JPH09306489A - Nonaqueous electrolyte secondary battery negative electrode material, manufacture of this nonaqueous electrolyte secondary battery negative electrode material and nonaqueous electrolyte secondary battery using this negative electrode material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode material of high capacity having a good cycle characteristic and a secondary battery of high reliability having high energy density. SOLUTION: In a nonaqueous electrolyte secondary battery having a negative/positive electrode formed of a carbon material capable of doping/dedoping lithium and a nonaqueous electrolyte formed by dissolving an electrolyte in a nonaqueous solvent, the negative electrode material is formed by crushing precursor graphitized fiber 20 having a different crystal part 21 periodically in a fiber lengthwise direction, a fiber-shaped carbon material has 50 or less aspect ratio and 1.5m<2> /g or less specific surface area by a BET method. The negative electrode material, after forming an organic material in a fiber shape, is made infusible, the carbon material is formed by heat treating. In the case of forming the organic material into a fiber shape, it is formed while applying a magnetic field in a pulse shape to a delivery spinning delivery hole or while applying an ultrasonic vibration to the delivery spinning delivery hole. The nonaqueous electrolyte secondary battery is constituted by using this negative electrode material.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a negative electrode material for a lithium ion secondary battery and a secondary battery using the same, and more particularly to using a fibrous carbon material as the negative electrode material.

[0002]

2. Description of the Related Art Recent remarkable advances in electronic technology have made electronic devices smaller and lighter one after another. Along with this, demands for batteries as portable power sources that are smaller, lighter, and have higher energy density are increasing.

Conventionally, an aqueous solution type battery such as a lead battery or a nickel-cadmium battery has been mainly used as a secondary battery for general use. These batteries can satisfy the cycle characteristics to some extent, but cannot be said to be satisfactory in terms of battery weight and energy density. On the other hand, research and development of non-aqueous electrolyte secondary batteries using lithium or a lithium alloy for the negative electrode have been actively conducted in recent years. This battery has high energy density, low self-discharge, and excellent characteristics such as light weight, but as the charge and discharge cycle progresses, lithium grows into dendrite-like crystals during charging and reaches the positive electrode, causing an internal short circuit. However, it was a major obstacle to practical use.

As a solution to such a problem, a non-aqueous electrolyte secondary battery using a carbon material for the negative electrode, that is, a so-called lithium ion secondary battery has been receiving attention. The lithium-ion secondary battery utilizes doping / dedoping of lithium between carbon layers for the negative electrode reaction, and no dendrite-like deposition is observed during charging even if the charging / discharging cycle progresses, and good charging / discharging It shows the cycle characteristics.

By the way, although there are several carbon materials that can be used as the negative electrode, the first practical materials are coke and glassy carbon. These are materials having low crystallinity obtained by heat-treating an organic material at a relatively low temperature, but they have been commercialized as a practical battery using an electrolytic solution containing PC (propylene carbonate) as a main component. More recently, when PC was used as the main solvent, even graphites that could not be used as the negative electrode reached a level where they could be used by using an electrolytic solution containing EC (ethylene carbonate) as a main component.

[0006] Graphites, which are scaly, are relatively easily available and have been widely used as conductive materials for alkaline batteries. These graphites have higher crystallinity and higher true density than the non-graphitizable carbon material. Therefore, if the negative electrode is constituted by this, a high electrode filling property is obtained and the energy density of the battery is increased. From this, it can be said that graphites are promising materials as negative electrode materials.

However, most of the above-mentioned carbon materials are in the form of blocks having a particle size larger than that actually used in batteries, and are pulverized into powder to be used. Therefore, even if the carbon structure is controlled microscopically or macroscopically by physical or chemical treatment, the structure is disturbed by pulverization, and the effect cannot be sufficiently obtained.

On the other hand, fibrous carbon (carbon fiber) obtained by carbonizing fibrous organic matter
Is relatively easy to control the carbon structure, and has recently attracted attention. The structure largely reflects the structure of the precursor organic fiber. As the organic fibers, there are fibers made from polymers such as polyacrylonitrile, pitches such as petroleum pitch, and fibers made from further oriented mesophase pitch. The fibers are spun into fibers. However, in all cases, when heat-treated during carbonization, they were melted and destroyed the fiber structure.

Therefore, carbonization is usually performed after the fiber surface is infusibilized by oxidation or the like. The fibrous carbon thus obtained has a cross-sectional structure derived from an organic fiber structure, and has a higher-order structure such as a concentrically oriented onion skin type, a radially oriented radial type, or an isotropic random type. Show. Graphite fibers obtained by subjecting these to graphitization have high true density and relatively high crystallinity, and thus are promising as a negative electrode material for non-aqueous electrolyte secondary batteries.

