KR20160024088A - Electrode assembly for secondary battery - Google Patents

Abstract

The present invention relates to an electrode assembly. In particular, according to a lithium secondary battery including multi-row laminated electrodes, a conductive intermediate layer is interposed between the multi-row laminated electrodes, thereby reducing interface resistance. Accordingly, output and lifespan improving effects are ensured.

Description

ELECTRODE ASSEMBLY FOR SECONDARY BATTERY Technical Field [1] The present invention relates to an electrode assembly for a secondary battery,

The present invention relates to an electrode assembly, and more particularly, to a lithium secondary battery including a multi-layer stacked electrode, in which an interfacial resistance is reduced by interposing a conductive intermediate layer between multiple stacked electrodes, .

With the development of technology and demand for mobile devices, it is urgently required to develop a small secondary battery which is light and long-lasting, highly reliable, and high-performance. In addition, there is a growing demand for the development of large-sized rechargeable batteries for efficient use of electric vehicles and idle idle electric power, which are solutions to environmental and energy problems. To meet this demand, lithium secondary batteries have been studied so far.

The lithium secondary battery can be classified into a lithium metal battery using an organic solvent electrolyte and a lithium polymer battery using a lithium ion battery and a solid polymer electrolyte depending on the type of electrolyte.

Of these, the lithium polymer battery has a stable electrolyte due to the solid electrolyte, and it can be manufactured in a form having a high energy density in various sizes and shapes depending on the application, and it is expected to be continuously developed in the future have.

On the other hand, as the number of charge / discharge cycles of lithium secondary battery increases, the resistance component is generated in the interface between the cathode active material and the electrolyte, the interface between the anode active material and the electrolyte, and the electrolyte itself, .

Particularly, the resistance component is generated mainly by the decomposition reaction of the electrolyte generated on the anode side. The decomposition reaction of the electrolyte generates a lot of gas to decrease the contact inside the cell to increase the resistance, or increase the viscosity of the electrolyte, The life of the battery and the capacity of the battery are reduced.

In connection with the present invention, Korean Patent Laid-Open Publication No. 10-2013-011697 (published Oct. 10, 2013) discloses an electrode assembly, but does not mention a technical means for solving the above problems.

An object of the present invention is to provide a lithium secondary battery including a multi-layer stacked electrode in which resistance problems are solved by interposing a conductive intermediate layer between multiple stacked electrodes to reduce the interfacial resistance, And an electrode assembly for a secondary battery.

Disclosed is a lithium secondary battery including a multi-layered electrode. The electrode assembly for a secondary battery has an effect of reducing the interfacial resistance and improving the output and lifetime by interposing a conductive intermediate layer between the electrodes.

According to the electrode assembly for a secondary battery of the present invention, it is possible to reduce the resistance to all the electrodes by including the multi-layer stacked electrodes, and to prevent the interface resistance that may be generated at the interface of the multi- So that the effect of improving the output and lifetime of the secondary battery can be obtained.

1 is a cross-sectional view of an electrode assembly of the present invention.
2 is a cross-sectional view of a first electrode portion included in the electrode assembly of the present invention.
3 is a sectional view of a second electrode portion included in the electrode assembly of the present invention.
4 is a cross-sectional view of an electrode assembly according to an embodiment of the present invention.
5 is a cross-sectional view of an electrochemical device including an electrode assembly according to an embodiment of the present invention.
6 is a cross-sectional view of another electrochemical device including an electrode assembly according to an embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention, and how to accomplish them, will become apparent by reference to the embodiments described in detail below with reference to the accompanying drawings. However, it should be understood that the present invention is not limited to the disclosed embodiments, but may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. It is to be understood that the invention is not limited to the disclosed embodiments but is to be accorded the widest scope of the invention. Like reference numerals refer to like elements throughout the specification.

Hereinafter, an electrode assembly for a secondary battery according to the present invention will be described in detail with reference to the accompanying drawings.

The electrode assembly of the present invention includes a first electrode portion, a second electrode portion, and a separator separating the first electrode portion and the second electrode portion, wherein the first electrode portion or the second electrode portion includes at least two units And a conductive intermediate layer interposed between the unit electrodes.

1 is a cross-sectional view of an electrode assembly of the present invention.

1, the electrode assembly of the present invention includes a first electrode unit 101, a second electrode unit 102, and a first electrode unit 101 and a second electrode unit 102, which separate the first electrode unit 101 and the second electrode unit 102 And a separation membrane 103 as shown in Fig.

2 and 3, the first electrode unit 101 or the second electrode unit 102 may include two or more unit electrodes in order to lower the resistance to the entire electrodes. have.

