Investigation of distribution of relaxation times responding to valve-regulated lead acid batteries degradation process

Electrochemical impedance spectroscopy (EIS), as a non-destructive evaluation technique, is extensively utilized in analyzing the degradation process of batteries. The distribution of relaxation times (DRT) serves as a powerful tool, eliminating the need for prior knowledge required by the traditional equivalent circuits model (ECM), in interpreting EIS. Valve-regulated lead-acid (VRLA) batteries, are commonly used as backup power sources in critical applications and represent one of the most widely used battery types, yet their degradation is commonly overlooked and necessitates further research. Therefore, this paper provides the first comprehensive DRT analysis of the float charging aging process of VRLA batteries through aging experiments. Based on the results, this paper identifies the optimal range of the regularization parameter (λ) in calculating the DRT of VRLA batteries as between 10^–6 and 10^–5. Based on this, it is determined that VRLA DRT exhibits four peaks regardless of changes in state of health (SOH) and state of charge (SOC). Additionally, it is found that the P1 peak in the high-frequency region has a good linear relationship with both SOH and SOC, with linear fitting coefficients of 0.861 and 0.991, respectively. This finding aids in the application of DRT for the state diagnosis of VRLA batteries, offering a DRT approach for VRLA degradation studies.