Battery case, battery cell including the same, and method for manufacturing the battery cell

Abstract

The present invention relates to a battery case including a first heat-sealable resin layer, a moisture-blocking metal layer, a second resin layer for protecting internal components from the outside, and a heat-dissipating layer including a carbon material and a binder, the heat-dissipating layer being attached to the surface of the second resin layer and having a thickness of 40 nm to 800 nm. The present invention also relates to a battery case that has improved heat dissipation performance while minimizing an increase in the thickness of the battery case, a battery cell including the same, and a method for manufacturing the battery cell.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0132102, filed October 4, 2023, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a pouch-type battery case including a carbon coating layer, a pouch-type battery cell including the same, and a method for manufacturing the pouch-type battery cell. More specifically, the present invention relates to a pouch-type battery case including a carbon coating layer that can prevent heat transfer generated during charging and discharging processes, thereby preventing further fires and explosions. [Background technology]

[0003] Lithium secondary batteries, which are rechargeable and have high energy density, are attracting attention as a new energy source with environmentally friendly properties, as they can dramatically reduce the use of fossil fuels and do not produce by-products due to energy consumption.

[0004] Lithium secondary batteries can be classified according to their shape, and more specifically, they can be classified into cylindrical battery cells and prismatic battery cells manufactured by inserting an electrode assembly into a metal can, and pouch battery cells manufactured by inserting an electrode assembly into a battery case formed from a laminate sheet including a resin layer and a metal layer.

[0005] Among these, the pouch-type battery cell has the advantages of being easily deformable and having a high energy density.

[0006] However, the resin layer of the laminate sheet is made of a material such as nylon or polyethylene terephthalate, which reduces heat dissipation performance, making it vulnerable to heat generation that occurs during charging and discharging of the secondary battery.In addition, the discharge rate increases with temperature rise, which causes a problem of a rapid decrease in the usable time of the battery.

[0007] When the temperature of a battery cell exceeds a certain temperature due to heat generation in a secondary battery, the electrode assembly or electrolyte decomposes, generating a large amount of gas. The gas generated in the battery cell increases the internal pressure of the battery cell, causing swelling, in which the battery cell itself expands. The swelling can cause dimensional changes in multiple pouch-type battery cells arranged inside the battery pack, leading to problems such as deformation of the pack case.

[0008] Therefore, various methods have been attempted to reduce the heat generation phenomenon of pouch-type battery cells.

[0009] Patent Document 1 relates to a pouch-type battery packaging material including an outermost layer of heat-resistant resin, a barrier layer containing aluminum or an aluminum alloy, and an innermost layer of thermoplastic resin, and at least one of the constituent layers of the packaging material includes a heat-dissipating layer containing a carbon material or a separate additional heat-dissipating layer containing a carbon material and a binder resin. It discloses that with this configuration, when the internal temperature of the battery rises rapidly due to overcharging or an internal short circuit caused by an abnormal reaction inside the lithium secondary battery, or when the battery is exposed to a high-temperature environment, the carbon material dissipates heat from the packaging material, thereby delaying and suppressing the rise in the internal temperature of the battery.

[0010] Patent Document 1 discloses the results of adding a heat-dissipating layer having a thickness of 1 μm or more to a packaging material and measuring the degree of cooling of the packaging material over time.

[0011] Patent Document 1 shows that the thicker the heat dissipation layer, the better the heat dissipation performance. However, there is a problem in that using a thick heat dissipation layer for heat dissipation performance increases the total thickness of the packaging material.

[0012] Therefore, there is a need to develop a pouch-type battery case that minimizes an increase in thickness of the pouch-type battery case while improving heat dissipation properties. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] Korean Patent Application Publication No. 10-2013-0011977 Summary of the Invention [Problem to be solved by the invention]

[0014] The present invention has been made to solve the above problems, and aims to provide a pouch-type battery case that minimizes an increase in the thickness of the pouch-type battery case and significantly improves heat dissipation performance, a pouch-type battery cell including the same, and a method for manufacturing the pouch-type battery cell. [Means for solving the problem]

[0015] To achieve this object, the battery case of the present invention includes a first resin layer having heat-sealing properties, a metal layer having moisture-blocking properties, a second resin layer for protecting internal components from the outside, and a heat-dissipating layer containing a carbon material and a binder, the heat-dissipating layer being attached to the surface of the second resin layer, and the heat-dissipating layer having a thickness of 40 nm to 800 nm.

