Negative electrode active material for lithium secondary battery, method for producing the same, and lithium secondary battery including the same

Abstract

The present invention relates to a method for producing a negative electrode active material for a lithium secondary battery, the method including the steps of: preparing artificial graphite; mixing the artificial graphite with a liquid coating material to form a coating layer that covers the artificial graphite; and carbonizing the artificial graphite with the coating layer formed thereon, wherein the liquid coating material has a viscosity of 300 to 25,000 mPa s at 35° C.; and a lithium secondary battery including the negative electrode active material produced from the method.

Description

[Technical Field]

[0001] The present invention relates to a negative electrode active material for a lithium secondary battery, a method for producing the same, and a lithium secondary battery including the same. Specifically, the present invention relates to a negative electrode active material for a lithium secondary battery having excellent electrode adhesion, a method for producing the same, and a lithium secondary battery including the same. [Background technology]

[0002] Graphite-based / carbon-based negative electrode active materials used in lithium secondary batteries have an electrode potential close to that of lithium metal, and therefore undergo minimal change in their crystalline structure during the intercalation and deintercalation processes of ionic lithium, enabling sustained and repeated oxidation-reduction reactions in the electrode, thereby enabling lithium secondary batteries to exhibit high capacity and excellent lifespan.

[0003] Carbon-based anode active materials come in a variety of forms, including crystalline carbon materials such as natural graphite and artificial graphite, and amorphous carbon materials such as hard carbon and soft carbon. Among these, graphite-based active materials are the most widely used, as they offer excellent reversibility and improve the lifespan characteristics of lithium secondary batteries. Because graphite-based active materials have a lower discharge voltage of -0.2 V compared to lithium, batteries using graphite-based active materials can exhibit a high discharge voltage of 3.6 V, offering numerous advantages in terms of energy density for lithium secondary batteries.

[0004] Artificial graphite, a crystalline carbon material, is created by applying high thermal energy of over 2,700°C to create a graphite crystalline structure. This gives it a more stable crystalline structure than natural graphite, resulting in less change in the crystalline structure even with repeated charging and discharging of lithium ions, resulting in a relatively long lifespan. In general, artificial graphite-based negative electrode active materials have a lifespan two to three times longer than natural graphite.

[0005] Soft carbon and hard carbon, which are amorphous carbon materials with an unstabilized crystal structure, allow lithium ions to penetrate more easily, which increases the charge / discharge rate and makes them suitable for use in electrodes that require high-speed charging.

[0006] In general, the carbonaceous materials are mixed together in a certain ratio in consideration of the life and output characteristics of the lithium secondary battery to be used.

[0007] Meanwhile, improving the high-temperature performance (high-temperature storage characteristics and high-temperature cycle characteristics) of lithium secondary batteries is an important issue. If the total internal pore volume is high after the negative electrode active material is applied to the current collector and rolled, the high-temperature performance of the negative electrode is likely to decrease. Therefore, it is necessary to improve the high-temperature performance of lithium secondary batteries by minimizing the changes in the electrode structure and total internal pore volume that occur during electrode rolling.

[0008] In particular, when developing negative electrode materials for rapid charging secondary batteries, there is a growing demand for improved high-temperature properties.

[0009] Due to technological development and increasing demand for mobile devices, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which exhibit high energy density and working potential, long cycle life, and low self-discharge rate, have been commercialized and are widely used.

[0010] In addition, as interest in environmental issues grows, there is growing interest in electric vehicles and hybrid electric vehicles as alternatives to vehicles that use fossil fuels such as gasoline and diesel vehicles, which are one of the main causes of air pollution. Research into the use of lithium secondary batteries as a power source for such electric vehicles and hybrid electric vehicles is being actively conducted.

[0011] A lithium secondary battery is generally composed of a positive electrode containing a positive active material, a negative electrode containing a negative active material, a separator, and an electrolyte, and is charged and discharged by the intercalation-decalation of lithium ions. Lithium secondary batteries have the advantages of high energy density, large electromotive force, and high capacity, and are therefore used in a variety of fields.

[0012] In particular, with the recent rapid rise of electric vehicles (EVs), expectations for lithium-ion secondary batteries are increasing, with demands for improvements in fast charging characteristics while maintaining existing capacity. To improve fast charging, the negative electrode active material, which is responsible for storing lithium ions during charging, must fulfill this role. As these materials are primarily made up of carbon / graphite-based materials, it is important to form a stable SEI (solid electrolyte interface) during charging.

