Negative active material, method for preparing the same, and negative electrode and secondary battery comprising the same

Abstract

This invention relates to a negative electrode active material comprising natural graphite, wherein the D of the negative electrode active material is... 90 For D 10 The ratio of D 90 / D 10 The strength is 2.0–2.2, and the tap density is 1.11 g / cm³. 3 ~1.19g / cm 3 Furthermore, the specific surface area of ​​BET is 2.02 m². 2 / g~2.30m 2 / g.

Description

Technical Field

[0001] Cross-reference to related applications

[0002] This application claims the benefit of Korean Patent Application No. 10-2019-0161897, filed on December 6, 2019, with the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0004] This invention relates to a negative electrode active material, its preparation method, and a negative electrode and secondary battery containing the same. Background Technology

[0005] With rising energy prices due to the depletion of fossil fuels and increased concern about environmental pollution, environmentally friendly alternative energy sources have become an essential element of future life.

[0006] In particular, with the development of technology and increasing demand for mobile devices, the demand for secondary batteries as an environmentally friendly energy source has increased rapidly.

[0007] Typically, lithium metal is used as the negative electrode in secondary batteries. However, due to the danger of short circuits caused by dendrite formation and the resulting explosions, carbon-based active materials capable of reversibly inserting and deintercalating lithium ions while maintaining structural and electrical properties have begun to be used.

[0008] Various types of carbon-based active materials have been used, such as artificial graphite, natural graphite, and hard carbon. Among them, graphite-based active materials, with their excellent reversibility, are the most widely used, ensuring the lifespan of lithium-ion batteries. Because graphite-based active materials have a lower discharge voltage of -0.2V compared to lithium, batteries using graphite-based active materials can exhibit a higher discharge voltage of 3.6V, thus providing many advantages in terms of energy density for lithium-ion batteries.

[0009] Among graphite-based active materials, natural graphite, in particular, exhibits higher output and capacity compared to other carbon-based active materials such as synthetic graphite, and possesses excellent adhesion, thus offering advantages such as reduced binder usage and the ability to achieve high-capacity, high-density negative electrodes. However, compared to synthetic graphite, typical natural graphite has far too many internal pores. Therefore, the problem lies in the severe cyclic swelling caused by electrolyte side reactions as charging and discharging continue, which may limit its application despite the aforementioned advantages.

[0010] To prevent the cyclic expansion problem of natural graphite, a mixture of natural and artificial graphite in a certain ratio can be used as the negative electrode active material. However, even in this case, natural graphite is still inferior to artificial graphite in preventing cyclic expansion caused by charging and discharging. Therefore, when natural graphite is used in the negative electrode, it cannot adequately prevent thickness expansion.

[0011] Therefore, there is a need to develop a negative electrode active material that can leverage the high output and capacity of natural graphite while preventing the problem of cyclic expansion.

[0012] Although Japanese Patent Publication No. 4403327 discloses graphite powder for use as a negative electrode in lithium-ion secondary batteries, the publication does not propose an alternative solution to the aforementioned problem.

[0013] [Existing Technical Documents]

[0014] [Patent Literature]

[0015] Japanese Patent Publication No. 4403327 Summary of the Invention

[0016] Technical issues

[0017] One aspect of the present invention provides a negative electrode active material comprising natural graphite, said negative electrode active material exhibiting the excellent output and capacity characteristics of natural graphite while effectively preventing cycle expansion problems caused by electrolyte side reactions.

[0018] Another aspect of the present invention provides a method for preparing a negative electrode active material, wherein the method includes a step of pressurizing natural graphite by cold isostatic pressing, thereby effectively preventing the problem of cyclic expansion of natural graphite.

[0019] Another aspect of the present invention provides a negative electrode and a secondary battery comprising the above-described negative electrode active material.

[0020] Technical solution

[0021] According to one aspect of the present invention, a negative electrode active material is provided, comprising natural graphite, wherein the D of the negative electrode active material is... 90 For D 10 The ratio (i.e., D) 90 / D 10 The viscosity is 2.0–2.2; the tap density is 1.11 g / cm³. 3 Up to 1.19 g / cm 3 Furthermore, the specific surface area of ​​BET is 2.02m². 2 / g to 2.30m 2 / g.

[0022] According to another aspect of the present invention, a method for preparing a negative electrode active material is provided, the method comprising pressing natural graphite by cold isostatic pressing, and D-type deionization of the pressed natural graphite. 90 For D 10 The ratio of D 90 / D 10 Adjust to 2.0–2.2, wherein the adjusted D 90 / D 10 The natural graphite described herein has a density of 2.02 μm. 2 / g to 2.30m 2 BET specific surface area / g and 1.11g / cm² 3 Up to 1.19 g / cm 3 The tap density.

[0023] According to another aspect of the present invention, a negative electrode is provided, the negative electrode comprising a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector, wherein the negative electrode active material layer comprises the aforementioned negative electrode active material.

[0024] According to another aspect of the present invention, a secondary battery is provided, the secondary battery comprising the aforementioned negative electrode, a positive electrode opposite to the negative electrode, a separator disposed between the negative electrode and the positive electrode, and an electrolyte.

[0025] Beneficial effects

[0026] D in the particle size distribution of the negative electrode active material of the present invention 10 With D 90 The ratio, tap density, and BET specific surface area are adjusted to desired levels within a specific range, thus enabling smooth packing of active material particles when applied to the negative electrode. This effectively prevents cycling expansion caused by electrolyte side reactions and thickness expansion of the negative electrode active material layer. Therefore, the output and capacity characteristics of natural graphite can be effectively exhibited while improving lifetime characteristics.

[0027] Furthermore, in the method for preparing the negative electrode active material of the present invention, to achieve the aforementioned negative electrode active material, natural graphite is pressurized by cold isostatic pressing (CIP), and the particle size, tap density, and specific surface area of ​​the active material are adjusted. Therefore, according to the preparation method of the present invention, the micropores present within natural graphite or the negative electrode active material can be reduced or eliminated, thereby reducing the specific surface area of ​​the active material and promoting particle packing, thus effectively preventing the expansion of the active material caused by charging and discharging. Detailed Implementation

[0028] It will be understood that the words or terms used in the specification and claims of this invention should not be construed as having the meanings defined in commonly used dictionaries. It should also be understood that, based on the principle that the inventor can appropriately define the meanings of words or terms to best interpret the invention, these words or terms should be interpreted as having meanings consistent with their meanings in the context of the relevant field and technical idea of ​​this invention.

