Negative active material for rechargeable lithium battery, negative electrode for rechargeable lithium battery and rechargable lithium battery

Abstract

The present invention relates to a negative electrode active material for a lithium secondary battery, a negative electrode for a lithium secondary battery including the same, and a lithium secondary battery including the same, wherein the negative electrode active material for the secondary battery comprises spherical graphite; and an amorphous carbon layer surrounding the spherical graphite, and wherein the volume ratio of the total volume of pores having a diameter of 100 to 1000 nm to the total volume of pores of the negative electrode active material is 3% or less, and the orientation ratio of the negative electrode active material is 90 or less.

Description

Technology Field

[0001] The invention relates to a negative electrode active material for a lithium secondary battery, a negative electrode for a lithium secondary battery containing the same, and a lithium secondary battery containing the same. Background Technology

[0003] With the recent rapid proliferation of battery-powered electronic devices such as mobile phones, laptop computers, and electric vehicles, the demand for high-energy-density, high-capacity rechargeable batteries is increasing rapidly. Accordingly, research and development to improve the performance of lithium-ion batteries is actively underway.

[0004] A lithium secondary battery is a battery comprising a positive electrode and a negative electrode containing an active material capable of lithium ion intercalation and deintercalation, and an electrolyte, which produces electrical energy through oxidation and reduction reactions when lithium ions are intercalated or deintercalated from the positive and negative electrodes.

[0005] Generally, electrode plates for lithium secondary batteries are manufactured by a wet method using a solvent such as water or N-methylpyrrolidone. Alternatively, electrode plates for lithium secondary batteries may be manufactured by a dry method without using the above solvent.

[0006] The above dry method may include detailed processes such as a mixing process for mixing an active material, a binder, etc., instead of using the above solvent, a process for fiberizing the binder and kneading the active material, and a process for dissolving the dough produced by the kneading process. It may be desirable for the above active material to have excellent dispersibility and not break during the kneading and dissolving processes. The problem to be solved

[0008] One embodiment provides a negative electrode active material for a lithium secondary battery that is free from cracking, breaking, and damage.

[0009] Another embodiment provides a negative electrode for a lithium secondary battery comprising the above-mentioned negative electrode active material and a lithium secondary battery comprising the same. means of solving the problem

[0011] One embodiment is a negative electrode active material for a lithium secondary battery, wherein the negative electrode active material comprises spherical graphite; and an amorphous carbon layer surrounding the spherical graphite, and the volume ratio of the total volume of pores having a diameter of 100 to 1000 nm to the total volume of pores of the negative electrode active material is 3% or less, and the orientation ratio of the negative electrode active material is 90 or less.

[0012] Another embodiment provides a negative electrode for a lithium secondary battery comprising the negative electrode active material for the lithium secondary battery.

[0013] Another embodiment provides a lithium secondary battery comprising a negative electrode including a negative electrode active material for the lithium secondary battery; and a positive electrode. Effects of the invention

[0015] The negative electrode active material for a secondary battery according to one embodiment had no cracking, breaking, or damage during the manufacture of the dry negative electrode, resulting in high manufacturing efficiency of the dry negative electrode and high battery efficiency. Brief explanation of the drawing

[0017] Figure 1 is a graph showing the result of cumulative pore volume (Y-axis, incremental pore volume, unit: mL / g) according to pore diameter (X-axis, pore width, unit: μm) for each of the cathode active material and natural graphite according to one embodiment. In Figure 1, the solid line represents the cathode active material, and the dotted line represents the result of natural graphite. FIGS. 2 to 5 are cross-sectional views schematically illustrating a lithium secondary battery according to one embodiment. Figure 6 is a scanning electron microscope (SEM) image of the negative electrode active material of Example 1. Figure 7 is an SEM image of the cathode active material of Comparative Example 1. Specific details for implementing the invention

[0018] Hereinafter, embodiments of the present invention will be described in detail. However, these are presented as examples and are not intended to limit the present invention, and the present invention is defined only by the scope of the claims set forth below.

[0019] Unless otherwise specifically stated in this specification, when a part such as a layer, film, region, plate, etc. is described as being "on" another part, this includes not only cases where it is "immediately on" another part, but also cases where there is another part in between.

[0020] Unless otherwise specified in this specification, a singular form may also include a plural form. Additionally, unless otherwise specified, "A or B" may mean "including A, including B, or including A and B."

[0021] In this specification, "combination of these" may mean a mixture of components, a laminate, a composite, a copolymer, an alloy, a blend, and a reaction product, etc.

[0022] Unless otherwise defined in this specification, the particle size may be the average particle size. Additionally, the particle size refers to the average particle size (D50), which means the diameter of the particle whose cumulative volume in the particle size distribution is 50% by volume. The average particle size (D50) may be measured by methods widely known to those skilled in the art, for example, by measuring with a particle size analyzer, or by measuring with a transmission electron microscope (TEM) image or a scanning electron microscope (SEM) image. Alternatively, the average particle size (D50) value may be obtained by measuring using a measuring device utilizing dynamic light scattering, performing data analysis to count the number of particles for each particle size range, and then calculating from this. Alternatively, it may be measured using a laser diffraction method. When measuring by laser diffraction, more specifically, after dispersing the particles to be measured in a dispersion medium, they are introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000) and irradiated with ultrasound of about 28 kHz at an output of 60 W, and then the average particle size (D50) at 50% of the particle size distribution in the measuring device can be calculated.

[0023] In this specification, the 'diameter' of a pore refers to the longest diameter of the pore.

[0024] The above 'longest diameter of the pore' may refer to the diameter of the pore when the cross-section of the pore is a perfect circle. The above 'longest diameter of the pore' may refer to the length of the longest side of the cross-section of the pore when the cross-section of the pore is not a circle.

[0025] The above 'maximum pore diameter' can be measured by image analysis of the cross-section of the cathode active material using a scanning electron microscope (SEM), Barrett-Joyner-Halenda (BJH) analysis, or a mercury impregnation method (mercury intrusion method).

[0026] Negative electrode active material for lithium secondary batteries

[0027] The lithium negative electrode active material (hereinafter referred to as the negative electrode active material) is densified so that there is no breakage, fracture, or damage during the manufacturing process of the negative electrode, particularly during the manufacturing process of the dry negative electrode, thereby significantly increasing the manufacturing efficiency of the dry negative electrode and the battery efficiency. The manufacturing process of the dry negative electrode may essentially include mixing, kneading, and grinding of the negative electrode active material instead of including a solvent.

