Shaping natural flake graphite to D50 19–20 μm is a critical pre‑spheroidization stage for lithium‑ion battery anode manufacturing. This process is not heavy crushing; it uses controlled low‑to‑medium mechanical impact, particle‑to‑particle collision and friction to trim flake edges while locking median particle size in the 19–20 μm window. The goal is to deliver narrow PSD, low over‑fine fraction and moderately rounded precursor powder ready for subsequent full spheroidization, instead of generating excessive submicron dust which hurts tap density and cycle performance.
1. Raw material pre-treatment before shaping
Consistent feedstock is the foundation to stabilize D50 19–20 μm.
- Carbon purity: ≥99.9% purified natural flake graphite; magnetic impurities must be minimized to avoid anode metal contamination.
- Moisture: control total moisture ≤0.5%. High moisture causes agglomeration, unstable airflow classification and uneven shaping force.
- Pre‑screening: remove oversized lumps and foreign contaminants. Recommended feed precursor D50 is around 21–23 μm from primary JCSM710 grinding mill. This narrow starting PSD greatly reduces shaping load and makes D50 19–20 μm easier to control.
2. Core shaping principle (JACAN integrated shaping & air classification system)
The shaping unit adopts closed negative‑pressure turbo classifier mill, matching the JCSM series platform.
- Quantitative feeding: pre‑ground flake graphite (D50 21–23 μm) enters the shaping chamber via screw feeder.
- Controlled low‑energy shaping: particles are accelerated by high‑speed rotor pins. Forces are dominated by edge polishing, curling and inter‑particle friction, rather than brute fracture. Sharp flake corners are peeled and folded; bulk flake splitting is suppressed to limit ultra‑fine dust.
- Air transport to top classification zone: shaped powder flows upward with circulating negative‑pressure airflow.
- Dynamic turbo classification to fix D50 19–20 μm:
- Tunable classifier wheel speed is the primary knob for median particle size. Higher wheel speed cuts finer particles; lower speed allows larger particles to pass.
- Particles meeting D50 19–20 μm pass through classifier wheel and go to cyclone + pulse collector as qualified precursor for spheroidization.
- Over‑size particles slide back to shaping chamber for re‑shaping; ultra‑fine dust is separated out and recycled separately.
- Non‑metallic wear liners and rotor protection: ceramic or polyurethane liners are used to prevent iron contamination for battery‑grade anode graphite.
3. Key adjustable process parameters for D50 19–20μm target
- Rotor speed: Keep at moderate level. Too high rotor speed creates massive fines and pushes D50 below 19 μm; too low leaves sharp flake edges and D50 exceeds 20 μm.
- Classifier wheel frequency: Fine tune this parameter to lock D50 within 19–20 μm. This is the most sensitive parameter for median particle size.
- System air volume: Stable negative‑pressure airflow ensures consistent particle residence time inside shaping chamber. Higher airflow shortens residence time and reduces over‑shaping risk.
- Feed rate: Constant feeding avoids material accumulation. Overfeeding causes incomplete shaping and broad PSD; underfeeding increases particle over‑impact and fines.
- Circulation cycles: Natural flake graphite usually runs multiple closed‑loop recirculations, gradually rounding flakes while slowly reducing D50 from 21–23 μm down to 19–20 μm.
4. In‑line quality monitoring during shaping
- Sampling at outlet to test PSD (D50, D10, D97). Target D50 19–20 μm, narrow distribution with low fine tail.
- Tap density check: tap density rises gradually as edges are rounded, without heavy particle breakdown.
- Sphericity check: precursor sphericity typically reaches 0.75–0.82 at this stage; full spheroidization equipment will further lift sphericity above 0.85.
- Metal impurity inspection: online magnetic separation removes ferromagnetic wear debris before powder enters spheroidization unit.
5. Common troubleshooting
- D50 <19 μm, too many fine powders
Cause: excessive rotor impact, classifier wheel speed too high, too many recirculation passes.
Solution: reduce rotor speed, lower classifier RPM, shorten shaping residence time, adjust airflow to discharge fines earlier. - D50 >20 μm, particles still sharp flaky
Cause: insufficient shaping energy, feed contains coarse tails, classifier wheel speed too low.
Solution: slightly raise rotor speed, increase classifier rotation speed, re‑check primary grinding PSD to remove oversize feed. - D50 hits 19–20 μm but high fines and low tap density
Cause: over‑impact, particle fracture instead of edge rounding.
Solution: switch to gentler shaping mode, optimize particle‑to‑particle collision ratio and reduce direct hammer impact.
6. Process handover to spheroidization
Once shaped powder meets D50 19–20 μm with narrow PSD and low fines, it is pneumatically conveyed to dedicated spheroidization machine. This precursor reduces spheroidization load, improves spheroidization yield and avoids excessive size shrinkage during the subsequent rounding stage.
To shape natural graphite to D50 19–20 μm for spheroidization, the production line starts with purified, dried pre‑ground feed (D50 21–23 μm from JCSM710 mill). The shaping stage uses low‑energy impact and friction to trim flake edges, paired with variable‑frequency turbo air classification in closed negative pressure loop. Tuning classifier wheel speed, rotor speed, airflow and feed rate enables stable control of D50 19–20 μm, delivering qualified low‑impurity precursor powder for the next spheroidization process for lithium battery anode.
