Unlocking the significant role of shell material for lithium-ion battery safety

The cylindrical lithium-ion battery has been widely used in 3C, xEVs, and energy storage applications and its safety sits as one of the primary barriers in the further development of its application. Among all cell components, the battery shell plays a key role to provide the mechanical integrity of the lithium-ion battery upon external mechanical loading. In the present study, target battery shells are extracted from commercially available 18,650 NCA (Nickel Cobalt Aluminum Oxide)/graphite cells. The detailed material analysis is conducted to reveal a full understanding of the material. Then, the dynamic behavior of the battery shell material is experimentally investigated. Both theoretical constitutive and numerical models have been developed, capable to describe mechanical behaviors of the battery shell material upon impact loading. It is the first time to discover that the strain rate effect of the shell material shall be considered for the mechanical integrity of the battery and high strength of the shell material may contribute to an early short-circuit triggering. The quantitative relationship is also established between short-circuit and material strength. Results lay a solid foundation towards providing a theoretical safety design guidance for the shell material choice of cylindrical lithium-ion batteries. [Display omitted] •Dynamic experiments were designed and conducted for battery shell•Mechanical behaviors were studied considering direction, strain rate and stress triaxiality index•A strain rate dependent constitutive model with fracture criterion was established•Finite element models were established to verify the constitutive model•Strain rate and strength effect on short-circuit property were discussed