Negative electrode and secondary battery comprising the same

Abstract

The present invention relates to a negative electrode excellent in rapid charging performance and life characteristics, and a secondary battery comprising the same, and to a negative electrode and a secondary battery comprising the same, the negative electrode comprising a current collector and a negative electrode active material layer formed on the current collector, wherein the negative electrode active material layer comprises a negative electrode active material comprising first uncoated artificial graphite particles and second uncoated artificial graphite particles at a weight ratio of 4:6 to 6:4, the first uncoated artificial graphite particles each being a single particle having an average particle diameter (D 50 ) of 5-7 μm, and the second uncoated artificial graphite particles having an average particle diameter (D 50 ) of 20-25 μm and being secondary particles formed by aggregation of a plurality of primary particles. The present invention relates to a negative electrode excellent in rapid charging performance and life characteristics, and a secondary battery comprising the same, and to a negative electrode and a secondary battery comprising the same, the negative electrode comprising a current collector and a negative electrode active material layer formed on the current collector, wherein the negative electrode active material layer comprises a negative electrode active material comprising first uncoated artificial graphite particles and second uncoated artificial graphite particles at a weight ratio of 4:6 to 6:4, the first uncoated artificial graphite particles each being a single particle having an average particle diameter (D 50 ) of 5-7 μm, and the second uncoated artificial graphite particles having an average particle diameter (D 50 ) of 20-25 μm and being secondary particles formed by aggregation of a plurality of primary particles.

Description

Technical Field

[0001] Cross-reference to related applications

[0002] This application claims priority and benefit to Korean Patent Application No. 10-2020-0083507, filed on July 7, 2020, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0004] This invention relates to a negative electrode with excellent fast charging performance and lifespan characteristics, and a secondary battery containing the negative electrode. Specifically, it relates to a negative electrode containing a negative electrode active material, the negative electrode active material comprising both uncoated artificial graphite particles as single particles and uncoated artificial graphite particles as secondary particles formed by the aggregation of multiple primary particles; and a secondary battery containing the negative electrode. Background Technology

[0005] With the rapid increase in fossil fuel use, the demand for alternative or clean energy sources is constantly growing, and the field of power generation and energy storage using electrochemical reactions has been the most actively studied to meet this growing demand.

[0006] Representative examples of electrochemical devices utilizing electrochemical energy include secondary batteries, whose applications are gradually expanding. Recently, with the development of technology and increased demand for portable devices such as laptops, mobile phones, and cameras, the demand for secondary batteries as an energy source has increased dramatically. Furthermore, to improve the ease of use of secondary batteries, charging time needs to be shortened, thus requiring excellent fast-charging performance.

[0007] A secondary battery typically consists of a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode contains an active material that allows lithium ions released from the positive electrode to intercalate and deintercalate.

[0008] As the negative electrode active material, graphite-based active materials, such as natural graphite and synthetic graphite, are typically used. The advantage of natural graphite, which has been used in the past, is its low cost and excellent cost-effectiveness. However, due to its irregular structure, it presents problems such as irreversible reactions caused by electrolyte penetration or decomposition when applied to batteries. On the other hand, the advantage of synthetic graphite, which has been used in the past, is its excellent initial charge / discharge efficiency. However, it exhibits a lower discharge capacity than natural graphite, resulting in a deterioration in battery capacity and energy density.

[0009] To address these issues, previous methods have included negative electrode active materials made by mixing typical natural and artificial graphite, and negative electrode active materials formed with an amorphous carbon coating on typical natural or artificial graphite. However, these methods have resulted in deterioration in fast charging performance and room temperature lifespan characteristics.

[0010] Therefore, there is a need for a negative electrode containing a negative electrode material that enables the realization of secondary batteries with high energy density and excellent fast charging performance and lifespan characteristics.

[0011] [Related Technical Documents]

[0012] [Patent Literature]

[0013] Japanese Patent Publication No. 2019-179687 Summary of the Invention

[0014] Technical issues

[0015] This invention relates to a negative electrode having high energy density, excellent fast charging performance and excellent lifespan characteristics, and a secondary battery comprising said negative electrode.

[0016] Technical solution

[0017] One aspect of the present invention provides a negative electrode comprising a current collector and a negative electrode active material layer formed on the current collector, wherein the negative electrode active material layer comprises a negative electrode active material comprising a first uncoated artificial graphite particles and a second uncoated artificial graphite particles in a weight ratio of 4:6 to 6:4, wherein the first uncoated artificial graphite particles have an average particle size (D) of [missing information]. 50 The first uncoated artificial graphite particles are single particles ranging from 5 μm to 7 μm in size, while the second uncoated artificial graphite particles are formed by the aggregation of multiple primary particles and have an average particle size (D). 50 ) are secondary particles ranging from 20μm to 25μm.

[0018] Another aspect of the present invention provides a secondary battery comprising the negative electrode.

[0019] Beneficial effects

[0020] According to the present invention, since the negative electrode contains a negative electrode active material, the negative electrode active material contains a first uncoated artificial graphite particles and a second uncoated artificial graphite particles in a specific weight ratio, wherein the first uncoated artificial graphite particles have an average particle size (D) of [missing information]. 50 The first uncoated artificial graphite particles are single particles ranging from 5 μm to 7 μm in size, while the second uncoated artificial graphite particles are formed by the aggregation of multiple primary particles and have an average particle size (D). 50The single particles are secondary particles ranging from 20μm to 25μm in size. These single particles fill the empty spaces between the secondary particles to reduce voids. The single particles are soft and can absorb impacts between the secondary particles, thus minimizing physical damage and structural changes to the electrode during rolling. This allows for smooth rolling of the electrode to achieve a thin electrode, ultimately resulting in a thin battery and improving its energy density. Furthermore, it improves the battery's fast-charging performance and lifespan characteristics. Detailed Implementation

[0021] The invention will now be described in more detail to aid in understanding it.

