KR102317512B1 - Negative active material for lithium secondary battery, method for preparing the same and lithium secondary battery including the same - Google Patents

Abstract

The present invention relates to (i) crystalline earth-like graphite aggregate particles having an average particle diameter of 1 to 5 μm; and (ii) a coating layer formed on the surface of the crystalline earth graphite agglomerate particles, comprising at least one element selected from P, B, O, F and N, and at least one carbon material selected from amorphous carbon and semi-crystalline carbon. Containing composite particles comprising a coating layer, wherein the composite particles are bonded by the carbon material to have an assembled structure, an anode active material for a lithium secondary battery, a method for manufacturing the same, and the anode active material As for a lithium secondary battery, the anode active material for a lithium secondary battery according to the present invention can implement a lithium secondary battery having a high capacity and excellent high rate charge/discharge characteristics, long life characteristics and high temperature characteristics.

Description

Anode active material for lithium secondary battery, manufacturing method thereof, and lithium secondary battery comprising same

The present invention relates to an anode active material for a lithium secondary battery, a manufacturing method thereof, and a lithium secondary battery comprising the anode active material for a lithium secondary battery.

Currently, carbon materials are mainly used as anode active materials for lithium secondary batteries, and they are classified into crystalline graphite and amorphous carbon. The amorphous carbon includes soft carbon obtained by calcining coal-based pitch or petroleum-based pitch at high temperature, hard carbon obtained by calcining polymer resin such as phenol resin, and the like, and exhibits excellent charge/discharge output characteristics. . However, the amorphous carbon has a problem in that the discharge specific capacity and the coulombic efficiency are lower than that of the crystalline graphite.

The crystalline graphite is classified into natural graphite and artificial graphite, and among them, natural graphite is inexpensive and exhibits electrochemical properties similar to those of artificial graphite, and thus has high utility as an anode active material.

In the case of charging and discharging of a lithium secondary battery, in the crystalline graphite-based negative active material, the high-rate charging and discharging rates are determined according to the lithium ion diffusion rate in the graphite particles, so the output characteristics at high rates are highly dependent on the size of the graphite particles. Currently, crystalline natural graphite is generally made of flake graphite assembled in a spherical shape, but the output characteristics at high rates are insufficient, so it cannot be applied as an anode active material for lithium secondary batteries that require high output and long life characteristics in the future. It is currently being limited. In addition, when the flaky graphite is granulated in a spherical shape, an irreversible reaction proceeds due to a reaction with the electrolyte penetrating inside as the charge/discharge cycle proceeds, forming an excessive SEI (solid electrolyte interphase) film, resulting in swelling. There is a problem in that the characteristics of the electrode are deteriorated. Furthermore, insufficient charging/discharging cycle characteristics at a high temperature of 45° C. or higher is also known as a problem to be solved in order to realize a high-performance battery.

On the other hand, microcrystalline graphite as natural graphite is usually present in a state in which primary particles of 1 μm or less are agglomerated and agglomerated, and the agglomerated earthy graphite is separated and agglomerated by a mechanical method using a jet mill, etc. In the case of pulverization, the size of the earth-like graphite aggregates can be adjusted in the agglomerated state.

Since the size of the primary particles in the earth graphite agglomerate may be 1 μm or less, more specifically 0.5 μm or less, the diffusion distance of lithium ions in the graphite primary particles is very short, so insertion and desorption of lithium ions are easy As a result, high-rate charge-discharge characteristics are very good. Moreover, in the case of earth-based natural graphite, it is known that the sizes of La and Lc, which indicate the crystallite size, are smaller than that of impression natural graphite. Therefore, when it is used as a negative electrode material for lithium secondary batteries, lithium insertion and desorption is expected to be easier. .

After separation and pulverization by a mechanical method using a jet mill, etc., the average particle diameter of the earth graphite aggregate may be generally 4 µm or less, specifically 3 µm or less, and more specifically 2 µm or less. However, in the case of the earth graphite aggregate, it is generally difficult to separate only the primary particles, so that two or more primary particles exist in an aggregated state.

In the case of the earth graphite agglomerate, the specific surface area is large, and when the earth graphite particles are directly exposed to an electrolyte, a side reaction occurs and the performance as an anode active material for a lithium secondary battery is deteriorated. In addition, as an active material having a large specific surface area is used, energy density is lowered by using a large amount of binder in manufacturing the electrode, and the mixing time of the slurry is prolonged, thereby reducing process efficiency, and thus there is a difficulty in manufacturing the slurry.

In order to solve this problem, Korean Patent Registration No. 10-1004443 and Korean Patent Registration No. 10-1131937 disclose an anode active material for a lithium secondary battery in which the earth graphite particles are dispersed in an amorphous and semi-crystalline carbon matrix.

