Second life batteries lifespan: Rest of useful life and environmental analysis

Road transportation is heading towards electrification using Li-ion batteries to power electric vehicles offering eight or ten years' warrant. After that, batteries are considered inappropriate for traction services but they still have 80% of its original capacity. On the other hand, energy storage devices will have an important role in the electricity market. Being Li-ion batteries still too expensive to provide such services with economic profit, the idea to reuse affordable electric vehicle batteries for a 2nd life originated the Sunbatt project, connecting the automotive and electricity sectors. The battery reuse is, by itself, a path towards sustainability, but the cleanliness of energy storage also depends on the electricity generation power sources and the battery ageing or lifespan. This paper analyses the rest of useful life of 2nd life batteries on four different stationary applications, which are: Support to fast electric vehicle charges, self-consumption, area regulation and transmission deferral. To do so, it takes advantage of an equivalent electric battery-ageing model that simulates the battery capacity fade through its use. This model runs on Matlab and includes several ageing mechanisms, such as calendar ageing, C-rate, Depth-of-Discharge, temperature and voltage. Results show that 2nd life battery lifespan clearly depends on its use, going from about 30 years in fast electric vehicle charge support applications to around 6 years in area regulation grid services. Additionally, this study analyses the day-to-day emissions from electricity generation in Spain, and states that grid oriented energy storage applications will hardly offer environmental benefits in the nearby future. On the other hand, applications that go by the hand of renewable power sources, such as self-consumption applications, are much more appropriate.