KR20130037150A - Negative active material for rechargeable lithium battery, method of preparing the same, and rechargeable lithium battery including the same - Google Patents

Abstract

PURPOSE: A negative electrode active material for lithium secondary batteries is provided to improve charging and discharging efficiency, to have high capacity, and to have excellent power performance, and to have high energy density. CONSTITUTION: A negative electrode active material(1) for lithium secondary batteries comprises a core particle(2) which includes at least one selected from amorphous hard carbon and amorphous semi-crystalline soft carbon; and a shell layer located on the surface of the core particle. The shell layer includes amorphous graphite(3), and amorphous or semicrystalline carbon(4). The average particle diameter of the core particle is 2-20 micron. A lithium secondary battery includes the negative electrode, which includes the negative electrode active material, positive electrode, and electrolyte.

Description

TECHNICAL FIELD The present invention relates to a negative active material for a lithium secondary battery, a method for producing the negative active material, and a lithium secondary battery including the same. [0001] The present invention relates to a negative active material for a lithium secondary battery,

The present invention provides a negative electrode active material for a lithium secondary battery, a method for producing the same, and a lithium secondary battery comprising the same.

As technology development and demand for mobile devices are increasing, the demand for secondary batteries as energy sources is rapidly increasing. Lithium secondary batteries, which have high energy density and voltage and long cycle life and low self-discharge rate, are commercialized Widely used.

Carbon materials are mainly used as negative electrode active materials of such lithium secondary batteries, and carbon materials capable of inserting and desorbing lithium are largely classified into crystalline graphite and amorphous carbon materials. The amorphous carbon material is further subdivided into amorphous hard carbon and semicrystalline soft carbon.

The amorphous hard carbon is carbon that maintains low crystalline properties even when heat treated at a graphitization temperature or higher, and the semicrystalline soft carbon is carbon which is changed to crystalline graphite when heat treated at a graphitization temperature or higher. Unlike crystalline graphite, in which the insertion and desorption of lithium is limited only to the edge surface and thus the charge / discharge output characteristics are lowered, the amorphous hard carbon and the semi-crystalline soft carbon are omnidirectional due to structural defects and micropores developed on the carbon surface and inside. In particular, since lithium insertion and desorption are performed, more excellent output characteristics can be exhibited. Due to such excellent output characteristics, it is recently used or planned as a negative electrode material of medium and large lithium secondary batteries such as energy storage devices and electric vehicles.

However, the amorphous hard carbon and the semi-crystalline soft carbon are made of amorphous particles having irregular shapes and sharp edges because of lower discharge specificity and coulombic efficiency than crystalline graphite and generally undergoing grinding after carbonization. Such a shape may cause pinholes in the separator during battery manufacture by applying to the negative electrode, which may cause deterioration of battery stability, and due to the amorphous particle shape, there is a disadvantage in that energy density per unit volume is lowered in electrode design.

One embodiment of the present invention is to provide a negative electrode active material for lithium secondary batteries having improved charging and discharging efficiency, high capacity, excellent output characteristics, and high energy density per unit volume during electrode production.

Another embodiment of the present invention is to provide a method of manufacturing the negative electrode active material for the lithium secondary battery.

Another embodiment of the present invention is to provide a lithium secondary battery including the negative electrode active material for the lithium secondary battery.

One embodiment of the present invention is a core particle comprising at least one selected from amorphous amorphous hard carbon and amorphous semi-crystalline soft carbon; And a shell layer disposed on the surface of the core particles, wherein the shell layer provides earth-based graphite having an average particle diameter of 0.1 to 5 μm, and an anode active material for a lithium secondary battery including amorphous or semicrystalline carbon.

The average particle diameter of the core particles may be 2 to 20 ㎛.

The core particles may be included in 5 to 98% by weight based on the total amount of the negative electrode active material.

The soil graphite may be included in an amount of 1 to 90% by weight based on the total amount of the negative electrode active material.

The amorphous or semicrystalline carbon may be sucrose, methylene diphenyl diisocyanate, polyurethane, Phenolic resin, naphthalene resin, polyvinyl alcohol, polyvinyl chloride, furfuryl alcohol, polyacrylonitrile, polyamide, furan resin, cellulose, styrene, polyimide, epoxy resin, vinyl chloride resin, coal pitch, It may be formed from a carbon precursor including at least one selected from petroleum pitch, mesophase pitch, tar and low molecular weight heavy oil.

The amorphous or semicrystalline carbon may be included in an amount of 1 to 94% by weight based on the total amount of the negative electrode active material.

The shell layer may further include at least one fibrous carbon selected from polyacrylonitrile-based carbon fibers, rayon-based carbon fibers, pitch-based carbon fibers, carbon nanotubes, and vapor-grown carbon fibers (VGCF).

The shell layer may have a thickness of 0.2 μm to 10 μm.

The negative active material may further include a coating layer disposed on the surface of the shell layer and including amorphous or semi-crystalline carbon, and the thickness of the coating layer may be 0.01 to 5 μm.

The average particle diameter of the negative electrode active material may be 2 to 40 ㎛.

Another embodiment of the present invention provides a surface of a core particle including at least one selected from amorphous amorphous hard carbon and amorphous semicrystalline soft carbon, earth graphite having an average particle diameter of 0.1 to 5 μm, and amorphous or quasi Coating with a mixture of crystalline carbon precursors to obtain composite particles; And heat treating the composite particles. The present invention also provides a method for manufacturing a negative electrode active material for a lithium secondary battery.

The mixture may further include at least one fibrous carbon selected from polyacrylonitrile-based carbon fibers, rayon-based carbon fibers, pitch-based carbon fibers, carbon nanotubes, and vapor-grown carbon fibers (VGCF).

The method of manufacturing the negative active material may further include coating the surface of the composite particle with the amorphous or semicrystalline carbon precursor.

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

The heat treatment may be performed at a temperature of 500 to 2500 ℃.