Examples of important physical property parameters of such fibrous carbon include, for example, JP-A-7-85862 and JP-A-7-8562.
There is an aspect ratio (fiber length / fiber diameter) shown in -142059. It is disclosed that the smaller the value, the better the characteristics of the negative electrode material.

However, in the fibrous carbon described above, the orientation state of the cross section of the fiber varies in the fiber length direction, so that cracks are likely to occur in the fiber axis direction during crushing, and it is difficult to crush as compared with the conventional lumpy carbon material. It was difficult to obtain a crushed powder having certain physical property parameters including the aspect ratio.

[0012]

SUMMARY OF THE INVENTION Therefore, the object of the present invention is to introduce a structure that is easily crushed into graphitized fibrous carbon, which is a precursor of crushed powder of fibrous carbon as a negative electrode material, to improve its physical properties. The purpose of the present invention is to easily obtain a practical negative electrode material with less variation in parameters, and to provide a highly reliable non-aqueous electrolyte secondary battery with a high energy density by using this material for the negative electrode. Is.

[0013]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and a negative electrode and a positive electrode made of a carbon material capable of being doped with lithium and dedoped, and a nonaqueous electrolysis in which an electrolyte is dissolved in a nonaqueous solvent. In a non-aqueous electrolyte secondary battery containing a liquid, the negative electrode material is a fibrous carbon material formed by pulverizing fibrous carbon having cross-sections with different crystal structures periodically in the fiber length direction. And

The carbon material has an aspect ratio of 50 or less and a BET specific surface area of 1.5.
It is assumed to be m ² / g or less.

Further, the negative electrode material is a carbon material obtained by infusible and heat-treating an organic raw material formed into a fibrous shape, and a fiber having cross-sections having different crystal structures in the fiber length direction. It is formed by a manufacturing method in which carbonaceous carbon is crushed to form.

Further, when the organic raw material is formed into a fibrous shape, it is formed while applying a magnetic field in a pulse shape to the discharge spinning discharge hole, or while applying ultrasonic vibration to the discharge spinning discharge hole. The manufacturing method is used.

Further, in the non-aqueous electrolyte secondary battery comprising a negative electrode and a positive electrode made of a carbon material capable of being doped and dedoped with lithium, and a non-aqueous electrolytic solution in which an electrolyte is dissolved in a non-aqueous solvent, A non-aqueous electrolyte secondary battery is constructed using a negative electrode material to solve the above problems.

As described above, the present invention uses, as a precursor, graphitized fibrous carbon having a cross-section portion having a different crystal structure at a specific or constant cycle in the fiber length direction, and crushing the precursor. A pulverized powder of fibrous carbon having a constant aspect ratio can be easily produced. This fibrous pulverized carbon powder can realize a lower aspect ratio and specific surface area, and easily obtain a high-performance negative electrode material. Also, by using this for the negative electrode, it has a high energy density, a long cycle life, and a high reliability. A high secondary battery can be obtained.

[0019]

FIG. 1 shows an embodiment of the present invention.
Or, it demonstrates with reference to FIG. FIG. 1 is a diagram for explaining the formation of fibrous carbon according to the present invention, (a) shows a precursor graphitized fiber, and (b) is a fibrous carbon obtained by crushing the precursor graphitized fiber. The sample powder of is shown. FIG. 2 is a side sectional view of a tubular battery using fibrous carbon according to the present invention. FIG. 3 is a diagram showing the relationship between the aspect ratio of the fibrous carbon and the capacity retention rate according to the present invention.

In order to solve the above-mentioned problems, the present inventors have used, as a precursor, a graphitized fibrous carbon having a portion having a different crystal structure in a cross section at a specific or constant period in the fiber length direction. It was found that by using it, it is possible to easily produce a pulverized fibrous carbon powder having a constant aspect ratio.

In the present invention, as shown in FIG. 1, graphitized fibrous carbon (hereinafter, simply referred to as "precursor graphitized fiber") serving as a precursor of fibrous carbon ground powder (hereinafter, simply referred to as "ground powder"). The sample powder 2 has a cross section having different crystal structures in a specific or constant period (FIG. 1 shows a periodic structure of length l) in the fiber length direction, and the sample powder 2 is crushed.
A pulverized powder of 2 is formed. Since the different crystal parts 21 having different crystal structures have different crystal orientations, the different crystal parts 21 are more likely to be broken than the parts during pulverization, and the sample powder 22 having a constant fiber length can be easily produced. The fiber diameter is d.

When the fibrous carbon is produced, polymers such as polyacrylonitrile and rayon as starting materials, petroleum pitch, coal pitch, synthetic pitch, and the like, at a maximum of about 400 ° C. for any time. Pitches such as mesophase pitch in which aromatic rings are condensed or polycyclic to have a laminated orientation by holding or accelerating the polymerization by adding an acid or the like can be used.

