JP2013222550A - Negative electrode material, negative electrode and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode material capable of being suitably used for manufacturing a lithium ion secondary battery small in a characteristic difference between individuals.SOLUTION: A first half cell is manufactured by applying a negative electrode material on a copper foil, forming an electrode at a pressing pressure of 125 kg/cm, using lithium metal as a counter electrode, and using an electrolyte obtained by adding LiPFat a rate of 1 mol/dminto a mixed solvent including an ethylene carbonate and a diethyl carbonate mixed at a volume ratio of 1:1. A second half cell is manufactured in the same manner as for the first half cell except that the pressing pressure is 250 kg/cm. In a negative electrode material of the present invention, a relationship of X-X≤20 mAh/g is satisfied, where X[mAh/g] represents an initial discharge capacity per unit weight of the electrode included in the first half cell, and X[ mAh/g] represents an initial discharge capacity per unit weight of the electrode included in the second half cell.

Description

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

  Conventionally, a carbon material has been used for a negative electrode of a lithium ion secondary battery (see, for example, Patent Document 1). This is because even if the charge / discharge cycle proceeds, dendritic lithium is hardly deposited on the negative electrode using the carbon material, and the safety is relatively high.

  However, conventionally, even when the same manufactured material is used, there has been a problem that a characteristic difference may be large among a plurality of manufactured lithium ion secondary batteries. This is considered to be due to the following reasons. That is, normally, the negative electrode is manufactured by applying a negative electrode material containing a carbon material on a sheet-like current collector, pressing the material, and increasing the density of the negative electrode material layer formed of the negative electrode material. It is formed. However, it is extremely difficult to strictly control the pressure when pressing the negative electrode material. And it is thought that the difference of the density of the negative electrode material layer formed by this difference in pressure arises, and as a result, the characteristic difference between lithium ion secondary batteries arises. In particular, from the viewpoint of productivity and the like, the negative electrode material is generally pressed by a roll press. However, in the roll press, it is particularly difficult to strictly adjust the pressing force (pressing pressure), The above tendency becomes more prominent.

JP-A-5-74457

  An object of the present invention is to provide a lithium ion secondary battery having a small characteristic difference between individuals, and to provide a negative electrode that can be suitably applied to a lithium ion secondary battery having a small characteristic difference between individuals. Another object of the present invention is to provide a negative electrode material that can be suitably used for the manufacture of a lithium ion secondary battery having a small characteristic difference between individuals.

Such an object is achieved by the present invention described in the following (1) to (14).
(1) A negative electrode material including a carbon material used in a lithium ion secondary battery,
A negative electrode material is applied on a copper foil, an electrode is formed at a pressing pressure of 125 kg / cm, lithium metal is used as a counter electrode, and ethylene carbonate and diethyl carbonate are mixed at a volume ratio of 1: 1 as an electrolyte. The initial discharge capacity per unit weight of the electrode of the first half cell when the first half cell is made using LiPF ₆ added at a ratio of 1 mol / dm ³ to the mixed solvent is X ₁ [ mAh / g]
The initial discharge capacity per unit weight of the electrode included in the second half cell when the second half cell is manufactured in the same manner as the first half cell except that the pressing pressure is 250 kg / cm is X ₂ [mAh / g]
A negative electrode material characterized by satisfying a relationship of X ₁ -X ₂ ≦ 20 mAh / g.

  (2) The negative electrode material according to (1), wherein the carbon material includes amorphous carbon.

  (3) The material for a negative electrode according to (2), wherein the carbon material includes graphite in addition to the amorphous carbon.

(4) When the content of the amorphous carbon in the negative electrode material is X _H [mass%] and the content of the graphite in the negative electrode material is X _G [mass%], 1 ≦ X _G The negative electrode material according to the above (3), which satisfies the relationship / X _H ≦ 25.

(5) Under the following conditions (A) to (E), the positron lifetime of the amorphous carbon measured by the positron annihilation method is 370 picoseconds or more and 480 picoseconds or less,
(A) Positron beam source: A positron is generated from an electron / positron pair 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
The half width of a peak observed near 285 eV measured by X-ray Photoelectron Spectroscopy (XPS method) is 0.8 eV or more and 1.8 eV or less, according to any one of (2) to (4) above Negative electrode material.

  (6) The negative electrode material according to any one of (1) to (5), wherein the negative electrode material contains a conductive additive.

  (7) The negative electrode material according to (6), wherein the content of the conductive additive with respect to 100 parts by mass of the carbon material is 0.5 part by mass or more and 20 parts by mass or less.

  (8) The negative electrode material according to any one of (1) to (7), wherein the negative electrode material contains styrene-butadiene rubber.

  (9) The negative electrode material according to (8), wherein the content of the styrene-butadiene rubber with respect to 100 parts by mass of the carbon material is 0.1 parts by mass or more and 15 parts by mass or less.

  (10) The negative electrode material according to any one of (1) to (9), wherein the negative electrode material contains carboxymethylcellulose.

  (11) The negative electrode material according to (10), wherein a content of the carboxymethyl cellulose with respect to 100 parts by mass of the carbon material is 0.1 parts by mass or more and 15 parts by mass or less.

  (12) A negative electrode manufactured using the negative electrode material according to any one of (1) to (11) above.

(13) A negative electrode material layer formed using the negative electrode material according to any one of (1) to (11) above on a current collector,
The negative electrode material layer has a porosity of 10% by volume or more and 70% by volume or less.

  (14) A lithium ion secondary battery manufactured using the negative electrode material according to any one of (1) to (11) above.

  According to the present invention, it is possible to provide a lithium ion secondary battery having a small characteristic difference between individuals, and to provide a negative electrode that can be suitably applied to a lithium ion secondary battery having a small characteristic difference between individuals. Moreover, the negative electrode material which can be used suitably for manufacture of a lithium ion secondary battery with a small characteristic difference between individuals can be 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.
<Material for negative electrode>
First, the negative electrode material of the present invention will be described.

  By the way, conventionally, a carbon material has been used for a 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 the safety is relatively high.

