JP5994319B2 - Method for producing composite graphite particles for non-aqueous secondary battery, composite graphite particles obtained by the production method, negative electrode, and non-aqueous secondary battery - Google Patents

Description

  The present invention relates to a method for producing composite graphite particles for non-aqueous secondary batteries used in non-aqueous secondary batteries, composite graphite particles obtained by the production method, a negative electrode formed using the particles, and a negative electrode. The present invention relates to a non-aqueous secondary battery.

  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. Conventionally, higher capacity of lithium ion secondary batteries has been widely studied, but in recent years, due to the increasing demand for higher performance of lithium ion secondary batteries, further increase in capacity, large current charge / discharge characteristics, high temperature storage characteristics, It is required to satisfy high cycle characteristics.

  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, the amorphous carbon material has a problem that the reversible capacity is small in a material range that can be put into practical use, and it is difficult to increase the density of the active material layer, so that the capacity cannot be increased. It is known that a graphite material has a capacity close to 372 mAh / g, which is the theoretical capacity of lithium storage, and is preferable as an active material. On the other hand, when the active material layer containing the negative electrode material is densified to increase the capacity, the destruction / deformation of the material increases the irreversible capacity of charge / discharge during the initial cycle, decreases the large current charge / discharge characteristics, There was a problem of decline.

In order to solve the above-mentioned problems, for example, as a carbon material, in Patent Document 1, mechanical energy treatment is applied to the graphite carbon particles on the scale to make it spherical, thereby improving the filling property and the large current discharge characteristics. Is disclosed.
In Patent Literature 2, natural graphite having a low Tap density and a binder are mixed to obtain a mixture, and the binder is carbonized by primary heating at 700 to 1500 ° C, and then secondary heating at 2400 to 3000 ° C. Further, a method for producing a carbon composite material having good large current charge / discharge characteristics by simultaneously purifying natural graphite and graphitizing a carbonized binder has been disclosed.

  In Patent Document 3, composite graphite particles in which spherical graphite particles having a specific structure and physical properties and binder graphite are combined are used as the negative electrode active material, which is favorable even when the negative electrode active material layer is densified. That exhibit high current charge / discharge characteristics.

Japanese Patent No. 3534391 JP 2000-086343 A JP 2008-181870 A

However, according to the study by the present inventors, in the technique described in Patent Document 1, since the internal void amount is large and soft due to the structure in which the flaky graphite is folded, the graphite particles are formed when the density of the negative electrode active material layer is increased. Graphite particles that are easily deformed and are simply spheroidized from flaky graphite have a problem in that the large current charge / discharge characteristics and cycle characteristics are remarkably deteriorated.
In the technology described in Patent Document 2, since the scale material or scale-like natural graphite having a low Tap density is assumed as a starting material, the movement of Li ions is slow particularly when the active material layer is densified, In addition, since there is no special provision in the binder, charge / discharge reactivity is inferior, it is difficult to increase the density of the active material layer and increase the capacity of the battery, and the large current charge / discharge characteristics are insufficient.

  In the technique described in Patent Document 3, suppression of charge / discharge irreversible capacity during the initial cycle was observed, but since there is no special provision in the binder, reduction in charge / discharge reactivity and increase in interface resistance were observed. Further improvement was required for the required high cycle characteristics and large current charge / discharge characteristics at low temperatures. In addition, there is a problem in that gas generation during storage at high temperatures is large, and battery swelling associated therewith is large. In other words, as can be seen from the above-mentioned patent documents, the technical improvement of the binder has not been considered so important in the past.

  Therefore, the present invention has been made in view of the background art, and the problem is that even when the density of the negative electrode active material layer is increased, the charge / discharge irreversible capacity seen during the initial cycle is sufficiently small and high. Provided negative electrode material for producing lithium ion secondary battery having input / output characteristics, high temperature storage characteristics, and high cycle characteristics, and as a result, has high capacity, high input / output characteristics, high temperature storage characteristics, and high cycle characteristics The object is to provide a lithium ion secondary battery.

  As a result of intensive studies to solve the above problems, the inventors of the present invention mixed graphite particles and graphitized material of a graphitizable binder and calcined them to produce graphite-coated graphite (in this specification, non-aqueous two-dimensional graphite). When producing composite graphite particles for non-aqueous secondary batteries using a graphitizable binder that satisfies specific conditions, and using it as a negative electrode material, Even when the active material layer is densified, the charge / discharge irreversible capacity seen during the initial cycle is sufficiently small, and it is possible to satisfy large current charge / discharge characteristics, high temperature storage characteristics, and high cycle characteristics. As a result, it was found that a lithium ion secondary battery having high capacity, high input / output characteristics, high temperature storage characteristics, and high cycle characteristics can be obtained, and the present invention has been achieved.

That is, the gist of the present invention is a method for producing composite graphite particles (C) for non-aqueous secondary batteries in which graphite particles (A) and graphitizable binder (B) are mixed and fired, and can be graphitized. The binder (B) satisfies the following condition (1). The present invention resides in a method for producing composite graphite particles for a non-aqueous secondary battery.
Condition (1): The plane distance (d002) of the 002 plane by the X-ray wide angle diffraction method of the carbon powder obtained by graphitizing the graphitizable binder (B) is 0.3357 nm or more and 0.34 nm or less, and Lc (004) is 10 nm or more and 500 nm or less.

  The composite graphite particles for non-aqueous secondary batteries obtained by the production method of the present invention can be used as a negative electrode material for non-aqueous secondary batteries, resulting in high capacity, high input / output characteristics, high-temperature storage characteristics, and high cycle characteristics. The non-aqueous secondary battery which has can be provided. Moreover, according to the manufacturing method of the negative electrode material for non-aqueous secondary batteries of this invention, it becomes possible to manufacture the negative electrode material which has the above-mentioned advantage in a simple process.

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.
<Graphite particles (A)>
Although the graphite particle (A) which is a raw material of the composite graphite particle for non-aqueous secondary batteries of this invention is shown below as an example, it is not restrict | limited in particular.

-Types of graphite particles (A) Examples of the graphite particles (A) include carbon materials having various degrees of graphitization from graphite to amorphous ones.
In addition, graphite or a carbon material having a low degree of graphitization is particularly preferable in that it can be easily obtained commercially.

Note that it is preferable to use graphite as the graphite particles (A) because the effect of improving the charge / discharge characteristics at a high current density is remarkably 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. Further, those having a high degree of graphitization are preferred, and specifically, those having a (002) plane spacing (d002) of less than 3.37 mm (0.337 nm) by X-ray wide angle diffraction method are preferred.

  Specific examples of artificial graphite include coal tar pitch, coal heavy oil, atmospheric residue, petroleum heavy oil, aromatic hydrocarbon, nitrogen-containing cyclic compound, sulfur-containing cyclic compound, polyphenylene, polyvinyl chloride, Organic substances such as polyvinyl alcohol, polyacrylonitrile, polyvinyl butyral, natural polymer, polyphenylene sulfide, polyphenylene oxide, furfuryl alcohol resin, phenol-formaldehyde resin, and imide resin are usually in a temperature range of 2500 ° C. or higher and usually 3200 ° C. or lower. Baked with and graphitized.