In particular, when the mesophase pitch is used, the mesophase content greatly affects the spinnability, the physical properties of fibrous carbon, and the electrical and chemical properties. The mesophase content is preferably 60% or more, and 95
% Or more is more preferable. If it is less than this range, the crystal orientation is poor and the capacity of the material itself is lowered, which is not preferable.

When the organic carbon which is the fibrous carbon precursor 20 of the present invention is produced, the above-mentioned polymers and pitches are heated, brought into a molten state, and molded and spun by discharge or the like. In this case, each organic substance has a different melting point,
The optimum spinning temperature can be appropriately selected for each.

The structure of the fibrous carbon largely reflects the structure of the precursor organic fiber. Therefore, the different crystal portion 21 of the precursor graphitized fiber 20 of the present invention needs to be formed by controlling the crystal orientation at the time of spinning the organic fiber.

As a method of controlling the crystal orientation at the time of spinning the organic fiber, there is a method of making the flow of the pitch in the discharge holes turbulent at a constant length during discharge.
This includes a method in which a fine hole is provided in the discharge hole to blow out a gas such as air, and a method in which the discharge hole is vibrated by ultrasonic waves or the like. In addition, the property that the pitches as a material are oriented with respect to the magnetic field may be used.

Although any method other than the above method for controlling the crystal orientation can be used, the important point is that the different crystal part 2 is used.
1 is the ratio and interval contained in the precursor graphitized fiber 20. Further, the different crystal portion 21 may be present so as to be distributed over the entire cross section of the precursor graphitized fiber 20, or may be present in a part thereof. The presence of the different crystal portion 21 can be appropriately selected according to the required physical property parameter of the pulverized powder, but if the content of the different crystal portion 21 increases, the intercalation capacity may decrease, and the content of Is preferably less.

Since the orientation of the different crystal portion 21 must be broken perpendicularly to the fiber axis due to crushing or the like, it is preferable that the foreign crystal portion 21 be oriented more perpendicular to the fiber cross section. The smaller angle formed by the different crystal portion 21 with respect to the fiber axis is 60 °
The above is preferable, and 80 ° or more is more preferable.

When the distance W existing in the precursor graphitized fiber 20 where the different crystal portion 21 is present is short, a material having a small aspect ratio can be obtained, while the content of the different crystal portion 21 becomes high.
Intercalation capacity may be reduced. Further, when the distance W is long, the material has a large aspect ratio, but the content ratio of the different crystal portion 21 is low, so that the capacity loss is small. Therefore, although it can be appropriately selected according to the required physical property parameters and capacity of the pulverized powder, 1 is preferably d or more and 100 d or less with respect to the fiber diameter d.

The organic fiber, which is a precursor of fibrous carbon, is infusibilized after spinning and before heat treatment. Although the specific means is not limited, for example, a wet method using an aqueous solution of nitric acid, mixed acid, sulfuric acid, hypochlorous acid, or the like, or a dry method using an oxidizing gas (air, oxygen), sulfur, ammonia nitrate,
A reaction with a solid reagent such as ammonium persulfate or ferric chloride is used. Moreover, when performing the said process, you may draw or tension a fiber.

The above infusibilized organic fibers are heat-treated in a stream of inert gas such as nitrogen. The conditions are as follows: carbonization at 300 to 700 ° C. and then in a stream of inert gas at every heating rate. Min 1-100 ° C, ultimate temperature 900-15
Calcination is performed at a temperature of 00 ° C. for a holding time of about 0 to 30 hours, and in order to obtain a graphitized product, it is preferable to perform heat treatment at 2000 ° C. or higher, preferably 2500 ° C. or higher. Of course, in some cases, the carbonization and calcination operations may be omitted. The fibrous carbon of the present invention graphitized by heat treatment at a high temperature of 2500 ° C. or higher has a true density close to that of artificial graphite and a high electrode packing density is obtained, which is preferable.

The produced fibrous carbon is classified or ground and classified to be used as a negative electrode material. Grinding may be carried out before or after carbonization, calcination, or during the temperature rising process before graphitization. In this case, the heat treatment for graphitization is finally performed in the powder state.

The main structure of fibrous carbon for the function of the negative electrode material of the present invention is classified according to its cross-sectional structure. There are onion skin type with concentric orientation, radial type with radial orientation, isotropic random type, etc., and the present invention can be applied to any of them. In particular, the radial type or the random radial type in which the radial type and the random type are mixed is preferable.

The present invention is intended to easily produce a material having a smaller aspect ratio, but in order to obtain a high performance negative electrode material, the crushed powder preferably has an aspect ratio of 50 or less, and 10 or less. More preferable. The fiber diameter d of the precursor graphitized fiber 20 is preferably 5 μm or more and 100 μm or less, more preferably 10 μm or more and 60 μm or less. The smaller the fiber diameter, the larger the specific surface area, and the larger the fiber diameter, the lower the effect of imparting the fiber shape, which is not preferable.

