Patent Publication Number: US-2023147796-A1

Title: Method for Manufacturing Battery Cell Stack

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method for manufacturing a battery cell stack. 
     2. Description of the Related Art 
     Research into a rechargeable secondary battery capable of being charged and discharged has been actively conducted in accordance with the development of state-of-the-art fields such as a digital camera, a cellular phone, a laptop computer, a hybrid automobile and the like. Examples of the secondary battery may include a nickel-cadmium battery, a nickel-metal hydride battery, a nickel-hydrogen battery, and a lithium secondary battery. Among them, since the lithium secondary batteries have a high operating voltage and excellent energy density characteristics per unit weight, they are used as a power source for portable electronic devices. Alternately, a plurality of lithium secondary batteries are connected in series, and then used in a high-output hybrid vehicle or an electric vehicle. 
     When used in the high-output hybrid vehicle or electric vehicle, in order to increase capacity and output of the secondary battery, a plurality of secondary batteries may be connected and used in a form of one battery module and a battery pack. In order to configure the above-described battery module or battery pack, various fastening parts or cooling equipment are required. However, these fastening parts or cooling equipment cause an increase in manufacturing costs while increasing volume and weight thereof, and also lead to a decrease in output in proportion to the increased volume and weight. 
     A method for manufacturing a cell stack forming a battery module by attaching a tape type adhesive to cell surfaces is also used. However, processes and equipment for inputting the tape and removing a release paper are complicated, and waste such as release paper may be generated in large quantities during manufacturing the battery module. 
     In addition, the tape type adhesive is formed with a uniform thickness, whereas a surface deformation occurs in the battery cell by swelling which causes the cell to expand due to repeated charging and discharging of the battery, and the flatness is changed, such that an effective adhesion area is reduced and an adhesive force of the adhesive is not properly expressed. This may further deteriorate stability and reliability of the battery module. 
     PRIOR ART DOCUMENT 
     Patent Document 
     Korean Patent Laid-Open Publication No. 10-2021-0056824 
     SUMMARY OF THE INVENTION 
     An object of embodiments of the present invention is to provide a method for manufacturing a battery cell stack with improved stability and reliability, by using an adhesive resin composition including a solvent-free adhesive, and applying a thickness pattern to an application method, thus to increase an effective adhesion area of the battery cell. 
     To achieve the above object, according to an aspect of the present invention, there is provided a method for manufacturing a battery cell stack, which includes: an application step of spraying an adhesive resin composition on one surface of a battery cell in one direction by a plurality of nozzles, wherein the nozzles are disposed in a direction different from the one direction, and at least two nozzles of the plurality of nozzles apply the adhesive resin composition in amounts different from each other. 
     In some embodiments, nozzles located on an outside may apply the adhesive resin composition to the one surface of the battery cell in an amount larger than that of nozzles located on an inside. 
     In some embodiments, at least one of the nozzles may gradually decrease the application amount of the adhesive resin composition from a portion where the application starts (“application start portion) to a predetermined portion. In some embodiments, at least one of the nozzles may gradually increase the application amount of the adhesive resin composition from the predetermined portion to a portion where the application ends (“application end portion”). 
     In some embodiments, at least one nozzle of the plurality of nozzles may gradually decrease the application amount of the adhesive resin composition from the application start portion to the predetermined portion, and may gradually increase the application amount of the adhesive resin composition from the predetermined portion to the application end portion. 
     In some embodiments, at least two nozzles of the plurality of nozzles may gradually decrease the application amount of the adhesive resin composition from the application start portion to the predetermined portion, and may gradually increase the application amount of the adhesive resin composition from the predetermined portion to the application end portion, wherein points where the decrease in the application amount of each nozzle ends or points where the increase in the application amount starts may be different from each other. 
     In some embodiments, the predetermined portion may correspond to a convex portion of one surface of the battery cell. 
     In some embodiments, in the application step, at least one of the battery cell and the nozzle may move in one direction. 
     In some embodiments, the adhesive resin composition may include a solvent-free adhesive. 
     In some embodiments, the solvent-free adhesive may include one or more selected from the group consisting of an ethylene vinyl acetate resin, polyamide resin, fatty acid polyamide resin, polyester resin, polyurethane resin, polyolefin resin, styrene resin and rubber resin. 
     In some embodiments, the solvent-free adhesive may be a pressure sensitive adhesive (PSA). 
     In some embodiments, the adhesive resin composition may include at least one of a phosphorus-based flame retardant and a nitrogen-based flame retardant. 
