WO2018097594A1 - Positive electrode for secondary battery, method for manufacturing same and lithium secondary battery comprising same - Google Patents

Abstract

The present invention relates to a method for manufacturing a positive electrode for a secondary battery, the method comprising the steps of: spreading a first positive electrode slurry comprising a first positive electrode active material onto a positive electrode current collector; forming a first positive electrode mixture layer by primarily rolling the first positive electrode slurry that has been spread; spreading a second positive electrode slurry comprising a second positive electrode active material onto the first positive electrode mixture layer that has been formed; and forming a second positive electrode mixture layer laminated on the first positive electrode mixture layer by secondarily rolling the second positive electrode slurry that has been spread. A positive electrode for a secondary battery manufactured as such allows for greatly reducing the elongation of the lower-layer part of an electrode adjacent to the positive electrode current collector, thereby enabling puncture resistance to increase when a metal body such as a nail penetrates the electrode from the outside. Accordingly, a positive electrode for a secondary battery and a secondary battery comprising same may be provided, the positive electrode having improved stability by which a battery ignition or explosion due to an overcurrent may be prevented by means of overcurrent inhibition.

Description

Secondary battery positive electrode, manufacturing method thereof and lithium secondary battery comprising same

Citation with Related Applications

This application claims the benefit of priority based on Korean Patent Application No. 10-2016-0156827 dated November 23, 2016 and Korean Patent Application No. 10-2017-0155472 dated November 21, 2017. All content disclosed in the literature is included as part of this specification.

Field of technology

The present invention relates to a positive electrode for a secondary battery, a manufacturing method thereof, and a lithium secondary battery including the same.

As technology development and demand for mobile devices increase, the demand for secondary batteries as a source of energy is rapidly increasing. Among such secondary batteries, lithium secondary batteries having high energy density and voltage, long cycle life, and low self discharge rate have been commercialized and widely used.

Lithium transition metal composite oxide is used as a positive electrode active material of a lithium secondary battery, and among these, lithium cobalt composite metal oxide of LiCoO ₂ having a high operating voltage and excellent capacity characteristics is mainly used. However, since LiCoO ₂ is very poor in thermal properties due to destabilization of crystal structure due to de-lithium and is expensive, there is a limit to using LiCoO ₂ as a power source in fields such as electric vehicles.

As a material for replacing LiCoO ₂ , lithium manganese composite metal oxides (such as LiMnO ₂ or LiMn ₂ O ₄ ), lithium iron phosphate compounds (such as LiFePO ₄ ), or lithium nickel composite metal oxides (such as LiNiO ₂ ) have been developed. Among them, research and development of lithium nickel composite metal oxides having a high reversible capacity of about 200mAh / g and which is easy to implement a large-capacity battery have been actively studied. However, LiNiO ₂ has a poor thermal stability as compared to LiCoO _2, and when an internal short circuit occurs due to pressure from the outside in a charged state, the positive electrode active material itself is decomposed to cause the battery to rupture and ignite.

Accordingly, as a method for improving low thermal stability while maintaining excellent reversible capacity of LiNiO ₂ , a method of replacing a portion of nickel (Ni) with cobalt (Co) or manganese (Mn) has been proposed. However, LiNi _{1 - α} Co _α O ₂ (α = 0.1 ~ 0.3) in which a part of nickel is substituted with cobalt shows excellent charge / discharge characteristics and life characteristics, but has a problem of low thermal stability. In the case of nickel manganese lithium composite metal oxide in which a part of Ni is substituted with Mn having excellent thermal stability and nickel cobalt manganese lithium composite metal oxide substituted with Mn and Co (hereinafter, simply referred to as 'NCM lithium oxide') Although it has the advantage of excellent cycle characteristics and thermal stability, its low penetration resistance prevents internal short circuits when penetrating metals such as nails, which can cause serious problems in terms of safety such as fire or explosion due to instantaneous overcurrent. have.

The present invention has a high capacity, high output performance, excellent cycle characteristics and thermal stability, but also to provide a secondary battery positive electrode and a secondary battery comprising the same to increase the penetration resistance when a metal body such as a nail penetrates the electrode from the outside will be.

The present invention comprises the steps of applying a first positive electrode slurry comprising a first positive electrode active material on the current collector; Rolling the first cathode after applying the first cathode slurry to form a first cathode mixture layer; Applying a second positive electrode slurry comprising a second positive electrode active material on the formed first positive electrode mixture layer; And forming a second positive electrode mixture layer laminated on the first positive electrode mixture layer by rolling the second positive electrode slurry after coating the second positive electrode slurry to provide a method of manufacturing a positive electrode for a secondary battery.

In addition, the present invention is a positive electrode current collector; A first positive electrode mixture layer laminated on the positive electrode current collector and including a first positive electrode active material; And a second positive electrode mixture layer stacked on the first positive electrode mixture layer and including a second positive electrode active material, wherein the difference in elongation between the first positive electrode mixture layer and the second positive electrode mixture layer is 0.1 to 1.0%. It provides a positive electrode for a secondary battery.

