Lithium-ion cells with high performance electrolytes and silicon oxide active materials that provide long cycle life, fast charging and high thermal stability

Abstract

The improved electrolyte for lithium-based cells may include a combination of lithium hexafluorophosphate and a di-salt of lithium bis(fluorosulfonyl)imide or lithium bis(trifluoromethanesulfonyl)imide, and a solvent including dimethyl carbonate, ethyl methyl carbonate, and 5 to 25 volume percent fluoroethylene carbonate. The improved electrolyte may include additives triethyl phosphate, ethoxy(pentafluoro)cyclotriphosphazene, 1,3-propane sultone, or mixtures thereof, and may have limited small amounts of additional co-solvents and / or lithium-free organic additives. The improved electrolyte may be used to make lithium-based cells with silicon-based active materials as the negative electrode and nickel-rich lithium metal oxide as the positive electrode. The lithium-based cells may achieve good thermal stability along with high energy, high power, fast charging, and long cycle life.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Patent Application No. 63 / 196,536 to Dong et al., entitled “Lithium Ion Cells With High Performance Electrolyte and Silicon Oxide Active Materials Achieving Long Cycle Life, Fast Charge and High Thermal Stability,” filed June 3, 2021, which is incorporated by reference herein.

[0002] The present invention relates to the assembly of cells with electrolytes that have been discovered to provide good cycleability, reduced outgassing, and stability in a wide range of commercial applications while functioning with negative electrodes incorporating high capacity silicon oxide active materials. [Background technology]

[0003] Lithium batteries are widely used in consumer electronic and electrical devices due to their relatively high energy density. For some current commercially available batteries, the anode material can be graphite, and the cathode material can include lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), lithium iron phosphate (LiFePO4), lithium nickel oxide (LiNiO2), lithium nickel cobalt oxide (LiNiCoO2), lithium nickel cobalt manganese oxide (LiNiMnCoO2), lithium nickel cobalt aluminum oxide (LiNiCoAlO2), etc. For the anode, lithium titanate is an alternative to graphite with good cycling properties, but with a lower energy density. Other alternatives to graphite, such as tin oxide and silicon, have the potential to provide increased energy density. However, some high capacity anode materials have been found to be 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, especially for silicon. Structural changes and large volume changes can compromise the structural integrity of the electrode, thereby reducing cycling efficiency. [Brief description of the drawings]

[0004] [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 showing the gassing performance of electrolytes E1-E4 in pouch cells held at 65° C. The plot shows the percent change in pouch cell thickness as a function of time. The electrode active materials were NMC622 for the positive electrode active material and silicon oxide composite SOC for the negative electrode active material. [Figure 3A] 1 is a plot of normalized capacity as a function of cycle number for coin cells made with electrolytes E1-E4. The coin cells were cycled at 1C 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 3B] FIG. 3B is a plot of non-normalized specific discharge capacity based on the weight of positive electrode active material for the data shown in FIG. 3A. [Figure 3C] FIG. 3B is a plot of normalized capacity as a function of cycle number for the coin cells described in FIG. 3A when cycling is performed at a 4C charge / 1C discharge rate. [Figure 3D] FIG. 3D is a plot of non-normalized specific discharge capacity based on the weight of positive electrode active material for the data shown in FIG. 3C. [Figure 3E] FIG. 3B is a plot of the discharge capacity as a function of cycle number for the coin cell described in FIG. 3A when cycling is performed at various charge and discharge rates. [Figure 4A] 1 is a plot of normalized capacity as a function of cycle number for coin cells made with electrolytes E1, E5, and E9. 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 SOC for the negative electrode active material. [Figure 4B] FIG. 4B is a plot of non-normalized specific discharge capacity based on the weight of positive electrode active material for the data shown in FIG. 4A. [Figure 5A]1 is a plot of normalized capacity as a function of cycle number for coin cells made with electrolytes E1 and E5. The coin cells were cycled at C / 3 charge / C / 3 discharge and 1C charge / 1C discharge rates. The electrode active materials were NMC811 for the positive electrode active material and SOC for the negative electrode active material. [Figure 5B] FIG. 5B is a plot of non-normalized specific discharge capacity based on the weight of positive electrode active material for the data shown in FIG. 5A. [Figure 5C] FIG. 5B is a plot of normalized capacity as a function of cycle number for the coin cell described in FIG. 5A when cycling is performed at 4C charge / 1C discharge rate (room temperature) and 1C charge / 1C discharge rate (45° C.). [Figure 5D] FIG. 5D is a plot of non-normalized specific discharge capacity based on the weight of positive electrode active material for the data shown in FIG. 5C. [Figure 6A] 5 is a plot of normalized capacity as a function of cycle number for coin cells made with electrolytes E1 and E3. The coin cells were cycled as described in FIG. 5C. The electrode active materials were NMC811 for the positive electrode active material and SOC for the negative electrode active material. [Figure 6B] FIG. 6B is a plot of non-normalized specific discharge capacity based on the weight of positive electrode active material for the data shown in FIG. 6A. [Figure 7A] 5 is a plot of normalized capacity as a function of cycle number for coin cells made with electrolytes E1 and E6. The coin cells were cycled as described in FIG. 5C. The electrode active materials were NMC811 for the positive electrode active material and SOC for the negative electrode active material. [Figure 7B] FIG. 7B is a plot of non-normalized specific discharge capacity based on the weight of positive electrode active material for the data shown in FIG. 7A. [Figure 8A] 5 is a plot of normalized capacity as a function of cycle number for coin cells made with electrolytes E1 and E7. The coin cells were cycled as described in FIG. 5C. The electrode active materials were NMC811 for the positive electrode active material and SOC for the negative electrode active material. [Figure 8B] FIG. 8B is a plot of non-normalized specific discharge capacity based on the weight of positive electrode active material for the data shown in FIG. 8A. [Figure 9A] 5 is a plot of normalized capacity as a function of cycle number for coin cells made with electrolytes E1 and E8. The coin cells were cycled as described in FIG. 5C. The electrode active materials were NMC811 for the positive electrode active material and SOC for the negative electrode active material. [Figure 9B] FIG. 9B is a plot of non-normalized specific discharge capacity based on the weight of positive electrode active material for the data shown in FIG. 9A. [Figure 10] 1 is a plot showing the gassing performance of electrolytes E1, E2, E10, and E21-E24 in pouch cells held at 65° C. The plot shows the percent change in pouch cell thickness as a function of time. The electrode active materials were NMC622 for the positive electrode active material and SOC for the negative electrode active material. [Figure 11A] 5 is a plot of normalized capacity as a function of cycle number for coin cells made with electrolytes E1 and E21. The coin cells were cycled as described in FIG. 5C, except that all cycles were performed at room temperature. The electrode active materials were NMC622 for the positive electrode active material and SOC for the negative electrode active material. [Figure 11B] FIG. 11B is a plot of non-normalized specific discharge capacity based on the weight of positive electrode active material for the data shown in FIG. [Figure 12A] 5 is a plot of normalized capacity as a function of cycle number for coin cells made with electrolytes E1 and E22. The coin cells were cycled as described in FIG. 5C, except that the cycling was performed at room temperature. The electrode active materials were NMC622 for the positive electrode active material and SOC for the negative electrode active material. [Figure 12B] FIG. 12B is a plot of non-normalized specific discharge capacity based on the weight of positive electrode active material for the data shown in FIG. [Figure 13A]5 is a plot of normalized capacity as a function of cycle number for coin cells made with electrolytes E1 and E23. The coin cells were cycled as described in FIG. 5C, except that the cycling was performed at room temperature. The electrode active materials were NMC622 for the positive electrode active material and SOC for the negative electrode active material. [Figure 13B] FIG. 13B is a plot of non-normalized specific discharge capacity based on the weight of positive electrode active material for the data shown in FIG. [Figure 14A] 5 is a plot of normalized capacity as a function of cycle number for coin cells made with electrolytes E1 and E24. The coin cells were cycled as described in FIG. 5C, except that the cycling was performed at room temperature. The electrode active materials were NMC622 for the positive electrode active material and SOC for the negative electrode active material. [Figure 14B] FIG. 14B is a plot of non-normalized specific discharge capacity based on the weight of positive electrode active material for the data shown in FIG. [Figure 15A] 5 is a plot of normalized capacity as a function of cycle number for coin cells made with electrolytes E1 and E25. The coin cells were cycled as described in FIG. 5C, except that the cycling was performed at room temperature. The electrode active materials were NMC622 for the positive electrode active material and SOC for the negative electrode active material. [Figure 15B] FIG. 15B is a plot of non-normalized specific discharge capacity based on the weight of positive electrode active material for the data shown in FIG. [Figure 16] 1 is a plot of the non-normalized specific discharge capacity at various rates for coin cells made with electrolytes E1 and E10-E12. Data is based on the weight of the positive electrode active material. The electrode active materials were NMC622 for the positive electrode active material and silicon oxide composite SOC for the negative electrode active material. [Figure 17]1 is a plot of the non-normalized specific discharge capacity at various rates for coin cells made with electrolytes E10, E11, and E13. Data is based on the weight of the positive electrode active material. The electrode active materials were NMC622 for the positive electrode active material and silicon oxide composite SOC for the negative electrode active material. [Figure 18] 1 is a plot of normalized 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 19A] 1 is a plot of the non-normalized specific discharge capacity as a function of cycle number for coin cells made with electrolytes E2 and E15. Data is based on the weight of the positive electrode active material. The coin cells were cycled at different charge rates as described in Example 8. The electrode active materials were NMC811 for the positive electrode active material and silicon oxide composite SOC for the negative electrode active material. [Figure 19B] 19B is a plot of normalized capacity as a function of cycle number for the coin cells described in FIG. 19A. The coin cells were cycled at a charge rate of 1C and a discharge rate of 1C. The electrode active materials were NMC811 for the positive electrode active material and silicon oxide composite SOC for the negative electrode active material. [Figure 19C] 1 is a plot of non-normalized specific discharge capacity based on the weight of the positive electrode active material. Cycling is performed at 4C charge / 1C discharge rate (room temperature). [Figure 20A] 1 is a plot of normalized capacity as a function of cycle number for pouch cells made with electrolytes E3, E5, and E7. The pouch cells were cycled at a 1C charge / 1C discharge rate. The electrode active materials were commercial single crystal NMC811 for the positive electrode active material and silicon oxide composite SOC for the negative electrode active material. [Figure 20B] FIG. 20B is a plot of non-normalized specific discharge capacity based on the weight of positive electrode active material for the data shown in FIG. [Figure 21A]FIG. 20B is a plot of normalized capacity as a function of cycle number for the pouch cell described in FIG. 20A when cycling is performed at a 4C charge / 1C discharge rate. [Figure 21B] FIG. 21B is a plot of non-normalized specific discharge capacity based on the weight of positive electrode active material for the data shown in FIG. [Figure 22A] 1 is a plot of normalized capacity as a function of cycle number for pouch cells fabricated with electrolyte E3 and commercially available single crystal NMC811 as the cathode active material. The pouch cells were cycled at a 1C charge / 1C discharge rate. [Figure 22B] FIG. 22B is a plot of non-normalized specific discharge capacity based on the weight of positive electrode active material for the data shown in FIG. 22A. [Figure 23A] 1 is a plot of normalized capacity as a function of cycle number for pouch cells fabricated with electrolyte E3 and commercially available single crystal NMC811 as the cathode active material. The pouch cells were cycled at a 4C charge / 1C discharge rate. [Figure 23B] FIG. 23B is a plot of non-normalized specific discharge capacity based on the weight of positive electrode active material for the data shown in FIG. [Figure 24A] 1 is a plot of normalized capacity as a function of cycle number for pouch cells fabricated with electrolyte E3 and commercially available single crystal NMC811 as the cathode active material. The pouch cells were cycled at a 1C charge / 1C discharge rate and a temperature of 45° C. [Figure 24B] FIG. 24B is a plot of non-normalized specific discharge capacity based on the weight of positive electrode active material for the data shown in FIG. [Diagram 25] 1 is a plot of the specific capacity based on the weight of the positive active material as a function of cycle number for coin cells made with E1, E26, and E27. The cycles were performed at a 1C charge / 1C discharge rate from 4.2 V to 2.5 V. [Figure 26]1 is a plot of the specific capacity based on the weight of the positive active material as a function of cycle number for coin cells made with E1, E26, and E27. Cycles were performed at a 4C charge / 1C discharge rate from 4.2V to 2.5V. [Figure 27A] 1 is a plot of the specific capacity based on the weight of the positive active material as a function of cycle number for coin cells made with E3, E28, and E29. The cycles were performed at a 4C charge / 1C discharge rate from 4.2V to 2.5V. [Figure 27B] FIG. 27B is a plot of capacity retention of the data shown in FIG. 27A. [Figure 28] 1 shows percent thickness change versus storage time at 65° C. for pouch cells having a SOC anode and NMC811 cathode in combination with E30-32 electrolyte. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0005] In a first aspect, the present invention provides an electrolyte for a lithium-based cell comprising: about 1.1 M to about 2.2 M lithium salt consisting essentially of about 0.05 M to about 0.6 M LiPF6, about 0.75 M to about 1.8 M lithium bis(fluorosulfonyl)imide (LiFSI) or lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and up to about 5 mole percent of optional other lithium salts; a solvent consisting essentially of about 5 volume percent (vol%) to about 25 volume% fluoroethylene carbonate, about 50 volume% to about 90 volume% dimethyl carbonate, ethyl methyl carbonate, or mixtures thereof, and 0 to about 35 volume% of an optional co-solvent selected from the group consisting of propylene carbonate, ethyl acetate, methyl acetate, propyl acetate, and mixtures thereof; up to about 10 weight percent (wt%) of an optional additive selected from the group consisting of triethyl phosphate (TEP), ethoxy(pentafluoro)cyclotriphosphazene (PFPN), 1,3-propane sultone (PS), and mixtures thereof; and about 5% by weight or less of additional co-solvents and / or lithium-free organic additives. The present invention relates to an electrolyte consisting essentially of:

