KR102049438B1 - Electrode having dual layer structure, method for preparing thereof and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention is an electrode current collector; An intermediate layer formed on at least one surface of the electrode current collector; And an electrode active material layer formed on the intermediate layer, wherein the intermediate layer includes a first binder and a conductive material, the electrode active material layer includes a second binder, a conductive material and an electrode active material, and the first binder is crosslinked. The present invention relates to an electrode having a double layer structure, a method for preparing the same, and a lithium secondary battery including the same.

Description

Electrode having dual layer structure, method for preparing same, and lithium secondary battery comprising same

The present invention is an electrode current collector; An intermediate layer formed on at least one surface of the electrode current collector; And an electrode active material layer formed on the intermediate layer, wherein the intermediate layer includes a first binder and a conductive material, the electrode active material layer includes a second binder, a conductive material, and an electrode active material, and the first binder is crosslinked. The present invention relates to an electrode having a double layer structure, a method for preparing the same, and a lithium secondary battery including the same.

In response to the rapid development of the communication industry such as the electronics industry and various information and communication including mobile communication, in response to the demand for thin and short electronic devices, notebooks, netbooks, tablet PCs, mobile phones, smartphones, PDAs, digital cameras, camcorders, etc. BACKGROUND ART Portable electronic products and communication terminals have been widely used. Accordingly, interest in development of batteries which are driving power sources for these devices has been increasing.

In addition, according to the development of electric vehicles such as hydrogen electric vehicles, hybrid vehicles, fuel cell vehicles, a great deal of attention is focused on the development of high performance, large capacity, high density, high output, high stability, and has a fast charge and discharge speed characteristics The development of batteries is also a big issue.

Batteries, a device that converts chemical energy into electrical energy, are classified into primary cells, secondary batteries, fuel cells, and solar cells, depending on the types and characteristics of basic materials.

Since the dual primary battery produces energy through irreversible reactions such as manganese batteries, alkaline batteries, and mercury batteries, the primary batteries have a large capacity but are not recyclable, and thus have various problems such as energy inefficiency and environmental pollution.

Secondary batteries include lead-acid batteries, nickel-metal hydride batteries, nickel-cadmium batteries, lithium-ion batteries, lithium polymer batteries, and lithium metal batteries, and the charging and discharging are repeated using a reversible interconversion between chemical and electrical energy. As a chemical battery that can be, it operates by a reversible reaction has the advantages of recycling and environmentally friendly.

The secondary battery has four basic components: a positive electrode and a negative electrode, a separator, and an electrolyte.

The anode and the cathode are electrodes in which energy is converted and stored, such as oxidation / reduction, and have positive and negative potentials, respectively. The separator is positioned between the anode and the cathode to maintain electrical insulation and to provide a path for charge movement. In addition, the electrolyte serves as a medium for charge transfer.

Each electrode includes each electrode active material, and each active material used in a lithium secondary battery which is currently receiving the most attention among secondary batteries is as follows.

Most of the positive electrode active material is a material capable of intercalating lithium ions, and lithium cobalt oxide (Li _x CoO ₂ ), lithium nickel oxide (Li _x NiO ₂ ), lithium nickel cobalt oxide (Li _x (NiCo) O ₂ ), Oxides such as lithium nickel cobalt manganese oxide (Li _x (NiCoMn) O ₂ ), spinel-type lithium manganese oxide (Li _x Mn ₂ O ₄ ), manganese dioxide (MnO ₂ ), or lithium iron phosphate (Li _x FePO ₄ ), lithium Olivine type, such as manganese phosphate (Li _x MnPO ₄ ), or NASICON type phosphates, silicates, silicates, sulfates or polymer materials.

As the negative electrode active material, a lithium metal, an alloy thereof, or a compound in which lithium ions may be intercalated may be used. A polymer material or a carbon material may be used, and graphite or egg such as artificial or natural graphite may be used. Graphitizable carbon (hard-carbon), or graphitizable carbon (soft-carbon), carbon nanotube (CNT), carbon nanofiber (CNF), carbon nano Carbon based such as wall (carbon nonawall, CNW) and the like can be used.

