Preparation And Electrochemical Performance Of LiMn₂O₄ Cathode Material

Nowadays,the problem of energy is very severe,lithium ion battery arises at the moment and has been widely used.The anode material is the key factor to influence the performance of lithium ion battery.The traditional cathode is LiCoO2,but it is replaced by other anode materials gradually,due to its high cost of materials,low capacity utilization,and serious environmental pollution.Spinel LiMn2O4 with rich raw materials,low cost,high safety,environmentally friendly and a series of advantages has becoming the most development potential anode material,and replacing LiCoO2 anode material.However,because of the dissolution of manganese in LiMn2O4,the capacity attenuated seriously in the process of charge-discharge,and cycle stability declined.To overcome the inherent shortcomings of materials,researchers have changed the synthesis method and synthesized different microstructure of product to improve the electrochemical performance of materials,spherical material is the developing direction of lithium ion battery cathode material.This thesis studied two synthesis methods and got different microstructure of samples to increase the reversible capacity and cycle stability of the material.In this paper,spinel LiMn2O4 cathode materials were successfully synthesized by the citric acid complex method.The product was characterized by XRD,SEM and electrochemical performance analysis,and it was studied that the influence of parameters of synthesis process on the material structure,morphology and electrochemical properties.As the drying temperature of the precursor is 150 ?,n(Li):n(Mn)=1.05:2,calcination temperature is 800 ?,the obtained powders have complete spinel structure,regular morphology of particles and uniform size distribution;it showed the highest initial discharge specific capacity in the process of charging-discharging,110.55 mAh·g-1,and after 30 cycles,the as-prepared LiMn2O4,retained 98.01%of its initial discharge capacities at 0.2C rate.Spherical porous LiMn2O4 particles were synthesized by combining the citric acid complex method with spray drying method,and the optimal parameters of synthesis process are determined.At 400 ?,spherical precursor convert to spinel LiMn2O4 completely,and better crystallized spherical micro porous LiMn2O4 were obtained at 700?,size distribution of the particles obtained at 700 ? is 2.0 to 3.5 ?m,and the porous particles wall are composed of 25-52 nm grains.The specific surface area of the product is 4.018 m2·g-1.The sample obtained at 700 "C has the highest initial discharge specific capacity of 123.85 mAh·g-1 at 0.2 C,between 3.0 and 4.5 V,after 30 cycles,it retained 97%of its initial discharge specific capacity.Adding excess lithium hydroxide to material,lithium plays the role of doping in materials,and lithium-rich spinel lithium manganite material is obtained,the product is pure,and there is none of impure phase.With the increasing of the content of lithium hydroxide,the specific capacity of the material is declining,however,after 30cycles,the retention of capacity in the process of charging-discharging is almost 100%.