State of Charge Dependent Mechanical Integrity Behavior of 18650 Lithium-ion Batteries

Abstract

Understanding the mechanism of mechanical deformation/stress-induced electrical failure of lithium–ion batteries (LIBs) is important in crash-safety design of power LIBs. The state of charge (SOC) of LIBs is a critical factor in their electrochemical performance; however, the influence of SOC with mechanical integrity of LIBs remains unclear. This study investigates the electrochemical failure behaviors of LIBs with various SOCs under both compression and bending loadings, underpinned by the short circuit phenomenon. Mechanical behaviors of the whole LIB body, which is regarded as an intact structure, were analyzed in terms of structure stiffness. Results showed that the mechanical behaviors of LIBs depend highly on SOC. Experimental verification on the cathode and anode sheet compression tests show that higher SOC with more lithium inserted in the anode leads to higher structure stiffness. In the bending tests, failure strain upon occurrence of short circuit has an inverse linear relationship with the SOC value. These results may shed light on the fundamental physical mechanism of mechanical integrity LIBs in relation to inherent electrochemical status.

Integrated computation model of lithium-ion battery subject to nail penetration

“…This observation indicates that the drop in mechanical load cannot be used as the indicator for the cathode-anode short circuit of the jellyroll. Similar qualitative phenomena were also observed in the bending and indentation mechanical tests, thereby showing that the internal short circuit occurred after the force drop, whereas the internal short circuit occurred before the buckling in compression tests in previous investigations [18,50].…”

“…In Stage I (the mechanical deformation stage), the jellyroll experienced elastic and plastic mechanical deformations until it buckled while sustaining nearly constant electrochemical properties, except for a minor voltage increase reported in Ref. [50]. The cathode and the anode in the outer layers progressively failed.…”

“…A previous study [50] conducted compression experiments on LIBs with various SOCs, and the results showed that the internal short displacement and the SOC exhibited a linear relationship, with a highly similar slope to that in Eq. (31).…”

“…The mechanical behaviors of LIBs have been proven to be SOC dependent in previous studies [50], where LIBs with high SOCs have exhibited high stiffness. Consequently, the reaction force of LIBs with high SOCs is considerable during nail penetration, as shown in Fig.…”

Computational model of 18650 lithium-ion battery with coupled strain rate and SOC dependencies

“…1(a). A large number of mechanical experiments have been studied for this type of battery [31], discovering that the mechanical properties are related to SOCs where the maximum contribution of SOC for the difference in force capacity can be up to 40%. It is true that battery shell's mechanical behavior plays an important role in overall LIB's mechanical behavior; however, the jellyroll contributes more for bearing force than the shell, demonstrated in the comparison of Figs.…”