Electrode for secondary battery and secondary battery including the same

Abstract

The present invention provides an electrode for a secondary battery, comprising: a dry electrode film including an active material, a conductive material, and a fibrillated binder; and a current collector on which the electrode film is laminated; wherein the conductive material includes carbon fiber; and a secondary battery including the electrode.

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0096481, filed on July 22, 2021, and all the contents disclosed in the documents of the corresponding Korean patent application are incorporated herein by reference in their entirety.

[0002] The present invention relates to an electrode for a secondary battery and a secondary battery including the same.

Background Art

[0003] Recently, there has been an increasing interest in energy storage technologies. As the application fields have expanded to mobile phones, camcorders, laptop computers, and even the energy of electric vehicles, efforts in the research and development of electrochemical devices have gradually materialized.

[0004] Electrochemical devices are the most spotlighted fields in such aspects, and among them, the development of rechargeable secondary batteries has become the focus of interest. Recently, in the development of secondary batteries, research and development on new electrode and battery designs have been actively conducted to improve the capacity density and specific energy.

[0005] Among currently commercialized secondary batteries, lithium secondary batteries have attracted attention for their advantages of higher operating voltage and much larger energy density compared to conventional batteries.

[0006] On the other hand, with the expansion and development of the applications of secondary batteries, continuous improvements in reducing the resistance, increasing the capacity, improving mechanical properties, and enhancing productivity of electrodes have been required.

[0007] An electrode for a secondary battery is usually manufactured by laminating an electrode active material layer formed by binding an active material and, if necessary, a conductive material used with a binder on a current collector. Specifically, a method of applying a slurry containing an electrode active material, a binder, a conductive material, etc. on a current collector and removing the solvent by heat or the like is generally used. However, the above method has the disadvantage that the solvent must be removed from the electrode slurry, which reduces the economy and productivity.

[0008] Therefore, in order to improve such disadvantages, a method of manufacturing an electrode without using an electrode slurry has been proposed. That is, after mixing an active material, a binder, and a conductive material without a liquid medium such as a solvent or a dispersion medium, a technique of passing the powder mixture through a rolling roll to manufacture an electrode film has been actively developed. Generally, a binder called "fibrillizable binders" or "fibril-forming binders" is used in such a method. The binder binds the active material and the conductive material while being microfibrillated, enabling the manufacture of a free-standing electrode film. The electrode film manufactured in this way is used for electrode manufacturing by laminating it on a current collector.

[0009] The above conventional method provides various advantages compared to the method of applying an electrode slurry. However, when manufacturing an electrode by the above method, the strength of the electrode film used in the free-standing film is not sufficiently maintained, which acts as a cause for reducing the productivity of the lamination process on the current collector. In particular, due to the development direction of reducing the usage amount of the binder in order to develop a high-capacity and high-efficiency battery, the above problems act as major obstacle factors in the development of secondary batteries.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

[0011] The present invention has been devised to solve the above problems of the prior art, and an object thereof is to provide an electrode for a secondary battery including a free-standing dry electrode film having excellent strength and a secondary battery including the same. Means for Solving the Problems

[0012] To achieve the above object, the present invention provides a dry electrode film including an active material, a conductive material, and a fibrillated binder; and a current collector on which the electrode film is laminated; and provides an electrode for a secondary battery in which the conductive material includes carbon fibers.

[0013] The present invention also provides a secondary battery including the above electrode. Advantages of the Invention

[0014] The electrode for a secondary battery of the present invention includes a free-standing dry electrode film having excellent strength, thereby greatly reducing the defective rate caused by insufficient strength of the electrode film during electrode manufacturing, and thereby providing the effect of significantly improving the productivity of electrode manufacturing.

[0015] Further, by improving the charge / discharge characteristics, life characteristics, etc. of the battery due to the reduction of the defective rate as described above, the effect of greatly improving the quality of the battery is provided. Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Best Mode for Carrying Out the Invention

[0017] Hereinafter, the present invention will be described in more detail to facilitate understanding of the present invention.

[0018] The terms and words used in this specification and claims should not be construed in a limited sense in accordance with ordinary or dictionary meanings. The inventor must interpret them in a meaning and concept that conforms to the technical idea of the present invention in accordance with the principle that the inventor can appropriately define the concept of the terms in order to explain his invention in the best way.

