How To Achieve Graphite Anode Sphericity ≥0.85 By Spheroidization Modification

Sphericity ≥0.85 is the standard threshold for commercial near‑spherical natural graphite anode. It cannot be achieved by one‑pass simple grinding. It relies on qualified potato‑shaped precursor, closed‑loop vortex spheroidization, balanced mechanical collision, precise air classification and strict in‑line morphology monitoring. The core idea is to fold and curl flake platelets into compact near‑spherical granules by particle‑to‑particle collision, while avoiding excessive particle fracture which generates ultra‑fine dust.

1. Precursor Material Qualification (Prerequisite)

Poor precursor is the main reason that sphericity cannot reach ≥0.85.

• Morphology: Feed must be potato‑shaped graphite, not flat raw flakes. Sharp edges should already be partially trimmed in pre‑shaping stage.
• PSD: Narrow particle distribution, low coarse tail and limited fine fraction. For example, D50 16–17 μm potato‑shaped precursor for final spheroidization.
• Purity: Carbon ≥99.9%, ferromagnetic metal impurities removed by magnetic separation.
• Moisture: ≤0.5%. High moisture causes agglomeration, particle adhesion on chamber wall and incomplete curling.
• Flake thickness control: Retain properly thick flakes; ultra‑thin flakes easily break into fine fragments instead of folding into spherical particles.

2. Equipment Selection: Closed Negative‑Pressure Vortex Spheroidization System

Use JACAN integrated spheroidization unit with high‑speed pin rotor and built‑in turbo classifier.

• The chamber adopts ceramic or PU non‑metallic liners and pins to prevent iron contamination.
• The whole system runs under stable negative pressure to avoid powder leakage and maintain consistent airflow circulation.
• The design prioritizes particle‑to‑particle collision rather than direct hammer impact on particles, so flakes fold instead of being smashed.

3. Key Parameter Tuning To Hit Sphericity ≥0.85

Rotor speed (main energy knob for sphericity)

Increase rotor speed to raise collision intensity, which promotes flake folding and edge polishing to lift sphericity.

• Too low rotor speed: insufficient vortex energy; flakes remain flat, sphericity stuck below 0.85.
• Too high rotor speed: over‑impact breaks particles into fines, D50 shrinks sharply, tap density drops.
• Operation strategy: Start at medium speed, increase step by step, sample sphericity after each adjustment, stop raising speed once sphericity reaches target.

Classifier wheel frequency

Controls final D50 and removes incompletely spheroidized coarse particles.

• Oversized particles with low sphericity are rejected and returned to spheroidization chamber for re‑circulation.
• Ultra‑fine fragments generated by over‑crushing are separated and discharged independently to avoid broadening PSD.
• Fine‑tune classifier speed together with rotor speed to lock target D50 while accumulating enough reshaping cycles.

System air volume & negative pressure

Airflow controls particle residence time inside vortex chamber.

• Lower airflow: longer residence time, more collision cycles, helps lift sphericity, but higher risk of over‑grinding.
• Higher airflow: shortens residence time, prevents over‑fragmentation, but insufficient collision leads to low sphericity.
• Keep airflow stable during continuous production; airflow fluctuation causes inconsistent sphericity between batches.

Feed rate

Constant low‑fluctuation feeding is critical.

• Overfeeding: particles cannot get enough collision, incomplete folding, low sphericity.
• Underfeeding: particles collide with rotor pins too frequently, fracture into fines.

Closed‑loop recirculation cycles

Multiple closed recirculation passes are required to reach sphericity ≥0.85.
Each circulation gradually curls flake edges and wraps flakes into compact granules. Particles with incomplete sphericity are continuously sent back to vortex chamber for repeated reshaping until morphology meets requirement.

Important: Do not blindly increase circulation times. Too many cycles will break particles into fines and degrade tap density.

4. In‑Line Quality Inspection & Feedback Control

Sphericity is measured by SEM image analysis (particle circularity). Set up periodic sampling loop:

1. Test sphericity, PSD, tap density and SSA.
2. If sphericity <0.85: slightly increase rotor speed or extend circulation time, check if feed still contains flat flakes.
3. If sphericity ≥0.85 but too many fines: reduce rotor speed, increase airflow to shorten residence time.
4. Target benchmark: Sphericity ≥0.85, narrow PSD, stable tap density and controlled specific surface area.

5. Common Barriers To Reach Sphericity ≥0.85 & Solutions

1. Sphericity stuck at 0.80–0.84, obvious flaky fragments
   Cause: Precursor still has many sharp flat flakes; rotor energy insufficient; recirculation times not enough.
   Solution: Optimize upstream potato‑shaping stage; moderately raise rotor speed; extend closed‑loop recirculation.
2. Sphericity reaches ≥0.85 but D50 drops heavily, high SSA and low tap density
   Cause: Excessive impact energy; over‑circulation; particle fracture instead of folding.
   Solution: Reduce rotor speed; raise airflow to cut residence time; separate fine powder earlier by classifier.
3. Batch‑to‑batch sphericity fluctuation
   Cause: Unstable feed PSD or moisture; airflow/negative pressure drift; inconsistent feeding.
   Solution: Stabilize precursor quality; maintain constant negative pressure; install continuous feeding monitor.

6. Post‑Spheroidization Treatment

After sphericity hits ≥0.85, the qualified near‑spherical graphite goes through magnetic separation again to remove metal wear debris. Then it is ready for carbon coating and high‑temperature carbonization. Carbon coating does not improve sphericity, but protects the spherical particle structure during lithium intercalation and de‑intercalation.

To achieve graphite anode sphericity ≥0.85, the whole process starts with qualified potato‑shaped precursor. Adopt closed negative‑pressure vortex spheroidization system to realize repeated mild particle‑to‑particle collision and flake folding. Adjust rotor speed, classifier frequency, airflow and feed rate, and apply multi‑pass closed‑loop recirculation. Real‑time morphology sampling and parameter feedback are required to ensure sphericity ≥0.85 while avoiding excessive fine powder generation. Integrated air classification removes incompletely spheroidized coarse particles and excess fines, delivering high‑performance near‑spherical graphite precursor for lithium battery anode.