JP2015079680A - Conductive carbon and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide conductive carbon which enables the materialization of a lithium ion secondary battery having a high energy density.SOLUTION: Conductive carbon according to the present invention is produced by the process of oxidation of a carbon raw material having cavities. The conductive carbon comprises a hydrophilic solid phase component. The hydrophilic solid phase component has crystallites; the size La of the crystallite including no torsion in a graphene plane direction, and the size Leq of the crystallite including torsion in the graphene plane direction, which are calculated from Raman spectra, satisfy the following relation: 1.0≤Leq/La≤1.55, where 1.3≤La≤1.5 and 1.5≤Leq≤2.3. In the Raman spectra of the hydrophilic solid phase component, the percentage of a peak area of an amorphous component band near 1510 cmto a peak area in a range of 980-1780 cmis in a range of 13-19%. In the conductive carbon, the number of micropores of a radius of 1.2 nm is 0.4-0.6 times that in the carbon raw material. The conductive carbon is caused to spread like paste by application of pressure thereto.

Description

  The present invention relates to conductive carbon that provides a lithium ion secondary battery having a high energy density and a method for producing the same.

  Lithium ion secondary batteries that use non-aqueous electrolytes with high energy density are widely used as power sources for information devices such as mobile phones and laptop computers. The performance of these information devices and the amount of information handled In order to cope with an increase in power consumption associated with an increase in the energy consumption, an improvement in the energy density of the lithium ion secondary battery is desired. In addition, from the viewpoints of reducing oil consumption, mitigating air pollution, and reducing the amount of carbon dioxide that causes global warming, we are working on low-pollution vehicles such as electric vehicles and hybrid vehicles that replace gasoline and diesel vehicles. Expectations are increasing, and it is desired to develop a large-sized lithium ion secondary battery having a high energy density as a motor drive power source for these low-pollution vehicles.

  The lithium ion secondary battery includes a positive electrode including a positive electrode active material that reversibly stores and releases lithium, a negative electrode including a negative electrode active material that reversibly stores and releases lithium, and a lithium salt dissolved in a non-aqueous solvent. An electrolyte solution. The positive electrode active material and the negative electrode active material constituting the positive electrode and the negative electrode are generally used in the form of a composite material with a conductive agent. As the conductive agent, conductive carbon such as carbon black, natural graphite, artificial graphite, or carbon nanotube is used. Conductive carbon is used in combination with a low-conductivity active material to play a role in imparting conductivity to the composite material. In addition to this, it acts as a matrix that absorbs volume changes associated with the insertion and extraction of lithium in the active material. It also acts to secure an electron conduction path even if the active material is mechanically damaged.

  By the way, a composite material of these active materials and conductive carbon is manufactured by a method of mixing particles of active material and conductive carbon. However, conductive carbon basically has the energy density of a lithium ion secondary battery. Since it does not contribute to improvement, in order to obtain a lithium ion secondary battery having a high energy density, it is necessary to decrease the amount of conductive carbon per unit volume and increase the amount of active material. Therefore, studies have been made to increase the amount of active material per unit volume by improving the dispersibility of conductive carbon or reducing the structure of conductive carbon, thereby bringing the distance between active material particles closer. Yes.

  For example, Patent Document 1 (Japanese Patent Laid-Open No. 2004-134304) includes a carbon material having a small average particle diameter of 10 to 100 nm (acetylene black in the examples) and a blackening degree of 1.20 or more. A non-aqueous secondary battery including a positive electrode having the following is disclosed. The paint used to make the positive electrode is a mixture of the positive electrode active material, the carbon material, the binder, and the solvent, a high-speed rotating homogenizer-type disperser, and a high shear dispersing device such as a planetary mixer having three or more rotating shafts. Dispersing or adding a dispersion in which the mixture of the carbon material, binder and solvent is dispersed in a strong shearing dispersion device to a paste in which a mixture of the positive electrode active material, the binder and the solvent is dispersed, and further dispersing It is obtained by letting. By using a device having a strong shearing force, a carbon material that is difficult to disperse due to a small particle diameter is uniformly dispersed.

Further, Patent Document 2 (Japanese Patent Laid-Open No. 2009-35598) discloses a non-made of acetylene black having a BET specific surface area of 30 to 90 m ² / g, a DBP absorption of 50 to 120 mL / 100 g, and a pH of 9 or more. A conductive agent for an aqueous secondary battery electrode is disclosed. A mixture of the acetylene black and the active material is dispersed in a liquid containing a binder to prepare a slurry, and this slurry is applied to a current collector and dried to form an electrode of a secondary battery. Since acetylene black having the above characteristics has a lower structure than ketjen black and conventional acetylene black, the bulk density of the mixture with the active material is improved, and the battery capacity is improved.

JP 2004-134304 A JP 2009-35598 A

  Lithium ion secondary batteries are always required to further improve energy density. However, as a result of investigations by the inventors, it is difficult to efficiently enter the conductive carbon between the active material particles even in the method as described in Patent Document 1 or Patent Document 2, and therefore, between the active material particles. It was difficult to increase the amount of the active material per unit volume by approaching the distance. For this reason, there is a limit to the improvement in energy density by the positive electrode and / or the negative electrode using a composite material of an active material and conductive carbon.

  Accordingly, an object of the present invention is to provide a conductive carbon that leads to a lithium ion secondary battery having a high energy density, and a method for producing the same.

  As a result of intensive studies, the inventors have configured a lithium ion secondary battery electrode using a composite material of conductive carbon and active material obtained by subjecting conductive carbon having voids to strong oxidation treatment. Then, it discovered that an electrode density rose significantly. As a result of detailed analysis of the conductive carbon used, the number of pores having a radius of 1.2 nm recognized in the primary particles of the conductive carbon is the number of pores having a radius of 1.2 nm in the conductive carbon used as a raw material. The hydrophilic solid phase component contained in the conductive carbon has a crystallite size in a specific range, and is formed by oxidizing the conjugated double bond of the conductive carbon. It has been found that the electrode density is remarkably improved when carbon contains a large amount of amorphous components bonded by single bonds.

