Patent Publication Number: US-2021167416-A1

Title: Lithium ion secondary battery, and system for and method of manufacturing same

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims priority to Korean Patent Application No. 10-2019-0156296, filed Nov. 29, 2019, the entire contents of which is incorporated herein for all purposes by this reference. 
     BACKGROUND 
     Field of the Disclosure 
     The present disclosure relates to a lithium ion secondary battery and a system for and method of manufacturing same. More particularly, the present disclosure relates to a lithium ion secondary battery with improved quick charging characteristics and a system for and method of manufacturing same. 
     Description of the Related Art 
     In electric vehicles, the mileage per charge is used as an indicator of the performance. The mileage per charge increases with energy density of each battery cell or with the number of battery cells mounted in an electric vehicle. When increasing the mileage per charge by increasing the energy density of each battery cell or the number of battery cells mounted in an electric vehicle, there are problems such as technical limitations and rising costs. For this reason, quick charging technology has been recently paid attention. When vehicle batteries can be charged fast, the charging time per charge decreases, resulting in convenient use of electric vehicles. That is, it is possible to improve customer satisfaction for electric vehicles without increasing the battery cost. 
     However, when a charge current is excessively higher than a predetermined level when a lithium ion secondary battery is quick-charged to reduce charging time, lithium precipitation and electrolyte reaction byproducts occur on an anode arranged to face trimmed surfaces of a cathode. The materials accumulate more and more with charge and discharge cycles of a lithium ion secondary battery, resulting in damage to a separator. This consequently results in short-circuiting and ignition. 
     The foregoing is intended merely to aid in understanding the background of the present disclosure and therefore should not be interpreted to admit that the present disclosure falls within the purview of the related art that is already known to those skilled in the art. 
     SUMMARY 
     The present disclosure is provided to propose a solution to the above problems occurring in the related art. A first objective of the present disclosure is to provide a lithium ion secondary battery in which a resistive layer is formed on a trimmed surface of a cathode electrode, in which the resistive layer restricts movement of electrons or lithium ions moving through the trimmed surface of the cathode, thereby minimizing the amount of lithium precipitation and the amount of electrolyte reaction byproducts formed on the trimmed surface of the cathode electrode, resulting in improvement in quick charge characteristics. In addition, due to the presence of the resistive layer on the trimmed surface of the cathode electrode, material cost is reduced. A second objective of the present disclosure is to provide a system for manufacturing a lithium ion secondary battery. A third objective of the present disclosure is to provide a method of manufacturing a lithium ion secondary battery. 
     In order to accomplish the first objective, according to one aspect of the present disclosure, there is provided a lithium ion secondary battery including: a cathode including a cathode current collector and a cathode coating layer formed on a surface of the cathode current collector; resistive layers formed on respective side surfaces at respective ends of the cathode; an anode including an anode current collector and an anode coating layer formed on a surfaced of the anode current collector; and a separator disposed between the cathode and the anode. 
     The resistive layer may be made of a mixture of a conductive material and a binder. 
     The conductive material and the binder may be mixed at a ratio of 1:1.1 to 1:10. 
     The resistive layers formed on the respective side surfaces at the respective ends of the cathode may be coated with a mixture solution of a binder and a solvent. 
     The binder may include one or more materials selected from the group consisting of carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), polyacrylic acid (PAA), poly(vinylidene fluoride) (PVdF), poly(vinyl alcohol) (PVA), and polyimide (PI). 
     The solvent may include one or more materials selected from the group consisting of alcohol, pure water, methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMA), and tetrahydrofuran (THF). 
     The concentration of the mixture solution may be in a range of from 0.5% to 20%. 
     The mixture solution may include a solvent, one or more monomers, and an initiator. 
     The monomer may include a vinyl group, an alkyl group, or any combination of a vinyl group and an alkyl group. 
     The monomer may include: at least one material selected from the group consisting of alkyl methacrylate, alkyl acrylate, acrylonitrile, alkyl acetate, styrene, and butadiene; vinyl alcohol; or a combination of vinyl alcohol and at least one material selected from the group consisting of alkyl methacrylate, alkyl acrylate, acrylonitrile, alkyl acetate, styrene, and butadiene. 
     The concentration of the initiator may be 0.5% to 5% by weight with respect to the total weight of the monomer. 
     The mixture solution may include a metal oxide or a metal hydroxide in a concentration of 0.5% to 5% with respect to the total weight of the mixture solution. 
