Cobalt sulfide and nickel sulfide synthesized by hydrothermal method in application for anode materials of Lithium-ion batteries

• Main Authors: OU YANG, PO YU, 歐陽伯禹
• Other Authors: WANG, CHAO HONG
• Format: Others
• Language: zh-TW
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/wxg5b9

碩士 === 國立中正大學 === 化學工程研究所 === 107 === Abstract Among kinds of anode materials, metal sulfides can form various sulfides, which have huge development potential. Unfortunately, they suffer from large volume expansion, leading to broken structure of electrode materials during lithiation/delithiation cycles. In this work, cobalt sulfide and nickel sulfide were made from one-step hydrothermal method. A excellent conductive commercial graphite sheet was added to changing original morphology of sulfides and minified particle size in order to overcome the disadvantage of volume expansion. Different adhesives was used to get better mixing ratio of the slurry. To enhance the electrochemical performance of cobalt sulfide and nickel sulfide, FEC was added in order that the denser SEI film was formed to promote cycle life. The capacity of cobalt sulfides was 674mAh/g at first cycle. After 50 cycles, cobalt sulfides exhibited a capacity of 289mAh/g. When 5wt.%FEC was added, cobalt sulfides have a great capacity retention up to 95.4% and a high reversible capacity of 666mAh/g after 50 cycles. After adding 5wt.%FEC, the capacity of nickel sulfides was increasing from 453mAh/g to 597mAh/g through 50 cycling test. All of the electrochemical performance was gained noticeable rising. Finally, the ratio of metal ions and sulfur ions was slightly changed, and the parameters of temperature and time were adjusted to synthesize high-purity cobalt sulfide and nickel sulfide. The optimum synthesis condition of nickel was tested and compared with the original condition. Otherwise, adding FEC in electrolyte let nickel sulfide stable during cycling test. The electrode activation was occurred, resulting in the first cycle coulombic efficiency was not good, but the cycle stability was excellent. After adding 5wt.% FEC, the capacity of nickel sulfide was up to 900mAh/g through 50 cycling test. Modulating the parameter did not rise the performance of cobalt sulfide and even decreased a lot. Therefore, it was reasonable to doubt if the particle size and commercial graphite sheet was the key point. The capacity did not fall to 200mAh/g when the commercial graphite sheet and FEC was adding during the synthesized process. However, the capacity of 600mAh/g was maintained after cycles. The particle size and commercial graphite sheet was not only important key to influence electrochemical performance but also reducing the stress of volume expansion and complete electrode. Key words：hydrothermal method、cobalt sulfide、nickel sulfide、lithium-ion battery