Synergistic cobalt doping and dual-carbon coating Na4Mn3(PO4)2P2O7 microspheres as high-performance cathode for sodium-ion batteries

Abstract

Na₄Mn₃(PO₄)₂P₂O₇ (NMPP) cathode materials exhibit promising application potential in sodium-ion batteries (SIBs), leveraging its cost-competitive advantages and high theoretical energy density. However, its low conductivity and Jahn–Teller effect induced by Mn³⁺ ions result in rapid capacity fading and lattice distortion, severely limiting its practical application in SIBs. In this study, we propose a synergistic optimization strategy combining cobalt doping with dual-carbon coating to enhance the electrochemical performance of the cathode material. Systematic investigations demonstrate that Co²⁺ substitution effectively regulates the electronic structure, enhancing redox activity in the high-voltage region (> 4.1 V) while suppressing Jahn–Teller lattice distortion of Mn³⁺, thereby accelerating Na⁺ diffusion kinetics and improving cycling stability. Furthermore, the dual-carbon microsphere structure formed by rGO and amorphous carbon composite coating establishes an efficient conductive network, enhancing the structural stability and conductivity. The optimized NMC_1.0PP@rGO delivers a high initial discharge capacity of 116.43 mA h g⁻¹ at 0.1C and demonstrates superior cycling stability with 80.7% capacity retention after 200 cycles at 5C, along with Coulombic efficiency exceeding 99%. This work provides a rational strategy to enhance the electrochemical performance of NMPP, highlighting its promising application prospects for manganese-based mixed phosphate materials.

Graphical abstract

A synergistic optimization strategy of cobalt doping and dual-carbon coating is applied to enhance the electrochemical performance of the Na₄Mn₃(PO₄)₂P₂O₇ cathode material. Appropriate cobalt substitution effectively alleviates Jahn–Teller distortion, improves the phase purity, and increases the redox activity in the high-voltage region. Meanwhile, a dual-carbon-coated microsphere architecture formed by rGO and amorphous carbon establishes an efficient conductive network. The optimized NMC_1.0PP@rGO cathode demonstrates a high reversible capacity of 116.43 mAh g⁻¹ at 0.1C and superior cycling stability with 80.7% capacity retention after 200 cycles at 5C.