Mitigating high-temperature degradation of Nb-doped Ni-rich cathodes through surface stabilization

초록

Various hetero-element doping strategies have been widely investigated and have improved the cycle life of Nirich cathode materials. However, these approaches primarily focus on enhancing structural stability or controlling particle morphology to reduce microcrack formation, while overlooking the detrimental effects of the increased surface area. This provides additional reactive sites for residual lithium compounds, thereby exacerbating side reactions with the electrolyte and promoting extensive gas evolution. Consequently, suppressing parasitic reactions during the high-temperature operation of Ni-rich cathodes remains challenging. In this study, we employed a synergistic surface modification strategy comprising a washing process and an additional fluorine coating to develop an F-coated cathode material based on Nb-treated Li[Ni0.921Co0.040Mn0.020Al0.014Nb0.005]O2. The proposed strategy effectively passivates both grain boundaries and particle surfaces by forming lithium niobate and a stable lithium fluoride coating layer. Accordingly, the pouch-type full cell incorporating the developed cathode exhibited an excellent cycling retention of 81.5% after 1400 cycles at 45 degrees C, even at a charging C-rate of 2 C. Notably, isothermal microcalorimetry analysis revealed a significant reduction in heat generation for the modified cathode, clearly demonstrating the effectiveness of the proposed strategy. Overall, this synergistic surface engineering strategy overcomes the inherent limitations of Ni-rich cathode materials, providing a viable pathway for the development of stable, high-energy lithium-ion batteries operating at elevated temperatures.

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