Synergistic effect of reducing volume expansion and improving electrochemical performance through a LiF-based SEI formation on SiOx/C electrodes

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SiOx/C electrodes are widely used due to their high lithium storage capacities and cycling stabilities. However, the SiOx/C electrode exhibits large volume expansion and unstable SEI layer formation during cycling. In this work, a carbon tetrafluoride (CF4) plasma was used to introduce C-F bonds onto the electrode surface to form a LiF-based SEI layer on a SiOx/C electrode (SGE) to improve its mechanical and electrochemical properties. The fluorinated SiOx/C electrode (FSGE) subjected to the CF4 plasma treatment for 10 min mitigated 2.5 times the volume expansion compared to the SGE by forming a LiF-based SEI layer to increase the mechanical properties. This mitigation of FSGE volume expansion resulted in excellent long-term cycling stability of 83 % for 100 cycles (1C). In addition, the LiF-based SEI layer formed on the FSGE increased the mobility of Li ions, resulting in 1.2 times better cycle stability than that of SGE at a high rate (10C). Thus, the improvement in the electrochemical performance achieved by reducing the volume expansion of SiOx in the electrode and enhancing the Li-ion conductivity was attributed to the stable LiF SEI layer formed with semi-ionic CF bonds introduced by the CF4 plasma.