JP7102868B2 - Artificial graphite-based negative electrode material, negative electrode for non-aqueous secondary batteries and non-aqueous secondary batteries - Google Patents

Description

The present invention relates to an artificial graphite-based negative electrode material having high discharge capacity and Coulomb efficiency, and excellent capacity retention rate and quick charge characteristics. The present invention also relates to a negative electrode for a non-aqueous secondary battery and a non-aqueous secondary battery containing the artificial graphite-based negative electrode material.

In recent years, with the miniaturization of electronic devices, the demand for high-capacity secondary batteries has been increasing. In particular, non-aqueous secondary batteries having a higher energy density and excellent rapid charge / discharge characteristics than nickel-cadmium batteries and nickel-hydrogen batteries, particularly lithium-ion secondary batteries, are attracting attention. In particular, a non-aqueous lithium secondary battery consisting of a positive electrode and a negative electrode capable of storing and releasing lithium ions and a non-aqueous electrolytic solution in which lithium salts such as LiPF ₆ and LiBF ₄ are dissolved has been developed and put into practical use.

Various negative electrode materials have been proposed for this non-aqueous lithium secondary battery, but graphite such as natural graphite or coke is used because of its high capacity and excellent flatness of discharge potential. Graphite carbon materials such as artificial graphite, graphitized mesophase pitch, and graphitized carbon fiber obtained by chemical conversion are used. In addition, an amorphous carbon material is also used because it is relatively stable with respect to some electrolytic solutions. Furthermore, the surface of the graphite particles is coated or adhered with amorphous carbon, and the graphite has a high capacity and a small irreversible capacity, and the amorphous carbon has excellent stability with an electrolytic solution. Carbon materials that also have characteristics are also used.

Among these, artificial graphite has the advantage of excellent battery life. Artificial graphite is roughly classified into artificial graphite having an isotropic structure and artificial graphite having an anisotropic structure according to the difference in crystal structure. Further, for each of these, there are artificial graphite composed of a single particle and artificial graphite obtained by granulating a single particle.

Artificial graphite having an isotropic structure is inferior in battery capacity to that having an anisotropic structure. In addition, although artificial graphite composed of granulated particles has an advantage of excellent quick charging characteristics, single particles are more advantageous from the viewpoint of battery life because the granulated particles may collapse due to repeated use. Is.

That is, the artificial graphite particles having an anisotropic structure composed of a single particle have a large battery capacity and are good in terms of battery life. Examples of artificial graphite particles derived from an anisotropic structure composed of a single particle include negative electrode materials disclosed in Patent Documents 1 and 2.

Japanese Patent No. 5461746 Japanese Unexamined Patent Publication No. 2014-167905

According to the studies by the present inventors, in Patent Documents 1 and 2, after mixing coal tar pitch having an anisotropic structure or coal tar pitch having an isotropic structure with needle coke powder, graphitization treatment is performed. Therefore, the coating on the surface of the graphite particles is graphitized, which is insufficient in terms of quick charging characteristics.

An object of the present invention is to provide an artificial graphite-based negative electrode material having high discharge capacity and Coulomb efficiency, and excellent capacity retention rate and quick charge characteristics. Another object of the present invention is to provide a negative electrode for a non-aqueous secondary battery and a non-aqueous secondary battery obtained by using this artificial graphite-based negative electrode material.

As a result of studies by the present inventors on the above problems, it is an artificial graphite-based negative electrode material composed of single graphite particles and derived from needle coke, which is at least partially coated with amorphous carbon. Furthermore, it has been found that the above-mentioned problems can be solved by a negative electrode material having a specific particle size distribution. That is, the gist of the present invention is as follows.

[1] An artificial graphite-based negative electrode material composed of a single particle, which satisfies the following conditions (1) to (3).
Condition (1): At least a part is coated with amorphous carbon.
Condition (2): The surface spacing (d002) of the 002 planes measured by the X-ray diffraction method (XRD) is 0.338 nm or less.
Condition (3): In the volume reference particle diameter, the median diameter (d50) is 9.0 to 25.0 μm, and the particle diameter (d10) of the 10% integrating portion from the small particle side is 0.5 to 5.4 μm. be.

[2] The artificial graphite-based negative electrode material according to [1], wherein the O / C represented by the following formula 1 is 0.1 to 1.5 mol% or less.
Equation 1: O / C (mol%) = [[O-atomic concentration obtained based on the peak area of the spectrum of O1s in the X-ray photoelectron spectroscopy analysis] / [Peak area of the spectrum of C1s in the X-ray photoelectron spectroscopy analysis] C atom concentration obtained based on]] × 100

[3] The artificial graphite-based negative electrode material according to [1] or [2], wherein the Raman R value represented by the following formula 2 is 0.05 or more and 0.8 or less.
Equation 2: [Raman R value] = [Intensity IB of peak _{P B} near 1360 cm ^-1 in Raman spectrum analysis] / [Intensity _IA of peak PA near 1580 cm ^-1 in Raman spectrum analysis]

[4] A current collector and an active material layer formed on the current collector are provided, and the active material layer contains the negative electrode material according to any one of [1] to [3]. Negative electrode for non-aqueous secondary batteries.

