Degradation analysis and doping modification optimization for high-voltage P-type layered cathode in sodium-ion batteries

Advancing high-voltage stability of layered sodium-ion oxides represents a pivotal avenue for their progress in energy storage applications. Despite this, a comprehensive understanding of the mechanisms underpinning their structural deterioration at elevated voltages remains insufficiently explored. In this study, we unveil a layer delamination phenomenon of Na0.67Ni0.3Mn0.7O2 (NNM) within the 2.0-4.3 V voltage, attributed to considerable volumetric fluctuations along the c-axis and lattice oxygen reactions induced by the simultaneous Ni3+/Ni4+ and anion redox reactions. By introducing Mg doping to diminished Ni-O antibonding, the anion oxidation-reduction reactions are effectively mitigated, and the structural integrity of the P2 phase remains firmly intact, safeguarding active sites and precluding the formation of novel interfaces. The Na0.67Mg0.05Ni0.25Mn0.7O2 (NMNM-5) exhibits a specific capacity of 100.7 mA h g , signifying an 83% improvement compared to the NNM material within the voltage of 2.0-4.3 V. This investigation underscores the intricate interplay between high-voltage stability and structural degradation mechanisms in layered sodium-ion oxides.(c) 2023 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press. All rights reserved.