[0016] In the battery case, the carbon material may be at least one selected from the group consisting of graphite, carbon nanotubes (CNTs), single-walled carbon nanotubes (SWNTs), graphene, and activated carbon fiber (ACF).

[0017] In the battery case, the carbon material may be graphene manufactured by a liquid phase exfoliation method.

[0018] In the battery case, the heat dissipation layer may have a thickness of 80 nm to 800 nm.

[0019] The binder may be included in the battery case in a range of 0.01 wt % to 5 wt % based on the total weight of the solid content.

[0020] In the battery case, the binder may be at least one selected from the group consisting of epoxy-based, acrylic-based, hydrocarbon-based, polyester-based, vinyl-based, urethane-based, and acrylate-based binders, or a copolymer containing any of these.

[0021] The battery cell includes a battery case, an electrode assembly is accommodated inside the battery case, a sealing portion is formed around the outer periphery of a cup portion in which the electrode assembly is accommodated, electrode leads connected to electrode tabs of the electrode assembly extend outward from the sealing portion of the battery case, and a heat dissipation layer is formed on the outer surface of the battery case.

[0022] The present invention provides a method for manufacturing the battery cell, and in one embodiment, the method includes the steps of preparing a battery case made of a laminate sheet including a first resin layer, a metal layer, and a second resin layer, preparing a solution for a heat dissipation layer including a carbon material and a binder, forming a heat dissipation layer on the battery case, and accommodating an electrode assembly in the battery case and then sealing the battery case.

[0023] The step of forming the heat-dissipating layer may be performed using a gravure coating method.

[0024] The present invention also provides a method for manufacturing the battery cell, and in another embodiment, the method includes the steps of preparing a battery case made of a laminate sheet including a first resin layer, a metal layer, and a second resin layer, accommodating an electrode assembly in the battery case and then sealing the battery case, preparing a solution for a heat dissipation layer including a carbon material and a binder, and forming a heat dissipation layer on the battery case.

[0025] In the method for manufacturing the battery cell, the step of forming the heat dissipation layer may be performed using a dip coating method.

[0026] Furthermore, the present invention can also be provided in the form of various combinations of means for solving the above problems. [Effects of the Invention]

[0027] As described above, the battery case according to the present invention exhibits high heat dissipation performance even when the heat dissipation layer has a thickness on the order of several tens to several hundreds of nanometers.

[0028] Reducing the thickness of the heat dissipation layer also reduces manufacturing costs, manages heat more efficiently, shortens product life, and reduces the risk of breakdowns and fires.

[0029] In addition, the increase in the thickness of the battery case can be minimized, thereby improving the energy density. [Brief explanation of the drawings]

[0030] [Figure 1] 1A and 1B are a perspective view and a partial vertical cross-sectional view of a pouch-type battery cell according to the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0031] Hereinafter, with reference to the accompanying drawings, a detailed description will be given of an embodiment of the present invention that will enable a person skilled in the art to easily carry out the present invention. In describing the operation principle of the embodiment of the present invention in detail, detailed description of related well-known functions or configurations will be omitted if it is determined that such detailed description may unnecessarily obscure the gist of the present invention.

[0032] Throughout the drawings, the same reference numerals are used for parts having similar functions and actions. Throughout the specification, when a part is said to be connected to another part, this includes not only a direct connection but also an indirect connection via another element therebetween. Furthermore, unless otherwise specified, "including a certain element" does not mean that other elements are excluded, but that other elements may also be included.

[0033] Descriptions that limit or specify additional elements are applicable to all inventions and are not limited to a particular invention unless otherwise limited.

[0034] Throughout the description and claims of this invention, the singular includes the plural unless otherwise stated.

