JP2011243567A - Negative electrode material for lithium ion secondary battery and method of manufacturing the same, negative electrode for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbonaceous material with which high discharge capacity and high initial charge/discharge efficiency, and further superior rate characteristics and cycle characteristics are obtained.SOLUTION: The present invention relates to the negative electrode material for the lithium ion secondary battery which has a graphite core material 12 made of a graphite material with high crystallinity and a carbonaceous coating layer 16 with low crystallinity covering a surface of the core material, and has no pore 14 on its surface, in which the graphite core material has pores and is in a substantially spherical shape in a state of a single particle having no carbonaceous coating layer. A pore volume of pores of 0.01-100 μm measured by a mercury penetration method after the negative electrode material for the lithium ion secondary battery is pulverized is 0.05-0.4 cm/g. When dof the negative electrode material for the lithium ion secondary battery is equal to or less than 0.3360 nm, an R value (I(1360)/I(1580)) of the negative electrode material for the lithium ion secondary battery in a Raman spectrum is 0.3-1.0.

Description

  The present invention relates to a negative electrode material for a lithium ion secondary battery containing a carbonaceous material, a negative electrode for a lithium ion secondary battery, and a lithium ion excellent in rate characteristics and cycle characteristics with high capacity, high charge / discharge efficiency using the negative electrode. The present invention relates to a secondary battery.

In recent years, with the miniaturization or high performance of electronic devices, there has been a demand for higher energy density of batteries. In such a situation, a lithium ion secondary battery having a higher energy density than other secondary batteries has attracted particular attention. The lithium ion secondary battery has a negative electrode, a positive electrode, and a non-aqueous electrolyte as main components, and acts as a secondary battery by moving lithium ions between the negative electrode and the positive electrode during a discharging process and a charging process. Currently, graphite is widely used as a negative electrode material for the lithium ion secondary battery.
As the crystallinity of graphite increases, the discharge capacity increases. However, as the crystallinity develops, the reactive active site called the edge surface also increases, which may increase the irreversible capacity during the first charge / discharge. In addition, it is essential to increase the density of the electrodes in order to increase the capacity of the battery. However, since the development of crystallinity leads to softening of the particles, pressing the electrode coated with graphite particles causes the particles to be easily crushed. Oriented in the direction. Such particle orientation decreases the permeability of the electrolytic solution and the diffusibility of lithium ions, which may cause a decrease in rate characteristics and cycle characteristics.

  Patent Document 1 describes a method for producing a carbon material in which a coating layer is formed on a core material having specific structural parameters obtained by grinding graphite or the like. Although there is no description about the shape of the core material, it is difficult to obtain a core material having specific structural parameters with good reproducibility.

Patent Document 2 describes a material in which a plurality of flat graphite particles are assembled or bonded non-parallelly. Even in this material, the characteristic deterioration due to the high crystallinity of graphite as described above is unavoidable, but the particle orientation is reduced by gathering or bonding non-parallelly. However, in recent lithium ion secondary batteries, it is necessary to further increase the electrode density in order to increase the capacity. For this reason, in a situation where a high pressing pressure is applied to the electrode, the particles are still crushed. As a result, the orientation is increased and the battery characteristics are lowered.
Patent Document 3 discloses a material characterized in that a plurality of flat graphite particles are aggregated or bonded non-parallelly.
Patent Document 4 describes a negative electrode material having a massive structure in which a plurality of flat graphite fine particles are aggregated or bonded, and a carbonaceous material formed on the surface of the graphite particles.
Patent Document 5 describes a secondary battery electrode material having composite particles containing a plurality of particles and a coating layer covering the particles, and the surface of the electrode material has pores.

Patent Document 6 describes a negative electrode active material for a secondary battery in which a base material obtained by firing a mixture of graphite powder, carbon, and metal silicon is coated with a carbon precursor or a mixture of a carbon precursor and carbon black. ing.
Patent Document 7 describes a cathode active material for a secondary battery having a graphite core having pores and metal nanoparticles and amorphous carbon in the pores.

  As described above, in the prior art, there are descriptions of negative electrode materials for lithium ion secondary batteries using various carbon materials, but higher performance materials are desired.

Japanese Patent Laid-Open No. 10-36108 Japanese Patent No. 3213575 Japanese Patent Laid-Open No. 10-236809 Reissue WO2005 / 024980 JP 2005-158721 A JP 2008-186732 A JP 2009-266795 A

  The present invention has been made in view of the above situation, that is, when used as a negative electrode material for a lithium ion secondary battery, a high discharge capacity, a high initial charge / discharge efficiency, and an excellent rate characteristic ( An object is to provide a carbonaceous material capable of obtaining rapid charge / discharge efficiency and cycle characteristics. Moreover, it aims at providing the manufacturing method of the carbonaceous material, the negative electrode containing the carbonaceous material, and the lithium ion secondary battery using the negative electrode.

As a result of intensive studies to achieve the above object, the present inventor has found that a graphite core material made of highly crystalline graphite having a specific shape and characteristics and a low crystalline carbonaceous material covering the surface of the core material The present inventors have found that a negative electrode material having a coating layer is excellent in the above characteristics, and have reached the present invention.
That is, the present invention provides the following.
(1) A negative electrode material for a lithium ion secondary battery, comprising a graphite core material made of highly crystalline graphite and a low crystalline carbonaceous coating layer covering the surface of the core material,
The surface of the negative electrode material for lithium ion secondary batteries has no pores, the graphite core has pores,
The graphite core is substantially spherical in the form of a single particle having no carbonaceous coating layer,
The pore volume of the graphite core material is such that the pore volume of 0.01 to 100 μm measured by the mercury intrusion method after pulverizing the negative electrode material for a lithium ion secondary battery is 0.05 to 0.4 cm ³ / g. ,
D _{002 of the} negative electrode material for a lithium ion secondary battery: 0.3360 nm or less,
The ratio of the R value of the negative electrode material for a lithium ion secondary battery (in the Raman spectrum using argon ion laser with a wavelength of 514.5 nm, a peak intensity of 1360 cm ^-1 to the peak intensity of ^{1580cm -1 (I1580) (I1360)} (I1360 / I1580)): A negative electrode material for a lithium ion secondary battery that is 0.3 to 1.0.

