Synergistically stabilized O3-type layered oxide cathodes via phase regulation of multi-cation doping enable high-performance sodium-ion batteries

Abstract

O3-type layered oxides, as high-capacity cathode materials for sodium-ion batteries (SIBs), face practical limitations due to poor structural stability, high Na+ diffusion barriers, and inadequate rate performance. This work proposes a Ca/Cu/Ti co-doping strategy and systematically regulates the crystal phase among 24 types of layered oxides, from P2-, mixed P2/O3- to O3-type phase, by precisely controlling the Na content and adjusting the transition metal layer microenvironment. The optimum O3-type Na0.80Ca0.06Ni0.48Mn0.40Cu0.06Ti0.06O2 delivers a high initial capacity of 151.37 mAh g−1 at 1 C (120 mA g−1) with 102.56 mAh g−1 retained after 200 cycles, while maintaining 80.67% capacity retention after 100 cycles at 0.1 C. Mechanistic studies and theoretical calculations demonstrate that an optimal Ca/Cu/Ti doping improves the Na+ diffusion kinetics, where Na vacancies activate Cu/Ni redox activity to sustain capacity under Na+-deficient conditions, and effectively suppresses Mn activity, thereby simultaneously enhancing the cycling stability of cathodes. This work provides a wide range of component-phase regulation, achieving highly stable Na-deficient O3-type layered oxides through a multi-cation trace doping strategy for SIBs.