NCM powder caking during dry grinding and classification is mainly caused by residual lithium on particle surfaces, moisture absorption, fine particle cohesion, local overheating, and static electricity. Caking forms soft or hard agglomerates, which disturbs particle size distribution, widens span, reduces tap density, and damages battery consistency. Based on JACAN’s NCM dry processing technology from ncm-mill.com, multiple combined measures can effectively stop NCM powder caking in the grinding circuit.
1. Strictly control raw material moisture and residual lithium
Raw material pretreatment is the first barrier against caking.
- Keep raw NCM moisture extremely low, typically below 0.1%. Even trace water reacts with surface lithium compounds to form sticky lithium hydroxide and lithium carbonate, which glue fine particles together into cakes.
- Control residual lithium content of incoming calcined NCM. Too high residual lithium increases surface stickiness, making fines prone to re-agglomeration under mechanical collision and heat during grinding. Low-residual-lithium feedstock greatly reduces caking tendency.
2. Maintain low and stable process temperature inside the mill circuit
Local temperature rise is a major trigger for NCM caking.
- For air classifier mills or jet mills processing high-nickel NCM, adopt closed-loop nitrogen inert gas as the process medium. Nitrogen carries away frictional heat continuously and avoids hot spots.
- Install temperature sensors with safety interlocks. If powder outlet temperature exceeds the set threshold, the system automatically reduces feed rate or adjusts gas flow to cool the material. Avoid thermal softening of surface lithium salts which causes particle adhesion.
3. Eliminate static accumulation in powder and pipeline
Fine NCM particles easily build static charge during high-speed collision and pneumatic conveying. Static attraction pulls small particles together and causes powder adhesion on chamber walls, classifier rotors and pipe surfaces, gradually forming cake layers.
- Full grounding of all equipment: grinding chamber, classifier, cyclone separator, bag filter and conveying pipelines.
- Use conductive ceramic or PU linings. Conductive lining dissipates static charges without introducing metal contamination.
- Properly adjust nitrogen dew point. Slightly controlled gas humidity helps static dissipation, but dew point must stay low enough to prevent moisture-induced caking.
4. Optimize grinding and classification parameters for gentle de-agglomeration
Over-grinding generates excessive ultra-fine fines, which have high specific surface area and are the main fraction responsible for caking.
- Tune rotor speed, gas flow and feed rate to break only soft calcined agglomerates instead of smashing primary particles. Reduce generation of excessive submicron fines.
- Set sharp top-cut classification to remove oversized particles while avoiding over-circulation of ultra-fine powder inside the closed loop. Too much fine powder circulating repeatedly raises caking risk.
- Prevent material dead zones in mill and classifier housing. Smooth internal geometry reduces powder buildup and cake growth.
5. Inert closed-loop atmosphere and low dew-point gas protection
Ambient air contains oxygen and moisture, both accelerate surface side reactions and caking for high-nickel NCM.
- Run the whole grinding-classification system under sealed nitrogen atmosphere. Keep oxygen and dew point at specified low levels to block water adsorption and surface lithium compound formation.
- Maintain slight negative pressure inside the line to prevent humid outside air leakage into the process loop.
6. Periodic online cleaning and system maintenance
Even with optimized operation, thin powder layers may slowly accumulate.
- Configure periodic pulse back-blow cleaning for cyclone and filter units to remove adhered powder before it hardens into cakes.
- Schedule regular inspection of classifier wheel, liner and pipe bends to clear built-up deposits. Hard cake pieces that fall off will contaminate finished PSD and create batch defects.
Preventing NCM powder caking during grinding relies on a combined strategy: low-moisture low-residual-lithium raw feed, nitrogen closed-loop inert environment with low dew point, static dissipation design, temperature interlock protection, optimized gentle de-agglomeration parameters, and regular system cleaning. These measures minimize fine particle adhesion and re-agglomeration, stabilizing PSD, tap density and powder flowability for battery-grade NCM cathode material.