[0013] Among these, artificial graphite is being adopted most readily from the standpoint of fast charging and lifespan (stability), and this trend is expected to continue in the future.

[0014] To obtain artificial graphite, coke particles and binder materials are mixed and heat-treated to produce secondary particles, but this process is difficult to build the necessary equipment, and there are problems with contamination in certain areas during actual production. It is also difficult to guarantee uniformity in terms of batch quality. Therefore, it is necessary to minimize the number of processes. Summary of the Invention [Problem to be solved by the invention]

[0015] An embodiment of the present invention provides a negative electrode active material for a lithium secondary battery that is manufactured without an assembly process, a manufacturing method thereof, and a secondary battery including the same.

[0016] An embodiment of the present invention provides a negative electrode active material for a lithium secondary battery, which is manufactured using a liquid coating material without an assembly process, a manufacturing method thereof, and a secondary battery including the same. [Means for solving the problem]

[0017] According to one embodiment of the present invention, a negative electrode active material for a lithium secondary battery includes: preparing artificial graphite; mixing the artificial graphite with a liquid coating material to form a coating layer that coats the artificial graphite; and carbonizing the artificial graphite with the coating layer formed thereon, wherein the liquid coating material has a viscosity of 300 to 25,000 mPa s at 35°C.

[0018] In the step of forming the coating layer, the content of the liquid coating material is 5 to 30 parts by weight based on 100 parts by weight of the artificial graphite.

[0019] In the step of forming the coating layer, the amount of fixed carbon in the liquid coating material at 25° C. is 15 to 60% by weight.

[0020] The step of preparing the artificial graphite includes the steps of crushing coke and graphitizing the coke.

[0021] In the step of preparing artificial graphite, the artificial graphite is coal-based coke-derived artificial graphite, petroleum-based coke-derived artificial graphite, or a mixture thereof.

[0022] The artificial graphite is a mixture of artificial graphite derived from coal-based coke and artificial graphite derived from petroleum-based coke, with 50 parts by weight or more of artificial graphite derived from petroleum-based coke mixed with 100 parts by weight of the mixture.

[0023] In the step of preparing artificial graphite, the particle size SPAN ((D90-D10) / D50) of the artificial graphite is 0.7 to 2.5.

[0024] In the step of forming a coating layer, the liquid coating material is a graphitizable carbon precursor or a non-graphitizable carbon precursor.

[0025] The carbonization temperature is 800 to 2000°C.

[0026] In the step of forming the coating layer, the artificial graphite and the liquid coating material are mixed at a temperature of 50° C. or less.

[0027] According to one embodiment of the present invention, there is provided a negative electrode active material for a lithium secondary battery, comprising: artificial graphite; and a carbon coating layer formed on the surface of the artificial graphite; wherein the carbon coating layer is a carbonized liquid coating layer having a viscosity of 300 to 25,000 mPa·s at 35°C.

[0028] The artificial graphite is artificial graphite derived from coal-based coke, artificial graphite derived from petroleum-based coke, or a mixture thereof.

[0029] The artificial graphite is a mixture of artificial graphite derived from coal-based coke and artificial graphite derived from petroleum-based coke, with the amount of artificial graphite derived from petroleum-based coke being 50 parts by weight or more per 100 parts by weight of the mixture.

[0030] A lithium secondary battery according to one embodiment of the present invention includes a negative electrode including a negative electrode active material prepared by the method for preparing a negative electrode active material for a lithium secondary battery; a positive electrode; and an electrolyte. [Effects of the Invention]

[0031] The negative electrode active material for a lithium secondary battery, the manufacturing method thereof, and the secondary battery including the same according to an embodiment of the present invention may not require an assembly process by controlling the viscosity of the liquid coating material used.

[0032] The negative electrode active material for a lithium secondary battery, the method for manufacturing the same, and the secondary battery including the same according to one embodiment of the present invention have excellent electrode adhesion.

