Negative electrode active material for lithium secondary battery, negative electrode and lithium secondary battery

Abstract

The negative electrode active material for lithium secondary battery of the present invention is composed of 50 The carbon-based primary particles are composed of synthetic graphite secondary particles assembled from carbon-based primary particles having an average particle size (D 50 ) is a particle group and the average particle size (D 50 ) is a particle group of b, and b<0.6a. The present invention has secondary particles assembled from carbon-based primary particles with different average particle sizes, thereby showing a sharply increased tap density and having the advantages of excellent negative electrode adhesion and high-temperature storage performance.

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2020-0142661, filed on October 30, 2020, and the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a negative electrode active material for a lithium secondary battery, a negative electrode and a lithium secondary battery, and more particularly to a negative electrode active material for a lithium secondary battery, a negative electrode and a lithium secondary battery in which the adhesion and rolling rate of the negative electrode can be improved by increasing the tap density of the negative electrode active material. Background Art

[0003] With the rapid increase in the use of fossil fuels, the demand for alternative and clean energy is increasing. Therefore, the fields related to power generation and storage using electrochemical reactions are currently the most actively researched.

[0004] A representative example of an electrochemical device using this electrochemical energy is a secondary battery, and the scope of use of the secondary battery is gradually expanding. Recently, with the technological development of portable devices such as portable computers, portable phones and cameras and the increase in their demand, the demand for secondary batteries as energy sources is also growing rapidly. Typically, a secondary battery is composed of a positive electrode, a negative electrode, an electrolyte and a separator. The negative electrode comprises a negative electrode active material that inserts and extracts lithium ions from the positive electrode, and a graphite-based active material such as natural graphite or artificial graphite can be used as the negative electrode active material.

[0005] The artificial graphite is mainly used in the form of secondary particles. To this end, usually, coke, which is a material of primary particles, is granulated into secondary particles, which are graphitized by heat treatment to obtain artificial graphite in the form of secondary particles.

[0006] Here, when following a general manufacturing method in which the size of the primary particles is not controlled, artificial graphite in the form of secondary particles has limitations in increasing the tap density (less than 1.1 g / cc) due to its irregular shape, and if the tap density is low, the solid content of the slurry for forming the negative electrode becomes low, resulting in decreased adhesion and a lower rolling rate during the electrode manufacturing process.

[0007] Therefore, in order to increase the tap density of artificial graphite, a method of mixing primary particles and secondary particles has been proposed. However, there are problems such as swelling due to increased orientation of the negative electrode or degradation of fast charging performance.

[0008] Korean Patent Publication No. 2020-0076504 discloses a technology that uses a negative electrode active material containing raw coke with controlled particle size to improve the discharge capacity and charge / discharge efficiency of a secondary battery, as well as the high-rate discharge and charge output characteristics of the secondary battery. However, since the technology uses raw coke as a material, it requires an additional process of carbonizing the secondary particles.

[0009] Therefore, there is a need for a technology that can increase the tap density while following the conventional artificial graphite manufacturing process without requiring an additional process. Summary of the Invention

[0010]

Technical Issues

[0011] The present invention is believed to solve at least some of the above problems. For example, one aspect of the present invention provides a negative electrode active material for a lithium secondary battery that can improve tap density without requiring an additional step in a conventional process for manufacturing secondary particle artificial graphite.

[0012]

Technical solution

[0013] The negative electrode active material for a lithium secondary battery according to the present invention is prepared by mixing particles having different average particle sizes (D 50 ) of carbon-based primary particles granulated to obtain artificial graphite secondary particles, wherein the carbon-based primary particles have an average particle size (D 50 ) is a particle group A and the average particle size (D 50 ) is a particle group B with b, and b<0.6a.

[0014] Here, the tap density may be equal to or greater than 1.1 g / cc and may preferably be within a range of 1.2 to 1.4 g / cc.

[0015] In one embodiment of the present invention, a may be in the range of 11 to 15 μm.

[0016] In one embodiment of the present invention, the carbon-based primary particles may further include a particle group C having an average particle size of c, and c <b。

[0017] In one embodiment of the present invention, c<0.4a.

