JP6757704B2 - Method for manufacturing negative electrode active material for lithium ion capacitors - Google Patents

Description

The present invention relates to a method for producing a negative electrode active material used in a lithium ion capacitor.

A lithium-ion capacitor is a device that uses activated carbon for the positive electrode and a pre-doped carbon material for the negative electrode, and has the characteristics of a lithium-ion battery and an electric double-layer capacitor. It has a higher output density than a lithium-ion battery and is an electric double-layer capacitor. Since the energy density is higher than that of the above, it is expected to be used in fields such as wind power generation, power leveling in solar power generation, instantaneous voltage drop compensation device, construction machinery such as forklifts, and various moving objects related to transportation. There is.

Lithium-ion batteries are widely used as a power source for automobiles in the transportation field, but they have a problem of high output characteristics and deterioration when charging and discharging are repeated. The electric double layer capacitor, which seems to be able to complement this, is satisfied with the output characteristics and the repetitive charge / discharge characteristics, but has a drawback that the energy density is not sufficiently high.
On the other hand, a lithium ion capacitor using a carbon material in which lithium ions are pre-doped into the negative electrode material in advance can increase the capacity and lower the potential of the negative electrode, so that the energy density is four times or more that of a conventional electric double layer capacitor. It is said that it exhibits excellent characteristics even in high temperature loads and long-term charge / discharge cycles.

Since materials with relatively low crystallinity such as hard carbon and soft carbon have been used for the conventional negative electrode active material of lithium ion capacitors, it is difficult to keep the internal resistance of the negative electrode active material sufficiently low. Yes, it was limited to some of the expected uses.

In order to popularize lithium ion capacitors, it is necessary to keep the internal resistance of the negative electrode active material sufficiently low, and as one of the means, it is also necessary to keep the electrical resistance value of the carbon material, which is the negative electrode active material, low. is there.

JP-A-2008-130890 Japanese Patent No. 5041351 Japanese Unexamined Patent Publication No. 2015-70032

From basic physical properties to application development, Kazuyoshi Tanaka et al., Kagaku-Dojin (2011) New Carbon Industry Toshinori Ishikawa, Michi Nagaoki, Modern Editing Company (1980) Introduction to New Carbon Materials Society of Carbon Materials (1996) Carbon Materials Engineering Michio Inagaki, Nikkan Kogyosha (1985)

Conventionally, the negative electrode active material of a lithium ion capacitor has been obtained by carbonizing after adding a crosslinked structure by blowing air when melting a phenol resin, a furan resin, and an optically isotropic pitch. It is a material having low crystallinity capable of high-speed charging and discharging such as hard carbon, soft carbon obtained by carbonizing pitch, carbon black, and composites thereof. In order to enhance the effect of high-speed charging and discharging, measures have been taken to reduce the particle size of the active material and increase the specific surface area. However, since the material has low crystallinity and a relatively high electrical resistance value, the internal resistance of the lithium ion capacitor is high.
On the other hand, the present invention reduces the internal resistance of the lithium ion capacitor without affecting the performance of the lithium ion capacitor, and brings about an increase in the capacity of the lithium ion capacitor and an improvement in energy density. The purpose is to provide the substance.

The interplanetary distance d ₍₀₀₂₎ of the carbon crystal network layer by X-ray diffraction is 0.3400 to 0.3770 nm inside the low crystal carbon particles, d ₍₀₀₂₎ is 0.3354 to 0.3360 nm, and the average particle diameter is A composite particle containing at least one graphite particle of 0.8 to 3.0 μm, having an average particle diameter of 2.0 to 6.0 μm, a maximum particle diameter of 50 μm or less, and a BET method specific surface area of 5.0 to 15.0 m ² /. g, The pore volume of micropores with a pore diameter of 2 nm or less is 2% or less of the total pore volume, the maximum adsorption amount of nitrogen gas by adsorption and desorption of nitrogen at liquid nitrogen temperature is 10 cm ³ / g or more, and flaxseed oil absorption amount 90 to 150 ml It is a negative electrode active material for a lithium ion capacitor having a tap density of 0.25 g / cm ³ or more and a tap density of 0.25 g / cm.

