KR20170130843A - Negative electrode active material for lithium secondary battery and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a cathodic active material for a lithium secondary battery, including defect graphite of which ID/IG band ratio value is 0.2-1.0. The defect graphite includes: 5-20% by volume of a rhombohedral structure in a crystal structure; and at least one selected from a functional group comprising a carboxyl group, a hydroxyl group, an ester group, an aldehyde group, a ketone group, and an ether group. When TPD-MS (temperature-rising and secession) is conducted to the cathodic active material, measured amounts of H2O and CO2 account for 180-300 parts by weight and 80-250 parts by weight respectively in proportion to 100 parts by weight of H2O and CO2. The cathodic active material includes a rhombohedral structure in a crystal structure, and also, includes defect graphite including a functional group in the surface. As such, the present invention is capable of improving low temperature performance of a lithium secondary battery and improving initial efficiency by having excellent durability to propylene carbonate, thereby being usefully applied to the manufacture of a lithium secondary battery.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a negative electrode active material for a lithium secondary battery, and a lithium secondary battery including the negative active material. 2. Description of the Related Art [0002]

The present invention relates to a negative electrode active material for a lithium secondary battery and a lithium secondary battery comprising the same. More particularly, the present invention relates to a lithium secondary battery including a defect graphite having a defective region in a crystal structure, And a lithium secondary battery including the negative active material.

As technology development and demand for mobile devices have increased, there has been a rapid increase in demand for secondary batteries as energy sources. Among such secondary batteries, lithium secondary batteries, which exhibit high energy density and operating potential, long cycle life, Batteries have been commercialized and widely used.

The lithium secondary battery generally comprises a cathode including a cathode active material, a cathode including a cathode active material, a separator, and an electrolyte, and is charged and discharged by intercalation-decalation of lithium ions. The lithium secondary battery has a high energy density, a large electromotive force, and a high capacity, so it is applied to various fields.

Metal oxides such as LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ and LiNiO ₂ are used as the positive electrode active material constituting the positive electrode of the lithium secondary battery. Examples of the negative electrode active material composing the negative electrode include metal lithium, graphite A carbon based meterial such as activated carbon or silicon oxide (SiO _x ) is used. Among the above-mentioned negative electrode active materials, metal lithium is mainly used. However, as charging and discharging cycles are progressed, lithium atoms are grown on the surface of metal lithium, thereby damaging the separator and damaging the battery. Recently, carbonaceous materials are mainly used.

In the currently commercialized lithium secondary battery, graphite carbon materials exhibiting high capacity and long life characteristics are mainly used as negative electrode active materials. However, when the propylene carbonate (PC) is mixed with an electrolyte to improve the low-temperature performance of the electrolyte, the propylene carbonate is destroyed by exfoliation of each layer constituting the interlayer structure of the graphite carbonaceous material .

Therefore, in order to solve the problem of peeling and destroying the interlayer structure of the graphite carbonaceous material of propylene carbonate as described above, in the case of graphite having a small surface defect or functional group content, propylene carbonate is not used, When there is a necessity to use it unavoidably, a method of passing through a high temperature activation process is used.

However, when using an ethylene / ethylene terephthalate (EC) based ternary / three-component electrolyte without the addition of propylene carbonate as the electrolyte, there is a limitation of the use temperature due to the high melting point of the ethylene carbonate, And a significant deterioration in battery performance. When the battery is subjected to a high-temperature activation process, there is a problem in that it takes time and cost to manufacture the secondary battery.

Therefore, there is a need to develop a new technique capable of reducing side reactions between propylene carbonate and graphite carbonaceous material.

SUMMARY OF THE INVENTION The present invention provides a negative active material for a lithium secondary battery capable of solving the problem caused by side reactions between an anode active material and propylene carbonate.

It is another object of the present invention to provide a negative electrode for a lithium secondary battery including the negative electrode active material for a lithium secondary battery and a lithium secondary battery including the same.

In order to solve the above problems,

And a defect graphite having an I _D / I _G band ratio of from 0.2 to 1.0, the negative active material comprising:

Wherein the defect graphite comprises 5 to 20% by volume of a rhombohedral structure in the crystal structure, and the surface of the defect graphite has a rhombohedral structure in which the functional graphite has a surface functional group selected from the group consisting of carboxyl group, hydroxyl group, ester group, aldehyde group, Comprising at least one selected,

The amount of H ₂ O and CO ₂ measured when TPD-MS (temperature elevation desorption method) was performed on the negative electrode active material for lithium secondary battery was such that the amounts of H ₂ O and CO ₂ measured for natural graphite were 100 weight And 180 parts by weight to 300 parts by weight and 80 parts by weight to 250 parts by weight, respectively, of the negative active material for a lithium secondary battery.

