The influence of crack on the Si anode performance in Na- and Mg-ion batteries: An atomic multiscale study

Abstract

Based on multiscale simulations coupled with quantum mechanical and molecular mechanical methods, we present the impact of crack on the performance of Si anode in Na-ion batteries (NIBs) and Mg-ion batteries (MIBs). We found that crack can offer more stable sites to host interstitials than defect-free Si and form binding energy gradients near the crack front. Moreover, the crack tip may significantly enhance the binding strength, enabling it to insert Na and Mg into the Si anode thermodynamically. The crack creates a fast channel into the tip along its propagation direction, causing Na and Mg to accumulate at the crack tip, similar to the case of Li. Furthermore, since diffusion out is more challenging, Na and Mg prefer to diffuse into the crack. Finally, the crack may trap interstitials and lower the charging and discharging rate of NIBs and MIBs.