The d _{(002) of} graphite is 0.3354 to 0.3360 nm, and the electrical resistivity is as low as 0.1 mΩcm (1 μΩm), which is a value that can be said to be a metal. In the case of artificial graphite, generally, when the carbonization temperature (graphiteization temperature) is 2800 ° C. or higher, d ₍₀₀₂₎ is 0.3354 to 0.3360 nm, which shows a low electrical resistance value, but conversely, the carbonization temperature is 2800 ° C. As the value becomes lower, the crystallinity of the obtained graphite decreases, and d ₍₀₀₂₎ becomes larger than 0.3360 nm accordingly, and the electric resistance value increases accordingly.
Low crystalline carbon has a carbonization temperature of 800 to 1300 ° C., d ₍₀₀₂₎ of 0.3400 to 0.3770 nm, and a high electrical resistance value.
By including graphite powder having d ₍₀₀₂₎ of 0.3354 to 0.3360 nm in the conventionally used low crystalline carbon, low resistance is achieved without changing the surface state.

The particles of artificial graphite or natural graphite contained inside the low crystalline carbon are preferably those having a high degree of crystallinity for the purpose of suppressing the electric resistance value of the carbon material which is the negative electrode active material. That is, the smaller the interplanetary distance d _{(002) of the} carbon network layer is, the better, and those having 0.3354 to 0.3360 nm are appropriately selected.
If it is less than 0.3354 nm, it is impossible due to the crystal structure of graphite, and if it is larger than 0.3360 nm, the crystallinity cannot be said to be sufficiently high and it is not preferable. When d ₍₀₀₂₎ is 0.3354 to 0.3360 nm, Lc indicating the thickness of the laminated carbon network layer and La indicating the spread of the carbon network surface are preferably larger than 100 nm in most cases. However, it is possible to use either Lc or La, or even when both Lc and La are less than 100 nm.

The particle size of the artificial graphite or natural graphite particles preferably has a volume cumulative average particle size of 0.8 to 3.0 μm. Those smaller than 0.8 μm are difficult to obtain because it is difficult to mass-produce them industrially, and those larger than 3.0 μm are graphite particles contained in low crystalline carbon in order to obtain the desired particle size by pulverization after firing. Even itself is crushed, the active crushed surface is exposed, and decomposition of the electrolytic solution and gas generation are promoted, which is not preferable. Further, the shape of the graphite particles to be used is not particularly limited, and flat, crushed, spherical, fibrous, and other shapes may be used without any particular problem. Since the oil absorption amount and the specific surface area differ depending on the shape of the graphite particles, it is necessary to appropriately adjust the pitch and the blending amount of the graphite particles.
Further, as the graphite particles, artificial graphite and natural graphite may be used alone, in combination, two or more kinds having different particle sizes may be used in combination, or two or more kinds having different grain shapes and types may be used in combination.

As the pitch used as a precursor of low crystalline carbon, the binder pitch used when producing a general artificial graphite material such as an artificial graphite electrode is suitable, the density is 1.26 to 1.30 g / cm ³ , and the softening point. The temperature is 80 to 120 ° C., the quinoline insoluble content is 7 to 15%, the toluene insoluble content is 25 to 40%, and the fixed carbon content is 53 to 65%.
Further, in general, when a binder pitch having a softening point of 80 to 120 ° C. is carbonized at 800 to 1200 ° C., the residual carbonization ratio is approximately 65 to 70%.

Regarding the composition of the pitch and the graphite particles, in terms of weight, 250 to 500 parts by weight of the graphite particles is preferable with respect to 100 parts by weight of the pitch, and more preferably 300 to 400 parts by weight, considering the residual carbonization ratio of the pitch after carbonization. Is. If the number of graphite particles is more than 500 parts by weight, it is difficult to sufficiently include the graphite particles in the low crystalline carbon. When the negative electrode is prepared with even a part of the graphite particles exposed, it is difficult to sufficiently suppress the decomposition of the electrolytic solution on the negative electrode and it is difficult to prevent gas generation. Therefore, if it is less than 250 parts by weight, the baked product is hard. It becomes a large lump, which makes it difficult to crush, and even the graphite particles themselves contained in the low crystal carbon are crushed in order to obtain the desired particle size by crushing, and the frequency of crushing the low crystal carbon derived from the pitch increases. It is not preferable because it promotes the decomposition of the electrolytic solution by increasing the specific surface area.

