Lithium ion battery

Abstract

To solve the problem of suppressing electrochemical resolution such as a lithium ion battery or an electrolyte in a negative electrode of a lithium ion capacitor, reducing an irreversible capacity, improving a cycle characteristic, or expanding a use temperature range.SOLUTION: A negative electrode for a power storage device, includes: a negative electrode collector; a negative electrode active material layer having a plurality of particle-like negative electrode active materials on the negative electrode collector; and a coated film coating one part of each particle-like negative electrode active material. The coated film is a film having an insulation property and lithium ion conductivity.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a negative electrode for an electricity storage device, a method for producing the same, and an electricity storage device. [Background technology]

[0002] In recent years, non-aqueous secondary batteries such as lithium-ion batteries (LIBs) and lithium-ion capacitors ( The development of various types of energy storage devices, such as LICs and air batteries, is currently underway. Lithium-ion batteries, which have a high energy density, are used in mobile phones, smartphones, and laptops. Electrical equipment such as portable information terminals (e.g., personal computers), portable music players, and digital cameras, Or medical equipment, hybrid vehicles (HEV), electric vehicles (EV), or plug-in hybrid vehicles Development of the semiconductor industry, including next-generation clean energy vehicles such as hybrid vehicles (PHEVs) Demand for it has expanded rapidly, and it has become a key source of rechargeable energy in today's information society. It has become an essential part of the meeting.

[0003] The negative electrode for the storage device of the lithium-ion battery or lithium-ion capacitor is a current collector (hereinafter referred to as a negative electrode current collector) and an active material layer (hereinafter referred to as a negative electrode active material) provided on the surface of the negative electrode current collector. The negative electrode active material layer is a structure having at least the above-mentioned structure. The active material (hereinafter referred to as the negative electrode) is carbon or silicon, which can store and release lithium ions. It contains the active material.

[0004] Currently, negative electrodes using graphite-based carbon materials, which are common as negative electrodes for lithium-ion batteries, are, for example, Graphite is the negative electrode active material, and acetylene black (AB) is the conductive additive. ) and PVDF, a resin used as a binder, to form a slurry. It is produced by applying the above to a current collector and drying it.

[0005] The negative electrodes of such lithium-ion batteries and lithium-ion capacitors have extremely high electrode potentials. Therefore, electrolytes using organic solvents are subject to reduction and decomposition. The range of potential within which a liquid does not undergo electrolysis is called the potential window. Essentially, the negative electrode must have an electrode potential within the potential window of the electrolyte. The negative electrode potential of lithium-ion batteries and lithium-ion capacitors is within the potential window of almost all electrolytes. In fact, the decomposition products form a passive film (solid electrolyte film, SEI) on the surface of the negative electrode. (Solid Electrolyte Interphase) is formed. This coating prevents further reduction and decomposition. By using a low electrode potential, lithium ions can be inserted into the negative electrode (see, for example, See 1).

[0006] However, the surface coating of the negative electrode made of such electrolyte decomposition products is kinetically Since the solution is suppressed, deterioration progresses gradually, and the film is not sufficiently stable. The decomposition reaction is accelerated, which causes serious problems in high temperature environments. This leads to irreversible capacity formation and a loss of part of the discharge capacity. There is a need for a coating on the surface of a negative electrode that can be formed without loss of conductivity. [Prior art documents] [Non-patent literature]

[0007] [Non-Patent Document 1] Zenpachi Ogumi, editor, "Lithium Secondary Batteries", Ohmsha, March 20, 2008, 1st edition, 1st printing, pp.116-118 Summary of the Invention [Problem to be solved by the invention]

[0008] The coating on the surface of the conventional negative electrode is believed to be formed by the battery reaction during charging. The charge used to form the film cannot be discharged. This reduced the initial capacity of the lithium-ion battery.

[0009] Furthermore, even if the coating formed on the surface of the negative electrode during the first charge is sufficiently stable and completely absorbs the electrolyte, It cannot be said that decomposition is suppressed, and it is thought that decomposition of the electrolyte will progress especially at high temperatures. are.

[0010] As the electrochemical decomposition of the electrolyte progresses, the amount of lithium responsible for charging and discharging decreases. Therefore, when charging and discharging are repeated, the lithium Sum-ion batteries eventually lose capacity. Also, the electrochemical reaction is more rapid at higher temperatures. Therefore, the more repeatedly charged and discharged a lithium-ion battery is at high temperatures, the faster the capacity decreases. The small becomes large.

[0011] The above issues are not limited to lithium-ion batteries, but also apply to lithium-ion capacitors. This can be said.

[0012] Therefore, one aspect of the present invention is to provide a method for manufacturing a lithium ion battery or a lithium ion capacitor using an initial capacity This reduces the occurrence of irreversible capacity, which causes a decrease in the amount of electrolyte in the negative electrode. The objective of the present invention is to suppress the decomposition of the cellulose.

[0013] Another aspect of the present invention is a method for charging and discharging a lithium ion battery or a lithium ion capacitor. By suppressing the decomposition reaction of the electrolyte, etc., which occurs as a side reaction during repeated charging and discharging, The objective is to improve the cycle characteristics of lithium-ion batteries or lithium-ion capacitors. The subject is...

[0014] In addition, one aspect of the present invention is to suppress the decomposition reaction of the electrolyte, which is accelerated at high temperatures, and to perform high-temperature charge / discharge By preventing the capacity loss in the lithium-ion battery or lithium-ion capacitor, The objective of this invention is to expand the operating temperature range of the capacitor.

[0015] Another embodiment of the present invention is to provide a negative electrode for a power storage device that solves the above problems.

[0016] Another embodiment of the present invention is to provide a power storage device including the power storage device negative electrode.

[0017] Furthermore, one embodiment of the present invention provides a method for manufacturing the negative electrode for a power storage device. [Means for solving the problem]

[0018] The decomposition of the electrolyte is thought to occur electrochemically. The materials are generally graphite or silicon, which have relatively high electrical conductivity. Even silicon has high electrical conductivity when lithium is inserted. Therefore, the decomposition reaction of the electrolyte proceeds on the surface of the negative electrode active material.

[0019] On the other hand, the negative electrodes of lithium-ion batteries and lithium-ion capacitors are charged and discharged at a constant rate. To maintain this, a granular negative electrode active material with an average particle size of several hundred nanometers to several tens of micrometers is used. Therefore, the negative electrode can be considered as a porous electrode where granular negative electrode active material is aggregated. The surface area is large. Therefore, the area available for the battery reaction is large, and the decomposition reaction of the electrolyte is also increased. do.

[0020] Therefore, by coating the surface of the negative electrode active material with an insulating metal oxide, it is possible to occupy a large area of ​​the electrode. This can prevent decomposition of the electrolyte on the surface of the negative electrode active material.

[0021] Therefore, one embodiment of the present invention is a negative electrode current collector and a plurality of particles of a negative electrode active material on the negative electrode current collector. and a coating that covers a portion of the granular negative electrode active material, wherein the coating The negative electrode for a power storage device is a film having insulating properties and lithium ion conductivity.

[0022] The negative electrode active material is a granular material. For example, the average particle size is 6 μm or more and 30 μm or less. A negative electrode active material having a molecular weight of m or less can be used.

[0023] The negative electrode active material is a material that can dissolve and deposit metals or insert and remove metal ions. There is no particular limitation as long as the material is used. Examples of the negative electrode active material include lithium metal and carbon-based Materials such as silicon, silicon alloys, and tin can be used.

[0024] Lithium metal has a low oxidation-reduction potential (-3.045 V vs. the standard hydrogen electrode) and is lightweight and and high specific capacity per volume (3860mAh / g and 2062mAh / cm, respectively) 3 ) is therefore preferable.

[0025] Carbon materials include graphite, easily graphitizable carbon (soft carbon), and non-graphitizable carbon (hard carbon). Examples of such materials include graphene, carbon black, graphene nanotubes, graphene nanofibers, and graphene nanofibers.

[0026] Graphite includes mesocarbon microbeads (MCMB), coke-based artificial graphite, and pitch. Examples of such graphite include artificial graphite such as spheroidized artificial graphite, and natural graphite such as spheroidized natural graphite.

[0027] When lithium ions are inserted into graphite (when lithium-graphite intercalation compounds are formed), It exhibits a potential as noble as lithium metal (0.1-0.3V vs. Li + / Li). This This allows lithium-ion batteries to exhibit high operating voltages. Relatively high capacity per volume, small volume expansion, and low cost compared to lithium metal This is preferable because it has advantages such as high safety.

[0028] As a negative electrode active material, charge / discharge reactions occur through alloying and dealloying reactions with lithium metal. Alloy materials that can be used are also usable. For example, Al, Si, Ge, Sn, Pb, S Examples of the material include a material containing at least one of b, Bi, Ag, Zn, Cd, In, Ga, etc. These elements have a large capacity compared to carbon, and silicon in particular has a theoretical capacity of 4200 m Ah / g, which is dramatically high. For this reason, it is preferable to use silicon as the negative electrode active material. Examples of alloy materials using such elements include SiO, Mg2Si, Mg2Ge, SnO, SnO2, Mg2Sn, SnS2, V2Sn3, FeSn2, CoSn2, Ni 3Sn2, Cu6Sn5, Ag3Sn, Ag3Sb, Ni2MnSb, CeSb3, La Examples include Sn3, La3Co2Sn7, CoSb3, InSb, and SbSn.

[0029] In addition, titanium dioxide (TiO2) and lithium titanium oxide (Li4T i5O 12 ), lithium-graphite intercalation compound (Li x C6), niobium oxide (Nb2O5), Oxides such as tungsten oxide (WO2) and molybdenum oxide (MoO2) can be used. Cut.

[0030] In addition, the negative electrode active material is a nitride of lithium and transition metals, which has a Li3N structure. i 3-x M x N (M=Co, Ni, Cu) can be used. For example, Li 2.6 C o 0.4 N3 is preferable because it exhibits a large charge / discharge capacity (900 mAh / g).

[0031] When a nitride of lithium and a transition metal is used, the negative electrode active material contains lithium ions, so the positive electrode Combine with materials such as V2O5 and Cr3O8 that do not contain lithium ions as electrode active materials Even when a material containing lithium ions is used as the positive electrode active material, By removing the lithium ions in advance, the negative electrode active material is a mixture of lithium and transition metals. Nitrides can be used.

[0032] In addition, a material that undergoes a conversion reaction can also be used as the negative electrode active material. , cobalt oxide (CoO), nickel oxide (NiO), iron oxide (FeO), etc. A transition metal oxide that does not undergo an alloying reaction with the negative electrode active material may be used. Further materials that undergo a reaction include Fe2O3, CuO, Cu2O, RuO2, and Cr2O Third order oxide, CoS 0.89 , NiS, CuS and other sulfides, Zn3N2, Cu3N, G Nitrides such as e3N4, phosphides such as NiP2, FeP2, CoP3, FeF3, BiF3 This also occurs with fluorides such as those mentioned above. Since the potential of the fluorides is high, they are not suitable for use as positive electrode active materials. That's fine.

[0033] The carrier ions are the lithium ions used in lithium ion batteries or lithium ion capacitors. In addition to lithium ions, alkali metal ions such as sodium and potassium, calcium, strontium, alkaline earth metal ions such as potassium and barium, beryllium ions, or magnesium ions Muion et al.

