JP6080653B2 - Negative electrode composite - Google Patents

Description

  The present invention relates to a negative electrode composite material.

In the current lithium ion battery, an organic electrolyte is mainly used as an electrolyte.
Although organic electrolytes exhibit high ionic conductivity, the electrolytes are liquid and flammable, so there are concerns about risks such as leakage and ignition when used as batteries. As a next-generation lithium ion battery that solves this problem, an all-solid-state lithium ion battery using a sulfide-based solid electrolyte with higher safety has been developed (Patent Document 1).

  Batteries for electric vehicle applications and the like are required to have a high energy density. Although silicon has a high theoretical capacity and a battery using a silicon-based negative electrode active material as a negative electrode active material is disclosed (Patent Documents 2 and 3), charge / discharge cycle characteristics are not sufficient.

  In addition, although there is a disclosure of a new silicon-based negative electrode active material for a liquid-type lithium ion battery, the characteristics when an all-solid-state lithium ion battery is made are not clear (Patent Document 4).

JP 2005-228570 A JP 2010-003679 A JP 2003-331828 A International Publication No. 2013/027686

  An object of the present invention is to provide a novel negative electrode mixture capable of obtaining an all solid lithium battery having high charge / discharge cycle characteristics.

According to the present invention, the following negative electrode mixture and the like are provided.
1. (A) A substantially spherical composite active material that contains graphite and a battery active material that can be combined with lithium ions and satisfies the following condition (1); and (b) a negative electrode composite containing a solid electrolyte.
(1) The area ratio of the graphite exposed on the surface of the composite active material observed by scanning electron microscope observation at an acceleration voltage of 10 kV or less is 95% or more.
2. (C) A substantially spherical composite active material that contains graphite and a battery active material that can be combined with lithium ions, and is produced by the production method of (2) below, and (b) a negative electrode mixture containing a solid electrolyte.
(2) A mixing step of mixing a graphite having a specific surface area of 30 m ² / g or more and a battery active material that can be combined with lithium ions to obtain a mixture;
A method for producing a composite active material, comprising: subjecting the mixture to a spheronization treatment to produce a substantially spherical composite active material containing a battery active material that can be combined with graphite and lithium ions.
3. 3. The negative electrode composite material according to 1 or 2, wherein the graphite is expanded graphite.
4). The negative electrode composite material according to any one of 1 to 3, wherein the battery active material that can be combined with lithium ions contains at least one element selected from the group consisting of silicon, tin, aluminum, antimony, and indium.
5. The negative electrode composite material in any one of 1-4 whose tap density of the said composite active material is 0.8 g / cm < ³ > or more.
6). The negative electrode mixture in any one of 1-5 whose specific surface area of the said composite active material is 5-100 m < ² > / g.
7). The negative electrode composite material according to any one of 1 to 6, wherein an average particle diameter of the battery active material that can be combined with the lithium ions is 1 μm or less.
8). The negative electrode composite material according to any one of 1 to 7, wherein the solid electrolyte is a lithium ion conductive inorganic solid electrolyte containing Li, P, and S.
9. The negative electrode composite material according to any one of 1 to 8, wherein the solid electrolyte is a lithium ion conductive inorganic solid electrolyte that satisfies a composition represented by the following formula (I).
Li _a M _b P _c S _d (I)
(In the formula (I), M represents an element selected from B, Zn, Si, Cu, Ga, or Ge.
a to d indicate the composition ratio of each element, and a: b: c: d satisfies 1 to 12: 0 to 0.2: 1: 2 to 9. )
10. The negative electrode composite material according to any one of 1 to 9, wherein the solid electrolyte is glass ceramics.
11. The negative electrode composite material according to any one of 1 to 10, wherein the solid electrolyte is a glass ceramic having a crystallinity of 50% or more.
12 The negative electrode composite material according to any one of 2 to 11, wherein the solid electrolyte is produced using at least P ₂ S ₅ and Li ₂ S.
13. A mixing step of mixing a graphite having a specific surface area of 30 m ² / g or more and a battery active material capable of combining with lithium ions to obtain a mixture;
Spheronization step of producing a substantially spherical composite active material containing a battery active material that can be combined with graphite and lithium ions by subjecting the mixture to spheroidization;
A method for producing a negative electrode mixture, comprising a step of mixing the composite active material and a solid electrolyte.
A negative electrode composite produced by the production method according to 14.13.
15. A negative electrode comprising the negative electrode mixture according to any one of 1 to 12 and 14.
16. A negative electrode produced from the negative electrode composite material according to any one of 1 to 12 and 14.
A lithium secondary battery including the negative electrode according to 17.15 or 16.
A device comprising the lithium secondary battery according to 18.17.

  ADVANTAGE OF THE INVENTION According to this invention, the novel negative electrode compound material which can obtain the all-solid-state lithium battery with high charging / discharging cycling characteristics can be provided.

FIG. 1 (A) is a diagram showing an XRD diffraction pattern (*: peak derived from expanded graphite, +: peak derived from Si) of the composite active material prepared in Example 1, and FIG. It is a figure which shows the XRD diffraction pattern (*: peak derived from expanded graphite, +: peak derived from Si) of the mixture of expanded graphite and a standard silicon sample. FIG. 2 is a secondary electron image (acceleration voltage 10 kV) obtained by SEM (scanning electron microscope) of the composite active material manufactured in Example 1. FIG. 2A shows a magnification of 500 times and FIG. ) Is a magnification of 2000 times.

One form of the negative electrode mixture of the present invention is
(A) a substantially spherical composite active material containing graphite and a battery active material that can be combined with lithium ions and satisfying the following condition (1); and (b) a solid electrolyte.
(1) The area ratio of the graphite exposed on the surface of the composite active material observed by scanning electron microscope (SEM) observation at an acceleration voltage of 10 kV or less is 95% or more.

Another form of the negative electrode composite of the present invention includes (c) a battery active material that can be combined with graphite and lithium ions, and is a substantially spherical composite active material manufactured by the manufacturing method of (2) below. And (b) including a solid electrolyte.
(2) A mixing step of mixing a graphite having a specific surface area of 30 m ² / g or more and a battery active material that can be combined with lithium ions to obtain a mixture;
A method for producing a composite active material, comprising: subjecting the mixture to a spheronization treatment to produce a substantially spherical composite active material containing a battery active material that can be combined with graphite and lithium ions.

[Composite active material and production method]
Below, the composite active material used for the negative electrode composite material of this invention and its manufacturing method are explained in full detail.
First, the features of the present invention compared with the prior art will be described in detail.
As one of the features of the method for producing a composite active material used for the negative electrode composite of the present invention, a graphite having a specific surface area is used, and a mixture of battery active material combined with graphite and lithium ions is used. The point which has performed the spheroidization process is mentioned. More specifically, first, a battery active material (preferably a graphite active material) is preferably used on the graphite surface by utilizing a huge space or surface area of graphite having a predetermined specific surface area such as expanded graphite or exfoliated graphite (flaky graphite). Highly uniform dispersion of finely divided battery active material). Thereafter, by subjecting the obtained battery active material highly dispersed graphite composition to spheronization treatment, it becomes possible to enhance the adhesion between graphite and the battery active material based on the high adhesion between the graphite AB surfaces. The composite active material obtained by the above procedure is an extremely thin graphite sheet having a large specific surface area, and has a shape that encloses the battery active material. Therefore, the composite active material used for the negative electrode composite of the present invention is incomparable with the contact frequency and adhesion between graphite and the battery active material as compared with the conventional composite active material for lithium secondary battery. It is good. As a result, it is possible to impart high conductivity to the battery active material and to avoid the loss of the conductive path due to the particle collapse of the battery active material associated with the charge / discharge cycle, resulting in a high cycle of the lithium secondary battery. Characteristics can be realized.

Conventionally, a composite active material for a lithium secondary battery composed of graphite and a battery active material has intentionally provided a space for expansion relaxation in the composite active material in order to reduce the volume expansion and contraction of the battery active material. However, the composite active material used in the negative electrode composite of the present invention has a graphite AB surface that has a strong expansion of the battery active material by dispersing graphite and the battery active material as high as possible with a completely opposite concept and further pressing them. Contained inside, the conductivity is maintained and the deformation of the composite active material is suppressed.
Furthermore, even if the battery active material undergoes physical deformation such as pulverization along with the charge / discharge cycle, the battery active material is maintained in a state of being sandwiched between graphite layers whose interlayer distance can be adjusted flexibly. This conductivity is maintained.

  Furthermore, by making this composite active material into a spherical molding material, the powdered battery active material can be prevented from falling off from the flaky graphite layer enclosing it. Alternatively, the composite active material obtained by performing the spheronization treatment has a structure in which the graphite edge surface is not substantially exposed to the outer surface by spheronization. Furthermore, if necessary, by covering the surface with CVD carbon, it is possible to obtain an edgeless structure in which the battery active material or the graphite edge surface is not exposed on the surface of the composite active material for a lithium secondary battery. The composite active material having such a structure exhibits better safety.

