In-Situ Nanoindentation and Finite Element Analysis for Evaluating the Young’s Modulus of Anode Current Collectors in Lithium-ion Batteries

As the utilization of lithium-ion batteries in electric vehicles becomes increasingly prevalent, there has been a growing focus on the mechanical properties of lithium-ion battery cores. The current collector significantly impacts the tensile properties of the electrode and the internal fracture of the battery cell. The stripping process tends to cause additional damage to the current collector, so tensile testing is not able to obtain in-situ mechanical properties of the current collector. Therefore, nanoindentation tests are required to acquire the in situ mechanical properties of the current collector. Nanoindentation testing represents the primary methodology for the determination of the mechanical properties of thin films. The Oliver-Pharr method is the standard approach used by commercial indentation instruments for the evaluation of mechanical properties in materials. Nevertheless, this approach is constrained by the limitations imposed by the sample boundary conditions. To obtain an accurate measurement of the Young’s modulus of the current collector in situ, nanoindentation tests were conducted on the current collector. The results of the nanoindentation test indicate that the calculated Young’s modulus falls within an acceptable error range only when a suitable indentation depth is employed. A finite element model was constructed for simulating the nanoindentation test. The results of the simulation analysis demonstrate that the material elasticity model exhibits a decline with increasing indentation depth. The analysis revealed that the nanoindentation test results in the in-plane direction of the film are influenced by two primary factors: surface roughness and sample thickness. Furthermore, we present a correction formula for the Young’s modulus of the sample measured without satisfying this condition, derived through a parametric study. The findings of this study offer guidance for implementing the Oliver-Pharr method to assess the Young’s modulus of current collectors.