Phosphite　derivatives　as　film　forming　additives　can　effectively　improve　the　electrochemical　performance　of　cathodes　in　Li-ion　batteries　(LIBs).　In　this　work,　ethyl　bis(trimethylsilyl)　phosphite　(TMSPE),　which　contains　trimethylsilyl　and　ethyl　functional　groups,　is　used　as　a　P-based　additive　for　improving　the　electrochemical　performance　of　a　Li1.144Ni0.136Co0.136Mn0.544O2　cathode.　Further,　the　comparative　evaluation　of　tris(trimethylsilyl)　phosphite　(TMSPi),　TMSPE,　and　triethyl　phosphite　(TEP)　as　phosphite-based　additives　for　Li1.144Ni0.136Co0.136Mn0.544O2/Li　cells　at　45　degrees　C　under　a　high　voltage　is　also　presented.　Theoretical　calculations　and　surface　characterization　revealed　that　TMSPE　formed　a　thinner　and　stable　cathode　electrolyte　interphase　(CEI)　on　the　surface　of　Li1.144Ni0.136Co0.136Mn0.544O2,　which　has　lower　interfacial　impedance,　stronger　HF　elimination,　and　transition　metal　dissolution　inhibition,　resulting　in　the　best　cell　performance　among　the　three　phosphite-based　additives.