  The characteristics representing the structural characteristics of the composite active material used for the negative electrode composite of the present invention are substantially spherical in shape, and 2 of the composite active material using a scanning electron microscope at a low acceleration voltage of 10 kV or less. When the secondary electron image is observed, the area ratio of the graphite exposed on the surface of the composite active material is 95% or more. That is, the battery active material is substantially encapsulated in the composite active material. Further, in the secondary electron image, it is possible to directly observe the battery active material encapsulated while being transmitted through the thin graphite layer and sandwiched in the graphite layer.

  Further, in X-ray diffraction, almost no peak due to an intercalation compound intercalated between graphite layers is observed, and this composite active material is a composite composed of a mechanical mixture of graphite and a battery active material. Recognize. By encapsulating the fine battery active material with the graphite sheet having such a small thickness as described above, the battery active material can be highly dispersed and closely adhered between the graphite sheets. As a result, it is extremely high by taking advantage of the fact that a large battery capacity is originally derived from a non-conductive or low-conductive battery active material, and further, the diffusion distance of lithium ions in the material caused by the fine battery active material is small. A composite active material for a lithium secondary battery capable of producing a lithium secondary battery having charge / discharge rate characteristics and good cycle characteristics can be provided.

First, the manufacturing method of the composite active material used for the negative electrode composite material of the present invention will be described in detail, and the aspect of the composite active material manufactured thereafter will be described in detail.
The method for producing a composite active material used for the negative electrode composite of the present invention includes a mixing step of mixing a predetermined graphite and a battery active material that can be combined with lithium ions, and a spheronization step of subjecting the obtained mixture to a spheronization treatment With.
Below, the material used and the procedure are explained in full detail for every process.

<Mixing process>
The mixing step is a step of obtaining a mixture by mixing graphite having a specific surface area of 30 m ² / g or more and a battery active material that can be combined with lithium ions (hereinafter also simply referred to as a battery active material). By carrying out this step, it is possible to obtain a mixture in which the battery active material is uniformly mixed on a very wide graphite surface and the battery active material is dispersed extremely highly. As will be described later, since graphite has a large area, the battery active material dispersed and adhered to the graphite surface in the mixture is sandwiched between the graphites by applying a slight pressure to the graphite. (In other words, it is included).
First, materials (graphite, battery active material, etc.) used in this step will be described in detail, and then the procedure of this step will be described in detail.

(graphite)
The graphite contained in the composite active material has a specific surface area of 30 m ² / g or more. If it is in the said range, the composite active material in which the battery active material was highly disperse | distributed on the graphite surface of a high surface area (preferably thin thickness) will be obtained. As a result, the battery material using this composite active material exhibits a large charge / discharge capacity and good cycle characteristics. Especially, 40 m < ² > / g or more is preferable and 60 m < ² > / g or more is more preferable at the point which the cycling characteristics of the lithium secondary battery using this composite active material are more excellent. The upper limit is not particularly limited, but the specific surface area is preferably 200 m ² / g or less in that the production procedure is complicated and the synthesis is difficult.

When the specific surface area of graphite is less than 30 m ² / g, mixing of the graphite and the battery active material becomes non-uniform, and the battery active material falls off during molding, the battery active material is exposed to the surface of the molded composite, etc. As a result, the charge / discharge amount and cycle characteristics of the lithium secondary battery using the composite active material are inferior.
In addition, the specific surface area of graphite is measured using the BET method (JIS Z 8830, one point method) by nitrogen adsorption.

The graphite includes a layer in which a plurality of graphene sheets are stacked in the direction in which the graphite surfaces are overlapped, and the graphene sheets are bonded to each other mainly by van der Waals force.
The average thickness of the layer of the graphene sheets stacked in the graphite having the predetermined specific surface area is preferably 29 nm or less in view of more excellent charge / discharge amount and cycle characteristics of the lithium secondary battery using the composite active material. 22 nm or less is more preferable. The lower limit is not particularly limited, but is usually 4.4 nm or more because the production procedure becomes complicated.

In general, the thickness of a single graphene sheet is said to be as thin as 0.34 nm. When the average thickness is less than 18 nm, the specific surface area is calculated to be greater than about 50 m ² / g. Further, the graphene single sheet has a theoretical value of specific surface area reaching 2630 m ² / g.
The average thickness is measured by observing graphite by electron microscope observation (TEM), measuring the thickness of 10 or more layers of the graphene sheet laminated in graphite, and arithmetically averaging the values. An average thickness is obtained.

The lower limit of the bulk specific gravity of the graphite used is not particularly limited, but is preferably 0.01 g / cm ³ or more and 0.02 g / cm ^{3 in} that the battery active material is more uniformly and highly dispersed in the graphite. ³ or more is more preferable. The upper limit is often 0.05 g / cm ³ or less because of manufacturing problems.
In addition, as a measuring method of bulk specific gravity, it inserts in a 500 ml glass measuring cylinder so that a sample may not be compressed, and calculates | requires by dividing the sample weight by a sample volume.

As graphite, a commercially available product may be used, or it may be produced by a known method. So-called expanded graphite or flaky graphite can be used.
As a method for producing expanded graphite, for example, after immersing graphite (for example, flaky graphite) in acid at room temperature, the obtained acid-treated graphite is subjected to heat treatment (preferably treated at 700 to 1000 ° C.). Can be manufactured. More specifically, after scaly natural graphite is immersed in a mixed acid of 9 parts by weight of sulfuric acid and 1 part by weight of nitric acid for about 1 hour, the acid is removed, followed by washing and drying. Then, expanded graphite is obtained by putting the obtained acid-treated graphite into a furnace at about 850 ° C. Note that expanded graphite can also be obtained by using graphite formed with an interlayer compound such as alkali metal instead of acid-treated graphite.

Although the bulk density of the acid-treated graphite obtained above is not particularly limited, 0.6 g / cm ³ or more is preferable and 0.7 g / cm ³ or more is more preferable in view of sufficient expansion of the acid-treated graphite. The upper limit is not particularly limited, but is often 1.0 g / cm ³ or less due to manufacturing problems.
The bulk density is measured by inserting a sample into a 100 ml glass graduated cylinder so as not to be compressed and dividing the sample weight by the sample volume.

As a method for producing flaky graphite, the expanded graphite hinge part is destroyed by dispersing the expanded graphite in a solvent and then treating it with an ultrasonic treatment or a pulverizer (for example, a stone mill) that applies a large shear stress. In addition, flaky graphite in which about 50 (preferably 10 to 150) graphene sheets are laminated can be obtained.
Note that the number of graphene sheets constituting the expanded graphite exhibiting the above specific surface area and the number of graphene sheets constituting the flaky graphite obtained by pulverizing the graphite are estimated to be basically the same.

(Battery active material)
The battery active material used in this step is a battery active material (preferably a negative electrode active material) that can be combined with lithium ions. In other words, any substance (for example, metal, metal carbide, nitride, oxide, or the like) that can occlude and release lithium ions by combining with lithium ions may be used. For example, a metal or nonmetal capable of absorbing and releasing lithium ions, or a metal oxide capable of being alloyed with lithium. Preferably, it is a negative electrode active material.

More specifically, silicon (silicon: Si), tin (Sn), aluminum (Al), antimony (Sb), zinc (Zn), bismuth (Bi), cadmium (Cd), lead (Pb), indium ( In), silver (Ag), gallium (Ga), germanium (Ge), or other metals (metals that can be alloyed with lithium) or alloys containing these metals (for example, Si alloys, Sb alloys, Sn alloys, In alloys) Or metal oxides (metal oxides that can be alloyed with lithium) such as SnO and SnO ₂ .

Among them, the battery active material is at least one selected from the group consisting of Si, Sn, Al, Sb and In in that the theoretical capacity and cycle characteristics of the lithium secondary battery obtained using the obtained composite active material are more excellent. It is preferable to contain a seed element, and it is more preferable to contain a Si or Sn element. Most preferably, the battery active material contains Si.

  In addition, about this alloy, the alloy containing the metal which does not occlude and discharge | release lithium ion other than the alloy which consists of a combination of the above-mentioned metal may be sufficient. In this case, the content of the metal that can be alloyed with the lithium in the alloy is preferably larger. Judging from the uniformity of particles and the cycle characteristics determined by the secondary electron image obtained by SEM observation, the upper limit of the metal content is preferably 70% by mass, and more preferably 60% by mass or less.

The shape of the battery active material to be used is not particularly limited, and any shape such as powder, plate, granule, fiber, lump, and sphere can be used.
The average particle size of the battery active material to be used is 1 μm or less in terms of further suppressing the battery active material from dropping off when the graphite and the battery active material are combined, or the expansion failure of the battery active material accompanying the cycle. Is preferably 0.5 μm or less, and more preferably 0.1 μm or less. The lower limit is not particularly limited and is preferably smaller. In a normal pulverization method, it is possible to produce a fine powder having an average particle size of about 0.01 μm, and a powder having this size can be used effectively.
As a method for measuring the average particle size, a laser diffraction type particle size distribution measuring device is used.

