JP6120626B2 - Method for producing composite carbon material for non-aqueous secondary battery - Google Patents

Description

  The present invention relates to a composite carbon material for a non-aqueous secondary battery used for a non-aqueous secondary battery, a negative electrode formed using the material, and a non-aqueous secondary battery having the negative electrode.

In recent years, demand for high-capacity secondary batteries has increased with the downsizing of electronic devices. In particular, lithium ion secondary batteries having higher energy density and excellent large current charge / discharge characteristics have attracted attention as compared to nickel / cadmium batteries and nickel / hydrogen batteries.
As a negative electrode material of a lithium ion secondary battery, graphite material and amorphous carbon are often used in terms of cost and durability. However, amorphous carbon material has a small reversible capacity within the range of materials that can be put to practical use, and graphite material breaks down when the active material layer containing the negative electrode material is densified for high capacity. As a result, the irreversible charge / discharge capacity at the initial cycle increases, and as a result, there is a problem that the capacity cannot be increased.

In order to solve the above problems, for example, Patent Document 1 discloses a graphite powder coated with graphite used for a negative electrode material for a lithium secondary battery. By covering the surface of the graphite powder with graphite, it is considered that the substantial surface area for desorbing lithium ions is increased, and the cycle characteristics can be improved with a high capacity.
Further, Patent Document 2 discloses a method for producing a negative electrode material for a lithium ion secondary battery containing isotropic graphite that is isotropically pressurized with spheroidized graphite and densified.
Patent Document 3 discloses a lithium ion characterized in that a coating layer made of carbide is formed on the surface of pressurized graphite particles obtained by pressurizing natural graphite spheroidized particles and / or natural graphite agglomerated particles. A graphite material for a secondary battery is disclosed.

Japanese Patent No. 30543379 Japanese Patent Laying-Open No. 2005-50807 JP 2011-060465 A

However, according to the study by the present inventors, in the technique described in Patent Document 1, graphite coated with graphite is disclosed. This graphite is a graphite powder having a high capacity and low capacity loss of a lithium secondary battery. Thus, although the initial efficiency and the cycle maintenance ratio were improved, the generation of the storage gas was not particularly reduced.
On the other hand, there is a description about a lithium ion secondary battery that is made dense by isotropically pressurizing spheroidized graphite and has excellent load characteristics, cycle characteristics, etc., but this method destroys the surface structure of graphite. There was a problem that the generation of storage gas was not reduced.

Patent Document 3 discloses a graphite material for a lithium ion secondary battery in which a coating layer made of carbide is formed on the surface of pressurized graphite particles obtained by pressurizing natural graphite spheroidized particles and / or natural graphite agglomerated particles. However, such a carbon material cannot satisfy the required performance of the market.
Therefore, the present invention has been made in view of such background art, and the problem is to adapt to market demands, so that the reduction in the generation of stored gas is further improved while maintaining the improvement in initial efficiency and cycle maintenance ratio. Another object is to provide a lithium ion secondary battery.

As a result of intensive studies to solve the above problems, the present inventors applied a composite carbon material for a non-aqueous secondary battery in which a carbon material subjected to isotropic pressure treatment and a graphite material are combined to a negative electrode. As a result, it was found that a lithium ion secondary battery in which the reduction of the generation of the storage gas was further improved while maintaining the improvement in the initial efficiency and the cycle maintenance ratio was obtained, and the present invention was achieved.
That is, the gist of the present invention resides in a composite carbon material for a non-aqueous secondary battery in which an isotropic pressure-treated carbon material and a graphite material are combined.

The composite carbon material for a non-aqueous secondary battery in which the carbon material subjected to the isotropic pressure treatment of the present invention and the graphite material are combined is more electrolyzed by using it as a composite carbon material for a non-aqueous secondary battery. It is possible to obtain a high-capacity non-aqueous secondary battery in which not only the reaction with the liquid is suppressed and the deterioration during the cycle is small, but also the expansion of the electrode and the generation of gas are small.
The details of the mechanism of the effect are not clear here, but as a result of the study by the inventors, it is surprising to combine the isotropic pressure treatment technology, which is a completely different effect technology, with the technology of combining the graphite material. It is thought that the side reaction with the electrolytic solution can be remarkably suppressed, and as a result, the initial irreversible capacity can be reduced and the generation of gas can be suppressed.

Hereinafter, the contents of the present invention will be described in detail. The description of the invention constituent elements described below is an example (representative example) of an embodiment of the present invention, and the present invention is not limited to these forms unless it exceeds the gist.
<Carbon material that is a raw material for composite carbon materials for non-aqueous secondary batteries>
Although the carbon material which is a raw material of the composite carbon material for non-aqueous secondary batteries of this invention is shown below as an example, it is not restrict | limited in particular. In addition, the carbon material which is a raw material means the carbon material before an isotropic pressurization process.

-Kind of carbon material Examples of the carbon material include carbon materials having various degrees of graphitization from graphite to amorphous materials.
In addition, graphite or a carbon material having a low degree of graphitization is particularly preferable in that it can be easily obtained commercially. It is preferable to use such graphite as a carbon material because the effect of improving charge / discharge characteristics at a high current density is significantly greater than when other negative electrode active materials are used.

As the graphite, either natural graphite or artificial graphite may be used. As graphite, those with few impurities are preferable, and they are used after being subjected to various purification treatments as necessary.
Specific examples of natural graphite include scaly graphite, scaly graphite, and soil graphite. Examples of artificial graphite include graphite particles such as coke, needle coke, and high-density carbon material produced by high-temperature heat treatment of pitch raw materials. Preferred examples of artificial graphite, which is spherical natural graphite from the viewpoint of low cost and ease of electrode production, include coal tar pitch, coal-based heavy oil, atmospheric heavy oil, petroleum-based heavy oil. Oil, aromatic hydrocarbon, nitrogen-containing cyclic compound, sulfur-containing cyclic compound, polyphenylene, polyvinyl chloride, polyvinyl alcohol, polyacrylonitrile, polyvinyl butyral, natural polymer, polyphenylene sulfide, polyphenylene oxide, furfuryl alcohol resin, phenol- Examples thereof include those obtained by baking and graphitizing organic substances such as formaldehyde resin and imide resin at a temperature of usually 2500 ° C. or higher and usually 3200 ° C. or lower.

As the carbon material, particles such as metal particles and metal oxide particles may be appropriately mixed and used in an arbitrary combination with the carbon material. Further, a plurality of materials may be mixed in each particle. For example, carbonaceous particles having a structure in which the surface of graphite is coated with a carbon material having a low degree of graphitization, or particles obtained by re-graphitizing a carbon material with an appropriate organic substance may be used. Furthermore, the composite particles may contain a metal that can be alloyed with Li, such as Sn, Si, Al, Bi.

-Physical property of carbon material The carbon material which is a raw material of the composite carbon material for non-aqueous secondary batteries of this invention shows the following physical properties. In addition, there is no restriction | limiting in particular in the measuring method in this invention, According to the measuring method as described in an Example, unless there is a special situation. In addition, the physical property etc. of the carbon material which is the raw material shown below show the physical property before performing an isotropic pressurization process.

(1) d002 of carbon material
The d value (interlayer distance) of the lattice plane (002 plane) determined by X-ray diffraction by the Gakushin method is usually 0.335 nm or more and less than 0.340 nm. Here, the d value is preferably 0.339 nm or less, more preferably 0.337 nm or less. If the d value is too large, the crystallinity may decrease and the initial irreversible capacity may increase. On the other hand, 0.335 nm is a theoretical value of graphite.

(2) Surface Functional Group Amount of Carbon Material The carbon material that is the raw material of the composite carbon material for non-aqueous secondary batteries of the present invention has a surface functional group amount O / C value represented by the following formula 1 of usually 1%. It is 4% or less, preferably 2% or more and 3.6% or less, and more preferably 2.6% or more and 3% or less. If this surface functional group amount O / C value is too small, the affinity with the binder decreases, the interaction between the negative electrode surface and the coating material becomes weak, and the coating material tends to be peeled off. If the / C value is too large, it becomes difficult to adjust the O / C value, and there is a tendency that the manufacturing process needs to be performed for a long time or the number of steps needs to be increased, resulting in a decrease in productivity and cost. There is a risk of rising.

Formula 1
O / C value (%) = O atom concentration determined based on the peak area of the O1s spectrum in X-ray photoelectron spectroscopy (XPS) analysis / C atom concentration determined based on the peak area of the C1s spectrum in XPS analysis × 100
The amount of surface functional groups in the present invention can be measured using X-ray photoelectron spectroscopy (XPS).

  The surface functional group amount O / C value is measured using an X-ray photoelectron spectrometer as an X-ray photoelectron spectroscopy measurement, the measurement target is placed on a sample stage so that the surface is flat, and the Kα ray of aluminum is used as an X-ray source. The spectra of C1s (280 to 300 eV) and O1s (525 to 545 eV) are measured by multiplex measurement. The obtained C1s peak top is corrected to be 284.3 eV, the peak areas of the C1s and O1s spectra are obtained, and the device sensitivity coefficient is multiplied to calculate the surface atomic concentrations of C and O, respectively. The obtained O / C atomic concentration ratio O / C (O atom concentration / C atom concentration) is defined as the surface functional group amount O / C value of the carbon material.

(3) Carbon material particle size (d50)
The particle size of the carbon material that is the raw material of the composite carbon material for a non-aqueous secondary battery of the present invention is not particularly limited, but as a range to be used, d50 is usually 50 μm or less, preferably 30 μm or less, more preferably 25 μm. It is as follows. Moreover, it is 1 micrometer or more normally, Preferably it is 4 micrometers or more, More preferably, it is 10 micrometers or more. If this particle size is too large, there is a tendency for inconveniences in the process such as striping when it is made into a plate, and if the particle size is too small, the surface area becomes too large and the activity with the electrolyte is suppressed. Tend to be difficult.

The particle size is measured by suspending 0.01 g of a carbon material in 10 mL of a 0.2% by mass aqueous solution of polyoxyethylene sorbitan monolaurate, which is a surfactant, and measuring a commercially available laser diffraction / scattering particle size distribution. The sample was introduced into the apparatus, irradiated with 28 kHz ultrasonic waves at an output of 60 W for 1 minute, and then measured as a volume-based median diameter in the measuring apparatus, which is defined as d50 in the present invention.

(4) BET specific surface area (SA) of carbon material
About the specific surface area measured by BET method of the carbon material which is a raw material of the composite carbon material for non-aqueous secondary batteries of this invention, it is 4 m < ² > / g or more normally, Preferably it is 5 m < ² > / g or more. Moreover, it is 11 m < ² > / g or less normally, Preferably it is 9 m < ² > / g or less, More preferably, it is 8 m < ² > / g or less. If the specific surface area is too small, there are few sites where Li enters and exits, and the high-speed charge / discharge characteristic output characteristics are inferior. Therefore, there is a tendency that a high capacity battery cannot be manufactured.
In addition, the measuring method of a BET specific surface area is measured by a BET 1 point method by a nitrogen gas adsorption circulation method using a specific surface area measuring device.

(5) X-ray structural analysis (XRD) of carbon materials
Rhombedral obtained from X-ray structural analysis (XRD) of carbon material
The abundance ratio (3R / 2H) of Hexagonal crystals with respect to normal is usually 0.2.
0 or more and 0.25 or more are preferable, and 0.3 or more are more preferable. If 3R / 2H is too small, the high-speed charge / discharge characteristics tend to be reduced.