  However, conventionally, even when the same manufactured material is used, there has been a problem that a characteristic difference may be large among a plurality of manufactured lithium ion secondary batteries. This is considered to be due to the following reasons. That is, normally, the negative electrode is manufactured by applying a negative electrode material containing a carbon material on a sheet-like current collector, pressing the material, and increasing the density of the negative electrode material layer formed of the negative electrode material. It is formed. However, it is extremely difficult to strictly control the pressure when pressing the negative electrode material. And it is thought that the difference of the density of the negative electrode material layer formed by this difference in pressure arises, and as a result, the characteristic difference between lithium ion secondary batteries arises. In particular, from the viewpoint of productivity and the like, the negative electrode material is generally pressed by a roll press. However, in the roll press, it is particularly difficult to strictly adjust the pressing force (pressing pressure), The above tendency becomes more prominent.

Therefore, the present inventor has conducted intensive research for the purpose of solving the above problems, and has reached the present invention. That is, the negative electrode material of the present invention is provided with a negative electrode material on a copper foil, an electrode is formed with a press pressure of 125 kg / cm, lithium metal is used as a counter electrode, and ethylene carbonate and diethyl carbonate are used as an electrolyte. Unit of the electrode included in the first half cell, using a mixed solvent in which LiPF ₆ is added at a ratio of 1 mol / dm ³ to a mixed solvent in which the volume ratio of 1: 1 is mixed. When the second half cell is manufactured in the same manner as the first half cell except that the initial discharge capacity per weight is X ₁ [mAh / g] and the pressing pressure is 250 kg / cm, When the initial discharge capacity per unit weight of the electrode of the half cell is X ₂ [mAh / g], the relationship of X ₁ −X ₂ ≦ 20 mAh / g is satisfied. And features.

  With such a configuration, the above problems can be solved. That is, it is possible to provide a negative electrode material that can be suitably used for manufacturing a lithium ion secondary battery having a small characteristic difference between individuals without strictly controlling the pressure when pressing the negative electrode material. it can. In addition, it is possible to make the difference in characteristics among individual lithium ion secondary batteries sufficiently small without strictly controlling the pressure when pressing the negative electrode material. Thus, the yield can be improved, and as a result, the productivity of the lithium ion secondary battery can be improved.

On the other hand, when the above conditions are not satisfied, the excellent effects as described above cannot be obtained. That is, if the value of X ₁ -X ₂ is greater than 20 mAh / g, the lithium ion secondary battery obtained when the pressure when pressing the negative electrode material changes during the production of the lithium ion secondary battery. The difference in characteristics between individuals becomes abruptly large, and it becomes difficult to guarantee the stability of the quality of the lithium ion secondary battery. Moreover, in order to make the difference in characteristics between individual lithium ion secondary batteries produced sufficiently small, it is conceivable to strictly control the pressure when pressing the negative electrode material. In this case, the productivity of the lithium ion secondary battery is significantly reduced.

  In addition, “charging” for the half cell means moving lithium ions from an electrode made of lithium metal to an electrode made of a material containing a carbon material by applying a voltage, and “discharging” means This refers to a phenomenon in which lithium ions move from an electrode made of a material containing a carbon material to an electrode made of lithium metal.

As described above, in the present invention, the relationship X ₁ −X ₂ ≦ 20 mAh / g may be satisfied, but it is preferable that the relationship X ₁ −X ₂ ≦ 15 mAh / g is satisfied, and X ₁ −X _It is more preferable to satisfy the relationship of ₂ ≦ 10 mAh / g. Thereby, the effects as described above can be made more remarkable.

  The electrode used for the measurement of the half cell can be suitably produced as follows. That is, a predetermined amount of the negative electrode material of the present invention is applied on a copper foil as a current collector, preliminarily dried at 60 ° C. for 2 hours, and then vacuum-dried at 120 ° C. for 15 hours. By pressing with a pressing pressure (125 kg / cm or 250 kg / cm) and cutting out to a predetermined size, the electrode can be suitably manufactured.

  In the half cell, a negative electrode (an electrode manufactured using the negative electrode material of the present invention) composed of a negative electrode material layer and a negative electrode current collector has a disc shape with a diameter of 13 mm, and the negative electrode material layer has a thickness of The counter electrode (electrode composed of Li) can be a disk having a diameter of 12 mm and a thickness of 1 mm.

The half cell may have a 2032 coin cell shape.
Hereinafter, the constituent components of the negative electrode material of the present invention will be described in detail.

<Carbon material>
The negative electrode material of the present invention contains a carbon material.

  The negative electrode material of the present invention preferably contains at least amorphous carbon as a carbon material. Thereby, the effect that it is excellent in the rapid charge / discharge characteristic in low temperature (for example, -20 degreeC) is acquired.

  The carbon material constituting the negative electrode material preferably contains graphite in addition to amorphous carbon. Thereby, in addition to a large charge capacity and high safety, a negative electrode with particularly excellent initial charge / discharge efficiency can be obtained.

  In the present invention, the ratio of the sum of the total volume of the mesopores and the total volume of the macropores with respect to the total pore volume of the carbon material is 80% or more and 98% or less, and the unit weight per unit weight of the carbon material. The volume of the macropores is preferably 0.005 ml / g or more and 0.030 ml / g or less. Thereby, the charge / discharge capacity and current density during charge / discharge of the lithium ion secondary battery produced using the negative electrode material of the present invention can be made particularly excellent.

  As described above, the ratio of the sum of the total volume of mesopores and the total volume of macropores to the total pore volume of the carbon material is preferably 80% or more and 98% or less, but 85% or more and 95%. More preferably, it is 85% or more and 92% or less. Thereby, the effects as described above can be exhibited more remarkably.

  As described above, the macropore volume per unit weight of the carbon material is preferably 0.005 ml / g or more and 0.030 ml / g or less, but 0.007 ml / g or more and 0.025 ml / g. The following is more preferable. Thereby, the effects as described above can be exhibited more remarkably.

  The mesopore volume per unit weight of the carbon material is preferably 0.001 ml / g or more and 0.025 ml / g or less, more preferably 0.003 ml / g or more and 0.020 ml / g or less. preferable.

  The ratio of the total volume of mesopores to the total pore volume of the carbon material is preferably 20% or more and 50% or less, and more preferably 30% or more and 45% or less.

