KR20180080495A - Electrode Assembly Comprising One-sided Coating Electrode of Improved Mechanical Strength - Google Patents

Abstract

The present invention is an electrode of a structure which has a plurality of unit cells stacked while a separating film or separating sheet are interposed. The unit cells include bi-cells with electrodes which are respectively located at the both outside surfaces and have same polarity with each other. The outermost unit cells of the electrode assembly respectively include at least one one-sided electrode which is coated with an electrode mixture only at the one surface of a current collector, and the rest unit cells except the outermost unit cells are composed of double-sided electrodes which are coated with an electrode mixture at the both sides of a current collector. A first current collector of the one-sided electrode has 150 to 500% of mechanical strength with respect to a second current collector of double-sided electrode which has same polarity with the one-sided current collector.

Description

[0001] Electrode Assembly Comprising One-sided Coating Electrode of Improved Mechanical Strength [

The present invention is directed to an electrode assembly comprising a cross-sectional electrode of improved mechanical 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.

The lithium secondary battery includes an electrode assembly in which a positive electrode plate, a negative electrode plate, and a separator are stacked, and a battery case that encloses and seals the electrode assembly.

In the electrode assembly, the positive electrode plate and the negative electrode plate may be a stacked electrode assembly having a structure in which an electrode mixture is coated on a current collector made of a thin metal plate such as aluminum or copper, and the separator is interposed therebetween A lamination electrode assembly in which the electrode plates are laminated to each other, or a lamination / stacked electrode assembly in which the stacked electrode assemblies are adhered, or a structure in which the stacked electrode assemblies are wound on the separation film Stacked / folded electrode assemblies.

Generally, the plate-shaped electrode assembly is housed in a pouch-shaped battery case and then used through an activation process. Since the pouch-shaped battery case has a lower strength than a rectangular metal case or a cylindrical battery case, There is a problem that deformation can easily occur.

Therefore, there is an attempt to increase the strength or elasticity of the battery case itself in order to protect the electrode assembly inside the pouch-shaped battery case from external pressure. This is essentially due to the prevention of short circuit, ignition, To reduce the risk of.

Thus, there is a high need for a technique for a high-efficiency secondary battery that can increase the strength of the electrode current collector and prevent the increase in thickness, maintain the existing electrical characteristics, and can be used for mid- to large-sized devices.

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 conducted intensive research and various experiments, and as will be described later, each outermost unit cell includes at least one cross-section electrode coated with an electrode mixture only on one surface of the current collector And the unit cells other than the outermost unit cells are composed of double-sided electrodes coated with an electrode mixture on both sides of the current collector, and the first current collector of the single-sided electrode has a high mechanical The present invention has been accomplished based on the discovery that an electrode assembly configured to have high strength has an effect of improving safety against an external impact.

To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, an electrode assembly according to the present invention includes a plurality of unit cells stacked with a separator or a separator interposed therebetween, Wherein each of the outermost unit cells of the electrode assembly includes at least one cross-section electrode coated with an electrode mixture only on one surface of the current collector, The unit cells other than the outermost unit cells are composed of double-sided electrodes coated with an electrode compound on both sides of the current collector, and the first current collector of the single-sided electrode is a double-sided electrode having the same polarity as the cross- And may have a mechanical strength of 150% to 500% with respect to the second current collector.

As described above, in the case where a cross-sectional electrode is used for each outermost unit cell of the electrode assembly, the cross-sectional electrode may be in a state where the electrode active material is not coated on the outer surface, and when an external impact using a needle- The direct contact with the conductive active material can be prevented, so that the safety against external impact can be improved.

The mechanical strength of the first current collector for a single-sided electrode included in the outermost unit cell can be used as it has a remarkably high strength as compared with the mechanical strength of the second current collector for a double-sided electrode. Can be solved.

