JP2019033102A - Negative electrode material for lithium ion secondary battery, negative electrode for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Abstract

To provide a negative electrode material for a lithium ion secondary battery, capable of constructing a lithium ion secondary battery having excellent initial charging capacity, initial charging and discharging efficiency, and life.SOLUTION: A negative electrode material for a lithium ion secondary battery includes: a silicon oxide particle; a simple substance of a carbon existed in a part or a whole part of a front surface of the silicon oxide particle; and an organic material existed in one part or the whole part of the front surface of the silicon oxide particle in which the simple substance of the carbon is existed in the surface.SELECTED DRAWING: None

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 using an element having a high theoretical capacity and capable of occluding and releasing lithium ions (hereinafter also referred to as “specific element”. The element containing the specific element is also referred to as “specific element body”). Material 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 a silicon crystal obtained by the Scherrer method based on the half-value width of the diffraction line is disclosed in Patent Document 1. The surface of a particle having a structure in which silicon crystallites are dispersed in a silicon compound and having a size of 1 to 500 nm is coated with carbon. A silicon 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 accompanying the 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 2-30 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 technique 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 secondary lithium ion 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 technique of Patent Document 3, the negative electrode material effective for non-aqueous electrolyte secondary battery negative electrode having excellent cycle characteristics is obtained by solving the expansion of the electrode, which is a defect of silicon oxide, and the expansion of the battery due to gas generation. It is supposed to be done.

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 to be able to release more ions. 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 and the initial charge / discharge efficiency. On the other hand, further improvement of the life of the lithium ion secondary battery using the recovery rate after charging and discharging as an index is also an important issue.
The present invention has been made in view of the above requirements, and has an initial discharge capacity, an initial charge / discharge efficiency, and a negative electrode material for a lithium ion secondary battery excellent in life, a negative electrode for a lithium ion secondary battery, and a lithium ion secondary. It is an object to provide a battery.

Specific means for solving the above problems are as follows.
<1> Silicon oxide particles, a simple substance of carbon existing on a part or all of the surface of the silicon oxide particle, and a part or all of the surface of the silicon oxide particle where the simple substance of carbon exists on the surface A negative electrode material for a lithium ion secondary battery, comprising: an organic substance present.

<2> The negative electrode material for a lithium ion secondary battery according to <1>, wherein the organic material includes a water-soluble organic material having at least one selected from the group consisting of a carboxyl group and a hydroxy group.

<3> The first component, wherein the organic substance is at least one selected from the group consisting of polysaccharides, gelatin, casein, and water-soluble polyether, and monosaccharides, disaccharides, oligosaccharides, amino acids, gallic acid, tannins, saccharin And a second component that is at least one selected from the group consisting of a saccharin salt and a butynediol, The negative electrode material for a lithium ion secondary battery according to <1> or <2>.

<4> Any one of <1> to <3>, wherein the content ratio of the carbon simple substance is 0.5 mass% to 10.0 mass% of the total amount of the silicon oxide particles and the carbon simple substance. The negative electrode material for lithium ion secondary batteries as described in 2.

<5> An X-ray diffraction spectrum using CuKα rays as a radiation source has a diffraction peak attributed to Si (111), and the silicon crystallite size calculated from the diffraction peak is 2.0 nm to 8. The negative electrode material for a lithium ion secondary battery according to any one of <1> to <4>, which is 0 nm.

<6> A negative electrode for a lithium ion secondary battery, comprising: a current collector; and a negative electrode material layer including the negative electrode material according to any one of <1> to <5>, provided on the current collector. .

A lithium ion secondary battery comprising a <7> positive electrode, a negative electrode for a lithium ion secondary battery according to <6>, 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 the initial stage discharge capacity, initial stage charge / discharge efficiency, and lifetime 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 the carbon simple substance 10 in the negative electrode material, and (B) describes another aspect of the state of the carbon simple substance 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.
Furthermore, in this specification, the amount in the composition is the total amount 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. means.

<Anode material for lithium ion secondary battery>
The negative electrode material for a lithium ion secondary battery of the present invention (hereinafter sometimes abbreviated as “negative electrode material”) is composed of silicon oxide particles and a simple substance of carbon existing on part or all of the surface of the silicon oxide particles. And part or all of the surface of silicon oxide particles having carbon alone (hereinafter, silicon oxide particles having carbon alone may be abbreviated as “SiO-C particles”). And organic matter present in A lithium ion secondary battery using the negative electrode material of the present invention having such a configuration is excellent in initial discharge capacity, initial charge / discharge efficiency, and recovery rate after charge / discharge.