Due to carbonization, the pitch undergoes thermal decomposition and polycondensation, and the pitch, which is an organic substance, changes to carbon, which is an inorganic substance. The residual carbonization rate varies depending on the properties of the pitch used and the carbonization temperature, but in general, the residual carbonization rate when a binder pitch having a softening point of 80 to 120 ° C. is carbonized at 800 to 1200 ° C. is approximately 65 to 70%. The pitch and the blending amount of the graphite particles may be appropriately adjusted in consideration of the residual coal ratio in advance. In order to sufficiently include graphite particles having a volume cumulative average particle diameter of 0.8 to 3.0 μm used in the present invention in the low crystalline carbon, the weight ratio of the low crystalline carbon to the graphite particles is 1: 3. It is 5 to 1 to 7.2.

An object of the present invention is to reduce the internal resistance of a lithium ion capacitor, and by including graphite particles having high crystallinity and a low electric resistance value in the main low crystal carbon, the lithium ion capacitor can be provided. It brings about a decrease in internal resistance. Graphite particles promote the decomposition of the electrolytic solution at the time of pre-doping lithium on the surface thereof and cause gas generation. Therefore, the graphite particles are included inside the low crystalline carbon so as not to be exposed on the surface.

The structure of a carbon material is represented by the plane orientation of a small hexagonal network composed of carbon atoms, the size of the region, and the aggregated state, and is anisotropic under a polarizing microscope. It is observed as an aggregate of plane orientation regions with. Specifically, when observed under a polarizing microscope, the optically anisotropic part changes color in the order of yellow, pink, blue, and yellow again when observed while rotating the sample table, but the isotropic part. Remains pink.
In the present invention, the low crystalline carbon derived from the pitch exhibits optical isotropic properties, and the graphite particles included therein exhibit optical anisotropy. The negative electrode active material powder obtained by the present invention is dispersed in an epoxy resin to which a curing agent has been added, and then the structure of the particles is included in the low crystalline carbon by observing the cross section of the graphite particles by leaving, curing, and polishing. The graphite particles can be confirmed for each particle.

It is also important that the specific surface area contributed by the pores of effective size is large in order to enhance the effect corresponding to high-speed charging and discharging.
In the pore structure of the negative electrode active material of the present invention, as shown in FIG. 1, the relative pressure (P / P ₀ ) of nitrogen gas is ₀ in the isotherm adsorption isotherm in the adsorption / desorption of nitrogen gas at the liquid nitrogen temperature. The amount of nitrogen gas adsorbed is small up to around 8, and increases sharply when it exceeds 0.8.
In the isotherm adsorption line for adsorption and desorption of nitrogen gas, the relative pressure (P / P ₀ ) of nitrogen gas is around 0.99, and the adsorption amount of nitrogen gas is 10 cm ³ / g or more.
The BET method specific surface area is 5.0 to 15.0 m ² / g.
The specific surface area of the micropores having a pore diameter of 2 nm or less is 0.5 m ² / g or less, and the pore volume of the micropores is 2% or less of the total pore volume.

The particle size distribution of the negative electrode active material of the present invention corresponds to high-speed charging and discharging more effectively as composite particles formed by including graphite particles having a volume cumulative average particle diameter of 0.8 to 3.0 μm in low crystalline carbon. Considering the particle size that can be produced, D ₁₀ is 1.0 to 3.5 μm, D ₅₀ (average particle size) is 2.0 to 6.0 μm, and D ₉₀ is 4.0 to 15.0 μm. D ₁₀₀ (maximum particle size) is 50 μm or less.

