Patent Publication Number: US-2023160087-A1

Title: Method of producing a graphene film

Description:
RELATIONSHIP TO OTHER APPLICATIONS 
     This application claims the benefit of U.S. provisional patent application Ser. No. 63/282,178 filed Nov. 23, 2021 to the same inventors. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to graphene film production and, more particularly, to a method of producing a graphene film on an anode. 
     BACKGROUND OF THE INVENTION 
     Metal oxides are conventionally used in battery manufacturing. However, such materials have relatively low conductivity and tensile strength which often results in the battery quickly losing the ability to fully charge after a given number of cycles as well as not being able to handle the size fluctuations when the battery heats up and cools off. Graphene is a material having the very significant electricity and heat conductivity properties. Additionally, graphene is also over one hundred times stronger than steel making it suitable for physically demanding applications such as the expansion and compression of a battery as it gets hot and then cools. 
     Graphene is conventionally produced using micro mechanical exfoliation, chemical vapor deposition, graphite oxide reduction and organic synthesis. These methods, however, have many limitations such as being hard to produce high quality graphene, extremely high costs and oxidation or defects. Graphene has largely been too cost-prohibitive to use effectively in batteries. 
     SUMMARY OF THE INVENTION 
     A graphene composite film is produced for application to an anode for a battery. A graphene dispersion is peeled off of a graphite solvent ultrasonically. The graphene material is them mixed with organic amine salt to be charged. Electrophoretic deposition is used to turn the graphene into a film. The film is then passed through a heat treatment to remove the organic amine salt. The resulting film is a highly conductive graphene film with a two-dimensional structure. 
     A significant advantage provided by the present invention is that it is a low-cost process. Another advantage provided by the present invention is that it is easy to scale. 
    
    
     
