NCA (Nickel-Cobalt-Aluminum) cathode material is highly heat-sensitive, with strong tendency toward fine particle re-agglomeration and surface side reactions. Controlling its particle size distribution (PSD) including D10, D50, D90 and span follows a similar dry de-agglomeration framework as NCM, yet with stricter temperature, inert atmosphere and raw material specifications. This content is adapted from JACAN powder processing technical knowledge on ncm-mill.com.
1. Raw material quality control before grinding
The starting calcined NCA powder defines the baseline PSD and agglomerate strength.
- Control calcination parameters: Calcination temperature and holding time determine primary particle size and agglomerate hardness. Higher sintering temperature produces larger, harder primary particles; insufficient calcination creates soft, fragile grains that easily form excessive ultra-fines during de-agglomeration.
- Strictly limit incoming moisture below 0.1%. Trace moisture reacts with surface residual lithium, forming sticky lithium salts that cause re-agglomeration and distort PSD measurement.
- Restrict residual lithium content. NCA has higher nickel content than most NCM grades, so excess residual lithium significantly increases particle adhesion and caking during grinding.
- Pre-screen raw feed to remove oversized hard agglomerates before entering the grinding circuit, preventing abnormal coarse peaks in the final PSD curve.
2. Select suitable grinding and classification equipment
Mechanical impact equipment such as standard air classifier mills carries high local heat risk for NCA.
- Fluidized bed spiral jet mill + high-precision ultra-fine classifier: Preferred industrial solution for NCA. It uses particle-to-particle collision with minimal frictional heat. Ceramic-lined chambers eliminate metal contamination. The high-speed classifier wheel provides sharp cut-point to separate coarse material and return oversize fractions back to grinding.
- Avoid conventional ACM for high-nickel NCA mass production. Rotor friction generates hot spots, which trigger NCA surface degradation and fines re-agglomeration, broadening PSD span.
3. Closed-loop inert gas system and temperature interlock
NCA is more susceptible to thermal and oxidative degradation than NCM.
- Run the whole grinding-classification circuit under sealed nitrogen atmosphere. Maintain low dew point and low oxygen concentration to block moisture and oxygen ingress.
- Install distributed temperature sensors with safety interlocks. When powder outlet temperature exceeds the preset threshold, the system automatically reduces feed rate or increases nitrogen flow for cooling. Thermal runaway of surface lithium compounds will otherwise create pseudo-agglomerates and shift D50 upward.
- Keep slight negative pressure inside the pipeline to prevent humid ambient air leakage through flanges and shaft seals.
4. Tune process parameters to stabilize PSD and span
Key adjustable parameters work together to lock target D50 and narrow span:
- Classifier wheel speed: Primary lever for cut size. Higher speed yields finer finished powder; lower speed allows coarser particles to pass. Small speed adjustments directly change D90 and span.
- Nitrogen jet pressure: Higher pressure enhances particle collision energy for finer de-agglomeration. Excess pressure creates excessive ultra-fine fines, broadening span and worsening powder flow.
- Feed rate: Stable, low feed rate ensures uniform de-agglomeration. Overfeeding causes incomplete breakup of agglomerates and inconsistent batch PSD.
- Gas flow rate: Controls particle residence time in the grinding zone. Too long residence time generates excess fines; too short leads to residual coarse agglomerates.
The target span for qualified NCA cathode powder is normally kept below 1.0, with premium grades controlled between 0.6–0.9.
5. Anti-static and anti-re-agglomeration design
Fine NCA particles build static easily during pneumatic transport, which pulls fines together and creates false coarse peaks in PSD.
- Fully ground all process units: mill chamber, classifier, cyclone, filter and pipelines.
- Apply conductive ceramic or conductive PU linings to dissipate static without introducing metal impurities.
- Optimize flow field to rapidly carry away freshly generated fines, reducing secondary collision and re-agglomeration inside the loop.
6. Online monitoring and batch quality verification
- Deploy online particle size monitoring to track D10, D50, D90 and span continuously.
- Regular off-line laser PSD sampling and Karl Fischer moisture testing. If span widens or D50 drifts, check for material buildup on classifier wheel, gas dew point fluctuation or raw material variation.
- Periodic pulse back-blow cleaning for cyclone and filter to remove accumulated powder deposits, which will otherwise break off as large chunks and contaminate PSD.
Controlling PSD for NCA cathode relies on integrated management: qualified low-moisture low-residual-lithium calcined feedstock, spiral jet mill paired with high-precision classifier, sealed low-dew-point nitrogen closed loop, temperature interlock protection, optimized process parameters, static elimination, plus continuous PSD monitoring. This maintains stable D50, controlled Dmax and narrow span while protecting NCA’s sensitive crystal structure from thermal degradation.
