KR20230045568A - Electrode assembly for a rechargeable battery and a rechargeable battery comprising the same - Google Patents

Abstract

The present invention relates to an electrode assembly for a secondary battery and a secondary battery including the same. The electrode assembly includes an electrode structure including a positive electrode, a negative electrode, and a solid electrolyte layer disposed between the positive electrode and the negative electrode. A polymer layer is formed at both ends of the electrode assembly. According to the present invention, it is possible to effectively control changes in the internal pressure of a battery due to changes in volume.

Description

Electrode assembly for secondary battery and secondary battery including the same

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.

With the development of technology and increase in demand for mobile devices, the demand for secondary batteries is also rapidly increasing. Among them, lithium secondary batteries with high energy density and operating voltage and excellent preservation and lifespan characteristics are used for various mobile devices as well as various electronic products. It is widely used as an energy source.

Secondary batteries are roughly classified into cylindrical batteries, prismatic batteries, and pouch-type batteries according to their external and internal structural features. Among them, prismatic batteries and pouch-type batteries that can be stacked with high integration and have a small width compared to the length receive special attention. are receiving

In addition, secondary batteries are attracting attention as an energy source for electric vehicles, hybrid electric vehicles, etc., which are proposed as a solution to air pollution such as existing gasoline vehicles and diesel vehicles using fossil fuels. Therefore, the types of applications using secondary batteries are becoming very diversified due to the advantages of secondary batteries, and it is expected that secondary batteries will be applied to more fields and products than now.

As the application fields and products of secondary batteries diversify in this way, the types of batteries are also diversified to provide output and capacity suitable for them. In addition, there is a strong demand for miniaturization and weight reduction of batteries applied to the related fields and products.

For example, small mobile devices such as mobile phones, PDAs, digital cameras, notebook computers, etc., use one or two or three or four small and lightweight battery cells per device in accordance with the trend of miniaturization and thinning of corresponding products. On the other hand, in medium and large-sized devices such as electric vehicles and hybrid electric vehicles, due to the need for high power and large capacity, battery modules electrically connecting a plurality of battery cells (also referred to as "medium-large battery packs") are used. Battery modules Since the size and weight of are directly related to the accommodation space and output of the medium-large sized device, manufacturers are trying to manufacture battery modules that are as compact and lightweight as possible.

A conventional pouch-type battery is formed by adhering both sides, which are contact parts, to upper and lower ends in a state in which an electrode assembly is housed in an exterior member composed of two upper and lower units and a receiving part formed on an inner surface thereof. The external mounting material is composed of a laminate structure of a resin layer / metal foil layer / resin layer, and can be bonded by mutually fusing the resin layers by applying heat and pressure to both sides and upper and lower ends that are in contact with each other. In some cases, using an adhesive can be glued. Since the both sides are in direct contact with the same resin layer of the upper and lower exterior members, uniform sealing is possible by melting. On the other hand, since the electrode leads protrude from the upper and lower ends, heat is applied between the electrode leads and the sealing member on the film to improve sealing performance in consideration of the thickness of the electrode leads and heterogeneity with the exterior member material. to fuse

However, as the pouch-type secondary battery repeatedly expands and contracts during charging and discharging, the internal pressure of the battery changes. Due to this, there was a problem of adversely affecting the life of the battery.

That is, since the change in the internal pressure of the battery adversely affects the life of the battery, there is a need to develop a technology capable of effectively controlling the change in the internal pressure of the battery.

Republic of Korea Patent Publication No. 2014-0141825 Republic of Korea Patent Publication No. 2021-0039213

The present invention is to solve the above problems, to provide an electrode assembly capable of effectively controlling the change in internal pressure due to the change in the volume of the battery and a pouch-type secondary battery including the same in order to characterize the lifespan of the secondary battery. do.

In order to achieve the above object, the present invention is 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, comprising polymer layers at both ends of the electrode assembly An electrode assembly is provided.

In addition, 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.

In addition, the present invention provides an electrode assembly in which the thickness of the polymer layer satisfies Equation 1 below.

[Equation 1]

Thickness (μm) ≥ 2.5 (μm cm ² /mAh pcs) x X (mAh/cm ² ) x Y (pcs)

(In the above formula 1,

X represents the capacity per unit area of the positive electrode,

Y represents the number of anodes of the electrode assembly.)

