JP2008251523A - Negative electrode material for nonaqueous electrolyte secondary battery, negative electrode for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery which is excellent in discharging load characteristics and cycle characteristics and has a high battery capacity, to provide a negative electrode for the nonaqueous electrolyte secondary battery, and to provide a negative electrode material for the nonaqueous electrolyte secondary battery. <P>SOLUTION: The negative electrode material for the nonaqueous electrolyte secondary battery is obtained at least by a mixture of a substance A and a substance B having different particle diameter distributions, and (i) an average particle diameter (D50) of the substance A is 18 μm or more and 40 μm or less, (ii) an average particle diameter of the substance B is 1 μm or more and 15 μm or less, (iii) a difference of the average particle diameter of the substance A and the average particle diameter of the substance B is 5 μm or more, (iv) a ratio of the substance B against a total volume of the substance A and the substance B is 10 wt.% ore more, and (v) a value of a standard deviation of the anode material for the nonaqueous electrolyte secondary battery obtained from the particle diameter distribution is 0.250 or more. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a negative electrode material for a non-aqueous electrolyte secondary battery, a negative electrode for a non-aqueous electrolyte secondary battery using the negative electrode material, and a discharge load characteristic, a cycle characteristic and a high battery capacity using the negative electrode. The present invention relates to a nonaqueous electrolyte secondary battery suitable for portable electronic devices, electric vehicles, power storage, and the like.

  With the reduction in size and weight of electronic devices such as mobile phones and notebook computers, non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries are required to have higher energy density. Current non-aqueous electrolyte secondary batteries generally use lithium oxide as a positive electrode active material (positive electrode material) and a carbon material as a negative electrode active material (negative electrode material). In order to improve battery performance, It is important to improve the characteristics of the positive electrode material and the negative electrode material.

  The carbon material used for the negative electrode material is classified into two types. One is an amorphous carbon material with a low degree of crystallinity, and the other is a graphite material with a high degree of crystallinity. Currently, graphite materials are mainly used in mobile phones and notebook computers. . This graphite material has a higher true density than the amorphous carbon material and is effective for increasing the energy density of the battery. However, the theoretical capacity is determined to be 372 mAh / g, and it corresponds to further increase in capacity. It is a difficult situation.

In order to provide a non-aqueous solvent secondary battery that maintains a high discharge capacity comparable to that of graphite while keeping the irreversible capacity very low and improving the charge / discharge efficiency and stability to the electrolyte. A non-aqueous solvent comprising a composite carbonaceous material obtained by adhering an organic carbide such that the amount of residual carbon with respect to 100 parts by weight of the graphitic carbonaceous material is 0.1 to 12 parts by weight on the surface of the carbonaceous material. An electrode material for a secondary battery is disclosed (see Patent Document 1).
JP-A-10-158005

  The present invention relates to a non-aqueous electrolyte secondary battery excellent in discharge load characteristics, cycle characteristics and high battery capacity, a negative electrode for a non-aqueous electrolyte secondary battery and a negative electrode for a non-aqueous electrolyte secondary battery for obtaining the same. The purpose is to provide materials.

  As a result of studies to achieve the above objective, two types of substances with different particle size distributions are mixed together to broaden the particle size distribution, thereby reducing voids between particles and increasing the electrode orientation at higher density. It was found that the liquid injection property can be improved, and the cycle characteristics and discharge load characteristics are also improved.

That is, the present invention is (1) a negative electrode material for a non-aqueous electrolyte secondary battery obtained by mixing at least a substance A and a substance B having different particle size distributions,
(I) The average particle diameter (D50) of the substance A is 18 μm or more and 40 μm or less,
(Ii) The average particle diameter (D50) of the substance B is 1 μm or more and 15 μm or less,
(Iii) The difference between the average particle diameter of the substance A and the average particle diameter of the substance B is 5 μm or more,
(Iv) The ratio of the substance B to the total amount of the substance A and the substance B is 10% by weight or more,
(V) The standard deviation value of the negative electrode material for a nonaqueous electrolyte secondary battery obtained from the particle size distribution is 0.250 or more, and is larger than the standard deviation values of the substance A and the substance B.
The present invention relates to a negative electrode material for a non-aqueous electrolyte secondary battery.