  In addition, as a method for obtaining the battery active material having the predetermined average particle diameter, the battery active material is pulverized by using a known apparatus such as a stirring tank type stirring mill (bead mill, etc.) to obtain the above-mentioned particle diameter. It is possible to obtain a small powder.

(Process procedure)
The method for mixing the graphite and the battery active material described above is not particularly limited, and a known method can be employed, and examples thereof include so-called dry processing or wet processing. In addition, the aspect of a wet process is preferable from the point which the graphite and battery active material in the obtained mixture mix more uniformly.
As the dry process, for example, there is a method of adding the above-described graphite and the battery active material to a known stirrer (for example, a Henschel mixer) and mixing them.

Examples of the wet treatment include a method of dispersing the above-described graphite and battery active material in a solvent, mixing and stirring the obtained solution, and removing the solvent.
The type of the solvent used in the wet treatment is not particularly limited as long as it can disperse graphite and the battery active material. For example, alcohol solvents (eg, methanol, ethanol, isopropanol), ketone solvents (eg, acetone, methyl ethyl ketone, cyclohexanone), amide solvents (eg, formamide, dimethylacetamide, N-methylpyrrolidone, N-ethylpyrrolidone), Nitrile solvents (eg acetonitrile, propionitrile), ester solvents (eg methyl acetate, ethyl acetate), carbonate solvents (eg dimethyl carbonate, diethyl carbonate), ether solvents (eg cellosolve), halogens Examples thereof include a solvent, water, and a mixture thereof.
Among these, alcohol solvents are preferable in that the cycle characteristics of the lithium secondary battery using the obtained composite active material are more excellent.

In the wet processing, the conditions for mixing and stirring the graphite and the battery active material are not particularly limited, and optimal conditions are appropriately selected according to the materials used. Usually, the stirring time is preferably about 1 to 2 hours in that the cycle characteristics of the lithium secondary battery using the obtained composite active material are more excellent as a result of more uniform dispersion of graphite and the battery active material.
Moreover, you may add an ultrasonic wave at the time of a stirring process as needed.

  The method for removing the solvent is not particularly limited, and examples thereof include a method using a known apparatus (for example, an evaporator).

  The mixing ratio of graphite and the battery active material is not particularly limited, but the battery active material is 10 to 10 parts by mass with respect to 100 parts by mass of graphite in that the cycle characteristics of the lithium secondary battery using the obtained composite active material are more excellent. It is preferable to mix 230 mass parts, and it is more preferable to mix 40-150 mass parts.

  Further, the amount of the solvent used is not particularly limited, but as a result of achieving a higher degree of dispersion, the cycle characteristics of the lithium secondary battery using the resulting composite active material are more excellent, with respect to 100 parts by mass of graphite. It is preferable to mix 3000-15000 mass parts of solvent, and it is more preferable to mix 5000-7000 mass parts.

<Spheronization process>
The spheronization step is a step of producing a substantially spherical composite active material containing a battery active material that can be combined with graphite and lithium ions by subjecting the mixture to a spheronization treatment.
By carrying out this step, the graphite sheet is folded into a spherical shape so as to take in the battery active material therein. At that time, the edge portion of the graphite is folded inside, and a structure that is not substantially exposed on the surface of the formed composite active material is obtained.

Below, the difference in the mechanism in the spheronization process between when the flaky graphite is used and when the graphite having a large specific surface area (expanded graphite or flaky graphite) is used will be described in detail.
For example, as described in Japanese Patent Application Laid-Open No. 2008-27897, when scaly graphite and a battery active material are placed in a high-speed air stream, the major axis direction of the graphite, that is, the AB surface of the graphite is aligned in the direction of the air stream. Then, it collides with a pin or a collision plate provided perpendicular to the air flow, the graphite AB surface is compressed and deformed, and as a result, it is spheroidized by sandwiching the battery active material. In this case, most of the battery active material existing on the graphite surface is separated from the graphite surface by the impact at the time of collision, and only the battery active material that happens to be sandwiched between the graphite AB surfaces is sandwiched between the graphite layers.

  On the other hand, in the present invention, for example, when the graphite having a large specific surface area to be used is expanded graphite, the long axis of the expanded graphite is in the direction of the graphite C axis, and when the graphite is placed in a high-speed air stream, Are arranged in the direction of airflow and collide with pins and collision plates. As a result, the graphite C-axis is first compressed, and the graphite changes to a state close to that before expansion. This means that the battery active material adhering to the AB surface of graphite is crushed by graphite, and the battery active material is completely sandwiched between the graphite layers. The graphite once compressed in the C-axis direction changes to a structure in which the AB surface is a major axis, and eventually changes to a sphere-forming body in which the graphite AB surface is folded.

In the case of flaky graphite, compression in the direction parallel to the graphite AB surface and compression in the direction perpendicular to the graphite AB surface are simultaneously received. However, since the modulus of elasticity of the graphite AB surface is low, compression between the graphite AB and the graphite AB surface is easy. The battery active material adhered and deformed to adhere to the flaky graphite surface is preceded by the action of being sandwiched in the graphite AB plane. Thereafter, deformation of the graphite AB surface having a high elastic modulus occurs, and spheroidization proceeds.
Further, since expanded graphite or flaky graphite has a small thickness of the laminated graphene sheet layer constituting it, it goes without saying that the AB surface can be easily deformed with a smaller compressive force in the AB surface direction. .

  The method of spheroidizing treatment is not particularly limited as long as it is a pulverizer capable of mainly applying impact stress. Examples of the pulverizer include a high-speed rotational impact pulverizer. More specifically, a sample mill, a hammer mill, a pin mill, or the like can be used. Among these, a pin mill is preferable in that the graphite and the battery active material are more uniformly mixed, and the resulting lithium secondary battery using the composite active material has more excellent cycle characteristics.

  Examples of high-speed rotary impact type pulverizers include those that collide a sample with a rotor that rotates at high speed and achieve miniaturization by the impact force. For example, a hammer with a fixed or swing type impactor attached to the rotor Mill type hammer type, pin mill type rotary disc type with a pin and impact head attached to a rotating disc, an axial flow type that crushes while the sample is conveyed in the shaft direction, and an annular type that refines particles in a narrow annular part Examples include molds. More specifically, a hammer mill, a pin mill, a screen mill, a turbo mill, a centrifugal classification mill, and the like can be given.

  When this step is performed with the high-speed rotational impact pulverizer, the spheronization is preferably performed at a rotation speed of usually 100 rpm or more, preferably 1500 rpm or more, and usually 20000 rpm or less. Grinding progresses from spheroidization due to excessive impact force. Therefore, the collision speed is preferably about 20 m / second to 100 m / second.

Unlike pulverization, since the spheronization treatment is carried out with a low impact force, it is usually preferable to perform a circulation treatment in this step. The processing time varies depending on the type of the pulverizer to be used, the amount charged, and the like, but is usually within 2 minutes, and the processing time can be completed in about 10 seconds if the apparatus is provided with an appropriate pin or collision plate. .
The spheronization treatment is preferably performed in air. If the same treatment is performed with nitrogen, there is a risk of fire when released to the atmosphere.

<Composite active material>
The composite active material obtained through the above-described steps is substantially spherical and contains graphite and a battery active material.
Hereinafter, the obtained composite active material will be described in detail.

The shape of the composite active material has a substantially spherical shape by the above treatment. The term “substantially spherical” means that the composite active material has a rounded structure and does not have sharp edges (peaks or twills) that are commonly found in crushed grains.
More specifically, the substantially spherical shape means that the aspect ratio (major axis / minor axis), which is the ratio of the major axis to the minor axis, is in the range of 1 to 3 (1-2 in that the effect of the present invention is more excellent). More preferably) the shape of composite active material particles. The aspect ratio means a value (arithmetic average value) obtained by calculating the long diameter / short diameter of each particle for at least 100 particles and arithmetically averaging them.

  The minor axis in the above is the distance between two parallel lines that are in contact with the outside of the particles observed by a scanning electron microscope or the like and that are the shortest distance among the combinations of two parallel lines that sandwich the particles. On the other hand, the major axis is the two parallel lines perpendicular to the parallel line that determines the minor axis, and the distance between the two parallel lines that is the longest interval among the combination of two parallel lines that touch the outside of the particle It is. The rectangle formed by these four lines is the size that the particles just fit within.

The area ratio of the graphite exposed on the surface of the composite active material for a lithium secondary battery observed by scanning electron microscope (SEM) observation at an acceleration voltage of 10 kV or less is 95% or more. Among these, 98% or more is more preferable, and 99% or more is more preferable. The upper limit is not particularly limited and may be 100%. If the area ratio is within the above range, the amount of the battery active material exposed on the surface of the composite active material is small, and as a result, the cycle characteristics and the like are excellent.
When the area ratio is out of the above range (less than 95%), the battery active material is likely to fall off, resulting in poor cycle characteristics.
As a method for measuring the area ratio, at least 100 composite active materials are observed with a scanning electron microscope (preferably at a magnification of 2000 times or more) at an acceleration voltage of 10 kV or less, and graphite occupies the surface of each composite active material. It is the value which measured the area ratio of and calculated them arithmetically.

