JP2015020921A - Silicon nanowire, silicon nanowire structure and method for producing the same, and nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a silicon nanowire structure having good electrical connection and a high stress relaxation property in a large amount at low cost.SOLUTION: There are used: silicon nanowires which comprises a crystalline silicon core, an amorphous layer for covering the crystalline silicon core and SiOoxide film, where the amorphous layer is composed of amorphous silicon or amorphous SiO(x<2); and a silicon nanowire structure in which the silicon nanowires are connected. There is provided a method for producing the silicon nanowire structure in which an organic silane containing no oxygen is thermally decomposed using the organic silane and an organic solvent containing no oxygen in the molecule including 0.3 to 5.0 wt.% of water or an organic substance containing oxygen in the molecule. In particular, it is preferable that the thermal decomposition is carried out in a reactor pressure vessel, the pressure is 2 MPa or more and 20 MPa or less and the temperature is 350°C or more and 500°C or less.

Description

  The present invention relates to a silicon nanowire having a dimension on the order of nanometers, a silicon nanowire structure in which a plurality of silicon nanowires are joined, and the like.

  Fibrous structures with minor axis dimensions on the order of nanometers are unique and useful, such as quantum mechanical behavior due to quantum size effects, unique catalytic ability due to increased specific surface area, stress relaxation and flexibility Has characteristics.

  Examples of such materials include silicon nanowires and structures in which silicon nanowires are integrated. Nanowires are characterized as one-dimensional, small scale, high surface area wire-like materials that exhibit quantum mechanical electron transport, glitter due to quantum size effects, stress relaxation, and the like. Such materials are important for certain medical, electronics and lithium ion battery applications.

  Conventionally, for the production of silicon nanowires, the VLS (Vapor-Liquid-Solid) method using supersaturated growth from alloy droplets and the SFLS (Superfluid-Liquid-Solid) method, as well as the silicon suboxide as a starting point for wire growth. A bottom-up method using an OAG (Oxide-Assisted Growth) method, a top-down method such as photolithography for cutting a wire-like structure from a silicon substrate, or a wet etching method has been used.

  In the VLS method, when a metal catalyst such as gold, iron, or nickel is heated and a silicon source is supplied, silicon crystals are precipitated from alloy droplets of the metal catalyst and silicon, and silicon nanowires can be obtained. In the VLS method, a chemical vapor deposition method in which a substrate carrying a catalyst metal is heated to 500 ° C. to 1200 ° C. to supply a silicon source gas such as silane, and a mixture and alloy of silicon and a metal catalyst are irradiated with a laser. There is a laser ablation method. In the chemical vapor deposition method, a large-scale apparatus such as a vacuum vessel is required, and there is a problem that it is difficult to scale up by simply expanding dimensions. In addition, the laser ablation method has a problem that since it requires laser irradiation, it is difficult to scale up by enlarging the dimensions and the synthesis efficiency is low. Furthermore, in any of the methods, since a metal catalyst is required, the metal catalyst is contained as an impurity in the silicon nanowire, and gold used for the catalyst to form a droplet alloy at a low temperature is expensive. there were.

In the OAG method, SiO gas is generated by irradiating a material mixed with Si and SiO ₂ at a ratio of 1: 1 to form a silicon oxide in a fluid state at 880 ° C. to 1150 ° C. Silicon deposited from silicon oxide forms nanowires, and silicon nanowires can be obtained. In the OAG method, no metal catalyst is used. However, since laser irradiation is performed, it is difficult to scale up and the synthesis efficiency is low.

  In the SFLS method, silicon nanowires can be obtained by heating and pressurizing a liquid containing organosilane to a supercritical or subcritical state of 400 ° C. to 500 ° C. together with a metal catalyst such as gold. However, since a metal catalyst is required, there is a problem that the metal catalyst is contained as an impurity in the silicon nanowire, and gold used as the catalyst is expensive.

