Electrode assembly and lithium secondary battery including the same

Abstract

The present disclosure relates to an electrode assembly including: an electrode laminate including a positive electrode including a positive electrode active material layer, a negative electrode including a negative electrode active material layer, and a separator interposed between the positive electrode and the negative electrode; and at least one fixing member configured to fix the electrode laminate by surrounding the electrode laminate in the full width direction, in which the positive electrode includes a positive electrode change portion in which the thickness of the positive electrode active material layer is reduced; and at least one fixing member is provided so as to overlap a region corresponding to the positive electrode change portion.

Description

Technical Field

[0001] This application claims the benefit of Korean Patent Application No. 10-2022-0183641, filed on Dec. 23, 2022, the disclosure of which is incorporated herein by reference in its entirety.

[0002] The present disclosure relates to an electrode assembly and a lithium secondary battery including the electrode assembly, and more particularly, to an electrode assembly developed to suppress lithium plating in an electrode changing portion and a lithium secondary battery including the electrode assembly. Background Art

[0003] With the development of technologies such as electric vehicles, energy storage systems (ESSs), and portable electronic devices, the demand for lithium secondary batteries as an energy source has rapidly increased.

[0004] According to the material of the case accommodating the electrode assembly, lithium secondary batteries can be classified into a pouch type, a can type, etc., and according to the manufacturing method and form, the electrode assembly can be classified into a wound type (rolled type), a stacked type (laminated type), a stacked lamination type, a stacked folding type, etc.

[0005] Among them, a pouch type secondary battery is manufactured by pressing a flexible pouch film laminate to form a cup portion, accommodating the electrode assembly in the cup portion, injecting an electrolyte, and then sealing a sealing portion, and a can type secondary battery is manufactured by accommodating the electrode assembly in a can made of a metal material, injecting an electrolyte, and then assembling a top cover on the can to seal the can.

[0006] The electrode assembly has a structure including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, and the positive electrode and the negative electrode are respectively manufactured by coating a current collector with an electrode paste to form an active material layer and then drying and rolling. When manufacturing the electrode by coating the electrode paste, a changing portion where the thickness of the active material layer gradually decreases is formed at the end of the active material layer. In the region where the electrode changing portion is formed, the distance between the positive electrode active material layer and the negative electrode active material layer increases, and the adhesion to the separator decreases, so that lithium plating may occur.

[0007] In addition, in a lithium secondary battery, as charging and discharging are repeated, the electrolyte is consumed and the amount of the electrolyte decreases, and when the amount of the electrolyte in the battery decreases, the electrolyte does not reach the end of the electrode, thereby deteriorating the electrolyte impregnation ability. Therefore, the mobility of lithium ions deteriorates, and lithium plating may occur.

[0008] Meanwhile, since lithium secondary batteries have recently been used as power sources for electric vehicles, lithium secondary batteries having a relatively long overall length compared to the full width (hereinafter referred to as "long battery cells" for convenience) have been developed in consideration of the battery accommodation space and position. Compared with conventional lithium secondary batteries, the lithium secondary battery having such a long battery cell structure has the advantages of high capacity and excellent space efficiency, but there are the following limitations: as the charge and discharge are repeated, the pressing force at the end of the electrode assembly near the electrode tab decreases, so the adhesion between the separator and the electrode decreases, thereby further increasing lithium plating.

[0009] Therefore, it is necessary to develop an electrode assembly that can prevent lithium plating in the electrode changing portion and a lithium secondary battery including the electrode assembly. SUMMARY OF THE INVENTION

[0010] TECHNICAL PROBLEM

[0011] To solve the above limitations, one aspect of the present disclosure provides an electrode assembly that is developed to improve the adhesion between the electrode and the separator by disposing a fixing member to overlap with the positive electrode changing portion, and to suppress the occurrence of the lithium plating phenomenon by maintaining the pressing force at the end of the electrode assembly.

[0012] Another aspect of the present disclosure provides a lithium secondary battery that can prevent deterioration of battery performance and safety due to lithium precipitation by including the electrode assembly.

[0013] TECHNICAL SOLUTION

[0014] According to one aspect of the present disclosure, there is provided an electrode assembly including: an electrode stack including a positive electrode, a negative electrode, and a separator, the positive electrode including a positive electrode active material layer, the negative electrode including a negative electrode active material layer, and the separator being interposed between the positive electrode and the negative electrode; and at least one fixing member that fixes the electrode stack by surrounding the electrode stack in the full width direction. In this case, the positive electrode includes a positive electrode changing portion where the thickness of the positive electrode active material layer decreases; and at least one fixing member is disposed to overlap with a region corresponding to the positive electrode changing portion.

