Exploring the Wrinkling of Lithium-ion Battery Electrode Coating

In the precision domain of Lithium-ion Battery manufacturing, the coating process stands as a core link, exerting a crucial influence on the quality of electrode sheets and the ultimate performance of batteries. Imagine that a lithium - battery is like the "heart" of an electronic device, and the electrode sheet is a key structure of this "heart". The quality of coating directly determines whether the "heart" can beat stably and efficiently. However, in the actual production process, the thorny problem of wrinkling in electrode - sheet coating persists. It is not only like a "destroyer" lurking in the dark, quietly eroding product quality, but also greatly affects production efficiency and cost control. Today, let's delve into the mysteries behind the wrinkling of electrode - sheet coating together, providing comprehensive and practical countermeasures for practitioners in the lithium - battery industry.

I. Wrinkling of Coated Electrode Sheets: A "Performance Killer" Not to Be Ignored
Once wrinkling occurs in coated electrode sheets, its impact is far more than just a matter of surface aesthetics. Analyzing from the perspective of battery performance, this problem is like a "time - bomb", potentially triggering a series of serious consequences at any time.
The risk of electrode - sheet short - circuit is like a sword hanging high. The presence of wrinkled areas disrupts the original well - insulated and orderly - arranged electrode - sheet structure. The distance between the positive and negative electrodes is abnormally shortened in local areas, creating conditions for short - circuits. Once a short - circuit occurs, the current inside the battery will get out of control, not only causing the battery to fail instantly but also potentially leading to more serious safety issues such as heating and fire.

The occurrence of lithium - plating is also a major hidden danger brought about by wrinkled electrode sheets. Due to uneven coating, there are differences in electrode thickness in different parts. This makes the deposition and dissolution of lithium during the charging and discharging process of the battery unable to proceed uniformly. In some areas, the deposition rate of lithium is too fast, forming lithium dendrites. Lithium dendrites are like sharp "thorns". As the battery continues to charge and discharge, they may gradually grow and penetrate the separator, ultimately leading to a short - circuit between the positive and negative electrodes, seriously affecting the consistency and safety of the battery.

Moreover, the decline in the battery's cycle performance is also closely related to the wrinkling of electrode sheets. The wrinkled electrode sheets cannot maintain a stable structure and good contact inside the battery, which will hinder the reaction kinetics during the charging and discharging process of the battery. As the number of cycles increases, the attenuation rate of battery capacity accelerates, and the cycle life is thus greatly shortened. For lithium - battery application scenarios that pursue long life and high performance, this is undoubtedly a fatal blow.
II. Multidimensional Exploration: The Root Causes and Solutions of Wrinkling in Coated Electrode Sheets
(I) Slurry: The "Sorrow" of the Foundation
1. The Subtle Balance of Slurry Viscosity

Slurry viscosity is like a precise balance. Both too high and too low viscosities will disrupt the uniformity of coating. When the viscosity is too high, the slurry becomes "thick and viscous", making it difficult to spread smoothly on the substrate during the coating process, and prone to local accumulation. When the viscosity is too low, the slurry is like an "uncontrolled water flow", unable to adhere evenly to the substrate, resulting in phenomena such as dripping and missing coating.
Solutions: According to the precise requirements of the coating process, just like a fine bartender, adjust the slurry viscosity to the optimal range by subtly changing the solvent ratio or adding an appropriate amount of thickener/diluent. At the same time, use a rheometer, a "precision detector", to carefully test the viscosity curve, ensuring that the fluidity of the slurry at different shear rates can perfectly match the coating process.
2. Precise Control of Solid Content