[0018] In one embodiment of the present invention, c<0.6b.

[0019] The average particle size (D 50 ) is in the range of 10 to 25 μm.

[0020] In one embodiment of the present invention, the secondary particles comprise an adhesive binder between the primary particles.

[0021] In one embodiment of the present invention, the carbon-based primary particles are composed of one or a combination of two or more selected from the group consisting of petroleum coke, pitch coke, and needle coke.

[0022] The present invention provides a negative electrode comprising the negative electrode active material for a lithium secondary battery.

[0023] The present invention provides a lithium secondary battery comprising the above-mentioned negative electrode active material for lithium secondary batteries.

[0024] The method for manufacturing a negative electrode active material for a lithium secondary battery according to the present invention comprises: 50 ) of carbon-based primary particles; forming secondary particles by mixing with a bonding binder; and graphitizing the secondary particles.

[0025] In one embodiment of the present invention, the carbon-based primary particles have an average particle size (D 50 ) is a particle group A and the average particle size (D 50 ) is a particle group B of b, and the mixing ratio of the particle group A and the particle group B is in the range of 2:1 to 1:2 by weight.

[0026] In one embodiment of the present invention, the carbon-based primary particles further comprise an average particle size (D 50 ) is a particle group C having c, and the content of the particle group C corresponds to 5% to 25% of the total weight of the particle group A and the particle group B.

[0027] Beneficial effects

[0028] In the present invention, since the secondary particles are granulated from carbon-based primary particles having different average particle sizes, relatively small primary particles are filled in the pores of relatively large primary particles, thereby significantly improving the tap density, which shows the effect of increasing the adhesion and high-temperature storage performance of the negative electrode. DETAILED DESCRIPTION

[0029] Hereinafter, the present invention will be described in detail. The terms and words used in this specification and claims should not be construed as limited to common or dictionary terms, and the inventors may appropriately define the concepts of the terms to best describe their invention. The terms and words should be interpreted as meanings and concepts consistent with the technical concept of the present invention.

[0030] In the present application, it should be understood that terms such as “including” or “having” are intended to indicate the features, numbers, steps, operations, constituent elements, parts or combinations thereof described in the specification, and they do not preclude the possibility of the existence or addition of one or more other features or numbers, steps, operations, constituent elements, parts or combinations thereof.

[0031] In this manual, D 50 It can be defined as the particle size corresponding to 50% of the volume cumulative amount in the particle size distribution curve, D max It can be defined as the maximum particle size among the particle sizes shown in the particle size distribution curve, and D min It can be defined as the smallest particle size among the particle sizes shown in the particle size distribution curve. 50 、D min and D max The particle size distribution (PSD) derived by laser diffraction can be used for measurement. The laser diffraction method is generally capable of measuring particle sizes from the submicron region to several mm and can obtain highly reproducible and high-resolution results.

[0032] In this specification, the tap density may be a density calculated by putting 40 g of negative electrode active material particles in a container and vibrating the container 1000 times.

[0033] Hereinafter, the present invention will be described in detail.

[0034] <Negative Electrode Active Materials for Lithium Secondary Batteries>

[0035] The negative electrode active material for a lithium secondary battery according to the present invention is prepared by mixing particles having different average particle sizes (D 50 ) of carbon-based primary particles granulated to obtain artificial graphite secondary particles, wherein the carbon-based primary particles have an average particle size (D 50 ) is a particle group A and the average particle size (D 50 ) is a particle group B with b, and b<0.6a.

[0036] In this specification, the term "primary particle" refers to an original particle when another particle is formed from a specific particle, and a secondary particle may be formed by aggregation or granulation of a plurality of primary particles.

[0037] In this specification, the term "secondary particles" refers to physically distinguishable large particles that can be formed by aggregation or granulation of primary particles.

[0038] In this specification, "granulation" of primary particles means forming secondary particles by spontaneous or artificial aggregation of a plurality of primary particles.