In order to solve the above-mentioned other problems,

A negative electrode for a lithium secondary battery including the negative active material for a lithium secondary battery, and a lithium secondary battery including the negative electrode for the lithium secondary battery.

Since the negative electrode active material for a lithium secondary battery of the present invention contains a rhombohedral structure in the crystal structure and contains defective graphite containing a functional group on its surface, it exhibits excellent durability against propylene carbonate, The low temperature performance of the battery can be improved and the initial efficiency can be improved, so that the lithium secondary battery can be usefully used.

Hereinafter, the present invention will be described in detail in order to facilitate understanding of the present invention.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

The negative electrode active material for a lithium secondary battery according to the present invention is a negative active material for a lithium secondary battery including a defect graphite having an I _D / I _G band ratio value of 0.2 to 1.0. The defect graphite has a rhombohedral structure within the crystal structure, And 5 to 20% by volume of the structure, and the surface of the negative electrode includes at least one selected from the group consisting of a carboxyl group, a hydroxyl group, an ester group, an aldehyde group, a ketone group and an ether group as a functional group, When the amounts of H ₂ O and CO ₂ measured when the TPD-MS (temperature elevation desorption method) were performed on the active material were 100 parts by weight each of H ₂ O and CO ₂ measured for natural graphite, respectively 180 to 300 parts by weight, and 80 to 250 parts by weight.

The defect graphite has a maximum peak intensity of the D band at 1360 + - 50 cm < ^-1 > relative to the maximum peak intensity (IG) of the G band at 1580 + ^- 50 cm < ^-1 > obtained by Raman spectroscopy using a laser with a wavelength of 532 nm I _D ) may be 0.2 to 1.0, and more preferably 0.2 to 0.5, in terms of the average value of the ratio (I _D / I _G ).

The peak present in the region around the wavenumber 1580 cm ^-1 in the Raman spectrum of the defect graphite is referred to as a G band, which indicates a carbon crystal having no structural defects as a peak indicating sp ² bonds in the defect graphite. On the other hand, the peak present in the region near the wavenumber 1360 cm ^-1 in the Raman spectrum is referred to as a D band, which is a peak indicating sp ³ bond in the defect graphite, in which the atomic bond formed by the sp ² bond is broken to form an sp ³ bond . Since the D band increases when disorder or defect existing in the defect graphite is generated, the D band maximum peak intensity I _D to the maximum peak intensity I G of the G band The ratio (I _D / I _G ) can be calculated to quantitatively evaluate the degree of disorder or defect generation.

In the present invention, the G band of the Raman spectrum for the defect graphite may be a peak present in a wavenumber range of 1580 ± 50 cm ^-1 , and the D band may be a peak present in a wavenumber range of 1360 ± 50 cm ^-1 . The wave number range for the G band and D band corresponds to a range that can be shifted according to the laser light source used in the Raman analysis method. The Raman value used in the present invention is not particularly limited, but can be measured at a laser wavelength of 532 nm using a DXR Raman Microscope (Thermo Electron Scientific Instruments LLC).

The defect graphite may include a rhombohedral structure in a crystal structure of a graphite structure, a defect region in addition to the Rombo-hydral structure, and a hexagonal system structure.

The graphite structure is a thermodynamically stable graphite crystal structure in which each carbon atom of graphite is composed of a planar layer having three nearest neighboring carbons at a distance of 142 pm and the carbon atoms are arranged in regular hexagonal rings . In addition, the planar layer may be formed by a method in which the other half of the carbon atoms is above or below the middle of the six-atom ring above or below the next layer, while half of the carbon atoms are directly above or below another carbon atom. pm. [Literature (Chemical Society, May 20, 2001, Sehwa, Graphite Structure)]. This can be expressed in ABAB form in the order of lamination of hexagonal graphite. In the specification of the present invention, the hexagonal structure refers to this laminated structure.

In the specification of the present invention, the defective region is a region in which a part of carbon atoms constituting the planar layer is lost in one layer or a plurality of layers of the planar layer constituting the crystal structure of the graphite, Or a hole or the like.

The rhombohydral structure (rhombohedral structure) in which the defect graphite is contained in the crystal structure may be 5 vol.% To 20 vol.%, Specifically 7 vol.% To 15 vol.%, And the lapping order may be represented by ABCABC. The ratio of the Rombo-hydral structure and the hexagonal structure can be determined by analyzing the peak and intensity ratio of X-ray diffraction.