The fiber diameter and fiber length are obtained by observing the pulverized powder with an electron microscope or the like. The value obtained by dividing the fiber length by the fiber diameter is defined as the aspect ratio of the pulverized powder.
This measurement was performed on 10 crushed powders, and the average value of each was defined as the fiber diameter d, the fiber length l, and the aspect ratio A.

Further, by satisfying the physical property values described below, a more practical negative electrode material can be obtained.

To obtain a higher electrode packing density, the true density of the graphitized fibrous carbon is preferably 2.1 g / cm ³ or more, more preferably 2.18 g / cm ³ or more. The true density of graphite material (Pycnometer method using butanol solvent) is
The crystal structure parameters such as the (002) plane distance and the C-axis crystallite thickness of the (002) plane, which are determined by the crystallinity and obtained by the X-ray diffraction method (Gakushin method), are used as an index. In order to obtain a material with high true density, it is preferable that the crystallinity is high, and the (002) plane spacing obtained by X-ray diffraction is preferably less than 0.340 nm, more preferably 0.335 nm or more and 0.337 nm or less. . The C-axis crystallite thickness of the (002) plane is preferably 14.0 nm or more and 30.0 nm.
The above is more preferred.

In order to obtain good cycle characteristics, it is preferable to use a material having a bulk density of 0.4 g / cm ³ or more. The negative electrode composed of a graphite material having a bulk density of 0.4 g / cm ³ or more has a good electrode structure, and it is unlikely that the graphite material peels off from the negative electrode mixture layer. Therefore, a long cycle life can be obtained.

The bulk density regulated by the present invention is JIS
It is the value determined by the method described in K-1469.
If a graphite material with this value of 0.4 g / cm ³ or more is used,
Although a sufficiently long cycle life can be obtained, the bulk density is preferably 0.5 g / cm ³ or more, and more preferably the bulk density is 0.1 g / cm ³ .
It is preferable to use a material of 7 g / cm ³ or more.

Bulk Density Measuring Method The bulk density measuring method will be described below. A graduated cylinder having a capacity of 100 cm ³ whose mass has been measured in advance is tilted, and 100 cm ³ of the sample powder is gradually added to this. And
The total mass is measured with a minimum scale of 0.1 g, and the mass of the graduated cylinder is subtracted from the mass to determine the mass of the sample powder.

Next, a graduated cylinder charged with the sample powder is capped with a cork, and the graduated cylinder in that state is dropped 50 times from a height of about 5 cm with respect to the rubber plate. As a result, the sample powder in the graduated cylinder is compressed,
Read the volume V of the compressed sample powder. And
The bulk density (g / cm ³ ) is calculated by the following formula (1).

D = W / V (1) where D: bulk density (g / cm ³ ) W: mass of sample powder in graduated cylinder (g) V: sample powder in graduated cylinder after 50 drops Volume of (cm ³ )

Further, when the average value of the shape parameter x expressed by the equation (2) is 125 or less, the cycle characteristics are further improved. That is, a typical shape of the graphite material powder is a flat columnar shape or a rectangular parallelepiped shape. When the thickness of the thinnest part of this graphite material powder is T, the length of the longest part is L, and the length in the direction orthogonal to the major axis corresponding to the depth is W, L The product of the values obtained by dividing each W by T is the shape parameter x. The smaller the shape parameter x, the higher the height with respect to the bottom area and the smaller the flatness.

X = (W / T) × (L / T) (2) Here, x: shape parameter T: thickness of the thinnest part of the powder L: length of the powder in the major axis direction W: Length of powder in the direction orthogonal to the long axis

Further, the average shape parameter xave. Is obtained by the following actual measurement. First, the graphite sample powder is SE
Observe using M (scanning electron microscope), and select 10 powders in which the length of the longest part is ± 30% of the average particle size. Then, the shape parameter x is calculated from the equation (2) for each of the 10 selected powders, and the average thereof is calculated. The calculated average value is the average shape parameter xave. The above effect can be obtained when the average shape parameter xave. Of the graphite powder is 125 or less, but preferably 2 or more and 115 or less, more preferably 2 or more and 100 or less.

When a material having a specific surface area of 9 m ² / g or less is used, a longer cycle life can be obtained. It is considered that the submicron particles adhering to the graphite particles influence the decrease in bulk density, and the specific surface area increases when the particles adhere, so even if the particle size is similar, the specific surface area The use of small graphite powder is not affected by the fine particles, a high bulk density is obtained, and as a result, cycle characteristics are improved.

However, the specific surface area as referred to herein means that measured and determined by the BET method. If the specific surface area of the graphite powder is 9 m ² / g or less, the above effect is sufficiently obtained, but preferably 7 m ² / g or less, more preferably 5 m
² / g or less is preferable.

