Study On Synthesis And Properties Of LiMn₂O₄ Cathode Material For Lithium Ion Battery

Rapid progress has been made in the research on lithium ion batteries due to its superior performance for recent years. These properties, however, are greatly affected by the selection and preparation of the materials, such as the electrode materials, the electrolytes and separators, particularly the cathode materials. LiMn₂O₄ is one of the most promising cathode materials for high voltage, low cost and non-toxicity. The quality of the LiMn₂O₄ powders strongly depends on the synthesis method and conditions, which determine the physical and chemical properties of the material, such as particle size, lattice parameters, stoichiometry and average Mn valence. This work concentrates on the preparation technique, structure and properties of LiMn₂O₄. In this paper, the spinel LiMn₂O₄ was synthesized by cellulose-citric acid-metal salts method, ultrasonic coordination precursor method and low-heating solid state method. The thermo-decomposing process of the precursors was studied by TG/DTA. The synthesized materials were characterized by X-ray diffraction, scanning electron microscope. Details of how varying the initial synthesis conditions affected the capacity and cycling performance of LiMn₂O₄ are discussed.(1) A technique was employed to synthesize spinel LiMn₂O₄ cathode materials by adding cellulose and citric acid to an aqueous solution of lithium and manganese salts. XRD, SEM, were used to examine the structural characteristics. The single phase with the spinel structure can be easily obtained by optimizing the processing parameters. Various synthesis conditions such as the calcination temperature and the citric acid-to-metal ion molar ratio (R) were investigated to determine the ideal conditions for preparing LiMn₂O₄ with the best electrochemical characteristics. The optimal synthesis conditions were found to be R=1/3 and a calcination temperature of 800℃. The initial discharge capacityof the material synthesized using the above conditions was 134 mAh g'1, and the discharge capacity after 40 cycles was 125mAh g"1, at a current density of 0.15 mA cm"2 between 3.0 and 4.35 V. The LiMn2O4 synthesized by such processing also has a good electrochemical performance, compared with LiMn2O4 produce by sol-gel method and reduce the price by cut down the content of organic acid,(2) A new route with ultrasonic for LiMr^CU used for lithium ion battery has been developed. This processing is simpler than normal route of preparing LiM^CV Phase structure was effected by citric acid addition, pre-sinter temperature and calcining temperature. The initial discharge capacity of the material synthesized at 800°C by the method was 133.7 mAh g"'and the discharge capacity after 45 cycles was 112.3 mAh g"1, at a current density of 0.3 mA cm'2 between 3.0 and 4.35 V.(3) The cathode material LiMn2-xCrxC>4 was prepared by ultrasonic coordination precursor method. The synthesized materials are characterized by X-ray diffraction, scanning electron microscopy, cyclic voltammetry and charge-discharge testing. The result showed that when the doping content of Cr was small, the materials can keep the spinel structure, has preferred surface morphology and improve the cycle properties. But its specific capacity was decreasing with the increasing of content of Cr. The loss of capacity of LiMn1.95Cro.05O4 was only 6.5% after 80 cycles. Compared with the same material made by other methods, the ultrasonic coordination precursor method can be employed to synthesized cathode material for lithium-ion battery as a new route.(4) The cathode material LiM^Cu was prepared by low-heating solid state coordination method. The spinel LiM^CM can be obtained by calcining in air at 550°C for 10 h in a muffle furnace in system 1. The optimal synthesis temperature was 550°C. The initial discharge capacity of the material synthesized using the above conditions was 116.3 mAh g'1, and the loss of capacity was only 5.1 % after 40 cycles, at a current density of 0.3 mAcm"2 between 3.0 and 4.35 V.Adding suitable amount of PEG-400 and NaCl, the spinel LiMn2O4 can be obtained by calcining in air at 300 °C for 10 h and there is trend of self-organization rod at 500°C.