KR102469471B1 - Cathode for lithium rechargeable battery, and lithium rechargeable battery including the same - Google Patents

Abstract

In the present invention, in attaching the positive electrode tab to the positive electrode current collector, an insulating layer that can be formed with a thin thickness replaces the adhesive tape, and the insulating layer is implemented with a composition that exhibits sufficient resistance to mechanical shock from the outside of the battery. A positive electrode and a lithium secondary battery are provided.

Description

Positive electrode for lithium secondary battery and secondary battery including the same

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

Recently, as a driving source for not only small electronic devices such as mobile devices, but also large electronic devices such as electric vehicles (EVs), lithium secondary batteries are in the limelight.

These lithium secondary batteries can be classified into lithium ion batteries, lithium ion polymer batteries, and lithium polymer batteries according to the type of separator and electrolyte used, and can be classified into cylindrical, prismatic, coin, pouch, etc. depending on the shape. .

Among them, a cylindrical battery is a type in which a negative electrode, a separator, and a positive electrode are sequentially stacked and then stored in a battery container in a spiral wound state. Such a cylindrical battery can be driven by attaching an electrode tab to a portion (ie, uncoated portion) of each electrode current collector to which the active material is not applied, and electrically connecting it to an electrode lead to form an electrode terminal.

In general, when attaching the positive electrode tab to the uncoated portion of the positive electrode current collector, an adhesive tape made of a polymer material is used. This is to prevent a short circuit between the positive electrode and the negative electrode due to foreign substances inside the battery and to protect the positive electrode current collector uncoated portion (specifically, in the electrode current collector uncoated portion, the exposed portion excluding the region to which the electrode tab is attached).

However, when such an adhesive tape is used, other components (eg, a separator) in the battery may be ruptured due to its thickness, and a short circuit between the positive electrode and the negative electrode may occur at the ruptured portion, thereby improving battery safety. There is a problem with deterioration. In addition, there is a limit to the adhesive force by the adhesive tape, there is a problem that is vulnerable to mechanical shock from the outside of the battery.

In the present invention, in attaching the positive electrode tab to the positive electrode current collector, an insulating layer that can be formed with a thin thickness replaces the adhesive tape, and the insulating layer is implemented with a composition that exhibits sufficient resistance to mechanical shock from the outside of the battery. A positive electrode and a lithium secondary battery are provided.

Specifically, in one embodiment of the present invention, a positive electrode plate comprising a positive electrode current collector, a positive electrode active material layer formed on the positive electrode current collector, and a positive electrode current collector uncoated portion on which the positive electrode active material layer is not formed; a positive electrode tab positioned on the positive electrode current collector uncoated portion; And located on the positive electrode tab, including alumina (Alumina, Al ₂ O ₃ ), a polymer, and a thickener as solid content, wherein the alumina content is 27 wt% or more among the total solid content (100 wt%) An insulating layer; It provides a positive electrode for a lithium secondary battery comprising a.

In addition, another embodiment of the present invention provides a lithium secondary battery including the positive electrode of the above embodiment.

The positive electrode according to one embodiment of the present invention prevents rupture of other components (eg, a separator) in the battery, and thus, short circuit between the positive electrode and the negative electrode can be suppressed. In addition, it is possible to express sufficient resistance to mechanical shock from the outside of the battery.

Accordingly, safety of the lithium secondary battery to which the positive electrode according to the embodiment is applied may be improved.

1 illustrates an anode structure according to the embodiment.
2 is an exploded perspective view of the lithium secondary battery according to the embodiment.

In the present specification, when a certain component is said to "include", it means that it may further include other components without excluding other components unless otherwise stated. As used throughout this specification, the terms "about," "substantially," and the like are used at or approximating that value when manufacturing and material tolerances inherent in the stated meaning are given, and do not convey the understanding of this application. Accurate or absolute figures are used to help prevent exploitation by unscrupulous infringers of the disclosed disclosure. The term "step of (doing)" or "step of" as used throughout the present specification does not mean "step for".

