disclosure.

[0064] For improved cycling of the negative electrode, nanoscale conductive additives in particulate form or combinations thereof have been found to be particularly desirable. Nanoscale conductive carbon generally refers to particles of elemental carbon with high surface area, with at least two dimensions of the primary particle being submicron. Suitable nanoscale conductive carbons include, for example, carbon black, carbon nanotubes, and carbon nanofibers. In some embodiments, the nanoscale conductive carbon additive used in the negative electrode can include carbon nanotubes, carbon nanofibers, carbon nanoparticles (e.g., carbon black), or combinations thereof. Other nanoscale conductive additives include, for example, metal nanoparticles, metal nanofibers, metal nanowires, other metal nanoparticles, and combinations thereof, such as silver nanoparticles, silver nanowires, and the like. In some embodiments, to achieve improved performance, the conductive additive can have a conductivity of at least about 40 S / cm, in some embodiments at least about 50 S / cm, and in further embodiments at least about 60 S / cm. One of ordinary skill in the art will recognize that additional ranges of particle loading and conductivity within the explicit ranges above are contemplated and are within the present disclosure.

[0065] The electrical conductivity, which is the reciprocal of the resistance, may be reported by the vendor, and is generally measured using a specific technique developed by the vendor. For example, the measurement of the electrical resistance of carbon black is performed between two copper electrodes using Super P™ carbon black. See Timcal Graphite & Carbon, A Synopsis of Analytical Procedures, 2008, www.timcal.com). Appropriate supplemental conductive additives can also be added to provide longer cycling stability. Some suppliers also list the conductive carbon concentration to achieve the conductive percolation threshold.

[0066] Carbon black means a synthetic carbon material and may alternatively be designated as acetylene black, furnace black, thermal black or other names that suggest a synthetic approach. Carbon black is generally described as amorphous carbon, although in at least some forms of carbon black there is a suggestion of small domains of short or medium range that correspond to graphite or diamond crystal structures. However, for practical purposes the material can be considered to be amorphous. Based on ISO Technical Specification 80004-1 (2010), carbon black is a nanostructured material. Although the primary particles of carbon black can range up to tens of nanometers, the primary particles are generally rigidly fused into chains or other aggregates, and the smallest dispersed units can be considered to be about 80 nm to 800 nm, which is still submicron. Carbon blacks synthesized to provide the desired level of electrical conductivity are commercially available, such as Super-P® (Timcal), Ketjenblack® (Akzo Nobel), Shawinigan Black® (Chevron-Phillips), and Black Pearls 2000® (Cabot).

[0067] Carbon nanofibers are high aspect ratio fibers that generally contain graphene layers in the form of plates, cones, or other shapes, while carbon nanotubes contain graphene sheets folded into tubes. Carbon nanofibers have diameters of 250 nm or less and are commercially available, for example, from Pyrograf® carbon nanofibers (Pyrograf Products, Inc.) or American Elements, Inc. Carbon nanotubes have been found to be desirable conductive additives that can improve the cycling performance of either positive or negative electrodes. Single-wall or multi-wall carbon nanotubes are also available from American Elements, Inc. (CA, USA), Cnano Technologies (China), Fuji, Inc. (Japan), Alfa Aesar (MA, USA) or NanoLabs (MA, USA).

[0068] The negative electrodes used in the cells described herein may have high active material loading levels with appropriately high electrode density. For a particular active material loading level, density is inversely proportional to thickness, so that an electrode with a higher density will be thinner than an electrode with a lower density. The loading is equal to density multiplied by thickness. In some embodiments, the battery negative electrode has a density of at least about 1.5 mg / cm 2 and in other embodiments, about 2 mg / cm 2 ~about 8mg / cm 2 and in a further embodiment about 2.5 mg / cm 2 ~about 6mg / cm 2 and in another embodiment about 3 mg / cm 2 ~about 5mg / cm 2 In some embodiments, the negative electrode of the battery has a negative electrode active material loading level of about 0.5 g / cc (cc=cubic centimeter (cm 3In some embodiments, the silicon oxide-based electrode has an active material density of from about 0.6 g / cc to about 1.5 g / cc, and in other embodiments from about 0.7 g / cc to about 1.3 g / cc. Similarly, the silicon oxide-based electrode may have an average dry thickness of at least about 15 microns, and in further embodiments at least about 20 microns, and in additional embodiments from about 25 microns to about 75 microns. The resulting silicon oxide-based electrode has an active material density of at least about 3.5 mAh / cm 2 and in further embodiments at least about 4.5 mAh / cm 2 and in additional embodiments at least about 6 mAh / cm 2 A person of ordinary skill in the art will recognize that additional ranges of active material loading levels and electrode densities within the explicit ranges above are contemplated and are within the present disclosure.

[0069] High capacity silicon-based anode materials Generally, the battery design herein is based on a high capacity anode active material. Specifically, the anode active material generally has a specific capacity of at least about 800 mAh / g, in further embodiments at least about 900 mAh / g, in additional embodiments at least about 1000 mAh / g, in some embodiments at least about 1150 mAh / g, and in other embodiments at least about 1400 mAh / g when cycled at a rate of C / 10 against lithium metal at 0.005V to 1.5V. Thus, the specific capacity of the negative electrode active material can be evaluated in a cell with a lithium metal counter electrode. However, in the batteries described herein, the negative electrode can exhibit a reasonably similar specific capacity when cycled against a high capacity lithium metal oxide positive electrode active material. In batteries using non-lithium metal electrodes, the specific capacity of each electrode can be evaluated by dividing the battery capacity by the weight of each of the active materials. As described herein, by combining silicon-based active materials and graphitic carbon active materials, good capacity is observed and desirable cycling results can be obtained.

[0070] Elemental silicon, silicon alloys, silicon composites, etc. may have a low potential relative to lithium metal, similar to graphite. However, elemental silicon undergoes very large volume changes upon alloying with lithium. Large volume expansions on the order of 2-4 times or more of the initial volume have been observed, and the large volume changes are associated with a significant decrease in the cycling stability of batteries with silicon-based anodes.

[0071] The cells described herein can use commercially available silicon suboxide, elemental silicon and carbon composites. Other formulations of silicon-based negative electrode active materials with high capacity and suitable cycling properties have also been developed. Below are described some silicon-based compositions that can replace commercially available SiO-based compositions and provide promising alternatives. The improved electrolyte formulations described herein have been found to be particularly effective with silicon-based negative electrode active materials and blends of silicon-based active materials with graphite.

[0072] Silicon-based high capacity materials in the negative electrode of a lithium-based battery may also exhibit high irreversible capacity loss (IRCL) in some formulations in the first charge / discharge cycle of the battery. The high IRCL of silicon-based anodes may consume a significant portion of the capacity available for the energy output of the battery. Since the cathode, i.e., the positive electrode, supplies all the lithium in conventional lithium-ion batteries, high IRCL in the anode, i.e., the negative electrode, may result in a low energy battery. To compensate for the high anode IRCL, supplemental lithium can be added directly or indirectly to the negative electrode material to compensate for the IRCL. The use of supplemental lithium to improve the performance of silicon-based electrodes is also described in the '694 patent and the '228 patent, both of which are incorporated herein by reference. The use of supplemental lithium in improved battery designs is further described below.

[0073] The anode, or negative electrode, of the battery described herein can use nanostructured active silicon-based materials to better accommodate volume expansion and thus maintain mechanical electrode stability and battery cycle life. Nanostructured silicon-based negative electrode compositions are disclosed in the '694 application, the '228 patent, and U.S. Pat. No. 9,139,441 to Anguchamy et al., entitled "Porous Silicon Based Anode Material Formed Using Metal Reduction" ('441 patent), which is incorporated herein by reference. Suitable nanostructured silicon can include, for example, nanoporous silicon and nanoparticulate silicon. Nanostructured silicon can also be formed into composites with carbon and / or alloys with other metallic elements. The goal of the design of improved silicon-based materials is to further stabilize the negative electrode material with cycling while maintaining high specific capacity and, in some embodiments, reducing irreversible capacity loss at the first charge and discharge cycle. Additionally, pyrolytic carbon coatings have also been observed to stabilize silicon-based materials with respect to battery performance.

[0074] Desirable high capacity anode active materials may include porous silicon (pSi)-based materials and / or composites of porous silicon-based materials. In general, pSi-based materials include highly porous crystalline silicon that can provide high surface area and / or high porosity relative to bulk silicon. Although nanostructured porous silicon can be formed by a variety of approaches, such as electrochemical etching of silicon wafers, particularly good battery performance has been obtained from nanostructured porous silicon obtained by metal reduction of silicon oxide powder. In particular, the material has particularly good cycling properties while maintaining a high specific capacity. Formation of composites of pSi-based materials with carbon-based materials or metals may further mechanically stabilize the anode for improved cycling. Additional description of pSi-based materials from reduction of silicon oxide can be found in the '441 patent referenced above.

