A Novel Electrolyte Additive Enables High-Voltage Operation of Nickel-Rich Oxide/Graphite Cells.

Nickel-rich oxide/graphite cells under high voltage operation provide high energy density but present short cycle life because of the parasitic electrolyte decomposition reactions. In this work, we report a novel electrolyte additive, N,O-bis(trimehylsilyl)-trifluoroacetamide (NOB), which enables nickel-rich oxide/graphite cells to operate stably under high voltage. When evaluated in a nickel-rich oxide-based full cell, LiNi0.5Co0.2Mn0.3O2 (NCM523)/graphite using a carbonate electrolyte, 1 wt % NOB provides the cell with capacity retention improved from 38% to 73% after 100 cycles at 1C under 4.5 V. It is found that NOB is able to eliminate hydrogen fluoride in the electrolyte. The radicals resulting from the interaction of NOB with the fluoride ion can be preferentially oxidized on the cathode compared with the electrolyte solvents, with its reaction products constructing N-containing interphases simultaneously on the cathode and anode, which suppress the parasitic electrolyte decomposition reactions, leading to the significantly improved cycle stability of nickel-rich oxide/graphite cells under high voltage.

Tailoring Low-Temperature Performance of a Lithium-Ion Battery via Rational Designing Interphase on an Anode.

Performances of lithium-ion batteries at subambient temperatures are extremely restricted by the resistive interphases originated from electrolyte decomposition, especially on the anode surface. This work reports a novel strategy that an anode interphase of low impedance is constructed by applying an electrolyte additive dimethyl sulfite (DMS). Electrochemical measurements indicate that the as-constructed interphase provides graphite/LiNi0.5Co0.2Mn0.3O2 pouch cells with excellent low-temperature performance, outperforming the interphase constructed by 1,3,2-dioxathiolane 2,2-dioxide (DTD), a common commercially used electrolyte additive. Spectral characterizations in combination with theoretical calculations demonstrate that the improved performance is attributed to the unique molecular structure of DMS, which presents appropriate reduction activity and constructs the more stable and ionically conductive anode interphase due to the weaker combination of its reduction product with lithium ions than DTD. This rational design of interphases via an additive structure has been proven to be a low cost but rather an effective approach to tailor the performances of lithium-ion batteries.