On the other hand, in the case of composite particles in which the earth graphite agglomerate is assembled with hard carbon or soft carbon, the properties as a negative active material for a lithium secondary battery depend largely on the internal structure of the composite particle and the characteristics of the hard carbon or soft carbon.

In addition, when carbon precursors such as coal-based pitch and petroleum-based pitch are used as binders when assembling the composite particles, melting occurs during heat treatment for carbonization of the precursor after assembly, resulting in poor coating and assembly state for the earth graphite aggregate In addition, since the composite particles contain amorphous hard carbon or low crystalline soft carbon having a lower specific capacity than crystalline graphite, there is also a problem in that the specific capacity is lower than that of pure graphite.

Korean Patent Registration No. 10-1004443 (Registration Date: 2010.12.21) Korean Patent Registration No. 10-1131937 (Registration Date: 2012.03.23) Korean Patent No. 10-1126937 (Registration Date: 2012.03.07) Korean Patent Publication No. 10-2013-0071070 (published on: June 28, 2013) Korean Patent Registration No. 10-1002539 (Registration Date: 2010.12.13) Korean Patent Registration No. 10-0570617 (Registration Date: 2006.04.06.)

The technical problem to be solved by the present invention is to provide a graphite-based negative active material for a lithium secondary battery having a high capacity and excellent in high output characteristics, long life characteristics and high temperature characteristics, a method for manufacturing the same, and a lithium secondary battery including the negative electrode active material.

In order to achieve the above technical object, the present invention is (i) crystalline earth graphite aggregate particles having an average particle diameter of 1 to 5 ㎛; and (ii) a coating layer formed on the surface of the crystalline earth graphite agglomerate particles, comprising at least one element selected from P, B, O, F and N, and at least one carbon material selected from amorphous carbon and semi-crystalline carbon. It proposes a negative active material for a lithium secondary battery, comprising composite particles comprising a coating layer, wherein the composite particles are bonded by the carbon material to have an assembled structure.

In addition, the crystalline earth graphite agglomerate particles, proposes a negative active material for a lithium secondary battery, characterized in that obtained by separating or pulverizing the earth graphite agglomerate mass.

In addition, for a lithium secondary battery, characterized in that a chemical bond is formed between one or more elements selected from P, B, O, F and N included in the coating layer of the composite particles and two or more elements selected from carbon constituting the carbon material An anode active material is proposed.

In addition, the coating layer proposes a negative active material for a lithium secondary battery, characterized in that it further comprises nano-sized pores.

In addition, the carbon material, 5 to 50 parts by weight based on 100 parts by weight of the negative electrode active material is proposed, characterized in that included in the negative active material for a lithium secondary battery.

In addition, the coating layer proposes a negative active material for a lithium secondary battery, characterized in that it contains 0.0001 to 50% by weight of one or more elements selected from P, B, O, F and N.

In addition, an anode active material for a lithium secondary battery, characterized in that the average particle diameter of the anode active material is 3 to 40 ㎛.

In addition, it proposes a negative active material for a lithium secondary battery, characterized in that it further comprises a carbon coating layer made of at least one carbon material selected from amorphous carbon and semi-crystalline carbon.

In addition, the thickness of the carbon coating layer proposes a negative active material for a lithium secondary battery, characterized in that 0.01 to 5㎛.

And, in another aspect of the present invention, separating or pulverizing the earthy graphite agglomerate mass to prepare crystalline earthy graphite agglomerate particles having an average particle diameter of 1 to 5 μm; coating the surface of the crystalline earth graphite agglomerate particle with at least one carbon precursor selected from an amorphous carbon precursor and a semi-crystalline carbon precursor; The crystalline earth-like graphite aggregate particles coated with the carbon precursor, H ₃ PO ₄ , H ₃ BO ₃ , P ₂ O ₅ , (NH ₄ ) ₂ S ₂ O ₈ , H ₂ O ₂ , NH ₄ F, and NH ₄ preparing a composite particle precursor by oxidation treatment in an aqueous solution containing at least one oxidizing agent selected from PF _{6 ;} preparing an anode active material precursor by assembling the composite particle precursor; and heat-treating the anode active material precursor.

In addition, the amorphous carbon precursor is citric acid, stearic acid, sucrose, phenol resin, naphthalene resin, polyvinyl alcohol resin, furfuryl alcohol resin, polyacrylonitrile resin, polyamide resin, It is selected from the group consisting of furan resin, cellulose resin, styrene resin, polyimide resin, epoxy resin and vinyl chloride resin, and the semi-crystalline carbon precursor is coal-based pitch, petroleum-based pitch, polyvinyl chloride, anthracene oil, FCC decant oil. , mesophase pitch, tar, or a method for producing a negative active material for a lithium secondary battery, characterized in that selected from the group consisting of low molecular weight heavy oil.