[0022] The terms and words used in this specification and claims should not be construed as limited to their common or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical scope of the invention, based on the principle that the inventors can appropriately define the concepts of the terms in order to best describe the invention.

[0023] The terminology used in this specification is for the purpose of describing exemplary embodiments only and is not intended to limit the invention. Unless the context clearly indicates otherwise, the singular forms “a,” “an,” and “described” are also intended to include the plural forms.

[0024] It should be understood that the terms “comprising,” “containing,” “including,” “having,” and / or “having” as used herein indicate the presence of the stated feature, number, step, operation, element, component, and / or combination thereof, but do not preclude the presence or addition of one or more other features, numbers, steps, operations, elements, components, and / or combinations thereof.

[0025] In this specification, D 50 It can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve (the curve on the particle size distribution map). D can be measured, for example, using laser diffraction. 50 Laser diffraction typically enables the measurement of particle sizes ranging from submicron to millimeters, and can produce results with high reproducibility and high resolution.

[0026] <Negative electrode>

[0027] According to one embodiment of the present invention, the negative electrode comprises a current collector and a negative electrode active material layer formed on the current collector, wherein the negative electrode active material layer comprises a negative electrode active material, the negative electrode active material comprising a first uncoated artificial graphite particles and a second uncoated artificial graphite particles in a weight ratio of 4:6 to 6:4, wherein the first uncoated artificial graphite particles have an average particle size (D) of [missing information]. 50The first uncoated artificial graphite particles are single particles ranging from 5 μm to 7 μm in size, while the second uncoated artificial graphite particles are formed by the aggregation of multiple primary particles and have an average particle size (D). 50 ) are secondary particles ranging from 20μm to 25μm.

[0028] In this specification, "primary particle" means a single particle, and "secondary particle" means an aggregate formed by bringing together multiple primary particles through an intentional assembly or bonding process.

[0029] The negative electrode includes a current collector and a layer of negative electrode active material formed on the current collector.

[0030] The current collector is used to support the negative electrode active material layer.

[0031] There are no particular limitations on the current collector, as long as it does not cause a chemical change in the battery and is conductive. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, and aluminum or stainless steel with a surface treated with carbon, nickel, titanium, silver, etc., can be used as current collectors. Specifically, transition metals such as copper and nickel, which readily adsorb carbon, can be used as current collectors. The thickness of the current collector can be from 6 μm to 20 μm, but is not limited to this.

[0032] A negative electrode active material layer is formed on the current collector. The negative electrode active material layer may be disposed on at least one surface of the current collector, specifically on one or both surfaces of the current collector.

[0033] The negative electrode active material layer comprises a negative electrode active material. The negative electrode active material layer may also comprise conductive materials, adhesives, etc.

[0034] The negative electrode active material comprises a first uncoated artificial graphite particle and a second uncoated artificial graphite particle. Specifically, the negative electrode active material may be composed of the first uncoated artificial graphite particle and the second uncoated artificial graphite particle. That is, the negative electrode active material may consist solely of the first uncoated artificial graphite particle and the second uncoated artificial graphite particle.

[0035] In this specification, uncoated artificial graphite particles mean artificial graphite particles that are not coated, and mean that the entire surface of the artificial graphite is exposed.

[0036] The negative electrode active material does not crack during rolling because it contains only uncoated active material, meaning it suffers less physical damage and thus can maintain the structure of the negative electrode well.

[0037] Because the negative electrode active material contains single and secondary particles of a specific size in a specific weight ratio, it can be rolled smoothly during the manufacturing of the negative electrode, thereby not only reducing the thickness of the negative electrode and ultimately the thickness of the battery, but also realizing a battery with high energy density, and improving the battery's fast charging performance and lifespan characteristics.

[0038] The first uncoated artificial graphite particle has an average particle size (D) 50 Single particles ranging from 5 μm to 7 μm in size. When the average particle size (D) of a single particle... 50 When the particle size is less than 5 μm, the small particle size may lead to an increase in the specific surface area and a decrease in the capacity of the active material. Conversely, when the average particle size of a single particle is less than 5 μm, it may lead to an increase in the specific surface area and a decrease in the capacity of the active material. 50 When the particle size exceeds 7μm, the particle size is too large to densely fill the empty space of the secondary particles, and therefore the calendering performance may deteriorate.

[0039] The second uncoated artificial graphite particle has an average particle size (D) 50 Secondary particles with a diameter of 20 μm to 25 μm. When the average particle size (D) of the secondary particles... 50 When the average particle size (D) of the secondary particles is less than 20 μm, the specific surface area of ​​the active material increases, which may lead to a deterioration in high-temperature performance. 50 When the particle size exceeds 25 μm, battery performance, such as fast charging and output, may deteriorate. Specifically, the average particle size (D) of the secondary particles... 50 The average particle size can be from 21 μm to 24 μm, more specifically from 22 μm to 23 μm. When the average particle size of the secondary particles falls within the above range, the secondary particles can be mixed with the single particles within an appropriate range to maximize the rolling performance of the electrode.

[0040] The second uncoated artificial graphite particle is a secondary particle formed by the aggregation of multiple primary particles, wherein the average particle size (D) of the primary particles constituting the secondary particle is... 50 The diameter can be from 7 μm to 9 μm. When the average particle size (D) of the primary particles constituting the second uncoated artificial graphite particles... 50 When falling within the above range, the appropriate primary particle size enables the maintenance of sufficiently high capacity and high levels of battery performance such as fast charging and output.

[0041] To improve energy density and charging performance, in the second uncoated artificial graphite particles, the average particle size (D) of the primary particles constituting the secondary particles is... 50 The average particle size (D) of the secondary particles formed by the aggregation of multiple primary particles is... 50 The ratio can be from 1:2 to 1.5, specifically from 1:2 to 1:3.