Accordingly, the present invention is a conductive carbon for an electrode of a lithium ion secondary battery obtained by oxidizing a carbon raw material having voids, and includes a hydrophilic solid phase component, and the hydrophilic solid component. The crystallite size La that does not include a twist in the graphene plane direction calculated from the Raman spectrum of the phase component, and the crystallite size Leq that includes a twist in the graphene plane direction are 1.3 ≦ La ≦ 1.5, and 1.5 ≦ Leq ≦ 2.3 and 1.0 ≦ Leq / La ≦ 1.55, and the peak of the amorphous component band near 1510 cm ⁻¹ in the Raman spectrum of the hydrophilic solid phase component area, the ratio to the peak area ranging 980～1780Cm ^-1 is in the range of 13 to 19%, and the radius of the conductive carbon 1.2n The number of pores, to conductive carbon, which is a 0.4 to 0.6 times the number of pores of radius 1.2nm in the carbon raw material.

In the present invention, the ratio of the number of pores having a radius of 1.2 nm means the ratio of the number of pores having a radius of 1.2 nm in the pore distribution measurement according to JIS Z8831-2. The “hydrophilic solid phase component” of conductive carbon means a portion collected by the following method. That is, conductive carbon powder having a mass of 1/1000 of pure water is added to 20 to 100 mL of pure water, and the conductive carbon is sufficiently dispersed in pure water by performing ultrasonic irradiation for 10 to 60 minutes. After allowing the dispersion to stand for 10 to 60 minutes, the supernatant is collected. A portion collected as a solid from the supernatant by centrifugation is a “hydrophilic solid phase component”. Further, the Raman spectrum in the hydrophilic solid phase component is used after being waveform-separated as follows. For Raman spectra obtained using a laser Raman spectrophotometer (excitation light: argon ion laser; wavelength 514.5 nm), using fitting analysis software of analysis software (spectra manager),
Component a: peak; 1180 cm ^-1 vicinity Component b: peak; 1350 cm ^-1 vicinity: D-band component c: Peak; 1510 cm ^-1 vicinity component d: Peak; 1590 cm ^-1 vicinity: G band component e: peak; 1610 cm ^-1 Near component f: peak; around 2700 cm ⁻¹ : 2D band,
Component g: Peak; Near 2900 cm ⁻¹ : For the seven components of the D + G band, the wave number and the half value width are varied so that the wave number and the half value width of each component are within the following ranges using the waveform of the Gauss / Lorentz mixed function. Then, waveform separation is performed by the least square method.
Component a: wave number 1127-1208 cm ⁻¹ , half width 144-311 cm ⁻¹
Component b: Wave number 1343 to 1358 cm ⁻¹ , Half width 101 to 227 cm ⁻¹
Component c: wave number 1489-1545 cm ⁻¹ , full width at half maximum 110-206 cm ⁻¹
Component d: Wave number 1571 to 1598 cm ⁻¹ , Half width 46 to 101 cm ⁻¹
Component e: wave number 1599-1624 cm < ^-1 >, half value width 31-72 cm < ^-1 >.
Component f: wave number 2680-2730 cm ⁻¹ , full width at half maximum 100-280 cm ⁻¹
Component g: wave number 2900-2945 cm ⁻¹ , full width at half maximum 100-280 cm ⁻¹

Using the component d obtained as a result of the waveform separation, that is, the peak area of the G band, the component b, that is, the peak area of the D band, and the component f, that is, the peak area of the 2D band, La and Leq are in accordance with the following expressions: Calculated.
La = 4.4 × (G band peak area / D band peak area)
Leq = 8.8 × (2D band peak area / D band peak area).

The relationship between La and Leq is conceptually shown below. (A) shows a crystallite having a twist on the graphene surface, and (B) shows a crystallite having no twist on the graphene surface. The farther the value of Leq / La is from 1, the more crystallites having the twisted portion shown in (A). It is also known that the value of Leq / La increases as the value of La increases.

Below, the components ae in a Raman spectrum, its origin, and the bonding state of carbon are shown. Among these, a band near 1510 cm ⁻¹ , that is, component c is a peak derived from a carbon single bond (SP ³ hybrid) formed by strongly oxidizing a conjugated double bond (SP ² hybrid) of conductive carbon. It is therefore called an amorphous component band. The peak area of the component c obtained as a result of the waveform separation is the peak area of the amorphous component band. The peak area in the range of 980 to 1780 cm ⁻¹ corresponds to the sum of the peak areas of components a to e. Hereinafter, the ratio of the peak area of the amorphous component band near 1510 cm ⁻¹ to the peak area in the range of 980 to 1780 cm ⁻¹ in the Raman spectrum of the hydrophilic solid phase component is represented as “amorphous component ratio”.

  The hydrophilic solid phase component in the conductive carbon of the present invention is compared with the hydrophilic solid phase component of conductive carbon such as ketjen black and acetylene black conventionally used for forming electrodes of lithium ion secondary batteries. Thus, the values of La and Leq are small, the twist on the graphene surface judged by using the value of Leq / La is small, and the amorphous component ratio is high.

