WO2012133700A1

WO2012133700A1 - Carbon material and negative electrode for nonaqueous secondary battery and nonaqueous secondary battery

Info

Publication number: WO2012133700A1
Application number: PCT/JP2012/058473
Authority: WO
Inventors: 信亨石渡; 山田　俊介; 宇尾野　宏之
Original assignee: 三菱化学株式会社
Priority date: 2011-03-30
Filing date: 2012-03-29
Publication date: 2012-10-04
Also published as: KR20140010406A; CN103460459B; KR101952464B1; CN103460459A; JP2012216537A

Abstract

The purpose of the present invention is to provide a carbon material for a nonaqueous secondary battery for fabricating a nonaqueous secondary battery, and among the same, a lithium ion secondary battery, having superior cycle characteristics in addition to superior high initial capacity and rate characteristics. The present invention relates to a carbon material for a nonaqueous secondary battery that contains natural graphite particles (a) with an internal porosity of 1 - 20% and carbonaceous composite particles (b) for which dibutyl phthalate oil absorption is 0.31 - 0.85 mL/g or less.

Description

Non-aqueous secondary battery carbon material, negative electrode, and non-aqueous secondary battery

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

In recent years, demand for high-capacity secondary batteries has increased with the downsizing of electronic devices. In particular, lithium ion secondary batteries having higher energy density and excellent large current charge / discharge characteristics have attracted attention as compared to nickel / cadmium batteries and nickel / hydrogen batteries.
It is known to use graphite as a carbon material for a lithium ion secondary battery. In particular, when graphite having a high degree of graphitization is used as a negative electrode active material for a lithium ion secondary battery, a capacity close to 372 mAh / g, which is the theoretical capacity of lithium occlusion of graphite, is obtained, and further, cost and durability are also improved. Since it is excellent, it is known that it is preferable as an active material.

Therefore, as a negative electrode material, Patent Document 1 proposes a carbon material that has been spheroidized using mechanical energy treatment. In Patent Document 2, 1 to 50% by mass of a graphitization catalyst is added to and mixed with a graphitizable aggregate or graphite and a graphitizable binder, and calcined at 2000 ° C. or higher so that the graphitization catalyst is removed. Carbon materials that have been graphitized and then ground have been proposed. Patent Document 3 proposes a carbon material in which spheroidized graphite is coated with graphite.

However, the above carbon material cannot satisfy the required characteristics such as initial efficiency, cycle characteristics, and load characteristics in a well-balanced manner, and needs to be improved.
Therefore, as methods for satisfying the above-described required characteristics, Patent Document 4 discloses a method of pressure-treating spherical graphite isotropically (hereinafter sometimes referred to as “CIP treatment”), and Patent Document 5 discloses a patent. It is disclosed that a negative electrode material as described in Document 2 is subjected to CIP treatment.

Japanese Laid-Open Patent Publication No. 10-158005 Japanese Unexamined Patent Publication No. 2000-340232 Japanese Unexamined Patent Publication No. 2007-042611 Japanese Unexamined Patent Publication No. 2005-50807 Japanese Unexamined Patent Publication No. 2000-294243

However, according to the study by the present inventors, as described above, even when the carbon materials described in Patent Documents 1 to 3 are used as the negative electrode material of the non-aqueous secondary battery, high capacity, excellent cycle characteristics, and high load characteristics are obtained. There was room for improvement in terms of maintaining
Further, even when the carbon material described in Patent Document 4 is used as a negative electrode material for a non-aqueous secondary battery, since the graphite is only pressure-treated, the electrode density is high, the irreversible capacity is increased, However, there is room for improvement because it is impossible to secure the immersion property of the electrolytic solution into the carbon material. Further, Patent Document 5 discloses a technique for subjecting the negative electrode material to isotropic pressure treatment, but there is room for improvement in terms of reducing the irreversible capacity as in Patent Document 4.

Therefore, the present invention has been made in view of such problems, and suppresses the reaction between the surface of the carbon material and the non-aqueous electrolyte and impairs the immersion of the electrolyte when used as a battery electrode. In addition, the present invention provides a carbon material for producing a non-aqueous secondary battery, in particular, a lithium ion secondary battery having excellent initial capacity and rate characteristics, and further excellent cycle characteristics. It aims at providing the non-aqueous secondary battery excellent in the characteristic, especially a lithium ion secondary battery.

As a result of intensive studies to solve the above-mentioned problems, the present inventors have selected two types of carbon materials from among the many carbon materials for negative electrodes that have been proposed so far, and carbon materials containing these carbon materials. Surprisingly, it has been found that a lithium ion secondary battery excellent in both cycle characteristics and initial capacity can be obtained by applying to a carbon material for a non-aqueous secondary battery, and the present invention has been completed.

That is, the gist of the present invention is shown in the following <1> to <7>.
<1> Natural graphite particles (a) having an internal porosity of 1% or more and 20% or less and carbonaceous material composite particles (b) having a dibutyl phthalate oil absorption of 0.31 mL / g or more and 0.85 mL / g or less And a carbon material for a non-aqueous secondary battery.
<2> The carbon material for a non-aqueous secondary battery according to <1>, wherein the carbonaceous material composite particles (b) are carbonaceous material-coated graphite.
<3> The natural graphite particles (a) have irregularities on the surface, and the diameter (D) of the irregularities of the irregularities is 0 with respect to the average particle diameter (d50) of the natural graphite particles (a). The carbon material for nonaqueous secondary batteries according to <1> or <2>, wherein the carbon material is 15 times or more and 7 times or less.
<4> The specific surface area of the carbonaceous material composite particles (b) is 0.5 m ² / g or more and 6.5 m ² / g or less, the Raman R value is 0.03 or more and 0.19 or less, and the tap density is 0. .7g / cm ³ or more, a non-aqueous secondary battery carbon material according to any one of 1.2 g / cm ³ or less is the <1> to <3>.
<5> The mass ratio ((a) / {(a) + (b)}) of the natural graphite particles (a) and the carbonaceous material composite particles (b) is 0.1 or more and 0.9 or less. The carbon material for a non-aqueous secondary battery according to any one of <1> to <4>.
<6> A negative electrode for a non-aqueous secondary battery comprising a current collector and an active material layer formed on the current collector, wherein the active material layer is any one of the items <1> to <5> A negative electrode for a non-aqueous secondary battery, comprising the carbon material for a non-aqueous secondary battery according to claim 1.
<7> A nonaqueous secondary battery comprising a positive electrode and a negative electrode, and an electrolyte, wherein the negative electrode is the negative electrode for a nonaqueous secondary battery according to <6>.

By using the carbon material for a non-aqueous secondary battery according to the present invention, a non-aqueous secondary battery excellent in both cycle characteristics and initial capacity can be provided.

FIG. 1 is a diagram showing an SEM photograph of natural graphite particles (a) and the diameter (D) of the approximate circle of the concave surface in the irregularities on the surface of the natural graphite particles (a). FIG. 2 is an explanatory view showing a method for calculating the amount of internal voids by Hg porosimetry measurement.

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.
Here, “wt%” is synonymous with “mass%” and “part by weight” is synonymous with “part by mass”.

<Natural graphite particles (a)>
In this specification, the natural graphite particles (a) represent natural graphite particles (a) capable of occluding and releasing lithium ions, and satisfy the condition that at least the internal porosity is 1% or more and 20% or less.
(1) Physical properties of natural graphite particles (a) The natural graphite particles (a) in the present invention preferably exhibit the following physical properties.
(I) Internal porosity The internal porosity of the natural graphite particles (a) is 1% or more, preferably 3% or more, more preferably 5% or more, and further preferably 7% or more. Moreover, it is 20% or less, Preferably it is 18% or less, More preferably, it is 15% or less, More preferably, it is 12% or less. If the internal porosity is too small, the amount of liquid in the particles tends to decrease, and charge / discharge characteristics tend to deteriorate. If the internal porosity is too large, there are few interparticle voids in the case of an electrode, and the electrolyte diffuses. Tend to be insufficient.