[0042] The average particle size (D) of the first uncoated artificial graphite particles 50 ) and the average particle size (D) of the second uncoated artificial graphite particles 50 The ratio can be from 1:3 to 1:5, specifically from 1:3 to 1:4.5, and more specifically from 1:3 to 1:4. When the average particle size (D) of the first uncoated artificial graphite particles... 50 ) and the average particle size (D) of the second uncoated artificial graphite particles 50 When the ratio of the first uncoated artificial graphite particles to the second uncoated artificial graphite particles falls within the above range, the first uncoated artificial graphite particles can fill the gaps between the particles to prepare a high-density negative electrode active material, thereby improving the fast charging performance and / or lifespan characteristics of the battery.

[0043] The nip pressure during tandem rolling of the negative electrode active material can be below 8 tons / cm, specifically from 4 tons / cm to 8 tons / cm, and more specifically from 4 tons / cm to 6 tons / cm. In this invention, the nip pressure during tandem rolling is measured by physical rolling after the unrolled negative electrode has been coated and dried under vacuum. A nip pressure within the above range during tandem rolling of the negative electrode active material is advantageous for subjecting less physical force during the rolling process used to manufacture the electrode and for achieving thinner electrodes. The nip pressure during tandem rolling can be measured in a rolling mill equipped with a nip pressure sensor.

[0044] The tap density of the negative electrode active material can be from 1.00 g / cc to 1.20 g / cc, specifically from 1.14 g / cc to 1.18 g / cc. When the tap density of the negative electrode active material falls within the above range, the tap density is high enough to allow for the fabrication of a low-thickness electrode coating.

[0045] The tap density is the mass per unit volume of a powder composed of particles, referring to the density obtained by continuously tapping or vibrating to fill the voids between particles. Factors affecting tap density include particle size distribution, moisture content, particle shape, and cohesion. The flowability and compressibility of a material can be predicted using tap density. The tap density can be measured based on ASTM D4781 and can be calculated using the formula TD = W / V (TD: tap density, W: sample weight (g), V: sample volume after tapping).

[0046] The BET specific surface area of ​​the negative electrode active material can be 1.0 m². 2 / g to 2.5m 2 / g. Specifically, the BET specific surface area of ​​the negative electrode active material can be 1.4m². 2 / g to 2.0m 2 / g, more specifically 1.5m 2 / g to 1.9m 2 / g. The BET specific surface area can be measured using a BEL adsorption meter (BEL Japan). When the BET specific surface area of ​​the negative electrode active material falls within the above range, high-temperature performance can be maintained at a high level.

[0047] The pore volume of the negative electrode active material layer can be 10 cm³. 3 / g to 20cm 3 / g. Specifically, the pore volume of the negative electrode active material layer can be 10 cm³. 3 / g to 15cm 3 / g, more specifically 15cm 3 / g to 20cm 3 / g. When the pore volume of the negative electrode active material layer falls within the above range, high-temperature battery performance, such as high-temperature cycling characteristics and high-temperature storage, can be maintained at a high level.

[0048] The negative electrode active material may be included in the negative electrode active material layer in an amount of 90% to 99% by weight, specifically 92% to 97% by weight. When the content of the negative electrode active material falls within the above range, the required battery capacity can be achieved.

[0049] The first uncoated artificial graphite particles can be prepared by mixing coke with binder pitch and heat-treating the mixture at high temperature (i.e., graphitization). The coke can be needle coke and / or isotropic coke, and the coke and binder pitch can be mixed in a weight ratio of 80:20 to 95:5.

[0050] The second uncoated artificial graphite particles can be prepared by mixing coke with binder pitch, heat-treating the mixture at high temperature to prepare primary particles, mixing the primary particles with binder pitch, and heat-treating the mixture at high temperature (specifically, between 2,500°C and 3,200°C). Since the binder pitch is graphitized through heat treatment at high temperature, second uncoated artificial graphite particles without coating materials such as amorphous carbon can be prepared. The coke can be needle-shaped coke and / or isotropic coke, and the coke and binder pitch can be mixed in a weight ratio of 80:20 to 95:5, as can the primary particles and binder pitch.

[0051] There are no particular limitations on the conductive material, as long as it does not cause a chemical change in the battery and is conductive. For example, graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal cracking black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; fluorocarbons; metal powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives can be used as the conductive material.

[0052] The conductive material preferably comprises at least one selected from carbon black and carbon nanotubes, and more preferably comprises carbon nanotubes.

[0053] The conductive material may be included in the negative electrode active material layer in an amount of 0.1% to 1.0% by weight, specifically 0.3% to 0.7% by weight. The content of the conductive material within the above range helps to maintain adequate electrical contact and prevent capacity degradation.

[0054] The adhesive may contain at least one selected from the group consisting of: polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and materials wherein hydrogen is replaced by Li, Na, Ca, etc., and may also contain various copolymers thereof.

[0055] The adhesive may be included in the negative electrode active material layer in an amount of less than 30% by weight, specifically from 0.1% to 30% by weight. When the content of the adhesive meets the above range, an adhesion effect due to the use of the adhesive can be exhibited, and the desired negative electrode unit volume capacity can be maintained.

[0056] By comprising a negative electrode active material, the pore resistance of the negative electrode can be below 9 ohms. The negative electrode active material comprises, in a specific weight ratio, first uncoated artificial graphite particles and second uncoated artificial graphite particles, wherein the first uncoated artificial graphite particles have an average particle size (D...). 50 The first uncoated artificial graphite particles are single particles ranging from 5 μm to 7 μm in size, while the second uncoated artificial graphite particles are formed by the aggregation of multiple primary particles and have an average particle size (D). 50The particles are secondary particles with a size of 20 μm to 25 μm. The pore resistance of the negative electrode is preferably 6 ohms to 9 ohms. When the pore resistance of the negative electrode falls within the above range, the pore resistance in the electrolyte can be minimized, and the lithium-ion diffusion path can be minimized.