In order to obtain high safety and reliability as a practical battery, the cumulative 10% particle size is 3 μm or more in the particle size distribution obtained by the laser diffraction method,
And the cumulative 50% particle size is 10 μm or more, and the cumulative 9%
It is desirable to use graphite powder having a 0% particle size of 70 μm or less.

It is preferable that the graphite powder with which the electrode is filled should have a particle size distribution with a range so that the graphite powder can be packed more efficiently, and that it is closer to the normal distribution. However, the battery may generate heat in an abnormal situation such as overcharging, and if the number of particles with small particle size is large, the heat generation temperature tends to be high, which is not preferable.

In addition, when the battery is charged, graphite intercalation helium ions are inserted, so that the crystallite expands by about 10% and presses the positive electrode and the separator in the battery, causing an initial defect such as an internal short circuit during the first charge. Although it tends to occur, it is not preferable when the distribution of large particles is large, because the incidence of defects tends to increase.

Therefore, by using the graphite powder having a particle size distribution in which particles having a large particle size to particles having a small particle size are well-balanced, a practical battery having high reliability can be obtained. If the shape of the particle size distribution is closer to the normal distribution, the particles can be packed more efficiently, but in the particle size distribution obtained by the laser diffraction method, the cumulative 10% particle size is 3 μm or more, and the cumulative 50% particle size is 10 μm or more, In addition, it is desirable to use graphite powder having a cumulative 90% particle size of 70 μm or less, and especially when the cumulative 90% particle size is 60 μm or less, initial defects are greatly reduced.

In order to improve the heavy load characteristics of a practical battery, the average value of the breaking strength of graphite particles is 6.0.
It is desirable to be kgf / mm ² or more. The load characteristics are affected by the ease with which ions move during discharge, but particularly when there are many holes in the electrodes, a sufficient amount of the electrolytic solution is present, so that good characteristics are exhibited. On the other hand, a graphite material with high crystallinity has a hexagonal graphite net plane developed in the a-axis direction, and a c-axis crystal is formed by stacking the graphite hexagonal net planes. Since it is a bond, it is easily deformed by stress. Therefore, when the graphite powder particles are compression-molded and filled in the electrode, they are more easily crushed than the carbonaceous material fired at a low temperature, and it is possible to secure pores. difficult. Therefore, the higher the fracture strength of the graphite powder particles, the less likely they are to be crushed, and the easier it is to create voids, which makes it possible to improve the load characteristics.

However, the average value of the breaking strength of the graphite particles as used herein means that which is obtained by the following actual measurement. A Shimadzu micro compression tester (MCTM-500) manufactured by Shimadzu Corporation is used as a breaking strength measuring device. First, the graphite sample powder is observed with an attached optical microscope, and 10 powders in which the length of the longest part is ± 10% of the average particle size are selected. Then, a load is applied to each of the 10 selected powders, the breaking strength of the particles is measured, and the average thereof is calculated. This calculated average value is the average value of the breaking strength of the graphite particles. In order to obtain good load characteristics, it is preferable that the average breaking strength of the graphite particles is 6 kgf / mm ² or more.

On the other hand, the positive electrode material used in combination with the negative electrode made of such fibrous carbon or graphitized fibrous carbon is not particularly limited, but preferably contains a sufficient amount of Li, for example, the general formula LiMO ₂ (However, M
Represents at least one of Co, Ni, Mn, Fe, Al, V, and Ti. ), A composite metal oxide composed of lithium and a transition metal, an intercalation compound containing Li, and the like are preferable.

In particular, since the present invention is aimed at achieving a high capacity, the positive electrode should be charged at 250 mAh or more per 1 g of the negative electrode carbon material in a steady state (for example, after repeating charging and discharging about 5 times). It is necessary to contain Li corresponding to the discharge capacity, and Li corresponding to the charge / discharge capacity of 300 mAh or more.
It is more preferred to include

It is not always necessary that Li is supplied from the positive electrode material, and the point is that Li corresponding to a charge / discharge capacity of 250 mAh or more per 1 g of carbon material should be present in the battery system. Further, the amount of Li will be determined by measuring the discharge capacity of the battery.

In the nonaqueous electrolytic solution used in the nonaqueous electrolytic solution secondary battery of the present invention, a nonaqueous electrolytic solution obtained by dissolving an electrolyte in a nonaqueous solvent is used as the electrolytic solution. Here, in the present invention, since the graphite material is used for the negative electrode, conventional PC cannot be used as the main solvent of the non-aqueous solvent, and it is premised that other solvents are used. EC is most preferred as the main solvent, but compounds having a structure in which the hydrogen element of EC is replaced with a halogen element are also suitable.

