Carbon composite active material, electrode, and secondary battery

Abstract

Provided is a carbon composite active material comprising particles of an electrode active material and a surface layer covering the particles. The surface layer comprises a coating material containing a graphene material and a binder. The graphene material includes, at a terminal, an anionic functional group and a counter cation of the anionic functional group, and a peak intensity ratio (ID / IG) of a D band and a G band of a Raman spectrum obtained by Raman spectroscopy is 0.50 or less. In the carbon composite active material, the content of the graphene material is 0.1-2.2 mass%, and the content of the binder is 0.01-0.7 mass%.

Description

Carbon composite active material, electrode, secondary battery

[0001] The present disclosure relates to a carbon composite active material, an electrode, and a secondary battery.

[0002] With the trend toward smaller and lighter electronic materials and the advancement of hybrid and electric vehicles (HEVs) and electric vehicles (EVs), there is a demand for smaller, larger-capacity secondary batteries, which are the driving sources for these vehicles. Among secondary batteries, various technological developments are being conducted for lithium-ion secondary batteries, which have the advantages of high voltage and high energy density.

[0003] Patent Document 1 discloses a technique for using a composite as a positive electrode active material for a lithium-ion secondary battery, which is formed by adhering a large number of particles of a carbon material (such as acetylene black) as a conductive additive to the surface of a phosphoric acid compound, and which has a specific surface area per unit mass of the positive electrode active material of a predetermined value or more. While phosphoric acid compounds have advantages such as high safety, they have the problem of low electronic conductivity. However, it has been reported that the composite increases the contact area between the positive electrode active material and the conductive additive, thereby improving electronic conductivity.

[0004] However, acetylene black is a bulky particle with an average particle size of several tens to several hundreds of nanometers, and contact with the active material is point contact with high contact resistance. In an active material layer where the active material and the conductive additive are connected by point contact, it is difficult to form a network for electronic conduction, resulting in low electronic conductivity. To improve electronic conductivity, it is necessary to increase the amount of conductive additive to increase the number of contact points. However, increasing the amount of conductive additive reduces the ratio of the active material in the electrode, which leads to a problem of reducing the discharge capacity of a secondary battery using the electrode.

[0005] Patent Document 2 discloses a technology using graphene as a conductive additive contained in a positive electrode active material layer. In a positive electrode active material layer using graphene as a conductive additive, graphene and an active material, and graphene and graphene are connected by surface contact to form an electronic conduction network. An active material layer having conductive paths connected by surface contact has high electronic conductivity, so there is no need to increase the amount of conductive additive to improve electronic conductivity, as in Patent Document 1, and the problem of a decrease in discharge capacity due to an increase in the amount of conductive additive does not occur.

[0006] Patent Literature 2 teaches that in order to form an electron conductive network in a positive electrode active material layer using graphene as a conductive additive, graphene must first be uniformly dispersed in a dispersion medium. It also discloses that a positive electrode paste is prepared by adding graphene oxide to a dispersion medium together with an active material and a binder, and then the dispersed graphene oxide is reduced by heat treatment to form graphene. In this case, an electron conductive network is formed in the active material layer, exhibiting excellent electron conductivity. On the other hand, when a positive electrode active material layer prepared by adding graphene as a conductive additive to a dispersion medium together with an active material and a binder was examined, the dispersibility was found to be insufficient, resulting in the failure of the formation of a network for electron conduction in the positive electrode active material layer. Similar results were also obtained when a positive electrode active material layer was prepared by adding graphene obtained by reducing graphene oxide to a dispersion medium instead of graphene as a conductive additive. That is, Patent Literature 2 describes a technology that requires a process of preparing a positive electrode paste using graphene oxide, followed by heat treatment to remove oxygen from the graphene oxide, thereby forming a graphene-containing positive electrode active material layer.

[0007] The technology of Patent Document 2, which requires the heat treatment, has a problem that if the heat treatment is insufficient, a large amount of oxygen remains, an electron conduction network is not sufficiently formed, and the electron conductivity is reduced. On the other hand, if the heat treatment is excessive, the active material may be altered or the binder may be decomposed, resulting in a decrease in discharge capacity.

[0008] JP 2002-110162 A JP 2020-21745 A

[0009] In recent years, there has been a demand for improved rate characteristics, i.e., discharge characteristics at high current values, in secondary batteries, but sufficient rate characteristics have not yet been obtained in either of the techniques disclosed in Patent Documents 1 and 2. The present disclosure has been made in view of the above-described circumstances, and aims to provide a carbon composite active material capable of improving the rate characteristics of secondary batteries, and to provide related techniques.

[0010] To achieve the above object, the present disclosure provides the following means.

[0011] <Carbon composite active material> [1] A carbon composite active material comprising particles of an electrode active material and a surface layer covering the particles, wherein the surface layer is made of a coating material containing a graphene material and a binder, the graphene material contains an anionic functional group and a counter cation of the anionic functional group at an end, and the peak intensity ratio (I Ｄ / I Ｇ ) is 0.50 or less, and the content of the graphene material in the carbon composite active material is 0.1 to 2.2 mass %, and the content of the binder in the carbon composite active material is 0.01 to 0.7 mass %. [2] The carbon composite active material of [1], wherein a content ratio of the graphene material to the binder is 3 to 30. [3] The carbon composite active material of [1] or [2], wherein a ratio (DG / DA) of a plane direction size DG of the graphene material to a particle size DA of the electrode active material is 0.002 to 3.000. [4] The carbon composite active material of any of [1] to [3], wherein the electrode active material is a positive electrode active material. [5] The carbon composite active material of any of [1] to [4], wherein the electrode active material is a negative electrode active material. [6] The carbon composite active material of [4], wherein the positive electrode active material is a lithium-containing composite oxide. [7] The carbon composite active material according to [6], wherein the lithium-containing composite oxide has at least one crystal structure selected from the group consisting of an olivine type, a layered rock salt type, and a spinel type. [8] The carbon composite active material according to [5], wherein the negative electrode active material is at least one selected from the group consisting of graphite, SiOx (0≦x<2), and lithium titanate. [9] The carbon composite active material according to any one of [1] to [8], wherein the binder contains at least one selected from the group consisting of a fluororesin, an olefin resin, a vinyl resin, a polyamide, a polyimide, a polyether, a polysaccharide, and a rubber. <Electrode>

[10] An electrode formed using a slurry containing the carbon composite active material according to any one of [1] to [9]. <Secondary battery>

[11] A secondary battery comprising the electrode according to

[10] .

[0012] According to the present disclosure, it is possible to provide a carbon composite active material that can improve the rate characteristics of a secondary battery.

