All-solid-state lithium-ion batteries are promising candidates to overcome safety and energy limitations of common lithium-ion batteries. Although excellent results have been reported for sulfide based electrolytes on a small scale, classical slurry-based lithium-ion processing fails to reproduce the same performance in a larger cell. In this lecture, scalable concepts for material and component development are presented.
Herein, the solid-state technology is firstly combined with PVD-based, scalable silicon anode concepts developed at Fraunhofer IWS. The columnar structure of the anode has a 1D breathing mechanism similar to lithium, which preserves the interface toward the electrolyte. Stable cycling is demonstrated for more than 100 cycles with a high coulombic efficiency (CE) of 99.7–99.9% in full cells with industrially relevant areal loadings of 3.5 mAh/cm².
To reduce the necessary stack pressure and anode breathing, which is of immense importance for its final application, we investigated silicon-carbon void structures with silicon contents of up to 37 wt% in solid state batteries. The carbon matrix enables enhanced performance and lifetime of the Si-C composites compared to bare silicon nanoparticles in half-cells even at high loadings of up to 7.4 mAh cm-2. The solid electrolyte (Li6PS5Cl, 3 mS cm-1) does not penetrate the Si-C void structure resulting in less side reactions and higher initial coulombic efficiency compared to a liquid electrolyte (72.7 % vs. 31.0 %), which eliminates the need for prelithiation. During galvanostatic cycling, full cells with a low overbalancing of the anode showed high capacity retention of up to 87.7 % after 50 cycles.
In addition, an open microporous carbon as 3D host stabilizing metallic or cluster-type lithium is presented. 7Li NMR reveals a novel hitherto unknown lithiation mechanism via extended Li-cluster, and a high reversible capacity of up to 825 mAh/g is gained at potentials close to 0 V vs. Li/Li+. This new lithium/carbon hybrid anode concept suppresses dendrite formation at room temperature at high areal loading (> 3.3 mAh/cm²).
The so-called DRYtraec® process had been developed as a viable approach to replace slurry-based binders by a fibrous PTFE one in NMC/sulfidic-electrolyte cathode composites. This process has been now applied to the fabrication of thin argyrodite separator films and evaluated in comparision with slurry-based coating approaches.
The presented approaches are important steps for multi-layered prototype all-solid state pouch cells.