Capacity Degradation In Lithium-Ion Batteries

Due to increasing gas prices and the dwindling of our planet’s finite oil resources, the hope for the future is to utilize electric vehicles. However, in the early transition stage of vehicle electrification, electric vehicles are more expensive than vehicles operating on internal combustion engines. Lithium-ion batteries are used because they exhibit high energy density, superior energy-to-weight ratio, and low-self discharge. However, safety issues and performance degradation due to aging related factors have become obstacles to the full market penetration of vehicles adopting this battery technology. As a result, consumers are reluctant to buy without knowing how long their investment will last. Recognizing this issue, several lithium-ion battery cells were tested in order to understand the aging of lithium-ion cells. One symptom of the aging process is capacity loss. Over time, the battery will be unable to retain as much capacity as compared to new, and eventually it becomes inapplicable. The cells underwent testing in a Peltier junction, and were subjected to different conditions of temperatures and charge/discharge that a battery would undergo in an electric vehicle. The capacity of these cells were measured once every few weeks using the Arbin BT-2000 tester attached to the Peltier junctions. This capacity is determined in ampere-hours and is visualized in MATLAB. In the end, this knowledge of capacity degradation will help give the consumers the understanding of electric vehicles for them to make an informed purchase