Binder for secondary batteries and lithium secondary battery using the same

Binder for Silicon Anodes Using Dopamine-PAA Copolymer and Polyaniline Ion-Crosslinking

This technology is a secondary battery material that uses a binder composed of a random copolymer of dopamine and polyacrylic acid segments, ionically crosslinked with 10 wt% polyaniline, for silicon electrode active materials.

While silicon has a theoretical capacity approximately 10 times higher than graphite, it expands by about 400% during lithiation, leading to pulverization and side reactions with the electrolyte. Conventional polymer binders fail to hold silicon particles together during contraction, causing a rapid loss in capacity due to the disruption of electron transport pathways.

In this technology, the catechol groups of dopamine form hydrogen bonds with the silicon surface to provide strong adhesion, while the carboxylic acid of polyacrylic acid and the nitrogen of polyaniline form ionic crosslinks to ensure both mechanical strength and electrical conductivity. With a peel strength of 0.6–0.7 N, the binder maintains the electrode structure despite repeated volume changes. It can be applied to high-energy-density silicon anode lithium secondary batteries for electric vehicles and energy storage systems, mitigating the cycle life degradation that has hindered the commercialization of silicon anodes.

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Key Features:

• A binder composite consisting of a first copolymer, which is a random copolymer of dopamine segments and hydrophilic polyacrylic acid segments, ionically bonded with a second copolymer, polyaniline.
• A binder for silicon electrode active materials in which the second copolymer is included at 10 wt% relative to the weight of the first copolymer, crosslinked via ionic bonding between the negative charge of the carboxylic acid and the positive charge of the nitrogen.
• A lithium secondary battery comprising a silicon electrode that forms hydrogen bonds with dopamine segments and the binder, exhibiting a peel strength of 0.6–0.7 N.
• A binder manufacturing method in which a first copolymer, synthesized with dopamine and hydrophilic segments in a weight ratio of 5:95 to 15:85, is bonded with a second copolymer at 20–40℃.

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This invention was developed with support from the Ministry of Education for the development of blue carbon biomass-based source materials and the establishment of a marine resource recycling platform.

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