  The present invention also relates to (2) the negative electrode material for a non-aqueous electrolyte secondary battery according to (1), wherein either one or both of the substance A and the substance B is a carbon material.

  The present invention also relates to (3) the negative electrode material for a non-aqueous electrolyte secondary battery according to (1) or (2), wherein either one or both of the substance A and the substance B is graphite.

  Further, the present invention is (4) a graphite obtained by collecting or combining a plurality of flat graphite fine particles so that their orientation planes are not parallel to each other. The present invention relates to a negative electrode material.

  Moreover, this invention uses the negative electrode material for nonaqueous electrolyte secondary batteries as described in any one of (5) said (1)-(4), The nonaqueous electrolyte secondary characterized by the above-mentioned. The present invention relates to a negative electrode for a battery.

  The present invention also relates to (6) a nonaqueous electrolyte secondary battery comprising the negative electrode for a nonaqueous electrolyte secondary battery described in (5) above.

  According to the present invention, a nonaqueous electrolyte secondary battery excellent in discharge load characteristics, cycle characteristics, and high battery capacity, a negative electrode for a nonaqueous electrolyte secondary battery for obtaining the same, and a nonaqueous electrolyte secondary battery A negative electrode material can be provided.

  Hereinafter, the present invention will be described in detail.

<Negative electrode material for non-aqueous electrolyte secondary battery>
The negative electrode material for a non-aqueous electrolyte secondary battery according to the present invention is a negative electrode material for a non-aqueous electrolyte secondary battery obtained by mixing at least a substance A and a substance B having different particle size distributions. The average particle diameter (D50) of the substance A is 18 μm or more and 40 μm or less, (ii) the average particle diameter (D50) of the substance B is 1 μm or more and 15 μm or less, and (iii) the average particle diameter of the substance A and the above The difference in the average particle diameter of the substance B is 5 μm or more, (iv) the ratio of the substance B to the total amount of the substance A and the substance B is 10% by weight or more, and (v) obtained from the particle size distribution. The standard deviation value of the negative electrode material for a non-aqueous electrolyte secondary battery is 0.250 or more and is larger than the standard deviation values of the substance A and the substance B.

  The negative electrode material for a non-aqueous electrolyte secondary battery of the present invention can be produced by mixing at least substances A and B having different particle size distributions. Here, the particle size distribution can be measured using, for example, a particle size distribution measuring apparatus using a laser light scattering method (for example, SALD-3000 manufactured by Shimadzu Corporation). Further, the mixing of the substance A and the substance B can be performed using, for example, a known mixing apparatus at room temperature, and the means and conditions thereof are not particularly limited. For example, a ribbon type mixer, a V type mixer, It is performed mechanically using a conical mixer, a planetary mixer, a raker, or the like.

Moreover, it is preferable that one or both of the substance A and the substance B is a carbon material, more preferably a carbon material. From the viewpoint of increasing the filling amount of the electrode, either one or both are It is even more preferable that it is graphite, and it is particularly preferable that both are graphite. Here, examples of the carbon material include graphite (crystalline carbon), graphitizable carbon (amorphous carbon), non-graphitizable carbon (amorphous carbon), and the like. The graphitizable carbon is a carbon material that easily develops into a graphite structure when heat-treated at a temperature of 2000 ° C. or higher, and has a true density of less than 2220 kg / m ³ , such as coke and carbon fiber. Is mentioned. Examples of the graphite include natural graphite and artificial graphite obtained by heat-treating easily graphitizable carbon at a high temperature. The true density is 2220 kg / m ³ or more. The artificial graphite is preferably graphite having voids inside the particles, in which a plurality of flat graphite fine particles are aggregated or bonded so that the orientation planes are non-parallel (Japanese Patent Laid-Open No. 10-158005). (See publications). Non-graphitizable carbon is a carbon material that does not reach a graphite structure even when subjected to high temperature treatment, and has a true density of less than 2220 kg / m ³ , and examples thereof include furfuryl alcohol resin. The true density can be obtained by a butanol method based on JIS R7212. In the present invention, the specific combination of the substance A and the substance B is preferably graphite and graphite, or graphite and graphitizable carbon, and more preferably graphite and graphite.

