KR20150052004A - Electrode material for lithium ion secondary batteries, method for producing same, and lithium ion secondary battery - Google Patents

Abstract

Disclosed is an electrode material for a lithium ion secondary battery capable of maintaining a large current charge / discharge over a long life span, and capable of realizing a high capacity lithium ion secondary battery, a production method thereof, and a lithium ion secondary battery. An electrode material for a lithium ion secondary battery, comprising an active material and a conductive material, wherein the active material is a lithium-containing complex oxide, tin oxide or silicon oxide, and contains amorphous carbon, carbon nanotube and carbon black as a conductive material, And covers part or all of the surface of the active material by carbon.

Description

TECHNICAL FIELD [0001] The present invention relates to an electrode material for a lithium ion secondary battery, a method for producing the electrode material, and a lithium ion secondary battery. BACKGROUND ART < RTI ID = 0.0 >

The present invention relates to an electrode material for a lithium ion secondary battery, a production method thereof, and a lithium ion secondary battery. More particularly, the present invention relates to a technology for increasing the capacity of a lithium ion secondary battery.

The lithium ion secondary battery in which the negative electrode is formed by a material capable of intercalating and deintercalating lithium ions can suppress the precipitation of the dendrive as compared with a lithium battery in which the negative electrode is formed by metal lithium. Accordingly, the lithium ion secondary battery has an advantage that it is possible to provide a battery having a high energy density with a high capacity after the battery is short-circuited to improve safety.

Recently, this lithium ion secondary battery is required to have a further high capacity, and as a battery for power system use, it is required to improve the large current charging / discharging performance by reducing the battery resistance. Therefore, it is necessary to increase the capacity of the lithium metal oxide positive electrode material and the carbonaceous negative electrode material, which are conventionally used as the battery reaction materials, to set the particle size of the reactive material particles, to increase the electrode area by the particle specific surface area and the battery design, And the like have been devised.

However, these designs lead to an increase in binder due to hardening of the particle size and increase of the specific surface area. As a result, there is a tendency to reverse the high capacity, or to peel off the metallic foil from the metal foil, There is a case. In order to solve such a problem, studies have been made to change the type of binder and increase the binding property with foil. However, this method has the problem that the battery capacity can be increased, but improvement of the large current charge / Is insufficient.

As a result, the conventional lithium ion secondary battery is inferior in charging / discharging characteristics of a large current as compared with a secondary battery such as a nickel-cadmium battery or a nickel metal hydride battery, and this becomes a large performance barrier, and electric power tools and hybrid cars Development for use was difficult. As a method for reducing the electrode resistance of a lithium ion secondary battery using a carbon conductive material, for example, a large-current charger is proposed (see, for example, Patent Document 1).

On the other hand, in recent years, olivine-type lithium iron phosphate (LiFePO ₄ ) has attracted attention as a positive electrode material for a lithium ion secondary battery from the viewpoint of safety and cost-consciousness. However, since this material has a large resistance, (See, for example, Patent Document 2). Therefore, in order to solve the problem of lowering the resistance of the olivine type lithium iron phosphate, various investigations have been made to combine olivine type lithium iron phosphate and graphite, which is a conductive material, into an electrode material (see, for example, 3 and 4).

Japanese Patent Application Laid-Open No. 2005-19399 Japanese Patent Publication No. 2000-509193 Japanese Patent Laid-Open No. 2002-75364 Japanese Patent Application Laid-Open No. 2011-108522

However, in the lithium ion secondary battery described in Patent Document 1, when the charging / discharging cycle by the large current is repeated, the conductive path of the particles between the positive and negative electrodes is damaged by the expansion and contraction of the positive and negative electrode materials, and as a result, There is a problem that it is lost. On the other hand, with respect to the electrode material using olivine-type iron phosphate lithium, the performance of the electrode material is improved by the composite of graphite, but since olivine-type lithium iron phosphate has a smaller capacity per volume than other active materials, .

Accordingly, it is an object of the present invention to provide an electrode material for a lithium ion secondary battery capable of maintaining a large current charge / discharge over a long period of life and capable of realizing a high capacity lithium ion secondary battery, a method for producing the same, and a lithium ion secondary battery .

An electrode material for a lithium ion secondary battery according to the present invention is an electrode material for a lithium ion secondary battery containing an active material and a conductive material, wherein the active material is a lithium-containing complex oxide, tin oxide or silicon oxide, A tube, and carbon black, and the amorphous carbon covers part or all of the surface of the active material.

The covering ratio of the surface of the active material with the amorphous carbon may be, for example, 10 to 95%.

