Graphite-based negative electrode active material, method for manufacturing same, and negative electrode and lithium secondary battery comprising same

Abstract

The present invention relates to a graphite-based negative electrode active material having excellent rapid charging performance and a method for manufacturing same, the graphite-based negative electrode active material comprising artificial graphite having a plane spacing d(002) of the (002) plane of 0.3360 nm to 0.3370 nm and a c-axis direction crystallite size Lc of 30.0 nm to 38.5 nm.

Description

Graphite-based negative electrode active material, method for producing the same, negative electrode and lithium secondary battery containing the same

[0001] This application claims the benefit of priority from Korean Patent Application No. 10-2024-0096748, filed July 22, 2024, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a graphite-based negative electrode active material having excellent rapid charging performance, a method for producing the same, and a negative electrode and a lithium secondary battery including the same.

[0003] Due to the rapid increase in fossil fuel use, the demand for alternative or clean energy is increasing, and as part of this, the most actively researched field is power generation and storage using electrochemical reactions.

[0004] Secondary batteries are a representative example of electrochemical devices that utilize electrochemical energy, and their applications are expanding. Recently, the demand for secondary batteries as an energy source for electronic devices and battery-powered vehicles has been rapidly increasing. A secondary battery typically consists of a cathode, an anode, an electrolyte, and a separator. The anode contains an anode active material that inserts and deintercalates lithium ions from the cathode. Carbon-based active materials, such as natural graphite or artificial graphite, are commonly used as anode active materials.

[0005] With the recent increase in demand for electric vehicles and other devices, the development of secondary batteries with superior rapid charging performance is becoming increasingly necessary. Because the charging speed of a secondary battery is influenced more by the cathode than the anode, research is underway to improve the charging performance of the cathode material to enhance the rapid charging performance of secondary batteries.

[0006] To this end, technologies utilizing Si-based anode active materials with superior rapid-charge performance have been proposed. However, Si-based anode active materials exhibit significant volume changes during charge and discharge, leading to reduced cycle life characteristics when applied. Furthermore, Si-based anode active materials are more expensive than carbon-based anode active materials, increasing the overall cost of the battery.

[0007] Therefore, there is a need for a method to improve the charging performance of carbon-based negative electrode active materials that have small volume changes during charging and discharging and are relatively inexpensive.

[0008] The present invention is intended to solve the above-mentioned problems, and to provide a graphite-based negative electrode active material having a small graphite crystal size and excellent rapid charging performance by including cavities in the crystal structure, and a method for manufacturing the same.

[0009] In addition, the present invention seeks to provide a negative electrode and a lithium secondary battery having excellent rapid charging performance, including the graphite-based negative electrode active material as described above.

[0010] [1] The present invention provides a method for producing a graphite-based negative electrode active material, comprising the steps of: forming a precursor having an oxygen content of 3 wt% to 15 wt% by crushing and assembling a carbon-based raw material; and graphitizing the precursor to produce artificial graphite having a (002) plane spacing d(002) of 0.3360 nm to 0.3370 nm and a c-axis direction crystallite size Lc of 30.0 nm to 38.5 nm.

[0011] [2] The present invention provides a method for producing a graphite-based negative electrode active material, wherein the carbon-based raw material in the above [1] includes needle cokes, mosaic cokes, coaltar pitch, resin pitch, soft carbone, or a combination thereof.

[0012] [3] The present invention provides a method for producing a graphite-based negative electrode active material, wherein, in the step of forming a precursor having an oxygen content of 3 wt% to 15 wt% in the above [1] or [2], at least one of the pulverization and granulation is performed while raising the temperature to 200 to 300°C in an oxygen atmosphere.

[0013] [4] The present invention provides a method for producing a graphite-based negative electrode active material, wherein, in the above [3], the temperature increasing is performed at a temperature increasing rate of 1°C / min to 20°C / min.

[0014] [5] The present invention provides a method for producing a graphite-based negative electrode active material, wherein the step of forming a precursor having an oxygen content of 3 wt% to 15 wt% in the above [1] or [2] is performed by crushing and assembling the raw material, and then supplying air at 100°C to 300°C to bring it into contact.

[0015] [6] The present invention provides a method for producing a graphite-based negative electrode active material, which further comprises, after the step of producing the artificial graphite in at least one of the above [1] to [5], a step of mixing the artificial graphite and a carbonaceous material and then carbonizing the mixture to form a carbon coating layer.

[0016] [7] The present invention provides a method for producing a graphite-based negative electrode active material, wherein the carbonaceous material is pitch in the above [6].

[0017] [8] The present invention provides a method for producing a graphite-based negative electrode active material, wherein, in at least one of the above [1] to [7], the artificial graphite includes a cavity in a crystal lattice.