  In the present invention, (i) the average particle diameter (D50) of the substance A is 18 μm or more and 40 μm or less, preferably 18 μm or more and 30 μm or less, and more preferably 20 μm or more and 25 μm or less. When the average particle size of the substance A is less than 18 μm, the specific surface area is increased, whereby the charge / discharge efficiency is lowered, and the clay of the paste containing the negative electrode material and the binder used when applied to the electrode is improved. When the average particle size of the substance A is more than 40 μm, the specific surface area is reduced, whereby the charge / discharge efficiency is improved, but the discharge load characteristics are lowered.

  In the present invention, (ii) the average particle diameter (D50) of the substance B is 1 μm or more and 15 μm or less, preferably 3 μm or more and 15 μm or less, and more preferably 3 μm or more and 10 μm or less. If the average particle diameter of the substance B is less than 1 μm, the particles are likely to aggregate with each other and difficult to be uniformly mixed with the substance A, so that the charge / discharge efficiency decreases. If the average particle diameter of the substance B exceeds 15 μm, the average particle diameter is close to that of the substance A, and it is not expected to suppress the electrode orientation and improve the liquid injection property at high density, and the discharge load characteristics and the cycle maintenance ratio decrease. .

  In the present invention, (iii) the difference between the average particle diameter of the substance A and the average particle diameter of the substance B is 5 μm or more, preferably 10 μm or more and 30 μm or less. If the difference in the average particle diameter is less than 5 μm, there is no difference in the average particle diameter between the substance A and the substance B, and it is not expected to suppress the electrode orientation and improve the liquid injection property at high density. Maintenance rate decreases.

  The average particle size (D50) in the present invention is a particle size in which the cumulative volume of the particle size distribution is 50% by volume, and is usually a laser diffraction method, for example, a laser diffraction type particle size distribution measuring device (Shimadzu Corporation). This can be measured using a SALD-3000J manufactured by Seisakusho.

  In the present invention, (iv) the ratio of the substance B to the total amount of the substance A and the substance B is 10% by weight or more, preferably 30% by weight or more. When the ratio of the substance B is less than 10% by weight, the particle size distribution becomes sharp, and improvement in electrode orientation and liquid injection property in the expected high density cannot be expected, and the discharge load characteristics and cycle maintenance ratio are lowered. In addition, since the applicability | paintability with respect to an electrode will deteriorate and charging / discharging efficiency will fall when the mixture ratio of the substance B in a negative electrode material increases, the ratio of the substance B contained in the negative electrode material of this invention is 60. It is preferably no more than wt%, more preferably no more than 40 wt%. In the present invention, the ratio of the substance A to the total amount of the substance A and the substance B is 90% by weight or more, preferably 70% by weight or less.

In the present invention, the standard deviation value of the negative electrode material for a non-aqueous electrolyte secondary battery obtained from (v) particle size distribution is 0.250 or more, preferably 0.300 to 0.400. . If the value of the standard deviation of the negative electrode material for a non-aqueous electrolyte secondary battery is less than 0.250, higher electrode density cannot be expected. The standard deviation value of the negative electrode material for a non-aqueous electrolyte secondary battery is preferably larger than the standard deviation values of the substance A and the substance B, and is larger by 0.050 or more. Here, the standard deviation is a standard deviation defined on a logarithmic scale, and can be calculated by, for example, analysis software belonging to a laser diffraction particle size distribution measuring apparatus (SALD-3000J, manufactured by Shimadzu Corporation). it can.
The average particle size of the negative electrode material for a non-aqueous electrolyte secondary battery of the present invention is preferably 10 μm or more and 40 μm or less, more preferably 10 μm or more and 30 μm or less, and preferably 10 μm or more and 25 μm or less. Particularly preferred. When the average particle diameter of the negative electrode material for a non-aqueous electrolyte secondary battery exceeds 40 μm, the electrode surface is uneven, and a short circuit is likely to occur. On the other hand, when the average particle diameter is less than 10 μm, the specific surface area increases, the electrode coatability and the adhesion tend to deteriorate, and the safety tends to decrease.

