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Continuous Drying Furnaces for Lithium-Ion Battery Electrode Substrate Dehydration (Absolute Drying) Processes

Achieving a Continuous Dehydration (Absolute Drying) Process

NGK has successfully combined its proprietary wavelength-control heater with a slalom configured roll-to-roll furnace that allows continuous conveying, transforming the conventional batch process for lithium-ion battery electrode substrate dehydration into a continuous process. This eliminates deformation defects and reduces drying times, revolutionizing the manufacturing process.

Schematic image of slalom-configured roll-to-roll furnace

Conventional Lithium-Ion Battery Electrode Substrate Dehydration (Absolute Drying) Process and Issues Involved

The most common lithium-ion battery electrode substrate dehydration (absolute drying) process is vacuum batch drying. Vacuum batch drying raises the following issues:

(1)Dehydration (absolute drying) processing is performed in batches

Using vacuum batch drying furnaces for dehydration (absolute drying) processes creates the following issues due to the long processing times required for vacuum batch drying furnaces:

  • Roll inventory awaiting drying builds up, forming bottlenecks.
  • A drying chamber is required for the roll inventory. This chamber takes up space and requires temperature and humidity control.
The dehydration (absolute drying) process following continious production is performed in batches.

(2)Dehydration processing in roll form

Using vacuum batch drying furnaces for dehydration (absolute drying) processes creates the following issues due to dehydration being performed in roll form:

  • Productivity is reduced by the long processing time taken until complete dehydration (absolute drying).
  • Drying in roll form results in uneven drying between the roll exterior and center.
  • Drying in roll form and in a vacuum causes sheet deformation.

Features of Slalom-Configured Roll-to-Roll Furnaces Using Wavelength-Control Heaters

Replacing vacuum batch drying furnaces with NGK slalom-configured roll-to-roll furnaces incorporating wavelength-control heaters offers the following advantages:

(1)Allows continuous dehydration (absolute drying).

The dehydration (absolute drying) process is performed continuously for each roll. This provides the following benefits:

  • Eliminates the need for roll form drying space.
  • Eliminates the need for drying chamber temperature/humidity control.
The roll-to-roll furnaces allow continuous dehydration (absolute drying).

(2)Enables sheet form dehydration (absolute drying).

Dehydration is possible in sheet form in the dehydration (absolute drying) process. Sheet form drying provides the following benefits:

  • Cuts the processing time required to achieve complete dehydration (absolute drying), improving productivity.
  • Eliminates overlapping of the sheets for uniform drying.
  • Sheets do not deform.
Figure comparing drying in rolls and drying in sheets.

(3)Allows dehydration (absolute drying) at low temperatures.

NGK’s proprietary wavelength-control heater (patented) enables rapid dehydration (absolute drying) of moisture from thousands of ppm to hundreds of ppm at atmospheric pressure and low temperatures (100 to 200 °C).
The wavelength-control heater incorporates the world’s first technology that allows selective emission of infrared radiation at the wavelengths absorbed by the solvent, allowing solvent drying without raising the temperature of the coating layer or substrate.

Wavelength-control heater

(4)Energy savings and CO2 reductions

A drying chamber is no longer required for rolls, halving the amount of dry air needed and helping to reduce energy consumption and CO2 emissions.

(5)Space savings

The slalom-configured roll-to-roll furnace (patented) is more compact than conventional straight-configured roll-to-roll furnaces. This saves still more space beyond the process space saved by eliminating the roll drying chamber.

Figure showing space saving.

Summary of Features

Item Vacuum batch type Slalom-configured roll-to-roll furnace incorporating wavelength-control heaters Remarks
Productivity Poor due to batch system Continuous production for each roll Eliminates the need for vacuum and drying chamber; eliminates inventory buildup awaiting dehydration (absolute drying).
Dehydration time/temperature Approx. 1 day Approx. 10 mins Cuts dehydration times to less than 1/100, even at the same dehydration temperature.
Dehydration (absolute drying) performance Approx. 1,000 ppm Approx. 200 to 600 ppm Improves dehydration (absolute drying) performance.
Substrate dehydration variations Susceptible Does not occur Dehydrates substrate (absolutely dry) while spread out, eliminating dehydration variations.
Substrate deformation Susceptible Does not occur Dehydrates lithium-ion battery electrode substrate (absolutely dry) at normal pressure, eliminating deformation.
Energy savings/CO2 reductions - More energy efficient than vacuum batch system Eliminating the roll drying chamber cuts dry air volumes by more than half.
Space savings - Space savings compared to vacuum batch system Requires less than half the space taken by a vacuum batch furnace; eliminates the need for drying chamber space.

Test Facility

NGK provides a slalom-configured roll-to-roll furnace incorporating wavelength-control heaters for test purposes to allow customers to perform test drying using actual production conditions before purchasing. This allows testing under a wide range of conditions while adjusting parameters such as dew point, feed speed, furnace internal gas flow rate, and heater output to suit individual film and substrate coatings (solvent type, thickness, initial moisture content) and requirements and restrictions, such as temperature resistance.

Overview of test facility
Inside the drying chamber

Test Facility Specifications

Item Specifications
Film/substrate width Max. 700 mm
Film/substrate length (in-out) 13.2 m
Film/substrate thickness 100 to 200 µm
Roll diameter Max. 400 mm
Core 3-inch or 6-inch (adapter compatible)
Feed speed 10 to 200 m/min
Tension control Normal: 50 to 150 N (supported range: 10 to 200 N)
Furnace internal temperature Normal: 80 to 200 °C (supported range: 50 to 250 °C)
Cleanliness level 10,000
Atmosphere Atmospheric air, dry atmosphere (atmospheric air, dew point -40 °C)
Heaters 33 sets, with individual variable output control (max. 120 kW)
Utilities Electricity: 200 V, 3-phase, 600AT/600AF
Supply/exhaust: 10 Nm3/min
*Also compatible with 380 V.

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