First, the first electrode unit 101 will be described with reference to FIG.

In the present invention, the first electrode unit 101 may be an anode. The first electrode unit 101 includes a positive electrode active material layer 11 coated on both surfaces of a current collector 10 made of a thin metal plate (for example, aluminum foil) having excellent conductivity. As the active material, chalcogenide compounds are used. For example, composite metal oxides such as LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiNi _{1 -x} Co _x O ₂ (0 <x <1) and LiMnO ₂ are used , But the material is not limited in the present invention.

In the present invention, the first electrode unit 101 may include two or more unit electrodes 101-a and 101-b. As shown in FIG. 2, when two or more unit electrodes are stacked in multiple layers, the resistance to electrodes can be reduced in inverse proportion to the number of stacked electrodes.

In order to solve this problem, in the present invention, a conductive intermediate layer 15 is interposed between two or more unit electrodes which are stacked in layers. . Since the conductive intermediate layer 15 can also be applied to the second electrode portion 102, the structure of the second electrode portion 102 will be described first.

The second electrode unit 102 will be described with reference to FIG.

In the present invention, the second electrode unit 102 may be a negative electrode. The second electrode portion 102 includes a negative electrode active material layer 12 coated on both surfaces of a current collector 20 made of a conductive metal thin plate (for example, copper or nickel foil). As the active material, carbon-based materials, Si, Sn, tin oxides, tin alloy composites, transition metal oxides, lithium metal nitrides, lithium metal oxides, and the like are used, but the present invention is not limited thereto.

In the present invention, the second electrode unit 102 may include two or more unit electrodes 102-a and 102-b. As shown in FIG. 3, when two or more unit electrodes are stacked in multiple layers, the resistance to electrodes can be reduced in inverse proportion to the number of stacked electrodes.

In order to solve this problem, in the present invention, a conductive intermediate layer 15 is interposed between two or more unit electrodes which are stacked in layers. .

In the present invention, the conductive intermediate layer 15 is formed of graphite, carbon nanotubes, carbon black, acetylene black, ketjen black, blast furnace black, carbon fiber, VGCF And a conductive paste containing at least one conductive material selected from the group consisting of a conductive paste and a conductive paste.

Here, the viscosity of the conductive paste is preferably selected according to the particle shape and surface condition of the first electrode, that is, the anode, and the solid content is varied according to the viscosity. Specifically, when the viscosity of the conductive paste is less than 100 cp, the solid content is less than 35 wt%, the viscosity is less than 100 cp and less than 500, the solid content is 35 to 50 wt%, and the viscosity is more than 500 cp to less than 35000 cp. Is more than 50% by weight.

Here, the conductive material may be at least 98 parts by weight based on 100 parts by weight of the conductive paste. When the content of the conductive material is less than 98 parts by weight, the content of the binder increases and the resistance of the electrode interface increases. That is, the preferable content of the conductive material capable of improving the binding force with the electrode and the conductivity is 98 parts by weight or more.

Here, the binder for preparing the conductive paste may include at least one selected from PVDF, NMP, and CMC / SBR.

Here, the average particle size of the conductive material included in the conductive intermediate layer may be 10 to 50 탆, excluding the carbon nanotubes, and the specific surface area may be 30 to 15000 m ² / g. For carbon nanotubes, the diameter may be between 5 and 200 nm.

Here, the conductive material included in the conductive intermediate layer may be surface-treated so as to be well dispersed in the conductive paste. Specifically, a compound treated so that an oxygen-containing group is contained on the surface of the conductive substance may be used. In order to facilitate the dispersion of the conductive material, the binder in the conductive paste may also include a dispersant or a dispersion medium.

Here, the thickness of the conductive intermediate layer may be 1 to 5 占 퐉, more preferably 1 to 3 占 퐉. When the thickness of the conductive intermediate layer exceeds 5 탆, the ohmic resistance increases to increase the interfacial resistance. On the other hand, when the thickness of the conductive intermediate layer is less than 1 탆, the conductive paste There is a problem that the resistance is similarly increased because the bonding force is impaired due to permeation into the pores in the electrode.

4, the electrode assembly according to an embodiment of the present invention includes a plurality of first electrode units 101 and a plurality of second electrode units 102 alternately laminated, And the first electrode unit 101 and the second electrode unit 102 may be separated from each other.

The first electrode unit 101 and the second electrode unit 102 are as described above and the separation membrane 103 is configured to separate the first electrode unit 101 and the second electrode unit 102 from each other. Propylene, and a copolymer of polyethylene and polypropylene. However, the material is not limited in the present embodiment.