In the negative electrode active material of the present invention, a binder, a conductive auxiliary agent, and a dispersion medium are mixed to prepare a slurry, which is then applied to a metal leaf current collector. At this time, it is important to prepare a slurry having good dispersion stability. is there. In addition, the characteristic index required for the active material is the oil absorption amount, and there is an appropriate oil absorption amount range in order to prevent the dispersion stability of the slurry and the deformation of the edge portion of the coating film immediately after application, and the linseed oil oil absorption amount is 90. ~ 150 ml / 100 g is preferable. At this time, the tap density of the active material is 0.25 g / cm ³ or more.

The method for producing the negative electrode active material for a lithium ion capacitor of the present invention will be described below, but only an example is given, and a precursor containing at least one graphite particle inside the pitch is not necessarily used by this method. Other methods may be used as long as they can be obtained.

<Mixing and stirring>
In order to obtain a precursor in which at least one graphite particle is contained in the pitch, a predetermined amount of pitch and graphite particles are mixed and stirred at a temperature equal to or higher than the softening point of the pitch using a heating kneader or the like. Since a pitch having a softening point of 80 to 120 ° C. is preferably used, in this case, mixing and stirring are performed for 1 to 3 hours while heating at a temperature of 140 to 180 ° C. above the softening point.

<Carbonization>
In order to carbonize the mixed mixture of pitch and graphite particles, it is placed in a metal container and held at 800 to 1200 ° C. for 1 to 10 hours while raising the temperature at 5 to 10 ° C./h in a non-oxidizing atmosphere. And bake. The atmosphere at the time of firing has no problem as long as it is a non-oxidizing atmosphere, and examples thereof include a nitrogen atmosphere, a carbon dioxide gas atmosphere, an argon atmosphere, and a non-oxidizing self-atmosphere generated by thermal decomposition of pitch.

<Crushing>
After being carbonized by firing, it is taken out of a metal container and crushed. Finally, use a jet mill, impeller mill, turbo mill, pin mill, ACM palberizer, etc. to appropriately adjust the input amount per hour, the number of rotations of the crushed teeth, and the amount of air in the case of a continuous type or jet mill. However, if the product is a large lump taken out from the metal container, it can be pre-crushed by using a jaw crusher, a rotoplex, an Orient mill, a hammer crusher or the like, if necessary.
In the present invention, an impeller mill IMP-400 manufactured by Seishin Enterprise Co., Ltd. was used as a crusher, and the raw material input speed was 35 kg / h, the impeller rotation speed was 3560 rpm, and the air volume was 35 m ³ / min.
If the power at the time of pulverization is insufficient, a predetermined particle size cannot be obtained, and conversely, if the power is excessive and over-pulverization occurs, the surface or cross section of the graphite particles contained in the low crystal carbon is exposed, which is not preferable.

<Sieve>
Since the pulverized product contains coarse powder, it is treated with a vibrating sieve, an ultrasonic sieve, or the like having a mesh with an opening of 32 to 38 μm in order to remove the coarse powder. Although an airflow type classifier can be used, it is not preferable from the viewpoint of profitability.

The physical properties and performance of the pitch, graphite particles, which are the raw materials used in the present invention, and the negative electrode active material for a lithium ion capacitor, which contains graphite particles in the low crystalline carbon of the present invention, were measured by the methods described below. ..

<Particle size>
The average particle size and particle size distribution are measured by adding a small amount of surfactant as a dispersant to water using the laser diffraction type particle size distribution measuring device MT3300EX manufactured by Nikkiso Co., Ltd. and ultrasonically dispersing the sample. did. The cumulative curve is calculated with the total volume of the powders used in the test as 100%, and the cumulative curve is 10, 50, 90, and 100% when integrated from the small particle diameter side to the large particle diameter side. The particle diameters of the points were D ₁₀ , D ₅₀ , D ₉₀ , and D ₁₀₀ (μm), respectively. Note that D ₅₀ represents the average particle size and D ₁₀₀ represents the maximum particle size.

<Pitch density>
A method for measuring pitch density is shown in JIS K 2425. The density of pitches with softening points of 70 to 90 ° C. is 1.26 to 1.27 g / cm ³ at 20 ° C. The pitch used in the present invention has a softening point of 105 ° C. and a density of 1.30 g / cm ³ .