[0029] The terminology used herein is for the purpose of describing particular exemplary embodiments only and is not intended to limit the invention. Unless the context clearly indicates otherwise, singular terms may include plural forms.

[0030] It should also be understood that, when used in this specification, the terms “comprising,” “including,” or “having” indicate the presence of the stated features, quantities, steps, elements, or combinations thereof, but do not exclude the presence or addition of one or more other features, quantities, steps, elements, or combinations thereof.

[0031] In this specification, D 50 D 10 and D 90 This can be defined as the particle size at 50%, 10%, and 90% of the cumulative volume on the particle size distribution curve, respectively. D 50 D 10 and D 90 This can be measured using methods such as laser diffraction. Laser diffraction can typically measure particle sizes from the submicron region to a few millimeters, thus providing highly reproducible and high-resolution results.

[0032] The invention will be described in detail below.

[0033] <Negative Electrode Active Materials>

[0034] This invention relates to a negative electrode active material, and more specifically to a negative electrode active material for lithium secondary batteries.

[0035] Specifically, the negative electrode active material of the present invention comprises natural graphite, and D 90 For D 10 The ratio (i.e., D) 90 / D 10 The strength is 2.0–2.2, and the tap density is 1.11 g / cm³. 3 Up to 1.19 g / cm 3 Furthermore, the specific surface area of ​​BET is 2.02 m². 2 / g to 2.30m 2 / g.

[0036] The negative electrode active material of the present invention is a negative electrode active material containing natural graphite, characterized by its D 90 / D10 The tap density and BET specific surface area are controlled within the aforementioned ranges. The negative electrode active material is a material from which the pores of natural graphite, which cause electrolyte side reactions and cycling expansion problems, have been sufficiently removed, and it has a uniform particle size distribution. Therefore, when applied to the negative electrode, it can promote particle aggregation, maintain a small electrode thickness after coating, reduce thickness changes during electrode rolling to the target thickness, and has a small electrode orientation value, allowing for the manufacture of an electrode that is advantageous in terms of electrode expansion. This effectively prevents cycling expansion problems caused by charging / discharging of the negative electrode and the resulting increase in negative electrode thickness. Furthermore, it has a D value adjusted to the aforementioned range. 90 / D 10 The negative electrode active material with tap density and BET specific surface area is a material from which the pores inside the particles have been sufficiently removed, thereby preventing the cycling expansion problem caused by electrolyte side reactions to an excellent level.

[0037] The negative electrode active material contains natural graphite.

[0038] Because the negative electrode active material uses natural graphite, it has the advantages of high output and capacity compared to using other carbon-based active materials such as artificial graphite. Specifically, the negative electrode active material may contain natural graphite with a theoretical capacity of 360 mAh / g or more.

[0039] The negative electrode active material may also include a carbon coating formed on the natural graphite.

[0040] The carbon coating can help improve the structural stability of the active material. Additionally, the carbon coating can reduce the pores present in natural graphite and decrease the BET specific surface area to a desired level, thereby effectively preventing side reactions with the electrolyte.

[0041] In order to prevent side reactions with the electrolyte, sufficiently improve structural stability, and prevent the inhibition of lithium insertion / extraction due to over-formation, the carbon coating may be included in the negative electrode active material in an amount of 2% to 7% by weight, preferably 3% to 6% by weight, more preferably 4% to 5% by weight.

[0042] The negative electrode active material may be spherical. In this specification, "spherical" encompasses not only a perfectly spherical shape but also a slightly deformed but generally spherical form.

[0043] When the negative electrode active material is spherical, it can promote the accumulation between active material particles, thereby reducing the thickness expansion problem of the negative electrode active material caused by charging / discharging to an even better level.

[0044] The spherical negative electrode active material can be realized from spherical natural graphite, or a negative electrode active material comprising spherical natural graphite and a carbon coating formed on the spherical natural graphite.

[0045] The negative electrode active material D 90 For D 10 The ratio of D 90 / D 10 It ranges from 2.0 to 2.2.

[0046] By D 90 / D 10 By adjusting to the above level, the negative electrode active material can have active material particles with uniform particle size. Therefore, when the negative electrode active material is applied to the negative electrode, the packing degree of the active material particles can be improved, and particle deformation can be prevented during the rolling of the negative electrode. Thus, mechanical expansion of the negative electrode and / or cyclic expansion caused by electrolyte side reactions can be prevented.

[0047] If the D of the negative electrode active material 90 / D 10 If the density exceeds 2.2, particle packing cannot be promoted, and electrolyte side reactions may be exacerbated due to increased porosity between particles. Furthermore, it may not effectively prevent negative electrode thickness expansion caused by charging / discharging. Additionally, volume expansion caused by charging / discharging of relatively large particles may locally exacerbate swelling. If the D of the negative electrode active material... 90 / D 10 If the particle size is less than 2.0, it becomes practically difficult to achieve a negative electrode active material with such a particle size distribution.

[0048] The negative electrode active material D 90 / D 10 The value can preferably be 2.05 to 2.12, and when it is within the above range, the problem of cyclic expansion caused by electrolyte side reactions can be prevented at an even better level, and the lithium insertion / extraction can be promoted due to the shortening of the lithium ion entry / extraction path.

[0049] The tap density of the negative electrode active material is 1.11 g / cm³. 3 Up to 1.19 g / cm 3 .

[0050] Tap density can be defined as the apparent density calculated by measuring the final volume, which is obtained by filling a container with negative electrode active material and then vibrating the container a specific number of times. Specifically, tap density can be defined as the apparent density calculated by measuring the final volume, which is obtained by filling 40g of negative electrode active material into a cylindrical container with a diameter of 30mm and a capacity of 100mL, and then vibrating the container up and down 1,000 times with an amplitude of 14mm.

[0051] Anode active materials with tap density within the above range can be evaluated as having improved spherical properties. Therefore, when anodes are manufactured using said anode active materials, the degree of packing between active material particles is improved, and the mechanical stress on the active material particles during electrode rolling can be reduced, which is advantageous in preventing swelling.