<Negative electrode for non-aqueous electrolyte secondary battery>
The negative electrode for a non-aqueous electrolyte secondary battery according to the present invention uses the negative electrode material for a non-aqueous electrolyte secondary battery according to the present invention. For example, the negative electrode material for a non-aqueous electrolyte secondary battery according to the present invention, an organic type A binder (binder) and various additives added as necessary are kneaded with a solvent, etc., with a stirrer, ball mill, super sand mill, pressure kneader, etc. Then, this is applied to the current collector by a known method such as a metal mask printing method, electrostatic coating method, dip coating method, spray coating method, roll coating method, doctor blade method, gravure coating method, screen printing method, etc. It can be formed by drying and, if necessary, compression molding by a molding method such as a roll press. Alternatively, the paste-like negative electrode material slurry can be formed into a sheet shape, a pellet shape, or the like, and then integrated with the current collector by a forming method such as a roll press.

  Examples of the organic binder include polyethylene, polypropylene, ethylene propylene terpolymer, butadiene rubber, styrene butadiene rubber, and butyl rubber; methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, and hydroxyethyl acrylate. Ethylenically unsaturated carboxylic acid esters such as hydroxyethyl methacrylate; ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid and maleic acid; unsaturated nitriles such as acrylonitrile and methacrylonitrile; Polymer compounds with high ionic conductivity such as vinylidene fluoride, polyethylene oxide, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, etc. There can be used. The organic binder is preferably contained in an amount of 1 to 20 parts by weight with respect to 100 parts by weight of the mixture of the negative electrode material for a non-aqueous electrolyte secondary battery of the present invention and the organic binder.

  Moreover, as said solvent, the solvent which can melt | dissolve or disperse | distribute a binder normally is used, For example, organic solvents, such as N-methyl-2-pyrrolidone and N, N- dimethylformamide, can be illustrated. The amount of the solvent used is not particularly limited as long as it is in a paste form. For example, it is usually about 60 to 150 parts by weight, preferably 60 parts per 100 parts by weight of the negative electrode material for a nonaqueous electrolyte secondary battery of the present invention. About 100 parts by weight.

  Moreover, the thickener of a negative electrode material slurry can also be used as said additive. Examples of the thickener include carboxymethyl cellulose, sodium carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, polyacrylic acid (salt), oxidized starch, phosphorylated starch, and casein. Moreover, you may mix a conductive support agent in order to improve the electroconductivity as an electrode as said additive. Examples of the conductive auxiliary agent include natural graphite, artificial graphite, carbon black (for example, acetylene black, thermal black, furnace black), graphite, conductive oxide, nitride, and the like. Two or more types can be used in combination. The amount of such an additive used is not particularly limited as long as it does not deteriorate the characteristics of the secondary battery, but 1 to the total amount of the negative electrode material for non-aqueous electrolyte secondary battery and the additive of the present invention. About 10% by weight is preferable, and about 1 to 5% by weight is more preferable.

Moreover, as said collector, well-known things, such as foil, meshes, such as aluminum, nickel, copper, can be used, for example. The coating amount of the current collector of the negative electrode material paste is not particularly limited, preferably about 5 to 15 mg / cm ^2, about 7~13mg / cm ² is more preferable.

<Nonaqueous electrolyte secondary battery>
The non-aqueous electrolyte secondary battery of the present invention uses the negative electrode for a non-aqueous electrolyte secondary battery of the present invention. For example, the negative electrode for a non-aqueous electrolyte secondary battery of the present invention and a positive electrode are interposed via a separator. Can be obtained by injecting an electrolytic solution. A typical example of the non-aqueous electrolyte secondary battery is a lithium ion secondary battery. In addition, a gasket, a sealing plate, a case, and the like that are usually used in the field may be further provided.