[0033] According to an embodiment of the present invention, a negative electrode active material for a lithium secondary battery, a manufacturing method thereof, and a secondary battery including the same do not require a separate assembly process, and therefore, an artificial graphite negative electrode material composed of single particles can be provided. DETAILED DESCRIPTION OF THE INVENTION

[0034] Terms such as "first," "second," and "third" are used to describe various parts, components, regions, layers, and / or sections, but are not limited thereto. These terms are used only to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Therefore, a first part, component, region, layer, or section described below may be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0035] The terminology used herein is merely for the purpose of referring to particular embodiments and is not intended to limit the present invention. As used herein, the singular forms "a," "an," and "the" include the plural forms unless the context clearly dictates otherwise. As used in the specification, the term "comprising" refers to the inclusion of certain features, regions, integers, steps, operations, elements, and / or components, and does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0036] When a part is referred to as being "on" or "above" another part, this can be directly on or above the other part, or with other parts in between. In contrast, when a part is referred to as being "directly on" another part, there are no other parts in between.

[0037] Unless otherwise specified, % means % by weight, and 1 ppm is 0.0001% by weight.

[0038] In one embodiment of the present invention, the inclusion of an additional element means that an additional amount of the additional element is included in place of the remaining iron (Fe).

[0039] Unless otherwise defined, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by a person of ordinary skill in the art to which this invention belongs. Terms defined in commonly used dictionaries are additionally interpreted to have a meaning consistent with the relevant technical literature and the presently disclosed content, and are not interpreted in an ideal or overly formal sense unless otherwise defined.

[0040] While the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein, the present invention will be described in detail below so that those skilled in the art can easily practice the present invention.

[0041] Each stage will be examined in detail below.

[0042] A method for preparing a negative electrode active material for a lithium secondary battery according to one embodiment of the present invention includes the steps of: preparing artificial graphite; mixing the artificial graphite with a liquid coating material to form a coating layer that coats the artificial graphite; and carbonizing the artificial graphite with the coating layer formed thereon.

[0043] In the method for manufacturing the negative electrode active material for a secondary battery, the step of preparing artificial graphite includes the steps of crushing coke and graphitizing the coke.

[0044] In addition, in the step of preparing the artificial graphite, the artificial graphite may be artificial graphite derived from coal-based coke, artificial graphite derived from petroleum-based coke, or a mixture thereof. That is, the artificial graphite may be obtained by pulverizing and graphitizing coal-based coke, petroleum-based coke, or a mixture thereof.

[0045] In addition, in the step of preparing artificial graphite, when the artificial graphite is a mixture of coal-based coke-derived artificial graphite and petroleum-based coke-derived artificial graphite, the petroleum-based coke artificial graphite may be mixed in an amount of 50 parts by weight or more for 100 parts by weight of the mixture of coal-based coke-derived artificial graphite and petroleum-based coke-derived artificial graphite.

[0046] That is, the coke used in the step of preparing artificial graphite may be coal-based coke, petroleum-based coke, or a mixture thereof. When a mixture of coal-based coke and petroleum-based coke is used, the petroleum-based coke may be contained in an amount of less than 50 parts by weight per 100 parts by weight of the mixture.

[0047] The coal-based coke or petroleum-based coke may be needle coke, isotropic coke, or a mixture thereof, and the coal-based coke or petroleum-based coke may be green coke, calcined coke, or a mixture thereof.

[0048] Furthermore, the artificial graphite according to the present invention is not assembled. That is, the artificial graphite is a primary particle or a single particle itself, and is not assembled. Therefore, the artificial graphite used as a raw material in the method for manufacturing a negative electrode active material does not include a soft carbon adhesive or a hard carbon adhesive.

[0049] The pulverization method used in the step of pulverizing coke included in the step of preparing artificial graphite is not limited as long as it can adjust the particle size to the size described below, and for example, a jet mill, a pin mill, an air classifier mill, a Raymond mill, a jaw crusher, etc. can be used. The pulverized coke can be classified using a suitable sieve.

[0050] In the step of preparing the artificial graphite, the particle size SPAN ((D90-D10) / D50) of the artificial graphite is 0.7 to 2.5. The particle size D50 of the artificial graphite is 10 to 20 μm, D10 is 5 μm or more, and D90 is 40 μm or less. In addition, if a mixture of coal-based coke-derived artificial graphite and petroleum-based coke-derived artificial graphite is used, it is preferable that the particle sizes of the two are similar.

[0051] In the step of preparing artificial graphite, the graphitization temperature in the step of graphitizing coke is 2200 to 3000°C, and the graphitization treatment time is 3 hours or more.