Another embodiment of the present invention is a negative electrode comprising the negative electrode active material; anode; And it provides a lithium secondary battery comprising an electrolyte solution.

Other details of the embodiments of the present invention are included in the following detailed description.

It is possible to implement a lithium secondary battery having improved charge and discharge efficiency, high capacity, and excellent output characteristics.

1 is a schematic cross-sectional view of a negative electrode active material according to an embodiment.
2 is a schematic cross-sectional view of a negative electrode active material according to another embodiment.
3 to 12 are scanning electron microscope (SEM) photographs of negative electrode active materials according to Examples 1 to 10, respectively.
13 to 16 are scanning electron microscope (SEM) photographs of negative electrode active materials according to Comparative Examples 1 to 4, respectively.
17 is a scanning electron microscope (SEM) photograph of the earthy graphite used in Examples 9 and 10.
18 is a scanning electron microscope (SEM) photograph of the impression graphite used in Comparative Examples 3 and 4.
19 is a particle size distribution diagram of earthy graphite used in Examples 1 to 8. FIG.
20 is a particle size distribution diagram of earthy graphite used in Examples 9 and 10. FIG.
21 is a particle size distribution diagram of impression graphite used in Comparative Examples 3 and 4. FIG.
22 shows X-ray diffraction patterns of the negative active materials according to Examples 1 and 2 and Comparative Example 1. FIG.
23 shows X-ray diffraction patterns of the negative active materials according to Examples 4 to 6 and Comparative Example 2. FIG.
24 shows X-ray diffraction patterns of the negative active materials according to Example 9 and Comparative Example 3. FIG.
25 shows X-ray diffraction patterns of the negative active materials according to Example 10 and Comparative Example 4. FIG.

Hereinafter, embodiments of the present invention will be described in detail. However, this is presented as an example, by which the present invention is not limited and the present invention is defined only by the scope of the claims to be described later.

The negative electrode active material according to one embodiment may be described with reference to FIG. 1.

1 is a schematic cross-sectional view of a negative electrode active material according to an embodiment.

Referring to FIG. 1, the negative electrode active material 1 according to the embodiment may be formed of a core layer 2 and a shell layer located on the surface of the core particle 2. Specifically, the shell layer may have a shape surrounding the core particles 2.

The core particle 2 may include at least one selected from amorphous amorphous hard carbon and amorphous semicrystalline soft carbon.

The shell layer may comprise earthy graphite 3 and amorphous or semicrystalline carbon 4. The amorphous or quasicrystalline carbon 4 may bond the earth graphite 3 to each other and may coat the surface of the earth graphite 3. In addition, the amorphous or semi-crystalline carbon 4 may coat the surface of the core particle 2 while bonding the earth graphite 3 and the core particle 2 to each other.

Amorphous amorphous hard carbon or amorphous semicrystalline soft carbon used as the core particles has good output characteristics of the battery when used as a negative electrode material, but has low initial efficiency, low storage capacity of lithium ions, and sharp edges. As a result, the packing density is low and the separator may be damaged.

It shows high output capacity due to high capacity and fine particles of earth graphite, but when the electrode is manufactured by fine earth graphite itself, the initial efficiency is low due to the high specific surface area, and excessive binder is consumed when the electrode is manufactured. There is a problem that the process efficiency is lowered.

According to one embodiment, by using the amorphous amorphous hard carbon or the amorphous semi-crystalline soft carbon as a core particle and having a structure of coating the surface of the core particle with the earth graphite and the amorphous or semi-crystalline carbon, The lithium storage capacity is large, the initial efficiency is improved, and lithium ions are easily moved during charging and discharging, so the output characteristics are excellent and the charging and discharging efficiency is excellent. In addition, the problems caused by the amorphous shape of the amorphous amorphous hard carbon or the amorphous semicrystalline soft carbon also cause the surface of the amorphous amorphous hard carbon or the amorphous semicrystalline soft carbon to have the soil graphite and the amorphous and semicrystalline particles. This can be solved by forming a shell layer composed of carbon.

The average particle diameter of the core particles may be 2 to 20 μm, specifically 3 to 10 μm. When the core particles have an average particle diameter in the above range, the coating for forming the shell layer with the earthy graphite is well made, and thus can be usefully applied to a lithium secondary battery having high capacity and excellent output characteristics.

The amorphous hard carbon is sucrose (sucrose), phenol resin (phenol resin), furan resin (furan resin), furfuryl alcohol (furfuryl alcohol), polyacrylonitrile, polyimide (polyimide), epoxy resin (epoxy resin), methylene diphenyl diisocyanate, polyurethane, cellulose, styrene, citric acid, stearic acid, polyvinylidene fluoride, carboxymethyl cellulose (CMC), hydroxypropyl Selected from cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated ethylene-propylene-diene monomer (EPDM), starch, glucose, gelatin and sugars At least one carbonaceous material formed by carbonization may be used.

The amorphous semicrystalline soft carbon may be formed by carbonizing at least one carbonaceous material selected from polyvinyl alcohol, polyvinyl chloride, coal-based pitch, petroleum-based pitch, mesophase pitch, and low molecular weight heavy oil.

The core particles may be included in 5 to 98% by weight, specifically, 20 to 90% by weight based on the total amount of the negative electrode active material. When the core particles are included in the above range, the shell layer may be formed at an appropriate ratio around the core particles, thereby exhibiting excellent output characteristics and improving capacity.

The soil graphite may have an average particle diameter of 0.1 to 5 µm, specifically 0.1 to 3 µm, and more specifically 0.1 to 2 µm. When the earth graphite having an average particle diameter in the above range is used, the diffusion rate of lithium ions during charging and discharging is shortened, so that the high rate characteristics are improved as the diffusion is easy inside. That is, since the insertion and desorption reaction of lithium ions occur rapidly between the graphite layers of the earth graphite, it may exhibit excellent output characteristics and improve capacity.

