KR101952464B1 - Carbon material and negative electrode for nonaqueous secondary battery and nonaqueous secondary battery - Google Patents

Abstract

An object of the present invention is to provide a non-aqueous secondary battery excellent in cycle characteristics in addition to high initial capacity and rate characteristics, and particularly to a carbon material for a non-aqueous secondary battery for producing a lithium ion secondary battery. The present invention relates to a non-aqueous secondary battery containing carbonaceous composite particles (b) having a natural graphite particle (a) having an internal porosity of 1% or more and 20% or less and a carbonaceous composite particle (b) having a dibutyl phthalate oil absorption of 0.31 ml / g or more and 0.85 ml / .

Description

TECHNICAL FIELD [0001] The present invention relates to a carbon material for a non-aqueous secondary battery, a carbon material for the non-aqueous secondary battery, a negative electrode, and a non-aqueous secondary battery,

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

2. Description of the Related Art In recent years, with the miniaturization of electronic devices, there has been an increasing demand for secondary batteries of high capacity. Particularly, lithium ion secondary batteries having higher energy density and excellent high current charging / discharging characteristics are attracting attention as compared with nickel-cadmium batteries and nickel-hydrogen batteries.

It is known to use graphite as a carbon material of 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, it is possible to obtain a capacity close to 372 mAh / g, which is the theoretical capacity of lithium ion storage of graphite, Is known.

Thus, in Patent Document 1, as a negative electrode material, a carbon material subjected to spheroidization treatment by using mechanical energy treatment has been proposed. In Patent Document 2, graphite-forming aggregates or graphite-graphitizable binders are added with graphite catalyst in an amount of 1 to 50 mass%, mixed and calcined and graphitized at a temperature of 2000 ° C or higher so that the graphitization catalyst is removed Crushed carbon materials have been proposed. Patent Document 3 proposes a carbon material coated with graphite in the spheroidizing graphite.

However, in the above-mentioned carbon materials, the required characteristics such as the initial efficiency, the cycle characteristics, the load characteristics, and the like were not satisfactorily satisfactorily satisfactorily and the improvement was required.

As a method for satisfying the above-described required characteristics, Patent Document 4 discloses a method of isotropically pressurizing the spheroidal graphite (hereinafter sometimes referred to as " CIP processing "), CIP treatment is applied to the negative electrode material described in Patent Document 2.

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

However, according to the investigations of the present inventors, it has been found that, even when the carbon materials described in the above-mentioned Patent Documents 1 to 3 are used as the negative electrode material of the non-aqueous secondary battery, the high capacity, excellent cycle characteristics, There was room.

In addition, even if the carbon material described in Patent Document 4 is used as the negative electrode material of the non-aqueous secondary battery, since the graphite is simply subjected to the pressure treatment, the density of the electrode is high and the irreversible capacity becomes large. There is room for improvement in that it can not secure sediment. Patent Document 5 discloses a technique of performing isotropic pressing processing on an anode material. However, as in Patent Document 4, there is room for improvement in reducing irreversible capacity.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is an object of the present invention to provide a non-aqueous electrolyte secondary battery which suppresses the reaction between a surface of a carbonaceous material and a non-aqueous electrolyte, A nonaqueous secondary battery excellent in cycle characteristics and a carbonaceous material for producing a lithium ion secondary battery, and as a result, a nonaqueous secondary battery having a high capacity and excellent cycle characteristics, It is an object of the present invention to provide an ion secondary battery.

The inventors of the present invention have conducted intensive studies to solve the above problems. As a result, the inventors have found that two types of carbon materials, which are selected from a large number of carbon materials for an anode, have been selected so far and carbon materials containing them are used as non- The present inventors have found that a lithium ion secondary battery having both excellent cycle characteristics and initial capacity can be obtained unexpectedly, thereby completing the present invention.

That is, the gist of the present invention is shown in the following <1> to <7>.

(1) A carbon material for a non-aqueous secondary battery, comprising (a) natural graphite particles having an internal porosity of 1% or more and 20% or less and carbonaceous composite particles (b) having a dibasic phthalate oil absorption of 0.31 ml / g or more and 0.85 ml / .

<2> The carbonaceous material for a non-aqueous secondary battery according to <1>, wherein the carbonaceous particulate composite particle (b) is carbon dioxide-coated graphite.

(3) The natural graphite particle (a) has unevenness on its surface, and the diameter (D) of the recessed portion of the unevenness is 0.15 times or more and 7 times Or less based on the total weight of the non-aqueous secondary battery.

Wherein the carbonaceous particulate composite particle (b) has 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 / cm 3 or more and 1.2 g / The carbon material for a non-aqueous secondary battery according to any one of <1> to <3>.

<5> The method for producing a carbon black according to <1> to <4>, wherein the mass ratio (a) / {(a) + (b)}) of the natural graphite particles (a) A carbonaceous material for a non-aqueous secondary battery according to any one of claims 1 to 3.

<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 contains the carbonaceous material for a non-aqueous secondary battery according to any one of <1> to <5> Negative electrode for non - aqueous secondary battery.

<7> A nonaqueous secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode is a negative electrode for a nonaqueous secondary battery as described in <6> above.

By using the carbonaceous material for a non-aqueous secondary battery according to the present invention, it is possible to provide a non-aqueous secondary battery having excellent cycle characteristics and initial capacity.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a SEM photograph of a natural graphite particle (a) and a diagram showing the diameter (D) of an approximate circle of a concave surface on the surface of the natural graphite particle (a).
Fig. 2 is an explanatory view showing a method of calculating the internal void amount by the Hg capturing system measurement.

Hereinafter, the contents of the present invention will be described in detail. The description of the constituent elements of the invention described below is an example (representative example) of the embodiment of the present invention, and the present invention is not limited to these embodiments unless the gist of the present invention is deviated.

Here, &quot; weight% &quot; means &quot; mass% &quot; and &quot; weight portion &quot;

&Lt; Natural graphite particles (a) &gt;

In the present specification, the natural graphite particles (a) represent natural graphite particles (a) capable of intercalating and deintercalating lithium ions, and satisfy at least an internal porosity of 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 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, further preferably 7% or more. And is 20% or less, preferably 18% or less, more preferably 15% or less, further preferably 12% or less. If the internal porosity is too small, the amount of liquid in the particles tends to be low, and the charge / discharge characteristics tend to deteriorate. When the internal porosity is too large, there is a tendency that the diffusion of the electrolytic solution becomes insufficient, .

As shown in Fig. 2, for example, the internal porosity is determined by the tangent line M with respect to the minimum value of the slope on the basis of the pore distribution (integral curve) L obtained by the known Hg porosimetry measurement (mercury porosimetry) And the branch point P of the tangent line M and the integral curve L is obtained and the pore volume smaller than the branch point is defined as the amount of pores in the particle (cm 3 / g) (V). The internal porosity can be calculated from the obtained amount of pores in the particles and the true density of the graphite. The true density of graphite used for the calculation is 2.26 g / cm 3, which is the true density of graphite in general. The calculation formula is shown in Equation (1).

Equation 1

Internal porosity (%) = [amount of pores in particles / {amount of pores in particles + (1 / true density of graphite)}] x 100

(Ii) the ratio of the diameter (D) of the concave portion to the average particle diameter (d50) (diameter (D) / d50 of the concave portion)

The use of graphite particles (unevenness formed) subjected to surface roughening treatment by applying mechanical energy to natural graphite particles (a) reduces the internal porosity and increases the packing density of the particles, And is more preferable in that it becomes difficult.