  In the X-ray structural analysis (XRD) measurement method, a 0.2 mm sample plate is filled so that the carbon material is not oriented, and is measured with an X-ray diffractometer at an output of 30 kV and 200 mA with CuKα rays. After subtracting the background from the obtained 3R (101) near 43.4 ° and 2H (101) near 44.5 °, the intensity ratio 3R (101) / 2H (101) can be calculated. .

(6) Tap density of carbon material The tap density of the carbon material which is the raw material of the composite carbon material for a non-aqueous secondary battery of the present invention is usually preferably 0.7 g / cm ³ or more, preferably 0.8 g / cm ³ or more. 1 g / cm ³ or more is more preferable. Moreover, 1.3 g / cm ³ or less and 1.2 g / cm ³ or less are usually preferable, and 1.1 g / cm ³ or less is more preferable. If the tap density is too low, the high-speed charge / discharge characteristics are inferior. If the tap density is too high, the intra-particle carbon density increases, the rollability is insufficient, and it may be difficult to form a high-density negative electrode sheet.

In the present invention, the tap density is filled with a powder density measuring device by dropping a carbon material through a sieve having a diameter of 1.6 cm and a volume capacity of 20 cm ³ through a sieve having an opening of 300 μm to fill the cell. After that, a tap having a stroke length of 10 mm is performed 1000 times, and the density obtained from the volume at that time and the weight of the sample is defined as the tap density.

(7) Raman R value of the carbon material as a raw material for non-aqueous secondary battery composite carbon material of the Raman spectra (Raman) spectrum invention carbon material, the intensity _{I A} of the peak _{P A} in the vicinity of 1580 cm ^-1, 1360 cm ^-1 was measured and the intensity _{I B} of the vicinity of the peak _{P B,} defined by calculating the intensity ratio _{R (R = I B / I} a). The value is usually 0.15 or more, preferably 0.4 or less, and more preferably 0.3 or less. When the Raman R value is less than this range, the crystallinity of the particle surface becomes too high, and when the density is increased, the crystals tend to be oriented in the direction parallel to the electrode plate, and the load characteristics tend to be lowered. On the other hand, if it exceeds this range, the crystal on the particle surface will be disturbed, the reactivity with the electrolyte will increase, and the charge / discharge efficiency will tend to decrease and gas generation will increase.

The Raman spectrum can be measured with a Raman spectrometer. Specifically, the sample particles are naturally dropped into the measurement cell to fill the sample, and the measurement cell is rotated in a plane perpendicular to the laser beam while irradiating the measurement cell with an argon ion laser beam. Measure.
Argon ion laser light wavelength: 532 nm
Laser power on sample: 25 mW
Resolution: 4cm ^-1
Measurement range: 1100 cm ^{−1 to} 1730 cm ⁻¹
Peak intensity measurement, peak half-width measurement: background processing, smoothing processing (convolution 5 points by simple averaging)

(8) Total pore volume of carbon material The total pore volume of the carbon material, which is the raw material of the composite carbon material for non-aqueous secondary batteries of the present invention, is a value measured using a mercury intrusion method (mercury porosimetry). Yes, usually 0.4 mL / g or more, preferably 0.5 mL / g or more, more preferably 0.55 mL / g or more, still more preferably 0.58 mL / g or more, particularly preferably 0.6 mL / g or more. Moreover, it is 0.95 mL / g or less normally, Preferably it is 0.93 mL / g or less, More preferably, it is 0.9 mL / g or less.

  If the total pore volume is below the above range, the number of voids that can be infiltrated by the non-aqueous electrolyte solution tends to be small, and when lithium ions are rapidly charged and discharged, lithium ions are not inserted and released in time, and lithium metal is deposited accordingly. Characteristics tend to deteriorate. On the other hand, if it exceeds the above range, the binder is easily absorbed into the gap during electrode plate production, and accordingly, the electrode plate strength and initial efficiency tend to be reduced.

(9) Pore volume in the range of 10 nm to 1000 nm of the carbon material The pore volume in the range of 10 nm to 1000 nm of the carbon material that is the raw material of the composite carbon material for the non-aqueous secondary battery of the present invention is determined by mercury intrusion method (mercury Is a value measured using a porosimetry), usually 0.05 mL / g or more, preferably 0.07 mL / g or more, more preferably 0.1 mL / g or more, and usually 0.3 mL / g or less. Preferably, it is 0.28 mL / g or less, More preferably, it is 0.25 mL / g or less.
When the pore volume in the range of 10 nm to 1000 nm is less than the above range, voids into which the non-aqueous electrolyte solution can enter decrease, so that when lithium ion is rapidly charged / discharged, lithium ion insertion / desorption is not in time, and accordingly lithium ion There is a tendency for the metal to precipitate and the cycle characteristics to deteriorate. On the other hand, if it exceeds the above range, the binder is easily absorbed into the gap during electrode plate production, and accordingly, the electrode plate strength and initial efficiency tend to be reduced.

(10) Carbon Material Production Method The carbon material that is the raw material of the composite carbon material for the non-aqueous secondary battery of the present invention is not particularly limited, but as described above, natural graphite, artificial graphite, coke powder, and needle coke. Powders, powders of graphitized resin, and the like can be used. Of these, natural graphite is preferable, and spheroidized natural graphite subjected to spheronization treatment is particularly preferable. Below, the manufacturing method of spherical natural graphite is described as an example.

The carbon material used as the raw material for the composite carbon material for non-aqueous secondary batteries of the present invention is subjected to the spheroidization step by the above surface treatment, whereby the scale-like natural graphite is folded or the peripheral edge portion is spherically pulverized. As a result, fine particles of 5 μm or less generated mainly by grinding adhere to the spherical base particles, and the surface functional group amount O / C value of the carbon material after the surface treatment is usually 1% or more and 4%. It manufactures by performing a spheronization process on the conditions used as follows. In this case, it is preferable to carry out in an active atmosphere so that the oxidation reaction of the graphite surface can be advanced by the energy of mechanical treatment and acidic functional groups can be introduced into the graphite surface. As an apparatus used for the spheroidization treatment, for example, an apparatus that repeatedly gives mechanical action such as compression, friction, shearing force, etc. including the interaction of particles mainly with impact force to the particles can be used.

  Specifically, it has a rotor with a large number of blades installed inside the casing, and mechanical action such as impact compression, friction, shearing force, etc. on the carbon material introduced inside the rotor by rotating at high speed. An apparatus that provides a surface treatment is preferable. Moreover, it is preferable to have a mechanism that repeatedly gives mechanical action by circulating the carbon material. Preferable apparatuses include, for example, a hybridization system (manufactured by Nara Machinery Co., Ltd.), kryptron (manufactured by Earth Technica Co., Ltd.), CF mill (manufactured by Ube Industries, Ltd.), mechanofusion system (manufactured by Hosokawa Micron Corporation), Etc.). Among these, a hybridization system manufactured by Nara Machinery Co., Ltd. is preferable.

  For example, when processing using the above-mentioned apparatus, the peripheral speed of the rotating rotor is usually 30 to 100 m / sec, preferably 40 to 100 m / sec, and more preferably 50 to 100 m / sec. The treatment can be performed by simply passing a carbonaceous material, but it is usually preferable to circulate or stay in the apparatus for 30 seconds or longer, and circulate or stay in the apparatus for 1 minute or longer.

<Organic compounds that are raw materials for composite carbon materials for non-aqueous secondary batteries>
The organic compound that is the other raw material of the composite carbon material for a non-aqueous secondary battery of the present invention preferably satisfies the following physical properties.
The organic compound in the present invention is a raw material that becomes a graphite material by firing. Here, the graphite material is graphite having a d value of less than 0.340 nm.

-Kind of organic compound As an organic compound, the compound as described in the following (a) or (b) is preferable.
(A) Coal heavy oil, DC heavy oil, cracked heavy oil, aromatic hydrocarbon, N ring compound, S ring compound, polyphenylene, organic synthetic polymer, natural polymer, thermoplastic resin and An easily graphitizable organic material capable of carbonization or graphitization selected from the group consisting of thermosetting resins.
(B) An easily graphitizable organic substance that can be carbonized or graphitized is dissolved in a low-molecular organic solvent.

  The coal-based heavy oil is preferably a coal tar pitch from a soft pitch to a hard pitch, dry distillation liquefied oil, etc., and the DC heavy oil is preferably an atmospheric residue, a vacuum residue, etc. As the heavy petroleum oil, ethylene tar or the like by-produced during thermal decomposition of crude oil, naphtha or the like is preferable, and as the aromatic hydrocarbon, acenaphthylene, decacyclene, anthracene, phenanthrene or the like is preferable, and the N-ring compound is , Phenazine, acridine and the like are preferable, the S ring compound is preferably thiophene, bithiophene and the like, the polyphenylene is preferably biphenyl, terphenyl and the like, and the organic synthetic polymer is polyvinyl chloride, polyvinyl alcohol, Polyvinyl butyral, insolubilized products of these, polyacrylonitrile , Polypyrrole, polythiophene, polystyrene and the like are preferable, the natural polymer is preferably a polysaccharide such as cellulose, lignin, mannan, polygalacturonic acid, chitosan, saccharose, etc., and the thermoplastic resin is polyphenylene sulfide, Polyphenylene oxide and the like are preferable, and as the thermosetting resin, a furfuryl alcohol resin, a phenol-formaldehyde resin, an imide resin, and the like are preferable. Among these, coal-based heavy oil, direct-current heavy oil, and cracked heavy petroleum oil are preferable because fine irregularities are easily formed on the surface of the graphite particles.

-Physical properties of organic compounds (1) X-ray parameters (d002 value)
The interplanar spacing (d002) of the 002 plane according to the X-ray wide angle diffraction method of the carbon powder obtained by graphitizing only the organic compound is usually 0.3357 nm or more, preferably 0.3358 nm or more, more preferably 0.3359 nm or more. It is. Moreover, it is 0.340 nm or less normally, Preferably it is 0.338 nm or less, More preferably, it is 0.337 nm or less. If the d002 value is too large, it indicates that the crystallinity is low, and the composite carbon material for non-aqueous secondary batteries may become particles with low crystallinity and the charge / discharge capacity may be reduced. There is a risk that the discharge reactivity will be reduced, resulting in an increase in gas generation during high temperature storage and a decrease in large current charge / discharge characteristics.

(2) Crystallite size (Lc (004))
The crystallite size (Lc (004)) of the carbon material determined by X-ray diffraction of the carbon powder obtained by graphitizing the organic compound is usually 10 nm or more, preferably 30 nm or more, more preferably It is 50 nm or more. Moreover, it is 500 nm or less normally, Preferably it is 400 nm or less, More preferably, it is 300 nm or less. If the crystallite size is too large, the composite carbon material for non-aqueous secondary batteries tends to have low crystallinity and the charge / discharge capacity tends to decrease, and if the crystallite size is too small, the charge / discharge reactivity decreases. In addition, there is a tendency for increased gas generation during storage at high temperatures and reduced large current charge / discharge characteristics.

(3) Softening point The softening point of the organic compound is usually 300 ° C or lower, preferably 200 ° C or lower, more preferably 150 ° C or lower, and further preferably 100 ° C or lower. If the softening point is too high, it is difficult to uniformly mix the carbon material with the carbon material, and it may be necessary to carry out the mixing at a high temperature. Although a minimum in particular is not restrict | limited, Usually, it is 40 degreeC or more.
(4) Quinoline insoluble matter (QI), toluene insoluble matter (TI)
The quinoline insoluble content of the organic compound is usually 0.6% or more, preferably 1% or more, more preferably 5% or more, still more preferably 6% or more, and particularly preferably 8% or more. Further, it is usually 30% or less, preferably 25% or less, more preferably 20% or less, still more preferably 15% or less, and particularly preferably 12% or less.