[0075] With respect to composites, nanostructured silicon components can be combined with, for example, carbon nanoparticles and / or carbon nanofibers in an intimate composite. The components can be, for example, ground to form a composite in which the materials are intimately associated. In general, such associations are believed to have mechanical characteristics such as softer silicon coated on or mechanically fixed to a harder carbon material. In additional or alternative embodiments, silicon can be ground together with metal powders to form alloys that may have corresponding nanostructures. Carbon components can be combined with silicon-metal alloys to form multi-component composites.

[0076] A carbon coating can also be applied onto the silicon-based material to improve electrical conductivity. The carbon coating also appears to stabilize the silicon-based material with respect to improved cycling and reduced irreversible capacity loss. The desired carbon coating can be formed by pyrolyzing an organic composition. The organic composition can be pyrolyzed at relatively high temperatures, for example, about 800°C to about 900°C, to form a hard amorphous coating. In some embodiments, the desired organic composition can be dissolved in a suitable solvent, such as water and / or a volatile organic solvent, for combination with the silicon-based component. This dispersion can be thoroughly mixed with the silicon-based composition. After drying the mixture to remove the solvent, the dried mixture with the silicon-based material coated with the carbon precursor can be heated in an oxygen-free atmosphere to pyrolyze the organic composition, such as organic polymers, some low molecular solid organic compositions, to form the carbon coating.

[0077] Similar to silicon, oxygen-deficient silicon oxides, such as silicon oxide, SiO x(0.1≦x≦1.9) can be intercalated / alloyed with lithium so that oxygen-deficient silicon oxide can function as an active material in lithium-ion batteries. These oxygen-deficient silicon oxide materials are generally referred to as silicon oxide-based materials, and in some embodiments can contain various amounts of silicon, silicon oxide, and silicon dioxide. Oxygen-deficient silicon oxide can incorporate relatively large amounts of lithium so that the material can exhibit large specific capacity. However, silicon oxide is generally observed to have a capacity that degrades rapidly with battery cycling, similar to that observed for elemental silicon.

[0078] Silicon oxide-based compositions can be formed into composites with high capacity and very good cycling properties, as described in the above-referenced '228 patent. In particular, oxygen-deficient silicon oxide can be surprisingly formed into composites with conductive materials, such as conductive carbon or metal powders, which significantly improve cycling while providing high specific capacitance values. Furthermore, milling silicon oxide into smaller particles, such as submicron structured materials, can further improve the performance of the material.

[0079] In general, a wide range of composites may be used and may include silicon oxide, carbon components such as graphite particles (Gr), inert metal powders (M), elemental silicon (Si), especially nanoparticles, pyrolytic carbon coatings (HC), carbon nanofibers (CNF) or combinations thereof. The component structure may or may not correspond to the structure of the components within the composite. Thus, the general composition of the composite may be expressed as αSiO-βGr-χHC-δM-εCNF-φSi, where α, β, χ, δ, ε and φ are relative weights that may be selected such that α+β+χ+δ+ε+φ=1. In general, 0.35<α<1, 0≦β<0.6, 0≦χ<0.65, 0≦δ<0.65, 0≦ε<0.65 and 0≦φ<0.65. Certain subsets of these composite ranges are of particular interest. In some embodiments, a composite of SiO and one or more carbon-based components is desired and can be represented by the formula αSiO-βGr-χHC-εCNF, where 0.35<α<0.9, 0≦β<0.6, 0≦χ<0.65, and 0≦ε<0.65 (δ=0 and φ=0); in further embodiments, 0.35<α<0.8, 0.1≦β<0.6, 0.0≦χ<0.55, and 0≦ε<0.55; in some embodiments, 0.35<α<0.8, 0≦β<0.45, 0.0≦χ<0.55, and 0.1≦ε<0.65, and in additional embodiments, 0.35<α<0.8, 0≦β<0.55, 0.1≦χ<0.65, and 0≦ε<0.55. In additional or alternative embodiments, a composite of SiO, an inert metal powder, and optionally one or more conductive carbon components can be formed, which can be represented by the formula αSiO-βGr-χHC-δM-εCNF, where 0.35<α<1, 0≦β<0.55, 0≦χ<0.55, 0.1≦δ<0.65, and 0≦ε<0.55.In further additional or alternative embodiments, a composite of SiO and elemental silicon and optionally one or more conductive carbon components can be formed, which can be represented by the formula αSiO-βGr-χHC-εCNF-φSi, where 0.35<α<1, 0≦β<0.55, 0≦χ<0.55, 0≦ε<0.55 and 0.1≦φ<0.65, and in further embodiments, 0.35<α<1, 0≦β<0.45, 0.1≦χ<0.55, 0≦ε<0.45 and 0.1≦φ<0.55. One of ordinary skill in the art will recognize that additional ranges within the explicit ranges above are contemplated and are within the present disclosure. As used herein, the reference to a composite refers to the application of significant binding forces, such as HEMM milling, to intimately associate the materials, as opposed to a simple blend that would not be considered to form a composite.

[0080] Various Si-SiO x A solution-based approach for the synthesis of SiO-CM (M=metal) composites is described in U.S. Patent Application to Han et al., entitled "Silicon-Based Active Materials for Lithium Ion Batteries and Synthesis With Solution Processing," which is incorporated herein by reference. Silicon-based carbon composites using graphene sheets are described in U.S. Patent No. 10,886,526 to Anguchamy et al., entitled "Silicon-Silicon Oxide-Carbon Composites For Lithium Battery Electrodes and Methods for Forming the Composites," which is incorporated herein by reference. x -Si-C or SiO x Commercially available materials believed to include -Si composites are used in the example batteries.

[0081] positive electrode Using the improved negative electrodes described above, a variety of positive electrode chemistries can be effectively implemented. Selected compositions can be blended into the positive electrode with appropriate binders and conductive materials. This section focuses on positive electrode active materials that are particularly desirable for high voltage cycling and reasonably high capacity. This section also describes the overall electrode composition and properties.

[0082] The desired application of the final cell may influence the selection of the positive electrode composition to some extent. In this regard, a wide range of compositions are described below. For automotive and similar applications, certain positive electrode chemistries have been found to be desirable for achieving high energy density with cycling over 600 cycles while maintaining at least 80% capacity. In particular, nickel-rich lithium nickel manganese cobalt oxide provides long cycling performance based on the improved electrolyte described herein. In another embodiment, blending a blend of nickel-rich lithium nickel manganese cobalt oxide and (lithium + manganese) rich lithium nickel manganese cobalt oxide provides desirable positive electrode performance. Furthermore, nickel-rich lithium nickel manganese cobalt oxide alone as an active material can provide desirable high energy density with average discharge voltage with good cycling when combined with the silicon-based negative electrode described herein. Below, an example is given for nickel-rich lithium nickel manganese cobalt oxide alone.

[0083] Nickel-rich lithium nickel manganese cobalt oxide (N-NMC) can provide desirable cycling and capacity characteristics for the lithium-ion batteries described herein. In particular, nickel-rich compositions have the formula LiNi x Mn y Co z O 2(wherein x+y+z≈1, 0.45≦x, 0.025≦y, z≦0.35, and in further embodiments 0.50≦x, 0.03≦y, z≦0.325, and 0.55≦x, 0.04≦y, z≦0.3). It is noted that NMC and NCM are used interchangeably in the art. The amount of nickel can affect the selected charge voltage to balance cycle stability and discharge energy density. For values ​​of x in the range of 0.525≦x≦0.7, the selected charge voltage can be 4.25V to 4.375V. For values ​​of x in the range of 0.7≦x≦0.9, the selected charge voltage can be 4.05V to 4.325V. As examples, NMC811 (x=0.8, y=z=0.1) or NMC622 (x=0.6, y=z=0.2) are provided at a charging voltage of 4.2V. One of ordinary skill in the art will recognize that additional ranges of compositions and selected charging voltages within the above explicit ranges are contemplated and are within the scope of the present disclosure. These compositions have been found to provide relatively stable high voltage cycling, good capacity, and desirable impedance. N-NMC powders can be synthesized using techniques such as co-precipitation, which are further described below, and are available from BASF (Germany), TODA (Japan), L&F Materials Corp. (Korea), Unicore (Belgium), and Jinhe Materials Corp. (China). Commercially available formulations of these compounds include, for example, LiNi 0.5 Mn 0.3 Co 0.2 O 2 (BASF), LiNi 0.6 Mn 0.2 Co 0.2 O 2 (L&F,Korea and Umicore,Belgium), LiNi 0.8 Mn 0.1 Co 0.1 O 2 (L&F, Korea, BASF, Germany, Umicore, Belgium and LG Chemical, Korea).

[0084] For N-NMC compositions, as the amount of nickel increases, the average voltage tends to be slightly higher, but the charge voltage for stable cycling tends to be slightly lower as the amount of nickel increases. Thus, while N-NMC active materials can provide good cycling and reasonably high capacity and energy density, the choice of active material can come at a cost.