(Silicon oxide particles)
The negative electrode material of the present invention contains silicon oxide particles. The silicon oxide constituting the silicon oxide particles may be an oxide containing a silicon atom, and examples thereof include silicon monoxide (also referred to as silicon oxide), silicon dioxide, and silicon suboxide. These may be used individually by 1 type and may be used in combination of multiple types.
Among silicon oxides, silicon oxide and silicon dioxide are generally represented as silicon monoxide (SiO) and silicon dioxide (SiO ₂ ), respectively, but the surface state (eg, the presence of an oxide film) or Depending on the state of formation of the compound, the measured value (or conversion value) of the contained element may be represented by the composition formula SiOx (x is 0 <x ≦ 2). In this case, the silicon oxide according to the present invention is also used. . 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 a silicon oxide, silicon monoxide, etc.

  The silicon oxide particles preferably have a structure in which silicon crystallites are dispersed in silicon oxide. In the case where silicon crystallites are dispersed in silicon oxide particles, when X-ray powder diffraction (XRD) measurement using CuKα rays as a radiation source is performed, Si (111) is around 2θ = 28.4 °. A diffraction peak attributed to is observed. When silicon crystallites are present in the silicon oxide particles, it is easy to obtain a high initial discharge capacity and a good initial charge / discharge efficiency.

The size of silicon crystallites is preferably 8.0 nm or less, and more preferably 6.0 nm or less. When the crystallite size is 8.0 nm or less, the silicon crystallites are less likely to be localized in the silicon oxide particles, so that lithium ions are easily diffused in the silicon oxide particles, and good charge / discharge is achieved. Capacity is easy to obtain.
Further, the size of the silicon crystallite is preferably 2.0 nm or more, and more preferably 3.0 nm or more. When the crystallite size is 2.0 nm or more, the reaction between lithium ions and silicon oxide is controlled, and good charge / discharge efficiency is easily obtained.

  The size of the silicon crystallite is the half-value width of the diffraction peak around 2θ = 28.4 ° attributed to Si (111) obtained by powder X-ray diffraction analysis using a CuKα ray having a wavelength of 0.154056 nm as a radiation source. Therefore, it can be obtained using Scherrer's equation.

  The structure in which silicon crystallites are dispersed in the silicon oxide particles is produced by, for example, heat-treating the silicon oxide particles in a temperature range of 700 ° C. to 1300 ° C. in an inert atmosphere to disproportionate. Can do. Moreover, it can produce by adjusting the heating temperature in the heat processing for providing the simple substance of below-mentioned carbon to a silicon oxide particle. 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.

  The silicon oxide particles can be produced by pulverizing and classifying when a bulk silicon oxide having a size of 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 obtained by secondary pulverization is preferably 0.1 μm to 20 μm, preferably 0.5 μm to 10 μm, in accordance with the final desired negative electrode material size. More preferred. The average particle diameter is the 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.

(Carbon simple substance)
The negative electrode material of the present invention contains a simple substance of carbon existing on a part or all of the surface of silicon oxide particles. The presence of carbon alone on part or all of the surface of the silicon oxide particles can alleviate expansion and contraction associated with insertion and extraction of lithium ions, and decrease the capacity of silicon oxide per unit mass. Can be suppressed. For this reason, it is considered that the initial discharge capacity and the initial charge / discharge efficiency are improved.

  The content of the simple carbon is preferably 0.5% by mass to 10.0% by mass in the total amount of the silicon oxide particles and the simple carbon. By setting it as such a structure, it exists in the tendency for the initial stage discharge capacity and initial stage charge-and-discharge efficiency to improve more. The carbon content is preferably 1.0% by mass to 9.0% by mass, and more preferably 2.0% by mass to 8.0% by mass.

  The content (mass basis) of the simple substance of carbon can be obtained by high-frequency firing-infrared analysis. In the high-frequency firing-infrared analysis method, for example, a carbon-sulfur simultaneous analyzer (CSLS600, LECO Japan LLC) can be used. At this time, the negative electrode material is heated to a temperature at which the organic matter is decomposed or higher (for example, 300 ° C.), and carbon derived from the organic matter is removed in advance, so that the amount of carbon in the total amount of silicon oxide particles and carbon alone The content rate of a simple substance can be measured.

The simple substance of carbon is preferably low crystalline. Low crystallinity means that the R value obtained by the method shown below is 0.5 or more.
Single 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, in the vicinity of 1580 cm ^-1 and Ig, the both peaks When the intensity ratio 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. 0.8 to 1.2 or less is more preferable. 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 usually a peak identified as corresponding to a single 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.

  The method for imparting simple carbon to the surface of the silicon oxide particles is not particularly limited, and examples thereof include a wet mixing method, a dry mixing method, and a chemical vapor deposition method. The wet mixing method or the dry mixing method is preferable from the viewpoint that the reaction system can be uniformly controlled and the shape of the negative electrode material can be maintained.

