WO2015137034A1

WO2015137034A1 - Negative electrode material for electricity storage devices

Info

Publication number: WO2015137034A1
Application number: PCT/JP2015/053670
Authority: WO
Inventors: 友紀廣野; 哲嗣久世; 哲朗仮屋; 澤田　俊之
Original assignee: 山陽特殊製鋼株式会社
Priority date: 2014-03-13
Filing date: 2015-02-10
Publication date: 2015-09-17
Also published as: CN106104863A; TWI650895B; KR20160132384A; JP6374678B2; JP2015176674A; CN106104863B; TW201537812A

Abstract

The present invention provides a material which is able to provide a negative electrode having high capacity, excellent electrical conductivity and excellent durability. A negative electrode (12) is provided with a collector (18) and a plurality of particles (22) that are affixed to the surface of the collector (18). The particles (22) are formed of an Si-based alloy. This alloy has (1) an Si phase that is mainly composed of Si and has a crystallite size of 30 nm or less, and (2) a compound phase that contains Si and Al, and additionally contains Cr or Ti, while having a crystallite size of 40 nm or less. It is preferable that the compound phase contains Si, Cr, Ti and Al. It is preferable that the Si phase contains Al that is solid-solved in Si.

Description

Negative electrode materials for electricity storage devices

Cross-reference of related applications

This application claims priority based on Japanese Patent Application No. 2014-050541 filed on March 13, 2014, the entire disclosure of which is incorporated herein by reference.

The present invention relates to a material suitable for a negative electrode of a power storage device such as a lithium ion secondary battery, an all solid lithium ion secondary battery, or a hybrid capacitor.

In recent years, cellular phones, portable music players, portable terminals, and the like are rapidly spreading. These portable devices include a lithium ion secondary battery. Furthermore, the electric vehicle and the hybrid vehicle also include a lithium ion secondary battery. In a lithium ion secondary battery, the negative electrode occludes lithium ions during charging. When the lithium ion secondary battery is used, lithium ions are released from the negative electrode. The negative electrode has a current collector and an active material fixed to the surface of the current collector.

As the active material in the negative electrode, carbon-based materials such as natural graphite, artificial graphite and coke are used. However, the theoretical capacity of the carbon-based material for lithium ions is only 372 mAh / g. Therefore, an active material having a large capacity is desired.

Si is attracting attention as an active material in the negative electrode. Si reacts with lithium ions. This reaction forms a compound. A typical compound is Li ₂₂ Si ₅ . By this reaction, a large amount of lithium ions is occluded in the negative electrode. Si can increase the storage capacity of the negative electrode.

When the active material layer containing Si occludes lithium ions, the active material layer expands due to the generation of the aforementioned compound. The expansion coefficient of the active material is about 400%. When lithium ions are released from the active material layer, the active material layer contracts. The active material is detached from the current collector due to repeated expansion and contraction. This drop off reduces the storage capacity. The lifetime of the conventional lithium ion secondary battery in which the negative electrode contains Si is not long.

In the active material made of Si, only the surface thereof reacts with lithium ions during charging. In this active material, the inside does not react with lithium ions. In other words, only the surface of the active material expands due to occlusion of lithium ions. Cracks are generated on this surface. At the time of the next charging, lithium ions enter through the crack and further generate a crack. By repeating the generation of the cracks, the active material is pulverized. Due to the pulverization, conduction between the active material and the active material adjacent thereto is inhibited. Micronization reduces the storage capacity. The lifetime of the conventional lithium ion secondary battery in which the negative electrode contains Si is not long.

Si is inferior in ionic conductivity compared to carbon-based materials and metal materials. In a negative electrode using Si, a carbon-based material may be used together with Si. Efficient lithium ion transfer is achieved by the carbon-based material. However, even in this negative electrode, further improvement in conductivity is desired.

An active material in which a Si phase is covered with an intermetallic compound is disclosed in Japanese Patent Application Laid-Open No. 2001-297757. This intermetallic compound is typically produced by the reaction of Si with a transition metal. This intermetallic compound can compensate for the disadvantages of Si. A similar active material is also disclosed in JP-A-10-31804.

An electrode in which a conductive layer is laminated on the surface of an active material layer containing Si is disclosed in Japanese Patent Application Laid-Open No. 2004-228059. Typically, the conductive layer includes Cu. This conductive layer can compensate for the disadvantages of Si. A similar electrode is also disclosed in JP-A-2005-44672.