     In some embodiments, the application of the adhesive resin composition may be performed at 140 to 200° C. 
     In some embodiments, the resin layer may have a thickness of 0.01 mm to 0.10 mm after application. 
     According to the embodiments of the present invention, the adhesive resin composition is applied to one surface of a non-flat battery cell, and the application amount is controlled according to portions to be applied, so that the one surface may bring into contact with a surface of another battery cell adhered thereon in an opposition state over an entire area in which the adhesive resin composition is applied. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG.  1    is a schematic view illustrating a method for manufacturing a battery cell stack according to an exemplary embodiment; 
         FIG.  2    is a schematic view illustrating a method for manufacturing a battery cell stack according to another exemplary embodiment; 
         FIG.  3    is a cross-sectional view illustrating a shape taken along on line A-A′ in  FIG.  2   ; 
         FIG.  4    is a cross-sectional view illustrating a shape taken along on line B-B′ in  FIG.  2   ; 
         FIG.  5    is a view illustrating a battery cell stack manufactured according to an exemplary embodiment; 
         FIG.  6    is a cross-sectional view illustrating a shape taken along on line A-A′ in  FIG.  5   ; and 
         FIG.  7    is a cross-sectional view illustrating a shape taken along on line B-B′ in  FIG.  5   . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In descriptions of the embodiments of the present invention, publicly known techniques that are judged to be able to make the purport of the present invention unnecessarily obscure will not be described in detail. Referring to the drawings, wherein like reference characters designate like or corresponding parts throughout the several views. In addition, the terms as used herein are defined by taking functions of the present invention into account and may be changed according to the custom or intention of users or operators. Therefore, definition of the terms should be made according to the overall disclosure set forth herein. 
     It should be understood that the technical spirit and scope of the present invention are defined by the appended claims, and the following embodiments are only made to efficiently describe the present invention to persons having common knowledge in the technical field to which the present invention pertains. 
     As used herein, the term “adhesive resin composition” refers to a composition including a resin component. The adhesive resin composition may be an adhesion composition or an adhesive composition. 
     As used herein, the term “solvent-free adhesive” refers to a thermoplastic adhesive which is made of a thermoplastic resin without using a solvent or other solvents, and is capable of being melted at a melting point or more, and then solidified by cooling. The solvent-free adhesive is a hot-melt adhesive which is applied to a material to be adhered in a liquid state at a high temperature, and exhibits an adhesive force by dissipating heat to the surface of the material to be adhered and surroundings after compression, thus to be cooled and solidified within a few seconds. 
     As used herein, the term “pressure sensitive adhesive (PSA)” refers to an adhesive on which an adhesive material acts when applying pressure on the adhesive so as to adhere it to an adhesive surface. 
     A battery cell stack according to an embodiment of the present invention may be widely used in various devices requiring electricity storage, such as an energy storage system (ESS) as well as a vehicle. 
     Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings. However, these are merely illustrative examples and the present invention is not limited thereto. 
       FIGS.  1  to  4    are schematic views illustrating a method for manufacturing a battery cell stack according to exemplary embodiments, respectively, and  FIGS.  5  to  7    are schematic views of a battery cell stack manufactured according to exemplary embodiments, respectively. 
     Referring to  FIGS.  1  to  4   , methods for manufacturing a battery cell stack  100  according to exemplary embodiments of the present invention include an application step of spraying an adhesive resin composition for forming a resin layer  130  to one surface of a battery cell  110  in one direction by a plurality of nozzles  120 , respectively. 
     The battery cell  110  according to an embodiment of the present invention is a general battery cell. The battery cell  110  may be configured in a form in which an electrode assembly and an electrolyte are accommodated in a pouch. The electrode assembly includes a plurality of electrode plates and electrode tabs, and is accommodated in the pouch. Herein, the electrode plate includes a cathode plate and an anode plate, and the electrode assembly may be configured in a stacked form so that the cathode plate and the anode plate have wide surfaces facing each other with a separator interposed therebetween. 
     The battery cell  110  may be supplied through a supply device such as a guide roller or a conveyor belt (not shown). The nozzle  120  may apply an adhesive resin composition to one surface of the battery cell  110  to form the resin layer  130  on one surface of the battery cell  110 . The nozzle  120  may receive the adhesive resin composition from a device such as a storage tank. The nozzle  120  may apply the adhesive resin composition to one surface of the battery cell  110  in a spray method while selectively controlling a spray height and a spray angle. For example, the nozzle  120  may be a spray nozzle which sprays the adhesive resin composition extruded from a melt extruder in the spray method by receiving air heated under high pressure through an air compressor. 
