JP5561225B2 - Carbon material for lithium ion secondary battery, negative electrode material for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Description

  The present invention relates to a carbon material for a lithium ion secondary battery, a negative electrode material for a lithium ion secondary battery, and a lithium ion secondary battery.

Conventionally, a carbon material has been used for the negative electrode of a lithium ion secondary battery. This is because even if the charge / discharge cycle proceeds, dendritic lithium is hardly deposited on the negative electrode using the carbon material, and safety is guaranteed.
For example, Patent Document 1 discloses that the pore volume occupied by pores having a nitrogen content of 0.1 to 5.0% by weight and a pore diameter exceeding 0.33 nm is 0.1 to 50.0 ml / kg. A carbon material having a pore volume of 50.0 ml / kg or less is disclosed in Patent Document 2 by carbonizing a specific resin composition.

Patent Document 3 discloses a carbon material having a spin concentration of 1 × 10 ^{18 to} 3 × 10 ¹⁸ spins / g at 25 ° C. measured by an electron spin resonance method.

JP 2006-083012 A JP 2004-303428 A JP H10-247495

  In recent years, development of lithium ion batteries with higher charge capacity, discharge capacity, and charge / discharge efficiency has been demanded. However, it is difficult to meet such demands using the conventional carbon materials disclosed in Patent Documents 1 and 2. That is, the conventional carbon materials disclosed in Patent Documents 1 and 2 relate to pores through which gas can enter from the surface of the carbon material, and improve charge and discharge efficiency by reducing surface reaction, etc. Carbon materials including improvements have not been developed. In addition, in the carbon material disclosed in Patent Document 3, the improvement of the discharge capacity and the charge / discharge efficiency is studied by adjusting the number of unpaired electrons in the material, but it does not necessarily satisfy the required characteristics. There wasn't.

According to the present invention,
A carbon material for a lithium ion secondary battery obtained by carbonizing a resin or a resin composition,
Under the following conditions (A) to (E), the positron lifetime measured by the positron annihilation method is 370 picoseconds or more and 480 picoseconds or less,
(A) Positron beam source: Electron / positron pair generation using an electron accelerator to generate positrons (B) Gamma ray detector: BaF ₂ scintillator and photomultiplier tube (C) Measurement temperature and atmosphere: 25 ° C. in vacuum (D) Count of annihilation γ-ray: 3 × 10 ⁶ or more (E) Positron beam energy: 10 KeV
A carbon material for a lithium ion secondary battery is provided, wherein a spin concentration measured by an electron spin resonance method is 5 × 10 ¹⁶ spins / g or more and 2 × 10 ¹⁸ spins / g or less.

By using such a carbon material for a lithium ion secondary battery, it is possible to provide a lithium ion battery having a high charge capacity and a high discharge capacity and a charge / discharge efficiency of a certain value or more.
That is, according to the present invention, it is possible to provide a lithium ion battery excellent in the balance of charge capacity, discharge capacity and charge / discharge efficiency.

  Furthermore, according to this invention, the lithium ion secondary battery containing the negative electrode material for lithium ion secondary batteries containing the carbon material for lithium ion secondary batteries mentioned above and this negative electrode material for lithium ion secondary batteries can also be provided.

  ADVANTAGE OF THE INVENTION According to this invention, the carbon material for lithium ion secondary batteries which can provide the lithium ion battery which has high charge capacity, discharge capacity, and was excellent in the balance of charge capacity, discharge capacity, and charge / discharge efficiency, lithium ion secondary A negative electrode material for a battery and a lithium ion secondary battery are provided.

It is a figure which shows the relationship between the count number of annihilation gamma rays, and positron annihilation time. It is a schematic diagram of a lithium ion secondary battery.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(Carbon material for lithium ion secondary battery)
First, the outline | summary of the carbon material for lithium ion secondary batteries of this invention (henceforth a carbon material may be demonstrated).
The carbon material for a lithium ion secondary battery of the present invention is a carbon material for a lithium ion secondary battery obtained by carbonizing a resin or a resin composition,
Under the following conditions (A) to (E), the positron lifetime measured by the positron annihilation method is 370 picoseconds or more and 480 picoseconds or less,
(A) Positron beam source: Electron / positron pairs are generated using an electron accelerator to generate positrons. (B) Gamma ray detector: BaF ₂ scintillator and photomultiplier tube (C) Measurement temperature and atmosphere: 25 ° C. in vacuum (D) Count of annihilation γ-ray: 3 × 10 ⁶ or more (E) Positron beam energy: 10 KeV
A carbon material for a lithium ion secondary battery, wherein a spin concentration measured by an electron spin resonance method is 5 × 10 ¹⁶ spins / g or more and 2 × 10 ¹⁸ spins / g or less.

Next, the carbon material for a lithium ion secondary battery will be described in detail.
The carbon material for a lithium ion secondary battery is obtained by carbonizing a resin or a resin composition.
Although it does not specifically limit as resin contained in resin or a resin composition, For example, a thermosetting resin or a thermoplastic resin can be contained. As the resin, one kind or a combination of two or more kinds can be used.
Further, as will be described later, the resin composition contains the above resin as a main component and can contain a curing agent, an additive and the like.

  Here, the thermosetting resin is not particularly limited. For example, a phenol resin such as a novolac type phenol resin or a resol type phenol resin, an epoxy resin such as a bisphenol type epoxy resin or a novolac type epoxy resin, a melamine resin, a urea resin, or aniline. Examples thereof include resins, cyanate resins, furan resins, ketone resins, unsaturated polyester resins, and urethane resins. In addition, modified products obtained by modifying these with various components can also be used.