Further, the area ratio of the battery active material exposed on the surface of the composite active material for a lithium secondary battery observed by observation with a scanning electron microscope at an acceleration voltage of 10 kV or less is preferably 5% or less. Among these, 2% or less is more preferable, and 1% or less is more preferable. A minimum in particular is not restrict | limited, 0% is mentioned. If the area ratio is within the above range, the amount of the battery active material exposed on the surface of the composite active material is small, and as a result, the cycle characteristics and the like are excellent.
As a method for measuring the area ratio, at least 100 composite active materials are observed with a scanning electron microscope (preferably at a magnification of 2000 times or more) at an acceleration voltage of 10 kV or less, and a battery occupying the surface of each composite active material It is a value obtained by measuring the area ratio of the active material and arithmetically averaging them.

  Further, as a feature of the composite active material, when observed with a scanning electron microscope at an acceleration voltage of 10 kV or less, the battery active material encapsulated in a state of being sandwiched in the graphite layer through the thin graphite layer can be directly observed. .

  Moreover, as a preferable aspect of a composite active material, the aspect which the edge part of graphite is not exposed on the surface substantially is mentioned. Since the edge portion is not exposed on the surface, the decomposition of the electrolytic solution and the destruction of the graphite, which are likely to occur during the charge / discharge cycle, are further suppressed, and as a result, the cycle characteristics are improved.

The content of the battery active material in the composite active material can be appropriately adjusted depending on the content of graphite and the battery active material in the mixing step described above.
Among them, the content of the battery active material is preferably 10% by mass or more, and 20% by mass with respect to the total amount of the composite active material in that the cycle characteristics of the lithium secondary battery using the obtained composite active material are more excellent. Is more preferable, and 30% by mass or more is particularly preferable. As an upper limit, 70 mass% or less is preferable, and 60 mass% or less is more preferable.
Even when the content of the battery active material is within the above range in the obtained composite active material, the area ratio of graphite exposed on the surface of the composite active material is within the above range.
When the battery active material is Si, when the content of Si in the composite active material is 30% by mass, the charge / discharge capacity derived only from Si is about 1200 mAh / g.

The particle size (D50: 50% volume particle size) of the composite active material is not particularly limited, but is preferably 2 to 30 μm in terms of more excellent cycle characteristics of the lithium secondary battery using the resulting composite active material, 20 micrometers is more preferable and 5-15 micrometers is still more preferable.
The particle size (D90: 90% volume particle size) is not particularly limited, but is preferably 7 to 30 μm, more preferably 10 to 25 μm in terms of more excellent cycle characteristics of the lithium secondary battery using the obtained composite active material. More preferred.
Further, the particle size (D10: 10% volume particle size) is not particularly limited, but 1 to 10 μm is preferable and 2 to 3 μm is preferable in that the cycle characteristics of the lithium secondary battery using the obtained composite active material are more excellent. More preferred.

D10, D50, and D90 correspond to the particle sizes of 10%, 50%, and 90% from the fine particle side of the cumulative particle size distribution measured by the laser diffraction scattering method, respectively.
In the measurement, the composite active material is added to the liquid and mixed vigorously while using ultrasonic waves or the like, and the prepared dispersion is introduced as a sample into the apparatus for measurement. As the liquid, it is preferable to use water, alcohol, or a low-volatile organic solvent for work. At this time, the obtained particle size distribution diagram preferably shows a normal distribution.

The bulk density of the composite active material is not particularly limited, but is preferably 0.5 g / cm ³ or more and more preferably 0.7 g / cm ³ or more in order to increase the capacity per volume of the composite active material to be obtained. The upper limit is not particularly limited.
The method for measuring the bulk density is the same as the method for measuring the bulk density of graphite described above, except that a 25 ml graduated cylinder is used.

The tap density of the composite active material is not particularly limited, but is preferably 0.8 g / cm ³ or more and more preferably 1.0 g / cm ³ or more in order to increase the capacity per volume of the composite active material to be obtained. The upper limit is not particularly limited, but is preferably 1.6 g / cm ³ or less.
The tap density is measured by putting the sample in a 25 ml graduated cylinder, tapping, and dividing the sample weight at the time when the change in capacity disappears by the sample volume.

The specific surface area (BET specific surface area) of the composite active material is not particularly limited, but is preferably 5 m ² / g or more, more preferably 8 m ² / g in terms of better cycle characteristics of the lithium secondary battery using the resulting composite active material. The above is more preferable. The upper limit is not particularly limited, but is preferably 100 m ² / g or less.
The measurement method of the specific surface area (BET specific surface area) of the composite active material is measured by a nitrogen adsorption one-point method after vacuum drying the sample at 300 ° C. for 30 minutes.

If necessary, the surface of the composite active material can be coated with carbon. By performing this treatment, the surface area of the composite active material can be adjusted, and the electrochemical stability can be enhanced.
The method of coating with carbon is not particularly limited, and examples thereof include a CVD method. More specifically, it is preferable to perform a CVD process at 750 to 1100 ° C. by flowing a gas such as toluene.

[Solid electrolyte]
The solid electrolyte used for the negative electrode mixture of the present invention is, for example, an oxide solid electrolyte or a sulfide solid electrolyte.
(1) Oxide-based solid electrolyte The oxide-based solid electrolyte includes a crystal having a perovskite structure such as LiN, LISICON, Thio-LISON, La _0.55 Li _0.35 TiO ₃ ; LiTi having a NASICON type structure ₂ P ₃ O ₁₂ ; an electrolyte obtained by crystallizing these, and the like.

(2) Sulfide-based solid electrolyte The sulfide-based solid electrolyte is preferably a lithium ion conductive inorganic solid electrolyte containing Li, P, and S, and more preferably lithium ions satisfying the composition represented by the following formula (I) Conductive inorganic solid electrolyte.
Li _a M _b P _c S _d (I)
In the formula (I), M represents an element selected from B, Zn, Si, Cu, Ga, or Ge.
a to d indicate the composition ratio of each element, and a: b: c: d satisfies 1 to 12: 0 to 0.2: 1: 2 to 9.
Preferably, b is 0, more preferably the ratio of a, c and d (a: c: d) is a: c: d = 1 to 9: 1: 3-7, more preferably a: c: d = 1.5-4: 1: 3.25-4.5.
As will be described later, the composition ratio of each element can be controlled by adjusting the blending amount of the raw material compound in producing the sulfide-based solid electrolyte.

The sulfide-based solid electrolyte may be amorphous (glass) or crystallized (glass ceramics), or only partially crystallized.
Here, when crystallized, the ion conductivity may be higher than that of amorphous, and in that case, it is preferable to crystallize.

Examples of the crystal structure of the sulfide-based solid electrolyte include, for example, Li ₇ PS ₆ structure, Li ₄ P ₂ S ₆ structure, Li ₃ PS ₄ structure, Li ₄ SiS ₄ structure disclosed in JP 2002-109955 A, Li ₂ SiS ₃ structure, Li ₇ P ₃ S ₁₁ structure disclosed in JP-A-2005-228570 and International Publication No. 2007/065539 are preferable. If these crystal structures are used, the ionic conductivity is higher than that of the amorphous body. Can be increased.
Here, the crystallized portion of the sulfide-based solid electrolyte may consist of only one crystal structure or may have a plurality of crystal structures.

In particular, Li ₇ P ₃ S ₁₁ can be cited as a crystal structure of a sulfide-based solid electrolyte having high ionic conductivity.
The Li ₇ P ₃ S ₁₁ structure has 2θ = 17.8 ± 0.3 deg, 18.2 ± 0.3 deg, 19.8 ± 0.3 deg, 21 in X-ray diffraction (CuKα: λ = 1.5418４). It has diffraction peaks at .8 ± 0.3 deg, 23.8 ± 0.3 deg, 25.9 ± 0.3 deg, 29.5 ± 0.3 deg, 30.0 ± 0.3 deg.

The degree of crystallinity of the sulfide-based solid electrolyte (the degree of crystallinity of the crystal structure having higher ionic conductivity than that of the amorphous body) is preferably 50% or more, more preferably 60% or more.
This is because when the crystallinity of the sulfide-based solid electrolyte is less than 50%, the effect of increasing the ionic conductivity by crystallization is reduced.
The degree of crystallinity can be measured by using an NMR spectrum apparatus. Specifically, a solid ³¹ P-NMR spectrum of a sulfide-based solid electrolyte was measured, and the resonance line observed at 70-120 ppm was separated into a Gaussian curve using a nonlinear least square method. It can be measured by determining the area ratio of each curve.

The sulfide-based solid electrolyte can be produced by the following method.
The raw materials for the sulfide-based solid electrolyte are Li ₂ S (lithium sulfide), P ₂ S ₃ (phosphorus trisulfide), P ₂ S ₅ (phosphorus pentasulfide), SiS ₂ (silicon sulfide), Li ₄ SiO _4. (Lithium orthosilicate), Al ₂ S ₃ (aluminum sulfide), single phosphorus (P), single sulfur (S), silicon (Si), GeS ₂ (germanium sulfide), B ₂ S ₃ (diboron trisulfide) ), Li ₃ PO ₄ (lithium phosphate), Li ₄ GeO ₄ (lithium germanate), LiBO ₂ (lithium metaborate), LiAlO ₃ (lithium aluminate), or the like can be used.
Preferred raw materials for sulfide-based solid electrolytes are Li ₂ S (lithium sulfide) and P ₂ S ₅ (diphosphorus pentasulfide).

