JP5994571B2 - Negative electrode material for lithium ion secondary battery and lithium ion secondary battery - Google Patents

Description

  The present invention relates to a negative electrode material for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery using the same, and more particularly to a negative electrode material for a lithium ion secondary battery and a lithium ion secondary battery using the same.

  Non-aqueous electrolyte secondary batteries are being developed as secondary batteries having a high energy density. Among these, lithium ion secondary batteries (hereinafter also referred to as “lithium ion batteries”) have a particularly high energy density, and are attracting attention as secondary batteries for electric vehicles or power storage. Examples of electric vehicle applications include zero emission electric vehicles not equipped with engines, hybrid electric vehicles equipped with both engines and secondary batteries, and plug-in electric vehicles charged from a system power source. Moreover, as an electric power storage use, the use as a stationary power storage system which stores electric power and supplies electric power at the time of the emergency which the electric power system was interrupted | blocked can be mentioned, for example.

  In the above applications, excellent durability to charge / discharge cycles is required. However, when the number of charge / discharge cycles is increased in a non-aqueous electrolyte secondary battery, there has been a problem that the capacity of the negative electrode is reduced and the battery characteristics are deteriorated.

For example, Patent Document 1 includes a positive electrode having a positive electrode mixture layer including a positive electrode active material containing lithium and a negative electrode active material as a technique for suppressing a decrease in capacity of the negative electrode accompanying an increase in the number of charge / discharge cycles. A battery element comprising a negative electrode having a negative electrode mixture layer, a separator, the positive electrode mixture layer, and a gel electrolyte layer containing a gel electrolyte between the negative electrode mixture layer and the separator is used as a laminate laminate outer material. The negative electrode active material contained is composed of a mixture of a plurality of types of mesophase carbon microbeads having different average particle diameters, which are composed of a surface portion having a low crystallinity and an internal portion having a high crystallinity. At least a large particle size mesophase carbon microbead with an average particle size of 20 μm or more and 40 μm or less and a small particle size mesophase with an average particle size of 5 μm or more and 16 μm or less The average particle size of the mesophase carbon microbeads with a small particle size is 0.55 times or less than the average particle size of the mesophase carbon microbeads with a large particle size. when arranged microbeads in particle size in ascending order, a particle size of 10% counted from smaller particle size side and D _10, a particle size of 50% counted from smaller particle size side and D _50, from the small diameter side the particle size of 90% th when the D _90, describes a non-aqueous electrolyte battery having a particle size distribution satisfying the relationship shown by the specific formula. This document uses a negative electrode active material for a negative electrode in a non-aqueous electrolyte battery as described above, which is a mixture of a plurality of types of carbonaceous materials having different average particle diameters with controlled particle size distribution regions. It is described that the energy density can be increased without deteriorating the characteristics.

According to Patent Document 2, the average particle size is 10 to 50 μm, the true density is 2200 kg / m ³ or more, the 002 plane spacing (d002) of graphite is less than 0.337 nm, the bulk density is 800 to 1000 kg / m ³ , the ratio The surface area is 3000 to 5000 m ² / kg, and the ratio (I ₁₃₄₀ / I ₁₅₈₀ ) of the peak area (I ₁₃₄₀ ) near 1340 cm ⁻¹ to the peak area (I ₁₅₈₀ ) near 1580 cm ^{−1 in the} Raman spectrum is 0.1 to Non-aqueous electrolyte secondary battery negative electrode having a structure in which 0.3, an aspect ratio is 5 or less, a plurality of flat graphite particles are aggregated or bonded non-parallel to each other, and have voids in the particles The graphite particles for use are described. In this document, when the above graphite particles are used as a negative electrode material for a non-aqueous electrolyte secondary battery, electrode coating properties, electrode adhesion, rapid charge / discharge characteristics, first charge / discharge characteristics are improved, and high capacity In addition, it is described that a non-aqueous electrolyte secondary battery excellent in rapid charge / discharge characteristics, little cycle deterioration, and excellent in safety can be provided.

  Patent Document 3 is a nonaqueous electrolyte secondary battery comprising a positive electrode, a negative electrode containing a negative electrode active material, and a nonaqueous electrolyte, wherein the negative electrode has a pore diameter of 0.15 cc / Cumulative pore distribution curve from 40% to 60% in the range of pore diameters from 0.001 μm to 10 μm at g˜0.35 cc / g with a peak in pore volume diameter of 0.4-3.5 μm in increased volume pore distribution %, The cumulative pore distribution curve has a cumulative diameter of 80%, 70%, 60%, and 20% satisfying a specific formula, and the negative electrode active material is A composite graphite material in which a carbon material layer having lower crystallinity than the particles is formed on at least a part of the surface of the graphite material particles, and has a particle size distribution satisfying a specific formula, and the increased volume pore distribution curve And the negative electrode active material particle diameter (D50) at a cumulative 50% of the negative electrode active material satisfies a specific formula A nonaqueous electrolyte secondary battery is described. This document describes that the above configuration can provide a non-aqueous electrolyte secondary battery with improved charge / discharge cycle life.

Japanese Patent No. 4120262 Japanese Patent No. 4635413 Japanese Patent No. 4776190

  As described above, a technique for improving the charge / discharge cycle life in the non-aqueous electrolyte secondary battery has been developed, but there still remains a problem of a decrease in capacity of the negative electrode accompanying an increase in the number of charge / discharge cycles.

  Therefore, the present invention provides a negative electrode material for a non-aqueous electrolyte secondary battery in which a capacity decrease accompanying an increase in the number of charge / discharge cycles is substantially suppressed, and a long-life non-aqueous electrolyte solution using the same. An object is to provide a secondary battery.

In order to solve the above problems, the negative electrode active material of the present invention is made of a powder containing graphite particles, and when the particle diameter in the cumulative volume of 10% of the powder is D ₁₀ and the particle diameter in the cumulative volume of 50% is D ₅₀ The particle size ratio D ₁₀ / D ₅₀ is in the range of 0.1 to 0.52, D ₁₀ is in the range of 1.2 to 9.2 μm, D ₅₀ is in the range of ₁₀ to 18.5 μm, and the specific surface area of the powder is 3.0. It is in the range of ~ 6.5 m ² / g.

  According to the present invention, there is provided a negative electrode material for a non-aqueous electrolyte secondary battery in which a decrease in capacity accompanying an increase in the number of charge / discharge cycles is substantially suppressed, and a long-life non-aqueous electrolyte secondary battery using the same. It becomes possible to provide.

  Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

It is a schematic diagram which shows one Embodiment of the lithium ion battery of this invention. It is a mimetic diagram showing one embodiment of a system of a lithium ion battery module of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail.
<1. Negative electrode active material>
The negative electrode active material of the present invention can be suitably used as a negative electrode material for a non-aqueous electrolyte secondary battery. In this specification, “non-aqueous electrolyte secondary battery” (hereinafter also referred to as “secondary battery”) is a secondary battery using a non-aqueous electrolyte in which an electrolyte is dissolved or dispersed in a non-aqueous organic solvent. It means an electrochemical device that stores (charges) or uses (discharges) electrical energy as the electrolyte is occluded or released from the electrode in the non-aqueous electrolyte. Examples of the non-aqueous electrolyte secondary battery include a lithium ion battery.

The present inventors have found that by using a graphite particles having a particle size distribution specified in the particle size (hereinafter respectively also described as D ₁₀ or D _50.) At 10% or 50% cumulative volume in the negative electrode, the volume of graphite particles It has been found that the stress inside the negative electrode due to the change is relaxed and the charge / discharge cycle life of the non-aqueous electrolyte secondary battery is improved. Therefore, the negative electrode active material of the present invention is made of a powder containing graphite particles in which D ₁₀ and D ₅₀ are specified.

  Further, in order to extend the charge / discharge cycle life of the negative electrode without increasing the irreversible capacity and / or deteriorating the storage characteristics, a powder containing graphite particles whose surface is coated with a carbonaceous material is used as the negative electrode active material. It is more desirable.

  Examples of the graphite particles include, but are not limited to, particles containing, as a main component, artificial or natural graphite having a graphite structure. It is preferably made of graphite particles produced by heat treatment such as coke powder or pitch. A graphitizable binder (for example, various pitches such as coal-based, petroleum-based or artificial, organic materials such as tar, thermosetting resin, or thermoplastic resin) may be blended into graphite particles, followed by firing and graphitization. . Considering that the graphite particles are granulated by the binder, it is preferable that the graphite particles have an average particle size of 1/2 or less of the finally obtained graphite particles. For example, graphite particles having an average particle size of 10 μm or more can be obtained by adding a pitch-based binder and baking the coke powder having an average particle size of 5 μm as it is or after pulverization. Alternatively, if desired, a part of the above graphite particles can be replaced with non-graphite particles. In this case, examples of the non-graphite particles include carbon black and an amorphous carbon material synthesized by pyrolyzing a 5-membered or 6-membered cyclic hydrocarbon compound or an oxygen-containing cyclic organic compound. it can. When the non-graphite particles are used, the blending ratio of the graphite particles to the non-graphite particles may be appropriately set within the range satisfying the negative electrode filling property and the particle size distribution condition of the negative electrode active material described below. For example, the blending ratio of graphite particles to non-graphite particles is excellent in terms of charging characteristics and cycle life if the graphite particles are in the range of 10 to 50% by weight with respect to the total weight of the graphite particles and non-graphite particles. A negative electrode having a high capacity and an excellent cycle life can be obtained by setting the graphite particles in the range of 50 to 100% by weight.

