Investigation of CO2 emissions in usage phase due to an electric vehicle — Study of battery degradation impact on emissions

The CO₂ emissions due to an electric vehicle in usage phase were estimated in this study. In usage phase, there is a possibility that indirect emissions due to electric vehicles are increased by the variation of vehicles´ performance, such as electricity consumption. In this paper, the impact of battery degradation on the vehicle´s indirect emissions was focused on and the variation of energy efficiency, and influence of battery replacement of an electric vehicle were investigated. Battery degradation is one of several significant factors that can influence indirect emissions, because batteries are the single energy source of electric vehicles and batteries´ degradations will influence vehicles´ performance directly. In addition, batteries are large components in electric vehicles and their replacements also have large impacts on indirect emissions. The variation of energy efficiency by battery degradation was investigated by drive tests with a test electric vehicle. Both the timing and impact of battery replacement on indirect CO₂ emissions were estimated through the test of Li-ion battery cells. From the results, it was expected that battery replacement would have larger impact on indirect CO₂ emissions than the variation of energy efficiency. The obtained estimation of indirect CO₂ emissions for 100,000 km driving was compared with the emissions from an internal combustion engine vehicle.