<Pitch softening point>
Measurement was performed using glycerin by the softening point test method specified in JIS K 2207 "Petroleum asphalt" or JIS K 2425 "Creosote oil / processed tar / tar pitch test method (ring ball method)".
In the ring-and-ball method, water is used as a heat medium up to 80 ° C., and glycerin is used above that. Automatic measuring devices for measuring softening points are also widespread, and examples thereof include asp-6 manufactured by Tanaka Kagaku Kikai Seisakusho Co., Ltd., RKA5 manufactured by Anton Paar Japan K.K., and EX-719PD4 manufactured by Daiichi Rika Co., Ltd. As another method, the measurement by the meterer softening point measurement method in which the bias with the JIS method is corrected is also performed. As the device, there are DP70 and DP90 of METTLER TOLEDO Co., Ltd.

<True density of negative electrode active material and graphite particles>
It was determined by a low volume expansion method (helium gas substitution method) using the true density measuring device AccuPyc1330-1 manufactured by Micromeritics.

<X-ray diffraction test results>
The interplanetary distance d _{(002) of the} carbon network layer, Lc indicating the thickness of the laminated carbon network layer, and La indicating the extent of the carbon network surface are X-rays using CuKα rays by the Ultra3 system manufactured by Rigaku Co., Ltd. The voltage applied to the wire tube was 40 kV, and the current was 20 mA. The scanning speed of the counter was 2 ° / min, the scanning range was 10 ° to 90 °, and measurements were taken at 0.02 ° intervals. The value of d ₍₀₀₂₎ is the position (angle) of the peak of the (002) plane whose diffraction angle 2θ is near 26 ° and the (111) plane of metallic silicon whose diffraction angle 2θ is about 28 °, which is added in advance as an internal standard. From the peak position (angle) of, the Lc value is the half width of the peak of the (002) plane whose diffraction angle 2θ is near 26 ° and the metal silicon whose diffraction angle 2θ is about 28 °, which is added in advance as an internal standard. From the half width of the peak of the (111) plane, the value of La is the half width of the peak of the peak of the (110) plane where the diffraction angle 2θ is around 77.6 °, and the diffraction angle 2θ added in advance as an internal standard is 76. It was calculated from the half width of the peak of the (331) plane of metallic silicon near 4 °, respectively, based on the Gakushin method.

<Specific surface area, pore volume, and maximum adsorption amount>
The specific surface area, pore volume, and maximum adsorption amount were measured by adsorption and desorption of nitrogen gas, and the measuring device was carried out at liquid nitrogen temperature using an automatic specific surface area / pore distribution measuring device TriStar3000 manufactured by Micromeritics. ..

The specific surface area was determined by the multipoint method of BET, which is calculated by evaluating the amount of nitrogen gas adsorbed from the adsorption isotherm as a monolayer.
P / V (P _0- P) = (1 / VmC) + {(C-1) / VmC} (P / P ₀ ) ... (1)
S = kVm ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ (2)
P ₀ : Saturated vapor pressure P: Adsorption equilibrium pressure V: Adsorption amount at adsorption equilibrium pressure P Vm: Adsorption amount of monolayer layer C: Parameters related to heat of adsorption, etc. S: Specific surface area k: Nitrogen single molecule occupied area: 0.162 nm ²

The total pore volume was determined from the amount of saturated adsorbed gas near the equilibrium relative pressure P / P ₀ = 0.99 obtained from the adsorption isotherm.
The micropore volume having a pore size of 2 nm or less was determined by a t-plot method in which the adsorption amount was plotted against the thickness t of the nitrogen gas adsorption film. The thickness of the adsorption membrane is in the range of 0.35 to 0.50 nm, and the Harkins & Jura formula t = [13.99 / {0.034-log (P / P ₀ )}] ^0.5 ... 3)
Obtained by.
P ₀ : Saturated vapor pressure P: Adsorption equilibrium pressure

<Oil absorption>
The oil absorption was measured according to JIS K6217 using flaxseed oil using an absorption measuring device S-410 manufactured by Asahi Soken Co., Ltd. Linseed oil is supplied while stirring the sample powder, and the change in torque at that time is measured. The torque varies depending on the structure of the sample powder, but 70% of the maximum torque was read as the end point and converted into the amount of linseed oil per 100 g of the sample.