JP 2001-297757 A JP 10-31804 A JP 2004-228059 A JP 2005-44672 A

In a conventional electrode including an active material in which the Si phase is covered with an intermetallic compound, dropping and pulverization of the active material are not sufficiently suppressed.

In a conventional electrode in which an active material layer and a conductive layer are laminated, means such as plating is used to form the conductive layer. It takes time to form the conductive layer. Furthermore, it is difficult to control the thickness of the conductive layer.

The same problem occurs in power storage devices other than lithium ion secondary batteries.

An object of the present invention is to provide a material capable of obtaining a negative electrode having a large capacity and excellent ion conductivity and durability.

According to one aspect of the present invention, the Si-based alloy is made of Si-based alloy.
(1) Si phase whose main component is Si and whose crystallite size is 30 nm or less,
And (2) A negative electrode material for an electricity storage device is provided that has a compound phase containing Si and Al, further containing Cr or Ti, and having a crystallite size of 40 nm or less.

According to a preferred embodiment, the compound phase contains Si, Al, Cr and Ti.

According to a preferred embodiment, the Si phase contains Al that is solid-solved in Si. Preferably, the Si-based alloy further has an Al single phase.

According to a preferred embodiment, the total content of Cr and Ti (atomic composition percentage) in the alloy is 0.05 at. % Or more and 30 at. % Or less. Preferably, the Al content is 0.05 at. % Or more and 15 at. % Or less.

According to a preferred embodiment, the ratio of the Si content (at.%) To the total content (at.%) Of Cr, Ti and Al in the alloy (Si / (Cr + Ti + Al)) is 1.00 or more and 7 .00 or less.

According to a preferred embodiment, the total content of Ti and Al in the alloy is 1.00 at. % Or more 25.00 at. % Or less.

According to a preferred embodiment, the ratio of Al content (at.%) To the total content (at.%) Of Cr, Ti and Al in the alloy (Al / (Cr + Ti + Al)) is 0.01 or more and 0. .50 or less. Preferably, the ratio (Al / (Cr + Ti + Al)) is 0.04 or more and 0.40 or less.

According to a preferred embodiment, the alloy contains one or more elements selected from the group consisting of Cu, V, Mn, Fe, Ni, Nb, Zn and Zr. The total content of these elements is 0.05 at. % Or more and 15 at. % Or less.

According to a preferred embodiment, the alloy contains one or more elements selected from the group consisting of Mg, B, P, Ga and C. The total content of these elements is 0.05 at. % Or more and 10 at. % Or less.

According to a preferred embodiment, the alloy contains N. The N content is 0.001 mass% or more and 1 mass% or less.

According to another aspect of the present invention, it comprises a current collector and a number of particles fixed to the surface of the current collector,
The particles are made of a Si-based alloy,
This Si alloy is
(1) Si phase whose main component is Si and whose crystallite size is 30 nm or less,
And (2) A negative electrode for an electricity storage device is provided that has a compound phase containing Si and Al, further containing Cr or Ti, and having a crystallite size of 40 nm or less.

According to still another aspect of the present invention, a positive electrode and a negative electrode are provided,
The negative electrode comprises a current collector and a number of particles fixed to the surface of the current collector;
The particles are made of a Si-based alloy,
This Si alloy is
(1) Si phase whose main component is Si and whose crystallite size is 30 nm or less,
And (2) An electricity storage device including a compound phase containing Si and Al, further containing Cr or Ti, and having a crystallite size of 40 nm or less is provided.

The negative electrode containing the material according to the present invention has a large capacity and is excellent in ion conductivity and durability.

FIG. 1 is a conceptual diagram showing a lithium ion secondary battery as an electricity storage device according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing a part of the negative electrode of the battery of FIG. FIG. 3 is an SEM image showing the Si—Si ₂ Cr eutectic alloy contained in the negative electrode particles of FIG. FIG. 4 is an XRD chart of a Si—Si ₂ (Cr, Ti) -based eutectic alloy contained in the negative electrode particles of FIG. FIG. 5 is an XRD chart of a Si—Si ₂ (Cr, Ti) -based eutectic alloy contained in the negative electrode particles of FIG. FIG. 6 is an XRD chart of a Si—Si ₂ (Cr, Ti) -based eutectic alloy contained in the negative electrode particles of FIG. FIG. 7 is a TEM image showing an alloy contained in the negative electrode particles of FIG.

Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

The lithium ion secondary battery 2 conceptually shown in FIG. 1 includes a tank 4, an electrolytic solution 6, a separator 8, a positive electrode 10, and a negative electrode 12. The electrolytic solution 6 is stored in the tank 4. This electrolytic solution 6 contains lithium ions. The separator 8 partitions the tank 4 into a positive electrode chamber 14 and a negative electrode chamber 16. The separator 8 prevents contact between the positive electrode 10 and the negative electrode 12. The separator 8 has a large number of holes (not shown). Lithium ions can pass through this hole. The positive electrode 10 is immersed in the electrolytic solution 6 in the positive electrode chamber 14. The negative electrode 12 is immersed in the electrolytic solution 6 in the negative electrode chamber 16.

FIG. 2 shows a part of the negative electrode 12. The negative electrode 12 includes a current collector 18 and an active material layer 20. The active material layer 20 includes a large number of particles 22. The particles 22 are fixed to other particles 22 that are in contact with the particles 22. The particles 22 that come into contact with the current collector 18 are fixed to the current collector 18. The active material layer 20 is porous.

The material (negative electrode material) of the particles 22 is a Si-based alloy. This alloy has a Si phase and a compound phase. The main component of the Si phase is Si. The crystallite size of the Si phase is 30 nm or less. The compound phase contains Si and Al. The compound phase further contains Cr or Ti. The crystallite size of the compound phase is 40 nm or less.

As described above, Si reacts with lithium ions. Since the Si phase contains Si as a main component, the negative electrode 12 including the Si phase can occlude a large amount of lithium ions. The Si phase can increase the storage capacity of the negative electrode 12. From the viewpoint of storage capacity, the Si content in the Si phase is 50 at. % Or more, 60 at. % Or more, more preferably 70 at. % Or more is particularly preferable.

The Si phase may contain elements other than Si. A typical element is Al. Si is inherently inferior in electrical conductivity. On the other hand, Al is excellent in electrical conductivity. In an alloy in which the Si phase contains Al, a large storage capacity is achieved and excellent electrical conductivity is achieved.

Preferably, Al is dissolved in Si in the Si phase. This solid solution increases the electrical conductivity of the Si phase. Al is soft. Al relieves stress caused by expansion during charging and contraction during discharging. This negative electrode 12 is excellent in durability.

When the alloy contains a large amount of Al, a part of Al is dissolved in Si, and the remaining Al forms a single phase. The single phase of Al is contained in the compound phase and dispersed in this compound phase. This single Al phase also increases the electrical conductivity of the alloy.

The compound phase can contain Cr together with Si. This compound phase contains a Si—Cr compound. A specific example of the compound is Si ₂ Cr. Si ₂ Cr can cause a eutectic reaction with the Si phase. In other words, the particles 22 can be formed from a Si—Si ₂ Cr eutectic alloy.

FIG. 3 is an SEM image showing the Si—Si ₂ Cr eutectic alloy. In FIG. 3, the Si phase is shown in black, and the Si ₂ Cr phase is shown in white. As is clear from FIG. 3, the Si phase is extremely fine, and the Si ₂ Cr phase is also extremely fine. This compound phase relieves stress caused by expansion during charge and contraction during discharge.

The compound phase may contain Ti instead of Cr. In this compound phase, the Si—Ti compound relieves stress.

It is preferred that the compound phase contains both Cr and Ti. In this compound phase, a part of Cr in the Si—Si ₂ Cr eutectic alloy is substituted with Ti. In other words, the compound phase includes a Si—Cr—Ti compound.

4 to 6 are charts showing the results of X-ray diffraction of a Si—Si ₂ (Cr, Ti) -based eutectic alloy. FIG. 4 is a chart of a eutectic alloy containing no Ti. FIG. 5 is a chart of a eutectic alloy having a ratio (Cr / Ti) of 50/50. FIG. 6 is a chart of a eutectic alloy having a ratio (Cr / Ti) of 25/75. 4 to 6, it is estimated that the added Ti increases the lattice constant without changing the crystal structure.

In the particles 22 having a compound phase having a large lattice constant, it is estimated that lithium ions pass smoothly through the silicide. In the lithium ion secondary battery using a eutectic alloy of Si and silicide, as far as the present inventor knows, no studies have been made so far.

Compounds such as Si ₂ Cr and Si ₂ (Cr, Ti) are presumed to improve the electrical conductivity of the particles 22.

