Understanding the role of porosity in carbon monolayers for their use as anode material for Li-ion batteries: A first principle study

With the aid of density functional theory (DFT) calculations, different models of porous carbon monolayers were proposed for the development of anode materials for lithium-ion batteries (LIB). Special attention was given to the pore size effect in the storage process and diffusion of Li ions. Porous carbon models were formed from the pristine graphene structure, by removing carbon atoms that mimic the pore formation. DFT calculations showed that the fundamental planar structure of graphene is preserved upon pore formation. The electronic structure properties of carbon are drastically altered with the enlargement of the pore size according to the introduced vacancies, allowing effective Li-ion adsorption in larger pores. Calculations based on atoms in molecules theory indicate that the Li ions interact with the pores via an electrostatic-type attraction, comparable to that of a hydrogen bonding. The porous carbon models exhibit the availability to retain a massive number of Li ions at the surface by keeping the original planarity of graphene. This is intimately related to an enhanced theoretical specific capacity that raises with increasing pore size. Such capacities are in close agreement with experimental data. Therefore, the formation of the pores improves Li ions diffusion compared to the pristine graphene. This is of special interest for the design of improved anode materials for Li ion batteries. This theoretical methodology can be applied as an auxiliary tool to tailor porous carbon materials intended to be used in Li ion batteries.