     The application may be performed in one direction, and a plurality of the nozzles  120  may be provided and disposed side by side in a direction different from the one direction in which the application is performed. The arrangement direction of the nozzles  120  is not particularly limited as long as it is a direction in which the adhesive resin composition can be applied to one surface of the battery cell  110 , and for example, may be a direction orthogonal or oblique direction to the application direction, but it is not limited thereto. 
     As shown in  FIGS.  3  and  4   , at least two nozzles of the plurality of nozzles  120  may apply the adhesive resin composition to one surface of the battery cell  110  in amounts different from each other in order to increase an effective adhesion area of the battery cell  110  when manufacturing the battery cell stack  100 . 
     As a specific embodiment, since a central portion of the battery cell  110  may be inflated more convexly than an outer portion, nozzles  120  located on an outside may apply the adhesive resin composition to one surface of the battery cell  110  in a larger amount than that of nozzles located on an inside. 
     As a specific embodiment, when a thickness of the battery cell  110  is increased from a portion where the application starts (“application start portion) to a predetermined portion, the nozzles  120  may apply the adhesive resin composition so as to gradually decrease the application amount thereof from the application start portion to a portion where the thickness of the battery cell  110  is increased in order to increase the effective adhesion area of the battery cell  110 . In addition, when the thickness of the battery cell  110  is decreased from the predetermined portion to a portion where the application ends (“application end portion”), the nozzles  120  may apply the adhesive resin composition so as to gradually increase the application amount thereof from the predetermined portion where the thickness begins to decrease to the application end portion in order to increase the effective adhesion area of the battery cell  110 . 
     As a specific embodiment, when the thickness of the battery cell  110  is increased and then decreased, at least one nozzle of the plurality of nozzles  120  may apply the adhesive resin composition so as to gradually decrease the application amount thereof from the application start portion to the predetermined portion, and then gradually increase the application amount of the adhesive resin composition from the predetermined portion to the application end portion. 
     As a specific embodiment, when the portions where the thickness of the battery cell  110  is increased and then decreased in one direction to be applied differ from each other depending on the positions of the respective nozzles  120  for applying the corresponding portions, in the respective nozzles  120 , points where the decrease in the application amount of each nozzle ends or points where the increase in the application amount starts may be different from each other. 
     The predetermined portion may correspond to a convex portion or the thickest portion of one surface of the battery cell  110 . 
     As a specific embodiment, the application may be performed in a state in which the nozzles  120  are fixed while the battery cell  110  moves in one direction. On the other hand, the application may also be performed in a state in which the battery cell  110  is fixed while the nozzles  120  move in one direction. In addition, the application may also be performed while the nozzles  120  move at speeds different from each other. 
     In some embodiments, a composition of the resin layer  130  (“resin layer  130  composition”) applied to one surface of the battery cell  110  through the nozzles  120  may include a solvent-free adhesive material, preferably a pressure sensitive adhesive (PSA) material, and more preferably a solvent-free or hot-melt coatable pressure sensitive adhesive. 
     In some embodiments, an applicator including the nozzle  120  may include a controller which executes a pre-stored processing program to control operations of the nozzles  120 . Therefore, as described above, it is possible to apply the resin layer  130  composition on one surface of the battery cell  110  by determining the application amount depending on the portion of the battery cell  110 . 
     In some embodiments, the applicator including the nozzle  120  may include a sensor capable of detecting a surface height of the battery cell  110  to determine the application amount of the resin layer  130  composition sprayed from the nozzles  120  and apply the composition depending on the detected surface height. 
     In some embodiments, the solvent-free adhesive may include one or more selected from the group consisting of an ethylene vinyl acetate resin, polyamide resin, fatty acid polyamide resin, polyester resin, polyurethane resin, polyolefin resin, styrene resin and rubber resin. 
     In some embodiments, the resin layer  130  may include a flame retardant. Since the resin layer  130  including a solvent-free adhesive may be applied in a spray method, in order to simultaneously exhibit effective flame retardancy while exhibiting appropriate physical properties, the flame retardant preferably includes one or more of a phosphorus-based flame retardant and a nitrogen-based flame retardant. 
     In some exemplary embodiments, the phosphorus-based flame retardant may include a phosphate compound, a phosphonate compound, a phosphinate compound, a phosphine oxide compound, a phosphazene compound, or metal salts thereof and the like. These compounds may be used alone or in combination of two or more thereof. 
