KR20200091563A - Dual coated separators and lithium secondary battery comprising the same - Google Patents

Abstract

Disclosed is a double-coated separator for a lithium secondary battery capable of preventing the generation of static electricity. According to an aspect of the present invention, a double-coated separator comprises: a substrate; a ceramic layer coated on the substrate; and an antistatic layer coated on the ceramic layer.

Description

Double coated separator and lithium secondary battery comprising the same {DUAL COATED SEPARATORS AND LITHIUM SECONDARY BATTERY COMPRISING THE SAME}

The present invention relates to a double-coated separator for lithium secondary batteries that can prevent the generation of static electricity.

Generally, a lithium secondary battery has a higher operating voltage and a higher energy density than a lead battery or a nickel/cadmium battery by accommodating an electroactive material. Accordingly, lithium secondary batteries are used as energy storage means for electric vehicles (EVs) and hybrid electric vehicles (HEVs).

Securing the safety of electric vehicles is an important issue. The purpose of the separator in a lithium secondary battery is to block the physical contact between the positive electrode and the negative electrode, thereby preventing the risk of ignition and explosion due to heat generated during contact between the positive electrode and the negative electrode. The separator applied to the existing lithium secondary battery uses a polyolefin-based porous substrate, and the polyolefin melts in a high-temperature atmosphere during overcharging, closing the pores of the separator and blocking the current, thereby preventing overcharge from proceeding and ensuring safety. .

In order to improve the mechanical strength and safety of lithium secondary batteries, a technique of coating a ceramic having high physical strength such as Al ₂ O ₃ on a porous separator has been introduced and utilized. However, as the demand for a large-capacity and high-energy density of lithium secondary batteries for electric vehicles gradually increases, safety becomes relatively weak, and more excellent mechanical strength and thermal stability are required.

In the case of patent document 1, the thickness of the separation membrane or the thickness of the coating layer is not limited, but when applied to a thin separation membrane, it is possible to induce a micro short due to the conductive polymer due to the penetration of the back side, and there is no ceramic coating layer, so lithium secondary It is difficult to satisfy the penetration stability required for the battery.

On the other hand, when coating a ceramic such as MgOH ₂ , it may improve safety, but it is difficult to apply practically because it is susceptible to moisture and generates static electricity. When the static electricity generation is severe, the alignment of the positive electrode and the negative electrode is distorted and a defect occurs in the process of manufacturing the lithium secondary battery, and when it is severe, the risk of ignition/explosion increases. In order to prevent this, there is a limit to lowering the process speed.

Korean Patent Publication No. 10-2015-0118468 (2015.10.22)

The present invention prevents electrostatic charge by introducing a conductive anti-static coating layer on the ceramic coating separator having a high static electricity generation, and improves the processability and improves the penetration stability and output required in the lithium secondary battery, and a double coating separator comprising the same It is intended to provide a lithium secondary battery.

As a technical means for achieving the above-described technical problem, the double coated separator according to an aspect of the present invention is a substrate; A ceramic layer coated on the substrate; It includes; anti-static layer coated on the ceramic layer.

In addition, the ceramic layer is coated on one surface of the substrate and may be coated to face the anode.

In addition, the ceramic layer is coated on both sides of the substrate, and the antistatic layer may be coated on one surface to face the cathode or the anode.

In addition, the antistatic layer may be coated on one surface to face the anode.

In addition, the ceramic layer may include at least one of Al ₂ O ₃ , AlOOH and Mg(OH) ₂ .

In addition, the thickness of the substrate is 5 to 11㎛, the thickness of the ceramic layer may be 4㎛ or less.

Further, the thickness of the antistatic layer may be 1 μm or less.

In addition, the anti-static layer may include one or more from the group consisting of poly-3,4-ethylenedioxythiophene:polystyrene sulfonate (PEDOT:PSS), carbon nanotubes (CNT) and graphene. .

In addition, the antistatic layer may further include at least one of acrylic acid, acrylic amine, and carboxylic acid.

In addition, the poly-3,4-ethylene dioxythiophene: polystyrene sulfonate (PEDOT: PSS) may have a weight ratio of 1:5 or more.

A lithium secondary battery according to an aspect of the present invention includes a positive electrode; cathode; Electrolyte; And a separator positioned between the anode and the cathode, and the separator includes the separator.

The lithium secondary battery including the double-coated separator according to the disclosed embodiment is coated with an antistatic layer on the ceramic coating layer, thereby preventing an increase in ion conductivity resistance at the surface of the separator by the ceramic layer and improving the output of the anode to improve the output of the cell. It can be expected to improve properties and stability.

