Preparation And Modification Of LiMn₂O₄ Cathode Material For Lithium-ion Batteries

Spinel LiMn₂O₄ has become the most promising cathode material for lithium-ion batteries due to its wide sources,low price,easy synthesis and no pollution properties.However,LiMn₂O₄ has its own defects that manganese ions are easily dissolved and structural instability,leading to rapid decay of capacity during the battery cycle,which limits its development.In this paper,improved synthesis method,bulk phase doping and surface modification were used to enhance the structural stability and overcome the problem of rapid capacity decay of LiMn₂O₄ at normal and high temperature.All these effectively revamp the defects of LiMn₂O₄ cathode material.The following studies was carried out to improve the electrochemical performance of LiMn₂O₄:1.Pure phase LiMn₂O₄ was synthesized by sol-gel method,using citric acid,tartaric acid and ethylenediamine tetraacetic acid as chelating agents.The effects of different chelating agents on the structure,morphology and electrochemical properties of LiMn₂O₄were investigated.It was shown that the best chelating agent was ethylenediamine tetraacetic acid,and the synthesized LiMn₂O₄ possess a complete spinel structure with sharp edges and corners.The first discharge specific capacity was 116.6 mAh·g^-1at 0.2 C,and the capacity conservation rate reached 86.7%after 50 cycles at the condition of 0.1 C rate.2.The best chelating agent ethylenediamine tetraacetic acid was used to prepare Al,Co,Mg three-element co-doped LiMn₂O₄ cathode material by sol-gel method.The phase structure analysis indicated that ternary co-doping did not change the original crystal structure of spinel LiMn₂O₄.After doping,the particle size decreased.The analysis result indicated that the electrochemical performance have been significantly improved.The structural stability of the material at high temperature was improved by a ternary co-doping method,which reduces the polarization,and greatly improved the cycle performance and rate performance.When the doping amount of Co and Mg was constant?0.05?,the Al doping amount was 0.02,obtained LiAl_0.02Co_0.05Mg_0.05Mn_1.88O₄ sample which exhibits the best electrochemical performance.The capacity retention rate reached 94.7%after 40 cycles at a rate of 0.1 C at 55?.3.Fe₂O₃ of different quality was coated on LiMn₂O₄ surface by co-precipitation method.The analysis result indicated that the coating effectively prevented the the corrosion of the cathode material by the electrolyte,reducing the polarization of the battery,making the material structure more stable,and improving the electrochemical performance of the material.The sample coated with 3wt.%Fe₂O₃ exhibited the best electrochemical performance.It delivered initial discharge capacity of 113 mAh·g^-1at a rate of 0.1 C,and the capacity conservation rate reached 86.7%after 50 cycles.On the basis of the coprecipitation method,the ternary co-doped LiAl_0.02Co_0.05Mg_0.05Mn_1.88O₄ as matrix material was further coated with Fe₂O₃.It indicated that original spinel structure was not changed by coating,and the electrochemical performance was further enhanced at high temperature.The capacity conservation rate of the synthesis of LiAl_0.02Co_0.05Mg_0.05Mn_1.88O₄/Fe₂O₃ reached 98.2%after40 cycles at high temperature.At the high current density of 5.0 C,the discharge specific capacity can still reach 94 mAh·g^-1.