Cyclability improvement of high voltage lithium cobalt oxide/graphite battery by use of lithium difluoro(oxalate)borate electrolyte additive

In order to overcome severe capacity fading of LiCoO 2 /graphite lithium-ion battery at a high voltage, lithium difluoro(oxalate)borate (LiDFOB) was investigated as an electrolyte additive. Electrochemical tests demonstrate that by adding 1 wt.% LiDFOB into a carbonate electrolyte, the capacity retention of the battery after 300 cycles at 1 C between 3.0 and 4.5 V is improved from 42.1 to 80.2%. With the help of computational calculations and physical characterization techniques, we found that the LiDFOB strongly coordinates with Co ions, which inhibits the dissolution of cobalt from bulk LiCoO 2 and prevents Co deposition on the anode. Meanwhile, the LiDFOB additive form stable, uniform, and thin surface films simultaneously on positive and negative of the LiCoO 2 /graphite battery, inhibiting the electrolyte decomposition and leading to the improvement of the batteries performance.