Further, conventionally, in a silicon nanowire integrated structure, an electrode formed by placing a silicon source into thermal plasma and entwining a plurality of nanowires in which a crystalline silicon core is coated with SiO ₂ as an oxide is entangled with metal fine particles. A method of depositing a material on a support (Patent Document 1), a structure in which silicon nanowires arranged substantially in one direction have a layer made of silicon or silicon oxide that connects the nanowires (Patent Document 2), etc. There is.

JP 2010-192444 A Special table 2009-523923

  However, as described above, in the VLS method and the SFLS method, there is a problem that, in addition to using an expensive catalyst metal, the catalyst metal is taken into the silicon nanowire as a contamination to form a defect level. In addition, the production of nanowires by the OAG method requires a high temperature of 850 ° C. or higher, and since ablation particles and gas are used as raw materials, high density synthesis is difficult, and there is a problem that it is not suitable for mass production.

In addition, although the electrical connection of the nanowires included in the structure described in Patent Document 1 is well maintained between the nanowires and the metal fine particles, SiO ₂ having high insulating properties is formed at the contact portion between the nanowires. Intervening, electrical connection is not good. In the structure described in Patent Document 2, since the nanowires are oriented in one direction, there is a problem that a direction in which stress due to deformation is released is limited.

  The present invention has been made in view of the above-described problems, and the object of the present invention is to provide a silicon nanowire structure with good electrical connection and high stress relaxation, and to reduce the cost of the structure. To get in large quantities.

In order to achieve the above-described object, the present invention has the following features.
(1) It has a crystalline silicon core, an amorphous layer covering the crystalline silicon core, and a SiO ₂ oxide film covering the amorphous layer, and the amorphous layer is made of amorphous silicon or amorphous SiO _x (x <2). Silicon nanowires characterized by that.
(2) It has a crystalline silicon core, an amorphous layer covering the crystalline silicon core, and a SiO ₂ oxide film covering the amorphous layer, and the amorphous layer is made of amorphous silicon or amorphous SiO _x (x <2). A silicon nanowire structure including a silicon nanowire, wherein the silicon nanowire has a structure in which a plurality of the silicon nanowires are connected.
(3) The silicon nanowire structure according to (2), wherein a plurality of the silicon nanowires have a structure in which the amorphous layers are in contact with each other.
(4) The silicon nanowire structure according to (2) or (3), wherein an average aspect ratio obtained by dividing the length of the silicon nanowire by the diameter of the silicon nanowire is 10 or more.
(5) The silicon nanowire according to (1), wherein a diameter of the crystalline silicon core of the silicon nanowire is 1 to 50 nm, and a thickness of the amorphous layer is 10 to 100 nm.
(6) It has a positive electrode capable of inserting and extracting lithium ions, a negative electrode having an active material layer on a current collector, and a separator disposed between the positive electrode and the negative electrode, and has lithium ion conductivity. A nonaqueous electrolyte secondary battery in which the positive electrode, the negative electrode, and the separator are provided in an electrolyte, wherein the active material layer of the negative electrode includes a crystalline silicon core, and an amorphous layer that covers the crystalline silicon core. A silicon nanowire characterized by comprising an amorphous layer or a SiO ₂ oxide film covering the amorphous layer, wherein the amorphous layer is made of amorphous silicon or amorphous SiO _x (x <2). A non-aqueous electrolyte secondary battery.
(7) In a reaction of thermally decomposing the organic silane using an organic silane that does not contain oxygen and an organic solvent that does not contain oxygen in the molecule, A method for producing a silicon nanowire structure, comprising adding an organic substance having a thermal decomposition reaction.
(8) The production of the silicon nanowire structure according to (7), wherein the thermal decomposition is performed in a pressure vessel, the pressure is 2 MPa or more and 20 MPa or less, and the temperature is 350 ° C. or more and 500 ° C. or less. Method.
(9) Any one or more selected from the group consisting of water, an organic substance having oxygen in the molecule, water, alcohol, ketone, carboxylic acid, aldehyde, ether, carboxylic anhydride, percarboxylic acid, carboxylic acid ester The method for producing a silicon nanowire structure according to (7) or (8), wherein
(10) The method for producing a silicon nanowire structure according to (9), wherein the water or the organic substance having oxygen in the molecule is water.
(11) The method for producing a silicon nanowire structure according to any one of (7) to (10), wherein the organic solvent is an aromatic hydrocarbon.
(12) The organic silane is any one of phenylsilane, diphenylsilane, triphenylsilane, tetraphenylsilane, diethylsilane, triethylsilane, tetraethylsilane, tetramethylsilane, or a mixture thereof. A method for producing a silicon nanowire structure according to any one of 7) to (11).
(13) The method for producing a silicon nanowire structure according to any one of (7) to (12), wherein the nanowire is formed simultaneously with the production of the silicon nanowire structure.

