Direct Assessment of Separator Strain in Li-Ion Batteries at the Onset of Mechanically Induced Short Circuit

Abstract

In the literature, mechanical deformation of Li-ion batteries (LIB) is characterized in terms of global or volumetric strain of the entire cell to develop load vs. strain plots. In characterizing the mechano-electrical–thermal–chemical interaction of the battery in relation to internal short circuit (ISC) due to mechanical load, these estimated strains are “indirect strains” at best. Direct evaluation of “internal local strains” between the layers, particularly, in the first separator layer should be a critical material parameter as it relates to separator rupture and should be the key link in ISC in LIBs. We make an effort to assess “internal local strains” which is not reported elsewhere, first by using the Oak Ridge National Laboratory (ORNL) approach to use plastic deformation of aluminum casing to “freeze” deformation states of the LIBs followed by microscopy to image undeformed and deformed cells. An image analysis procedure is developed to estimate transverse compression strains in the cells, e.g., in Cu anode, Al cathode, and the polymeric separator. The local strain experienced by the polymeric separator nearest to ball indentation is found to be close to 65–70% and this strain level is much higher than 40–50% maximum average strains estimated for the same sample.

Multifunctional sandwich panel design with lithium-ion polymer batteries

“…Pouching of cells has been shown to dramatically improve most mechanical properties of Li-ion cells, compared to those without a pouch [17]. To-date most studies on the mechanical performance of Li-ion batteries have focused on the relationship between mechanical loading and the onset of an internal short circuit [17–22]. Li-ion pouch batteries have been subjected to a range of mechanical tests including out-of-plane compression, in-plane compression, punch indentation, impact and three-point bending tests [17–22].…”

“…To-date most studies on the mechanical performance of Li-ion batteries have focused on the relationship between mechanical loading and the onset of an internal short circuit [17–22]. Li-ion pouch batteries have been subjected to a range of mechanical tests including out-of-plane compression, in-plane compression, punch indentation, impact and three-point bending tests [17–22]. However, to the best knowledge of the authors, no study has characterized the shear properties of a Li-ion battery, which are critical in mechanical design.…”

Energy Storage Structural Composites with Integrated Lithium‐Ion Batteries: A Review

“…Most studies at the single battery level have focused on the relationship between the type and magnitude of mechanical loads and the onset of internal short circuiting due to damage. [ 27–35 ] LiPo batteries are anisotropic in their mechanical properties, which have been characterized in multiple directions. The properties of LiPo batteries have been measured for different mechanical conditions, including out‐of‐plane compression, [ 27 ] in‐plane compression, [ 27,36–38 ] punch indentation, [ 27,30,33–35,37 ] impact, [ 31 ] nail penetration, [ 39,40 ] three‐point bending, [ 27,28,37 ] and tension.…”

“…[ 27–35 ] LiPo batteries are anisotropic in their mechanical properties, which have been characterized in multiple directions. The properties of LiPo batteries have been measured for different mechanical conditions, including out‐of‐plane compression, [ 27 ] in‐plane compression, [ 27,36–38 ] punch indentation, [ 27,30,33–35,37 ] impact, [ 31 ] nail penetration, [ 39,40 ] three‐point bending, [ 27,28,37 ] and tension. [ 38 ] Under load, the internal components of LiPo batteries are prone to delaminate and buckle due to the weak shear and/or tension strength between individual electrode layers.…”

“…While most studies into the mechanical properties of lithium‐ion batteries have focused on prismatic LiPo batteries, [ 26,27,30,33,37,42 ] cylindrical 18 650 batteries have also been used in battery packs for automotive and other applications. Compared with other lithium‐ion battery geometries, cylindrical batteries are often cheaper and have superior energy density, although with inferior power density.…”