Apparatus and Method for Processing Battery Electrodes

Abstract

An apparatus for processing battery electrodes includes: a microwave applicator cavity with slots on opposite ends to allow a continuous sheet to move through the cavity in a first direction; a processing chamber constructed of microwave-transparent material, disposed within the applicator cavity and surrounding the continuous sheet, the processing chamber having slots to allow the continuous sheet to pass through it; a microwave power supply to deliver power to the applicator cavity; a source of heated gas providing a controlled gas flow through the processing chamber in a direction opposite the first direction; and, at least one non-contacting temperature measuring device positioned to measure a surface temperature at a selected location on the continuous sheet as it passes through the processing chamber. The apparatus is particularly suited for removing polar solvents from porous electrode coatings. A related method is also disclosed.

We claim: 
     
         1 . A method for processing battery electrodes comprising:
 depositing an electrode material as a wet slurry containing a solvent onto a continuous substrate;   passing said coated substrate through a microwave-transparent processing chamber disposed within a microwave applicator cavity; and,   applying microwave power to said applicator cavity to heat said solvent while simultaneously introducing heated gas from a source external to said processing chamber so that said gas passes through said processing chamber in the direction opposite to the direction of movement of the coated substrate in order that dry gas enters said processing chamber adjacent to the dry end of said coated substrate and moist gas exits said processing chamber adjacent to the wet end of said coated substrate.   
     
     
         2 . The method of  claim 1  wherein said coating is deposited on said substrate by a process selected from the group consisting of: casting; doctor blading; spray coating, dip coating, screen printing, and extrusion. 
     
     
         3 . The method of  claim 1  wherein said solvent is a polar solvent selected from the group consisting of: water; N-methyl-2-pyrrolidone, ethanol, methanol, isopropanol, acetone, n-propanol, n-butanol, formic acid, propylene carbonate, ethyl acetate, dimethyl sulfoxide, acetonitrile, dimethyl formamide, tetrahydrofuran, and dichloromethane. 
     
     
         4 . The method of  claim 1  wherein said microwave power is supplied in a sweeping fashion over a selected bandwidth. 
     
     
         5 . The method of  claim 3  wherein said heated gas is introduced at a temperature less than 240° C. 
     
     
         6 . The method of  claim 1  wherein said moist gas is extracted from said processing chamber at a rate equal to the rate at which said heated gas is introduced into said processing chamber so that neutral pressure is maintained in said processing chamber. 
     
     
         7 . The method of  claim 1  further including the step of pre-drying said gas to a selected relative humidity before heating and delivering said gas to said processing chamber. 
     
     
         8 . The method of  claim 1  further including the step of calendaring said coated substrate after it exits from said processing chamber. 
     
     
         9 . The method of  claim 1  further including the step of passing said coated substrate through a heated drying oven after it exits from said processing chamber. 
     
     
         10 . The method of  claim 1  wherein said electrode material contains a binder phase and said coating is dried at such a rate that the concentration of said binder adjacent to a free surface is no more than 1.3 times the concentration of said binder adjacent to said substrate. 
     
     
         11 . A method for processing battery electrodes comprising:
 depositing an electrode material as a wet slurry containing a selected solvent onto a continuous substrate;   passing said coated substrate through a microwave-transparent processing chamber disposed within a microwave applicator cavity;   applying microwave power to said applicator cavity to heat said solvent while simultaneously introducing heated gas from a source external to said processing chamber so that said gas passes through said processing chamber in the direction opposite to the direction of movement of the coated substrate in order that dry gas enters said processing chamber adjacent to the dry end of said coated substrate and moist gas exits said processing chamber adjacent to the wet end of said coated substrate; and,   passing said coated substrate out of said applicator cavity and through a second chamber for further processing via conventional heating.   
     
     
         12 . The method of  claim 11  wherein said wet slurry is deposited on said substrate by a process selected from the group consisting of: casting; doctor blading; spray coating, dip coating, screen printing, and extrusion. 
     
     
         13 . The method of  claim 11  wherein said solvent is a polar solvent selected from the group consisting of: water; N-methyl-2-pyrrolidone, ethanol, methanol, isopropanol, acetone, n-propanol, n-butanol, formic acid, propylene carbonate, ethyl acetate, dimethyl sulfoxide, acetonitrile, dimethyl formamide, tetrahydrofuran, and dichloromethane. 
     
     
         14 . The method of  claim 11  wherein said microwave power is supplied in a sweeping fashion over a selected bandwidth. 
     
     
         15 . The method of  claim 13  wherein said heated gas is introduced at a temperature less than 240° C. 
     
     
         16 . The method of  claim 11  wherein said moist gas is extracted from said processing chamber at a rate equal to the rate at which said heated gas is introduced into said processing chamber so that neutral pressure is maintained in said processing chamber. 
     
     
         17 . The method of  claim 11  further including the step of pre-drying said gas to a selected relative humidity before heating and delivering said gas to said processing chamber. 
     
     
         18 . The method of  claim 11  further including the step of calendaring said coated substrate after it exits from said processing chamber. 
     
     
         19 . The method of  claim 11  wherein said electrode material contains a binder phase and said coating is dried at such a rate that the concentration of said binder adjacent to a free surface is no more than 1.3 times the concentration of said binder adjacent to said substrate.