The defect graphite contained in the negative electrode active material for a lithium secondary battery according to the present invention contains 5 vol% to 20 vol% of the Romboh hydral structure within the crystal volume. Therefore, the defect graphite has a stacking fault due to lithium insertion (I.e., a phenomenon of widening of the layers adjacent to the layer) is not formed, thereby making it difficult for the solvent to coextensive with the layered structure, thereby making the layered structure more durable, thereby enhancing the durability against propylene carbonate.

When the Romboh hydral structure is less than 5 vol%, it is difficult to expect improvement in durability against propylene carbonate due to the inclusion of the defect graphite. Thus, the lithium secondary battery including the negative active material for a lithium secondary battery including the defect graphite There is a problem in that the initial efficiency is deteriorated and the reversible capacity is decreased. When the Romboh hydral structure exceeds 20 vol%, the fraction of the Romboh hydral structure in the defect graphite becomes excessively high, There is a problem that the reaction can be suppressed.

By applying external pressure in a direction parallel to each of the planar layers constituting the graphite structure in the graphite structure of the defect graphite through pulverization or the like, a part of the planar layer is separated from the original position And may be formed by layer slipping.

Carbon atoms constituting one planar layer in the graphite structure of the defect graphite are connected by SP bonds to form strong bonds, but attraction due to wander walls force acts between the planar layers, so that relatively small external pressure The slip between the planar layers can be induced.

Therefore, the external pressure applied by the milling does not affect SP bonding of the carbon atoms forming one planar layer in the graphite structure of the crystalline carbon, and may be stronger than the van der Waals force between the planar layers.

The pulverization may be carried out by a conventional milling process and may be carried out by a conventional milling process which may be carried out by a conventional milling machine such as a friction mill, an attrition mill, a disk mill, a vibrating mill, a stirring mill, a sand mill, a ball mill, Or by one or more means selected from the group consisting of:

The defect graphite includes at least one functional group selected from the group consisting of a carboxyl group, a hydroxyl group, an ester group, an aldehyde group, a ketone group, and an ether group as a functional group on the surface, Or both. The amount of H ₂ O measured when TPD-MS (temperature elevation desorption) is performed on the anode active material for lithium secondary batteries may be 180 to 300 parts by weight, specifically 200 to 250 parts by weight, and CO ₂ may be 80 to 250 parts by weight, specifically 120 to 180 parts by weight. In this case, the relation that is when the amount of H ₂ O and CO ₂ measured when the amount of H ₂ O and CO ₂ have been subjected to TPD-MS for the natural graphite hayeoteul each 100 parts by weight.

When the amount of the H ₂ O measured is less than 180 parts by weight when the TPD-MS (temperature elevation desorption method) is performed on the anode active material for the lithium secondary battery, when propylene carbonate (PC) is mixed with the electrolyte, There is a problem of graphite exfoliation and output performance deterioration due to the propylene carbonate. When the amount exceeds 300 parts by weight, initial efficiency and life performance may be deteriorated. When the amount of CO ₂ is less than 80 parts by weight, there is a problem that the propylene carbonate is mixed with the electrolytic solution and the graphite peeling and the output performance deteriorate due to the use of the propylene carbonate. When the amount exceeds 250 parts by weight, May occur.

H ₂ O and CO ₂ measured when the TPD-MS is performed may be derived from a functional group included in the surface of the defect graphite, the functional group may be located in a defect region of the defect graphite, In the formation of the region, a nonporous electron pair may be formed by bonding with oxygen in the atmosphere.

The total amount of the surface functional groups contained in the defect graphite may be 0.5% to 5%, and more specifically, 1 to 3%, and more specifically, 1.5 to 2.5% of the surface elements of the defect graphite.

When the total amount of the surface functional groups is 0.5% or more, the effect of effectively exfoliating between layers due to propylene carbonate can be effectively exerted. When the total amount of the surface functional groups is 5% or less, irreversible There is no problem that the capacity is excessively increased.

The amount of the functional group can be measured by using TPD-MS (Temperature Programmed Desorption and Decomposition-Mass Spectroscopy). The temperature elevation desorption method is a method of analyzing the chemical properties of a sample by measuring a trace gas component generated and desorbed when the sample is heated, an amount of generated gas, and a generated temperature. A mass spectrometer (MS) can be used for analyzing an inorganic gas having a sufficient detection sensitivity in a low mass region of m / z = 2 to 200. For example, the total amount of the functional groups and the surface functional groups contained in the defect graphite may be H ₂ O (m / z = 18), CO ₂ (m / z) generated when the temperature is raised from room temperature to 1,000 using a TPD- = 44), and other gas components can be analyzed by a mass spectrometer and then obtained therefrom.

