KR20120096898A - Negative active material having high density and anode for lithium secondary battery containing the same - Google Patents

Abstract

PURPOSE: A negative electrode active material for a lithium secondary battery is provided to improve electrode density while widening a pore size distribution of a negative electrode active material. CONSTITUTION: A negative electrode active material for a lithium secondary battery comprises a first carbon based negative electrode active material in which an amorphous layer that polyvinyl alcohol is sintered is coated on a crystalline core; a flake graphite with low orientation; and a second carbon based negative electrode active material in which an amorphous layer that pitch is sintered coated on a crystalline core. The content of the amorphous layer derived from the polyvinyl alcohol is 0.5-10 weight% based on total weight of the first carbon based negative electrode active material, and the content of the amorphous layer derived from the pitch is 0.5-10 weight% based on total weight of the second carbon based negative electrode active material.

Description

High Density Negative Active Material and Negative Active Material Having High Density and Anode for Lithium Secondary Battery Containing The Same

The present invention relates to a high-density negative electrode active material and a negative electrode for a lithium secondary battery including the same, and more particularly, a first carbon-based negative electrode active material coated with an amorphous layer obtained by firing a polyvinyl alcohol on a crystalline core; Low orientation flake graphite; And a negative electrode active material for a lithium secondary battery in which a second carbon-based negative electrode active material coated with an amorphous layer coated with a pitch is fired in a crystalline core and lithium having an electrode density of 1.63 g / cc or more under a pressure condition of 12 to 16 mPa. It relates to a negative electrode for a secondary battery.

As the development and demand for mobile devices increases, the demand for secondary batteries as energy sources is rapidly increasing. Among them, lithium secondary batteries with high energy density and voltage, long cycle life, and low self discharge rate It is commercially used and widely used.

Lithium-containing cobalt oxide (LiCoO ₂ ) is mainly used as a positive electrode active material of the lithium secondary battery. In addition, lithium-containing manganese oxide such as spinel crystal structure LiMn ₂ O ₄ , lithium-containing nickel oxide (LiNiO ₂ ), and the like are also used. have.

Meanwhile, a carbon-based active material is mainly used as the negative electrode active material, and the carbon-based active material includes crystalline carbon such as natural graphite and artificial graphite, and amorphous such as soft carbon and hard carbon. There is system carbon.

The carbon-based active material used as the negative electrode active material has a very low discharge potential of about -3 V relative to the standard hydrogen electrode potential, and exhibits a very reversible charge and discharge behavior due to the uniaxial orientation of the graphite layer. The electrode life cycle (cycle life) is shown.

In addition, since the electrode potential at the time of charging Li ions can exhibit a potential almost similar to that of pure lithium metal as 0 V Li / Li ⁺ , it has the advantage that higher energy can be obtained when configuring an oxide-based positive electrode and a battery.

However, due to the continuous development of secondary batteries, the natural graphite-based material as a negative electrode active material reaches its theoretical maximum capacity of 372 mAh / g (844 mAh / cc), which is limited in capacity increase, and thus, a rapidly changing next generation mobile device. It is difficult to play a sufficient role as an energy source for devices, electric vehicles, and power storage devices.

In addition, the battery capacity depends on how many active materials are placed in the limited battery, but the carbon-based negative active material is loaded with carbon having a sp ² hybrid orbit regularly arranged to form a plane, and the planes are stacked and the hardness is weak. If the loading amount is increased, the base surfaces are in surface contact with each other, so that pores on the electrode surface are reduced, so that impregnation of the electrolyte is difficult, and mobility of lithium ions is also reduced. Furthermore, after filling the negative electrode active material to the negative electrode current collector during the production of the negative electrode, the porosity of the surface during the press (press) is further lowered.

Therefore, there is an urgent need for techniques for high density and high capacity of carbon materials as negative electrode active materials.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-mentioned problems of the prior art and the technical problems required from the past.

The inventors of the present application, after in-depth study and various experiments, when mixing three kinds of negative electrode active materials having a predetermined shape and structure, confirms that the pore size distribution of the negative electrode active material is expanded while having a high electrode density. The present invention was completed.