In the case of earth graphite constituting the shell layer, it is excellent in crystallinity, inexpensive, and easily atomized. In general, crystalline graphite is divided into artificial graphite and natural graphite, the artificial graphite is manufactured by heat treatment at a high temperature of 2800 ℃ or more bar price is very expensive, the natural graphite is made of flake-type and earth graphite Are distinguished. In the case of the impression graphite, it is very difficult to atomize in the state of maintaining the crystallinity, while in the case of the earthy graphite is very easy to atomize in the state of maintaining the crystallinity can be usefully used as the graphite constituting the shell layer.

In more detail, the earth graphite is a kind of natural graphite and may also be referred to as microcrystalline graphite. The earthy graphite is in a state in which fine particles having an average particle diameter of about 1 μm or less are agglomerated, and the aggregated graphite mass has an average particle diameter of about 0.1 to 50 μm, which is a state in which a plurality of flaky wide plate particles are overlapped and are about 100 to 200 μm. It is distinguished from impression graphite having an average particle diameter of. When the ground graphite is pulverized by a milling process, the term "pulverization" is used, but the structure is close to the concept of "separating" the aggregated state, while graphite crystallinity is maintained after pulverization. In the case of pulverization, the pulverized plate particles are separated from each other in that crystallinity may be lowered during the crushing process.

Tohsang the graphite may be a non-(I ₁₃₆₀ / I ₁₅₈₀₎ of 0.1 to 0.5 of the peak intensity (I ₁₃₆₀₎ of 1360㎝ ^-1 to a peak intensity (I ₁₅₈₀₎ of one 1580㎝ ^-1 in Raman spectrum, specifically May be 0.1 to 0.3. If the ratio of the peak intensity (I ₁₃₆₀ / I ₁₅₈₀₎ the ratio of Tohsang graphite peak strength of which can be seen the surface crystallinity, the through (I ₁₃₆₀ / I ₁₅₈₀₎ is within the above range is maintained crystallinity as excellent initial Excellent charging and discharging efficiency

The soil graphite may be included in an amount of 1 to 90% by weight, specifically, 5 to 70% by weight based on the total amount of the negative electrode active material. When the earthy graphite is included in the above range, the earthy graphite may form a shell layer at an appropriate ratio around the core particles, thereby exhibiting excellent output characteristics and improving capacity.

The amorphous or semicrystalline carbon may be sucrose, methylene diphenyl diisocyanate, polyurethane, Phenolic resin, naphthalene resin, polyvinyl alcohol, polyvinyl chloride, furfuryl alcohol, polyacrylonitrile, polyamide, furan resin, cellulose, styrene, polyimide, epoxy resin, vinyl chloride resin, coal pitch, One formed from a carbon precursor comprising at least one selected from petroleum pitch, mesophase pitch, tar and low molecular weight heavy oil can be used.

The amorphous or semicrystalline carbon may be included in an amount of 1 to 94% by weight, specifically, 15 to 75% by weight, based on the total amount of the negative electrode active material. When the amorphous or quasi-crystalline carbon is included in the above range, it is possible to implement a high capacity lithium secondary battery by sufficiently bonding the earth graphites.

The shell layer may further include fibrous carbon in addition to the earth graphite and the amorphous or semicrystalline carbon.

 The fibrous carbon may be at least one selected from polyacrylonitrile-based carbon fibers, rayon-based carbon fibers, pitch-based carbon fibers, carbon nanotubes, and vapor-grown carbon fibers (VGCF).

The fibrous carbon may have a diameter of 1 to 1000 nm and a length of 0.5 to 20 um.

The thickness of the shell layer may be 0.2 to 10 μm, specifically 1 to 7 μm. When the shell layer is formed to a thickness within the above range, the earth graphite is present at an appropriate ratio, thereby realizing a lithium secondary battery having excellent output characteristics and high capacity.

The negative electrode active material 1 may be manufactured by the following method.

The surface of the core particles may be coated with a mixture of the earthy graphite and an amorphous or quasi-crystalline carbon precursor to obtain composite particles, and the composite particles may be heat-treated to prepare the negative electrode active material.

The soil graphite may use fine particles having an average particle diameter of 0.1 to 5 μm, which may be obtained by grinding or separating the soil graphite.

The grinding may be performed by a conventional milling process. Specifically, the milling process may include a ball mill, an attention mill, a vibration mill, a disk mill, a jet mill, a rotor mill, and the like. Can be carried out using a milling apparatus.

The grinding speed (rpm) and grinding time for the grinding may be appropriately adjusted by those skilled in the art according to the type of milling apparatus, the content of the material to be treated and the like.

The amorphous or semi-crystalline carbon precursor is sucrose (sucrose), methylene diphenyl diisocyanate, polyurethane, Phenolic resin, naphthalene resin, polyvinyl alcohol, polyvinyl chloride, furfuryl alcohol, polyacrylonitrile, polyamide, furan resin, cellulose, styrene, polyimide, epoxy resin, vinyl chloride resin, coal pitch, At least one selected from petroleum pitch, mesophase pitch, tar and low molecular weight heavy oil can be used.

The mixture coated on the surface of the core particles may further include fibrous carbon. The content of the fibrous carbon is as described above.

The coating method for obtaining the composite particles may use a mechanochemical method such as a blade, a mechano-fusion, a hybridizer, which can give a shear force, and also Spray drying or emulsion may be used, but is not limited thereto.

For example, a rotor blade mill (Fritsch), a hybridizer (Nara), a mechano-fusion (mechano-), which is a dry coating equipment, may be used for the core particles, the earth graphite, and the amorphous or semi-crystalline carbon precursor. fusion, Hosokawa) or the like, to impart a strong mechanical shear force at a temperature above the softening point of the amorphous or semicrystalline carbon precursor and coated with the mixture of the earthy graphite and the amorphous or semicrystalline carbon precursor on the surface of the amorphous or semicrystalline core particle. The composite particle in which the shell layer was formed is manufactured. The amorphous or semi-crystalline carbon precursor carbonization heat treatment step of the composite particles is carried out.

