阅读说明：本技术 用于锂二次电池的负极、制备所述负极的方法和包括所述负极的锂二次电池 (Negative electrode for lithium secondary battery, method of preparing the same, and lithium secondary battery including the same ) 是由 蔡午秉 禹相昱 金帝映 于 2019-03-18 设计创作，主要内容包括：本发明涉及一种用于锂二次电池的负极、一种制备所述负极的方法、一种通过对所述负极进行预锂化来制备预锂化负极的方法、以及一种包括所述负极的锂二次电池。具体地,通过预锂化确保负极的初始可逆性,根据本发明的负极能够增加电池容量并改善电化学性能,并且根据本发明的负极能够允许锂离子在预锂化期间不损失地扩散到负极活性材料层中。(The present invention relates to an anode for a lithium secondary battery, a method of preparing the anode, a method of preparing a prelithiated anode by prelithiating the anode, and a lithium secondary battery including the anode. Specifically, the anode according to the present invention can increase the battery capacity and improve the electrochemical performance by ensuring the initial reversibility of the anode through pre-lithiation, and the anode according to the present invention can allow lithium ions to diffuse into the anode active material layer without loss during pre-lithiation.)

1. An anode for a lithium secondary battery, comprising:

a negative electrode current collector;

a first anode active material layer formed on the anode current collector and including a first anode active material; and

a second anode active material layer formed on the first anode active material layer and including a second anode active material on a surface of which an inorganic coating layer is formed,

wherein the second anode active material having the inorganic coating layer formed on a surface thereof contains lithium in at least one of the inorganic coating layer and the second anode active material.

2. The anode for a lithium secondary battery according to claim 1, wherein the inorganic coating layer comprises at least one selected from the group consisting of a metal halide, a metal carbonate, and a metal oxide.

3. The anode for a lithium secondary battery according to claim 1, wherein the inorganic coating layer comprises one or more selected from the group consisting of LiF, Li₂CO₃、Li₂O、Al₂O₃、SiO₂And ZrO₂At least one of the group consisting of.

4. The anode for a lithium secondary battery according to claim 1, wherein the first anode active material and the second anode active material are each independently one or more anode active materials selected from the group consisting of: a carbon-based material; one or more selected from the group consisting of Si, Sn, Al, Sb and Zn or an oxide thereof; and is selected from the group consisting of Co_x1O_y1(1≤x1≤3,1≤y1≤4)、Ni_x2O_y2(1≤x2≤3,1≤y2≤4)、Fe_x3O_y3(1≤x3≤3,1≤y3≤4)、TiO₂、MoO₂、V₂O₅And Li₄Ti₅O₁₂Metal oxides of the group consisting.

5. The anode for a lithium secondary battery according to claim 1, wherein the first anode active material is a silicon-based anode active material.

6. The anode for a lithium secondary battery according to claim 1, wherein the second anode active material is one or more selected from the group consisting of lithiated graphene, lithiated silicon, and lithiated graphite.

7. An anode for a lithium secondary battery, comprising:

a negative electrode current collector;

a first anode active material layer formed on the anode current collector and including a first anode active material; and

a second anode active material layer formed on the first anode active material layer and including a second anode active material on a surface of which an inorganic coating layer is formed,

wherein the first anode active material layer contains lithium, and the lithium is diffused in the form of lithium ions or exists in a form combined with the first anode active material, and the second anode active material layer having the inorganic coating layer formed on a surface thereof contains lithium in at least one of the inorganic coating layer and the second anode active material.

8. A method of preparing the anode for a lithium secondary battery of claim 1, comprising the steps of:

forming a first anode active material layer including a first anode active material on the anode current collector;

forming an inorganic coating layer on a surface of the second anode active material; and

forming a second anode active material layer on the first anode active material layer, the second anode active material layer including the second anode active material having the inorganic coating formed on a surface thereof and including lithium in at least one of the inorganic coating or the second anode active material.

9. A method of preparing the anode for a lithium secondary battery of claim 7, comprising the steps of:

forming a first anode active material layer including a first anode active material on the anode current collector;

forming an inorganic coating layer on a surface of the second anode active material;

forming a second anode active material layer on the first anode active material layer, the second anode active material layer including the second anode active material having the inorganic coating formed on a surface thereof and including lithium in at least one of the inorganic coating or the second anode active material; and

the anode in which the first anode active material layer and the second anode active material layer are formed on the anode current collector is impregnated with a prelithiation solution to perform prelithiation, so that lithium is contained in the first anode active material layer.