(A) relative to d50 of the natural graphite particles (a), assuming that the concave portion of the surface of the natural graphite particles (a) is a circle and the diameter of the approximate circle is (D) The ratio of the diameter D of the concave portion (diameter (D) / d50 of the concave portion) is usually 0.15 times or more and 7 times or less. Preferably 0.2 times or more, and more preferably 0.3 times or more. The upper limit is usually 7 times or less, preferably 5 times or less, and more preferably 3 times or less.

(The diameter (D) / d50 of the concave portion) is too large, the particles tend to become flat and tend to be easily oriented in the direction parallel to the electrode when the electrode is used. When the ratio of the diameter (D / d50) of the concave portion of the natural graphite particles (a) is too small, the contactability between the particles becomes poor when the electrode is used, and sufficient cycle characteristics tend not to be obtained.

The diameter D of the concave portion of the natural graphite particles (a) is calculated using an SEM image.

The measurement method of the SEM image is, for example, measurement with an acceleration voltage of 5 kV using VE-7800 manufactured by Keyens Co., Ltd.

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 defined as the diameter (D) of the concave portion of the natural graphite particle (a). The diameter d of the concave portion (d) / d50 is calculated using d50 of the natural graphite particles (a) measured by the following measurement method.

An SEM image of the natural graphite particles (a) used in Example 1 and Comparative Example 3 as an example and a circle approximating a concave portion are shown in Fig.

The diameter D of the concave portion is usually 0.1 占 퐉 or more, preferably 1 占 퐉 or more, more preferably 5 占 퐉 or more, further preferably 10 占 퐉 or more and usually 100 占 퐉 or less, preferably 70 占 퐉 or less, More preferably 50 m or less, and further preferably 30 m or less. If the diameter D is excessively large, the concavo-convex shape becomes gentle so that it becomes flat and tends to be oriented parallel to the electrodes when used as an electrode. On the other hand, when the diameter D is too small, It tends to get worse.

The average particle diameter (d50) was 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, Was introduced into a laser diffraction / scattering type particle size distribution measuring apparatus &quot; HORIBA manufactured by LA-920 &quot;, and ultrasonic waves of 28 kHz were irradiated at 60 W for 1 minute and then measured as a median diameter based on volume in a measuring apparatus. .

The average particle size (d50) of the natural graphite particles (a) is usually 5 占 퐉 or more, preferably 10 占 퐉 or more, more preferably 15 占 퐉 or more and usually 40 占 퐉 or less, preferably 35 占 퐉 or less Preferably 30 mu m or less. If the average particle diameter is too small, the specific surface area becomes large and the irreversible capacity tends to be hard to be prevented from increasing. On the other hand, if the average particle diameter is too large, the contact area between the electrolyte solution and the carbonaceous particulate composite particles (b) is reduced, thereby making it difficult to prevent the rapid charge / discharge characteristics from being degraded.

(Iii) X-ray parameters

The crystallite size (Lc) in the c-axis direction and the crystallite size (La) in the a-axis direction of the natural graphite particles (a) obtained by X-ray diffraction of the natural graphite particles (a) And more preferably 100 nm or more. When the crystallite size is within this range, the amount of lithium that can be charged into the natural graphite particles (a) is increased, which is preferable because a high capacity can be easily obtained.

(Iv) Raman R value, Raman half width

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

When the Raman R value is too small, the crystallinity of the particle surface becomes excessively high, and the sites where Li ions enter the interlayer tends to decrease with charge and discharge. That is, the chargeability of water may be lowered. When the density of the negative electrode obtained by applying the active material layer containing the natural graphite particles (a) to the collector is increased, the crystal tends to be oriented in the direction parallel to the electrode plate, . When the Raman value R is 0.1 or more, a preferable coating film is formed on the surface of the negative electrode, thereby improving the storage characteristics, cycle characteristics, and load characteristics.

On the other hand, if the value of Raman R is too large, the crystallinity of the particle surface is lowered and the reactivity with the non-aqueous liquid electrolyte is increased, which tends to cause a decrease in charging / discharging efficiency and an increase in gas generation.

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 usually 100 cm ^-1 or less, preferably 80 cm ^-1 or less, more preferably 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 excessively high, and the sites where Li ions enter the interlayer tends to decrease with the charge and discharge. That is, the chargeability of water may be lowered. Further, when the density is increased by pressing the negative electrode obtained by applying the active material layer containing the natural graphite particles (a) to the current collector, the crystal tends to be oriented in the direction parallel to the electrode plate, .

On the other hand, if the Raman half-width is too large, the crystallinity of the particle surface is lowered, and the reactivity with the non-aqueous liquid electrolyte increases, thereby decreasing the charge-discharge efficiency and increasing the generation of gas.

The measurement of the Raman spectra can be performed by filling the sample in a measurement cell by dropping it in a measurement cell using a Raman spectroscope (for example, a Raman spectrometer manufactured by Nippon Bunko), irradiating the sample surface in the cell with argon ion laser light, And rotating it in a plane perpendicular to the light.

The intensity I _A of the peak P _{A in} the vicinity of 1580 cm ^-1 and the intensity I _B of the peak P _{B in} the vicinity of 1360 cm ^-1 were measured for the obtained Raman spectra and the intensity ratio R (R = I _B / I _A ) . The Raman R value calculated by this measurement is defined as the Raman R value of the negative electrode active material of the present invention. The half width of the peak P _{A in} the vicinity of 1580 cm ^-1 of the obtained spectrum is measured and defined as the half width of the negative electrode active material of the present invention.

The measurement conditions of the above-mentioned Raman spectrum are as follows.

· Argon ion laser wavelength: 514.5 nm

· Laser power on sample: 15 ~ 25 mW

Resolution: 10-20 cm ^-1

Measuring range: 1100 cm ^-1 to 1730 cm ^-1

· Raman R value, Raman half width analysis: Background processing · Smoothing processing (simple average, convolution 5 points)

(V) BET specific surface area

The BET specific surface area (SA) of the natural graphite particles (a) is a value of a specific surface area measured by the BET method, usually 0.1 m 2 · g ^-1 or more, preferably 0.7 m 2 · g ^-1 or more, 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 ㎡ · g ^-1 or less, particularly preferably 10 ㎡ · g ^-1 or less.

When the BET specific surface area is too small, the water solubility of lithium ions tends to deteriorate at the time of charging, and lithium tends to precipitate from the surface of the electrode, 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 liquid electrolyte is increased and the generation of gas tends to be increased, so that it tends to be difficult to obtain a preferable battery.

The specific surface area by the BET method can be measured by, for example, preliminary drying at 350 DEG C for 15 minutes under nitrogen flow to the sample using a surface area meter (automatic surface area measuring apparatus manufactured by Okura Riken Co., Ltd.) The nitrogen adsorption BET 1-point method by the gas flow method using the nitrogen helium mixed gas accurately adjusted so that the relative pressure value becomes 0.3. The specific surface area determined by this 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 at least 0.1 g · cm ^-3 , preferably at least 0.5 g · cm ^-3 , more preferably at least 0.7 g · cm ^-3 , particularly preferably at least 0.8 g · cm &lt; ^-3 &gt; and is usually not more than 2 g · cm ^-3 , preferably not more than 1.8 g · cm ^-3 , more preferably not more than 1.6 g · cm ^-3 .

If the tap density is too small, the charge density tends not to rise when the negative electrode is used, and it tends to be difficult to obtain a high capacity battery. On the other hand, if the tap density is excessively large, voids between the particles in the electrode become excessively small, and conductivity between particles tends to be hard to be secured, so that it is difficult to obtain desirable battery characteristics.

