KR102459625B1 - Electrode assembly, Lihtium battery comprising electrode assembly, and Preparation method thereof - Google Patents

Abstract

a first portion in contact with the positive electrode active material layer and the negative electrode active material layer; and a second portion not in contact with the positive electrode active material layer and the negative electrode active material layer, wherein a ratio (T1/T2) of the thickness (T1) of the first portion to the thickness (T2) of the second portion is T1/T2 <0.97 composite separator a positive electrode including the positive electrode active material layer disposed on a first portion of one surface of the composite separator; and a negative electrode including the negative electrode active material layer disposed on the first portion of the other surface of the composite separator; an electrode assembly including the same, a lithium battery including the same, and a method of manufacturing an electrode assembly are provided.

Description

Electrode assembly, lithium battery and electrode assembly manufacturing method employing the same

It relates to an electrode assembly, a lithium battery employing the same, and a method for manufacturing an electrode assembly.

In order to meet the miniaturization and high performance of various devices, miniaturization and weight reduction of lithium batteries are becoming important. In addition, in order to be applied to fields such as electric vehicles, the discharge capacity, energy density, and cycle characteristics of lithium batteries are becoming important. In order to meet the above use, a lithium battery having a large discharge capacity per unit volume, high energy density, and excellent lifespan characteristics is required.

In a lithium battery, a separator is disposed between the positive electrode and the negative electrode to prevent a short circuit. An electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrodes is wound to have a jelly roll shape, and in the electrode assembly, the jelly roll is rolled to improve adhesion between the positive electrode/negative electrode and the separator.

As separators for lithium batteries, olefinic polymers are widely used. Olefin-based polymers have excellent flexibility, but have low strength when immersed in an electrolyte, and short circuits may occur in the battery due to rapid thermal contraction at a high temperature of 100° C. or higher. Accordingly, a separator having improved strength and heat resistance by coating a ceramic on one surface of a porous olefinic polymer substrate is provided. The ceramic-coated separator has a low adhesion between the negative electrode and the positive electrode, so the battery volume changes rapidly during charging and discharging, so that the battery is easily deformed.

In order to improve adhesion between a ceramic coated separator and an anode/cathode, a separator in which a binder is added on a ceramic is provided. In the separator in which the binder is added to the ceramic, the porosity is lowered and the internal resistance is increased, or the lithium battery is easily deteriorated due to swelling in the electrolyte of the binder.

Accordingly, there is a need for a separator that overcomes the limitations of the prior art and provides improved energy density and charge/discharge characteristics by having improved adhesion and air permeability.

One aspect is to provide an electrode assembly including a composite separator having improved adhesion to an anode and air permeability.

Another aspect is to provide a lithium battery including the electrode assembly.

Another aspect is to provide a method of manufacturing the electrode assembly.

According to one aspect,

a first portion in contact with the positive electrode active material layer and the negative electrode active material layer; and

It includes a second portion not in contact with the positive electrode active material layer and the negative electrode active material layer,

a composite separator in which a ratio (T1/T2) of the thickness (T1) of the first part and the thickness (T2) of the second part is T1/T2<0.97;

a positive electrode including the positive electrode active material layer disposed on a first portion of one surface of the composite separator; and

An electrode assembly including a; a negative electrode including the negative electrode active material layer disposed on the first portion of the other surface of the composite separator is provided.

according to the other side

Including the electrode assembly according to the above,

A lithium battery in which the electrode assembly is wound in the form of a jelly roll is provided.

According to another aspect,

Preparing a jelly roll by winding an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode;

thermally softening the jelly roll under pressure and pre-charging;

hot rolling the filled jelly roll;

cold rolling the filled jelly roll; and

There is provided a method of manufacturing an electrode assembly comprising; a chemical conversion step of charging and discharging the charged jelly roll under pressure.

According to one aspect, energy density and charge/discharge characteristics of a lithium battery may be improved by employing a composite binder.

1 is a schematic diagram of a composite separator according to an exemplary embodiment.
2 is a schematic diagram of a lithium battery according to an exemplary embodiment.
<Explanation of symbols for main parts of the drawing>
1: Lithium battery 2: Anode
3: positive electrode 4: separator
5: Battery case 6: Cap assembly

Hereinafter, an electrode assembly according to exemplary embodiments and a lithium battery employing the same will be described in more detail.

An electrode assembly according to an embodiment includes a first portion in contact with a positive electrode active material layer and a negative electrode active material layer; and a second portion not in contact with the positive electrode active material layer and the negative electrode active material layer, wherein a ratio (T1/T2) of the thickness (T1) of the first portion to the thickness (T2) of the second portion is T1/T2 <0.97 composite separator; a positive electrode including the positive electrode active material layer disposed on a first portion of one surface of the composite separator; and an anode including the anode active material layer disposed on a first portion of the other surface of the composite separator. In the composite separator included in the electrode assembly, the thickness of the first portion in contact with the electrode active material layer including the positive electrode active material layer and/or the negative electrode active material layer is less than 97% compared to the thickness of the second portion not in contact with the electrode active material layer. Accordingly, since the volume of the electrode assembly including the separator and the electrode is reduced, the energy density per unit volume of the lithium battery including the electrode assembly may be improved. In addition, since the composite separator has excellent adhesion between the electrode active material layer and the composite separator, the volume change during charging and discharging of the lithium battery is suppressed. have.

For example, in the composite separator, a ratio (T1/T2) of the thickness T1 of the first portion to the thickness T2 of the second portion may be 0.80<T1/T2<0.96. For example, in the composite separator, a ratio (T1/T2) of the thickness T1 of the first portion to the thickness T2 of the second portion may be 0.84<T1/T2<0.95. For example, in the composite separator, a ratio (T1/T2) of the thickness T1 of the first portion to the thickness T2 of the second portion may be 0.85<T1/T2<0.95. For example, in the composite separator, a ratio (T1/T2) of the thickness T1 of the first portion to the thickness T2 of the second portion may be 0.86≤T1/T2≤0.93. In the composite separator, when the ratio (T1/T2) of the thickness T1 of the first part to the thickness T2 of the second part exceeds the above range, adhesion between the separator and the electrode may be poor. In the composite separator, if the ratio (T1/T2) of the thickness T1 of the first part to the thickness T2 of the second part is smaller than the above range, the volume of the separator is excessively contracted to cause a short circuit of the battery, or the separator Lithium battery may not work because the pores of the battery are clogged and internal resistance increases rapidly.

The composite separator may include a porous substrate; and a coating layer disposed on at least one surface of the porous substrate, wherein the coating layer may include a binder and a filler.

For example, the coating layer may be disposed on one or both surfaces of the porous substrate. In addition, the coating layer may be an organic layer including organic particles as a binder and filler, an inorganic layer including inorganic particles as a binder and filler, and an organic/inorganic layer including a binder and organic particles and inorganic particles. In addition, the coating layer may have a single-layer or multi-layer structure.

For example, the coating layer may be disposed on only one surface of the porous substrate, and the coating layer may not be disposed on the other surface. The coating layer disposed on only one surface of the porous substrate may be an organic layer, an inorganic layer, or an organic/inorganic layer. In addition, the coating layer may have a multilayer structure. In the multi-layered coating layer, layers selected from an organic layer, an inorganic layer, and an organic/inorganic layer may be arbitrarily disposed. The multi-layer structure may be a two-layer structure, a three-layer structure, or a four-layer structure, but is not necessarily limited to such a structure and may be selected according to required separator characteristics.

For example, coating layers may be respectively disposed on both surfaces of the porous substrate. Each of the coating layers disposed on both surfaces of the porous substrate may be an organic layer, an inorganic layer, or an organic/inorganic layer independently of each other. In addition, one or more of the coating layers disposed on both surfaces of the porous substrate may have a multi-layer structure. In the multi-layered coating layer, layers selected from an organic layer, an inorganic layer, and an organic/inorganic layer may be arbitrarily disposed. The multi-layer structure may be a two-layer structure, a three-layer structure, or a four-layer structure, but is not necessarily limited to such a structure and may be selected according to required separator characteristics.

For example, in an electrode assembly in the form of a jelly roll in which anode/composite separator/cathode are overlapped and wound, the ratio (ratio, T1/T2) of the thickness (T1) of the first part to the thickness (T2) of the second part of the composite separator ) may be T1/T2<0.97. When the electrode assembly in the form of jelly roll goes through the pressure initial filling step, hot rolling step, cold rolling step, and pressurization step, the fillers dispersed in the coating layer are rearranged and uniformly disposed on the surface of the active material layer along the surface of the active material layer do. Accordingly, the composite separator may have a reduced coating layer thickness at a portion in contact with the positive active material layer and/or the negative active material layer. In addition, by gel-sol conversion and sol-gel conversion of the binder included in the coating layer, the coating layer may have improved adhesion between the positive electrode active material layer and/or the negative electrode active material layer.