[0006] In a further aspect, the present invention provides a lithium ion cell comprising: a negative electrode 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, the active material comprising 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 polymeric 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, the lithium salt comprising about 60 mole percent to about 100 mole percent LiTFSI, and the non-aqueous solvent comprising about 5% to about 25% by volume fluoroethylene carbonate, 50% to 90% by volume dimethyl carbonate, ethyl methyl carbonate, or mixtures thereof, and up to about 35% by volume of an optional co-solvent selected from the group consisting of propylene carbonate, ethyl acetate, methyl acetate, propyl acetate, and mixtures thereof; A container for enclosing the negative electrode, the positive electrode, the separator, and the electrolyte; and having a room temperature discharge specific capacity at a rate of 4C of at least about 120 mAh / g between 2.5 V and a selected charging voltage based on the weight of the cathode active material.

[0007] In a further aspect, the present invention provides a lithium ion cell comprising: a negative electrode 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, the active material comprising 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 polymeric binder; a separator between the negative electrode and the positive electrode; an electrolyte comprising about 1.0 M to about 2.5 M lithium salt and a non-aqueous solvent, the lithium salt comprising about 60 mole percent to about 100 mole percent LiTFSI, and the non-aqueous solvent comprising about 5 volume percent to about 25 volume percent fluoroethylene carbonate; A container for enclosing the negative electrode, the positive electrode, the separator, and the electrolyte; and having a room temperature discharge specific capacity at a rate of 4C of at least about 120 mAh / g between 2.5 V and a selected charging voltage based on the weight of the cathode active material; The present invention relates to a lithium-ion cell that, when cycled at room temperature between 2.5V and a selected charging voltage from the 7th cycle to the 700th cycle at a rate of 4C, has a capacity at the 700th cycle that is at least about 80% of the capacity at the 7th cycle.

[0008] In a further aspect, the present invention provides a lithium ion cell comprising: a negative electrode 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, the active material comprising 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 polymeric binder; a separator between the negative electrode and the positive electrode; an electrolyte comprising about 1.1M to about 2.2M of a lithium salt and a non-aqueous solvent, the lithium salt comprising about 90 mole percent to about 100 mole percent of LiPF6, and the non-aqueous solvent comprising about 5% to about 25% by volume of fluoroethylene carbonate, 50% to 80% by volume of dimethyl carbonate, ethyl methyl carbonate, or mixtures thereof, about 5% to about 15% by volume of propylene carbonate, and about 5% to about 20% by volume of methyl acetate, ethyl acetate, propyl acetate, or mixtures thereof; A container for enclosing the negative electrode, the positive electrode, the separator, and the electrolyte; and having a room temperature discharge specific capacity at a rate of 4C between 2.5V and a selected charge voltage based on the weight of the cathode active material of at least about 120 mAh / g, and when cycled at room temperature between 2.5V and the selected charge voltage at a rate of 1C from the 7th cycle to the 650th cycle, having a capacity at the 650th cycle that is at least about 80% of the capacity at the 7th cycle.

[0009] The lithium-ion batteries described herein may achieve high energy, high power, rapid charging, and long cycle life with good thermal stability. The lithium-ion cells have been developed with novel electrolyte formulations that, in combination with a negative electrode dominated by silicon-based active materials, improve cycle life and thermal stability. In the illustrated embodiment, the lithium-ion cells use nickel-rich cathode materials paired with SiOx-graphite composite anodes. To achieve long cycle life while maintaining high energy, various SiOx anode formulations have been described in previous patent applications. In this application, the lithium-ion cells have been developed using electrolyte formulations that improve cycle life, fast charge cycles, and thermal stability using the applicant's adaptation of high performance electrode designs. With regard to formulating practical cells for vehicle applications, electrolytes have been developed that can reduce gassing from the cells without sacrificing cycle performance or high rate capability that allows high power and / or fast charging. In some embodiments, the lithium-ion cells described herein exhibit improved gassing behavior along with improved safety due to the higher thermal decomposition temperature of the salts used.

[0010] In some embodiments, the electrolyte is based on a mixture of lithium salts, LiPF6, LiFSI (lithium bis(fluorosulfonyl)imide), LiTFSI (lithium bis(trifluoromethanesulfonyl)imide) in a blended organic solvent, while in other embodiments, the improved low gassing electrolyte is based essentially only on LiPF6 with a blend of organic solvents resulting in improved properties. The blended organic solvent typically includes fluoroethylene carbonate and additional solvents, e.g., co-solvents such as dimethyl carbonate, ethyl methyl carbonate, and / or propylene carbonate. In some embodiments, the electrolyte formulation may use different types of additives and / or co-solvents to enhance certain performance characteristics. For example, co-solvents such as methyl acetate and ethyl acetate can increase the conductivity of the electrolyte, additives such as TEP (triethyl phosphite) and PS (1,3-propane sultone) can reduce gassing, and PFPN (ethoxy(pentafluoro)cyclotriphosphazene) can increase flame retardancy. The low gassing electrolyte based on LiPF6 includes an organic solvent with a co-solvent such as an alkyl acetate, e.g., methyl acetate or ethyl acetate. The low gassing electrolyte is advantageous for cell manufacturing because it exhibits comparable cycling at moderate charge rates and low gassing. The mixed lithium salt electrolyte described herein can provide lower gassing while providing good cycling at high charge rates.

[0011] The electrolytes and corresponding electrodes described herein are designed to provide the key properties required for commercial cells that use a relatively large percentage of silicon-based negative electrode active material. Applicant has been able to achieve proper cycling of silicon-based negative electrodes for vehicle applications of secondary lithium-ion cells. In particular, the combination of high power and high energy properties is particularly desirable for flying vehicles. Flying vehicles require high power during takeoff and landing. Since landing obviously occurs at the end of the flight, high power must be available after a suitable consumption of battery capacity to provide a reasonable distance for the flight. Planned and developing flying vehicles include, for example, vertical takeoff taxis, drones, and the like. Other high performance applications, such as high performance cars and boats and some commercial vehicles, can similarly provide certain performance advantages based on the availability of high power cells.

[0012] Lithium has been used in both primary and secondary cells. Attractive features of lithium for use in cells or batteries are its light weight and the fact that it is the most electropositive metal, and aspects of these features can be advantageously incorporated in lithium-based cells. Certain metals, metal oxides, and carbonaceous materials are known to incorporate lithium ions from the electrolyte into their structure by intercalation, alloying, or similar mechanisms. The positive electrode of a lithium-based cell generally includes an active material that reversibly intercalates / alloys with lithium. A lithium-ion cell generally refers to a cell in which the negative electrode active material is also a lithium intercalation / alloying material. A lithium cell generally refers to a cell in which the negative electrode active material is lithium metal or an alloy thereof. As used herein and for convenience, the terms cell and battery and variations thereof are used interchangeably unless a clear distinction is made.

[0013] The cells described herein are lithium-ion cells that use a non-aqueous electrolyte solution containing lithium cations and appropriate anions, although electrolytes are also suitable for lithium cells. For secondary lithium-ion batteries during charging, oxidation occurs at the cathode (positive electrode), where lithium ions are extracted and electrons are released. During discharge, reduction occurs at the cathode, where lithium ions are inserted and electrons are consumed. Similarly, during charging, reduction occurs at the anode (negative electrode), where lithium ions are taken up and electrons are consumed. During discharge, oxidation also occurs at the anode, where lithium ions and electrons are released. Unless otherwise specified, performance values ​​described herein are at room temperature, i.e., about 23±2° C.

[0014] The term "element" is used herein to mean an element that has the appropriate oxidation state when it is in a composition, and when it is shown to be in its elemental form, M 0 The term "metal" is used in the conventional manner to mean a member of the Periodic Table found in Table 1. A metal element therefore generally exists only in the metallic state of its elemental form or in a suitable alloy of the metal's elemental form. That is, metal oxides or other metal compositions other than metal alloys are generally not metals.

[0015] When using lithium-ion batteries, the uptake and release of lithium from the positive and negative electrodes induces changes in the structure of the electroactive materials. As long as these changes are essentially reversible, cycling does not change the capacity of the materials. However, it has been observed that cycling reduces the capacity of the active materials to a greater or lesser extent. Thus, after a number of cycles, the performance of the cell becomes less than acceptable and the cell is replaced. The first cycle of the cell also generally experiences an irreversible capacity loss that is significantly greater than the capacity loss per cycle in subsequent cycles. The irreversible capacity loss (IRCL) is the difference between the charge capacity and the first discharge capacity of a new cell. Positive electrodes based on lithium metal oxides may exhibit some IRCL, resulting in some replenishment of the negative electrode in terms of available lithium for cycling. The irreversible capacity loss may result in a corresponding decrease in the capacity, energy and power of the cell due to changes in the cell materials during the initial cycles.

[0016] Elemental silicon and other silicon-based active materials are of great interest as potential anode materials due to silicon's extremely high specific capacity for lithium uptake and release. Elemental silicon forms alloys with lithium, and is theoretically capable of having a lithium content corresponding to five or more lithium atoms per silicon atom (e.g., Li 4.4 Silicon has a theoretical specific capacity of about 4000-4400 mAh / g, which is significantly greater than the theoretical capacity of about 370 mAh / g for graphite. Graphite is believed to intercalate lithium to a level of about one lithium atom per six carbon atoms (LiC6). Elemental silicon, silicon alloys, silicon composites, etc., may also have low potentials relative to lithium metal, similar to graphite. However, upon alloying with lithium, silicon undergoes very large volume changes. Large volume expansions of about 2-3 times the initial volume or more have been observed, and the large volume changes are associated with a significant decrease in the cycling stability of batteries with silicon-based anodes. Silicon suboxide, i.e., SiO, where x<2, is a xIt has also been found that silicon dioxide is a desirable active material for lithium-based batteries. It can have high specific capacity for lithium alloying in some embodiments. By referring to silicon suboxide, silicon dioxide can be recognized as a fully oxidized form of silicon. For convenience, silicon suboxide can be generally referred to as silicon oxide, which is not limited to silicon monoxide (SiO) unless otherwise indicated. Silicon oxide is a material that is widely used in various fields, and the terminology may vary slightly depending on the field. Silicon oxide can also be referred to as SiO2.

[0017] In particularly interesting embodiments, the silicon-based active material may include a composite with elemental silicon, silicon suboxide, and / or carbon as the primary active material. Silicon suboxide has been found to be particularly effective in achieving longer cycle stability. Carbon may be incorporated into the composite active material to stabilize the silicon-based active material and increase electrical conductivity. For carbon composites with nanoscale elemental silicon and / or silicon oxide, long cycle stability remains challenging, but the applicant has had great success with cycle stability in cells designed for both consumer electronics and vehicle applications. Although longer cycle stability is exemplified herein using a mixture of electroactive graphite and silicon-based composites, depending on the application, suitable cycles may also be achieved using silicon-based composites as the sole negative electrode active material. As described in more detail below, the silicon-based electrode may further include an additional conductive source, such as nanoscale carbon.

[0018] As used herein, active materials for lithium-ion secondary cells generally include, for example, a positive electrode (i.e., cathode) active material having a moderately high average voltage relative to lithium, and a silicon-based active material for the negative electrode (i.e., anode). In general, a variety of cathode materials can be used. For example, it is possible to use commercially available cathode active materials with existing available commercial products. Such cathode active materials include, for example, lithium cobalt oxide (LiCoO2), LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 LiNiCoAlO2 (L333 or NMC111), LiNiCoAlO2 (NCA), other lithium nickel manganese cobalt oxides (NMC), LiMn2O4 (lithium manganese oxide spinel), modified forms thereof or mixtures thereof.