  By using the above graphite particles and, if desired, graphite particles containing non-graphite particles as the material of the negative electrode active material, it is possible to produce a long-life non-aqueous electrolyte secondary battery with excellent charge / discharge cycle life characteristics It becomes.

  The shape of the graphite particles is preferably spherical, massive or flat spherical. In this case, the average particle size of the graphite particles is preferably in the range of 1 to several tens of μm, and more preferably in the range of 10 to 18.5 μm. When the average particle size exceeds the above range, it is difficult to control the particle size distribution of the negative electrode active material to the range described below, which is not preferable. Alternatively, the shape of the graphite particles may be a shape having a large aspect ratio such as a flake shape or a fiber shape. However, the aspect ratio of the entire core material is preferably in the range of 1 to 5, and more preferably in the range of 1 to 3. In this case, the c-axis length of the core material crystal (hereinafter also referred to as “Lc”) is not particularly limited as long as it satisfies the above aspect ratio. When the aspect ratio exceeds the above range, the ratio of large amorphous particles increases, and even if the particle size distribution of the negative electrode active material is controlled to the range described below, the amorphous particles lower the negative electrode fillability. Therefore, it is not preferable.

  In addition, although the average particle diameter of graphite particle | grains is not limited, For example, it can be determined using the particle size distribution measuring apparatus (for example, microtrack) using laser scattering. Further, the c-axis length (Lc) of the core material crystal is not limited, but can be determined by, for example, an X-ray diffraction method using CuKα rays as an X-ray source.

Regarding the crystallinity of the graphite particles, the distance of the graphite plane index (002) (hereinafter also referred to as “d ₀₀₂ ”) is preferably in the range of 0.3345 to 0.3370 nm. When _d002 is in the above range, the occlusion amount of the electrolyte (for example, lithium ion) at a low negative electrode potential increases, and the energy (Wh) of the resulting nonaqueous electrolyte secondary battery increases, which is preferable. .

The distance (d ₀₀₂ ) of the graphite plane index (002) of the graphite crystal is not limited, but can be determined by, for example, an X-ray wide angle diffraction method using CuKα rays as an X-ray source.

  The graphite particles may be prepared by a method known in the technical field. For example, the materials described above are mixed and pulverized at a predetermined blending ratio, pressure-molded, and then fired in an inert gas atmosphere. Thereafter, the fired product obtained can be pulverized to obtain fine core material powder containing graphite. In the above method, examples of the pulverizing means include a hammer mill. Moreover, nitrogen or argon can be mentioned as an inert gas. The firing temperature is preferably in the range of 400 to 3000 ° C. The firing time is preferably in the range of 1 to 50 hours. The higher the temperature, the shorter the firing time required for graphitization.

  The graphite particles may have a form in which a coating layer is disposed on the surface of a core material containing graphite. For example, a so-called core / shell structure in which a coating layer is formed on the surface of a core material made of graphite is preferable. The coating layer preferably has a thickness in the range of 5 to 200 nm. When the thickness of the coating layer exceeds 5 nm, the organic solvent in the electrolytic solution penetrates the coating layer and hardly reaches the core material surface, resulting in a reductive decomposition reaction of the organic solvent on the surface. This is preferable because the possibility is reduced. Moreover, it is preferable that the thickness of the coating layer is less than 200 nm because diffusion of an electrolyte such as lithium ion is not inhibited, and as a result, the capacity at a large current decreases. In addition, the thickness of the coating layer is appropriately set in the preparation of the coating layer described below, with respect to the mixing ratio of the carbonaceous material and the core material forming the coating layer and / or the conditions of the heat treatment or pyrolysis treatment. Can be adjusted.

  The coating layer preferably has a dense structure rather than a porous structure. In the case of a dense structure, the organic solvent in the electrolytic solution is prevented from penetrating the coating layer and reaching the core material surface, and as a result, the possibility of reductive decomposition reaction of the organic solvent on the surface is reduced. ,preferable.

  Although the thickness and structure of the coating layer are not limited, for example, using a focused ion beam (FIB) processing apparatus, a cross-section of the core material particle on which the coating layer is formed, It can be determined by measuring the thickness and structure of the coating layer using a transmission electron microscope (TEM).

  The coating layer contains carbon as a main component. Examples of the material for the covering layer include, but are not limited to, a phenolic resin (for example, novolac-type phenolic resin) and a carbonaceous material that is a polycyclic aromatic hydrocarbon such as naphthalene, anthracene, and creosote oil. Can do. In this case, for example, after immersing and dispersing the core material described above in a solution containing the carbonaceous material in an organic solvent, the core material is filtered, dried and heat-treated, A core material having a coating layer formed on the surface can be prepared. The temperature of the heat treatment is preferably in the range of 200 to 1000 ° C, and more preferably in the range of 500 to 800 ° C. The heat treatment time is preferably in the range of 1 to 50 hours. When the temperature of the heat treatment is in the range of 500 to 800 ° C., the bulk modulus of the coating layer is smaller than the bulk modulus of the core material, which is more preferable.

  Alternatively, as the material for the coating layer, polyvinyl alcohol, or an oxygen-containing organic compound such as polyvinyl chloride or polyvinyl pyrrolidone may be used. In this case, for example, after mixing the above-described compound and the core material described above, the core material having a coating layer formed on the surface thereof is prepared by heating the mixture to thermally decompose the compound. Can do. The pyrolysis temperature is preferably in the range of 200 to 400 ° C, more preferably in the range of 300 to 400 ° C. The thermal decomposition time is preferably in the range of 1 to 50 hours. When the temperature of thermal decomposition is in the range of 300 to 400 ° C., the coating layer formed by the thermally decomposed compound is firmly bonded to the core material, and thus is more preferable.

  The coating layer may contain a small amount of nitrogen, phosphorus, oxygen, alkali metal, alkaline earth metal, or transition metal in addition to the carbon derived from the carbonaceous material. For example, when the surface concentration of the element is determined by an X-ray photoelectron spectrometer, the atomic concentration may be included in the range of 0.01 to 10 atomic% with respect to carbon. By adding an element other than carbon, an effect of increasing the strength of the coating layer and / or suppressing the decomposition reaction of the electrolytic solution can be obtained. The carbon concentration is preferably 90 atomic% or more.

  The method for measuring the carbon content contained in the coating layer is not limited, but the weight of the coating layer is obtained from the weight measurement before and after the formation of the coating layer, and the carbon content is calculated from the atomic concentration. can do.

  By disposing a coating layer containing the above carbonaceous material and other materials on the surface of the core material, the organic solvent in the electrolytic solution prevents the penetration of the coating layer and reaches the core material, while lithium. An electrolyte such as ions can pass through the coating layer and contact the core material.

  However, the first object of the present invention is to improve the cycle life of the negative electrode by reducing the stress inside the negative electrode. Therefore, the coating of the graphite particle surface is not essential. This is because the volume change of the graphite particles accompanying the charge / discharge cycle is hardly affected by the presence or absence of coating on the surface of the graphite particles.

In addition to the graphite particles, the powder constituting the negative electrode active material of the present invention may further include particles of other materials that can electrochemically occlude and / or release electrolytes such as lithium ions. You can also. Examples of the other materials include carbon materials having a graphite surface index (002) distance (d ₀₀₂ ) larger than 0.3370 nm, such as expanded graphite, pitch-based amorphous carbonaceous material, silicon carbide, and needle coke or petroleum. An amorphous carbon material produced from coke or the like can be mentioned. Particles of an amorphous carbon material such as a pitch-based amorphous carbonaceous material such as tar pitch or coal tar or amorphous silicon carbide are preferred. Since the particle | grains of said other material are amorphous, it can be used for the negative electrode active material of this invention, without arrange | positioning a coating layer on the surface. In addition, the particles of the other materials are more excellent in charge / discharge rate characteristics than the graphite particles. When the negative electrode active material of the present invention is composed of a powder containing graphite particles and particles of other materials, the mixing ratio of the particles of other materials to the graphite particles is the negative electrode filling property and the particle size distribution condition of the negative electrode active material described below. May be set as appropriate within a range satisfying the above. For example, the blending ratio of graphite particles to other material particles is 50% by volume or more, preferably 50 to 90% by volume of graphite particles with respect to the total volume of the graphite particles and other material particles. The cycle life of graphite can be improved. When the negative electrode active material of the present invention contains particles of the other material, it is possible to improve the charge / discharge rate characteristics in addition to the improvement of the cycle life of the negative electrode active material. In particular, if 10% or more of low crystalline carbon (which is exemplified by the amorphous carbon material) having a small volume change during charge / discharge cycles compared to graphite particles is added, voids around the low crystalline carbon particles are reduced. It can absorb the volume increase of graphite (about 10%) during charging. Therefore, cycle life can be improved by making the compounding ratio of the graphite particles less than 90% by volume. Moreover, by setting the blending ratio of the graphite particles to 50% by volume or more, it is possible to avoid a decrease in the capacity density of the negative electrode, which is caused by an excessive blending ratio of the particles of the other materials with respect to the graphite particles.