[0018] [9] The present invention provides a graphite-based negative electrode active material including artificial graphite having a plane spacing d(002) of a (002) plane of 0.3360 nm to 0.3370 nm and a c-axis direction crystallite size Lc of 30.0 nm to 38.5 nm.

[0019]

[0010] The present invention provides a graphite-based negative electrode active material, wherein the tap density of the graphite-based negative electrode active material is 0.90 g / cc or more in the above [9].

[0020]

[0011] The present invention provides a graphite-based negative electrode active material, wherein the artificial graphite is produced by graphitizing a precursor having an oxygen content of 3 wt% to 15 wt% in the above [9] or

[0010] .

[0021]

[0012] The present invention provides a negative electrode comprising a graphite-based negative electrode active material of any one of the above [9] to

[0011] .

[0022]

[0013] The present invention provides a negative electrode having an SOC value of 35% or more at which lithium precipitation occurs when a half-cell manufactured with the negative electrode and the lithium metal counter electrode in the above

[0012] is charged at 3C.

[0023]

[0014] The present invention provides a lithium secondary battery including the negative electrode of

[0012] or

[0013] .

[0024] The present invention controls the oxygen content of a precursor during the production of artificial graphite, thereby preventing the crystal structure from being transformed into an sp2 structure in the carbonization temperature range of the graphitization process, thereby enabling the production of artificial graphite having a small crystal size and containing cavities within the crystal structure.

[0025] In addition, when manufacturing artificial graphite using a precursor having a relatively high oxygen content as in the present invention, the content of highly volatile organic components in the precursor is reduced, so that the volatile components are reduced in the carbonization temperature range, and thus high-density artificial graphite can be manufactured, and thus a graphite-based negative electrode active material having excellent mechanical properties and less particle breakage can be manufactured.

[0026] The graphite-based negative electrode active material according to the present invention comprises artificial graphite having a smaller crystallite size and pores within its crystal structure compared to conventional materials. Therefore, the lithium ion mobility within the artificial graphite is high, the lithium ion migration path is short, and the insertion / de-insertion of lithium ions is easy, thereby providing excellent charging performance. Therefore, when the graphite-based negative electrode active material of the present invention is applied, a lithium secondary battery with excellent rapid charging performance can be realized.

[0027] Terms or words used in this specification and the scope of the claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0028] The terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

[0029] In this specification, it should be understood that the terms “include,” “comprising,” or “having” are intended to specify the presence of a feature, number, step, component, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0030]

[0031] Method for manufacturing graphite-based negative electrode active material

[0032] First, a method for manufacturing a graphite-based negative electrode active material according to the present invention will be described.

[0033] The method for manufacturing a graphite-based negative electrode active material according to the present invention comprises the steps of (1) pulverizing and granulating a carbon-based raw material to form a precursor having an oxygen content of 3 wt% to 15 wt%, and (2) graphitizing the precursor to manufacture a graphite-based negative electrode active material, and, if necessary, may further comprise the step of (3) mixing the precursor and a carbonaceous material after the graphitization step and then carbonizing the precursor to form a carbon coating layer.

[0034]

[0035] Hereinafter, each step of the manufacturing method according to the present invention will be described in detail.

[0036]

[0037] (1) Precursor formation stage

[0038] First, a carbon-based raw material is prepared, crushed and assembled to form a precursor having an oxygen content of 3 wt% to 15 wt%, preferably 3 wt% to 10 wt%.

[0039] Specifically, by controlling the temperature and atmosphere of the pulverization and / or assembly process of the carbon-based raw material, or by additionally performing a surface modification process after the pulverization and assembly of the carbon-based raw material is completed, a precursor having an oxygen content of 3 wt% to 15 wt%, preferably 3 wt% to 10 wt%, can be formed.

[0040] When the precursor's oxygen content satisfies the above range, artificial graphite with excellent rapid charging performance and capacity characteristics can be manufactured. More specifically, when the precursor's oxygen content is less than 3 wt%, cavity formation may decrease during the assembly process and surface density may deteriorate. When the precursor's oxygen content exceeds 15 wt%, assembly strength may deteriorate.

[0041] When the precursor has a high oxygen content, the transformation of the amorphous sp3 structure into the crystalline sp2 structure is hindered by oxygen at temperatures between 900℃ and 1300℃ (carbonization temperature range). Accordingly, when a precursor with a high oxygen content is used, crystallization occurs in a state with a relatively large amorphous structure compared to when a precursor with a low oxygen content is used, resulting in the formation of cavities within the crystal structure and the formation of small graphite crystals.