[0039] The carbon-based primary particles are composed of one or a combination of two or more selected from the group consisting of petroleum coke, pitch coke, and needle coke.

[0040] In the present invention, the particle size of the carbon-based primary particles is controlled to improve the tap density of the negative electrode active material composed of the artificial graphite of the secondary particles.50 ) of primary particles to reduce the internal pores formed between the particles, thereby improving the tap density. The inventors of the present invention have found that when the carbon-based primary particles contain an average particle size (D 50 ) is a particle group A and the average particle size (D 50 ) is a particle group B with b and b<0.6a, the tap density of the secondary particles of the artificial graphite becomes equal to or greater than 1.1 g / cc and the present invention is completed.

[0041] According to one embodiment of the present invention, by controlling the average particle size (D 50 ) is a particle group A and the average particle size (D 50 ) is the particle size and mixing ratio of the particle group B of b, and a negative electrode active material for a lithium secondary battery with a tap density in the range of 1.2 to 1.4 g / cc can be provided. In addition, when a negative electrode forming slurry is manufactured using a negative electrode active material having a tap density equal to or greater than 1.1 g / cc, the solid content in the slurry can be made equal to or greater than 56 weight %. Therefore, since the migration of the binder is limited during the drying process, the adhesion between the negative electrode and the current collector can be improved, and since the electrode thickness is reduced, the calendering rate during the calendering process can be increased, and by reducing damage to the electrode, high temperature storage performance can be improved.

[0042] According to one embodiment of the present invention, the average particle size (D50) of the particle group A is a, and the average particle size a is in the range of 11 to 15 μm, preferably 12 to 13 μm.

[0043] According to one embodiment of the present invention, the carbon-based primary particles include, in addition to the average particle size (D 50 ) is a particle group A and the average particle size (D 50 ) is b, a particle group C with an average particle size of c may also be included. In this case, c is smaller than b. Since the particle group C with an average particle size of c is filled in the pores formed by the particle group A with an average particle size (D50) of a and the particle group B with an average particle size (D50) of b, the tap density can be further improved. In this case, in order to maximize the improvement effect of the tap density, preferably c<0.4a and c<0.6b.

[0044] The secondary particles of the present invention can be formed by granulating carbon-based primary particles. That is, the secondary particles can be a structure formed by the aggregation of primary particles. The secondary particles can contain an adhesive binder that causes the primary particles to aggregate. The adhesive binder is located between the primary particles to provide adhesion between the primary particles, thereby forming the secondary particles by granulating the primary particles. Some examples of the adhesive binder include one or a combination of two or more selected from the group consisting of petroleum-based asphalt, coal-based asphalt, and mesophase asphalt.

[0045] Likewise, the average particle size (D) of artificial graphite secondary particles obtained by granulating carbon-based primary particles of controlled particle size is 50 ) may be in the range of 10 to 25 μm, preferably 11 to 20 μm. When the above range is satisfied, the negative electrode active material particles may be uniformly dispersed in the negative electrode slurry, and the charging performance of the battery may also be improved.

[0046] <Method for producing negative electrode active material for lithium secondary battery>

[0047] The method for manufacturing a negative electrode active material for a lithium secondary battery according to the present invention may include: 50 ) of carbon-based primary particles; forming secondary particles by mixing with a bonding binder; and graphitizing the secondary particles.

[0048] In the method for producing the negative electrode active material of the present invention, the mixing for producing the negative electrode active material can be performed by simple mixing or mechanical grinding using a method known in the related art. For example, the mixing can be performed using only a mortar, or can be performed by rotating at a speed of 100 to 1000 rpm using a blade grinder or a ball mill to mechanically apply compressive stress.

[0049] With different average particle size (D 50 The mixing step of carbon-based primary particles is a step of controlling the diameter of the primary particles, and includes adjusting the average particle size (D 50 ) is a particle group A and the average particle size (D 50 ) is a step of preparing and mixing particle group B of b. The mixing ratio of the particle group A to the particle group B is preferably in the range of 2:1 to 1:2. When the mixing ratio is satisfied, the tap density improvement effect can be maximized.