(2) A lithium ion secondary battery negative electrode using the lithium ion secondary battery negative electrode material described in (1) above.
(3) The lithium ion secondary battery negative electrode according to (2), wherein the negative electrode has an electrode density of 1.7 to 1.9 g / cm ³ .
(4) A lithium ion secondary battery having the negative electrode according to (2) or (3).
(5) A mixture of inorganic fine particles and a carbonaceous precursor is heated at 2500 ° C. or higher to decompose and evaporate the inorganic fine particles to obtain pores and graphitize the carbonaceous precursor to obtain graphite having pores. A graphitization step for obtaining a porous core material, an attachment step for attaching a carbonaceous precursor to the surface of the graphite core material obtained in the graphitization step, and a graphitic material to which a carbonaceous precursor is attached in the attachment step The above (1) characterized by comprising a firing step of heating the core material at a temperature of 1100 ° C. or higher and 1500 ° C. or lower to obtain a negative electrode material having a carbonaceous coating layer having no voids on the surface of the graphite core material. The manufacturing method of the negative electrode material for lithium ion secondary batteries as described in 2 ..

  The present invention provides a carbonaceous material having good discharge capacity, initial charge / discharge efficiency, rate characteristics, and cycle characteristics as a negative electrode material for a lithium ion secondary battery. Therefore, the lithium ion secondary battery using the carbonaceous material of the present invention satisfies the recent demand for higher energy density of the battery, and is effective in reducing the size and performance of the mounted equipment.

It is typical sectional drawing of the negative electrode carbonaceous material of this invention. It is sectional drawing of the evaluation battery for evaluating the battery characteristic of the negative electrode of this invention.

Hereinafter, the present invention will be described more specifically.
The negative electrode material for a lithium ion secondary battery (hereinafter sometimes referred to as negative electrode carbonaceous material or carbonaceous material) 10 according to the present invention has at least two parts having different crystallinity as shown in a cross-sectional view in FIG. The graphite core material 12 has high crystallinity compared to the crystallinity of the carbonaceous coating layer 16 on the surface, and the highly crystalline portion of the graphite core material is flat or scaly. The carbonaceous coating layer 16 is not an aggregate of particles, and the carbonaceous coating layer 16 has no voids and has voids or pores 14 in the highly crystalline part.

[Negative carbonaceous material]
The negative electrode carbonaceous material of the present invention has an average particle diameter in terms of volume and is preferably 1 to 100 μm, particularly 1 to 50 μm, and more preferably 1 to 30 μm. If the thickness is 1 μm or more, the filling density of the negative electrode can be increased, so that the discharge capacity per volume is improved, and if it is 100 μm or less, cycle characteristics and rate characteristics are improved. The average particle diameter in terms of volume is a particle diameter at which the cumulative frequency of particle size distribution is 50% by volume by a laser diffraction particle size distribution meter.

The specific surface area of the negative electrode carbonaceous material of the present invention is preferably 10 m ² / g or less, particularly 5 m ² / g or less, and more preferably 3.5 m ² / g or less. If the specific surface area is within the above range, the initial charge / discharge efficiency is improved.
The average crystallinity of the negative electrode carbonaceous material can be determined from the interplanar spacing (d ₀₀₂ ) of the carbon network layer and the size of the crystallite in the C-axis direction (Lc) in the X-ray wide angle diffraction method. . That is, using a CuKα ray as an X-ray source and high-purity silicon as a standard substance, a (002) diffraction peak is measured for a carbonaceous material, and d ₀₀₂ and Lc are calculated from the peak position and its half width, respectively. To do. The calculation method is in accordance with the Gakushin Law, and a specific method is described in “Carbon Fiber” (Modern Editorial Company, published in March 1986), pages 733 to 742.
From the viewpoint of developing a high discharge capacity, d ₀₀₂ and Lc, which are indicators of the degree of development of the graphite structure of the negative electrode carbonaceous material of the present invention, are d ₀₀₂ ≦ 0.3360 nm and Lc ≧ 40 nm. It is preferable that d ₀₀₂ ≦ 0.3359 nm and Lc ≧ 50 nm are particularly preferable. When d ₀₀₂ > 0.3360 nm and Lc <40 nm, the degree of development of the graphite structure is low. Therefore, when it is used as the negative electrode of a lithium ion secondary battery, the lithium doping amount is small and a high discharge capacity is obtained. It may not be obtained.

Negative electrode carbonaceous material of the invention, R value is the peak intensity ratio of 1360 cm ^-1 relative to 1580 cm ^-1 with an argon laser Raman spectrum is 0.3 to 1.0. This means that the surface crystallinity is low, and if the peak intensity ratio is within the above range, the initial charge / discharge efficiency is improved and the rate characteristics and cycle characteristics are improved. The R value is preferably 0.35 to 0.8, and more preferably 0.35 to 0.65.
The negative electrode carbonaceous material of the present invention can be contained within the range not impairing the object of the present invention by mixing different types of graphite materials, carbonaceous materials such as amorphous hard carbon, organic matter, metals, metal compounds, etc. Or you may coat. The carbonaceous material of the present invention may be subjected to various chemical treatments in the liquid phase, gas phase, and solid phase, heat treatment, physical treatment, oxidation treatment, and the like.

<Graphitic core>
The graphite core material, which is a highly crystalline part of the carbonaceous material of the present invention, is substantially spherical in the form of single particles not having a carbonaceous coating layer, and is not scale-like or flat. The aspect ratio is 3 or less, preferably 1 to 2, more preferably less than 1 to 1.8. The aspect ratio is calculated by observing the graphite core material particles with an SEM and measuring and averaging the ratio of 50 major axes and minor axes.
The graphite core material may be a single particle or a granulated body in which a plurality of particles are aggregated or bonded.
Similarly to the negative electrode carbonaceous material, the crystallinity of the graphite core particles can be expressed by d ₀₀₂ and Lc, and d ₀₀₂ is preferably 0.3360 nm or less and Lc is preferably 40 nm or more.
There are pores in the graphite core. As will be described later, since the voids or pores do not exist in the low crystalline carbonaceous coating layer of the present invention, the porosity of the present invention can be measured for the entire negative electrode carbonaceous material and the negative electrode carbonaceous material is pulverized. In addition, the mercury intrusion method is applied.
The pore volume of the graphite core material is such that the pore volume of 0.01 to 100 μm measured by mercury porosimetry after pulverizing the negative electrode carbonaceous material is 0.05 to 0.4 cm ³ / g.
If the pores of the graphite core material inside the particles are within this range, the expansion associated with charging is absorbed and the electrolyte is retained, so that lithium ions are not depleted even during high-speed charging. The pore volume of the graphite core material is preferably 0.08 to 0.4 cm ³ / g, more preferably 0.1 to 0.4 cm ³ / g.
Here, g per unit mass of the pore volume of the graphite core material cm ³ / g indicates the mass of the graphite core material. The mass of the graphite core material is obtained by measuring the amount of TG (weight reduction) of the negative electrode carbonaceous material to obtain the ratio of the low crystalline carbonaceous coating layer, and calculating the ratio of the low crystalline carbonaceous coating layer from the mass of the negative carbonaceous material. It calculated | required from the quantity which deducted mass. The TG (weight loss) measurement is described in detail in the Examples section.
The shape and state of the pores existing in the graphite core material are not limited, and the pores may be dispersed, may be present near the center, or reach the surface of the graphite core material. It may be a void.

