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A study on the effects of SEI improving by wetting and formation temperature for fast charging of lithium-ion cell

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Title
A study on the effects of SEI improving by wetting and formation temperature for fast charging of lithium-ion cell
Author
Baek, Daewon
Advisor
Jeong, Kyeong-Min
Issue Date
2020-08
Publisher
Graduate School of UNIST
Abstract
Rapid charging technologies of lithium-ion batteries is required for electric vehicles. In electrochemical engineering, it is available to increase the energy density and rate capability by decreasing overpotential. However, lithium-ion batteries have unwanted Li plating problems that cause capacity degradation at rapid charging rates. In this experiment, we study the effects of homogeneity and composition of solid electrolyte interphase on rapid charge cycle performance of LiNi0.8Co0.1Mn0.1O2/graphite-silicon full cells to improve Li ion transfer in SEI. To control homogeneity and composition of the SEI layer which affects the Li dendrite problem, we experiment with a change of electrode wetting and initial charge temperature as SEI modification methods. Contact angle was experimented to compare the degree of electrolyte wetting into electrodes which was put in two different temperature, based on capillary rise principle. In chemical analysis of SEI, the inorganic components of SEI on anode surface such as LiF and Li2CO3 were found to be more compact and homogeneous in 45°C aging and 40°C formation condition compared to 25°C aging condition. In addition, when the 40°C formation condition was performed, the amount of Li2CO3 increased, so that a change of the SEI component was found. In analysis of difference between electrode surface and electrode inner SEI, in the case of 25°C aging condition, unstable formation of LiF generated in the electrode inner SEI might be also reason of the increased impedance of SEI, with inhomogeneous inorganic components in electrode surface SEI. As a result, although full cell in both 45°C aging condition and 40°C formation condition consumed more Li ions during pre-cycling, those clearly exhibited a superior rapid charge cyclability respectively by 5.8% and 13% than the baseline condition at 3C/1C cycle test.
Description
Department of Energy Engineering (Battery Science and Technology)
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