[0034] The coating that coats such granular negative electrode active material may contain niobium, titanium, vanadium, tantalum, or the like. Zirconium, tungsten, zirconium, molybdenum, hafnium, chromium, aluminum or or silicon oxide film, or an oxide film containing one of these elements and lithium. Such a coating can be used to prevent the negative electrode surface from being coated with decomposition products of conventional electrolytes. This film is sufficiently dense compared to the coating formed on the surface.

[0035] For example, niobium oxide (Nb2O5) has an electronic conductivity of 10 -9 S / cm 2 and low, high absolute Therefore, the niobium oxide film prevents the electrochemical decomposition reaction between the negative electrode active material and the electrolyte. On the other hand, the lithium diffusion coefficient of niobium oxide is 10 -9 cm 2 / sec, and high It has high lithium ion conductivity, which allows lithium ions to pass through. be.

[0036] Therefore, when the coating of the negative electrode active material has carrier ion conductivity, the carrier ions The negative electrode active material can permeate the coating, allowing the battery reaction to occur. By having insulating properties, it is possible to suppress the reaction between the electrolyte solution and the negative electrode active material. The metal oxide film is preferably made of a material with a high diffusion coefficient of carrier ions, and is as thin as possible. The thickness of the coating is preferably 5 nm or more and 50 nm or less. Desirable.

[0037] On the other hand, in the case of a negative electrode active material that is completely insulated from the surroundings, electrons can move freely inside and outside the negative electrode active material. Since the movement of the negative electrode active material is suppressed, the battery reaction cannot occur. However, in order to secure a path for electron conduction with the outside, the negative electrode active material must be completely covered by a coating. The surrounding area is not covered, and at least a part of the negative electrode active material is exposed without being covered by the coating. In this way, it is necessary to form a coating that covers a part of the granular negative electrode active material. By forming it on the surface of the electrode active material, it enables the battery reaction of the negative electrode active material while preventing the decomposition of the electrolyte. The reaction can be suppressed.

[0038] In addition, one aspect of the present invention is a method for preparing a metal alkoxide, a stabilizer, and a solvent, the method comprising: adding a granular black powder to a solution containing the metal alkoxide, a stabilizer, and a solvent; Lead is dispersed to prepare a dispersion solution, and metal alkoxide is subjected to hydrolysis and condensation reactions to form a gel. By solubilizing the graphite particles, a gel containing the metal of the metal alkoxide is attached to the surface of the graphite particles. By baking the gel through heat treatment, a metal oxide film is formed on the surface of the granular graphite, and the metal A slurry containing granular graphite on which an oxide film was formed and a binder was applied onto a negative electrode current collector. This is a method for producing a negative electrode for an electricity storage device, which is then fired.

[0039] The metal oxide film that covers the surface of the negative electrode active material can be formed by a sol-gel method. The sol-gel method is a process in which a solution of metal alkoxides or metal salts is subjected to hydrolysis and polycondensation. This method involves forming a gel that has lost its fluidity through a reaction, and then baking this gel to form a thin film. The lubrication method is a method for forming thin films from a liquid phase, so the raw materials must be mixed homogeneously at the molecular level. For this reason, the negative electrode active material such as graphite is added to the raw material of the metal oxide film at the solvent stage. By adding the active material, it is possible to easily disperse the active material in the gel. A metal oxide film is formed on the surface of the material.

[0040] Here, in order for the negative electrode active material to undergo a battery reaction, the metal oxide film that covers the negative electrode active material must be The film must be permeable to carrier ions such as lithium ions. A material with a high diffusion coefficient of carrier ions is preferred, and the insulating coating is as thin as possible. In terms of thin film formation, the sol-gel method is the optimum method.

[0041] On the other hand, in the case of a negative electrode active material that is completely insulated from the surroundings, electrons can move freely inside and outside the negative electrode active material. Since the movement of the negative electrode active material is suppressed, the battery reaction cannot occur. In order to secure a path for electron conduction with the outside, the negative electrode active material is made of metal oxide. The surrounding area is not completely covered, and at least a part of the negative electrode active material is exposed. For this reason, metal oxides can be formed thinly enough using sol-gel It is best to use the method.

[0042] From the above, it is possible to form a granular negative electrode active material having insulating and lithium ion conductive properties on the surface thereof. By forming a coating, the electric current in a lithium ion battery or a lithium ion capacitor can be reduced. The decomposition reaction of the solution can be suppressed. [Effects of the Invention]

[0043] According to one aspect of the present invention, the initial capacity of a lithium ion battery or a lithium ion capacitor can be This reduces the occurrence of irreversible capacity that causes a decrease in capacity, and prevents electrochemical breakdown of the electrolyte at the negative electrode. The solution can be constrained.

[0044] Furthermore, according to one aspect of the present invention, a method for charging and discharging a lithium ion battery or a lithium ion capacitor is provided. Suppresses the decomposition reaction of the electrolyte, etc., which occurs as a side reaction during repeated charging and discharging. and improving the cycle characteristics of the lithium ion battery or lithium ion capacitor. can be done.

[0045] In addition, according to one aspect of the present invention, the decomposition reaction of the electrolyte, which is accelerated at high temperatures, is suppressed, and high-temperature charging is possible. By preventing the loss of capacity during discharge, the lithium-ion battery or The operating temperature range of the capacitor can be expanded.

[0046] According to one embodiment of the present invention, a negative electrode for a power storage device that solves the above problems can be provided. do.

[0047] According to one embodiment of the present invention, a power storage device including the power storage device negative electrode can be provided. do.

[0048] According to one embodiment of the present invention, a method for manufacturing the negative electrode for a power storage device can be provided. [Brief explanation of the drawings]

[0049] [Figure 1] 1A and 1B are diagrams illustrating a negative electrode active material having a coating; [Figure 2] 1A to 1C are diagrams illustrating a method for manufacturing a coating. [Figure 3] FIG. [Figure 4] FIG. [Figure 5] FIG. 1 is a diagram illustrating a coin-type lithium-ion battery. [Figure 6] FIG. 1 is a diagram illustrating a laminated lithium-ion battery. [Figure 7] FIG. 1 is a diagram illustrating a cylindrical lithium-ion battery. [Figure 8] FIG. 1 is a diagram illustrating an electrical device. [Figure 9] FIG. 1 is a diagram illustrating an electrical device. [Figure 10] FIG. 1 is a diagram illustrating an electrical device. [Figure 11] X-ray diffraction spectrum. [Figure 12] SEM image. [Figure 13] SEM image. [Figure 14] TEM image. [Figure 15] TEM image. [Figure 16] CV measurement results. [Figure 17] CV measurement results. [Figure 18] CV measurement results. [Figure 19] TEM image. [Figure 20] FIG. [Figure 21] FIG. [Figure 22] FIG. [Figure 23] FIG. 1 is a diagram showing a film formation model. [Figure 24] FIG. [Figure 25] Arrhenius plot. [Figure 26] FIG. [Figure 27] FIG. [Figure 28] SEM image. [Figure 29] Photograph and schematic diagram of a laminated secondary battery. [Figure 30] FIG. [Figure 31] FIG. [Figure 32] FIG. DETAILED DESCRIPTION OF THE INVENTION

[0050] Hereinafter, embodiments will be described with reference to the drawings. The present invention can be implemented in various forms and in various ways without departing from the spirit and scope of the present invention. It will be readily apparent to those skilled in the art that various modifications may be made to the design and details of the present invention. The present invention should not be construed as being limited to the following description of the embodiments.

[0051] (Embodiment 1) In this embodiment, a negative electrode active material having a coating film capable of suppressing the decomposition reaction of the electrolyte is The structure will be explained using FIG.

[0052] 1(A) and 1(B) are diagrams showing the negative electrode active material used in the negative electrode for the power storage device according to the present invention. The negative electrode active material 101 is in the form of particles, fine particles, or powder (hereinafter referred to as "granular"). The particulate negative electrode active material 101 does not necessarily have to be spherical, and each shape may be any shape. The granular negative electrode active material 101 may have any shape different from each other. The negative electrode active material can be used with an average particle size that is normally used as a negative electrode active material. For example, it is possible to use a negative electrode active material having an average particle size of 6 μm or more and 30 μm or less. As long as the shape is as described above, the manufacturing method is not particularly limited.

[0053] As the material for the negative electrode active material 101, graphite, which is a carbon material commonly used in the field of electricity storage, can be used. Graphite can be classified into soft carbon and hard carbon as low crystalline carbon, and highly crystalline carbon as Natural graphite, kish graphite, pyrolytic carbon, liquid crystal pitch-based carbon fiber, mesocarbon microfiber Examples include clobeads (MCMB), liquid crystal pitch, petroleum or coal-based coke, etc.

[0054] Alternatively, a material that undergoes an alloying / dealloying reaction with carrier ions that transfer charges may be used. Such materials include, for example, magnesium, calcium, aluminum, silicon, Germanium, tin, lead, arsenic, antimony, bismuth, silver, gold, zinc, cadmium, water Examples include silver.

[0055] A coating 102 is provided on the surface of such a granular negative electrode active material 101. ), the coating 102 does not cover the entire surface of the granular negative electrode active material 101. Therefore, the surface of the granular negative electrode active material 101 is partially covered with the coating 102. The particulate negative electrode active material 10 has a region covered with the particulate negative electrode active material 10 and a region not covered with the particulate negative electrode active material 10. The coating 102 covering the granular negative electrode active material 101 is formed to cover several pcs of the surface area of ​​the granular negative electrode active material 101 as shown in FIG. It may also be a membrane having a relatively large surface area, occupying one cent to several tens of percent. Alternatively, the negative electrode may be a film having a very small surface area as shown in FIG. 1(B). The size of the coating 102 to be attached to the surface of the active material 101 is determined by the conditions of the sol-gel method described later and This can be adjusted appropriately depending on the surface shape and surface condition of the negative electrode active material used.

[0056] The material of the coating 102 may be niobium, titanium, vanadium, tantalum, tungsten, zirconium, or the like. any one of nium, molybdenum, hafnium, chromium, aluminum, or silicon or an oxide film containing any one of these elements and lithium can be used. Such a coating 102 is formed on the surface of the negative electrode active material by the decomposition products of the conventional electrolyte. This is a sufficiently dense film compared to the coating that is used.

[0057] For example, niobium oxide (Nb2O5) has an electronic conductivity of 10 -9 S / cm 2 and low, high absolute Therefore, the niobium oxide film prevents the electrochemical decomposition reaction between the negative electrode active material and the electrolyte. On the other hand, the lithium diffusion coefficient of niobium oxide is 10 -9 cm 2 / sec, and high It has high lithium ion conductivity, which allows lithium ions to pass through. be.

[0058] Therefore, when the coating 102 of the negative electrode active material 101 has carrier ion conductivity, the carrier Ions can pass through this film 102, and the negative electrode active material 101 can carry out a battery reaction. On the other hand, since the coating 102 has insulating properties, the electrolyte and the negative electrode active material 101 can be easily mixed. Therefore, the coating 102 has a high diffusion coefficient of carrier ions. The film 102 is preferably made of a thin insulating material and is preferably as thin as possible. The thickness is preferably 5 nm or more and 50 nm or less.

[0059] On the other hand, in the case of the negative electrode active material 101 that is completely insulated from the surroundings, electrons Since the free movement of the electrolyte between the inside and outside of the battery is restricted, the battery reaction cannot occur. In order to ensure a path for electron conduction between the negative electrode active material 101 and the outside, The negative electrode active material 101 is not completely covered with the coating 102. In any case, it is necessary that a part of the negative electrode active material 101 is exposed without being covered by the coating film 102. In this way, the coating 102 that covers a part of the granular negative electrode active material 101 is formed on the negative electrode active material 10. By forming the negative electrode active material 101 on the surface of the negative electrode active material 101, the battery reaction of the negative electrode active material 101 can be performed while preventing the decomposition of the electrolyte. The reaction can be suppressed.

