JP6615431B2 - Negative electrode material for lithium ion secondary battery, negative electrode for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Description

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

At present, graphite is mainly used as a negative electrode material for lithium ion secondary batteries, and it is known that graphite has a theoretical capacity limit of 372 mAh / g in discharge capacity. In recent years, with the improvement in performance of mobile devices such as mobile phones, notebook computers and tablet terminals, the demand for higher capacity of lithium ion secondary batteries has become stronger, and the further increase in capacity of lithium ion secondary batteries has increased. There is a need for achievable negative electrode materials.
Therefore, a negative electrode material using an element having a high theoretical capacity and capable of occluding and releasing lithium ions (hereinafter also referred to as “specific element”. Also, a material containing the specific element is also referred to as “specific element body”). Development is active.

  As the specific element, silicon, tin, lead, aluminum and the like are well known. Among them, silicon oxide, which is one of the specific element bodies, has advantages such as higher capacity, lower cost and better workability than negative electrode materials made of other specific elements. Research is particularly active.

  On the other hand, these specific element bodies are known to undergo large volume expansion when alloyed by charging. Such volume expansion makes the specific element bodies themselves finer, and further, the structure of the negative electrode material using these elements is broken and the conductivity is cut. Therefore, it has been a problem that the capacity of the lithium ion secondary battery is remarkably reduced as the cycle progresses.

For example, in Patent Document 1, a diffraction peak attributed to Si (111) is observed in X-ray diffraction, and the silicon crystal obtained by the Scherrer method based on the half-value width of the diffraction line is observed in Patent Document 1. Conductive silicon for negative electrode material of non-aqueous electrolyte secondary battery, having a size of 1 to 500 nm, wherein the surface of particles having a structure in which silicon microcrystals are dispersed in a silicon compound is coated with carbon A composite is disclosed.
According to the technique of Patent Document 1, silicon microcrystals or fine particles are dispersed in an inert and strong substance, for example, silicon dioxide, and carbon for imparting conductivity to at least a part of the surface is fused. By doing so, it is said that the structure is stable with respect to the volume change caused by insertion and extraction of lithium as well as the surface conductivity, and as a result, the long-term stability and the initial efficiency are improved.

Moreover, in patent document 2, it is the electroconductive powder which coat | covered the surface of the material which can occlude and discharge | release lithium ion with a graphite film | membrane, a graphite coating amount is 3 to 40 weight%, and a BET specific surface area is ² to 30 m < ² > / g. a is, graphite coating, according to the Raman spectrum, the Raman shift is the negative electrode material for a nonaqueous electrolyte secondary battery characterized by having a spectrum of graphite structure-specific are disclosed in the vicinity of 1330 cm ^-1 and 1580 cm ^-1 ing.
According to the technology of Patent Document 2, by controlling the physical properties of a graphite film covering the surface of a material capable of occluding and releasing lithium ions within a specific range, a lithium ion secondary that can reach a characteristic level required by the market. It is said that the negative electrode of a battery is obtained.

In Patent Document 3, a negative electrode material used in the negative electrode for a secondary battery with a nonaqueous electrolyte, negative electrode material, the carbon film on the surface of the silicon oxide particles represented by the general formula SiO _x There is disclosed a negative electrode material for a non-aqueous electrolyte secondary battery, characterized in that it is coated and the carbon film is subjected to a thermal plasma treatment.
According to the technology of Patent Document 3, it solves the electrode expansion and the battery expansion caused by gas generation, which are disadvantages when using silicon oxide, and is effective as a negative electrode for non-aqueous electrolyte secondary batteries with excellent cycle characteristics. Negative electrode material is obtained.

Japanese Patent No. 3952180 Japanese Patent No. 4171897 JP 2011-90869 A

However, when silicon oxide, which is one of the specific element bodies, is used as the negative electrode material, the initial charge / discharge efficiency is low, and the battery capacity of the positive electrode is excessive when applied to an actual battery. Even in this technology, the feature of silicon oxide having a high capacity could not be fully utilized in an actual lithium ion secondary battery. In addition, as a negative electrode material to be applied to lithium ion secondary batteries suitable for higher performance of mobile devices and the like in the future, not only can a large amount of lithium ions be stored (high charge capacity), but also stored lithium It is necessary that the performance is not easily lowered even when more ions are released and repeated charge and discharge are performed. Therefore, as a negative electrode material that contributes to further improving the performance of the lithium ion secondary battery, it is important to improve the initial discharge capacity, the initial charge / discharge efficiency, and the cycle characteristics.
The present invention has been made in view of the above requirements, and has a negative electrode material for a lithium ion secondary battery, a negative electrode for a lithium ion secondary battery, and a lithium ion secondary battery that are excellent in initial discharge capacity, initial charge / discharge efficiency, and cycle characteristics. It is an object to provide a battery.

  Specific means for solving the above problems are as follows.

<1> In an X-ray diffraction spectrum in which part or all of the surface of silicon oxide particles has carbon, the carbon is contained in an amount of 0.5% by mass to 10% by mass, and CuKα rays are used as a radiation source. A negative electrode material for a lithium ion secondary battery having a diffraction peak attributed to Si (111) and having a silicon crystallite size of 2.0 nm to 8.0 nm calculated from the diffraction peak.

<2> The negative electrode material for a lithium ion secondary battery according to <1>, wherein the carbon is low crystalline carbon.

<3> a current collector and a negative electrode material layer comprising the negative electrode material for lithium ion secondary batteries according to <1> or <2>, provided on the current collector,
A negative electrode for a lithium ion secondary battery.

A lithium ion secondary battery provided with a <4> positive electrode, the negative electrode for lithium ion secondary batteries as described in said <3>, and an electrolyte.

  ADVANTAGE OF THE INVENTION According to this invention, the negative electrode material for lithium ion secondary batteries, the negative electrode for lithium ion secondary batteries, and a lithium ion secondary battery which are excellent in initial stage discharge capacity, initial stage charge / discharge efficiency, and cycling characteristics can be provided.