  The toluene insoluble content is usually 16% or more, preferably 20% or more, more preferably 25% or more. Moreover, it is 60% or less normally, Preferably it is 50% or less, More preferably, it is 40% or less. When the quinoline insoluble content and the toluene insoluble content are within this range, the charge / discharge reactivity becomes a preferable range because the crystallinity of the carbon material for the non-aqueous secondary battery becomes a preferable range, so the charge / discharge capacity is improved, There is a tendency to reduce gas generation during storage at high temperatures, to improve large current charge / discharge characteristics, and to improve cycle characteristics.

In addition, the measuring method of a quinoline insoluble content (QI) and a toluene insoluble content (TI) shall follow the method as described in an Example.
(5) Residual carbon ratio The residual carbon ratio of the organic compound is not particularly limited, but is usually 1% by mass or more, preferably 10% by mass or more, more preferably 20% by mass or more, and further preferably 30% by mass or more. Usually, it is 80 mass% or less, Preferably it is 70% or less, More preferably, it is 60 mass% or less. If it is in the said range, since it becomes easy to become uniform composite graphite particle and it is excellent in productivity, it is preferable. Here, the residual carbon ratio is a value obtained from the yield of the organic compound before and after firing, and can be obtained, for example, by the method described in JIS K2270.

(6) Elementary hydrogen ratio (H / C)
The hydrogen atom ratio (H / C) of the organic compound is usually 0.03 or more, preferably 0.035 or more, more preferably 0.04 or more, and preferably 0.15 or less, more preferably 0.8. It is 10 or less, more preferably 0.06 or less, and particularly preferably 0.043 or less. If the hydrogen source ratio is too large, the irreversible capacity at the beginning of the cycle may increase.If the hydrogen source ratio is too small, the charge / discharge reactivity decreases, increasing gas generation during high-temperature storage, There is a tendency for large-current charge / discharge characteristics to decrease. In addition, the measuring method of hydrogen raw material ratio (H / C) shall follow the method as described in an Example.

<Method for producing composite carbon material for non-aqueous secondary battery>
The method for producing the composite carbon material for the non-aqueous secondary battery is not particularly limited as long as the isotropic pressure-treated carbon material and the graphite material are composited. For example, the carbon material isotropically pressurized. After the treatment, the organic compound may be mixed and fired, or the above-described carbon material and the organic compound for obtaining the graphite part may be mixed, and the resulting mixture may be fired. The carbon material is subjected to isotropic pressure treatment by pressurization and then crushed, mixed with an organic compound, and the resulting mixture may be fired and pulverized, or the above-described carbon material and graphite portion may be combined. When mixing with the organic compound to obtain and performing the firing treatment on the resulting mixture, the carbon material is mixed with the organic compound and isotropically pressurized with pressure, and then the resulting mixture is fired. Composite carbon for non-aqueous secondary batteries used in the present invention by pulverization treatment It can be produced. In the production method of the present invention, as a preferred embodiment, after mixing an organic compound and a carbon material (hereinafter also referred to as a mixture), isotropic pressure treatment is performed on the mixture.

In the manufacturing method described above, a composite carbon material for a non-aqueous secondary battery in which a carbon material subjected to isotropic pressure treatment and a graphite material is combined is manufactured. "" Includes, for example, "a carbon material provided with a graphite layer on at least a part of its surface". Specifically, it includes not only a form in which the graphite material layer covers part or all of the surface of the carbon material particles in a layered manner, but also a form in which the graphite material layer adheres to or adheres to part or all of the surface. The graphite material layer may be provided so as to cover the entire surface, or a part thereof may be coated, attached, or attached.
In the following, a preferred embodiment of a production method in which an organic compound and a carbon material are mixed and then subjected to isotropic pressure treatment on the mixture will be specifically described.

-Step of mixing an organic compound and a carbon material as a raw material Mixing of a carbon material and an organic compound can be performed by a conventional method. The mixing temperature is usually from room temperature to 150 ° C., more preferably from 50 to 150 ° C., and further preferably in a heated state of from 100 to 130 ° C.
The mixing amount of the organic compound with respect to the carbon material is adjusted and mixed so that the organic compound is usually 1% by mass or more, preferably 5% by mass or more, more preferably 10% by mass or more with respect to the carbon material. The upper limit is an amount such that this ratio is usually 60% by mass or less, preferably 40% by mass or less, and more preferably 30% by mass or less. If the amount of the organic compound mixed is too large, the charge / discharge capacity decreases, and the press load required for high-density rolling of the active material layer applied to the current collector increases, resulting in a non-aqueous secondary battery. It may be difficult to increase the capacity. On the other hand, if the mixing amount of the organic compound is too small, particles may be destroyed or deformed when the active material layer applied to the current collector is rolled to a high density, and good large current charge / discharge characteristics may not be obtained. is there.

When mixing with the carbon material, the organic compound is preferably diluted with an organic solvent. The reason for diluting is that by diluting with an organic solvent, the viscosity of the organic compound to be mixed is lowered, and the carbon material can be coated more uniformly and efficiently.
Organic solvents include pentane, hexane, isohexane, heptane, octane, isooctane, decane, dimethylbutane, cyclohexane, methylcyclohexane and other hydrocarbons, ethyl ether, isopropyl ether, diisoamyl ether, methylphenyl ether, amylphenyl ether. , Ethers such as ethyl benzyl ether, ketones such as acetone, methyl acetone, methyl ethyl ketone, methyl isobutyl ketone, diethyl ketone, methyl formate, ethyl formate, isobutyl formate, methyl acetate, isoamyl acetate, methoxybutyl acetate, cyclohexyl acetate, methyl butyrate, Esters such as ethyl butyrate, butyl benzoate, isoamyl benzoate, benzene, toluene, xylene, ethylbenzene, diethylbenzene, isopropylben Aromatic hydrocarbons such as but not limited to benzene, amylbenzene, diamylbenzene, triamylbenzene, tetraamylbenzene, dodecylbenzene, didodecylbenzene, amyltoluene, tetralin, cyclohexylbenzene, etc. . Moreover, what mixed these 2 or more types may be used. Among these, benzene, toluene, and xylene are organic solvents having a relatively high boiling point and a low viscosity, and are particularly preferable in that the concentration change due to volatilization hardly occurs and the viscosity of the organic compound can be lowered.

  The dilution ratio is usually 5% by mass or more, preferably 25% by mass or more, more preferably 40% by mass or more, and further preferably 50% by mass with respect to the total mass of the organic solvent and the organic compound. These are usually 90% by mass or less, preferably 80% by mass or less, more preferably 70% by mass or less, and still more preferably 60% by mass or less. If the dilution ratio is too large, the concentration of the organic compound tends to decrease, and there is a tendency that the carbon material cannot be coated efficiently. If the dilution ratio is too small, the organic compound concentration does not sufficiently decrease and the carbon material is efficiently removed. Tends to be unable to be coated.

Mixing is usually carried out under normal pressure, but if desired, it can also be carried out under reduced pressure or under pressure. Mixing can be carried out either batchwise or continuously. In any case, mixing efficiency can be improved by using a combination of an apparatus suitable for rough mixing and an apparatus suitable for fine mixing.
As a batch type mixing device, a single blade is used in the tank, such as a mixer that revolves while the two frame molds rotate, a dissolver that is a high-speed high-shear mixer, and a butterfly mixer for high viscosity. A device having a structure for stirring and dispersing, a so-called kneader type device having a structure in which a stirring blade such as a sigma type rotates along the side surface of a semi-cylindrical mixing tank, and a trimix type device having three stirring blades A so-called bead mill type apparatus having a rotating disk and a dispersion medium in a container is used.

  It also has a container with a paddle that is rotated by a shaft, and the inner wall surface of the container is formed substantially along the outermost line of rotation of the paddle, preferably in a long twin cylinder shape, and the paddle has side surfaces facing each other. A device having a structure in which many pairs are arranged in the axial direction of the shaft so as to be slidably engaged (for example, KRC reactor manufactured by Kurimoto Iron Works, SC processor, TEM manufactured by Toshiba Machine Celmac, TEX-K manufactured by Nippon Steel Works) Etc.), and a container having a plurality of pavement or sawtooth paddles fixed to the shaft and arranged in multiple phases, the inner wall surface of which is the outermost line of rotation of the paddle Substantially along the (externally heated) device, preferably in the form of a cylinder (for example, a Redige mixer manufactured by Redige, a flow share mixer manufactured by Taiyo Kiko Co., Ltd., a Tsukishima Machine Co., Ltd. T dryer, etc.) can also be used.

In order to perform mixing in a continuous manner, a pipeline mixer, a continuous bead mill, or the like may be used.
The viscosity of the mixture obtained in this step is usually 100 cP or less, preferably 70 cP or less, more preferably 50 cP or less. Moreover, it is 1 cP or more normally, Preferably it is 10 cP or more. If the viscosity is too high, deterioration during cycling tends to occur, and cycle characteristics tend to deteriorate.

-Process of isotropic pressure treatment of a mixture of carbon material and organic compound Graphite composite carbon material manufactured without isotropic pressure treatment of a mixture containing at least a carbon material and an organic compound has very small pores inside the particle. In contrast, the graphite composite carbon material produced by isotropic pressure treatment of a mixture containing at least a carbon material and an organic compound has moderate pores inside the particles. As a result, the non-aqueous electrolyte can appropriately enter during charging / discharging, which tends to improve large current charging / discharging characteristics and cycle characteristics, which is preferable. Although the detailed reason for having the pores in the particles within a preferable range is not clear, the void opening is appropriately blocked by isotropic pressure treatment with the organic compound sucked into the internal void of the carbon material. In addition, it is considered that the gas component generated from the organic compound in the subsequent baking treatment is appropriately prevented from coming out of the internal voids of the carbon material, and as a result, pores are introduced into the particles.

The method for pressure molding is not particularly limited, and a roll compactor, roll press, rivet machine, CIP, uniaxial molding machine, tablet machine, and the like can be used.
Further, if necessary, the carbon material can be molded simultaneously with the press according to the pattern carved in the roll. Moreover, the method of exhausting the air which exists between carbon material particles and vacuum-pressing can also be applied.

Note that isotropic pressure treatment is preferable because flattening of particles hardly occurs, a spherical shape can be maintained, and a decrease in fluidity when formed into a paint can be prevented.
At a pressure of pressurizing the carbon material is not particularly limited, usually 50 kgf / cm ² or higher, preferably 100 kgf / cm ² or more, more preferably 300 kgf / cm ² or more, most preferably 1000 kgf / cm ² or more is there. The upper limit of the isotropic pressure treatment is not particularly limited, but is usually 2000 kgf / cm ² or less, preferably 1500 kgf / cm ² or less. When the pressure is too low, strong granulation is not achieved and the internal voids tend not to decrease, and when the pressure is too high, the cost of the process tends to increase.

The pressurizing time is usually 0.1 seconds or longer, preferably 3 seconds or longer, more preferably 1 minute or longer. Moreover, it is 30 minutes or less normally, Preferably it is 10 minutes or less, More preferably, it is 3 minutes or less. If the time is too long, it adversely affects the manufacturing process. On the other hand, if the time is too short, strong granulation is not achieved and the internal voids tend not to decrease.
The carbon material obtained by the isotropic pressure treatment preferably exhibits the following physical properties.

