Capacity Recovery Effect in Commercial LiFePO4 / Graphite Cells
Franz B. Spingler, Maik Naumann, Andreas Jossen
Abstract
We report a significant capacity recovery effect of more than 10% after continuous shallow cycling of commercial LiFePO4/Graphite cells. In a previous study on a LiFePO4/Graphite cell, we observed that capacity losses were more severe with shallow cycles than with full cycles. Herein, the effects of shallow cycling on aging are investigated in detail using three different LiFePO4/Graphite cell models, two 26650-type and one 18650-type. It is shown that a large portion of the capacity losses that occur with shallow cycling can be recovered by holding the cells at 0% or 100% state of charge. Differential voltage analysis and post-mortem experiments suggest that these capacity losses are caused by strongly non-uniform lithium distributions in the electrodes. Hypothetical mechanisms are presented and discussed that could lead to such non-uniform distributions of lithium.