Synthesis And Electrochemical Research Of Li₄Mn₅O₁₂ As Cathode Materials For Lithium-ion Batteries

Lithium-ion battery has been considered as one of the most promising green secondary batteries due to its excellent properties such as high working voltage, long cycling life, high specific energy, and environmental friendliness. Because of the high cost and toxicity of commercial LiCoO2 cathode material, the search for an alternative cathode material is pressing. Spinel lithium manganese oxide LiMn2O4 is a prospective alternative material for its low cost, easy preparation, high safety and nontoxicity. However, LiMn2O4 exhibits poor cycling stability, especially at elevated temperatures, which limits its commercialization. The substitution of Mn3+ by Li+ to form Li4Mn5O12 (Li1+0.33Mn2-0.33O4) can increase the valence of manganese so as to relieve the Jahn-teller distortion, leading to improved cycling stability.The Li-rich spinel Li4Mn5O12 powder was successfully prepared by oxidizing coprecipitation method. It was found that lithium excess helps to obtain a pure Li4Mn5O12 phase. Li4Mn5O12 particles had rod like morphology as observed by scanning electron microscope (SEM). With the increase of lithium, the particles transformed from nanorods into nanoplates, and then aggregated to form micron-sized secondary particles at last. At a low rate of 0.1 C, The sample prepared using a high concentration of LiOH showed a higher initial discharge capacity reached 161.1 mAh-g"1, close to its theoretic capacity (163 mAh·g-1). In contrast, the sample prepared a low concentration of LiOH exhibited a higher capacity and a better cycling stability at a high rate of 2 C.Nanosized Li4Mn5O12 powder with grain size of 20-50 nm has been synthesized by a spray-drying-assisted solid state method. The X-ray diffraction (XRD) indicated that the resultant was well crystallized and the SEM showed that the powder was composed of cube-like particles with smooth surface. The effect of spray drying and drying temperature on the microstructure and electrochemical performance of the final products have been investigated. It was found that the sample exhibit a good electrochemical performance at 3 V. The materials gave a discharge capacity of 158.7 mAh·g-1 in the first cycle at 0.5 C, and a capacity of above 80 mAh·g-1 was still kept after 300 cycles.The Li-rich spinel Li4Mn5O12 powder was prepared by multi-step and one-step template method without any catalyst and organic solvent. Compared with the sample obtained by multi-step route, the sample by one-step route showed a better crystallinity. The precursor particles prepared by hydrothermal-assisted route showed is fine with smooth surface. The electrochemical results indicated that the sample by one-step route gave a higher capacity than the sample by multi-step route (increased by 40～50 mAh·g-1 on average).