KR20220139717A - Electrode for secondary battery and lithium secondary battery including the same - Google Patents

Abstract

An electrode for a secondary battery according to exemplary embodiments can include: an electrode current collector; an electrode active material layer formed on the electrode current collector; and a coating layer formed on the electrode active material layer and including rod-type inorganic particles and resin particles having a unit represented by chemical formula 1.

Description

Electrode for a secondary battery and a lithium secondary battery comprising the same

The present invention relates to an electrode for a secondary battery and a lithium secondary battery including the same. More particularly, it relates to an electrode for a secondary battery including an insulating layer and a lithium secondary battery including the same.

A secondary battery is a battery that can be repeatedly charged and discharged, and is widely applied as a power source for portable electronic devices such as mobile phones and notebook PCs.

For example, the secondary battery includes a lithium secondary battery, a nickel cadmium battery, and a nickel hydrogen battery. Among them, lithium secondary batteries are being actively researched and developed in that they have high operating voltage and energy density per unit weight, and are advantageous for charging speed and weight reduction.

For example, a lithium secondary battery may include a positive electrode, a negative electrode, and an electrode assembly having a separator interposed between the positive electrode and the negative electrode. In addition, the lithium secondary battery may include an electrode assembly and a case (eg, cylindrical, prismatic, pouch-type) containing an electrolyte impregnating the electrode assembly.

For example, the separator should have insulating properties and ion permeability to allow the electrolyte to pass smoothly while electrically insulating the anode and the cathode. In addition, with the recent development of high-energy lithium secondary batteries, the demand for a separator with improved high-temperature stability is increasing.

However, polyolefin-based microporous membranes commonly used as substrates for separation membranes have a problem with poor heat resistance, such as melting at high temperatures.

In order to solve the above problems, for example, Korean Patent Registration No. 10-1447565 discloses a separator in which inorganic particles are coated on a polyolefin-based substrate.

Republic of Korea Patent No. 10-1447565

One object of the present invention is to provide a secondary battery including a separator having excellent ion permeability and high temperature stability.

One object of the present invention is to provide a secondary battery having excellent energy density.

An electrode for a secondary battery according to exemplary embodiments may include an electrode current collector; an electrode active material layer formed on the electrode current collector; and a coating layer formed on the electrode active material layer and including rod-type inorganic particles and resin particles including units of Formula 1 below.

[Formula 1]

(In Formula 1, R ₁ and R ₂ are each independently hydrogen, halogen, or a C ₁ to C ₆ alkyl group, and at least one of R ₁ and R ₂ is halogen).

In one embodiment, the coating layer may be in direct contact with the electrode active material layer.

In one embodiment, the resin particles may include a repeating unit represented by the following formula (2).

[Formula 2]

(In Formula 2, R ₁ to R ₄ are each independently hydrogen or a C ₁ to C ₆ alkyl group, R ₅ and R ₆ are each independently hydrogen, halogen or a C ₁ to C ₆ alkyl group, R ₅ and at least one of R ₆ is halogen).

In one embodiment, in Formula 2, R ₁ to R ₄ may be hydrogen, R ₅ and R ₆ may be each independently hydrogen or halogen, and at least one of R ₅ and R ₆ may be halogen.

In one embodiment, the ratio of the long axis length of the inorganic particles to the diameter length of the resin particles may be 3 to 5.

In one embodiment, the aspect ratio of the inorganic particles may be 6 to 8.

In one embodiment, the long axis length of the inorganic particles may be 0.3 to 10 μm.

In one embodiment, the inorganic particles may include bohemite particles.

In one embodiment, the diameter of the resin particles may be 0.1 to 2 ㎛.

In one embodiment, the ratio of the weight of the inorganic particles to the weight of the resin particles in the coating layer may be 0.7 to 8.5.

In one embodiment, the air permeability measured by the Gurley method of the coating layer may be 50 to 175 sec / 100cc.

In one embodiment, the thickness of the coating layer may be 0.1 to 15 ㎛.

A lithium secondary battery according to an exemplary embodiment may include a positive electrode and a negative electrode facing the positive electrode, and at least one of the positive electrode and the negative electrode may be an electrode for the secondary battery.

In one embodiment, the secondary battery electrode is provided as the negative electrode, the positive electrode includes a positive electrode active material layer, the positive electrode active material layer may be in direct contact with the coating layer included in the negative electrode.

In one embodiment, the secondary battery electrode is provided as the positive electrode, the negative electrode includes a negative active material layer, the negative active material layer may be in direct contact with the coating layer included in the positive electrode.

