What Are the Common Defects in Lithium-ion Battery Electrode Calendering?

A detailed analysis of 12 issues, their causes, and improvement measures

Calendering is a core process in the manufacturing of lithium-ion battery electrodes, directly determining the energy density, cycle life, and safety of the battery cell. In actual production, various defects can easily occur after calendering due to factors such as equipment, process parameters, and materials. Drawing on technical data from "Lithium-ion Battery Experts" (Lidianpai), this article systematically outlines the identification criteria and control measures for 12 types of common defects, providing a reference for on-site process optimization.

Strip breakage is the most severe failure in calendering, primarily caused by five major risk factors:

1. Hard particles/impurities: These puncture the foil, manifesting as bright spots detected by CCD, pinholes in the foil, or indentations on the roller surface. Control measures include strictly managing coating cleanliness and performing microscopic inspection on the first article.

2. Sudden changes in thickness/areal density: Excessive stress occurs at the transition between thick and thin sections; issues include online thickness deviations exceeding ±2μm, spikes in the areal density curve, and micro-cracks at porosity sites. It is necessary to stabilize coating quality and eliminate thickness fluctuations.

3. Loss of closed-loop pressure control: Instantaneous pressure spikes exceeding 15% or increased roller gap deviation. Appropriate linear loads must be matched, and pressure curves monitored with alarms set for limit violations.

4. Tension fluctuations: Fluctuations exceeding ±5%, frequent EPC (Edge Position Control) corrections, or uneven winding. Tension across the entire line must be stabilized, and linked deceleration protection implemented.

5. Roller surface material adhesion/damage: Periodic defects on the electrode (spacing equals roller circumference) or scratches on the roller surface. Regular cleaning of the roller surface and the establishment of inspection and replacement standards are required.

ACEY-MRP100L electrode calendering machine is mainly suitable for manual rolling of battery materials in the laboratory. It is especially suitable for thinning and increasing the density of lithium battery pole plates of clean energy materials . This machine adopts gear transmission to realize the roll pressing, the rolling thickness can be adjusted, and it is easy to use.

Roller adhesion leads to coating transfer and strip breakage; the primary causes are excessive residual solvent (>0.5%) or insufficient drying. Identification criteria include tearing marks on the electrode surface, material buildup on the roller, and a tacky coating. Control measures include optimizing the oven temperature gradient to strictly control residual solvent levels to ≤0.3%; using hot calendering (85–110°C) to soften the binder; reducing calendering speed to lower peel force; and regularly cleaning the roller surface.

Thickness deviation can trigger lithium plating and winding difficulties. Transverse unevenness is often caused by uneven coating or unbalanced roll gaps; longitudinal unevenness usually stems from areal density drift or roll eccentricity. Detection: Online thickness gauge readings exceeding transverse/longitudinal tolerances; offline sampling showing excessive deviation. Control: Prioritize inspecting the coating process; activate AGC (Automatic Gauge Control) for closed-loop thickness control; regularly calibrate roll coaxiality; strictly control incoming material for wavy edges.

A springback rate ≥5% is abnormal and easily leads to uneven winding. The primary causes are material stress release and insufficient drying. Control measures include optimizing the formulation to reduce stress, extending drying time to fully remove moisture, and strictly controlling coating thickness tolerances.

Often caused by thick coating edges or non-parallel rolls. Prevention requires a trapezoidal transition at the coating edge and regular calibration of roll parallelism.

The coated area elongates while the uncoated area (margin) remains unchanged; the excess length forms waves. Causes: Excessive compaction density, small roll diameter, or tension mismatch. Prevention: Optimize compaction density design, select large-diameter rolls, match upstream and downstream tension, and verify wavy edge thresholds during first-article inspection.

Aluminum foil has poor ductility (deformation difference of 0.5%–1.2% between coated and uncoated areas); while performance isn't affected, quality control is. Prevention: Use IHA (Induction Heating) for pre-stretching the cathode (reducing deformation difference to <0.1%); use hot roll pressing at 60–100°C to improve aluminum foil ductility; for the anode, apply 3–5 layers of Teflon tape for adjustment.

Failure to meet compaction density targets directly reduces energy density. Primary causes: Insufficient pressure or excessively hard material. Control measures: Match pressure to material type (150–250 kN/m for NCM; 200–300 kN/m for LFP); control cathode particle size (D50 = 8–12 μm); mandate inspection of compacted density for the first unit and conduct spot checks every 2 hours.

Edge stress concentration leads to powder shedding or strip breakage. Prevention/Control: Use gradient pressurization (pre-compression at 80–100 kN/m followed by main compression); implement a trapezoidal transition at the coating edge; raise roller temperature to 40–60°C to soften the material; inspect edge condition on the first unit of every roll.

Caused by foreign matter during coating or excessive calendering pressure; affects safety. Control: Strictly control fluctuations in coating area density and prevent foreign matter contamination; avoid calendering pressures exceeding material limits; perform full-surface visual inspection on the first unit; use high-magnification microscopy to spot-check for pinholes and cracks.

Caused by foreign matter adhering to the roller surface or surface damage (roughness Ra > 0.2 μm). Control: Clean roller surfaces with anhydrous ethanol before calendering; regularly regrind or replace rollers; inspect roller surfaces before and during shifts; stop the machine immediately if periodic marks are detected.

Caused by roller surface wear, excessive bearing clearance, or uneven incoming material thickness, leading to electrode sheet slippage. Control: Regularly replace worn rollers and bearings; strictly control the thickness stability of incoming materials; standardize operations and prohibit arbitrary parameter adjustments; immediately investigate roller surfaces and incoming materials if thickness drift is detected.

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