KR20150043769A - Anode for lithium secondary battery, preparation method thereof and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to an anode comprising an anode collector, a first anode active material layer including a layered structure of lithium-nickel compound oxide formed on at least one side of the anode collector, and a second anode active material layer including a spinel structure of lithium-manganese oxide formed on the first anode active material layer; a preparation method thereof; and a lithium secondary battery comprising the same. The lithium secondary battery comprising the anode can have a high battery capacity by the layered structure of lithium-nickel compound oxide active material included in the first anode active material layer, as well as high heat stability by the spinel structure of lithium-manganese oxide active material included in the second anode active material.

Description

[0001] The present invention relates to a positive electrode for a lithium secondary battery, a method for producing the same, and a lithium secondary battery comprising the same.

The present invention relates to a lithium secondary battery comprising a positive electrode collector, a first positive electrode active material layer including a lithium-nickel composite oxide active material layered on at least one side of the positive electrode collector, and a spinel- Based active material layer, a method for producing the same, and a lithium secondary battery including the anode active material layer.

As technology development and demand for mobile devices are increasing, the demand for secondary batteries as energy sources is rapidly increasing. Among such secondary batteries, lithium secondary batteries having high energy density and voltage, long cycle life and low self- It has been commercialized and widely used.

The lithium secondary battery includes an electrode assembly having a microporous separation membrane interposed between a positive electrode containing a positive electrode active material capable of intercalating and deintercalating lithium ions and a negative electrode containing a negative active material capable of intercalating and deintercalating lithium ions, Means a battery containing a non-aqueous electrolyte.

Examples of the positive electrode active material of the lithium secondary battery include transition metal oxides such as lithium cobalt oxide (LiCoO ₂ ), lithium-manganese oxide (LiMn ₂ O ₄ ) or lithium nickel oxide (LiNiO ₂ ) And a composite oxide in which some of them are substituted with other transition metals.

Of the above cathode active materials, LiCoO ₂ has excellent properties such as excellent cycle characteristics and is widely used at present. However, LiCoO ₂ has low safety, is expensive due to the resource limit of cobalt as a raw material, and is used as a power source for fields such as electric vehicles There is a limit.

Lithium-manganese-based oxides such as LiMnO ₂ or LiMn ₂ O ₄ have the advantage of using manganese which is abundant in resources and environment-friendly as a raw material, and thus attracts much attention as a cathode active material capable of replacing LiCoO ₂ . However, these lithium-manganese-based oxides are disadvantageous in that they are small in capacity and poor in cycle characteristics, and have a disadvantage in that when the lithium-manganese-based oxide is directly applied on a current collector and formed, It has a disadvantage that the manganese oxide is damaged due to tearing of the current collector.

On the other hand, LiNiO _2, such as a lithium nickel based oxide is time, the reversible capacity of the bar, the doped LiNiO ₂ having a high discharge capacity when charged to 4.3 V, while the cost is cheaper than the cobalt oxide is the capacity of LiCoO ₂ (about 165 lt; / RTI > (mAh / g).

Therefore, in spite of a slightly low average discharge voltage and volumetric density, the compatibilized battery including LiNiO ₂ cathode active material has an improved energy density. Therefore, in order to develop a high capacity battery, Research is actively under way. However, although the LiNiO ₂ cathode active material has an advantage of a high capacity, it has a disadvantage that its thermal stability is low and its cell stability is poor and the discharge operating voltage is low.

Thus, a lithium transition metal oxide in which a part of nickel is substituted with another transition metal such as manganese or cobalt has been proposed. However, such metal-substituted nickel-based lithium-transition metal oxides have an advantage in that they have excellent cycle characteristics and capacity characteristics. However, even in this case, the cycle characteristics are drastically decreased during long-term use and the swelling, And low chemical stability are not sufficiently solved. Accordingly, there is a high need for a technique capable of solving the problem of high-temperature safety while using a lithium-nickel-based positive electrode active material suitable for high capacity.

Disclosure of Invention Technical Problem [8] Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a lithium secondary battery comprising a lithium secondary battery comprising a lithium secondary battery, And to provide a positive electrode excellent in capacity characteristics and thermal stability by preventing the current collector from being damaged during the roll press process by sequentially forming the positive electrode active material layer.

