KR20100071786A - Secondary battery having enhanced uniformity of temperature distribution - Google Patents

Abstract

PURPOSE: A secondary battery including an electrode assembly is provided to extend the lifetime of the battery by maintaining the temperature uniformity by varying the thickness of the center and the outside of the cell of the electrode assembly. CONSTITUTION: An electrode assembly of a secondary battery includes a structure by successively laminating a positive electrode, a negative electrode and a separator in between the electrodes. The thickness deviation of an electrode current collector of the electrode assembly is 2~20 microns. A unit cell included inside the assembly is either a full cell including electrodes with different structures, or a bicell including the electrodes with the same structure. The electrode assembly is a stack and folding type.

Description

Secondary battery having enhanced uniformity of temperature distribution

The present invention relates to a secondary battery in which the thickness of the electrode current collector is variously designed such that the thickness of the electrode current collector is made thicker at the center of the cell and the thickness becomes thinner toward the outside, thereby improving the temperature uniformity inside and outside the cell.

Recently, secondary batteries capable of charging and discharging have been widely used as energy sources of wireless mobile devices. In addition, the secondary battery is an electric vehicle (EV), a hybrid electric vehicle (HEV), a parallel hybrid electric vehicle that has been proposed as a solution to solve air pollution of conventional gasoline and diesel vehicles using fossil fuels. It is also attracting attention as a power source such as PHEV).

One or two or four battery cells are used for small mobile devices, whereas medium and large battery modules, which are electrically connected to a plurality of battery cells, are used for medium and large devices such as automobiles due to the need for high output and large capacity.

Since medium and large battery modules are preferably manufactured in a small size and weight, square batteries, pouch-type batteries, etc., which can be charged with high integration and have a small weight to capacity, are mainly used as battery cells of medium and large battery modules. In particular, a pouch-type battery using an aluminum laminate sheet or the like as an exterior member has attracted much attention in recent years due to its advantages such as low weight, low manufacturing cost, and easy deformation.

On the other hand, since the required characteristics are different depending on the type of device in which the medium-large battery module is used, the secondary battery constituting the battery module is also required to be different in terms of output and capacity. For example, a high capacity battery is preferable for a battery module for an electric vehicle (EV), a high output battery is preferable for a battery module for a hybrid electric vehicle (HEV), and a high capacity for a battery module for a hybrid hybrid electric vehicle (PHEV). And high power batteries are preferred.

According to the shape of the battery case, secondary batteries are classified into cylindrical batteries and rectangular batteries in which the electrode assembly is embedded in a cylindrical or rectangular metal can, and pouch-type batteries in which the electrode assembly is embedded in a pouch type case of an aluminum laminate sheet. .

In addition, the electrode assembly embedded in the battery case is a power generator capable of charging and discharging composed of a laminated structure of the anode / separator / cathode, a jelly-roll type wound through a separator between the long sheet-type anode and cathode coated with the active material And a plurality of positive and negative electrodes of a predetermined size, which are sequentially stacked in a state of being interposed in a separator. Among them, the jelly-roll type electrode assembly has advantages of easy manufacturing and high energy density per weight.

The jelly-roll type electrode assembly is formed by laminating a long sheet-shaped anode and a cathode with a separator interposed therebetween, and then winding it roundly to form a cross-sectional circular structure, or by winding in such a circular structure and compressing in one direction to form a substantially flat plate-shaped cross-section. Can be made into a structure

The conventional winding type battery as described above is a jelly-roll type electrode assembly in which long sheets of positive and negative electrodes are insulated and stacked by a separator, and the electrode current collectors of the respective electrodes use a constant thickness, and thus, in the manufacturing process, It is difficult to apply electrode collectors having various thicknesses by electrode position (center, outer).

Therefore, there was always a temperature difference between the center and the outside of the cell due to the cell heat generation characteristics during discharge, and there was a problem in that the center of the cell deteriorated more accelerated than the outside by the temperature difference.

Therefore, the present invention is to improve the performance of the battery by solving a number of problems of the conventional secondary battery caused by the temperature difference according to the position of the electrode during discharge by using an electrode current collector having a constant thickness.

Accordingly, the present invention recognizes that it is necessary to maintain a uniform temperature distribution inside the cell to reduce the deterioration caused by the temperature difference inside the cell as described above. Although it is difficult to make it very different in the manufacturing process, in stack type cells, the thickness of the current collector is applied differently for each bi-cell to obtain a hint from the cell manufacturing, and the heat dissipation in the center and the outside of the cell is balanced. In order to solve the above problem, the thickness of the current collector is thickened at the center of the cell, and the thickness of the current collector is made thinner at the center of the cell.