[0019] The terms used in this specification are merely used to explain exemplary embodiments and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0020] In this specification, terms such as "comprising", "including" or "having" are intended to specify the presence of implemented features, numbers, steps, components, or combinations thereof, and should be understood as not precluding the presence or addition possibility of one or more other features, numbers, steps, components, or combinations thereof.

[0021] The electrode for a secondary battery of the present invention includes a dry electrode film containing an active material, a conductive material, and a fibrillated binder; and a current collector on which the electrode film is laminated; and is characterized in that the conductive material contains carbon fibers.

[0022] In this field, various forms of dry electrode films have been proposed. However, when the strength of the electrode film is not maintained, for example, it is difficult to apply to a secondary battery through a roll to roll process, etc. Therefore, strength is a very important factor in the electrode film.

[0023] The present invention is characterized in that a carbon fiber is included as a conductive material in an electrode film to improve the strength of the electrode film.

[0024] In one embodiment of the present invention, it is preferable that the average diameter of the carbon fiber is the same as or larger than the average particle diameter of the active material particles. When the average diameter of the carbon fiber is smaller than the average particle diameter of the active material particles, it is difficult to expect an improvement in strength by the carbon fiber. This is because when the diameter of the carbon fiber is smaller than the particle diameter of the active material in the dry electrode film, the carbon fiber is not firmly fixed between the active material particles. Conversely, when the diameter of the carbon fiber is larger than the particle diameter of the active material, the carbon fiber is firmly fixed in the dry electrode film, so the strength of the dry electrode film is greatly improved.

[0025] In one embodiment of the present invention, the average diameter of the carbon fiber is 1 to 10 times, preferably 1.1 to 5 times, more preferably 1.2 to 2 times the average particle diameter of the active material particles. When the average diameter of the carbon fiber is less than 1 time the average particle diameter of the active material particles, the effect of improving the strength of the electrode film is not significant, and when it exceeds 10 times, the volume of the carbon fiber occupies most of the electrode area and the energy density becomes very low, which is not preferable in terms of the uniformity of the electrode.

[0026] In one embodiment of the present invention, the average diameter of the carbon fiber is 0.05 μm to 100 μm, and the average particle diameter of the active material particles is 0.01 μm to 20 μm.

[0027] In one embodiment of the present invention, the carbon fiber can be included in an amount of 0.1 to 5% by weight based on the total weight of the electrode film. When the carbon fiber is included in an amount of 0.1% by weight, it is difficult to expect an improvement in strength effect, and when it exceeds 5% by weight, the electrode energy density becomes low, which is not preferable for the production of high-capacity batteries.

[0028] In one embodiment of the present invention, the length of the carbon fiber is 5 μm to 1500 μm, preferably 100 μm to 1000 μm, more preferably 200 μm to 800 μm.

[0029] Hereinafter, the present invention will be described for each constituent component.

[0030] <Active material> In the active material, all components normally used for the positive electrode and the negative electrode can be used. Specifically, for example, when the active material is a positive electrode active material, LiCoO2, LiNiO2, LiMn2O4, LiCoPO4, LiFePO4, and LiNi 1-x-y-z Co x M1 y M2 z O2 (where M1 and M2 are each independently selected from the group consisting of Al, Ni, Co, Fe, Mn, V, Cr, Ti, W, Ta, Mg, and Mo, and x, y, and z are each independently 0 ≤ x < 0.5, 0 ≤ y < 0.5, 0 ≤ z < 0.5, 0 < x + y + z ≤ 1 as the atomic fraction of the oxide composition elements) can be included in any one active material particle selected from the group consisting of or a mixture of two or more of these.

[0031] Also, when the electrode active material is a negative electrode active material, natural graphite or artificial graphite (such as mesocarbon microbeads (MCMB), pyrolytic carbon, mesophase pitch based carbon fiber, mesophase pitches, petroleum or coal tar pitch derived cokes, etc.); lithium-containing titanium composite oxide (LTO), Si, Sn, Li, Zn, Mg, Cd, Ce, Ni, or Fe metals (Me); alloys composed of the metals (Me); oxides of the metals (MeO x , e.g., SIO); and any one active material selected from the group consisting of composites of the metals (Me) and carbon or a mixture of two or more of these.

[0032] The active material can be contained, for example, in an amount of 85 to 98% by weight based on the total weight of the electrode film.

