Date of Award
Master of Science
Deyang Qu, Junjie Niu
In this study, we demonstrate that the low temperature power capability of a Li-ion battery can be substantially improved not by adding exotic additives into the electrolyte, but by rational design of the composition of the most commonly used solvents. Through the detailed analysis with electrochemical impedance spectroscopy, the formation of a homogenous solid electrolyte interphase (SEI) layer on the carbon anode surface is critical to ensure the performance of a Li-ion battery in a wide temperature range. Subsequent post mortem analysis after cycling of the negative electrode by XPS revealed that all the electrolyte compositions form similar compounds in the solid electrolyte interphase. However, the higher capacity low temperature solvents showed a higher percentage of LiF and a lower percentage of carbon containing species such as lithium carbonate and lithium ethylene di-carbonate. The electrolyte composition where cyclic carbonates make up less than 25 % of the total solvent showed increased low temperature performance. Additionally, solvent composition with higher percentage of linear short chain carbonates also showed an improvement in low temperature performance. Lastly, there was no significant impact seen with high temperature performances in nearly all the combinations investigated.
Chang, Jeremy, "Effects of Electrolyte Formulation on Graphite Anode for Wide Temperature Application" (2017). Theses and Dissertations. 1594.