Accordingly, an object of the present invention is to provide a negative electrode active material for a lithium secondary battery and an anode including the same, while increasing the pore size distribution of the negative electrode active material and increasing electrode density.

According to the present invention, a negative active material for a rechargeable lithium battery according to the present invention includes a first carbon-based negative active material coated with an amorphous layer obtained by firing a polyvinyl alcohol on a crystalline core; Low orientation flake graphite; And a second carbon-based negative active material coated with an amorphous layer obtained by firing a pitch to the crystalline core.

In the negative electrode active material according to the present invention, since the first and second carbon-based negative electrode active materials are positioned between the base surfaces of the low oriented flaky graphite, the voids do not decrease even when the loading amount is increased, and thus the mobility of lithium ions is not reduced. As a result, high-speed charging and discharging is possible.

In addition, the negative electrode active material according to the present invention is formed by baking a polyvinyl alcohol or pitch from the first and second carbon-based negative electrode active material formed on the surface of the crystalline core, thereby increasing the hardness of the crystalline core, rolling It is stable even at the time of showing a high electrode density, there is an effect of improving the life characteristics because there is little change in the structure even during repeated charging and discharging.

In the first carbon-based negative electrode active material according to the present invention, for example, low molecular weight (Mw. 850,000 to 1,000,000) polyvinyl alcohol is maintained in a gaseous state, and then put the crystalline core of natural graphite in a firing furnace 800 ℃ to 1000 It can be prepared by plastic coating in the temperature range of ℃.

In addition, the second carbon-based negative active material according to the present invention may be prepared by, for example, mixing the pitch and the crystalline core of natural graphite in a calcination furnace and then firing coating at a temperature range of 800 ° C to 1000 ° C.

The content of the polyvinyl alcohol-derived amorphous layer and the pitch-derived amorphous layer may be 0.5 wt% to 10 wt% with respect to the weight of the first carbon-based negative electrode active material or the second carbon-based negative electrode active material. If the content is too small, it may be difficult to achieve the effects described above, on the contrary, if too large, the thickness of the amorphous coating layer is excessively increased, which is not preferable because it may interfere with the mobility of lithium ions.

In one preferred embodiment, the first carbon-based negative active material is spherical, has an average particle diameter of 18 μm to 25 μm and a specific surface area of 3.3 m ² / g to 5.1 m ² / g and has a pressure of 1.50 at a pressure of 12 to 16 mPa. It may be a material having a compression density of g / cc to 1.85 g / cc.

In addition, the second carbon-based negative active material is spherical, has an average particle diameter of 13 μm to 18 μm and a specific surface area of 2.0 m ² / g to 4.0 m ² / g, and 1.50 g / cc at a pressure of 13 to 14 mPa. And a material having a compressive density of from 1.70 g / cc.

Meanwhile, in the negative active material of the present invention, the flaky graphite may be a material having an average particle diameter of 18 μm to 25 μm and a specific surface area of 2.0 m ² / g to 4.0 m ² / g.

For reference, when the width direction of flaky graphite is X and the longitudinal direction is Y, the degree of orientation when Y is longer than general flaky graphite is referred to as 'high orientation', and when Y is shorter than general flaky graphite. The degree of orientation of is referred to as 'low orientation'. Thus, the 'low orientation' means that Y of flaky graphite is relatively shorter than general flaky graphite.

Specifically, in the present specification, low oriented flaky graphite means a material having a compressive density of 1.50 g / cc to 1.85 g / cc at a pressure of 12 to 16 mPa, and high oriented flaky graphite is generally used. As flaky graphite, it means a material having a compressive density of 1.8 to 2.0 g / cc under a pressure of 12 to 16 mPa.

In addition, the low-oriented flake graphite may be defined as a material having a lattice constant a in the base plane of 2.4640 Å or more and a lattice constant c in the stacking direction of 6.7120 Å or more in a hexagonal crystal structure.