[0042] Meanwhile, in the case of carbonaceous raw materials such as coke or soft carbon, a swelling phenomenon may occur in which the volume expands as highly volatile organic hydrocarbons rapidly volatilize in the temperature range of 600 to 900℃. When such swelling occurs, the density of the artificial graphite decreases, which causes problems such as poor mechanical properties and particle breakage. However, when the oxygen content in the precursor is high as in the present invention, the content of highly volatile organic hydrocarbons in the raw material decreases, so the phenomenon of a rapid increase in the volatilization amount in the temperature range below 1000℃ can be suppressed, and accordingly, artificial graphite with a high density can be manufactured.

[0043]

[0044] Meanwhile, the carbon-based raw material may include needle cokes, mosaic cokes, coaltar pitch, resin pitch, soft carbone, or a combination thereof, and preferably may include needle cokes, mosaic cokes, soft carbone, or a combination thereof.

[0045] Once the above carbon-based raw material is prepared, the carbon-based raw material is pulverized. The pulverization can be performed using a pulverization method generally known in the art, such as a jet mill, hammer mill, roller mill, pin mill, vibration mill, impact mill, etc., and the method is not particularly limited. During the pulverization, the type of pulverizer and the type of pulverization can be appropriately selected depending on the type of the carbon-based raw material.

[0046] The above grinding is performed to obtain the average particle size (D) of the carbonaceous raw material. 50 ) can be performed so that the particle size of the raw material is 1 ㎛ to 20 ㎛, preferably 5 ㎛ to 15 ㎛. If the particle size of the raw material after grinding is too small, the discharge capacity may decrease, and if the particle size is too large, the rapid charging performance may decrease.

[0047] Meanwhile, the average particle diameter (D) of the above carbon-based raw material 50 ) can be prepared by diluting the sample to 1 wt% in deionized water, and then measuring the volume cumulative particle size distribution by laser diffraction method using a particle size measuring device (Microtrac s3500).

[0048] Next, once the carbon-based raw material has been crushed to an appropriate size, a granulation process is performed. This granulation process can be performed, for example, by placing the crushed particles into a mixing device such as Mechanofusion or Nobilta and applying mechanical compression and / or shear force. Meanwhile, during the granulation process, a binder such as pitch, polyvinyl alcohol, starch, or carboxymethyl cellulose may be additionally added to the mixing device, if necessary.

[0049]

[0050] According to one embodiment, the crushing and / or granulating process may be performed while heating in an oxygen atmosphere. Here, the oxygen atmosphere refers to a gaseous atmosphere containing 20 mass% or more of oxygen, including an atmospheric atmosphere.

[0051] Meanwhile, the temperature increase can be performed up to 200°C to 300°C, and the temperature increase rate is preferably 1°C / min to 20°C / min, preferably 2°C / min to 10°C / min.

[0052] When the crushing and / or granulation is performed under the oxygen atmosphere and elevated temperature conditions as described above, the particle surface is modified by an oxidation reaction to form a precursor having a higher oxygen content than before, specifically, an oxygen content of 3 wt% to 15 wt%, preferably 3 wt% to 10 wt%.

[0053]

[0054] According to another embodiment, after the pulverization and assembly process of the carbon-based raw material, a process of supplying high-temperature air (air blowing) to the assembled particles (precursor) to bring them into contact with each other can be additionally performed, thereby forming a precursor having a higher oxygen content than before, specifically, an oxygen content of 3 wt% to 15 wt%, preferably 3 wt% to 10 wt%.

[0055] When a process of contacting high-temperature air as described above is additionally performed, the crushing and / or granulating process may be performed in an oxygen atmosphere and elevated temperature conditions as in the above-described embodiment, or may be performed at room temperature.

[0056] In the process of contacting the above-described high-temperature air, the temperature of the air may be 100°C to 300°C, preferably 130°C to 250°C. When the high-temperature air contacts the precursor as described above, the surface of the precursor is oxidized, forming a precursor with a high oxygen content. When the temperature of the air contacting the precursor is less than 100°C, it is difficult for the oxygen content of the precursor to exceed 3 wt%, and when it exceeds 300°C, problems such as a reduction or removal of binders such as pitch may occur.

[0057] When a binder such as pitch is used in the assembly process, the temperature of the air may be lower than the softening point of the binder. For example, the temperature of the air may be 10°C to 60°C, preferably 30°C to 50°C lower than the softening point of the binder.