[0050] In one embodiment of the present invention, the particles have different average particle sizes (D 50 The mixing step of carbon-based primary particles may further include the following steps in addition to the average particle size (D 50 ) is a particle group A and the average particle size (D 50 ) is b and the average particle size (D 50 ) is a step of adding particle group C of c. At this time, the content of the particle group C is preferably in the range of 5 wt % to 25 wt % of the total weight of the particle group A and the particle group B, because the improvement effect of the tap density can be maximized within this range.

[0051] Since the specific numerical ranges and relationships of a, b and c have been described in detail above, further description will be omitted.

[0052] The step of forming secondary particles by mixing an adhesive binder may include mixing and stirring the adhesive binder with carbon-based primary particles of controlled particle size. This allows the carbon-based primary particles to aggregate and form particles. The adhesive binder may be coal-based pitch or petroleum-based pitch, and the mixing and stirring may be performed at a temperature of 200 to 900°C, specifically 300 to 500°C.

[0053] The step of graphitizing the secondary particles may include a process of graphitizing the secondary particles formed of a mixture of carbon-based primary particles and an adhesive binder through calcination.

[0054] The calcination may be performed by heating at a temperature of 2500° C. to 3500° C., specifically, at a temperature of 2800° C. to 3200° C. The average particle size (D 50 ) can be in the range of 10 to 25 μm.

[0055] <Negative electrode>

[0056] The present invention provides a negative electrode for a secondary battery containing the negative electrode active material.

[0057] The negative electrode for a lithium secondary battery includes a negative electrode current collector and a negative electrode active material layer.

[0058] Any negative electrode current collector commonly used in the art can be used as the negative electrode current collector. For example, any negative electrode current collector having high conductivity and not causing chemical changes to the lithium secondary battery can be used as the negative electrode current collector. For example, the negative electrode current collector can be made of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, a product obtained by surface-treating copper or stainless steel with carbon, nickel, titanium, silver, etc., or an aluminum-cadmium alloy.

[0059] Furthermore, in the negative electrode current collector, fine concavoconvexities may be formed on the surface to improve the binding force of the negative electrode active material, and it may be used in various forms such as film, sheet, foil, net, porous body, foam, and non-woven fabric.

[0060] The negative electrode current collector may generally have a thickness of 3 to 500 μm.

[0061] The negative electrode active material layer is formed on the negative electrode current collector.

[0062] The negative electrode active material layer comprises the present invention by mixing the particles having different average particle sizes (D 50 The negative electrode active material for a lithium secondary battery is an artificial graphite secondary particle obtained by granulating carbon-based primary particles of a lithium secondary battery. The content of the negative electrode active material for a lithium secondary battery can be in the range of 80% to 90% by weight of the total weight of the negative electrode active material layer.

[0063] In addition to the negative electrode active material, the negative electrode active material layer may further include at least one selected from a binder and a conductive material.

[0064] The binder is a component that facilitates bonding between the conductive material, the active material, and the current collector, and is generally added in an amount of 1 wt % to 30 wt % based on the total weight of the negative electrode active material layer.

[0065] Examples of such binders include polyvinylidene fluoride (PVdF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various combinations thereof.

[0066] The conductive material is a component for further improving conductivity of the negative electrode active material, and may be added in an amount of 1 wt % to 30 wt % based on the total weight of the negative electrode active material layer.

[0067] Such a conductive material is not particularly limited as long as it has conductivity without causing chemical changes in the battery, and examples thereof 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 fibers and metal fibers; fluorocarbons; metal powders such as aluminum and nickel powders; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives. Specific examples of commercially available conductive materials include acetylene black series (Chevron Chemical Company), Denka black (Denka Singapore Private Limited), Gulf Oil Company products, Ketjen black, EC series (Armak Company), Vulcan XC-72 (Cabot Company), and Super P (Timcal Company).

[0068] The negative electrode active material layer may be manufactured by mixing a negative electrode active material for a lithium secondary battery with at least one additive selected from a binder and a conductive material in a solvent to prepare a negative electrode slurry, applying the negative electrode slurry on the negative electrode collector, and rolling and drying the negative electrode collector.