[5] A non-aqueous secondary battery including a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode is a negative electrode for a non-aqueous secondary battery according to [4].

According to the present invention, an artificial graphite-based negative electrode material having high discharge capacity and coulombic efficiency, excellent capacity retention rate and quick charge characteristics, and a negative electrode for a non-aqueous secondary battery and a non-aqueous secondary battery containing the same are provided. ..

Hereinafter, the present invention will be described in detail, but the present invention is not limited to the following description, and can be arbitrarily modified and carried out without departing from the gist of the present invention. In addition, in this invention, when a numerical value or a physical property value is put before and after using "-", it is used as including the value before and after that.

[Artificial graphite-based negative electrode material]
The artificial graphite-based negative electrode material of the present invention is an artificial graphite-based negative electrode material composed of a single particle, and satisfies the following conditions (1) to (3). Hereinafter, the artificial graphite-based negative electrode material of the present invention may be simply referred to as “the negative electrode material of the present invention”.
Condition (1): At least a part is coated with amorphous carbon.
Condition (2): The surface spacing (d002) of the 002 planes measured by the X-ray diffraction method (XRD) is 0.338 nm or less.
Condition (3): In the volume reference particle diameter, the median diameter (d50) is 9.0 to 25.0 μm, and the particle diameter (d10) of the 10% integrating portion from the small particle side is 0.5 to 5.4 μm. be.

[Coating with amorphous carbon]
As described in the above condition (1), the negative electrode material of the present invention is at least partially coated with amorphous carbon. As a result, the negative electrode material of the present invention has good discharge capacity and initial Coulomb efficiency.

[Surface spacing of 002 surfaces (d002)]
In the negative electrode material of the present invention, as described in the above condition (2), the surface spacing (d002) of the 002 surfaces measured by the X-ray diffraction method (XRD) is 0.338 nm or less, and preferably 0.337 nm or less. Yes, more preferably 0.336 nm or less. d002 is a value indicating the bulk crystallinity of the negative electrode material. The smaller the value of d002, the higher the crystallinity of the carbon material, and the amount of lithium entering the graphite layers approaches the theoretical value, so that the capacity increases. To increase. If the crystallinity is too low, it tends to be difficult to exhibit the excellent battery characteristics of high capacity and low irreversible capacity when highly crystalline graphite is used for the electrode. Further, since the negative electrode material of the present invention is carbonaceous-derived artificial graphite having an anisotropic structure, d002 is in the above range. On the other hand, in the case of artificial graphite having an isotropic structure, d002 is larger than 0.338 nm, which is clearly distinguished from the negative electrode material of the present invention in its crystal structure.

X-ray diffraction is measured by the following method. First, about 15% by weight of the total amount of X-ray standard high-purity silicon powder is added to carbon powder and mixed, and CuKα ray monochromated with a graphite monochromator is used as the radiation source, and the reflection diffraction method is used. The wide-angle X-ray diffraction curve is measured. Then, the interplanar spacing (d002) and the crystallite size (Lc) are determined using the Gakushin method.

[Particle size distribution (d50, d10 and d90)]
As described in the above condition (3), the negative electrode material of the present invention has a median diameter (d50) of 9.0 to 25.0 μm in a volume reference particle diameter, and a particle diameter (d10) of a 10% integrating portion from the small particle side. ) Is 0.5 to 5.4 μm.

When d50 is within the range of the condition (3), the battery capacity becomes good. Further, from the viewpoint of making these better, d50 is preferably 10.0 μm or more, more preferably 11.0 μm or more, while preferably 20.0 μm or less, more preferably 18.0 μm. It is as follows.

When d10 is in the range of the condition (3), the quick charge characteristic becomes good. Further, from the viewpoint of making these better, d10 is preferably 1.0 μm or more, more preferably 2.0 μm or more, and on the other hand, preferably 5.3 μm or less.

Further, in the negative electrode material of the present invention, the particle diameter (d90) of the 90% integrating portion from the small particle side is preferably 20.0 μm or more, more preferably 22.0 μm or more, from the viewpoint of quick chargeability. Further, the d90 of the negative electrode material of the present invention is preferably 30.0 μm or less, more preferably 29.0 μm or less, from the viewpoint of quick charging characteristics.

A laser diffraction method in which 0.01 g of a negative electrode material is suspended in approximately 150 mL of a 0.1% by volume aqueous solution of polyoxyethylene (20) sorbitan monolaurate (Zeen 20 (registered trademark)), which is a surfactant. By measuring the volume-based particle size distribution using a particle size distribution meter (LA-920 manufactured by Horiba Seisakusho), the median diameter (d50), the d10 particle size of the 10% integration part from the small particle side, and the d90 grain of the 90% integration part. The diameter can be calculated. The measurement conditions are ultrasonic dispersion for 1 minute, ultrasonic intensity 4, circulation speed 2, and relative refractive index 1.50.

