Binders - Battery Design

Binders are crucial for holding active materials and conductive additives together, ensuring adhesion to the current collector and preventing disintegration during charge/discharge cycles.

The most common binders are:

CMC (Carboxymethyl Cellulose): used as a binder and as a thickener, particularly in anodes. Refining Carboxymethyl Cellulose.
PAA (Polyacrylic Acid): used as a binder in silicon anodes due to flexibility.
PTFE (Polytetrafluoroethylene): used in the past, for both anodes and cathodes due to its high chemical and thermal resistance.
PVDF (Polyvinylidene Fluoride): widely used, especially for cathodes, known for its good mechanical, chemical, and electrochemical properties.
SBR (Styrene Butadiene Rubber): commonly used as an anode binder, known for its versatility and electrochemical performance.

Self-Healing (Dynamic) Binders

These advanced polymers utilize reversible bonds—such as the “molecular pulley” design combining polyrotaxane and PAA. When the silicon expands, the polymer network stretches and bonds temporarily dissociate to dissipate stress; when the silicon contracts, the bonds autonomously reassemble to “heal” microcracks in the electrode.

Aqueous Binder Systems: SBR/CMC

Styrene butadiene rubber (SBR) paired with carboxymethyl cellulose (CMC) is the dominant binder pairing for graphite and silicon-graphite anodes, and the pairing is a good illustration of why “binder system” is often a more accurate term than “binder” on its own. CMC is dissolved in water first, where it acts as a thickener and dispersant that controls the viscosity of the electrode slurry and coats the surface of the active material and conductive carbon; the SBR latex is then added as the actual elastomeric binder. The two play different roles: CMC’s carboxyl and hydroxyl groups give strong adhesion to the copper current collector and to graphite particle surfaces, while SBR supplies the mechanical flexibility needed to survive the repeated graphite expansion that comes with lithiation.

The appeal of SBR/CMC over PVDF for anode coating is mostly a manufacturing story rather than a pure performance one. PVDF is normally processed from N-methyl-2-pyrrolidone (NMP), a solvent that has to be recovered out of the electrode under tightly controlled conditions because it is expensive and classified as toxic to reproduction in the EU — coating lines running PVDF need enclosed drying ovens with solvent-recovery systems to avoid venting it to atmosphere. Water-based SBR/CMC slurries remove that recovery loop entirely, which is a large part of why aqueous anode coating is now close to universal across the industry despite PVDF’s earlier head start [1][2]. The trade-off runs the other way at the drying stage: residual moisture in an aqueous anode reacts with the electrolyte and degrades the SEI in the finished cell, so aqueous-coated anodes typically need a longer dry-out and an additional vacuum bake before cell assembly than a solvent-based equivalent.

Low-Fluorine and Fluorine-Free Cathode Binders

Cathodes have mostly stayed on PVDF rather than following anodes to an aqueous binder. PVDF is electrochemically stable at cathode potentials in a way SBR is not, and NMP-based coating tolerates aggressive cathode chemistries better than water does — many high-nickel NMC precursors react with residual moisture, raising slurry pH and causing gassing or gelling problems in aqueous cathode formulations. That is starting to change, for two separate reasons: regulatory pressure on fluoropolymers as a class, and a technical weakness specific to PVDF.

On the regulatory side, PVDF falls within the broad per- and polyfluoroalkyl substances (PFAS) definition used in the EU’s proposed PFAS restriction. As of September 2026 that restriction has not been finalised: the European Chemicals Agency’s Risk Assessment Committee adopted its opinion in March 2026, a final public consultation on the Socio-Economic Analysis Committee’s draft opinion ran to 25 May 2026, and the Committee is expected to issue its final opinion by the end of 2026, after which the European Commission still has to decide on and adopt any actual restriction [3]. Nothing is banned yet, but battery-grade PVDF is one of the higher-profile uses under scrutiny, and cell and material manufacturers are not waiting for the restriction to be finalised before developing alternatives.

Separately from regulation, PVDF has a genuine technical weakness with high-nickel NMC cathodes: it does not bond as strongly to the microcracked surface these cathodes develop on cycling, so cracks propagate faster and expose fresh surface to electrolyte attack and transition-metal dissolution. Recent published work on fluorine-free binder strategies for high-nickel cathodes has focused on replacing PVDF with binders that chemically anchor to the cathode surface rather than relying on PVDF’s weaker adhesion, reporting improved capacity retention on high-nickel chemistries as a result [4]. Polyacrylic acid (PAA) and PAA-based copolymers, already established on the anode side, are the leading fluorine-free candidates on cathodes too, though matching PVDF’s oxidative stability above roughly 4.3 V remains the open problem most of this research is trying to solve.