Although it is reactive with a graphite material like PC, a small amount of EC is used as a main solvent or a compound having a structure in which a hydrogen atom of EC is replaced with a halogen element. Good properties are obtained by substituting with a binary solvent. As the second component solvent, PC, butylene carbonate, 1,2-dimethoxyethane, 1,
2-diethoxymethane, γ-butyrolactone, valerolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-
Dioxolane, sulfolane, methylsulfolane and the like can be used, and the addition amount thereof is preferably less than 10 Vol%.

To further complete the present invention, a third solvent is added to the main solvent or a mixed solvent of the main solvent and the second component solvent to improve the conductivity and suppress the decomposition of EC. The low temperature characteristics may be improved and the reactivity with lithium metal may be lowered to improve the safety.

As the solvent for the third component, first, DEC
A chain ester carbonate such as (diethyl carbonate) or DMC (dimethyl carbonate) is suitable. Also, ME
Asymmetric chain ester carbonate such as C (methyl ethyl carbonate) or MPC (methyl propyl carbonate) is preferable. The volume ratio of the main solvent or the mixed solvent of the main solvent and the second component solvent of the chain carbonate as the third component (main solvent or the mixed solvent of the main solvent and the second component solvent: the third component solvent) is the volume. The ratio is preferably 10:90 to 60:40, more preferably 15:85 to 40:60.

Further, as the solvent for the third component, MEC and D
It may be a mixed solvent with MC. The MEC-DMC mixing ratio is preferably in a range represented by 1/9 ≦ d / m ≦ 8/2, where MEC capacity is m and DMC capacity is d. Further, the MEC-DMC mixing ratio of the main solvent, or the mixed solvent of the main solvent and the second component solvent and the solvent of the third component, when the MEC capacity is m, the DMC capacity is d, and the total amount of the solvent is T, 3/10 ≦ (m + d) / T ≦ 7/1
The range shown by 0 is preferable.

As the electrolyte which can be dissolved in such a non-aqueous solvent, one or more kinds can be used as a mixture as long as they are used in the battery of this type. For example, LiPF ₆ is preferable, but LiClO 4, LiAsF ₆ , Li
BF ₄ , LiB (C ₆ H ₅ ) ₄ , CH ₃ SO ₃ Li, C
_{F 3 SO 3 Li, LiN (} CF 3 SO 2) 2, LiC
(CF ₃ SO ₂ ) ₃ , LiCl, LiBr and the like can also be used.

Hereinafter, the present invention will be described with reference to specific examples, but the present invention is not limited to these examples and may be used for other means for embodying the technical idea of the present invention. I can't wait for the matter.

Example 1 First, a negative electrode material was produced as follows. Keep the petroleum pitch in an inert gas atmosphere at 425 ° C for 5 hours,
A petroleum-based mesophase pitch having a softening point of 230 ° C. was obtained. At this time, the mesophase content rate was 91%. Discharge spinning of the obtained petroleum mesophase pitch at a constant extrusion pressure at 300 ° C. while applying a magnetic field in a pulse shape at a constant time interval using a discharge hole having an inner diameter of 20 μm that incorporates a small probe for applying a magnetic field. Then, an organic fiber was obtained. Then, this was infusibilized at 260 ° C. and calcined at a temperature of 1000 ° C. in an inert atmosphere to obtain fibrous carbon. Further, it was heat-treated at a temperature of 3000 ° C. in an inert atmosphere to obtain a precursor graphitized fiber 20 as shown in FIG. 1, which was further air-ground to give a sample powder 22. The aspect ratio of the obtained sample powder 22 was A = 1.3, and the specific surface area was 0.9 mm ² / g.

Next, using the sample powder as a negative electrode material,
A cylindrical non-aqueous electrolyte secondary battery was actually manufactured. The structure of the battery is shown in FIG.

The negative electrode 1 was manufactured as follows. 90 parts by weight of the above graphite powder and 10 parts by weight of polyvinylidene fluoride (PVDF) as a binder are mixed to prepare a negative electrode mixture,
It was dispersed in N-methylpyrrolidone as a solvent to form a slurry (paste form). The negative electrode current collector 10 has a thickness of 10
A band-shaped negative electrode 1 was prepared by applying a negative electrode mixture slurry on both sides of this current collector using a band-shaped copper foil having a thickness of μm, drying it, and then compression molding it at a constant pressure.

The positive electrode 2 was manufactured as follows. First, a positive electrode active material was prepared as follows. Lithium carbonate 0.
5 mol and 1 mol of cobalt carbonate are mixed and the mixture is calcined in air at a temperature of 900 ° C. for 5 hours. As a result of X-ray diffraction measurement of the obtained material, it was in good agreement with the peak of LiCoO ₂ registered in the JCPDS file.