For example, as shown in FIG. 2, the internal porosity is tangent to the minimum slope value based on the pore distribution (integral curve) (L) obtained by the known Hg porosimetry measurement (mercury intrusion method). (M) is subtracted to determine the branch point (P) of the tangent line (M) and the integral curve (L), and the pore volume smaller than the branch point is determined as the intra-particle pore volume (cm ³ / g) (V ). The internal porosity can be calculated from the amount of pores in the particles obtained and the true density of graphite. The true density of graphite used for calculation is 2.26 g / cm ³ , which is the true density of general graphite. The calculation formula is shown in Formula 1.

Formula 1
Internal porosity (%) = [intraparticle pore volume / {intraparticle pore volume + (1 / true graphite density)}] × 100

(Ii) Ratio of the diameter (D) of the concave portion to the average particle diameter (d50) (diameter of the concave portion (D) / d50)
For natural graphite particles (a), the use of graphite particles whose surface is roughened by applying mechanical energy (formed with irregularities) as a raw material reduces the internal porosity and increases the packing density of the particles. From the viewpoint that it is difficult to orient in the electrode.
Assuming that the concave portion of the surface of the SEM image of the natural graphite particles (a) is a circle and assuming that the diameter of the approximate circle is (D), the natural graphite particles (a) with respect to d50 of the natural graphite particles (a) The ratio of the diameter (D) of the concave portion on the surface (the diameter (D) / d50 of the concave portion) is usually 0.15 times or more and 7 times or less. Preferably it is 0.2 times or more, more preferably 0.3 times or more. Further, the upper limit is usually 7 times or less, preferably 5 times or less, more preferably 3 times or less.
If the ratio of (the diameter of the concave portion (D) / d50) is too large, the particles tend to be flat and tend to be oriented in a direction parallel to the electrode when formed into an electrode. Moreover, when the ratio of the (diameter (D) / d50) portion of the concave portion of the natural graphite particle (a) is too small, the contact property between the particles is deteriorated when the electrode is formed, and sufficient cycle characteristics tend not to be obtained. is there.

The diameter (D) of the concave portion of the natural graphite particles (a) is calculated using an SEM image.
As a measuring method of the SEM image, for example, VE-7800 manufactured by Keyence Corporation is used, and measurement is performed at an acceleration voltage of 5 kV.
An approximate circle is drawn assuming that the concave portion of the surface of the obtained natural graphite particle (a) is a circle, and the diameter of the approximate circle is the diameter (D) of the concave portion of the natural graphite particle (a). And Then, using the d50 of the natural graphite particles (a) measured by the following measuring method, the diameter of the concave portion (D) / d50 is calculated.
As an example, an SEM image of the natural graphite particles (a) used in Example 1 and Comparative Example 3 and a circle approximating the concave portion are shown in FIG.

The diameter (D) of the concave portion is usually 0.1 μm or more, preferably 1 μm or more, more preferably 5 μm or more, further preferably 10 μm or more, and usually 100 μm or less, preferably 70 μm or less, more preferably 50 μm or less, and further Preferably it is 30 micrometers or less. If this diameter (D) is too large, the uneven shape becomes gentle, so that it becomes flat particles, and when it is made into an electrode, it tends to be oriented parallel to the electrode, while the diameter (D) is If it is too small, the contact between the particles tends to deteriorate.

The average particle size d50 is measured by first suspending 0.01 g of a sample in 10 mL of a 0.2 mass% aqueous solution of polyoxyethylene sorbitan monolaurate (for example, Tween 20 (registered trademark)) as a surfactant. And introduced into 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 measured as a volume-based median diameter in the measuring device Is d50.

The average particle diameter (d50) of the natural graphite particles (a) is usually 5 μm or more, preferably 10 μm or more, more preferably 15 μm or more, and usually 40 μm or less, preferably 35 μm or less, more preferably 30 μm or less. . If the average particle size is too small, the specific surface area tends to be large and it is difficult to prevent an increase in irreversible capacity. Moreover, when an average particle diameter is too large, it will become difficult to prevent the rapid charge / discharge property fall by the contact area of electrolyte solution and carbonaceous material composite particle (b) reducing.

(Iii) X-ray parameters The crystallite size (Lc) in the c-axis direction and the crystallite size in the a-axis direction of the natural graphite particles (a) determined by X-ray diffraction by the Gakushin method of natural graphite particles (a) La) is preferably 30 nm or more, and more preferably 100 nm or more. If the crystallite size is within this range, the amount of lithium that can be charged into the natural graphite particles (a) increases, and a high capacity is easily obtained, which is preferable.

(Iv) Raman R value, Raman half value width The Raman R value of the natural graphite particles (a) is a value measured by using an argon ion laser Raman spectrum method, and is usually 0.01 or more, preferably 0.03 or more. More preferably, it is 0.1 or more, usually 1.5 or less, preferably 1.2 or less, more preferably 1 or less, and particularly preferably 0.5 or less.

When the Raman R value is too small, the crystallinity of the particle surface becomes too high, and there is a tendency that the number of sites where Li ions enter the interlayer is reduced with charge / discharge. That is, charge acceptance may be reduced. In addition, when densification is performed by pressing a negative electrode obtained by applying an active material layer containing natural graphite particles (a) to a current collector, crystals are easily oriented in a direction parallel to the electrode plate, The load characteristics may be degraded. A Raman R value of 0.1 or more is more preferable because a suitable film can be formed on the negative electrode surface, thereby improving storage characteristics, cycle characteristics, and load characteristics.
On the other hand, if the Raman R value is too large, the crystallinity of the particle surface is lowered, the reactivity with the non-aqueous electrolyte solution is increased, and the charge / discharge efficiency is decreased and the gas generation is increased.

The Raman half width of the peak in the vicinity of 1580 cm ^{−1 of the} negative electrode active material is not particularly limited, but is usually 10 cm ⁻¹ or more, preferably 15 cm ⁻¹ or more, and is usually 100 cm ⁻¹ or less, preferably 80 cm ⁻¹ or less. More preferably, it is 60 cm ⁻¹ or less, particularly preferably 40 cm ⁻¹ or less.
When the Raman half-width is too small, the crystallinity of the particle surface becomes too high, and there is a tendency that the number of sites where Li ions enter the interlayer is reduced with charge / discharge. That is, charge acceptance may be reduced. In addition, when densification is performed by pressing a negative electrode obtained by applying an active material layer containing natural graphite particles (a) to a current collector, crystals are easily oriented in a direction parallel to the electrode plate, There is a tendency for load characteristics to deteriorate.
On the other hand, if the Raman half width is too large, the crystallinity of the particle surface decreases, the reactivity with the non-aqueous electrolyte increases, and the charge / discharge efficiency tends to decrease and gas generation increases.

The Raman spectrum is measured by using a Raman spectrometer (for example, a Raman spectrometer manufactured by JASCO Corporation) to drop the sample naturally into the measurement cell, filling it, and irradiating the sample surface in the cell with argon ion laser light. However, the cell is rotated in a plane perpendicular to the laser beam.
The resulting Raman spectrum, the intensity _{I A} of the peak _{P A} in the vicinity of 1580 cm ^-1, and measuring the intensity _{I B} of a peak _{P B} in the vicinity of 1360 cm ^-1, the intensity ratio _{_{R (R = I B / I}} A) Is calculated. The Raman R value calculated by the measurement is defined as the Raman R value of the negative electrode active material of the present invention. Further, the half width of the peak P _A in the vicinity of 1580 cm ^-1 of the resulting Raman spectrum was measured, which is defined as the Raman half-value width of the negative electrode active material of the present invention.