  The present inventors used the negative electrode active material by adjusting the four types of physical properties described below to a suitable range in the negative electrode active material comprising a powder containing graphite particles having a particle size distribution of the present invention. The secondary battery was found to be a long-life secondary battery in which the capacity reduction accompanying an increase in the number of charge / discharge cycles was substantially suppressed without causing an increase in irreversible capacity and / or deterioration in storage characteristics. .

First, the negative electrode active material of the present invention preferably has a plane index (002) distance (d ₀₀₂ ) in the range of 0.3345 to 0.3370 nm. The powder of the negative electrode active material in which _d002 is in the above range contains graphite crystals. Therefore, by using a negative electrode active material having d _{002 in the} above range, a high capacity negative electrode can be obtained.

The distance (d ₀₀₂ ) of the surface index (002) of the negative electrode active material is not limited, but can be determined by, for example, an X-ray wide angle diffraction method using CuKα rays as an X-ray source.

Second, the negative electrode active material of the present invention preferably has a specific surface area of 3.0 to 6.5 m ² / g. When the specific surface area exceeds the above range, although the occlusion / release rate of the electrolyte (for example, lithium ion) on the particle surface of the negative electrode active material is increased, the site of the decomposition reaction of the electrolytic solution is increased, which is not preferable. Therefore, by using a negative electrode active material having a specific surface area in the above range, it is possible to obtain a negative electrode having a high capacity and a long life while improving both negative electrode performance and suppressing deterioration. Moreover, if the specific surface area is in the range of 4.0 to 5.5 m ² / g, a negative electrode having a higher capacity and a longer life can be provided.

  The specific surface area of the negative electrode active material is not limited, but can be determined using, for example, a known BET specific surface area measurement apparatus utilizing gas adsorption. The specific surface area can be adjusted by the particle size distribution or the degree of surface coating.

Third, in the Raman spectrum, the ratio of the peak intensity in the 1360 cm ⁻¹ (D band) region to the peak intensity in the 1580 cm ⁻¹ (G band) region in the Raman spectrum (I ₁₃₆₀ / I ₁₅₈₀ ) Is preferably in the range of 0.1 to 0.6, more preferably in the range of 0.1 to 0.3. In the Raman spectrum of graphite, the absorption in the D band region shows a turbulent structure, and the absorption in the G band region shows a graphite crystal structure. The use of graphite particles having a low crystalline carbonaceous coating layer on the surface of a graphite core material is more desirable because it facilitates suppressing decomposition of the electrolyte. In the case of the Raman spectrum of the negative electrode active material of the present invention, the absorption in the G band region becomes stronger as the crystallinity of the coating layer becomes higher (closer to the crystal of graphite), and the absorption in the D band region becomes more amorphous. Become stronger. That is, the peak intensity ratio is an index representing the degree of amorphousness of the graphite particle surface. When the peak intensity ratio is in the range of 0.1 to 0.3, the coating layer has crystallinity close to that of the core material. Such a negative electrode active material is more preferable because not only the coating layer is not easily destroyed during high-density pressure molding, but also the coating layer is difficult to peel off from the surface of the core material during a charge / discharge cycle. Therefore, by using a negative electrode active material having a peak intensity ratio (I ₁₃₆₀ / I ₁₅₈₀ ) in the above range, a negative electrode having a high capacity and a long life can be obtained.

  Further, by using a negative electrode active material in which the ratio of the peak intensities is in the above range and the thickness of the coating layer is in the above range, it is possible to obtain a negative electrode having a higher capacity and a longer life.

Note that the ratio of the peak intensity of I ₁₃₆₀ / I ₁₅₈₀ of the negative electrode active material is not limited, but, for example, a Raman spectrum is measured using a known laser Raman spectrometer using an argon laser, and 1360 cm ^−1. (D band) and 1580 cm ^-1 (G band) peak in the wave number region are detected, and the ratio of peak intensity in the 1360 cm ^-1 (D band) region to the peak intensity in the 1580 cm ^-1 (G band) region ( It can be determined by calculating I ₁₃₆₀ / I ₁₅₈₀ ).

Fourth, the negative electrode active material of the present invention, D ₁₀ particle size of 10% cumulative volume of the powder of the negative electrode active material, when the particle diameter at a cumulative volume of 50% was D _50, D ₁₀ is 1.2 to 9.2 A range of μm is preferred. Further, D ₅₀ is preferably in the range of 10 to 18.5 μm. Here, when the negative electrode active material of the present invention is composed only of graphite particle powder, the D ₁₀ and D ₅₀ are determined based on the particle size distribution of the graphite particle powder. Further, when the negative electrode active material of the present invention is composed of a powder containing graphite particles and particles of other materials, the D ₁₀ and D ₅₀ have a particle size distribution of the entire powder containing graphite particles and particles of other materials. To be determined. When D ₅₀ is in the above range, in the secondary battery using the negative electrode active material, the stress inside the negative electrode is reduced and the cycle life is improved. Furthermore, it is preferable because the irreversible capacity is low and the capacity is high. In particular, when D ₅₀ is in a range exceeding 18.5 μm, the specific surface area becomes small and the reaction area related to charge / discharge decreases. A secondary battery using such a negative electrode active material is not preferable because high-rate discharge characteristics are lowered. The particle size ratio D ₁₀ / D ₅₀ is preferably in the range of 0.1 to 0.52, and more preferably in the range of 0.29 to 0.47. When the particle size ratio D ₁₀ / D ₅₀ is in the range of 0.1 to 0.52, the tap density of the powder of the negative electrode active material is increased, and it is easy to ensure contact between the particles. A secondary battery using such a negative electrode active material is preferable because it has a high capacity retention rate and a long life. Further, when the particle size ratio D ₁₀ / D ₅₀ is in the range of 0.29 to 0.47, the specific surface area of the negative electrode active material powder decreases. A secondary battery using such a negative electrode active material is preferable because the irreversible capacity of the negative electrode is reduced.

D ₁₀ / D ₅₀ , D ₁₀ and D ₅₀ are not limited, but, for example, the particle size of the powder of the negative electrode active material suspended in water using a particle size distribution measuring device utilizing laser scattering It can be determined by measuring the distribution.

  Examples of means for adjusting the four physical properties of the negative electrode active material of the present invention to the above ranges include classification treatments known in the art. For example, a powder containing graphite particles and optionally particles of other materials is prepared by the method described above, and the powder is classified into particles having a particle size of several stages using an airflow classifier or sieve classification. . Then, the powder of the negative electrode active material which has a suitable physical property can be obtained by adjusting the mixing ratio of each particle group suitably, and mixing.

  By using the negative electrode active material having the above-mentioned characteristics, the long-life is substantially suppressed from being reduced in capacity with an increase in the number of charge / discharge cycles without causing an increase in irreversible capacity and / or deterioration in storage characteristics. A secondary battery can be obtained.

<2. Negative electrode>
The negative electrode active material of the present invention can be suitably used as a negative electrode material for non-aqueous electrolyte secondary batteries (for example, lithium ion batteries). Therefore, the present invention also relates to a negative electrode having a current collector and a negative electrode mixture layer containing the negative electrode active material of the present invention. In the examples of the present specification, the negative electrode was prepared using graphite particles in which the surface of the core material made of graphite was coated with low crystalline carbon. However, the negative electrode was prepared using uncoated graphite particles. The contribution to the volume change accompanying charging / discharging is the same. Therefore, in the negative electrode of the present invention, graphite particles not coated on the surface may be mixed and used.

  The current collector used in the negative electrode of the present invention may be any current collector commonly used in the technical field. Examples of the material for the current collector include copper, stainless steel, titanium, and nickel. For example, a copper foil having a thickness of 10 to 100 μm, a copper perforated foil having a thickness of 10 to 100 μm and a hole diameter of 0.1 to 10 mm, an expanded metal or a foamed metal plate is preferable.

  The negative electrode mixture layer contained in the negative electrode of the present invention usually contains a binder in addition to the negative electrode active material of the present invention. The binder may be any binder commonly used in the technical field. For example, mention may be made of styrene-butadiene rubber, carboxymethylcellulose and polyvinylidene fluoride (PVDF), and mixtures thereof. A mixture of styrene-butadiene rubber and carboxymethylcellulose is preferred.

  In the negative electrode of the present invention, the negative electrode mixture layer is disposed on the surface of the current collector. For example, the negative electrode mixture layer is preferably adhered to the surface of the current collector. In this case, the thickness of the negative electrode mixture layer is not particularly limited, but is preferably in the range of 1 to 100 μm. In particular, when the thickness is in the range of 1 to 50 μm, it is possible to reduce the voltage loss due to the resistance of the negative electrode even if the current density flowing through the negative electrode increases.

