Surface Coatings of Nickel-Rich NCM Based Cathode Active Materials for Improved Electrochemical Performance of Lithium-Ion Batteries

Abstract

Ni-rich NCM based cathodes are considered the most promising cathode candidates for next-generation high-performance Lithium-ion batteries (LIBs). Despite very good electrochemical performance, Ni-rich NCM based cathodes still suffer practical cycling problems, which need to be addressed before their successful commercialization. Surface modification by coating has become one of the feasible approaches to tackle these issues and in turn improve the electrochemical performance. However, the most common coating methods are rather complex, time-consuming and expensive. Thus, a practical coating technique for the commercialization of these cathodes is highly needed. The main objective of this thesis is the development of such an efficient coating process that not only improves the electrochemical performance of Ni-rich NCM based cathodes but also brings them one step closer to their successful commercialization. For this purpose, several simple, low-temperature, cost-effective coating processes have been developed. The developed coating processes resulted in very homogenous and conformal coatings, which in turn led to an improvement in the C-rate performance, long-term cycling stability, and particle cracking of Ni-rich NCM based cathodes in LIBs. Several coating materials have been tested and reported for NCM based cathode. However, due to their different properties, one standardized coating material has not been agreed upon. Nevertheless, Al2O3 based coating materials are considered as most promising coating material. Thus the major part of this thesis focuses upon Al2O3 and its analogous as coating material. In addition, a Li4Ti5O12 based coating has also been tested due to its increasing popularity among coating materials. It has been found that the physical properties of a coating such as coating homogeneity, conformity and thickness, as well the coating’s chemical composition can have a significant effect on the electrochemical performance of NCM based cathodes. Furthermore, it is demonstrated that a post-annealing step after coating can play a crucial role in improving the electrochemical performance of NCM based cathodes, as it helps in improving the ionic conductivity of the coating layer due to the insertion of Li+-ion inside the coating layer. In addition, in-depth investigations have been performed to understand the beneficial effect of the coatings on the electrochemical performance of NCM based cathodes, which allowed better insights into the ongoing degradation mechanism of NCM based cathodes during cycling. The knowledge gained in this thesis is considered to be imperative for further developments of surface coating strategies. To conclude, this thesis offers various practical surface coating strategies for Ni-rich NCM based cathodes. The developed coating strategies are very simple, easy, cost- effective, environment friendly, and significantly improve the electrochemical performance of NCM based LIBs. These improvements combined with the potential of these coating strategies for scalability make them suitable for large-scale industrial application and in turn for the commercialization of Ni-rich NCM cathodes for next-generation LIBS. Last but not the least, the in-depth knowledge regarding the impact of coatings during electrochemical cycling on Ni-rich NCM provides a strong fundamental for further future research.