JP2019012646A - 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 in which a long life and high efficiency lithium ion secondary battery can be obtained as compared with a case where a conventional silicon is used although a silicon having high electric capacity is used as compared with a case where conventional graphite is used as an electrode active material, a negative electrode for a lithium ion secondary battery including the negative electrode material, and a lithium ion secondary battery including the negative electrode.SOLUTION: A negative electrode material for a lithium ion secondary battery includes a particle containing silicon and lithium silicate, a carbon present on at least a part of the surface of the particle, and a phosphate compound present on at least a part of the outermost surface of the particle.SELECTED DRAWING: Figure 1

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.

  Lithium ion secondary batteries are lighter and have higher charge / discharge capacity than other secondary batteries such as nickel cadmium batteries, nickel metal hydride batteries, and lead acid batteries. Is expected as a power source. In order to spread electric vehicles, hybrid electric vehicles, etc., it is important to further increase the capacity of lithium ion secondary batteries.

  In order to increase the electric capacity of a lithium ion secondary battery, the use of silicon as a negative electrode active material has attracted attention. In general, graphite is used as a negative electrode active material used in a lithium ion secondary battery, and the theoretical electric capacity of graphite is 372 mAh / g. The theoretical electric capacity of silicon is 4200 mAh / g, which is about 11 times that of graphite, and silicon can be said to be an effective material for increasing the electric capacity of lithium ion secondary batteries.

  However, silicon has a property of expanding in volume at the time of charging, and the theoretical volume expansion rate at the time of full charging is 400%. The volume expansion of silicon not only causes deterioration of the electrode of the lithium ion secondary battery, but also gives a problem to the shape stability of the battery itself. Moreover, there is a problem that the silicon itself collapses or is pulverized by repeating the expansion and contraction of the volume due to charge and discharge, thereby reducing the charge and discharge efficiency and life. Furthermore, since silicon has a high activity of decomposing electrolyte solution on the surface, it is also a problem that the initial irreversible capacity is larger than that of graphite.

  As a means for relieving the stress caused by the volume expansion of silicon, a composite of silicon and lithium silicate has been studied (see Patent Document 1 and Patent Document 2). This method can improve the charge / discharge cycle characteristics of a lithium ion secondary battery using a non-aqueous electrode.

  Further, as means for suppressing the electrolyte decomposition activity on the surface of silicon, the coating treatment on the surface of silicon-containing particles such as composite particles of silicon and lithium silicate has been performed so far (see Patent Documents 2 and 3). Has been studied. This method can reduce the initial irreversible capacity derived from silicon.

Japanese Patent Laid-Open No. 2006-66529 JP-A-2015-156328 Japanese Patent Laid-Open No. 2006-81922

  However, in the method of compounding silicon and lithium silicate described in Patent Document 1 and Patent Document 2, since lithium silicate exhibits water solubility and strong basicity, an aqueous electrode (that is, when preparing a negative electrode) When the negative electrode material is an electrode including a step of dispersing with a water-based solvent, the binding property of the electrode is lowered. Therefore, this method is not suitable for a lithium ion secondary battery using an aqueous electrode. Further, even by the method of performing the coating treatment as described in Patent Document 2 and Patent Document 3, it is impossible to prevent a decrease in the binding property of the aqueous electrode due to lithium silicate.

  Therefore, when increasing the electric capacity of a lithium ion secondary battery using a water-based electrode using silicon, stress relaxation due to volume expansion of silicon, suppression of silicon collapse, and electrolyte decomposition activity on the surface of silicon are performed. Therefore, it is necessary to improve the binding property of the electrode even when using particles containing silicon and lithium silicate.

  The present disclosure includes a negative electrode material for a lithium ion secondary battery, which can improve the initial capacity and the initial efficiency of the lithium ion secondary battery, and suppress the decrease in electrode binding properties, and the negative electrode material. An object is to provide a negative electrode for a lithium ion secondary battery and a lithium ion secondary battery including the negative electrode.

Means for solving the above problems include the following embodiments.
<1> A lithium ion secondary battery comprising: particles containing silicon and lithium silicate; carbon present on at least a part of the surface of the particle; and a phosphate compound existing on at least a part of the outermost surface of the particle. Negative electrode material.
<2> The specific surface area determined from nitrogen adsorption measurements at 77K is ^{0.1 m 2 /g~3.0 m 2 / g} , negative for a lithium ion secondary battery according to <1> electrode material.
<3> The negative electrode material for a lithium ion secondary battery according to <1> or <2>, wherein the average particle size (50% D) is 0.5 μm to 20 μm.
<4> A negative electrode for a lithium ion secondary battery, comprising the negative electrode material for a lithium ion secondary battery according to any one of <1> to <3>.
<5> A lithium ion secondary battery comprising the negative electrode for a lithium ion secondary battery according to <4>.

  According to the present disclosure, a negative electrode material for a lithium ion secondary battery, which can improve the initial capacity and initial efficiency of a lithium ion secondary battery, and suppress the decrease in electrode binding property, the negative electrode material A negative electrode for a lithium ion secondary battery to be contained, and a lithium ion secondary battery including the negative electrode are provided.

It is a figure showing the specific example of the negative electrode material for lithium ion secondary batteries of this indication. It is a figure showing the specific example of the negative electrode material for lithium ion secondary batteries of this indication.

