Formation mechanism of protective interphase for high voltage cathodes by phenyl trifluoromethyl sulfide

The formation mechanism of protective interphases on high voltage cathodes of lithium ion batteries, resulting from phenyl trifluoromethyl sulfide (PTS) as an electrolyte additive, is understood through theoretical calculations, and confirmed by evaluating the cyclic stability of a lithium-rich cathode, Li1·2Mn0·54Ni0·13Co0·13O2, in the electrolytes with and without PTS. It is found that PTS is oxidized through the transferring of one fluorine atom from methyl to phenyl and the subsequent breaking of bond S–C in phenyl, yielding fluorobenzene and sulfur-contained radical that construct mainly the protective interphase. With this interphase formed from PTS, the cyclic stability of Li1·2Mn0·54Ni0·13Co0·13O2 is significantly improved. The capacity retention of Li1·2Mn0·54Ni0·13Co0·13O2 in 1.0 M LiPF6-EC/EMC/DEC (3/5/2 by weight) at 0.5C after 200 cycles is enhanced from 39% to 83% by adding 0.5% PTS.