This LiCoO ₂ was crushed to obtain a LiCoO ₂ powder having a cumulative 50% particle size of 15 μm obtained by a laser diffraction method. Then, 95 parts by weight of this LiCoO ₂ powder and 5 parts by weight of lithium carbonate powder were mixed to obtain 91 parts of this mixture.
By weight, 6 parts by weight of graphite as a conductive agent and 3 parts by weight of polyvinylidene fluoride as a binder were mixed to prepare a positive electrode mixture, which was dispersed in N-methylpyrrolidone to form a slurry (paste form).

A strip-shaped aluminum foil having a thickness of 20 μm was used as the positive electrode current collector 11, and the positive electrode mixture slurry was uniformly applied to both surfaces of the current collector, dried, and then compression molded to obtain the strip-shaped positive electrode 2. Was produced.

Then, the strip-shaped negative electrode 1 and the strip-shaped positive electrode 2 produced as described above were made to have a thickness of 25 μm as shown in FIG.
A negative electrode 1, a separator 3, a positive electrode 2, and a separator 3 are laminated in this order through a separator 3 made of a microporous polypropylene film of m and then wound many times to have an outer diameter of 18 mm.
A spirally wound electrode body was prepared.

The spirally wound electrode body thus produced was
It was housed in a nickel-plated iron battery can 5. Then, the insulating plates 4 are arranged on the upper and lower surfaces of the spiral type electrode, and the positive electrode lead 13 made of aluminum is led out from the positive electrode current collector 11 to the battery lid 7, and the negative electrode lead 12 made of nickel is connected to the negative electrode current collector 10. Was welded to the battery can 5.

Into the battery can 5, an electrolytic solution prepared by dissolving LiPF ₆ at a ratio of 1 mol / l in a mixed solvent of EC and DMC in an equal volume was injected. Then, by caulking the battery can 5 through a sealing gasket 6 whose surface is coated with asphalt, a safety valve device 8 having a current interruption mechanism, P
The TC element 9 and the battery lid 7 were fixed, the airtightness inside the battery was maintained, and a cylindrical nonaqueous electrolyte secondary battery having a diameter of 18 mm and a height of 65 mm was produced.

Example 2 A cylindrical non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1 except that discharge spinning was carried out under different applied magnetic field pulse conditions to obtain organic fibers. The aspect ratio of the obtained test powder was A = 3.3 and the specific surface area was 0.8 m ² / g.

Example 3 A cylindrical non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that discharge spinning was performed by changing the applied pulse conditions of the magnetic field to obtain organic fibers. The aspect ratio of the obtained test powder was A = 7.0, and the specific surface area was 1.2 m ² / g.

Example 4 Cylindrical non-aqueous electrolyte secondary solution was obtained in the same manner as in Example 1 except that ultrasonic waves were applied to the tip of the discharge hole in pulses instead of the magnetic field to carry out discharge spinning to obtain organic fibers. A battery was made. The aspect ratio of the obtained test powder was A = 9.3, and the specific surface area was 1.
It was 3 m ² / g.

Example 5 The same as Example 1 except that a discharge hole having pores inside was used instead of the magnetic field, and discharge was spun while ejecting air in a pulse shape from the pores to obtain an organic fiber. To produce a cylindrical non-aqueous electrolyte secondary battery. The aspect ratio of the obtained test powder was A = 41.0, and the specific surface area was 1.5 m ² / g.

Comparative Example 1 A cylindrical non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that no magnetic field was applied to the discharge holes. The obtained test powder has an aspect ratio of A = 64 and a specific surface area of 2.0 m.
² / g.

Table 1 shows the results of measuring the charge / discharge capacity of the fibrous carbon used in each of the examples and comparative examples.

[Table 1]

Charging / Discharging Capacity Measuring Method The charging / discharging capacity measuring method will be described below. The measurement was performed by making a test cell described below. In producing the test cell, first, the sample powder was preheated in an Ar atmosphere under the conditions of a temperature rising rate of about 30 ° C./minute, an ultimate temperature of 600 ° C., and an ultimate temperature holding time of 1 hour. Then, polyvinylidene fluoride in an amount equivalent to 10% by weight was added as a binder, dimethylformamide was mixed as a solvent, and dried to prepare a sample mix. The 37 mg was weighed, and the diameter was 15.5 with the Ni mesh as the current collector.
mm pellets were formed to prepare a working electrode.