It is a schematic sectional drawing which shows an example of a structure of the negative electrode material of this invention. It is a schematic sectional drawing which shows another example of a structure of the negative electrode material of this invention. It is a schematic sectional drawing which shows another example of a structure of the negative electrode material of this invention. It is a schematic sectional drawing which shows another example of a structure of the negative electrode material of this invention. It is a schematic sectional drawing which shows another example of a structure of the negative electrode material of this invention. It is sectional drawing to which some negative electrode materials of FIGS. 1-3 were expanded. (A) illustrates one aspect of the state of carbon 10 in the negative electrode material, and (B) describes another aspect of the state of carbon 10 in the negative electrode material.

In the present specification, a numerical range indicated using “to” indicates a range including the numerical values described before and after “to” as the minimum value and the maximum value, respectively.
Further, in the present specification, the amount of each component in the composition is the amount of each of the plurality of substances present in the composition unless there is a specific indication when there are a plurality of substances corresponding to each component in the composition. It means the total amount.

<Anode material for lithium ion secondary battery>
The negative electrode material for a lithium ion secondary battery of the present invention (hereinafter may be abbreviated as “negative electrode material”) has carbon in part or all of the surface of the silicon oxide particles, and the carbon has a value of 0.00. 5% to 10% by mass, having a diffraction peak attributed to Si (111) in an X-ray diffraction spectrum using CuKα rays as a radiation source, and the size of silicon crystallites calculated from the diffraction peak Is 2.0 nm to 8.0 nm. By adopting such a configuration, expansion and contraction associated with insertion and extraction of lithium ions can be mitigated and capacity decrease per unit mass can be suppressed, so that the initial discharge capacity and initial charge / discharge can be suppressed. Excellent efficiency and cycle characteristics.

(Silicon oxide particles)
The material for the silicon oxide particles according to the present invention may be any oxide containing silicon atoms, and examples thereof include silicon monoxide (also referred to as silicon oxide), silicon dioxide, and silicon suboxide. These may be used alone or in combination of two or more. Silicon oxide and silicon dioxide are generally represented as silicon monoxide (SiO) and silicon dioxide (SiO ₂ ), respectively, depending on the surface state (eg, the presence of an oxide film) and the state of compound formation. As a measured value (or converted value) of an element to be obtained, there is a case where it is represented by a composition formula SiOx (x is 0 <x ≦ 2). Note that the value of x can be calculated, for example, by quantifying oxygen contained in silicon oxide by an inert gas melting-non-dispersive infrared absorption method. In addition, when a disproportionation reaction of silicon oxide (2SiO → Si + SiO ₂ ) is involved in the production process of the negative electrode material of the present invention, the chemical reaction includes silicon and silicon dioxide (in some cases, silicon oxide). In this case, the silicon oxide according to the present invention is used.
Silicon oxide can be obtained, for example, by a known sublimation method in which a gas of silicon monoxide generated by heating a mixture of silicon dioxide and metal silicon is cooled and precipitated. Moreover, it can obtain from a market as silicon oxide, silicon monoxide, Silicon Monooxide, etc.

  The silicon oxide particles have a structure in which silicon crystallites are dispersed in silicon oxide. When silicon crystallites are dispersed in silicon oxide, a diffraction peak attributed to Si (111) is shown in an X-ray diffraction spectrum using CuKα rays as a radiation source.

  The size of silicon crystallites contained in the silicon oxide is 2.0 nm to 8.0 nm. If the crystallite size of silicon is less than 2.0 nm, lithium ions and silicon oxide are likely to react with each other, and the initial charge capacity is increased, so that the charge / discharge efficiency tends to be low. In addition, if the size of the silicon crystallites exceeds 8.0 nm, the silicon crystallites are likely to be localized in the silicon oxide, and lithium ions are less likely to diffuse in the silicon oxide. There is a tendency for characteristics to deteriorate. The size of the silicon crystallite is preferably 3.0 nm or more, and more preferably 4.0 nm or more. Further, from the viewpoint of discharge capacity, it is preferably 6.0 nm or less, and more preferably 5.0 nm or less.

  The size of the silicon crystallite is the size of the silicon single crystal contained in the silicon oxide, and is calculated from the diffraction peak attributed to Si (111) in the X-ray diffraction (XRD) spectrum. Specifically, based on the Scherrer equation from the half-value width of the diffraction peak near 2θ = 28.4 ° attributed to Si (111) in the X-ray diffraction spectrum using CuKα rays with a wavelength of 0.154056 nm as the radiation source. Is calculated.

  In addition, the state in which the silicon crystallites are dispersed in the silicon oxide can be confirmed by the presence of a diffraction peak attributed to Si (111) in the X-ray diffraction spectrum. For example, the silicon oxide can be oxidized using a transmission electron microscope. When physical particles are observed, the presence of silicon crystals in the amorphous silicon oxide can be confirmed.

  A structure in which silicon crystallites are dispersed in silicon oxide can be produced, for example, by heat-treating silicon oxide in a temperature range of 700 ° C. to 1300 ° C. in an inert atmosphere to disproportionate. Moreover, it can produce by adjusting the heating temperature and heat processing time in the heat processing for providing the below-mentioned carbon to a silicon oxide particle.

  The method for producing silicon oxide in which silicon crystallites are dispersed is not particularly limited. For example, silicon oxide is crystallized in silicon oxide by heat treatment in a temperature range of 700 ° C. to 1300 ° C., preferably in a temperature range of 800 ° C. to 1200 ° C., under an inert atmosphere. Can be produced. From the viewpoint of generating silicon crystallites in a desired size, the heat treatment temperature is preferably higher than 850 ° C., more preferably 900 ° C. or higher. The heat treatment temperature is preferably less than 1150 ° C, and more preferably 1100 ° C or less.