Accordingly, an object of the present invention is to provide an electrode assembly and a secondary battery including the same which can maintain a uniform temperature distribution in the cell because the cell life is different depending on the temperature distribution inside the cell due to heat generated during high-output discharge. have.

As the present invention, the thickness of the electrode current collector can be variously designed to maintain temperature uniformity inside and outside the cell, thereby extending the life of the cell.

The electrode assembly of the present invention for achieving the above object is an electrode assembly having a structure in which the positive electrode and the negative electrode are cut in a predetermined size unit and sequentially stacked through a separator, and the electrode assembly of the center and the outer portion of the electrode assembly is sequentially stacked. It is characterized in that the thickness of the electrode current collector is configured differently so that the total thickness deviation is from 2 to 20 mu m.

In addition, a pouch type secondary battery for achieving another object of the present invention is characterized in that it comprises the electrode assembly.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

The present invention has a basic structure of a stacked electrode assembly made of a plate-like structure by cutting the positive electrode and the negative electrode in a unit of a predetermined size and sequentially stacking them through a separator, in stacking the unit cells. The thickness of the current collector of the unit cell is designed to be different so that the unit cell having a thicker current collector thickness is located at the center and the unit cell having a thinner current collector thickness is located at the outside.

That is, the electrode assembly according to the present invention makes a bicell or a full cell as a unit cell of a small unit in a stacked manner as shown in FIG. The 'full cell' is a unit cell composed of a unit structure of an anode, a separator, and a cathode, and is a cell in which an anode and a cathode are located at both sides of the cell, respectively. Such a full cell may include an anode / separator / cathode cell and an anode / separator / cathode / separator / anode / separator / cathode cell having the most basic structure. In order to configure an electrochemical cell such as a secondary battery using such a full cell, a plurality of full cells should be stacked such that the positive electrode and the negative electrode face each other with the separation film interposed therebetween.

The 'bicell' is a unit cell in which the same electrode is positioned at both sides of the cell, such as a unit structure of an anode / 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 battery using such a bicell, a bicell and a cathode, a separator, an anode, a separator, and a cathode structure of the anode / separator / cathode / separator / anode structure with the separator film interposed therebetween. A plurality of bicells should be stacked so that the bicells face each other.

In the present invention, when manufacturing the full cell or bicell, the thickness of the current collector is differently prepared for each part. That is, as shown in FIG. 1, a plurality of bicells 10 having a stacked structure of an anode (cathode) / separator / cathode (anode) / separator / anode (cathode) are formed on a continuous separation film 30 having a long length. In the above, it is preferable that the thickness variation between the current collectors of the respective bicells located in the center of the cell and the current collectors of the respective bicells located outside the cell is in a range of 2 to 20 μm. In the present invention, "bicell located at the center of the cell" and "bicell located at the outer side of the cell" means a position in the structure of the cell after the final folding of the above-described bicell.

Therefore, the bi-cell located at the starting point of folding the plurality of bi-cells is located at the center after the final folding, so when the plurality of bi-cells are placed on the separation film as shown in FIG. When the seventh bicell is the folding start point (when folding in the arrow direction), the thickness of the current collector used in the seventh bicell is configured to be the thickest.

In the case of the current collector used in the seventh bi-cell, it is preferable to form a thick 4 to 40% of 5 to 50 ㎛ thickness of the positive or negative electrode current collector used in general.

In addition, the current collector used in each bicell from the seventh bicell to the first bicell, sequential in the 4 to 40% thin thickness range of 5 to 50 ㎛ thickness of the positive or negative electrode current collector commonly used It is preferable to form so as to be thin.

Specifically, according to one preferred embodiment of the present invention, as shown in FIG. 2, it is also possible to form a tapered state in which the thickness of the current collector becomes thinner from the center to the outside. That is, when the thickness of the positive electrode and the negative electrode current collector of the seventh bicell is 50 μm, the thicknesses of the positive electrode and the negative electrode current collector of the sixth bicell adjacent to the seventh bicell may be 4 to the seventh bicell. 10% to 45 to 48㎛ reduced, and the thickness of the positive electrode and the negative electrode current collector of the fifth bi-cell adjacent to the sixth bi-cell reduced by 8 to 20% compared to the seventh bi-cell 40 to 46 ㎛ In this way, the thickness of the bicell may be gradually reduced toward the end of the folding starting point.

In addition to the above-described method, any method that can change the thickness of the bi-cell located in the center and the bi-cell located outside is not particularly limited.