Fluctuations in solid content are one of the important factors causing wrinkling of electrode sheets. When the solid content is too high, it is like applying a strong "shrinking force" to the coating during the drying process. The shrinkage stress of the coating increases during drying, resulting in uneven tension and thus wrinkles. When the solid content is too low, the slurry becomes "weak and powerless", unable to adhere firmly to the substrate, and may even slip during the coating process, causing uneven stress on the substrate and ultimately leading to wrinkling.
Solutions: During the slurry preparation process, strictly control the solid - content ratio in the slurry formula, like a guard strictly guarding a treasury. Use precision metering equipment to ensure that the feeding of each raw material is accurate. At the same time, regularly detect the solid content of the slurry, just like a doctor regularly checking a patient's physical indicators. Once fluctuations are detected, adjust the stirring and mixing time in a timely manner to ensure the uniformity of the slurry.
3. The Key Mission of Slurry Dispersion

Uneven slurry dispersion is like having "lumps" in a pot of delicious soup. Local aggregation of particles causes the local thickness of the coating layer to increase abnormally. This not only破坏了 the flatness of the coating but also can cause the substrate to bend or wrinkle.
Solutions: Use high - efficiency dispersion equipment, such as a high - speed mixer, which is like a powerful "mixing master", to fully disperse the particles in the slurry. Or optimize the homogenization process to fundamentally ensure that the slurry is uniform and free of particle agglomeration.
(II) Substrate: The "Foundation" of Stability

1. The Principle of Uniform Substrate Tension During the coating process, the tension of the substrate is like a tightly - stretched string. Any unevenness may cause "out - of - tune" situations. Unilateral tight - loose differences in the transverse width or longitudinal tight - loose fluctuations will lead to uneven tension distribution and thus wrinkling.
Solutions: First, you can try to replace the substrate with a higher - quality one or appropriately increase the unwinding tension of the substrate, but be careful not to overdo it, just like grasping the tightness of a string. At the same time, detect and correct the deformation of the substrate during the production process in a timely manner.
2. The Art of Matching Substrate Tension Mismatched substrate tension is like two people walking together with inconsistent paces, prone to "stumbles". The appearance of vertical and oblique wrinkles is often closely related to mismatched substrate tension.
Solutions: Follow the principle that "the thinner the substrate and the narrower the width, the smaller the tension", just like following the laws of nature. In equipment operation, use the setting methods of constant - tension unwinding and taper - tension winding to ensure that the substrate is always in a stable tension state throughout the coating process.
3. Countermeasures for the Deformation of the Substrate Itself Different substrates, such as ultra - thin copper - aluminum foils and composite copper - aluminum foils, may undergo irreversible deformation under the action of temperature or tension, like being under a magic spell, resulting in wrinkling phenomena such as orange peel or bulging.
Solutions: Without affecting the drying effect, appropriately reduce the temperature of the heating roller or the oven, just like cooling down a feverish patient. At the same time, reduce the unwinding tension and appropriately increase the winding tension. By adjusting the balance of tension, relieve the deformation of the substrate.
4. Solutions for Substrate Edge Sagging Slight edge sagging of the substrate may still勉强 maintain production under the action of reducing tension and adjusting the regulating roller, but severe edge sagging is like a large crack in the foundation of a house. The material is extremely prone to wrinkling when passing through the roller.
Solutions: Decisively replace the substrate material with a higher - quality one to fundamentally solve the problem and ensure the smooth progress of production.
(III) Operation and Process: The "Essence" of Precision