The measurement conditions of the above Raman spectrum are as follows.
Argon ion laser wavelength: 514.5nm
・ Laser power on the sample: 15-25mW
・ Resolution: 10-20cm ^-1
Measurement range: 1100 cm ⁻¹ to 1730 cm ⁻¹
・ Raman R value, Raman half-width analysis: Background processing ・ Smoothing processing (simple average, 5 points of convolution)

(V) BET specific surface area The BET specific surface area (SA) of the natural graphite particles (a) is a value of the specific surface area measured using the BET method, and is usually 0.1 m ² · g ⁻¹ or more, preferably 0.8. 7 m ² · g ⁻¹ or more, more preferably 1.0 m ² · g ⁻¹ or more, particularly preferably 1.5 m ² · g ⁻¹ or more, and usually 20 m ² · g ⁻¹ or less, preferably 17 m. ² · g ⁻¹ or less, more preferably 14 m ² · g ⁻¹ or less, particularly preferably 10 m ² · g ⁻¹ or less.

If the value of the BET specific surface area is too small, the acceptability of lithium ions tends to deteriorate during charging, lithium tends to precipitate on the electrode surface, and the stability tends to decrease. On the other hand, if the value of the BET specific surface area is too large, the reactivity with the non-aqueous electrolyte increases, gas generation tends to increase, and a preferable battery tends to be difficult to obtain.
The specific surface area is measured by the BET method using, for example, a surface area meter (a fully automated surface area measuring device manufactured by Okura Riken), preliminarily drying the sample at 350 ° C. for 15 minutes under a nitrogen flow, and then measuring nitrogen against atmospheric pressure. A nitrogen adsorption BET one-point method using a gas flow method is performed using a nitrogen-helium mixed gas that is accurately adjusted so that the relative pressure value of the gas becomes 0.3. The specific surface area obtained by the measurement is defined as the BET specific surface area of the natural graphite particles (a) of the present invention.

(Vi) Tap density The tap density of the natural graphite particles (a) is usually 0.1 g · cm ⁻³ or more, preferably 0.5 g · cm ⁻³ or more, more preferably 0.7 g · cm ⁻³ or more, particularly Preferably, it is 0.8 g · cm ⁻³ or more, usually 2 g · cm ⁻³ or less, preferably 1.8 g · cm ⁻³ or less, more preferably 1.6 g · cm ⁻³ or less.
If the tap density is too small, it is difficult to increase the packing density when the negative electrode is used, and it is difficult to obtain a high-capacity battery. On the other hand, if the tap density is too high, there are too few voids between the particles in the electrode, and it is difficult to ensure conductivity between the particles, and it is difficult to obtain preferable battery characteristics.

The tap density is measured by passing the sample through a sieve having a mesh size of 300 μm, dropping the sample onto a tapping cell of, for example, 20 cm ³ and filling the sample to the upper end surface of the cell, and then measuring a powder density measuring instrument (for example, Seishin Enterprise Co., Ltd.). The tap density is calculated from the volume at that time and the mass of the sample. The tap density calculated by the measurement is defined as the tap density of the natural graphite particles (a) of the present invention.

(Vii) Orientation ratio The orientation ratio of the natural graphite particles (a) is usually 0.005 or more, preferably 0.01 or more, more preferably 0.015 or more, and usually 0.6 or less. Preferably it is 0.5 or less, more preferably 0.4 or less. When the orientation ratio is below the above range, the high-speed charge / discharge characteristics may tend to be reduced. In addition, 0.6 which is the normal upper limit of the said range is a theoretical upper limit of the orientation ratio of a carbonaceous material.

The orientation ratio is measured by X-ray diffraction measurement after pressure-molding the sample. For example, a molded body obtained by filling 0.47 g of a sample into a molding machine having a diameter of 17 mm and compressing it with 58.8 MN · m ⁻² and a load of 600 kg becomes the same surface as the surface of the measurement sample holder using clay. Then, the X-ray diffraction is measured. From the (110) diffraction and (004) diffraction peak intensities of the obtained carbon, a ratio represented by {(110) diffraction peak intensity / (004) diffraction peak intensity} is calculated. The orientation ratio calculated by the measurement is defined as the orientation ratio of the natural graphite particles (a) of the present invention.

The X-ray diffraction measurement conditions are as follows. “2θ” indicates a diffraction angle.
・ Target: Cu (Kα ray) graphite monochromator ・ Slit: Divergent slit = 0.5 degree Light receiving slit = 0.15 mm
Scattering slit = 0.5 degrees ・ Measurement range, step angle and measurement time:
(110) plane: 75 degrees ≦ 2θ ≦ 80 degrees, 1 degree / 60 seconds (004) plane; 52 degrees ≦ 2θ ≦ 57 degrees, 1 degree / 60 seconds

(2) Shape of natural graphite particles (a) The natural graphite particles (a) in the present invention preferably have irregularities on the surface as shown in FIG. Of the irregularities, the convex portion is a portion that maintains the roundness of the spheroidized graphite as it is, and the concave portion is a pressure treatment, preferably by other graphite particles by an isotropically pressurized CIP treatment. It means the compressed part.

(3) Manufacturing method of natural graphite particle (a) The manufacturing method of the natural graphite particle (a) of the present invention is not particularly limited as long as the physical properties described above are satisfied. An example of a preferable production method is described below.
For example, the natural graphite particles (a) are preferably subjected to a step (pressure treatment) for molding the raw natural graphite particles under pressure.

Natural graphite particles (a) and types of raw natural graphite particles Natural graphite is easily available commercially, and can theoretically have a high charge / discharge capacity of 372 mAh / g. This is preferable because the effect of improving charge / discharge characteristics at a high current density is remarkably greater than when a negative electrode active material is used.

Natural graphite is preferably one having few impurities, and is 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 (d ₀₀₂ ) of less than 3.37 mm (0.337 nm) by X-ray wide angle diffraction method are preferred.
As natural graphite, for example, highly purified flaky graphite or spheroidized graphite can be used. Among these, spherical graphite subjected to spheroidizing treatment is particularly preferable from the viewpoint of particle filling properties and charge / discharge rate characteristics.

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

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

・ Process to form raw natural graphite particles by pressure (pressure treatment)
In this step, the raw natural graphite particles are pressed and molded. Preferably, isotropic pressure treatment (CIP) is performed. In addition, it is preferable to perform isotropic pressing of the raw natural graphite particles because a predetermined internal porosity is obtained by forming irregularities on the surface of the graphite particles and uniformly reducing the interparticle voids.

The method of molding by pressure treatment is not particularly limited, and isotropic pressure treatment is preferably performed with a hydrostatic pressure press, a roll compactor, a roll press, a pricket machine, and a tablet machine.
Further, if necessary, the graphite particles can be molded simultaneously with the press according to the pattern carved in the roll. Moreover, the method of exhausting the air which exists between graphite particles and vacuum-pressing can also be applied.

The pressure for pressurizing the feed natural graphite particles is not particularly limited, usually 50 kgf / cm ² or higher, preferably 100 kgf / cm ^2, more preferably 300 kgf / cm ² or more, more preferably 500 kgf / cm ² or more Particularly preferably, it is 700 kgf / cm ² or more. The upper limit of the pressure treatment is not particularly limited, but is usually 2000 kgf / cm ² or less, preferably 1800 kgf / cm ² or less, more preferably 1600 kgf / cm ² or less, and further preferably 1500 kgf / cm ² or less.
If the pressure is too low, the amount of voids in the particles and the formation of irregularities on the particle surface tend to be insufficient, and if the pressure is too high, extra force is required at the time of pulverization and the particles are destroyed. There is a tendency that the characteristics cannot be fully exhibited.

The pressurizing time is usually 1 minute or longer, preferably 2 minutes or longer, more preferably 3 minutes or longer, and further preferably 4 minutes or longer. Moreover, it is normally 30 minutes or less, Preferably it is 25 minutes or less, More preferably, it is 20 minutes or less, More preferably, it is 15 minutes or less. When the time is too long, the productivity tends to be remarkably lowered, and when the time is too short, the treatment is not sufficiently performed.
If necessary, a step of crushing the pressure-treated natural graphite may be performed. The shape is arbitrary, but is usually granular with an average particle size (d50) of 2 to 50 μm. It is preferable to grind and classify so that the average particle size is 5 to 35 μm, particularly 8 to 30 μm.

