Boosting fast electrode reaction kinetics of silicon suboxide anodes by fluoroethylene carbonate-based electrolyte

Abstract

The growing demand for electric vehicles has led to an urgent need for higher-energy-density batteries. Silicon (Si) has been regarded as an alternative to graphite as an anode material owing to its high theoretical capacity. Nevertheless, the large volume change in Si during repeated charge/discharge causes serious particle fracture, leading to rapid capacity degradation. Silicon suboxide (SiOx) anodes show better cycling performance than Si because of their alleviated volume variation, yet still have unsatisfactory electrode reaction kinetics. Herein, fluoroethylene carbonate (FEC)-based electrolyte is proposed to enhance the electrochemical properties of SiOx anodes. A higher specific capacity of ∼1500 mAh g−1 at 0.5 A g−1 and an excellent rate capability of ∼1050 mAh g−1 at 4 A g−1 are obtained for the SiOx anode, which ensures an 83.5% capacity retention of SiOx||LiFePO4 cells after 300 cycles. The theoretical calculations and experimental studies reveal that FEC forms a weakly solvating electrolyte, enabling easier Li-ion desolvation and fast electrode reaction kinetics. Moreover, FEC reinforces the Li+-anion coordination owing to its weak solvating capability, thus a LiF-rich electrode/electrolyte interphase is formed through the co-decomposition of FEC and PF6− anions, leading to a tough SEI film formation with rapid ionic conductivity and good mechanical property.