<Carbonaceous coating layer>
There is a low crystalline carbonaceous coating layer 16 on the surface of the graphite core 12. The mass percentage of the carbonaceous coating layer which is a low crystalline part in the negative electrode carbonaceous material 10 of the present invention is 1 to 50 mass%, preferably 1 to 20 mass%, more preferably 1 to 10 mass% of the whole negative electrode carbonaceous material. %. The mass percentage can be obtained by TG (weight loss) measurement or the like.
In the present invention, the carbonaceous coating layer is substantially free of pores. This can be confirmed by SEM observation of the negative electrode carbonaceous material at 10,000 to 100,000 times and no pores. The reason why pores are not provided in the carbonaceous coating layer (or problems when voids exist in the surface layer) is that the surface layer prevents the negative electrode carbonaceous material particles from being crushed when the electrode is pressed, In this case, the particle orientation is suppressed.
However, if pores are present in the surface layer, the strength of the surface layer itself may decrease, thereby reducing the effect of suppressing particle orientation, and further, the charge / discharge efficiency of the secondary battery may decrease due to generation of cracks or cracks.

[Production method]
The negative electrode carbonaceous material of the present invention is a carbonaceous particle having at least two parts having different crystallinity, the internal crystallinity is higher than the surface crystallinity, and the highly crystalline part is a scaly particle. It may be produced by any method as long as it is a method capable of producing a carbonaceous material having pores in the highly crystalline portion instead of an aggregate. An example of the production method of the present invention is shown below.

After dispersing inorganic fine particles (average particle diameter: 0.01 to 0.3 μm) such as silica and iron oxide in a carbon precursor solution (for example, coal tar pitch dissolved in oil in tar), the solvent is removed, The resulting mixture of pitch and inorganic fine particles is graphitized at a temperature of 2500 ° C. or higher, whereby the pitch portion is graphitized and the inorganic fine particles are volatilized to form pores therein. After pulverizing and classifying this graphitized product to an appropriate particle size to obtain a graphite core material, it is dispersed again in the same carbonaceous material solution as described above, and then the solvent is removed. By heat-treating the mixture at 1100 ° C. to 1500 ° C. for carbonization, a composite in which the surface of the graphitized product (graphite core material) is coated with a low crystalline layer is formed.
The graphitization temperature is preferably 2500 ° C to 4000 ° C, more preferably 2500 ° C to 3500 ° C. Within this range, the crystallinity and the degree of pores of the graphite core material are appropriate.
The heat treatment temperature is preferably more than 1100 ° C. to 1500 ° C. or less. When the temperature is within the above range, a negative electrode carbonaceous material having a sufficiently low R value is obtained. The presence or absence of pores on the surface of the low crystalline layer can be controlled by changing the carbon precursor solution used, specifically the pitch type, viscosity, and drying conditions (temperature, pressure). Control to prevent voids and pores. The target negative electrode carbonaceous material particles can be obtained by classifying the composite to have an appropriate particle size. The absence of pores in the low crystalline coating layer can be confirmed by SEM observation of the particle cross section.

The mass percentage of the low crystalline part in the carbonaceous material of the present invention is 1 to 50% by mass, preferably 1 to 20% by mass, and more preferably 1 to 10% by mass with respect to the whole negative electrode carbonaceous material. The mass percentage can be obtained by TG (weight loss) measurement or the like.
When the negative electrode carbonaceous material of the present invention is used, the mechanism by which the initial charge / discharge efficiency, rate characteristics, cycle characteristics and the like are improved is not clear, but is estimated as follows. That is, since the surface has a low crystalline part, the electrolytic solution is hardly decomposed on the graphite edge surface. In addition, the low crystalline portion on the surface is harder than the internal high crystalline portion, preventing the particles from being crushed when the electrode is pressed, and suppressing the particle orientation in the electrode. Further, the pores of the graphite core material inside the particles absorb expansion due to charging, and also serve to retain the electrolyte, so that lithium ions are not depleted even during high-speed charging. It is considered that favorable rate characteristics and cycle characteristics are expressed by these factors.

[Negative electrode]
The present invention is a negative electrode for a lithium ion secondary battery containing the negative electrode carbonaceous material, and a lithium ion secondary battery using the negative electrode.
<Binder>
The negative electrode for a lithium ion secondary battery of the present invention is produced according to a normal negative electrode molding method, but is not limited as long as it is a method capable of obtaining a chemically and electrochemically stable negative electrode. When preparing the negative electrode, it is preferable to use a negative electrode mixture prepared in advance by adding a binder to the negative electrode carbonaceous material of the present invention. As the binder, those showing chemical and electrochemical stability with respect to the electrolyte are preferable. For example, fluorine-based resin powders such as polytetrafluoroethylene and polyvinylidene fluoride, and resin powders such as polyethylene and polyvinyl alcohol Carboxymethyl cellulose and the like are used. These can also be used together. A binder is normally used in the ratio of about 1-20 mass% in the whole quantity of a negative electrode mixture.
The electrode density of the negative electrode is such that the thickness of the current collector is t ₁ [cm], the mass per unit area is W ₁ [g / cm ² ], and the mass ratio of the negative electrode carbonaceous material of the present invention is P [%]. A negative electrode mixture having a thickness t ₂ [cm] manufactured by applying and pressing a negative electrode mixture paste with a binder to be punched is punched out in a predetermined area S [cm ² ], and the mass of the negative electrode after punching is defined as W _2. When [g], it can be obtained by the following formula. In addition, the said mass is the value measured with the top plate type automatic balance and thickness with the micrometer.
Electrode density [g / cm ³ ] = {(W ₂ / S−W ₁ ) / (t ₂ −t ₁ )} × (P / 100), preferably 1.5 to 2.0 g / cm ³ 1.7 to 1.9 g / cm ³ is more preferable.