[0013] The present disclosure will be described in detail below with reference to one embodiment. In this specification, the expression "XX to YY" means "XX or more and YY or less." Furthermore, in this specification, for numerical ranges (e.g., ranges of content, etc.), lower and upper limits described in stages can be independently combined. Furthermore, in the numerical ranges described in this specification, the upper or lower limit of the numerical range may be replaced with a value shown in an example.

[0014] [Carbon Composite Active Material] The carbon composite active material of the present disclosure is a carbon composite active material comprising particles of an electrode active material and a surface layer covering the particles, wherein the surface layer is made of a coating material containing a graphene material and a binder, the graphene material contains an anionic functional group and a counter cation of the anionic functional group at an end, and the peak intensity ratio (I Ｄ / I Ｇ ) is 0.50 or less, and the content of the graphene material in the carbon composite active material is 0.1 to 2.2 mass %, and the content of the binder is 0.01 to 0.7 mass %.

[0015] The graphene material contained in the surface layer of the carbon composite active material of the present disclosure is a graphene material obtained by introducing a modifying group into a base material, graphene. Specifically, the graphene material contains an anionic functional group and a counter cation of the anionic functional group at an end, and has a Raman spectrum of 1300 to 1400 cm －１ The D band peak intensity I in the range Ｄ and 1550-1650 cm －１ The G-band peak intensity I in the range Ｇ The peak intensity ratio (I Ｄ / I Ｇ ) is a graphene material having a refractive index of 0.50 or less.

[0016] From the viewpoint of improving ionic conductivity, it is preferable that the graphene material has some structural defects. When the graphene material contains structural defects, ions can move through the structural defects, thereby improving ionic conductivity. On the other hand, if the graphene material has too many structural defects, it will have low conductivity. The structural defects in the graphene material can be measured by Raman spectroscopy. The D band is a peak derived from defects in the graphene material, and the G band is a peak derived from the graphite structure of the graphene material. In a perfect graphite crystal, I Ｄ However, as the symmetry of the graphite structure is lost, the peak of I Ｄ As the peaks become more intense and the graphene material has more structural defects, the peak intensity ratio (I Ｄ / I Ｇ In a graphene material containing an anionic functional group and a counter cation of the anionic functional group at its terminal, the peak intensity ratio (I Ｄ / I Ｇ By using a graphene material having a peak intensity ratio (I) of 0.50 or less as a conductive additive, it is possible to achieve both ionic conductivity and electrical conductivity. Ｄ / I Ｇ The lower limit of the peak intensity ratio (I) is not limited, but from the viewpoint of current manufacturing technology, it may be 0.10 or more. Ｄ / I Ｇ ) may be 0.10 to 0.50, 0.11 to 0.40, or 0.12 to 0.30. All of the peak intensity ratios are measured using a solid-state laser as the excitation laser at an excitation wavelength of 514.79 nm. In Raman spectroscopy, graphene powder has a peak intensity of 1570 cm －１ Nearby and 1345cm －１ It has a peak near

[0017] (Graphene) In the present disclosure, graphene refers to a one-atom-thick sp ２ It refers to a flake-like sheet material in which sheets of bonded carbon atoms (single-layer graphene) are stacked together, and the number of layers in the stack may be less than 100, less than 50, or less than 20.

[0018] The average particle size of graphene is not particularly limited, but in one embodiment, from the viewpoint of dispersibility, it may be 0.5 to 15 μm, 1.0 to 10 μm, or 1.5 to 5 μm. In the present disclosure, the average particle size of graphene refers to the particle size (D50) at which the cumulative number in the particle size distribution is 50%. The average particle size of graphene can be measured using a laser diffraction particle size distribution meter (for example, MT3300EXII, manufactured by Microtrackbell Corporation).

[0019] Graphene having the above average particle size can be obtained by pulverizing a carbon material having a particle size of 1 to 700 μm using a known pulverizer. The carbon material may have a particle size of 3 to 500 μm, 5 to 300 μm, or 10 to 200 μm. Examples of known pulverizers include dry pulverizers such as a ball mill, planetary mill, stirring mill, bead mill, jet mill, hammer mill, and high-speed stirrer, and may also be a ball mill, planetary mill, stirring mill, or bead mill that uses media. From the viewpoint of improving productivity, it is preferable that the rotation speed for stirring is high and the stirring time is short.

[0020] The carbon atom content in graphene is not particularly limited and may be 95 mass % or more, 99 mass % or more, or 100 mass %. The impurity substance content in graphene is not particularly limited and may be 5 mass % or less, 1 mass % or less, or 0 mass %.

[0021] From the viewpoint of dispersibility, the thickness of graphene may be 0.3 to 60.0 nm, 0.3 to 30.0 nm, or 0.6 to 12.0 nm. The "thickness" referred to here refers to the thickness of one layer in the case of a single layer, and refers to the thickness of the entire layer in the case of a multilayer. The thickness of graphene can be measured using, for example, an atomic force microscope.

[0022] (Modifying Group) In graphene materials, the modifying group introduced into the base graphene consists of an anionic functional group and a counter cation of the anionic functional group. It is inferred that the anionic functional group binds to the edge of the graphene particle, and the counter cation is attracted around the negatively charged graphene.

[0023] As described below, during the production of graphene materials, the grinding of graphene is promoted, and radicals are generated on the fracture surfaces of the graphene during grinding. It is believed that the counter anions of the water-soluble salt bond to the graphene through a weak acid liberation reaction between the radicals generated on the fracture surfaces of the graphene and a weak acid. The bond may be a covalent bond, an ionic bond, or a coordinate bond. Alternatively, a component of the water-soluble salt may be physically adsorbed to the carbon material.

[0024] The mechanical energy generated during the crushing process promotes the reaction between radicals generated at the fractured surfaces of the graphene and weak acid salts (e.g., lithium acetate), resulting in bonding.

[0025] When a solvent is added to a graphene material in which a modifying group has been introduced to the graphene, the counter cation dissociates in the solvent, and an electrostatic repulsion acts on the graphene to which the anionic functional group is bonded. As a result, the graphene material has good dispersibility when dispersed in a solvent and is resistant to re-aggregation.

[0026] By bonding an anionic modification group to graphene, the graphene has the characteristic of being highly negatively charged in the dispersion liquid. As the amount of negative charge increases, the dispersibility index, which will be described later, increases. General-purpose graphene (for example, a commercially available product: graphene nanoplate (manufactured by XG Science, product name: R10)) and crushed products of graphite alone have a small amount of negative charge, and van der Waals forces become dominant, so they aggregate and the dispersibility index decreases.

