Effect of lithium salt type on silicon anode for lithium-ion batteries

Silicon (Si) is one of the most promising anode materials in the next generation of Li-ion batteries. However, the application of Si is restricted by its unsatisfactory electrochemical performance. This work investigates the influence of lithium salt type on the electrochemical performance of Si anode, and shows that lithium salt type plays an importing role in determining the electrochemical performance of Si anode. Through investigation and optimization, lithium hexafluorophosphate (LiPF6)-lithium bis(fluorosulfonyl)imide (LiFSI)-lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) ternary composite lithium salt with a mole ratio of 7:1:2 exhibits the best cycling stability and rate capability. It retains a high capacity of 1879.8 mAh g−1 after 400 cycles at 0.5 C charge and discharge, and still maintains 1851.4 mAh g−1 at 30 C; which are significantly higher than the 583.3 and 316.4 mAh g−1 of the LiPF6-based electrolyte under the same conditions. The underlying mechanism is investigated, and the results indicate that the lithium type has an effect on both the Si anode and the lithium counter electrode, and the synergistic effect of LiPF6-LiFSI-LiTFSI enables high-rate and long-cycle Si anodes.