Sodium Adsorption and Mobility in a Pillared Graphene Structure

Sodium-ion batteries are generally considered a promising alternative to lithium-ion batteries due to the abundance and low cost of sodium. However, their main limitation is the lack of an appropriate anode, since the usual graphite electrode used in lithium batteries is incompatible with the larger ionic radius of sodium. In this work, the theoretical behavior of pillared graphene as a possible anode is analyzed via computational simulations based on Density Functional Theory (DFT) using the FIREBALL program. The structural relaxation results reveal that staggered pillars are more stable than the aligned alternative. The adsorption energy of sodium is shown to be significantly higher than for graphite, with a maximum value of −2.23 eV, leading to an important energetic benefit. The diffusion analysis shows high mobility for sodium, with migration barriers comparable to those of lithium ions both in the flat regions of the structure and close to the nanotubes. The values are comparable to those of the standard graphite used in current batteries. Finally, the charge analysis confirms significant electronic transfer from both sodium and lithium to the lattice. These data indicate that pillared graphene can be a good candidate for the optimization of charge dynamics in sodium-ion batteries.