Rational design of yolk-shell CoFe₂O₄ nanospheres towards enhanced lithium storage performance

Co–Fe bimetal oxides have attracted increasing attention owing to their high theoretical capacity and multiple electrochemically active sites for lithium-ion battery which widely applied in electric/hybrid electric vehicles and renewable energy storage. However, Co–Fe bimetal oxides still suffer from the inherently poor conductivity and severe volume change upon lithiation/delithiation process, thus resulting in poor cycle stability. Herein, the yolk-shell CoFe₂O₄ nanospheres were prepared by a solvothermal method and subsequent calcination strategy. The phase and morphology can affect the electrochemical storage performance by adjusting the annealing temperature. Benefiting from the unique structure, the yolk-shell CoFe₂O₄ electrode displayed improved lithium storage performance and excellent rate capability, delivering a reversible capacity of ~ 912.7 mAh g⁻¹ at 200 mA g⁻¹ and 694.3 mAh g⁻¹ at even a high current density of 1000 mA g⁻¹. More importantly, this novel strategy can be commonly used to design various other bimetal oxides with novel nanostructures, which is promising for developing advanced electrodes for high-performance energy storage devices.