Carbon nitrides as cathode materials for aluminium ion batteries

Density functional theory calculations are used to determine the suitability of carbon nitrides as potential cathode materials for aluminium ion batteries (AIB). Our calculations reveal that, compared to graphene, carbon nitrides with only pyridinic and pyrrolic nitrogen result in a decline in performance whereas carbon nitrides with only graphitic nitrogen show significantly improved performance. Two different two-dimensional carbon nitrides with graphitic nitrogen only, honeycomb structured graphene-like C11N and C4N which features defects, are tested and compared with graphene as potential cathode materials. It is found that the AlCl4 binds more strongly to carbon nitrides (−3.47 eV to −3.58 eV) than to graphene (−2.21 eV). This higher binding energy significantly reduces AlCl4 agglomeration, suggesting a higher storage capacity of C11N (184 mAh g−1) than graphene (155 mAh g−1) and lower emission of chlorine. The AlCl4 can move on the surface of C4N/C11N without significant energy barrier which will facilitate fast charging. Finally it can be concluded that carbon nitrides with graphitic nitrogen and graphene-like honeycomb structures are more suitable for the AIBs and a small percentage of graphitic nitrogen doping could significantly improve the storage capacity of the AIB with fast charging, lower anion agglomeration rate and low chlorine emission.