Spheroidization modification is a core mechanical reshaping process for natural flake graphite anode. It converts flat, platelet‑like flake graphite into near‑spherical graphite particles by repeated controlled impact, inter‑particle collision and friction. This process greatly improves tap density, powder flowability and electrode compaction performance, which is essential for lithium‑ion battery energy density and cycle life.
This spheroidization stage comes after primary grinding and pre‑shaping (potato‑shaping). It is a closed negative‑pressure loop process, not simple crushing. The target is to raise particle sphericity to ≥0.85 while locking D50 within the designed particle size window, and minimize excessive fine powder generation.
1. Feedstock Requirements Before Spheroidization
The incoming material is pre‑shaped potato‑like graphite precursor, not raw flake graphite.
- PSD: Stabilized D50 (such as 16–17 μm, 19–20 μm), narrow particle distribution, low coarse tail and controlled fine fraction.
- Purity: Carbon ≥99.9%; ferromagnetic metal impurities removed by magnetic separation.
- Moisture: ≤0.5%. High moisture causes particle agglomeration, wall adhesion and unstable classification.
- Morphology: Pre‑curled potato‑shaped particles, sharp flake edges already partially trimmed. Good precursor reduces spheroidization load and improves yield.
2. Core Working Principle & Step‑by‑Step Spheroidization Process
JACAN spheroidization system adopts high‑speed rotor vortex shaping chamber with built‑in turbo air classifier, running under fully closed negative pressure.
- Continuous feeding
Quantitative screw feeder sends pre‑shaped graphite powder into the center of spheroidization chamber. - Vortex high‑energy reshaping
High‑speed pin rotor accelerates graphite particles to form strong vortex flow. Particles collide heavily with each other instead of direct hammer impact.
Flat flake fragments are folded, curled and wrapped together. Sharp corners are continuously polished. The flakes assemble into compact near‑spherical granules.
The key difference from pre‑shaping: spheroidization uses higher collision intensity and multiple closed‑loop recirculation cycles to lift sphericity significantly, while strictly avoiding over‑fragmentation into ultra‑fine dust. - Air conveying to turbo classification zone
Under circulating negative‑pressure airflow, powder flows upward to top classification rotor. - Dynamic air classification & closed‑loop recirculation
Variable‑frequency classifier wheel generates adjustable centrifugal force:
- Qualified near‑spherical particles with target D50 pass through classifier wheel and are collected by cyclone and pulse dust collector.
- Incompletely spheroidized irregular particles and oversized particles are rejected by centrifugal force, slide back to spheroidization chamber for repeated reshaping.
- Excess ultra‑fine powder is separated and discharged independently to prevent PSD broadening and excessive specific surface area (SSA).
- Anti‑contamination protection
Ceramic or PU non‑metallic liners and rotor pins are used inside the chamber to cut iron contamination, meeting battery‑grade anode purity standards.
3. Key Controllable Process Parameters
- Rotor speed: The main knob for sphericity. Higher rotor speed delivers stronger vortex collision and higher sphericity, but risks over‑grinding and D50 shrinkage. Lower speed cannot fully fold flakes and sphericity remains low.
- Classifier wheel frequency: Controls final D50. Higher classifier speed removes coarser particles and reduces median particle size.
- System air volume & negative pressure: Stabilizes particle residence time in vortex chamber. Stable airflow ensures consistent collision times per particle.
- Feed rate: Constant feeding is required. Overfeeding leads to insufficient collision and low sphericity; underfeeding causes over‑impact and excess fines.
- Closed‑loop recirculation times: Multiple cycles are necessary. Each pass gradually improves roundness, until sphericity reaches target ≥0.85.
4. Post‑Process Inspection & Quality Indicators
After spheroidization, finished powder is sampled and tested:
- Particle morphology: Near‑spherical shape, sphericity ≥0.85
- PSD: D50, D10, D97, narrow span, limited fine tail
- Tap density: Remarkably increased compared with potato‑shaped precursor
- Specific surface area: Controlled within specification; too many fines will raise SSA and reduce first‑cycle efficiency
- Metal impurity: Low ferromagnetic impurity for battery safety
5. Next Step: Carbon Coating (Surface Modification)
Mechanical spheroidization only changes particle geometry. To further reduce surface reactivity and improve cycle performance, carbon coating is usually applied after spheroidization. Pitch or resin is coated on graphite particle surface, followed by high‑temperature carbonization, forming a uniform soft carbon layer. This is the final surface modification for commercial spherical graphite anode.
6. Common Troubleshooting
- Low sphericity, still obvious flaky fragments
Cause: Insufficient rotor energy, insufficient recirculation cycles, unstable feeding.
Solution: Increase rotor speed appropriately, extend closed‑loop circulation, stabilize feed rate. - Sphericity meets target but D50 drops too much, many fine particles
Cause: Excessive impact energy, too many recirculation passes, classifier speed too high.
Solution: Reduce rotor speed, lower classifier RPM, separate fine fractions earlier. - High sphericity but low tap density
Cause: Over‑fragmentation, large amount of submicron fines generated during spheroidization.
Solution: Reduce collision intensity, optimize particle‑to‑particle collision ratio, adjust classification cut‑point.
Spheroidization modification for lithium battery graphite anode is a closed‑loop vortex mechanical reshaping process. Pre‑shaped potato graphite precursor enters the spheroidization chamber, and repeated inter‑particle collision and folding convert flakes into near‑spherical particles. By tuning rotor speed, classifier frequency, airflow and feed rate, manufacturers control sphericity and lock target D50. Air classification removes oversized particles and excess fines. The spheroidized graphite obtains higher tap density and better flowability, ready for subsequent carbon coating and high‑temperature treatment for lithium‑ion battery anode production.