[0015] Meanwhile, the negative electrode may include a negative electrode changing portion where the thickness of the negative electrode active material layer decreases, and the fixing member may be disposed to overlap with at least a part of a region corresponding to the negative electrode changing portion.

[0016] Meanwhile, in the electrode stack, the ratio (L / W) of the overall length (L) to the full width (W) of the electrode stack may be at least 3, and preferably, the ratio (L / W) of the overall length (L) to the full width (W) may be 3 to 7.

[0017] The electrode assembly according to the present disclosure may include 2 to 10 fixing members, wherein a plurality of fixing members may be disposed at symmetric left and right positions in the total length direction, and preferably, a plurality of fixing members may be arranged at equal intervals.

[0018] The fixing member may include a porous structure, specifically, it may be a tape having an adhesive layer formed on one surface of a substrate having a porous structure.

[0019] The width of the fixing member may be 10 mm to 50 mm.

[0020] According to another aspect of the present disclosure, a lithium secondary battery is provided, including the electrode assembly according to the present disclosure, an electrolyte, and a battery case accommodating the electrode assembly and the electrolyte. In this case, the battery case may be a pouch-type battery case.

[0021] Advantageous Effects

[0022] In the electrode assembly according to the present disclosure, the fixing member is disposed to overlap with the region where the positive electrode variation portion is formed, thereby firmly maintaining the close contact between the electrode variation portion and the separator. Therefore, it is possible to minimize the decrease in lithium mobility due to poor interfacial adhesion between the electrode variation portion and the separator, thereby preventing lithium from precipitating from the electrode variation portion.

[0023] In addition, when the fixing member is disposed in a long battery cell in which the total length is longer than the total width as in the present disclosure, it is possible to suppress the decrease in the pressing force at the end of the electrode assembly due to the charge and discharge process, thereby minimizing the reduction of the electrolyte in the electrode variation portion and preventing the deterioration of battery performance.

[0024] Therefore, when the electrode assembly according to the present disclosure is applied, excellent performance and safety can be achieved until the end of the life of the lithium secondary battery. Brief Description of the Drawings

[0025] Figure 1 is a top view of an electrode assembly according to an embodiment of the present disclosure;

[0026] Figure 2 is a cross-sectional view of an electrode laminate according to an embodiment of the present disclosure;

[0027] Figure 3 is a photograph showing the state after cycling of a lithium secondary battery including an electrode assembly manufactured by an example; and

[0028] Figure 4 is a photograph showing the state after cycling of a lithium secondary battery including an electrode assembly manufactured by a comparative example. Detailed Description of the Embodiments

[0029] In the following, the present disclosure will be described in detail.

[0030] As a result of extensive repeated research on developing a lithium secondary battery that can achieve excellent performance and safety until the end of battery life, the present inventors have found that when forming an electrode assembly, the electrode laminate is fixed with a fixing member, and the fixing member is arranged to overlap with the region of the positive electrode change portion. Thus, even when repeated charge and discharge are performed, not only is the interfacial adhesion between the electrode change portion and the separator improved, but also a relatively uniform pressing force is maintained up to the end of the electrode assembly. As a result, until the end of battery life, the deterioration of battery performance is minimized, and excellent safety is achieved by suppressing ignition and / or explosion caused by lithium plating, thereby completing the present disclosure.

[0031] Specifically, an electrode assembly according to the present disclosure includes: an electrode laminate including a positive electrode, a negative electrode, and a separator; and at least one fixing member that fixes the electrode laminate by surrounding the outer surface of the electrode laminate in the full-width direction, wherein at least one fixing member is arranged to overlap with the region corresponding to the positive electrode change portion.

[0032] When the fixing member is arranged to overlap with the region of the positive electrode change portion as described above, the distance between the electrode change portion and the separator is maintained by the fixing member, and even if the volume change of the positive electrode active material layer and / or the negative electrode active material layer is caused by repeated charge and discharge, the fixing member prevents the distance between the electrode change portion and the separator from increasing. Therefore, even when repeated charge and discharge are performed, the interfacial adhesion between the separator and the electrode and the impregnation property of the electrolyte can be maintained at the end of the electrode assembly, thereby suppressing the occurrence of lithium plating caused by the deterioration of lithium mobility.

