Retention of lithium atoms by A@C20 (A = Li, Na and K) metallofullerenes: possible anodes for batteries?

Abstract

We have investigated the electronic properties of lithium, sodium, and potassium doped endohedrally on C₂₀ fullerenes, through DFT calculations. The dipolar moment, average binding energies, cohesion energy, |HOMO–LUMO| energy gaps and NBO population analysis are expressed as functions of Li amount. The electrons transferred by lithium are distributed on the surface of the C₂₀. The excess charge induces a decrease in the gap value, which allows the structure to behave like a semiconductor material. The obtained results indicate that the C₂₀ fullerenes are highly efficient in adsorbing Li atoms, as the retention capacity of Li@C₂₀, Na@C₂₀, and K@C₂₀ exceeds 1458.9, 1146.3, and 907.4 mA h g⁻¹, respectively. The Li@C₂₀ complex provides a maximum voltage of 1.1 V. The insertion of Na and K increases the adsorption energy, so the voltage also increases to 2.2 and 2.4 V. This makes them an alternative for energy storage.