[0069] The solvent may include water or an organic solvent such as NMP (N-methyl-2-pyrrolidone), and may be used in an amount that provides a desired viscosity when the negative electrode active material and optionally a binder and a conductive material are included. For example, the concentration of the solid containing the negative electrode active material for a lithium secondary battery and optionally a binder and a conductive material may be in the range of 50% by weight to 95% by weight.

[0070] <Lithium Secondary Battery>

[0071] In addition, the present invention provides a lithium secondary battery comprising the above-mentioned negative electrode for lithium secondary battery.

[0072] The lithium secondary battery may include a negative electrode for a lithium secondary battery, a positive electrode for a lithium secondary battery, and a separator interposed between the negative electrode for a lithium secondary battery and the positive electrode for a lithium secondary battery.

[0073] Specifically, the lithium secondary battery of the present invention can be manufactured by injecting a non-aqueous electrolyte into an electrode structure, wherein the electrode structure is composed of a negative electrode for a lithium secondary battery, a positive electrode for a lithium secondary battery, and a separator inserted between the negative electrode for a lithium secondary battery and the positive electrode for a lithium secondary battery. In this case, the positive electrode, negative electrode, and separator commonly used to manufacture lithium secondary batteries can be used as the positive electrode, negative electrode, and separator forming the electrode structure.

[0074] At this time, the positive electrode may be manufactured by coating a positive electrode active material slurry containing a positive electrode active material and optionally a binder, a conductive material, and a solvent on a positive electrode current collector, followed by drying and rolling.

[0075] The positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes in the battery. Examples of the positive electrode current collector include stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, etc.

[0076] The positive electrode active material is a compound capable of reversibly inserting and extracting lithium, and may specifically include a lithium composite metal oxide containing lithium and at least one metal such as cobalt, manganese, nickel or aluminum. More specifically, some examples of the lithium composite metal oxide include lithium manganese oxide (e.g., LiMnO2, LiMn2O4, etc.), lithium cobalt oxide (e.g., LiCoO2, etc.), lithium nickel oxide (e.g., LiNiO2, etc.), lithium nickel manganese oxide (e.g., LiNi 1-Y Mn Y O2 (here 0 <Y<1)、LiMn 2- z Ni z O4 (where 0<Z<2), etc.), lithium nickel cobalt oxide (e.g., LiNi 1-Y1 Co Y1O2 (where 0 < Y1 < 1, etc.), lithium manganese cobalt oxide (e.g., LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-z1 Co z1 O4 (where 0 < Z1 < 2, etc.), lithium nickel manganese cobalt oxide (e.g., Li(Ni p Co q Mn r1 )O2 (where 0 < p < 1, 0 < q < 1, 0 < r1 < 1, p + q + r1 = 1) or Li(Ni p1 Co q1 Mn r2 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r2 < 2, p1 + q1 + r2 = 2), etc.) and lithium nickel cobalt transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r3 M S2 )O2 (where M is one selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo; p2, q2, r3, and s2 are atomic fractions of each independent element; and 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < s2 < 1, p2 + q2 + r3 + s2 = 1), etc.), and one or a mixture of two or more thereof can be used. Here, in terms of improving the capacity characteristics and stability of the battery, the lithium composite metal oxide can be LiCoO2, LiMnO2, LiNiO2, lithium nickel manganese cobalt oxide (e.g., Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2 or Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, etc.) or lithium nickel cobalt aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 )O2, etc.), and considering the significance of the improvement effect brought by controlling the content ratio and type of the elements forming the lithium composite metal oxide, the lithium composite metal oxide can be Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co0.15 )O2 or Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, and a mixture of one or more types can be used.

[0077] The positive electrode active material may be included in an amount of 80 wt % to 99 wt % based on the total weight of each positive electrode mixture.

[0078] As a component that helps to bind the active material to the conductive material and to the current collector, the binder is added in an amount of 1% to 30% by weight based on the total weight of the positive electrode mixture. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, various copolymers, and the like.