[0052] If the tap density of the negative electrode active material is less than 1.11 g / cm³ 3 When the tap density of an active material is such that it has relatively low sphericity, the electrode thickness increases when the negative electrode active material layer is coated, and the thickness variation is large during rolling to the target thickness after coating the negative electrode active material layer, requiring excessive force to be applied. Therefore, electrodes manufactured using negative electrode active materials with such tap density have high electrode orientation, but are disadvantageous in terms of negative electrode expansion performance. On the other hand, when the tap density of the negative electrode active material is greater than 1.19 g / cm³... 3 In order to achieve the above-mentioned tap density, natural graphite needs to undergo multiple spheroidization processes. In order to reduce the increase in the specific surface area of ​​natural graphite due to the multiple spheroidization processes, excessive use of binders (such as asphalt) is required, which may lead to excessive degradation of output characteristics and charge / discharge efficiency.

[0053] Preferably, the tap density of the negative electrode active material can be 1.14 g / cm³. 3 Up to 1.17 g / cm 3 When within the above range, the cyclic expansion problem caused by electrolyte side reactions can be prevented at an even better level, the sphericity of the negative electrode active material can be improved to the desired level, and the arrangement of the active material in the negative electrode can be well achieved, thus being preferred in terms of shortening the movement path of lithium ions and promoting lithium insertion / extraction.

[0054] The BET specific surface area of ​​the negative electrode active material is 2.02 m². 2 / g to 2.30m 2 / g.

[0055] Natural graphite typically has a large specific surface area due to the presence of pores on its surface and within, thus exacerbating the problem of cyclic expansion caused by electrolyte side reactions. However, the negative electrode active material of the present invention, although using natural graphite, adjusts the BET specific surface area range to the aforementioned level, thereby effectively preventing electrolyte side reactions.

[0056] If the BET specific surface area of ​​the negative electrode active material exceeds 2.30 m² 2 If the BET specific surface area of ​​the negative electrode active material is less than 2.02 m² / g, the side reactions in the electrolyte will intensify, and the irreversible reactions of the negative electrode active material will increase, thereby reducing efficiency and preventing the output and capacity characteristics of natural graphite from being fully realized. 2 If the output characteristics of natural graphite are reduced to a certain value (e.g.), the output characteristics may deteriorate, making it a less desirable option.

[0057] The BET specific surface area of ​​the negative electrode active material can be 2.02 m². 2 / g to 2.30m 2 / g, preferably 2.05m 2 / g to 2.15m 2 / g. When within the above range, it is advantageous in improving lifetime performance and high-temperature storage performance by preventing swelling problems without deteriorating the output characteristics of natural graphite.

[0058] The BET specific surface area can be determined by measuring the D of the negative electrode active material. 90 / D 10 The process involves adjusting the tap density to the aforementioned range and processing the natural graphite using the cold isostatic pressing (CIP) method, described later. Natural graphite typically has a relatively large BET specific surface area due to the pores present on its surface and within it, thus exhibiting a problem of exacerbated side reactions with the electrolyte. Furthermore, to reduce the high BET specific surface area of ​​natural graphite, the formation of an excessive carbon coating can be considered. However, this method leads to a deterioration of the output characteristics of the natural graphite and is therefore not preferred. However, in this invention, the D... 90 / D 10 The tap density is controlled within the above range, and the amount and area of ​​pores can be effectively controlled through the CIP process. As a result, the BET specific surface area of ​​the negative electrode active material is reduced to the required level, thereby preventing side reactions with the electrolyte, thus improving the lifetime characteristics of the negative electrode active material, and preferably achieving the high output characteristics of natural graphite.

[0059] The BET specific surface area of ​​the negative electrode active material can be measured, for example, using the Brunauer-Emmett-Teller (BET) measurement method with an adsorbed gas such as nitrogen and a BELSORP (BET device) from Bell Japan.

[0060] The negative electrode active material D 50 The average particle size is between 6 μm and 15 μm. When the negative electrode active material has an average particle size (D) within the above range... 50 This prevents the problems of increased specific surface area and exacerbated electrolyte side reactions that occur when the average particle size is too small, and the lithium diffusion distance is kept at an appropriate level, thus making it preferred in terms of exhibiting the output performance and fast charging performance of natural graphite.

[0061] The negative electrode active material D 50 The particle size can preferably be from 8 μm to 12 μm, more preferably from 9.5 μm to 11.5 μm, and even more preferably from 10.2 μm to 10.8 μm. When within the above range, the particle packing performance is improved and the porosity between particles is reduced, resulting in excellent anti-swelling properties. Furthermore, lithium can be smoothly inserted / extracted even at high C-rates, thus it is also preferred in terms of improving fast charging performance.

[0062] <Methods for preparing negative electrode active materials>

[0063] In addition, the present invention provides a method for preparing a negative electrode active material.

[0064] Specifically, the method for preparing the negative electrode active material of the present invention includes pressing natural graphite by cold isostatic pressing, and then pressing the pressed natural graphite into D... 90 For D 10 The ratio (i.e., D) 90 / D 10 Adjust to 2.0–2.2, wherein the adjusted D 90 / D 10 The natural graphite described herein has a density of 2.02 μm. 2 / g to 2.30m 2 BET specific surface area / g and 1.11g / cm² 3 Up to 1.19 g / cm 3 The tap density.

[0065] The natural graphite can be spherical. The spherical natural graphite can be prepared by spherizing flake-like natural graphite, and when the natural graphite is spherical, it can promote the stacking between active material particles, thereby reducing the thickness expansion problem of the negative electrode active material caused by charging / discharging to a level that is even better.

[0066] The flake-like natural graphite is prepared from natural graphite raw materials (e.g., collected from graphite ore), specifically, it can be prepared by, for example, pulverizing the natural graphite raw materials, removing impurities by alkali treatment and / or acid treatment, washing, drying and sieving.

[0067] Spherical natural graphite can be prepared by spheroidizing the flake-like natural graphite. Specifically, the spheroidization can be carried out using a vortex mill.

