Effects of Defective Boron Nitride Additives on Lithium-Ion Conductivity and Hydrogen-Desorption Properties of LiAlH4

Abstract

The lithium-ion conductivity and hydrogen-desorption properties of lithium alanate (LiAlH4)/boron nitride (BN) composites were investigated. The effects of boron nitrides with different structures (hexagonal (h-BN), turbostratic (t-BN), and cubic (c-BN)) on the properties were demonstrated. Compared with milled LiAlH4, the ion conductivity was improved in the h-BN and t-BN composites. Among the composites, the t-BN composite showed the highest conductivity and lowest activation energy (Ea) for ion conduction. In the 40 wt % t-BN composite, the conductivity at 80 °C reached as high as 1.1 × 10–3 S cm–1. Impedance plots that correspond to the interfacial conductivity were observed, which implies the appearance of LiAlH4/t-BN interfacial ion conduction. Ball-milling of LiAlH4 with BN caused the partial replacement of aluminum with boron to form LiBH4 phase, which would cause the Ea decrease. The LiAlH4 melting and hydrogen-desorption temperature decreased in the t-BN composite. In the c-BN composite, a large amount of stainless steel impurity during ball-milling caused desorption without melting. This study suggests that the addition of defective boron nitride like t-BN can be a useful strategy to improve the lithium-ion conductivity of complex hydrides. The t-BN additive effects on the hydrogen-desorption properties, which are different from transition metal catalysts, were also demonstrated.