In addition, the present invention provides a lithium secondary battery including the positive electrode.

The secondary battery positive electrode manufactured according to the manufacturing method of the present invention can increase the penetration resistance when a metal body such as a nail penetrates the electrode from the outside by greatly reducing the elongation of the lower layer of the electrode adjacent to the positive electrode current collector. Accordingly, it is possible to provide a secondary battery positive electrode and a secondary battery including the same, in which stability of the secondary battery, which is improved by preventing overcurrent, thereby preventing ignition or explosion of the battery due to the overcurrent.

1 to 4 is a view schematically showing a method for manufacturing a positive electrode for a secondary battery according to an embodiment of the present invention.

5 is a graph showing the penetration resistance of the positive electrode for a secondary battery manufactured according to Examples and Comparative Examples of the present invention.

Hereinafter, the present invention will be described in more detail to aid in understanding the present invention. At this time, the terms or words used in the present specification and claims should not be construed as being limited to the ordinary or dictionary meanings, and the inventors appropriately define the concept of terms in order to explain their invention in the best way. It should be interpreted as meaning and concept corresponding to the technical idea of the present invention based on the principle that it can.

The accompanying drawings are intended to explain the invention clearly, and are not limited to the embodiments of the drawings. Shapes and sizes of the elements in the drawings may be exaggerated for clarity, and parts not related to the description are omitted, and the same elements within the scope of the same idea will be described using the same reference numerals.

Method of manufacturing a positive electrode for a secondary battery of the present invention comprises the steps of applying a first positive electrode slurry containing a first positive electrode active material on a positive electrode current collector; Rolling the first cathode after applying the first cathode slurry to form a first cathode mixture layer; Applying a second positive electrode slurry comprising a second positive electrode active material on the formed first positive electrode mixture layer; And rolling the second cathode after applying the second positive electrode slurry to form a second positive electrode mixture layer laminated on the first positive electrode mixture layer.

The average particle diameter (D ₅₀ ) of the first positive electrode active material may be 5 to 80% of the average particle diameter (D ₅₀ ) of the second positive electrode active material.

That is, relative to the average particle diameter (D ₅₀₎ is smaller the average particle size of the first cathode active material in the positive electrode collector so as to be adjacent to the coating on the lower part of the electrode, and the relative (D ₅₀₎ is larger according to the second embodiment of the present invention The positive electrode active material may be coated on the upper layer of the electrode. As a result, the first positive electrode mixture layer adjacent to the positive electrode current collector may have low elongation, and the second positive electrode mixture layer positioned at the upper layer of the electrode may have a relatively high elongation.

In the present invention, the average particle diameter (D ₅₀ ) may be defined as a particle size corresponding to 50% of the cumulative volume in the particle size distribution curve. The average particle diameter D ₅₀ may be measured using, for example, a laser diffraction method. For example, the measuring method of the average particle diameter (D ₅₀ ) of the positive electrode active material is dispersed in the dispersion medium particles in a dispersion medium, and then introduced into a commercially available laser diffraction particle size measuring apparatus (for example, Microtrac MT 3000) to After irradiating an ultrasonic wave of 28 kHz with an output of 60 W, the average particle diameter D ₅₀ corresponding to 50% of the volume accumulation amount in the measuring device can be calculated.

In the present invention, the elongation of each positive electrode mixture layer means a value measured using the UTM equipment, and when the positive electrode mixture layer is stretched at a rate of about 5 mm / min after mounting the positive electrode mixture layer, the electrode (anode) Elongation is measured by changing the length until the mixture layer) is stretched to the maximum.

On the other hand, conventionally, when forming a positive electrode having a multi-layered structure, since the slurry is applied in multiple layers and then rolled at a time, the layer located in the lower layer of the electrode has a poor rolling rate and has a limit in reducing the elongation.

However, in the present invention, after applying the first positive electrode slurry for forming the first positive electrode mixture layer close to the positive electrode current collector, the first roll is first rolled, and then the second positive electrode slurry for forming the second positive electrode mixture layer is applied again, and then secondly. By rolling a positive electrode having a multilayer structure, the rolling ratio of the first positive electrode mixture layer in the lower electrode portion of the electrode layer was improved, thereby effectively reducing the elongation of the first positive electrode mixture layer adjacent to the positive electrode current collector, thereby effectively reducing the metal body from the outside. In the case of penetrating, the penetration resistance was significantly increased, and the overcurrent was suppressed to prevent the battery from igniting or exploding due to the overcurrent.

1 is a view schematically showing a method for manufacturing a cathode for a secondary battery according to an embodiment of the present invention.

