Secondary battery separator comprising a cellulose coating layer and manufacturing method thereof

Inorganic-free heat-resistant separator with a dual-phase nano/micro cellulose fiber structure

This technology forms a uniform cellulose coating layer—consisting of a continuous phase of cellulose nanofibers and a dispersed phase of microfibers—on a porous support using a carboxymethyl cellulose (CMC) dispersant with specific degrees of substitution, polymerization, and zeta potential.

Conventional polyolefin separators suffer from low thermal stability, leading to shrinkage at high temperatures. Furthermore, binders used in inorganic particle coatings often clog pores, reducing ion conductivity and making it difficult to achieve a uniform coating.

This technology replaces synthetic polymer binders with a CMC dispersant to maximize the dispersibility of cellulose microfibers and nanofibers. This ensures high puncture strength, excellent air permeability, low thermal shrinkage, and improved ion conductivity without the need for inorganic materials. Ideal for high-power electric tools and EV batteries where thermal shrinkage is a concern, this technology enhances both heat resistance and mechanical strength using only a lightweight cellulose layer, eliminating the need for ceramic coatings.

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Key Features:

• Cellulose coating layer where multiple cellulose nanofibers form a continuous phase through chain entanglement
• Cellulose microfibers forming a dispersed phase, included at 5 to 200 parts by weight per 100 parts by weight of cellulose nanofibers
• Carboxymethyl cellulose dispersant with a degree of ether substitution of 0.5 to 1.0 and a weight-average molecular weight of 200,000 to 400,000 g/mol
• Step of applying a coating composition to a porous support, prepared by adding the dispersant, cellulose microfibers, and cellulose nanofibers to a solvent in that order

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This invention was developed with support from the Korea Forest Service for the design and manufacturing technology of nanocellulose-coated separators.

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