[0079] The conductive material is generally added in an amount of 1 wt % to 30 wt % based on the total weight of the positive electrode mixture.

[0080] Such a conductive material is not particularly limited as long as it has conductivity without causing chemical changes in the battery, and examples thereof include graphite; carbonaceous materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; fluorocarbons; metal powders such as aluminum and nickel powders; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives. Specific examples of commercially available conductive materials include acetylene black series (Chevron Chemical Company), Danka Black (Danka Singapore Pte. Ltd.), Gulf Oil Company products, Ketjen black, EC series (Armak Corporation), Vulcan XC-72 (Cabot Corporation), and Super P (Timcal Corporation).

[0081] The solvent may include an organic solvent such as NMP (N-methyl-2-pyrrolidone), and may be used in an amount that becomes a desired viscosity when a positive electrode active material and optionally a binder and a conductive material are included.

[0082] In a lithium secondary battery, the diaphragm is used to separate the negative electrode from the positive electrode and provide a path for the movement of lithium ions, and any diaphragm commonly used in lithium secondary batteries can be used without any particular restrictions. In particular, a diaphragm with high electrolyte moisture retention and low electrolyte ion movement resistance is preferred. Specifically, a porous polymer film can be used, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer and an ethylene / methacrylate copolymer. In addition, a non-woven fabric made of a conventional porous non-woven fabric such as a high melting point glass fiber, polyethylene terephthalate fiber, etc. can be used. In order to ensure heat resistance or mechanical strength, a coating diaphragm containing a ceramic component or a polymer material can be used, and can optionally be used in a single-layer or multilayer structure.

[0083] Examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries, but the present invention is not limited to these examples.

[0084] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0085] The organic solvent may be any organic solvent capable of acting as a medium through which ions participating in the electrochemical reaction of the battery can move. Specifically, some examples of the organic solvent may include: ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents; carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethanol and isopropanol; nitriles such as R-CN; amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolane. Among them, carbonate solvents are preferred, and a mixture of a cyclic carbonate (such as ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant and a chain carbonate compound (such as ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) with low viscosity is more preferred because the mixture can improve the charge / discharge performance of the battery. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1:1 to about 1:9, the electrolyte can have excellent performance.

[0086] The lithium salt can be used without any particular restriction, as long as it is a compound that can provide lithium ions for lithium secondary batteries. Specifically, LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI or LiB(C2O4)2 can be used as the lithium salt. The concentration of the lithium salt is preferably in the range of 0.1 to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity so that it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0087] Since the lithium secondary battery according to the present invention consistently exhibits excellent discharge capacity, rapid charging characteristics, and capacity retention, it can be used in portable devices such as mobile phones, laptop computers, digital cameras, and electric vehicles (HEVs) such as hybrid electric vehicles, and is particularly useful as a battery constituting a medium-to-large battery module. Therefore, the present invention also provides a medium-to-large battery module comprising the aforementioned secondary battery as a unit cell.

[0088] Such medium and large battery modules can be preferably applied to power sources requiring high power and large capacity, such as electric vehicles, hybrid electric vehicles, power storage devices, and the like.

[0089] Hereinafter, the present invention will be described in detail with reference to Examples. However, embodiments according to the present invention may be modified into various other forms, and the scope of the present invention should not be construed as being limited to the following examples. The embodiments of the present invention are provided to more fully describe the present invention to those skilled in the art.

[0090] Example 1

[0091] Coke primary particles were pulverized to prepare a particle group (particle group D) having an average particle size of 13 μm in the pulverized particles and a particle group (particle group E) having an average particle size of 7 μm in the pulverized particles.

[0092] After the particle group D and the particle group E were mixed at a weight ratio of 1:1, 11 parts by weight of asphalt having a softening point of 120° C. was mixed based on 100 parts by weight of the mixture. Thereafter, they were mixed for 3 hours using a heatable mixer to prepare secondary particles.

[0093] Thereafter, they were graphitized by heating to 3000° C. to produce a negative electrode active material having an average particle size of 18 μm.

