New class of nonaqueous electrolytes for long-life and safe lithium-ion batteries

Long-life and safe lithium-ion batteries have been long pursued to enable electrification of the transportation system and for grid applications. However, the poor safety characteristics of lithium-ion batteries have been the major bottleneck for the widespread deployment of this promising technology. Here, we report a novel nonaqueous Li2B12F12-xHx electrolyte, using lithium difluoro(oxalato)borate as an electrolyte additive, that has superior performance to the conventional LiPF6-based electrolyte with regard to cycle life and safety, including tolerance to both overcharge and thermal abuse. Cells tested with the Li2B12F9H3-based electrolyte maintained about 70% initial capacity when cycled at 55 °C for 1,200 cycles, and the intrinsic overcharge protection mechanism was active up to 450 overcharge abuse cycles. Results from in situ high-energy X-ray diffraction showed that the thermal decomposition of the delithiated Li1-x[Ni1/3Mn1/3Co1/3]0.9O2 cathode was delayed by about 20 °C when using the Li2B12F12-based electrolyte. Safe lithium-ion batteries require stable electrolytes with high chemical resistance and high thermal tolerance. Chen et al. find a solid lithium-salt electrolyte that is able to give rise to a prolonged battery life and a delayed decomposition of battery cathodes.