Referring to FIG. 1, in the method of manufacturing a cathode for a secondary battery according to an embodiment of the present invention, first, a first cathode slurry 21 ′ including a first cathode active material is coated on a cathode current collector 10.

The average particle diameter (D ₅₀ ) of the first positive electrode active material may be 5 to 80% of the average particle diameter (D ₅₀ ) of the second positive electrode active material.

Specifically, the average particle diameter (D ₅₀ ) of the first positive electrode active material may be 1 to 15㎛. Even more preferably, the average particle diameter (D ₅₀ ) of the first positive electrode active material may be 1 to 10 μm, more preferably 2 to 8 μm. When the average particle diameter (D ₅₀ ) of the first positive electrode active material is less than 1 μm, an electrode side reaction may occur or dispersibility may not be easy in an electrode manufacturing process, and when the average particle diameter exceeds 15 μm, adhesive strength with a positive electrode current collector This decreases, and the elongation of the first positive electrode mixture layer increases, so that the effect of improving stability may be insignificant.

On the other hand, the positive electrode current collector 10 is not particularly limited as long as it has conductivity without causing chemical changes in the battery, and is not limited to, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surfaces. The surface-treated with carbon, nickel, titanium, silver, etc. can be used. In addition, the positive electrode current collector 10 may have a thickness of about 3 to 500 μm, and may form fine irregularities on the surface of the positive electrode current collector 10 to increase the adhesion of the positive electrode active material. For example, it can be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven body.

The first positive electrode slurry 21 ′ may further include a conductive material, a binder, and a solvent in addition to the first positive electrode active material, and may further include additives such as fillers in the slurry as necessary.

Next, referring to FIG. 2, the first positive electrode slurry 21 ′ is first rolled to form a first positive electrode mixture layer 21.

As such, one embodiment of the present invention includes a cathode active material having a relatively small average particle diameter in the first cathode slurry 21 ′ adjacent to the cathode current collector 10, and is first rolled first to form a first cathode mixture layer ( 21), the first positive electrode mixture layer 21 can be formed with a significantly reduced elongation.

Next, referring to FIG. 3, a second positive electrode slurry 22 ′ including a second positive electrode active material is coated on the formed first positive electrode mixture layer 21.

The second positive electrode active material may be large particle size having a relatively larger average particle diameter (D ₅₀ ) than the first positive electrode active material.

Specifically, the average particle diameter (D ₅₀ ) of the second positive electrode active material may be 10 to 100㎛. Even more preferably, the average particle diameter (D ₅₀ ) of the second positive electrode active material may be 10 to 50㎛, more preferably 10 to 30㎛. When the average particle diameter (D ₅₀ ) of the second positive electrode active material is less than 10 μm, there may be a difficulty in the process of rolling during the electrode manufacturing process, and when the average particle diameter exceeds 100 μm, output characteristics may be reduced.

The second positive electrode slurry 22 ′ may further include a conductive material, a binder, and a solvent in addition to the second positive electrode active material, and may further include additives such as fillers in the slurry as necessary.

The first positive electrode active material and / or the second positive electrode active material may include a lithium transition metal oxide represented by Formula 1 below.

[Formula 1]

Li _a Ni _1-xy Co _x Mn _y M _z O ₂

In the above formula, M is at least one element selected from the group consisting of Al, Zr, Ti, Mg, Ta, Nb, Mo and Cr, 0.9≤a≤1.5, 0≤x≤0.5, 0≤y≤0.5, 0 ≦ z ≦ 0.1 and 0 ≦ x + y ≦ 0.7.

However, the first positive electrode active material and / or the second positive electrode active material are not necessarily limited to the lithium transition metal oxide represented by Chemical Formula 1, and the first positive electrode active material and / or the second positive electrode active material may be lithium cobalt oxide (LiCoO _2). ), A layered compound such as lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; Lithium manganese oxides such as Li _{1 + x1} Mn _2-x1 O ₄ (where x ₁ is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ ; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiV ₃ O ₄ , V ₂ O ₅ , Cu ₂ V ₂ O _7, and the like; Chemical Formula LiNi _{1 - x2} M ¹ _x2 O ₂ Ni-site type lithium nickel oxide represented by (wherein M ¹ = Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x ₂ = 0.01 to 0.3); Formula LiMn _2-x3 M ² _x3 O ₂ , wherein M ² = Co, Ni, Fe, Cr, Zn or Ta, and x ₃ = 0.01 to 0.1, or Li ₂ Mn ₃ M ³ O ₈ , wherein M ³ = Fe, Co, Ni, Cu or Zn) lithium manganese composite oxide; A spinel structure lithium manganese composite oxide represented by LiNi _x4 Mn _{2 - x4} O ₄ (where x ₄ = 0.01 to 1); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with alkaline earth metal ions; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ and the like.

Meanwhile, the first and second positive electrode active materials may include lithium transition metal oxides of the same composition, or may include lithium transition metal oxides of different compositions.