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

In addition, the heat treatment may be carried out at a temperature of 500 to 2500 ℃, specifically may be carried out at a temperature of 700 to 2000 ℃. When the heat treatment is performed in the above temperature range, fine pores of the amorphous amorphous hard carbon are maintained, and the semicrystalline state of the amorphous semicrystalline soft carbon is maintained, so that the capacity and output characteristics are excellent, and the amorphous or semicrystalline carbon precursor Fully carbonization can occur.

The negative electrode active material according to another embodiment may be described with reference to FIG. 2.

2 is a schematic cross-sectional view of a negative electrode active material according to another embodiment.

Referring to FIG. 2, the negative electrode active material 6 may include a core particle 2, a shell layer positioned on the surface of the core particle 2, and a coating layer 5 positioned on the surface of the shell layer. Specifically, the shell layer may be in the form of surrounding the core particles (2), the coating layer 5 may be in the form of surrounding the shell layer.

The shell layer may comprise earthy graphite 3 and amorphous or semicrystalline carbon 4.

Details of the core particles and the shell layer are as described above.

The coating layer 5 may include amorphous or semicrystalline carbon. The amorphous or semicrystalline carbon is as described above.

When the earth graphite is coated with the amorphous or semicrystalline carbon and coated on the surface of the core particles, the capacity is improved when a shell layer is formed, and the graphite edge surface when the amorphous or semicrystalline carbon is further coated on the shell layer. The initial charge and discharge efficiency may be improved by reducing the exposure of and reducing the exposure of the core particles surface of amorphous amorphous hard carbon or amorphous semicrystalline soft carbon.

The thickness of the coating layer may be 0.01 to 5 ㎛, specifically 0.1 to 3 ㎛. When the thickness of the coating layer is formed in the above range, the exposure of the graphite edge surface is reduced, and the exposure of the core particle surface of amorphous amorphous hard carbon or amorphous semicrystalline soft carbon is reduced, thereby increasing initial charge and discharge efficiency, and outputting It is possible to implement a lithium secondary battery having excellent characteristics and improved charge / discharge cycle characteristics with high capacity.

The negative electrode active material 6 may be manufactured by the following method.

After coating the surface of the core particles with a mixture of the earth graphite and an amorphous or semi-crystalline carbon precursor to obtain a composite particle, after coating the surface of the composite particles with the amorphous or semi-crystalline carbon precursor, the coated composite The negative electrode active material may be prepared by heat treating the particles.

The soil graphite and the amorphous or semicrystalline carbon precursor are as described above, and the atmosphere and temperature of the heat treatment are also as described above.

The shape of the negative active material according to the exemplary embodiment illustrated through FIGS. 1 and 2 may be spherical, but is not limited thereto.

The average particle diameter of the negative electrode active material may be 2 to 40 μm, specifically 5 to 30 μm. When the negative electrode active material has an average particle diameter in the above range, excellent electrode manufacturing process efficiency and electrode density can be obtained.

According to another embodiment of the present invention, there is provided a lithium secondary battery including a cathode including a cathode active material capable of intercalating and deintercalating lithium ions, a cathode including the anode active material, and an electrolyte solution .

The lithium secondary battery may be classified into a lithium ion battery, a lithium ion polymer battery, and a lithium polymer battery according to the type of separator and electrolyte used, and may be classified into a cylindrical shape, a square shape, a coin type, a pouch type, etc., Depending on the size, it can be divided into bulk type and thin film type. The structure and the manufacturing method of these cells are well known in the art, and 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 a negative electrode active material layer, and then coating it on a negative electrode current collector such as copper.

The binder may be polyvinyl alcohol, carboxymethyl cellulose / styrene-butadiene rubber, hydroxypropylene cellulose, diacetylene cellulose, polyvinylchloride, polyvinylpyrrolidone, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene or Polypropylene, polyacrylic acid, etc. can be used 1 type or in mixture of 1 or more types, It is not limited to this.

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

The conductive material is not particularly limited as long as it has conductivity without causing chemical changes to the battery. Specifically, graphite such as natural graphite and artificial graphite; Carbon blacks such as acetylene black, Ketjen black, channel black, furnace black, lamp black and summer black; Conductive fibers such as carbon fiber and metal fiber; 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; Conductive materials, such as a polyphenylene derivative, can be used 1 type or in mixture of 1 or more types.

The positive electrode includes a positive electrode active material, and as the positive electrode active material, a compound capable of reversible intercalation and deintercalation of lithium (lithiated intercalation compound) may be used. Specifically, the layered compound which is at least one selected from cobalt, manganese and nickel and at least one of a composite oxide of lithium; Or a spinel compound of at least one selected from titanium, vanadium, and manganese and at least one of a complex oxide of lithium; Or an olivine mixture of at least one selected from iron, cobalt, manganese and nickel and at least one of complex oxides with lithium and phosphorus; Or a vanadium compound can be used.

Like the negative electrode, the positive electrode may also be prepared by mixing the positive electrode active material, a binder, and optionally a conductive material 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 solution 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, chloroborane lithium, lower aliphatic carboxylate lithium, lithium 4-phenylborate, and imide.

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, But are not limited to, ricifrcr, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, An ether, a methyl ethyl pyrophosphate, an ethyl propionate, a methyl ethyl ketone derivative, a methyl ethyl ketone derivative, a methyl ethyl ketone derivative, Etc. may be used.

Examples of the organic solid electrolytic solution include a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene and an ionic dissociation group And the like can be used.

The inorganic solid electrolyte may be 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 − Nitrides, halides, sulfates, and the like of Li, such as LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ , may be used.

For the purpose of improving the charge and discharge characteristics, flame retardancy and the like, for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexa phosphate 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 can be added.

In addition, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further included to impart nonflammability, and carbon dioxide gas may be further included to improve high temperature storage characteristics.

