KR20160140507A - Electrode assembly with directional thickness and Lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a lithium secondary battery including an electrode assembly, ensuring compact volume while reducing resistance and heat emission of cells when at least two cells, using the electrode collector having gradually varying thickness, are stacked. According to the present invention, it is possible to resolve an issue associated with an increase in resistance and heat emission, and an unnecessary increase in the volume of the lithium secondary battery can be avoided as well.

Description

[0001] The present invention relates to an electrode assembly having thickness directionality and a lithium secondary battery including the same,

The present invention relates to an electrode assembly having thickness directionality and a lithium secondary battery including the electrode assembly.

A rechargeable secondary battery is widely used as an energy source for wireless mobile devices. In addition, the secondary battery is an electric vehicle (EV), a hybrid electric vehicle (HEV), and a parallel hybrid electric vehicle (hereinafter referred to as a " hybrid electric vehicle ") which are proposed as solutions for the air pollution of existing gasoline vehicles and diesel vehicles using fossil fuels PHEV), and the like.

One example of the secondary battery is a pouch-type secondary battery in which an electrode assembly is embedded in a pouch-shaped case made of a laminate sheet. The pouch-type secondary battery is also becoming larger in recent years as it is used not only as an energy source for mobile devices but also as a vehicle power source. As a result, the metal foil used as an electrode current collector is becoming larger At the same time, the thickness is becoming thinner. As a result, not only the resistance of the metal foil increases but also the resistance of the cell manufactured using the metal foil increases and the heat generation is increased.

Accordingly, it is an object of the present invention to solve the problem of increase in resistance and heat generation of a secondary battery caused by enlargement of the electrode current collector and a small thickness.

In addition, the present invention solves the problem of increase in resistance and heat generation of the secondary battery and makes the secondary battery compact.

According to an aspect of the present invention, there is provided an electrode assembly comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, wherein the positive electrode includes a positive electrode active material layer formed on both surfaces of the positive electrode collector, Wherein the positive electrode collector and the negative electrode collector each have a thickness thinner from the proximal end of the tab to the distal end of the tab, The positive electrode active material is formed to have the same thickness throughout the positive electrode collector, the negative electrode active material is formed to have the same thickness throughout the negative electrode collector, the positive electrode and the negative electrode are laminated, The electrode assembly being laminated so as to face the tab portion of the negative electrode in the opposite direction.

Each of the positive electrode collector and the negative electrode collector may have a thickness thinning at the same rate of change throughout the current collector.

The tab proximal end of each of the positive electrode collector and the negative electrode collector has a thickness of 5 to 50 占 퐉 and the tab distal end may have a thickness greater than 0 and thinner than the tab proximal end.

Alternatively, the tab proximal end of each of the cathode current collector and the anode current collector may have a thickness of 5 to 50 占 퐉, and the tab distal end may have a thickness in a numerical range of more than 2 占 퐉 and not more than 80% of the tab proximal end thickness.

In addition, the electrode assembly may be a stacked electrode assembly or a stacked and folded electrode assembly including two or more unit cell cells.

According to one aspect of the present invention, there is provided an electrode assembly in which an electrode active material layer is coated with a uniform thickness on both sides of a directional electrode current collector having a thicker thickness at a position where the electron movement amount is large.

That is, in the electrode current collector according to an embodiment of the present invention, the proximal portion of the tab having a large amount of electron movement is formed to have a thicker thickness to solve the problem of resistance increase and heat generation, Thereby preventing an unnecessary increase in the volume of the cell, as well as facilitating lithium insertion / removal in the electrode active material layer.

According to an aspect of the present invention, there is provided an electrode assembly and a lithium secondary battery including at least two such electrode assemblies, wherein the positive electrode tab portion and the negative electrode tab portion are laminated so as to face in opposite directions, A compact lithium secondary battery can be obtained.