[0033] Figure 1 A top view of an electrode assembly according to an embodiment of the present disclosure is shown, and Figure 2 A cross-sectional view of an electrode laminate according to the present disclosure is shown. In the following, the present disclosure will be described in more detail with reference to the drawings. However, the following drawings are only examples for describing the present disclosure, and the scope of the present disclosure is not limited to the scope described in the drawings, and various modifications can be made within the scope of the present disclosure without impairing the purpose and spirit of the present disclosure.

[0034] As Figure 1 shown, according to the present disclosure, the electrode assembly 1 includes an electrode laminate 100 and at least one fixing member 200 that fixes the electrode laminate 100 by surrounding the electrode laminate 100 in the full-width direction.

[0035] Referring to Figure 2, the electrode laminate 100 includes a positive electrode 10, a negative electrode 20, and a separator 30. The positive electrode 10 includes positive electrode active material layers 12a and 12b, the negative electrode 20 includes negative electrode active material layers 22a and 22b, and the separator 30 is interposed between the positive electrode 10 and the negative electrode 20. The electrode laminate 100 may be a laminated electrode laminate formed by cutting a positive electrode, a separator, and a negative electrode into a predetermined size and then laminating them.

[0036] For example, the positive electrode 10 may have a structure in which the positive electrode active material layers 12a and 12b are formed on one surface or both surfaces of the positive electrode current collector 14, and the positive electrode active material layer includes a positive electrode central portion 12a in which the thickness of the positive electrode active material layer remains relatively constant and a positive electrode varying portion 12b in which the thickness of the positive electrode active material layer decreases. In addition, the positive electrode 10 includes a positive electrode tab 16 for electrically connecting to an external power source.

[0037] The positive electrode 10 of the lithium secondary battery is manufactured by coating one surface or both surfaces of the positive electrode current collector 14 with a positive electrode paste (prepared by dispersing a positive electrode active material, a conductive agent, and a binder in a solvent such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water), removing the solvent of the positive electrode paste through a drying process, and then winding the positive electrode current collector 14. When the positive electrode active material layer is formed by the wet coating method as described above, the amount of the positive electrode paste coated at the end of the positive electrode active material layer decreases, thereby forming the positive electrode varying portion 12b.

[0038] Meanwhile, various positive electrode current collectors used in the art can be used as the positive electrode current collector 14. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc. can be used as the positive electrode current collector. The positive electrode current collector generally may have a thickness of 3 μm to 500 μm, and microscopic irregularities may be formed on the surface of the positive electrode current collector to increase the adhesiveness of the positive electrode active material. The positive electrode current collector can be used in various shapes, for example, a film, a sheet, a foil, a net, a porous body, a foam body, a non-woven fabric body, etc.

[0039] Meanwhile, the positive electrode active material layers 12a and 12b may contain a positive electrode active material, a conductive agent, and a binder.

[0040] The positive electrode active material is a compound capable of reversibly inserting and extracting lithium, and various positive electrode active materials used in the art can be used, and its type is not particularly limited. For example, as the positive electrode active material, a lithium iron phosphate-based oxide (for example, LiFe 1-x M xPO4, 0 ≤ x1), lithium manganese-based oxides (e.g., LiMnO2, LiMn2O4, etc.), lithium cobalt-based oxides (e.g., LiCoO2, etc.), lithium nickel manganese-based oxides (e.g., LiNi 1-Y Mn Y O2 (0 < Y < 1), LiMn 2-Z Ni Z O4 (0 < Z < 2)), lithium nickel cobalt-based oxides (e.g., LiNi 1-Y1 Co Yl O2 (0 < Y1 < 1)), lithium manganese cobalt-based oxides (e.g., LiCo 1-Y2 Mn Y2 O2 (0 < Y2 < 1), LiMn 2-Z1 Co Z1 O4 (0 < Z1 < 2)), lithium nickel manganese cobalt-based oxides (e.g., Li(Ni p1 Co q1 Mn r1 )O2 (0 < p1 < 1, 0 < q1 < 1, 0 < r1 < 1 and p1 + q1 + r1 = 1) or Li(Ni p2 Co q2 Mn r2 )O4 (0 < p2 < 2, 0 < q2 < 2, 0 < r2 < 2 and p2 + q2 + r2 = 2)) or lithium nickel cobalt transition metal (M) oxides (e.g., Li(Ni p3 Co q3 Mn r3 M s3 )O2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, p3, q3, r3, and s3 are the atomic fractions of the independent elements, respectively, and 0 < p3 < 1, 0 < q3 < 1, 0 < r3 < 1, 0 < s3 < 1 and p2 + q2 + r3 + s2 = 1) or combinations thereof.

[0041] Relative to the total weight of the positive electrode active material layer, it may contain 80 wt% to 99 wt%, preferably 85 wt% to 99 wt%, more preferably 90 wt% to 99 wt% of the positive electrode active material.