Another object of the present invention is to provide a method of manufacturing the anode.

It is still another object of the present invention to provide a lithium secondary battery having high capacity characteristics including the positive electrode and excellent thermal stability.

According to an aspect of the present invention, there is provided a lithium secondary battery comprising a positive electrode collector, a first positive electrode active material layer including a layered lithium-nickel composite oxide active material formed on at least one surface of the positive electrode collector, And a second cathode active material layer containing a lithium-manganese oxide active material having a spinel structure formed on the cathode active material layer.

Further, the present invention provides a method for manufacturing a lithium secondary battery, comprising the steps of: (1) forming a first cathode active material layer by coating a cathode active material composition obtained by mixing a layered lithium-nickel composite oxide active material, a binder and a conductive material on a cathode current collector; And forming a second cathode active material layer by coating a second cathode active material composition obtained by mixing a lithium manganese oxide active material having a spinel structure, a binder and a conductive material on the first cathode active material layer (step 2) A method of manufacturing an anode is provided.

In addition, the present invention provides a lithium secondary battery comprising a positive electrode and a negative electrode including a different kind of positive electrode active material layer of the first positive electrode active material layer and the second positive electrode active material layer, a separator interposed between the positive electrode and the negative electrode, and an electrolyte .

The positive electrode comprising a different kind of positive electrode active material layer in which the first positive electrode active material layer and the second positive electrode active material layer according to the present invention are sequentially formed is a layered lithium-nickel alloy having a surface with relatively rounded irregularities formed on the positive electrode collector A second cathode active material layer including a lithium-manganese-based oxide active material having a spinel structure having a surface on which an angular polygonal concavo-convex structure is formed on the first cathode active material layer is formed as a first cathode active material layer containing a composite oxide active material, The second positive electrode active material layer does not directly contact the positive electrode collector at the time of sintering the roll press, so that damage to the current collector can be prevented.

Also, the lithium secondary battery according to the present invention includes a positive electrode in which a first positive electrode active material layer and a second positive electrode active material layer are sequentially formed, so that a layered lithium-nickel composite oxide active material contained in the first positive electrode active material layer And has high thermal stability due to the lithium-manganese oxide active material having a spinel structure contained in the second positive electrode active material layer.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments of the invention and, together with the description of the invention, It should not be construed as limited.
1 is a scanning electron microscope (SEM) image of a layered lithium-nickel composite oxide active material and (b) a spinel-structured lithium-manganese-based oxide active material according to an embodiment of the present invention.
2 is a cross-sectional view of a positive electrode comprising a first positive electrode active material layer and a second positive electrode active material layer according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail in order to facilitate understanding of the present invention.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

The positive electrode comprising the different kind of positive electrode active material layer of the present invention comprises a positive electrode collector; A first cathode active material layer including a layered lithium-nickel composite oxide active material formed on at least one surface of the cathode current collector; And a second positive electrode active material layer including a lithium-manganese oxide active material having a spinel structure formed on the first positive electrode active material layer.

The positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, carbon, nickel , Titanium or silver, or the like may be used.

The cathode current collector according to a preferred embodiment of the present invention may have a first cathode active material layer formed on opposite sides or at least one side of the cathode current collector. Preferably, the first cathode active material layer is formed on one surface of the cathode current collector .

The first cathode active material layer according to a preferred embodiment of the present invention may include a layered lithium-nickel composite oxide active material.

In addition, the second cathode active material layer according to a preferred embodiment of the present invention may include a lithium-manganese oxide active material having a spinel structure.

The lithium-nickel composite oxide active material having the layered structure exhibits a high discharge capacity when charged at 4.3 V and at a lower cost than the conventional cobalt-based oxide. Particularly, since the lithium-nickel composite oxide active material having the layered structure has a layered crystal structure, the diffusion path of lithium in the oxide is two-dimensional and the volume output density of the electrode is excellent. Therefore, it is used as a cathode active material which is important for a battery requiring high energy density.

However, the lithium-nickel composite oxide active material having the layered structure has a problem that the stability of the battery is deteriorated due to its low thermal properties. To overcome this problem, a nickel-manganese oxide active material having a spinel structure, However, since the lithium-manganese oxide active material having a spinel structure having a surface with irregularly angled polygonal shapes is used, it is difficult to roll-press the lithium-nickel composite oxide active material. There is a problem that the positive electrode current collector is damaged by tearing or the like during the process.

