Negative electrode and secondary battery including the same

Abstract

The present invention relates to a negative electrode including a negative electrode current collector, a lower negative electrode active material layer disposed on the negative electrode current collector, and an upper negative electrode active material layer disposed on the lower negative electrode active material layer, the lower negative electrode active material layer including a first negative electrode active material including natural graphite particles and a second negative electrode active material including artificial graphite particles in a primary particle form, the upper negative electrode active material layer including a third negative electrode active material including artificial graphite particles in a secondary particle form formed by granulating two or more primary particles, and the first negative electrode active material has a pore volume of 0.06 mL / g or less as measured by a mercury porosimeter measurement method.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0184261, filed December 21, 2021, and all contents disclosed in the documents of that Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a negative electrode and a secondary battery including the same. [Background technology]

[0003] With the depletion of fossil fuels causing rising energy costs and increasing concerns about environmental pollution, alternative, environmentally friendly energy sources have become an essential factor for future life.

[0004] In particular, with technological development and increasing demand for mobile devices, the demand for secondary batteries as an environmentally friendly alternative energy source is rapidly increasing.

[0005] In the secondary battery, lithium metal has been used as the negative electrode in the past. However, due to the risk of battery short circuit due to the formation of dendrites and the resulting risk of explosion, the use of carbon-based active materials, which allow reversible intercalation and deintercalation of lithium ions and maintain structural and electrical properties, has been attracting attention.

[0006] The carbon-based active material is available in various forms, including artificial graphite, natural graphite, and hard carbon. Among these, graphite-based active materials are the most widely used, as they have excellent reversibility and can ensure the life characteristics of lithium secondary batteries. Because the graphite-based active material has a lower discharge voltage of -0.2 V compared to lithium, batteries using the graphite-based active material can exhibit a high discharge voltage of 3.6 V, offering many advantages in terms of the energy density of lithium batteries.

[0007] Among these, natural graphite has the advantage of exhibiting higher output and capacity than other carbon-based active materials such as artificial graphite, and its excellent adhesive strength allows for a reduction in the amount of binder used, thereby enabling the realization of a high-capacity, high-density anode. However, natural graphite has the problem of reduced anode durability due to a high degree of electrolyte side reaction, and its high degree of orientation is unfavorable for cycle expansion characteristics.

[0008] Therefore, there is a need to develop a negative electrode active material that can exhibit the high output and capacity of natural graphite while preventing the problem of cycle expansion.

[0009] Japanese Patent Registration Publication No. 4403327 discloses graphite powder for the negative electrode of a lithium ion secondary battery, but fails to provide an alternative solution to the above-mentioned problems. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Patent No. 4403327 Summary of the Invention [Problem to be solved by the invention]

[0011] An object of the present invention is to provide a negative electrode that has high energy density, excellent fast charging performance, and improved negative electrode adhesion, and can effectively prevent cycle swelling problems.

[0012] Another object of the present invention is to provide a secondary battery including the above-mentioned negative electrode. [Means for solving the problem]

[0013] The present invention provides a negative electrode comprising: a negative electrode current collector; a lower negative electrode active material layer disposed on the negative electrode current collector; and an upper negative electrode active material layer disposed on the lower negative electrode active material layer, wherein the lower negative electrode active material layer comprises a first negative electrode active material including natural graphite particles and a second negative electrode active material including artificial graphite particles in the form of primary particles; and the upper negative electrode active material layer comprises a third negative electrode active material including artificial graphite particles in the form of secondary particles formed by granulating two or more primary particles, and the first negative electrode active material has a pore volume of 0.06 mL / g or less as measured by mercury porosimetry.

[0014] The present invention also provides a secondary battery including the above-mentioned negative electrode, a positive electrode facing the negative electrode, a separator interposed between the negative electrode and the positive electrode, and an electrolyte. [Effects of the Invention]

[0015] The anode of the present invention includes a double-layered anode active material layer, wherein the lower anode active material layer includes a first anode active material including natural graphite particles and a second anode active material including primary particle artificial graphite particles, and the upper anode active material layer includes a third anode active material including secondary particle artificial graphite particles, and the first anode active material has a void volume measured by mercury porosimetry within a specific range. The first and second anode active materials included in the lower anode active material layer improve adhesion to the anode current collector, thereby improving anode capacity and reducing cycle swelling. The third anode active material included in the upper anode active material layer improves fast charge performance. The anode of the present invention has high energy density, excellent fast charge performance, improved anode adhesion, and reduced cycle swelling. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a schematic side view illustrating a negative electrode according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] The terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as having meanings and concepts that are consistent with the technical idea of ​​the present invention, based on the principle that inventors can appropriately define the concepts of terms in order to best explain their inventions.

[0018] The terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the present invention. The singular expressions include the plural expressions unless the context clearly indicates otherwise.

[0019] It should be understood that in this specification, the terms "comprises," "includes," "has," and the like specify the presence of embodied features, numbers, steps, components, or combinations thereof, but do not preclude the possible presence or addition of one or more different features, numbers, steps, components, or combinations thereof.

[0020] In this specification, D 50 can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve. 50 can be measured using, for example, a laser diffraction method. The laser diffraction method generally enables measurement of particle sizes from the submicron range to several mm, and can provide results with high reproducibility and high resolution.

[0021] In this specification, the BET specific surface area can be measured by the BET (Brunauer-Emmett-Teller) measurement method using an adsorption gas such as nitrogen and a BELSORP (BET equipment) manufactured by BEL JAPAN.

[0022] The present invention will be specifically described below with reference to the drawings, specifically, Fig. 1 is a schematic side view for explaining a negative electrode according to the present invention.

[0023] <Negative electrode> The present invention relates to a negative electrode, specifically to a negative electrode for a lithium secondary battery.

[0024] Referring to FIG. 1, an anode 10 of the present invention includes an anode current collector 100, a lower anode active material layer 210 disposed on the anode current collector 100, and an upper anode active material layer 220 disposed on the lower anode active material layer 210. The lower anode active material layer 210 includes a first anode active material including natural graphite particles and a second anode active material including artificial graphite particles in the form of primary particles. The upper anode active material layer 220 includes a third anode active material including artificial graphite particles in the form of secondary particles formed by granulating two or more primary particles. The first anode active material has a pore volume of 0.06 mL / g or less as measured by a mercury porosimeter.

[0025] According to the anode of the present invention, the first anode active material and the second anode active material contained in the lower anode active material layer improve adhesion with the anode current collector, thereby improving anode capacity and reducing cycle expansion. The third anode active material contained in the upper anode active material layer improves fast charge performance, thereby providing high energy density, excellent fast charge performance, improved anode adhesion, and reduced cycle expansion.