In this regard, Figure 8 shows the relationship between the pressure and the compressive density of the low-oriented flake graphite of one embodiment of the present invention and the low-oriented flake graphite of the comparative example, Figure 9 is a low-oriented flake of an embodiment of the present invention The lattice constant a and the lattice constant c in the lamination direction in the hexagonal crystal structure of the phase graphite and the low-orientation flaky graphite of the comparative example are shown.

Since the negative electrode active material according to the present invention includes high-density, high-capacity spherical first and second carbon-based negative electrode active materials, the electrode density is remarkably improved and battery capacity is increased.

For example, the content of the three components may be, for example, 35 wt% to 52.5 wt% of the first carbon-based negative active material, 7.5 wt% to 15 wt% of the low-oriented flaky graphite, and 2 carbon-based negative active material may range from 40% by weight to 50% by weight.

The present invention also provides a negative electrode for a rechargeable lithium battery having an electrode density of 1.63 g / cc or more under a pressure condition of 12 to 16 mPa is applied to the current collector to the negative electrode active material.

For example, the negative electrode may be manufactured by coating and drying a negative electrode active material on a negative electrode current collector, and optionally further include components such as a conductive agent, a binder, and a filler as described above.

The negative electrode collector is generally made to have a thickness of 3 to 500 mu m. Such an anode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, and may be formed of a material such as copper, stainless steel, aluminum, nickel, titanium, fired carbon, surface of copper or stainless steel A surface treated with carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. In addition, fine concavities and convexities may be formed on the surface to enhance the bonding strength of the negative electrode active material, and may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), cellulose, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated Cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers, and the like. have.

The conductive agent is not particularly limited as long as it has conductivity without causing chemical change in the battery. Examples of the conductive agent include graphite such as natural graphite and artificial graphite; Carbon black such as carbon black, 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 polyphenylene derivatives and the like can be used. Specific examples of commercially available conducting agents include acetylene black Chevron Chemical Company, Denka Singapore Private Limited, Gulf Oil Company, Ketjenblack, EC series (Armak Company), Vulcan XC-72 (Cabot Company), and Super P (Timcal).

In some cases, a filler may be optionally added as a component to suppress the expansion of the negative electrode. Such a filler is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery, and examples thereof include olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

As the dispersion, isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, and the like may be typically used.

The method of evenly applying the paste of the electrode material to the metal material can be selected from known methods or performed by a new suitable method in consideration of the properties of the material. For example, it is preferable to disperse the paste onto the current collector and then to disperse the paste uniformly using a doctor blade or the like. In some cases, a method of distributing and dispersing in one process may be used. In addition, die casting, comma coating, screen printing, or the like may be used. Alternatively, molding on a separate substrate may be performed by pressing or lamination. You may join.

Drying of the paste applied on the metal plate is preferably dried for 1 to 3 days in a vacuum oven at 50 to 200 ℃.

The present invention also provides a lithium secondary battery comprising an electrode assembly facing a positive electrode including a positive electrode active material represented by the following Chemical Formulas 1 and 2 with a separator interposed therebetween, and a lithium salt-containing non-aqueous electrolyte. To provide.

Li _x M _{1 - y} M ' _y O _{2 - z} A _z (1)

In the above formula

0 <x <1.2;

0 ≦ y ≦ 0.9;

0 ≦ z ≦ 0.3;

M and M 'are each independently at least one metal or transition metal cation of + 2-valent to + 4-valent oxidation water;

A is a -1 or -divalent anion.

Li _a M _{2 - b} M ' _b O _{4 - c} A _c (2)

In the above formula

0 <a <1.2;

0 ≦ b ≦ 0.5;

0 ≦ c ≦ 0.3;

M and M 'are each independently at least one metal or transition metal cation of + 2-valent to + 4-valent oxidation water;

A is a -1 or -divalent anion.

As one preferred example, M in Formula 1 may be at least one selected from the group consisting of Co, Mn, and Ni, and M 'may be at least one selected from the group consisting of Al, Mg, and Ti.

In addition, in Formula 2, M is Mn, and M 'may be at least one selected from the group consisting of Co, Mn, Ni, Al, Mg, and Ti.