The electrode can generally be prepared by applying an electrode active material slurry on an electrode current collector and drying to form an electrode active material layer. The electrode active material slurry generally contains other additives such as an electrode active material, a conductive material, a binder, and a dispersion medium. It is included. Specifically, the electrode may be manufactured by weighing and mixing the materials constituting the electrode active material slurry, coating and drying the electrode on a current collector, and then rolling. .

As described above, the electrode generally has a structure of an electrode current collector and an electrode active material layer formed on the electrode current collector, or includes a binder and a conductive material between the electrode current collector and the electrode active material layer in order to increase the performance of the electrode. It has a structure in which an intermediate layer is further formed.

However, in the case of the electrode having the intermediate layer as described above, the network path between the conductive materials is broken by the expansion of the binder occurring at a predetermined temperature or more, and a short circuit may occur, thereby degrading the performance of the battery including the electrode. Therefore, there is a need for the development of high output high stability electrodes.

KR 10-2011-0111236 A

The present invention has been made to solve the above problems, and an object of the present invention is to provide an electrode having a double layer structure including an intermediate layer containing a cross-linked polyolefin resin, the short circuit of the conductive material is prevented.

Another object of the present invention is to provide a method of manufacturing the electrode of the double layer structure.

Still another object of the present invention is to provide a lithium secondary battery including the electrode.

In order to solve the above problems, the present invention is an electrode current collector; An intermediate layer formed on at least one surface of the electrode current collector; And an electrode active material layer formed on the intermediate layer, wherein the intermediate layer includes a first binder and a conductive material, the electrode active material layer includes a second binder, a conductive material, and an electrode active material, and the first binder is crosslinked. The present invention provides an electrode having a double layer structure, which is a polyolefin resin.

In addition, the present invention comprises the steps of preparing a conductive material pre-dispersion slurry (step 1); Coating the conductive material line dispersion slurry on at least one surface of an electrode current collector to form an intermediate layer including a first binder (step 2); And forming an electrode active material layer by coating an electrode active material slurry on the intermediate layer (step 3), wherein the first binder is a cross-linked polyolefin-based resin. to provide.

In addition, the present invention provides a lithium secondary battery including the electrode of the double layer structure.

The electrode having a double layer structure according to the present invention uses the polyolefin resin crosslinked with the first binder included in the intermediate layer so that the first binder itself is broken at a high temperature (eg, 130 ° C. to 150 ° C.) (zipper bag effect). Short circuit of the conductive material due to expansion of the binder can be prevented.

The following drawings, which are attached to this specification, illustrate exemplary embodiments of the present invention, and together with the contents of the present invention serve to further understand the technical idea of the present invention, the present invention is limited to the matters described in such drawings. It should not be construed as limited.
Figure 1 schematically shows a short circuit phenomenon of the conductive material due to the expansion of the binder in the electrode according to the prior art.
2 is a graph showing the resistance characteristic behavior by heat of a lithium secondary battery including a positive electrode having a double layer structure having an intermediate layer including a cross-linked polyolefin-based resin according to an embodiment of the present invention.

Hereinafter, the present invention will be described in more detail to aid in understanding the present invention.

The terms or words used in this specification and claims should not be construed as being limited to the common or dictionary meanings, and the inventors may appropriately define the concept of terms in order to best describe their invention. It should be interpreted as meaning and concept corresponding to the technical idea of the present invention based on the principle that the present invention.

The present invention is an electrode current collector; Provided is a double layered electrode in which an intermediate layer and an electrode active material layer are sequentially stacked.

An electrode of the dual layer structure according to an embodiment of the present invention is an electrode current collector; An intermediate layer formed on at least one surface of the electrode current collector; And an electrode active material layer formed on the intermediate layer, wherein the intermediate layer includes a first binder and a conductive material, the electrode active material layer includes a second binder, a conductive material and an electrode active material, and the first binder is crosslinked. It is characterized in that the polyolefin resin.