In addition, the present invention provides an electrode assembly in which the polymer layer is made of rubber or silicone resin.

In addition, the present invention provides an electrode assembly in which the solid electrolyte layer includes a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a polymer-based solid electrolyte, or two or more of them.

In addition, the present invention provides an electrode assembly in which the solid electrolyte layer is a sulfide-based solid electrolyte having an Argyrodite structure.

In addition, in the present invention, the solid electrolyte layer is one selected from the group consisting of Li ₂ SP ₂ S ₅ , Li ₆ PS ₅ Cl, Li ₁₀ GeP ₂ S ₁₂ , Li ₃ PS ₄ , and Li ₇ P ₃ S ₁₁ It provides an electrode assembly that includes the above.

In addition, the present invention provides an electrode assembly, wherein the electrode assembly includes a structure in which 1 to 100 of the electrode structures are stacked.

In addition, the present invention provides an electrode assembly in which the positive electrode includes a positive electrode active material, a sulfide-based solid electrolyte, a conductive material and a binder.

In addition, the present invention provides a pouch type secondary battery including the electrode assembly.

The electrode assembly according to the present invention includes a polymer layer having a specific yield strength and a specific thickness at both ends of the electrode assembly, so that the internal pressure of the battery is changed by the change in volume occurring during charging and discharging of the secondary battery. can be effectively controlled.

In this way, life characteristics of the secondary battery can be improved by effectively controlling the change in internal pressure generated during charging/discharging of the secondary battery.

1 is a cross-sectional view of a conventional representative pouch-type secondary battery.
2 is a cross-sectional view of a pouch type secondary battery according to the present invention.
3 is a graph showing 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.
4 is a graph showing life characteristics (capacity retention rate) of pouch-type secondary batteries manufactured according to Example 6 and Comparative Example 5 of the present invention.

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

Referring to FIG. 1 , in a conventional pouch-type secondary battery, a stack-type electrode assembly 100 in which a plurality of electrode structures are stacked is disposed 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 laminated on both sides of a negative electrode current collector 101, a positive electrode in which a positive electrode active material layer 104 is laminated on both sides of a positive electrode current collector 103, and the above It consists of a solid electrolyte layer 105 interposed between an anode and a cathode.

Such a conventional pouch-type secondary battery has a problem in that the internal pressure of the battery changes due to the volume change of the electrode assembly while the battery itself repeatedly expands and contracts during the charging and discharging process, thereby shortening the life of the battery.

In order to solve the above conventional problems, the present invention is 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, including polymer layers at both ends of the electrode assembly. It provides an electrode assembly that

In one embodiment of the present invention, the electrode assembly may be the electrode assembly 200 shown in FIG. 2 .

Specifically, referring to FIG. 2, the electrode assembly according to the present invention includes a negative electrode in which a negative electrode active material layer 202 is laminated on both sides of a negative electrode current collector 201, and a positive electrode active material layer on both sides of a positive electrode current collector 203 ( 204) may have a structure in which a positive electrode is stacked, a solid electrolyte layer 205 interposed between the positive electrode and the negative electrode, and a polymer layer 206 are additionally disposed at both ends.

In one embodiment of the present invention, the positive current collector 201 and the negative current collector 203 may be extended to form an electrode tab, respectively, and the electrode tab may extend to one side of the battery case. The electrode tabs may be fused together with one side of the battery case to form an electrode lead extending or exposed to the outside of the battery case.

In another embodiment of the present invention, the polymer layer 206 of the electrode assembly may cover the entire surfaces of adjacent anodes and cathodes.

In another embodiment of the present invention, the area of the polymer layer 206 of the electrode assembly may be equal to or greater than the area of adjacent anodes and cathodes.

In one embodiment of the present invention, the polymer layer may be an elastic body having elasticity capable of appropriately responding to internal pressure in order to control a change in internal pressure according to a change in volume of a pouch-type secondary battery.

In another embodiment of the present invention, the yield strength of the polymer layer (Yield strength) may be 5Mpa or more and 20Mpa or less. More specifically, the yield strength of the polymer layer may be 5Mpa or more, 6Mpa or more, 7Mpa or more, 8Mpa or more, 9Mpa or more, 10Mpa or more, 11Mpa or more, 12Mpa or more, 20Mpa or less, 19Mpa or less, 18Mpa or less, It may be 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.

