Shabaz Khan

Date of Award

1-1-2019

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Energy Systems Engineering

First Advisor

Michael D. Mann

Abstract

Climate change is a big concern among the people. Day by day people are trying to increase the use of the sustainable energy in every sector of their life. Like other sectors, transportation sector manufacturers are beginning to shifting from fossil fuels based models to electric models. Manufacturers are trying to introduce electrified models from bicycles to cars. For energy storage, these electrified models are highly dependent on the battery. Lithium-ion cells have a high energy density, no memory effect, long cycle life and low self discharge quality, and are therefor highly used from portable electronics to electric vehicles everywhere. A main concern with a rechargeable battery is that it needs to recharge in regular intervals. This charging procedure is time consuming and can have a great impact on the total capacity of the battery, cycle life, and charging efficiency (or energy efficiency). A gasoline-base vehicle takes 3-5 minutes to fill the gas tank, but, an electric vehicle may need up to 10-12 hours (depend on the battery pack capacity) to be fully charged. For that, electric vehicles can become unreliable under emergency conditions and a deterent to regular users. As a result, charging technology has become a major concern among the manufacturers of electric vehicles. Using fast charging techniques can create unwanted side effects, like, thermal runaway, capacity fade, lithium platting and other electrochemical changes. In this thesis we developed an optimal fast charging technique for lithium-ion cells, which will be able to charge the cell faster compared with present industrial charging methods and maintain the long cycle life without significant decay of the capcity. We used 18650 lithium-ion cells for testing. During testing continuous cycling test was stopped when the capacity degraded by 20% of it’s original capacity. We compared our proposed fast charging technique with an available industrial charging technique. Due to differences in the charging times, when our proposed fast charging technique goes through more than 1600 cycles, the industrial charging technique had completed only 660 cycles. For comparision purposes, we chose 600 cycles as the common comparision point. We had found that our proposed technique took an average 63.7 minutes to charge 100% of the cell after 600th cycle. At the same time, the industrial charging technique took an average of 150 minutes to charge 100% of the cell. From this comparision it was clear the our proposed method is 135% faster than the available industrial charging technique. Capacity degradation was 10.5% for the fast charging technique and 6.6% for the industrial charging. As a result, we can say our proposed fast charging technique is faster and capabale of maintaining the capacity degradation rate within reasonable limits.

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