The amorphous carbon may be a thermal decomposition product of an organic substance.

When the electrode material for a lithium ion secondary battery of the present invention is used for a positive electrode material, examples of the active material include LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , Li (Mn _a Ni _b Co _c ) O ₂ + b + c = 1 and 0 <a <1, 0 <b <1, 0 <c <1), Li (Al _d Ni _e Co _f ) O ₂ d <1, 0 <e < 1, 0 <f <1), xLi 2 MnO 3 - (1-x) LiMO 2 ( stage, 0 <x <1) and _{LiNi g Mn (2-g)} O 4 ( However, one type of lithium-containing complex oxide selected from the group consisting of 0 < g < 2) can be used.

When the electrode material for a lithium ion secondary battery of the present invention is used for an anode material, for example, Li ₄ Ti ₅ O ₁₂ , tin oxide containing metal tin, or silicon oxide containing metal silicon can be used as the active material .

Alternatively, when the electrode material for a lithium ion secondary battery of the present invention is used for an anode material, a mixture of tin oxide containing metal tin or silicon oxide containing metal tin and graphite may be used as the active material.

A method of manufacturing an electrode material for a lithium ion secondary battery according to the present invention is characterized by comprising the steps of mixing an active material, an organic material which forms amorphous carbon by thermal decomposition, a carbon nanotube, and carbon black in a solvent, And then heating to form amorphous carbon derived from the organic material on the surface of the active material, and a step of smashing the mixture after heating.

Another method for producing an electrode material for a lithium ion secondary battery according to the present invention includes the steps of mixing an active material, a carbon nanotube, and carbon black in a solvent; drying the mixture obtained by the mixing and then heating; And the step of crushing the mixture after the heating, wherein either or both of the carbon nanotubes and the carbon black contain amorphous carbon.

The lithium ion secondary battery according to the present invention uses the above-described electrode material for a lithium ion secondary battery.

According to the present invention, it is possible to maintain a large current charge / discharge over a long period of life and realize a lithium ion secondary battery with a high capacity.

Hereinafter, the present invention will be described in detail. The present invention is not limited to the embodiments described below.

(First Embodiment)

First, the electrode material according to the first embodiment of the present invention will be described. The electrode material of the present embodiment is used for a lithium ion secondary battery and contains lithium-containing complex oxide, tin oxide or silicon oxide as an active material, and contains amorphous carbon, carbon nanotube and carbon black as a conductive material. In the electrode material of the present embodiment, part or all of the surface of the active material is covered with amorphous carbon, which is a conductive material.

Thus, in the electrode material of the present embodiment, the amorphous carbon is electrically connected to the active material by covering the surface of the active material, and the carbon nanotube contacts both amorphous carbon and carbon black to electrically connect them. The carbon black forms a conductive network over the entire electrode and also electrically connects with the current collector.

[Amorphous carbon]

The amorphous carbon, which is a conductive material, is carbon having a low crystallinity (low graphitization degree) and low crystallinity makes it possible to coat the surface of the active material. On the other hand, carbon having a high crystallinity (high graphitization degree) has a layered structure peculiar to graphite, and each of the carbon layers has a gentle bond by van der Waals force, so that peeling occurs in a direction perpendicular to the layer easy. Therefore, it is not suitable for covering the surface of the active material.

The covering ratio of the surface of the active material with the amorphous carbon is preferably 10 to 95%, and more preferably 20 to 95%, when the entire surface of the active material is 100%. If the coating rate is less than 10%, the electrical connection between the active material and the amorphous carbon may become insufficient. Further, as the covering ratio is larger, the coating ratio by the amorphous carbon may be 100% since it is advantageous for the electrical connection. However, there is a concern that the lithium ion penetrates into the active material during charging and discharging, , It is preferable that the covering ratio by the amorphous carbon is 95% or less.

The amorphous carbon used in the electrode material of the present embodiment is not particularly limited except that the crystallinity is low (the degree of graphitization is low), but it is preferable that the amorphous carbon is formed by thermal decomposition of an organic material. As a result, the coated state of the surface of the active material by the amorphous carbon can be improved. Examples of organic substances that form amorphous carbon by thermal decomposition include glucose (C ₆ H ₁₂ O ₆ ), sucrose (C ₁₂ H ₂₂ O ₁₁ ), dextrin ((C ₆ H ₁₂ O ₅ ) _n ), ascorbic acid (C ₆ H ₈ O ₆ ), carboxymethyl cellulose (CMC), polyvinyl pyrrolidone (PVP), polyallylamine hydrochloride (PAH), polyacrylate (PAA), polyvinyl alcohol And coal pitch.

