Tailoring the Interfacial Behavior to Stabilize Iron Oxalate Anode for Boosting Ultrahigh Lithium Storage

Iron (II) oxalate has attracted considerable attention for energy storage and conversion applications, particularly as a low-cost, high-capacity anode material for lithium-ion batteries. However, its poor electronic conductivity and the loss of active components during cycling severely limit its lithium storage performance. Here, we propose a facile and universal surface functionalization strategy that inhibits direct contact between electrode particles and electrolyte, thereby mitigating the loss of active components. This is achieved by carbonizing carboxymethyl cellulose (CMC) to generate a carbon layer enriched with carbonyl functional groups. Benefiting from the regulation of SEI formation by the carbonyl-rich layer and the improved adsorption of reaction intermediates, the optimized composite delivers a high reversible capacity of 1652 mAh g^-1 at 0.5 A g^-1 and retains 517 mAh g^-1 even at an ultrahigh current density of 15 A g^-1. This strategy not only significantly enhances the lithium storage capability of iron oxalate but also provides a general approach for engineering the surface chemistry of oxalate-based materials toward high-performance electrochemical energy storage.