The effect of chemical doping on the lithiation processes of the crystalline Si anode ‒ A first-principles study

We employed first-principles calculations to investigate the effect of chemical doping on the lithiation kinetics and dynamic properties of the c–Si anode. Our ab initio molecular dynamics simulations reveal that phosphorous/arsenic doping can greatly enhance the lithiation kinetics of c–Si, whereas boron doping is unable to produce such an improvement. Our calculations also show that boron doping could enhance Li insertion into c–Si, but phosphorous/arsenic doping tends to increase the insertion energy of Li ions. Although the migration energy barriers of Li ions may slightly increase (decrease) in the boron-(phosphorus-/arsenic-)doped c–Si, these changes were only effective within the range of the nearest-neighbor distance from dopants. Furthermore, it was found that the phosphorus-/arsenic-doped Si can be more ductile and can more easily undergo plastic deformation upon lithiation, while the c–Si matrix becomes more brittle and stiffer when doped with boron. Our simulation results also demonstrate that phosphorous- and arsenic-doping can effectively speed up the Li-induced structural amorphization of c–Si while boron doping appears to severely slow it down. These findings unambiguously indicate that the induced mechanical softening of the c–Si bond network can be the primary factor that leads to the enhanced lithiation kinetics in the n-type doped c–Si anodes.