Electrode assembly for secondary battery and secondary battery containing the same

Abstract

The present invention provides an electrode assembly including a plurality of electrode structures each including a positive electrode, a negative electrode, and a solid electrolyte layer disposed between the positive electrode and the negative electrode, the electrode assembly including a polymer layer on both ends of the electrode assembly, and a secondary battery including the electrode assembly.

Description

[Technical Field]

[0001] This application claims the benefit of priority under Korean Patent Application No. 10-2021-0128239 dated September 28, 2021, and Korean Patent Application No. 10-2022-0121373 dated September 26, 2022, and incorporates all the contents disclosed in the relevant Korean patent applications as part of this specification.

[0002] The present invention relates to an electrode assembly for a secondary battery and a secondary battery containing the same, and more particularly to an electrode assembly for a secondary battery and a secondary battery containing the same that can improve battery life. [Background technology]

[0003] With technological advancements and increasing demand for mobile devices, the demand for rechargeable batteries has also surged. Among these, lithium-ion batteries, which have high energy density and operating voltage, as well as excellent storage and lifespan characteristics, are widely used as an energy source not only for various mobile devices but also for a wide range of electronic products.

[0004] Secondary batteries are broadly classified into cylindrical batteries, prismatic batteries, and pouch-type batteries based on their external and internal structural characteristics. Among these, prismatic batteries and pouch-type batteries, which can be stacked with a high degree of integration and have a narrow width relative to their length, are attracting particular attention.

[0005] Furthermore, secondary batteries are attracting attention as an energy source for electric vehicles and hybrid electric vehicles, which are being presented as solutions to address air pollution caused by existing gasoline and diesel vehicles that use fossil fuels. Therefore, the types of applications using secondary batteries are becoming increasingly diverse due to their advantages, and it is expected that secondary batteries will be applied to many more fields and products in the future.

[0006] As the application fields and products of secondary batteries diversify, the types of batteries themselves are also diversifying to provide the appropriate output and capacity. At the same time, there is a strong demand for smaller and lighter batteries to be used in these fields and products.

[0007] For example, small mobile devices such as mobile phones, PDAs, digital cameras, and laptops use one, two, or three small, lightweight battery cells per device to match the trend towards miniaturization and thinning of these products. On the other hand, medium- and large-sized devices such as electric vehicles and hybrid electric vehicles use battery modules (also called "medium- and large-sized battery packs") that electrically connect numerous battery cells to meet the need for high output and large capacity. However, the size and weight of the battery module are directly related to the space required to house the medium- and large-sized device and its output, so manufacturers strive to produce battery modules that are as small and lightweight as possible.

[0008] Conventional pouch-type batteries are formed by housing an electrode assembly in an outer casing consisting of two upper and lower units and a storage compartment formed on its inner surface, and then bonding the contact points, namely both sides, the upper end, and the lower end. The outer casing has a laminate structure of resin layer / metal foil layer / resin layer, and can be bonded by applying heat and pressure to the two contacting sides, the upper end, and the lower end to fuse the resin layers together, or in some cases, by using an adhesive. Since the same resin layer of the upper and lower outer casings is in direct contact with both sides, uniform sealing is possible by melting. On the other hand, since electrode leads protrude from the upper and lower ends, a film-like sealing member is interposed between the electrode leads and the outer casing material to enhance sealing performance, taking into account the thickness of the electrode leads and their different properties from the outer casing material, and then heat-sealing is performed.

[0009] However, pouch-type rechargeable batteries undergo repeated expansion and contraction during the charging and discharging process, causing changes in the internal pressure of the battery. This poses a problem that negatively impacts the battery's lifespan.

[0010] That is, since the change in the internal pressure of the battery affects the battery life, it is necessary to develop a technology that can effectively control such a change in the internal pressure of the battery.

Prior Art Documents

Patent Documents

[0011]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0012] The present invention is for solving the above problems, and in order to improve the life characteristics of a secondary battery, it aims to provide an electrode assembly capable of effectively controlling the change in internal pressure due to the volume change of the battery and a pouch - type secondary battery including the same.

Means for Solving the Problems

[0013] To achieve the above object, the present invention provides an electrode assembly including an electrode structure including a positive electrode, a negative electrode, and a solid electrolyte layer disposed between the positive electrode and the negative electrode, and polymer layers at both ends of the electrode assembly.

