A joint research team—led by Professor Ki-Jae Kim from the Department of Energy Science and the Department of Future Energy Engineering

f Sungkyunkwan University(SKKU), alongside Professor Jang Wook Choi's research team from Seoul National University—has developed a high-performance "hybrid polymer binder" for thick-film electrodes. This breakthrough significantly boosts the energy density of lithium-ion batteries while extending their lifespan. The study proposes a practical strategy to overcome chronic binder migration issues and performance degradation that occur during the conventional wet-manufacturing process when making electrodes thicker to increase battery capacity for electric vehicles (EVs) and smartphones.

Recently, the battery academia and industry have actively researched "high-loading electrode" technology. This involves stacking more nickel-rich layered cathode materials into thicker layers to increase EV driving ranges. However, the conventionally used PVDF (polyvinylidene fluoride) binder suffers from a critical drawback during the drying process of thick electrode manufacturing: the binder tends to float to the top, causing the electrode to crack or crumble easily. This severely weakens the mechanical strength and lithium-ion conductivity of the electrode, leading to a sharp decline in battery lifespan.

To tackle this challenge, Professor Ki-Jae Kim's joint research team blended two polymers with completely different properties: Spandex (SPDX), a highly elastic apparel fabric, and Poly(acrylic acid) (PAA). They applied this combination to the electrode as a novel "Dual-Acting Hybrid Polymer (DHP)" binder. Thanks to spandex's excellent elasticity and PAA’s superior molecular interaction with internal electrode components, this new binder maintains a robust structure that prevents cracking or crumbling, even when applied to exceptionally thick electrodes.

Experimental results showed that the electrode using the newly developed binder exhibited nearly twice the adhesive strength of conventional PVDF binders. Notably, the team identified a new operational mechanism during the initial charge/discharge cycles: the binder spontaneously forms a "Li-PAA interface" that accelerates lithium-ion migration. This enables faster and more uniform lithium-ion transport within the thick-film electrode, significantly enhancing its electrochemical performance.

Furthermore, the research team validated the new hybrid binder by fabricating large-capacity, commercial-grade pouch-type cells. The results were remarkable: while batteries with conventional binders suffered a sharp drop in capacity and failed after approximately 95 cycles, the batteries using the new hybrid binder stably maintained 86.8% of their initial capacity even after more than 200 charge/discharge cycles—effectively more than doubling the lifespan.

This research carries immense industrial value because it allows manufacturers to produce high-capacity batteries using existing "wet manufacturing processes" without needing to alter production lines or invest in new equipment. It stands as an exemplary case of solving a practical industrial bottleneck by effectively harnessing the physical/chemical properties and ion-transport mechanisms of polymers.

"Previously, increasing electrode thickness and size was limited by binder and processing issues, which restricted overall battery performance. We overcame this hurdle by efficiently combining the advantages of spandex and poly(acrylic acid)," said Professor Ki-Jae Kim. "This binder technology is highly adaptable to the industry as it utilizes current wet production lines without adopting dry-processing technologies, which have recently attracted attention as next-generation battery manufacturing methods. We expect it to play a pivotal role in extending the driving range of next-generation electric vehicles."

This research was supported by the Ministry of Science and ICT and the National Research Foundation of Korea (NRF) through the projects: Development of Modular LEA (Lithium Electrode Assembly) Core Technology for Universal Utilization of Lithium Metal Anodes and Training Future Leading Talents to Respond to Industrial Demand for Breakthrough Next-Generation Secondary Batteries.