Extreme Fast Charge Challenges for Lithium-Ion Battery: Variability and Positive Electrode Issues

Enabling a 10 min fast charge for electric vehicles is a possible route to reduce range anxiety and increase the utility of electric vehicles. While lithium plating during fast charging is a known challenge, the full suite of limitations which occur in full cells during a 10 min fast charge are unknown. In the present work the central constraints of extreme fast charging are explored through extensive experiments and analysis in single layer graphite/NMC532 pouch cells. Methods of developing fast-charging protocols considering the impedance and transport limitations are presented and the relative benefits of altering the charging rate, profile, relaxation, etc., are investigated. Analysis during and at the end of cycling identified both known and unexpected aging pathways. The most distinct outcomes from the work are a significant increase in cell-to-cell variability as the number of fast charge cycles increase [up to 11% (1σ)] and the identification of distinct aging of the NMC532 positive electrode including cracking of the secondary particles and a trend toward under-lithiation of the positive electrode. While significant aging of the positive electrode was observed, only a few conditions had discernible Li plating and no distinct reversible Li signature was seen during periodic reference performance tests.