Diethyl (4-isopropylbenzyl) phosphonate as an electrolyte additive for LiNi0.5Mn1.5O4 cathode for high-voltage Li-ion battery

Diethyl (4-isopropylbenzyl) phosphonate (DLPP) was applied as a positive film forming additive for LiNi_0.5Mn_1.5O₄ (LNMO) cathode. The rate and cycling performances of LNMO have been improved by adding 1 wt.% DLPP in carbonate electrolyte. The DFT calculation and LSV test shows that DLPP can preferentially oxidize decomposition during charging process, which inhibits the continuous electrolyte decomposition and promotes the formation of a protective cathode layer. LNMO/Li half-cell using the electrolyte with 1 wt.% DLPP delivers better rate capabilities and capacity retention of 92.8% after 200 cycles at 3 C (86.8% with STD electrolyte). SEM and XRD tests of the electrode after cycling show that DLPP can significantly stabilize the LNMO/electrolyte interface and crystal structures.