Triethanolamine borate as a surface stabilizing bifunctional additive for Ni‐rich layered oxide cathode

Ni-rich cathode materials have been receiving substantial highlight because of its large specific capacity, however, they suffer from inferior cycling results owing to occurring undesired reactions in the cell. Herein, triethanolamine borate (TEAB), containing borate and ethanolamine groups, is proposed as a functional additive because it spontaneously suppresses electrolyte decomposition while inhibiting Ni dissolution in Ni-rich cathodes. The electrochemical oxidation of TEAB first generates borate-based cathode-electrolyte interphases for the Ni-rich cathode, which effectively suppress the electrolyte decomposition. A cell controlled with TEAB showed a greatly decreased internal pressure, which improved the safety performance of the cell. Notably, even the inclusion of 0.1% TEAB in the cell markedly increased the cycling performance from 32.0% to 63.2%. Cells cycled with TEAB showed stable retention rate after 100 cycles at high temperature. Results of high-temperature storage of the cells confirmed improvements as changes in the open-circuit potentials, thickness of the cell, and the recovery rate for specific capacity. TEAB is also efficient for suppressing Ni dissolution because TEAB selectively scavenges fluoride species by a chemical scavenging reaction. The cell evaluated with TEAB-containing electrolyte exhibited a releasing 140.3 ppm of dissolved Ni, whereas the cell evaluated with bare electrolyte released 643.6 ppm.