Grinding and shaping (spheroidization) is the core mechanical processing stage for graphite anode. For natural flake graphite, it converts flat flake particles into near‑spherical morphology; for artificial graphite (calcined petroleum coke), it breaks irregular angular coke particles, optimizes particle‑size distribution and tap density. This process liberates surface‑bonded gangue impurities, removes sharp edges, narrows PSD, improves powder flowability and electrode compaction density. Closed‑loop impact grinding with integrated air classification is the mainstream industrial solution for mass‑production anode lines.
Key distinction: Grinding mainly realizes particle‑size reduction and impurity liberation; shaping / spheroidization modifies particle morphology with moderate mechanical force, avoids excessive over‑crushing and excessive ultrafine powder generation.
Full Industrial Workflow
Natural flake graphite workflow
Flotation graphite concentrate → initial sieving (‑100 mesh) → drying → pre‑grinding → multi‑stage closed‑loop shaping/spheroidization → air classification → high‑intensity magnetic separation → purification → carbon coating.
Artificial graphite (calcined coke) workflow
Green coke → pre‑crushing → drying → calcination → grinding & shaping → classification → magnetic separation → pitch mixing → carbon coating → graphitization.
Step‑by‑step process description
Step 1: Pre‑grinding (particle‑size reduction & impurity liberation)
Raw feed enters impact‑type grinding host with non‑metallic ceramic/polyurethane lining to avoid secondary iron contamination.
- Natural flake graphite feed: after initial 100‑mesh screening, D50 = 70‑110 μm. Target after pre‑grinding: D50 = 21‑23 μm. Mechanical impact and shear break composite particles, liberate silicate and metal impurities adhered to flake edges.
- Calcined coke for artificial graphite: feed size ≤5 mm; pre‑grinding target D50 = 18‑22 μm, break angular coke fragments.
Closed‑loop configuration: integrated dynamic air classifier separates finished‑size powder; coarse particles return back to grinding chamber for re‑processing. Oversized particles cannot enter shaping stage. Excess ultrafine powder (<2 μm) is continuously discharged as tailings to prevent high‑BET and low initial coulomb efficiency risk.
Step 2: Multi‑stage closed‑loop shaping / spheroidization
Shaping adopts moderate‑energy repeated collision, friction and shear, not high‑intensity crushing.
- Natural flake graphite: flat flakes are curled, folded and wrapped into potato‑shaped near‑spherical particles; sharp corners are worn away. Multi‑pass circulation is typical for industrial lines.
- Artificial graphite calcined coke: angular particle edges are rounded, reduce particle aspect ratio.
Key control parameters:
- Rotor / shaping wheel speed: 3600‑6000 rpm; too high speed creates excessive ultrafine powder; too low gives poor sphericity.
- Air volume & classifier wheel speed: precisely cut PSD, control D10/D50/D90.
- System runs under negative‑pressure closed environment, prevents dust leakage and air‑induced surface oxidation.
Target indicators after shaping:
- D50: 15‑18 μm (standard anode grade); customized 10‑22 μm range for different battery systems.
- Sphericity ≥0.85‑0.90 for natural spherical graphite.
- Tap density ≥0.85 g/cm³.
- Specific surface area BET: 3‑6 m²/g (controlled to avoid severe SEI side‑reaction).
Step 3: Post‑shaping classification and impurity removal
- Air classification: Strictly separate oversize particles and ultrafine tailings, obtain narrow particle‑size distribution.
- High‑intensity magnetic separation: Remove ferromagnetic metal impurities generated by equipment wear, reduce magnetic foreign substances down to ppm‑level.
All powder‑contact surfaces adopt non‑metallic lining; steel components are forbidden for direct powder contact.
Step 4: Post‑process handling
After grinding‑shaping, natural graphite goes to chemical purification to reach fixed carbon ≥99.95 %. Artificial graphite powder enters pitch high‑speed mixing for carbon‑coating pretreatment.
Critical process pitfalls & troubleshooting
| Problem | Root Cause | Countermeasure |
|---|---|---|
| Low tap density, poor sphericity | Insufficient shaping cycles; rotor speed too low | Increase closed‑loop circulation passes; raise shaping rotor speed within safe window |
| Too many ultrafine powders, high BET | Over‑grinding, excessive mechanical energy input | Tune classifier wheel speed; reduce rotor speed; timely discharge fine tailings |
| Increased iron‑based magnetic impurities | Steel lining / steel rotor contact powder | Upgrade to ceramic‑polyurethane wear‑resistant lining |
| Wide particle‑size distribution | Poor closed‑loop classification efficiency | Check classifier rotor clearance; optimize system air volume |
| Low spheroidization yield | Raw feed particle size out‑of‑spec; flake thickness uneven | Stabilize pre‑grinding outlet D50; control feed quality |
Difference between natural graphite and artificial graphite grinding‑shaping
- Natural flake graphite: Main goal is morphological spheroidization; multiple closed‑loop shaping cycles are required; yield is a key economic indicator. Impurities are liberated during grinding for subsequent magnetic separation and chemical purification.
- Artificial graphite (calcined coke): Main goal is particle‑size control and edge rounding; less folding‑wrapping deformation compared with flake graphite; PSD control is more critical.
