Amorphous aluminum-based oxychloride superionic conductors via cation–oxygen coupled modification for durable high-rate all-solid-state lithium batteries

Abstract

Al-based chlorides have garnered significant attention as promising solid electrolytes (SEs) due to their low cost and elemental abundance. However, the strong lattice ordering and the dense coordination framework of Li₃AlCl₆ result in intrinsically low ionic conductivity at room temperature, severely limiting its practical applicability. In contrast, the absence of grain boundaries in amorphous SEs enables intimate solid–solid contact and uniform Li⁺ transport, offering an effective pathway toward high-performance all-solid-state lithium batteries (ASSLBs). In this work, we propose a heterovalent cation–anion co-doping strategy of introducing Zr, an earth-abundant and low-cost element, and Hf coexisting with Zr in zircon minerals, along with partial substitution of Cl⁻ by O²⁻ to markedly enhance ionic conductivity. The resulting amorphous electrolytes, Li_2.7Al_0.7Zr_0.3Cl_3.3O_1.35 and Li_2.7Al_0.7Hf_0.3Cl_3.3O_1.35, exhibit ionic conductivities of 1.63 and 1.65 mS cm⁻¹, respectively, nearly two orders of magnitude higher than that of Li₃AlCl₆. Structural analysis reveals that the co-doping of O²⁻ with Zr⁴⁺/Hf⁴⁺ induces a highly disordered local structure, thereby facilitating Li⁺ migration. Furthermore, Li_2.7Al_0.7Zr_0.3Cl_3.3O_1.35 demonstrates high electrochemical stability and a low estimated cost of 45.96 USD kg⁻¹. The LiIn|Li₁₀GeP₂S₁₂|Li_2.7Al_0.7Zr_0.3Cl_3.3O_1.35|LiNi_0.83Co_0.12Mn_0.05O₂ full cell retains 90.3% capacity after 4000 cycles at 5C, highlighting the great potential of amorphous aluminum-based SEs for next-generation ASSLBs.