Secondary agglomeration of LFP means qualified fine powder re‑clumps after grinding/classification during pneumatic conveying, silo storage and transfer. It is caused by moisture absorption, static electricity, excessive particle collision, high residence time and improper flow aid. Once secondary agglomerates form, tap density drops and PSD becomes unstable, which seriously affects downstream electrode coating.
1. Control gas humidity and oxygen in conveying pipeline
LFP fine powder is highly hygroscopic. Water molecules act as a binder between particles and trigger agglomeration.
- Use dry carrier gas: dew point controlled below -40 ℃. For high-end grades, adopt nitrogen instead of air.
- Keep the whole conveying system airtight; prevent ambient humid air from leaking into negative-pressure pipelines.
- Maintain low relative humidity (<40% RH) in silo rooms and packaging areas.
- Insulate pipelines to avoid cold wall condensation.
2. Optimize pneumatic conveying mode and velocity
High-speed dilute-phase conveying creates frequent particle-particle and particle-wall collisions, which compacts fine powder and forms soft agglomerates.
- Prefer dense-phase low-speed conveying for long-distance transfer. Low particle velocity reduces collision energy and minimizes re-agglomeration.
- If dilute negative pressure is required (short distance after the mill), limit airflow velocity reasonably. Do not blindly increase fan speed.
- Avoid sudden pipeline cross-section expansion, which causes powder deposition and stacking.
3. Static elimination design
Static charge makes fine LFP particles attract each other and stick to pipe walls, forming wall deposits that fall off as agglomerates.
- Continuously ground all equipment, pipelines, elbows and valves with low-resistance grounding cables.
- Use anti-static materials for contact surfaces: anti-static PU or ceramic lining.
- Install static eliminators at key transfer points such as cyclone outlet and silo inlet.
- Avoid sharp bends; use long-radius elbows to reduce friction charging.
4. Silo and buffer vessel design to avoid powder compaction
Fine LFP powder tends to bridge and compact under its own weight inside silos. Compaction leads to secondary agglomeration.
- Use mass-flow silo design instead of funnel flow, so powder flows uniformly without dead zones.
- Bin activators / low-pressure air fluidization at silo bottom: gentle fluidization to break bridging, avoid strong vibration or high-pressure air blasting (strong disturbance will increase agglomeration).
- Control silo filling height to reduce static pressure on the powder bed. Avoid long-term static storage inside silos.
- Shorten residence time: transfer powder to packaging promptly; do not store finished powder for extended periods.
5. Pipeline layout optimization
- Reduce the number of elbows, tee joints and diversion valves. Each bend increases particle friction and wall buildup.
- All elbows adopt long-radius ceramic-lined design.
- Use smooth inner surface for all wetted parts, reduce surface roughness that traps fine powder.
- Install periodic mild pulse blow cleaning for pipe wall deposits, prevent accumulated powder from peeling into agglomerates.
6. Process parameter matching at the grinding outlet
The powder status at mill outlet directly affects conveying stability.
- Control powder temperature: excessive heat from grinding increases electrostatic attraction; install cooling if necessary.
- Keep powder moisture low before entering conveying pipeline.
- Avoid over-grinding: ultra-fine submicron fractions raise the tendency of secondary agglomeration. Set the classifier cut point properly to reduce excess fines.
7. Optional trace flow aid (limited use for battery materials)
Only use after material validation, because additives may affect electrochemical performance.
- Trace fumed silica can reduce inter-particle adhesion, but battery customers often restrict foreign additives.
- Most LFP production lines avoid adding flow aids and rely purely on mechanical & gas environment control.
8. Online monitoring and early warning
- Install online PSD sampling points after conveying and before packaging, to detect secondary agglomeration in real time.
- Monitor dew point, static voltage, powder temperature and silo level.
- When agglomeration appears, the PLC automatically reduces conveying speed or adjusts carrier gas dew point.
The core strategy to prevent LFP secondary agglomeration during conveying is: low-humidity carrier gas, low conveying velocity, full static elimination, mass-flow silo design, minimized dead zones and short powder residence time. Dense-phase pneumatic conveying is the preferred transfer method for finished LFP powder, as it greatly reduces particle collision compared with dilute-phase conveying.
