PTFE-Based Solvent-Free Electrode Manufacturing Process for Lithium-Ion Batteries and Solid-State Batteries
Authors: Hwang Insung 
Published: December 2024

As the global energy and climate crisis continues to escalate, the importance of secondary batteries is continuously growing. The current generation's lithium-ion battery technology has received widespread attention from various sectors worldwide, experiencing explosive growth. However, it seems to be entering a saturation phase in terms of technological advancement. Most research has primarily focused on material-centric approaches, such as High-Ni cathode materials and Si-based anode materials, to improve battery energy density. Research on electrode manufacturing processes has been relatively lacking. However, in recent years, dry electrode manufacturing processes have gained significant attention, owing to the distinct features and advantages over conventional slurry-based electrode processes.

Firstly, thick electrode formation is required to enhance battery energy density. In conventional slurry processes, difficulties arise in manufacturing thick electrodes due to binder and conductive material migration issues, leading to decreased electrode performance. In contrast, dry processes eliminate the solvent drying stage, avoiding the aforementioned issues and enabling easier manufacturing of high-performance thick electrodes, thus effectively improving battery energy density. Additionally, dry processes offer advantages in terms of cost and environmental impact. Slurry processes require substantial energy input for solvent drying, necessitating large-scale equipment and incurring high costs. Moreover, harmful NMP vapor emissions during electrode drying require additional expenses for solvent recovery systems. In contrast, dry processes eliminate the need for solvent drying, offering environmental and cost advantages and often being labeled as low-carbon environmentally friendly processes.

There are various types of 'dry electrode manufacturing processes' because absence of any solvent is the only requirement to be considered as a dry process. Among them, currently, the most commercially viable dry manufacturing technology utilizes PTFE fibrillation, initially patented by Maxwell in the United States and extensively promoted by Tesla. This technique involves mixing and kneading active materials, conductive additives, and PTFE without solvents, shaping them into film form. Notably, the resulting electrode layer exists as a free-standing film, distinct from being directly coated on a substrate.

This presentation will introduce the manufacturing technology of lithium secondary battery thick electrodes using PTFE fibrillation-based dry processes, as well as the manufacturing technology of cathodes for all-solid-state batteries(ASSBs). For the dry manufacturing process of thick electrodes of lithium ion batteries, key factors needed to be deeply explored will be introduced, based on every process stage. Along with an overview of materials, equipment, and processes, basic research results on the mechanical and electrochemical properties of dry thick electrodes manufactured through dry processes will be shared.

Furthermore, research results on the application of dry manufacturing processes to sulfide-based solid-state batteries, which is considered as a promising application area, will be introduced. Due to its excellent ionic conductivity and superior ductility, sulfide-based solid electrolytes like LPSCl are considered the most promising solid electrolyte for ASSBs. However, they are too much vulnerable to polar solvents, which poses a challenge when using slurry-based electrode manufacturing processes. To overcome this issue, research has been conducted on the development of composite cathodes based on sulfide-based solid electrolytes using solvent-free dry manufacturing processes, especially PTFE-based process, achieving scale-up possibility of manufacturing processes. The manufacturing of large-area solid-state battery cathode free-standing films with widths exceeding 200mm and theoretically infinite lengths was possible, exhibiting enough mechanical strength and flexibility for roll-to-roll processes. In pouch cell systems, composed of dry-manufactured composite cathode, LPSCl membrane, and Ag/C anode, initial discharge capacity of up to 200 mAh/g was achieved, demonstrating the potential for commercialization of sulfide-based all-solid-state batteries.