The first current collector having a thickness smaller than that of the second current collector may be used for the unit cells other than the outermost unit cells in the electrode assembly, thereby reducing the overall thickness of the electrode assembly. Therefore, the loading amount of the electrode active material corresponding to the reduced thickness of the electrode current collector can be increased, so that the capacity of the battery can be increased.

The electrode assembly includes a stacked (stacked) electrode assembly in which a plurality of positive electrodes and negative electrodes cut in a predetermined size unit are sequentially stacked with a separator interposed therebetween, a stacked (stacked) electrode assembly in which a predetermined unit of positive and negative electrodes are stacked A stack-folding type electrode assembly in which a bi-cell or full-cell is wound in a separator sheet, or a lamination-stack type electrode assembly in which electrode assemblies are stacked in a stacked state Type electrode assembly.

In one specific example, in the outermost unit cells, the electrode located on the outer surface of the electrode assembly is a cross-sectional electrode, and the electrodes other than the cross-sectional electrode may be double-sided electrodes. As described above, since the electrodes other than the outermost electrodes of the electrode assembly are formed of double-sided electrodes, the capacity of the battery can be prevented from being reduced as compared with the case where only the single electrodes are used.

The cross-sectional electrodes positioned on both outer surfaces of the electrode assembly may be electrodes of the same polarity. Preferably, the cross-sectional electrodes located on both outer surfaces of the electrode assembly may be an anode. In this way, when the anode is disposed on each of the outer surfaces on both sides of the electrode assembly, the manufacturing process can be facilitated, and the strength of the aluminum or stainless foil used as the anode current collector is generally used as the anode current collector The strength of the copper foil is excellent compared with the strength of the copper foil, thereby improving the mechanical strength of the battery cell.

As described above, it is preferable that the anode is located on each outermost side of the electrode assembly. The first current collector and the second current collector may each be a cathode current collector, and the mechanical strength of the first current collector is, It is possible to provide an electrode assembly having improved strength as a whole. In addition, since the durability against external physical impact is improved, explosion and ignition can be prevented

The unit cells other than the outermost unit cells may be a bi-cell composed of double-sided electrodes. In order to prevent the capacity of the battery from decreasing, a double-sided electrode is preferably used. Since the unit cell having the same polarity is used as the anode, it is possible to prevent the occurrence of errors in the electrode direction design in the process of manufacturing the battery cell, thereby facilitating the design of the whole process.

In one specific example, the first current collector has 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% Alloy, and the second current collector may be made of aluminum or an aluminum alloy.

When the content of iron contained in the first current collector is greater than 75 atomic% or less than 12 atomic%, corrosion is less liable to occur due to a small increase in corrosion resistance obtained by adding chromium, which is not preferable .

The first current collector 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 Element, and can be configured to have the characteristics of a desired current collector by selectively including such elements.

The content of the added metal element may be 1 to 10 atomic%, more specifically 2 to 8 atomic%, based on the total amount of the metal elements constituting the first current collector. When the content of the added metal is less than 1 atomic% based on the content of all the metal elements, 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% It is not preferable because the content of the components is relatively reduced.

In the electrode assembly according to the present invention, when the thicknesses of the first current collector and the second current collector are the same, the first current collector has a higher mechanical equivalent to 150% to 500% based on the mechanical strength of the second current collector The thickness of the first current collector may be smaller than the thickness of the second current collector in order to increase the capacity of the battery without deteriorating the overall strength of the electrode assembly. In detail, the thickness of the first current collector may be 20% to 100% of the thickness of the second current collector. More specifically, the thickness of the first current collector may be 30% 80%.

If the thickness of the first current collector is less than 20% of the thickness of the second current collector, it is difficult to achieve the object of manufacturing an electrode assembly having an improved strength. When the thickness of the first current collector is greater than 100% Which is undesirable.

In the electrode assembly according to the present invention, when the thickness of the first current collector included in the outermost unit cells and having a mechanical strength higher than the mechanical strength of the second current collector is greater than the thickness of the second current collector, The strength of the electrode assembly can be effectively improved. Therefore, the thickness of the first current collector may be, for example, 110% to 400% of the thickness of the second current collector, and more specifically, 150% to 300%.

