Lithium-ion secondary battery

Abstract

To provide a method for forming graphene with a practically uniform thickness on an object with uneven or complex shapes on the surface, in particular, an object with a three-dimensional structure on the surface or with a curved surface due to particularly complicated uneven shapes.SOLUTION: A method for manufacturing a graphene-coated object having an uneven surface, comprising: immersing an object and an electrode in a solution including graphene oxide; and applying voltage to the object and the electrode. At this time, the object serves as an anode. Graphene oxide is attracted to the anode because of being negatively charged, and deposited on the surface of the object to have a practically even thickness. A portion where graphene oxide is deposited is unlikely coated with another graphene oxide. Thus, deposited graphene oxide is reduced to graphene, whereby graphene can be formed to have a practically even thickness on the object having surface with complex unevenness.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for producing a graphene-coated object using single-layer graphene, which is a sheet of a one-atom-thick carbon molecule having a π bond, or multilayer graphene in which two or more and 100 or less single-layer graphene sheets are stacked, and further relates to multilayer graphene and a method for producing the same. In this specification, single-layer graphene and multilayer graphene are collectively referred to simply as graphene. Further, the present invention relates to a negative electrode of a secondary battery using a carbon-based film, and a secondary battery using the same.

[0002]

Background Art

[0003] Graphene has been attempted to be applied to various products due to its excellent electrical properties such as high conductivity and mobility, and physical properties such as flexibility and mechanical strength (see Patent Documents 1 to 3).

[0004] Here, in a secondary battery, which is a rechargeable power storage device sold as a product, a carbon material such as graphite (graphite) is used as its negative electrode. Graphite has a regular planar arrangement of carbons having sp 2 hybrid orbitals and has a laminated crystal structure. Charge and discharge of the secondary battery are performed by utilizing the occlusion of lithium ions from the positive electrode between the layers of the laminated crystal structure.

[0005] In addition to graphite, carbon materials suitable as negative electrode materials for lithium ion secondary batteries have been studied (Patent Document 4). Such carbon materials have a high lithium occlusion and release capacity as a negative electrode material for lithium ion secondary batteries and are difficult to break even when subjected to continuous charge and discharge. To solve the problem, the carbon contains carbon particles having voids inside and containing a metal that forms an alloy with lithium. The carbon particles are contained.

[0006] An electromotive force substance that is directly involved in the battery reaction and generates electric power is called an active material of the battery. From the viewpoint of increasing the output of the secondary battery, it is preferable to reduce the particle diameter of the active material of the electrode. However, when the particle diameter is reduced, a conductive aid and a binder are required to efficiently construct a conductive network. However, there is a problem that the capacity per unit volume of the electrode decreases due to the conductive aid and the binder. Therefore, a battery that is held using whiskers on the surface of the active material layer and the current collector without using a conductive aid or a binder has been studied (Patent Document 5). In Patent Document 5, lithium manganate, lithium nickelate, lithium cobaltate, lithium iron phosphate, lithium titanate, graphite, and hard carbon are described as the materials of the active material, and carbon, potassium titanate, titanium carbide, silicon carbide, titanium dioxide, zinc oxide, magnesium oxide, tin dioxide, and indium oxide are described as the materials of the whiskers. When lithium released from the positive electrode is occluded in the negative electrode, it is known to expand and eventually pulverize. To solve this problem, a configuration has been proposed in which particles of a metal or semi-metal that forms a lithium alloy are used as nuclei and the nuclei of the particles are coated with carbon (Patent Document 6). In Patent Document 6, it is described that silicon is preferable as the particles serving as nuclei, and a chemical vapor deposition treatment method is described as the method for coating with carbon.

[0007]

Prior Art Documents

Patent Documents

[0008] ​​​​​​​​​

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Summary of the Invention

Problems to be Solved by the Invention

[0009] As described in Patent Documents 1 to 3, the methods for producing graphene are roughly classified into a vapor-phase growth (CVD) method and a coating method. The CVD method is, for example, as described in Patent Document 1 or Patent Document 2 wherein a metal serving as a catalyst is heated and hydrocarbon gas is passed therethrough to grow graphene on the catalyst.

[0010] Also, the coating method is, as described in Patent Document 3, to disperse graphene oxide obtained by oxidizing graphite in a solution, apply this to form a graphene oxide film and further reduce this to obtain graphene.

[0011] It is possible to obtain graphene on a flat surface by any of these methods. However, it is difficult to form graphene on an object having a concavo-convex or complex-shaped surface, particularly an object having a three-dimensional structure on the surface due to a complex concavo-convex shape, or an object having a curved surface. CVD In the method, since graphene is formed only on the catalyst, the formed graphene needs to be peeled off and transferred to the target object. At this time, it was impossible to transfer it to an object having an uneven shape or a complex shape on the surface, or an object having a curved surface. Also, in the coating method, it is difficult to form graphene with a practically uniform thickness on the concave and convex portions of an object having unevenness. In the case of a surface having a three-dimensional structure due to a complex uneven shape, it was difficult to form graphene sufficiently inside the structure. Generally, on the convex portion, the graphene becomes thin and in some cases, graphene cannot be formed. Also, in the concave portion, the graphene becomes excessively thick or graphene is not formed up to the inside of the concave portion, and a space is formed between the graphene and the concave portion. An object of the present invention is to provide graphene formed on an object having such an uneven shape or a complex shape on the surface, particularly an object having a three-dimensional structure on the surface due to a complex uneven shape, or an object having a curved surface. Another object of the present invention is to provide a method for forming graphene on such an object. Another object of the present invention is to provide a device having graphene formed on such an object. Also, in a secondary battery, in the configuration of Patent Document 4, since there are voids inside, there is waste in the arrangement of the number of carbon particles. In the configurations of Patent Documents 4 to 6, the active material is in the form of particles and there are limitations in the absorption and release of lithium ions. Therefore, an object of the present invention is to use a non-spherical material, particularly a film-like carbon-based material, as the electrode material.

Means for Solving the Problems

[0012]

[0013]

[0014]

[0015] One aspect of the present invention will be described. First, graphene oxide is dispersed in a suitable solution. Graphene oxide is a single-layer or laminated multi-layer graphene sheet which is a sheet of carbon molecules with a single atomic layer, and a part of the edge of a graphene sheet of a certain size is terminated with a carboxyl group (-COOH). Therefore, in a solution such as water, hydrogen ions are detached from the carboxyl group, and the graphene oxide itself is negatively charged. Utilizing this property, a coating of graphene oxide is formed on the surface of an object by electrophoresis. That is, an object serving as an anode for forming graphene and a cathode are immersed in a dispersion of graphene oxide, and a potential difference is applied between the anode and the cathode, whereby the negatively charged graphene oxide is attracted to the anode and adheres to the surface of the object, forming graphene oxide that covers the surface of the object.

[0016] When forming graphene oxide on the surface of an object by electrophoresis, the graphene oxide adheres to a portion of the object surface other than the portion where graphene oxide has already adhered. In other words, it is difficult for other graphene oxide to adhere to the portion where graphene oxide has already adhered. FIGS. 1(A)-(C) schematically show the state of graphene oxide adhering to the surface of an object. In the case where graphene oxide 102 has already adhered on the surface of a columnar object 101 immersed in a suitable solution 100, other graphene oxide 103 does not adhere on the already adhered graphene oxide 102, but adheres to the portion of the object surface where graphene oxide has not yet adhered (see FIGS. 1(A) and (B)). This is because graphene oxide is an insulator with a sufficiently low conductivity compared to graphene, so electrophoretic electrodeposition does not proceed at the portion adhered to the object surface. Also , graphene oxide is negatively charged, and graphene oxides repel each other electrostatically. The surface of graphene oxide that adheres to the object surface is where the carboxyl groups from which hydrogen ions have detached adhere to the object. The carboxyl groups from which hydrogen ions have detached can also bond with the object and can be neutralized. On the other hand, the carboxyl groups on the solution side surface of the adhered graphene oxide, that is, the carboxyl groups on the exposed surface, still have hydrogen ions detached and are negatively charged. Therefore, after the object is completely covered by graphene oxide, it is more difficult to be further covered by other graphene oxides (see Fig. 1(C)).

[0017] Since the coating with graphene oxide is carried out through such a process, the thickness of the graphene oxide formed on the surface of the object becomes practically uniform. It becomes approximately uniform. Furthermore, even for an object whose surface has an uneven shape or a complex shape on the surface, or an object having a curved surface, it is also possible to effectively attach graphene oxide in principle. In particular, when the object has a three-dimensional structure on the surface due to a complex concave-convex shape, even in this case, since the size of graphene oxide is much smaller than the size of the object forming the structure, it is possible to move between complex three-dimensional structures, so it is possible to attach graphene oxide even inside the structure. The graphene oxide that has entered the structure will adhere to other parts except for the parts where graphene oxide has already adhered.

[0018] Thereafter, by heating the graphene oxide in an appropriate atmosphere such as in a vacuum or a reducing atmosphere, the graphene oxide can be reduced to form graphene on the surface of the object. Note that graphene may contain elements other than carbon and oxygen at 15 atomic % or less, and also Elements other than carbon may be included at 30 atomic % or less. The shape and size of the object to be coated also matter, but the length of one side of the graphene oxide used is preferably 10 μm or less. This is to enable more dense and reliable coating of the surface of an object having an uneven shape or a complex shape.

[0019] Note that the surface of the object to be formed with graphene may exhibit conductivity, or a non-conductive substance may be present on the surface of the object to the extent that electrodeposition by electrophoresis is possible.

[0020] Further, in one aspect of the present invention, a film-like carbon-based material (carbon-based film ) is used as the electrode material of the secondary battery. The film-like carbon-based material is provided so as to be in contact with the convex portions of the uneven shape and cover the uneven shape. That is, the film-like carbon-based material can be provided across the convex portions. The uneven shape may be an uneven shape formed on the current collector or an uneven shape composed of the active material.

