KR20170058061A - Lithium Secondary Battery Using Laminate Sheet with Enhanced Strength - Google Patents

Abstract

The present invention relates to a secondary battery in which an electrode assembly impregnated with an electrolyte is sealed in a pouch-shaped battery case. The battery case is made of a laminate sheet including a resin layer, at least one metal layer, and a sealant layer. The metal layer is made of alloy having a content of iron (Fe) of 50 to 80 atomic%, a content of chromium (Cr) of 10 to 40 atomic%, and a content of nickel (Ni) of 5 atomic% to 30 atomic%.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a lithium secondary battery using a laminate sheet having improved strength,

The present invention relates to a lithium secondary battery using a laminate sheet having improved strength.

As technology development and demand for mobile devices are increasing, the demand for batteries as energy sources is rapidly increasing, and accordingly, a lot of researches on batteries capable of meeting various demands have been conducted.

Typically, in terms of the shape of a battery, there is a high demand for a prismatic secondary battery and a pouch-type secondary battery which can be applied to products such as mobile phones with a small thickness, and has advantages such as high energy density, discharge voltage, There is a high demand for lithium secondary batteries such as lithium ion batteries and lithium ion polymer batteries.

Recently, a pouch-shaped battery having a structure in which a stacked or stacked / folded electrode assembly is embedded in a pouch-shaped battery case of an aluminum laminate sheet is attracting much attention due to low manufacturing cost, small weight, Its usage is also gradually increasing.

In this regard, FIG. 1 schematically shows a general structure of a conventional pouch-type secondary battery.

1, the battery case 100 includes a main body 103 having a storage portion 101 for mounting an electrode assembly (not shown) and a main body 103, And a lid 102 of a type that can be used.

Therefore, after the electrode assembly is attached to the housing portion 101 of the battery case 100, the pouch type secondary battery is bent at the connection portion between the main body 103 and the lid 102 to seal the housing portion 101 The lid 102 and the three sealing portions of the main body 103 except for the bent portion are thermally fused.

2 is a cross-sectional view of a laminate sheet for forming a battery case 101 in the secondary battery of FIG.

Referring to FIG. 2, the laminate sheet 200 includes an outer coating layer 203 forming an outermost layer, a metal barrier layer 202 preventing penetration of a material, and an inner sealant layer 201 for sealing.

The inner sealant layer 201 serves to provide sealing property by mutually heat-sealing by heat and pressure applied while the electrode assembly is embedded, and is mainly composed of CPP (unleaded polypropylene film).

Aluminum (Al) may be used for the metal barrier layer 202 so as to exhibit a function of preventing foreign matter from entering or leaking.

In the case of applying heat to the sealing portions of the main body 103 and the lid 102 in which the inner sealant layer 201 corresponding to the innermost layer face each other in the thermal fusion process, the inner sealant layer 201 is melted The main body 103 and the lid 102 are joined and sealed by fusion.

However, during the manufacturing process of the battery, the metal barrier layer 202 may be exposed while the outer coating layer and / or the inner sealant layer 201 are partially broken due to a local excessive stress applied or excessive heat fusion .

In this case, since the sealing property of the battery is lowered, there is a problem that the electrolytic solution leaks to the outside or moisture from the outside can penetrate into the battery. When the exposed aluminum layer comes into contact with the electrolytic solution or the electrode tab, Is destroyed.

At this time, aluminum as a barrier layer has a large difference in electromotive force from nickel as an electrode lead and a connecting member. Therefore, when the secondary battery is charged and discharged in the above-described electrically connected state, corrosion of aluminum proceeds.

As a result, water introduced through the outer coating layer having no water barrier property flows into the battery case through fine cracks formed in the aluminum layer, causing swelling of the battery, resulting in deterioration of the safety of the lithium secondary battery, Deterioration of long-term storage property, reduction of insulation resistance, and the like.