  The negative electrode of the present invention can be produced by a method known in the art. The negative electrode active material of the present invention is usually in the form of particles or lumps. For this reason, the negative electrode active material and the binder described above are mixed to prepare a negative electrode mixture, and the negative electrode active material and the binder powder are bonded together in the negative electrode mixture. Next, the negative electrode mixture may be attached to the current collector, and the negative electrode mixture layer may be adhered to the surface of the current collector. For example, the negative electrode active material and a binder are mixed in a solvent to prepare a dispersion or slurry of the negative electrode mixture. When particles exceeding the preferred thickness of the negative electrode mixture layer are present in the powder of the negative electrode active material used for the negative electrode mixture, coarse particles are previously obtained by classification treatment such as air flow classification or sieve classification. It is preferable to remove. The mixing and dispersing treatment can be performed using a kneader or a dispersing machine known in the art. What is necessary is just to select suitably the solvent for preparing the dispersion liquid or slurry of a negative mix based on the binder used. For example, when the binder is styrene-butadiene rubber, water is preferably used, and when the binder is PVDF, 1-methyl-2-pyrrolidone is preferably used. The dispersion or slurry of the negative electrode mixture is adhered to the current collector by a doctor blade method, a dipping method, a spray method or the like (attachment step). Thereafter, the current collector to which the negative electrode mixture dispersion or slurry is adhered is dried to evaporate and remove the solvent (drying step). Subsequently, a negative electrode can be produced by press-molding the current collector and the negative electrode mixture layer by a roll press or the like (molding step). In the above method, the negative electrode mixture layer in a multilayer form can be arranged on the surface of the current collector by repeating a plurality of times from the attaching step to the drying step.

  In the negative electrode of the present invention, the inventors of the present invention have a uniform arrangement of voids formed by particles of a plurality of negative electrode active materials, so that a secondary battery including the negative electrode has increased irreversible capacity and / or storage. It has been found that a long-life secondary battery is obtained in which a decrease in capacity accompanying an increase in the number of charge / discharge cycles is substantially suppressed without causing deterioration of characteristics.

  For example, the peak of the differential pore volume measured by the mercury intrusion method is preferably 1 μm or less. Further, the ratio of the total volume of pores having a pore diameter of less than 1 μm to the total volume of pores having a pore diameter of 1 μm or more is preferably 3 or more. When the ratio of the peak of the differential pore volume and the total volume of the pores is in the above range, it is preferable because the electrolyte can be uniformly permeated into the negative electrode while relaxing the volume change during the charge / discharge cycle. . By using a negative electrode having the above characteristics for a secondary battery, a long-life secondary battery can be obtained.

  In addition, the ratio of the total volume of the pores related to the pore diameter of less than 1 μm to the total volume of the pores related to the peak of the differential pore volume measured by the mercury intrusion method and the pore diameter of 1 μm or more is not limited. However, it can be determined, for example, by measuring the pore volume distribution of the negative electrode of the present invention using a pore volume measuring device (mercury porosimeter).

<3. Lithium-ion battery>
The negative electrode of the present invention can be suitably used as a negative electrode for non-aqueous electrolyte secondary batteries, particularly lithium ion batteries. Therefore, the present invention also relates to a lithium ion battery comprising the above negative electrode, a positive electrode, and an electrolyte.
One embodiment of a lithium ion battery produced using the negative electrode of the present invention is shown in FIG.

  As shown in FIG. 1, a lithium ion battery 101 of the present invention includes a negative electrode 112, a positive electrode 110, and an electrolyte. The lithium ion battery 101 includes a separator 111, a battery can 113, a positive current collector tab 114, a negative current collector tab 115, an inner lid 116, an internal pressure release valve 117, a gasket 118, a positive temperature coefficient, as will be described below. (PTC: Positive temperature coefficient) It is also possible to provide a battery lid 120 that also serves as a resistance element 119 and a positive electrode external terminal. The battery lid 120 can be an integral part composed of an inner lid 116, an internal pressure release valve 117, a gasket 118, and a PTC resistance element 119.

  The positive electrode 110 includes a current collector and a positive electrode mixture layer that is disposed on the surface of the current collector and includes a positive electrode active material and a binder.

Examples of the positive electrode active material include LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ , Li ₄ Mn ₅ O ₁₂ , LiMn _2-x M _x O ₂ ( However, M = Co, Ni, Fe, Cr, Zn, Ta, x = 0.01-0.2), Li ₂ Mn ₃ MO ₈ (M = Fe, Co, Ni, Cu, Zn), Li _1-x A _x Mn ₂ O ₄ (A = Mg, Ba, B, Al, Fe, Co, Ni, Cr, Zn, Ca, x = 0.01 to 0.1), LiNi _1-x M _x O ₂ (where M = Co, Fe, Ga, x = 0.01 to 0.2), LiFeO ₂ , Fe ₂ (SO ₄ ) ₃ , LiCo _1-x M _x O ₂ (where M = Ni, Fe, Mn, x = 0.01 to 0.2), LiNi _1-x M _x O ₂ (M = Mn, Fe, Co, Al, Ga, Ca, Mg, x = 0.01-0.2), Fe (MoO ₄ ) ₃ , FeF ₃ , LiFePO ₄ and LiMnPO ₄ etc. Can be mentioned.

  Examples of the binder include styrene-butadiene rubber, carboxymethyl cellulose, polyvinylidene fluoride (PVDF), and mixtures thereof.

  The positive electrode active material is an oxide and has high electric resistance. For this reason, the positive electrode mixture layer usually further includes a conductive agent containing carbon powder as a main component in order to supplement the electrical conductivity of the positive electrode active material. Examples of the conductive agent include acetylene black, carbon black, and carbon materials such as graphite or amorphous carbon. In order to form an electronic network inside the positive electrode, the particle size of the conductive agent is preferably less than the average particle size of the positive electrode active material, and more preferably 1/10 or less of the average particle size of the positive electrode active material. . The average particle diameter of the positive electrode active material can be determined by the same method as the average particle diameter of the negative electrode active material described above.

  The current collector may be any current collector commonly used in the art. The same material as that of the negative electrode current collector described above can be used.

  Although a suitable positive electrode material has been exemplified here, the effect of the present invention is not limited by the type of the positive electrode material. Therefore, various positive electrode materials known in the art can be used.

  In the positive electrode, the positive electrode mixture layer is disposed on the surface of the current collector. For example, the positive electrode mixture layer is preferably bonded to the surface of the current collector. In this case, the thickness of the positive electrode mixture layer is not particularly limited, but is preferably in the range of 1 to 100 μm. In particular, when the thickness is in the range of 1 to 50 μm, the voltage loss due to the resistance of the positive electrode can be reduced even if the current density flowing through the negative electrode is increased.

  What is necessary is just to produce the positive electrode of this invention by the method similar to the preparation method of the negative electrode demonstrated above.

  Next, the configuration of the lithium ion battery of the present invention including the negative electrode and the positive electrode described above will be further described with reference to FIG.

  The separator 111 is inserted between the positive electrode 110 and the negative electrode 112 described above to prevent a short circuit between the positive electrode 110 and the negative electrode 112. As the separator 111, for example, a polyolefin polymer sheet containing polyethylene or polypropylene as a main component, or a sheet having a multilayer structure in which a fluorine polymer sheet represented by a polyolefin polymer and tetrafluoropolyethylene is welded, Furthermore, the nonwoven fabric which consists of a synthetic fiber of a cellulose fiber or polyacrylonitrile can be mentioned. A mixture of ceramics and a binder may be formed in a thin layer on the surface of the separator 111 so that the separator 111 does not shrink when the battery temperature becomes high. Since the separator 111 needs to allow lithium ions to pass through during charging and discharging of the battery, it can be generally used if the pore diameter is 0.01 to 10 μm and the porosity is 20 to 90%.

  The separator 111 is also inserted between the battery can 113 and the electrode disposed at the end of the electrode group consisting of a plurality of positive electrodes 110, negative electrodes 112 and the separator 111, and the positive electrode 110 and the negative electrode 112 through the battery can 113. Prevent short circuit between.

  The upper part of the laminate composed of the positive electrode 110, the negative electrode 112, and the separator 111 is electrically connected to an external terminal via a lead wire. The positive electrode 110 is connected to the inner lid 116 via the positive electrode current collecting tab 114. The negative electrode 112 is connected to the battery can 113 via a negative electrode current collecting tab 115. The current collecting tabs 114 and 115 can take any shape such as a wire shape or a plate shape. If the material has a structure that can reduce the ohmic loss when a current is passed and does not react with the electrolyte, the shape, number, and / or material of the current collecting tabs 114 and 115 are the same as those of the battery can 113. It can be arbitrarily selected depending on the structure.

  The positive temperature coefficient (PTC) resistance element 119 is arranged to stop charging / discharging of the lithium ion battery 101 and protect the battery when the temperature inside the battery becomes high.