[0014] Also, the present invention provides an electrode assembly in which the yield strength of the polymer layer is 5 MPa or more and 20 MPa or less.

[0015] Also, the present invention provides an electrode assembly in which the thickness of the polymer layer satisfies the following Equation 1.

[0016] [Equation 1] Thickness (μm) ≥ 2.5 (μm·cm 2 / mAh·piece) × X (mAh / cm 2 ) × Y (piece) (In the above formula 1, The above X represents the capacitance per unit area of ​​the positive electrode. Y indicates the number of positive electrodes in the electrode assembly.

[0017] Furthermore, the present invention provides an electrode assembly in which the polymer layer is made of rubber or silicone resin.

[0018] Furthermore, the present invention provides an electrode assembly in which the solid electrolyte layer contains a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a polymer-based solid electrolyte, or two or more of these.

[0019] Furthermore, the present invention provides an electrode assembly in which the solid electrolyte layer is a sulfide-based solid electrolyte with an argyrodite structure.

[0020] Furthermore, the present invention relates to a solid electrolyte layer that is Li2S-P2S5, Li6PS5Cl, Li 10 GeP2S 12 Li3PS4 and Li7P3S 11 The present invention provides an electrode assembly that includes one or more selected from the group consisting of the following.

[0021] Furthermore, the present invention provides an electrode assembly in which the electrode assembly includes a structure in which 1 to 100 of the electrode structures are stacked.

[0022] Furthermore, the present invention provides an electrode assembly in which the positive electrode comprises a positive electrode active material, a sulfide-based solid electrolyte, a conductive material, and a binder.

[0023] Furthermore, the present invention provides a pouch-type secondary battery including the electrode assembly. [Effects of the Invention]

[0024] The electrode assembly according to the present invention includes polymer layers with specific yield strength and thickness at both ends of the electrode assembly, thereby effectively controlling the change in internal pressure of the battery caused by volume changes during charging and discharging of the secondary battery.

[0025] In this way, by effectively controlling the changes in internal pressure that occur during the charging and discharging of secondary batteries, the lifespan characteristics of secondary batteries can be improved. [Brief explanation of the drawing]

[0026] [Figure 1] This is a cross-sectional view of a typical conventional pouch-type rechargeable battery. [Figure 2] This is a cross-sectional view of a pouch-type secondary battery according to the present invention. [Figure 3] This graph shows the life characteristics (capacity retention rate) of pouch-type secondary batteries manufactured according to Examples 1 to 5 and Comparative Examples 1 to 4 of the present invention. [Figure 4] This graph shows the life characteristics (capacity retention rate) of pouch-type secondary batteries manufactured according to Example 6 and Comparative Example 5 of the present invention. [Modes for carrying out the invention]

[0027] The present invention will be described in more detail below with reference to drawings illustrating embodiments of the present invention, but the scope of the present invention is not limited thereto.

[0028] In a conventional pouch-type secondary battery, as shown in Figure 1, a stack-type electrode assembly 100 is arranged inside a pouch-type battery case 106, with multiple electrode structures stacked on top of each other. The electrode assembly 100 consists of a negative electrode with negative electrode active material layers 102 stacked on both sides of a negative electrode current collector 101, a positive electrode with positive electrode active material layers 104 stacked on both sides of a positive electrode current collector 103, and a solid electrolyte layer 105 interposed between the positive electrode and the negative electrode.

[0029] Conventional pouch-type rechargeable batteries have a problem in that during the charging and discharging process, the battery itself expands and contracts repeatedly, causing changes in the internal pressure of the battery due to volume changes in the electrode assembly, which shortens the battery's lifespan.

[0030] To solve the aforementioned problems of the prior art, the present invention provides an electrode assembly comprising an electrode structure including a positive electrode, a negative electrode, and a solid electrolyte layer disposed between the positive electrode and the negative electrode, wherein the electrode assembly includes polymer layers at both ends.

[0031] In one embodiment of the present invention, the electrode assembly may be the electrode assembly 200 shown in Figure 2.

[0032] Specifically, referring to Figure 2, the electrode assembly according to the present invention can have a negative electrode in which a negative electrode active material layer 202 is laminated on both sides of a negative electrode current collector 201, a positive electrode in which a positive electrode active material layer 204 is laminated on both sides of a positive electrode current collector 203, a solid electrolyte layer 205 interposed between the positive electrode and the negative electrode, and polymer layers 206 further arranged at both ends.