[0021] The present invention can provide a carbon-based film in close contact with the convex portions as the electrode material of the secondary battery. That is, a carbon-based film can be provided around the convex portions.

[0022] The film-like carbon-based material has 2 or more and 1000 or less, preferably 100 or more and 300 or less graphenes. When 2 to 3 graphenes are stacked, the film thickness of the film-like carbon-based material becomes a film thickness of 1 nm to 2 nm. The film-like carbon-based material may be amorphous or crystalline.

[0023] At the convex portions, the length with respect to the diameter is 2 to 10000 times, preferably 10 to 100 times ​​​​​​​It is columnar. If it is long, it is difficult to form the convex portion perpendicular to the current collector, and the convex portion will bend or lie horizontally with respect to the current collector. Also, depending on the material of the convex portion, the convex portion may bend. From such a state, it can be expressed as whisker-shaped (bearded).

Advantages of the Invention

[0024] It is possible to form graphene on the surface of an object whose surface has an uneven shape or a complex shape, particularly an object having a three-dimensional structure on the surface due to a complex concave-convex shape, or an object whose surface is a curved surface, which was difficult with conventional methods. Also, in an object whose surface has an uneven shape or a complex shape, particularly an object having a three-dimensional structure on the surface due to a complex concave-convex shape, or an object whose surface is a curved surface, graphene can be formed with a practically uniform thickness even inside the structure.

[0025] In addition, even in an object whose surface is covered with graphene having a practically uniform thickness, even if the object expands due to some factor, it is possible to prevent the object from being crushed because graphene has sufficient flexibility.

[0026] When a film-like carbon-based material is used as the electrode material of a secondary battery, as the negative electrode active material, it has the advantage of a short diffusion path of lithium in the active material. As the conductive assistant, it has the advantage of being able to construct a wide-range conductive network.

[0027] Also, when a film-like carbon-based material is used as the electrode material of a secondary battery, as the negative electrode active material, it has the advantage of a short diffusion path of lithium in the active material. As the conductive assistant, it has the advantage of being able to construct a wide-range conductive network.

Brief Description of the Drawings

[0028]

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Mode for Carrying Out the Invention

[0029] Hereinafter, embodiments will be described. However, the embodiments can be implemented in many different modes and it is possible to variously change its form and details without departing from the spirit and its scope. Those skilled in the art can easily understand that it can be obtained. Therefore, the present invention is not construed as being limited to the description of the following embodiments. It is not construed as being limited to the description of the following embodiments.

[0030] (Embodiment 1) In this embodiment, a method for forming graphene on the surface of an object will be described. Graphite oxide is obtained by oxidizing graphite to produce graphite oxide and applying ultrasonic vibration thereto. For details, reference may be made to Patent Document 3. Also, commercially available graphene oxide may be used. It may be used.

[0031] Graphene oxide is dispersed in a solvent such as water, chloroform, N,N-dimethylformamide ( DMF), or N-methylpyrrolidone (NMP). The solvent is preferably a polar solvent. The concentration of graphene oxide may be 0 to 10 g per liter. .1 g to 10 g per liter.

[0032] Fig. 2 shows a diagram of the apparatus used in this embodiment. A solution 201 in which graphene oxide is dispersed is placed in a container 200, and an object 202 to which graphene is to be attached is placed therein, and this is used as the anode. A solution 201 in which graphene oxide is dispersed is placed in a container 200, and an object 202 to which graphene is to be attached is placed therein, and this is used as the anode. Also, a conductor 203 serving as the cathode is placed in the solution, and an appropriate voltage (for example , 5 V to 20 V) is applied between the anode and the cathode to perform electrophoretic deposition (such an electrodeposition method will be referred to as the electrophoresis method hereinafter). The voltage does not have to be constant. By measuring the amount of charge flowing between the anode and the cathode, the thickness of the graphene oxide attached to the object can be estimated. is referred to as the electrophoresis method hereinafter). The voltage does not have to be constant. By measuring the amount of charge flowing between the anode and the cathode, the thickness of the graphene oxide attached to the object can be estimated. The attachment of graphene oxide to the anode stops when the anode is entirely covered. Therefore, by grasping in advance the time required to completely cover the anode with graphene oxide The attachment of graphene oxide to the anode stops when the anode is entirely covered. Therefore, by grasping in advance the time required to completely cover the anode with graphene oxide , it is possible to complete the complete coverage in the shortest time. , it is possible to complete the complete coverage in the shortest time.

[0033] Once the attachment of graphene oxide is completed, the object is lifted out of the solution and dried. Further, it is heated at a temperature of 150°C or higher, preferably 200°C or higher, in a vacuum or a reducing atmosphere such as an inert gas (nitrogen or noble gas, etc.). The higher the heating temperature and the longer the heating time, the better the reduction of graphene oxide and the higher the purity of the obtained graphene (i.e., the lower the concentration of elements other than carbon). It is known that graphene oxide is reduced at a heating temperature of 100°C or higher. Although it is more preferable to heat at a higher temperature, the heating temperature should be determined in consideration of the reactivity with the object. The higher the heating temperature and the longer the heating time, the better the reduction of graphene oxide and the higher the purity of the obtained graphene (i.e., the lower the concentration of elements other than carbon). it is heated at a temperature of 150°C or higher, preferably 200°C or higher, in a vacuum or a reducing atmosphere such as an inert gas (nitrogen or noble gas, etc.). The higher the heating temperature and the longer the heating time, the better the reduction of graphene oxide and the higher the purity of the obtained graphene (i.e., the lower the concentration of elements other than carbon). It is known that graphene oxide is reduced at a heating temperature of 100°C or higher. Although it is more preferable to heat at a higher temperature, the heating temperature should be determined in consideration of the reactivity with the object. it is heated at a temperature of 150°C or higher, preferably 200°C or higher, in a vacuum or a reducing atmosphere such as an inert gas (nitrogen or noble gas, etc.). The higher the heating temperature and the longer the heating time, the better the reduction of graphene oxide and the higher the purity of the obtained graphene (i.e., the lower the concentration of elements other than carbon). It is known that graphene oxide is reduced at a heating temperature of 100°C or higher. Although it is more preferable to heat at a higher temperature, the heating temperature should be determined in consideration of the reactivity with the object. it is heated at a temperature of 150°C or higher, preferably 200°C or higher, in a vacuum or a reducing atmosphere such as an inert gas (nitrogen or noble gas, etc.). The higher the heating temperature and the longer the heating time, the better the reduction of graphene oxide and the higher the purity of the obtained graphene (i.e., the lower the concentration of elements other than carbon). It is known that graphene oxide is reduced at a heating temperature of 100°C or higher. Although it is more preferable to heat at a higher temperature, the heating temperature should be determined in consideration of the reactivity with the object. it is heated at a temperature of 150°C or higher, preferably 200°C or higher, in a vacuum or a reducing atmosphere such as an inert gas (nitrogen or noble gas, etc.). The higher the heating temperature and the longer the heating time, the better the reduction of graphene oxide and the higher the purity of the obtained graphene (i.e., the lower the concentration of elements other than carbon). It is known that graphene oxide is reduced at a heating temperature of 100°C or higher. Although it is more preferable to heat at a higher temperature, the heating temperature should be determined in consideration of the reactivity with the object.

[0034] In addition, in order to increase the electron conductivity of the obtained graphene, the above heat treatment is preferably a high-temperature treatment. For example, when graphene oxide on a glass substrate is heated and reduced to graphene, the resistivity of multilayer graphene is about 240 MΩcm at a heating temperature of 100°C (for 1 hour), but becomes 4 kΩcm at a heating temperature of 200°C (for 1 hour), and 2.8 Ωcm at 300°C (for 1 hour) (all are the average values of 8 samples). In addition, in order to increase the electron conductivity of the obtained graphene, the above heat treatment is preferably a high-temperature treatment. For example, when graphene oxide on a glass substrate is heated and reduced to graphene, the resistivity of multilayer graphene is about 240 MΩcm at a heating temperature of 100°C (for 1 hour), but becomes 4 kΩcm at a heating temperature of 200°C (for 1 hour), and 2.8 Ωcm at 300°C (for 1 hour) (all are the average values of 8 samples). In addition, in order to increase the electron conductivity of the obtained graphene, the above heat treatment is preferably a high-temperature treatment. For example, when graphene oxide on a glass substrate is heated and reduced to graphene, the resistivity of multilayer graphene is about 240 MΩcm at a heating temperature of 100°C (for 1 hour), but becomes 4 kΩcm at a heating temperature of 200°C (for 1 hour), and 2.8 Ωcm at 300°C (for 1 hour) (all are the average values of 8 samples). In addition, in order to increase the electron conductivity of the obtained graphene, the above heat treatment is preferably a high-temperature treatment. For example, when graphene oxide on a glass substrate is heated and reduced to graphene, the resistivity of multilayer graphene is about 240 MΩcm at a heating temperature of 100°C (for 1 hour), but becomes 4 kΩcm at a heating temperature of 200°C (for 1 hour), and 2.8 Ωcm at 300°C (for 1 hour) (all are the average values of 8 samples). In addition, in order to increase the electron conductivity of the obtained graphene, the above heat treatment is preferably a high-temperature treatment. For example, when graphene oxide on a glass substrate is heated and reduced to graphene, the resistivity of multilayer graphene is about 240 MΩcm at a heating temperature of 100°C (for 1 hour), but becomes 4 kΩcm at a heating temperature of 200°C (for 1 hour), and 2.8 Ωcm at 300°C (for 1 hour) (all are the average values of 8 samples).