  The shape of the electrode group consisting of a plurality of positive electrodes 110, negative electrodes 112, and separators 111 may be a wound shape, may be a shape that is wound into an arbitrary shape such as a flat shape, or a strip shape. There may be. Various shapes can be taken. The shape of the battery container can be selected from any shape such as a cylindrical shape, a flat oval shape, or a square shape according to the shape of the electrode group. In this case, the battery container may be configured to be integrated with the bottom surface member such as the battery can 113, or may be configured such that the battery cover is attached to the bottom surface of the battery container and the negative electrode is connected to the battery cover. A battery container having an arbitrary shape and configuration can be used according to the shape of the electrode group and / or the terminal attachment method without affecting the effects of the present invention.

  The material of the battery container may be appropriately selected from materials that are corrosion resistant to the nonaqueous electrolyte, such as aluminum, stainless steel, or nickel-plated steel. In addition, when the battery container is electrically connected to the positive electrode current collecting tab or the negative electrode current collecting tab, the material is deteriorated due to corrosion of the battery container and / or alloying with lithium ions in a portion in contact with the nonaqueous electrolyte. Select the lead wire material to prevent this from occurring.

  The battery lid 120 can be attached to the battery can 113 by a method such as caulking, welding, or adhesion.

  An electrolyte solution is injected into the battery can 113 in which the electrode group is inserted, and the electrolyte solution is held on the surfaces of the positive electrode 110, the negative electrode 112, and the separator 111 and in the pores.

  The electrolytic solution is not limited to the organic solvent, the type of electrolyte, and / or the mixing ratio of the organic solvent, and any electrolytic solution known in the art can be used. Examples of the organic solvent used in the electrolytic solution include propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 1,2-dimethoxyethane, and 2-methyl. Tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, methyl propionate, ethyl propionate, phosphate triester, trimethoxymethane, dioxolane, diethyl ether, sulfolane, 3-methyl-2-oxazolidinone, Non-aqueous solvents selected from tetrahydrofuran, 1,2-diethoxyethane, chloroethylene carbonate, chloropropylene carbonate, and the like, and mixtures thereof can be mentioned. . Solvents other than those described above may be used as long as they are organic solvents that do not decompose on the positive electrode or negative electrode used in the lithium ion battery of the present invention.

Further, as the electrolyte used in the electrolytic solution, for example, represented by _{LiPF 6, LiBF 4, LiClO 4} , LiCF 3 SO 3, LiCF 3 CO 2, LiAsF 6, LiSbF 6, and lithium trifluoromethane sulfonimide The lithium salt selected from the imide salt of lithium etc. can be mentioned. Any electrolyte other than those described above may be used as long as the electrolyte does not decompose on the positive electrode or the negative electrode used in the lithium ion battery of the present invention.

A particularly preferable electrolytic solution is a mixture of ethylene carbonate and propylene carbonate, dimethyl carbonate, diethyl carbonate or ethyl methyl carbonate, and lithium hexafluorophosphate (LiPF ₆ ) or lithium borofluoride (LiBF ₄ ) as an electrolyte. It is a dissolved solution.

Alternatively, an ionic liquid can be used as the electrolytic solution. Examples of the ionic liquid include 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF ₄ ), a lithium salt LiN (SO ₂ CF ₃ ) ₂ (LiTFSI), a mixed complex of triglyme and tetraglyme. And cyclic quaternary ammonium cations (for example, N-methyl-N-propylpyrrolidinium) and imide anions (for example, bis (fluorosulfonyl) imide). Any ionic liquid other than those described above may be used as long as it does not decompose on the positive electrode or negative electrode used in the lithium ion battery of the present invention.

  The method of injecting the electrolytic solution into the battery container may be appropriately selected based on the shape of the battery container. As the method, for example, there is a method of removing the battery lid 120 from the battery can 113 and adding it directly to the electrode group, or a method of adding from a liquid inlet provided in the battery lid 120.

  The lithium ion battery of the present invention is a solid polymer electrolyte (hereinafter also referred to as “polymer electrolyte”) in which an ion conductive polymer contains the above electrolyte instead of using the electrolyte solution, or a polymer electrolyte and the non-aqueous electrolyte. A mixture with an electrolytic solution (hereinafter also referred to as “gel electrolyte”) may be used. When a polymer electrolyte or a gel electrolyte is used, there is an advantage that the separator is not necessary. Examples of the monomer unit of the ion conductive polymer include ethylene oxide, acrylonitrile, polyvinylidene fluoride, methyl methacrylate and hexafluoropropylene.

  The lithium ion battery of the present invention may be used alone or in the form of a module in which a plurality of lithium ion batteries are connected.

  One embodiment of a system of a lithium ion battery module produced using the lithium ion battery of the present invention is shown in FIG.

  As shown in FIG. 2, the module 201 of the lithium ion battery of the present invention includes a plurality of lithium ion batteries 202. The positive external terminal 203 and the negative external terminal 205 of the plurality of lithium ion batteries 202 can be connected to each other by a terminal 204. The eight lithium ion batteries 202 in FIG. 2 are connected in series. The lithium ion battery 202 included in the module 201 of the lithium ion battery is arranged in an appropriate position by the module container 206 in some cases.

  Further, the lithium ion battery module 201 of the present invention includes a positive external terminal 207, a negative external terminal 208, a charging circuit 210, an arithmetic control unit 209, a power line 212, a signal line 213, and an external power cable 214 as desired. The system S1 of the lithium ion battery module can be provided. The system S1 is connected to an external power source or an external load (indicated as 211 in FIG. 2) and can be charged and discharged.

  As described above in detail, the negative electrode active material and the negative electrode of the present invention are substantially suppressed from being reduced in capacity due to an increase in the number of charge / discharge cycles. Compared to products, it can have a longer life. Therefore, the lithium ion battery and the module thereof according to the present invention are not limited to consumer electronics such as portable electronic devices, mobile phones or electric tools, but also electric vehicles, trains, storage batteries for storing renewable energy, unmanned mobile vehicles, or nursing care devices. It can be used for a power source such as. Further, the lithium ion battery and the module thereof of the present invention can be applied to a power supply of a logistics train for searching for the moon or Mars. In addition, space suits, space stations, structures on earth or other celestial bodies, or living spaces (whether sealed or open), spacecraft for interplanetary movement, planet rover, underwater or underwater. It can also be used for various power sources such as air conditioning, temperature control, purification of sewage or air, or power for various spaces such as closed space, submarine or fish observation equipment.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the technical scope of the present invention is not limited to these examples.

<Production Example 1: Negative electrode active material>
[1: Preparation of graphite particle powder (1)]
50 parts by weight of coke powder having an average particle diameter of 5 μm, 20 parts by weight of tar pitch, 7 parts by weight of silicon carbide having an average particle diameter of 48 μm and 10 parts by weight of coal tar were heated at 200 ° C. for 1 hour with mixing. The obtained mixture was pulverized using a hammer mill, and the mixture was compressed using a hydraulic press and formed into pellets. Next, it was fired at 2800 ° C. for 20 hours in a nitrogen atmosphere to enhance the crystallinity of graphite. The fired product obtained was pulverized using a hammer mill to obtain fine graphite particle powder. This powder was adjusted to an average particle size of 20 μm using an air classifier. This powder is referred to as graphite particle powder 1.

The particle size distribution of graphite powder suspended in water was measured using a particle size distribution measuring device (Horiba, LA-920) using laser scattering. The particle size at which the cumulative volume percentage of the graphite powder is 50%, referred to as D _50. Similarly, the particle size of which cumulative percentage becomes 10%, and D _10. When the particle size distribution of the graphite particle powder 1 prepared above was analyzed using a particle size distribution measuring apparatus, D ₅₀ was 18 to 19 μm.

[2: Preparation of graphite particle powder (2)]
50 parts by weight of coke powder having an average particle diameter of 5 μm, 20 parts by weight of tar pitch, 7 parts by weight of silicon carbide having an average particle diameter of 48 μm, 10 parts by weight of coal tar and 1 part by weight of naphthalene were mixed. The obtained mixture was pulverized using a hammer mill and pressed into a pellet using a hydraulic press. Next, it was fired at 2000 ° C. in a nitrogen atmosphere to obtain a graphite fired product with slightly low crystallinity. The obtained fired product was pulverized using a hammer mill and fired at 2800 ° C. for 20 hours in a nitrogen atmosphere to obtain graphite particle powder. This powder was adjusted to an average particle size of 10 μm using an air classifier. This powder is referred to as graphite particle powder 2.

[3: Preparation of graphite particle powder with coating layer]
100 parts by weight of the graphite particle powder 1 or 2 prepared above was immersed in 160 parts by weight of a novolac type phenol resin methanol solution (manufactured by Hitachi Chemical Co., Ltd.). Graphite particle powder was dispersed using methanol to prepare a mixture solution of graphite particles and phenol resin. From this solution, a mixture of graphite particles and phenol resin was collected by filtration and dried in vacuum at 80 ° C. for 24 hours. The dried mixture was heated at 400 ° C. for 10 hours to obtain graphite particle powder in which a coating layer containing carbon as a main component was formed on the surface of the graphite core material. The powder obtained from the graphite particle powder 1 or 2 is referred to as graphite particle powder 1 or 2 having a coating layer formed, respectively.

