Preparation Of Li₂MnO₃Cathode Materials For Lithium-ion Batteries And Modifications

The lithium ion battery with specific energy is demanded by the development of electronic products, especially the development and application of new energy vehicles. But it is difficult to meet the needs of high energy density for the lithium ion battery with traditional cathode materials. So the developing of new high-capacity lithium-ion battery cathode materials is an urgent need. Much attention is paid on the layered structure of Li2MnO3based cathode materials. Because they are proved to have high theoretical capacity, good environmental compatibility and cheap raw material. But the application of these materials has been restricted by their low conductivity. In this paper nanometer scale Li2Mn03was successfully synthesized by gel combustion synthesis method and modified with Co addition.The effects of the amount of citric acid, calcination temperature, calcination time and the addition amount of L1NO3on structure, morphology and electrochemical performance of material powders were discussed. The increasing of the amount of citric acid, the calcination temperature and time extension can promote the growth of the crystal structure and expand the material particles particle size. Experiments show that pure Li2MnO3can be obtained with this method at600℃and above600℃. When0.5was chosen to be the ratio of citric acid and metal ion, a overdose of LiNO3in5%at600℃with12hours, the pure Li2MnO3obtained in optimized process showed the best electrochemical performance with50nm particle size. Its initial discharge capacity is up to195mAh/g at a current density of4.58mA/g,2.0-4.6V voltage range.The Co-Li2MnO3test results indicated the amount of citric acid, calcination temperature and calcination time have a great influence on structure, morphology and electrochemical performance of Co-Li2MnO3material powders. The material crystallinity and powder particle size increases with the calcination temperature and time enhance. Citric acid addition can promote crystal growth within a certain range; too much citric acid will cause incomplete combustion. The molar ratio of citric acid and metal ion for0.5,700℃calcining12hours is a better process condition for preparing Co-Li2MnO3materials by gel combustion synthesis method. Under these conditions, the discharge capacity of Co-Li2MnO3material increases with the cobalt content increasing.Material discharge capacity (130mAh/g to253mAh/g) and stability (the capacity retention rate from76.92%to93.81%) have been substantially improved by increasing cobalt content (0%to20%). Co-Li2MnO3with the20%Co content has the best electrical properties. Its grain size is about100nm. When the current density of4.58mA/g increased to13.74mA/g, the capacity is just reduced by20mAh/g after30cycles. Cobalt addition can reduce the impedance value in charge-discharge process and improve materials rate performance.