Effects of Charge Cutoff Potential on an Electrolyte Additive for LiNi0.6Co0.2Mn0.2O2-Mesocarbon Microbead Full Cells

摘要

Tris(trimethylsilyl)phosphite (TMSPi) has been reported to be an excellent electrolyte additive. However, scarce reports exist on the effect of the charge cutoff potential on the cyclic stability using high-performance LiNi0.6Co0.2Mn0.2O2 (NCM622)-mesocarbon microbead (MCMB) full cells. Herein, a high-loading and repeatable NCM622-MCMB coin-type full cell is successfully prepared, and the role of TMSPi on such a full cell at charge cutoff potentials of 4.25 and 4.45 V is studied. Theoretical calculations and detailed analyses reveal that it is oxidized in the first charging process due to its unsaturated P-O bonds, thus forming a stable P-O-F-rich cathode electrolyte interphase and preventing severe decomposition of the electrolyte over NCM622 during long-term cycling. In addition, the P-O and Si-O bonds of TMSPi both display HF-scavenging ability. Moreover, TMSPi may react directly with the LiPF6-based electrolyte to form some intermediate products that can be reduced on the MCMB electrode, thereby modifying the solid electrolyte interphase and improving the stability of MCMB during lithium intercalation.