  Further, as the graphite particles having a low graphitization degree, those obtained by firing an organic substance at a temperature of usually 2500 ° C. or lower are used. Specific examples of organic substances include coal-based heavy oils such as coal tar pitch and dry-distilled liquefied oil; straight-run heavy oils such as atmospheric residual oil and vacuum residual oil; by-product during thermal decomposition of crude oil, naphtha, etc. Petroleum heavy oils such as cracked heavy oils such as ethylene tar; Aromatic hydrocarbons such as acenaphthylene, decacyclene and anthracene; Nitrogen-containing cyclic compounds such as phenazine and acridine; Sulfur-containing cyclic compounds such as thiophene; Aliphatic cyclic compounds; polyphenylenes such as biphenyl and terphenyl; polyvinyl esters such as polyvinyl chloride, polyvinyl acetate and polyvinyl butyral; and thermoplastic polymers such as polyvinyl alcohol.

  Further, when obtaining graphite particles having a low degree of graphitization, the firing temperature of the organic substance is usually 600 ° C. or higher, preferably 900 ° C. or higher, more preferably 950 ° C. or higher. The upper limit varies depending on the desired degree of graphitization imparted to the graphite particles, but is usually 2500 ° C. or lower, preferably 2000 ° C. or lower, more preferably 1400 ° C. or lower. At the time of baking, acids such as phosphoric acid, boric acid and hydrochloric acid, and alkalis such as sodium hydroxide may be mixed with the organic matter.

  The graphite particles (A) may be used by appropriately mixing particles such as metal particles and metal oxide particles with the graphite particles (A) in any combination. 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 aggregating graphite particles with an appropriate organic substance and regraphitizing 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 graphite particle (A) The graphite particle (A) in 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.
(1) Surface Functional Group Amount of Graphite Particle (A) Graphite particle (A) which is a composite graphite particle for a non-aqueous secondary battery of the present invention has a surface functional group amount O / C value represented by the following formula 1. Is usually 1% or more and 4 or less, more preferably 2% or more and 3.6% or less, and most preferably 2.6% or more and 3% or less. If this surface functional group amount O / C value is too small, the large current charge / discharge characteristics may be reduced. If it is too large, the charge / discharge irreversible capacity at the beginning of the cycle will increase, making it difficult to adjust the O / C value. 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, which may lead to a decrease in productivity and an increase in cost.
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 atomic concentration ratio O / C of O and C (O atomic concentration / C atomic concentration) is defined as the surface functional group amount O / C value of the carbon material.

(2) Particle size of graphite particles (A) The particle size of the graphite particles (A) 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 or less. It is usually 1 μm or more, preferably 4 μm or more, more preferably 10 μm or more. If this particle size range is exceeded, inconveniences such as striping often occur when the plate is made, and if it is less than this, the surface area becomes too large and the activity with the electrolyte is suppressed. Becomes difficult.

  The particle size is measured by suspending 0.01 g of graphite particles in 10 mL of a 0.2% by weight 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.

(3) BET specific surface area (SA) of graphite particles (A)
The specific surface area of the graphite particles (A) of the present invention measured by the BET method is usually 4 m ² / g or more, preferably 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. When the specific surface area is below this range, there are few sites where Li enters and exits, and the high-speed charge / discharge characteristic output characteristics are inferior. On the other hand, when the specific surface area exceeds this range, the activity of the active material with respect to the electrolytic solution becomes excessive. Since the irreversible capacity becomes large, a high-capacity battery may not 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.
(4) X-ray structural analysis (XRD) of graphite particles (A)
The interplanar spacing (d002) of the 002 plane determined from the X-ray diffraction of the graphite particles (A) by the Gakushin method is preferably 0.337 nm or less, more preferably 0.3365 nm or less, still more preferably 0.336 nm or less, Lc Is preferably 90 nm or more. By setting the 002-plane spacing (d002) and Lc of the spheroidized graphite particles before being coated with graphitic carbon within the above range, a high-capacity electrode that is less likely to be reduced in capacity due to an increase in irreversible capacity can be obtained.

From the X-ray structural analysis (XRD) of graphite particles (A),
The abundance ratio (3R / 2H) of the hexagonal crystal to the rhombohedral crystal is preferably 0.20 or more. If 3R / 2H is below this range, the high-speed charge / discharge characteristics may be degraded.
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. .

(5) Tap density of graphite particles (A) The tap density of the graphite particles (A) of the present invention is usually preferably 0.5 g / cm ³ or more, more preferably 0.7 g / cm ³ or more, and 1 g / cm ^3. The above is more preferable. Moreover, 1.3 g / cm < ³ > or less is preferable normally and 1.1 g / cm < ³ > or less is more preferable. If the tap density is too low, sufficient continuous voids are not secured especially in the electrode rolled to a high density, and the mobility of Li ions in the electrolyte that is not held in the voids is reduced, resulting in large current charge / discharge characteristics. Tends to decrease. When the tap density is too high, the carbon density in the particle 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 measured by using a powder density measuring device to drop the carbon material into a cylindrical tap cell having a diameter of 1.6 cm and a volume capacity of 20 cm ³ through a sieve having a mesh 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.
(6) the intensity of the Raman R value is an intensity _{I A} of the peak _{P A} in the vicinity of 1580 cm ^-1, a peak _{P B} in the vicinity of 1360 cm ^-1 in the Raman spectrum (Raman) spectrum graphite particles (A) of the graphite particles (A) It was measured and I _B, defined by calculating the intensity ratio _{R (R = I B / I} a). The value is preferably 0.15 or more. Further, it is preferably 0.4 or less, and more preferably 0.3 or less. If the Raman R value is below this range, the crystallinity of the particle surface becomes too high, and when the density is increased, the crystals are likely to be oriented in a direction parallel to the electrode plate, which may lead to a reduction in load characteristics. On the other hand, if it exceeds this range, the crystal on the particle surface is disturbed, the reactivity with the electrolytic solution is increased, and the charge / discharge efficiency may be lowered and the gas generation may be increased.

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: 514.5 nm
Laser power on sample: 25 mW
Resolution: 4cm ^-1
Measurement ^range: 1100cm ^-1 ~1730cm -1 peak intensity measurement, peak half-width measurement: background processing, smoothing processing (convolution 5 points by a simple average)
-Manufacturing method of graphite particles (A)
The graphite particles (A) of the present invention are not particularly limited as long as they are graphitized carbon particles, but natural graphite, artificial graphite, coke powder, needle coke powder, resin graphitized powder Etc. Of these, natural graphite is preferable, and spheroidal graphite subjected to spheroidizing treatment is particularly preferable.

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 when the rotor rotates at high speed, mechanical action such as impact compression, friction, shearing force, etc. is applied to the carbon material introduced inside. 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.

  The graphite particles of the present invention are pulverized into base particles that are made spherical by spheroidizing the scale-like natural graphite by applying the spheronization step by the surface treatment described above, or by pulverizing the peripheral edge portion into spheres. Produced by performing spheronization treatment under the condition that the resulting fine powder of 5 μm or less adheres and the surface functional group amount O / C value of the surface-treated graphite particles is 1% or more and 4% or less. Is done. 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. For example, when processing using the above-mentioned apparatus, the peripheral speed of the rotating rotor is preferably 30 to 100 m / sec, more preferably 40 to 100 m / sec, and 50 to 100 m / sec. Is more preferable. The treatment can be performed by simply passing a carbonaceous material, but it is preferable to circulate or stay in the apparatus for 30 seconds or longer, and it is preferable to circulate or stay in the apparatus for 1 minute or longer. More preferred.