In addition, the heat treatment proposes a method of manufacturing a negative active material for a lithium secondary battery, characterized in that performed at 700 to 3200 ℃.

In addition, the heat treatment proposes a method of manufacturing an anode active material for a lithium secondary battery, characterized in that it is performed in an atmosphere of one kind of gas selected from nitrogen gas, argon gas, and hydrogen gas, or a mixed gas atmosphere of two or more kinds, or a vacuum atmosphere.

And, in another aspect of the present invention, a lithium secondary battery including the negative active material is proposed.

The anode active material for a lithium secondary battery according to the present invention can implement a lithium secondary battery having a high capacity and excellent high rate charge/discharge characteristics, long lifespan characteristics and high temperature characteristics.

1 is a schematic cross-sectional view of an anode active material according to an embodiment of the present invention.
2(a) and 2(b) are schematic cross-sectional views and scanning electron microscope (SEM) images of crystalline earth-like graphite aggregate particles included in the composite particles of the negative electrode active material according to the present invention, respectively.
3 is a schematic cross-sectional view of an anode active material according to another embodiment of the present invention.
4 to 7 are X-ray photoelectron spectroscopy (XPS) analysis results of the negative active materials according to Examples 1 to 4, respectively.
8 is an X-ray photoelectron spectroscopy (XPS) analysis result of the negative active material according to Comparative Example 1. Referring to FIG.
9 shows the capacity according to the cycle at 45 ℃ of the negative active material according to Example 4 and Comparative Example 1.
10 shows the cycle coulombic efficiency at 45° C. of the negative active materials according to Example 4 and Comparative Example 1. FIG.

In describing the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted.

Since the embodiment according to the concept of the present invention may have various changes and may have various forms, specific embodiments will be illustrated in the drawings and described in detail in the present specification or application. However, this is not intended to limit the embodiment according to the concept of the present invention with respect to a specific disclosed form, and should be understood to include all changes, equivalents or substitutes included in the spirit and scope of the present invention.

The terms used herein are used only to describe specific embodiments, and are not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In this specification, terms such as "comprises" or "have" are intended to designate that the described features, numbers, steps, operations, components, parts, or combinations thereof exist, and include one or more other features or numbers. , it is to be understood that it does not preclude the possibility of the presence or addition of steps, operations, components, parts, or combinations thereof.

Hereinafter, the present invention will be described in detail.

1 is a schematic cross-sectional view of an anode active material according to an embodiment of the present invention.

Referring to FIG. 1 , the negative active material 1 according to an embodiment of the present invention is a composite particle comprising a crystalline earth graphite aggregate particle 11 and a coating layer 12 formed on the surface of the crystalline earth graphite aggregate particle. It has an assembled structure bonded by the carbon material.

As the crystalline earth graphite aggregate particles 11, fine particles having an average particle diameter of 1 to 5 μm may be used, and more preferably, aggregate particles having an average particle size of 1 to 3 μm may be used.

When crystalline graphite having an average particle diameter in the above range is used, a negative active material having excellent high rate characteristics and excellent cycle characteristics can be provided as lithium insertion and desorption reactions are easy.

As shown in FIGS. 2A and 2B , the crystalline earthy graphite agglomerate particles 11 have a form in which a plurality of earthy graphite fine particles 21 having a flake or amorphous form are agglomerated and aggregated.

The coating layer 12 contains at least one element of P, B, O, F, and N, exists between the elements or in a state in which the element and a carbon atom are bonded, and is made of amorphous or semi-crystalline carbon or a combination thereof. , may include a plurality of nano-sized pores 13 .

The coating layer 12 not only coats the surface of the crystalline earth graphite aggregate particles 11, but also includes at least one carbon material selected from amorphous carbon and semi-crystalline carbon included in the coating layer between neighboring crystalline earth graphite aggregate particles. It serves to bind the crystalline earth graphite aggregate particles to each other while located in the

The carbon material may be mixed in an amount of 5 to 50 parts by weight, specifically 5 to 30 parts by weight, based on 100 parts by weight of the crystalline earth graphite aggregate particles.

When the carbon material is used within the content range, uniform coating of the surfaces of the crystalline earth graphite aggregate particles is possible, and the granulation through bonding of the crystalline earth graphite aggregate particles is easy.

In addition, heterogeneous elements other than carbon (P, B, O, F, N, etc.) in the carbon material may be included in an amount of 0.0001 to 50 wt%. When the heterogeneous element is included in less than 0.0001 weight %, it is difficult to expect a sufficient effect according to the addition of the heterogeneous element. It is difficult to expect an increase in capacity and an improvement in charging/discharging speed.

The anode active material 1 according to the present invention is assembled by bonding to each other by one or more carbon materials selected from amorphous carbon and semi-crystalline carbon serving as a binder in which crystalline earth graphite aggregate particles 11 are included in the coating layer 12 . It has a spherical structure and its shape may be spherical.

