Fast Room-Temperature Mg Conductivity in Mg(BH)·1.6NH-AlO Nanocomposites.

Design of new functional materials with fast Mg-ion mobility is crucial for the development of competitive solid-state magnesium batteries. Herein, we present new nanocomposites, Mg(BH)·1.6NH-AlO, reaching a high magnesium conductivity of σ(Mg) = 2.5 × 10 S cm at 22 °C assigned to favorable interfaces between amorphous state Mg(BH)·1.6NH; inert and insulating AlO nanoparticles; and a minor fraction of crystalline material, mainly Mg(BH)·2NH. Furthermore, quasi-elastic neutron scattering reveals that the Mg-ion mobility in the solid state appears to be correlated to relatively slow motion of NH molecules rather than the fast dynamics of BH complexes. The nanocomposite is compatible with a metallic Mg anode and shows stable Mg stripping/plating in a symmetric cell and an electrochemical stability of ∼1.2 V. The nanocomposite has high mechanical stability and ductility and is a promising Mg electrolyte for future solid-state magnesium batteries.