The improved cycling stability of nanostructured NiCo2O4 anodes for lithium and sodium ion batteries.

Developing the high-capacity anode materials such as conversion-type metal oxides which possess both Li and Na storage activity is very practical for the high-energy Li-ion battery (LIB) and Na-ion battery (LIB). Herein, we use NiCo₂O₄ anodes as a model to investigate the morphology evolution which accounts for the poor cycling performance and understand the effect of structure optimization on the electrochemical performance. Three NiCo₂O₄ samples with different morphologies of microspheres, nanospheres and nanosheets are synthesized. Firstly, the serious structural degradation of NiCo₂O₄ microspheres is observed whether it works as a LIB or SIB anode. In addition, a significant difference between the lithiation and sodiation capacity of NiCo₂O₄ materials reveals Na⁺ ions only partially intercalated in NiCo₂O₄ and the conversion reaction limited by the strain. Next, NiCo₂O₄ nanosheets on Ni foam as a binder-free anode for the LIB are investigated which suggest the positive effect of 3D nanostructures on the morphology stability. As a result, NiCo₂O₄ nanosheets deliver a high lithiation capacity of 1092 mAh g⁻¹ after 100 cycles at 0.5 A g⁻¹ and an excellent rate capacity of 643 mAh g⁻¹ at 4 A g⁻¹. Finally, NiCo₂O₄ nanospheres are evaluted as a SIB anode which indicate the smaller particle size of active materials is beneficial to the release of stress and structure stability during discharge–charge processes. Relatively speaking, the nano sheet structure is with the best electrochemical performance based on the capacity retention. A rational design of the electrode' architecture is very important for the conversion-type 3d transition metal oxide anodes for the advanced LIB and SIB. [ABSTRACT FROM AUTHOR]