Synthesis And Modification Of LiMn₂O₄ As Cathode Material For Lithium-ion Batteries

During these years, many investigations have been made on the cathode materials of lithium-ion rechargeable bateries. LiCoO2 has been commercialized for its high potential, high capacity and excellent recharge ability. LiNiO2 has also been developed as the substitutive cathode. However, cobalt and nickel compounds have economic and environmental problems, and the preparation of stoichiometric LiNiO2 is extremely difficult.Lithium-ion batteries have a good prospect in application for its favorable advantages of high voltage, high specific capacity, long cycling life and non-pollution.Cathode is the key of the development of lithium-ion batteries. LiMn2O4 spinel is believed to be the most promising cathode material for lithium-ion batteries.because.of its abundant resources, low cost, simple synthesis processing environmental friendly nature. However, the low initial capacity and poor cyclability prevent LiMn2O4 spinel from wide application. Several mechanism about the attenuation of LiMn2O4 spinel and some ways to improve the performance of this cathode material has been illuminated in the paper.In the present work, LiMn2O4 spinel compound was synthesized by means of the so called sol-gel process. The effects of the calcination process on the structure and properties of the LiMn2O4 spinel materials were discussed.The experimental results show that pure spinel phase of LiMn2O4 cathode was obtained under the experimental conditions of 750℃. Heating process was divided into 3 stages, i.e.150℃8 h—650℃12 h—750℃12 h. Their structure and electrochemical properties were characterized by means of XRD, SEM techniques. The initial discharge specific capacity of LiMn2O4 is 127.9 mAh/g, The LiMn2O4 spinel compound has a high capacity retention of 89.8% after 35 cycles.The important investigation points in the present thesis was modification of LiMn2O4 by ions-doping. Ni2+andF--doping spinels (LiNixMn2-xO4-yFy (x=0.03,0.05,0.1;y=0,0.05,0.1)) were prepared.The effects of sintering temperature and dopant content were studied. Their structure and electrochemical properties were characterized by means of XRD,SEM techniques. The LiNi0.1Mn1.9O3.95F0.05 powder with high discharge capacity and cycling performance is prepared at sintering temperature of 750℃. The initial discharge specific capacity of LiNi0.1Mn1.9O3.95F0.05 is 106.1 mAh/g,The powder has a high capacity retention of 96.5% after 35 cycles.Cr2+and F-doping spinels (LiCrixMn1.97O4-yFy (x=0.03,0.05,0.1 ; y=0,0.05,0.1)) were prepared. The effects of sintering temperature and dopant content were discussed. Their structure and electrochemical properties were characterized by means of XRD,SEM techniques. The LiCr0.1Mn1.9O3.95F0.05 powder with high discharge capacity and cycling performance is prepared at sintering temperature of 750℃. The initial discharge specific capacity of LiCr0.1Mn1.9O3.95F0.05 is 110.9 mAh/g, The powder has a high capacity retention of 97.9% after 35 cycles.Generally speaking, the cycling performance of spinel LiMn2O4 was evidently improved through cation doping even though the specific capacity of materials were reduced to some extent. Howere, the specific capacity of spinel LiMn2O4 was evidently improved through anion doping even though the cycling performance of materials were reduced to some extent. In order to improve electrochemical properties of spinel LiMn2O4, we will look for the ideal doping ions and gain the best ratio in the future.