Investigation on topographic, electrochemical and thermal features of aging lithium-ion cells induced by overcharge/over-discharge cycling

The present study prepared five types of cells (the fresh cells, the cells degraded to 90 % and 80 % SOH (state of health) after overcharge cycling and the cells degraded to 90 % and 80 % SOH after over-discharge cycling) to illustrate the topographic, electrochemical and thermal features of aged cells induced by overcharge and over-discharge cycling. Cell's internal resistance aggravates significantly after overcharge and over-discharge cycling, notably for the charge transfer impedance and Warburg impedance. Both electrodes become expanded along the overcharge and over-discharge cycle. The lattice of positive electrode materials varies and the graphite degree of the negative electrode material decreases following the overcharge and over-discharge cycle; meanwhile, the passivation layer of the positive electrode material is revealed to grow obviously and the transition metal dissolution is found to aggravate. The thermal stability of the aged positive electrode materials is somewhat decreased, which further leads to the aggravation of thermal runaway behaviors for the aged cells; moreover, the severity exacerbates with the deepening of cell aging. In comparison with overcharge, the aging induced by over-discharge seems to decline the safety of cells more.