By satisfying the range of the yield strength, the polymer layer can apply a constant pressure to the battery assembly during driving to bring the lithium metal layer forming the negative electrode into contact with the solid electrolyte layer at a constant pressure. formation can be inhibited. In addition, the polymer layer contracts by an amount corresponding to the expansion volume of the electrode assembly during operation of the battery, thereby ensuring structural stability of the battery.

When the yield strength of the polymer layer is out of the above range, the internal pressure of the pouch type secondary battery cannot be effectively controlled, so the yield strength of the polymer layer preferably satisfies the above range.

In one embodiment of the present invention, the thickness of the polymer layer may satisfy Equation 1 below.

[Equation 1]

Thickness (㎛) ≥2.5 (㎛ cm ² /mAh · piece) x X (mAh/cm ² ) x Y (piece)

(In the above formula 1,

X represents the capacity per unit area of the positive electrode,

Y represents the number of anodes of the electrode assembly.)

The polymer layer serves to buffer the volume change of the electrode assembly during operation of the battery, and preferably has a sufficient thickness to buffer the volume change of the electrode assembly.

That is, when the thickness of the polymer layer of the present invention does not satisfy the above range, the thickness of the polymer layer satisfies the above range because the internal pressure of the electrode assembly cannot be effectively controlled because the volume change of the electrode assembly cannot be sufficiently buffered. It is desirable to do

However, if the thickness of the polymer layer is too thick, the volume of the battery may be excessively large, which is undesirable. Therefore, the thickness of the polymer layer is preferably 5,000 μm or less. The thickness of the polymer layer may be, for example, 3,000 μm or less, 1,000 μm or less, 500 μm or less, or 100 μm or less, but is not limited thereto.

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

As long as the polymer layer can cover the surfaces of the positive electrode and the negative electrode at both ends of the battery assembly, and has a uniform thickness and uniform yield strength as long as it does not affect the driving of the battery, the type and composition of the polymer layer are not limited. don't

The polymer layer may be a silicone rubber pad from the point of view of maintaining a uniform thickness and uniform yield strength without affecting the operation of the battery.

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

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.

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

The solid electrolyte layer may preferably include a sulfide-based solid electrolyte, and examples of the sulfide-based solid electrolyte include lithium sulfide, silicon sulfide, germanium sulfide, and boron sulfide. Specific examples of such a solid electrolyte include an LPS type solid electrolyte such as Li ₂ SP ₂ S ₅ , Li _3.833 Sn _0.833 As _0.166 S ₄ , Li ₄ SnS ₄ , Li _3.25 Ge _0.25 P _0.75 S ₄ , B ₂ S ₃ -Li ₂ S, xLi ₂ S-(100-x)P ₂ S ₅ (x=70~80), Li ₂ S-SiS ₂ -Li ₃ N, Li ₂ SP ₂ S ₅ -LiI, Li ₂ S-SiS ₂ -LiI, Li ₂ SB ₂ S ₃ -LiI, Li ₃ N, LISICON, LIPON (Li _3+y PO _4-x N _x ), Thio-LISICON (Li _3.25 Ge _0.25 P _0.75 S ₄ ), Li ₂ O- Al ₂ O ₃ -TiO ₂ -P ₂ O ₅ (LATP); and the like.

The solid electrolyte layer preferably includes one or more selected from the group consisting of Li ₂ SP ₂ S ₅ , Li ₆ PS ₅ Cl, Li ₁₀ GeP ₂ S ₁₂ , Li ₃ PS ₄ , and Li ₇ P ₃ S ₁₁ can do.

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

In one 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.

In another embodiment of the present invention, the binder may be cross-linked. In the positive electrode active material layer, the sulfide-based solid electrolyte may be included in an amount of 5 parts by weight to 100 parts by weight based on 100 parts by weight of the positive electrode active material. In addition, the binder may be included in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the positive electrode active material layer, and the conductive material may be included in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the positive electrode active material layer.

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, since the crosslinking proceeds throughout the entire electrode assembly after the entire electrode assembly is impregnated with the crosslinking agent solution, crosslinking of the binder may be formed even between the interface such as the electrode and the solid electrolyte. Alternatively, in another embodiment of the present invention, depending on the object to be impregnated with the crosslinking agent solution, the crosslinking may be performed only within the anode.