  Using a focused ion beam (FIB) processing device (Hitachi High-Technologies, FB-2100), cut out the cross section of graphite particle powder 1 and 2 on which the coating layer was formed, and transmission electron microscope (TEM) (Hitachi High-Technologies, The thickness of the coating layer was measured using a field emission transmission electron microscope (HF-3300). As a result, the thickness of the graphite particle powder 1 or 2 on which the coating layer was formed was 20 ± 5 nm.

[4: Classification of graphite particle powder with coating layer (1)]
Using a wind classifier, the graphite particle powder 1 on which the coating layer prepared above was formed was classified into coarse particles having a particle size of 50 μm or more and large particles having a particle size of less than 50 μm. The average particle diameter D ₅₀ of the powder composed of the large particles was 18.7 μm.

Next, the large particles having a particle size of less than 50 μm were classified into medium particles having a particle size of 15 μm or more and small particles having a particle size of less than 15 μm using an air flow classifier. The average particle diameter D ₅₀ of the powder composed of the small particles, measured using a particle size distribution measuring apparatus, was 8.2 μm.

Using a planetary mixer (Primics, Hibismix 2P-03 type), a predetermined amount of the powder composed of the large particles and the powder composed of the small particles were mixed based on the volume ratio and sufficiently stirred. Let the obtained graphite particle powder be Examples 1-6 (NM1-6).
The powder composed of the large particles is referred to as Comparative Example 1 (NM13).

[5: Classification of graphite particle powder with coating layer (2)]
In the procedure of classification (1) described above, the graphite particle powder 1 with the coating layer is changed to the graphite particle powder 2 with the coating layer, and coarse particles with a particle size of 50 μm or more, particle size of 15 μm. Thus, the particles were classified into large particles having a particle size of less than 50 μm and small particles having a particle size of less than 15 μm.

Next, the small particles having a particle size of less than 15 μm were classified by using an air flow classifier to obtain fine particles having a particle size of less than 10 μm. The average particle diameter D ₅₀ of the powder composed of the fine particles was measured using a particle size distribution measuring apparatus, and 6.4 μm was obtained.

  Using a planetary mixer (Primics, Hibismix 2P-03 type), a predetermined amount of the powder composed of the large particles and the powder composed of the fine particles were mixed based on the volume ratio and sufficiently stirred. The obtained graphite particle powder was used as the graphite particle powder of Examples 7 to 11 (NM7 to 11) and Comparative Examples 2 and 3 (NM13 and 14).

  In the classification treatment, the classification time was extended to obtain extremely small fine particle powder having an average particle diameter of 1 to 2 μm. The obtained small particle size powder and large particle powder (average particle size 18.7 μm) were mixed. The obtained graphite particle powder is referred to as Example 12 (NM12).

Mixing ratio of classified particles when preparing the graphite particle powders of Examples 1 to 12 and Comparative Examples 1 to 3, and D ₁₀ and D ₅₀ measured using a particle size distribution measuring device and their particle size ratio D ₁₀ / The value of D ₅₀ is shown in Table 1.

[6: Physical property analysis of graphite particle powder with coating layer]
The distance (d ₀₀₂ ) between the plane index (002) planes of the graphite crystals contained in the graphite particle powders of Examples 1 to 12 and Comparative Examples 1 to 3 was determined by the X-ray wide angle diffraction method. A micro X-ray diffractometer (Rigaku, RU-200) was used as the X-ray diffractometer, and CuKα was used as the X-ray source.

  As shown in Table 2, it was revealed that the powders of Examples 1 to 12 and Comparative Examples 1 to 3 contained a core material having graphite crystals inside the particles.

  The c-axis length (hereinafter referred to as Lc) of the graphite crystal prepared above was in the range of 20 to 90 nm. However, the present invention is not limited by the range of Lc under the conditions where the effects of the present invention can be obtained.

  The specific surface areas of the graphite particle powders of Examples 1 to 12 and Comparative Examples 1 to 3 were determined using a BET specific surface area measuring device (counterchrome, AUTOSORB-1) using gas adsorption. Nitrogen was used as the adsorption gas.

The Raman spectra of Examples 1 to 12 and Comparative Examples 1 to 3 were measured using a laser Raman spectrometer (JASCO, NRS-2100). As the laser beam, an argon laser was used. The sample powder is irradiated with an argon laser and the scattered light is dispersed to detect peaks in the wave number region of 1360 cm ^-1 (D band) and 1580 cm ^-1 (G band), and 1580 cm ^-1 (G band). The ratio (I ₁₃₆₀ / I ₁₅₈₀ ) of the peak intensity of the 1360 cm ⁻¹ (D band) region to the peak intensity of the region was calculated.

The spacing (d ₀₀₂ ) of the plane index (002) plane, specific surface area, ratio of Raman peak intensity (I ₁₃₆₀ / I ₁₅₈₀ ) and the graphite particle powders (negative electrode active materials) of Examples 1 to 12 and Comparative Examples 1 to 3 Table 2 shows the thickness of the coating layer.

<Production Example 2: Negative electrode>
[1: Production of negative electrode]
98 parts by weight of negative electrode active materials containing graphite particles of Examples 1 to 12 and Comparative Examples 1 to 3 were separately weighed, and water was used as a solvent, and a planetary mixer (Primics, Hibismix 2P-03) was used. And stirred. To this, carboxymethylcellulose and a binder were added in this order and mixed well to prepare a slurry. The binder was 1 part by weight of styrene-butadiene rubber and 1 part by weight of carboxymethyl cellulose. The obtained slurry was applied to a copper current collector foil (thickness 10 μm) using a blade coater. Subsequently, it vacuum-dried in the temperature range of 60-120 degreeC, the water | moisture content was removed, and the electrode was compressed with the roll press machine, and the negative electrode was obtained. The density of the obtained negative electrode mixtures of Examples 1 to 12 and Comparative Examples 1 to ³ was 1.5 g / cm ³ . The negative electrodes of Examples 1 to 12 and Comparative Examples 1 to 3 are denoted as NM1 to 12 and NM13 to 15.

[2: Differential pore volume distribution of negative electrode]
The pore volume distribution of the negative electrodes of Examples 1 to 12 and Comparative Examples 1 to 3 was determined by a mercury intrusion method (mercury porosimeter). Further, the ratio of the total volume of pores having a pore diameter of less than 1 μm to the total volume of pores having a pore diameter of 1 μm or more was calculated.

  As a result, the peak of the differential pore volume of the negative electrodes of Examples 1 to 12 and Comparative Examples 1 to 3 was in the range of 0.1 to 1 μm. Table 3 shows the ratio of the total volume of pores having a pore diameter of less than 1 μm to the total volume of pores having a pore diameter of 1 μm or more.

<Production Example 3: Lithium-ion battery>
[1: Fabrication of positive electrode]
In this example, LiNi _1/3 Mn _1/3 Co _1/3 O ₂ was used as the positive electrode active material.
89 parts by weight of LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , 4 parts by weight of acetylene black and 7 parts by weight of PVDF are dispersed in a solvent (1-methyl-2-pyrrolidone) to form a positive electrode composite. An agent slurry was prepared. The slurry was adhered to a current collector (material: aluminum, thickness: 20 μm). Thereafter, the positive electrode was dried in a vacuum at a temperature range of 60 to 120 ° C., and the current collector to which the positive electrode mixture layer was adhered was pressure-formed by a roll press to produce a positive electrode.

[2: Fabrication of lithium-ion battery]
Using the negative electrodes of Examples 1 to 12 and Comparative Examples 1 to 3 and the positive electrode described above, five lithium ion batteries were prepared in the following procedure. FIG. 1 shows lithium ion batteries produced using the negative electrodes of Examples 1 to 12 and Comparative Examples 1 to 3.

  The separator 111 was inserted between the negative electrode 112 of Examples 1 to 12 and Comparative Examples 1 to 3 and the positive electrode 110 produced by the above procedure, and the negative electrode 112 (active material weight; 10 g) and the positive electrode 110 (active Short circuit between material weight; 28 g) was prevented. The separator 111 is a microporous sheet having a three-layer structure in which polyethylene is adhered to both sides of polypropylene, having a pore diameter of 0.05 to 0.2 μm, a thickness of 25 μm, and a porosity of 45 ± 5%. Using. A laminate composed of the positive electrode 110, the negative electrode 112, and the separator 111 was inserted into a battery can 113 made of nickel-plated steel. A separator 111 was also inserted between the electrode arranged at the end of the laminate and the battery can 113 to prevent a short circuit between the positive electrode 110 and the negative electrode 112 through the battery can 113.

