The Research On Preparation And Coating Modification Of LiMn₂O₄ With Special Morphology

Lithium-ion batteries have attracted widespread attention owing to their high specific energy density,long cycle life,no memory effect,and environmental friendly.Besides,the cathode electrode materials are the key parts which limit the electrochemical performance of lithium-ion batteries.Spinel LiMn₂O₄ is a promising cathode material due to its rich material source,low cost,and environmental friendly.However,the rate performance of common spinel LiMn₂O₄ unable to meet the requirements for some applications,and the severe degradation of circulating capacity at high temperatures has also limited its wide application.Compared with ordinary microspheres LiMn₂O₄ positive electrode materials,LiMn₂O₄ cathode materials with hollow and porous microsphere structure exhibit larger specific surface area and shorter Li⁺ion transport channels,which can achieve the purpose of improving material rate performance.Furthermore,coating modification is one of the most efficacious ways to improve the high temperature cycling performance of LiMn₂O₄ positive electrode materials,and Al₂O₃ is one of the most widely used coating materials due to its lower material cost and mature coating methods.Co-precipitation method was used to fabricate Li Mn₂O₄ cathode materials with two kinds of special morphology of hollow structure and porous microsphere structure,respectively.Then the porous microsphere structured LiMn₂O₄ material was modified by alumina coating.Firstly,hollow structured LiMn₂O₄ cathode material was prepared by co-precipitation using a mixed solution of sodium hydroxide and sodium carbonate as precipitants.The hollow LiMn₂O₄ has a unique cavity structure,which can provide a large specific surface area and shorten Li⁺ion transmission channel.Moreover,this unique cavity structure can also achieve the purpose of improving material rate performance.The hollow structured LiMn₂O₄ cathode material was charged and discharged under 0.2 C rate at room temperature.Its initial discharge specific capacity is 122.0 mAh g^-1 and the capacity retention rate can reach 97.5%after 100 cycles.When the rate increased to 10 C,the discharge specific capacity could retain 84 mAh g^-1.Secondly,a porous LiMn₂O₄ microspheres cathode material was prepared by precipitation method.This material retained part of the hollow structure cavity,filled with some LiMn₂O₄particles in the cavity.Moreover,the particles were free to form a channel structure which can promote the contact of the electrolyte with the electrode material and provide a better rate performance.The porous LiMn₂O₄ microspheres cathode material was charged and discharged with 0.5 C rate at room temperature.The material showed a high initial discharge specific capacity of 133.3 mAh g^-1 and the capacity retention rate of 84.2%after 100 cycles.And at the10 C rate,the discharge specific capacity can reach 90.9 mAh g^-1.Finally,the porous LiMn₂O₄microspheres cathode material was modified by Al₂O₃ with the optimum coating amount of 3wt%.The coated LiMn₂O₄ material was discharged under 0.5 C rate at room temperature,and the initial discharge specific capacity was 129.6 mAh g^-1.After 100 cycles,the capacity retention rate could reach 98.8%.When the rate increased to 5 C,the material still showed a high initial discharge specific capacity of 107.5 m Ah g^-1 as well as a high the capacity retention rate of 89.7%.In this work,LiMn₂O₄ cathode materials with hollow and porous microsphere structure were prepared to investigate the effect of special morphology LiMn₂O₄ materials on the electrochemical performance of the battery,which provided a new idea for the modification of LiMn₂O₄ cathode materials.Moreover,porous Li Mn₂O₄ microspheres with Al₂O₃ coating also provides a novel idea for coating modification.