Theoretical insights into nitrogen fixation on Ti2C and Ti2CO2 in a lithium–nitrogen battery

Abstract

Recently, the first lithium–nitrogen (Li–N₂) battery was designed, achieving a reversible electrochemical reaction between N₂ and Li₃N under ambient conditions (Ma et al., Chem, 2017, 2, 525–532). However, the performance of a Li–N₂ battery is limited by the weak interaction between the carbon cloth cathode substrate and N₂. In the present work, we theoretically evaluate a Ti₂C monolayer as a potential cathode substrate to improve the performance of an Li–N₂ battery. Our results reveal that N₂ interacts strongly with the bare Ti₂C substrate with low adsorption energy and a lot of electron transfer, and the existence of Li atoms facilitates N₂ 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 N₂ fixation, hinders the dissociation and increases the overpotential of the electrochemical reaction. According to the present theoretical calculations, Ti₂CO₂ will be lithiated to Ti₂CO₂Li₂ in the initial discharge state, and the lithiated Ti₂CO₂ substrate can decrease discharge and charge overpotentials in comparison to a bare Ti₂CO₂ substrate. Our work is the first theoretical report on the mechanism of an Li–N₂ battery on a Ti₂C cathode substrate, which provides a feasible strategy for efficient N₂ fixation and reduction.