In the composite separator, the porous substrate may be a porous membrane including polyolefin. Polyolefin has an excellent short circuit prevention effect and can also improve battery stability by a shutdown effect. For example, the porous substrate may be a film made of a resin such as polyethylene, polypropylene, polybutene, polyolefin such as polyvinyl chloride, and a mixture or copolymer thereof, but is not necessarily limited thereto and may be used in the art. Any porous membrane is possible. For example, a porous membrane made of a polyolefin-based resin; a porous membrane woven with polyolefin-based fibers; nonwoven fabric comprising polyolefin; An aggregation of insulating material particles, etc. may be used. For example, a porous membrane containing polyolefin has excellent applicability of a binder solution for producing a coating layer formed on the base layer, and increases the capacity per unit volume by increasing the ratio of active materials in the battery by thinning the film thickness of the composite separator. can

For example, the polyolefin used as the material of the porous substrate may be a homopolymer, a copolymer such as polyethylene or polypropylene, or a mixture thereof. The polyethylene may be low-density, medium-density, or high-density polyethylene, and from the viewpoint of mechanical strength, high-density polyethylene may be used. In addition, two or more types of polyethylene may be mixed for the purpose of providing flexibility. The polymerization catalyst used for the preparation of polyethylene is not particularly limited, and a Ziegler-Natta catalyst, a Phillips catalyst, or a metallocene catalyst may be used. From the viewpoint of reconciling mechanical strength and high permeability, the weight average molecular weight of polyethylene may be 100,000 to 12 million, for example, 200,000 to 3 million. Polypropylene may be a homopolymer, a random copolymer, or a block copolymer, and may be used alone or in combination of two or more thereof. In addition, the polymerization catalyst is not particularly limited, and a Ziegler-Natta catalyst or a metallocene catalyst may be used. Also, stereoregularity is not particularly limited, and isotactic, syndiotactic or atactic may be used, but inexpensive isotactic polypropylene may be used. In addition, additives such as polyolefins other than polyethylene or polypropylene and antioxidants may be added to the polyolefin within the scope not impairing the effects of the present invention.

For example, the porous substrate includes polyolefin such as polyethylene and polypropylene, and a multilayer film of two or more layers may be used, a polyethylene/polypropylene two-layer separator, a polyethylene/polypropylene/polyethylene three-layer separator, polypropylene/polyethylene/ A mixed multilayer film such as a polypropylene three-layer separator may be used, but is not limited thereto, and any material and configuration that can be used as a porous substrate in the art may be used.

For example, the porous substrate may include a diene-based polymer prepared by polymerizing a monomer composition including a diene-based monomer. The diene-based monomer may be a conjugated diene-based monomer or a non-conjugated diene-based monomer. For example, the diene-based monomer is 1,3-butadiene, isoprene, 2-chloro-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 1 ,3-pentadiene, chloroprene, vinylpyridine, vinylnorbornene, dicyclopentadiene and at least one selected from the group consisting of 1,4-hexadiene, but is not necessarily limited thereto, and as a diene-based monomer in the art Anything that can be used is possible.

In the composite separator, the thickness of the porous substrate may be 1 μm to 100 μm. For example, the thickness of the porous substrate may be 1 μm to 30 μm. For example, the thickness of the porous substrate may be 5 μm to 20 μm. For example, the thickness of the porous substrate may be 5 μm to 15 μm. For example, the thickness of the porous substrate may be 5 μm to 10 μm. If the thickness of the porous substrate is less than 1 μm, it may be difficult to maintain the mechanical properties of the composite separator, and if the thickness of the porous substrate is more than 100 μm, the internal resistance of the lithium battery may increase.

In the composite separator, the porosity of the porous substrate may be 5% to 95%. If the porosity is less than 5%, the internal resistance of the lithium battery may increase, and if the porosity is more than 95%, it may be difficult to maintain the mechanical properties of the porous substrate.

In the composite separator, the pore size of the porous substrate may be 0.01 μm to 50 μm. For example, in the composite separator, the pore size of the porous substrate may be 0.01 μm to 20 μm. For example, in the composite separator, the pore size of the porous substrate may be 0.01 μm to 10 μm. If the pore size of the porous substrate is less than 0.01 μm, the internal resistance of the lithium battery may increase, and if the pore size of the porous substrate exceeds 50 μm, it may be difficult to maintain the mechanical properties of the porous substrate.

In the composite separator, the coating layer includes a filler. The filler is not particularly limited, and any filler that can be used as a filler in the art is possible.

In the composite separator, the filler may serve as a support. When the separator is about to shrink at a high temperature, the filler supports the separator to suppress the shrinkage of the separator. When the coating layer disposed on the composite separator includes a filler, sufficient porosity may be secured and mechanical properties may be improved. A lithium battery including such a composite separator may secure improved stability.

The average particle diameter of the filler included in the coating layer may be 300 nm to 2 μm. For example, the average particle diameter of the filler may be 300 nm to 1.5 μm. For example, the average particle diameter of the filler may be 300 nm to 1.0 μm. Such an average particle diameter can be defined as the number average particle diameter of the particles measured using a laser scattering particle size distribution meter (eg, Horiba LA-920). By using a filler having an average particle diameter of the filler, it is easy to form the coating layer to an appropriate thickness, and the composite separator including the coating layer including the filler may have an appropriate porosity. If the average particle diameter of the filler is less than 300 nm, the mechanical properties of the composite separator may be deteriorated.

The filler included in the coating layer may be inorganic particles, organic particles, or a combination thereof.

The inorganic particles may be metal oxides, metalloid oxides, or a combination thereof. Specifically, the inorganic particles may be alumina, silica, boehmite, magnesia, or a combination thereof. The alumina, silica, and the like have a small particle size, so it is easy to make a dispersion. For example, the inorganic particles are Al ₂ O ₃ , SiO ₂ , TiO ₂ , SnO ₂ , CeO ₂ , NiO, CaO, ZnO, MgO, ZrO ₂ , Y ₂ O ₃ , SrTiO ₃ , BaTiO ₃ , MgF ₂ , Mg(OH) ₂ , or a combination thereof.

The inorganic particles may be in the form of a sphere, a plate, or a fiber, but is not limited thereto, and any form that can be used in the art may be used.

The plate-shaped inorganic particles include, for example, alumina and boehmite. In this case, the reduction in the area of the separator at a high temperature can be further suppressed, a relatively large porosity can be secured, and characteristics can be improved during the penetration evaluation of the lithium battery.

When the inorganic particles are plate-shaped or fibrous, an aspect ratio of the inorganic particles may be about 1:5 to 1:100. For example, the aspect ratio may be about 1:10 to 1:100. For example, the aspect ratio may be about 1:5 to 1:50. For example, the aspect ratio may be about 1:10 to 1:50.

The ratio of the length of the long axis to the minor axis on the flat surface of the plate-shaped inorganic particles may be 1 to 3. For example, the ratio of the length of the major axis to the minor axis on the flat surface may be 1 to 2. For example, the ratio of the length of the major axis to the minor axis on the flat surface may be about 1. The aspect ratio and the ratio of the length of the major axis to the minor axis may be measured through a scanning electron microscope (SEM). In the aspect ratio and the length range of the minor axis to the major axis, the contraction of the separator may be suppressed, the relatively improved porosity may be secured, and the penetration characteristics of the lithium battery may be improved.

When the inorganic particles are plate-shaped, the average angle of the flat surface of the inorganic particles with respect to one surface of the porous substrate may be 0 to 30 degrees. For example, the angle of the flat surface of the inorganic particles with respect to one surface of the porous substrate may converge to 0 degrees. That is, one surface of the porous substrate and the flat surface of the inorganic particles may be parallel. For example, when the average angle of the flat surface of the inorganic compound with respect to one surface of the porous substrate is within the above range, thermal contraction of the porous substrate may be effectively prevented, thereby providing a separator with reduced shrinkage.

The organic particles may be cross-linked polymers. The organic particles may be highly crosslinked polymers that do not exhibit a glass transition temperature (Tg). When a highly crosslinked polymer is used, heat resistance is improved, and shrinkage of the porous substrate can be effectively suppressed at high temperatures.

Organic particles include, for example, acrylate-based compounds and derivatives thereof, diallyl phthalate-based compounds and derivatives thereof, polyimide-based compounds and derivatives thereof, polyurethane-based compounds and derivatives thereof, copolymers thereof, or combinations thereof. However, it is not limited thereto, and any one that can be used as a filler in the art is possible. For example, the filler may be cross-linked polystyrene particles or cross-linked polymethyl methacrylate particles.