     In order to accomplish the second objective of the present disclosure, according to one aspect, there is provided a lithium ion secondary battery manufacturing system including: a cutter/coater configured to trim a cathode electrode to have a predetermined size and to coat trimmed surfaces at respective ends of the cathode electrode with a coating solution to form resistive layers on the respective trimmed surfaces; an electrode feeder configured to feed the cathode electrode to the cutter/coater; an electrode discharger configured to discharge the trimmed and coated cathode electrode from the cutter/coater; and a coating solution feeder configured to feed the coating solution to the cutter/coater. 
     The system may further include at least one device selected from among: a coating solution container for storing the coating solution; a vacuum device configured to create a negative pressure at around the trimmed surfaces of the cathode electrode before the coating solution is sprayed by the cutter/coater and configured to remove the residue of the coating solution after the coating solution is sprayed; a cleaning solution feeder configured to feed a cleaning solution to the trimmed surfaces of the cathode electrode; a particle remover configured to remove particles escaping from the trimmed surfaces of the cathode electrode; and a dryer configured to dry the coated surfaces of the cathode electrode. 
     The cutter/coater may include an upper mold and a lower mold. 
     The upper mold may include: a cutter being vertically movable and configured to trim the cathode electrode; a fixing part configured to fix the cathode electrode when trimming the cathode electrode; and a coater configured to spray the coating solution to the trimmed surfaces of the cathode electrode. 
     The lower mold may include: a mounting portion in which the cathode electrode is mounted; and a support portion that is vertically movable, that supports the cathode electrode mounted in the mounting portion from the sides of the cathode electrode, that moves downward when both sides of the cathode electrode is trimmed by the cutter, and that supports the cathode electrode from the trimmed side surfaces. 
     In order to accomplish the third objective of the present disclosure, according to one aspect, there is provided a method of manufacturing a lithium ion secondary battery, the method including: loading a cathode electrode into a cutter/coater; lowering an upper mold of the cutter/coater to move a cutter downward while fixing a cathode electrode with a fixing part in order to trim the cathode electrode to have a predetermined size; moving the cuter upward while fixing the trimmed cathode electrode with the fixing part; spraying a coating solution to form resistance layers on respective trimmed surfaces of the cathode electrode; and unloading the trimmed and coated cathode electrode. 
     The method may further include a step of removing particles escaping from the trimmed surfaces of the cathode electrode before the coating of the trimmed surfaces of the cathode electrode. 
     The method may further include a step of drying the trimmed and coated cathode electrode before the unloading of the trimmed and coated cathode electrode. 
     The method may further include a step of stacking multiple cathode electrodes trimmed to have a predetermined size and a step of forming restive layers on trimmed surfaces of the multiple cathode electrodes stacked on each other after the moving of the cutter while fixing the cathode electrodes. 
     According to the present disclosure, since the resistive layers are formed on the respective trimmed surfaces of the cathode electrode, it is possible to restrict the movement of electrons or lithium ions moving out through the trimmed surfaces the cathode electrode, thereby minimizing the amount of lithium precipitation and the amount of electrolyte reaction by-products accumulated on the trimmed surfaces of the cathode electrode, resulting in improvement in quick charge characteristics. In addition, since the thickness of the cathode electrode increases due to the presence of the resistive layers, it is possible to reduce the material cost. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view illustrating a conventional lithium ion secondary battery in which lithium precipitates or electrolyte reaction byproducts occur on an anode arranged to face a section of a cathode during quick charging of the lithium ion secondary battery; 
         FIG. 2  is a schematic view illustrating the construction of a lithium ion secondary battery according to one exemplary embodiment of the present disclosure; 
         FIG. 3  is an enlarged view of a portion A of  FIG. 2 ; 
         FIG. 4  is an enlarged view of a portion B of  FIG. 3 ; 
         FIG. 5  is a view illustrating the overall construction of a lithium ion secondary battery manufacturing system according to one exemplary embodiment of the present disclosure; 
         FIG. 6  is a view illustrating the overall construction of a lithium ion secondary battery manufacturing system according to another exemplary embodiment of the present disclosure; 
         FIG. 7  is a view illustrating a method of manufacturing a lithium ion secondary battery, according to a first exemplary embodiment of the present disclosure; 
         FIG. 8  is a view illustrating a method of manufacturing a lithium ion secondary battery, according to a second exemplary embodiment of the present disclosure; and 
         FIG. 9  is a view illustrating a method of manufacturing a lithium ion secondary battery, according to a third exemplary embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, exemplary embodiments of the present disclosure will be described with reference to the accompanying drawings. Prior to giving the following detailed description of the present disclosure, it should be noted that the terms and words used in the specification and the claims should not be construed as being limited to ordinary meanings or dictionary definitions but should be construed in a sense and concept consistent with the technical idea of the present disclosure, on the basis that the inventor can properly define the concept of a term to describe its invention in the best way possible. 
