S. Schweizer, J.J. Low, L. Subramanian
Keywords: battery, silicon anode, mechanical properties, porosity, carbon coating, molecular dynamics
Summary:Lithium(Li)-ion batteries are widely used in portable electronic devices. Their use as energy storage system in other important industrial fields - such as electric vehicles, wind turbines, or photo voltaic plants - is limited by their storage capacity. The latter is governed by the electrode material . To satisfy the increasing requirements of industry and consumers, novel powerful anode materials need to be developed. Silicon (Si) is regarded as an exceedingly promising anode material for several reasons: It’s theoretical capacity is more than ten times higher compared to graphite which is used for state-of-the art battery anodes. Moreover, Si combines low cost and low toxicity with a high abundance . Pure Si-based electrodes have, however, one major drawback. They experience large volume changes during charging and discharging which induces pulverization of the electrode and fast fading of the capacity . In order to overcome these problems, different kinds of nanostructured Si materials have been designed. Promising approaches range from porous over composite to core-shell structures and it has been shown that these materials improve the performance significantly [see e.g. 1-5 and references therein]. Here, we address mechanical properties of porous carbon-coated Si which are important for the stability and durability of the anode. Molecular dynamics (MD) simulations have been performed to model regular micro- and mesoporous Si as well as amorphous porous Si. Carbon has been inserted into the porous Si structures and we have systematically analyzed how pore size, carbon coating, and defects in the coating affect the elasticity of the material by calculating Young’s modulus. Our results show that the mechanical properties are influenced by the carbon coating and suggest that it can be used to tune the stability of this important class of electrode material. References:  D. Ma, Z. Cao , A. Hu, Nano-Micro Lett. (2014) 6(4):347-358.  C.-M. Park, J.-H. Kim, H. Kim H.-J. Sohn, Chem. Soc. Rev. (2010) 39:3115-3141.  X. Li et al., Nature Communications (2014) 5:4105.  Z. Sun, S. Tao, X. Song, P. Zhang, L. Gaoz. J. Electrochem. Soc. (2015) 162(8):A1530-A1536.  S. Fang, Z. Tong, P. Nie, G. Liu, X. Zhang,ACS Appl. Mater. Interfaces (2017) 9:18766-18773.