[0035] Throughout the description and claims, "or" includes "and" unless otherwise stated. Thus, "comprising A or B" means the three cases of including A, including B, or including both A and B.

[0036] The battery case according to the present invention may be a pouch-type battery case made of a laminate sheet including a resin layer and a metal layer. Specifically, the battery case may include a first resin layer having heat-sealing properties for sealing a battery cell, a metal layer having moisture-blocking properties, a second resin layer for protecting an internal electrode assembly from the outside, and a heat-dissipating layer including a carbon material and a binder, the heat-dissipating layer being attached to a surface of the second resin layer, and the thickness of the heat-dissipating layer may be 40 nm to 800 nm.

[0037] Specifically, the first resin layer can be made of a polymer resin that has heat-sealing properties, low moisture absorption for the electrolyte solution, and is not swollen or corroded by the electrolyte solution, and can be made of, for example, a non-oriented polypropylene film (CPP).

[0038] The metal layer may be made of aluminum (Al) or an aluminum alloy to enhance the strength of the battery case in addition to preventing the inflow of foreign substances such as gas and moisture and the outflow of the electrolyte.

[0039] The second resin layer must have excellent resistance to the external environment and therefore must have tensile strength and weather resistance above a predetermined value. In this regard, the polymer resin of the second resin layer may include polyethylene naphthalate (PEN), polyethylene terephthalate (PET), or oriented nylon, which have excellent tensile strength and weather resistance.

[0040] The heat dissipation layer includes a carbon material and a binder for binding the carbon material, and the carbon material may be at least one selected from the group consisting of graphite, carbon nanotubes (CNTs), single-walled carbon nanotubes (SWNTs), graphene, and activated carbon fiber (ACF), and in particular, graphene.

[0041] Graphene is a structure in which hexagons consisting of six carbon atoms are connected to form a two-dimensional single layer, and has a different structure from graphite, which has a three-dimensional structure formed by stacking multiple layers of carbon nanotubes, which have a tubular one-dimensional structure.

[0042] Such graphene has an electron mobility of 50,000 cm 2 / Vs or higher, and when electrons move, they exhibit the same speed as a beam of light, as if they had zero mass. Graphene also boasts structural and chemical stability, excellent thermal conductivity, and is made solely of the relatively light element carbon, making it easy to fabricate one- or two-dimensional nanopatterns. Above all, graphene sheets are an inexpensive material, making them more cost-competitive than existing nanomaterials.

[0043] In the pouch-type battery case according to the present invention, the first resin layer has a thickness of 10 μm to 50 μm, the metal layer has a thickness of 20 μm to 150 μm, and the second resin layer has a thickness of 5 μm to 40 μm. If the thickness of each layer of the pouch-type battery case is too thin, it is difficult to expect improved blocking function and strength against substances, while if it is too thick, it is undesirable because it reduces processability and causes an increase in sheet thickness.

[0044] The thickness of the heat dissipation layer is 40 nm to 800 nm, and more specifically, 80 nm to 800 nm. If the thickness of the heat dissipation layer is thinner than 40 nm, the heat dissipation performance may be reduced, which may cause safety issues, and if the thickness is thicker than 800 nm, the effect of improving heat dissipation may be reduced and costs may increase significantly, which is not preferable.

[0045] The binder may be one or more selected from the group consisting of epoxy, acrylic, hydrocarbon, polyester, vinyl, and urethane binders, or a copolymer containing any of these, such as polyvinylidene fluoride, polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polyacrylonitrile, polyvinylacetate, ethylene-vinylacetate copolymer, polyimide, or polyethylene oxide.

[0046] The acrylic binder may be at least one selected from the group consisting of methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, isobutyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, and lauryl (meth)acrylate.

[0047] The binder may be included in an amount of 0.01 wt% to 5 wt% based on the total weight of the solid content, and more specifically, in an amount of 0.1 wt% to 1 wt%.

[0048] If the binder content is less than 0.01 wt% based on the total weight of the solid content, a decrease in surface adhesive strength may occur, and if it is more than 5 wt%, a decrease in heat dissipation properties may occur, which is not preferable.