<Binder that can be graphitized (B)>
The graphitizable binder (B) that is a raw material of the composite graphite particles for non-aqueous secondary batteries of the present invention (also referred to as composite graphite particles in the present invention) is not particularly limited as long as the following conditions are satisfied. Condition: Carbon powder obtained by graphitizing the graphitizable binder (B) has a surface spacing (d002) of 002 planes by an X-ray wide angle diffraction method of 0.3357 nm to 0.34 nm and Lc (004 ) Is 10 nm or more and 500 nm or less.

The carbon powder obtained by the graphitization treatment in the present specification is subjected to the graphitization treatment under the following conditions.
Conditions: 100 g of binder (B) is baked in a nitrogen atmosphere at 1000 ° C. for 1 hour and 3000 ° C. for 3 hours.
Preferred conditions are described below.

-Types of graphitizable binder (B) The graphitizable binder (B) is not particularly limited as long as it is carbonaceous that can be graphitized by firing. Among them, binder pitch is preferable, specifically, petroleum-based and coal-based condensed polycyclic aromatics from tar, soft pitch to hard pitch are used, and coal-based heavy oils such as impregnated pitch, coal tar pitch, and coal liquefied oil are used. More preferred are straight-run heavy oils such as fine oils and asphaltenes, and petroleum heavy oils such as cracked heavy oils.

-Physical properties of graphitizable binder (B) (1) X-ray parameters (d002 value)
The interplanar spacing (d002) of the 002 plane by the X-ray wide angle diffraction method of the carbon powder obtained by graphitizing the graphitizable binder (B) is preferably 0.3357 nm or more, more preferably 0.3358 nm or more, More preferably, it is 0.3359 nm or more, 0.34 nm or less, preferably 0.338 nm or less, more preferably 0.337 nm or less. If the d002 value is too large, it indicates that the crystallinity is low, and the composite graphite particles (C) may become particles having low crystallinity, resulting in a decrease in charge / discharge capacity. If d002 is too small, the charge / discharge reactivity may be reduced. There is a risk that gas generation will increase during high-temperature storage and large current charge / discharge characteristics may deteriorate.

(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 graphitizable binder (B) is 10 nm or more, preferably 30 nm or more. , More preferably 50 nm or more, and 500 nm or less, preferably 300 nm or less, more preferably 100 nm or less. Normally, Lc (004) obtained by X-ray diffraction by the Gakushin method has an upper limit of 100 nm due to the problem of measurement accuracy, and more than that is described as> 100 nm. However, with recent improvements in measurement accuracy, it is no longer necessary to consider 100 nm as the measurement limit. In the examples, it is described as a reference value.

If Lc (004) is too large, the composite graphite particles (C) tend to have low crystallinity and the charge / discharge capacity tends to decrease. If Lc (004) is too small, the charge / discharge reactivity decreases. Therefore, there is a tendency for gas generation to increase during high-temperature storage, and large current charge / discharge characteristics to decrease.
(3) Softening point The softening point of the graphitizable binder (B) is usually 400 ° C or lower, preferably 300 ° C or lower, more preferably 200 ° C or lower, and further preferably 150 ° C or lower. When the softening point is too high, it becomes difficult to uniformly mix with the graphite particles, and it may be necessary to carry out the mixing at a high temperature. The lower limit is not particularly limited, but is usually 40 ° C. or higher.

(4) Residual carbon ratio The residual carbon ratio of the graphitizable binder (B) is not particularly limited, but is usually 1% by mass or more,
Preferably it is 10 mass% or more, More preferably, it is 20 mass% or more, More preferably, it is 30 mass% or more, Usually 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 graphitizable binder (B) before and after firing, and can be obtained, for example, by the method described in JIS K2270.

(5) Quinoline insoluble matter (QI), toluene insoluble matter (TI)
The quinoline insoluble content of the graphitizable binder (B) is usually 0.6% or more, preferably 3% or more, more preferably 5% or more, still more preferably 10% or more, and usually 30% or less, more Preferably it is 25% or less, More preferably, it is 20% or less, Most preferably, it is 15% or less.

If there is too much quinoline insoluble matter, the irreversible capacity of charge / discharge at the beginning of the cycle may increase, and if there is too little quinoline insoluble matter, charge / discharge reactivity will decrease, resulting in increased gas generation during high temperature storage, large current Charge / discharge characteristics and cycle characteristics tend to deteriorate.
Toluene insoluble content is usually 10% or more, preferably 17% or more, more preferably 20% or more, further preferably 25% or more, and usually 60% or less, preferably 50% or less, more preferably 40% or less. is there. If there is too much toluene insoluble matter, the charge / discharge irreversible capacity at the beginning of the cycle may increase, and if there is too little toluene insoluble matter, charge / discharge reactivity will decrease, increasing gas generation during high-temperature storage, Large current charge / discharge characteristics and cycle characteristics tend to deteriorate.

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.
The quinoline insoluble content of the carbon powder obtained by graphitizing the graphitizable binder (B) (the quinoline insoluble content of the graphitizable binder (B) (%) / residual carbon ratio (%) ) Is usually 1.2% or more, preferably 5% or more, more preferably 10% or more, still more preferably 15% or more, and usually 50% or less, more preferably 40% or less, still more preferably 30%. Hereinafter, it is particularly preferably 20% or less.

  If the quinoline insoluble content of the carbon powder obtained by graphitizing the graphitizable binder (B) is too large, the charge / discharge irreversible capacity at the beginning of the cycle tends to increase. When the quinoline insoluble content of the carbon powder obtained by graphitizing (B) is too small, the charge / discharge reactivity is lowered, resulting in increased gas generation during high temperature storage, large current charge / discharge characteristics, and cycle characteristics. Tend.

Toluene insoluble content of carbon powder obtained by graphitizing graphitizable binder (B) (toluene insoluble content of graphitizable binder (B) (%) / residual carbon ratio (%) ) Is usually at least 15%, preferably at least 25%, more preferably at least 30%, even more preferably at least 35%, and usually at most 90%, preferably at most 80%, more preferably at most 60%. . If the carbon powder obtained by graphitizing the graphitizable binder (B) has too much toluene insoluble content, the charge / discharge irreversible capacity at the beginning of the cycle tends to increase. When the toluene insoluble content of the carbon powder obtained by graphitizing (B) is too small, the charge / discharge reactivity is lowered, resulting in increased gas generation during high temperature storage, large current charge / discharge characteristics, and cycle characteristics. Tend.

(6) Elementary hydrogen ratio (H / C)
The hydrogen source ratio (H / C) of the graphitizable binder (B) 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, it is 0.10 or less, More preferably, it is 0.06 or less, Most preferably, it is 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 graphite particles (C) for non-aqueous secondary batteries>
The method for producing composite graphite particles (C) for non-aqueous secondary batteries is to use the above-described graphite particles (A) and a graphitizable binder (B) for obtaining a graphite-coated portion as raw materials. By combining specific raw materials, the composite graphite particles (C) for non-aqueous secondary batteries of the present invention can be produced.

  More specifically, the composite graphite particles (C) for non-aqueous secondary batteries of the present invention are mixed with a binder containing graphite particles (A) and a specific graphitizable binder (B), and subjected to a graphitization treatment. It is manufactured by. If produced using at least a graphitizable binder (B) satisfying the following conditions as a graphitizable binder (B) as a raw material when producing composite graphite particles (C) for non-aqueous secondary batteries The method for producing the negative electrode material of the present invention is not particularly limited.