<Carbonaceous composite particles (b)>
The carbonaceous material composite particles (b) are not particularly limited as long as the carbonaceous material is composited, and are not particularly limited as long as the physical properties described below are satisfied.
(1) Physical properties of carbonaceous material composite particles (b) The physical properties of carbonaceous material composite particles (b) are measured according to the methods described in natural graphite particles (a) unless otherwise specified.

(I) DBP (dibutyl phthalate) oil absorption amount The carbonaceous material composite particles (b) of the present invention generally have a dibutyl phthalate oil absorption amount (hereinafter referred to as “DBP oil absorption amount”) of 0.31 mL / g or more and 0.85 mL. / G or less, preferably 0.42 mL / g or more, more preferably 0.45 mL / g or more, still more preferably 0.50 mL / g or more, and the upper limit is preferably 0.85 mL / g or less. Is 0.80 mL / g or less, more preferably 0.76 mL / g or less.
If the DBP oil absorption is less than this range, there will be less voids that can be infiltrated by the non-aqueous electrolyte solution, so lithium ion insertion / desorption will not be in time when rapid charge / discharge is performed, and lithium metal will be deposited accordingly. Cycle characteristics tend to deteriorate. On the other hand, if it is larger than this range, the binder is likely to be absorbed into the gap during electrode plate production, and accordingly, the electrode plate strength and initial efficiency tend to be reduced.

In addition, the measurement of DBP oil absorption amount can be performed in the following procedures using a measurement material.
The measurement of DBP oil absorption is based on the viscosity of JIS K6217 standard, 40 g of measurement material is added, the dropping speed is 4 ml / min, the rotation speed is 125 rpm, and the measurement is performed until the maximum value of torque is confirmed. It is defined by a value calculated from the amount of dropped oil when a torque of 70% of the maximum torque is shown in a range in which the maximum torque is shown.

(Ii) BET specific surface area The specific surface area of the carbonaceous material composite particles (b) of the present invention is a value of the specific surface area measured using the BET method, and is usually 0.5 m ² · g ⁻¹ or more and 6.5 m ^2. g ^-1 or less, preferably 1.0 m ² · g ^-1 or more, more preferably 1.3 m ² · g ^-1 or more, particularly preferably 1.5 m ² · g ^-1 or more, and usually 6.5m against ² · ^{g -1} or less, preferably 6.0 m ² · ^{g -1} or less, more preferably 5.5 m ² · ^{g -1} or less, particularly preferably 5.0 m ² · ^{g -1} or less It is.
When the value of the specific surface area is less than this range, the lithium ion acceptability tends to deteriorate during charging when used as a negative electrode material, lithium metal tends to precipitate on the electrode surface, and the cycle characteristics tend to deteriorate. On the other hand, if it exceeds this range, when used as a negative electrode material, the reactivity with the non-aqueous electrolyte increases, the initial charge / discharge efficiency tends to decrease, and a preferable battery is difficult to obtain.

(Iii) Raman R value, Raman half-value width The Raman R value of the particles composed of the carbonaceous material composite particle (b) of the present invention is a value measured using an argon ion laser Raman spectrum method, and is usually 0.03 or more and 0. .19 or less, preferably 0.05 or more, more preferably 0.07 or more, and usually 0.19 or less, preferably 0.18 or less, more preferably 0.16 or less, particularly Preferably it is 0.14 or less.

When the Raman R value is lower than the above range, the crystallinity of the particle surface becomes too high, and there are cases where the number of sites where lithium ions enter between the layers becomes smaller along with charge / discharge. That is, the charge acceptance may be reduced and the cycle characteristics may be deteriorated. In addition, when the negative electrode is densified by applying it to the current collector and then pressing it, the crystals are likely to be oriented in a direction parallel to the electrode plate, which may lead to a decrease in load characteristics. On the other hand, when the above range is exceeded, the crystallinity of the particle surface is lowered, the reactivity with the non-aqueous electrolyte is increased, and the initial efficiency may be lowered and the gas generation may be increased.

(Iv) Surface functional group amount O / C
As for the surface functional group amount O / C of the carbonaceous material composite particles (b) of the present invention, the value of O / C represented by the following formula 2 is usually 0.1% or more, preferably 0.2% or more, more preferably Is 0.3% or more, particularly preferably 0.5 or more, and is usually 2.2% or less, preferably 2.0% or less, and more preferably 1.8% or less. If the surface functional group amount O / C is too small, the reactivity with the electrolytic solution is poor, and stable SEI formation cannot be performed, and the cycle characteristics may be deteriorated. On the other hand, if the surface functional group amount O / C is too large, the crystal on the particle surface is disturbed, the reactivity with the electrolytic solution is increased, and there is a risk of increasing the irreversible capacity and increasing gas generation.

Formula 2
O / C (%) = {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 surface functional group amount O / C in the present invention can be measured using X-ray photoelectron spectroscopy (XPS).
The surface functional group amount O / C is measured by using an X-ray photoelectron spectrometer as an X-ray photoelectron spectroscopy measurement, placing the object to be measured on a sample stage so that the surface is flat, and using Kα rays of aluminum as an X-ray source. The spectra of C1s (280 to 300 eV) and O1s (525 to 545 eV) are measured by plex measurement. The obtained C1s peak top is corrected to be 284.3 eV, the peak areas of the C1s and O1s spectra are obtained, and the device sensitivity coefficient is multiplied to calculate the surface atomic concentrations of C and O, respectively. The obtained O / C atomic concentration ratio O / C (O atomic concentration / C atomic concentration) is defined as the surface functional group amount O / C of the negative electrode material.

(V) Tap density The tap density of the carbonaceous material composite particles (b) of the present invention is usually 0.7 g · cm ⁻³ or more, preferably 0.8 g · cm ⁻³ or more, more preferably 0.9 g · cm ^{−. 3} or more, usually 1.25 g · cm ⁻³ or less, preferably 1.2 g · cm ⁻³ or less, more preferably 1.18 g · cm ⁻³ or less, particularly preferably 1.15 g · cm ^−3. It is as follows.
In particular, it is preferably 0.7 g · cm ⁻³ or more and 1.2 g · cm ⁻³ or less.
When the tap density is below the above range, the packing density is difficult to increase when used as a negative electrode, and a high-capacity battery may not be obtained. On the other hand, when the above range is exceeded, there are too few voids between particles in the electrode, it is difficult to ensure conductivity between the particles, and it may be difficult to obtain preferable battery characteristics.

(Vi) Average particle diameter d50
The volume-based average particle diameter of the carbonaceous material composite particles (b) of the present invention is such that the volume-based average particle diameter d50 (median diameter) determined by the laser diffraction / scattering method is usually 1 μm or more, preferably 3 μm or more, more preferably. Is 5 μm or more, particularly preferably 7 μm or more, and is usually 100 μm or less, preferably 50 μm or less, more preferably 40 μm or less, particularly preferably 30 μm or less.
If the average particle size d50 is too small, the irreversible capacity may increase, leading to loss of initial battery capacity. On the other hand, if it is too large, it tends to be a non-uniform coating surface when an electrode is produced by coating, which may be undesirable in the battery production process.

(Vii) X-ray parameter The crystallite size (Lc) in the c-axis direction and the crystallite size in the a-axis direction of the carbonaceous material obtained by X-ray diffraction of the carbonaceous material composite particles (b) of the present invention by the Gakushin method. (La) is preferably 30 nm or more, and more preferably 100 nm or more. If the crystallite size is in this range, the amount of lithium that can be charged in the negative electrode material is increased, and a high capacity is easily obtained, which is preferable.

