Synergistic Cu/F Co-doped P2-Na 0.67 Ni 0.33 Mn 0.67 O 2 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 0.67 Ni 0.33 Mn 0.67 O 2 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 0.1 C and exhibits excellent cycling stability with 88.07% capacity retention after 100 cycles at 1 C. 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.