  The positive electrode can be obtained by forming a positive electrode material layer containing a positive electrode active material, a conductive agent and the like on the current collector surface in the same manner as the negative electrode.

As the positive electrode active material is not particularly limited, for _{example, LiNiO 2, LiCoO 2, LiMn} 2 O 4, LiMnO 2, LiCo 0.33 Ni 0.33 Mn 0.33 O 2 and lithium composite oxides and Cr ₃ O ₈ , Cr ₂ O ₅ , V ₂ O ₅ , V ₆ O ₁₃ , VO ₂ , MnO ₂ , TiO ₂ , MoV ₂ O ₈ , TiS ₂ , V ₂ S ₅ , VS ₂ , MoS ₂ , MoS ₃ , Conductive polymers such as polyaniline and polypyrrole, porous carbon and the like can be used alone or in combination. Examples of the conductive agent include natural graphite, artificial graphite, carbon black, and acetylene black.

Examples of the electrolytic solution include LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiClF ₄ , LiSbF ₆ , LiAlO ₄ , LiAlCl ₄ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ). ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiCl, LiI, LiSO ₃ CF _{3 and} other lithium salts (electrolytes) that produce anions that are difficult to solvate, such as carbonates, lactones, chain ethers, cyclic A so-called organic electrolytic solution dissolved in a non-aqueous solvent such as ethers, sulfolanes, sulfoxides, nitriles, amides, polyoxyalkylene glycols or the like is used.

  Specific examples of the non-aqueous solvent include ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, cyclopentanone, sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane, dimethyl sulfoxide, and 3-methyl. -1,3-oxazolidine-2-one, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, methyl butyl carbonate, ethyl propyl carbonate, ethyl butyl carbonate, 1,2-dimethoxy Ethane, dimethyl ether, diethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 4-methyldioxolane, 1,3-dioxolane, aceto Nitrile, propionitrile, benzonitrile, N, N-dimethylformamide, N, N-dimethylacetamide, diethylene glycol, methyl acetate, ethyl acetate, etc. can be used, and these solvents can be used alone or as a mixture of two or more. It may be.

  Further, the concentration of the electrolyte is not particularly limited, but is preferably 0.3 to 5 mol, more preferably 0.5 to 3 mol, and 0.8 to 1 with respect to 1 L of the electrolytic solution. Particularly preferred is .5 moles.

  As said separator, the nonwoven fabric, cloth, porous film which combined polyolefin, such as polyethylene and a polypropylene, a porous film, or those combined can be used, for example. In addition, when it is set as the structure where the positive electrode and negative electrode of the secondary battery which are produced do not contact directly during use, it is not necessary to use a separator.

  Further, the structure of the non-aqueous electrolyte secondary battery of the present invention is not particularly limited. Usually, a positive electrode and a negative electrode, and a separator provided as necessary, are wound in a flat spiral shape to form a wound electrode plate. It is common to form a group or to laminate them as a flat plate to form a laminated electrode plate group and to enclose these electrode plate groups in an exterior body. In addition, the nonaqueous electrolyte secondary battery of the present invention can have any form such as a paper type, a button type, a coin type, a stacked type, a square type, and a cylindrical type. In addition, the partial cross section front view of an example of a cylindrical lithium ion secondary battery is shown in FIG. 1 as an example of a non-aqueous electrolyte secondary battery. The cylindrical lithium ion secondary battery shown in FIG. 1 is obtained by winding a positive electrode 1 processed into a thin plate shape and a negative electrode 2 processed in the same manner through a separator 3 made of polyethylene microporous membrane, This is inserted into a metal battery can 7 and sealed. The positive electrode 1 is bonded to the positive electrode lid 6 via the positive electrode tab 4, and the negative electrode 2 is bonded to the battery bottom via the negative electrode tab 5. The positive electrode lid 6 is fixed to a battery can (negative electrode can) 7 with a gasket 8.