<Manufacture of negative electrode>
More specifically, first, the negative electrode carbonaceous material of the present invention is adjusted to a desired particle size by classification, etc., and the mixture obtained by mixing with a binder is dispersed in a solvent to prepare a negative electrode mixture in the form of a paste. To do. That is, a slurry obtained by mixing the negative electrode material of the present invention and a binder with a solvent such as water, isopropyl alcohol, N-methylpyrrolidone, dimethylformamide, and the like, a known stirrer, mixer, kneader, A paste is prepared by stirring and mixing using a kneader or the like. When the paste is applied to one or both sides of the current collector and dried, a negative electrode in which the negative electrode mixture layer is uniformly and firmly bonded is obtained. The film thickness of the negative electrode mixture layer is 10 to 200 μm, preferably 20 to 100 μm.
The negative electrode of the present invention can also be produced by dry-mixing the carbonaceous material of the present invention and resin powders such as polyethylene and polyvinyl alcohol and hot pressing in a mold.
When the negative electrode mixture layer is formed and then pressure bonding such as pressurization is performed, the adhesive strength between the negative electrode mixture layer and the current collector can be further increased.

The shape of the current collector used for producing the negative electrode is not particularly limited, but may be a foil shape, a mesh shape, a net shape such as expanded metal, or the like. The material for the current collector is preferably copper, stainless steel, nickel or the like. The thickness of the current collector is preferably about 5 to 20 μm in the case of a foil.
It should be noted that the negative electrode of the present invention can be included even if different types of graphite materials, carbonaceous materials such as amorphous hard carbon, organic substances, metals, metal compounds, and the like are mixed within a range that does not impair the object of the present invention. Alternatively, it may be coated or laminated.

[Positive electrode]
The positive electrode is formed, for example, by applying a positive electrode mixture comprising a positive electrode material, a binder and a conductive agent to the surface of the current collector. The positive electrode material (positive electrode active material) is preferably selected from materials that can occlude / release a sufficient amount of lithium, and lithium such as lithium-containing transition metal oxides, transition metal chalcogenides, vanadium oxides, and lithium compounds thereof. containing compound, the general formula _{M x Mo 6 S 8-Y} (M in the formula is a transition metal element of at least one, X is 0 ≦ X ≦ 4, Y is a number in the range from 0 ≦ Y ≦ 1) Chevrel phase compounds, activated carbon, activated carbon fibers and the like. Vanadium oxide _is one represented by _{V 2 O 5, V 6 O} 13, V 2 O 4, V 3 O 8.

The lithium-containing transition metal oxide is a composite oxide of lithium and a transition metal, and may be a solid solution of lithium and two or more transition metals. The composite oxide may be used alone or in combination of two or more. Specifically, the lithium-containing transition metal oxide is LiM ¹ _1-X M ² _x O ₂ (wherein M ¹ and M ² are at least one transition metal element, and X is in a range of 0 ≦ X ≦ 1. LiM ¹ _1-Y M ² _Y O ₄ (wherein M ¹ and M ² are at least one transition metal element, and Y is a value in the range of 0 ≦ Y ≦ 1). Indicated. The transition metal elements represented by M ¹ and M ² are Co, Ni, Mn, Cr, Ti, V, Fe, Zn, Al, In, Sn, etc., preferably Co, Fe, Mn, Ti, Cr , V, Al, etc. Preferred examples include LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiNi _0.9 Co _0.1 O ₂ , LiNi _0.5 Co _0.5 O ₂ , and the like.

<Production of positive electrode>
Examples of the lithium-containing transition metal oxide include lithium, transition metal oxides, hydroxides, salts, and the like as starting materials, and these starting materials are mixed in accordance with the composition of the desired metal oxide, and are mixed under an oxygen atmosphere. It can be obtained by firing at a temperature of ˜1000 ° C.
The positive electrode active material may be used alone or in combination of two or more. For example, a carbonate such as lithium carbonate can be added to the positive electrode. Moreover, when forming a positive electrode, conventionally well-known various additives, such as a electrically conductive agent and a binder, can be used suitably.
The positive electrode is produced by applying a positive electrode mixture comprising the positive electrode material, a binder, and a conductive agent for imparting conductivity to the positive electrode on both sides of the current collector to form a positive electrode mixture layer. As the binder, the same one as that used for producing the negative electrode can be used. As the conductive agent, known materials such as graphitized materials and carbon black are used.
The shape of the current collector is not particularly limited, but a foil shape or a mesh shape such as a mesh or expanded metal is used. The material of the current collector is aluminum, stainless steel, nickel or the like. The thickness is preferably 10 to 40 μm.
Similarly to the negative electrode, the positive electrode mixture may be formed in a paste by dispersing the positive electrode mixture in a solvent, and the paste-like positive electrode mixture may be applied to a current collector and dried to form a positive electrode mixture layer. After forming the agent layer, pressure bonding such as press pressing may be further performed. As a result, the positive electrode mixture layer is uniformly and firmly bonded to the current collector.

[Nonaqueous electrolyte]
The non-aqueous electrolyte used in the lithium ion secondary battery of the present invention, an electrolyte salt used in the conventional non-aqueous _{electrolyte, LiPF 6, LiBF 4, LiA} s F 6, LiClO 4, LiB (C 6 _{H 5), LiCl, LiBr,} LiCF 3 SO 3, LiCH 3 SO 3, LiN (CF 3 SO 2) 2, LiC (CF 3 SO 2) 3, LiN (CF 3 CH 2 OSO 2) 2, LiN (CF _{3 CF 2 OSO 2) 2,} LiN (HCF 2 CF 2 CH 2 OSO 2) 2, LiN ((CF 3) 2 CHOSO 2) 2, LiB [{C 6 H 3 (CF 3) 2}] 4, LiAlCl ₄ and lithium salts such as LiSiF ₆ can be used.
From the viewpoint of oxidation stability, LiPF ₆ and LiBF ₄ are particularly preferable.
The electrolyte salt concentration in the electrolytic solution is preferably 0.1 to 5 mo1 / 1, and more preferably 0.5 to 3.0 mol / 1.
The non-aqueous electrolyte may be a liquid non-aqueous electrolyte or a polymer electrolyte such as a solid electrolyte or a gel electrolyte. In the former case, the non-aqueous electrolyte battery is configured as a so-called lithium ion secondary battery, and in the latter case, the non-aqueous electrolyte battery is configured as a polymer electrolyte battery such as a polymer solid electrolyte or a polymer gel electrolyte battery. .

  As a solvent for preparing the nonaqueous electrolyte solution, carbonates such as ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate, 1,1- or 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, 1,3-dioxolane, 4-methyl-1,3-dioxolane, ethers such as anisole and diethyl ether, thioethers such as sulfolane and methylsulfolane, acetonitrile, chloronitrile, propionitrile, etc. Nitrile, trimethyl borate, tetramethyl silicate, nitromethane, dimethylformamide, N-methylpyrrolidone, ethyl acetate, trimethyl orthoformate, nitrobenzene, benzoyl chloride, Benzoyl, tetrahydrothiophene, dimethyl sulfoxide, 3-methyl-2-oxazolidone, ethylene glycol, aprotic organic solvents such as dimethyl sulfite may be used.

