Yolk-shell structured ZnCo₂O₄ spheres anchored on reduced graphene oxide with enhance lithium/sodium storage performance

Transition metal oxides are expected to replace commercial graphite for the next generation of secondary battery anode materials. However, the capacity decreases rapidly due to poor conductivity and volume expansion during operation. In this study, we first designed a yolk-shell structured ZnCo₂O₄ sphere, and then combined it with reduced graphene oxide through an electrostatic interaction process. The prepared ZnCo₂O₄/RGO showed enhanced lithium/sodium storage performance. Specifically, it can provide 997.2 mA h g⁻¹ (for LIBs, 500 cycles) and 280 mA h g⁻¹ (for SIBs,1000 cycles) reversible capacities at 1.0 A g⁻¹ current density, respectively. These superior properties are derived from their unique structure. On the one hand, the gap between the yolk and shells not only provides a shorter Li⁺/Na⁺ diffusion distance, but also the electrolyte can be in sufficient contact with the anode material to induce a rapid surface reaction; on the other hand, the introduction of graphene can effectively buffer the large volume expansion of the cycle and maintain the structural integrity of the electrode material.