Fast ion-conducting high-entropy garnet solid-state electrolytes with excellent air stability

The garnet-type electrolyte is one of the most promising solid-state electrolytes due to its high ionic conductivity and wide electrochemical window. However, such electrolytes generate Li₂CO₃ in the air, leading to an increase in impedance, which greatly limits their practical application. In turn, high-entropy ceramics can improve phase stability due to the high entropy effect. Herein, the high-entropy garnet (HEG) Li_6.2La₃(Zr_0.2Hf_0.2Ti_0.2Nb_0.2Ta_0.2)₂O₁₂ (LL(ZrHfTiNbTa)O) solid-state electrolyte was synthesized by the solid-state reaction method. The XRD, XPS, EIS, and SEM characterizations indicated that LL(ZrHfTiNbTa)O electrolyte has excellent air stability. The room temperature conductivity of LL(ZrHfTiNbTa)O can be maintained at ~1.42×10^-4 S/cm after exposure to air for 2 months. Single-element doped garnets were synthesized to explain the role of different elements and the mechanism of air stabilization. In addition, the Li/LL(ZrHfTiNbTa)O/Li symmetric cell cycle is stable over 600 h and the critical current density (CCD) is 1.24 mA cm^-2, indicating remarkable stability of the Li/LL(ZrHfTiNbTa)O interface. Moreover, the LiFePO₄/LL(ZrHfTiNbTa)O/Li cell shows excellent rate performance at 30 ℃. These results suggest that high entropy ceramics can be one of the strategies to improve the performance of solid-state electrolytes in the future due to their unique effects.