Unanticipated Mechanism of the Trimethylsilyl Motif in Electrolyte Additives on Nickel-Rich Cathodes in Lithium-Ion Batteries

The introduction of a trimethylsilyl (TMS) motif in electrolyte additives for lithium-ion batteries is regarded as an effectual approach to remove corrosive hydrofluoric acid (HF) that structurally and compositionally damages the electrode–electrolyte interface and gives rise to transition metal dissolution from the cathode. Herein, we present that electrolyte additives with TMS moieties lead to continued capacity loss of polycrystalline (PC)-LiNi0.8Co0.1Mn0.1O2 (NCM811) cathodes coupled with graphite anodes compared to additives without TMS as the cycle progresses. Through a comparative study using electrolyte additives with and without TMS moieties, it is revealed that the TMS group is prone to react with residual lithium compounds, in particular, lithium hydroxide (LiOH) on the PC-NCM811 cathode, and the resulting TMS-OH triggers the decomposition of PF5 created by the autocatalytic decomposition of LiPF6 that generates reactive species, namely, HF and POF3. This work aims to offer a way to build favorable interface structures for Ni-rich cathodes covered with residual lithium compounds through a study to figure out the roles of TMS moieties of electrolyte additives.