The secondary battery according to exemplary embodiments may not include a separate separator including a polyolefin-based membrane as a substrate. Accordingly, the energy density of the secondary battery may be further improved.

In the secondary battery according to exemplary embodiments, a coating layer capable of replacing a conventional separator may be formed on an electrode. Accordingly, the energy density of the secondary battery may be further improved.

In some embodiments, the coating layer may have excellent heat resistance by including resin particles and inorganic particles including specific chemical units. Accordingly, a secondary battery having excellent high-temperature stability can be realized.

In some embodiments, a ratio of a length of a diameter of the resin particle to a length of a long axis of the inorganic particle may satisfy a specific range. Accordingly, the coating layer has excellent air permeability, thereby realizing a secondary battery having more improved operational stability.

1 is a schematic cross-sectional view showing a cathode according to an exemplary embodiment.
2 and 3 are schematic cross-sectional views and plan views, respectively, of a lithium secondary battery according to an exemplary embodiment.

An electrode for a secondary battery according to exemplary embodiments may include an electrode current collector; an electrode active material layer formed on the electrode current collector; and a coating layer formed on the electrode active material layer, wherein the coating layer may include rod-type inorganic particles and resin particles including units of Formula 1 below.

[Formula 1]

In Formula 1, R ₁ and R ₂ may each independently represent hydrogen, a halogen, or a C ₁ to C ₆ alkyl group, and at least one of R ₁ and R ₂ may be a halogen.

A secondary battery according to example embodiments may include the electrode. For example, the coating layer may replace a separator including a polyolefin-based membrane. In this case, the thickness of the battery can be further reduced and the energy density can be improved. In addition, the coating layer may have excellent heat resistance by including the collection particles and inorganic particles. Accordingly, a secondary battery having excellent high-temperature stability can be realized.

Hereinafter, an electrode for a secondary battery and a secondary battery according to exemplary embodiments will be described in more detail with reference to the drawings.

1 is a schematic cross-sectional view showing a cathode according to an exemplary embodiment.

2 and 3 are schematic cross-sectional views and plan views, respectively, of a secondary battery according to an exemplary embodiment.

1 , an electrode for a secondary battery according to exemplary embodiments includes an electrode current collector 40; an electrode active material layer 90 formed on the electrode current collector 40; and a coating layer 140 formed on the electrode active material layer 90 .

The electrode active material layer 90 may be formed on one surface of the electrode current collector 40 , and may be formed on both surfaces (eg, upper and lower surfaces).

For example, the coating layer 140 may be formed to directly contact the electrode active material layer 90 . In this case, the energy density of the secondary battery can be further improved.

In one embodiment, the secondary battery electrode may be applied to the negative electrode. For example, the electrode current collector 40 may be the negative electrode current collector 125 , and the electrode active material layer 90 may be the negative electrode active material layer 120 .

In one embodiment, the secondary battery electrode may be applied to the positive electrode. For example, the electrode current collector 40 may be the positive electrode current collector 105 , and the electrode active material layer 90 may be the positive electrode active material layer 110 .

In an embodiment, the coating layer 140 may include rod-type inorganic particles and resin particles including units of Formula 1 below. In this case, a secondary battery having excellent high-temperature stability can be realized.

[Formula 1]

In Formula 1, R ₁ and R ₂ are each independently hydrogen, a halogen, or a C ₁ to C ₆ alkyl group, and at least one of R ₁ and R ₂ may be a halogen. In addition, * may mean a bond.

The rod type particles may mean particles having a shape other than 1 in aspect ratio (long axis length/thickness), and may also include a fibrous shape.

The shape of the cross-section of the rod-shaped particles (eg, a cross-section perpendicular to the direction of the major axis length) is not particularly limited. For example, the cross-section of the rod-shaped particle may be a circle, an ellipse, or a polygon, and the rod-shaped particle may have a cylindrical shape, a polygonal columnar shape, or the like.

For example, the 'thickness' of a bar type is the diameter length of the cross-section perpendicular to the longitudinal direction of the major axis (the diameter of the circumscribed circle when the cross-section is polygonal, and the average length of the longest and shortest diameters when the cross-section is an ellipse) can mean, and the 'major axis' of the bar type may mean the height and length of the column.

In one embodiment, the resin particles may include a repeating unit represented by the following formula (2). In this case, a secondary battery having more improved high-temperature stability can be implemented.

[Formula 2]

In Formula 2, R ₁ to R ₄ are each independently hydrogen or a C ₁ to C ₆ alkyl group, R ₅ and R ₆ are each independently hydrogen, halogen or a C ₁ to C ₆ alkyl group, R ₅ and R At least one of ₆ may be halogen.

