Modeling Inhomogeneities during Parallel-Connected Fast Charging of Lithium-Ion Battery Systems

Abstract

Parallel connections of lithium-ion cells in battery systems lead to current distributions between the cells, which impacts fast charging capabilities. This study examines the influence of interconnection resistance, format, electrode design, cell-to-cell variations, and temperature differences on system inhomogeneity and identifies anode potential safety margins that ensure safe charging without lithium plating. To this end, a physico-chemical parameterization of the Molicel INR21700-P45B is presented. An optimized fast-charging profile enables charging from 10%–80% cell capacity in under 10 minutes. The experimental application of the fast-charging profile yielded a result of over 300 equivalent full cycles before reaching 90% state of health. Furthermore, the cell model is scaled to different parallel-connected systems in an extensive simulation study. The interconnection resistance, and analogously the internal-to-interconnection resistance ratio, was found to be the primary factor influencing inhomogeneity in high parallel configurations, whereas cell-to-cell resistance variations are the most significant determinant in low parallel configurations. Variations in cooling were found to be more impactful than initial temperature disparities.