[Surface functional group amount O / C value (mol%)]
The O / C value obtained from XPS and represented by the following formula 1 is preferably 0.1 mol% or more, more preferably 0.2 mol% or more, still more preferably 0.3 mol% or more, while preferably. It is 1.5 mol% or less, more preferably 1.3 mol% or less, still more preferably 1.1 mol% or less. When the surface functional group amount O / C value is within the above range, the desolvation reactivity of Li ions and the electrolytic solution solvent on the negative electrode surface is promoted, the rapid charge / discharge characteristics are improved, and the side reaction with the electrolytic solution occurs. It tends to be suppressed and the charge / discharge efficiency becomes good.
Equation 1: O / C (mol%) = [[O-atomic concentration obtained based on the peak area of the spectrum of O1s in the X-ray photoelectron spectroscopy analysis] / [Peak area of the spectrum of C1s in the X-ray photoelectron spectroscopy analysis] C atom concentration obtained based on]] × 100

In calculating the surface functional group amount O / C value, an X-ray photoelectron spectrometer was used as an X-ray photoelectron spectroscopy measurement, the measurement target was placed on a sample table so that the surface was flat, and X-rays of aluminum Kα rays were emitted. As a source, the spectra of C1s (280 to 298 eV) and O1s (526 to 542 eV) are measured. The peak top of the obtained C1s is charge-corrected as 284.6 eV, the peak areas of the spectra of C1s and O1s are obtained, and further multiplied by the device sensitivity coefficient to calculate the surface atomic concentrations of C and O, respectively. The obtained atomic concentration ratio O / C (O atomic concentration / C atomic concentration) of O and C is defined as the surface functional group amount O / C value of the carbon material.

[Raman R value]
The negative electrode material of the present invention has a Raman R value represented by the following formula 1 of preferably 0.05 or more, more preferably 0.1 or more, still more preferably 0.15 or more. Further, it is preferably 0.8 or less, more preferably 0.6 or less, still more preferably 0.4 or less. If the Raman R value is too small, it indicates that the crystallinity of the surface of the negative electrode material is too high, and the low temperature input / output characteristics may be deteriorated due to the difficulty of inserting and removing Li ions. On the other hand, if the Raman R value is too large, the influence of the irreversible capacity of amorphous carbon increases and the side reaction with the electrolytic solution increases, resulting in a decrease in the initial charge / discharge efficiency of the lithium ion secondary battery and an increase in the amount of gas generated. The battery capacity tends to decrease.
Equation 2: [Raman R value] = [Intensity IB of peak _{P B} near 1360 cm ^-1 in Raman spectrum analysis] / [Intensity _IA of peak PA near 1580 cm ^-1 in Raman spectrum analysis]

In the present invention, the Raman _R value is the intensity _IA of the peak PA near 1580 cm ^-1 and the intensity IB of the peak _{P B near} 1360 cm ^-1 in the Raman spectrum obtained by Raman spectroscopy for the negative electrode material of the present invention. _{Is defined as the intensity ratio (IB / I A )} when measured. The term "near 1580 cm ^-1 " refers to the range of 1580 to 1620 cm ^-1 , and the term "near 1360 cm ^-1 " refers to the range of 1350 to 1370 cm ^-1 .

In the present invention, the Raman R value can be obtained by the following method. In Raman spectrum analysis using _Almega XR manufactured by Thermo Fisher Scientific Co., Ltd. and using a semiconductor laser beam with a wavelength of 532 nm, the intensity of peak PA near 1580 cm ^-1 and the intensity of peak _{P B in} the range of 1360 cm ^-1 . IB is measured and the ratio of its intensities _R = _IB / _IA is determined. In the preparation of the sample, the powder is filled in the cell by natural drop, and the cell is rotated in a plane perpendicular to the laser beam while irradiating the sample surface in the cell with the laser beam to perform the measurement.
Laser power on sample: 2 mW or less Resolution: Approximately 10 cm ^-1
Measurement range: 400 cm ^-1 to 4000 cm ^-1
Peak intensity measurement, peak half width measurement: background processing, averaging of multiple spectra

[Production method]
In the negative electrode material of the present invention, coal tar pitch is heat-polymerized to produce raw coke, which is crushed and classified to form raw coke powder, then graphitized, and further mixed and heated with an amorphous carbon precursor. It can be produced by performing a coating treatment of amorphous carbon. In order to control the conditions (3) to d10 and d50, it is preferable to obtain raw coke and then pulverize and classify it, and to coat it with amorphous carbon and then sieve it to adjust the particle size. In particular, raw coke powder having different particle size distributions is prepared in advance, and each of them is used to produce artificial graphite coated with amorphous carbon, and these are appropriately mixed to control the condition (3) to be satisfied. This is preferable because it is easy to control the particle size distribution.