[0033] <Conductive material> In one embodiment of the present invention, other conductive materials other than the carbon fiber can be further included as the conductive material. Such a conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the secondary battery. For example, carbon blacks such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; one or more selected from polyphenylene derivatives and the like can be used.

[0034] The conductive material can be contained, for example, in an amount of 1 to 10% by weight, specifically 2 to 5% by weight based on the total weight of the electrode film.

[0035] Other conductive materials other than the carbon fiber can be contained in an amount of 1 to 5% by weight based on the total weight of the electrode film.

[0036] <Binder> In one embodiment of the present invention, the fibrillated binder can contain any one or more of polyvinylidene fluoride - hexafluoropropylene and polytetrafluoroethylene, and polytetrafluoroethylene can preferably be used.

[0037] Further, the electrode for a secondary battery of the present invention can further contain other binders other than the binder. Among the other binders, any substance that can assist in binding the active material and the conductive material and adhering to the current collector can be used without limitation. Specifically, non - acrylic polymers or acrylic polymers can be used as the binder.

[0038] As the acrylic polymer, any polymer can be used without limitation as long as at least one repeating unit of the binder polymer is derived from an acrylic monomer. In the acrylic monomer, alkyl acrylate, alkyl methacrylate, isoalkyl (meth)acrylate, etc. are possible. At this time, "alkyl" is an alkyl group having 1 to 10 carbon atoms, and more specifically, an alkyl group having 1 to 5 carbon atoms. Specific examples of the acrylic monomer include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, and the like.

[0039] The acrylic polymer is a homopolymer composed of one repeating unit derived from an acrylic monomer, or a copolymer containing repeating units derived from two or more acrylic monomers, or a mixture of two or more of these.

[0040] In addition, the acrylic polymer is a copolymer of one or more non-acrylic monomers and an acrylate monomer, such as one or more selected from the group consisting of acrylate-styrene-butadiene rubber, acrylate-acrylonitrile-styrene-butadiene rubber, methyl acrylate-styrene-butadiene rubber, methyl acrylate-acrylonitrile-styrene-butadiene rubber, ethyl acrylate-styrene-butadiene rubber, ethyl acrylate-acrylonitrile-styrene-butadiene rubber, propyl acrylate-styrene-butadiene rubber, propyl acrylate-acrylonitrile-styrene-butadiene rubber, butyl acrylate-styrene-butadiene rubber, and butyl acrylate-acrylonitrile-styrene-butadiene rubber. In the case of a copolymer of a non-acrylic monomer and an acrylate monomer, the weight percentage of the repeating unit derived from the acrylate monomer is 5 to 45% by weight, and more specifically, 5 to 35% by weight.

[0041] Further, the acrylic polymer may be a mixture of two or more homopolyacrylic polymers, a mixture of two or more acrylic copolymers, or a mixture of copolymers of two or more non-acrylic monomers and acrylate monomers, and is also a mixture of two or more among homopolyacrylic polymers, acrylic copolymers, and copolymers of non-acrylic monomers and acrylate monomers.

[0042] The non-acrylic polymer means a polymer containing one or more repeating units derived from monomers other than acrylic, and specifically, a homopolymer composed of one kind of repeating unit, a copolymer containing two or more different repeating units, a mixture of two or more different homopolymers, or a mixture of two or more of these.

[0043] Specific examples of the non-acrylic polymer include styrene-butadiene rubber (SBR), a mixture of polystyrene and polybutadiene, polyvinylidene fluoride (PVDF), polyvinylidene fluoride-cohexafluoropropylene, polyvinylidene fluoride-cotrichloroethylene, polytetrafluoroethylene (PTFE), polyvinylpyrrolidone, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, and carboxyl methyl cellulose (CMC), and one or a mixture of two or more of these can be used. Among these, polyvinylidene fluoride (PVDF), polyethylene oxide (PEO), etc. can preferably be used.

[0044] In one embodiment of the present invention, the total binder content including the fibrillated binder is 0.01 to 5% by weight, specifically 1 to 4% by weight based on the total weight of the electrode film. When the content of the binder satisfies such a range, the adhesive force between the electrode active material layer and the current collector is improved, and by improving the adhesive force, the electrode resistance can be reduced, electrode detachment can be prevented even after the degradation of the cell, and the migration of the binder to the electrode surface can be suppressed to improve the ionic conductivity and electrical conductivity in the electrode.

