Understanding Cell Degradation As a Function of Fast Charging

Abstract

The results of this work aim to inform development of charging protocols that are less damaging to cell health. To that end, degradation during fast charging is observed through capacity limited charging with rates ranging from 1C to 8C and SOCs ranging from 10-100%. This test matrix probes various failure modes including metallic deposition of lithium at the anode, continued formation of SEI, and full cell impedance rise. Reference electrode testing and harvested electrodes transferred to half cells are used in order to deconvolute these degradation modes.Through these experiments, we find that impedance rise is a function of charging rate alone and not on the amount of capacity passed at each cycle. Accordingly, limiting charging to a narrow SOC can delay cell aging, but not prevent eventual degradation. Particle cracking in the cathode is identified as the likely mechanism for impedance rise, supporting the notion that electrode design is essential to enabling fast charging.