When the non-aqueous electrolyte is a polymer electrolyte such as a polymer solid electrolyte or a polymer gel electrolyte, it is preferable to use a polymer gelled with a plasticizer (non-aqueous electrolyte) as a matrix. Examples of the polymer constituting the matrix include ether-based polymer compounds such as polyethylene oxide and cross-linked products thereof, polymethacrylate-based polymer compounds, polyacrylate-based polymer compounds, polyvinylidene fluoride, and vinylidene fluoride-hexafluoropropylene. It is particularly preferable to use a fluorine-based polymer compound such as a copolymer.
The polymer solid electrolyte or polymer gel electrolyte is mixed with a plasticizer, and as the plasticizer, the electrolyte salt and the non-aqueous solvent can be used. In the case of a polymer gel electrolyte, the concentration of the electrolyte salt in the nonaqueous electrolytic solution that is a plasticizer is preferably 0.1 to 5 mol / 1, and more preferably 0.5 to 2.0 mol / 1.

The method for producing the polymer solid electrolyte is not particularly limited. For example, a method of mixing a polymer compound constituting a matrix, a lithium salt, and a nonaqueous solvent (plasticizer) and heating to melt the polymer compound, an organic solvent A method in which a polymer compound, a lithium salt, and a non-aqueous solvent (plasticizer) are dissolved in, and an organic solvent for mixing is evaporated, a polymerizable monomer, a lithium salt, and a non-aqueous solvent (plasticizer) are mixed, and the mixture is mixed Examples thereof include a method of polymerizing a polymerizable monomer by irradiating an ultraviolet ray, an electron beam, a molecular beam or the like to obtain a polymer.
Here, the ratio of the non-aqueous solvent (plasticizer) in the solid electrolyte is preferably 10 to 90% by mass, and more preferably 30 to 80% by mass. If it is less than 10% by mass, the electrical conductivity will be low, and if it exceeds 90% by mass, the mechanical strength will be weak and film formation will be difficult.

[Separator]
In the lithium ion secondary battery of the present invention, a separator can also be used. Although the material of a separator is not specifically limited, For example, a woven fabric, a nonwoven fabric, a synthetic resin microporous film, etc. can be used. As a material for the separator, a microporous membrane made of synthetic resin is suitable. Among them, a polyolefin microporous membrane is suitable in terms of thickness, membrane strength, and membrane resistance. Specifically, polyethylene and polypropylene microporous membranes, or microporous membranes composed of these are suitable.

[Lithium ion secondary battery]
The lithium ion secondary battery of the present invention is configured by laminating the negative electrode, the positive electrode, and the nonaqueous electrolyte having the above-described configuration in the order of, for example, the negative electrode, the nonaqueous electrolyte, and the positive electrode, and accommodating the laminate in the battery exterior material. The Further, a non-aqueous electrolyte may be disposed outside the negative electrode and the positive electrode.
In addition, the structure of the lithium ion secondary battery of the present invention is not particularly limited, and the shape and form thereof are not particularly limited, and are cylindrical, depending on the application, mounted equipment, required charge / discharge capacity, and the like. , Square shape, coin shape, button shape, and the like. In order to obtain a sealed nonaqueous electrolyte battery with higher safety, it is preferable to use a battery equipped with means for detecting an increase in the internal pressure of the battery and shutting off the current when an abnormality such as overcharging occurs.
In the case where the lithium ion secondary battery is a polymer solid electrolyte battery or a polymer gel electrolyte battery, a structure in which the lithium ion secondary battery is enclosed in a laminate film may be used.

  EXAMPLES Next, although an Example demonstrates this invention concretely, this invention is not limited to these Examples. In the following examples and comparative examples, as shown in FIG. 2, a current collector (negative electrode) 7b having a negative electrode carbonaceous material of the present invention attached to at least a part of the surface and a counter electrode (positive electrode) 4 made of lithium foil. A button-type secondary battery for single electrode evaluation composed of An actual battery can be produced according to a known method based on the concept of the present invention.

[Example 1]
[Production of carbonaceous materials]
Using a biaxial heating kneader, iron oxide fine particles (average particle diameter: 0.05 μm) were added to a solution obtained by mixing coal oil with coal tar pitch (manufactured by JFE Chemical Co., Ltd., PK-E). Kneaded for hours. At that time, the solid content ratio (mass ratio, the same applies hereinafter) was prepared from coal tar pitch: iron oxide fine particles and 95: 5. After kneading, a vacuum was applied to remove the solvent in the kneaded product.
The obtained kneaded material is roughly pulverized to about 1 mm using a cutter mill and then placed in a graphite crucible. First, the mixture is held at 500 ° C. for 6 hours in an argon atmosphere to reduce the volatile content to 5% or less, and then 3000 ° C. And graphitized for 3 hours.
The graphitized product was pulverized with an atomizer so that the average particle size was 10 μm, and the obtained graphite core material particles were observed with an SEM to determine the ratio of 50 major axes to minor axes as an aspect ratio. The results are shown in Table 1. The d ₀₀₂ of the graphite core material particles was 0.3357 nm.
Next, the graphite core material was kneaded with a coal tar pitch solution at 150 ° C. for 1 hour using a biaxial heating kneader in the same manner as described above. At that time, the solid content ratio was adjusted to 10:90 with coal tar pitch: the graphite core material. After kneading, the solvent in the kneaded product was removed by heating at normal pressure.
The obtained kneaded material was put in a graphite crucible and first held at 500 ° C. for 6 hours under an argon atmosphere to reduce the volatile content to 5% or less, and then carbonized at 1500 ° C. for 3 hours. This kneaded product was pulverized with an atomizer so that the average particle size was 20 μm, and the intended carbonaceous material was obtained.

[Preparation of negative electrode mixture paste]
90% by mass of the carbonaceous material and 10% by mass of polyvinylidene fluoride were placed in N-methylpyrrolidone, and stirred and mixed at 2000 rpm for 30 minutes using a homomixer to prepare an organic solvent-based negative electrode mixture.
[Production of working electrode (negative electrode)]
The negative electrode mixture paste was applied to a copper foil with a uniform thickness, the solvent was volatilized in a vacuum at 90 ° C., dried, and the negative electrode mixture layer was pressed by a hand press. The copper foil and the negative electrode mixture layer were punched into a cylindrical shape having a diameter of 15.5 mm to prepare a working electrode (negative electrode) composed of a current collector and a negative electrode mixture adhered to the current collector.

