Enhanced performance of natural graphite in Li-ion battery by oxalatoborate coating

We report an effect of surface modification on the performance of natural graphite in Li-ion battery. A graphite electrode was treated with a mixed solution of H3BO3 and H2C2O4 (2:3 molar ratio) in methanol, followed by condensation at 100–110 °C under vacuum. The above treatments result in formation of oxalatoborate coating on the graphite surface. It is shown that the resulting coating can effectively increase reversibility of the initial forming cycle of Li/graphite half-cell. More interestingly, such a coating significantly suppresses self-delithiation of the lithiated graphite, which hence increases the storage performance of Li-ion battery, especially at elevated temperatures. With progressive cycling, the coated graphite shows excellent capacity retention while the control one starts fast capacity fading from around 70th cycle.