The positive electrode constituting the bicell and the full cell is manufactured by applying the slurry of the positive electrode active material, the conductive material, and the binder on a positive electrode current collector, followed by drying, and optionally, a filler is further added to the mixture.

The positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery. For example, the positive electrode current collector is not limited to the surface of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel. Surface-treated with carbon, nickel, titanium, silver, and the like can be used.

The current collector may form fine irregularities on its surface to increase the adhesion of the positive electrode active material, and may be in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

Specific examples of the positive electrode active material of the present invention 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 , LiMnO _2, and the like; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ , Cu ₂ V ₂ O ₇ and the like; Ni-site type lithium nickel oxide represented by the formula LiNi _1-x MxO ₂ , wherein 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 , wherein 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, Lithium manganese composite oxide represented by Ni, Cu, or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with alkaline earth metal ions; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ , and the like. However, the present invention is not limited to these. Preferably, the positive electrode 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 the bonding of the active material and the conductive material to the current collector, and is generally added in an amount of 1 to 50 wt% based on the total weight of the electrode mixture. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoro Low ethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, fluorine rubber, various copolymers thereof, and the like.

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 mixture. Such a conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery, and examples thereof include graphite such as natural graphite and artificial graphite; Carbon blacks 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 powder, aluminum powder and nickel powder; Conductive whiskeys 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 the 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. Examples of the filler include olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

The negative electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery. For example, the negative electrode current collector may be formed on a surface of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper, or stainless steel. Surface-treated with carbon, nickel, titanium, silver and the like, aluminum-cadmium alloy and the like can be used. In addition, like the positive electrode current collector, fine concavities and convexities may be formed on the surface to enhance the bonding strength of the negative electrode active material, and may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The negative electrode material may be, for example, carbon such as hardly graphitized carbon or graphite carbon; Li _x Fe ₂ O ₃ (0 ≦ x ≦ 1), LixWO ₂ (0 ≦ x ≦ 1), Sn _x Me _1-x Me ' _y O _z (Me: Mn, Fe, Pb, Ge; Me': Al Metal complex oxides such as B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen, 0 <x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8); Lithium metal; Lithium alloys; Silicon-based alloys; Tin-based alloys; 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 oxides such as Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used.

Further details of the electrode assembly of the stack / foldable structure are disclosed in Korean Patent Application Publication Nos. 2001-0082058, 2001-0082059, and 2001-0082060 to the present applicants. Is incorporated by reference.

Since the stack / foldable electrode assembly of the present invention is a form of winding unit cells of a predetermined unit, the formation process of the stacked stack is relatively simple, and since some unit cells are selectively changed, a desired battery is manufactured. In the process of manufacturing the battery according to the predetermined structure is not a significant change to the conventional process.

The separator is interposed between the positive electrode plate and the negative electrode plate to prevent shorts that may occur between the positive electrode plate and the negative electrode plate. The separator is usually formed of thermoplastic resin such as polyethylene (PE), polypropylene (PP), and the surface thereof has a porous membrane structure. Such a porous membrane structure becomes an insulating film because the separator melts when the temperature rises inside the battery and becomes close to the melting point of the thermoplastic resin.

As the present invention, the thickness of the electrode current collector can be variously designed to maintain temperature uniformity inside and outside the cell, thereby extending the life of the cell.

1 illustrates a state in which a plurality of bicells are placed on a separation film,

2 illustrates a state in which a plurality of bicells having current collectors having different thicknesses are positioned on a separation film according to an embodiment of the present invention.

Claims (10)

An electrode assembly having a structure in which a positive electrode and a negative electrode are cut in a predetermined size and stacked sequentially through a separator, so that the thickness deviation of the electrode collector in the center and outside of the electrode assembly is between 2 and 20 μm. An electrode assembly comprising different thicknesses. The electrode assembly according to claim 1, wherein the electrode current collector is either positive electrode or negative electrode. The electrode assembly of claim 11, wherein the unit cell is a full cell having different structures on both sides of the electrode. The electrode assembly of claim 1, wherein the unit cell is a bicell having a structure in which electrodes on both sides are the same. The electrode assembly of claim 1, wherein the electrode assembly is a stack & folding type. Electrochemical device comprising an electrode assembly according to any one of claims 1 to 5. The electrochemical device of claim 6, wherein the electrochemical device is a secondary battery. 8. The electrochemical device of claim 7, wherein the secondary battery is a lithium secondary battery. A high output large-capacity battery pack comprising a battery cell according to any one of claims 7 to 8. The medium-large battery pack of claim 9, wherein the battery pack is used as a power source for an electric vehicle, a hybrid electric vehicle, an electric bicycle, and an electric motorcycle.

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