Binary metal oxide NiCo₂O₄ is a promising anode material for future Li-ion batteries (LIBs) and Na-ion batteries (SIBs) owing to its inherited characteristics of high theoretical capacity and low cost.^1,2 In particular, NiCo₂O₄ possesses high electrical conductivity, reversible capacity and mechanical stability than single-component metal oxides NiO and Co₃O_4.^3,4 However, the large volume change and sluggish kinetics during the charge/discharge process result in a short cycling life and poor rate performance, which limits its practical application.⁵

The electrochemical performance of an active material highly depends on its structure (both primary and secondary structures).⁶ Therefore, tailored architecture design and surface engineering of NiCo₂O₄ are highly desirable to secure both the high transport kinetics and sustain the structure integrity for high rate and long life.

In this study, one-dimensional (1D) porous NiCo₂O₄ microrods and microspheres are successfully synthesized by a simple solvothermal method using different solvents followed by calcination. The solvothermal process and solvents employed in the synthesis play crucial role in determining the final morphologies of NiCo₂O₄. Compared with NiCo₂O₄ microspheres, the porous microrods exhibit much better Li- and Na-ion storage properties owing to the 1D geometry to facilitate fast ion transport and the porous structure to accommodate volume expansion of NiCo₂O₄ during ion insertion. The porous NiCo₂O₄ microrods display high initial charge capacity (1046.1 mAh g^-1 at 100 mA g^-1), long cycling stability (719 mAh g^-1 after 600 cycles at 500 mA g^-1), and rate capability for lithium-ion batteries. They also show better performance in sodium-ion batteries. This work may provide a facile way for fabricating novel structured metal oxide anode materials for batteries.

Figure 1. (Left) SEM images of the 1D porous NiCo₂O₄ microrods and microspheres for LIBs and SIBs respectively. (Right) Rate performances at various current densities of LIBs and SIBs.

References

1. Zheng, F. C.; Zhu, D. Q.; Chen, Q. W. ACS Applied Materials & Interfaces 2014, 6, (12), 9256-9264.
2. Lee, Y.; Kim, M. G.; Cho, J. Nano letters 2008, 8, (3), 957-961.
3. Li, B.; Feng, J.; Qian, Y.; Xiong, S. Journal of Materials Chemistry A 2015, 3, (19), 10336-10344.
4. Jadhav, H. S.; Kalubarme, R. S.; Park, C. N.; Kim, J.; Park, C. J. Nanoscale 2014, 6, (17), 10071-10076.
5. Chen, J.; Ru, Q.; Mo, Y.; Hu, S. RSC Advances 2015, 5, (90), 73783-73792.
6. Ye, J.; Liu, W.; Cai, J.; Chen, S.; Zhao, X.; Zhou, H.; Qi, L. Journal of the American Chemical Society 2010, 133, (4), 933-940.