(Viii) Orientation ratio The orientation ratio of the carbonaceous material composite particles (b) of the present invention is usually 0.005 or more, preferably 0.01 or more, more preferably 0.015 or more, and usually 0. .67 or less, preferably 0.5 or less, more preferably 0.4 or less.
When the orientation ratio is below the above range, the high-density charge / discharge characteristics tend to be reduced. In addition, the normal upper limit of the said range is a theoretical upper limit of the orientation ratio of a carbonaceous material.

(2) Form and structure of carbonaceous material composite particles (b) The form of the particles composed of the carbonaceous material composite particles (b) of the present invention is not particularly limited, but may be spherical, elliptical, massive, plate-like, polygonal, etc. Among them, a spherical shape, an elliptical shape, a lump shape, and a polygonal shape are preferable because the particle filling property can be improved when the negative electrode is used.

Further, the carbonaceous material composite particles (b) satisfy the above-described physical properties, and are not particularly limited as long as the carbonaceous material is composited. Specific examples thereof include graphite particles having a carbon layer.
Graphite particles are, for example, naturally produced graphite in the form of scales, lumps or plates, and artificial graphite produced by heating petroleum coke, coal pitch coke, coal needle coke, mesophase pitch, etc. to 2500 ° C. or higher. It is possible to use spheroidized graphite particles formed into particles by applying a crystallization treatment. Among these, spheroidized natural graphite is particularly preferable.
Examples of the carbon layer include those made of amorphous carbon or graphite. The form of the graphite particles provided with the carbon layer is preferably a graphite (carbonaceous material-coated graphite) structure coated with a carbonaceous material, and is coated with amorphous carbon-coated graphite particles and graphite material. Graphite particles are more preferable, and graphite particles coated with a graphite material are particularly preferable from the viewpoint that the particle surface that is an interface with the electrolytic solution can be efficiently modified.
“Coated with a carbonaceous material” can be expressed as “a carbon layer is provided on at least a part of the surface”, and the carbon layer covers not only a part or all of the surface of the graphite particles in a layered manner, It includes a form in which the carbon layer adheres or adheres to part or all of the surface. The carbon layer may be provided so as to cover the entire surface, or a part of the carbon layer may be covered or attached / attached.

(3) Production method of carbonaceous material composite particles (b) The carbonaceous material composite particles (b) may be produced by any production method as long as they have the above properties. It can be obtained by referring to the production methods described in 2007-042611 and International Publication No. 2006-025377.

Specifically, the carbon material described in the natural graphite particles (a) described above can be used as a raw material. Among these, for example, naturally produced graphite in scale-like, scale-like, plate-like and massive shapes, and artificial graphite produced by heating petroleum coke, coal pitch coke, coal needle coke and mesophase pitch at 2500 ° C. or more. The spherical graphite particles produced by applying the mechanical energy treatment as described above are preferably used as raw materials. Furthermore, the use of graphite particles that have been roughened by applying mechanical energy to the spheroidized graphite particles (formed with irregularities) as raw materials increases the packing density of the particles by reducing internal voids. Further, it is more preferable in that it is difficult to align in the electrode.

When the carbonaceous material composite particles (b) are graphite particles coated with a graphite material, the carbonaceous material-coated graphite particles are added to the spheroidized graphite particles, petroleum-based and coal-based tars and pitches, polyvinyl alcohol, By mixing a resin such as acrylonitrile, phenolic resin and cellulose with a solvent if necessary, and firing in a non-oxidizing atmosphere, preferably 1500 ° C. or higher, more preferably 1800 ° C., particularly preferably 2000 ° C. or higher. can get. After the firing, pulverization classification may be performed as necessary.

The coverage indicating the amount of graphitic carbon covering the spheroidized graphite particles is preferably in the range of 0.1 to 50%, more preferably in the range of 0.5 to 30%. A range of ˜20% is particularly preferred.
By reducing the coverage to 0.1% or more, the effect of reducing the irreversible capacity by coating with graphitic carbon, that is, the irreversible generated by coating the irreversible capacity of the spheroidized graphite particles as the core with graphite carbon The capacity reduction effect can be fully utilized.
Further, by setting the coverage to 50% or less, it is performed to restore the particles bound after the firing by preventing the binding force between the particles due to the coated graphitic carbon after firing becoming too strong. In the pulverization step, operations such as increasing the number of pulverization rotations or multistage pulverization can be eliminated. Further, by setting the coverage to 50% or less, the binding force between the particles of the coated graphitic carbon is strengthened, thereby preventing an increase in irreversible capacity due to an increase in the BET specific surface area of the graphite carbon-coated graphite particles. Can do.

<Carbon material for non-aqueous secondary batteries>
The carbon material for a non-aqueous secondary battery according to the present invention is a mixture containing at least natural graphite particles (a) and carbonaceous material composite particles (b). Moreover, the negative electrode material of the present invention exhibits the effects of the present invention by appropriately selecting the natural graphite particles (a) and the carbonaceous material composite particles (b) under the specific conditions described above, regardless of the production method, and mixing them. can do.

(1) Method of mixing natural graphite particles (a) and carbonaceous material composite particles (b) The apparatus used for mixing with natural graphite particles (a) and carbonaceous material composite particles (b) is not particularly limited. In the case of a rotary mixer, a cylindrical mixer, a twin cylindrical mixer, a double cone mixer, a regular cubic mixer, a vertical mixer; in the case of a fixed mixer, a spiral mixer, Ribbon type mixers, Muller type mixers, Helical Flight type mixers, Pugmill type mixers, fluidized type mixers, and the like can be used.

(2) Mixing ratio of natural graphite particles (a) and carbonaceous material composite particles (b) The negative electrode material of the present invention is a mixed carbon material containing the above natural graphite particles (a) and carbonaceous material composite particles (b). . In the negative electrode material of the present invention, the ratio of the natural graphite particles (a) to the total amount of the natural graphite particles (a) and the carbonaceous material composite particles (b) (mass ratio (a) / ((a) + (b))) is And usually 0.1 or more and 0.9 or less, preferably 0.2 or more, more preferably 0.3 or more, and usually 0.9 or less, preferably 0.8 or less, more preferably 0. 7 or less, more preferably 0.6 or less.

When the ratio of the natural graphite particles (a) to the total amount of the natural graphite particles (a) and the carbonaceous material composite particles (b) is too large, it is difficult to prevent an increase in irreversible capacity. In addition, if the proportion of the natural graphite particles (a) is too small, there is a tendency that the cycle characteristics, which are particularly excellent characteristics of the natural graphite particles (a), cannot be fully utilized, and the carbon for non-aqueous secondary batteries is apt to be obtained. It tends to be difficult to obtain better cycle characteristics as a material.

(3) Physical properties of non-aqueous secondary battery carbon material The non-aqueous secondary battery carbon material according to the present invention includes at least natural graphite particles (a) and carbonaceous material composite particles (b). However, typical physical property values thereof are shown below.
(I) BET specific surface area of the non-aqueous secondary battery carbon material having a specific surface area of the present invention according to the BET method is preferably usually ^{10 m} 2 / g or less, and more preferably less ^7m 2 / g . Further, it is preferably ^2m 2 / g or more, more preferably ^3m 2 / g or more.
If the specific surface area of the carbon material for a non-aqueous secondary battery of the present invention is too large, it tends to be difficult to prevent a decrease in capacity due to an increase in irreversible capacity. On the other hand, if the specific surface area is too small, the contact area between the electrolytic solution and the negative electrode material becomes small, so that sufficient charge / discharge load characteristics tend not to be obtained.

(Ii) (002) plane spacing (d ₀₀₂ )
The interplanar spacing (d ₀₀₂ ) of the (002) plane of the carbon material for a non-aqueous secondary battery of the present invention by X-ray wide angle diffraction method is usually 3.37 mm or less, preferably 3.36 mm or less. The crystallite size Lc is usually 900 mm or more, preferably 950 mm or more. If the face spacing (d ₀₀₂ ) of the (002) plane is too large, the crystallinity of most parts excluding the surface of the carbon material particles will be low, and the irreversible capacity as seen in the amorphous carbon material will be large. There is a tendency to see a decrease in capacity. If the crystallite size Lc is too small, the crystallinity tends to be low.