[0019] Nickel-rich lithium nickel cobalt manganese oxide (LiNi x Mn y Co z O2, 0.45≦x, 0.05≦y, z≦0.35) may be of interest due to their lower cost and lower risk of flammability versus lithium cobalt oxide, as well as their ability to cycle in the desired voltage range. In particular, desirable cycling results can be obtained from nickel-rich lithium nickel manganese cobalt oxide (N-NMC), which has the formula LiNi x Mn y Co zO2, where x≧0.45 and x+y+z≈1, and certain cathode compositions of particular interest are described below. In the industry, both NCM and NMC are used interchangeably, with cobalt and manganese listed in the corresponding order, and the designations are equivalent and based only on personal preference. Lithium cobalt oxide can also be stabilized to effectively cycle at higher voltages, as described in U.S. Patent No. 10,193,135 to Sharma et al., entitled "Positive Electrode Active Materials With Composite Coatings for High Energy Density Secondary Batteries and Corresponding Processes," incorporated herein by reference.

[0020] For lithium-ion cell design, electrolytes are established based on electrode design and cell performance criteria. The improved electrolytes described herein provide excellent power and energy output while providing excellent cycling performance. The adjustment of various parameters provides a matrix where all parts of the parameter matrix are suitable to work together to achieve the target performance. The combination of the improved electrolytes and corresponding electrodes allows for fast charging and significantly reduced gassing while maintaining good cycling even in cells containing relatively large amounts of silicon-based active materials.

[0021] electrolyte Desirable electrolytes can be based on a mixture of lithium salts: lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiN(FSO2)2 or LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiN(SO2CF3)2 or LiTFSI) in a blended organic solvent. In some embodiments, the electrolyte is essentially based on LiPF6 as the sole lithium salt. In some embodiments, the improved electrolyte comprises a mixture of LiPF6 and LiFSI or a mixture of LiPF6 and LiTFSI. In some embodiments, the improved electrolyte comprises a mixture of LiPF6 and LiFSI or a mixture of LiPF6 and LiTFSI, with the majority of the lithium salt being LiFSI or LiTFSI. More generally, the electrolyte consists essentially of a particular lithium salt, a blend of non-aqueous solvents and possible additives including narrow ranges of optional additional components. These electrolytes provide the desired high power cell performance described herein, and acceptable optional components can be used to fine-tune the specific performance criteria for a particular application.

[0022] 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 and summarized in Table 2. LiFSI is thermally stable up to 200 °C, and when used in battery constructions 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>LiPF6>LiTFSi>LiClO4>LiBF4) when measured for solutions containing lithium salts in 30 / 70 vol.% EC / EMC. Selected properties of lithium tetrafluoroborate (LiBF4) and lithium perchlorate (LiClO4) are shown in Table 1.

[0023] [Table 1]

[0024] The properties of the electrolytes containing different lithium salts are shown in Table 2. The electrolytes are E10 to E12 shown in Table 5.

[0025] [Table 2]

[0026] In some embodiments, the improved high power electrolyte comprises a blended organic solvent, typically consisting essentially of fluoroethylene carbonate (FEC) and additional solvents such as dimethyl carbonate (DMC) and / or ethyl methyl carbonate (EMC). In some embodiments, the electrolyte formulation may use different types of additives and / or co-solvents to enhance certain performance characteristics. For example, co-solvents such as propylene carbonate (PC), methyl acetate (MA) and ethyl acetate (EA) can increase the conductivity of the electrolyte, while triethyl phosphite ((C2H5O)3P or TEP) or 1,3-propane sultone (C3H6OSO2 or PS) can reduce gassing, and ethoxy(pentafluoro)cyclotriphosphazene ((C2H5O)F5N3P3) or PFPN) can increase flame retardancy.

[0027] The lithium salt is dissolved in a non-aqueous solvent. In some embodiments, the non-aqueous solvent generally comprises a majority of EMC and / or DMC by volume, a moderate amount of FEC, and generally lesser amounts of PC, acetate, or mixtures thereof, optionally as a secondary solvent or co-solvent. In some embodiments, additional additives may be included for safety concerns and / or to further reduce gassing as described above. Improved rate performance is obtained by using EMC instead of DMC.

[0028] In some embodiments, the electrolyte comprises a lithium salt in a non-aqueous solvent at a concentration of about 1.1 M to about 2.2 M. The lithium salt generally comprises or consists essentially of (LiTFSI or LiFSI) and LiPF6 in a molar ratio of about 3:1 to about 1.25:1, in further embodiments from about 2.5:1 to about 1.35:1, and in other embodiments from about 2.25:1 to about 1.45:1. Another way to express the amounts of these salts is the respective molar ratios. In mixed lithium salt embodiments, the electrolyte may have about 0.05M to about 0.4M LiPF6, in further embodiments about 0.075M to about 0.375M, and in other embodiments about 0.1M to about 0.35M LiPF6 and about 0.7M to about 2.15M (LiFSI or LiTFSI), in further embodiments about 0.8M to about 2M, and in other embodiments about 0.9M to about 1.9M (LiFSI or LiTFSI). Some low gassing electrolytes are formed with LiPF6 as essentially the sole lithium salt. In the case of mixed salt electrolytes or LiPF6-based electrolytes, any additional lithium salts in the electrolyte are present in an amount of about 10 mole percent (mol%) or less of the total lithium salts, in other embodiments about 7.5 mol% or less, in further embodiments about 5 mol% or less, in further embodiments about 2 mol% or less, and in some embodiments about 1 mol% or less. A person of ordinary skill in the art will recognize that additional ranges of lithium salt concentrations within the above explicit ranges are contemplated and are within the scope of the present disclosure.

[0029] Other lithium salts include, for example, lithium 4-pyridyltrimethylborate (LiB(CHN)(OMe) or LPTB), lithium bis(oxalato)borate (LiB(C0) or LiBOB), lithium difluoro(oxalato)borate (LiBF(C0) or LiFOB), lithium bis(monofluoromalonato)borate (LiBFMB), (LiB(Lithium tetracyanoborate (LiB(CN))), lithium bis(perf Lithium fluoroethanesulfonyl)imide (LiN(SO2CF3)2 or LiBETI), lithium cyclodifluoromethane-1,1-bis(sulfonyl)imide (LiDMSI), lithium dicyano-trifluoromethyl-imidazole (LiTDI), lithium dicyano-pentafluoroethyl-imidazole (LiPDI), lithium dicyano-heptafluoropropyl-imidazole (LiHDI), lithium fluoroalkylphosphate (LiFAP or LiF x (C y F 2y+1 ) z , (wherein x=1-3, y=1-3 and x+z=6), lithium dicyanotriazolate (LiDCTA), lithium tris(trifluoromethylsulfonyl)methanide (LiTriTFSM), lithium tricyanomethanide (LiTCM), lithium trifluoromethanesulfonate (lithium triflate or LiSO3CF3), lithium borohydride (LiBH4), lithium perchlorate (LiClO4) and mixtures.

[0030] The non-aqueous solvent generally comprises about 50 to about 90 volume percent (EMC, DMC or mixtures thereof), about 5 to about 25 volume percent FEC, optionally about 5 to about 15 volume percent PC, optionally about 5 to about 15 volume percent alkyl acetate (methyl acetate, ethyl acetate, propyl acetate, other C3-C10 alkyl acetates or mixtures thereof) and up to about 10 volume percent other organic liquids / additives. As exemplified herein, electrolytes with EMC provide lower gassing and desirable cycles. In further embodiments, the electrolyte comprises about 60 volume percent to about 80 volume percent EMC or DMC or a mixture of DMC and EMC, about 9 volume percent to about 20 volume percent FEC, optionally 5 volume percent to about 10 volume percent PC, and optionally about 5 volume percent to about 10 volume percent alkyl acetate. With regard to other optional co-solvent additives, in some embodiments, the electrolyte comprises about 7 volume percent or less, in further embodiments about 5 volume percent or less, in further embodiments about 2 volume percent or less, and in some embodiments about 1 volume percent or less of total co-solvent additives. Other optional co-solvent additives refer to co-solvents other than PC and alkyl acetate. 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 present disclosure. A more detailed discussion of electrolyte formulations is provided below.

[0031] The electrolyte optionally includes other cyclic carbonates (e.g., butylene carbonate (BC), vinylene carbonate and its derivatives, and vinyl ethylene carbonate (VEC)), lactones (e.g., gamma-butyrolactone (GBL), gamma-valerolactone (GVL), and alpha-angelicalactone (AGL)), other linear carbonates (e.g., diethyl carbonate (DEC), methyl propyl carbonate (MPC), dipropyl carbonate (DPC), methyl butyl carbonate (MBC), and dibutyl carbonate (DBC), ethers (e.g., tetrahydrofuran (THF), 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane ... Other co-solvents may be included, such as diethyl ether (DME), 1,2-diethoxyethane and 1,2-dibutoxyethane), nitriles (e.g., acetonitrile and adiponitrile), esters (e.g., methyl propionate, methyl pivalate, butyl pivalate and octyl pivalate), amides (e.g., dimethylformamide), and combinations thereof. Generally, the electrolyte is free of ethylene carbonate (EC) or contains very small amounts (less than 0.5% by volume) of EC, since silicon-based anodes generally do not cycle well with EC solvents. A person of ordinary skill in the art will recognize that additional ranges of additive concentrations within the explicit ranges above are contemplated and are within the present disclosure.

[0032] Other optional additives can provide anti-gassing effects, reduce flammability, and / or provide other safety effects, as described above. Any additive that helps maintain the desired cycling stability can be selected.

[0033] The electrolyte can include a non-ionic organic additive at a concentration of 0 to about 10 weight percent, in further embodiments from about 0 to about 7 weight percent, and in other embodiments from about 0.1 weight percent to about 5 weight percent. In some embodiments, the non-ionic organic additive can be selected from the group consisting of TEP, PS, PFPN, LPTB, propene sultone, sulfones such as dimethyl sulfone or divinyl sulfone, dioxasilane-2,2-dioxide (DTD), phenyl trifluoromethyl sulfide (PTS), trivinylcyclotriboroxane (tVCBO), phenylboronic acid ethylene glycol ester (PBE), trimethyl borate (TMB), triethyl borate (TEB), tris(trimethylsilyl) phosphite (TMSPi), and organic phosphates such as trimethyl phosphate and trioctyl phosphate. A person of ordinary skill in the art will recognize that additional ranges of additive concentrations within the explicit ranges above are contemplated and are within the present disclosure.

[0034] The use of FEC to reduce corrosion of aluminum current collectors with electrolytes using LiFSI is described in JP 2014-203748 to Shinya et al., entitled "Nonaqueous Electrolyte Solution for Lithium Ion Secondary Batteries and Lithium Ion Secondary Battery Having the Same," which is incorporated herein by reference. An electrolyte using a blend of lithium salts, LiPF6 and LiFSI, for use with silicon-based electrodes is described in U.S. Patent Application Publication No. 2020 / 0168955 to Simanuki et al., entitled "Lithium Ion Secondary Battery," which is incorporated herein by reference (hereinafter the '955 application). The '955 application focuses on the impregnation of dialkyl sultone additives with certain solvents. Objectives described in the '955 application for the new additive include reducing the swelling of the active material with the incorporation of lithium, which is speculated to aid in "durability." The electrolytes described herein have a variety of formulations that provide improved high power battery performance while maintaining good cycling using silicon-based anode active materials.

[0035] Applicant has achieved very good cycling of silicon-based electrodes using previously developed electrolytes as 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 the cycle life performance of silicon-based cells, the work herein is directed to reducing gassing and improving stability, which is desirable for widespread commercial applications. The reference electrolyte used in the examples is based on the electrolyte in the '901 Application, and is described as E1, with no special meaning to the nomenclature.

[0036] In some embodiments, the electrolyte formulations described in this work exhibit better thermal properties and reduced gassing while exhibiting cycle life comparable to or better than a reference electrolyte formulation consisting of LiPF6 salt in FEC and DMC solvent. As exemplified herein, a first family of electrolytes has a formulation having a blend of LiPF6 and LiTFSI salts in a solvent consisting of FEC, EMC, PC, and either MA or EA. A second family of novel electrolytes has LiPF6 salt in a solvent consisting of FEC, EMC, PC, and either MA or EA, optionally with DMC. The electrolytes are also exemplified by the individual salts LiPF6, LiFSI, or LiTFSI in a solvent consisting of FEC, EMC, and PC. These exemplified electrolytes suggest other variations within these clear teachings.