FIG. 1 shows an SEM image of a lithium-manganese oxide (LMO) active material having a spinel structure and a lithium-nickel composite oxide (NMC) active material layer having a layered structure. As shown in FIG. 1A, the lithium-nickel composite oxide active material having a layered structure has a surface having a relatively rounded concavo-convex surface, and the lithium-manganese oxide active material having a spinel structure, as shown in FIG. Lt; / RTI >

Therefore, the positive electrode comprising the different kinds of positive electrode active material layers of the first positive electrode active material layer and the second positive electrode active material layer of the present invention has a lamellar structure of lithium-nickel composite oxide having a surface on which high-capacity characteristics and relatively round- Nickel composite oxide (see FIG. 1A) active material layer is formed on the first positive electrode active material layer, and a lithium-manganese composite oxide having a spinel structure having an uneven surface formed on the first positive electrode active material layer, A second cathode active material layer containing a lithium-manganese oxide active material of the spinel structure is formed directly on the cathode current collector in the roll press process by forming a second cathode active material layer containing a lithium-manganese oxide active material (see FIG. 1B) It is possible to prevent the current collector from being damaged, and at the same time, it can have high capacity characteristics and high thermal stability.

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

FIG. 2 is a cross-sectional view of a positive electrode including a first positive electrode active material layer and a second positive electrode active material layer according to a preferred embodiment of the present invention. FIG.

The positive electrode 100 including a heterogeneous positive electrode active material layer according to a preferred embodiment of the present invention includes a first positive electrode active material layer 10 including a layered lithium-nickel composite oxide active material formed on at least one surface of a positive electrode collector 10, And a second cathode active material layer 30 including a lithium-manganese-based oxide active material having a spinel structure formed on the first cathode active material layer 20, as shown in FIG.

The first cathode active material layer 20 according to an embodiment of the present invention may include a layered lithium-nickel composite oxide active material. In addition, the first cathode active material layer 20 may include a binder and a conductive material.

The layered lithium-nickel composite oxide active material contained in the first positive electrode active material layer 20 may be represented by the following formula (1).

[Chemical Formula 1]

Li _x Ni _a Mn _b Co _c O _2-y D _y

0.5, 0? B? 0.5, 0? C? 0.5, 0? Y? 0.1, and D is at least one element selected from the group consisting of S, F and P .

Preferably, the layered lithium-nickel composite oxide active material is at least one selected from the group consisting of LiNiO ₂ , LiNi _0.8 Mn _0.1 Co _0.1 O _2, and LiNi _{0 .6} Mn _{0 .2} Co _{0 .2} O ₂ Lt; / RTI >

On the other hand, the binder is a component that assists in bonding of the active material to the conductive material and bonding to the current collector, and may be usually added in an amount of 1% by weight to 30% by weight based on the total amount of the cathode active material composition. Examples of such binders include vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HEP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, Polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM) Sulfonated EPDM, styrene butylene rubber (SBR), and fluorine rubber, or a mixture of two or more thereof.

The conductive material may be added in an amount of 0.05 wt% to 5 wt% based on the total weight of the first cathode active material composition. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing side reactions with other elements of the battery. For example, graphite such as natural graphite or artificial graphite; Carbon black (super-p), acetylene black; Carbon black such as Ketjen black, channel black, purne 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 whiskers 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 second cathode active material layer 30 according to a preferred embodiment of the present invention may include a spinel-type lithium-manganese-based oxide active material. In addition, the second cathode active material layer 30 may include a binder and a conductive material.

The lithium-manganese oxide active material having a spinel structure included in the second positive electrode active material layer 30 may be represented by the following formula (2).

(2)

Li _x Mn _(2-y) M _y O ₄

In the above formula, 1? X? 1.2, 0? Y? 0.2, M is at least one element selected from the group consisting of Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, , W, P, Ti, and Bi.

Preferably, the spinel structure lithium-manganese oxide active material is LiMn ₂ O ₄ or LiCoMnO ₄ can be a.

The thickness ratio of the first cathode active material layer 20 and the second cathode active material layer 30 according to a preferred embodiment of the present invention can be appropriately adjusted according to the target battery capacity, To 97: 3.