<Coal tar pitch>
In the present invention, the "coal tar pitch" means a mixture obtained by distilling and refining coal tar obtained by carbonization of coal. The components of coal tar pitch usually include naphthalene, acenaphthene, phenoxybenzene, methylnaphthalene, and other polycyclic aromatic compounds having three or more rings. The quinoline insoluble content of coal tar pitch used as a raw material is usually less than 5% by weight, preferably 3% by weight or less, and more preferably 1% by weight or less.

<Heat polymerization>
Raw coke can be obtained by heating and polymerizing the coal tar pitch at 400 to 700 ° C. The heating temperature in this step is preferably 450 to 600 ° C. Further, this heat treatment is usually performed in an atmosphere of an inert gas such as nitrogen gas.

<Crushing and classification>
The obtained raw coke is preferably pulverized and classified into raw coke powder. In particular, it is preferable to adjust the particle size of the raw coke powder by classification so as to satisfy the condition (3).

Examples of the coarse crusher used for the crushing process include a jaw crusher, an impact type crusher, a cone crusher and the like, examples of an intermediate crusher include a roll crusher and a hammer mill, and examples of a fine crusher include a ball mill and vibration. Examples include mills, pin mills, stirring mills, jet mills and the like.

As the conditions for the classification treatment, those having a mesh opening of preferably 75 μm or less are used. When artificial graphite having a different particle size distribution is mixed in a later step, raw coke powder having a different particle size distribution may be prepared in advance by using one having a different mesh size at this stage.

The apparatus used for the classification process is not particularly limited, but for example, in the case of dry sieving: a rotary sieving, a swaying sieving, a oscillating sieving, a vibrating sieving, etc. can be used, and in the case of a dry air flow sieving. : Gravity type classifier, inertial force type classifier, centrifugal force type classifier (classifier, cyclone, etc.) can be used, and in the case of wet sieving: mechanical wet classifier, hydraulic classifier, sedimentation classifier, A centrifugal wet classifier or the like can be used.

<Graphitization>
Artificial graphite can be obtained by heating the raw coke powder to 2800 to 3300 ° C. and graphitizing it. At this time, the heating condition is preferably 2800 ° C. or higher from the viewpoint of volatilizing impurities derived from the raw material to obtain artificial graphite having high crystallinity, and more preferably 2900 ° C. or higher from this viewpoint. Further, the temperature of 3300 ° C. or lower is preferable from the viewpoint of preventing excess energy consumption after the progress of graphitization is stopped, and more preferably 3200 ° C. or lower from this viewpoint. A raw coke powder baked at 700 ° C. to 1800 ° C. before graphitization may be used.

<Amorphous carbon coating treatment>
Condition (1) is satisfied by mixing the artificial graphite obtained by graphitization with an amorphous carbon precursor (raw material of amorphous carbon) and firing it.

The amorphous carbon precursor is not particularly limited, but is a coal-based heavy oil such as coal tar, coal tar pitch, and dry distillate liquefied oil; a direct-retaining heavy oil such as normal pressure residual oil and reduced pressure residual oil; crude oil. Petroleum-based heavy oils such as decomposition-type heavy oils such as ethylene tar, which are by-produced during thermal decomposition of naphtha, etc .; Sulfur-containing cyclic compounds such as adamantan; aliphatic cyclic compounds such as adamantan; polyphenylene such as biphenyl and terphenyl, polyvinyl esters such as polyvinyl chloride, polyvinyl acetate and polyvinyl butyral, and organic substances such as thermoplastic polymers such as polyvinyl alcohol. Can be mentioned. These organic precursors may be used alone or in combination of two or more.

The firing of the amorphous carbon coating treatment is usually carried out in an inert gas such as nitrogen or argon. The heat treatment temperature at this time is usually 800 ° C. or higher, preferably 900 ° C. or higher, more preferably 1000 ° C. or higher, while it is usually 1300 ° C. or lower, preferably 1200 ° C. or lower. The heat treatment time may be until the amorphous carbon precursor is amorphous carbonized, and is usually 10 minutes to 24 hours.

<Adjustment of particle size distribution>
It is preferable to adjust the particle size of the obtained artificial graphite coated with amorphous carbon by using a sieve. Further, in order to adjust the particle size distribution, it is preferable to adjust the particle size by mixing with those having different particle size distributions.

[Negative electrode for non-aqueous secondary batteries]
The negative electrode for a non-aqueous secondary battery of the present invention (hereinafter, may be referred to as “negative electrode of the present invention”) includes a current collector and an active material layer formed on the current collector. The active material layer contains the negative electrode material of the present invention.

In order to produce a negative electrode using the negative electrode material of the present invention, a slurry in which a binder resin is mixed with the negative electrode material is made into a slurry with an aqueous or organic medium, and if necessary, a thickener is added thereto and applied to a current collector. Then dry it.