  Hereinafter, embodiments for carrying out the present invention will be described in detail. However, the present invention is not limited to the following embodiments. In the following embodiments, the components (including element steps and the like) are not essential unless otherwise specified. The same applies to numerical values and ranges thereof, and the present invention is not limited thereto.

In the present disclosure, the term “process” includes a process that is independent of other processes and includes the process if the purpose of the process is achieved even if it cannot be clearly distinguished from the other processes. .
In the present disclosure, the numerical ranges indicated using “to” include numerical values described before and after “to” as the minimum value and the maximum value, respectively.
In the numerical ranges described stepwise in the present disclosure, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of another numerical description. . Further, in the numerical ranges described in the present disclosure, the upper limit value or the lower limit value of the numerical range may be replaced with the values shown in the examples.
In the present disclosure, each component may contain a plurality of corresponding substances. When multiple types of substances corresponding to each component are present in the composition, the content or content of each component is the total content or content of the multiple types of substances present in the composition unless otherwise specified. Means quantity.
In the present disclosure, a plurality of particles corresponding to each component may be included. When a plurality of particles corresponding to each component are present in the composition, the particle diameter of each component means a value for a mixture of the plurality of particles present in the composition unless otherwise specified.
In the present disclosure, the term “layer” or “film” includes only a part of the region in addition to the case where the layer or film is formed over the entire region. The case where it is formed is also included.
In the present disclosure, the term “lamination” indicates that layers are stacked, and two or more layers may be combined, or two or more layers may be detachable.
In the present disclosure, “(meth) acrylate” means at least one of acrylate and methacrylate, and “(meth) acrylonitrile” means at least one of acrylonitrile and methacrylonitrile.

<Anode material for lithium ion secondary battery>
The negative electrode material for a lithium ion secondary battery of the present disclosure includes particles containing silicon and lithium silicate; carbon existing on at least a part of the surface of the particles; and phosphorus existing on at least a part of the outermost surface of the particles. An acid compound. Hereinafter, the negative electrode material for a lithium ion secondary battery of the present disclosure is also simply referred to as “negative electrode material”.
According to the negative electrode material for a lithium ion secondary battery of the present disclosure, it is possible to improve the initial capacity and the initial efficiency of the lithium ion secondary battery, and to suppress the decrease in electrode binding properties. The reason for the above effect is not necessarily clear, but can be considered as follows.
Since the negative electrode material for a lithium ion secondary battery of the present disclosure uses silicon which is a high capacity negative electrode active material, the initial capacity is improved when a lithium ion secondary battery is manufactured. On the other hand, since particles containing silicon and lithium silicate instead of silicon alone are used as the negative electrode active material, stress due to the volume expansion of silicon can be relieved, and as a result, collapse of the negative electrode material can be suppressed. . Furthermore, the presence of carbon and phosphate compounds on the surface of particles containing silicon and lithium silicate reduces the contact surface with the electrolyte solution on the silicon surface and suppresses the decomposition activity of the electrolyte solution on the silicon surface. The Therefore, it is considered that the initial efficiency is improved. In addition, the presence of carbon and phosphate compounds on the surface of particles containing silicon and lithium silicate improves the water resistance of particles containing silicon and lithium silicate, and suppresses elution of silicon and lithium silicate. . As a result, even when a water-based electrode is used, it is considered that the increase in pH of the slurry can be suppressed and the binding property of the electrode can be improved.

(Particles containing silicon and lithium silicate)
The negative electrode material for a lithium ion secondary battery of the present disclosure has particles containing silicon and lithium silicate. Particles containing silicon and lithium silicate can occlude and release lithium ions. The particles containing silicon and lithium silicate may be particles having a total of 100% purity of silicon and lithium silicate, and may contain a trace amount of impurity elements.

The silicon contained in the particles may be crystalline, amorphous, or a mixture thereof.
The content of silicon in the particles containing silicon and lithium silicate is not particularly limited, and is preferably 30% by mass to 80% by mass with respect to the particles containing silicon and lithium silicate, and 40% by mass to 70% by mass. % Is more preferable.

The composition of the lithium silicate contained in the particles is not particularly limited. From the viewpoint of obtaining high cycle characteristics, Li ₄ SiO ₄ , Li ₂ Si ₂ O ₅ , Li ₆ Si ₂ O ₇ , or Li ₂ SiO ₃ is preferable. Lithium silicate may contain 1 type independently, and 2 or more types of mixtures may be sufficient as it.
Content of the lithium silicate in the particle | grains containing a silicon | silicone and lithium silicate is not specifically limited, It is preferable that it is 20 mass%-70 mass% with respect to the particle | grains containing a silicon | silicone and lithium silicate, 30 mass%-60 mass%. More preferably, it is mass%.

The method for producing particles containing silicon and lithium silicate is not particularly limited. One example is in-bulk reforming. In bulk modification, particles containing silicon and lithium silicate can be obtained by selectively changing part of the SiO ₂ component present in the silicon-based material to lithium silicate by an electrochemical method. . As the silicon-based material used for modification in the bulk, metallic silicon, silicon dioxide, or the like can be used alone or in combination of two or more. As the lithium silicate to be generated, Li ₄ SiO ₄ , Li ₂ Si ₂ O ₅ , Li ₆ Si ₂ O ₇ , and Li ₂ SiO ₃ tend to exhibit particularly good characteristics.
When particles containing silicon and lithium silicate are produced using such in-bulk modification, silicate formation in the silicon region can be reduced or avoided, and the material tends to be stable in the atmosphere.

