Compositionally Tuned High‐Entropy Li‐Garnet Electrolyte for Advanced Solid‐State Batteries

The advancement of all‐solid‐state lithium batteries (ASSLBs) hinges on developing highly conductive and chemically stable solid electrolytes. High‐entropy ceramics leveraged from high configurational entropy and synergistic interactions among the elements have emerged as a rapidly expanding class of high‐entropy materials, attracting significant attention due to their exceptional properties. Here, a high‐entropy Li‐stuffed garnet (HEG) solid electrolyte, Li 7 La 3 Zr 0.5 Hf 0.5 Sc 0.5 Nb 0.25 Ta 0.25 O 1 2 , crystallizing in a highly Li + conductive (≈1.25 × 10 −4 S cm −1 at room temperature) cubic phase, is reported. Electrochemical evaluations demonstrate excellent stability against lithium metal, with symmetric Li|HEG|Li cells sustaining stable Li plating/stripping beyond 550 cycles at 0.4 mA cm −2 . Furthermore, full‐cell integration with LiFePO 4 cathodes exhibits high capacity retention (≈99% over 500 cycles), confirming its potential for high‐performance ASSLBs. Further, the HEG solid electrolyte is compatible with high‐voltage LiMn 2 O 4 cathode (mass loading ≈16.6 mg cm −2 ), retaining 96% capacity over 100 cycles (at 0.2C). These findings establish a framework for tailoring high‐entropy garnet electrolytes, paving the way for next‐generation solid‐state battery technologies.