The crystallite size of the Si phase is 30 nm or less. In the Si phase having a crystallite size of 30 nm or less, pulverization due to reaction with lithium ions is suppressed. In the battery having this Si phase, the discharge capacity is easily maintained. From this viewpoint, the crystallite size is preferably 25 nm or less, particularly preferably 10 nm or less.

The control of the crystallite size of the Si phase can be performed by controlling the cooling rate at the time of solidification after dissolving the raw material powder in place of or in addition to the control of the above components. Specific examples include a water atomizing method, a single roll quenching method, a twin roll quenching method, a gas atomizing method, a disk atomizing method, and a centrifugal atomizing method. When the cooling effect is insufficient in these methods, mechanical milling or the like may be performed. Examples of the milling method include a ball mill method, a bead mill method, a planetary ball mill method, an attritor method, and a vibration ball mill method.

The crystallite size of the compound phase is 40 nm or less. A compound phase having a crystallite size of 40 nm or less has a high yield stress. Since this compound phase is excellent in ductility and toughness, cracks are unlikely to occur. This compound phase is excellent in electrical conductivity. This compound phase contacts the Si phase with a large specific surface area. The compound phase that comes into contact with the Si phase with a large specific surface area relieves stress caused by expansion during charge and contraction during discharge. The compound phase that contacts the Si phase with a large specific surface area is excellent in electrical conductivity with the Si phase. This compound phase prevents electrical isolation of the Si phase. From these viewpoints, the crystallite size of the compound phase is preferably 20 nm or less, and particularly preferably 10 nm or less.

The crystallite size of the compound phase can be controlled by controlling the cooling rate during solidification after dissolving the raw material powder. Specific examples include a water atomizing method, a single roll quenching method, a twin roll quenching method, a gas atomizing method, a disk atomizing method, and a centrifugal atomizing method. When the cooling effect is insufficient in these methods, mechanical milling or the like may be performed. Examples of the milling method include a ball mill method, a bead mill method, a planetary ball mill method, an attritor method, and a vibration ball mill method.

The crystallite size can be measured directly with a transmission electron microscope (TEM). In addition, the crystallite size can be confirmed by powder X-ray diffraction. In X-ray diffraction, CuKα rays having a wavelength of 1.54059 Å are used as an X-ray source. The measurement is performed in the range of 2θ between 20 degrees and 80 degrees. In the obtained diffraction spectrum, a broader diffraction peak is observed as the crystallite size is smaller. From the full width at half maximum of the peak obtained by powder X-ray diffraction analysis, the following Scherrer equation can be used to determine the crystallite size.
D = (K × λ) / (β × cos θ)
In this equation, D represents the crystallite size (angstrom), K represents Scherrer's constant, λ represents the wavelength of the X-ray tube, and β represents the broadening of the diffraction line depending on the crystallite size. , Θ represents the diffraction angle.

FIG. 7 shows that the total amount of Cr and Ti is 23 at. It is a cross-sectional organization chart by the transmission electron micrograph of the alloy which is%. According to energy dispersive X-ray analysis,
Analysis location 1: Si-12.28 at. % Cr-11.84 at. % Ti
Analysis location 2: Si-10.37 at. % Cr-10.04 at. % Ti
Analysis location 3: Si-11.69 at. % Cr-11.35 at. % Ti
Met. As is apparent from this structure chart, the crystallite size is about 20 nm. As is clear from this structure chart, a microstructure in which the Si phase and the compound phase are mixed is obtained in the alloy.

The total content of Cr and Ti in the alloy is 0.05 at. % Or more and 30 at. % Or less is preferable. Total content is 0.05 at. If the alloy is at least%, a Si phase with a small crystallite size can be obtained. From this viewpoint, the total content is 12 at. % Or more is particularly preferable. Total content is 30 at. For alloys that are less than or equal to%, a compound phase with a small crystallite size can be obtained. From this viewpoint, the total content is 25 at. % Or less is particularly preferable.

As described above, Al contributes to the electrical conductivity of the alloy. From the viewpoint of electric conductivity, 0.2 at. % Or more and 0.5 at. % Or less of Al is preferably dissolved.

Al content in the alloy is 0.05 at. % Or more and 15 at. % Or less is preferable. This content is 0.05 at. % Or more of the alloy is excellent in electrical conductivity. From this viewpoint, the content is 0.2 at. % Or more is particularly preferable. This content is 15 at. In an alloy that is less than or equal to%, the reaction between Si and lithium ions is difficult to be inhibited. From this viewpoint, the content is 10 at. % Or less is particularly preferable.

