Investigation of Characteristics Regarding Lithium-ion Battery Cells for an Electric Race Car Application

摘要

The objective of this paper is to investigate the performance, build quality and safety aspects of the lithium-ion battery cell used in the battery package of the Revolve NTNU 2016 electric race car, called Gnist. Cell testing revealed that the chosen cell can deliver charging currents of 70A for 300ms, 56A for 1000ms and maximum amplitude of 80A, i.e. the cell is able to deliver the maximum power requirements of the car's motors. Entropy was found to have a significant impact on heat generation, as charging has a cooling effect on the cell in most of the charge range. Removing charge bursts proved very disadvantageous in this context, as the decline in temperature was only 2.1°C while the decline in discharge capacity was 60%. Degradation testing showed that surrounding temperature is the most influential factor. When running two similar tests, one at 35°C and another at 25°C, the latter only degraded to 98.1% capacity after 221.5 normalised cycles while the former had a capacity of 93.1% after 245.3 normalised cycles. Furthermore, it was found that applying charging bursts would improve cycle life. When running the same test protocol with 35°C, but with no charging bursts, capacity was 90.3% after 147.8 normalised cycles.