Examples of the inert atmosphere include a nitrogen atmosphere and an argon atmosphere. The heat treatment time can be appropriately selected according to the heat treatment temperature and the like. For example, it is preferably 1 hour to 10 hours, and more preferably 2 hours to 7 hours.
In addition, there exists a tendency for the magnitude | size of the silicon crystallite to become large, so that the heating temperature at the time of heat processing becomes high, and heating time becomes long. Therefore, it is preferable to select the heat treatment temperature and the heat treatment time so that the silicon crystallite size is in a desired range. For example, when the heat treatment time is 2 hours to 7 hours, the heat treatment temperature is preferably higher than 850 ° C. and lower than 1150 ° C., more preferably 900 ° C. or higher and 1100 ° C. or lower.

  The silicon oxide to be subjected to the heat treatment is preferably pulverized and classified when a lump of about several cm square is prepared. Specifically, it is preferable to firstly perform primary pulverization and classification to a size that can be charged into a fine pulverizer, and then secondary pulverize this with a fine pulverizer.

  The average particle diameter of the silicon oxide particles is not particularly limited. For example, the average particle diameter of the silicon oxide particles is preferably 0.1 μm to 20 μm from the viewpoint of the initial discharge capacity and cycle characteristics in accordance with the final desired negative electrode material size. More preferably, it is 5 μm to 10 μm. The average particle diameter is a volume cumulative 50% particle diameter (D50%) of the particle size distribution. Hereinafter, the same applies to the description of the average particle diameter. For measuring the average particle diameter, a known method such as a laser diffraction particle size distribution analyzer can be employed.

  Furthermore, the negative electrode material of the present invention has carbon in part or all of the surface of the silicon oxide particles, and the carbon is included in the entire negative electrode material in an amount of 0.5 mass% to 10 mass%. With such a configuration, initial discharge capacity, initial charge / discharge efficiency, and cycle characteristics are improved. In the whole negative electrode material, carbon is preferably contained at 1.0% by mass to 9.0% by mass, more preferably 2.0% by mass to 8.0% by mass, and 3.0% by mass. More preferably, it is contained at ˜7.0% by mass.

  The carbon content (mass basis) in the whole negative electrode material can be determined by high-frequency firing-infrared analysis. In the high-frequency firing-infrared analysis method, for example, a carbon-sulfur simultaneous analyzer (LECO Japan GK, CSLS600) can be applied.

  The negative electrode material of the present invention has carbon in part or all of the surface of the silicon oxide particles. 1 to 4 are schematic cross-sectional views showing examples of the configuration of the negative electrode material of the present invention. In FIG. 1, carbon 10 covers the entire surface of silicon oxide 20. In FIG. 2, the carbon 10 covers the entire surface of the silicon oxide 20, but the thickness varies. Moreover, in FIG. 3, carbon 10 exists partially on the surface of the silicon oxide 20, and the surface of the silicon oxide 20 is partially exposed. In FIG. 4, carbon 10 particles having a particle diameter smaller than that of the silicon oxide 20 are present on the surface of the silicon oxide 20. In FIG. 5, it is a modification of FIG. 4, and the particle shape of the carbon 10 is scaly. 1 to 5, the shape of the silicon oxide 20 is schematically represented in a spherical shape (a circle as a cross-sectional shape), but a spherical shape, a block shape, a scale shape, or a polygonal cross-sectional shape. (A shape with corners) or the like may be used.

FIG. 6 is an enlarged cross-sectional view of a part of the negative electrode material of FIGS. 1 to 3. FIG. 6A illustrates one embodiment of the shape of carbon 10 in the negative electrode material, and FIG. Another aspect of the shape of the carbon 10 in the material will be described. In the case of FIGS. 1 to 3, even if the carbon 10 is entirely composed of carbon as shown in FIG. 6 (A), the carbon 10 is composed of carbon fine particles 12 as shown in FIG. 6 (B). It may be. Although FIG. 6B shows the carbon 10 with the contour shape of the carbon fine particles 12 remaining, the carbon fine particles 12 may be bonded to each other. When the carbon fine particles 12 are bonded to each other, the carbon 10 may be entirely composed of carbon, but voids may be included in a part of the carbon 10. In this way, voids may be included in part of the carbon 10.
When carbon 10 is a particle, as shown in FIG. 4, the carbon 10 particle is partially present on the surface of silicon oxide 20, and the surface of silicon oxide 20 may not be partially covered. However, as shown in FIG. 6B, carbon 10 particles may be present on the entire surface of the silicon oxide 20.

The carbon on the surface of the silicon oxide particles is preferably low crystalline. That carbon is low crystalline means that it is 0.5 or more in the following R value.
Carbon, in a profile obtained by laser Raman spectroscopy of the excitation wavelength 532 nm, the intensity of the peak appearing the intensity of the peak appearing in the vicinity of 1360 cm ^-1 Id, around 1580 cm ^-1 and Ig, the intensity ratio of the two peaks When Id / Ig (also expressed as D / G) is an R value, the R value is preferably 0.5 to 1.5, more preferably 0.7 to 1.3, 0 More preferably, it is 8 to 1.2.
When the R value is 0.5 to 1.5, the particle surface is coated with low crystalline carbon in which carbon crystallites are randomly oriented, so that the reactivity with the electrolytic solution can be reduced, and the cycle characteristics tend to be improved. There is.

Here, the peak appearing in the vicinity of 1360 cm ⁻¹ is a peak that is usually identified as corresponding to the amorphous structure of carbon, for example, a peak observed at 1300 cm ^{−1 to} 1400 cm ⁻¹ . Also, the peak appearing near 1580 cm ^-1, generally a peak identified as corresponding to the graphite crystal structure, for ^example, refers to peaks observed at 1530cm ^-1 ~1630cm -1.
Incidentally, R value Raman spectrum measuring apparatus (e.g., NSR-1000 type, manufactured by JASCO Corporation) was used, the ^{1050cm -1 ~1750cm} -1 as a baseline for the measurement range ^{(830cm -1 ~1940cm} -1) Can be sought.