[0028] The above-described negative electrode active material comprises spherical graphite; and an amorphous carbon layer surrounding the spherical graphite. The negative electrode active material has a volume ratio of the total volume of pores with a diameter of 100 to 1000 nm to the total volume of pores of 3% or less, and an orientation ratio of 90 or less.

[0029] The above total pores include only open pores, excluding closed pores among the pores contained within the cathode active material. The volume of the above total pores may be the total volume of open pores formed within the cathode active material, regardless of their diameter.

[0030] The pores having a diameter of 100 to 1000 nm may be pores contained within the cathode active material. The pores having a diameter of 100 to 1000 nm are not restricted in shape as long as they have the diameter range.

[0031] In one embodiment, the total pores contained within the cathode active material may have a diameter distribution of 10 nm to 6000 nm.

[0032] The above volume ratio is the ratio of the total volume of pores with a diameter of 100 to 1000 nm to the total pore volume contained within the cathode active material.

[0033] According to one embodiment, the total volume of the pores may be 0.1 mL / g to 0.5 mL / g, for example, 0.3 mL / g to 0.5 mL / g, and this can be measured by a mercury impregnation method.

[0034] According to one embodiment, the total volume of the pores having a diameter of 100 to 1000 nm may be 0.01 mL / g to 0.07 mL / g, for example, 0.03 mL / g to 0.06 mL / g, and this can be measured by a mercury impregnation method.

[0035] In one embodiment, the volume ratio may be obtained by dividing the volume of a pore with a diameter of 100 to 1000 nm by the true density of graphite (about 2.2 g / cc). The true density may be measured by a method known to those skilled in the art. For example, the true density may be measured using a method applying Archimedes' principle or by using a gas pycnometer. For example, the true density may be measured using a Micrometrics Accupyc II 1340 apparatus with 1.0 g of cathode active material using a gas method with helium gas.

[0036] In the above-mentioned cathode active material, the volume ratio of pores with a diameter of 100 to 1000 nm was considered. This is explained with reference to FIG. 1.

[0037] Figure 1 is a graph showing the cumulative pore volume (Y-axis, incremental pore volume, unit: mL / g) according to pore diameter (X-axis, pore width, unit: μm) for a cathode active material according to one embodiment and conventional natural graphite, respectively.

[0038] Referring to FIG. 1, it can be seen that the pore distribution of the cathode active material according to one embodiment and natural graphite is significantly different in the pore region with a diameter of 100 to 1000 nm.

[0039] As shown in the experimental examples below, it was confirmed that the above-mentioned cathode active material had a higher dry cathode manufacturing efficiency and higher cell efficiency compared to the above-mentioned natural graphite when subjected to the same dry cathode manufacturing process. Accordingly, it was confirmed that the manufacturing of the dry cathode can be influenced by the volume ratio of the total volume of pores having a diameter of 100 to 1000 nm, for example, 300 to 1000 nm, for example, 400 to 1000 nm.

[0040] According to one embodiment, the volume ratio of the total volume of pores with a diameter of 300 to 1000 nm to the total volume of pores in the cathode active material may be 3% or less.

[0041] According to one embodiment, the volume ratio of the total volume of pores with a diameter of 400 to 1000 nm to the total volume of pores in the cathode active material may be 3% or less.

[0042] According to one embodiment, the volume ratio may be greater than 0% and less than or equal to 3%, 1 to 3%, 1 to 2.5%, or 2 to 3%.

[0043] The above-mentioned negative electrode active material has an orientation ratio of 90 or less. Within the above orientation ratio range, the active material in the dry negative electrode can be oriented in a state where it stands at a certain angle with respect to the current collector, so that the movement of lithium ions during charging and discharging can occur more easily and the resistance to movement of the electrolyte within the negative electrode can be reduced, thereby increasing the efficiency of the dry negative electrode, for example, the initial efficiency, and shortening the electrolyte impregnation time of the negative electrode active material even after the rolling process during the dry negative electrode manufacturing process.

[0044] According to one embodiment, the orientation ratio may be 50 to 80, 60 to 80, or 70 to 80. When the orientation ratio is 50 or more and 80 or less, the degree of rolling of the negative electrode active material during the rolling process in the manufacturing process of the dry negative electrode can be increased to increase the energy density of the battery.

[0045] According to one embodiment, the orientation ratio can be calculated according to Equation 1 below.

[0046] [Equation 1]

[0047] Orientation ratio = I(110)) / I(002)

[0048] (In the above Equation 1,

[0049] I(110) is the peak intensity of the (110) plane when XRD measuring the above negative electrode active material.

[0050] I(002) is the peak intensity of the (002) plane during XRD measurement of the above-mentioned cathode active material.

[0051] According to one embodiment, the XRD measurement was performed using the CuKα line as the target line.

[0052] Even when the above-mentioned negative electrode active material is included in a dry negative electrode plate, substantially the same peak intensity can be obtained by XRD measurement. That is, even in the XRD measurement of the above-mentioned dry negative electrode plate, the negative electrode active material having an orientation degree of 90 or less is included.

[0053] The above-mentioned negative electrode active material is spherical, and since its shape is spherical, it can be well dispersed throughout the negative electrode, thereby reducing the expansion rate during charging and discharging. In addition, when the above-mentioned negative electrode active material is mixed with crystalline carbon, the spherical negative electrode active material can be better inserted between the crystalline carbons, allowing it to be better dispersed throughout the negative electrode.

[0054] According to one embodiment, the cathode active material is spherical, with a sphericity (S) represented by Equation 2 below of 0.8 to 1.0:

[0055] [Equation 2]

[0056] Sphericity (S) = 4π × A / B 2

[0057] (In the above Equation 2,

[0058] A is the total area of ​​the negative electrode active material, and

[0059] B is the circumference of the shape of the negative electrode active material)

[0060] According to one embodiment, the above B may be the shape of an actual negative electrode active material.

[0061] The degree of sphericity of the above-described cathode active material may be a value obtained when a three-dimensional particle is projected onto a two-dimensional plane. For example, the degree of sphericity may be the ratio of the boundary of a circle having the same area as the boundary of the actual particle shape.

