Stable Photothermal Conversion Fillers Enable Subzero‐Temperature Applications of PEO‐Based Solid‐State Lithium Batteries via In Situ Self‐Heating

ABSTRACT Low‐temperature operational reliability remains a critical bottleneck for all‐solid‐state batteries (ASSBs). Polyethylene oxide (PEO)‐based solid‐state electrolytes (SSEs), the most widely studied SSE system, typically exhibit ionic conductivities as low as 10 −6 S cm −1 at ambient temperature, necessitating battery operation at 60°C–80°C. This external heating requirement consumes extra electrical energy and severely limits the application of PEO‐based ASSBs under low‐temperature conditions. Here, we introduce lithiated poly(3,4‐dioxythiophene) (LiPHT) photothermal conversion filler into PEO‐based SSEs, which significantly enhances the ionic conductivity to 1.34 × 10 −4 S cm −1 while simultaneously broadening the electrochemical window to 4.55 V vs. Li/Li + at room temperature. By utilizing the PEO‐LiPHT composite layer as both a “heater” and the electrolyte layer within the transparent battery, the device exhibits efficient photothermal conversion and rapid light‐induced heating. Benefiting from the in situ photothermal self‐heating effect that elevates the actual internal cell temperature to the optimal operating range of PEO electrolytes, the ASSB demonstrates a high discharge capacity of 131.3 mA h g −1 at 0.5 C under an ambient temperature of −15°C. This work offers a viable pathway to circumvent the intrinsic low‐temperature limitation of PEO‐based electrolytes, facilitating the development of high‐performance ASSBs for subzero‐temperature applications.