Ultrasonic Spray Coating 2D Materials on Copper Foil: Process Feasibility and Equipment Solutions for Lithium Battery Current Collectors
1. Project Background
In lithium battery materials research, some customers want to deposit 2D material aqueous dispersions uniformly onto copper foil surfaces to prepare functional interfacial thin films.
These materials may include graphene, graphene oxide, MXene, or other layered nanosheet materials.
The coating objective may be to improve interfacial contact between copper foil and anode materials, investigate conductive undercoatings, modify lithium metal deposition behavior, or develop other functional electrode layers.
Because 2D material aqueous dispersions may exhibit low solid content, nanosheet aggregation, and sensitivity to drying conditions, selecting an appropriate precision coating process is important.
Ultrasonic spray coating is one technical approach that can be evaluated for feasibility.
2. Basic Principle of Ultrasonic Spray Coating for 2D Materials
Ultrasonic spray coating equipment uses high-frequency vibration at an ultrasonic nozzle to atomize a suitable liquid dispersion into droplets.
The droplets are subsequently transported toward the copper foil surface by a controlled gas flow.
Using a precision liquid delivery system and programmable motion platform, the effects of liquid flow rate, scan speed, and number of coating passes can be investigated.
Unlike conventional processes designed to produce relatively thick wet films, ultrasonic spray coating can use multiple thin-layer deposition passes to gradually build up the target dry coating mass per unit area.
However, passing 2D material nanosheets through an ultrasonic nozzle does not necessarily make them thinner or improve their dispersion.
Nozzle compatibility must be confirmed through testing with the actual dispersion.
3. Feasibility Requirements for Ultrasonic Spray Coating of 2D Material Aqueous Dispersions
3.1 Adequate Dispersion Stability
The dispersion should maintain acceptable uniformity during liquid delivery and spraying.
If the material sediments or aggregates rapidly, coating loading may vary over time.
3.2 Nanosheet Size Compatibility with the Spray System
2D materials have lateral dimensions and may contain aggregates.
It is necessary to confirm that the material can pass through the liquid delivery system and nozzle consistently while maintaining acceptable atomization.
Spray compatibility cannot be determined solely from the material name.
3.3 Appropriate Wetting of Copper Foil
After the spray droplets reach the copper foil, they should form a deposition pattern compatible with the coating objective.
Insufficient wetting may cause dewetting and exposed regions.
Excessive spreading combined with high wet deposition amounts may result in flowing or localized accumulation.
3.4 Material-Compatible Drying Conditions
Water must be removed under suitable processing conditions.
Copper foil surface changes, 2D material oxidation, coating cracking, and nanosheet redistribution should all be considered during drying trials.
3.5 Compliance with Final Functional Requirements
A uniform coating appearance is only an initial indicator.
For conductive interfacial layers, electrical properties must be measured.
For lithium metal deposition research, lithium deposition behavior must be evaluated.
For silicon-based anode interfaces, bonding with the active material layer and cycling performance require further assessment.
4. Main Components of an Ultrasonic Spray Coating System
4.1 Precision Liquid Delivery System
The liquid delivery system transports the 2D material aqueous dispersion to the spray nozzle at a controlled rate.
Depending on dispersion characteristics, appropriate stirring or circulation methods may be investigated to reduce the effects of sedimentation.
4.2 Ultrasonic Spray Coating Module
The ultrasonic spray module atomizes the dispersion and produces the spray.
Nozzle selection should consider liquid properties, nanosheet dimensions, and the target coating area. The appropriate configuration must be established through practical testing.
4.3 Copper Foil Holding Platform
For sheet-based coating, a suitable flat holding mechanism can be used.
Thin copper foil may wrinkle or curl, so substrate flatness requires attention.
If vacuum holding is used, the system should be evaluated to ensure that the holding method does not cause unacceptable surface marks or damage.
4.4 Motion Control System
The motion control system manages the relative movement between the spray nozzle and copper foil.
Scan speed, spray path, spray pattern overlap, and multiple deposition passes can be investigated.
4.5 Drying System
The drying system removes water and helps form the target coating.
Controlled temperature, airflow, and residence time can be investigated according to material compatibility.
4.6 Exhaust and Safety System
2D materials may become airborne as aerosols during spraying. Appropriate enclosure, exhaust ventilation, and particle capture should therefore be considered.
Even when water is used as the dispersion medium, occupational exposure risks must be evaluated.
5. Recommended Sample Coating Process
Step 1: Confirm the Material and Coating Objective
The customer should provide the 2D material type, dispersion solid content, nanosheet size information, and solvent and additive composition.
Copper foil thickness, surface condition, target coating area, and final application should also be identified.
Step 2: Evaluate Dispersion Compatibility
First, test whether the dispersion can be delivered and atomized consistently.
Observe sedimentation, aggregation, abnormal spray behavior, or liquid delivery blockage.
If the dispersion is unstable, formulation issues should be addressed before simply increasing the number of spray passes.
Step 3: Evaluate Copper Foil Wetting
Perform small-area deposition trials using representative copper foil.
Observe droplet spreading, contraction, and surface coverage after drying.
If necessary, copper foil cleaning or other validated surface treatments can be investigated.
Step 4: Conduct Initial Single-Pass Spray Testing
Perform an initial spray trial on a relatively small area to confirm whether the spray can form an acceptable deposited layer.
Record liquid flow rate, scan speed, nozzle position, and substrate conditions.
Step 5: Investigate Multiple Thin-Layer Passes
After establishing single-pass feasibility, investigate whether additional scan passes help achieve the target coating.