The ratio of the total volume of macropores to the total pore volume of the carbon material is preferably 30% or more and 70% or less, and more preferably 40% or more and 60% or less.
Hereinafter, the case where the carbon material includes graphite and amorphous carbon will be mainly described.

[Graphite]
Graphite is one of the allotropes of carbon, and is a hexagonal hexagonal plate crystal material that forms a layered lattice made of layers of six-carbon rings.

  The particle size (average particle size) at the time of 50% accumulation in the volume-based cumulative distribution of graphite is preferably 5 μm or more and 50 μm or less, and more preferably 5 μm or more and 30 μm or less. This makes it possible to produce a high-density electrode while maintaining high charge / discharge efficiency.

  The content of graphite in the carbon material is preferably 50% by weight or more and 96.2% by weight or less, more preferably 55% by weight or more and 95% by weight or less, and 60% by weight or more and 83.3% by weight. More preferably, it is as follows. When the graphite content is within the above range, the charge / discharge efficiency can be increased, the cycle stability can be further improved, and the input / output characteristics of a large current can be further improved.

[Amorphous carbon]
Amorphous carbon, unlike graphite, is an amorphous (amorphous) carbon material.
Amorphous carbon can be suitably obtained by carbonizing a resin or resin composition.

  The particle size (average particle size) at 50% accumulation in the volume-based cumulative distribution of amorphous carbon is preferably 1 μm or more and 50 μm or less, and more preferably 2 μm or more and 30 μm or less. Thereby, a high-density electrode can be produced.

  The content of amorphous carbon in the carbon material is preferably 3.8 wt% or more and 50 wt% or less, more preferably 5.0 wt% or more and 45 wt% or less, and 16.7 wt%. % To 40% by weight is more preferable. Thereby, the stability at the time of cycling and the input / output characteristics of a large current can be more effectively enhanced without impairing the excellent charge / discharge efficiency.

When the negative electrode material of the present invention contains amorphous carbon and graphite, the content of the amorphous carbon in the negative electrode material is X _H [mass%], and the content of the graphite in the negative electrode material Is preferably X _G [mass%], preferably satisfies the relationship of 1 ≦ X _G / X _H ≦ 25, more preferably satisfies the relationship of 1.2 ≦ X _G / X _H ≦ 19. More preferably, the relationship of 1.5 ≦ X _G / X _H ≦ 6 is satisfied. By satisfying such a relationship, the stability during cycling and the input / output characteristics of a large current can be further effectively improved without impairing the excellent charge / discharge efficiency.

  The resin used as the raw material for amorphous carbon or the resin contained in the resin composition is not particularly limited. For example, a thermosetting resin, a thermoplastic resin, or petroleum-based tar produced as a by-product during production of ethylene and Petroleum, coal-based tar or pitch, such as pitch, coal tar produced during coal carbonization, heavy components and pitch obtained by distilling off low boiling components of coal tar, tar and pitch obtained by coal liquefaction, and Those obtained by crosslinking the tar, pitch and the like can be contained, and one or more of these can be used in combination.

  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, and further, a crosslinking treatment by oxidation or the like can be appropriately performed. it can.

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

  The thermoplastic resin is not particularly limited, and examples thereof include 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.

  In particular, a thermosetting resin is preferable as a resin as a main component used in the production of amorphous carbon. Thereby, the storage stability (long-term storage characteristics) of the negative electrode material can be made particularly excellent.

  In particular, among thermosetting resins, those selected from novolac type phenol resins, resol type phenol resins, melamine resins, furan resins, aniline resins, and modified products thereof are preferable. Thereby, the charge / discharge efficiency can be made particularly excellent. In addition, the degree of freedom in designing the carbon material is widened and can be manufactured at a low price. Further, the stability during cycling and the input / output characteristics of a large current can be further improved.

Moreover, when using a thermosetting resin, the hardening | curing agent can be used together.
The curing agent to be used is not particularly limited. For example, in the case of a novolac type phenol resin, hexamethylenetetramine, resol type phenol resin, polyacetal, paraform and the like can be used. In the case of epoxy resin, 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, resol type phenol resins, etc. 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 embodiment is used in a smaller amount than usual or without using a curing agent. You can also.

  Moreover, in the resin composition as a raw material of amorphous carbon, an additive can be blended in addition to the above components.

  Although it does not specifically limit as an additive used here, For example, the carbon material precursor carbonized at 200 to 800 degreeC, an organic acid, an inorganic acid, a nitrogen-containing compound, an oxygen-containing compound, an aromatic compound, and And non-ferrous metal elements. These additives can be used alone or in combination of two or more depending on the type and properties of the resin used.

  As a resin used as a raw material for amorphous carbon, 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, amorphous carbon containing nitrogen can be obtained. When nitrogen is contained in amorphous carbon, suitable electrical characteristics can be imparted to amorphous carbon (carbon material) depending on 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.

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, polyphthalamide, and the like.

Moreover, the following can be illustrated as resin other than nitrogen-containing resin.
Examples of the thermosetting resin include a phenol resin, an epoxy resin, a furan resin, and an 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. For example, hexamethylenetetramine, which is a curing agent for a novolac type phenol resin, and aliphatic polyamine, which is a curing agent for an epoxy resin. Besides aromatic polyamines, dicyandiamide and the like, in addition to the curing agent component, amine compounds that do not function as curing agents, ammonium salts, nitrates, nitro compounds, and other nitrogen-containing compounds 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.

  The resin composition used as the raw material for amorphous carbon or the nitrogen content in the resin is not particularly limited, but is preferably 5% by weight or more and 65% by weight or less, preferably 10% by weight or more and 20% by weight or less. More preferably.

  The carbon atom content in the amorphous carbon obtained by carbonizing the resin composition or resin is preferably 95% by weight or more, and the nitrogen atom content is preferably 0.5% by weight. The content is preferably 5% by weight or less.