  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 the carbon source solution is adhered to the surface of the silicon oxide particles, and a solvent is used as necessary. Then, the carbon source can be carbonized by heat treatment in an inert atmosphere to give a simple substance of carbon. 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. The simple substance of carbon can be provided 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 the chemical vapor deposition method, a known method can be applied. For example, the silicon oxide particles are heat-treated in an atmosphere containing a gas obtained by vaporizing a carbon source, thereby imparting simple carbon to the surface of the silicon oxide particles. can do.

  In the case of applying carbon simple substance to the surface of 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 simple substance by heat treatment. Specifically, polymer compounds such as phenol resin, styrene resin, polyvinyl alcohol, polyvinyl chloride, polyvinyl acetate, polybutyral; ethylene heavy end pitch, coal-based pitch, petroleum pitch, coal tar pitch, asphalt decomposition pitch, Examples thereof include PVC pitches produced by thermally decomposing polyvinyl chloride and the like, naphthalene pitches such as naphthalene pitch produced by polymerizing in the presence of a super strong acid, and polysaccharides such as starch and cellulose. 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 chemical vapor deposition, the carbon source can be gaseous or easily gasified among aliphatic hydrocarbons, aromatic hydrocarbons, alicyclic hydrocarbons, etc. Preference is given to using possible compounds. 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 the simple substance of carbon low crystalline and from the viewpoint of generating silicon crystallites in a desired size, it is preferably 1300 ° C. or less, more preferably 1200 ° C. or less, and more preferably 1100 ° C. More preferably, it is as follows.

  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, 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.

  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 a simple substance of carbon to the surface of silicon oxide particles, for example, as a simple substance of carbon imparted to the surface of silicon oxide particles, amorphous carbon such as soft carbon or hard carbon; graphite A method using a carbonaceous material such as; According to this method, a negative electrode material having a shape in which the carbon simple substance 10 is present as the particle on the surface of the silicon oxide particle 20 as shown in FIG. 4 and FIG. As a method using a carbonaceous substance, a wet mixing method or a dry mixing method can be applied.

  When applying the wet mixing method, the carbonaceous material particles and the organic compound (compound capable of leaving carbon alone by heat treatment) are mixed to form a mixture, and the mixture and the silicon oxide particles are mixed. Is further produced by attaching the mixture to the surface of the silicon oxide particles and heat-treating the mixture. The organic compound is not particularly limited as long as it is a compound that can leave a simple 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 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 performing. 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 particles. The heat treatment conditions for applying the dry mixing method can be the heat treatment conditions for carbonizing the carbon source.

(organic matter)
The negative electrode material of this invention contains the organic substance which exists in a part or all of the surface of SiO-C particle | grains. By including the organic substance, the specific surface area of the negative electrode material is reduced, and the reaction with the electrolytic solution is suppressed. Therefore, it is considered that the recovery rate after charging and discharging is improved.

  Furthermore, when the negative electrode material contains an organic substance, the capacity retention rate can be improved without using fluoroethylene carbonate (FEC). FEC is generally used as an additive for an electrolytic solution in order to suppress a reaction with the electrolytic solution caused by expansion and contraction of silicon when silicon is used as a negative electrode active material. However, FEC may decompose and generate gas. By using the negative electrode material of the present invention, it becomes possible to omit or reduce the amount of FEC, and to prevent or suppress the generation of gas due to the decomposition of FEC.

  The organic matter content is preferably 0.1% by mass to 2.0% by mass in the whole negative electrode material. Within the above range, the effect of improving the recovery rate after charging and discharging tends to be sufficiently obtained while suppressing the decrease in conductivity. The organic content in the whole negative electrode material is preferably 0.2% by mass to 1.5% by mass, and more preferably 0.3% by mass to 1.0% by mass.

Whether or not the negative electrode material has an organic substance is, for example, heated to a temperature (for example, 300 ° C.) that is higher than the temperature at which the organic substance decomposes and is lower than the temperature at which the simple substance of carbon decomposes. And it can confirm by measuring the mass of the negative electrode material after organic substance decomposed | disassembled. Specifically, when the mass of the negative electrode material before heating is Ag, and the mass of the negative electrode material after heating is Bg, the mass change rate represented by {(AB) / A} × 100 is 0. If it is 1% or more, it can be determined that the negative electrode material contains an organic substance.
The rate of change is preferably 0.1% to 2.0%, and more preferably 0.3% to 1.0%. When the rate of change is 0.1% or more, a sufficient amount of organic matter is present on the surface of the SiO—C particles, and the effects of the present invention tend to be sufficiently obtained.

