Reactivity of TiH2 hydride with lithium ion: Evidence for a new conversion mechanism

The electrochemical reactivity of the face centered cubic (fcc) TiH2 hydride with lithium ion was studied. A full discharge capacity of 1072 mAh/g at an average potential of 0.2 V can be achieved when the TiH2 hydride electrode is ground with 10wt% of carbon. From X-ray diffraction (XRD) characterization of the electrodes, dehydrogenation of the titanium hydride via an electrochemical process occurs following different reaction steps. From 0 to 0.34 Li, an fcc delta-TiH2-x solid solution is formed according to the reaction delta-TiH2 (fcc) + 0.34 Li -> delta TiH1.66 (fcc) + 0.34 LiH. Pursuing the dehydrogenation process from 0.34 to 1, the cubic solid solution delta-TiH2-x reacts with lithium ion and transforms partially an a distorted face centered orthorhombic phase delta-TiH (fco). At this stage, the absence of hexagonal close-packed (hcp) alpha-Ti formation is attributed to the peritectic transformation: hcp alpha-Ti(H) + fcc alpha-TiH2-x -> delta-TiH. From 1 to 2 Li, a usual conversion mechanism is observed leading to the formation of hcp alpha-Ti and LiH according to the reaction delta-TiH2-x (fcc) <-> delta-TiH (fco) -- Li -> alpha-Ti (hcp) + LiH. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.