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 δ-TiH2−x solid solution is formed according to the reaction δ-TiH2 (fcc) + 0.34 Li → δ TiH1.66 (fcc) + 0.34 LiH. Pursuing the dehydrogenation process from 0.34 to 1, the cubic solid solution δ-TiH2−x reacts with lithium ion and transforms partially in a distorted face centered orthorhombic phase δ-TiH (fco). At this stage, the absence of hexagonal close-packed (hcp) α-Ti formation is attributed to the peritectic transformation: hcp α-Ti(H) + fcc δ-TiH2−x → δ-TiH. From 1 to 2 Li, a usual conversion mechanism is observed leading to the formation of hcp α-Ti and LiH according to the reaction δ-TiH2−x (fcc) ↔ δ-TiH (fco) + Li → α-Ti (hcp) + LiH.

► Electrochemical reactivity of the fcc-TiH2 hydride with lithium ion.
► New conversion mechanism, involving a solid solution and a metastable phase.
► A fcc δ-TiH2−x solid solution is first formed (0–0.34 Li).
► It is followed by the formation of a distorted fco phase δ-TiH (0.34–1 Li).
► A conversion mechanism is finally observed leading to hcp α-Ti and LiH (1–2 Li).