In Formula 1 or 2, A is preferably one or more selected from the group consisting of halogen, S and N.

Looking at the specific manufacturing method of the positive electrode as follows.

First, a paste is prepared by adding and stirring a positive electrode active material of the present invention and a binder and a conductive agent in an amount of 1 to 20% by weight with respect to the positive electrode active material, and then applying it to a metal plate for current collector and compressing the paste. After drying, a laminate electrode can be prepared.

The cathode current collector generally has a thickness of 3 to 500 mu m. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery. For example, the surface of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel Surface treated with carbon, nickel, titanium, silver, or the like can be used. Like the negative electrode current collector, the current collector may form fine irregularities on its surface to increase the adhesion of the positive electrode active material, and may be in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The separator is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally from 0.01 to 10 ㎛ ㎛, thickness is generally 5 ~ 300 ㎛. As such a separator, for example, olefin polymers such as chemical resistance and hydrophobic polypropylene; Sheet or nonwoven fabric made of glass fiber or polyethylene; Kraft paper or the like is used. Typical examples currently on the market include Celgard series (Celgard ^R 2400, 2300 (manufactured by Hoechest Celanese Corp.), polypropylene separator (manufactured by Ube Industries Ltd. or Pall RAI), polyethylene series (Tonen or Entek), etc.).

In some cases, a gel polymer electrolyte may be coated on the separator to increase battery stability. Representative examples of such gel polymers include polyethylene oxide, polyvinylidene fluoride, polyacrylonitrile, and the like.

When a solid electrolyte such as a polymer is used as an electrolyte, the solid electrolyte may also serve as a separation membrane.

The said lithium salt containing non-aqueous electrolyte consists of a nonaqueous electrolyte and lithium. As the non-aqueous electrolyte, a non-aqueous electrolyte, a solid electrolyte, an inorganic solid electrolyte and the like are used.

As said non-aqueous electrolyte, N-methyl- 2-pyrrolidinone, a propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, for example , Gamma-butylo lactone, 1,2-dimethoxy ethane, 1,2-diethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolon, 4-methyl-1,3-dioxene, diethyl ether, formamide, dimethylformamide, dioxolon, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxy methane, dioxolon Aprotic organic solvents such as derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl pyroionate and ethyl propionate can be used. Can be.

Examples of the organic solid electrolyte include a polymer electrolyte such as 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 fluoride, Polymers containing ionic dissociation groups, and the like can be used.

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

The lithium salt is a material that is readily soluble in the non-aqueous electrolyte, for example, 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, LiSCN, LiC (CF 3 SO 2) 3, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, 4-phenylborate, imide, and the like can be used.

For the purpose of improving the charge / discharge characteristics and the flame retardancy, the electrolytic solution is preferably mixed with an organic solvent such as pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, . In some cases, in order to impart nonflammability, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further included, and carbon dioxide gas may be further included to improve high temperature storage characteristics, and FEC (Fluoro-Ethylene Carbonate) may be further included. ), PRS (Propene sultone) may be further included.

The secondary battery according to the present invention has a high electrode density and a loading amount, as can be seen in the following Examples, Experimental Examples, etc., so that a high capacity is possible, and in particular, it can be preferably used as a constituent battery of a medium-large battery module. have. Accordingly, the present invention also provides a medium-large battery module including the secondary battery as a unit cell.

The medium-large battery module may be preferably applied to a power source that requires high output and large capacity, such as an electric vehicle, a hybrid electric vehicle, and a power storage device.

Since the construction of the medium-large battery module and its manufacturing method are well known in the art, a description thereof will be omitted.

As described above, since the first and second carbon-based negative active materials of a specific shape and structure are located between the base surfaces of the low-orientation flaky graphite, the negative electrode active material according to the present invention does not decrease the void even when the loading amount is increased. In addition, the mobility of lithium ions is not reduced, and thus high-speed charging and discharging is possible.

In addition, the negative electrode active material according to the present invention may preferably include high-density, high-capacity spherical first and second carbon-based negative electrode active materials, thereby increasing the battery density by increasing the electrode density.