[0057] The pore resistance can be defined as the resistance value obtained by injecting a lithium-ion-containing electrolyte into a symmetric cell, which uses the negative electrode of a lithium secondary battery as both the working electrode and the counter electrode, and then performing electrochemical impedance spectroscopy (EIS) analysis. Since the pore resistance is measured by EIS analysis of a symmetric cell, only lithium ions from the electrolyte are present, thus allowing for an objective measurement of the lithium-ion diffusion resistance in the negative electrode.

[0058] Secondary batteries

[0059] A secondary battery according to another embodiment of the present invention includes a negative electrode, and the negative electrode is the same as the negative electrode described above.

[0060] Specifically, the secondary battery may include: the aforementioned negative electrode; a positive electrode; a separator inserted between the negative electrode and the positive electrode; and an electrolyte, wherein the negative electrode is the same as the aforementioned negative electrode. Since the negative electrode has already been described above, its detailed description will be omitted.

[0061] The positive electrode comprises a positive current collector and a positive active material layer formed on the current collector, wherein the positive active material layer comprises a positive active material, and the positive active material may be: a layered compound, such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound replaced by one or more transition metals; lithium iron oxide, such as LiFe3O4; lithium manganese oxide, such as Li 1+c1 Mn 2-c1 O4 (0≤c1≤0.33), LiMnO3, LiMn2O3, LiMnO2, etc.; lithium copper oxide (Li2CuO2); vanadium oxides, such as LiV3O8, V2O5, Cu2V2O7, etc.; and those with the chemical formula LiNi 1-c2 M c2 O2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01 ≤ c2 ≤ 0.3) represents a Ni-site type lithium nickel oxide; LiMn 2-c3 M c3A lithium manganese composite oxide represented by O2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and 0.01 ≤ c3 ≤ 0.1) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); or LiMn2O4, in which some Li ions in the chemical formula have been replaced by alkaline earth metal ions.

[0062] The positive electrode active material is preferably selected from lithium cobalt oxide, lithium nickel oxide, and Li a Ni x1 Co y1 Mn z1 O2 (0.9 ≤ a ≤ 1.1, 0.6 ≤ x1 < 1.0, 0 < y1 < 0.4, 0 < z1 < 0.4), or one or more of them.

[0063] In the positive electrode, there is no particular limitation on the positive electrode current collector as long as it does not cause chemical changes in the battery and has conductivity. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel treated with carbon, nickel, titanium, silver, etc. on the surface can be used as the positive electrode current collector. In addition, the thickness of the positive electrode current collector can generally be 3 μm to 500 μm, and fine irregularities are formed on its surface to improve the adhesion of the positive electrode active material. Furthermore, the positive electrode current collector can be used in any of various forms such as films, sheets, foils, meshes, porous materials, foams, non-woven fabrics, etc.

[0064] In addition to containing the above positive electrode active material, the positive electrode active material layer may further contain a positive electrode conductive material and a positive electrode binder.

[0065] In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and any conductive material that does not cause chemical changes in the battery and has electron conductivity can be used without particular limitation. Specific examples of the conductive material include: graphites such as natural graphite and artificial graphite; carbon materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking carbon black, carbon fiber; metal powders or metal fibers containing copper, nickel, aluminum, silver, etc.; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives, and they can be used alone or in the form of a combination of two or more of them.

[0066] Furthermore, the positive electrode adhesive is used to improve the cohesive force between the positive electrode active material particles and the adhesion force between the positive electrode active material and the positive electrode current collector. Specific examples of the adhesive include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof, which can be used alone or in combination of two or more of them.

[0067] The separator serves to separate the negative electrode from the positive electrode and provide a channel for lithium-ion migration. Any separator commonly used in secondary batteries can be used without particular limitation. In particular, separators exhibiting low resistance to electrolyte ion migration and excellent electrolyte impregnation capabilities are preferred. Specifically, porous polymer membranes can be used, such as porous polymer membranes made from polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, ethylene / methacrylate copolymers, etc., or stacked structures of two or more layers thereof. Alternatively, typical porous nonwoven fabrics can be used, such as nonwoven fabrics made from high-melting-point glass fibers, polyethylene terephthalate fibers, etc. Alternatively, coated separators containing ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength; optionally, the separator can be used in the form of a single-layer or multi-layer structure.

[0068] Examples of electrolytes include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, inorganic solid electrolytes, molten inorganic electrolytes, etc., which can be used to manufacture lithium secondary batteries, but the present invention is not limited thereto.

[0069] Specifically, the electrolyte may contain non-aqueous organic solvents and metal salts.

[0070] As the aforementioned non-aqueous organic solvent, aprotic organic solvents such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butyl carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, ethyl propionate, etc., can be used.

[0071] In carbonate-based organic solvents, ethylene carbonate and propylene carbonate, as cyclic carbonates, are particularly preferred because they are high-viscosity organic solvents and have high dielectric constants, thus satisfactorily dissociating lithium salts. Electrolytes with high conductivity can be prepared by using mixtures formed by mixing such cyclic carbonates with low-viscosity, low-dielectric-constant linear carbonates such as dimethyl carbonate and diethyl carbonate in appropriate ratios. Therefore, the use of such mixtures is more preferred.

[0072] Lithium salts can be used as the metal salts, and these lithium salts are substances that are readily soluble in non-aqueous electrolytes. For example, one or more anions selected from the group consisting of F can be used as the anion of the lithium salt. - 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 - .

[0073] In addition to the electrolyte components mentioned above, to improve battery life characteristics, suppress battery capacity reduction, and improve battery discharge capacity, the electrolyte may also contain one or more additives selected from the following: alkylene carbonate halide compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether, hexamethylphosphoryltriamine, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted... Alzolidinediones, N,N-substituted imidazolidinedions, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol, aluminum trichloride, etc.