[0068] The method for preparing the negative electrode active material of the present invention includes the step of pressurizing natural graphite by cold isostatic pressing. Cold isostatic pressing can effectively remove or reduce the pores present in the negative electrode active material containing natural graphite, and can reduce the specific surface area of ​​the natural graphite to an appropriate level, thereby effectively preventing the cyclic expansion problem of the negative electrode active material prepared thereby (a problem caused by electrolyte side reactions).

[0069] The "cold isostatic pressing" method, or CIP, refers to a forming method in which powder is filled into a mold and compressed in an infinite number of axial directions using hydrostatic pressure. In other words, according to the CIP process, the powder can be compressed isotropically, thereby uniformly removing or reducing the pores present in the formed negative electrode active material. Due to the reduction in pores, the reaction area between the natural graphite and the electrolyte under pressure during the CIP process is reduced. This significantly reduces side reactions with the electrolyte and improves the battery's lifespan characteristics.

[0070] The pressurization can be carried out at a pressure of 80 MPa to 150 MPa, preferably 85 MPa to 100 MPa. When within the above pressure range, the pores of the particles can be filled to the desired level, thereby effectively preventing side reactions with the electrolyte and preventing damage to the negative electrode active material that may be caused by using excessive pressure, which is therefore preferred.

[0071] The pressurization can be applied for 30 seconds to 1,200 seconds, preferably 50 seconds to 600 seconds, and more preferably 60 seconds to 300 seconds. Within these ranges, the BET specific surface area of ​​the negative electrode active material can be reduced to the desired level, and is therefore preferred.

[0072] The method for preparing the negative electrode active material of the present invention may further include the step of forming a carbon coating on natural graphite after pressurizing it. The carbon coating can compensate for damage or breakage of the natural graphite that may occur during pressurization, crushing, sieving, acid / alkali treatment processes, etc., reduce the increase in the BET specific surface area of ​​the natural graphite due to the crushing, etc., and improve the mechanical stability of the negative electrode active material.

[0073] The carbon coating can be formed by providing spherical natural graphite with at least one precursor selected from the group consisting of pitch, rayon, and polyacrylonitrile resins, and then heat-treating the precursor to cause thermal decomposition. In terms of forming a uniform carbon coating and preventing over-formation of the carbon coating, the heat treatment process for forming the carbon coating can be carried out in a temperature range of 1,100°C to 1,500°C, more preferably 1,200°C to 1,300°C.

[0074] The carbon coating can be formed in an amount of 2% to 7% by weight, preferably 3% to 6% by weight, and more preferably 4% to 5% by weight, based on the total weight of the natural graphite and the carbon coating. In this case, the prevention of side reactions with the electrolyte and structural stability can be sufficiently improved, while preventing lithium insertion / extraction barriers caused by excessive formation of the carbon coating.

[0075] The method for preparing the negative electrode active material of the present invention includes pressing natural graphite into D 90 For D 10 The ratio of D 90 / D 10 The steps are to adjust to 2.0 to 2.2, preferably 2.05 to 2.12.

[0076] With D adjusted to the above range 90 / D 10 The aforementioned negative electrode active material has a uniform particle size distribution. Therefore, when applied to the negative electrode, the degree of particle packing is excellent, and it can effectively prevent the cycling expansion problem caused by the charging / discharging of the negative electrode and the resulting increase in negative electrode thickness.

[0077] The step of adjusting the particle size distribution of the pressurized natural graphite can be carried out, for example, by sieving, which is a well-known method in the art for adjusting the particle size distribution.

[0078] When a carbon coating is formed on the pressurized natural graphite, the step of adjusting the particle size distribution can be performed before or after the formation of the carbon coating.

[0079] The method for preparing the negative electrode active material of the present invention may further include D-processing the pressurized natural graphite. 50 The step involves adjusting the particle size to 6 μm to 15 μm, preferably 8 μm to 12 μm, more preferably 9.5 μm to 11.5 μm, and even more preferably 10.2 μm to 10.8 μm. When the average particle size is adjusted to the above range, the particle packing performance is improved and the porosity between particles is reduced, resulting in excellent anti-swelling properties. Furthermore, due to the small particle size, lithium can be smoothly inserted / extracted even at high C rates, thus it is also preferred in terms of improving fast charging performance.

[0080] The step of adjusting the particle size distribution of the pressurized natural graphite can be carried out, for example, by sieving, which is a well-known method in the art for adjusting the particle size distribution.

[0081] When a carbon coating is formed on the pressurized natural graphite, the step of adjusting the particle size distribution can be performed before or after the formation of the carbon coating.

[0082] With adjusted D 90 / D 10 The BET specific surface area of ​​natural graphite or natural graphite with a carbon coating is 2.02 m². 2 / g to 2.30m 2 / g. When within the above range, the pores present in the natural graphite are controlled to the desired level, thereby effectively preventing side reactions with the electrolyte. Having adjusted D 90 / D 10 The BET specific surface area of ​​the natural graphite or natural graphite with a carbon coating is preferably 2.05 m². 2 / g to 2.15m 2 / g.

[0083] The aforementioned BET specific surface area range can be achieved, for example, by pressurizing the natural graphite using the aforementioned cold isostatic pressing method, adjusting the processing conditions of the cold isostatic pressing method, or adjusting the intensity during crushing or disintegration, the content of the precursor used to form the carbon coating, the heat treatment temperature during the formation of the carbon coating, etc.

[0084] With adjusted D 90 / D 10 The tap density of natural graphite or natural graphite with a carbon coating is 1.11 g / cm³. 3 Up to 1.19 g / cm 3 Anode active materials with tap density within the aforementioned range can be evaluated as having improved sphericity. Therefore, when anodes are manufactured using said anode active materials, the degree of packing between active material particles is improved, and the mechanical stress on the active material particles during electrode rolling can be reduced, which is advantageous in preventing swelling.

[0085] Preferably, it has an adjusted D 90 / D 10 The tap density of natural graphite or natural graphite with a carbon coating can be 1.14 g / cm³. 3 Up to 1.17 g / cm 3Furthermore, when applied to the negative electrode, it can promote the accumulation between particles, keep the thickness of the coated electrode small, reduce thickness changes during the rolling of the electrode to the target thickness, result in a small electrode orientation value, and can produce an electrode that is favorable in terms of electrode expansion, thereby effectively preventing cyclic expansion problems, swelling phenomena, and the resulting increase in the thickness of the negative electrode caused by charging / discharging of the negative electrode.