[0035] In this way, the graphene oxide attached to the surface of the object is reduced to graphene. At this time, adjacent graphenes are bonded to each other, and as a whole, a larger sheet-like or mesh-like network is formed (hereinafter, such a network formed by such graphene is called a graphene network). The graphene formed in this way is formed with a substantially uniform thickness on both the concave and convex portions of the object, even if the object has concavities and convexities. The same applies to the case where the object has a curved surface. At this time, adjacent graphenes are bonded to each other, and as a whole, a larger sheet-like or mesh-like network is formed (hereinafter, such a network formed by such graphene is called a graphene network). The graphene formed in this way is formed with a substantially uniform thickness on both the concave and convex portions of the object, even if the object has concavities and convexities. The same applies to the case where the object has a curved surface. At this time, adjacent graphenes are bonded to each other, and as a whole, a larger sheet-like or mesh-like network is formed (hereinafter, such a network formed by such graphene is called a graphene network). The graphene formed in this way is formed with a substantially uniform thickness on both the concave and convex portions of the object, even if the object has concavities and convexities. The same applies to the case where the object has a curved surface. At this time, adjacent graphenes are bonded to each other, and as a whole, a larger sheet-like or mesh-like network is formed (hereinafter, such a network formed by such graphene is called a graphene network). The graphene formed in this way is formed with a substantially uniform thickness on both the concave and convex portions of the object, even if the object has concavities and convexities. The same applies to the case where the object has a curved surface. At this time, adjacent graphenes are bonded to each other, and as a whole, a larger sheet-like or mesh-like network is formed (hereinafter, such a network formed by such graphene is called a graphene network). The graphene formed in this way is formed with a substantially uniform thickness on both the concave and convex portions of the object, even if the object has concavities and convexities. The same applies to the case where the object has a curved surface.

[0036] (Embodiment 2) In this embodiment, an electrode having a film-like carbon-based material will be described.

[0037] As shown in FIG. 11, the electrode has a current collector 1100 and a film-like carbon-based material 1102 . The film-like carbon-based material 1102 may be provided on the current collector 1100, but it is preferably held so as to increase the surface area. For example, it is held by a plurality of convex portions 1101 (each being denoted as 1101a to 1101e) on the current collector 1100. That is, the film-like carbon-based material 1102 can be provided over the plurality of convex portions 1101.

[0038] The film-like carbon-based material 1102 has graphene 1104 in which one or more and 1000 or less, preferably 100 or more and 300 or less layers are laminated. The graphene network is different from graphite in any of the following points. · In the stacking direction (Z-axis direction), it is bonded by van der Waals force. · The number of stacked layers is large. · The ends of the layers are misaligned. · The number of carbon ring members constituting one layer is large, for example, 9 or more, and the gap is wide.

[0039] The graphene network having any one of the above characteristics can increase the lithium ion occlusion rate. Furthermore, since it is film-like, it is advantageous for the occlusion and release of lithium ions.

[0040] When two or three layers are laminated, the film thickness of the film-like carbon-based material becomes a film thickness of 1 nm to 2 nm. The film-like carbon-based material may be amorphous or crystalline.

[0041] Such a film-like carbon-based material has conductivity. The film-like carbon-based material is used as a conductive assistant for the negative electrode. ​​​​It can be used. Since the film-like carbon-based material has a large surface area, it is effective as a conductive aid. It is.

[0042] The film-like carbon-based material can be used as the active material of the negative electrode. Lithium is occluded in the film-like carbon-based material. The number of graphene sheets is preferably 1 or more and 1000 or less, more preferably 100 or more and 300 or less. This is because the larger the number of graphene sheets, the more efficiently lithium can be occluded. It is.

[0043] For a film-like carbon-based material, compared with the spherical case, it can construct its own conductive network. Since it also has the functions of a binder and a conductive aid, the addition of a binder and a conductive aid can be reduced or omitted. Therefore, the amount of the active material can be increased. It has the functions of a binder and a conductive aid, so the addition of a binder and a conductive aid can be reduced or omitted. Therefore, the amount of the active material can be increased. It is. It can be.

[0044] The film-like carbon-based material may be provided so as to cover the surfaces of the plurality of convex portions 1101, that is, along the plurality of convex portions 11 01a to 1101e. It may be provided without creating a space between adjacent convex portions. For example, it is provided so that no space is created between the convex portion 1101a and the convex portion 1101b. The amount of graphene can be increased. It may be provided so that no space is created between the convex portion 1101a and the convex portion 1101b. The amount of graphene can be increased. It can be.

[0045] To provide the film-like carbon-based material along the plurality of convex portions 1101, an electrophoresis method is used. It is a method of applying a voltage for a certain period of time using an aqueous solution in which graphene oxide is dispersed. The production conditions and the like will be described in the following examples. It is a method of applying a voltage for a certain period of time using an aqueous solution in which graphene oxide is dispersed. The production conditions and the like will be described in the following examples. The production conditions and the like will be described in the following examples.

[0046] Also, as a method different from the electrophoresis method, a dipping method can be used to provide a film-like carbon-based material along the plurality of convex portions 1101. The dipping method is a method of dispersing graphene oxide in water. The dipping method is a method of dispersing graphene oxide in water. A method of immersing a current collector provided with a plurality of convex portions in a solution without applying a voltage. In this case, a space may be formed between the plurality of convex portions 1101 and the film-like carbon-based material.

[0047] Such a plurality of convex portions 1101 can be formed on the surface of the current collector 1100. Also, a plurality of convex portions 1101 can be formed by scraping the surface of the current collector 1100.

[0048] The plurality of convex portions 1101a to 1101e have a diameter of 50 nm or more and 10 μm or less, preferably 500 nm or more and 3 μm or less. The length along the axis of the convex portion is 0.5 μm or more and 1000 μm or less, preferably 1 μm or more and 100 μm or less. The length with respect to the diameter satisfies 2 to 10000 times, preferably 10 to 100 times. Its shape is called columnar. The side surface of the convex portion may have a roundness. Its shape is called cylindrical. Further, the tip of the convex portion preferably has a roundness . The roundness prevents cracks or breakage in the film-like carbon-based material. The convex portion may be spherical or hemispherical (dome-shaped).

[0049] The shape of the plurality of convex portions can also be whisker-like (bearded). In this case, the plurality of convex portions have different shapes from each other. Since the whisker-like convex portions are long, it is difficult to form them perpendicular to the current collector , and the whisker-like convex portions may bend, lie horizontally with respect to the current collector, entangle with nearby whisker-like convex portions , or cross-link with nearby whisker-like convex portions. Also, one whisker-like convex portion may draw a circle.

[0050] Silicon whiskers having silicon can be used for the whisker-like convex portions. The plurality of convex portions, including silicon whiskers, may be amorphous or crystalline ​ If it is amorphous, it is less likely to break compared to the crystalline case. Also, if it is a silicon whisker , it is preferable that the core part has crystallinity and the periphery of the core part is amorphous. In addition to a certain strength, it can be provided with resistance to breakage.

[0051] If it is a negative electrode having a silicon whisker and a film-like carbon-based material, both can be used as active materials. It is possible to provide a negative electrode that combines the lithium storage characteristics of silicon and the lithium storage characteristics of carbon. That is, it is possible to provide a negative electrode with a high lithium storage capacity by adding the lithium storage capacity of carbon to the lithium storage ability of silicon.

[0052] Also, the shape and arrangement of the plurality of convex portions 1101a to 1101e are not particularly limited as long as they can support the film-like carbon-based material. Even one convex portion can support the film-like carbon-based material. If it is a film-like carbon-based material supported by one convex portion, it will hang down toward the current collector. The film-like carbon-based material can have a larger surface area when it hangs down toward the current collector.

[0053] As described above, in the convex portion, if it is long, there is a risk of breakage. When lithium is occluded in the convex portion, the risk of breakage becomes even higher. Such breakage of the convex portion can be prevented by the film-like carbon-based material.

[0054] When such a film-like carbon-based material is used for the negative electrode of a secondary battery, it is advantageous for the absorption and release of lithium ions compared to the spherical case. Furthermore, if it is graphene having a layer structure of 2 or more and 1000 or less, preferably 100 or more and 300 or less layers, lithium is occluded between the layers. Therefore, lithium can be more efficiently occluded than in the case of spherical active material.

[0055] (Embodiment 3) In this embodiment, a structure in which a carbon-based material is provided around a plurality of convex portions 1101 will be described. do.

[0056] As shown in FIG. 12, it has a carbon-based material 1103 that covers a plurality of convex portions 1101. Carbon The - based material 1103 has 1 or more and 1000 or less, preferably 100 or more and 300 or less graphene 1104. When two to three graphene sheets are stacked, the film thickness of the carbon-based material becomes 1 nm to 2 nm. The carbon-based material may be amorphous or crystalline.

[0057] For other configurations, reference can be made to Embodiment 2, and a film-like carbon-based material 1102 can be provided.

[0058] The carbon-based material has conductivity. Therefore, it can be used as a conductive additive for the negative electrode. When a film-like carbon-based material 1102 as shown in Embodiment 2 is provided, together with the carbon-based material 1103, a plurality of carbon-based materials are provided, enhancing the function as a conductive additive.

[0059] In addition, the carbon-based material can be used as an active material. When a film-like carbon-based material 1102 as shown in Embodiment 2 is provided, the carbon-based material 1103 can be used as an active material together with the film-like carbon-based material 1102. Also, when the carbon-based material 1103 is used as an active material, the film-like carbon-based material 1102 can also function as a conductive additive. In any case, providing a plurality of carbon-based materials improves the function as an electrode.

[0060] ​​​​​​​​​ (Embodiment 4) In this embodiment, the form of the laminated secondary battery having the negative electrode according to the present invention will be described.