<Tap density>
It was calculated from the volume after exactly 30 g of the sample was weighed and put into a 100 ml graduated cylinder and tapped 700 times with a stroke of 10 mm.

<Initial charge / discharge capacity>
For the initial charge capacity, prepare an aqueous slurry by combining 2 parts by weight each of SBR and CMC as a binder with respect to 100 parts by weight of the negative electrode active material, and apply it on a copper foil using a doctor blade at 120 ° C. After drying with, and applying a roll press, an electrode having a thickness of 60 μm was punched into φ12. A lithium metal is used as a counter electrode, and the electrodes are opposed to each other via a separator to form an electrode group, and then an electrolytic solution of 1M LiPF ₆ / EC: DEC (3: 7) is added to form a coin cell, and a current value of 0.5 mA is formed. After constant current charging at / cm ² until the voltage value reached 0.01 V, constant current charging was performed until the current value reached 0.01 mA / cm ² . After the charging was completed, a constant current discharge was performed at a current value of 0.5 mA / cm2, and the discharge was completed when the voltage value reached 1.5 V.

Hard carbon obtained by carbonizing the conventionally used phenol resin, furan resin, and optically isotropic pitch after adding a crosslinked structure by blowing air at the time of melting, or soft obtained by carbonizing the pitch. The internal resistance of a lithium-ion capacitor is obtained by including graphite particles with high crystallinity and low electrical resistance in a low-crystal carbon material using carbon and carbon black, which has low crystallinity and relatively high electrical resistance. Was able to be reduced.

The isotherm adsorption diagram of nitrogen gas at the liquid nitrogen temperature of Example 1. FIG. 6 is an isothermal adsorption diagram of nitrogen gas at the liquid nitrogen temperature of Comparative Example 3.

Examples and comparative examples of the present invention will be described below.
<Example 1>
Density 1.30 g / cm ³ , softening point 105 ° C, quinoline insoluble content 11%, carbon-based optically isotropic binder pitch 100 parts by weight and D ₁₀ = 1.55 μm, D ₅₀ = 2.49 μm, D ₉₀ = 4.23 μm, D ₁₀₀ = 7.07 μm, carbon mesh surface interlayer distance d ₍₀₀₂₎ is 0.3360 nm, BET specific surface area is 22.61 m ² / g, flaxseed oil absorption is 106 ml / 100 g, true density is 2. 330 parts by weight of artificial graphite particles having a tap density of 23 g / cm ³ and a tap density of 0.21 g / cm ³ were put into a heating kneader and kneaded at 160 ° C. for 3 hours. After transferring this kneaded product to a metal container, the temperature was raised at 5 ° C./h in a non-oxidizing atmosphere, and the mixture was held at 1000 ° C. for 2 hours for firing. Then, by pulverizing and passing through a sieve having a mesh size of 38 μm, graphite particles are formed inside low crystalline carbon of D ₁₀ = 2.32 μm, D ₅₀ = 4.26 μm, D ₉₀ = 8.42 μm, and D ₁₀₀ = 16.58 μm. The encapsulated carbon particles were obtained. The d ₍₀₀₂₎ of the obtained carbon particles was 0.3360 nm, the BET specific surface area was 5.65 m ² / g, the linseed oil oil absorption was 119 ml / 100 g, the true density was 2.13 g / cm ³ , and the tap density was 0. It was .43 g / cm ³ .
FIG. 1 shows an isothermal adsorption diagram of nitrogen gas adsorption / desorption at the liquid nitrogen temperature of Example 1. When the relative pressure (P / P ₀ ) of nitrogen gas is low up to around 0.8, the amount of nitrogen gas adsorbed is small, and when it exceeds 0.8, it is observed to increase rapidly, and isotherm adsorption during adsorption and desorption of nitrogen gas. In the diagram, the relative pressure (P / P ₀ ) of nitrogen gas is around 0.99, and the amount of nitrogen gas adsorbed is 40 cm ³ / g.

