The Properties and Surface Modification of LiNi0.5Mn1.5O4 Cathode Material for Lithium-ion Battery

• Main Authors: Yan-Ting Chen, 陳彥廷
• Other Authors: I-Ming Hung
• Format: Others
• Language: zh-TW
• Online Access: http://ndltd.ncl.edu.tw/handle/47278672149629160876

碩士 === 元智大學 === 化學工程與材料科學學系 === 101 === The spinel LiNi0.5Mn1.5O4 cathode material has been successfully prepared by sol-gel method. The effects of pH conditions, calcining temperature, time and the mo-lar ratio of citric acid on the structural and morphological characterization and elec-trochemical performance of the products were investigated by XRD, SEM, cyclic voltammetry and galvanostatic charge-discharge tests in detail. The results show that all the parameters in this study have a remarkable impact on the crystallinity, the purity, the Mn3+ amount and the particle size distribution. Among the all of samples, LiNi0.5Mn1.5O4 synthesized by pH 7; calcined at 850 oC for 12h and molar ratio = 2 of citric acid / metal demonstrated the most excellent electrochemical performance. It delivers high initial capacity of 130.8 mAhg-1 at 0.2 C, and high rate discharge capa-bility of 112.1 mAhg-1 and 84.1 mAhg-1 at 2 C and 5 C, respectively. Therefore, the optimal method to prepare LiNi0.5Mn1.5O4 was observed in first part of this study. In the second part, we want to improve the electrochemical performances of LiNi0.5Mn1.5O4. Therefore, La0.6Sr0.4Co0.8Fe0.2O3- (LSCF)－coated 5 V spinel LiNi0.5Mn1.5O4 as cathode was prepared by same route with ball-milling. The electro-chemical properties of coated－LiNi0.5Mn1.5O4 were also investigated by galvanostatic charged / discharged tests, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) ,too. It was found that the LSCF－coated LiNi0.5Mn1.5O4 samples showed lower lithium-ion diffusion resistance and charge transfer resistance than uncoated LiNi0.5Mn1.5O4. After surface modification, the discharge capacity at high C-rate was enhance from 58.8 mAhg-1 to 107.8 mAhg-1. The improved electro-chemical performance of the surface modification samples can be attributed to the de-creasing contact area between the electrode and electrolyte during electrochemical cycling and enhance the electronic conductivity by LSCF－coated layer. As the re-sults, the surface coating with LSCF is an effective approach to improve the electro-chemical performance especially at the high C－rate.