Tailoring Microstructures and Ionic Conductivities of Li1+XAlxGe2–X(PO4)3 (LAGP) Solid Electrolytes for All-Solid-State Batteries

Abstract

Lithium ion batteries (LIBs) have been successfully utilized as power sources for various electronic devices (e.g. mobile phone, remote controller, lab-top, etc.). Recently, the application of LIBs is extending to emerging markets such as electric vehicles (EVs) and energy storage systems (ESSs) for grid-supporting. Unfortunately, conventional LIBs still suffer from safety issues associated with the use of flammable organic electrolytes. To overcome such limitation of LIBs, many attentions have been devoted to the development of all-solid-state batteries (ASBs) that are employing solid electrolytes with excellent structural and electrochemical stabilities. Li1+xAlxGe2–x(PO4)3 (LAGP) is a kind of potential solid electrolytes with a NASICON structure. It offers relatively high bulk ionic conductivity (~10-4 Scm-1) with a wide electrochemical window and great moisture tolerance.[2] Owing to these advantages, LAGP can be a great option as a practical solid electrolyte for realizing ASBs. However, there are some technical issues to be resolved before commercial use of LAGP solid electrolytes as follow; i) a low ionic conductivity arising from the high boundary resistance and ii) a high synthesis temperature (i.e. energy consumable process). In this work, the microstructures of LAGP solid electrolyte are tailored by addition of Bi2O3 and B2O3 with a purpose of improving the ionic conductivity and reducing the fabrication temperature. Based on various structural and electrochemical analyses, we investigate the correlation between microstructure and ionic conductivity of LAGP. In practice, Bi2O3 is able to improve the structural integrity of LAGP with turning down of the sintering temperature, leading to the densification of LAGP [1] and, on the other hand, B2O3 facilitates the grain growth of LAGP during synthesis.[3] As a result of co-addition of Bi2O3 and B2O3, the ionic conductivity of LAGP solid electrolyte increases about one order of magnitude higher than pristine LAGP. This work will provide a practical guideline to develop a highly reliable solid electrolytes for ABSs. (Figure 1 image) SD Lee and KN Jung, ChemSusChem 10, 2175 (2017)Masashi Kotobuki, Keigo Hoshina, Yasuhiro Isshiki, Phosphorus Research Bulletin 24, 061 (2010)Harsharaj S. Jadhav, Ramchandra S. Kalubarme, Seong-Yong Jang, KN Jung, Mo, Dalton Trans. 43, 11723 (2014) Figure 1