The defect graphite may have an average particle diameter (D ₅₀ ) of 5 to 40 μm, specifically, a particle diameter of 10 to 30 μm, and more specifically, a particle diameter of 10 to 20 μm.

When the average particle size of the defect graphite is 5 탆 or more, the particle size is too small to prevent problems related to safety, and when the electrode has an appropriate volume per volume and the average particle diameter is 40 탆 or less, The slurry can be suitably coated to a uniform thickness upon coating the slurry to form the electrode.

In the present invention, the average particle size (D ₅₀ ) of the defect graphite can be defined as a particle size on the basis of 50% of the particle size distribution. The average particle diameter is not particularly limited, but can be measured using, for example, a laser diffraction method or a scanning electron microscope (SEM) photograph. In the laser diffraction method, it is generally possible to measure the particle diameter of about several millimeters from the submicron region, and high reproducibility and high degradability can be obtained.

The defect graphite may have a specific surface area of 2.5 m ² / g to 4.0 m ² / g, and more specifically, a specific surface area of 3.0 m ² / g to 3.5 m ² / g.

When the specific surface area of the defect graphite is less than 2.5 m ² / g, when the propylene carbonate is mixed with the electrolytic solution, the graphite peeling and the output performance deteriorate due to the propylene carbonate. When the specific surface area exceeds 4.0 m ² / g, And degradation of lifetime performance may occur.

Meanwhile, the negative electrode active material for a lithium secondary battery may further include a second graphite having an I _D / I _G band ratio of less than 0.2, specifically 0.15 to less than 0.2 in Raman spectroscopy.

The negative electrode active material for a lithium secondary battery may include the defective graphite and the second graphite in a weight ratio of 30:70 to 90:10, and more specifically 60:40 to 70:30 by weight.

If the amount of the second graphite exceeds 70 parts by weight with respect to 30 parts by weight of the defect graphite, the graphite peeling due to the propylene carbonate and the deterioration of output performance may occur when the propylene carbonate is mixed with the electrolyte solution. When the amount of the second graphite is less than 10 parts by weight based on the weight, the high temperature storage performance may be insufficient as compared with conventional graphite.

Therefore, when the defect graphite and the second graphite are contained in the weight ratio of 30:70 to 90:10, deterioration of the high temperature storage performance can be prevented and the graphite layer separation by the electrolyte solution propylene carbonate can be prevented.

The average particle diameter (D ₅₀₎ of the second graphite may be similar to the average particle diameter (D ₅₀₎ of the defective graphite. For example, the second graphite may have an average particle diameter (D ₅₀ ) of 5 to 40 μm, specifically, a particle diameter of 10 to 30 μm, and more specifically, a particle diameter of 10 to 20 μm.

The defect graphite and the second graphite may be graphite carbonaceous materials having a graphite structure, and may be low-crystalline carbon or high-crystallinity carbon. Examples of the low crystalline carbon include soft carbon and hard carbon. Examples of the highly crystalline carbon include natural graphite, kish graphite, pyrolytic carbon, High temperature sintered carbon such as mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitch derived cokes. In addition, specifically, the second graphite may be natural graphite or artificial graphite.

As described above, the negative electrode active material for a lithium secondary battery including the defect graphite and the second graphite may have a specific surface area of 2.0 m ² / g to 3.0 m ² / g, specifically 2.3 m ² / g to 2.6 m ² / g. ≪ / RTI >

If the specific surface area of the negative electrode active material for a lithium secondary battery including the defect graphite and the second graphite is less than 2.0 m ² / g, when the propylene carbonate is mixed with the electrolyte, the graphite peeling due to the propylene carbonate and the deterioration of the output performance may occur If it exceeds 3.0 m ² / g, initial efficiency decrease and lifetime performance deterioration may occur.

The negative electrode active material for a lithium secondary battery may further include another negative electrode active material. Examples of the negative electrode active material other than the negative electrode active material for the lithium secondary battery include a carbon material such as an amorphous carbon or a carbon composite material, lithium metal, silicon or tin, which is commonly used lithium ions can be occluded and released.

The negative electrode active material for a lithium secondary battery can be used for a negative electrode for a lithium secondary battery. Accordingly, the present invention provides a negative electrode for a lithium secondary battery comprising the negative active material for the lithium secondary battery.