[0052] In the method for manufacturing a negative electrode active material for a secondary battery, the liquid coating material in the step of forming the coating layer has a viscosity of 300 to 25,000 mPa s at 35°C. Specifically, the liquid coating material has a viscosity of 1,000 to 15,000 mPa s at 35°C. More specifically, the liquid coating material has a viscosity of 8,000 to 10,000 mPa s at 35°C.

[0053] If the viscosity of the liquid coating material is too low, it will have poor wettability and separate from the base material, resulting in incomplete coating of the base material. However, if the viscosity of the liquid coating material is too high, the viscosity will be too high and the liquid will have properties closer to a solid than a liquid, causing phase separation and resulting in incomplete coating of the base material. In other words, good coating of the base material can only be achieved if the viscosity range is met.

[0054] In addition, by controlling the viscosity of the liquid coating material within the above range in the method for manufacturing an anode active material for a lithium secondary battery according to the present invention, it is possible to immediately coat artificial graphite composed of single particles, i.e., primary particles only. Furthermore, it is possible to provide an anode active material with excellent electrode adhesion without a separate assembly process, thereby achieving energy and cost reductions during the process.

[0055] Additionally, in the coating layer formation step, the liquid coating material should have a fixed carbon content (residual carbon content) of 15-60% by weight at 25°C. If the fixed carbon content is too low, the mixer rotation speed must be increased when mixing with the artificial graphite to function as a coating material. As the rotation speed increases, the temperature inside the mixer and the mixture rises, which can lead to performance degradation. On the other hand, if the fixed carbon content is too high, liquefaction becomes difficult, preventing the benefits of the liquid coating from being achieved and requiring more complex processing steps.

[0056] In the step of forming the coating layer, the liquid coating material is not limited as long as it satisfies the above-mentioned viscosity and fixed carbon content.

[0057] The liquid coating material may be a graphitizable carbon (soft carbon) precursor or a non-graphitizable carbon (hard carbon) precursor among amorphous carbon-based materials. The graphitizable carbon precursor may be coal-based pitch, petroleum-based pitch, or coal tar. Therefore, when a graphitizable carbon-based precursor material is used, its structural stability can be enhanced after carbonization by heat treatment. The non-graphitizable carbon (hard carbon) may be polyimide resin, furan resin, phenol resin, polyvinyl alcohol resin, cellulose resin, epoxy resin, polystyrene resin, etc. The non-graphitizable carbon-based precursor material may also have enhanced structural stability after carbonization by heat treatment.

[0058] For example, the liquid coating material may be one or more selected from the group consisting of liquid phenol resin, liquid petroleum pitch, liquid coal pitch, and coal tar, i.e., liquid phenol resin, liquid petroleum pitch, liquid coal pitch, coal tar, etc., and may satisfy the above-mentioned viscosity and fixed carbon ranges.

[0059] In addition, in the step of forming the coating layer, the content of the liquid coating material relative to 100 parts by weight of the artificial graphite is 5 to 30 parts by weight. Specifically, the content of the liquid coating material relative to 100 parts by weight of the artificial graphite may be 10 to 30 parts by weight or 15 to 25 parts by weight. If the content of the liquid coating material does not satisfy the above range, the electrode adhesive strength of the negative electrode active material is insufficient for use in products (for example, 300 gf / cm 2 There is a problem below.

[0060] In the step of forming the coating layer, the artificial graphite and the liquid coating material are mixed at a temperature of 50° C. or less.

[0061] The mixing time of the artificial graphite and the liquid coating material and the mixer speed (e.g., the rotation speed (rpm) in the case of a rotary mixer) can be adjusted depending on the viscosity of the liquid coating material. If the viscosity of the liquid coating material is too low, it is better to increase the mixing time and increase the mixer speed to ensure good substrate coating. Conversely, if the viscosity of the liquid coating material is too high, it is better to shorten the mixing time and decrease the mixer speed to ensure good substrate coating. The preferred mixing rotation speed is 100 rpm or more, and the mixing time is 15 minutes or more. If the time is too short, the substrate will not be completely coated.

[0062] In addition, in the step of forming the coating layer, the liquid coating material is charged into the mixing reactor above the artificial graphite, in order to spread and coat the liquid coating material as uniformly as possible on the artificial graphite.

[0063] The mixing reactor may have one or more rotating parts, and preferably has two or more rotating parts, and the two or more rotating parts may simultaneously revolve around their own axes.

