Preparation And Modification Of LiMnPO₄ Cathode Material By Solvothermal Method For Li-ion Batteries

To meet the increasing demand for clean,high efficient,sustainable energy,the research on Lithium-ion batteries with better performance has attracted more and more attention.LiMnPO₄ material is considered as an promising cathode material for Lithiun-ion batteries due to its high energy density,low cost and environmental benign nature.However,low electronic conductivity and Lithium-ion diffusion rate of the material limit its application.In this paper,we adopt the solvothermal method to prepare LiMnPO₄ material,and high performance material has been synthesized by adjusting preparation condition,surface surfactant modification and carbon coating.Firstly,LiMnPO₄ materials with different morphology and particle size have been prepared by changing the ratio and adding order of the rectants.Results show that the material has better electrochemical performance when the ratio of LiOH/MnSO₄ is 2.7or 3.0 and adding order is MnSO₄,H₃PO₄,LiOH.To further improve the performance of the material,five kinds of surfactants are added into the reaction system and LiMnPO₄ materials with different morphology and particle size have been obtained.Nanoplates assembled in layer-by-layer material and square structure material are obtained respectively when the surfactant is CTAB and Triton X-100.The two kinds of material with smaller particle size,which exhibit discharge capacities of 157.9 and148.2 mA h g^-1 respectively,possess better electrochemical performances.Secondly,the material is modified by surface coating.The amount and effect of pyrolytic carbon and graphene on the performance of material was investigated.Pyrolytic carbon coating can enhance the surface electronic conductivity of LiMnPO₄nanoplates,which plays a major role in improving the performances of the material.Graphene can enhance the ionic conductivity between nanoplates,and then improve the electrochemical properties of the material.Electrochemical measurements indicate that LiMnPO₄ electrode with 4%pyrolytic carbon and 2%graphene exhibits better electrochemical performances.In addition,preparation of graphene and solvothermal synthesis of LiMn PO₄/G composite have been explored.