[0033] In one embodiment of the present invention, the negative electrode current collector 201 and the positive electrode current collector 203 can be extended to form electrode taps, and the electrode taps can be extended to one side of the battery case. The electrode taps can be fused together with one side of the battery case to form electrode leads that are extended to or exposed outside the battery case.

[0034] In another embodiment of the present invention, the polymer layer 206 of the electrode assembly may be configured to cover the entire surfaces of the contacting positive and negative electrodes.

[0035] In another embodiment of the present invention, the polymer layer 206 of the electrode assembly may be the same as or larger than the area of ​​the positive and negative electrodes in contact with it.

[0036] In one embodiment of the present invention, the polymer layer may be an elastic body having elastic force that can appropriately respond to the internal pressure in order to control the change in internal pressure due to the volume change of the pouch-type secondary battery.

[0037] In other embodiments of the present invention, the yield strength of the polymer layer may be 5 MPa or more and 20 MPa or less. More specifically, the yield strength of the polymer layer may be 5 MPa or more, 6 MPa or more, 7 MPa or more, 8 MPa or more, 9 MPa or more, 10 MPa or more, 11 MPa or more, 12 MPa or more, and may be 20 MPa or less, 19 MPa or less, 18 MPa or less, 17 MPa or less, 16 MPa or less, 15 MPa or less, 14 MPa or less, or 13 MPa or less, but is not limited thereto.

[0038] The polymer layer satisfies the yield strength range, thereby applying a constant pressure to the battery assembly during operation, allowing the lithium metal layer forming the negative electrode to come into contact with the solid electrolyte layer at a constant pressure, thereby suppressing the formation of lithium dendrites. Furthermore, the polymer layer contracts by an amount corresponding to the volume expansion of the electrode assembly during battery operation, thereby ensuring the structural stability of the battery.

[0039] If the yield strength of the polymer layer falls outside the range, the internal pressure of the pouch-type secondary battery cannot be effectively controlled; therefore, it is preferable that the yield strength of the polymer layer stays within the range.

[0040] In one embodiment of the present invention, the thickness of the polymer layer may satisfy the following formula 1.

[0041] [Formula 1] Thickness (μm) ≥ 2.5 (μm·cm) 2 / mAh·pieces) × X (mAh / cm²) 2 )×Y(pieces) (In the above formula 1, The above X represents the capacitance per unit area of ​​the positive electrode. Y indicates the number of positive electrodes in the electrode assembly.

[0042] The polymer layer serves to buffer the volume change of the electrode assembly during battery operation, and it is preferable that it has sufficient thickness to buffer such volume changes of the electrode assembly.

[0043] In other words, if the thickness of the polymer layer in the present invention does not meet the above range, it is not possible to adequately buffer the volume change of the electrode assembly, and the internal pressure of the electrode assembly cannot be effectively controlled. Therefore, it is preferable that the thickness of the polymer layer meets the above range.

[0044] However, if the polymer layer is too thick, the volume of the battery becomes too large, which is undesirable, so the thickness of the polymer layer is preferably 5000 μm or less. The thickness of the polymer layer may be, for example, 3000 μm or less, 1000 μm or less, 500 μm or less, or 100 μm or less, but is not limited to these.

[0045] In one embodiment of the present invention, the polymer layer may be an elastic body, and the elastic body may be made of rubber or silicone resin, but is not limited thereto.

[0046] The polymer layer only needs to be able to cover the surfaces of the positive and negative electrodes at both ends of the battery assembly, and its type and composition are not limited as long as it has a uniform thickness and uniform yield strength, as long as it does not affect the operation of the battery.

[0047] The polymer layer may be a silicone rubber pad, from the viewpoint of maintaining a uniform thickness and uniform yield strength without affecting the operation of the battery.

[0048] In one embodiment of the present invention, the solid electrolyte layer is not limited to any particular component and may include one or more inorganic solid electrolytes such as crystalline solid electrolytes, amorphous solid electrolytes, and glass-ceramic solid electrolytes.

[0049] In one embodiment of the present invention, the solid electrolyte layer may include a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a polymer-based solid electrolyte, or two or more of these.

[0050] In another embodiment of the present invention, the solid electrolyte layer may include a sulfide-based solid electrolyte having an argyrodite structure.