(Iii) Tap density The tap density of the carbon material for a non-aqueous secondary battery of the present invention is usually 1.2 g / cm ³ or less, preferably 1.1 g / cm ³ or less, more preferably 1.0 g / cm ³ or less. It is. Moreover, it is 0.8 g / cm ³ or more, preferably 0.9 g / cm ³ or more.
When the tap density of the negative electrode material is too large, there is a tendency that it is difficult to take contact between particles when an electrode is formed. On the other hand, if the tap density is too small, the slurry characteristics when the electrode is produced deteriorates, and the production of the electrode tends to be difficult.

(Iv) 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 non-aqueous secondary battery carbon material for the Raman R value present invention is usually 0. 001 or more, preferably 0.005 or more, more preferably 0.01 or more, and usually 0.7 or less, preferably 0.6 or less, more preferably 0.5 or less.
If the Raman R value is too small, 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, and the load characteristics may be deteriorated. On the other hand, if the Raman R value is too large, the crystal on the particle surface is disturbed, the reactivity with the electrolytic solution increases, and the charge / discharge efficiency tends to decrease and the gas generation tends to increase.

(V) Aspect ratio The aspect ratio of the carbon material for a non-aqueous secondary battery of the present invention is usually 15 or less, preferably 10 or less, more preferably 5 or less. When the aspect ratio is too large, there is a tendency to be oriented when the electrode is formed.

(Vi) Average particle diameter The average particle diameter (d50) of the carbon material for non-aqueous secondary batteries of the present invention is usually 5 μm or more, preferably 10 μm or more, more preferably 15 μm or more, and usually 35 μm or less, preferably 30 μm. Hereinafter, it is more preferably 25 μm or less. If the average particle size is too small, the specific surface area tends to be large and it is difficult to prevent an increase in irreversible capacity. Moreover, when an average particle diameter is too large, it will become difficult to prevent the rapid charge / discharge property fall by the contact area of electrolyte solution and carbonaceous material composite particle (b) reducing.

<Negative electrode>
In order to produce a negative electrode using the negative electrode material of the present invention, a negative electrode material blended with a binder resin is made into a slurry with an aqueous or organic medium, and if necessary, a thickener is added to the current collector. What is necessary is just to apply | coat and dry.
As the binder resin, it is preferable to use a resin that is stable with respect to the non-aqueous electrolyte and water-insoluble. For example, rubbery polymers such as styrene, butadiene rubber, isoprene rubber and ethylene / propylene rubber; synthetic resins such as polyethylene, polypropylene, polyethylene terephthalate and aromatic polyamide; styrene / butadiene / styrene block copolymers and hydrogenated products thereof , Thermoplastic elastomers such as styrene / ethylene / butadiene, styrene copolymers, styrene / isoprene and styrene block copolymers and hydrides thereof; syndiotactic-1,2-polybutadiene, ethylene / vinyl acetate copolymers, and Soft resinous polymers such as copolymers of ethylene and α-olefins having 3 to 12 carbon atoms; polytetrafluoroethylene / ethylene copolymers, polyvinylidene fluoride, polypentafluoropropylene and polyhexene And fluorinated polymers such as hexafluoropropylene may be used.
Examples of the organic medium include N-methylpyrrolidone and dimethylformamide.

The binding resin provides sufficient binding force between the negative electrode materials and between the negative electrode material and the current collector, and can prevent the battery capacity from being reduced and the recycling characteristics from deteriorating due to the separation of the negative electrode material from the negative electrode. It is usually preferable to use 0.1 parts by weight or more, preferably 0.2 parts by weight or more with respect to 100 parts by weight.
In addition, since the capacity of the negative electrode can be prevented, and problems such as preventing lithium ions from entering and leaving the negative electrode material can be prevented, the binder resin should be 10 parts by weight or less with respect to 100 parts by weight of the negative electrode material. Is preferable, and it is more preferable to set it as 7 weight part or less.

As the thickener added to the slurry of the negative electrode material and the binder resin, for example, water-soluble celluloses such as carboxymethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose, polyvinyl alcohol, polyethylene glycol, and the like may be used. Of these, carboxymethylcellulose is preferred. The thickener is preferably used in an amount of usually 0.1 to 10 parts by weight, preferably 0.2 to 7 parts by weight, with respect to 100 parts by weight of the negative electrode material. The strength tends to be difficult to maintain, and too much binder resin leads to a decrease in battery capacity and an increase in resistance.

As the negative electrode current collector, for example, copper, copper alloy, stainless steel, nickel, titanium, and carbon that are conventionally known to be usable for this purpose may be used. The shape of the current collector is usually a sheet, and those having irregularities on the surface thereof, or those using a net, punching metal, or the like are preferable.
After applying and drying the slurry of the negative electrode material and the binder resin to the current collector, pressurize to increase the density of the electrode formed on the current collector, thereby increasing the battery capacity per unit volume of the negative electrode layer Is preferred. The density of the electrode is usually 1.2 g / cm ³ or more, preferably 1.3 g / cm ³ or more, and usually 1.8 g / cm ³ or less, preferably 1.6 g / cm ³ or less.

If the density of the electrode is too small, it tends to be difficult to prevent a decrease in battery capacity accompanying an increase in electrode thickness. Also, if the electrode density is too large, the amount of electrolyte solution retained in the voids decreases as the interparticle voids in the electrode decrease, and it becomes difficult to prevent the rapid charge / discharge characteristics from being lowered due to the low mobility of Li ions. Tend.

[Non-aqueous secondary battery]
The non-aqueous secondary battery according to the present invention can be produced according to a conventional method except that the above negative electrode is used.
Examples of the positive electrode material include a lithium cobalt composite oxide having a basic composition represented by LiCoO ₂ ; a lithium nickel composite oxide represented by LiNiO ₂ ; a lithium manganese composite oxide represented by LiMnO ₂ and LiMn ₂ O ₄ . Lithium transition metal composite oxides such as, transition metal oxides such as manganese dioxide, and composite oxide mixtures thereof may be used.
Furthermore, TiS ₂ , FeS ₂ , Nb ₃ S ₄ , Mo ₃ S ₄ , CoS ₂ , V ₂ O ₅ , CrO ₃ , V ₃ O ₃ , FeO ₂ , GeO ₂ and LiNi _0.33 Mn _0.33 Co _{0 .33} O ₂ or the like can also be used.

A positive electrode can be produced by slurrying a mixture of the positive electrode material and a binder resin with an appropriate solvent, and applying and drying to a current collector. The slurry preferably contains a conductive material such as acetylene black and ketjen black. Moreover, you may contain a thickener as desired. As the thickener and the binder resin, those well-known in this application, for example, those exemplified as those used for producing the negative electrode may be used.

The blending ratio of the conductive agent with respect to 100 parts by weight of the positive electrode material is usually 0.2 parts by weight or more, preferably 0.5 parts by weight or more, more preferably 1 part by weight or more, and usually 20 parts by weight or less, preferably 15 parts by weight. Below, more preferably 10 parts by weight or less.
The blending ratio of the binder resin to 100 parts by weight of the positive electrode material is preferably 0.2 to 10 parts by weight, particularly preferably 0.5 to 7 parts by weight when the binder resin is slurried with water. When the binder resin is slurried with an organic solvent that dissolves the binder resin such as N-methylpyrrolidone, the amount is preferably 0.5 to 20 parts by weight, particularly 1 to 15 parts by weight.

Examples of the positive electrode current collector include aluminum, titanium, zirconium, hafnium, niobium and tantalum, and alloys thereof. Of these, aluminum, titanium and tantalum and alloys thereof are preferred, and aluminum and alloys thereof are most preferred.