[Production of counter electrode (positive electrode)]
A lithium metal foil is pressed against a nickel net and punched into a circular shape with a diameter of 15.5 mm. A current collector made of nickel net and a counter electrode made of a lithium metal foil (thickness 0.5 mm) in close contact with the current collector ( Positive electrode) was prepared.
[Electrolyte, separator]
LiPF ₆ was dissolved at a concentration of 1 mol / L in a mixed solvent of ethylene carbonate 33 vol 1% -methyl ethyl carbonate 67 vol% to prepare a non-aqueous electrolyte. The obtained nonaqueous electrolytic solution was impregnated into a polypropylene porous body (thickness 20 μm) to produce a separator impregnated with the electrolytic solution.

[Production of evaluation battery]
A button-type secondary battery shown in FIG. 2 was produced as an evaluation battery.
The exterior cup 1 and the exterior can 3 were sealed by interposing an insulating gasket 6 at the peripheral portion thereof and caulking both peripheral portions. In the inside, in order from the inner surface of the outer can 3, a current collector 7 a made of nickel net, a cylindrical counter electrode (positive electrode) 4 made of lithium foil, a separator 5 impregnated with an electrolytic solution, and a copper foil with Si attached thereto. It is a battery system in which the current collector 7b is laminated.
In the evaluation battery, the separator 5 impregnated with the electrolytic solution was laminated between the current collector 7b and the counter electrode 4 in close contact with the current collector 7a, and then the current collector 7b was placed in the outer cup 1 4 is accommodated in the outer can 3, the outer cup 1 and the outer can 3 are combined, and further, an insulating gasket 6 is interposed between the outer peripheral portion of the outer cup 1 and the outer can 3, and both peripheral portions are caulked and sealed. And made.
The physical properties of the base material and the carbonaceous material were measured by the following methods. The measurement results and evaluation results are shown in Table 1.

[Surface observation of carbonaceous materials]
A negative electrode carbonaceous material was embedded in a resin and polished. The cross section (inside) of the low crystalline carbonaceous coating layer or the outer surface of the negative electrode carbonaceous material was observed by SEM (magnification: 10,000 times) to confirm the presence or absence of voids. As a result, as shown in Table 1, pores on the outer surface of the negative electrode carbonaceous material were not recognized in the examples. The pores of the graphite core other than the surface were measured by a mercury intrusion method after pulverizing the particles as described above.
[TG (weight loss) measurement]
The sample was heated to 600 ° C. at a rate of 10 ° C./min in a nitrogen atmosphere, and when the temperature reached 600 ° C., the inflow gas was switched from nitrogen gas to a mixed gas of nitrogen and air of 50:50 (vol% ratio). Hold for 5 hours. Then, it cooled to room temperature, measured the mass of the remaining sample, and calculated | required the ratio which the mass decreased. The ratio of this mass reduction was taken as the ratio of the coating layer.
[X-ray diffraction of carbonaceous materials]
A (002) diffraction peak was measured using CuKα ray as an X-ray source and high-purity silicon as a standard substance, and d ₀₀₂ was calculated from the peak position and half width thereof. The calculation method follows the Japan Science and Technology Act (measurement method defined by the 117th Committee of the Japan Society for the Promotion of Science). Specifically, “Carbon Fiber” (written by Suguro Otani, Modern Editorial Company, published in March 1986) ) Pp. 733-742 and the like.
[Raman spectroscopy]
The R value of the carbonaceous material by Raman spectroscopy is analyzed using a Raman spectrometer [NR-1100: manufactured by JASCO Corporation]. D band 1360 cm ^-1 peak intensity (ID), to measure the peak intensity of G-band 1580cm ^-1 (IG). And intensity ratio ID / IG was made into R value.

[Charge / discharge test]
After constant current charging of 0.9 mA until the circuit voltage reaches 0 mV, switching to constant voltage charging when the circuit voltage reaches 0 mV, and the charge capacity is obtained from the amount of current during which the current value reaches 20 μA. It was. Then, it rested for 10 minutes. Next, constant current discharge was performed until the circuit voltage reached 1.5 V at a current value of 0.9 mA, and the discharge capacity was determined from the amount of electricity supplied during this period. This was the first cycle. Next, charging and discharging were performed in the same manner as in the first cycle with a charging current of 0.5 C and a discharging current of 2 C. The current values of 0.5C and 2C were calculated from the discharge capacity of the first cycle and the weight of the negative electrode active material.
The first charge / discharge loss was calculated from the following equation (1).
Initial charge / discharge loss = charge capacity of the first cycle-discharge capacity of the first cycle (1)
The 2C discharge rate was calculated from the following equation (2).
2C discharge rate (%) = 100 × (discharge capacity at 2C current value / discharge capacity of first cycle) (2)
In this test, the process of occluding lithium ions in the negative electrode material was charged, and the process of detaching lithium ions from the negative electrode material was discharge.

[Cycle characteristics]
The cycle characteristics were measured as follows. After constant current charging at a 0.5 C current value until the circuit voltage reached 0 mV, switching to constant voltage charging was continued until the current value reached 20 μA, and then rested for 10 minutes. Next, constant current discharge was performed at a current value of 0.5 C until the circuit voltage reached 1.5V. This charging / discharging was repeated 50 times, and the cycle characteristics were calculated from the obtained discharge capacity using the following equation.
Cycle characteristics = (discharge capacity in the 50th cycle / discharge capacity in the first cycle) × 100
[Electrode density]
Negative electrode mixture paste with a binder in which the thickness of the current collector is t ₁ [cm], the mass per unit area is W ₁ [g / cm ² ], and the mass ratio of the negative electrode carbonaceous material is P [%] When a negative electrode having a thickness t ₂ [cm] produced by applying and pressing is applied with a predetermined area S [cm ² ], and the mass of the negative electrode after punching is W ₂ [g], the following formula It can ask for. In addition, the said mass is the value measured with the top plate type automatic balance and thickness with the micrometer.
Electrode density [g / cm ³ ] = {(W ₂ / S−W ₁ ) / (t ₂ −t ₁ )} × (P / 100)

[Example 2]
A carbonaceous material (a negative electrode material for a lithium ion secondary battery) was prepared in the same manner as in Example 1 except that the iron oxide fine particles were changed to silica fine particles (average particle diameter: 0.05 μm) in Example 1, and the negative electrode composite was prepared. The preparation of the agent, the production of the negative electrode, the production of the lithium ion secondary battery and the characteristics evaluation were performed. The evaluation results are also shown in Table 1.