[0086] The aforementioned tap density range can be achieved by adjusting the spheroidization processing conditions of flake-like natural graphite.

[0087] The negative electrode active material prepared by the method of preparing negative electrode active material according to the present invention has a D 90 / D 10 The BET specific surface area and tap density can be achieved by adjusting the spheroidization process of natural graphite, the pressure applied by cold isostatic pressing, the carbon coating formation process, and / or the sieving process. The resulting negative electrode active material exhibits excellent particle packing characteristics, prevents cycling expansion caused by electrolyte side reactions and thickness expansion of the negative electrode active material layer, and maximizes the output characteristics of natural graphite.

[0088] <Negative electrode>

[0089] In addition, the present invention provides a negative electrode comprising the above-mentioned negative electrode active material.

[0090] Specifically, the negative electrode of the present invention includes a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector, wherein the negative electrode active material layer includes the aforementioned negative electrode active material.

[0091] The negative electrode current collector can typically have a thickness of 3 μm to 500 μm. The negative electrode current collector is not particularly limited, as long as it has high conductivity without causing chemical changes in the battery; for example, it can contain at least one material selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, and aluminum-cadmium alloys. Furthermore, the negative electrode current collector can have fine irregularities formed on its surface, thereby enhancing the adhesion of the negative electrode active material. Additionally, the negative electrode current collector can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0092] The negative electrode active material layer comprises the aforementioned negative electrode active material.

[0093] The negative electrode active material layer may also contain other active materials known in the art without degrading the effectiveness of the present invention. Specifically, it may contain one or more of the following materials selected from the group consisting of: carbonaceous materials; metals such as lithium-containing titanium oxide (LTO), Si, Sn, Li, Zn, Mg, Cd, Ce, Ni or Fe; alloys of said metals; oxides of said metals; and complexes of said metals and carbon.

[0094] The negative electrode active material may be included in the negative electrode active material layer in an amount of 80% to 99% by weight, preferably 90% to 98% by weight.

[0095] In addition, the negative electrode active material layer may selectively include at least one additive selected from the group consisting of binders, thickeners and conductive materials, in addition to the negative electrode active material.

[0096] The adhesive is a component that facilitates the bonding between the conductive material, the active material, and the current collector, and can be added to the negative electrode active material layer in an amount of 1% to 30% by weight. Examples of the adhesive may include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile rubber, fluororubber, and various copolymers thereof.

[0097] As the thickener, any thickener typically used in lithium secondary batteries can be used, and one example is carboxymethyl cellulose (CMC).

[0098] The conductive material is a component used to further improve the conductivity of the negative electrode active material, and can be added to the negative electrode active material layer in an amount of 1% to 20% by weight. The conductive material is not particularly limited, as long as it is conductive and does not cause chemical changes in the battery. For example, graphite, such as natural or artificial graphite; carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermally cracked carbon black; conductive fibers, such as carbon fibers and metal fibers; fluorocarbons; metal powders, such as aluminum powder and nickel powder; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; or conductive materials, such as polyphenylene derivatives, etc. Specific examples of commercially available conductive materials may include Chevron Chemical Company’s acetylene black series, Denka Singapore Private Limited’s Danka Black, Gulf Oil Company’s products, Armak’s Ketjen Black and EC series, Cabot Company’s Vulcan XC-72, and Timcal Company’s Super P.

[0099] Because the negative electrode according to the present invention contains the aforementioned negative electrode active material, the stacking of active material particles in the negative electrode can be smoothly achieved, and the problems of cyclic expansion caused by electrolyte side reactions and thickness expansion of the negative electrode active material layer can be effectively prevented. Therefore, the output and capacity characteristics of natural graphite can be effectively exhibited while improving lifetime characteristics.

[0100] When performing X-ray diffraction analysis on the negative electrode, the orientation index of the area ratio I(004) / I(110) can be from 9 to 15, preferably from 9 to 12. When within the above range, the negative electrode active material can expand in multiple directions, which is preferred in terms of preventing swelling and improving lifetime characteristics.

[0101] Secondary batteries

[0102] In addition, the present invention provides a lithium secondary battery comprising the above-mentioned negative electrode for a secondary battery.

[0103] Specifically, the lithium secondary battery includes the aforementioned negative electrode, a positive electrode opposite to the negative electrode, a separator inserted between the negative electrode and the positive electrode, and an electrolyte.

[0104] The positive electrode may include a positive electrode current collector and a layer of positive electrode active material formed on the positive electrode current collector.

[0105] The positive electrode current collector is not particularly limited, as long as it is conductive and will not cause chemical changes in the battery. For example, the positive electrode current collector may contain at least one material selected from the group consisting of stainless steel, aluminum, nickel, titanium, and sintered carbon.

[0106] The positive current collector can typically have a thickness of 3 μm to 500 μm.

[0107] The positive electrode active material layer is formed on the positive electrode current collector and contains positive electrode active material.

[0108] The positive electrode active material is a compound capable of reversibly inserting and deintercalating lithium, and specifically, it may comprise a lithium composite metal oxide containing one or more metals such as cobalt, manganese, nickel, or aluminum, and lithium. More specifically, the lithium composite metal oxide may be a lithium-manganese oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt oxide (e.g., LiCoO2, etc.), a lithium-nickel oxide (e.g., LiNiO2, etc.), or a lithium-nickel-manganese oxide (e.g., LiNi...). 1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-z Ni z O4 (where 0 < Z < 2), etc.), lithium-nickel-cobalt oxides (e.g., LiNi), 1-Y1 Co Y1 O2 (where 0 < Y1 < 1), etc.), lithium-manganese-cobalt oxides (e.g., LiCo). 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-z1 Co z1 O4 (where 0 < Z1 < 2), etc.), lithium-nickel-manganese-cobalt oxides (e.g., Li(Ni) p Co q Mn r1 O2 (where 0 < p < 1, 0 < q < 1, 0 < r1 < 1, p + q + r1 = 1), or Li (Ni p1 Co q1 Mn r2 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r2 < 2, p1 + q1 + r2 = 2) etc.), or lithium-nickel-cobalt-transition metal (M) oxides (e.g., Li(Ni) p2 Co q2 Mn r3 A S2The lithium composite metal oxide can be any one of the following: O2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r3, and s2 are atomic fractions of independent elements, where 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < s2 < 1, p2 + q2 + r3 + s2 = 1), etc., and can contain any one of these or a mixture of two or more of them. Due to the fact that it can increase the capacity characteristics and stability of the battery, the lithium composite metal oxide can be LiCoO2, LiMnO2, LiNiO2, lithium nickel-manganese-cobalt oxide (e.g., Li(Ni...)...). 0.6 Mn 0.2 Co 0.2 O2, Li(Ni) 0.5 Mn 0.3 Co 0.2 O2 or Li(Ni) 0.8 Mn 0.1 Co 0.1 (O2, etc.) or lithium nickel cobalt aluminum oxide (e.g., Li(Ni) 0.8 Co 0.15 Al 0.05 O2, etc.

