Li<sub>3–<i>x</i></sub>Zr<sub><i>x</i></sub>(Ho/Lu)<sub>1–<i>x</i></sub>Cl<sub>6</sub> Solid Electrolytes Enable Ultrahigh-Loading\nSolid-State Batteries\nwith a Prelithiated Si Anode

We report two new families of lithium metal chloride\nsolid electrolytes\nLi_3–<i>x</i>Zr_<i>x</i>(M)_1–<i>x</i>Cl₆ (0 ≤ <i>x</i> ≤ 0.8; M = Ho or Lu) with ionic conductivities\nof up to 1.8 mS cm^–1 and a low activation energy\nof 0.34 eV. Structural elucidation <i>via</i> high-resolution\nneutron diffraction determines the Li ion distribution in trigonal\nLi₃HoCl₆, orthorhombic-I Li₃LuCl₆, and orthorhombic-II Li_2.4Zr_0.6(Ho/Lu)_0.4Cl₆. The last compound exhibits well-connected\nLi-ion pathways and abundant Li-ion carriers/vacancies to promote\ndiffusion. All-solid-state batteries with Li_2.6Zr_0.4(Ho/Lu)_0.6Cl₆ solid electrolytes and NCM85\ncathodes exhibit stable cycling up to 4.6 V vs Li⁺/Li,\nwhich is even preserved up to 4.8 V. Stable cathode interphases are\nformed for both electrolytes upon cycling to 4.3, 4.6, and 4.8 V cutoff\npotentials, as identified by a ToF-SIMS analysis. Solid-state cells\nwith a prelithiated Li_0.7Si anode exhibit a significantly\nincreased initial coulombic efficiency of 94.5% compared to Si and\na high areal capacity of up to 16.3 mAh·cm^–2.