Depressed P3–O3′ phase transition in an O3-type layered cathode for advanced sodium-ion batteries

Abstract

O3-type layered oxides are regarded as promising cathode materials for sodium-ion batteries (SIBs). However, they commonly exhibit complex phase transitions and sluggish Na⁺ kinetics, thus incurring poor capacity retention and rate capability. Here, O3-Na_0.993Ni_0.382Mn_0.428Cu_0.098Sn_0.049O₂ is obtained with Cu²⁺ and Sn⁴⁺ doped into the transition metal layers. It is found that the dopants Sn and Cu can enhance the electrostatic interactions between Na and O and improve the electrical conductivity, respectively. This reinforces its structure stability upon Na⁺ (de)intercalation and suppresses the Na⁺/vacancy rearrangement and the P3 → O3′ phase transition at high voltages. It exhibits a smooth charge/discharge curve, excellent cycling performance (80.7% capacity retention after 500 cycles) and good rate capability (108.5 mA h g⁻¹ at 1000 mA g⁻¹). This study provides new insights into designing novel layered oxide cathode materials for SIBs.