The tap density was measured by passing the sample through a sieve having an interval of 300 占 퐉 and dropping the sample into, for example, a 20 cm3 tapping cell to fill the sample up to the top surface of the cell, Tapping with a stroke length of 10 mm is performed 1000 times, and 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 powder 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 0.5 or less, more preferably 0.4 or less . If the orientation ratio is less than the above range, the high-speed charge / discharge characteristics tend to be lowered. A typical upper limit of 0.6 in the above range is the theoretical upper limit value of the orientation ratio of the carbonaceous material.

The orientation ratio is measured by X-ray diffraction measurement after press molding the sample. For example, 0.47 g of a sample was charged into a molding machine having a diameter of 17 mm, compressed to 58.8 MN · m ^-2 and a load of 600 kg, and the formed body was set to be flush with the surface of the sample holder for measurement using clay to obtain X Ray diffraction is measured. The ratio represented by {(110) diffraction peak intensity / (004) diffraction peak intensity} is calculated from the peak intensity of (110) diffraction and (004) diffraction of the obtained carbon. The orientation ratio calculated by this 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. Further, &quot; 2 &amp;thetas; &quot; indicates a diffraction angle.

· Target: Cu (Kα line) graphite monochrometer

Slit: divergence slit = 0.5 degree

         Receiving slit = 0.15 mm

         Scattering slit = 0.5 degree

· Measuring range, step angle and measuring time:

  (110) plane; 75 degrees ≤ 2θ ≤ 80 degrees, 1 degree / 60 seconds

  (004) plane; 52 degrees ≤ 2θ ≤ 57 degrees, 1 degree / 60 seconds

(2) The shape of the natural graphite particles (a)

As shown in Fig. 1, the natural graphite particles (a) in the present invention preferably have irregularities on their surfaces. The convex portion in the concavo-convex portion refers to a portion retaining the roundness of spheroidized graphite as it is, and the concave portion means a portion compressed by other graphite particles by a pressurizing treatment, preferably an isotropically pressurized CIP treatment do.

(3) Production method of natural graphite particles (a)

The method for producing the natural graphite particles (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 will be described below.

For example, the natural graphite particles (a) are preferably subjected to a step of pressurizing the raw natural graphite particles (pressing treatment).

Natural graphite particles (a) and natural graphite particles as raw materials

Natural graphite is commercially available and can theoretically have a high charging / discharging capacity of 372 mAh / g, and the effect of improving the charging / discharging characteristics at a high current density is remarkably larger than that of other negative electrode active materials Therefore, it is preferable.

As the natural graphite, it is preferable that the amount of impurities is small, and it is used after being subjected to various purification treatments as necessary. In addition, it is preferable that the degree of graphitization is large. Specifically, it is preferable that the plane interval (d ₀₀₂ ) of the (002) plane by the X-ray diffraction method is less than 3.37 Å (0.337 nm).

As the natural graphite, for example, scaly graphite or sphered graphite which has been highly purified can be used. Among them, spheroidal graphite subjected to sphering treatment is particularly preferable from the viewpoint of particle filling property and charge / discharge rate characteristic.

As the device used in the sphering process, for example, an apparatus for imparting mechanical action such as compression, friction, shear force and the like repeatedly to particles, including interaction of particles mainly with an impact force, can be used.

Specifically, there is a rotor having a plurality of blades installed in a casing. By rotating the rotor at a high speed, a mechanical action such as impact compression, friction, and shearing force is applied to the carbon material introduced into the casing, Is preferable. It is also preferable that a mechanism for repeating the mechanical action by circulating the carbon material is provided.

As a preferable apparatus, for example, a hybridization system (manufactured by Nara Machinery &amp; Manufacturing Co., Ltd.), Cryptron (manufactured by Earth Techica), CF mill (manufactured by Ube Kosan Co., Ltd.), a mechanofusion system (manufactured by Hosokawa Micron Co., Composer (manufactured by TOKUJI KABUSHIKI KAISHA), and the like. Of these, a hybridization system manufactured by Nara Machinery &amp;

For example, in the case of processing using the above-described apparatus, the main speed of the rotating rotor is preferably 30 to 100 m / sec, more preferably 40 to 100 m / sec, and most preferably 50 to 100 m / . In the spheroidizing treatment, it is possible to simply pass the carbonaceous material through the inside of the device. However, it is preferable to circulate or stay inside the device for 30 seconds or longer, and the inside of the device is circulated or stagnated for 1 minute or more More preferable.

· Process of molding natural graphite particles by pressurization (pressure treatment)

In this step, raw natural graphite particles are formed by pressurization. Preferably, pressure application (CIP) is performed isotropically. Further, it is preferable to pressurize the raw material natural graphite particles isotropically so that irregularities are formed on the surface of the graphite particles to uniformly reduce voids in the particles, thereby obtaining a predetermined internal porosity.

The method of molding by pressure treatment is not particularly limited, and it is preferable that the pressure is isotropically pressed by an hydrostatic press machine, a roll compactor, a roll press, a frying machine, and a tablet machine.

If necessary, the graphite particles may be molded simultaneously with the pressing under the pattern engraved on the roll. It is also possible to apply a method of evacuating air present between graphite particles and vacuum pressing.

The pressure for pressurizing the raw material natural graphite particles is not particularly limited, but is usually 50 kgf / cm2 or more, preferably 100 kgf / cm2 or more, more preferably 300 kgf / cm2 or more, still more preferably 500 Kgf / cm2 or more, particularly preferably 700 kgf / cm2 or more. The upper limit of the pressure treatment is not particularly limited, but it is usually 2000 kgf / cm 2 or lower, preferably 1800 kgf / cm 2 or lower, more preferably 1600 kgf / cm 2 or lower, still more preferably 1500 kgf / Or less.

If the pressure is too low, the amount of porosity in the particle and the formation of irregularities on the particle surface tends to become insufficient. When the pressure is too high, a useless force is required at the time of pulverization, There is a tendency that it can not be exercised sufficiently.

The pressing time is usually 1 minute or more, preferably 2 minutes or more, more preferably 3 minutes or more, further preferably 4 minutes or more. It is usually not more than 30 minutes, preferably not more than 25 minutes, more preferably not more than 20 minutes, more preferably not more than 15 minutes. If the time is excessively long, the productivity tends to remarkably decrease, and if the time is too short, the treatment tends not to be sufficiently performed.

If necessary, a step of crushing the natural graphite subjected to pressure treatment may be carried out. The shape thereof is arbitrary, but it is usually a granular shape having an average particle diameter (d50) of 2 to 50 μm. It is preferable to pulverize and classify the particles so that the average particle diameter becomes 5 to 35 μm, particularly 8 to 30 μm.

<Carbonaceous particulate composite (b)>

The carbonaceous particulate composite (b) is not particularly limited as long as it is a composite of carbonaceous substances, and is not particularly limited as long as the properties described below are satisfied.

(1) Physical properties of carbonaceous composite particles (b)

The method of measuring the physical properties of the carbonaceous particulate composite particle (b) is to be in accordance with the method described in the natural graphite particles (a), unless otherwise specified.

(I) DBP (dibutyl phthalate) oil absorption

The dibutyl phthalate oil absorption amount (hereinafter referred to as "DBP oil absorption amount") of the carbonaceous particulate composite particle (b) of the present invention is generally 0.31 ml / g or more and 0.85 ml / g or less, preferably 0.42 ml / G or more, more preferably 0.50 ml / g or more, and the upper limit is usually 0.80 ml / g or less, preferably 0.80 ml / g or less, more preferably 0.76 ml / g or less.