[0049] Graphene can be produced by a variety of methods, including mechanical exfoliation, epitaxial growth, thermal expansion, chemical functionalization, and gas-phase organic solvent dispersion. On an industrial scale, the most widely used methods are direct growth of graphene from a copper plate or catalyst substrate by chemical vapor deposition, and production of reduced graphene by oxidizing graphite to separate graphene oxide and then reducing the separated graphene oxide with a reducing agent or heat treatment.

[0050] However, chemical vapor deposition has the drawback of being difficult to apply to large areas, especially when transferring large areas to glass surfaces. The reduced graphene method, which involves producing graphene oxide from graphite and then reducing it, not only requires many steps, resulting in very low productivity, but also in the loss of the inherent physical properties of graphene.

[0051] The carbon material constituting the heat dissipation layer according to the present invention may include graphene manufactured by a liquid phase exfoliation method.

[0052] The liquid phase exfoliation method was devised to maintain the physical and electrical properties of graphene, and is a method for forming graphene without functional groups, which can prevent defects that occur when producing reduced graphene oxide (rGO) using chemical exfoliation. The liquid phase exfoliation method induces intercalation of graphite using an ionic substance and an organic solvent, disperses the intercalated graphite, and then separates the layers of the dispersed solution using ultracentrifugation to separate single-layer graphene.

[0053] Graphene produced by the liquid phase exfoliation method has better dispersibility than graphene produced by the existing CVD method or oxidation / reduction method, so a uniform coating layer can be formed without the use of a separate dispersant.In addition, because the liquid phase exfoliation method provides excellent crystallinity, when coated as a film, it has excellent adhesive strength due to π-π stacking.

[0054] The present invention provides a battery cell including the battery case, and the battery cell may be a pouch-type battery cell. Figure 1 shows a perspective view and a partial vertical cross-sectional view of a pouch-type battery cell according to the present invention.

[0055] Referring to FIG. 1, a pouch-type battery cell 100 has an electrode assembly 300 housed inside a pouch-type battery case 200, a sealing portion 202 formed around the outer periphery of a cup portion 201 in which the electrode assembly 300 is housed, an electrode lead 310 connected to an electrode tab of the electrode assembly 300 extends outward from the sealing portion 202 of the pouch-type battery case 200, and a heat dissipation layer 240 is provided on the outer surface of the pouch-type battery case 200.

[0056] A first embodiment of a method for manufacturing such a pouch-type battery cell includes the steps of preparing a pouch-type battery case made of a laminate sheet including a first resin layer, a metal layer, and a second resin layer, preparing a solution for a heat dissipation layer including a carbon material and a binder, forming a heat dissipation layer in the pouch-type battery case, and accommodating an electrode assembly in the pouch-type battery case and then sealing it.

[0057] The step of forming the heat-dissipating layer may be performed by coating the heat-dissipating layer on the outer surface of the second resin layer using a gravure coating method.

[0058] In the gravure coating method, a solution for the heat dissipation layer is prepared by adding 0.01 wt% to 1 wt% of an acrylic binder to the graphene ink prepared by the liquid phase exfoliation method.

[0059] Before forming the cup portion of the pouch-type battery case, the solution for the heat-dissipating layer is coated on the outer surface of the second resin layer by gravure coating to form a heat-dissipating layer.

[0060] A cup portion is formed in the pouch-type battery case having the heat dissipation layer formed therein, and the electrode assembly is accommodated therein, followed by heat sealing to manufacture a pouch-type battery cell.

[0061] The gravure coating method can form a heat dissipation layer with a uniform thickness, but since a pouch-type battery cell is manufactured using a coated pouch-type battery case, the heat dissipation layer is not formed on the electrode leads, lead films, etc.

[0062] As a method for manufacturing a pouch-type battery cell, the second embodiment may include the steps of preparing a pouch-type battery case made of a laminate sheet including a first resin layer, a metal layer, and a second resin layer, housing an electrode assembly in the pouch-type battery case and then sealing it, preparing a solution for a heat dissipation layer including a carbon material and a binder, and forming a heat dissipation layer on the pouch-type battery case.

