Understanding the Degradation Mechanism of Lithium Nickel Oxide Cathode for Li-Ion Batteries

Abstract

Nowadays, Li-ion battery technology has become one of the best performing energy storage devices and holds the best promise to power the upcoming electrical vehicles (EV).1 Continuous search of cathode materials with even better performance and lower cost ($/Wh) led to numerous layered lithium transition metal oxides, such as LiNixMnyCozO2 and LiNixCoyAlzO2 (0 < x, y, z <1). Recently, there is an emerging interest on developing Ni-rich cathode materials because a higher level of Ni incorporation can lead to a higher practical capacity.2 This is resulted from the electronic configuration of Ni3+ (3d7), allowing the removal of electrons only from the eg band, therefore, the loss of oxygen occurs at a higher charge state.3 On the other hand, a higher Ni content may result in a severe capacity fade during cycling, likely due to the structural transformation in the bulk and at the surface.4, 5 A combination of different transition metals in these LiNixMnyCozO2 or LiNixCoyAlzO2 further increases the complexity of the problem because of the phase separations and side reactions with electrolyte resulting from the difference in chemical and electrochemical reactivity of the transition metals. We have reported the synthesis of high-performance LiNiO2 6, here, we will use it as a model system to reveal the intrinsic performance degradation mechanism originating from the high Ni content for those complex R-3m layered oxides. The phase transition, charge compensation and local chemical environment of Ni in the bulk and at the surface of LiNiO2 were investigated by a variety of bulk and surface characterization techniques for different terms of cycling. We revealed the phase transition from original hexagonal (H1) phase to another two hexagonal (H2+H3) phases and observed a gradual loss of H3 phase features over the extended charges. The reduction in Ni redox activity occurred in both charge and discharge states, and it appeared both in the bulk and at the surface over the extended cycles. The destruction in crystal structure, and Ni redox activity simultaneously contributed to the cycling performance decay of LiNiO2. Reference 1. M. S. Whittingham, Chemical Reviews, 2004, 104, 4271-4301. 2. M. H. Choi, C. S. Yoon, S. T. Myung, B. B. Lim, S. Komaba and Y. K. Sun, Journal of the Electrochemical Society, 2015, 162, A2313-A2318. 3. M. Balasubramanian, X. Sun, X. Q. Yang and J. McBreen, Journal of Power Sources, 2001, 92, 1-8. 4. P. F. Yan, J. M. Zheng, D. P. Lv, Y. Wei, J. X. Zheng, Z. G. Wang, S. Kuppan, J. G. Yu, L. L. Luo, D. Edwards, M. Olszta, K. Amine, J. Liu, J. Xiao, F. Pan, G. Y. Chen, J. G. Zhang and C. M. Wang, Chemistry of Materials, 2015, 27, 5393-5401. 5. J. M. Zheng, W. H. Kan and A. Manthiram, Acs Applied Materials & Interfaces, 2015, 7, 6926-6934. 6. J. Xu, F. Lin, D. Nordlund, E. J. Crumlin, F. Wang, J. Bai, M. M. Doeff and W. Tong, Chemical Communications, 2016, 52, 4239-4242.