Modifying High-Voltage Olivine-Type LiMnPO₄ Cathode via Mg Substitution in High-Orientation Crystal

The LiMnPO₄ material with Mg²⁺ ion substitution in transition metal site is successfully obtained by a facile solvothermal method combining with the subsequent spray drying and pyrolysis. The TEM image shows the controlled crystalline orientation of the primary Mg-doped LiMnPO₄ particle, and the three-dimensional (3D) hierarchical micronano structure and the electronic structure of the Mg-doped material are investigated by the reconstructed nanotomography and X-ray absorption spectroscopy, respectively. The uniformity of Mg²⁺ ions substitution at the secondary particle level is confirmed by the transmission X-ray microscopy combined with X-ray absorption near edge structure. The prepared material exhibits an excellent electrochemical performance with the capacity of 156 mAh/g at the rate of 0.1 C, and good capacity retention of 100% after 400 cycles at the rate of 1 C. The in operando synchrotron X-ray diffraction data indicate that the performance improvement of the Mg-doped materials is attributed to the changed electrochemical reaction mechanism from the typical two-phase reaction for pristine LiMnPO₄ material to the two-phase reaction combined with the single-phase (solid-solution) reaction process. These findings provide a new approach and understanding on developing high-energy cathode materials for lithium-ion batteries.