  The thermoplastic resin is not particularly limited. For example, polyethylene, polystyrene, polyacrylonitrile, acrylonitrile-styrene (AS) resin, acrylonitrile-butadiene-styrene (ABS) resin, polypropylene, vinyl chloride, methacrylic resin, polyethylene terephthalate, Polyamide, polycarbonate, polyacetal, polyphenylene ether, polybutylene terephthalate, polyphenylene sulfide, polysulfone, polyethersulfone, polyetheretherketone, polyetherimide, polyamideimide, polyimide, polyphthalamide, and the like can be given.

A thermosetting resin is preferable as the resin as the main component used in the carbon material of the present invention. Thereby, the remaining carbon rate of a carbon material can be raised more.
And among thermosetting resins, those selected from novolak-type phenol resins, resol-type phenol resins, melamine resins, furan resins, aniline resins, and modified products thereof are preferable. Thereby, the freedom degree of design of a carbon material spreads and it can manufacture at low cost.

Moreover, when using a thermosetting resin, the hardening | curing agent can be used together.
Although it does not specifically limit as a hardening | curing agent used here, For example, in the case of a novolak-type phenol resin, a hexamethylene tetramine, a resol type phenol resin, a polyacetal, paraform etc. can be used. In the case of epoxy resins, known as epoxy resins such as polyamine compounds such as aliphatic polyamines and aromatic polyamines, acid anhydrides, imidazole compounds, dicyandiamide, novolac-type phenol resins, bisphenol-type phenol resins, and resol-type phenol resins. Can be used.
In addition, even if it is a thermosetting resin that normally uses a predetermined amount of a curing agent, the resin composition used in the present invention may use a smaller amount than usual or may be used without using a curing agent. You can also

Moreover, in the resin composition used by this invention, an additive can be mix | blended besides this.
Although it does not specifically limit as an additive used here, For example, the carbon material precursor carbonized at 200-800 degreeC, a graphite and graphite modifier, an organic acid, an inorganic acid, a nitrogen-containing compound, an oxygen-containing compound, aromatic Group compounds and non-ferrous metal elements.
The above additives may be used alone or in combination of two or more depending on the type and properties of the resin used.

  As a resin used for the carbon material of the present invention, nitrogen-containing resins described later may be included as a main component resin. Moreover, when the nitrogen-containing resin is not contained in the main component resin, at least one kind of nitrogen-containing compound may be included as a component other than the main component resin, or the nitrogen-containing resin is included as the main component resin. In addition, a nitrogen-containing compound may be included as a component other than the main component resin. By carbonizing such a resin, a carbon material containing nitrogen can be obtained.

Here, the following can be illustrated as nitrogen-containing resin.
Examples of thermosetting resins include melamine resins, urea resins, aniline resins, cyanate resins, urethane resins, phenol resins modified with nitrogen-containing components such as amines, and epoxy resins.
Examples of the thermoplastic resin include polyacrylonitrile, acrylonitrile-styrene (AS) resin, acrylonitrile-butadiene-styrene (ABS) resin, polyamide, polyetherimide, polyamideimide, polyimide, and polyphthalamide.

Moreover, the following can be illustrated as resin other than nitrogen-containing resin.
Examples of the thermosetting resin include phenol resin, epoxy resin, furan resin, and unsaturated polyester resin.

  Examples of the thermoplastic resin include polyethylene, polystyrene, polypropylene, vinyl chloride, methacrylic resin, polyethylene terephthalate, polycarbonate, polyacetal, polyphenylene ether, polybutylene terephthalate, polyphenylene sulfide, polysulfone, polyethersulfone, and polyetheretherketone. .

In addition, when a nitrogen-containing compound is used as a component other than the main component resin, the type thereof is not particularly limited. In addition to the aromatic polyamine, dicyandiamide and the like, besides the curing agent component, a compound containing nitrogen such as an amine compound, ammonium salt, nitrate, nitro compound which does not function as a curing agent can be used.
As the nitrogen-containing compound, one type may be used or two or more types may be used in combination, whether or not the main component resin contains nitrogen-containing resins.

Although it does not specifically limit as resin content used for the carbon material of this invention, or nitrogen content in resin, It is preferable that it is 5.0 to 65.0 weight%. More preferably, it is 10.0-20.0 weight%.
By performing the carbonization treatment of such a resin composition or resin, the carbon atom content in the carbon material finally obtained is 95.0 wt% or more, and the nitrogen atom content is 0.5 to 5.0 wt%. % Is preferred.
Thus, by containing 0.5 wt% or more, particularly 1.0 wt% or more of nitrogen atoms, it is possible to impart electrical characteristics suitable for the carbon material due to the electronegativity of nitrogen. Thereby, occlusion and discharge | release of lithium ion can be accelerated | stimulated and a high charging / discharging characteristic can be provided.

  Further, by setting the nitrogen atom to 5.0 wt% or less, particularly 3.0 wt% or less, the electrical characteristics imparted to the carbon material are suppressed from becoming excessively strong, and the occluded lithium ions are nitrogen. Prevents electroadsorption with atoms. Thereby, an increase in irreversible capacity can be suppressed and high charge / discharge characteristics can be obtained.

