DFT study of lithium adsorption on silicon quantum dots for battery applications

Understanding lithium (Li) adsorption in silicon quantum dots (SiQDs) is crucial for optimizing Li-ion battery (LIB) anode materials. We systematically investigated Li adsorption in ten hydrogenated SiQDs (Si₁₀H₁₆, Si₁₄H₂₀, Si₁₈H₂₄, Si₂₂H₂₈, Si₂₆H₃₀, Si₃₀H₃₄, Si₃₅H₃₆, Si₃₉H₄₀, Si₄₄H₄₂, and Si₄₈H₄₆) across five adsorption sites (bridge(B), on-top(T), hollow-tetrahedral inner(Td_inner), hollow-tetrahedral surface(Td_surface), and hollow-hexagonal(Hex)), utilizing density functional theory (DFT) with the M06–2X hybrid functional and 6-31G+(d) basis set. Findings identify Td_inner as the most favorable adsorption site, with a binding energy (E_bind) of 0.80–1.00 eV, dependent on SiQD size. The adsorption site exerts a more pronounced impact on E_bind than the cluster size. Multiple adsorptions in SiQDs show increased E_bind per Li atom with Li atom number. Molecular volume changes, independent of Li atom number but site-dependent, exhibit a maximum of 2.51 %. SiQD energy gap, influencing conductivity, varies with size, larger SiQDs being more conductive, especially with Li adsorption. Conclusively, our study recommends large-sized SiQDs as optimal LIB anode materials, offering high capacity, minimal volume expansion, and reasonable conductivity. This research addresses a theoretical gap, illuminating the impact of Li adsorption on SiQD molecular volumes and electronic structures, aiding in the design of enhanced capacity silicon anodes for LIB.