In addition, the thickness of the first positive electrode active material layer 20 is preferably 13 to 990 탆. If the thickness of the first cathode active material layer is less than 13 탆, it may be difficult to obtain the desired capacity of the secondary battery. If the thickness exceeds 990 탆, the capacity of the secondary battery may increase but due to the side reaction with the electrolyte The negative reactants adversely affect the separator or the negative electrode, thereby deteriorating the cycle characteristics.

Further, the thickness of the second cathode active material layer 30 is 1 占 퐉 to 10 占 퐉. If the thickness of the second cathode active material layer is less than 1 탆, it is difficult to achieve the effect of improving the battery stability by compensating the low thermal properties of the lithium-nickel composite oxide. If the thickness is more than 10 탆, A capacity loss due to the second cathode active material layer 30 may occur.

The second cathode active material layer 30 may be equal to or more than the coating area of the first cathode active material layer 20 so that the first cathode active material layer 20 may be completely covered.

The present invention also provides a method of manufacturing a positive electrode comprising a first positive electrode active material layer and a second positive electrode active material layer.

The method for producing a positive electrode comprising the different kind of positive electrode active material layer of the present invention comprises coating a first positive electrode active material composition obtained by mixing a layered lithium-nickel composite oxide active material, a binder and a conductive material on a positive electrode collector, Forming an active material layer (step 1); And forming a second cathode active material layer by coating a second cathode active material composition obtained by mixing a lithium-manganese oxide active material having a spinel structure, a binder and a conductive material on the first cathode active material layer (step 2) .

The step 1 is a step of forming a first cathode active material layer including a layered lithium-nickel composite oxide active material having a high capacity characteristic on at least one surface of a cathode current collector, and a method commonly used in the art .

For example, the first cathode active material composition is prepared by mixing and stirring the lithium-nickel composite oxide active material, the binder, the conductive material and, if necessary, the dispersant, and then applying the composition to the cathode current collector, The positive electrode active material layer can be formed.

The layered lithium-nickel composite oxide active material of the present invention may be 60 wt% to 97 wt%, preferably 90 wt% to 97 wt%, based on the total amount of the first cathode active material composition.

It is preferable that the method of the present invention further comprises a step of drying after the step 1 at a temperature range of 70 ° C to 120 ° C. The drying can be performed until the first cathode active material layer is completely dried. The drying time is not particularly limited, but it may be preferable to perform the drying in the temperature range described above for 10 minutes to 60 minutes, for example.

Step 2 is a step for forming a second cathode active material layer including a lithium-manganese oxide active material having a spinel structure having high thermal stability on the first cathode active material layer, Can be performed.

For example, the second cathode active material composition is prepared by mixing and stirring the spinel-type lithium-manganese oxide active material, the binder and the conductive material, and if necessary, the dispersant, and then coating the first cathode active material layer with the first cathode active material A second cathode active material layer may be formed on the layer.

The lithium-manganese oxide active material of the spinel structure of the present invention may be 60 wt% to 97 wt%, preferably 90 wt% to 97 wt%, based on the total amount of the second cathode active material composition.

Preferably, the method of the present invention further comprises a different drying step of performing a primary drying at a room temperature after the step 2, the secondary drying after the step 2, and a secondary drying at a temperature range of 70 ° C to 120 ° C. The drying time is not particularly limited, but may be, for example, primary drying for 10 minutes to 60 minutes at room temperature, and secondary drying for 10 minutes to 60 minutes at the temperature range described above. At this time, when the secondary drying is performed without performing the primary drying at room temperature, the bonding property with the first cathode active material layer may be deteriorated.

In addition, the present invention provides a lithium secondary battery comprising a cathode and an anode including the above-mentioned different kind of cathode active material layer, a separator interposed between the cathode and the anode, and an electrolyte.

The lithium secondary battery of the present invention comprises a first anode active material layer including a layered lithium-nickel composite oxide active material having a high capacity and a second anode including a lithium-manganese oxide active material having a spinel structure excellent in thermal stability A separator interposed between the anode and the cathode, and an electrolyte. The anode and the cathode are made of a heterogeneous cathode active material layer in which an active material layer is sequentially stacked.