[0051] The solid electrolyte layer may preferably include a sulfide-based solid electrolyte. Examples of such sulfide-based solid electrolytes include lithium sulfide, silicon sulfide, germanium sulfide, and boron sulfide. Specific examples of such solid electrolytes include LPS-type solid electrolytes such as Li2S-P2S5, Li 3.833 Sn 0.833 As 0.166 S4, Li4SnS4, Li 3.25 Ge 0.25 P 0.75 S4, B2S3-Li2S, xLi2S-(100-x)P2S5 (x = 70 to 80), Li2S-SiS2-Li3N, Li2S-P2S5-LiI, Li2S-SiS2-LiI, Li2S-B2S3-LiI, Li3N, LISICON, LIPON (Li 3+y PO 4-x N x ), Thio-LISICON (Li 3.25 Ge 0.25 P 0.75 S4), Li2O-Al2O3-TiO2-P2O5 (LATP), and the like.

[0052] The solid electrolyte layer may preferably include one or more selected from the group consisting of Li2S-P2S5, Li6PS5Cl, Li 10 GeP2S 12 , Li3PS4, and Li7P3S 11 .

[0053] In one embodiment of the present invention, the electrode assembly may include a plurality of electrode structures. For example, it may include 1 to 100 electrode structures. Preferably, it may include 1 to 50 electrode structures.

[0054] In one embodiment of the present invention, the positive electrode may consist of a positive electrode active material layer and a positive electrode current collector, and the positive electrode active material layer may include a positive electrode active material, a sulfide-based solid electrolyte, a conductive material, and a binder.

[0055] In another embodiment of the present invention, the binder may be crosslinked. The sulfide-based solid electrolyte in the positive electrode active material layer may be present in a ratio of 5 to 100 parts by weight relative to 100 parts by weight of the positive electrode active material. The binder may be present in a ratio of 0.1 to 10 parts by weight relative to 100 parts by weight of the positive electrode active material layer, and the conductive material may be present in a ratio of 0.1 to 10 parts by weight relative to 100 parts by weight of the positive electrode active material layer.

[0056] In one embodiment of the present invention, the crosslinking of the binder in the positive electrode active material layer can be performed by adding a crosslinking agent solution. According to another embodiment of the present invention, the crosslinking is performed throughout the entire electrode assembly after the entire electrode assembly has been impregnated with the crosslinking agent solution, so that the binder can be crosslinked even between interfaces such as the electrode and the solid electrolyte. Alternatively, in another embodiment of the present invention, the crosslinking may be performed only within the positive electrode depending on the object being impregnated with the crosslinking agent solution.

[0057] In one embodiment of the present invention, the positive electrode active material layer has its mechanical properties, such as elasticity and rigidity, improved by the crosslinking of the binder. This allows the positive electrode active material layer to suppress or mitigate the effects of expansion and / or contraction of the positive electrode active material during charging and discharging, and maintains adhesion at the interface between the positive electrode active material layer and the solid electrolyte layer, thereby providing an all-solid-state battery with excellent cycle characteristics.

[0058] In one embodiment of the present invention, the binder includes a rubber-based binder resin. The rubber-based binder resin can be dissolved in a nonpolar solvent. When sulfide-based solid electrolyte components come into contact with polar solvents, physical properties such as decreased ionic conductivity may occur. In this invention, the use of a nonpolar solvent is eliminated during electrode manufacturing, and a rubber-based binder resin with high solubility in a nonpolar solvent is used as the binder component. In one embodiment of the present invention, the rubber-based binder resin can be selected and used if it dissolves in the solvent at a concentration of 50% or more by weight, 70% or more by weight, 90% or more by weight, or 99% or more by weight, based on approximately 25°C. Furthermore, the solvent can include a nonpolar solvent with a polarity index of 0 to 3 and / or a dielectric constant of less than 5. By using a nonpolar solvent in this way, it is possible to prevent the decrease in ionic conductivity of the sulfide-based solid electrolyte caused by the use of a polar solvent.