The nitrogen content in the carbon material of the present invention is not limited to the nitrogen content in the resin composition or the resin, but is subjected to a condition for carbonizing the resin composition or the resin, or a curing treatment or a pre-carbonization treatment before the carbonization treatment. In some cases, these conditions can also be adjusted by appropriately setting.
For example, as a method of obtaining the carbon material having the nitrogen content as described above, the nitrogen content in the resin composition or the resin is set as a predetermined value, and conditions for carbonizing the resin composition, particularly the final temperature are adjusted. There are methods.

  The method for preparing the resin composition used for the carbon material of the present invention is not particularly limited. For example, the above main component resin and other components are blended in a predetermined ratio, and these are melt mixed. These components can be prepared by dissolving them in a solvent and mixing them, or by pulverizing and mixing these components.

In the carbon material, the nitrogen content is measured by a thermal conductivity method.
In this method, a measurement sample is converted into a simple gas (CO ₂ , H ₂ O, and N ₂ ) using a combustion method, and then the gasified sample is homogenized and then passed through a column. . Thereby, these gas is isolate | separated in steps and content of carbon, hydrogen, and nitrogen can be measured from each thermal conductivity.
In the present invention, an element analysis measuring device “PE2400” manufactured by PerkinElmer Co., Ltd. was used.

The carbon material of the present invention has a positron lifetime measured by the positron annihilation method of 370 picoseconds or more, preferably 380 picoseconds or more. Further, the carbon material of the present invention has a positron lifetime measured by a positron annihilation method of 480 picoseconds or less, preferably 460 picoseconds or less.
When the positron lifetime measured by the positron annihilation method is not less than 370 picoseconds and not more than 480 picoseconds, it can be said that a void having a size in which lithium easily enters and exits is formed in the carbon material, as will be described later. It is possible to obtain a carbon material that can increase the discharge capacity, has a high charge capacity, a high discharge capacity, and has a charge / discharge efficiency of a certain degree or more, that is, a carbon material that has an excellent balance of charge capacity, discharge capacity, and charge / discharge efficiency. it can.

Here, the relationship between the positron lifetime and the void size will be described.
The positron lifetime method is a method for measuring the size of the void by measuring the time from when the positron (e ⁺ ) enters the sample until it disappears.
A positron is an antimatter of electrons and has the same static mass as an electron, but its charge is positive.
It is known that when a positron enters a substance, it becomes a pair (positron-electron pair (positronium)) with an electron and then disappears. When a positron is injected into the carbon material, the positron (e ⁺ ) is combined with one of the electrons struck out in the polymer to form positronium. Positronium is trapped in a portion having a low electron density in the polymer material, that is, a local void in the polymer, and overlaps with the electron cloud emitted from the void wall and disappears. When positronium is present in voids in the polymer, the size of the voids and the annihilation lifetime of positronium are inversely related. That is, when the void is small, the overlap between the positronium and the surrounding electrons is increased, and the positron annihilation lifetime is shortened. On the other hand, when the void is large, the probability that positronium disappears by overlapping with other electrons oozing out from the void wall is lowered, and the annihilation lifetime of positronium is increased. Therefore, the size of the voids in the carbon material can be evaluated by measuring the annihilation lifetime of positronium.
As described above, the positron incident on the carbon material loses energy, and then forms positronium and disappears together with the electron. At this time, γ rays are emitted from the carbon material.
Accordingly, the emitted γ rays serve as a measurement end signal.
For the measurement of positron annihilation lifetime, often used radioactive isotopes ^{22 Na} as that of an electron accelerator and generic as positron source. ²² Na emits positrons and 1.28 MeV gamma rays simultaneously when β ⁺ decays to ²² Ne. The positron incident on the carbon material emits 511 keV gamma rays through an annihilation process. Therefore, the annihilation lifetime of the positron can be obtained by measuring the time difference between the 1.28 MeV γ ray and the 511 kev γ ray as the end signal. Specifically, a positron lifetime spectrum as shown in FIG. 1 is obtained. The slope A of the positron lifetime spectrum indicates the positron lifetime, and the positron lifetime of the carbon material can be grasped from the positron lifetime spectrum.
When an electron accelerator is used as the positron source, electron / positron pair generation is caused by the braking X-rays generated by irradiating the target made of tantalum or tungsten with an electron beam to generate positrons. In the case of an electron accelerator, the time when the positron beam is incident on the sample is set as a measurement start point (corresponding to the start signal in the ²² Na), and the end signal is measured on the same principle as in the case of ²² Na.

Conventionally, as disclosed in Patent Documents 1 and ₂ , the pore volume and the pore diameter are measured by a gas adsorption method using CO ₂ , and the diameter and the capacity are capable of inserting and extracting lithium. A carbon material with pores was developed. However, it was very difficult to improve the charge capacity and the discharge capacity even when a carbon material having pores satisfying the conditions disclosed in Patent Documents 1 and 2 was used.
This is probably because carbon dioxide molecules have a molecular diameter of 0.33 nm, which is much larger than lithium ions (ion radius is about 0.06 nm). Lithium ions can enter and exit even very small pores that cannot be detected by the gas adsorption method using carbon dioxide. Therefore, the gas adsorption method using CO ₂ can absorb and release lithium ions. It is difficult to estimate the hole accurately. For this reason, it is considered that a carbon material having optimum pores capable of inserting and extracting lithium ions could not be obtained.
On the other hand, since the positron used in the positron annihilation method is very small, it is possible to accurately estimate the optimum hole for insertion and extraction of lithium ions. Therefore, by manufacturing a carbon material having a positron lifetime of 370 picoseconds or more and 480 picoseconds or less as measured by the positron annihilation method, it is possible to increase the charge capacity and the discharge capacity.
When the positron lifetime measured by the positron annihilation method is less than 370 picoseconds, the pore size is too small and it becomes difficult to occlude and release lithium ions. In addition, when the positron lifetime measured by the positron annihilation method exceeds 480 picoseconds, the amount of occlusion of lithium is increased, but it is assumed that lithium is less likely to be released due to an increase in electrostatic capacity due to intrusion of other substances such as an electrolytic solution. Is done.