10. The method of claim 9, wherein the prelithiation solution includes an ionizable lithium salt and an organic solvent.

11. The method of claim 9, wherein the impregnating is carried out at a temperature in the range of 10 ℃ to 200 ℃ for 2 hours to 48 hours.

12. A lithium secondary battery comprising the anode for a lithium secondary battery according to claim 1 or 7.

Technical Field

Cross Reference to Related Applications

This application claims priority and benefit to korean patent application No. 10-2018-0038716 filed by the korean intellectual property office at 4/3 in 2018, the entire contents of which are incorporated herein by reference.

Background

As the technical development and demand for mobile devices increase, the demand for secondary batteries as energy sources is rapidly increasing. Among these secondary batteries, lithium secondary batteries exhibiting high energy density and operating potential, long cycle life, and low self-discharge rate have been commercialized and widely used.

Furthermore, such as LiCoO₂、LiMnO₂、LiMn₂O₄Or LiCrO₂Is used as a positive electrode active material forming a positive electrode of a lithium secondary battery, and lithium metal (metal lithium), carbon-based materials such as graphite (graphite), activated carbon (activated carbon) or the like, or carbon-based materials such as silicon oxide (SiO) are used_x) Or the like is used as a negative electrode active material forming the negative electrode. In the above-described anode active material, lithium metal is primarily used initially, but as charge and discharge cycles progress, lithium atoms grow on the surface of lithium metal, causing damage to the separator and the battery, and therefore, carbon-based materials have been mainly used recently. However, in the case of the carbon-based material, since the theoretical capacity is only about 400mAh/g, there is a disadvantage that the capacity is small. Therefore, various studies have been made to replace the carbon-based material with a silicon (Si) based material having a high theoretical capacity (4,200mAh/g) as an anode active material.

The lithium secondary battery is charged and discharged while lithium ions of a positive electrode active material of a positive electrode are intercalated into/deintercalated from a negative electrode active material of a negative electrode.

Theoretically, the intercalation and deintercalation reactions of lithium in the anode active material are completely reversible, but actually more lithium is consumed than the theoretical capacity of the anode active material, and only a part of lithium is recovered during discharge. Therefore, after the second cycle, a smaller amount of lithium ions are intercalated during charging, but almost all of the intercalated lithium ions are deintercalated during discharging. The capacity difference exhibited in the first charge-discharge reaction is called irreversible capacity loss. Since a commercial lithium secondary battery is manufactured in a state where lithium ions are supplied from a cathode and lithium is not present in an anode, it is very important to minimize irreversible capacity loss during initial charge and discharge.

It is known that such initial irreversible capacity loss is mainly caused by an Electrolyte decomposition (Electrolyte decomposition) reaction on the surface of the anode active material, and a Solid Electrolyte Interface (SEI) is formed on the surface of the anode active material by an electrochemical reaction through the Electrolyte decomposition. The formation of SEI causes a problem of irreversible capacity loss due to consumption of a large amount of lithium ions, but SEI formed at the start of charging prevents lithium ions from reacting with an anode or other materials during charging and discharging and serves as an Ion Tunnel (Ion Tunnel) through which only lithium ions pass, thereby further suppressing decomposition reaction of an electrolyte and contributing to improvement of cycle characteristics of a lithium secondary battery.

Therefore, a method for improving the initial irreversible capacity loss caused by the formation of SEI or the like is required. One of these methods is to perform pre-lithiation (pre-lithiation) before manufacturing a lithium secondary battery so as to undergo side reactions occurring during first charging in advance. As described above, in the case where the prelithiation is performed, when charging and discharging are performed on the actually manufactured secondary battery, there are advantages in that: since the first cycle is performed in a state where the irreversible capacity loss is reduced, the initial irreversible capacity loss can be reduced.

Examples of the conventional prelithiation method include a method of depositing lithium on a negative electrode and a method of directly contacting lithium with a negative electrode. For example, a lithiated material layer for prelithiation may be formed on the anode active material layer, but the lithiated material is easily oxidized and thus easily oxidized when exposed to moisture or oxygen.

