Tris(trimethylsilyl)borate (TMSB) is applied to suppress the self-discharge of charged LiNi1/3Co1/3Mn1/3O2 (LNCM) under high potential. The contribution of TMSB is understood via physical and electrochemical characterizations. It is found that the charged LNCM under 4.5V suffers serious self-discharge: potential drops to 0.5V and crystal structure collapses, but this self-discharge is effectively suppressed by applying TMSB in a standard (STD) electrolyte. Different from the failure from cycling, which is caused mainly by the electrochemical oxidation decomposition of electrolyte, the self-discharge results from the interaction between charged LNCM and electrolyte. TMSB is preferentially oxidized in comparison with STD electrolyte, generating a solid electrolyte interphase film on LNCM, which avoids the direct contact between LNCM and electrolyte and thus suppresses the self-discharge of the charged LNCM.