The compositionally tuned high-entropy Li-garnet solid electrolyte exhibits high conductivity and excellent electrochemical performance in symmetric and full cells.

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, Li₇La₃Zr_0.5Hf_0.5Sc_0.5Nb_0.25Ta_0.25O_{1 2}, crystallizing in a highly Li⁺ conductive (≈1.25 × 10⁻⁴S 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 LiFePO₄ 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 LiMn₂O₄ 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.