Therefore, there is a need to develop an anode for a lithium secondary battery capable of achieving more efficient prelithiation.

Disclosure of Invention

[ problem ] to

An object of the present invention is to provide an anode for a lithium secondary battery capable of securing initial reversibility of the anode and allowing diffusion of lithium ions into an anode active material without loss due to moisture, oxidation, or the like, a method for efficiently producing the anode, and a lithium secondary battery including the anode.

[ solution ]

In order to achieve the object, the present invention provides an anode for a lithium secondary battery comprising:

a negative electrode current collector;

a first anode active material layer formed on the anode current collector and including a first anode active material; and

a second anode active material layer formed on the first anode active material layer and including a second anode active material,

an inorganic coating layer is formed on a surface of the second negative electrode active material, wherein the second negative electrode active material having the inorganic coating layer formed on the surface thereof contains lithium in at least one of the inorganic coating layer and the second negative electrode active material.

The inorganic coating layer may include at least one selected from the group consisting of metal halides, metal carbonates, and metal oxides, and particularly, the inorganic coating layer may include LiF, Li₂CO₃、Li₂O、Al₂O₃、SiO₂And ZrO₂One or more of (a).

The first anode active material and the second anode active material may each independently be: a carbon-based material; one or more selected from the group consisting of Si, Sn, Al, Sb and Zn or an oxide thereof; or Co_x1O_y1(1≤x1≤3,1≤y1≤4)、Ni_x2O_y2(1≤x2≤3,1≤y2≤4)、Fe_x3O_y3(1≤x3≤3,1≤y3≤4)、TiO₂、MoO₂、V₂O₅Or Li₄Ti₅O₁₂。

Specifically, the first negative electrode active material may be a silicon-based negative electrode active material, and the second negative electrode active material may be lithiated graphene, lithiated silicon, or lithiated graphite.

Further, the present invention provides an anode for a lithium secondary battery including:

a negative electrode current collector;

a first anode active material layer formed on the anode current collector and including a first anode active material; and

a second anode active material layer formed on the first anode active material layer and including a second anode active material on a surface of which an inorganic coating layer is formed,

wherein the first negative electrode active material layer contains lithium, and the lithium is diffused in the form of lithium ions or exists in a form combined with the first negative electrode active material,

and the second anode active material layer having the inorganic coating layer formed on the surface thereof contains lithium in at least one of the inorganic coating layer and the second anode active material.

In addition to this, the present invention is,

the present invention provides a method of preparing an anode for a lithium secondary battery, the method comprising the steps of:

forming a first anode active material layer including a first anode active material on the anode current collector;

forming an inorganic coating layer on a surface of the second anode active material; and

forming a second anode active material layer on the first anode active material layer, the second anode active material layer including a second anode active material having an inorganic coating formed on a surface thereof, and including lithium in at least one of the inorganic coating or the second anode active material.

Further, the present invention provides a method of preparing an anode for a lithium secondary battery, the method comprising the steps of:

forming a first anode active material layer including a first anode active material on the anode current collector;

forming an inorganic coating layer on a surface of the second anode active material;

forming a second anode active material layer on the first anode active material layer, the second anode active material layer including a second anode active material having an inorganic coating formed on a surface thereof and containing lithium in at least one of the inorganic coating or the second anode active material; and

the anode in which the first anode active material layer and the second anode active material layer are formed on the anode current collector is impregnated with a prelithiation solution to perform prelithiation, so that lithium is contained in the first anode active material layer.

The prelithiation solution includes an ionizable lithium salt and an organic solvent, and the impregnation may be performed at a temperature in the range of 10 ℃ to 200 ℃ for 2 hours to 48 hours.

Further, the present invention provides a lithium secondary battery including the anode for a lithium secondary battery.

[ advantageous effects ]

In the anode according to the present invention including the first anode active material layer containing lithium and the second anode active material layer having the inorganic coating layer formed thereon, the second anode active material is resistant to moisture or oxidation due to being coated with the inorganic coating layer, so that lithium ions diffused into the first anode active material layer are not consumed during the subsequent prelithiation. In addition, the prelithiated anode according to the present invention can ensure initial reversibility of the anode, thereby improving electrochemical performance of the lithium secondary battery.