  The number of pores having a radius of 1.2 nm in the conductive carbon satisfies the above range with respect to the number of pores having a radius of 1.2 nm in the carbon raw material, and the hydrophilic solid phase components La and Leq are When the range is satisfied and the amorphous component ratio of the hydrophilic solid phase component satisfies the above range, the conductive carbon has high flexibility, and when pressure is applied to the conductive carbon, the carbon The particles become deformed and spread like a paste. Therefore, the positive electrode active material or the negative electrode active material and the conductive carbon of the present invention are added to a solvent in which a binder is dissolved as necessary and kneaded sufficiently, and the obtained kneaded product is used for a lithium ion secondary battery. After coating on the current collector for constituting the positive electrode or the negative electrode and drying as necessary, when the coating film is subjected to a rolling treatment, the conductive carbon of the present invention spreads in the form of a paste due to the pressure. The material particles approach each other, and the conductive carbon of the present invention is extruded and filled in the gap formed between the adjacent active materials. As a result, the amount of the active material per unit volume of the positive electrode or negative electrode obtained after the rolling treatment increases, and an electrode having a high electrode density can be stably obtained. The number of pores having a radius of 1.2 nm in the conductive carbon is larger than the above range with respect to the number of pores having a radius of 1.2 nm in the carbon raw material, or the values of La, Leq, and Leq / La are as described above. If the ratio is larger than the range or the amorphous component ratio is smaller than the above range, the flexibility of the conductive carbon is observed to be reduced, and thus the electrode density of the positive electrode or the negative electrode obtained after the rolling process is observed to be reduced. . The number of pores having a radius of 1.2 nm in the conductive carbon is smaller than the above range with respect to the number of pores having a radius of 1.2 nm in the carbon raw material, and the values of La, Leq, and Leq / La are more than the above range. It is recognized that a conductive carbon that is small and has an amorphous component ratio larger than the above range is difficult to produce, and the effect of improving the electrode density tends to be saturated.

  The conductive carbon of the present invention can be produced by oxidizing a carbon material having voids. By this oxidation treatment, the pores in the primary particles of the carbon raw material are crushed due to the crushing of the carbon raw material and the reaction of the surface functional groups, etc. A flexible conductive carbon having a hydrophilic solid phase component having an amorphous component ratio in the specific range and having La and Leq in the specific range is obtained by cutting the crystallites in the graphene plane direction particularly at a twisted portion. can get. Depending on the oxidation treatment using a solid carbon raw material, it is difficult to obtain conductive carbon having a hydrophilic solid phase component having an amorphous component ratio in the specific range and having La and Leq in the specific range. .

  The conductive carbon of the present invention has high flexibility, and when pressure is applied to the conductive carbon, the carbon particles are deformed and spread in a paste shape. In the production of an electrode of a lithium ion secondary battery, when pressure is applied to a composite material in which an active material capable of reversibly occluding and releasing lithium and the conductive carbon of the present invention is applied, the pressure causes the conductive of the present invention to The conductive carbon spreads in the form of a paste, the active material particles approach each other, and the conductive carbon of the present invention is extruded and filled into the gap formed between the adjacent active materials. As a result, the amount of active material per unit volume in the electrode increases and the electrode density increases, resulting in an improvement in the energy density of the battery.

It is the figure which compared the pore distribution of the conductive carbon of an Example and a comparative example. It is the figure which compared the press fit analysis result of the conductive carbon of an Example and a comparative example. It is the figure which compared the ultraviolet visible spectrum about the water-soluble part of the electroconductive carbon of an Example and a comparative example. It is the figure which compared the Raman spectrum of the hydrophilic solid-phase component of the conductive carbon of an Example and a comparative example. It is a SEM photograph of the conductive carbon of an example and a comparative example. It is the figure which showed the relationship between Leq and an electrode density. It is the figure which showed the relationship between an amorphous component rate and an electrode density.

  The conductive carbon of the present invention has high flexibility, and when pressure is applied to the conductive carbon, the carbon particles are deformed and spread like a paste. This property is crushed by strong oxidation of the carbon raw material. This is mainly caused by the reaction of the surface functional groups and the hydrophilic solid phase component contained in the conductive carbon. The number of pores having a radius of 1.2 nm in the conductive carbon obtained as a result of strong oxidation of the carbon material is reduced to 0.4 to 0.6 times the number of pores having a radius of 1.2 nm in the carbon material. Further, a crystallite size La not including a twist in the graphene plane direction calculated from a Raman spectrum of the hydrophilic solid phase component and a crystallite size Leq including a twist in the graphene plane direction are 1.3 ≦ La ≦ 1. 5 and 1.5 ≦ Leq ≦ 2.3 and 1.0 ≦ Leq / La ≦ 1.55, and the amorphous component ratio calculated from the Raman spectrum of this hydrophilic solid phase component is It is 13 to 19%, preferably 14 to 18%. The hydrophilic solid phase component in the conductive carbon of the present invention is compared with the hydrophilic solid phase component of conductive carbon such as ketjen black and acetylene black conventionally used for forming electrodes of lithium ion secondary batteries. Thus, the values of La and Leq are small, the twist on the graphene surface judged by using the value of Leq / La is small, and the amorphous component ratio is high.

The conductive carbon of the present invention can be obtained by subjecting a carbon raw material having voids to a strong oxidation treatment. In addition to the pores of the porous carbon powder, the voids include ketchen black internal voids, carbon nanofibers and carbon nanotubes, and intertube voids. In the course of strong oxidation treatment, the specific surface area of the conductive carbon decreases due to the crushing of the carbon raw material or the reaction of the surface functional groups, and the pores in the primary particles of the carbon raw material are crushed. The number of pores having a radius of 1.2 nm in the obtained conductive carbon is reduced to 0.4 to 0.6 times the number of pores having a radius of 1.2 nm in the carbon raw material. Moreover, the specific surface area of the conductive carbon obtained is generally in the range of 650 to 800 cm ² / g. The specific surface area means a value measured according to JIS Z8830. In addition, during the process of strong oxidation, the conjugated double bonds of conductive carbon are oxidized and a lot of amorphous components are generated, causing crystallite fracture, particularly fracture in the twisted portion of the graphene surface, and the specific relationship described above. Conductive carbon containing a hydrophilic solid phase component having La, Leq and an amorphous component ratio satisfying the above is obtained.