[0026] [Negative electrode current collector 100] The negative electrode current collector 100 may be any negative electrode current collector commonly used in the art, and is not particularly limited as long as it does not cause chemical changes in the lithium secondary battery and has high conductivity. For example, the negative electrode current collector 100 may include at least one selected from copper, stainless steel, aluminum, nickel, titanium, sintered carbon, and an aluminum-cadmium alloy, preferably copper.

[0027] The negative electrode current collector 100 may have fine irregularities on its surface to strengthen the binding force of the negative electrode active material, and may be used in various forms such as a film, a sheet, a foil, a mesh, a porous body, a foam, or a nonwoven fabric.

[0028] The negative electrode current collector 100 may generally have a thickness of 3 μm to 500 μm.

[0029] [Lower negative electrode active material layer 210] The lower negative electrode active material layer 210 is disposed on the negative electrode current collector 100 .

[0030] The lower negative electrode active material layer 210 may be disposed on at least one surface, specifically, one or both surfaces, of the negative electrode current collector 100 .

[0031] The lower negative electrode active material layer 210 includes a first negative electrode active material and a second negative electrode active material.

[0032] The first negative electrode active material includes natural graphite particles, which can improve adhesion between the lower negative electrode active material layer and the negative electrode current collector, thereby improving the capacity of the negative electrode.

[0033] The pore volume of the first negative electrode active material measured by mercury porosimetry is 0.06 mL / g or less.

[0034] Mercury porosimetry (Hg porosimetry) is a measurement method that can measure the size, porosity, and pore volume of voids present on the surface of a sample by injecting mercury into the sample. Unlike the BET nitrogen adsorption method, the Hg porosimetry method injects mercury, rather than gas, into the sample, allowing it to measure large voids within a negative electrode active material, specifically void volumes with sizes on the order of approximately 5 nm to 1,000 nm. On the other hand, the BET nitrogen adsorption method measures void volume by adsorbing nitrogen gas into the sample, allowing it to measure the presence, specific surface area, and pore volume of small voids, specifically voids with sizes on the order of several nm to 100 nm, but has limitations in measuring voids larger than 100 nm. In this respect, the measurement ranges of voids by the Hg porosimetry method and the BET nitrogen adsorption method are considered to be different from each other.

[0035] The first negative electrode active material has a pore volume measured by mercury porosimetry adjusted to the above-mentioned level, thereby reducing the ratio, content, or volume of large pores within the particles, e.g., pores with a pore size of 100 nm or greater. The lower negative electrode active material layer includes the first negative electrode active material, thereby improving electrode adhesion and negative electrode energy density and reducing cycle expansion. Furthermore, the first negative electrode active material is included in the lower negative electrode active material layer together with a second negative electrode active material (described below), thereby further improving the negative electrode adhesion and reducing cycle expansion.

[0036] For example, if the pore volume of the first negative electrode active material measured by mercury porosimetry exceeds 0.06 mL / g, the cycle expansion cannot be sufficiently reduced, and the occurrence of negative electrode swelling may increase.

[0037] Specifically, the pore volume of the first negative electrode active material measured by mercury porosimetry may be 0.001 mL / g to 0.06 mL / g, more specifically 0.010 mL / g to 0.045 mL / g. When the pore volume is within this range, the above-mentioned effects of improving the energy density of the negative electrode, improving the rapid charging performance, improving the negative electrode adhesion, and reducing cycle expansion can be further improved.

[0038] The first negative electrode active material has a BET specific surface area of ​​0.6 m 2 / g~2.5m 2 / g, specifically 1.5m 2 / g~2.2m 2 When the negative electrode active material has a specific surface area of ​​the above level, it can ensure a sufficient contact area with the electrolyte, thereby improving output characteristics and further improving the effects of preventing the electrolyte side reaction and reducing cycle expansion.

[0039] The BET specific surface area can be measured by the Brunauer-Emmett-Teller (BET) method. For example, the BET specific surface area can be measured by the BET 6-point method using a porosimetry analyzer (Belsorp-II mini, Bell Japan Inc.) and a nitrogen gas adsorption flow method.

[0040] The average particle size (D 50 The average particle size (D ) of the negative electrode active material may be 8 μm to 25 μm, specifically 12 μm to 20 μm, and more specifically 15 μm to 20 μm. 50 ) is adjusted to the above range, the BET specific surface area is adjusted to a preferred level, the voids between particles are reduced, and swelling is prevented, and problems such as significant volume expansion during charge and discharge due to an excessively large average particle size of natural graphite particles and reduced fast charge performance due to an increased lithium diffusion distance are prevented.

[0041] The first negative electrode active material may be spherical. When the first negative electrode active material is spherical, a smooth pore structure is maintained when the first negative electrode active material is included in a negative electrode, thereby ensuring a diffusion path for lithium ions and improving the output characteristics of the negative electrode. Furthermore, when the first negative electrode active material is spherical, adhesive strength within the negative electrode can be improved, allowing for a relative reduction in the amount of binder used, which can be advantageous for reducing output characteristics and resistance. In this specification, the term "spherical" refers to a shape that is not only perfectly spherical, but also includes shapes that are substantially spherical even if slightly crushed.

[0042] The tap density of the first negative electrode active material may be 1.0 g / cc to 1.3 g / cc, specifically 1.05 g / cc to 1.30 g / cc, and more specifically 1.11 g / cc to 1.20 g / cc, which is preferable in terms of improving the sphericity of the negative electrode active material and reducing the degree of cycle expansion of a negative electrode containing the same.

[0043] The tap density can be determined, for example, by filling 40 g of the first negative electrode active material into a cylindrical container having a diameter of 30 mm and a capacity of 100 mL, vibrating the container up and down 1,000 times with an amplitude of 10 mm, measuring the final volume, and calculating the apparent density.

[0044] The first negative electrode active material may further include an amorphous carbon coating layer located on at least a portion of the surface of the natural graphite particle.

[0045] The amorphous carbon coating layer can reduce the specific surface area of ​​the first anode active material, improve cell performance, and facilitate lithium ion mobility, thereby reducing resistance and improving fast charging performance. More specifically, the first anode active material can be composed of the natural graphite particles and the amorphous carbon coating layer.

[0046] The amorphous carbon coating layer may be included in the first negative electrode active material in an amount of 1 wt % to 10 wt %, specifically 2 wt % to 5 wt %.

[0047] The method for preparing the first negative electrode active material is not particularly limited as long as it can adjust the pore volume measured by mercury porosimetry to the above-mentioned level. More specifically, the first negative electrode active material may be prepared by a method including the following steps:

[0048] (a) isostatically pressing a natural graphite raw material; (b) mixing the isostatically pressed natural graphite raw material and a binder material to produce a mixture; (c) heat treating the mixture to carbonize it; and (d) crushing the carbonized mixture

[0049] According to the manufacturing method, the natural graphite raw material is isostatically pressed, mixed with the isostatically pressed natural graphite binder material, heat-treated, carbonized, and then crushed to prepare the first negative electrode active material.