[0059] In one embodiment of the present invention, the positive electrode active material is a layered compound such as lithium manganese composite oxide (LiMn2O4, LiMnO2, etc.), lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; chemical formula Li 1+x Mn 2-x Lithium manganese oxides such as O4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiFe3O4, V2O5, Cu2V2O7; chemical formula LiNi 1-x M x Ni-site type lithium nickel oxide represented as O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x = 0.01 to 0.3); chemical formula LiMn 2-x M xLithium manganese composite oxides represented as O2 (where M = Co, Ni, Fe, Cr, Zn, or Ta, and x = 0.01 to 0.1) or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu, or Zn); LiMn2O4 in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion; disulfide compounds; and may contain one or more of the following: Fe2(MoO4)3.

[0060] In one embodiment of the present invention, the binder may include a rubber-based binder resin. PVdF-based binder resins and acrylic-based binder resins used in electrode binders have low solubility in nonpolar solvents, making electrode slurry production difficult. Therefore, in the present invention, a rubber-based resin with high solubility in nonpolar solvents is used as the binder. In one embodiment of the present invention, the rubber-based binder resin may include one or more selected from the group consisting of natural rubber, butyl rubber, bromo-butyl rubber, chlorinated butyl rubber, styrene-isoprene rubber, styrene-ethylene-butylene-styrene rubber, acrylonitrile-butadiene-styrene rubber, polybutadiene rubber, nitrile-butadiene rubber, styrene-butadiene rubber, styrene-butadiene-styrene rubber (SBS), and EPDM (ethylene propylene diene monomer) rubber.

[0061] In one embodiment of the present invention, the conductive material may be any one selected from the group consisting of, for example, graphite, carbon black, carbon fiber or metal fiber, metal powder, conductive whisker, conductive metal oxide, activated carbon, and polyphenylene derivative, or a mixture of two or more of these conductive materials. More specifically, it may be one selected from the group consisting of natural graphite, artificial graphite, super-p, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, denka black, aluminum powder, nickel powder, zinc oxide, potassium titanate, and titanium oxide, or a mixture of two or more of these conductive materials.

[0062] In one embodiment of the present invention, the negative electrode may include a negative electrode active material laminated on a negative electrode current collector. Examples of the negative electrode active material include carbon such as lithium metal oxide, graphitizable carbon, and graphite-based carbon; Li x Fe2O3 (0 ≤ x ≤ 1), Li x WO2 (0 ≤ x ≤ 1), Sn x Me 1-x Me' y O z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8), etc. metal composite oxides; lithium metal; lithium alloy; silicon-based alloy; tin-based alloy; metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, Bi2O5; conductive polymers such as polyacetylene; Li-Co-Ni-based materials; one or a mixture of two or more selected from titanium oxides.

[0063] In one embodiment of the present invention, the positive electrode current collector and the negative electrode current collector are not particularly limited as long as they have high conductivity without causing a chemical change in the battery, and for example, stainless steel, copper, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. can be used.

[0064] The present invention provides a pouch-type secondary battery that houses the electrode assembly described above.

[0065] Specifically, after sequentially stacking the positive electrode, solid electrolyte layer, and negative electrode as described above, laminating them to produce a unit electrode structure, then interposing a solid electrolyte layer between multiple unit electrode structures to produce a stack of unit electrode structures, then stacking the polymer layers described above on both ends of the stack of unit electrode structures, and finally housing them in a pouch-type battery case and sealing them, a pouch-type secondary battery can be manufactured.

[0066] The following are preferred embodiments to aid in understanding the present invention, but these embodiments are provided only to facilitate understanding the present invention and the invention is not limited thereto.

[0067] Examples - Manufacturing of pouch-type rechargeable batteries 1. Example 1 A positive electrode active material slurry was prepared by mixing a positive electrode active material, an argyrodite-structured sulfide-based solid electrolyte (Li6PS5Cl), a conductive material, and a binder in a mass ratio of 80:15:1:4. The positive electrode active material slurry was then loaded onto an aluminum current collector at a loading rate of 4 mAh / cm². 2 After coating the material to achieve the desired consistency, it was dried to produce the positive electrode. Lithium metal was compressed onto copper foil to a thickness of 20 μm and used as the negative electrode. For the solid electrolyte layer, an argyrodite-structured sulfide-based solid electrolyte (Li6PS5Cl) was used.

[0068] A unit electrode structure was manufactured by sequentially stacking the positive electrode, solid electrolyte layer, and negative electrode, and then laminating them. Two of these unit electrode structures were prepared, and a stack of unit electrode structures was manufactured by stacking the solid electrolyte layer between the positive electrode of each unit electrode structure and the other unit electrode structure.

