Effect of Microwave Processing on the Microstructure and Grain Boundary Conductivity of Lithium-Aluminum-Germanium-Phosphate and Lithium Iron Phosphate for Solid State Battery Applications

Solid state electrolytes (SSE) represent a significant advancement over liquid electrolytes in terms of safety, reliability, and energy density, but maximizing ionic conductivity requires high temperature thermal processing, which can lead to development of secondary phases. In addition, high temperature processing may hinder interfacing with cathode materials. This report demonstrates rapid microwave processing of lithium-aluminum-germanium phosphate (LAGP) electrolyte materials from source powders and subsequent co-processing with lithium-iron-phosphate (LFP) cathode interfaces. Scanning electron microscopy (SEM) was used to characterize structural evolution as well as LAGP/LFP interfaces, while X-ray diffraction and energy dispersive X-ray spectroscopy (EDS) were used to characterize phase purity and elemental diffusion. Electrochemical impedance spectroscopy (EIS) data were used to determine ionic conductivity. LAGP shows evidence of a microwave effect, as efficient absorption of microwaves results in samples with porous, low-density microstructures and improved grain boundary conductivity. LFP was observed to have moderate and controllable absorption of microwaves.