Here, the first binder and the second binder may be the same or different from each other. That is, the first binder and the second binder may be the same kind of crosslinked polyolefin resin or heterogeneous crosslinked polyolefin resin.

Specifically, the first binder included in the intermediate layer may be a cross-linked polyolefin-based resin, the cross-linked polyolefin-based resin is formed by cross-linking the polyolefin-based resin together with the polyolefin-based resin in the conductive material line dispersion slurry to be described later It may be crosslinked by the included crosslinking agent. The polyolefin-based resin may be one or more selected from the group consisting of polyethylene, polypropylene and modified polypropylene, and the modified polypropylene may be modified by maleic acid.

The crosslinking degree of the crosslinked polyolefin-based resin included in the intermediate layer may be 20 to 80, specifically 30 to 50. Here, a crosslinking degree shows the degree of crosslinking of the said polyolefin resin.

The electrode according to the present invention includes a cross-linked polyolefin-based resin in the intermediate layer, the cross-linked polyolefin resin acts as a PTC (Positive Temperature Coefficient) material to generate a short circuit of the conductive material due to the expansion of the binder (see Fig. 1) Can be prevented. As a result, the lithium secondary battery including the electrode may exhibit high power and high stability.

As described above, the second binder may be a crosslinked polyolefin resin of the same kind as the first binder, or a heterogeneous crosslinked polyolefin resin. In this case, the degree of crosslinking of the second binder may be 20 to 100, and specifically 40 to 95.

In addition, the electrode active material layer may further include a third binder, and the third binder may include, for example, vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HEP) and polyvinylidene fluoride. , Polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, It may be one or more selected from the group consisting of polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butyrene rubber (SBR) and fluorine rubber.

The electrode active material according to the present invention may be a positive electrode active material, and the positive electrode active material is any one selected from the group consisting of oxides of the following Chemical Formulas 1 to 3, and V ₂ O ₅ , TiS, MoS, or a mixture of two or more thereof Can be.

[Formula 1]

Li _{1 + x} [Ni _a Co _b Mn _c ] O ₂ (−0.5 ≦ x ≦ 0.6, 0 ≦ a, b, c ≦ 1, x + a + b + c = 1);

[Formula 2]

LiMn _{2 - x} M _x O ₄ (M is one or more elements selected from the group consisting of Ni, Co, Fe, P, S, Zr, Ti, and Al, 0 ≦ x ≦ 2);

[Formula 3]

Li _{1 + a} Fe _{1 - x} M _x (PO _{4 -b} ) X _b (M is Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn and Y At least one element selected from the group consisting of: X is at least one element selected from the group consisting of F, S, and N, and -0.5 ≤ a ≤ +0.5, 0 ≤ x ≤ 0.5, 0 ≤ b ≤ 0.1)

Specifically, the positive electrode active material is LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li [Ni _a Co _b Mn _c ] O ₂ (0 <a, b, c ≤ 1, a + b + c = 1 And) and LiFePO ₄ It may be one or more selected from the group consisting of.

The intermediate layer according to the present invention may have a thickness of 0.5 μm to 1.5 μm, and the electrode active material layer may have a thickness of 40 μm to 120 μm.

In addition, the present invention provides a method of manufacturing the electrode of the double layer structure.

Method for producing an electrode of the double layer structure according to an embodiment of the present invention comprises the steps of preparing a conductive material pre-dispersion slurry (step 1); Coating the conductive material line dispersion slurry on at least one surface of an electrode current collector to form an intermediate layer including a first binder (step 2); And forming an electrode active material layer including a second binder by coating an electrode active material slurry on the intermediate layer (step 3), wherein the first binder is a crosslinked polyolefin resin.

The electrode according to the present invention may be a positive electrode or a negative electrode. When the electrode is a positive electrode, the electrode active material may be a positive electrode active material, and when the electrode is a negative electrode, the electrode active material may be a negative electrode active material. That is, the manufacturing method of the electrode according to the present invention is not particularly limited to the positive electrode and the negative electrode and can be easily applied to any electrode, and to the electrode active material (for example, positive electrode active material or negative electrode active material) used for the production of each electrode. It is thus possible to produce different electrodes. Specifically, the manufacturing method may be easier to manufacture a positive electrode. Accordingly, the term electrode used in an electrode, an electrode active material, an electrode current collector, and the like, which will be described later, may mean both a positive electrode and a negative electrode unless specifically defined.