Thus, there is a high need for a technique for preventing deformation of the cell due to an external impact and corrosion caused by an electrolyte by increasing the mechanical strength of the pouch-shaped battery case.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems of the prior art and the technical problems required from the past.

The inventors of the present application have found that when the material of the metal barrier layer of the laminate sheet constituting the pouch-shaped battery case is used as a metal having a specific component, the mechanical strength is improved, The present invention has been completed.

Therefore, since the rigidity of the battery cell as a whole is improved, damage of the battery cell due to an external impact can be prevented, and a secondary battery which can be widely used for a smart device, an attaching / detaching device, and the like can be provided.

To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a pouch type secondary battery according to the present invention is a secondary battery in which an electrode assembly is sealed in a pouch-shaped battery case in a state of being impregnated with an electrolyte, And a sealant layer, wherein the metal layer has a content of iron (Fe) of 50 atom% to 80 atom%, a content of chromium (Cr) of 10 atom% to 40 atom% Ni) is 5 atom% to 30 atom%.

As described above, the secondary battery according to the present invention is formed of a laminate sheet containing at least one metal layer containing a predetermined amount of iron, chromium and nickel, and has a higher mechanical strength than a conventional laminate sheet containing aluminum . Therefore, it is possible to safely protect the electrode assembly from an external impact, prevent deformation of the cell due to impact, and prevent the conventional metal layer containing aluminum from being corroded by the electrolyte solution.

In one specific example, the metal layer is made of an alloy having a content of iron of 55 atom% to 75 atom%, a content of chromium of 12 atom% to 30 atom%, and a content of nickel of 8 atom% to 20 atom% . When the content of iron contained in the metal layer is more than 75 atomic% or the content of chromium is less than 12 atomic%, it is not preferable since corrosion resistance tends to occur because the increase in corrosion resistance obtained by adding chromium is small.

Meanwhile, the metal layer may include at least one metal selected from the group consisting of tungsten (W), vanadium (V), copper (Cu), silicon (Si), manganese (Mn), carbon (C), and molybdenum And can be configured to have the characteristics of a desired metal layer by selectively including such elements.

The content of the added metal may be 1 to 10 atomic%, more specifically 2 to 8 atomic%, based on the entire content of the metal layer. When the content of the added metal is less than 1 atomic% based on the total content of the metal layer, it is difficult to exhibit the effect of the desired alloy such as strength and / or electrical conductivity. When the added metal content is larger than 10 atomic% The content is relatively undesirable.

In one specific example, the thickness of the laminate sheet may be from 70 μm to 150 μm, in particular from 80 μm to 140 μm, and more specifically from 100 μm to 130 μm. When the thickness of the laminate sheet is less than 70 mu m, the thickness of the metal layer is also reduced proportionally, so that the battery cell is protected from external shocks And when it is larger than 150 탆, the weight and volume of the whole secondary battery are increased, so that the applied device may be limited, which is not preferable.

In the secondary battery according to the present invention, the metal layer may have a structure in which a chromium oxide film is formed on the surface, and the film is formed by combining chromium contained in the metal layer with oxygen to form an oxide film in the air to oxidize and corrode the metal layer. . Specifically, the chromium oxide film may be made of chromium trivalent oxide (Cr ₂ O ₃ ).

For example, the thickness of the chromium oxide film may be 10 A to 30 A, and more specifically, 15 A to 25 A, for example. When the thickness of the chromium oxide film is thinner than 10 Å, it is not sufficient to prevent penetration of the outside air. When it is thicker than 30 Å, the content of chromium for film formation is increased, So that the desired physical properties can not be exhibited.

Meanwhile, in order to improve the bonding strength between the metal layer and the resin layer, and between the metal layer and the sealant layer, irregularities may be formed on the upper surface and / or the lower surface of the metal layer. Specifically, the surface of the metal layer can be chemically and / or physically treated so that a plurality of irregularities can be formed. Such irregularities can be formed by performing sandblasting, chemical etching, or the like on the surface of the metal layer, It is expected that the adhesive strength can be improved.