Drawings

Fig. 1 is a view illustrating formation of an inorganic coating layer on a second anode active material.

Fig. 2 is a simplified diagram showing a production process of the anode of the present invention.

Detailed Description

Hereinafter, the present invention will be described in further detail.

The terms used in the present specification and claims should not be construed as limited to conventional meanings or literal meanings, but should be construed to have meanings and concepts corresponding to technical ideas of the present invention based on the principle that the inventor can appropriately define the concepts of the terms to explain his invention by the most preferable method.

Negative electrode

The anode according to the present invention includes:

a negative electrode current collector;

a first anode active material layer formed on the anode current collector and including a first anode active material; and

a second anode active material layer formed on the first anode active material layer and including a second anode active material,

an inorganic coating layer is formed on a surface of the second negative electrode active material, wherein the second negative electrode active material layer having the inorganic coating layer formed on the surface thereof contains lithium in at least one of the inorganic coating layer and the second negative electrode active material.

The inorganic coating layer may include at least one selected from the group consisting of metal halides, metal carbonates, and metal oxides. The inorganic coating may comprise a material selected from the group consisting of LiF, Li₂CO₃、Li₂O、Al₂O₃、SiO₂And ZrO₂At least one of the group consisting of.

The first anode active material and the second anode active material may each independently be: a carbon-based material; one or more selected from the group consisting of Si, Sn, Al, Sb and Zn or an oxide thereof; or Co_x1O_y1(1≤x1≤3,1≤y1≤4)、Ni_x2O_y2(1≤x2≤3,1≤y2≤4)、Fe_x3O_y3(1≤x3≤3,1≤y3≤4)、TiO₂、MoO₂、V₂O₅Or Li₄Ti₅O₁₂。

Specifically, the first negative electrode active material as the silicon-based negative electrode active material includes silicon (Si), a silicon-based alloy, silicon oxide (SiO)_x,0<x is less than or equal to 2) or the like.

In addition, the first negative electrode active material layer may further include a carbon-based negative electrode active material such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon, in addition to the silicon-based negative electrode active material. In this case, the first anode active material layer may include a carbon-based anode active material and a silicon-based anode active material in a weight ratio of 99:1 to 50:50, preferably 95:5 to 80: 20.

When the content of the silicon-based negative active material is less than the above range, it is difficult to increase the energy density of the battery, and thus it is difficult to achieve high capacity of the battery. When the amount of the silicon-based anode active material exceeds the above range, the volume expansion degree of the anode may increase.

In addition, the second anode active material may be lithiated graphene, lithiated silicon, or lithiated graphite.

The negative electrode for a lithium secondary battery is a negative electrode before pre-lithiation. Lithium of the second anode active material may be diffused into the first anode active material through a prelithiation process.

The prelithiated negative electrode according to the present invention, as described above, comprises:

a negative electrode current collector;

a first anode active material layer formed on the anode current collector and including a first anode active material; and

a second anode active material layer formed on the first anode active material layer and including a second anode active material on a surface of which an inorganic coating layer is formed,

wherein the first negative electrode active material layer contains lithium, and the lithium is diffused in the form of lithium ions or exists in a form combined with the first negative electrode active material,

and the second anode active material layer having the inorganic coating layer formed on the surface thereof contains lithium in at least one of the inorganic coating layer and the second anode active material.

In the prelithiation anode, lithium in a second anode active material layer present in the anode before prelithiation is diffused into a first anode active material so that lithium is diffused in the form of lithium ions or exists in a form combined with the first anode active material.

Method for preparing negative electrode

The method for preparing an anode for a lithium secondary battery according to the present invention includes the following steps (see fig. 1 and 2).

First, the anode 132 before pre-lithiation in the anode for a lithium secondary battery according to the present invention is prepared by the following steps:

forming a first anode active material layer 122 including a first anode active material on the anode current collector 120;

forming an inorganic coating layer 114 on a surface of the second anode active material 112;

a second anode active material layer 116 is formed on the first anode active material layer 122, the second anode active material layer 116 including a second anode active material 112 having an inorganic coating 114 formed on a surface thereof and including lithium in at least one of the inorganic coating 114 or the second anode active material 112.

