New Electrolyte Additives for High Voltage Lithium Ion Batteries

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The degradation of lithium ion batteries (LIBs) with cycling results from reactions of electrolyte at both anode and cathode, leading to increased cell impedance from continual formation of solid electrolyte interphases (SEIs). One of the economic ways to improve battery cycling performance is to utilize sacrificial additives that could form thin and stable SEIs to prevent continual electrolyte reactions at both electrodes. In this presentation, three trimethylsilyl based malonate esters have been used as additives in 1.0 M LiPF6/ethylene carbonate (EC)-dimethyl carbonate (DMC)-diethyl carbonate (DEC) (1-1-1, by v) baseline electrolyte for LiNi0.80Co0.15Al0.05O2 (NCA) based high voltage lithium ion batteries. The NCA half-cells with 5 wt.% additive exhibit higher capacity retention than that in the baseline electrolyte at different upper cut off voltages, that is, 4.2, 4.3, 4.4 and 4.5 V vs. Li/Li+. Scanning electron microscope (SEM) show that the additive successfully prevents the formation of thick solid electrolyte interphase (SEI) films on the surface of the NCA electrodes. X-ray diffraction (XRD) further reveals that the crystal structure of NCA is also maintained in the electrolyte with 5 wt.% additive at high cut off voltages. Besides beneficial to NCA cathode, the BTMSMFM additive also ensures better cycling performance of the graphite based half-cells and NCA/graphite full-cells, and thus is a promising additive for application in rechargeable lithium ion batteries.