In this specification, the term "combination of these" included in the expression of the Markush form means a mixture or combination of one or more selected from the group consisting of the components described in the expression of the Markush form, It means including one or more selected from the group consisting of.

Based on the above definition, embodiments of the present invention will be described in detail. However, these are presented as examples, and thereby the present invention is not limited and the present invention is only defined by the scope of the claims to be described later.

Anode for Lithium Secondary Battery

In one embodiment of the present invention, a positive electrode plate comprising a positive electrode current collector, a positive electrode active material layer formed on the positive electrode current collector, and a positive electrode current collector uncoated portion on which the positive electrode active material layer is not formed; a positive electrode tab positioned on the positive electrode current collector uncoated portion; And located on the positive electrode tab, including alumina (Alumina, Al ₂ O ₃ ), a polymer, and a thickener as solid content, wherein the alumina content is 27 wt% or more among the total solid content (100 wt%) An insulating layer; It provides a positive electrode for a lithium secondary battery comprising a.

In the anode of the embodiment, the insulating layer can be formed to a thinner thickness than the adhesive tape of the problem pointed out above. Thus, the positive electrode including the insulating layer can suppress a short circuit between the positive electrode and the negative electrode due to the metal foreign matter generated during the battery manufacturing process.

In addition, in the positive electrode of one embodiment, the insulating layer may exhibit sufficient resistance to mechanical shock from the outside of the battery. Specifically, in the solids constituting the insulating layer, when the alumina content is 27% by weight, specifically 29% by weight or more of the total amount of solids (100% by weight), the insulating layer is sufficient against mechanical shock from the outside of the battery. strength can be expressed. This fact is demonstrated from examples described later.

Hereinafter, the anode of the embodiment will be described in more detail.

Anode mechanical properties

The positive electrode of one embodiment may have a puncture strength of 0.6 kgf or more, which is related to the composition of solids constituting the insulating layer.

Specifically, when the alumina content of the total solid content (100 wt%) is 27 wt%, for example, 29 wt% or more, the positive electrode has a puncture strength of 0.6 kgf or more, for example, 0.67 kgf or more. It may have sufficient strength.

insulation layer ingredient

In the anode of the embodiment, the solid component constituting the insulating layer includes a polymer and a thickener in addition to the alumina described above.

As the polymer, a polymer having adhesive strength, for example, at least one selected from the group consisting of styrene-butadiene rubber (SBR) and polyvinylidene fluoride (PVDF) may be used. .

The purpose of its use lies in adhesive strength, and as its content increases, its adhesive strength increases, and as its amount decreases, the content of the alumina can be increased. For example, the content of the polymer may be controlled to 69.5% by weight or more and 72.5% by weight or less based on the total solid content (100% by weight) of the insulating layer. When this is satisfied, the insulating layer can exhibit sufficient adhesive strength, the composition for forming the insulating layer has an appropriate viscosity, and the workability of the insulating layer forming process can be improved, but is not limited thereto.

In the case of the thickener, a material having dispersibility, for example, at least one selected from the group consisting of carboxy methyl cellulose (CMC) and polyacrylic acid (PAA) may be used. .

This may serve as a dispersing agent so that the alumina can be well dispersed in the slurry. Accordingly, the thickener may be used in a minimum amount at a level capable of properly securing the dispersibility of the alumina. For example, the content of the thickener may be controlled to 0.5 wt% or more and 1.5 wt% or less based on the total solid content (100 wt%) of the insulating layer. When this is satisfied, the adhesive strength of the insulating layer to the positive electrode tab and the positive electrode current collector uncoated portion (specifically, in the positive electrode current collector uncoated portion, the exposed portion excluding the region to which the positive electrode tab is attached) is excellently expressed. The composition for forming the insulating layer may have an appropriate viscosity, and the workability of the insulating layer forming process may be improved.

bipolar structure

1 illustrates the anode structure of one embodiment, and is a view from above after placing the anode current collector (not shown) at the bottom of the paper and sequentially stacking the remaining components. The following description can be understood with reference to FIG. 1 .

