Theoretical insights into nitrogen fixation on Ti 2 C and Ti 2 CO 2 in a lithium–nitrogen battery

Recently, the first lithium–nitrogen (Li–N 2 ) battery was designed, achieving a reversible electrochemical reaction between N 2 and Li 3 N under ambient conditions (Ma et al. , Chem , 2017, 2 , 525–532). However, the performance of a Li–N 2 battery is limited by the weak interaction between the carbon cloth cathode substrate and N 2 . In the present work, we theoretically evaluate a Ti 2 C monolayer as a potential cathode substrate to improve the performance of an Li–N 2 battery. Our results reveal that N 2 interacts strongly with the bare Ti 2 C substrate with low adsorption energy and a lot of electron transfer, and the existence of Li atoms facilitates N 2 dissociation. The estimated discharge and charge overpotentials of this novel electrochemical system are less than 0.55 V. With regard to the typical surface termination, the oxygen (O) termination weakens the N 2 fixation, hinders the dissociation and increases the overpotential of the electrochemical reaction. According to the present theoretical calculations, Ti 2 CO 2 will be lithiated to Ti 2 CO 2 Li 2 in the initial discharge state, and the lithiated Ti 2 CO 2 substrate can decrease discharge and charge overpotentials in comparison to a bare Ti 2 CO 2 substrate. Our work is the first theoretical report on the mechanism of an Li–N 2 battery on a Ti 2 C cathode substrate, which provides a feasible strategy for efficient N 2 fixation and reduction.