The separator may exist between the positive electrode and the negative electrode according to the type of the lithium secondary battery. As the separator, an insulating thin film having high ion permeability and mechanical strength may be used. The pore diameter of the separator may be 0.01 to 10 mu m and the thickness may be 5 to 300 mu m.

Specifically, the separator may include an olefin polymer such as polypropylene having chemical resistance and hydrophobicity; Sheets or nonwovens made of glass fibers, polyethylene, and the like can 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, preferred examples and comparative examples of the present invention are described. However, the following embodiments are merely preferred embodiments of the present invention, and the present invention is not limited to the following embodiments.

Example  One

50% by weight of soft carbon having an average particle diameter of 11 µm, 30% by weight of earthy graphite having an average particle diameter of 1.7 µm, and 20% by weight of petroleum pitch at a rotor blade mill (seconds to minutes at 5000 to 20000 rpm) Rotated) to obtain a composite particle powder having a surface of the soft carbon coated with a mixture of the earthy graphite and the petroleum pitch. The obtained composite particle powder was heat-treated at 1200 ° C. for 1 hour at an elevated temperature rate of 5 ° C./min in argon atmosphere, and then cooled to prepare a negative electrode active material having an average particle diameter of 13.9 μm.

Example  2

30% by weight of soft carbon with an average particle diameter of 11 μm, 50% by weight of earthy graphite with an average particle diameter of 1.7 μm, and 20% by weight of petroleum pitch are rotated at a rotor mill (several minutes to minutes at 5000 to 20000 rpm). ), To obtain a composite particle powder having a surface of the soft carbon coated with a mixture of the earthy graphite and the petroleum pitch. The obtained composite particle powder was heat-treated at 1200 ° C. for 1 hour at an elevated temperature rate of 5 ° C./min in argon atmosphere, and then cooled to prepare a negative electrode active material having an average particle diameter of 17.2 μm.

Example  3

50% by weight of soft carbon with an average particle diameter of 6 μm, 30% by weight of earthy graphite with an average particle diameter of 1.7 μm, and 20% by weight of petroleum pitch are rotated at a rotor mill (several minutes to minutes at 5000 to 20000 rpm). ), To obtain a composite particle powder having a surface of the soft carbon coated with a mixture of the earthy graphite and the petroleum pitch. The obtained composite particle powder was heat-treated at 1200 ° C. for 1 hour at an elevated temperature rate of 5 ° C./min in argon atmosphere, and then cooled to prepare a negative electrode active material having an average particle diameter of 15.6 μm.

Example  4

70% by weight of hard carbon with an average particle diameter of 9 μm, 10% by weight of earthy graphite with an average particle diameter of 1.7 μm, and 20% by weight of petroleum pitch are rotated at a rotor mill (several minutes to minutes at 5000 to 20000 rpm). ), To obtain a composite particle powder having a surface of the hard carbon coated with a mixture of the earthy graphite and the petroleum pitch. The obtained composite particle powder was heat-treated at 1200 ° C. for 1 hour at an elevated temperature rate of 5 ° C./min in argon atmosphere, and then cooled to prepare a negative electrode active material having an average particle diameter of 13.5 μm.

Example  5

50% by weight of hard carbon with an average particle diameter of 9 μm, 30% by weight of earthy graphite with an average particle diameter of 1.7 μm, and 20% by weight of petroleum pitch are rotated at a rotor mill (several minutes to minutes at 5000 to 20000 rpm). ), To obtain a composite particle powder having a surface of the hard carbon coated with a mixture of the earthy graphite and the petroleum pitch. The obtained composite particle powder was heat-treated at 1200 ° C. for 1 hour at an elevated temperature rate of 5 ° C./min in an argon atmosphere, and then cooled to prepare a negative electrode active material having an average particle diameter of 14.8 μm.

Example  6

30% by weight of hard carbon with an average particle diameter of 9 μm, 50% by weight of earthy graphite with an average particle diameter of 1.7 μm, and 20% by weight of petroleum pitch are rotated at a rotor mill (several minutes to minutes at 5000 to 20000 rpm). ), To obtain a composite particle powder having a surface of the hard carbon coated with a mixture of the earthy graphite and the petroleum pitch. The obtained composite particle powder was heat-treated at 1200 ° C. for 1 hour at an elevated temperature rate of 5 ° C./min in argon atmosphere, and then cooled to prepare a negative electrode active material having an average particle diameter of 18.3 μm.

Example  7

40 wt% of hard carbon having an average particle diameter of 9 μm, 30 wt% of earthy graphite having an average particle diameter of 1.7 μm, 10 wt% of vapor-grown carbon fiber (VGCF) having a diameter of 160 nm and a length of 10 μm, and 20 wt% of petroleum pitch % Was added to a rotor mill (rotated at 5000 to 20000 rpm in a few seconds to several minutes) to obtain a composite particle powder in which the surface of the hard carbon was coated with a mixture of the earthy graphite and the petroleum pitch. The obtained composite particle powder was heat-treated at 1200 ° C. for 1 hour at an elevated temperature rate of 5 ° C./min in argon atmosphere, and then cooled to prepare a negative electrode active material having an average particle diameter of 15.3 μm.

Example  8

30% by weight of hard carbon with an average particle diameter of 9 μm, 50% by weight of earthy graphite with an average particle diameter of 1.7 μm, and 20% by weight of petroleum pitch are rotated at a rotor mill (several minutes to minutes at 5000 to 20000 rpm). ), To obtain a first composite particle powder having a surface of the hard carbon coated with a mixture of the earth graphite and the petroleum pitch. 90 wt% of the obtained first composite particle powder and 10 wt% of petroleum pitch were introduced into the mixer to obtain a second composite grain powder having the surface of the first composite grain powder coated with the petroleum pitch. The obtained second composite particle powder was heat-treated at 1200 ° C. for 1 hour at an elevated temperature rate of 5 ° C./min in argon atmosphere, and then cooled to prepare a negative electrode active material having an average particle diameter of 18.8 μm.