[0074] According to another embodiment of the present invention, a battery module comprising the aforementioned secondary battery as a unit cell and a battery pack comprising the battery module are provided. Since the battery module and battery pack comprise secondary batteries with high capacity, high rate capability, and high cycle performance, they can be used as power sources for medium to large-sized devices selected from groups consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and energy storage systems.

[0075] Exemplary embodiments of the invention will be described below to aid in understanding the invention. However, it will be apparent to those skilled in the art that the exemplary embodiments presented herein are intended to illustrate the invention, and that various changes and modifications can be made within the scope and spirit of the invention; therefore, it is self-evident that the invention covers all such changes and modifications, provided they fall within the scope of the appended claims.

[0076] Examples and Comparative Examples

[0077] Example 1: Preparation of the negative electrode

[0078] The average particle size (D) was prepared. 50 Single particles with an average particle size of 6 μm were used as the first uncoated artificial graphite particles. These were prepared by passing multiple primary particles (average particle size (D...)... 50 Secondary particles formed by the aggregation of 8μm particles (average particle size (D)) 50 The second uncoated artificial graphite particles consist of 22.5 μm particles.

[0079] Specifically, the second uncoated artificial graphite particles are prepared by pulverizing coke raw materials into particles with an average particle size (D). 50 The coke with a particle size of 8 μm was used; the pulverized coke and pitch were mixed to prepare a granulated intermediate in the form of secondary particles; the intermediate was heat-treated by slowly raising the temperature to 3000°C, holding the temperature at 3000°C for 60 hours, and then slowly lowering the temperature to room temperature to induce graphitization and secondary granulation; and the average particle size (D) of the secondary particles was... 50 The thickness was adjusted to 22.5 μm. In this case, the total heat treatment time for the intermediate was 2 weeks.

[0080] The first uncoated artificial graphite particles and the second uncoated artificial graphite particles were mixed in a 5:5 weight ratio, and this mixture was used as the negative electrode active material (BET specific surface area: 1.5m²). 2 / g), using styrene-butadiene rubber (SBR) as the adhesive, CNT as the conductive material, and carboxymethyl cellulose (CMC) as the thickener.

[0081] A negative electrode slurry was prepared by adding 96.45 parts by weight of negative electrode active material, 1.9 parts by weight of binder, 0.5 parts by weight of conductive material, and 1.15 parts by weight of thickener to 10 parts by weight of distilled water. The negative electrode slurry was then mixed at a concentration of 10 mg / cm³. 2 The negative electrode paste was applied to an 8μm thick copper foil (current collector) and then dried. In this case, the circulating air temperature was 130°C. Subsequently, the current collector coated with the negative electrode paste was rolled, dried in a vacuum oven set to 130°C for 1 hour, and then cut into 15.2cm pieces. 2 The shape is rectangular, thus creating a negative electrode containing a layer of negative electrode active material.

[0082] The pressure of the pressing zone when the negative electrode active material is rolled in series is 4.5 tons / cm.

[0083] Example 2: Preparation of the negative electrode

[0084] The negative electrode was manufactured in the same manner as in Example 1, except that a mixture prepared by mixing the first uncoated artificial graphite particles and the second uncoated artificial graphite particles of Example 1 in a weight ratio of 4:6 was used as the negative electrode active material.

[0085] The BET specific surface area of ​​the negative electrode active material is 1.6 m². 2 / g. The pressing pressure of the negative electrode active material when rolled in series is 5.5 tons / cm.

[0086] Example 3: Preparation of the negative electrode

[0087] The negative electrode was manufactured in the same manner as in Example 1, except that a mixture prepared by mixing the first uncoated artificial graphite particles and the second uncoated artificial graphite particles of Example 1 in a weight ratio of 6:4 was used as the negative electrode active material.

[0088] The BET specific surface area of ​​the negative electrode active material is 1.5 m². 2 / g. The pressing pressure of the negative electrode active material when rolled in series is 6.5 tons / cm.

[0089] Example 4: Preparation of the negative electrode

[0090] The average particle size (D) was prepared. 50 A single particle with a size of 5 μm was used as the first uncoated artificial graphite particle.

[0091] The negative electrode was manufactured in the same manner as in Example 1, except that the first uncoated artificial graphite particles described above were used instead of the first uncoated artificial graphite particles of Example 1.

[0092] The BET specific surface area of ​​the negative electrode active material is 1.7 m². 2 / g. The pressing pressure of the negative electrode active material when rolled in series is 7.5 tons / cm.

[0093] Example 5: Preparation of the negative electrode

[0094] The average particle size (D) was prepared. 50 A single particle with a size of 7 μm was used as the first uncoated artificial graphite particle.

[0095] The negative electrode was manufactured in the same manner as in Example 1, except that the first uncoated artificial graphite particles described above were used instead of the first uncoated artificial graphite particles of Example 1.

[0096] The BET specific surface area of ​​the negative electrode active material is 1.6 m². 2 / g. The pressing pressure of the negative electrode active material when rolled in series is 6.5 tons / cm.

[0097] Example 6: Preparation of the negative electrode

[0098] Prepared by passing through multiple primary particles (average particle size (D) 50 Secondary particles formed by the aggregation of 6μm (average particle size (D)) 50 Uncoated artificial graphite particles (20μm):

[0099] Specifically, the uncoated artificial graphite particles are prepared by pulverizing coke raw materials into particles with an average particle size (D). 50 The coke with a particle size of 6 μm was pulverized and mixed with pitch to prepare a granulated intermediate in the form of secondary particles. The intermediate was then heat-treated by slowly raising the temperature to 3000°C, maintaining the temperature at 3000°C for 60 hours, and then slowly lowering the temperature to room temperature to induce graphitization and secondary granulation. The average particle size (D) of the secondary particles was then... 50 The thickness was adjusted to 20 μm. In this case, the total heat treatment time for the intermediate was 2 weeks.