Step 1 is a step for producing a highly dispersible conductive material pre-dispersion slurry, the conductive material pre-dispersion slurry may be prepared by adding and mixing a conductive material and a crosslinking agent to the polyolefin resin.

The polyolefin resin, the conductive material and the crosslinking agent may be mixed in a weight ratio of 79: 20: 1 to 90: 5: 5.

The mixing is not particularly limited, but may be performed by high shear mixing. The high shear mixing is not particularly limited, but is performed using a high shear mixer such as a microfludizer, a bead mill, a fil mixer, or a planetary dispersive mixer. It may be, specifically, may be performed under a pressure condition of 20,000 psi to 40,000 psi pressure or a stirring speed of 10,000 rpm to 200,000 rpm.

The polyolefin resin may be as described above.

The conductive material is not particularly limited as long as it is conductive without causing side reactions with other elements of the battery. Examples of the conductive material include graphite such as natural graphite and artificial graphite; Carbon blacks such as carbon black (super-p), 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 whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials, such as a polyphenylene derivative, can be used.

As described above, the crosslinking agent crosslinks the polyolefin-based resin to form a crosslinked polyolefin-based resin, and the degree of crosslinking may be controlled by the coating described below. The crosslinking agent may be one or more selected from the group consisting of phenol resins, melamine resins, epoxy resins, imide resins, and polyethylene glycols.

Step 2 is a step for forming an intermediate layer by coating the conductive material pre-dispersion slurry on at least one surface of the electrode current collector, the coating is applied to at least one surface of the electrode current collector slurry and dried Can be done.

The electrode current collector may be generally used having a thickness of 3 μm to 500 μm, and is not particularly limited as long as it has high conductivity without causing chemical change in the battery. For example, copper, stainless steel, aluminum, nickel , Titanium, calcined carbon, or a surface treated with carbon, nickel, titanium, silver, or the like on the surface of aluminum or stainless steel may be used.

The coating of step 2 may be carried out by applying and drying as described above, the coating is not particularly limited and may be carried out by conventional methods known in the art, for example, the conductive material pre-dispersion slurry is After spraying or dispensing on the whole, it may be performed by uniformly dispersing using a doctor blade or the like. In addition, the method may be performed by a die casting method, a comma coating method, a screen printing method, or the like.

The drying may be performed by heat treatment for 10 hours to 24 hours in the temperature range of 140 ℃ to 160 ℃. The production method according to the present invention may form a cross-linked polyolefin resin by applying a conductive material pre-dispersion slurry containing the polyolefin resin and a crosslinking agent on at least one surface of an electrode current collector and heat treatment it by the drying method, The degree of crosslinking of the crosslinked polyolefin resin may be adjusted according to the heat treatment conditions.

Step 3 is a step for preparing an electrode having a double layer structure by forming an electrode active material layer on the intermediate layer, it may be performed by coating an electrode active material slurry on the intermediate layer.

The electrode active material slurry may include a polyolefin resin, a conductive material, a crosslinking agent, and an electrode active material, or may include a polyolefin resin, a conductive material, a crosslinking agent, a third binder, and an electrode active material. In this case, the electrode active material slurry may be prepared by mixing a polyolefin-based resin, a conductive material and a crosslinking agent to prepare a pre-dispersed solution of the conductive material, and then adding and mixing the electrode active material. The three binders may be mixed together with the conductive material linear dispersion solution.

Specifically, the electrode active material slurry may include a third binder, the electrode active material slurry is a polyolefin resin, a crosslinking agent, a third binder, a conductive material and the electrode active material 0.9: 0.1: 2: 2: 95 to 4.5 It may be included in a weight ratio of: 0.5: 2: 2: 91.

