Producing NCM cathode powder with particle size below 1 μm via dry ultrafine grinding is technically challenging. NCM particles are prone to re‑agglomeration, heat-induced surface degradation and residual lithium side reactions when ground to submicron range. Based on JACAN dry processing technology from ncm-mill.com, submicron NCM can be achieved by selecting suitable grinding equipment, closed inert gas system, optimized classification and strict process control.
1. Select proper grinding equipment
Conventional air classifier mills (ACM) struggle to reliably produce large volumes of submicron NCM because mechanical impact generates friction heat and excessive fine particles easily re-agglomerate.
- Fluidized bed spiral jet mill: The preferred equipment for submicron NCM. It relies on high-speed particle-to-particle collision driven by high-pressure nitrogen. No rotating grinding rotor, so less frictional heat and low metal contamination. It can break agglomerates down to below 1 μm when paired with high-precision ultra-fine classifier.
- Ultra-fine air classifier mill: Only for limited lab or small-batch submicron trials. Requires low feed rate and full ceramic lining. Not recommended for mass production of high-nickel NCM due to heat risk.
2. Adopt closed-loop nitrogen inert atmosphere system
Submicron NCM has extremely high specific surface area. It readily absorbs moisture and oxygen, triggering re-agglomeration and surface degradation.
- Use dry nitrogen as grinding and conveying medium, maintain low dew point and low oxygen content in the circuit.
- Maintain slight negative pressure to prevent humid ambient air leakage.
- Install temperature and dew point interlocks to avoid hot spots and moisture condensation, which would cause fines to stick back together and falsify particle size results.
3. High-precision ultra-fine classification
Submicron grinding cannot be separated from sharp ultra-fine classification. The classifier cuts coarse particles and circulates unqualified material back to grinding zone.
- Deploy high-speed vertical ultra-fine classifier wheel with narrow clearance. It provides sharp cut-point to separate submicron finished powder and return oversize particles.
- Tune classifier wheel speed and nitrogen gas flow to precisely control D50 below 1 μm and restrain span. Without precise classification, many pseudo-agglomerates will remain, and laser PSD test will show larger particle size than actual primary particles.
4. Raw material and feed condition control
- Feed NCM must be pre-dried to moisture <0.1% to eliminate moisture-induced adhesion of submicron fines.
- Control residual lithium of incoming NCM. High residual lithium makes submicron particles sticky and promotes re-agglomeration.
- Use very low and stable feed rate. Overfeeding causes incomplete grinding and unstable PSD. Consistent feeding is critical for continuous submicron production.
5. Anti-re-agglomeration and anti-static design
Submicron NCM fines generate strong van der Waals force and static charge, the main reasons for re-agglomeration.
- Full ceramic or conductive PU linings and complete equipment grounding to dissipate static charge.
- Optimize nitrogen flow field to quickly carry away freshly generated submicron particles, reducing particle collision chance inside the mill that causes re-agglomeration.
- Avoid over-grinding. Excess ultra-fine fraction further increases cohesion and worsens powder flowability.
6. Limitations for battery-grade NCM
For most lithium-ion battery applications, NCM cathode powder is not ground below 1 μm routinely. Submicron NCM sharply increases specific surface area, which raises residual lithium, worsens powder flowability and reduces tap density. It may also cause higher electrolyte side reactions inside cells. Submicron NCM is usually only for special formulations such as coating precursors or customized lab materials.
To achieve NCM ultrafine grinding below 1 μm, the standard solution is fluidized bed spiral jet mill combined with high-speed ultra-fine classifier, operating in sealed low-dew-point nitrogen closed loop. Strict raw material moisture/residual lithium control, static elimination and stable low feed rate are mandatory. Users must understand that submicron NCM brings trade-offs in tap density, flowability and electrochemical stability, so this process is only applied for special customized requirements rather than standard battery cathode powder.