[0037] Electronic vehicles are of primary interest for lithium-ion cells for commercial applications. Suitable vehicles include, for example, automobiles, trucks, vans, sport utility vehicles, crossover styles, commercial trucks, construction equipment, utility vehicles such as forklifts, manned flying vehicles such as personal air vehicles, unmanned ground vehicles such as tractors, people movers, unmanned flying vehicles such as drones, and similar vehicles. In these applications, it may be desirable to use pouch-type cells with flexible housings. In flexible housings, it may be desirable to incorporate the cells into a battery pack that holds the cells within a predetermined volume. Such volumetric constraint effects are also exhibited with cells assembled in a metal container, such as the coin cell embodiment used in the examples. Positioning the cells in the pack can be equivalent to clamping the cells to control the decomposition of the electrode stack, which can impair cycling. In the following examples, cell expansion is tested for unclamped pouch cells to test the effects of gassing. In the constrained configuration, the cells cannot expand, but gassing is manifested through an increase in pressure. The increase in pressure can be exacerbated by an increase in temperature. For these reasons, cycling performance at 45° C. may reflect the ability to control gassing.

[0038] 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 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 Asahi Kasei (Japan). Ceramic-polymer composite materials have also been developed for the separator. These ceramic composite separators can be stable at high temperatures, and the composite materials can reduce fire risks. Polymer ceramic composites for lithium ion battery separators are sold under the trademarks Separion® by Evonik Industries, Germany, Lielsort® by Tiejin Lielsort Korea Co., Ltd., and Q-Series ceramic coated polymer separators from Celgard®. It is also possible to form the separator using a porous polymer sheet coated with a gel-forming polymer. The design of such separators is 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.

[0039] 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.

[0040] 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 single electrode pair or multiple electrode pairs 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 over multiple cycling of the battery.

[0041] 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 into 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 to complete the cell. 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.

[0042] 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 used effectively in other situations.

[0043] 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.

[0044] 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.

[0045] The electrode stack can 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.

[0046] 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.

[0047] 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, air vehicles, or other vehicles. However, the improved anode described herein can be effectively used for consumer electronics applications that can be based on smaller cell configurations. A general design for consumer electronics cells using silicon-based active materials is described in U.S. Patent Application Publication No. 2015 / 0050535 to Amiruddin et al., entitled "Lithium Ion Batteries With High Capacity Anode Active Material and Good Cycling for Consumer Electronics" (hereinafter the '535 application), which is incorporated herein by reference. It should be noted that automobiles can also use smaller consumer electronics cells, and Tesla cars are currently known for using thousands of small consumer electronics cells in their battery packs. Generally, within certain ranges, larger cells / batteries can achieve greater energy densities. It may be desirable to select a positive electrode active material based on a particular application to balance various considerations such as energy density.

[0048] 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. FIG. 1A shows the length "L" of the electrode core 104, and FIG. 1C shows the width "W" such that the area of ​​the electrode is defined as L×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 sheet-like 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. Design of cells using high capacity silicon-based active materials to achieve specific total cell capacities is described in U.S. Pat. No. 9,780,358 to Masarapu et al., entitled "Battery Designs With High Capacity Anode Materials and Cathode Materials," which is incorporated herein by reference.

[0049] 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.

[0050] 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. In the following sections, the characteristics of certain negative and positive electrode layers are described.

[0051] 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 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.

[0052] negative electrode The basic electrode design includes a blend of active composition, polymer binder and conductive diluent. As mentioned above, in some embodiments, the improved electrode design may include a polymer binder blend and a blend of active composition and a nanoscale conductive carbon additive. The active material blend may include, in some embodiments, a silicon-based active material such as a majority of silicon oxide composite and at least 10 weight percent of separate graphite. It has also been discovered that stabilization of electrode cycling with silicon-based active material can be obtained by blending polyimide to provide high mechanical strength with a more deformable polymer portion that still provides good electrode performance in a synergistic binder blend. Although graphite can provide electrical conductivity to the electrode, nevertheless, in some embodiments, the amount of separate nanoscale conductive carbon can be significant to the ability to produce long-term cycling anodes. In general, graphite is electrochemically active, but nanoscale conductive carbon is not considered to be electrochemically active. These improved design aspects are therefore incorporated into the electrode along with further previously discovered silicon-based electrode improvements.

[0053] There has been considerable interest in high capacity anode active materials based on silicon. Until the applicant's recent work, silicon based active materials have generally not achieved cycling stability suitable for automotive applications for batteries containing significant amounts of silicon. The '535 application demonstrated successful cycling suitable for consumer electronics applications and the like, up to about 200-300 cycles at at least 80% of the initial capacity value. The applicant has had particular success with cycling stability, achieved primarily with materials based on silicon oxide composites. The applicant's development of improved electrode structures along with suitable electrolytes has enabled the characterization of cells based primarily on silicon based active materials while achieving cycling suitable for vehicular applications. As demonstrated herein, electrodes are provided that are successfully cycled at high power for over 800 cycles without experiencing less than 80% capacity fade while cycling over a wide voltage range at reasonable rates. Thus, the present work is directed toward extending cycling stability into the realm suitable for vehicular use. In particular, flying vehicles are particularly dependent on high power performance.

[0054] As described herein, the active composition blended with silicon-based active material and graphitic carbon provides improved cycling results. 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 additional embodiments at least about 1000 mAh / g, and in other embodiments at least about 1100 mAh / g, cycled at a rate of C / 3 from 5 millivolts (mV) to 1.5 V against lithium metal. 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 95% by weight of silicon-based active material, and in additional embodiments from about 60% by weight to about 90% by weight of silicon-based active material. Correspondingly, the blended active material can include from about 5% graphite to about 65% graphite, in further embodiments from about 7% graphite to about 60% graphite, in additional embodiments from about 8% graphite to about 55% graphite, and in other embodiments from about 10% graphite to about 50% graphite. A person of ordinary skill in the art will recognize that additional ranges of specific discharge capacity and concentrations of silicon-based active materials within the explicit ranges above are contemplated and are within the present disclosure.

[0055] Similar to silicon, oxygen-deficient silicon oxides, e.g., silicon oxide, SiO x(0.1≦x≦1.9) can be intercalated / alloyed with lithium so that the oxygen-deficient silicon oxide functions as an active material in a lithium-based cell. Silicon oxide can incorporate relatively large amounts of lithium, and therefore can exhibit large specific capacity. However, silicon oxide is generally observed to have a relatively fast capacity degradation with cell cycling. Commercially available silicon-based materials, including SiO, from several sources, can be composites with carbon and silicon nanocrystals, and are available from Alfa Aesar (USA), Sigma-Aldrich (USA), Shin-Etsu Chemical Co., Ltd. (Japan), Osaka Titanium Co., Ltd. (Japan), Nanostructured and Amorphous Materials Corp. (USA). Additional specific suitable formulations of silicon-based compositions are further described below. Applicants have achieved cycle stabilization of silicon oxide-based composite active materials with improved electrode formulations, and these advances are continued herein to further improve rate capability and corresponding power output. In some embodiments, for extended cycle life with an acceptable decrease in specific capacity, it may be desirable to have a negative electrode that includes a combination of a graphitic carbon active material and a silicon-based active material, and the excellent cycle performance exemplified herein uses such an active material blend.

[0056] As described above and in detail below, suitable silicon-based active materials may include composites with carbon components. The silicon-based active materials are described in detail in the following sections. 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 believed 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, which is not present in the composite in the active material blend. The following examples are based on commercially available composite compositions believed to contain primarily silicon suboxide and some amount of elemental silicon crystals and elemental carbon in the combined composite particulate materials.

[0057] 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. The graphitic form of crystalline carbon is capable of intercalating lithium, and is therefore an established electrochemically active material for lithium-ion batteries.

[0058] The graphite particles can 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 can have a D50 (mass median diameter) of about 5 microns to about 50 microns, in further embodiments about 7 microns to about 45 microns, and in additional embodiments about 10 microns to about 8 microns to about 40 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 ~ approx. 25m 2 / g, and in a further embodiment about 1.25 m 2 / g~about 20m 2 / g and in a further embodiment, about 1.5 m 2 / g ~ approx. 12m 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.

[0059] 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 includes at least about 5% by weight of a polymer having a low modulus, and 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, as further defined below. A person of ordinary skill in the art will recognize that additional ranges of amounts of polymer within the explicit ranges above are contemplated and are within the present disclosure. The polymers of the blend can be selected to be soluble in the same solvent.

[0060] Since silicon-based materials undergo large volume changes during cycling, electrode design is an important aspect in the construction of cells with silicon-based anodes to achieve desirable cycling. Part of the electrode design includes the selection of a polymer binder that helps maintain the electrode integrity during cycling. Significant cell engineering was required to achieve stable cycling of silicon-based active materials in cells with adequate capacity and energy density. Applicants initially achieved significant progress in cycling anodes with silicon-based active materials using polyimide binders and nanoscale carbon conductive materials. See U.S. Pat. No. 10,290,871 to Masarapu et al., entitled "Battery Cell Engineering and Design to Reach High energy," which is incorporated herein by reference. High tensile strength and high elongation were believed to be important features of polyimides that contribute to cycling properties. Polyimide binders have been processable with organic solvents, but more recently developed polyimides are water processable. See UBE Industries polyimides.

[0061] Polyimides were initially identified as useful polymeric binders for silicon-based materials due to their mechanical strength. Thus, polyimides provide some stability to the electrode due to the mechanical forces of the polymer as the active material changes with lithium uptake or release. With polyimide binders, good cycling has been achieved, particularly for consumer electronics. See applicant's '535 application, supra. Applicant has subsequently discovered that blending polyimides with more elastic polymers further improves electrode performance. See U.S. Pat. No. 11,094,925 to Venkatachalam et al., entitled "Electrodes with Silicon Oxide Active Materials, for Lithium Ion Cells Achieving High Capacity, High Energy Density and Long Cycle Life Performance," incorporated herein by reference (the '925 patent). Suitable water-based binders have also now been identified as an alternative, more environmentally friendly approach to solvent-based polymeric binders. See U.S. Patent Application Publication No. 2022 / 0006090 to Hayes et al., entitled "Lithium Ion Cells With Silicon Based Active Materials and Negative Electrodes With Water Based Binders Having Good Adhesion and Cohesion," which is incorporated herein by reference. Although the examples herein are based on organic solvent processed binders, applicants have achieved similar good cycling with both solvent-based and water-based negative electrode binders.

[0062] 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 3 shows the sources of high tensile strength polyimide polymers and the corresponding polyimide polymer names.

[0063] [Table 3]

[0064] The polyimide polymer can 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 can also have relatively high elongation values. Elongation value is the amount of elongation that a polymer can withstand before tearing. In some embodiments, the polyimide can 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 ​​can 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.

[0065] 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, polyvinylidene fluoride (PVDF), cellulose, such as 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 4.

[0066] [Table 4]

[0067] PVDF, CMC, and SBR are commercially available from a number of sources. LiPAA can be prepared from lithium hydroxide (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.

[0068] 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.

[0069] 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.

[0070] Higher active material loadings of the binder are possible. In some embodiments, the negative electrode has about 75% to about 92% by weight of the negative electrode active material, in other embodiments about 77% to about 90% by weight of the negative electrode active material, and in further embodiments about 78% to about 88% by weight of the negative electrode active material. In some embodiments, the negative electrode has about 6% to about 20% by weight of the polymer binder, in other embodiments about 7% to 19% by weight of the polymer binder, and in further embodiments about 8% to 18% by weight of the polymer binder. In some embodiments, the negative electrode also includes about 1% to about 7% by weight of nanoscale conductive carbon, in further embodiments about 1.5% to about 6.5% by weight, and in additional embodiments about 2% to about 6% by weight of 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.

[0071] For improved cycling of the negative electrode, nanoscale carbon additives 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 may include carbon nanotubes, carbon nanofibers, carbon nanoparticles (e.g., carbon black), or combinations thereof. In some embodiments, to achieve improved performance, the conductive additive may 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.

[0072] 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.

[0073] Carbon black means a synthetic carbon material and may alternatively be referred to 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).

[0074] 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).

[0075] The negative electrodes used in the cells described herein can 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 4.5mg / 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 yet another embodiment, 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 additional embodiments from about 0.7 g / cc to about 1.3 g / cc. Similarly, the silicon oxide based electrode can have an average dry thickness of at least about 15 microns, 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.

[0076] 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 comparable 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.

[0077] Elemental silicon, silicon alloys, silicon composites, etc. can have a low potential relative to lithium metal similar to graphite. However, elemental silicon undergoes a very large volume change 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.

[0078] 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.

[0079] 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.

[0080] 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 on cycling while maintaining high specific capacity and, in some embodiments, reducing irreversible capacity loss in the first charge and discharge cycle. Additionally, pyrolytic carbon coatings have also been observed to stabilize silicon-based materials with respect to battery performance.

[0081] 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 can 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.

[0082] 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.

[0083] 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.

[0084] 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 the oxygen-deficient silicon oxide can function as an active material in a lithium-ion battery. 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. The oxygen-deficient silicon oxide can incorporate relatively large amounts of lithium so that the material can exhibit a 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.

