Ruthenium nitride thin films with ZnS type cubic structure are successfully and reproducibly deposited by pulsed-DC magnetron sputtering. Their electrochemical behavior as negative electrode for Li-ion microbatteries is investigated by cyclic voltammetry and galvanostatic experiments. The influence of the film thickness and the rate capability are reported and discussed. A specific capacity of about 400 mA h g (1) is proved to be stable at C/2 over 20 cycles at a mean voltage of 0.25 V vs. Li+/Li and attractive specific capacities varying from 100 to 300 mu A h cm (2) can be reached depending on the thickness in the range 250 nm-850 nm. XRD, SEM, HRTEM, electron diffraction and EELS are used to understand the electrochemical mechanism of RuN with lithium. Electrochemical properties and structural characterization support the occurrence of a reversible conversion reaction of RuN into Ru metal and Li3N. (C) 2015 Elsevier Ltd. All rights reserved.