| Summary: | 碩士 === 國立中央大學 === 化學學系 === 106 === Safety is the primary issues in all aspects of lithium ion battery applications. This issue is becoming even more important with the increasing adaption for advanced electronic devices and in electric car applications where higher power and energy density are required. Longer cycle life, stable high temperature performance and safety in these advances lithium ion batteries become highly critical. It is known that electrolyte will react with the active material under the charge/discharge cycle, causing the lithium salt in the electrolyte to decompose which releases heat. In over-charging and over-heating conditions, the cathode material releases oxygen which increases internal pressure and further raised the cell temperature. This which eventually causes the breakdown (termination) of the battery, or even worse causes the cell to burst and explode, accompanying with burning of the released electrolytes.
In this study, we will exam the boosting of performance on lithium battery by two new types of electrolyte additives; mPhMI and p-PhMI in terms of lengthening cycle life stability and improving safety. While mPhMI is prepared by copolymerization of 1,3-dimethyl-barbituric acid (1,3-DBTA) with Bis(4-meleimido phenoxy)phenyl phosphine oxide (PhMI), p-PhMI is the homo-polymerization of PhMI monomers alone. In the copolymer mPhMI, phosphorus atoms in PhMI unit can reduce the release of oxygen and inhibit the electrolyte decomposition, and 1,3-DBTA is found to serve additional function to capture free radicals which hinders the combustion reaction. These additives have the advantage of forming a stable SEI layer over coating the electrode to improve the lithium battery long cycle performance and improve safety. The cycle life test shows that with the addition of mPhMI and p-PhMI in the electrode, the capacity retention are 86.93% and 90.59%, respectively after 80 cycles. The XPS spectrum provides the direct evidence to the reduction of lithium salt decomposition on the SEI layer in presence of the electrolyte additives. SEM study also suggested negligible change of the pore structure on surface of the SEI layer and the development of crack on cathode particles, after 100 repeated cycles in presence of these electrolyte additives.
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