[0069] Subsequently, an electrode assembly was manufactured by layering silicone rubber pads, each 20 μm thick and with a yield strength of 5 MPa, as polymer layers on both ends of the stack of the unit electrode structures.

[0070] After placing the electrode assembly into a pouch-type battery case, it was sealed to manufacture a pouch-type secondary battery.

[0071] 2. Example 2 A pouch-type secondary battery was manufactured in the same manner as in Example 1, except that the yield strength of the silicone rubber pad was 10 MPa.

[0072] 3. Example 3 A pouch-type secondary battery was manufactured in the same manner as in Example 1, except that the yield strength of the silicone rubber pad was 20 MPa.

[0073] 4. Example 4 A pouch-type secondary battery was manufactured in the same manner as in Example 1, except that the thickness of the silicone rubber pad was 50 μm.

[0074] 5. Example 5 A pouch-type secondary battery was manufactured in the same manner as in Example 1, except that the thickness of the silicone rubber pad was 100 μm.

[0075] 6. Example 6 The positive electrode active material slurry is loaded onto an aluminum current collector with a loading capacity of 3 mAh / cm². 2 The material was applied in the same manner as in Example 1, except that the thickness of the silicone rubber pad was 15 μm.

[0076] Comparative Example 1. Comparative Example 1 A pouch-type secondary battery was manufactured in the same manner as in Example 1, except that it did not include a silicone rubber pad.

[0077] 2. Comparative Example 2 A pouch-type secondary battery was manufactured in the same manner as in Example 1, except that the yield strength of the silicone rubber pad was 3 MPa.

[0078] 3. Comparative Example 3 A pouch-type secondary battery was manufactured in the same manner as in Example 1, except that the yield strength of the silicone rubber pad was 30 MPa.

[0079] 4. Comparative Example 4 A pouch-type secondary battery was manufactured in the same manner as in Example 1, except that the thickness of the silicone rubber pad was 15 μm.

[0080] 5. Comparative Example 5 A pouch-type secondary battery was manufactured in the same manner as in Example 6, except that the thickness of the silicone rubber pad was 10 μm.

[0081] Experimental example 1. Measurement of volume change that occurs during charging / discharging of pouch-type rechargeable batteries. The volume change that occurs during charging and discharging was measured for the pouch-type secondary batteries according to Examples 1 to 5 and Comparative Examples 1 to 4.

[0082] Specifically, the pouch-type secondary batteries described in Examples 1 to 5 and Comparative Examples 1 to 4 underwent an initial (single) charge-discharge cycle at room temperature using an electrochemical charger, and the volume of the pouch-type secondary battery was then measured. In the charge-discharge cycle, charging was performed by applying current at a current density of 0.1C up to a voltage of 4.2V, and discharging was performed at the same current density down to 3.0V. This is defined as the initial volume.

[0083] Subsequently, after performing this charge-discharge cycle a total of 100 times, the volume was measured. This volume is defined as the final volume.

[0084] The volume change rate (%) is calculated by substituting the measured initial and final volumes into Equation 2 below and is shown in Table 1.

[0085] [Formula 2] Volume change rate (%) = {(Final volume - Initial volume) / Initial volume} × 100 (%)

[0086] [Table 1]

[0087] Referring to Table 1 above, it was confirmed that the pouch-type secondary batteries according to Examples 1 to 5 of the present invention effectively control changes in internal pressure compared to the pouch-type secondary batteries according to Comparative Examples 1, 2, and 4.

[0088] On the other hand, in the case of the pouch-type secondary battery according to Comparative Example 3, the yield strength of the silicone rubber pad was too high, so although the volume change of the pouch-type secondary battery was small, the internal pressure of the pouch-type secondary battery became too high, causing a short circuit, which rapidly deteriorated the life characteristics.

[0089] 2. Evaluation of the life characteristics of pouch-type rechargeable batteries The capacity retention rate was measured using the pouch-type secondary batteries described in Examples 1 to 6 and Comparative Examples 1 to 5 in the following manner. The results are shown in Table 2, Figure 3, and Figure 4.