Conditions: The surface distance (d002) of the 002 plane by the X-ray wide angle diffraction method of the carbon powder obtained by graphitization is 0.3357 nm or more and 0.340 nm or less, and Lc (004) is 10 nm or more and 500 nm or less.
As a specific method, when the graphite particles (A) and the graphitizable binder (B) are mixed, the graphitizable binder (B) for obtaining a graphite-coated portion is used as it is and graphitized. A method of obtaining a composite graphite particle (C) for a non-aqueous secondary battery by graphitizing a mixture of a possible binder (B) and graphite particles (A), a part of the graphitizable binder (B) described above Carbonized amorphous carbon powder is prepared in advance, mixed with graphite particles (A), graphitized and combined, and the aforementioned amorphous carbon powder is prepared in advance. A method of mixing graphite particles (A), amorphous carbon powder, and a graphitizable binder (B), and performing a graphitization treatment to form a composite can be employed. In the latter two methods of preparing amorphous carbon powder in advance, it is preferable to use amorphous carbon having an average particle size of 1/10 or less of the average particle size of the graphite particles (A). . In addition, by applying mechanical energy such as pulverization to amorphous carbon and graphite particles prepared in advance, it is possible to adopt a method in which the other is involved in one or a structure that is electrostatically attached. is there. Among these, when mixing the graphite particles (A) and the graphitizable binder (B), the graphitizable binder (B) is used as it is by using the graphitizable binder (B) for obtaining the graphite-coated portion. ) And graphite particles (A) are preferably graphitized to obtain composite graphite particles (C) for non-aqueous secondary batteries. As described above, in the production method of the present invention, it is only necessary that the binder (B) that can be graphitized as a binder is used as at least a raw material. For example, after mixing other binders that do not satisfy the above conditions, After further mixing (B), a graphitization treatment may be performed.

A more specific manufacturing process for obtaining composite graphite particles (C) for non-aqueous secondary batteries in the present invention is divided into the following three processes.
First step: Graphite particles, a graphitizable binder (B), and, if necessary, a solvent are mixed using various commercially available mixers and kneaders to obtain a mixture.
In the graphitizable binder (B), the ratio of the binder-derived carbon component occupying the composite graphite particles (C) for non-aqueous secondary batteries that have been graphitized by carbonization / graphitization is usually 1% by mass or more. , Preferably 5% by mass or more, and more preferably 10% by mass or more. As the upper limit, 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 binder (B) that can be graphitized is too large, the charge / discharge capacity is reduced, and the press load necessary for high-density rolling of the active material layer applied to the current collector is increased. As a result, it may be difficult to increase the capacity of the non-aqueous secondary battery. On the other hand, if the amount of the binder (B) is too small, when the active material layer applied to the current collector is rolled to a high density, the particles may be destroyed and deformed, and good large current charge / discharge characteristics may not be obtained. is there.

  The amount of the binder (B) added is the mass ratio of the graphite particles (A) and the binder (B), and the binder (B) is usually 1 or more, preferably 10 or more, with respect to the graphite particles (A) 100. More preferably, it is 19 or more, More preferably, it is 21 or more, Usually, 200 or less, Preferably it is 100 or less, More preferably, it is 70 or less, More preferably, it is 50 or less. When the amount of the binder (B) added is within the above range, it is preferable because uniform composite graphite particles are easily obtained and the productivity is excellent.

The amount of the binder (B) -derived carbon component in the composite graphite particles is controlled by the amount of the binder (B) added at the stage before mixing. For example, when the residual carbon ratio of the binder obtained by the method described in JIS K2270 is p%, 100 / p times the desired amount of binder (B) is added.
In order to increase the charge / discharge capacity and improve the pressability, a graphitization catalyst may be added when mixing the graphite particles and the binder (B). Examples of the graphitization catalyst include metals such as iron, nickel, titanium, silicon, and boron, and compounds such as carbides, oxides, and nitrides thereof. Of these, silicon, silicon compounds, iron, and iron compounds are preferable, and silicon carbide is particularly preferable among silicon compounds, and iron oxide is particularly preferable among iron compounds. When silicon or a silicon compound is used as the graphitization catalyst, all of the silicon carbide produced by heating is pyrolyzed at a temperature of 2800 ° C. or more to grow graphite with extremely good crystallinity, and when the silicon is volatilized, the graphite crystal Since pores are formed between them, the charge transfer reaction and diffusion of lithium ions inside the particles can be promoted, and the battery performance can be improved. Further, when iron or a compound thereof is used as the graphitization catalyst, graphite having good crystallinity can be grown by the mechanism of dissolution and precipitation of carbon in the catalyst, and the same effect as silicon can be exhibited. The addition amount of these graphitization catalysts is usually 30% by mass or less, preferably 20% by mass or less, more preferably 10% by mass or less, and particularly preferably 5% by mass or less with respect to the carbonaceous primary particles as a raw material. . When there are too many graphitization catalysts, graphitization will advance too much and the characteristic at the time of lithium ion secondary battery manufacture, especially the problem that immersion property may not be enough may arise. At the same time, the strength of the particles may decrease because of the formation of pores in the composite graphite particles, and as a result, the surface may be smoothed in the pressing step during electrode plate preparation, and ion migration may be inhibited. On the other hand, if there is too little graphitization catalyst, graphitization is insufficient and there is a problem of reduction in charge / discharge capacity when a non-aqueous secondary battery is made, and high pressure is required in the pressing process during electrode plate production. It may be difficult to increase the density. In addition, due to the absence of an appropriate amount of pores in the composite graphite particles, the strength of the particles becomes too high, and high pressure is required when the active material layer applied to the current collector is pressed to a predetermined bulk density. In some cases, it is difficult to increase the density of the negative electrode active material layer.

  The raw materials such as the graphite particles, the binder (B) and the graphitization catalyst added if desired are first mixed under heating. As a result, the liquid binder (B) is attached to the graphite particles and the raw material that does not melt at the mixing temperature. In this case, all the raw materials may be charged into the mixer and mixing and heating may be performed at the same time, or components other than the binder (B) may be charged into the mixer and heated with stirring, after the temperature has risen to the mixing temperature. A binder (B) at room temperature or in a vulcanized molten state may be charged.

  The heating temperature at the time of mixing is not lower than the softening point of the binder (B) and is usually 10 ° C or higher than the softening point, preferably 20 ° C or higher than the softening point, usually 450 ° C or lower, preferably 250 ° C or lower. Done in If the heating temperature is too low, the viscosity of the binder (B) may become high and mixing may be difficult. If the heating temperature is too high, the viscosity of the mixed system becomes too high due to volatilization and polycondensation of the binder (B). There is a fear.

  As the mixer, a model having a stirring blade is preferable, and a general-purpose device such as a Z type or a gusset type may be used as the stirring blade. The amount of the raw material charged into the mixer is usually 10% by volume or more, preferably 15% by volume or more, and 50% by volume or less, preferably 30% by volume or less of the volume of the mixer. The mixing time is required for 5 minutes or longer, and at most, it takes up to a time when a large viscosity change occurs due to volatilization of volatile matter, and is usually 30 to 120 minutes. The mixer is preferably preheated to the mixing temperature prior to mixing.