[0062] The area represented by the value A above refers to the area of ​​a circle having the same perimeter as B, obtained by acquiring an SEM image of the electrode cross-section using a CP-SEM (controlled pressure scanning electron microscope) and calculating the actual perimeter length (B) of the particle through the Image J program using this cross-section image. According to one embodiment, the actual perimeter length may be the length obtained along the perimeter even if the particle shape is not a perfect sphere and there are uneven regions.

[0063] According to one embodiment, the degree of sphericity of the cathode active material may be 0.8 to 0.99, 0.92 to 0.98, or 0.92 to 0.95. Within this range, efficiency during charging and discharging can be increased, and cracking and breakage during dry electrode manufacturing can be significantly reduced.

[0064] The above-mentioned spherical graphite may be a secondary particle assembled from a plurality of natural graphite primary particles.

[0065] The above primary particles may have an average particle size D50 of 1 to 15 μm. When assembled within the above particle size range, the occurrence of internal pores can be reduced. According to one embodiment, the above primary particles may have an average particle size of 1 to 13 μm or 5 to 10 μm.

[0066] The above secondary particles may have an average particle size D50 of 5 to 30 μm. Within the above particle size range, cracking and breakage of the negative electrode active material during the kneading and disintegration processes in the dry electrode manufacturing process may be reduced. According to one embodiment, the above secondary particles may have an average particle size of 10 to 15 μm or 10 to 20 μm.

[0067] The number of primary particles constituting the secondary particles is not particularly limited as long as they can form secondary particles. For example, it may be 2 to 50, 2 to 30, or 2 to 10.

[0068] The above natural graphite may be graphite having a long axis and a short axis. The length of the long axis of the above natural graphite may be 5 to 15 μm. Within this range, it may be non-oriented, the number of lithium ion movement ports may increase, thereby improving rate characteristics, and it may have appropriate edge portions, thus maintaining efficiency appropriately.

[0069] In the above amorphous carbon layer, the amorphous carbon may be soft carbon, hard carbon, mesophase pitch carbide, calcined coke, or a combination thereof.

[0070] The above amorphous carbon layer may have a thickness of 1 nm to 2 µm, 1 nm to 500 nm, 10 nm to 300 nm, or 20 nm to 200 nm. Within the above range, the degree of cracking and breakage during dry electrode manufacturing can be reduced, thereby increasing the efficiency of dry electrode manufacturing.

[0071] According to one embodiment, a portion of the space surrounded by the primary particles in the cathode active material may be filled with the amorphous carbon. This can be achieved by the amorphous carbon precursor easily penetrating into the pores formed inside the secondary assembled particles by compression molding as described below, and then carbonizing. This can further reduce the volume ratio of the aforementioned pores.

[0072] According to one embodiment, the spherical graphite and amorphous carbon among the cathode active materials may be included in a weight ratio of spherical graphite to amorphous carbon of 90:10 to 99:1, for example, 93:7 to 95:5, based on a total of 100 parts by weight. Within this range, side reactions with the electrolyte are reduced and rate characteristics can be further improved.

[0073] A cathode active material according to one embodiment may have a low specific surface area, i.e., a low BET specific surface area, and the specific surface area may be 3 m² / g or less, for example, 0.5 m² / g to 3 m² / g, 0.8 m² / g to 3 m² / g, or 0.8 m² / g to 1.5 m² / g or 2 m² / g to 3 m² / g.

[0074] The above-mentioned cathode active material can be manufactured by the following process.

[0075] The primary particles are aggregated into secondary particles by performing a spheroidization process using a spheroidization device. The spheroidization process can be performed by introducing the primary particles into the spheroidization device and rotating the inner container. The spheroidization process can produce secondary particles in which natural graphite primary particles are aggregated and which contain pores inside.

[0076] A mixture is prepared by mixing the above-mentioned secondary particles with an amorphous carbon precursor.

[0077] The above amorphous carbon precursor may be included in the mixture in an amount of 10% by weight or less, for example, more than 1% by weight and 8% by weight or less, or 5 to 7% by weight. Within this range, there may be an optimal effect on the internal density and initial efficiency of the negative electrode active material.

[0078] The above amorphous carbon precursor is not particularly limited as long as it is a material that is carbonized. Examples of the above amorphous carbon precursor may include one or more types of pitch carbon such as synthetic pitch, petroleum-based pitch, and coal-based pitch.

[0079] Then, the above mixture is compression molded.

[0080] The above compression molding can further reduce the volume ratio of the total volume of the pores with a diameter of 100 to 1000 nm by increasing the degree to which the amorphous carbon precursor penetrates into the pores inside the secondary particles, and can also suppress side reactions between the negative electrode active material and the electrolyte.

[0081] The above compression molding can be performed at a pressure sufficient to maintain the spherical shape of the obtained product, particularly the final product, the cathode active material. The pressure can be, for example, greater than 0 MPa and less than or equal to 100 MPa, greater than 30 MPa and less than or equal to 90 MPa, or between 50 and 80 MPa. Within the above pressure range, porosity can be reduced while maintaining the spherical shape of the cathode active material without generating fine particles.

[0082] According to one embodiment, the compression molding can be performed by cold isostatic pressing (CIP).

[0083] The above compression molded product can be heat-treated to convert the amorphous carbon precursor into an amorphous carbon layer. Since the compression molding is performed by a cold isostatic pressing method, it is easy to manufacture a negative electrode active material that satisfies the volume ratio of the pores described above.

[0084] The heat treatment may be performed at a temperature of 1000 to 1500°C, for example, 1100 to 1400°C, 1100 to 1300°C, or 1200 to 1300°C. The heat treatment may be performed for 1 to 20 hours, for example, 10 to 18 hours, 14 to 17 hours, or 14 to 16 hours. Within this range, not only the amorphous carbon precursor on the surface of the compression molded article but also the amorphous carbon precursor that has penetrated into the pores inside the secondary particles may be converted into amorphous carbon, thereby further reducing the volume ratio of the total volume of the pores having a diameter of 100 to 1000 nm.

[0085] The above heat treatment is for carbonizing the amorphous carbon precursor and can be carried out in a nitrogen atmosphere, a helium atmosphere, or a combination thereof.

[0086] <Cathode for Lithium Secondary Batteries>

[0087] A negative electrode for a lithium secondary battery comprises a negative electrode active material layer, and the negative electrode active material layer comprises the negative electrode active material described above.