The conductive material included in the first positive electrode slurry and / or the second positive electrode slurry is not particularly limited as long as it has conductivity without causing chemical changes in the battery. Examples thereof include graphite such as natural graphite and artificial graphite; Carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black and carbon fiber; Metal powder or metal fibers such as copper, nickel, aluminum, and silver; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Or conductive polymers such as polyphenylene derivatives. The conductive material may be included in an amount of 1 wt% to 30 wt% with respect to the total weight of the positive electrode mixture layer.

Meanwhile, the binder included in the first positive electrode slurry and / or the second positive electrode slurry serves to improve adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC). ), Starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubbers, or various copolymers thereof, and the like, and one or a mixture of two or more thereof may be used. The binder may be included in an amount of 1 wt% to 30 wt% with respect to the total weight of the positive electrode mixture layer.

The solvent may be a solvent generally used in the art, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone or acetone. Water, and the like, one of these alone or a mixture of two or more thereof may be used. The amount of the solvent is sufficient to dissolve or disperse the positive electrode active material, the conductive material, and the binder in consideration of the coating thickness of the slurry and the production yield, and to have a viscosity that can exhibit excellent thickness uniformity in the coating for the production of the positive electrode. Do.

Next, referring to FIG. 4, after coating the second positive electrode slurry 22 ′, the second positive electrode mixture layer 22 formed on the first positive electrode mixture layer 21 is rolled to form a second positive electrode mixture layer 22. 100) is prepared.

The positive electrode 100 according to the embodiment of the present invention manufactured as described above includes a first positive electrode active material having a small average particle diameter (D ₅₀ ) relative to the first positive electrode mixture layer 21, which is an electrode lower layer, and is an upper electrode of an electrode. The second positive electrode mixture layer 22 includes a second positive electrode active material having a relatively large average particle diameter D ₅₀ , thereby reducing the elongation of the first positive electrode mixture layer 21 and reducing the elongation of the second positive electrode mixture layer 22. Is increased, and further, the first positive electrode mixture layer 21 is formed by first rolling the first positive electrode slurry 21 'first after applying the first positive electrode slurry 21' after applying all of the positive electrode slurry forming the multilayer. As a result, the reduction of the elongation of the first positive electrode mixture layer 21 could be maximized. In this way, the elongation of the first positive electrode mixture layer 21 adjacent to the positive electrode current collector is effectively reduced to significantly increase the penetration resistance when the metal body penetrates the electrode from the outside, and suppresses the overcurrent to ignite the battery due to the overcurrent. Or to prevent explosion.

The difference in elongation between the first positive electrode mixture layer 21 and the second positive electrode mixture layer 22 manufactured according to an embodiment of the present invention may be 0.1 to 1.0%, more preferably 0.2 to 0.7%. Can be. The elongation of each positive electrode mixture layer in the present invention is a value measured by using a UTM equipment, and when the positive electrode mixture layer is stretched at a speed of about 5 mm / min after mounting the positive electrode mixture layer, the positive electrode mixture layer is the maximum compared to the existing positive electrode mixture layer length. The elongation was measured through the change in length until stretched to.

As such, the reduction in elongation of the lower electrode portion is maximized, but the upper electrode portion is formed of an anode active material having a small specific surface area to maximize the difference in elongation between the lower electrode portion and the upper layer portion, thereby increasing the penetration resistance and improving cell performance such as life characteristics. Can be.

Specifically, the elongation of the first positive electrode mixture layer 21 may be 0.2 to 1.2%, more preferably 0.2 to 0.5%.

When the elongation of the first positive electrode mixture layer 21 adjacent to the positive electrode current collector 10 satisfies the above range, the penetration resistance when the metal body penetrates the electrode from the outside can be significantly increased, and the overcurrent through the penetration resistance is increased. Prevention of production can improve safety.

In addition, the elongation of the second positive electrode mixture layer 22 may be 0.6 to 2.0%, and more preferably 0.6 to 0.9%.

Since the elongation of the second positive electrode mixture layer 22 positioned in the upper electrode portion satisfies the above range, the elongation of the entire positive electrode can be maintained at a predetermined level or more, and a problem that breakage occurs in the rolling process during the electrode fabrication process can be prevented. .

In addition, the total elongation of the positive electrode 100 including the first positive electrode mixture layer 21 and the second positive electrode mixture layer 22 manufactured as described above may be less than 1.4%. By varying the average particle diameter (D ₅₀ ) of the positive electrode active material included in the first positive electrode mixture layer 21 and the second positive electrode mixture layer 22 as described above, by producing a positive electrode through the secondary rolling manufacturing process The difference in elongation between the first positive electrode mixture layer 21 and the second positive electrode mixture layer 22 may be 0.1 to 1.0%, more preferably 0.2 to 0.7%, and further, the total elongation of the positive electrode may be less than 1.4%. Can be.

