Study on the interface between sulfide-based solid electrolytes and high-capacity electrode materials

Abstract

There is a growing trend of interest in all-solid-state batteries utilizing solid electrolytes for improved battery energy storage density and safety. However, limitations exist due to the low oxidation stability of sulfide-based SEs and the non-fluidic nature of solids, particularly at the interface between high-capacity electrode active materials such as polycrystalline LiNi0.8Co0.1Mn0.1O2 cathode active material and Lithium (Li) metal anode, both electrochemically and physically unstable. In Chapter III, to mitigate the oxidation decomposition reactions of Li6PS5Cl within the cathode mixture and the capacity loss of LiNi0.8Co0.1Mn0.1O2 due to sulfide-based gas penetration between grains, ZnO was mixed into the cathode composite. The semiconducting properties of ZnO and its affinity for sulfide-based gases were expected to adjust the electronic conductivity within the cathode mixture, aiming to alleviate the oxidation decomposition reactions of LiNi0.8Co0.1Mn0.1O2 and reduce the capacity loss caused by sulfide-based gas penetration between grains, thereby enhancing the initial reversible capacity of the full cell and increasing capacity retention during subsequent cycles. Nano-sized gaps or voids exist between the Li metal anode and Li6PS5Cl, leading to uneven Li-ion flux due to irregular physical contact, resulting in crack formation, dendrite growth, and void formation during further plating/stripping processes. In Chapter Ⅳ, to enhance physical contact and facilitate uniform and rapid charge transfer, a carbon protective layer with a PVA-g-PAA binder was utilized. The binder facilitates Li-ion transport and also helps prevent layer cracking during repeated Li volume changes throughout the cycle due to its excellent adhesive properties. Additionally, In Chapter Ⅴ, porous structures were employed to reduce the occurrence of reductive decomposition reactions between Li and the solid electrolyte. It is anticipated that porous structures synthesized using non-solvent induced phase separation will help Li to deposit internally or underneath the layer. By preventing direct contact between Li and the solid electrolyte, cell overpotential can be reduced, and the lifespan characteristics can be improved.