The effects of pulsed charging on lithium ion cells

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Gaddes, Daniel William
Joshi, Yogendra
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As part of this thesis, the effects of pulsed charging on lithium-ion batteries were investigated. Pulsed charging is an alternative method of charging batteries in which the charge current is interrupted by periods of no current and discharge. It has been suggested in past research that this method can both charge the cell faster and improve the lifetime of the cell through improving the internal kinetics. Based on past literature, influential parameters of the pulse protocol were identified. In this thesis these values were tested through both single charge and lifetime measurements to analyze the impact on charge rate and lifetime. Additionally, a mathematical model was developed to analyze the cell under pulsing for internal conditions which cannot be easily measured experimentally. As part of the single charge testing, the pulse parameters that were determined to be most influential, the frequency of the pulses, the magnitude of the charging current, the root mean squared current value, the discharge capacity, and the ratio of discharge capacity to charge capacity, were analyzed. After this, two pulsing plans were selected to be tested to evaluate the impact on aging mechanisms and the lifetime of the cells. These plans were also analyzed within an electrochemical model, based on the Doyle, Fuller, Newman model to analyze any potential differences on the internal kinetics. The results of these tests were compared to cells charged under the constant current constant voltage condition, using an equivalent mean current for all tests and one hour to charge the cell. The results indicated that pulses with constant currents and pulse duration do not produce positive effects, as all parameters are dominated by the higher current magnitude required by the pulse method to maintain an equivalent mean current. Preliminary analysis of a different pulsing plan, in which the current begins high but decreases as the cell charges does result in a greater capacity before reaching the upper voltage limit, as well as a greater capacity within one hour, and is a potential area for further research.
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