Tris(trimethylsilyl)phosphate (TMSP) has been investigated as an additive to form a modified solid electrolyte interface (SEI) on lithium rich cathode material Li[Li0.2Ni0.13Mn0.54Co0.13]O2 and improve its electrochemical performances. Linear sweep voltammetry (LSV) results show that TMSP additive decomposes at the potential ca. 4.1V, lower than that of electrolyte solvent decomposition. The morphology images via TEM clearly demonstrate a continuous interfacial layer formed on the cathode surface after initial cycles. XPS results prove that the components of SEI are mainly derived from the decomposition of TMSP. The Li[Li0.2Ni0.13Mn0.54Co0.13]O2 cathode materials cycled in 1.0 wt% TMSP-containing electrolyte demonstrate obvious enhancement in its cycling stability and capacity retention reaches 91.1% after 50 cycles. The improved performances are ascribed to modified SEI which tightly covers on cathode particle, and effectively avoids a direct contact between cathode active material and electrolyte, leading to the stabilized interfacial structures.