[0064] The unreacted area of ​​the mixer reactor may be 10% or less of the total area, and the unreacted area refers to the part of the reactor that is not in contact with the rotating part of the mixer reactor.

[0065] In the method for manufacturing a negative electrode active material for a secondary battery, the step of carbonizing the artificial graphite having the coating layer formed thereon is carried out at a carbonization temperature of 800 to 2000°C. Specifically, the carbonization temperature is 1000 to 1500°C or 1200 to 1500°C. Specifically, the temperature is raised to the carbonization temperature at a rate of 3 to 8°C / min, and the carbonization can be carried out by maintaining the temperature at the carbonization temperature for 1 to 5 hours. If the carbonization temperature is too low, the volatile matter removal rate is low, resulting in poor quality of the final product. If the carbonization temperature is too high, unnecessary energy consumption occurs at temperatures close to graphitization.

[0066] According to one embodiment of the present invention, there is provided a negative electrode active material for a lithium secondary battery, comprising: artificial graphite; and a carbon coating layer formed on the surface of the artificial graphite; wherein the carbon coating layer is a carbonized liquid coating layer having a viscosity of 300 to 25,000 mPa s at 35°C.

[0067] The artificial graphite contained in the negative electrode active material for a lithium secondary battery is artificial graphite derived from coal-based coke, artificial graphite derived from petroleum-based coke, or a mixture thereof.

[0068] Furthermore, when the artificial graphite is a mixture of coal-based coke-derived artificial graphite and petroleum-based coke-derived artificial graphite, the amount of petroleum-based coke-derived artificial graphite may be 50 parts by weight or more per 100 parts by weight of the mixture of coal-based coke-derived artificial graphite and petroleum-based coke-derived artificial graphite.

[0069] A lithium secondary battery according to an embodiment of the present invention includes a negative electrode including the negative electrode active material prepared by the above-described method, a positive electrode, and an electrolyte. Specifically, the lithium secondary battery may further include a separator disposed between the positive electrode and the negative electrode.

[0070] The negative electrode may be manufactured by mixing the negative electrode active material manufactured according to one embodiment of the present invention, a binder, and optionally a conductive material to prepare a composition for forming a negative electrode active material layer, and then coating the composition on a negative electrode current collector.

[0071] The negative electrode current collector may be, for example, copper foil, nickel foil, stainless steel, titanium foil, nickel foam, copper foam, a conductive metal-coated polymer substrate, or a combination thereof.

[0072] The binder may be, but is not limited to, polyvinyl alcohol, carboxymethyl cellulose / styrene-butadiene rubber, hydroxypropylene cellulose, diacetylene cellulose, polyvinyl chloride, polyvinylpyrrolidone, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, or polypropylene, and may be mixed in an amount of 1 wt % to 30 wt % based on the total amount of the composition for forming the negative electrode active material layer.

[0073] The conductive material is not particularly limited as long as it does not induce chemical changes in the battery and is conductive, and specific examples include graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber and metal fiber; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskey such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives. The conductive material may be mixed in an amount of 0.1 wt % to 30 wt % with respect to the total amount of the composition for forming the negative electrode active material layer.

[0074] The positive electrode may be fabricated by mixing a positive electrode active material, a binder, and optionally a conductive material to form a composition for forming a positive electrode active material layer, and then coating the composition on a positive electrode current collector, using the same binder and conductive material as in the negative electrode.

[0075] The positive electrode current collector may be, for example, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, or the like.

[0076] The positive electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium (lithiated intercalation compound).