  According to the present invention, silicon nanowire structures having good electrical connection and high stress relaxation properties can be obtained in large quantities at low cost.

Sectional drawing of the silicon nanowire 1 which concerns on embodiment of this invention. Sectional drawing of the silicon nanowire structure 11 which concerns on embodiment of this invention. Sectional drawing of the silicon nanowire structure 13 which concerns on embodiment of this invention. (A)-(e) The figure which shows the formation process of the silicon nanowire or silicon nanowire structure which concerns on embodiment of this invention. The figure which shows the time change of the organic silane density | concentration and water density | concentration in a reaction system. (A), (b) The figure explaining formation of the branched structure joined by the crystalline silicon core 3. FIG. (A), (b) The figure explaining formation of the branched structure joined by the amorphous layer 5. FIG. The figure explaining the structure of the silicon nanowire structure 33. FIG. (A)-(d) The scanning electron micrograph of the silicon nanowire structure which concerns on Examples 1-4. (A)-(d) The scanning electron micrograph of the silicon nanowire structure which concerns on Examples 5-8. The scanning electron micrograph of the silicon nanowire structure which concerns on the comparative example 1. 1 is a transmission electron micrograph of silicon nanowires according to Example 1. FIG. The elemental analysis result of the silicon nanowire which concerns on Example 1. FIG. 4 is a transmission electron micrograph of silicon nanowires according to Example 3. FIG. The elemental analysis result of the silicon nanowire which concerns on Example 3. FIG. (A) Transmission electron micrograph of the edge part of the silicon nanowire which concerns on Example 3, (b) The enlarged view of an edge part. 4 is a transmission electron micrograph of a bonded portion of a silicon nanowire structure according to Example 3. FIG.

(Silicon nanowire 1)
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a cross-sectional view of a silicon nanowire 1 according to an embodiment of the present invention. The silicon nanowire 1 is wire-like or fiber-like silicon. Silicon nanowires 1, a crystalline silicon core 3 made of crystalline silicon, covering the amorphous layer 5 made of amorphous silicon or amorphous _SiO x (x <2), further, SiO ₂ oxide film made of amorphous layer 5 of SiO ₂ 7 has the structure which covers.

As will be described later, the silicon nanowire 1 is formed by depositing an amorphous layer 5 around the crystalline silicon core 3 after the crystalline silicon core 3 is formed. Thereafter, by touching the outside air, silicon or SiO _x of the amorphous layer 5 on the surface is oxidized to SiO ₂ to form the SiO ₂ oxide film 7.

  It is preferable that the average of aspect ratios obtained by dividing the length of one silicon nanowire 1 constituting a silicon nanowire structure described later by the diameter is 10 or more. When the aspect ratio is less than 10, the silicon nanowire 1 is in a particle or rod shape, and it is difficult to form a silicon nanowire structure. Therefore, the average aspect ratio of the silicon nanowires constituting the silicon nanowire structure is desirably 10 or more, and more desirably, the aspect ratio of all the silicon nanowires constituting the silicon nanowire structure is 10 or more. Is desirable. Moreover, it can prevent a crack at the time of expansion / contraction as a fibrous silicon nanowire.

  The diameter of the silicon nanowire 1 is 1 μm or less, preferably 500 nm or less, and more preferably 300 nm or less.

  The diameter of the crystalline silicon core 3 of the silicon nanowire 1 is preferably 1 to 50 nm, and the thickness of the amorphous layer 5 is preferably 10 to 100 nm.