  From the viewpoint of efficiently presenting an organic substance on part or all of the surface of the SiO-C particles, the organic substance preferably contains a water-soluble organic substance, and has at least one selected from the group consisting of a carboxyl group and a hydroxy group. More preferably, it contains a water-soluble organic substance.

  The organic substance is one or more selected from the group consisting of polysaccharides, gelatin, casein and water-soluble polyether as the first component, and monosaccharides, disaccharides, oligosaccharides, amino acids, gallic acid as the second component, And one or more selected from the group consisting of tannin, saccharin, saccharin salt and butynediol. In the present invention, a polysaccharide means a compound having a structure in which 10 or more monosaccharide molecules are bonded, and an oligosaccharide means a compound having a structure in which 3 to 10 monosaccharide molecules are bonded.

Specific examples of polysaccharides include starch, starch derivatives, dextrin, dextrin derivatives, cyclodextrin, cellulose derivatives, alginic acid, alginic acid derivatives, pullulan, glycogen, agarose, carrageenan, pectin, lignin derivatives, xyloglucan, etc. Can be mentioned.
Specific examples of monosaccharides include arabinose, glucose, mannose, and galactose.
Specific examples of the disaccharide include sucrose, maltose, lactose, cellobiose and trehalose.
Specific examples of the oligosaccharide include raffinose, stachyose, maltotriose and the like.
Specific amino acids include glycine, alanine, valine, leucine, isoleucine, serine, threonine, cysteine, cystine, methionine, aspartic acid, glutamic acid, lysine, arginine, phenylalanine, tyrosine, histidine, tryptophan, proline, oxyproline, glycine And sylglycine.
Specific examples of tannins include tea catechin and straw catechin.

  The first component preferably contains at least one polysaccharide, and more preferably at least one selected from the group consisting of starch, dextrin and pullulan. The first component is considered to decrease the specific surface area by being present so as to cover part or all of the surface of the negative electrode material. As a result, the reaction between the negative electrode material and the electrolytic solution is suppressed, which is considered to contribute to the improvement of the life of the lithium ion secondary battery.

  The second component preferably includes at least one selected from the group consisting of disaccharides and monosaccharides, and more preferably includes at least one selected from the group consisting of maltose, lactose, trehalose and glucose. It is considered that the second component is taken into the first component and suppresses the solubility of the precipitated film formed from the first component in water or the electrolytic solution.

  When the organic substance includes the first component and the second component, the mass ratio (first component: second component) is preferably 1: 1 to 25: 1, and preferably 3: 1 to 20: 1. Is more preferably 5: 1 to 15: 1. When the mass ratio is within the above range, the retention rate and the recovery rate of the storage characteristics tend to be improved.

There is no particular limitation on the method for causing the organic substance to be present on part or all of the surface of the SiO—C particles. For example, the organic substance can be attached to the SiO-C particles by putting the SiO-C particles in a liquid in which the organic substance is dissolved or dispersed and stirring as necessary. Thereafter, the SiO—C particles to which the organic matter adheres are taken out from the liquid and dried as necessary, whereby the SiO—C particles to which the organic matter adheres to the surface can be obtained.
The temperature of the aqueous solution during stirring is not particularly limited, and can be selected from, for example, 5 ° C to 95 ° C. The temperature in particular at the time of drying is not restrict | limited, For example, it can select from 50 to 200 degreeC. The content rate of the organic substance in the aqueous solution is not particularly limited, and can be selected from, for example, 0.1% by mass to 20% by mass.

Hereinafter, an example of the negative electrode material of the present invention will be described with reference to the drawings.
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, the carbon simple substance 10 covers the entire surface of the silicon oxide particles 20. In FIG. 2, the simple substance of carbon 10 covers the entire surface of the silicon oxide particles 20, but the thickness varies. In FIG. 3, the simple substance of carbon 10 is partially present on the surface of the silicon oxide particle 20, and the surface of the silicon oxide particle 20 is partially exposed. In FIG. 4, carbon single-particle particles 10 having a particle diameter smaller than that of the silicon oxide particles 20 are present on the surface of the silicon oxide particles 20. FIG. 5 is a modification of FIG. 4, and the particle shape of the carbon simple substance 10 is scaly. 1 to 5, the surface of silicon oxide particles 20 (SiO—C particles) on which carbon simple substance 10 exists in this state is covered with organic substance 16.
1 to 5, the shape of the silicon oxide particles 20 is schematically represented in a spherical shape (a circle as a cross-sectional shape), but the spherical shape, the block shape, the scale shape, and the cross-sectional shape are polygonal. It may be any shape (cornered shape) or the like. 1 to 5, the entire surface of silicon oxide particles 20 (SiO-C particles) on which carbon simple substance 10 is present is covered with organic substance 16, but the present invention is not limited to this. A part may be coated.

