Mechanical properties of electrochemically lithiated Sn

Abstract

Sn is a promising Li ion battery anode with high theoretical capacity, but it can easily pulverize due to repeated application of extreme volumetric strain of 260% during cycling. Sn is a low melting point metal with low modulus and therefore has previously been proposed to be a fracture resistant anode due to its the ability to relax stresses via plasticity and creep deformations. In this study, intrinsic mechanical properties of lithiated Sn at various stages in the lithiation were evaluated using nanoindentation experiments using a special setup. In order to avoid oxidation of the highly reactive lithiated Sn, nanoindentation was performed on specimens submerged in a mineral oil bath. After careful calibration, hardness and modulus of different phases of lithiated Sn were evaluated. With an increase in the lithium content, both the modulus and hardness of the lithiated Sn decreased, as expected, where the modulus and hardness are 28.6 GPa and 0.37 GPa, respectively, for fully lithiated Sn (Li22Sn5) and 58.0 GPa and 0.77 GPa, respectively, for unlithiated Sn. This is the first report on the mechanical properties of lithiated Sn, which is expected to be of importance in theoretical analysis of the diffusion induced stresses in Sn anodes.