Ageing Estimation of Lithium-Ion Batteries Applied to a Three-Wheel PHEV Roadster

Predicting the ageing behaviour of a lithium-ion battery is a challenging difficulty in plug-in hybrid electric vehicles applications. Invoking the expensive price of the energy density linked with considerable performances degradation over cycling, it is worth considering a battery lifetime optimization in the design process. The degradation will materialize by a capacity loss and an increase of the internal resistance. Capacity loss will affect the autonomy of the vehicle while an increase of the internal resistance will lead to an increase of the battery power losses and overheating. In the paper, the lifetime of a PHEV roadster battery pack is estimated by applying a real-life current discharge pattern, instead of the common ageing experiments based on constant current discharge patterns. A current cycle corresponding to a roadster power load has been used as input. This work involves an accelerated ageing experiment of individual LiFePO₄ battery cells through cycling. The cycle applied is derived from a speed cycle comprised of three parts: urban roads, rural roads and highways. For more than 1400 cycles, the capacity, internal resistance, voltage, current and temperature have been monitored.