Residual Capacity Estimation of Valve-regulated Lead-acid (VRLA) Batteries for Second-use

Valve-regulated lead-acid (VRLA) batteries widely used in substations still have large residual capacities when they are retired, so they can be used secondly in energy storage systems. To enhance the economic and technical performance of second-used VRLA batteries, the estimations of battery’s residual capacity before and during second-use are essential, which are the two main topics of this paper. First, based on the electrochemical impedance spectroscopy (EIS) of retired VRLA batteries, an equivalent circuit model is established as the basis for subsequent research. Then, the relationship between the EIS and the residual capacity of the retired VRLA battery that has not been put into second-use is studied by theoretical analysis and experiment research. It is found that the impedance at 0.01Hz (capacitance) and 50Hz (resistance) can be used to select batteries that need restoration and the irreparable batteries respectively. Moreover, the test results of charge-discharge cycles show that the residual capacity of the retired VRLA battery that has been put into second-use can be estimated using battery’s open-circuit voltage and DC impedance, both of which are easy to measure for batteries in operation. The residual capacity estimation methods lay a theoretical foundation for the second-use of retired VRLA batteries, thus promoting resource recycling and producing social and economic values simultaneously.