[0027] The anionic functional group constituting the modifying group may be at least one selected from the group consisting of a carboxy group, a carbonate group, a sulfonic acid group, and a phosphate group, or may be a carboxy group or a carbonate group, from the viewpoint of the dissociation property of the counter cation of the anionic functional group.

[0028] From the viewpoint of ionization tendency, the counter cation constituting the modifying group may be at least one selected from the group consisting of potassium ion, sodium ion, lithium ion, barium ion, calcium ion, magnesium ion, rubidium ion, and ammonium ion, or may be a potassium ion, a lithium ion, or a sodium ion.

[0029] When the modifying group is composed of an anionic functional group and a counter cation of the anionic functional group, the concentration of the counter cation contained in the graphene material may be 50 to 15,000 ppm by mass, 50 to 13,000 ppm by mass, 50 to 10,000 ppm by mass, 50 to 5,000 ppm by mass, or 100 to 5,000 ppm by mass. When the concentration of the counter cation is 50 ppm by mass or more, the dispersibility of the graphene material in the solvent can be further improved. When the concentration is 15,000 ppm by mass or less, the electrostatic repulsive force acting on the graphene material in the solvent becomes stronger, and the graphene material can better maintain its dispersed state in the solvent. The concentration of counter cations contained in the graphene material can be measured by ICP-OES (Inductively Coupled Plasma Optical Emission Spectrometry) or ICP-MS (Inductively Coupled Plasma Mass Spectrometry). Specifically, it can be measured by the method described in the examples.

[0030] (pH) The pH (25°C) of a dispersion obtained by dispersing a graphene material (concentration: 0.3% by mass) in a mixed solvent containing deionized water and 2-propanol in a volume ratio of 6:4 may be 5.1 to 8.1, 5.5 to 8.0, or 6.0 to 7.9. When the pH of a graphene material having a modifying group consisting of an anionic functional group and a counter cation of the anionic functional group is within the above range, the counter cation is easily dissociated in the solvent, and the anionic functional group is easily charged. As a result, electrostatic repulsion acts on the graphene to which the anionic functional group is bonded, thereby further improving the dispersibility of the graphene material in the solvent and making it less likely to re-aggregate. The pH can be adjusted within the above range by appropriately adjusting the properties of the graphene, the type of water-soluble salt, the compounding ratio of graphene to the water-soluble salt, and the mixing and grinding conditions.

[0031] (Particle size) In a volume-based particle size cumulative distribution measured by a laser diffraction scattering method, the cumulative 50% particle size (D50) from the small particle side of the graphene material may be 0.5 to 15.0 μm. When the particle size D50 is 0.5 μm or more, the crystallinity of the graphene material is more easily maintained and dispersibility is improved. When the particle size (D50) is 15.0 μm or less, the crystallinity of the graphene material is maintained and dispersibility is further improved. The particle size (D50) may be 1.0 to 10.0 μm, or 1.5 to 5.0 μm.

[0032] (Dispersion Index) The graphene material may have a dispersion index of 20 to 70% as calculated by the following <Equation 1>: <Equation 1> Dispersion Index (X) [%] = [(Absorbance) / (Absorbance Coefficient × Cell Thickness) / (Initial Concentration)] × 100 (In Equation 1, the absorbance coefficient is 3200 (L / g m), the cell thickness is 0.0001 (m), and the initial concentration is the solids concentration when the graphene material is dispersed in a mixed solvent of deionized water and 2-propanol (IPA) in a volume ratio of deionized water:IPA = 6:4, and is 3 (g / L).)

[0033] When the dispersion index is 20% or more, the graphene material has good dispersibility, and when it is 70% or less, the interparticle distance between graphene materials is maintained and aggregation can be reduced. The dispersion index may be 25 to 65%, or may be 30 to 60%. The dispersion index can be set within the above range by appropriately adjusting the average particle size of the carbon material as the base material, the water-soluble salt concentration, the pH of the solvent, and the conductivity of the solvent.

[0034] The larger the absolute value of the zeta potential of the graphene material, the stronger the electrostatic repulsion between the graphene materials, resulting in more stable dispersibility. From the viewpoint of further enhancing the dispersibility of the graphene material, the absolute value of the zeta potential of the graphene material may be 30 to 60 mV, 30 to 55 mV, or 30 to 50 mV.

[0035] (Method for Producing Graphene Material) Examples of methods for producing a graphene material include a method in which a water-soluble salt is added to graphene and mixed in a dry state, and the resulting mixture is washed with water. Anions liberated from the water-soluble salt bond with graphene and are incorporated into the graphene, thereby facilitating exfoliation and pulverization of the graphene. Note that in the present disclosure, "pulverization" is not limited to crushing or disintegration for downsizing the graphene from that used as a raw material, but also includes the purpose of simply breaking down the agglomerations of graphene.

[0036] The graphene described above can be used. The water-soluble salt is not particularly limited as long as it is a salt that is soluble in water. Specific examples of the water-soluble salt include tripotassium citrate, potassium tartrate, potassium acetate, potassium glutamate, potassium carbonate, and tripotassium phosphate. Further examples include salts in which the potassium in these water-soluble salts is replaced with sodium, lithium, barium, calcium, magnesium, rubidium, and ammonium, respectively. The water-soluble salt may be used alone or in combination of two or more.

[0037] The blending amount of the water-soluble salt may be 1 to 500 parts by mass, 10 to 400 parts by mass, or 100 to 300 parts by mass relative to 100 parts by mass of the carbon material. When the blending amount of the water-soluble salt is 1 part by mass or more, dispersibility in a solvent is improved by the generation of a graphene material, and when it is 500 parts by mass or less, reaction and adsorption of an excess of the water-soluble salt can be reduced.

[0038] The environmental conditions for mixing and pulverizing the water-soluble salt and graphene are not particularly limited. The pulverization may be performed under similar environmental conditions to those used for the pulverization described above, such as room temperature (25°C) in air, a nitrogen atmosphere, or an inert gas environment such as argon. Furthermore, the pulverization may be performed at a high or low temperature, or under a pressurized or reduced pressure environment, as necessary. The pulverization apparatus and examples thereof are as described above, and known apparatuses can be used without limitation. Examples of suitable pulverization apparatuses include dry pulverization apparatuses such as a ball mill, a bead mill, a jet mill, a hammer mill, and a high-speed agitator. The processing conditions may be adjusted appropriately depending on the type of carbon material, particle size, and the like.

[0039] After mixing the water-soluble salt and graphene, the resulting mixture is washed with water. This removes excess water-soluble salt. The amount of water added during the water washing is not particularly limited, as long as it is an amount sufficient to obtain a suspension. Heating may be performed as necessary. For example, water is added in an amount 10 to 10,000 times the total mass of the water-soluble salt and the carbon material, and the mixture is mixed and stirred. The number of water washings may be, for example, 2 to 10 times, or 2 to 8 times. The water washing conditions may be appropriately set depending on the types of graphene and water-soluble salt used, etc.

