Characteristics of interface between solid electrolyte and electrode in all-solid-state batteries prepared by spark plasma sintering

Interface issues impede the development of all-solid-state lithium batteries (ASSLiBs). To resolve these issues, it is crucial to understand characteristics of electrode-electrolyte interface. Herein, all-solid-state symmetrical batteries and full batteries were prepared by spark plasma sintering (SPS) at 500 °C and 650 °C, using Li1.5Al0.5Ge1.5(PO4)3 (LAGP) and LiFePO4 (LFP) as solid electrolyte and electrode. The microstructures and electrochemical performances of the LFP/LAGP interface and LAGP/LFP interface (different sintering current directions) were investigated. The results showed that no interface layer was formed at the LFP/LAGP interface and LAGP/LFP interface at 500 °C; however, various interface layers were formed at 650 °C. At the 650-LFP/LAGP interface, an Al-poor layer and a Fe-rich Li-poor layer composed of Fe2P2O7 were found, while at the 650-LAGP/LFP interface, an Al-rich Li-poor layer composed of AlPO4 was found. The interfaces sintered at 500 °C had small impedance and were able to electrochemically cycle, while those sintered at 650 °C showed large impedance and were not able to electrochemically cycle. Furthermore, the 500-LAGP/LFP interface showed better cycle stability than the 500-LFP/LAGP interface. Thus, it is concluded that the sintering temperature and sintering current direction play important roles in the ASSLiBs preparation. The formation mechanism of the interface microstructures under the SPS was also discussed.