The separator is a key inner component of a lithium-ion battery and has a decisive effect on safety and electrochemical performance. In wet-coated separator manufacturing, the dispersion quality of the slurry directly determines coating uniformity and separator performance. As the core equipment for nano-dispersing the slurry, the bead mill (sand mill) uses mechanical grinding forces to solve the problem of ultrafine dispersion of ceramic particles, polymers and special powders, making it a key technology for better separators.
1. What separator coating slurries need from fine grinding
Ceramic coating slurries for lithium battery separators consist mainly of four components: ceramic particles (such as alumina or boehmite), binder (such as PVDF or PVA), solvent (water- or oil-based) and functional additives. The size distribution and dispersion of the ceramic particles are decisive for coating performance:
Coarse particles (>1 μm) make the coating surface rough and porosity uneven, reducing puncture strength
Nanoparticles (<100 nm) agglomerate easily because of their high specific surface area, creating local defects
Power batteries place higher demands on separators: high heat resistance (thermal shrinkage ≤3% above 130 °C), ultra-thin coatings (≤1.5 μm) and high ionic conductivity. Nano materials such as γ-alumina (dv50 = 5-100 nm) can form dense thin coatings but are very hard to disperse in deionized water, where van der Waals forces cause strong agglomeration that conventional stirring cannot break. High-intensity shear grinding in a bead mill is the key to overcoming this dispersion bottleneck.
2. Bead mill principle and equipment innovation
In a bead mill, grinding media (usually 0.3-2 mm zirconia beads) driven by a high-speed rotor create multi-directional impact and shear fields that break and disperse particles. In separator slurry processing, development has focused on three directions:
1. Better nano-dispersion
- INFOR pin and turbine bead mills use a gentle grinding strategy with 0.1-2 mm zirconia beads
- Ceramic particles can be refined to 200 nm-2 μm
- Axial separators and ceramic separation systems prevent slurry degradation from temperature rise during grinding
- INFOR nano bead mills optimize energy conversion efficiency
- The particle size distribution is concentrated, with less coarse-particle tailing
- Excellent adaptability to low- and medium-viscosity slurries
2. Intelligent and modular design
- PLC control enables one-button closed-loop operation
- Speed (800-1,400 rpm), flow (0.5-5 m³/h) and other parameters adjust dynamically
- Manual errors are greatly reduced
- The grinding chamber can be all-ceramic or fitted with PU-coated rotors as required
- Metal contamination is avoided, meeting battery material purity requirements (e.g. Fe content <1 ppm)
3. High-efficiency grinding
- INFOR dynamic plus static discharge technology
- Can form a fully automatic line with high-speed dispersers and transfer tanks
- Zero batch-to-batch variation in boehmite, alumina and other inorganic slurries
- Large throughput per pass and high capacity
The bead mill has evolved from a simple size-reduction machine into a "molecular-level designer" of separator performance. With breakthroughs by Chinese manufacturers in nano bead mills, China's lithium battery materials industry is steadily reducing its reliance on imports. Leading companies such as SEMCORP and Putailai have raised China's global separator market share from under 30% to over 65% through vertical integration of equipment, materials and process (base film, coating and bead milling). In future, bead mill technology will continue to underpin new fields such as solid electrolyte slurries and nanocomposite coatings.