Stress homogenization enabled by a layered composite electrolyte for high-performance all-solid-state lithium metal batteries

The growing demand for high-energy-density and high-safety batteries has spurred research interest in all-solid-state lithium metal batteries. As the core constituent, solid polymer electrolytes exhibit improved interfacial compatibility compared with their inorganic counterparts. However, their further applications are impeded by suboptimal ionic conductivity and stress-induced uncontrolled Li deposition. Here, guided by in-situ stress imaging and multiphysical field simulations, we develop a layered composite electrolyte that simultaneously provides continuous ion-conduction pathways and modulates stress distribution for homogeneous Li deposition. Consequently, the layered electrolyte enables stable Li plating/stripping in a symmetric coin cell up to 3000 h with current density of 0.1 mA/cm² and cutoff capacity of 0.05 mAh/cm² at 60 °C. Most importantly, the Li|Layered electrolyte|LiFePO₄ coin cell maintains a capacity retention of 84.3% after 400 cycles with 0.2C (34 mA/g) even at 30 °C. The corresponding pouch cell (nominal capacity of 7.65 mAh) delivers an initial discharge capacity of 6.3 mAh at 0.2C (1.53 mA) and 60 °C under a stack pressure of 100 kPa, achieving a capacity retention of 85.7% after 100 cycles. Our study reveals a strategy for utilizing structured solid electrolytes to modulate stress evolution and Li deposition for high-performance all-solid-state lithium metal batteries.