[0040] After washing with water, a filter may be used for filtration. The optimum pore size of the filter is selected depending on the application of the obtained graphene material. The obtained graphene material may be dried and extracted as a powder, or it may be dispersed in a liquid or used as a paste. Drying can be performed by any method. For example, the graphene material can be dried by spray drying.

[0041] <Binder> The binder contained in the surface layer of the carbon composite active material according to the present disclosure serves to bind the electrode active material and the graphene material together, and may include at least one selected from the group consisting of fluororesin, olefin resin, vinyl resin, polyamide, polyimide, polyether, polysaccharide, and rubber. For example, the material may be a fluororesin such as poly(vinyldifluoroethylene) (PVDF), poly(vinyldifluoroethylene-co-hexafluoropropylene) (PVDF-HFP), poly(tetrafluoroethylene) (PTFE), or ethylene tetrafluoroethylene (ETFE); an olefin resin such as polyethylene (PE) or polypropylene (PP); a vinyl resin such as polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyacrylic acid (PAA), or lithium polyacrylic acid (LiPAA); a polyamide (PA); a polyimide (PI); a polyether such as poly(ethylene) oxide (PEO); a polysaccharide such as cellulose, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, or regenerated cellulose; or a rubber such as fluororubber, styrene-butadiene rubber (SBR), ethylene propylene diene rubber (EPDM), or sulfonated EPDM.

[0042] <Electrode Active Material> In the carbon composite active material of the present disclosure, the electrode active material may be a positive electrode active material or a negative electrode active material.

[0043] (Positive Electrode Active Material) The positive electrode active material may be a lithium-containing composite oxide having at least one crystal structure selected from the group consisting of an olivine type, a layered rock salt type, and a spinel type.

[0044] The lithium-containing composite oxide having an olivine structure is represented by the general formula LiMPO ４ (M is one or more of Fe(II), Mn(II), Co(II), and Ni(II)). ４ Representative examples include LiFePO ４ , LiNiPO ４ , LiCoPO ４ , LiMnPO ４ , LiFeａ Ni ｂ P.O. ４ , LiFe ａ Co ｂ P.O. ４ , LiFe ａ Mn ｂ P.O. ４ , LiNi ａ Co ｂ P.O. ４ , LiNi ａ Mn ｂ P.O. ４ (a+b is 1 or less, 0<a<1, 0<b<1), LiFe ｃ Ni ｄ Co ｅ P.O. ４ , LiFe ｃ Ni ｄ Mn ｅ P.O. ４ , LiNi ｃ Co ｄ Mn ｅ P.O. ４ (c+d+e is 1 or less, 0<c<1, 0<d<1, 0<e<1), LiFe ｆ Ni ｇ Co ｈ Mn ｉ P.O. ４ (f+g+h+i is 1 or less, 0<f<1, 0<g<1, 0<h<1, 0<i<1), etc.

[0045] The lithium-containing composite oxide having a layered rock salt crystal structure is lithium cobalt oxide (LiCoO ２ ), LiNiO ２ , LiMnO ２ , Li ２ MnO ３ , LiNi ０．８ Co ０．２ O ２ NiCo-based alloys (general formula: LiNi ｘ Co １－ｘ O ２ (0<x<1)), LiNi ０．５ Mn ０．５ O ２ NiMn-based alloys (general formula: LiNi ｘ Mn １－ｘ O ２ (0<x<1)), LiNi １／３ Mn１／３ Co １／３ O ２ NiMnCo-based alloys (also called NMC) such as LiNi ｘ Mn ｙ Co １－ｘ－ｙ O ２ (x>0, y>0, x+y<1)) ０．８ Co ０．１５ Al ０．０５ ) O ２ , Li ２ MnO ３ -LiMO ２ (M=Co, Ni, Mn) or the like may also be used.

[0046] The lithium-containing composite oxide having a spinel-type crystal structure is LiMn ２ O ４ , Li １＋ｘ Mn ２－ｘ O ４ , Li(MnAl) ２ O ４ , LiMn １．５ Ni ０．５ O ４ may be.

[0047] The positive electrode active material is represented by the general formula Li （２－ｊ） MSiO ４ (M is one or more of Fe(II), Mn(II), Co(II), and Ni(II), and 0≦j≦2) may be a composite oxide represented by the general formula Li （２－ｊ） MSiO ４ Representative examples include Li （２－ｊ） FeSiO ４ , Li （２－ｊ） NiSiO ４ , Li （２－ｊ） CoSiO ４ , Li （２－ｊ） MnSiO ４ , Li （２－ｊ） Fe ｋ Ni ｌ SiO ４ , Li （２－ｊ） Fe ｋ Co ｌ SiO ４ , Li （２－ｊ） Fe ｋ Mn ｌ SiO ４, Li （２－ｊ） Ni ｋ Co ｌ SiO ４ , Li （２－ｊ） Ni ｋ Mn ｌ SiO ４ (k+l is 1 or less, 0<k<1, 0<l<1), Li （２－ｊ） Fe ｍ Ni ｎ Co ｑ SiO ４ , Li （２－ｊ） Fe ｍ Ni ｎ Mn ｑ SiO ４ , Li （２－ｊ） Ni ｍ Co ｎ Mn ｑ SiO ４ (m+n+q is 1 or less, 0<m<1, 0<n<1, 0<q<1), Li （２－ｊ） Fe ｒ Ni ｓ Co ｔ Mn ｕ SiO ４ (r+s+t+u is 1 or less, 0<r<1, 0<s<1, 0<t<1, 0<u<1), etc.

[0048] (Negative electrode active material) The negative electrode active material may be a carbon material such as natural graphite, artificial graphite, mesocarbon microbeads, mesocarbon fiber (MCF), cokes, glassy carbon, or a fired organic compound; a silicon-containing material SiOx (0≦x<2), a metal capable of combining with lithium such as Sn or aluminum, an alloy thereof, a composite material of such a metal and a carbon material, or lithium titanate (Li ４ Ti ５ O １２ ), SnO ２ The negative electrode active material may be at least one selected from the group consisting of graphite, SiOx (0≦x<2), and lithium titanate.

[0049] The shape of the active material is not particularly limited, and examples thereof include spherical, non-spherical, scale-like, and plate-like shapes. The active material may also be hollow particles having a void in the center. When the active material is in the form of particles, the average particle size may be 1 nm or more and 100 μm or less, 100 nm or more and 50 μm or less, or 1000 nm or more and 25 μm or less. The average particle size in the present disclosure refers to the particle diameter D50 at which the cumulative number of particles in the particle size distribution reaches 50%, and can be measured using a laser diffraction particle size distribution analyzer.