When amorphous carbon is formed on the surface of the active material by using these organic materials, a mixture obtained by mixing, for example, an active material, carbon nanotubes, carbon black and an organic material in a solvent may be dried and then heated.

Further, the present inventors have found that when either or both of the carbon nanotubes and the carbon black contain amorphous carbon, the surface of the active material can be coated with amorphous carbon well without using an organic material decomposing to form amorphous carbon . In this case, the mixture obtained by mixing the active material, the carbon nanotubes, and the carbon black in a solvent can be dried and then heated. The carbon nanotubes or carbon black containing amorphous carbon referred to herein include, for example, carbon nanotubes having an amorphous carbon layer covering the surface of a tube body (see Japanese Patent Application Laid-Open No. 2004-299986).

[Carbon nanotubes]

The carbon nanotube as the conductive material preferably has a fiber diameter of 5 to 50 nm and a specific surface area of 50 to 400 m2 / g. In the electrode material of the present embodiment, the carbon nanotubes are electrically connected by bonding with the amorphous carbon coated on the surface of the active material. As used herein, &quot; bonding &quot; includes bonding by covalent bond or van der Waals force.

The reason why the carbon nanotubes are bonded to the amorphous carbon is that the carbon nanotubes are fibrous particles and can be in line contact with the amorphous carbon layer coated on the surface of the active material. On the other hand, since carbon black is a spherical particle, it can not be in point contact with amorphous carbon, and sufficient bonding can not be obtained. The method of bonding the amorphous carbon to the carbon nanotube is not particularly limited. For example, in the case of a method of decomposing organic matter by heating to form amorphous carbon on the surface of the active material, The bond between the carbon and the carbon nanotube is also formed at the same time.

Further, in the electrode material of the present embodiment, the carbon nanotubes are electrically connected by bonding with carbon black. The method of bonding the carbon nanotubes to the carbon black is not particularly limited. For example, there are a method of introducing carbon nanotubes into the carbon black to produce carbon black by thermally decomposing hydrocarbons, (Japanese Unexamined Patent Application Publication No. 2009-503182), a method in which a hydrocarbon containing a catalyst for forming a carbon nanotube is supplied and bonded in a state in which an acetylene gas is thermally decomposed, a method in which carbon nanotubes and carbon black are mixed with hydrocarbons A method in which the carbonized raw material liquid is dispersed in a carbonization raw material liquid such as an alcohol to cause carbonization of the carbonized raw material liquid in a liquid or gasified state by an operation such as heating to bond the carbon nanotubes and carbon black to each other, And a method of bonding by a chemical method.

As a method for bonding the carbon nanotubes and the carbon black by a mechanochemical method, there is a method of using a medium agitating type mixer such as a bead mill, a vibration mill and a ball mill. In this case, for example, when an active material, an organic material decomposing to form amorphous carbon, a carbon nanotube, and carbon black are mixed in a solvent, or an active material and either or both of carbon nanotubes containing amorphous carbon And a carbon nanotube and a carbon black may be bonded using a mechanochemical method when the carbon black is mixed in a solvent, or may be bonded at the time of heating after mixing.

[Carbon black]

Carbon black, which is a conductive material, is preferably acetylene black or furnace black, and more preferably acetylene black having a relatively small content of impurities that may affect battery performance. The specific surface area of the carbon black is preferably smaller than the specific surface area of the carbon nanotubes and is preferably 10 to 200 m 2 / g. The carbon black to be used for the electrode material of the present embodiment is preferably not more than 1.0% by mass as specified in JIS K 1469.

In the electrode material of the present embodiment, the carbon black is not only electrically coupled with the carbon nanotubes as described above, but also forms a conductive network over the entire electrode and electrically connects with the current collector. The reason why carbon black can form a conductive network over the entire electrode is that carbon black is different from carbon nanotubes and is spherical particles and has good dispersibility and is therefore widely distributed over the entire electrode. The reason why the carbon black can be electrically connected to the carbon nanotube or the current collector is because the spherical primary particles have a unique high-order structure connected in a chain and conduction is easy even though they are spherical particles.

[Active Material]

The electrode active material of the present embodiment is a lithium-containing complex oxide, tin oxide, or silicon oxide. For example, when the electrode material of the present embodiment is used as the positive electrode material, LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , Li (Mn _a Ni _b Co _c ) O ₂ (where a + b + c = 1 In addition, 0 <a <1, 0 < b <1, 0 <c <1), Al d Ni e Co f (Li) O 2 ( stage, d + e + f = 1 In addition, 0 <d <1, 0 < e <1, 0 <f < 1), xLi 2 MnO 3 - (1-x) LiMO 2 ( stage, 0 <x <1) and _{LiNi g Mn (2-g)} O 4 ( However, 0 <g < 2) may be used as the positive electrode active material.