<Example 2>
Instead of the artificial graphite particles used in Example 1, D ₁₀ = 1.66 μm, D ₅₀ = 2.74 μm, D ₉₀ = 4.80 μm, D ₁₀₀ = 8.39 μm, the interlayer distance d ₍₀₀₂₎ of the carbon mesh surface. ₎ Is 0.3354 nm, BET specific surface area is 17.05 m ² / g, flaxseed oil absorption amount is 101 ml / 100 g, true density is 2.23 g / cm ³ , and tap density is 0.27 g / cm ³ . Others were the same as in Example 1.
D ₁₀ = 2.64 μm, D ₅₀ = 5.08 μm, D ₉₀ = 9.97 μm, D ₁₀₀ = 19.66 μm, d ₍₀₀₂₎ is 0.3354 nm, BET specific surface area is 7.48 m ² / g, oil absorption. Carbon particles in which graphite particles were contained inside low crystalline carbon having an amount of 133 ml / 100 g and a true density of 2.19 g / cm ³ and a tap density of 0.37 g / cm ³ were obtained.

<Comparative example 1>
The artificial graphite particles used in Example 1 were used as they were.

<Comparative example 2>
Example 1 using 100 parts by weight of the pitch used in Example 1 and 74 parts by weight of acetylene black (BET specific surface area: 39.0 m ² / g, d ₍₀₀₂₎ : 0.3539 nm, average particle size 48 nm). D ₁₀ = 1.56 μm, D ₅₀ = 2.62 μm, D ₉₀ = 4.73 μm, D ₁₀₀ = 8.39 μm, d ₍₀₀₂₎ is 0.3539 nm, and the BET specific surface area is 24. Low crystalline carbon particles having a tap density of 48 m ² / g, an oil absorption of 79 ml / 100 g, and a tap density of 0.50 g / cm ³ were obtained.

<Comparative example 3>
100 parts by weight of pitch used in Example 1, D ₁₀ = 2.60 μm, D ₅₀ = 7.34 μm, D ₉₀ = 15.90 μm, D ₁₀₀ = 32.78 μm, d ₍₀₀₂₎ is 0.3455 nm, BET ratio. The same treatment as in Example 1 was carried out using 500 parts by weight of calcined coal-based coke having a surface area of 8.67 m ² / g, and D ₁₀ = 5.58 μm, D ₅₀ = 11.22 μm, D ₉₀ =. 21.87 μm, D ₁₀₀ = 38.86 μm, d ₍₀₀₂₎ is 0.3455 nm, BET specific surface area is 2.02 m ² / g, oil absorption is 84 ml / 100 g, tap density is 0.75 g / cm ³ low crystalline carbon Obtained particles of.
FIG. 2 shows an isothermal adsorption diagram of Comparative Example 3 in the adsorption / desorption of nitrogen gas at the liquid nitrogen temperature. The relative pressure of nitrogen gas (P / P ₀ ) slightly increased around 1.0, but the rapid increase in the amount of nitrogen gas adsorbed as in the examples was not observed.

<Comparative example 4>
The same treatment as in Example 1 was carried out using 100 parts by weight of the pitch used in Example 1 and 220 parts by weight of artificial graphite particles, but after firing, it became an integrated strong mass and could be taken out from the metal container. I couldn't do it, so I canceled it.

Table 1 Examples and the low-crystalline carbon from a pitch of Comparative Example d _(002), carbon particles such as artificial graphite particles or carbon black mixed with a pitch d _(002), carbon particles obtained by firing Shows average particle size, maximum particle size, oil absorption, and tap density.

In Table 1, the Comparative Example 1 does not include a low crystalline carbon only graphite particles, the d ₍₀₀₂₎ column of the low crystalline carbon from pitch have as a blank, column d ₍₀₀₂₎ of the inclusion particles It is d ₍₀₀₂₎ of the artificial graphite particle of Example 1. Further, Comparative Example 2 is a mixture of pitch and acetylene black, and the value of d ₍₀₀₂₎ of acetylene black is entered in the d ₍₀₀₂₎ column of the _contained particles, and Comparative Example 3 is It is a value of d ₍₀₀₂₎ of calcined coke.

Table 2 shows the characteristics such as the specific surface area of the carbon particles of Examples and Comparative Examples, the total pore volume, the micropore volume, the ratio of the micropore volume to the total pore volume, and the amount of nitrogen gas adsorbed.