Hereinafter, a sulfide-based solid electrolyte using Li ₂ S (lithium sulfide) and P ₂ S ₅ (diphosphorus pentasulfide) as a raw material for the sulfide-based solid electrolyte will be described.

Lithium sulfide can be manufactured by the method of Unexamined-Japanese-Patent No. 7-330312, Unexamined-Japanese-Patent No. 9-283156, Unexamined-Japanese-Patent No. 2010-163356, and Unexamined-Japanese-Patent No. 2011-84438, for example.
In JP 2010-163356 A, lithium hydroxide and hydrogen sulfide are reacted at 70 ° C. to 300 ° C. in a hydrocarbon organic solvent to produce lithium hydrosulfide, and then this reaction solution is dehydrosulfurized. To synthesize lithium sulfide. In JP 2011-84438 A, lithium hydroxide and hydrogen sulfide are reacted at 10 ° C. to 100 ° C. in an aqueous solvent to produce lithium hydrosulfide, and then this reaction solution is dehydrosulfurized. To synthesize lithium sulfide.

Although there is no restriction | limiting in particular, the lithium sulfide used for manufacture of sulfide type solid electrolyte has a high purity.
The lithium sulfide preferably has a total lithium oxide lithium salt content of 0.15% by mass or less, more preferably 0.1% by mass or less, and a lithium N-methylaminobutyrate content. The content is preferably 0.15% by mass or less, more preferably 0.1% by mass or less.

When the total content of the lithium salt of the sulfur oxide is 0.15% by mass or less, the sulfide-based solid electrolyte obtained by the melt quenching method or the mechanical milling method is a glassy sulfide-based solid electrolyte (fully amorphous). Quality). On the other hand, when the total content of the lithium salt of sulfur oxide exceeds 0.15% by mass, the obtained electrolyte may become a crystallized product from the beginning, and the ionic conductivity of the crystallized product is low. Further, even if this crystallized product is subjected to a heat treatment, the crystallized product is not changed, and there is a possibility that a sulfide-based solid electrolyte having high ion conductivity cannot be obtained. In addition, when the content of lithium N-methylaminobutyrate is 0.15% by mass or less, a deteriorated product of lithium N-methylaminobutyrate does not deteriorate the cycle performance of the lithium ion battery.
When lithium sulfide with reduced impurities is used as described above, a sulfide-based solid electrolyte having high ionic conductivity can be obtained.

The lithium sulfides described in JP-A-7-330312 and JP-A-9-283156 preferably contain a lithium salt of sulfur oxide and the like, and thus are preferably purified.
In the case of purifying lithium sulfide, a preferable purification method includes, for example, a purification method described in International Publication No. 2005/40039. Specifically, the lithium sulfide obtained as described above is purified by washing at a temperature of 100 ° C. or higher using an organic solvent.
In addition, since lithium sulfide manufactured by the manufacturing method of lithium sulfide described in JP 2010-163356 A has a very small content of lithium salt of sulfur oxide, etc., manufacture of a sulfide-based solid electrolyte without purification Can be used.

The phosphorous pentasulfide (P ₂ S ₅ ) used for the production of the sulfide-based solid electrolyte can be used without particular limitation as long as it is industrially produced and sold.

When a sulfide-based solid electrolyte is produced using lithium sulfide and diphosphorus pentasulfide, the ratio (molar ratio) between lithium sulfide and diphosphorus pentasulfide is usually Li ₂ S: P ₂ S ₅ = 50: 50˜ 80:20, preferably 60:40 to 80:20, more preferably 65:35 to 78:22, and most preferably 68:32 to 76:24.

As a method for producing a glassy sulfide-based solid electrolyte using lithium sulfide (Li ₂ S) and diphosphorus pentasulfide (P ₂ S ₅ ), a melt quenching method, a mechanical milling method (MM method), an organic solvent There is a slurry method in which the raw materials are reacted.

(A) Melting and quenching method The melting and quenching method is described in, for example, Japanese Patent Application Laid-Open No. 6-279049 and International Publication No. 2005/119706. Specifically, a predetermined amount of P ₂ S ₅ and Li ₂ S mixed in a mortar and pelletized are placed in a carbon-coated quartz tube and vacuum-sealed. After reacting at a predetermined reaction temperature, it is put into ice and rapidly cooled to obtain a glassy sulfide-based solid electrolyte.
The reaction temperature is preferably 400 ° C to 1000 ° C, more preferably 800 ° C to 900 ° C.
The reaction time is preferably 0.1 hour to 12 hours, more preferably 1 to 12 hours.
The quenching temperature of the reaction product is usually 10 ° C. or less, preferably 0 ° C. or less, and the cooling rate is usually about 1 to 10,000 K / sec, preferably 10 to 10,000 K / sec.

(B) Mechanical milling method The mechanical milling method is described in, for example, JP-A-11-134937, JP-A-2004-348972, and JP-A-2004-34897.
For example, a predetermined amount of P ₂ S ₅ and Li ₂ S are mixed in a mortar and reacted for a predetermined time using various ball mills or the like to obtain a glassy sulfide-based solid electrolyte.
The mechanical milling method using the above raw materials can be reacted at room temperature. According to the mechanical milling method, since a glassy sulfide-based solid electrolyte can be produced at room temperature, there is an advantage that a raw material is not thermally decomposed and a glassy sulfide-based solid electrolyte having a charged composition can be obtained. is there. The mechanical milling method also has an advantage that the glassy sulfide-based solid electrolyte can be finely powdered simultaneously with the production of the glassy sulfide-based solid electrolyte.

For the mechanical milling method, various types such as a rotating ball mill, a rolling ball mill, a vibrating ball mill, and a planetary ball mill can be used. Incidentally, as described in JP 2010-90003 A, balls of a ball mill may be used by mixing balls having different diameters.
As a condition of the mechanical milling method, for example, when a planetary ball mill is used, the rotation speed may be several tens to several hundreds of revolutions / minute, and the treatment may be performed for 0.5 hours to 100 hours. At this time, it is preferable that the raw material be 60 ° C. or higher and 160 ° C. or lower.
As described in JP 2009-110920 A and JP 2009-211950 A, an organic solvent may be added to the raw material to form a slurry, and the slurry may be mechanically milled. Moreover, you may adjust the temperature in the mill in the case of a mechanical milling process as described in Unexamined-Japanese-Patent No. 2010-30889.

(C) Slurry method The slurry method is described in, for example, International Publication No. 2004/093099 and International Publication No. 2009/047977.
Specifically, a glassy sulfide-based solid electrolyte is obtained by reacting a predetermined amount of phosphorous pentasulfide (P ₂ S ₅ ) particles and lithium sulfide (Li ₂ S) particles in an organic solvent for a predetermined time. It is done.
Here, as described in Japanese Patent Application Laid-Open No. 2010-140893, in order to advance the reaction, the slurry containing the raw material may be reacted while being circulated between the bead mill and the reaction vessel. Further, as described in International Publication No. 2009/047977, when the raw material lithium sulfide is pulverized in advance, the reaction can proceed efficiently. In addition, as described in JP2011-136899A, polar solvents having a solubility parameter of 9.0 or more (for example, methanol, diethylcarnate, acetonitrile, etc.) in order to increase the specific surface area of the raw material lithium sulfide. ) For a predetermined time.

The organic solvent used in the slurry method is not particularly limited, but an aprotic organic solvent is particularly preferable.
Aprotic organic solvents include aprotic organic solvents (for example, hydrocarbon organic solvents), aprotic polar organic compounds (for example, amide compounds, lactam compounds, urea compounds, organic sulfur compounds, cyclic organophosphorus compounds, etc. ) And can be suitably used as a single solvent or as a mixed solvent.

As the hydrocarbon organic solvent which is an aprotic organic solvent, a saturated hydrocarbon solvent, an unsaturated hydrocarbon solvent or an aromatic hydrocarbon solvent can be used, and as the saturated hydrocarbon solvent, hexane, pentane, 2-ethylhexane , Heptane, decane, cyclohexane, etc., unsaturated hydrocarbon solvents include hexene, heptene, cyclohexene, etc., and aromatic hydrocarbon solvents include toluene, xylene, decalin, 1, 2, 3, 4 -Tetrahydronaphthalene etc. are mentioned. Among these hydrocarbons, toluene and xylene are particularly preferable.
The hydrocarbon solvent is preferably dehydrated in advance. Specifically, the water content is preferably 100 ppm by weight or less, and particularly preferably 30 ppm by weight or less.
In addition, you may add another solvent to a hydrocarbon type solvent as needed. Specific examples include ketones such as acetone and methyl ethyl ketone, ethers such as tetrahydrofuran, alcohols such as ethanol and butanol, esters such as ethyl acetate, and halogenated hydrocarbons such as dichloromethane and chlorobenzene.