The ratio (Si / (Cr + Ti + Al)) of the Si content (at.%) To the total content (at.%) Of Cr, Ti and Al in the alloy is preferably 1.00 or more and 7.00 or less. An alloy having a ratio (Si / (Cr + Ti + Al)) of 1.00 or more has a large discharge capacity. In this respect, the ratio (Si / (Cr + Ti + Al)) is particularly preferably equal to or greater than 2.00. In an alloy having a ratio (Si / (Cr + Ti + Al)) of 7.00 or less, stress caused by expansion during charge and contraction during discharge is alleviated. Furthermore, in an alloy having a ratio (Si / (Cr + Ti + Al)) of 7.00 or less, a charging reaction and a discharging reaction can be performed smoothly. From these viewpoints, the ratio (Si / (Cr + Ti + Al)) is particularly preferably 6.00 or less.

The total content of Ti and Al in the alloy is 1.00 at. % Or more 25.00 at. % Or less is preferable. Total content is 1.00 at. % Or more of the alloy is excellent in electrical conductivity. From this viewpoint, the total content is 3.00 at. % Or more is particularly preferable. Total content is 25.00 at. % Or less of the alloy can contribute to the high capacity of the battery 2 and excellent cycle characteristics. From this viewpoint, the total content is 20.00 at. % Or less is particularly preferable.

The ratio (Al / (Cr + Ti + Al)) of the Al content (at.%) To the total content (at.%) Of Cr, Ti and Al in the alloy is preferably 0.01 or more and 0.50 or less. In an alloy having a ratio (Al / (Cr + Ti + Al)) of 0.01 or more, the Si phase is excellent in electrical conductivity. Furthermore, this alloy is also excellent in electrical conductivity between the Si phase and the compound phase. From these viewpoints, the ratio (Al / (Cr + Ti + Al)) is particularly preferably 0.04 or more. In an alloy having a ratio (Al / (Cr + Ti + Al)) of 0.50 or less, the Si phase is not easily covered with Al. In this alloy, Al does not inhibit the reaction between Si and lithium ions. The discharge capacity of this alloy is large. The discharge capacity retention rate of this alloy is large. From these viewpoints, the ratio (Al / (Cr + Ti + Al)) is particularly preferably 0.40 or less.

Preferably, the alloy includes one or more elements selected from the group consisting of Cu, V, Mn, Fe, Ni, Nb, Zn, and Zr. Since these elements can form a eutectic alloy with Si, a fine Si phase can be generated. These elements can form a compound that is flexible and excellent in electrical conductivity. This compound surrounds the Si phase. This compound relieves stress caused by expansion during charging and contraction during discharging. This compound prevents electrical isolation of the Si phase. From these viewpoints, the total content of these elements is 0.05 at. % Or more, 0.1 at. % Or more is particularly preferable. From the viewpoint that the discharge capacity of the alloy is large, the total content of these elements is 15 at. % Or less, preferably 9 at. % Or less is particularly preferable.

Preferably, the alloy contains one or more elements selected from the group consisting of Mg, B, P, Ga and C. These elements can form a compound that is flexible and excellent in electrical conductivity. This compound surrounds the Si phase. This compound relieves stress caused by expansion during charging and contraction during discharging. This compound prevents electrical isolation of the Si phase. From these viewpoints, the total content of these elements is 0.05 at. % Or more, 0.1 at. % Or more is particularly preferable. From the viewpoint that the discharge capacity of the alloy is large, the total content of these elements is 10 at. % Or less, preferably 7 at. % Or less is particularly preferable.

In an alloy containing B, the Si phase may have a P-type semiconductor structure. This Si phase is excellent in electrical conductivity.

In an alloy containing P, the Si phase may have an N-type semiconductor structure. This Si phase is excellent in electrical conductivity.

The alloy may contain Co, Pd, Bi, In, Sb, Sn, or Mo. These elements can also contribute to the improvement of the discharge capacity retention rate. The total content of these elements is 0.05 at. % Or more and 10 at. % Or less is preferable.

Preferably, the alloy contains N. An alloy containing N is brittle. With this alloy, small particle sizes can be easily achieved. In this respect, the N content (mass percentage) is preferably equal to or greater than 0.001 mass%, and particularly preferably equal to or greater than 0.01 mass%. From the viewpoint of preventing the separation of the particles 22 at the negative electrode and the viewpoint of preventing the electrical isolation of the particles 22, the N content is preferably 1 mass% or less, and particularly preferably 0.1 mass% or less.