-The step of firing the mixture Specifically, the mixture is heated in a non-oxidizing atmosphere, preferably under a flow of nitrogen, argon, carbon dioxide, etc., to graphitize the organic compound, and thus a composite coal for non-aqueous secondary batteries. This is a process for producing a material (also referred to as graphitization treatment).
The firing temperature varies depending on the organic compound used for the preparation of the mixture, but when obtaining a composite carbon material for a non-aqueous secondary battery in which a graphite material is composited, it may be at or above the temperature at which the organic compound graphitizes, Specifically, it is normally graphitized by heating to 2000 ° C. or higher, preferably 2500 ° C. or higher, more preferably 2700 ° C. or higher. If the heating temperature is too high, the sublimation of graphite becomes remarkable, so the upper limit of the superheating temperature is usually 3300 ° C. or lower, preferably 3100 ° C. or lower and 3000 ° C. or lower. In addition, you may perform a de-VM baking process once at 1000 degreeC before performing a graphitization process.

In the firing treatment conditions, the heat history temperature condition, the temperature rise rate, the cooling rate, the heat treatment time, etc. are appropriately set. Further, after heat treatment in a relatively low temperature region, the temperature can be raised to a predetermined temperature. In addition, the reactor used for this process may be a batch type or a continuous type, and may be one or more.
The furnace used for firing is not particularly limited as long as the above requirements are satisfied. For example, a reactor such as a shuttle furnace, a tunnel furnace, a lead hammer furnace, a rotary kiln, an autoclave, a coker (heat treatment tank for coke production), a Tamman furnace, As the Atchison furnace and heating method, a high-frequency induction heating furnace, direct resistance heating, indirect resistance heating, direct combustion heating, radiant heat heating, or the like can be used. During the treatment, stirring may be performed as necessary.

The composite carbon material that has undergone the above-described steps is subjected to powder processing such as pulverization, crushing, and classification again as necessary to obtain a composite carbon material for a non-aqueous secondary battery.
There are no particular restrictions on the apparatus used for pulverization and pulverization, for example, the coarse pulverizer includes a shearing mill, jaw crusher, impact crusher, cone crusher, etc., and the intermediate pulverizer includes roll crusher, hammer mill, etc. Examples of the pulverizer include a ball mill, a vibration mill, a pin mill, a stirring mill, and a jet mill.

  There is no particular limitation on the apparatus used for classification, but for example, in the case of dry sieving, a rotary sieving, a swaying sieving, a rotating sieving, a vibrating sieving, etc. can be used. In this case, gravity classifier, inertial classifier, centrifugal classifier (classifier, cyclone, etc.) can be used, wet sieving, mechanical wet classifier, hydraulic classifier, sedimentation classifier A centrifugal wet classifier or the like can be used.

<Composite carbon material for non-aqueous secondary batteries>
The composite carbon material for non-aqueous secondary batteries obtained by the above manufacturing method has the following characteristics.
(1) 002 plane spacing (d002)
The interplanar spacing (d002) of the 002 plane by the X-ray wide angle diffraction method of the composite carbon material for non-aqueous secondary batteries is usually 3.37 mm or less and Lc is usually 900 mm or more. The 002 plane spacing (d002) by X-ray wide angle diffractometry is 3.37 mm or less and Lc is 900 mm or more, which means that most of the crystallinity excluding the surface of the composite carbon material for non-aqueous secondary batteries. This indicates that the composite carbon material is a high-capacity electrode that does not cause a reduction in capacity due to the large irreversible capacity found in amorphous carbon materials.

(2) Tap density The tap density (Tap density) of the composite carbon material for non-aqueous secondary batteries is usually 0.8 g / cm ³ or more, preferably 0.85 g / cm ³ or more, more preferably 1 g / cm. ³ or more, more preferably 1.1 g / cm ³ or more.
That the tap density of the composite carbon material for non-aqueous secondary batteries is 0.8 g / cm ³ or more is one of the indicators that the composite carbon material for non-aqueous secondary batteries has a spherical shape. . When the tap density is less than 0.8 g / cm ³ , this is one of the indicators that the spherical carbon material, which is the raw material of the composite carbon material for non-aqueous secondary batteries, is not sufficient spherical particles. If the tap density is less than 0.8 g / cm ³ , sufficient continuous voids are not secured in the electrode, and the mobility of Li ions in the electrolyte that are not held in the voids is reduced, thereby reducing rapid charge / discharge characteristics. Tend to.

(3) Raman R value is the peak intensity ratio in the vicinity of 1360 cm ^-1 to the peak intensity near 1580 cm ^-1 in the argon ion laser Raman spectrum of the Raman R value for nonaqueous secondary batteries composite carbon material is usually 0.45 or less , Preferably 0.40 or less, more preferably 0.35 or less, usually 0.20 or more, preferably 0.23 or more, more preferably 0.25 or more. If the Raman value is within this range, the crystallinity on the surface of the negative electrode active material is in an appropriate range, which is preferable because high output is easily obtained.

(4) Specific surface area by BET method The specific surface area by the BET method of the composite carbon material for non-aqueous secondary batteries is usually 15 m ² / g or less, preferably 7 m ² / g or less, more preferably 6.5 m ² / g or less. More preferably, it is 5 m ² / g or less, particularly preferably 4.3 m ² / g or less, usually 0.1 m ² / g or more, preferably 0.7 m ² / g or more, more preferably 1 m ² / g or more. It is. If the specific surface area is too large, the reactivity between the portion exposed to the electrolyte when used as the negative electrode active material and the electrolyte increases, gas generation tends to increase, and a favorable battery tends to be difficult to obtain. If it is too small, the lithium acceptability tends to deteriorate during charging when used as a negative electrode active material.

(5) Total pore volume The total pore volume of the composite carbon material for a non-aqueous secondary battery is a value measured using a mercury intrusion method (mercury porosimetry), and usually 0.3 mL / g or more, preferably 0.4 mL / g or more, more preferably 0.46 mL / g or more, particularly preferably 0.55 mL / g or more,
Usually, it is 1 mL / g or less, Preferably it is 0.8 mL / g or less, More preferably, it is 0.6 mL / g or less.

  If the total pore volume is below the above range, the number of voids that can be infiltrated by the non-aqueous electrolyte solution tends to be small, and when lithium ions are rapidly charged and discharged, lithium ions are not inserted and released in time, and lithium metal is deposited accordingly. Characteristics tend to deteriorate. On the other hand, if it exceeds the above range, the binder is easily absorbed into the gap during electrode plate production, and accordingly, the electrode plate strength and initial efficiency tend to be reduced.

(6) Pore volume in the range of 10 nm to 1000 nm The pore volume in the range of 10 nm to 1000 nm of the composite carbon material for non-aqueous secondary batteries is a value measured using a mercury intrusion method (mercury porosimetry), Usually 0.031 mL / g or more, preferably 0.04 mL / g or more, more preferably 0.07 mL / g or more, and usually 0.3 mL / g or less, preferably 0.11 mL / g or less. is there. When the pore volume in the range of 10 nm to 1000 nm is less than the above range, voids into which the non-aqueous electrolyte solution can enter decrease, so that when lithium ion is rapidly charged / discharged, lithium ion insertion / desorption is not in time, and accordingly lithium ion There is a tendency for the metal to precipitate and the cycle characteristics to deteriorate. On the other hand, if it exceeds the above range, the binder is easily absorbed into the gap during electrode plate production, and accordingly, the electrode plate strength and initial efficiency tend to be reduced.

(6) Volume-based average particle diameter (d50)
The volume-based average particle size of the composite carbon material for non-aqueous secondary batteries is usually 50 μm or less, preferably 40 μm or less, more preferably 30 μm or less, still more preferably 20 μm or less, usually 5 μm or more, preferably 10 μm or more, More preferably, it is 16 micrometers or more, More preferably, it is 16.9 micrometers or more. If the average particle size is too large, a large amount of binder tends to be required, and if the average particle size is too small, high current density charge / discharge characteristics tend to decrease.

(7) Coverage The composite carbon material for a non-aqueous secondary battery of the present invention is preferably coated with a graphite material. This coverage is usually 1% by mass or more, preferably 5% by mass or more, more preferably 8% by mass or more, and further preferably 11% or more, and usually 40% by mass or less, preferably 30% by mass or less, more Preferably it is 25 mass% or less, More preferably, it is 19 mass% or less, More preferably, it is 17 mass% or less. If this content is too high, the packing density is difficult to increase when it is made into an electrode, so there is a tendency to require an excessive press load, and the low crystalline portion of the negative electrode material increases, so when assembling the battery The reversible capacity tends to be small. If it is too small, the graphite material is not uniformly coated on the scale graphite and strong granulation is not performed, and the particle size tends to be small when pulverized after firing. In addition, the content rate (coverage) of the graphite material derived from the organic compound of the carbon material for electrodes finally obtained is measured by the amount of the carbon material to be used, the amount of the organic compound, and the micro method of JIS K 2270. It can be calculated by the following formula based on the remaining carbon ratio.
Covering rate of graphitic material derived from organic compound (%) = (mass of organic compound × remaining carbon ratio × 100) / (mass of carbon material + mass of organic compound × remaining carbon ratio)

(8) Intraparticle porosity The intraparticle particle porosity of the composite carbon material for non-aqueous secondary batteries of the present invention is usually 30% or less, preferably 25% or less, more preferably 20% or less, and usually 5% or more. , Preferably 7% or more, more preferably 10% or more. If the intra-particle porosity is too large, the organic compound to be mixed will be wasted into the internal voids of the carbon material, and there is a tendency that the carbon material cannot be efficiently coated, and if the intra-particle porosity is too small There is an excess of organic compounds to be mixed, and the carbon materials tend to agglomerate with each other so that the carbon materials cannot be efficiently coated.
In addition, the measuring method of the particle | grain porosity is according to the measuring method of an Example.

(9) Orientation ratio (110/004)
The orientation ratio of the powder of the composite carbon material for a non-aqueous secondary battery of the present invention is usually 0.1 or more, preferably 0.27 or more, more preferably 0.29 or more, and further preferably 0.3 or more. Particularly preferably, it is 0.4 or more, and is usually 0.7 or less, preferably 0.6 or less, more preferably 0.5 or less. When the orientation ratio is below the above range, the high-density charge / discharge characteristics may tend to deteriorate. In addition, the normal upper limit of the said range is a theoretical upper limit of the orientation ratio of a carbonaceous material.

The orientation ratio is measured by X-ray diffraction after pressure-molding the sample. Set the molded body obtained by filling 0.47 g of the sample into a molding machine with a diameter of 17 mm and compressing it with 58.8MN · m ^{-2 so} that it is flush with the surface of the sample holder for measurement. X-ray diffraction is measured. From the (110) diffraction and (004) diffraction peak intensities of the obtained carbon, a ratio represented by (110) diffraction peak intensity / (004) diffraction peak intensity is calculated. The orientation ratio calculated by the measurement is defined as the orientation ratio of the negative electrode material of the present invention.

<Mixing with other materials>
The composite carbon material for a non-aqueous secondary battery of the present invention may contain other materials defined below. Combinations of composite carbon materials for non-aqueous secondary batteries and other materials should be used suitably as negative electrode materials for lithium ion secondary batteries by using one or a combination of two or more in any composition and combination. Can do.

  When mixing other materials to the above-mentioned non-aqueous secondary battery composite carbon material, the mixing ratio of the non-aqueous secondary battery composite carbon material to the total amount of the non-aqueous secondary battery composite carbon material and other materials is: Although there is no restriction | limiting in particular, Usually, it is 10 mass% or more, Preferably it is 20 mass% or more, and is 90 mass% or less normally, Preferably it is the range of 80 mass% or less. When the mixing ratio of other materials is less than the above range, the added effect tends to hardly appear. On the other hand, if it exceeds the above range, the characteristics of the composite carbon material for non-aqueous secondary batteries tend to hardly appear.

<Other materials>
Other materials include natural graphite, artificial graphite, coated graphite obtained by coating a non-pressurized carbon material with amorphous carbon or graphite, amorphous carbon, metal particles, and metal compounds. Is used. Any one of these materials may be used alone, or two or more of these materials may be used in any combination and composition.