[0060] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0061] (Embodiment 2) In this embodiment, a method for producing a coating on a granular negative electrode active material according to the present invention will be described with reference to FIG. This will be used to explain.

[0062] First, in step S150, a metal alkoxide and a stabilizer are added to a solvent and stirred. A solution is prepared. For example, toluene can be used as a solvent. Alternatively, in step S150, the following can be used: Silicon alkoxide and a stabilizer are added to a solvent and stirred to prepare a solution.

[0063] In addition, the metal alkoxide may contain a desired compound that will become a metal oxide film that is formed as a coating of the negative electrode active material. Select a metal.

[0064] Next, in step S151, a granular negative electrode active material such as graphite is added to the solution and stirred. A solvent such as toluene is added and stirred to make the solution thick and paste-like. The surface of the substrate is coated with metal alkoxide or silicon alkoxide. Steps S150 and S151 are preferably performed in a low humidity environment such as a dry room. is to suppress the progress of the hydrolysis reaction.

[0065] Next, in steps S152 and S153, a granular negative electrode is formed by using a sol-gel method. The metal alkoxide or silicon alkoxide on the surface of the electrode active material is gelled.

[0066] First, in step S152, a small amount of water is added to a solution containing a negative electrode active material such as graphite. By adding water, the metal alkoxide or silicon alkoxide reacts with water (hydrolysis reaction) ) to produce a sol-like decomposition product. Here, the sol-like state means that solid particles are roughly dispersed in the liquid. The addition of a small amount of water prevents the negative electrode active material from dissolving in the solution when it is exposed to the air. For example, a metal alkoxide may be added with nitrogen to the metal alkoxide. When Nb(OEt)5, a type of alkoxide, is used, the hydrolysis reaction is The reaction is shown in 1.

[0067] Nb(OEt)5+5H2O→Nb(OEt) 5-x (OH) x +xEtOH+(5-x )H2O (x is a positive number less than or equal to 5.) (Equation 1)

[0068] Alternatively, for example, when Si(OEt)4, which is a type of silicon alkoxide, is used, The hydrolysis reaction is shown in Equation 2.

[0069] Si(OEt)4 + 4H2O → Si(OEt) 4-x (OH) x +xEtOH+(4-x )H2O (x is a positive number less than or equal to 4) (Equation 2)

[0070] Next, in step S153, the solated decomposition product is dehydrated and condensed to form a gel-like reaction product. Here, the term "gel-like" refers to the state in which the fluid sol-like decomposition product has solidified, and The attractive interactions between the particles create a three-dimensional network structure. When Nb(OEt)5, a type of alkoxide, is used, the condensation reaction is shown in Reaction Scheme 3. The reaction is as shown.

[0071] 2Nb(OEt) 5-x (OH) x →[Nb(OEt) 5-x (OH) x-1 ]-O-[ Nb(OEt) 5-x (OH) x-1 ]+H2O (x is a positive number less than or equal to 5.) (Equation 3 )

[0072] Alternatively, for example, when Si(OEt)4, a type of silicon alkoxide, is used, The condensation reaction is shown in Equation 4.

[0073] 2Si(OEt) 4-x (OH) x →(OEt) 4-x (OH) x-1 Si-O-Si( OH) x-1 (OEt) 4-x +H2O (x is a positive number less than or equal to 4) (Equation 4)

[0074] This process forms a gel-like reaction product that adheres to the surface of the granular negative electrode active material. For convenience, the sol formation by the hydrolysis reaction and the gel formation by the condensation reaction are considered as mentioned above. Although the above steps are described as two separate steps, S152 and S153, in reality, Both reactions occur almost simultaneously. Metal alkoxides or silicon-containing alkoxides are This is because the structure gradually changes to a stable gel-like substance depending on the temperature and water. do.

[0075] Thereafter, in step S154, the dispersion is baked under atmospheric pressure to form a metal oxide film or The sintering temperature is 1000°C, and the sintering temperature is 1000°C. The temperature is 300°C or higher and 900°C or lower, preferably 500°C or higher and 800°C or lower.

[0076] Through the above steps, a negative electrode covered with a film made of a metal oxide film or a silicon oxide film is obtained. In this way, when a coating is formed on the negative electrode active material using the sol-gel method, It can be applied to negative electrode active materials with complex shapes, and can form coatings in large quantities. This makes it an ideal manufacturing method for mass production.

[0077] (Embodiment 3) In this embodiment, a negative electrode for a power storage device using a granular negative electrode active material having a coating and a method for manufacturing the same The method will be explained with reference to FIG.

[0078] As shown in FIG. 3(A), the negative electrode 200 includes a negative electrode current collector 201 and a negative electrode layer 202 on both sides of the negative electrode current collector 201. Alternatively, the negative electrode active material layer 202 is provided on one surface (both surfaces are shown in the figure).

[0079] The negative electrode current collector 201 is made of a conductive material that does not alloy with carrier ions such as lithium. It is made of highly durable materials such as stainless steel, iron, aluminum, copper, and nickel. Alternatively, aluminum-nickel alloys, aluminum, or titanium can be used. An alloy material such as a copper alloy may be used. The negative electrode current collector 201 may be in the form of a foil, a plate (sheet) or the like. Shapes such as a metal plate, a mesh plate, a punched metal plate, an expanded metal plate, etc. can be used as appropriate. The negative electrode current collector 201 preferably has a thickness of 10 μm or more and 30 μm or less.

[0080] The negative electrode active material layer 202 is provided on one or both surfaces of the negative electrode current collector 201. 02 is a metal oxide film or silicon oxide film described in the first or second embodiment. The negative electrode active material is in the form of particles covered with a coating made of the above.

[0081] In this embodiment, a conductive additive and a binder (binding agent) are added to the above-mentioned negative electrode active material, and mixed. The negative electrode active material layer 202 prepared by baking is used.

[0082] The negative electrode active material layer 202 will be described with reference to FIG. 3B. The negative electrode active material layer 202 is the same as that shown in Embodiment 1 or 2. The negative electrode active material 203 is in the form of particles, the conductive additive 204 is in the form of particles, and the binder (not shown) is in the form of particles. As described in the previous embodiment, the negative electrode active material 203 is a metal oxide film or a silicon oxide film. It is covered with a coating made of polyimide.

[0083] The conductive additive 204 improves the conductivity between the negative electrode active material 203 and between the negative electrode active material 203 and the negative electrode current collector 201. It is preferable to add the conductive additive 20 to the negative electrode active material layer 202. For 4, a material with a large specific surface area is desirable, and acetylene black (AB) etc. In addition, carbon materials such as carbon nanotubes, graphene, and fullerenes are used. An example in which graphene is used will be described later.

[0084] The binder may be any binder that binds the negative electrode active material, the conductive additive, and the current collector. Examples of materials include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexyl Tetrafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer Polymer, styrene-butadiene copolymer rubber, polytetrafluoroethylene, polypropylene Resin materials such as polyethylene and polyimide can be used.

[0085] The negative electrode 200 is fabricated as follows: First, the negative electrode 200 is fabricated by the method described in the second embodiment. The granular negative electrode active material having the coating is mixed with a vinylidene fluoride polymer such as polyvinylidene fluoride. The mixture is mixed with a solvent such as NMP (N-methylpyrrolidone) to form a slurry. do.

[0086] Next, the slurry is applied to one or both surfaces of the negative electrode current collector 201 and dried. When the process is performed on both sides of the negative electrode current collector 201, the negative electrode active material layer is formed on both sides simultaneously or one side at a time. Then, the negative electrode 200 is manufactured by rolling using a roll press. do.

[0087] Next, an example in which graphene is used as a conductive additive added to the negative electrode active material layer 202 will be described with reference to FIG. 3(C) and (D) will be used to explain.

[0088] Here, in this specification, graphene refers to a single layer of graphene or a layer of graphene having 2 to 100 layers. Single-layer graphene is a sheet of carbon molecules with a single atomic layer. Graphene oxide refers to the compound obtained by oxidizing the graphene. When graphene oxide is reduced to form graphene, the Not all of the oxygen contained in the graphene is released, and some of the oxygen remains in the graphene. If it contains, the proportion of oxygen is 2 atomic % or more and 20 atomic % or less of the total, Preferably, it is 3 atomic % or more and 15 atomic % or less.

[0089] When multilayer graphene oxide is reduced to multilayer graphene, the interlayer distance is 0.34 nm or more and 0.5 nm or less, preferably 0.38 nm or more and 0.42 nm or less, and more preferably The interlayer distance of graphite is generally between 0.39 nm and 0.41 nm. The thickness of the multilayer graphene layer used in the power storage device of one embodiment of the present invention is Since the interlayer distance can be increased, the power storage device according to one embodiment of the present invention can The multilayer graphene used allows carrier ions to move more easily between layers than graphite. It becomes easy.

[0090] FIG. 3C is a plan view of a part of the negative electrode active material layer 202 using graphene. The electrode active material layer 202 is made of a granular negative electrode active material 203 and a layer covering a plurality of the granular negative electrode active material 203. The negative electrode active material 203 is composed of particles of graphene 205 packed therein. A binder not shown may be added, but it is necessary to add a binder to bind the graphenes 205 together. If the binder is contained in an amount sufficient to function as a binder, the addition of the binder is The negative electrode active material layer 202 in plan view is made up of a plurality of granular negative electrode active material 20 The surface of the negative electrode active material 203 is covered with different graphene 205. 3 may be exposed.

[0091] FIG. 3D is a cross-sectional view of a part of the negative electrode active material layer 202 in FIG. 3C. and a graphite layer covering the negative electrode active material 203 in a plan view of the negative electrode active material layer 202. In the cross-sectional view, the graphene 205 is observed as a line. The same graphene or multiple graphenes overlap with multiple negative electrode active materials 203, or The negative electrode active material particles 203 are contained within the same graphene or a plurality of graphenes. Note that the graphene 205 has a bag shape and contains a plurality of negative electrode active materials. In addition, the graphene 205 has a partially open area, and in this area, the load The electrode active material 203 may be exposed.

[0092] The thickness of the negative electrode active material layer 202 is selected from the range of 20 μm to 150 μm. .

[0093] The negative electrode active material layer 202 may be pre-doped with lithium. As a method, a lithium layer may be formed on the surface of the negative electrode active material layer 202 by sputtering. Alternatively, by providing a lithium foil on the surface of the negative electrode active material layer 202, O2 can be pre-doped with lithium.

[0094] In addition, the negative electrode active material 203 may expand in volume due to the absorption of carrier ions. For this reason, the negative electrode active material layer becomes brittle during charging and discharging, and part of the negative electrode active material layer collapses. As a result, the reliability of the electricity storage device, such as cycle characteristics, decreases.

[0095] That is, there is no need to use a binder when forming the negative electrode active material layer 202, and the negative electrode active material layer 202 is formed by a constant weight (a certain amount). In the negative electrode active material layer 202 (of a constant volume), the amount of the negative electrode active material can be increased. Therefore, the charge / discharge capacity per electrode weight (electrode volume) can be increased.

[0096] The graphene 205 has conductivity and is in contact with the plurality of negative electrode active materials 203. In other words, when forming the negative electrode active material layer 202, the conductive additive In the negative electrode active material layer 202 of a certain weight (certain volume), Therefore, the charge / discharge capacity per electrode weight (electrode volume) can be increased. It can be increased.