The positive current collector uncoated portion (not shown) may be positioned in a direction parallel to a winding end of the positive current collector. At this time, a portion of the positive electrode tab (not shown) is located on the positive electrode current collector uncoated portion, and the remaining portion 102 is located outside the positive electrode current collector uncoated portion, so that an end extending from the positive electrode plate is formed. can be made to form.

In addition, the insulating layer may be positioned 103a on a partial region of the cathode tab positioned on the non-coated portion of the cathode current collector. Specifically, the insulating layer may be formed on a partial region 103a of the positive electrode tab positioned on the uncoated portion of the positive electrode current collector; In the positive electrode current collector uncoated portion, an exposed portion 103b excluding an area where the positive electrode tab is attached; and on a partial region 103c of the positive electrode active material layer; respectively, they may be collectively covered.

If, in the anode structure as described above, if a generally known adhesive tape is used instead of the insulating layer, the anode may have a non-uniform thickness. That is, in the positive electrode to which the adhesive tape is applied, the height from the lowermost positive electrode current collector to the uppermost adhesive tape may vary depending on the position of the adhesive tape (ie, 103a, 103b, alc 103c). Therefore, when a cylindrical battery is implemented by winding the positive electrode to which the adhesive tape is applied together with the separator and the negative electrode, the adhesive tape acts as a step and the separator in direct contact with the positive electrode is ruptured during impact or bar crush test of the battery to which the tape is applied. , an anode-cathode short circuit may occur in that area.

On the other hand, since the anode of the embodiment has an insulating layer having a thinner thickness than a generally known adhesive tape, the insulating layer does not act as a level difference. Thus, even if an external shock is applied to the battery, the separator in direct contact with the positive electrode is not ruptured, thereby preventing an anode-cathode short circuit.

Specifically, in the positive electrode of the embodiment, the thickness ratio of the insulating layer and the electrode tab may be 1:4 to 1:10. When this range is satisfied, other components (eg, a separator) in the battery may not be ruptured by the insulating layer, and short circuit between the positive electrode and the negative electrode may be prevented.

For example, the thickness of the electrode tab may be 80 μm to 100 μm, and the thickness of the insulating layer may be 10 μm to 20 μm according to the thickness ratio, which is only an example and the embodiment is limited thereto It doesn't work.

As a more detailed example, the cathode current collector is generally made to have a thickness of 3 to 500 μm. The positive electrode current collector is not particularly limited as long as it does not cause chemical change in the battery and has high conductivity. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or aluminum or stainless steel. A surface treated with carbon, nickel, titanium, silver, etc. may be used. The current collector may form fine irregularities on its surface to increase the adhesion of the positive electrode active material, and various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven fabrics are possible.

Meanwhile, the insulating layer may be formed to have a length of 1 mm to 3 mm in the extension direction of the electrode tab from the lower end of the electrode tab, and on the other hand, the insulating layer may be formed in the extension direction of the electrode tab from the lower end of the electrode tab. It may be formed to cover 1% to 50% of the total length of the electrode tab.

Outside of the above range, when the insulating layer is formed to a thickness of less than 1 mm in the extension direction of the electrode tab or is formed to less than 1% of the total length of the electrode tab, sufficient insulation cannot be secured, and internal short circuit may occur, If it exceeds the above range and is formed to exceed 3 mm in the extension direction of the electrode tab or is formed to exceed 50% of the total length of the electrode tab, an excessive amount of the insulating composition is used, so the process cost increases and the electrode tab It is not preferable because it is difficult to sufficiently secure a connection area with electrode leads for electrical connection, which is the original purpose.

Of course, the insulating layer may be formed in a shape overlapping a portion where the electrode active material is applied in a range of 0.5 mm or less.

In addition, the insulating layer may be formed with the same width as the width of the electrode tab perpendicular to the extension direction of the electrode tab of the electrode tab, but is not limited thereto, and a part of the upper end where the electrode tab of the electrode current collector is formed It can also be formed over a wider range to cover.

cathode active material layer

Meanwhile, the positive electrode active material layer may further include a binder, a conductive material, and a filler in addition to the positive electrode active material.

