Quantitative analysis of aging and detection of commercial 18650 lithium-ion battery under slight overcharging cycling

Lithium-ion batteries are widely used in electric vehicles to solve the problems of greenhouse gas emission. However, overcharging occurs due to the inconsistency of lithium-ion batteries, malfunction of charge control and inappropriate battery management. In order to solve the safety and cycle life problems of batteries suffering slight overcharging, quantitative analysis of the aging behavior, aging mechanisms and detection of slight overcharging cycling are studied in this manuscript. The results indicate that the cycle life of battery decreases linearly and exponentially with the upper cut-off voltage increasing when capacity and resistance are used as the threshold of the end of life respectively. The batteries have tolerance to slight overcharging with voltage lower than 4.6 V. The generated gas is not the main aging mechanism. Loss of active material is the main aging mechanism when the batteries are cycled at 4.4 V. Charging stress is the key factor triggering the loss of active material. The main aging mechanism becomes to be loss of lithium with the increase of voltage and cycle number due to the electrolyte oxidation, reduction and lithium plating. The differential voltage, coulombic efficiency and fast resistance increase are used as warming parameters of slight overcharging cycling.