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 LiCoO2/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 LiCoO2 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 LiCoO2/graphite battery, inhibiting the electrolyte decomposition and leading to the improvement of the batteries performance.