       DESCRIPTION OF THE FIGURES OF THE DRAWINGS 
       The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and 
         FIG.  1    is a process diagram illustrating an exemplary embodiment of the present invention, according to a preferred embodiment of the present invention; 
         FIG.  2    is a process diagram illustrating exemplary details of step one of the exemplary process of  FIG.  1    of the present invention, according to a preferred embodiment of the present invention; 
         FIG.  3    is a process diagram illustrating exemplary details of step two of the exemplary process of  FIG.  1    of the present invention, according to a preferred embodiment of the present invention; 
         FIG.  4    is a process diagram illustrating exemplary details of step three of the exemplary process of  FIG.  1    of the present invention, according to a preferred embodiment of the present invention; and 
         FIG.  5    is a process diagram illustrating exemplary details of step four of the exemplary process of  FIG.  1    of the present invention, according to a preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG.  1    is a process diagram illustrating an exemplary embodiment of the process  100  for making and adhering a graphene film, according to a preferred embodiment of the present invention. In step  102 , equipment for the process is made ready, including an ultrasonic tank, a centrifuge, a vacuum furnace, and associated containers. In step  104 , a graphene dispersion is created, as will be described in more detail in regard to  FIG.  2   . In step  106 , the graphene dispersion is positively charged, as will be described in more detail in regard to  FIG.  3   . In step  108 , a conductive film is prepared by electrophoretic deposition, as will be described in more detail in regard to  FIG.  4   . In step  110 , the organic amine salt used to charge the graphene dispersion in step  106  is removed, as will be described in more detail in regard to  FIG.  5   . Step  112  is to collect the graphene-coated anode or anodes as the final product of the process. 
       FIG.  2    is a process diagram illustrating exemplary details of step  104  of the exemplary process  100  of  FIG.  1    of the present invention, according to a preferred embodiment of the present invention. Step  202  begins the step  104  of creating a graphene dispersion. In step  204 , graphite is added to an organic solvent in the ratio of graphite to organic solvent of 1 g:10 ml. The organic solvent is preferably NMP(1-methyl-2-pyrrolidone). In particular embodiments, the organic solvent may be, for non-limiting examples, acetone, methanol, or ethanol. The graphite and organic solvent mixture is placed in an ultrasonic chamber operating at 210 Watts for a period of between thirty minutes to one-hundred-twenty minutes to obtain a graphite dispersion. In step  206 , the graphite dispersion is placed in a vacuum furnace heated at a rate of ten degrees Celsius per minute under the protection of nitrogen. In step  208 , the graphite dispersion is heated for one to four hours at a temperature ranging from four hundred degrees Celsius to about eight hundred degrees Celsius and then passively cooled to room temperature to obtain solvent-intercalated expanded graphite. In step  210 , the solvent-intercalated expanded graphite is added to additional organic solvent to achieve a solid content of one gram of solvent-intercalated expanded graphite per liter of organic solvent. In step  212 , the solution created in step  210  is subjected to ultrasonic energy at two hundred and ten Watts for a period in the range of one hour to ten hours. In step  214 , the solution created in, step  212  is paced in a centrifuge and centrifuged at four thousand revolutions per minute for a period in the range of thirty minutes to one-hundred twenty minutes to obtain a graphene solid content in the graphene dispersion in the range of 0.01 grams of graphene per liter of organic solvent and 0.1 grams of graphene per liter of organic solvent.  FIG.  3    is a process diagram illustrating exemplary details of step  106  of the exemplary process  100  of  FIG.  1    of the present invention, according to a preferred embodiment of the present invention. The purpose of step  106  is to positively charge the graphene dispersion. In step  302 , the process continues with the graphene dispersion produced in step  212 . In step  304 , organic amine salt is dissolved, into the organic solvent in a ratio of one gram per liter to create an amine salt solution. The organic amine salt used is, for non-limiting examples, aniline hydrochloride or benzidine dihydrochloride, which contain aromatic structural groups and negative ions of Cl − , NO3 − , and SO4 2− . In step  306 , the amine salt solution is added to the graphene dispersion from step  212 . In step  308 , the solution created in step  306  is subjected to ultrasonic energy at two hundred and ten Watts for a period ranging from ten minutes to thirty minutes. In step  310 , the result of step  308 , a positively charged graphene dispersion, is collected. 
       FIG.  4    is a process diagram illustrating exemplary details of step  108  of the exemplary process  100  of  FIG.  1    of the present invention, according to a preferred embodiment of the present invention. Step  402  begins the preparation of a conductive film by electrophoretic deposition. In step  404 , The graphene dispersion obtained in step  310 , above, is used as the electrophoresis of a electrophoretic liquid. In step  406 , an electrical current is applied across the positive and negative plates for the electrophoresis. The plates are preferably spaced apart by a gap in the range of one millimeter to fifty millimeters and most preferably fifteen millimeters. In step  408 , the temperature of the electrophoretic liquid is maintained at approximately sixty degrees Celsius. In step  410 , a graphene film deposits on the negative pole piece, or anode, over approximately five minutes. In step  412 , the negative pole piece with the graphene film coating it is collected. 
       FIG.  5    is a process diagram illustrating exemplary details of step  110  of the exemplary process  100  of  FIG.  1    of the present invention, according to a preferred embodiment of the present invention. Step  502  begins the removal of organic amine salt by heat. In step  504 , the graphene film deposited on the negative pole piece is heated in a reducing gas, such as nitrogen. In Step  506 , the heat is increased at a rate of ten degrees Celsius per minute to a final temperature within the range of two hundred degrees Celsius and eight hundred degrees Celsius. In step  508 , the temperature is maintained in a range between four hundred degrees Celsius and six hundred degrees Celsius for approximately four hours. In step  510 , the graphene-coated negative pole piece is passively cooled to room temperature by simply turning off the heat. In step  512 , the negative pole piece having the highly conductive graphene film deposited on the negative pole piece, is collected for use in making a battery. 
     The result of process  100  is a conductive graphene composite film that can be used in a variety of battery applications such as lithium polymer pouch to lithium ion cylindrical battery cells. 
     The process  100  may be used to apply graphene composite conductive film to an anode of a lithium polymer battery to increase power density and life cycles A single sheet, or several sheets, may be applied depending on application. When a battery charges, the battery may swell and then compress as it cools. This is a physically taxing, but increased conductivity reduces resistance and therefor heat and the attendant swelling of the battery. 
     Graphene resolves three key deficiencies in batteries: conductivity (heat generation), power density, and life cycles. 
     The following claims include some functional claiming and do not include any statements of intended purpose.