The resulting mixture may be used as it is in a de-VM firing process for the purpose of removing volatile components (hereinafter abbreviated as “VM”) and carbonizing, but is molded and removed for easy handling. It is preferable to use for a VM baking process.
The molding method is not particularly limited as long as the shape can be maintained, and extrusion molding, mold molding, isostatic pressing, and the like can be employed. Among these, compared with the extrusion molding in which the particles are easily oriented in the molded body, mold molding and isostatic pressing in which the particle orientation is kept at random are preferable.

  The molding temperature may be room temperature (cold) or under heating (hot, temperature above the softening point of the binder). In the case of cold molding, it is desirable to preliminarily crush the mixture that has been cooled after mixing to a maximum dimension of 1 mm or less in order to improve moldability and obtain uniformity of the molded body. The shape and size of the molded body are not particularly limited, but in hot forming, if the molded body is too large, there is a problem that it takes time to perform uniform preheating prior to molding. It is preferable to set it as the magnitude | size.

If the molding pressure is too high, removal of devolatilized components through the pores of the molded body (de-VM) becomes difficult, and carbonaceous particles that are not perfect circles may be oriented, making pulverization in subsequent processes difficult. Therefore, the upper limit of the molding pressure is usually 3 tf / cm ² (294 MPa) or less, preferably 1500 kgf / cm ² (49 MPa) or less, more preferably 600 kgf / cm ² (0
. 98 MPa) or less. The lower limit pressure is not particularly limited, but is preferably set to such an extent that the shape of the molded body can be maintained in the VM removal step.

  Second step: The obtained mixture or molded body is heated and subjected to de-VM firing to obtain an intermediate substance from which volatile components (VM) generated from the graphite particles, the solvent, and the graphitizable binder (B) are removed. . The de-VM firing is usually performed at a temperature of 600 ° C. or higher, preferably 650 ° C. or higher, usually 1300 ° C. or lower, preferably 1100 ° C. or lower, usually for 0.1 hour to 10 hours. In order to prevent oxidation, heating is usually performed in a non-oxidizing atmosphere in which an inert gas such as nitrogen or argon is circulated or a granular carbon material such as breeze or packing coke is filled in the gap.

  Equipment used for de-VM firing is, for example, a reaction furnace 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), an electric furnace, a gas furnace, etc. There is no particular limitation if possible. The heating rate during heating is desirably a low speed for removal of volatile components, and usually from 3 to 100 ° C. from around 200 ° C. where low-boiling components start to volatilize to around 700 ° C. where only hydrogen is generated. The temperature is raised at / hr. During the treatment, stirring may be performed as necessary.

  The mixture or molded body obtained by the de-VM firing is then heated at a high temperature and graphitized. The heating temperature during graphitization is usually 2600 ° C. or higher, preferably 2800 ° C. or higher. Moreover, since the sublimation of graphite will become remarkable when heating temperature is too high, 3300 degrees C or less is preferable. The heating time may be performed until the binder (B) becomes graphite, and is usually 1 to 24 hours.

  In order to prevent oxidation, the atmosphere during graphitization is performed under a non-oxidizing atmosphere in which an inert gas such as nitrogen or argon is circulated or granular graphite particles such as breeze or packing coke are filled in the gap. The equipment used for graphitization is not particularly limited as long as it meets the above purpose, such as an electric furnace, a gas furnace, an electrode material Atchison furnace, etc. The heating rate, cooling rate, heat treatment time, etc. are acceptable for the equipment used. It can be set arbitrarily within the range.

  Third step: The non-aqueous secondary battery composite graphite particles (C) are subjected to powder processing such as pulverization, pulverization, grinding, and classification as required. There are no particular restrictions on the apparatus used for pulverization, for example, the coarse pulverizer includes a shearing mill, jaw crusher, impact crusher, cone crusher, etc., and the intermediate pulverizer includes a roll crusher, hammer mill, etc. Examples of the fine 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 graphite particles for non-aqueous secondary batteries (C)>
The composite graphite particles (C) for non-aqueous secondary batteries obtained by the above production method have the following characteristics.
(1) 002 plane spacing (d002)
The interplanar spacing (d002) of the 002 plane determined by X-ray diffraction by the Gakushin method of the composite graphite particles (C) for non-aqueous secondary batteries is usually 0.337 nm or less, preferably 0.3365 nm or less, more preferably 0. It is preferable that 336 nm or less and Lc be 90 nm or more. The fact that the interplanar spacing (d002) of the 002 plane by X-ray wide angle diffraction method is 0.337 nm or less and Lc is 90 nm or more is that most of the composite graphite particles (C) for non-aqueous secondary batteries excluding the surface of the particles. The high crystallinity indicates that the 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.

The tap density of (2) a tap density non-aqueous secondary battery composite graphite particle (C) is usually 0.7 g / cm ³ or more, 1.35 g / cm ³ or more.
If the tap density is too small, sufficient continuous voids are not secured especially in the electrode rolled to a high density, and the mobility of Li ions in the electrolyte that is not retained in the voids is reduced, resulting in large current charge / discharge characteristics. Tends to decrease. When the tap density is too high, the carbon density in the particle increases, the rollability is insufficient, and it may be difficult to form a high-density negative electrode sheet.

(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 graphite particle (C) is usually 0. 01 or more, preferably 0.05 or more, and usually 0.3 or less, preferably 0.25 or less, more preferably 0.2 or less. If the Raman R value is too large, the crystal on the particle surface is disturbed, and the reactivity with the electrolytic solution tends to increase, leading to a decrease in efficiency. If the Raman value is too small, the charge / discharge reactivity is lowered and stored at high temperatures. There is a tendency to increase gas generation at the time and to reduce large current charge / discharge characteristics.

(4) Specific surface area by BET method The specific surface area by the BET method of the composite graphite particles (C) for non-aqueous secondary batteries is usually 0.5 m ² / g or more, preferably 1.0 m ² / g or more, preferably 8 m. ² / g or less, and more preferably not more than ^7m 2 / g. If the specific surface area is too large, the reactivity with the electrolyte may increase, leading to a decrease in charge / discharge efficiency. If the specific surface area is too small, the charge / discharge reactivity will decrease, resulting in increased gas generation during high-temperature storage. There is a tendency for the current charge / discharge characteristics to decrease.

(5) Pore capacity The pore capacity in the range of 10 nm to 100000 nm of the composite graphite particles (C) for non-aqueous secondary batteries by mercury intrusion method is usually 5 ml / g or less, preferably 3 ml / g or less, more preferably Is 2 ml / g or less, usually 0.01 ml / g or more, preferably 0.05 ml / g or more, more preferably 0.1 ml / g or more, and the pore volume in the range of 250 to 2500 nm is Usually, 0.001 ml / g or more, preferably 0.002 ml / g or more, more preferably 0.005 ml / g or more, usually 1 ml / g or less, preferably 0.9 ml / g or less, more preferably 0 0.7 ml / g or less. If the amount of pores is too large, the specific surface area resulting from the pores will increase, and excessive reaction with the electrolyte will tend to increase the irreversible capacity. There is a tendency to decrease.

(6) Average particle diameter (d50)
The average particle diameter (d50) of the composite graphite particles (C) for non-aqueous secondary batteries is usually 40 μm or less, preferably 30 μm or less, more preferably 25 μm or less, and usually 3 μm or more, preferably 4 μm or more. Preferably it is 5 micrometers or more. If the average particle size is too large, exceeding this particle size range will often cause inconveniences in the process of striping, etc., and if it falls below this particle size range, the surface area will become too large. It tends to be difficult to suppress the activity with the electrolytic solution.