The filler may be secondary particles formed by aggregation of primary particles. In the separator including the filler, which is a secondary particle, the porosity of the coating layer is increased, so that a lithium battery having excellent high output characteristics can be provided.

In the composite separator, a coating layer may be disposed on both surfaces of the porous substrate. The thickness of the coating layer may be 0.1 to 5 μm, 0.5 to 5 μm, or 0.5 to 3 μm based on one surface. When the thickness of the coating layer satisfies the above range, a composite separator including the same may provide improved adhesion and air permeability. In addition, since the coating layer is disposed on both sides of the porous substrate, the adhesion between the composite binder and the electrode active material layer may be further improved, and thus the volume change of the lithium battery may be suppressed. For example, referring to FIG. 1 , coating layers 12 and 13 including a binder and a filler may be respectively disposed on both surfaces of the porous substrate 11 in the composite separator. The thickness T of the composite separator is the sum of the thicknesses of the porous substrate 11 and the coating layers 12 and 13 . The thickness T1 of the first portion is the sum of the thicknesses of the substrate 11 and the coating layers 12 and 13 of the composite separator in contact with the positive electrode active material layer and the negative electrode active material layer. The thickness T2 of the second portion is the sum of the thicknesses of the substrate 11 and the coating layers 12 and 13 of the composite separator that are not in contact with the positive electrode active material layer and the negative electrode active material layer.

The coating layers disposed on both surfaces of the composite separator may have the same composition. By disposing the coating layer having the same composition on both surfaces of the composite separator, the same adhesive force acts on the electrode active material layer on one surface and the other surface of the composite separator, so that the volume change of the lithium battery can be uniformly suppressed.

In the composite separator, the coating layer may include a blend of a binder and a filler. The coating layer may include a blend of a binder and a filler in which the binder and the filler are uniformly mixed. Since the coating layer includes a blend of a binder and a filler, the adhesion between the porous substrate and the electrode active material layer may be further improved as compared to a multilayer structure in which the binder and the filler are disposed as separate layers.

The coating layer may be formed by mixing a filler and a binder composition to prepare a composition for forming a coating layer, and then applying it on a porous substrate. A method of applying the composition for forming the coating layer is not particularly limited and any method that can be used in the art is possible. For example, it may be formed by a method such as printing, compression, press-fitting, roller application, blade application, bristle application, dipping application, spray application, or flow-on application.

The content of the filler may be 90% or less based on the total weight of the binder and the filler in the coating layer. If the content of the filler in the coating layer is more than 90%, the content of the binder is too low, the adhesive force between the composite separator and the electrode active material layer may be reduced.

For example, the binder:filler ratio in the coating layer may be 1:1 to 1:8. For example, the binder:filler ratio in the coating layer may be 1:1.5 to 1:7. For example, the binder:filler ratio in the coating layer may be 1:2 to 1:6. For example, the binder:filler ratio in the coating layer may be 1:2 to 1:5. In the ratio range of the binder and the filler, improved adhesion and air permeability can be obtained at the same time. When the ratio of the filler is lower than the above range, the adhesive strength is improved, but the air permeability is excessively lowered, and the internal resistance of the lithium battery may be excessively increased.

The binder included in the coating layer may have a swelling (swelling) of 250% or less after being left in the electrolyte at 45°C for 24 hours. For example, the binder included in the coating layer may have a swelling (swelling) of 200% or less after being left in the electrolyte at 45°C for 24 hours. For example, the binder included in the coating layer may have a swelling (swelling) of 180% or less after being left in the electrolyte at 45°C for 24 hours. For example, the binder included in the coating layer may have a swelling (swelling) of 160% or less after being left in the electrolyte at 45° C. for 24 hours. For example, the binder included in the coating layer may have a swelling (swelling) of 150% or less after being left in the electrolyte at 45°C for 24 hours. Since the binder included in the coating layer has low swelling with respect to the electrolyte, the stability of the separator may be improved. When the swelling of the binder included in the coating layer with respect to the electrolyte solution is excessively large (250% or more), the adhesive force between the composite separator and the electrode active material layer is reduced, the volume of the lithium battery is increased, and the lifespan characteristics of the lithium battery may be reduced. Swelling is defined as the ratio of the mass of the membrane to the mass of the initial membrane, which is increased after making a 100 μm thick membrane with the binder used in the membrane coating layer and immersing it in the electrolyte at a constant temperature for 1 day. As the electrolyte, the electrolyte described in the lithium battery section below may be used.

The binder included in the coating layer may be a fluorine-based polymer. The binder included in the coating layer may be a fluorine-based polymer in which part or all of hydrogen connected to carbon included in the binder is substituted with fluorine. For example, the fluorine-based polymer may be a polymer including a repeating unit derived from at least one monomer selected from vinylidine fluoride monomer, ethylene tetrafluoride monomer, and propylene hexafluoride. For example, the binder included in the coating layer may be a fluorine-based homopolymer.

The binder included in the coating layer may be a copolymer. The binder included in the coating layer may be a fluorine-based copolymer.

The fluorine-based copolymer included in the coating layer may be a copolymer of an ethylene tetrafluoride monomer and another monomer. Another monomer used together with the ethylene tetrafluoride monomer may be at least one fluorine-containing monomer selected from the group consisting of vinylidene fluoride, hexafluoropropylene, chlorotrifluoroethylene, and perfluoroalkyl vinyl ether. For example, the fluorine-based copolymer included in the coating layer is an ethylene tetrafluoride-vinylidene fluoride copolymer, an ethylene tetrafluoride-hexafluoropropylene copolymer, an ethylene tetrafluoride-chlorotrifluoroethylene copolymer, and an ethylene tetrafluoride. - It may be a perfluoroalkyl vinyl ether or the like. For example, in the fluorine-based copolymer included in the coating layer, the amount of ethylene tetrafluoride monomer units may be 10 mol% or more. For example, in the fluorine-based copolymer included in the coating layer, the amount of ethylene tetrafluoride monomer units may be 30 mol% or more. For example, in the fluorine-based copolymer included in the coating layer, the amount of ethylene tetrafluoride monomer units may be 50 mol% or more. For example, the amount of ethylene tetrafluoride monomer units in the fluorine-based copolymer included in the coating layer may be 70 mol% or more. For example, in the fluorine-based copolymer included in the coating layer, the amount of ethylene tetrafluoride monomer units may be 90 mol% or more.

Alternatively, the fluorine-based copolymer included in the coating layer may be a copolymer of vinylidine fluoride monomer and another monomer. For example, the fluorine-based copolymer included in the coating layer is a copolymer of vinylidene fluoride monomer and one or more fluorine-containing monomers selected from the group consisting of hexafluoropropylene, chlorotrifluoroethylene, fluorovinyl and perfluoroalkyl vinyl ether. may be synthetic. Specifically, the vinylidine-based monomer may be a vinylidene fluoride homopolymer, a vinylidene fluoride-hexafluoropropylene copolymer, a vinylidene fluoride-chlorotrifluoroethylene copolymer, or the like. For example, the fluorine-based copolymer included in the coating layer may contain 50 mol% or more of vinylidene fluoride-based monomer units. For example, the fluorine-based copolymer included in the coating layer may include 60 mol% or more of vinylidene fluoride-based monomer units. For example, the fluorine-based copolymer included in the coating layer may contain 70 mol% or more of vinylidene fluoride-based monomer units. For example, the fluorine-based copolymer included in the coating layer may contain 80 mol% or more of vinylidene fluoride-based monomer units. For example, the fluorine-based copolymer included in the coating layer may include 90 mol% or more of vinylidene fluoride-based monomer units.

The fluorine-based polymer included in the coating layer may additionally include a hydrophilic functional group. By additionally including the hydrophilic functional group, the adhesion strength with the electrode active material layer may be improved. The hydrophilic functional group is a polar functional group.

The hydrophilic functional group additionally included in the fluorine-based polymer included in the coating layer may be at least one selected from the group consisting of a carboxylic acid group, a sulfonic acid group, a phosphoric acid group, an acid anhydride group, a hydroxyl group, and salts thereof, but is not necessarily limited thereto. Anything that can be used as a hydrophilic functional group in the technical field is possible.

