Ammine Magnesium Borohydride Nanocomposites for All-Solid-State Magnesium Batteries
Yigang Yan, Jakob B. Grinderslev, Mathias Jørgensen, Lasse N. Skov, Jørgen Skibsted, Torben R. Jensen
Abstract
Magnesium batteries are considered promising solutions for future energy storage beyond the lithium-ion battery era. However, the development of magnesium batteries is hindered by the lack of suitable electrolytes. Here we present solid Mg2+ electrolytes based on ammine magnesium borohydride composites, Mg(BH4)2·xNH3, which have conductivities ca. three orders of magnitude higher than the parent compounds (x = 1, 2, 3, and 6). A nanocomposite formed by the Mg(BH4)2·xNH3 composite and MgO nanoparticles exhibits outstanding Mg2+ conductivity of the order of 10–5 S cm–1 at room temperature and around 10–3 S cm–1 at moderate temperature (ca. 70 °C), with an activation energy for Mg2+ conduction of Ea ∼108 kJ/mol (1.12 eV) and high thermal stability (Tdec = 120 °C). Characterization using solid-state nuclear magnetic resonance, powder X-ray diffraction, and transmission electron microscopy reveals that the high Mg2+ conductivity is attributed to amorphization of Mg(BH4)2·xNH3 resulting in a highly dynamic state. This nanocomposite is compatible with a Mg metal anode and allows stable Mg plating/stripping (at least 100 cycles) in a symmetric cell. The results represent a major advancement of solid-state multivalent ion conductors here demonstrated for Mg2+.