[0058] The contact time of the precursor with the high temperature air can be appropriately controlled depending on the temperature of the air, and can be, for example, 20 to 150 minutes, 30 to 140 minutes, or 60 to 120 minutes. The higher the temperature of the air, the shorter the contact time can be. For example, when the temperature of the air is 50℃ lower than the softening point of the binder, the contact time can be about 100 to 140 minutes, and when the temperature of the air is 30℃ lower than the softening point of the binder, the contact time can be about 20 to 40 minutes. When the contact time with the high temperature air satisfies the above range, it is easy to control the oxygen content of the precursor to 3 wt% to 15 wt%. If the contact time is too short, the surface modification is not sufficient, making it difficult to reach the target oxygen content, and if the contact time is too long, the problem of the binder such as pitch being reduced or removed may occur.

[0059]

[0060] (2) Graphitization process

[0061] When a precursor having an oxygen content of 3 wt% to 15 wt% is produced through the above process, it is graphitized to produce artificial graphite.

[0062] The above graphitization step can be performed using a graphitization device and method well known in the art. For example, the graphitization step can be performed by introducing the precursor into a graphitization furnace such as an Acheson graphitization furnace, a box type graphitization furnace, or a lengthwise graphitization furnace, and raising the temperature to 2,000°C to 3,500°C, 2,500°C to 3,500°C, or 2,800°C to 3,500°C.

[0063]

[0064] As described above, when a graphitization process is performed using a precursor having an oxygen content of 3 wt% to 15 wt%, the conversion of an amorphous structure into a crystalline structure in the carbonization temperature range is hindered by the oxygen contained in the precursor, and as a result, crystallization occurs with a relatively high amorphous content, so that cavities are formed within the crystal structure and the crystallite size is formed relatively small.

[0065]

[0066] Specifically, the artificial graphite according to the present invention may include cavities within its crystal structure. When cavities are formed within the crystal structure, lithium ion mobility within the artificial graphite is enhanced, thereby improving rapid charging performance.

[0067] Meanwhile, when vacancies are included in the crystal structure, the spacing d(002) of the (002) plane becomes relatively large, and the crystallite size Lc in the c-axis direction becomes relatively small. Therefore, whether or not vacancies are included in the crystal structure can be revealed through the d(002) and Lc values. The artificial graphite manufactured according to the method of the present invention has a spacing d(002) of the (002) plane measured by XRD of 0.3360 nm or more, preferably 0.3360 nm to 0.3370 nm, more preferably 0.3360 nm to 0.3365 nm, and a crystallite size Lc in the c-axis direction measured by XRD of 38.5 nm or less, preferably 30.0 nm to 38.5 nm, more preferably 34 nm to 38.5 nm.

[0068]

[0069] (3) Carbonization process

[0070] Meanwhile, although not essential, an additional step of mixing the artificial graphite and a carbonaceous material and then carbonizing the mixture to form a carbon coating layer may be performed after the step of manufacturing the artificial graphite.

[0071] When a carbon coating layer is formed on the surface of artificial graphite, the bonding of the artificial graphite particles constituting the assembled particles becomes stronger, which can improve the stability of the assembled particles during charging and discharging, and further improve the rapid charging performance.

[0072] The carbonaceous material may be, for example, pitch, and generally used solid pitch or liquid pitch may be applied. The solid pitch may be obtained by crushing coal tar pitch, petroleum pitch, synthetic pitch, wood tar pitch, etc. The liquid pitch may be manufactured by dissolving liquid resin or solid pitch in a solvent, coating, and then carbonizing. At this time, the solvent that may be used is hexane, toluene, tetrahydrofuran (THF), quinoline, N-methylpyrrolidone (NMP), ethanol, etc.

[0073] Meanwhile, the carbonaceous material may be mixed in an amount of 1 to 10 parts by weight, 1 to 5 parts by weight, or 3 to 5 parts by weight, based on 100 parts by weight of artificial graphite. When the amount of the carbonaceous material mixed satisfies the above range, the assembly stability of the graphite-based negative electrode active material is improved, and the rapid charging performance is improved. If the content of the carbonaceous material is too low, the effect of improving the assembly stability and rapid charging performance is minimal, and if it is too high, the carbon coating layer may be formed too thick, which may deteriorate the electrochemical properties.

[0074] The mixing of the above artificial graphite and carbonaceous material can be performed by methods generally known in the art, and is not particularly limited. For example, the mixing can be performed using a mechanochemical method such as a two-roll kneader, a blade, a mechanomicro system, an extruder, a ball mill, a planetary mill, a mechanofusion system, a nobilta, hydridization, or a rotary ball mill, or using a spray drying method, an emulsion method, or the like.

[0075] When the artificial graphite and the carbonaceous material are homogeneously mixed, a carbon coating layer is formed by carbonizing at a temperature of 1,000°C to 1,600°C, preferably 1,200°C to 1,400°C. At this time, the carbonization treatment time may be, for example, 18 to 30 hours or 20 to 26 hours. When the carbonization treatment temperature and time satisfy the above range, carbon stabilization sufficiently progresses, impurities in the carbonaceous material are almost removed, and the surface properties of the coating can be prevented from being modified due to excessively high temperatures.