The negative electrode for a lithium secondary battery can be used as a negative electrode of a lithium secondary battery. Accordingly, the present invention provides a lithium secondary battery including the negative electrode for the lithium secondary battery.

The lithium secondary battery may include a positive electrode, a negative electrode for the lithium secondary battery, and a separator interposed between the positive electrode and the negative electrode.

The anode may be prepared by a conventional method known in the art. For example, a slurry may be prepared by mixing and stirring a solvent, a binder, a conductive material, and a dispersant as necessary in a cathode active material, and then coating (coating) the mixture on a current collector of a metal material, have.

The current collector of the metal material is a metal having high conductivity and is a metal which can easily adhere to the slurry of the cathode active material and is not particularly limited as long as it has high conductivity without causing chemical change in the battery in the voltage range of the battery But not limited to, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, or the like. In addition, fine unevenness may be formed on the surface of the current collector to increase the adhesive force of the positive electrode active material. The current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric, and may have a thickness of 3 to 500 μm.

The cathode active material is selected from the group consisting of lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), Li [Ni _x Co _y Mn _z Mv] O ₂ Y, z? 0.5, 0? V? 0.1 and x + y + z + v = 1), Li (Li _a M _{ba -b 'M' b ') O} 2 - c a c ( wherein, 0≤a≤0.2, 0.6≤b≤1, 0≤b'≤0.2, 0≤c≤0.2 and; M is Mn and, Ni M, at least one selected from the group consisting of Al, Mg and B, A is at least one selected from the group consisting of P, F, S, and N), or a compound substituted with one or more transition metals; Lithium manganese oxides such as Li _{1 + y} Mn _{2 - y} O ₄ (where y is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ and LiMnO ₂ ; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ and Cu ₂ V ₂ O ₇ ; Formula _{LiNi 1 - y M y O 2} ( where, the M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, y = 0.01 - 0.3 Im) Ni site type lithium nickel oxide which is represented by; Formula _{LiMn 2-y M y O 2} ( where, M = Co, Ni, Fe , Cr, and Zn, or Ta, y = 0.01 - 0.1 Im) or Li ₂ Mn ₃ MO ₈ (where, M = Fe, Co, Ni, Cu, or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with an alkaline earth metal ion; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ , and the like. However, the present invention is not limited to these.

Examples of the solvent for forming the anode include organic solvents such as NMP (N-methylpyrrolidone), DMF (dimethylformamide), acetone, and dimethylacetamide, and water. These solvents may be used alone or in combination of two or more Can be mixed and used. The amount of the solvent used is sufficient to dissolve and disperse the cathode active material, the binder and the conductive material in consideration of the coating thickness of the slurry and the production yield.

Examples of the binder include polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, Polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM) Sulfonated EPDM, styrene butadiene rubber (SBR), fluorine rubber, poly acrylic acid, and polymers in which hydrogen is substituted with Li, Na, or Ca, or Various kinds of binder polymers such as various copolymers can be used.

The conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, and examples thereof include graphite such as natural graphite and artificial graphite; Carbon black such as acetylene black, Ketjen black, channel black, panes black, lamp black, and thermal black; Conductive fibers such as carbon fiber and metal fiber; Conductive tubes such as carbon nanotubes; Metal powders such as fluorocarbon, aluminum and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used. The conductive material may be used in an amount of 1 wt% to 20 wt% based on the total weight of the positive electrode slurry.

The dispersing agent may be an aqueous dispersing agent or an organic dispersing agent such as N-methyl-2-pyrrolidone.

The negative electrode may be prepared by a conventional method known in the art. For example, the negative electrode active material, the additives such as the binder and the conductive material are mixed and stirred to prepare the negative electrode active material slurry, And then compressed.

Examples of the solvent for forming the negative electrode include organic solvents such as NMP (N-methylpyrrolidone), DMF (dimethylformamide), acetone, and dimethylacetamide, and water. These solvents may be used alone or in combination of two or more Can be mixed and used. The amount of the solvent to be used is sufficient to dissolve and disperse the negative electrode active material, the binder and the conductive material in consideration of the coating thickness of the slurry and the production yield.

The binder may be used to bind the negative electrode active material particles to maintain the formed body. Any conventional binder used in preparing the slurry for the negative electrode active material is not particularly limited, and examples thereof include polyvinyl alcohol, carboxymethyl cellulose, Polyvinylidene fluoride (PTFE), polyvinylidene fluoride (PVdF), polyethylene or polypropylene, and the like can be used. In addition, an acrylic resin such as acrylic resin (polyvinyl chloride), polyvinyl pyrrolidone, polytetrafluoroethylene Acrylonitrile-butadiene rubber, styrene-butadiene rubber, styrene-butadiene rubber, and acrylic rubber, or a mixture of two or more thereof. The aqueous binders are economical, environmentally friendly, harmless to the health of workers, and are superior to non-aqueous binders, and have a better binding effect than non-aqueous binders. Thus, the ratio of the active materials of the same volume can be increased and the capacity of the aqueous binders can be increased. Preferably styrene-butadiene rubber can be used.