[0050] The natural graphite raw material may be spherical natural graphite particles.

[0051] The isostatic pressing process can be cold isostatic pressing or hot isostatic pressing.

[0052] The isostatic pressing treatment can be carried out at a pressure of 20 MPa to 100 MPa, specifically at a pressure of 45 MPa to 95 MPa. By carrying out the isostatic pressing treatment within this pressure range, it is possible to reduce voids within the natural graphite raw material and prevent an increase in defects in the natural graphite raw material due to pressing at an excessive pressure.

[0053] The isostatic pressing may be performed for 0.1 to 20 minutes, specifically 0.5 to 3 minutes, and when the time is within this range, it is preferable in that the desired physical properties of the first negative electrode active material can be appropriately adjusted and maintained.

[0054] The binder material may include at least one selected from the group consisting of a polymer resin and a pitch. Specifically, the polymer resin may include at least one selected from the group consisting of sucrose, phenol resin, naphthalene resin, polyvinyl alcohol resin, furfuryl alcohol resin, polyacrylonitrile resin, polyamide resin, furan resin, cellulose resin, styrene resin, polyimide resin, epoxy resin, vinyl chloride resin, and polyvinyl chloride. The pitch may include at least one selected from the group consisting of coal-based pitch, petroleum-based pitch, and mesophase pitch.

[0055] The natural graphite raw material and the binder substance can be mixed at a weight ratio of 100:4 to 100:14, specifically at a weight ratio of 100:5 to 100:10.

[0056] The heat treatment of the mixture may be carried out at 1,000 to 1,500°C, specifically 1,150 to 1,300°C, and carbonization of the binder material may be preferably carried out within this range. The heat treatment may be carried out for 20 to 48 hours.

[0057] After the carbonized mixture is crushed, a sieving process may be further performed. The crushing and sieving may be performed to determine the average particle size (D 50 ) range can be satisfied.

[0058] The lower negative electrode active material layer includes a second negative electrode active material. The second negative electrode active material includes primary particle-shaped artificial graphite particles. Specifically, the second negative electrode active material may consist solely of primary particle-shaped artificial graphite particles.

[0059] The lower negative electrode active material layer includes a second negative electrode active material in addition to the first negative electrode active material, thereby achieving fast charging characteristics and low cycle expansion of the negative electrode. In particular, the second negative electrode active material includes primary particle artificial graphite particles rather than secondary particle artificial graphite particles. Primary particle artificial graphite particles have a higher tap density than secondary particle artificial graphite particles, improving the packing of the lower negative electrode active material layer, allowing for a thinner electrode and improved energy density. Furthermore, the second negative electrode active material includes primary particle artificial graphite particles, which have excellent cycle expansion performance, and therefore reduces cycle expansion to an excellent level when mixed with the first negative electrode active material.

[0060] Here, the term "primary particle-form artificial graphite particles" may refer to single particle-form artificial graphite particles, and is used as a term to distinguish it from "secondary particle-form artificial graphite particles," which are aggregates of two or more primary particle-form artificial graphite particles aggregated by an intentional granulation or bonding process.

[0061] The average particle size (D 50 ) may be 4 μm to 13 μm, specifically 7 μm to 10 μm. When the specific surface area of ​​the second negative electrode active material is within this range, the specific surface area of ​​the second negative electrode active material can be reduced to a preferred level, which not only helps to improve the capacity of the negative electrode but also allows the second negative electrode active material to densely fill voids formed between the first negative electrode active material particles, which will be described later, and thus improves rolling performance.

[0062] The BET specific surface area of ​​the second negative electrode active material is 0.1 m 2 / g~3.0m 2 / g, specifically 0.8m 2 / g~1.5m 2 / g, and when it is within the above range, it is preferable in terms of suppressing side reactions and reducing resistance. The BET specific surface area can be measured using a BEL Sorption instrument (manufactured by BEL Japan).

[0063] The second negative electrode active material may be spherical. When the second negative electrode active material is spherical, a smooth pore structure is maintained when the second negative electrode active material is included in a negative electrode, thereby ensuring a diffusion path for lithium ions and improving the output characteristics of the negative electrode.

[0064] The tap density of the second negative electrode active material may be 1.0 g / cc to 1.3 g / cc, specifically 1.15 g / cc to 1.30 g / cc, which is preferable in terms of improving the sphericity of the negative electrode active material and reducing the degree of cycle expansion of a negative electrode containing the negative electrode active material.

[0065] The weight ratio of the first negative electrode active material to the second negative electrode active material may be 50:50 to 90:10, which is preferable in that the energy density and cycle expansion characteristics can be simultaneously improved to desirable levels.

[0066] The average particle size (D 50 ) relative to the average particle size (D 50 The ratio of (a) to (b) may be 1 to 8, specifically 1.5 to 3.0, and when it is within this range, it is preferable in that it can minimize electrolyte side reactions and improve cycle expansion characteristics.

[0067] The total weight of the first and second negative electrode active materials may be 80% to 99% by weight, preferably 90% to 98% by weight, based on the weight of the lower negative electrode active material layer 210.

[0068] In addition, the lower negative electrode active material layer 210 may further include, in addition to the first negative electrode active material and the second negative electrode active material, at least one additive selected from the group consisting of a binder, a thickener, and a conductive material.

[0069] The binder, which serves to bind the conductive material, active material, and current collector, may be added in an amount of 1 to 30 wt % to the lower negative electrode active material layer 210. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers thereof.

[0070] The thickener may be any thickener that has been used in lithium secondary batteries, and an example thereof is carboxymethyl cellulose (CMC).

[0071] The conductive material is a component for further improving the conductivity of the negative electrode material and may be added in an amount of 1 to 20 wt % to the lower negative electrode active material layer 210. The conductive material is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity, 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 fiber and metal fiber; metal powders such as carbon fluoride, aluminum, 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. Specific examples of commercially available conductive materials include acetylene black-based products from Chevron Chemical Company, Denka Singapore Private Limited, Gulf Oil Company, Ketjenblack, EC-based products (manufactured by Armak Company), Vulcan XC-72 (manufactured by Cabot Company), and Super P (manufactured by Timcal).

[0072] [Top negative electrode active material layer 220] The upper negative electrode active material layer 220 is disposed on the lower negative electrode active material layer 210. Specifically, the upper negative electrode active material layer 220 may be formed on one side of the lower negative electrode active material layer 210 that does not face the negative electrode current collector 100. If the lower negative electrode active material layers are formed on both sides of the negative electrode current collector, the upper negative electrode active material layers may be disposed on the lower negative electrode active material layers formed on both sides of the negative electrode current collector, respectively.

