Optimal concentration of electrolyte additive for cyclic stability improvement of high-voltage cathode of lithium-ion battery

Additives that can be oxidized preferentially to the baseline electrolyte are possible of forming a protective cathode interphase, but less attention has been paid to the effect of the additive concentration. Herein, this issue is addressed by evaluating the effect of an easily oxidizable electrolyte additive, tripropyl borate (TPB), on the cyclic stability of high-voltage cathode, LiNi0.5Mn1.5O4. It is found that the optimal concentration of TPB is 1 wt.% for the best cyclic stability of LiNi0.5Mn1.5O4 and the discharge capacity of LiNi0.5Mn1.5O4 will decrease when TPB concentration is lower or higher than this concentration. This effect is related to the resulting interphase from TPB, which cannot provide sufficient protection for the structural integrity of LiNi0.5Mn1.5O4 when it is formed in the electrolyte with lower concentrations of TPB, while shows an increased interfacial impedance of LiNi0.5Mn1.5O4/electrolyte when it is formed from higher concentrations of TPB.