[0050] <Combination of Electrode Active Material, Graphene Material, and Binder> The combination of the electrode active material, graphene material, and binder may be performed by mechanically attaching the graphene material and the binder to the surface of the electrode active material. Mechanical attachment means repeatedly applying shear or compressive force to a mixture of the materials to fix the materials together. This is a combination by a so-called mechanical combination method.

[0051] The specific method of mechanical compounding is not particularly limited, and may be a known compounding method. Dry compounding or wet compounding may be used. For example, a binder may be added and dispersed in a deionized water / IPA solution containing isopropyl alcohol and deionized water, and then a graphene material may be added and ultrasonically dispersed, followed by centrifugation to prepare a graphene dispersion. An active material may be mixed with the graphene dispersion, suction filtered, and then dried to obtain a carbon composite active material.

[0052] The content of the graphene material in the carbon composite active material may be 0.1 to 2.2 mass%, 0.1 to 2.0 mass%, or 0.1 to 0.5 mass%. By setting the content of the highly conductive graphene material having anionic functional groups within the above range, the local electronic conductivity and ionic conductivity of the active material particle surface are improved.

[0053] The content of the binder in the carbon composite active material may be 0.01 to 0.7% by mass, 0.01 to 0.25% by mass, or 0.01 to 0.06% by mass. By setting the content of the binder within the above range, it is possible to ensure the effect of holding the graphene material on the surface of the active material, while avoiding a deterioration in battery characteristics due to a loss of the reactive surface area of ​​the electrode active material, and to maintain good battery characteristics.

[0054] In the carbon composite active material, the content ratio of the graphene material to the binder, in mass ratio, may be 3 to 30, 15 to 30, or 25 to 30. When the content ratio is within the above range, the internal resistance (electron / lithium ion transfer resistance) of a secondary battery using an electrode formed using the carbon composite active material is reduced, and the rate characteristics are improved.

[0055] In the obtained carbon composite active material, the ratio (DG / DA) of the planar size DG of the graphene material to the particle size DA of the electrode active material may be 0.002 to 3.000, 0.003 to 0.400, or 0.020 to 0.100. When DG / DA is 3.000 or less, the graphene material can be easily coated on the surfaces of the electrode active material particles, and when DG / DA is 0.002 or more, the internal resistance (electron / lithium ion transfer resistance) of a secondary battery using an electrode formed with the carbon composite active material is reduced, thereby improving the rate characteristics.

[0056] The planar size DG of the graphene material refers to the planar size, i.e., the long side of the plate-like graphene material. Specifically, it can be measured by the method described in the Examples.

[0057] The particle size DA of the electrode active material refers to the average of the longest and shortest diameters of the electrode active material particles, and can be measured by the method described in the Examples.

[0058] [Electrode] The electrode of the present disclosure can be formed using a slurry containing a carbon composite active material. The configuration and manufacturing method of the electrode are not particularly limited and may follow a known form. By using an electrode formed using a slurry containing the carbon composite active material, the rate characteristics of the battery are improved. There are a wide variety of electrode structures that can achieve this effect, and it is impossible or impractical with current technology to specify in detail and fully describe the structure according to one embodiment.

[0059] For example, in one embodiment, a positive electrode for a lithium secondary battery can be produced by mixing the carbon composite active material, a conductive additive, a binder, and a solvent to obtain a slurry, applying the slurry onto a positive electrode current collector, and drying the slurry.

[0060] Examples of the conductive additive include carbon materials such as Ketjen black, metal materials such as Al, conductive oxides, etc. Examples of the binder include polyvinylidene fluoride, acrylic resins, polytetrafluoroethylene resins, etc.

[0061] As the solvent, N-methylpyrrolidone or the like can be used. As the positive electrode current collector, a metal thin film mainly containing aluminum or the like can be used. The thickness of the positive electrode current collector is not particularly limited, but can be, for example, 5 to 50 μm.

[0062] The method for applying the slurry onto the current collector is not particularly limited, and examples thereof include a doctor blade method, a dipping method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, brush coating, etc. The amount of the slurry to be applied is not particularly limited, and can be appropriately set depending on the desired thickness of the electrode mixture layer, etc.

[0063] The method for drying the slurry on the current collector is not particularly limited, and examples thereof include drying with warm air, hot air, or low-humidity air, vacuum drying, and drying by irradiation with (far) infrared rays, electron beams, or the like. Drying conditions can be set appropriately, and the drying temperature may be 50 to 250°C, or 80 to 200°C. The drying time is not particularly limited, and is usually within a range of 10 to 60 minutes. The electrode may be stabilized by pressing after drying. Examples of pressing methods include die pressing and calendar pressing, but are not limited thereto.

[0064] [Secondary Battery] The secondary battery of the present disclosure includes the above-described electrode. That is, in the secondary battery of the present disclosure, at least one of the positive electrode and the negative electrode is the electrode of the present disclosure. The secondary battery of the present disclosure has a high discharge capacity. When one of the positive electrode and the negative electrode is the electrode of the present disclosure and the other is not the electrode of the present disclosure, the other electrode is not particularly limited, and any electrode can be used.

[0065] The secondary battery of the present disclosure may be a lithium ion secondary battery.

[0066] The secondary battery of the present disclosure may include an electrolyte layer in addition to the electrodes described above. The secondary battery of the present disclosure is, for example, stacked such that the positive electrode and the negative electrode face each other via the electrolyte layer. The electrolyte layer may be composed of an electrolytic solution or a solid electrolyte. When the electrolyte layer is an electrolytic solution, it may be a nonaqueous electrolytic solution obtained by dissolving an electrolyte salt in a nonaqueous solvent. Examples of non-aqueous solvents include ethylene carbonate, fluoroethylene carbonate, chloroethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, cyclopentanone, cyclohexylbenzene, sulfolane, propane sultone, 3-methyl sulfolane, 2,4-dimethyl sulfolane, 3-methyl-1,3-oxazolidin-2-one, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, butyl methyl carbonate, ethyl propyl carbonate, butyl ethyl carbonate, dipropyl carbonate, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate, ethyl acetate, trimethyl phosphate, and triethyl phosphate. These may be used alone or in combination of two or more. Examples of electrolyte salts include lithium salts. The lithium salt is not particularly limited as long as it dissolves in a non-aqueous solvent and exhibits high ionic conductivity, and can be appropriately selected depending on the purpose. For example, lithium hexafluorophosphate (LiPF ６ ), lithium tetrafluoroborate (LiBF ４ ) etc.