In some embodiments, in Formula 2, R ₁ to R ₄ may be hydrogen, R ₅ and R ₆ may be each independently hydrogen or halogen, and at least one of R ₅ and R ₆ may be halogen.

In some embodiments, in Formula 2, R ₁ to R ₄ may be hydrogen, R ₅ may be halogen, and R ₆ may be hydrogen. In this case, a secondary battery having more improved high-temperature stability can be implemented.

For example, the halogen may be one of F, Cl, Br and I. In some embodiments, the halogen may be F or Cl.

In one embodiment, the resin particles may be spherical. For example, the sphericity of the resin particles may be 0.1 to 1.0, 0.3 to 1.0, or 0.5 to 1.0.

In one embodiment, the ratio of the long axis length of the inorganic particles to the diameter length of the resin particles may be 3 to 5. In this case, the coating layer 140 may have excellent air permeability, and a secondary battery having improved operational stability and high temperature stability may be realized.

For example, the diameter length of the resin particle and the long axis length of the inorganic particle may mean a length measured based on a scanning electron microscope (SEM) image of the coating layer 140 .

For example, the diameter length of the resin particle is the diameter length of the circle when the SEM image (two-dimensional) of the resin particle is the cause, and the average length of the longest and shortest diameters of the ellipse in the case of an ellipse, a polygon case, it may mean the diameter and length of the circumscribed circle.

In an embodiment, the aspect ratio of the inorganic particles may be more than 1 and less than 50, more than 1 and less than 25, 1.5 to 15, 2 to 10, or 6 to 8. In this case, the air permeability of the coating layer 140 may be further improved.

In an embodiment, the long axis length of the inorganic particles may be 0.1 to 15 μm, 0.3 to 10 μm, 0.5 to 7.5 μm, or 1 to 6 μm. In this case, the air permeability of the coating layer 140 may be further improved.

In an embodiment, the diameter length of the resin particles may be 0.1 to 2 μm, 0.25 to 1.5 μm, or 0.5 to 1.25 μm. In this case, the coating layer 140 may exhibit excellent air permeability.

In an embodiment, the inorganic particles may include at least one of bohemite, MgO, Mg(OH) ₂ , BaSO 3 , silica (SiO ₂ ), and alumina (Al ₂ O ₃ ).

In some embodiments, the inorganic particles may include boehmite particles. In this case, it is easy to satisfy the ratio of the long axis length to the diameter length of the resin particles described above, and the coating layer 140 may exhibit excellent air permeability and heat resistance.

In one embodiment, the ratio of the weight of the inorganic particles to the weight of the resin particles in the coating layer 140 may be 0.5 to 12, preferably 0.7 to 8.5, and more preferably 1 to 5.0.

In one embodiment, the coating layer 140 may further include a binder. In this case, the adhesive force between the coating layer 140 and the electrode active material layer 90 may be increased. In addition, adhesion between the resin particles and the inorganic particles in the coating layer 140 may be increased. Accordingly, the operational stability of the battery may be further improved.

In some embodiments, the binder may include at least one of a rubber-based binder and a fluorine-based binder. For example, the rubber-based binder may include styrene-butadiene rubber (SBR), and the fluorine-based binder may include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co- HFP) and the like.

In one embodiment, when the secondary battery electrode is applied to the negative electrode 130 , the coating layer 140 may include the fluorine-based binder. In addition, the anode active material layer 120 may include the rubber-based binder.

In one embodiment, when the electrode for a secondary battery is applied to the positive electrode 110 , the coating layer 140 may include the rubber-based binder. In addition, the positive active material layer 110 may include the fluorine-based binder.

As described above, when the electrode active material layer and the coating layer include different binders, the dispersion medium of the electrode active material layer slurry and the coating layer slurry may be different from each other during electrode manufacturing. Accordingly, it is possible to prevent the electrode active material layer from being deteriorated by the dispersion medium of the coating layer slurry.

In some embodiments, the binder may include spherical binder particles (eg, SBR particles).

In some embodiments, a ratio of a major axis length of the inorganic particle to a diameter length of the spherical binder particle may be 3 to 5. In this case, the coating layer 140 may ensure excellent air permeability. In addition, the adhesive force between the coating layer 140 and the electrode active material layer 90 and the adhesive force between the resin particles and the inorganic particles in the coating layer 140 may be increased.

In some embodiments, the coating layer 140 may include 10 to 55% by weight of the resin particles, 40 to 85% by weight of the inorganic particles, and 1 to 10% by weight of the binder. Alternatively, the coating layer 140 may include 15 to 45% by weight of the resin particles, 50 to 88% by weight of the inorganic particles, and 1 to 10% by weight of the binder. In this case, the coating layer 140 may exhibit better air permeability, heat resistance, and adhesion.