[0088] Accordingly, the above-mentioned cathode includes a cathode active material satisfying the orientation ratio, thereby facilitating the movement of lithium ions during charging and discharging and reducing the resistance to electrolyte movement within the cathode, which can result in high initial efficiency. Additionally, the above-mentioned cathode includes a cathode active material satisfying the volume ratio, which can increase the manufacturing efficiency of the cathode. In particular, compared to a wet cathode, a dry cathode is manufactured by a process involving the grinding of the cathode active material without a solvent; since the cathode active material satisfies the volume ratio, there is no breakage, fragmentation, or damage, which can significantly increase the manufacturing efficiency of the dry cathode.

[0089] In one embodiment, the above-described cathode active material may be included in an amount of 95% or more by weight, for example, 95 to 100% by weight or 100% by weight, among the total cathode active material of the cathode active material layer.

[0090] The above-described cathode active material layer may additionally include a cathode active material different from the above-described cathode active material, in addition to the above-described cathode active material. For convenience, the cathode active material according to the above-described embodiment is referred to as the first cathode active material, and the additionally included cathode active material is referred to as the second cathode active material.

[0091] The second negative electrode active material may further include a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide.

[0092] A material capable of reversibly intercalating / deintercalating the above lithium ions may be a carbon-based negative electrode active material, such as crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, etc.

[0093] As the above lithium metal alloy, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn may be used.

[0094] As a material capable of doping and undoping the above lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material may be used. The Si-based negative electrode active material may be silicon, a silicon-carbon composite, SiOx (0 < x < 2), a Si-Q alloy (wherein Q is selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof), or a combination thereof. The Sn-based negative electrode active material may be Sn, SnO2, a Sn-based alloy, or a combination thereof.

[0095] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite may be in the form of silicon particles and amorphous carbon coated on the surface of the silicon particles. For example, it may include a secondary particle (core) assembled from silicon primary particles and an amorphous carbon coating layer (shell) located on the surface of the secondary particle. The amorphous carbon may also be located between the silicon primary particles, so that, for example, the silicon primary particles may be coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0096] The silicon-carbon composite may further include crystalline carbon. For example, the silicon-carbon composite may include a core comprising crystalline carbon and silicon particles and an amorphous carbon coating layer located on the surface of the core.

[0097] The above Si-based or Sn-based negative electrode active material can be used in combination with a carbon-based negative electrode active material.

[0098] (bookbinder)

[0099] The above negative electrode active material layer may further include a binder in addition to the above negative electrode active material.

[0100] The above binder serves to effectively bond the negative active materials to each other and also to effectively bond the negative active materials to the current collector. As the binder, a non-aqueous binder, an aqueous binder, or a combination thereof may be used.

[0101] Examples of the above-mentioned non-aqueous binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0102] The above-mentioned water-based binder may be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylenepropylenediene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0103] When a water-based binder is used as the above-mentioned cathode binder, a cellulose-based compound capable of imparting viscosity may be further included. As this cellulose-based compound, one or more types such as carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or alkali metal salts thereof may be mixed and used. Na, K, or Li may be used as the alkali metal.

[0104] In one embodiment, the cathode is a dry cathode, and the dry cathode will be described in detail below.

[0105] The above negative electrode active material layer may include a first binder.

[0106] The first binder described above may be included without particular limitation as long as it is capable of being fiberized in the manufacturing step of the dry cathode described below. The fiberization may include a process of micronizing and dividing the polymer. For example, the fiberization may be performed using mechanical shear force, etc. The surface of the fiberized polymer fiber is loosened to generate a large number of microfibers, and the dry cathode may be manufactured by causing the generated microfibers to intertwine with the cathode active material and / or the conductive material described below.

[0107] In one embodiment, the first binder may comprise polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyolefin, or a mixture thereof. Specifically, the first binder may comprise polytetrafluoroethylene, and more specifically, may be polytetrafluoroethylene. Specifically, one or more of the polytetrafluoroethylene and polyvinylidene fluoride (PVDF) may be included in an amount of 60% or more by weight, for example, 90 to 100% by weight, or 100% by weight, based on the total weight of the first binder.

[0108] In one embodiment, the first binder may be included in the cathode active material layer in a fibrous state.

[0109] In one embodiment, the cathode active material layer may comprise 80 to 99.5 weight% of the cathode active material, for example, 90 to 99.5 weight%, and 0.5 to 20 weight% of the first binder, for example, 0.5 to 10 weight%. Within this range, the manufacture of a dry cathode may be easy, and the binding force between the materials constituting the electrode may be improved by the fibrous binder.

[0110] The above-mentioned negative electrode active material layer further comprises a second binder, and the second binder may comprise a non-fibrotic binder. For example, the non-fibrotic binder may comprise one or more of polyethylene oxide and polyvinylidene fluoride-co-hexafluoropropylene.

[0111] The cathode active material layer (which may be referred to as a dry electrode film) for the above dry cathode can be manufactured by the following steps.

[0112] (a) A process for preparing a powdered mixture comprising the above-mentioned negative electrode active material; and a binder comprising the above-mentioned first binder;

[0113] (b) a kneading process for mixing the above powdered mixture;

[0114] (c) a disintegration process for obtaining electrode powder by crushing the mixture mass produced by the above kneading process; and

[0115] (d) A process of obtaining a dry electrode film by calendering the above electrode powder.

[0116] First, a powder mixture is prepared by mixing the above-mentioned cathode active material and a binder containing the first binder. The mixing is performed so that the cathode active material and the binder are uniformly distributed within the mixture, and since the mixture is in powder form, it is not limited to any method that enables simple mixing thereof. However, since the mixture is intended to manufacture a dry electrode film, it does not contain a solvent. The mixing can be performed by dry mixing, for example, by introducing the materials into a device such as a blender. The mixture may further include the above-mentioned conductive material.

[0117] In one embodiment, the mixing time is not particularly limited but can be performed for 1 second to 10 minutes. Meanwhile, the mixing speed is not particularly limited but can be appropriately controlled within a range of about 3,000 rpm to 30,000 rpm. As a specific example, the mixing can be prepared by mixing in a mixer at 5,000 rpm to 20,000 rpm for 30 seconds to 2 minutes, specifically at 10,000 rpm to 15,000 rpm for 30 seconds to 5 minutes, in terms of controlling high uniformity and the degree of crystallinity of the binder resin.

