Morphology‐Regulated Structural Dynamics and Stress Mitigation Enable Stable Chloride Storage for Bismuth Oxychloride Cathodes

ABSTRACT Layered metal oxychlorides, featuring robust M–O frameworks and high theoretical capacities from conversion‐type Cl ⁻ storage, represent a compelling class of cathode materials for Chloride‐ion batteries (CIBs). Nevertheless, the large volume fluctuations inherent to conversion reactions often cause structural degradation and poor cycling reversibility. Here, we introduce a morphology‐regulated strategy to modulate the structural dynamics of bismuth oxychloride (BiOCl) cathodes. BiOCl materials with pH‐dependent morphologies ranging from nanoplates to submicron spheres were synthesized via hydrothermal crystallization, where the evolution was controlled by a dynamic balance between self‐assembly and recrystallization. Nanoplates (BiOCl‐N) exhibit superior Cl‐storage capability, enabled by a high surface area, open mesoporous architecture, and accelerated ion diffusion. In situ XRD and ex situ XPS confirm a highly reversible Bi ³⁺ /Bi ⁰ redox process in BiOCl‐N, accompanied by dynamic Bi–O bond reconfiguration coupled with Cl ⁻ migration. In contrast, bulk BiOCl‐B and spherical BiOCl‐S suffer from sluggish kinetics and incomplete reoxidation. Consequently, BiOCl‐N maintains 158.5 mAh g ⁻¹ after 200 cycles at 200 mA g ⁻¹ , over twofold the retention of bulk BiOCl‐B. Finite element analysis reveals the lowest interfacial stress during cycling, indicating that morphology control effectively mitigates stress‐induced collapse. This work underscores morphology engineering as an intrinsic route to stabilize phase transitions and enable high‐performance CIBs.