Ethylene carbonate (hereinafter also referred to as “EC”) and ethyl methyl carbonate (hereinafter also referred to as “EMC”) were mixed at a mixing ratio of 1: 2 (volume ratio) to prepare an EC and EMC mixed solvent. LiPF ₆ was dissolved in this mixed solvent to prepare a solution containing 1M LiPF ₆ in EC and EMC mixed solvent. Further, 1% by weight of vinylene carbonate was added to the total weight of the solution to prepare an electrolytic solution containing 1M LiPF ₆ as an electrolyte.

  The electrolyte prepared above was injected into the battery can 113 in which the laminate was inserted, and the electrolyte was held on the surfaces of the positive electrode 110, the negative electrode 112, and the separator 111 and inside the pores.

  One end of the positive electrode current collecting tab 114 was connected to the positive electrode 110 of the laminate, and the other end was connected to the inner lid 116. Also, one end of the negative electrode current collecting tab 115 was connected to the negative electrode 112 of the laminate, and the other end was connected to the battery can 113. The positive electrode current collecting tab 114 and the negative electrode current collecting tab 115 were made of aluminum foil and nickel foil, respectively.

  An inner lid 116, an internal pressure release valve 117, a gasket 118 and a positive temperature coefficient (PTC) resistance element 119 were attached to the battery lid 120. The PTC resistance element 119 was used to stop charging / discharging of the lithium ion battery 101 and protect the battery when the temperature inside the battery became high. The battery lid 120 and the battery can 113 were brought into close contact, and the battery lid 120 was attached to the battery can 113 by caulking to produce a lithium ion battery 101. Let the obtained lithium ion battery be the lithium ion battery of Examples 1-12 (B1-12) and Comparative Examples 1-3 (B13-15).

  The weight of the negative electrode active material used for each lithium ion battery was 10 ± 0.1 g. The weight of the positive electrode active material was 28 ± 0.3 g. Based on the above negative electrode weight and positive electrode weight, the rated capacity (calculated value) of each lithium ion battery was calculated to be 3.5 Ah.

[3: Performance evaluation of lithium-ion battery]
The lithium ion batteries of Examples 1 to 12 (B1 to 12) and Comparative Examples 1 to 3 (B13 to 15) were subjected to initial aging treatment according to the following procedure.

  Each lithium ion battery was charged from an open circuit state. The current was 3.5 A, the voltage was maintained when 4.2 V was reached, and charging was continued until the current reached 0.1 A. Thereafter, a 30-minute rest period was provided, and discharging was started at 3.5 A. When the battery voltage reached 3.0 V, the discharge was stopped and a 30-minute pause was performed. In the same procedure as described above, charging and discharging were repeated 5 times to complete the initial aging process of the lithium ion battery. The initial capacity was calculated by dividing the discharge capacity of the last cycle (5th cycle) by the weight of the negative electrode active material (10 ± 0.1 g).

  Next, in the above-described initial aging procedure, the current value during discharge was increased to 10.5 A (current value equivalent to 3C) without changing the charging conditions, and the 3C discharge capacity density was measured.

  In addition, a charge / discharge test of 300 cycles was performed in the same procedure as the above initial aging, and the capacity retention rate (%) was calculated by dividing the discharge capacity density of the last cycle (300th cycle) by the initial value.

  Table 4 shows the initial capacity, 3C discharge capacity density, and capacity retention rate of the lithium ion batteries of Examples 1 to 12 (B1 to 12) and Comparative Examples 1 to 3 (B13 to 15).

  As shown in Table 4, high initial capacity densities were obtained with the lithium ion batteries of Examples 1 to 12 (B1 to 12), and a high discharge capacity density of 340 mAh / g or more was obtained. In the lithium ion batteries of Examples 1 to 12, it was considered that a high discharge capacity density was obtained because the filling state of the particles inside the negative electrode was improved and the electronic network was improved. Further, the 3C discharge capacity tended to increase as the mixing ratio of the small particle size particles increased. In particular, the 3C discharge capacity density of the negative electrode of Example 12 was increased. In these lithium ion batteries, in addition to the improvement of the electronic network, it is considered that the increase in the specific surface area improved the high rate discharge characteristics.

  Even after 300 cycles of charge and discharge tests were performed under the initial aging conditions, the lithium ion batteries of Examples 1 to 12 exhibited a high capacity retention rate of 96% or more.

  In contrast, the lithium ion battery of Comparative Example 1 had a lower initial capacity density than the lithium ion batteries of Examples 1-12. This is probably because the lithium ion battery of Comparative Example 1 had a poor electronic network and increased the resistance of the negative electrode. As a result, in the lithium ion battery of Comparative Example 1, both the 3C discharge capacity and the capacity retention rate after 300 cycles were reduced as compared with the lithium ion batteries of Examples 1-12.

  The negative electrode active material of Comparative Example 2 used for the lithium ion battery of Comparative Example 2 has a mixing ratio of large and small graphite particles in a range close to the mixing ratio of the negative electrode active material of Example 7. (table 1). However, in the lithium ion battery of Comparative Example 2, all of the initial capacity density, 3C discharge capacity, and capacity retention after 300 cycles were lower than in the case of the lithium ion battery of Example 7.

The lithium ion battery of Comparative Example 3 had higher initial capacity density and 3C discharge capacity than the lithium ion battery of Example 12. Since the negative electrode active material of Comparative Example 3 used for the lithium ion battery of Comparative Example 3 has a higher proportion of small particle size particles in the mixing ratio of the graphite particle powder than the negative electrode active material of Example 12 (Table 1) The specific surface area of the negative electrode active material of Comparative Example 3 is larger than that of the negative electrode active material of Example 12 (Table 2). Thereby, the negative electrode active material of Comparative Example 3 increases the reaction area related to charge / discharge compared with the negative electrode active material of Example 12, resulting in the initial capacity density and 3C discharge of the lithium ion battery of Comparative Example 3 The capacity is considered to be higher than that in Example 12. On the other hand, since the specific surface area of the negative electrode active material of Comparative Example 3 was as extremely large as 6.9 m ² / g, the capacity retention rate after 300 cycles was considered to be low. From the results of Example 12 and Comparative Example 3, there is an upper limit value of the specific surface area for obtaining a high capacity retention ratio at an intermediate position between the specific surface areas of both negative electrode active materials, and the upper limit value is estimated to be 6.5.

Further, the lithium ion batteries of Comparative Examples 1 and 2 had a lower 3C discharge capacity than the lithium ion battery of Example 1. Since D ₅₀ of the negative electrode active material of Comparative Example 1 and 2 used in the lithium ion battery of Comparative Example 1 and 2 are large value centered on 18.5 (Table 1), the negative active in Comparative Examples 1 and 2 The material has a specific surface area smaller than that of the negative electrode active material of Example 1 (Table 2). Thereby, the negative electrode active material of Comparative Examples 1 and 2 has a reduced reaction area for charge and discharge compared to the negative electrode active material of Example 1, resulting in 3C discharge of the lithium ion batteries of Comparative Examples 1 and 2 The capacity is considered to be lower than that in Example 1. Therefore, it can be concluded that the upper limit value of D ₅₀ for ensuring high rate discharge characteristics is 18.5 μm.

  From the above results, it became clear that the following relationship exists between the specifications of the negative electrode active material and the negative electrode and the performance of the lithium ion battery using the negative electrode. Note that the present invention is not limited to the following actions and principles.

First, the particle size ratio D ₁₀ / D _{50 of the} negative electrode active material powder containing graphite particles is in the range of 0.1 to 0.52, D ₁₀ is in the range of 1.2 to 9.2 μm, and D ₅₀ is in the range of ₁₀ to 18.5 μm. When the specific surface area of the powder is in the range of 3.0 to 6.5 m ² / g, the negative electrode and lithium ion battery using the negative electrode active material are the negative electrode and lithium ion using the negative electrode active material of Comparative Example 1. Performance that exceeds the battery can be exhibited. For example, the initial capacity density can reach 350 mAh / g or more, and the capacity retention rate can reach 96% or more.

If the particle diameter ratio D ₁₀ / D ₅₀ of the graphite particles contained in the powder of the anode active material is in the range of 0.29 to 0.47, the negative electrode and the performance of the lithium ion battery using the negative electrode active material is more increased. For example, the initial capacity density reaches 352 mAh / g or more, and the 3C (1/3 hour rate) discharge capacity density reaches 343 mAh / g. In other words, it was found that, within the above range, the capacity retention rate was 96% or more, and both the life and high rate discharge characteristics were excellent. In addition, in the case of the negative electrode active material of Example 1 that deviates from the above range of the particle size ratio, the 3C discharge capacity is slightly reduced, so that the preferable upper limit of D ₁₀ / D ₅₀ is between 0.47 and 0.52. It is supported that there is.

When the particle size ratio D ₁₀ / D _{50 of the} graphite particles contained in the powder of the negative electrode active material is in the range of 0.1 to 0.35, the discharge capacity density of the negative electrode and the lithium ion battery using the negative electrode active material is further improved. For example, the 3C discharge capacity density can reach 357 mAh / g. The lithium ion batteries using the negative electrode active materials of Examples 9 to 12 included in the above range have the highest discharge capacity density.