A further example of a method for producing particles containing silicon and lithium silicate is a pre-doping method. In the pre-doping method, a silicon-based material and lithium metal are kneaded in the presence of a solvent.
As a silicon-based material used in the pre-doping method, silicon fine particles are contained in silicate particles or silicon oxide particles represented by SiO _x (0.5 ≦ x ≦ 2.0, preferably 0.5 ≦ x <1.6). Examples of the material dispersed therein. Of the particles having a fine structure in which silicon fine particles are dispersed in the silicate, the silicate is preferably inactive. Among silicates and silicon oxides, silicon dioxide is preferable from the viewpoint of ease of production.

As a further example of the method for producing particles containing silicon and lithium silicate, there is a thermal doping method. In the thermal doping method, for example, a mixture containing lithium silicate and SiO _z powder (0.5 ≦ x ≦ 2.0, preferably 1.0 ≦ z <1.6) that generates SiO gas is an inert gas. The reaction is conducted by heating at a temperature of 900 ° C. to 1300 ° C. under an atmosphere or reduced pressure to obtain particles containing silicon and lithium silicate.

As a further example of the method for producing particles containing silicon and lithium silicate, there is a method of performing mechanical alloying after disproportionation reaction by heat. By heating the silicon monoxide particles to 1000 ° C. to 1500 ° C. under an inert atmosphere, a disproportionation reaction occurs, and silicon and silicon dioxide are dispersed in the particles. By fusing the obtained particles and lithium silicate with a mechanical alloy, particles containing silicon and lithium silicate can be obtained.
Silicon and lithium silicate may be used as materials to be fused by mechanical alloy. As lithium silicate, Li ₄ SiO ₄ , Li ₂ Si ₂ O ₅ , Li ₆ Si ₂ O ₇ , and Li ₂ SiO ₃ tend to exhibit particularly good characteristics.

  The average particle diameter (50% D) of the particles containing silicon and lithium silicate is not particularly limited. From the viewpoint of adjusting the particle diameter of a negative electrode material for a lithium ion secondary battery to be described later to an appropriate range, the average particle diameter (50% D) is preferably 0.3 μm to 20 μm, and preferably 0.3 μm to 15 μm. It is more preferable. In addition, the measuring method of an average particle diameter (50% D) can be measured by the method similar to the measuring method of the average particle diameter of the negative electrode material for lithium ion secondary batteries mentioned later.

(carbon)
The negative electrode material of this indication has carbon which exists in at least one part of the surface of the particle | grains containing a silicon and lithium silicate. Carbon may be present on the entire surface of the particles containing silicon and lithium silicate, or may be present only on a part of the surface. The manner in which carbon is present on the surface of the particle containing silicon and lithium silicate is not particularly limited, and may be chemically bonded or may not exist via a chemical bond. Hereinafter, the carbon layer formed so as to exist on at least part of the surface of the particle containing silicon and lithium silicate is also referred to as a carbon layer.

  The ratio of carbon to particles containing silicon and lithium silicate is not particularly limited, and is preferably 0.001 to 0.3 by mass ratio. When the ratio of the carbon layer to the particles containing silicon and lithium silicate (mass ratio) is 0.001 or more, good life characteristics and charge / discharge capacity tend to be obtained when a lithium ion secondary battery is obtained. If it is 0.3 or less, good initial charge / discharge efficiency and energy density tend to be obtained when a lithium ion secondary battery is obtained. The ratio of the carbon layer to the particles containing silicon and lithium silicate can be calculated from the weight of the particles containing silicon and lithium silicate, the mass of the carbon precursor serving as the carbon layer, and the carbonization rate of the carbon precursor.

  The carbon layer may be formed, for example, by attaching an organic compound (also referred to as a carbon precursor) that leaves carbonaceous matter by heat treatment to the surface of the particles containing silicon and lithium silicate, and then firing.

  There is no particular limitation on the method of attaching the organic compound to the surface of the particles containing silicon and lithium silicate, and the particles containing silicon and lithium silicate are dispersed in a mixed solution in which the organic compound is dissolved or dispersed in a solvent. Wet method to remove the solvent after mixing, a dry method in which particles containing silicon and lithium silicate and organic compound are mixed with each other, and mechanical energy is applied to the mixture, and a vapor phase method such as CVD method, etc. Is mentioned.

  There is no restriction | limiting in particular in the organic compound in the case of making an organic compound adhere to the surface of the particle | grains containing a silicon | silicone and lithium silicate, High molecular compounds, such as a thermoplastic resin and a thermosetting resin, etc. can be used. For example, when a thermoplastic resin is used, it is carbonized via the liquid phase and a carbon layer having a relatively small specific surface area is generated. The presence of this carbon layer on the surface of particles containing silicon and lithium silicate is preferable because the specific surface area of the negative electrode material is also relatively small, and as a result, the initial irreversible capacity of the lithium ion secondary battery tends to be small. An organic compound may be used individually by 1 type, and may use 2 or more types together.

  The thermoplastic resin used in the case of using a thermoplastic resin is not particularly limited, and ethylene heavy end pitch, crude oil pitch, coal tar pitch, asphalt decomposition pitch, pitch generated by pyrolyzing polyvinyl chloride, etc., naphthalene, etc. are super strong acids. A synthetic pitch produced by polymerization in the presence may be used. Further, polyvinyl chloride, polyvinyl alcohol, polyvinyl acetate, polyvinyl butyral, or the like may be used as the thermoplastic resin. Natural products such as starch and cellulose may also be used. A thermoplastic resin may be used individually by 1 type, and may use 2 or more types together.