[0109] Based on the total weight of the positive electrode active material layer, the positive electrode active material may be included in an amount of 80% to 99% by weight.

[0110] In addition to the aforementioned positive electrode active material, the positive electrode active material layer may also selectively contain at least one additive selected from the group consisting of binders and conductive materials.

[0111] The adhesive is a component that facilitates the bonding of active materials, conductive materials, etc., and to the current collector, and is typically added in an amount of 1% to 30% by weight based on the total weight of the positive electrode active material layer. Examples of the adhesive may include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers thereof.

[0112] The conductive material is not particularly limited, as long as it is conductive and will not cause chemical changes in the battery. For example, graphite; carbonaceous materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermally cracked black; conductive fibers such as carbon fibers and metal fibers; fluorocarbons; metal powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive materials such as polyphenylene derivatives, etc. Specific examples of commercially available conductive materials may include Chevron Chemical Company's acetylene black series, Denka Singapore Private Limited's Denka Black, Gulf Oil Company's products, Armak's Ketjen black and EC series, Cabot Company's Vulcan XC-72, and Timcal Company's Super P.

[0113] Based on the total weight of the positive electrode active material layer, the conductive material may be included in an amount of 1% to 30% by weight.

[0114] The positive electrode active material layer can be prepared by adding an additive containing positive electrode active material and selective binder and / or conductive material to a solvent to prepare a positive electrode slurry, then applying the slurry to the positive electrode current collector, and then rolling and drying it.

[0115] The solvent may include an organic solvent such as N-methyl-2-pyrrolidone (NMP), and its amount may be such that a preferred viscosity is achieved when the positive electrode active material, as well as selective binders and conductive materials, are included. For example, the solvent content may be such that the concentration of the solids containing the positive electrode active material and selective binders and conductive materials is 50% to 95% by weight, preferably 70% to 90% by weight.

[0116] In the lithium secondary battery, a separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator can be used without particular limitation, as long as it is a separator commonly used in secondary batteries. In particular, separators with excellent moisture-holding capacity for the electrolyte and low resistance to ion movement within the electrolyte are preferred. Specifically, porous polymer membranes can be used, such as porous polymer membranes made from polyolefin polymers like ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminates of two or more layers thereof. Furthermore, typical porous nonwoven fabrics can be used, such as nonwoven fabrics formed from high-melting-point glass fibers, polyethylene terephthalate fibers, etc. Moreover, separators coated with ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and can be selectively used in single-layer or multi-layer structures.

[0117] In addition, the electrolyte used in this invention can be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, etc., which can be used to manufacture lithium secondary batteries, but is not limited to these.

[0118] Specifically, the electrolyte may contain an organic solvent and a lithium salt.

[0119] Any organic solvent can be used without particular limitation, as long as it can serve as a medium through which the ions involved in the electrochemical reactions of the battery can move. Specifically, as said organic solvents, ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone can be used; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic 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 ethanol and isopropanol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic C2 to C20 hydrocarbon group, and may contain double bonds, aromatic rings, or ether bonds); amides such as dimethylformamide; dioxolane solvents such as 1,3-dioxolane; or sulfolane. Among the solvents described above, carbonate solvents are preferred, and more preferably, mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant, which can increase the charge / discharge performance of the battery, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate). In this case, when the cyclic carbonate and the linear carbonate are mixed in a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte can be excellent.

[0120] Any compound can be used as the lithium salt without particular limitation, as long as it can provide lithium ions used in lithium secondary batteries. Specifically, LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, etc., can be used as the lithium salt. The lithium salt can be used in a concentration range of 0.1M to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte has suitable conductivity and viscosity, thereby exhibiting excellent performance, and lithium ions can move efficiently.

[0121] As described above, the secondary battery according to the present invention can be used in portable devices such as mobile phones, laptops, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs). In particular, it can be preferably used as a constituent battery of medium-to-large-sized battery modules. Therefore, the present invention also provides a medium-to-large-sized battery module comprising the secondary battery described above as a unit cell.

[0122] The medium-to-large battery modules described above can be preferably applied to power sources that require high output and large capacity, such as electric vehicles, hybrid electric vehicles, and energy storage devices.

[0123] Embodiments of the invention will be described in detail below, so that those skilled in the art can readily implement the invention. However, the invention may be embodied in many different forms and is not limited to the embodiments set forth herein.

[0124] Examples and Comparative Examples

[0125] Example 1: Preparation of negative electrode active material

[0126] Natural graphite raw materials are collected from graphite ore using flotation, and the natural graphite raw materials are treated with acid or alkali to remove impurities, then washed and dried to prepare flake natural graphite. The flake natural graphite obtained above is spheroidized using a vortex mill, treated with sulfuric acid to remove impurities, and then dried to prepare spherical natural graphite.

[0127] The spherical natural graphite was filled into a mold and pressurized using a cold isostatic pressing (CIP) method. During the pressurization, the pressure was 90 MPa and the pressurization was carried out for 100 seconds.

[0128] Pressurized spherical natural graphite is mixed with bitumen with a softening point of 175°C to 185°C, and the mixture is heat-treated in an inert atmosphere at 1,250°C for 24 hours by drying to form a carbon coating on the spherical natural graphite.