(Silicon nanowire structure)
FIG. 2 is a cross-sectional view of the joint portion of the silicon nanowire structure 11 according to the embodiment of the present invention. The silicon nanowire structure 11 is formed by bonding two or more silicon nanowires 1, and a network structure is formed by the plurality of silicon nanowires 1. In FIG. 2, it is joined in a T shape, but it may be a cross shape or an L shape. Further, in FIG. 2, two silicon nanowires 1 are illustrated as being bonded at a right angle, but can be bonded at an arbitrary angle other than a right angle.

Further, in the silicon nanowire structure 11, the silicon nanowires 1 are bonded to each other through the amorphous layer 5. Since SiO ₂ is not interposed at the bonding location of the silicon nanowires 1, the silicon nanowires 1 are electrically connected to each other. This is formed when the amorphous layers 5 are joined to each other while the amorphous layers 5 are being deposited when the two crystalline silicon cores 3 are sufficiently close. Since the formation of the silicon nanowire and the formation of the silicon nanowire structure 11 or 13 are performed at the same time, it is possible to obtain a silicon nanowire structure having a network structure by bonding the silicon nanowires before the SiO ₂ oxide film 7 is formed. it can. Further, since the SiO ₂ oxide film 7 is formed after the amorphous layer 5 is formed, the SiO ₂ oxide films 7 are also connected.

Further, in the silicon nanowire structure 13 shown in FIG. 3, not only the silicon nanowires 1 are bonded together by the amorphous layer 5 but also the crystalline silicon cores 3 are bonded together. Since the crystalline silicon cores 3 having good electrical conductivity are joined, the silicon nanowires 1 are electrically connected to each other more satisfactorily. The silicon nanowire structure 13 is formed when a growth nucleus is generated on the side wall during the growth of the crystalline silicon core 3 and another crystalline silicon core 3 grows therefrom. Thereafter, an amorphous layer 5 and a SiO ₂ oxide film 7 are formed.

(effect)
Since the silicon nanowire 1 has a fibrous structure, when used as a negative electrode active material of a non-aqueous electrolyte secondary battery, even if it expands / contracts during insertion / release of lithium ions, stress can be released and cracked. Can be prevented.

  Since the silicon nanowire 1 has a one-dimensional conductive path, when used as a negative electrode active material for a non-aqueous electrolyte secondary battery, the silicon nanowire 1 has a conduction path in the entire silicon nanowire 1 as compared to a particulate negative electrode active material. Can be obtained.

  Since the silicon nanowire 1 has a small diameter, a quantum size effect is obtained, and an increase in band gap, an increase in light emission efficiency due to direct transition, a high mobility of electrons, and the like are exhibited.

In the silicon nanowire structures 11 and 13, the silicon nanowires 1 are joined together by the amorphous layer 5, and since there is no highly insulating SiO _{2 at} the joining portion between the silicon nanowires 1, the silicon nanowires 1 are electrically good. Connected to.

(Method for producing silicon nanowires)
The silicon nanowire 1 or the silicon nanowire structures 11 and 13 use 0.3 to 5.0% by weight of water or a molecule in a reaction in which the organic silane is thermally decomposed using an organic solvent that does not contain oxygen in the molecule. It can be obtained by carrying out a thermal decomposition reaction by adding an organic substance having oxygen.

  Specifically, the thermal decomposition of the organosilane is performed in a pressure vessel, and the pressure is preferably 2 MPa or more and 20 MPa or less, and the temperature is 350 ° C. or more and 500 ° C. or less. This is because, under these conditions, the thermal decomposition of the organosilane proceeds at a sufficient rate and silicon is deposited.