  The solvent for dissolving or dispersing the organic compound is not particularly limited. A solvent may be used individually by 1 type and may use 2 or more types together. In order to improve the coating effect, the affinity between the surface of the silicon particles and the organic compound may be improved by adding a surfactant, a dispersing agent or the like.

  When the organic compound is pitches, tetrahydrofuran, toluene, xylene, benzene, quinoline, pyridine, a mixture of relatively low boiling point liquid substances (creosote oil) produced in coal dry distillation, etc. may be used as the solvent. . Further, when the organic compound is polyvinyl chloride, tetrahydrofuran, cyclohexanone, nitrobenzene or the like may be used as a solvent. When the organic compound is polyvinyl acetate, polyvinyl butyral, etc., alcohols, esters, ketones, etc. may be used as the solvent. When the organic compound is polyvinyl alcohol, water or the like may be used as a solvent. When water is used as a solvent, mixing or dispersion of particles containing silicon and lithium silicate in the solvent is promoted, and adhesion between the organic compound and particles containing silicon and lithium silicate is improved. A surfactant may be added.

  The removal of the solvent may be performed by heating in a normal pressure or reduced pressure atmosphere. The temperature at the time of solvent removal is preferably 200 ° C. or lower when the atmosphere is air. When the removal temperature is 200 ° C. or lower, the reaction between oxygen in the atmosphere, the organic compound, and the solvent (especially when creosote oil is used) is suppressed, and there is a tendency that fluctuation in the amount of carbon generated by firing can be suppressed. . Moreover, it exists in the tendency which tends to express a desired characteristic as a negative electrode material by making porous.

Moreover, the firing conditions of the particles containing silicon and lithium silicate to which the organic compound is attached may be determined as appropriate in consideration of the carbonization rate of the organic compound, and are not particularly limited. Baking is preferably performed in a non-oxidizing atmosphere in the range of 700 ° C to 1400 ° C, more preferably 700 ° C to 900 ° C. When the firing temperature is 700 ° C. or more, the initial irreversible capacity of the lithium ion secondary battery tends to be suppressed, and when the firing temperature is 1400 ° C. or less, an increase in production cost tends to be suppressed. In addition, even if it heats exceeding 1400 degreeC, there is almost no change in the performance as a negative electrode material.
Examples of the non-oxidizing atmosphere include an inert gas atmosphere such as nitrogen, argon, and helium, a vacuum atmosphere, and a circulated combustion exhaust gas atmosphere.

  Prior to firing, the particles containing silicon and lithium silicate to which an organic compound is attached may be heat-treated at a temperature of 150 ° C. to 300 ° C. For example, when polyvinyl alcohol is used as the organic compound, the carbonization rate tends to be increased by such heat treatment.

(Phosphate compound)
The negative electrode material of the present disclosure has a phosphoric acid compound present on at least a part of the outermost surface of particles containing silicon and lithium silicate. The phosphoric acid compound may be present on the entire outermost surface of the particles containing silicon and lithium silicate, or may be present only on a part thereof. The manner in which the phosphate compound is present is not particularly limited, and may be chemically bonded to the components present on the surface of the particles containing silicon and silicate containing carbon as described above. It may exist without intervention.

  The method for causing the phosphate compound to exist is not particularly limited. For example, the particles containing silicon and silicate containing carbon on the surface after firing as described above may be crushed as necessary. Then, after classifying or sieving, the particles containing silicon and silicate containing carbon on the surface are dispersed and mixed in a solution in which the phosphate compound is dissolved or dispersed, and then the solvent is removed to remove phosphorus. The method of providing an acid compound is mentioned.

  The phosphoric acid compound is not particularly limited, and from the viewpoint of improving water resistance and not inhibiting the conductivity as the negative electrode material, a surfactant-based phosphate compound or a nonionic surfactant-based phosphate compound is preferable. More preferred are ether type nonionic surfactant phosphates, amino ether type nonionic surfactant phosphates, ether ester type nonionic surfactant phosphates, and alkanolamide type fatty acid ester phosphates, polyoxyethylene alkyl ether phosphates Polyoxyethylene allyl phenyl ether phosphate, fatty acid methyl ester ethoxyl phosphate, polyoxyethylene alkylphenyl ether phosphate, polyoxyethylene polyoxypropylene glycol phosphate are more preferable. A phosphoric acid compound may be used individually by 1 type, and may use 2 or more types together.

  The abundance of the phosphoric acid compound is not particularly limited, and is 0.5% by mass to 3% by mass with respect to the total amount of the negative electrode material from the viewpoint of improving water resistance and not inhibiting the conductivity as the negative electrode material. It is preferable. The abundance of the phosphate compound can be calculated from the difference in dry weight before and after the application of the phosphate compound.

  The solvent for dissolving or dispersing the phosphate compound is not particularly limited. A solvent may be used individually by 1 type and may use 2 or more types together. In order to improve the coating effect, the affinity between the organic compound and the surface of the particles containing silicon and silicate containing carbon may be increased by adding a surfactant, a dispersing agent, or the like. For example, alcohols, esters, ketones, and the like may be used as substances that increase the affinity of organic compounds.