  The non-aqueous electrolyte secondary battery of the present invention is superior in discharge load characteristics, cycle characteristics, high battery capacity, and safety compared to non-aqueous electrolyte secondary batteries using a conventional carbon material for the negative electrode. It is suitable as a power source and auxiliary power source for various electronic / electrical equipment, automobiles, power storage and the like.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited by description of the said Example.

<Preparation of negative electrode material for non-aqueous electrolyte secondary battery>
(Examples 1-6, Comparative Examples 1-9)
As shown in Tables 1 and 2, Substance A and Substance B having different particle size distributions were mixed for 10 minutes using a V-type mixer to prepare a negative electrode material for a non-aqueous electrolyte secondary battery. The average particle diameter, standard deviation, true density of substance A and substance B, and the average particle diameter and standard deviation of the negative electrode material for nonaqueous electrolyte secondary batteries were measured as follows.

  In addition, it is as follows about the manufacturing method of the artificial graphite used in each Example and the comparative example as the substance A and the substance B, natural graphite, and amorphous carbon. Moreover, the unit of the mixing ratio of the substance A and the substance B in Tables 1-2 is a weight part.

(Physical property measurement)
Average particle size: Laser diffraction type particle size distribution measuring device (manufactured by Shimadzu Corporation) was prepared by dispersing a sample (substance A, substance B or negative electrode material for non-aqueous electrolyte secondary battery) in purified water together with a surfactant. , SALD-3000J) was measured by laser diffraction while circulating with a pump while applying ultrasonic waves. The particle diameter at which the cumulative volume of the obtained particle diameter distribution was 50% by volume was defined as the average particle diameter (D50).

  Standard deviation: It was calculated by analysis software belonging to a laser diffraction type particle size distribution measuring apparatus (manufactured by Shimadzu Corporation, SALD-3000J).

  True density: Measured by a butanol method based on JIS R7212.

(Carbon material used as substance A or substance B)
(A) Artificial graphite 100 parts by weight of coke powder having an average particle diameter of 5 μm, 30 parts by weight of tar pitch, 30 parts by weight of silicon carbide having an average particle diameter of 48 μm, and 20 parts by weight of coal tar are mixed at 270 ° C. for 1 hour. Mixed. The obtained mixture was pulverized, pressed into pellets, pre-fired at 1000 ° C. in nitrogen, and then graphitized at 3000 ° C. using an Atchison furnace. The graphite block obtained as described above was pulverized by using a hammer mill or a jet mill and appropriately selecting the pulverization conditions so that the average particle diameter of the resulting artificial graphite would be a desired value. The pulverized artificial graphite was then passed through a 250 mesh standard sieve. According to the scanning electron microscope (SEM) photograph of the obtained artificial graphite, the graphite particles had a structure in which a plurality of flat particles were aggregated or bonded so that their orientation planes were non-parallel.

(B) Natural Graphite Natural graphite produced in China was pulverized using a hammer mill or a jet mill with appropriate selection of pulverization conditions so that the average particle diameter of the natural graphite obtained would be a desired value. The ground natural graphite was then passed through a 250 mesh standard sieve.

(C) Amorphous carbon Coal coke was pulverized by using a hammer mill or a jet mill and appropriately selecting the pulverization conditions so that the average particle diameter of the obtained amorphous carbon would be a desired value. . The ground amorphous carbon was then passed through a 250 mesh standard sieve.

<Evaluation of negative electrode material>
Using the negative electrode materials for non-aqueous electrolyte secondary batteries obtained in the above examples and comparative examples, lithium ion secondary batteries were produced as follows.

(Preparation of negative electrode)
98% by weight of the negative electrode material for each non-aqueous electrolyte secondary battery, 1% by weight of styrene butadiene rubber (manufactured by Zeon Corporation, trade name “BM-400B”) as a binder, and carboxymethyl cellulose (first) as a thickener Kogyo Seiyaku Co., Ltd.) 1% by weight was mixed and dispersed in water to obtain a uniform slurry. This slurry was applied to the surface of a 40 μm thick copper foil, dried at 80 ° C. and 140 ° C., pressure-molded, and cut into a size of φ9.5 mm to produce a negative electrode.

