New High-Entropy Zirconium-Based Solid-State Electrolyte: Balancing High Conductivity and High Voltage

Solid-state electrolytes (SSEs) exhibit both high ionic conductivity and electrochemical stability, which are essential for next-generation all-solid-state batteries (ASSBs). In this study, a high-entropy strategy was employed to modify two distinct structural phases of Li₂ZrCl₆ (LZC), resulting in a low-crystallinity (lc-) form of Li_1.92(ZrHf)_0.25(InTaNb)_0.16Cl₆ and a high-crystallinity (hc-) form of Li_1.8(ZrHfInTaNb)_0.2Cl₆. This approach overcomes the typical trade-offs encountered in chloride-based SSEs, achieving high ionic conductivities of 1.0 and 0.968 mS cm^{- 1} at 25°C, respectively, while maintaining an excellent oxidation potential exceeding 4.6 V (relative to Li⁺/Li). Furthermore, the lc phase benefits from an entropy-driven amorphization process, resulting in an amorphous phase content of 72.77%. In contrast, the hc phase exhibits lattice contraction and the disappearance of atomic positions, thereby optimizing Li⁺ migration. A full cell employing a Li-In anode and sc-NCM83 cathode demonstrated outstanding rate performance and long-term stability, retaining over 80% capacity after 1600 cycles at 5C. This work validates the general applicability of the high-entropy design in tuning the properties of SSEs across different crystalline states.