Surface-Engineered LLZO-PVDF Solid-State Electrolyte for Enhanced Solid-State Lithium Battery Performance

Abstract

The transition from laboratory-scale fabrication to industrial manufacturing remains a major challenge for the commercialization of composite solid electrolytes (CSEs) in all-solid-state batteries. PEO is limited by its low voltage stability, which motivates the use of PVDF-based electrolytes; however, PVDF systems also suffer from dehydrofluorination, particularly in the presence of LLZO, so we shifted to PVDF-HFP. Although the electrochemical and mechanical properties of PVDF-HFP/LLZO systems have been widely studied, scalable and continuous production methods compatible with industrial requirements are still limited. Conventional batch casting and static drying approaches suffer from low throughput, limited reproducibility, and poor process control for large-area films. In addition, the use of volatile organic solvents such as acetone raises concerns regarding safety, environmental impact, and large-scale applicability. Processing of PVDF-HFP typically relies on N-methyl-2-pyrrolidone (NMP) as a coating solvent, which raises environmental and health concerns due to its toxicological profile. These limitations have driven the search for safer and more sustainable alternatives, such as γ-valerolactone (GVL), for solid electrolyte fabrication. To address these limitations, this work first investigates γ-valerolactone (GVL) as a greener and less toxic solvent alternative for the preparation of composite electrolyte slurries. The results demonstrate that GVL-based systems can achieve comparable dispersion quality and suitable rheological properties for coating processes, while offering advantages in terms of reduced toxicity and improved sustainability. These findings highlight the potential of GVL as a viable solvent for environmentally responsible large-scale electrolyte production. Building on this, a roll-to-roll (R2R) continuous coating and drying platform was developed by modifying a commercial 3D printer into a multifunctional manufacturing system for solid electrolyte films. The system integrates either Mayer rod or slot-die coating techniques to enable precise thickness control and uniform deposition of PVDF-HFP/LLZO composite slurries onto flexible substrates. A downstream heated calendaring mill simultaneously applies pressure and thermal energy, promoting solvent removal, reducing porosity, and improving interfacial contact between polymer and ceramic phases. The platform allows systematic control over key processing parameters, including coating speed, drying temperature, and deposition method, enabling process optimization for scale-up. Continuous calendaring-assisted drying enhances film cohesion and mechanical integrity while maintaining compatibility with high ceramic loadings required for improved ionic conductivity. Stable and repeatable operation was successfully demonstrated at the pilot laboratory scale, confirming the feasibility of extended continuous production. In a nutshell, this study presents a practical and adaptable pathway for scaling up the production of PVDF-HFP/LLZO composite solid electrolytes. By integrating sustainable solvent selection with continuous manufacturing techniques, it establishes a foundation for producing uniform, mechanically robust electrolyte films suitable for next-generation solid-state battery applications. Here, we evaluate γ-valerolactone (GVL), a promising green-solvent based on its closeness to NMP in the Hansen Solubility Space. Through this study, we highlight that GVL is a promising candidate currently available that merits further investigation.