As the binder resin, it is preferable to use a resin that is stable to a non-aqueous electrolytic solution and is water-insoluble. For example, rubber-like polymers such as styrene / butadiene rubber, isoprene rubber and ethylene / propylene rubber; synthetic resins such as polyethylene, polypropylene, polyethylene terephthalate, polyimide, polyacrylic acid, and aromatic polyamide; both styrene / butadiene / styrene blocks. Polymers and their hydrogenated products, styrene / ethylene / butadiene, styrene copolymers, styrene / isoprene and styrene block copolymers, and thermoplastic elastomers such as hydrides thereof; Soft resinous polymers such as vinyl acetate copolymers and copolymers of ethylene and α-olefins having 3 to 12 carbon atoms; polytetrafluoroethylene / ethylene copolymers, polyvinidene fluoride, polypentafluoro A fluorinated polymer such as propylene and polyhexafluoropropylene can be used. As the organic medium, for example, N-methylpyrrolidone and dimethylformamide can be used.

It is preferable to use 0.1 part by weight or more, preferably 0.2 part by weight or more of the binder resin with respect to 100 parts by weight of the negative electrode material. By setting the amount of the binder resin to 0.1 parts by weight or more with respect to 100 parts by weight of the negative electrode material, the binding force between the negative electrode materials and between the negative electrode material and the current collector becomes sufficient, and the negative electrode material can be separated from the negative electrode material. It is possible to prevent a decrease in battery capacity and deterioration of recycling characteristics due to peeling.

The amount of the binder resin used is preferably 10 parts by weight or less, more preferably 7 parts by weight or less, based on 100 parts by weight of the negative electrode material. By setting the amount of the binder resin to 10 parts by weight or less with respect to 100 parts by weight of the negative electrode material, it is possible to prevent a decrease in the capacity of the negative electrode and prevent alkaline ions such as lithium ions from entering and exiting the negative electrode material. You can prevent problems.

Examples of the thickener to be added to the slurry include water-soluble celluloses such as carboxymethyl cellulose, methyl cellulose, hydroxyethyl cellulose and hydroxypropyl cellulose, polyvinyl alcohol, polyethylene glycol and the like. Of these, carboxymethyl cellulose is preferred. The thickener is preferably used so as to be usually 0.1 to 10 parts by weight, particularly 0.2 to 7 parts by weight, based on 100 parts by weight of the negative electrode material.

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

After applying the negative electrode material and the binder resin slurry to the current collector and drying it, pressurize it to increase the density of the active material layer formed on the current collector, and increase the density of the battery per unit volume of the negative electrode active material layer. It is preferable to increase the capacity. The density of the active material layer is preferably in the range of 1.2 to 1.8 g / cm ³ , and more preferably 1.3 to 1.6 g / cm ³ . By setting the density of the active material layer to the above lower limit value or more, it is possible to prevent a decrease in battery capacity due to an increase in the thickness of the electrodes. Further, by setting the density of the active material layer to the above upper limit value or less, the amount of the electrolytic solution held in the voids decreases as the interparticle voids in the electrode decrease, and the mobility of alkaline ions such as lithium ions becomes small. It is possible to prevent the rapid charge / discharge property from becoming small.

The pore volume in the range of 10 nm to 100,000 nm by the mercury injection method of the negative electrode active material layer formed by using the negative electrode material of the present invention is preferably 0.05 mL / g, and is 0.1 ml / g or more. Is more preferable. By setting the pore volume to 0.05 mL / g or more, the area of entry and exit of alkaline ions such as lithium ions becomes large.

[Non-aqueous secondary battery]
The non-aqueous secondary battery of the present invention is a non-aqueous secondary battery including a positive electrode, a negative electrode, and an electrolyte, and uses the negative electrode of the present invention as the negative electrode. In particular, the positive electrode and the negative electrode used in the non-aqueous secondary battery of the present invention are usually preferably lithium ion secondary batteries capable of storing and releasing Li ions.

The non-aqueous secondary battery of the present invention can be manufactured according to a conventional method except that the above-mentioned negative electrode of the present invention is used. In particular, in the non-aqueous secondary battery of the present invention, the values of [Negative electrode capacity] / [Positive electrode capacity] are preferably designed to be 1.01 to 1.5, and are designed to be 1.2 to 1.4. Is more preferable.

[Positive electrode]
Examples of the positive electrode material used as the active material for the positive electrode of the non-aqueous secondary battery of the present invention include a lithium cobalt composite oxide having a basic composition represented by LiCoO ₂ , a lithium nickel composite oxide represented by LiNiO ₂ , and LiMnO. A lithium transition metal composite oxide such as a lithium manganese composite oxide represented by ₂ and LiMn ₂ O ₄ , a transition metal oxide such as manganese dioxide, and a mixture of these composite oxides 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 , LiFePO ₄ , etc. may be used.

A positive electrode can be produced by slurrying the positive electrode material with a binder resin with an appropriate solvent, applying it to a current collector, and drying it. It is preferable that the slurry contains a conductive material such as acetylene black or ketjen black. Further, a thickener may be contained if necessary. As the binder and the thickener, those known for this purpose, for example, those exemplified as those used for manufacturing a negative electrode can be used.