     The exemplary embodiments described herein and the configurations illustrated in the drawings are presented for illustrative purposes and do not exhaustively represent the technical spirit of the present invention. Accordingly, it should be appreciated that there will be various equivalents and modifications that can replace the exemplary embodiments and the configurations at the time at which the present application is filed. 
       FIG. 2  is a schematic view illustrating the construction of a lithium ion secondary battery according to one exemplary embodiment of the present disclosure,  FIG. 3  is an enlarged view of a portion A of  FIG. 2 , and  FIG. 4  is an enlarged view of a portion B of  FIG. 3 . 
     Referring to  FIG. 2 , a lithium ion secondary battery according to one exemplary embodiment of the present disclosure includes a cathode electrode  10 , a resistive layer  14 , an anode electrode  20 , and a separator  30 . The lithium ion secondary battery may further include a cathode tab  40 , an anode tab  50 , and a casing  60 . 
     The cathode electrode  10  includes a cathode current collector  11  and a cathode coating layer  12  coated on the surface of the cathode current collector  11 . The cathode current collector  11  can be made of any conductive material. Depending on embodiment, the cathode current collector  11  may be made of aluminum, stainless steel, or nickel-plated steel. 
     The cathode coating layer  12  is formed on the surface of the cathode current collector  11 . The cathode coating layer  12  includes a cathode active layer made of a cathode active material and a binder and a conductive material formed on the cathode active layer. For example, the cathode active material may be a solid solution oxide containing lithium. However, the cathode active material is not limited to a specific material if the material can electrochemically absorb and release lithium ions. 
     The anode electrode  20  includes an anode current collector  21  and an anode coating layer  22  coated on the surface of the anode current collector  21 . The anode current collector  21  can be made of any conductive material. Depending on embodiment, the anode current collector  11  may be made of copper, aluminum, stainless steel, or nickel-plated steel. However, the material of the anode current collector  11  is not limited thereto. 
     The anode coating layer  22  is formed on the surface of the anode current collector  21 . The anode coating layer  12  includes an anode active layer made of an anode active material and a binder and a conductive material formed on the anode active layer. Here, the anode active materials include metal-based active materials and carbon-based active materials. The metal-based active materials include silicon-based active materials, tin-based active materials, and any combination thereof. The carbon-based active material is a material that contains carbon (atoms) and which can electrochemically absorb and release lithium ions. Examples of the carbon-based active material include a graphite active material, artificial graphite, natural graphite, a mixture of artificial graphite and natural graphite, natural graphite coated with artificial graphite, but are not limited thereto. 
     The separator  30  is positioned between the cathode electrode  10  and the anode electrode  20  to electrically isolate the cathode electrode  10  and the anode electrode  20  from each other. The separator  30  is a porous membrane allowing ions to pass through so that the ions can move between the cathode electrode  10  and the anode electrode  20 . 
     The cathode electrode tab  40  is welded to a portion of the cathode current collector  11  at a position where the coating layer is not formed, thereby allowing electric charges to flow to the outside. 
     The anode tab  50  is welded to a portion of the anode current collector  21  at a position where the coating layer is not formed, thereby allowing electric charges to flow to the outside. 
     The casing  60  serves to isolate the electrode assembly contained in the casing, thereby preventing the electrode assembly from being exposed to ambient air and moisture. 
     The resistive layers  14  are the key element of the present disclosure and they are layers respectively formed on both end faces of the cathode electrode  10 . The end faces of the cathode electrode  10  mean cross-sections of the cathode electrode. 
     The resistive layers  14  are made of a mixture of a conductive material and a binder. Specifically, the mixing ratio of the conductive material and the binder that constitute the resistive layer  14  may be in a range of 1:1.1 to 1:10. 
     Referring to  FIGS. 3 and 4 , the resistive layer  14  is made of a mixture of the conductive material  141  and the binder  142 , and the resistive layer  14  can be called a highly contained binder layer in which the content of the binder is relatively high in comparison with the other portions of the cathode coating layer so that the electric conductivity of the resistive layer  14  is relatively low. Here, the binder may be polymer  121 . 
