Simply put, viscosity is the slurry's resistance to flow. Think of the difference between honey and water: honey has high viscosity and flows slowly, while water has low viscosity and pours instantly. In coating, viscosity directly affects slurry leveling, uniformity, and dry film thickness.

Viscosity too high: The slurry behaves like "glue" making it difficult to spread. This results in uneven coating thickness, edge buildup, and even nozzle blockage.

Viscosity too low: The slurry is "as thin as water" prone to sagging, pinholes, and even cracking of the coating.

A lithium battery manufacturer experienced a 10% fluctuation in anode slurry viscosity, which led to a 15% drop in battery capacity consistency — causing direct losses of over tens of millions RMB.

● Cathode Materials (e.g., NCM, LFP):
High viscosity (1,000–10,000 mPa·s) is required to keep solid particles suspended and prevent sedimentation. However, excessive viscosity can reduce solid content, negatively affecting energy density.

● Anode Materials (e.g., Graphite, Si-C):
Lower viscosity (500–5,000 mPa·s) is needed to promote carbon material dispersion and minimize agglomeration.

Key Tip: Add binders such as CMC or SBR to strike a balance between viscosity and dispersion.

Photoresist viscosity must be precisely controlled in the 1–100 mPa·s range.

● Viscosity too low: Coating is too thin, causing excessive light penetration during exposure and resulting in blurred patterns.

● Viscosity too high: Uneven surface tension occurs, leading to "orange peel" defects.

Advanced Technology: Some companies control the molecular weight distribution of photoresist to limit viscosity fluctuations to <1%, achieving a 30% improvement in yield.

Catalyst slurries (e.g., Pt/C) must balance high solid content with low viscosity; otherwise, spray coating equipment is prone to clogging.

● Solution: Apply nano-scale dispersion technology to reduce viscosity by 50% while increasing solid content by 20%.

● Solvent System: Aqueous slurries have low viscosity but can corrode equipment, while oil-based slurries have higher viscosity but double the cost.

● Solid Particles: Smaller particle sizes increase viscosity (e.g., nano-silicon anodes can have viscosities up to 10 times higher than conventional graphite).

● Additives: Dispersants reduce viscosity, thickeners increase it, but potential side effects—such as bubbles or gelation—must be carefully considered.

● Temperature Control: Viscosity decreases as temperature rises (e.g., PVDF slurry viscosity drops by 20% for every 10°C increase).

● Shear Rate: High-speed stirring can temporarily reduce viscosity, but it recovers after stopping — special attention is needed for thixotropic materials.

● Online Monitoring: Use rotothinner viscometers or rheometers to provide real-time feedback to the coating machine’s closed-loop control system.

● Slot-Die Coating: Suitable for high-viscosity slurries (>5000 mPa·s), but requires high-pressure pump support.

● Micro-Gravure Coating: Covers a wide viscosity range (100–5000 mPa·s), but is highly influenced by slurry flow behavior.

● Spray Coating: Only suitable for ultra-low viscosity (<100 mPa·s), but suffers from low material utilization efficiency.