Electrode assembly for secondary battery, and secondary battery comprising the same

Abstract

To provide an electrode assembly capable of effectively controlling a change in internal pressure due to a change in the volume of a secondary battery to improve the lifetime property of the battery, and a pouch-type secondary battery comprising the same.SOLUTION: The electrode assembly includes: a plurality of electrode structures, each comprising a positive electrode, a negative electrode and a solid electrolyte layer between the positive and negative electrodes; and polymer layers at both ends of the electrode assembly. Also provided is a secondary battery comprising the same.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0128239 filed September 28, 2021 and Korean Patent Application No. 10-2022-0121373 filed September 26, 2022, and the entire contents disclosed in the documents of the relevant Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to an electrode assembly for a secondary battery and a secondary battery including the same, and more particularly to an electrode assembly for a secondary battery capable of improving battery life and a secondary battery including the same. [Background technology]

[0003] Due to technological development and increasing demand for mobile devices, the demand for secondary batteries is also rapidly increasing. Among them, lithium secondary batteries, which have high energy density and operating voltage, as well as excellent storage and life characteristics, are widely used as an energy source for various electronic products as well as various mobile devices.

[0004] Secondary batteries are roughly classified into cylindrical batteries, prismatic batteries, and pouch-type batteries depending on their external and internal structural characteristics. Among them, prismatic batteries and pouch-type batteries, which can be stacked with high density and have a narrow width relative to their length, are attracting particular attention.

[0005] Secondary batteries are also attracting attention as an energy source for electric vehicles and hybrid electric vehicles, which are being proposed as a solution to address air pollution caused by existing gasoline and diesel vehicles that use fossil fuels. As a result, the types of applications using secondary batteries are becoming increasingly diverse due to the advantages of secondary batteries, and secondary batteries are expected to be applied to more fields and products in the future.

[0006] As the application fields and products of secondary batteries become more diverse, the types of batteries are also becoming more diverse to provide the appropriate output and capacity. At the same time, there is a strong demand for batteries applied to these fields and products to be smaller and lighter.

[0007] For example, small mobile devices such as mobile phones, PDAs, digital cameras, and laptops use one, two, or even three small and lightweight battery cells per device in response to the trend toward smaller, lighter, and thinner products. Meanwhile, medium- to large-sized devices such as electric vehicles and hybrid electric vehicles require high output and large capacity, so battery modules (also called "medium- to large-sized battery packs") in which multiple battery cells are electrically connected are used. Since the size and weight of a battery module are directly related to the storage space and output of the medium- to large-sized device, manufacturers are striving to produce battery modules that are as small and lightweight as possible.

[0008] Conventional pouch-type batteries are formed by bonding the two sides and the upper and lower ends of a housing formed on the inner surface of a two-unit exterior member, consisting of an upper and lower unit, with an electrode assembly housed inside the housing. The housing member has a laminate structure of a resin layer / metal foil layer / resin layer. The two sides and the upper and lower ends are bonded by applying heat and pressure to fuse the resin layers together, and in some cases, adhesives can also be used. The two sides are directly connected to the same resin layers of the upper and lower exterior members, allowing for a uniform seal through fusion. Meanwhile, because electrode leads protrude from the upper and lower ends, a film-like sealing material is interposed between the electrode leads and the housing member material, and heat-sealed to enhance sealing, taking into account the thickness of the electrode leads and the heterogeneity of the housing member material.

[0009] However, pouch-type secondary batteries repeatedly expand and contract during charging and discharging, causing changes in the internal pressure of the battery, which can adversely affect the battery's lifespan.

[0010] That is, since changes in the internal pressure of a battery have a negative effect on the battery life, there is a need to develop a technology that can effectively control such changes in the internal pressure of a battery. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Korean Patent Publication No. 2014-0141825 [Patent Document 2] Korean Patent Publication No. 2021-0039213 Summary of the Invention [Problem to be solved by the invention]

[0012] The present invention aims to solve the above problems and to provide an electrode assembly and a pouch-type secondary battery including the same that can effectively control changes in internal pressure due to changes in battery volume in order to improve the life characteristics of the secondary battery. [Means for solving the problem]

[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, the electrode assembly including a polymer layer on both ends of the electrode assembly.