[0076] The carbon coating layer formed as described above may be made of amorphous or crystalline carbon.

[0077]

[0078] Graphite-based negative electrode active material

[0079] The graphite-based negative electrode active material according to the present invention includes artificial graphite in which the spacing d(002) of the (002) plane measured by XRD is 0.3360 nm or more, preferably 0.3360 nm to 0.3370 nm, more preferably 0.3360 nm to 0.3365 nm, and the crystallite size Lc in the c-axis direction measured by XRD is 38.5 nm or less, preferably 30.0 nm to 38.5 nm, more preferably 34 nm to 38.5 nm.

[0080] When d(002) and Lc of artificial graphite satisfy the above range, excellent rapid charging performance can be realized. Specifically, when d(002) and Lc of artificial graphite satisfy the above range, it can be seen that cavities are formed between the crystal lattices, and when cavities are included in the crystal structure, lithium ion mobility is improved within the artificial graphite, thereby improving rapid charging performance.

[0081] Meanwhile, artificial graphite having d(002) and Lc satisfying the above ranges can be manufactured by graphitizing a precursor having an oxygen content of 3 wt% to 15 wt%, and specifically, can be manufactured according to the method of the present invention described above.

[0082] Meanwhile, the graphite-based negative electrode active material may further include a carbon-based coating layer on the surface of the artificial graphite. The carbon-based coating layer may be formed by mixing a carbonaceous material, such as pitch, with the artificial graphite and then carbonizing it. The method for forming the carbon-based coating layer is the same as described above, so a detailed description is omitted.

[0083]

[0084] The above graphite-based negative electrode active material may have a tap density of 0.90 g / cc or more, preferably 1.00 g / cc to 1.30 g / cc, and more preferably 1.00 g / cc to 1.20 g / cc. When the tap density satisfies the above range, a high electrode density can be realized, resulting in excellent capacity characteristics.

[0085]

[0086] cathode

[0087] Next, the cathode according to the present invention will be described.

[0088] The negative electrode according to the present invention comprises the graphite-based negative electrode active material according to the present invention, as described above, as a negative electrode active material. For example, the negative electrode may comprise a negative electrode active material layer comprising the graphite-based negative electrode active material according to the present invention, and specifically, the negative electrode may comprise a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector.

[0089] Meanwhile, the negative electrode active material may be made of a graphite-based negative electrode active material according to the present invention, or may be used by mixing other types of negative electrode active materials (e.g., natural graphite, silicon-based negative electrode active material, etc.) other than the graphite-based negative electrode active material.

[0090] The negative active material may be included in an amount of 90 wt% to 99.5 wt%, 93 wt% to 99 wt%, or 95 wt% to 98.5 wt% based on the total weight of the negative active material layer.

[0091] The negative electrode current collector is not particularly limited as long as it is conductive and does not cause chemical changes in the battery. The negative electrode current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc., and the material of the negative electrode current collector may be, for example, copper, nickel, stainless steel, nickel, titanium, calcined carbon, or a combination thereof. The positive electrode current collector may typically have a thickness of 3 to 500 μm. If necessary, the positive electrode current collector may have fine unevenness formed on the surface to strengthen the bonding strength of the positive electrode active material.

[0092] The negative electrode active material layer may be disposed on the current collector. The negative electrode active material layer may be disposed on at least one surface of the current collector, and specifically, may be disposed on one surface or both surfaces.

[0093] Meanwhile, the negative electrode active material layer may further include at least one of a binder and a conductive material in addition to the negative electrode active material.

[0094] The above binder may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluoroelastomer, polyacrylic acid, and materials in which hydrogens thereof are substituted with Li, Na, Ca, etc., and may also include various copolymers thereof.

[0095] The binder may be included in an amount of 0.1 wt% to 8 wt%, 0.5 wt% to 5 wt%, or 0.8 wt% to 4 wt% based on the total weight of the negative electrode active material layer.

[0096]

[0097] The conductive material is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, paneth black, lamp black, thermal black, and the like; conductive fibers such as carbon fiber or metal fiber; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0098] The conductive material may be included in an amount of 0.1 wt% to 8 wt%, 0.5 wt% to 5 wt%, or 0.8 wt% to 4 wt% based on the total weight of the negative electrode active material layer.

[0099]

[0100] The above negative electrode can be manufactured by mixing a negative electrode active material and optionally a binder and a conductive material in a solvent such as NMP (N-methyl-2-pyrrolidone), water, etc. to prepare a negative electrode slurry, then coating the negative electrode slurry on a negative electrode current collector, drying, and rolling.