In one specific example, the cross-sectional electrode has a structure in which an electrode mixture is applied to only one surface of the first current collector, and an electrode mixture is applied to one surface of the first current collector facing the both surface electrodes, May be a structure facing the outside of the electrode assembly. Therefore, even if there is an external impact using the needle-like conductor or the like on the battery cell, the direct contact between the electrode assembly and the needle-shaped conductor can be prevented by using the first current collector having a high mechanical strength, thereby reducing the risk of explosion or ignition .

The present invention also provides a secondary battery in which the electrode assembly is embedded in a battery case. The battery case is made of a laminate sheet including a resin layer and a metal layer, and the metal layer may be made of the same material as the first collector. In this case, since the battery case including the metal layer of the same material as the first current collector having a relatively high mechanical strength is used, the safety of the secondary battery can be further improved.

The battery case may be formed of a laminate sheet including a resin layer and a metal layer, and the metal layer may be made of the same material as the second collector.

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, in the electrode assembly according to the present invention, the outermost unit cells each include at least one cross-section electrode coated with an electrode mixture only on one surface of the current collector, The other unit cells are composed of double-sided electrodes coated with an electrode mixture on both sides of the current collector, the first current collector of the single-sided electrode is configured to have a high mechanical strength with respect to the second current collector of the double- An improved electrode current collector can be provided and durability against external physical impact can be improved, thereby preventing explosion and ignition.

In addition, since the electrode current collector having a relatively high mechanical strength is used, the thickness of the electrode current collector can be reduced. On the other hand, when the coating amount of the active material is increased, Can be obtained.

1 is a side schematic view of an electrode assembly according to one embodiment;
2 is a side schematic view of bicells according to one embodiment;
3 is a side schematic view of bicells according to another embodiment;
4 is a side schematic view of a stack-folding electrode assembly comprised of the bi-cells of FIGS. 2 and 3; And
5 is a side schematic view of a lamination-stacked electrode assembly composed of bi-cells of Figs. 2 and 3. Fig.

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.

1 schematically shows a side view of an electrode assembly according to the present invention.

Referring to FIG. 1, an electrode assembly 100 is formed by winding seven unit cells 110, 120, 130, 140, 150, 160, and 170 in a long sheet-like separation membrane 181 And the unit cells 110, 120, 130, 140, 150, 160, and 170 are formed of bi-cells in which electrodes disposed on both outer surfaces of the unit cells are the same electrode as an anode or a cathode. Although the electrode assembly 100 is composed of seven unit cells, the number of unit cells is not particularly limited as long as the electrodes located at both ends of the electrode assembly are bi-cells composed of positive electrodes.

Figures 2 and 3 illustrate bi-cells according to one specific embodiment. 2 and 3, the bi-cells of FIG. 2 are composed of double-sided electrodes coated with an electrode mixture on both sides of the electrode assembly, and the bi-cells of FIG. 3 are coated with an electrode mixture only on one surface of the electrode assembly End electrodes and double-sided electrodes.

The double-sided electrodes shown in Fig. 2 include an A-type bi-cell in which an anode 201, a cathode 202 and an anode 201 are sequentially stacked with a separator 203 therebetween, a cathode 202, A cathode mix material 211 is coated on both sides of the cathode current collector and a cathode mixture 212 is coated on both sides of the anode current collector 201 have.

3 includes a cross-sectional anode 301, a double-sided cathode 302, and a double-sided anode 305 to which a mixture is applied on only one side of the current collector. The cross-sectional cathode 304, the double- And a double-sided cathode 302.

The positive electrode 301 is coated with a positive electrode mixture 312 on only one side of the current collector 311 facing the double-side negative electrode 302. The positive electrode mixture 302 is coated on both sides of the negative electrode collector 321 with a negative electrode mixture And the positive electrode mixture agent 312 is applied to both surfaces of the current collector 313. The current collector 311 may be made of a material having a higher strength than the mechanical strength of the current collector 313 and the thickness of the current collector 311 may be relatively smaller than the thickness of the current collector 313 Or may be made of a larger thickness.