In addition, the carbon material of the present invention has a spin concentration measured by an electron spin resonance method of 5 × 10 ¹⁶ spins / g or more and 2 × 10 ¹⁸ spins / g or less.
When the spin concentration in the electron spin resonance method is 5 × 10 ¹⁶ spins / g or more and 2 × 10 ¹⁸ spins / g or less, it can be said that the conductivity in the material is optimized as described later. The associated high efficiency is possible.

Here, the relationship between the spin concentration and the conductivity will be described.
The electron spin resonance method is one of spectroscopic methods for detecting unpaired electrons in a material. An electron has a property called spin, and when an unpaired electron is placed in a static magnetic field, the unpaired electron absorbs a microwave of a specific frequency, and the energy level of the spin transitions to a higher level. The electron spin resonance method detects unpaired electrons by utilizing this phenomenon. The absorption intensity of the electron spin resonance method is proportional to the number of unpaired electrons, and the concentration of unpaired electrons in the material, that is, the spin concentration can be obtained by comparing the concentration of unpaired electrons with a known standard sample.
Generally, it is known that the spin concentration in a material is related to the electrical resistivity, and it is said that the electrical resistivity decreases as the spin concentration increases.

When the spin concentration in the electron spin resonance method is less than 5 × 10 ¹⁶ spins / g, the spin concentration is low and the electric resistivity is high, and high efficiency is not accompanied even if the charge capacity is high. On the other hand, when the spin concentration exceeds 2 × 10 ¹⁸ spins / g, the unpaired electron density in the material increases, and the opportunity to react with the electrolytic solution increases, resulting in a decrease in efficiency due to an increase in irreversible capacity.
On the other hand, when the spin concentration is 5 × 10 ¹⁶ spins / g or more and 2 × 10 ¹⁸ spins / g or less, the electrical resistivity in the material is small and the irreversible capacity can be kept to a minimum. It is estimated that the accompanying high efficiency is possible.

The carbon material of the present invention preferably has an (002) plane average plane distance d002 of 3.40 mm or more and 3.90 mm or less calculated from the wide angle X diffraction method using the Bragg equation. When the average interplanar distance d002 is 3.40 mm or more, particularly 3.60 mm or more, it is difficult to cause shrinkage / expansion between layers accompanying occlusion of lithium ions, so that it is possible to suppress a decrease in charge / discharge cycle performance.
On the other hand, when the average interplanar distance d002 is 3.90 mm or less, particularly 3.80 mm or less, lithium ions are occluded / desorbed smoothly, and a decrease in charge / discharge efficiency can be suppressed.
Furthermore, in the carbon material of the present invention, the crystallite size Lc in the c-axis direction (the (002) plane orthogonal direction) is preferably 8 to 50 mm.
By setting Lc to 8 mm or more, particularly 9 mm or more, there is an effect that a carbon interlayer space capable of inserting and extracting lithium ions is formed, and a sufficient charge / discharge capacity can be obtained. By doing so, it is possible to suppress the collapse of the carbon laminate structure due to the insertion / desorption of lithium ions and the reductive decomposition of the electrolytic solution, and to suppress the decrease in charge / discharge efficiency and charge / discharge cycle performance.
Lc is calculated as follows.
It was determined from the half width of the 002 plane peak and the diffraction angle in the spectrum obtained from the X-ray diffraction measurement using the following Scherrer equation.
Lc = 0.94 λ / (βcos θ) (Scherrer equation)
Lc: crystallite size λ: wavelength of characteristic X-ray K _α1 output from the cathode β: half width of peak (radian)
θ: Spectral reflection angle

The X-ray diffraction spectrum of the carbon material of the present invention is measured by an X-ray diffractometer “XRD-7000” manufactured by Shimadzu Corporation. The method for measuring the average spacing in the carbon material of the present invention is as follows.
From the spectrum calculated | required from the X-ray-diffraction measurement of the carbon material of this invention, average surface space | interval d (nm) was computed from the following Bragg formulas.
λ = 2d _hkl sinθ Bragg equation (d _hkl = d ₀₀₂ )
λ: wavelength of characteristic X-ray K _α1 output from the cathode θ: reflection angle of spectrum

