Aluminium doping in single-crystal nickel-rich cathodes: insights into electrochemical degradation and enhancement

Single-crystal nickel-rich cathode materials are considered one of the most promising candidates for automobile Li-ion batteries due to their high compacted density and superior cycling stability. In this work, we conduct a comparative study of single-crystal Ni-rich ternary NCM and quaternary NCMA with aluminum doping, and it is found that Al doping applied to a quaternary NCMA sample can maintain superior electrochemical performance with a significantly reduced direct current resistance (DCR). In contrast, the ternary NCM samples demonstrate a notable capacity decay to only 76.7% after 100 cycles at 2.75-4.3 V, compared to 85.9% for the NCMA. Synchrotron-based characterizations combined with high-resolution transmission electron microscopy reveal that the surface microstructural and bulk structural stability has been greatly enhanced after Al doping thereby substantially reducing DCR and improving the operational lifespan and efficiency of the batteries. It is hoped this work will provide a deep understanding of the electrochemical degradation and enhancement mechanism of the single-crystal Ni-rich cathodes, offering critical insights into the development of high-energy-density cathode materials for next-generation lithium-ion batteries.