[0085] 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.

[0086] In general, a wide range of composites is available 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 can 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, which would not be considered to form a composite.

[0087] Various Si-SiO x A solution-based approach for the synthesis of SiO-CM (M=metal) composites is described in U.S. Patent Application Publication No. 2014 / 0308585 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 Application Publication No. 2014 / 0370387 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.

[0088] The capacity of the anode significantly affects the energy density of the battery. The higher the specific capacity of the anode material, the lower the weight of the anode in the same power cell. When the negative electrode is made of a silicon-based material, the electrode can have a discharge specific capacity at a C / 3 rate of about 800 mAh / g to 2500 mAh / g at a C / 3 discharge of 1.5 V to 5 mV vs. lithium metal, in further embodiments about 900 mAh / g to about 2300 mAh / g, and in other embodiments about 950 mAh / g to about 2200 mAh / g. A person of ordinary skill in the art will recognize that additional ranges of discharge specific capacity within the explicit ranges above are contemplated and are within the present disclosure.

[0089] 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.

[0090] 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 together with cycling over 600 cycles while maintaining at least 80% capacity, although some materials show promising results with somewhat lower cycling stability. In particular, nickel-rich lithium nickel manganese cobalt oxide provides very 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.

[0091] 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 zO2, where 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. In some embodiments, y and z are approximately equal. The amount of nickel can affect the selected charging voltage to balance cycling stability and discharge energy density. For values ​​of x in the range of 0.525≦x≦0.7, the selected charging voltage can be 4.25V to 4.375V. For values ​​of x in the range of 0.7≦x≦0.9, the selected charging voltage can be 4.05V to 4.325V. 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 and are available from BASF Corp. (Germany), TODA Corp. (Japan), L&F Materials Corp. (Korea), Umicore NV (Belgium), and Ningbo Jinhe New Materials Co., Ltd. (China). Commercially available formulations of these compounds include, for example, LiNi 0.5 Mn 0.3 Co 0.2 O2 (BASF), LiNi 0.6 Mn 0.2 Co 0.2 O2 (L&F, Korea and Umicore, Belgium), LiNi 0.8 Mn 0.1 Co 0.1 O2 (L&F, Korea, BASF, Germany, Umicore, Belgium and LG Chemical, Korea).

[0092] 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.

[0093] As noted above, desirable blends can include N-NMC and (lithium-rich + manganese-rich) lithium nickel manganese cobalt oxide (LM-NMC or HCMR™). For the active material blend for the positive electrode, the active material can include about 3% to about 85% by weight of LM-NMC. 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 δO2 (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 can 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.

[0094] 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, which are generally considered to be electrochemically inert during battery cycling, can include metal fluorides, metal oxides, or non-fluoride halides of metals. Improved metal fluoride coatings with appropriately designed thicknesses are 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.

[0095] The positive electrode active material is lithium cobalt oxide, LiNi 0.33 Mn 0.33 Co 0.33 O2(NMC111), LiNi 0.8 Co 0.15 Al 0.05O2 (NCA), lithium manganese oxide (LiMn2O4), lithium metal phosphates such as lithium iron phosphate (LiFePO4), 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.

[0096] 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 can be large. In some embodiments, the positive electrode includes about 85% to about 99% by weight of the positive electrode active material, in other embodiments about 90% to about 98% by weight of the positive electrode active material, and in further embodiments about 95% to about 97.5% by weight of the positive electrode active material. In some embodiments, the positive electrode has about 0.75% to about 10% by weight of the polymer binder, in other embodiments about 0.8% to about 7.5% by weight of the polymer binder, and in further embodiments about 0.9% to about 5% by weight of the polymer binder.

[0097] In general, the positive electrode composition can also include a conductive additive different from the electroactive composition. In some embodiments, the positive electrode can have 0.4 wt % to about 12 wt % of the conductive additive, in further embodiments about 0.45 wt % to about 7 wt %, and in other embodiments about 0.5 wt % to about 5 wt % of the conductive additive. A person of ordinary skill in the art will recognize that additional ranges of particle loadings within the explicit ranges above are contemplated and are within the present disclosure. The active materials for the positive electrode are described above. Suitable polymer binders for the positive electrode include, for example, PVDF, polyethylene oxide, polyimide, polyethylene, polypropylene, polytetrafluoroethylene, polyacrylate, rubber, such as ethylene-propylene-diene monomer (EPDM) rubber or SBR, copolymers thereof, or mixtures thereof. For the positive electrode, PVDF can be used with good results, and the example positive electrode uses a PVDF binder. The conductive additives have been described in detail for the negative electrode, and nanoscale conductive carbon can be effectively used for the positive electrode.

[0098] 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 mg / cm 2 ~about 40mg / cm 2 and in other embodiments, about 12 mg / cm 2 ~Approx. 37.5mg / cm 2 and in a further embodiment about 13 mg / cm 2 ~about 35mg / cm 2 and in other embodiments 20 mg / cm 2 ~Approx. 32.5mg / 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 can have a thickness of positive electrode material on each side of the current collector, after pressing and drying, of from about 45 microns to about 300 microns, in some embodiments from about 80 microns to about 275 microns, and in additional embodiments 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.

[0099] 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 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.

[0100] Depending on the approach for the introduction of supplemental lithium, the positive electrode may initially contain 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 into 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 supplemental electrode may contain elemental lithium, lithium alloys and / or other sacrificial lithium sources in addition to other electrode components.

[0101] In some embodiments, at least a portion of the supplemental lithium is initially associated with the negative electrode. For example, the supplemental lithium may be in the form of a lithium alloy or other lithium source that is more electronegative than the negative electrode active material. The elemental lithium may be in the form of a thin film, lithium alloy foil, and / or powder, such as those formed by vapor deposition, sputtering, or ablation. Elemental lithium, especially in powder form, may be coated to stabilize the lithium for handling purposes. Commercially available lithium powders, such as powders from FMC Corporation, are 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 electrodes are internally conductive, there is no need to close the circuit to obtain electron flow from the reaction. During this process, a solid electrolyte interface (SEI) layer may 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 in the same electrode.

[0102] 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. In additional or alternative embodiments, the supplemental lithium is disposed along the electrode surface. For example, the negative electrode can include an active layer having an active negative electrode composition and a supplemental lithium source layer on the surface of the active layer. 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 the surface of the active layer. In alternative configurations, 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.

[0103] 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 a lithium foil, a lithium alloy foil, or a lithium source material in a polymer binder, optionally with a conductive powder, which is in direct contact with a 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 some embodiments, the lithium source in the electrode may be assembled into a cell together 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.

[0104] 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.

[0105] 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 about 3% to about 55% of the capacity, in additional embodiments about 5% to about 52.5% of the capacity, and in some embodiments about 5% to about 50% 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.

[0106] 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.

[0107] Testing of the active materials is carried out in lithium cells that use lithium metal electrodes. Such cells are commonly referred to as 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, as opposed to its usual role as the negative electrode in lithium-ion cells.

[0108] The positive electrode active material capacity 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. Lithium is then de-intercalated 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 vs. lithium metal based on the voltage of the final anode vs. lithium metal. Similarly, for a given silicon-based electrode, the insertion and extraction capabilities can be evaluated using a battery having a positive electrode with 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 deintercalated / dealloyed to 1.5 V at a rate of C / 20. 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, which 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 balance after the formation cycle or several formation cycles may be desirable in that the balance is more based on the conditions during battery use.

[0109] In most commercially available carbon-based batteries, an excess of about 7-10% 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 may be inactive in the cell after the first charge-discharge cycle, adding significant deadweight to the battery.

[0110] 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 in subsequent cycles several cycles later, 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 the selected rate used in that cycle, and these capacities can be estimated from the electrode performance.

[0111] As mentioned above, supplemental lithium can be introduced in various ways. If supplemental lithium is introduced to the negative electrode active material before the assembly of the cell, the negative electrode can show a significant reduction in irreversible capacity loss compared to other approaches for introducing supplemental lithium. Without wishing to be limited by theory, material changes related to irreversible capacity loss can occur during the prelithiation process performed in the assembly of the cell. With reduced irreversible capacity loss, the electrode balance (positive electrode capacity vs. negative electrode capacity) has less initial imbalance to adjust from the IRCL. A similar way to consider this situation is that the negative electrode capacity has already been adjusted to account for supplemental lithium, so that the measured capacity of the negative electrode can be considered as a virtual total capacity minus the supplemental lithium provided to the negative electrode active material. For these embodiments, it is still valid to consider the fourth cycle capacity to evaluate the balance, but it is possible that the fourth cycle capacity is more similar to the first cycle capacity.

[0112] 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.

[0113] 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, when 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. In a robust battery design, at least about 10% additional negative electrode may be desirable in 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 design described below.

[0114] Cell performance characteristics The combination of design features described herein can provide longer cycle stability while maintaining the desired high power cell performance. In certain applications, it may be important to maintain power capability in the latter half of the cell's life before charging. 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.

[0115] The selected charge voltage may be influenced by the positive electrode active material. Typically, the selected charge voltage for these cells is about 4.05V-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 can exhibit very good cycling performance resulting in high power generation with high discharge rates. In some embodiments, the cells exhibit a discharge capacity at the 700th cycle of at least about 75%, in other embodiments at least about 80%, of the 6th cycle capacity discharged at room temperature from the selected charge voltage to 2.5V at a 1C rate or a 4C rate, and in additional embodiments, at the 700th cycle, at least about 82% of the 6th cycle discharge capacity when cycled at room temperature from the selected charge voltage to 2.5V at a 1C charge rate. 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. EXAMPLES

[0116] General Methods and Materials. The general methods and materials are described in the '925 patent 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. Specifically, the active material for the positive electrode was of the formula LiNi 0.6 Mn 0.2 Co 0.2 O2(NMC622) or LiNi 0.8 Mn 0.1 Co 0.1 The active material for the positive electrode was a commercially available lithium nickel manganese cobalt oxide with 02 (NMC811). NMC811 is commercially available from different sources as polycrystalline or single crystal, and different examples were carried out using each of these as the active material for the positive electrode. The negative electrode active material was a commercially available SiO-Si-C (SiOx) composite (denoted as SOC) blended with electrochemically active graphite.

[0117] The positive electrode was blended with 1% to 4% by weight of PVDF binder and 1% to 3% by weight of nanoscale carbon to have an active material loading of about 93% to 97.5% by weight. The cathode material was blended with NMP solvent, spread on an aluminum foil current collector, pressed, and dried.

[0118] To form a negative electrode using a silicon oxide-based active material, the active material is, unless otherwise specified, 65% to 80% by weight of a commercially available silicon oxide / silicon / carbon composite (herein referred to as SiO xThe negative electrodes were formed by blending powders of SiO2 / Si / C (denoted as SiO2 / Si / C) with the remainder (20 wt%-35 wt%) of electroactive graphite (KS 6 composite graphite, Imerys SA). The negative electrode active material was thoroughly mixed with 1 wt%-7 wt% nanoscale carbon conductive additive to form a homogenous powder mixture. The negative electrodes had 2-6 wt% carbon nanotubes as conductive additive. The powder components of the electrode, active material, and carbon nanotubes were mixed to form a homogenous powder mixture. The negative electrodes had 1-7 wt% lower modulus binder and 7-15 wt% polyimide. The weight ratio of lower modulus binder to polyimide was 0.714.

[0119] To form the negative electrode, a blend of the polymer binder, polyimide binder, and low modulus binder was mixed with NMP (Sigma-Aldrich) and stirred overnight to form a polymer binder-NMP solution. The homogenous powder mixture was then added to the polymer binder-NMP solution and mixed for approximately 2 hours to form a homogenous slurry. The slurry was applied onto a copper foil current collector to form a wet film, and the laminated current collector was dried in a vacuum oven to remove the NMP and harden the polymer. The laminated current collector was then pressed between the rollers of a sheet mill to obtain the desired laminate thickness. The dried laminate contained 2-20% by weight of binder, with the remainder of the electrode contributed by the powder. The negative electrode was electrochemically prelithiated with enough lithium to compensate for 100%-160% of the lithium loss due to irreversible capacity loss of the anode.

[0120] 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.

[0121] 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 Ah at a discharge rate of C / 3 at 30°C.

[0122] The electrolyte salts, solvents, co-solvents and additives used in the examples are listed in Table 5. In the examples that follow, cell performance is evaluated based on selected electrolytes.

[0123] [Table 5]

[0124] [Table 6]

[0125] Example 1 – Gassing performance of LiPF6 / LiTFSI electrolyte with various solvents In this example, gassing from cells made with the various electrolytes described herein is investigated.