Meanwhile, the thickness ratio of the first and second positive electrode mixture layers 21 and 22 may be 1: 1 to 1: 8. Specifically, the thickness of the first positive electrode mixture layer 21 may be 15 to 40 μm, and the thickness of the second positive electrode mixture layer 22 may be 30 to 80 μm.

In addition, an embodiment of the present invention provides a secondary battery positive electrode 100 manufactured according to the manufacturing method.

Specifically, the positive electrode 100 according to an embodiment of the present invention is a positive electrode current collector (10); A first positive electrode mixture layer 21 stacked on the positive electrode current collector 10 and including a first positive electrode active material; And a second positive electrode mixture layer 22 stacked on the first positive electrode mixture layer 21 and including a second positive electrode active material, wherein the first positive electrode mixture layer 21 and the second positive electrode mixture layer are included. The difference in elongation of (22) is 0.1 to 1.0%. In addition, more preferably, the difference in elongation between the first positive electrode mixture layer 21 and the second positive electrode mixture layer 22 may be 0.2 to 0.7%.

The average particle diameter (D ₅₀ ) of the first positive electrode active material may be 5 to 80% of the average particle diameter (D ₅₀ ) of the second positive electrode active material, and more preferably, the average particle diameter (D ₅₀ ) of the first positive electrode active material. Silver may be 1 to 15 μm, and the average particle diameter (D ₅₀ ) of the second positive electrode active material may be 10 to 100 μm.

The positive electrode 100 according to the exemplary embodiment of the present invention is formed by first rolling the first positive electrode mixture layer 21 including the first positive electrode active material having a relatively small average particle diameter (D ₅₀ ), and having a relatively average particle diameter. The second positive electrode active material having a large (D ₅₀ ) is formed by rolling the second positive electrode mixture layer 22 containing the secondary to reduce the difference in elongation between the first positive electrode mixture layer 21 and the second positive electrode mixture layer 22. It can be 0.1 to 1.0%. More preferably, the difference in elongation between the first positive electrode mixture layer 21 and the second positive electrode mixture layer 22 may be 0.2 to 0.7%.

Specifically, the elongation of the first positive electrode mixture layer 21 may be 0.2 to 1.2%, more preferably 0.2 to 0.5%, and the elongation of the second positive electrode mixture layer 22 may be 0.6 to 2.0. %, And may be more preferably 0.6 to 0.9%.

In addition, the total elongation of the positive electrode 100 including the first positive electrode mixture layer 21 and the second positive electrode mixture layer 22 may be less than 1.4%.

In addition, the porosity of the first positive electrode mixture layer 21 may be 18 to 34%, and the porosity of the second positive electrode mixture layer 22 may be 20 to 40%.

The first positive electrode mixture layer 21 not only contains a relatively small particle size of the positive electrode active material, but also firstly rolled the first positive electrode slurry after applying the first positive electrode slurry to form a first positive electrode mixture layer, thereby improving the rolling ratio. And the porosity was also reduced.

Through this, the penetration resistance was significantly increased by maximizing the elongation difference between the lower and upper electrodes, and the overcurrent was suppressed to prevent the battery from ignition or explosion due to the overcurrent, and the cell performance such as the lifespan characteristics could be improved. It was made.

In addition, the description of the overlapping parts of the method for manufacturing the secondary battery positive electrode according to the embodiment of the present invention described above is omitted, but may be applied in the same manner as described in the manufacturing method.

In addition, an embodiment of the present invention provides an electrochemical device including the anode. The electrochemical device may be specifically a battery, a capacitor, or the like, and more specifically, a lithium secondary battery.

The lithium secondary battery specifically includes a positive electrode, a negative electrode positioned to face the positive electrode, a separator and an electrolyte interposed between the positive electrode and the negative electrode, and the positive electrode is as described above. The lithium secondary battery may further include a battery case accommodating the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member sealing the battery case.

In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode mixture layer located on the negative electrode current collector.

The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery. For example, the negative electrode current collector may be formed on a surface of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper, or stainless steel. Surface-treated with carbon, nickel, titanium, silver, and the like, aluminum-cadmium alloy and the like can be used. In addition, the negative electrode current collector may have a thickness of about 3 μm to 500 μm, and like the positive electrode current collector, fine unevenness may be formed on the surface of the negative electrode current collector to enhance the bonding force of the negative electrode active material. For example, it can be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven body.

The negative electrode mixture layer includes a binder and a conductive material together with the negative electrode active material. For example, the negative electrode mixture layer is coated with a negative electrode active material, and optionally a composition for forming a negative electrode mixture layer including a binder and a conductive material on a negative electrode current collector and dried, or the composition for forming the negative electrode mixture layer on a separate support The film obtained by casting in and then peeling off from this support may be prepared by laminating onto a negative electrode current collector.