Although there is no restriction | limiting in particular as a method to provide carbon on the surface of a silicon oxide particle, Methods, such as a wet mixing method, a dry-type mixing method, a chemical vapor deposition method, are mentioned. From the viewpoint of uniform and easy control of the reaction system and maintaining the shape of the negative electrode material, a wet mixing method or a dry mixing method is preferable.
In the case of the wet mixing method, for example, silicon oxide particles and a solution in which a carbon source is dissolved in a solvent are mixed, and a solution containing the carbon source is attached to the surface of the silicon oxide particles, as necessary. The carbon source can be carbonized by removing the solvent and then heat-treating under an inert atmosphere, and carbon can be imparted to the surface of the silicon oxide particles. In addition, when a carbon source does not melt | dissolve in a solvent, it can also be set as the dispersion liquid which disperse | distributed the carbon source in the dispersion medium.
In the case of the dry mixing method, for example, silicon oxide particles and a carbon source are mixed in a solid state to form a mixture, and the carbon source is carbonized by heat-treating the mixture in an inert atmosphere, thereby oxidizing silicon. Carbon can be imparted to the surface of the product particles. In addition, when mixing a silicon oxide particle and a carbon source, you may perform the process (for example, mechanochemical process) which adds mechanical energy.
In the case of chemical vapor deposition, a known method can be applied. For example, by applying heat treatment to silicon oxide particles in an atmosphere containing a gas obtained by vaporizing a carbon source, carbon is imparted to the surface of the silicon oxide particles. Can do.

  When carbon is imparted to the surface of the silicon oxide particles by the above method, the carbon source is not particularly limited as long as it is a compound that can leave carbon by heat treatment. Specific examples of carbon sources include polymer compounds such as phenol resin, styrene resin, polyvinyl alcohol, polyvinyl chloride, polyvinyl acetate, and polybutyral; ethylene heavy end pitch, coal pitch, petroleum pitch, coal tar pitch, asphalt decomposition And pitches such as naphthalene pitch produced by polymerizing PVC pitch, naphthalene, etc. in the presence of a super strong acid; polysaccharides such as starch, cellulose; and the like. These carbon sources may be used alone or in combination of two or more.

  When carbon is applied to the surface of silicon oxide particles by a chemical vapor deposition method, the carbon source is a gaseous or easily vaporizable compound among aliphatic hydrocarbons, aromatic hydrocarbons, alicyclic hydrocarbons, etc. Is preferably used. Specific examples include methane, ethane, propane, toluene, benzene, xylene, styrene, naphthalene, cresol, anthracene, and derivatives thereof. These carbon sources may be used alone or in combination of two or more.

  The heat treatment temperature for carbonizing the carbon source is not particularly limited as long as the carbon source is carbonized, and is preferably 700 ° C. or higher, more preferably 800 ° C. or higher, and 900 ° C. or higher. More preferably it is. Further, from the viewpoint of making carbon low crystalline, the heat treatment temperature is preferably 1300 ° C. or less, more preferably 1200 ° C. or less, further preferably 1150 ° C. or less, and more preferably 1100 ° C. or less. It is particularly preferred.

  The heat treatment time is appropriately selected depending on the type of carbon source used and the amount of the carbon source used, and is preferably 1 hour to 10 hours, for example, and more preferably 2 hours to 7 hours.

  Note that the heat treatment is preferably performed in an inert atmosphere such as nitrogen or argon. The heat treatment apparatus is not particularly limited as long as a reaction apparatus having a heating mechanism is used, and examples thereof include a heating apparatus capable of processing by a continuous method, a batch method, or the like. Specifically, a fluidized bed reaction furnace, a rotary furnace, a vertical moving bed reaction furnace, a tunnel furnace, a batch furnace or the like can be appropriately selected according to the purpose.

  When the carbon is formed by heat treatment of a carbon source, the heat treatment of the carbon source may also serve as a disproportionation treatment of silicon oxide. As heat treatment conditions in this case, from the viewpoint of obtaining a negative electrode material having a desired silicon crystallite size, it is preferable that the temperature is higher than 850 ° C. and lower than 1150 ° C. for 1 hour to 10 hours, and 900 ° C. to 1100 More preferably, it is 2 to 7 hours at ° C.

  The heat-treated product obtained by the heat treatment is preferably crushed because individual particles may be aggregated. Moreover, when adjustment to a desired average particle diameter is required, you may further grind | pulverize.

  Further, as another method for imparting carbon to the surface of silicon oxide particles, for example, as a carbon source to be imparted to the surface of silicon oxide particles, amorphous carbon such as soft carbon and hard carbon; graphite; Examples include a method using a carbonaceous material. According to this method, a negative electrode material having a shape in which carbon 10 is present on the surface of the silicon oxide particle 20 as a particle as shown in FIGS. 4 and 5 can also be produced. As the method using the carbonaceous material, the wet mixing method or the dry mixing method can be applied.

  When applying the wet mixing method, fine particles of the carbonaceous material and an organic compound (compound capable of leaving carbon by heat treatment) as a binder are mixed to form a mixture, and the mixture and the silicon oxide particles are further mixed. By mixing, the mixture is made to adhere to the surface of the silicon oxide particles and heat-treated. The organic compound is not particularly limited as long as it is a compound that can leave carbon by heat treatment. The heat treatment conditions for applying the wet mixing method can be the heat treatment conditions for carbonizing the carbon source.

  When applying the dry mixing method, carbonaceous fine particles and silicon oxide particles are mixed in a solid state to form a mixture, and mechanical energy is applied to the mixture (for example, mechanochemical treatment). It is produced by. Even when the dry mixing method is applied, it is preferable to perform a heat treatment in order to generate silicon crystallites in the silicon oxide. The heat treatment conditions for applying the dry mixing method can be the heat treatment conditions for carbonizing the carbon source.

  The volume-based average particle diameter (D50%) of the negative electrode material is preferably 0.1 μm to 20 μm, and more preferably 0.5 μm to 10 μm. When the average particle size is 20 μm or less, the distribution of the negative electrode material in the negative electrode is made uniform, and further, the expansion and contraction during charge / discharge are made uniform, and the deterioration of cycle characteristics tends to be suppressed. Further, when the average particle diameter is 0.1 μm or more, the negative electrode density tends to increase and the capacity tends to be increased.