  The removal of the solvent may be performed by heating in a normal pressure or reduced pressure atmosphere. The temperature for removing the solvent is preferably 150 ° C. or lower when the atmosphere is air. When the removal temperature is 150 ° C. or lower, the reaction between oxygen in the atmosphere, the phosphoric acid compound, and the solvent can be suppressed, and fluctuations in the adhesion amount of the phosphoric acid compound tend to be suppressed. Moreover, it exists in the tendency which tends to express a desired characteristic as a negative electrode material by making porous.

  The particles containing silicon and silicate in which a phosphoric acid compound is present on the outermost surface and containing silicate are subjected to crushing treatment, classification treatment, or sieving treatment as necessary, and lithium ions of the present disclosure You may obtain the negative electrode material for secondary batteries.

The negative electrode material for a lithium ion secondary battery of the present disclosure is preferably a specific surface area determined from nitrogen adsorption measurements at 77K is ^{0.1m 2 /g~3.0m 2 / g, 0.2m} 2 / g~ more preferably 2.0 m ² / ^g, further preferably 0.5m ² /g~1.0m 2 / g. When the specific surface area is 0.1 m ² / g or more, the input characteristics tend to be good. Moreover, when the specific surface area is 3.0 m ² / g or less, carbon existing on the surface of the particles containing silicon and lithium silicate can be prevented from becoming porous for some reason, and the lithium ion secondary battery There is a tendency to suppress the increase in the first irreversible capacity. In addition, the specific surface area by nitrogen adsorption can be calculated | required using the BET method from the adsorption isotherm obtained from the nitrogen adsorption measurement in 77K.

The average particle diameter of the negative electrode material for a lithium ion secondary battery of the present disclosure is not particularly limited. The average particle size (50% D) is preferably 0.5 μm to 20 μm.
When the average particle size is 0.5 μm or more, the specific surface area does not become too large and the initial charge / discharge efficiency of the lithium ion secondary battery tends to be good. Furthermore, it is in the tendency for the contact of particle | grains to be maintained favorable and for the fall of charging / discharging capacity to be suppressed. Moreover, it exists in the tendency which can suppress that the purity falls by the influence of surface oxidation, a charge / discharge capacity falls, and the charge / discharge capacity per unit volume falls by the fall of a bulk density.
On the other hand, when the average particle size is 20 μm or less, unevenness on the electrode surface is suppressed, and it tends to be possible to suppress a short circuit of the battery. Further, the diffusion distance of Li from the particle surface to the inside However, the charge / discharge capacity of the lithium ion secondary battery tends to be kept good. Moreover, when performing the process of adhering carbon, it tends to be easy to suppress a decrease in cycle performance caused by a decrease in the amount of deposited carbon. Furthermore, it tends to be easy to suppress particle cracking caused by expansion and contraction of intra-particle silicon during charging and discharging, and deterioration of cycle characteristics due to this.

The average particle size is measured by the following method.
A measurement sample is placed in a 0.01% by weight aqueous solution of a surfactant (Esomine T / 15, manufactured by Lion Corporation) and dispersed with a vibration stirrer. The obtained dispersion is put into a sample water tank of a laser diffraction particle size distribution analyzer (SALD-3000J, manufactured by Shimadzu Corporation), circulated with a pump while applying ultrasonic waves, and measured by a laser diffraction method. The volume cumulative 50% particle size (50% D) of the obtained particle size distribution is defined as the average particle size. The measurement conditions are as follows.
・ Light source: Red semiconductor laser (690nm)
Absorbance: 0.10 to 0.15
-Refractive index: 2.00 to 0.20

Specific examples of the negative electrode material for a lithium ion secondary battery of the present disclosure are shown in FIGS. 1 and 2.
In FIG. 1, the negative electrode material 10 includes particles 12 containing silicon and lithium silicate; carbon 14 present on at least a part of the surface of the particles; and phosphate compound 16 present on at least a part of the outermost surface of the particles. Have In FIG. 1, carbon 14 is present on the entire surface of particles 12 containing silicon and lithium silicate, and phosphoric acid compound 16 covers the entire outermost surface of particles 12 containing lithium silicate.
In FIG. 2, the negative electrode material 20 includes particles 22 containing silicon and lithium silicate; carbon 24 existing on at least a part of the surface of the particles; and phosphate compound 26 existing on at least a part of the outermost surface of the particles. Have In FIG. 2, carbon 24 is present on part of the surface of the particle 22 containing silicon and lithium silicate, and the phosphoric acid compound 26 is present on part of the outermost surface of the particle 22 containing lithium silicate.
In addition, the negative electrode material for lithium ion secondary batteries of this indication is not limited to the specific example described in drawing. Moreover, the size of each structure in the drawings is conceptual, and the relative relationship between the structures is not limited to this.

<Anode for lithium ion secondary battery>
The negative electrode for lithium ion secondary batteries in the present disclosure contains the negative electrode material for lithium ion secondary batteries of the present disclosure.
In one embodiment, the negative electrode for a lithium ion secondary battery is obtained by using a negative electrode material for a lithium ion secondary battery of the present disclosure and a dispersing device such as a stirrer, a ball mill, a super sand mill, and a pressure kneader together with an organic binder. A negative electrode material slurry is prepared by kneading and applied to a current collector to form a negative electrode layer, or a paste-like negative electrode material slurry is formed into a sheet shape, a pellet shape, etc. It can be obtained by integrating with the body.