At this time, the third binder is a vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HEP), polyvinylidene fluoride (polyvinylidene fluoride), polyacrylonitrile (polyacrylonitrile), polymethyl meta as described above Polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene- It may be one or more selected from the group consisting of diene monomer (EPDM), sulfonated EPDM, styrene butyrene rubber (SBR) and fluorine rubber.

The electrode according to the present invention may be a positive electrode or a negative electrode as described above, and thus the electrode active material may be a positive electrode active material or a negative electrode active material.

The cathode active material may be as described above.

The negative electrode active material is not particularly limited and may be a carbon material, lithium metal, silicon, tin, or the like, in which lithium ions commonly known in the art may be occluded and released. Preferably, the carbon material may be used, and as the carbon material, both low crystalline carbon and high crystalline carbon may be used. The low crystalline carbon includes soft carbon and hard carbon, and the high crystalline carbon includes natural graphite, kish graphite, pyrolytic carbon, and liquid crystal pitch carbon fiber. high temperature calcined carbon such as mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitch derived cokes.

The conductive material may be as described above, and the electrode active material slurry may further include additives such as a filler and a dispersion medium, as necessary, in addition to the above-described active ingredient.

The filler may be used as necessary to control the expansion of the electrode, if necessary, and is not particularly limited as long as it is a fibrous material without causing chemical change in the battery. For example, an olefin polymer such as polyethylene or polypropylene may be used. ; It may be a fibrous material such as glass fiber, carbon fiber.

The dispersion medium is not particularly limited, but may be, for example, isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or the like.

The coating of step 3 includes an application step and a drying step, the application is not particularly limited and may be carried out by conventional methods known in the art, specifically, may be as described above.

The drying may be performed by heat treatment for 10 hours to 24 hours in the temperature range of 120 ℃ to 140 ℃.

In addition, the present invention provides a lithium secondary battery including the electrode of the double layer structure.

The lithium secondary battery according to an embodiment of the present invention is characterized by including a separator and an electrolyte interposed between the positive electrode, the negative electrode and the positive electrode and the negative electrode.

At this time, any one or more of the positive electrode and the negative electrode may be an electrode of the aforementioned double layer structure.

The separator may be an insulating thin film having high ion permeability and mechanical strength, and may generally have a pore diameter of 0.01 μm to 10 μm and a thickness of 5 μm to 300 μm. Such separators may be made of porous polymer films such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, yetherin / hexene copolymers and polyolefin-based polymers such as ethylene / methacrylate copolymers. It may be used as a lamination or or a conventional porous non-woven fabric, for example, a non-woven fabric made of glass fibers, polyethylene terephthalate fibers of high melting point, etc. may be used, but is not limited thereto.

In addition, the electrolyte may include an organic solvent and a lithium salt commonly used in the electrolyte, and are not particularly limited.

With the lithium salt of the anion is ^{F -, Cl -, I -} , NO 3 -, N (CN) 2 -, BF 4 -, ClO 4 -, PF 6 -, (CF 3) 2 PF 4 -, (CF 3 ^{_{) 3 PF 3 -, (CF}} 3) 4 PF 2 -, (CF 3) 5 PF -, (CF 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO 3 -, (CF 3 SO 2 _{^{) 2 N -, (FSO 2}} ) 2 N -, CF 3 CF 2 (CF 3) 2 CO -, (CF 3 CO 2) 2 CH -, (SF 5) 3 C -, (CF 3 SO 2) 3 _{^{C -, CF 3 (CF 2}} ) 7 SO 3 -, CF 3 CO 2 -, CH 3 CO 2 -, SCN - , and _{(CF 3 CF 2 SO 2)} 2 N - it may be at least one member selected from the group consisting of .

Typical organic solvents include propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, dipropyl carbonate, dimetal sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane and vinylene. It may be one or more selected from the group consisting of carbonate, sulfolane, gamma-butyrolactone, propylene sulfite and tetrahydrofuran.

In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates among the carbonate-based organic solvents, are highly viscous organic solvents, and thus may be preferably used because they dissociate lithium salts in the electrolyte well. Such cyclic carbonates, dimethyl carbonates and diethyl When a low viscosity, low dielectric constant linear carbonate, such as carbonate, is mixed and used in an appropriate ratio, an electrolyte having high electrical conductivity can be prepared, and thus it can be more preferably used.

