Numerical Modeling of Fracture-Resistant Sn Micropillars as Anode for Lithium Ion Batteries

Sn possesses three times higher capacity in comparison to graphite anode (372 mAhg(-1)) that makes it a promising candidate for enhanced performance Li ion batteries. Contrary to Si, Sn is compliant and ductile in nature and thus is expected to readily relax the Li diffusion-induced stresses. The low melting point of Sn additionally allows for stress relaxations from time-dependent or creep deformations even at room temperature. In this study, numerical modeling is used to reveal the significance of plasticity and creep-based stress relaxations in the Sn working electrode. The maximum elastic tensile hoop stresses for 1 mu m micropillar size with 1C charging rate conditions reduces down from similar to 1 GPa to similar to 200 MPa when Sn is allowed to plastically deform at a yield strength of similar to 150 MPa. After experimentally determining the creep response of Sn micropillars, creep deformations are incorporated in numerical modeling to show that the maximum tensile hoop stress is further reduced to similar to 0.45 MPa under the same conditions. Lastly, the Li-induced stresses are analyzed for different micropillar sizes to evaluate the critical size to prevent fracture, which is determined to be similar to 5.3 mu m for C/10 charging rate, which is significantly larger than that in Si.