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

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, the effect of electrode-preparation methods on electrochemical performance of electrodes with Li + -containing organic ionic plastic crystals (OIPCs) as solid electrolytes has yet to be investigated. Here, we prepared various Si−OIPC composite electrodes using four different methods and measured their electrochemical performance to decipher the method−structure−property relationship for high-performing SSBs. Si−OIPC composite electrodes containing 50 mol% LiFSI in N -ethyl- N -methylpyrrolidinium bis(fluorosulfonyl)imide ([C 2 mpyr][FSI]) showed the highest initial Coulombic efficiency and cyclability. Three out of the four methods provided the Si−Li 0.50 [C 2 mpyr] 0.50 [FSI] electrodes with relatively large capacity retentions that were close to that of the Si electrode in a liquid electrolyte solution. Elemental analysis of electrode cross-sections showed homogeneous distribution of Li 0.50 [C 2 mpyr] 0.50 [FSI], except for those prepared by the drop-cast method, suggesting that well-designed methods can establish the long-range ion-conduction network in the electrode necessary 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.