For example, the introduction of a polar functional group into the fluorine-based polymer included in the coating layer is performed by adding a monomer containing a carboxylic acid group, a sulfonic acid group, a phosphoric acid group, an acid anhydride group and a hydroxyl group and a salt thereof to the fluorine-containing monomer mixture and polymerization It can be carried out by

Monocarboxylic acid and its derivative(s), dicarboxylic acid, these derivatives, etc. are mentioned as a monomer which has a carboxylic acid group. Examples of the monocarboxylic acid include acrylic acid, methacrylic acid, and crotonic acid. Examples of the monocarboxylic acid derivative include 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, α-chloro-β-E-methoxy acrylic acid, and β-diaminoacrylic acid. can As dicarboxylic acid, maleic acid, fumaric acid, itaconic acid, etc. are mentioned. Examples of the dicarboxylic acid derivative include methyl allyl maleate such as methyl maleic acid, dimethyl maleic acid, phenyl maleic acid, chloromaleic acid, dichloro maleic acid and fluoromaleic acid, diphenyl maleate, nonyl maleate, decyl maleate, dodecyl maleate, octadecyl maleate, and maleic acid. maleic acid salts such as fluoroalkyl; and the like. Moreover, an acid anhydride which produces|generates a carboxyl group by hydrolysis can also be used. Examples of the acid anhydride of dicarboxylic acid include maleic anhydride, acrylic anhydride, methyl maleic anhydride, and dimethyl maleic anhydride. In addition, monoethyl maleate, diethyl maleate, monobutyl maleate, dibutyl maleate, monoethyl fumarate, diethyl fumarate, monobutyl fumarate, dibutyl fumarate, monocyclohexyl fumarate, dicyclohexyl fumarate, mono itaconic acid and monoesters and diesters of α,β-ethylenically unsaturated polycarboxylic acids such as ethyl, diethyl itaconate, monobutyl itaconate, and dibutyl itaconate.

Examples of the monomer having a sulfonic acid group include vinylsulfonic acid, methylvinylsulfonic acid, (meth)allylsulfonic acid, styrenesulfonic acid, (meth)acrylic acid-2-sulfonate ethyl, 2-acrylamide-2-methylpropanesulfonic acid, 3-allyloxy-2- Hydroxypropanesulfonic acid etc. are mentioned.

Examples of the monomer having a phosphoric acid group include 2-(meth)acryloyloxyethyl phosphate, methyl-2-(meth)acryloyloxyethyl phosphate, and ethyl-(meth)acryloyloxyethyl phosphate.

Examples of the monomer having a hydroxyl group include ethylenically unsaturated alcohols such as (meth)allyl alcohol, 3-butene-1-ol, and 5-hexen-1-ol; Acrylic acid-2-hydroxyethyl, acrylic acid-2-hydroxypropyl, methacrylic acid-2-hydroxyethyl, methacrylic acid-2-hydroxypropyl, di-2-hydroxyethyl maleate, di4-hydroxy maleate alkanol esters of ethylenically unsaturated carboxylic acids such as butyl and di2-hydroxypropyl itaconic acid; is represented by the general formula CH ₂ =CR ¹ -COO-(C _n H _{2 n} O) _m -H (m is an integer from 2 to 9, n is an integer from 2 to 4, R ¹ represents hydrogen or a methyl group) esters of polyalkylene glycol and (meth)acrylic acid; Monohydroxy esters of dicarboxylic acids such as 2-hydroxyethyl-2'-(meth)acryloyloxyphthalate and 2-hydroxyethyl-2'-(meth)acryloyloxysuccinate (meth)acrylic acid esters; vinyl ethers such as 2-hydroxyethyl vinyl ether and 2-hydroxypropyl vinyl ether; (meth) allyl-2-hydroxyethyl ether, (meth) allyl-2-hydroxypropyl ether, (meth) allyl-3-hydroxypropyl ether, (meth) allyl-2-hydroxybutyl ether, (meth) ) mono(meth)allyl ethers of alkylene glycols such as allyl-3-hydroxybutyl ether, (meth)allyl-4-hydroxybutyl ether, and (meth)allyl-6-hydroxyhexyl ether; polyoxyalkylene glycol (meth) monoallyl ethers such as diethylene glycol mono (meth) allyl ether and dipropylene glycol mono (meth) allyl ether; Halogen of (poly)alkylene glycol, such as glycerol mono(meth)allyl ether, (meth)allyl-2-chloro-3-hydroxypropyl ether, and (meth)allyl-2-hydroxy-3-chloropropyl ether and mono (meth) allyl ether of a hydroxy substituent; mono(meth)allyl ethers of polyhydric phenols such as eugenol and isoeugenol and halogen-substituted products thereof; (meth)allylthioethers of alkylene glycols, such as (meth)allyl-2-hydroxyethyl thioether and (meth)allyl-2-hydroxypropyl thioether; and the like.

Among them, in terms of excellent adhesion to the electrode active material layer, the hydrophilic group may be a carboxylic acid group or a sulfonic acid group. In particular, a carboxylic acid group may be used in that transition metal ions eluted from the positive electrode active material layer can be collected with high efficiency.

The content of the repeating unit including the hydrophilic functional group included in the fluorine-based polymer included in the coating layer may be 10 mol% or less. For example, the content of the repeating unit including a hydrophilic functional group included in the fluorine-based polymer included in the coating layer may be greater than 0 to 9 mol% or less. For example, the content of the repeating unit including a hydrophilic functional group included in the fluorine-based polymer included in the coating layer may be greater than 0 to 8 mol% or less. For example, the content of the repeating unit including a hydrophilic functional group included in the fluorine-based polymer included in the coating layer may be greater than 0 to 7 mol% or less. For example, the content of the repeating unit including a hydrophilic functional group included in the fluorine-based polymer included in the coating layer may be greater than 0 to 5 mol% or less. When the content of the repeating unit including the hydrophilic functional group is too large, the flexibility of the electrode assembly may be reduced.

For example, the fluorine-based polymer included in the coating layer may be a fluorine-based copolymer. The fluorine-based copolymer may include a repeating unit derived from vinylidene fluoride, a repeating unit derived from hexafluoropropylene, and a repeating unit derived from a carboxyl group-containing monomer. For example, in the fluorine-based copolymer, the content of the repeating unit derived from hexafluoropropylene is 4 wt% to 10 wt%, and the content of the repeating unit derived from the carboxyl group-containing monomer is 1 wt% to 7 wt%, The remaining amount may include a repeating unit derived from vinylidene fluoride. For example, in the fluorine-based copolymer, 4 wt% to 10 wt% of a repeating unit derived from hexafluoropropylene, 1 wt% to 7 wt% of a repeating unit derived from a carboxyl group-containing monomer, and a repeating unit derived from vinylidene fluoride 83 It may contain from % to 94% by weight. By using the composite separator in which the fluorine-based copolymer having such a repeating unit composition is applied to the coating layer, the binding force between the composite separator and the electrode (positive and negative electrode) is improved, and the thickness ratio (T1/T2) of the composite separator in a certain range can be obtained. .

The weight average molecular weight of the fluorine-based polymer included in the coating layer may be 100,000 daltons or more. For example, the weight average molecular weight of the fluorine-based polymer included in the coating layer may be 100,000 to 1,500,000 daltons. For example, the weight average molecular weight of the fluorine-based polymer included in the coating layer may be 300,000 to 1,500,000 daltons. For example, the weight average molecular weight of the fluorine-based polymer included in the coating layer may be 500,000 to 1,500,000 daltons. For example, the weight average molecular weight of the fluorine-based polymer included in the coating layer may be 1,000,000 to 1,500,000 daltons. The weight average molecular weight is a polystyrene conversion value by gel permeation chromatography. Adhesion to the positive electrode active material layer may be further improved within the weight average molecular weight range of the fluorine-based polymer included in the coating layer. When the weight average molecular weight of the fluorine-based polymer included in the coating layer is too small, the adhesion is reduced, and when the weight average molecular weight is large, the preparation of the binder composition is not easy.

The adhesive strength between the composite separator and the negative electrode may be 0.01 to 1.4 kgf/mm. For example, the adhesive strength between the composite separator and the negative electrode may be 0.1 to 1.0 kgf/mm. For example, the adhesive strength between the composite separator and the negative electrode may be 0.2 to 0.8 kgf/mm. In the above adhesive strength range, the volume change of the lithium battery can be effectively suppressed. For the measurement of adhesive strength, refer to the method disclosed in the adhesive force test of Evaluation Example 3.

The air permeability of the composite separator may be 170 to 900 sec/100ml. For example, the air permeability of the composite separator may be 170 to 800 sec/100ml. For example, the air permeability of the composite separator may be 170 to 700 sec/100ml. For example, the air permeability of the composite separator may be 170 to 600 sec/100ml. For example, the air permeability of the composite separator may be 170 to 500 sec/100ml. For example, the air permeability of the composite separator may be 170 to 400 sec/100ml. For example, the air permeability of the composite separator may be 170 to 300 sec/100ml. For example, the air permeability of the composite separator may be 170 to 250 sec/100ml. An increase in the internal resistance of the lithium battery in the air permeability range can be effectively suppressed. For the air permeability measurement, refer to the method disclosed in the air permeability evaluation of Evaluation Example 4.