In one embodiment of the present invention, the positive electrode active material layer suppresses this effect even if the positive electrode active material expands and/or contracts during charging and discharging because mechanical properties such as elasticity and rigidity of the positive electrode are improved by crosslinking the binder. Alternatively, it may be relieved, and the adhesion of the interface between the positive electrode active material layer and the solid electrolyte layer is maintained to provide an all-solid-state battery with excellent cycle characteristics.

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. When the sulfide-based solid electrolyte component comes into contact with a polar solvent, deterioration in physical properties such as deterioration in ionic conductivity may occur. Therefore, in the present invention, when manufacturing an electrode, a non-polar solvent is used instead of a polar solvent, and a rubber-based binder resin having high solubility in non-polar solvents is used as a component of the binder. In one embodiment of the present invention, the rubber-based binder resin is selected to dissolve at least 50% by weight, at least 70% by weight, at least 90% by weight, or at least 99% by weight based on the solvent used at about 25 ° C. and can be used. In addition, the solvent includes a non-polar solvent, and a polarity index of 0 to 3 and/or a dielectric constant of less than 5 may be used. By using the non-polar solvent as described above, it is possible to prevent a decrease in ionic conductivity of the sulfide-based solid electrolyte due to the use of a polar solvent.

In one embodiment of the present invention, the positive electrode active material is a layered compound such as lithium manganese composite oxide (LiMn ₂ O ₄ , LiMnO ₂ , etc.), lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or one or compounds substituted with more transition metals; lithium manganese oxides such as Li _1+x Mn _2-x O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ ; lithium copper oxide (Li ₂ CuO ₂ ); vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ , and Cu ₂ V ₂ O ₇ ; Ni site type lithium nickel oxide represented by the formula LiNi _1-x M _x O ₂ , where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3; Formula LiMn _2-x M _x O ₂ where M = Co, Ni, Fe, Cr, Zn or Ta and x = 0.01 to 0.1 or Li ₂ Mn ₃ MO ₈ where M = Fe, Co, Ni, Cu or Zn) lithium manganese composite oxide; LiMn ₂ O ₄ in which Li part of the formula is substituted with an alkaline earth metal ion; disulfide compounds; Fe ₂ (MoO ₄ ) ₃ may include one type or a mixture of two or more types.

In one embodiment of the present invention, the binder may include a rubber-based binder resin. Since PVdF-based binder resins or acrylic binder resins used as electrode binders have low solubility in non-polar solvents, it is difficult to prepare electrode slurries. Therefore, in the present invention, a rubber-based resin having high solubility in a non-polar solvent is used as a binder. In one embodiment of the present invention, the rubber-based binder resin is natural rubber, butyl-based rubber, bromo-butyl-based rubber, chlorinated butyl-based rubber, styrene-isoprene-based rubber, styrene-ethylene-butylene- A group consisting of styrene-based rubber, acrylonitrile-butadiene-styrene-based rubber, polybutadiene-based rubber, nitrile-butadiene-based rubber, styrene-butadiene-based rubber, styrene-butadiene-styrene-based rubber (SBS), and EPDM (ethylene propylene diene monomer)-based rubber It may include one or more selected from.

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

In one embodiment of the present invention, the negative electrode may include a negative electrode active material stacked on a negative electrode current collector, and the negative electrode active material may include carbon such as lithium metal oxide, non-graphitizable carbon, and graphite-based carbon; Li _x Fe ₂ O ₃ (0≤x≤1), Li _x WO ₂ (0≤x≤1), Sn _x Me _1-x Me' _y O _z (Me: Mn, Fe, Pb, Ge; Me' : Metal composite oxides such as Al, B, P, Si, elements of groups 1, 2, and 3 of the periodic table, halogens, 0<x≤1;1≤y≤3;1≤z≤8); lithium metal; lithium alloy; silicon-based alloys; tin-based alloys; SnO, SnO2, PbO, PbO ₂ , Pb ₂ O ₃ , Pb ₃ O ₄ , Sb ₂ O ₃ , Sb ₂ O ₄ , Sb ₂ O ₅ , GeO, GeO ₂ , Bi ₂ O ₃ , Bi ₂ O ₄ , Bi ₂ O ₅ and other metal oxides; conductive polymers such as polyacetylene; Li-Co-Ni based materials; It may include one or a mixture of two or more selected from titanium oxide.