As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; Metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys or Al alloys; Metal oxides capable of doping and undoping lithium, such as SiO _β (0 <β <2), SnO ₂ , vanadium oxide, and lithium vanadium oxide; Or a composite including the metallic compound and the carbonaceous material, such as a Si-C composite or a Sn-C composite, and any one or a mixture of two or more thereof may be used. In addition, a metal lithium thin film may be used as the anode active material. As the carbon material, both low crystalline carbon and high crystalline carbon can be used. Soft crystalline carbon and hard carbon are typical low crystalline carbon, and high crystalline carbon is amorphous, plate, scaly, spherical or fibrous natural graphite or artificial graphite, Kish graphite (Kish) graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitch High-temperature calcined carbon such as derived cokes is typical.

In addition, the binder and the conductive material may be the same as described above in the positive electrode.

On the other hand, in the lithium secondary battery, the separator is to separate the negative electrode and the positive electrode and to provide a passage for the movement of lithium ions, if it is usually used as a separator in a lithium secondary battery can be used without particular limitation, in particular in the ion transfer of the electrolyte It is desirable to have a low resistance against the electrolyte and excellent electrolytic solution-moisture capability. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer or the like Laminate structures of two or more layers may be used. In addition, conventional porous nonwoven fabrics such as nonwoven fabrics made of high melting point glass fibers, polyethylene terephthalate fibers and the like may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may be optionally used as a single layer or a multilayer structure.

In addition, examples of the electrolyte used in the present invention include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, and the like, which can be used in manufacturing a lithium secondary battery. It doesn't happen.

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

The organic solvent may be used without particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may be an ester solvent such as methyl acetate, ethyl acetate, γ-butyrolactone or ε-caprolactone; Ether solvents such as dibutyl ether or tetrahydrofuran; Ketone solvents such as cyclohexanone; Aromatic hydrocarbon solvents such as benzene and fluorobenzene; Dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate, Carbonate solvents such as PC); Alcohol solvents such as ethyl alcohol and isopropyl alcohol; Nitriles such as R-CN (R is a C2 to C20 linear, branched or cyclic hydrocarbon group, which may include a double bond aromatic ring or an ether bond); Amides such as dimethylformamide; Dioxolanes such as 1,3-dioxolane; Or sulfolanes may be used. Of these, carbonate-based solvents are preferable, and cyclic carbonates having high ionic conductivity and high dielectric constant (for example, ethylene carbonate or propylene carbonate) that can improve the charge and discharge performance of a battery, and low viscosity linear carbonate compounds ( For example, a mixture of ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate and the like is more preferable. In this case, when the cyclic carbonate and the chain carbonate are mixed and used 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 as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt is LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAl0 ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (C ₂ F ₅ SO ₃ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ . LiCl, LiI, or LiB (C ₂ O ₄ ) ₂ and the like can be used. The concentration of the lithium salt is preferably used within the range of 0.1M to 2.0M. When the concentration of the lithium salt is included in the above range, since the electrolyte has an appropriate conductivity and viscosity, it can exhibit excellent electrolyte performance, and lithium ions can move effectively.

The electrolyte includes, in addition to the electrolyte components, haloalkylene carbonate-based compounds such as difluoroethylene carbonate for the purpose of improving the life characteristics of the battery, suppressing the reduction of the battery capacity, and improving the discharge capacity of the battery; Or pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N, N One or more additives such as -substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol or aluminum trichloride may be included. In this case, the additive may be included in an amount of 0.1% by weight to 5% by weight based on the total weight of the electrolyte.

As described above, since the lithium secondary battery including the cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, portable devices such as mobile phones, notebook computers, digital cameras, and hybrid electric vehicles ( It is useful for electric vehicle fields such as hybrid electric vehicle (HEV).

Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

The battery module or the battery pack is a power tool (Power Tool); Electric vehicles including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); Or it can be used as a power source for any one or more of the system for power storage.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily practice the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

Example 1

LiNi ₀ having an average particle diameter (D ₅₀ ) of 5 μm as the first positive electrode active material _{. 6} Mn _{0 . 2} Co _{0 . 2} O ₂ , carbon black and PVdF binder were mixed in an N-methylpyrrolidone solvent in a weight ratio of 89: 6: 5 to prepare a first positive electrode slurry.

The first positive electrode slurry was applied to an aluminum current collector, dried at 130 ° C., and rolled to form a first positive electrode mixture layer.

In addition, as the second positive electrode active material, LiNi ₀ having an average particle diameter (D ₅₀ ) of 11 μm _{. 6} Mn _{0 . 2} Co _{0 . 2} O ₂ , carbon black, and PVdF binder were mixed in an N-methylpyrrolidone solvent in a ratio of 89: 6: 5 by weight to prepare a second positive electrode slurry.