A lithium battery according to another embodiment includes the above-described electrode assembly, and the electrode assembly is wound in the form of a jelly roll. Since the lithium battery includes the above-described composite separator, adhesion between the electrodes (positive electrode and negative electrode) and the composite separator is increased, and thus volume change during charging and discharging of the lithium battery can be suppressed. Accordingly, deterioration of the lithium battery accompanying the volume change of the lithium battery is suppressed, and thus the lifespan characteristics of the lithium battery may be improved.

The first portion of the composite separator is a portion on which the positive electrode active material layer and the negative electrode active material layer are disposed, and the second portion of the composite separator is a portion where the positive electrode active material layer and the negative electrode active material layer are not disposed, for example, a terminal portion of the composite separator.

A lithium battery according to another embodiment includes a positive electrode; cathode; organic electrolyte; and the above-described separator between the positive electrode and the negative electrode. By including the separator, stability and lifespan characteristics of a lithium battery may be improved.

The lithium battery may be manufactured, for example, by the following method.

First, an anode active material composition in which an anode active material, a conductive material, a binder, and a solvent are mixed is prepared. The negative electrode active material composition is directly coated on a metal current collector to prepare a negative electrode plate. Alternatively, the negative electrode active material composition may be cast on a separate support, and then a film peeled from the support may be laminated on a metal current collector to manufacture a negative electrode plate. The negative electrode is not limited to the above-mentioned types and may be of a type other than the above-mentioned types.

The negative active material may be a non-carbon-based material. For example, the negative active material includes at least one selected from the group consisting of a metal capable of forming an alloy with lithium, an alloy of a metal capable of forming an alloy with lithium, and an oxide of a metal capable of forming an alloy with lithium can do.

For example, the metal alloyable with lithium is Si, Sn, Al, Ge, Pb, Bi, Sb Si-Y alloy (wherein Y is an alkali metal, an alkaline earth metal, a group 13-16 element, a transition metal, a rare earth element, or It may be a combination element thereof, but not Si), a Sn-Y alloy (wherein Y is an alkali metal, alkaline earth metal, group 13-16 element, transition metal, rare earth element, or a combination element thereof, not Sn), etc. . The element Y includes Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ge, P, As, Sb, Bi, S, Se, Te, Po, or a combination thereof.

For example, the transition metal oxide may be lithium titanium oxide, vanadium oxide, lithium vanadium oxide, or the like.

For example, the non-transition metal oxide may be SnO ₂ , SiO _x (0<x<2), or the like.

Specifically, the negative active material is Si, Sn, Pb, Ge, Al, SiOx (0<x≤2), SnOy (0<y≤2), Li ₄ Ti ₅ O ₁₂ , TiO ₂ , LiTiO ₃ , Li ₂ Ti ₃ O ₇ It may be at least one selected from the group consisting of, but is not necessarily limited thereto, and any non-carbon-based negative active material used in the art may be used.

In addition, a composite of the non-carbon-based negative active material and the carbon-based material may be used, and a carbon-based negative active material may be additionally included in addition to the non-carbon-based material.

The carbon-based material may be crystalline carbon, amorphous carbon, or a mixture thereof. The crystalline carbon may be graphite, such as non-shaped, plate-shaped, flake-shaped, spherical or fibrous natural graphite or artificial graphite, and the amorphous carbon is soft carbon (low-temperature calcined carbon). Alternatively, it may be hard carbon, mesophase pitch carbide, calcined coke, or the like.

As the conductive material, acetylene black, ketjen black, natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, copper, nickel, aluminum, silver metal powder such as silver, metal fiber, etc. can be used, In addition, one type or a mixture of one or more conductive materials such as polyphenylene derivatives may be used, but the present invention is not limited thereto, and any conductive material that can be used as a conductive material in the art may be used. In addition, the above-described crystalline carbon-based material may be added as a conductive material.

Examples of the binder include vinylidene fluoride/hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene and mixtures thereof, or styrene butadiene rubber-based polymer. may be used, but is not limited thereto, and any binder that can be used as a binder in the art may be used.

As the solvent, N-methylpyrrolidone, acetone, or water may be used, but the solvent is not limited thereto and any solvent that can be used in the art may be used.

The content of the anode active material, the conductive material, the binder, and the solvent is a level commonly used in a lithium battery. At least one of the conductive material, the binder, and the solvent may be omitted depending on the use and configuration of the lithium battery.

Meanwhile, the binder used for manufacturing the negative electrode may be the same as the binder composition included in the coating layer of the separator.

Next, a positive electrode active material composition in which a positive electrode active material, a conductive material, a binder, and a solvent are mixed is prepared. The positive electrode active material composition is directly coated and dried on a metal current collector to prepare a positive electrode plate. Alternatively, the positive electrode active material composition may be cast on a separate support, and then a film peeled from the support may be laminated on a metal current collector to manufacture a positive electrode plate.

The cathode active material may include at least one selected from the group consisting of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, and lithium manganese oxide, but is not necessarily limited thereto. Any positive electrode active material available in can be used.

For example, Li _a A _1-b B _b D ₂ (wherein 0.90 ≤ a ≤ 1.8, and 0 ≤ b ≤ 0.5); Li _a E _1-b B _b O _2-c D _c (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); LiE _2-b B _b O _4-c D _c (wherein 0 ≤ b ≤ 0.5 and 0 ≤ c ≤ 0.05); Li _a Ni _1-bc Co _b B _c D _α (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); Li _a Ni _1-bc Co _b B _c O _2-α F _α (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _1-bc Co _b B _c O _2-α F ₂ (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _1-bc Mn _b B _c D _α (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); Li _a Ni _1-bc Mn _b B _c O _2-α F _α (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _1-bc Mn _b B _c O _2-α F ₂ (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _b E _c G _d O ₂ (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0.001 ≤ d ≤ 0.1); Li _a Ni _b Co _c Mn _d GeO ₂ (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, 0.001 ≤ e ≤ 0.1); Li _a NiG _b O ₂ (in the above formula, 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li _a CoG _b O ₂ (in the above formula, 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li _a MnG _b O ₂ (in the above formula, 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li _a Mn ₂ G _b O ₄ (in the above formula, 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); QO ₂ ; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LiIO ₂ ; LiNiVO ₄ ; Li _(3-f) J ₂ (PO ₄ ) ₃ (0 ≤ f ≤ 2); Li _(3-f) Fe ₂ (PO ₄ ) ₃ (0 ≤ f ≤ 2); A compound represented by any one of the formulas of LiFePO ₄ may be used:

In the above formula, A is Ni, Co, Mn, or a combination thereof; B is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P, or a combination thereof; E is Co, Mn, or a combination thereof; F is F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; Q is Ti, Mo, Mn, or a combination thereof; I is Cr, V, Fe, Sc, Y, or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

Of course, a compound having a coating layer on the surface of the compound may be used, or a mixture of the compound and a compound having a coating layer may be used. The coating layer may include a coating element compound of oxide or hydroxide of the coating element, oxyhydroxide of the coating element, oxycarbonate of the coating element, or hydroxycarbonate of the coating element. The compound constituting these coating layers may be amorphous or crystalline. As the coating element included in the coating layer, Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof may be used. In the coating layer forming process, any coating method may be used as long as the compound can be coated by a method that does not adversely affect the physical properties of the positive electrode active material (eg, spray coating, dipping method, etc.) by using these elements in the compound. Since the content can be well understood by those engaged in the field, a detailed description thereof will be omitted.

For example, LiNiO ₂ , LiCoO ₂ , LiMn _x O _2x (x=1, 2), LiNi _1-x Mn _x O ₂ (0<x<1), LiNi _1-x- yCo _x Mn _y O ₂ ( 0≤x≤0.5, 0≤y≤0.5), LiFeO ₂ , V ₂ O ₅ , TiS, MoS, etc. may be used.

In the cathode active material composition, the same conductive material, binder and solvent may be used as in the case of the anode active material composition. Meanwhile, it is also possible to form pores in the electrode plate by further adding a plasticizer to the positive electrode active material composition and/or the negative electrode active material composition.

The content of the positive electrode active material, the conductive material, the general binder, and the solvent is at a level commonly used in a lithium battery. At least one of the conductive material, the general binder, and the solvent may be omitted depending on the use and configuration of the lithium battery.

Meanwhile, the binder used for manufacturing the positive electrode may be the same as the binder composition included in the coating layer of the separator.

Next, the above-described composite separator is disposed between the positive electrode and the negative electrode.

