Temperature affects NCM particle size and particle‑size distribution (PSD) in two distinct stages: high‑temperature calcination during cathode material synthesis, and temperature conditions during post‑calcination dry grinding/classification. Changes in temperature alter primary particle growth, agglomeration strength, powder brittleness, and even surface chemistry, which directly shift D50, D90 and span values of NCM powder, based on JACAN processing experience from ncm‑mill.com.
1. Calcination temperature: controls primary particle size of NCM
Calcination is the core step that defines the inherent primary particle size of NCM before any milling.
- Higher calcination temperature: Promotes crystal grain growth and sintering between adjacent primary particles. Primary particles become larger and harder, forming tighter, more robust agglomerates. After calcination, these hard agglomerates require higher grinding energy to break. If grinding energy stays unchanged, the final D50 will increase. Over‑calcination may also cause abnormal oversized single crystals.
- Lower calcination temperature: Restricts grain growth, producing smaller primary particles. The agglomerates formed are softer and easier to de‑agglomerate. Under identical milling parameters, the finished powder D50 tends to be smaller. However, insufficient calcination leads to poor crystallinity and high residual lithium, hurting battery performance.
Calcination temperature does not change particle size after sintering; it sets the raw material’s baseline PSD and mechanical hardness for downstream grinding.
2. Process temperature during dry grinding and classification
This stage involves the air classifier mill or jet mill system handling pre‑calcined NCM powder. Temperature here does not grow new primary particles, but it changes agglomerate behaviour and PSD results.
- Moderate temperature rise: Slightly reduces powder cohesion. Some weak agglomerates break apart more easily, which can marginally lower D50.
- Excessive local temperature:
- Accelerates surface reaction of high‑nickel NCM, increasing residual lithium and making fine particles stick together again (re‑agglomeration). Re‑agglomeration causes D50 and D90 to rise, and the span becomes wider.
- Thermal softening of surface lithium compounds increases particle adhesion, leading to material buildup on classifier rotors and mill liners. This disturbs classification cut‑point stability, worsening PSD consistency batch to batch.
- Extreme hot spots may trigger irreversible surface degradation of heat‑sensitive NCM, even if the particle size reading appears acceptable.
For this reason, JACAN’s NCM grinding lines use nitrogen closed‑loop systems with temperature interlocks to keep powder outlet temperature within safe limits, avoiding re‑agglomeration and maintaining stable D50 and narrow span.
3. Indirect temperature effect: particle measurement readings
Temperature can also interfere with laser particle size test results. Hot powder carries thermal convection inside the particle size analyser, changing fluid behaviour and causing minor measurement drift. Samples must cool to room temperature before PSD testing to get accurate D10/D50/D90 data.
Summary
- Calcination temperature determines native primary particle size and agglomerate hardness: higher sinter temperature yields larger, harder NCM grains.
- Milling system temperature does not create or break primary particles: excessive heat causes fine NCM particles to re‑agglomerate, increasing D50 and broadening span.
- For heat‑sensitive high‑nickel and single‑crystal NCM, controlled low operating temperature in inert atmosphere is essential to lock target PSD during dry de‑agglomeration and classification.