[0085] For N-NMC compositions, as the amount of nickel increases, the average voltage tends to be slightly higher, but the charge voltage for stable cycling tends to be slightly lower as the amount of nickel increases. Thus, while N-NMC active materials can provide good cycling and reasonably high capacity and energy density, the choice of active material can come at a cost.

[0086] As noted above, desirable blends may include N-NMC and (lithium-rich + manganese-rich) lithium nickel manganese cobalt oxide (LM-NMC or HCMR®). These compositions have the formula Li 1+b Ni α Mn β Co γ A δ O 2-z F z (wherein b+α+β+γ+δ≈1, b is in the range of about 0.04 to about 0.3, α is in the range of 0 to about 0.4, β is in the range of about 0.2 to about 0.65, γ is in the range of 0 to about 0.46, δ is in the range of about 0 to about 0.15, and z is in the range of 0 to 0.2, with the proviso that α and γ are not both 0, and A is a metal other than lithium, manganese, nickel, and cobalt). In some embodiments, A can be Mg, Sr, Ba, Cd, Zn, Al, Ga, B, Zr, Ti, Ca, Ce, Y, Nb, Cr, Fe, V, or combinations thereof. In additional or alternative embodiments, Li 1+b Ni α Mn β Co γ A δ O 2(where 0.05≦b≦0.125, 0.225≦α≦0.35, 0.35≦β≦0.45, 0.15≦γ≦0.3, 0≦δ≦0.05) and up to 5 mole percent of the oxygen may also be replaced with a fluorine dopant. A person of ordinary skill in the art will recognize that additional ranges of compositions within the explicit ranges above are contemplated and are within the present disclosure. As described in U.S. Pat. No. 8,928,286 to Amiruddin et al., entitled "Very Long Cycling of Lithium Batteries With Lithium Rich Cathode Materials," which is incorporated herein by reference, long-term cycling stability has been achieved at relatively high cycling voltages for (lithium + manganese) rich NMC active materials.

[0087] LM-NMC cathode materials can be advantageously synthesized by co-precipitation and sol-gel processes. In some embodiments, the cathode materials are synthesized by precipitating a mixed metal hydroxide or carbonate composition from a solution containing +2 cations, the hydroxide or carbonate composition having a selected composition. The metal hydroxide or carbonate precipitate is then subjected to one or more heat treatments to form a crystalline layered lithium metal oxide composition.

[0088] It has been found that for LM-NMC positive electrode active materials, the performance of the corresponding cells can be improved by applying a coating on the material. Suitable coating materials that are generally considered to be electrochemically inert during battery cycling can include metal fluorides, metal oxides, or non-fluoride halides of metals. It has been found that for LM-NMC positive electrode active materials, the performance of the corresponding cells can be improved by applying a coating on the material. Suitable coating materials that are generally considered to be electrochemically inert during battery cycling can include metal fluorides, metal oxides, or non-fluoride halides of metals. An improved metal fluoride coating with a properly designed thickness is described in published U.S. Patent No. 9,843,041 to Lopez et al., entitled "Coated Positive Electrode Materials for Lithium Ion Batteries," which is incorporated herein by reference.

[0089] The positive electrode active material may optionally contain 0 to 25 weight percent of an additional active material, such as lithium cobalt oxide, LiNi 0.33 Mn 0.33 Co 0.33 O 2 (NMC111), LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA), and mixtures thereof. A person of ordinary skill in the art will recognize that additional ranges of composition blends within the explicit ranges above are contemplated and are within the present disclosure.

[0090] As described above, the positive electrode generally includes an active material and a conductive material in a binder. The loading of active material in the electrode may be large. In some embodiments, the positive electrode includes about 85 to about 99% positive electrode active material, in other embodiments about 90 to about 98% positive electrode active material, and in further embodiments about 95 to about 97.5% positive electrode active material. In some embodiments, the positive electrode has about 0.75 to about 10% polymer binder, in other embodiments about 0.8 to about 7.5% polymer binder, and in further embodiments about 0.9 to about 5% polymer binder. In general, the positive electrode composition may also include a conductive additive different from the electroactive composition. Suitable nanoscale conductive particles are as described above with respect to the negative electrode, and these may be used in the positive electrode as well. In some embodiments, the positive electrode may have 0.4 weight percent to about 12 weight percent conductive additive, in further embodiments about 0.45 weight percent to about 7 weight percent, and in other embodiments about 0.5 weight percent to about 5 weight percent conductive additive. A person of ordinary skill in the art will recognize that additional ranges of particle loading within the explicit ranges above are contemplated and are within the present disclosure. The positive electrode active material is as described above. Suitable polymer binders for the positive electrode include, for example, PVDF, PEO, polyimide, polyethylene, polypropylene, polytetrafluoroethylene, polyacrylate, rubber, such as ethylene-propylene-diene monomer (EPDM) rubber or SBR, copolymers thereof, or mixtures thereof. Good results can be obtained using PVDF for the positive electrode, and the positive electrode in the examples uses a PVDF binder. Water-based binders, as described above, can also be used for the positive electrode. Conductive additives are detailed for the negative electrode, and nanoscale conductive carbon can be effectively used for the positive electrode.

[0091] For a particular loading level, electrode density (of active material) is inversely proportional to thickness, so that electrodes with higher density will be thinner than electrodes with lower density. The loading is equal to density multiplied by thickness. In some embodiments, the battery positive electrode has a loading of about 10 to about 40 mg / cm. 2and in other embodiments, from about 12 to about 37.5 mg / cm 2 and in additional embodiments from about 13 to about 35 mg / cm 2 and in other embodiments, 20 to about 32.5 mg / cm 2 In some embodiments, the positive electrode of the battery has an active material density of from about 2.5 g / cc to about 4.6 g / cc in some embodiments, from about 3.0 g / cc to about 4.4 g / cc in other embodiments, and from about 3.25 g / cc to about 4.3 g / cc in additional embodiments. In further embodiments, the positive electrode, after pressing and drying, can have a thickness of positive electrode material on each side of the current collector of from about 45 microns to about 300 microns, from about 80 microns to about 275 microns in some embodiments, and from about 90 microns to about 250 microns. One of ordinary skill in the art will recognize that additional ranges of active material loading levels, electrode thicknesses, and electrode densities within the explicit ranges above are contemplated and are within the present disclosure.

[0092] Supplemental Lithium The improved high energy battery design described herein generally includes supplemental lithium, and this section relates to an approach for incorporating supplemental lithium for suitable embodiments. In general, for cells using silicon-based negative electrode active materials, the incorporation of supplemental lithium is desirable because the material may exhibit relatively high irreversible capacity loss during initial charging of the battery. Supplemental lithium also surprisingly stabilizes cycling of LM-NMC. Although various approaches can be used for the introduction of supplemental lithium into the battery, after the corresponding initial reaction and / or charging, the negative electrode is associated with an excess amount of lithium for cycling from the supplemental lithium. For the negative electrode in a battery with supplemental lithium, the structure and / or composition of the negative electrode may change compared to its initial structure and composition after the first cycle and after additional cycles. Generally, the positive electrode is provided with extractable lithium, and the start-up or formation of the cell requires an initial charge to extract lithium from the positive electrode, which is generally equal to or greater than the cycle capacity. The supplemental lithium can be considered as a supplement to the initial lithium contained in the positive electrode active material.

[0093] Depending on the approach for the introduction of supplemental lithium, the positive electrode may initially include a source of supplemental lithium and / or a sacrificial electrode containing supplemental lithium may be introduced. Additionally or alternatively, the supplemental lithium may be associated with the negative electrode. In some embodiments, the supplemental lithium may be introduced to the negative electrode using electrochemical methods as opposed to purely chemical or mechanical methods. If the supplemental lithium is initially placed in the positive electrode or another electrode, the negative electrode may be in an unchanged form without the presence of lithium until the battery is charged or at least until the circuit between the negative electrode and the electrode with the supplemental lithium is closed in the presence of the electrolyte and separator. For example, the positive electrode or the supplemental electrode may include elemental lithium, lithium alloys and / or other sacrificial lithium sources in addition to other electrode components.

[0094] When the positive electrode contains sacrificial lithium, the lithium of the sacrificial lithium source is loaded into the negative electrode during the charging reaction. The voltage during charging based on the sacrificial lithium source can be significantly different from the voltage during charging based on the positive electrode active material. For example, elemental lithium in the positive electrode can charge the negative electrode active material without applying an external voltage, since oxidation of elemental lithium can drive the reaction as long as the circuit is closed. For some sacrificial lithium source materials, an external voltage is applied to oxidize the sacrificial lithium source in the positive electrode and drive lithium into the negative electrode active material. Charging can generally be performed using constant current, stepwise constant voltage charging, or other convenient charging schemes. However, at the end of the charging process, the battery must be charged to the desired voltage, which also involves extraction (e.g., deintercalation or dealloying) of lithium from the positive electrode active material.