Furthermore, the carbon material of the present invention preferably has a specific surface area of 15 m ² / g or less and 1 m ² / g or more according to the BET three-point method in nitrogen adsorption.
Reaction with a carbon material and electrolyte solution can be suppressed because the specific surface area by BET 3 point method in nitrogen adsorption is 15 m < ² > / g or less.
Moreover, there exists an effect that appropriate permeability to the carbon material of electrolyte solution is acquired by making the specific surface area by BET 3 point method in nitrogen adsorption into 1 m < ² > / g or more.
The calculation method of the specific surface area is as follows.
The monomolecular adsorption amount Wm was calculated from the following formula (1), the total surface area Total was calculated from the following formula (2), and the specific surface area S was calculated from the following formula (3).
1 / [W (Po / P-1) = (C-1) / WmC (P / Po) / WmC (1)
In the formula (1), P: pressure of the adsorbate gas in the adsorption equilibrium, Po: saturated vapor pressure of the adsorbate at the adsorption temperature, W: adsorption amount at the adsorption equilibrium pressure P, Wm: monomolecular layer adsorption amount, C : Constant on the magnitude of the interaction between the solid surface and the adsorbate (C = exp {(E1-E2) RT}) [E1: heat of adsorption of the first layer (kJ / mol), E2: measurement temperature of the adsorbate Liquefaction heat (kJ / mol)]
Total = (WmNAcs) M (2)
In formula (2), N: Avogadro number, M: molecular weight, Acs: adsorption cross section S = Total / w (3)
In formula (3), w: sample weight (g)

The carbon material as described above can be manufactured as follows.
First, a resin or resin composition to be carbonized is manufactured.
The apparatus for preparing the resin composition is not particularly limited. For example, when melt mixing is performed, a kneading apparatus such as a kneading roll, a single screw or a twin screw kneader can be used. Moreover, when performing melt | dissolution mixing, mixing apparatuses, such as a Henschel mixer and a disperser, can be used. And when performing pulverization mixing, apparatuses, such as a hammer mill and a jet mill, can be used, for example.
The resin composition thus obtained may be one obtained by physically mixing a plurality of types of components, or is applied during mixing (stirring, kneading, etc.) during preparation of the resin composition. A part of the material may be chemically reacted with mechanical energy and thermal energy converted from the mechanical energy. Specifically, a mechanochemical reaction using mechanical energy or a chemical reaction using thermal energy may be performed.

The carbon material of the present invention is obtained by carbonizing the above resin composition or resin.
Although it does not specifically limit as conditions for carbonization here, For example, it heats up from normal temperature at 1-200 degreeC / hour, and is hold | maintained at 800-3000 degreeC for 0.1 to 50 hours, Preferably it is 0.5 to 10 hours Can be done. The atmosphere during the carbonization treatment is an inert atmosphere such as nitrogen or helium gas, or a substantially inert atmosphere where a trace amount of oxygen is present in the inert gas, or a reducing gas atmosphere. Is preferred. By doing in this way, thermal decomposition (oxidative decomposition) of resin can be suppressed and a desired carbon material can be obtained.
Conditions such as temperature and time during the carbonization can be adjusted as appropriate in order to optimize the characteristics of the carbon material.

In addition, before performing the said carbonization process, a pre carbonization process can be performed.
Although it does not specifically limit as conditions of a pre carbonization process here, For example, it can carry out at 200-600 degreeC for 1 to 10 hours. Thus, even if the resin composition or the resin is infusibilized by performing the pre-carbonization treatment before the carbonization treatment, and the resin composition or the resin is pulverized before the carbonization treatment step, the resin composition after the pulverization is performed. It is possible to prevent the object or resin from being re-fused during the carbonization treatment, and to obtain a desired carbon material efficiently.
At this time, as an example of a method for obtaining a carbon material having a positron lifetime measured by a positron annihilation method of 370 picoseconds or more and 480 picoseconds or less, a pre-carbonization treatment is performed in the absence of a reducing gas or an inert gas. Can be done.

Further, when a thermosetting resin or a polymerizable polymer compound is used as the resin constituting the carbon material, the resin composition or the resin can be cured before the pre-carbonization treatment.
Although it does not specifically limit as a hardening processing method, For example, it can carry out by the method of giving the heat quantity which can perform a hardening reaction to a resin composition, the method of thermosetting, or the method of using resin and a hardening | curing agent together. Thereby, since the pre-carbonization treatment can be performed substantially in the solid phase, the carbonization treatment or the pre-carbonization treatment can be performed in a state in which the resin structure is maintained to some extent, and the structure and characteristics of the carbon material can be controlled. become.

  In addition, when performing the carbonization treatment or the pre-carbonization treatment, a metal, a pigment, a lubricant, an antistatic agent, an antioxidant, or the like is added to the resin composition to impart desired characteristics to the carbon material. You can also.

When the said hardening process and / or pre carbonization process are performed, you may grind | pulverize a processed material after the said carbonization process after that. In such a case, variation in the thermal history during the carbonization treatment can be reduced, and the uniformity of the surface state of the carbon material can be improved. And the handleability of a processed material can be made favorable.
Further, in order to obtain a carbon material having a positron lifetime measured by a positron annihilation method of 370 picoseconds or more and 480 picoseconds or less, for example, after carbonization treatment, if necessary, in the presence of a reducing gas or an inert gas, You may naturally cool to 800-500 degreeC, and may cool at 100 degreeC / hour until it becomes 100 degrees C or less after that.
By doing in this way, the crack of the carbon material by rapid cooling is suppressed, and the positron lifetime measured by the positron annihilation method is 370 picoseconds or more and 480 picoseconds or less because it can maintain the formed voids. It is estimated that the material can be obtained.

(Lithium secondary battery)
Next, an embodiment of a negative electrode material for a secondary battery (hereinafter simply referred to as “negative electrode material”) of the present invention and a lithium secondary battery (hereinafter simply referred to as “secondary battery”) which is an embodiment using the same. explain.