If the DBP oil absorption is less than this range, the voids in which the non-aqueous liquid electrolyte can penetrate are reduced, so that when the rapid charging / discharging is performed, the intercalation / deintercalation of lithium ions is delayed and lithium metal precipitates and the cycle characteristics deteriorate There is a tendency. On the other hand, if it is larger than this range, the binder tends to be absorbed into the voids during the production of the electrode plate, and accordingly, the strength of the electrode plate tends to decrease or the initial efficiency tends to decrease.

Further, the measurement of the DBP oil absorption can be carried out in the following order using the measurement material.

The measurement of the DBP oil absorption was carried out in accordance with the viscosity of JIS K 6217 standard until the maximum value of the torque was confirmed at a dropping rate of 4 ml / min and a rotation speed of 125 rpm, , And a value calculated from the dropping flow rate when a torque of 70% of the maximum torque is shown in the range from the start of measurement to the maximum torque.

(Ii) BET specific surface area

The specific surface area of the carbonaceous particulate composite particle (b) of the present invention is a value of a specific surface area measured by a BET method, and is usually from 0.5 m 2 · g ^-1 to 6.5 m 2 · g ^-1 , · g ^-1, and, more preferably at 1.3 ㎡ · g ^-1 or more, and particularly preferably not less than 1.5 ㎡ · g ^-1, again, typically 6.5 g · ㎡ about ^-1 or less, preferably 6.0 ㎡ · g ^-1 or less, more preferably 5.5 m 2 · g ^-1 or less, and particularly preferably 5.0 m 2 · g ^-1 or less.

If the value of the specific surface area is below this range, the water solubility of lithium ions tends to deteriorate at the time of charging in the case of being used as the negative electrode material, and lithium metal tends to precipitate from the electrode surface, and the cycle characteristic tends to deteriorate. On the other hand, when it exceeds this range, the reactivity with the nonaqueous electrolyte solution increases when used as a negative electrode material, and the initial charge-discharge efficiency tends to be lowered, making it difficult to obtain a preferable battery.

(Iii) Raman R value, Raman half width

The Raman R value of the particles composed of the carbonaceous particulate composite particle (b) of the present invention is a value measured using an argon ion laser lambs spectrum method, and is usually 0.03 or more and 0.19 or less, preferably 0.05 or more, 0.07 or more, and usually 0.19 or less, preferably 0.18 or less, more preferably 0.16 or less, particularly preferably 0.14 or less.

When the Raman R value is less than the above range, the crystallinity of the particle surface becomes excessively high, and the sites where the lithium ions enter the interlayer between the charge and discharge may be reduced. That is, there are cases where the chargeability is deteriorated and the cycle characteristics are deteriorated. In addition, when the negative electrode is densified by applying it to the current collector after pressing it, the crystal tends to be oriented in the direction parallel to the electrode plate, resulting in a decrease in load characteristics. On the other hand, if it exceeds the above range, the crystallinity of the particle surface is lowered and the reactivity with the non-aqueous liquid electrolyte is increased, which may cause the initial efficiency to be lowered and the gas generation to be increased.

(Iv) Surface functional group amount O / C

The surface functional group amount O / C of the carbon-carbon composite particle (b) of the present invention is usually 0.1% or more, preferably 0.2% or more, more preferably 0.3% or more, Particularly preferably not less than 0.5, and usually not more than 2.2%, preferably not more than 2.0%, more preferably not more than 1.8%. If the amount of the surface functional group O / C is too small, the reactivity with the electrolytic solution is insufficient, and stable SEI formation can not be carried out, thereby deteriorating the cycle characteristics. On the other hand, if the amount of the surface functional group O / C is excessively large, the crystal surface of the particles is disturbed and reactivity with the electrolyte increases, which may increase the irreversible capacity and increase the generation of gas.

Equation 2

O / C (%) = {O atom concentration determined based on the peak area of spectrum of O1s in the X-ray photoelectron spectroscopy (XPS) analysis / C atom obtained based on the peak area of spectrum of C1s in XPS analysis Concentration} x 100

The surface functional group amount O / C in the present invention can be measured by X-ray photoelectron spectroscopy (XPS).

The surface functional group amount O / C was measured by X-ray photoelectron spectroscopy using an X-ray photoelectron spectroscope, placing the object to be measured on the sample table so as to flatten the surface, using the Kα line of aluminum as an X-ray source, , C1s (280 to 300 eV) and O1s (525 to 545 eV) are measured. The peak height of the obtained C1s peak is adjusted to 284.3 eV, and the peak area of the spectrum of C1s and O1s is obtained. The peak atomic concentration of C and O is then calculated by multiplying the peak area by the device sensitivity coefficient. The atomic concentration ratio O / C (O atom concentration / C atom concentration) of O and C obtained is defined as the surface functional group amount O / C of the negative electrode material.

(V) Tap density

The tap density of the carbonaceous particulate composite particle (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, It is 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, and particularly preferably 1.15 g · cm ^-3 or less.

Among them, it is preferable that the thickness is 0.7 g · cm ^-3 or more and 1.2 g · cm ^-3 or less.

If the tap density is less than the above range, the charging density tends not to rise when used as a negative electrode, and a high capacity battery may not be obtained. On the other hand, if it exceeds the above range, the voids between the particles in the electrode become too small to secure the conductivity between the particles, which makes it difficult to obtain desirable battery characteristics.

(Vi) average particle diameter (d50)

The volume-based average particle diameter of the carbon-matter complex particles (b) of the present invention is preferably 1 mu m or more, more preferably 3 mu m or more, in terms of volume average d50 (median diameter) determined by laser diffraction / scattering method More preferably not less than 5 mu m, particularly preferably not less than 7 mu m, and usually not more than 100 mu m, preferably not more than 50 mu m, further preferably not more than 40 mu m, particularly preferably not more than 30 mu m.

If the average particle diameter (d50) is too small, the irreversible capacity increases and the initial battery capacity may be lost. On the other hand, if it is too large, it may be unfavorable in the manufacturing process of the battery because the electrode is likely to become uneven (coated) when it is produced by coating.

(Ⅶ) X-ray parameters

The crystallite size (Lc) in the c-axis direction and the crystallite size (La) in the a-axis direction of the carbonaceous material obtained by X-ray diffraction of the carbonaceous particulate composite particle (b) of the present invention are 30 nm or more More preferably 100 nm or more. When the crystallite size is within this range, the amount of lithium that can be charged into the negative electrode material increases, which is preferable because a high capacity can be easily obtained.

(Ⅷ) Orientation ratio

The orientation ratio of the powder of the carbonaceous particulate composite particle (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, Is not more than 0.4.

If the orientation ratio is less than the above range, the high-density charge-discharge characteristics tend to be lowered. Further, a typical upper limit of the above range is the theoretical upper limit value of the orientation ratio of the carbonaceous material.

(2) Form and structure of carbonaceous composite particle (b)

The shape of the particles composed of the carbonaceous particulate composite particle (b) of the present invention is not particularly limited, and examples thereof include spherical, oval, massive, plate, and polygonal shapes. Among them, spherical, oval, The filling property of the particles can be improved when the shape is a negative electrode.

The carbonaceous particulate composite particles (b) are not particularly limited as long as they satisfy the above-described physical properties and the carbonaceous material is complex, and specifically include graphite particles having a carbon layer.

