Editor's Note
In the future, as power batteries face higher demands in terms of range, safety, longevity, and cost efficiency, significant transformations will occur in the production processes of both positive and negative electrode materials, along with a surge in adhesive research and development. Innovation in adhesives will continue to drive progress in battery technology.
"Adhesive is easy to make, but it's extremely difficult to do it right," said Li Rengui, General Manager of Chengdu Zhongkelaifang Energy Technology Co., Ltd., at the 2017 Senior Industrial Lithium Conference. Using a humorous tone, he described how his company has spent 17 years deeply focusing on adhesive development, treating it like a "glue" that holds everything together.
In reality, both the positive and negative electrode materials, along with conductive agents, are inorganic powders. To ensure they adhere properly to the metal current collector during electrode sheet formation, adhesives act like glue. However, due to the complex chemical reactions within lithium batteries, achieving a stable and reliable bonding effect is no easy task.
From the perspective of electrode sheet processing, lithium battery adhesives must meet four key requirements: first, maintaining slurry viscosity over time without settling or failing; second, dissolving into a high-concentration solution with lower heat of vaporization; third, being easy to form without rebounding during rolling; and fourth, offering flexibility to prevent fragmentation when the electrode breaks.
Additionally, the binder in lithium batteries accounts for 1-2% of the total weight and plays a crucial role. Due to the unique properties of the binder polymer, it can unexpectedly influence battery performance.
According to a long-term study by Japan’s JSR Co., Ltd., adhesives not only fulfill basic application needs but also significantly impact battery performance. Their influence includes bond strength, migration inhibition, internal resistance, expansion control, and cycle life.
Li Rengui noted that after three years of rapid lithium battery development, adhesive applications have become relatively mature. Commercially, they are mainly divided into water-based and oil-based adhesives. The positive electrode material typically uses an oily binder—PVDF—which requires NMP solvent and generates harmful substances. The negative electrode material, on the other hand, mainly uses aqueous binders such as polypropylene or SBR emulsions.
As lithium batteries evolve toward higher energy density, improved safety, and lower costs, adhesives face even greater challenges. These include reduced binder content, better high-temperature storage performance, enhanced electrode flexibility, and excellent roll peeling force.
For example, Solvay Specialty Polymers introduced a new PVDF adhesive that reduces binder usage, thereby increasing battery activity and energy density. This new product uses 30% less binder than previous versions and is expected to improve battery reliability by 15%, effectively extending its lifespan by at least one year.
As a leader in the domestic battery adhesive industry, Zhongkelaifang's team comes from the Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences. Over 17 years, they've focused on adhesive R&D, and their methods and results offer valuable insights for domestic competitors.
Take LA136D, a new negative electrode adhesive, as an example. The team began by designing the material's molecular structure, considering flexibility and electrochemical resistance. Next, they adjusted the secondary structure through molecular weight control. Finally, they achieved outstanding battery performance through the tertiary structure.
From a basic performance standpoint, LA136D has a decomposition temperature of 280°C and an electrochemical window exceeding 6V. Its most notable feature is its strong adhesion, which outperforms current mainstream SBR water-based adhesives, even with reduced usage.
Comparison of Adhesion Between LA136D and SBR
Moreover, LA136D shows a clear advantage in electrolyte swelling. When tested in an aluminum-plastic pouch sealed environment at 70°C for 24 hours using EC:DEC (3:7), LA136D absorbed 10.60% of the electrolyte, compared to 34.95% for SBR.
When applied to the same battery system, LA136D demonstrates superior dispersion of conductive agents and greatly improves the high-speed coating process. From a performance perspective, batteries using LA136D exhibit excellent power characteristics, particularly in low-temperature charge and discharge performance and reduced internal resistance at high temperatures.
It’s worth noting that LA136D is just one example of Zhongkelaifang’s ongoing adhesive innovation. Looking ahead, as power batteries demand higher endurance, safety, service life, and cost-efficiency, the production of positive and negative electrode materials—and consequently adhesives—will undergo major changes. More research and development will take place, driving the continuous creation of newer, more advanced adhesives.
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