FIG. 6 is an enlarged cross-sectional view of a part of the negative electrode material of FIGS. 1 to 3, and FIG. 6A illustrates one mode of the shape of the carbon simple substance 10 in the negative electrode material, and FIG. Then, the other aspect of the shape of the carbon simple substance 10 in a negative electrode material is demonstrated. In the case of FIGS. 1 to 3, even if the carbon simple substance 10 is entirely composed of carbon simple substance as shown in FIG. 6A, the carbon simple substance 10 is carbon as shown in FIG. 6B. The particles 12 may be configured. Although FIG. 6B shows a state in which the contour shape of the carbon particles 12 remains in the carbon simple substance 10, the carbon particles 12 may be bonded to each other. When the carbon particles 12 are bonded to each other, the carbon simple substance 10 may be entirely composed of the carbon simple substance, but a void may be included in a part of the carbon simple substance 10. Thus, a void may be included in a part of the carbon simple substance 10.
When the carbon simple substance 10 is a particle, as shown in FIG. 4, the carbon simple substance 10 particles are partially present on the surface of the silicon oxide particles 20, and the surface of the silicon oxide particles 20 is partially exposed. Alternatively, as shown in FIG. 6B, particles of the carbon simple substance 10 may exist on the entire surface of the silicon oxide particles 20.

  The volume-based average particle diameter of the negative electrode material of the present invention 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 at the time of charge and discharge are made uniform, so that the deterioration of cycle characteristics can 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 increase.

The specific surface area of the negative electrode material of the present invention is ^preferably 0.1m ² /g~15.0m 2 / ^g, more preferably 0.5m ² /g~10.0m 2 / g, 1 more preferably from ^{.0m 2 / g~7m 2 / g,} 1.0m 2 if /g~3.0m particularly preferably a specific surface area that is ² / g is less than 15.0 m ² / g, obtained The increase in the first irreversible capacity of the lithium ion secondary battery is 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 between the negative electrode material and the electrolytic solution increases, and the charge / discharge efficiency increases. 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 of the present invention has a carbon content of 0.5% to 10.0% by mass, an organic content of 0.1% to 2.0% by mass, silicon The crystallite size is preferably 2.0 nm to 8.0 nm or less, the carbon content is 1.0 mass% to 9.0 mass%, and the organic content is 0.2%. More preferably, the silicon crystallite size is 3.0 nm to 6.0 nm or less.

The negative electrode material of the present invention may be used in combination with a carbon-based 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-based negative electrode material used in combination, an improvement in charge and discharge efficiency, an improvement in cycle characteristics, an electrode expansion suppression effect, and the like can be obtained.
Conventionally known carbon-based negative electrode materials include natural graphite such as flaky natural graphite, spherical natural graphite obtained by spheroidizing flaky natural graphite, artificial graphite, amorphous carbon, and the like. Further, these carbon-based negative electrode materials may further have carbon on a part or all of the surface thereof. One or more of these carbon-based negative electrode materials may be used by mixing 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-based negative electrode material, the ratio (A: B) of the negative electrode material (A) of the present invention to the carbon-based negative electrode material (B) is appropriately determined according to the purpose. It is possible to adjust. For example, from the viewpoint of the effect of suppressing the expansion of the electrode, the mass is preferably 0.1: 99.9 to 20:80, and more preferably 0.5: 99.5 to 15:85. 1: 99-10: 90 is more preferable.

<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”) comprises a current collector and a negative electrode material for the lithium ion secondary battery of the present invention provided on the current collector. And a material layer. For example, the negative electrode for a lithium ion secondary battery of the present invention includes a negative electrode material for a lithium ion secondary battery of the present invention, an organic binder, a solvent such as a solvent or water, and, if necessary, a thickener, a conductive aid, By preparing a coating liquid in which a known carbon-based negative electrode material or the like is mixed and applying this coating liquid to a current collector, the solvent or water is dried, and pressure forming is performed to form a negative electrode material layer. can get. Generally, it is kneaded with an organic binder, a solvent or the like, and formed into a sheet shape, a pellet shape or the like.