[0061] FIG. 13(A) is a plan view of a laminated secondary battery 1301, and a cross-sectional view taken along the dash-dotted line A-B in FIG. 13(A) is shown in FIG. 13(B). The laminated secondary battery 1301 shown in FIG. 13(A) has a power storage cell 1305 inside an exterior member 1303. Further, it has a terminal portion 1307 and a terminal portion 1309 connected to the power storage cell 1305. The exterior member 1303 can be made of a laminate film, a polymer film, a metal film, a metal case, a plastic case, etc. As shown in FIG. 13(B), the power storage cell 1305 has a negative electrode 1313, a positive electrode 1315, a separator 1317, and an electrolytic solution 1319. The separator 1317 is provided between the negative electrode 1313 and the positive electrode 1315. The exterior member 1303 is filled with the electrolytic solution 1319. As shown in FIG. 13(B), the power storage cell 1305 has a negative electrode 1313, a positive electrode 1315, a separator 1317, and an electrolytic solution 1319. The separator 1317 is provided between the negative electrode 1313 and the positive electrode 1315. The exterior member 1303 is filled with the electrolytic solution 1319. As shown in FIG. 13(B), the power storage cell 1305 has a negative electrode 1313, a positive electrode 1315, a separator 1317, and an electrolytic solution 1319. The separator 1317 is provided between the negative electrode 1313 and the positive electrode 1315. The exterior member 1303 is filled with the electrolytic solution 1319. As shown in FIG. 13(B), the power storage cell 1305 has a negative electrode 1313, a positive electrode 1315, a separator 1317, and an electrolytic solution 1319. The separator 1317 is provided between the negative electrode 1313 and the positive electrode 1315. The exterior member 1303 is filled with the electrolytic solution 1319. As shown in FIG. 13(B), the power storage cell 1305 has a negative electrode 1313, a positive electrode 1315, a separator 1317, and an electrolytic solution 1319. The separator 1317 is provided between the negative electrode 1313 and the positive electrode 1315. The exterior member 1303 is filled with the electrolytic solution 1319.

[0062] As shown in FIG. 13(B), the power storage cell 1305 has a negative electrode 1313, a positive electrode 1315, a separator 1317, and an electrolytic solution 1319. The separator 1317 is provided between the negative electrode 1313 and the positive electrode 1315. The exterior member 1303 is filled with the electrolytic solution 1319. As shown in FIG. 13(B), the power storage cell 1305 has a negative electrode 1313, a positive electrode 1315, a separator 1317, and an electrolytic solution 1319. The separator 1317 is provided between the negative electrode 1313 and the positive electrode 1315. The exterior member 1303 is filled with the electrolytic solution 1319. As shown in FIG. 13(B), the power storage cell 1305 has a negative electrode 1313, a positive electrode 1315, a separator 1317, and an electrolytic solution 1319. The separator 1317 is provided between the negative electrode 1313 and the positive electrode 1315. The exterior member 1303 is filled with the electrolytic solution 1319. As shown in FIG. 13(B), the power storage cell 1305 has a negative electrode 1313, a positive electrode 1315, a separator 1317, and an electrolytic solution 1319. The separator 1317 is provided between the negative electrode 1313 and the positive electrode 1315. The exterior member 1303 is filled with the electrolytic solution 1319.

[0063] The negative electrode 1313 is configured with reference to the above embodiment and has at least a negative electrode current collector 1321 and a negative electrode active material layer 1323. The positive electrode 1315 has at least a positive electrode current collector 1325 and a positive electrode active material 1327. The negative electrode active material layer 1323 can be provided on one or both surfaces of the negative electrode current collector 1321. That is, a film-like carbon-based material may be formed on one surface of the negative electrode current collector 1321, or a film-like carbon-based material may be formed on both surfaces. The positive electrode active material layer 1327 is provided on one or both surfaces of the positive electrode current collector 1325. The negative electrode 1313 is configured with reference to the above embodiment and has at least a negative electrode current collector 1321 and a negative electrode active material layer 1323. The positive electrode 1315 has at least a positive electrode current collector 1325 and a positive electrode active material 1327. The negative electrode active material layer 1323 can be provided on one or both surfaces of the negative electrode current collector 1321. That is, a film-like carbon-based material may be formed on one surface of the negative electrode current collector 1321, or a film-like carbon-based material may be formed on both surfaces. The positive electrode active material layer 1327 is provided on one or both surfaces of the positive electrode current collector 1325. The negative electrode 1313 is configured with reference to the above embodiment and has at least a negative electrode current collector 1321 and a negative electrode active material layer 1323. The positive electrode 1315 has at least a positive electrode current collector 1325 and a positive electrode active material 1327. The negative electrode active material layer 1323 can be provided on one or both surfaces of the negative electrode current collector 1321. That is, a film-like carbon-based material may be formed on one surface of the negative electrode current collector 1321, or a film-like carbon-based material may be formed on both surfaces. The positive electrode active material layer 1327 is provided on one or both surfaces of the positive electrode current collector 1325. The negative electrode 1313 is configured with reference to the above embodiment and has at least a negative electrode current collector 1321 and a negative electrode active material layer 1323. The positive electrode 1315 has at least a positive electrode current collector 1325 and a positive electrode active material 1327. The negative electrode active material layer 1323 can be provided on one or both surfaces of the negative electrode current collector 1321. That is, a film-like carbon-based material may be formed on one surface of the negative electrode current collector 1321, or a film-like carbon-based material may be formed on both surfaces. The positive electrode active material layer 1327 is provided on one or both surfaces of the positive electrode current collector 1325. The negative electrode 1313 is configured with reference to the above embodiment and has at least a negative electrode current collector 1321 and a negative electrode active material layer 1323. The positive electrode 1315 has at least a positive electrode current collector 1325 and a positive electrode active material 1327. The negative electrode active material layer 1323 can be provided on one or both surfaces of the negative electrode current collector 1321. That is, a film-like carbon-based material may be formed on one surface of the negative electrode current collector 1321, or a film-like carbon-based material may be formed on both surfaces. The positive electrode active material layer 1327 is provided on one or both surfaces of the positive electrode current collector 1325. The negative electrode 1313 is configured with reference to the above embodiment and has at least a negative electrode current collector 1321 and a negative electrode active material layer 1323. The positive electrode 1315 has at least a positive electrode current collector 1325 and a positive electrode active material 1327. The negative electrode active material layer 1323 can be provided on one or both surfaces of the negative electrode current collector 1321. That is, a film-like carbon-based material may be formed on one surface of the negative electrode current collector 1321, or a film-like carbon-based material may be formed on both surfaces. The positive electrode active material layer 1327 is provided on one or both surfaces of the positive electrode current collector 1325.

[0064] Further, the negative electrode current collector 1321 is connected to the terminal portion 1309. Also, the positive electrode current collector 132 5 is connected to the terminal portion 1307. Further, a part of each of the terminal portion 1307 and the terminal portion 1309 is led out to the outside of the exterior member 1303.

[0065] In this embodiment, a thin secondary battery sealed as an external form of the laminate type secondary battery 1301 is shown, but the present invention is not limited to this, and as the external form of the secondary battery, various shapes such as a button type, a cylindrical type, or a rectangular type can be used. Further, in this embodiment, although a structure in which a positive electrode, a negative electrode, and a separator are laminated is shown, a structure in which the positive electrode, the negative electrode, and the separator are wound may also be used.

[0066] As the material of the positive electrode current collector 1325, aluminum, stainless steel, or the like is used. The shape of the positive electrode current collector 1325 can be made into a foil shape, a plate shape, a net shape, or the like.

[0067] The positive electrode active material layer 1327 can use LiFeO2, LiCoO2, LiNiO2, LiMn2O 4, LiFePO4, LiCoPO4, LiNiPO4, LiMn2PO4, V2O5, Cr2O5, MnO2, and other lithium compounds as materials. Note that when the carrier ion is an alkali metal ion, an alkaline earth metal ion, a beryllium ion, or a magnesium ion other than a lithium ion, as the positive electrode active material layer 1327, instead of lithium in the lithium compound, an alkali metal (for example, sodium or potassium, etc.), an alkaline earth metal (for example, calcium, strontium, or barium, etc.), beryllium, or magnesium may be used.

[0068] ​​​​​​As the solute of the electrolytic solution 1319, a material having lithium ions which are carrier ions is used. Examples of the solute of the electrolytic solution 1319 include lithium salts such as LiClO4, LiAsF6, LiBF4 , LiPF6, Li(C2F5SO2)2N, etc. In addition, when the carrier ions are alkali metal ions or alkaline earth metal ions other than lithium, as the solute of the electrolytic solution 1319, alkali metal salts (for example, sodium salts or potassium salts etc.), alkaline earth metal salts (for example, calcium salts, strontium salts or barium salts etc.), beryllium salts or magnesium salts, etc. can be used.

[0069] Also, as the solvent of the electrolytic solution 1319, a material capable of transferring lithium ions is used. As the solvent of the electrolytic solution 1319, an aprotic organic solvent is preferable. Examples of the aprotic organic solvent include, for example, ethylene carbonate, propylene carbonate, dimethyl carbonate , diethyl carbonate, γ-butyrolactone, acetonitrile, dimethoxyethane and tetrahydrofuran, etc., and one or more of these can be used. Also, by using a gellable polymer material as the solvent of the electrolytic solution 1319, the safety including the leakage property is enhanced, and the thinning and weight reduction of the secondary battery 1301 become possible. Representative examples of the gellable polymer material include silicone gel, acrylic gel, acrylonitrile gel , polyethylene oxide, polypropylene oxide or fluorine-based polymer, etc.

[0070] As the electrolytic solution 1319, a solid electrolytic solution such as Li3PO4 can be used.

[0071] Separator 1317 uses an insulating porous body. Examples of the material of separator 1317 include cellulose (paper), polyethylene, polypropylene, and the like.