     As described above, according to one exemplary embodiment of the present disclosure, the resistive layers formed on the respective side surfaces of the cathode electrode restrict the movement of electrons or lithium ions at the side surfaces of the cathode electrode during the quick charging of the lithium ion secondary battery, thereby minimizing the lithium metal precipitation and the electrolyte reaction byproducts on the anode electrode to improve the quick charge characteristics. 
     On the other hand, the resistive layers  14  formed on the respective side surfaces (i.e. end faces) of the cathode electrode  10  may be formed by coating the side surfaces of the cathode electrode with a mixture solution of a binder and a solvent. According to an embodiment of the present disclosure, the resistive layers  14  are formed by coating the side surfaces (i.e., end faces) of the cathode electrode  10  with a mixture solution, in which various coating methods such as spray coating, electro spray coating (ESC), brush coating, and slit-nozzle coating can be used. 
     The binder is composed of one or more materials selected from the group consisting of carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), polyacrylic acid (PAA), poly(vinylidene fluoride) (PVdF), poly(vinyl alcohol) (PVA), and polyimide (PI). The solvent is composed of one or more materials selected from the group consisting of alcohol, pure water, -methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMA), and tetrahydrofuran (THF) 
     Depending on embodiment, the concentration of the mixture solution may be in a range of 0.5% to 20%. Here, when the concentration of the mixture solution is 0.5% or less, the solvent may penetrate excessively deep into the cathode electrode. On the contrary, when the concentration of the mixture solution is 20% or more, the solvent cannot penetrate into the cathode electrode, resulting in poor coating. Therefore, the concentration of the mixture solution is preferably in a range of 0.5% to 20%. However, this range is only an example, and the concentration of the mixture solution may vary depending on the coating method, the type of the binder, and the pores of the cathode electrode. 
     The mixture solution may include a solvent, one or more monomers, and an initiator. The monomer may be a vinyl group, an alkyl group, or any combination of the vinyl group and the alkyl group. 
     The monomer may be at least one material selected from the group consisting of alkyl methacrylate, alkyl acrylate, acrylonitrile, alkyl acetate, styrene, and butadiene; or vinyl alcohol; or a combination of vinyl alcohol and at least one material selected from the group consisting of alkyl methacrylate, alkyl acrylate, acrylonitrile, alkyl acetate, styrene, and butadiene. 
     The concentration of the initiator is 0.5% to 5% by weight with respect to the total weight of the monomer. 
     Alternatively, the mixture solution may contain a metal oxide or a metal hydroxide in a concentration of 0.5% to 5% with respect to the total weight of the mixture solution. Here, the metal oxide or the metal hydroxide is contained in the mixture solution to enable an operator to easily discern whether the resistive layers are coated on the trimmed surfaces or not when forming the resistive layers by applying the mixture solution to the trimmed surfaces of the cathode electrode. 
     Specifically, the metal oxide may be SiO 2 , Al 2 O 3 , Al 2 (OH) 3 , TiO 2 , Mg(OH) 2 , BaS0 4 , TiO 2 , SnO 2 , CeO 2 , ZrO 2 , BaTiO 3 , Y 2 O 3  or B 2 O 3 . In this case, D50 of the metal oxide may be 0.1 μm to 2 μm. 
     On the other hand, the metal hydroxide may be Al(OH) 3  or Mg(OH) 2 . 
       FIG. 5  is a view illustrating the overall construction of a lithium ion secondary battery manufacturing system according to one exemplary embodiment of the present disclosure. Referring to  FIG. 5 , a lithium ion secondary battery manufacturing system according to one exemplary embodiment of the present disclosure includes a cutter/coater  100 , an electrode feeder  200 , an electrode discharger  300 , and a coating solution feeder  400 . The system may further include at least one device selected from among a coating solution container  500 , a vacuum device  600 , a cleaning solution feeder  700 , a particle remover  800 , and a dryer  900 . 
     The cutter/coater  100  trims a cathode electrode to have a predetermined size and coats the surfaces of the cathode electrode, which are exposed through the trimming of the cathode electrode, with a coating solution, thereby forming resistive layers on the respective trimmed surfaces of the cathode electrode. Specifically, the cutter/coater  100  includes an upper mold  110  and a lower mold  130 . 
     More specifically, the upper mold includes a cutter  111  movable up and down and configured to trim the cathode electrode, a fixing part  112  for fixing the cathode electrode when trimming the cathode electrode, and a coater  113  for spraying a coating solution to the trimmed surfaces of the cathode electrode. Here, as illustrated in  FIG. 5 , the upper mold  110  may be provided with an elastic member, and the elastic member may be compressed or decompressed when the cutter  111  moves upward or downward. 