FIG. 2 is a schematic diagram showing the configuration of the embodiment of the secondary battery.
The secondary battery 10 includes a negative electrode 13 composed of a negative electrode material 12 and a negative electrode current collector 14, a positive electrode 21 composed of a positive electrode material 20 and a positive electrode current collector 22, an electrolyte solution 16, and a separator 18. Is included.

  In the negative electrode 13, as the negative electrode current collector 14, for example, a copper foil or a nickel foil can be used. And the negative electrode material 12 uses the carbon material of this invention.

The negative electrode material of the present invention is manufactured, for example, as follows.
1 to 30 parts by weight of an organic polymer binder (fluorine polymer including polyethylene, polypropylene, etc., rubbery polymer such as butyl rubber and butadiene rubber) and an appropriate amount of viscosity with respect to 100 parts by weight of the carbon material. An adjustment solvent (N-methyl-2-pyrrolidone, dimethylformamide, etc.) is added and kneaded, and the paste-like mixture is molded into a sheet or pellet by compression molding, roll molding, etc. 12 can be obtained.
And the negative electrode 13 can be manufactured by laminating | stacking with the negative electrode collector 14. FIG.

  Further, 1 to 30 parts by weight of an organic polymer binder (fluorine polymer including polyethylene, polypropylene, etc., rubbery polymer such as butyl rubber, butadiene rubber, etc.) and an appropriate amount with respect to 100 parts by weight of the carbon material. A viscosity adjusting solvent (N-methyl-2-pyrrolidone, dimethylformamide, etc.) was added and kneaded, and the slurry mixture was used as the negative electrode material 12, and this was applied to the negative electrode current collector 14 and molded. Thus, the negative electrode 13 can also be manufactured.

As the electrolytic solution 16, a solution obtained by dissolving a lithium salt serving as an electrolyte in a non-aqueous solvent is used.
As this non-aqueous solvent, it is possible to use a mixture of cyclic esters such as propylene carbonate, ethylene carbonate and γ-butyrolactone, chain esters such as dimethyl carbonate and diethyl carbonate, and chain ethers such as dimethoxyethane. it can.
As the electrolyte, lithium metal salts such as LiClO ₄ and LiPF ₆ , tetraalkylammonium salts, and the like can be used. Further, the above salts can be mixed with polyethylene oxide, polyacrylonitrile, etc. and used as a solid electrolyte.

  Although it does not specifically limit as the separator 18, For example, porous films, such as polyethylene and a polypropylene, a nonwoven fabric, etc. can be used.

In the cathode 21, and is not particularly limited as cathode material 20, such as lithium cobalt oxide (LiCoO _2), lithium nickel oxide (LiNiO _2), composite oxides such as lithium manganese oxide (LiMn ₂ O _4), Conductive polymers such as polyaniline and polypyrrole can be used.
As the positive electrode current collector 22, for example, an aluminum foil can be used.
And the positive electrode 21 in this embodiment can be manufactured with the manufacturing method of the known positive electrode.

  It should be noted that the present invention is not limited to the above-described embodiments, and modifications, improvements, and the like within the scope that can achieve the object of the present invention are included in the present invention.

  The present invention will be described below with reference to examples. However, the present invention is not limited to the examples. In the examples and comparative examples, “parts” represents “parts by weight” and “%” represents “% by weight”.

First, measurement methods in the following examples and comparative examples will be described.
(1. Method for measuring positron lifetime by positron lifetime method)
Using a positron / positronium lifetime measurement / nanopore measurement device (manufactured by National Institute of Advanced Industrial Science and Technology), the electromagnetic wave (annihilation γ-ray) generated when the positron disappears was measured to measure the positron lifetime.
Specifically, it is as follows.
(A) Positron beam source: Using the electron accelerator of National Institute of Advanced Industrial Science and Technology (AIST), positrons are generated from electron / positron pair generation (the electron accelerator irradiates a target (tantalum) with an electron beam, Causes generation of electron-positron pairs, generating positrons)
(B) Gamma ray detector: BaF ₂ scintillator and photomultiplier tube (C) Measurement temperature and atmosphere: 25 ° C. in vacuum (1 × 10 ⁻⁵ Pa (1 × 10 ⁻⁷ Torr))
(D) Count of annihilation γ rays: 3 × 10 ⁶ or more (E) Positron beam energy: 10 keV
(F) Sample size: Apply powder to sample holder (aluminum plate) with thickness of 0.1mm

(2. Analysis of surface condition by ESR measurement)
The absorption intensity of the electromagnetic field was measured using JES-FR80 manufactured by JEOL.
Specifically, it is as follows.
(G) Device name: JES-FR80 (manufactured by JEOL)
(H) Measurement temperature: 23 ± 1 ° C
(I) Magnetic field range: 330 ± 100 mT
The g value was determined using a signal of Mn ²⁺ ions doped in magnesium oxide measured in the same manner as the measurement sample. The spin concentration of the measurement sample was calculated using the peak area of the electron spin resonance spectrum of the measurement sample and the peak area of the electron spin resonance spectrum of the standard sample for spin concentration measurement (TEMPOL) obtained by the same measurement.