  Thus, by containing 0.5% by weight or more, particularly 1.0% by weight or more of nitrogen atoms, it is possible to impart electrical characteristics suitable for amorphous carbon depending on 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% by weight or less, particularly 3% by weight or less, the electrical characteristics imparted to the amorphous carbon are suppressed from becoming excessively strong, and the occluded lithium ions are nitrogenated. Prevents electroadsorption with atoms. Thereby, an increase in irreversible capacity can be suppressed and high charge / discharge characteristics can be obtained.

  Nitrogen content in amorphous carbon is the above-mentioned resin composition or nitrogen content in the resin, as well as conditions for carbonizing the resin composition or resin, and when curing or pre-carbonization is performed before carbonization. In addition, these conditions can also be adjusted by appropriately setting.

  For example, as a method for 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, in particular, the final temperature is adjusted. There are methods.

  The method for preparing a resin composition used as a raw material for amorphous carbon is not particularly limited, for example, a method of blending the above main component resin and other components at a predetermined ratio, and melt-mixing them, It can be prepared by a method in which these components are dissolved in a solvent and mixed, or a method in which these components are pulverized and mixed.

In the present specification, 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.

Further, the amorphous carbon constituting the negative electrode material of the present invention preferably has a positron lifetime measured by a positron annihilation method of 370 picoseconds or more and 480 picoseconds or less, and 380 picoseconds or more and 460 picoseconds or less. More preferably.
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 amorphous carbon as described later. The charge capacity and discharge capacity of the ion secondary battery can be further increased.

Note that the measurement of the positron lifetime by the positron annihilation method is performed under the following conditions.
(A) Positron beam source: A positron is generated from an electron / positron pair 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

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 the positronium overlaps with other electrons that have exuded from the void wall and disappears becomes low, and the annihilation lifetime of the positronium becomes long. 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.

  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 the case of amorphous carbon, the half width of the peak observed around 285 eV measured by XPS method is preferably 0.8 eV or more and 1.8 eV or less, more preferably 0.9 eV or more and 1.6 eV or less. preferable. When the half-value width of the peak observed around 285 eV measured by XPS method is 1.8 eV or less, most of the elements present on the amorphous carbon surface are due to inactive C—C bonds, etc. A functional group or impurity that reacts with an active substance related to ion conduction such as ions is substantially absent. Moreover, when the half width of the peak recognized in the vicinity of 285 eV is 0.8 eV or more, problems such as excessive crystallization do not occur. Therefore, when the half width of the peak observed in the vicinity of 285 eV measured by the XPS method is 0.8 eV or more and 1.8 eV or less, a decrease in charge / discharge efficiency due to irreversible capacity is suppressed.

Next, the relationship between the XPS measurement and the surface state will be described.
The XPS measurement method irradiates the surface of a solid sample with X-rays and measures the kinetic energy of photoelectrons emitted from the excited atoms. As a result, the binding energy of electrons in the atoms (a value specific to each atom is determined). It is a method for identifying constituent elements present on the surface.

  The surface state can also be analyzed by the FT-IR method, which identifies chemical bonds existing about 1 μm from the surface, whereas the XPS measurement method identifies elements present several kilometers from the surface. be able to. From this, it is preferable to use the XPS measurement method to identify the functional group closer to the surface.

Amorphous carbon preferably has an average interplanar spacing d ₀₀₂ of (002) planes of 3.4 to 3.9 mm calculated from the wide-angle X-ray diffraction method using the Bragg equation. When the average interplanar distance d ₀₀₂ is 3.4 mm or more, particularly 3.6 mm or more, the interlayer contraction / expansion due to the occlusion of lithium ions is less likely to occur, so that the reduction in charge / discharge cycle performance can be suppressed.

On the other hand, when the average interplanar distance d ₀₀₂ is 3.9 mm or less, particularly 3.8 mm or less, lithium ions are smoothly occluded / desorbed, and a decrease in charge / discharge efficiency can be suppressed.

  Further, the amorphous carbon preferably has a crystallite size Lc in the c-axis direction (the (002) plane orthogonal direction) of 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 = 0.94λ / (βcosθ) (Scherrer equation)
Lc: Crystallite size λ: Characteristic X-ray Kα1 wavelength output from the cathode β: Half width of peak (radian)
θ: Reflection angle of spectrum

  The X-ray diffraction spectrum in the amorphous carbon is measured by an X-ray diffraction apparatus “XRD-7000” manufactured by Shimadzu Corporation. The method for measuring the average interplanar spacing in amorphous carbon is as follows.

  From the spectrum obtained from the X-ray diffraction measurement of amorphous carbon, the average interplanar spacing d was calculated from the following Bragg equation.

λ = 2d _hkl sin θ (Bragg equation) (d _hkl = d ₀₀₂ )
λ: wavelength of characteristic X-ray Kα1 output from the cathode θ: reflection angle of spectrum

Further, the amorphous carbon 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 amorphous carbon as described above can be produced as follows in a typical example of a resin or a resin composition.

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.

Amorphous carbon is obtained by carbonizing the above resin composition or resin.
Here, the conditions for the carbonization treatment are not particularly limited. For example, the temperature is raised from room temperature to 1 ° C./hour to 200 ° C./hour, and from 800 ° C. to 3000 ° C., 0.1 to 50 hours, preferably Can be carried out by holding for 0.5 hours or more and 10 hours or less. 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 carbonization can be adjusted as appropriate in order to optimize the characteristics of amorphous carbon.

  In addition, in order to obtain a carbon material having a peak half-value width measured in the vicinity of 285 eV measured by the XPS method of 0.8 eV or more and 1.8 eV or less, conditions may be appropriately determined according to the resin or the like. The temperature during the carbonization treatment may be set to 1000 ° C. or higher, and the temperature increase rate may be set to less than 200 ° C./hour.

  By doing so, the surface of the amorphous carbon is caused by an inactive functional group or the like, and the half width of the peak observed near 285 eV measured by XPS method is 0.8 eV or more and 1.8 eV or less. It is estimated that crystalline carbon can be obtained.

In addition, before performing the said carbonization process, a pre carbonization process can be performed.
Although it does not specifically limit as conditions for pre carbonization here, For example, it can carry out at 200 degreeC or more and 600 degrees C or less for 1 hour or more and 10 hours or less. Thus, even if the resin composition or 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 or the resin can be prevented from being re-fused during carbonization, and a desired carbon material can be obtained efficiently.