In addition, the electrolyte may be pyridine, triethyl phosphate, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexa phosphate triamide, nitrobenzene derivative, if necessary, in order to improve charge / discharge characteristics and flame retardancy characteristics. , Sulfur, quinone imine dye, N-substituted oxazolidinone, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol, aluminum trichloride, and the like. . In some cases, the solvent may further include a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride to impart nonflammability, may further include carbon dioxide gas to improve high temperature storage characteristics, and may further include fluoro-ethylene carbonate. ), Propene sulfone (PRS), and fluoro-propylene carbonate (FPC).

In the lithium secondary battery of the present invention, an electrode assembly is formed by disposing a separator between a positive electrode and a negative electrode, and the electrode assembly may be manufactured by putting an electrolyte into a cylindrical battery case or a square battery case. Alternatively, after stacking the electrode assembly, it may be prepared by impregnating it in an electrolyte and sealing the resultant obtained in a battery case.

The battery case used in the present invention may be adopted that is commonly used in the art, there is no limitation on the appearance according to the use of the battery, for example, cylindrical, square, pouch type or coin using a can (coin) type and the like.

The lithium secondary battery according to the present invention may not only be used in a battery cell used as a power source for a small device, but also preferably used as a unit battery in a medium-large battery module including a plurality of battery cells. Preferred examples of the medium and large devices include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, power storage systems, and the like.

Hereinafter, the present invention will be described in more detail with reference to the following examples and experimental examples. However, the following Examples and Experimental Examples are provided to illustrate the present invention, and the scope of the present invention is not limited only to these examples.

Example

Microfluluene of polyethylene (density: 0.97 g / cm ³ , average particle diameter: 0.5 μm), epoxy resin (DER ^TM 317, DOW Chem.) And denka black (BET = 60 m ² / g, DBP = 200 ml / 100 g) It was dispersed under a pressure of 25,000 psi using a die (MN400BF, Micro Knox Inc.) and applied on an aluminum thin film with a thickness of 1.5 ㎛. In this case, the polyethylene, epoxy resin and denka black were used in a weight ratio of 79: 1: 20. Thereafter, vacuum drying was performed at 120 ° C. for 10 hours to form an intermediate layer on the aluminum thin film.

Polyethylene (density: 0.97 g / cm ³ , average particle diameter: 0.5 μm), epoxy resin (DER ^TM 317, DOW Chem.), Polyvinylidene fluoride (PVDF) and denka black (BET = 60 m ² / g, DBP = 200 ml / 100 g) was mixed to prepare a conductive material predispersion solution, and LiCoO ₂ was added to prepare a cathode active material slurry. At this time, the positive electrode active material slurry contained polyethylene, epoxy resin, polyvinylidene fluoride, denka black and LiCoO ₂ in a weight ratio of 0.9: 0.1: 2: 2: 95. The prepared positive electrode active material slurry was applied to the intermediate layer with a thickness of 40 μm and vacuum dried at 140 ° C. for 10 hours to prepare a positive electrode having a double layer structure.

Lithium metal was used as a negative electrode, and an electrode assembly was prepared by interposing a cell guard as a separator between the negative electrode and the positive electrode. This was punched into a coin shape, and 1M LiPF6 was dissolved in a mixed solvent of propylene carbonate (PC), ethylmethyl carbonate (EMC) and ethylene carbonate (EC) (PC: EMC: EC = 3: 4: 3). Injected to produce an experimental lithium secondary battery.

Comparative example

Polyethylene (density: 0.97 g / cm ³ , average particle diameter: 0.5 μm), epoxy resin (DER ^TM 317, DOW Chem.) And denka black (BET = 60 m ² / g, DBP = 200 ml / 100 g) were mixed A conductive material predispersion solution was prepared, and LiCoO ₂ was added to prepare a cathode active material slurry. At this time, the positive electrode active material slurry contained denka black and LiCoO ₂ in a weight ratio of 2: 1. The prepared positive electrode active material slurry was applied to a positive electrode current collector to a thickness of 40 ㎛ and vacuum-dried at 140 ℃ for 10 hours to prepare a positive electrode of a double layer structure.