[0118] Next, a kneading process, i.e., a mixing process, is performed on the mixture obtained above to fiberize the binder. The kneading is a step of forming a mixture mass with a solid content of 100% by weight by combining or linking the cathode active material and / or the conductive material as the binder fiberizes.

[0119] Specifically, the mixing of step (b) can be controlled at a speed of 10 rpm to 100 rpm. For example, the mixing can be controlled at a speed of 40 rpm to 70 rpm. The mixing can be performed for 1 minute to 30 minutes. For example, it can be performed for 3 minutes to 7 minutes at a speed of 40 rpm to 70 rpm. Meanwhile, the mixing can be controlled such that the shear stress is in the range of 10 / s to 500 / s. In a specific embodiment of the present invention, the mixing can be performed for 1 minute to 30 minutes and the shear stress can be controlled in the range of 30 / s to 100 / s.

[0120] The above mixing step can be performed under high temperature and pressure conditions above atmospheric pressure, and more specifically, under pressure conditions higher than atmospheric pressure. More specifically, the mixing can be performed on the mixture in a range of 70°C to 200°C, specifically 90°C to 150°C.

[0121] In addition, it can be performed at a pressure above atmospheric pressure, specifically at a pressure of 1 atm to 3 atm, and more specifically at 1.1 atm to 3 atm. If performed outside the above range at a pressure too high, it is undesirable because excessive shear force and pressure may be applied, which may cause the formed fibers to be cut or the density of the mixture lumps to become too high. That is, according to the present invention, the intended effect of the present invention can be achieved when a low-shear mixing process is performed under high temperature and pressure above atmospheric pressure conditions instead of high-shear mixing.

[0122] Next, a disintegration step is performed in which the mass of the mixture produced through the above kneading process is crushed again to obtain a powder for the electrode.

[0123] Specifically, although the mixture mass produced through the above kneading may be calendered immediately, in this case, the mixture mass may need to be pressed under high pressure and high temperature to produce a thin film. Consequently, problems may arise where the film density becomes too high or a uniform film cannot be obtained; therefore, the produced mixture mass undergoes the aforementioned crushing step.

[0124] The grinding described above is not limited but may be performed using known grinding devices such as blenders or grinders. The speed of the grinding may be controlled within a range of 3,000 rpm to 30,000 rpm. The grinding time may be appropriately controlled within a range of 1 second to 10 minutes. The grinding speed and time are not specifically limited to the above ranges. As a specific example, the grinding may be performed at a speed of 5,000 rpm to 20,000 rpm for 30 seconds to 10 minutes, or at a speed of 10,000 rpm to 18,000 rpm for 30 seconds to 5 minutes. By performing sufficient grinding within the above ranges, it is easy to form into a film and the degree of fine powder generation can be reduced.

[0125] A dry electrode film is manufactured by heating and pressing the above electrode powder. Specifically, the electrode powder obtained by completing the grinding step as described above is fed into a calendering process.

[0126] The electrode powder is heat-pressed by a calendering process and processed into a sheet-shaped film. The calendering process may be performed by a pair of opposing calendering rollers. The calendering process may be performed by the electrode powder passing through a plurality of calendering rollers.

[0127] The above electrode powder may be pretreated before performing the calendering process.

[0128] The above pretreatment process can be performed by applying heat to the electrode powder so that the temperature of the powder is maintained at 80°C or higher, preferably 100°C or higher, for a predetermined period of time. The time of the pretreatment process can be performed for 1 minute or more and can be appropriately adjusted depending on the amount of powder. For example, the temperature of the powder can be maintained at a temperature of 80°C or higher for 1 minute or more, or at a temperature of 100°C or higher for 1 minute or more. Alternatively, the heating temperature of the electrode powder is preferably controlled to be below the melting point of the binder resin to prevent deterioration of the electrode components contained in the electrode powder, for example, the binder resin used. For example, it can be controlled to 320°C or lower. The above pretreatment process can be performed using a commonly used heating device, such as a convection oven or an infrared heating device. At this time, it is preferable that the electrode powder be stirred so that it does not remain stagnant while being heated.

[0129] After step (d) above, an additional step of rolling the dry electrode film and laminating it with a current collector described below may be performed.

[0130] Meanwhile, in one embodiment of the present invention, the dry electrode film may have a thickness of 100 μm to 200 μm, but is not particularly limited thereto. For example, the dry electrode film may have a thickness of 100 μm to 150 μm.

[0131] (Challenge)

[0132] The above-mentioned cathode active material layer may further include a conductive material.

[0133] The above conductive material is not particularly limited as long as it possesses conductivity without causing chemical changes in the battery. For example, the above conductive material may include graphite such as natural graphite or artificial graphite; carbon black-based compounds such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; conductive fibers such as carbon fibers or metal fibers; metal powders such as carbon fluoride, aluminum, or nickel powder; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive materials such as polyphenylene derivatives. In detail, to ensure uniform mixing of the conductive material and to improve conductivity, it may include one or more selected from the group consisting of activated carbon, graphite, carbon black, and carbon nanotubes, and more specifically, it may include activated carbon.

[0134] In one embodiment, the negative electrode active material layer may comprise 80 to 99 weight% of the negative electrode active material, for example, 90 to 99.5 weight%, 0.5 to 20 weight% of the binder, for example, 0.5 to 10 weight%, and 0.5 to 20 weight% of the conductive material, for example, 0.5 to 10 weight%. Within the above range, the manufacture of a dry electrode film may be easy, and there may be an effect of imparting electronic conductivity.

[0135] The above cathode may further include a current collector located on one surface of the cathode active material layer.

[0136] The above current collector is not particularly limited as long as it provides high conductivity without causing chemical changes in the battery. For example, the above current collector may be stainless steel, aluminum, nickel, titanium, calcined carbon, copper, or aluminum or stainless steel, copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a polymer substrate coated with a conductive metal that has been surface-treated with carbon, nickel, titanium, silver, etc. The current collector may also form fine irregularities on its surface to increase the adhesion of the negative electrode active material, and various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics are possible.

[0137] The above current collector may have a thickness of 10㎛ to 50㎛, but is not specifically limited thereto. For example, the above current collector may have a thickness of 10㎛ to 20㎛.

[0138] Lithium secondary battery

[0139] Another embodiment provides a lithium secondary battery comprising the above-mentioned negative electrode active material.

