Synergistic structural stabilization and interface engineering of LiMn0.6Fe0.4PO4 cathodes via Nb5+ doping and second-time carbon coating for lithium-ion batteries

Olivine-structured LiMn x Fe 1-x PO 4 (LMFP) has garnered significant attention as a cathode material for lithium-ion batteries (LIBs) due to its high energy density and low cost. However, its widespread application is limited by its inherently low electronic and ionic conductivities, as well as structural instability arising from the Jahn-Teller distortion of Mn 3+ ions and interfacial side reactions. To address these challenges, this study developed an innovative synergistic modification strategy combining Nb 5+ doping with second-time carbon coating to prepare high-performance LiMn 0.6 Fe 0.4 PO 4 /C cathode materials. Nb 5+ doping stabilizes the crystal structure during cycling by strengthening M-O bonding interactions, thus effectively alleviating the Jahn-Teller distortion of Mn 3+ . Meanwhile, uniform carbon coating layer effectively suppresses electrolyte attack on the material and mitigates Mn dissolution. Furthermore, the synergistic effects of Nb 5+ doping and second-time carbon coating significantly enhance the Li + /e − transport efficiency of the material by narrowing the band gap and constructing a continuous conductive network. As a result, the dual-modified LMFP/DC-2Nb electrode exhibits significantly enhanced cycling stability and rate capability, delivering an initial discharge capacity of 158.3 mAh g −1 at 0.1 C and achieving 93.2 % capacity retention at 1 C after 700 cycles. Moreover, a high specific capacity of 156.2 mAh g −1 is delivered after 200 cycles at 1 C and 50 °C with negligible capacity fading, and a discharge capacity of 119.8 mAh g −1 is maintained even at a high rate of 5 C. The synergistic modification strategy holds great potential for application and offers broad prospects for the design and development of high-energy-density, low-cost, and high-performance lithium-ion batteries.