Dry versus aqueous: the binder logic of two electrode routes

Where the two routes divide

Wet electrodes disperse active material, conductive additive and binder in a solvent, coat the slurry and then dry it; aqueous processing replaces the solvent with water. Dry electrodes use no solvent at all: powders are mixed, formed into a film and pressed onto the current collector, removing the coating-and-drying line and solvent recovery.

That difference sets the binder’s form: wet processing needs polymers that dissolve or disperse, while dry processing needs materials that form a network under mechanical force.

Dry: the binder moves from liquid to fibre

Today’s dry electrodes rely mainly on polytetrafluoroethylene (PTFE). In high-shear mixing, PTFE particles are drawn into fine fibres that cradle the active particles like a web before the mass is calendered into a film. The process is short, solvent-free and suited to thick electrodes, but the challenges are clear: PTFE is a fluoropolymer within the scope of the EU’s PFAS restriction proposal, and it has reductive-stability issues at low anode potentials. Fraunhofer and others are developing fluorine-free dry binders.

Aqueous: the mature anode mainstream

Aqueous processing is already the industry mainstream for anodes, with a mature SBR + CMC system and supply chain, and cathodes are following with LFP as the starting point. Its key variables sit in the slurry: dispersion stability, the rheology window and binder migration during drying decide electrode quality.

Side by side: one goal, two logics

Binder form: a fibrillating powder for dry, latex or water-soluble polymers for aqueous. Key process: shear mixing and calendered film formation for dry; mixing, coating and drying for aqueous. Advantages: dry is short and suits thick electrodes; aqueous is mature and free of organic solvent. Challenges: fluorinated materials and uniformity for dry; cathode water sensitivity and drying capacity for aqueous. Evaluation focus: film strength, fibre network and thickness uniformity for dry; slurry stability, peel and residual water for aqueous.

The two routes will coexist for a long time. Dry electrodes are in early industrialisation, and wet processing remains the industry mainstream.

CASU’s view

We evaluate dry and aqueous processing as separate routes, with their own binder forms, process windows and test methods, and we do not transfer experience from one to the other. For most projects, the more robust path is to realise the full potential of aqueous systems while tracking dry and fluorine-free binders closely.