[0100] The negative electrode was manufactured in the same manner as in Example 1, except that the above-mentioned uncoated artificial graphite particles were used as the second uncoated artificial graphite particles instead of the second uncoated artificial graphite particles in Example 1.

[0101] The BET specific surface area of ​​the negative electrode active material is 1.9 m². 2 / g. The pressing pressure of the negative electrode active material when rolled in series is 5.5 tons / cm.

[0102] Example 7: Preparation of the negative electrode

[0103] Prepared by passing through multiple primary particles (average particle size (D) 50 Secondary particles formed by the aggregation of 6μm (average particle size (D)) 50 Uncoated artificial graphite particles (25μm):

[0104] Specifically, the uncoated artificial graphite particles are prepared by pulverizing coke raw materials into particles with an average particle size (D). 50 The coke with a particle size of 6 μm was pulverized and mixed with pitch to prepare a granulated intermediate in the form of secondary particles. The intermediate was then heat-treated by slowly raising the temperature to 3000°C, maintaining the temperature at 3000°C for 60 hours, and then slowly lowering the temperature to room temperature to induce graphitization and secondary granulation. The average particle size (D) of the secondary particles was then... 50 The thickness is adjusted to 25 μm. In this case, the total heat treatment time for the intermediate is 2 weeks.

[0105] The negative electrode was manufactured in the same manner as in Example 1, except that the above-mentioned uncoated artificial graphite particles were used as the second uncoated artificial graphite particles instead of the second uncoated artificial graphite particles in Example 1.

[0106] The BET specific surface area of ​​the negative electrode active material is 1.6 m². 2 / g. The pressing pressure of the negative electrode active material when rolled in series is 5.5 tons / cm.

[0107] Comparative Example 1: Preparation of the negative electrode

[0108] The average particle size (D) was prepared. 50 A single particle with a size of 4 μm was used as the first uncoated artificial graphite particle.

[0109] The negative electrode was manufactured in the same manner as in Example 1, except that the first uncoated artificial graphite particles described above were used instead of the first uncoated artificial graphite particles of Example 1.

[0110] The BET specific surface area of ​​the negative electrode active material is 1.5 m². 2 / g. The pressing pressure of the negative electrode active material when rolled in series is 9.5 tons / cm.

[0111] Comparative Example 2: Preparation of the Negative Electrode

[0112] The average particle size (D) was prepared. 50A single particle with a size of 8 μm was used as the first uncoated artificial graphite particle.

[0113] The negative electrode was manufactured in the same manner as in Example 1, except that the first uncoated artificial graphite particles described above were used instead of the first uncoated artificial graphite particles of Example 1.

[0114] The BET specific surface area of ​​the negative electrode active material is 1.6 m². 2 / g. The pressing pressure of the negative electrode active material when rolled in series is 8.5 tons / cm.

[0115] Comparative Example 3: Preparation of the Negative Electrode

[0116] Prepared by passing through multiple primary particles (average particle size (D) 50 Secondary particles formed by the aggregation of 8μm particles (average particle size (D)) 50 Uncoated artificial graphite particles (19μm):

[0117] Specifically, the uncoated artificial graphite particles are prepared by pulverizing coke raw materials into particles with an average particle size (D). 50 The coke with a particle size of 8 μm was pulverized and mixed with pitch to prepare a granulated intermediate in the form of secondary particles. The intermediate was then heat-treated by slowly raising the temperature to 3000°C, maintaining the temperature at 3000°C for 60 hours, and then slowly lowering the temperature to room temperature to induce graphitization and secondary granulation. The average particle size (D) of the secondary particles was then... 50 The thickness was adjusted to 19 μm. In this case, the total heat treatment time for the intermediate was 2 weeks.

[0118] The negative electrode was manufactured in the same manner as in Example 1, except that the above-mentioned uncoated artificial graphite particles were used as the second uncoated artificial graphite particles instead of the second uncoated artificial graphite particles in Example 1.

[0119] The BET specific surface area of ​​the negative electrode active material is 1.7 m². 2 / g. The pressing pressure of the negative electrode active material when rolled in series is 9.5 tons / cm.

[0120] Comparative Example 4: Preparation of the Negative Electrode

[0121] Prepared by passing through multiple primary particles (average particle size (D) 50 Secondary particles formed by the aggregation of 8μm particles (average particle size (D)) 50 Uncoated artificial graphite particles (26μm):

[0122] Specifically, the uncoated artificial graphite particles are prepared by pulverizing coke raw materials into particles with an average particle size (D).50 The coke with a particle size of 6 μm was pulverized and mixed with pitch to prepare a granulated intermediate in the form of secondary particles. The intermediate was then heat-treated by slowly raising the temperature to 3000°C, maintaining the temperature at 3000°C for 60 hours, and then slowly lowering the temperature to room temperature to induce graphitization and secondary granulation. The average particle size (D) of the secondary particles was then... 50 The thickness was adjusted to 26 μm. In this case, the total heat treatment time for the intermediate was 2 weeks.

[0123] The negative electrode was manufactured in the same manner as in Example 1, except that the above-mentioned uncoated artificial graphite particles were used as the second uncoated artificial graphite particles instead of the second uncoated artificial graphite particles in Example 1.

[0124] The BET specific surface area of ​​the negative electrode active material is 1.5 m². 2 / g. The pressing pressure of the negative electrode active material when rolled in series is 8.5 tons / cm.

[0125] Comparative Example 5: Preparation of the Negative Electrode

[0126] The negative electrode was manufactured in the same manner as in Example 1, except that a mixture prepared by mixing the first uncoated artificial graphite particles and the second uncoated artificial graphite particles of Example 1 in a weight ratio of 3:7 was used as the negative electrode active material.

