Elucidating the Effect of Borate Additive in High‐Voltage Electrolyte for Li‐Rich Layered Oxide Materials

Lithium-rich layered oxides (LRLO) have attracted great interest for high-energy Li-ion batteries due to their high theoretical capacity. However, capacity decay and voltage fade during the cycling impede the practical application of LRLO. Herein, the use of lithium bis-(oxalate)borate (LiBOB) as an electrolyte additive is reported to improve the cycling stability in high voltage LRLO/graphite full cells. The cell with LiBOB-containing electrolyte delivers 248 mAh g(-1) initial capacity and shows no capacity decay after 70 cycles as well as 95.5% retention after 150 cycles over 4.5 V cycling. A systematic mechanism study for the LiBOB-enabled cycling performance improvement is conducted. Analytical electron microscopy under cryo-condition confirms the formation of a uniform interphase and less phase transformation on the LRLO particle, accompanied by less voltage decay in the cathode. The formation of B-F species is identified in the cycled electrolyte, elucidating the HF scavenger effect of LiBOB. Due to less HF corrosion on both electrode interphases, a reduced amount of transition metal dissolution and redeposition on the graphite is proved, thereby mitigating the capacity decay in LRLO/graphite full cells. These findings suggest that the borate additive is a promising strategy to optimize high voltage electrolyte for the industrialization of LRLO.