[0067] The concentration of the electrolyte salt is not particularly limited and can be appropriately selected depending on the purpose. From the viewpoints of lithium ion mobility and viscosity, the concentration may be 0.5 to 3.0 mol / L or 0.8 to 1.5 mol / L in the non-aqueous solvent.

[0068] (Separator) A separator is provided between the positive electrode and the negative electrode to prevent short-circuiting between the positive electrode and the negative electrode. Examples of separator materials include paper such as kraft paper, vinylon-mixed paper, and synthetic pulp-mixed paper, cellophane, polyethylene graft membrane, polyolefin nonwoven fabric such as polypropylene melt-blown nonwoven fabric, polyamide nonwoven fabric, glass fiber nonwoven fabric, and micropore membrane. The size of the separator is not particularly limited as long as it can be used in an electrochemical element. The separator may have a single-layer structure or a laminated structure. When a solid electrolyte is used, the separator can be omitted.

[0069] The secondary battery of the present disclosure has excellent rate characteristics. The secondary battery of the present disclosure may have a capacity retention rate of more than 60.4%, or even 70% or more at a 5C rate.

[0070] The present disclosure will now be described in detail with reference to examples, but the present disclosure is not limited to these examples.

[0071] <Preparation of Graphene Material> (Synthesis Example 1 - Graphene Material-1) 4 g of natural graphite (ACB-50, manufactured by Nippon Graphite Industries Co., Ltd., average particle size 350 μm) and 8 g of potassium L-glutamate were weighed out in a nitrogen atmosphere at room temperature (25°C) and milled for 40 minutes using a planetary ball mill (manufactured by Fritsch, model: P-6, ball diameter 10 mm, rotation speed 540 rpm). The milled mixture was then washed with deionized water, filtered, and dried at 60°C to obtain graphene material-1. 0.3 g of the obtained graphene material-1 was added to 100 mL of a mixed solvent of deionized water and 2-propanol (IPA) (volume ratio: 60 / 40), and ultrasonicated for 3 minutes using an ultrasonic homogenizer (UH-600S, manufactured by SMT Corporation) with a 26 mm diameter tip to obtain a dispersion. The resulting dispersion was sprayed onto a mica plate to prepare a measurement sample. The measurement sample was observed using an atomic force microscope (Hitachi High-Tech Corporation, model: AFM5300E) to measure the thickness of graphene material-1. As a result, it was confirmed that the thickness was 0.99 nm, the number of graphene layers was equivalent to three or less, and that natural graphite had been exfoliated between the layers to form graphene. The obtained graphene material-1 was placed in a platinum crucible, incinerated, and dissolved in a hydrochloric acid solution by alkali fusion. This was diluted with ultrapure water, and the target cation was quantitatively analyzed using an ICP optical emission spectrometer (Analytik Jena, model: PQ9000 Elite). As a result, it was confirmed that the counter cation, potassium, was contained in an amount of 2,200 ppm by mass.

[0072] (Synthesis Example 2 - Graphene Material-2) At room temperature (25°C) in a nitrogen atmosphere, 4 g of natural graphite (F#2, manufactured by Nippon Graphite Industries Co., Ltd., average particle size 130 μm) and 8 g of lithium acetate were weighed and ground for 40 minutes using a planetary ball mill (manufactured by Fritsch, model: P-6, ball diameter 10 mm, rotation speed 540 rpm). The mixture was then washed with deionized water, filtered, and dried at 60°C to obtain graphene material-2. The target cation was quantitatively analyzed using the same method as in Synthesis Example 1. As a result, it was confirmed that the counter cation, lithium element, was contained in an amount of 3,100 ppm by mass.

[0073] (Synthesis Example 3 - Graphene Material-3) At room temperature (25°C) in a nitrogen atmosphere, 4 g of natural graphite (F#1, manufactured by Nippon Graphite Industries Co., Ltd., average particle size 350 μm), 8 g of tripotassium citrate, and 25 ml of IPA were weighed and ground for 40 minutes using a planetary ball mill (manufactured by Fritsch, model: P-6, ball diameter 10 mm, rotation speed 540 rpm). The mixture was then washed with deionized water, filtered, and dried at 60°C to obtain graphene material-3. The target cation was quantitatively analyzed using the same method as in Synthesis Example 1. As a result, it was confirmed that the counter cation, potassium, was contained in an amount of 1700 ppm by mass.

[0074] (Synthesis Example 4 - Graphene Material-4) At room temperature (25°C) in a nitrogen atmosphere, 4 g of natural graphite (F#1, manufactured by Nippon Graphite Industries Co., Ltd., average particle size 350 μm), 8 g of lithium citrate, and 25 ml of IPA were weighed and ground for 40 minutes using a planetary ball mill (manufactured by Fritsch, model: P-6, ball diameter 10 mm, rotation speed 540 rpm). The mixture was then washed with deionized water, filtered, and dried at 60°C to obtain graphene material-4. The target cation was quantitatively analyzed using the same method as in Synthesis Example 1. As a result, it was confirmed that the counter cation, lithium element, was contained in an amount of 2800 ppm by mass.

[0075] <Preparation of Carbon Composite Active Material> (Preparation Example 1 for Example 1) 0.02 g of a binder (carboxymethyl cellulose (CMC)) was added and dispersed in 100 g of a deionized water / IPA solution consisting of isopropyl alcohol and deionized water, and then 0.65 g of graphene material-1 was added and ultrasonically dispersed, followed by centrifugation to prepare a graphene dispersion. 150 g of a positive electrode active material (lithium nickel oxide) was mixed with the graphene dispersion, and the mixture was suction filtered and dried to obtain carbon composite active material-1. The graphene material content in carbon composite active material-1 was 0.26 mass %, and the binder content was 0.01 mass %.

