Spheroidization to D50 19–20 μm is a two‑stage dry mechanical reshaping workflow for natural flake graphite anode. The first stage uses JCSM710 classifier mill to reduce raw flakes to D50 21–23 μm precursor; the second stage adopts JACAN vortex spheroidizer with built‑in turbo classifier to trim, fold and curl flat flakes into near‑spherical particles, locking D50 within 19–20 μm and reaching sphericity ≥0.85. This process improves tap density, powder flowability and electrode compaction for lithium‑ion battery anodes, while controlling excessive fine powder generation.
1. Raw Material & Precursor Preparation
The feed for spheroidization must be pre‑ground graphite from JCSM710 mill, not raw large flake graphite.
- Precursor PSD: D50 21–23 μm, narrow particle distribution, low coarse tail and limited fine fraction.
- Purity: Carbon ≥99.9%, ferromagnetic metal impurities removed by magnetic separation.
- Moisture: ≤0.5%. High moisture causes powder agglomeration, wall adhesion and unstable airflow classification.
- Morphology: Partially trimmed flake edges; avoid ultra‑thin fragile flakes which easily fracture into fines during spheroidization.
2. Working Principle of Closed Negative‑Pressure Vortex Spheroidization System
The whole line runs under fully closed negative pressure to prevent graphite leakage and stabilize particle residence time.
- Quantitative feeding: Screw feeder continuously sends D50 21–23 μm pre‑shaped graphite into the center of the spheroidization chamber.
- Vortex particle‑to‑particle collision & curling: High‑speed pin rotor creates strong vortex flow. The dominant force is inter‑particle friction and mild collision rather than direct hammer impact. Sharp flake edges are polished and folded inward, turning flat platelets into compact near‑spherical granules.
- Air conveying to turbo classifier: Airflow carries shaped powder upward to the top variable‑frequency classification wheel.
- Dynamic closed‑loop classification:
- Qualified near‑spherical particles with D50 19–20 μm pass through classifier gaps and are collected by cyclone and pulse dust collector.
- Incompletely spheroidized, oversized particles are rejected by centrifugal force and slide back to spheroidization chamber for repeated recirculation reshaping.
- Excess ultra‑fine dust is separated and discharged independently to avoid PSD broadening and high specific surface area.
- Anti‑contamination design: Ceramic or PU non‑metallic liners and rotor pins minimize iron contamination for battery‑grade requirements.
3. Key Adjustable Process Parameters For D50 19–20μm Target
Rotor speed (sphericity control)
Set to medium‑high level to generate enough vortex energy for flake curling.
- Too low: insufficient collision; flakes remain flat, sphericity below 0.85.
- Too high: violent impact fractures particles; D50 drops below 19 μm and SSA rises sharply.
Strategy: Increase rotor speed step by step, sample sphericity after each adjustment.
Classifier wheel frequency (primary D50 tuning knob)
Higher classifier wheel speed cuts finer particles and reduces median particle size; lower speed allows larger particles to pass. Fine tune in small increments to stabilize D50 between 19–20 μm.
System air volume & negative pressure
Controls particle residence time inside vortex chamber.
- Slightly lower airflow extends residence time for more edge curling, helping lift sphericity.
- Too low airflow causes over‑grinding and fines; too high airflow shortens residence time and leaves incomplete spheroidization.
Feed rate
Maintain steady, constant feeding. Overfeeding leads to insufficient collision and low sphericity; underfeeding increases particle‑rotor contact and generates fine fragments.
Closed‑loop recirculation cycles
Multiple gentle recirculation passes are required to fold flakes into near‑spherical shape. Each cycle improves sphericity gradually. Stop recirculation once D50 and sphericity hit targets to avoid over‑processing.
4. In‑Line Quality Monitoring
- PSD: D50 19–20 μm, narrow span, controlled D10/D97, low fine tail.
- Morphology & sphericity: SEM inspection, sphericity ≥0.85, compact near‑spherical shape.
- Tap density: obvious increase compared with D50 21–23 μm precursor.
- SSA: kept within target range, no abnormal rise caused by fractured particles.
- Impurity: low ferromagnetic metal content after secondary magnetic separation.
5. Common Troubleshooting
- D50 <19 μm, many fine fragments
Cause: Excessive rotor speed, too many recirculation cycles, classifier speed too high.
Solution: Reduce rotor speed, lower classifier RPM, increase airflow to shorten residence time. - D50 >20 μm, particles still flaky, sphericity <0.85
Cause: Insufficient vortex energy, incomplete recirculation, precursor with coarse flakes.
Solution: Raise rotor speed moderately, increase classifier wheel speed, re‑check upstream pre‑grinding PSD. - D50 in 19–20 μm but low tap density and high SSA
Cause: Particle fracture instead of gentle edge curling.
Solution: Reduce collision intensity, optimize particle‑to‑particle collision ratio, adjust classification cut‑point to remove free fines.
6. Subsequent Process
After spheroidization and inspection, qualified D50 19–20 μm near‑spherical graphite proceeds to mild surface modification (low‑load carbon coating), carbonization, soft de‑agglomeration and screening, to become finished lithium battery anode material.
To spheroidize natural flake graphite to D50 19–20 μm for lithium battery anode, first pre‑grind raw flakes to D50 21–23 μm using JCSM710 mill. Then feed the precursor into JACAN closed negative‑pressure vortex spheroidization system. By tuning rotor speed, classifier frequency, airflow and feed rate, combined with multi‑pass closed‑loop recirculation, flat graphite flakes are folded and polished into near‑spherical particles with sphericity ≥0.85. Integrated turbo classification locks D50 at 19–20 μm and removes excess fines, delivering high‑performance spheroidized graphite precursor ready for carbon coating.