[0095] In some embodiments, at least a portion of the supplemental lithium is initially associated with the negative electrode. For example, the supplemental lithium can be in the form of elemental lithium, a lithium alloy, or other lithium source that is more electronegative than the negative electrode active material. The elemental lithium can be in the form of a thin film, lithium or lithium alloy foil, and / or powder, such as formed by deposition, sputtering, or ablation. The elemental lithium, particularly in powder form or powder dispersed in a non-aqueous solvent, can be coated to stabilize the lithium for handling purposes, and a commercial lithium powder dispersion available from Livent Corporation is sold with a proprietary coating for stability. This coating generally does not change the performance of the lithium powder for electrochemical applications. After contacting the negative electrode with the electrolyte, a reaction can occur and the supplemental lithium is transported to the negative electrode active material. Because the electrode is internally conductive, it is not necessary to close the circuit to obtain electron flow from the reaction. During this process, at least a partial solid electrolyte interface (SEI) layer can also be formed. Thus, the supplemental lithium is loaded into the negative electrode active material, at least a portion of which is generally consumed in the formation of the SEI layer. The supplemental lithium placed in the negative electrode should be more electronegative than the negative electrode active material so that application of a voltage will not cause reaction between the active material and the supplemental lithium source at the same electrode.

[0096] In some embodiments, the supplemental lithium associated with the negative electrode can be incorporated as a powder within the negative electrode. In particular, the negative electrode can include an active negative electrode composition, a supplemental lithium source in a polymer binder matrix, and, if present, a conductive powder. The supplemental lithium source layer can include a lithium or lithium alloy foil sheet, a supplemental lithium powder in a polymer binder, and / or particles of a supplemental lithium source material disposed on a surface of the active layer. In an alternative configuration, the supplemental lithium source layer is between the active layer and the current collector. In some embodiments, the negative electrode can also include a supplemental lithium source layer on both surfaces of the active layer.

[0097] The arrangement for carrying out the electrochemical pre-loading of lithium may include an electrode having a silicon-based active material formed on a current collector, which is placed in a container containing an electrolyte and a sheet of lithium source material in contact with the electrode. The sheet of lithium source material may include lithium foil, lithium alloy foil, or lithium source material in a polymer binder, optionally with a conductive powder, which is in direct contact with the negative electrode pre-loaded with lithium so that electrons can flow between the materials to maintain electrical neutrality while the respective reactions are occurring. In a subsequent reaction, lithium is loaded into the silicon-based active material via intercalation, alloying, etc. In an alternative or additional embodiment, the negative electrode active material may be mixed into the electrolyte and lithium source material to incorporate supplemental lithium before forming into an electrode with a polymer binder so that the respective materials can react spontaneously in the electrolyte. In some embodiments, the lithium source in the electrode may be assembled into a cell with the electrodes pre-loaded with lithium. A separator may be placed between the respective electrodes. A current may be passed between the electrodes to provide a controlled electrochemical pre-lithiation.

[0098] In some embodiments, the lithium source in the electrode can be assembled into a cell with the electrodes preloaded with lithium. A separator can be placed between each electrode. A current can be passed between the electrodes to provide a controlled electrochemical prelithiation. Depending on the composition of the lithium source, a voltage may or may not be required to promote lithium deposition in the silicon-based active material. An apparatus for carrying out this lithiation process can include a container that houses an electrolyte and a cell that includes an electrode to be used as the negative electrode of the final battery, a current collector, a separator, and a sacrificial electrode that includes a lithium source such as lithium metal foil, with the separator between the sacrificial electrode and the electrode with the silicon-based active material. Convenient sacrificial electrodes can include lithium foil, lithium powder or lithium alloy embedded in a polymer, although any electrode with extractable lithium can be used. The container for the lithiation cell can include a conventional battery housing, a beaker, or other convenient structure. This configuration offers the advantage that the current can be measured to measure the degree of lithiation of the negative electrode. Furthermore, negative electrodes with near full lithium loading of the negative electrode active material can be cycled one or more times, allowing for a desired degree of control over the formation of the SEI layer during the lithium preloading of the negative electrode active material, thus allowing the negative electrode to be fully formed during the fabrication of the negative electrode with a selected lithium preloading.

[0099] In alternative or additional embodiments, the negative electrode active material can be mixed with the electrolyte and a lithium source material for incorporating supplemental lithium before being formed into an electrode with a polymer binder so that the respective materials can react spontaneously in the electrolyte. Commercially available SiO-Si-C composite compositions are currently available from Shin-Etsu Chemical Co., Ltd. (Japan), such as their KSC series products. Various approaches for incorporating supplemental lithium into cells are described in U.S. Patent No. 9,166,222 to Amiruddin et al., entitled "Lithium Ion Batteries With Supplemental Lithium," which is incorporated herein by reference.

[0100] Generally, for embodiments in which supplemental lithium is used, the amount of supplemental lithium preloaded or loadable into the active composition can be at least about 2.5% of the capacity, in further embodiments from about 3 percent to about 55 percent of the capacity, in additional embodiments from about 5 percent to about 52.5 percent of the capacity, and in some embodiments from about 5 percent to about 50 percent of the negative electrode active material capacity. The supplemental lithium can be selected to generally balance the IRCL of the negative electrode, although other amounts of supplemental lithium can be used as desired. In some embodiments, the supplemental lithium added is an amount having an oxidation capacity corresponding to 60% to 180% of the first cycle IRCL of the negative electrode, in further embodiments, this is 80% to 165%, and in other embodiments, this is 90% to 155%. A person of ordinary skill in the art will recognize that additional ranges of percentages within the explicit ranges above are contemplated and are within the present disclosure. Thus, with the addition of supplemental lithium, the contribution to the IRCL of the negative electrode can be effectively reduced or eliminated such that the measured IRCL of the battery represents a partial or majority contribution from the IRCL of the positive electrode that is not reduced by the presence of supplemental lithium. A person of ordinary skill in the art will recognize that additional ranges of IRCL within the explicit ranges above are contemplated and are within the present disclosure.

[0101] Cathode and anode balance It has been found that the overall performance of a battery depends on the capacity of both the negative and positive electrodes and their relative balance. It has been found that the balance of electrodes is important in terms of achieving particularly high energy density and good cycling characteristics for the battery. In some embodiments, a sacrifice may be made in terms of achieving longer cycling stability and energy density. To achieve longer cycling stability, it may be desirable to balance the battery to achieve a relatively low energy density, but to use a battery that is suitable for stable long-term use in a wider range of operating parameters. With properly selected active materials, a desired electrode design, and an improved electrolyte formulation, high energy density is still obtainable while obtaining cycling of more than 800 cycles with a capacity fade of 80% or less. Electrode balance can be evaluated in several different ways, which can work effectively when the specific evaluation approach is properly considered.

[0102] Testing of the active materials is carried out in lithium cells that use lithium metal electrodes. Such cells are commonly called half cells, in contrast to lithium-ion cells (called full cells) in which both electrodes contain lithium alloy or intercalation materials. In half cells that use silicon-based electrodes, the lithium electrode functions as the negative electrode and the silicon-based electrode functions as the positive electrode, opposite to its usual role as the negative electrode in lithium-ion cells.

[0103] The capacity of the positive electrode active material can be estimated from the capacity of the material, which can be measured by cycling the material against lithium metal foil. For example, for a given positive electrode, the capacity can be evaluated by determining the insertion and extraction capacity during the first charge / discharge cycle. At this time, lithium is deintercalated or extracted from the positive electrode to a selected voltage based on the material chemistry and the selected charging voltage of the cell design (typically 4.2V to 4.5V), and intercalated or inserted back into the positive electrode at a rate of C / 20 to 2V with a small adjustment, typically 0.1V, to a higher charging voltage relative to lithium metal based on the voltage of the final anode relative to lithium metal. For positive electrode active materials, the choice of charging voltage determines the capacity of the cell and can be selected in part for a particular material to promote a particular cycling stability, voltage profile during cycling, and impedance during cycling.

[0104] Similarly, for a given silicon-based electrode, the insertion and extraction capabilities can be evaluated using a battery having a positive electrode containing a silicon-based active material and a lithium foil negative electrode. This capacity is evaluated by determining the insertion and extraction capacity of the battery during the first charge / discharge cycle in which lithium is intercalated / alloyed into the silicon-based electrode to 5 mV and de-intercalated / de-alloyed to 1.5 V at a rate of C / 20.

[0105] In actual use, the observed capacity may vary from the tested capacity due to various factors such as high rate operation and changes in voltage range, which may be due to battery design and the composition of the counter electrode that is not lithium metal. For some evaluation approaches, subsequent capacity after the first cycle can be used to evaluate the electrode balance, and higher discharge rates such as C / 3 or C / 10 can be used if necessary. The use of a formation cycle or a balance after several formation cycles can be desirable in that the balance is more based on the conditions during battery use.

[0106] In most commercially available carbon-based batteries, an excess of about 5-10% anode over cathode is used to prevent lithium plating. One major concern with excess anode is that it increases the cell weight, lowering the cell's energy density. Compared to graphite, which has a first cycle IRCL of about 7%, high capacity silicon-based anodes can have an IRCL ranging from about 10% to about 40%. A large portion of the capacity can become inactive in the cell after the first charge-discharge cycle, adding significant deadweight to the battery.