[0014] The present invention also provides an electrode assembly in which the polymer layer has a yield strength of 5 MPa or more and 20 MPa or less.

[0015] The present invention also provides an electrode assembly in which the thickness of the polymer layer satisfies the following formula 1:

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

[0017] The present invention also provides an electrode assembly, wherein the polymer layer is made of rubber or silicone resin.

[0018] The present invention also provides an electrode assembly, wherein the solid electrolyte layer is a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a polymer-based solid electrolyte, or a mixture of two or more of these.

[0019] The present invention also provides an electrode assembly, wherein the solid electrolyte layer is a sulfide-based solid electrolyte having an argyrodite structure.

[0020] The present invention also provides a method for manufacturing a solid electrolyte layer comprising: 10 GeP2S 12 , Li3PS4, and Li7P3S 11 The present invention provides an electrode assembly comprising one or more selected from the group consisting of:

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

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

[0023] The present invention also 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 having a specific yield strength and a specific thickness at both ends of the electrode assembly, thereby effectively controlling changes in the internal pressure of the battery due to volume changes that occur during charging and discharging of the secondary battery.

[0025] In this way, by effectively controlling the change in internal pressure that occurs during charging and discharging of the secondary battery, the life characteristics of the secondary battery can be improved. [Brief explanation of the drawings]

[0026] [Figure 1] FIG. 1 is a cross-sectional view of a typical conventional pouch-type secondary battery. [Figure 2] 1 is a cross-sectional view of a pouch-type secondary battery according to the present invention. [Figure 3] 1 is a graph showing the life characteristics (capacity retention rate) of pouch-type secondary batteries manufactured in Examples 1 to 5 of the present invention and Comparative Examples 1 to 4. [Figure 4] 1 is a graph showing the life characteristics (capacity retention rate) of pouch-type secondary batteries manufactured in Example 6 of the present invention and Comparative Example 5. DETAILED DESCRIPTION OF THE INVENTION

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

[0028] 1, a conventional pouch-type secondary battery includes a stacked electrode assembly 100 in which a plurality of electrode structures are stacked inside a pouch-type battery case 106. The electrode assembly 100 includes a negative electrode in which a negative electrode active material layer 102 is stacked on both sides of a negative electrode current collector 101, a positive electrode in which a positive electrode active material layer 104 is 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] Such conventional pouch-type secondary batteries have a problem in that the battery itself repeatedly expands and contracts during charging and discharging, causing changes in the volume of the electrode assembly and resulting in changes in the internal pressure of the battery, which shortens the battery's lifespan.

[0030] In order to solve the above-mentioned problems, 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, the electrode assembly including a polymer layer on both ends of the electrode assembly.

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

[0032] Specifically, referring to FIG. 2, the electrode assembly according to the present invention may have a structure in which anode active material layers 202 are laminated on both sides of anode current collector 201, cathode active material layers 204 are laminated on both sides of cathode current collector 203, solid electrolyte layer 205 is interposed between the cathode and anode, and polymer layers 206 are further disposed on both ends.

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

[0034] In another embodiment of the present invention, the polymer layer 206 of the electrode assembly may be in a form that covers the entire surfaces of the adjacent positive and negative electrodes.

[0035] In another embodiment of the present invention, the polymer layer 206 of the electrode assembly may have an area equal to or greater than the area of the adjacent positive and negative electrodes.

[0036] In an embodiment of the present invention, the polymer layer may be an elastic material having elasticity capable of appropriately responding to internal pressure in order to control changes in internal pressure due to volume changes of the pouch-type secondary battery.

