The extensive studies over the last decade have established Na-ion batteries (NIBs) as one of the cheaper alternatives to Li-ion batteries (LIBs) [1-2]. P2-type Na
0.67Ni
0.33Mn
0.67O
2 has stood out among layered oxide based electrode materials providing the best over-all electrochemical performance. The electrodes can exert up to 92.5% of its theoretical capacity (160 mAhg
-1) at a voltage higher than 3 V accounted for the Ni
2+/Ni
4+ redox. However, at higher voltages, electrodes suffer irreversibility due to P2-O2 structural transition [3]. Recent studies in suppressing this transition by partial substitution with various metals on either Ni or Mn lattice site have suggested enhancing cycling stability [4-7]. In this study, a novel cathode material with Ti-substitution on Ni site, P2-type Na
0.67Ni
0.25Ti
0.08Mn
0.67O
2 has been synthesized via solid-state synthesis method and characterized electrochemically. Na
0.67Ni
0.25Ti
0.08Mn
0.67O
2 electrodes have been observed to be highly reversible at higher voltage ranges. The
electrodes have an initial discharge capacity of 125 mAhg
-1 and can retain around 84% of this capacity (105 mAhg
-1) even after 50 cycles at 0.1C when cycled at an upper cut-off voltage of 4.3 V (Figure 1). Na
0.67Ni
0.25Ti
0.08Mn
0.67O
2 electrodes are believed to suppress the irreversible P2-O2 transformation by diverting the charging reaction through a more reversible P2-OP4 transition.
References
[1] A. Eftekhari, D. W. Kim, J. Power Sources 2018, 395, 336-348.
[2] J. Y. Hwang, S. T. Myung, Y. K. Sun, Chem. Soc. Rev. 2017. 46, 3529-3614.
[3] G. Singh, N. Tapia-Ruiz, J.M. Lopez del Amo, U. Maitra, J.W. Somerville, A.R. Armstrong, J. Martinez de Ilarduya, T. Rojo, P.G. Bruce, Chem. Mater. 2016, 28, 5087-5094.
[4] T. Y. Yu, J. Y. Hwang, D. Aurbach, Y. K. Sun, ACS Appl. Mater. Interfaces 2017, 9, 44534-44541.
[5] K. Kubota, Y. Yoda, S. Komaba, J. Electrochem. Soc. 2017, 164, A2368-A2373.
[6] J. Xu, D. H. Lee, R. J. Clément, X. Yu, M. Leskes, A. J. Pell, G. Pintacuda, X. Q. Yang, C. P. Grey, Y. S. Meng, Chem. Mater. 2014, 26, 1260-1269.
[7] W. Zhao, A. Tanaka, K. Momosaki, S. Yamamoto, F. Zhang, Q. Guo, H. Noguchi, Electrochim. Acta 2015, 170, 171-181.