(3. Average spacing (d002), crystallite size in the c-axis direction (Lc))
The average interplanar spacing was measured using an X-ray diffractometer “XRD-7000” manufactured by Shimadzu Corporation.
From the spectrum calculated | required from the X-ray-diffraction measurement of a carbon material, average surface space | interval d002 (nm) was computed from the following Bragg formulas.
λ = 2d _hkl sinθ Bragg equation (d _hkl = d ₀₀₂ )
λ: Wavelength of characteristic X-ray K _α1 output from the cathode θ: Reflection angle of spectrum Further, Lc was measured as follows.
It was determined from the half width of the 002 plane peak and the diffraction angle in the spectrum obtained from the X-ray diffraction measurement using the following Scherrer equation.
Lc = 0.94 λ / (βcos θ) (Scherrer equation)
Lc: crystallite size λ: wavelength of characteristic X-ray K _α1 output from the cathode β: half width of peak (radian)
θ: Spectral reflection angle

(4. Specific surface area)
It measured by the BET 3 point method in nitrogen adsorption | suction using the Yuasa company make Nova-1200 apparatus. A specific calculation method is as described in the above embodiment.

(5. Carbon content, nitrogen content)
The measurement was performed using an elemental analysis measuring device “PE2400” manufactured by PerkinElmer. The measurement sample is converted into CO ₂ , H ₂ O, and N ₂ using a combustion method, and then the gasified sample is homogenized and then passed through the column. Thereby, these gases were separated stepwise, and the contents of carbon, hydrogen, and nitrogen were measured from the respective thermal conductivities.
A) Carbon content The obtained carbon material was dried at 110 ° C./vacuum for 3 hours, and then the carbon composition ratio was measured using an elemental analyzer.
B) Nitrogen content The obtained carbon material was dried at 110 ° C./vacuum for 3 hours, and then the nitrogen composition was measured using an elemental analyzer.

(6. Charge capacity, discharge capacity, charge / discharge efficiency)
(1) Manufacture of a bipolar coin cell for secondary battery evaluation 10 parts of polyvinylidene fluoride as a binder and N-methyl-2- 2 as a diluting solvent with respect to 100 parts of the carbon material obtained in each example and comparative example A suitable amount of pyrrolidone was added and mixed to prepare a slurry-like negative electrode mixture. The prepared negative electrode slurry-like mixture was applied to both sides of 18 μm copper foil, and then vacuum-dried at 110 ° C. for 1 hour. After vacuum drying, the electrode was pressure-formed by a roll press. This was cut out as a circle having a diameter of 16.156 mm to produce a negative electrode.
The positive electrode was evaluated with a bipolar coin cell using lithium metal. As the electrolytic solution, a solution obtained by dissolving 1 mol / liter of lithium perchlorate in a mixed solution of ethylene carbonate and diethyl carbonate having a volume ratio of 1: 1 was used.

(2) Evaluation of Charging Capacity and Discharging Capacity The charging condition was that charging was stopped at a constant current of 25 mA / g until it reached 1 mV, and then the charging was terminated when the current attenuated to 1.25 mA / g with 1 mV holding. The cut-off potential under discharge conditions was 1.5V.

(3) Evaluation of charge / discharge efficiency Based on the value obtained in the above (2), the charge / discharge efficiency was calculated by the following formula.
Charge / discharge efficiency (%) = [discharge capacity / charge capacity] × 100

Example 1
As a resin composition, phenol resin PR-217 (manufactured by Sumitomo Bakelite Co., Ltd.) was processed in the order of the following steps (a) to (f) to obtain a carbon material.
(A) Temperature reduction from room temperature to 500 ° C. at 100 ° C./hour without any of reducing gas replacement, inert gas replacement, reducing gas flow and inert gas flow (b) Reducing gas replacement and inert gas replacement Then, after degreasing treatment at 500 ° C. for 2 hours without cooling gas flow and inert gas flow, cooling (c) fine pulverization with a vibrating ball mill (d) from room temperature to 1200 under substitution and flow of inert gas (nitrogen) (E) Carbonization for 8 hours at 1200 ° C. under an inert gas (nitrogen) flow (f) After natural cooling to 600 ° C. under an inert gas (nitrogen) flow, 600 Cooling from 100 ° C to 100 ° C or less at 100 ° C / hour

(Example 2)
In Example 1, 100 parts of aniline using aniline resin (synthesized by the following method) instead of phenol resin, 697 parts of 37% formaldehyde aqueous solution, 2 parts of oxalic acid, 3 ports equipped with a stirrer and a cooling pipe The flask was placed in a flask, reacted at 100 ° C. for 3 hours, and then dehydrated to obtain 110 parts of aniline resin. The obtained aniline resin had a weight average molecular weight of about 800.
The resin composition obtained by pulverizing and mixing 100 parts of the aniline resin and 10 parts of hexamethylenetetramine obtained as described above was treated in the same process as in Example 1 to obtain a carbon material.

(Example 3)
The same resin composition as in Example 2 was used.
Further, in the treatment of the resin composition, a carbon material was obtained in the same manner as in Example 2 except that the steps (d) and (e) were performed as follows.
(D) Under inert gas (nitrogen) substitution and flow, temperature rise from room temperature to 1100 ° C. at 100 ° C./hour (e) Carbonization treatment at 1100 ° C. for 8 hours under flow of inert gas (nitrogen)

(Comparative Example 1)
A carbon material composed of graphite (mesophase carbon microbeads) was prepared.