[0077] The positive electrode active material may be one or more of composite oxides of lithium and cobalt, manganese, nickel, or a combination thereof, and a specific example thereof may be a compound represented by any one of the following chemical formulas: Li a A 1-b R b D2 (wherein 0.90≦a≦1.8 and 0≦b≦0.5); Li a E 1-b R b O 2-c D c (wherein 0.90≦a≦1.8, 0≦b≦0.5, and 0≦c≦0.05); LiE 2-b R b O 4-c D c (wherein 0≦b≦0.5, 0≦c≦0.05); Li a Ni 1-b-c Co b R c D α (wherein 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0<α≦2); Li a Ni 1-b-c Co b R c O 2-α Z α (wherein 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0<α<2); Li a Ni 1-b-c Co b R c O 2-α Z2 (wherein 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0<α<2); Li a Ni 1-b-c Mn b R c D α (wherein 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0<α≦2); Li a Ni 1-b-c Mn b R c O 2-αZ α (wherein 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0<α<2); Li a Ni 1-b-c Mn b R c O 2-α Z2 (wherein 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0<α<2); Li a Ni b E c G d O2 (wherein 0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, and 0.001≦d≦0.1); Li a Ni b Co c Mn d GeO2 (wherein 0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0≦d≦0.5, and 0.001≦e≦0.1); Li a NiG b O2 (wherein 0.90≦a≦1.8 and 0.001≦b≦0.1); Li a CoG b O2 (wherein 0.90≦a≦1.8 and 0.001≦b≦0.1); Li a MnG b O2 (wherein 0.90≦a≦1.8 and 0.001≦b≦0.1); Li a Mn2G b O4 (wherein 0.90≦a≦1.8 and 0.001≦b≦0.1); QO2; QS2; LiQS2; V2O5; LiV2O5; LiTO2; LiNiVO4; Li (3-f) J2(PO4)3(0≦f≦2);Li (3-f) Fe2(PO4)3(0≦f≦2); and LiFePO4.

[0078] In the above chemical formula, A is Ni, Co, Mn, or a combination thereof; R is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P, or a combination thereof; E is Co, Mn, or a combination thereof; Z is F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; Q is Ti, Mo, Mn, or a combination thereof; T is Cr, V, Fe, Sc, Y, or a combination thereof; and J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

[0079] The electrolyte filled in the lithium secondary battery may be a non-aqueous electrolyte or a known solid electrolyte, and may be one in which a lithium salt is dissolved.

[0080] The lithium salt may be, for example, one or more selected from the group consisting of LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, LiSbF6, LiAlO4, LiAlCl4, LiCl, and LiI.

[0081] Examples of solvents for the non-aqueous electrolyte include, but are not limited to, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate; chain carbonates such as dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate; esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and γ-butyrolactone; ethers such as 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,2-dioxane, and 2-methyltetrahydrofuran; nitriles such as acetonitrile; and amides such as dimethylformamide. These solvents can be used alone or in combination. A mixed solvent of a cyclic carbonate and a chain carbonate is particularly preferred.

[0082] The electrolyte may be a gel polymer electrolyte in which a polymer electrolyte such as polyethylene oxide or polyacrylonitrile is impregnated with an electrolytic solution, or an inorganic solid electrolyte such as LiI or Li3N.

[0083] The separator can be a sheet or nonwoven fabric made of chemically resistant and hydrophobic olefin polymers such as polypropylene, glass fiber, polyethylene, etc. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte can also serve as the separator. [Example]

[0084] While the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein, the present invention will be described in detail below so that those skilled in the art can easily practice the present invention.

[0085] "Experimental Example 1 - Experiment on electrode adhesive strength depending on base material configuration" A negative electrode active material was prepared according to the composition shown in Table 1 below. In Table 1 below, particle size Span means (D90-D10) / D50. The liquid coating material was mixed with the base material at 20 wt % and mixed for 30 minutes using a Nauta Mixer at 150 rpm. The base material outside the coating material was then carbonized at 1200°C. The temperature was increased to the carbonization temperature at a rate of 5°C / min, and the mixture was maintained at the carbonization temperature for 3 hours, after which it was naturally cooled to 100°C, yielding a negative electrode active material.

[0086] 97 wt % of the prepared negative active material, 2 wt % of a binder containing carboxymethyl cellulose and styrene butadiene rubber, and 1 wt % of Super P conductive material were mixed in distilled water solvent to prepare a negative active material slurry.

[0087] The negative electrode active material slurry was applied to a copper (Cu) current collector, dried at 100°C for 10 minutes, and then pressed with a roll press. The time point at which detachment occurred during drying in a vacuum oven at 100°C was then measured. If no detachment occurred within 12 hours under the specified conditions, the electrode could be used, so the measurement was continued for up to 12 hours. In this case, detachment refers to the separation of the negative electrode active material from the Cu plate, which is the negative electrode current collector.

[0088] The electrode density of the vacuum-dried negative electrode was 1.5 to 1.7 g / cc.

[0089] [Table 1]

[0090] Looking at the results in Table 1, natural graphite in categories 1 and 2 was measured to have low electrode adhesive strength when liquid phenol resin and liquid petroleum pitch were used as the liquid coating material.