     As a specific example, the phosphorus-based flame retardant may include diphenyl phosphate, diaryl phosphate, triphenyl phosphate, tricresyl phosphate, trizyrenyl phosphate, tri(2,6-dimethylphenyl)phosphate, tri(2,4,6-trimethylphenyl)phosphate, tri(2,4-di-tert-butylphenyl)phosphate, tri(2,6-dimethylphenyl)phosphate, bisphenol-A bis(diphenylphosphate), resorcinol bis(diphenylphosphate), resorcinol bis[bis(2,6-dimethylphenyl)phosphate], resorcinol bis[bis(2,4-di-tert-butylphenyl)phosphate], hydroquinone bis[bis(2,6-dimethylphenyl)phosphate], hydroquinone bis[bis(2,4-di-tert-butylphenyl)phosphate], an oligomeric phosphoric acid ester compound, and the like, but it is not limited thereto. These compounds may be applied alone or in a form of a mixture of two or more thereof. 
     As a specific example, the nitrogen-based flame retardant may include melamine and melamine derivatives. These may be used alone or in combination of two or more thereof. 
     As a specific example, the nitrogen-based flame retardant may include melamine, melamine phosphate, melamine cyanurate, etc., but it is not limited thereto. These may be applied alone or in a form of a mixture of two or more thereof. 
     In some embodiments, the flame retardant may be included in a ratio of 10 to 50 parts by weight (“wt. parts”) based on 100 wt. parts of the resin layer. 
     The contents of the above-described phosphorus-based flame retardant and the nitrogen-based flame retardant are preferably added and used alone or in the same proportion as each other in a sum of both retardants. If the proportion of the flame retardant is less than 10 wt. parts, the flame retardancy is insufficient, whereas if it exceeds 50 wt. parts, physical properties such as an adhesive force or workability when applying the resin layer may be deteriorated. 
     In some embodiments, the resin layer  120  may have a softening point of about 60 to 140° C., and preferably about 80 to 105° C. In the above softening point range, when a defect occurs during manufacturing the battery cell stack  100 , a rework is easily performed and a damage to the cell may be minimized, as well as the resin layer  120  may be easily removed when recycling the battery cell stack  100 . Whereas, if the softening point is less than 60° C., the viscosity of the resin layer  130  composition is increased, such that nozzle clogging of an applicator or scattering of the resin layer  130  composition may occur when applying the resin layer, and re-liquefaction may occur in the resin layer  130  due to heat generated from the battery cell  110 , and thereby causing the impact resistance of the battery cell stack  100  to be deteriorated. If the softening point exceeds 140° C., a damage due to heat may occur in the battery cell  110  when the resin layer  130  is re-liquefied. 
     The resin layer  120  may be formed in a form of a relatively thin layer compared to the battery cell  110 . In this case, the resin layer  120  may have a thickness within a range of 0.01 to 0.10 mm, or 0.02 to 0.08 mm, or about 0.03 to 0.05 mm, for example. If the resin layer  120  is less than 0.01 mm, a fixing force between the battery cells  110  is weakened to cause a reduction in the stability of the battery cell stack  100 , whereas if it exceeds 0.10 mm, insulation properties may be deteriorated. The thickness may be a thickness of the thinnest portion, a thickness of the thickest portion, or an average thickness of the resin layer  120 . 
     Referring to  FIGS.  5  to  7   , the battery cell stack  100  manufactured according to exemplary embodiments of the present invention is configured by stacking a plurality of battery cells  110 . The battery cells  110  may be vertically erected and stacked in a left-and-right direction (i.e., in a horizontal direction), but may be horizontally laid down and stacked in an up-and-down direction (i.e., in a vertical direction) as necessary. 
     The battery cell  110  may be fixed by the resin layer  130 . For example, the resin layer  130  may be formed on the outer surface of the battery cell  110  to be mutually fixed to the battery cell  110  adjacent thereto. 
     Meanwhile, in some embodiments, after the application step, an additional battery cell  120  may be stacked again on the applied resin layer  130  composition to manufacture the battery cell stack  100 . The stacking of the battery cells  120  may be performed continuously after application of the resin layer  130  composition. In addition, the process of re-applying the resin layer  130  composition on the stacked battery cell  120  and stacking the additional battery cell  120  again may be repeatedly performed. 
     DESCRIPTION OF REFERENCE NUMERALS 
     
         
           100 : Battery cell stack 
           110 : Battery cell 
           120 : Nozzle 
           130 : Resin layer