Available Discharge Capacity Estimation According to C-rate Variation of Second-Used Battery

As the number of used batteries increases, recycling the used batteries becomes an issue. One of the most notable ways to recycle used batteries is to create a new energy storage system with a used battery. In case of used battery, however, the life expectancy is low. Therefore, if a used battery is required to construct a low-cost system to perform a grid-scale energy storage, it should be considered how to use batteries efficiently. The fresh-battery oriented state-of-charge (SOC) or state-of-health (SOH) algorithms such as Kalman filter or extended Kalman filter which require the internal parameter of battery is not proper for used battery system. In general, experimental steps to measure the internal parameters of a battery take a long time. Whereas, the ampere counting method is almost real time process, so more appropriate for the used battery system. Basically, it can be used only with measuring the available discharge capacity of a battery. However, in the case of used lithium-ion battery, the variation of the available discharge capacity is greater as the C-rate changes, than that of the fresh battery is. In this paper, algorithm for estimation about available discharge capacity according to C-rate of second used battery is proposed. Since the proposed algorithm in this paper estimates the available discharge capacity according to the C-rate and SOH variations, it can minimize an error of the ampere counting. Since the base of the algorithm is ampere counting, it does not require a high-performance computing processor. Therefore, this second used battery system can be configured in low cost.