Moisture is a hidden but impactful variable in NCM powder dry grinding. Even trace water reacts with surface residual lithium, forming sticky lithium hydroxide and lithium carbonate. This creates re‑agglomeration and caking, which falsely raises D50 and widens PSD span. High moisture also causes powder adhesion on mill liners, classifier wheels and pipeline walls, destabilizing particle size consistency. Based on JACAN NCM processing technology from ncm-mill.com, the following measures control moisture and protect target particle size.
1. Raw material incoming inspection and pre-drying
The first moisture control point starts before grinding.
- Test the moisture content of calcined NCM feedstock. Reject batches exceeding the threshold; for battery-grade NCM, raw powder moisture must be kept below 0.1%.
- Apply low-temperature vacuum drying for damp incoming material. Drying temperature must be carefully limited to avoid triggering NCM surface degradation or residual lithium side reactions. After drying, the material is transferred immediately into a sealed, low-dew-point hopper to prevent re-absorption of ambient moisture.
2. Maintain low dew-point inert gas in the closed grinding loop
Ambient air contains water vapor that rapidly adsorbs onto high-surface-area NCM fines.
- Run the whole grinding-classification circuit under sealed nitrogen atmosphere. Use a gas drying system to maintain nitrogen dew point at a low set value, blocking water vapor ingress.
- Keep slight negative pressure inside the system to prevent humid outside air from leaking through flange joints, shaft seals or filter housings. Any air leakage introduces moisture and creates local agglomerates that distort PSD results.
3. Equipment sealing and insulation to avoid condensation
Temperature drop on cold equipment surfaces causes water condensation, which wets NCM powder and creates sticky cakes.
- Inspect and maintain all seals on the mill, classifier, cyclone, filter and powder transfer pipes. Replace worn gaskets regularly.
- Apply thermal insulation on pipework and vessel walls to prevent cold spots. Condensation must be eliminated, as even tiny water droplets cause localized particle agglomeration and inconsistent D50.
4. Optimize process temperature to reduce moisture adsorption
Fine NCM particles absorb moisture faster at low temperatures. Excessive heat also accelerates surface lithium reactions.
- Maintain stable, moderate powder temperature inside the loop via gas flow cooling and temperature interlock controls. Avoid large temperature fluctuations that shift moisture adsorption behaviour.
- Prevent overheating, which can drive surface side reactions; the combination of heat plus trace moisture is the biggest driver of hard agglomerates that particle size testing cannot easily distinguish from primary particles.
5. Post-grinding powder handling and storage
Moisture pickup after grinding can ruin already qualified PSD.
- Collect finished NCM powder under inert gas protection. Transfer powder into moisture-barrier aluminum bags with nitrogen blanketing immediately after collection.
- Store finished powder in a temperature- and humidity-controlled dry room. Avoid prolonged exposure to normal atmosphere before battery electrode manufacturing.
6. Online monitoring and sampling verification
- Install dew point and moisture sensors in the nitrogen loop to continuously track gas conditions.
- Take regular powder samples for Karl Fischer moisture testing and laser PSD analysis. If moisture rises, adjust gas drying or stop feeding before agglomeration shifts particle size outside specification.
Controlling moisture to stabilize NCM particle size relies on a full-chain strategy: qualified low-moisture feedstock with optional pre-drying, sealed nitrogen closed-loop with low dew point, well-maintained equipment sealing and anti-condensation design, stable process temperature, and inert post-processing packaging. This prevents moisture-induced re-agglomeration, caking and PSD drift during dry de-agglomeration and classification.
