| Summary: | 碩士 === 國立臺灣科技大學 === 化學工程系 === 102 === A need for improved and efficient energy storage technology is pragmatic for the sustainable development of our society. With this respect, the development of electrochemical energy storage technologies, such as lithium ion batteries, will play a grand role in the advancement of alternative renewable energy sources. Such battery technologies employ redox reactions with intercalation reactions in crystalline metal oxides, where lithium ions act as charge carriers to produce efficient and high power energy storage options. Therefore, a comprehensive understanding of the important processes occurring in lithium ion battery by using either computational or experimental approach will help to develop batteries with better performance.
The adsorption and decomposition mechanism of electrolyte on the cathode surface is one of the governing factors which control the stability, capacity and cyclic life. In this thesis, first principles calculations are used to study the adsorption and surface catalyzed decomposition mechanisms of ethylene carbonate on the (100) surface of fully discharged LiMn2O4. Six different adsorption configuration of EC on LiMn2O4 (100) surface was found by using GGA+U approximation. The adsorption strength and electronic properties of each site was then discussed by using density of states (DOS), projected density of states (PDOS) and electron density difference (EDD). Moreover, the initial decomposition mechanisms of EC on LiMn2O4 (100) surface is investigated by examining the minimum energy path between these two minima using the climbing image nudged elastic band reaction-pathway sampling scheme. In all sites, an electron transfer from the surface to the adsorbate was observed resulting in weakening and subsequent breaking of C-O bond and formation of open chain radical. Even though adsorption and decomposition reaction can occur on the (100) surface of LiMn2O4, for all configurations studied, the results show that the generation of gas is highly unlikely to occur at normal condition. In order to investigate the catalytic effect of the surface on the EC decomposition reaction, DFT calculations for the gas phase molecular decomposition of EC are performed and discussed in detail. In general, this work aims to give an insight about the initial stages in surface catalyzed electrolyte decomposition reactions on spinel cathode structure.
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