As the electrolytic solution, a solution in which various lithium salts are dissolved in a conventionally known non-aqueous solvent can be used.
Examples of the non-aqueous solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate; chain carbonates such as dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; cyclic esters such as γ-butyrolactone; Cyclic ethers such as 2-methyltetrahydrofuran, tetrahydrofuran, 1,2-dimethyltetrahydrofuran and 1,3-dioxolane; chain ethers such as 1,2-dimethoxyethane may be used.
Usually some of these are used together. Among these, it is preferable to use a cyclic carbonate and a chain carbonate, or another solvent in combination with this.

Further, vinylene carbonate, vinyl ethylene carbonate, succinic anhydride, maleic anhydride, propane sultone, diethylsulfone, and other compounds such as difluorophosphate such as lithium difluorophosphate may be added to the electrolytic solution. Furthermore, an overcharge inhibitor such as diphenyl ether and cyclohexylbenzene may be added.

Examples of the electrolyte dissolved in the non-aqueous solvent include LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (CF ₃ CF ₂ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) _{3 and the} like can be used. The concentration of the electrolyte in the electrolytic solution is usually 0.5 to 2 mol / L, preferably 0.6 to 1.5 mol / L.

For the separator interposed between the positive electrode and the negative electrode, it is preferable to use a porous sheet or non-woven fabric of polyolefin such as polyethylene or polypropylene.
In the non-aqueous secondary battery according to the present invention, the capacity ratio of the negative electrode / positive electrode is preferably designed to be 1.01 to 1.5, and designing to 1.2 to 1.4 can suppress deterioration of the battery. To more preferable.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples.
[Physical property evaluation of negative electrode carbon material (carbon material)]
(1) Internal porosity The internal porosity of the natural graphite particles (a) was calculated by Hg porosimetry analysis. First, the measurement method of Hg porosimetry accurately weighs the powder, pretreats it under vacuum (50 μm / Hg × 10 minutes), and then uses a micromeritics autopore IV9520 type and pore distribution by mercury porosimetry. Was measured.

Based on the obtained pore distribution (integral curve) (L), the internal porosity is calculated by drawing a tangent line (M) with respect to the minimum value of the slope and calculating a branch point (P) between the tangent line and the integral curve. The pore volume smaller than that is determined and defined as the pore volume (V) in the particle (FIG. 2). The internal porosity was calculated from the amount of pores in the obtained particles and the true density of graphite. The true density of graphite used for the calculation was 2.26 g / cm ^3, which is the true density of general graphite. The calculation formula is shown in Formula 1.

(2) Diameter D / d50 for the recess
Of the irregularities on the surface of the natural graphite particles (a), the diameter (D) in the approximate circle for the concave portion was determined from the SEM image and the cross-sectional SEM image. The SEM image was measured using VE-7800 manufactured by Keyence Corporation at an acceleration voltage of 5 kV. Assuming that the concave portion of the SEM image of the obtained natural graphite particles (a) is a circle, a circle approximation is performed, and the diameter of the approximate circle is the diameter (D) of the concave portion of the natural graphite particles (a). . As an example, a circle approximate to the SEM image of the natural graphite particles (a) used in Example 1 and Comparative Example 3 is shown in FIG.
The average particle size (d50) of the natural graphite particles (a) was adjusted to 10 mL of a 0.2% by weight aqueous solution of polyoxyethylene sorbitan monolaurate (for example, Tween 20 (registered trademark)) as a surfactant. 01 g was suspended, introduced into a commercially available laser diffraction / scattering particle size distribution analyzer “LA-920 manufactured by HORIBA”, irradiated with 28 kHz ultrasonic waves at an output of 60 W for 1 minute, and then the volume-based median diameter in the measuring device Was measured as an average particle diameter (d50).

(3) Dibutyl phthalate (DBP) oil absorption The DBP oil absorption was measured as one of the physical properties of carbonaceous material-coated graphite particles in the carbonaceous material composite particles (b) of the present invention.

The DBP oil absorption was measured using the negative electrode material according to the following procedure.
The measurement of DBP oil absorption is based on the viscosity of JIS K6217 standard, 40 g of measurement material is added, the dropping speed is 4 ml / min, the rotation speed is 125 rpm, and the measurement is performed until the maximum value of torque is confirmed. It was defined by a value calculated from the amount of dropped oil when a torque of 70% of the maximum torque was shown in the range between showing the maximum torque.

(4) BET specific surface area (SA)
The specific surface area of the carbonaceous material composite particles (b) was measured by a BET one-point method using a specific surface area measuring device (AMS8000, manufactured by Okura Riken Co., Ltd.) by a nitrogen gas adsorption flow method. After filling the cell with 0.4 g of sample and heating to 350 ° C., pre-treatment, cooling to liquid nitrogen temperature, saturated adsorption of 30% nitrogen and 70% He gas, then heating to room temperature The amount of desorbed gas was measured, and the specific surface area was calculated from the obtained results by the usual BET method.

(5) Tap density The tap density of the carbonaceous material composite particles (b) is 1.6 cm in diameter and 20 cm ³ in volume capacity using a powder density measuring device (Tap Denser KYT-4000, manufactured by Seishin Enterprise Co., Ltd.). The sample was dropped into a cylindrical tap cell through a sieve having an opening of 300 μm, and the cell was fully filled, and then the volume and the weight of the sample after 1000 taps with a stroke length of 10 mm were obtained.

(6) Raman R value Using a laser Raman spectrophotometer (NR-1800, manufactured by JASCO Corp.), the sample is naturally dropped into the measurement cell to fill the sample, and the measurement cell is irradiated with argon ion laser light. The carbonaceous material composite particles (b) were measured under the following conditions while rotating the measurement cell in a plane perpendicular to the argon ion laser beam.

Argon ion laser light wavelength: 514.5 nm
Laser power on sample: 25 mW
Resolution: 4cm ^-1
Measurement range: 1100 cm ⁻¹ to 1730 cm ⁻¹
Peak intensity measurement, peak half-width measurement: background processing, smoothing processing (convolution 5 points by simple averaging)
The Raman R value is the maximum peak _P A (G band) and 1358cm ^-1 near the maximum peak _P B (D band) and the ratio of the peak intensity I of around 1580 cm ^-1, ie defined in _I B / _{I A} ( F. Tuinstra, JL Koenig, J. Chem. Phys, 53, 1126 [1970]).

[Preparation of negative electrode sheet]
Using the obtained negative electrode carbon material containing natural graphite particles (a) and carbonaceous material composite particles (b), an electrode plate having an active material layer having an active material layer density of 1.75 ± 0.03 g / cm ³ is produced. did.
Specifically, 20.00 ± 0.02 g (in terms of solid content) of a 1% by mass carboxymethylcellulose Na salt (Serogen 4H, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was added to 20.00 ± 0.02 g of the negative electrode carbon material. 0.200 g), and 0.5 ± 0.02 g (0.1 g in terms of solid content) of a styrene-butadiene rubber aqueous dispersion (BM400B, manufactured by Nippon Zeon Co., Ltd.) having a weight average molecular weight of 270,000, using a hybrid mixer manufactured by Keyence. The mixture was stirred for 5 minutes and defoamed for 30 seconds to obtain a slurry.
The slurry is applied to a width of 5 cm by a doctor blade method so that the negative electrode material adheres to 12.8 ± 0.2 mg / cm ² on a 18 μm-thick copper foil as a current collector, and air-dried at room temperature. Went. Furthermore, after drying at 110 degreeC for 30 minutes, it roll-pressed using the roller with a diameter of 20 cm, and it adjusted so that the density of an active material layer might be 1.75 g / cm < ³ >, and obtained the negative electrode sheet.

[Evaluation of negative electrode sheet]
The initial capacity and cycle retention of the negative electrode sheet produced by the above method were measured by the following methods. The results are shown in Table 1.

