Micro- and nano-structural design strategies towards polycrystalline nickel-rich layered cathode materials

Polycrystalline nickel-rich layered transition metal oxides (NRLOs) are promising cathodes in commercial lithium-ion batteries, especially applied in the electric vehicle market. However, they suffer from serious structural degradation by forming micro-/nano-cracks along grain boundaries and severe electrochemical performance deterioration caused by high Ni3+/4+ reactivity. Although doping and coating strategies have been proven to effectively retard the onset of the damage, they are unable to overcome the inherent degradation. Nevertheless, micro- and nano-structural modifications of the NRLOs can directly counter their intrinsic degradation. Herein, this review focuses on the structure-activity relationship of NRLOs from their bulk microstructure to final battery performances. Firstly, the recent progress in different kinds of microstructures in NRLOs including core-shell structures, heterostructures, equiaxed or radially elongated structures in primary particles and their composites is clarified and summarized systematically. Then, their corresponding synthesis strategies, formation and modification mechanism are discussed in detail. Finally, future perspectives of the development of NRLOs with micro- and nano-structure modifications are presented to promote their large-scale application.