[0072] When the film-like carbon-based material of the present invention is used as the negative electrode material of a secondary battery, the lithium storage efficiency of the secondary battery can be improved.

[0073] (Embodiment 5) As an example of a secondary battery according to an aspect of the present invention, the structure of a coin-type secondary battery will be described with reference to FIG. 8.

[0074] As shown in FIG. 8, the coin-type secondary battery includes a negative electrode 804, a positive electrode 832, a separator 81 0, an electrolytic solution (not shown), a housing 806, and a housing 844. In addition, it has a ring-shaped insulator 820, a spacer 840, and a washer 842.

[0075] The negative electrode 804 has a negative electrode active material layer 802 on a negative electrode current collector 800. As the negative electrode active material layer 80 2, silicon having a whisker-like structure with its surface sufficiently and uniformly coated with graphene is used. That is, when the film-like carbon-based material of the present invention is used as the negative electrode material of a secondary battery, the lithium storage efficiency of the secondary battery can be improved. Further, as the negative electrode current collector 800, for example copper may be used.

[0076] As the material of the positive electrode current collector 828, aluminum may be used. The positive electrode active material layer 830 may be obtained by applying a slurry in which particles of a positive electrode active material are mixed with a binder and a conductive assistant onto the positive electrode current collector 82 8 and drying it.

[0077] Examples of the material of the positive electrode active material include lithium cobaltate, lithium iron phosphate, and manganese phosphate​​ Lithium, lithium manganese silicate, lithium iron silicate, etc. can be used, but not limited to these. The particle size of the active material particles is preferably 20 nm to 100 nm. Also, carbohydrates such as glucose are mixed during firing so that the positive electrode active material particles are coated with carbon. This treatment increases the conductivity.

[0078] As the electrolyte, a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) dissolved with LiPF6 may be used, but not limited to this.

[0079] For the separator 810, an insulator with pores (for example, polypropylene) may be used, or a solid electrolyte that allows lithium ions to permeate may be used.

[0080] The housing 806, housing 844, spacer 840, and washer 842 are preferably made of metal (for example, stainless steel). The housing 806 and housing 844 have the function of electrically connecting the negative electrode 804 and the positive electrode 832 to the outside.

[0081] These negative electrode 804, positive electrode 832, and separator 810 are impregnated with the electrolyte, and as shown in FIG. 8, with the housing 806 facing down, the negative electrode 804, separator 810, ring-shaped insulator 820 , positive electrode 832, spacer 840, washer 842, and housing 844 are laminated in this order, and the housing 806 and housing 844 are crimped to fabricate a coin-type secondary battery.

[0082] This embodiment can be implemented in appropriate combination with other embodiments.

[0083] (Embodiment 6) The secondary battery according to one aspect of the present invention can be used as a power source for various electric devices driven by electric power. It can be used.

[0084] Specific examples of electric devices using the secondary battery according to one aspect of the present invention include display devices, lighting devices, desktop or notebook personal computers, image playback devices that play still images or moving images stored on recording media such as DVDs (Digital Versatile Discs), mobile phones, portable game machines, portable information terminals, e-books, video cameras, digital still cameras, high-frequency heating devices such as microwave ovens, electric rice cookers, washing machines, air conditioning equipment such as air conditioners, refrigerators, freezers, refrigerator-freezers, DNA preservation freezers, dialysis devices, etc. In addition, mobile bodies propelled by electric motors using the power from the secondary battery are also included in the category of electric devices. Examples of the above mobile bodies include, for example, electric vehicles, hybrid vehicles (hybrid cars) having both an internal combustion engine and an electric motor, and motorized bicycles including electric assist bicycles. For example, electric vehicles, hybrid vehicles (hybrid cars) having both an internal combustion engine and an electric motor, and motorized bicycles including electric assist bicycles.

[0085] Note that the above electric devices can use the secondary battery according to one aspect of the present invention as a secondary battery (referred to as the main power source) that supplies almost all of the power consumption. Alternatively, the above electric devices can use the secondary battery according to one aspect of the present invention as a secondary battery (referred to as an uninterruptible power supply) that can supply power to the electric device when the power supply from the above main power source or commercial power source stops. Alternatively, the above electric devices can use the secondary battery according to one aspect of the present invention as a secondary battery (referred to as an auxiliary power source) that supplies power to the electric device in parallel with the power supply from the above main power source or commercial power source to the electric device. It can be used. When the power supply from the above main power source or commercial power source stops, it can supply power to the electric device. The secondary battery according to one aspect of the present invention can be used as a secondary battery (referred to as an uninterruptible power supply) that can supply power to the electric device. It can be used. Alternatively, the above electric devices can use the secondary battery according to one aspect of the present invention as a secondary battery (referred to as an auxiliary power source) that supplies power to the electric device in parallel with the power supply from the above main power source or commercial power source to the electric device. It can be used.

[0086] Figure 9 shows the specific configuration of the above electrical device. In Figure 9, the display device 5000 is an example of an electrical device using the secondary battery 5004 according to one aspect of the present invention. Specifically, the display device 5000 corresponds to a display device for receiving TV broadcasts, and includes a housing 5001, a display unit 5002, a speaker unit 5003, a secondary battery 5004, and the like. The secondary battery 5004 according to one aspect of the present invention is provided inside the housing 5001. The display device 5000 can receive power supply from a commercial power source, or can also use the power stored in the secondary battery 5004. Therefore, even when power supply from the commercial power source cannot be received due to a power outage or the like, by using the secondary battery 5004 according to one aspect of the present invention as an uninterruptible power supply, the display device 5000 can be used. The display unit 5002 can be provided with a light-emitting device having a light-emitting element such as a liquid crystal display device or an organic EL element in each pixel, an electrophoretic display device, a DMD (Digital Micromirror Device), a PDP (Plasma Display Panel), a FED (Field Emission Display), or the like, and a semiconductor display device can be used. In addition, the display device includes not only a display device for receiving TV broadcasts but also all display devices for personal computers, advertising displays, and the like for all information displays. In Figure 9, the stationary lighting device 5100 is an example of an electrical device using the secondary battery 5103 according to one aspect of the present invention. Specifically, the lighting device 5100 includes a housing 5101, a light source 5102, a secondary battery 5103, and the like. In Figure 9, the secondary battery 5103 is located inside the housing 510

[0087] source 5102, a secondary battery 5103, and the like. In Figure 9, the secondary battery 5103 is located inside the housing 510 source 5102, a secondary battery 5103, and the like. In Figure 9, the secondary battery 5103 is located inside the housing 510 source 5102, a secondary battery 5103, and the like. In Figure 9, the secondary battery 5103 is located inside the housing 510 source 5102, a secondary battery 5103, and the like. In Figure 9, the secondary battery 5103 is located inside the housing 510

[0088] source 5102, a secondary battery 5103, and the like. In Figure 9, the secondary battery 5103 is located inside the housing 510 source 5102, a secondary battery 5103, and the like. In Figure 9, the secondary battery 5103 is located inside the housing 510

[0089] In Figure 9, the stationary lighting device 5100 is an example of an electrical device using the secondary battery 51 03 according to one aspect of the present invention. Specifically, the lighting device 5100 includes a housing 5101, a light source 5102, a secondary battery 5103, and the like. In Figure 9, the secondary battery 5103 is located inside the housing 510 ​Illustrated is a case where it is installed inside the ceiling 5104 where the light source 5102 is installed However, the secondary battery 5103 may be provided inside the housing 5101. The lighting device 5100 can receive power supply from a commercial power source, or can use the power stored in the secondary battery 5103 Therefore, even when the power supply from the commercial power source cannot be received due to a power outage or the like, the secondary battery 5103 according to one aspect of the present invention is used as an uninterruptible power supply so that the lighting device 5100 can be used

[0090] In addition, in FIG. 9, an example of a fixed-type lighting device 5100 provided on the ceiling 5104 is illustrated However, the secondary battery according to one aspect of the present invention can be used not only for the ceiling 5104 but also for, for example, a fixed-type lighting device provided on a side wall 5105, a floor 5 106, a window 5107, etc., or can be used for a tabletop type lighting device or the like

[0091] In addition, as the light source 5102, an artificial light source that artificially obtains light using power can be used Specifically, an incandescent bulb, a discharge lamp such as a fluorescent lamp, and a light emitting element such as an LED or an organic EL element are examples of the above artificial light source

[0092] In FIG. 9, an air conditioner having an indoor unit 5200 and an outdoor unit 5204 is an example of an electric device using the secondary battery 5203 according to one aspect of the present invention. Specifically, the indoor unit 5200 has a housing 5201, an air outlet 5202, a secondary battery 5203, etc. In FIG. 9 an example of the case where the secondary battery 5203 is provided in the indoor unit 5200 is illustrated, but the secondary battery 5203 may be provided in the outdoor unit 5204. Alternatively, the indoor unit 5200 and the outdoor unit 5204 ​​A secondary battery 5203 may be provided in both the indoor unit 5200 and the outdoor unit 5204. The air conditioner can receive power supply from a commercial power source or use the power stored in the secondary battery 5203. In particular, when the secondary battery 520 3 is provided in both the indoor unit 5200 and the outdoor unit 5204, even when power supply from the commercial power source cannot be received due to a power outage or the like, by using the secondary battery 5203 according to an aspect of the present invention as an uninterruptible power supply, the air conditioner can be used.

[0093] Note that in FIG. 9, a separate type air conditioner composed of an indoor unit and an outdoor unit is illustrated, but the secondary battery according to an aspect of the present invention can also be used in an integrated type air conditioner having the functions of the indoor unit and the outdoor unit in one housing.