For example, the size of the concavities and convexities is not particularly limited, but may be a maximum diameter of 10 占 퐉 to 200 占 퐉, specifically, 30 占 퐉 to 170 占 퐉, so as to provide a high bonding force between the layers, Specifically, it may be 50 [mu] m to 150 [mu] m. If the size of the concavities and convexities is less than 10 m, it is difficult to exert the effect of improving the adhesive strength. If it is more than 200 m, the thickness of the gas absorption layer is increased to increase the thickness of the entire laminate sheet. It is not preferable.

In addition to forming the concavities and convexities on the surface of the metal layer, a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven fabric or the like may be added in order to increase the bonding force with the resin layer and the sealant layer.

In one specific example, the laminate sheet may be comprised of one metal layer, and in such a case, the thickness of the metal layer may be in the range of 10 탆 to 100 탆 within the range of the thickness of the laminate sheet described above. And more specifically from 15 [mu] m to 80 [mu] m. When the thickness of the metal layer is thinner than 10 탆, the effect of improving the mechanical strength is difficult to exhibit. When the thickness of the metal layer is thicker than 100 탆, the thickness of the laminate sheet is increased, which makes it difficult to provide a compact secondary battery.

In another specific example, the laminate sheet may be of a construction comprising two metal layers. When two metal layers are included, it is preferable to use a metal layer having a thickness smaller than that of one metal layer, in order to prevent the thickness of the entire laminate sheet from being increased. 50 mu m, and more specifically, 25 mu m to 40 mu m.

In this case, it is preferable that the metal layer included in the laminate sheet is positioned so as not to be adjacent to each other in consideration of bonding force with other layers. For example, the first resin layer, the first metal layer, the second resin layer, And a sealant layer may be stacked in this order.

The adhesive layer may further include an adhesive layer between the resin layer and the metal layer and between the metal layer and the sealant layer to increase the bonding force between layers made of different materials. The adhesive layer may be an epoxy, phenol, melamine, polyimide , Polyester-based materials, urethane-based materials, polyethylene terephthalate-based materials, and polyether urethane-based materials.

The present invention also provides a battery pack including the secondary battery as a unit battery and a device including the battery pack as a power source.

Specifically, the battery pack may be used as a power source for devices requiring high temperature safety, long cycle characteristics, and high rate characteristics. Examples of such devices include mobile electronic devices, wearable electronic devices, A power tool powered by a battery-powered motor; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), and the like; An electric motorcycle including an electric bike (E-bike) and an electric scooter (E-scooter); An electric golf cart; And a power storage system, but the present invention is not limited thereto.

The middle- or large-sized battery module is configured to include a plurality of battery cells, and accordingly, the cost of the members used for manufacturing the battery cell greatly affects the manufacturing cost of the entire battery module. Therefore, It can be particularly preferably applied to a battery module.

The structure of these devices and their fabrication methods are well known in the art, and a detailed description thereof will be omitted herein.

As described above, since the secondary battery according to the present invention uses a laminated sheet including a metal layer containing iron (Fe), chromium (Cr), and nickel (Ni) at a certain ratio, mechanical strength is improved It is possible to prevent the damage caused by the physical impact on the bar and the outside.

In addition, since the corrosion caused by the electrolytic solution is reduced, safety of the secondary battery is improved, life characteristics and long-term storage characteristics are improved, and problems such as reduction in insulation resistance can be solved.

1 is an exploded perspective view of a general structure of a conventional pouch type secondary battery;
2 is a schematic view of a cross-sectional structure of a conventional laminate sheet;
3 is a schematic cross-sectional view of a laminate sheet according to one embodiment of the present invention;
4 is a schematic cross-sectional view of a laminate sheet according to another embodiment;
5 is a schematic cross-sectional view of a metal layer according to one embodiment; And
6 is a cross-sectional schematic diagram of a laminate sheet according to another embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings, but the present invention is not limited by the scope of the present invention.

