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

TL;DR

This study synthesizes Ti-V hydrides via mechanochemistry, investigates their structure and electrochemical behavior as anodes in lithium and sodium-ion batteries, revealing tunable conversion potentials and kinetic limitations.

Contribution

It introduces a novel mechanochemical synthesis method for Ti-V hydrides and explores their conversion reactions in Li and Na batteries, highlighting composition-dependent electrochemical properties.

Findings

Ti1-xVxH2 hydrides are formed with x<0.8 and crystallize in a fluorite structure.

The lattice parameter decreases linearly with V content, destabilizing the hydrides.

Hydrides show potential for tunable conversion reactions in lithium-ion batteries.

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 can be gradually tuned with the vanadium content due to its destabilization effect. 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