| Summary: | 碩士 === 國立臺灣科技大學 === 化學工程系 === 99 === Recently, additives for cathode material in lithium ion battery have been considerably received a great attention. In this work, several hyperbranch polymers with different degree of branch for A2B3-type additive have been successfully synthesized. After electrochemical process, these additives form the SEI layer on the surface of lithium cobalt oxide (LiCoO2, cathode material), which can enhance the thermal stability of lithium cobalt oxide in battery system. In order to discuss the performance outcome and to find out the reaction mechanism for the synthesized additives, model compound and linear polymer with the same repeat unit of hyperbranch polymer were also observed as additives in the battery system. After 5 cycles ( the SEI layer is completely formed), the full charge of electrode was analyzed using DSC test. The resulting test showed two phenomenon (1) the higher degree of branch of polymers provides outstanding enhancement of thermal stability (2) the higher molecular weight of additives can have a good thermal stability due to their stable structure. So that, these additives can give better thermal stability when added in the electrode. However, the cycling performance showed that the higher molecular weight results in (1) blocking of Li+ ion transport which made low cycling performance (2) reducing the ability of additives to be dispersed in the electrode which caused the SEI layer could not totally cover on the lithium cobalt oxide to achieve a good thermal stability enhancement.
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