In one embodiment, the air permeability measured by the Gurley method of the coating layer 140 may be 50 to 175 sec / 100cc. In this case, a secondary battery having excellent high-temperature stability and output stability can be implemented. For example, as the air permeability of the coating layer 140 decreases, the thermal stability of the coating layer 140 may be inferior. Also, as the air permeability of the coating layer 140 increases, the output characteristics of the secondary battery may deteriorate. Therefore, having the air permeability in the above-described range may be advantageous in realizing a secondary battery having excellent operational stability.

In one embodiment, the thickness of the coating layer 140 may be 0.1 to 15 μm, preferably 0.1 to 10 μm. In this case, the energy density of the battery can be further improved.

The electrode according to the above-described exemplary embodiments may be applied to at least one of a positive electrode and a negative electrode of a lithium secondary battery.

In one embodiment, in order to improve the thickness and energy density of the battery, the above-described electrode may be applied to only one of the positive electrode and the negative electrode.

Hereinafter, a lithium secondary battery according to exemplary embodiments will be described in more detail with reference to FIGS. 2 and 3 . For convenience of description, the case in which the above-described electrode is applied to the negative electrode will be described as an example. However, as described above, the above-described electrode may be applied to the positive electrode, or may be applied to both the negative electrode and the positive electrode.

Referring to FIG. 2 , the lithium secondary battery may include a positive electrode 100 and a negative electrode 130 facing the positive electrode 100 .

For example, the positive electrode 100 may include a positive electrode current collector 105 and a positive electrode active material layer 110 on the positive electrode current collector 105 .

The positive electrode active material layer 110 may be formed on one or both surfaces (ie, upper and lower surfaces) of the positive electrode current collector 105 .

The positive electrode active material layer 110 may include a positive electrode active material and, if necessary, a positive electrode binder and a conductive material.

For the positive electrode 100 , for example, a positive electrode slurry is prepared by mixing and stirring a positive electrode active material, a positive electrode binder, a conductive material, a dispersion medium, and the like, and then the positive electrode slurry is applied on the positive electrode current collector 105 , dried and rolled. can be manufactured.

The positive electrode current collector 105 may include, for example, stainless steel, nickel, aluminum, titanium, copper or an alloy thereof, and more preferably, may include aluminum or an aluminum alloy.

The positive active material may be a material capable of reversible insertion and deintercalation of lithium ions. The positive active material may be, for example, a lithium metal oxide including a metal element such as nickel, cobalt, manganese, or aluminum.

In one embodiment, the lithium metal oxide may include nickel in an amount of 80 mol% or more, preferably 85 mol% or more, more preferably 90 mol% or more, of all elements except lithium and oxygen.

In one embodiment, the lithium metal oxide may be represented by the following formula (3).

[Formula 3]

Li _x Ni _a Co _b M _c O _y

In Formula 3, M is at least one of Al, Zr, Ti, B, Mg, Mn, Ba, Si, Y, W, and Sr, 0.9≤x≤1.1, 1.9≤y≤2.1, 0.8≤a≤1, 0≤c/(a+b)≤0.13 and 0≤c≤0.11.

In some embodiments, 0.85≤a≤1, more preferably 0.9≤a≤1.

In some embodiments, Mc may be Mn or Al.

In some embodiments, the lithium metal oxide may further include a coating element or a doping element. For example, the coating element or doping element may include Al, Ti, Ba, Zr, Si, B, Mg, P, Sr, W, La, alloys thereof, or oxides thereof. These may be used alone or in combination of two or more.

The positive electrode binder is, for example, polyvinylidene fluoride (PVDF; polyvinylidenefluoride, vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyacrylonitrile (polyacrylonitrile), polymethylmethacrylic an organic binder such as polymethylmethacrylate, an aqueous binder such as styrene-butadiene rubber (SBR), etc. Also, the positive electrode binder may be used together with a thickener such as carboxymethyl cellulose (CMC).

The conductive material may include, for example, a carbon-based conductive material such as graphite, carbon black, graphene, and carbon nanotubes; and a metal-based conductive material such as a perovskite material such as tin, tin oxide, titanium oxide, LaSrCoO3, or LaSrMnO3.

The negative electrode 130 may include a negative electrode current collector 125 , a negative electrode active material layer 120 on the negative electrode current collector 125 , and a coating layer 140 on the negative electrode active material layer 120 .

The anode active material layer 120 may be formed on one or both surfaces (ie, upper and lower surfaces) of the anode current collector 125 .

