Synthesis And Characterization Of LiMnPO₄ Positive Materials For Li-ion Battery

The continuous exploitation of new energy source has become important foundation for sustainable development of the human society. Batteries with high standand are required along with the development of science and technology. The new types of the rechargeable Li-ion batteries with high capacity, low consumption, environmentaly friendly and light mass, have been intensively interested.Since A. K. Padhi made the pioneering work in phosphate system, a large number of researchers start to join the ranks. Lithium iron phosphate(LiFePO4)is a new type of lithium-ion battery cathode material:the material is non-toxic, environmentally benign, abundant supply, has high capacity, cycling performance and excellent thermal stability, particularly in the large-scale lithium ion batteries. Lithium manganese phosphate has the similar structure and Li+diffusion channels as Lithium iron phosphate.In this paper, we will report the sol-gel and solide-state method for producing LiMnPO4. We examines the factors that influencing the performance and stability of this material, and gropes the best respectively conditions.In the sol-gel method, lithium carbonate, manganese citrate complexes, ammonium dihydrogenphosphate and citric acid dissolved in water were heated at 60℃under stirring after adjusting the pH to 0.5-3.7 by adding concentrated HNO3 and ammonia. The dried green solid was heated at 120℃to get rid of water before annealing at 500-600℃for 3 h in Ar-H2. We examines the influence of calcinated temperature, PH and the dosage of citric acid. All of the conditions have great influences on the sample. The results showing when the PH=3.2., citric aci:citric acid manganese=1:1. annealing at 550℃for 3 h, the sample has the best performance, the firstdischarge capacity is 118.1mAh/g. after 20 cycles, the discharge capacity was 108.1mAh/g.In the solid-state methods, lithium carbonate, manganous carbonate and ammonium dihydrogenphosphate are the reactants. We examines the effects of the different carbon source, the carbon content, reaction temperature and times, the proportation of the lithium and manganese ere investigated. Among them, the the different carbon source, reaction temperature and the proportation of the lithium and manganese have great influences on the sample. The results show that the sample with addition of 6% resorcinol formaldehyde resin as the carbon source synthesized at 600℃for 3h show the best performance:The initial discharge capacity was 121.6mAh/g at 0.02C and an overall reversible capacity of 110mAh/g has been retained after 20 cycles. While at 0.1C, the discharge capacity was 110mAh/g and more than 60mAh/g at 1C.