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

Summary 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. Triethanolamine borate (TEAB), a bifunctional additive containing borate and ethanolamine groups, is proposed which can spontaneously suppress electrolyte decomposition and inhibit Ni dissolution in Ni‐rich cathodes. The electrochemical oxidation of TEAB first generates borate‐based cathode‐electrolyte interphases for the Ni‐rich cathode and it effectively suppresses the electrolyte decomposition occurring at the interface between the cathode and the electrolyte. A cell controlled with TEAB showed a greatly decreased internal pressure, which improved the safety performance of the cell. High temperature storage tests confirmed improvements as changes in the open‐circuit potential, in the cell thickness, and in the recovery rate for specific capacity. As a result, even the inclusion of 0.1% TEAB in the cell markedly increases the cycling performance from 32.0% to 63.2%.