[0140] The above secondary battery may include a negative electrode for a secondary battery comprising the above negative electrode active material; and a positive electrode. The negative electrode for the secondary battery is substantially the same as described above.

[0141] anode

[0142] A positive electrode for a secondary battery may include a current collector and a positive electrode active material layer formed on the current collector. The positive electrode active material layer may include a positive electrode active material and may further include a binder and / or a conductive material.

[0143] For example, the above anode may further include an additive that can serve as a sacrificial anode.

[0144] The content of the positive active material is 90% to 99.5% by weight with respect to 100% by weight of the positive active material layer, and the content of the binder and the conductive material may each be 0.5% to 5% by weight with respect to 100% by weight of the positive active material layer.

[0145] As a positive electrode active material, a compound capable of reversible intercalation and deintercalation of lithium (a lithated intercalation compound) may be used. Specifically, one or more composite oxides of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof may be used.

[0146] The above composite oxide may be a lithium transition metal composite oxide, and specific examples include a lithium nickel-based oxide, a lithium cobalt-based oxide, a lithium manganese-based oxide, a lithium iron phosphate-based compound, a cobalt-free nickel-manganese-based oxide, or a combination thereof.

[0147] As an example, a compound represented by any one of the following chemical formulas may be used. Li a A 1-b X b O 2-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); Li a Mn 2-b X b O 4-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); Li a Ni 1-b-c Co b X c O 2-α D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α<2); Li a Ni 1-b-c Mn b X c O 2-α D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α<2); Li a Nib Co c L 1 d G e O2(0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, 0≤e≤0.1); Li a NiG b O2(0.90≤a≤1.8, 0.001≤b≤0.1); Li a CoG b O2(0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn 1-b G b O2(0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn2G b O4(0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn 1-g G g PO4(0.90≤a≤1.8, 0≤g≤0.5); Li (3-f) Fe2(PO4)3(0≤f≤2); Li a FePO4(0.90≤a≤1.8).

[0148] In the above chemical formula, A is Ni, Co, Mn, or a combination thereof; X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; L 1 is Mn, Al, or a combination thereof.

[0149] For example, the above-mentioned positive electrode active material may be a high-nickel positive electrode active material in which the nickel content relative to 100 mol% of the metal excluding lithium in the lithium transition metal composite oxide is 80 mol% or more, 85 mol% or more, 90 mol% or more, 91 mol% or more, or 94 mol% or more and 99 mol% or less. The high-nickel positive electrode active material can achieve high capacity and can be applied to high-capacity, high-density lithium secondary batteries.

[0150] The above binder serves to adhere the positive active material particles well to each other and also to adhere the positive active material well to the current collector. Representative examples of binders include, but are not limited to, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, nylon, etc.

[0151] The above conductive material is used to impart conductivity to the electrode, and any electronically conductive material that does not cause chemical changes can be used in the battery being constructed. Examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube; metal-based materials in the form of metal powder or metal fibers containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0152] Al may be used as the current collector mentioned above, but is not limited thereto.

[0153] The above secondary battery may further include an electrolyte.

[0154] electrolyte

[0155] The electrolyte for secondary batteries contains a non-aqueous organic solvent and a lithium salt.

[0156] The above-mentioned non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0157] The above-mentioned non-aqueous organic solvent may be a carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvent, an aprotic solvent, or a combination thereof.

[0158] The above carbonate-based solvents may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc.

[0159] Ester-based solvents such as methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methylpropionate, ethylpropionate, decanolide, mevalonolactone, valerolactone, and caprolactone may be used.

[0160] As ether-based solvents, dibutyl ether, tetraglame, diglame, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. may be used. Additionally, as ketone-based solvents, cyclohexanone, etc. may be used. As alcohol-based solvents, ethyl alcohol, isopropyl alcohol, etc. may be used, and as aprotic solvents, nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double bond, an aromatic ring, or an ether group); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane, 1,4-dioxolane; sulfolanes, etc. may be used.

[0161] The above-mentioned non-aqueous organic solvent can be used alone or in a mixture of two or more types.

[0162] In addition, when using a carbonate-based solvent, a mixture of cyclic carbonates and chain carbonates can be used, and the cyclic carbonates and chain carbonates can be mixed in a volume ratio of 1:1 to 1:9.

[0163] The above lithium salt is a substance that dissolves in an organic solvent and acts as a source of lithium ions within the battery, enabling the basic operation of a lithium secondary battery and facilitating the movement of lithium ions between the anode and cathode. Representative examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1 It may include one or more selected from SO2)(x and y are integers from 1 to 20), lithium trifluoromethane sulfonate, lithium tetrafluoroethane sulfonate, lithium difluorobis(oxalate)phosphate (LiDFOB), and lithium bis(oxalate)borate (LiBOB).

[0164] The above secondary battery may further include a separator.

[0165] separator

[0166] Depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. As such a separator, polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films of two or more layers thereof may be used, and of course, mixed multilayer films such as polyethylene / polypropylene two-layer separators, polyethylene / polypropylene / polyethylene three-layer separators, and polypropylene / polyethylene / polypropylene three-layer separators may be used.

[0167] The above separator may include a porous substrate and a coating layer comprising an organic material, an inorganic material, or a combination thereof located on one or both sides of the porous substrate.

[0168] The porous substrate may be a polymer membrane formed from any one of the following: polyolefins such as polyethylene and polypropylene; polyesters such as polyethylene terephthalate and polybutylene terephthalate; polyacetal; polyamide; polyimide; polycarbonate; polyetherketone; polyaryletherketone; polyetherimide; polyamideimide; polybenzimidazole; polyethersulfone; polyphenylene oxide; cyclic olefin copolymer; polyphenylene sulfide; polyethylene naphthalate; glass fiber; Teflon; and polytetrafluoroethylene, or a copolymer or mixture of two or more of these.

[0169] The above organic material may include a polyvinylidene fluoride-based polymer or a (meth)acrylic-based polymer.

[0170] The above inorganic materials are Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, It may include, but is not limited to, inorganic particles selected from SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof.

[0171] The above organic and inorganic materials may exist mixed in a single coating layer, or may exist in a stacked form with a coating layer containing organic materials and a coating layer containing inorganic materials.

