Ultimate Design Principles and Fabrication Process for High Energy Density Solid State Pouch Cells Based on Solid Polymer Electrolytes

Solid-state lithium batteries have become promising alternatives to the conventional lithium-ion chemistries for pursuing enhanced safety and higher energy density. Owing to the advancement in the solid electrolytes and the active materials, its energy-storing characteristics are getting evolved in the lab-scale environment, but it is still far from the practical cell engineering perspectives. Here, we are proposing an ultimate design principle for building practically energy-dense solid-state batteries from the microstructure of electrodes to the entire cell architecture. The impact of multiscale parameters on the cell energy density was mathematically evaluated such as 1) gravimetric/volumetric composition, 2) apparent density, 3) areal loading amount in the electrode level, 4) the types of anode materials, 5) the thickness of solid electrolyte membrane, 6) the electrode sheet stacking number, and 7) the cell size. Not only just designing the electrochemical cells, but the fabrication process developments are also quite important to demonstrate the design methodology. To validate our design logic, we also suggest adequate processing methods and made double-layer stacked 200 mAh scale solid-state pouch cells based on the solid polymer electrolyte with PVDF-HFP conjugated to lithium salts and plasticizer as a model system. Thanks to the NCM622-based high active material composition (94 wt%), the areal capacity (> 4 mAh cm−1) using WIP (warm isostatic press) densification with the freestanding thin lithium metal anode (40 μm), we could verify the energy density as high as 227 Wh kg−1 including the whole-cell package, which was certified by the third-party organization. This design principle and the developed process can be applied to the various kind of solid-state batteries, so it might guide the research community to rationally achieve the practical high energy density milestone.