  As the natural graphite, for example, a highly purified carbon material or a spherical natural graphite can be used. In the present invention, high purification means that ash contained in low-purity natural graphite is usually treated in an acid such as hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, or a combination of a plurality of acid treatment steps. It means an operation of dissolving and removing metal and metal, etc., and usually, after the acid treatment step, a water washing treatment or the like is performed to remove the acid content used in the high purification treatment step. Moreover, you may evaporate and remove ash, a metal, etc. by processing at high temperature 2000 degreeC or more instead of an acid treatment process. Moreover, you may remove ash, a metal, etc. by processing in halogen gas atmosphere, such as chlorine gas, at the time of high temperature heat processing. Furthermore, these methods may be used in any combination.

  The volume-based average particle diameter of natural graphite is usually 8 μm or more, preferably 12 μm or more, and usually 60 μm or less, preferably 40 μm or less. If the average particle size is too large, exceeding this particle size range tends to cause inconveniences in the process such as striping when the plate is formed, and the charge / discharge load characteristics tend to decrease. On the other hand, if the particle size is below this range, the surface area tends to be too large and it becomes difficult to suppress the activity with the electrolyte.

Natural graphite has a BET specific surface area of usually 3.5 m ² / g or more, preferably 4.5 m ² / g or more, and usually 8 m ² / g or less, preferably 6 m ² / g or less. If the specific surface area is too large, the reactivity between the portion exposed to the electrolyte and the electrolyte when used as the negative electrode active material increases, and the charge / discharge efficiency tends to decrease and gas generation tends to increase, making it difficult to obtain a favorable battery. If the specific surface area is too small, the lithium acceptability tends to deteriorate during charging when used as a negative electrode active material.

The tap density of natural graphite is usually preferably 0.6 g / cm ³ or more, 0.7 g / cm ³ or more, more preferably 0.8 g / cm ³ or more, and further preferably 0.85 g / cm ³ or more. Moreover, 1.3 g / cm ³ or less and 1.2 g / cm ³ or less are usually preferable, and 1.1 g / cm ³ or less is more preferable. If the tap density is too low, the high-speed charge / discharge characteristics are inferior. If the tap density is too high, the intra-particle carbon density increases, the rollability is insufficient, and it may be difficult to form a high-density negative electrode sheet.

Examples of the artificial graphite include particles obtained by graphitizing a carbon material. For example, a single graphite precursor particle is fired while being powdered, a graphitized particle, and a plurality of graphite precursor particles are molded and fired. Granulated particles that have been graphitized and crushed can be used.
The volume-based average particle size of artificial graphite is usually 5 μm or more, preferably 10 μm or more, and usually 60 μm or less, preferably 40 μm, more preferably 30 μm or less. If the average particle size is too large, exceeding this particle size range tends to cause inconveniences in the process such as striping when the plate is formed, and the charge / discharge load characteristics tend to decrease. On the other hand, if the particle size is below this range, the surface area tends to be too large and it becomes difficult to suppress the activity with the electrolyte.

The artificial graphite has a BET specific surface area of usually 0.5 m ² / g or more, preferably 1.0 m ² / g or more, and usually 8 m ² / g or less, preferably 6 m ² / g or less, more preferably 4 m ^2. / G or less. If the specific surface area is too large, the reactivity between the portion exposed to the electrolyte and the electrolyte when used as the negative electrode active material increases, and the charge / discharge efficiency tends to decrease and gas generation tends to increase, making it difficult to obtain a favorable battery. If the specific surface area is too small, the lithium acceptability tends to deteriorate during charging when used as a negative electrode active material.

Further, the tap density of the artificial graphite is usually preferably 0.6 g / cm ³ or more, 0.7 g / cm ³ or more, more preferably 0.8 g / cm ³ or more, and further preferably 0.85 g / cm ³ or more. Moreover, normally 1.5 g / cm < ³ > or less and 1.4 g / cm < ³ > or less are preferable, and 1.3 g / cm < ³ > or less is more preferable. If the tap density is too low, the high-speed charge / discharge characteristics are inferior. If the tap density is too high, the intra-particle carbon density increases, the rollability is insufficient, and it may be difficult to form a high-density negative electrode sheet.

As the coated graphite obtained by coating a non-pressurized carbon material with amorphous carbon or a graphite material, for example, natural graphite or artificial graphite that has not been pressure-treated is coated with an amorphous precursor, baked and / or Graphitized particles, or particles obtained by coating amorphous with CVD on natural graphite or artificial graphite that has not been subjected to pressure treatment can be used.
The volume-based average particle diameter of the coated graphite is usually 8 μm or more, preferably 12 μm or more, and usually 60 μm or less, preferably 40 μm or less. If the average particle size is too large, exceeding this particle size range tends to cause inconveniences in the process such as striping when the plate is formed, and the charge / discharge load characteristics tend to decrease. On the other hand, if the particle size is below this range, the surface area tends to be too large and it becomes difficult to suppress the activity with the electrolyte.

The BET specific surface area of the coated graphite is usually 1 m ² / g or more, preferably 2 m ² / g or more, more preferably 2.5 m ² / g or more, and usually 8 m ² / g or less, preferably 6 m ² / g. Hereinafter, the range is more preferably 4 m ² / g or less. If the specific surface area is too large, the reactivity between the portion exposed to the electrolyte and the electrolyte when used as the negative electrode active material increases, and the charge / discharge efficiency tends to decrease and gas generation tends to increase, making it difficult to obtain a favorable battery. If the specific surface area is too small, the lithium acceptability tends to deteriorate during charging when used as a negative electrode active material.

The tap density of the coated graphite is usually preferably 0.6 g / cm ³ or more, 0.7 g / cm ³ or more, more preferably 0.8 g / cm ³ or more, and further preferably 0.85 g / cm ³ or more. Moreover, 1.3 g / cm ³ or less and 1.2 g / cm ³ or less are usually preferable, and 1.1 g / cm ³ or less is more preferable. If the tap density is too low, the high-speed charge / discharge characteristics are inferior. If the tap density is too high, the intra-particle carbon density increases, the rollability is insufficient, and it may be difficult to form a high-density negative electrode sheet.

As amorphous carbon, for example, particles obtained by firing a bulk mesophase or particles obtained by infusibilizing an easily graphitizable organic compound and firing can be used.
The volume-based average particle size of the amorphous carbon is usually in the range of 5 μm or more, preferably 12 μm or more, and usually 60 μm or less, preferably 40 μm or less. If the average particle size is too large, exceeding this particle size range tends to cause inconveniences in the process such as striping when the plate is formed, and the charge / discharge load characteristics tend to decrease. On the other hand, if the particle size is below this range, the surface area tends to be too large and it becomes difficult to suppress the activity with the electrolyte.

The BET specific surface area of amorphous carbon is usually 1 m ² / g or more, preferably 2 m ² / g or more, more preferably 2.5 m ² / g or more, and usually 8 m ² / g or less, preferably 6 m ^2. / G or less, more preferably 4 m ² / g or less. If the specific surface area is too large, the reactivity between the portion exposed to the electrolyte and the electrolyte when used as the negative electrode active material increases, and the charge / discharge efficiency tends to decrease and gas generation tends to increase, making it difficult to obtain a favorable battery. If the specific surface area is too small, the lithium acceptability tends to deteriorate during charging when used as a negative electrode active material.

Moreover, the tap density of amorphous carbon is usually preferably 0.6 g / cm ³ or more, preferably 0.7 g / cm ³ or more, more preferably 0.8 g / cm ³ or more, and further more preferably 0.85 g / cm ³ or more. preferable. Moreover, 1.3 g / cm ³ or less and 1.2 g / cm ³ or less are usually preferable, and 1.1 g / cm ³ or less is more preferable. If the tap density is too low, the high-speed charge / discharge characteristics are inferior. If the tap density is too high, the intra-particle carbon density increases, the rollability is insufficient, and it may be difficult to form a high-density negative electrode sheet.

  Examples of metal particles include Fe, Co, Sb, Bi, Pb, Ni, Ag, Si, Sn, Al, Zr, Cr, P, S, V, Mn, Nb, Mo, Cu, Zn, Ge, In A metal selected from the group consisting of Ti and the like or a compound thereof is preferable. Further, an alloy composed of two or more kinds of metals may be used, and the metal particles may be alloy particles formed of two or more kinds of metal elements. Among these, a metal selected from the group consisting of Si, Sn, As, Sb, Al, Zn, and W or a compound thereof is preferable.

  The volume-based average particle diameter of the metal particles is usually in the range of 5 μm or more, preferably 12 μm or more, and usually 60 μm or less, preferably 40 μm or less. If the average particle size is too large, exceeding this particle size range tends to cause inconveniences in the process such as striping when the plate is formed, and the charge / discharge load characteristics tend to decrease. On the other hand, if the particle size is below this range, the surface area tends to be too large and it becomes difficult to suppress the activity with the electrolyte.

The BET specific surface area of the metal particles is usually 1 m ² / g or more, preferably 2 m ² / g or more, more preferably 2.5 m ² / g or more, and usually 8 m ² / g or less, preferably 6 m ² / g. Hereinafter, the range is more preferably 4 m ² / g or less. If the specific surface area is too large, the reactivity between the portion exposed to the electrolyte and the electrolyte when used as the negative electrode active material increases, and the charge / discharge efficiency tends to decrease and gas generation tends to increase, making it difficult to obtain a favorable battery. If the specific surface area is too small, the lithium acceptability tends to deteriorate during charging when used as a negative electrode active material.

Further, the tap density of the metal particles is usually preferably 0.6 g / cm ³ or more, 0.7 g / cm ³ or more, more preferably 0.8 g / cm ³ or more, and further preferably 0.85 g / cm ³ or more. Moreover, 1.3 g / cm ³ or less and 1.2 g / cm ³ or less are usually preferable, and 1.1 g / cm ³ or less is more preferable. If the tap density is too low, the high-speed charge / discharge characteristics are inferior. If the tap density is too high, the intra-particle metal density increases, the rollability is insufficient, and it may be difficult to form a high-density negative electrode sheet.

Examples of the metal compound include metal oxides, metal nitrides, metal carbides, and the like. Moreover, you may use the alloy which consists of 2 or more types of metals.
Among these, Si or Si compound is preferable in terms of increasing capacity. Specific examples of the Si compound include SiOx, SiNx, SiCx, SiZxOy (Z = C, N) and the like, and preferably SiOx when expressed by a general formula. The general formula SiOx is obtained using Si dioxide (SiO ₂ ) and metal Si (Si) as raw materials, and the value of x is usually 0 ≦ x <2. SiOx has a larger theoretical capacity than graphite. Furthermore, amorphous Si or nano-sized Si crystals easily allow alkali ions such as lithium ions to enter and exit, so that a high capacity can be obtained.

Specifically, it is expressed as SiOx, and x is usually 0 ≦ x <2, more preferably 0.2 or more and 1.8 or less, and still more preferably 0.4 or more. 6 or less, particularly preferably 0.6 or more and 1,4 or less. Within this range, the capacity is high and at the same time Li
It becomes possible to reduce the irreversible capacity due to the bond between oxygen and oxygen.
The volume-based average particle size of the metal compound is usually 5 μm or more, preferably 12 μm or more, and usually 60 μm or less, preferably 40 μm or less. If the average particle size is too large, exceeding this particle size range tends to cause inconveniences in the process such as striping when the plate is formed, and the charge / discharge load characteristics tend to decrease. On the other hand, if the particle size is below this range, the surface area tends to be too large and it becomes difficult to suppress the activity with the electrolyte.