[0129] The spherical natural graphite with a carbon coating is broken down, sieved, and de-ironized, and the 10% volumetric cumulative diameter D of its particle size distribution is reduced. 10 50% of the cumulative volume diameter D 50 and 90% of the cumulative volume diameter D 90 The anode active material of Example 1 was prepared by adjusting the micrometer to 7.4 μm, 10.7 μm and 15.5 μm respectively.

[0130] At this point, the carbon coating is formed to account for 4.5% by weight of the total weight of the negative electrode active material based on Example 1.

[0131] Example 2: Preparation of negative electrode active material

[0132] The negative electrode active material was prepared in the same manner as in Example 1, but the difference from Example 1 was that different spheroidizing processing conditions and sieving conditions were applied, and the carbon coating was formed at 5% by weight based on the total weight of the negative electrode active material.

[0133] The negative electrode active material D 10 D 50 D 90 The corresponding sizes are 7.3 μm, 10.0 μm, and 14.6 μm.

[0134] Comparative Example 1: Preparation of Negative Electrode Active Materials

[0135] The negative electrode active material was prepared in the same manner as in Example 1, but the difference from Example 1 was that different spheroidizing processing conditions and sieving conditions were applied, and the carbon coating was formed at 5% by weight based on the total weight of the negative electrode active material.

[0136] The negative electrode active material D 10 D 50 D 90 The corresponding sizes are 6.4 μm, 9.0 μm, and 13.6 μm.

[0137] Comparative Example 2: Preparation of Negative Electrode Active Materials

[0138] The negative electrode active material was prepared in the same manner as in Example 1, but the difference from Example 1 was that different spheroidizing and sieving conditions were applied, and the carbon coating was formed at 4% by weight based on the total weight of the negative electrode active material.

[0139] The negative electrode active material D10 D 50 D 90 The corresponding sizes are 6.8 μm, 11.0 μm, and 19.1 μm.

[0140] Comparative Example 3: Preparation of Negative Electrode Active Materials

[0141] The negative electrode active material was prepared in the same manner as in Example 1, but the difference from Example 1 was that different spheroidizing processing conditions and sieving conditions were applied, the carbon coating was formed at 5% by weight based on the total weight of the negative electrode active material, and the pressure was applied for 400 seconds by cold isostatic pressing (CIP).

[0142] The negative electrode active material D 10 D 50 D 90 The corresponding sizes are 7.0 μm, 10.0 μm, and 15.4 μm.

[0143] Comparative Example 4: Preparation of Negative Electrode Active Materials

[0144] The negative electrode active material was prepared in the same manner as in Example 1, but the difference from Example 1 was that different spheroidizing processing conditions and sieving conditions were applied, the carbon coating was formed at 5% by weight based on the total weight of the negative electrode active material, and no pressure was applied by the cold isostatic pressing (CIP) method.

[0145] The negative electrode active material D 10 D 50 D 90 The corresponding sizes are 6.3 μm, 9.0 μm, and 15.5 μm.

[0146] Comparative Example 5: Preparation of Negative Electrode Active Materials

[0147] The negative electrode active material was prepared in the same manner as in Example 1, but the difference from Example 1 was that different spheroidizing and sieving conditions were applied, and the carbon coating was formed at 4% by weight based on the total weight of the negative electrode active material.

[0148] The negative electrode active material D 10 D 50 D 90 The corresponding sizes are 7.5 μm, 11.0 μm, and 16.5 μm.

[0149] Comparative Example 6: Preparation of Negative Electrode Active Materials

[0150] The negative electrode active material was prepared in the same manner as in Example 1, but the difference was that spherical natural graphite and excess pitch were mixed, and the heat treatment of the mixture of spherical natural graphite and pitch was carried out at 3,000°C instead of 1,250°C. The carbon coating was formed at 10% by weight based on the total weight of the negative electrode active material, and no pressure was applied by cold isostatic pressing (CIP).

[0151] The negative electrode active material D 10 D 50 D 90 The corresponding sizes are 6.8 μm, 10.0 μm, and 14.8 μm.

[0152] The D values ​​of the negative electrode active materials prepared in Examples 1, 2, and Comparative Examples 1 to 6 were measured respectively. 50 D 10 D 90 The specific surface area and tap density of BET are shown in Table 1 below.

[0153] [Table 1]

[0154]

[0155] The tap density was obtained by measuring the final volume and calculating the apparent density. The final volume was obtained by filling 40g of negative electrode active material into a cylindrical container with a diameter of 30mm and a capacity of 100mL, and then vibrating the container up and down 1,000 times with an amplitude of 14mm.

[0156] The BET specific surface area of ​​the negative electrode active material was measured by pretreating the negative electrode active material at 130°C and then measuring it using nitrogen gas with a BELSORP (BET device) from BEL JAPAN Co. using the Brunauer-Emmett-Teller (BET) measurement method.

[0157] Experimental Example

[0158] <Manufacturing the Negative Electrode>

[0159] The negative electrode active material prepared in Example 1, Super C65 as a conductive material, styrene-butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener were mixed in a weight ratio of 96.6:1:1.3:1.1, and then water was added to prepare a negative electrode slurry. The negative electrode slurry was then coated onto copper foil, vacuum dried at approximately 130°C for 8 hours, and then rolled to produce an area of ​​1.4875 cm². 2The negative electrode. At this point, the loading of the fabricated negative electrode is 3.6 mAh / cm³. 2 .

[0160] The negative electrodes of Examples 2 and Comparative Examples 1 to 6 were manufactured in the same manner as in Example 1, except that the negative electrode active material of Examples 2 and Comparative Examples 1 to 6 was used instead of the negative electrode active material of Example 1.

[0161] Experimental Example 1: Swelling Evaluation

[0162] Manufacturing of Secondary Batteries

[0163] LiCoO2 as the positive electrode active material, Li-435 (manufactured by Denka Co., Ltd.) as the conductive material, KF9700 (manufactured by Kureha Co., Ltd.) as the binder, and BH-730H (manufactured by Zeon Co., Ltd.) as the thickener were mixed in a weight ratio of 97.68:1.20:1.00:0.12. N-methylpyrrolidone (NMP) was then added as a solvent to prepare the positive electrode slurry. The slurry was applied to aluminum foil, vacuum dried at approximately 130°C for 8 hours, and then rolled to produce a slurry with an area of ​​1.7671 cm². 2 The positive electrode. At this point, the loading of the fabricated positive electrode is 3.4 mAh / cm³. 2 .