[0094] In FIG. 9, the electric refrigerator 5300 is an example of an electric device using the secondary battery 5304 according to an aspect of the present invention. Specifically, the electric refrigerator 5300 includes a housing 5301, a door 5302 for the storage compartment, a door 5303 for the freezer compartment, a secondary battery 5304, etc. In FIG. 9, the secondary battery 5304 is provided inside the housing 5301. The electric refrigerator 5300 can receive power supply from a commercial power source or use the power stored in the secondary battery 5304. Therefore, even when power supply from the commercial power source cannot be received due to a power outage or the like, by using the secondary battery 5304 according to an aspect of the present invention as an uninterruptible power supply, the electric refrigerator 5300 can be used.

[0095] Among the above-described electric devices, high-frequency heating devices such as microwave ovens, electric Electrical appliances require high power for a short period of time. Therefore, they need to supplement the power that cannot be supplied by commercial power sources. By using a secondary battery according to one embodiment of the present invention as an auxiliary power source for supporting This can prevent the commercial power breaker from tripping when using the device.

[0096] In addition, during periods when electrical equipment is not being used, the total amount of power that can be supplied by commercial power suppliers is also a concern. During the time period when the ratio of the amount of electricity actually used (called the electricity usage rate) is low, By storing power in the secondary battery, it is possible to prevent the power usage rate from increasing outside the above time periods. For example, in the case of the electric refrigerator-freezer 5300, when the temperature is low, the refrigerator compartment door 53 02, during the night when the freezer door 5303 is not opened or closed, power is supplied to the secondary battery 5304. Then, as the temperature rises, the refrigerator door 5302 and the freezer door 5303 are opened and closed. During the daytime, when the vehicle is turned on, the secondary battery 5304 is used as an auxiliary power source, thereby reducing the power consumption during the daytime. The rate can be kept low.

[0097] This embodiment mode can be implemented in appropriate combination with any of the above embodiment modes. EXAMPLES

[0098] In this embodiment, a graph was applied to the whisker-shaped silicon surface by the electrophoresis method shown in the first embodiment. The sample in which laphene was formed (hereinafter referred to as sample A) will be described. A number of silicon spurs 300 are formed on the titanium sheet, and various types of silicon spurs are formed on the titanium sheet as shown in FIG. Therefore, the sample surface on which graphene is formed has a cylindrical shape extending in a single direction. The presence of the whisker-like silicon 300 gives rise to a complex three-dimensional structure.

[0099] An aqueous solution in which graphene oxide was dispersed was prepared as follows. Graphite (flake carbon) and concentrated sulfuric acid were mixed, potassium permanganate was added, and the mixture was stirred for 2 hours. Then, pure water was added, the mixture was heated and stirred for 15 minutes, and hydrogen peroxide solution was further added to obtain a yellowish-brown solution containing graphite oxide. Further, this was filtered, hydrochloric acid was added to the precipitate for washing, and after washing, it was washed with pure water. Then, ultrasonic treatment was performed for 2 hours to convert graphite oxide into graphene oxide, and an aqueous solution in which graphene oxide was dispersed was obtained.

[0100] This aqueous solution was immersed with the above whisker-shaped silicon together with the titanium sheet, and on the other hand, a stainless steel plate was immersed as the other electrode. Here, the distance between the titanium sheet and the stainless steel plate was set to 1 cm. Then, with the titanium sheet as the anode and the stainless steel plate as the cathode, a voltage of 10 V was applied for 30 seconds. The amount of charge that flowed during this time was 0.089 C. A schematic diagram of the device is shown in Figure 2. shown.

[0101] Thereafter, the titanium sheet was taken out, dried, and further heated in a vacuum (0.1 Pa or less) at 3 00 °C for 10 hours. Sample A was prepared in this way. An observation of the surface of the obtained whisker-shaped silicon is shown in Figure 3(B). At first glance, no obvious difference is observed from Figure 3(A) before the formation of graphene, but black portions are confirmed in patches on the surface of the whiskers in a mottled pattern. This is considered to be a portion where the number of stacked graphene sheets constituting the multilayer graphene is large and thus the thickness is increased. On the other hand, this difference in the number of stacked graphene sheets does not affect the practical uniformity to such an extent. Also, a filamentous or film-like object is observed spanning between the whiskers in the center of the photograph. like state.

[0102] From Raman spectroscopy, since the peaks of the D band and G band, which are characteristics of graphene, were observed at any position on the whiskers, it is considered that almost the entire surface of the whiskers is covered with graphene. Fig. 10(A) shows the result of Raman spectroscopic measurement of whisker-shaped silicon without graphene coating. In contrast, Fig. 10(B) shows the result of Raman spectroscopic measurement of whisker-shaped silicon coated with graphene. In Fig. 10(B), peaks that are not seen in Fig. 10(A) are confirmed at around 1340 cm and around 1580 cm. The peak observed at around 1340 cm is a peak derived from the D band, and is observed when there are defects or impurities in graphene. Also, the peak observed at around 1580 cm is derived from the G band. Fig. 7 shows a cross-sectional observation photograph of a whisker coated with graphene. Fig. 7(A) shows a cross-section of a cylindrical whisker observed by a transmission electron microscope. The circular part is the silicon whisker 700, and extremely thin graphene is formed around it. Also, for observation, a thick carbon deposition film 701 is provided on the outermost surface. An enlarged view of a part of Fig. 7(A) is shown in Fig. 7(B). The left side is a part of the whisker 700, and extremely thin graphene 702 is formed at the end thereof. Its thickness is about 1 to 2 nm, which is equivalent to 2 to 3 layers of single-layer graphene. In the observed sample, a natural oxide film 703 is formed between the whisker-shaped silicon and graphene. A non-conductive natural oxide film 703 is formed on the silicon -3 -3

[0103] -3 -3

[0103] Even if there is, it can be seen that graphene can be sufficiently formed in the electrophoresis method. be seen.

[0104] The whiskers shown in Fig. 7(A) have a crystalline center part 704 as the core in a circular cross-section, which is composed of silicon (crystalline silicon). On the other hand, the outer shell part 705 that thickly covers the periphery of the center part 704 is composed of amorphous silicon (amorphous silicon). Crystalline silicon and amorphous silicon can be discriminated as differences in contrast in a transmission electron micrograph as shown in Fig. 7(A). When the configuration of this embodiment is applied to the electrode of a secondary battery, it is more resistant to the volume change of the electrode accompanying the occlusion and release of ions such as lithium that become carriers than when using whiskers composed only of crystalline silicon as the active material, and the electrode is less likely to be damaged. In particular, since carriers are more easily occluded in amorphous than in crystalline, the capacity of the secondary battery can be improved by forming the outer shell part 705 thickly. than when using whiskers composed only of crystalline silicon as the active material, it is more resistant to the volume change of the electrode accompanying the occlusion and release of ions such as lithium that become carriers, and the electrode is less likely to be damaged. In particular, since carriers are more easily occluded in amorphous than in crystalline, the capacity of the secondary battery can be improved by forming the outer shell part 705 thickly. 5 is composed of amorphous silicon (amorphous silicon). Crystalline silicon and amorphous silicon can be discriminated as differences in contrast in a transmission electron micrograph as shown in Fig. 7(A). When the configuration of this embodiment is applied to the electrode of a secondary battery, it is more resistant to the volume change of the electrode accompanying the occlusion and release of ions such as lithium that become carriers than when using whiskers composed only of crystalline silicon as the active material, and the electrode is less likely to be damaged. In particular, since carriers are more easily occluded in amorphous than in crystalline, the capacity of the secondary battery can be improved by forming the outer shell part 70 5 thickly. and release, and the electrode is less likely to be damaged. In particular, since carriers are more easily occluded in amorphous than in crystalline, the capacity of the secondary battery can be improved by forming the outer shell part 70 5 thickly. 5 thickly, the capacity of the secondary battery can be improved.

[0105] As a comparative example, graphene was produced by a coating method on the surface of whisker-shaped silicon (sample B). In sample B, after immersing the titanium sheet together in the same solution in which graphene oxide was dispersed as in sample A, it was pulled up. Then, sample B was dried and heated under the same conditions as sample A. In this heating process, graphene oxide is reduced to graphene. In this heating process, graphene oxide is reduced to graphene.

[0106] Fig. 4(A) shows the state of the surface of sample B. As shown in Fig. 4(A), it can be confirmed that graphene is formed in a film-like manner so as to connect between the convex portions of the whisker-shaped silicon. However, due to the presence of this film-like graphene, it is not clear which silicon under the film is. It is not clear whether such a state has been achieved. Also, the film-like graphene has been partially formed. There are also some areas where the graphene thickness is not uniform, and it is clear that the thickness of the graphene varies greatly even within the same sample. It is possible that...

[0107] When the cross section of the recess in FIG. 4(A) is observed to confirm the state of the recess, it is found as shown in FIG. 4(B). As shown in FIG. 1, there is a gap between the graphene-containing film-like layer 400 and the recess of the whisker-like silicon 401. It was found that a gap 402 was formed. The whisker-like silicon 40 It was found that no graphene was formed on the surface of 1. A carbon deposition film was formed on this graphene, so in Figure 4(B) It should be noted that there is a vapor-deposited carbon film on the surface.

[0108] In this way, the coating method is not able to produce graphene that sufficiently covers the surface of objects with complex shapes and structures. In addition, the thickness of the graphene varies between samples and the thickness of the sample is very thin. There was a large variability, making it difficult to control the thickness of the graphene.

[0109] In contrast, in the electrophoretic method, once graphene oxide is attached to the area, other graphene oxides are not attached. This makes it difficult for bacteria to adhere to the surface, making it possible to form a uniform coating with excellent reproducibility. As described above, the formation of graphene by the electrophoretic method shown in the first embodiment is more advantageous than the coating method. The results showed that the results were highly uniform and reliable. EXAMPLES

[0110] In this example, graphene was formed on the surface of a whisker-like silicon, and this was then ionized with lithium ions. The results are compared between the negative electrode of a lithium secondary battery and the negative electrode without any surface treatment. The electrolytic solution used in a lithium-ion secondary battery reacts with an electrode (especially the negative electrode), and it is known that a compound film formed by decomposing the electrolytic solution is formed on the electrode surface. It is known that a compound film is formed on the surface of the electrode by decomposing the electrolytic solution.