As described above, the negative active material according to the present invention, in which composite particles including crystalline earth graphite aggregate particles are combined and granulated by a carbon material, is one of the problems of conventional commercial spheroidized natural graphite even during repeated charging and discharging. Phosphorus swelling is suppressed and the surface stability of the crystalline earth graphite agglomerate particles is improved, thereby suppressing side reactions with the electrolyte, which not only improves long life characteristics but also shows stable charging and discharging characteristics at high temperatures.

On the other hand, the average particle diameter of the negative active material according to the present invention may be 3 to 40 ㎛, more preferably 5 to 30 ㎛. When the negative active material has an average particle diameter in the above range, excellent electrode manufacturing process efficiency and electrode density can be obtained.

3 is a schematic cross-sectional view of an anode active material according to another embodiment of the present invention.

Referring to FIG. 3 , the anode active material 2 according to another embodiment of the present invention is a carbon coating layer made of one or more carbon materials selected from amorphous carbon and semi-crystalline carbon on the surface of the anode active material 1 of FIG. 1 . (14) is further included.

The thickness of the carbon coating layer 14 may be 0.01 to 5 μm, more preferably 0.1 to 3 μm.

Another embodiment of the present invention provides a method of manufacturing the negative active material for a lithium secondary battery.

According to the manufacturing method of the negative electrode active material for a lithium secondary battery according to the present invention, first, the crystalline earthy graphite aggregate particles obtained by separating or pulverizing the earthy graphite aggregate and having an average particle diameter of 1 to 5 μm are prepared, and the prepared crystalline The surface of the earthy graphite agglomerate particles is coated with one or more carbon precursors selected from an amorphous carbon precursor and a semi-crystalline carbon precursor, and the crystalline earthy graphite agglomerate particles coated with the carbon precursor are treated with H ₃ PO ₄ , H ₃ BO ₃ , P _{2 O 5, (NH 4) 2} S 2 O 8, H 2 O 2, NH 4 F, NH 4 PF oxidation treatment in that contains at least one aqueous solution of an oxidizing agent, such as ₆ to produce a composite particle precursor, said composite particles The anode active material precursor is prepared by assembling the precursor, and the anode active material precursor is heat-treated to prepare the anode active material.

Hereinafter, each step of the method for manufacturing the negative active material for a lithium secondary battery according to the present invention will be described in detail.

First, in order to prepare crystalline earthy graphite aggregate particles having an average particle diameter of 1 to 5 μm, a process of separating or pulverizing the earthy graphite aggregate is performed, wherein the separation or grinding is performed by a conventional milling process, For example, a milling device such as a ball mill, an attrition mill, a vibration mill, a disk mill, a jet mill, and a rotor mill is used. to do it At this time, the grinding speed (rpm) and grinding time for grinding can be appropriately adjusted by a person skilled in the art according to the type of milling apparatus, the content of the material to be treated, and the like. In addition, the separation and pulverization may be performed through an ultrasonic process.

Next, the process of coating the surface of the crystalline earth-like graphite aggregate particles obtained through separation or pulverization with one or more carbon precursors selected from an amorphous carbon precursor and a semi-crystalline carbon precursor may be performed by dry or wet methods. When using the dry method, a mixture of one or more carbon precursor particles selected as an amorphous carbon precursor and a semi-crystalline carbon precursor and the crystalline earthy graphite aggregate particles are put into equipment to which a shear force can be applied, and the coating is carried out by the wet method. In this case, at least one carbon precursor selected as the amorphous carbon precursor and the semi-crystalline carbon precursor and the crystalline earth graphite aggregate particles are uniformly mixed in a solvent, the mixture is dried, and the dried mixture is processed to an appropriate size and coated prepared composite particle precursor. Here, the solvent is N-methylpyrrolidone, dimethylformamide, toluene, ethylene, dimethylacetamide, acetone, methylethylketone, hexane, tetrahydrofuran, decane, ethanol, methanol, isopropanol, water, ethyl acetate, or these combinations of can be used.

At this time, as the carbon precursor for forming the carbon material, coal-based pitch and petroleum-based pitch are preferable, but citric acid, stearic acid, sucrose, polyvinylidene fluoride, carboxymethyl cellulose (CMC), hydroxypropyl cellulose, regenerated cellulose, polyvinyl Pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, starch, phenolic resin, furan resin, furfuryl alcohol, polyacrylic acid, sodium polyacrylic acid, polyacrylo Nitrile, polyimide, epoxy resin, cellulose, styrene, polyvinyl alcohol, polyvinyl chloride, mesoface pitch, low molecular weight heavy oil, glucose, gelatin, sugar, or a combination thereof may be used.