On the other hand, when the electrode material of the present embodiment is used as an anode material, Li ₄ Ti ₅ O ₁₂ , tin oxide containing metal tin, silicon oxide containing metal silicon, or the like can be used as the active material. As the negative electrode active material, tin oxide containing metal tin or silicon oxide containing metal silicon may be mixed with graphite.

In addition, it is difficult to improve the battery capacity per volume in a lithium-containing phosphate such as LiFePO ₄ (olivine type iron phosphate), LiMnPO ₄ , LiMnXFe _(1-X) PO ₄ and the like. Therefore, Inappropriate.

[Manufacturing method]

The method for producing the electrode material of the present embodiment is not particularly limited, and for example, a method of mixing an active material, an organic material that forms amorphous carbon by thermal decomposition, a carbon nanotube, and carbon black in a solvent, And then heating the mixture to form an amorphous carbon derived from an organic material on the surface of the active material and a step of crushing the mixture after heating. When it is produced by this method, it is preferable to use an organic substance which is dissolved in a solvent and then decomposes at the time of heating to form amorphous carbon.

The electrode material of the present embodiment may be formed by a step of mixing the active material, the carbon nanotubes and the carbon black in a solvent by using a material containing amorphous carbon in one or both of the carbon nanotubes and carbon black, Drying the mixture obtained by the above-mentioned method, and then heating, and a step of pulverizing the mixture after heating.

The mixing process in each of the above-mentioned production methods can be carried out using a mixer such as a brain ball, a universal mixer, a Henschel mixer or a ribbon blender, or a medium agitating mixer such as a bead mill, a vibration mill or a ball mill. The solvent used in the mixing step may be water, but in order to improve the dispersibility of the carbon nanotubes and carbon black, a mixed solvent of water and alcohol or a nonaqueous solvent such as alcohol is preferable.

When the active material is a tin oxide containing metal tin or a silicon oxide containing metal silicon or a mixture of these with graphite, the solvent in the mixing step may be added to prevent hydrolysis of metal tin or metal silicon, In order to improve the dispersibility, it is preferable to use a non-aqueous solvent such as alcohol.

After the mixing step, the obtained mixture is dried to remove the solvent. The method of drying the mixture is not particularly limited, but in the case of using an organic material that forms amorphous carbon by thermal decomposition, care must be taken to prevent the organic material from being removed together with the solvent as a filtrate. Therefore, in addition to filtration, freeze drying, vacuum drying, vacuum drying, or vibrating flow drying may be applied to the drying of the mixture.

After drying, or after drying, the mixture is heated. In the case of using an organic material which forms amorphous carbon by thermal decomposition, amorphous carbon is formed from the organic material by heating, and the amorphous carbon covers the surface of the active material, and the amorphous carbon and the carbon nanotube bond, A bond between the carbon nanotubes and the carbon black is formed. When carbon nanotubes containing amorphous carbon or carbon black containing amorphous carbon are used, the amorphous carbon contained in the carbon nanotubes and / or carbon black covers the surface of the active material, The bonding of the carbon nanotubes and the bonding of the carbon nanotubes and the carbon black are formed.

The conditions such as temperature and atmosphere at the time of heating the mixture differ depending on the active material used. The atmosphere is preferably an inert atmosphere or a reducing atmosphere in order to prevent oxidation of the carbon-based material. Further, the active _{material, LiCoO 2, LiMn 2 O 4} , LiNiO 2, Li (Mn a Ni b Co c) O 2 ( However, a + b + c = 1 In addition, 0 <a <1, 0 < b <1, 0 <c <1), Li (Al d Ni e Co f) O 2 ( stage, d + e + f = 1 In addition, 0 <d <1, 0 < e <1, 0 <f <1), xLi 2 In the case of using an oxide-based positive electrode active material such as MnO ₃ - (1-x) LiMO ₂ (where 0 <x <1) and LiNi _g Mn _(2-g) O ₄ , An oxidizing atmosphere such as dry air is preferably used in order to prevent reduction decomposition of the active material itself. Further, in the case of using an organic material which forms amorphous carbon by thermal decomposition, it is preferable to heat at a relatively low temperature of 200 to 400 캜 so that the organic material is decomposed without burning.