[0063] The method for manufacturing a pouch-type battery cell according to the second embodiment differs from the method for manufacturing a pouch-type battery cell according to the first embodiment in that the step of forming a heat dissipation layer is performed after assembling the pouch-type battery cell.

[0064] Specifically, a solution for the heat dissipation layer is prepared by adding 0.01 wt% to 1 wt% of an acrylic binder to graphene ink prepared by the liquid phase exfoliation method.

[0065] A dip coating method can be used in which the remaining parts of the assembled pouch-type battery cell, excluding the electrode leads, are dipped into the heat dissipation layer solution to be coated.

[0066] The dip coating method has low process costs and can form a heat dissipation layer on all parts except the electrode leads, but has the disadvantages of not producing a uniform thickness of the heat dissipation layer and requiring a large amount of solution for forming the heat dissipation layer.

[0067] The present invention will be described below with reference to examples, but these are for easier understanding of the present invention and are not intended to limit the scope of the present invention.

[0068] Example 1 1 g of graphene ink prepared by the liquid phase exfoliation method and 0.1 g of an acrylic binder were added to 100 ml of ethanol as a solvent to prepare a solution for the heat dissipation layer.

[0069] The heat-dissipating layer solution was coated on the outer surface of the second resin layer of the pouch-shaped battery case by gravure coating to a thickness of 40 nm to form a heat-dissipating layer.

[0070] A cup portion was formed in the thus manufactured pouch-type battery case, and the electrode assembly was accommodated therein. Then, the outer periphery of the cup portion was subjected to heat sealing by heating and pressing, thereby manufacturing 10 pouch-type battery cells.

[0071] <Example 2> Ten pouch-type battery cells were manufactured in the same manner as in Example 1, except that the heat dissipation layer was formed to a thickness of 80 nm.

[0072] Example 3 Ten pouch-type battery cells were manufactured in the same manner as in Example 1, except that the heat dissipation layer was formed to a thickness of 200 nm.

[0073] Example 4 Ten pouch-type battery cells were manufactured in the same manner as in Example 1, except that the heat dissipation layer was formed to a thickness of 400 nm.

[0074] <Example 5> Ten pouch-type battery cells were manufactured in the same manner as in Example 1, except that the heat dissipation layer was formed to a thickness of 800 nm.

[0075] <Comparative Example> Ten pouch-type battery cells were manufactured in the same manner as in Example 1 using a pouch-type battery case without a heat-dissipating layer.

[0076] <Hot boxテスト> In order to check the heat dissipation performance of the pouch-type battery cells manufactured in Examples 1 to 5 and Comparative Example, fully charged pouch-type battery cells were placed in a chamber, and the temperature of the chamber was increased from room temperature at a rate of 5°C / min until it reached 140°C. After that, the temperature was maintained for 1 hour, and the presence or absence of damage to the pouch-type battery cells was checked.

[0077] The results and the cost of the heat dissipation layer by thickness are shown in Table 1 below.

[0078] <Adhesion test> For the pouch-type battery cases with heat dissipation layers formed thereon, prepared in Examples 1 to 5, a scratch was made on the surface of the heat dissipation layer by cross-hatching lines with an area of ​​10 mm x 10 mm using a cross hatch cutter, and then tape was applied. The tape was rubbed with a uniform force, and then the tape was peeled off, and the number of peeled pieces of the heat dissipation layer was counted.

[0079] The number of such heat dissipation layer pieces was used to indicate the magnitude of the adhesive strength of the heat dissipation layer as a numerical value from 0B to 5B.

[0080] Specifically, the adhesion test can be carried out according to the standards KS M ISO 2409 and ASTM D3359.

[0081] In the comparative example shown in Table 1 below, a pouch-type battery case without a heat-dissipating layer was used, so the adhesive strength of the heat-dissipating layer could not be measured.

