“Solid-in-Solid” Electrolyte via Scalable Melting Infiltration Method for High-Voltage Solid-State Lithium Metal Batteries

Solid electrolytes are critical to enabling safe and high-energy-density batteries, yet their practical deployment is impeded by poor electrochemical stability, inadequate interfacial contact, and challenging manufacturing processes. Here, we introduce a novel “solid-in-solid” electrolyte architecture comprising a porous Li zeolite electrolyte (LiX) infiltrated with a melt-processable plastic crystal electrolyte (PCE). This LiX–PCE electrolyte achieves an ionic conductivity of 0.55 mS/cm at 20 °C, alongside improved electrochemical stability over pure PCE. Solid-state nuclear magnetic resonance reveals three Li⁺ transport pathways: through LiX, through PCE, and via ion exchange at phase boundaries. Leveraging the melt-processability of the PCE, we proposed a roll-to-roll-compatible melt infiltration strategy for scalable solid-state battery (SSB) fabrication with the LiX–PCE electrolyte. The SSBs demonstrate excellent rate performance (over 12C), 93% capacity retention after 200 cycles, and 4.5V compatibility. This work elucidates critical design principles for high-performance solid-state electrolytes and presents a viable path toward practical fast-charging, high-power SSBs.