Furthermore, the negative electrode active material according to the present invention has a polyvinyl alcohol or an amorphous coating layer calcined pitch is formed on the surface of the crystalline core to maintain the shape of the crystalline core, so that even when repeated charging and discharging, there is little change in structure, improving the life characteristics It is effective.

1 is a graph comparing the pore distribution of Preparation Example (first carbon-based negative electrode active material) and Comparative Example 1 at an electrode density of 1.63 g / cc;
FIG. 2 is a graph comparing the pore distribution of Preparation Example (low-oriented scaly graphite) and Comparative Example 2 at an electrode density of 1.63 g / cc;
3 is a graph comparing the pore distribution of Examples 1 and 4 and Comparative Example 3 according to the present invention at an electrode density of 1.71 g / cc;
4 is a graph comparing the electrolyte solution impregnation times of Examples 1 to 4 and Comparative Examples 3 and 4 according to the present invention at an electrode density of 1.71 g / cc;
5 is a graph comparing the electrochemical characteristics of Examples 1 and 4 and Comparative Example 3 according to the present invention at an electrode density of 1.71 g / cc;
Figure 6 is a graph comparing the increase and decrease of the negative electrode hardness according to the difference in the mixing ratio of the three mixed negative electrode active material of Examples 1 and 4 and Comparative Example 3 according to the present invention;
7 is a graph comparing fast charging characteristics of Examples 1 and 4 and Comparative Example 3 according to the present invention at an electrode density of 1.71 g / cc;
8 is a graph comparing the relationship between the pressure and the compressive density of the low-oriented flake graphite of one embodiment of the present invention and the low-oriented flake graphite of the comparative example;
FIG. 9 is a graph showing the lattice constant a and the lattice constant c in the lamination direction in the hexagonal crystal structure of the low oriented flaky graphite of the embodiment and the low oriented flaky graphite of the comparative example.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the following Examples are provided to illustrate the present invention, and the scope of the present invention is not limited thereto.

<Production Example>

Preparation of the First Carbon-Based Anode Active Material

A polyvinyl alcohol resin was applied to the surface of natural graphite and calcined at a temperature of 800 ° C. to 1000 ° C. to prepare a spherical first carbon-based negative electrode active material coated with an amorphous layer in an amount of 1.0 wt% on the surface of natural graphite. The first carbon-based negative electrode active material has an average particle diameter of 20 µm, a specific surface area of 3.5 m ² / g, and a compressive density of 1.68 g / cc under 14 mPa pressure.

Preparation of Second Carbon-Based Anode Active Material

Pitch was applied to the surface of the natural graphite and calcined at a temperature of 800 ℃ to 1000 ℃ to prepare a spherical second carbon-based negative active material coated with an amorphous layer in an amount of 3.0% by weight on the surface of the natural graphite. The second carbon-based negative electrode active material has an average particle diameter of 16 µm, a specific surface area of 3.4 m ² / g, and a compression density of 1.60 g / cc under 14 mPa pressure.

Preparation of Low Oriented Flaky Graphite

A low orientation inflated graphite having an average particle diameter of 22 µm, a specific surface area of 2.6 m ² / g, and a compression density of 1.69 g / cc at 14 mPa pressure was prepared.

Hereinafter, a mixed negative electrode active material was prepared based on the materials prepared or prepared in the above. Therefore, unless otherwise stated below, the first carbon-based negative electrode active material, the second carbon-based negative electrode active material, and the low oriented flaky graphite refer to materials prepared or prepared in the preparation example.

&Lt; Example 1 >

A mixed negative electrode active material was prepared by mixing 42.5% by weight of the first carbon-based negative electrode active material, 7.5% by weight of low-oriented flaky graphite, and 50% by weight of the second carbon-based negative electrode active material.

<Example 2>

A mixed negative electrode active material was prepared by mixing 35% by weight of the first carbon-based negative electrode active material, 15% by weight of low-oriented flaky graphite, and 50% by weight of the second carbon-based negative electrode active material.