[0126] The lithium ion cells have a positive electrode with SOC anode and NMC622 in combination with E2-E9 electrolytes, which may show less gassing compared to batteries with known electrolytes. Figure 2 shows the percent thickness change versus storage time at 65°C for electrolytes E1-E4 used in combination with pouch cells with NMC622 cathode and SOC anode. The electrolyte filled pouch cells are stored at 65°C and thickness is measured at 48 hour intervals. After each measurement from the cell removed from the oven, the cell is allowed to rest at room temperature for 30 minutes. After cooling to room temperature, thickness is measured again and the cell is returned to the oven for the next interval. As shown in Figure 2, the pouch cell using E1 electrolyte showed a larger and less desirable change in thickness over 48 hours compared to the pouch cells with E2, E3, and E4 electrolytes.

[0127] Example 2 - Cycling performance of LiPF6 / LiTFSI electrolyte at various rates with various solvents In this example, the cycling performance is investigated using electrolytes having different amounts of FEC along with various other solvent components.

[0128] Lithium-ion batteries, when used in combination with electrolytes E2, E3, and E4, may exhibit improved or comparable cycling compared to batteries containing known electrolytes with reduced gassing. Coin cells using NMC622 positive active material and SOC anodes were fabricated using each of electrolytes E1-E4. The cycling performance of the coin cells under various conditions was measured and the results are shown in Figures 3A-3E. For cycling, two cycles were performed at C / 10 rate, cycles 3 and 4 at C / 5 rate, cycles 4 and 5 at C / 3 rate, and cycles 7 and beyond were performed at the desired test rate for longer cycles. Every 50 cycles, a cycle was performed at C / 3 to check the cell performance. This cycling format was used for the other examples unless otherwise indicated. Figure 3A is a plot of normalized capacity as a function of cycle number for coin cells cycled from 4.3V to 2.5V at 1C charge / 1C discharge rate. Electrolytes E2, E3, and E4 show similar cycling behavior compared to E1. All cells achieved more than 700 cycles at 1C / 1C charge and discharge rates before the capacity dropped to less than 80% of the capacity at the 7th cycle. Figure 3B shows a plot of the non-normalized specific discharge capacity for the data shown in Figure 3A. As used herein, the non-normalized specific discharge capacity is reported based on the weight of the positive electrode active material.

[0129] FIG. 3C is a plot of normalized capacity as a function of cycle number for coin cells cycled at 4C charge / 1C discharge rates. A 1C charge / 1C discharge cycle was performed every 50 cycles to check the cell performance. E3 and E4 electrolytes show similar cycling behavior compared to E1, while E2 is worse than E1. This suggests that a slightly higher FEC concentration is beneficial for high rate charging without sacrificing cycling performance. E1, E3, and E4 achieved at least 750 cycles before the capacity dropped below 80% of the second cycle capacity. FIG. 3D shows a plot of the non-normalized specific capacity for the data shown in FIG. 3C.

[0130] Figure 3E is a plot of the discharge capacity as a function of cycle number for coin cells cycled at various discharge rates. The charge rate protocol utilized in generating these data is listed in Table 6.

[0131] [Table 7]

[0132] Electrolytes E2, E3 and E4 showed lower rate capacity at higher than 2C charge / 1C discharge rate compared to E1 electrolyte. The lower rate capacity of E2, E3 and E4 may be due to the use of EMC compared to DMC in E1. Comparable or higher ionic conductivity is expected for E2, E3 and E4 compared to E1.

[0133] Example 3 - Cycling performance of LiPF6 / LiTFSI electrolyte with various solvents, additives and co-solvents Cycling performance was measured for electrolytes E5 containing 0.5-5 wt% PFPN and E9 containing 0.1-2 wt% LPTB and 5-30 wt% EA to determine the effect of additives and co-solvents. Coin cells with NMC622 positive active material and SOC anodes were fabricated with electrolytes E5 and E9, respectively. Figure 4A is a plot of normalized capacity as a function of cycle number for coin cells cycled at 4C charge / 1C discharge rates at 45°C. A 1C rate capacity check was performed every 50 cycles. Figure 4B is a plot of the non-normalized specific capacity for the data shown in Figure 4A. Improved cycling performance was observed for electrolytes E5 (E3+PFPN) and E9 (E2+LPTB and EA) compared to electrolyte E1, except for an initial drop in short cycles.

[0134] Example 4 - Cycling performance of LiPF6 / LiTFSI electrolyte with selected solvents, additives and co-solvents and NMC811 positive electrode active material This example shows cycling results for cells using NMC811 active material with the same silicon-based anode and with various electrolytes described herein.

[0135] Coin cells using NMC811 positive active material and SOC anode were fabricated using electrolytes E1 and E5, respectively. The cycling performance of the coin cells was measured as described for Example 2, and the results are shown in Figures 5A-5D. Figure 5A is a plot of normalized capacity as a function of cycle number for coin cells cycled at C / 3 charge-discharge rate and 1C / 1C charge-discharge rate. Comparable cycle life was obtained for E5 compared to E1, with cells based on each electrolyte cycled for over 900 cycles while achieving 80% capacity for the 7th cycle. Figure 5B shows a plot of the unnormalized specific capacity of the data shown in Figure 5A.

[0136] FIG. 5C is a plot of normalized capacity as a function of cycle number for coin cells cycled at 4C / 1C charge-discharge rate (room temperature) and 1C / 1C charge-discharge rate (45° C.). Compared to E1, superior cycle life is predicted for E5. FIG. 5D shows a plot of the non-normalized specific capacity of the data shown in FIG. 5C. In general, under high rate or high temperature conditions, E5 had better cycling performance than E1 for NMC811. Electrolyte E5 contained additive PFPN.

[0137] FIG. 6A is a plot of normalized capacity as a function of cycle number for coin cells made with electrolytes E1 and E3. The coin cells were cycled as described in FIG. 5C. The electrode active materials were NMC811 for the positive electrode active material and SOC for the negative electrode active material. The cells were cycled at 1C charge / 1C discharge at 45° C. or 4C charge / 1C discharge at room temperature. At 1C / 45° C., E1 and E3 electrolytes performed similarly, but at 4C / 1C cycling, E3 electrolyte did not perform as well as E1 electrolyte. FIG. 6B shows a plot of the unnormalized specific capacity of the data shown in FIG. 6A.

[0138] FIG. 7A is a plot of normalized capacity as a function of cycle number for coin cells made with electrolytes E1 and E6. The coin cells were cycled again at 1C charge / 1C discharge at 45° C. and 4C / 1C discharge at room temperature. The electrode active materials were NMC811 for the positive electrode active material and SOC for the negative electrode active material. E6 had slightly better cycling performance at 45° C., but significantly worse high-rate cycling performance. FIG. 7B is a plot of the unnormalized specific capacity of the data shown in FIG. 7A.

[0139] FIG. 8A is a plot of normalized capacity as a function of cycle number for coin cells made with electrolytes E1 and E7. Electrolyte E7 contained additive TEP. The coin cells were cycled again at 1C charge / 1C discharge at 45° C. and 4C / 1C discharge at room temperature. The electrode active materials were NMC811 for the positive electrode active material and SOC for the negative electrode active material. Compared to E1, the cell with electrolyte E7 showed good high temperature cycling but poor high rate cycling. FIG. 8B is a plot of the unnormalized specific capacity of the data shown in FIG. 8A.

[0140] FIG. 9A is a plot of normalized capacity as a function of cycle number for coin cells made with electrolytes E1 and E8. Electrolyte E8 also contained additive TEP. The coin cells were cycled at 1C charge / 1C discharge at 45° C. and 4C / 1C at room temperature. The electrode active materials were NMC811 for the positive electrode active material and SOC for the negative electrode active material. The performance of the cells with electrolyte E8 was similar to that of the cells with electrolyte E7. Although the high charge rate performance of the cells with electrolytes E7 and E8 is inferior to that of the cells with electrolyte E1, these cells still cycle well for over 700 cycles at 80% capacity. FIG. 9B shows a plot of the unnormalized specific capacity of the data shown in FIG. 9A.

[0141] The data in Example 4 show improved cycle life of electrolytes E3 and E5-E8 with PFPN, TEP and combination of PFPN and TEP compared to E1 electrolyte. In particular, E5 shows better cycle life at both 1C / 1C and 4C / 1C rates and better 1C / 1C cycle when stored at 45° C.

[0142] Example 5 – Gassing behavior of LiPF6 electrolyte with various co-solvents In this example, the swelling behavior of pouch cells formed with electrolytes selected from Table 3 is investigated.

[0143] Lithium ion cells with SOC anodes and NMC622 cathodes were prepared in combination with the E21-E24 electrolytes and the reference electrolyte E1 and tested as described above for Example 2. Figure 10 shows the percent change in thickness versus storage time at 65°C for the E21-E24 electrolytes and the E1, E2 and E10 electrolytes used in combination with the pouch cells. As shown in Figure 10, the pouch cell with the baseline E1 electrolyte showed the greatest undesirable change in thickness over the 48 hour period compared to the other pouch cells.

[0144] Example 6 – Cycling performance of LiPF6 electrolyte with various co-solvents The cycling performance at different rates was measured for coin cells using E21-E25 electrolytes. The data for each of the E21-E25 electrolytes are shown in comparison with that for E1 electrolyte.

[0145] FIG. 11A is a plot of normalized capacity as a function of cycle number for coin cells made with electrolytes E1 and E21. The coin cells were cycled as described in FIG. 5C, except that all cycles were performed at room temperature. The electrode active materials were NMC622 for the positive electrode active material and SOC for the negative electrode active material. Electrolyte E21 exhibited similar behavior to E1 when a 1C charge / 1C discharge rate was used, but exhibited inferior behavior when a 4C charge / 1C discharge rate was used. FIG. 11B is a plot of the unnormalized specific discharge capacity of the data shown in FIG. 11A.

[0146] FIG. 12A is a plot of normalized capacity as a function of cycle number for coin cells made with electrolytes E1 and E22. The coin cells were cycled as described in FIG. 5C, except that cycling was performed at room temperature. The electrode active materials were NMC622 for the positive electrode active material and SOC for the negative electrode active material. Electrolyte E22 exhibited similar behavior to E1 when a 1C charge / 1C discharge rate was used, but exhibited inferior behavior when a 4C charge / 1C discharge rate was used. FIG. 12B is a plot of the unnormalized specific capacity of the data shown in FIG. 12A.

[0147] FIG. 13A is a plot of normalized capacity as a function of cycle number for coin cells made with electrolytes E1 and E23. The coin cells were cycled as described in FIG. 5C, except that cycling was performed at room temperature. The electrode active materials were NMC622 for the positive electrode active material and SOC for the negative electrode active material. Electrolyte E23 performed poorly compared to E1 when 1C charge / 1C discharge and 4C charge / 1C discharge rates were used. FIG. 13B is a plot of the unnormalized specific capacity of the data shown in FIG. 13A.

[0148] FIG. 14A is a plot of normalized capacity as a function of cycle number for coin cells made with electrolytes E1 and E24. The coin cells were cycled as described in FIG. 5C, except that cycling was performed at room temperature. The electrode active materials were NMC622 for the positive electrode active material and SOC for the negative electrode active material. Electrolyte E24 performed poorly compared to E1 when 1C charge / 1C discharge and 4C charge / 1C discharge rates were utilized. FIG. 14B is a plot of the unnormalized specific capacity of the data shown in FIG. 14A.

[0149] FIG. 15A is a plot of normalized capacity as a function of cycle number for coin cells made with electrolytes E1 and E25. The coin cells were cycled as described in FIG. 5C, except that the cells were cycled at room temperature. The electrode active materials were NMC622 for the positive electrode active material and SOC for the negative electrode active material. Electrolyte E25 exhibited similar behavior to E1 when a 1C charge / 1C discharge rate was used, but exhibited inferior behavior when a 4C charge / 1C discharge rate was used. FIG. 15B is a plot of the unnormalized specific capacity of the data shown in FIG. 15A.

[0150] The data suggests that when a single salt LiPF6 electrolyte is utilized, similar results can be obtained by substituting DMC for EMC, but inferior results are obtained in most cases, regardless of whether a co-solvent is present in the electrolyte.

[0151] Example 7 - Cycling performance of electrolytes with different lithium salts including LiPF6 / LiFSI at different rates The discharge capacities at different discharge rates as a function of cycle number were measured for coin cells with electrolytes E1 and E10-E13, including the single salt electrolytes LiPF6, LiFSI and LiTFSI, and the two-salt electrolyte LiPF6 / LiFSI.

[0152] The fast charge test protocol for evaluating the rate capability is shown in Table 7.

[0153] [Table 8]

[0154] FIG. 16 is a plot of the discharge capacity as a function of cycle number for coin cells made with electrolytes E1 and E10-E12 (all single salt electrolytes), cycled according to the test protocol shown in Table 7. The electrode active materials were NMC622 for the positive electrode active material and silicon oxide composite SOC for the negative electrode active material. Electrolyte E11 with LiFSI showed improved 4C discharge compared to E1. Electrolytes E10-E12 showed rate performance as a function of conductivity, i.e., LiFSI>LiPF6>LiFSI.

