Controllable Synthesis Of High-performance LiMnPO₄ Cathode Material By Solvothermal Method

Olivine-type LiMnPO4 has been considering as a promising cathode for next-generation high-power lithium ion batteries due to its environmental benignancy, low cost and excellent thermal stability. However, the bad electrochemical performance of LiMnP04, which results from the 1D lithium diffusion path channel, the poor electron and ion conductivity and the John-Teller lattice dissordtion arround Mn3+, has made it difficult to practical use. Up to now, carbon coating and decreasing the particle size are the efficient way to enhence the properties.Here we synthesized LiFePO4 nanoparticles using EG-based solvothermal method, confirming the ratio of the raw material and the mixing sequence are the key factor during the solvothermal process. Beside, by adding the amout of H3PO4 and changing the mixing sequence in the precursor, we controllable prepared a series of LiFePO4 nanoparticles with different morphology.Based on the above research, we report here a simple solvothermal synthesis of LiMnPO4 nanocrystals using LiOH·H2O, H3PO4 and MnSO4·H2O as precursor and ethylene glycol as reaction medium. We found that the ratio of the starting materials exerts a great influence on the morphology, size and crystal orientation of LiMnP04 nanocrystals. We confirmed the critical role that H+ concentration plays in altering the crystallization habit of LiMnPO4. The results showed that after carbon coating, the plate-like LiMnP04, which was synthesized from the precursor with a LiOH/H3PO4/MnSO4 ratio of 3:1.1:1, exhibited the best electrochemical performance, yielding a discharge capacity of 108.2 mAh g-1 at 10 C and keeping a discharge capacity of 133.5 mAh g-1 after 100 cycles at 0.5 C.Besides, we successfully observed the morphological transformations of LiMnPO4 nanocrystals upon solvothermal treatment, just by gradually increasing the amount of H3PO4 in the precursor. The LiMnPO4 nanocrystal turns from the spindle-like morphology to the plate-like structure dramatically, and then the nano-plate become larger and randomly shaped as the increase of the H3PO4. The electrochemical performance of the as prepared LiMnPO4 products exhibit a regular changes with the increase of H3PO4. The correlation between the LiMnPO4 crystal morphology and the electrochemical performance is investigated and discussed. All of the plate-like LiMnP04 samples exhibited the excellent rate and cycling performance for the fast electron and Li+ ion transformation, in comparison to other particles.