Lithium metal was used as a negative electrode, and an electrode assembly was prepared by interposing a cell guard as a separator between the negative electrode and the positive electrode. This was punched into a coin shape, and 1M LiPF6 was dissolved in a mixed solvent of propylene carbonate (PC), ethylmethyl carbonate (EMC) and ethylene carbonate (EC) (PC: EMC: EC = 2: 3: 5). Injected to produce an experimental lithium secondary battery.

Experimental Example

The effect of PTC (positive temperature coefficient) of each lithium secondary battery produced in the above Examples and Comparative Examples was analyzed. The results are shown in Table 1 and FIG. 2.

In this case, the PTC effect was analyzed by checking the resistance while increasing the temperature of each lithium secondary battery at 5 ℃ / min in the oven to determine the interval (PCT effect) that the resistance is increased rapidly compared to the initial resistance.

division Resistance zoom temperature (℃) Example 130 Comparative example -

As shown in Table 1, the lithium secondary battery of the embodiment including a positive electrode having a double layer structure having an intermediate layer according to the present invention exhibits a PTC effect of a sudden increase in resistance at a specific temperature, while having a positive electrode having no intermediate layer according to the present invention. In the lithium secondary battery of the comparative example including no spikes of resistance was observed in the tested temperature range.

In addition, as shown in Figure 2, the lithium secondary battery of the embodiment according to the present invention shows a resistance increase level of less than 2 times compared to the initial resistance before 130 ℃, the resistance rapidly increases when the time exceeds 130 ℃ Although the PTC effect was clearly shown, the lithium secondary battery of the comparative example did not show a sharp increase in resistance compared to the initial resistance within the experimental temperature conditions.

The above results indicate that a bilayer positive electrode having an intermediate layer including a crosslinked polyolefin-based resin according to the present invention and a lithium secondary battery using the same have self-functional properties that can suppress a short circuit caused by a specific phenomenon occurring in the battery. Indicates that it can.

Claims (27)