[0073] The upper negative electrode active material layer 220 includes a third negative electrode active material. The third negative electrode active material includes artificial graphite particles in the form of secondary particles formed by granulating two or more primary particles. The artificial graphite particles in the form of secondary particles include voids formed between the primary particles, allowing lithium ions to diffuse smoothly through the voids.

[0074] The upper anode active material layer is disposed on the upper part of the anode and includes a third anode active material including artificial graphite particles in the form of secondary particles, thereby facilitating the diffusion of lithium ions and thereby further improving the fast charging performance of the anode.

[0075] The secondary particle-form artificial graphite particles have an average particle size (D 50 When the average particle size of the primary artificial graphite particles contained in the uncoated artificial graphite particles is within the above range, the capacity can be adjusted to a preferred level, and the average particle size (D 50 ) can be prevented from being too large, thereby preventing a decrease in fast charging performance.

[0076] The third negative electrode active material may further include an amorphous carbon coating layer disposed on the secondary particle-type artificial graphite particles, and the amorphous carbon coating layer may be included in the third negative electrode active material in an amount of 1 wt % to 10 wt %, specifically 2 wt % to 5 wt %.

[0077] The amorphous carbon coating layer can be formed by adding a carbon precursor to the secondary particle-form artificial graphite particles and then heat-treating the mixture. The carbon precursor can be, but is not limited to, a polymer resin such as sucrose, phenol resin, naphthalene resin, polyvinyl alcohol resin, furfuryl alcohol resin, polyacrylonitrile resin, polyamide resin, furan resin, cellulose resin, styrene resin, polyimide resin, epoxy resin, vinyl chloride resin, or polyvinyl chloride; or a pitch such as coal-based pitch, petroleum-based pitch, or mesophase pitch. The heat-treatment temperature can be 1,000°C to 1,800°C.

[0078] The average particle size (D 50 ) may be 15 μm to 25 μm, specifically 17 μm to 22 μm. When the particle size is within this range, a decrease in fast charging performance due to excessive particle size is prevented, and the specific surface area of ​​the active material is adjusted to a preferred level, which is favorable for improving high-temperature performance.

[0079] The third negative electrode active material has a BET specific surface area of ​​0.1 m 2 / g~3.0m 2 / g, specifically 0.6m 2 / g~1.0m 2 / g, and when it is within this range, it is preferable in that electrolyte side reactions can be minimized.

[0080] The third negative electrode active material may have a tap density of 1.0 g / cc or less, in the range of 0.85 g / cc to 0.99 g / cc.

[0081] The weight of the third negative electrode active material may be 80% to 99% by weight, preferably 90% to 98% by weight, based on the weight of the upper negative electrode active material layer 220.

[0082] In addition, the upper negative electrode active material layer 220 may further include, in addition to the third negative electrode active material, at least one additive selected from the group consisting of a binder, a thickener, and a conductive material.

[0083] The binder is a component that helps bind the conductive material, active material, and current collector, and may be added in an amount of 1 to 30 wt % to the upper negative electrode active material layer 220. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers thereof.

[0084] The thickener may be any thickener that has been used in lithium secondary batteries, and an example thereof is carboxymethyl cellulose (CMC).

[0085] The conductive material is a component for further improving the conductivity of the negative electrode material and may be added in an amount of 1 to 20 wt % into the upper negative electrode active material layer 220. The conductive material is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity, 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 fiber and metal fiber; metal powders such as carbon fluoride, aluminum, 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. Specific examples of commercially available conductive materials include acetylene black-based products from Chevron Chemical Company, Denka Singapore Private Limited, Gulf Oil Company, Ketjenblack, EC-based products (manufactured by Armak Company), Vulcan XC-72 (manufactured by Cabot Company), and Super P (manufactured by Timcal).

[0086] The sum of the thickness of the lower negative electrode active material layer 210 and the thickness of the upper negative electrode active material layer 220 may be 30 μm to 200 μm, specifically 100 μm to 150 μm, and more specifically 110 μm to 130 μm.

[0087] The ratio of the thickness of the lower negative electrode active material layer to the thickness of the upper negative electrode active material layer may be 1:0.5 to 1:2, specifically 1:0.8 to 1:1.3, which is preferable in that the overall charge / discharge performance, adhesive strength, and energy density of the negative electrode can be improved simultaneously.

[0088] The sum of the loading amount of the lower negative electrode active material layer and the loading amount of the upper negative electrode active material layer is 3 mAh / cm2 ~4mAh / cm 2 , specifically 3.4mAh / cm 2 ~3.8mAh / cm 2 It can be.

[0089] The ratio of the loading amount of the lower negative electrode active material layer to the loading amount of the upper negative electrode active material layer may be 1:0.5 to 1:2, specifically 1:0.8 to 1:1.3, which is preferable in that the overall charge / discharge performance, adhesion, and energy density of the negative electrode can be improved simultaneously.

[0090] The method for manufacturing the negative electrode is not particularly limited as long as it can achieve the lower and upper negative electrode active material layers having the above-described characteristics. For example, a negative electrode according to the present invention can be manufactured by adding a first negative electrode active material, a second negative electrode active material, and at least one additive selected from a binder, a conductive material, and a thickener to a solvent to prepare a slurry for the lower negative electrode active material layer, adding the third negative electrode active material and, optionally, at least one additive selected from a binder, a conductive material, and a thickener to a solvent to prepare a slurry for the upper negative electrode active material layer, and then applying the resulting slurry to a negative electrode current collector. More specifically, a negative electrode according to the present invention can be manufactured by applying the slurry for the lower negative electrode active material layer to a negative electrode current collector, rolling, and drying the slurry for the upper negative electrode active material layer, and then applying the slurry for the upper negative electrode active material layer to the lower negative electrode active material layer, rolling, and drying the resulting slurry for the upper negative electrode active material layer. Meanwhile, the anode according to the present invention may be manufactured by applying the slurry for the lower anode active material layer onto the anode current collector while substantially simultaneously applying the slurry for the upper anode active material layer onto the slurry for the lower anode active material layer, followed by rolling and drying.

[0091] <Secondary battery> The present invention also provides a secondary battery including the above-mentioned negative electrode. Specifically, the secondary battery may be a lithium secondary battery.

[0092] Specifically, the secondary battery includes the above-described negative electrode, a positive electrode facing the negative electrode, a separator interposed between the negative electrode and the positive electrode, and an electrolyte.

[0093] The positive electrode can include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector.

[0094] <000,0416>The positive electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or those obtained by surface treatment of the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. can be used.

[0095] Generally, the positive electrode current collector can have a thickness of 3 μm to 500 μm.

[0096] The positive electrode active material layer is formed on the positive electrode current collector and contains a positive electrode active material.