  The amount of the raw material added to the organic solvent is preferably such that the raw materials lithium sulfide and diphosphorus pentasulfide are in the form of a solution or slurry. Usually, the amount of the raw material (total amount) added to 1 liter of the organic solvent is about 0.001 kg or more and 1 kg or less, preferably 0.005 kg or more and 0.5 kg or less, and more preferably 0.01 kg or more to 0. 3 kg.

  In the slurry method, the reaction temperature is preferably 20 ° C. or higher and 80 ° C. or lower, more preferably 20 ° C. or higher and 60 ° C. or lower. The reaction time is preferably 1 hour or longer and 16 hours or shorter, more preferably 2 hours or longer and 14 hours or shorter.

  Manufacturing conditions such as temperature conditions, processing time, and charge of the melt quenching method, mechanical milling method and slurry method can be appropriately adjusted according to the equipment used.

A method for producing a crystalline sulfide solid electrolyte is disclosed in Japanese Patent Application Laid-Open No. 2005-228570, International Publication No. 2007/065539, and Japanese Patent Application Laid-Open No. 2002-109955.
Specifically, a crystalline sulfide solid electrolyte is obtained by heat-treating the glassy sulfide solid electrolyte obtained by the above-described method at a predetermined temperature.

The glassy sulfide-based solid electrolyte is preferably heated in an environment with a dew point of −40 ° C. or less, and more preferably in an environment with a dew point of −60 ° C. or less.
The pressure during heating may be normal pressure or reduced pressure, and the atmosphere during heating may be air or an inert atmosphere. Furthermore, you may heat in a solvent as it describes in Unexamined-Japanese-Patent No. 2010-186744.

The heating conditions for producing a sulfide-based solid electrolyte having a Li ₇ P ₃ S ₁₁ crystal structure include the following.
The heat treatment temperature is preferably 180 ° C. or higher and 330 ° C. or lower, more preferably 200 ° C. or higher and 320 ° C. or lower, and particularly preferably 210 ° C. or higher and 310 ° C. or lower. If the temperature is lower than 180 ° C., a sulfide-based solid electrolyte having a high degree of crystallinity may be difficult to obtain. If the temperature is higher than 330 ° C., a sulfide-based solid electrolyte having a crystal structure having a low ionic conductivity may be generated.
When the heat treatment temperature is 180 ° C. or higher and 210 ° C. or lower, the heat treatment time is preferably 3 hours or longer and 240 hours or shorter, and particularly preferably 4 hours or longer and 230 hours or shorter. Further, when the heat treatment temperature is higher than 210 ° C and lower than or equal to 330 ° C, it is preferably 0.1 hours or longer and 240 hours or shorter, more preferably 0.2 hours or longer and 235 hours or shorter, and further preferably 0.3 hours or longer and 230 hours or shorter. .
If the heat treatment time is shorter than 0.1 hour, a sulfide-based solid electrolyte with a high degree of crystallinity may be difficult to obtain. If longer than 240 hours, a sulfide-based solid electrolyte with a low degree of crystallinity may be generated. .

When producing a sulfide-based solid electrolyte having a Li ₇ PS ₆ crystal structure, a Li ₄ P ₂ S ₆ crystal structure, a Li ₃ PS ₄ crystal structure, a Li ₄ SiS ₄ crystal structure, or a Li ₂ SiS ₃ crystal structure, these A sulfide-based solid electrolyte having a crystal structure can be produced by a known method, for example, a method disclosed in JP-A-2002-109955.

[Other ingredients]
In addition to the composite active material for lithium secondary batteries and the solid electrolyte, the negative electrode mixture of the present invention may contain other optional components such as a binder.
Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), fluorine-containing resins such as fluororubber; thermoplastic resins such as polypropylene and polyethylene; ethylene-propylene-dienemer (EPDM), sulfonated EPDM, natural Butyl rubber (NBR) or the like can be used alone or as a mixture of two or more.
In addition, an aqueous dispersion of cellulose or styrene butadiene rubber (SBR), which is an aqueous binder, can also be used.

[Composition of negative electrode mixture]
The weight ratio of the composite active material for a lithium secondary battery and the solid electrolyte contained in the negative electrode mixture of the present invention is, for example, 90:10 to 30:70 (weight ratio), and preferably 80:20 to 40:60 ( Weight ratio).

  The negative electrode composite of the present invention may consist only of a composite active material for lithium secondary batteries and a solid electrolyte, or may consist essentially of a composite active material for lithium secondary batteries and a solid electrolyte. In the present invention, “substantially” means that the content of the composite active material for lithium secondary battery and the solid electrolyte in the negative electrode mixture is, for example, 90 wt% or more, 95 wt% or more, 97 wt% or more, or It means 99% by weight or more.

[Method for producing negative electrode mixture]
The negative electrode composite of the present invention can be produced by mixing a material containing a composite active material and a solid electrolyte.
The mixing method of the materials can be used without any particular limitation, for example, dry mixing using a mortar, ball mill, bead mill, jet mill, planetary ball mill, vibrating ball mill, pin mill, sand mill, cutter mill; and in an organic solvent After the raw materials are dispersed in the mixture, mixing using a mortar, ball mill, bead mill, planetary ball mill, vibrating ball mill, pin mill, sand mill, and fill mix, and then wet mixing for removing the solvent can be applied.

[Lithium secondary battery]
The negative electrode mixture of the present invention can be suitably used as a material for the negative electrode layer of a lithium secondary battery. The lithium secondary battery of the present invention is an all-solid battery including a positive electrode layer, an electrolyte layer, and a negative electrode layer in this order, and the negative electrode layer includes the negative electrode mixture of the present invention.

The composite active material described above is useful as an active material used for battery materials (electrode materials) used in lithium secondary batteries.
Features of the battery material using the composite active material include that a capacity close to the theoretical value of the battery material is obtained, that the cycle characteristics are good, and that the rate characteristics are excellent. The reason why the capacity close to the theoretical value of the battery material can be obtained is that graphite having excellent conductivity can sufficiently exist around the refined battery active material. In addition, the reason why the cycle characteristics are good is that even if the battery active material is pulverized with the cycle, the battery active material does not lose the conductive path because it is tightly wrapped in the thin graphite layer. It is done. Furthermore, the reason why the rate characteristics are excellent is that the diffusion distance of Li ions is small as a result of the refinement of the battery active material. In particular, it is theoretically clear that the rate characteristics become better as the particle size becomes smaller, but in an environment in which the battery active material further refined with the cycle does not fall off and is securely held in a thin graphite layer. This is achieved only when a sufficient conductive path is secured.

Hereinafter, each layer of the lithium ion battery of the present invention will be described.
(1) Negative electrode layer The negative electrode layer (hereinafter also simply referred to as “negative electrode”) is a layer containing the negative electrode mixture of the present invention or a layer produced from the negative electrode mixture of the present invention.
A negative electrode layer should just contain the negative electrode compound material of this invention, and may consist only of the negative electrode compound material of this invention.
The thickness of the negative electrode layer is preferably from 100 nm to 5 mm, more preferably from 1 μm to 3 mm, and even more preferably from 5 μm to 1 mm.
A negative electrode layer can be manufactured by a well-known method, for example, can be manufactured by the apply | coating method and an electrostatic method (an electrostatic spray method, an electrostatic screen method, etc.).

(2) Electrolyte layer The electrolyte layer is a layer containing a solid electrolyte. Examples of the solid electrolyte constituting the electrolyte layer include the oxide-based solid electrolyte described above, and a polymer-based solid electrolyte in addition to the sulfide-based solid electrolyte.
As the polymer solid electrolyte, as disclosed in, for example, JP-A-2010-262860, it is used as a polymer electrolyte such as fluororesin, polyethylene oxide, polyacrylonitrile, polyacrylate, and derivatives and copolymers thereof. Materials that can be used.
Examples of the fluororesin that is a polymer-based solid electrolyte include a polymer containing, as a structural unit, vinylidene fluoride (VdF), hexafluoropropylene (HFP), tetrafluoroethylene (TFE), or a derivative thereof. Specifically, homopolymers such as polyvinylidene fluoride (PVdF), polyhexafluoropropylene (PHFP), polytetrafluoroethylene (PTFE); a copolymer of VdF and HFP (hereinafter, this copolymer is referred to as “P (VdF-HFP) ") and the like, and binary copolymers and ternary copolymers.

  The electrolyte layer may consist only of a solid electrolyte, and may further contain a binder. As the binder, the same binder as that of the negative electrode mixture of the present invention can be used.

The thickness of the electrolyte layer is preferably 0.001 mm or more and 1 mm or less.
The solid electrolyte of the electrolyte layer is preferably fused. The fusion means that a part of the solid electrolyte particles is dissolved and the dissolved part is integrated with other solid electrolyte particles. The electrolyte layer may be a solid electrolyte plate, and the plate includes a case where a part or all of the solid electrolyte particles are dissolved to form a plate.
The electrolyte layer can be manufactured by a known method, for example, by a coating method or an electrostatic method (an electrostatic spray method, an electrostatic screen method, or the like).