  At this time, as an example of a method for obtaining amorphous carbon having a positron lifetime measured by the positron annihilation method of 370 picoseconds or more and 480 picoseconds or less, in the absence of a reducing gas or an inert gas, Carburizing treatment is performed.

  Further, when a thermosetting resin or a polymerizable polymer compound is used as the resin for producing amorphous carbon, 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 hardening reaction to a resin composition, the method of thermosetting, or the method of using resin and a hardening | curing agent together. As a result, the pre-carbonization treatment can be performed substantially in the solid phase, so that the carbonization treatment or the pre-carbonization treatment can be performed while maintaining the resin structure to some extent, and the structure and characteristics of the amorphous carbon can be controlled. become able to.

  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 curing treatment and / or the pre-carbonization treatment are performed, the processed product may be pulverized before the carbonization treatment. In such a case, variation in thermal history during carbonization can be reduced, and the uniformity of the surface state of amorphous carbon can be improved. And the handleability of a processed material can be made favorable.

  Further, in order to obtain amorphous carbon having a positron lifetime measured by the positron annihilation method of 370 picoseconds or more and 480 picoseconds or less, for example, in the presence of a reducing gas or an inert gas after carbonization treatment as necessary. Then, it may be naturally cooled to 500 ° C. or higher and 800 ° C. or lower, and then cooled at 100 ° C./hour until it becomes 100 ° C. or lower.

  By doing so, cracks of amorphous carbon due to rapid cooling are suppressed, and the formed voids can be maintained, so that the positron lifetime measured by the positron annihilation method is 370 picoseconds or more and 480 picoseconds or less. It is speculated that some amorphous carbon can be obtained.

<Conductive aid>
The negative electrode material of the present invention may contain a conductive additive in addition to the carbon material. Thereby, the electroconductivity of a negative electrode improves and the heat_generation | fever by an electrical resistance can be prevented more effectively.

  In this invention, a conductive support agent means the material with high electroconductivity added in order to improve the electroconductivity of a negative electrode.

  As the conductive assistant, for example, carbon black such as acetylene black and furnace black, vapor grown carbon fiber (VGCF), fine carbon fiber such as carbon nanotube, and the like can be used.

  When the negative electrode material contains a conductive additive, the content of the conductive additive with respect to 100 parts by mass of the carbon material is preferably 0.5 parts by mass or more and 20 parts by mass or less, and preferably 1 part by mass or more and 10 parts by mass or less. It is more preferable that Thereby, higher electroconductivity can be provided, preventing the side reaction of Li and a conductive support material.

<Styrene-butadiene rubber>
The negative electrode material of the present invention may contain styrene-butadiene rubber. Thereby, the negative electrode material can be suitably bonded to the current collector in a small amount.

  When the negative electrode material includes styrene-butadiene rubber, the content of the styrene-butadiene rubber with respect to 100 parts by mass of the carbon material is preferably 0.1 parts by mass or more and 15 parts by mass or less, and 0.5 parts by mass or more. More preferably, it is 10 parts by mass or less. Thereby, the negative electrode material can be suitably bonded to the current collector while preventing an increase in the electric resistance of the negative electrode.

<Carboxymethylcellulose>
Moreover, the negative electrode material of the present invention may contain carboxymethyl cellulose. Thereby, the viscosity at the time of apply | coating the material for negative electrodes on a collector is increased, and thickness control of a negative electrode becomes easier.

  When the negative electrode material contains carboxymethyl cellulose, the content of carboxymethyl cellulose with respect to 100 parts by mass of the carbon material is preferably 0.1 parts by mass or more and 15 parts by mass or less, and 0.5 parts by mass or more and 10 parts by mass or less. It is more preferable that Thereby, the viscosity at the time of apply | coating the negative electrode material on a collector is prevented, preventing the increase in the electrical resistance of a negative electrode, and thickness control of a negative electrode becomes easier.

<Other ingredients>
Moreover, the negative electrode material of the present invention may contain components other than those described above (other components). Examples of such components include organic polymer binders (for example, fluorine-based polymers including polyethylene and polypropylene, rubbery polymers such as butyl rubber), viscosity adjusting solvents (for example, water, N- Methyl-2-pyrrolidone, dimethylformamide and the like).

<Negative electrode / Lithium ion secondary battery>
Next, the negative electrode and lithium ion secondary battery (hereinafter, also simply referred to as “secondary battery”) of the present invention will be described.

  The negative electrode of the present invention is produced using the negative electrode material of the present invention as described above. Thereby, the negative electrode which can be applied suitably for a lithium ion secondary battery with a large charge capacity and high safety can be provided. The lithium ion secondary battery of the present invention is manufactured using the negative electrode material of the present invention. Thereby, a lithium ion secondary battery with a large charge capacity and high safety can be provided.

Hereinafter, preferred embodiments of the negative electrode and the lithium ion secondary battery of the present invention will be described.
FIG. 2 is a schematic diagram of a lithium ion secondary battery.
As shown in FIG. 2, the secondary battery 10 includes a negative electrode 13, a positive electrode 21, an electrolytic solution 16, and a separator 18.

As shown in FIG. 2, the negative electrode 13 includes a negative electrode material layer 12 and a negative electrode current collector 14.
The negative electrode current collector 14 is made of, for example, copper foil or nickel foil.
The negative electrode material layer 12 is formed using the negative electrode material of the present invention as described above.
The negative electrode 13 can be manufactured as follows, for example.
The negative electrode 13 can be manufactured, for example, by the following manufacturing method.

  That is, the negative electrode 13 has a coating process for coating the negative electrode material of the present invention as described above on the sheet-like negative electrode current collector 14 to form a coating film, and a pressing process for pressing the coating film. It can be manufactured using a method.

  In the manufacture of the negative electrode 13, the negative electrode current collector 14 to which the negative electrode material is applied may have a size corresponding to the negative electrode 13 to be included in the lithium ion secondary battery 10 to be finally manufactured. Although it is good, from the viewpoint of productivity, the negative electrode current collector 14 coated with the negative electrode material is cut after at least the coating step, and the lithium ion secondary battery 10 to be finally manufactured is provided. A size corresponding to the power negative electrode 13 is preferable.