[0127] The BET specific surface area of ​​the negative electrode active material is 1.8 m². 2 / g. The pressing pressure of the negative electrode active material when rolled in series is 10.5 tons / cm.

[0128] Comparative Example 6: Preparation of the Negative Electrode

[0129] The negative electrode was manufactured in the same manner as in Example 1, except that a mixture prepared by mixing the first uncoated artificial graphite particles and the second uncoated artificial graphite particles of Example 1 in a weight ratio of 7:3 was used as the negative electrode active material.

[0130] The BET specific surface area of ​​the negative electrode active material is 1.7 m². 2 / g. The pressing pressure of the negative electrode active material when rolled in series is 11.5 tons / cm.

[0131] Comparative Example 7: Preparation of the Negative Electrode

[0132] The average particle size (D) was prepared. 50 A single particle with a size of 9 μm was used as the first uncoated artificial graphite particle.

[0133] Prepared by passing through multiple primary particles (average particle size (D)50 Secondary particles formed by the aggregation of 4μm (average particle size (D)) 50 The second uncoated artificial graphite particles consist of 17.5 μm.

[0134] Specifically, the second uncoated artificial graphite particles are prepared by pulverizing coke raw materials into particles with an average particle size (D). 50 The coke with a particle size of 4 μm was pulverized and mixed with pitch to prepare a granulated intermediate in the form of secondary particles. The intermediate was then heat-treated by slowly raising the temperature to 3000°C, maintaining the temperature at 3000°C for 60 hours, and then slowly lowering the temperature to room temperature to induce graphitization and secondary granulation. The average particle size (D) of the secondary particles was then... 50 The thickness was adjusted to 17.5 μm. In this case, the total heat treatment time for the intermediate was 2 weeks.

[0135] The negative electrode was manufactured in the same manner as in Example 1, except that a mixture prepared by mixing the first uncoated artificial graphite particles and the second uncoated artificial graphite particles in a weight ratio of 3:7 was used as the negative electrode active material.

[0136] The BET specific surface area of ​​the negative electrode active material is 1.5 m². 2 / g. The pressing pressure of the negative electrode active material when rolled in series is 5.5 tons / cm.

[0137] Comparative Example 8: Preparation of the Negative Electrode

[0138] 90 parts by weight of the first uncoated artificial graphite particles from Example 1 were mixed with 10 parts by weight of asphalt, and the mixture was heat-treated at 1200°C for 10 hours to prepare soft carbon-coated artificial graphite particles (average particle size (D)). 50 (6.5μm).

[0139] The negative electrode was manufactured in the same manner as in Example 1, except that a mixture prepared by mixing the soft carbon-coated artificial graphite particles with the second uncoated artificial graphite particles of Example 1 in a weight ratio of 3:7 was used as the negative electrode active material.

[0140] The BET specific surface area of ​​the negative electrode active material is 1.1 m². 2 / g. The pressing pressure of the negative electrode active material when rolled in series is 6.5 tons / cm.

[0141] Comparative Example 9: Preparation of the Negative Electrode

[0142] The negative electrode was manufactured in the same manner as in Example 1, except that only the second uncoated artificial graphite particles from Example 1 were used as the negative electrode active material.

[0143] The BET specific surface area of ​​the negative electrode active material is 0.9 m². 2 / g. The pressing pressure of the negative electrode active material when rolled in series is 7.5 tons / cm.

[0144] Comparative Example 10: Preparation of the Negative Electrode

[0145] 90 parts by weight of the second uncoated artificial graphite particles from Example 1 were mixed with 10 parts by weight of asphalt, and the mixture was heat-treated at 1200°C for 10 hours to prepare soft carbon-coated artificial graphite particles (average particle size (D)). 50 :23μm).

[0146] The negative electrode was manufactured in the same manner as in Example 1, except that soft carbon-coated artificial graphite particles were used as the negative electrode active material.

[0147] The BET specific surface area of ​​the negative electrode active material is 0.8 m². 2 / g. The pressing pressure of the negative electrode active material when rolled in series is 10.5 tons / cm.

[0148] Comparative Example 11: Preparation of the negative electrode

[0149] The negative electrode was manufactured in the same manner as in Example 1, except that only the first uncoated artificial graphite particles of Example 1 were used as the negative electrode active material.

[0150] The BET specific surface area of ​​the negative electrode active material is 1.2 m². 2 / g. The pressing pressure of the negative electrode active material when rolled in series is 11.5 tons / cm.

[0151] Comparative Example 12: Preparation of the Negative Electrode

[0152] The negative electrode was manufactured in the same manner as in Example 1, except that natural graphite (POSCOCHEMICAL, PAS-C3B) was used as the negative electrode active material.

[0153] The average particle size (D) of the secondary particles contained in the natural graphite 50 The micrometer diameter (μm) is 22.5 μm, and the specific surface area of ​​BET is 2.9 m². 2 / g, the pressing pressure of the negative electrode active material when rolled in series is 9.5 tons / cm.

[0154] [Table 1]

[0155]

[0156] Preparation Example

[0157] Batteries were manufactured using the negative electrodes of Examples 1 to 7 and Comparative Examples 1 to 12 as follows.

[0158] LCO (as the positive electrode active material), carbon black-based conductive material, and PVDF powder (as a binder) were mixed in an N-methyl-2-pyrrolidone solvent at a weight ratio of 92:2:6 to prepare the positive electrode slurry.

[0159] The prepared positive electrode slurry was applied to a 20 μm thick positive electrode current collector, so that the loading per unit area (mg / cm²) was achieved. 2 The sample was 23.4 mg, dried in a vacuum oven set at 130°C for 1 hour, and rolled at a pressure of 15 MPa while passing through rollers heated at 80°C, thereby producing a positive electrode with a final thickness (current collector + active material layer) of 72.5 μm.

