Investigation On Cathode Materials Based On Manganese For Lithium-ion Batteries

With the rapid development of electronic facilities as well as energy and environmental concerning, people make high demands on batteries. Lithium-ion batteries are widely used for their favorable advantages of high voltage, big specific capacity, long cycling life and non-pollution. Transitional metal oxides with high inserted potential are usually used as cathode material of Li-ion batteries. At present, layered compounds LiCoO₂, LiNiO₂ and spinel LiMn₂O₄ are extensively studied. Spinel LiMn₂O₄ is considered as one of the most promising cathode materials for Li-ion because of its high voltage, high safety, low cost, easy recycling and environmental affinity among these materials.The spinel LiMn₂O₄ cathode material was prepared by sol-gel method on the basis of traditional solid-state reaction, and was modified by ion doping and surface coating. Besides, the 5V cathode material LiNio.5Mn1.5O4 and 1.5V anode material were prepared by solid-state method, and composed new battery system Li₄Ti₅O₁₂/LiNi_0.5Mn_1.5O₄ successfully. The structure, morphology and electrochemical performance of the materials were analysed by means of X-ray diffraction (XRD), scanning electric microscopy (SEM), charge-discharge at constant current, cyclic voltammety (CV), AC impedance (EIS) as well as various electrochemical analysis methods.The results show that the radius of the doped Cr³⁺, Ni²⁺, Co³⁺, Mg²⁺ are closed to Mn³⁺, the ions have incorporated into the host structure forming a solid solution easily. As the doping content increases, the first discharge specific capacity of samples are reduces, but the structural stability and cycle performances are improved. Together with the advantages of single ion doping, two and multiple doping was carried out in article. Although F-doped samples have decreased the average valence of manganese and have higher specific capacity, the increase of Jahn-Teller distortion and Mn dissolution lead to poor cycle performance. The materials have not only high reversible capacity but also well cycleability by F-Co-Cr ion co-doping. The property of LiCo_0.025Cr_0.025Mn_1.95F_0.05O_3.95 cathode material is the best, under the condition of 55℃, the first discharge specific capacity is 117.1mAh·g^-1, the capacity loss is only 11.78% after 30th cycles.The LiCoO₂ coated on parent material can be synthesized by sol-gel method, and the LiCoO₂ coated LiCr_xMn_2-xO₄ samples with smooth appearance, improve the resist ability of corrosion and decrease the dissolution of Mn to electrolyte. Among the samples, the material 5%LiCoO₂-coated LiCr_0.05Mn_1.95O₄ had better electrochemical properties, the first discharge specific capacity is 122.3mAh·g^-1, after 50 cycles, the discharge specific capacity keeps above 112.4mAh·g^-1.Besides, the test and analysis of the new battery system Li₄Ti₅O₁₂/LiNi_0.5Mn_1.5O₄ show that the cathode and anode material all exhibited spinel structure, the first discharge specific capacity is 124.31mAh·g^-1, after 50 cycles the capacity retention is 93.32%, compared with the battery system C/LiMn₂O₄, the properties improved about 10%, indicated that the charge-discharge and cycle performance of the battery system Li₄Ti₅O₁₂/LiNi_0.5Mn_1.5O₄ is very well.