  The water or the organic substance having oxygen in the molecule is at least one selected from the group consisting of water, alcohol, ketone, carboxylic acid, aldehyde, ether, carboxylic anhydride, percarboxylic acid, and carboxylic acid ester. It is preferable. As the alcohol, methanol, ethanol, propanol, butanol, ethylene glycol, glycerin, 1,2-propanediol and the like can be used. As the ketone, acetone, 2-butanone and the like can be used, and as the carboxylic acid, formic acid, acetic acid, propionic acid, butyric acid and the like can be used. As the aldehyde, formaldehyde, acetaldehyde, propionaldehyde, etc. can be used, as the ether, dimethyl ether, ethyl methyl ether, diethyl ether, oxetane, tetrahydrofuran, tetrahydropyran, etc. can be used, and as the carboxylic acid anhydride, acetic anhydride, anhydrous Benzoic acid or the like can be used, and peracetic acid or the like can be used as the percarboxylic acid, and methyl acetate, ethyl acetate, propyl acetate, phenyl acetate, methyl benzoate, ethyl benzoate, or the like can be used as the carboxylic acid ester. In particular, it is preferable to use water among water or an organic substance having oxygen in the molecule.

  The organic solvent containing no oxygen in the molecule is preferably an aromatic hydrocarbon. As such aromatic hydrocarbon, benzene, toluene, xylene and the like can be used. Due to the presence of the organic solvent, the pressure in the reaction vessel can be increased and the thermal decomposition can proceed efficiently.

  The organic silane not containing oxygen is preferably phenylsilane, diphenylsilane, triphenylsilane, tetraphenylsilane, diethylsilane, triethylsilane, tetraethylsilane, tetramethylsilane, or a mixture thereof.

(Formation process of silicon nanowire 1)
4 (a) to 4 (e) are diagrams showing a process of forming silicon nanowires. In FIG. 4, phenylsilane is used as the organic silane, and water is used as water or an organic substance having oxygen in the molecule. First, as shown in FIG. 4A, the phenylsilane 21 is thermally decomposed to produce silane 23. Next, as shown in FIG. 4B, the silane 23 and the water 25 react to produce a silicon oxide 27 made of SiOx (0 <x <2). Next, as shown in FIG. 4C, silicon atoms are supplied from the silane 23 to the silicon oxide 27. The silicon oxide 27 discharges silicon atoms that are excessive to maintain a stable composition. Since the discharged silicon atoms are arranged at a stable position in terms of energy, crystalline silicon is formed, and a crystalline silicon core 3 is formed. Next, as shown in FIG. 4 (d), amorphous silicon or amorphous SiO _x is deposited on the surface of the crystalline silicon core 3 to form an amorphous layer 5. Thereafter, as shown in FIG. 4E, the surface of the amorphous layer 5 is oxidized by being exposed to the outside air, and the SiO ₂ oxide film 7 is formed.

  FIG. 5 is a diagram showing temporal changes in the organic silane concentration and the water concentration in the reaction system. When the concentration of the water or water, which is an organic substance having oxygen in the molecule, is higher than a certain ratio, the reaction of silane and water proceeds as shown in FIG. Nuclei are generated and the crystalline silicon core 3 grows. On the other hand, when the concentration of water is lower than a certain ratio, amorphous silicon or amorphous SiOx is generated from silane and deposited at random as shown in FIG. 4D, so that the amorphous layer 5 is formed. From the above points, in the reaction system according to the embodiment of the present invention, since both the organic silane concentration and the water concentration are high at the initial stage of the reaction, both the generation of the silicon oxide 27 and the growth of the crystalline silicon core 3 occur. This is the crystal growth mode that occurs. Thereafter, when water is used to generate the silicon oxide 27 and the water concentration is lowered, the amorphous layer growth mode in which the amorphous layer 5 grows is set. The reaction stops when the organosilane concentration decreases.

(Process of forming silicon nanowire structure 11 or 13)
In the process of growing the crystalline silicon core 3 as shown in FIG. 4C, water may act on the side wall of the crystalline silicon core 3 to form the silicon oxide 27 as shown in FIG. 6A. . As shown in FIG. 6B, when the crystalline silicon core 3 is generated from the silicon oxide 27 on the side wall, a silicon nanowire structure 29 having a branched structure in which the crystalline silicon cores 3 are joined to each other is generated. After such a branched structure is repeatedly generated to form a network structure, the amorphous layer 5 is deposited, and when the SiO ₂ oxide film 7 is further formed, a silicon nanowire structure 13 is obtained.