  The organic binder is not particularly limited, and ethylene such as styrene-butadiene copolymer, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, (meth) acrylonitrile, hydroxyethyl (meth) acrylate, and the like. Unsaturated carboxylic acid ester; ethylenically unsaturated carboxylic acid such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, maleic acid; polyvinylidene fluoride, polyethylene oxide, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, etc. And a high molecular compound having a large ion conductivity. An organic binder may be used individually by 1 type, and may use 2 or more types together. Content of an organic binder is not specifically limited, It is preferable to contain 1-20 mass parts with respect to a total of 100 mass parts of the negative electrode material for lithium ion secondary batteries, and an organic binder.

  A thickener for adjusting the viscosity may be added to the negative electrode material slurry. The thickener is not particularly limited, and carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, polyacrylic acid (or a salt thereof), oxidized starch, phosphorylated starch, casein and the like can be used. A thickener may be used individually by 1 type and may use 2 or more types together.

  Moreover, you may mix a conductive support material with the said negative electrode material slurry. The conductive auxiliary material is not particularly limited, and examples thereof include carbon black, graphite, acetylene black, oxides or nitrides exhibiting conductivity. The usage-amount of a conductive support agent is good about 1 mass%-15 mass% of a negative electrode material.

  The material and shape of the current collector are not particularly limited, and a strip-shaped current collector made of aluminum, copper, nickel, titanium, stainless steel, or the like in a foil shape, a punched foil shape, a mesh shape, or the like can be used. Also, porous materials such as porous metal (foamed metal) and carbon paper can be used.

When a negative electrode material slurry is applied to a current collector to obtain a negative electrode for a lithium ion secondary battery, the method of applying the negative electrode material slurry to the current collector is not particularly limited, and a metal mask printing method, electrostatic coating method, dipping Known methods such as a coating method, a spray coating method, a roll coating method, a doctor blade method, a gravure coating method, and a screen printing method may be used. After the application, rolling treatment with a flat plate press, a calender roll or the like may be performed as necessary.
When the negative electrode material slurry is formed into a sheet shape, pellet shape, etc., and this is integrated with a current collector to obtain a negative electrode for a lithium ion secondary battery, the negative electrode material formed into a sheet shape, pellet shape, etc. The method for integrating the slurry and the current collector is not particularly limited, and may be performed by a known method such as a roll, a press, or a combination thereof.

<Lithium ion secondary battery>
The lithium ion secondary battery of the present disclosure includes the negative electrode for a lithium ion secondary battery of the present disclosure. A lithium ion secondary battery can be obtained, for example, by disposing a negative electrode for a lithium ion secondary battery and a positive electrode facing each other with a separator interposed therebetween and injecting an electrolytic solution.

  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 in this case, a strip-shaped current collector made of a metal or an alloy such as aluminum, titanium, or stainless steel in a foil shape, a punched foil shape, a mesh shape, or the like can be used.

The positive electrode material used for the positive electrode layer is not particularly limited. For example, a metal compound, metal oxide, metal sulfide, or conductive polymer material that can be doped or intercalated with lithium ions may be used. For example, lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganate (LiMnO ₂ ), and their double oxides (LiCo _x Ni _y Mn _z O ₂ , X + Y + Z = 1), lithium manganese spinel (LiMn ₂ O ₄ ), lithium vanadium compound, V ₂ O ₅ , V ₆ O ₁₃ , VO ₂ , MnO ₂ , TiO ₂ , MoV ₂ O ₈ , TiS ₂ , V ₂ S ₅ , VS ₂ , MoS ₂ , MoS ₃ , Cr ₃ O ₈ , Cr ₂ O ₅ , olivine-type LiMPO ₄ (M represents Co, Ni, Mn, or Fe), conductive polymers such as polyacetylene, polyaniline, polypyrrole, polythiophene, polyacene, porous carbon, etc. Can be used. The positive electrode material may be used alone or in combination of two or more.

  Examples of the separator include non-woven fabrics, cloths, microporous films, or a combination thereof, mainly composed of polyolefins such as polyethylene and polypropylene. In addition, when it is the structure where the positive electrode and negative electrode of a lithium ion secondary battery to produce are not in direct contact, it is not necessary to use a separator.

Examples of the electrolyte include lithium salts such as LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiSO ₃ CF ₃ , ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, cyclopentanone, sulfolane, and 3-methyl. Sulfolane, 2,4-dimethylsulfolane, 3-methyl-1,3-oxazolidine-2-one, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, butyl methyl carbonate, ethyl propyl carbonate, butyl Ethyl carbonate, dipropyl carbonate, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate, vinegar A so-called organic electrolyte solution in which a simple substance such as ethyl acid or a mixture of two or more components is dissolved in a non-aqueous solvent may be used.

  Further, as the electrolytic solution, an aqueous solvent such as lithium salt hydrate (normal temperature molten hydrate (hydrate melt)) may be used.

  The structure of the lithium ion secondary battery of the present disclosure is not particularly limited. For example, a positive electrode and a negative electrode, and a separator provided as necessary, are wound into a flat spiral to form a wound electrode group, or these are laminated as a flat plate to form a stacked electrode group, The structure which enclosed these electrode groups in the exterior body is mentioned.

  The shape of the lithium ion secondary battery of the present disclosure is not particularly limited, and can be used as a paper-type battery, a button-type battery, a coin-type battery, a stacked battery, a cylindrical battery, or the like.