Subsequently, the crystalline earth-like graphite aggregate particles coated with one or more carbon precursors selected as the amorphous carbon precursor and the semi-crystalline carbon precursor are mixed with H ₃ PO ₄ , H ₃ BO ₃ , P ₂ O ₅ , (NH ₄ ) ₂ S ₂ O ₈ , H ₂ O ₂ , NH ₄ F, NH ₄ PF _{6 In} an aqueous solution containing at least one of the oxidizing agents, after oxidation treatment, elements constituting the oxidizing agent during heat treatment (eg, P, B, O, F) , N, etc.) reacts with the carbon precursor to form a stable coating layer by chemical bonding. A uniform coating is possible and a coating layer including a plurality of nano-sized pores can be obtained after carbonization.

Then, the composite particle precursor that has undergone the oxidation treatment process is put into a spheroidization assembly equipment to prepare a negative active material precursor having a spherical shape.

Next, the anode active material is prepared by heat-treating the anode active material precursor at a temperature in the range of 700 to 3200 °C.

The heat treatment may be performed in an atmosphere containing nitrogen, argon, hydrogen, or a mixed gas thereof, or under vacuum.

Furthermore, the step of forming a carbon coating layer made of amorphous or semi-crystalline carbon on the surface of the anode active material particles prepared as described above may be additionally performed. Accordingly, it is possible to implement a lithium secondary battery with increased initial charge/discharge efficiency, excellent output characteristics, and improved charge/discharge cycle characteristics.

Amorphous or low-crystalline carbon forming the carbon coating layer is citric acid, stearic acid, sucrose, polyvinylidene fluoride, naphthalene resin, carboxymethyl cellulose (CMC), hydroxypropyl cellulose, regenerated Cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, starch, phenolic resin, furan resin, furfuryl alcohol, polyacrylic acid, sodium polyacrylate , polyacrylonitrile, polyimide, epoxy resin, cellulose, styrene, polyvinyl alcohol, polyvinyl chloride, coal-based pitch, petroleum-based pitch, mesophase pitch, low molecular weight heavy oil, glucose, block-copolymer, It may be formed from at least one or more carbon precursors selected from polyols, gelatins and saccharides.

The anode active material prepared according to the above-described manufacturing method and obtained by coating the surface of the crystalline earth graphite aggregate particles with a carbon material and combining and granulating the crystalline earth graphite aggregate particles increases the lithium storage capacity, and the carbon material inside the negative active material High-output characteristics can be improved because lithium can easily move through the passage made of In addition, the coating layer including the carbon material is chemically stable, and by suppressing side reactions with the electrolyte, it is possible to suppress the swelling phenomenon and improve the charging and discharging characteristics at a long life and high temperature.

In another embodiment, the present invention provides a lithium secondary battery including a negative electrode including the negative active material, a positive electrode, and an electrolyte.

Lithium secondary batteries can be classified into lithium ion batteries, lithium ion polymer batteries, and lithium polymer batteries depending on the type of separator and electrolyte used, and can be classified into cylindrical, prismatic, coin-type, pouch-type, etc. according to the shape, According to the size, it can be divided into a bulk type and a thin film type. Since the structure and manufacturing method of these batteries are well known in the art, a detailed description thereof will be omitted.

The negative electrode may be prepared by mixing the above-described negative electrode active material, a binder, and optionally a conductive material to prepare a composition for forming the negative electrode active material layer, and then applying the composition to the negative electrode current collector.

Examples of the binder include polyvinyl alcohol, carboxymethyl cellulose/styrene-butadiene rubber, hydroxypropylene cellulose, diacetylene cellulose, polyvinyl chloride, polyvinylpyrrolidone, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene or Polypropylene or the like may be used, but is not limited thereto.

The binder may be mixed in an amount of 1 to 30% by weight based on the total amount of the composition for forming the anode active material layer.

The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and specifically, graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; A conductive material such as a polyphenylene derivative may be used.

The conductive material may be mixed in an amount of 0.1 to 30% by weight based on the total amount of the composition for forming the negative active material layer.

The negative electrode current collector may have a thickness of 3 to 500 μm. Examples of the anode current collector may include stainless steel, aluminum, nickel, titanium, calcined carbon, or one in which the surface of aluminum or stainless steel is surface-treated with carbon, nickel, titanium, silver, or the like. The negative electrode current collector may increase the adhesion of the negative electrode active material by forming fine irregularities on the surface thereof, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven body are possible.

The positive electrode includes a positive electrode active material, and a compound capable of reversible intercalation and deintercalation of lithium (a lithiated intercalation compound) may be used as the positive electrode active material. Specifically, at least one selected from cobalt, manganese, and nickel and at least one of a composite oxide of lithium can be used.

The positive electrode may also be prepared by mixing the positive electrode active material, the binder, and optionally a conductive material in the same manner as the negative electrode to prepare a composition for forming a positive electrode active material layer, and then applying the composition to a positive electrode current collector such as aluminum.