  Further, the structure is cut in the course of strong oxidation treatment for the carbon raw material. The height of the structure is represented by the DBP oil absorption, but in the preferred form of the conductive carbon of the present invention, the DBP oil absorption is in the range of 100 to 200 mL / 100 g. The DBP oil absorption is a value measured according to JIS K 6217-4.

The conductive carbon of the present invention is
(A1) a step of treating the carbon material having voids with an acid,
(B1) a step of mixing the product after the acid treatment and the transition metal compound,
(C1) pulverizing the obtained mixture to cause a mechanochemical reaction;
(D1) a step of heating the product after the mechanochemical reaction in a non-oxidizing atmosphere, and
(E1) It can obtain suitably by the 1st manufacturing method including the process of removing the said transition metal compound and / or its reaction product from the product after a heating.

  In the first production method, carbon having voids such as porous carbon powder, ketjen black, carnon nanofiber, and carbon nanotube is used as the carbon raw material. As such a carbon raw material, ketjen black is preferable. Even when solid carbon is used as a raw material and the same treatment as in the first production method is performed, it is difficult to obtain the conductive carbon of the present invention.

  In the step (a1), the carbon raw material is immersed in an acid and left standing. As the acid, it is possible to use acids usually used for the oxidation treatment of carbon, such as nitric acid, a nitric acid-sulfuric acid mixture, and a hypochlorous acid aqueous solution. The immersion time depends on the acid concentration and the amount of the carbon raw material to be treated, but is generally in the range of 5 minutes to 1 hour. The acid-treated carbon is sufficiently washed with water and dried, and then mixed with the transition metal compound in the step (b1).

  The transition metal compound added to the carbon raw material in the step (b1) includes transition metal halides, nitrates, sulfates, carbonates and other inorganic metal salts, formate salts, acetate salts, oxalate salts, methoxides, ethoxides, isoforms. An organic metal salt such as propoxide or a mixture thereof can be used. These compounds may be used alone or in combination of two or more. You may mix and use the compound containing a different transition metal by predetermined amount. Moreover, as long as the reaction is not adversely affected, a compound other than the transition metal compound, for example, an alkali metal compound may be added together. Since the conductive carbon of the present invention is used in the production of an electrode of a lithium ion secondary battery by being mixed with an active material capable of reversibly occluding and releasing lithium, a compound of an element constituting the active material is used. Addition to the carbon raw material is preferable because it can prevent an element that can be an impurity from being mixed into the active material.

  In step (c1), the mixture obtained in step (b1) is pulverized to cause a mechanochemical reaction. Examples of a pulverizer for this reaction include a lyker, ball mill, bead mill, rod mill, roller mill, stirring mill, planetary mill, vibration mill, hybridizer, mechanochemical compounding apparatus, and jet mill. The pulverization time depends on the pulverizer to be used, the amount of carbon to be treated, and the like, and is not strictly limited, but is generally in the range of 5 minutes to 3 hours. The step (d1) is performed in a non-oxidizing atmosphere such as a nitrogen atmosphere or an argon atmosphere. The heating temperature and the heating time are appropriately selected according to the transition metal compound used. In the subsequent step (e1), the transition metal compound and / or the reaction product thereof is removed from the heated product by means such as dissolution with an acid, and then thoroughly washed and dried, whereby the conductive material of the present invention is obtained. Sex carbon can be obtained.

  In the first production method, in the step (c1), the transition metal compound acts so as to promote the oxidation of the carbon raw material by a mechanochemical reaction, and the oxidation of the carbon raw material proceeds rapidly. By this oxidation, the pores in the primary particles of the carbon raw material are crushed due to the crushing of the carbon raw material and the reaction of the surface functional groups, etc., and at the same time, the conjugated double bonds of the conductive carbon are oxidized to produce a lot of amorphous components, The crystallites in the direction of the graphene plane are cut particularly at the twisted portions, and flexible conductive carbon is obtained.

The conductive carbon of the present invention also has
(A2) a step of mixing a carbon raw material having voids and a transition metal compound,
(B2) heating the resulting mixture in an oxidizing atmosphere; and
(C2) It can obtain suitably by the 2nd manufacturing method including the process of removing the said transition metal compound and / or its reaction product from the product after a heating.

  Also in the second manufacturing method, carbon having voids such as porous carbon powder, ketjen black, carnon nanofiber, and carbon nanotube is used as the carbon raw material. As such a carbon raw material, ketjen black is preferable. Even when solid carbon is used as a raw material and the same treatment as in the second production method is performed, it is difficult to obtain the conductive carbon of the present invention.

  Examples of the transition metal compound added to the carbon raw material in the step (a2) include transition metal halides, nitrates, sulfates, carbonates, and other inorganic metal salts, formate salts, acetate salts, oxalate salts, methoxides, ethoxides, isoforms. An organic metal salt such as propoxide or a mixture thereof can be used. These compounds may be used alone or in combination of two or more. You may mix and use the compound containing a different metal by predetermined amount. Moreover, as long as the reaction is not adversely affected, a compound other than the transition metal compound, for example, an alkali metal compound may be added together. Since this conductive carbon is used mixed with an active material in the manufacture of an electrode of a lithium ion secondary battery, when an elemental compound constituting the active material is added to the carbon raw material, it becomes an impurity with respect to the active material. This is preferable because it is possible to prevent mixing of possible elements.

  The step (b2) is performed in an oxygen-containing atmosphere, for example, air, and is performed at a temperature at which carbon does not disappear, preferably at a temperature of 200 to 350 ° C. In the subsequent step (c2), the transition metal compound and / or the reaction product thereof is removed from the heated product by means such as dissolution with an acid, and then thoroughly washed and dried, whereby the conductive material of the present invention is obtained. Sex carbon can be obtained.