In the negative electrode, the negative electrode active material is typically a carbonaceous material, lithium metal, silicon or tin capable of intercalating and deintercalating lithium ions. Preferably, carbon materials can be used, and carbon materials such as low-crystalline carbon and highly-crystalline carbon can be used. Examples of low crystalline carbon include soft carbon and hard carbon. Examples of highly crystalline carbon include natural graphite, Kish graphite, pyrolytic carbon, liquid crystal pitch carbon High temperature calcined carbon such as mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitch derived cokes.

As the binder used for the cathode, those which can be commonly used in the art can be used as the anode. The negative electrode may be prepared by preparing a negative electrode active material composition by mixing and stirring the negative electrode active material and the additives, applying the negative electrode active material composition to the current collector, and compressing the negative electrode active material composition to produce a negative electrode.

As the separator, a conventional porous polymer film conventionally used as a separator, such as a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer The porous polymer film made of a polymer may be used alone or in a laminated form, or a nonwoven fabric made of a conventional porous nonwoven fabric such as a glass fiber having a high melting point, polyethylene terephthalate fiber or the like may be used. no.

In addition, the electrolyte may include an organic solvent and a lithium salt which are conventionally used in an electrolyte, and is not particularly limited.

With the lithium salt of the anion is ^{F -, Cl -, I -} , NO 3 -, N (CN) 2 -, BF 4 -, ClO 4 -, PF 6 -, (CF 3) 2 PF 4 -, (CF 3 ^{_{) 3 PF 3 -, (CF}} 3) 4 PF 2 -, (CF 3) 5 PF -, (CF 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO 3 -, (CF 3 SO 2 _{^{) 2 N -, (FSO 2}} ) 2 N -, CF 3 CF 2 (CF 3) 2 CO -, (CF 3 SO 2) 2 CH -, (SF 5) 3 C -, (CF 3 SO 2) 3 _{^{C -, CF 3 (CF 2}} ) 7 SO 3 -, CF 3 CO 2 -, CH 3 CO 2 -, SCN - , and _{(CF 3 CF 2 SO 2)} 2 N - be at least one selected from the group consisting of have.

Examples of the organic solvent include propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate , Sulfolane, gamma-butyrolactone, propylene sulfite, and tetrahydrofuran.

In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates in the carbonate-based organic solvent, can be preferably used because they have high permittivity as a high-viscosity organic solvent and dissociate the lithium salt in the electrolyte well. To such a cyclic carbonate, dimethyl carbonate and diethyl When a low viscosity, low dielectric constant linear carbonate such as carbonate is mixed in an appropriate ratio, an electrolyte having a high electric conductivity can be prepared, and thus it can be more preferably used.

In addition, the electrolyte of the present invention may further include an additive such as an overcharge inhibitor or the like, which is usually included in the electrolyte, if necessary.

The lithium secondary battery of the present invention can be manufactured by disposing a separator between an anode and a cathode to form an electrode assembly, inserting the electrode assembly into a cylindrical battery case or a prismatic battery case, and injecting an electrolyte. Alternatively, the electrode assembly may be laminated, impregnated with the electrolyte, and the resultant may be sealed in a battery case.

The battery case used in the present invention may be of any type that is commonly used in the art, and is not limited in its external shape depending on the use of the battery. For example, a cylindrical case, a square type, a pouch type, (coin) type or the like.

The lithium secondary battery according to the present invention can be used not only in a battery cell used as a power source of a small device but also as a unit cell in a middle- or large-sized battery module including a plurality of battery cells. Preferable examples of the above medium and large-sized devices include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric power storage systems, and the like.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to examples. However, the embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

Example : Heterogeneous anode As the active material layer  Preparation of Lithium Secondary Battery Containing Constituted Positive Electrode

1) Preparation of a positive electrode comprising a heterogeneous positive electrode active material layer

A layered structure of lithium - LiNi _{0 .6} Mn _{0 .2} to nickel-based complex oxide active material, Co _{0 .2} O ₂ 96% by weight, polyvinylidene fluoride, 2% by weight super-p 2 wt% and a binder of a conductive material Were mixed to prepare a first cathode active material composition. The first cathode active material composition was applied to an aluminum (Al) current collector thin film having a thickness of about 20 탆 and dried at about 80 캜 for 20 minutes to obtain a first cathode active material layer.