The electrolyte is a lithium salt; and non-aqueous organic solvents, organic solid electrolytes, inorganic solid electrolytes, and the like.

The lithium salt is LiCl, LiBr, LiI, LiClO ₄ ,LiBF ₄ ,LiB ₁₀ Cl ₁₀ ,LiPF ₆ ,LiCF ₃ SO ₃ ,LiCF ₃ CO ₂ ,LiAsF ₆ ,LiSbF ₆ , _{LiAlCl 4} ,CH ₃ SO ₃ Li,CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium 4-phenyl borate, imide, or the like may be used.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydro Roxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate Ester, trimethoxy methane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl pyropionate, ethyl propionate etc. may be used.

Examples of the organic solid electrolyte include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphoric acid ester polymers, poly agitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, and ionic dissociation groups. polymers and the like may be used.

As the inorganic solid electrolyte, Li ₃ N,LiI,Li ₅ NI ₂ ,Li ₃ N-LiI-LiOH,LiSiO ₄ ,LiSiO ₄ -LiI-LiOH,Li ₂ SiS ₃ ,Li ₄ SiO ₄ ,Li ₄ SiO ₄ - the _{LiI-LiOH, Li 3 PO 4} -Li 2 S-SiS 2 and Li nitrides, halides, sulfates, etc. may be used.

The electrolyte solution is for the purpose of improving charge/discharge characteristics, flame retardancy, etc., for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene Derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxy ethanol, aluminum trichloride and the like may be added.

In addition, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further included in order to impart incombustibility, and carbon dioxide gas may be further included in order to improve high temperature storage characteristics.

A separator may exist between the positive electrode and the negative electrode depending on the type of the lithium secondary battery. As such a separator, an insulating thin film having high ion permeability and mechanical strength may be used. The separator may have a pore diameter of 0.01 to 10 μm and a thickness of 5 to 300 μm.

Specifically, the separator may include an olefin-based polymer such as chemical-resistant and hydrophobic polypropylene; A sheet or nonwoven fabric made of glass fiber, polyethylene, etc. may be used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.

Hereinafter, examples will be given to describe the present specification in detail. However, the embodiments according to the present specification may be modified in various other forms, and the scope of the present specification is not to be construed as being limited to the embodiments described below. The embodiments of the present specification are provided to more completely explain the present specification to those of ordinary skill in the art.

Example 1

Coal-based pitch (20% after carbonization) was coated on crystalline earth graphite aggregate particles having an average particle diameter of 1.7 μm obtained by separation or pulverization by a jet mill method, and then 5 parts by weight of _{P 2} O _{5 compared to the pitch precursor was dissolved} After adding to water, the mixture was stirred at room temperature for 1 hour and then dried. An anode active material precursor having a spherical shape is prepared by inputting the dried composite particle precursor into a spheroidization assembly equipment. The obtained powder was heat-treated at 1200° C. for 1 hour at a temperature increase rate of 5° C./min in an argon atmosphere, and then furnace cooled to prepare an anode active material having an average particle diameter of 15 μm.

Example 2

A negative active material was prepared in the same manner as in Example 1, except that water in which 10 parts by weight of _{P 2} O ₅ was dissolved compared to the pitch precursor was used.

Example 3

A negative active material was prepared in the same manner as in Example 1, except that water in which 15 parts by weight of _{P 2} O ₅ was dissolved compared to the pitch precursor was used.

Example 4

An anode active material was prepared in the same manner as in Example 1, except that water in which 20 parts by weight of _{P 2} O ₅ was dissolved compared to the pitch precursor was used.

Comparative Example 1

An anode active material was prepared in the same manner as in Examples 1 to 4, except that water not containing _{P 2} O _{5 was used.}

Evaluation 1: Surface composition analysis

For each of the negative active materials prepared in Examples 1 to 4 and Comparative Example 1, the binding energy between the elements was measured using an X-ray photoelectron spectroscopy (XPS), and the results are shown in FIGS. 4 to 8 .

4 to 7, in the case of Examples 1 to 4, a peak related to P is observed in the energy range of 125 eV to 140 eV, and _{the binding of P=O, C 3} P=O, C ₃ -P, and CP is confirmed. And as a result of measuring through the ratio of the area of the peaks appearing at each binding energy, it was found that as the _{amount of P 2} O ₅ increased, the CP bond increased and the C ₃ P=O and C ₃ -P bonds slightly decreased.

Meanwhile, in the case of Comparative Example 1, as shown in FIG. 8, no peak was observed in the energy range of 125 eV to 140 eV. From this, it can be confirmed that the carbon material surrounding the surface of the crystalline earth graphite agglomerate particle of the negative electrode active material is effectively modified _{through the P 2} O _{5 addition process.}

Evaluation 2: Characterization of reversible capacity

Each of the negative active materials prepared in Examples 1 to 4 and Comparative Example 1 was mixed with CMC/SBR (carboxymethyl cellulose/styrene-butadiene rubber) in distilled water in a weight ratio of 96:4 to prepare a negative electrode slurry. The negative electrode slurry was coated on a copper foil, dried and compressed to prepare each negative electrode.

