Lithium cobalt oxide (LCO) is widely used in high-energy-density lithium-ion batteries for consumer electronics. Compared with NCM and NCA, LCO has high hardness, relatively good thermal stability at moderate processing temperatures, but its surface is sensitive to moisture. Excess heat and water will trigger surface lithium precipitation, degrade electrochemical performance, and increase powder agglomeration. This article draws on JACAN dry processing technical experience from ncm-mill.com.
1. Raw material pretreatment before grinding
Calcined LCO exists as soft secondary agglomerates formed by tightly bonded primary crystals. The goal of grinding is de-agglomeration instead of smashing primary particles.
- Control incoming moisture below 0.1%. LCO readily absorbs moisture; water reacts with residual lithium to form sticky lithium salts, causing re-agglomeration and unstable PSD.
- Inspect and screen raw feedstock to remove large hard agglomerates and foreign impurities, avoiding abnormal coarse peaks in final particle size distribution.
- Check residual lithium level. High residual lithium increases particle adhesion, which leads to material sticking on mill liners and classifier wheels.
2. Equipment selection for LCO grinding
Two main dry grinding options are available for industrial LCO processing:
- Air Classifier Mill (ACM)
Suitable for conventional mass production of LCO. It delivers high throughput and moderate fineness. Full ceramic lining is required to eliminate metal contamination. Local frictional heat must be controlled. It works well for target D50 from 2 μm to 10 μm. - Fluidized bed spiral jet mill
Preferred for high-end LCO requiring narrower PSD, lower metal impurity, and finer size. Less frictional heat is generated. It is the better choice for ultra-fine LCO grades with strict electrochemical requirements. Jet milling can achieve D50 down to ~1 μm under optimized conditions.
Note: Wet bead milling is only used for lab nano LCO preparation, not standard mass production of commercial LCO cathode powder.
3. Key process parameter tuning
Adjust these parameters to stabilize D50, D90 and span:
- Classifier wheel speed: The primary control parameter. Higher speed creates a finer cut point and reduces D50; lower speed allows coarser particles to pass through.
- Gas flow rate: Controls particle residence time in the grinding zone. Higher airflow quickly carries finished fines out and prevents over-grinding.
- Feed rate: Maintain steady and uniform feeding. Overfeeding leads to incomplete de-agglomeration and larger D50. Too low feed rate generates excessive ultra-fine fines and broadens span.
- Jet pressure (jet mill only): Higher nitrogen pressure enhances particle collision for finer de-agglomeration, at the cost of higher gas consumption.
The typical target span for commercial LCO powder is below 1.0.
4. Atmosphere, temperature and anti-static control
LCO is less heat-sensitive than high-nickel NCA/NCM, but moisture and static still cause quality drift.
- Use dry air or nitrogen as the process gas. Nitrogen closed-loop is recommended for premium high-voltage LCO grades to suppress surface side reactions.
- Install temperature monitoring. Restrict local hot spots; high temperature accelerates surface lithium precipitation and re-agglomeration.
- Full grounding for all equipment and conductive ceramic linings to dissipate static charge, reduce wall adhesion and fines clustering.
- Keep slight negative pressure in the circuit to block humid ambient air ingress.
5. Quality monitoring and maintenance
- Use offline laser particle size testing, or install online PSD monitoring to continuously track D10, D50, D90 and span.
- Pulse back-blow cleaning for cyclone and bag filter to remove accumulated powder cake. Falling cake chunks will introduce coarse contaminants and destroy PSD consistency.
- Regularly inspect classifier wheel and liner for powder buildup, which changes classification cut-point over time.
6. Typical PSD target for commercial LCO
- Standard consumer battery LCO: D50 3–8 μm, span <1.0
- High-rate ultra-fine LCO: D50 1–3 μm, span <0.9
LCO grinding is mainly dry de-agglomeration of calcined secondary agglomerates. Air classifier mills are widely adopted for large-volume standard LCO, while spiral jet mills are used for high-purity, narrow-span premium LCO. Stable low-moisture feedstock, optimized classifier and gas parameters, static elimination, and continuous PSD monitoring are required to maintain target particle size while avoiding surface lithium precipitation and particle re-agglomeration.