The graphite particles can be produced, for example, on artificial graphite produced by heating natural graphite in the form of scales, masses or platelets, petroleum coke, coal pitch coke, coal needle coke and mesophase pitch at 2500 DEG C or higher, Spheroidized graphite particles formed into granules can be used by the treatment. Of these, spheroidized natural graphite is particularly preferable.

The carbon layer may be composed of amorphous carbon or graphite.

The shape of the graphite particles having a carbon layer is preferably a structure of graphite (carbonaceous coated graphite) coated with carbonaceous material, more preferably graphite particles coated with amorphous carbon or graphite particles coated with graphite , And graphite particles coated with graphite are particularly preferable because they can efficiently modify the particle surface, which is the interface with the electrolytic solution.

The term &quot; coated with carbonaceous material &quot; can also be expressed as &quot; having a carbon layer on at least a part of the surface &quot;, and not only the form in which the carbon layer covers part or all of the surface of the graphite particles in layers, But also includes a form that is attached to or adheres to a part or all of the body. The carbon layer may be provided so as to cover the entire surface, or may be partially covered or attached or adhered.

(3) Method for producing carbonaceous composite particles (b)

The carbonaceous particulate composite particle (b) may be produced by any production method as long as it has the above properties. For example, with reference to the production method described in Japanese Patent Application Laid-Open No. 2007-042611 or International Publication No. 2006-025377 .

Specifically, a carbon material described in the above-mentioned natural graphite particles (a) can be used as a raw material. Among them, for example, graphite produced in the form of scales, scales, plates and masses, and graphite produced by heating petroleum coke, coal pitch coke, coal needle coke and mesophase pitch at 2500 ° C or higher It is preferable to use spherical graphite particles prepared by applying mechanical energy treatment as described above to an artificial graphite as a raw material. Further, the use of graphite particles (irregularities formed) subjected to surface roughening treatment by applying mechanical energy to the spheroidized graphite particles as a raw material increases the filling density of the particles by reducing internal voids, Which is more preferable in view of difficulty.

When the carbonaceous particulate composite particles (b) are graphite particles coated with graphite, the graphite particles coated with carbonaceous substance are obtained by mixing petroleum and coal tar and pitch, and polyvinyl alcohol, polyacrylonitrile , Phenol resin and cellulose are mixed with a solvent or the like if necessary and the mixture is calcined in a non-oxidizing atmosphere at preferably 1,500 ° C or higher, more preferably 1,800 ° C or higher, particularly preferably 2,000 ° C or higher . After the calcination, the pulverization and classification may be carried out as necessary.

The coating ratio indicating the amount of graphitic carbon coating the spheroidized graphite particles is preferably in the range of 0.1 to 50%, more preferably in the range of 0.5 to 30%, and more preferably in the range of 1 to 20% Particularly preferred.

By setting the covering ratio to 0.1% or more, the effect of reducing irreversible capacity due to coating with graphite carbon, that is, the effect of reducing the irreversible capacity generated by covering the irreversible capacity of spherical graphite particles as nuclei with graphite carbon I can save enough.

In addition, by setting the coating ratio to 50% or less, it is possible to prevent the cohesive force between the particles due to the coated graphite carbon after firing from being excessively strengthened, so that in the pulverizing step carried out to return the particles bound to the original particles after the firing, It is not necessary to increase the number of revolutions or to perform multi-stage pulverization. Further, by setting the coating ratio to 50% or less, an increase in the irreversible capacity due to an increase in the BET specific surface area of the graphite carbon-coated graphite particles can be prevented as the binding force of the particles with the coated graphite carbon becomes stronger.

<Charcoal material for non-aqueous secondary battery>

The carbonaceous material for a non-aqueous secondary battery according to the present invention is a mixture containing at least natural graphite particles (a) and carbonaceous composite particles (b). The negative electrode material of the present invention can exhibit the effect of the present invention by appropriately selecting natural graphite particles (a) and carbonaceous composite particles (b) under the above-described specific conditions irrespective of the production method and mixing them .

(1) Method of mixing natural graphite particles (a) and carbonaceous composite particles (b)

The apparatus used for mixing the natural graphite particles (a) and the carbonaceous particulate composite particles (b) is not particularly limited. For example, in the case of a rotary mixer, a cylindrical mixer, a twin cylindrical mixer, Cubic mixer, hoe mixer; In the case of a stationary mixer, a helical mixer, a ribbon mixer, a Muller mixer, a Helical Flight mixer, a Pugmill mixer, a fluidizing mixer, or the like can be used.

(2) The mixing ratio of the natural graphite particles (a) and the carbonaceous composite particles (b)

The negative electrode material of the present invention is a mixed carbon material containing the above-mentioned natural graphite particles (a) and carbonaceous composite particles (b). The ratio (mass ratio (a) / (a) + (b)) of the natural graphite particles (a) to the total amount of the natural graphite particles (a) and the carbonaceous composite particles (b) Is 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, further preferably 0.6 or less.

If the ratio of the natural graphite particles (a) to the total amount of the natural graphite particles (a) and the carbonaceous composite particles (b) is excessively large, the increase of the irreversible capacity tends to be difficult to prevent. When the proportion of the natural graphite particles (a) is too small, the electrode tends to be an electrode which can not fully utilize the cyclic characteristics, which is a particularly excellent characteristic of the natural graphite particles (a). As the carbonaceous material for nonaqueous secondary batteries, It tends to be difficult to obtain.

(3) Properties of carbonaceous materials for non-aqueous secondary batteries

The carbonaceous material for a non-aqueous secondary battery according to the present invention contains at least natural graphite particles (a) and carbonaceous composite particles (b). Typical physical property values thereof are shown below.

(I) Specific surface area by BET method

The specific surface area of the carbonaceous material for a non-aqueous secondary battery of the present invention by the BET method is preferably 10 m 2 / g or less, and more preferably 7 m 2 / g or less. Further, it is preferably at least 2 m 2 / g, more preferably at least 3 m 2 / g.

If the specific surface area of the carbonaceous material for a non-aqueous secondary battery of the present invention is excessively large, it is difficult to prevent the capacity from decreasing due to the increase of the irreversible capacity. If the specific surface area is too small, the contact area between the electrolyte solution and the negative electrode material becomes small, so that sufficient charge / discharge load characteristics tend not to be obtained.

(Ii) the surface interval (d ₀₀₂ ) of the ( ₀₀₂ )

The plane spacing (d ₀₀₂ ) of the (002) plane of the carbon material for a non-aqueous secondary battery of the present invention by the X-ray wide angle diffraction method is usually 3.37 Å or less, preferably 3.36 Å or less. The crystallite size Lc is usually 900 A or more, preferably 950 A or more. (002) plane of the plane interval (d ₀₀₂₎ is too large, most of the part determines the exception of the particle surface of the carbon material property becomes low, the tendency for the irreversible capacity can be seen in an amorphous carbon material, the capacity reduction due to a large have. When the crystallite size Lc is too small, crystallinity tends to be lowered.

(Iii) tap density

The tap density of the carbonaceous material for a non-aqueous secondary battery of the present invention is usually 1.2 g / cm3 or less, preferably 1.1 g / cm3 or less, and more preferably 1.0 g / cm3 or less. Also, it is 0.8 g / cm 3 or more, preferably 0.9 g / cm 3 or more.

