One-Stop Solution Guide for Battery Binder Issues

On the production frontlines of lithium battery slurry mixing, coating, and subsequent assembly, slurry sedimentation, gelation (jelly-like consistency), and coating head blockages are three persistent "ailments" that trouble process engineers. These issues can further trigger chain reactions like electrode cracking, film delamination, and battery deformation. Such instabilities not only lead to poor electrode consistency but also directly drag down production yield and capacity.

Often, we tend to adjust the mixing process or solid content, overlooking the critical role of a minor yet pivotal component in the formula – the binder. This article will start from the micro-mechanisms of binders, unravel the complexities layer by layer, and provide a "one-stop" troubleshooting and solution guide for the aforementioned problems.

I. How to Address Slurry Sedimentation?

Causes:

(1) The selected CMC type is unsuitable. The degree of substitution (DS) and molecular weight of CMC can affect slurry stability. For instance, CMC with low DS has poor hydrophilicity but good wettability for graphite; however, it offers weak slurry suspension capability.

(2) Insufficient CMC usage, failing to effectively suspend the slurry components.

(3) Too much CMC participating in the kneading process, leading to insufficient free CMC available between particles for suspension, often resulting in poor slurry stability.

(4) High mechanical shear forces or fluctuations in slurry pH may cause SBR demulsification, leading to slurry sedimentation.

Solutions:

(1) Switch to or blend with CMC having high DS and large molecular weight. For example, using a combination of WSC (low molecular weight, low DS, good graphite wettability, weak suspension) and CMC2200 in mass production formulas can significantly improve slurry stability.

(2) Increasing CMC dosage is one of the most effective means to enhance slurry stability, but a balance must be found considering process capability and the battery's low-temperature performance.

(3) Reducing the amount of CMC involved in kneading and increasing the content of free CMC can improve slurry stability to a certain extent.

(4) After adding SBR to the slurry system, reduce the stirring speed of the planetary mixer to prevent demulsification.

Explore our battery equipment customization services for optimized slurry mixing processes.

II. Filter Blockage During Filtration – What to Do?

Causes:

(1) Poor wetting of active materials, leading to inadequate dispersion.

(2) SBR demulsification causing filtration failure.

Solutions:

(1) Adopt a kneading process to improve dispersion.

(2) After adding SBR to the slurry system, reduce the stirring speed to prevent demulsification.

III. How to Handle Slurry Gelation?

Causes: Gelation primarily falls into two categories: physical gel and chemical gel.

(1) Physical Gel: Caused by cathode active material, conductive carbon black (SP), or solvent NMP absorbing moisture, or excessive environmental humidity. Particles are surrounded by PVDF polymer chains. When water content exceeds limits, chain movement is hindered, leading to inter-chain entanglement, reduced slurry fluidity, and gelation.

(2) Chemical Gel: Prone to occur during the processing or storage of high-nickel or high-alkalinity active materials. In the high pH environment created by basic residues, the PVDF polymer backbone readily undergoes dehydrofluorination (loss of HF), forming double bonds. Existing water or amines in the solvent can then attack these double bonds, causing cross-linking. This severely reduces production capacity and deteriorates battery performance. Generally, gelation worsens with increased alkalinity of the active material.

Solutions:

(1) Physical Gel: Control by strictly managing moisture in raw materials and the environment, and employing appropriate stirring speeds during slurry storage.

(2) Chemical Gel: Can be mitigated through the following methods:

* Dry active materials and conductive carbon before dispersion to remove adsorbed water; use higher purity NMP.
* Strictly control environmental humidity during the mixing process.

* Source NCM materials with reduced surface free Li to lower alkalinity.

* Develop Anti-gel PVDF. The development strategy involves grafting other monomer units (e.g., vinyl ether, hexafluoropropylene, tetrafluoroethylene) to replace H/F in the -CH2-CF2- unit, inhibiting continuous HF loss and reducing cross-linking sites.

* Develop non-PVDF cathode binders. Since the above methods cannot completely inhibit PVDF dehydrofluorination, risks remain when using highly alkaline cathodes (high-nickel, NCA) or functional additives (alkaline Li2CO3). Developing alternative binders aims to solve this issue thoroughly.

Learn about our advanced battery materials, including specialized binders.

IV. Poor Coated Electrode Appearance (Cracking)

Causes:

(1) The binder itself has a high glass transition temperature (Tg), causing its film-forming temperature to exceed the coating temperature. Difficult film formation leads to electrode cracking.