[0042] The conductive agent is used to provide conductivity to the electrode. Among them, any conductive agent can be used without particular limitation as long as it has appropriate electronic conductivity and does not cause adverse chemical changes in the battery. Specific examples of the conductive agent can include, for example, graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, and carbon nanotube; powders or fibers of metals such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and any one of them can be used alone or a mixture of two or more of them can be used. Relative to the total weight of the positive electrode active material layer, the amount of the conductive agent can generally be 1 wt% to 30 wt%, preferably 1 wt% to 20 wt%, and more preferably 1 wt% to 10 wt%.

[0043] The binder is used to improve the adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples of the binder can include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one of them can be used alone or a mixture of two or more of them can be used. Relative to the total weight of the positive electrode active material layer, the amount of the binder can be 1 wt% to 30 wt%, preferably 1 wt% to 20 wt%, and more preferably 1 wt% to 10 wt%.

[0044] Next, the negative electrode 20 may have a structure in which the negative electrode active material layers 22a and 22b are formed on one surface or two surfaces of the negative electrode current collector 24. The negative electrode active material layer includes a negative electrode central portion 22a with a relatively constant thickness of the negative electrode active material layer and a negative electrode variable portion 22b with a reduced thickness of the negative electrode active material layer. In addition, the negative electrode 20 includes a negative electrode tab 26 for electrically connecting to an external power source.

[0045] The negative electrode 20 of a lithium secondary battery is manufactured by coating one or both surfaces of a negative electrode current collector 24 with a negative electrode paste (prepared by dispersing a negative electrode active material, a conductive agent, and a binder in a solvent such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water), removing the solvent of the negative electrode paste through a drying process, and then winding the negative electrode current collector 14. When the negative electrode active material layer is formed by the wet coating method as described above, the amount of the negative electrode paste coated at the end of the negative electrode active material layer decreases, thereby forming a negative electrode variable portion 22b. Although it varies depending on the negative electrode loading and coating conditions, the negative electrode variable portion 22b is generally formed to be longer than the positive electrode variable portion 12b.

[0046] As the negative electrode current collector, those commonly used in the art can be used. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, copper or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc., and aluminum cadmium alloy can be used as the negative electrode current collector. The negative electrode current collector generally can have a thickness of 3 μm to 500 μm, and similar to the positive electrode current collector, micro irregularities can be formed on the surface of the current collector to improve the adhesion of the negative electrode active material. For example, the negative electrode current collector can be used in various shapes, such as a film, a sheet, a foil, a net, a porous body, a foam body, and a non-woven fabric body.

[0047] Meanwhile, the negative electrode active material layer can contain a negative electrode active material, a conductive agent, and a binder.

[0048] As the negative electrode active material, compounds capable of reversibly intercalating and deintercalating lithium, which are commonly used in the art, can be used, and their types are not particularly limited. Specific examples of the negative electrode active material can include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, or amorphous carbon; silicon-based materials such as Si, Si-Me alloy (where Me is at least one selected from the group consisting of Al, Sn, Mg, Cu, Fe, Pb, Zn, Mn, Cr, Ti, and Ni), SiO y (where 0 < y < 2) or Si-C composite materials; lithium metal thin films; metal materials such as Sn or Al that can be alloyed with lithium; and any one of them or a mixture of two or more of them can be used.

[0049] Relative to the total weight of the negative electrode active material layer, the negative electrode active material can be contained in an amount of 80 wt% to 99 wt%, preferably 85 wt% to 99 wt%, more preferably 90 wt% to 99 wt%.

[0050] The conductive agent is used to provide conductivity to the negative electrode. Among them, any conductive agent can be used without particular limitation as long as it has appropriate electronic conductivity and does not cause adverse chemical changes in the battery. Specific examples of the conductive agent can include, for example, graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal carbon black, carbon fiber, and carbon nanotube; powders or fibers of metals such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and any one of them can be used alone or a mixture of two or more of them can be used. Relative to the total weight of the negative electrode active material layer, the amount of the conductive agent is generally 1 wt% to 30 wt%, preferably 1 wt% to 20 wt%, more preferably 1 wt% to 10 wt%.

[0051] The binder is used to improve the adhesion between the negative electrode active material particles and the adhesion between the negative electrode active material and the negative electrode current collector. Specific examples of the binder can include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one of them can be used alone or a mixture of two or more of them can be used. Relative to the total weight of the negative electrode active material layer, the amount of the binder can be 1 wt% to 30 wt%, preferably 1 wt% to 20 wt%, more preferably 1 wt% to 10 wt%.

