Feed rate represents the mass flow rate of calcined NCM clinker entering the jet‑milling system, directly determining particle concentration inside the grinding chamber and classification zone. It strongly influences collision efficiency, particle‑interference effect, classification sharpness and final powder fineness (D50, D97, Dmax). Under fixed grinding pressure, classifier speed and system airflow, improper feed rate will cause fineness drift, coarse particle leakage or over‑grinding. This paper analyzes how feed rate changes NCM powder fineness, internal mechanism, parameter matching and practical operating guidelines for ternary cathode production.
1. Core Mechanism
Feed rate decides solid‑gas ratio within jet mill:
- High feed rate → higher particle loading. Numerous NCM particles crowd the collision zone; particles shield one another, reducing effective collision probability and impact energy. In the classifier, dense particle clouds create particle‑interference effect, which weakens centrifugal‑drag separation. Coarse agglomerates are easily entrained into finished products.
- Low feed rate → lower particle concentration. Each particle obtains sufficient acceleration energy for collision; residence time inside closed‑loop becomes longer. Particles experience repeated impacts, tending to produce finer powder with more ultrafine fractions.
Important note: Feed rate indirectly affects fineness by changing grinding efficiency and classification effect. It cannot independently set final fineness; it must work together with grinding pressure and classifier wheel speed.
2. Effect of Increasing Feed Rate (Higher Throughput)
With other parameters kept constant:
- Fineness becomes coarser: D50, D97 and Dmax increase. Unbroken sintered agglomerates rise due to insufficient collision energy per particle.
- Classification sharpness declines, PSD span widens. Particle‑interference causes coarse bypass, raising risk of oversized killer‑particle leakage.
- BET specific surface area decreases, as fewer ultrafine fragments are generated.
- Production capacity improves, yet product quality stability deteriorates.
- Severe over‑feeding may trigger powder accumulation inside grinding chamber or pipeline, leading to unstable system operation.
For high‑nickel NCM, excessive feed rate is a frequent cause of intermittent Dmax spikes in mass production. Even if grinding pressure and classifier speed are set correctly, over‑feeding will still produce out‑of‑spec coarse powder.
3. Effect of Reducing Feed Rate (Lower Throughput)
- Powder becomes finer: D50 and D97 decrease. More agglomerates are disassembled by sufficient particle‑to‑particle collision.
- Extended particle residence time in closed‑loop circulation raises over‑grinding risk. Complete secondary particles may fracture, generating large amounts of sub‑micron fines.
- D10 drops sharply, BET rises obviously; span may increase due to excess ultrafine fractions.
- High‑nickel NCM exposes more fresh surface, becoming more sensitive to moisture and residual lithium, bringing higher gas‑generation risk in cells.
- Production throughput declines significantly, raising unit‑processing cost.
Too low feed rate wastes nitrogen consumption and aggravates particle pulverization, which should be avoided even if target fineness can be achieved.
4. Interaction with Other Key Parameters
4.1 Matching with grinding pressure
At high feed rate, higher grinding pressure is required to maintain collision intensity. If feed rate rises without pressure adjustment, fineness turns coarser.
Reducing feed rate amplifies the effect of grinding pressure; over‑grinding easily occurs even under medium pressure.
4.2 Matching with classifier wheel speed
When feed rate increases, particle load to the classifier rises. If wheel speed stays unchanged, coarse leakage appears. Simply raising classifier speed cannot fully offset the negative impact of high particle concentration. Reducing feed load is more effective for restoring classification sharpness.
4.3 Gravimetric feeding requirement
Volumetric feeding cannot maintain stable actual mass flow. Powder fluidity fluctuation will cause real‑world feed‑rate drift, leading to batch‑to‑batch fineness deviation. Gravimetric screw feeder with buffer hopper is preferred for NCM production to eliminate material bridging and lump surging.
5. Practical Operation Principles for NCM
- Determine the maximum allowable feed rate under target PSD specification. Do not blindly pursue throughput at the cost of fineness and Dmax control. High‑nickel grades normally adopt relatively conservative feed‑rate window.
- When fineness becomes coarser: Do not raise grinding pressure or classifier speed at once. First check whether actual feed rate exceeds the process window.
- Avoid large‑range sudden feed‑rate adjustment. Any change of feed rate should be followed by PSD testing for D50, D97, Dmax, span and BET.
- For existing production lines, perform feed‑rate gradient test to find the balance point between throughput and powder quality.
6. Troubleshooting Table
| Phenomenon | Root Cause Related to Feed Rate | Recommended Countermeasure |
|---|---|---|
| D50 and Dmax get coarser, span widens | Feed rate too high, particle interference reduces classification efficiency | Reduce feed rate moderately; check gravimetric feeder stability |
| D50 is too fine, high BET and many ultrafine fines | Feed rate too low, long residence time causes over‑grinding | Appropriately increase feed rate; re‑calibrate process parameters |
| Fineness drifts randomly batch‑to‑batch | Unstable feed rate caused by hopper bridging | Install anti‑bridging device; verify gravimetric feeder accuracy |
| Dmax still high after raising classifier speed | Over‑feeding leads to coarse bypass | Lower feed load instead of further increasing wheel speed |
Feed rate exerts significant indirect influence on NCM powder fineness by altering particle concentration, collision efficiency and classification performance. Higher feed rate tends to produce coarser powder and raises oversized‑particle risk. Lower feed rate delivers finer fineness yet brings obvious over‑grinding risk. Feed‑rate adjustment must coordinate with grinding pressure and classifier parameters. Stable gravimetric feeding is essential to guarantee consistent fineness across batches for ternary cathode powder.