Further, the method of preparing the prelithiated anode 134 for a lithium secondary battery according to the present invention is obtained by:

forming a first anode active material layer 122 including a first anode active material on the anode current collector 120;

forming an inorganic coating layer 114 on a surface of the second anode active material 112;

forming a second anode active material layer 116 on the first anode active material layer 122, the second anode active material layer 116 including a second anode active material 112 having an inorganic coating 114 formed on a surface thereof and containing lithium in at least one of the inorganic coating 114 or the second anode active material 112; and

the anode 132 in which the first anode active material layer 122 and the second anode active material layer 116 are formed on the anode current collector 120 is impregnated with a prelithiation solution to perform prelithiation, so that lithium is contained in the first anode active material layer.

The first anode active material layer 122 may be formed by: dissolving or dispersing a first anode active material, a conductive material and/or a binder in a solvent to prepare an anode composite, applying the anode composite to at least one surface of an anode current collector, and drying and pressing the anode composite; or the first anode active material layer 122 may be formed by: the anode material was cast on a separate support, and the film separated from the support was laminated on an anode current collector.

The second anode active material layer 116 may be formed by: dissolving or dispersing the second anode active material 112 having the inorganic coating layer 114 formed thereon, a conductive material, and/or a binder in a solvent to prepare an anode composite, applying the anode composite to at least one surface of an anode current collector, and drying and pressing the anode composite; or the second anode active material layer 116 may be formed by: the anode material was cast on a separate support, and the film separated from the support was laminated on an anode current collector. One or more of the inorganic coating 114 and the second negative active material 112 includes lithium.

The anode current collector is not particularly limited as long as it has high conductivity and does not cause chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, aluminum-cadmium alloy, or the like may be used. In addition, the anode current collector may have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the binding force of the anode active material. For example, the anode current collector may be used in various forms such as a film, a sheet, a foil, a mesh, a porous body, a foam, a non-woven fabric, and the like.

The first anode active material and the second anode active material may be each included in an amount of 80 to 99 wt%, more specifically, 85 to 98 wt%, based on the total weight of the first anode active material layer and the second anode active material layer. When the content is within the above range, excellent capacity characteristics may be exhibited.

The conductive material is used to impart conductivity to the electrode, and is not particularly limited as long as it has conductivity without causing chemical changes in the corresponding battery. Specific examples of the conductive material may include: graphite, such as natural graphite or artificial graphite; a carbonaceous material such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, or carbon fiber; powders or fibers of metals such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive polymers such as polyphenylene derivatives; and the like, any one of them or a mixture of two or more of them may be used. The conductive material may be included in an amount of 1 to 30 wt% based on the total weight of the anode active material layer.

In addition, the binder serves to enhance cohesion between the anode active material particles and binding force between the anode active material and the current collector. Specific examples of the binder include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile (polyacrylonitrile), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, various copolymers thereof, and the like, any one of them or a mixture of two or more of them may be used. The binder may be included in an amount of 1 to 30 wt% based on the total weight of the anode active material layer.

In addition, the solvent used in the preparation of the anode composite may be a solvent commonly used in the related art. For example, dimethyl sulfoxide (DMSO), isopropyl alcohol (isopropyl alcohol), N-methylpyrrolidone (NMP), acetone (acetone), water, or the like may be used alone or in combination. The amount of the solvent used may be appropriately adjusted according to the application thickness of the slurry, production yield, viscosity, and the like.

The prelithiation solution is a solution comprising an ionizable lithium salt and an organic solvent. The anode may be prelithiated by impregnating the anode with a prelithiation solution before the electrode assembly is assembled, or may be prelithiated by an injected electrolyte solution (corresponding to the prelithiation solution) after the battery is assembled.