[0097] The positive electrode active material can include a compound capable of reversible intercalation and deintercalation of lithium, specifically, a lithium composite metal oxide containing one or more metals such as cobalt, manganese, nickel, or aluminum and lithium. More specifically, the lithium composite metal oxide is a lithium-manganese-based oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt-based oxide (e.g., LiCoO2, etc.), a lithium-nickel-based oxide (e.g., LiNiO2, etc.), a lithium-nickel-manganese-based oxide (e.g., LiNi 1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-z Ni z O4 (where 0 < Z < 2), etc.), a lithium-nickel-cobalt-based oxide (e.g., LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1), etc.), a lithium-manganese-cobalt-based oxide (e.g., LiCo 1-Y2 MnY2 O2 (where 0 < Y2 < 1), LiMn 2-z1 Co z1 O4 (where 0 < Z1 < 2), etc.), lithium-nickel-manganese-cobalt-based 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.), or lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r3 M S2 )O2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r3, and s2 are, as atomic fractions of independent elements, 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < s2 < 1, and p2 + q2 + r3 + s2 = 1), etc.), and one or more of these compounds can be included. Among them, in terms of being able to enhance the capacity characteristics and stability of the battery, the lithium composite metal oxide is 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 Mn 0.15 Co 0.05 )O2, etc.).

[0098] The positive electrode active material can be contained in an amount of 80% to 99% by weight based on the total weight of the positive electrode active material layer.

[0099] The positive electrode active material layer may further contain, in addition to the above-mentioned positive electrode active material, at least one additive selected from the group consisting of a binder and a conductive material.

[0100] The binder is a component that helps bind the active material and conductive material together and to the current collector, and is typically added in an amount of 1 to 30 wt % based on the total weight of the positive electrode active material layer. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers.

[0101] The conductive material is not particularly limited as long as it does not cause chemical changes in the battery and is conductive, and examples thereof include graphite; carbon-based materials such as carbon black, 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 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-based products from Chevron Chemical Company, Denka Singapore Private Limited, and Gulf Oil Company, as well as Ketjenblack, EC-based products (manufactured by Armak Company), Vulcan XC-72 (manufactured by Cabot Company), and Super P (manufactured by Timcal).

[0102] The conductive material may be contained in an amount of 1 to 30% by weight based on the total weight of the positive electrode active material layer.

[0103] The positive electrode active material layer may be manufactured by preparing a positive electrode slurry by adding a positive electrode active material and, optionally, an additive including a binder and / or a conductive material to a solvent, and then coating, rolling, and drying the slurry on the positive electrode current collector.

[0104] The solvent may include an organic solvent such as NMP (N-methyl-2-pyrrolidone), and may be used in an amount that provides a desired viscosity when the positive electrode active material, and optionally, a binder and a conductive material, are included. For example, the solvent may be included so that the concentration of the solids, including the positive electrode active material, and optionally, a binder and a conductive material, is 50 wt % to 95 wt %, preferably 70 wt % to 90 wt %.

[0105] In the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without limitation. In particular, a separator with low resistance to electrolyte ion movement and excellent electrolyte humidification ability is preferred. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof can be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material can also be used, and can be used in a single-layer or multi-layer structure.

[0106] Furthermore, examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the production of lithium secondary batteries, but are not limited to these.

[0107] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0108] The organic solvent can be any organic solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent that can be used include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether and tetrahydrofuran; ketone-based solvents such as cyclohexanone; aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (R is a C2-C20 linear, branched, or cyclic hydrocarbon group that may contain a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; and sulfolanes. Among these, carbonate-based solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and a high dielectric constant, which can improve the charge / discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred. In this case, the cyclic carbonate and the linear carbonate are mixed in a volume ratio of about 1:1 to about 1:9, which allows the electrolyte to exhibit excellent performance.

[0109] The lithium salt may be any compound capable of providing lithium ions used in lithium secondary batteries. Specifically, examples of the lithium salt include LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, and LiB(C2O4)2. The lithium salt is preferably used at a concentration in the range of 0.1 to 2.0 M. When the lithium salt concentration is within this range, the electrolyte has appropriate conductivity and viscosity, resulting in excellent electrolyte performance and efficient lithium ion migration.

[0110] As described above, the secondary battery according to the present invention is useful in portable devices such as mobile phones, notebook computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs), and is particularly suitable as a component battery of a medium- to large-sized battery module. Accordingly, the present invention also provides a medium- to large-sized battery module including the above-described secondary battery as a unit cell.

[0111] Such a medium- to large-sized battery module can be preferably applied to power sources that require high output and large capacity, such as electric vehicles, hybrid electric vehicles, and power storage devices.

[0112] Although the present invention may be embodied in various different forms, it is not intended to be limited to the embodiments set forth herein, and the present invention may be practiced in various different forms, without departing from the spirit or scope of the present invention.

[0113] Examples and Comparative Examples Example 1: Preparation of negative electrode <Production of the first negative electrode active material, the second negative electrode active material, and the third negative electrode active material> 1. Preparation of the First Negative Electrode Active Material As the natural graphite raw material, spherical natural graphite particles (average particle size (D 50 The spherical natural graphite particles were subjected to cold isostatic pressing at a pressure of 90 MPa for 1 minute.

[0114] The isostatically pressed spherical natural graphite particles were mixed with pitch as a binder in a weight ratio of 100:6, and the mixture was carbonized by heat treatment at 1,250°C for 24 hours. The carbonized mixture was then crushed and sieved to prepare a first negative electrode active material in which an amorphous carbon coating layer was formed on natural graphite particles.

[0115] The first negative electrode active material has an average particle size (D 50 ) is 17 μm, and the BET specific surface area is 1.8 m 2 / g and the tap density was 1.12 g / cc.

[0116] An amorphous carbon coating layer was formed on the first negative electrode active material in an amount of 3 wt %.

[0117] The pore volume of the first negative electrode active material measured by mercury porosimetry was 0.042 mL / g.

[0118] 2. Preparation of the Second Negative Electrode Active Material The primary particle form is spherical artificial graphite particles with an average particle size (D 50 ) is 9 μm, and the BET specific surface area is 1.27 m 2 / g and a tap density of 1.23 g / cc was used as the second negative electrode active material.

[0119] 3. Preparation of the Third Negative Electrode Active Material Multiple primary artificial graphite particles (average particle size (D 50 Artificial graphite particles (average particle size (D): approximately 11 μm) in the form of secondary particles agglomerated 50 ):18 μm) was prepared.

[0120] Specifically, the artificial graphite particles are obtained by dissolving the coke raw material into particles having an average particle size (D 50The coke is pulverized with coke having an average particle diameter (D) of about 11 μm, and the pulverized coke is mixed with pitch to produce an intermediate granulated in the form of secondary particles. The temperature is gradually increased to 3,000°C, maintained at 3,000°C for 60 hours, and then gradually decreased to room temperature for heat treatment to graphitize and secondary particles. The average particle diameter (D) of the secondary particles is then measured. 50 The total heat treatment time for the intermediate was 2 weeks.

