Insight into fast charging/discharging aging mechanism and degradation-safety analytics of 18650 lithium-ion batteries

As an unavoidable factor in the practical use of lithium-ion batteries, cyclic aging will lead to problems such as capacity decline, impedance increase, as well as polarization deepening. To better identify the influence of cyclic aging on safety performance, we carried out aging cycles on commercial 18650 lithium-ion batteries through fast charge/discharge mode. Thermal abuse test was conducted to characterize safety performance. The results indicated that the aging process is nonlinear and presents a three-stage change. Increased charge/discharge rate may significantly exacerbate aging state, making the three-stage of aging intersect with each other. In addition, cells with 2C/3C showed higher temperatures during cycling as compared with normally cycled fresh cells. The thermal abuse test results showed that aged cells have better thermal stability than the fresh cells, but much higher thermal runaway temperature was observed, which could be related to flammable gas and exothermic reactions occurring during fast charge/discharge process. This study indicates that aged cells within products such as electric vehicles are more likely to trigger the spread of thermal runaway.