Synergistic Cu/F co-doped P2-Na0.67Ni0.33Mn0.67O2 microsphere cathodes for enhanced sodium storage via dual doping and structural design

Abstract

The development of high-performance cathode materials is crucial for advancing sodium-ion batteries (SIBs). P2-type layered transition-metal oxides are promising cathode candidates, yet they suffer from capacity fading and poor rate performance, primarily due to irreversible phase transitions, Jahn–Teller distortion, and interfacial side reactions. To address these challenges, we report a Cu/F co-doped P2-Na_0.67Ni_0.33Mn_0.67O₂ cathode with a unique microsphere architecture. The microsphere structure reduces interfacial side reactions, while the synergistic effect of co-doping plays a key role: the Cu²⁺/Cu³⁺ redox couple elevates the operating voltage, and F⁻ doping enhances lattice stability and suppresses Jahn–Teller distortion. The optimized electrode delivers a high specific capacity of 139.6 mA h g⁻¹ at 0.1C and exhibits excellent cycling stability with 88.07% capacity retention after 100 cycles at 1C. In situ XRD reveals a highly reversible solid-solution reaction with a minimal volume change of only 1.5%. This comprehensive modification strategy provides a new avenue for designing high-stability layered oxide cathodes suitable for practical sodium-ion batteries.