FIG. 1 is a side view schematically showing a general electrode form including an electrode current collector, an electrode tab extending from the electrode current collector, and an active material layer formed on both surfaces of the electrode current collector, the active material layer being coated with a uniform thickness.
FIG. 2 is a cross-sectional view of an electrode collector having a thickness symmetrically and gradually changing up and down with respect to the center of a side surface of the electrode collector, an electrode tab extending from the electrode collector, FIG. 2 is a side view schematically showing an electrode according to an embodiment of the present invention, including an active material layer formed in a conventional manner.
FIG. 3 is a schematic side view of a bipolar electrode assembly formed by stacking an anode and a cathode according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms, and the inventor should appropriately interpret the concepts of the terms appropriately It should be construed in accordance with the meaning and concept consistent with the technical idea of the present invention based on the principle that it can be defined.

Therefore, the embodiments described in the present specification and the configurations shown in the drawings are only the most preferred embodiments of the present invention and do not represent all the technical ideas of the present invention. Therefore, It is to be understood that equivalents and modifications are possible.

FIG. 1 is a side view schematically showing an embodiment of a general electrode including an electrode current collector, an electrode tab extending from the electrode current collector, and an active material layer coated on both surfaces of the electrode current collector with a uniform thickness.

More specifically, the electrode active material layer 120 is coated on both surfaces of the electrode current collector 110 with a uniform thickness, and the electrode tab 130 is extended to the electrode current collector 110, (110) are formed to have the same thickness irrespective of their positions.

FIG. 2 is a side view schematically showing an electrode according to an embodiment of the present invention, including an electrode current collector, an electrode tab extending from the electrode current collector, and an active material layer coated on both surfaces of the electrode current collector.

2, the electrode current collector has the largest thickness at the proximal end of the electrode tab 230, and the thickness of the electrode current collector gradually decreases to have the thinnest thickness at the distal end of the electrode tab 230, And an electrode active material layer 220 is formed on both sides of the current collector.

The term "proximal end of a tab" or "proximal end of an electrode tab" in the present specification means a portion 'p' which is an end located closest to the electrode tab in the electrode current collector shown in FIG. 2, Quot; or " distal end of the electrode tab " is understood to mean a portion " d ", which is the end farthest from the electrode tab in the electrode current collector shown in Fig.

The structure of the electrode current collector is characterized in that the electron movement amount is reflected in the thickness setting. That is, as shown in FIG. 2, the electrode tab and / or the electrode lead are designed to have the thickest thickness at the proximal end of the electrode tab, which is relatively large in electron transfer, and is located far away from the electrode tab and / Is designed so that the thickness becomes thinner toward the distal end of the electrode tab.

The proximal end of the electrode tab in the electrode current collector may have a thickness of 5 to 50 占 퐉. Also, the electrode tab distal end may have a thickness greater than 0 占 퐉 and thinner than the electrode tab proximal end. Alternatively, the electrode tab distal end may have a thickness in the numerical range greater than 2 [mu] m and less than 80% of the electrode tab proximal end thickness.

The electrode current collector may have the same thickness change rate at all positions of the electrode current collector. However, the electrode current collector may be stacked so that the positive electrode and the negative electrode are in contact with each other to form an electrode assembly. The present invention is not limited thereto.

The positive electrode current collector is not particularly limited as long as it has high conductivity without causing a chemical change in the battery. For example, the positive electrode current collector may be made of stainless steel, aluminum, nickel, titanium, sintered carbon, , Nickel, titanium, silver, or the like may be used. The positive electrode current collector may have fine unevenness on the surface thereof to increase the adhesive force of the positive electrode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible.

The negative electrode current collector is not particularly limited as long as it has electrical conductivity without causing chemical change in the battery. For example, the negative electrode current collector may be made of carbon, stainless steel, aluminum, nickel, titanium, sintered carbon, , Nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. In addition, like the positive electrode collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

The method of changing the thickness of the current collector is not particularly limited. However, when the current collector is rolled in a normal temperature or a warm state, the thickness of the current collector can be controlled by adjusting the rolling strength.

