First-principles study of interstitial Li effects on the electronic, structural and diffusion properties of highly boron-doped porous silicon

Silicon-based anodes for Li-ion batteries have been the subject of intense research due to their high storage capacity, low working potential, and abundant resources. Nevertheless, the low electrical conductivity, large volume changes and slow Li ion diffusivity in silicon have hampered its performance. In this work, we modelled B-doped porous silicon passivated with hydrogen to analyse the effect of interstitial Li atoms on its electronic, structural, and diffusion properties by the density functional theory (DFT). Results show that high boron doping induces metallic properties in porous silicon, which are also improved by interstitial Li atoms. The metallic behaviour of porous Si is detailed by the calculations of the effective masses and the Fermi surfaces. Conversely, the B atoms produce volumetric compression, which partially compensates for the volumetric expansion generated by the interstitial Li atoms. Furthermore, the bulk moduli of the B-doped porous structure and the Bdoped porous structure with the highest Li concentration here considered show a variation of 0.2 % and 0.37 %, respectively. These results suggest that the addition of large amounts of B and Li atoms slightly reduces the hydrostatic compressive strength of the porous silicon. Finally, we found that the dopant contributes to the asymmetric Li diffusion activation since the energy barrier of 0.86 eV must be overcome when Li migration occurs from the interior to the edge of the wall. In contrast, in the opposite direction, the energy barrier increases to 1.43 eV. This implies that the Li atom could preferentially be stored in the pore surface area.