How to produce spherical LFP particles through grinding

Dry post‑sinter grinding (jet mill / ACM mill) cannot create spherical primary LFP particles from irregular fragments by mechanical rounding / ball‑on‑particle polishing. Grinding only breaks particles; it does not reshape sharp‑fractured grains into smooth spheres. True spherical LFP (spherical secondary granules) is formed in the precursor stage by wet bead milling + spray‑drying granulation, followed by high‑temperature sintering. Post‑sinter grinding only preserves pre‑formed spherical secondary‑particle morphology, rather than generating sphericity.

1. Core concept distinction

1. Spherical secondary particles (industrial spherical LFP)
   Spherical agglomerates (5‑20 μm secondary spheres), assembled by many sub‑micron primary LFP grains inside each spherical granule. Sphericity comes from spray‑drying droplet shrinkage during precursor processing, not grinding.
2. Primary‑particle morphology
   Olivine LFP primary grains are intrinsically potato‑shaped / sub‑rounded crystals. Mechanical grinding can only fracture them into sharp‑edged fragments; dry grinding has no polishing mechanism to turn irregular pieces into spherical primary particles.
3. Role of post‑sinter grinding: deagglomeration only, preserve existing spherical secondary granules, do not re‑shape particles.

2. Full industrial route for spherical LFP (grinding position in workflow)

1. Wet bead milling of precursor slurry
   Wet‑mill raw material mixture (Fe‑source, Li‑source, P‑source, carbon source) down to sub‑micron primary particles, achieve homogeneous dispersion in water‑based slurry.

This is precursor wet grinding; not post‑sinter dry grinding.

2. Spray‑drying granulation (key spherization step)
   Atomize slurry into fine droplets; solvent evaporates inside hot drying tower, self‑assembly forms compact spherical precursor secondary granules.
3. High‑temperature inert‑atmosphere sintering
   Spherical precursor granules transform into LFP olivine phase; internal primary grains grow, carbon coating forms. Output sintered powder with spherical secondary‑particle structure.
4. Dry ceramic‑lined jet‑mill / ACM closed‑loop processing
   Only break soft sinter‑bonded agglomerates between spherical secondary particles; keep each spherical secondary granule intact. This step adjusts PSD, removes oversized lumps, preserves sphericity, does not create spheres.

3. How to preserve spherical secondary‑particle morphology during post‑sinter dry grinding

If you already have sintered spherical LFP granules, improper dry grinding will shatter spherical secondary particles into irregular fragments. Follow these rules to retain spherical shape:

Jet mill configuration

1. Use minimum effective grinding pressure for deagglomeration. Higher pressure causes particle‑to‑particle impact that cracks spherical secondary spheres.
2. Stable and sufficient feed rate; avoid under‑feeding. Low feed rate amplifies collision energy and breaks spherical granules.
3. Closed‑loop turbo classifier set for sharp cut‑point. Discharge qualified material promptly; prevent spherical particles from long‑time repeated circulation inside grinding chamber.
4. Gentle upstream full‑ceramic pre‑breaking for hard sintered lumps. Hard lumps will smash surrounding spherical secondary particles during high‑energy collision.

Ceramic‑lined ACM (air classifier mill)

1. Operate at moderate rotor tip‑speed, prioritize shear‑based deagglomeration instead of violent impact. High rotor speed fractures spherical secondary granules.
2. Loss‑in‑weight stable feeding; prevent particle‑on‑rotor direct impact.
3. Optimize secondary dispersing air in classifier zone to separate inter‑granule agglomerates, reduce grinding‑zone load.

Material requirement

Full high‑purity alumina ceramic wetted‑parts to avoid metal contamination; monolithic sintered ceramic instead of thin coatings.

Monitoring indicators for spherical morphology retention

1. SEM inspection: Spherical secondary granules remain intact; minimal broken fragments. If many shattered irregular pieces appear, grinding energy is too high.
2. BET specific surface area: Abnormal BET jump signals spherical‑granule fracture.
3. Tap density: Tap density drops sharply when spherical secondary particles are destroyed.
4. PSD curve: Avoid large increase of sub‑micron fine‑particle tail.

4. What cannot be achieved by post‑sinter dry grinding

1. Cannot take irregular sintered LFP powder and “grind‑polish” into spherical particles. Impact fracture produces sharp fragments instead of rounded spheres.
2. Cannot turn non‑spherical primary crystals into spherical primary grains.
3. High‑energy dry ball‑milling must be avoided for spherical LFP post‑processing; ball impact destroys spherical secondary granules completely.

5. Common misconception

Some equipment datasheets mention jet‑milled “potato‑like / near‑spherical powder”. This refers to preserving the original rounded secondary‑particle shape inherited from spray‑dried sintered feedstock, not that jet milling reshapes irregular particles into spheres.

Grinding alone cannot produce spherical LFP particles. True spherical secondary LFP granules are realized by precursor wet bead milling + spray‑drying granulation + sintering. Post‑sinter dry grinding (jet mill / ACM) only acts as low‑damage deagglomeration step: separate soft agglomerates between spherical granules while preserving original spherical secondary‑particle morphology. Excessive grinding energy shatters spherical structures and degrades tap density and electrochemical performance.