[0107] For high capacity anode materials, the negative electrode irreversible capacity loss is generally greater than the positive electrode irreversible capacity loss, which results in additional lithium availability for the cell. If the negative electrode has a significantly higher irreversible capacity loss than the positive electrode, the initial charge of the negative electrode will consume lithium irreversibly, so that during subsequent discharge, the negative electrode cannot supply enough lithium to provide the positive electrode with enough lithium to meet the full lithium acceptance capacity of the positive electrode. This will waste positive electrode capacity and correspondingly increase the weight that does not contribute to cycling. Most or all of the lithium loss from the net IRCL (negative electrode IRCL-positive electrode IRCL) can be made up by supplemental lithium as described above. The assessment of the electrode balance during the first formation cycle may or may not take into account supplemental lithium. In the formation cycle or subsequent cycles after several cycles, any excess amount of supplemental lithium that is not consumed for IRCL will generally be alloyed into the anode material. The electrode balance can be assessed during a cycling stage after formation, such as the fourth cycle at a selected rate, and these capacities can be estimated from the electrode performance.

[0108] From the perspective of providing stable longer term cycling performance, it may be desirable to balance the electrodes to effectively use both electrode capacities and to avoid plating of lithium metal during cycling. Generally, electrode balance is considered during assembly of the electrodes with reference to the initial capacity of the electrodes relative to lithium metal.

[0109] Generally, the battery life can be selected to end when the energy output at a constant discharge rate drops by about 20% from the initial capacity, but other values ​​can be selected as necessary. For the materials described herein, the capacity drop due to cycling of the negative electrode is generally greater than that of the positive electrode, so avoiding lithium metal deposition due to cycling suggests a higher excess capacity of the negative electrode to further stabilize cycling. Generally, if the negative electrode capacity decreases about twice as fast as the positive electrode capacity, it may be desirable to include at least 10% additional negative electrode capacity to accommodate cycling. For a robust battery design, at least about 10% additional negative electrode may be desirable under various discharge conditions. In general, the balance can be selected such that the initial negative electrode charge capacity, evaluated at a C / 20 rate from open circuit voltage to 1.5 V vs. lithium, is about 110% to about 195%, in further embodiments about 120% to about 185%, and in additional embodiments about 130% to about 190% of the initial positive electrode charge capacity at a C / 20 rate from open circuit to the charge voltage of the cell design (generally 4.2 V to 4.6 V) plus any supplemental lithium oxidation capacity. Alternatively, the electrode balance can be evaluated at the fourth cycle at a C / 10 or C / 3 discharge rate with the negative electrode capacity relative to the positive electrode capacity being about 110% to about 195%, in further embodiments about 120% to about 185%, and in additional embodiments about 130% to about 190%. One of ordinary skill in the art will recognize that additional ranges of balance within the above explicit ranges are contemplated and are within the present disclosure. Such balance is described in the battery designs described below.

[0110] Cell performance Cell performance characteristics The combination of design features and the described electrolytes can provide longer cycling stability while maintaining the desired high power cell performance. In certain applications, maintaining power capability in the latter half of the cell's life before charging can be important. In other words, to be a practical solution, the cell must have high rate capability and high capacity while maintaining cycle life. To achieve long-term high power cycling, the improved electrolytes described above must be used along with a balance of cell design parameters, especially the negative electrode. The selected charging voltage is influenced by the positive electrode active material. The cell can exhibit high capacity at rapid discharge rates. In some embodiments, at room temperature, the specific capacity from the selected charging voltage to 2.5V can be at least about 135mAh / g based on the positive electrode active material weight at a discharge rate of 5C.

[0111] Typically, the selected charge voltage for these cells is about 4.05V to 4.4V. As noted above, the anode is designed to have a low voltage relative to elemental lithium over the relevant voltage range, so the selected charge voltage is typically based on the cathode active material. The cells may exhibit very good cycling performance resulting in high power generation with high discharge rates. In some embodiments, the cells may exhibit a discharge capacity at the 700th cycle of at least about 75%, and in other embodiments at least about 80%, of the 6th cycle capacity discharged at a rate of 4C from the selected charge voltage to 2.5V at room temperature, and in additional embodiments may exhibit a discharge capacity at the 700th cycle of at least about 82% of the 6th cycle discharge capacity when cycled at a charge rate of 1C from the selected charge voltage to 2.5V at room temperature. Similarly, the battery may exhibit a discharge capacity at the 825th cycle of at least about 75%, and in other embodiments at least about 80%, of the sixth cycle capacity discharged at a 1C rate from the selected charge voltage to 2.5V at room temperature, and in additional embodiments may exhibit a discharge capacity at the 825th cycle of at least about 82.5% of the sixth cycle discharge capacity when cycled at a 1C rate from the selected charge voltage to 2.5V at room temperature. A person of ordinary skill in the art will recognize that additional ranges within the explicit ranges above are contemplated and are within the present disclosure.

[0112] The power capability can be tested as a function of the state of charge of the cell. The cell can be discharged at a rate of 1C. Then, after every 10% drop in state of charge, a 30 second 5C discharge pulse can be applied to the cell. The power is calculated as voltage times current, where the current is evaluated as voltage divided by resistance (R). The evaluation is summarized in equations (1) and (2) below. Based on the power exhibited during the 30 second pulse, the power output of the cell can be reported as kW / kg. The available power can then be evaluated as a function of voltage at the state of charge at which the pulse is delivered. At a 70% state of charge, the cell may exhibit a power output greater than about 2kW / kg. R dischg pulse =ΔV / ΔI=(Vt0-Vt1) / (It0-It1) (1) Discharge pulse output capacity = Vmin × (OCV pulse -Vmin) / R dischg pulse (2) EXAMPLES

[0113] General Methods and Materials. General methods and materials are described in the '047 and '925 patents referenced above. The electrolyte formulations were tested by incorporation into coin and pouch cells using NMC positive and negative electrodes incorporating a blend of silicon oxide-based composite and graphite as the active material.

[0114] The active material for the positive electrode is of the formula LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC622) or LiNi 0.8 Mn 0.1 Co 0.1 O 2 The cathode material was a commercially available lithium nickel manganese cobalt oxide having a cation content of 1.0 to 1.5% by weight (NMC811). NMC811 is commercially available from different sources as polycrystalline or single crystalline, and different examples were carried out using each of these as the active material for the cathode. The cathode had an active material loading of about 93% to 97.5% by weight blended with 1% to 4% by weight PVDF binder and 1% to 3% by weight nanoscale carbon. The cathode material was blended with NMP solvent, spread on an aluminum foil current collector, pressed, and dried.

[0115] The negative electrode active material was a commercially available SiO-Si-C (SiOx) composite blended with electrochemically active graphite. Unless otherwise noted, 80 wt% to 100 wt% of the SiO-Si-C composite as powder was blended with up to 20 wt% of electroactive graphite (KS6 synthetic graphite, Imerys SA). The resulting negative electrode active material was thoroughly mixed with 1 wt% to 7 wt% of single-walled or multi-walled carbon nanotubes as a conductive additive to form a homogenous powder mixture.

[0116] To form the negative electrodes, one of two different formulations was used. One formulation, containing 7% to 15% by weight of polyimide binder and 1% to 7% by weight of low modulus binder, was mixed with NMP (Sigma-Aldrich) and stirred overnight to form a polymer binder-NMP solution. The weight ratio of low modulus binder to polyimide binder was 0.714. The homogenous powder mixture was then added to the polymer binder blend-NMP solution and mixed for approximately 2 hours to form a homogenous slurry. This slurry was applied onto a copper foil current collector to form a thin wet film, and the laminated current collector was dried in a vacuum oven to remove the NMP and cure the polymer. The dried laminate contained 2 to 20% by weight of binder, with the remainder of the electrode contributed by powder. The other formulation contained a commercially available water-based binder of polyacrylate / polyamide components.

[0117] The loading of the negative electrode active material is about 4.0-4.8 mg / cm 2 The negative electrode was electrochemically prelithiated with enough lithium (powder) to compensate for 100%-160% of the lithium loss due to the irreversible capacity loss of the anode.

[0118] To form coin cells, a portion of the negative electrode was cut to size along with the separator, and a portion of the positive electrode was also cut to size. The negative electrode capacity at cycle 4 was balanced at 105%-150% of the positive electrode capacity at cycle 4. The separator for these cells was a Celgard® porous polymer membrane. The electrodes with the separator between them were placed into a coin cell housing. An electrolyte selected as described below was placed into the cell, and the cell was sealed.

[0119] For some examples, pouch cells with designs similar to those shown in Figures 1A-1D were prepared as follows. Prismatic pouch cells had approximate dimensions of 145 mm x 64 mm x 7.7 mm (thickness), ignoring the tabs. Electrodes were formed as described above, and the separator sheet was pleated with the plated electrodes placed in the folds of the separator. The separator for the pouch cells was a porous polymer composite sheet with a gel-forming polymer coating. Supplemental lithium was provided by applying lithium powder (SLMP®, Livent Corp.) to the negative electrode surface prior to assembly to supplement approximately 100%-160% of the IRCL of the silicon-based negative electrode active material. The battery was designed to have a total capacity of approximately 11-12 Ah at 30°C and a discharge rate of C / 3.