The binder may be contained in an amount of 10 wt% or less, specifically 0.1 wt% to 10 wt%, based on the total weight of the slurry for the negative electrode active material. If the content of the binder is less than 0.1 wt%, the effect of the binder is insufficient, which is undesirable. If the content of the binder is more than 10 wt%, the relative content of the active material may decrease to increase the binder content. not.

The conductive material is not particularly limited as long as it has conductivity without causing chemical changes in the battery, and examples of the conductive material include 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 fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; And conductive materials such as polyphenylene derivatives. The conductive material may be used in an amount of 1 wt% to 9 wt% with respect to the total weight of the slurry for the negative electrode active material.

The negative electrode collector used in the negative electrode according to an embodiment of the present invention may have a thickness of 3 to 500 mu m. The negative electrode current collector is not particularly limited as long as it has electrical conductivity without causing a chemical change in the battery. For example, carbon, Nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. In addition, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

As the separator, a conventional porous polymer film conventionally used as a separator, such as a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene-butene copolymer, an ethylene-hexene copolymer and an ethylene-methacrylate copolymer Porous nonwoven fabric such as high melting point glass fiber, polyethylene terephthalate fiber or the like may be used as the nonwoven fabric, but the present invention is not limited thereto.

The lithium salt that can be used as the electrolyte used in the present invention may be any of those commonly used in electrolytes for lithium secondary batteries, and examples thereof include F ^- , Cl ^- , Br ^- , I ^- , NO _{3 ^{-, N (CN) 2 -}} , BF 4 -, ClO 4 -, PF 6 -, (CF 3) 2 PF 4 -, (CF 3) 3 PF 3 -, (CF 3) 4 PF 2 -, (CF ^{_{3) 5 PF -, (CF}} 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO 3 -, (CF 3 SO 2) 2 N -, (FSO 2) 2 N -, CF 3 CF 2 ^{_{(CF 3) 2 CO -,}} (CF 3 SO 2) 2 CH -, (SF 5) 3 C -, (CF 3 SO 2) 3 C -, CF 3 (CF 2) 7 SO 3 -, CF 3 CO ₂ ^- , CH ₃ CO ₂ ^- , SCN ^-, and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- .

Examples of the organic solvent included in the electrolytic solution include propylene carbonate (PC), ethylene carbonate (EC), ethylene carbonate (EC), and the like. ), Diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane , Vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite, and tetrahydrofuran, or a mixture of two or more thereof. Specifically, ethylene carbonate and propylene carbonate, which are cyclic carbonates in the carbonate-based organic solvent, can be preferably used because they have high permittivity as a high viscosity organic solvent and dissociate the lithium salt in the electrolyte well. The cyclic carbonates include dimethyl carbonate and di Low-dielectric-constant linear carbonates such as ethyl carbonate can be mixed in an appropriate ratio to form an electrolytic solution having a high electrical conductivity. In particular, since the lithium secondary battery including the negative electrode active material for a lithium secondary battery of the present invention has excellent propylene carbonate property including graphite having an alkaline carbonate layer formed on its surface, the lithium secondary battery can exhibit excellent low temperature performance Preferably, it may contain the propylene carbonate.

Alternatively, the electrolytic solution stored in accordance with the present invention may further include an additive such as an overcharge inhibitor or the like contained in an ordinary electrolytic solution.

The external shape of the lithium secondary battery of the present invention is not particularly limited, but may be a cylindrical shape, a square shape, a pouch shape, a coin shape, or the like using a can.

The lithium secondary battery according to the present invention can be used not only in a battery cell used as a power source of a small device but also as a unit cell in a middle- or large-sized battery module including a plurality of battery cells.

Preferable examples of the above medium and large-sized devices include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and electric power storage systems.