[0037] In another embodiment 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, or 12 MPa or more, or 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, so that a constant pressure is applied to the battery assembly during operation, allowing the lithium metal layer forming the anode to contact the solid electrolyte layer with a constant pressure, thereby suppressing the formation of lithium dendrites.Furthermore, the polymer layer contracts by an amount corresponding to the expansion volume of the electrode assembly during battery operation, thereby ensuring the structural stability of the battery.

[0039] If the yield strength of the polymer layer is outside this range, the internal pressure of the pouch-type secondary battery cannot be effectively controlled, so it is preferable that the yield strength of the polymer layer be within this 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·pcs)×X(mAh / cm 2 )×Y(pieces) (In the above formula 1, X represents the capacity 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 operation of the battery, and preferably has a thickness sufficient to buffer such volume change of the electrode assembly.

[0043] That is, if the thickness of the polymer layer of the present invention does not satisfy the above range, it will not be possible to sufficiently buffer the volume change of the electrode assembly and effectively control the internal pressure of the electrode assembly. Therefore, it is preferable that the thickness of the polymer layer satisfies the above range.

[0044] However, if the thickness of the polymer layer is too thick, the volume of the battery will be 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, but is not limited to, 3000 μm or less, 1000 μm or less, 500 μm or less, or 100 μm or less.

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

[0046] The polymer layer may be any type or composition as long as it covers the surfaces of the positive and negative electrodes at both ends of the battery assembly, has a uniform thickness, and has a uniform yield strength, and 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 a uniform yield strength without affecting the operation of the battery.

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

[0049] In one embodiment of the present invention, the solid electrolyte layer may be a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a polymer-based solid electrolyte, or a mixture of 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, and 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=70~80), 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), etc.

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

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

[0054] In an embodiment of the present invention, the positive electrode may include 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 may be included in the positive electrode active material layer 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 included 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 included 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, cross-linking of the binder in the positive electrode active material layer may be performed by introducing a cross-linking agent solution. According to another embodiment of the present invention, the cross-linking is performed throughout the electrode assembly after the entire electrode assembly is impregnated with the cross-linking agent solution, so that cross-linking of the binder may also be formed between interfaces such as the electrode and the solid electrolyte. Alternatively, in another embodiment of the present invention, the cross-linking may be performed only within the positive electrode depending on the target impregnated with the cross-linking agent solution.

[0057] In one embodiment of the present invention, the binder in the cathode active material layer is cross-linked, thereby improving mechanical properties such as elasticity and rigidity of the cathode. Therefore, even if the cathode active material expands and / or contracts during charge and discharge, the cathode active material layer can suppress or mitigate such effects. Furthermore, the adhesion at the interface between the cathode active material layer and the solid electrolyte layer is maintained, 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 may be dissolved in a non-polar solvent. Contact with a polar solvent can cause deterioration of physical properties, such as a decrease in ionic conductivity. Therefore, in the present invention, a non-polar solvent is used instead of a polar solvent during electrode fabrication, and a rubber-based binder resin with high solubility in the non-polar solvent is used as the binder component. In one embodiment of the present invention, the rubber-based binder resin may be selected to be soluble in the solvent used at a concentration of 50 wt % or more, 70 wt % or more, 90 wt % or more, or 99 wt % or more at about 25°C. The solvent may include a non-polar solvent, and may have a polarity index of 0 to 3 and / or a dielectric constant of less than 5. The use of a non-polar solvent can prevent a decrease in the ionic conductivity of the sulfide-based solid electrolyte due to 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; 1+x Mn 2-x Lithium manganese oxides such as LiMnO4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiFe3O4, V2O5, and Cu2V2O7; and the chemical formula LiNi 1-x M x Ni-site type lithium nickel oxide represented by the formula LiMnO2 (where M=Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x=0.01 to 0.3). 2-x M xThe compounds may include one or a mixture of two or more of the following: lithium manganese composite oxides represented by Li2Mn3MO8 (where M is Co, Ni, Fe, Cr, Zn, or Ta, and x is 0.01 to 0.1); LiMn2O4, in which part of the Li in the chemical formula is replaced with an alkaline earth metal ion; disulfide compounds; and 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 as electrode binders have low solubility in non-polar solvents, making it difficult to prepare electrode slurry. Therefore, in the present invention, a rubber-based resin with high solubility in non-polar solvents is used as the binder. In one embodiment of the present invention, the rubber-based binder resin may include at least one selected from the group consisting of natural rubber, butyl-based rubber, bromobutyl-based rubber, chlorinated butyl-based rubber, styrene-isoprene-based rubber, styrene-ethylene-butylene-styrene-based rubber, acrylonitrile-butadiene-styrene-based rubber, polybutadiene-based rubber, nitrile butadiene-based rubber, styrene butadiene-styrene-based rubber (SBS), and EPDM (ethylene propylene diene monomer)-based 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; and one or a mixture of two or more selected from titanium oxides.