[0094] Example 2

[0095] Coke primary particles were pulverized to prepare a particle group (particle group E) having an average particle size of 7 μm and a particle group (particle group F) having an average particle size of 4 μm. The particles were then mixed.

[0096] Thereafter, by performing granulation and graphitization in the same manner as in Example 1, a negative electrode active material having an average particle size of 12 μm was produced.

[0097] Example 3

[0098] Primary coke particles were pulverized to prepare a particle group having an average particle size of 13 μm (Particle Group D), a particle group having an average particle size of 7 μm (Particle Group E), and a particle group having an average particle size of 4 μm (Particle Group F). The mixture ratio of Particle Group D to Particle Group E was 1:1 by weight, and 20 parts by weight of Particle Group F was added based on the total weight of Particle Group D and Particle Group E.

[0099] Thereafter, by performing granulation and graphitization in the same manner as in Example 1, a negative electrode active material having an average particle size of 15 μm was produced.

[0100] Comparative Example 1

[0101] By granulating and graphitizing the particle group D in Example 1, a negative electrode active material having an average particle size of 20 μm was produced.

[0102] Comparative Example 2

[0103] By granulating and graphitizing the particle group E in Example 1, a negative electrode active material having an average particle size of 15 μm was produced.

[0104] Comparative Example 3

[0105] By granulating and graphitizing the particle group F in Example 2, a negative electrode active material having an average particle size of 7 μm was produced.

[0106] Comparative Example 4

[0107] A negative electrode active material was prepared, which was obtained by mixing the negative electrode active material of Comparative Example 1 and the negative electrode active material of Comparative Example 3 at a weight ratio of 1:1.

[0108] Experimental Example 1: Measurement of tap density

[0109] 40 g of each of the negative electrode active material particles of Examples 1 to 3 and Comparative Examples 1 to 4 were placed in a container and then vibrated 1000 times. Thereafter, the tap density was calculated, and the results are shown in Table 1.

[0110] Experimental Example 2: Evaluation of Negative Electrode Adhesion

[0111] A negative electrode slurry was prepared by dispersing 96 parts by weight of the negative electrode active material, 0.5 parts by weight of carbon black conductive material, 2.3 parts by weight of SBR binder, and 1.2 parts by weight of CMC in distilled water. This slurry was then applied to a 15 μm copper current collector and dried to produce the negative electrode. The circulating air temperature was 110°C. The negative electrode was then rolled and dried in a vacuum oven at 130°C for 2 hours.

[0112] For each of the negative electrode active materials of Examples 2 to 3 and Comparative Examples 1 to 4, each negative electrode was manufactured in the same manner.

[0113] The negative electrode was cut into 20 mm x 150 mm pieces and then mounted in the center of a 25 mm x 75 mm glass slide. The current collector was then peeled off using a UTM (Uniform Mass Spectrometer) to measure its peel strength. The average peel strength of five or more measurements was calculated and evaluated. The results are shown in Table 1.

[0114] Experimental Example 3: Evaluation of Battery Capacity and High-Temperature Life Performance

[0115] Li[Ni 0.6 Mn 0.2 Co 0.2 ]O2 was used as a positive electrode active material. A positive electrode slurry was manufactured by mixing the positive electrode active material, carbon black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder in a weight ratio of 94:4:2 in N-methyl-2-pyrrolidone. The prepared positive electrode slurry was applied on an aluminum metal film having a thickness of 15 μm as a positive electrode current collector, and then dried. At this time, the temperature of the circulating air was 110°C. Thereafter, it was dried in a vacuum oven at a temperature of 130°C for 2 hours, thereby manufacturing a positive electrode including a positive electrode active material layer.

[0116] The negative electrode, the manufactured positive electrode, and the porous polypropylene separator were assembled in a stacked manner, and a lithium secondary battery was manufactured by injecting an electrolyte into the assembled battery.