The BET specific surface area of the metal compound is usually 1 m ² / g or more, preferably 2 m ² / g or more, more preferably 2.5 m ² / g or more, and usually 8 m ² / g or less, preferably 6 m ² / g. Hereinafter, the range is more preferably 4 m ² / g or less. If the specific surface area is too large, the reactivity between the portion exposed to the electrolyte and the electrolyte when used as the negative electrode active material increases, and the charge / discharge efficiency tends to decrease and gas generation tends to increase, making it difficult to obtain a favorable battery. If the specific surface area is too small, the lithium acceptability tends to deteriorate during charging when used as a negative electrode active material.

Further, the tap density of the metal compound is usually preferably 0.6 g / cm ³ or more, 0.7 g / cm ³ or more, more preferably 0.8 g / cm ³ or more, and further preferably 0.85 g / cm ³ or more. Moreover, 1.3 g / cm ³ or less and 1.2 g / cm ³ or less are usually preferable, and 1.1 g / cm ³ or less is more preferable. If the tap density is too low, the high-speed charge / discharge characteristics are inferior. If the tap density is too high, the intra-particle metal density increases, the rollability is insufficient, and it may be difficult to form a high-density negative electrode sheet.

<Mixed carbon material for non-aqueous secondary battery and other materials>
There are no particular restrictions on the device used for mixing the composite carbon material for non-aqueous secondary batteries and other materials. For example, in the case of a rotary mixer: a cylindrical mixer, a twin cylinder mixer, a double mixer For conical mixers, regular cubic mixers, vertical mixers, fixed mixers: spiral mixers, ribbon mixers, Muller mixers, Helical Flyt mixers, Pugmill
A mold mixer, a fluidized mixer, or the like can be used.

<Mixed material of composite carbon material for non-aqueous secondary battery and other materials>
The physical properties of the mixed material of the composite carbon material for non-aqueous secondary batteries and other materials are preferably as follows.
The volume-based average particle diameter of the mixed material of the composite carbon material for non-aqueous secondary batteries of the present invention and other materials is usually 5 μm or more, preferably 10 μm or more, and usually 60 μm or less, preferably 40 μm or less. is there. If the average particle size is too large, exceeding this particle size range tends to cause inconveniences in the process such as striping when the plate is formed, and the charge / discharge load characteristics tend to decrease. On the other hand, if the particle size is below this range, the surface area tends to be too large and it becomes difficult to suppress the activity with the electrolyte.

The BET specific surface area of the mixed material of the composite carbon material for non-aqueous secondary batteries of the present invention and other materials is usually 1.5 m ² / g or more, preferably 2.0 m ² / g or more, and usually 8 m. ² / g or less, preferably 6 m ² / g or less. If the specific surface area is too large, the reactivity between the portion exposed to the electrolyte and the electrolyte when used as the negative electrode active material increases, and the charge / discharge efficiency tends to decrease and gas generation tends to increase, making it difficult to obtain a favorable battery. If the specific surface area is too small, the lithium acceptability tends to deteriorate during charging when used as a negative electrode active material.

Further, the tap density of the mixed material of the composite carbon material for non-aqueous secondary battery of the present invention and other materials is usually preferably 0.6 g / cm ³ or more, preferably 0.7 g / cm ³ or more, and 0.8 g / cm 2. cm ³ or more is more preferable, and 0.85 g / cm ³ or more is more preferable. And usually 1.4 g / cm ³ or less, preferably 1.3 g / cm ³ or less, 1.2 g / cm ³ or less is more preferable. If the tap density is too low, the high-speed charge / discharge characteristics are inferior. If the tap density is too high, the intra-particle carbon density increases, the rollability is insufficient, and it may be difficult to form a high-density negative electrode sheet.

<Negative electrode for non-aqueous secondary battery>
A negative electrode for a non-aqueous secondary battery of the present invention (hereinafter also referred to as an “electrode sheet” as appropriate) includes a current collector and an active material layer formed on the current collector, and the active material layer is at least the present material layer. The composite carbon material for non-aqueous secondary batteries of the invention is contained. More preferably, it contains a binder.

  As the binder, one having an olefinically unsaturated bond in the molecule is used. The type is not particularly limited, and specific examples include styrene-butadiene rubber, styrene / isoprene / styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, and ethylene / propylene / diene copolymer. By using such a binder having an olefinically unsaturated bond, the swellability of the active material layer with respect to the electrolytic solution can be reduced. Of these, styrene-butadiene rubber is preferred because of its availability.

  By using a binder having such an olefinically unsaturated bond in combination with the above active material, the strength of the negative electrode plate can be increased. When the strength of the negative electrode is high, deterioration of the negative electrode due to charge / discharge is suppressed, and the cycle life can be extended. In addition, since the negative electrode according to the present invention has high adhesive strength between the active material layer and the current collector, even when the binder content in the active material layer is reduced, the negative electrode is wound to produce a battery. It is speculated that the problem that the active material layer peels from the current collector does not occur.

As the binder having an olefinically unsaturated bond in the molecule, one having a large molecular weight or one having a large proportion of unsaturated bonds is desirable. Specifically, in the case of a binder having a large molecular weight, it is desirable that the weight average molecular weight is usually 10,000 or more, preferably 50,000 or more, and usually 1,000,000 or less, preferably 300,000 or less. In the case of a binder having a large proportion of unsaturated bonds, the number of moles of olefinically unsaturated bonds per gram of all binders is usually 2.5 × 10 ⁻⁷ mol or more, preferably 8 × 10 ⁻⁷ mol. In addition, it is desirable that the amount is usually in the range of 1 × 10 ⁻⁶ mol or less, preferably 5 × 10 ⁻⁶ mol or less. The binder only needs to satisfy at least one of these regulations regarding molecular weight and regulations regarding the proportion of unsaturated bonds, but it is more preferable to satisfy both regulations simultaneously. When the molecular weight of the binder having an olefinically unsaturated bond is too small, the mechanical strength is inferior, and when it is too large, the flexibility is inferior. Moreover, if the ratio of the olefinically unsaturated bond in the binder is too small, the effect of improving the strength is reduced, and if it is too large, the flexibility is poor.

The binder having an olefinically unsaturated bond has a degree of unsaturation of usually 15% or more, preferably 20% or more, more preferably 40% or more, and usually 90% or less, preferably 80% or less. Is desirable. The degree of unsaturation represents the ratio (%) of the double bond to the repeating unit of the polymer.
In the present invention, a binder that does not have an olefinically unsaturated bond can also be used in combination with the above-described binder that has an olefinically unsaturated bond as long as the effects of the present invention are not lost. The mixing ratio of the binder having no olefinically unsaturated bond to the binder having an olefinically unsaturated bond is usually 150% by mass or less, preferably 120% by mass or less.

By using a binder that does not have an olefinically unsaturated bond, the coatability can be improved. However, if the combined amount is too large, the strength of the active material layer is lowered.
Examples of the binder having no olefinic unsaturated bond include thickening polysaccharides such as methylcellulose, carboxymethylcellulose, starch, carrageenan, pullulan, guar gum, xanthan gum (xanthan gum), polyethers such as polyethylene oxide and polypropylene oxide, Vinyl alcohols such as polyvinyl alcohol and polyvinyl butyral, polyacids such as polyacrylic acid and polymethacrylic acid, or metal salts of these polymers, fluorine-containing polymers such as polyvinylidene fluoride, alkane polymers such as polyethylene and polypropylene, and these A copolymer etc. are mentioned.

  When the carbon material of the present invention is used in combination with the above-mentioned binder having an olefinically unsaturated bond, the ratio of the binder used for the active material layer can be reduced as compared with the conventional material. Specifically, the negative electrode material of the present invention and a binder (in some cases, it may be a mixture of a binder having an unsaturated bond and a binder having no unsaturated bond as described above). The mass ratio is usually 90/10 or more, preferably 95/5 or more, and usually 99.9 / 0.1 or less, preferably 99.5 / 0.5 or less in terms of the respective dry mass ratios. is there. If the binder ratio is too high, the capacity is likely to decrease and the resistance is increased. If the binder ratio is too small, the electrode plate strength is inferior.

  The negative electrode of the present invention is formed by dispersing the above-described negative electrode material of the present invention and a binder in a dispersion medium to form a slurry, which is applied to a current collector. As the dispersion medium, an organic solvent such as alcohol or water can be used. If necessary, a conductive agent may be added to the slurry. Examples of the conductive agent include carbon black such as acetylene black, ketjen black, and furnace black, and fine powder made of Cu, Ni having an average particle diameter of 1 μm or less, or an alloy thereof. The addition amount of the conductive agent is usually about 10% by mass or less with respect to the negative electrode material of the present invention.

A conventionally well-known thing can be used as a collector which apply | coats a slurry. Specific examples include metal thin films such as rolled copper foil, electrolytic copper foil, and stainless steel foil. The thickness of the current collector is usually 4 μm or more, preferably 6 μm or more, and usually 30 μm or less, preferably 20 μm or less.
This slurry was applied to a width of 5 cm using a doctor blade so that the negative electrode material was 14.5 ± 0.3 mg / cm ² on a 18 μm-thick copper foil as a current collector, and air-dried at room temperature. Went. Further, after drying at 110 ° C. for 30 minutes, roll pressing was performed using a roller having a diameter of 20 cm to adjust the density of the active material layer to 1.70 ± 0.03 g / cm ³ to obtain an electrode sheet.

After applying the slurry on the current collector, the slurry is usually dried at a temperature of 60 ° C. or higher, preferably 80 ° C. or higher, and usually 200 ° C. or lower, preferably 195 ° C. or lower, in dry air or an inert atmosphere. A physical layer is formed.
The thickness of the active material layer obtained by applying and drying the slurry is usually 5 μm or more, preferably 20 μm or more, more preferably 30 μm or more, and usually 200 μm or less, preferably 100 μm or less, more preferably 75 μm or less. . If the active material layer is too thin, it is not practical as a negative electrode because of the balance with the particle size of the active material, and if it is too thick, it is difficult to obtain a sufficient Li occlusion / release function for high-density current values.

The density of the composite carbon material for the non-aqueous secondary battery in the active material layer varies depending on the application, but is usually 1.55 g / cm ³ or more, preferably 1.6 g / cm ³ or more, more preferably in applications where the capacity is important. it is 1.65 g / cm ³ or more, further preferably 1.7 g / cm ³ or more. If the density is too low, the capacity of the battery per unit volume is not always sufficient. Moreover, since a rate characteristic will fall when a density is too high, it is 1.9 g / cm < ³ > or less normally.

  When producing the negative electrode for non-aqueous secondary batteries using the composite carbon material for non-aqueous secondary batteries of the present invention described above, the method and selection of other materials are not particularly limited. Moreover, when producing a lithium ion secondary battery using this negative electrode, there is no particular limitation on the selection of members necessary for the battery configuration such as the positive electrode and the electrolytic solution constituting the lithium ion secondary battery. Hereinafter, the details of the negative electrode for lithium ion secondary batteries and the lithium ion secondary battery using the negative electrode material of the present invention will be exemplified, but the materials that can be used and the method of production are not limited to the following specific examples. Absent.

<Non-aqueous secondary battery>
The basic configuration of the non-aqueous secondary battery of the present invention, particularly the lithium ion secondary battery, is the same as that of a conventionally known lithium ion secondary battery, and usually includes a positive electrode and a negative electrode capable of inserting and extracting lithium ions, and an electrolyte. Is provided. The negative electrode of the present invention described above is used as the negative electrode.
The positive electrode is obtained by forming a positive electrode active material layer containing a positive electrode active material and a binder on a current collector.