Figs. 3 and 4 each schematically show a cross section of a laminate sheet according to the present invention. 3, the laminate sheet 300 has a structure corresponding to the laminate sheet of FIG. 2 in that the inner sealant layer 301, the metal layer 302, and the outer resin layer 303 are laminated in this order, 2 is different from the laminated sheet of FIG. 2 in that the laminated sheet 302 has a structure in which iron, chromium, and nickel are contained in a certain amount. The thickness D of the laminate sheet 300 is formed within the range of 70 占 퐉 to 150 占 퐉 and the thickness d1 of the metal layer 302 is in the range of 70 占 퐉 to 150 占 퐉. Is formed in the range of 10 mu m to 100 mu m.

4, the laminate sheet 310 has a structure in which an inner sealant layer 311, a metal layer 312 and an outer resin layer 313 are stacked in this order. In order to improve the corrosion resistance of the metal layer, A chromium oxide film 320 is formed to a thickness of 10 Å to 30 Å.

5 schematically shows a cross section of a metal layer according to one embodiment. 5, irregularities 341 are formed on the upper surface and the lower surface of the metal layer 340. The irregularities 341 may be formed only on one surface of the upper surface or the lower surface of the metal layer 340, The size and the number of the irregularities can be formed differently depending on the thickness of the metal layer and the thickness of the laminate sheet.

The structure of the metal layer having the unevenness is not limited to the case where the metal layer is one, such as the laminate sheets 300 and 310 shown in FIGS. 3 and 4, but also a structure in which two or more metal layers are included Can also be used.

6 schematically shows a cross section of a laminate sheet according to still another embodiment of the present invention. 6, the laminate sheet 400 includes a first resin layer 405, a first metal layer 404, a second resin layer 403, a second metal layer 402, and a sealant layer 401 in this order As a structure in a laminated form, two metal layers 402 and 404 are included. Therefore, it is possible to provide a secondary battery with improved mechanical strength. However, the thickness d2 of the metal layers 402 and 404 is preferably in the range of 10 占 퐉 to 30 占 퐉 in order to prevent the overall thickness from increasing as compared with the laminate sheets 300 and 310 of Figs. 3 and 4 including one metal layer. And is formed to be thinner than the thickness d1 of the metal layer. In addition, the thicknesses d2 of the metal layers 402 and 404 may be equal to each other, and structures having different thicknesses may be included in the scope of the present invention.

Hereinafter, the present invention will be further described with reference to examples and the like. However, the following examples are intended to illustrate the present invention and the scope of the present invention is not limited thereto.

<Examples>

A battery case was formed using a laminate sheet including a metal layer made of a laminate sheet having a thickness of 114 탆, a metal content of 60 atomic%, a chromium content of 20 atomic%, and a nickel content of 20 atomic% , And a positive electrode / separator / negative electrode laminated in the battery case.

A liquid electrolyte in which LiPF ₆ was dissolved in 1.0 M of ethylene carbonate (EC): propylene carbonate (PC): propylene propionate (PP) in a ratio of 30: 10: 60 wt% The battery was impregnated for 2 days. After the impregnation for 2 days, the formation process was carried out and degassing and resealing, side trimming, Hot Press, and discharge filling process were carried out to complete the battery.

&Lt; Comparative Example 1 &

A secondary battery was fabricated in the same manner as in the above example except that the thickness of the laminate sheet was 150 占 퐉 and the metal layer was made of aluminum material in the above example.

&Lt; Comparative Example 2 &

In the examples, a secondary battery was manufactured in the same manner as in the above example except that a laminate sheet composed of a metal layer made of an aluminum material having a thickness of 71 탆 was used and an AFL separation membrane was used.

<Experimental Example>

In order to measure the stiffness of the secondary batteries manufactured in each of the above-described Examples and Comparative Examples 1 and 2, a 3-point bending machine was used to apply tension to 2.0 mm based on the initial state, The results are shown in Table 1 below.