[0172] secondary battery

[0173] Secondary batteries can be classified into cylindrical, prismatic, pouch, coin, etc., depending on their shape. FIGS. 2 to 5 are schematic diagrams illustrating a lithium secondary battery according to one embodiment, where FIG. 2 is a cylindrical battery, FIG. 3 is a prismatic battery, and FIGS. 4 and 5 are pouch-type batteries. Referring to FIGS. 2 to 5, the lithium secondary battery (100) may include an electrode assembly (40) with a separator (30) interposed between a positive electrode (10) and a negative electrode (20), and a case (50) in which the electrode assembly (40) is housed. The positive electrode (10), the negative electrode (20), and the separator (30) may be impregnated with an electrolyte (not shown). The lithium secondary battery (100) may include a sealing member (60) that seals the case (50) as in FIG. 2. In addition, in FIG. 3, the lithium secondary battery (100) may include a positive lead tab (11) and a positive terminal (12), a negative lead tab (21) and a negative terminal (22). As shown in FIG. 4 and FIG. 5, the lithium secondary battery (100) may include electrode tabs (70), namely a positive tab (71) and a negative tab (72), which serve as electrical passages for inducing current formed in the electrode assembly (40) to the outside.

[0174] A lithium secondary battery according to one embodiment of the present invention may be applied to automobiles, mobile phones, and / or various types of electric devices, etc., but the present invention is not limited thereto.

[0176] Examples and comparative examples of the present invention are described below. However, the following examples are merely one example of the present invention, and the present invention is not limited to the following examples.

[0178] Example 1

[0179] (1) A flaky natural graphite raw material with an average particle size D50 of 120㎛ was finely divided into primary particles with an average particle size D50 of 6㎛ using an air-flow grinding method. The primary particles were then finely divided into secondary particles with an average particle size D50 of 15㎛ using a spheroidizing device.

[0180] The above secondary particles and pitch carbon were mixed in a weight ratio of 93:7 based on a total of 100 parts by weight, and the mixture was subjected to a compression molding process using a cold isostatic pressing method at a pressure of 80 MPa.

[0181] Next, the obtained compression molded product was heat-treated for 16 hours in a kiln at a maximum temperature of 1100 to 1300°C under N2 atmosphere conditions to produce a cathode active material.

[0182] SEM images of the manufactured cathode active material are shown in Fig. 6. As shown in Fig. 6, it can be confirmed that the cathode active material is densified.

[0183] The sphericity of the manufactured cathode active material is 0.9. The sphericity was measured using a Malvern Morphologi 4 as a sphericity analyzer. For the manufactured cathode active material, the values ​​of A and B in Equation 1 above were determined, and then calculated according to Equation 1 above.

[0184] (2) 98.5 wt% of the above-prepared cathode active material and 1.5 wt% of a mixture of polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) as binders were put into a blender without a solvent and mixed at 10,000 rpm for 1 minute to obtain a mixture. The obtained mixture was put into a kneader and kneaded at 110°C at a speed of 60 rpm for 5 minutes to obtain a mass of the mixture, and then the mass of the mixture was put into a blender and ground at 10,000 rpm for 40 seconds to obtain an electrode powder. Afterwards, the electrode powder was repeatedly compressed using a calender roll (roll diameter: 200 mm, roll temperature: 80°C) to obtain a cathode active material layer (thickness 150 μm).

[0185] The above-mentioned cathode active material layer was laminated onto a copper foil and rolled to manufacture a dry cathode plate.

[0186] A half-cell was manufactured using the above dry negative electrode plate, lithium metal counter electrode, and electrolyte. The electrolyte is a mixed solvent of ethylene carbonate and dimethyl carbonate (3:7 volume ratio) in which 1M LiPF4 is dissolved.

[0187] Example 2

[0188] A dry cathode plate was manufactured using the same method as in Example 1, except that when manufacturing the cathode active material in Example 1, the primary particles had an average particle size D50 of 5 μm.

[0189] Example 3

[0190] A dry cathode plate was manufactured using a cathode active material in the same manner as in Example 1, except that the secondary particles and pitch carbon were mixed in a weight ratio of 95:5 based on a total of 100 parts by weight in Example 1.

[0191] Comparative Example 1

[0192] Flake-shaped natural graphite raw material with an average particle size D50 of 120㎛ was finely granulated into primary particles with an average particle size D50 of 20㎛ using an air-stream grinding method. The primary particles were granulated into secondary particles with an average particle size D50 of 15㎛ using a spheroidizing device.

[0193] A negative electrode active material was prepared by mixing pitch carbon with the secondary particles in a weight ratio of 93:7 of the total 100 parts by weight of the secondary particles and pitch carbon, and heat-treating it in a kiln at 1100 to 1300°C for 16 hours.

[0194] SEM images of the manufactured cathode active material are shown in Fig. 7. As shown in Fig. 7, it can be confirmed that there are relatively more pores compared to Fig. 6.

[0195] A dry cathode plate was manufactured using the above-mentioned cathode active material in the same manner as in Example 1.

[0196] Comparative Example 2

[0197] A negative electrode active material was prepared in the same manner as in Comparative Example 1, except that it was finely divided into primary particles with an average particle size D50 of 17 μm, and a dry negative electrode plate was prepared in the same manner as in Example 1 using the prepared negative electrode active material.

[0198] Comparative Example 3

[0199] A negative electrode active material was prepared in the same manner as in Comparative Example 1, except that the secondary particles and pitch carbon were changed to a weight ratio of 95:5 based on a total of 100 parts by weight in Comparative Example 1, and a dry negative electrode plate was prepared in the same manner as in Example 1 using the prepared negative electrode active material.

[0200] Comparative Example 4

[0201] A negative electrode active material was prepared in the same manner as in Comparative Example 1, except that the weight ratio of secondary particles and pitch carbon was changed to 97:3 based on a total of 100 parts by weight in Comparative Example 1, and a dry negative electrode plate was prepared in the same manner as in Example 1 using the prepared negative electrode active material.

[0202] (Experimental Example)

[0203] Volume Ratio (Unit: %):

[0204] The volume ratio was measured by the mercury impregnation method. For the cathode active materials of the examples and comparative examples, the Hg Intrusion Porosimeter (Micromertics, AutoPore V) was used for measurement. The cathode active material was placed in a special sample cup and surrounded with mercury, and a pressure of 0.2 to 60,000 psi was applied to inject mercury into the cathode active material. Then, the cumulative pore volume of 0.1 μm to 1 μm was obtained by measuring the volume change of the mercury, and the volume ratio was calculated by dividing it by the true density value of graphite (approx. 2.2 g / cc).

