ABSTRACT Chloride-based Li2FeCl4 has emerged as a promising candidate high-voltage, highly deformable cathode material for all-solid-state lithium-ion batteries. However, further enhancement of Li-ion conductivity is required for practical application. In this study, we synthesized Br-substituted Li2FeCl3.8Br0.2 and examined how partial anion substitution influences both the crystal structure and Li-ion conductivity. X-ray diffraction confirmed that a single-phase cubic framework was retained and that the lattice constant remained unchanged despite Br incorporation. As a result of AC impedance measurements, the ionic conductivity was confirmed to increase approximately twofold, from 2.0 × 10−5 S/cm for the pristine material to 4.0 × 10−5 S/cm for the Br-substituted sample. In an effort to uncover the underlying mechanism of this enhancement, first-principles calculations (Density Functional Theory) combined with genetic algorithm – driven structural optimization were performed. The calculations indicated that Br substitution promoted a more disordered occupancy of Li ions across the sites along the conduction pathways. These results demonstrate that targeted anion substitution effectively tunes the Li-site energy landscape and controls Li-ion conductivity in chloride cathode materials.

Direct regeneration has emerged as a promising approach, owing to its economic and environmental advantages. However, the efficiency of lithium replenishment and phase reconstruction-the core steps in the regeneration process-is critically hindered by the inert rock-salt phase of spent cathode materials. Herein, we propose a segregation-assisted regeneration strategy that leverages the segregation behavior of high-valence elements to regulate reaction thermodynamics during the regeneration process, thereby preferentially inducing the in situ transformation of the NiO-type rock-salt phase. This transformation facilitates Li-ion diffusion, accelerates the reconstruction of the layered structure, and enhances the overall structural stability. As proof of concept, tungsten (W6+) is introduced into the regeneration process of spent LiNi0.5Co0.2Mn0.3O2 (NCM523) cathodes, leading to the formation of Li-W-Ni-O compounds and Li2WO4, which collectively facilitate the direct regeneration of the degraded material. The regenerated NCM523 delivers a high reversible capacity of 150 mAh g-1 at 0.5 C, outperforming commercial counterparts, and retains 83% of its capacity after 800 cycles in a 1.1 Ah pouch cell. Moreover, this strategy demonstrates broad applicability to other degraded layered cathode materials, including LiNi0.6Co0.2Mn0.2O2 and LiNi0.8Co0.1Mn0.1O2. This work provides a scalable, energy-efficient, and sustainable route for regenerating spent cathodes.

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