Cation-inversion-controlled ion–electron coupling and conversion dynamics in CoFe₂O₄ sodium-ion anodes

Sodium-ion batteries offer a resource-abundant and cost-effective platform for large-scale energy storage, yet conversion-type anodes remain constrained by coupled transport limitations, reaction heterogeneity, structural evolution, and interfacial degradation. For spinel CoFe₂O₄, the role of cation inversion remains unresolved because its effects are intertwined with particle geometry, electronic connectivity, conversion-product formation, and solid-electrolyte interphase growth. Here, a three-dimensional, multiscale, and uncertainty-aware multiphysics framework was developed by sequentially coupling an isolated octahedral particle model with a representative volume element of the composite electrode. The framework resolves solid-state Na-ion transport, concentrated-electrolyte behavior, charge conservation, Butler–Volmer kinetics, conversion to Co, Fe, and Na₂O, irreversible sodium consumption, porosity evolution, interfacial-film growth, contact resistance, and spatial reaction redistribution. Alternative constitutive-model families were propagated to avoid imposing a predetermined inversion optimum. Within the controlled modeling framework, cation inversion was predicted to modulate the coupled balance among ionic redistribution, electronic conduction, interfacial consumption, and product-layer evolution. Under reference conditions, the accessible capacity increased from approximately 480 to 690 mAh g⁻¹ within the favorable intermediate-inversion region, before decreasing to approximately 570 mAh g⁻¹ at full inversion. Intermediate inversion also promoted deeper conversion, more uniform reaction, improved utilization, and lower polarization. Overall, the framework links crystallographic disorder to mesoscale reaction-field evolution and provides transferable design guidance for conversion-type electrode materials.

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