[0101]

[0102] Since the negative electrode according to the present invention includes a graphite-based negative electrode active material including artificial graphite having a smaller crystal size than conventional ones and containing pores in the crystal structure, the mobility of lithium ions in the negative electrode active material is excellent, and the insertion / de-insertion of lithium ions is easy, resulting in excellent rapid charging performance.

[0103] The rapid charge performance of the negative electrode can be evaluated through the SOC value at which lithium precipitation occurs when a half-cell manufactured with the negative electrode and the lithium metal counter electrode is charged at 3C. While the SOC at which lithium precipitation occurs when a half-cell manufactured using a negative electrode using a conventional graphite-based negative electrode active material is charged at 3C is less than 35%, the SOC at which lithium precipitation occurs when a half-cell manufactured using the negative electrode according to the present invention is charged at 3C is 35% or more, which is higher than that of the conventional negative electrode. This shows that the rapid charge performance of the negative electrode using the negative electrode active material according to the present invention is superior to that of the conventional negative electrode.

[0104]

[0105] lithium secondary battery

[0106] Next, a lithium secondary battery according to the present invention will be described.

[0107] A lithium secondary battery according to the present invention comprises the anode according to the present invention described above. Specifically, the secondary battery according to the present invention may comprise the anode described above; a cathode facing the cathode; a separator interposed between the cathode and the anode; and an electrolyte.

[0108] Since the cathode has been described above, the components excluding the cathode will be described below.

[0109] The above positive electrode may include a positive electrode current collector; and a positive electrode active material layer formed on the positive electrode current collector.

[0110] The positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. The positive electrode current collector can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc., and the material of the positive electrode current collector can be, for example, aluminum, stainless steel, nickel, titanium, sintered carbon, an aluminum-cadmium alloy, or a combination thereof. The positive electrode current collector can typically have a thickness of 3 to 500 μm. If necessary, the positive electrode current collector can form fine unevenness on the surface to strengthen the bonding strength of the positive electrode active material.

[0111] Meanwhile, the positive electrode active material layer includes a positive electrode active material and may further include a conductive material and a binder, if necessary.

[0112] As the positive electrode active material, various positive electrode active materials used in the relevant technical field can be used without limitation and are not particularly limited. For example, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; LiFe 1-a Mn a Lithium phosphate compounds such as PO4(O≤a≤1); chemical formula Li 1+c1 Mn 2-c1 Lithium manganese oxides such as O4(0≤c1≤0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; chemical formula LiNi 1-c2 M c2 Lithium nickel oxide represented by O2 (wherein, M is at least one selected from the group consisting of Co, Mn, Al, Zr, Y, W, Mo, Cu, Fe, Mg, B, and Ga, and satisfies 0.01≤c2≤0.3); chemical formula LiMn 2-c3 M c3Examples thereof include, but are not limited to, lithium manganese composite oxides represented by O2 (wherein, M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01≤c3≤0.1) or Li2Mn3M'O8 (wherein, M' is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn).

[0113] The above binder is a component that assists in the binding of the active material and the conductive material and the binding to the current collector, and specifically, may include at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber, preferably polyvinylidene fluoride.

[0114] The conductive material may be used to assist and improve conductivity in a secondary battery, and is not particularly limited as long as it has conductivity without causing chemical changes. Specifically, the conductive material may include at least one selected from the group consisting of graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, paneth black, lamp black, thermal black; conductive fibers such as carbon fibers or metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, and nickel powders; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and polyphenylene derivatives.

[0115] The above positive electrode can be manufactured by mixing a positive electrode active material and optionally a binder and a conductive material in an organic solvent such as NMP (N-methyl-2-pyrrolidone) to prepare a positive electrode slurry, then coating the positive electrode slurry on a positive electrode current collector, drying, and rolling.

[0116]

[0117] The above separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. If it is a separator commonly used in lithium secondary batteries, it can be used without any special restrictions. For example, the separator may include a polyolefin-based polymer film such as an ethylene homopolymer, a propylene homopolymer, an ethylene / propylene copolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminate of two or more layers thereof, and / or a non-woven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, or the like as a substrate. Meanwhile, a coated separator containing a ceramic component and / or a polymer material on the substrate may be used to secure heat resistance or mechanical strength.

[0118]

[0119] Next, examples of the electrolyte include, but are not limited to, 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 manufacture of secondary batteries.

[0120] For example, the electrolyte may include an organic solvent and a lithium salt.

[0121] The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may include ester solvents such as methyl acetate, ethyl acetate, gamma-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; R-CN (R is C2 to C 20 Nitriles such as a straight-chain, branched, or cyclic hydrocarbon group, which may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, carbonate solvents are preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of a battery and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferable.