[0090] (1) Specifically, the pouch-type secondary batteries according to Examples 1 to 5 and Comparative Examples 1 to 4 underwent initial (single) charge-discharge cycles at room temperature using an electrochemical charger. During these charge-discharge cycles, charging was performed by applying current at a rate of 0.1 C to a voltage of 4.2 V, and discharging was performed at the same current density to a voltage of 3.0 V. A total of 100 such charge-discharge cycles were performed.

[0091] The capacity of each battery was measured during the charging and discharging process described above.

[0092] Based on this, the capacity retention rate of each battery is calculated using the following formula 3, and the results are shown in Table 2 below.

[0093] [Formula 3] Capacity retention rate (%) = (Capacity after 100 cycles / Initial capacity) × 100

[0094] [Table 2]

[0095] As shown in Table 2 above, it was confirmed that the capacity retention rate of the pouch-type secondary batteries according to Examples 1 to 5 of the present invention was significantly improved compared to the pouch-type secondary batteries according to Comparative Examples 1 to 4.

[0096] (2) In addition, the pouch-type secondary batteries of Example 6 and Comparative Example 5 were subjected to an initial (single) charge-discharge cycle at room temperature using an electrochemical charge-discharger. During the charge-discharge cycle, charging was performed by applying current at a current density of 0.1C up to a voltage of 4.2V, and discharging was performed at the same current density up to 3.0V. A total of 50 such charge-discharge cycles were performed.

[0097] The capacity of each battery was measured during the charging and discharging process described above, and the results are shown in Figure 4.

[0098] As shown in Figure 4, it was confirmed that the capacity retention rate of the pouch-type secondary battery according to Example 6 of the present invention was significantly improved compared to the pouch-type secondary battery according to Comparative Example 5.

[0099] (3) Considering these points, it was confirmed that in the pouch-type secondary battery of the present invention, when elastic bodies with a yield strength of 5 to 20 MPa and a thickness satisfying the following formula 1 are placed at both ends of the stack of the unit electrode assembly, the life characteristics are significantly improved.

[0100] [Formula 1] Thickness (μm) ≥ 2.5 (μm·cm) 2 / mAh·pieces) × X (mAh / cm²) 2 )×Y(pieces) (In Equation 1 above, X represents the capacity per unit area of ​​the positive electrode, and Y represents the number of positive electrodes in the pouch-type secondary battery.)

[0101] Any simple modifications or changes to the present invention fall within the scope of the present invention, and the specific scope of protection of the present invention is clarified by the appended claims. [Explanation of symbols]

[0102] 10, 20: Pouch-type rechargeable battery 100, 200: Electrode assembly 101, 201: Negative electrode current collector 102, 202: Negative electrode active material layer 103, 203: Positive electrode current collector 104, 204: Positive electrode active material layer 105, 205: Solid electrolyte layer 106, 207: Battery case

Claims

1. An electrode assembly comprising an electrode structure including a positive electrode, a negative electrode, and a solid electrolyte layer disposed between the positive electrode and the negative electrode, The electrode assembly includes polymer layers only at both ends in the stacking direction, The yield strength of the polymer layer is 5 MPa or more and 20 MPa or less. The thickness of the polymer layer satisfies the following formula 1, The solid electrolyte layer is a sulfide-based solid electrolyte with an argyrodite structure. The aforementioned polymer layer is made of an elastic material, An electrode assembly having a polymer layer thickness of 100 μm or less: [Formula 1] Thickness (μm) ≥ 2.5 (μm·cm) ２ / mAh・pcs)×X(mAh / cm ２ ) x Y (pieces) (In the above formula 1, The above X represents the capacitance per unit area of ​​the positive electrode. Y indicates the number of positive electrodes in the electrode assembly.

2. The electrode assembly according to claim 1, characterized in that the polymer layer is made of rubber or silicone resin.

3. where the solid electrolyte layer contains Li ２ S - P ２ S ５ , Li ６ PS ５ , Li １０ GeP ２ S １２ , Li ３ PS ４ , and Li ７ P ３ S １１ The electrode assembly according to claim 1, characterized in that it contains one or more selected from the group consisting of

4. The electrode assembly according to claim 1, characterized in that the electrode assembly includes a structure in which 1 to 100 of the electrode structures are stacked.

5. The electrode assembly according to claim 1, characterized in that the positive electrode comprises a positive electrode active material, a sulfide-based solid electrolyte, a conductive material, and a binder.

6. A pouch-type secondary battery comprising the electrode assembly described in claim 1.

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