The cathode active material may include layered compounds such as lithium cobalt oxide (LiCoO ₂ ) and lithium nickel oxide (LiNiO ₂ ), or compounds substituted with one or more transition metals; lithium manganese oxides such as Li _1+x Mn _2-x O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ ; lithium copper oxide (Li ₂ CuO ₂ ); vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ , and Cu ₂ V ₂ O ₇ ; Ni site type lithium nickel oxide represented by the formula LiNi _{1 - x} M _x O ₂ (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3); Formula LiMn _{2 -x} M _x O ₂ where M = Co, Ni, Fe, Cr, Zn or Ta and x = 0.01 to 0.1 or Li ₂ Mn ₃ MO ₈ where M = Fe, Co, Ni, Cu or Zn) lithium manganese composite oxide; lithium manganese composite oxide of spinel structure represented by LiNi _x Mn _{2 - x} O ₄ ; LiMn ₂ O ₄ in which Li part of the formula is substituted with an alkaline earth metal ion; disulfide compounds; Fe ₂ (MoO ₄ ) ₃ etc. are mentioned, but it is not limited only to these.

The binder is a component that assists in the bonding of the active material and the conductive material and the bonding to the current collector, and is typically added in an amount of 1 to 30% by weight based on the total weight of the electrode mixture layer including the electrode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butyrene rubber, fluororubber, various copolymers, and the like.

The conductive material is typically added in an amount of 1 to 50% by weight based on the total weight of the mixture including the negative electrode active material. The conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

The filler is selectively used as a component that suppresses expansion of the negative electrode, and is not particularly limited as long as it is a fibrous material without causing chemical change in the battery. For example, olefinic polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

lithium secondary battery

In another embodiment of the present invention, a lithium secondary battery including the positive electrode according to the embodiment is provided.

2 is an exploded perspective view of the lithium secondary battery according to the embodiment. Referring to FIG. 2 , the lithium secondary battery 100 has a cylindrical shape, and includes a negative electrode 112, a positive electrode 114, a separator 113 disposed between the negative electrode 112 and the positive electrode 114, and the negative electrode 112 ), an electrolyte (not shown) impregnated in the positive electrode 114 and the separator 113, the battery container 120, and the sealing member 140 for sealing the battery container 120. It is composed of main parts. The lithium secondary battery 100 is configured by sequentially stacking a negative electrode 112, a separator 113, and a positive electrode 114, and then storing them in a battery container 120 in a spiral wound state.

Here, a cylindrical lithium secondary battery is exemplified through FIG. 2 , but the positive electrode according to the embodiment may be applied to lithium secondary batteries of other shapes such as a prismatic shape, a coin shape, and a pouch type as well as a cylindrical shape.

Description of the positive electrode according to the embodiment is as described above, and components of the lithium secondary battery other than the positive electrode will be described in detail below. However, the following description is only an example and can be changed according to what is known in the art.

The negative electrode may include a negative electrode current collector and a negative electrode active material coated on a surface thereof. In this case, as in the case of the positive electrode, a binder, a conductive material, and a filler may be further mixed and applied to the negative electrode current collector as necessary in addition to the negative electrode active material.

The negative electrode active material may be carbon such as non-graphitizing carbon or graphite-based carbon; Li _x Fe ₂ O ₃ (0≤x≤1), Li _x WO ₂ (0≤x≤1), Sn _x Me _{1 - x} Me' _y O _z (Me: Mn, Fe, Pb, Ge; Me' : Metal complex oxides such as Al, B, P, Si, elements of groups 1, 2, and 3 of the periodic table, halogens, 0<x≤1;1≤y≤3;1≤z≤8); lithium metal; lithium alloy; silicon-based alloys; tin-based alloys; SnO, SnO ₂ , PbO, PbO ₂ , Pb ₂ O ₃ , Pb ₃ O ₄ , Sb ₂ O ₃ , Sb ₂ O ₄ , Sb ₂ O ₅ , GeO, GeO ₂ , Bi ₂ O ₃ , Bi ₂ O ₄ , metal oxides such as Bi ₂ O ₅ ; conductive polymers such as polyacetylene; Li-Co-Ni based materials; titanium oxide; Lithium titanium oxide and the like can be used.