1 is a view showing a cross-section of a double coated separator according to an embodiment of the present invention.
2 and 3 is a view showing a cross-section of the double coating separator according to another embodiment of the present invention together with the positive electrode and the negative electrode.
4 is a graph showing the discharge capacity in the rate-specific discharge experiments of Examples and Comparative Examples of the present invention.

The same reference numerals refer to the same components throughout the specification. This specification does not describe all elements of the embodiments, and overlaps between general content or embodiments in the technical field to which the present invention pertains are omitted.

Throughout the specification, when a part “includes” a certain component, it means that the component may further include other components, not to exclude other components, unless otherwise stated.

Singular expressions include plural expressions, unless the context clearly has an exception.

Hereinafter, embodiments according to the present invention will be described in detail with reference to the accompanying drawings. First, a description will be given of a lithium secondary battery, and then a detailed description will be given of a double coated separator according to the disclosed embodiment.

Lithium secondary batteries generally include a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode, the negative electrode, and the electrolyte may be all those commonly used in manufacturing lithium secondary batteries.

The electrode may be formed by applying an electrode slurry mixed with an electrode active material, a conductive material, a solvent, and a binder on an electrode current collector to a predetermined thickness, and then drying and rolling the electrode slurry.

The electrode current collector is not particularly limited as long as it has high conductivity without causing a chemical change in the lithium secondary battery, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or the surface of aluminum or stainless steel. The surface treatment with carbon, nickel, titanium, silver, or the like may be used. It is also possible to increase the adhesion of the positive electrode active material by forming fine irregularities on the surface of the current collector, and various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics are possible.

The negative electrode active material used in manufacturing the negative electrode may be any negative electrode active material capable of intercalation or deintercalation of lithium ions. The negative electrode active material may be formed of any one or a combination of two or more selected from the group consisting of a material capable of reversibly storing and removing lithium, a metal material capable of alloying with lithium, and mixtures thereof.

At least one material selected from the group consisting of artificial graphite, natural graphite, graphitized carbon fiber, graphitized mesocarbon microbeads, fullerene and amorphous carbon may be used as a material capable of reversibly occluding or deintercalating lithium. have.

Amorphous carbons include hard carbon, coke, MCMB fired at 1500°C or lower, and MPCF. In addition, at least one metal selected from the group consisting of Al, Si, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Ni, Ti, Mn, and Ge may be used as a metal capable of alloying with lithium. . These metal materials can be used alone or in combination or alloying. In addition, the metal can be used as a composite mixed with a carbon-based material.

The negative electrode active material may include silicon. It may also include a graphite-silicon composite. The negative electrode active material containing silicon is meant to include silicon oxide, silicon particles, silicon alloy particles, and the like. Representative examples of the alloy include, but are not limited to, solid elements such as aluminum (Al), manganese (Mn), iron (Fe), and titanium (Ti), intermetallic compounds, and process alloys.

The positive electrode active material includes a compound capable of reversible intercalation or deintercalation of lithium. Specifically, the positive electrode active material may be one or more of a complex oxide of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof.

The conductive material is for improving electrical conductivity, and is not particularly limited as long as it is an electronically conductive material that does not cause a chemical change in the lithium secondary battery. For example, graphite, such as natural graphite and 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 powder, aluminum powder, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

Examples of the binder include carboxymethyl cellulose (CMC), a water-based binder used for the negative electrode, Styrene-butadiene Rubber (SBR), and polyvinylidene fluoride (PVDF) used for the positive electrode. Can be used.

When the negative electrode contains a graphite and silicon composite, the binder is Heparin in which Heparin and Dopamine are polymerized to suppress the adhesive strength and bulk expansion of the water-based binder CMC/SBR used for the graphite-based negative electrode and the silicon-based negative electrode to improve adhesion. And a binder in which a polymer binder such as LiPAA (Lithium polyacrylate) is mixed.

The electrode according to the disclosed embodiment may further include other components, such as a dispersion medium, a viscosity modifier, and a filler, as additives, in addition to the above-described electrode active material, conductive material, and binder.

The electrolyte includes a lithium salt and a non-aqueous organic solvent, and may further include additives for improving charge/discharge characteristics, prevention of overcharge, and the like. As the lithium salt, for example, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiCl, LiBr, LiI, LiB ₁₀ Cl ₁₀ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, LiN(SO ₂ C ₂ F ₅ ) ₂ , Li(CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiB(C ₆ H ₅ ) ₄ , Li( SO ₂ F) ₂ N (LiFSI) and (CF ₃ SO ₂ ) ₂ NLi may be used by mixing one or two or more selected from the group consisting of NLi.