[0120] The electrolyte salts, solvents, co-solvents and additives used in the examples are shown in Table 4.

[0121] [Table 4]

[0122] Example 1 – Comparison of lithium salts The purpose of this example is to explore the basic charging characteristics of cells using various lithium salts.

[0123] The electrode active materials were NMC622 for the positive electrode active material and silicon oxide composite SOC for the negative electrode active material. Figure 2 is a plot of the specific capacity as a function of cycles performed at different charge rates for coin cells made with electrolytes E1, E13, and E19. Each coin cell was subjected to 28 cycles of the charge rate protocol as detailed in Table 5. The charge rate protocol indicates the charge and discharge rates used per cycle and the number of cycles for each charge / discharge rate. Cycles 9-26 were performed at various specified constant current rates under fast charge conditions with a cutoff of 15 minutes or an upper voltage limit of 4.3 V. The lower voltage limit was 2.5 V.

[0124] [Table 5]

[0125] From this data, the cells using electrolyte 1 containing LiFSI have the following characteristics: 6 Compared with the cells using electrolytes 13 and 19 containing LiFSI and LiPF, the cells showed higher capacity for all cycles, especially in the fast charge cycle, suggesting that this salt is particularly supportive of fast charging. 6 Despite the similar electrical conductivity of LiPF 6 The capacity of the electrolyte containing E1 was low, indicating a low charging capability. For all three coin cells, the final two cycles at lower charge / discharge rates indicate that the rapid charging cycles did not cause significant irreversible changes in the active materials. The conductivity of E1, E13, and E19 was 8.31 mS / cm, respectively. 1 , 5.6mS / cm 1 and 7.64 mS / cm 1 It was.

[0126] Example 2 - LiFSI-based electrolyte This example explores the properties of electrolytes incorporating various concentrations of LiFSI as the lithium salt.

[0127] Figure 3 shows LiPF 6 Figure 1 shows a combined plot of conductivity and viscosity as a function of increasing concentration (left to right) of LiFSI shown in Table 4, with , held constant. Viscosity increased steadily while conductivity peaked, remained constant, and then dropped sharply above 1.75 M. In general, low viscosity and high ionic conductivity can be desirable, but in-cell testing shows these relationships in more complex terms.

[0128] LiPF 6Discharge rate evaluations were performed on coin cells assembled with electrolytes E5-E7, which correspond to the electrolytes exhibiting the highest conductivity as shown in Figure 3, along with electrolyte E17, which contains only lithium salt. The electrode active materials were NMC622 for the positive electrode active material and silicon oxide composite SOC for the negative electrode active material. Figure 4 plots the capacity as a function of cycles along with the corresponding charge rates for electrolytes E5-E7 and E17. Each coin cell followed the charge rate protocol detailed in Table 6.

[0129] [Table 6]

[0130] All three electrolytes, E5–E7, showed similar capacity for cycling up to about 1C, but differences between them became increasingly apparent as the discharge rate increased and the capacity decreased above 1C. Electrolyte E7 showed the best high-rate performance, while LiPF 6 The electrolyte containing only 17 showed the poorest high-rate performance. All four electrolytes showed a decrease in capacity with increasing discharge rate, but the final C / 3 charge / discharge cycle indicated that none of the four cells sustained irreversible damage from the rapid charge / discharge cycle.

[0131] Similar assembled coin cells using electrolytes E5-E7 and E17 were tested using the charge rate protocol detailed in Table 7. In this test, for cycles 3-15, the charge rate was increased from 1C to 5C and the discharge remained the same at 1C. The results are shown in Figure 5. E5-E7 showed similar capacity throughout the test, with electrolyte E5 performing slightly better and E17 performing slightly worse compared to E5-E7. Two final C / 3 charge / discharge cycles showed that the cells were not irreversibly damaged during the rapid discharge cycles.

[0132] [Table 7]

[0133] Similar assembled coin cells using electrolytes E5-E7 and E17 were evaluated for long cycling over the voltage range of 4.3V-2.5V. Each cell was cycled for 48 cycles at 4C charge (15 min constant current and constant voltage) + 1C discharge followed by C / 3 charge + C / 3 discharge cycles (cap check). Fade checks at C / 3 charge discharge (cap check) were performed every 50 cycles at C / 3 charge. Capacity results as a function of cycle are shown in Figure 6A for E5, Figure 6B for E6, Figure 6C for E7, and Figure 6D for E17. The horizontal lines indicate the 80% capacity fade cutoff at C / 3 and 4C discharge rates. Cells using all electrolytes showed good cycling performance. All four electrolytes showed capacity loss over the test period, but all electrolytes well beyond 600 cycles with 80% fade.

[0134] Example 3 - LiFSI / LiPF 6 Comparison of combinations The lithium salt combinations were evaluated using the same charge / discharge rate sequence as listed in Table 6, except for the second 5C cycle. Figure 7 is a plot of capacity as a function of cycles at specific charge / discharge rates for coin cells assembled using electrolytes E2, E3, E7, E9, E17 and E18. The electrode active materials were NMC811 for the positive electrode active material and silicon oxide composite SOC for the negative electrode active material. Each coin cell followed the charge rate protocol detailed in Table 6, with a voltage range of 4.2V to 2.5V. Differences between the electrolytes became increasingly evident as the discharge rate increased and capacity decreased after 1C. Electrolytes E7 and E9 had the highest concentration of LiFSI and showed the best high rate performance, while LiPF 6 E17 and E18, which contained only ZnO, showed the poorest high-rate performance. All six electrolytes showed a decrease in capacity with increasing discharge rate, but the final C3 charge / discharge cycle confirmed that the cells did not exhibit significant irreversible capacity loss over the cycles tested.

[0135] Example 4 – Comparison of Solvent Combinations Various solvent combinations were evaluated using an array of charge / discharge rates detailed in Table 8 similar to Table 6. Figure 8 is a plot showing the specific capacity as a function of cycle number for coin cells assembled with electrolytes E9, E14-E16 and E20-E22. Comparing the specific capacity of electrolytes E14-E16 shows that DEC provides better performance compared to FEMC and OTE is better than both DEC and FEMC. Electrolytes E20-E22 provide improved performance compared to similar electrolytes E14-E16, especially for E16 with OTE. Electrolytes E9 (with additives PC and MA) and E22 (with OTE) performed better compared to all other electrolytes. All electrolytes showed capacity loss during the test. The capacities obtained at the final C / 3 and 1C charge / discharge steps did not show significant irreversible capacity change.

[0136] [Table 8]

[0137] Figures 9A-9G are plots of normalized capacity as a function of cycle number for coin cells assembled with electrolytes E7, E9, E14, E15, E20, E21, and E22, respectively. In this study, charge / discharge was performed at a rate of 1C in the voltage range of 4.2V-2.5V to test the long cycling performance. From the comparison of normalized capacity, electrolytes E20-E22 performed better than E9, E14, and E15, which are similar to each other. E7, E21, and E22 performed better than E9.

[0138] Example 5 - Large pouch cell The electrolytes were evaluated in large format pouch cells assembled as described above and designed to have a total capacity of approximately 11-12 Ah at a discharge rate of C / 3 at 30 °C. Studies were carried out over the voltage range of 4.2 V to 2.5 V.

[0139] Figure 10 shows plots of power output as a function of cell voltage for electrolytes E7, E9-E12 and E17. The pouch cells were charged to 4.2V with constant current and constant voltage charging. Power output and resistance were measured with 5C, 30 second discharge pulses at every 10% state of charge (SOC). After each discharge pulse, the cells were discharged at a C / 3 rate to the next SOC level based on the cell voltage. LiFSI and LiPF 6 The electrolytes E7, E9 and E11 contain LiTFSI and LiPF 6 The results are superior to those of electrolytes E10 and E12, which contain E7 and E9. Electrolyte E11 also showed good power behavior. Overall, E7 and E9 showed superior power performance to the other electrolyte formulations.

[0140] Normalized capacity (normalized to C / 3 capacity) plots showing the long cycling performance of electrolytes E7 and E9-E12 in large format pouch cells are shown in Figures 11A-11J. For cells made with E7, E9, E10, E11 and E12, respectively, the data shown in Figures 11A-11E was obtained by cycling the cells at 1C charge and discharge. For cells made with E7, E9, E10, E11 and E12, respectively, the data shown in Figures 11F-11J was obtained by cycling the cells at 3C charge and 1C discharge with C / 3 cap check every 48 cycles. The 3C charge was performed with a 20 minute 3C charge step followed by a 10 minute constant voltage charge for a total charge process of 30 minutes. Particularly good cycling performance was observed for E7 and E9, but reasonable cycling performance was observed for all cells tested. Electrolyte E7 performed nearly identically to E9 under 3C / 1C conditions.

