Study on actual Ah-throughput-based health indicator of battery module consisting of inconsistent cells for its second life

Abstract

In this Letter, an actual Ah-throughput-based novel health indicator (HI) of battery module is proposed for its second life. The state of health (SOH) of a battery cell is generally evaluated by the cell capacity. However, it is difficult to define the SOH of a battery module since it consists of inconsistently aged cells. To represent module aging and the inconsistency, this Letter utilizes the actual Ah-throughput, which is the total amount of current suppliable to a load, as the module HI. Ah-throughput is affected by loss from cell balancing control, which is necessary for the safe and efficient operation of a battery system. The larger the inconsistency, the more balancing operation is needed. Therefore, the proposed HI can evaluate the module health reflecting the inconsistency from a balancing perspective. For the implementation of the HI, its derivation and calculation algorithm are presented. Finally, the effectiveness is verified by various case studies with an experimental setup consisting of a series-connected cells and an active cell balancer.