The ionizable lithium salt comprises Li⁺As cations, and the anion may be selected from the group consisting of F^-、Cl^-、Br^-、I^-、NO₃ ^-、N(CN)₂ ^-、BF₄ ^-、ClO₄ ^-、AlO₄ ^-、AlCl₄ ^-、PF₆ ^-、SbF₆ ^-、AsF₆ ^-、B₁₀Cl₁₀ ^-、BF₂C₂O₄ ^-、BC₄O₈ ^-、PF₄C₂O₄ ^-、PF₂C₄O₈ ^-、(CF₃)₂PF₄ ^-、(CF₃)₃PF₃ ^-、(CF₃)₄PF₂ ^-、(CF₃)₅PF^-、(CF₃)₆P^-、CF₃SO₃ ^-、C₄F₉SO₃ ^-、CF₃CF₂SO₃ ^-、(CF₃SO₂)₂N^-、(FSO₂)₂N^-、CF₃CF₂(CF₃)₂CO^-、(CF₃SO₂)₂CH^-、CH₃SO₃ ^-、CF₃(CF₂)₇SO₃ ^-、CF₃CO₂ ^-、CH₃CO₂ ^-、SCN^-And (CF)₃CF₂SO₂)₂N^-A group of which.

The organic solvent may be one or more selected from the group consisting of: a cyclic carbonate-based organic solvent selected from the group consisting of ethylene carbonate, 1, 2-butylene carbonate, 2, 3-butylene carbonate, 1, 2-pentylene carbonate, 2, 3-pentylene carbonate, vinylene carbonate, and fluoroethylene carbonate (FEC); a linear carbonate-based organic solvent selected from the group consisting of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate and ethylene propylene carbonate; a linear ester-based organic solvent selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate.

The impregnation may be carried out at a temperature ranging from 10 ℃ to 200 ℃ for 2 hours to 48 hours.

When lithium in the second anode active material layer 116 of the present invention is diffused into the first anode active material layer 122 as an underlying layer through the prelithiation process, prelithiation occurs. Thus, a prelithiated anode 134 including a first anode active material layer 122' into which lithium ions have diffused through prelithiation may be prepared.

In the prelithiated anode 134, the lithium concentration of the second anode active material layer 116 'after prelithiation is lower than the lithium concentration of the second anode active material layer 116 before prelithiation, and lithium is present in the first anode active material layer 122' corresponding to the reduced amount.

Lithium secondary battery

Next, a lithium secondary battery according to the present invention will be described.

The anode prepared according to the present invention can be effectively used to prepare a lithium secondary battery.

Specifically, a lithium secondary battery according to the present invention includes an anode, a cathode disposed opposite to the anode, a separator interposed between the anode and the cathode, and an electrolyte. Here, the anode is an anode prepared according to the present invention as described above.

In addition, the secondary battery may optionally further include: a battery container accommodating an electrode assembly composed of a positive electrode, a negative electrode and a separator; and a sealing member sealing the battery container.

A lithium secondary battery may be prepared according to a conventional secondary battery preparation method, except for using the anode according to the present invention.

In the secondary battery, the positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector.

The positive electrode may be prepared according to a conventional positive electrode preparation method well known in the related art. For example, the positive electrode may be prepared by: dissolving or dispersing components (i.e., a cathode active material, a conductive material, and/or a binder) forming a cathode active material layer in a solvent to prepare a cathode composite, applying the cathode composite onto at least one surface of a cathode current collector, and drying and pressing the cathode composite; alternatively, the positive electrode may be prepared by: the positive electrode composite material is cast on a separate support, and then the film separated from the support is laminated on a positive electrode current collector.

The positive electrode current collector is not particularly limited as long as it has conductivity and does not cause chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like may be used. In addition, the cathode current collector may generally have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the binding force of the cathode active material. For example, the cathode current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, and the like.

Examples of the positive electrode active material may include, but are not limited to: such as lithium cobalt oxide (LiCoO)₂) And lithium nickel oxide (LiNiO)₂) Such layered compounds, or compounds substituted with one or more transition metals; lithium manganese oxides, such as of formula Li_1+yMn_2-yO₄(wherein y is 0 to 0.33), LiMnO₃、LiMn₂O₃、LiMnO₂And compounds represented by the like; lithium copper oxide (Li)₂CuO₂) (ii) a Vanadium oxides, such as LiV₃O₈、LiV₃O₄、V₂O₅、Cu₂V₂O₇And the like; from the formula LiNi_1-yM_yO₂(wherein M ═ Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and y ═ 0.01 to 0.3) represents a Ni-site type lithium nickel oxide; of the formula LiMn_{2- y}M_yO₂(where M ═ Co, Ni, Fe, Cr, Zn or Ta, and y ═ 0.01 to 0.1) or the formula Li₂Mn₃MO₈(wherein M ═ Fe, Co, Ni, Cu, or Zn); LiMn₂O₄Wherein a portion of Li is substituted with alkaline earth metal ions; a disulfide compound; fe₂(MoO₄)₃And the like.

