Defect-engineered N/Te-doped graphene for lithium adsorption and voltage behavior: a first-principles study

First-principles density functional theory was used to study lithium adsorption on vacancy-defected graphene doped with nitrogen (N) and tellurium (Te), in view of lithium-ion battery anodes. Thirteen configurations, from pristine and monovacancy to mono-, bi-, tri-doped and co-doped systems, were analyzed for adsorption, electronic structure, and open-circuit voltages (OCVs). The systems with voltages in or near the 0.1-1.0 V range favoured for anodes were then taken to the lowest-energy dopant arrangement and lithium adsorption site found in a configurational search. Pristine and lightly nitrogen-doped graphene bind lithium only weakly, with incomplete transfer of the lithium 2 s electron, and give negative voltages. Heavier doping or a vacancy switches the interaction to chemisorption with near-complete ionization, and the strength of this chemisorption sets the OCV. The bare monovacancy, which adopts a reconstructed 5|9 structure, binds lithium with an OCV of 1.10 V, just above the 0.1-1.0 V range; tellurium decoration brings the voltage into this range: G@2Te-Li (0.48 V), G@3Te-Li (0.69 V) and the Te-rich co-doped G@2Te@1N-Li (0.95 V) are held by a mix of van der Waals and ionic anchoring, revealed by non-covalent interaction analysis. Heavy pyridinic nitrogen doping (G@3N-Li) opens a direct 0.41 eV gap and binds lithium very strongly (E _ads = -4.89 eV, OCV = 2.97 V), whereas co-doped systems with a single Te atom or two N atoms remain outside the range. Within the single-lithium, dilute limit considered here, tellurium-decorated vacancies therefore offer the most balanced lithium binding among the configurations examined.