  The organic binder is not particularly limited. Ethylene such as styrene-butadiene copolymer; methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, (meth) acrylonitrile, hydroxyethyl (meth) acrylate, etc. (Meth) acrylic copolymer obtained by copolymerization of an ethylenically unsaturated carboxylic acid ester and an ethylenically unsaturated carboxylic acid such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, maleic acid; polyvinylidene fluoride , Polymer compounds such as polyethylene oxide, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polyimide, polyamideimide, and the like. “(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 the heat treatment temperature during the preparation of the negative electrode is low as described later, 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 layer of the lithium ion secondary battery negative electrode material is preferably 0.1% by mass to 20% by mass, and preferably 0.2% by mass to 20% by mass. More preferably, it is 0.3 to 15% by mass.
When the content ratio of the organic binder is 0.1% by mass or more, the adhesion is good, and the destruction of the negative electrode due to expansion and contraction during charge / discharge is suppressed. On the other hand, it can suppress that electrode resistance becomes large because it is 20 mass% or less.

Furthermore, as a thickener for adjusting the viscosity, carboxymethylcellulose, methylcellulose, hydroxymethylcellulose, ethylcellulose, polyvinyl alcohol, polyacrylic acid (salt), oxidized starch, phosphorylated starch, casein, and the like are the organic binders described above. May be used together.
A solvent may be used as necessary when mixing the organic binder. The solvent is not particularly limited, and N-methylpyrrolidone, dimethylacetamide, dimethylformamide, γ-butyrolactone and the like are used.

  In addition, you may add a conductive support agent to a coating liquid. Examples of the conductive assistant include carbon black, acetylene black, conductive oxide, and conductive nitride. 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, and is a metal mask printing method, electrostatic coating method, dip coating method, spray coating method, roll coating method, doctor blade method, gravure coating method, screen printing. Law. After the application, it is preferable to perform a pressure treatment with a flat plate press, a calender roll or the like, if necessary.
Moreover, the integration of the coating liquid and the current collector formed into a sheet shape, a pellet shape, or the like can be performed by, for example, integration by a roll, integration by a press, or integration by a combination thereof.

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 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, and improves 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 ^{1.4g / cm 3 ~1.9g / cm 3} , a 1.5g / cm ³ ~1.85g / cm 3 it is more ^preferable, and further preferably from ^{1.6g / cm 3 ~1.8g / 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, a negative electrode of the present invention, and an electrolyte.
The negative electrode of the present invention can be formed into a lithium ion secondary battery by, for example, disposing a positive electrode 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 of the present invention. As the current collector in the positive electrode, the same current collector as described in the negative electrode of the present invention 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), and lithium manganate (LiMnO ₂₎ or the like.

The positive electrode is prepared by mixing the above positive electrode material, an organic binder such as polyvinylidene fluoride, and a solvent such as N-methyl-2-pyrrolidone or γ-butyllactone, and preparing this positive electrode coating solution. The liquid can be applied to at least one surface of a current collector such as an aluminum foil, and then the solvent can be removed by drying, followed by pressure treatment 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, conductive oxide, and conductive nitride. 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, 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, LiC ( CF ₃ SO ₂ ) ₃ , LiCl, LiI and the like.

  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 include a paper separator, a polypropylene separator, a polyethylene separator, a glass fiber separator, and the like.

  The method for producing the lithium ion secondary battery is not particularly limited. For example, it can be manufactured by the following steps. First, two electrodes, 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 the 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, and examples include lithium ion secondary batteries such as paper batteries, button batteries, coin batteries, stacked batteries, cylindrical batteries, and prismatic batteries. .

  The negative electrode material for a lithium ion secondary battery according to the present invention is not limited to a lithium ion secondary battery, and can be applied to all electrochemical devices having a charging / discharging mechanism for insertion / extraction of lithium ions.

  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, Standard: 10 mm to 30 mm square) was coarsely pulverized with a mortar to obtain silicon oxide particles. The silicon oxide particles were further pulverized by a vibration mill (small vibration mill NB-0, manufactured by Nichito Kagaku Co., Ltd.) and then sized with a 300M (300 mesh) test sieve, and the average particle diameter D50 was 5 μm. Silicon oxide particles were obtained. The average particle size was measured by the following method.

<Measurement of average particle diameter>
A measurement sample (5 mg) was placed in a 0.01% by weight aqueous solution of a surfactant (Esomine T / 15, Lion Co., Ltd.) 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.
・ Light source: Red semiconductor laser (690nm)
Absorbance: 0.10 to 0.15
-Refractive index: 2.00-0.20

  950 g of the obtained silicon oxide particles and 50 g of coal-based pitch (fixed carbon 50%) were put into a mixing device (Rocking Mixer RM-10G, Aichi Electric Co., Ltd.), mixed for 5 minutes, and then heat-treated container made of alumina. 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 SiO-C particles. Next, 0.7 g of pullulan as an organic substance was dissolved in 1 liter of pure water, 100 g of SiO-C particles were added, and the mixture was stirred with a homogenizer for 10 minutes for dispersion treatment. Thereafter, 0.1 g of trehalose was added and dried in a thermostatic bath at 150 ° C. for 12 hours to obtain SiO—C particles to which an organic substance as a negative electrode material was adhered.