[0160] In Examples 1 to 7 and Comparative Examples 1 to 12, a porous polyethylene separator was inserted between each negative electrode and the positive electrode to assemble the battery in a stacked manner. An electrolyte (ethylene carbonate (EC) / ethyl methyl carbonate (EMC) = 1:4 (volume ratio), lithium hexafluorophosphate (LiPF6, 1M) and ethylene carbonate (VC) at a content of 0.5% by weight of the electrolyte) was injected into the assembled battery to manufacture each lithium secondary battery.

[0161] Experimental Example

[0162] Experimental Example 1: Evaluation of Battery Energy Density

[0163] The volumetric energy density per unit volume of each negative electrode of Examples 1 to 7 and Comparative Examples 1 to 12 was measured using a PNE charger / discharger (PNE Solution Corporation). The results are shown in Table 2 below.

[0164] Experimental Example 2: Evaluation of Battery Life Characteristics

[0165] The manufactured batteries were charged and discharged as follows: the charging range was set from SOC 0% to SOC 100%, the first cycle was performed at a current rate of 0.1C, the second cycle at a current rate of 0.2C, the third cycle at 0.5C, and so on up to the 100th cycle. The charging performance of the battery was then calculated using Equation 1 below. The results are shown in Table 2 below.

[0166] [Formula 1]

[0167] Charging performance (%) = [Charging capacity after 100 cycles / Initial charging capacity] × 100

[0168] Experimental Example 3: Evaluation of Negative Electrode Hole Resistance

[0169] The negative electrodes of Examples 1 to 7 and Comparative Examples 1 to 12 were used as both the working electrode and the counter electrode, and a polyethylene diaphragm was inserted between the working electrode and the counter electrode to prepare an electrode assembly. A symmetrical single cell was fabricated by injecting an electrolyte prepared by dissolving 1M LiPF6 in a solvent obtained by mixing ethylene carbonate (EC) and diethylene carbonate (EMC) in a 1:4 volume ratio into the electrode assembly.

[0170] Using an electrochemical impedance spectroscopy instrument at 10 6 The impedance of a symmetrical single cell was measured in the frequency range of Hz to 0.05Hz, separating the electrolyte resistance and pore resistance, and the pore resistance was measured. The results are shown in Table 2 below.

[0171] [Table 2]

[0172]

[0173] Referring to Table 2, it can be confirmed that the negative electrodes of Examples 1 to 7 according to the present invention exhibit higher energy densities compared to the negative electrodes of Comparative Examples 1 to 12. This is because the negative electrodes of Examples 1 to 5 contain negative electrode active materials, which are contained in a specific weight ratio as an average particle size (D). 50 Uncoated artificial graphite particles with a single particle size of 5 μm to 7 μm, and uncoated artificial graphite particles formed by the aggregation of multiple primary particles with an average particle size (D) 50 Uncoated artificial graphite particles with a secondary particle size of 20μm to 25μm were used to roll the electrode in series. The pressure in the low-pressure zone was measured, so the electrode could be rolled smoothly even with relatively small force, thus achieving a thin electrode.

[0174] Furthermore, it can be confirmed that, compared with batteries containing the negative electrode of the comparative example, batteries containing the negative electrode of Embodiments 1 to 7 according to the present invention exhibit significantly superior charging performance.

[0175] Furthermore, it can be confirmed that the negative electrode according to the present invention exhibits a low pore resistance of less than 9 ohms. Therefore, it is evident that the negative electrode according to the present invention can maintain high charging characteristics by reducing resistance to electrolyte diffusion while sufficiently preserving the electrode structure.

Claims

1. A negative electrode, said negative electrode comprising a current collector and a layer of negative electrode active material formed on said current collector, The negative electrode active material layer contains a negative electrode active material. The negative electrode active material comprises a first uncoated artificial graphite particle and a second uncoated artificial graphite particle in a weight ratio of 4:6 to 6:

4. The first uncoated artificial graphite particle has an average particle size D. 50 Single particles ranging from 5 μm to 7 μm, and The second uncoated artificial graphite particles are formed by the aggregation of multiple primary particles and have an average particle size D. 50 Secondary particles ranging from 20 μm to 25 μm. Uncoated artificial graphite particles refer to artificial graphite particles that are not coated, and mean that the entire surface of the artificial graphite is exposed. The BET specific surface area of ​​the negative electrode active material is 1.0 m². 2 / g to 2.5m 2 / g.

2. The negative electrode according to claim 1, wherein the negative electrode active material is composed of the first uncoated artificial graphite particles and the second uncoated artificial graphite particles.

3. The negative electrode according to claim 1, wherein the secondary particles are of average particle size D 50 It is formed by the aggregation of multiple primary particles ranging from 7μm to 9μm.

4. The negative electrode according to claim 1, wherein the tap density of the negative electrode active material is from 1.00 g / cc to 1.20 g / cc.

5. The negative electrode according to claim 1, wherein the pore volume of the negative electrode active material layer is 10 cm³. 3 / g to 20cm 3 / g.

6. The negative electrode according to claim 1, wherein the negative electrode active material is contained in the negative electrode active material layer in an amount of 90% to 99% by weight.

7. The negative electrode according to claim 1, wherein the negative electrode active material layer further comprises a conductive material. The conductive material is included in the negative electrode active material layer in an amount of 0.1% to 1.0% by weight.

8. The negative electrode according to claim 7, wherein the conductive material comprises at least one selected from carbon black and carbon nanotubes.

9. The negative electrode according to claim 1, wherein the pore resistance of the negative electrode is less than 9 ohms.

10. A secondary battery, the secondary battery comprising: The negative electrode according to any one of claims 1 to 9; positive electrode; A diaphragm inserted between the negative electrode and the positive electrode; and Electrolytes.

Images