Electrode current collectors;
An intermediate layer formed on at least one surface of the electrode current collector; And
An electrode active material layer formed on the intermediate layer,
The intermediate layer includes a first binder and a conductive material,
The electrode active material layer includes a second binder, a third binder, a conductive material and an electrode active material,
The first binder is a crosslinked polyolefin resin,
The second binder is a crosslinked polyolefin resin,
The third binder is vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HEP), polyvinylidene fluoride (polyvinylidene fluoride), polyacrylonitrile (polyacrylonitrile), polymethyl methacrylate (polymethylmethacrylate), Polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), Electrode having a double layer structure, characterized in that at least one member selected from the group consisting of sulfonated EPDM, styrene butyrene rubber (SBR) and fluorine rubber.
The method according to claim 1,
The polyolefin resin is a double layer electrode, characterized in that at least one selected from the group consisting of polyethylene, polypropylene, modified polypropylene.
delete delete delete The method according to claim 1,
The conductive material may be natural graphite, artificial graphite, carbon black (super-p), acetylene black, ketjen black, channel black, furnace black, lamp black, summer black, carbon fiber, metal fiber, carbon fluoride, aluminum, nickel powder, A bilayer electrode, characterized in that at least one member selected from the group consisting of zinc oxide, potassium titanate and titanium oxide.
The method according to claim 1,
The electrode active material is a double layer electrode, characterized in that the positive electrode active material.
The method according to claim 7,
The positive electrode active material is an electrode having a double layer structure, characterized in that the oxide of Formula 1 to Formula 3, and any one selected from the group consisting of V ₂ O ₅ , TiS, MoS or a mixture of two or more thereof.
[Formula 1]
Li _{1 + x} [Ni _a Co _b Mn _c ] O ₂ (−0.5 ≦ x ≦ 0.6, 0 ≦ a, b, c ≦ 1, x + a + b + c = 1);
[Formula 2]
LiMn _{2 - x} M _x O ₄ (M is one or more elements selected from the group consisting of Ni, Co, Fe, P, S, Zr, Ti, and Al, 0 ≦ x ≦ 2);
[Formula 3]
Li _{1 + a} Fe _{1 - x} M _x (PO _{4 -b} ) X _b (M is Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn and Y At least one element selected from the group consisting of: X is at least one element selected from the group consisting of F, S, and N, and -0.5 ≤ a ≤ +0.5, 0 ≤ x ≤ 0.5, 0 ≤ b ≤ 0.1)
The method according to claim 7,
The positive electrode active material is LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li [Ni _a Co _b Mn _c ] O ₂ (0 <a, b, c ≤ 1, a + b + c = 1) and The electrode of the double layer structure, characterized in that at least one member selected from the group consisting of LiFePO ₄ .
The method according to claim 1,
The crosslinking degree of the first binder is 20 to 80, characterized in that the electrode of the double layer structure.
The method according to claim 1,
The crosslinking degree of the first binder is 30 to 50, characterized in that the electrode of the double layer structure.
The method according to claim 1,
The degree of crosslinking of the second binder is 20 to 100, characterized in that the electrode of the double layer structure.
The method according to claim 1,
The degree of crosslinking of the second binder is 40 to 95, characterized in that the electrode of a double layer structure.
The method according to claim 1,
The intermediate layer electrode of a double layer structure, characterized in that having a thickness of 0.5 ㎛ to 1.5 ㎛.
The method according to claim 1,
The electrode active material layer has a thickness of 40 ㎛ to 120 ㎛ electrode, characterized in that the double layer structure.
1) preparing a conductive material pre-dispersion slurry prepared by mixing a polyolefin resin, a conductive material and a crosslinking agent;
2) coating the conductive material line dispersion slurry on at least one surface of an electrode current collector to form an intermediate layer including a first binder; And
3) coating an electrode active material slurry prepared by mixing a polyolefin resin, a conductive material, a crosslinking agent, a third binder and an electrode active material on the intermediate layer to form an electrode active material layer including a second binder and a third binder. Including,
The first binder is a crosslinked polyolefin resin,
The second binder is a crosslinked polyolefin resin,
The third binder is vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HEP), polyvinylidene fluoride (polyvinylidene fluoride), polyacrylonitrile (polyacrylonitrile), polymethyl methacrylate (polymethylmethacrylate), Polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), Method for producing an electrode having a double layer structure, characterized in that at least one member selected from the group consisting of sulfonated EPDM, styrene butyrene rubber (SBR) and fluorine rubber.
delete The method according to claim 16,
The mixing method of the electrode of the double layer structure, characterized in that carried out through high shear mixing.
The method according to claim 16,
The polyolefin resin, the conductive material and the crosslinking agent is a method of manufacturing a double layer electrode, characterized in that mixed in a weight ratio of 79: 20: 1 to 90: 5: 5.
The method according to claim 16,
The coating of step 2) comprises an application step and a drying step,
The drying is a method of manufacturing an electrode having a double layer structure, characterized in that performed by heat treatment for 10 hours to 24 hours in the temperature range of 140 ℃ to 160 ℃.
delete The method according to claim 16,
The electrode active material slurry
A method for producing an electrode having a double layer structure, wherein a polyolefin resin, a crosslinking agent, a third binder, and a conductive material are mixed to prepare a conductive material predispersion solution, and then an electrode active material is added and mixed.
delete delete The method according to claim 16,
The coating of step 3) comprises an application step and a drying step,
The drying is a method for producing an electrode having a double layer structure, characterized in that carried out by heat treatment for 10 to 24 hours in a temperature range of 120 ℃ to 140 ℃.
The method according to claim 16,
The crosslinking agent is a phenol resin, melamine resin, epoxy resin, imide-based resin, polyethylene glycol manufacturing method of a double layer structure, characterized in that at least one member selected from the group consisting of.
A lithium secondary battery comprising the electrode of the double layer structure of claim 1.

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