As the non-aqueous organic solvent, carbonate, ester, ether, or ketone may be used alone or in combination. The carbonate includes dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), ethylmethyl carbonate (EMC) ethylene carbonate (EC), Propylene carbonate (PC), butylene carbonate (BC), fluoroethylene carbonate (FEC), vinylene carbonate (VC), and the like can be used. As the ester, γ-butyrolactone (GBL), n-methyl acetate , n-ethyl acetate, n-propyl acetate, and the like, and dibutyl ether and the like may be used as the ether, but is not limited thereto.

In addition, the non-aqueous organic solvent may further include an aromatic hydrocarbon-based organic solvent. Specific examples of the aromatic hydrocarbon-based organic solvent include benzene, fluorobenzene, bromobenzene, chlorobenzene, cyclohexylbenzene, isopropylbenzene, n-butylbenzene, octylbenzene, toluene, xylene, mesitylene, and the like. And may be used alone or in combination.

The separator is a lithium secondary battery to provide a path for transporting lithium ions, and to physically separate both electrodes. If a separator is usually used as a material for a separator in a lithium secondary battery, it can be used without particular limitation, and particularly, ion transport of electrolytes It is preferable that the resistance is low and the electrolyte-moisturizing ability is excellent.

For example, the separator substrate is a conventional porous polymer film, for example, a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer. The prepared porous polymer film may be used alone or in a laminate.

On the other hand, in order to improve the mechanical strength and safety of the lithium secondary battery, a technique of coating a ceramic with high physical strength on a porous separator has been introduced and utilized. In particular, in the case of a ceramic coating separator, static electricity is easily generated depending on the type of ceramic in the process of winding or folding the electrodes constituting the electrode assembly, and when winding or folding due to the generated static electricity, poor insertion of the anode electrode body, anode tab There is a problem that a process defect such as a position defect occurs. This tends to cause the positive and negative electrodes to short circuit, and may lead to ignition/explosion hazards.

Likewise, static electricity is easily generated in a polyolefin-based separator without a ceramic layer coated thereon. When only the conductive polymer is coated without coating the ceramic layer, when the separator heat shrinks, it is highly likely to cause a short circuit between the positive electrode and the negative electrode. In particular, there is a risk of ignition/explosion because it is very weak in safety such as penetration, high temperature short circuit, and heat exposure required in the battery cell.

Even in the case of a separator having a thickness of 15 µm or less, which has recently been developed, micro-shorting may occur due to the conductive polymer being coated when coated on both sides. This results in poor cell performance, poor quality, and poor safety.

The present invention aims to improve the processability by preventing the electrostatic charging and improve the output at the same time, through the stability of the penetration of the lithium secondary battery by introducing an antistatic coating layer to the separation membrane having high static electricity to prevent the above-mentioned problems in advance. have.

The double-coated separator according to an aspect of the present invention includes a substrate; A ceramic layer coated on the substrate; It includes; anti-static layer coated on the ceramic layer.

1 is a view showing a cross-section of a double coated separator according to an embodiment of the present invention.

Referring to FIG. 1, in the double coated separator according to the present invention, a ceramic layer may be coated on a base material serving as a base material of the separator, and an antistatic layer may be coated on the ceramic layer.

2 and 3 is a view showing a cross-section of the double coated separator according to another embodiment of the present invention together with the positive electrode and the negative electrode. Together with FIG. 1, the structure of the double coated separator of the present invention will be described with reference to FIGS. 2 and 3.

2 and 3, the ceramic layer may be coated on one side or both sides of the substrate. When the ceramic layer is coated on both sides of the substrate, there are two locations where the antistatic layer can be coated, but the antistatic layer should be present only on one side of the separator. The antistatic layer has a great effect of suppressing the generation of static electricity when coated to face the anode. Therefore, when the ceramic layer is coated on both sides of the substrate, the antistatic layer may be coated to face the cathode or the anode, but may preferably be coated on the ceramic layer to face the anode. Meanwhile, when the ceramic layer is coated on only one surface of the substrate, it may be coated to face the anode, such as the antistatic layer.

The base material, which is the base material of the double-coated separation membrane, is not limited in its components, and may have a thickness in the range of 5 to 11 μm.

The ceramic layer may be selected and coated with at least one of Al ₂ O ₃ , AlOOH and Mg(OH) ₂ , and in the case of a separation membrane coated with Mg(OH) ₂ alone, the antistatic and surface resistance values by the antistatic layer coating This appears excellent. By coating the separator thinly with ceramics having high heat resistance, the separator shrinks due to heat, thereby preventing the occurrence of an internal short circuit in which the positive electrode and the negative electrode contact. The total thickness of the ceramic layer coated on one or both sides of the substrate may be 4 μm or less.

The antistatic layer may include one or more types of poly-3,4-ethylenedioxythiophene: polystyrene sulfonate (PEDOT:PSS), carbon nanotube (CNT), and graphene.

