Preparation and electrical properties of NASICON-type structured Li1.4Al0.4Ti1.6(PO4)3 glass-ceramics by the citric acid-assisted sol–gel method

Lithium-ion conducting Li1.4Al0.4Ti1.6(PO4)3 glass-ceramics with ultrapure NASICON-type phase were synthesized by a citric acid-assisted sol–gel method and characterized by TGA-DSC, XRD, transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM) and complex impedance techniques. The influence of molar ratio of citric acid to cations as well as pH value on the formation of Li1.4Al0.4Ti1.6(PO4)3 sol was studied. Experimental results indicated that the citric acid-assisted sol–gel method made it possible to obtain well crystallized glass-ceramics of Li1.4Al0.4Ti1.6(PO4)3 at a much lower temperature within a shorter synthesis time in comparison to conventional solid-state reaction methods. The optimized conditions for citrate-based preparation process were at the molar ratio (R) of [H3Cit + glycol] / [Li+ + Al3+ + Ti4+] = 4 and pH = 7, respectively. Highly pure and ultrafine powders were obtained by heating the amorphous powders got from the sol–gel process at a temperature between 800 and 1000 °C. The highest room temperature bulk and total Li+ conductivities were 2.09 × 10− 3 S/cm and 6.13 × 10− 4 S/cm, respectively. And the bulk activation energy as low as 0.29 eV was obtained for the same specimen prepared at 950 °C for 6 h. The high conductivity, good chemical stability and easy fabrication of the glass-ceramics suggest it to be a promising candidate as solid electrolyte for all-solid-state Li-ion rechargeable batteries.