(3) Positive Electrode Layer The positive electrode layer (hereinafter also simply referred to as “positive electrode”) is a layer containing a positive electrode active material.
The positive electrode active material is a material capable of inserting and removing lithium ions, and those known as a positive electrode active material in the battery field can be used.
Examples of the positive electrode active material include V ₂ O ₅ , LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li (Ni _a Co _b Mn _c ) O ₂ (where 0 <a <1, 0 <b <1, 0 <c <1, a + b + c = 1), LiNi _1-Y Co _{Y 2} O ₂ , LiCo _1-Y Mn _{Y 2} O ₂ , LiNi _1-Y Mn _{Y 2} O ₂ (where 0 ≦ Y <1) _{, Li (Ni a Co b Mn} c) O 4 (0 <a <2,0 <b <2,0 <c <2, a + b + c = 2), LiMn 2-Z Ni Z O 4, LiMn 2-Z CoZO ₄ (where 0 <Z <2), LiCoPO ₄ , and LiFePO ₄ .
In the sulfide-based positive electrode active material, titanium sulfide (TiS ₂ ), molybdenum sulfide (MoS ₂ ), iron sulfide (FeS, FeS ₂ ), copper sulfide (CuS), nickel sulfide (Ni ₃ S ₂ ), etc. can be used. TiS ₂ is preferable.
In the oxide-based positive electrode active material, bismuth oxide (Bi ₂ O ₃ ), bismuth leadate (Bi ₂ Pb ₂ O ₅ ), copper oxide (CuO), vanadium oxide (V ₆ O ₁₃ ), lithium cobalt oxide (LiCoO ₂₎ ), Lithium nickelate (LiNiO ₂ ), lithium manganate (LiMnO ₂ ), and the like. It is also possible to use a mixture of these. Preferably, lithium cobaltate can be used.
In addition, Li _x CoO ₂ , Li _x NiO ₂ , Li _x Mn ₂ O ₄ , Li _x FePO ₄ , Li _x CoPO ₄ , Li _x Mn _1/3 Ni _1/3 Co _1/3 O ₂ , Li _x Mn _{1 .5} Ni _0.5 O ₂ and the like can also be used (X is 0.1 to 0.9.)

In addition to the above, niobium selenide (NbSe ₃ ), organic disulfide compounds shown below, carbon sulfide compounds shown below, sulfur, lithium sulfide, metal indium and the like can be used as the positive electrode active material, preferably sulfur, lithium sulfide is there.
(In Formulas (A) to (C), X is a substituent, n and m are each independently an integer of 1 to 2, and p and q are each independently an integer of 1 to 4.
In formula (D), Z is -S- or -NH-, respectively, and n is an integer of 2 to 300 repetitions. )
(In the formula, n and m are each an integer of 1 or more.)

The positive electrode layer may further contain a solid electrolyte and / or a conductive aid.
Examples of the solid electrolyte included in the positive electrode layer include the same as the solid electrolyte of the negative electrode layer and the electrolyte layer.
The conductive auxiliary agent only needs to have conductivity, and its electronic conductivity is preferably 1 × 10 ³ S / cm or more, more preferably 1 × 10 ⁵ S / cm or more. Examples of the conductive aid include substances selected from carbon materials, metal powders and metal compounds, and mixtures thereof.
Specific examples of conductive aids are preferably carbon materials, nickel, copper, aluminum, indium, silver, cobalt, magnesium, lithium, chromium, gold, ruthenium, platinum, beryllium, iridium, molybdenum, niobium, osnium, rhodium, A substance containing at least one element selected from the group consisting of tungsten and zinc, and more preferably a carbon simple substance having a high conductivity, or a carbon material other than simple carbon; nickel, copper, silver, cobalt, magnesium, lithium, ruthenium , Gold, platinum, niobium, osnium or rhodium, simple metals, mixtures or compounds.
Specific examples of carbon materials include carbon blacks such as ketjen black, acetylene black, denka black, thermal black, and channel black; graphite, carbon fiber, activated carbon, and the like. These may be used alone or in combination of two or more. Is possible. Among these, acetylene black, denka black, and ketjen black having high electron conductivity are preferable.

The thickness of the positive electrode is preferably 0.01 mm or more and 10 mm or less.
The positive electrode layer can be manufactured by a known method, for example, by a coating method or an electrostatic method (electrostatic spray method, electrostatic screen method, etc.).

(4) Current Collector The lithium secondary battery of the present invention may further include a current collector, and a known current collector can be used as the current collector.
The current collector is a layer in which a layer made of a metal that reacts with a sulfide-based solid electrolyte, such as Au, Pt, Al, or Cu, is further coated with Au, conductive carbon, or the like.

[Equipment with lithium secondary battery]
The lithium secondary battery using the negative electrode mixture of the present invention can be provided in various devices. Specifically, it can be used as a battery for a portable information terminal, a portable electronic device, a small household power storage device, a motorcycle using a motor as a power source, an electric vehicle, a hybrid electric vehicle, or the like.

Production Example 1 Production of Solid Electrolyte (1) Production of Lithium Sulfide Production and purification of lithium sulfide were carried out in the same manner as in Example of International Publication No. 2005/040039. Specifically, it is as follows.
A 10-liter autoclave equipped with a stirring blade was charged with 3326.4 g (33.6 mol) of N-methyl-2-pyrrolidone (NMP) and 287.4 g (12 mol) of lithium hydroxide at 130 ° C. while stirring at 300 rpm. The temperature was raised to. After the temperature rise, hydrogen sulfide was blown into the liquid at a supply rate of 3 liters / minute for 2 hours.

  Subsequently, this reaction solution was heated in a nitrogen stream (200 cc / min) to dehydrosulfide a part of the reacted hydrogen sulfide. As the temperature increased, water produced as a by-product due to the reaction between hydrogen sulfide and lithium hydroxide began to evaporate, but this water was condensed by the condenser and extracted out of the system. While water was distilled out of the system, the temperature of the reaction solution rose, but when the temperature reached 180 ° C., the temperature increase was stopped and the temperature was kept constant. After the dehydrosulfurization reaction was completed (about 80 minutes), the reaction was completed to obtain lithium sulfide.

(2) Purification of lithium sulfide After decanting NMP in the 500 mL slurry reaction solution (NMP-lithium sulfide slurry) obtained in (1) above, 100 mL of dehydrated NMP was added and stirred at 105 ° C. for about 1 hour. . NMP was decanted at that temperature. Further, 100 mL of NMP was added, stirred at 105 ° C. for about 1 hour, NMP was decanted at that temperature, and the same operation was repeated a total of 4 times. After completion of decantation, lithium sulfide was dried for 3 hours under a nitrogen stream at 230 ° C. (temperature higher than the boiling point of NMP) and normal pressure. The impurity content in the obtained lithium sulfide was measured.

Incidentally, lithium sulfite _(Li 2 _SO 3), the content of each sulfur oxide lithium sulfate _(Li 2 SO ₄₎ and lithium thiosulfate _{(Li 2 S 2 O 3)} , and N- methylamino acid lithium (LMAB) Was quantified by ion chromatography. As a result, the total content of sulfur oxides was 0.13% by mass, and LMAB was 0.07% by mass.

(3) Production of solid electrolyte The solid electrolyte was obtained by the following method. According to the method described in WO 2005/040039, the (1) and high purity _Li 2 _{S0.6508g (0.01417mol)} prepared in _(2), P 2 _{S 5} (manufactured by Aldrich) 1. 3492 g (0.00607 mol) was mixed well, and the mixed powder was put into an alumina pot and completely sealed. This pot was attached to a planetary ball mill. First, milling was performed at a low speed (85 rpm) for several minutes in order to sufficiently mix the starting materials. Thereafter, the rotational speed was gradually increased to 370 rpm, and mechanical milling was performed for 20 hours.

It was confirmed by X-ray measurement that the obtained powder was vitrified. Next, this powder was heat-treated at 300 ° C. for 2 hours to obtain a solid electrolyte.
The ionic conductivity was measured by an AC impedance method (measurement frequency: 100 Hz to 15 MHz) and found to be 1.0 × 10 ⁻³ S / cm at room temperature.

Production Example 2 Production of Graphite-Si Composite (1) Preparation of Expanded Graphite After immersing scaly natural graphite with an average particle diameter of 1 mm in a mixed acid of 9 parts by weight of sulfuric acid and 1 part by weight of nitric acid at room temperature for 1 hour, a No3 glass filter Then, mixed acid was removed to obtain acid-treated graphite. Further, the acid-treated graphite was washed with water and dried. When 5 g of dried acid-treated graphite was stirred in 100 g of distilled water and the pH was measured after 1 hour, the pH was 6.7. The dried acid-treated graphite was put into a vertical electric furnace under a nitrogen atmosphere set at 850 ° C. to obtain expanded graphite. The bulk density of the acid-treated graphite was 0.78 g / cm ³ . The specific surface area of the expanded graphite was 42 m ² / g, the bulk specific gravity was 0.023 g / cm ³ , and the average thickness of the layers of the laminated graphene sheets was 21 nm.