  Applications of the lithium ion secondary battery of the present disclosure are not particularly limited, and examples include applications such as electric vehicles and power tools.

  Next, although the said embodiment is described in more detail with the following example, these Examples do not restrict | limit the said embodiment.

Example 1
A raw material in which metal silicon and silicon dioxide were mixed was placed in a reaction furnace, the atmosphere was reduced to a vacuum degree of 15 Pa to vaporize the raw material, and this was deposited on an adsorption plate, and then cooled sufficiently. Thereafter, the deposit was taken out and pulverized with a ball mill, and the particle size was adjusted to obtain a powder. The produced powder was subjected to bulk modification by an electrochemical method in a 1: 1 (volume ratio) mixed solvent of propylene carbonate and ethylene carbonate to obtain particles containing silicon and lithium silicate. 100 g of particles containing silicon and lithium silicate and 10 g of coal tar pitch were mixed at room temperature (25 ° C.), respectively, and then heated to 800 ° C. at a temperature rising rate of 300 ° C./hour under nitrogen flow. Carbon was deposited by holding for a period of time. The resulting particles were crushed and passed through a 250 mesh standard sieve. 2 g of the obtained particles, 2 g of polyoxyethylene alkyl ether phosphate manufactured by ADEKA CORPORATION, and 38 g of isopropanol were mixed and stirred at a rate of 20 rotations / minute (rpm) with MIXROTOR MR-5 manufactured by ASONE CORPORATION. The obtained mixed liquid was filtered and dried at 105 ° C. for 2 hours to obtain a negative electrode material 1 having an average particle diameter of 16.8 μm.

(Example 2)
A raw material in which metal silicon and silicon dioxide were mixed was placed in a reaction furnace, the atmosphere was reduced to a vacuum degree of 15 Pa to vaporize the raw material, and this was deposited on an adsorption plate, and then cooled sufficiently. Thereafter, the deposit was taken out and pulverized with a ball mill, and the particle size was adjusted to obtain a powder. The produced powder was subjected to bulk modification by an electrochemical method in a 1: 1 (volume ratio) mixed solvent of propylene carbonate and ethylene carbonate to obtain particles containing silicon and lithium silicate. 100 g of particles containing silicon and lithium silicate and 10 g of coal tar pitch were mixed at room temperature (25 ° C.), respectively, and then heated to 800 ° C. at a temperature rising rate of 300 ° C./hour under nitrogen flow. Carbon was deposited by holding for a period of time. The resulting particles were crushed and passed through a 250 mesh standard sieve. 2 g of the obtained particles, 4 g of polyoxyethylene alkyl ether phosphate manufactured by Adeka Corporation and 36 g of isopropanol were mixed, and the mixture was stirred at a speed of 20 rotations / minute (rpm) with MIXROTOR MR-5 manufactured by ASONE Corporation. The obtained mixed liquid was filtered and dried at 105 ° C. for 2 hours to obtain a negative electrode material 2 having an average particle diameter of 17.3 μm.

(Example 3)
A raw material in which metal silicon and silicon dioxide were mixed was placed in a reaction furnace, the atmosphere was reduced to a vacuum degree of 15 Pa to vaporize the raw material, and this was deposited on an adsorption plate, and then cooled sufficiently. Thereafter, the deposit was taken out and pulverized with a ball mill, and the particle size was adjusted to obtain a powder. The produced powder was subjected to bulk modification by an electrochemical method in a 1: 1 (volume ratio) mixed solvent of propylene carbonate and ethylene carbonate to obtain particles containing silicon and lithium silicate. 100 g of particles containing silicon and lithium silicate and 10 g of coal tar pitch were mixed at room temperature (25 ° C.), respectively, and then heated to 800 ° C. at a temperature rising rate of 300 ° C./hour under nitrogen flow. Carbon was deposited by holding for a period of time. The resulting particles were crushed and passed through a 250 mesh standard sieve. 6 g of the obtained particles, 2 g of polyoxyethylene alkyl ether phosphate manufactured by ADEKA CORPORATION, and 34 g of isopropanol were mixed, and the mixture was stirred at a speed of 20 revolutions / minute (rpm) with MIXROTOR MR-5 manufactured by ASONE CORPORATION. The obtained mixed liquid was filtered and dried at 105 ° C. for 2 hours to obtain a negative electrode material 3 having an average particle diameter of 17.8 μm.

  The physical property values and electrical characteristics of the negative electrode materials 1 to 3 obtained in Examples 1 to 3 were measured as follows. The measurement results are shown in Table 1. For comparison, as Comparative Example 1, particles containing carbon-coated silicon and silicate (average particle diameter: 15.0 μm) were used as the negative electrode material.

[Average particle size]
2 g of the obtained negative electrode material sample was placed in a 0.01% by mass aqueous solution of a surfactant (Esomine T / 15, manufactured by Lion Corporation) and dispersed with a vibration stirrer. The obtained dispersion was placed in a sample water tank of a laser diffraction particle size distribution measuring apparatus (SALD-3000J, manufactured by Shimadzu Corporation). Subsequently, it was made to circulate with a pump, applying an ultrasonic wave, and the average particle diameter was measured with the laser diffraction type. The volume cumulative 50% particle size (50% D) of the obtained particle size distribution was defined as the average particle size. The measurement conditions were as follows.
・ Light source: Red semiconductor laser (690nm)
Absorbance: 0.10 to 0.15
-Refractive index: 2.00 to 0.20

[Specific surface area]
After 1 g of the obtained negative electrode material sample was vacuum-dried at 200 ° C. for 2 hours, nitrogen adsorption at a liquid nitrogen temperature (77 K) was measured by a multipoint method using ASAP2010 manufactured by Micromeritics, and calculated according to the BET method.

