Influence of circuit design on load distribution and performance of parallel-connected Lithium ion cells for photovoltaic home storage systems

Abstract

In parallel cell circuits within Lithium ion home storage systems, both the components as well as the topological structure of the circuit have an enormous influence on the current distribution among the individual cells and as consequence on the battery lifetime. For large battery assemblies welding techniques are often used for which a weldable current collector is needed. Due to the high specific resistance of the commonly used materials, this resistance measurably influences the current distribution.In this paper the current distribution in battery modules with Li ion cells connected in parallel has been measured and modelled. The cell internal resistance, the current collector resistance and the topology of the circuitry have been varied in order to determine the influence of each of these parameters on the current distribution. Model calculations for the cycle lifetime of battery modules have been performed assuming realistic charge and discharge profiles matching the conditions to be found in commercially available home storage systems.From the experimental data and the modeling results the most important parameters determining the homogeneity of the current distribution and the cycle lifetime of the battery modules have been extracted. Finally, design recommendations for Li ion batteries with cells connected in parallel are derived.