The blending amount of the conductive material is preferably 0.5 to 20 parts by weight, more preferably 1 to 15 parts by weight, based on 100 parts by weight of the positive electrode material. The blending amount of the thickener is preferably 0.2 to 10 parts by weight, more preferably 0.5 to 7 parts by weight, based on 100 parts by weight of the positive electrode material. Further, the blending amount of the binder resin with respect 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, when the binder resin is slurried with water. When the binder resin is slurryed with an organic solvent that dissolves the binder resin such as N-methylpyrrolidone, 0.5 to 20 parts by weight is preferable, and 1 to 15 parts by weight is more preferable.

Examples of the positive electrode current collector include aluminum, titanium, zirconium, hafnium, niobium, tantalum and the like, and alloys thereof. Among these, aluminum, titanium and tantalum and their alloys are preferable, and aluminum and its alloys are most preferable.

[Electrolytic solution]
As the electrolytic solution, a solution obtained by dissolving various lithium salts in a conventionally known non-aqueous solvent can be used.

Examples of the non-aqueous solvent include cyclic carbonates such as ethylene carbonate, fluoroethylene carbonate, propylene carbonate, butylene carbonate and vinylene carbonate, chain carbonates such as dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate, and cyclic esters such as γ-butyrolactone. , Crown ether, cyclic ethers such as 2-methyltetrahydrofuran, tetrahydrofuran, 1,2-dimethyltetrahydrofuran and 1,3-dioxolane, chain ethers such as 1,2-dimethoxyethane and the like may be used. Usually, two or more of these are mixed and used. Of these, it is preferable to use cyclic carbonate and chain carbonate, or a mixture thereof with another solvent.

Compounds such as vinylene carbonate, vinylethylene carbonate, succinic anhydride, maleic anhydride, propane sultone and diethylsulfone, and difluorophosphates such as lithium difluorophosphate may be added to the electrolytic solution. Further, an overcharge inhibitor such as diphenyl ether and cyclohexylbenzene may be added.

Examples of the electrolyte to be dissolved in a 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 , and LiN (CF ₃ ). Examples thereof include 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.

[Separator]
It is preferable to use a separator interposed between the positive electrode and the negative electrode. As such a separator, it is preferable to use a porous sheet of polyolefin such as polyethylene or polypropylene or a non-woven fabric.

Hereinafter, the present invention will be described in more detail with reference to Examples. In the following examples and comparative examples, the measurement method of each characteristic is as follows.

<Manufacturing of negative electrode sheet>
Using the negative electrode materials prepared in the following Examples and Comparative Examples as the negative electrode material, a electrode plate having an active material layer having an active material layer density of 1.50 ± 0.03 g / cm ³ was prepared. Specifically, 20.00 ± 0.02 g of the negative electrode material, 20.00 ± 0.02 g of a 1 wt% carboxymethyl cellulose sodium salt aqueous solution (0.200 g in terms of solid content), and styrene having a weight average molecular weight of 270,000. -Add 0.50 ± 0.05 g (0.2 g in terms of solid content) of butadiene rubber aqueous dispersion, stir for 5 minutes with a hybrid mixer manufactured by Keyence, and defoam for 30 seconds to obtain a slurry.

This slurry was applied to a width of 5 cm using a doctor blade so that the negative electrode material adhered to 10.0 ± 0.3 mg / cm ² on a copper foil having a thickness of 10 μm, which is a current collector, and air-dried at room temperature. Was done. After further drying at 110 ° C. for 30 minutes, roll pressing was performed using a roller having a diameter of 20 cm to adjust the density of the active material layer to 1.50 ± 0.03 g / cm ³ to obtain an electrode sheet.

<Manufacturing of lithium-ion secondary battery (2016 coin type battery)>
The negative electrode sheet produced by the above method was punched into a disk shape having a diameter of 12.5 mm, and the lithium metal foil was punched into a disk shape having a diameter of 14 mm to serve as a counter electrode. Between the two electrodes, a separator (porous polyethylene film) is impregnated with an electrolytic solution in which LiPF ₆ is dissolved at 1 mol / L in a mixed solvent of ethylene carbonate and ethyl methyl carbonate (volume ratio = 3: 7). , 2016 coin type batteries were prepared respectively.

<Discharge capacity, initial Coulomb efficiency>
Using the above-mentioned lithium ion secondary battery (2016 coin type battery), the discharge capacity at the time of charging and discharging the battery was measured by the following measuring method.

Using the non-aqueous secondary battery (coin type battery) produced by the above method, the discharge capacity (mAh / g) at the time of battery charging / discharging was measured by the following measuring method. The current density of 0.05C is charged to 5 mV with respect to the lithium counter electrode, the current density is charged to 0.005 C at a constant voltage of 5 mV, lithium is doped into the negative electrode, and then the current density is 0.1 C. The current was discharged to 1.5 V with respect to the lithium counter electrode. In this initial cycle, the initial Coulomb efficiency (= (initial discharge capacity / initial charge capacity) × 100 (%)) was calculated. Subsequently, the second and third times were charged at 10 mV and 0.005 Ccut by cc-cv charging at the same current density, and the discharge was performed at 0.1 C and 1.5 V at all times.