The cathode slit 304 has a cathode mixture 322 coated on only one side of the current collector 321 facing the anode 305. The anode on both sides of the cathode 304 is coated on both sides of the cathode collector 311 with a cathode mixture The anode mixture 302 is coated on both sides of the current collector 323 with a cathode mixture 322 applied thereto. The current collector 321 may be made of a material having a higher strength than the mechanical strength of the current collector 323 and the thickness of the current collector 321 is relatively small Or may be made of a larger thickness.

Figs. 4 and 5 schematically show a side view of an electrode assembly composed of the unit cells shown in Figs. 2 and 3. Fig. 4 and 5, the electrode assembly 400 shown in FIG. 4 includes stacked unit cells 410, 420, 430, 440, and 450 formed on a long sheet-like separator 461, The electrode assembly 500 of FIG. 5 is a folding type electrode assembly in which the unit cells 510, 520, 530, 540 and 550 are stacked and the separator 561 is interposed between the unit cells Stacked electrode assemblies are manufactured by a method of adhering them to each other.

The outermost electrode of the electrode assembly 400 has a positive electrode, the outermost positive electrode is a one-side positive electrode coated with a positive electrode mixture only in an inner direction of the current collector, and the remaining electrodes except the outermost positive electrode are double- . The collector of the one-sided anode is made of a material having a relatively high mechanical strength as compared with the current collector of the double-sided electrode, can be formed to have a relatively thin thickness, and can have a relatively large thickness for increasing the strength.

The outermost electrode of the electrode assembly 500 has a positive electrode, the outermost positive electrode is a one-side positive electrode coated with a positive electrode mixture only in an inner direction of the current collector, and the remaining electrodes except the outermost positive electrode are double- . The collector of the one-sided anode is made of a material having a relatively high mechanical strength as compared with the current collector of the double-sided electrode, can be formed to have a relatively thin thickness, and can have a relatively large thickness for increasing the strength.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings, but it should be understood that the scope of the present invention is not limited thereto.

≪ Example 1 >

The stack-folding type electrode assembly of FIG. 4 is fabricated such that a cross-section anode is located on both sides of the electrode assembly in the outermost unit cell.

LiCoO ₂ was used as a positive electrode active material, and N-methyl-2-pyrrolidone (NMP) as a solvent was added to 96% by weight of LiCoO ₂ and 2.0% by weight of Super-P The slurry of the positive electrode mixture was coated, dried and pressed on one surface of a current collector having an iron content of 74 at%, a chromium content of 18 at% and a nickel content of 8 at% and a thickness of 10 μm A cross section anode was prepared. The positive electrode active material was coated on both sides of an aluminum foil having a thickness of 12 占 퐉, dried and pressed to prepare a double-sided positive electrode.

Artificial graphite was used as the negative electrode active material. An anode mixture slurry was prepared by adding 96.3% by weight of artificial graphite, 1.0% by weight of Super-P (conductive agent) and 2.7% by weight of PVdF (binder) The negative electrode was prepared by coating, drying and pressing on both sides of copper foil having a thickness of 10 μm.

Manufacture of Secondary Battery

After the bi-cells as shown in FIGS. 2 and 3 were produced with the separator interposed between the positive electrode and the negative electrode, five bi-cells were positioned on the long sheet-like separation film so that the bi- The electrode assembly was assembled into a pouch-type battery case, and then a 1M LiPF ₆ carbonate-based solution electrolyte was injected to complete the secondary battery.

≪ Example 2 >

A secondary battery was manufactured in the same manner as in Example 1, except that the thickness of the single-sided positive electrode current collector was 20 m.