In one embodiment of the present invention, the positive and negative current collectors are not particularly limited as long as they do not cause chemical change in the battery and have high conductivity. 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.

The present invention provides a pouch-type secondary battery in which the above-described electrode assembly is housed therein.

Specifically, after sequentially stacking the above-described positive electrode, solid electrolyte layer, and negative electrode, lamination is performed to prepare a unit electrode structure, and then a solid electrolyte layer is interposed between a plurality of unit electrode structures to manufacture a stack of unit electrode structures. After that, the above-described polymer layers are laminated on both ends of the stack of unit electrode structures, stored in a pouch-type battery case, and then sealed to manufacture a pouch-type secondary battery.

Hereinafter, preferred embodiments are presented to aid understanding of the present invention, but the following examples are provided to more easily understand the present invention, but the present invention is not limited thereto.

Example

- Manufacture of pouch type secondary battery

1. Example 1

A cathode active material slurry was prepared by mixing the cathode active material, an argyrodite structured sulfide-based solid electrolyte (Li ₆ PS ₅ Cl), a conductive material, and a binder in a mass ratio of 80:15:1:4. The positive electrode active material slurry was applied to an aluminum current collector in a loading amount of 4 mAh/cm ² and then dried to prepare a positive electrode. Lithium metal was pressed onto a copper foil to a thickness of 20 μm and used as a negative electrode. A sulfide-based solid electrolyte (Li ₆ PS ₅ Cl) having an argyrodite structure was used as the solid electrolyte layer.

After sequentially stacking the positive electrode, the solid electrolyte layer, and the negative electrode, a unit electrode structure was prepared by lamination. Two unit electrode structures were prepared, and a solid electrolyte layer was laminated between the anode of each unit electrode structure and another unit electrode structure to prepare a stack of unit electrode structures.

Subsequently, an electrode assembly was manufactured by attaching a silicone rubber pad having a thickness of 20 μm and a yield strength of 5 Mpa as a polymer layer to both ends of the stack of unit electrode structures.

After storing the electrode assembly in a pouch-type battery case, it was sealed to manufacture a pouch-type secondary battery.

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.

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.

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.

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.

6. Example 6

A pouch-type secondary battery was prepared in the same manner as in Example 1, except that the cathode active material slurry was applied to the aluminum current collector in a loading amount of 3mAh/cm ² and the thickness of the silicone rubber pad was 15㎛. did

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.

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.

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.

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.

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.

Experimental example

1. Measurement of volume change occurring during charging/discharging of a pouch-type secondary battery

Volume change occurring during charging/discharging of the pouch-type secondary batteries according to Examples 1 to 5 and Comparative Examples 1 to 4 was measured.

Specifically, the pouch-type secondary battery according to Examples 1 to 5 and Comparative Examples 1 to 4 was initially charged and discharged at room temperature using an electrochemical charger and discharger, and then the pouch-type secondary battery The volume was measured. In the charge/discharge, charging was performed by applying a current at a current density of 0.1 C-rate to a voltage of 4.2V, and discharging was performed at the same current density to 3.0V. This is defined as the initial volume.

Thereafter, after performing such charging and discharging a total of 100 times, the volume was measured. This is defined as the final volume.

The volume change rate (%) was calculated by substituting the measured values of the initial volume and the final volume into Equation 2 below, and is shown in Table 1.

[Equation 2]

Volume change rate (%) = {(final volume - initial volume)/initial volume} × 100 (%)

Volume change (%) Example 1 2 Example 2 2 Example 3 2 Example 4 2 Example 5 2 Comparative Example 1 6 Comparative Example 2 6 Comparative Example 3 2 Comparative Example 4 5

Referring to Table 1, it can be confirmed that the pouch-type secondary batteries according to Examples 1 to 5 of the present invention effectively control the change in internal pressure compared to the pouch-type secondary batteries according to Comparative Examples 1 to 2 and 4. there was.

On the other hand, in the case of the pouch-type secondary battery according to Comparative Example 3, since the yield strength of the silicone rubber pad is too large, the volume change of the pouch-type secondary battery is small, but the pressure inside the pouch-type secondary battery is excessively high, resulting in a short circuit. , which led to rapid deterioration of life characteristics.

2. Evaluation of Life Characteristics of Pouch-type Secondary Batteries

Capacity retention was measured using the pouch-type secondary batteries according to Examples 1 to 6 and Comparative Examples 1 to 5 in the following manner. The results according to this are shown in Table 2, FIGS. 3 and 4.