The value obtained by dividing the discharge capacity of the third cycle by the discharge capacity of the first cycle in the total of three cycles was calculated as the cycle maintenance rate [%].

<Evaluation of quick charge characteristics>
Using the non-aqueous secondary battery (coin type battery) produced by the above method, the discharge capacity (mAh / g) at the time of battery charging / discharging was measured by the following measuring method. The current density of 0.05C is charged to 5 mV with respect to the lithium counter electrode, the current density is charged to 0.005 C at a constant voltage of 5 mV, lithium is doped into the negative electrode, and then the current density is 0.1 C. The current was discharged to 1.5 V with respect to the lithium counter electrode. Subsequently, the second and third times were charged at 10 mV and 0.005 Ccut by cc-cv charging at the same current density, and the discharge was performed at 0.1 C and 1.5 V at all times.

The current density was 3C, and the lithium counter electrode was charged with cc until the capacity per gram of the negative electrode material reached 360 mAh / g, and the potential change in the process was measured. The value (dV / dQ) obtained by differentiating the obtained potential value with the current value was plotted against the charge rate (= charged capacity [mAh / g] / discharge capacity in the third cycle of cc-cv, hereinafter referred to as SOC). The quick charge characteristic was evaluated from the dV / dQ value of the peak peak confirmed at SOC = 0 to 15% of this differential curve.

<Manufacturing of artificial graphites A to C>
Coal tar pitch (quinoline insoluble content: less than 1% by weight) was heated at 500 ° C. for 24 hours to obtain raw coke. The obtained raw coke powder was classified by 75 um, and the one having an average particle diameter of 13 μm was designated as raw coke powder A, and the one having an average particle diameter of 8 μm was designated as raw coke powder B. Each of the raw coke powders A and B was heated at 3000 ° C. for 40 hours to graphitize. Graphitized raw coke powder A is referred to as artificial graphite C.

100 parts by weight of each graphitized product of the raw coke powders A and B was mixed with heavy oil. Each of these was coated with amorphous carbon by heating at 1300 ° C. The graphitized product of raw coke powder A was coated with amorphous carbon, further pulverized by a pulverizer, and then passed through a 45 μm sieve to obtain artificial graphite A. Further, the graphitized product of raw coke powder B was coated with amorphous carbon, further pulverized by a pulverizer, and then a 45 μm sieve was added to obtain artificial graphite B.

[Example 1]
The negative electrode material 1 was manufactured by mixing artificial graphites A and B with (artificial graphite A) :( artificial graphite B) = 7: 3 (weight ratio). Various physical properties of the negative electrode material 1 were evaluated. Further, the negative electrode material 1 was used to prepare a negative electrode sheet and a lithium ion secondary battery, and various evaluations were performed. The results are shown in Tables 1 and 2 below.

[Example 2]
The negative electrode material 2 was manufactured by mixing artificial graphites A and B with artificial graphite A: artificial graphite B = 5: 5 (weight ratio). Various evaluations were performed in the same manner as in Example 1 except that the negative electrode material 2 was used instead of the negative electrode material 1. The results are shown in Tables 1 and 2.

[Comparative Example 1]
The negative electrode material 3 was manufactured using artificial graphite C. Various evaluations were carried out in the same manner as in Example 1 except that the negative electrode material 3 was used instead of the negative electrode material 1. The results are shown in Tables 1 and 2.

[Comparative Example 2]
The negative electrode material 4 was manufactured using artificial graphite B. Various evaluations were carried out in the same manner as in Example 1 except that the negative electrode material 4 was used instead of the negative electrode material 1. The results are shown in Tables 1 and 2.

[Comparative Example 3]
The negative electrode material 5 was manufactured by mixing artificial graphites A and B with artificial graphite A: artificial graphite B = 8: 2 [weight ratio]. Various evaluations were performed in the same manner as in Example 1 except that the negative electrode material 5 was used instead of the negative electrode material 1. The results are shown in Tables 1 and 2.

[Comparative Example 4]
The negative electrode material 6 was produced by mixing artificial graphites A and B with artificial graphite A: artificial graphite B = 9: 1 [weight ratio]. Various evaluations were performed in the same manner as in Example 1 except that the negative electrode material 6 was used instead of the negative electrode material 1. The results are shown in Tables 1 and 2.

[Discussion of results]
From the result of Comparative Example 1 in which the amorphous coating is not applied, it is confirmed that the irreversible capacity becomes large. In the present invention, in order to prevent this irreversible capacitance, artificial graphites A and B in which a part of the particles are amorphous-coated are used in Examples 1 and 2 and Comparative Examples 2 and 4.