[0045] <Current collector> In the current collector, known current collectors used in secondary batteries can be used without limitation. For example, stainless steel, aluminum, nickel, titanium, fired carbon, copper; stainless steel surface-treated with carbon, nickel, titanium or silver; aluminum-cadmium alloy; non-conductive polymer surface-treated with a conductive material; non-conductive polymer surface-treated with a metal; and conductive polymers and the like can be used.

[0046] <Manufacture of electrode> Hereinafter, the manufacturing method of the electrode for a secondary battery of the present invention will be described with examples.

[0047] The manufacturing method of the electrode according to one embodiment of the present invention includes a step of dry-mixing an active material, a conductive material, and a binder to produce a mixture (primary mixing); a step of applying a high shear force to the mixture (secondary mixing); a step of pressing the secondary mixture to produce a free-standing film; and a step of positioning the free-standing electrode film on a current collector and rolling it.

[0048] The high shear force is 50 N to 1000 N. Here, since the active material, the conductive material, and the binder are the same as those described above, the description is omitted.

[0049] The mixture can be produced by dry mixing the active material, the conductive material, and the binder. The dry mixing means mixing without a solvent. The dry mixing can be carried out by using a stirring device and mixing at 600 rpm to 20000 rpm, specifically 1000 rpm to 12000 rpm, for 0.5 minutes to 10 minutes at a temperature below normal temperature.

[0050] The step of applying the high shear force can be carried out before positioning the mixture on the current collector. The step of applying the high shear force can include shear-compressing the mixture to apply the high shear force. Specifically, when using a device for applying shear force, such as PBV-0.1L (Irie Shokai), the mixture can be shear-compressed at 10 rpm to 100 rpm for 1 minute to 10 minutes to apply the high shear force. However, it is not necessarily limited to such a method.

[0051] When applying a high shear force to the mixture, the active material, binder, and conductive material in the mixture may become entangled with each other, thereby forming granules in which the conductive material, active material, and binder are aggregated. Therefore, due to the presence of the granules, the active material and the binder can be supported by the carbon fiber conductive material and the binding force can be increased. This facilitates the step of disposing the mixture on the current collector.

[0052] The high shear force is 50 N to 1000 N, specifically 100 N to 500 N, and more specifically 100 N to 300 N. In the present invention, a high shear force within this range can be applied to induce an entanglement phenomenon such as that of carbon fiber.

[0053] In the step of manufacturing the free-standing film, pressing can be carried out by using a two-roll mill MR-3 (Inoue Seisakusho) or the like.

[0054] The step of rolling the current collector on which the free-standing film is positioned can be carried out through a roll press method.

[0055] <Manufacture of secondary battery> The present invention also relates to a secondary battery including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, wherein one or more of the positive electrode and the negative electrode are the electrodes described above. When the electrode according to the present invention is used only for one of the positive electrode and the negative electrode, other electrodes can be used without limitation to electrodes known in this field.

[0056] Hereinafter, examples of the secondary battery will be given and described. Specifically, an example of a lithium secondary battery will be given and described.

[0057] In the lithium secondary battery, the separator can be a porous polymer film commonly used as a separator, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, etc., can be used alone or in a laminated form. Also, an insulating thin film having high ion permeability and mechanical strength can be used. The separator can include a stability-reinforced separator (SRS) having an organic / inorganic composite porous coating layer in which inorganic particles are connected and fixed on the surface of a separator substrate such as a porous polymer film through a binder polymer and thinly coated. In addition, ordinary porous non-woven fabrics, for example, non-woven fabrics made of high-melting glass fibers, polyethylene terephthalate fibers, etc., can be used, and the above-mentioned organic / inorganic composite porous coating layer can also be applied on the porous non-woven fabric, and the form is not limited thereto.

[0058] The lithium secondary battery of the present invention can be manufactured by housing the positive and negative electrode assemblies in a battery case and injecting an electrolyte.

[0059] The electrolyte can contain a lithium salt and an organic solvent for dissolving the same. Any lithium salt that is commonly used in electrolytes for secondary batteries can be used without limitation. For example, as the anion of the lithium salt, F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - can be used, and one selected from the group consisting of them can be used.

