Mechanical properties of amorphous LixSi alloys: a reactive force field study

Silicon is a high-capacity anode material for lithium-ion batteries. Electrochemical cycling of Si electrodes usually produces amorphous LixSi (a-LixSi) alloys at room temperature. Despite intensive investigation of the electrochemical behaviors of a-LixSi alloys, their mechanical properties and underlying atomistic mechanisms remain largely unexplored. Here we perform molecular dynamics simulations to characterize the mechanical properties of a-LixSi with a newly developed reactive force field (ReaxFF). We compute the yield and fracture strengths of a-LixSi alloys under a variety of chemomechanical loading conditions, including the constrained thin-film lithiation, biaxial compression, uniaxial tension and compression. Effects of loading sequence and stress state are investigated to correlate the mechanical responses with the dominant atomic bonding, featuring a transition from the covalent to the metallic glass characteristics with increasing Li concentration. The results provide mechanistic insights for interpreting experiments, understanding properties and designing new experiments on aLixSi alloys, which are essential to the development of durable Si electrodes for high-performance lithium-ion batteries. (Some figures may appear in colour only in the online journal) 0965-0393/13/074002+15$33.00 © 2013 IOP Publishing Ltd Printed in the UK & the USA 1 Modelling Simul. Mater. Sci. Eng. 21 (2013) 074002 F Fan et al