<Example 3>

A mixed negative electrode active material was prepared by mixing 52.5 wt% of the first carbon-based negative electrode active material, 7.5 wt% of the low orientation flaky graphite, and 40 wt% of the second carbon-based negative electrode active material.

<Example 4>

A mixed negative electrode active material was prepared by mixing 45% by weight of the first carbon-based negative electrode active material, 15% by weight of low-oriented flaky graphite, and 40% by weight of the second carbon-based negative electrode active material.

Battery cell  Produce

The three mixed negative electrode active materials of Examples 1 to 4 prepared above, CMC and SBR as a binder were mixed in a ratio (weight ratio) of 98.0: 1.0: 1.0, stirred with distilled water as a solvent, and then a metal current collector. It was coated on phosphorus copper (Cu) foil. This was dried for 2 hours or more in a vacuum oven at 120 ℃ to prepare a negative electrode.

An electrode assembly was prepared using a porous separator made of LiCoO ₂ and polypropylene as the cathode and the anode.

1 M LiPF ₆ Coinlf cell and full cell were prepared using an ethylene carbonate (EC) and dimethyl carbonate (DMC) solution having a volume ratio of 1: 1 dissolved as an electrolyte.

&Lt; Comparative Example 1 &

A spherical carbon-based negative electrode active material having an average particle diameter of 22 m, a specific surface area of 5.1 m ² / g, and a compressive density of 1.50 g / cc to 1.85 g / cc at 14 mPa pressure was prepared.

Comparative Example 2

Highly oriented flaky graphite having an average particle diameter of 20 to 24 µm, a specific surface area of 4.0 m ² / g, and a compressive density of 1.8 to 2.0 g / cc under 14 mPa pressure was prepared as a negative electrode active material.

&Lt; Comparative Example 3 &

A mixed negative electrode active material was prepared by mixing 42.5 wt% of the negative active material of Comparative Example 1, 7.5 wt% of the highly oriented flaky graphite of Comparative Example 2, and 50 wt% of the second carbon-based negative active material.

&Lt; Comparative Example 4 &

Pitch is applied to the surface of natural graphite and calcined at a temperature of 800 ° C. to 1000 ° C., and an amorphous layer is coated on the surface of natural graphite in an amount of 3.0% by weight, the average particle diameter is 20 μm, and the specific surface area is 3.4 m ² / g. , Spherical pitch-coated calcined anode material having a compression density of 1.60 g / cc under 14 mPa pressure was prepared.

A mixed negative electrode active material was prepared by mixing a 42.5 wt% pitch coated calcined negative electrode material with a 7.5 wt% high orientation flaky graphite of Comparative Example 2 and a 50 wt% second carbon-based negative active material.

<Experimental Example 1>

The pore size distribution of the first carbon-based negative electrode active material of Preparation Example and the carbon-based negative electrode active material of Comparative Example 1 was compared under an electrode density of 1.63 g / cc, and the results are shown in FIG. 1. Pore size distributions were compared by mercury porosimetry (compare distributions by the amount of liquid mercury (Hg) absorbed).

Referring to FIG. 1, it can be seen that the first carbon-based negative electrode active material of Preparation Example has a higher amount of mercury absorbed in a portion having a larger pore size than the carbon-based negative electrode active material of Comparative Example 1. This means that the first carbon-based negative electrode active material of Preparation Example is composed of pores having larger internal pores than the carbon-based negative electrode active material of Comparative Example 1.

<Experimental Example 2>

The pore size distribution of the low-orientation flaky graphite of Preparation Example and the high-orientation flaky graphite of Comparative Example 2 was compared under the electrode density condition of 1.63 g / cc, and the results are shown in FIG. 2.

Referring to FIG. 2, it can be seen that the low-orientation flaky graphite of Preparation Example compared to the high-orientation flaky graphite of Comparative Example 2 has a large amount of mercury absorbed in a portion having a large pore size. This means that the low-orientation flaky graphite of Preparation Example is composed of pores having a larger internal void than that of the high-orientation scaly graphite of Comparative Example 2.