Test the stiffness of the battery cell atom% The alloy of iron (60), Cr (20), Ni (20) Al (150 탆) Al (71 탆) Force (gf) 22,214 17,887 16,190

As shown in the above table, the secondary battery manufactured in the example was measured to require a force of 22, 214 gf when a deformation of 2 mm occurred. This result shows that the secondary battery of Comparative Example 1 requires 17, 887 gf of force during the deformation of 2 mm, and the secondary battery of Comparative Example 2 requires about 16 and 190 gf of force, 124% and about 137% of the force is needed.

Considering that the thickness of the laminate sheet of Example 1 is 114 占 퐉 and the thickness of the laminate sheet of Comparative Example 1 is 150 占 퐉, in the case of Example 1, even though a thinner thickness laminate sheet is used, It can be seen that the material is made of a material having greater rigidity as the force is required. As a result, the safety of the secondary battery according to the present invention is remarkably improved because the risk of shape deformation of the battery due to an external impact is reduced.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (18)

A secondary battery in which an electrode assembly is sealed in an interior of a pouch-shaped battery case in a state of being impregnated with an electrolyte,
Wherein the battery case is made of a laminate sheet including a resin layer, at least one metal layer, and a sealant layer,
Wherein the metal layer contains 50 atom% to 80 atom% of iron (Fe), 10 atom% to 40 atom% of chromium (Cr) and 5 atom% to 30 atom% of nickel (Ni) Wherein the secondary battery is made of an alloy. The metal layer according to claim 1, wherein the metal layer is made of an alloy having an iron content of 55 to 75 atomic%, a chromium content of 12 to 30 atomic%, and a nickel content of 8 to 20 atomic% And a secondary battery. The method according to claim 1, wherein the metal layer is formed of a material selected from the group consisting of tungsten (W), vanadium (V), copper (Cu), silicon (Si), manganese (Mn), carbon (C), and molybdenum Wherein the secondary battery further comprises a metal or more. 4. The secondary battery according to claim 3, wherein the content of the added metal is 1 at% to 10 at% based on the total content of the metal layer. The secondary battery according to claim 1, wherein the thickness of the laminate sheet is 70 탆 to 150 탆. The secondary battery according to claim 1, wherein the metal layer has a chromium oxide film formed on its surface. The secondary battery according to claim 6, wherein the chromium oxide film is made of chromium trivalent oxide (Cr ₂ O ₃ ). The secondary battery according to claim 6, wherein the thickness of the chromium oxide film is 10 A to 30 A. The secondary battery according to claim 1, wherein concave and convex portions are formed on an upper surface and / or a lower surface of the metal layer. The secondary battery according to claim 1, wherein the laminate sheet comprises one metal layer. The secondary battery according to claim 10, wherein the thickness of the metal layer is 10 탆 to 100 탆. The secondary battery according to claim 1, wherein the laminate sheet includes two metal layers. 13. The secondary battery according to claim 12, wherein the laminate sheet comprises a first resin layer, a first metal layer, a second resin layer, a second metal layer, and a sealant layer laminated in this order. 13. The secondary battery according to claim 12, wherein the thickness of the metal layer is 10 [mu] m to 50 [mu] m. The adhesive layer according to claim 1, further comprising an adhesive layer between the resin layer and the metal layer, and between the metal layer and the sealant layer, wherein the adhesive layer is an epoxy, phenol, melamine, polyimide, polyester, Polyethylene terephthalate-based materials, and polyether urethane-based materials. A battery pack comprising a unit battery according to any one of claims 1 to 15. A device comprising the battery pack according to claim 16 as a power source. 18. The apparatus of claim 17, wherein the device is a mobile device, a wearable device, a power tool powered by a battery-based motor, An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), and the like; An electric motorcycle including an electric bike (E-bike) and an electric scooter (E-scooter); An electric golf cart; Wherein the system is a system for power storage.

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