Influence of electrolyte presence on the vibration behavior of a Li-ion pouch cell and on the mechanical characteristics of its incorporated [formula omitted]-coated polyolefin separator

Abstract

Quality improvement of battery crash simulation models is essential for realistic mechanically induced short-circuit prediction in modern electric vehicles, where the battery is part of the load path. In this paper, the electrolyte influence on the mechanical behavior of a commercial pouch cell and its incorporated Al2O3-coated separator is investigated. To mechanically characterize the separator, both compression and tensile tests were performed. Modal analyses were performed to determine the damping behavior and dynamic stiffness of a normally conditioned cell (wet) and a cell without electrolyte (dry). In the tensile tests, a slight anisotropy and an increase in stiffness, triggered by higher test speeds, were observed. The wet specimens soaked in substitute electrolyte mixture showed longer elongation to failure with a stiffer response than the dry specimens under tensile loading. In the compression tests, exactly the opposite mechanical response of wet and dry specimens was measured. From the modal analyses, a stiffening of the dry cell could be determined. Based on the component tests, a finite element model of the separator was developed in LS-DYNA, enabling prediction of the deformation behavior of the separator under mechanical loads — this can be further used in high-fidelity cell simulation models.