[0121] The artificial graphite particles were mixed with pitch and then heat-treated at 1,200° C. for 24 hours to form an amorphous carbon coating layer on the artificial graphite particles, which was used as a third negative electrode active material.

[0122] The amorphous carbon coating layer was contained in the third negative electrode active material at 3.5 wt %.

[0123] The average particle size (D 50 ) is 18 μm, and the BET specific surface area is 0.75 m 2 / g and the tap density was 0.92 g / cc.

[0124] <Production of negative electrodes> 1. Preparation of slurry for the lower negative electrode active material layer A mixture of the first negative electrode active material and the second negative electrode active material in a weight ratio of 60:40, carbon black as a conductive material, styrene-butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener was mixed in a weight ratio of 96.1:1.0:1.7:1.2, and water was added to prepare a slurry for the lower negative electrode active material layer.

[0125] 2. Preparation of slurry for upper negative electrode active material layer A third negative electrode active material, carbon black as a conductive material, styrene-butadiene (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener were mixed in a weight ratio of 95.3:1.0:2.5:1.2, and water was added to prepare a slurry for the upper negative electrode active material layer.

[0126] 3. Formation of the lower and upper negative electrode active material layers The slurry for the lower negative electrode active material layer prepared above was coated on a copper foil (thickness: 15 μm) as a negative electrode current collector, and substantially simultaneously, the slurry for the upper negative electrode active material layer prepared above was coated on the coated slurry for the lower negative electrode active material layer. The resulting mixture was rolled and dried in a vacuum oven at 130°C for 10 hours to prepare a negative electrode in which the negative electrode current collector, the lower negative electrode active material layer, and the upper negative electrode active material layer were sequentially stacked.

[0127] The loading capacity of the lower negative electrode active material layer is 1.8 mAh / cm 2 The loading amount of the upper negative electrode active material layer is 1.8 mAh / cm 2 The sum of the loading amounts of the lower and upper negative electrode active material layers is 3.6 mAh / cm 2 It was.

[0128] Example 2: Preparation of negative electrode <Production of the first negative electrode active material, the second negative electrode active material, and the third negative electrode active material> 1. Preparation of the First Negative Electrode Active Material As a natural graphite raw material, the average particle size (D 50 A first negative electrode active material was prepared in the same manner as in Example 1, except that spherical natural graphite particles having a particle diameter of 18 μm were used.

[0129] The first negative electrode active material has an average particle size (D 50 ) is 18 μm, and the BET specific surface area is 1.8 m 2 / g, the tap density was 1.13 g / cc, and the pore volume measured by mercury porosimetry was 0.041 mL / g.

[0130] 2. Preparation of the Second Negative Electrode Active Material The primary particle form is spherical artificial graphite particles with an average particle size (D 50 ) is 8 μm, and the BET specific surface area is 1.30 m 2 / g and a tap density of 1.25 g / cc was used as the second negative electrode active material.

[0131] 3. Preparation of the Third Negative Electrode Active Material Multiple primary artificial graphite particles (average particle size (D 50 : Approximately 11.5 μm) are agglomerated secondary particles of artificial graphite particles (average particle size (D 50 ):19 μm) was prepared.

[0132] Specifically, the artificial graphite particles are obtained by dissolving the coke raw material into particles having an average particle size (D 50 The coke is pulverized with coke having an average particle diameter (D) of about 11.5 μm, and the pulverized coke is mixed with pitch to produce an intermediate granulated in the form of secondary particles. The temperature is gradually increased to 3,000°C, maintained at 3,000°C for 60 hours, and then gradually decreased to room temperature for heat treatment to graphitize and secondary particles. The average particle diameter (D) of the secondary particles is then measured. 50 ) was adjusted to 19 μm, and the total heat treatment time of the intermediate was 2 weeks.

[0133] The artificial graphite particles were mixed with pitch and then heat-treated at 1,200° C. for 24 hours to form an amorphous carbon coating layer on the artificial graphite particles, which was used as a third negative electrode active material.

[0134] The amorphous carbon coating layer was contained in the third negative electrode active material at 3.5 wt %.

[0135] The average particle size (D 50 ) is 19 μm, and the BET specific surface area is 0.7 m 2 / g and the tap density was 0.90 g / cc.

[0136] <Production of negative electrodes> A negative electrode was fabricated in the same manner as in Example 1, except that the first negative electrode active material, the second negative electrode active material, and the third negative electrode active material prepared above were used and the first negative electrode active material and the second negative electrode active material were mixed in a weight ratio of 70:30 when fabricating the lower negative electrode active material layer.

[0137] Example 3: Preparation of negative electrode <Production of the first negative electrode active material, the second negative electrode active material, and the third negative electrode active material> 1. Preparation of the First Negative Electrode Active Material As a natural graphite raw material, the average particle size (D 50 A first negative electrode active material was prepared in the same manner as in Example 1, except that spherical natural graphite particles having a particle diameter of 18 μm were used.

[0138] The first negative electrode active material has an average particle size (D 50 ) is 18 μm, and the BET specific surface area is 1.8 m 2 / g, the tap density was 1.14 g / cc, and the pore volume measured by mercury porosimetry was 0.039 mL / g.

[0139] 2. Preparation of the Second Negative Electrode Active Material The same second negative electrode active material as that used in Example 2 was prepared.

[0140] 3. Preparation of the Third Negative Electrode Active Material The same third negative electrode active material as that used in Example 1 was prepared.

[0141] <Production of negative electrodes> A negative electrode was fabricated in the same manner as in Example 1, except that the first negative electrode active material, the second negative electrode active material, and the third negative electrode active material prepared above were used, and the first negative electrode active material and the second negative electrode active material were mixed in a weight ratio of 90:10 when fabricating the lower negative electrode active material layer.

[0142] Comparative Example 1: Production of negative electrode 1. Preparation of slurry for the lower negative electrode active material layer A negative electrode active material was produced in the same manner as the method for producing the first negative electrode active material in Example 1, except that the isostatic pressing treatment was not performed.

[0143] The average particle size (D 50 ) is 18 μm, and the specific surface area is 2.7 m 2 / g, tap density was 1.10 g / cc, and the pore volume measured by mercury porosimetry was 0.080 mL / g.

[0144] The negative electrode active material, carbon black as a conductive material, styrene-butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener were mixed in a weight ratio of 96.1:1.0:1.7:1.2, and water was added to prepare a slurry for the lower negative electrode active material layer.

[0145] 2. Preparation of slurry for upper negative electrode active material layer The same negative electrode active material as the third negative electrode active material prepared in Example 2 was prepared as a negative electrode active material.

[0146] The negative electrode active material, carbon black as a conductive material, styrene-butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener were mixed in a weight ratio of 95.3:1.0:2.5:1.2, and water was added to prepare a slurry for the upper negative electrode active material layer.