[0097] In addition, the graphene 205 provides an efficient and sufficient electron conduction path to the negative electrode active material layer 202. Therefore, the conductivity of the negative electrode 200 can be improved.

[0098] Graphene 205 also functions as a negative electrode active material capable of absorbing and releasing carrier ions. Therefore, the charge capacity of the negative electrode 200 can be improved.

[0099] Next, a method for forming the negative electrode active material layer 202 shown in FIGS.

[0100] First, the coating-having negative electrode active material particles 203 described in Embodiment 1 or 2, A dispersion containing graphene oxide is kneaded to form a slurry.

[0101] Next, the above slurry is applied onto the negative electrode current collector 201. Next, vacuum drying is performed for a certain period of time. The solvent is removed from the slurry applied to the negative electrode current collector 201 by a roll press. The material is rolled using a machine.

[0102] After that, we investigated the electrochemical reduction of graphene oxide using electrical energy and the thermal treatment. Thermal reduction of graphene oxide produces graphene 205. In particular, electrochemical When a reduction treatment is performed, the graphene formed by the heat treatment has a π bond. The proportion of double-bonded carbon-carbon bonds increases, resulting in highly conductive graphene205. By the above steps, graphene can be formed on one or both surfaces of the negative electrode current collector 201. The negative electrode active material layer 202 can be formed by using the conductive additive, and the negative electrode 200 can be manufactured. It is possible.

[0103] (Fourth embodiment) In this embodiment, a structure and a manufacturing method of a lithium ion battery as a power storage device will be described. do.

[0104] (positive electrode) First, the positive electrode and the method for producing the same will be described.

[0105] 4A is a cross-sectional view of a positive electrode 250. The positive electrode 250 has a positive electrode active material on a positive electrode current collector 251. A layer of matrix 252 is formed.

[0106] The positive electrode current collector 251 may be made of stainless steel, gold, platinum, zinc, iron, copper, aluminum, titanium, etc. Highly conductive materials such as metals and alloys thereof can be used. Elements that improve heat resistance, such as silicon, titanium, neodymium, scandium, and molybdenum, are added. Aluminum alloys that react with silicon to form silicide can also be used. The metal element may be a metal element that reacts with silicon to form silicide. These include zirconium, titanium, hafnium, vanadium, niobium, tantalum, and chromium. The positive electrode current collector 251 is made of a foil. , plate (sheet), mesh, punched metal, expanded metal, etc. It can be used.

[0107] The positive electrode active material layer 252 contains a conductive additive and a binder (binding agent) in addition to the positive electrode active material. Good too.

[0108] The positive electrode active material of the positive electrode active material layer 252 is, for example, a carrier ion such as a lithium ion. A material that allows for insertion and desorption of lithium ions can be used. The active material may have, for example, an olivine type crystal structure, a layered rock salt type crystal structure, or a spinel Examples of the lithium-containing composite oxide include those having a crystal structure of the above type.

[0109] Examples of lithium-containing composite oxides having an olivine-type crystal structure include those represented by the general formula LiM PO4 (M is one or more of Fe(II), Mn(II), Co(II), and Ni(II)) A typical example of the general formula LiMPO4 is LiFePO 4, LiNiPO4, LiCoPO4, LiMnPO4, LiFe a Ni b PO4, Li Fe a Co b PO4, LiFe a Mn b PO4, LiNi a Co b PO4, LiNi a M n b PO4(a+b is less than 1, 0 <a<1、0<b<1)、LiFe c Ni d Co e PO 4. LiFe c Ni d Mn e PO4, LiNi c Co d Mn e PO4(c+d+e is 1 or more bottom, 0 <c<1、0<d<1、0<e<1)、LiFe f Ni g Co h Mni PO4(f +g+h+i is 1 or less, 0 < f < 1, 0 < g < 1, 0 < h < 1, 0 < i < 1), etc. can be mentioned. These are mentioned.

[0110] In particular, LiFePO4 satisfies the requirements for a cathode active material, such as safety, stability, high capacity density, high potential, and the presence of lithium ions that can be extracted during initial oxidation (charging), in a balanced manner. Therefore, it is preferable.

[0111] Examples of lithium-containing composite oxides having a layered rock salt crystal structure include lithium cobalt oxide (LiCoO2), LiNiO2, LiMnO2, Li2MnO3, LiNi 8Co 0. 8Co 0.2 O2, etc. of the NiCo system (general formula is LiNi x Co 1-x O2(0 < x < 1) ), LiNi 0.5 Mn 0.5 O2, etc. of the NiMn system (general formula is LiNi x Mn 1-x O 2(0 < x < 1)), LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2, etc. of the NiMnCo system (also called N MC. General formula is LiNi x Mn y Co 1-x-y O2(x > 0, y > 0, x + y < 1)) can be mentioned. Further, Li(Ni 0.8 Co 0.15 Al 0.05 )O2, Li2MnO3 - LiMO2(M = Co, Ni, Mn), etc. can also be mentioned.

[0112] In particular, LiCoO2 is preferable because it has advantages such as a large capacity, being more stable in the air compared to LiNiO2, and being thermally more stable compared to Li NiO2.

[0113] Examples of lithium-containing composite oxides having a spinel-type crystal structure include LiMnO 4. Li 1+x Mn 2-x O4, Li(MnAl)2O4, LiMn 1.5 Ni 0.5 O 4, etc.

[0114] Lithium-containing composite oxides with spinel-type crystal structure containing manganese, such as LiMn2O4 The material contains a small amount of lithium nickel oxide (LiNiO2 or LiNi 1-x MO2 (M = Co, A Mixing with other additives such as manganese elution and electrolyte decomposition has the advantage of suppressing the dissolution of manganese. Yes, and preferable.

[0115] In addition, the positive electrode active material is a compound of the general formula Li (2-j) MSiO4 (M is Fe(II), Mn (II), Co(II), Ni(II), or a composite oxide represented by 0≦j≦2) It can be used. (2-j) A typical example of MSiO4 is Li (2-j ) FeSiO4, Li (2-j) NiSiO4, Li (2-j) CoSiO4, Li (2 -j) MnSiO4, Li (2-j) Fe k Ni l SiO4, Li (2-j) Fe k Co l SiO4, Li (2-j) Fe k Mn l SiO4, Li (2-j) Ni k Co l SiO 4. Li (2-j) Ni k Mn lSiO4 (where k + l is 1 or less, 0 < k < 1, 0 < l < 1) , Li (2-j) Fe m Ni n Co q SiO4, Li (2-j) Fe m Ni n Mn q Si O4, Li (2-j) Ni m Co n Mn q SiO4 (where m + n + q is 1 or less, 0 < m < 1, 0 < n < 1, 0 < q < 1), Li (2-j) Fe r Ni s Co t Mn u SiO4 (where r + s + t + u is 1 or less, 0 < r < 1, 0 < s < 1, 0 < t < 1, 0 < u < 1) and the like can be mentioned .

[0116] Also, as the positive electrode active material, A x M2(XO4)3 (A = Li, Na, Mg, M = Fe, M n, Ti, V, Nb, Al, X = S, P, Mo, W, As, Si) represented by the general formula of the nashi con type compound can be used. Examples of the nashicon type compound include Fe2(MnO4) 3, Fe2(SO4)3, Li3Fe2(PO4)3 and the like. Also, as the positive electrode active material Li2MPO4F, Li2MP2O7, Li5MO4 (M = Fe, Mn) represented by the general formula, perovskite type fluorides such as NaF3, FeF3, metal chalcogenides (sulfides, selenides, tellurides) such as TiS2, M oS2, lithium-containing composite oxides having an inverse spinel type crystal structure such as LiMVO4, vanadium oxide systems (V2O 5, V6O , LiV3O8, etc.), manganese oxide systems, organic sulfur systems and other materials can be used 13 . ​

[0117] In addition, the carrier ions are alkali metal ions other than lithium ions, alkaline earth metal ions, etc. In the case of ions, beryllium ions, or magnesium ions, the positive electrode active material layer 252 In the lithium compounds and lithium-containing composite oxides, lithium is replaced by a Alkaline metals (e.g., sodium and potassium), alkaline earth metals (e.g., calcium Alternatively, other metals such as tungsten, strontium, barium, beryllium, or magnesium may be used.

[0118] Furthermore, the positive electrode active material layer 252 is not limited to being formed directly on the positive electrode current collector 251 . Between the positive electrode current collector 251 and the positive electrode active material layer 252, 2, and an adhesion layer for reducing the irregularities on the surface of the positive electrode current collector 251. a planarizing layer for dissipating heat, a heat dissipation layer for dissipating heat, and a layer for applying heat to the positive electrode current collector 251 or the positive electrode active material layer 252. A functional layer such as a stress relief layer for relieving stress may be formed using a conductive material such as metal. stomach.

[0119] FIG. 4(B) is a plan view of the positive electrode active material layer 252. The particulate positive electrode active material 253 capable of absorbing and releasing ions is used. Graphene 25 in which the positive electrode active material 253 is packed while covering the plurality of positive electrode active materials 253 4. The surfaces of a plurality of positive electrode active materials 253 are covered with different graphenes 254. In addition, the positive electrode active material 253 may be partially exposed.

[0120] The particle size of the positive electrode active material 253 is preferably 20 nm or more and 100 nm or less. Since electrons move within 253, the particle size of the positive electrode active material 253 is preferably smaller.

[0121] Furthermore, sufficient characteristics can be obtained even if the surface of the positive electrode active material 253 is not coated with a graphite layer. However, when graphene is used in combination with a positive electrode active material coated with a graphite layer, This is more preferable because the carrier hops between the positive electrode active materials, causing a current to flow.

[0122] FIG. 4(C) is a cross-sectional view of a portion of the positive electrode active material layer 252 in FIG. 4(B). The positive electrode active material 253 is covered with graphene 254. The graphene is observed as a line in the cross-sectional view. In other words, the positive electrode active material is contained in the same graphene or between multiple graphenes. The graphene has a bag-like shape, and a plurality of positive electrode active materials are present inside the bag-like shape. In some cases, a plurality of positive electrode active materials are enclosed within the graphene. Material may be exposed.

[0123] The thickness of the positive electrode active material layer 252 is selected from the range of 20 μm to 100 μm. The thickness of the positive electrode active material layer 252 is adjusted appropriately to prevent cracks and peeling. It is preferable that:

[0124] The positive electrode active material layer 252 is formed of acetylene having a volume that is 0.1 to 10 times the volume of graphene. Black particles and carbon particles such as carbon nanofibers with one-dimensional expansion, A known conductive additive may be included.

[0125] Depending on the material of the positive electrode active material, the volume may expand due to the absorption of ions that act as carriers. As a result, the positive electrode active material layer becomes brittle during charging and discharging, and part of the positive electrode active material layer is broken off. However, the positive electrode active material is charged, and the reliability of the power storage device is reduced. Even if the volume expands due to discharge, the graphene covers the surrounding area, so graphene is a positive electrode active material In other words, graphene can prevent the dispersion of the positive electrode active material layer and the collapse of the positive electrode active material layer. This has the function of maintaining the bond between the positive electrode active materials even if the volume of the positive electrode active materials increases or decreases. .

[0126] In addition, graphene 254 is in contact with multiple positive electrode active materials and functions as a conductive additive. In addition, it has the function of retaining a positive electrode active material that can absorb and release carrier ions. Therefore, there is no need to mix a binder into the positive electrode active material layer, and the amount of positive electrode active material per positive electrode active material layer is It is possible to increase the discharge capacity of the non-aqueous secondary battery.

