How to Adjust D50 in Ultrafine Grinding of NCM

Two main industrial equipment systems: fluidized‑bed jet mill (mainstream for NCM) and ACM air classifier mill (not recommended for high‑nickel EV grade). Below focuses on jet‑mill system with external turbo classifier.

1. Jet mill parameters to tune D50

1.1 Nozzle grinding pressure

• Increase nozzle pressure: Higher gas kinetic energy, stronger particle‑to‑particle collision. More agglomerates break, partial secondary spheres crack → D50 decreases. Risk: over‑pressure generates excessive sub‑micron fines.
• Decrease nozzle pressure: Lower collision energy, only break weak sinter necks; secondary spheres remain intact → D50 becomes larger. Hard agglomerates may remain, D99 rises.

1.2 Feed rate

• Reduce feed rate: Less material inside grinding chamber, higher collision frequency → finer product, D50 goes down. Risk of over‑grinding.
• Increase feed rate: Particle crowding cushions collision impact; particles pass through with less breakage → coarser output, D50 increases. Risk: incomplete de‑agglomeration, high Dmax.

1.3 Built‑in jet‑mill classifier wheel speed

Many jet mills have an internal turbine classifier:

• Raise internal classifier speed: Smaller cut‑size; coarse particles return to grinding zone → D50 decreases.
• Lower internal classifier speed: Coarser cut‑size, fewer re‑circulated coarse particles → D50 increases.

2. External independent turbo air classifier (big lever for finished‑powder D50)

When jet mill feeds to separate external closed‑loop classifier, this unit strongly shapes final D50 without extra grinding damage.

• Increase external classifier wheel speed: Finer cut‑point; more coarse particles are circulated back to jet mill → finished powder D50 decreases.
• Decrease external classifier wheel speed: Allow larger particles to pass to product → D50 increases.
• System air flow: Higher air flow can carry larger particles, slightly raise D50; lower airflow yields finer D50.

Note: When raising classifier speed to lower D50, pay attention to D10 / SSA: avoid accumulating too many ultra‑fine fractions.

3. Upstream adjustment (largest D50 influence)

Grinding can only fine‑tune D50. If you need a big D50 change, modify upstream:

1. Precursor co‑precipitation: Adjust ammonia concentration, pH, seed addition, residence time in CSTR to change precursor D50. Final NCM D50 largely inherits precursor.
2. Sintering profile: Higher sinter temperature / longer hold time grows primary grains and slightly increases secondary‑particle rigidity; indirectly affects how easily particles break in grinding. Cannot make large D50 shift.

4. Operation guidance for polycrystalline NCM811 (EV‑grade example target D50:8‑11 μm)

To lower D50 (within safe window)

1. Moderately raise jet‑mill nozzle pressure (do not max‑out).
2. Slightly reduce feed throughput.
3. Increase internal or external classifier wheel speed step‑by‑step.
4. Monitor: D50, D10, D99, span, SSA. Stop if D10 drops sharply (sign of secondary‑sphere crushing).

To raise D50

1. Lower jet‑mill nozzle pressure to reduce collision energy.
2. Increase feed rate.
3. Decrease classifier wheel speed, allow larger particles into finished product.
4. Check D99/Dmax: ensure oversized killer particles do not jump up.

5. Common pitfalls & constraints

1. ❌ Do not use grinding to cut D50 by >2‑3 μm from incoming feed. This will fracture secondary spheres, broaden PSD, increase residual alkali and moisture sensitivity for high‑nickel NCM. If you need much smaller D50, change precursor specification.
2. ❌ Do not only watch D50. Always track D10, D99, span and SSA together. Same D50 can have completely different PSD tails.
3. For single‑crystal NCM: material is more brittle. Use lower jet‑mill energy; rely more on classifier wheel speed to tune D50 instead of raising grinding pressure.
4. High‑nickel NCM: whole grinding‑classification loop must run under N₂ inert atmosphere; newly fractured surfaces readily absorb moisture and form residual lithium.

Quick troubleshooting