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

As the use 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 metal collector exerts a significant impact on the tensile properties of the electrode and also on the internal fracture of the cell. Tensile tests are unable to obtain the mechanical properties of the collector in situ, and the stripping process tends to cause additional damage to the collector. Therefore, nanoindentation tests are required to gain the mechanical properties of the collector. Nanoindentation testing represents the primary methodology for the determination of the mechanical properties of thin films. Commercial indentation instruments typically employ the Oliver-Pharr method for the assessment of material mechanical properties. However, this method is subject to limitations due to the constraints imposed by sample boundary conditions. In order to obtain an accurate measurement of the elastic modulus of the collector in situ, nanoindentation tests were performed on the collector. The results of the nanoindentation test demonstrate that the calculated elastic modulus is within an acceptable error range only when a suitable indentation depth is employed. A finite element model was developed for use in 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 elastic modulus of the sample measured without satisfying this condition, derived through a parametric study. The findings of this study offer a guidance for the implementation of the Oliver-Pharr method for the assessment of the elastic modulus of collectors.