[0127] Next, a method for manufacturing the positive electrode active material layer 252 will be described.

[0128] First, a slurry containing particulate positive electrode active material and graphene oxide is formed. After the slurry is applied onto the dielectric 251, a reduction treatment is performed by heating in a reducing atmosphere. The positive electrode active material is baked, and oxygen contained in the graphene oxide is desorbed, resulting in the graphene Note that not all of the oxygen contained in graphene oxide is released, and some of the oxygen remains in the graphene. By the above steps, a positive electrode active material layer 252 is formed on the positive electrode current collector 251. As a result, the conductivity of the positive electrode active material layer 252 is increased.

[0129] Graphene oxide contains oxygen and therefore becomes negatively charged in polar solvents. The phenanthrene disperses in the polar solvent, so the positive electrode active material contained in the slurry does not aggregate. This makes it difficult for the particle size of the positive electrode active material to increase due to aggregation. This facilitates the movement of electrons within the electrode active material, thereby increasing the conductivity of the positive electrode active material layer.

[0130] Next, one embodiment of the structure and manufacturing method of a lithium ion battery will be described with reference to FIG. Here, the cross-sectional structure of a lithium-ion battery is explained below.

[0131] (coin-type lithium-ion battery) FIG. 5(A) is an external view of a coin-type (single-layer flat) lithium-ion battery, and FIG. 5(B) ) is a cross-sectional view thereof.

[0132] The coin-type lithium ion battery 300 has a positive electrode can 301 that also serves as a positive electrode terminal and a negative electrode can 302 that also serves as a negative electrode terminal. The negative electrode can 302 is insulated and sealed with a gasket 303 made of polypropylene or the like. The positive electrode 304 is composed of a positive electrode current collector 305 and a positive electrode active material provided in contact with the positive electrode current collector. The negative electrode 307 is formed by a negative electrode current collector 308 and a conductive layer 306 in contact therewith. The negative electrode active material layer 309 is formed by the positive electrode active material layer 306 and the negative electrode active material layer 309. Between the electrolyte layer 309 and the separator 310, there is an electrolyte (not shown).

[0133] The negative electrode 307 is the negative electrode described in any of the first to third embodiments. The positive electrode 250 described in the embodiment can be used.

[0134] The separator 310 may be made of cellulose (paper), or porous polypropylene, polypropylene, or An insulator such as ethylene can be used.

[0135] The electrolytic solution uses a material having carrier ions as an electrolyte. Typical examples of the electrolyte include: is LiClO4, LiAsF6, LiAlCl4, LiSCN, LiBr, LiI, L i2SO4, Li2B 10 Cl 10 , Li2B 12 Cl 12 , LiCF3SO3, LiC 4F9SO3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiN(CF 3SO2)2, LiN(C4F9SO2)(CF3SO2), LiN(C2F5SO2) There are two classes of lithium salts.

[0136] In addition, the carrier ions are alkali metal ions other than lithium ions, alkaline earth metal ions, etc. In the case of lithium ions, beryllium ions, or magnesium ions, the electrolyte is In the humic salts, instead of lithium, an alkali metal (e.g., sodium or potassium) , alkaline earth metals (e.g., calcium, strontium, barium, etc.), beryllium Alternatively, magnesium may be used.

[0137] In addition, a material that can transport carrier ions is used as the solvent for the electrolyte. The solvent is preferably an aprotic organic solvent. Typical examples of the aprotic organic solvent include: , ethylene carbonate (EC), propylene carbonate, butylene carbonate, Ethylene carbonate, vinylene carbonate, dimethyl carbonate, diethyl carbonate Carbonate (DEC), Ethyl methyl carbonate (EMC), γ-butyrolactone, γ -Valerolactone, methyl formate, methyl acetate, methyl butyrate, 1,3-dioxane, 1,4 -Dioxane, dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile Tolyl, benzonitrile, dimethoxyethane, tetrahydrofuran, sulfolane, sulfur One or more of these can be used. By using a gelling polymer material, safety against leakage etc. is improved. This makes it possible to make lithium-ion batteries thinner and lighter. Representative examples of polymer materials that can be gelled include Silicone gel, acrylic gel, acrylonitrile gel, polyethylene oxide , polypropylene oxide, fluorine-based polymers, etc. Also, as a solvent for the electrolyte, By using one or more ionic liquids (room temperature molten salts) that are flame-retardant and non-volatile, Even if the internal temperature of the lithium-ion battery rises due to an internal short circuit or overcharging, the secondary battery will not be damaged. This can prevent cracks and fires.

[0138] In addition, instead of the electrolyte solution, solid electrolytes containing inorganic materials such as sulfides and oxides, and P A solid electrolyte containing a polymer material such as EO (polyethylene oxide) can be used. When a solid electrolyte is used, the separator is not required. Since it can be integrated, there is no risk of leakage, and safety is improved dramatically.

[0139] The positive electrode can 301 and the negative electrode can 302 are made of a material that is resistant to liquids such as electrolytes during charging and discharging of the secondary battery. Metals such as nickel, aluminum, and titanium that are corrosion-resistant, alloys of these metals, and Alloys of metals with other metals (e.g., stainless steel, etc.), laminations of the metals, and the metals and the above-mentioned Lamination with alloys (e.g., stainless steel, aluminum, etc.), lamination of the metal with other metals A layer (e.g., nickel, iron, nickel, etc.) can be used. 304 and the negative electrode can 302 are electrically connected to the negative electrode 307, respectively.

[0140] The negative electrode 307, the positive electrode 304, and the separator 310 are impregnated with an electrolyte, and as shown in FIG. As shown, the positive electrode can 301 is placed downwards, and the positive electrode 304, separator 310, negative electrode 307, and negative electrode The cans 302 are stacked in this order, and the positive electrode can 301 and the negative electrode can 302 are secured together with a gasket 303 interposed therebetween. The coin-shaped lithium ion battery 300 is manufactured by crimping.

[0141] (Laminated lithium-ion battery) Next, an example of a laminated lithium ion battery will be described with reference to FIG.

[0142] The laminated lithium ion battery 400 shown in FIG. 6 includes a positive electrode current collector 401 and a positive electrode active material. A positive electrode 403 having a porous layer 402, a separator 407, a negative electrode current collector 404, and a negative electrode active material The negative electrode 406 having the porous layer 405 is laminated, and the laminate is enclosed in an outer casing 409 and an electrolyte 408 is poured into the outer casing 409. In FIG. 6, the laminated lithium ion battery 400 is a sheet-shaped positive electrode The structure shows a stack of one electrode 403 and one negative electrode 406, but in order to increase the battery capacity, It is preferable to wind the laminate structure or stack a plurality of sheets of the laminate structure and then laminate them. In particular, when the lithium ion battery is in the form of a laminate, the battery has flexibility. Therefore, it is suitable for applications that require flexibility.

[0143] In the laminated lithium ion battery 400 shown in FIG. The electrode current collector 404 also serves as a terminal for electrical contact with the outside. The current collector 401 and the negative electrode current collector 404 are arranged so as to be partially exposed to the outside from the exterior body 409. It will be placed.

[0144] In the laminated lithium ion battery 400, the exterior body 409 is made of, for example, polyethylene. Made of materials such as polyethylene, polypropylene, polycarbonate, ionomer, polyamide, etc. On the inner surface, a thin metal film with excellent flexibility, such as aluminum, stainless steel, copper, or nickel, is installed. Further, a polyamide resin, polyester resin or the like is applied on the metal thin film as the outer surface of the exterior body. A laminate film having a three-layer structure with an insulating synthetic resin film can be used. This three-layer structure prevents electrolyte and gas from permeating and ensures insulation. In addition, it has resistance to electrolyte.

[0145] (cylindrical lithium-ion battery) Next, an example of a cylindrical lithium ion battery will be described with reference to FIG. As shown in FIG. 7(A), the lithium ion battery 500 has a positive electrode cap (battery cover) 5 on the top surface. 501, and a battery can (external can) 502 on the side and bottom. and the battery can (external can) 502 are insulated by a gasket (insulating packing) 510. There are.

[0146] Fig. 7(B) is a schematic diagram showing the cross section of a cylindrical lithium ion battery. Inside the battery can 502, a strip-shaped positive electrode 504 and a strip-shaped negative electrode 506 are sandwiched between a separator 505. The battery element is sandwiched between the center pin and wound around the center pin. The battery can 502 is closed at one end and open at the other end. 502 is a nickel-based material that has corrosion resistance to liquids such as electrolytes during charging and discharging of secondary batteries. Metals such as nickel, aluminum, and titanium, alloys of these metals, and alloys of these metals with other metals (e.g., stainless steel), lamination of the metal, lamination of the metal and the above-mentioned alloy (e.g., For example, stainless steel or aluminum), lamination of the metal with other metals (for example, nickel \iron\nickel, etc.) can be used. The battery element with the separator wound around it is sandwiched between a pair of opposing insulating plates 508 and 509. The inside of the battery can 502 in which the battery element is provided is filled with an electrolyte (not shown). The electrolyte is the same as that used in coin-type and laminated lithium-ion batteries. can be used.

[0147] The positive electrode 504 and the negative electrode 506 are the same as the positive electrode and the negative electrode of the coin-type lithium ion battery described above. The positive and negative electrodes used in cylindrical lithium ion batteries are wound. The positive electrode 504 is provided with a positive electrode terminal (positive electrode terminal). A negative electrode terminal (negative electrode current collecting lead) 507 is connected to the negative electrode 506. The positive electrode terminal 503 and the negative electrode terminal 507 are both made of a metal material such as aluminum. The positive terminal 503 is connected to the safety valve mechanism 512, and the negative terminal 507 is connected to the battery can. The safety valve mechanism 512 is made of a PTC element (Positive Temperature Coefficient). ve Temperature Coefficient) 511 via positive cap The safety valve mechanism 512 is electrically connected to the battery 501. If the temperature exceeds the limit, the electrical connection between the positive electrode cap 501 and the positive electrode 504 is cut off. The PTC element 511 is a thermosensitive resistor whose resistance increases when the temperature rises. The PTC element prevents abnormal heat generation by limiting the amount of current through an increase in resistance. Barium titanate (BaTiO3) based semiconductor ceramics and the like can be used.

[0148] In this embodiment, the lithium ion battery may be a coin type, a laminate type, or a cylindrical type. Although this figure shows a sealed lithium-ion battery, other sealed lithium-ion batteries and prismatic lithium-ion batteries are also included. Lithium ion batteries of various shapes, such as lithium ion batteries, can be used. and a structure in which a plurality of separators are stacked, and a structure in which a positive electrode, a negative electrode, and a separator are wound may be.

[0149] The lithium ion battery 300, the lithium ion battery 400, and the lithium ion battery The negative electrode of the ON battery 500 is a negative electrode for a power storage device according to one embodiment of the present invention. For lithium ion battery 300, lithium ion battery 400, lithium ion battery 5 00 cycle characteristics can be improved. This can suppress the deterioration of the battery, and furthermore, it is possible to provide a lithium ion battery with good high-temperature characteristics.

[0150] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0151] (Embodiment 5) In this embodiment, a lithium ion capacitor will be described as the power storage device.