(7) Surface layer functional group amount (O / C)
The functional group amount (O / C value) represented by the following formula 2 of the surface layer of the composite graphite particles (C) for non-aqueous secondary batteries is usually 0.1% or more, preferably 0.3% or more. Preferably it is 0.5% or more. Further, it is usually 3% or less, preferably 2.5% or less, more preferably 2% or less. If the surface functional group amount O / C value is too small, the desolvation reactivity of Li ions and the electrolyte solvent on the surface of the negative electrode active material is lowered, and the large current charge / discharge characteristics may be lowered. There is a possibility that the reactivity with the electrolyte increases and the charge / discharge efficiency decreases.
Formula 2
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 atomic concentration ratio O / C of O and C (O atomic concentration / C atomic concentration) is defined as the surface functional group amount O / C value of the carbon material.

(8) Graphite crystal orientation ratio (I (110) / I (004))
Intensity ratio R of peaks corresponding to lattice planes (110) and (004) of composite graphite particles (C) for non-aqueous secondary batteries obtained by wide-angle X-ray diffraction measurement (= I (110) / I (004) ) Is usually 0.50 or less, preferably 0.40 or less, more preferably 0.30 or less, and usually 0.05 or more, preferably 0.10 or more, more preferably 0.15 or more. . When the powder orientation ratio is less than the above range, the expansion of the electrode at the time of charging the battery tends to increase, and the cycle characteristics tend to be deteriorated due to the dropping of the active material due to the expansion and contraction during the cycle test. On the other hand, when the powder orientation ratio exceeds the above range, it may be difficult to increase the active material filling density of the electrode by pressing.

(9) Average circularity Circularity given by the following formula measured for particles having a particle diameter of 10 μm to 40 μm of the composite graphite particles (C) for non-aqueous secondary batteries (= circumference of a circle having the same area as the particle projected area) Long / peripheral length of the projected particle image) is usually 0.85 or more, preferably 0.90 or more, more preferably 0.93 or more. When the average circularity is below this range, the large current charge / discharge characteristics tend to be reduced.

(10) Coverage The composite graphite particles (C) for non-aqueous secondary batteries of the present invention are coated with a graphite material. This coverage is usually 1% or more, preferably 5% or more, more preferably 8% or more, more preferably 11% or more, and usually 20% or less, preferably 19% or less, more preferably 17% or less. It is. If the content is too large, the low crystalline portion of the negative electrode material increases, and the reversible capacity when the battery is assembled tends to be small. If the content is too small, the low crystalline portion is not uniformly coated on the scale graphite. At the same time, strong granulation is not achieved, and the particle size tends to be small when pulverized after firing. In addition, the content rate (coverage) of the carbide derived from the binder of the composite graphite particles (C) for the non-aqueous secondary battery finally obtained is the amount of the carbon material used, the amount of the binder, and the microscopic value of JIS K 2270. It can be calculated by the following formula based on the residual carbon ratio measured by the method.

Covering ratio of carbide derived from binder (%) = (mass of binder × residual carbon ratio × 100) /
(Mass of graphite particles + mass of binder x residual carbon ratio)
<Negative electrode material for non-aqueous secondary battery (E)>
The composite graphite particles (C) for non-aqueous secondary batteries of the present invention can be suitably used as a negative electrode material for non-aqueous secondary batteries, either alone or in combination of two or more in any composition and combination. However, one kind or two or more kinds may be mixed with another kind or two or more kinds of other carbon materials (D), and this may be used as a negative electrode material for a non-aqueous secondary battery, preferably a lithium ion secondary battery. . In the present invention, these mixtures are also referred to as negative electrode materials (E) for non-aqueous secondary batteries.

  When other carbon material (D) is mixed with the above-mentioned non-aqueous secondary battery composite graphite particles (C), the non-aqueous system with respect to the total amount of the non-aqueous secondary battery composite graphite particles (C) and the other carbon material (D). The mixing ratio of the composite graphite particles (C) for secondary batteries is usually 10% by mass or more, preferably 20% by mass or more, and usually 90% by mass or less, preferably 80% by mass or less. When the mixing ratio of the other carbon material (D) 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 graphite particles (C) for non-aqueous secondary batteries tend to hardly appear.

In addition, as the carbon material (D), a material selected from natural graphite, artificial graphite, amorphous-coated graphite, and amorphous carbon 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 natural graphite, for example, highly purified flaky graphite or spheroidized graphite can be used. 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. 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.

Examples of the artificial graphite include particles obtained by graphitizing a carbon material. For example, particles obtained by firing and graphitizing a single graphite precursor particle while it is powdered can be used.
As amorphous-coated graphite, for example, natural graphite or artificial graphite coated with an amorphous precursor pair and fired, or natural graphite or artificial graphite coated with amorphous by CVD can be used.

As amorphous carbon, for example, particles obtained by calcining bulk mesophase or particles obtained by infusibilizing a graphitizable binder (B) and calcining can be used.
The apparatus used for mixing the composite graphite particles (C) for non-aqueous secondary batteries and other carbon materials (D) is not particularly limited. For example, in the case of a rotary mixer: a cylindrical mixer, a twin cylinder Type mixer, double cone mixer, regular cubic mixer, vertical mixer, stationary mixer: spiral mixer, ribbon mixer, Muller mixer, Helical Flight mixer, Pugmill A mold mixer, a fluidized mixer, or the like can be used.

<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. It contains the negative electrode material (E) for non-aqueous secondary batteries of the invention. More preferably, it contains a binder. The binder here means a binder added for the purpose of binding the active materials and holding the active material layer on the current collector when producing a negative electrode for a non-aqueous secondary battery, and graphite. It is different from the binder (B) which can be converted.

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 ratio of unsaturated bonds, the number of moles of olefinically unsaturated bonds per gram of all binders is usually 2.5 × 10 ⁻⁷ or more, preferably 8 × 10 ⁻⁷ or more, In addition, it is usually 1 × 10 ⁻⁶ or less, preferably 5 × 10 ⁻⁶ 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.

  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 non-aqueous secondary battery negative electrode material (E) in the active material layer varies depending on the application, the application that emphasizes capacity, preferably 1.55 g / cm ³ or more, especially 1.60 g / cm ³ or more, further 1.65 g / cm ³ or more, in particular 1.70 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, 1.9 g / cm < ³ > or less is preferable.

  When producing the negative electrode for non-aqueous secondary batteries using the negative electrode material for non-aqueous secondary batteries (E) 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 non-aqueous secondary battery or lithium ion secondary battery, and can normally occlude and release lithium ions. A positive electrode, a negative electrode, and an electrolyte are 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 NiPS ₃ and FePS ₃ , selenium compounds of transition metals such as VSe ₂ and NbSe ₃ , Fe0.25V0.75S ₂ , Na0.1CrS ₂ composite oxide of a transition metal such _as, LiCoS _2, LiNiS 2 composite sulfide of a transition metal, such as and the like.