The specific surface area of the negative electrode material is preferably 0.1m ² / g~15m ² / g, more preferably ^{0.5m 2 / g~10m 2 / g,} 1.0m 2 / g~7m More preferably, it is ² / g. When the specific surface area is 15 m ² / g or less, an increase in the first irreversible capacity of the obtained lithium ion secondary battery tends to be suppressed. Furthermore, an increase in the amount of binder used can be suppressed when producing the negative electrode. When the specific surface area is 0.1 m ² / g or more, the contact area with the electrolytic solution increases, and the charge / discharge efficiency tends to increase. For the measurement of the specific surface area, a known method such as the BET method (nitrogen gas adsorption method) can be employed.

  The negative electrode material preferably contains carbon in an amount of 0.5 mass% to 10 mass%, and the silicon crystallite size is preferably 2.0 nm to 8.0 nm, and the carbon is 1.0 mass%. More preferably, it is contained at ˜9.0% by mass, and the crystallite size of silicon is from 3.0 nm to 6.0 nm.

The negative electrode material of the present invention may be used in combination with a carbon negative electrode material conventionally known as an active material for a negative electrode of a lithium ion secondary battery, if necessary. Depending on the type of carbon negative electrode material used in combination, an improvement in charge / discharge efficiency, an improvement in cycle characteristics, an effect of suppressing the expansion of the electrode, and the like are obtained.
Conventionally known carbon anode materials include natural graphite such as flaky natural graphite, spherical natural graphite obtained by spheroidizing flaky natural graphite, artificial graphite, and amorphous carbon. Moreover, these carbon negative electrode materials may further have carbon in part or all of the surface thereof. These carbon negative electrode materials may be used alone or in combination with the negative electrode material of the present invention.

  When the negative electrode material of the present invention is used in combination with a carbon negative electrode material, the ratio (SiO-C: C) of the negative electrode material of the present invention (denoted as SiO-C) and the carbon negative electrode material (denoted as C) is For example, from the viewpoint of the effect of suppressing the expansion of the electrode, it is preferably 0.1: 99.9 to 20:80 on the mass basis, Is more preferably 99.5 to 15:85, and still more preferably 1:99 to 10:90.

<Anode for lithium ion secondary battery>
The negative electrode for a lithium ion secondary battery of the present invention (hereinafter sometimes abbreviated as “negative electrode”) is a negative electrode material comprising a current collector and the negative electrode material for a lithium ion secondary battery provided on the current collector. And a layer. For example, the negative electrode for a lithium ion secondary battery of the present invention is conventionally known as the negative electrode material for a lithium ion secondary battery, an organic binder, a solvent, a solvent such as water, and, if necessary, a thickener, a conductive aid. It is obtained by preparing a coating liquid in which the carbon negative electrode material and the like are mixed, applying the coating liquid to a current collector, removing the solvent or water, and performing pressure molding to form a negative electrode material layer. . A sheet material obtained by kneading the negative electrode material for lithium ion secondary battery, an organic binder, a solvent, etc., a kneaded material such as a pellet, and the like are stacked on a current collector and integrated by a roll, a press, etc. You may produce the negative electrode for ion secondary batteries.

  The organic binder is not particularly limited. For example, styrene-butadiene copolymer; methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, (meth) acrylonitrile, hydroxyethyl (meth) acrylate, and the like. A (meth) acrylic copolymer obtained by copolymerizing an ethylenically unsaturated carboxylic acid ester of the above and an ethylenically unsaturated carboxylic acid such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid and maleic acid; And polymer compounds such as vinylidene chloride, polyethylene oxide, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polyimide, and polyamideimide. “(Meth) acrylate” means “acrylate” and “methacrylate” corresponding thereto. The same applies to other similar expressions such as “(meth) acrylic copolymer”.

  These organic binders include those dispersed or dissolved in water or those dissolved in an organic solvent such as N-methyl-2-pyrrolidone (NMP) depending on the respective physical properties. Among these, an organic binder whose main skeleton is polyacrylonitrile, polyimide or polyamideimide is preferable because of its excellent adhesion, and as described later, the heat treatment temperature during the preparation of the negative electrode is low, and the flexibility of the electrode is excellent. Therefore, an organic binder whose main skeleton is polyacrylonitrile is more preferable. Examples of the organic binder having polyacrylonitrile as a main skeleton include, for example, a product obtained by adding acrylic acid for imparting adhesiveness and a linear ether group for imparting flexibility to a polyacrylonitrile skeleton (LSR7 (trade name), Hitachi Kasei Co., Ltd.) can be used.

The content ratio of the organic binder in the negative electrode material layer of the lithium ion secondary battery negative electrode is preferably 0.1% by mass to 20% by mass, and more preferably 0.2% by mass to 20% by mass. Preferably, it is 0.3 mass%-15 mass%.
Adhesiveness is good when the content ratio of the organic binder is 0.1% by mass or more, and the negative electrode tends to be prevented from being destroyed by expansion and contraction during charge and discharge. On the other hand, when it is 20% by mass or less, the electrode resistance tends to be suppressed from increasing.

Further, as a thickener for adjusting the viscosity, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, polyacrylic acid or a salt thereof, oxidized starch, phosphorylated starch, casein, etc., the organic binder described above May be used together.
The solvent used for mixing the organic binder is not particularly limited, and N-methyl-2-pyrrolidone, dimethylacetamide, dimethylformamide, γ-butyrolactone and the like are used.

  In addition, you may add a conductive support agent to the said coating liquid. Examples of the conductive assistant include carbon black, acetylene black, oxides showing conductivity, and nitrides showing conductivity. These conductive assistants may be used alone or in combination of two or more. It is preferable that the content rate of a conductive support agent is 0.1 mass%-20 mass% in a negative electrode material layer (100 mass%).

