Abstract
Recently, lithium ion batteries (LIBs) have received great attention as a suitable power source for electric vehicles (EVs) because of its highest energy and power densities among currently available energy storage systems. For successful implementation the achievable energy density of current LIBs should be further improved to meet the industrial requirements. In this respect, the development of advanced materials is crucial for improving the energy density of LIBs. During the last decade, layered lithium transition metal oxides (e.g., LiMO2, M = transition metal) have been used as the most popular cathode materials in commercial LIBs [1]. From a structural point of view, Li+ can be reversibly inserted and extracted in the given structure based on the redox reactions of transition metals. Therefore, the choice of transition metals is crucial for determining the electrochemical properties of these cathode materials. By increasing the Ni concentration, the reversible capacity of the cathode materials can be effectively increased due to the double redox reaction of Ni2+/Ni4+. In practice, high-Ni layered cathode materials (Ni > 80%) can offer a high reversible capacity over 200 mAh g-1 [2]. As a result of increasing the Ni concentration, however, the cathode materials suffer from poor cycle performance and thermal stability mainly induced by side reactions with electrolyte and residual Li at the surface. To overcome these limitations, effective surface coatings are required to make the surface more stable and suppress undesirable side reactions [3]. Herein, we propose a surface coating with LiNbO3 onto NCM811 cathode material to minimize undesirable side reactions as well as improve the thermal stability [4]. Thanks to the high ionic conductivity and thermal resistance of LiNbO3, LiNbO3 coated NCM811 exhibit much improved cycle performance and rate capabilities even at high operating temperature of 60 oC. Moreover, we also investigate the effect of LiNbO3 crystallinity on the electrochemical properties of LiNbO3 coated NCM811. It would provide a practical guideline for the development of a highly reliable high-capacity cathode material for EV applications.
References:
[1] M. M. Thackeray, J. Electrochem. Soc. 142 (1995) 2558-2563.
[2] P. Hou, J. Yin, M. Ding, J. Huang, X. Xu, Small 13 (2017) 1701802.
[3] Z. Chen, D. Chao, J. Lin, Z. Shen, Mater. Res. Bull. 96 (2017) 491-502.
[4] M. Gellert, K. I. Gries, J. Sann, E. Pfeifer, K. Volz, B. Roling, Solid State Ion. 287 (2016) 8-12.