Mechanochemical synthesis of pseudobinary Ti-V hydrides and their conversion reaction with Li and Na

Abstract

Lithium-ion batteries (LiBs) based on insertion electrodes reach intrinsic capacity limits. Performance improvements and cost reduction require alternative reaction mechanisms and novel battery chemistries such as conversion reactions and sodium-ion batteries (NaBs), respectively. We here study the formation of Ti1-xVxH2 hydrides (0 ≤ x ≤ 1) and their electrochemical properties as anodes in LiBs and NaBs half-cells. Hydrides were synthesized by mechanochemistry of the metal powders under hydrogen atmosphere (PH2 ∼ 8 MPa). For V contents below 80 at. % (x < 0.8), single-phase pseudobinary dihydride compounds Ti1-xVxH2 are formed. They crystallize in the fluorite-type structure and are highly nanostructured (crystallite size ≤ 10 nm). Their lattice parameter decreases linearly with the V content leading to hydride destabilization. Electrochemical studies were first carried out in Li-ion half cells with full conversion between Ti1-xVxH2 hydrides and lithium. The potential of the conversion reaction is gradually tuned with the vanadium content as result of the hydride induced destabilization. Furthermore, different paths for the conversion reaction are observed for Ti-rich (x ≤ 0.25) and V-rich (x ≥ 0.7) alloys. Na-ion half-cell measurements prove the reactivity between (V, Ti)H2 hydrides and sodium, albeit with significant kinetic limitations.