Example

Hereinafter, the present invention will be described in more detail with reference to Examples and Experimental Examples, but the present invention is not limited by these Examples and Experimental Examples. The embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

Example 1: Negative electrode active material

Mosaic coke was finely pulverized and mixed with a pitch binder to form graphite first, then graphitized through firing at 3000 DEG C in a nitrogen atmosphere, and then washed to obtain 200 g of artificial graphite. The mixture was milled for 2 hours at 1,000 rpm using a spindle mill to obtain an average particle size (D ₅₀ ) of 18 μm. The rhombohedral structure of the crystal structure was 9.3% by volume and the specific surface area is 3.0 m ² / g and, TPD-MS (Frontier lab 2020iD , Agilent 6890 / 5973N, EQC-0120) and the amount of H ₂ O 225% by weight as determined using the amount of CO ₂ 135% by weight (hereinafter referred to as , And the amount of H ₂ O and CO ₂ measured for the natural graphite used in Comparative Example 1 was set to 100 wt%, thereby preparing a defect graphite.

(IG) of the G band at 1580 ± 50 cm ^-1 obtained by Raman spectroscopy [using DXR Raman Microscope (Thermo Electron Scientific Instruments LLC)] using a laser with a wavelength of 532 nm for the defect graphite The ratio (I _D / I _G ) of the maximum peak intensity ( _{D D} ) of the D band at 1360 ± 50 cm ^-1 was 0.222.

Example 2: Negative electrode active material

60 g of the defect graphite prepared in Example 1 was mixed with 40 g of natural graphite to prepare an anode active material.

The anode active material thus prepared had a rhombohydral structure of 6.4% by volume in the crystal structure and a specific surface area of 2.7 m ² / g. H ₂ O ₂ as measured by TPD-MS (Frontier lab 2020iD, Agilent 6890 / 5973N, EQC- The amount of O was 152 wt%, and the amount of CO ₂ was 68 wt%.

Example 3: Negative electrode active material

90 g of the defect graphite prepared in Example 1 was finely pulverized and mixed with a pitch binder to form graphite first, then graphitized at 3,000 占 폚 in a nitrogen atmosphere, And 10 g of artificial graphite to prepare an anode active material.

The prepared negative electrode active material had a rhombohydral structure in the crystal structure of 8.6% by volume and a specific surface area of 3.3 m ² / g, and H ₂ (weight average molecular weight: 20,000) as measured by TPD-MS (Frontier lab 2020iD, Agilent 6890 / 5973N, EQC- The amount of O was 218% by weight, and the amount of CO ₂ was 128% by weight.

Comparative Example 1: Negative electrode active material

The natural graphite used in Example 2 was used as the negative electrode active material.

Comparative Example 2: Negative electrode active material

10 g of the defect graphite prepared in Example 1 was finely pulverized and mixed with a pitch binder to form graphite first, then graphitized at 3,000 占 폚 in a nitrogen atmosphere and then washed And 90 g of artificial graphite to prepare an anode active material.

The prepared negative electrode active material had a rhombohydral structure in the crystal structure of 2.8% by volume and a specific surface area of 1.7 m ² / g. H ₂ O ₂ as measured by TPD-MS (Frontier lab 2020iD, Agilent 6890 / 5973N, EQC- The amount of O was 159% by weight, and the amount of CO ₂ was 75% by weight.

Example 4: Preparation of negative electrode and lithium secondary battery

≪ Preparation of negative electrode &

A mixture obtained by mixing the negative electrode active material prepared in Example 1, super c65 (manufacturer) as a conductive material, and polyvinylidene (PVdF) as a binder in a solvent N-methylpyrrolidone (NMP) was mixed at a weight ratio of 94: To prepare a uniform negative electrode active material slurry.

The prepared negative electrode active material slurry was coated on one side of the copper current collector to a thickness of 65 탆, dried and rolled, and punched to a predetermined size to prepare a negative electrode.

≪ Production of lithium secondary battery >

(EC), propylene carbonate (PC), and ethylmethyl carbonate (EMC) were mixed at a ratio of 20:10:70 by using a Li metal as a counter electrode, and a polyolefin separator interposed between the cathode and the Li metal. By volume of a 1 M LiPF ₆ solution was injected into a mixed solvent to prepare a coin type half cell.

Examples 5 and 6: Preparation of negative electrode and lithium secondary battery

A coin-shaped half cell was prepared in the same manner as in Example 4 except that the negative electrode active material prepared in Example 2 was used instead of the negative electrode active material prepared in Example 1 .

Comparative Examples 3 and 4

In the same manner as in Example 4 except that the negative electrode active materials of Comparative Examples 1 and 2 were used in place of the negative electrode active material prepared in Example 1 as the negative active material in Example 4, .

