Insight into structural and electrochemical properties of Mg‐doped LiMnPO 4 /C cathode materials with first‐principles calculation and experimental verification

Abstract

The LiMnPO₄ material has the advantages of abundant raw materials, safety and environmental protection, low price, high theoretical capacity, high stable working voltage platform and so on, showing great potential in lithium-ion batteries. Dissimilar metal ion doping can essentially improve the electronic conductivity of LiMnPO₄ and the material's charge and discharge performance, which is an ideal method to improve the electrochemical performance of LiMnPO₄. In this paper, the optimal doping concentration of Mg-doped solid solution material was calculated by first principles. At the same time, the corresponding content of LiMn_1−xMg_xPO₄/C cathode material was synthesized by hydrothermal method for experimental verification, so as to prepare the cathode material with excellent electrochemical performance. The results show that the doping of Mg cations does not change the phase of the main phase, but significantly changes the crystal structure parameters. The regulation of the band width directly affects the electronic conductivity of the material, which is directly proportional to the electrochemical performance. EIS and CV test results show that a proper amount of magnesium doping can effectively reduce the impedance of the material, and can effectively alleviate the polarization phenomenon of LiMnPO₄ electrode material, accelerate the diffusion rate of Li⁺, and it is easier to obtain high capacity battery. LiMn_23/24Mg_1/24PO₄/C showed the best electrochemical performance, with an initial capacity of 153.8 mAh/g at 0.05C ratio and a capacity retention rate of 97.5% after 100 cycles at 0.05C ratio. The theoretical calculation is in good agreement with the experimental results, which indicates that the theoretical calculation based on first principles can effectively provide a more reliable theoretical basis for experimental design and subsequent improvement.