  In the second production method, the transition metal compound acts as a catalyst for oxidizing the carbon raw material in the heating step in the oxidizing atmosphere, and the oxidation of the carbon raw material proceeds rapidly. By this oxidation, the pores in the primary particles of the carbon raw material are crushed due to the crushing of the carbon raw material and the reaction of the surface functional groups, etc., and at the same time, the conjugated double bonds of the conductive carbon are oxidized to produce a lot of amorphous components, The crystallites in the direction of the graphene plane are cut particularly at the twisted portions, and flexible conductive carbon is obtained.

  The conductive carbon of the present invention is obtained by subjecting a carbon raw material having voids to a strong oxidation treatment, and it is also possible to promote the oxidation of the carbon raw material by a method other than the first manufacturing method and the second manufacturing method. is there.

  The conductive carbon of the present invention is used for producing an electrode of this battery in the form of a composite material with active material particles operable as a positive electrode active material or a negative electrode active material of a lithium ion secondary battery. In general, the positive electrode active material or the negative electrode active material and the conductive carbon of the present invention are added to a solvent in which a binder is dissolved as necessary and sufficiently kneaded. After apply | coating on the electrical power collector for comprising the positive electrode or negative electrode of a secondary battery, and drying as needed, an electrode is manufactured by performing a rolling process to a coating film.

  As a positive electrode active material and a negative electrode active material, the active material currently used in the conventional lithium ion secondary battery is used without limitation. The active material may be a single compound or a mixture of two or more compounds.

Examples of positive electrode active materials include layered rock salt type LiMO ₂ , layered Li ₂ MnO ₃ —LiMO ₂ solid solution, and spinel type LiM ₂ O ₄ (wherein M is Mn, Fe, Co, Ni, or these Meaning a combination). Specific examples of these include LiCoO ₂ , LiNiO ₂ , LiNi _4/5 Co _1/5 O ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNi _1/2 Mn _1/2 O ₂ , LiFeO ₂ , LiMnO ₂ , Li ₂ MnO ₃ —LiCoO _2, Li ₂ MnO ₃ —LiNiO ₂ , Li ₂ MnO ₃ —LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , Li ₂ MnO ₃ —LiNi _1/2 Mn _1/2 O ₂ , Li ₂ MnO ₃ —LiNi _1/2 Mn _1/2 O ₂ —LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiMn ₂ O ₄ , LiMn _3/2 Ni _1/2 O ₄ may be mentioned.

Examples of positive electrode active materials also include sulfur and sulfides such as Li ₂ S, TiS ₂ , MoS ₂ , FeS ₂ , VS ₂ , Cr _1/2 V _1/2 S ₂ , NbSe ₃ , VSe ₂ , NbSe _3. In addition to selenides such as Cr ₂ O ₅ , Cr ₃ O ₈ , VO ₂ , V ₃ O ₈ , V ₂ O ₅ , V ₆ O ₁₃ , LiNi _0.8 Co _0.15 Al _{0. 05} O ₂ , LiVOPO ₄ , LiV ₃ O ₅ , LiV ₃ O ₈ , MoV ₂ O ₈ , Li ₂ FeSiO ₄ , Li ₂ MnSiO ₄ , LiFePO ₄ , LiFe _1/2 Mn _1/2 PO ₄ , LiMnPO ₄ , Li A composite oxide such as ₃ V ₂ (PO ₄ ) ₃ can be given.

Examples of the negative electrode active material include Fe ₂ O ₃ , MnO, MnO ₂ , Mn ₂ O ₃ , Mn ₃ O ₄ , CoO, Co ₃ O ₄ , NiO, Ni ₂ O ₃ , TiO, TiO ₂ , SnO, SnO ₂ , oxides such as SiO ₂ , RuO ₂ , WO, WO ₂ , ZnO, metals such as Sn, Si, Al, Zn, composite oxides such as LiVO ₂ , Li ₃ VO ₄ , Li ₄ Ti ₅ O ₁₂ , Examples thereof include nitrides such as Li _2.6 Co _0.4 N, Ge ₃ N ₄ , Zn ₃ N ₂ , and Cu ₃ N.

  As the current collector, a conductive material such as platinum, gold, nickel, aluminum, titanium, steel, or carbon can be used. As the shape of the current collector, any shape such as a film shape, a foil shape, a plate shape, a net shape, an expanded metal shape, and a cylindrical shape can be adopted.

  As the binder, known binders such as polytetrafluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, polyvinyl fluoride, and carboxymethyl cellulose are used. The content of the binder is preferably 1 to 30% by mass with respect to the total amount of the mixed material. If it is 1% by mass or less, the strength of the active material layer is not sufficient, and if it is 30% by mass or more, disadvantages such as a decrease in the discharge capacity of the negative electrode and an excessive internal resistance occur.

  The particles of the active material have a size capable of entering a gap formed by coarse particles having a particle size of 1 μm or more, preferably 5 μm or more and adjacent coarse particles, preferably 1/5 or less of the coarse particles, particularly Preferably, it contains fine particles having a particle size of 1/10 or less. The particle size of the active material particles can be confirmed by SEM photographs. The surface of the fine particles is coated with the conductive carbon of the present invention, and after the rolling process, the fine particles are closely packed in the gap formed by the adjacent coarse particles together with the conductive carbon of the present invention, Therefore, the energy density of the lithium ion secondary battery is further improved.

  In addition, the conductive carbon of the present invention may be used in combination with conductive carbon such as acetylene black and carbon nanofibers used for electrodes of conventional lithium ion secondary batteries. The surface of the conventional conductive carbon is covered with the conductive carbon of the present invention, and after the rolling process, the conventional conductive carbon is closely packed in the gap formed by the adjacent coarse particles together with the conductive carbon of the present invention. Since the conductivity of the entire electrode material is improved, the energy density of the lithium ion secondary battery is further improved.

  The present invention will be described with reference to the following examples, but the present invention is not limited to the following examples.

