Study on xLiBH₄-NaBH₄ (x = 1.6, 2.3, and 4) composites with enhanced lithium ionic conductivity

In the present work, ball-milled xLiBH₄-NaBH₄ (x = 1.6, 2.3, 4) composites were investigated as fast ionic conductors. It was found that the conductivity σ of xLiBH₄-NaBH₄ (x = 1.6, 2.3, 4) composites could attain 10⁻² S cm⁻¹ when temperature is higher than 373 K. Meanwhile, these σ values are one or two orders of magnitude higher than that of pristine LiBH₄ at temperatures below 373 K. A window voltage of 4.5 V was identified by means of the cyclic voltammetry (CV) measurements on xLiBH₄-NaBH₄ (x = 1.6, 2.3, 4) composites for 5 cycles. The structural stability of xLiBH₄-NaBH₄ (x = 1.6, 2.3, 4) composites before and after CV tests were demonstrated by X-ray diffraction (XRD) and Fourier Transform infrared spectroscopy (FTIR). They are also very stable during the ramping from room temperature to 393 K. Measurements by differential scanning calorimetry (DSC) observed that both transition enthalpies and transition temperatures were all reduced, implying that the high temperature phase of LiBH₄ was stabilized. Such phenomenon facilitates the enhancement of lithium mobility in these composites.