[0155] FIG. 17 is a plot of the discharge capacity as a function of cycle number for coin cells made with electrolytes E10 and E11 single salt electrolytes and electrolyte E13 dual salt electrolyte. The cycles were performed according to the test protocol shown in Table 7. The electrode active materials were NMC622 for the positive active material and silicon oxide composite SOC for the negative active material. Electrolyte E13 showed similar "15min-4C charge" performance as electrolyte E10. The dual salt LiPF6 / LiFSI electrolyte showed similar performance as the single salt LiFSI electrolyte.

[0156] FIG. 18 is a plot of normalized capacity as a function of cycle number for coin cells made with electrolyte E14 two-salt LiPF6 / LiFSI electrolyte. The concentrations of each salt LiPF6 and LiFSI in E14 were the same, but the concentration of LiFSI was higher than that of LiPF6 in E13. 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.

[0157] The mixed salt system of LiFSI and LiPF6 electrolyte appeared to show better 4C charging performance than the pure LiFSI cell, but showed one instance of performance degradation likely due to a manufacturing defect.

[0158] Example 8 - Cycling performance of LiPF6 / LiFSI and LiPF6 / LiTFSI electrolytes without low boiling point solvent FIG. 19A is a plot of the non-normalized specific discharge capacity as a function of cycle number for coin cells made with electrolytes E2 and E15. Electrolyte E15 contains a di-salt electrolyte LiPF6 / LiFSI together with a co-solvent PC with a boiling point of 242° C. Electrolyte E2 contains the same di-salt combination and co-solvent PC in addition to a co-solvent EA with a boiling point of 77° C. Data is based on the weight of the positive electrode active material. The electrode active materials are NMC811 for the positive electrode active material and silicon oxide composite SOC for the negative electrode active material. The coin cells were cycled at different charge rates according to the charge rate protocol shown in Table 8 below.

[0159] [Table 9]

[0160] From this data, it can be seen that E15 exceeds or is comparable to E2. Thus, by using a solvent that does not contain low boiling point components, it is possible to obtain good high-rate cycle performance.

[0161] Figure 19B is a plot of normalized capacity as a function of the number of 1C charge / 1C discharge rate cycles of coin cells. The coin cells were cycled at 1C charge / 1C discharge rates. The electrode active materials are NMC811 for the positive electrode active material and silicon oxide composite SOC for the negative electrode active material. Figure 19C is a plot of the non-normalized specific discharge capacity cycled at 4C charge and 1C discharge rates based on the weight of the positive electrode active material of the data shown in Figure 19B.

[0162] Example 9 – Cycling performance of LiPF6 / LiTFSI electrolyte in a pouch cell In this example, the cycling performance of various electrolytes in a pouch battery or cell is investigated. Pouch cells with NMC811 positive active material and SOC anode were fabricated with E3, E5, and E7 electrolytes. The pouch cells had an energy density of 315Wh / kg based on the total cell weight and a capacity of 12Ah at C / 3. The cycling performance of the pouch cells was measured under various conditions and the results are shown in Figures 20A-21B.

[0163] Figure 20A is a plot of normalized capacity as a function of cycle number for pouch cells cycled from 4.2 V to 2.5 V at 1C charge / 1C discharge rates. Electrolytes E3, E5, and E7 showed similar cycling behavior, undergoing 1000 cycles without the normalized capacity dropping below 90%. Figure 20B shows a plot of the unnormalized specific discharge capacity based on the weight of the positive electrode active material for the data shown in Figure 20A.

[0164] FIG. 21A is a plot of normalized capacity as a function of cycle number for pouch cells cycled from 4.2V to 2.5V at 4C charge / 1C discharge rates. A C / 3 cap check was performed every 50 cycles. Electrolytes E3, E5, and E7 showed similar cycling behavior, with 1000 cycles performed without the normalized capacity dropping below 90%. Electrolyte E3 showed cycling behavior with 1200 cycles performed without the normalized capacity dropping below 90%. FIG. 21B shows a plot of the unnormalized specific discharge capacity based on the weight of the positive electrode active material for the data shown in FIG. 21A.

[0165] Example 10 - Cycling performance of LiPF6 / LiTFSI electrolyte in pouch cells containing various positive electrode active materials In this example, we investigate the cycling performance of E3 in pouch cells containing various positive electrode active materials. The NCM811 cathode is monocrystalline in nature compared to previously reported polycrystalline NCM811 cathodes. This pouch cell had an energy density of 325 Wh / kg based on the total cell weight and a capacity of 12 Ah at C / 3. The cycling performance of the pouch cell under various conditions was measured and the results are shown in Figures 22A-24B.

[0166] Figure 22A is a plot of normalized capacity as a function of cycle number for a pouch cell cycled from 4.2 V to 2.5 V at 1 C charge / 1 C discharge rate. After 800 cycles, the normalized capacity of the cell remained greater than 80%. Figure 22B shows a plot of the unnormalized specific discharge capacity based on the weight of the positive electrode active material for the data shown in Figure 22A.

[0167] FIG. 23A is a plot of normalized capacity as a function of cycle number for a pouch cell cycled from 4.2V to 2.5V at a 4C charge / 1C discharge rate. A C / 3 cap check was performed every 50 cycles. After 600 cycles, the normalized capacity of the cell remained greater than 80%. FIG. 23B shows a plot of the unnormalized specific discharge capacity based on the weight of the positive electrode active material for the data shown in FIG. 23A.

[0168] FIG. 24A is a plot of normalized capacity as a function of cycle number for a pouch cell cycled from 4.2 V to 2.5 V at 1C charge / 1C discharge rate, where the pouch cell cycling was performed at 45° C. After 500 cycles, the normalized capacity of the cell remained greater than 90%. FIG. 24B shows a plot of the unnormalized specific discharge capacity based on the weight of the positive electrode active material for the data shown in FIG. 24A.

[0169] Example 11 - Cycling performance of electrolyte with additive PS The cycling performance of coin cells fabricated using E1, E3, and E26-E29 with electrolytes containing PS as an additive was measured. The coin cells contain single crystal NCM811 positive electrode active material and SOC negative electrode. The cycling performance of the coin cells under various conditions was measured and the results are shown in Figures 25, 26, 27A, and 27B.

[0170] 25 is a plot of the specific capacity based on the weight of the positive active material as a function of cycle number for coin cells made with E1, E26, and E27. Cycling was performed at 1C charge / 1C discharge rate from 4.2 V to 2.5 V. The data shows that the specific capacity begins to decline after about 150 cycles and rapidly deteriorates after about 300 cycles.

[0171] Figure 26 is a plot of the specific capacity based on the weight of the positive active material as a function of cycle number for coin cells made with E1, E26 and E27. Cycling was performed from 4.2V to 2.5V at a 4C charge / 1C discharge rate. A C / 3 cap check was performed every 50 cycles. The data shows that the specific capacity starts to decline after about 400 cycles.

[0172] FIG. 27A is a plot of the specific capacity based on the weight of the positive active material as a function of cycle number for coin cells made with E3, E28, and E29. Cycling was performed from 4.2V to 2.5V at a 4C charge / 1C discharge rate. A C / 3 cap check was performed every 50 cycles. The data shows that the specific capacity decreases after about 350 cycles. FIG. 27B is a plot of the capacity retention of the data shown in FIG. 27A. The data is similar to that shown in FIG. 27A.

[0173] Example 12 – Gassing behavior of electrolytes with various additives Pouch cells with SOC anodes and NMC622 cathodes in combination with E30-32 electrolyte were fabricated and tested as described above for Example 1. Figure 28 shows the percent cell thickness change versus storage time at 65° C. The data shows that the addition of PFPN to the electrolyte reduces gassing, and the addition of PFPN and PS reduces gassing even further.

[0174] 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 this 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. An electrolyte for a lithium-based cell, comprising: About 0.05 M to about 0.6 M of LiPF ６ , about 1.1 M to about 2.2 M of a lithium salt consisting essentially of about 0.75 M to about 1.8 M of lithium bis(fluorosulfonyl)imide (LiFSI) or lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and an optional other lithium salt of about 5 mole percent or less; a solvent consisting essentially of about 5 volume percent (vol%) to about 25 vol% of fluoroethylene carbonate, about 50 vol% to about 90 vol% of dimethyl carbonate, ethyl methyl carbonate or a mixture thereof, and 0 to about 35 vol% of an optional co-solvent selected from the group consisting of propylene carbonate, ethyl acetate, methyl acetate, propyl acetate and mixtures thereof; an optional additive selected from the group consisting of triethyl phosphate (TEP), ethoxy(pentafluoro)cyclotriphosphazene (PFPN), 1,3-propanesultone (PS) and mixtures thereof, in an amount of about 10 weight percent (wt%) or less; about 5 wt% or less of an additional co-solvent and / or a lithium-free organic additive and consisting essentially of these components.

2. The lithium salt consists essentially of from about 0.3 M to about 0.6 M of LiPF ６ and from about 0.8 M to about 1.4 M of LiTFSI, and the solvent consists essentially of from about 60 vol% to about 80 vol% of ethyl methyl carbonate and from about 5 vol% to about 20 vol% of fluoroethylene carbonate, the electrolyte according to claim 1.

3. The electrolyte according to claim 2, wherein the optional additive comprises about 0.5 to about 5 wt% of PFPN.

4. The electrolyte according to claim 2, wherein the optional co-solvent comprises about 5 vol% to about 15 vol% of propylene carbonate.

5. The electrolyte according to claim 2, wherein the optional additive comprises about 0.5 wt% to about 3 wt% of TEP.

6. The electrolyte according to claim 2, wherein the optional additive comprises about 0.5 to about 5 wt% of PS.

7. The electrolyte according to any one of claims 1 to 3 or 5 or 6, wherein the solvent consists essentially of about 60 vol% to about 75 vol% of ethyl methyl carbonate, about 10 vol% to about 20 vol% of fluoroethylene carbonate, and 5 vol% to 25 vol% of a co-solvent selected from the group consisting of propylene carbonate, ethyl acetate, methyl acetate, propyl acetate and mixtures thereof.

8. A lithium-ion cell, comprising: a negative electrode comprising about 75 wt% to about 96 wt% of an anode active material, about 0.1 wt% to about 7 wt% of a nanoscale conductive carbon, and about 4 wt% to about 20 wt% of a polymer binder, wherein the anode active material comprises about 45 wt% to about 100% of a silicon-based active material and 0 to about 55 wt% of graphite carbon; a positive electrode comprising a cathode active material, a conductive carbon and a polymer binder, wherein the cathode active material comprises a lithium metal oxide; a separator between the negative electrode and the positive electrode; An electrolyte comprising a lithium salt and a non-aqueous solvent in amounts of about 1.1 M to about 2.2 M, wherein the lithium salt comprises about 60 mol% to about 100 mol% of LiTFSI, and the non-aqueous solvent comprises about 5 vol% to about 25 vol% of fluoroethylene carbonate, 50 vol% to 90 vol% of dimethyl carbonate, ethyl methyl carbonate or a mixture thereof, and an optional co-solvent selected from the group consisting of propylene carbonate, ethyl acetate, methyl acetate, propyl acetate and mixtures thereof in an amount of about 35 vol% or less; A container encapsulating the negative electrode, the positive electrode, the separator and the electrolyte A lithium ion cell having a room temperature discharge specific capacity of at least about 120 mAh / g at a rate of 4C between 2.5 V and a selected charge voltage based on the weight of the cathode active material.

9. The lithium ion cell according to claim 8, wherein the silicon-based active material comprises a silicon-silicon oxide-carbon composite material.

10. The graphite carbon has a BET surface area of about 1 m ２ / g to about 20 m ２ / g, the lithium ion cell according to claim 8.

11. The lithium ion cell according to claim 8, wherein the polymer binder of the negative electrode comprises a blend of polyimide and a water-based polymer binder.

12. The lithium ion cell according to claim 8, wherein the polymer binder of the negative electrode comprises a blend of at least about 50 wt% of polyimide and a second polymer binder selected from the group consisting of polyvinylidene fluoride, cellulose, styrene-butadiene rubber, lithiated polyacrylic acid, copolymers thereof and mixtures thereof, the polyimide has an elongation rate of at least about 40%, and the second polymer binder has a greater elasticity than that of the polyimide.

13. The lithium ion cell according to claim 8, wherein the polymer binder of the negative electrode comprises a water-soluble binder.

14. The lithium ion cell according to claim 13, wherein the water-soluble binder comprises poly(acrylamide-co-acrylate) having at least about 5 mol% of acrylate moieties and at least about 5 mol% of acrylamide moieties.