The anode active material layer 120 may include an anode active material, if necessary, an anode binder and a conductive material.

The negative electrode 130 is, for example, by mixing and stirring the negative electrode active material, the negative electrode binder, the conductive material, the solvent, etc. to prepare a negative electrode slurry, then coating the negative electrode slurry on the negative electrode current collector 125, drying and rolling can be manufactured.

The negative electrode current collector 125 may include, for example, gold, stainless steel, nickel, aluminum, titanium, copper or an alloy thereof, and more preferably, may include copper or a copper alloy.

The negative active material may be a material capable of intercalating and deintercalating lithium ions. The negative active material may include, for example, a carbon-based negative active material; silicon-based negative active material; lithium alloy; and the like.

The carbon-based negative active material may include, for example, crystalline carbon, amorphous carbon, carbon composite material, carbon fiber, and the like.

The amorphous carbon may be, for example, hard carbon, coke, mesocarbon microbead (MCMB) calcined at 1500° C. or lower, mesophase pitch-based carbon fiber (MPCF), etc. . The crystalline carbon may be, for example, natural graphite, graphitized coke, graphitized MCMB, graphitized MPCF, or the like.

The silicon-based material may include, for example, Si, SiO _x (0<x<2), Si/C, SiO/C, or Si-Metal.

The lithium alloy may include, for example, a metal element such as aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, and indium.

The negative electrode binder and the conductive material may be substantially the same as or similar to the above-described positive electrode binder and conductive material. The negative electrode binder may be, for example, an aqueous binder such as styrene-butadiene rubber (SBR) for compatibility with the carbon-based active material, and may be used together with a thickener such as carboxymethyl cellulose (CMC).

A separator (not shown) may be interposed between the anode 100 and the cathode 130 .

The separator may include a porous polymer film made of a polyolefin-based polymer, such as an ethylene homopolymer, a propylene homopolymer, an ethylene/butene copolymer, an ethylene/hexene copolymer, or an ethylene/methacrylate copolymer.

In one embodiment, the lithium secondary battery may not include a separate separator between the positive electrode 100 and the negative electrode 130 .

In one embodiment, the lithium secondary battery may not include a polyolefin-based film between the positive electrode 100 and the negative electrode 130 .

For example, the above-described electrode for a secondary battery is provided as the negative electrode 130 , and the coating layer 140 and the positive electrode active material layer 110 may directly contact each other.

For example, the above-described electrode for a secondary battery is provided as the positive electrode 100 , and the coating layer 140 and the negative active material layer 120 may directly contact each other.

In the lithium secondary battery according to exemplary embodiments, the coating layer 140 may serve as a separator. Accordingly, since a separate separator may not be included, the thickness and energy density of the secondary battery may be further improved.

An electrode cell may be formed including the anode 100 and the cathode 130 . Also, a plurality of electrode cells may be stacked to form the electrode assembly 150 .

Referring to FIG. 3 , the lithium secondary battery includes a positive electrode lead 107 connected to the positive electrode 100 and protruding to the outside of the case 160 ; and a negative electrode lead 127 connected to the negative electrode 130 and protruding to the outside of the case 160 .

For example, the positive electrode 100 and the positive electrode lead 107 may be electrically connected. Similarly, the negative electrode 130 and the negative lead 127 may be electrically connected.

For example, the positive electrode lead 107 may be electrically connected to the positive electrode current collector 105 . In addition, the negative lead 130 may be electrically connected to the negative current collector 125 .

For example, the positive electrode current collector 105 may include a protrusion (positive electrode tab, not shown) on one side. The positive electrode active material layer 110 may not be formed on the positive electrode tab. The positive electrode tab may be integral with the positive electrode current collector 105 or may be connected by welding or the like. The positive electrode current collector 105 and the positive electrode lead 107 may be electrically connected through the positive electrode tab.

Similarly, the negative electrode current collector 125 may include a protrusion (negative electrode tab, not shown) on one side. The negative electrode active material layer 120 may not be formed on the negative electrode tab. The negative electrode tab may be integral with the negative electrode current collector 125 or may be connected by welding or the like. The negative electrode current collector 125 and the negative electrode lead 127 may be electrically connected through the negative electrode tab.

In an embodiment, the electrode assembly 150 may include a plurality of positive electrodes and a plurality of negative electrodes. For example, a plurality of anodes and cathodes may be alternately disposed with each other. Accordingly, the lithium secondary battery may include a plurality of positive electrode tabs and a plurality of negative electrode tabs protruding from each of the plurality of positive electrodes and the plurality of negative electrodes.