Examples of the positive electrode active material include metal chalcogen compounds that can occlude and release alkali metal cations such as lithium ions during charge and discharge. Examples of metal chalcogen compounds include vanadium oxide, molybdenum oxide, manganese oxide, chromium oxide, titanium oxide, tungsten oxide and other transition metal oxides, vanadium sulfide, molybdenum sulfide. , Transition metal sulfides such as titanium sulfide, transition metal sulfides such as NiS ₃ and FePS ₃ , selenium compounds of transition metals such as VSe ₂ and NbSe ₃ , Fe _0.25 V _0. Examples thereof include composite oxides of transition metals such as ₇₅ S ₂ and Na _0.1 CrS ₂ and composite sulfides of transition metals such as LiCoS ₂ and LiNiS ₂ .

Among these, V ₂ O ₅ , V ₅ O ₁₃ , VO ₂ , Cr ₂ O ₅ , MnO ₂ , TiO ₂ , MoV ₂ O ₈ , LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , TiS ₂ , V ₂ S ₅ , C
r _0.25 V _0.75 S ₂ , Cr _0.5 V _0.5 S _{2 and the} like are preferable, and LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ and some of these transition metals are particularly preferable. Lithium transition metal composite oxide substituted with a metal. These positive electrode active materials may be used alone or in combination.

  A known binder can be arbitrarily selected and used as the binder for binding the positive electrode active material. Examples include inorganic compounds such as silicate and water glass, and resins having no unsaturated bond such as Teflon (registered trademark) and polyvinylidene fluoride. Among these, a resin having no unsaturated bond is preferable. If a resin having an unsaturated bond is used as the resin for binding the positive electrode active material, the resin may be decomposed during the oxidation reaction. The weight average molecular weight of these resins is usually 10,000 or more, preferably 100,000 or more, and usually 3 million or less, preferably 1 million or less.

The positive electrode active material layer may contain a conductive material in order to improve the conductivity of the electrode. The conductive agent is not particularly limited as long as it can be mixed with an active material in an appropriate amount to impart conductivity, but is usually carbon powder such as acetylene black, carbon black, and graphite, various metal fibers, powder, and foil. Etc.
The positive electrode plate is formed by slurrying a positive electrode active material or a binder with a solvent in the same manner as in the production of the negative electrode as described above, and applying and drying on a current collector. As the positive electrode current collector, aluminum, nickel, stainless steel (SUS), or the like is used, but is not limited at all.

As the electrolyte, a non-aqueous electrolyte obtained by dissolving a lithium salt in a non-aqueous solvent, or a gel, rubber, or solid sheet obtained by using an organic polymer compound or the like from the non-aqueous electrolyte is used.
The non-aqueous solvent used in the non-aqueous electrolyte is not particularly limited, and can be appropriately selected from known non-aqueous solvents that have been conventionally proposed as solvents for non-aqueous electrolytes. For example, chain carbonates such as diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate; cyclic carbonates such as ethylene carbonate, propylene carbonate, and butylene carbonate; chain ethers such as 1,2-dimethoxyethane; tetrahydrofuran, 2-methyl Examples include cyclic ethers such as tetrahydrofuran, sulfolane, and 1,3-dioxolane; chain esters such as methyl formate, methyl acetate, and methyl propionate; and cyclic esters such as γ-butyrolactone and γ-valerolactone.

  Any one of these non-aqueous solvents may be used alone, or two or more thereof may be mixed and used. In the case of a mixed solvent, a combination of a mixed solvent containing a cyclic carbonate and a chain carbonate is preferable, and the cyclic carbonate is a mixed solvent of ethylene carbonate and propylene carbonate. This is particularly preferable from the viewpoint that the impossible characteristics are improved. Among these, propylene carbonate is preferably in a range of 2% by mass to 80% by mass, more preferably in a range of 5% by mass to 70% by mass, and further in a range of 10% by mass to 60% by mass with respect to the entire non-aqueous solvent. preferable. When the proportion of propylene carbonate is lower than the above, the ionic conductivity at low temperature decreases, and when the proportion of propylene carbonate is higher than the above, when a graphite-based electrode is used, propylene carbonate solvated with lithium ions enters between the graphite phases. The co-insertion causes a delamination degradation of the graphite-based negative electrode active material, and there is a problem that a sufficient capacity cannot be obtained.

The lithium salt used in the non-aqueous electrolytic solution is not particularly limited, and can be appropriately selected from known lithium salts that can be used for this purpose. For example, halides such as LiCl and LiBr, perhalogenates such as LiClO ₄ , LiBrO ₄ and LiClO ₄ , inorganic lithium salts such as inorganic fluoride salts such as LiPF ₆ , LiBF ₄ and LiAsF ₆ , LiCF ₃ SO ₃ , Fluorine-containing organic lithium salts such as perfluoroalkanesulfonic acid salts such as LiC ₄ F ₉ SO ₃ and perfluoroalkanesulfonic acid imide salts such as Li trifluorosulfonimide ((CF ₃ SO ₂ ) ₂ NLi) Of these, LiClO ₄ , LiPF ₆ , and LiBF ₄ are preferable.

Lithium salts may be used alone or in combination of two or more. The concentration of the lithium salt in the nonaqueous electrolytic solution is usually in the range of 0.5 mol / L or more and 2.0 mol / L or less.
In addition, when an organic polymer compound is included in the above non-aqueous electrolyte and used in the form of a gel, rubber, or solid sheet, specific examples of the organic polymer compound include polyethylene oxide, polypropylene oxide, and the like. Polyether polymer compounds; Cross-linked polymers of polyether polymer compounds; Vinyl alcohol polymer compounds such as polyvinyl alcohol and polyvinyl butyral; Insolubilized vinyl alcohol polymer compounds; Polyepichlorohydrin; Polyphosphazene; Siloxane; vinyl polymer compounds such as polyvinylpyrrolidone, polyvinylidene carbonate, polyacrylonitrile; poly (ω-methoxyoligooxyethylene methacrylate), poly (ω-methoxyoligooxyethylene methacrylate-co-methyl methacrylate) Rate) and polymer copolymers such as poly (hexafluoropropylene-vinylidene fluoride).

  The non-aqueous electrolyte solution described above may further contain a film forming agent. Specific examples of the film forming agent include carbonate compounds such as vinylene carbonate, vinyl ethyl carbonate, and methylphenyl carbonate; alken sulfides such as ethylene sulfide and propylene sulfide; sultone compounds such as 1,3-propane sultone and 1,4-butane sultone And acid anhydrides such as maleic acid anhydride and succinic acid anhydride. Furthermore, an overcharge inhibitor such as diphenyl ether or cyclohexylbenzene may be added. When the above additives are used, the content is usually 10% by mass or less, preferably 8% by mass or less, more preferably 5% by mass or less, and particularly preferably 2% by mass or less. If the content of the additive is too large, other battery characteristics such as an increase in initial irreversible capacity, low temperature characteristics, and deterioration in rate characteristics may be adversely affected.

Further, as the electrolyte, a polymer solid electrolyte which is a conductor of an alkali metal cation such as lithium ion can be used. Examples of the polymer solid electrolyte include a polymer in which a lithium salt is dissolved in the aforementioned polyether polymer compound, and a polymer in which the terminal hydroxyl group of the polyether is substituted with an alkoxide.
In order to prevent a short circuit between the electrodes, a porous separator such as a porous film or a nonwoven fabric is usually interposed between the positive electrode and the negative electrode. In this case, the nonaqueous electrolytic solution is used by impregnating a porous separator. As a material for the separator, polyolefin such as polyethylene and polypropylene, polyethersulfone, and the like are used, and polyolefin is preferable.

  The form of the lithium ion secondary battery of the present invention is not particularly limited. Examples include a cylinder type in which a sheet electrode and a separator are spiral, a cylinder type having an inside-out structure in which a pellet electrode and a separator are combined, a coin type in which a pellet electrode and a separator are stacked, and the like. In addition, by storing batteries of these forms in an optional outer case, the battery can be used in an arbitrary shape such as a coin shape, a cylindrical shape, or a square shape.

  The procedure for assembling the lithium ion secondary battery of the present invention is not particularly limited, and may be assembled by an appropriate procedure according to the structure of the battery. For example, the negative electrode is placed on the outer case, and the electrolytic solution is placed thereon. A separator is provided, and a positive electrode is placed so as to face the negative electrode, and it is caulked together with a gasket and a sealing plate to form a battery.

<Battery performance>
The battery produced as described above exhibits the following performance.
The output is usually 1.0 W or more, preferably 1.5 W or more, more preferably 1.8 W or more. If the output is too low, when a lithium ion secondary battery is used as a power source for an electric vehicle, large energy cannot be taken out at the time of start and acceleration, and large energy generated at the time of deceleration cannot be efficiently regenerated.
The cycle maintenance ratio is usually 70% or more, preferably 75% or more, more preferably 80% or more. If the cycle maintenance ratio is too low, it is not suitable for applications in which charging and discharging are repeated and used for a long period of time.

EXAMPLES Next, specific embodiments of the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.
(Measuring method)
(1) Particle size A solution obtained by adding about 20 mg of carbon powder to about 1 ml of a 2 (volume)% aqueous solution of polyoxyethylene (20) sorbitan monolaurate and dispersing it in about 200 ml of ion-exchanged water is a laser diffraction type. A volume-based particle size distribution was measured using a particle size distribution meter (LA-920, manufactured by Horiba, Ltd.), and a 50% cumulative particle size d50 was determined. The measurement conditions are ultrasonic dispersion for 1 minute, ultrasonic intensity 2, circulation speed 2, and relative refractive index 1.50.

(2) Tap density The tap density is a powder density measuring device manufactured by Seishin Enterprise Co., Ltd. “Tap Denser KYT-4000”, and is open to a cylindrical tap cell having a diameter of 1.6 cm and a volume capacity of 20 cm ^3. After dropping the carbon material through a 300 μm sieve and filling the cell completely, tap with a stroke length of 10 mm is performed 1000 times, and the density obtained from the volume and the weight of the sample is defined as the tap density.

(3) BET specific surface area (SA)
The BET specific surface area is measured by, for example, using a specific surface area measuring device “AMS8000” manufactured by Okura Riken Co., Ltd., by the nitrogen gas adsorption flow method, using the BET one-point method. Specifically, 0.4 g of sample (carbon material) is filled in a cell, heated to 350 ° C., pretreated, cooled to liquid nitrogen temperature, and saturated with 30% nitrogen and 70% He gas. The amount of gas adsorbed and then heated to room temperature and desorbed was measured, and the specific surface area was calculated from the obtained results by a normal BET method.

(4) Orientation ratio The sample was measured by X-ray diffraction after being pressure-molded. Set the molded body obtained by filling 0.47 g of the sample into a molding machine with a diameter of 17 mm and compressing it with 58.8MN · m ^{-2 so} that it is flush with the surface of the sample holder for measurement. X-ray diffraction is measured. From the (110) diffraction and (004) diffraction peak intensities of the obtained carbon, a ratio represented by (110) diffraction peak intensity / (004) diffraction peak intensity is calculated. It was calculated by the measurement.

(5) Pore volume As a measurement of the mercury intrusion method, using a mercury porosimeter (Autopore 9520 manufactured by Micromeritex Co., Ltd.), a sample (negative electrode material) was weighed in an amount of about 0.2 g in a powder cell, room temperature, After degassing pretreatment for 10 minutes under vacuum (50 μmHg or less), the pressure was reduced stepwise to 4 psia, mercury was introduced, the pressure was increased stepwise from 4 psia to 40000 psia, and the pressure was further decreased to 25 psia. The pore distribution was calculated from the obtained mercury intrusion curve using the Washburn equation. The surface tension of mercury is 485 dyne / cm.
The contact angle was calculated as 140 °.
Here, it is considered that the pore volume in the range of 10 nm to 1000 nm mainly reflects the amount of internal voids of the graphite particles, and it is estimated that the larger the pore volume in the range of 10 nm to 1000 nm, the more voids inside the particles. Is done.