≪ Comparative Example 1 &

The secondary battery was fabricated in the same manner as in Example 1 except that all the double-sided positive electrode current collectors constituting the electrode assembly were made of aluminum foil having a thickness of 12 탆 and the single-sided positive electrode collector was composed of aluminum foil having a thickness of 20 탆. .

<Experimental Example 1>

In order to measure the safety of the secondary batteries manufactured in Examples 1 and 2 and Comparative Example 1, they were prepared in a fully charged state of 4.35V. Using a nail penetration tester, a 2.5 mm diameter nail made of iron was passed through the center of the secondary battery to measure ignition.

At this time, the penetration speed of the nail was constant at 12 m / min, and the results are summarized in Table 1 below.

Whether ignited Example 1 No ignition Example 2 No ignition Comparative Example 1 Ignited

As shown in Table 1, the secondary batteries according to the present invention were not short-circuited and ignited, while the secondary batteries of Comparative Example 1 were short-circuited and ignited.

As described above, since the electrode assembly according to the present invention has a structure including a current collector having a high strength in the outermost unit cell, it is possible to provide a secondary battery having high safety against external impact.

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 (17)

An electrode assembly having a structure in which a plurality of unit cells are stacked with a separator or a separator interposed therebetween,
Wherein the unit cells include bi-cells having polarities identical to each other, the electrodes disposed on both outer sides of the unit cells;
Each of the outermost unit cells of the electrode assembly includes at least one cross-section electrode coated with an electrode mixture only on one surface of the current collector, and the unit cells other than the outermost unit cells include electrodes Sided electrodes to which a compound is applied;
Wherein the first current collector of the cross-sectional electrode has a mechanical strength of 150% to 500% with respect to the second current collector of the double-sided electrode having the same polarity as the cross-sectional electrode. The electrode assembly of claim 1, wherein the electrode assembly is a stacked electrode assembly, a stack-folding electrode assembly, or a lamination-stacked electrode assembly. The electrode assembly according to claim 1, wherein, in the outermost unit cells, the electrode located on the outer surface of the electrode assembly is a cross-sectional electrode, and the remaining electrodes except for the cross-sectional electrode are two-sided electrodes. The electrode assembly according to claim 3, wherein the cross-sectional electrodes located on both outer surfaces of the electrode assembly are electrodes having the same polarity. The electrode assembly according to claim 4, wherein the cross-sectional electrodes located on both outer surfaces of the electrode assembly are anodes. The electrode assembly according to claim 1, wherein the first current collector and the second current collector are cathode current collectors. The electrode assembly according to claim 1, wherein the unit cells other than the outermost unit cells are bi-cells formed of double-sided electrodes. The method according to claim 1,
Wherein the first current collector 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%;
Wherein the second current collector is made of aluminum or an aluminum alloy. The method according to claim 8, wherein the first current collector 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 Further comprising one or more selected metallic elements. &Lt; RTI ID = 0.0 &gt; 11. &lt; / RTI &gt; The electrode assembly according to claim 9, wherein the content of the added metal element is 1 at% to 10 at% based on the total amount of the metal elements constituting the first current collector. The electrode assembly according to claim 1, wherein the thickness of the first current collector is 20% to 100% of the thickness of the second current collector. The electrode assembly according to claim 10, wherein the thickness of the first current collector is 30% to 80% of the thickness of the second current collector. The electrode assembly according to claim 1, wherein the thickness of the first current collector is 110% to 400% of the thickness of the second current collector. The electrode assembly according to claim 1, wherein the cross-sectional electrode has an electrode mixture applied on one surface of a first current collector facing the double-sided electrode, and the other surface opposite to the one surface is directed to the outside of the electrode assembly . The secondary battery according to claim 1, wherein the electrode assembly is embedded in a battery case. 16. The secondary battery according to claim 15, wherein the battery case is made of a laminate sheet including a resin layer and a metal layer, and the metal layer is made of the same material as the first collector. 16. The secondary battery according to claim 15, wherein the battery case is made of a laminate sheet including a resin layer and a metal layer, and the metal layer is made of the same material as the second current collector.

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