[0076] (Preparation Example 2 - For Example 2) Carbon composite active material-2 was obtained by the same method as in Preparation Example 1, except that the amount of binder (carboxymethyl cellulose (CMC)) added was 0.09 g, graphene material-2 was used instead of graphene material-1, and the amount of graphene material-2 added was 3.32 g. The graphene material content in carbon composite active material-2 was 1.29 mass%, and the binder content was 0.05 mass%. (Preparation Example 3 - For Example 3) Carbon composite active material-3 was obtained by the same method as in Preparation Example 1, except that the amount of binder (carboxymethyl cellulose (CMC)) added was 0.01 g, graphene material-3 was used instead of graphene material-1, and the amount of graphene material-3 added was 0.36 g. Carbon composite active material-3 was obtained by the same method as in Preparation Example 1. The graphene material content in carbon composite active material-3 was 0.14 mass%, and the binder content was 0.01 mass%. (Preparation Example 4 - For Example 4) Carbon composite active material-4 was obtained by the same method as in Preparation Example 1, except that the amount of binder (carboxymethyl cellulose (CMC)) added was 0.02 g, graphene material-3 was used instead of graphene material-1, and the amount of graphene material-3 added was 0.74 g. The graphene material content in carbon composite active material-4 was 0.32 mass%, and the binder content was 0.01 mass%. (Preparation Example 5 - For Example 5) Carbon composite active material-5 was obtained by the same method as in Preparation Example 1, except that the amount of binder (carboxymethyl cellulose (CMC)) added was 0.12 g, graphene material-4 was used instead of graphene material-1, and the amount of graphene material-4 added was 5.85 g. The graphene material content in carbon composite active material-5 was 1.74 mass%, and the binder content was 0.06 mass%. (Preparation Example 6 - For Example 6) Carbon composite active material-6 was obtained in the same manner as in Preparation Example 1, except that the amount of binder (carboxymethyl cellulose (CMC)) added was 0.12 g and the amount of graphene material-1 added was 7.54 g. The graphene material content in carbon composite active material-6 was 1.87 mass %, and the binder content was 0.23 mass %.(Preparation Example 7 - For Example 7) Carbon composite active material-7 was obtained in the same manner as in Preparation Example 1, except that the amount of binder (carboxymethyl cellulose (CMC)) added was 1.19 g, graphene material-3 was used instead of graphene material-1, and the amount of graphene material-3 added was 8.36 g. The graphene material content in carbon composite active material-7 was 1.95 mass%, and the binder content was 0.65 mass%.

[0077] (Preparation Example 8 for Comparative Example 2) Carbon composite active material-8 was obtained in the same manner as in Preparation Example 1, except that the amount of binder (carboxymethyl cellulose (CMC)) added was 0.15 g, graphene material-3 was used instead of graphene material-1, and the amount of graphene material-3 added was 9.40 g. The graphene material content in carbon composite active material-8 was 2.22 mass%, and the binder content was 0.08 mass%.

[0078] (Preparation Example 9 - For Comparative Example 3) Carbon composite active material-9 was obtained by the same method as in Preparation Example 1, except that the amount of binder (carboxymethyl cellulose (CMC)) added was 1.30 g, graphene material-3 was used instead of graphene material-1, and the amount of graphene material-3 added was 4.01 g. The graphene material content in carbon composite active material-9 was 1.03 mass%, and the binder content was 0.77 mass%. (Preparation Example 10 - For Comparative Example 4) Carbon composite active material-10 was obtained by the same method as in Preparation Example 1, except that the amount of binder (carboxymethyl cellulose (CMC)) added was 0.08 g, acetylene black (Li-100, manufactured by Denka Co., Ltd.) was used instead of the graphene material, and the amount added was 0.45 g. Carbon composite active material-10 had a carbon material content of 0.19 mass%, and the binder content was 0.04 mass%.

[0079] <Peak intensity ratio of graphene material (I Ｄ / I Ｇ )> Graphene material-1 to graphene material-4 and acetylene black were used as measurement powders, and the peak intensity ratios (I Ｄ / I Ｇ) was calculated. The calculation results are shown in Table 1 (Examples 1 to 7) and Table 2 (Comparative Examples 1 to 4). 0.3 g of the powder to be measured was added to 100 mL of a mixed solvent of deionized water and IPA (volume ratio: 60 / 40), and ultrasonic treatment was performed for 3 minutes using an ultrasonic homogenizer (UH-600S, manufactured by SMT Corporation) with a tip size of 26 mmφ to prepare a dispersion with a solids concentration of 3 g / L. 100 mL of the dispersion was transferred using a dropper to two 50 mL centrifuge tubes and centrifuged for 10 minutes at 25°C and 1000 rpm using a centrifuge (CR21N, manufactured by Hitachi Koki Co., Ltd.). The supernatant of the dispersion after centrifugation was dropped onto a membrane filter with a pore size of 5 μm and suction filtered. Raman spectroscopy was performed on the sample on the membrane filter using a laser Raman spectrometer (HR-800, manufactured by Horiba, Ltd.). The measurement conditions were a laser wavelength of 514.79 nm and a measurement wave number of 100 to 4000 cm －１ In the obtained spectrum, 1300 to 1400 cm －１ The D band peak intensity I in the range Ｄ , and 1550 to 1650 cm －１ The G-band peak intensity I in the range Ｇ From the peak intensity ratio (I Ｄ / I Ｇ ) was calculated.

[0080] <DG / DA> The carbon composite active material was embedded in a thermosetting resin and then thinned. TEM observation of the particle cross section was performed using an atomic resolution analytical electron microscope (JEOL Ltd., JEM-ARM200F NEOARM). The size of the graphene particles attached to the active material particle surface was measured at 20 random locations, and the average value was taken as DG (μm). The length of the longest part (major axis, μm) and the length of the shortest part (minor axis, μm) of 20 randomly selected electrode active material particles were measured using a scanning electron microscope (Hitachi High-Tech Corporation, Model S-3400NX). The value calculated by (major axis + minor axis) / 2 was averaged for 20 particles to give DA (μm).

[0081] <Preparation of secondary battery>

[0082] (Example 1) (1) Preparation of Positive Electrode Slurry Carbon composite active substance material-1, acetylene black and carbon nanotubes as conductive additives, and polyvinylidene fluoride (PVDF) as a binder were added to N-methylpyrrolidone (NMP) in a mass ratio of lithium nickel oxide:acetylene black:carbon nanotubes:PVDF=92:2:2:4, and the mixture was stirred for 15 minutes at a rotation speed of 20 m / s using a FILMICS stirrer (model number: 80, manufactured by PRIMIX Corporation) to prepare a positive electrode slurry.

[0083] (2) Preparation of Negative Electrode Slurry Spherical graphite and Si as negative electrode active materials, graphite as a conductive additive, and carboxymethyl cellulose (CMC) as a binder were added to a mixed solvent of deionized water and 2-propanol (IPA) in a volume ratio of 6:4 so that the mass ratio of graphite:Si:graphite:CMC was 80:12:4:4, and the mixture was stirred for 30 minutes at a rotation speed of 30 m / s using a Filmix stirrer (model number: 80, manufactured by Primix Corporation) to prepare a negative electrode slurry.

[0084] (3) Preparation of negative electrode and positive electrode The prepared negative electrode slurry and positive electrode slurry were each coated on one side of a current collector foil (SUS foil) using a bar coater (IMC-7000, manufactured by Imoto Machinery Co., Ltd.). The coated current collector foil was dried at 85 ° C. for 24 hours using an explosion-proof dryer (SAFWTY OVEN SPHH-100, manufactured by ESPEC Corporation) to prepare a negative electrode and a positive electrode.