(6) Softening point, quinoline insoluble matter (QI), toluene insoluble matter (TI)
The softening point of organic compounds, quinoline insoluble matter (QI), toluene insoluble matter (TI) are JIS K
The measurement was performed in accordance with 2425.
(7) Remaining charcoal rate The remaining charcoal rate of the organic compound was measured in accordance with JIS K2270.
(8) Hydrogen source ratio (H / C)
The atomic ratio (H / C) calculated | required from the amount of hydrogen measured with the elemental analyzer (CHN meter) and the amount of carbon was computed.

Example 1
Using the spheronized natural graphite described in Comparative Example 2 in Table 1 below as a carbon material, the above spheronized natural graphite and an organic compound are mixed at a mass ratio of 100: 20, and put into a kneader for 20 minutes. Combined. The composite is subjected to isotropic pressure treatment at 1000 kgf / cm ² for 2 minutes using a CIP molding machine to raise the temperature from room temperature to 1000 ° C. in an electric furnace, and further maintained at 1000 ° C. Thus, de-VM firing was performed. Thereafter, this fired body was heated at 3000 ° C. to be graphitized. The obtained molded body was crushed and finely pulverized to obtain a negative electrode material 1 in which the surface of spherical natural graphite particles was coated with a graphite material.

From the firing yield, it was confirmed that the obtained composite carbon material powder (negative electrode material 1) was coated with 10% by mass of a graphite material.
The organic compound has a residual carbon ratio of 50%, a quinoline insoluble content of 10%, a toluene insoluble content of 30%, H / C of 0.041, a softening point of 80 ° C., and graphitized and then pulverized. A heavy oil having a 002 plane spacing (d002) of 0.3360 nm and Lc (004) of 67 nm by X-ray wide angle diffraction of the carbon powder obtained by the treatment was used.
Table 1 shows the powder properties of the composite carbon material and natural graphite, and Table 2 shows the battery evaluation results.

-Production of positive electrode, negative electrode, electrolyte and battery Production of negative electrode The negative electrode material 1 of Example 1 was used as the negative electrode active material, and 98% by mass of the negative electrode active material, 1% by mass of sodium carboxymethylcellulose as a thickener and binder, respectively. Then, 1% by mass of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber 40% by mass) was added and mixed by biaxial kneading to form a slurry. The obtained slurry was coated on one side of 18 μm rolled copper foil, dried, and rolled with a press. The active material layer size was 32 mm in width, 42 mm in length, and the uncoated part as a current collector tab welded part. It cut out in the shape which has and was set as the negative electrode. At this time, the density of the active material of the negative electrode was 1.8 g / cm ³ .

Production of Positive Electrode The positive electrode active material is a lithium transition metal composite oxide synthesized by the following method, and is represented by the composition formula LiMn _0.33 Ni _0.33 Co _0.33 O ₂ . Mn ₃ O ₄ as a manganese raw material, NiO as a nickel raw material, and Co (OH) ₂ as a cobalt raw material are weighed so as to have a molar ratio of Mn: Ni: Co = 1: 1: 1, and pure water is added thereto. In addition, it was made into a slurry, and while being stirred, the solid content in the slurry was wet pulverized so as to have a median diameter of 0.2 μm using a circulating medium stirring wet bead mill.

The obtained slurry was spray-dried with a spray drier to obtain substantially spherical granulated particles having a particle size of about 5 μm and consisting only of manganese raw material, nickel raw material and cobalt raw material. To the obtained granulated particles, LiOH powder having an average particle size (d50) of 3 μm was added so that the ratio of the number of moles of Li to the total number of moles of Mn, Ni, and Co was 1.05. It mixed with the mixer and the mixed powder of the granulated particle of nickel raw material, cobalt raw material, manganese raw material, and lithium raw material was obtained. This mixed powder was calcined at 950 ° C. for 12 hours under air flow (climbing temperature 5 ° C./min), then crushed and passed through a sieve having an opening of 45 μm to obtain a positive electrode active material. The positive electrode active material had a BET specific surface area of 1 m ² / g, an average primary particle size of 1 μm, an average particle size (d50) of 8 μm, and a tap density of 1.7 g / cm ³ .

90% by mass of the positive electrode active material described above, 7% by mass of acetylene black as a conductive material, and 3% by mass of polyvinylidene fluoride (PVdF) as a binder were mixed in an N-methylpyrrolidone solvent, Slurried. The obtained slurry was applied to a 15 μm aluminum foil, dried, and rolled to a thickness of 100 μm with a press machine. The positive electrode active material layer had a width of 30 mm, a length of 40 mm, and an uncoated part for current collection. It was cut out into a shape having a positive electrode. The density of the positive electrode active material layer was 2.6 g / cm ³ .

Preparation of electrolyte solution Lithium hexafluorophosphate (LiPF) sufficiently dried at a concentration of 1 mol / L in a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (volume ratio 3: 7) under an inert atmosphere ₆ ) was dissolved. Furthermore, what added 1 mass% of vinylene carbonate (VC) to the electrolyte solution was used.

Production of Battery One positive electrode and one negative electrode were arranged so that the active material surfaces face each other, and a separator (25 μm) of a porous polyethylene sheet was sandwiched between the electrodes. At this time, the positive electrode active material surface was faced so as not to deviate from the negative electrode active material surface. A current collector tab is welded to the uncoated portion of each of the positive electrode and the negative electrode to form an electrode body, and a laminate sheet (total thickness) in which a polypropylene film, an aluminum foil having a thickness of 0.04 mm, and a nylon film are laminated in this order. 0.1 mm) was sandwiched with a laminate sheet so that the polypropylene film was on the inner surface side, and the area without electrodes was heat-sealed except for one piece for injecting the electrolyte solution.

Thereafter, 200 μL of a non-aqueous electrolyte was injected into the active material layer, sufficiently infiltrated into the electrode, and sealed to produce a laminate cell. The rated capacity of this battery is 40 mAh.
Cycle maintenance rate measurement Under a 25 ° C. environment, voltage range 4.2 to 3.0 V, current value 0.2 C (the rated capacity due to the discharge capacity at 1 hour rate is 1 C, and the same applies hereinafter) ) Initial conditioning was performed. Further, after aging, a cycle test was conducted. Using the discharge capacity at the first cycle as a reference, the cycle maintenance factor was calculated from the discharge capacity at the 200th cycle according to the following equation.

Cycle maintenance rate = discharge capacity at 200th cycle / discharge capacity at the first cycle × 100
Evaluation of high-temperature storage characteristics (amount of stored gas)
After charging at a constant current of 0.2 C in an environment of 25 ° C., this was stored at 85 ° C. for 24 hours. After the battery was cooled to room temperature, it was immersed in an ethanol bath and the volume was measured. The amount of gas generated from the volume change was determined.
The linear pressure (kg / 5 cm) necessary for rolling so that the density of the negative electrode active material layer of the press load was 1.8 g / cm ³ was used.

Example 2
In Example 1, the negative electrode material 2 was obtained similarly to Example 1 except having mixed by the mass ratio of 100: 30. It was confirmed that the obtained composite carbon material powder (negative electrode material 1) was coated with 15% by mass of a graphite material.
The powder physical properties of the obtained composite carbon material are shown in Table 1, and the battery evaluation results are shown in Table 2.

Comparative Example 1
Using the spheronized natural graphite described in Comparative Example 2 in Table 1 below as a carbon material, the above spheronized natural graphite and an organic compound are mixed at a mass ratio of 100: 30, put into a kneader, and 20 minutes. Combined. The composite is subjected to anisotropic pressure treatment at ² kgf / cm ² (0.20 MPa) for 1 minute using a mold press molding machine to form a molded body, which is 1000 ° C. from room temperature in an electric furnace.
The temperature was raised to 0 ° C. and VM removal treatment was performed. The fired body was graphitized at 3000 ° C. in the same manner as in Example 1 to obtain a negative electrode material 3. The powder physical properties of the obtained composite carbon material are shown in Table 1, and the battery evaluation results are shown in Table 2.

  The organic compound has a residual carbon ratio of 50%, quinoline insoluble content ≦ 0.5%, toluene insoluble content 16%, H / C 0.044, softening point 80 ° C., and after graphitization A heavy oil having a 002 plane spacing (d002) of 0.3356 nm and Lc (004) of> 100 nm (reference value 550 nm) by X-ray wide-angle diffraction of carbon powder obtained by pulverization was used. . It was confirmed that the obtained composite carbon material powder (negative electrode material 3) was coated with 15% by mass of a graphite material.

Comparative Example 2
Spheroidized graphite shown in Table 1 was used as the negative electrode material 4 as it was. The battery evaluation results are shown in Table 2.

  From the above results, the negative electrode materials 1 and 2 that are the composite carbon materials of Examples 1 and 2 are superior in both the cycle retention ratio and the amount of generated storage gas compared to the negative electrode material 3 that is the conventional negative electrode material. I understood. Further, the negative electrode material 4 was poor in initial efficiency as compared with Examples 1 and 2.

  The composite carbon material of the present invention is not only excellent in initial efficiency by being used as a negative electrode material for a non-aqueous secondary battery, but also has a high cycle retention rate and a low storage gas generation amount. Material can be provided.

Claims (7)

After carbon material that is spheroidized natural graphite is isotropically pressed, a mixture obtained by mixing the carbon material and an organic compound, or a carbon material that is spheroidized natural graphite and an organic compound are mixed. after the mixture obtained was treated isotropic pressure, fired to the organic compound to graphite pledge, and the carbon material and the graphite pledge is a composite carbon material for a nonaqueous secondary battery complexed A method for producing a composite carbon material for a non-aqueous secondary battery, wherein the orientation ratio (110/004) of the obtained composite carbon material is 0.29 or more and 0.7 or less . 2. The method for producing a composite carbon material for a non-aqueous secondary battery according to claim 1 , wherein the composite carbon material obtained has a volume-based average particle size (d50) of 16.9 μm or more and 50 μm or less. The specific surface area of the composite carbon material obtained is 0.1 m 2 / ^g or more, a manufacturing method of the nonaqueous secondary battery composite carbon material according to claim 1 or 2, characterized in that 15 m 2 / ^g or less. Nonaqueous secondary battery composite carbon material according to any one of claims 1 to 3, the coverage of the graphite material in the resulting composite carbon material is equal to or less than 40 wt% or more 1 wt% Manufacturing method . The said organic compound is at least any one chosen from the following (a) or (b), The composite carbon material for non-aqueous secondary batteries of any one of Claims 1-4 characterized by the above-mentioned. Manufacturing method.
(A) Coal heavy oil, DC heavy oil, cracked heavy oil, aromatic hydrocarbon, N ring compound, S ring compound, polyphenylene, organic synthetic polymer, natural polymer, thermoplastic resin and Carbonitizable or graphitizable easily graphitizable organic material selected from the group consisting of thermosetting resins
(B) Carbonized or graphitizable easily graphitizable organic substance dissolved in a low molecular organic solvent 6. The composite for a non-aqueous secondary battery according to claim 1, wherein a total pore volume of the obtained composite carbon material is 0.46 mL / g or more and 1 mL / g or less. Carbon material manufacturing method . The pore volume in the range of 10 nm to 1000 nm of the obtained composite carbon material is 0.031 mL / g or more and 0.3 mL / g or less, according to any one of claims 1 to 6. A method for producing a composite carbon material for a non-aqueous secondary battery .