[0152] Lithium ion capacitors are electric double layer capacitors (EDLCs) that use carbon materials as the positive electrode. It is a hybrid capacitor that combines the negative electrode of a lithium-ion battery with the positive electrode This is an asymmetric capacitor with a different negative electrode storage principle. The positive electrode forms an electric double layer and the physical action The negative electrode is charged and discharged by the chemical action of lithium. By using a negative electrode in which lithium is absorbed in advance into the negative electrode active material such as carbon material, Compared to electric double layer capacitors that use activated carbon for the electrodes, the energy density has been dramatically improved. There are.

[0153] The lithium ion capacitor is a lithium ion battery having a positive electrode active material layer of the lithium ion battery shown in the fourth embodiment. Instead, a material capable of reversibly carrying at least one of lithium ions and anions is used. Such materials include, for example, activated carbon, conductive polymers, polyacene-based organic semiconducting materials, and the like. Conductor (PAS), etc.

[0154] Lithium-ion capacitors have high charge / discharge efficiency, can be charged and discharged rapidly, and can be used repeatedly. It also has a long lifespan due to use.

[0155] The negative electrode of such a lithium ion capacitor may be a lithium ion capacitor for use in the power storage device described in any of the first to third embodiments. This suppresses the generation of initial irreversible capacity and improves cycle characteristics. In addition, a power storage device having excellent high-temperature characteristics can be manufactured. This can be done.

[0156] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0157] (Embodiment 6) The power storage device according to one embodiment of the present invention can be used as a power source for various electric devices driven by electric power. It is possible.

[0158] Specific examples of electrical devices using a power storage device according to one embodiment of the present invention include displays such as televisions and monitors. display devices, lighting equipment, desktop or notebook personal computers, Word processors processors, DVD (Digital Versatile Disc) and other recording media Image playback devices that play back stored still or moving images, portable CD players, radios, Tape recorders, headphone stereos, stereos, table clocks, wall clocks, cordless phones Handsets, transceivers, portable radios, mobile phones, car phones, portable game consoles, calculators, mobile phones Portable information terminals, electronic organizers, e-books, electronic translators, voice input devices, video cameras, digital Still cameras, toys, electric shavers, microwave ovens and other high-frequency heating devices, electric rice cookers, Washing machines, vacuum cleaners, water heaters, electric fans, hair dryers, air conditioners, humidifiers, dehumidifiers air conditioning equipment such as electric appliances, dishwashers, dish dryers, clothes dryers, futon dryers, electric refrigerators, Air freezers, electric refrigerators and freezers, freezers for DNA storage, flashlights, power tools such as chainsaws , smoke detectors, medical equipment such as dialysis machines, etc. Furthermore, emergency lights, traffic lights, belts, etc. Conveyors, elevators, escalators, industrial robots, power storage systems, power leveling Examples include industrial equipment such as energy storage devices for smart grids and energy conservation. Mobile bodies propelled by electric motors using electric power are also included in the category of electrical equipment. Examples of the above-mentioned mobile bodies include electric vehicles (EVs), hybrid vehicles that combine an internal combustion engine and an electric motor, and Hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), and their tires and wheels Tracked vehicles, including electrically assisted bicycles, motorcycles, Electric wheelchairs, golf carts, small or large boats, submarines, helicopters, aircraft, location shooting Examples include satellites, space probes, interplanetary probes, and spacecraft.

[0159] The electrical equipment is powered by a power supply according to one embodiment of the present invention. Alternatively, the electrical equipment can be powered by the main power supply or the commercial power supply. Uninterruptible power supply that can supply power to electrical equipment when the power supply from The power storage device according to one embodiment of the present invention can be used as a power source. The device supplies power to electrical equipment in parallel with the supply of power to the electrical equipment from the main power supply or commercial power supply. The power storage device of one embodiment of the present invention can be used as an auxiliary power source for supplying power. Cut.

[0160] 8 shows a specific configuration of the above-mentioned electrical device. In FIG. 8, a display device 600 is a display device according to the present invention. 6 is an example of an electrical device using the power storage device 604 according to one embodiment of the present invention. 600 corresponds to a display device for receiving TV broadcasts, and includes a housing 601, a display unit 602, a speaker unit 603, and a 3, a power storage device 604, and the like. The power storage device 604 according to one embodiment of the present invention is The display device 600 can also be supplied with power from a commercial power source. In addition, the power stored in the power storage device 604 can be used. Even when power cannot be supplied from a commercial power source, the power storage device 604 of one embodiment of the present invention can be used By using it as an uninterruptible power supply, the display device 600 can be used.

[0161] The display unit 602 is a light-emitting device having a light-emitting element such as a liquid crystal display device or an organic EL element in each pixel. Device, electrophoretic display, DMD (Digital Micromirror Device) e), PDP (Plasma Display Panel), FED (Field E A semiconductor display device such as a mission display can be used.

[0162] In addition to TV broadcast reception, display devices are also used for personal computers and advertising displays. , including all display devices for displaying information.

[0163] In FIG. 8, a stationary lighting device 610 includes a power storage device 613 according to one embodiment of the present invention. Specifically, the lighting device 610 includes a housing 611, a light source 612, 8, the power storage device 613 is disposed between the housing 611 and the light source 612. Although the example shown is that the power storage device 61 is installed inside a ceiling 614, 3 may be provided inside the housing 611. The lighting device 610 receives power from a commercial power source. The power supply can be received, or the power stored in the power storage device 613 can be used. Therefore, even when power cannot be supplied from a commercial power source due to a power outage or the like, one aspect of the present invention can be used. By using the power storage device 613 as an uninterruptible power supply, the lighting device 610 can be used. This becomes:

[0164] Although FIG. 8 illustrates a fixed lighting device 610 installed on the ceiling 614, The power storage device of one embodiment of the present invention can be mounted on any surface other than the ceiling 614, such as a side wall 615, a floor 616, or a window 617. It can be used for a fixed lighting device installed in a room such as a building, or for a tabletop lighting device. It can be used anywhere.

[0165] The light source 612 may be an artificial light source that artificially obtains light using electricity. Specifically, incandescent lamps, fluorescent lamps and other discharge lamps, and light-emitting elements such as LEDs and organic EL elements An example of the artificial light source is a lamp.

[0166] In FIG. 8, an air conditioner having an indoor unit 620 and an outdoor unit 624 is 6 is an example of an electric appliance using a power storage device 623 according to one embodiment. 8, the power storage device 623 is a housing 621, an air outlet 622, a power storage device 623, and the like. Although the case where the power storage device 623 is provided in the indoor unit 620 is illustrated, the power storage device 623 is provided in the outdoor unit 624. Alternatively, the power storage device 62 may be provided in both the indoor unit 620 and the outdoor unit 624. 3 may be provided. The air conditioner may be supplied with power from a commercial power source. Alternatively, the electric power stored in the power storage device 623 can be used. When the power storage device 623 is provided in both the outdoor unit 624 and the outdoor unit 620, if a power outage occurs, Even when power cannot be supplied from a power source, the power storage device 623 of one embodiment of the present invention can be continuously operated. By using it as a power source, it becomes possible to use an air conditioner.

[0167] Note that Figure 8 shows an example of a separate-type air conditioner consisting of an indoor unit and an outdoor unit. However, it is an integrated air conditioner that has the functions of both the indoor unit and the outdoor unit in a single housing. The power storage device according to one embodiment of the present invention can also be used in the inverter.

[0168] In FIG. 8, an electric refrigerator-freezer 630 uses a power storage device 634 of one embodiment of the present invention. Specifically, the electric refrigerator-freezer 630 includes a housing 631, a refrigerator compartment door 632, and a 32, a freezer door 633, a power storage device 634, etc. In FIG. The electric refrigerator-freezer 630 is provided inside a body 631. The electric refrigerator-freezer 630 is supplied with power from a commercial power source. Alternatively, the power stored in the power storage device 634 can be used. Even when power cannot be supplied from a commercial power source due to a power outage or the like, the present invention By using the power storage device 634 as an uninterruptible power supply, the electric refrigerator-freezer 630 can be used. become.

[0169] Among the above-mentioned electrical appliances, high-frequency heating devices such as microwave ovens and electric rice cookers Equipment requires high power for a short period of time, so it supplements the power that cannot be supplied by commercial power. By using a power storage device according to one embodiment of the present invention as an auxiliary power source for This prevents the commercial power breaker from tripping during use.

[0170] In addition, during periods when electrical equipment is not in use, especially when the total amount of power that can be supplied by the commercial power supplier is low, During times when the percentage of electricity actually used (called the electricity usage rate) is low, By storing power in the device, it is possible to prevent power usage rates from increasing outside of the above time periods. For example, in the case of an electric refrigerator-freezer 630, when the temperature is low, the refrigerator compartment door 632, During the night when the freezer compartment door 633 is not opened or closed, power is stored in the power storage device 634. In the daytime, when the temperature rises and the refrigerator door 632 and the freezer door 633 are opened and closed, In this case, by using the power storage device 634 as an auxiliary power source, the power usage rate during the day can be kept low. This can be done.

[0171] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0172] (Embodiment 7) Next, a portable information terminal, which is an example of an electrical device, will be described with reference to FIG.

[0173] 9(A) and 9(B) show a foldable tablet terminal 650. 6 shows the tablet terminal 650 in an open state. The tablet terminal 650 includes a housing 651, a display unit 652a, and a display 652b, a display mode changeover switch 653, a power switch 654, a power saving mode changeover switch The switch 655 and the operation switch 656 are provided.

[0174] A part of the display unit 652a can be used as a touch panel area 657a, and the displayed operation Data can be input by touching the operation key 658. For example, half of the area has a display function and the other half has a touch function. Although the display unit 652a has a configuration having a panel function, it is not limited to this configuration. For example, the entire surface of the display unit 652a may have a touch panel function. The keyboard buttons are displayed on the display unit 652b to function as a touch panel, and the display unit 652b is used as a display screen. It is possible.

[0175] Similarly to the display section 652a, the display section 652b can also be touched by touching a part of the display section 652b. The area 657b of the touch panel can be used as the keyboard display switch. By touching the position where the replacement button 659 is displayed with a finger or a stylus, the display unit 65 Keyboard buttons can be displayed on 2b.

[0176] In addition, when the area 657a of the touch panel and the area 657b of the touch panel are touched at the same time, You can also input it.

[0177] A display mode changeover switch 653 changes the display orientation between portrait and landscape. You can select between black and white and color display. The Touch 655 is a tablet device that detects external light during use using a built-in light sensor. The tablet device has a light sensor that can adjust the display brightness to suit the amount of light. In addition, it also incorporates other detection devices such as gyro, acceleration sensor, etc. to detect tilt. It is also acceptable to do so.

[0178] FIG. 9A shows an example in which the display area of ​​the display unit 652b is the same as that of the display unit 652a. There is no particular limitation on the size of the image, and the size of one image may be different from the other image. For example, one of the display panels may be capable of displaying a higher resolution image than the other. Good too.

[0179] FIG. 9B shows the tablet terminal 650 in a closed state. The tablet terminal 650 includes a housing 651, a solar cell 652, and a battery 653. 60, includes a charge / discharge control circuit 670, a battery 671, and a DC / DC converter 672. In FIG. 9B, a battery 671 and a DC / DC converter are used as an example of the charge / discharge control circuit 670. The battery 671 is the same as that in the above embodiment. The power storage device described above is included.

[0180] The tablet terminal 650 can be folded in half, so when not in use, the housing 651 can be closed. Therefore, the display units 652a and 652b can be protected, and the display units 652a and 652b can be The tablet terminal 650 is highly durable and reliable for long-term use. This can be done.

