Management of imbalances in parallel-connected lithium-ion battery packs

Uneven electrical current distribution in a parallel-connected lithium-ion battery pack can result in different degradation rates and overcurrent issues in the cells. Understanding the electrical current dynamics can enhance configuration design and battery management of parallel connections. This paper presents an experimental investigation of the current distribution for various discharge C-rates of both parallel-connected LiFePO4 and Li(NiCoAl)O2 cells. A first-order Thevenin model for current distribution calculation was applied to assess the maximum discharge current discrepancy between cells when the number of cells increases. This study reveals why balancing circuits are seldom implemented on cells in a parallel connection, and provides guidance on reducing cell imbalances by managing battery operation in terms of state of charge range and discharge C-rates, as well as improving connection design.