In an embodiment, the positive electrode tabs (or negative electrode tabs) may be laminated, compressed, and welded to form a positive electrode tab stack (or negative electrode tab stack). The positive electrode tab stack may be electrically connected to the positive electrode lead 107 . In addition, the negative electrode tab stack may be electrically connected to the negative electrode lead 127 .

The electrode assembly 150 may be accommodated together with the electrolyte in the case 160 to form a lithium secondary battery.

The electrolyte may include, for example, a lithium salt, and the lithium salt may be accommodated in a case in a non-aqueous electrolyte state together with an organic solvent.

The lithium salt may be, for example, represented by Li ⁺ X ⁻ .

The anion (X ^- ) of the lithium salt is, for example, F ^- , Cl ^- , Br ^- , 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 ^- may be any one selected from. In some embodiments, the lithium salt may include at least one of LiBF ₄ and LiPF ₆ .

The organic solvent is, for example, ethylene carbonate (EC; ethylene carbonate), propylene carbonate (PC; propylene carbonate), dimethyl carbonate (DMC; dimethyl carbonate), diethyl carbonate (DEC; diethyl carbonate), ethyl methyl carbonate ( EMC; ethyl methyl carbonate), methyl propyl carbonate, dipropyl carbonate, dimethyl sulfate, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite and tetrahydrofuran It may include any one or more selected from the like.

The lithium secondary battery may be manufactured, for example, in a cylindrical shape, a prismatic shape, a pouch type, or a coin type.

Hereinafter, preferred examples and comparative examples of the present invention will be described. However, the following examples are only preferred examples of the present invention, and the present invention is not limited thereto.

Hereinafter, preferred examples and comparative examples of the present invention will be described. However, the following examples are only preferred examples of the present invention, and the present invention is not limited thereto.

[Example 1]

1. Preparation of slurry for coating layer formation

Chloroprene rubber particles (hereinafter, CR particles) and boehmite particles (hereinafter, BM particles) were prepared, and then classified according to diameter and long axis.

CR particles (diameter 1.5 μm), BM particles (long axis 5.7 μm, aspect ratio about 7), styrene-butadiene rubber (SBR) particles and carboxymethyl cellulose (CMC) were dispersed in distilled water at a weight ratio of 35:60:3.5:1.5 to disperse the positive electrode A slurry for forming a coating layer was prepared.

2. Preparation of positive and negative electrodes

(1) Preparation of anode with coating layer

Li(Ni _0.8 Co _0.1 Mn _0.1 )O ₂ A cathode active material, carbon black, and PVDF were mixed in a weight ratio of 92:5:3 to prepare a slurry for forming a cathode active material layer.

The slurry for forming the positive electrode active material layer was uniformly coated on an area of an aluminum foil (thickness: 15 μm) having a projection on one side except for the projection, dried, and then rolled to prepare a positive electrode.

The slurry for forming the positive electrode coating layer was applied and dried on the positive electrode to prepare the positive electrode of Example 1 in which the coating layer (thickness: 5 μm) was formed.

(2) Preparation of negative electrode

A negative active material, SBR, and CMC, in which artificial graphite and natural graphite were mixed in a weight ratio of 7:3, were mixed in a weight ratio of 97:1:2 to prepare a slurry for forming a negative electrode active material layer.

The slurry for forming the negative electrode active material layer was uniformly coated on an area excluding the projections of the copper foil (thickness: 15 μm) having projections on one side, dried, and then rolled to prepare the negative electrode of Example 1.

3. Preparation of lithium secondary battery samples

The positive electrode and the negative electrode were laminated to form an electrode assembly. Next, the positive electrode lead and the negative electrode lead were respectively welded and connected to the protrusion (positive electrode tab) of the positive electrode and the protrusion (negative electrode tab) of the negative electrode.

The electrode assembly was accommodated in a pouch (case) so that some regions of the positive electrode lead and the negative electrode lead were exposed to the outside, and three surfaces except for the electrolyte injection part were sealed.

After injecting the electrolyte and sealing the electrolyte injection part, the lithium secondary battery sample was prepared by immersion for 12 hours.

As the electrolyte, a 1 M LiPF ₆ solution (a mixed solvent of EC/EMC/DEC at a volume ratio of 25:30:45) was prepared, and then, based on the total weight of the electrolyte, 1wt% of FEC (Fluoroethylene carbonate), VC (Vinylethylene carbonate) 0.3wt%, LiPO2F2 (Lithium difluorophosphate) 1.0wt%, PS (1,3-Propane sultone) 0.5wt% and PRS (Prop-1-ene-1,3-sultone) 0.5wt% added and mixed did.

