BACKGROUND

Field

The present application relates generally to electrolytes for energy storage devices. In particular, the present application relates to electrolytes and additives for use in lithium-ion energy storage devices with silicon-based anode materials.

Description of the Related Art

As the demands for both zero-emission electric vehicles and grid-based energy storage systems increase, lower costs and improvements in energy density, power density, and safety of lithium (Li)-ion batteries are highly desirable. Enabling the high energy density and safety of Li-ion batteries requires the development of high-capacity, and high-voltage cathodes, high-capacity anodes and accordingly functional electrolytes with high voltage stability, interfacial compatibility with electrodes and safety.

A lithium-ion battery typically includes a separator and/or electrolyte between an anode and a cathode. In one class of batteries, the separator, cathode and anode materials are individually formed into sheets or films. Sheets of the cathode, separator and anode are subsequently stacked or rolled with the separator separating the cathode and anode (e.g., electrodes) to form the battery. Typical electrodes include electro-chemically active material layers on electrically conductive metals (e.g., aluminum and copper). Films can be rolled or cut into pieces which are then layered into stacks. The stacks are of alternating electro-chemically active materials with the separator between them.

Si is one of the most promising anode materials for Li-ion batteries due to its high specific gravimetric and volumetric capacity (3579 mAh/g and 2194 mAh/cm3vs. 372 mAh/g and 719 mAh/cm3for graphite), and low lithiation potential (<0.4 V vs. Li/Li+). Among the various cathodes presently available, layered lithium transition-metal oxides such as Ni-rich Li[NixCoyMn(Al)1-x-y]O2(NCM or NCA) are the most promising ones due to their high theoretical capacity (˜280 mAh/g) and relatively high average operating potential (3.6 V vs Li/Li+). Coupling Si anodes with high-voltage Ni rich NCM (or NCA) cathodes can deliver more energy than conventional Li-ion batteries with graphite-based anodes, due to the high capacity of these new electrodes. However, both Si-based anodes and high-voltage Ni rich NCM (or NCA) cathodes face formidable technological challenges, and long-term cycling stability with high-Si anodes paired with NCM or NCA cathodes has yet to be achieved.

For anodes, silicon-based materials can provide significant improvement in energy density. However, the large volumetric expansion (>300%) during the Li alloying/dealloying processes can lead to disintegration of the active material and the loss of electrical conduction paths, thereby reducing the cycling life of the battery. In addition, an unstable solid electrolyte interphase (SEI) layer can develop on the surface of the cycled anodes, and leads to an endless exposure of Si particle surfaces to the liquid electrolyte. This results in an irreversible capacity loss at each cycle due to the reduction at the low potential where the liquid electrolyte reacts with the exposed surface of the Si anode. In addition, oxidative instability of the conventional non-aqueous electrolyte takes place at voltages beyond 4.5 V, which can lead to accelerated decay of cycling performance. Because of the generally inferior cycle life of Si compared to graphite, only a small amount of Si or Si alloy is used in conventional anode materials.

The NCM (or NCA) cathode usually suffers from an inferior stability and a low capacity retention at a high cut-off potential. The reasons can be ascribed to the unstable surface layer's gradual exfoliation, the continuous electrolyte decomposition, and the transition metal ion dissolution into electrolyte solution. In order to make good use of Si anode//NCM or NCA cathode-based Li-ion battery systems, the aforementioned barriers need to be overcome.

One strategy for overcoming these barriers includes exploring new electrolyte additives in order to make good use of Si anode//NCM or NCA cathode-based full cells. The next generation of electrolyte additives to be developed should be able to form a uniform, stable SEI layer on the surface of Si anodes. This layer should have low impedance and be electronically insulating, but ionically conductive to Li-ion. Additionally, the SEI layer formed by the additive should have excellent elasticity and mechanical strength to overcome the problem of expansion and shrinkage of the Si anode volume. On the cathode side, the ideal additives should be oxidized preferentially to the solvent molecule in the bare electrolyte, resulting in a protective cathode electrolyte interphase (CEI) film formed on the surface of the NCM (or NCA). At the same time, it should help alleviate the dissolution phenomenon of transition metal ions and decrease surface resistance on cathode side. In addition, they could help improve the physical properties of the electrolyte such as ionic conductivity, viscosity, and wettability.