(2) In water-based binders, severe shrinkage during water loss in curing can cause overall electrode cracking, e.g., in aqueous PAA systems.

Example: Polyacrylic acid polymers are rigid with poor flexibility. During electrode manufacturing, large-area curling and cracking can occur, leading to very low production yield in coating and winding.

PAA electrode showing curling and cracking during processing

Solutions:

(1) If poor coating appearance is due to the binder's high film-forming temperature, switch to a binder with a lower film-forming temperature.
(2) For aqueous PAA systems, adding EC as a plasticizer significantly helps improve electrode cracking.

Mandrel test demonstrating improved electrode flexibility

V. Poor Coated Electrode Appearance (Bubbles)

Causes:

(1) Insoluble fibers in CMC can cause granular bubbles during coating.

(2) Excessive emulsifier in SBR. Emulsifiers act like surfactants, stabilizing bubble surface tension and preventing bubble removal.

Emulsifier stabilizing foam

Solutions:

(1) Use CMC with low insoluble content, e.g., replacing CMC2200 with MAC500 in some EV production formulas.
(2) Reduce the amount of emulsifier in the SBR used.

VI. Battery Gassing at High Temperature?

Cause: When polymer molecules contain many polar functional groups, they tend to absorb moisture. This moisture can react with lithium ions during high-temperature storage, generating hydrogen gas.

Solution: Control moisture content within the cell and/or employ high-temperature, high-State-of-Charge (SOC) formation processes.

Example: Cells using SD-3 binder showed significant swelling due to gassing during 85°C storage. By controlling cell moisture below 100ppm and using a high SOC formation process, the high-temperature storage issue was markedly improved.

VII. Rapid Capacity Fade in High-Temperature Cycling?

Causes:

(1) Excessive binder swelling at high temperature, disrupting the continuous conductive network between particles.
(2) Poor stability of the binder at high temperature, leading to dissolution or chemical reaction with Li.
(3) After high-temperature exposure to electrolyte, the binder's strength decreases, failing to effectively suppress active material pulverization during cycling.

Solutions:

(1) Select or blend binders with higher Tg, appropriately reducing their affinity with the electrolyte to minimize high-temperature swelling damage.

(2) For silicon anode materials with large cycling expansion, use high-modulus binders like PA/PI/PAI types to effectively suppress or reduce silicon particle cracking and pulverization during cycling.

VIII. Battery Prone to Deformation?

Cause: When the polymer binder is too rigid, it creates significant internal stress within the electrode. During charge/discharge cycles, the release of this internal stress can cause electrode twisting and deformation, ultimately leading to battery deformation.

Solution: Add plasticizers to reduce internal electrode stress.

Example: BI-4 binder showed excellent kinetic performance in CEs but caused severe battery deformation. To mitigate this, 2wt% EC additive was introduced during slurry mixing. EC, a small molecule plasticizer, volatilizes completely during electrode drying, thus having no significant impact on cell electrical performance while greatly improving the deformation issue.

Conclusion

Although binders constitute just a "drop in the ocean" of the electrode formula, they hold the key to slurry rheology and dispersion stability. Facing challenges like sedimentation, gelation, blockages, and their derivative issues like electrode cracking and high-temperature gassing, single-dimensional process adjustments often only address the symptoms, not the root cause. Only by deeply understanding the binder's molecular structure, dissolution characteristics, and interaction with active materials can we accurately identify the "ailment" and prescribe the right remedy. We hope the approach provided in this article offer valuable technical reference for optimizing your slurry system, adjusting process parameters, and enhancing the quality of electrode manufacturing.

About TOB NEW ENERGY

TOB NEW ENERGY is a premier provider of comprehensive solutions for the battery industry and R&D sectors. We specialize in delivering end-to-end battery production lines, pilot lines, and experimental lines tailored to your specific budget and output requirements. Our services encompass everything from design and facility construction to equipment selection, supply, installation, commissioning, and staff training.

We pride ourselves on offering cutting-edge battery technology support, including expertise in solid-state batteries, sodium-ion batteries, lithium-sulfur batteries, and dry electrode technology. Our dedicated team of battery experts provides technical guidance to enhance product performance across capacity, rate capability, cycle life, and safety.

Furthermore, we supply a wide range of customized equipment for all stages from lab to pilot to mass production, alongside a comprehensive portfolio of advanced battery materials to support your research and development endeavors. Trust TOB NEW ENERGY for all your battery manufacturing and R&D needs.

Contact us today to discuss how we can power your innovation.