In addition, the present invention may include an electrochemical device in which the above-described electrode assembly is superimposed on a base unit and each of the superimposed portions has a separation film interposed therebetween.

5 and 6, the first electrode unit 101, the second electrode unit 102, and the separator (not shown) for separating the first electrode unit 101 and the second electrode unit 102 103 are stacked on a base unit, and a separation film 201 is disposed on each of the overlapped portions.

Here, although the separation film 201 is interposed at a different position from the separation membrane 103, other materials including the material can be considered to be the same at a level acceptable to those skilled in the art.

Specifically, as shown in FIG. 5, the electrochemical device of the present invention may have a configuration in which a plurality of electrode assemblies are alternately stacked, and a separation film 201 is formed in a zigzag shape to separate the alternately stacked electrode assemblies.

6, the electrochemical device of the present invention is manufactured by placing a plurality of electrode assemblies on a separation film 103 in a predetermined pattern and winding the separation film 103, Assemblies &lt; / RTI &gt;

Example

Hereinafter, the configuration and operation of the present invention will be described in more detail with reference to preferred embodiments of the present invention. It is to be understood, however, that the same is by way of illustration and example only and is not to be construed in a limiting sense.

The contents not described here are sufficiently technically inferior to those skilled in the art, and a description thereof will be omitted.

Example  One

(Anode manufacture)

The slurry was dispersed in NMP at a weight ratio of Li (Ni / Co / Mn) O2: carbon black: PVDF = 94: 3: 3 to prepare a slurry. The slurry was coated on both sides of aluminum foil, The unit anode was prepared by pressing. The thickness of the double-coated anode was 140 탆.

 (Cathode manufacture)

The slurry was dispersed in NMP at a weight ratio of graphite: acetylene black: PVDF = 93: 1: 6 to prepare a slurry. The slurry was coated on both surfaces of a copper foil and sufficiently dried at 130 ° C. The thickness of the double coated cathode was 135 mu m.

(Preparation of conductive intermediate layer)

The slurry was dispersed in water at a weight ratio of furnace black: CMC / SBR = 98: 2 to prepare a slurry. The slurry was coated on the anode-coated electrode to a thickness of 1 to 5 μm to prepare a conductive intermediate layer. The coating area must be coated between the same type of electrodes facing each other.

(Preparation of electrode assembly)

A 16 占 퐉 -thick polypropylene film having a microporous structure as a separator was used as the first polymer separator, and a polyvinylidene fluoride-chlorotrifluoroethylene copolymer 32008 of Solvey Polymer was used as a gelling secondary polymer Multilayer polymer films were used.

A unit anode coated on both surfaces of a positive electrode current collector prepared above was cut except for a place where tabs were to be formed in a rectangle having a size of 7.8 cm x 10.6 cm and another unit anode prepared by the same method was cut in the same manner Then, the unit anode was overlaid, and the prepared conductive intermediate layer was positioned at the interface between the unit anodes. In order to reduce the interfacial resistance, the positive electrode assembly was manufactured by passing the conductive paste coated on the positive electrode through a roll laminator having a temperature of 140 ° C and thermally fusing.

On the other hand, after cutting the negative electrode coated on both surfaces of the negative electrode collector with the exception of the place where tabs were to be formed into a rectangular shape with a size of 80 cm x 108 cm, the multi-layered polymer film prepared above was placed between the positive electrode and the negative electrode at 84 cm × 112 cm to produce an electrode assembly of FIG.

 (Manufacture of electrochemical device)

The electrode assembly manufactured as described above was superimposed like the structure of FIG. 5, and the multilayer polymer film prepared above was assembled so as to be located in a zigzag shape in the overlapping portions of the electrode assemblies.

(Battery manufacturing)

The prepared electrochemical device was placed in an aluminum laminate packaging material, and an electrolyte of EC / EMC / DEC / PC in LiPF6 was injected and packed.

Comparative Example  One

(Anode manufacture)

The slurry was dispersed in NMP at a weight ratio of Li (Ni / Co / Mn) O2: carbon black: PVDF = 94: 3: 3 to prepare a slurry. The slurry was coated on both sides of aluminum foil, The unit anode was prepared by pressing. The thickness of the double-coated anode was 140 탆.

(Cathode manufacture)

The slurry was dispersed in NMP at a weight ratio of graphite: acetylene black: PVDF = 93: 1: 6 to prepare a slurry. The slurry was coated on both surfaces of a copper foil and sufficiently dried at 130 ° C. The thickness of the double coated cathode was 135 mu m.

