Two-dimensional nanostructures have attracted increasing interest due to their fascinating properties and broad applications. In this study, we carry out first-principles studies on the electronic properties of MXenes and investigate their application in lithium-ion batteries. Herein, we focus on the transition-metal nitride monolayers M_i+1N_i; where M = Ta, Ti, and V; i = 1 and 2. We find that these monolayers are metallic and most of them show non-magnetic behavior, with the exception of the anti-ferromagnetic Ti₂N and ferromagnetic Ti₃N₂. Our calculations show that Li atoms can be easily transported on the surfaces of the monolayers, with negligible barriers as low as 0.017 eV on Ti₂N, because of low adsorption energy and long binding distance. We further show that these monolayers remain metallic under full Li-intercalation and have low open circuit voltages. In particular, the Ti₂N monolayer shows the best performance with an open circuit voltage of 0.53 V and the highest specific capacity of 487 mA h g⁻¹. Our calculations predict that transition-metal nitride monolayers may be applied in lithium ion batteries with improved performance.