[0063] In an embodiment of the present invention, the positive electrode current collector and the negative electrode current collector may be made of any material having high conductivity without causing any chemical change in the battery. For example, stainless steel, copper, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like may be used.

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

[0065] Specifically, the above-described positive electrode, solid electrolyte layer, and negative electrode are sequentially stacked and then laminated to manufacture a unit electrode structure. Then, a solid electrolyte layer is interposed between a plurality of unit electrode structures to manufacture a stack of unit electrode structures. Then, the above-described polymer layer is laminated on both ends of the stack of unit electrode structures. The stack is then housed in a pouch-type battery case and sealed to manufacture a pouch-type secondary battery.

[0066] Preferred examples are presented below to aid in understanding the present invention. However, the following examples are provided merely to facilitate understanding of the present invention, and the present invention is not limited thereto.

[0067] Example -Manufacture of pouch-type secondary batteries 1. Example 1 The positive electrode active material, an argyrodite-structured sulfide-based solid electrolyte (Li6PS5Cl), a conductive material, and a binder were mixed in a mass ratio of 80:15:1:4 to prepare a positive electrode active material slurry. The positive electrode active material slurry was applied to an aluminum current collector at a loading rate of 4 mAh / cm. 2 The cathode was fabricated by applying the coating to a thickness of 20 μm and then drying. Lithium metal was pressed onto copper foil to form the anode. The solid electrolyte layer used was a sulfide-based solid electrolyte (Li6PS5Cl) with an argyrodite structure.

[0068] The positive electrode, solid electrolyte layer, and negative electrode were sequentially stacked and then laminated to produce a unit electrode structure. Two unit electrode structures were prepared, and a solid electrolyte layer was stacked between the positive electrode of each unit electrode structure and the other unit electrode structure to produce a stack of unit electrode structures.

[0069] Thereafter, silicone rubber pads having a thickness of 20 μm and a yield strength of 5 MPa as polymer layers were laminated on both ends of the stack of unit electrode structures to manufacture an electrode assembly.

[0070] The electrode assembly was housed in a pouch-type battery case and sealed to prepare 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 was loaded onto an aluminum current collector at a rate of 3 mAh / cm 2 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.

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

[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 changes that occur during charging / discharging of pouch-type secondary batteries The pouch-type secondary batteries according to Examples 1 to 5 and Comparative Examples 1 to 4 were measured for volume changes occurring during charging / discharging.

[0082] Specifically, the pouch-type secondary batteries according to Examples 1 to 5 and Comparative Examples 1 to 4 were subjected to an initial charge / discharge cycle (single cycle) at room temperature using an electrochemical charge / discharge machine, and then the volumes of the pouch-type secondary batteries were measured. Charging was performed by applying a current at a current density of 0.1 C up to a voltage of 4.2 V, and discharging was performed at the same current density up to 3.0 V. This volume was defined as the initial volume.

[0083] After this charge / discharge cycle was repeated 100 times, the volume was measured and defined as the final volume.

[0084] The measured values of the initial volume and the final volume were substituted into the following formula 2 to calculate the volume change rate (%), which is shown in Table 1.