     The lower mold  130  includes a mounting portion  131  in which the cathode electrode can be mounted and a support portion  132  movable upward and downward. The support portion  132  supports the cathode electrode mounted in the mounting portion from the sides of the cathode electrode. The support portion  132  moves downward when the cathode electrode is trimmed by the cutter and supports the cathode electrode from the trimmed surfaces. Here, as illustrated in  FIG. 5 , the lower mold  130  may be provided with an elastic member, and the elastic member may be compressed or decompressed when the support portion  132  moves upward or downward. 
     The electrode feeder  200  is a device for supplying the cathode electrode to the cutter/coater  100 , and the electrode discharger  300  is a device for discharging the trimmed and coated cathode electrode from the cutter/coater  100 . The coating solution feeder  400  is a device for supplying the coating solution to the cutter/coater  100 . 
     The coating solution container  500  may be a device that serves to store the coating solution. The vacuum device  600  creates a negative pressure around the trimmed surfaces (i.e., end faces) of the cathode electrode before the coating solution is sprayed to trimmed surfaces by the cutter/coater and removes the remaining coating solution on the trimmed surfaces before the coating is finished. 
     The cleaning solution feeder  700  is a device for supplying the cleaning solution to the trimmed surfaces of the cathode electrode. The particle remover  800  serves to remove the particles escaping from the trimmed surfaces of the cathode electrode after the cathode electrode is trimmed. The dryer  900  is a device that serves to dry the coated trimmed surfaces of the cathode electrode. 
       FIG. 6  is a view illustrating the overall construction of a lithium ion secondary battery manufacturing system according to another exemplary embodiment of the present disclosure. Referring to  FIG. 6 , in a lithium ion secondary battery manufacturing system according to another exemplary embodiment of the present disclosure, a cutter  910  and a coater  920  are separated from each other. The lithium ion secondary battery manufacturing system according to this exemplary embodiment is the same as the lithium ion secondary battery manufacturing system according to the former exemplary embodiment except for the cutter  910  and the coater  920  are separated from each other. Therefore, the points that are common between the former exemplary embodiment and the present exemplary embodiment will not be described. 
       FIG. 7  is a view illustrating a method of manufacturing a lithium ion secondary battery, according to a first exemplary embodiment of the present disclosure,  FIG. 8  is a view illustrating a method of manufacturing a lithium ion secondary battery, according to a second exemplary embodiment of the present disclosure, and  FIG. 9  is a view illustrating a method of manufacturing a lithium ion secondary battery, according to a third exemplary embodiment of the present disclosure. 
     Referring to  FIG. 7 , the method according to the first exemplary embodiment of the present disclosure includes: Step S 100  of loading a cathode electrode into a cutter/coater; Step S 200  of lowering an upper mold of the cutter/coater to move a cutter downward while fixing the cathode electrode with a fixing part in order to trim the cathode electrode to have a predetermined size; Step S 300  of moving the cuter upward while fixing the trimmed cathode electrode with the fixing part; Step S 400  of spraying a coating solution to form resistance layers on respective trimmed surfaces of the cathode electrode; and Step S 500  of unloading the cathode electrode with the coated trimmed surfaces. 
     Referring to  FIG. 8 , the method according to the second embodiment of the present disclosure may further include Step S 350  of removing particles escaping from the trimmed surfaces of the cathode electrode in comparison with the method according to the first exemplary embodiment, in which Step S 350  is performed before Step S 400  at which the trimmed surfaces of the cathode electrode are coated. 
     The method according to the second embodiment may further include Step S 450  of drying the coated trimmed surfaces of the cathode electrode in comparison with the method according to the first exemplary embodiment, in which Step S 450  is performed before Step S 500  at which the cathode electrode having undergone the trimming and the coating is unloaded. 
     Referring to  FIG. 9 , the method according to the third embodiment of the present invention may further include Step S 330  of stacking multiple cathode electrodes that are trimmed to have a predetermined size and of forming resistive layers on the trimmed surfaces of the multiple cathode electrodes stacked on each other in comparison with the first embodiment or the second embodiment, in which Step S 330  is performed after Step S 300  at which the cutter is moved upward while the trimmed cathode electrode is fixed. 
     Although the present disclosure has been described and illustrated with reference to the particular embodiments thereof, it will be apparent to a person skilled in the art that various improvements and modifications of the present disclosure can be made without departing from the technical idea of the present disclosure provided by the following claims.