Particles (powder) can be produced by a single roll cooling method, a gas atomizing method, a disk atomizing method or the like. In order to obtain particles 22 having a small size, it is necessary to quench the molten raw material. The cooling rate is preferably 100 ° C./s or more.

In the single roll cooling method, raw materials are put into a quartz tube having pores at the bottom. This raw material is heated and melted by a high frequency induction furnace in an argon gas atmosphere. The raw material flowing out from the pores is dropped on the surface of the copper roll and cooled to obtain a ribbon. This ribbon is put into the pot together with the ball. Examples of the ball material include zirconia, SUS304, and SUJ2. Examples of the pot material include zirconia, SUS304, and SUJ2. The pot is filled with argon gas and the pot is sealed. The ribbon is pulverized by milling to obtain particles 22. Examples of milling include a ball mill, a bead mill, a planetary ball mill, an attritor, and a vibrating ball mill.

In the gas atomization method, raw materials are put into a quartz crucible having pores at the bottom. This raw material is heated and melted by a high frequency induction furnace in an argon gas atmosphere. In an argon gas atmosphere, argon gas is injected onto the raw material flowing out from the pores. The raw material is quenched and solidified to obtain particles 22.

In the disc atomization method, raw materials are put into a quartz crucible having pores at the bottom. This raw material is heated and melted by a high frequency induction furnace in an argon gas atmosphere. In an argon gas atmosphere, the raw material flowing out from the pores is dropped onto a disk that rotates at high speed. The rotation speed is 40000 rpm to 60000 rpm. The raw material is rapidly cooled by the disk and solidified to obtain a powder. This powder is put into a pot together with a ball. Examples of the ball material include zirconia, SUS304, and SUJ2. Examples of the pot material include zirconia, SUS304, and SUJ2. The pot is filled with argon gas and the pot is sealed. The ribbon is pulverized by milling to obtain particles 22. Examples of milling include a ball mill, a bead mill, a planetary ball mill, an attritor, and a vibrating ball mill.

Hereinafter, the effects of the present invention will be clarified by examples. However, the present invention should not be interpreted in a limited manner based on the description of the examples.

The effect of the negative electrode material according to the present invention was confirmed using a bipolar coin cell. First, raw materials having the compositions shown in Tables 1 to 5 were prepared. Particles were produced from each raw material by the above-described single roll cooling method, gas atomization method or disk atomization method. A large number of particles, a conductive material (acetylene black), a binder (polyimide, polyvinylidene fluoride, etc.) and a dispersion (N-methylpyrrolidone) were mixed to obtain a slurry. This slurry was apply | coated on the copper foil which is a collector. This slurry was dried under reduced pressure using a vacuum dryer. The drying temperature was 200 ° C. or higher when polyimide was the binder, and 160 ° C. or higher when polyvinylidene fluoride was the binder. The solvent was evaporated by this drying to obtain an active material layer. The active material layer and the copper foil were pressed with a roll. This active material layer and copper foil were punched into a shape suitable for a coin-type cell to obtain a negative electrode.

A mixed solvent of ethylene carbonate and dimethyl carbonate was prepared as an electrolytic solution. The mass ratio of both was 3: 7. Furthermore, lithium hexafluorophosphate (LiPF ₆ ) was prepared as a supporting electrolyte. The amount of the supporting electrolyte is 1 mol with respect to the electrolytic solution. This supporting electrolyte was dissolved in the electrolytic solution.

A separator and a positive electrode having a shape suitable for a coin-type cell were prepared. This positive electrode is made of lithium. The separator was immersed in the electrolytic solution under reduced pressure and allowed to stand for 5 hours to fully infiltrate the separator with the electrolytic solution.

A negative electrode, a separator and a positive electrode were incorporated in the tank. The tank was filled with an electrolytic solution to obtain a coin-type cell. In addition, it is necessary to handle electrolyte solution in the inert atmosphere by which dew point control was carried out. Therefore, the cell was assembled in a glove box with an inert atmosphere.

In Tables 1 to 5 below, No. Nos. 1 to 66 are compositions of negative electrode materials according to examples of the present invention. 67 to 74 are compositions of the negative electrode material according to the comparative example.

In the coin-type cell, charging was performed until the potential difference between the positive electrode and the negative electrode became 0 V under the conditions that the temperature was 25 ° C. and the current density was 0.50 mA / cm ² . Thereafter, discharging was performed until the potential difference became 1.5V. This charge and discharge was repeated 50 cycles. The initial discharge capacity X and the discharge capacity Y after 50 cycles of charging and discharging were measured. Furthermore, the ratio (maintenance rate) of the discharge capacity Y to the discharge capacity X was calculated. The results are shown in Tables 6 to 8 below.