Among _{these, V 2 O 5, V 5} O 13, VO 2, Cr 2 O 5, MnO 2, TiO, MoV 2 O 8, LiCoO 2, LiNiO 2, LiMn 2 O 4, TiS 2, V 2 S 5 Cr0.25V0.75S ₂ , Cr0.5V0.5S _{2 and the} like are preferable, and LiCoO ₂ , LiNiO ₂ , LiMn ₂ O _4, and lithium transitions in which some of these transition metals are replaced with other metals are particularly preferable. It is a metal complex oxide. 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 current collector of the positive electrode, aluminum, nickel, 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 is lowered, and when the proportion of propylene carbonate is higher than the above, when a graphite electrode is used, the PC solvated with Li ions coexists between the graphite phases. Insertion causes delamination degradation of the graphite-based negative electrode active material, and there is a problem that 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, Li
Halides such as Cl 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 , LiC ₄ Fluorine-containing organic lithium salts such as perfluoroalkanesulfonic acid salts such as F ₉ SO ₃ and perfluoroalkanesulfonic acid imide salts such as Li trifluorosulfonimide ((CF ₃ SO ₂ ) ₂ NLi), etc. 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 non-aqueous electrolyte is usually in the range of 0.5M to 2.0M.

  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 salt of Li 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 load reverse capacity is usually 50 mAh / g or less, preferably 40 mAh / g or less, more preferably 35 mAh / g or less. The amount of cell swelling during the high temperature durability test is usually 0.66 ml or less, preferably 0.64 ml or less, more preferably 0.62 ml or less, and further preferably 0.60 ml or less. The cycle maintenance ratio is usually 60% or more, preferably 70% or more, more preferably 75% or more, and further preferably 80% or more.

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) Surface functional group amount The surface functional group amount is measured using X-ray photoelectron spectroscopy (XPS).

The surface functional group amount O / C value is measured using an X-ray photoelectron spectrometer (ESCA manufactured by ULVAC-PHI) as the X-ray photoelectron spectroscopy measurement, and the measurement target (graphite material) is placed on the sample stage so that the surface becomes flat. The spectrum of C1s (280 to 300 eV) and O1s (525 to 545 eV) is measured by multiplex measurement using an aluminum Kα ray as an X-ray source. 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. The obtained atomic concentration ratio O / C (O atomic concentration / C atomic concentration) of O and C is defined as the surface functional group amount O / C value of the carbon material, and can be calculated specifically by the following formula 1. .
Formula 3
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
(2) Particle size The particle size was measured by adding 0.01 g of carbon material to 10 mL of 0.2% by weight aqueous solution of polyoxyethylene sorbitan monolaurate (for example, Tween 20 (registered trademark)) as a surfactant. Was suspended in a commercially available laser diffraction / scattering particle size distribution measuring device “LA-920 manufactured by HORIBA”, irradiated with 28 kHz ultrasonic waves at an output of 60 W for 1 minute, and then used as a volume-based median diameter in the measuring device. The measured value is defined as d50 in the present invention.

(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 single point method. Specifically, 0.4 g of a 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) X-ray structural analysis (XRD)
The X-ray structural analysis (XRD) measurement method is performed by filling a sample plate of 0.2 mm with about 15% X-ray standard high purity silicon powder mixed with carbon powder so as not to be oriented. Measured with a diffraction device (for example, JDX-3500, manufactured by JEOL Ltd.) with CuKα rays at an output of 30 kV and 200 mA. Using the Gakushin method, the interplanar spacing (d002) and crystallite size (Lc (004)) of the 002 plane were determined. Also, 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) is obtained. Calculated.

(5) Tap density The tap density is a powder density measuring instrument manufactured by Seishin Enterprise Co., Ltd. “Tap Denser KYT-4000”, with a diameter of 1.6 cm and a volume capacity of 20 cm ^{3 in} a cylindrical tap cell. 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.

(6) Raman spectrum (Raman) spectrum The Raman spectrum can be measured with a Raman spectrometer: "Raman spectrometer manufactured by JASCO Corporation". 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: 514.5 nm
Laser power on sample: 25 mW
Resolution: 4cm ^-1
Measurement ^range: 1100cm ^-1 ~1730cm -1 peak intensity measurement, peak half-width measurement: background processing, smoothing processing (convolution 5 points by a simple average)
(7) Remaining charcoal ratio The remaining charcoal ratio of the graphitizable binder (B) was measured in accordance with JIS K2270.

(8) Softening point, quinoline insoluble matter (QI), toluene insoluble matter (TI)
The softening point, quinoline insoluble content (QI), and toluene insoluble content (TI) of the graphitizable binder (B) were measured in accordance with JIS K2425.
(9) Hydrogen elementary ratio (H / C) The atomic ratio (H / C) determined from the amount of hydrogen and the amount of carbon measured with an elemental analyzer (CHN meter) was calculated.

(10) Irreversible Capacity, Discharge Capacity, Initial Efficiency Measurement Method Using a non-aqueous secondary battery, the irreversible capacity / discharge capacity during battery charge / discharge was measured by the following measurement method.
After charging to 5 mV with respect to the lithium counter electrode at a current density of 0.16 mA / cm ² , and further charging until the charge capacity value becomes 350 mAh / g at a constant voltage of 5 mV, after doping lithium in the negative electrode, 0 The battery was discharged to 1.5 V with respect to the lithium counter electrode at a current density of .33 mA / cm ² . Subsequently, the second and third times were charged at 10 mV and 0.005 Ccut by cc-cv charging at the same current density, and the discharge was discharged to 1.5 V at 0.04 C at all times. The sum of the difference between the charge capacity and the discharge capacity for a total of three cycles was calculated as an irreversible capacity. Further, the discharge capacity at the third cycle was defined as the discharge capacity of the material, the discharge capacity at the third cycle / (the discharge capacity at the third cycle + the sum of the difference between the charge capacity and the discharge capacity at the third cycle).

(11) Method for measuring cell swell amount during high-temperature endurance test After a laminate-type battery produced by the method described below is left for 12 hours, the potential difference between both electrodes is 4.1 V at a current density of 0.2 CmA / cm3. Then, the battery was charged, and then discharged at 0.2 CmA / cm3 until 3V was reached. This was repeated twice, and further charging was carried out with the same current value until the potential difference between both electrodes reached 4.2V. The amount of swelling a (mL) generated so far was measured by the immersion volume method (solvent replacement method based on Archimedes' principle). Then, it was left in an 85 ° C. constant temperature bath for 24 hours, and the amount b (mL) of further swelling was obtained, and “a + b (mL)” was defined as “cell swelling amount during a high temperature durability test”. The results in Table 3 were obtained by measuring each of the two laminated batteries and calculating the average value.

(12) Measuring method of cycle retention rate A laminate type battery manufactured by the method described later is repeatedly charged to 4.2 V at 0.8 C and discharged to 3.0 V at 0.5 C, with respect to the discharge capacity at the first cycle. The ratio of discharge capacity at the 200th cycle × 100 was defined as the cycle retention rate (%). (Production of electrode sheet)
Using the carbon material of the present invention as the negative electrode material, an electrode plate having an active material layer with an active material layer density of 1.70 ± 0.03 g / cm ³ was produced. Specifically, 20.00 ± 0.02 g of a negative electrode material, 20.00 ± 0.02 g of a 1% by mass aqueous solution of carboxymethylcellulose sodium salt (0.200 g in terms of solid content), and styrene having a weight average molecular weight of 270,000 -Aqueous dispersion of butadiene rubber 0.50 ± 0.05 g (0.2 g in terms of solid content) was stirred for 5 minutes with a hybrid mixer manufactured by Keyence, and defoamed for 30 seconds to obtain a slurry.
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.

