Lithium-ion battery slurry is a complex, multi-phase, non-Newtonian fluid. Anode slurry is composed of a mixture of active material (graphite), conductive agents (such as carbon black, CNTs, and VGCF), binders, thickeners, and a solvent (deionized water). Cathode slurry consists of active material, conductive agents, binders, and a solvent. Since active materials, conductive agents, and solvents do not adhere to metal electrodes on their own, they cannot be formed into the electrode sheets required for lithium-ion battery manufacturing. The binder is a crucial component of the slurry; it bonds various particles together to create an adhesive mixture that firmly attaches to the metal foil. Although binders typically account for only about 1% of the total mass, they play a pivotal role—often described as "small but mighty"—in the battery's function.

From the perspective of electrode sheet processing, the key performance requirements for binders are as follows:

1. Capable of maintaining stable slurry viscosity over extended periods; the slurry does not settle or lose effectiveness during storage.

2. Dissolves to form high-concentration solutions and requires a low heat of vaporization.

3. Easy to shape during calendering without spring-back.

4. Exhibits flexibility; does not shatter into fragments if the electrode cracks.

Binders are not only critical to the manufacturing process of lithium-ion batteries but also significantly influence their electrochemical performance. Consequently, binders must possess the following characteristics:

•     1. Ability to effectively maintain the state of the active material.

•     2. Good adhesion to metal foils, ensuring no delamination occurs due to exposure to electrolytes or the charge-discharge process.

•     3. Good electrochemical stability across a wide voltage range.

•     4. High melting point and low swelling rate. The structural integrity of the binder-active material combination must remain stable even at high temperatures. Binders typically exhibit swelling; excessive swelling impairs electrical conductivity between the active material and the current collector, leading to battery capacity fade, so the swelling rate must be controlled.

•     5. Good ionic and electronic conductivity.

  Binders can be categorized into water-based and solvent-based (oil-based) types. Common solvent-based binders include PVDF homopolymers and copolymers, which typically utilize solvents such as NMP (N-Methyl-2-pyrrolidone) or DMF (N,N-Dimethylformamide). In battery systems employing Lithium Iron Phosphate (LFP) or NCM (Nickel-Cobalt-Manganese) ternary materials as the cathode, PVDF is generally selected as the cathode binder. PVDF exists in both powder and gel forms; the powder appears as white granules, while the gel form is a pale yellow, transparent colloid with a viscosity of approximately 5,000–8,000 mPa·s. Mature processes exist for both adding PVDF powder directly during slurry mixing and preparing a gel prior to the mixing process; the difference lies in the specific processing steps—even with identical solid content and feed ratios—resulting in variations in the final slurry viscosity.

 Common water-based binders include SBR (styrene-butadiene rubber emulsion), CMC (carboxymethyl cellulose), PTFE (polytetrafluoroethylene emulsion), and PAA (polyacrylate). Initially, solvent-based binders like PVDF were used for anode slurry mixing; however, due to concerns regarding severe internal polarization—and given that water-based binders are more environmentally friendly and capable of performing the necessary binding function—the industry has largely shifted toward using water-based binders for anodes. Graphite-based anodes commonly employ a combination of SBR and CMC. While both contribute to adhesion, SBR functions primarily as the binder, whereas CMC acts as a thickener (stabilizing the slurry). The rationale for using this synergistic SBR-CMC combination is as follows:

     1. SBR offers superior binding strength but is prone to emulsion breakdown (coagulation) during prolonged mixing, which compromises its structure and reduces adhesion; consequently, SBR is typically added during the final stages of mixing. Furthermore, SBR’s dispersion performance is inferior to that of CMC, and excessive SBR usage leads to significant swelling; thus, SBR cannot serve as the sole binder.

  2. CMC is highly effective at dispersing graphite anode particles. In aqueous solution, CMC dissociates into sodium ions and anions; as the CMC concentration increases, these dissociation products adsorb onto the graphite particle surfaces, creating electrostatic repulsion between particles and achieving excellent dispersion. However, CMC has a critical drawback: it is brittle. If CMC were used exclusively as the binder, the graphite anode layer would be prone to structural collapse and severe powder shedding during the calendering (pressing) and slitting processes.

Currently, no single "perfect" binder meets all the aforementioned requirements. The approach involves selecting binders that best satisfy the necessary physical processing and electrochemical criteria. With the evolution of lithium-ion battery technology—and driven by cost and environmental considerations—there is a gradual shift toward water-based binders. Recent technological advancements have even introduced binder-free designs, a trend worth continued monitoring.