Lithium battery pole piece burrs refer to tiny protrusions or uneven defects on the edge during the pole piece cutting or slitting process. Burrs can cause internal short circuits in the battery, increase self-discharge, and even thermal runaway, which is a key issue affecting battery safety and performance. The following is a systematic analysis of its causes and solutions:
Causes of burrs
1.Material factors:
- Current collector material: Copper foil or aluminum foil has insufficient ductility (such as too high hardness), and is easy to break and form burrs when cutting.
- Pole coating characteristics:
- Poor adhesion between the coating and the current collector, the coating peels off and forms burrs when cutting;
- Uneven coating (too thick or cracked edges), rough edges after cutting.
- Drying process defects: Insufficient drying after coating leads to low mechanical strength of the coating, which is easy to break when cutting.
2.Process factors
- Die-cutting tool status:
- The tool is worn, blunted or has an uneven edge, making it impossible to achieve clean cutting;
- The tool and the pole piece material are poorly matched (such as improper tool angle or material).
- Die-cutting parameter settings:
- Cutting pressure and speed do not match (excessive pressure causes material tearing, and too fast speed causes edge burrs);
- Improper die-cutting temperature control (such as heat-affected zone causing material deformation during laser cutting).
- Pole piece tension control:
- Uneven tension during winding and unwinding, pole piece shifts or vibrates during cutting;
- Uneven support platform for pole piece, uneven local force during cutting.
3.Environmental and equipment factors
- Workshop cleanliness: Dust pollution adheres to the surface of the tool or electrode, interfering with cutting accuracy.
- Equipment vibration: The mechanical stability of the die-cutting machine or slitting machine is insufficient, resulting in deviation in cutting action.
Solutions
1.Material optimization
- Improvement of current collector:
- Use high-purity copper foil/aluminum foil with better ductility (such as adding trace alloy elements);
- Adjust the hardness and toughness of the current collector through annealing process.
- Coating optimization:
- Improve the dispersion of slurry and ensure coating uniformity (such as optimizing the stirring process);
- Increase the adhesion between the coating and the current collector (such as adding high-performance binders PVDF or CMC);
- Optimize the drying process (gradient heating, precise humidity control) to enhance the mechanical strength of the coating.
2.Process Improvement
- Tool management and parameter adjustment:
- Regularly check the degree of tool wear and replace or grind in time;
- Optimize tool angle (such as using sharp cutting edge and reducing tool gap);
- Adjust cutting parameters (reduce cutting speed and pressurize in stages to reduce stress concentration).
- Tension and equipment stability control:
- Install high-precision tension sensors to achieve dynamic tension closed-loop control;
- Strengthen equipment rigidity and reduce vibration (such as using shock-proof platforms and regularly calibrating transmission components).
- Laser cutting replaces traditional die cutting:
- Using ultra-short pulse laser (such as picosecond/femtosecond laser) to reduce heat-affected zone and improve cutting accuracy;
- Optimizing laser parameters (power, frequency, spot size) to adapt to different pole piece thicknesses.
3.Environment and detection methods
- Environmental control:
- Maintain constant temperature and humidity in the workshop (such as temperature 25±2°C, humidity ≤30%);
- Add dust removal equipment (such as HEPA filter) to reduce dust pollution.
- Online inspection and sorting:
- Introducing the automatic optical inspection (AOI) system to monitor the edge quality of the electrode in real time;
- Combining AI image recognition technology to automatically remove the electrode with excessive burrs.
4.Post-processing technology
- Burr grinding: Use precision brushes or plasma treatment to remove tiny burrs on the edge of the pole piece;
- Edge coating repair: Repair coating damage caused by cutting through local re-coating or infiltration process.
Industry Trends and Innovation Directions
- Intelligent cutting process: Based on big data and machine learning, cutting parameters are adjusted in real time to adapt to material fluctuations.
- Composite current collector applications: such as copper-polymer-copper (CPC) composite foil, which improves ductility and reduces cutting burrs.
- Dry electrode technology: Through solvent-free dry coating process, the brittleness of the coating caused by solvent residue is avoided, and the burrs are indirectly reduced.
The control of pole piece burrs requires coordinated optimization from multiple dimensions of materials, processes, and equipment. The core lies in improving cutting accuracy and material adaptability. In the future, with the application of laser technology, intelligent detection and new materials, the burr problem is expected to be further reduced, thereby improving the safety and consistency of lithium batteries.