[0141] Figure 12 is a plot showing the capacity as a function of cycle at 30°C for two large format pouch cells. Electrolyte 9 was used for both cell 1 and cell 2, and the cells were subjected to 1C charge / discharge cycling. The cells easily exceeded 600 cycles with greater than 90% capacity retention.

[0142] Example 6 – Coin Cell Cycling The electrolytes were evaluated in coin cells assembled as described above. Electrolyte E7 was used in cells 3 and 4, and E17 in cells 5 and 6. The cells were subjected to 1C charge / discharge cycling. The normalized capacity in percent as a function of cycles is shown in Figure 13A. The coulombic efficiency ((discharge capacity / charge capacity) x 100%) as a function of cycles is shown in Figure 13B.

[0143] Example 7 - Large pouch cell Electrolyte E7 was evaluated in large format pouch cells assembled as described above and designed to have a total capacity of approximately 32 Ah at a discharge rate of C / 3 at 30 °C. Studies were performed over a voltage range of 4.2 V to 2.5 V. Figure 14A is a plot of normalized capacity as a function of cycle number for cells cycled at 1C charge / 1C discharge rates. The electrode active materials were NMC811 for the positive active material and silicon oxide composite (SOC) for the negative active material. Resistance was monitored to ensure low growth towards end of life such that the resistance at 50% state of charge did not exceed 2.5 times the resistance value at cycle 0. Figure 14B is a plot of resistance as a function of percent SOC at various cycles from 0 to 900. The pouch cells were cycled at 1C charge / 1C discharge rates with a 1C Hybrid Pulsed Power Characterization (HPPC) pulse (30 seconds) every 100 cycles.

[0144] FIG. 15A is a plot of voltage as a function of capacity for large format pouch cells made with electrolyte E7 when charged at rates from C to 6C. The cells are charged at a constant rate until a charge voltage of 4.2V is reached, and then charged at constant voltage until the current falls below a threshold or the cell reaches its maximum time. The charge rate protocol is detailed in Table 9. The final capacity of the cell charged at 1C was slightly higher, while the charge capacities of the cells charged at 2C to 6C were approximately the same.

[0145] [Table 9]

[0146] FIG. 15B is a plot of voltage as a function of capacity for the pouch cell described in FIG. 15A when discharged at various rates from C / 10 to 12 C. The cell was charged at C / 3 and discharged at rates from C / 10 to 12 C. Even at 12 C it shows a discharge capacity of over 18 Ah, indicating very high rate capability.

[0147] The above embodiments are illustrative and not limiting. Additional embodiments are within the scope of the claims. In addition, although the present invention has been described with reference to specific embodiments, those skilled in the art will recognize that changes in form and detail may be made without departing from the spirit and scope of the present invention. Any incorporation by reference of the above documents is limited to not incorporating subject matter contrary to the explicit disclosure of the present specification. To the extent that a particular structure, composition and / or process is described herein by components, elements, ingredients, or other divisions, the disclosure of the present specification is understood to encompass, unless otherwise specified, embodiments that include the particular embodiment, the particular component, element, ingredient, other division, or combination thereof, as set forth in the present discussion, as well as embodiments that consist essentially of such particular component, ingredient, other division, or combination thereof, which may include additional features that do not alter the basic nature of the subject matter.

Claims

1. 1. A high-rate capable electrolyte for a lithium-based cell, comprising: About 0.05M to about 0.8M LiPF ６ about 1.3 M to about 2.5 M lithium salt consisting of about 0.8 M to about 2.1 M lithium bis(fluorosulfonyl)imide (LiFSI) or lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and up to about 5 mole percent of optional other lithium salts; about 5 weight percent (wt %) to about 25 wt % fluoroethylene carbonate; from about 65% to about 95% by weight of a co-solvent consisting of at least about 30% by weight dimethyl carbonate, 0 to about 50% by weight diethyl carbonate, 0 to about 50% by weight hydrofluoroether, from about 0 to about 50% by weight fluorinated linear carbonate, from about 0 to about 20% by weight propylene carbonate, from about 0 to about 20% by weight alkyl acetate, and mixtures thereof, wherein the weight percentages of fluoroethylene carbonate and co-solvent add up to 100% by weight; and about 10 weight percent or less of optional additives based on the total electrolyte weight. High rate compatible electrolyte.

2. The lithium salt is about 0.1 M to about 0.4 M LiPF ６ 10. The high rate capable electrolyte of claim 1 consisting essentially of LiFSI and LiFSI.

3. The solvent is about 5% to about 25% by weight of fluoroethylene carbonate; and about 75% to about 95% by weight of dimethyl carbonate 3. The high rate capable electrolyte of claim 1 or 2, consisting essentially of

4. 3. The high rate capable electrolyte of claim 1 or 2, wherein the co-solvent consists essentially of dimethyl carbonate, propylene carbonate, and alkyl acetate.

5. 3. The high rate capable electrolyte of claim 1 or 2, wherein the co-solvent consists essentially of dimethyl carbonate and a linear fluorocarbonate.

6. The electrolyte of claim 5 , wherein the linear fluorocarbonate comprises fluoroethyl methyl carbonate.

7. The linear fluorocarbonate is CF ３ CH ２ O(CO)OCH ３ 6. The electrolyte of claim 5, wherein:

8. Dimethyl carbonate vs. CF ３ CH ２ O(CO)OCH ３ 8. The electrolyte of claim 7, wherein the weight ratio of is from about 1:0.6 to about 1:1.

2.

9. 3. The electrolyte of claim 1, wherein the co-solvent consists essentially of dimethyl carbonate and a hydrofluoroether.

10. The hydrofluoroether is CHF ２ (CF ２ ) ３ CH ２ OCF ２ CHF ２ 10. The electrolyte of claim 9 comprising:

11. Dimethyl carbonate vs. CHF ２ (CF ２ ) ３ CH ２ OCF ２ CHF ２ 11. The electrolyte of claim 10, wherein the weight ratio of is from about 1:0.6 to about 1:1.

2.

12. 2. The electrolyte of claim 1, wherein the optional additive is selected from the group consisting of triethyl phosphate (TEP), ethoxy(pentafluoro)cyclotriphosphazene (PFPN), 1,3-propane sultone (PS), and mixtures thereof.

13. 13. The electrolyte of claim 12 comprising from about 0.1% to about 5% by weight of the additive.

14. The optional lithium salt additive is LiBF ４ , LiBOB, LiBFP, LiDFOB or mixtures thereof.

15. 15. The electrolyte of claim 14, wherein the lithium salt comprises from about 0.1 mole percent to about 2.5 mole percent of a lithium salt additive.

16. About 0.05M to about 0.4M LiPF ６ and about 1.5 M to about 2.1 M lithium bis(fluorosulfonyl)imide (LiFSI) and a co-solvent consisting of about 35 wt % to about 70 wt % dimethyl carbonate, 0 to about 50 wt % hydrofluoroether, about 0 to about 50 wt % fluorinated linear carbonate, about 0 to about 20 wt % propylene carbonate, about 0 to about 20 wt % alkyl acetate, and mixtures thereof, wherein the combined weight percentage of the hydrofluoroether, fluorinated linear carbonate, propylene carbonate, and alkyl acetate is at least about 10 wt %.

17. A lithium ion cell, an anode comprising about 75% to about 96% by weight of an active material, about 0.1% to about 7% by weight of nanoscale conductive particles, and about 4% to about 20% by weight of a polymer binder, wherein the active material comprises about 45% to about 100% by weight of a silicon-based active material and 0% to about 55% by weight of graphitic carbon; a positive electrode comprising lithium metal oxide, conductive particles and a polymer binder; a separator between the negative electrode and the positive electrode; an electrolyte comprising about 1.1 M to about 2.2 M lithium salt and a non-aqueous solvent, wherein the lithium salt comprises about 60 mole percent to about 100 mole percent LiFSI, LiTFSI, or a mixture thereof, and the non-aqueous solvent comprises about 5 wt % to about 25 wt % fluoroethylene carbonate, 35 wt % to 90 wt % dimethyl carbonate, and 0 to about 50 wt % diethyl carbonate, a hydrofluoroether, a fluoroalkyl carbonate, propylene carbonate, ethyl acetate, methyl acetate, propyl acetate, or a mixture thereof, wherein the weight percentages are based on the solvent; A container enclosing the negative electrode, the positive electrode, the separator, and the electrolyte and a discharge specific capacity at a rate of 4 C between 2.5 V and a selected charge voltage of at least about 120 mAh / g based on the weight of the cathode active material, and an impedance of about 10 mOhms or less at the 600th cycle at a 30% state of charge.

18. 18. The lithium-ion cell of claim 17, wherein the silicon-based active material comprises a silicon-silicon oxide carbon composite.

19. The graphite carbon is about 1 m ２ / g ~ approx. 20m ２ 19. The lithium-ion cell of claim 17 or 18, having a BET surface area of ​​0.1g / g.