In an electrode assembly including a positive electrode/separator/negative electrode, the separator disposed between the positive electrode and the negative electrode includes a first portion in contact with the electrode active material layer as described above; and a second portion not in contact with the electrode active material layer, wherein a ratio (T1/T2) of the thickness (T1) of the first portion and the thickness (T2) of the second portion is T1/T2<0.97. is a separator.

The composite separator may be separately prepared and disposed between the positive electrode and the negative electrode. Alternatively, in the composite separator, after winding an electrode assembly including a positive electrode/separator/negative electrode in the form of a jelly roll, the jelly roll is accommodated in a battery case or pouch, and the jelly roll is thermally pressed under pressure in the battery case or pouch body accommodated. It can be prepared by pre-charging with softening, hot rolling the filled jelly rolls, cold rolling the filled jelly rolls, and passing through the conversion steps of charging and discharging the filled jelly rolls under pressure. . For a more specific manufacturing method of the composite separator, refer to the following composite separator manufacturing method.

Next, the electrolyte is prepared.

The electrolyte may be in a liquid or gel state.

For example, the electrolyte may be an organic electrolyte. In addition, the electrolyte may be a solid. For example, it may be boron oxide, lithium oxynitride, etc., but is not limited thereto, and any solid electrolyte that can be used as a solid electrolyte in the art may be used. The solid electrolyte may be formed on the negative electrode by a method such as sputtering.

For example, an organic electrolyte may be prepared. The organic electrolyte may be prepared by dissolving a lithium salt in an organic solvent.

The organic solvent may be used as long as it can be used as an organic solvent in the art. For example, propylene carbonate, ethylene carbonate, fluoroethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, dibutyl carbonate , benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, dioxolane, 4-methyldioxolane, N,N-dimethylformamide, dimethylacetamide, dimethyl sulfoxide , dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, diethylene glycol, dimethyl ether, or mixtures thereof.

The lithium salt may also be used as long as it can be used as a lithium salt in the art. For example, LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li(CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiAlO ₂ , LiAlCl ₄ , LiN(C _x F _2x+1 SO ₂ )(C _y F _2y+1 SO ₂ ) (where x and y are natural numbers), LiCl, LiI, or a mixture thereof.

As shown in FIG. 2 , the lithium battery 1 includes a positive electrode 3 , a negative electrode 2 , and a separator 4 . The above-described positive electrode 3 , negative electrode 2 , and separator 4 are wound or folded in the form of a jelly roll and accommodated in the battery case 5 . Then, an organic electrolyte is injected into the battery case 5 and sealed with a cap assembly 6 to complete the lithium battery 1 . The battery case may have a cylindrical shape, a prismatic shape, a thin film type, or the like. For example, the lithium battery may be a thin film battery. The lithium battery may be a lithium ion battery. The lithium battery may be a lithium polymer battery.

A separator may be disposed between the positive electrode and the negative electrode to form an electrode assembly. After the electrode assembly is laminated in a bi-cell structure or wound in the form of a jelly roll, it is impregnated with an organic electrolyte, and the obtained result is accommodated in a pouch and sealed to complete a lithium ion polymer battery.

In addition, a plurality of the electrode assembly is stacked to form a battery pack, and the battery pack can be used in any device requiring high capacity and high output. For example, it can be used in a laptop, a smartphone, an electric vehicle, and the like.

In particular, the lithium battery is suitable for an electric vehicle (EV) because it has excellent high rate characteristics and lifespan characteristics. For example, it is suitable for a hybrid vehicle such as a plug-in hybrid electric vehicle (PHEV).

A method for manufacturing a composite separator according to another embodiment includes: preparing a jelly roll by winding an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; pre-charging the jelly roll while thermally softening it under pressure; hot rolling the filled jelly roll; cold rolling the filled jelly roll; and a formation step of charging and discharging the charged jelly roll under pressure. The composite separator manufactured by the composite separator manufacturing method includes: a first portion in contact with the electrode active material layer; and a second portion not in contact with the electrode active material layer, wherein a ratio (T1/T2) of the thickness T1 of the first portion to the thickness T2 of the second portion is T1/T2<0.97.

Preparing a jelly roll by winding an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode may be performed in a conventional general method. In the separator interposed between the positive electrode and the negative electrode, the portion in contact with the positive electrode active material layer of the positive electrode and the negative electrode active material layer of the negative electrode is a first portion (eg, a mixture portion), the positive electrode active material layer of the positive electrode and the negative electrode active material layer of the negative electrode The non-contact part is the second part (eg, the uncoated part).

The gel-to-sol transition of the binder including the coating layer disposed on the separator for thermal softening in the initial pre-charging step of thermal softening the jelly roll under pressure It can be initially charged while maintaining a low temperature compared to the temperature. The temperature at which the jelly roll is maintained may be any temperature lower than the transition temperature from the gel to the sol of the binder included in the coating layer disposed on the separator, but may be, for example, 40 to 80°C. . The pressure applied to the jelly roll may be 100 to 300 kgf/cm ² , but is not necessarily limited to this range and may be adjusted according to the required physical properties of the composite separator. The time for which the pressure is applied to the jelly roll may be 0.1 to 10 hours, but is not necessarily limited to this range and may be adjusted according to the required physical properties of the composite separator. For example, the time the pressure is applied to the jelly roll may be 0.1 to 5 hours. For example, the time the pressure is applied to the jelly roll may be 0.1 to 2 hours. Initial charging can be done up to 50% of the SOC.

The hot rolling of the filled jelly roll may be performed at a temperature at which the binder including the coating layer disposed on the separator transitions from gel to sol. For example, the temperature at which the jelly roll is maintained in the hot rolling step may be 70 to 90° C., but is not necessarily limited to this range, and may be determined according to the type of binder included in the coating layer. The pressure applied to the jelly roll in the hot rolling step may be 100 to 250 kgf/cm ² , but is not necessarily limited to this range and may be adjusted according to the required physical properties of the composite separator. The time the pressure is applied to the jelly roll may be less than 180 seconds. For example, the time the pressure is applied to the jelly roll may be 10 to 170 seconds. For example, the time the pressure is applied to the jelly roll may be 10 to 150 seconds. In the step of hot rolling, the binder included in the coating layer undergoes a phase change from gel to sol, thereby increasing adhesion with the electrode active material layer.

The cold rolling of the filled jelly roll may be performed at a temperature lower than the temperature at which the binder including the coating layer disposed on the separator transitions from gel to sol. For example, the temperature at which the jelly roll is maintained in the cold rolling step may be 40° C. or less, but is not necessarily limited to this range, and may be determined according to the type of binder included in the coating layer. The pressure applied to the jelly roll in the cold rolling step may be 100 to 250 kgf/cm ² , but is not necessarily limited to this range and may be adjusted according to the required physical properties of the composite separator. The time the pressure is applied to the jelly roll may be less than 120 seconds. For example, the time the pressure is applied to the jelly roll may be 10 to 110 seconds. For example, the time for which the pressure is applied to the jelly roll may be 10 to 100 seconds. In the cold rolling step, the adhesion between the binder included in the coating layer and the electrode active material layer may be further strengthened by the anchoring effect.

The formation step of charging and discharging the charged jelly roll under pressure is a temperature lower than the temperature at which the transition from the gel to the sol of the binder including the coating layer disposed on the separator is lower and higher than the cold rolling step. can be performed in For example, the temperature at which the jelly roll is maintained in the pressurization step may be 40 to 70° C., but is not necessarily limited to this range, and may be determined according to the type of binder included in the coating layer. The pressure applied to the jelly roll in the pressurization step may be 100 to 250 kgf/cm ² , but is not necessarily limited to this range and may be adjusted according to the required physical properties of the composite separator. The time for applying pressure to the jelly roll in the pressurization step may be 0.1 to 10 hours, but is not necessarily limited to this range and may be adjusted according to the required physical properties of the composite separator. For example, the time the pressure is applied to the jelly roll may be 0.1 to 5 hours. For example, the time the pressure is applied to the jelly roll may be 0.1 to 2 hours. Charging and discharging may be performed 2 to 7 times in the pressurization step, but it is not necessarily limited to this range and may be adjusted according to the required physical properties of the composite separator. The thickness of the composite separator can be adjusted in the pressurization step.

The composite separator, which has undergone the pressure initial charging step, the hot rolling step, the cold rolling step, and the pressurization step, may include a first portion in contact with the electrode active material layer; and a second portion not in contact with the electrode active material layer, wherein a ratio (T1/T2) of the thickness (T1) of the first portion and the thickness (T2) of the second portion is T1/T2<0.97, Since excellent adhesion and air permeability are provided, energy density per unit volume and charge/discharge characteristics of a lithium battery employing the composite separator are improved.