A lithium-manganese-based oxide active material having a spinel structure is coated on the surface of the first cathode active material layer formed on the current collector with LiMn ₂ O ₄ , 2 wt% of super-p as a conductive material and 2 wt% of polyvinylidene fluoride as a binder, and dried at room temperature for 20 minutes, and then dried at about 80 ° C for 20 minutes And dried to form a second cathode active material layer. At this time, the thickness ratio of the first cathode active material layer and the second cathode active material layer was 99: 1. Thereafter, a roll press was performed to produce a positive electrode including a different kind of positive electrode active material layer.

2) Manufacture of cathode

As negative active material, 96.3 wt% of carbon powder, 1.0 wt% of super-p as a conductive material, 1.5 wt% and 1.2 wt% of SBR and carboxymethyl cellulose (CMC) as a binder were added to NMP as a solvent to prepare an anode material composition . The negative electrode material composition was coated on a copper (Cu) thin film as an anode current collector having a thickness of 10 mu m and dried to produce a negative electrode, followed by roll pressing to produce a negative electrode.

3) Preparation of lithium secondary battery

Aqueous electrolyte was prepared by adding an organic solvent having a composition of ethylene carbonate (EC): propylene carbonate (PC): diethyl carbonate (DEC) = 3: 2: 5 (volume ratio) and 1.0M of LiPF ₆ .

After the polyolefin separator was interposed between the positive electrode and the negative electrode, the electrolyte solution was injected to prepare a lithium secondary battery.

Comparative Example : Preparation of Lithium Secondary Battery Containing a Positive Electrode Consisting of a Single Layer

As a cathode active material on an aluminum (Al) thin film _{LiNi 0 .6 Mn 0 .2 Co 0} .2 O , and is of a coin type in the same manner as in Example ₂ except that a single coating and using a mixture of LiMn ₂ O ₄ Thereby preparing a lithium secondary battery.

Experimental Example : Impact test

Impact tests were carried out for comparative analysis of the lithium secondary batteries comprising a lithium secondary battery comprising a positive electrode active material layer of the above embodiment and a positive electrode composed of a single layer of a comparative example.

The impact test was carried out by measuring the volume of the battery charged at 4.2 V and measuring the diameter of 15.8 mm and the weight of 9.1 kg at a height of 610 ± 25 mm.

As a result, a lithium-nickel composite oxide active material having a layered structure is coated on the positive electrode current collector to form a first positive electrode active material layer, and then a lithium-manganese oxide active material having a spinel structure is coated on the first positive electrode active material layer It was confirmed that the anode (Example) in which the second cathode active material layer was formed by drying did not cause ignition and explosion upon impact.

On the other hand, in the case of a positive electrode (comparative example) in which a lithium-nickel composite oxide active material and a lithium-manganese oxide active material are mixed and simultaneously coated and dried on a positive electrode current collector to form a single positive electrode active material layer, ignition and explosion The safety of the battery deteriorated.

This is because, in the case of the positive electrode of the comparative example, a mixture of the lithium-nickel composite oxide active material and the lithium-manganese oxide active material is applied to the positive electrode collector to form a single positive electrode active material layer and a roll press process is performed, It is considered that the lithium-manganese oxide active material having a polygonal concavo-convex surface has damage such as tearing of the positive electrode collector, resulting in degraded battery safety.

On the other hand, in the case of the positive electrode of the embodiment, the first positive electrode active material layer containing the lithium-nickel composite oxide active material is formed on the positive electrode current collector, and then the second positive electrode active material layer including the lithium-manganese oxide active material is formed The lithium-manganese oxide active material having a surface formed with angled polygonal irregularities by performing a roll press process does not directly contact the positive electrode collector, thereby preventing damage to the positive electrode collector, thereby greatly improving battery safety. I think.