If the tap density of the negative electrode material is excessively large, it tends to be difficult to obtain contact points between particles when the electrode material is used as an electrode. In addition, if the tap density is too small, the slurry characteristics at the time of production of the electrode deteriorate, and the production of the electrode tends to become difficult.

(Iv) the value of Raman R

The Raman R value, which is the peak intensity ratio in the vicinity of 1360 cm ^-1 to the peak intensity at about 1580 cm ^-1 in the Argon ion laser spectrum of the carbonaceous material for a nonaqueous secondary battery of the present invention, is usually 0.001 or more, preferably 0.005 More preferably not less than 0.01, and usually not more than 0.7, preferably not more than 0.6, more preferably not more than 0.5.

If the value of Raman R is too small, the crystallinity of the particle surface becomes excessively high, and when the density is increased, the crystal tends to be aligned in the direction parallel to the electrode plate, and the load characteristic may be deteriorated. On the other hand, if the value of Raman R is too large, the crystals on the surface of the particles are disturbed and reactivity with the electrolytic solution increases, which tends to result in reduction of charging / discharging efficiency and increase of gas generation.

(V) Aspect ratio

The aspect ratio of the carbonaceous material for a non-aqueous secondary battery of the present invention is usually 15 or less, preferably 10 or less, and more preferably 5 or less. If the aspect ratio is too large, it tends to be easily oriented when formed into an electrode.

(Vi) average particle diameter

The average particle size (d50) of the carbonaceous material for a non-aqueous secondary battery of the present invention is usually 5 占 퐉 or more, preferably 10 占 퐉 or more, more preferably 15 占 퐉 or more, and usually 35 占 퐉 or less, preferably 30 占 퐉 or less, And more preferably 25 m or less. If the average particle diameter is too small, the specific surface area becomes large and the irreversible capacity tends to be hard to be prevented from increasing. On the other hand, if the average particle diameter is too large, the contact area between the electrolyte solution and the carbonaceous particulate composite particles (b) is reduced, thereby making it difficult to prevent the rapid charge / discharge characteristics from being degraded.

<Negative electrode>

In order to produce a negative electrode using the negative electrode material of the present invention, a negative electrode material may be prepared by blending a binder resin with an aqueous or organic medium, adding a thickener to the negative electrode material and applying it to the collector, do.

As the binder resin, it is preferable to use a binder which is stable with respect to the nonaqueous electrolyte solution and is insoluble in water. For example, rubber-like polymers such as styrene, butadiene rubber, isoprene rubber and ethylene-propylene rubber; Synthetic resins such as polyethylene, polypropylene, polyethylene terephthalate and aromatic polyamide; A thermoplastic elastomer such as styrene-butadiene-styrene block copolymer or its hydrogenated product, styrene-ethylene-butadiene, styrene copolymer, styrene-isoprene, styrene block copolymer and hydrogenated product thereof; A soft dendritic polymer such as a syndiotactic-1,2-polybutadiene, an ethylene-vinyl acetate copolymer, and a copolymer of ethylene and an? -Olefin having 3 to 12 carbon atoms; Fluorinated polymers such as polytetrafluoroethylene-ethylene copolymer, polyvinylidene fluoride, polypentafluoropropylene, and polyhexafluoropropylene can be used.

Examples of the organic medium include N-methylpyrrolidone and dimethylformamide.

It is preferable that 100 parts by weight of the negative electrode material is mixed with 100 parts by weight of the negative electrode material in order to prevent the deterioration of the battery capacity and the recycling characteristics of the negative electrode material due to the sufficient adhesion force between the negative electrode materials and the negative electrode material, It is preferable to use 0.1 parts by weight or more, preferably 0.2 parts by weight or more.

In order to prevent a reduction in the capacity of the negative electrode and to prevent problems such as interfering with the entry and exit of lithium ions into the negative electrode material, the amount of the binder resin is preferably 10 parts by weight or less based on 100 parts by weight of the negative electrode material And more preferably 7 parts by weight or less.

As the thickening material to be added to the slurry of the negative electrode material and the binder resin, for example, water-soluble cellulose such as carboxymethylcellulose, methylcellulose, hydroxyethylcellulose and hydroxypropylcellulose, polyvinyl alcohol and polyethylene glycol do. Among them, carboxymethylcellulose is preferable. It is preferable that the thickening material is used in an amount of usually 0.1 to 10 parts by weight, preferably 0.2 to 7 parts by weight, based on 100 parts by weight of the negative electrode material. If the amount of the binder resin is too small, , And if the binder resin is too large, the battery capacity decreases and the resistance increases.

As the negative electrode current collector, for example, copper, copper alloy, stainless steel, nickel, titanium, carbon, and the like, which are conventionally known to be usable for this purpose, may be used. The shape of the current collector is usually in the form of a sheet, and irregularities are formed on the surface thereof, and it is also preferable to use a net and a punching metal or the like.

After the negative electrode material and the binder resin slurry are coated and dried on the current collector, it is preferable to increase the electrode density formed on the current collector by pressurization, thereby increasing the battery capacity per unit volume of the negative electrode layer. The density of the electrode is usually 1.2 g / cm3 or more, preferably 1.3 g / cm3 or more, and usually 1.8 g / cm3 or less, preferably 1.6 g / cm3 or less.

When the density of the electrode is excessively small, it is difficult to prevent the decrease in the battery capacity accompanying the increase in the thickness of the electrode. On the other hand, if the electrode density is too large, the amount of the electrolytic solution retained in the voids decreases with the reduction of intergranular voids in the electrode, and the mobility of Li ions tends to be reduced, making it difficult to prevent the rapid charge / discharge characteristics from being lowered.

[Non-aqueous secondary battery]

The nonaqueous secondary battery according to the present invention can be produced by a conventional method except that the negative electrode is used.

As the positive electrode material, for example, a lithium-cobalt composite oxide whose basic composition is represented by LiCoO ₂ ; Lithium nickel composite oxide represented by LiNiO _2; Lithium-transition metal composite oxides such as lithium manganese composite oxides represented by LiMnO ₂ and LiMn ₂ O ₄ , transition metal oxides such as manganese dioxide, and mixtures of these complex oxides may be used.

Further, 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 , It can also be used.

A positive electrode can be prepared by forming a slurry of a mixture of the positive electrode material and a binder resin with an appropriate solvent, applying the resultant to a current collector, and drying the resultant. It is preferable that the slurry contains a conductive material such as acetylene black and ketjen black. It is also possible to add a thickening material as desired. As the thickening material and the binder resin, those known in this application, for example those used for the production of a negative electrode, may be used.

The mixing ratio of the conductive agent 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, usually 20 parts by weight or less, preferably 15 parts by weight or less , And 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, more preferably 0.5 to 7 parts by weight, in the case of slurrying the binder resin with water. When the binder resin is slurried with an organic solvent which dissolves a binder resin such as N-methylpyrrolidone, the amount is preferably 0.5 to 20 parts by weight, particularly preferably 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 preferable, and aluminum and alloys thereof are most preferable.

The electrolytic solution may also be prepared by dissolving various lithium salts in a conventionally known nonaqueous solvent.

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? -butyrolactone; Cyclic ethers such as crown ether, 2-methyltetrahydrofuran, tetrahydrofuran, 1,2-dimethyltetrahydrofuran and 1,3-dioxolane; Chain ethers such as 1,2-dimethoxyethane and the like may be used.

Normally, some of them are used in combination. Among them, it is preferable to use a cyclic carbonate and a chain carbonate or another solvent in combination.