[0085] [Formula 2] Volume change rate (%) = {(final volume - initial volume) / initial volume} x 100 (%)

[0086] [Table 1]

[0087] Referring to Table 1, it can be seen that the pouch-type secondary batteries according to Examples 1 to 5 of the present invention can effectively control the change 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 the volume change of the pouch-type secondary battery was small, but the internal pressure of the pouch-type secondary battery became too high, causing a short circuit, which resulted in a rapid deterioration of the life characteristics.

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

[0090] (1) Specifically, the pouch-type secondary batteries according to Examples 1 to 5 and Comparative Examples 1 to 4 were subjected to an initial charge / discharge cycle at room temperature using an electrochemical charge / discharge machine. Charging was performed by applying a current at a current density of 0.1 C rate up to a voltage of 4.2 V, and discharging was performed at the same current density down to 3.0 V. This cycle was repeated 100 times in total.

[0091] The capacity of each battery was measured during the above-described charge and discharge process.

[0092] As a result, the capacity retention rate of each battery was 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) x 100

[0094] [Table 2]

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

[0096] (2) The pouch-type secondary batteries according to Example 6 and Comparative Example 5 were subjected to an initial charge / discharge cycle at room temperature using an electrochemical charge / discharge machine. Charging was performed by applying a current at a current density of 0.1 C up to a voltage of 4.2 V, and discharging was performed at the same current density down to 3.0 V. This cycle was repeated a total of 50 times.

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

[0098] As shown in FIG. 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 that of the pouch-type secondary battery according to Comparative Example 5.

[0099] (3) Considering these points, it has been confirmed that in the pouch-type secondary battery of the present invention, when an elastic body having a yield strength of 5 to 20 MPa and a thickness satisfying the following formula 1 is disposed on both ends of the stack of unit electrode assemblies, the life characteristics are significantly improved.

[0100] [Formula 1] Thickness (μm) ≥ 2.5 (μm cm 2 / mAh·pcs)×X(mAh / cm 2 )×Y(pieces) (In the formula 1, 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 variations of the present invention fall within the scope of the present invention, and the specific scope of protection of the present invention will be defined by the appended claims. [Explanation of symbols]

[0102] 10, 20: Pouch-type secondary 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 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, The electrode assembly includes a polymer layer on each end of the electrode assembly.

2. The electrode assembly according to claim 1 , wherein the polymer layer has a yield strength of 5 MPa to 20 MPa.

3. 2. The electrode assembly according to claim 1, wherein the thickness of the polymer layer satisfies the following formula 1: [Formula 1] Thickness (μm) ≧ 2.5 (μm cm ２ / mAh・pcs)×X(mAh / cm ２ ) x Y (pieces) (In the above formula 1, X represents the capacity per unit area of the positive electrode, Y indicates the number of positive electrodes in the electrode assembly).

4. The electrode assembly according to claim 1 , wherein the polymer layer is made of rubber or silicone resin.

5. 2. The electrode assembly according to claim 1, wherein the solid electrolyte layer comprises a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a polymer-based solid electrolyte, or two or more of these.

6. 2. The electrode assembly according to claim 1, wherein the solid electrolyte layer is a sulfide-based solid electrolyte having an argyrodite structure.

7. The solid electrolyte layer is Li ２ S-P ２ S ５ , Li ６ P.S. ５ Cl, Li １０ GeP ２ S １２ , Li ３ P.S. ４ , and Li ７ P ３ S １１ The electrode assembly according to claim 1 , comprising at least one selected from the group consisting of:

8. The electrode assembly according to claim 1 , wherein the electrode assembly comprises 1 to 100 stacked electrode structures.

9. The electrode assembly according to claim 1 , wherein the positive electrode comprises a positive electrode active material, a sulfide-based solid electrolyte, a conductive material, and a binder.

10. A pouch-type secondary battery comprising the electrode assembly according to claim 1.

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