Low temperature sintering of fully inorganic all-solid-state batteries - Impact of interfaces on full cell performance

One of the necessary prerequisites to advance the electrochemical performance of Li7La3Zr2O12 (LLZ) based all-solid-state lithium batteries is the manufacturing of dense composite cathodes from cathode active material (CAM) and the LLZ ceramic solid electrolyte. However, free co-sintering of LLZ and CAM mixtures requires temperatures above 1000 degrees C which often leads to decomposition and secondary phase formation, especially for high energy CAMs. In our study we present a completely dry processing route which is fast, free of any sintering additives and coatings and suitable to fabricate dense mixed cathodes, pure LLZ separators and multilayers of the two. Through application of high mechanical pressure during Field-Assisted Sintering we were able to reduce the sintering temperature down to 675-750 degrees C with dwell times as low as 10 min, while still obtaining 95% theoretical density for LCO/LLZ mixtures. The low sintering temperature is suitable for high energy CAMs, but leads to a significant effect of surface impurities, especially from powder handling in air, and affects the crystallinity of the CAM/LLZ interface. In the present paper we investigate the impact of resulting interfaces on the ionic conductivity, the interfacial impedance and the cycling stability of produced cells and propose the optimization strategy.

Automated summary

The study introduces a completely dry processing route for manufacturing dense composite cathodes, pure LLZ separators, and multilayers of the two through high mechanical pressure during Field-Assisted Sintering. The low sintering temperature achieved is suitable for high energy CAMs but leads to surface impurities affecting the crystallinity of the CAM/LLZ interface. Investigating the impact of resulting interfaces on ionic conductivity, interfacial impedance, and cycling stability of produced cells, an optimization strategy is proposed.