How to Break Soft Agglomerates in NCM Powder

Soft agglomerates of NCM are loose particle clusters held together by static electricity, van‑der‑Waals force or trace moisture, without sintered necks between particles. Individual spherical secondary particles remain intact. If not dispersed, these clusters behave as fake coarse particles in classification: they are mistakenly rejected back to grinding chamber, raise circulation ratio, increase energy consumption and risk of over‑grinding. Soft agglomerates cannot be eliminated by raising jet‑mill grinding pressure; higher pressure will break real secondary spheres. This article describes identification and practical industrial solutions for closed‑loop jet‑mill production of NCM cathode powder.

1. Distinguish soft agglomerates vs hard sintered agglomerates

Common site mistake: treat soft agglomerates as hard agglomerates and increase grinding pressure, triggering over‑grinding.

2. Root causes of soft agglomerates in NCM

1. Static electricity: High‑nickel NCM has high surface resistance. Friction in conveying and classification generates static charge; particles attract one another to form loose clusters.
2. Trace moisture: High dew‑point circulating nitrogen or air ingress creates liquid‑bridge adhesion between particles. High‑nickel NCM easily absorbs moisture, aggravates agglomeration.
3. Particle‑particle collision in closed‑loop circulation enhances static accumulation.
4. Poor flow‑field dispersion before classification zone, particles are not fully separated.

3. Core solution 1: Optimize classifier secondary‑air (most effective for jet‑mill line)

Secondary‑air provides high‑shear gas flow at classifier inlet, dispersing soft clusters before particles enter rotor separation zone.

1. Ensure classifier is equipped with independent secondary‑air inlet channel. Classifiers without dedicated secondary‑air cannot effectively eliminate soft agglomerates.
2. Increase secondary‑air flow step‑by‑step: inject shear gas to tear loose static clusters into discrete individual spheres.
3. Do not over‑increase secondary‑air: excessive secondary‑air disturbs main flow‑field, reduces classification sharpness and causes coarse bypass.
4. Effect verification: After adjustment, return‑stream sample shows fewer intact qualified spheres; circulation ratio decreases.

Secondary‑air can break soft static clusters, cannot break calcination‑generated hard sintered agglomerates.

4. Core solution 2: Static elimination across whole system

1. Reliable grounding for jet‑mill body, classifier, cyclone, filter and all pipelines; eliminate static charge accumulation.
2. Use anti‑static lining for powder‑contact pipelines and hoppers to reduce frictional charging.
3. Avoid excessively high circulation ratio: long‑time repeated circulation increases particle friction and static build‑up. Follow minimum‑sufficient classifier‑speed principle to reduce circulation load.

5. Core solution 3: Strictly control gas‑source dew‑point

Moisture is a major driver of soft agglomeration for high‑nickel NCM.

1. Closed‑loop circulating nitrogen dew‑point should be maintained ≤‑40 ℃.
2. Inspect system sealing; prevent humid ambient air leakage into jet‑mill loop.
3. Check nitrogen dryer performance; prevent dew‑point drift during long‑time continuous production.

6. Process‑parameter optimization (do not touch grinding pressure)

1. Main airflow & classifier‑speed matching: Improper speed‑airflow matching worsens particle aggregation before classification. Optimize recipe to achieve good particle dispersion inside flow‑field.
2. Stabilize feeding rate: Avoid ultra‑low feed rate. Low particle concentration intensifies friction‑induced static charging. Maintain optimal gas‑solid ratio.
3. Do not solve fake coarse D90 caused by soft agglomerates by raising grinding pressure or rotor speed. Higher rotor speed increases circulation ratio and makes static agglomeration worse.

7. Pre‑treatment and auxiliary dispersion methods

1. Pre‑dispersion before feeding: Use low‑shear air‑dispersion device or ultrasonic vibration sieve for calcined clinker before entering jet‑mill; break large soft agglomerates in advance.
2. Equipment maintenance: Keep classifier volute and pipeline clean. Powder buildup creates dead zones where particles aggregate. Periodic cleaning reduces agglomeration sources.
3. For lab / wet‑process: ultrasonic dispersion is effective to break soft agglomerates during PSD testing, but cannot be directly applied to dry industrial production.

8. Verification method for soft‑agglomerate improvement

1. PSD comparison: Run ultrasonic dispersion in laser particle‑size test. If after‑sonication PSD narrows obviously, soft agglomeration exists. After process adjustment, the gap between “with‑sonication” and “without‑sonication” PSD should shrink.
2. SEM observation: Check whether powder exists as discrete individual spheres instead of loose clusters.
3. Monitor circulation‑return stream: Reduction of qualified fine particles in return flow proves soft‑agglomerate dispersion works.
4. BET remains stable: No obvious BET increase, confirming no over‑grinding occurs.

9. Typical on‑site troubleshooting table

Soft agglomerates in NCM powder are caused by static electricity and trace moisture. Do not use grinding impact to solve soft agglomeration. The priority measures are: optimize classifier secondary‑air shear dispersion, full‑system static elimination, control nitrogen dew‑point, and reduce circulation ratio. Always distinguish soft agglomerates from hard sintered agglomerates via ultrasonic PSD test and SEM to avoid unnecessary over‑grinding of spherical secondary particles.