[0052] Next, the separator 30 isolates the negative electrode and the positive electrode and provides a migration path for lithium ions. Among them, any separator can be used as the separator without particular limitation as long as it is commonly used in lithium secondary batteries. Specifically, a porous polymer membrane, for example, a porous polymer membrane prepared from a polyolefin-based polymer (such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer), or a laminated structure having two or more layers thereof can be used as the separator. In addition, conventional porous non-woven fabrics, for example, non-woven fabrics formed from high-melting-point glass fibers or polyethylene terephthalate fibers, can be used. In addition, a coated separator including a ceramic component or a polymer material can be used to ensure heat resistance or mechanical strength.

[0053] According to the present disclosure, when there is an electrode changing portion where the thickness of the active material layer included at the ends of the positive electrode and the negative electrode is reduced, the separator and the electrode active material layer do not adhere to the electrode changing portion, so that the lithium mobility is reduced compared with the central portion of the electrode. Therefore, a lithium plating phenomenon occurs in which the lithium ions generated in the positive electrode do not embed in the negative electrode and precipitate from the surface of the negative electrode during the discharging process. In addition, when the overall length of the electrode assembly increases, the pressing force at the end of the electrode assembly decreases. Therefore, the adhesiveness with the separator at the end of the electrode assembly further decreases, and when the electrolyte is consumed due to repeated charge and discharge, the electrolyte does not contact the electrode changing portion, thereby accelerating the battery performance degradation and lithium plating.

[0054] To solve this limitation, the fixing member 200 is provided to overlap with the positive electrode changing portion 12b, thereby improving the adhesiveness between the positive electrode changing portion 12b and the separator 30. When the fixing member 200 is provided according to the present disclosure, the reduction in lithium mobility due to the defect of the interfacial adhesion between the electrode changing portion and the separator can be minimized, and the reduction in the pressing force at the end of the electrode assembly due to the progress of charge and discharge can be suppressed, thereby minimizing the phenomenon of electrolyte reduction in the electrode changing portion.

[0055] More preferably, the fixing member 200 can be provided to overlap at least a part of the region corresponding to the negative electrode changing portion 22b. When the fixing member 200 is provided to overlap at least a part of the negative electrode changing portion, both the interfacial adhesion force between the positive electrode and the separator and the interfacial adhesion force between the negative electrode and the separator increase, so that the effects of suppressing lithium plating and performance degradation can be more excellent.

[0056] Meanwhile, in the electrode laminate, the ratio (L / W) of the overall length (L) to the overall width (W) can be at least 3, preferably 3 to 7, and more preferably 4 to 6. In this case, the overall width and the overall length respectively refer to the length in the width direction and the length in the length direction of the component having the largest size among the positive electrode, the negative electrode, and the separator constituting the electrode laminate. When the ratio of the overall length to the overall width of the electrode laminate is at least 3, the advantage is that a high capacity can be achieved. However, when the overall length is longer than the overall width, the pressing force of the battery cell at the end in the overall length direction weakens, and when the electrolyte is consumed due to charge and discharge, there may be a limitation in the deterioration of the electrolyte impregnation ability at the end. However, as in the present disclosure, when the fixing member is provided to overlap with the positive electrode changing portion, a relatively uniform pressing force is maintained until the end of the electrode laminate, so this limitation can be solved.

[0057] Specifically, the overall width of the electrode laminate according to the present disclosure may be from 50 mm to 200 mm, preferably from 70 mm to 200 mm, more preferably from 70 mm to 150 mm, and the overall length may be from 200 mm to 1000 mm, preferably from 300 mm to 800 mm, more preferably from 400 mm to 600 mm.

[0058] Meanwhile, the fixing member 200 may include a porous structure. When the fixing member includes a porous structure, the electrolytic solution can pass through the fixing member, and the electrode laminate can be impregnated with the electrolytic solution, thereby preventing the electrolytic solution impregnation ability of the electrode laminate from deteriorating due to the fixing member. Specifically, the fixing member 200 may be a finishing tape having an adhesive layer formed on one surface of a base material layer made of a polymer material having a porous structure, but is not limited thereto. For example, the polymer material may be polyethylene terephthalate (PET), polyvinyl chloride (PVC), polyethylene (PE), etc., but is not limited thereto.