[0181] In addition, the tablet terminals shown in Fig. 9(A) and Fig. 9(B) can also display various information ( Functions that display still images, videos, text images, etc., calendars, dates, or times, etc. A function to display information on the display unit, and a touch input device to operate or edit the information displayed on the display unit by touch input. It can have functions such as the ability to control processing by various software (programs), etc. can.

[0182] The solar cell 660 attached to the surface of the tablet terminal supplies power to the touch panel, display, The solar cell 660 can supply the power to a display unit, a video signal processor, etc. 651 can be provided on one or both sides of the battery 671, and the battery 671 can be efficiently charged. Note that the battery 671 can be a power storage device according to one embodiment of the present invention. The use of such a device has the advantage of enabling miniaturization.

[0183] The configuration and operation of the charge / discharge control circuit 670 shown in FIG. 9(B) are shown in block diagram form in FIG. 9(C). 9(C) shows a solar cell 660, a battery 671, a DCD Regarding the C converter 672, the converter 673, the switches SW1 to SW3, and the display unit 652 The figure shows a battery 671, a DC-DC converter 672, a converter 673, and a switch. The switches SW1 to SW3 correspond to the charge / discharge control circuit 670 shown in FIG. 9(B). do.

[0184] First, an example of operation when solar cell 660 generates power using external light will be described. The power generated by the solar cell 660 is converted into a voltage for charging the battery 671. The voltage is increased or decreased by the CDC converter 672. When power is being used from the battery 660, the switch SW1 is turned on, and the converter 673 The voltage is increased or decreased to the voltage required for the display unit 652. When not displaying the battery 671, turn SW1 off and SW2 on. The configuration may be such that electricity is supplied.

[0185] The solar cell 660 is shown as an example of a power generating means, but is not particularly limited thereto. Other power generation methods such as piezoelectric elements (piezoelectric elements) and thermoelectric elements (Peltier elements) For example, the power may be transmitted and received wirelessly (contactlessly). It is also possible to combine it with a contactless power transmission module that charges the battery, or other charging means. You may do so.

[0186] Furthermore, if the power storage device described in the above embodiment is provided, the electric device shown in FIG. It goes without saying that the present invention is not limited to the above.

[0187] (Embodiment 8) Furthermore, an example of a mobile object, which is an example of an electrical device, will be described with reference to FIG.

[0188] The power storage device described in the above embodiment can be used as a battery for control. The battery is charged by external power supply using plug-in technology or wireless power supply. In addition, if the moving object is an electric railway vehicle, power can be supplied from overhead lines or conductive rails. It can be charged by

[0189] 10(A) and (B) show an example of an electric vehicle. The electric vehicle 680 has a battery. The power of the battery 681 is output by a control circuit 682. The force is adjusted and supplied to the drive unit 683. The control circuit 682 includes a ROM (not shown), It is controlled by a processing unit 684 having RAM, a CPU, etc.

[0190] The drive unit 683 is a DC motor or an AC motor alone, or a combination of a motor and an internal combustion engine. The processing device 684 is configured to receive operation information (acceleration , deceleration, stopping, etc.) and driving information (uphill and downhill slopes, load information on the drive wheels, etc.) Based on the input information, the control circuit 682 outputs a control signal to the control circuit 682. The control signal from the processing unit 684 adjusts the electrical energy supplied from the battery 681. In case an AC motor is installed, the output of the drive unit 683 is controlled by adjusting the speed. However, it also has a built-in inverter that converts direct current to alternating current.

[0191] The battery 681 can be charged by an external power supply using plug-in technology. For example, the battery 681 can be charged from a commercial power source through a power plug. It is converted into a constant DC voltage with a constant voltage value through a conversion device such as an AC / DC converter. The power storage device of one embodiment of the present invention is mounted as the battery 681. This will contribute to increasing the capacity of batteries and improve convenience. In addition, by improving the characteristics of the battery 681, the battery 681 itself can be made smaller and lighter. If this is possible, it will contribute to reducing the vehicle's weight, thereby improving fuel efficiency.

[0192] Note that the electric devices are not particularly limited to the above-described electric devices as long as they include the power storage device of one embodiment of the present invention. Needless to say, this is not possible.

[0193] This embodiment mode can be implemented in appropriate combination with other embodiment modes. [Example]

[0194] The present invention will be specifically described below using examples. It is not limited to only

[0195] (Evaluation of coating by XRD) Niobium oxide was analyzed by X-ray diffraction (XRD). Here, graphite was not used, and gel-like niobium was formed by the sol-gel method. The niobium oxide produced by forming a powder was measured by placing it in a crucible and firing it at 600°C for 3 hours. The results of the measurement using X-ray diffraction are shown in FIG.

[0196] In FIG. 11, the horizontal axis represents the X-ray diffraction angle, and the vertical axis represents the X-ray diffraction intensity. The peak in the torr represents the intensity of X-ray reflection from the crystal lattice plane. The higher the intensity and the narrower the half-width, This indicates high crystallinity. The crystal lattice planes correspond to the X-ray diffraction angles, and the crystal structure and If the crystal lattice plane is different, the position where the peak appears in the X-ray diffraction spectrum (diffraction angle 2θ) will be different. do.

[0197] From the measurement results shown in Figure 11, the coating formed by the sol-gel method is in the space group P63 / mmc It was confirmed that the material was Nb2O5 with a hexagonal crystal structure.

[0198] The niobium oxide sample used for this X-ray diffraction measurement was fired at 600°C. However, the same crystalline structure was confirmed even when fired at 500°C. In the case of low-temperature firing at up to 300° C., amorphous fine particles are formed.

[0199] (Preparation of coated graphite granules) Next, a negative electrode active material having a niobium oxide film as a coating was prepared. First, as shown in the second embodiment, graphite manufactured by Nippon Chem. )5 and ethyl acetoacetate, which acts as a stabilizer, are added to toluene and stirred to obtain Nb(OE A toluene solution of Nb(OEt)5 was prepared. The compounding ratio of this solution was 3.14 × 1 0 ―4 mol, ethyl acetoacetate 6.28 x 10 ―4 mol, toluene was 2 ml Next, in a dry room environment, the negative electrode active material, Nb(OEt)5, was dissolved in a toluene solution. Granular graphite was added and stirred. The solution was then kept at 50°C for 3 hours in a humid environment. By doing so, Nb(OEt)5 in a toluene solution containing graphite was dehydrated. That is, the Nb(OEt)5 in the solution was gradually reacted with the moisture in the air. Each of the compounds was subjected to hydrolysis and subsequently condensed by dehydration. Niobium gel was attached to the surface of granular graphite. The mixture was baked for a certain period of time to produce granular graphite covered with a film of niobium oxide.

[0200] (Observation of the coating using an electron microscope) Figures 12 and 13 show SEM (Scanning Electron Microscopy) images of granular graphite. Microscope observation images are shown in Fig. 12(A) and Fig. 12(B). This is an SEM image of unformed granular graphite 700. Figure 12(A) is a 3000x magnification. Figure 12(B) is an SEM image of a part of the same, magnified 5000 times. Approximately 20 μm granular graphite 700 is observed, but the surface is rough and there are smaller particles. The appearance of aggregation is confirmed.

[0201] 13(A) and (B) show the graphite particles shown in FIG. 12, which have been treated with an acid by the sol-gel method. The graphite granules 701 are shown in Figure 13( In the SEM images of (A) and (B), the graphite granules are shown in dark gray. The white, spotted areas on the surface are the areas where the niobium oxide film 702 is formed. In the SEM image, the contrast difference indicates the area where the niobium oxide film is formed and the area where it is formed. The niobium oxide film covers the surface of the granular graphite 701. It was confirmed that it covered only a portion of the surface without completely covering it.

[0202] Next, the cross section of the granular graphite coated with the niobium oxide film by the sol-gel method was measured using a TE Observation by M (Transmission Electron Microscope) TEM images are shown in Figures 14 and 15.

[0203] Figure 14 is a TEM image of the cross section of a single particle of granular graphite 703. Niobium oxide Granular graphite 703 coated with a film was placed on a silicon wafer, and the graphite was used for sample processing and observation. It was covered with a bare film 704 and a tungsten film 706 .

[0204] The layer structure inside the granular graphite 703 can be seen. In the cross section of graphite 703, black niobium oxide films can be seen in places on the outline. do.

[0205] A TEM image obtained by enlarging the area enclosed by the dashed line in FIG. 14 is shown in FIG. 15(A). A niobium oxide film, which appears black in the TEM image, is confirmed on the surface of 03. An enlarged TEM image of the area within the dashed frame in Figure 5(A) is shown in Figure 15(B). The niobium oxide film 705 formed on the surface is formed along the surface of the granular graphite 703. The thin-sectioned specimen for TEM observation has a thickness in the depth direction, and the graphite to be observed is granular. Although it is not easy to evaluate the film thickness due to its shape, the results of this observation indicate that the niobium oxide film 705 The thickness was confirmed to be approximately 10 nm to 20 nm.

[0206] From the above results of electron microscope observations using SEM and TEM, it is clear that sol-gel annealing occurs on the surface of the granular graphite. Niobium oxide films were formed by the sol-gel method. It was found that the niobium oxide film was a very thin film with a thickness of about 10 nm to 20 nm. In addition, the niobium oxide film does not cover the entire surface of the granular graphite, but only partially covers the surface. It was found that there is.

[0207] (CV measurement 1) Next, whether or not the coating film according to the present invention exhibits a lithium ion insertion / extraction reaction is determined by: Confirmed by cyclic voltammetry (CV). I acknowledged it.

[0208] A three-electrode cell was used for CV measurement, and the working electrode was a granular graphite coated with a niobium oxide film. The active material layer was made of a lithium metal, and the reference and counter electrodes were made of a 1M lithium hexafluorophosphate electrolyte. LiPF6 was dissolved in ethylene carbonate (EC) solution (1 mol / L) and diethyl carbonate. The sample was dissolved in a mixture of 1:1 volume of diethyl ether (DEC) and 1:1 volume of diethyl ether (DEC). , Scan rate 0.2 mV / sec, Scan range 0 V to 2.5 V (vs. Li + / Li) for 3 cycles I went there.

[0209] The cyclic voltammogram showing the results of the CV measurement is shown in Figure 16. The measurement results for three cycles are shown for the range of 0V to 2V. This is focused on the potential around 1.5 to 2 V in the cycle. During the insertion, a change in the current value appears within the lower dotted circle in the figure. This indicates that the niobium oxide film covering the surface of the graphite particles reacted with lithium during the insertion of the ions. It is something that is.

[0210] On the other hand, for comparison, the same graphite as above was measured under the same conditions without being coated with a niobium oxide film. The measurement results are shown in FIG. 17. As shown in FIG. 17(B), in the vicinity of 1.5 to 2 V, Therefore, the change in the current value shown in Figure 16(B) is This confirms that this indicates a reaction between niobium and the niobium oxide film.

[0211] (CV measurement 2) Next, to directly confirm the suppression of the reaction between graphite and the electrolyte by the niobium oxide coating, CV measurements were carried out using a HOPG film as the active material.

[0212] HOPG(Highly Oriented Pyrolytic Graphite) Highly oriented pyrolytic graphite (highly oriented pyrolytic graphite) has a thin plate shape and a flat surface, so it can be used as a coating. It is easy to completely cover the surface of the HOPG film with a niobium oxide film.