[0111] Such a compound film is called SEI (Solid Electrolyte Interface), and it is considered necessary to mitigate and stabilize the reaction between the electrode and the electrolyte. However, since its thickness is determined by the combination of the electrode and the electrolyte, it may become thicker than necessary. However, since its thickness is determined by the combination of the electrode and the electrolyte, it may become thicker than necessary. As adverse effects associated with SEI formation, there are a decrease in Coulomb efficiency, a decrease in lithium ion conductivity between the electrode and the electrolytic solution, and consumption of the electrolytic solution. Conventionally, in order to suppress the generation of such SEI, attempts have been made to coat the electrode surface by vapor deposition or CVD method.

[0112] As adverse effects associated with SEI formation, there are a decrease in Coulomb efficiency, a decrease in lithium ion conductivity between the electrode and the electrolytic solution, and consumption of the electrolytic solution. Conventionally, in order to suppress the generation of such SEI, attempts have been made to coat the electrode surface by vapor deposition or CVD method. However, since it is preferable that the electrode of the lithium-ion secondary battery has a larger surface area, for example, it is preferable to use a complex shape such as whisker-shaped silicon. However, conventional vapor deposition methods and CVD methods cannot sufficiently coat the surface of an object with a complex shape. On the other hand, with the method shown in Embodiment 1 or Example 1, even the surface of an object having a plurality of whisker-shaped silicon with a complex shape can be appropriately coated. Thereby, it becomes possible to increase the surface area of the electrode while suppressing excessive generation of SEI. However, since it is preferable that the electrode of the lithium-ion secondary battery has a larger surface area, for example, it is preferable to use a complex shape such as whisker-shaped silicon. However, conventional vapor deposition methods and CVD methods cannot sufficiently coat the surface of an object with a complex shape. On the other hand, with the method shown in Embodiment 1 or Example 1, even the surface of an object having a plurality of whisker-shaped silicon with a complex shape can be appropriately coated. Thereby, it becomes possible to increase the surface area of the electrode while suppressing excessive generation of SEI.

[0113] However, since it is preferable that the electrode of the lithium-ion secondary battery has a larger surface area, for example, it is preferable to use a complex shape such as whisker-shaped silicon. However, conventional vapor deposition methods and CVD methods cannot sufficiently coat the surface of an object with a complex shape. On the other hand, with the method shown in Embodiment 1 or Example 1, even the surface of an object having a plurality of whisker-shaped silicon with a complex shape can be appropriately coated. Thereby, it becomes possible to increase the surface area of the electrode while suppressing excessive generation of SEI. However, since it is preferable that the electrode of the lithium-ion secondary battery has a larger surface area, for example, it is preferable to use a complex shape such as whisker-shaped silicon. However, conventional vapor deposition methods and CVD methods cannot sufficiently coat the surface of an object with a complex shape. On the other hand, with the method shown in Embodiment 1 or Example 1, even the surface of an object having a plurality of whisker-shaped silicon with a complex shape can be appropriately coated. Thereby, it becomes possible to increase the surface area of the electrode while suppressing excessive generation of SEI. However, since it is preferable that the electrode of the lithium-ion secondary battery has a larger surface area, for example, it is preferable to use a complex shape such as whisker-shaped silicon. However, conventional vapor deposition methods and CVD methods cannot sufficiently coat the surface of an object with a complex shape. On the other hand, with the method shown in Embodiment 1 or Example 1, even the surface of an object having a plurality of whisker-shaped silicon with a complex shape can be appropriately coated. Thereby, it becomes possible to increase the surface area of the electrode while suppressing excessive generation of SEI. However, since it is preferable that the electrode of the lithium-ion secondary battery has a larger surface area, for example, it is preferable to use a complex shape such as whisker-shaped silicon. However, conventional vapor deposition methods and CVD methods cannot sufficiently coat the surface of an object with a complex shape. On the other hand, with the method shown in Embodiment 1 or Example 1, even the surface of an object having a plurality of whisker-shaped silicon with a complex shape can be appropriately coated. Thereby, it becomes possible to increase the surface area of the electrode while suppressing excessive generation of SEI. However, since it is preferable that the electrode of the lithium-ion secondary battery has a larger surface area, for example, it is preferable to use a complex shape such as whisker-shaped silicon. However, conventional vapor deposition methods and CVD methods cannot sufficiently coat the surface of an object with a complex shape. On the other hand, with the method shown in Embodiment 1 or Example 1, even the surface of an object having a plurality of whisker-shaped silicon with a complex shape can be appropriately coated. Thereby, it becomes possible to increase the surface area of the electrode while suppressing excessive generation of SEI. However, since it is preferable that the electrode of the lithium-ion secondary battery has a larger surface area, for example, it is preferable to use a complex shape such as whisker-shaped silicon. However, conventional vapor deposition methods and CVD methods cannot sufficiently coat the surface of an object with a complex shape. On the other hand, with the method shown in Embodiment 1 or Example 1, even the surface of an object having a plurality of whisker-shaped silicon with a complex shape can be appropriately coated. Thereby, it becomes possible to increase the surface area of the electrode while suppressing excessive generation of SEI.

[0114] In this example, two types of samples, Sample C and Sample D, were prepared. Sample C has a plurality of whisker-shaped silicon on which no treatment was performed on the surface, and the initial surface state is shown in FIG. 3 ( Sample C has a plurality of whisker-shaped silicon on which no treatment was performed on the surface, and the initial surface state is shown in FIG. 3 ( It is equivalent to that shown in (A). Sample D has a plurality of whisker-shaped silicon with graphene formed on the surface by the method shown in Example 1, and the initial surface state is equivalent to that shown in Fig. 3(B). Next, cyclic voltammetry (CV) measurements were performed on the sample coated with graphene and the sample without any treatment, respectively. For the measurement, a three-electrode cell was used, with whisker-shaped silicon as the working electrode, metallic lithium as the reference electrode and the counter electrode, and a mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) (volume ratio 1:1) with lithium hexafluorophosphate (LiPF6) dissolved at a concentration of 1 mol / L as the electrolyte. The measurement was carried out at a scanning rate of 0.1 mV / second and a scanning range of 0 V to 1 V (vs. Li / Li ) for 10 cycles. However, the first cycle starts the scan from the open circuit potential.

[0115] Next, for the sample treated with graphene coating and the sample without any treatment, cyclic voltammetry (CV) measurements were carried out. For the measurement, a three-electrode cell was used, with whisker-shaped silicon as the working electrode, metallic lithium as the reference electrode and the counter electrode, and a mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) (volume ratio 1:1) with lithium hexafluorophosphate (LiPF6) dissolved at a concentration of 1 mol / L as the electrolyte. For the measurement, a three-electrode cell was used, with whisker-shaped silicon as the working electrode, metallic lithium as the reference electrode and the counter electrode, and a mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) (volume ratio 1:1) with lithium hexafluorophosphate (LiPF6) dissolved at a concentration of 1 mol / L as the electrolyte. The measurement was carried out at a scanning rate of 0.1 mV / second and a scanning range of 0 V to 1 V (vs. Li / Li For the measurement, a three-electrode cell was used, with whisker-shaped silicon as the working electrode, metallic lithium as the reference electrode and the counter electrode, and a mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) (volume ratio 1:1) with lithium hexafluorophosphate (LiPF6) dissolved at a concentration of 1 mol / L as the electrolyte. The measurement was carried out at a scanning rate of 0.1 mV / second and a scanning range of 0 V to 1 V (vs. Li / Li (volume ratio 1:1) with lithium hexafluorophosphate (LiPF6) dissolved at a concentration of 1 mol / L was used, and the measurement was carried out at a scanning rate of 0.1 mV / second and a scanning range of 0 V to 1 V (vs. Li / Li (volume ratio 1:1) with lithium hexafluorophosphate (LiPF6) dissolved at a concentration of 1 mol / L was used, and the measurement was carried out at a scanning rate of 0.1 mV / second and a scanning range of 0 V to 1 V (vs. Li / Li + ) for 10 cycles. However, the first cycle starts the scan from the open circuit potential.

[0116] From the CV measurement results, Fig. 5 shows a graph focusing on the reduction current at the high potential in the first cycle. The reduction current increases rapidly from around 0.20 V (vs. Li / Li + ), indicating that the alloying reaction between silicon and lithium is occurring. The reduction current at a potential higher than 0.20 V (vs. Li / Li Li / Li + ) is due to the decomposition reaction that is unnecessary for the battery, and it is known that a surface film is formed on the electrode surface by this decomposition reaction. It is desirable that this surface film is thinner. As shown in Fig. 5, the reduction current of the sample treated with graphene coating was smaller at higher potentials. This indicates that the formation of a film on the surface of the electrode (here, whisker-shaped silicon) is suppressed due to the presence of graphene. As shown in Fig. 5, the reduction current of the sample treated with graphene coating was smaller at higher potentials. This indicates that the formation of a film on the surface of the electrode (here, whisker-shaped silicon) is suppressed due to the presence of graphene. As shown in Fig. 5, the reduction current of the sample treated with graphene coating was smaller at higher potentials. This indicates that the formation of a film on the surface of the electrode (here, whisker-shaped silicon) is suppressed due to the presence of graphene. As shown in Fig. 5, the reduction current of the sample treated with graphene coating was smaller at higher potentials. This indicates that the formation of a film on the surface of the electrode (here, whisker-shaped silicon) is suppressed due to the presence of graphene.

