The ionic conductivities, stabilities and ionic mobilities of xLiBH₄-Li₂NH (x = 1, 2, 4) composites as fast ion conductor

LiBH₄ possesses high ionic conductivity (σ) at a temperature over 373 K and wide window voltage over 5 V, but low σ value below 373 K. Li₂NH owns excellent ionic conductivity at low temperature but performs in a narrow window voltage (only 0.7 V). xLiBH₄-Li₂NH composites (x = 1, 2, 4) were therefore synthesized to eliminate their respective drawbacks. By alternating current impedance spectra, we observed that xLiBH₄-Li₂NH (x = 1, 2, 4) composites offer σ of 10⁻² Scm⁻¹ at a temperature over 373 K, and lift σ value by 100 times from that of LiBH₄ at a temperature below 373 K. According to the cyclic voltammetry (CV for 10 cycles) results, the window voltage of 3 V can be achieved for LiBH₄-Li₂NH (1:1). X-ray diffraction (XRD) and Fourier Transform infrared spectroscopy (FTIR) measurements on xLiBH₄-Li₂NH (x = 1, 2, 4) samples inform that original phases were well preserved after ball milling and temperature ramping. Their chemical stabilities were also demonstrated by differential scanning calorimetry (DSC) measurements. The enhanced lithium mobility at low temperature in LiBH₄-Li₂NH should be ascribed to the favorable boundaries between both phases according to the investigations by both in-situ nuclear magnetic resonance (NMR) and high-resolution transmission electron microscope (HRTEM). However, at a temperature above 373 K, the enhanced ionic mobility of LiBH₄-Li₂NH should be mainly contributed by HT-LiBH₄ phase.