The negative electrode materials of Examples 1 to 11 include a Si phase and an Al—Si—Cr compound phase. The crystallite size of the Si phase is 30 nm or less, and the crystallite size of the compound phase is 40 nm or less.

For example, the negative electrode material of Example 4 includes a Si phase and a compound phase as described above. In this negative electrode material, since the crystallite size of the Si phase is 3 nm, this crystallite size is included in the range of “30 nm or less”. In this negative electrode material, since the crystallite size of the compound phase is 4 nm, this crystallite size is included in the range of “40 nm or less”. In the cell using this negative electrode material, the initial discharge capacity is as large as 1423 mAh / g, and the discharge capacity retention rate after 50 cycles is as large as 82%.

The negative electrode materials of Examples 12 to 22 include a Si phase and an Al—Si—Ti compound phase. The crystallite size of the Si phase is 30 nm or less, and the crystallite size of the compound phase is 40 nm or less.

For example, the negative electrode material of Example 14 includes a Si phase and a compound phase as described above. In this negative electrode material, since the crystallite size of the Si phase is 7 nm, this crystallite size is included in the range of “30 nm or less”. In this negative electrode material, since the crystallite size of the compound phase is 9 nm, this crystallite size is included in the range of “40 nm or less”. In the cell using this negative electrode material, the initial discharge capacity is as large as 1578 mAh / g, and the discharge capacity maintenance ratio after 50 cycles is as large as 88%.

The negative electrode materials of Examples 23 to 36 include a Si phase and an Al—Si—Cr—Ti compound phase. The crystallite size of the Si phase is 30 nm or less, and the crystallite size of the compound phase is 40 nm or less.

For example, the negative electrode material of Example 25 includes a Si phase and a compound phase as described above. In this negative electrode material, since the crystallite size of the Si phase is 1 nm, this crystallite size is included in the range of “30 nm or less”. In this negative electrode material, since the crystallite size of the compound phase is 3 nm, this crystallite size is included in the range of “40 nm or less”. In the cell using this negative electrode material, the initial discharge capacity is as large as 1291 mAh / g, and the discharge capacity retention rate after 50 cycles is as large as 94%.

The negative electrode materials of Examples 37 to 49 include a Si phase and a compound phase. Each compound phase contains Al, Si, Cr and Ti. This compound phase further contains other additive elements (Cu, V, Mn, Fe, Ni, Nb, Pd, Zn, Zr, Mg, B, P, Ga, C, or N). The crystallite size of the Si phase is 30 nm or less, and the crystallite size of the compound phase is 40 nm or less.

For example, the negative electrode material of Example 49 includes a Si phase and a compound phase as described above. In this negative electrode material, since the crystallite size of the Si phase is 2 nm, this crystallite size is included in the range of “30 nm or less”. In this negative electrode material, since the crystallite size of the compound phase is 4 nm, this crystallite size is included in the range of “40 nm or less”. In the cell using this negative electrode material, the initial discharge capacity is as large as 1590 mAh / g, and the discharge capacity retention rate after 50 cycles is as large as 86%.

The negative electrode materials of Examples 50 to 66 include a Si phase and a compound phase. Each compound phase contains Al, Si, Cr and Ti. This compound phase further includes other additive elements (Cu, V, Mn, Fe, Ni, Nb, Pd, Zn, Zr, Mg, B, P, Ga, C, N, Co, Pd, Bi, In, Sb. , Sn or Mo). The crystallite size of the Si phase is 30 nm or less, and the crystallite size of the compound phase is 40 nm or less.

For example, the negative electrode material of Example 63 includes the Si phase and the compound phase as described above. In this negative electrode material, since the crystallite size of the Si phase is 3 nm, this crystallite size is included in the range of “30 nm or less”. In this negative electrode material, since the crystallite size of the compound phase is 6 nm, this crystallite size is included in the range of “40 nm or less”. In the cell using this negative electrode material, the initial discharge capacity is as large as 1654 mAh / g, and the discharge capacity retention rate after 50 cycles is as large as 82%.