The electrolytic solution may contain a compound such as vinylene carbonate, vinylethylene carbonate, succinic anhydride, maleic anhydride, propane sultone, and diethyl sulfone, or a difluorophosphate such as lithium difluorophosphate. An overcharge inhibitor such as diphenyl ether and cyclohexylbenzene may also be added.

As the non-aqueous electrolyte to be dissolved in a solvent, for _{example, 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 ) and LiC (CF ₃ SO ₂ ) ₃ . 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.

As the separator interposed between the positive electrode and the negative electrode, a porous sheet or nonwoven fabric of polyolefin such as polyethylene or polypropylene is preferably used.

In the nonaqueous secondary battery according to the present invention, it is preferable to design the capacity ratio of the negative electrode / the positive electrode to 1.01 to 1.5, and it is more preferable to design the ratio to 1.2 to 1.4 in view of suppressing deterioration of the battery.

Example

Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples.

[Evaluation of physical properties of negative electrode carbon material (carbon material)] [

(1) Internal porosity

The internal porosity of the natural graphite particles (a) was calculated by the Hg trap simulation. First, the method of measuring the Hg trap procedure was as follows: Powder was precisely weighed and subjected to pretreatment under vacuum (50 占 퐉 / Hgx 10 minutes), then pore distribution was measured by mercury porosimetry using Autopore IV9520 manufactured by Micromeritics Respectively.

The internal porosity is calculated by drawing a tangent line M with respect to the minimum value of the slope based on the obtained pore distribution (integral curve) L and obtaining the tangent point P of the tangent line and the integral curve, Is defined as the amount of pores in the particles (V) (Fig. 2). The internal porosity was calculated from the amount of pores in the obtained particles and the true density of the graphite.

The true density of the graphite used in the calculation was 2.26 g / cm 3 of the true density of graphite. The calculation formula is shown in Equation (1).

Equation 1

Internal porosity (%) = [amount of pores in particles / {amount of pores in particles + (1 / true density of graphite)}] x 100

(2) Diameter of concave portion D / d 50

From the SEM image and the cross-sectional SEM image, the diameter (D) in the approximate circle of the concave portion of the unevenness of the surface of the natural graphite particle (a) was determined. The measurement of the SEM image was carried out using VE-7800 manufactured by Keyens Co., Ltd. with an acceleration voltage of 5 kV. The obtained approximate circle of the natural graphite particle (a) is assumed to be a circle in the recessed portion of the SEM image, and the diameter of the approximate circle is defined as the diameter (D) of the concave portion of the natural graphite particle (a). A circle approximating an 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 measured by suspending 0.01 g of a sample in 10 ml of a 0.2 mass% aqueous solution of polyoxyethylene sorbitan monolaurate (e.g., Tween 20 (registered trademark)) as a surfactant, Was introduced into a commercially available laser diffraction / scattering type particle size distribution analyzer &quot; LA-920 manufactured by HORIBA &quot;, ultrasonic waves of 28 kHz were irradiated at 60 W for 1 minute, and then measured as median diameters based on volume And the average particle size (d50).

(3) Dibutyl phthalate (DBP) oil absorption

As one of physical properties of the carbonaceous material-coated graphite particles of the carbonaceous composite particles (b) of the present invention, the DBP oil absorption was measured.

The measurement of the DBP oil absorption was carried out in the following order using the negative electrode material.

The measurement of the DBP oil absorption was carried out in accordance with the viscosity of JIS K 6217 standard, until the maximum torque value was confirmed at a dropping rate of 4 ml / min and a rotation speed of 125 rpm, Was defined by the value calculated from the dropping flow rate when a torque of 70% of the maximum torque was expressed in the range from the start of measurement to the maximum torque.

(4) BET specific surface area (SA)

The specific surface area of the carbonaceous particulate composite particle (b) was measured by a BET one-point method by a nitrogen gas adsorption / distribution method using a specific surface area measuring device (AMS8000, manufactured by Okura Chemical Co., Ltd.). 0.4 g of the sample was charged into a cell and subjected to pretreatment by heating at 350 DEG C and then cooled to a liquid nitrogen temperature to saturate 30% of nitrogen gas and 70% of He gas to saturate and then heated to room temperature to remove the desorbed gas And the specific surface area was calculated from the obtained results by a conventional BET method.

(5) Tap density

The tap density of the carbonaceous particulate composite particles (b) was measured using a powder density meter (tap capacitor KYT-4000, manufactured by Seishin Enterprise Co., Ltd.) in a cylindrical tab cell having a diameter of 1.6 cm and a volume capacity of 20 cm 3, After passing through a sieve having a size of 300 mu m and dropping the sample, the cell was filled to full capacity, and then the volume after 1000 taps with a stroke length of 10 mm was obtained from the weight of the sample and the weight of the sample.

(6) The value of Raman R

A sample was filled in a measurement cell by dropping the sample in a measurement cell naturally using a laser Raman spectrophotometer (NR-1800, manufactured by Nippon Bunko), and the measurement cell was irradiated with argon ion laser light, The carbonaceous composite particles (b) were measured under the following conditions while being rotated in the plane.

Wavelength of argon ion laser light: 514.5 nm

Laser power on sample: 25 mW

Resolution: 4 cm ^-1

Measuring range: 1100 cm ^-1 to 1730 cm ^-1

Peak intensity measurement, peak half width measurement: background processing, smoothing processing (convolution 5 points by simple average)

The Raman R value was defined as the ratio of the peak intensity P _A (G band) near 1580 cm ^{-1 to} the peak intensity I of the maximum peak P _B (D band) near 1358 cm ^-1 , that is, I _B / I _A (F. Tuinstra, JL Koenig, J. Chem. Phys., 53, 1126 [1970]).

[Production of negative electrode sheet]

An electrode plate having an active material layer having an active material layer density of 1.75 ± 0.03 g / cm 3 was produced by using the negative electrode carbon material containing the obtained natural graphite particles (a) and the carbonaceous composite particles (b).

Specifically, 20.00 ± 0.02 g (0.200 g in terms of solid content) of an aqueous solution of 1 mass% carboxymethylcellulose Na salt (Serigene 4H, manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd.) was added to 20.00 ± 0.02 g of the negative electrode carbon material, 0.5 ± 0.02 g (0.1 g in terms of solid content) of a styrene-butadiene rubber aqueous disperser (BM400B, manufactured by Nippon Zeon Co., Ltd.) having a molecular weight of 270,000 was stirred with a hybrid mixer manufactured by Keith Corporation for 5 minutes and defoamed for 30 seconds to obtain a slurry.

The slurry was coated on a copper foil having a thickness of 18 탆 as a current collector with a width of 5 cm by a doctor blade method so that the negative electrode material was adhered at 12.8 ± 0.2 mg / cm 2, and air drying was performed at room temperature. Dried again at 110 캜 for 30 minutes, and then rolled using a roller having a diameter of 20 cm to adjust the density of the active material layer to 1.75 g / cm 3 to obtain a negative electrode sheet.

[Evaluation of negative electrode sheet]

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

(1) Manufacturing method of laminate type battery

The negative electrode sheet produced by the above method was cut into a rectangular shape of 6 cm x 4 cm to form a negative electrode, and a positive electrode made of LiCoO ₂ was cut out to have the same area and combined. Between the negative electrode and the positive electrode, LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate to 1.2 mol / l, and a separator (made by impregnating an electrolytic solution containing 2% by volume of vinylene carbonate as an additive Manufactured by Mitsui Chemicals, Inc.) was placed in the mold to prepare a laminate type battery. The cell was manufactured in a dry box in which the water content was adjusted to 20 ppm or less.

