Tailoring interlayer channels of iron oxalate by regulated stress in polymorphic structure to enhance the lithium storage

Abstract

Iron (II) oxalate is a cost-effective anode material with high theoretical capacity for lithium-ion batteries, yet its practical performance is hindered by sluggish lithium-ion diffusion and limited active site utilization. Here, inspired by dehydration-induced cracking in plant tissues, we propose a biomimetic strategy to engineer interlayer channels in iron oxalate to address these limitations. Specifically, a rod-like FeC₂O₄·2H₂O precursor composed of stacked lamellar particles with mixed α/β crystalline phases was synthesized by ethylene glycol assisted co-precipitation method. The regulated dehydration stress by polymorphic structure induced anisotropic shrinkage and multichannel formation of iron oxalate. A β-phase-rich composition (59.05 wt%) ensured rapid dehydration, while the α-phase (40.95 wt%) provided structural buffering. The resulting structure delivered an exceptional lithium storage capacity of 1144 mAh g⁻¹ at 0.5 A g⁻¹ and retained 709 mAh g⁻¹ at 5 A g⁻¹. This work demonstrates a biomimetic phase-engineering strategy for tuning interlayer structures in coordination compounds and offers a new route for designing single-layer structured oxalates by leveraging stress in polymorphic structure.