  Moreover, it is preferable that the negative electrode current collector 14 is wound in a roll shape, and a negative electrode material is coated on a portion fed from the roll by rotation.

  The conveying speed of the negative electrode current collector 14 subjected to the coating process is preferably 0.1 m / min or more and 5 m / min or less, and more preferably 0.5 m / min or more and 3 m / min or less. Thereby, the productivity of the lithium ion secondary battery 10 can be made particularly excellent while sufficiently reducing variation in characteristics due to uneven coating amount and uneven thickness of the negative electrode material layer 12.

  The negative electrode material can be applied using a known apparatus such as a gravure coater, a slit coater, a bar coater, or a doctor blade coater.

  Although the press process should just press the coating film formed using the material for negative electrodes, it is preferable to perform by a roll press. Thereby, the productivity of the lithium ion secondary battery 10 can be made particularly excellent. In addition, in the conventional negative electrode material, when the coating film formed using the negative electrode material is pressed by a roll press, there is a problem that a characteristic difference between individual lithium ion secondary batteries to be manufactured increases. However, in the present invention, even when a roll press is employed, it is possible to reliably prevent the above problems from occurring. That is, when the coating film formed using the negative electrode material is pressed by a roll press, the effects of the present invention are more remarkably exhibited.

  The pressing pressure in the pressing step is preferably 50 kg / cm or more and 400 kg / cm or less, and more preferably 100 kg / cm or more and 350 kg / cm or less. Thereby, the density of the negative electrode material layer 12 can be made higher, the charge / discharge capacity of the lithium ion secondary battery 10 can be made particularly excellent, and the productivity of the lithium ion secondary battery 10 is particularly excellent. Can be.

  When the pressing step is performed by roll pressing, the adjustment of the pressing pressure is performed by adjusting the gap between the negative electrode current collector 14 and the roll (roll gap) and the amount of the negative electrode material applied to the negative electrode current collector 14 per unit area. This can be done by adjusting.

  The porosity of the negative electrode material layer 12 is preferably 10% by volume or more and 70% by volume or less, and more preferably 20% by volume or more and 60% by volume or less. As a result, a negative electrode having a high density and easily infiltrated with the electrolytic solution can be obtained.

  The electrolyte solution 16 fills the space between the positive electrode 21 and the negative electrode 13 and is a layer in which lithium ions move by charge / discharge.

  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, chain ethers such as dimethoxyethane, and the like. 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 or the like and used as a solid electrolyte.

  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.

As shown in FIG. 2, the positive electrode 21 has a positive electrode material layer 20 and a positive electrode current collector 22.
The positive electrode material layer 20 is not particularly limited. For example, a composite oxide such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganese oxide (LiMn ₂ O ₄ ), or polyaniline is used. A conductive polymer such as 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.

  As mentioned above, although this invention was demonstrated based on suitable embodiment, this invention is not limited to these.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example and a comparative example, this invention is not limited to this. In the examples and comparative examples, “part” indicates “part by weight” and “%” indicates “% by weight”.

[1] Measuring Method First, measuring methods in the following examples and comparative examples will be described.

1. Particle size distribution Using a laser diffraction particle size distribution measuring device LA-920 manufactured by Horiba, Ltd., by laser diffraction, the particle size distribution of the carbon material, the particle size distribution of graphite constituting the carbon material, and the amorphous carbon constituting the carbon material The particle size distribution was measured. From the measurement results, for the carbon material, the particle diameter (D50, average particle diameter) at the time of 50% accumulation in the number-based cumulative distribution is obtained, and the graphite constituting the carbon material and the amorphous carbon constituting the carbon material , 50% cumulative particle size (D50, average particle size) was determined.

2. Measurement of size and abundance of vacancies in amorphous carbon Using a sample of Shimadzu Corporation's pore distribution measuring device “ASAP2010”, after preheating under vacuum at 623K, using nitrogen gas as the measurement gas The adsorption isotherm at 77K was measured, and the pore volume was calculated by the DH method. The sum of the volumes of pores having a diameter of 2 nm or more and less than 50 nm was defined as the mesopore volume, and the sum of the volumes of pores of 50 nm or more was defined as the macropore volume.

3. Measurement method of positron lifetime by positron lifetime method Using positron / positronium lifetime measurement / nano-hole measuring device (manufactured by National Institute of Advanced Industrial Science and Technology), measure electromagnetic wave (annihilation γ-ray) generated when positron disappears, The positron lifetime was measured.
Specifically, it is as follows.

(A) Positron beam source: National Institute of Advanced Industrial Science and Technology
Generating positrons from electron-positron pair generation (the electron accelerator
Irradiate get (tantalum) with electron beam to generate electron-positron pairs
Cause 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: Powder is applied to a sample holder (aluminum plate) with a thickness of 0.1 mm.

4). Analysis of surface condition by XPS measurement Using Escalab-220iXL (Thermo Fisher Scientific), measurement was performed under the following conditions, and the half width of the peak observed near 285 eV was obtained by the following calculation method. Calculated.

(Measurement condition)
X-ray source: Mg-Kα
Output: 12kV-10mA

(Method of calculation)
Based on the obtained spectrum, the peak intensity and the peak half-value width are obtained as follows.
In order to obtain the peak intensity, a baseline is drawn from both ends of the target peak, and the intensity from the baseline to the peak apex is defined as the peak intensity. This is because the base line of the spectrum usually obtained changes depending on the environment at the time of measurement, the difference in the sample, and the like. When a plurality of peaks overlap in the obtained spectrum, a baseline is drawn from both ends of the overlapping peaks. The half width of the peak is obtained by drawing a line parallel to the base line from a point having an intensity of ½ of the peak intensity obtained from the peak apex, and reading the energy at the intersection with both ends of the peak.

5. Average spacing (d ₀₀₂ ), 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 obtained from the X-ray diffraction measurement of the carbon material, the average interplanar distance d ₀₀₂ was calculated from the following Bragg equation.