Further, when the two crystalline silicon cores 3 are close to each other as shown in FIG. 7A, when the amorphous layer 5 is formed, as shown in FIG. Layer 5 may join. In this case, the silicon nanowire structure 31 in which the amorphous layers 5 are joined to each other and the amorphous layers 5 are joined is obtained. As shown in FIG. 8, when the amorphous layer 5 is formed in a state where a large number of crystalline silicon cores 3 are deposited, a silicon nanowire structure 33 in which a large number of silicon nanowires are connected by the amorphous layer 5 is obtained. When the SiO ₂ oxide film 7 is formed on the surfaces of the silicon nanowire structures 31 and 33, the silicon nanowire structure 11 is obtained.

(Effect of manufacturing method according to embodiment)
In the manufacturing method of the silicon nanowire or the silicon nanowire structure according to the embodiment of the present invention, since the metal catalyst is not used and water or an organic substance having oxygen in the molecule is used, the metal catalyst is not mixed into the silicon nanowire as an impurity. . Moreover, since a metal catalyst is not used, it can be produced at low cost.

  Since the thermal decomposition reaction of organosilane is used, silicon nanowires and the like can be formed in a low temperature environment of 500 ° C. or lower.

  Since silicon nanowires are obtained from the liquid phase using liquid organosilane, scale-up is easy. In addition, since the amount of silicon per volume is higher than when a gaseous raw material is used, the amount of silicon nanowires obtained is also large.

  Further, since the formation of the silicon nanowire and the formation of the network structure of the silicon nanowire structure are performed in one step, the silicon nanowire structure can be easily obtained.

(Use of silicon nanowire or silicon nanowire structure)
When using silicon nanowires or silicon nanowire structures as negative electrode active materials for non-aqueous electrolyte secondary batteries, copper foil, silicon nanowires or silicon nanowire structures, conductive additives, binders, thickeners, solvents, etc. The slurry kneaded is applied to form a negative electrode for a non-aqueous electrolyte secondary battery.

  For dispersion of silicon nanowires or silicon nanowire structures into a slurry, a general kneader can be used, and a device called a kneader, a stirrer, a disperser, a mixer, etc. that can prepare a slurry should be used. it can.

  The slurry can be applied by using a general coating apparatus capable of applying the slurry to the copper substrate, for example, a roll coater, a coater using a doctor blade, a comma coater, or a die coater.

  In the solid content of the slurry, the silicon nanowire or silicon nanowire structure is 25 to 90% by weight, the conductive additive is 5 to 70% by weight, the binder is 1 to 30% by weight, and the thickener is 0 to 25% by weight. including.

  When preparing an aqueous slurry, latex (dispersion of rubber fine particles) such as styrene / butadiene / rubber (SBR) can be used as a binder, and polysaccharides such as carboxymethylcellulose and methylcellulose as thickeners. Etc. are suitably used as one or a mixture of two or more. In preparing an organic slurry, polyvinylidene fluoride (PVdF) or the like can be used as a binder, and N-methyl-2-pyrrolidone can be used as a solvent.

  The conductive assistant is a powder made of at least one conductive material selected from the group consisting of carbon, copper, tin, zinc, nickel, and silver. A single powder of carbon, copper, tin, zinc, nickel, or silver may be used, or a powder of each alloy may be used. For example, general carbon black having an average particle diameter of 1 nm to 1 μm, such as furnace black or acetylene black, can be used.

  The average particle size of the conductive assistant refers to the average particle size of the primary particles. Even when the structure shape is highly developed such as acetylene black (AB), the average particle diameter can be defined by the primary particle diameter here, and the average particle diameter can be obtained by image analysis of the SEM photograph.

  The binder is a resin binder, and a fluororesin such as polyvinylidene fluoride (PVdF) and styrene butadiene rubber (SBR) or a rubber system, and an organic material such as polyimide (PI) or acrylic is used. Can do.