[0059] Preferably, the width of the fixing member 200 in the overall width direction of the electrode laminate is about 10 mm to 50 mm or about 20 mm to 40 mm. When the width of the fixing member 200 is too wide, the outer surface area of the electrode laminate 100 covered by the fixing member 200 increases, and the contact area with the electrolytic solution decreases, so the electrolytic solution impregnation ability may deteriorate, and when the width is too small, the fixing effect of the electrode laminate may deteriorate.

[0060] Meanwhile, the electrode assembly according to the present disclosure may include 2 to 10 fixing members, preferably 2 to 8 fixing members, more preferably 3 to 7 fixing members. In this case, the plurality of fixing members may be disposed at symmetric positions in the overall length direction, and preferably, the plurality of fixing members may be spaced apart at equal intervals. When the plurality of fixing members are arranged and disposed as described above, the electrode laminate of the long battery cell structure having a long overall length can be firmly fixed, and the pressing force can be prevented from varying according to the position of the electrode laminate.

[0061] Next, a lithium secondary battery according to the present disclosure will be described.

[0062] The lithium secondary battery according to the present disclosure includes: an electrode assembly according to the present disclosure; an electrolytic solution; and a battery case in which the electrode assembly and the electrolytic solution are accommodated. Since the electrode assembly has been described above, only other components will be described below.

[0063] The lithium secondary battery according to the present disclosure can be manufactured by a method of accommodating the electrode assembly in a battery case, injecting the electrolytic solution therein, and sealing the battery case.

[0064] In this case, for example, the battery case may be a pouch-type battery case.

[0065] The pouch-type battery case may include a barrier layer, a base layer provided on one surface of the barrier layer, and a sealant layer provided on the other surface of the barrier layer, and may include at least one cup portion recessed in one direction.

[0066] Specifically, the pouch-type battery case is flexible, and can be manufactured by inserting a pouch film stack in which the base layer, the barrier layer, and the sealant layer are sequentially laminated into a pressing molding device, and stretching the pouch film stack by applying pressure to a partial area of the pouch film stack with a punch, thereby forming a cup portion recessed in one direction.

[0067] In this case, the base layer is provided on the outermost layer of the pouch-type battery case to protect the electrode assembly from external impacts and electrically insulate the electrode assembly.

[0068] The base layer may be made of a polymer material, for example, at least one polymer material selected from the group consisting of polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymer, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, poly(p-phenylene benzobisoxazole), polyarylate, and Teflon.

[0069] The base layer may have a single-layer structure or a multi-layer structure in which different polymer films are laminated. When the base layer has a multi-layer structure, an adhesive layer may be interposed between the polymer films.

[0070] For example, the base layer may have a laminated structure of a polyethylene terephthalate (PET) film and a nylon film. In this case, preferably, the nylon film is provided on the barrier layer side (i.e., the inner side), and the polyethylene terephthalate film is provided on the surface side of the pouch.

[0071] Polyethylene terephthalate has excellent durability and electrical insulation properties. Therefore, when the PET film is provided on the surface side, excellent durability and insulation properties are exhibited. However, in the case of the PET film, since the adhesion to the aluminum alloy thin film constituting the barrier layer is weak and the stretching properties are different, when the PET film is provided on the barrier layer side, peeling between the base layer and the barrier layer may occur during the molding process, and since the barrier layer is not uniformly stretched, there may be limitations in deteriorated formability. On the other hand, since the nylon film has stretching properties similar to those of the aluminum alloy thin film constituting the barrier layer, when the nylon film is provided between the polyethylene terephthalate and the barrier layer, an effect of improving formability can be obtained.

[0072] The thickness of the polyethylene terephthalate film may be 5 μm to 20 μm, preferably 5 μm to 15 μm, more preferably 7 μm to 15 μm, and the thickness of the nylon film may be 10 μm to 40 μm, preferably 10 μm to 35 μm, more preferably 15 μm to 25 μm. When the thickness of the polyethylene terephthalate film and the nylon film meet the above ranges, the formability and rigidity after molding are excellent.

[0073] At the same time, the total thickness of the base layer may be 10 μm to 60 μm, preferably 20 μm to 50 μm, and more preferably 30 μm to 50 μm. When the base layer has a multilayer structure, the thickness is the thickness including the adhesive layer. When the base layer meets the above range, durability, insulation and formability are excellent. If the base layer is too thin, durability may deteriorate and damage to the base layer may occur during the molding process. If the base layer is too thick, formability may deteriorate, the total thickness of the soft pack may increase, and the battery accommodation space may be reduced, thereby reducing energy density.

[0074] The barrier layer is used to ensure the mechanical strength of the pouch-type battery case, block the entry of gas, moisture, etc. outside the secondary battery, and prevent leakage of the electrolyte.

