Using Triallyl Phosphate as Electrolyte Additive to Stabilize Electrode–Electrolyte Interface of LiNi_0.5Mn_1.5O₄/Graphite High Voltage Lithium Ion Cells

Using high voltage cathode materials is one of the main ways to improve energy density of Li ion batteries. However, the oxidation of commercial carbonate electrolyte on the cathode makes the batteries suffer serious capacity degradation. In this work triallyl phosphate (TAP) as an electrolyte additive is used to improve the cycle life of LiNi0.5Mn1.5O4 (LNMO)/graphite high voltage lithium ion cell. 1.0 wt % TAP has the best effect; it increases the retention rate of discharge capacity of the cell by about 20% compared with that without additive after 150 cycles at 0.2C. The results of electrochemical measurements, several spectral analyses, and theoretical calculation show that TAP can be electrochemically oxidized prior to the solvents EC and EMC and quickly forms a low molecular weight polymer deposit layer on the cathode, which can effectively prevent electrolyte oxidation and LNMO dissolution. In the absence of interference from electrolyte oxidation products, a dense SEI layer can be formed on the graphite anode whether TAP exists or not. Therefore, although TAP can also be electrochemically reduced to change the composition of the anode SEI layer, the improvement of the cycling performance of LNMO/graphite cell should be attributed to the oxidation reaction of TAP on the cathode.