Compared with Comparative Examples 3 and 4, Examples 1 and 2 exhibited a discharge capacity of 350 mAh / g or more, a Coulomb efficiency of 97% or more, and a capacity retention rate, and exhibited excellent characteristics as a negative electrode material for a lithium ion battery. In addition, SOC vs. obtained from the quick charge test. When the peak top values at SOC 0 to 15% at the initial stage of charging were compared from the dV / dQ curve, it was -0.0081 and -0.0076 in Examples 1 and 2, and 0.0023 and 0.0023 in Comparative Examples 3 and 4. Was obtained. SOC vs. charging process. Taking a positive value in the dV / dQ curve means that the potential rises in the region where the potential originally drops with charging. This phenomenon is called overshoot, and it is suggested that the electrical resistance may be high due to the resistance in the conduction of lithium ions between the electrode and the electrolyte and the crystallinity of the negative electrode material itself, as well as the surface condition and coating of the particles. It also has a great effect on the condition. Such anomalous potential behavior also puts an excessive load on the electrolyte. It is presumed that this is one of the causes of the decrease in the Coulomb efficiency and the cycle maintenance rate in Comparative Examples 3 and 4.

XRD, XPS, for the purpose of evaluating the crystallinity and particle surface state that determine the electrical conductivity of the carbon material for each of the negative electrode materials 1, 2, 5 and 6 used in Examples 1 and 2 and Comparative Examples 3 and 4. Evaluation was performed by Raman spectroscopy. From the results shown in Table 1, all of the negative electrode materials 1, 2, 5 and 6 had extremely high crystallinity of d002 <0.338 nm, La> 100 nm, and La> 100 nm from the XRD measurement.

On the other hand, the filling degree of the electrode was determined, and the particle size of the negative electrode material, which affects the affinity with the electrolytic solution, was also evaluated, and the results shown in Table 1 were obtained. From the results, it was confirmed that there was a tendency for the particle size distribution to change predominantly between Examples 1 and 2 and Comparative Examples 3 and 4, and the high discharge capacity, high Coulomb efficiency, and high cycle maintenance rate were confirmed within the range where the particle size distribution satisfied the condition (3). , It was confirmed that good quick charge characteristics are achieved at the same time.

Subsequently, in Comparative Example 2, the same high discharge capacity (first time; 351 mAh / g) and excellent quick charge characteristics (dV / dQ peak top value at SOC 0 to 15%; -0.0079) as in Examples 1 and 2 from Table 1 ), But it was confirmed that the Coulomb efficiency (96.7%) and cycle maintenance rate (96.0%) tended to decrease as compared with Examples 1 and 2. This suggests that in Comparative Example 2, since the negative electrode material is composed only of artificial graphite B having a small particle size, the contact area between the electrode and the electrolytic solution becomes excessive, and the electrolytic solution may be decomposed.

From the results of the particle size measurement of Comparative Example 2 (negative electrode material 4) shown in Table 1, the average particle size d10 was obtained as 3.6 μm. From the viewpoint of suppressing the decomposition of the electrolytic solution and maintaining the Coulomb efficiency and the cycle maintenance rate well, the result was obtained that it is desirable to set the particle size distribution within the range of the condition (3).

The artificial graphite-based negative electrode material of the present invention, and the negative electrode for non-aqueous secondary batteries and the non-aqueous secondary battery containing the same have high discharge capacity and Coulomb efficiency, and are excellent in capacity retention rate and quick charge characteristics, and thus are used in vehicles; Power tool applications: Can be suitably used for mobile device applications such as mobile phones and personal computers.

Claims (4)

An artificial graphite-based negative electrode material composed of a single particle, which satisfies the following conditions (1) to (3) and has an O / C of 0.1 to 1.5 mol% represented by the following formula 1. Negative electrode material.
Condition (1): At least a part is coated with amorphous carbon.
Condition (2): The surface spacing (d002) of the 002 planes measured by the X-ray diffraction method (XRD) is 0.338 nm or less.
Condition (3): In the volume reference particle diameter, the median diameter (d50) is 9.0 to 25.0 μm, and the particle diameter (d10) of the 10% integrating portion from the small particle side is 0.5 to 5.4 μm. be.
Equation 1: O / C (mol%) = [[O-atomic concentration obtained based on the peak area of the spectrum of O1s in the X-ray photoelectron spectroscopy analysis] / [Peak area of the spectrum of C1s in the X-ray photoelectron spectroscopy analysis] C atom concentration obtained based on]] × 100 The artificial graphite-based negative electrode material according to claim 1, wherein the Raman R value represented by the following formula 2 is 0.05 or more and 0.8 or less.
Equation 2: [Raman R value] = [Intensity IB of peak _{P B} near 1360 cm ^-1 in Raman spectrum analysis] / [Intensity _IA of peak PA near 1580 cm ^-1 in Raman spectrum analysis] 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 artificial graphite-based negative electrode material according to claim 1 or 2. .. 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 secondary battery according to claim 3.