According to an aspect of the present invention, there is provided a unit battery cell including the electrode current collector. In the present specification, 'unit cell' means a unit cell constituting a secondary battery, and may include a full cell or a bi-cell.

The 'full cell' is a cell having a unit structure of an anode / a separator / a cathode, and a cathode and a cathode are located on both sides of the cell. Such a full cell includes a cell made of a positive electrode / separator / negative electrode having the most basic structure, and a cell made of a positive electrode / separator / negative electrode / separator / positive electrode / separator / negative electrode. In order to construct an electrochemical cell such as a secondary cell using such a full cell, a plurality of full cells must be stacked such that the anode and the cathode face each other with the separation film interposed therebetween.

The 'bicell' is a unit cell in which the same electrode is located on both sides of a cell, such as a unit structure of a cathode / separator / cathode / separator / anode and a unit structure of a cathode / separator / anode / separator / cathode . In order to construct an electrochemical cell including a secondary cell using such a bi-cell, an A-type bi-cell having a positive electrode / separator / negative electrode / separator / positive electrode structure and a negative electrode / separator / positive electrode / separator / A plurality of bi-cells must be stacked so that the C-type bi-cells of the structure face each other.

According to an aspect of the present invention, there is provided a stacked type electrode assembly or a stacked and folded type electrode assembly assembled by stacking two or more unit battery cells.

The term "stacked electrode assembly" as used herein means an 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.

In the present specification, the term 'stack and folding type electrode assembly' refers to a stack and a folding type electrode assembly in which a bi-cell or a full cell, in which a predetermined unit of positive and negative electrodes are stacked with a separator interposed therebetween, The present invention is not limited thereto.

Each of the positive and negative electrodes constituting the unit battery cell includes an electrode current collector according to an embodiment of the present invention. The electrode active material layer is uniformly coated on both surfaces of the electrode current collector, The electrode according to one embodiment has a side of a parallelogram shape. If the change rate of the thickness of the electrode current collector is compensated for by varying the thickness of the active material layer of the electrode, that is, if the electrode is designed to have a rectangular side, smooth insertion / desorption of lithium ions from the inside of the thickly formed active material layer There is a problem that the insufficient lithium ion mobility of the stacked electrode assembly or the stacked and folded electrode assembly is further deteriorated.

A side view of a bi-cell formed by stacking an anode and a cathode according to an embodiment of the present invention is shown in FIG.

3, a cathode 300 'is disposed at the center of the unit cell, an anode 300 is disposed around the cathode 300', and a cathode 300 'is disposed on the other side of the anode 300 ') Are further disposed in the unit cell. A separator 400 is interposed between the anode 300 and the cathode 300 '.

Each of the positive electrode 300 and the negative electrode 300 'includes an electrode current collector 310 and 310', electrode tabs 330 and 330 'extending from the electrode current collectors 310 and 310' And active material layers 320 and 320 'coated on both sides of the entire body 310 and 310'.

The distal end portions of the positive electrode tabs 330 of the positive electrode 310 are laminated on the proximal end portions of the negative electrode tabs 330 'connected to the negative electrode collector 310' Can be made well and can be arranged so that unnecessary volume increase of the battery does not occur.

The positive electrode constituting the unit cell may be prepared by coating the positive electrode current collector with the slurry of the positive electrode active material, the conductive material and the binder, and drying the positive electrode current collector. Optionally, a filler may be further added to the mixture.

Specific examples of the positive electrode active material include a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or 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 and 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 ; Formula _{LiNi 1 - x M x O 2} ( where, the M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, x = 0.01 ~ 0.3 Im) Ni site type lithium nickel oxide which is represented by; Formula _{LiMn 2 - x M x O 2} ( where, M = Co, Ni, Fe , Cr, and Zn, or Ta, x = 0.01 ~ 0.1 Im) or Li ₂ Mn ₃ MO ₈ (where, M = Fe, Co, Ni, Cu, or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with an alkaline earth metal ion; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ , and the like. However, the present invention is not limited to these. Preferably, the cathode active material may be lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium manganese-cobalt-nickel oxide, or a combination of two or more thereof.