An electrode assembly was prepared by stacking the negative electrode and lithium metal as a positive electrode with a separator, Celgard, between the negative electrode and the positive electrode. _{Thereafter, an electrolyte solution in which 1M LiPF 6} was dissolved in a mixed solvent of diethyl carbonate (DEC) and ethylene carbonate (EC) (DEC:EC = 1:1) was added to prepare a coin-type half cell as a test cell.

The reversible capacity according to Examples 1 to 4 and Comparative Example 1 was measured using the prepared test cell in the following manner, and the results are shown in Table 1 below.

Charging was performed in CC/CV mode at a current density of 0.1C rate range, and the termination voltage was maintained at 0.005V, and discharging was performed in CC mode at a current density of 0.2C rate, and the termination voltage was maintained at 1.5V.

[Table 1]

From Table 1, it can be seen that the reversible capacity increases as the amount of _{P 2} O _{5 added increases.}

Evaluation 3: Characterization of high-rate charging

The high-rate charge/discharge characteristics according to Examples 1 to 4 and Comparative Example 1 were evaluated using the prepared test cell in the following manner, and the results are shown in Table 2 below.

Charging was performed in CC/CV mode at a current density of 0.2C to 5C rate, and the final voltage was maintained at 0.005V, and discharging was performed in CC mode at a current density of 0.2C rate, and the final voltage was maintained at 1.5V.

[Table 2]

From Table 2, it can be seen that Examples 1 to 4 have superior high-rate charging characteristics compared to Comparative Example 1. In addition, it can be seen that the high-rate charging characteristic is improved as the amount of _{P 2} O _{5 added increases.}

Evaluation 4: Characterization of High Rate Discharge

The high-rate discharge characteristics according to Examples 1 to 4 and Comparative Example 1 were evaluated using the prepared test cell in the following manner, and the results are shown in Table 3 below.

Charging was performed in CC/CV mode at a current density of 0.2C rate range, and the final voltage was maintained at 0.005V, and discharging was performed in CC mode at a given current density in the 0.2C to 10C rate range, and the final voltage was maintained at 0.005V. did.

[Table 3]

From Table 3, it can be seen that Examples 1 to 4 have superior high-rate discharge characteristics compared to Comparative Example 1. In addition, it can be seen that the high rate discharge characteristics are improved as the amount of _{P 2} O _{5 added increases.}

Evaluation 5: Cycle Characterization

The cycle characteristics according to Examples 1 to 4 and Comparative Example 1 were evaluated in the following manner using the prepared test cell, and the discharge capacity was measured after 100 cycles compared to the discharge capacity in the first cycle, and the result was It is shown in Table 4 below.

During charging, it was performed in CC/CV mode in the range of current density of 0.1C rate, and the termination voltage was maintained at 0.005V, and during discharging, discharging was completed in CC mode at a current density of 0.2C rate to 1.5V. Thereafter, only the current density was changed to 0.5 C, and charging and discharging were performed under the same conditions as above.

[Table 4]

From Table 4, it can be confirmed that the case of Examples 1 to 4 has excellent cycle characteristics compared to the case of Comparative Example 1. In addition, it can be seen that the cycle characteristics are improved as the amount of _{P 2} O _{5 added increases.}

Evaluation 6: Swelling Characterization

Using the prepared test cell, the electrode thickness was measured in the charged state during the cycle according to Example 4 and Comparative Example 1 in the following manner. The results are shown in Table 5.

[Table 5]

From Table 5, it can be confirmed that the case of Example 4 has superior swelling properties compared to the case of Comparative Example 1.

Evaluation 7: High-Temperature Cycle Characterization

The cycle characteristics according to Example 4 and Comparative Example 1 were evaluated in the following manner using the prepared test cell, and capacity maintenance and Coulombic efficiency were measured according to the high-temperature cycle, and the respective results are shown in FIG. 9 and It is shown in Figure 10.

During charging, it was performed in CC/CV mode in the range of current density of 0.1C rate, and the termination voltage was maintained at 0.005V. During discharging, discharging was completed at room temperature to 1.5V in CC mode at a current density of 0.2C rate. After that, only the current density was changed to 0.5 C, and charging and discharging were performed at 45° C. under the same conditions as above.

9 and 10, it can be confirmed that the case of Example 4 has superior capacity retention characteristics and charge/discharge coulombic efficiency characteristics according to a high-temperature cycle compared to the case of Comparative Example 1.