100: anode
10: positive collector
20: First cathode active material layer
30: Second cathode active material layer

Claims (19)

Anode collector;
A first cathode active material layer including a layered lithium-nickel composite oxide active material formed on at least one surface of the cathode current collector; And
And a second cathode active material layer comprising a lithium-manganese-based oxide active material having a spinel structure formed on the first cathode active material layer.
The method according to claim 1,
Wherein the layered lithium-nickel composite oxide active material is represented by the following formula (1): < EMI ID =
[Chemical Formula 1]
Li _x Ni _a Mn _b Co _c O _{2 - y} D _y
0.5, 0? B? 0.5, 0? C? 0.5, 0? Y? 0.1, D is at least one member selected from the group consisting of S, F and P Sake)
3. The method of claim 2,
Wherein the layered lithium-nickel composite oxide active material is at least one selected from the group consisting of LiNiO ₂ , LiNi _0.8 Mn _0.1 Co _0.1 O _2, and LiNi _{0 .6} Mn _{0 .2} Co _{0 .2} O ₂ anode.
The method according to claim 1,
The lithium-manganese oxide active material of the spinel structure is represented by the following formula (2)
(2)
Li _x Mn _(2-y) M _y O ₄
Wherein M is at least one element selected from the group consisting of Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, P, Ti and Bi)
5. The method of claim 4,
The spinel structure lithium-manganese oxide active material is LiMn ₂ O ₄ or Lt; _{RTI ID = 0.0} &gt; LiCoMnO4. &Lt; / _RTI &gt;
The method according to claim 1,
Wherein the thickness ratio of the first cathode active material layer to the second cathode active material layer is from 99: 1 to 93: 7.
The method according to claim 1,
Wherein the thickness of the first cathode active material layer is 13 占 퐉 to 990 占 퐉 and the thickness of the second cathode active material layer is 1 占 퐉 to 10 占 퐉.
1) forming a first cathode active material layer by coating a first cathode active material composition obtained by mixing a layered lithium-nickel composite oxide active material, a binder and a conductive material on a cathode current collector; And
2) coating a second cathode active material composition obtained by mixing a lithium manganese oxide active material having a spinel structure, a binder and a conductive material on the first cathode active material layer to form a second cathode active material layer.
9. The method of claim 8,
Wherein the layered lithium-nickel composite oxide active material is represented by the following formula (1): < EMI ID =
[Chemical Formula 1]
Li _x Ni _a Mn _b Co _c O _2-y D _y
0.5, 0? B? 0.5, 0? C? 0.5, 0? Y? 0.1, D is at least one member selected from the group consisting of S, F and P Sake)
10. The method of claim 9,
Wherein the layered lithium-nickel composite oxide active material is at least one selected from the group consisting of LiNiO ₂ , LiNi _0.8 Mn _0.1 Co _0.1 O _2, and LiNi _{0 .6} Mn _{0 .2} Co _{0 .2} O ₂ Gt;
9. The method of claim 8,
The lithium-manganese oxide active material having the spinel structure is represented by the following formula (2)
(2)
Li _x Mn _(2-y) M _y O ₄
Wherein M is at least one element selected from the group consisting of Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, P, Ti and Bi)
12. The method of claim 11,
The spinel structure lithium-manganese oxide active material is LiMn ₂ O ₄ or Lt; _{RTI ID = 0.0} &gt; LiCoMnO4. &Lt; / _RTI &gt;
9. The method of claim 8,
Wherein the layered lithium-nickel composite oxide active material is 60 wt% to 97 wt% based on the total amount of the first cathode active material composition.
9. The method of claim 8,
Wherein the lithium-manganese oxide active material of the spinel structure is 60 wt% to 97 wt% based on the total amount of the second cathode active material composition.
9. The method of claim 8,
The binder may be selected from the group consisting of vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HEP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, But are not limited to, alcohols, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer EPDM, styrene butylene rubber (SBR) and fluorine rubber, or a mixture of two or more thereof.
9. The method of claim 8,
Further comprising the step of drying after the step 1) in a temperature range of 70 ° C to 120 ° C.
9. The method of claim 8,
And a second drying step of first drying at room temperature after the step 2), and then secondary drying at a temperature ranging from 70 ° C to 120 ° C.
9. The method of claim 8,
Wherein the first cathode active material layer and the second cathode active material layer are coated to have a coating thickness ratio of 99: 1 to 97: 3.
A lithium secondary battery comprising: a positive electrode and a negative electrode of claim 1 comprising a first positive electrode active material layer and a second positive electrode active material layer; and a separator interposed between the positive electrode and the negative electrode, and an electrolyte.

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