[0085] (4) Preparation of Battery Components The dried negative and positive electrodes were each rolled using a small heated roll press (R-THCH1516, manufactured by Thank Metal Co., Ltd.), and the negative and positive electrodes were punched out to 16 mm diameter. As battery components, the positive electrode, the negative electrode, a separator (Ube Maxell CPORE (registered trademark) / thickness 0.025 mm / 19.5 mm diameter), and a coin cell were prepared, and dried in a pass box of a glove box (UNICO / UN-1000L) at a temperature of 85°C and a vacuum pressure of -0.1 MPa.

[0086] (5) Battery Fabrication The dried battery components were transferred from the pass box of the glove box to the main box, and the negative and positive electrodes were stacked in a coin cell with a separator interposed therebetween. 1 mL of electrolyte was then poured into the coin cell, and the coin cell was crimped using a manual coin crimping machine to fabricate a CR2032 coin cell (Battery-1). The fabricated battery was then removed from the glove box. The electrolyte contained lithium hexafluorophosphate (LiPF ６ A non-aqueous electrolyte solution was used in which ethylene carbonate (EC) and diethyl carbonate (DEC) were dissolved at a concentration of 1 mol / L in a mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of EC:DEC=50:50.

[0087] (Example 2) Battery-2 was produced in the same manner as Example 1, except that carbon composite active material-2 was used instead of carbon composite active material-1 in preparing the positive electrode slurry. (Example 3) Battery-3 was produced in the same manner as Example 1, except that carbon composite active material-3 was used instead of carbon composite active material-1 in preparing the positive electrode slurry. (Example 4) Battery-4 was produced in the same manner as Example 1, except that carbon composite active material-4 was used instead of carbon composite active material-1 in preparing the positive electrode slurry. (Example 5) Battery-5 was produced in the same manner as Example 1, except that carbon composite active material-5 was used instead of carbon composite active material-1 in preparing the positive electrode slurry. (Example 6) Battery-6 was produced in the same manner as Example 1, except that carbon composite active material-6 was used instead of carbon composite active material-1 in preparing the positive electrode slurry. (Example 7) Battery-7 was produced in the same manner as Example 1, except that carbon composite active material-7 was used instead of carbon composite active material-1 in preparing the positive electrode slurry. (Comparative Example 1) Battery-8 was produced in the same manner as Example 1, except that untreated positive electrode active material was used instead of carbon composite active material-1 in preparing the positive electrode slurry. (Comparative Example 2) Battery-9 was produced in the same manner as Example 1, except that carbon composite active material-8 was used instead of carbon composite active material-1 in preparing the positive electrode slurry. (Comparative Example 3) Battery-10 was produced in the same manner as Example 1, except that carbon composite active material-9 was used instead of carbon composite active material-1 in preparing the positive electrode slurry. (Comparative Example 4) Battery-11 was produced in the same manner as Example 1, except that carbon composite active material-10 was used instead of carbon composite active material-1 in preparing the positive electrode slurry.

[0088] <Capacity Retention Rate> Charge and discharge measurements were performed on Batteries-1 to -11 prepared in each Example and Comparative Example using a charge / discharge tester (TOSCAT-3100 manufactured by Toyo Systems Co., Ltd.). Charging was performed in a constant-temperature bath at 25°C, with the upper limit voltage set to 4.2 V from the OCV, in CC mode at 0.1 C, followed by charging in CV mode with a cutoff of 0.01 C. Discharging was performed at a lower limit voltage of 2.0 V, with the temperature of the constant-temperature bath maintained at 25°C, and discharges at 0.1 C and 5.0 C. The ratio of discharge capacity at this time = (discharge capacity at 5 C rate / discharge capacity at 0.5 C rate) × 100 was used as the capacity retention rate at 5 C rate. Based on the above measurement results, the electrodes were evaluated according to the following evaluation criteria. The results are shown in Table 1 (Examples 1 to 7) and Table 2 (Comparative Examples 1 to 4). [Evaluation criteria] ⊚: Capacity retention rate at 5C rate is 70% or more; ◯: Capacity retention rate at 5C rate is more than 60.4% and less than 70%; ×: Capacity retention rate at 5C rate is 60.4% or less

[0089]

[0090]

[0091] In all of the batteries equipped with the electrodes of Examples 1 to 7, i.e., the electrodes prepared using the slurries containing the specific carbon composite active material, the capacity retention rate at a 5C rate was greater than the reference value (60.4%), and improvement in rate characteristics was observed.

[0092] The carbon composite active material of the present disclosure is suitable for use as an active material for electrodes of secondary batteries in fields where improved rate characteristics are required.

Claims

1. A carbon composite active material comprising particles of an electrode active material and a surface layer covering the particles, wherein the surface layer is made of a coating material containing a graphene material and a binder, the graphene material contains an anionic functional group and a counter cation of the anionic functional group at its terminal, and the peak intensity ratio (I) of the D band to the G band in a Raman spectrum obtained by Raman spectroscopy measurement is Ｄ / I Ｇ ) is 0.50 or less, and the content of the graphene material in the carbon composite active material is 0.1 to 2.2 mass %, and the content of the binder in the carbon composite active material is 0.01 to 0.7 mass %.

2. The carbon composite active material according to claim 1, wherein the content ratio of the graphene material to the binder is 3 to 30 by mass.

3. The carbon composite active material according to claim 1 or 2, wherein the ratio (DG / DA) of the planar size DG of the graphene material to the particle size DA of the electrode active material is 0.002 to 3.

000.

4. The carbon composite active material according to any one of claims 1 to 3, wherein the electrode active material is a positive electrode active material.

5. The carbon composite active material according to any one of claims 1 to 4, wherein the electrode active material is a negative electrode active material.

6. The carbon composite active material according to claim 4, wherein the positive electrode active material is a lithium-containing composite oxide.

7. The carbon composite active material according to claim 6, wherein the lithium-containing composite oxide has at least one crystal structure selected from the group consisting of an olivine type, a layered rock salt type, and a spinel type.

8. The carbon composite active material according to claim 5, wherein the negative electrode active material is at least one selected from the group consisting of graphite, SiOx (0≦x<2), and lithium titanate.

9. The carbon composite active material according to any one of claims 1 to 8, wherein the binder comprises at least one selected from the group consisting of fluororesin, olefin resin, vinyl resin, polyamide, polyimide, polyether, polysaccharide, and rubber.

10. An electrode formed using a slurry containing the carbon composite active material according to any one of claims 1 to 9.

11. A secondary battery comprising the electrode according to claim 10.

Images