Intercalation-conversion and pseudocapacitive coupled sodium storage in binder-free ZnCo2O4 anode

Abstract

Sodium-ion batteries (SIBs) have emerged as a promising alternative to lithium-ion systems due to the abundance and cost-effectiveness of sodium resources

however, their development is hindered by the lack of high-performance anode materials. Spinel ZnCo<inf>2</inf>O<inf>4</inf> (ZCO) is considered a favorable candidate owing to its high theoretical capacity, multiple redox-active sites, and tunable morphology. Herein, ZCO is directly grown on nickel foam (NF) via a hydrothermal reaction, developing a binder-free ZCO/NF electrode. Urea is employed as a structure-directing agent, resulting in a unique neem leaf-like morphology of the ZCO/NF. Further, the ZCO/NF was structurally and morphologically characterized by physicochemical techniques. When evaluated as an anode material for SIBs, it demonstrated outstanding electrochemical performance. The ZCO/NF exhibited an irreversible discharge capacity of 1893.73 mAh/g and a reversible capacity of 863.79 mAh/g at a current density of 10 mA/g, along with excellent rate capability. At a current density of 50 mA/g, it retains 42.12% of its capacity after 300 cycles. This electrochemical performance of ZCO/NF is attributed to multiple sodium storage mechanisms, including conversion reactions, limited intercalation, and pseudocapacitive surface redox processes. This study highlights the potential of ZCO/NF as a high-performance, binder-free anode material for next-generation rechargeable energy storage systems. © 2025 Acta Materialia Inc.