1. The Importance of Tape - Joining Standards Improper operation during tape - joining is like misaligning the links when connecting a chain, resulting in unbalanced foil - tape tension and thus wrinkles.
Solutions: Follow the standard operating procedures for tape - joining strictly, with every step being accurate to ensure the balance of foil - tape tension, just like building a stable bridge.
2. The Necessity of Correct Tape - Threading When threading the tape without using the centering mode, it is like a person not walking on the right path, which will make the unwinding mechanism unstable and thus cause wrinkles.
Solutions: During the tape - threading process, ensure that the tape is threaded in the centering mode to keep the unwinding mechanism in a stable state at all times, laying the foundation for the smooth progress of the coating process.
3. Control Strategies for Tension Fluctuations Unreasonable speed setting of the tension roller or large fluctuations in the equipment motor frequency are like an unstable - speed car, which is likely to cause tension changes during the coating process and lead to wrinkling.
Solutions: First, ensure that the speed of the traction roller matches the coating speed perfectly to avoid tension fluctuations caused by speed differences. Second, regularly check the operating status of the equipment motor, just like checking the engine of a car, to ensure that the motor frequency fluctuation is within the allowable range. Once abnormal frequency fluctuations are detected, repair or replace the problem components, such as the motor controller or drive system, in a timely manner. In addition, install a real - time tension monitoring system, which is like installing an "intelligent brain" for the equipment. It can detect tension changes in real - time during operation and adjust automatically. Adopt closed - loop control technology to ensure that the tension is always maintained within a stable range. At the same time, regularly lubricate mechanical components to reduce the impact of equipment wear on tension fluctuations. Check whether the tension roller and its related components have abnormal looseness or wear and replace them in a timely manner.
4. Rational Adjustment of Heating Temperature When the solid content of the slurry is low and the coating layer is thick, high temperature and high wind frequency are required to dry the slurry. However, during the rapid drying process, the surface tension of the foil and the slurry changes. Especially, the slurry will shrink and wrinkle like a heated dough under the influence of temperature.
Solutions: Appropriately reduce the coating speed and at the same time reduce the heating temperature, just like slowing down a fast - running athlete, to make the drying process more stable and avoid wrinkling of the electrode sheet caused by excessive temperature changes.
5. The Key Role of Wind - Frequency Balance Uneven air volume at the upper and lower air outlets of the oven is like a strong wind blowing from one side, which will cause the electrode sheet to be unevenly stressed in the oven, shake greatly in the oven, resulting in cracking of the electrode sheet and even curling in severe cases.
Solutions: Fine - tune the opening of the upper and lower air nozzles of the coating, just like adjusting the water flow of a faucet, to accurately control the air volume until the coated strip passes through each section of the oven smoothly without shaking.
6. Optimization of Coating Thickness Selection Excessive coating thickness or high viscosity is like putting on overly thick clothes for a person, which may cause the substrate to slide and lead to wrinkling. **Solutions**: Reduce the coating thickness or choose a binder with a lower viscosity to make the coating more lightweight and adherent, avoiding wrinkling caused by coating problems.
(IV) Equipment: The "Precise Tool"