<Measurement method of carbon content>
The content rate of the simple substance of carbon 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. In addition, the adhering organic substance was previously removed by heat treatment at 300 ° C. for 2 hours.
・ 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 setting mode of the device ・ Combustible material: Fe + W / Sn
Standard sample: Leco 501-024 (C: 3.03% ± 0.04% S: 0.055% ± 0.002%)
-Number of measurements: 2 times (the value of carbon content in Table 1 is the average value of the 2 measurements)

<Measurement method of organic content>
The obtained negative electrode material was heated at 300 ° C. for 2 hours in an electric furnace under the atmosphere, and the mass before and after heating was measured. The mass (A) before heating was 1.0000 g, the mass (B) after heating was 0.9926 g, and the rate of change in mass was 0.74%.

<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 GK), nitrogen adsorption at a liquid nitrogen temperature (77K) was measured by a five-point method, and the BET method (relative pressure range: 0.05). 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 full width at half maximum of the peak attributed to Si (111) derived from the structure analysis software with the above settings was read, and the size of the silicon crystallite 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)
The negative electrode material powder (97.6 parts by mass), carboxymethylcellulose (CMC) (1.2 parts by mass), and styrene-butadiene rubber (SBR, 1.2 parts by mass) produced by the above method are kneaded to obtain a uniform slurry. Was made. This slurry is applied to the glossy surface of the electrolytic copper foil so that the coating amount is 10 mg / cm ² , preliminarily dried at 90 ° C. for 2 hours, and then 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, metallic lithium as a counter electrode, ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl methyl carbonate (EMC) containing 1M LiPF ₆ as an electrolyte (volume ratio 1: 1: A 2016 type coin cell was prepared using a mixed liquid of 1) and vinylene carbonate (VC) (1.0 mass%), 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)
<First discharge capacity, initial charge / discharge efficiency>
The resultant battery above, placed in a constant temperature bath maintained at 25 ℃, 0.45mA / cm ² after the constant current charging until 0V, the current at a constant voltage of 0V is 0.09 mA / cm ² The battery was further charged until it decayed to a value corresponding to, and the initial charge capacity was measured. After charging, the battery was discharged after a 30-minute pause. Discharge was performed at 0.45 mA / cm ² until the voltage reached 1.5 V, and the initial discharge capacity was measured. At this time, the capacity was converted per mass of the negative electrode material used. A value obtained by dividing the initial discharge capacity by the initial charge capacity was calculated as the initial charge / discharge efficiency (%). The results are shown in Table 1.

<Storage characteristics (life: maintenance rate and recovery rate)>
Each of the batteries obtained in the above was placed in a constant temperature bath maintained at 25 ° C., after constant current charging until 0V at 0.45 mA / cm ^2, current at a constant voltage of 0V is 0.09 mA / cm ² The battery was further charged until it decayed to a value corresponding to. After charging, after a 30-minute pause, the battery was discharged. Discharging was performed at 0.45 mA / cm ² until 1.5V was reached.
Next, after charging for the second cycle under the same conditions as described above, the battery was placed in a constant temperature bath maintained at 70 ° C. while being charged, and stored for 72 hours. Thereafter, it was again placed in a thermostatic bath maintained at 25 ° C. and discharged at 0.45 mA / cm ² until it reached 1.5V. The ratio of the discharge capacity immediately after storage at 70 ° C. to the initial discharge capacity was defined as the retention rate of the storage characteristics.
Subsequently, the charge / discharge test of the 3rd cycle was done on the same conditions as the above with a 25 degreeC thermostat. The ratio of the discharge capacity at the third cycle to the initial discharge capacity (discharge capacity at the third cycle / initial discharge capacity) was taken as the recovery rate of the storage characteristics.

<Cycle characteristics (10 cycle capacity retention rate)>
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 a cycle test was performed 10 times. The cycle characteristics were evaluated by the discharge capacity at the 10th cycle relative to the discharge capacity at the 1st cycle (discharge capacity at the 10th cycle / discharge capacity at the 1st cycle).

[Comparative Example 1]
A 2016 type coin cell was produced in the same manner as in Example 1 except that the step of attaching the organic substance to the sieved heat-treated product was not performed, and evaluation was performed in the same manner as in Example 1. The results are shown in Table 1. The “average particle diameter of the negative electrode material” in the table is the average particle diameter of SiO—C particles (in the case where organic substances are attached, SiO—C particles in a state where organic substances are attached).