[0147] 3. Formation of the lower and upper negative electrode active material layers A negative electrode was fabricated in the same manner as in Example 1, except that the above-prepared slurry for the lower negative electrode active material layer and the slurry for the upper negative electrode active material layer were used.

[0148] Comparative Example 2: Production of negative electrode 1. Preparation of slurry for the lower negative electrode active material layer The same negative electrode active material as the third negative electrode active material prepared in Example 2 was used as the negative electrode active material.

[0149] The negative electrode active material, carbon black as a conductive material, styrene-butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener were mixed in a weight ratio of 95.3:1.0:2.5:1.2, and water was added to prepare a slurry for the lower negative electrode active material layer.

[0150] 2. Preparation of slurry for upper negative electrode active material layer A negative electrode active material was produced in the same manner as the method for producing the first negative electrode active material in Example 1, except that the isostatic pressing treatment was not performed.

[0151] The average particle size (D 50 ) is 19 μm, and the specific surface area is 2.8 m 2 / g, tap density was 1.10 g / cc, and the pore volume measured by mercury porosimetry was 0.090 mL / g.

[0152] The negative electrode active material, carbon black as a conductive material, styrene-butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener were mixed in a weight ratio of 96.1:1.0:1.7:1.2, and water was added to prepare a slurry for the upper negative electrode active material layer.

[0153] 3. Formation of the lower and upper negative electrode active material layers A negative electrode was fabricated in the same manner as in Example 1, except that the above-prepared slurry for the lower negative electrode active material layer and the slurry for the upper negative electrode active material layer were used.

[0154] Comparative Example 3: Production of negative electrode 1. Preparation of slurry for the lower negative electrode active material layer The same slurry for the lower negative electrode active material layer as in Comparative Example 1 was prepared.

[0155] 2. Preparation of slurry for upper negative electrode active material layer The primary particle form is spherical artificial graphite particles with an average particle size (D 50 ) is 10 μm, and the BET specific surface area is 1.25 m 2 / g and a tap density of 1.15 g / cc was used as the negative electrode active material.

[0156] The negative electrode active material, carbon black as a conductive material, styrene-butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener were mixed in a weight ratio of 95.3:1.0:2.5:1.2, and water was added to prepare a slurry for the upper negative electrode active material layer.

[0157] 3. Formation of the lower and upper negative electrode active material layers A negative electrode was fabricated in the same manner as in Example 1, except that the above-prepared slurry for the lower negative electrode active material layer and the slurry for the upper negative electrode active material layer were used.

[0158] Comparative Example 4: Production of negative electrode 1. Preparation of slurry for the lower negative electrode active material layer The primary particle form is spherical artificial graphite particles with an average particle size (D 50 ) is 10 μm, and the BET specific surface area is 1.25 m 2 / g and a tap density of 1.15 g / cc was used as the negative electrode active material.

[0159] The negative electrode active material, carbon black as a conductive material, styrene-butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener were mixed in a weight ratio of 95.3:1.0:2.5:1.2, and water was added to prepare a slurry for the lower negative electrode active material layer.

[0160] 2. Preparation of slurry for upper negative electrode active material layer A negative electrode active material was produced in the same manner as the method for producing the first negative electrode active material in Example 1, except that the isostatic pressing treatment was not performed.

[0161] The average particle size (D 50 ) is 19 μm, and the specific surface area is 2.8 m 2 / g, tap density was 1.10 g / cc, and the pore volume measured by mercury porosimetry was 0.090 mL / g.

[0162] The negative electrode active material, carbon black as a conductive material, styrene-butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener were mixed in a weight ratio of 96.1:1.0:1.7:1.2, and water was added to prepare a slurry for the upper negative electrode active material layer.

[0163] 3. Formation of the lower and upper negative electrode active material layers A negative electrode was fabricated in the same manner as in Example 1, except that the above-prepared slurry for the lower negative electrode active material layer and the slurry for the upper negative electrode active material layer were used.

[0164] Comparative Example 5: Production of negative electrode <Production of the first negative electrode active material, the second negative electrode active material, and the third negative electrode active material> 1. Preparation of the First Negative Electrode Active Material A negative electrode active material was produced in the same manner as the method for producing the first negative electrode active material in Example 1, except that the isostatic pressing treatment was not performed.

[0165] The average particle size (D 50 ) is 18 μm, and the specific surface area is 2.7 m 2 / g, tap density was 1.10 g / cc, and the pore volume measured by mercury porosimetry was 0.080 mL / g.

[0166] 2. Preparation of the Second Negative Electrode Active Material The same second negative electrode active material as in Example 1 was prepared.

[0167] 3. Preparation of the Third Negative Electrode Active Material The same third negative electrode active material as in Example 1 was prepared.

[0168] <Production of negative electrodes> A negative electrode was fabricated in the same manner as in Example 1, except that the first, second, and third negative electrode active materials prepared above were used.

[0169] Comparative Example 6: Production of negative electrode 1. Preparation of slurry for the lower negative electrode active material layer The same second negative electrode active material as in Example 1 was prepared as a negative electrode active material.

[0170] The negative electrode active material, carbon black as a conductive material, styrene-butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener were mixed in a weight ratio of 95.3:1.0:2.5:1.2, and water was added to prepare a slurry for the lower negative electrode active material layer.

[0171] 2. Preparation of slurry for upper negative electrode active material layer The same negative electrode active material as the third negative electrode active material prepared in Example 2 was prepared as a negative electrode active material.

[0172] The negative electrode active material, carbon black as a conductive material, styrene-butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener were mixed in a weight ratio of 95.3:1.0:2.5:1.2, and water was added to prepare a slurry for the upper negative electrode active material layer.

[0173] 3. Formation of the lower and upper negative electrode active material layers A negative electrode was fabricated in the same manner as in Example 1, except that the above-prepared slurry for the lower negative electrode active material layer and the slurry for the upper negative electrode active material layer were used.

[0174] Comparative Example 7: Production of negative electrode 1. Preparation of slurry for the lower negative electrode active material layer As a natural graphite raw material, the average particle size (D 50 A negative electrode active material was prepared in the same manner as in Example 1, except that spherical natural graphite particles having a particle diameter of 18 μm were used and the pressure during the isostatic pressing treatment was 40 MPa.

[0175] The negative electrode active material has an average particle size (D 50 ) is 18 μm, and the BET specific surface area is 1.9 m 2 / g, tap density was 1.07 g / cc, and the pore volume measured by mercury porosimetry was 0.050 mL / g.

[0176] The negative electrode active material, carbon black as a conductive material, styrene-butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener were mixed in a weight ratio of 96.1:1.0:1.7:1.2, and water was added to prepare a slurry for the lower negative electrode active material layer.