On the other hand, in the case of using Li ₄ Ti ₅ O ₁₂ as the negative electrode active material, Li ₄ Ti ₅ O ₁₂ is difficult to decompose, and therefore it is preferable to heat it at 300 to 500 ° C which is slightly higher. When an active material mixed with tin oxide containing metal tin or graphite mixed therein is used, an inert gas such as argon or nitrogen can be used because the active material is not decomposed in an inert atmosphere or a reducing atmosphere. However, Since the melting point of metallic tin is low at 232 占 폚, it is preferable to heat at a temperature lower than 232 占 폚.

The active material is not decomposed even in an inert atmosphere or a reducing atmosphere, and the melting point of silicon is high at 1410 DEG C, so that the temperature of the active material in the vicinity of 1400 DEG C The heating can be performed in a wide range of temperature, and an inert gas such as argon or nitrogen can be used. After the heating, the mixture is released by coagulation to obtain the electrode material of the present embodiment.

The electrode material of the present embodiment improves the electron conduction network in the electrode and further facilitates the transfer of electrons between the active material, the conductive agent and the current collectors of the metal foil. Therefore, Compared to one electrode material, the electrode resistance is reduced, and a large current charge / discharge can be achieved. In addition, since the electrode material of the present embodiment has the optimum electrical connection between the active material, the conductive agent, and the current collectors of the metal foil, and can conduct with a small amount of conductive agent, The car becomes remarkable. In addition, as it is possible to use a small amount, it contributes to the improvement of the battery capacity.

Thus, by using the electrode material of the present embodiment, the ratio of the active material in the electrode material can be increased and the capacity of the lithium ion secondary battery can be increased.

(Second Embodiment)

Next, a lithium ion secondary battery according to a second embodiment of the present invention will be described. The lithium ion secondary battery of the present embodiment uses the above-described electrode material of the first embodiment in the above-mentioned positive electrode material and / or negative electrode material.

A general lithium ion secondary battery is composed of an electrode group formed by stacking or winding an electrode including a negative electrode and a positive electrode via a separator and an electrolyte solution in which the electrode group is immersed. The electrode is formed by coating an electrode material for a lithium ion secondary battery on a collector of a metal foil through an organic binder or the like.

In the case of forming the electrode of the lithium ion secondary battery using the electrode material of the first embodiment described above, the electrode material is kneaded with a solvent or a binder to form an electrode mixture (slurry). For example, in the case of forming a positive electrode, N-methylpyrrolidone (NMP) may be used as a solvent, and polyvinylidene fluoride (PVDF) may be used as a binder. Further, in the case of forming the negative electrode, water is used as a solvent, and carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR) are often used as a binder.

Then, the electrode mixture can be coated on the current collector of the metal foil and then subjected to pressure molding to produce an electrode. The active material is LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , Li (Mn _a Ni _b Co _c ) O ₂ (provided that a + b + c = 1 and 0 <a <1, 0 <b <_{<1), Li (Al d} Ni e Co f) O 2 ( stage, d + e + f = 1 In addition, 0 <d <1, 0 < e <1, 0 <f <1), xLi 2 MnO 3 - (1-x) LiMO ₂ (where 0 <x <1) and LiNi _g Mn _(2-g) O ₄ (where 0 <g <2), or a positive electrode active material Li ₄ In the case of Ti ₅ O ₁₂ , aluminum foil is used as the current collector. When the active material is tin oxide containing metal tin or silicon oxide containing metal silicon or a mixture of graphite and silicon tin, copper foil is used.

Examples of other materials used for the lithium ion secondary battery include a separator and an electrolytic solution. The separator is to electrically insulate the positive electrode and the negative electrode to retain the electrolyte solution, and may be made of a synthetic resin such as polyethylene or polypropylene or a nonwoven fabric made of cellulose. In order to improve the retention of the electrolytic solution, it is preferable to use a separator in the form of a porous film.

As the electrolytic solution in which the electrode group described above is immersed, it is preferable to use a nonaqueous electrolytic solution containing a lithium salt, an ion conductive polymer, or the like. Examples of the non-aqueous solvent of the nonaqueous electrolyte in the non-aqueous electrolyte solution containing the lithium salt include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC) Methyl ethyl carbonate (MEC), and the like. Examples of the lithium salt that can be dissolved in the nonaqueous solvent include lithium hexafluorophosphate (LiPF ₆ ), lithium borohydride (LiBF ₄ ), lithium trifluoromethanesulfonate (LiSO ₃ CF ₄ ), and the like.

Since the lithium ion secondary battery of the present embodiment uses the electrode material of the first embodiment described above, the large current charging / discharging can be maintained over a long life span, and is also a high capacity.

Example

Hereinafter, the effects of the present invention will be described in detail with reference to Examples and Comparative Examples of the present invention. In this embodiment, an electrode material was produced by the following method and its performance was evaluated.

