Enabling High‐Performance NASICON‐Based Solid‐State Lithium Metal Batteries Towards Practical Conditions

Solid-state lithium metal batteries (SSLMBs) are promising next-generation high-energy rechargeable batteries. However, the practical energy densities of the reported SSLMBs have been significantly overstated due to the use of thick solid-state electrolytes, thick lithium (Li) anodes, and thin cathodes. Here, a high-performance NASICON-based SSLMB using a thin (60 mu m) Li1.5Al0.5Ge1.5(PO4)(3) (LAGP) electrolyte, ultrathin (36 mu m) Li metal, and high-loading (8 mg cm(-2)) LiFePO4 (LFP) cathode is reported. The thin and dense LAGP electrolyte prepared by hot-pressing exhibits a high Li ionic conductivity of 1 x 10(-3) S cm(-1) at 80 degrees C. The assembled SSLMB can thus deliver an increased areal capacity of approximate to 1 mAh cm(-2) at C/5 with a high capacity retention of approximate to 96% after 50 cycles under 80 degrees C. Furthermore, it is revealed by synchrotron X-ray absorption spectroscopy and in situ high-energy X-ray diffraction that the side reactions between LAGP electrolyte and LFP cathode are significantly suppressed, while rational surface protection is required for Ni-rich layered cathodes. This study provides valuable insights and guidelines for the development of high-energy SSLMBs towards practical conditions.