Experimental Example 1: Evaluation of initial efficiency and cycle characteristics

The batteries prepared in Examples 4 to 6 and Comparative Examples 3 and 4 were charged at 4.2 V at a constant current (CC) of 0.8 C at 25 캜 and then charged at a constant voltage (CV) C (cut-off current). After that, it was left for 20 minutes and then discharged at a constant current (CC) of 0.8 C until it reached 2.5 V. [ This was repeated in 1 to 50 cycles. The results are shown in Table 1 below.

Experimental Example 2: Evaluation of rate characteristics

The cells manufactured in Examples 3 and 4 and Comparative Example 1 were measured for 2 C rate discharge capacity to calculate the ratio of 2 C rate discharge capacity to 0.1 C rate discharge capacity, Respectively.

Initial efficiency
(1 ^st discharging capacity / 1 ^st charging capacity) Capacity retention rate
@ 50 cycles Output performance
@ 2C / 0.1C High Temperature Storage Characteristics
@ 8 weeks / 60 ℃ storage Example 4 82% 91.8% 93% 80% Example 5 80% 90% 92% 89% Example 6 81% 90% 92.4% 82% Comparative Example 3 54% 68% 89% 92% Comparative Example 4 62% 71% 90% 90%

As can be seen from the above results, the amount of H ₂ O and the amount of CO ₂ , as measured by TPD-MS, containing defective graphite are respectively 180 parts by weight to 300 parts by weight, and 80 parts by weight to 250 parts by weight It was confirmed that the secondary batteries of Examples 4 to 6 each using the negative electrode active materials of Examples 1 to 3 satisfying the range exhibited excellent performance in all aspects of initial efficiency, capacity retention rate, output performance, and high-temperature storage characteristics .

On the other hand, the secondary battery of Comparative Example 3 using the negative electrode active material of Comparative Example 1 made of natural graphite containing no defect graphite, and the amount of H ₂ O and the amount of CO ₂ measured by TPD-MS were 180 parts by weight 300 parts by weight, and 80 parts by weight to 250 parts by weight of the negative electrode active material of Comparative Example 2, the secondary battery of Comparative Example 4 was inferior to the secondary batteries of Examples 4 to 6 in terms of initial efficiency and capacity retention rate And the output performance was relatively poor.

Thus, the appropriate amount of functional groups that can be estimated from the amount of H ₂ O and the amount of CO ₂ determined by the appropriate Rombohydral structure content, TPD-MS, and co-intercalation (co) of graphite propylene carbonate -intercalation) in the restraint.

Claims (11)

And a defect graphite having an I _D / I _G band ratio of from 0.2 to 1.0, the negative active material comprising:
Wherein the defect graphite comprises 5 to 20% by volume of a rhombohedral structure in the crystal structure, and the surface of the graphite has a rhombohedral structure in which the functional graphite has at least one functional group selected from the group consisting of carboxyl group, hydroxyl group, ester group, aldehyde group, Comprising at least one selected,
The amount of H ₂ O and CO ₂ measured when TPD-MS (temperature elevation desorption method) was performed on the negative electrode active material for lithium secondary battery was such that the amounts of H ₂ O and CO ₂ measured for natural graphite were 100 weight , And 180 parts by weight to 300 parts by weight and 80 parts by weight to 250 parts by weight, respectively, of the negative active material for a lithium secondary battery.
The method according to claim 1,
The defect is a graphite having an average particle diameter (D ₅₀₎ of from 5 to 40 ㎛, negative active material.
The method according to claim 1,
Wherein the defect graphite includes a defect region and a hexagonal system structure in addition to the Rombo-hydral structure in the crystal structure.
The method according to claim 1,
Wherein the defect graphite has a specific surface area of 2.5 m ² / g to 4.0 m ² / g.
The method according to claim 1,
Wherein the total amount of functional groups on the surface of the defect graphite is 0.5% to 5% of the surface elements of the defect graphite.
The method according to claim 1,
Wherein the negative electrode active material for a lithium secondary battery further comprises a second graphite having an I _D / I _G band ratio of less than 0.2 in Raman spectroscopy.
The method according to claim 6,
And the second graphite is natural graphite.
The method according to claim 6,
Wherein the negative electrode active material for a lithium secondary battery comprises the defective graphite and the second graphite at a weight ratio of 30:70 to 90:10.
The method according to claim 6,
Wherein the negative electrode active material for a lithium secondary battery has a specific surface area of 2.0 m ² / g to 3.0 m ² / g.
An anode for a lithium secondary battery comprising the anode active material for a lithium secondary battery according to any one of claims 1 to 9.
11. A lithium secondary battery comprising a negative electrode for a lithium secondary battery according to claim 10.