The second positive electrode slurry was applied onto the first positive electrode mixture layer, dried at 130 ° C., and then rolled to form a second positive electrode mixture layer to prepare a positive electrode (total elongation 1.1%). The thickness of the first positive electrode mixture layer was 30 μm, and the thickness of the second positive electrode mixture layer was 30 μm.

Example 2

The first positive electrode mixture layer was formed with an average particle diameter D ₅₀ of the first positive electrode active material as 4 μm, and the second positive electrode mixture layer was formed with an average particle diameter D ₅₀ of the second positive electrode active material 12 μm. It was prepared in the same manner as in Example 1 except that (Total elongation rate 1.05%) was prepared.

Comparative Example 1

LiNi ₀ having an average particle diameter of ₅₀ μm as a positive electrode active material _{. 6} Mn _{0 . 2} Co _{0 . A} positive electrode slurry was prepared by using ₂ O ₂ , the positive electrode slurry was applied to an aluminum current collector, and rolled to prepare a positive electrode in the same manner as in Example 1 except that the positive electrode of the single positive electrode mixture layer was prepared. .

Comparative Example 2

Except that the first positive electrode slurry was applied to an aluminum current collector, the second positive electrode slurry was applied immediately without rolling, and then rolled to produce a positive electrode including a first positive electrode mixture layer and a second positive electrode mixture layer. It carried out similarly to 1, and manufactured the positive electrode.

Comparative Example 3

LiNi ₀ having an average particle diameter of ₅₀ μm as a positive electrode active material _{. 6} Mn _{0 . 2} Co _{0 . A} positive electrode slurry was prepared using ₂ O ₂ , the positive electrode slurry was applied to an aluminum current collector, rolled to form a first positive electrode mixture layer, and then the positive electrode slurry was again applied onto the first positive electrode mixture layer The positive electrode was manufactured in the same manner as in Example 1 except that the second positive electrode mixture layer was rolled to form a positive electrode (total elongation 1.3%).

Preparation Example: Fabrication of Lithium Secondary Battery

A lithium secondary battery was manufactured using the positive electrodes prepared in Examples 1 and 2 and Comparative Examples 1 to 3, respectively.

First, as a negative electrode active material, a natural graphite, a carbon black conductive material, and a PVdF binder are mixed in an N-methylpyrrolidone solvent in a ratio of 85: 10: 5 by weight to prepare a composition for forming a negative electrode, which is applied to a copper current collector. To prepare a negative electrode.

An electrode assembly is prepared between the anodes and the cathodes prepared in Examples 1 and 2 and Comparative Examples 1 to 3 through a separator of porous polyethylene, and the electrode assembly is placed inside the case, and then the electrolyte is introduced into the case. Injected to prepare a lithium secondary battery. At this time, the electrolyte is prepared by dissolving 1.0M concentration of lithium hexafluorophosphate (LiPF ₆ ) in an organic solvent consisting of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate (mixing volume ratio of EC / DMC / EMC = 3/4/3). It was.

Experimental Example Penetration Resistance and Stability Evaluation

The lithium secondary batteries manufactured by using the positive electrodes prepared in Examples 1 and 2 and Comparative Examples 1 to 3, respectively, were subjected to a 5-8 mm diameter metal body at a speed of 25 ± 5 mm / sec in the same manner as the Chinese GB / T certification. Penetration resistance was measured through the resistance change after dropping and penetrating the cell. The results are shown in Table 1 and FIG. 5.

In addition, the lithium secondary battery manufactured by using the anodes prepared in Examples 1, 2 and Comparative Examples 1 to 3, respectively, 25 ± 5mm / sec. It was evaluated whether or not ignition when penetrating the cell by falling at a speed.

The results are shown in Table 1 below.

	First positive electrode mixture layer elongation (%)	2nd positive electrode mixture layer elongation (%)	Elongation Difference (%)	Penetration Resistance (Unit: Ω)	Explosion
Example 1	1.0	1.5	0.5	6.16	Unexploded
Example 2	0.9	1.6	0.7	6.0	Unexploded
Comparative Example 1	Single Layer 1.4		-	1.42	explosion
Comparative Example 2	1.41	1.5	0.09	2.48	explosion
Comparative Example 3	1.32	1.4	0.08	2.0	explosion

As can be seen from Table 1, the first positive electrode mixture layer was formed by using a relatively small particle positive electrode active material, and first rolled to form a first positive electrode mixture layer, and the second positive electrode mixture layer was rolled secondaryly using a relatively positive electrode active material having a relatively small diameter. The positive electrode of Examples 1 and 2 manufactured by forming a significantly increased the penetration resistance, thereby suppressing the overcurrent to prevent the explosion of the battery due to the overcurrent.