  In addition, a separator is disposed between the negative electrode and the positive electrode according to the present invention to form a battery element, and such a battery element is wound or laminated into a cylindrical battery case or a rectangular battery case. Thereafter, an electrolyte or an electrolytic solution can be injected to produce a nonaqueous electrolyte secondary battery.

Hereinafter, the present invention will be specifically described using examples and comparative examples.
[Example 1]
(Production of silicon nanowires or silicon nanowire structures)
1 ml of phenylsilane, 19 ml of dehydrated toluene and 0.175 ml of water were placed in a quartz crucible and mixed. The ratio of water in the reaction solution is 1% by mass. The crucible was placed in an autoclave and the inside of the furnace was replaced with inert nitrogen gas and sealed. The temperature was raised to 380 ° C., held for 2 hours, and then cooled to room temperature. The pressure in the autoclave was about 5 MPa. After cooling, the quartz crucible was taken out and a yellow powdery precipitate was collected.

  When the obtained powder was observed with a scanning electron microscope, innumerable nanowires having a diameter of about 150 nm to 300 nm were observed as shown in FIG.

[Examples 2 to 8]
Examples 2 to 8 were performed by changing the amount of phenylsilane, the amount of dehydrated toluene, the amount of water, and the heating temperature.

[Comparative Example 1]
The synthesis was performed under the same conditions as in Example 3 except that water was not added. Table 1 shows the conditions of Examples 1 to 8 and Comparative Example 1.

  Moreover, the result of having observed the powder of each Example and the comparative example with the scanning electron microscope is shown to FIG. 9 (a)-(d), FIG. 10 (a)-(d), and FIG. In Examples 1 to 8, silicon nanowires having a thickness of 300 nm or less were observed. On the other hand, in Comparative Example 1, particulate silicon having a particle size of 3 to 10 μm and flaky silicon having a thickness of about 1 μm were observed.

  When Examples 1 to 3 are compared, the diameter of the obtained silicon nanowires becomes thinner as the heating temperature increases to 450 ° C. in the order of Examples 1, 2, and 3.

  In Example 3, Example 5 and Example 7, the conditions were the same except that the amounts of phenylsilane and dehydrated toluene were changed. However, when the proportion of phenylsilane was increased, the amount of silicon nanowires produced decreased. ing.

  In addition, when Examples 3 and 4 were compared, when the amount of water was increased from 1 wt% to 3 wt%, branching increased and products other than silicon nanowires tended to increase. The same applies to the comparison between Examples 5 and 6 and the comparison between Examples 7 and 8.

  12 is a transmission electron microscope image of the silicon nanowire according to Example 1. FIG. The diameter of the silicon nanowire is about 250 nm. Further, a black crystalline silicon core having a thickness of about 10 nm was observed at the center of the silicon nanowire.

FIG. 13 shows the result of elemental analysis performed by EDX in the outer region 1 and the central region 2 of the same silicon nanowire. In the central region 2, the proportion of oxygen is small and the central portion is not oxidized. In the region 2 as well, since the measurement includes the SiO ₂ oxide film on the surface, oxygen is detected to some extent.

FIG. 14 is a transmission electron microscope image of the silicon nanowire according to Example 3. The diameter of the silicon nanowire is about 150 nm. A black crystalline silicon core with a thickness of about 30 nm is observed at the center of the silicon nanowire. An amorphous layer having a thickness of about 40 nm is formed outside the crystalline silicon core. A SiO ₂ oxide film having a thickness of about 20 nm is formed outside the amorphous layer.

  FIG. 15 shows the result of elemental analysis performed by EDX in the outer region 1 and the central region 2 of the same silicon nanowire. In the central region 2, the proportion of oxygen is small and the central portion is not oxidized.

  FIG. 16 is a transmission electron micrograph of another region of the silicon nanowire according to Example 3. As shown in FIG. 16A, the diameter of the silicon nanowire is about 50 nm, and as shown in the enlarged view of FIG. 16B, a crystalline silicon core having a diameter of about 5 nm is exposed at the end.