λ = 2d _hkl sin θ (Bragg equation) (d _hkl = d ₀₀₂ )
λ: wavelength of characteristic X-ray Kα1 output from the cathode θ: reflection angle of spectrum

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 = 0.94λ / (βcosθ) (Scherrer equation)
Lc: crystallite size λ: wavelength of characteristic X-ray Kα1 output from the cathode β: half width of peak (radian)
θ: Reflection angle of spectrum

6). Specific surface area It measured by the BET 3 point method in nitrogen adsorption | suction using the specific surface area measuring apparatus Nova-3200 made from Quantachrome. A specific calculation method is as described in the above embodiment.

7. Carbon content, nitrogen content Measured 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 amorphous carbon 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 amorphous carbon was dried at 110 ° C./vacuum for 3 hours, and then the nitrogen composition ratio was measured using an elemental analyzer.

8). Electrode porosity measurement (according to moisture absorption characteristics specification)
Measurement was performed by mercury porosimetry using a fully automatic pore distribution measuring device, Por Master 60-GT, manufactured by Quantachrome. The porosity was calculated from the following equation from the pore volume (P) obtained by injecting mercury into the sample cell containing the measurement sample and the bulk volume (V) of the sample.
Porosity = P / (P + V) × 100

9. Charge capacity, discharge capacity, charge / discharge efficiency, etc. (1) Manufacture of bipolar coin cell for secondary battery evaluation For each example and each comparative example, the negative electrode material was stirred and mixed with a mixer to form a slurry, This was applied to one side of an 18 μm copper foil, then pre-dried at 60 ° C. for 2 hours, and then vacuum-dried at 120 ° C. for 15 hours. After vacuum drying, pressing is performed so that the pressing pressure is 125 kg / cm, and this is cut into a disk shape having a diameter of 13 mm, and a current collector made of copper and a negative electrode material layer made of a dried material for negative electrode The negative electrode provided with these was produced.

A disc-shaped positive electrode having a diameter of 12 mm and a thickness of 1 mm was formed using lithium metal.
Then, using the negative electrode and the positive electrode produced as described above, LiPF ₆ was added at a ratio of 1 mol / dm ³ to a mixed solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 1 as an electrolytic solution. Was used to produce a 2032 type coin cell-shaped bipolar half cell.

Further, a 2032 type coin cell-shaped bipolar half cell was manufactured in the same manner as described above except that the pressing pressure was changed to 250 kg / cm.
These half cells were evaluated as follows.

(2) Initial charge capacity, initial discharge capacity Charging condition is that the battery is charged until it reaches 0V at a constant current of 25mA / g at 25 ° C, and then the charge ends when the current decays to 2.5mA / g with 0V holding. It was. The cut-off potential under discharge conditions was 1.5V.

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

(4) Evaluation of 60 cycle capacity retention ratio The ratio of the charge / discharge capacity obtained in (2) above and the discharge capacity after repeating charge / discharge 60 times was calculated by the following formula.

  60 cycle capacity retention rate (%) = [60th cycle discharge capacity / 1st cycle charge capacity] × 100

  The second and subsequent charging / discharging conditions were defined as charging termination when the current was attenuated to 12.5 mA / g with 1 mV holding after charging at a constant current of 250 mA / g until reaching 1 mV. The cut-off potential under discharge conditions was 1.5V.

(5) Large current characteristics Based on the value of the discharge capacity obtained in the above (2), the discharge value obtained by discharging at a current value of 1C, assuming that the current value that completes the discharge in 1 hour is 1C, The ratio of the discharge capacity obtained by discharging at a current value of 5C [5C discharge capacity / 1C discharge capacity] was used as an indicator of the large current characteristics.

[2] Production of negative electrode material (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 hard carbon as amorphous carbon.

(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

100 parts by weight of porous graphite (mesophase carbon microbeads) and 43 parts by weight of the obtained amorphous carbon were mixed using a mortar to obtain a carbon material.
Thereafter, the carbon material obtained as described above was mixed with styrene-butadiene rubber, carboxymethyl cellulose, and acetylene black as a conductive auxiliary agent at a ratio as shown in Table 1, whereby a negative electrode material ( Negative electrode material) was obtained.

(Examples 2 and 3)
A negative electrode material (negative electrode material) was obtained in the same manner as in Example 1 except that the contents of graphite and amorphous carbon were changed as shown in Table 1.

Example 4
The same resin composition as in Example 1 was used.
Moreover, the carbon material was obtained like Example 1 except the point which changed the process of (c) of Example 1 as follows in the process of a resin composition.

(C) Fine pulverization with a bead mill Thereafter, the carbon material was mixed with styrene-butadiene rubber, carboxymethyl cellulose, and acetylene black as a conductive auxiliary agent at a ratio as shown in Table 1, whereby a negative electrode material (negative electrode) Material).

(Example 5)
In Example 1, an aniline resin (synthesized by the following method) was used instead of the phenol resin.

  100 parts of aniline, 697 parts of 37% aqueous formaldehyde, and 2 parts of oxalic acid were placed in a three-necked flask equipped with a stirrer and a condenser, reacted at 100 ° C. for 3 hours, and 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 amorphous carbon. 100 parts by weight of porous graphite (mesophase carbon microbeads) and 67 parts by weight of the obtained amorphous carbon were mixed using a mortar to obtain a carbon material.

  Thereafter, the carbon material was mixed with styrene-butadiene rubber, carboxymethyl cellulose, and acetylene black as a conductive additive at a ratio as shown in Table 1 to obtain a negative electrode material (negative electrode material).

(Example 6)
The same resin composition as in Example 5 was used.

  Further, in the treatment of the resin composition, amorphous carbon was obtained in the same manner as in Example 5 except that the steps (d) and (e) of Example 1 were 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)

  100 parts by weight of porous graphite (mesophase carbon microbeads) and 43 parts by weight of the obtained amorphous carbon were mixed using a mortar to obtain a carbon material.

  Thereafter, the carbon material was mixed with styrene-butadiene rubber, carboxymethyl cellulose, and acetylene black as a conductive additive at a ratio as shown in Table 1 to obtain a negative electrode material (negative electrode material).