[0075] The barrier layer may be made of a metal material such as an aluminum alloy film. In this case, the aluminum alloy film may contain aluminum and may further contain, in addition to aluminum, one or more metal elements selected from the group consisting of iron (Fe), copper (Cu), chromium (Cr), manganese (Mn), nickel (Ni), magnesium (Mg), silicon (Si), and zinc (Zn).

[0076] The thickness of the barrier layer may be 40 to 100 μm, more preferably 50 to 80 μm, and more preferably 60 to 80 μm. When the thickness of the barrier layer satisfies the above range, formability is improved to increase the molding depth of the cup portion, or even when two cup portions are molded, cracks and / or pinholes are less likely to occur, thereby improving resistance to external stress after molding.

[0077] The sealant layer is attached by heat compression to seal the pouch-type battery case and is located on the inner layer of the battery case.

[0078] Since the sealant layer is the surface in contact with the electrolyte and electrode assembly after the soft pack is molded, the sealant layer should have insulation and corrosion resistance, and since its interior should be completely sealed to prevent material from moving between the inside and the outside, the sealant layer should have high sealing performance.

[0079] The sealant layer can be made of a polymeric material, for example, at least one selected from the group consisting of polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymers, polyacrylonitrile, polyimide, polyamide, cellulose, aromatic polyamide, nylon, polyester, poly(p-phenylene benzobisoxazole), polyarylate, and Teflon. Among these materials, particularly preferably, the sealant layer comprises polypropylene (PP) which has excellent mechanical properties (e.g., tensile strength, stiffness, surface hardness, abrasion resistance, and heat resistance) and excellent chemical properties (e.g., corrosion resistance).

[0080] More specifically, the sealant layer can comprise polypropylene, cast polypropylene (CPP), acid-modified polypropylene, a polypropylene-butene-ethylene copolymer, or a combination thereof.

[0081] The sealant layer can have a single-layer structure or can have a multi-layer structure including two or more layers made of different polymeric materials.

[0082] The total thickness of the sealant layer can be from 60 μm to 100 μm, preferably from 60 μm to 90 μm, more preferably from 70 μm to 90 μm. If the sealant layer is too thin, the sealing durability and insulation may deteriorate, and if the sealant layer is too thick, the curvature may deteriorate and the total thickness of the soft package stack may increase, resulting in a decrease in energy density per volume.

[0083] Next, the electrolyte is used to move lithium ions generated by the electrochemical reaction of the electrodes during charging and discharging of the secondary battery, and various electrolytes known in the art for lithium secondary batteries can be used, and their types are not particularly limited.

[0084] For example, the electrolyte can comprise an organic solvent and a lithium salt.

[0085] Any organic solvent can be used as the organic solvent without particular limitation, as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone can be used; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; or carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methylethyl carbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents such as ethanol and isopropanol; nitriles such as R-CN (where R is a linear, branched, or cyclic C2-C20 hydrocarbon group and may include double bonds, aromatic rings, or ether bonds); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolane can be used as the organic solvent. Among these solvents, carbonate-based solvents can be used. For example, a mixture of cyclic carbonates (such as ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant can be used, which can improve the charge-discharge performance of the battery, and low-viscosity linear carbonate-based compounds (such as ethylmethyl carbonate, dimethyl carbonate, or diethyl carbonate) can be used.

[0086] A lithium salt can be used without particular limitation as long as it is a compound that can provide lithium ions for use in a lithium secondary battery. Specifically, LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiA1O4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, etc. can be used as the lithium salt. Preferably, a lithium salt with a concentration range of 0.1 M to 5.0 M, preferably 0.1 M to 3.0 M is used. When the concentration of the lithium salt is within the above range, the electrolyte can have appropriate conductivity and viscosity, thereby exhibiting excellent performance, and lithium ions can move effectively.

[0087] To improve the life characteristics of the battery, suppress the reduction of the battery capacity, and increase the discharge capacity of the battery, in addition to the above electrolyte components, additives can be further included in the electrolyte.

[0088] Implementing the embodiments of the present disclosure

[0089] Hereinafter, the present disclosure will be described in more detail through specific examples.

[0090] Examples

[0091] Prepare a positive electrode with dimensions of 70 mm × 500 mm, a negative electrode with dimensions of 75 mm × 505 mm, and a separator with dimensions of 80 mm × 510 mm, and stack the positive electrode / separator / negative electrode in sequence to form an electrode laminate.