  FIG. 17 is a transmission electron micrograph of the bonded portion of the silicon nanowire structure according to Example 3. It can be seen that the silicon nanowires are joined together by the amorphous layer 5.

  The preferred embodiments of the present invention have been described above with reference to the accompanying drawings, but the present invention is not limited to such examples. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the technical idea disclosed in the present application, and these are naturally within the technical scope of the present invention. Understood.

1 ......... silicon nanowire 3 ......... crystal silicon core 5 ......... amorphous layer 7 ......... SiO ₂ oxide film 11 ......... silicon nanowire structure 13 ......... silicon nanowire structure 21 ......... phenylsilane 23 ……… Silane 25 ……… Water 27 ……… Silicon oxide 29 ……… Silicon nanowire structure 31 ……… Silicon nanowire structure 33 ……… Silicon nanowire structure

Claims (13)

A crystalline silicon core, an amorphous layer covering the crystalline silicon core, and a SiO ₂ oxide film covering the amorphous layer,
The silicon nanowire, wherein the amorphous layer is made of amorphous silicon or amorphous SiO _x (x <2). It has a crystalline silicon core, an amorphous layer covering the crystalline silicon core, and a SiO ₂ oxide film covering the amorphous layer, and the amorphous layer is made of amorphous silicon or amorphous SiO _x (x <2). Including silicon nanowires,
A silicon nanowire structure having a structure in which a plurality of the silicon nanowires are connected.   The silicon nanowire structure according to claim 2, wherein a plurality of the silicon nanowires have a structure in which the amorphous layers are connected to each other while being in contact with each other.   The silicon nanowire structure according to claim 2 or 3, wherein an average aspect ratio obtained by dividing the length of the silicon nanowire by the diameter of the silicon nanowire is 10 or more.   2. The silicon nanowire according to claim 1, wherein a diameter of the crystalline silicon core of the silicon nanowire is 1 to 50 nm, and a thickness of the amorphous layer is 10 to 100 nm. A positive electrode capable of inserting and extracting lithium ions;
A negative electrode having an active material layer on a current collector;
Having a separator disposed between the positive electrode and the negative electrode;
A non-aqueous electrolyte secondary battery in which the positive electrode, the negative electrode, and the separator are provided in an electrolyte having lithium ion conductivity,
The active material layer of the negative electrode includes a crystalline silicon core, an amorphous layer that covers the crystalline silicon core, and a SiO ₂ oxide film that covers the amorphous layer, and the amorphous layer is amorphous silicon or amorphous SiO _x ( A non-aqueous electrolyte secondary battery comprising a silicon nanowire characterized by comprising x <2).   In a reaction of thermally decomposing the organic silane using an organic silane that does not contain oxygen and an organic solvent that does not contain oxygen in the molecule, 0.3 to 5.0% by weight of water or an organic substance having oxygen in the molecule A method for producing a silicon nanowire structure, comprising adding and performing a thermal decomposition reaction.   The method for producing a silicon nanowire structure according to claim 7, wherein the thermal decomposition is performed in a pressure vessel, the pressure is 2 MPa or more and 20 MPa or less, and the temperature is 350 ° C or more and 500 ° C or less.   The water or the organic substance having oxygen in the molecule is at least one selected from the group consisting of water, alcohol, ketone, carboxylic acid, aldehyde, ether, carboxylic anhydride, percarboxylic acid, and carboxylic ester. The method for producing a silicon nanowire structure according to claim 7 or 8, wherein:   The method for producing a silicon nanowire structure according to claim 9, wherein the water or the organic substance having oxygen in the molecule is water.   The method for producing a silicon nanowire structure according to any one of claims 7 to 10, wherein the organic solvent is an aromatic hydrocarbon.   The organic silane is phenyl silane, diphenyl silane, triphenyl silane, tetraphenyl silane, diethyl silane, triethyl silane, tetraethyl silane, tetramethyl silane, or a mixture thereof. 11. The method for producing a silicon nanowire structure according to any one of 11 above. The method for producing a silicon nanowire structure according to any one of claims 7 to 12, wherein the nanowire is formed simultaneously with the production of the silicon nanowire structure.