The anode current collector is generally made to have a thickness of 3 to 500 μm. The negative electrode current collector is not particularly limited as long as it has conductivity without causing chemical change to the battery, and for example, the surface of copper, stainless steel, aluminum, nickel, titanium, fired carbon, copper or stainless steel. For the surface treatment with carbon, nickel, titanium, silver, etc., an aluminum-cadmium alloy, etc. may be used. In addition, like the positive electrode current collector, fine irregularities may be formed on the surface to enhance the bonding strength of the negative electrode active material, and may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

The separator may be an insulating thin film having high ion permeability and mechanical strength. The pore diameter of the separator is generally 0.01 to 10 μm, and the thickness is generally 5 to 300 μm. Examples of such separators and films include olefin-based polymers such as chemical-resistant and hydrophobic polypropylene; Sheets or non-woven fabrics made of glass fibers or polyethylene; Kraft paper or the like is used. Representative examples currently on the market include Celgard ^R 2400 and 2300 (manufactured by Hoechest Celanese Corp.), polypropylene separators (manufactured by Ube Industries Ltd. or Pall RAI), and polyethylene series (Tonen or Entek).

In some cases, a gel polymer electrolyte may be coated on the separator to increase battery stability. Representative examples of such gel polymers include polyethylene oxide, polyvinylidene fluoride, and polyacrylonitrile.

Meanwhile, when a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may serve as a separator.

The secondary battery has a structure in which such an electrode assembly is impregnated with a lithium salt-containing non-aqueous electrolyte.

The lithium salt-containing non-aqueous electrolyte is composed of a non-aqueous electrolyte and a lithium salt, and a non-aqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte, etc. are used as the non-aqueous electrolyte, but are not limited thereto.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, and gamma -Butylolactone, 1,2-dimethoxyethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethylsulfoxide, 1,3-dioxorane, formamide, dimethylformamide, dioxolane , acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triesters, trimethoxy methane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbo An aprotic organic solvent such as nate derivative, tetrahydrofuran derivative, ether, methyl propionate, or ethyl propionate may be used.

Examples of the organic solid electrolyte include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphoric acid ester polymers, poly agitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, A polymerizer containing an ionic dissociation group or the like can be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitride, halide, sulfate, and the like of Li such as Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ , etc. may be used.

The lithium salt is a material that is easily soluble in the non-aqueous electrolyte, and is, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, lithium chloroborane, lithium lower aliphatic carbonate, lithium 4 phenyl borate, imide and the like can be used.

In addition, for the purpose of improving charge and discharge characteristics, flame retardancy, etc. in the lithium salt-containing non-aqueous electrolyte, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, Hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol, aluminum trichloride etc. may be added. In some cases, halogen-containing solvents such as carbon tetrachloride and trifluoride ethylene may be further included to impart incombustibility, and carbon dioxide gas may be further included to improve high-temperature storage characteristics, and FEC (Fluoro-Ethylene Carbonate), PRS (Propene sultone), etc. may be further included.

In one specific example, a lithium salt such as LiPF ₆ , LiClO ₄ , LiBF ₄ , LiN(SO ₂ CF ₃ ) ₂ , a cyclic carbonate of EC or PC as a high dielectric solvent and a low viscosity solvent of DEC, DMC or EMC An electrolyte may be prepared by adding linear carbonate to a mixed solvent.

The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for a small device, but also can be preferably used as a unit battery in a medium or large battery module including a plurality of battery cells.

Hereinafter, preferred embodiments of the present invention, comparative examples in contrast thereto, and test examples for evaluating them are described. However, the following example is only a preferred embodiment of the present invention, but the present invention is not limited to the following example.

