Ni-based cathode materials for Na-ion batteries

Na-ion batteries (NIBs) have attracted significant attention owing to Na being an abundant resource that is uniformly distributed in the Earth's crust. Several 3d transition metal (TM) ions have been thoroughly investigated as charge compensators in single or multiple composition systems to enhance the electrochemical performance of cathodes for the practical applications. In this review, the composition-structure-property relationship of Ni-based cathodes has been reviewed as a design perspective for NIB's cathodes. The typical Ni-based cathode materials have been systematically summarized and comparatively analyzed, and it is demonstrated that Ni ions can be used to provide charge compensation. Moreover, Ni-based cathodes present high reversible capacity owing to the multi-electron redox reactions and suitable redox potential of Ni-ions redox. However, considering the abundance, cost, and hygroscopic properties of Ni element, the content of 0.15-0.35 per formula can be optimal for enhancing the performance of cathodes. Lastly, further perspectives on designing Ni-containing cathodes, including Ni-rich layered cathodes, have been discussed, which could promote the practical applications of NIBs for grid-scale energy storage in future.