The need for intermediate drying should be determined according to actual drying behavior.
Step 6: Dry and Inspect the Samples
After spraying, remove water under suitable conditions.
Inspect for coffee-ring patterns, dewetting, cracks, nanosheet aggregation, or poor adhesion.
Step 7: Perform Functional Testing
Conduct electrical, interfacial, or electrochemical testing according to the customer’s objectives.
Only appropriate functional validation can determine whether the coating meets the requirements of the intended battery application.
6. How to Calculate the Target Deposition Amount of 2D Materials
The amount of 2D material deposited can be expressed as dry mass per unit area.
Let:
- L = Target coating loading, in mg/cm².
- A = Coating area, in cm².
- m = Target deposited dry mass, in mg.
The relationship is:
m = L × A
For example, consider a hypothetical project used only to demonstrate the calculation:
- Copper foil coating area: 100 cm².
- Assumed target 2D material loading: 0.05 mg/cm².
The theoretical required dry mass is:
m = 0.05 × 100 = 5 mg
This is only a calculation example and does not represent a recommended coating loading.
If the dispersion contains other nonvolatile components, the mass of the 2D material itself must be distinguished from the total dry coating mass.
In addition, not all material delivered by the spray system will necessarily be deposited onto the copper foil.
Actual deposition efficiency must therefore be measured before determining the required dispersion volume.
7. Which Ultrasonic Spray Coating Parameters Need Optimization?
7.1 Dispersion Solid Content
Solid content affects the amount of dry material delivered per unit volume of liquid.
Very low concentrations may require more spray passes, while higher concentrations may influence dispersion stability and atomization.
7.2 Liquid Flow Rate
Liquid flow rate influences the amount of material entering the nozzle per unit time.
However, the actual coating loading also depends on deposition efficiency.
7.3 Nozzle-to-Substrate Distance
Spray distance affects the spray coverage area, droplet conditions upon reaching the substrate, and material utilization.
7.4 Scan Speed and Spray Pattern Overlap
Scan speed and overlap between adjacent spray paths affect in-plane coating distribution.
7.5 Copper Foil Temperature
Substrate temperature influences droplet wetting and water evaporation.
Excessively rapid drying may cause nanosheet accumulation, while prolonged wet-state residence time may also be undesirable.
7.6 Number of Spray Passes
Multiple thin-layer passes may help build up the target coating loading gradually.
However, if the previous layer is not sufficiently stable, subsequent droplets may rewet or disturb the existing coating.
8. How Should Coating Quality Be Evaluated?
A three-level evaluation approach is recommended.
8.1 Level One: Coating Appearance and Structure
Evaluate copper foil surface coverage, thickness distribution, nanosheet aggregation, and localized defects.
Depending on the sample, optical microscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), or other suitable techniques may be used.
8.2 Level Two: Interfacial and Electrical Properties
Depending on the target application, coating adhesion, surface resistance, contact resistance, and relevant material properties can be measured.
It is important to note that copper foil itself is highly conductive. Simply measuring the electrical resistance of the entire sample may not accurately represent the conductivity of the 2D material film.
8.3 Level Three: Battery Performance
If the objective is anode interface modification, testing should be performed in a relevant battery system.
Possible evaluations include cycling performance, impedance, rate capability, lithium deposition morphology, or other application-specific parameters.
Improved battery performance must not be inferred solely from coating uniformity.
9. From Sheet-Based Coating to Roll-to-Roll Copper Foil Processing
Once laboratory sample feasibility has been established, customers may consider increasing the coating area or adopting continuous copper foil processing.
A roll-to-roll ultrasonic spray coating system can be investigated as a subsequent equipment development option.
Potential system components include:
- Copper foil unwinding and rewinding.
- Precision web tension control.
- Continuous ultrasonic spray coating.
- Multiple spray nozzles or wide-area scanning.
- Multi-stage drying.
- Coating quality inspection.
However, the suitability of roll-to-roll production must be evaluated according to target throughput, copper foil width, material consumption, and drying requirements.
Successful small-area ultrasonic spray coating does not automatically demonstrate economic advantages at the intended industrial production speed.
10. Cheersonic Ultrasonic Spray Coating Equipment for 2D Material Coatings on Copper Foil
For lithium battery projects involving 2D material aqueous dispersions and copper foil substrates, Cheersonic can discuss precision ultrasonic spray coating processes and sample coating trials.
Customers can provide:
- 2D material type and dispersion information.
- Copper foil thickness and dimensions.
- Target coating area.
- Target dry coating loading or thickness.
- Current coating method and existing challenges.
- Single-sided coating requirements.
- Laboratory research or continuous production requirements.
Initial atomization testing, copper foil sample coating, and coating quality evaluation can help determine whether ultrasonic spray coating is suitable for the material system.
If further development is required, equipment automation and continuous processing options can then be investigated.
For more information about coating equipment solutions, visit:
Conclusion
Ultrasonic spray coating of 2D material aqueous dispersions onto copper foil is a precision functional coating process with potential value for experimental development.
Possible applications include lithium battery anode current collector modification, conductive interfacial layers, silicon-based anode research, and certain lithium metal battery interface engineering projects.
However, practical feasibility depends on dispersion stability, copper foil wettability, nozzle compatibility, drying behavior, and final battery performance.
For lithium battery manufacturers and research organizations, small-area sample coating trials are recommended to establish a suitable process window before selecting larger-area or continuous ultrasonic spray coating equipment.