[0060] As the organic solvent contained in the electrolyte, any solvent used in this field can be used without limitation. Typically, one or more selected from the group consisting of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite, and tetrahydrofuran can be used.

[0061] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are preferred as high-viscosity organic solvents because they have a high dielectric constant and can well dissociate lithium salts in the electrolyte, and a low-viscosity and low-dielectric-constant linear carbonate such as dimethyl carbonate and diethyl carbonate can be mixed with such a cyclic carbonate at an appropriate ratio to produce an electrolyte solution having high electrical conductivity and can be more preferably used.

[0062] Optionally, the electrolyte stored according to the present invention can further contain additives such as overcharge preventives contained in a normal electrolyte solution.

[0063] As the electrolyte, a known solid electrolyte can also be used.

[0064] The secondary battery according to an embodiment of the present invention is of a stack type, a winding type, a stack-and-folding type, or a cable type. Further, the secondary battery can be used not only as a battery cell used as a power source for a small device, but also as a unit cell in a medium- and large-sized battery module including a large number of battery cells. Preferred examples of the medium- and large-sized devices include electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, power storage systems, etc., and in particular, it can be usefully used in hybrid electric vehicles in areas where high output is required and batteries for new renewable energy storage.

[0065] Regarding the configuration and manufacturing method of the secondary battery of the present invention, the parts not described above can be applied without limitation to the configurations and manufacturing methods known in this field.

[0066] Hereinafter, examples will be given to specifically describe the present invention in detail. However, the examples according to the present invention may be deformed into several different forms, and the scope of the present invention should not be construed as being limited to the following examples. The examples of the present invention are provided to more fully explain the present invention to those with average knowledge in the industry.

[0067] Example 1: Production of the positive electrode 96 g of NCM powder (product name: GL80, LG Chem) which is positive electrode active material particles with an average particle size of 10 μm, 2 g of Li250 (Denka) as a conductive material, 1 g of carbon fiber with a diameter of 12 μm and a length of 200 μm, and 2 g of PTFE as a binder were mixed using a Lab Blender (Waring) at 5000 rpm for 1 minute without a solvent (primary mixing). Next, a shear force of 250 N was applied to the mixture (PBV-0.1L, Irie Shokai) to perform high-shear mixing (secondary mixing). Next, the kneaded secondary mixture was manufactured into a free-standing film using a Two roll mill MR-3 (Inoue). Thereafter, the free-standing film was placed on one surface of an aluminum current collector with a thickness of 15 μm and pressurized to manufacture a positive electrode.

[0068] Example 2: Production of the positive electrode A positive electrode was manufactured in the same manner as in Example 1, except that NCM powder (product name: GL80, LG Chem) which is positive electrode active material particles with an average particle size of 10 μm in Example 1 and carbon fiber with a diameter of 15 μm and a length of 500 μm were used.

[0069] Example 3: Production of the positive electrode A positive electrode was manufactured in the same manner as in Example 1, except that NCM powder (product name: GL80, LG Chem) which is positive electrode active material particles with an average particle size of 10 μm in Example 1 and carbon fiber with a diameter of 20 μm and a length of 800 μm were used.

[0070] Example 4: Production of the negative electrode A negative electrode was manufactured in the same manner as in Example 1, except that artificial graphite powder, which is a negative electrode active material with an average particle size of 7 μm, was used instead of the positive electrode active material in Example 1.

[0071] Comparative Example 1: Manufacture of Positive Electrode A positive electrode was manufactured in the same manner as in Example 1, except that NCM powder (trade name: GL80, manufactured by LG Chem), which is a positive electrode active material particle with an average particle size of 10 μm in Example 1, and carbon fiber with a diameter of 5 μm and a length of 150 μm were used.

[0072] Comparative Example 2: Manufacture of Positive Electrode A positive electrode was manufactured in the same manner as in Example 1, except that NCM powder (trade name: GL80, manufactured by LG Chem), which is a positive electrode active material particle with an average particle size of 10 μm in Example 1, and carbon fiber with a diameter of 8 μm and a length of 100 μm were used.

[0073] Comparative Example 3: Manufacture of Positive Electrode A positive electrode was manufactured in the same manner as in Example 1, except that NCM powder (trade name: GL80, manufactured by LG Chem), which is a positive electrode active material particle with an average particle size of 5 μm in Example 1, and carbon fiber with a diameter of 56 μm and a length of 100 μm were used.