The structure of the test cell is as follows. Cell shape: coin type cell (diameter 20 mm, thickness 2.5 m
m) Counter electrode: Li metal Separator: Polypropylene porous membrane Electrolyte: LiPF ₆ dissolved in a mixed solvent of EC and DEC (volume ratio 1: 1) at a concentration of 1 mol / l

Using the test cell having the above structure, carbon material 1
The capacity per gram was measured. Doping of lithium into the working electrode (charging: strictly speaking, in this test method, discharging is not charging in the process of doping the carbon material with lithium, but this doping process is convenient for the actual battery. Is charged, and the dedoping process is called discharge.) Is a constant current of 1 mA per cell, 0 V (Li / Li
⁺ ) Constant current constant voltage method for charging and discharging (de-doping process)
Was calculated with a constant current of 1 mA per cell up to a terminal voltage of 1.5 V, the discharge capacity at this time was taken as the capacity, and the value obtained by subtracting the discharge capacity from the charge capacity was taken as the capacity loss.

With respect to the tubular batteries produced in the respective examples and comparative examples, the charging current was 1 A and the maximum charging voltage was 4.2 V.
5h constant current constant voltage charging, then discharge current 700
The charging / discharging cycle of discharging to 2.75 V at mA was repeated, and the ratio of the capacity at the 100th cycle to the capacity at the second cycle (capacity retention rate) was obtained. The results of the capacity retention rate at the 200th cycle relative to the second cycle are shown in Table 1 above
It was shown to. The relationship between the aspect ratio A and the capacity retention rate is shown in FIG.

From the above results, the fibrous carbon powder according to the manufacturing method of the present invention easily realized a low aspect ratio, and by using this as the negative electrode material, the cycle characteristics were excellent as compared with the material of the comparative example. It was revealed that a non-aqueous secondary battery can be obtained.

[0084]

As is apparent from the above description, the present invention is, as described above, a graphitized fibrous material having a cross-section portion having a different crystal structure in a specific or constant period in the fiber length direction. By using carbon as a precursor and crushing it as a precursor, it is possible to easily produce a pulverized fibrous carbon powder having a constant aspect ratio. This fibrous pulverized carbon powder can realize a lower aspect ratio and specific surface area, and easily obtain a high-performance negative electrode material. Also, by using this for the negative electrode, it has a high energy density, a long cycle life, and a high reliability. A high secondary battery can be obtained.

[Brief description of drawings]

FIG. 1 is a view for explaining the formation of fibrous carbon according to the present invention, in which (a) shows a precursor graphitized fiber,
(B) shows a sample powder of fibrous carbon obtained by crushing the precursor graphitized fiber.

FIG. 2 is a side sectional view of a tubular battery using fibrous carbon according to the present invention.

FIG. 3 is a diagram showing the relationship between the aspect ratio and the capacity retention rate of fibrous carbon according to the present invention.

[Explanation of symbols]

1 ... Negative electrode, 2 ... Positive electrode, 3 ... Separator, 4 ... Insulating plate, 5
... Battery can 6 ... Sealing gasket, 7 ... Battery lid, 8 ... Safety valve device, 9
... PTC element 10 ... Negative electrode collector, 11 ... Positive electrode collector, 12 ... Negative electrode lead, 13 ... Positive electrode lead 14 ... Center pin, 20 ... Precursor graphitized fiber, 21 ...
Different crystal part 22 ... Sample powder

Claims (6)

[Claims] 1. A non-aqueous electrolyte secondary battery comprising a negative electrode and a positive electrode made of a carbon material capable of being doped and dedoped with lithium, and a non-aqueous electrolytic solution in which an electrolyte is dissolved in a non-aqueous solvent. The material is a fibrous carbon material formed by pulverizing fibrous carbon having cross-sections having different crystal structures periodically in the fiber length direction, and a negative electrode material for a non-aqueous electrolyte secondary battery. . 2. The aspect ratio is 50 or less, and B
The negative electrode material for a non-aqueous electrolyte secondary battery according to claim 1, which has a specific surface area of 1.5 m ² / g or less according to the ET method. 3. The negative electrode material is a carbon material obtained by infusible and heat-treating an organic raw material formed into a fibrous shape, and a fiber having cross-sections having different crystal structures in the fiber length direction. The method for producing a negative electrode material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the carbonaceous carbon is formed by crushing. 4. When forming the organic raw material into a fibrous shape,
The method for producing a negative electrode material for a non-aqueous electrolyte secondary battery according to claim 1, characterized in that the negative electrode material for a non-aqueous electrolyte secondary battery is formed by applying a magnetic field in a pulsed manner to a discharge spinning discharge hole. 5. When forming the organic raw material into a fibrous shape,
The method for producing a negative electrode material for a non-aqueous electrolyte secondary battery according to claim 1, which is formed while applying ultrasonic vibration to the discharge spinning discharge holes. 6. A non-aqueous electrolyte secondary battery comprising a negative electrode and a positive electrode made of a carbon material capable of being doped and dedoped with lithium, and a non-aqueous electrolyte solution in which an electrolyte is dissolved in a non-aqueous solvent. A non-aqueous electrolyte secondary battery using the negative electrode material for a non-aqueous electrolyte secondary battery according to 1.