Example 3
Using a biaxial heating kneader, iron oxide fine particles (average particle diameter: 0.05 μm) were added to an ethanol solution of a phenol resin (manufactured by Sumitomo Bakelite Co., Ltd.) and kneaded at 50 ° C. for 1 hour. At that time, the solid content ratio was 95: 5 with phenol resin: iron oxide fine particles. After kneading, a vacuum was applied to remove the solvent in the kneaded product. The obtained kneaded material was graphitized under the same conditions as in Example 1 and pulverized to produce a graphitized core material (d ₀₀₂ : 0.3359 nm). Using the coal-tar pitch solution as the graphitized core material, a carbonaceous material (a negative electrode material for a lithium ion secondary battery) is prepared in the same manner as in Example 1 to prepare a negative electrode mixture, a negative electrode, and lithium ions. A secondary battery was fabricated and evaluated. The evaluation results are also shown in Table 1.
Example 4
The graphite core material produced in Example 1 was kneaded with a coal tar pitch solution under the same conditions as in Example 1 and then carbonized at 1100 ° C. for 3 hours to produce a carbonaceous material (a negative electrode material for a lithium ion secondary battery). ) Was produced. In the same manner as in Example 1, preparation of the negative electrode mixture, preparation of the negative electrode, preparation of the lithium ion secondary battery, and property evaluation were performed. The evaluation results are also shown in Table 1.

Example 5
In Example 1, using a biaxial heating kneader, iron oxide fine particles were added to a solution obtained by mixing oil in tar with coal tar pitch, and when the mixture was kneaded at 150 ° C. for 1 hour, the solid content ratio was changed to coal tar pitch: iron oxide fine particles. Thus, a carbon material (a negative electrode material for a lithium ion secondary battery) was prepared in the same manner as in Example 1 except that the ratio was 98: 2, and a negative electrode mixture was prepared, a negative electrode was manufactured, and a lithium ion secondary battery was manufactured. Table 1 also shows the evaluation results obtained by evaluating the characteristics.

Example 6
In Example 1, using a biaxial heating kneader, iron oxide fine particles were added to a solution obtained by mixing oil in tar with coal tar pitch, and when the mixture was kneaded at 150 ° C. for 1 hour, the solid content ratio was changed to coal tar pitch: iron oxide fine particles. Thus, a carbon material (a negative electrode material for a lithium ion secondary battery) was prepared in the same manner as in Example 1 except that the ratio was 97: 3, and a negative electrode mixture was prepared, a negative electrode was manufactured, and a lithium ion secondary battery was manufactured. Table 1 also shows the evaluation results obtained by evaluating the characteristics.

Example 7
In Example 1, using a biaxial heating kneader, iron oxide fine particles were added to a solution obtained by mixing oil in tar with coal tar pitch, and when the mixture was kneaded at 150 ° C. for 1 hour, the solid content ratio was changed to coal tar pitch: iron oxide fine particles. Thus, a carbon material (a negative electrode material for a lithium ion secondary battery) was prepared in the same manner as in Example 1 except that the ratio was 94: 6, and a negative electrode mixture, a negative electrode, and a lithium ion secondary battery were prepared. Table 1 also shows the evaluation results obtained by evaluating the characteristics.

Example 8
In Example 1, when the graphite core material was kneaded with the coal tar pitch solution at 150 ° C. for 1 hour with a biaxial heating kneader, the solid content ratio was 5:95 with the coal tar pitch: the graphite core material. A carbon material (a negative electrode material for a lithium ion secondary battery) is prepared in the same manner as in Example 1 except that the preparation of the negative electrode mixture is performed. The evaluation results performed are also shown in Table 1.

Example 9
The carbonaceous material (lithium ion 2) was prepared in the same manner as in Example 1 except that the graphite core material produced in Example 1 was carbonized at 900 ° C. for 3 hours after kneading with a coal tar pitch solution under the same conditions as in Example 1. A negative electrode material for a secondary battery) was prepared, and a negative electrode mixture, a negative electrode, a lithium ion secondary battery, and characteristics were evaluated. The evaluation results are also shown in Table 1. The Lc value of the graphite core material used in the examples was 50 nm or more.

[Comparative Example 1]
A mixture of natural graphite (manufactured by Union Carbon Co., Ltd., BF15A, flake shaped, d ₀₀₂ : 0.3357 nm) and iron oxide fine particles (average particle diameter 0.05 μm) at 95: 5 is mixed with a biaxial heating kneader. It knead | mixed with the coal tar pitch solution at 150 degreeC for 1 hour. At that time, the solid content ratio was adjusted to be coal tar pitch: the mixture was 10:90. After kneading, a vacuum was applied to remove the solvent in the kneaded product. The obtained kneaded material is put into a graphite crucible, and first kept at 500 ° C. for 6 hours under an argon atmosphere to reduce the volatile content to 5% or less, then carbonized and pulverized at 1500 ° C. for 3 hours. A powder was obtained. In the same manner as in Example 1, the obtained carbide powder and coal tar pitch solution were kneaded, and in the same manner as in Example 1, a carbonaceous material (a negative electrode material for a lithium ion secondary battery) was produced. Preparation of a negative electrode mixture, preparation of a negative electrode, preparation of a lithium ion secondary battery, and characteristic evaluation were performed. The evaluation results are also shown in Table 1.

[Comparative Example 2]
In Example 1, graphite core particles (d ₀₀₂ : 0.3363 nm) were prepared in the same manner as in Example 1 except that the kneaded mixture of coal tar pitch and iron oxide was heat-treated at 2000 ° C. In the same manner as in Example 1, the graphite core material particles and coal tar pitch solution were kneaded, and in the same manner as in Example 1, a carbonaceous material (a negative electrode material for a lithium ion secondary battery) was produced. The preparation of the negative electrode mixture, the production of the negative electrode, the production of the lithium ion secondary battery, and the characteristics evaluation were performed. The evaluation results are also shown in Table 1.
[Comparative Example 3]
Graphite core particles (d ₀₀₂ : 0.3358 nm) were produced under the same conditions as in Example 1. In Example 1, a carbonaceous material (a negative electrode material for a lithium ion secondary battery) was prepared in the same manner as in Example 1 except that the graphite core particles and coal tar pitch were heat-treated at 2500 ° C. The preparation of the agent, the production of the negative electrode, the production of the lithium ion secondary battery and the characteristics evaluation were performed. The evaluation results are also shown in Table 1.