After the laminate-type battery prepared by the above method was left for 12 hours, the battery was charged at a current density of 0.2 CmA / cm 3 until the potential difference between both electrodes reached 4.1 V, and then 0.2 CmA / Cm &lt; 3 &gt;. This was repeated twice, and the current was again charged until the potential difference between both electrodes reached 4.2 V, and the battery was discharged to 3.0 V for conditioning.

(2) Method of measuring cycle retention rate

The laminate-type battery prepared by the method described later was charged to 0.8 V at 4.2 V, and discharging at 0.5 C to 3.0 V was repeated. The discharge capacity at the first cycle was regarded as the initial capacity. The discharging capacity at the 200th cycle with respect to the initial capacity x 100 was defined as the cycle holding ratio (%).

(3) Method of measuring rate characteristics

The discharge rate (%) of 1 C / 0.2 C was charged to 4.2 V at 0.5 C in the battery before the start of the cycle, and then charged to 4.2 V at 0.5 C to the discharge capacity when discharged to 3.0 V at 0.2 C, And was calculated from the ratio of the discharge capacity when discharging to 3.0 V at 1 C.

Method for preparing natural graphite particles (a)

Spheroidized graphite was processed by using a hydrostatic powder molding machine manufactured by Nihon R & D Co., Ltd. Spheroidized graphite was filled in a rubber container and pressurized with oil. The conditions were as follows: the pressing pressure was 1000 or 300 kgf / cm 2, and the pressing time was 5 minutes. The obtained molded product was pulverized with a hammer mill until the particle diameter became equal to the original spheroidizing graphite to obtain natural graphite particles (a).

The internal porosity of the obtained natural graphite particles (a) and the diameter (D) of the concave portion were measured by the above method. The inner porosity, and the diameter (D) / d50 of the concave portion are summarized in Table 1.

· Method for preparing carbon-carbon composite particles (b)

As raw material graphite, spherical natural graphite having a volume-based average particle diameter of 17 탆 was used. As the roughening process, raw graphite was pulverized at a revolution speed of 6900 rpm of Cryptron orbital manufactured by Earth Techica, and the pitch of the raw material organic material was mixed with 100 parts by weight of roughened graphite using a kneader at a ratio of 30 parts by weight. The resulting mixture was molded and fired in an inert atmosphere at 1000 占 폚, carbonized, and then graphitized at 3000 占 폚. The resulting graphite-covered graphite was pulverized and finely pulverized to obtain a powder sample of the carbonaceous composite particles (b). Table 1 shows the results (oil absorption amount, specific surface area, lemon R value, and tap density) of the obtained carbonaceous material-coated graphite.

(Examples 1 to 4)

The graphite-coated graphite, which is roughened as natural graphite particles (a) and carbonaceous substance-coated graphite as the carbonaceous composite particles (b), was mixed at a mass ratio (a) / (a + b) shown in Table 1. The negative electrode was produced using the obtained carbon material, and a laminate battery was produced by the above-mentioned method. From the initial discharge capacity and the discharge capacity at the 200th cycle, the maintenance rate of 200 cycles was calculated.

Further, after charging up to 4.2 V at 0.5 C, after charging to 4.2 V at 0.5 C with respect to the discharge capacity at discharge rate 0.2 C, examination of the discharge rate characteristic by the ratio of the discharge capacity at 1 C Respectively.

The results are shown in Table 1.

(Comparative Examples 1 to 4)

Electrodes were produced in the same manner as in Example 1 except that the carbon black composite particles (b) having the characteristics described in Table 1 and the carbon-dioxide composite particles (b) were mixed at the mass ratios shown in Table 1, (Comparative Examples 1 to 3). Further, an electrode was produced in the same manner as in Example 1 using the carbon-carbon composite particles (b) alone, and various measurements were carried out (Comparative Example 4). The results are shown in Table 1.

As can be seen from the above Examples and Comparative Examples, the improvement in the cycle retention ratio was remarkable in Examples 1 to 4 while maintaining the initial capacity by mixing the natural graphite particles (a) and the carbonaceous particulate composite particles (b) .

Particularly, in Examples 1 to 3 and Comparative Example 4, a mixture of the natural graphite particles (a) and the carbonaceous particulate composite particles (b) provides a very high cycle characteristic regardless of the mass ratio of (a) .

From the results of Examples 1 and 4 and Comparative Example 1, the natural graphite particles (a) were subjected to pressure treatment to lower the internal porosity, thereby remarkably improving the cycle characteristics. The internal porosity can be controlled by the pressure applied at the time of the pressurizing treatment, but the cycle characteristics are improved even when the internal porosity is reduced from 25% to 20% at the time of non-treatment.

As described above, the lithium ion secondary battery using the carbonaceous material for a non-aqueous secondary battery according to the present invention as an electrode can improve the cycle characteristics while maintaining a high initial discharge capacity and a discharge rate characteristic, . These properties are achieved by mixing the natural graphite particles (a) and the carbonaceous particulate composite particles (b) in the present invention.

Although the present invention has been described in detail with reference to specific embodiments thereof, it is apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention.

The present application is based on Japanese Patent Application (Japanese Patent Application No. 2011-075483) filed on March 30, 2011, the content of which is incorporated herein by reference.

Industrial availability

The carbonaceous material according to the present invention can be used as a carbonaceous material for a non-aqueous secondary battery to provide a non-aqueous secondary battery having excellent cycle characteristics while maintaining a high initial capacity and a high rate characteristic, and in particular, a lithium ion secondary battery.

D: Diameter of the approximate circle in the concave portion of the unevenness formed on the surface of the natural graphite particle (a)
L: Pore distribution in the measurement of Hg porosimetry (integral curve)
M: Tangent to the minimum value part of the slope of the integral curve in the Hg capture simulation
P: Integral curve and tangent point at the Hg capture system
V: amount of pores in the particle in measurement of Hg porosimetry

Claims (7)

(B) having a natural graphite particle (a) having an internal porosity of 1% or more and 20% or less and a dibasic phthalate oil absorption of 0.31 ml / g or more and 0.85 ml / g or less. The method according to claim 1,
Wherein the carbon-carbon composite particles (b) are carbon-dioxide-coated graphite particles. 3. The method according to claim 1 or 2,
Wherein the natural graphite particles (a) have irregularities on the surface and the ratio of the diameter (D) of the recessed portions of the unevenness to the average particle diameter (d50) of the natural graphite particles (a) Carbonaceous materials for water-based secondary batteries. 3. The method according to claim 1 or 2,
Wherein the carbonaceous particulate composite particle (b) has a specific surface area of 0.5 m 2 / g or more and 6.5 m 2 / g or less, a Raman value of 0.03 or more and 0.19 or less, and a tap density of 0.7 g / cm 3 or more and 1.2 g / Battery charcoal material. 3. The method according to claim 1 or 2,
Wherein the mass ratio ((a) / {(a) + (b)}) of the natural graphite particles (a) and the carbonaceous particulate composite particles (b) is 0.1 or more and 0.9 or less. A negative electrode for a non-aqueous secondary battery comprising a current collector and an active material layer formed on the current collector,
A negative electrode for a non-aqueous secondary battery, wherein the active material layer contains the carbonaceous material for a non-aqueous secondary battery according to any one of claims 1 to 3. 1. A non-aqueous secondary battery comprising a positive electrode, a negative electrode, and an electrolyte,
Wherein the negative electrode is the negative electrode for a non-aqueous liquid secondary battery according to claim 6.

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