Bi2O3-Added Li1.4Al0.4Ti1.6(PO4)3 with Enhanced Li-Ion Conductivity As a Solid Electrolyte for All-Solid-State Battery

Abstract

Lithium-ion battery (LIB) has been one of the most attractive energy sources for mobile devices, energy storage systems and electric vehicles, however, the safety issue is one of the remaining challenges for commercial LIBs. All-solid-state lithium battery with a solid electrolyte has been regarded as alternative technology for LIBs that use organic liquid electrolyte because of likely higher energy density and superior safety. Various solid electrolytes such as polymer, sulfides and oxides have been extensively studied to eliminate the flammable components in LIBs and to achieve the high lithium-ion conductivity required for the practical use [1,2]. Among the oxide-based solid electrolytes, NASICON-type Li1+xAlxTi2-x(PO4)3 (LATP) has received much attention due to its fast lithium conduction in the bulk at room temperature up to 1 mS cm-1 as well as its superior mechanical strength and chemical stability. However, the high grain boundary resistance of LATP gives a high total resistivity for the inorganic solid electrolyte, which hinders its application and use in all-solid state batteries. While the sintering process is one of the effective ways to minimize the grain boundary resistance of LATP by densification of oxide ceramics, the sintering temperature should be reduced with maintaining high density and lithium-ion conductivity. Bismuth oxide (Bi2O3) is a well-known sintering aid, which can promote densification and lower sintering temperature. In this work, we present the Bi2O3-added Li1.4Al0.4Ti1.6(PO4)3 as a solid electrolyte for all-solid-state battery. The high purity LATP nano-powders were synthesized by Pechini method and the Bi2O3-added LATP solid electrolytes with high density were fabricated via sintering process at various temperatures of 800 oC - 950 oC. Based on the analyses of structural and electrochemical properties for Bi2O3-added LATP electrolytes, the effects of Bi2O3 addition on the microstructure and the behavior of lithium ion conduction in LATP solid electrolyte were examined. The LATP with Bi2O3 sintered at 850 oC shows the enhanced lithium-ion conductivity (ca. 0.9 mS/cm) compared with that (ca. 0.4 mS/cm) of pristine LATP, which implies that added-Bi2O3 effectively promotes the densification of LATP and reduces the grain boundary resistance. The cycle performances and rate capabilities for the Li half-cells constructed with Bi2O3-added LATP were also compared with those of the cell with pristine LATP. Reference [1] P. Knauth, Solid State Ionics, 180 (2009) 911. [2] J. C. Bachman et al., Chem. Rev, 116 (2016) 140.