[0092] At this time, the positive electrode is prepared by coating an aluminum current collector with a length of 500 mm with a positive electrode paste, making the total length of the positive electrode active material layer 490 mm, then drying and winding the current collector and forming positive electrode variable portions with a length of 8 mm at both ends of the positive electrode active material layer.

[0093] In addition, the negative electrode is prepared by coating a copper current collector with a length of 505 mm with a negative electrode paste, making the total length of the negative electrode active material layer 495 mm, then drying and winding the current collector and forming negative electrode variable portions with a length of 10 mm at both ends of the negative electrode active material layer.

[0094] Next, five fixing members are wound around the outer surface of the electrode laminate in the full-width direction to manufacture an electrode assembly. At this time, the fixing members provided at both ends of the electrode laminate are set to be located 5 mm from the end of the positive electrode, and the distance between the fixing members is set to an equal interval. As the fixing member, a trimming tape with a width of 30 mm (0.022T, PET, Daehyun ST, ST-5595DG(HF)) is used.

[0095] Comparative Example

[0096] An electrode assembly is manufactured in the same manner as in the example, except that the fixing member is set to be located 30 mm from the end of the positive electrode.

[0097] Experimental Example

[0098] The electrode assemblies prepared in the examples and comparative examples are each accommodated in a soft-pack type battery case in which nylon / polyethylene terephthalate / Al alloy film / polypropylene are stacked in sequence and a cup portion is formed, an electrolyte is injected therein, and then the battery case is sealed to manufacture a lithium secondary battery.

[0099] Then, the manufactured lithium secondary battery is charged to 4.22 V at 0.33 °C and discharged to 2.5 V at 0.33 °C, which is set as one cycle, and 800 charge-discharge cycles are repeated, and then the electrode laminate is separated to visually confirm whether lithium plating occurs.

[0100] Figure 3 A photograph showing the state after 800 cycles of the lithium secondary battery using the electrode assembly of the example is shown. Figure 4 A photograph showing the state after 800 cycles of the lithium secondary battery using the electrode assembly of the comparative example is shown. Refer to Figure 3 andFigure 4 As can be seen, no lithium plating occurred in the lithium secondary battery using the electrode assembly of the use example, but lithium plating did occur in the lithium secondary battery using the electrode assembly of the comparative example.

[0101] [Description of Reference Numerals]

[0102] 1: Electrode assembly

[0103] 10: Positive electrode

[0104] 20: Negative electrode

[0105] 30: Separator

[0106] 100: Electrode laminate

[0107] 200: Fixing member

[0108] 300: Electrolyte

Claims

1. An electrode assembly, comprising: An electrode laminate including a positive electrode, a negative electrode, and a separator, the positive electrode including a positive electrode active material layer, the negative electrode including a negative electrode active material layer, and the separator being interposed between the positive electrode and the negative electrode; and At least one fixing member configured to fix the electrode laminate by surrounding the electrode laminate in the full-width direction, Wherein the positive electrode includes a positive electrode variation portion where the thickness of the positive electrode active material layer is reduced, and The at least one fixing member is disposed to overlap with a region corresponding to the positive electrode variation portion.

2. The electrode assembly according to claim 1, wherein, The negative electrode includes a negative electrode variation portion where the thickness of the negative electrode active material layer is reduced.

3. The electrode assembly according to claim 2, wherein, The fixing member is disposed to overlap with at least a part of a region corresponding to the negative electrode variation portion.

4. The electrode assembly according to claim 1, wherein, The ratio (L / W) of the overall length (L) to the overall width (W) of the electrode laminate is at least 3.

5. The electrode assembly according to claim 1, wherein, The ratio (L / W) of the overall length (L) to the overall width (W) of the electrode laminate is 3 to 7.

6. The electrode assembly according to claim 1, wherein, The electrode assembly includes 2 to 10 fixing members, and The plurality of fixing members are disposed at symmetric left and right positions in the overall length direction.

7. The electrode assembly according to claim 6, wherein, The plurality of fixing members are disposed to be spaced apart from each other at equal intervals.

8. The electrode assembly according to claim 1, wherein, The fixing member includes a porous structure.

9. The electrode assembly according to claim 1, wherein, The fixing member is a tape having an adhesive layer formed on one surface of a substrate having a porous structure.

10. The electrode assembly according to claim 1, wherein, The width of the fixing member is 10 mm to 50 mm.

11. A lithium secondary battery, comprising: The electrode assembly according to any one of claims 1 to 10; An electrolyte; And A battery case, wherein the electrode assembly and the electrolyte are accommodated in the battery case.

12. The lithium secondary battery according to claim 11, wherein, The battery case is a soft-pack type battery case.

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