  The material of the current collector is not particularly limited, and examples thereof include aluminum, copper, nickel, titanium, stainless steel, porous metal (foamed metal), and carbon paper. The shape of the current collector is not particularly limited, and examples thereof include a foil shape, a perforated foil shape, and a mesh shape.

The method for applying the coating solution to the current collector is not particularly limited. For example, a metal mask printing method, an electrostatic coating method, a dip coating method, a spray coating method, a roll coating method, a doctor blade method, a gravure coating method. And a screen printing method. After the application, it is preferable to perform a pressure treatment with a flat plate press, a calendar roll, or the like as necessary.
Further, the integration of the kneaded material and the current collector, which includes a component for constituting the negative electrode material layer and is formed into a sheet shape, a pellet shape, or the like, for example, integration by a roll, integration by a press, and It can carry out by integration by these combinations.

The negative electrode material layer formed on the current collector or the negative electrode material layer integrated with the current collector is preferably heat-treated according to the type of organic binder used. For example, when using an organic binder having polyacrylonitrile as the main skeleton, heat treatment is preferably performed at 100 ° C. to 180 ° C., and when using an organic binder having polyimide or polyamideimide as the main skeleton, 150 is used. It is preferable to heat-treat at a temperature of from 450C to 450C.
This heat treatment increases the strength by removing the solvent and curing the organic binder, thereby improving the adhesion between the negative electrode material and the adhesion between the negative electrode material and the current collector. Note that these heat treatments are preferably performed in an inert atmosphere such as helium, argon, nitrogen, or a vacuum atmosphere in order to prevent oxidation of the current collector during the treatment.

In addition, the negative electrode is preferably pressed (pressurized) before the heat treatment. The electrode density can be adjusted by applying pressure treatment. It The negative electrode for a lithium ion secondary battery of the present invention, it is preferable that the electrode density of ^{1.40g / cm 3 ~1.90g / cm 3} , a 1.50g / cm ³ ~1.85g / cm 3 it is more ^preferable, and further preferably from ^{1.60g / cm 3 ~1.80g / cm 3} . As the electrode density is higher, the volume capacity of the negative electrode tends to be improved, and the adhesion between the negative electrode material and the adhesion between the negative electrode material and the current collector tend to be improved.

<Lithium ion secondary battery>
The lithium ion secondary battery of the present invention includes a positive electrode, the negative electrode, and an electrolyte. The lithium ion secondary battery may further include a separator as necessary.
For example, the negative electrode can be a lithium ion secondary battery by disposing a positive electrode opposite to each other with a separator interposed therebetween and injecting an electrolytic solution containing an electrolyte.

  The positive electrode can be obtained by forming a positive electrode layer on the current collector surface in the same manner as the negative electrode. As the current collector for the positive electrode, the same current collector as described for the negative electrode can be used.

The material used for the positive electrode of the lithium ion secondary battery of the present invention (also referred to as positive electrode material) may be any compound that can be doped or intercalated with lithium ions, such as lithium cobaltate (LiCoO ₂ ), lithium nickelate. (LiNiO ₂₎ lithium manganate (LiMnO _2), and the like.

The positive electrode is prepared by mixing the positive electrode material described above, an organic binder such as polyvinylidene fluoride, and a solvent such as N-methyl-2-pyrrolidone or γ-butyrolactone, and this positive electrode coating solution Is applied to at least one surface of a current collector such as an aluminum foil, then the solvent is removed, and pressure treatment is performed as necessary.
In addition, you may add a conductive support agent to a positive electrode coating liquid. Examples of the conductive assistant include carbon black, acetylene black, oxides showing conductivity, and nitrides showing conductivity. These conductive assistants may be used alone or in combination of two or more.

  The electrolyte solution used for the lithium ion secondary battery of the present invention is not particularly limited, and a known one can be used. For example, a non-aqueous lithium ion secondary battery can be manufactured by using a solution obtained by dissolving an electrolyte in an organic solvent as the electrolytic solution.

As the electrolyte, for _{example, LiPF 6, LiClO 4, LiBF} 4, LiClF 4, LiAsF 6, LiSbF 6, LiAlO 4, LiAlCl 4, LiN (CF 3 SO 2) 2, LiN (C 2 F 5 SO 2) 2 and Examples include LiC (CF ₃ SO ₂ ) ₃ , LiCl, and LiI.

  The organic solvent only needs to dissolve the electrolyte, and examples thereof include propylene carbonate, ethylene carbonate, diethyl carbonate, ethyl methyl carbonate, vinyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, and 2-methyltetrahydrofuran.

  Various known separators can be used as the separator. Specific examples of the separator include a paper separator, a polypropylene separator, a polyethylene separator, a glass fiber separator, and the like.

  As a method for manufacturing a lithium ion secondary battery, for example, first, two electrodes of a positive electrode and a negative electrode are wound through a separator. The obtained spiral wound group is inserted into a battery can, and a tab terminal previously welded to a negative electrode current collector is welded to the bottom of the battery can. Inject the electrolyte into the obtained battery can, weld the tab terminal that was previously welded to the positive electrode current collector to the battery lid, and place the lid on the top of the battery can via an insulating gasket A battery is obtained by caulking and sealing the part where the lid and the battery can are in contact.

  The form of the lithium ion secondary battery of the present invention is not particularly limited. Specifically, a lithium ion secondary battery such as a paper type battery, a button type battery, a coin type battery, a stacked type battery, a cylindrical type battery, and a square type battery can be given.

  The above-described negative electrode material for a lithium ion secondary battery according to the present invention has been described as being used for a lithium ion secondary battery. However, it can be applied to any electrochemical device that uses a charge / discharge mechanism to insert and desorb lithium ions. It is.

  EXAMPLES Hereinafter, although a synthesis example, an Example, and a comparative example are given and this invention is demonstrated more concretely, this invention is not restrict | limited to the following Example. Unless otherwise specified, “part” and “%” are based on mass.