&Lt; Examples 1 to 8 &

Using the mixer, the active material, organic material, carbon nanotube, and carbon black shown in Table 1 below were mixed in a solvent. Thereafter, the electrode materials of Examples 1 to 8 were obtained by drying, heating and shredding. The conditions in each step are shown in Table 2 below.

&Lt; Example 9 >

(Mn (NO ₃ ) ₂ .6H ₂ O), nickel nitrate (Ni (NO ₃ ) ₂ .6H ₂ O) and cobalt nitrate (Co (NO ₃ ) ₂ .6H ₂ O) : Co = 4: 1: 1, and dissolved. Thereafter, lithium carbonate (Li ₂ CO ₃ ) was added in a molar ratio of Li ₂ CO ₃ : (Mn + Ni + Co) = 1.75: 1 in a nitrogen atmosphere and sufficiently stirred, filtered, washed, &Lt; / RTI &gt;

This was calcined at 500 ° C for 4 hours in the atmosphere, and then calcined at 900 ° C for 10 hours to obtain a black powder. For the obtained powder, it was a compound having the elemental analysis, and was subjected to X-ray diffraction _{measurement, 0.5Li 2 MnO 3 -0.5LiMn 1/} 3 Ni 1/3 the composition of Co _1/3 O _2.

Subsequently, a carbon nanotube whose surface was covered with an amorphous carbon layer was obtained by the method described in Example 1 of Japanese Patent Laid-Open No. 2004-299986. This and the above-mentioned black powder and carbon black were mixed in a solvent using a mixer. Thereafter, the electrode material of Example 9 was obtained by drying, heating and shredding. The materials used are shown in Table 1 below. The conditions in each step are shown in Table 2 below.

&Lt; Example 10 >

(NiCl ₂ .6H ₂ O) and manganese chloride (MnCl ₂ .4H ₂ O) were mixed at a molar ratio of Ni: Mn = 1: 3, and then ammonium oxalate ((NH ₄ ) ₂ C ₂ O ₄ H ₂ O) at a molar ratio of (Ni + Mn): C ₂ O ₄ = 5: 6. The mixture was dried at 110 DEG C for 2 hours and then calcined at 400 DEG C for 4 hours in the air.

Thereafter, lithium carbonate (Li ₂ CO ₃ ) was added and mixed in a molar ratio of Li: (Ni + Mn) = 1: 2, followed by mixing in air at 700 ° C for 48 hours to obtain a black powder. The obtained powder was subjected to elemental analysis and X-ray diffraction measurement, LiNi _0.5 Mn ₀ was a compound having a composition of _{1 0.5} O _4.

Subsequently, a carbon nanotube whose surface was covered with an amorphous carbon layer was obtained by the method described in Example 1 of Japanese Patent Laid-Open Publication No. 2004-299986. This and the above-mentioned black powder and carbon black were mixed in a solvent using a mixer. Thereafter, the electrode material of Example 10 was obtained by drying, heating and shredding. The materials used are shown in Table 1, and the conditions in each step are shown in Table 2 below.

The electrode materials of Examples 1 to 10 prepared by the above-described method were photographed in a reflection electron composition using a scanning electron microscope (JSM-7400F, manufactured by Nippon Denshi Kabushiki Kaisha), and a coating of amorphous carbon Respectively. Transmission electron beams (TEM) images of the electrode materials of Examples 1 to 10 were photographed using a transmission electron microscope (JEM-2010 manufactured by JEOL Ltd.), and the presence or absence of bonding between the amorphous carbon and the carbon nanotubes And whether or not the carbon nanotubes and the carbon black were bonded. The results are shown in Table 3 below.

As shown in Table 3, the electrode materials of Examples 1 to 10 had an amorphous carbon coverage of 10% or more. In all of the electrode materials of Examples 1 to 10, the amorphous carbon and the carbon nanotube bond, the carbon nanotube and the carbon black bond, and the carbon black formed the conductive network.

&Lt; Examples 11 to 20 &

Subsequently, electrodes (positive electrode and negative electrode) were formed by using the electrode materials of Examples 1 to 10, and lithium ion secondary batteries of Examples 11 to 20 were fabricated. Specifically, the electrode materials of Examples 1 to 10 and polyvinylidene fluoride (KF polymer solution manufactured by Kureha Kabushiki Kaisha) as a binder were mixed in a ratio of 95: 5 by mass ratio. N-methylpyrrolidone (product number 328634, manufactured by Sigma-Aldrich) was added as a dispersion solvent, and the resultant mixture was kneaded using a kneader (Hybis mix and Homodisper, manufactured by Primemix) to prepare an electrode mixture (slurry) Respectively.