(1) Specifically, the pouch-type secondary batteries according to Examples 1 to 5 and Comparative Examples 1 to 4 were initially charged and discharged at room temperature using an electrochemical charger and discharger. In the charge/discharge, charging was performed by applying a current at a current density of 0.1 C-rate to a voltage of 4.2V, and discharging was performed at the same current density to 3.0V. A total of 100 such charge/discharge cycles were performed.

The capacity of each battery was measured during the charging/discharging process as described above.

From this, the capacity retention rate of each battery was calculated as in Equation 3 below, and the results are shown in Table 2 below.

[Equation 3]

Capacity retention rate (%) = (capacity at 100 cycles/initial capacity) × 100

initial discharge capacity
(mAh/g) Discharge capacity after 100 cycles
(mAh/g) capacity retention rate
(%) Example 1 200 162 81 Example 2 200 164 82 Example 3 200 160 80 Example 4 200 162 81 Example 5 200 160 80 Comparative Example 1 170 20 12 Comparative Example 2 180 38 21 Comparative Example 3 200 30 15 Comparative Example 4 200 110 55

As shown in Table 2, 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.

(2) In addition, the pouch-type secondary battery according to Example 6 and Comparative Example 5 was initially charged and discharged at room temperature using an electrochemical charger and discharger. In the charge/discharge, charging was performed by applying a current at a current density of 0.1 C-rate to a voltage of 4.2V, and discharging was performed at the same current density to 3.0V. A total of 50 such charge/discharge cycles were performed.

The capacity of each battery was measured during the charging/discharging process as described above, and the results are shown in FIG. 4 .

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.

(3) Considering this point, in the pouch-type secondary battery of the present invention, an elastic body having a yield strength of 5 to 20 MPa and a thickness satisfying Equation 1 below is provided at both ends of the stack of unit electrode assemblies. In the case of arranging, it was confirmed that the life characteristics are remarkably improved.

[Equation 1]

Thickness (㎛) ≥2.5 (㎛ cm ² /mAh · piece) x X (mAh/cm ² ) x Y (piece)

(In Equation 1, X represents the capacity per unit area of the positive electrode, and Y represents the number of positive electrodes of the pouch-type secondary battery.)

All simple modifications or changes of the present invention belong to the scope of the present invention, and the specific protection scope of the present invention will be clarified by the appended claims.

10, 20: pouch type secondary battery
100, 200: electrode assembly
101, 201: negative current collector
102, 202: negative electrode active material layer
103, 203: positive current collector
104, 204: cathode active material layer
105, 205: solid electrolyte layer
106, 207: battery case

Claims (10)

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,
An electrode assembly comprising a polymer layer at both ends of the electrode assembly. According to claim 1,
Electrode assembly, characterized in that the yield strength (Yield strength) of the polymer layer is 5Mpa or more and 20Mpa or less. According to claim 1,
An electrode assembly, characterized in that the thickness of the polymer layer satisfies Equation 1 below.
[Equation 1]
Thickness (μm) ≥ 2.5 (μm cm ² /mAh pcs) x X (mAh/cm ² ) x Y (pcs)
(In the above formula 1,
X represents the capacity per unit area of the positive electrode,
Y represents the number of anodes of the electrode assembly.) According to claim 1,
The electrode assembly, characterized in that the polymer layer is made of rubber or silicone resin. According to claim 1,
The electrode assembly, characterized in that 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 them. According to claim 1,
The electrode assembly, characterized in that the solid electrolyte layer is a sulfide-based solid electrolyte having an azirodite structure. According to claim 1,
Characterized in that the solid electrolyte layer includes one or more selected from the group consisting of Li ₂ SP ₂ S ₅ , Li ₆ PS ₅ Cl, Li ₁₀ GeP ₂ S ₁₂ , Li ₃ PS ₄ , and Li ₇ P ₃ S ₁₁ Electrode assembly to be. According to claim 1,
The electrode assembly, characterized in that the electrode assembly comprises a structure in which 1 to 100 of the electrode structures are stacked. According to claim 1,
Electrode assembly, characterized in that the positive electrode comprises a positive electrode active material, a sulfide-based solid electrolyte, a conductive material and a binder. A pouch type secondary battery comprising the electrode assembly according to claim 1 .

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