Lithium Battery Coating Process: Main Causes of A&B Surface Misalignment and Related Improvement Measures

During the lithium battery coating process, misalignment of the A and B surfaces is a critical yet often overlooked issue that directly impacts battery capacity, safety, and cycle life. This misalignment manifests as deviations in coating areas or uneven thickness between the front and back surfaces, potentially leading to risks such as lithium plating and electrode sheet fracture. This article will analyze the multi-dimensional causes from equipment, process, material, and other aspects, while sharing key improvement measures to enhance battery quality consistency.

1. Main Causes of A&B Surface Misalignment

1.1Equipment Factors

Insufficient installation accuracy of backup roller/coating roller: Horizontal deviation, coaxial misalignment, or installation errors lead to coating displacement.

Positioning error of the coating head: Inadequate encoder/grating ruler precision or sensor signal drift.

Abnormal tension control: Uneven tension during unwinding/spooling causes foil stretching, deformation, or wrinkles.

1.2 Material Factors

Uneven ductility: Variations in foil ductility result in loss of control over coating gap.

Inadequate surface treatment: Surface oxides affect paste adhesion, indirectly causing positional deviation.

1.3Slurry Factors

Excessive viscosity: Poor leveling results in slurry accumulation and misalignment.

Significant surface tension differences: Uneven edge shrinkage of A/B side slurries.

1.4Process Parameters

Coating speed disparity: Different speeds between the two sides lead to inconsistent leveling rates.

Inconsistent drying conditions: Temperature differences in A/B side ovens cause varying substrate shrinkage.

2 Improvement Measures

2.1Equipment Optimization

Regularly calibrate coaxiality and horizontal alignment of coating rollers and backup rollers.

Replace high-precision encoders and grating rulers to ensure coating head positioning error ≤±0.1mm.

Optimize tension control systems (e.g., PID closed-loop control) to maintain substrate tension fluctuation ≤±3%.

2.2Foil Material Control

Select foils with consistent ductility (e.g., copper/aluminum foil with uniform tensile strength).

Enhance foil surface treatment processes (e.g., plasma cleaning or chemical passivation).

2.3Slurry Adjustment

Adjust slurry viscosity to optimal leveling range (anode: 10–12 Pa·s; cathode: 4–5 Pa·s).

Add surfactants (e.g., PVP or SDS) to balance surface tension differences between A/B side slurries.

2.4Process Parameter Optimization

Ensure A/B side coating speeds are consistent, with speed deviation <0.5 m/min.

Implement segmented temperature-controlled drying (low-temperature stage for stress relaxation, high-temperature stage for rapid curing), maintaining temperature difference ≤5℃.

3. Specific Troubleshooting Procedures

3.1Equipment Inspection

Use a laser interferometer to detect parallelism between coating rollers and backup rollers (error ≤0.02 mm/m).

Check servo motor and sensor signal stability (avoid signal drift exceeding 0.5% of full scale).

3.2Foil Evaluation

Sample testing for foil ductility (elongation at break deviation controlled within ±5%).

SEM observation of foil surface micropores/oxide layer thickness (must be <50 nm).

3.3Slurry Testing

Rheometer to measure A/B side slurry viscosity and thixotropic index (thixotropic loop area difference <5%).

Surface tensiometer to measure difference between two sides (must be <2 mN/m).

3.4Process Monitoring

Online laser thickness measurement system for real-time coating thickness monitoring (thickness fluctuation CV ≤1%).

Post-drying X-ray measurement of areal density (lateral consistency deviation <2%).

Conclusion: By implementing equipment calibration, material screening, slurry optimization, and closed-loop process parameter management, A&B surface misalignment can be controlled within ≤0.5 mm, ensuring consistent cell capacity and safety.