  The reason why the above advantageous effect was obtained is thought to be that the mixing ratio of the large particle size particles and the small particle size particles of the negative electrode active material powder containing graphite particles was within a suitable range. Such an effect is derived from the fact that the distribution of graphite particles is within the optimum range of the present invention. In the particle powder, the apparent negative electrode density is increased by the small particle diameter particles entering the voids formed by the plurality of large particle diameter particles. For this reason, even if it is a small press-molding pressure, a desired negative electrode density is easily realizable. Thereby, it can avoid that an excessive pressure is applied to a graphite particle and this particle | grain deform | transforms. As a result, it is considered that a desirable negative electrode structure was realized and the performance of the negative electrode was improved. The same effect can be obtained even if at least one of the large or small particle size graphite particles is replaced with graphite particles with little coating or uncoated graphite particles. This is because the volume change accompanying the charge / discharge cycle is not related to the presence or absence of coating.

  In the production of the negative electrode, when an excessive pressure is applied to specific graphite particles, minute cracks are formed in the particles. When a negative electrode of a lithium ion battery is produced using a negative electrode active material containing graphite particles with cracks formed, the graphite particles collapse based on the cracks due to charge / discharge cycles. Collapse of the graphite particles used in the negative electrode causes a decrease in capacity due to loss of the negative electrode active material. Moreover, since the surface of the reactive active graphite is exposed at the collapsed portion of the graphite particles, the decomposition reaction site of the electrolytic solution increases. As a result, a film resulting from the decomposition of the electrolytic solution is formed on the surface of the negative electrode. When such a film is formed, the capacity maintenance rate of the lithium ion battery is decreased and / or the direct current resistance is increased, and as a result, the life characteristics of the lithium ion battery are deteriorated.

  In the case of the negative electrode of this example, a desired negative electrode density can be easily realized with a small pressure forming pressure, and therefore it is possible to avoid deformation of graphite particles due to an excessive pressure forming pressure being applied. . Therefore, the above problem can be solved. Such an effect is derived from the fact that the distribution of graphite particles is within the optimum range of the present invention, and is independent of the presence or absence of coating on the graphite surface.

  In addition, in the case of the negative electrode of this example, since the small particle diameter enters the void formed by a plurality of large particle size graphite particles, not only the electrical contact between the graphite particles is good, but also the fine voids It is uniformly formed throughout the negative electrode. For this reason, about all the particles contained in a negative electrode, the volume change of this particle | grain accompanying a charging / discharging cycle is relieve | moderated. As described above, in the case of the negative electrode of this example, the total volume of the pores related to the pore diameter of 1 μm is a high ratio of 3 times or more the total volume of the pores related to the pore diameter of 1 μm or more, and the minute volume It was shown that simple pores were formed in the entire negative electrode (Table 3). When the size of voids between graphite particles contained in the negative electrode is inhomogeneous, the space between the particles gradually increases at the contact surface of multiple particles that form small voids due to the volume change during the charge / discharge cycle To do. As a result, an electrical contact failure occurs. Further, when an excessive stress is applied to specific graphite particles, the graphite particles in contact with each other are displaced, and a new graphite surface is exposed. Alternatively, the coating layer of graphite particles is destroyed, and the surface of the reactive active graphite is exposed. The decomposition reaction of the electrolytic solution newly proceeds at the exposed portion. As a result, the capacity of the negative electrode is reduced. Such a decrease in capacity is alleviated to some extent by the coating of the graphite particles, but the volume change of the graphite particles during charging / discharging is an essential cause.

  On the other hand, in the case of the negative electrode of this example, since the size of the voids between the graphite particles is substantially uniform, substantially uniform stress acts on all the particles during the charge / discharge cycle. By using the graphite particles having the optimum particle size distribution of the present invention, the stress inside the negative electrode can be equalized and the stress per particle can be reduced. As described above, in the case of the negative electrode of this example, it is possible to avoid applying an excessive stress to the specific graphite particles, so that the above problem can be solved.

<Production Example 4: Lithium-ion battery module system>
[1: Production of system]
Using the lithium ion battery of Example 1, a module (assembled battery) system was produced by the following procedure. FIG. 2 shows a module system of a lithium ion battery manufactured using the lithium ion battery of Example 1.

  Using the terminal 204, the positive electrode external terminal 203 and the negative electrode external terminal 205 of the lithium ion battery 202 of Example 1 were connected in series, and the module 201 was assembled. A positive electrode external terminal 207, a negative electrode external terminal 208, a charging circuit 210, a calculation control unit 209, a power supply load power supply 211, a power line 212, a signal line 213, and an external power cable 214 were connected to the module 201 to produce a system S1. .

  Further, a system S2 was produced in the same procedure as described above except that the lithium ion battery of Example 1 was changed to the lithium ion battery of Example 8 in the above procedure.

  Since this example was a test for confirming the effectiveness of the present invention, a power supply load power source 211 having both functions of supplying and consuming power is used for attaching an external power source or an external load. It was. The use of this does not make a difference in the effect of the present invention compared to an actual use of an electric vehicle such as an electric vehicle or a machine tool, or a distributed power storage system or a backup power supply system.

[2: System performance evaluation]
In the above systems S1 and S2, a charging current corresponding to a 1 hour rate (3.5 A) is passed from the charge / discharge circuit 210 to the positive external terminal 207 and the negative external terminal 208, and the constant voltage of 33.6 V is applied for 1 hour. Charged. The constant voltage value set here is eight times the constant voltage value 4.2 V of the unit cell described above. Electric power necessary for charging / discharging the module was supplied from a power supply load power supply 211.

  In the discharge test, a reverse current was passed from the positive external terminal 207 and the negative external terminal 208 to the charge / discharge circuit 210, and power was consumed by the power supply load power supply 211. The discharge current was 1 hour rate (discharge current 3.5 A), and discharging was performed until the voltage between the positive external terminal 207 and the negative external terminal 208 reached 24 V.

  When the charge / discharge test was performed under the above conditions, in the case of system S1, the initial performance was a charge capacity of 3.5 Ah and a discharge capacity of 3.4 to 3.5 Ah. When a charge / discharge cycle test of 300 cycles was further performed, in the case of system S1, the capacity maintenance rate was 91 to 93%, and in the case of system S2, the capacity maintenance rate was 94 to 95%.

  In addition, this invention is not limited to an above-described Example, Various modifications are included. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Further, it is possible to add, delete, and / or replace another configuration with respect to a part of the configuration of each embodiment.

101 ... Lithium ion battery
110 ... Positive electrode
111 ... Separator
112 ... Negative electrode
113 ... Battery can
114 ... Positive current collector tab
115… Negative electrode current collecting tab
116 ... Inner lid
117 ... Internal pressure release valve
118… Gasket
119… Positive temperature coefficient (PTC) resistance element
120 ... Battery cover
201 ... Module
202 ... Lithium ion battery
203 ... Lithium ion battery positive electrode external terminal
204 ... Terminal
205 ... Negative electrode external terminal of lithium-ion battery
206 ... Module container
207… Module positive external terminal
208 ... Negative external terminal of module
209 ... Calculation control unit
210 ... Charging circuit
211… Power supply for load supply
212 ... Power line
213 ... Signal line
214 ... External power cable

Claims (7)

The particle size ratio D ₁₀ / D ₅₀ is in the range of 0.1 to 0.35 , where the particle size is D ₁₀ when the cumulative particle size is 10% and the particle size when the cumulative particle size is 50% is D _50. A non-aqueous electrolyte in which D ₁₀ is in the range of 1.2 to 4.7 μm, D ₅₀ is in the range of 10.4 to 15.1 μm, and the specific surface area of the powder is in the range of 3.0 to 6.5 m ² / g Negative electrode active material for secondary battery . The non-aqueous electrolyte secondary according to claim 1, wherein the powder further includes particles of another material, and the graphite particles include 50% by volume or more based on a total volume of the graphite particles and the particles of the other material. Negative electrode active material for batteries . 3. The nonaqueous electrolyte secondary battery according to claim 1, wherein the graphite particles have a core material containing graphite, and a coating layer containing carbon as a main component disposed on the surface of the core material. use the negative electrode active material. 4. The negative electrode active material for a non-aqueous electrolyte secondary battery according to claim 3 , wherein the coating layer further contains nitrogen, phosphorus, oxygen, alkali metal, alkaline earth metal, or transition metal. A current collector, and a negative electrode mixture layer comprising a negative electrode active material for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 4 and a binder disposed on a surface of the current collector. The peak of differential pore volume measured by mercury porosimetry is a pore diameter of 1 μm or less, and the total volume of pores having a pore diameter of less than 1 μm with respect to the total volume of pores having a pore diameter of 1 μm or more. The negative electrode for nonaqueous electrolyte secondary batteries whose ratio is 3 or more. 6. A lithium ion secondary battery comprising the negative electrode for a non-aqueous electrolyte secondary battery according to claim 5 , a positive electrode, and an electrolyte. 7. A system of a lithium ion secondary battery module comprising a plurality of lithium ion secondary batteries according to claim 6 .

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