[Examples 2 to 4]

As shown in Table 1 below, it was carried out in the same manner as in Example 1, except that the ratio of the diameter of the CR particle and the length of the long axis of the BM particle was changed.

Since the application amount of the slurry for forming the positive electrode coating layer was kept the same, the thickness of the coating layer after drying was also changed according to the change in the length ratio.

[Examples 5 to 8]

As shown in Table 1 below, it was carried out in the same manner as in Example 1, except that the contents of the CR particles and BM particles (excluding the dispersion medium, based on the solid content) in the slurry for forming the positive electrode coating layer were changed.

Since the application amount of the slurry for forming the positive electrode coating layer was kept the same, the thickness of the coating layer after drying was also changed according to the change in the content ratio.

[Example 9]

CR particles, BM particles, and polyvinylidene fluoride (PVDF) were dispersed in NMP in a weight ratio of 35:60:5 to prepare a slurry for forming a negative electrode coating layer.

The slurry for forming the negative electrode coating layer was applied on the negative electrode and dried to prepare a negative electrode of Example 9 in which a coating layer (thickness: 5 μm) was formed.

The negative electrode of Example 9 was used instead of the negative electrode of Example 1, and the positive electrode was used without a coating layer.

Other than that, it carried out similarly to Example 1.

[Comparative Example 1]

Instead of the positive electrode of Example 1, a positive electrode having no coating layer was used. An electrode assembly was formed by interposing a PE separator (thickness: 18 μm) between the positive electrode and the negative electrode.

Other than that, it carried out similarly to Example 1.

[Comparative Example 2]

Instead of the positive electrode of Example 1, a positive electrode having no coating layer was used.

The slurry for forming the positive electrode coating layer of Example 1 was applied on a PE separator (thickness: 13 μm) and dried to prepare the separator of Comparative Example 2 in which the coating layer (thickness: 5 μm) was formed.

An electrode assembly was formed by interposing the separator of Comparative Example 2 between the positive electrode and the negative electrode.

Other than that, it carried out similarly to Example 1.

Experimental Example 1: Measurement of the ratio of the BM particle major axis length to the CR particle diameter length

Using a scanning electron microscope (SEM; Scanning Electron Microscope), the surface of the coating layer of Examples and Comparative Example 2 was observed.

After photographing three regions at different positions on the surface of the coating layer, the average A of the diameter lengths of the CR particles and the average B of the major axis lengths of the BM particles observed in the photographed regions were measured.

Using the measured A and B values, a ratio (B/A) value of the major axis length of the BM particles to the diameter length of the CR particles was calculated.

Experimental Example 2: Air permeability evaluation

The slurry for forming the positive electrode (or negative electrode) coating layer according to the embodiments was applied to a glass plate and dried to form a coating layer having the same thickness.

The coating layer was peeled off from the glass plate to prepare a coating layer sample. The air permeability (Gurley method) of the coating layer samples and the separator of Comparative Example 2 was measured.

Permeability was measured using a Gurley densometer according to ASTM D726. More specifically, under a pressure of 12.2 inH ₂ O, the time taken for 100 cc of air to pass through the cross section of the coating layer sample was measured.

Experimental Example 3: Operational stability evaluation

CC/CV charging (0.5C 4.3V 0.05C CUT-OFF) and CC discharge (1.0C 3.0V CUT-OFF) were repeated 300 times at room temperature for the lithium secondary battery samples of Examples and Comparative Examples.

For the lithium secondary battery sample, it was checked whether the operation was stopped due to a problem such as a short circuit during repeated charging and discharging 200 times, and it was described in the following evaluation criteria.

In case of interruption: ×

In case of 200 charging/discharging without any problem: ○

Experimental Example 4: Evaluation of expected energy density of large cells

In Examples and Comparative Examples, an expected energy density value when each electrode assembly was stacked 77 times as a unit cell was calculated.

Based on the expected energy density value of Comparative Example 1, the energy density increase values of Examples and Comparative Examples were calculated. The energy density increase value was calculated as follows. The following formula takes Example 1 as an example.

Energy density increase value (%) = (Expected energy density of Example 1 - Expected energy density of Comparative Example 1) / Expected energy density of Comparative Example 1 × 100 (%)

CR
particle
content
(wt%) BM particles
content
(wt%) CR particles
prepare
BM particle weight ratio B/A value
(length ratio) breathability
(sec/100cc) energy
density
increment
(%) work
stability Example 1 35 60 1.71 3.8 101 8 ○ Example 2 35 60 1.71 4.3 103 8 ○ Example 3 35 60 1.71 2.9 190 0.5 ○ Example 4 35 60 1.71 5.2 39 4 ○ Example 5 15 80 5.34 3.8 157 1.5 ○ Example 6 50 45 0.90 3.8 66 3 ○ Example 7 7.5 87.5 11.67 3.8 178 One ○ Example 8 60 35 0.58 3.8 49 3 ○ Example 9 35 60 1.71 3.8 111 8 ○ Comparative Example 1 - - - - 110 - ○ Comparative Example 2 35 60 1.71 3.8 158 -6 ○

Referring to Table 1, in the case of the secondary batteries of the Examples, the energy density increase value was more excellent.