[0122] The lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, or a combination thereof. The concentration of the lithium salt is preferably used within the range of 0.1 to 4.0 M, preferably 0.5 to 3.0 M, and more preferably 0.8 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0123] The above secondary battery can be manufactured by inserting a separator between the above-described negative electrode and positive electrode and then injecting an electrolyte according to a conventional secondary battery manufacturing method.

[0124]

[0125] The lithium secondary battery according to the present invention can be particularly useful as a power source for electric vehicles because it has excellent rapid charging performance by applying a negative electrode active material having excellent charging performance.

[0126]

[0127] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0128]

[0129] Comparative Example 1

[0130] Coke raw material was fed into a planetary milling crusher and ground to an average particle size (D50) of 8 μm. The crushed coke raw material and pitch were fed into a granulator and granulated to produce a precursor. The crushing and granulation were performed at room temperature, pressure, and in an air atmosphere.

[0131] The manufactured precursor was put into a graphitization furnace, heated to 3,000°C at a heating rate of 0.5°C / min, maintained for 12 hours, and then cooled to manufacture artificial graphite.

[0132]

[0133] Comparative Example 2

[0134] Precursors and artificial graphite were manufactured in the same manner as in Comparative Example 1, except that an air blowing process at 100°C for 1 hour was performed before putting them into a graphitization furnace after crushing and assembling.

[0135]

[0136] Example 1

[0137] Precursors and artificial graphite were manufactured in the same manner as in Comparative Example 1, except that an air blowing process at 170°C for 1 hour was performed before putting them into a graphitization furnace after crushing and assembling.

[0138]

[0139] Example 2

[0140] Precursors and artificial graphite were manufactured in the same manner as in Comparative Example 1, except that an air blowing process at 220°C for 1 hour was performed before putting them into a graphitization furnace after crushing and assembling.

[0141]

[0142] Example 3

[0143] Precursors and artificial graphite were manufactured in the same manner as in Comparative Example 1, except that an air blowing process at 300°C for 1 hour was performed before putting them into a graphitization furnace after crushing and assembling.

[0144]

[0145] Experimental Example 1 - Measurement of Precursor Oxygen Content

[0146] The precursors manufactured in Examples 1 to 3 and Comparative Examples 1 to 2 were collected and the element content of each precursor was measured using the following method. The measurement results are shown in Table 1 below.

[0147] <Method of measuring element content>

[0148] Each precursor was placed in an elemental analyzer and combusted while increasing the temperature. During the precursor combustion process, CO2, H2O, N2, and SO2 gases were mainly formed up to about 1000℃, and CO gas was generated as O was thermally decomposed around 1060℃. The generated gas was separated in a gas chromatography column (GC column), and the contents of C, H, N, O, and S were quantitatively analyzed using a thermal conductive detector.

[0149]

[0150] Comparative Example 1 Comparative Example 2 Example 1 Example 2 Example 3 C (wt%) 96.1 94.1 92.6 91.7 86.2 H (wt%) 2.2 3.4 2.8 2.5 3.9 N (wt%) 1.3 0.8 0.9 1.12.1 O (wt%) 0.3 1.6 3.6 4.6 7.7 S (wt%) 0.1 0.1 0.1 0.1 0.1

[0151] Experimental Example 2

[0152] The tap density and d(002) and Lc(002) of the artificial graphite manufactured according to Examples 1 to 3 and Comparative Examples 1 to 2 were measured using the following methods. The measurement results are shown in Table 2 below.

[0153] (1) Tap density (cc / g): After collecting 40 g of artificial graphite, it was placed in a sample container for tap density measurement with a volume indicated, and the volume after tapping 1000 times was measured to calculate the tap density.

[0154] (2) d(002) and Lc(002): The artificial graphite sample was placed in a powder measuring holder, and X-rays were irradiated to the surface of the sample under the following conditions using a Bruker D8 XRD device (Cu, λ=1.5418Å).

[0155] <XRD 측정 조건>

[0156] Opening degree: 0.5°

[0157] Fixed sample distance: 3mm

[0158] For 2θ= 20 ~ 80°, step size: 0.00428°

[0159] total scan time = approximately 75 minutes

[0160]

[0161] Experimental Example 3

[0162] An electrode assembly was manufactured by interposing a separator between the negative electrode and the lithium counter electrode manufactured in Examples 1 to 4 and Comparative Examples 1 to 3, and the electrode assembly was placed in a battery case, and then an electrolyte was injected to manufacture a coin-half cell.

[0163] The above coin half cell was charged at 3.0C, CC mode to obtain a charge profile according to SOC, and the inflection point in the charge profile was evaluated as the point at which lithium precipitation occurred, and the SOC value at which lithium precipitation occurred was measured.