< manufacturing example 1> insulation layer Preparation of Forming Composition

In each composition of Table 1 below, the solid content of SBR, CMC, and alumina (Al ₂ O ₃ ) were mixed, and 10 parts by weight of water as a solvent was added to 100 parts by weight of the total solid content to prepare a composition for forming each insulating layer. .

However, in the composition of Table 1 below, the total amount of SBR, CMC, and alumina (Al ₂ O ₃ ), which are solid components, is 100% by weight, each content is described, and the unit (% by weight) is omitted.

< manufacturing example 2> Manufacture of anode

(1) Formation of positive electrode active material layer

(Width: 600 mm) * (Length: 59 mm) * (Thickness: 17 ㎛) aluminum foil (Al-foil) cut into a positive electrode current collector, and a positive electrode active material layer is formed on one surface of the positive electrode current collector did

Specifically, the cathode active material LiNi _{0 . 8} Co _{0 . 1Mn0 . _ 1} O ₂ , Super-C65 as a conductive material, and KF1100 as a binder were mixed in a weight ratio of 96.5:1.5:2, and NMP as a solvent was added to form a slurry phase.

As shown in FIG. 1, the positive electrode active material slurry is not applied to the center of the positive electrode current collector in the transverse direction (ie, forming a non-coated area), and the non-coated portion is sandwiched between the non-coated portion and has a width of 160 mm. / 440 mm (both sides), 250㎛ thick. Thereafter, the cathode active material slurry applied to both sides of the uncoated portion was treated to form a dried cathode active material coating layer.

(2) anode of the tab Attach

(Width: 4 mm)*(Length: 70 mm)*(Thickness: 100 μm) was used as a cathode tab, and it was attached to the cathode current collector on which the cathode active material layer was formed.

Specifically, as shown in FIG. 1 , a portion of the positive electrode tab is positioned on the positive electrode current collector uncoated portion, and the remaining portion is located outside the positive electrode current collector uncoated portion and has an end extending from the positive electrode plate. placed to form. In the disposed positive electrode tab, an area located on the positive electrode collector uncoated portion is 220 mm ² .

After disposing the positive electrode tab as described above, each of the insulating compositions prepared in Preparation Example 1 was applied to a width of 20 mm and a thickness of 30 μm.

Specifically, as shown in FIG. 1 , the positive electrode tab positioned on the uncoated portion of the positive electrode current collector and the exposed portion of the uncoated portion are entirely covered, and each portion of the positive electrode active material coating layer on both sides of the uncoated portion is covered.

Thereafter, the applied insulating composition was treated by drying at 110oC for 10 min to form a dried insulating layer.

< Experimental example 1> Evaluation of the mechanical properties of the anode

(1) Evaluation of puncture strength

The puncture strength of each positive electrode of Preparation Example 2 was evaluated.

(2) Evaluation of impact strength

4.2V, a radius of 15.8 mm, and a 9.1 kg metal bar were dropped from a height of 61 cm toward each anode, and the impact strength of each anode of Preparation Example 2 was evaluated.

(3) bar crush (bar crush) evaluation

Using a metal bar of 4.2V and a radius of 75 cm, a bar crush impact was applied to each anode of Preparation Example 2 at a strain rate of 30%, and the results were evaluated.

The positive electrode mechanical property evaluation results are recorded in Table 1 below.

Alumina solid contents 25% 27% 29% Puncture Strength (kgf) 0.59 0.623 0.67 Impact test results 3/10
fail 0/10
fail 0/10
fail Bar crush test results 1/5
fail 0/5
fail 0/5
fail note comparative example Example Example

Referring to Table 1, when the alumina content in the solid content of the insulating layer is 0.27% by weight or more, it can be seen that the physical properties of the cathode are improved compared to the case where the alumina content is less than 0.27% by weight. Specifically, in the case of the former, it can be seen that the puncture strength of 0.6 kgf or more, the impact strength and the bar crush evaluation results are improved, and contribute to improving battery safety.