[Comparative Example 4]
Graphitization treatment of Example 1: Graphitization treatment at 3000 ° C. for 3 hours, followed by pulverization with an atomizer so that the average particle diameter becomes 20 μm without performing the subsequent treatment, and there is no low crystalline coating layer A carbonaceous material was obtained. In the other steps, as in Example 1, preparation of the negative electrode mixture, preparation of the negative electrode, preparation of the lithium ion secondary battery, and characteristic evaluation were performed. The evaluation results are also shown in Table 1.
[Comparative Example 5]
In Example 1, except that the kneaded product of the graphite core material particles and the coal tar pitch solution is heated and the solvent in the kneaded product is removed under vacuum, and the carbonaceous material ( A negative electrode material for a lithium ion secondary battery) was prepared, and a negative electrode mixture, a negative electrode, a lithium ion secondary battery, and characteristics were evaluated. The evaluation results are also shown in Table 1.
[Comparative Example 6]
A mixture of natural graphite (manufactured by Union Carbon Co., Ltd., BF15A, flake shaped, d ₀₀₂ : 0.3357 nm) and iron oxide fine particles (average particle diameter 0.05 μm) at 95: 5 is mixed with a biaxial heating kneader. It knead | mixed with the coal tar pitch solution at 150 degreeC for 1 hour. At that time, the solid content ratio was adjusted to 10:90 with the coal tar pitch: the mixture. After kneading, a vacuum was applied to remove the solvent in the kneaded product. The obtained kneaded material was put into a graphite crucible, and first kept at 500 ° C. for 6 hours under an argon atmosphere to reduce the volatile content to 5% or less, and then graphitized at 3000 ° C. for 3 hours.
The obtained graphitized product was pulverized to prepare a pulverized product. Using this, preparation of a negative electrode mixture, preparation of a negative electrode, preparation of a lithium ion secondary battery, and characteristic evaluation were performed. The evaluation results are also shown in Table 1.

[Comparative Example 7]
A kneaded product of a pulverized graphitized material (corresponding to graphite core particles) and a coal tar pitch solution produced in the same manner as in Comparative Example 6 was carbonized in the same manner as in Example 1 to obtain a carbonaceous material (lithium ion). A negative electrode material for a secondary battery) was prepared, and a negative electrode mixture was prepared, a negative electrode was manufactured, a lithium ion secondary battery was manufactured, and characteristics were evaluated. The evaluation results are also shown in Table 1.

[Comparative Example 8]
In Example 1, using a biaxial heating kneader, iron oxide fine particles were added to a solution obtained by mixing oil in tar with coal tar pitch, and when the mixture was kneaded at 150 ° C. for 1 hour, the solid content ratio was changed to coal tar pitch: iron oxide fine particles. Thus, a carbon material (a negative electrode material for a lithium ion secondary battery) was prepared in the same manner as in Example 1 except that 99.5: 0.5 was set, and a negative electrode mixture was prepared, a negative electrode was prepared, and lithium ion two Table 1 also shows the evaluation results of the production and characteristic evaluation of the secondary battery.

[Comparative Example 9]
In Example 1, using a biaxial heating kneader, iron oxide fine particles were added to a solution obtained by mixing oil in tar with coal tar pitch, and when the mixture was kneaded at 150 ° C. for 1 hour, the solid content ratio was changed to coal tar pitch: iron oxide fine particles. Thus, a carbon material (a negative electrode material for a lithium ion secondary battery) was produced in the same manner as in Example 1 except that the ratio was 90:10, and a negative electrode mixture was prepared, a negative electrode was produced, and a lithium ion secondary battery was produced. Table 1 also shows the evaluation results obtained by evaluating the characteristics.

From the comparison between Example 1 and Comparative Example 1, it can be seen that the 2C discharge rate and the cycle characteristics are inferior if the graphite core material particles of the negative electrode carbonaceous material do not have pores.
From a comparison between Example 1 and Comparative Example 2, it is found that the discharge capacity is inferior when the graphite core material of the negative electrode carbonaceous material has low crystallinity.
From comparison between Example 1 and Comparative Example 3, it can be seen that when the crystallinity near the surface of the negative electrode carbonaceous material is high, the initial charge / discharge loss, 2C discharge rate, and cycle characteristics are inferior.

  The negative electrode carbonaceous material of the present invention can be used for high-performance lithium ion secondary batteries ranging from small to large, taking advantage of the characteristics.

DESCRIPTION OF SYMBOLS 1 Exterior cup 2 Working electrode 3 Exterior can 4 Counter electrode 5 Electrolyte solution impregnation separator 6 Insulation gasket 7a, 7b Current collector 10 Negative electrode carbonaceous material 12 Graphite core material 14 Pore 16 Carbonaceous coating layer

Claims (5)

A negative electrode material for a lithium ion secondary battery having a graphite core material made of highly crystalline graphite and a low crystalline carbonaceous coating layer covering the surface of the core material,
The surface of the negative electrode material for lithium ion secondary batteries has no pores, the graphite core has pores,
The graphite core is substantially spherical in the form of a single particle having no carbonaceous coating layer,
The pore volume of the graphite core material is such that the pore volume of 0.01 to 100 μm measured by the mercury intrusion method after pulverizing the negative electrode material for a lithium ion secondary battery is 0.05 to 0.4 cm ³ / g. ,
D _{002 of the} negative electrode material for a lithium ion secondary battery: 0.3360 nm or less,
The ratio of the R value of the negative electrode material for a lithium ion secondary battery (in the Raman spectrum using argon ion laser with a wavelength of 514.5 nm, a peak intensity of 1360 cm ^-1 to the peak intensity of ^{1580cm -1 (I1580) (I1360)} (I1360 / I1580)): A negative electrode material for a lithium ion secondary battery that is 0.3 to 1.0.   A lithium ion secondary battery negative electrode using the negative electrode material for a lithium ion secondary battery according to claim 1. ^3. The lithium ion secondary battery negative electrode according to claim 2, wherein an electrode density of the negative electrode is 1.7 to 1.9 g / cm ³ .   The lithium ion secondary battery which has a negative electrode of Claim 2 or 3.   A mixture of inorganic fine particles and carbonaceous precursor is heated at 2500 ° C. or higher to decompose and evaporate the inorganic fine particles to obtain pores and graphitize the carbonaceous precursor to have a graphite core material having pores A graphitization step for obtaining a carbonaceous precursor on the surface of the graphite core obtained in the graphitization step, and a graphite core to which the carbonaceous precursor is attached in the attachment step 2. The lithium according to claim 1, further comprising a firing step of heating at a temperature of 1100 ° C. or more and 1500 ° C. or less to obtain a negative electrode material having a carbonaceous coating layer having no voids on the surface of the graphite core material. A method for producing a negative electrode material for an ion secondary battery.

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