1. Adjustment of the Parallelism of Guide Rolls From the perspective of equipment installation, even for equipment with extremely high precision, after long - term operation, due to the action of various tensions during the running of the coated sheet, the guide rolls may shift like a pushed - over benchmark. In actual production, when wrinkles occur, inexperienced personnel often blindly adjust the guide rolls, ignoring other real causes, making the non - parallelism of the guide rolls the main problem affecting wrinkling.
Solutions: First, measure and observe whether the left and right diameters of a single non - parallel guide roll are consistent. If not, directly replace the guide roll. If the left and right diameters are consistent, fine - adjustment is required. The specific adjustment method is as follows: Select a good reference point, first visually judge the parallelism, carefully observe the gap between the guide rolls, and then use auxiliary tools to measure. The most practical measurement method in engineering is to use a tape measure to bypass two guide rolls to form a closed - loop ellipse and read the circumference, and make corresponding adjustments according to the data differences, just like giving the equipment a precise "physical examination".
2. Inspection and Tightening of Roller Fastening Screws Loose roller fastening screws are like loose screws in a house, which will destroy the parallel state of each roller. At this time, wrinkling will occur accordingly.
Solutions: Regularly check the state of roller fastening screws. Once looseness is found, adjust and tighten them in a timely manner to ensure that each roller always maintains a stable parallel state.
3. Maintenance of Roller Surface Quality When the roughness of the roller surface exceeds the tolerance, it is not smooth enough and has obvious processing textures, which is like a bumpy road surface, causing wrinkling of the foil tape. If there are foreign matters adhered to the surface of the back roller and each passing roller, it will also affect the coating effect.
Solutions: For the situation where the roughness of the roller surface exceeds the tolerance, ask the manufacturer to replace it. If there are foreign matters adhered to the roller surface, clean them in a timely manner and pay attention not to damage the roller surface during the cleaning process to ensure that the roller surface always maintains a good state.
4. Optimization of Composite Pressure There may be unreasonable or improper installation of the cylinder, structure, and rubber roller in the equipment, resulting in inconsistent pressure on both sides of the rubber roller. In addition, the production switching of different - width products, especially when switching from a narrow - width to a wide - width product, will also cause uneven stress on the rubber roller, leading to indentation marks and even wrinkling.
Solutions: Regularly conduct carbon - paper tests, like giving the equipment a "pressure test", to check whether the composite pressure is consistent and adjust according to the results. Appropriately reduce the composite pressure to avoid excessive pressure settings. At the same time, reasonably arrange the production plan to avoid only producing narrow - width products for a long time, so that the rubber roller can be evenly stressed.
5. Precise Adjustment of Both - End Gaps In transfer - type coating, the both - end gaps refer to those between the coating roller and the back roller. In slit - extrusion coating, the both - end gaps refer to those between the lip and the substrate. Inconsistent both - end gaps are like asymmetrical blades of scissors, which will cause wrinkling of the electrode sheet.
Solutions: During the coating process, whether coating the first side or the second side, the operator should carefully adjust the both - end gaps, just like treating a precision instrument. Use precision tools such as feeler gauges and gap gauges to accurately measure and adjust to ensure the consistency of both - end gaps. At the same time, check the wear condition of the roller surface and repair or replace it in a timely manner. Introduce sensing equipment to real - time detect the state of both - end gaps and pressure distribution during the coating process, like installing a "real - time monitoring eye" for the equipment, and adjust in a timely manner. Add a gap - calibration link during product change - over or process adjustment to ensure that the equipment is always in the best state.
6. Rational Handling of Forced Deviation Correction If the deviation - correction device does not match properly or is not corrected reasonably when the substrate is running, it will lead to forced deviation correction. Especially when the unwinding and winding positions are not in a straight line, it is prone to snake - like phenomena or forced wrinkling.
Solutions: First, turn off the unwinding or winding deviation - correction device, let the substrate reach a stable position through natural running, and then turn on the deviation - correction, just like letting a lost ship adjust its course by itself first. Second, make good deviation - correction position markings and fix the reference positions of unwinding and winding to provide a stable reference for subsequent production.
7. Solutions for the Eccentricity of the Air - Expansion Shaft When one side of the air - expansion shaft has air and the other side has no air, the overall roll shape will become a "bullet - head shape", resulting in uneven stress and thus wrinkles.
Solutions: Replace the problematic air - expansion shaft in a timely manner. Before use, check whether the air - expansion shaft has air leakage or uneven inflation, just like checking whether a car tire has a leak, especially whether the airbag and sealing components are damaged. Once it is found that the air - expansion shaft cannot maintain uniform inflation, replace it immediately to avoid affecting the continuity of production. At the same time, strengthen the management of inflation operations. During operation, inflate evenly from both ends to ensure the pressure balance inside the air - expansion shaft. Set an appropriate air pressure according to the thickness of the substrate and the requirements of the coil tension to avoid insufficient or excessive inflation.
III. Conclusion

In the complex process of lithium - battery electrode - sheet coating, the wrinkling problem is like a puzzle hidden in a maze, involving multiple dimensions such as raw materials, substrates, equipment, and processes. Exploring its root causes and finding effective solutions not only requires us to have keen observation and rigorous analysis capabilities but also demands that we maintain a high degree of focus and a pursuit of excellence in every link. Through the comprehensive analysis of the causes of wrinkling in coated electrode sheets and the detailed elaboration of corresponding solutions in this article, it is hoped that it can provide practitioners in the lithium - battery industry with a practical "puzzle - solving guide", helping everyone effectively reduce the incidence of wrinkling problems in the production process, improve the quality of electrode - sheet coating, and inject strong impetus into the development of the lithium - battery industry. Let's work hand in hand, continue to explore on the path of pursuing excellence, and strive hard to promote lithium - battery technology to a new height.