As shown in Table 1, the BET specific surface area of Example 1 in which organic substances were adhered to SiO—C particles was 1.3 m ² / g, and Comparative Example 1 in which organic substances were not adhered to SiO—C particles was 3 Less than ² m ² / g. Furthermore, the recovery rate of the lithium ion secondary battery of Example 1 was 97.5%, which was larger than 96.3% of Comparative Example 1. From the above results, it is considered that the reduction of the BET specific surface area of the negative electrode material by attaching an organic substance to the SiO—C particles is related to the improvement of the recovery rate of the lithium ion secondary battery.

[Reference Example 1]
The step of attaching an organic substance to the SiO-C particles was not performed, and ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl methyl carbonate (EMC) containing 1 M LiPF ₆ as an electrolytic solution (volume ratio 1: A 2016-type coin cell was produced in the same manner as in Example 1 except that the mixed solution of 1: 1) was used, and evaluation was performed in the same manner as in Example 1. The results are shown in Table 2.

[Reference Example 2]
Same as Example 1 except that a mixed solution of ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl methyl carbonate (EMC) (volume ratio 1: 1: 1) containing 1M LiPF ₆ was used as the electrolyte. Thus, a 2016 type coin cell was produced and evaluated in the same manner as in Example 1. The results are shown in Table 2.

[Reference Example 3]
A 2016 type coin cell was prepared in the same manner as in Reference Example 1 except that a mixed liquid further containing fluoroethylene carbonate (FEC) (1.0% by mass) was used as the electrolytic solution, and evaluation was performed in the same manner as in Example 1. It was. The results are shown in Table 2.

[Reference Example 4]
A 2016 type coin cell was prepared in the same manner as in Reference Example 2 except that a mixed liquid further containing fluoroethylene carbonate (FEC) (1.0% by mass) was used as the electrolytic solution, and evaluation was performed in the same manner as in Example 1. It was. The results are shown in Table 2.

  As shown in the comparison between Reference Example 1 and Reference Example 3, when the electrolyte solution contained FEC, the capacity retention rate was higher than when it did not, and the cycle characteristics were excellent. On the other hand, as shown in the comparison between Reference Example 1 and Reference Example 2, when the organic substance is attached to the SiO—C particles, the capacity retention rate is higher than when the organic substance is not attached and the cycle characteristics are excellent. It was. Furthermore, the degree of improvement of the capacity retention rate when organic substances are adhered to the SiO—C particles is comparable to the degree of improvement of the capacity maintenance rate when the electrolytic solution contains FEC. From the above, it has been found that by using the negative electrode material of the present invention, the capacity retention rate can be sufficiently increased without adding FEC to the electrolytic solution, and the cycle characteristics are improved. Further, as shown in the comparison between Reference Example 3 and Reference Example 4, it was found that the use of the negative electrode material of the present invention provides an effect of improving cycle characteristics that cannot be achieved simply by adding FEC to the electrolytic solution.

10 Carbon simple substance 12 Carbon simple substance particle 16 Organic substance 20 Silicon oxide particle

Claims (7)

  Silicon oxide particles, carbon simple substance present on part or all of the surface of the silicon oxide particle, and organic substance present on part or all of the surface of the silicon oxide particle where the carbon simple substance exists on the surface And a negative electrode material for a lithium ion secondary battery.   2. The negative electrode material for a lithium ion secondary battery according to claim 1, wherein the organic material includes a water-soluble organic material having at least one selected from the group consisting of a carboxyl group and a hydroxy group.   The organic substance is at least one selected from the group consisting of polysaccharides, gelatin, casein, and water-soluble polyethers, and monosaccharides, disaccharides, oligosaccharides, amino acids, gallic acid, tannins, saccharin, and saccharin. 3. The negative electrode material for a lithium ion secondary battery according to claim 1, comprising a second component that is at least one selected from the group consisting of a salt and a butynediol.   The content rate of the said simple substance of carbon is 0.5 mass%-10.0 mass% of the total amount of a silicon oxide particle and the simple substance of carbon, It is any one of Claims 1-3. Negative electrode material for lithium ion secondary batteries.   An X-ray diffraction spectrum using CuKα rays as a radiation source has a diffraction peak attributed to Si (111), and the silicon crystallite size calculated from the diffraction peak is 2.0 nm to 8.0 nm. The negative electrode material for lithium ion secondary batteries according to any one of claims 1 to 4.   The negative electrode for lithium ion secondary batteries which has a collector and the negative electrode material layer containing the negative electrode material of any one of Claims 1-5 provided on the said collector.   A lithium ion secondary battery comprising: a positive electrode; a negative electrode for a lithium ion secondary battery according to claim 6; and an electrolyte.