The electrode mixture (slurry) was applied to an aluminum foil or a copper foil having a thickness of 20 占 퐉, and dried. Then, the electrode mixture was cut into 40 mm square pieces to obtain an electrode for a lithium secondary battery. As the separator for electrically isolating them, an olefin fiber nonwoven fabric having a size of 50 mm was used. A solution of lithium hexafluorophosphate (LiPF _6, manufactured by Stella Chemipa Co., Ltd.) was added to a solution of EC (ethylene carbonate, manufactured by Aldrich) and MEC (methyl ethyl carbonate, manufactured by Aldrich) in a volume ratio of 30:70, ) Dissolved in 1 mol / L was used.

Graphite (artificial graphite MCMB6-28 manufactured by Osaka Gas Co., Ltd.) was used as a negative electrode active material, acetylene black (HS-100 manufactured by Denki Kagaku Kogyo K. K.) and a binder Was mixed with polyvinylidene fluoride at a mass ratio of 95: 1: 4. Thereafter, a slurry was prepared in the same manner as in the above-described electrode material, coated on a copper foil having a thickness of 20 mu m and dried, and then a negative electrode cut into a 40 mm square was used. After terminals were connected to the positive electrode and the negative electrode, the whole was enclosed in an aluminum laminate package to form a 70 mm laminate battery.

The surface of the electrode was observed using a scanning electron microscope without using a part of the pressed electrode in a battery. Then, on the scanning electron beam (SEM) obtained, It was confirmed that carbon black forms a conductive network over the entire electrode. These results are shown in Table 4 above. Since formation of a conductive network by carbon black was confirmed on any of the electrode surfaces of Examples 1 to 10, it was presumed that the same conductive network was formed on the back surface of the electrode in contact with the metal foil as the current collector and was electrically connected to the current collector .

&Lt; Comparative Examples 1 to 10 &

Using the same active materials, carbon nanotubes, and carbon black as those of Examples 1 to 10, electrode materials of Comparative Examples 1 to 10 shown in Table 4 were produced. The electrode materials of Comparative Examples 1 to 10 were mixed so as to have a ratio of binder: remaining portion = 5: 95 in a mass ratio to a polyvinylidene fluoride (KF polymer solution manufactured by Kureha K.K.) as a binder, N-methylpyrrolidone was added and kneaded using a kneader to prepare an electrode mixture (slurry).

However, in Comparative Examples 1 to 8, instead of adding an organic substance decomposing to form amorphous carbon, instead of the carbon black produced when the organic substances used in Examples 1 to 8 were decomposed, Was added in an increased amount to the amount of carbon black of Examples 1 to 8. The types and blending amounts of the active material, the carbon nanotubes, and the carbon black in the electrode materials of Comparative Examples 1 to 10 are summarized in Table 4 below.

&Lt; Comparative Examples 11 to 12 >

An electrode material of Comparative Example 11 was prepared in the same manner as in Example 1 except that the amount of sucrose in Example 1 was changed from 3 g to 0.3 g. Specifically, an electrode material of Comparative Example 11 was obtained by mixing a conductive agent, an organic material that forms amorphous carbon by thermal decomposition, carbon nanotubes, and carbon black in a solvent using a mixer, followed by drying, heating, and shaking.

The covering ratio of the obtained amorphous carbon to the active material of the electrode material of Comparative Example 11 was measured in terms of the reflection electron composition obtained using a scanning electron microscope, and found to be 5%. Further, by the transmission electron beam (TEM) image obtained by using a transmission electron microscope (JEM-2010 manufactured by JEOL Ltd.), the presence or absence of bonding between the amorphous carbon and the carbon nanotube and the bonding between the carbon nanotube and the carbon black The binding between the carbon nanotubes and the carbon black was recognized, but the binding between the amorphous carbon and the carbon nanotubes was not recognized.

Subsequently, the electrode material of Comparative Example 11 was compounded with polyvinylidene fluoride as a binder in the same manner as in Example 10, N-methylpyrrolidone was added as a dispersion solvent, and kneaded using a kneader to prepare an electrode mixture (slurry) Respectively. A laminate-type battery of Comparative Example 12 was also produced using this electrode.

&Lt; Comparative Examples 13 to 22 >

The laminated cells of Comparative Examples 13 to 22 were produced in exactly the same manner as in Examples 11 to 20 except that the electrode mix prepared in Comparative Examples 1 to 10 was used for the electrodes.

