Solved the Challenges of Commercializing Next-Generation Secondary Batteries

Saenggiyun-DGIST Develops Thin-Film Cathode Technology for Aqueous Zinc-Ion Batteries
Higher Capacity and Durability Than Existing Technologies

Domestic researchers have solved the drawbacks of aqueous zinc-ion batteries, emerging as the next-generation secondary battery, unlocking the potential for large capacity and enhanced durability, thus paving the way for commercialization.

Dr. Chanhoon Kim of the Clean Wellbeing Research Group at Saenggiwon, showing the fabricated rear electrode. Photo by Saenggiwon

A joint research team from the Korea Institute of Industrial Technology and Daegu Gyeongbuk Institute of Science and Technology (DGIST) announced on the 25th that they have succeeded in developing a “thick-film cathode technology for aqueous zinc-ion batteries,” which are emerging as next-generation secondary batteries, providing a breakthrough in solving the biggest obstacle to commercialization: the low capacity per unit area.

Secondary batteries, once mainly used in small mobile devices, are now being applied to medium and large devices such as electric vehicles and energy storage systems (ESS), becoming a core of the future energy industry. However, recent frequent ESS fire accidents have raised safety concerns. The “aqueous zinc-ion battery” uses a water-based electrolyte, eliminating the risk of ignition and offering high safety. However, commercialization has been challenging due to a significant capacity drop when manufacturing “thick-film cathodes.” Thick-film cathodes are electrodes where active materials that generate electrical energy are coated thickly on a current collector, which serves as a pathway for electron movement. They are essential for improving the energy density of secondary batteries. Replacing four 30-micrometer (㎛) thick cathodes with one 120㎛ thick thick-film cathode reduces the battery thickness by more than 30% and increases energy density.

The research team solved the capacity degradation problem of aqueous zinc-ion batteries by imparting hydrophilicity to the cathode binder used in commercial lithium-ion batteries (an adhesive material added to help active materials and conductive agents adhere well to the current collector). Lithium-ion batteries use polyvinylidene fluoride (PVdF), a fluorine-based polymer, as a binder to adhere active materials and conductive agents to the current collector. However, PVdF is hydrophobic and does not bond well with water molecules, hindering the wetting of the finished cathode by the aqueous electrolyte. Conductive agents facilitate electron movement between the cathode and anode active materials.

Especially, the thicker the cathode, the higher the tortuosity, making it difficult for the aqueous electrolyte to penetrate inside the electrode. Cathodes that are not penetrated by the electrolyte suffer from poor zinc-ion supply, limiting the capacity realization of aqueous ion batteries. The research team solved this long-standing problem by simply sulfonating the existing lithium-ion battery binder to create a hydrophilic Sulfonated PVdF (S-PVdF). Sulfonation (Aromatic Sulfonation) is a substitution reaction used to increase the hydrophilicity of polymer electrolyte membranes for fuel cells. The reformed S-PVdF binder contains abundant sulfonate functional groups within its molecules,

which improves the wettability of the aqueous electrolyte and increases ionic conductivity by about ten times compared to conventional PVdF.

The sulfonate functional groups enhance the polarity of the S-PVdF binder, improving the dispersion of cathode active materials within the electrode. This advancement addresses the biggest challenge in manufacturing thick-film cathodes with high energy density: the uneven distribution and low adhesion of active materials, binders, and conductive agents within the electrode. Using the developed S-PVdF binder, a thick-film electrode with an active material loading of 6 mg/cm² was fabricated and analyzed, showing an initial reversible capacity increase of more than 20% compared to the conventional binder. Furthermore, over 3,000 cycles, it maintained consistently higher reversible capacity than cathodes using PVdF, effectively suppressing cathode dissolution and demonstrating more than twice the capacity retention rate even at high temperatures.

The research results were published online in April in the international energy journal Nano-Micro Letters (IF=26.6, JCR top 2.92%).

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