[Example 1]
(Preparation of negative electrode material)
Bulk silicon oxide (High Purity Chemical Laboratory Co., Ltd., standard 10 mm to 30 mm square) was coarsely pulverized with a mortar to obtain silicon oxide particles. The silicon oxide particles are further pulverized by a vibration mill (small vibration mill NB-0, Nichito Kagaku Co., Ltd.) and then sized with a 300M (300 mesh) test sieve to obtain fine particles having an average particle diameter of 5 μm. It was.

  995 g of the obtained silicon oxide fine particles and 10 g of coal-based pitch (fixed carbon 50%) are put into a mixing device (Rocking Mixer RM-10G, Aichi Electric Co., Ltd.) and mixed for 5 minutes, and then heat treatment made of alumina. The container was filled. After filling the heat treatment container, this was heat treated in an atmosphere firing furnace under a nitrogen atmosphere at 1000 ° C. for 5 hours to obtain a heat treated product.

  The obtained heat-treated product was crushed with a mortar and sieved with a 300M (300 mesh) test sieve to obtain a negative electrode material having an average particle diameter of 5.0 μm.

<Measurement of average particle diameter>
A measurement sample (5 mg) was placed in a 0.01% aqueous solution of a surfactant (Esomine T / 15, Lion Corporation) and dispersed with a vibration stirrer. The obtained dispersion was put into a sample water tank of a laser diffraction particle size distribution analyzer (SALD3000J, Shimadzu Corporation), circulated with a pump while applying ultrasonic waves, and measured by a laser diffraction method. The measurement conditions were as follows. The volume cumulative 50% particle size (D50%) of the obtained particle size distribution was defined as the average particle size. Hereinafter, in the examples, the average particle size was measured in the same manner.
・ Light source: Red semiconductor laser (690nm)
Absorbance: 0.10 to 0.15
-Refractive index: 2.00-0.20i

<Method for measuring carbon content>
The carbon content of the negative electrode material was measured by high-frequency firing-infrared analysis. The high-frequency firing-infrared analysis method is an analysis method in which a sample is heated and burned with an oxygen stream in a high-frequency furnace, carbon and sulfur in the sample are converted into CO ₂ and SO ₂ , respectively, and quantified by an infrared absorption method. The measuring apparatus and measurement conditions are as follows.
・ Device: Simultaneous carbon sulfur analyzer (CSLS600, LECO Japan GK)
・ Frequency: 18MHz
・ High frequency output: 1600W
Sample weight: about 0.05g
・ Analysis time: Automatic mode is used in the instrument setting mode.
Standard sample: Leco 501-224 (C: 3.03% ± 0.04%, S: 0.055% ± 0.002%)
-Number of measurements: 2 times (the value of carbon content in Table 2 is the average value of the two measurements)

<Measurement of R value>
Using the Raman spectrum measuring apparatus (NSR-1000 type, JASCO Corporation), the obtained spectrum was analyzed for the anode material with the following range as the baseline. The measurement conditions were as follows.
・ Laser wavelength: 532 nm
・ Irradiation intensity: 1.5mW (measured value with laser power monitor)
・ Irradiation time: 60 seconds ・ Irradiation area: 4 μm ²
Measurement range: 830 cm ^{−1 to} 1940 cm ⁻¹
Baseline: 1050 cm ^{−1 to} 1750 cm ⁻¹

The wave number of the obtained spectrum is the wave number of each peak obtained by measuring the reference substance inden (Wako Class 1, Wako Pure Chemical Industries, Ltd.) under the same conditions as described above, and the theoretical wave number of each peak of indene. Correction was performed using a calibration curve obtained from the difference between the two.
Among the profile obtained after the correction, 1360 cm ^-1 to the intensity of the peak appearing in the vicinity of Id, and Ig the intensity of a peak appearing near 1580 cm ^-1, at both peak intensity ratio Id / Ig of (D / G) It calculated | required as R value.

<Measurement of BET specific surface area>
Using a high-speed specific surface area / pore distribution measuring device (ASAP2020, Micromeritics Japan LLC), nitrogen adsorption at a liquid nitrogen temperature (77K) was measured by a five-point method, and the BET method (relative pressure range: 0.00). 05 to 0.2).

<Measurement of crystallite size of silicon>
The negative electrode material was analyzed using a powder X-ray diffractometer (MultiFlex (2 kW), Rigaku Corporation). The size of the silicon crystallite was calculated from the half width of the peak attributed to the crystal plane of Si (111) existing in the vicinity of 2θ = 28.4 °, using the Scherrer equation. The measurement conditions were as follows.
-Radiation source: CuKα ray (wavelength: 0.154056 nm)
Measurement range: 2θ = 10 ° to 40 °
・ Sampling step width: 0.02 °
・ Scanning speed: 1 ° / min ・ Tube current: 40 mA
・ Tube voltage: 40kV
・ Divergent slit: 1 °
・ Scatter slit: 1 °
・ Reception slit: 0.3mm

  The obtained profile was subjected to background (BG) removal and peak separation using the structure analysis software (JADE6, Rigaku Corporation) attached to the above apparatus with the following settings.

[Kα2 peak removal and background removal]
・ Kα1 / Kα2 intensity ratio: 2.0
BG curve up and down (σ) from BG point: 0.0

[Specify peak]
-Peak attributed to Si (111): 28.4 ° ± 0.3 °
・ Peak attributed to SiO ₂ : 21 ° ± 0.3 °

[Peak separation]
Profile shape function: Pseudo-Voigt
・ Background fixed

The half width of the peak attributed to Si (111) derived from the structure analysis software with the above settings was read, and the silicon crystallite size D was calculated from the following Scherrer equation.
D = Kλ / B cos θ
B = ( _Bobs ² −b ² ) ^1/2
D: Size of crystallite (nm)
K: Scherrer constant (0.94)
λ: Source wavelength (0.154056 nm)
θ: Measurement half-width peak angle B _obs : Half-width (measured value obtained from structural analysis software)
b: Measurement half width of standard silicon (Si)

(Production method of negative electrode)
3.75% by mass of negative electrode material powder prepared by the above method, 71.25% by mass of artificial graphite (Hitachi Chemical Co., Ltd.) as a carbon negative electrode material (produced negative electrode material: artificial graphite = 5: 95 (mass ratio)) , 15% by mass of acetylene black (Electrochemical Co., Ltd.) powder as a conductive additive, and an organic binder (LSR-7, Hitachi Chemical Co., Ltd.) having polyacrylonitrile as the main skeleton as a binder, then kneaded A uniform slurry was produced. In addition, the addition amount of the binder was adjusted so that it might become 10 mass% with respect to the total mass of a slurry. This slurry is applied to the glossy surface of the electrolytic copper foil so that the coating amount is 10 mg / cm ^2, and after preliminary drying at 90 ° C. for 2 hours, the density is 1.65 g / cm ³ with a roll press. Adjusted. Thereafter, a curing treatment was performed by drying at 120 ° C. for 4 hours in a vacuum atmosphere to obtain a negative electrode.