Claims (20)

1. Applying a first positive electrode slurry comprising a first positive electrode active material onto a positive electrode current collector;

   Rolling the first cathode after applying the first cathode slurry to form a first cathode mixture layer;

   Applying a second positive electrode slurry comprising a second positive electrode active material on the formed first positive electrode mixture layer; And

    Rolling the second cathode slurry after coating the second cathode slurry to form a second cathode mixture layer laminated on the first cathode mixture layer;

   Method of manufacturing a positive electrode for a secondary battery comprising a.
2. The method of claim 1,

   The average particle diameter (D ₅₀ ) of the first positive electrode active material is a method for producing a positive electrode for secondary batteries is 5 to 80% of the average particle diameter (D ₅₀ ) of the second positive electrode active material.
3. The method of claim 1,

   The average particle diameter (D ₅₀ ) of the first positive electrode active material is a manufacturing method of the positive electrode for secondary batteries.
4. The method of claim 1,

   The average particle diameter (D ₅₀ ) of the second positive electrode active material is a method for producing a positive electrode for secondary batteries.
5. The method of claim 1,

   Elongation of the first positive electrode mixture layer is a manufacturing method of the positive electrode for secondary batteries is 0.2 to 1.2%.
6. The method of claim 1,

   Elongation of the second positive electrode material mixture layer is a manufacturing method of the positive electrode for secondary batteries is 0.6 to 2.0%.
7. The method of claim 1,

   The difference in elongation between the first positive electrode mixture layer and the second positive electrode mixture layer is 0.1 to 1.0% of a method for manufacturing a positive electrode for a secondary battery.
8. The method of claim 1,

   The total elongation of the positive electrode including the first positive electrode mixture layer and the second positive electrode mixture layer is less than 1.4% of the manufacturing method of the positive electrode for secondary batteries.
9. The method of claim 1,

   At least one of the first positive electrode active material and the second positive electrode active material manufacturing method of a positive electrode for a secondary battery comprising a lithium transition metal oxide represented by the formula (1).

   [Formula 1]

   Li _a Ni _1-xy Co _x Mn _y M _z O ₂

   In the above formula, M is at least one element selected from the group consisting of Al, Zr, Ti, Mg, Ta, Nb, Mo, and Cr, and 0.9≤a≤1.5, 0≤x≤0.5, 0≤y≤0.5 , 0 ≦ z ≦ 0.1, 0 ≦ x + y ≦ 0.7.)
10. A positive electrode current collector;

    A first positive electrode mixture layer laminated on the positive electrode current collector and including a first positive electrode active material; And

    And a second positive electrode mixture layer stacked on the first positive electrode mixture layer and including a second positive electrode active material.

    The difference in elongation between the first positive electrode mixture layer and the second positive electrode mixture layer is 0.1 to 1.0% of a positive electrode for a secondary battery.
11. The method of claim 10,

    The difference in elongation between the first positive electrode mixture layer and the second positive electrode mixture layer is 0.2 to 0.7% of a positive electrode for a secondary battery.
12. The method of claim 10,

    The average particle diameter (D ₅₀ ) of the first positive electrode active material is a secondary battery positive electrode of 5 to 80% of the average particle diameter (D ₅₀ ) of the second positive electrode active material.
13. The method of claim 10,

    The average particle diameter (D ₅₀ ) of the first positive electrode active material is a positive electrode for secondary batteries.
14. The method of claim 10,

    The average particle diameter (D ₅₀ ) of the second cathode active material is a secondary battery positive electrode having a diameter of 10 to 100㎛.
15. The method of claim 10,

    Elongation of the first positive electrode mixture layer is 0.2 to 1.2% of a positive electrode for a secondary battery.
16. The method of claim 10,

    Elongation of the second positive electrode mixture layer is a positive electrode for secondary batteries is 0.6 to 2.0%.
17. The method of claim 10,

    The total elongation of the positive electrode including the first positive electrode mixture layer and the second positive electrode mixture layer is less than 1.4% of the positive electrode for secondary batteries.
18. The method of claim 10,

    The porosity of the first positive electrode mixture layer is 18 to 34% of a secondary battery positive electrode.
19. The method of claim 10,

    At least one of the first positive electrode active material and the second positive electrode active material includes a lithium transition metal oxide represented by Chemical Formula 1 below.

    [Formula 1]

    Li _a Ni _{1 -x- y} Co _x Mn _y M _z O ₂

    In the above formula, M is at least one element selected from the group consisting of Al, Zr, Ti, Mg, Ta, Nb, Mo and Cr, and 0.9≤a≤1.5, 0≤x≤0.5, 0≤y≤0.5 , 0 ≦ z ≦ 0.1, 0 ≦ x + y ≦ 0.7.)
20. An electrode assembly including an anode, a cathode, and a separator interposed between the anode and the cathode;

    A battery case incorporating the electrode assembly; And

    It includes; non-aqueous electrolyte injected into the battery case,

    The positive electrode is a lithium secondary battery is a positive electrode according to any one of claims 10 to 19.

Images