Analysis of the effect of buffer pads on the cycle life of lithium-ion pouch batteries

Lithium-ion batteries have the advantages of long cycle life, high specific capacity, low cost, and are widely used in electric vehicles and energy storage systems. However, the battery expansion problem after long-term charging and discharging has been one of the important factors restricting the further improvement of the cycle performance of Li-ion batteries. In order to reduce the negative impacts caused by battery expansion, this paper aims to analyze the application of different buffer pads between ternary lithium-ion soft pack batteries to provide a reference for improving the cycling performance of the batteries, evaluated by capacity test, internal resistance test, polarization degree test, and electrochemical impedance test. In order to refine the contribution of individual electrochemical processes to the battery impedance, the electrochemical AC impedance spectrum was analyzed using the distribution of relaxation time analysis technique (Distribution of relaxation, DRT), employing Relaxl S as analysis software. Compared to the batteries with other buffer pads, the batteries with ceramic aerogel buffer pads performed better, improved the capacity retention of the batteries by 4%, reduced the internal resistance by 13 mΩ, and exhibited the smallest degree of polarization, the smallest ohmic impedance, and the smallest Faraday impedance. In particular, the electrochemical processes of the batteries were analyzed by DRT technique, and it was found that the batteries with ceramic aerogel buffer pads showed better performance in contact impedance, impedance of Li-ion crossing the SEI membrane, and impedance of the liquid-phase diffusion process.