Table 3 shows the characteristics of lithium ion capacitors using carbon particles of Examples and Comparative Examples as a negative electrode active material.

Table 3 shows the initial charge / discharge capacity measurement results of Examples 1 and 2, Comparative Examples 1, 2 and 3.
In Examples 1 and 2, although the initial discharge capacity is lower than 360 mAh / g of Comparative Example 1 composed of only artificial graphite, it exceeds 335 mAh / g, and the charge / discharge efficiency exceeds 86% and is higher than that of Comparative Example 1. Shown. In Comparative Examples 2 and 3, the charge / discharge efficiency was low, and the initial discharge capacity was less than 250 mAh / g.

<Method of confirming graphite particles in low carbon particles>
The active material particles obtained in Examples 1 and 2 are placed on a fluororesin plate with a fluororesin ring having an inner diameter of φ25 × an outer diameter of φ30 × a height of 25 mm, and the active material particles are put into the ring for embedding. The main agent of the epoxy resin and the curing agent were mixed at a volume ratio of 9: 1 and poured from above. The volume ratio of the active material particles to the epoxy resin main agent to the curing agent was 1: 9: 1 at this time. This was left at room temperature (20 to 25 ° C.) for 10 hours to cure the epoxy resin to obtain a cured resin product in which the active material particles were dispersed in the resin. The cured resin was then polished with a plurality of abrasive papers until the cross sections of the plurality of active material particles were exposed to give a mirror surface.
Using this as a sample, observation with a polarizing microscope was carried out by changing the magnification and changing the incident angle of polarized light with respect to the cross section of the sample powder by rotating the sample table.
As a result of observation, in Example 1 a graphite particle portion showing optical anisotropy in which the color changes in the order of yellow, pink, blue, and yellow again inside the pink low crystal carbon portion showing optical isotropicity. Both and 2 were observed.

When the same observations as in Examples were performed on the particles of Comparative Examples 1, 2 and 3, only the particles showing optical anisotropy (graphite particles) were observed in Comparative Example 1. In Comparative Example 2, it is far more than the optically anisotropic part that is clearly discriminated as blue or yellow, which is observed when graphite or coke is observed in the same pink color showing optical isotropicity. A minute part of optical anisotropy, which was unclear and was finally recognized as blue or yellow by gazing, was observed. In Comparative Example 3, a coke particle portion showing optical anisotropy was observed inside the low crystal carbon portion showing optical isotropicity as in the example.

Claims (2)

The interplanetary distance d ₍₀₀₂₎ of the carbon crystal network layer by X-ray diffraction is 0.3400 to 0.3770 nm inside the low crystal carbon, d ₍₀₀₂₎ is 0.3354 to 0.3360 nm, and the average particle size is The average particle size is 2.0 to 6.0 μm, which includes at least one graphite particle of 0.8 to 3.0 μm, and the weight ratio of low crystalline carbon to graphite particles is 1: 3.5 to 1: 7. A manufacturing method for obtaining a negative electrode active material for a lithium ion capacitor, which is characterized by being 2.
A predetermined amount of pitch and graphite particles are stirred and mixed, and the mixture is heated at 5 to 10 ° C./h in a non-oxidizing atmosphere and held at 800 to 1200 ° C. for 1 to 10 hours for firing. The fired product is crushed to the extent that the included graphite particles are not exposed on the surface, the crushed material active material particles are hardened with an epoxy resin, and the obtained cured resin is polished with abrasive paper to give a mirror surface, and then by a polarization microscope. A method for producing a negative electrode active material for a lithium ion capacitor for confirming the presence of graphite particles. In claim 1, in the preparation of a sample in which the negative electrode active material for a lithium ion capacitor is hardened with an epoxy resin, a fluorine resin ring is placed on a fluorine resin plate and the negative electrode active material particles for a lithium ion capacitor are activated in the ring. A method for producing a negative electrode active material for a lithium ion capacitor, which is obtained by charging material particles and mixing a main agent of an epoxy resin for embedding resin and a curing agent at a volume ratio of 9: 1.