[0082] [Table 1]

[0083] The results of the adhesion test were as follows: 5B: The cut surface was clean and the grid squares were not separated; 4B: Small pieces of the coating were separated at the intersections (less than 5% of the grid area); 3B: Small pieces of the coating were separated along the edges at the intersections of the cut sections (5-15% of the grid area); 2B: The edges of the coating were separated along the cut surface and some of the squares were separated (15-35% of the grid area); 1B: The coating was peeled off significantly along the cut surface edges and the squares were separated (35-65% of the grid area); 0B: The coating was peeled off more than in 1B and separated (more than 65% of the grid area).

[0084] Referring to Table 1, it can be seen that 30% of the pouch-type battery cells of Example 1, which had a heat dissipation layer thickness of 40 nm, failed the hot box test, and 70% of the pouch-type battery cells of the comparative examples failed the test. However, the results show that 100% of the pouch-type battery cells of Examples 2 to 5, which had heat dissipation layer thicknesses of 80 nm to 800 nm, passed the hot box test.

[0085] As described above, the present invention uses graphene produced by the liquid phase exfoliation method as the heat dissipation layer, so that a separate dispersant is not required, and the heat dissipation performance is significantly improved even when the heat dissipation layer is formed to a thickness in the range of several tens to several hundreds of nanometers.

[0086] Those skilled in the art will be able to make various applications and modifications within the scope of the present invention based on the above content. [Explanation of symbols]

[0087] 100 pouch-type battery cells 200 Pouch-type battery case 201 Cup section 202 Sealing section 210 1st resin layer 220 metal layer 230 Second resin layer 240 heat dissipation layer 300 electrode assembly stereo 310 electrode リード

Claims

1. a first resin layer having thermal fusion properties; a metal layer having moisture-blocking properties; a second resin layer for protecting the internal components from the outside; a heat dissipation layer including a carbon material and a binder; Including, the heat dissipation layer is added to a surface of the second resin layer, The battery case, wherein the heat dissipation layer has a thickness of 40 nm to 800 nm.

2. 2. The battery case according to claim 1, wherein the carbon material is at least one selected from the group consisting of graphite, carbon nanotubes (CNTs), single-walled carbon nanotubes (SWNTs), graphene, and activated carbon fiber (ACF).

3. The battery case according to claim 2 , wherein the carbon material is graphene produced by a liquid phase exfoliation method.

4. 2. The battery case according to claim 1, wherein the heat dissipation layer has a thickness of 80 nm to 800 nm.

5. 2. The battery case according to claim 1, wherein the binder is contained in an amount ranging from 0.01 wt % to 5 wt % based on the total weight of the solid content.

6. 2. The battery case according to claim 1, wherein the binder is at least one selected from the group consisting of epoxy-based, acrylic-based, hydrocarbon-based, polyester-based, vinyl-based, urethane-based, and acrylate-based binders, or a copolymer containing any of these.

7. A battery cell including the battery case according to any one of claims 1 to 6, An electrode assembly is housed inside the battery case, A sealing portion is formed around the outer periphery of the cup portion in which the electrode assembly is accommodated. an electrode lead connected to the electrode tab of the electrode assembly extends outward from the sealing portion of the battery case; The heat dissipation layer is provided on the outer surface of the battery case.

8. The method for manufacturing a battery cell according to claim 7, preparing a battery case made of a laminate sheet including the first resin layer, the metal layer, and the second resin layer; preparing a solution for a heat-dissipating layer, the solution including the carbon material and a binder; forming the heat dissipation layer on the battery case; housing an electrode assembly in the battery case and then sealing the battery case; A method for manufacturing a battery cell, comprising:

9. The method of claim 8 , wherein the forming of the heat dissipation layer is performed using a gravure coating method.

10. The method for manufacturing a battery cell according to claim 7, preparing a battery case made of a laminate sheet including the first resin layer, the metal layer, and the second resin layer; housing an electrode assembly in the battery case and then sealing the battery case; preparing a solution for a heat-dissipating layer, the solution including the carbon material and a binder; forming the heat dissipation layer on the battery case; A method for manufacturing a battery cell, comprising:

11. The method of claim 10 , wherein the forming of the heat dissipation layer is performed using a dip coating method.

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