20. 18. The lithium-ion cell of claim 17, wherein the polymeric binder of the negative electrode comprises a blend of at least about 50% by weight of a polyimide and a second polymeric binder selected from the group consisting of polyvinylidene fluoride, cellulose, styrene-butadiene rubber, lithiated polyacrylic acid, copolymers thereof, and mixtures thereof, wherein the polyimide has an elongation of at least about 40%, and the second polymeric binder has an elasticity greater than that of the polyimide.

21. 20. The lithium-ion cell of claim 17, wherein the polymer binder of the negative electrode comprises a water-soluble binder.

22. 22. The lithium-ion cell of claim 21, wherein the water-soluble binder comprises poly(acrylamide-co-acrylate) having at least about 5 mole percent acrylate moieties and at least about 5 mole percent acrylamide moieties.

23. 22. The lithium ion cell of claim 21, wherein the water soluble binder comprises metal-polyacrylic acid / acrylate (M-PAA) moieties from the corresponding monomer, where M is a cation of lithium, sodium, potassium, or a mixture thereof.

24. The lithium metal oxide has the formula LiNi ｘ Mn ｙ Co ｚ O ２ 20. The lithium-ion cell of claim 17 comprising a lithium nickel cobalt manganese oxide generally represented by the formula: where 0.45≦x, 0.05≦y, z≦0.35, and x+y+z≈1.

25. 18. The lithium-ion cell of claim 17, further comprising supplemental lithium in an amount of about 80% to about 180% of the first cycle irreversible capacity loss of the negative electrode, and having a ratio of negative electrode capacity divided by positive electrode capacity at the fourth cycle at a C / 3 discharge rate of about 1.10 to about 1.

95.

26. The lithium salt is about 0.05M to about 0.8M LiPF ６ 18. The lithium-ion cell of claim 17, wherein the solvent comprises about 65% to about 95% by weight of a co-solvent consisting of at least about 30% by weight dimethyl carbonate, 0 to about 50% by weight diethyl carbonate, 0 to about 50% by weight hydrofluoroether, about 0 to about 50% by weight fluorinated linear carbonate, about 0 to about 20% by weight propylene carbonate, about 0 to about 20% by weight alkyl acetate, and mixtures thereof, the weight percentages of fluoroethylene carbonate and co-solvent adding up to 100% by weight.

27. The lithium salt is about 0.05M to about 0.4M LiPF ６ 18. The lithium-ion cell of claim 17, wherein the solvent comprises about 5% to about 20% by weight fluoroethylene carbonate and a co-solvent consisting essentially of about 35% to about 70% by weight dimethyl carbonate, 0 to about 50% by weight hydrofluoroether, about 0 to about 50% by weight fluorinated linear carbonate, about 0 to about 20% by weight propylene carbonate, about 0 to about 20% by weight alkyl acetate, and mixtures thereof, wherein the combined weight percentage of hydrofluoroether, fluorinated linear carbonate, propylene carbonate, and alkyl acetate is at least about 10% by weight.

28. 18. The lithium-ion cell of claim 17, wherein the negative electrode active material comprises about 60% to about 95% by weight silicon oxide-based material and about 5% to about 40% by weight graphite.

29. 18. The lithium-ion cell of claim 17, wherein when cycled at room temperature from the 10th cycle to the 600th cycle at a rate of 4C from 2.5V to the selected charging voltage, the cell has a capacity at the 600th cycle that is at least about 80% of the capacity at the 7th cycle.

30. 18. The lithium-ion cell of claim 17, wherein the impedance is less than or equal to about 10 mOhms at 30% state of charge at the 600th cycle, and the cell exhibits a power of at least 2 kW / kg for a 30 second discharge at 5C at 30% state of charge.

31. A lithium ion cell, an anode comprising about 75% to about 96% by weight of an active material, about 0.1% to about 7% by weight of nanoscale conductive carbon, and about 4% to about 20% by weight of a polymer binder, wherein the active material comprises about 45% to about 100% by weight of a silicon-based active material and 0 to about 55% by weight of graphitic carbon; a positive electrode comprising lithium metal oxide, conductive carbon and a polymer binder; a separator between the negative electrode and the positive electrode; an electrolyte comprising about 1.1 M to about 2.2 M lithium salt and a non-aqueous solvent, wherein the lithium salt comprises about 60 mole percent to about 100 mole percent LiFSI, LiTFSI, or a mixture thereof, and the non-aqueous solvent comprises about 5 wt % to about 25 wt % fluoroethylene carbonate, 35 wt % to 90 wt % dimethyl carbonate, and 0 to about 50 wt % diethyl carbonate, a hydrofluoroether, a fluoroalkyl carbonate, propylene carbonate, ethyl acetate, methyl acetate, propyl acetate, or a mixture thereof, wherein the weight percentages are based on the solvent; a container that encloses the negative electrode, the positive electrode, the separator, and the electrolyte; and a pulse power density at a 5C rate for a 30 second pulse at a 30% state of charge of at least about 2.0 kW / kg.

32. 32. The lithium-ion cell of claim 31, wherein the silicon-based active material comprises a silicon-silicon oxide carbon composite material.

33. The graphite carbon is about 1 m ２ / g ~ approx. 20m ２ 33. The lithium-ion cell of claim 31 or 32, having a BET surface area of ​​0.1g / g.

34. 32. The lithium-ion cell of claim 31 , wherein the polymeric binder of the negative electrode comprises a blend of at least about 50% by weight of a polyimide and a second polymeric binder selected from the group consisting of polyvinylidene fluoride, cellulose, styrene-butadiene rubber, lithiated polyacrylic acid, copolymers thereof, and mixtures thereof, wherein the polyimide has an elongation of at least about 40%, and the second polymeric binder has an elasticity greater than that of the polyimide.

35. 32. The lithium-ion cell of claim 31 , wherein the polymer binder of the negative electrode comprises a water-soluble binder.

36. 36. The lithium-ion cell of claim 35, wherein the water-soluble binder comprises poly(acrylamide-co-acrylate) having at least about 5 mole percent acrylate moieties and at least about 5 mole percent acrylamide moieties.

37. 36. The lithium ion cell of claim 35, wherein the water soluble binder comprises metal-polyacrylic acid / acrylate (M-PAA) moieties from the corresponding monomer, where M is a cation of lithium, sodium, potassium, or mixtures thereof.

38. The lithium metal oxide has the formula LiNi ｘ Mn ｙ Co ｚ O ２ 32. The lithium-ion cell of claim 31 comprising a lithium nickel cobalt manganese oxide generally represented by the formula: where 0.45≦x, 0.05≦y, z≦0.35, and x+y+z≈1.

39. 32. The lithium-ion cell of claim 31, further comprising supplemental lithium in an amount of about 80% to about 180% of the first cycle irreversible capacity loss of the negative electrode, and having a ratio of negative electrode capacity divided by positive electrode capacity at the fourth cycle at a C / 3 discharge rate of about 1.10 to about 1.

95.

40. The lithium salt is about 0.05M to about 0.8M LiPF ６ 32. The lithium-ion cell of claim 31 , comprising: the solvent comprising about 65% to about 95% by weight of a co-solvent consisting of at least about 30% by weight dimethyl carbonate, 0 to about 50% by weight diethyl carbonate, 0 to about 50% by weight hydrofluoroether, about 0 to about 50% by weight fluorinated linear carbonate, about 0 to about 20% by weight propylene carbonate, about 0 to about 20% by weight alkyl acetate, and mixtures thereof, the weight percentages of fluoroethylene carbonate and co-solvent adding up to 100% by weight.

41. The lithium salt is about 0.05M to about 0.4M LiPF ６ 32. The lithium-ion cell of claim 31 , wherein the solvent comprises about 5% to about 20% by weight fluoroethylene carbonate and a co-solvent consisting essentially of about 35% to about 70% by weight dimethyl carbonate, 0 to about 50% by weight hydrofluoroether, about 0 to about 50% by weight fluorinated linear carbonate, about 0 to about 20% by weight propylene carbonate, about 0 to about 20% by weight alkyl acetate, and mixtures thereof, wherein the combined weight percentage of hydrofluoroether, fluorinated linear carbonate, propylene carbonate, and alkyl acetate is at least about 10% by weight.

42. 32. The lithium-ion cell of claim 31, wherein the negative electrode active material comprises about 60% to about 95% by weight silicon oxide-based material and about 5% to about 40% by weight graphite.

43. 32. The lithium-ion cell of claim 31, wherein when cycled at room temperature from the 10th cycle to the 600th cycle at a rate of 4C from 2.5V to the selected charging voltage, the cell has a capacity at the 600th cycle that is at least about 80% of the capacity at the 7th cycle.

44. 32. The lithium-ion cell of claim 31, having a discharge specific capacity at a rate of 4 C between 2.5 V and a selected charge voltage of at least about 120 mAh / g based on the weight of the cathode active material, and an impedance of less than or equal to about 10 mOhms at the 600th cycle at a 30% state of charge.

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