Synergistic surface coating and doping modification strategy for high rate and stable LiFe_0.4Mn_0.6PO₄ cathode materials

The manganese-based olivine material LiMn_0.6Fe_0.4PO₄ (LMFP) has received significant attention for its higher energy density compared to commercial LiFePO₄ (LFP). However, the inherent low charge conduction rate and Jahn-Teller distortion of Mn³⁺ limit the rate performance and cycle life of LMFP, hindering further application. To address these issues, we developed a simple temperature-programmed calcination method to in-situ synthesize the LiFe_0.4Mn_0.6PO₄ materials (M-LMFP) with innovative carbon coating and phase (Fe₂P and amorphous Li₄P₂O₇) doping structures. The surface-doped Fe₂P expanded the local Li⁺ diffusion pathway along the [101] direction. These phases enhanced the electronic conductivity and Li-ion conductivity of the LMFP, thus significantly improving the rate capability (from 137.5 mAh/g to 151.6 mAh/g at 1C). Remarkably, the stabilized structure enabled the capacity retention from 69.8 % to 96.6 % after 500 cycles at 1 C. Moreover, the density functional theory (DFT) calculations revealed a reduced band gap and increased transition metal states close to the Fermi level in the M-LMFP, further explaining the excellent performance. In distinction to conventional doping and coating methods, this temperature-programmed calcination method depends only on the carbon and Fe-containing components derived directly from the raw materials. Surprisingly, the strategy in this work is extremely scalable and applicable on a large scale without introducing any additional reducing gases or cumbersome processes.