Lithium manganese oxide (LMO, spinel LiMn₂O₄) is a low-cost cathode material for lithium-ion batteries. LMO has unique characteristics: moderate hardness, susceptibility to manganese dissolution under high temperature and moisture, and easy formation of hard agglomerates during calcination. Its particle size control focuses on de-agglomeration while avoiding particle over-crushing and surface damage. This article is adapted from JACAN powder processing technical knowledge referenced from ncm-mill.com.
1. Raw material pre-control before grinding
Calcination parameters define the initial primary particle size and agglomerate hardness of LMO.
- Higher calcination temperature creates larger primary grains and harder agglomerates, requiring greater grinding energy. Lower calcination temperature yields smaller primary particles with weaker crystal integrity, which may generate excessive fines during de-agglomeration.
- Strictly control incoming raw material moisture below 0.2%. Moisture accelerates manganese ion leaching, promotes agglomerate sticking and distorts PSD test results.
- Pre-screen raw powder to remove oversized hard agglomerates and foreign debris, preventing abnormal coarse peaks in finished PSD.
- Check raw material pH and residual lithium. High residual lithium causes particle adhesion, powder buildup on mill components and unstable particle size.
2. Equipment selection for LMO processing
LMO is not as heat-sensitive as high-nickel NCM/NCA, so multiple dry grinding options are available.
- Air Classifier Mill (ACM): Mainstream mass-production choice for LMO. High throughput, lower operational cost. Full ceramic lining is adopted to prevent metal contamination. It is suitable for target D50 ranging from 2 μm to 10 μm.
- Fluidized bed spiral jet mill: Used for premium LMO requiring narrow PSD, low impurity and finer particle size. Low frictional heat minimizes surface degradation and manganese dissolution risk. Jet mill can reach D50 down to ~1 μm under optimized operation.
3. Core adjustable process parameters
These parameters directly tune D50, D90, D10 and span:
- Classifier wheel speed: The primary control factor. Higher speed delivers a finer cut point and smaller D50; lower speed allows coarser particles to pass.
- Gas flow rate: Adjusts particle residence time inside the grinding chamber. Higher airflow quickly carries qualified fines out and prevents over-grinding.
- Feed rate: Maintain consistent feeding. Overfeeding leads to incomplete de-agglomeration and larger D50. Too low feed rate creates excessive ultra-fine particles, broadening span and increasing specific surface area.
- Jet pressure (jet mill only): Increase nitrogen pressure to strengthen particle collision for finer de-agglomeration, at the expense of higher gas consumption.
Commercial LMO typically targets span below 1.0.
4. Process atmosphere and anti-agglomeration measures
LMO is vulnerable to moisture-induced manganese dissolution, even though it is less sensitive to oxidation than NCA/NCM.
- Dry air or nitrogen can serve as process gas. Nitrogen closed-loop is preferred for high-performance LMO grades to suppress surface side reactions.
- Keep slight negative pressure in the whole circuit to stop humid ambient air leaking into the system.
- Full grounding and conductive ceramic linings dissipate static electricity, reduce powder adhesion on chamber walls and restrain fines re-agglomeration.
- Control process temperature; avoid hot spots that accelerate manganese elution and powder caking.
5. Online monitoring and equipment maintenance
- Use offline laser PSD testing or install online particle size monitoring to continuously track D10, D50, D90 and span.
- Pulse back-blow cleaning for cyclone and filter units to clear accumulated powder cake. Large cake fragments falling into finished product will introduce coarse outliers and ruin PSD consistency.
- Regular inspection of classifier wheel and liners for powder deposition, which shifts classification cut-point over time.
6. Typical PSD targets for commercial LMO
- Standard power battery LMO: D50 3–8 μm, span <1.0
- High-rate fine LMO: D50 1–3 μm, span <0.9
LMO particle size control is based on dry de-agglomeration of calcined agglomerates rather than breaking primary crystals. Air classifier mills dominate mass production of standard LMO, while spiral jet mills are used for high-purity narrow-span premium LMO. Stable low-moisture feedstock, optimized classifier and gas parameters, static elimination and continuous PSD monitoring are essential. The process must avoid excess heat and moisture to prevent manganese dissolution while maintaining the target particle size distribution.
