Ultrafine-Grained Ni-Rich Layered Cathode for High-Performance Li-Ion Batteries

Currently, Li-ion batteries (LIBs) are the main power source for electric vehicles (EVs) because of their high energy density, excellent rate performance, and long cycle life. However, even EVs that are powered by state-of-the-art LIBs are unable to meet the driving range offered by internal combustion engine vehicles (ICEVs), which is typically 600–800 km. 1 The properties of LIBs are strongly related to the nature of positive electrodes (cathodes), and thus, the selection of appropriate cathodes is of paramount importance. Currently, Ni-rich layered LiMO 2 (M = Ni, Co, Mn, and/or Al) compounds are considered ideal cathode materials for EV batteries because their high capacity enables EVs to achieve high mileage per charge. Although Ni-rich layered cathodes are advantageous in terms of energy density and material cost, in general, they have considerably decreased cycling lifetimes with inferior thermal stabilities, which hinder their commercialization. The inherent structural instability of Ni-enriched layered oxide cathodes, particularly in the deeply charged state, leads to a build-up of mechanical strain. 2 The strain build-up causes the nucleation and propagation of microcracks, which enable electrolyte infiltration and accelerate structural deterioration, which has plagued attempts to stabilize the cycling performance of Ni-rich layered cathodes. 3 In this study, we demonstrate that limiting the primary particle size of the cathode resolves the capacity fading problem as nano-sized primary particles effectively relieve the high internal strain associated with the phase transition near charge end and fracture-toughen the cathode. Particle size refinement, achieved by inhibiting the grain growth during lithiation through the introduction of a high-valence dopant, imparts the necessary mechanical toughness to counter the high internal strain associated with the phase transition near charge end. The Li[Ni 0.95 Co 0.04 Mn 0.01 ]O 2 cathode, whose microstructure is engineered to mitigate the mechanical instability of Ni-rich layered cathodes, represents a next-generation, high energy-density cathode with a long cycle life and fast charging capability. Reference s : [1] K. B. Naceur, Tracking Clean Energy Progress (International Energy Agency, 2016). [2] H.-H. Ryu, K.-J. Park, C. S. Yoon and Y.-K. Sun, Chem. Mater. 30 (2018) 1155–1163. [3] G. W. Nam, N.-Y. Park, K.-J. Park, J. Yang, J. Liu, C. S. Yoon, Y.-K. Sun, ACS Energy Lett. 4 (2019) 2995–3001.