(1) Effect of Leq, Amorphous Component Ratio, and Micropore Reduction Rate / First Manufacturing Method Example 1
10 g of Ketjen black (trade name ECP600JP, manufactured by Ketjen Black International) was added to 300 mL of 60% nitric acid, and the resulting liquid was irradiated with ultrasonic waves for 10 minutes and then filtered to collect Ketjen black. The recovered ketjen black was washed with water three times and dried to obtain an acid-treated ketjen black. 0.5 g of this acid-treated ketjen black, 1.98 g of Fe (CH ₃ COO) ₂ , 0.77 g of Li (CH ₃ COO), 1.10 g of C ₆ H ₈ O ₇ .H ₂ O, and CH ₃ 1.32 g of COOH, 1.31 g of H ₃ PO ₄ and 120 mL of distilled water were mixed, and the resulting mixture was stirred with a stirrer for 1 hour and then evaporated to dryness at 100 ° C. in air to collect the mixture. . Next, the obtained mixture was introduced into a vibrating ball mill apparatus and pulverized at 20 hz for 10 minutes. The pulverized powder was heated in nitrogen at 700 ° C. for 3 minutes to obtain a composite in which LiFePO ₄ was supported on ketjen black.

1 g of the obtained complex is added to 100 mL of 30% hydrochloric acid aqueous solution, and the resulting liquid is dissolved in LiFePO ₄ while irradiating ultrasonic waves for 15 minutes, and the remaining solid is filtered and washed with water. And dried. A part of the solid after drying was heated to 900 ° C. in air by TG analysis, and the weight loss was measured. Until the weight loss was 100%, that is, it was confirmed that LiFePO ₄ did not remain, the steps of dissolving, filtering, washing and drying LiFePO _{4 with} the hydrochloric acid aqueous solution were repeated to obtain LiFePO ₄ -free conductive carbon. .

  Subsequently, the specific surface area and pore distribution were measured for the used ketjen black and the obtained conductive carbon, and the ratio of the number of pores having a radius of 1.2 nm was calculated. 40 mg of the obtained conductive carbon was added to 40 mL of pure water, and ultrasonic irradiation was performed for 30 minutes to disperse the carbon in pure water. The supernatant was collected, the supernatant was centrifuged, the solid phase portion was collected, and dried to obtain a hydrophilic solid phase component. About the obtained hydrophilic solid-phase component, the Raman spectrum was measured using the micro Raman measuring apparatus (Excitation light: Argon ion laser; Wavelength 514.5nm). From the obtained Raman spectrum, a crystallite size La not including a twist in the graphene plane direction, a crystallite size Leq including a twist in the graphene plane direction, Leq / La, and an amorphous component ratio were calculated.

Fe (CH ₃ COO) ₂ , Li (CH ₃ COO), C ₆ H ₈ O ₇ .H ₂ O, CH ₃ COOH and H ₃ PO ₄ are introduced into distilled water, and the resulting mixed solution Was stirred for 1 hour with a stirrer, evaporated to dryness at 100 ° C. in air, and then heated at 700 ° C. for 3 minutes in nitrogen to obtain LiFePO ₄ microparticles with a primary particle size of 100 nm. Next, commercially available LiFePO ₄ (primary particle diameter 0.5 to 1 μm, secondary particle diameter 2 to 3 μm), the obtained fine particles, and the conductive carbon are mixed in a ratio of 90: 9: 1, Furthermore, 5% by mass of the total polyvinylidene fluoride and an appropriate amount of N-methylpyrrolidone were added and kneaded sufficiently to form a slurry. The slurry was applied onto an aluminum foil, dried, and then subjected to a rolling treatment. The positive electrode of the lithium ion secondary battery was obtained. The electrode density was calculated from the measured values of the volume and weight of the electrode material on the aluminum foil.

Example 2
Among the procedures in Example 1, 0.5 g of acid-treated ketjen black, 1.98 g of Fe (CH ₃ COO) ₂ , 0.77 g of Li (CH ₃ COO), and C ₆ H ₈ O ₇ · H ₂ A portion where 1.10 g of O, 1.32 g of CH ₃ COOH, 1.31 g of H ₃ PO ₄ and 120 mL of distilled water are mixed, 1.8 g of acid-treated ketjen black, and Fe (CH ₃ COO) ₂ 1. 98 g, Li (CH ₃ COO) 0.77 g, C ₆ H ₈ O ₇ · H ₂ O 1.10 g, CH ₃ COOH 1.32 g, H ₃ PO ₄ 1.31 g, and distilled water 250 mL were mixed. The procedure of Example 1 was repeated except that the procedure was changed.

Example 3
Among the procedures in Example 1, 0.5 g of acid-treated ketjen black, 1.98 g of Fe (CH ₃ COO) ₂ , 0.77 g of Li (CH ₃ COO), and C ₆ H ₈ O ₇ · H ₂ A portion where 1.10 g of O, 1.32 g of CH ₃ COOH, 1.31 g of H ₃ PO ₄ and 120 mL of distilled water are mixed, 1.8 g of acid-treated ketjen black, Fe (CH ₃ COO) ₂ . 5 g, Li (CH ₃ COO) 0.19 g, C ₆ H ₈ O ₇ · H ₂ O 0.28 g, CH ₃ COOH 0.33 g, H ₃ PO ₄ 0.33 g, and distilled water 250 mL were mixed. The procedure of Example 1 was repeated except that the procedure was changed.

Comparative Example 1
The acid-treated ketjen black obtained in Example 1 was introduced into a vibrating ball mill apparatus and pulverized at 20 hz for 10 minutes. The pulverized powder was heated in nitrogen at 700 ° C. for 3 minutes. Next, the specific surface area and pore distribution were measured for the obtained conductive carbon, and the ratio of the pores with a radius of 1.2 nm to the number of pores in the ketjen black used as a raw material was calculated. 40 mg of the obtained conductive carbon was added to 40 mL of pure water, and the La, Leq, Leq / La, and amorphous component ratios of the hydrophilic solid phase components were calculated by the same procedure as in Example 1. Furthermore, using the resulting conductive carbon, to create a LiFePO ₄ containing cathode in the same procedure as in Example 1, was calculated electrode density.