[0177] 2. Preparation of slurry for upper negative electrode active material layer The same negative electrode active material as the third negative electrode active material prepared in Example 2 was prepared as a negative electrode active material.

[0178] The negative electrode active material, carbon black as a conductive material, styrene-butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener were mixed in a weight ratio of 95.3:1.0:2.5:1.2, and water was added to prepare a slurry for the upper negative electrode active material layer.

[0179] 3. Formation of the lower and upper negative electrode active material layers A negative electrode was fabricated in the same manner as in Example 1, except that the above-prepared slurry for the lower negative electrode active material layer and the slurry for the upper negative electrode active material layer were used.

[0180] Experimental Example Experimental example 1: Swelling evaluation <Lithium secondary battery manufacturing> A cathode slurry was prepared by mixing LiCoO2 as a cathode active material, Li-435 (Denka), KF9700 (Kureha), and BH-730H (Zeon) as a thickener in a weight ratio of 97.68:1.20:1.00:0.12, and adding N-methylpyrrolidone (NMP). The cathode slurry was applied to an aluminum foil, vacuum dried at about 130°C for 8 hours, and rolled to prepare a cathode. The cathode loading was about 3.4 mAh / cm. 2 It was manufactured to be.

[0181] Secondary batteries of Examples 1 to 3 and Comparative Examples 1 to 7 were fabricated by inserting a polyolefin separator between the negative and positive electrodes, and then injecting an electrolyte solution into the negative and positive electrodes. The electrolyte solution used was a non-aqueous electrolyte solvent made by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 2:8, to which vinylene carbonate (VC) was added at 0.5 wt % relative to the solvent, and LiPF6 was dissolved at 1 M.

[0182] <Swelling evaluation> The lithium secondary batteries of Examples 1 to 3 and Comparative Examples 1 to 7 were charged and discharged over a charge range of SOC0 to SOC95, with the first cycle at 0.1 C, the second cycle at 0.2 C, and the third to 50th cycles at 0.5 C. The swelling ratio was then measured and calculated according to the following equation. The results are shown in Table 1 below.

[0183] Swelling ratio (%) = {(t2-t1) / t1} × 100 (t1 is the thickness of the negative electrode for the secondary battery before the first charge-discharge cycle, and t2 is the thickness of the negative electrode for the secondary battery after the 50th charge-discharge cycle)

[0184] Experimental Example 2: Initial Discharge Capacity Evaluation <Manufacturing coin-type half-cell secondary batteries> A lithium metal counter electrode was used as the positive electrode.

[0185] Coin-type half-cell secondary batteries of Examples 1 to 3 and Comparative Examples 1 to 7 were fabricated by inserting a polyolefin separator between the negative and positive electrodes and then injecting an electrolyte solution into the batteries. The electrolyte solution was prepared by adding 0.5 wt % of vinylene carbonate (VC) to a non-aqueous electrolyte solvent made by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 2:8, and dissolving LiPF6 at 1M.

[0186] <Measurement of initial discharge capacity> The coin-type half-cell secondary battery was charged and discharged under the following charge and discharge conditions to measure the initial discharge capacity, and the results are shown in Table 1 below.

[0187] Charging conditions: CCCV mode, 0.1C charging, cut-off at 0.005C and 5mV Discharge conditions: CC mode, 0.1C discharge, cut-off at 1.5V

[0188] [Table 1]

[0189] Referring to Table 1, it can be seen that the negative electrodes and secondary batteries according to the embodiments of the present invention have an excellent level of energy density and an improved effect of reducing cycle swelling. [Explanation of symbols]

[0190] 10 negative electrode 100 Negative electrode current collector 210 Lower negative electrode active material layer 220 Upper negative electrode active material layer

Claims

1. a negative electrode current collector; a lower negative electrode active material layer disposed on the negative electrode current collector; an upper negative electrode active material layer disposed on the lower negative electrode active material layer, the lower negative electrode active material layer includes a first negative electrode active material including natural graphite particles and a second negative electrode active material including artificial graphite particles in the form of primary particles; the upper negative electrode active material layer includes a third negative electrode active material including artificial graphite particles in the form of secondary particles formed by granulating two or more primary particles; a pore volume of the first negative electrode active material measured by mercury porosimetry of 0.06 mL / g or less;

2. 2. The negative electrode according to claim 1, wherein the first negative electrode active material has a pore volume of 0.001 mL / g to 0.06 mL / g as measured by a mercury porosimeter.

3. The average particle size (D ５０ 2. The negative electrode according to claim 1, wherein the thickness of the first electrode is 8 μm to 25 μm.

4. The first negative electrode active material has a BET specific surface area of ​​0.6 m ２ / g to 2.5m ２ The negative electrode according to claim 1 , wherein the anode has a Cr content of 1.0 / g.

5. The average particle size (D ５０ 2. The negative electrode according to claim 1, wherein the thickness of the first electrode is 4 μm to 13 μm.

6. The BET specific surface area of ​​the second negative electrode active material is 0.1 m ２ / g to 3.0m ２ The negative electrode according to claim 1 , wherein the anode has a Cr content of 1.0 / g.

7. The average particle size (D ５０ 2. The negative electrode according to claim 1, wherein the thickness of the first electrode is 15 μm to 25 μm.

8. The third negative electrode active material has a BET specific surface area of ​​0.1 m ２ / g to 3.0m ２ The negative electrode according to claim 1 , wherein the anode has a Cr content of 1.0 / g.

9. 2. The negative electrode according to claim 1, wherein a weight ratio of the first negative electrode active material to the second negative electrode active material is 50:50 to 90:

10.

10. 2. The negative electrode of claim 1, wherein a total weight of the first negative electrode active material and the second negative electrode active material is 80 wt % to 99 wt % of a weight of the lower negative electrode active material layer.

11. The average particle size (D ５０ ) of the first negative electrode active material relative to the average particle size (D ５０ 2. The negative electrode according to claim 1, wherein the ratio of

12. 2. The negative electrode of claim 1, wherein a weight of the third negative electrode active material is 80% by weight to 99% by weight of a weight of the upper negative electrode active material layer.

13. 2. The negative electrode of claim 1, wherein a ratio of the thickness of the lower negative electrode active material layer to the thickness of the upper negative electrode active material layer is 1:0.5 to 1:

2.

14. 2. The negative electrode of claim 1, wherein a ratio of a loading amount of the lower negative electrode active material layer to a loading amount of the upper negative electrode active material layer is 1:0.5 to 1:

2.

15. An anode as described in claim 1, wherein the first anode active material further comprises an amorphous carbon coating layer located on at least a portion of the surface of the natural graphite particles.

16. The negative electrode according to any one of claims 1 to 15, a positive electrode facing the negative electrode; a separator interposed between the negative electrode and the positive electrode; and an electrolyte.

Images