(Preparation of non-aqueous secondary battery (2016 coin type battery))
The electrode sheet produced by the above method was punched into a disk shape with a diameter of 12.5 mm, and a lithium metal foil was punched into a disk shape with a diameter of 14 mm as a counter electrode. Between the two electrodes, A: an electrolytic solution in which LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate and ethyl methyl carbonate (volume ratio = 3: 7) so as to be 1 mol / L, B: ethylene carbonate and propylene carbonate Electrolyte solution in which LiPF ₆ was dissolved in a mixed solvent of 1 and diethyl carbonate (volume ratio = 2: 4: 4) to a concentration of 1 mol / L, C: mixed solvent of ethylene carbonate, propylene carbonate and diethyl carbonate (volume ratio) = 1: 5: 4) separator (made of a porous polyethylene film) impregnated with an electrolytic solution (represented as electrolytic solutions A, B, and C in the table, respectively) in which LiPF ₆ was dissolved to 1 mol / L ) And 2016 coin type batteries using the electrolytes A to C were produced.

(Production method of non-aqueous secondary battery (laminated battery))
The negative electrode sheet produced by the above method was cut into a square of 4 cm × 3 cm to form a negative electrode, and a positive electrode made of LiCoO 2 was cut out with the same area and combined. Between the negative electrode and the positive electrode, LiPF6 was dissolved in a mixed solvent of ethylene carbonate, ethylmethyl carbonate, and dimethyl carbonate (volume ratio = 20: 20: 60) to 1 mol / L, and vinylene carbonate was further added as an additive. A separator (made of a porous polyethylene film) impregnated with 2% by volume of an electrolytic solution was placed and a laminate type battery was produced.

(Type of raw material)
(1) Graphite particles (A)
In this example, the following natural graphite materials are used as the graphite particles (A).
Graphite particles (a): Particle size d50, tap density, specific surface area, d002, Lc (004), Raman R value, O / C measured by the above measurement method are 11.6 μm, 0.66 g / cm ³ , respectively. Spherical natural graphite particles of 8.6 m ^{2 /} g, 0.3356 nm,> 100 nm, 0.20, 2.3% Graphite particles (b): particle size d50, tap density, specific surface area measured by the above measurement method , D002, Lc (004), Raman R value, O / C are 16.4 μm, 1.02 g / cm ³ , 6.7 m ² / g, 0.3355 nm,> 100 nm, 0.26, 3.0%, respectively. Spherical natural graphite (2) Graphitizable binder (B)
In this example, the following binder pitch material is used as the graphitizable binder (B).

Binder pitch (a): Carbon powder obtained by graphitization and then pulverized by X-ray wide angle diffraction method has a 002 plane spacing (d002) of 0.3360 nm, Lc (004) of 67 nm, and a residual carbon ratio of Binder pitch with 50%, quinoline insoluble content 10%, toluene insoluble content 30%, H / C 0.041, softening point 80 ° C.
Binder Pitch (b): Carbon powder obtained by graphitization and then pulverized by X-ray wide angle diffraction method has a 002 plane spacing (d002) of 0.3356 nm and Lc (004)> 100 nm (reference value 550 nm). ), Binder pitch with a residual carbon ratio of 50%, quinoline insoluble content ≦ 0.5%, toluene insoluble content 16%, H / C 0.044, softening point 80 ° C.

Example 1
The graphite particles (a) and the binder pitch (a) were added at a mass ratio of 10 0: 30 and put into a kneader and mixed for 20 minutes. This mixture was molded as a molded body using a molding machine, heated from room temperature to 1000 ° C. in an electric furnace, and further held at 1000 ° C. to perform de-VM firing. Then, this fired body was graphitized by heating at 3000 ° C. The obtained graphite compact was roughly crushed and pulverized to obtain a graphite composite particle sample. With respect to this sample, the particle size d50, tap density, specific surface area, d002, Lc (004), Raman R value, and O / C were measured by the above measurement method. The results are shown in Table 2. It was confirmed that the obtained graphite composite particles were covered with 15% graphite. Moreover, according to the said measuring method, the irreversible capacity | capacitance, discharge capacity, initial efficiency, the amount of cell swelling at the time of a high temperature endurance test, and the cycle maintenance factor were measured. The results are shown in Table 3.

Comparative Example 1
A graphite composite particle sample was obtained in the same manner as in Example 1 except that the binder pitch (a) was changed to the binder pitch (b). It was confirmed that the obtained graphite composite particles were covered with 15% graphite. About this, the physical property and the battery characteristic were measured by the same method as Example 1. The results are shown in Tables 2 and 3.

Example 2
A graphite composite particle sample was obtained in the same manner as in Example 1 except that the graphite particles (a) were changed to the graphite particles (b). It was confirmed that the obtained graphite composite particles were covered with 15% graphite. About this, the physical property and the battery characteristic were measured by the same method as Example 1. The results are shown in Tables 2 and 3.

Comparative Example 2
A graphite composite particle sample was obtained in the same manner as in Example 2 except that the binder pitch (a) was changed to the binder pitch (b). It was confirmed that the obtained graphite composite particles were covered with 15% graphite. About this, the physical property and the battery characteristic were measured by the same method as Example 1. The results are shown in Tables 2 and 3.

Example 3
After adding graphite particles (b) and binder pitch (b) at a mass ratio of 100: 20 and mixing with a kneader, this mixture is further mixed with binder pitch (a) at a mass ratio of 120: 10, A graphite composite particle sample was obtained in the same manner as in Example 1 except that mixing was performed using a kneader. It was confirmed that the obtained graphite composite particles were covered with 15% graphite. About this, the physical property and the battery characteristic were measured by the same method as Example 1. The results are shown in Tables 2 and 3.

  Table 1 summarizes the types, mixing ratios, and electrode densities of the raw materials described in the above Examples and Comparative Examples.

  In each of Examples 1 to 3, Comparative Example 1 and Comparative Example 2 using a graphitizable binder having no specific physical properties by using a graphitizable binder having specific physical properties as described above. Compared with, the amount of cell swelling during the high temperature durability test was reduced. Further, in Example 1, the use of a graphitizable binder having specific physical properties resulted in a remarkable improvement in cycle retention compared to Comparative Example 1.

  By using the composite graphite particles of the present invention as a carbon material for a non-aqueous secondary battery, it is possible to provide a negative electrode material for a non-aqueous secondary battery with high capacity and good charge / discharge load characteristics. Moreover, according to the manufacturing method of the said material, since there are few processes, it can manufacture stably and efficiently and cheaply.

Claims (4)

A method for producing composite graphite particles (C) for a non-aqueous secondary battery in which graphite particles (A) and a graphitizable binder (B) are mixed and graphitized, wherein the graphitizable binder (B) The manufacturing method of the composite graphite particle (C) for non-aqueous secondary batteries characterized by satisfying the following condition (1).
Condition (1): The plane distance (d002) of the 002 plane by the X-ray wide angle diffraction method of the carbon powder obtained by graphitizing the graphitizable binder (B) is 0.3357 nm or more and 0.34 nm or less, and Lc (004) is 10 nm or more and 500 nm or less.   The method for producing composite graphite particles for a non-aqueous secondary battery according to claim 1, wherein the graphite particles (A) are at least one selected from natural graphite, artificial graphite, amorphous coated graphite, and amorphous carbon. .   The method for producing composite graphite particles for nonaqueous secondary batteries according to claim 1 or 2, wherein the graphite particles (A) are spherical natural graphite. The method for producing composite graphite particles for a non-aqueous secondary battery according to any one of claims 1 to 3, wherein the quinoline insoluble content in the graphitizable binder (B) is 0.6% or more and 30% or less .