Comparative Example 2
40 mg of the ketjen black raw material used in Example 1 was added to 40 mL of pure water, and La, Leq, Leq / La, and amorphous component ratios of hydrophilic solid phase components were calculated in the same procedure as in Example 1. did. Further, using this ketjen black raw material, a LiFePO ₄ -containing positive electrode was prepared in the same procedure as in Example 1, and the electrode density was calculated.

Table 1 shows the ratio of the number of pores having a radius of 1.2 nm between the obtained conductive carbon and the carbon raw material for the conductive carbons of Examples 1 to 3 and Comparative Examples 1 and 2, La, Leq, Leq. The values of / La, amorphous component ratio, and electrode density are shown together with the value of specific surface area. The ratio of the number of pores is larger than 0.6, and La and Leq of the hydrophilic solid phase component are 1.3 ≦ La ≦ 1.5, 1.5 ≦ Leq ≦ 2.3, and 1.0 Even if the conductive carbon of Comparative Examples 1 and 2 that does not satisfy the relationship of ≦ Leq / La ≦ 1.55 and the amorphous component ratio of the hydrophilic solid phase component is less than 13%, the electrode density does not increase, In other words, it can be seen that the amount of active material particles in the electrode material cannot be increased. Moreover, it can be seen from Table 1 that the specific surface area greatly decreases with the decrease in the pore number ratio.

  By comparing the conductive carbon (Ketjen Black raw material) of Comparative Example 2 with the conductive carbon obtained in Example 1, the carbon raw material acid treatment in Example 1 → metal compound mixing → pulverization → in nitrogen The effect of the heating process (hereinafter referred to as “strong oxidation process”) can be confirmed.

  FIG. 1 is a diagram showing the pore distribution measurement results for the conductive carbon of Comparative Example 2 and Example 1. As a result of the strong oxidation process, pores having a radius of about 25 nm or more observed in the carbon having a developed structure appearing in the A region almost disappear, and a radius of about 5 nm or less recognized in the primary particle appearing in the B region. It can be seen that the number of pores having a large decrease has been found. Therefore, it was found that the strong oxidation process cuts the structure and collapses the pores in the primary particles.

  FIG. 2 is a view showing the press-fitting analysis results for the 50 μm aggregates of conductive carbon of Comparative Example 2 and Example 1. In the measurement of the conductive carbon of Comparative Example 2, it can be seen that the indentation load increases rapidly in the vicinity of the indentation depth of about 10 μm, and the carbon particles of the aggregate are difficult to deform. On the other hand, in the measurement of the conductive carbon in Example 1, the indentation load increased gently while showing the vertical movement of the load several times in the indentation depth range of 0 to 20 μm. The vertical movement of the load observed at the indentation depth of about 4 to about 9 μm corresponds to the load fluctuation due to the fragile portion of the bond between the primary particles being cut, and is gentle in the range of the indentation depth of about 9 μm or more. The increase in load is considered to correspond to the flexible deformation of the primary particles. This flexible deformation is a major characteristic of the conductive carbon of the present invention.

The treatment of the strong oxidation process involves a change in the surface functional group of the carbon, and this change in the surface functional group can be confirmed by analyzing the hydrophilic portion of the conductive carbon. The ultraviolet-visible spectrum was measured for the remaining part from which the components were collected (the liquid phase part of the supernatant). FIG. 3 shows the UV-visible spectrum of the liquid phase portion of the conductive carbon of Comparative Example 2 and Example 1. In the spectrum of Example 1, a π → π ^* transition of a small fraction (small size graphene) that is not recognized in the spectrum of Comparative Example 2 is clearly recognized, and the graphene is reduced to a small size by the strong oxidation process. I found it cut.

FIG. 4 shows a Raman spectrum of 980 to 1780 cm ⁻¹ of the hydrophilic solid phase component of the conductive carbon of Comparative Example 2 and Example 1, and a waveform separation result thereof. In the spectrum for Example 1, compared with the spectrum for Comparative Example 2, the peak area of the component d derived from the ideal graphite is reduced, the peak area of the component c derived from the amorphous component, and the surface oxidized graphite. It can be seen that the peak area of the component e is increased. This indicates that in the course of the strong oxidation process, the conjugated double bond (SP ² hybrid) of the graphene carbon raw material was strongly oxidized, and a large amount of carbon single bond (SP ³ hybrid) part, that is, an amorphous component was generated. ing.

  FIG. 5 shows the conductive carbon of Example 1, the conductive carbon of Comparative Example 2, and the hydrophilic solid phase component of the conductive carbon of Example 1, respectively, dispersed in a dispersion medium, and the resulting dispersion is used as an aluminum foil. The SEM photograph which image | photographed the coating film apply | coated and dried on the top, and the SEM photograph image | photographed after performing a rolling process of the force of 300 kN to a coating film are shown. The conductive carbon coating film of Comparative Example 2 showed no significant change before and after the rolling treatment. However, in the conductive carbon coating film of Example 1, the unevenness of the surface was remarkably reduced by the rolling treatment, and the carbon spread in a paste form, as can be seen from the SEM photograph. Therefore, it can be seen that the properties of carbon are greatly changed by the strong oxidation treatment. When the SEM photograph of the coating film of the hydrophilic solid phase component of the conductive carbon of Example 1 is compared with the SEM photograph of the coating film of the conductive carbon of Example 1, the surface of the coating film of the hydrophilic solid phase component is rolled. It can be seen that the treatment is further flattened, and the carbon is further spread in a paste form. From this, it was thought that the property which spreads in the paste-like shape in the conductive carbon of Example 1 mainly originated from the hydrophilic solid phase component.

