Peng Zhongdong

Electrochemical characterization of surface-modified LiMn2O4 cathode materials for Li-ion batteries

To improve the performance, the surface of LiMn2O4 was coated with very fine MgO, Al2O3 and ZnO by sol-gel method, respectively. The structure and morphology of the coated materials were investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The charge and discharge performance of uncoated and surface modified LiMn2O4 spinel at 25°C and 55°C were tested, using a voltage window of 3.0–4.35 V and a current density of 0.1 C rate. There is a slight decrease in the initial discharge capacity relative to that of uncoated LiMn2O4, but the cycle ability of Li LiMn2O4 coated by metal-oxide has remarkably been improved. The EIS measurements of uncoated and Al2O3-coated LiMn2O4 were carried out by a model 273 A potentiostat/galvanistat controlled by a computer using M270 software, and using a frequency response analyzer (Zsimpwin) combined with a potentiostate (PAR 273). Consequently, the reason for the improved cycle properties is that the surface modification reduces the dissolution of Mn, which results from the suppression of the electrolyte decomposition, and suppresses the formation of passivation film that acts as an electronic insulating layer. In conclusion, the use of surface modification is an effective way to improve the electrochemical performance of LiMn2O4 cathode material for lithium batteries.

微波辅助固相法合成锂离子电池正极复合材料Li 2 FeSiO 4 /C

以Na 2 SiO 3 ·9H 2 O和FeCl 2 ·4H 2 O为原料, 采用低热固相反应获得了分散均匀的β-FeOOH/SiO 2 前驱体; 再以Li 2 CO 3 为锂源、聚乙烯醇和超导电炭黑为复合碳源, 通过微波辅助固相法合成了Li 2 FeSiO 4 /C材料. 通过X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)和恒电流充放电测试等方法对材料的结构、微观形貌及电化学性能进行表征. 650℃下微波处理12 min可获得结晶好、晶粒细小均匀的Li 2 FeSiO 4 /C材料; 在选用的微波合成体系下, 超导碳和聚乙烯醇热分解的无定形碳不仅利于合成反应的顺利进行, 而且提高了Li 2 FeSiO 4 的整体导电性能. 制备的复合正极材料在60 ℃下0.05 C 倍率首次放电容量为129.6 mAh/g, 0.5 C 倍率下为107.5 mAh/g, 0.5 C 下15次循环后保持为104.8 mAh/g, 具有较好的放电比容量和良好的循环稳定性能. 结果表明, 微波辅助固相合成工艺是制备Li 2 FeSiO 4 /C复合材料的一种很有前景的方法.以Na 2 SiO 3 ·9H 2 O和FeCl 2 ·4H 2 O为原料, 采用低热固相反应获得了分散均匀的β-FeOOH/SiO 2 前驱体; 再以Li 2 CO 3 为锂源、聚乙烯醇和超导电炭黑为复合碳源, 通过微波辅助固相法合成了Li 2 FeSiO 4 /C材料. 通过X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)和恒电流充放电测试等方法对材料的结构、微观形貌及电化学性能进行表征. 650℃下微波处理12 min可获得结晶好、晶粒细小均匀的Li 2 FeSiO 4 /C材料; 在选用的微波合成体系下, 超导碳和聚乙烯醇热分解的无定形碳不仅利于合成反应的顺利进行, 而且提高了Li 2 FeSiO 4 的整体导电性能. 制备的复合正极材料在60 ℃下0.05 C 倍率首次放电容量为129.6 mAh/g, 0.5 C 倍率下为107.5 mAh/g, 0.5 C 下15次循环后保持为104.8 mAh/g, 具有较好的放电比容量和良好的循环稳定性能. 结果表明, 微波辅助固相合成工艺是制备Li 2 FeSiO 4 /C复合材料的一种很有前景的方法.

Effect of la dopant on the structure and electrochemical properties of LiCoO2

The cathode material LiCo1−xLaxO2(x=0, 0.01, 0.02, 0.05) for Li-ion battery was prepared in solid phase. Effects of La dopant on the structure were analyzed by X-ray diffraction, and the morphology of the samples was observed by scanning electron microscopy. The results show that the structure of LiCoO2 becomes more and more non-perfect with the increasing content of La and some impurity peaks appear in the XRD pattern when the La content reaches 0.05. Meanwhile, a high synthesis temperature is advantageous to the intact and unitary compound. The initial discharge capacity of doped material containing La (x=0.01) synthesized at 900 °C reaches 160 mAh/g by charge-discharge test, which prior to that of non-doped material synthesized under the same condition. However, the increasing La content deteriorates the cycling performance. Therefore, the appropriate content of La is 0.01 and the optimum synthesis temperature is 900°C.