On the degradation of lithium-ion batteries over a current ripple effect

• A charging system simulates real-life EV battery fast chargers has been developed. • The battery degradation effect under the different AC current ripple signals has been studied. • Charge transference resistance has been revealed as a key factor for the measurement of the real state of battery-health. Fast charging is one of the key technologies for the massive deployment of electric vehicles. A fast charger is a power converter which transforms energy from the AC electricity grid into the rectified DC current needed to charge battery packs. Depending on the type of the charger used, the rectified DC current may inject harmonic current components to the pack. As fast charging is a relatively new technology, limited research output has been found on the application of repetitive cycle tests featuring realistic AC charging current content over a long time. However, several battery testing procedures such as variable power pulses, have been proposed and are widely used to estimate the lifespan of lithium-ion batteries, yet all of them based on well-filtered DC current charging. This article proposes a novel battery testing protocol featuring artificial AC waveform signals used to simulate a fast charger of poor quality applied to commercial electric vehicle batteries. The analysis based on the proposed advanced testing profile estimates that the impact of high amplitude current ripple on battery deterioration can be up to 15% and is capable of providing a robust estimation of the internal impedance associated with a 20% battery capacity loss.