[0164] A polyolefin separator was inserted between the negative electrode and the positive electrode manufactured in Examples 1, 2, and Comparative Examples 1 to 6, respectively, and then an electrolyte was injected therein to manufacture the full-cell secondary batteries of the examples and comparative examples. The electrolyte used was prepared by adding vinylene carbonate (VC) in an amount of 0.5% by weight based on the solvent to a non-aqueous electrolyte solvent (in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 1:4), and then dissolving 1M LiPF6 therein.

[0165] <Swelling Evaluation>

[0166] The lithium secondary batteries manufactured in Examples 1, 2, and Comparative Examples 1 to 6 were charged and discharged at 0.1C in the first cycle, at 0.2C in the second cycle, and at 0.5C from the third to the 30th cycle, with a charging range of SOC 0 to SOC 95. The swelling rate was then calculated using Equation 1 below.

[0167] [Formula 1]

[0168] Swelling rate (%) = {(t2-t1) / t1} × 100

[0169] (t1 is the thickness of the negative electrode of the secondary battery before the first charge / discharge cycle, and t2 is the thickness of the negative electrode of the secondary battery after the 30th charge / discharge cycle.)

[0170] [Table 2]

[0171] Swelling rate (%) Example 1 21 Example 2 22 Comparative Example 1 24 Comparative Example 2 26 Comparative Example 3 29 Comparative Example 4 26 Comparative Example 5 27 Comparative Example 6 30

[0172] Referring to Table 2, compared with the comparative examples, the negative electrode active materials of Examples 1 and 2 respectively prevented electrolyte side reactions and also prevented swelling to an excellent degree. In Examples 1 and 2, natural graphite was pressurized by cold isostatic pressing, and the D of the negative electrode active material... 90 / D 10 The tap density and BET specific surface area are adjusted to the required range.

[0173] Experiment Example 2: Fast Charging Performance Evaluation

[0174] <Manufacturing of Coin-Type Half-Cells>

[0175] The negative electrodes manufactured in Examples 1, 2, and Comparative Examples 1 to 6 were each stamped into the size of a coin cell, and then a polyolefin separator was inserted between the negative electrode and a lithium foil serving as the counter electrode. Subsequently, an electrolyte was injected to manufacture the respective coin-type half-cells of the Examples and Comparative Examples. In the electrolyte, 1 M of LiPF6 was dissolved in a solvent obtained by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a volume ratio of 20:80, and 0.5 wt% of vinylene carbonate (VC) additive was added.

[0176] <Fast Charging Performance Evaluation>

[0177] To confirm the fast charging characteristics of the negative electrodes prepared according to Examples 1 and 2 and Comparative Examples 1 to 6, a Li plating experiment was conducted.

[0178] The coin-type half-cells of the examples and comparative examples were subjected to three charge-discharge cycles at 0.1C, followed by charging at 3C for 15 minutes to determine the inflection points of the profile at the first derivative and dQ / dV, in order to quantify the SOC (%) of Li deposition, which is the SOC at which lithium deposition occurs on the negative electrode surface. The results are shown in Table 3.

[0179] [Table 3]

[0180] Analysis of the SOC (%) of Li Example 1 41 Example 2 42 Comparative Example 1 41 Comparative Example 2 37 Comparative Example 3 41 Comparative Example 4 41 Comparative Example 5 38 Comparative Example 6 36

[0181] Referring to Table 3, compared with the negative electrodes of Comparative Examples 2, 5 and 6, the negative electrodes of Examples 1 and 2 exhibited superior fast charging performance.

[0182] Although Comparative Examples 1, 3, and 4 showed the same level of fast charging performance as Example 1, their anti-swelling performance was poor compared to the above-described examples, and therefore they were not preferred.

Claims

1. A negative active material, comprising: a natural graphite with or without a carbon coating formed thereon, The D of the natural graphite thereon with or without a carbon coating 90 For D 10 The ratio of D 90 / D 10 The strength is 2.0–2.2; the tap density is 1.11 g / cm³. 3 Up to 1.19 g / cm 3 Furthermore, the specific surface area of ​​BET is 2.02m². 2 / g to 2.30m 2 / g, D90 of the natural graphite on which a carbon coating is formed or is not formed is 6 μm to 15 μm. 50 is 6 μm to 15 μm.

2. The negative active material according to claim 1, wherein the D50 of the negative active material is 2.05 to 2.

12. 90 / D 10 2.05 to 2.

12. 3.The negative active material according to claim 1, further comprising a carbon coating formed on the natural graphite. 4.The negative active material according to claim 3, wherein the carbon coating is contained in the negative active material in an amount of 2 to 7% by weight. 5.The negative active material according to claim 1, wherein the negative active material is spherical. 6.A method of manufacturing a negative active material, the method comprising: pressurizing a natural graphite by a cold isostatic pressing method; and D 90 The D 10 ratio D 90 / D 10 was adjusted to 2.0-2.2 and the D 50 of the pressurized natural graphite was adjusted to 6 μm to 15 μm, wherein the natural graphite having the adjusted D 90 / D 10 The natural graphite having a D 2 / g to 2.30 m 2 / g of BET specific surface area and 1.11 g / cm 3 to 1.19 g / cm 3 of tap density. 7.The method according to claim 6, further comprising forming a carbon coating on the natural graphite after the natural graphite is pressurized. 8.The method according to claim 7, wherein the carbon coating is formed in an amount of 2 to 7% by weight based on the total weight of the natural graphite and the carbon coating. 9.The method according to claim 6, wherein the pressurizing is performed at a pressure of 80 to 150 MPa. 10.The method according to claim 6, wherein the pressurizing is performed for a time of 30 to 1,200 seconds. 11.A negative electrode, comprising: a negative current collector; and a negative active material layer formed on the negative current collector, wherein the negative active material layer comprises the negative active material according to claim 1. 12.A secondary battery, comprising: the negative electrode according to claim 11; a positive electrode opposite to the negative electrode; a separator interposed between the positive electrode and the negative electrode; and an electrolyte.

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