In addition, when the alumina content in the solid content of the insulating layer is 0.27% by weight or more, compared to the case where the alumina content is less than 0.27% by weight, it can be confirmed that the rate-specific characteristics and lifespan characteristics of the lithium secondary battery are improved, and the mechanical properties are improved. can Specifically, in the case of the former, the driving condition of the lithium secondary battery or safety against external force is enhanced.

More specifically, even when the alumina content in the solid content of the insulating layer is 0.27% by weight or more, especially when it is 29% by weight or more, the mechanical properties of the positive electrode are improved, and the conditions of the battery to which it is applied or the safety against external forces are enhanced. You can check.

Although the embodiments of the present invention have been described above, those skilled in the art to which the present invention pertains will understand that the present invention can be implemented in other specific forms without changing the technical spirit or essential features.

Therefore, the embodiments described above should be understood as illustrative in all respects and not limiting. The scope of the present invention is indicated by the claims to be described later rather than the detailed description above, and all changes or modified forms derived from the meaning and scope of the claims and equivalent concepts thereof should be construed as being included in the scope of the present invention. .

102: positive electrode tab 103a, 103b, 103c: insulating layer
101a: positive electrode active material layer
100: lithium secondary battery 112: negative electrode
114: anode 113: separator
120: battery container 140: sealing member

Claims (15)

a positive electrode plate including a positive electrode current collector, a positive electrode active material layer formed on the positive electrode current collector, and a positive electrode current collector uncoated portion on which the positive electrode active material layer is not formed;
a positive electrode tab positioned on the positive electrode current collector uncoated portion; and
An insulating layer positioned on the positive electrode tab and including alumina (Alumina, Al ₂ O ₃ ), a polymer, and a thickener as solid content, wherein the alumina content is 29 wt% or more among the total solid content (100 wt%); include,
The puncture strength is 0.67 kgf or more,
A cathode for a lithium secondary battery.
According to claim 1,
The thickness ratio of the insulating layer and the positive electrode tab,
3:10 to 10:10,
A cathode for a lithium secondary battery.
delete delete delete According to claim 1,
The polymer,
Styrene-butadiene rubber (SBR), and polyvinylidene fluoride (Polyvinylidene fluoride, PVDF) comprising at least one selected from the group consisting of,
A cathode for a lithium secondary battery.
According to claim 1,
Of the total solid content of the insulating layer (100% by weight), the polymer is 69.5% by weight or more and 72.5% by weight or less,
A cathode for a lithium secondary battery.
According to claim 1,
The thickener
To include at least one member selected from the group consisting of carboxy methyl cellulose (CMC) and polyacrylic acid (PAA),
A cathode for a lithium secondary battery.
According to claim 1,
The thickener content is 0.5% by weight or more and 1.5% by weight or less of the total solid content of the insulating layer (100% by weight),
A cathode for a lithium secondary battery.
According to claim 1,
The positive current collector uncoated portion is located in a direction parallel to the winding end of the positive current collector,
The positive electrode active material layer is formed on both sides of the positive electrode current collector uncoated portion,
A cathode for a lithium secondary battery.
According to claim 10,
The positive electrode tab,
a partial area is located on the positive electrode current collector uncoated portion;
the remaining partial region is located outside the positive electrode current collector uncoated portion to form an end extending from the positive electrode plate;
A cathode for a lithium secondary battery.
According to claim 11,
The insulating layer is
Located on a partial region of the positive electrode tab located on the positive electrode current collector uncoated portion,
A cathode for a lithium secondary battery.
According to claim 12,
The insulating layer is
a partial area of the positive electrode tab positioned on the positive electrode current collector uncoated portion; In the positive electrode current collector uncoated portion, an exposed portion excluding an area to which the positive electrode tab is attached; And a partial region of the positive electrode active material layer;
A cathode for a lithium secondary battery.
A lithium secondary battery comprising the positive electrode of claim 1.
According to claim 14,
A lithium secondary battery that is a cylindrical battery.

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