(Production of lithium ion secondary battery)
The negative electrode prepared above was used as the working electrode, and 1 mm thick metal lithium was used as the counter electrode, and both electrodes were opposed to each other through a separator (manufactured by Asahi Kasei Co., Ltd., microporous olefin membrane). Further, a nonaqueous electrolyte solution containing 0.5% by weight of vinylene carbonate was injected into a mixed solution (3: 7 volume ratio) of 1.0M LiPF ₆ / ethylene carbonate and methyl ethyl carbonate, and a secondary lithium ion solution was obtained by a conventional method. A battery was produced.

  The following evaluation was performed about the obtained lithium ion secondary battery.

(Charge capacity / Discharge capacity)
The produced lithium ion secondary battery (electrode density: 1700 kg / m ³ ) in an atmosphere of 25 ° C. by a constant current constant voltage method, a constant current of 0.2 mA, a constant voltage of 0 V (Li / Li ⁺ ), and a cut current of 0.3. The battery was charged under the condition of 02 mA, and the charge capacity (kg / Ah) at this time was measured. Next, constant current discharge was performed by a constant current method until a constant current of 0.2 mA and a cut voltage of 1.5 V (Li / Li ⁺ ) were obtained, and the discharge capacity (kg / Ah) at this time was measured.

(Charge / discharge efficiency)
From the charge capacity and discharge capacity measured above, the charge / discharge efficiency (%) was calculated by the following formula.

Charging / discharging efficiency (%) = discharge capacity / charge capacity × 100
(Discharge load capacity)
The produced lithium ion secondary battery (electrode density: 1700 kg / m ³ ) in an atmosphere of 25 ° C. by a constant current constant voltage method, a constant current of 0.2 mA, a constant voltage of 0 V (Li / Li ⁺ ), and a cut current of 0.3. The battery was charged under the condition of 02 mA. Next, a constant current discharge is performed until a constant current of 5.0 mA and a cut voltage of 1.5 V (Li / Li ⁺ ) are obtained, and a discharge capacity (kg / Ah) at this time is measured. did.

(Cycle maintenance rate)
The produced lithium ion secondary battery (electrode density: 1700 kg / m ³ ) in an atmosphere at 25 ° C. is a constant current constant voltage method, a constant current of 0.4 mA, a constant voltage of 0 V (Li / Li ⁺ ), and a cut current of 0.5. The battery was charged under the condition of 02 mA. Subsequently, constant current discharge was performed by a constant current method until a constant current of 0.4 mA and a cut voltage of 1.5 V (Li / Li ⁺ ) were obtained, and the discharge capacity (kg / Ah) at this time was measured. This charge / discharge was repeated 300 times, and the ratio of the discharge capacity at the 300th cycle to the discharge capacity at the first cycle was calculated as the cycle maintenance ratio (%).

(Compressibility)
The negative electrode produced above was pressed at a linear pressure of 150 kg / cm, and the electrode density was measured.

  From Table 1 and Table 2, it can be seen that the negative electrode material of each example can provide a lithium ion secondary battery excellent in discharge load characteristics, cycle characteristics, and compressibility.

