Papers by Keyword: Spinel LiMn₂O₄

Abstract: Spinel LiMn₂O₄ nanorods were prepared by a hydrothermal method followed by solid-state lithiation. The produce β-MnO₂ nanowire as template, and LiOH·H₂O was used as lithium source. The spinel LiMn₂O₄ nanorods samples were characterized by SEM, XRD, (HR)TEM, and galvanostatic charge/discharge profile measurement. Compared with the LiMn₂O₄ nanoparticles, the LiMn₂O₄ nanorods showed superior cycling stability, better rate capability, good high temperature performance, and delivered a discharge capacity of 122 mAh/g (at 1 C, 100 cycles).

Abstract: Spinel LiMn₂O₄ was prepared by a molten-salt combustion synthesis using eutectic acetate salts as starting materials without any additional molten-salt at 400°C, 500°C, 600°C and 700°C for 3h. The experimental results show that the main phase of the produts is spinel LiMn₂O₄, and the impurities are Mn₂O₃ or Mn₃O₄. It has been found that elevated temperature was easy to generate Mn₃O₄, and low temperature was easy to generate Mn₂O₃. The product prepared at 600 °C is single phase LiMn₂O₄ and has good crystallinity. With increasing combustion reaction temperature, the particle sizes of the products were decreased. The product prepared at 600 °C has the highest initial specific capacity of 116.5 mAh•g^-1 at 0.2C, the capacity retention was only 77.2% after 50 cycles.

Abstract: Spinel LiMn₂O₄ cathode material was rapidly prepared by solid-state combustion synthesis which used lithium carbonate and manganese carbonate as raw materials and β-cyclodextrin as a fuel. The effects of amount of β-cyclodextrin and calcination temperature on their structure and electrochemical properties were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), galvanostatic charge-discharge test and cyclic voltammetry (CV). The optimal synthesis conditions were found to be 5 wt% β-cyclodextrin. Under these conditions, high-purity spinel LiMn₂O₄ was obtained, and its discharge specific capacity was 110.5 mAh/g in the first cycle and still retained at 99.9 mAh/g after 40 cycles.

Abstract: The LiMg_0.06Mn_1.94O₄ calcined at 500 °C for 3 hours then sintered at 600 °C, 700 °C and 800 °C for 3 hours by flameless liquid-phase combustion synthesis are prepared. Particle properties were characterized by X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy. Besides, galvanostatic tests and electrochemical impedance spectroscopy were performed to investigate the cycling performance. Particle properties analyses showed that LiMg_0.06Mn_1.94O₄ sintered at 600 °C has a single phase and the average grain size is about 80-200 nm with a little agglomeration, it also displays the highest initial capacity of 114.2 mAh/g and still remains 82.7% after 40 cycles. Results showed that sintered temperature by nitric acid assisted liquid-phase combustion method should be 600 °C.

Abstract: The spinel LiMn₂O₄ was synthesized by high temperature solid-state reaction and modified by coating carbon nanotubes (CNTs) which was used as the carbon source. The effect of different coated quantity on the electrochemical performance of spinel cathode materials was discussed. The morphology and structure of the material was characterized by SEM and XRD. The results indicated that the crystal grew well and morphology displayed excellently. Based on electrochemical performance test, the conclusion could be drawn: at 0.5C1C2C rate, the initial discharge capacity of LiMn₂O₄ coated by 5%wt CNTs was 100.5113.1103.6mAh/g respectively. After 20 cycles, the capacity maintained at 115.5111.3101.1mAh/g, which displayed better capacity retention.

Abstract: Many studies show spinel LiMn2O4 is one of the most promising cathode materials for lithium ion batteries. At present, urgent need is that capacity attenuation in the process of charge / discharge and cycle stability at high temperature are developed. The methods can be classified into bulk doped, surface coated and nanometer particles. Research progress about improving the electrochemical performance of spinel LiMn2O4 is summarized and further research trend is pointed out in this paper.

Abstract: Spinel LiMn₂O₄ was modified with Y₂O₃ coating by a chemical process. The crystal structures of the as-prepared samples were investigated by X-ray diffraction (XRD). The charge/discharge characteristics of the modified samples were evaluated at different rates between 3.0 and 4.4V. The discharge capacities of 2.0 wt.% Y₂O₃-coated LiMn₂O₄ are 116 mAh•g⁻¹, 99.7mAh•g⁻¹, 93.3mAh•g⁻¹ and 82.9mAh•g⁻¹ at 0.1C, 0.5C, 1C and 2C rates (at 20^◦C). The cycle abilities improvement of the spinel LiMn₂O₄ coated with Y₂O₃ are demonstrated at elevated temperature (55^◦C) and high rates (2C). From the analysis of electrochemical impedance spectroscopy (EIS), the improvement of cycle ability may be attributed to the suppression on the formation of the passivating films and the reduction of Mn dissolution, which result from the surface modification with Y₂O₃.

Abstract: Effect of calcination temperature on spinel LiMn₂O₄ by molten-salt flameless combustion synthesis using the lithium acetate (lithium nitrate), manganese acetate (manganese nitrate) as raw materials was studied. The structural characterization and morphology of the powder were measured by X-ray diffraction and Scanning electron microscopy. The results indicated that the main phase was LiMn₂O₄, which could be obtained at 400-700 °C. The product crystallinity and particle size increased with increasing calcination temperature, but the capacity and cyclic stability decreased. When LiMn₂O₄ was calcinated at 400 °C and 500°C, the initial specific capacity at 0.1C rate was 104.2 and 101.5 mAh·g^-1, respectively. After 30 cycles, the discharge capacity retention rate was 80.4 % and 83.5 %, respectively. The performance was the worst when LiMn₂O₄ was calcinated at 700°C, when the initial specific capacity was only 81.9 mAh·g^-1.

Abstract: A series of cathode materials for Li-ion battery, spinel LiMn_2-xCe_xO₄ (x=0-0.03), were synthesized by the method of solid-state reaction at high temperature. The XRD data showed that all the synthesis samples were pure spinel phase. The results of charge-discharge tests show that LiMn_1.98Ce_0.02O4 has the highest discharge specific capacity of 119.6 mAh/g, and the discharge specific capacity of the material was 108.5 mAh/g after 50 cycles at room temperature with a retention of 91.0%, and the coulombic coefficient was still high up to 99.8%.

Abstract: Single phase LiMn₂O₄ spinel powders have been prepared by solution combustion synthesis at 400 and 500°C using nitrate-acetate mixture raw materials without any fuels. The effect of single or double calcination has been studied contrastively. The phase composition and micro morphology are investigated by X-ray diffraction (XRD) and scanning electric microscope (SEM). The XRD results indicate that single phase LiMn₂O₄ can be obtained by single calcination at 400°C and 500°C, but there is Mn₂O₃ impurity in the sample prepared by double calcination at 500°C. SEM investigation exhibits that the particle size increases with raising calcination temperature or double calcination. The electrochemical performance tests indicates that the initial capacity, cyclic performance and rate capability of the samples prepared by single calcination are better than these of the samples prepared by double calcination.