[0074] Experimental Example 1: Measurement of Strength of Free-Standing Electrode The strength of the free-standing films manufactured in Examples 1 to 4 and the free-standing films manufactured in Comparative Examples 1 to 3 was measured using an Instron UTM equipment under the condition of 500 mm / min by the 180-degree peel measurement method, sampling electrodes with a width of 20 mm, a length of 200 mm, and a thickness of 200 μm.

[0075] The maximum value among the forces applied until no cracks occurred in the film during the measurement was evaluated as the strength of the free-standing film, and the measurement results are shown in Table 1 below.

[0076]

Table 1

[0077] Example 5 and Comparative Example 3: Manufacture of Lithium Secondary Battery Using the positive electrodes manufactured in Example 1, Comparative Example 1, and Comparative Example 3, the batteries of Example 5, Comparative Example 4, and Comparative Example 5 were manufactured respectively. The specific manufacturing method is as follows.

[0078] (1) Manufacture of Negative Electrode Natural graphite, carbon black conductive material, and PVDF binder as negative electrode active materials were mixed in a weight ratio of 85:10:5 in an N-methylpyrrolidone solvent to manufacture a negative electrode forming composition, and this was applied to a copper current collector to manufacture a negative electrode.

[0079] (2) Manufacture of Lithium Secondary Battery An electrode assembly was manufactured with a porous polyethylene separator interposed between each of the positive electrodes manufactured in Example 1, Comparative Example 1, and Comparative Example 3 and the negative electrode manufactured in (1) above. After positioning the electrode assembly inside the case, an electrolyte was injected into the case to manufacture a lithium secondary battery. At this time, the electrolyte was prepared by dissolving lithium hexafluorophosphate (LiPF6) with a concentration of 1.0 M in an organic solvent composed of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate (mixed volume ratio of EC / DMC / EMC = 3 / 4 / 3). Through this, the lithium secondary batteries of Example 5, Comparative Example 4, and Comparative Example 5 were manufactured.

[0080] Experimental Example 2: Evaluation of Initial Discharge Efficiency and Capacity Retention Rate of Lithium Secondary Battery Charging and discharging were performed on the secondary batteries of Example 5, Comparative Example 4, and Comparative Example 5, and the initial discharge efficiency and capacity retention rate were evaluated and described in Table 2 below. Charging and discharging were performed at 0.1C for 1 cycle and 2 cycles, and at 0.33C from 3 cycles to 49 cycles. The 50th cycle ended in a charged state (with lithium in the negative electrode).

[0081] Charging Conditions: CC (constant current) / CV (low voltage) (4.25V / 0.05C current cut-off) Discharge condition: CC (constant current) condition 3.0V The initial discharge efficiency and capacity retention rate were derived by the following calculations, respectively. Initial discharge efficiency (%) = (discharge capacity per cycle / charge capacity per cycle) × 100 Capacity retention rate (%) = (discharge capacity after 49 cycles / discharge capacity per cycle) × 100

[0082]

Table 2

Claims

1. A dry electrode film containing an active material, a conductive material, and a fibrillated binder, and a current collector on which the dry electrode film is laminated, wherein the conductive material includes carbon fibers, and an average diameter of the carbon fibers is 1 to 10 times a ratio of an average particle size of particles of the active material, and an electrode for a secondary battery is provided.

2. The electrode for a secondary battery according to claim 1, wherein the average diameter of the carbon fibers is 0.05 μm to 100 μm, and the average particle size of the particles of the active material is 0.01 μm to 20 μm.

3. The electrode for a secondary battery according to claim 1, wherein the carbon fibers are contained in an amount of 0.1 to 5% by weight based on the total weight of the electrode film.

4. The electrode for a secondary battery according to claim 3, wherein the conductive material further includes another conductive material other than carbon fibers in an amount of 1 to 5% by weight based on the total weight of the electrode film.

5. The electrode for a secondary battery according to claim 1, wherein the carbon fibers have a length of 5 μm to 1500 μm.

6. The electrode for a secondary battery according to claim 1, wherein the fibrillated binder includes any one or more of polyvinylidene fluoride - hexafluoropropylene and polytetrafluoroethylene.

7. A secondary battery including the electrode for a secondary battery according to claim 1.

8. The secondary battery according to claim 7, wherein the secondary battery is a lithium secondary battery.

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