[0117] The above sample C or sample D was used as the positive electrode, metallic lithium as the negative electrode, and ethylene carbon as the electrolyte. A mixture of 1:1 volumetric ratio of 6-fluoro-2,4-diethyl carbonate (EC) and diethyl carbonate (DEC) was added to the Lithium fluoride phosphate (LiPF6) was dissolved at a concentration of 1 mol / L, and the separator was A coin cell was fabricated using polypropylene with fine holes as the data collector. The in-cell was charged and discharged, and the change in capacity due to the release and absorption of lithium was measured. The current value for the first cycle was 50 μA, and for the second and subsequent cycles it was 4 mA. The range is 0.03 to 1.0 V (vs. Li / Li + ) was used.

[0118] As shown in FIG. 6(A), when lithium was repeatedly released and absorbed, both specimens C and D were easily The capacity of sample D decreases after 10 cycles, but the capacity increases after 10 cycles, and is larger than that of sample C. FIG. 6(B) shows the potential change due to the release (or absorption) of lithium in the 30th cycle. The relationship between the change in capacitance and the capacitance is shown in Fig. 1. Since the capacitance of sample D is larger than that of sample C, It has been found that the ion exchange membrane can release more lithium and absorb more lithium. This is believed to be because the SEI was not formed thicker in sample D. . EXAMPLES

[0119] In this example, silicon whiskers are used as the protrusions, and a film of carbonaceous material is deposited by electrophoresis. The case where the above-mentioned is formed will be described.

[0120] A titanium sheet with a purity of 99.5% and a thickness of 100 μm was prepared as a current collector. Silicon whiskers are formed. The silicon whiskers are formed by the LPCVD (Low Pres sure CVD) method. The flow rates of silane gas and nitrogen gas are used as the material gases and introduced into the reaction chamber as SiH4 / N2 = 300 sccm / 300 sccm. The pressure in the reaction chamber is set to 150 Pa, and the temperature in the reaction chamber is set to 550 °C. When the temperature of the current collector is raised, argon is introduced into the reaction chamber. The diameter of the silicon whiskers becomes 700 nm. As shown in Fig. 20 the central part A of the silicon whiskers has crystallinity, and the outer peripheral part B other than the central part is non- crystalline. The titanium sheet on which the silicon whiskers are formed is washed with 0.5% hydrofluoric acid for 10 minutes .

[0121] As shown in Fig. 14, the titanium sheet 1601 on which silicon whiskers are formed is immersed in an aqueous solution 1602 in which graphene oxide is dispersed. The aqueous solution was prepared as follows. Potassium permanganate was added to a mixture of graphite (scaly carbon) and concentrated sulfuric acid, and then stirred for 2 hours. Then, pure water was added, heated and stirred for 15 minutes, and hydrogen peroxide solution was further added to obtain a yellowish-brown solution containing graphene oxide. Further, this was filtered, hydrochloric acid was added, and then washed with pure water. Then, ultrasonic treatment was performed for 2 hours to convert graphene oxide into graphene, and an aqueous solution in which graphene was dispersed was obtained.

[0122] The whisker-like silicon on the titanium sheet was immersed in this aqueous solution together with the titanium sheet 1601, and a stainless steel plate (stainless steel plate) 1603 was immersed as an electrode. Here, the distance between the titanium sheet and the stainless steel plate was set to 1 cm. Then, with the titanium sheet as the anode and the stainless steel plate as the cathode, a voltage of 10 V was applied for 15 minutes using a power supply 1605. The current flowing during this period​ The charged amount is 0.223 C.

[0123] Thereafter, the titanium sheet was taken out and dried, and further heated in a vacuum (0.1 Pa or less) at 3 00 °C for 10 hours. Sample E was thus prepared. The TEM image of the surface of the obtained sample E is shown in Fig. 15. A film-like carbon-based material is observed to be spanning between the whiskers at the center of Fig. 15(A). Fig. 15(B) is an enlarged view of Fig. 15(A). From these, it can be seen that the film-like carbon-based material is provided from the rounded tip of the silicon whiskers forming the convex portion to the nearby silicon whiskers. When viewed from the tip of the silicon whiskers, the carbon-based material appears to be provided in a tent shape. .

[0124] When using electrophoresis, since the state of the film-like carbon-based material can be controlled by the charged amount, the reproducibility is high. Also, for a large area, a film-like carbon-based material can be formed. Moreover, it is easy to control the thickness of the film-like carbon-based material.

[0125] Fig. 16 shows the TEM image of the cross section along the dotted line in Fig. 15(A). The thickness of the film-like carbon-based material is 4.6 nm or more and 5.6 nm or less. 8 to 10 layers are stacked.

Example

[0126] As the conditions of electrophoresis, the TEM image of sample F when a voltage of 10 V is applied for 5 minutes is shown in Fig. 1 7. A film-like carbon-based material can be confirmed in part. The charged amount flowing during this is 0

[0127] A cycle test was conducted on sample E prepared as in Example 3. The conditions of the cycle test were as follows: sample E was used as the positive electrode, metallic lithium was used as the negative electrode, and a mixture of ethylene carbonate (EC) solution and diethyl carbonate (DEC) (volume ratio 1:1) with 1 mol / L of lithium hexafluorophosphate (LiPF6) dissolved therein was used as the electrolyte. A coin cell using microporous polypropylene as the separator was fabricated. Then, charge and discharge of the coin cell were carried out, and the change in the capacity of lithium insertion and extraction was measured. During charge and discharge, the rate of the first cycle was 0.2C, and the rate from the second cycle onwards was 0.5C. The potential range was 0.03 to 1.0 V (vs. Li / Li ). The cycle characteristics are shown in Fig. 18. In Fig. 18, the X-axis represents the number of cycles, and the Y-axis represents the capacity (mAh / g), indicating the change in capacity during lithium insertion. It can be seen that lithium insertion and extraction are possible . (Reference Example) A cycle test was conducted using the sample prepared by heat-treating and reducing graphene oxide as the positive electrode and metallic lithium as the negative electrode. The graphene oxide aqueous solution was dried, and then the positive electrode was fabricated by heating at 300°C for 10 hours in a vacuum (0.1 Pa or less). During charge and discharge, the current value was 1 μA, and the potential range was 0 to 1 V (vs. Li / Li + ). The other conditions were the same as in Example 4

[0128] . The cycle characteristics are shown in Fig. 19. In Fig. 19, the X-axis represents the number of cycles, and the Y-axis represents the capacity (mAh / g). (mAh / g), indicating the change in capacity during lithium insertion. It can be seen that lithium insertion and extraction are possible

[0129] . A cycle test was conducted using the sample prepared by heat-treating and reducing graphene oxide as the positive electrode and metallic lithium as the negative electrode. The graphene oxide aqueous solution was dried, and then the positive electrode was fabricated by heating at 300°C for 10 hours in a vacuum (0.1 Pa or less). During charge and discharge, the current value was 1 μA, and the potential range was 0 to 1 V (vs. Li / Li ). The other conditions were the same as in Example 4 . The cycle characteristics are shown in Fig. 19. In Fig. 19, the X-axis represents the number of cycles, and the Y-axis represents the capacity + (mAh / g). (mAh / g).

[0130] The cycle characteristics are shown in Fig. 19. In Fig. 19, the X-axis represents the number of cycles, and the Y-axis represents the capacity (mAh / g).

[0131] From the results of FIG. 19, it can be seen that even a film-like carbon-based material made using graphene obtained by heat treatment reduction has a function as an active material.

Explanation of Signs

[0132] 100 Solution 101 Object 102 Graphene oxide 103 Graphene oxide 200 Container 201 Solution 202 Object 203 Conductor 300 Whisker-like silicon 400 Film-like layer containing graphene 401 Whisker-like silicon 402 Space 700 Whisker 701 Carbon deposition film 702 Graphene 703 Natural oxide film 704 Central part 705 Outer shell part 800 Negative electrode current collector 802 Negative electrode active material layer 804 Negative electrode 806 Housing 810 Separator 820 Ring-shaped insulator 828 Positive electrode current collector 830 Positive electrode active material layer 832 Positive electrode 840 Spacer 842 Washer 844 Housing 1100 Current collector 1101 Protrusion 1101a Protrusion 1101b Protrusion 1101c Protrusion 1101d Protrusion 1101e Protrusion 1102 Film-like carbon-based material 1103 Carbon-based material 1104 Graphene 1301 Secondary battery 1303 Exterior member 1305 Storage battery cell 1313 Negative electrode 1315 Positive electrode 1317 Separator 1319 Electrolyte 1321 Negative electrode current collector 1323 Negative electrode active material layer 1325 Positive electrode current collector 1327 Positive electrode active material layer 5000 Display device 5001 Housing 5002 Display unit 5003 Speaker unit 5004 Secondary battery 5100 Lighting device 5101 Housing 5102 Light source 5103 Secondary battery 5104 Ceiling 5105 Side wall 5106 Floor 5107 Window 5200 Indoor unit 5201 Housing 5202 Air outlet 5203 Secondary battery 5300 Electric refrigerator-freezer 5301 Housing 5302 Door for refrigerator compartment 5303 Door for freezer compartment 5304 Secondary battery

Claims

1. A negative electrode having a plurality of silicons, having first graphene around the silicon, having second graphene across the plurality of silicons, wherein the silicon is composed of crystalline silicon in a central portion and amorphous silicon covering the crystalline silicon, A lithium-ion secondary battery in which, in a cross-sectional view, the thickness of the amorphous silicon is greater than the thickness of the crystalline silicon.

2. In claim 1, A lithium-ion secondary battery in which the first graphene can occlude and release lithium ions.

3. In claim 1 or claim 2, A lithium-ion secondary battery in which the second graphene can occlude and release lithium ions.

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