Synthesis and ionic transport mechanisms of α-LiAlO2

The pure phase alpha-LiAlO2 is synthesized by a solid-state reaction. The obtained product has nanocrystalline structure with the Li deficient regions near the surfaces. Combining X-ray diffraction (XRD) and thermogravimetry-differential scanning calorimetry (TG-DSC), the synthesis mechanism is revealed. The measured room temperature ionic conductivity of the alpha LiAlO2 ceramic pellet is as low as 10(-21) S. cm(-1). This could be caused by the absence of conduction pathways, as calculated from the bond-valence (BV) method. In addition, a first principles calculation is performed. The calculated result suggests that although the alpha-LiAlO2 bulk has the extremely low ionic conductivity, its ionic conductivity could be increased significantly when applied the bias voltage, which is due to the introduction of external lithium sources (lithium reservoirs of interstitials/vacancies) and external charge sources (electrons/holes). This may explain why alpha-LiAlO2 as the coating layer on cathode for Li ion batteries does not block the transport of lithium ions. (C) 2016 Elsevier B.V. All rights reserved.