Example  9

50% by weight of soft carbon with an average particle diameter of 11 µm, 30% by weight of earthy graphite with an average particle diameter of 3.5 µm, and 20% by weight of petroleum pitch at a rotor blade mill (several minutes to minutes at 5000 to 20000 rpm) Rotated) to obtain a composite particle powder having a surface of the soft carbon coated with a mixture of the earthy graphite and the petroleum pitch. The obtained composite particle powder was heat-treated at 1200 ° C. for 1 hour at an elevated temperature rate of 5 ° C./min in argon atmosphere, and then cooled to prepare a negative electrode active material having an average particle diameter of 13.5 μm.

Example  10

50% by weight of hard carbon with an average particle diameter of 9 µm, 30% by weight of earthy graphite with an average particle diameter of 3.5 µm, and 20% by weight of petroleum pitch at a rotor blade mill (several minutes to minutes at 5000 to 20000 rpm) Rotated) to obtain a composite particle powder having a surface of the hard carbon coated with a mixture of the earthy graphite and the petroleum pitch. The obtained composite particle powder was heat-treated at 1200 ° C. for 1 hour at an elevated temperature rate of 5 ° C./min in argon atmosphere, and then cooled to prepare a negative electrode active material having an average particle diameter of 14.2 μm.

Comparative example  One

Soft carbon having an average particle diameter of 11 μm was used as the negative electrode active material.

Comparative example  2

Hard carbon having an average particle diameter of 9 μm was used as a negative electrode active material.

Comparative example  3

50% by weight of soft carbon with an average particle diameter of 11 μm, 30% by weight of impression graphite with an average particle diameter of 3.2 μm, and 20% by weight of a petroleum pitch at a rotor blade mill (seconds to minutes at 5000 to 20000 rpm) Rotated) to obtain a composite particle powder having a surface of the soft carbon coated with a mixture of the impression graphite and the petroleum pitch. The obtained composite particle powder was heat-treated at 1200 ° C. for 1 hour at an elevated temperature rate of 5 ° C./min in an argon atmosphere, and then cooled to prepare a negative electrode active material having an average particle diameter of 13.4 μm.

Comparative example  4

50% by weight of hard carbon having an average particle diameter of 9 µm, 30% by weight of impression graphite having an average particle diameter of 3.2 µm, and 20% by weight of a petroleum pitch at a rotor blade mill (seconds to minutes at 5000 to 20000 rpm) Rotated) to obtain a composite particle powder having a surface of the soft carbon coated with a mixture of the earthy graphite and the petroleum pitch. The obtained composite particle powder was heat-treated at 1200 ° C. for 1 hour at an elevated temperature rate of 5 ° C./min in argon atmosphere, and then cooled to prepare a negative electrode active material having an average particle diameter of 14.3 μm.

Evaluation 1: Scanning Electron Microscope of Anode Active Material SEM Photo analysis

Scanning electron microscope (SEM) photographs of the negative active materials prepared in Examples 1 to 10 and Comparative Examples 1 and 4 are shown in FIGS. 3 to 16.

3 to 12 are scanning electron microscope (SEM) pictures of the negative electrode active materials according to Examples 1 to 10, and FIGS. 13 to 16 are scanning electron microscope (SEM) pictures of the negative electrode active materials according to Comparative Examples 1 to 4, respectively.

Referring to Figures 3 to 12, Examples 1 to 10 have a core-shell structure coated with earthy graphite and a semicrystalline carbon such as petroleum pitch on the surface of core particles such as hard carbon or soft carbon. You can check it. On the other hand, in Comparative Examples 1 and 2 it can be seen that only the core particles are present without coating, respectively, in Comparative Examples 3 and 4 on the surface of the core particles, such as hard carbon or soft carbon, impression graphite and petroleum-based It can be seen that the semi-crystalline carbon such as pitch has a core-shell structure coated. In addition, the negative electrode active materials of Examples 1 to 10 and Comparative Examples 3 and 4 having the core-shell structure have a spherical particle shape, whereas the negative electrode active materials of Comparative Examples 1 and 2 having only the core particles have sharp edge shapes. It can be seen that. In addition, it can be seen that the surface of the core particles is uniformly coated as the content of the soil graphite increases.

In addition, scanning electron microscope (SEM) images of the earth graphite used in Examples 9 and 10 and the impression graphite used in Comparative Examples 3 and 4 are shown in FIGS. 17 and 18.

17 is a scanning electron microscope (SEM) photograph of the earth graphite used in Examples 9 and 10, and FIG. 18 is a scanning electron microscope (SEM) photograph of the impression graphite used in Comparative Examples 3 and 4. FIG.

Referring to FIGS. 17 and 18, the earth-to-graphite used in Examples 9 and 10 was confirmed that the fine particles having an average particle diameter of about 1 μm or less aggregated to form a graphite mass having a size of about 3 μm. It can be seen that the impression graphite used in Figure 4 was formed by stacking several sheets of broad plate-like particles of several micrometers to form graphite having a size of about 3 micrometers.

Evaluation 2: Soil  Particle Size Distribution Analysis of Graphite

The particle size distribution of the earth graphite used in Examples 1 to 10 was measured by laser diffraction scattering particle size distribution measurement method, and the results are shown in FIGS. 19 and 20.

FIG. 19 is a particle size distribution diagram of soil graphite used in Examples 1 to 8, and FIG. 20 is a particle size distribution diagram of soil graphite used in Examples 9 and 10. FIG.

Referring to FIGS. 19 and 20, it can be seen that in Example 1 to 10, soil graphite having an average particle size range of 0.1 to 5 μm was used.

The particle size distribution of the impression graphite used in Comparative Examples 3 and 4 was measured by a laser diffraction scattering particle size distribution measurement method, and the results are shown in FIG. 21.

21 is a particle size distribution diagram of impression graphite used in Comparative Examples 3 and 4. FIG.

Referring to FIG. 21, it can be seen that in Comparative Examples 3 and 4, an impression graphite having an average particle size range of 0.1 to 5 μm was used.