The binder is a component that assists in bonding between the active material and the conductive material and bonding to the electrode current collector, and is usually added in an amount of 1 to 50 wt% based on the total weight of the electrode material mixture. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene Examples thereof include ethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, fluorine rubber and various copolymers thereof.

The conductive material is a component for further improving the conductivity of the electrode active material, and may be added in an amount of 1 to 20 wt% based on the total weight of the electrode material mixture. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, for example, graphite such as natural graphite or artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The filler is optionally used as a component for suppressing expansion of the anode, and is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery, and examples thereof include olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

The negative electrode material may be, for example, carbon such as non-graphitized carbon or graphite 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 complex oxides such as Al, B, P, Si, Group 1, Group 2 and Group 3 elements of the periodic table, Halogen; 0 < x &lt; Lithium metal; Lithium alloy; Silicon-based alloys; Tin alloy; _{SnO, SnO 2, 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 , and Bi ₂ O ₅ and the like; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used.

The separator is interposed between the positive electrode and the negative electrode to prevent a short circuit that may occur between the positive electrode and the negative electrode. The separator may be typically formed of a thermoplastic resin such as polyethylene (PE) or polypropylene (PP), and the surface of the separator may have a porous membrane structure, but is not limited thereto. Such a porous film structure becomes an insulating film by melting the separator and blocking pores when the temperature rises near the melting point of the thermoplastic resin due to the temperature rise inside the battery.

The material and shape of the positive electrode tab, the positive electrode lead, the negative electrode tab, and the negative electrode lead are not particularly limited and can be formed into materials and shapes commonly used in the art.

The secondary battery according to the present invention can be applied to a middle- or large-sized battery module or a battery pack using the unit battery. The middle- or large-sized battery module or the battery pack may be an electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), and a plug-in hybrid electric vehicle (PHEV). Electric truck; Electric commercial vehicle; Or a power storage system, as shown in FIG.

The middle- or large-sized battery module is configured to connect a plurality of unit cells in a serial manner or a serial / parallel manner to provide a large-capacity large-capacity battery, which is well known in the art.

In the foregoing detailed description of the present invention, specific examples have been described. However, various modifications are possible within the scope of the present invention. The technical idea of the present invention should not be limited to the embodiments of the present invention but should be determined by the equivalents of the claims and the claims.

Claims (6)

An electrode assembly comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode,
Wherein the positive electrode includes a positive electrode active material layer formed on both surfaces of the positive electrode collector,
The negative electrode includes a negative electrode active material layer formed on both surfaces of the negative electrode collector,
Each of the positive electrode collector and the negative electrode collector is thinned from the proximal end of the tab to the distal end of the tab and thinner at the same rate of change symmetrically at the top and bottom with respect to the side center,
The positive electrode active material is formed to have the same thickness throughout the positive electrode collector,
The negative electrode active material is formed to have the same thickness throughout the negative electrode collector
Wherein the positive electrode and the negative electrode are stacked such that the tab portion of the positive electrode is opposite to the tab portion of the negative electrode.
The method according to claim 1,
Wherein the positive electrode collector and the negative electrode collector each have a thickness thinned at the same thickness change rate throughout the current collector.
The method according to claim 1,
Wherein the tab proximal end of each of the cathode current collector and the anode current collector has a thickness of 5 to 50 占 퐉 and the tab distal end is greater than 0 and thinner than the tab proximal end.
The method according to claim 1,
Wherein the tab proximal end of each of the positive electrode collector and the negative electrode collector has a thickness of 5 to 50 占 퐉 and the tab distal end has a thickness in the numerical range of more than 2 占 퐉 and not more than 80% of the tab proximal end thickness. Assembly.
The method according to claim 1,
Wherein the electrode assembly is a stacked electrode assembly.
The method according to claim 1,
Wherein the electrode assembly is a stack and folding type electrode assembly.

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