Herein we demonstrate a new perspective that Li substitution in NFM cathode can facilitate Na diffusion due to the Jahn Teller (JT) effect resulted from high spin Mn ions. The ex situ soft X-ray adsorption spectroscopy (SXAS) qualitatively suggests that the amount of high spin Mn ions on the surface is larger than that in the bulk. The high spin Mn3+ ion has a half occupied majority spin eg orbital favoring a JT distortion.9 Previously, Li et al. has discussed that Jahn Teller effect can assist Na diffusion through integrated experimental and simulation study.10 In our study, the galvanostatic intermittent titration technique (GITT) result indeed indicated that Na diffusion in Li-NFM is larger than that in NFM. In addition, structural stability of Li-NFM cathode was confirmed by ex situ selected area electron diffraction (SAED) and high resolution transmission electron microscopy (HRTEM). When fully charged, the well-defined crystalline structure of Li-NFM cathode was partially damaged due to the stacking fault, resulting in diffusive ring on SAED pattern and disordered HRTEM image. However, after discharged, the diffusive ring disappears and long-term ordering appears on the SAED and HRTEM, respectively, suggesting reversible reconstruction of crystal structure and great structural stability.
1. J. Zhao, L. W. Zhao, N. Dimov, S. Okada and T. Nishida, J Electrochem Soc, 2013, 160, A3077-A3081.
2. D. Kim, E. Lee, M. Slater, W. Q. Lu, S. Rood and C. S. Johnson, Electrochem Commun, 2012, 18, 66-69.
3. N. Yabuuchi, M. Yano, H. Yoshida, S. Kuze and S. Komaba, J Electrochem Soc, 2013, 160, A3131-A3137.
4. D. D. Yuan, Y. X. Wang, Y. L. Cao, X. P. Ai and H. X. Yang, Acs Appl Mater Inter, 2015, 7, 8585-8591.
5. S. M. Zhang, Y. Liu, N. Zhang, K. Zhao, J. H. Yang and S. Y. He, J Power Sources, 2016, 329, 1-7.
6. S. M. Oh, S. T. Myung, J. Y. Hwang, B. Scrosati, K. Amine and Y. K. Sun, Chem Mater, 2014, 26, 6165-6171.
7. S. Y. Zheng, G. M. Zhong, M. J. McDonald, Z. L. Gong, R. Liu, W. Wen, C. Yang and Y. Yang, J Mater Chem A, 2016, 4, 9054-9062.
8. J. Xu, H. D. Liu and Y. S. Meng, Electrochem Commun, 2015, 60, 13-16.
9. D. J. Singh and W. E. Pickett, Phys Rev B, 1998, 57, 88-91.