All-solid-state batteries (ASSBs) employing inorganic solid electrolytes have been considered as promising candidates for next generation energy storage owing to their intrinsic safety performance and high energy density. Designing highly ionically conductive and (electro)chemically stable inorganic solid electrolytes utilizing cost-effective materials is of vital importance for the development of practical ASSBs. Herein, we report a series of new lithium-conducting superionic halides Li_2+xHf_1–xFe_xCl₆ that are free of rare-earth elements with high ionic conductivities up to 0.91 mS cm^–1 at 30 °C by aliovalent substitution with low-cost and earth-abundant Fe elements. By means of complementary characterization techniques and bond-valence site energy (BVSE) calculations, we gain insights into the influence of aliovalent doping engineering on the local structural environment and the underlying lithium-ion transport properties of Fe³⁺-substituted Li₂HfCl₆. Importantly, it is demonstrated that the prevalently existent distortion of octahedral structure and redistribution of the lithium ion induced by the aliovalent substitution strongly benefits the transport properties. Notably, the formation of infinitely 3D connected lithium-ion migration pathways comprised of a directly connected face-sharing octahedron along the c direction is revealed by structural analysis and theoretical calculations. Additionally, owing to the intrinsic oxidation tolerance of Fe³⁺-substituted Li₂HfCl₆, the fabricated bulk-type ASSBs with uncoated LiCoO₂ deliver an outstanding electrochemical performance.

中文翻译：

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用于全固态锂金属电池的具有优异离子电导率的低成本卤化物电解质 Li2+xHf1–xFexCl6

采用无机固体电解质的全固态电池（ASSB）因其固有的安全性能和高能量密度而被认为是下一代储能的有希望的候选者。利用具有成本效益的材料设计高离子导电性和（电）化学稳定性的无机固体电解质对于实用ASSB的开发至关重要。在此，我们报道了一系列新型锂导电超离子卤化物Li _{2+ x} Hf _{1– x} Fe _x Cl ₆，它们不含稀土元素，在30°C时通过异价离子电导率高达0.91 mS cm ^–1用低成本且地球储量丰富的铁元素替代。通过互补表征技术和键价位能量（BVSE）计算，我们深入了解了异价掺杂工程对局部结构环境的影响以及Fe ³⁺取代的Li ₂ HfCl ₆的潜在锂离子传输特性。重要的是，事实证明，普遍存在的八面体结构的扭曲和异价取代引起的锂离子的重新分布极大地有利于传输性能。值得注意的是，结构分析和理论计算揭示了由沿c方向直接连接的共面八面体组成的无限3D连接的锂离子迁移路径的形成。此外，由于Fe ³⁺取代的Li ₂ HfCl _{6的固有氧化耐受性，用未涂覆的LiCoO 2}制造的块状ASSB具有出色的电化学性能。