(Comparative Example 1)
Graphite (mesophase carbon microbeads) was prepared and used as a carbon material.
Thereafter, the carbon material was mixed with styrene-butadiene rubber, carboxymethyl cellulose, and acetylene black as a conductive additive at a ratio as shown in Table 1 to obtain a negative electrode material (negative electrode material).

(Comparative Example 2)
Amorphous carbon produced in the same manner as in Example 4 was used as it was without mixing with graphite.

  Thereafter, the carbon material was mixed with styrene-butadiene rubber, carboxymethyl cellulose, and acetylene black as a conductive additive at a ratio as shown in Table 1 to obtain a negative electrode material (negative electrode material).

(Comparative Example 3)
The same resin composition as in Example 1 was used.
Further, in the treatment of the resin composition, amorphous carbon was obtained in the same manner as in Example 1 except that the steps (d) and (e) of Example 1 were as follows.

(D) Temperature rise from room temperature to 1000 ° C. at 100 ° C./hour under inert gas (nitrogen) substitution and flow (e) Carbonization treatment at 1000 ° C. for 8 hours under flow of inert gas (nitrogen)

The obtained amorphous carbon was used as it was without mixing with graphite.
Thereafter, the carbon material was mixed with styrene-butadiene rubber, carboxymethyl cellulose, and acetylene black as a conductive additive at a ratio as shown in Table 1 to obtain a negative electrode material (negative electrode material).

[3] Results For each of the above examples and comparative examples, together with the composition of the negative electrode material (negative electrode material), the ratio of the total volume of mesopores to the total pore volume of the carbon material, the macropores relative to the total pore volume Total volume ratio, volume of macropores per unit weight of carbon material, volume of mesopores per unit weight of carbon material, D50, graphite constituting carbon material, D50 for amorphous carbon, content of graphite , Amorphous carbon content, positron lifetime for amorphous carbon, XPS, average interplanar spacing, crystallite size, specific surface area, carbon content, nitrogen content, porosity of negative electrode material layer It was shown in 1. In Table 1, the ratio of the total volume of the mesopores to the total pore volume of the carbon material is R1, the ratio of the total volume of the macropores to the total pore volume is R2, and the ratio of the macropores per unit weight of the carbon material The volume is represented by V ₁ and the volume of mesopores V ₂ per unit weight of the carbon material. In Table 1, regarding the components constituting the negative electrode material (negative electrode material), graphite is “GR”, amorphous carbon is “AM”, styrene-butadiene rubber is “SBR”, and carboxymethyl cellulose is “CMC”. Acetylene black is indicated by “AB”. Further, in Table 1, the carbon content in amorphous carbon is represented by X _C [wt%], and the nitrogen content in amorphous carbon is represented by X _N [wt%].

  Table 2 shows the charge capacity, discharge capacity, charge / discharge efficiency, etc., when the carbon materials obtained in each Example and each Comparative Example were used as the negative electrode. In Table 2, a half cell manufactured with a pressing pressure in the pressing step of 125 kg / cm is indicated as “HC125”, and a half cell manufactured with a pressing pressure in the pressing step as 250 kg / cm is indicated as “HC250”.

  As is apparent from the table, excellent results were obtained with the present invention, whereas satisfactory results were not obtained with the comparative example.

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

Claims (14)

A negative electrode material including a carbon material used in a lithium ion secondary battery,
A negative electrode material is applied on a copper foil, an electrode is formed at a pressing pressure of 125 kg / cm, lithium metal is used as a counter electrode, and ethylene carbonate and diethyl carbonate are mixed at a volume ratio of 1: 1 as an electrolyte. The initial discharge capacity per unit weight of the electrode of the first half cell when the first half cell is made using LiPF ₆ added at a ratio of 1 mol / dm ³ to the mixed solvent is X ₁ [ mAh / g]
The initial discharge capacity per unit weight of the electrode included in the second half cell when the second half cell is manufactured in the same manner as the first half cell except that the pressing pressure is 250 kg / cm is X ₂ [mAh / g]
A negative electrode material characterized by satisfying a relationship of X ₁ -X ₂ ≦ 20 mAh / g.   The negative electrode material according to claim 1, wherein the carbon material includes amorphous carbon.   The negative electrode material according to claim 2, wherein the carbon material includes graphite in addition to the amorphous carbon. When the content of the amorphous carbon in the negative electrode material is X _H [mass%] and the content of the graphite in the negative electrode material is X _G [mass%], 1 ≦ X _G / X _H The negative electrode material according to claim 3, satisfying a relationship of ≦ 25. Under the following conditions (A) to (E), the positron lifetime of the amorphous carbon measured by the positron annihilation method is 370 picoseconds or more and 480 picoseconds or less,
(A) Positron beam source: A positron is generated from an electron / positron pair 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
The half-value width of a peak observed around 285 eV measured by X-ray Photoelectron Spectroscopy (XPS method) is 0.8 eV or more and 1.8 eV or less, for a negative electrode according to any one of claims 2 to 4. material.   The negative electrode material according to any one of claims 1 to 5, wherein the negative electrode material contains a conductive additive.   The negative electrode material according to claim 6, wherein a content of the conductive additive with respect to 100 parts by mass of the carbon material is 0.5 parts by mass or more and 20 parts by mass or less.   The negative electrode material according to any one of claims 1 to 7, wherein the negative electrode material contains styrene-butadiene rubber.   The negative electrode material according to claim 8, wherein a content of the styrene-butadiene rubber with respect to 100 parts by mass of the carbon material is 0.1 parts by mass or more and 15 parts by mass or less.   The negative electrode material according to any one of claims 1 to 9, wherein the negative electrode material contains carboxymethylcellulose.   The negative electrode material according to claim 10, wherein a content of the carboxymethyl cellulose with respect to 100 parts by mass of the carbon material is 0.1 parts by mass or more and 15 parts by mass or less.   A negative electrode manufactured using the negative electrode material according to any one of claims 1 to 11. On the current collector, the negative electrode material layer formed using the negative electrode material according to any one of claims 1 to 11,
The negative electrode material layer has a porosity of 10% by volume or more and 70% by volume or less.   A lithium ion secondary battery manufactured using the negative electrode material according to any one of claims 1 to 11.

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