15. The water-soluble binder contains a metal-polyacrylic acid / acrylate (M-PAA) moiety from the corresponding monomer, and M is a cation of lithium, sodium, potassium, or a mixture thereof. The lithium ion cell according to claim 13.

16. The lithium metal oxide is of the formula LiNi ｘ Mn ｙ Co ｚ O ２ (wherein 0.45 ≦ x, 0.05 ≦ y, z ≦ 0.35, and x + y + z ≒ 1), and the lithium ion cell according to claim 8, comprising lithium nickel cobalt manganese oxide generally represented by the formula.

17. The lithium metal oxide has the formula Li １＋ｂ Ni α Mn β Co γ A δ O ２－ｚ F ｚ (where b + α + β + γ + δ ≒ 1, b ranges from about 0.04 to about 0.3, α ranges from 0 to about 0.4, β ranges from about 0.2 to about 0.65, γ ranges from 0 to about 0.46, δ ranges from about 0 to about 0.15, and z ranges from 0 to 0.2, provided that both α and γ are not 0, and A is a metal different from lithium, manganese, nickel, and cobalt), and further includes a lithium and manganese-rich lithium nickel manganese cobalt oxide represented by the formula, the lithium ion cell according to claim 16.

18. Further comprising a supplementary lithium in an amount of about 80% to about 180% of the irreversible capacity loss of the first cycle of the negative electrode, and having a ratio in the fourth cycle at a discharge rate of C / 3 of the negative electrode capacity divided by the positive electrode capacity of about 1.10 to about 1.

95. The lithium ion cell according to any one of claims 8 to 17.

19. The anode active material contains about 60% to about 95% by weight of a silicon oxide-based material and about 5% to about 40% by weight of graphite. The lithium ion cell according to any one of claims 8 to 17.

20. The solvent consists essentially of about 60% to about 85% by volume of ethyl methyl carbonate, about 10% to about 20% by volume of fluoroethylene carbonate, and an optional co-solvent selected from the group consisting of propylene carbonate, ethyl acetate, methyl acetate, propyl acetate, and mixtures thereof in an amount of 25% by volume or less. The lithium ion cell according to claim 8.

21. The lithium salt is from about 0.3 M to about 0.6 M of LiPF ６ and from about 0.8 M to about 1.4 M of LiTFSI and optionally up to about 5 mole percent of other lithium salts, the lithium ion cell according to claim 20, consisting essentially of.

22. The electrolyte is a lithium salt, a solvent, an optional additive selected from the group consisting of triethyl phosphate (TEP), ethoxy(pentafluoro)cyclotriphosphazene (PFPN), 1,3-propanesultone (PS), and mixtures thereof in an amount of about 10 weight percent (wt%) or less; an additional co-solvent and / or a lithium-free organic additive in an amount of about 5% by weight or less and consists essentially of the lithium ion cell according to claim 21.

23. When cycled at room temperature from the seventh cycle to the seven-hundredth cycle between 2.5 V and the selected charging voltage at a rate of 4C, having at least about 80% of the capacity in the seventh cycle at the seven-hundredth cycle. The lithium ion cell according to claim 8.

24. A lithium ion cell, An anode comprising from about 75 wt% to about 96 wt% active material, from about 0.1 wt% to about 7 wt% nanoscale conductive carbon, and from about 4 wt% to about 20 wt% polymer binder, wherein the active material comprises from about 45 wt% to about 100% silicon-based active material and from 0 wt% to about 55 wt% graphite carbon; A cathode comprising a lithium metal oxide, conductive carbon, and a polymer binder; A separator between the anode and the cathode; An electrolyte comprising from about 1.0 M to about 2.5 M lithium salt and a non-aqueous solvent, wherein the lithium salt comprises from about 60 mole percent to about 100 mole percent LiTFSI, and the non-aqueous solvent comprises from about 5 vol% to about 25 vol% fluoroethylene carbonate; A container encapsulating the anode, the cathode, the separator, and the electrolyte comprising, having a room temperature discharge specific capacity of at least about 120 mAh / g at a rate of 4C between 2.5 V and a selected charge voltage based on the weight of the cathode active material, A lithium ion cell having, at a rate of 4C, at least about 80% of the capacity at the 7th cycle at room temperature when cycled between 2.5 V and the selected charge voltage from the 7th cycle to the 700th cycle.

25. The lithium ion cell according to claim 24, wherein the container is a pouch.

26. The lithium ion cell according to claim 24, wherein the container is a canister, and the anode and the cathode are wound in a cylindrical or prismatic shape.

27. The lithium ion cell according to claim 24, wherein the non-aqueous solvent comprises from about 50 vol% to about 90 vol% dimethyl carbonate, ethyl methyl carbonate, or a mixture thereof, and an optional co-solvent selected from the group consisting of propylene carbonate, ethyl acetate, methyl acetate, propyl acetate, and mixtures thereof, in an amount of 35 vol% or less.

28. The lithium ion cell according to claim 24, wherein the silicon-based active material comprises a silicon-silicon oxide carbon composite material.

29. The graphite carbon is about 1 m ２ / g to about 20 m ２ / g and has a BET surface area, and the lithium ion cell according to claim 24.

30. The lithium ion cell according to claim 24, wherein the polymer binder of the anode comprises a blend of a polyimide and a water-based polymer binder.

31. The polymer binder of the negative electrode includes a blend of at least about 50 wt% polyimide and a second polymer binder selected from the group consisting of polyvinylidene fluoride, cellulose, styrene-butadiene rubber, lithiated polyacrylic acid, copolymers thereof, and mixtures thereof, the polyimide has an elongation rate of at least about 40%, and the second polymer binder has greater elasticity than that of the polyimide, the lithium ion cell according to claim 24.

32. The polymer binder of the negative electrode includes a water-soluble binder, the lithium ion cell according to claim 24.

33. The water-soluble binder includes poly(acrylamide-co-acrylate) having at least about 5 mol% acrylate moiety and at least about 5 mol% acrylamide moiety, the lithium ion cell according to claim 32.

34. The water-soluble binder includes a metal-polyacrylic acid / acrylate (M-PAA) moiety from the corresponding monomer, where M is a cation of lithium, sodium, potassium, or a mixture thereof, the lithium ion cell according to claim 32.

35. The lithium metal oxide is of the formula LiNi ｘ Mn ｙ Co ｚ O ２ (where 0.45 ≦ x, 0.05 ≦ y, z ≦ 0.35, and x + y + z ≒ 1), and the lithium ion cell according to claim 24, which contains lithium nickel cobalt manganese oxide generally represented by this formula.

36. Further includes supplementary lithium in an amount of about 80% to about 180% of the irreversible capacity loss of the first cycle of the negative electrode, having a ratio in the fourth cycle at a discharge rate of C / 3 of the negative electrode capacity divided by the positive electrode capacity of about 1.10 to about 1.95, the lithium ion cell according to any one of claims 24 to 35.

37. The negative electrode active material includes about 60 wt% to about 95 wt% silicon oxide-based material and about 5 wt% to about 40 wt% graphite, the lithium ion cell according to any one of claims 24 to 35.

38. The solvent consists essentially of about 60 vol% to about 85 vol% ethyl methyl carbonate, about 10 vol% to about 20 vol% fluoroethylene carbonate, and an optional co-solvent selected from the group consisting of propylene carbonate, ethyl acetate, methyl acetate, propyl acetate, and mixtures thereof in an amount of 25 vol% or less, the lithium ion cell according to claim 24.

39. The lithium salt consists essentially of about 0.3 M to about 0.6 M of LiPF ６ and about 0.8 M to about 1.4 M of LiTFSI and an optional other lithium salt of about 5 mole percent or less, the lithium ion cell according to claim 38.

40. The electrolyte is a lithium salt, a solvent, An optional additive selected from the group consisting of triethyl phosphate (TEP), ethoxy(pentafluoro)cyclotriphosphazene (PFPN), 1,3-propanesultone (PS), and mixtures thereof, in an amount of about 10 weight percent (wt%) or less; An additional co-solvent and / or a lithium-free organic additive in an amount of about 5 wt% or less The lithium ion cell according to claim 39, consisting essentially of.

41. A lithium ion cell, A negative electrode comprising about 75 wt% to about 96 wt% active material, about 0.1 wt% to about 7 wt% nanoscale conductive carbon, and about 4 wt% to about 20 wt% polymer binder, wherein the active material comprises about 45 wt% to about 100% silicon-based active material and 0 to about 55 wt% graphite carbon, the negative electrode; A positive electrode comprising a lithium metal oxide, conductive carbon, and a polymer binder; A separator between the negative electrode and the positive electrode; An electrolyte comprising a lithium salt and a non-aqueous solvent in amounts of from about 1.1 M to about 2.2 M, wherein the lithium salt comprises from about 90 mole percent to about 100 mole percent of LiPF ６ and the non-aqueous solvent comprises from about 5 vol% to about 25 vol% of fluoroethylene carbonate, from 50 vol% to 80 vol% of dimethyl carbonate, ethyl methyl carbonate or a mixture thereof, from about 5 vol% to about 15 vol% of propylene carbonate and from about 5 vol% to about 20 vol% of methyl acetate, ethyl acetate, propyl acetate or a mixture thereof; A container enclosing the negative electrode, the positive electrode, the separator, and the electrolyte Including, having a room temperature discharge specific capacity of at least about 120 mAh / g at a rate of 4C between 2.5V and a selected charge voltage based on the weight of the cathode active material, and at a rate of 1C, when cycled at room temperature from the 7th cycle to the 650th cycle between 2.5V and the selected charge voltage, having at the 650th cycle at least about 80% of the capacity at the 7th cycle. A lithium ion cell.

42. The non-aqueous solvent of the lithium ion cell according to claim 41, comprising about 50 vol% to about 90 vol% of dimethyl carbonate, ethyl methyl carbonate, or a mixture thereof, and an optional co-solvent selected from the group consisting of propylene carbonate, ethyl acetate, methyl acetate, propyl acetate, and mixtures thereof, in an amount of about 35 vol% or less.

43. The lithium ion cell according to claim 41, wherein the silicon-based active material comprises a silicon-silicon oxide carbon composite material.

44. The graphite carbon is about 1 m ２ / g to about 20 m ２ / g and has a BET surface area, and the lithium ion cell according to claim 41.

45. The lithium ion cell according to claim 41, wherein the polymer binder of the negative electrode comprises a blend of a polyimide and a water-based polymer binder.

46. The polymer binder of the negative electrode includes a blend of at least about 50 wt% of polyimide and a second polymer binder selected from the group consisting of polyvinylidene fluoride, cellulose, styrene-butadiene rubber, lithiated polyacrylic acid, copolymers thereof, and mixtures thereof, the polyimide has an elongation rate of at least about 40%, and the second polymer binder has an elasticity greater than that of the polyimide, the lithium ion cell according to claim 41.

47. The polymer binder of the negative electrode includes a water-soluble binder, the lithium ion cell according to claim 41.

48. The water-soluble binder includes poly(acrylamide-co-acrylate) having at least about 5 mol% acrylate moiety and at least about 5 mol% acrylamide moiety, the lithium ion cell according to claim 47.

49. The water-soluble binder includes a metal-polyacrylic acid / acrylate (M-PAA) moiety from the corresponding monomer, where M is a cation of lithium, sodium, potassium, or a mixture thereof, the lithium ion cell according to claim 47.

50. The lithium metal oxide is of the formula LiNi ｘ Mn ｙ Co ｚ O ２ (where 0.45 ≦ x, 0.05 ≦ y, z ≦ 0.35, and x + y + z ≒ 1), and includes lithium nickel cobalt manganese oxide, the lithium ion cell according to claim 41.

51. Further includes supplementary lithium in an amount of about 80% to about 180% of the irreversible capacity loss of the first cycle of the negative electrode, having a ratio in the fourth cycle at a discharge rate of C / 3 of the negative electrode capacity divided by the positive electrode capacity of about 1.10 to about 1.95, the lithium ion cell according to any one of claims 41 to 50.

52. The active material includes about 60 wt% to about 95 wt% of a silicon oxide-based material and about 5 wt% to about 40 wt% of graphite, the lithium ion cell according to claim 41.

53. The solvent consists essentially of about 60 vol% to about 75 vol% of ethyl methyl carbonate and about 10 vol% to about 20 vol% of fluoroethylene carbonate, the lithium ion cell according to claim 41.

54. The electrolyte is a lithium salt, a solvent, an optional additive selected from the group consisting of triethyl phosphate (TEP), ethoxy(pentafluoro)cyclotriphosphazene (PFPN), 1,3-propanesultone (PS), and mixtures thereof in an amount of about 10 weight percent (wt%) or less; an additional co-solvent and / or a lithium-free organic additive in an amount of about 5 wt% or less The lithium ion cell according to claim 53, which consists essentially of