A method for measuring the thickness of the first portion and the second portion is not particularly limited, and any method that can be used as a method for measuring the thickness of an electrode in the art may be used. For example, the thickness of the first portion and the second portion may be obtained from a cross-sectional image of the high magnification electrode assembly photographed using a scanning electron microscope or a transmission electron microscope.

This creative concept will be described in more detail through the following examples and comparative examples. However, the examples are provided to illustrate the present creative concept, and the scope of the present creative concept is not limited thereto.

(Manufacture of composite separator)

Preparation Example 1: Ceramic ratio (binder/ceramic) 1/3

A composition for forming a coating layer was prepared by mixing 25 parts by weight of a fluorine-based binder with 75 parts by weight of alumina (AES-11, Sumitomo Chemical Co., Ltd.) having an average particle diameter of 0.4 to 0.6 μm (volume basis D50) as inorganic particles. The binder includes a carboxyl group (-COOH) as a hydrophilic group, and is a fluorine-based binder that is a copolymer of vinylidene fluoride and hexafluoropropylene. The degree of swelling of the fluorine-based binder after standing in an electrolyte solution at 45° C. for 24 hours was 138%.

The composition for forming the coating layer was gravure-printed on both sides of a porous polyethylene substrate having a thickness of 7.5 μm to prepare a separator in which a blend coating layer of inorganic particles and a binder having a thickness of 1.5 μm was respectively disposed on both sides of the porous substrate. The thickness of the coating layer was 1.5 μm based on one surface. The thickness of the separator was 10.5 µm.

Preparation Example 2: Ceramic ratio (binder/ceramic) 1/2

A separator was prepared in the same manner as in Preparation Example 1, except that 67 parts by weight of the inorganic particles and 33 parts by weight of the binder were mixed.

Preparation Example 3: Ceramic ratio (binder/ceramic) 1/4.88

A separator was prepared in the same manner as in Preparation Example 1, except that 83 parts by weight of the inorganic particles and 17 parts by weight of the binder were mixed.

Preparation Example 4: Ceramic ratio (binder/ceramic) 1/1

A separator was prepared in the same manner as in Preparation Example 1, except that 50 parts by weight of the inorganic particles and 50 parts by weight of the binder were mixed.

Preparation Example 5: Ceramic Ratio (Binder/Ceramic) 1/8

A separator was prepared in the same manner as in Preparation Example 1, except that 89 parts by weight of the inorganic particles and 11 parts by weight of the binder were mixed.

Comparative Preparation Example 1:

A separator (Asahi, FD511D) in which a ceramic coating layer having a thickness of 2 μm is disposed on one surface of a porous substrate having a thickness of 7 μm, and an acrylic binder layer having a thickness of 0.15 μm is coated on one surface of the ceramic coating layer and the other surface of the porous substrate. It was obtained and used as it is. The degree of swelling after leaving the acrylic binder in an electrolyte solution at 45° C. for 24 hours was 600%.

Comparative Preparation Example 2:

A separator (SK, T14-715CB) in which a ceramic coating layer having a thickness of 2 μm is disposed on one surface of a porous substrate having a thickness of 12 μm was obtained and used as it is.

(Manufacture of lithium battery)

Example 1

(Production of cathode)

After mixing 97% by weight of graphite particles (C1SR, Japanese carbon) having an average particle diameter of 25㎛, 1.5% by weight of a styrene-butadiene rubber (SBR) binder (Zeon) and 1.5% by weight of carboxymethyl cellulose (CMC, NIPPON A&L), distilled water and stirred for 60 minutes using a mechanical stirrer to prepare a negative electrode active material slurry. The slurry was applied on a copper current collector with a thickness of 10 μm using a doctor blade, dried in a hot air dryer at 100° C. for 0.5 hours, dried again under vacuum and 120° C. conditions for 4 hours, and rolled by A negative electrode plate was manufactured.

(Manufacture of anode)

LiCoO ₂ 97% by weight, 1.5% by weight of carbon black powder as a conductive material, and 1.5% by weight of polyvinylidene fluoride (PVdF, SOLVAY) were mixed and added to N-methyl-2-pyrrolidone solvent, and then a mechanical stirrer was used. and stirred for 30 minutes to prepare a cathode active material slurry. The slurry was applied on an aluminum current collector with a thickness of 20 μm using a doctor blade, dried in a hot air dryer at 100° C. for 0.5 hours, dried again under vacuum and 120° C. conditions for 4 hours, and rolled A positive electrode plate was manufactured.

(electrode assembly jelly roll)

The separator prepared in Example 1 was interposed between the positive and negative plates prepared above and then wound to prepare an electrode assembly jelly roll. After inserting the jelly roll into the pouch and injecting the electrolyte, the pouch was vacuum sealed.

As the electrolyte, 1.3M of LiPF ₆ dissolved in a 3/5/2 (volume ratio) mixed solvent of ethylene carbonate (EC)/ethylmethyl carbonate (EMC)/diethyl carbonate (DEC) was used.

The jelly roll inserted in the pouch was pre-cahred up to 50% of the SOC while thermal softening at a temperature of 70° C. for 1 hour while applying a pressure of 250 kgf/cm ² .

The jelly roll was hot-pressed at a temperature of 85° C. for 180 seconds while applying a pressure of 200 kgf/cm ² . In the hot rolling process, as the binder transitions from a gel state to a sol state, an adhesive force is generated between the positive electrode/negative electrode and the separator.

Then, the jelly roll was cold-pressed at a temperature of 22-23° C. for 90 seconds while applying a pressure of 200 kgf/cm ² . During the hot rolling process, the binder was transferred from a sol state to a gel state.

Then, degassing from the pouch, and applying a pressure of 200 kgf / cm ² to the jelly roll, constant current charging at a temperature of 45 ° C. for 1 hour at a current of 0.2 C rate until the voltage reaches 4.3 V and constant voltage charging until the current reached 0.05C while maintaining 4.3V. Then, the formation step was performed by repeating the cycle of discharging at a constant current of 0.2C 5 times until the voltage reached 3.0V during discharging.

Examples 2 to 5

A lithium battery was manufactured in the same manner as in Example 1, except that the separators prepared in Preparation Examples 2 to 5 were respectively used.

Comparative Examples 1 to 2

Lithium batteries were respectively manufactured in the same manner as in Example 1, except that the separators prepared in Comparative Preparation Examples 1 and 2 were respectively used.

Evaluation Example 1: Separator thickness measurement

In the lithium batteries of Examples 1 to 5 and Comparative Examples 1 and 2 that have undergone the chemical conversion step, in the jelly roll stored in the pouch, the separator first region (mixture part) and the second region not in contact with the active material layer ( The thickness of the uncoated region) was measured, and the results are shown in Table 1. In Table 1 below, the thickness of the unused separator is T0, the thickness of the first region of the separator after formation is T1, the thickness of the second region of the separator after formation is T2, and the thickness ratio of the first region and the second region of the separator is T1/T2.

The thickness of the first region and the second region was measured from a scanning electron microscope cross-sectional image of the electrode assembly jelly roll.

T0 [μm] T1 [μm] T2 [μm] T1/T2 Example 1 10.5 9.0 10.2 0.88 Example 2 10.5 8.8 10.1 0.87 Example 3 10.5 9.2 10.3 0.89 Example 4 10.5 8.4 10.0 0.84 Example 5 10.5 9.8 10.3 0.95 Comparative Example 1 9.3 9.0 9.2 0.98 Comparative Example 2 14.0 13.5 13.9 0.99

As shown in Table 1 above, T1/T2 of the composite separators of Examples 1 to 5 was less than 0.97. On the other hand, T1/T2 of the composite separators of Comparative Examples 1 and 2 was 0.98 or more.

In the composite separators of Comparative Examples 1 and 2, the thickness T1 of the first region (mixture part) of the composite separator in contact with the active material layer did not change substantially due to the structure and content of the inorganic particles.

Evaluation Example 2: Measurement of Jelly Roll Electrode Assembly Thickness

The thickness of the jellyroll lithium battery (J1) before initial charging and the thickness (J2) of the jellyroll lithium batteries of Examples 1 to 5 and Comparative Examples 1 and 2 that were 100% SOC after passing through the formation step were measured, respectively, and the results were obtained. It is shown in Table 2 below.

J1 [mm] J2 [mm] Example 1 2.80 3.30 Example 2 2.80 3.28 Example 3 2.80 3.32 Example 4 2.80 3.26 Example 5 2.80 3.48 Comparative Example 1 2.78 3.35 Comparative Example 2 2.87 3.64

As shown in Table 2, the composite separators of Examples 1 to 4 had a thickness of the jelly roll when 100% SOC was charged, which was smaller than the thickness of the jelly roll of Comparative Examples 1 and 2, so the lithium batteries of Examples 1 to 4 were compared. A higher energy density per unit volume may be provided compared to the lithium batteries of Examples 1 and 2 .