  As a comparative example with respect to Example 1, Comparative Example 1 in which the average particle diameter of the material B is 17.6 μm and the standard deviation of the negative electrode material for a non-aqueous electrolyte secondary battery is 0.231 has a low cycle maintenance factor and electrode density. Comparative Example 2 in which the average particle size of material A is 45.3 μm and the average particle size of material B is 25.1 μm is low in discharge load capacity, cycle retention rate and electrode density, and the average particle size of material B is 0.00. Comparative Example 3 of 9 μm has low charge / discharge efficiency, cycle maintenance rate and electrode density, the average particle diameter of material B is 17.6 μm, the mixing ratio of substance B is 5% by weight, and the negative electrode for non-aqueous electrolyte secondary battery It turns out that the comparative example 4 whose standard deviation of material is 0.243 has a low cycle maintenance factor and electrode density. As a comparative example with respect to Example 2, the average particle size of material B was 19.8 μm, the difference between the average particle size of material A and the average particle size of material B was 0.5 μm, and the negative electrode material for a nonaqueous electrolyte secondary battery It can be seen that Comparative Example 5 having a standard deviation of 0.216 has a low discharge load capacity, cycle retention rate, and electrode density. As a comparative example with respect to Example 3, Comparative Example 6 in which the average particle size of material B is 19.8 μm and the standard deviation of the negative electrode material for nonaqueous electrolyte secondary batteries is 0.234 is the discharge load capacity, cycle retention rate, and It can be seen that the electrode density is low. As a comparative example for Example 4, the average particle size of material B was 17.6 μm, the difference between the average particle size of material A and the average particle size of material B was 2.7 μm, and the negative electrode material for nonaqueous electrolyte secondary batteries It can be seen that Comparative Example 7 having a standard deviation of 0.222 has a low discharge load capacity, cycle retention rate, and electrode density. As a comparative example with respect to Example 5, Comparative Example 8 in which the average particle size of material B is 19.8 μm and the standard deviation of the negative electrode material for nonaqueous electrolyte secondary batteries is 0.232 is the discharge load capacity, the cycle retention rate, and It can be seen that the electrode density is low. As a comparative example with respect to Example 6, the average particle diameter of material B is 17.6 μm, the difference between the average particle diameter of substance A and the average particle diameter of substance B is 2.2 μm, and the negative electrode material for a nonaqueous electrolyte secondary battery It can be seen that Comparative Example 9 having a standard deviation of 0.236 has a low cycle retention ratio and electrode density.

  Therefore, according to the present invention, it is possible to provide a nonaqueous electrolyte secondary battery excellent in discharge load characteristics, cycle characteristics and high battery capacity, a negative electrode for obtaining the same, and a negative electrode material for a nonaqueous electrolyte secondary battery. It becomes.

It is a section front view showing one embodiment of a nonaqueous electrolyte secondary battery (cylindrical lithium secondary battery).

Explanation of symbols

1: Positive electrode 2: Negative electrode 3: Separator 4: Positive electrode tab 5: Negative electrode tab 6: Positive electrode lid 7: Battery can (negative electrode can)
8: Gasket

Claims (6)

A negative electrode material for a non-aqueous electrolyte secondary battery obtained by mixing at least a substance A and a substance B having different particle size distributions,
(I) The average particle diameter (D50) of the substance A is 18 μm or more and 40 μm or less,
(Ii) The average particle diameter (D50) of the substance B is 1 μm or more and 15 μm or less,
(Iii) The difference between the average particle diameter of the substance A and the average particle diameter of the substance B is 5 μm or more,
(Iv) The ratio of the substance B to the total amount of the substance A and the substance B is 10% by weight or more,
(V) The standard deviation value of the negative electrode material for a nonaqueous electrolyte secondary battery obtained from the particle size distribution is 0.250 or more, and is larger than the standard deviation values of the substance A and the substance B.
The negative electrode material for nonaqueous electrolyte secondary batteries characterized by the above-mentioned.   2. The negative electrode material for a non-aqueous electrolyte secondary battery according to claim 1, wherein one or both of the substance A and the substance B is a carbon material.   3. The negative electrode material for a non-aqueous electrolyte secondary battery according to claim 1, wherein one or both of the substance A and the substance B is graphite.   The negative electrode material for a non-aqueous electrolyte secondary battery according to claim 3, wherein the graphite is graphite obtained by collecting or combining a plurality of flat graphite fine particles so that the orientation planes are non-parallel.   A negative electrode for a non-aqueous electrolyte secondary battery, comprising the negative electrode material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 4.   A non-aqueous electrolyte secondary battery comprising the negative electrode for a non-aqueous electrolyte secondary battery according to claim 5.

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