[0205] Memorial Stone

[0206] The orientation ratio was measured using the PANalytical X'Pert Pro as an XRD analysis device. The negative electrode active material of the example and comparative example was pressured to form a pellet of 1.65 g / cc, and then the ratio of the diffraction peak intensity I (002) of the (002) plane to the diffraction peak intensity I (110) of the (110) plane was determined by XRD diffraction analysis using Cuα rays.

[0207] Specific surface area (unit: g / m²) 2 ):

[0208] The BET specific surface area of ​​the negative electrode active materials of the examples and comparative examples can be measured using MOUNTECH’s Macsorb HM Model-1208.

[0209] Charge capacity, discharge capacity (above, unit: mAh / g), and initial efficiency (unit: %)

[0210] The above-mentioned manufactured half-cell was subjected to one charge / discharge cycle at 0.1C and one charge / discharge cycle at 0.2C within the range of 2.5V to 4.2V, followed by 500 charge / discharge cycles at 1C. The charge / discharge method and cut-off conditions are as follows.

[0211] Charging: Constant current-constant voltage, 4.2V / 0.01C cut-off

[0212] Discharge: Constant voltage, 2.5V cut-off

[0213] Initial efficiency was evaluated as the ratio of discharge capacity to charge capacity.

[0214] The results measured with the dry cathodes of the examples and comparative examples are as follows.

[0215] Volume ratio memorial stele specific surface area Charging capacity Discharge capacity Initial efficiency Comparative Example 1 4 130 6.5 405 353 87.2 Comparative Example 2 4.5 120 7.1 406 351 86.5 Comparative Example 3 5 125 5.8 397 350 88.1 Comparative Example 4 5 130 4.4 400 353 88.3 Example 1 2 80 2.7 388 355 91.5 Example 2 1.8 75 2.6 387 355 91.8 Example 3 2.2 70 3 390 356 91.3

[0216] As shown in Table 1 above, the dry negative electrode plate for the lithium secondary battery of the example contained a negative active material that was not broken, shattered, or damaged during the manufacture of the dry electrode plate, and thus the initial efficiency of the battery was high.

[0217] However, as shown in Table 1 above, the dry cathode of the comparative example, which did not satisfy the volume ratio and orientation ratio of the present case, had poor initial efficiency compared to the example.

[0219] Although preferred embodiments of the present invention have been described above, the present invention is not limited thereto and can be implemented with various modifications within the scope of the claims, the detailed description of the invention, and the attached drawings, and it is obvious that such modifications also fall within the scope of the present invention. Explanation of the symbols

[0221] 100: Lithium secondary battery 10: Positive electrode 11: Positive lead tab 12: Positive terminal 20: Cathode 21: Cathode lead tab 22: Negative terminal 30: Separator 40: Electrode assembly 50: Case 60: Sealing member 70: Electrode tab 71: Positive tab 72: Negative tab

Claims

Claim 1 A negative electrode active material for a lithium secondary battery, wherein the negative electrode active material comprises spherical graphite; and an amorphous carbon layer surrounding the spherical graphite, wherein the volume ratio of the total volume of pores having a diameter of 100 to 1000 nm to the total volume of pores is 3% or less, and the orientation ratio of the negative electrode active material is 90 or less. Claim 2 A negative electrode active material for a lithium secondary battery according to claim 1, wherein the entire pore is a pore contained within the negative electrode active material, and the pore having a diameter of 100 to 1000 nm is a pore contained within the negative electrode active material. Claim 3 A negative electrode active material for a lithium secondary battery, wherein, in claim 1, the total pores have a diameter of 10 nm to 6000 nm. Claim 4 A negative electrode active material for a lithium secondary battery according to claim 1, wherein the total pore volume is 0.1 mL / g to 0.5 mL / g and the volume of pores with a diameter of 100 to 1000 nm is 0.01 mL / g to 0.07 mL / g. Claim 5 In claim 1, the negative electrode active material is a negative electrode active material for a lithium secondary battery having a sphericity (S) represented by Equation 2 below of 0.8 to 1.0: [Equation 2] Sphericity (S) = 4π × A / B 2 (In Equation 2 above, A is the total area of ​​the negative electrode active material, and B is the perimeter of the shape of the negative electrode active material). Claim 6 In claim 1, the spherical graphite comprises natural graphite, a negative electrode active material for a lithium secondary battery. Claim 7 In claim 1, the spherical graphite comprises secondary particles formed by assembling a plurality of primary natural graphite particles, a negative electrode active material for a lithium secondary battery. Claim 8 A negative electrode active material for a lithium secondary battery according to claim 7, wherein a portion of the space surrounded by the primary particles among the negative electrode active material is filled with the amorphous carbon. Claim 9 A negative electrode active material for a lithium secondary battery according to claim 7, wherein the primary particles have an average particle size D50 of 1 to 15 μm and the secondary particles have an average particle size D50 of 5 to 30 μm. Claim 10 A negative electrode active material for a lithium secondary battery, wherein the amorphous carbon layer has a thickness of 1 nm to 2 μm in claim 1. Claim 11 A negative electrode active material for a lithium secondary battery according to claim 1, wherein the spherical graphite and amorphous carbon among the negative electrode active materials are included in a weight ratio of 90:10 to 99:1 based on a total of 100 parts by weight of spherical graphite : amorphous carbon. Claim 12 In claim 1, the negative electrode active material is a negative electrode active material for a lithium secondary battery having a specific surface area of ​​3 m² / g or less. Claim 13 A negative electrode for a lithium secondary battery comprising a negative electrode active material layer comprising a negative electrode active material for a lithium secondary battery according to any one of claims 1 to 12. Claim 14 A negative electrode for a lithium secondary battery according to claim 13, wherein the negative electrode active material layer comprises a binder, and the binder comprises one or more of polytetrafluoroethylene and polyvinylidene fluoride. Claim 15 A negative electrode for a lithium secondary battery according to claim 14, wherein the negative electrode active material layer comprises 80 to 99.5 weight% of the negative electrode active material and 0.5 to 20 weight% of the binder. Claim 16 In Clause 13, the above-mentioned cathode is a dry cathode, a cathode for a lithium secondary battery. Claim 17 A lithium secondary battery comprising a negative electrode active material for a lithium secondary battery according to any one of claims 1 to 12; and a positive electrode.

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