(1) Method for Producing Laminate Battery The negative electrode sheet produced by the above method was cut into a 6 cm × 4 cm rectangle to form a negative electrode, and a positive electrode made of LiCoO ₂ was cut out with the same area and combined. Electrolysis in which LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate so as to be 1.2 mol / L between the negative electrode and the positive electrode, and 2% by volume of vinylene carbonate was further added as an additive. A separator (made of a porous polyethylene film) impregnated with the liquid was placed to prepare a laminate type battery. The cell was produced in a dry box adjusted to a moisture value of 20 ppm or less.

The laminate type battery produced by the above method was left for 12 hours, and then charged at a current density of 0.2 CmA / cm ³ until the potential difference between both electrodes reached 4.1 V, and then until the voltage became 3 V. Discharge was performed at 2 CmA / cm ³ . This was repeated twice and further charged with the same current value until the potential difference between both electrodes reached 4.2 V, discharged to 3.0 V, and conditioned.

(2) Measuring method of cycle maintenance rate The laminate type battery produced by the method described later was repeatedly charged to 4.2V at 0.8C and discharged to 3.0V at 0.5C. The discharge capacity at the first cycle was set as the initial capacity. The discharge capacity at the 200th cycle with respect to the initial capacity × 100 was defined as the cycle maintenance ratio (%).

(3) Rate characteristic measurement method 1C / 0.2C discharge rate (%) is the battery before the start of the cycle when charged to 4.2V at 0.5C and subsequently discharged to 3.0V at 0.2C. It calculated from the ratio of the discharge capacity when charging to 4.2 V at 0.5 C and then discharging to 3.0 V at 1 C with respect to the discharge capacity.

-Preparation method of natural graphite particles (a) Spherical graphite was processed using a hydrostatic pressure powder molding apparatus manufactured by Nippon R & D Co., Ltd. Spherical graphite was filled in a rubber container and pressurized with oil. The conditions were a pressure of 1000 or 300 kgf / cm ² and a pressure time of 5 minutes to obtain a molded product. The obtained molded product was pulverized with a hammer mill until the particle size became equal to the original spheroidized graphite to obtain natural graphite particles (a).

The internal porosity and the diameter (D) of the concave portion of the obtained natural graphite particles (a) were measured by the above methods. Table 1 summarizes the values of the internal porosity and the diameter (D) / d50 of the concave portion.

-Preparation method of carbonaceous material composite particles (b) Spherical natural graphite having a volume-based average particle diameter of 17 μm was used as the raw material graphite. As a roughening step, raw material graphite was pulverized with a kryptron orb manufactured by Earth Technica Co., Ltd. at a rotational speed of 6900 rpm, and a kneader was used at a ratio of 30 parts by weight of the organic material pitch to 100 parts by weight of roughened graphite. And mixed. After the resulting mixture was molded, it was fired and carbonized at 1000 ° C. in an inert atmosphere, and further graphitized at 3000 ° C. The obtained graphite-coated graphite was roughly crushed and pulverized to obtain a powder sample of carbonaceous material composite particles (b). Table 1 summarizes the results of physical property evaluation (oil absorption amount, specific surface area, Raman R value, and tap density) of the obtained carbonaceous material-coated graphite.

(Examples 1 to 4)
Natural graphite particles (a) and graphitic material-coated graphite roughened as carbonaceous material-coated graphite as carbonaceous material composite particles (b) were mixed at a mass ratio (a) / (a + b) shown in Table 1. A negative electrode was produced using the obtained carbon material, a laminate type battery was produced by the above method, and a 200 cycle maintenance factor was calculated from the initial discharge capacity and the discharge capacity at the 200th cycle.
In addition, after charging to 4.2 V at 0.5 C, the discharge rate characteristics were examined by the ratio of the discharge capacity at 1 C to 0.5 C after charging to 4.2 V at 0.5 C to the discharge capacity at 0.2 C discharge rate. It was.
The results are shown in Table 1.

(Comparative Examples 1 to 4)
The same method as in Example 1, except that the natural graphite particles (a) having the characteristics described in Table 1 and the carbonaceous material composite particles (b) were mixed at a mass ratio described in Table 1 to obtain a carbon material. Electrodes were prepared and various measurements were performed (Comparative Examples 1 to 3). In addition, using the carbonaceous material composite particles (b) alone, electrodes were prepared in the same manner as in Example 1 and various measurements were performed (Comparative Example 4). The results are shown in Table 1.

As can be seen from the above Examples and Comparative Examples, the cycle retention rate is improved while maintaining the initial capacity by mixing the natural graphite particles (a) and the carbonaceous material composite particles (b) in Examples 1 to 4. Was noticeable.
Particularly in Examples 1 to 3 and Comparative Example 4, the mixture of natural graphite particles (a) and carbonaceous material composite particles (b) is very high regardless of the mass ratio of (a) and (b). It was found that cycle characteristics can be obtained.
Moreover, from the results of Examples 1 and 4 and Comparative Example 1, the cycle characteristics were significantly improved by subjecting the natural graphite particles (a) to pressure treatment to lower the internal porosity. The internal porosity can be controlled by the pressure applied during the pressure treatment, but the cycle characteristics improved even when the internal porosity was reduced from 25% to 20% when not treated.
As described above, the lithium ion secondary battery using the carbon material for a non-aqueous secondary battery according to the present invention as an electrode improves the cycle characteristics while maintaining high initial discharge capacity and discharge rate characteristics. The properties can be balanced. These characteristics are achieved for the first time by mixing the natural graphite particles (a) and the carbonaceous material composite particles (b) in the present invention.

Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.
This application is based on a Japanese patent application filed on March 30, 2011 (Japanese Patent Application No. 2011-075483), the contents of which are incorporated herein by reference.

The carbon material according to the present invention is used as a carbon material for a non-aqueous secondary battery, thereby maintaining a high initial capacity and a high rate characteristic, and a non-aqueous secondary battery excellent in cycle characteristics, particularly a lithium ion secondary battery. Can be provided.

D: Diameter of approximate circle in concave and convex portions formed on the surface of natural graphite particles (a) L: Pore distribution (integral curve) in Hg porosimetry measurement
M: tangent to the minimum value portion of the slope of the integral curve in the Hg porosimetry measurement P: branch point of the integral curve and the tangent line in the Hg porosimetry measurement V: amount of pores in the particle in the Hg porosimetry measurement

Claims

Contains natural graphite particles (a) having an internal porosity of 1% or more and 20% or less and carbonaceous material composite particles (b) having a dibutyl phthalate oil absorption of 0.31 mL / g or more and 0.85 mL / g or less. Carbon material for non-aqueous secondary batteries.
The carbon material for a non-aqueous secondary battery according to claim 1, wherein the carbonaceous material composite particles (b) are carbonaceous material-coated graphite particles.
The natural graphite particles (a) have irregularities on the surface, and the diameter (D) of the irregularities of the irregularities is 0.15 times the average particle diameter (d50) of the natural graphite particles (a). The carbon material for a non-aqueous secondary battery according to claim 1 or 2, wherein the carbon material is 7 times or less.
The carbonaceous material composite particles (b) have a specific surface area of 0.5 m 2 / g or more and 6.5 m 2 / g or less, a Raman R value of 0.03 or more and 0.19 or less, and a tap density of 0.7 g / The carbon material for a non-aqueous secondary battery according to any one of claims 1 to 3, wherein the carbon material is cm 3 or more and 1.2 g / cm 3 or less.
The mass ratio ((a) / {(a) + (b)}) of the natural graphite particles (a) and the carbonaceous material composite particles (b) is 0.1 or more and 0.9 or less. 5. The carbon material for a non-aqueous secondary battery according to any one of 4 above.
6. A negative electrode for a non-aqueous secondary battery comprising a current collector and an active material layer formed on the current collector, wherein the active material layer is according to any one of claims 1 to 5. A negative electrode for a non-aqueous secondary battery, comprising a carbon material for a non-aqueous secondary battery.
A non-aqueous secondary battery comprising a positive electrode and a negative electrode, and an electrolyte, wherein the negative electrode is a negative electrode for a non-aqueous secondary battery according to claim 6.