(Production of lithium ion secondary battery)
The electrode obtained above was used as a negative electrode, lithium metal as a counter electrode, and ethylene carbonate / ethyl methyl carbonate (3: 7 volume ratio) and vinyl carbonate (VC) (1.0% by mass) containing 1M LiPF ₆ as an electrolyte. A 2016 type coin cell was prepared using a mixed liquid of the above, a polyethylene microporous film having a thickness of 25 μm as a separator, and a copper plate having a thickness of 250 μm as a spacer.

(Battery evaluation)
<Initial charge capacity, initial discharge capacity, and initial charge / discharge efficiency>
The battery obtained above was placed in a thermostatic chamber maintained at 25 ° C., charged at a constant current of 0.43 mA (0.32 mA / cm ² ) until it reached 0 V, and then the current was 0 at a constant voltage of 0 V. The battery was further charged until it decayed to a value corresponding to 0.043 mA, and the initial charge capacity was measured. After charging, the battery was discharged after a 30-minute pause. Discharge was performed at 0.43 mA (0.32 mA / cm ² ) until it reached 1.5 V, and the initial discharge capacity was measured. At this time, the capacity was converted per mass of the used negative electrode material (total mass of the produced negative electrode material and artificial graphite mixed). A value obtained by dividing the initial discharge capacity by the initial charge capacity was calculated as the initial charge / discharge efficiency (%).

<Cycle characteristics>
Each battery obtained above was placed in a thermostat kept at 25 ° C., charged at 0.45 mA / cm ² until it became 0 V, and then at a constant voltage of 0 V, the current was 0.09 mA / cm. ^The battery was further charged until it decayed to a value corresponding to ² . After charging, the battery was discharged after a 30-minute pause. Discharging was performed at 0.45 mA / cm ² until 1.5V was reached. This charge-discharge was set as one cycle, and the cycle characteristics were evaluated by performing a cycle test 10 times.
Cycle characteristics = discharge capacity at 10th cycle / discharge capacity at 1st cycle

[Examples 2 to 11, Comparative Example 2]
In the production of the negative electrode material of Example 1, a negative electrode material was produced in the same manner as in Example 1 except that the mixing ratio of silicon oxide particles and coal pitch was changed as shown in Table 1 below, and the same evaluation was performed. Went.

[Comparative Example 1]
In the production of the negative electrode material of Example 1, the negative electrode material was produced in the same manner as in Example 1 except that the coal pitch was not mixed and only the silicon oxide particles were heat-treated, and the same evaluation was performed. It was. The evaluation results of the above examples and comparative examples are shown in Table 2 below.

  From the results of Table 2, the negative electrode materials for lithium ion secondary batteries shown in Examples 1 to 11 were compared with Comparative Example 1 in which carbon coating was not performed and in Comparative Example 2 in which the carbon coating amount exceeded 10% by mass. It can be seen that the material has a high discharge capacity, excellent initial charge / discharge efficiency, and excellent cycle characteristics.

[Examples 12 to 15]
In the production of the negative electrode material of Example 7, the heat treatment temperature was changed to 900 ° C. (Example 12), 950 ° C. (Example 13), 1050 ° C. (Example 14), and 1100 ° C. (Example 15), respectively. In the same manner as in Example 7, negative electrode materials were produced and evaluated in the same manner.

[Comparative Example 3]
In the production of the negative electrode material of Example 7, a negative electrode material was produced in the same manner as in Example 7 except that the heat treatment temperature was changed to 850 ° C., and the same evaluation was performed.
In the negative electrode material produced in Comparative Example 1, a diffraction peak attributed to Si (111) was not observed, so “ND” is described in Table 3.

[Comparative Example 4]
A negative electrode material was produced in the same manner as in Example 7 except that the heat treatment temperature was changed to 1150 ° C. in the production of the negative electrode material of Example 7, and the same evaluation was performed.

  From the results of Table 3, the negative electrode materials for lithium ion secondary batteries shown in Examples 12 to 15 are Comparative Example 3 in which silicon crystallites are not observed and Comparative Example in which the size of silicon crystallites is 11.0 nm. It can be seen that it is a negative electrode material having a large initial discharge capacity, excellent initial charge / discharge efficiency, and excellent cycle characteristics as compared with the negative electrode material No. 4.

10 carbon 12 carbon fine particles 20 silicon oxide particles

Claims (3)

A part or all of the surface of the silicon oxide particles has carbon, and the carbon is contained in an amount of 5% by mass to 10% by mass. In the X-ray diffraction spectrum using CuKα rays as a radiation source, Si (111) The crystallite size of silicon calculated from the diffraction peak is 2.0 nm to 8.0 nm.
The carbon has an R value of 0.5 or more ,
However, negative electrode materials for lithium ion secondary batteries excluding those doped with lithium, magnesium or calcium. A negative electrode material layer comprising a current collector and a negative electrode material for a lithium ion secondary battery according to claim 1 provided on the current collector,
A negative electrode for a lithium ion secondary battery.   A lithium ion secondary battery comprising: a positive electrode; a negative electrode for a lithium ion secondary battery according to claim 2; and an electrolyte.