On the other hand, in the case of the secondary battery of Comparative Example 2, by employing a separate PE substrate and forming a coating layer on the PE substrate, the energy density was rather reduced.

For example, depending on the difference in the B/A value, the air permeability may vary. Accordingly, in order to secure an appropriate level of air permeability, the thickness of the coating layer may be different, and the energy density may also be different. Therefore, it is possible to implement an excellent air permeability and energy density increase value through the adjustment of the B / A value.

In the case of Examples 1, 2 and 9, B/A values fell within a specific range, indicating better results in air permeability and energy density increase values.

Similarly, according to the difference in the content ratio between the CR particles and the BM particles, the air permeability, the thickness of the coating layer, and the energy density may be different. Therefore, excellent air permeability and energy density increase values can be realized by controlling the content ratio between the CR particles and the BM particles.

In the case of Examples 1, 2 and 9, the content ratio between the CR particles and the BM particles fell within a specific range, resulting in better results in terms of air permeability and energy density increase.

40: electrode current collector 90: electrode active material layer
100: positive electrode 105: positive electrode current collector
107: positive lead 110: positive active material layer
120: negative electrode active material layer 125: negative electrode current collector
127: negative lead 130: negative
140: coating layer 150: electrode assembly
160: case

Claims (15)

electrode current collector;
an electrode active material layer formed on the electrode current collector; and
A secondary battery electrode comprising a; a coating layer formed on the electrode active material layer, the coating layer including rod-type inorganic particles and resin particles including units of Formula 1 below:
[Formula 1]

(In Formula 1, R ₁ and R ₂ are each independently hydrogen, halogen, or a C ₁ to C ₆ alkyl group, and at least one of R ₁ and R ₂ is halogen). The electrode for a secondary battery according to claim 1, wherein the coating layer is in direct contact with the electrode active material layer. The electrode for a secondary battery according to claim 1, wherein the resin particle includes a repeating unit represented by the following Chemical Formula 2:
[Formula 2]

(In Formula 2, R ₁ to R ₄ are each independently hydrogen or a C ₁ to C ₆ alkyl group, R ₅ and R ₆ are each independently hydrogen, halogen or a C ₁ to C ₆ alkyl group, R ₅ and at least one of R ₆ is halogen). The method according to claim 3, In Formula 2, R ₁ To R ₄ Are hydrogen,
R ₅ and R ₆ are each independently hydrogen or halogen,
At least one of R ₅ and R ₆ is halogen, an electrode for a secondary battery. The electrode for a secondary battery according to claim 1, wherein a ratio of a major axis length of the inorganic particle to a diameter length of the resin particle is 3 to 5. The electrode for a secondary battery according to claim 1, wherein an aspect ratio of the inorganic particles is 6 to 8. The electrode for a secondary battery according to claim 1, wherein a major axis length of the inorganic particles is 0.3 to 10 μm. The electrode for a secondary battery according to claim 1, wherein the inorganic particles include bohemite particles. The electrode for a secondary battery according to claim 1, wherein the resin particles have a diameter of 0.1 to 2 μm. The electrode for a secondary battery according to claim 1, wherein a ratio of the weight of the inorganic particles to the weight of the resin particles in the coating layer is 0.7 to 8.5. The method according to claim 1, The air permeability measured by the Gurley method (Gurley method) of the coating layer is 50 to 175 sec / 100cc, the secondary battery electrode. The electrode for a secondary battery according to claim 1, wherein the coating layer has a thickness of 0.1 to 15 μm. a positive electrode, and a negative electrode opposite to the positive electrode;
At least one of the positive electrode and the negative electrode is an electrode for a secondary battery according to claim 1, a lithium secondary battery. 14. The method of claim 13,
The electrode for the secondary battery is provided as the negative electrode,
The positive electrode includes a positive electrode active material layer, the positive electrode active material layer is in direct contact with the coating layer included in the negative electrode, a lithium secondary battery. 14. The method of claim 13,
The electrode for the secondary battery is provided as the positive electrode,
The negative electrode includes a negative active material layer, wherein the negative active material layer is in direct contact with the coating layer included in the positive electrode, a lithium secondary battery.

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