(Preparation of electrode assembly)

A 16 占 퐉 -thick polypropylene film having a microporous structure as a separator was used as the first polymer separator, and a polyvinylidene fluoride-chlorotrifluoroethylene copolymer 32008 of Solvey Polymer was used as a gelling secondary polymer Multilayer polymer films were used.

The positive electrode material prepared in the above was coated on both surfaces of the positive electrode current collector. The positive electrode was cut into a rectangle having a size of 78 cm x 106 cm except for the place where the tab was to be formed. The negative electrode coated with the double- A rectangular electrode having a size of 108 cm was cut except for the place where the tab was to be cut to manufacture an electrode assembly.

(Manufacture of electrochemical device)

The electrode assembly manufactured as described above was superimposed as in the structure of FIG. 5, and the multilayer polymer film prepared above was laminated so as to be placed in a zigzag shape in the overlapping portions of the electrode assemblies.

(Battery manufacturing)

The prepared electrochemical device was placed in an aluminum laminate packaging material, and an electrolyte of EC / EMC / DEC / PC in LiPF6 was injected and packed.

Comparative Example  2

An electrode assembly, an electrochemical device, and a battery were produced in the same manner as in Example, but the conductive intermediate layer was not used at the interface between unit electrodes.

evaluation

The lifetime and the capacity of the battery prepared by the above Examples and Comparative Examples were measured, and the results are shown in Table 1 below.

Evaluation method of life characteristics:

Charging 2 C, 4.2 V (CC / CV), 0.1 C cut off, rest 10 min,

Discharge 2C, 2.5V (CV), rest 10min

In the above-described manner, the discharge capacity after charging was once cycled, and the cycle was continued until the discharge capacity deteriorated by 80%.

Capacity characteristics evaluation method:

Charging 1 C, 4.2 V (CC / CV), 0.1 C cut off, rest 10 min,

Discharge 1 C, 2.5 V (CV), rest 10 min

The capacity was confirmed by discharging in the same manner as described above.

EOL 80% Example 1 Comparative Example 1 Comparative Example 2 Life cycle 1037 748 1260 Capacity (mAh) 857 832 863

From the above results, it can be confirmed that the life characteristics and the capacity characteristics of Comparative Example 1 are significantly lower than those of Examples. This is because the resistance of the anode of Comparative Example 1 was large. Further, even when the positive electrode was laminated in multiple layers to reduce the resistance, in the case where the conductive intermediate layer was not interposed between the positive electrodes as in Comparative Example 2, the life characteristics and the capacity characteristics were not excellent due to the interface resistance.

In other words, according to the embodiment of the present invention, in order to solve the interfacial resistance that may be generated at the interface of the multi-layer stacked electrode while reducing the resistance applied to all the electrodes by including the multi-layer stacked electrode, The interfacial resistance is reduced, and the effect of improving the output and lifetime of the secondary battery can be obtained.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. These changes and modifications may be made without departing from the scope of the present invention. Accordingly, the scope of the present invention should be determined by the following claims.

Claims (10)

The electrode assembly includes a first electrode portion, a second electrode portion, and a separator separating the first electrode portion and the second electrode portion,
Wherein the first electrode unit or the second electrode unit includes two or more unit electrodes,
And a conductive intermediate layer is interposed in the interface between the unit electrodes.
The method according to claim 1,
Wherein the conductive intermediate layer is formed of a conductive paste containing at least one conductive material selected from graphite, carbon nanotubes, carbon black, acetylene black, ketjen black, blast furnace black, carbon fiber, and VGCF.
3. The method of claim 2,
Wherein the conductive material is present in an amount of 98 parts by weight or more based on 100 parts by weight of the conductive paste.
3. The method of claim 2,
Wherein an average particle size of the conductive material except for the carbon nanotubes is 10 to 50 mu m and a specific surface area is 30 to 15000 m &lt; ² &gt; / g.
3. The method of claim 2,
Wherein an average particle diameter of the conductive material, which is included in the conductive intermediate layer and is a carbon nanotube, is 5 to 200 nm.
3. The method of claim 2,
Wherein the conductive material contained in the conductive intermediate layer is surface-treated.
The method according to claim 1,
Wherein the thickness of the conductive intermediate layer is 1 to 5 占 퐉.
The method according to claim 1,
Wherein the first electrode portion is an anode and the second electrode portion is a cathode.
The method according to claim 1,
The plurality of first electrode portions and the plurality of second electrode portions are alternately laminated,
Wherein the separation membrane is formed in a zigzag shape to separate the first electrode part and the second electrode part alternately stacked.
The electrochemical device according to claim 1, wherein the electrode assembly is superimposed on a base unit, and each of the superimposed portions has a separation film interposed therebetween.

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