Evaluation Example 3: Adhesion (adhesive strength) test between the negative electrode and the composite separator

The jelly rolls were taken out from the pouches of Examples 1 to 5 and Comparative Examples 1 and 2 that had undergone the chemical conversion step, and the adhesion between the negative electrode and the composite separator was evaluated.

As for the adhesion force, a 180° peel test was performed (INSTRON) to measure the adhesion between the negative electrode active material layer and the composite separator. Specifically, after attaching the negative electrode active material layer and the composite separator assembly separated from the jelly roll that has undergone the chemical conversion step to the slide glass with double-sided tape, the adhesive strength measurer measures the adhesive strength (peel strength), which is the force it takes to detach in both directions at 180 degrees. The results are shown in Table 3 below.

Evaluation Example 4: Air permeability test of composite separator

The jelly rolls were taken out from the pouches of Examples 1 to 5 and Comparative Examples 1 and 2 that had undergone the chemical conversion step, and the composite separator was separated to evaluate air permeability.

The air permeability was measured using a Gurley type Densometer (No. 158) manufactured by Toyoseiki according to the JIS Gurley measurement method of the Japanese industrial standard, and the results are shown in Table 3 below.

Air permeability refers to the time (in seconds) it takes for 100 ml of air to pass through a 1 square inch composite separator under constant air pressure.

adhesion
[kgf/mm] breathability
[sec/100cc] Example 1 0.47 195 Example 2 0.55 227 Example 3 0.34 180 Example 4 0.87 430 Example 5 0.04 165 Comparative Example 1 1.51 1049 Comparative Example 2 - 150

As shown in Table 3, the composite separators of Examples 1 to 5 had improved air permeability compared to the composite separator of Comparative Example 1, and improved adhesion compared to the composite separator of Comparative Example 2.

Evaluation Example 5: Evaluation of charging and discharging characteristics (high rate characteristics)

The lithium battery that had undergone the formation step was charged with a constant current at 25° C. with a current of 0.2C rate until the voltage reached 4.45V (vs. Li), and was charged with a constant voltage until the current reached 0.01C while maintaining 4.45V. . Then, it was discharged at a constant current of 0.2C until the voltage reached 3.0V (vs. Li) during discharge. (1st cycle)

Subsequently, the lithium battery was charged with a constant current at 25° C. at a rate of 2.0C until the voltage reached 4.45V (vs. Li), and was charged with a constant voltage until the current reached 0.01C while maintaining 4.45V. Then, it was discharged at a constant current of 2.0C until the voltage reached 3.0V (vs. Li) during discharge. (Second cycle)

Some of the results of the charging and discharging experiments are shown in Table 4 below. The high rate characteristic is expressed by Equation 1 below.

<Equation 1>

High rate characteristic [%] = [2C (second cycle) discharge capacity/0.2C (first cycle) discharge capacity] × 100

High rate characteristic [%] Example 1 74.2 Example 2 72.7 Example 3 75.3 Example 4 50.4 Example 5 77.5 Comparative Example 1 70.4 Comparative Example 2 78.3

As shown in Table 4, the lithium batteries of Examples 1 to 3 and Example 5 had improved high-rate characteristics compared to the lithium battery of Comparative Example 1.

Although the lithium battery of Comparative Example 2 had excellent high-rate characteristics, as shown in Table 2 above, the adhesion to the negative electrode was poor.

Evaluation Example 6: Evaluation of charging and discharging characteristics (room temperature life characteristics)

The lithium battery that had undergone the formation step was charged with a constant current at 25° C. at a rate of 0.7 C until the voltage reached 4.35 V (vs. Li), and was charged with a constant voltage until the current reached 0.025 C while maintaining 4.35 V. . Then, the cycle of discharging at a constant current of 1.0C was repeated 500 times until the voltage reached 3.0V (vs. Li) during discharging.

Some of the results of the charging and discharging experiments are shown in Table 5 below. The room temperature capacity retention rate is expressed by Equation 2 below.

<Equation 2>

Room temperature capacity retention rate [%] = [discharge capacity at 500 ^th cycle/1 discharge capacity at ^st cycle] × 100

Room temperature capacity retention [%] Example 1 95.8 Example 2 95.2 Example 3 95.9 Example 4 92.3 Example 5 86.4 Comparative Example 1 78.6 Comparative Example 2 32.8

As shown in Table 5, the lithium batteries of Examples 1 to 5 had improved room temperature lifespan characteristics compared to the lithium batteries of Comparative Examples 1-2.

Evaluation Example 7: Evaluation of charging and discharging characteristics (high temperature life characteristics)

The lithium battery that had undergone the formation step was charged with a constant current at 45° C. at a rate of 0.7 C until the voltage reached 4.35 V (vs. Li), and was charged at a constant voltage until the current reached 0.025 C while maintaining 4.35 V. . Then, the cycle of discharging at a constant current of 1.0C was repeated 500 times until the voltage reached 3.0V (vs. Li) during discharging.

Some of the results of the charging and discharging experiments are shown in Table 6 below. The high-temperature capacity retention rate is expressed by the following Equation (2).

<Equation 2>

High-temperature capacity retention rate [%] = [discharge capacity at 500 ^th cycle/1 discharge capacity at ^st cycle] x 100

High temperature capacity retention rate [%] Example 1 92.9 Example 2 93.0 Example 3 93.1 Example 4 92.5 Example 5 55.3 Comparative Example 1 90.6 Comparative Example 2 32.7

As shown in Table 5, the lithium batteries of Examples 1 to 5 had improved high-temperature lifespan characteristics compared to the lithium batteries of Comparative Examples 1 and 2.

Claims (18)

a first portion in contact with the positive electrode active material layer and the negative electrode active material layer; and
It includes a second portion not in contact with the positive electrode active material layer and the negative electrode active material layer,
a composite separator in which a ratio (T1/T2) of the thickness T1 of the first part to the thickness T2 of the second part is 0.91<T1/T2<0.97;
a positive electrode including the positive electrode active material layer disposed on a first portion of one surface of the composite separator; and
a negative electrode including the negative electrode active material layer disposed on a first portion of the other surface of the composite separator; and
An electrode assembly in which the anode active material layer includes a carbon-based anode active material. The electrode assembly according to claim 1, wherein a ratio (T1/T2) of the thickness (T1) of the first part to the thickness (T2) of the second part is 0.91<T1/T2<0.95. The method according to claim 1, wherein the composite separator comprises:
porous substrate; and a coating layer disposed on at least one surface of the porous substrate,
An electrode assembly in which the coating layer includes a binder and a filler. The electrode assembly according to claim 3, wherein the coating layer is disposed on both surfaces of the porous substrate. The electrode assembly according to claim 4, wherein the coating layers disposed on both surfaces have the same composition. The electrode assembly of claim 3 , wherein the coating layer includes a blend of a binder and a filler. The electrode assembly according to claim 3, wherein the content of the filler is 90% or less based on the total weight of the binder and the filler in the coating layer. The electrode assembly according to claim 3, wherein a ratio of the binder to the filler is 1:2 to 1:6. The electrode assembly according to claim 3, wherein the swelling (swelling) is 250% or less after the binder is left in the electrolyte at 45°C for 24 hours. The electrode assembly according to claim 3, wherein the binder is a fluorine-based polymer. The electrode assembly according to claim 3, wherein the binder is a copolymer. The electrode assembly of claim 3 , wherein the binder includes a hydrophilic functional group. The electrode assembly according to claim 3, wherein the binder comprises a copolymer including a repeating unit derived from vinylidene fluoride, a repeating unit derived from hexafluoropropylene, and a repeating unit derived from a carboxyl group-containing monomer. The method according to claim 13, wherein the content of the repeating unit derived from hexafluoropropylene in the copolymer is 4 wt% to 10 wt%, and the content of the repeating unit derived from the carboxyl group-containing monomer is 1 wt% to 7 wt% electrode assembly. The electrode assembly according to claim 1, wherein the composite separator has a peel strength of 0.1 to 1.4 kgf/mm with respect to the negative electrode. The electrode assembly of claim 1, wherein the composite separator has a permeability of 170 to 400 sec/100ml. 17. It comprises the electrode assembly according to any one of claims 1 to 16,
A lithium battery in which the electrode assembly is wound in the form of a jelly roll. 17. A method of manufacturing an electrode assembly according to any one of claims 1 to 16, comprising:
Preparing a jelly roll by winding an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode;
pre-charging the jelly roll while thermally softening it under pressure;
hot rolling the filled jelly roll;
cold rolling the filled jelly roll; and
A method of manufacturing an electrode assembly comprising a; charging and discharging the charged jelly roll under pressure.

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