(Comparative Example 2)
A resin composition was prepared by pulverizing and mixing 30 parts of a novolac type phenol resin (PR-53195, manufactured by Sumitomo Bakelite Co., Ltd.), 3 parts of hexamethylenetetramine, and 70 parts of melamine resin.
The obtained resin composition was processed in the following steps to obtain a carbon material.
(G) Temperature rising from 100 ° C. to 200 ° C. at 20 ° C./hour under inert gas (nitrogen) flow (h) Heat treatment at 200 ° C. for 1 hour under inert gas (nitrogen) flow (c) Vibration Fine pulverization with a ball mill (i) Temperature increase from room temperature to 900 ° C. in an inert gas (nitrogen) atmosphere at 10 ° C./hour (j) Carbonization treatment at 900 ° C. in an inert gas (nitrogen) atmosphere for 10 hours ( f) After allowing to cool naturally to 600 ° C under inert gas (nitrogen) circulation, cooling from 600 ° C to 100 ° C or less at 100 ° C / hour

The carbon materials obtained in the above Examples and Comparative Examples were measured for positron lifetime, spin concentration, average interplanar spacing, crystallite size, specific surface area, carbon content, and nitrogen content. The results are shown in Table 1.
Table 2 shows the charge capacity, discharge capacity, and charge / discharge efficiency when the carbon materials obtained in the above Examples and Comparative Examples are used as the negative electrode.

Implementation in which the positron lifetime measured by the positron annihilation method is 370 picoseconds or more and 480 picoseconds or less, and the spin concentration measured by the electron spin resonance method is 5 × 10 ¹⁶ spins / g or more and 2 × 10 ¹⁸ spins / g or less. In Examples 1 to 3, all of the charge capacity and discharge capacity were very high, and the charge and discharge efficiency was as high as 75% or more.
In addition, the positron lifetime is 370 picoseconds or more and 480 picoseconds or less, and the spin concentration measured by the electron spin resonance method is 5 × 10 ¹⁶ spins / g or more and 2 × 10 ¹⁸ spins / g or less, In Examples 2 and 3 containing 1 wt% or more and 5 wt% or less of nitrogen atoms, the discharge capacity was also high.
As in Examples 2 and 3, the (002) plane average plane distance d calculated from the wide angle X diffraction method using the Bragg equation is 3.40 mm or more and 3.90 mm or less, and the positron lifetime is 370 picoseconds. As described above, since it is 480 picoseconds or less, in addition to the formation of pores of an effective size capable of reversibly occluding and releasing lithium ions, the carbon material contains 1.0 wt% or more of nitrogen atoms. By including 0.0 wt% or less, it is considered that suitable electrical characteristics can be imparted to the carbon material due to the electronegativity resulting from the optimum amount of nitrogen content. Thereby, it is presumed that occlusion / release of lithium ions is promoted and high charge / discharge characteristics can be obtained.
On the other hand, in Comparative Example 1, since the spin concentration measured by the electron spin resonance method is 5 × 10 ¹⁶ spins / g or more and 2 × 10 ¹⁸ spins / g or less and has an optimum conductivity, the charge / discharge efficiency is high. Although the positron lifetime is 370 picoseconds or less, the pore size is too small to absorb and release lithium ions, and both the charge capacity and the discharge capacity are low. Since the lifetime is 370 picoseconds or more and 480 picoseconds or less, lithium can be sufficiently occluded, and a high charge capacity is shown. However, since the spin concentration is 2 × 10 ¹⁸ spins / g or more, there is an excess of lithium. The irreversible capacity was increased and the charge / discharge efficiency was very low by promoting the reaction between the counter-electron and the electrolyte.

DESCRIPTION OF SYMBOLS 10 Secondary battery 12 Negative electrode material 14 Negative electrode collector 13 Negative electrode 20 Positive electrode material 22 Positive electrode collector 21 Positive electrode 16 Electrolytic solution 18 Separator

Claims (6)

A carbon material for a lithium ion secondary battery obtained by carbonizing a resin or a resin composition,
Under the following conditions (A) to (E), the positron lifetime measured by the positron annihilation method is 370 picoseconds or more and 480 picoseconds or less,
(A) Positron beam source: Generates positrons from electron / positron pairs using an electron accelerator (B) Gamma ray detector: BaF ₂ scintillator and photomultiplier tube (C) Measurement temperature and atmosphere: 25 ° C. in vacuum (D ) Count of annihilation γ-ray: 3 × 10 ⁶ or more (E) Positron beam energy: 10 keV
A carbon material for a lithium ion secondary battery, wherein a spin concentration measured by an electron spin resonance method is 5 × 10 ¹⁶ spins / g or more and 2 × 10 ¹⁸ spins / g or less. The carbon material for a lithium ion secondary battery according to claim 1,
The average spacing d of (002) planes calculated from the wide-angle X diffraction method using the Bragg equation is 3.4 mm or more and 3.9 mm or less, and the crystallite size Lc in the c-axis direction is 8 mm or more and 50 mm. The following carbon materials for lithium ion secondary batteries. The carbon material for a lithium ion secondary battery according to claim 1 or 2,
A carbon material for a lithium ion secondary battery having a specific surface area of 15 m ² / g or less and 1 m ² / g or more by a BET three-point method in nitrogen adsorption. The carbon material for a lithium ion secondary battery according to any one of claims 1 to 3,
A carbon material for a lithium ion secondary battery containing 95 wt% or more of carbon atoms and containing 0.5 wt% or more and 5 wt% or less of nitrogen atoms as elements other than carbon atoms.   The negative electrode material for lithium ion secondary batteries containing the carbon material for lithium ion secondary batteries in any one of Claims 1 thru | or 4.   The lithium ion secondary battery containing the negative electrode material for lithium ion secondary batteries of Claim 5.

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