A bi-functional lithium difluoro(oxalato)borate additive for lithium cobalt oxide/lithium nickel manganese cobalt oxide cathodes and silicon/graphite anodes in lithium-ion batteries at elevated temperatures

The Role of Additives in Improving Performance in High Voltage Lithium-Ion Batteries with Potentiostatic Holds

“…This work investigates some conclusions in the available literature of an additive molecule that decomposes on the charged cathode surface and passivates the surface against electrolyte oxidation. With the goal of increasing battery energy density for transportation applications, layered transition metal oxides cathodes of the form LiMO 2 (M = Ni, Co, Mn) have received significant attention.1-7 While these cathode materials have a high theoretical gravimetric capacity of ∼280 mAh/g, 8 achieving the high capacity of these materials requires very high charging voltages (>4.5V vs. Li + /Li), 2-4 above the stability range of conventional carbonate electrolytes.9,10 Enabling the additional high voltage capacity of the cathode materials requires new electrolytes that provide additional stability at high voltages at the charged cathode surface.The approach to creating compatible electrolytes has mainly fallen along two separate paths: either increasing the intrinsic anodic stability of the electrolyte, [11][12][13][14][15][16][17] or using a sacrificial component in small amounts (an additive) to "passivate" the cathode surface and inhibit continual electrolyte oxidation.18 20,32 have shown evidence of decomposition on various high voltage cathode surfaces through a variety of surface characterization techniques, including attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS).However, this cathode "passivation" is conventionally inferred through a combination of experimental results, such as increased capacity retention, voltammetric methods indicating a lower anodic stability attributed to additive oxidation, changes to the XPS and/or FTIR spectra of the cathode that include components of the additive, and decreased impedance after cycling. While the results provided by the previously mentioned characterization methods can be reconciled with the conclusion that cathode "passivation" led to the improvement, this mechanistic process can be more accurately evaluated by monitoring the electrolyte oxidation current at a charged cathode surface through potentiostatic holds.…”

“…18 20,32 have shown evidence of decomposition on various high voltage cathode surfaces through a variety of surface characterization techniques, including attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS).…”

“…[18][19][20][21][22][23] Among additives tested, vinylene carbonate, 21,24,25 phosphites, [26][27][28][29] fluorinated carbonates, 30,31 and borates 20,32 have shown evidence of decomposition on various high voltage cathode surfaces through a variety of surface characterization techniques, including attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS).…”

“…In this work, both of these components are evaluated separately, with the passivation determined during the potentiostatic hold, and the functionality determined during the z E-mail: zzhang@anl.gov post-hold cycling. In this way, this protocol distinguishes cathode passivation from other known mechanisms of performance improvement through the use of additives, including HF scavenging, [33][34] anode solid-electrolyte interphase (SEI) formation, 20,24,33 or prevention of transition metal ion dissolution. 26 For every electrolyte oxidation reaction, there is a compensating reduction reaction, and charge neutrality dictates that the electron transfer will not lead to net charging of either the electrolyte or the electrode.…”

Studies of the Capacity Fade Mechanisms of LiCoO2/Si-Alloy: Graphite Cells

“…For this reason, most of the full cells using nanosized silicon or micron sized silicon negative electrodes show poor capacity retention. 17,25,[34][35][36][37][38][39] …”