  FIG. 6 shows the relationship between Leq of the hydrophilic solid phase component of the conductive carbon of Examples 1 to 3 and Comparative Examples 1 and 2 and the electrode density. As is apparent from this figure, the electrode density is remarkably increased in the process in which Leq is decreased from 2.35 nm (Comparative Example 1) to 2.20 nm (Example 3). From this, it was considered that the twisted portion of the crystallites in the graphene surface direction was destroyed to a predetermined amount or more, which greatly contributed to the increase in electrode density.

  FIG. 7 shows the relationship between the amorphous component ratio of the hydrophilic solid phase component of the conductive carbon of Examples 1 to 3 and Comparative Examples 1 and 2 and the electrode density. As is clear from this figure, as the amorphous component rate increases, the electrode density increases remarkably, but when the amorphous component rate becomes 13% or more, the increase rate of the electrode density tends to be saturated. From this, it was found that by making the amorphous component 13% or more, an electrode of a lithium ion secondary battery having a high electrode density can be stably obtained with good reproducibility.

(2) Influence of structure Comparative example 3
As described above, the carbon structure is cut in the strong oxidation process. In order to investigate the influence of structure deterioration, although the DBP oil absorption of the conductive carbon of Example 1 is almost the same as the DBP oil absorption of 130 mL / 100 g, the hydrophilic solid phase component Leq is larger than the range of the present invention, and the amorphous component Commercially available conductive carbon (DBP oil absorption = 134.3 mL / 100 g) having a rate smaller than the range of the present invention was used instead of the conductive carbon of Example 1, and LiFePO ₄ was used in the same manner as in Example 1. The containing positive electrode was manufactured and the electrode density was calculated. The obtained electrode density was 2.4 g / cm ³ . From this result, it was found that the improvement of the electrode density cannot be achieved only by the deterioration of the structure.

(3) Influence of carbon raw material Comparative Example 4
Instead of ketjen black used as a carbon raw material in Example 1, solid acetylene black (primary particle diameter 40 nm) was used, and the procedure of Example 1 was repeated. As a result, even with strong oxidation treatment, Leq of the hydrophilic solid phase component does not decrease to the range of the present invention, the amorphous component ratio does not increase to the range of the present invention, and the electrode density is 2.35 g / cm ³ . An increase in electrode density was not achieved. Therefore, it was found that it is important to use a carbon material having voids as a raw material.

(4) Second Manufacturing Method Example 4
Ketchen Black (EC300J, manufactured by Ketjen Black International Co.) and 0.45 _g, and Co (CH 3 _COO) of ₂ · 4H 2 O 4.98g, and LiOH _· H 2 O1.6g, and distilled water 120mL mixture The resulting mixture was stirred with a stirrer for 1 hour, and the mixture was collected by filtration. Next, 1.5 g of LiOH.H ₂ O was mixed using an evaporator and then heated in air at 250 ° C. for 30 minutes to obtain a composite in which a lithium cobalt compound was supported on ketjen black. 1 g of the resulting complex was added to 100 mL of an aqueous solution in which concentrated sulfuric acid with a concentration of 98%, concentrated nitric acid with a concentration of 70% and hydrochloric acid with a concentration of 30% were mixed at a volume ratio of 1: 1: 1. The lithium cobalt compound in the composite was dissolved while irradiating with ultrasonic waves for 15 minutes, and the remaining solid was filtered, washed with water, and dried. A part of the solid after drying was heated to 900 ° C. in air by TG analysis, and the weight loss was measured. Until the weight loss is 100%, that is, it can be confirmed that the lithium cobalt compound does not remain, the steps of dissolving, filtering, washing and drying the lithium cobalt compound with the hydrochloric acid aqueous solution are repeated, and the lithium cobalt compound-free conductive carbon is obtained. Got.

  Subsequently, the specific surface area and pore distribution were measured for the used ketjen black and the obtained conductive carbon, and the ratio of the number of pores having a radius of 1.2 nm was calculated. 40 mg of the obtained conductive carbon was added to 40 mL of pure water, and ultrasonic irradiation was performed for 30 minutes to disperse the carbon in pure water. The supernatant was collected, the supernatant was centrifuged, the solid phase portion was collected, and dried to obtain a hydrophilic solid phase component. About the obtained hydrophilic solid-phase component, the Raman spectrum was measured using the micro Raman measuring apparatus (Excitation light: Argon ion laser; Wavelength 514.5nm). From the obtained Raman spectrum, La, Leq, Leq / La, and further the amorphous component ratio were calculated. The obtained conductive carbon exhibited a pore number reduction rate of 1.2 nm in radius, La, Leq, and Leq / La, which were substantially the same as the conductive carbon of Example 1, and an amorphous component rate.

  By using the conductive carbon of the present invention, a lithium ion secondary battery having a high energy density can be obtained.

Claims (2)

A conductive carbon for an electrode of a lithium ion secondary battery obtained by oxidizing a carbon raw material having voids,
A hydrophilic solid phase component,
The crystallite size La that does not include a twist in the graphene plane direction, and the crystallite size Leq that includes a twist in the graphene plane direction, calculated from the Raman spectrum of the hydrophilic solid phase component,
1.3 ≦ La ≦ 1.5, and
1.5 ≦ Leq ≦ 2.3, and
1.0 ≦ Leq / La ≦ 1.55
Satisfy the relationship
Wherein in the Raman spectrum of the hydrophilic solid phase component, the peak area of amorphous component band near 1510 cm ^-1, proportion of peak area in the range of 980～1780Cm ^-1 is the range of 13 to 19%, and,
The number of pores having a radius of 1.2 nm in the conductive carbon is 0.4 to 0.6 times the number of pores having a radius of 1.2 nm in the carbon raw material.   The conductive carbon according to claim 1, which is produced by oxidizing a carbon raw material having voids.