Fast charging technique for high power LiFePO4 batteries: A mechanistic analysis of aging

• Aging analysis of LiFePO4 cells cycled under standard and fast charge schemes.
• A high-fidelity mechanistic model was used to quantify the degradation modes.
• Similar cycle aging effects were found under both cycling schemes.
• Degradation is caused by a linear loss of Li inventory and loss of active material.
• Fast charging attained safe recharges without excess capacity fading from cycling.

One of the major issues hampering the acceptance of electric vehicles (EVs) is the anxiety associated with long charging time. Hence, the ability to fast charging lithium-ion battery (LIB) systems is gaining notable interest. However, fast charging is not tolerated by all LIB chemistries because it affects battery functionality and accelerates its aging processes. Here, we investigate the long-term effects of multistage fast charging on a commercial high power LiFePO4-based cell and compare it to another cell tested under standard charging. Coupling incremental capacity (IC) and IC peak area analysis together with mechanistic model simulations (‘Alawa’ toolbox with harvested half-cell data), we quantify the degradation modes that cause aging of the tested cells. The results show that the proposed fast charging technique caused similar aging effects as standard charging. The degradation is caused by a linear loss of lithium inventory, coupled with a less degree of linear loss of active material on the negative electrode. This study validates fast charging as a feasible mean of operation for this particular LIB chemistry and cell architecture. It also illustrates the benefits of a mechanistic approach to understand cell degradation on commercial cells.