As a result, when comparing the electrode pore distribution with reference to the results of FIGS. 1 and 2, the carbon-based negative electrode active material of Comparative Example 1 and the first carbon-based negative electrode active material of Preparation Example have similar characteristics in general, and The highly oriented flaky graphite and the low oriented flaky graphite of the preparation example have similar characteristics in general, but it can be seen that the first carbon-based negative electrode active material and the low oriented flaky graphite of the preparation have a relatively large pore distribution.

<Experimental Example 3>

The pore size distribution was compared with Comparative Example 3 based on Examples 1 and 4 having the least electrolyte impregnation time under an electrode density of 1.71 g / cc, and the results are shown in FIG. 3.

Referring to FIG. 3, it can be seen that Examples 1 and 4 compared to Comparative Example 3 have a large amount of mercury absorbed in a large pore size portion. This means that Examples 1 and 4 are composed of pores having larger internal voids than Comparative Example 3.

<Experimental Example 4>

The first carbon-based negative electrode active material (Preparation Example-a) and low-formation flaky graphite (Preparation Example-b) of the Preparation Example and the negative electrode active materials of Examples 1 to 4 and Comparative Examples 1 to 4 at an electrode density of 1.71 g / cc After the preparation of the pellets (pellets) each containing, after the impregnation of the pellet in 120 μl electrode solution was compared the natural impregnation time. That is, 120 μl of the electrolyte was dropped on the pellet surface, and then the amount absorbed was compared. The results are shown in FIG. 4.

Referring to FIG. 4, it can be seen that the impregnation time of Preparation Example-a and Preparation Example-b is less than that of Comparative Examples 1 and 2, respectively, and that of Examples 1 to 4 is less than that of Comparative Examples 3 and 4. can confirm.

<Experimental Example 5>

Electrochemical properties of Comparative Example 3 were compared with those of Examples 1 and 4 having the least electrolyte impregnation time under an electrode density of 1.71 g / cc, and the results are shown in FIG. 5.

Referring to FIG. 5, it is confirmed that Examples 1 and 4 have more charging capacity required to reach 0.1V under fast charging conditions than Comparative Example 3. This means that Li ions can be easily intercalated into the cathode layered structure. In other words, it can be seen that the division of the voltage stage is increased at the time of fast charging and the resistance at the time of insertion of Li ions is small.

<Experimental Example 6>

Based on Examples 1 and 4 having the least electrolyte impregnation time at an electrode density of 1.71 g / cc, the increase and decrease of the negative electrode hardness according to the difference in the mixing ratio of Comparative Example 3 and the mixed negative electrode active material were compared. Indicated.

Referring to FIG. 6, the density of pellets in Examples 1 and 4 was lower than that of Comparative Example 3, which indicates that the anode active materials according to Examples 1 and 4 had less structural deformation than the anode active materials of Comparative Example 3. it means.

Experimental Example 7

After fabricating the lithium secondary batteries including the negative electrode active materials of Examples 1 and 4 at an electrode density of 1.71 g / cc, the fast charging characteristics were compared with Comparative Example 3, and the results are shown in FIG. 7.

Referring to FIG. 7, it is confirmed from the current graph graph A that the constant current time (Constant-Current) was increased under the conditions of Examples 1 and 4 compared to Comparative Example 3. This means that there are many electrode pores under the conditions of Examples 1 and 4, so that Li ions are easily inserted into the layer in the cathode under the charging conditions.

Further, in the voltage graph V, it is confirmed that the voltages of Examples 1 and 4 are lower than those of Comparative Example 3 in the range of 0.0 (hour) to 0.3 (hour). This means that the resistance is low when the Li ions are inserted.