The negative electrode material of Comparative Example 67 has a Si phase crystallite size of 30 nm or less and a compound phase crystallite size of 40 nm or less, but does not contain Al. The negative electrode material of Comparative Example 68 does not contain Al, and the Si crystallite size exceeds 30 nm. The negative electrode material of Comparative Example 69 does not contain Al, and the crystallite size of the compound phase exceeds 40 nm. The negative electrode material of Comparative Example 70 does not contain Al, the Si phase crystallite size exceeds 30 nm, and the compound phase crystallite size exceeds 40 nm.

The negative electrode material of Comparative Example 71 has a Si phase crystallite size of 30 nm or less and a compound phase crystallite size of 40 nm or less, but does not contain Cr and Ti. The negative electrode material of Comparative Example 72 does not contain Cr and Ti, and the crystallite size of the Si phase exceeds 30 nm. The negative electrode material of Comparative Example 73 has a Si phase crystallite size of 30 nm or less, but does not contain Cr and Ti, and the compound phase crystallite size exceeds 40 nm. The negative electrode material of Comparative Example 74 does not contain Cr and Ti, the crystallite size of the Si phase exceeds 30 nm, and the crystallite size of the compound phase exceeds 40 nm.

From the evaluation results shown in Tables 6 to 8, the superiority of the present invention is clear.

The negative electrode described above can be applied not only to a lithium ion secondary battery but also to an electricity storage device such as an all-solid lithium ion secondary battery or a hybrid capacitor.

2 ... Lithium ion secondary battery 6 ... Electrolyte solution 8 ... Separator 10 ... Positive electrode 12 ... Negative electrode 18 ... Current collector 20 ... Active material layer 22 ... Particle

Claims

Made of Si-based alloy, this Si-based alloy
(1) Si phase whose main component is Si and whose crystallite size is 30 nm or less,
And (2) A negative electrode material for an electricity storage device comprising a compound phase containing Si and Al, further containing Cr or Ti, and having a crystallite size of 40 nm or less.
The negative electrode material according to claim 1, wherein the compound phase contains Si, Cr, Ti, and Al.
The Si phase contains Al that is dissolved in Si;
The negative electrode material according to claim 1, wherein the Si-based alloy further has an Al single phase.
The total content of Cr and Ti in the Si-based alloy is 0.05 at. % Or more and 30 at. %, And the Al content is 0.05 at. % Or more and 15 at. The negative electrode material according to claim 1 or 2, which is not more than%.
The ratio (Si / (Cr + Ti + Al)) of Si content (at.%) To the total content (at.%) Of Cr, Ti and Al in the Si-based alloy is 1.00 or more and 7.00 or less. The negative electrode material according to claim 1 or 2, wherein
The total content of Ti and Al in the Si-based alloy is 1.00 at. % Or more 25.00 at. The negative electrode material according to claim 1 or 2, which is not more than%.
The ratio of Al content (at.%) To the total content (at.%) Of Cr, Ti and Al in the Si-based alloy (Al / (Cr + Ti + Al)) is 0.01 or more and 0.50 or less. The negative electrode material according to claim 1 or 2, wherein
The negative electrode material according to claim 7, wherein the ratio (Al / (Cr + Ti + Al)) is 0.04 or more and 0.40 or less.
The Si-based alloy contains one or more elements selected from the group consisting of Cu, V, Mn, Fe, Ni, Nb, Zn, and Zr, and the total content of these elements is 0. .05at. % Or more and 15 at. The negative electrode material according to claim 1 or 2, which is not more than%.
The Si-based alloy contains one or more elements selected from the group consisting of Mg, B, P, Ga and C, and the total content of these elements is 0.05 at. % Or more and 10 at. The negative electrode material according to claim 1 or 2, which is not more than%.
The negative electrode material according to claim 1 or 2, wherein the Si-based alloy contains N, and the content of N is 0.001 mass% or more and 1 mass% or less.
A current collector and a large number of particles fixed to the surface of the current collector;
The particles are made of a Si-based alloy,
This Si alloy is
(1) Si phase whose main component is Si and whose crystallite size is 30 nm or less,
And (2) A negative electrode of an electricity storage device comprising a compound phase containing Si and Al, further containing Cr or Ti, and having a crystallite size of 40 nm or less.
A positive electrode and a negative electrode,
The negative electrode comprises a current collector and a number of particles fixed to the surface of the current collector;
The particles are made of a Si-based alloy,
This Si alloy is
(1) Si phase whose main component is Si and whose crystallite size is 30 nm or less,
And (2) An electricity storage device having a compound phase containing Si and Al, further containing Cr or Ti, and having a crystallite size of 40 nm or less.