Tailoring Silicon Composite Anodes with Li+-Doped Organic Ionic Plastic Crystals for Solid-State Batteries

Abstract Silicon is one of the highest-capacity anode active materials and, therefore, its use in solid-state batteries (SSBs) is expected to provide both high energy density and safety. Although the creation of solid-state Si electrodes via a scalable method is important from the perspective of battery production, its effect on electrochemical performance has yet to be clarified for the electrodes containing Li+-doped organic ionic plastic crystals (OIPCs) as solid electrolytes. Here, we made various Si−OIPC composite electrodes using four electrode-preparation methods and measured their electrochemical performances to decipher the method−structure−property relationship for high-performing SSBs. The Si−OIPC composite electrode containing 50 mol% LiFSI in N-ethyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide ([C2mpyr][FSI]) showed the highest initial Coulombic efficiency and cyclability. Three out of four methods provided the Si−Li0.50[C2mpyr]0.50[FSI] electrodes with relatively large capacity retentions that were close to that of the Si electrode in a liquid electrolyte. Elemental analysis for the electrode cross-sections resolved the homogeneous distribution of Li0.50[C2mpyr]0.50[FSI], except for the one made by the drop-casting method, suggesting that three methods can establish the long-range ion-conduction network in the electrode to improve the electrochemical stability of Si during cycling. This study clarifies the importance of the OIPC-incorporation method in fabricating highly functional OIPC-based electrodes for SSBs.