Those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims (19)

A first carbon-based negative active material coated with an amorphous layer obtained by calcining polyvinyl alcohol on a crystalline core; Low orientation flake graphite; And a second carbon-based negative electrode active material coated with an amorphous layer coated with a calcination pitch on a crystalline core. The negative active material of claim 1, wherein the polyvinyl alcohol-derived amorphous layer has a content of 0.5 wt% to 10 wt% based on the total weight of the first carbon-based negative active material. The negative active material of claim 1, wherein the first carbon-based negative electrode active material is spherical. The negative active material of claim 1, wherein the pitch-derived amorphous layer is present in an amount of 0.5 wt% to 10 wt% based on the total weight of the second carbon-based negative active material. The negative active material of claim 1, wherein the second carbon-based negative active material is spherical. According to claim 1, wherein the first carbon-based negative electrode active material based on the total weight of the negative electrode active material 35 to 52.5% by weight, low-oriented flaky graphite 7.5% to 15% by weight, and the second carbon-based negative electrode The negative active material for a lithium secondary battery, wherein the active material is mixed in a range of 40 wt% to 50 wt%. The method of claim 1, wherein the first carbon-based negative active material has an average particle diameter of 18 ㎛ to 25 ㎛ and a specific surface area of 3.3 m ² / g to 5.1 m ² / g and 1.50 g / cc at a pressure of 12 to 16 mPa The negative active material for a lithium secondary battery, characterized in that it has a compression density of 1.85 g / cc. The flaky graphite of claim 1, wherein the flaky graphite has an average particle diameter of 18 µm to 25 µm and a specific surface area of 2.0 m ² / g to 4.0 m ² / g, and is 1.50 g / cc to 1.85 at a pressure of 12 to 16 mPa. A negative active material for a lithium secondary battery, characterized in that it has a compression density of g / cc. The negative electrode active material of claim 1, wherein the flaky graphite has a lattice constant a in the base plane of at least 2.4640 Å and a lattice constant c in the stacking direction of at least 6.7120 에서 in a hexagonal crystal structure. The method of claim 1, wherein the second carbon-based negative electrode active material has an average particle diameter of 13 ㎛ to 18 ㎛ and a specific surface area of 2.0 m ² / g to 4.0 m ² / g, and 1.50 g / under a pressure of 12 to 16 mPa A negative active material for a lithium secondary battery, characterized in that it has a compression density of cc to 1.70 g / cc. The first carbon-based negative electrode active material coated with the amorphous layer calcined with polyvinyl alcohol on the crystalline core, the low-oriented flaky graphite, and the second carbon-based negative electrode active material coated with the amorphous layer calcined with pitch on the crystalline core were mixed. And an electrode density of 1.63 g / cc or more under a pressure condition of 12 to 16 mPa. A cathode according to claim 11;
A cathode for a lithium secondary battery coated with a coating solution containing a cathode active material for a lithium secondary battery represented by Formula 1 or Formula 2 below; And
An electrode assembly, characterized in that consisting of a porous separator:
Li _x M _{1 - y} M ' _y O _{2 - z} A _z (1)
In the above formula
0 <x <1.2;
0 ≦ y ≦ 0.9;
0 ≦ z ≦ 0.3;
M and M 'are each independently at least one metal or transition metal cation of + 2-valent to + 4-valent oxidation water;
A is a -1 or -divalent anion.
Li _a M _{2 - b} M ' _b O _{4 - c} A _c (2)
In the above formula
0 <a <1.2;
0 ≦ b ≦ 0.5;
0 ≦ c ≦ 0.3;
M and M 'are each independently at least one metal or transition metal cation of + 2-valent to + 4-valent oxidation water;
A is a -1 or -divalent anion. The electrode assembly of claim 12, wherein in Formula 1, M is at least one selected from the group consisting of Co, Mn, and Ni, and M 'is at least one selected from the group consisting of Al, Mg, and Ti. The electrode assembly of claim 12, wherein M in Formula 2 is Mn, and M 'is at least one selected from the group consisting of Co, Mn, Ni, Al, Mg, and Ti. The electrode assembly of claim 12, wherein A in Formula 1 or 2 is at least one selected from the group consisting of halogen, S, and N. A lithium secondary battery comprising the electrode assembly of claim 12. A battery module comprising the lithium secondary battery of claim 16 as a unit cell. An electric vehicle or a hybrid electric vehicle, comprising using the battery module according to claim 17 as a power source. A power storage device using the battery module according to claim 17 as a power source.

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