[0117] Thereafter, the lithium secondary battery was activated by charging the battery to SOC 30% at a current of 0.2C, and then charged in CC / CV mode (4.2V, 0.05C cut-off) and discharged in CC mode (0.2C current, 3.0V cut-off) three times. Thereafter, the secondary battery was repeatedly charged and discharged at a current of 1C in a chamber at a temperature of 45°C, and the capacity retention rates of the 100th, 200th, and 300th cycles were evaluated, and the results are shown in Table 1. The battery capacity and high temperature life performance of Table 1 represent the residual capacity at the 300th cycle and the capacity retention rate at the 300th cycle, and the capacity retention rate was calculated by substituting into the following equation (1).

[0118] Equation (1): Capacity retention (%) = (discharge capacity after high-temperature charge and discharge / initial discharge capacity) × 100

[0119] [Table 1]

[0120]

[0121] Referring to Table 1 above, the tap density of the negative electrode active materials of Examples 1 to 3 of the present invention is significantly better than the tap density of the negative electrode active materials of Comparative Examples 1 to 4. Therefore, since the solid concentration of the slurry of the negative electrode using the negative electrode active materials of Examples 1 to 3 is improved, the adhesion of the negative electrode using the negative electrode active materials of Examples 1 to 3 is significantly better than the adhesion of the negative electrode using the negative electrode active materials of Comparative Examples 1 to 4.

[0122] Furthermore, the secondary batteries using the negative active materials of Examples 1 to 3 exhibited better high-temperature lifespan than the comparative examples. This is likely because the negative active materials of the present invention affect rolling properties, reducing side reactions at the interface with the negative electrode.

[0123] The above description is only an explanation of the technical concept of the present invention, and those skilled in the art to which the present invention belongs can make various modifications and changes without departing from the essential features of the present invention. Therefore, the content disclosed in the present invention is not intended to limit the technical concept of the present invention, but is used to illustrate the present invention, and the scope of the technical concept of the present invention is not limited by these contents. The scope of protection of the present invention should be interpreted by the attached claims, and all technical concepts within the scope of their equivalents should be interpreted as included within the scope of the present invention.

Claims

1. A negative electrode active material for a lithium secondary battery, wherein the negative electrode active material is prepared by mixing particles having different average particle sizes D 50 The artificial graphite secondary particles are obtained by granulating the carbon primary particles. The carbon-based primary particles have an average particle size D 50 The particle group A and the average particle size D are 50 The particle group B is b, and b<0.6a, The carbon-based primary particles further comprise a particle group C with an average particle size of c, wherein c <b, wherein the tap density of the negative electrode active material is equal to or greater than 1.1 g / cc and less than or equal to 1.4 g / cc, and wherein a is in the range of 11 to 15 μm.

2. The negative electrode active material according to claim 1, wherein c<0.4a.

3. The negative electrode active material according to claim 2, wherein c<0.6b.

4. The negative electrode active material according to claim 1, wherein the average particle size D of the negative electrode active material particles is 50 In the range of 10 to 25 μm. 5 . The negative active material of claim 1 , wherein the secondary particles comprise an adhesive binder between the primary particles. 6 . The negative electrode active material according to claim 1 , wherein the carbon-based primary particles are composed of one or a combination of two or more selected from the group consisting of petroleum coke, pitch coke, and needle coke. 7 . A negative electrode comprising the negative electrode active material for a lithium secondary battery according to claim 1 . 8 . A lithium secondary battery comprising the negative electrode active material for a lithium secondary battery according to claim 1 .

9. A method for producing the negative electrode active material for a lithium secondary battery according to claim 1, the method comprising: Will have different average particle size D 50 A mixture of carbon-based primary particles; forming secondary particles by mixing with a gluing binder; as well as The secondary particles are graphitized.

10. The method of claim 9, wherein the carbon-based primary particles comprise an average particle size D 50 The particle group A and the average particle size D are 50 is a particle group B of b, and The mixing ratio of the particle group A to the particle group B is in the range of 2:1 to 1:2 by weight.

11. The method of claim 10, wherein the carbon-based primary particles further comprise an average particle size D 50 is a particle swarm C of c, and The content of the particle group C corresponds to 5% to 25% of the total weight of the particle group A and the particle group B.

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