(2) Mixing Step Metal Si (15 parts by mass) having an average particle size of 0.23 μm was charged into 3000 parts by mass of ethanol in a beaker and stirred for 2 minutes.
The expanded graphite (35 parts by mass) was added to ethanol in which metal Si was dispersed to prepare a uniformly mixed slurry containing expanded graphite and metal Si fine powder. Ethanol was recovered from this slurry using an evaporator to obtain a powder mixture.

(3) Spheronization process Using a pin mill (manufactured by Fritsch) (rotor diameter 10 cm, rotation speed: 8000 rpm, treatment time: 2 minutes), the powder mixture obtained above is granulated and formed into a spherical shape, A substantially spherical composite active material having a graphite content of 70% by mass and a metal Si content of 30% by mass was obtained.
The physical properties are as follows. Bulk density: 0.65 g / cm ³ , tap density: 1.15 g / cm ³ , particle size distribution D90: 25 μm, D50: 12 μm, D10: 4.5 μm, XRD: see FIG. 1A, specific surface area: 10.7 m ² / g, shape: SEM reference in FIG. 2, aspect ratio: 1.45.

As shown to FIG. 1A, the diffraction pattern of graphite and crystalline Si is recognized by XRD of the composite active material obtained above. From this, it is clear that the metal Si is dispersed in the graphite layer without changing to SiC or the like.
FIG. 1B shows a diffraction pattern of a mixed material of expanded graphite and a standard silicon substance before being combined with Si. When FIG. 1A is compared with FIG. 1B, there is no change in the diffraction pattern of the expanded graphite after being combined. From this, it can be seen that the metal Si fine particles are encapsulated by the folded graphite without intercalation of the metal Si fine particles between the graphite layers.

FIG. 2 is a view obtained by observing a secondary electron image of the composite active material using SEM at a low acceleration voltage of 10 kV or less. As can be seen from the figure, the particles of the battery active material Si metal can be clearly observed through the graphite skin.
From this, it can be directly observed that the composite active material has a structure in which the battery active material is sandwiched between thin graphite layers. It can also be confirmed at the same time that the battery active material exposed on the surface is extremely small and that the graphite edge surface is not present on the surface of the composite material.
More specifically, the area ratio of graphite exposed on the surface of the composite active material observed by SEM observation was 98%, and the area ratio of exposed Si metal was 2%. In addition, the average particle diameter of metal Si in the composite active material was almost the same as the average particle diameter in the mixing step.

Example 1
[Fabrication of half cell using negative electrode mixture]
(A) Preparation of negative electrode mixture The graphite-Si composite prepared in Production Example 2 was used as a negative electrode material (negative electrode active material). This negative electrode material and the solid electrolyte prepared in Production Example 1 were mixed at a mass ratio of 70:30 to obtain a negative electrode layer material (negative electrode mixture).

(B) Production of half cell 60 mg of the inorganic solid electrolyte powder, which is the solid electrolyte glass prepared in Production Example 1, was put into a ceramic cylinder having a diameter of 10 mm, and pressure-molded to form an electrolyte layer (electrolyte sheet, inorganic solid electrolyte powder basis weight) Amount: 76.4 mg / cm ² ).
Next, by pressure-molding the negative electrode mixture prepared in (a) (graphite-Si composite amount: 3.3 mg, negative electrode composite weight per unit area: 6.0 mg / cm ² ) in contact with the electrolyte layer, The working electrode was used. From the opposite side of the working electrode, a LiIn alloy foil was bonded as a reference electrode and a counter electrode, followed by pressure molding. Finally, the periphery of the cell was screwed at four positions every 90 degrees to pressurize in the stacking direction. In this way, a bipolar half cell having a three-layer structure was produced. The LiIn alloy can be used as a reference electrode because the Li desorption reaction potential is kept constant (0.62 V vs. Li / Li +) if the atomic ratio Li / In is 0.8 or less. It becomes possible.

[Evaluation of half cell using negative electrode composite]
The produced half cell was 1.0 mA / cm ² and the potential was 0.01 Vvs. Until Li / Li +, then 0.01 V vs. Li / Li + is, by inserting Li ions until 0.127mA / cm ^2, the potential 1.52Vvs at 1.0 mA / cm ^2. Li ions were desorbed to Li / Li +. The charge / discharge cycle was repeated under these conditions, and the Li ion desorption capacity retention ratio [%] after 50 cycles (Li ion desorption capacity at the 50th cycle / Li ion desorption capacity at the 1st cycle × 100) was calculated. The results are shown in Table 1.

Comparative Example 1
A half cell was prepared and evaluated in the same manner as in Example 1 except that Si powder (SIE19PB, particle size of 45 μm or less, 99.9%, manufactured by High Purity Science Laboratory) was used as the negative electrode active material. The results are shown in Table 1.

As shown in Table 1, Example 1 using a composite of graphite and Si, which is a conductive material, has improved cycle characteristics as compared with Comparative Example 1 that is Si alone.

The battery using the negative electrode composite material of the present invention can be used as a battery for a portable information terminal, a portable electronic device, a small electric power storage device for home use, a motorcycle using a motor as a power source, an electric vehicle, a hybrid electric vehicle, or the like. .

Claims (18)

(A) a spheroidized composite active material containing expanded graphite or flaky graphite and a battery active material that can be combined with lithium ions and satisfying the following condition (1); and (b) for an all solid lithium battery including a solid electrolyte . Negative electrode composite.
(1) The area ratio of the graphite exposed on the surface of the composite active material observed by scanning electron microscope observation at an acceleration voltage of 10 kV or less is 95% or more. (C) a spheroidized composite active material containing expanded graphite or flake graphite , and a battery active material that can be combined with lithium ions, and manufactured by the manufacturing method of (2) below, and (b) all including a solid electrolyte Negative electrode composite material for solid lithium batteries .
(2) A mixing step of mixing expanded graphite or flaky graphite having a specific surface area of 30 m ² / g or more and a battery active material that can be combined with lithium ions to obtain a mixture;
The mixture subjected to sphering treatment, and a sphering step of producing spherical composite active material containing expanded graphite or flake graphite, and lithium ions can compound a battery active material, method for producing a composite active material. The negative electrode composite material for an all-solid-state lithium battery according to claim 1 or 2, wherein the expanded graphite or flaky graphite is expanded graphite. The all-solid-state lithium in any one of Claims 1-3 in which the battery active material which can be combined with the said lithium ion contains at least 1 sort (s) of element chosen from the group which consists of silicon, tin, aluminum, antimony, and indium. Negative electrode composite for batteries . The negative electrode composite material for all-solid-state lithium batteries in any one of Claims 1-4 whose tap density of the said composite active material is 0.8 g / cm < ³ > or more. The negative electrode composite material for all-solid-state lithium batteries in any one of Claims 1-5 whose specific surface area of the said composite active material is 5-100 m < ² > / g. The negative electrode composite material for all-solid-state lithium batteries in any one of Claims 1-6 whose average particle diameter of the battery active material which can be combined with the said lithium ion is 1 micrometer or less. The negative electrode composite material for all-solid-state lithium batteries in any one of Claims 1-7 whose said solid electrolyte is a lithium ion conductive inorganic solid electrolyte containing Li, P, and S. The negative electrode composite material for all-solid-state lithium batteries in any one of Claims 1-8 whose said solid electrolyte is a lithium ion conductive inorganic solid electrolyte which satisfy | fills the composition shown to following formula (I).
Li _{a Mb} P _c S _d (I)
(In the formula (I), M represents an element selected from B, Zn, Si, Cu, Ga, or Ge.
a to d indicate the composition ratio of each element, and a: b: c: d satisfies 1 to 12: 0 to 0.2: 1: 2 to 9. ) The negative electrode composite material for all-solid-state lithium batteries in any one of Claims 1-9 whose said solid electrolyte is glass ceramics. The negative electrode composite material for all-solid-state lithium batteries in any one of Claims 1-10 whose said solid electrolyte is glass ceramics whose crystallinity degree is 50% or more. Wherein the solid electrolyte is one prepared by using at least P ₂ S ₅ and Li 2 _S, negative electrode composite for all-solid lithium battery according to any one of claims 2 to 11. A mixing step of mixing expanded graphite or flaky graphite having a specific surface area of 30 m ² / g or more and a battery active material that can be combined with lithium ions to obtain a mixture;
A spheronization step of subjecting the sphering treatment, to produce spherical composite active material containing expanded graphite or flake graphite, and lithium ions can compound battery active material to the mixture,
The manufacturing method of the negative mix for all-solid-state lithium batteries which has the process of mixing the said composite active material and solid electrolyte. A negative electrode composite material for an all solid lithium battery produced by the production method according to claim 13. The negative electrode for all-solid-state lithium batteries containing the negative mix in any one of Claims 1-12 and 14. The negative electrode for all-solid-state lithium batteries manufactured from the negative electrode compound material in any one of Claims 1-12 and 14. An all-solid lithium secondary battery comprising the negative electrode according to claim 15. An apparatus comprising the all-solid-state lithium secondary battery according to claim 17.