Tailoring percolative conduction networks and reaction interfaces via infusion of polymeric ionic conductor for high-performance solid-state batteries

Solid-state batteries (SSBs) offer a promising technical solution to meet the key requirements of future energy storage systems, i.e., safety and high energy density. However, the realization of SSBs is hindered by low electrode performance that results from poorly controlled solid-solid contacts. Herein, we propose an effective strategy for tailoring conductive networks and reaction interfaces via the viscosity-controlled infusion of a molten-state polymer electrolyte precursor (polymer ionic conductor, PIC) into a porous composite electrode (CE). A poly(ethylene glycol)-based PIC penetrates a three-dimensional pore network of the CE and transforms to a highly viscous, stable phase under battery operating conditions. The infused PIC enables the formation of percolating Li⁺ conduction pathways as well as intimate solid-solid reaction interfaces, which leads to the full utilization of the CE at high mass loadings. SSBs assembled with PIC-infused LiFePO₄-CEs exhibit superior capacity (154 mAh g⁻¹), rate-capability, and cycling stability than SSBs with unmodified CEs. Moreover, a 10 V-class, bipolar-pouch SSB fabricated using the PIC-infusion technology shows reversible charge–discharge operations without a considerable performance loss. This study demonstrates that the proposed microstructural engineering provides an effective approach to resolving the interfacial solid-solid contact issues of SSBs and can be used to fabricate safe, high-energy, long-cycling SSBs.