Weaving secondary battery electrodes with fibers and tying them like ropes for both durability and performance

(Press-News.org) A joint research team led by Dr. Gyujin Song of the Korea Institute of Energy Research (President: Yi, Chang-Keun, hereafter “KIER”), Dr. Kwon-Hyung Lee of the University of Cambridge, and Professor Tae-Hee Kim of the University of Ulsan has successfully developed a new dry-process manufacturing technology for secondary battery electrodes that overcomes the limitations of conventional electrode fabrication processes.

The technology developed by the research team is a dry manufacturing process that forms a dual-fibrous structure inside the electrode, simultaneously creating thin “thread-like” and thick “rope-like” fibers. This dual-fiber (dual-fibrous) architecture enables the technology to address both the low mixing strength and performance degradation issues of conventional dry processes at the same time.

Electrode manufacturing methods for secondary batteries are broadly divided into wet and dry processes, depending on whether a solvent is used. In the wet process, a binder* dissolved in a solvent is used as an adhesive, which ensures uniform mixing of the electrode materials. Owing to its high process reliability and advantages in securing performance, the wet process is currently the predominant method used for electrode fabrication.

* Binder: a polymer material used in manufacturing secondary-battery electrodes that holds together components such as the active material (which stores electrical energy) and the conductive additive (which carries electric current), so the electrode can stably maintain its form.

However, it relies on toxic organic solvents, which creates a heavy environmental burden, and the time required for drying and solvent recovery is long, leading to high production costs. As a result, there has recently been growing interest in developing dry-process technologies that do not use solvents.

The dry process does not use solvents, which allows for faster processing and helps reduce environmental pollution and energy consumption. However, because there is no solvent to dissolve the binder, only a limited range of binder materials can be used, such as polytetrafluoroethylene (PTFE)*, which stretches into fiber-like structures and physically holds the particles together.

* PTFE (Polytetrafluoroethylene): a material with excellent heat resistance and chemical resistance, widely known in everyday life as Teflon (a brand name of DuPont, USA) used for frying pan coatings.

As a result, in conventional dry processes it has been difficult to uniformly mix the electrode materials, and the low cohesion of the mixture has led to persistent concerns that the performance and durability of the finished batteries are degraded.

To overcome the structural limitations of the dry process, the researchers did not change the material of the conventional PTFE binder; instead, they controlled the physical structure of the same material to create a PTFE binder with a “dual-fiber” structure.

The research team designed an original multi-step process that divides the binder addition from a single step into two stages. First, they add a small amount of binder and carry out a primary mixing step, forming a fine, “thread-like” fibrous network that densely connects the active material and the conductive additive. Then, in a secondary mixing step, they add the remaining binder so that, while the existing fibrous network is maintained, an additional thick and robust “rope-like” fiber structure is formed.

The resulting fine, “thread-like” fibrous network uniformly disperses the constituent materials, such as the active material and conductive additive, thereby making the reactions more uniform and improving battery performance. In addition, the thick, “rope-like” fibers firmly bind the entire electrode together, significantly increasing its strength and mechanical stability and enhancing the durability required for mass-production processes.

In addition, analysis using electrochemical reaction-resistance mapping showed that all regions of the electrode exhibit fast and uniform reaction kinetics and resistance characteristics. This is a key factor in minimizing energy loss during battery operation, preventing performance degradation in specific areas, and thereby extending the overall lifetime of the cell.

In performance evaluations, the dry electrode developed by the research team achieved a high areal capacity of 10.1 mAh/cm². A pouch-type lithium metal anode cell using this electrode reached an energy density of 349 Wh/kg, about 40% higher than that of commercial electrodes, which are around 250 Wh/kg. In addition, a pouch cell using a graphite anode achieved an energy density of 291 Wh/kg, showing a value approximately 20% higher than that of a wet-process cell under the same conditions.

Dr. Gyujin Song, who led the research, stated, “This study is highly significant in that we have established an original process technology capable of simultaneously resolving the two core challenges of dry electrodes: electrochemical uniformity and mechanical durability. We expect it to not only enhance the cost competitiveness of the secondary battery industry, but also be applicable to electric vehicles and energy storage systems (ESS), which require high energy density.”

Meanwhile, this research was carried out with support from the Ministry of Science and ICT’s “Global TOP Research Program” and “Creative Allied Project,” and the results were published in the September issue of Energy & Environmental Science (IF 30.8), a world-renowned journal in the field of energy and the environment.

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