Wook Ahn

All‐solid‐state Li batteries (ASSLBs) are considered suitable candidates to replace conventional batteries utilizing liquid electrolytes. However, the applications of this type of batteries are limited owing to their narrow operating temperature range, low ionic conductivity, poor long‐term stability, and complex production process. Herein, a simple approach that combines all potential battery candidates that have been investigated over the last few years, including polyethylene oxide (PEO), Li 7 La 3 Zr 2 O 12 (LLZO), succinonitrile (SN), and Li salt (LiTFSI), is employed to solve the limitations of ASSLBs. LLZO codoped with Al 3+ and Nb 5+ (NAL) is synthesized at a low temperature using a modified sol‐gel Pechini method. NAL, along with SN, plays a critical role in improving the performance of the resultant solid polymer electrolyte, which can be operated at room temperature. The integrated electrolyte PEO/LiTFSI‐SN‐NAL (PLS‐NAL) delivers a high ionic conductivity of 3.09 × 10 −4 S cm −1 and an excellent Li‐ion transference number of 0.75 at room temperature. ASSLBs combining LiFePO 4 and PLS‐NAL exhibit excellent cycling stability at both room temperature and 45 °C with a high capacity retention of ≈90% after 200 cycles and cycle life of up to 400 cycles.