Synthesis and Surface Modification of High-voltage Cathode Materials for Lithium Ion Batteries

• Main Authors: Pei-Qi Chen, 陳佩琪
• Other Authors: Chien-Te Hsieh
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/du64xy

碩士 === 元智大學 === 化學工程與材料科學學系 === 105 === This study adopts co-precipitation followed by calcination process to synthesize LiMnxFe(1-x)PO4/C (LMFP/C) cathode materials for Li-ion batteries to overcome the low working potential, poor conductivity and low lithium-ion diffusion rate of LiFePO4 cathode. Ammonia is used to adjust the pH value of colloidal suspension, and the as-prepared precursors are calcined at 700°C in high-purity N2 atmosphere. The LMFP/C powders are systematically characterized by X-ray diffraction, scanning electron microscopy, cyclic voltammetry, and charge-discharge test at various C rates. It is confirmed the influence of pH value and the ratio of manganese and iron ions on the mean electrochemical performance is very evident. The results indicate that the LMFP/C powders possess a spherical-like shape and the cathode material prepared at pH=8, x=0.5 display better performance among the others. The specific capacity of LMFP/C cathodes can achieve as high as 128.2 mAh g-1 at 0.1C. This enhanced rate capability and improved capacity can be ascribed to the synergetic effect on the cathode that thin carbon layer and Mn doping in the LMFP/C structure with Mn high oxidation-reduction potential. The present works shed some lights on the importance of LMFP/C, which originated from the pH value and the different ratio of manganese and iron ions in co-precipitation route on the electrochemical performance of Li-ion batteries.