From this, the negative active material particles according to one embodiment are produced _{through the P 2} O ₅ addition process, the lithium storage capacity increases as the carbon material surrounding the surface of the crystalline earth graphite aggregate particles of the negative electrode active material is effectively reformed, and the High-output characteristics are improved because lithium moves easily through the passage made of the carbon material inside the negative electrode active material, and the carbon material is chemically stable to suppress side reactions with the electrolyte, thereby suppressing swelling, long lifespan and charging at high temperatures. It can be seen that the discharge characteristics are improved.

The present invention is not limited to the above embodiments, but can be manufactured in various different forms, and those of ordinary skill in the art to which the present invention pertains can take other specific forms without changing the technical spirit or essential features of the present invention. It will be understood that it can be implemented as Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive.

1, 2: negative active material
11: crystalline earth graphite aggregate particles
12: coating layer
13: nano-sized pores
14: carbon coating layer
21: crystalline earth graphite fine particles

Claims (14)

(i) crystalline earth graphite aggregate particles having an average particle diameter of 1 to 5 μm; and
(ii) a coating layer formed on the surface of the crystalline earth graphite agglomerate particles, the coating layer comprising at least one element selected from P, B, O, F and N, and at least one carbon material selected from amorphous carbon and semi-crystalline carbon Including composite particles comprising;
The negative active material for a lithium secondary battery, characterized in that the composite particles have a structure assembled by bonding by the carbon material. According to claim 1,
The crystalline earth graphite agglomerate particle is a negative active material for a lithium secondary battery, characterized in that obtained by separating or pulverizing the earth graphite agglomerate mass. According to claim 1,
A negative active material for a lithium secondary battery, characterized in that a chemical bond is formed between one or more elements selected from P, B, O, F and N included in the coating layer of the composite particles and two or more elements selected from carbon constituting the carbon material . According to claim 1,
The coating layer is an anode active material for a lithium secondary battery, characterized in that it further comprises nano-sized pores. According to claim 1,
The carbon material is an anode active material for a lithium secondary battery, characterized in that it is included in an amount of 5 to 50 parts by weight based on 100 parts by weight of the anode active material. According to claim 1,
The coating layer is an anode active material for a lithium secondary battery, characterized in that it comprises 0.0001 to 50% by weight of one or more elements selected from P, B, O, F and N. According to claim 1,
A negative active material for a lithium secondary battery, characterized in that the average particle diameter is 3 to 40 ㎛. According to claim 1,
A negative active material for a lithium secondary battery, characterized in that it further comprises a carbon coating layer made of at least one carbon material selected from amorphous carbon and semi-crystalline carbon. 9. The method of claim 8,
A negative active material for a lithium secondary battery, characterized in that the thickness of the carbon coating layer is 0.01 to 5 ㎛. Separating or pulverizing the earthy graphite agglomerate mass to prepare crystalline earthy graphite agglomerate particles having an average particle diameter of 1 to 5 μm;
coating the surface of the crystalline earth graphite agglomerate particle with at least one carbon precursor selected from an amorphous carbon precursor and a semi-crystalline carbon precursor;
The crystalline earthy graphite agglomerate particles coated with the carbon precursor, H ₃ PO ₄ , H ₃ BO ₃ , P ₂ O ₅ , (NH ₄ ) ₂ S ₂ O ₈ , H ₂ O ₂ , NH ₄ F, and NH ₄ preparing a composite particle precursor by oxidation treatment in an aqueous solution containing at least one oxidizing agent selected from PF _{6 ;}
preparing an anode active material precursor by assembling the composite particle precursor; and
heat-treating the anode active material precursor;
A method of manufacturing a negative active material for a lithium secondary battery comprising a. 11. The method of claim 10,
The amorphous carbon precursor is citric acid, stearic acid, sucrose, phenol resin, naphthalene resin, polyvinyl alcohol resin, furfuryl alcohol resin, polyacrylonitrile resin, polyamide resin, furan resin , is selected from the group consisting of a cellulose resin, a styrene resin, a polyimide resin, an epoxy resin, and a vinyl chloride resin,
The semi-crystalline carbon precursor is selected from the group consisting of coal-based pitch, petroleum-based pitch, polyvinyl chloride, anthracene oil, FCC decant oil, mesophase pitch, tar or low molecular weight heavy oil. manufacturing method. 11. The method of claim 10,
The heat treatment is a method of manufacturing a negative active material for a lithium secondary battery, characterized in that performed at 700 to 3200 ℃. 11. The method of claim 10,
The heat treatment is a method of manufacturing a negative active material for a lithium secondary battery, characterized in that it is performed in a nitrogen gas, argon gas and hydrogen gas, or a mixture of two or more kinds of gas atmosphere or vacuum atmosphere selected from the group consisting of hydrogen gas. A lithium secondary battery comprising the negative active material according to any one of claims 1 to 9.

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