Bicomponent electrolyte additive excelling fluoroethylene carbonate for high performance Si-based anodes and lithiated Si-S batteries

Si-based anode materials for advanced high energy Li-ion batteries and Li-S battery as a promising candidate for “beyond LIBs” have been intensively studied in recent years. Although FEC electrolyte additive plays an important role in improving the cycle stability of Si-based electrodes, its high temperature behavior is still unsatisfactory. Herein, a new bicomponent additive (LiPO₂F₂ + DMTFA) is proposed to replace FEC in LiPF₆/carbonate electrolyte. The resulting electrolyte shows high ionic conductivity (10.9 mS cm^-1), good anti-oxidation capability (>5 V vs. Li/Li⁺) and excellent compatibility with Si-based anodes even at elevated temperature. Moreover, this electrolyte is also fit for S@pPAN cathode developed for Li-S batteries. An in-situ lithiated Si-S@pPAN cell containing the proposed electrolyte delivers a high reversible capacity of about 1400 mA h g^-1 _sulfur with retention of 92.1% for 1000 cycles at 1 C and about 1350 mA h g^-1 _sulfur with a capacity retention of 94.8% for 2000 cycles at 2 C. Its rate performance has been also improved greatly. This cell system avoids some fatal flaws of conventional Li-S cells, including the Li dendrite formation and thermal instability. It is promising for the practical application.