[0164] In addition, the coin half-cell was charged at 0.1C in CCCV mode with a cut-off condition of 0.005V, and discharged to 1.5V at 0.1C in CC mode to measure the discharge capacity and initial efficiency.

[0165] The measurement results are shown in Table 2 below.

[0166] Comparative Example 1 Comparative Example 2 Example 1 Example 2 Example 3 Tap Density (cc / g) 1.00 1.02 1.11.08 1.06 d(002) (nm) 0.3358 0.3359 0.3361 0.3362 0.3364 Lc (nm) 39.4 38.8 38.1 38.0 37.5 Discharge Capacity (mAh / g) 355 354 351 350 347 Initial Capacity Efficiency (%) 9 39 39 39 39 33 C SOC (%) 33 34 36 38 39

[0167] Through the above Table 2, it can be confirmed that the artificial graphite of Examples 1 to 3 manufactured using a precursor having an oxygen content of 3 to 15 wt% had a (002) plane spacing d(002) of 0.3360 nm or more and a c-axis direction crystallite size Lc of 38.5 nm or less, thereby forming vacancies between the crystal lattices. In contrast, the artificial graphite of Comparative Examples 1 and 2 manufactured using a precursor having an oxygen content of less than 3 wt% had a (002) plane spacing d(002) of less than 0.3360 nm and a c-axis direction crystallite size Lc of more than 38.5 nm.

[0168] In addition, the tap density of the artificial graphite of Examples 1 to 3 was found to be higher than the tap density of the artificial graphite of Comparative Examples 1 to 2.

[0169] In addition, the coin half cell using the artificial graphite of Examples 1 to 3 showed a higher SOC value at which lithium precipitation occurred during 3C charging compared to the coin half cell using the artificial graphite of Comparative Examples 1 to 2, which shows that the rapid charging performance is improved when the artificial graphite of Examples 1 to 3 is applied.

Claims

1. A step of crushing and assembling carbon-based raw materials to form a precursor having an oxygen content of 3 wt% to 15 wt%; and A method for producing a graphite-based negative electrode active material, comprising the step of producing artificial graphite by graphitizing the precursor, wherein the (002) plane spacing d(002) is 0.3360 nm to 0.3370 nm and the c-axis direction crystallite size Lc is 30.0 nm to 38.5 nm.

2. In paragraph 1, A method for producing a graphite-based negative electrode active material, wherein the carbon-based raw material includes needle cokes, mosaic cokes, coaltar pitch, resin pitch, soft carbone, or a combination thereof.

3. In paragraph 1, A method for producing a graphite-based negative electrode active material, wherein the step of forming a precursor having an oxygen content of 3 wt% to 15 wt% is performed while at least one of the crushing and granulating is heated to 200 to 300°C in an oxygen atmosphere.

4. In paragraph 3, A method for producing a graphite-based negative electrode active material, wherein the above temperature raising is performed at a temperature raising rate of 1°C / min to 20°C / min.

5. In paragraph 1, A method for producing a graphite-based negative electrode active material, wherein the step of forming a precursor having an oxygen content of 3 wt% to 15 wt% is performed by crushing and assembling the raw material, and then supplying air at 100°C to 300°C to bring it into contact.

6. In paragraph 1, A method for producing a graphite-based negative electrode active material, further comprising a step of forming a carbon coating layer by mixing the artificial graphite and a carbonaceous material and then carbonizing the mixture after the step of producing the artificial graphite.

7. In paragraph 6, A method for producing a graphite-based negative electrode active material, wherein the carbonaceous material is pitch.

8. In paragraph 1, A method for producing a graphite-based negative electrode active material, wherein the above artificial graphite contains cavities within a crystal lattice.

9. A graphite-based negative electrode active material comprising artificial graphite having a plane spacing d(002) of 0.3360 nm to 0.3370 nm and a c-axis direction crystallite size Lc of 30.0 nm to 38.5 nm.

10. In paragraph 9, The above graphite-based negative electrode active material is a graphite-based negative electrode active material having a tap density of 0.90 g / cc or more.

11. In paragraph 9, The above artificial graphite is a graphite-based negative electrode active material manufactured by graphitizing a precursor having an oxygen content of 3 wt% to 15 wt%.

12. A negative electrode comprising a graphite-based negative electrode active material according to any one of claims 9 to 11.

13. In paragraph 12, A negative electrode having an SOC value of 35% or more at which lithium precipitation occurs when a half-cell manufactured with the above negative electrode and a lithium metal counter electrode is charged at 3C.

14. A lithium secondary battery comprising the negative electrode of claim 12.