[0091] In both categories 5 and 6, a mixture of coal-based and petroleum-based artificial graphite was used, but the results were contradictory. That is, when a mixture of coal-based and petroleum-based artificial graphite with similar particle sizes was used, excellent electrode adhesion was confirmed only when the petroleum-based artificial graphite was mixed in greater amounts than the coal-based. In other words, when artificial graphite was mixed and used, in cases such as category 6, where the particle size measurement laser peaks were distributed over two or more, it can be seen that electrode adhesion was poor.

[0092] "Experimental Example 2 - Adhesion force measurement based on viscosity of liquid coating material" A negative electrode was manufactured using the negative active material according to the composition shown in Table 2. The negative electrode was manufactured in the same manner as in Experimental Example 1.

[0093] The adhesive strength test was carried out by attaching the final electrode to a 25cm 2 They were cut to size and tested according to ASTM D4541 test method.

[0094] [Table 2]

[0095] The adhesive strength suitable for use as a negative electrode is 300gf / cm 2 Sections 7 to 10 differ only in the amount of liquid coating material relative to the base material, and the same base material and liquid coating material with the same viscosity were used. However, sections 7 and 10, which had a low or high amount of liquid coating material, showed low electrode adhesion.

[0096] The same base material was used in sections 11 and 13, and the amount of liquid coating material relative to the base material was also the same, but the coal tar used had different viscosities. As a result, section 13, which had a low viscosity of 270 mPas, showed low electrode adhesion. Therefore, it was found that the viscosity of the liquid coating material must be greater than 270 mPas.

[0097] Sections 12 and 14 showed the same results as sections 11 and 13.

[0098] For reference, when 25% by weight of liquid petroleum pitch is used as the liquid coating material on the same base material as before, and the viscosity of the liquid petroleum pitch is different between 250mPas and 450mPas, the adhesive strength when the viscosity is 250mPas is 80gf / cm 2 When the viscosity is too low, 450mPa, the adhesive strength is 590gf / cm 2 It was confirmed that this is shown in

[0099] The present invention is not limited to the examples, and can be manufactured in various different forms, and a person skilled in the art to which the present invention pertains can understand that the present invention can be embodied in other specific forms without changing the technical idea or essential features of the present invention. Therefore, it should be understood that the above example is illustrative in all respects and not limiting.

Claims

1. preparing primary particles of artificial graphite; mixing the artificial graphite with a liquid coating material to form a coating layer that covers the artificial graphite; and carbonizing the artificial graphite on which the coating layer is formed; The liquid coating material has a viscosity of 300 to 25,000 mPa·s at 35°C, In the step of forming the coating layer, the artificial graphite and the liquid coating material are mixed at a temperature of 50°C or less, and the content of the liquid coating material is 15 to 25 parts by weight per 100 parts by weight of the artificial graphite.

2. forming a coating layer; 2. The method for producing a negative electrode active material for a lithium secondary battery according to claim 1, wherein the liquid coating material has a fixed carbon content of 15 to 60% by weight at 25°C.

3. preparing artificial graphite; grinding the coke; and The method for producing a negative electrode active material for a lithium secondary battery according to claim 1 or 2, further comprising: graphitizing the coke.

4. preparing artificial graphite; 3. The method for producing a negative electrode active material for a lithium secondary battery according to claim 1, wherein the artificial graphite is artificial graphite derived from coal-based coke, artificial graphite derived from petroleum-based coke, or a mixture thereof.

5. The artificial graphite is a mixture of artificial graphite derived from coal-based coke and artificial graphite derived from petroleum-based coke, 5. The method for producing a negative electrode active material for a lithium secondary battery according to claim 4, wherein 50 parts by weight or more of artificial graphite derived from petroleum coke is mixed with 100 parts by weight of the mixture.

6. preparing artificial graphite; 6. The method for producing a negative electrode active material for a lithium secondary battery according to claim 1, wherein the particle size SPAN ((D90-D10) / D50) of the artificial graphite is 0.7 to 2.

5.

7. forming a coating layer; The method for producing a negative electrode active material for a lithium secondary battery according to claim 1 , wherein the liquid coating material is a graphitizable carbon precursor or a non-graphitizable carbon precursor.

8. The method for producing a negative electrode active material for a lithium secondary battery according to any one of claims 1 to 7, wherein the carbonization temperature in the carbonization step is 800 to 2000°C.

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