Evaluation 3: particle size distribution analysis of the negative electrode active material

The particle size distributions of the negative electrode active materials prepared in Examples 1 to 10 and Comparative Examples 1 to 4 were measured by laser diffraction scattering particle size distribution measurement method, and the results are shown in Table 1 below.

Example Comparative example One 2 3 4 5 6 7 8 9 10 One 2 3 4 Average particle size of the negative electrode active material (㎛) 13.9 17.2 15.6 13.5 14.8 18.3 15.3 18.8 13.5 14.2 11 9 13.4 14.3

Referring to Table 1, in comparison with the case of the negative electrode active material of Comparative Examples 1 and 2 consisting of only soft carbon or hard carbon, Examples 1 to 10 and Comparative Examples 3 and 4 having a structure coated with the surface of the core particles It can be seen that the average particle diameter of the negative electrode active material increases.

Evaluation 4: X-Ray of Anode Active Material diffraction  Pattern analysis

Crystallinity of the negative active materials prepared in Examples 1 and 2 and Comparative Example 1 was measured using an X-ray diffraction pattern analyzer, and the results are shown in FIG. 22.

22 shows X-ray diffraction patterns of the negative active materials according to Examples 1 and 2 and Comparative Example 1. FIG.

Referring to FIG. 22, it can be seen that in Examples 1 and 2, the intensity of the peak (002), which is the main peak of graphite, is increased and the half width thereof is decreased, compared with that of Comparative Example 1. It can be seen that this is due to the structure coated with earthy graphite having excellent crystallinity as compared with the case of only semicrystalline soft carbon. In addition, in the case of Example 2 with more content of earth graphite, it can be seen that the intensity of the peak is increased and the half width is reduced compared to Example 1.

In addition, the crystallinity of the negative active material prepared in Examples 4 to 6 and Comparative Example 2 was measured using an X-ray diffraction pattern analyzer, the results are shown in FIG.

23 shows X-ray diffraction patterns of the negative active materials according to Examples 4 to 6 and Comparative Example 2. FIG.

Referring to FIG. 23, it can be seen that in the case of Examples 4 to 6, the intensity of the peak (002), which is the main peak of graphite, is increased and the half width thereof is decreased, compared with the case of Comparative Example 2. It can be seen that this is due to the structure coated with earthy graphite having excellent crystallinity as compared with the case of only amorphous hard carbon. In addition, in Examples 4 to 6, it can be seen that as the content of the earth graphite increases, the intensity of the peak increases and the half width decreases.

In addition, the crystallinity of the negative electrode active material prepared in Example 9 and Comparative Example 3 was measured using an X-ray diffraction pattern analyzer, the results are shown in FIG.

24 shows X-ray diffraction patterns of the negative active materials according to Example 9 and Comparative Example 3. FIG.

Referring to FIG. 24, it can be seen that the negative active materials prepared in Example 9 and Comparative Example 3 showed the (002) peak, which is the main peak of graphite, which is obtained in Example 9 and Comparative Example 3 of earth graphite. This is due to the presence in the shell layer of the prepared negative electrode active material.

In addition, the crystallinity of the negative active material prepared in Example 10 and Comparative Example 4 was measured using an X-ray diffraction pattern analyzer, the results are shown in FIG.

25 shows X-ray diffraction patterns of the negative active materials according to Example 10 and Comparative Example 4. FIG.

Referring to FIG. 25, it can be seen that the negative active materials prepared in Example 10 and Comparative Example 4 showed the (002) peak, which is the main peak of graphite, which is the example of earthy graphite and impression graphite in Example 10 and Comparative Example 4. This is due to the presence in the shell layer of the prepared negative electrode active material.

(Manufacture of Test Cell)

Each negative electrode active material prepared in Examples 1 to 10 and Comparative Examples 1 to 4 was mixed with CMC / SBR (carboxymethyl cellulose / styrene-butadiene rubber) in distilled water at a weight ratio of 95: 5 to prepare a negative electrode slurry. Each negative electrode slurry was coated on a copper foil, followed by drying and pressing to prepare each negative electrode.

Using the negative electrode and lithium metal as positive electrodes, a cell guard, which is a separation membrane, was laminated between the negative electrode and the positive electrode to produce an electrode assembly. Thereafter, an electrolytic solution in which 1 M of 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 test cell.

Evaluation 5: initial Charging and discharging  Characterization

Using the prepared test cells, the initial charge and discharge characteristics according to Examples 1 to 10 and Comparative Examples 1 and 2 were evaluated in the following manner, and the results are shown in Table 2 below.

Charging was carried out in CC / CV mode with a current density of 0.2 mA / cm ² , the termination voltage was maintained at 0.01 V, and charging was terminated when the current was 0.02 mA. Discharge was performed in CC mode with a current density of 0.2 mA / cm ² , and the termination voltage was maintained at 2V.

Initial Reversible Capacity (mAh / g) Initial Efficiency (%) Example 1 281 89.4 Example 2 308 90.1 Example 3 287 89.4 Example 4 260 87.3 Example 5 276 88.7 Example 6 304 89.2 Example 7 282 88.5 Example 8 299 90.6 Example 9 283 89.3 Example 10 277 88.8 Comparative Example 1 231 83.5 Comparative Example 2 225 80.8

Through Table 2, in the case of Examples 1 to 10 using the negative electrode active material having a core-shell structure compared to the case of Comparative Examples 1 and 2 in which the shell layer does not exist, the initial reversible capacity and the initial efficiency are confirmed to increase. Can be.

From this, in the case of using the negative electrode active material of the core-shell structure according to one embodiment, the electrode exhibits a shape close to a spherical shape during manufacturing of the electrode and thus has high process efficiency. In addition, a high capacity can be achieved by the coated earth graphite, and by reducing the exposure of the porous surface of hard carbon or soft carbon as well as the edge surface of the earth graphite by amorphous or semi-crystalline carbon, a lithium secondary battery having excellent initial efficiency can be realized. have.