SUMMARY

In some aspects, energy storage devices are provided. In some embodiments, the energy storage device includes a first electrode and a second electrode, wherein at least one of the first electrode and the second electrode is a Si-based electrode. In some embodiments, the energy storage device includes a separator between the first electrode and the second electrode. In some embodiments, the energy storage device includes an electrolyte. In some embodiments, the energy storage device includes at least one electrolyte additive comprising a compound selected from Formulae (A), (B) and (C):



In some embodiments, each R1and R2is independently selected from the group consisting of


and absent thereby leaving a negative charge. In some embodiments, R is a C1-C3 alkyl. In some embodiments, X is selected from the group consisting of an alkylene optionally substituted by


or chloroalkyl, a cycloalkylene, and a heteroalkylene with at least one —O—.

In some embodiments, the second electrode is a Si-dominant electrode. In some embodiments, the second electrode comprises a self-supporting composite material film. In some embodiments, the composite material film comprises greater than 0% and less than about 90% by weight of silicon particles, and greater than 0% and less than about 90% by weight of one or more types of carbon phases, wherein at least one of the one or more types of carbon phases is a substantially continuous phase that holds the composite material film together such that the silicon particles are distributed throughout the composite material film.

In some embodiments, the electrolyte further comprises fluoroethylene carbonate (FEC). In some embodiments, the electrolyte is substantially free of non-fluorine containing cyclic carbonate.

In some embodiments, the electrolyte additive is selected from the group consisting of diallyl carbonate (DAC); diallyl pyrocarbonate (DAPC); diallyl (oxybis(ethane-2,1-diyl)) dicarbonate; 2-prop-2-enoxycarbonyloxyethyl prop-2-enyl carbonate; di(ethylene glycol) bis(allyl carbonate); 2-[2-(2-prop-2-enoxycarbonyloxyethoxy)ethoxy]ethyl prop-2-enyl carbonate; (prop-2-enoxycarbonylamino) prop-2-enyl carbonate; [4-(prop-2-enoxycarbonyloxymethyl)cyclohexyl]methyl prop-2-enyl carbonate; (2-methylcycloocten-1-yl) prop-1-en-2-yl carbonate; (2-methylcyclohepten-1-yl) prop-1-en-2-yl carbonate; prop-1-en-2-yl (2,6,6-trimethylcyclohexen-1-yl) carbonate; 2-methylallyl 2-methylcyclohex-1-enyl carbonate; prop-2-enyl (2,2,2-trichloro-1-propenoxycarbonyloxyethyl) carbonate; 2,5,8-trioxa-nonanedioic acid dimethallyl ester; 2-[2-(prop-2-enoxycarbonylamino)ethoxycarbonyloxy]ethyl 2-methylprop-2-enoate; Allyl cyclohexylidenemethyl carbonate; Allyl 6-methyl-1-cyclohexenyl carbonate; Allyl 2-ethylcyclohex-1-enyl carbonate; (2-Methylcyclohepten-1-yl) prop-1-en-2-yl carbonate; Allyl cyclopent-1-en-1-yl carbonate; Allyl cyclohex-1-en-1-yl carbonate; Allyl (4-phenylbut-3-en-2-yl) carbonate; Allyl 2-methyl-3,4-dihydronaphthalen-1-yl carbonate; Dimethallyl carbonate 4-prop-2-enoyloxybutyl 2-methylprop-2-enoate; [3-prop-2-enoxycarbonyloxy-2,2-bis(prop-2-enoxycarbonyloxymethyl)propyl] prop-2-enyl carbonate; prop-2-enyl 2-prop-2-enoxycarbonyloxypropanoate; and prop-2-enyl 2-prop-2-enoxycarbonyloxyprop-2-enoate.

