Optimisation of LiFe1−xMnxPO4 cathode material via a defect engineering strategy controlled by lattice mismatch

Olivine-structured LiFe (1− x ) Mn x PO 4 (LFMP) cathode materials are promising because they combine the excellent rate capability of LiFePO 4 with the high operating voltage of LiMnPO 4 . However, lattice distortion induced by the Jahn–Teller effect in Mn 3+ considerably impedes lithium-ion transport, limiting the full performance of cathode materials. To address this issue, this study proposes a defect engineering strategy based on lattice mismatch regulation, enabling the controlled design of dislocation defect types through precise adjustment of the Fe/Mn ratio. A comprehensive investigation of the underlying mechanisms reveals that an optimal Fe/Mn ratio generates specific local dislocation morphologies by controlling the degree of lattice mismatch. This effectively transforms Jahn–Teller induced lattice defects into channels that facilitate rapid lithium-ion transport, thereby improving electrochemical performance. Accordingly, LiFe 1− x Mn x PO 4 ( x = 0.3, 0.4, and 0.5) cathode materials are synthesised using a solid-state method. The best electrochemical performance is achieved at a Fe:Mn ratio of 6:4, delivering an initial discharge capacity of 178.3 mA h g −1 , a Coulombic efficiency of 94.3%, and a capacity retention rate of 96.5% after 1000 cycles at 1 C. This finding provides a new approach for developing high-performance electrode materials for lithium-ion batteries through defect engineering design strategies.