Cell balancing technology in battery packs

Batteries are a major source of power for mobile applications. As an electrochemical cell, a battery is highly dependent on operating conditions. Even the same type of battery may behave differently under different conditions. Lithium-ion batteries, which have lithium as the cathode and graphite as the anode, are the dominant battery type in the world. Their applications range from consumer electronics to electric vehicles. To satisfy different specifications of applications, battery packs with different terminal voltage and different capacity are used. In a battery pack, battery cells connect in series and in parallel. Series connections attain higher terminal voltage while parallel connections attain higher capacity. Although combining cells increases flexibility, it increases the failure rate as well. The state of the weakest cell determines the state of the entire battery pack. Minimizing the deviation among cells becomes a critical task because it can utilize most cells in the pack and hence prolong life of the pack. In this paper, a more intelligent balance method is proposed. It can charge weak cells more exactly and safely.