The conductive polymer PEDOT:PSS(poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) has excellent electrical conductivity and flexibility, by coating PEDOT:PSS on the ceramic layer, the ion conductivity at the surface of the separator by the ceramic layer It is possible to prevent an increase in resistance In addition, when PEDOT:PSS is coated to face the anode, the output of the anode can be improved to improve the output characteristics and stability of the cell.

In addition, the antistatic layer may further include at least one of acrylic acid, acrylic amine and carboxylic acid, and may be coated in combination with PEDOT:PSS, carbon nanotubes or graphene. Can.

In addition, the PEDOT:PSS may have a weight ratio of 1:5 or more.

The thickness of the antistatic layer may be 1 μm or less. The thickness of the antistatic layer should be controlled to satisfy the surface resistance value for preventing static electricity, and the surface resistance value for preventing static electricity is 10 ⁴ to 10 ⁹ Ω/cm 2, preferably 10 ⁵ to 10 ⁸ Ω/cm 2.

Example

Conductive polymer PEDOT:PSS and carbon nanotube CT-300 for preventing static electricity are coated on the ceramic layer coated porous separator by thickness, respectively, and the surface resistance is measured and shown in Table 1 below.

Antistatic layer PEDOT:PSS CT-300 Thickness(㎛) 0 One 2 One 3 6 Surface resistance (Ω/㎠) - 21,782 7,855 16,856 5,747 3,528

As described above, the surface resistance value for preventing static electricity is required to be 10 ⁴ Ω/cm 2 or more, and when the thickness of the antistatic layer exceeds 1 μm, the surface resistance value is too low. As the thickness of the antistatic layer increases, the conductivity improves, and thus has an improvement effect such as output, but is more suitable for conductivity than the antistatic effect, which is not preferable because it can degrade the insulating function of the separator.

Subsequently, in order to confirm the improvement of the output of the lithium secondary battery including the double coated separator according to the present invention, a rate-dependent discharge (C-rate) experiment was performed. A coin cell to which a double coating separator was applied according to an embodiment of the present invention (example) and a coin cell to which a general ceramic coating separator was applied (comparative example) were prepared and performance was evaluated.

division Discharge capacity (%) Example Comparative example 0.2C 100 100 0.5C 97.4 97.4 1C 93.4 93.1 2C 90.2 86.6

4 is a graph showing the discharge capacity in the rate-specific discharge experiments of Examples and Comparative Examples of the present invention.

Referring to Table 2 and FIG. 4, in the case of the embodiment of the present invention in which the antistatic layer was introduced, the discharge capacity was measured superior to that of the comparative example in the rate-specific discharge (C-rate) test. When applied to a lithium secondary battery, it means that the output can be improved.

As described above, the disclosed embodiments have been described with reference to the accompanying drawings. Those of ordinary skill in the art to which the present invention pertains will understand that the present invention may be practiced in different forms from the disclosed embodiments without changing the technical spirit or essential features of the present invention. The disclosed embodiments are illustrative and should not be construed as limiting.

1: Substrate 2: Ceramic layer
3: Antistatic layer

Claims (11)

materials;
A ceramic layer coated on the substrate;
A double coating separator comprising a; anti-static layer coated on the ceramic layer. According to claim 1,
The ceramic layer is coated on one surface of the substrate,
A double coated separator coated to face the anode. According to claim 1,
The ceramic layer is coated on both sides of the substrate,
The anti-static layer is a double coating separator is coated on one surface to face the negative electrode or the positive electrode. According to claim 3,
The anti-static layer is a double coating separator is coated on one surface to face the anode. According to claim 1,
The ceramic layer is a double coated separator comprising at least one of Al ₂ O ₃ , AlOOH and Mg(OH) ₂ . According to claim 1,
The thickness of the substrate is 5 to 11㎛,
The thickness of the ceramic layer is a double-coated separator of 4㎛ or less. According to claim 1,
The anti-static layer has a thickness of 1㎛ or less double coated separator. According to claim 1,
The antistatic layer
Poly-3,4-ethylene dioxythiophene: polystyrene sulfonate (PEDOT: PSS), carbon nanotubes (CNT) and graphene (graphene) at least one group comprising a double coating separator. The method of claim 8,
The antistatic layer,
Double coated separator further comprising at least one of acrylic acid, acrylic amine and carboxyl acid. The method of claim 8,
The poly-3,4-ethylene dioxythiophene: polystyrene sulfonate (PEDOT: PSS) is a double coating separator having a weight ratio of 1:5 or more. anode;
cathode;
Electrolyte; And
It includes; a separator located between the anode and the cathode;
The separator is a lithium secondary battery comprising the separator of any one of claims 1 to 10.

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