In addition, the binder and the conductive material may be the same as those for the negative electrode described above.

In addition, in the secondary battery, a separator separates the negative electrode and the positive electrode, and provides a path for lithium ion migration. The separator may be used without any particular limitation as long as it is generally used as a separator in a secondary battery. In particular, a separator having low resistance to the movement of ions of the electrolyte and excellent electrolyte impregnation is preferable. Specifically, a porous polymer film, for example, a porous polymer film formed of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene/butene copolymer, an ethylene/hexene copolymer, an ethylene/methacrylate copolymer, and the like, or a laminated structure having two or more layers thereof may be used. Further, a conventional porous nonwoven fabric, for example, a porous nonwoven fabric formed of glass fibers having a high melting point, polyethylene terephthalate fibers, or the like, may be used. Further, a coated separator including a ceramic component or a polymer material to secure heat resistance or mechanical strength may be used, and may be optionally used as a single layer or a multi-layer structure.

Further, examples of the electrolyte include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a melt-type inorganic electrolyte, and the like, which can be used to prepare a secondary battery, but are not limited thereto.

Specifically, the electrolyte may include an organic solvent and a lithium salt.

The organic solvent may be used without limitation as long as it can serve as a medium enabling movement of ions involved in the electrochemical reaction of the battery. Specifically, the organic solvent may be: ester-based solvents such as methyl acetate (methyl acetate), ethyl acetate (ethyl acetate), γ -butyrolactone (γ -butyrolactone), -caprolactone (-caprolone), and the like; ether-based solvents such as dibutyl ether (dibutyl ether), tetrahydrofuran (tetrahydrofuran), or the like; ketone based solvents such as cyclohexanone (cyclohexoxanone); aromatic hydrocarbon-based solvents such as benzene (bezene), fluorobenzene (fluorobenzene) and the like; carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methylethyl carbonate (MEC), ethylmethyl carbonate (EM C), Ethylene Carbonate (EC), Propylene Carbonate (PC) and the like; alcohol-based solvents such as ethanol, isopropanol, and the like; nitriles such as Ra-CN (where Ra is a linear, branched or cyclic C2 to C20 hydrocarbyl group and may include double-bonded aromatic rings or ether linkages); amides such as dimethylformamide; dioxolanes such as 1, 3-dioxolane; or sulfolane (sulfolane). Among them, a carbonate-based solvent is preferable, and a mixture of a cyclic carbonate (such as ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant, and a linear carbonate-based compound (for example, ethylmethyl carbonate, dimethyl carbonate, diethyl carbonate, etc.) having low viscosity, which are capable of improving the charge and discharge performance of the battery, is more preferable. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1:1 to 9, the performance of the electrolyte may be excellent.

The lithium salt may be used without particular limitation so long as it is a compound capable of providing lithium ions used in the lithium secondary battery. Specifically, the lithium salt may be LiPF₆、LiClO₄、LiAsF₆、LiBF₄、LiSbF₆、LiAlO₄、LiAlCl₄、LiCF₃SO₃、LiC₄F₉SO₃、LiN(C₂F₅SO₃)₂、LiN(C₂F₅SO₂)₂、LiN(CF₃SO₂)₂LiCl, LiI, or LiB (C)₂O₄)₂And the like. The concentration of the lithium salt is preferably in the range of 0.1M to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte has suitable conductivity and viscosity so that it can exhibit excellent electrolyte properties and lithium ions can be efficiently moved.

In addition to the above electrolyte components, in order to improve the life characteristics of a battery, suppress a decrease in the capacity of a battery, and improve the discharge capacity of a battery, one or more types of additives may be added to the electrolyte: such as a haloalkylene carbonate-based compound such as difluoroethylene carbonate and the like; or pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, ethylene glycol dimethyl ether (glyme), hexaphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, or the like. Here, the additive may be included in an amount of 0.1 to 5 wt% based on the total weight of the electrolyte.