[Discharge performance evaluation]

Then, discharge performance tests were conducted on the lithium ion secondary batteries (laminate batteries) of Examples 11 to 20 and Comparative Examples 12 to 22 produced by the above-described method. Specifically, it was confirmed that the charge / discharge efficiency became close to 100% after the first charge of each cell, and the constant current discharge was performed at a current density of 0.7 mA / cm 2 at 2.7 V (Examples 12, 15, 17, 17, and 19 were 1.2 V and 3.0 V in Example 20 and Comparative Example 22). The current value capable of charging / discharging the capacity (mAh) to 1 hour was set to &quot; 1C &quot;.

After charging and discharging for the first time, the charge was 4.3 V (2.8 V for Examples 12, 15 and 17 and Comparative Examples 14, 17 and 19, 4.8 V for Examples 19 and 21, 5.0 V for Examples 20 and 22 (At the time of 0.2 C constant current and at the end of the current of 0.05 C) and discharging is performed every cycle at 0.2 C, 0.33 C, 0.5 C, 1 C, 3 C, 5 C, The current value was gradually increased to the end of 1.2 V in Comparative Examples 14, 17 and 19, and the end of 3.0 V in Example 20 and Comparative Example 22, and the stopping was carried out for 10 minutes between them for charging and discharging, (%) Of the charge / discharge capacity with respect to the charge / discharge capacity of the capacitor C was regarded as the rate characteristic. Further, the DC resistance (DCR) of the battery was calculated from the I-V characteristic at the time of SOC (charge depth) of 50%. The DC resistance at the time of charging was referred to as &quot; charged DCR &quot; and the discharge was defined as &quot; discharge DCR &quot;. The results are summarized in Table 5 below.

As shown in Table 5, the lithium ion secondary batteries of Examples 11 to 20 using the electrode materials of Examples 1 to 10 had larger cell capacities than the lithium secondary batteries of Comparative Examples 12 to 22, The DC resistance in the discharge was low and the discharge performance was excellent. From these results, it was confirmed that according to the present invention, it is possible to maintain a large current charge / discharge over a long life span, and to realize a lithium ion secondary battery with a high capacity.

Claims (9)

An electrode material for a lithium ion secondary battery containing an active material and a conductive material,
The active material is a lithium-containing complex oxide, tin oxide or silicon oxide,
The conductive material is amorphous carbon, carbon nanotube, and carbon black,
And a part or all of the surface of the active material is covered with the amorphous carbon
Electrode material for lithium ion secondary battery. The electrode material for a lithium ion secondary battery according to claim 1, wherein the covering ratio of the surface of the active material to the amorphous carbon is 10 to 95%. The electrode material for a lithium ion secondary battery according to claim 1 or 2, wherein the amorphous carbon is a thermal decomposition product of an organic material. 4. The method according to any one of claims 1 to 3,
LiCoO ₂ ,
LiMn ₂ O ₄ ,
LiNiO _2,
Li (Mn _a Ni _b Co _c ) O ₂
1, 0 < b < 1, 0 < c < 1,
Li (Al _d Ni _e Co _f ) O ₂
D + e + f = 1 and 0 < d < 1, 0 &
xLi ₂ MnO ₃ - (1-x) LiMO ₂
However, 0 < x < 1,
And LiNi _g Mn _(2-g) O ₄
However, 0 < g < 2
Containing complex oxide selected from the group consisting of lithium,
An electrode material for a lithium ion secondary battery, which is used for a positive electrode material. The lithium secondary battery according to any one of claims 1 to 3, wherein the active material is Li ₄ Ti ₅ O ₁₂ , tin oxide containing metal tin, or silicon oxide containing metal silicon,
An electrode material for a lithium ion secondary battery, which is used for an anode material. The method according to any one of claims 1 to 3, wherein the active material is a mixture of tin oxide containing metal tin or silicon oxide containing metal silicon and graphite,
An electrode material for a lithium ion secondary battery, which is used for an anode material. A step of mixing an active material, an organic material that forms amorphous carbon by thermal decomposition, a carbon nanotube, and carbon black in a solvent,
Drying the mixture obtained by the mixing and then heating to form amorphous carbon derived from the organic material on the surface of the active material;
A step of crushing the mixture after the heating
Wherein the electrode material is a lithium ion secondary battery. A step of mixing the active material, the carbon nanotubes, and the carbon black in a solvent;
Drying the mixture obtained by the mixing and then heating,
A step of crushing the mixture after the heating
Lt; / RTI &gt;
Wherein either or both of the carbon nanotube and the carbon black contains amorphous carbon. A lithium ion secondary battery using the electrode material according to any one of claims 1 to 6.