Accelerated aging protocols design for Li-ion batteries based on equivalence of the degradation mechanisms

A reasonable and efficient accelerated aging protocol is crucial for the design and application of Li-ion batteries. Most of the current research on accelerated aging protocols simply apply higher level of stress to raise the acceleration rate, without considering the aging mechanism. However, the same capacity attenuation doesn't mean the same state of health, considering the nonequivalence of mechanism. For the first time, this study proposes a method to design the accelerated aging protocols completely equivalent to the normal aging state and have a high acceleration ratio. Firstly, two degradation mechanisms, loss of lithium inventory (LLI) and active materials of positive electrode (LAM_PE), are decoupled quantitatively for the normal aging process. The LLI accelerated protocol: The protocol involves two parts: first is charging at low-temperature. Charging with low rate under low temperature can generate large amount of plated lithium metal, second is resting at high-temperature(60 °C) after charging, which leads to transformation of the deposited lithium into SEI film faster because of Arrhenius formula. The resting temperature is not designed to be too high to avoid thermal runaway of battery. Secondly, different cycle protocols are designed to specifically accelerate single mechanism. The equivalence of these mechanisms is experimentally verified through CP-SEM, SEM-EDS, HRTEM and XPS. Finally, combined accelerated protocols are designed by combining and matching single accelerated protocols based on the proportions of degradation mechanisms during normal aging. Under these protocols, cells experience the same aging pathway as the normal aging ones. The proposed aging protocols could accelerate the battery aging experiment by 62 times and 39 times under the extreme and gentle conditions respectively. [Display omitted] •Decoupling LLI, LAM degradation mechanisms with single accelerated conditions•Designing and verifying combined accelerated protocols by matching two single accelerated conditions•Achieving high acceleration ratio while maintaining aging path equivalently