Improved Li-ion conductivity of 0.7Li4SiO4–0.3Li3PO4 by aluminum doping

Highlight
• Aluminum doping has been conducted for Li4SiO4-Li3PO4 solid solution (LSP).
• The Al-doped LSP (LASP) has much higher ionic conductivity than the undoped LSP.
• The ionic conductivity of LASP increases as the amount of dopant is increased.
• LASP has higher ionic conductivity and lower electron transport number.
• LASP appears to be a better solid electrolyte than LSP due to the above features.

The solid solution 0.7Li4SiO4–0.3Li3PO4 (LSP) is known to be a Li-ion conducting ceramic. Aluminum doping of it was carried out to increase the ionic conductivity. The aluminum-doped LSP (LASP) was prepared with different amounts of dopant, to examine the effect of the amount of dopant on the ionic conductivity. LASP was synthesized using a sol-gel reaction and subsequent calcination. The crystalline phase of the LASP was analyzed by powder X-ray diffraction (PXRD) and identified as the monoclinic phase of 0.7Li4 − yAlySiO4–0.3Li3PO4. However, addition of aluminum results in the precipitation of a secondary crystalline Li2SiO3 phase. Li-ion conductivity was estimated by using electrochemical impedance spectroscopic (EIS) analysis on an LASP pellet that had been sintered at 1000 °C. In spite of the precipitation of the Li2SiO3 phase, Li-ion conductivity was increased by aluminum doping at 150 °C to approximately 20 times that of the undoped material (LSP), which effect is considered to be associated with vacancies generated by the aluminum doping providing conducting paths for the Li-ion.