Evaluation 6: High Rate Charging Characterization

Using the prepared test cell was evaluated the high rate charging characteristics according to Examples 1 to 10 and Comparative Examples 1 to 4 in the following manner, the results are shown in Table 3 below.

Charging was carried out in CC mode at a current density of 50 to 1300 mA / g and the termination voltage was maintained at 0.01 V, discharge was conducted in CC mode at a current density of 50 mA / g and termination voltage was maintained at 2V.

Charging capacity (mAh / g) Current density
50 mA / g Current density
300 mA / g Current density
800 mA / g Current density
1300 mA / g Example 1 258 199 137 107 Example 2 281 227 135 96 Example 3 280 223 165 128 Example 4 226 180 137 115 Example 5 254 198 139 117 Example 6 280 232 155 119 Example 7 269 217 147 118 Example 8 274 222 144 107 Example 9 260 182 120 84 Example 10 253 178 112 80 Comparative Example 1 189 147 94 66 Comparative Example 2 184 146 94 79 Comparative Example 3 257 150 78 55 Comparative Example 4 251 168 89 64

Through Table 3, in the case of Examples 1 to 10 using the negative electrode active material having a core-shell structure it can be confirmed that the high rate charging characteristics are excellent compared to the case of Comparative Examples 1 and 2 where the shell layer does not exist.

In addition, in the case of Examples 9 and 10 using the negative electrode active material in which the earth phase graphite is present in the shell layer, it can be confirmed that the high rate charging characteristics are superior to those of Comparative Examples 3 and 4 using the negative electrode active material in which the impression graphite is present in the shell layer. have.

From this, high charge capacity can be exhibited by the earth graphite having a short diffusion distance of lithium and high charge capacity during high rate charging, thereby realizing a lithium secondary battery having excellent high rate characteristics.

The present invention is not limited to the above embodiments, but may be manufactured in various forms, and a person skilled in the art to which the present invention pertains has another specific form without changing the technical spirit or essential features of the present invention. It will be appreciated that the present invention may be practiced as. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

1, 6: negative electrode active material
2: core particle
3: soil graphite
4: amorphous or semicrystalline carbon
5: Coating layer

Claims (17)

A core particle comprising at least one selected from amorphous amorphous hard carbon and amorphous semicrystalline soft carbon; And
Shell layer located on the surface of the core particles
Including,
The shell layer comprises earthy graphite having an average particle diameter of 0.1 to 5 μm, and amorphous or semicrystalline carbon.
Negative electrode active material for lithium secondary battery.
The method of claim 1,
The average particle diameter of the core particles is 2 to 20 ㎛ negative electrode active material for a secondary battery.
The method of claim 1,
The core particle is a lithium secondary battery negative electrode active material is contained in 5 to 98% by weight based on the total amount of the negative electrode active material.
The method of claim 1,
The earth graphite is included in 1 to 90% by weight based on the total amount of the negative electrode active material negative electrode active material for a lithium secondary battery.
The method of claim 1,
The amorphous or semicrystalline carbon may be sucrose, methylene diphenyl diisocyanate, polyurethane, Phenolic resin, naphthalene resin, polyvinyl alcohol, polyvinyl chloride, furfuryl alcohol, polyacrylonitrile, polyamide, furan resin, cellulose, styrene, polyimide, epoxy resin, vinyl chloride resin, coal pitch, A negative electrode active material for a lithium secondary battery formed from a carbon precursor comprising at least one selected from petroleum pitch, mesophase pitch, tar and low molecular weight heavy oil.
The method of claim 1,
The amorphous or semi-crystalline carbon is 1 to 94% by weight based on the total amount of the negative electrode active material negative electrode active material for lithium secondary batteries.
The method of claim 1,
The shell layer further includes at least one fibrous carbon selected from polyacrylonitrile-based carbon fibers, rayon-based carbon fibers, pitch-based carbon fibers, carbon nanotubes, and vapor-grown carbon fibers (VGCF). .
The method of claim 1,
The shell layer has a thickness of about 0.2 μm to 10 μm.
The method of claim 1,
The negative active material is
Coating layer located on the surface of the shell layer and containing amorphous or semicrystalline carbon
A negative electrode active material for a lithium secondary battery further comprising.
10. The method of claim 9,
The thickness of the coating layer is a negative active material for a lithium secondary battery of 0.01 to 5 ㎛.
The method of claim 1,
An average particle diameter of the negative electrode active material is a negative active material for a lithium secondary battery of 2 to 40 ㎛.
The surface of the core particle comprising at least one selected from amorphous amorphous hard carbon and amorphous semicrystalline soft carbon is coated with a mixture of earthy graphite having an average particle diameter of 0.1 to 5 μm, and an amorphous or semicrystalline carbon precursor. Obtaining a composite particle; And
Heat treating the composite particles
Method for producing a negative electrode active material for a lithium secondary battery comprising a.
The method of claim 12,
The mixture of the negative electrode active material for a lithium secondary battery further comprises at least one fibrous carbon selected from polyacrylonitrile-based carbon fibers, rayon-based carbon fibers, pitch-based carbon fibers, carbon nanotubes and vapor-grown carbon fibers (VGCF) Manufacturing method.
The method of claim 12,
Method for producing the negative electrode active material
Coating the surface of the composite particle with the amorphous or semicrystalline carbon precursor
The manufacturing method of the negative electrode active material for lithium secondary batteries containing further.
The method of claim 12,
The heat treatment is a method for producing a negative electrode active material for a lithium secondary battery is carried out under an atmosphere containing nitrogen, argon, hydrogen or a mixed gas thereof, or under a vacuum.
The method of claim 12,
The heat treatment is a method of manufacturing a negative electrode active material for a lithium secondary battery is carried out at a temperature of 500 to 2500 ℃.
A negative electrode comprising the negative electrode active material of any one of claims 1 to 11;
anode; And
Electrolyte
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