[PH of slurry]
92.6% by mass and 1.2% by mass of the solid content of graphite-based negative electrode material, styrene butadiene rubber (SBR), and carboxymethyl cellulose (CMC), respectively, with respect to 5% by mass of the negative electrode material sample of each example and comparative example. And kneaded to prepare a paste-like negative electrode material slurry. The pH of the prepared negative electrode material slurry when immersed in water was measured with a compact pH meter LAQUATwin B-712 manufactured by Horiba, Ltd.

[Peel test]
92.6% by mass and 1.2% by mass of the solid content of graphite-based negative electrode material, styrene butadiene rubber (SBR), and carboxymethyl cellulose (CMC), respectively, with respect to 5% by mass of the negative electrode material sample of each example and comparative example. And it added so that it might become 1.2 mass%, and it knead | mixed, and produced the paste-form negative electrode material slurry. The prepared slurry was applied to an electrolytic copper foil having a thickness of 10 μm using a quarter having a thickness of 100 μm, and further dried at 105 ° C. to remove moisture, thereby preparing a sample electrode (negative electrode).
The produced electrode was cut out to a width of 10 mm, and peel strength was measured at a test speed of 100 mm / min by an autograph EZ-S manufactured by Shimadzu Corporation. The same test sample was measured 5 times, and the average value was calculated.

[Initial charge capacity and initial efficiency]
92.6% by mass and 1.2% by mass in terms of solid content of graphite-based negative electrode material, styrene butadiene rubber (SBR), and carboxymethyl cellulose (CMC), respectively, with respect to 5% by mass of the negative electrode material sample of each example and comparative example. % And 1.2% by mass and kneaded to prepare a paste-like negative electrode material slurry. This slurry was applied to an electrolytic copper foil with a thickness of 10 μm using a quarter with a thickness of 100 μm, and further dried at 105 ° C. to remove moisture, thereby preparing a sample electrode (negative electrode).

Next, after laminating the sample electrode, separator, and counter electrode (positive electrode) in this order, LiPF ₆ was mixed with ethylene carbonate (EC) and methyl ethyl carbonate (MEC) (EC and MEC are in a volume ratio of 3: 7). The solution was poured into a coin type battery. Metal lithium was used for the counter electrode, and a polyethylene microporous film having a thickness of 20 μm was used for the separator.

Between the sample electrode and the counter electrode of the obtained coin-type battery, it was charged to 0.06 V (V vs. Li / Li ⁺ ) with a constant current of 0.6 mA / cm ² , and then the current with a constant voltage of 0.6 V Was charged to 0.06 mA. Next, after a 30-minute rest period, a one-cycle test was performed to discharge to 1.0 V (V vs. Li / Li ⁺ ) at a constant current of 0.6 mA / cm ² to measure the initial charge capacity. Furthermore, the initial efficiency was calculated from the difference between the obtained initial charge capacity and the initial discharge capacity.

  Table 1 shows the measured physical property values.

As is clear from Table 1, when the negative electrode material for lithium ion secondary batteries of Examples 1 to 3 was used, the slurry was compared with the case of using the negative electrode material for lithium ion secondary batteries of Comparative Example 1. The pH when immersed in water is low, and the water resistance is improved. As a result, also in the peel test, the negative electrode for lithium ion secondary battery using the negative electrode material for lithium ion secondary battery of Examples 1 to 3 was lithium ion using the negative electrode material for lithium ion secondary battery of Comparative Example 1. It can be seen that the binding property is improved as compared with the negative electrode for the secondary battery.
Furthermore, the lithium ion secondary battery using the negative electrode material for lithium ion secondary batteries of Examples 1 to 3 is compared with the lithium ion secondary battery using the negative electrode material for lithium ion secondary battery of Comparative Example 1. Excellent initial charge capacity and initial efficiency.

  From the above, when the negative electrode material for a lithium ion secondary battery of the present disclosure is used, the initial charge capacity and the initial efficiency of the lithium ion secondary battery can be improved. Furthermore, the water resistance of the negative electrode material is improved, and as a result, the binding property of the electrode can be improved.

10 Negative electrode material 12 Particles containing silicon and lithium silicate 14 Carbon 16 Phosphoric acid compound 20 Negative electrode material 22 Particles containing silicon and lithium silicate 24 Carbon 26 Phosphoric acid compound

Claims (5)

Particles containing silicon and lithium silicate;
Carbon present on at least a portion of the surface of the particle; and
A phosphate compound present on at least a portion of the outermost surface of the particle;
A negative electrode material for a lithium ion secondary battery having: The specific surface area determined from nitrogen adsorption measurements at 77K is ^{0.1 m 2 /g~3.0 m 2 / g} , negative for a lithium ion secondary battery according to claim 1 electrode material.   The negative electrode material for a lithium ion secondary battery according to claim 1 or 2, wherein the average particle size (50% D) is 0.5 µm to 20 µm.   The negative electrode for lithium ion secondary batteries containing the negative electrode material for lithium ion secondary batteries of any one of Claims 1-3.   A lithium ion secondary battery comprising the negative electrode for a lithium ion secondary battery according to claim 4.