[0213] For example, FIG. 19 shows a case where a niobium oxide film 781 is formed on a glass substrate 780 by EB evaporation. This is a TEM image of the cross section of the sample. The TEM image has been rotated 90° counterclockwise. The right side of the photograph is the glass substrate 780. The surface of the glass substrate 780 is flat. The niobium oxide film 781 is formed on such a flat surface. As a result, the niobium oxide film 781 can be formed with a substantially uniform thickness (about 30 nm). As a result, the surface of the glass substrate 780 was completely covered with a niobium oxide film. For observation purposes, a carbon film 782 and a platinum film 783 are provided on the niobium oxide film 781 .

[0214] Similarly, a niobium oxide film with a thickness of approximately 10 nm was deposited on a HOPG film with a flat surface by EB evaporation. This resulted in the formation of a niobium oxide film that completely covered the surface of the HOPG film. It was.

[0215] The HOPG film with this coating was used as the working electrode, metallic lithium was used as the reference electrode and counter electrode, and the electrolyte was 1M lithium perchlorate (LiClO4) in ethylene carbonate (EC) solution (1 mo l / L) and diethyl carbonate (DEC) in a volume ratio of 1:1. For comparison, the same CV measurement was performed on an uncoated HOPG film. Measurements were carried out.

[0216] The results of the CV measurement are shown in Figure 18. Figure 18(A) shows the results of the CV measurement in the scanning range of 0V to 2V (vs. Li + / Li), the thick line indicates the HOPG film with a coating, and the thin line indicates the HOPG film without a coating. For comparison, the results for the HOPG film are shown in Fig. 18(B). This is an expanded view of the results for the V to 1.0 V range.

[0217] The surface of the HOPG film is a basal surface with low reactivity, so the value of the current that flows is small. In Figure 18(B), there is a voltage of 0.8 V (vs. Li), which is considered to be the decomposition of the EC / DEC electrolyte. + / Li) can be seen in the electrode using the HOPG film without a coating. However, the peaks of the HOPG film with the niobium oxide film formed on it were not observed. At the electrode, 0.8V (vs. Li + No peak was observed near the peak.

[0218] This suggests that when the negative electrode active material is coated with a niobium oxide film, the decomposition of the electrolyte is suppressed. It was confirmed that this is the case.

[0219] (Cycle characteristics evaluation) Next, a granular material having a niobium oxide film formed as a coating by the sol-gel method as described above was prepared. The negative electrode was fabricated using graphite as the negative electrode active material, and assembled into a full cell to cycle the secondary battery. The characteristics of the capacitor were measured.

[0220] The characteristics were evaluated in the form of a coin cell. The electrolyte was ethylene carbonate (EC). and diethyl carbonate (DEC) in a volume ratio of 1:1. Lithium fluorophosphate (LiPF6) was dissolved at a concentration of 1 mol / L. The separator is made of polypropylene (PP). The charge and discharge rate is 1C (charge in 1 hour). The voltage range was 2V to 4V. The ambient temperature was set to 60°C. went.

[0221] The cycle characteristics were evaluated using a negative electrode that used granular graphite coated with a niobium oxide film as the negative electrode active material. For comparison, the test was carried out on a negative electrode in which granular graphite without a coating was used as the negative electrode active material. Furthermore, for graphite with a niobium oxide film, the weight ratio of niobium oxide to graphite was The weight ratio of niobium oxide to graphite was 2. A sample with a concentration of 0.0 wt% was prepared.

[0222] The measurement results of the cycle characteristics are shown in Figure 20. The horizontal axis shows the number of cycles (times), and the vertical axis shows the secondary current. The discharge capacity (mAh / g) of the battery is shown. An electrode with a niobium weight ratio of 2.0 wt% and an electrode without a niobium oxide film were prepared. The number of measurement samples was n = 2. In the figure, the weight ratio of niobium oxide was set to 0.5 wt%. The cycle characteristics of the electrode are shown by curves 810a and 810b, and the weight ratio of niobium oxide is 2.0 wt. The cycle characteristics of the electrode with t% niobium oxide film are shown by curves 820a and 820b. The cycling characteristics of the uncharged electrode are shown by curves 830a and 830b.

[0223] As a result of the measurement, as shown by curves 830a and 830b, the grains without the coating made of niobium oxide were In the case of secondary batteries that use graphite as the negative electrode active material, the discharge capacity decreases as the number of cycles increases. In other words, the deterioration was significant.

[0224] In contrast, as shown by curves 810a, 810b, 820a, and 820b, the niobium oxide film In secondary batteries using granular graphite coated with However, there is no significant decrease in capacity compared to those without a coating, and there is no sign of deterioration. In particular, the deterioration was suppressed under the condition of an environmental temperature of 60°C. This has made it possible to improve cycle characteristics.

[0225] Furthermore, curves 810a and 810b show the results for the electrode containing 0.5 wt % niobium oxide. b and curves 820a and 820b, which are the results of an electrode with a weight ratio of niobium oxide of 2.0 wt %. In comparison, the electrode with 0.5 wt% niobium oxide maintains a higher discharge capacity. In addition, the charge-discharge efficiency per cycle was higher than that of a battery without a niobium oxide film. The electrode with a weight ratio of niobium oxide of 0.5 wt% had a 99.4%. The electrode with a weight ratio of niobium oxide of 2.0 wt% was 99.5%. Therefore, when a coating is used, the charge / discharge efficiency is improved compared to when no coating is used. Understood.

[0226] (evaluation) From the above, it is possible to prevent the occurrence of irreversible capacity that causes a decrease in the initial capacity of lithium-ion batteries. This reduced the amount of electrolyte in the negative electrode, and suppressed the electrochemical decomposition of the electrolyte. When a lithium-ion battery is repeatedly charged and discharged, the electrolyte, etc., is depleted as a side reaction during charging and discharging. By suppressing the decomposition reaction, the cycle characteristics of lithium-ion batteries can be improved. In addition, the decomposition reaction of the electrolyte, which accelerates at high temperatures, is suppressed, and the capacity during high-temperature charge and discharge is improved. Preventing this decrease makes it possible to expand the temperature range in which lithium-ion batteries can be used. [Example]

[0227] In this example, a negative electrode for a power storage device coated with silicon oxide was actually produced, and a A model of deterioration of the power storage device will be described.

[0228] (Example of electricity storage device) As an example, a negative electrode for a power storage device that was actually fabricated and a power storage device using the negative electrode will be described. do.

[0229] In this example, graphite particles on which silicon oxide was formed were prepared using a sol-gel method. The lead particles used were graphite manufactured by JFE Chemical Corporation. Add ethyl acetoacetate and toluene and stir to prepare a Si(OEt)4 toluene solution. At this time, the ratio of silicon oxide to be generated later was 1 wt% (weight percentage) of graphite. The amount of Si(OEt)4 was determined so that the solution would be 100% pure. Et)4 to 3.14 × 10 -4 mol, ethyl acetoacetate 6.28 x 10 -4 mol, Next, in a dry room environment, Si(OEt)4 toluene was added to 2 mL. Graphite was added to the solution and stirred. After this, the solution was kept at 70°C for 3 hours in a humid environment. By doing so, the Si(OEt)4 in the toluene solution containing graphite was dehydrated. That is, the Si(OEt)4 in the solution was gradually reacted with the moisture in the air to form a decomposition reaction and a condensation reaction. The mixture was then subjected to hydrolysis and subsequent dehydration to condense. The graphite is then baked at 500°C for 3 hours under atmospheric pressure, and a film of silicon oxide is formed. We prepared an electrode material containing particles. Furthermore, we mixed the electrode material with acetylene black and PVDF. The slurry formed by mixing the above is applied to a current collector and dried to form an electrode (also called electrode 1). The weight ratio of PVDF to graphite was 10 wt%.

[0230] When the electrode 1 was observed using a scanning electron microscope (also known as SEM), several It was found that particles were formed, and the average particle size of the multiple particles was approximately 9 μm.

[0231] In addition, observation of electrode 1 using a scanning transmission electron microscope (also known as STEM) and energy dispersive electron microscopy (EEM) were performed. The results of EDX showed that silicon was present in a portion of the surface area of ​​electrode 1. On the other hand, no silicon was detected in the EDX results of another area. This indicates that silicon oxide is formed on only part of the particle surface, not on the entire surface. It was found that this had been done.

[0232] (Cycle characteristics evaluation) a negative electrode using graphite particles on which silicon oxide is formed using the sol-gel method as a negative electrode active material; Batteries were fabricated using a positive electrode made of LiPO4 and a positive electrode made of LiPO4, and their cycle characteristics were compared.

[0233] The characteristics were evaluated in the form of a coin cell. The electrolyte was ethylene carbonate (EC). and diethyl carbonate (DEC) in a volume ratio of 3:7. The electrolyte used was lithium fluorophosphate (LiPF6) dissolved at a concentration of 1 mol / L. Polypropylene (PP) was used for the separator. The charge and discharge rate was 1C (charge in 1 hour). The test was performed in a voltage range of 2 V to 4 V. The ambient temperatures were 25°C, 50°C, 60°C, The cycle characteristics were measured at 70°C or 85°C for two samples each.

[0234] The data showing the cycle characteristics are shown in Figure 21. The horizontal axis shows the number of cycles (times), and the vertical axis shows the secondary As shown in Figure 21, as the ambient temperature increases, the discharge capacity of the battery decreases with the number of cycles. The decrease in capacity was observed to be significant.

[0235] For example, for a sample with an environmental temperature of 60°C, the change in the initial discharge capacity is calculated using a linear function. When approximating the value, the difference with the actual measurement became larger as the number of cycles increased. Even when the exponential function is used for approximation, the difference with the actual measurement increases as the number of cycles increases. (See Figure 22).

[0236] Therefore, we developed a model that has a small difference from the actual measurement even when the number of cycles increases, and we investigated the effect of changes in the environmental temperature. This was considered based on the tendency of the discharge capacity to decrease.

[0237] In the following, it is assumed that the decrease in discharge capacity of the secondary battery is caused entirely by the decomposition of solvent molecules. As shown in FIG. 23, in the sample of this example, there are four types of lithium ions in the electrolyte. When lithium ions are absorbed into the negative electrode, some of the solvent molecules are It is immediately decomposed on the surface of the negative electrode and forms a film (SEI). By repeating this process, the film Even when the entire negative electrode is covered with a film, the solvent molecules diffuse through the film. As a result, some of the film reaches the surface of the negative electrode. While growing.

[0238] When the above-mentioned film formation model is established, the film formation rate, i.e., the decomposition rate of the solvent molecules, It is believed that the diffusion coefficient of the solvent molecules in the coating can be determined. The diffusion distance of the solvent molecules can be expressed by Equation 5.

[0239]

number

[0240] where D is the diffusion coefficient of the solvent molecules in the coating, and t is the time for one charging cycle. Shows.

[0241] Therefore, when the thickness of the coating is T, the frequency with which the solvent molecules diffused in the coating reach the negative electrode surface is The degree is given by Equation 6.

[0242]

number

[0243] If the amount of charge required for film growth is B, the change in charge capacity q due to the number of cycles is expressed by the formula: It is represented as 7.

[0244]

number

[0245] Furthermore, t is expressed as in Equation 8, where C is the charge rate and q0 is the initial charge capacity.

[0246]

number

[0247] Therefore, the film growth per cycle is given by Equation 9.

[0248]

number

[0249] Here, A is a constant determined by the surface area of ​​the negative electrode, the concentration of the electrolyte, etc.

[0250] Using the formula 9 obtained above, we first calculate the cycle time for the sample with an environmental temperature of 60°C. The constant A was derived by analyzing the characteristics. Next, the analysis was performed based on the constant A obtained by the analysis. The diffusion coefficient D at other environmental temperatures was derived by using the above method. 24 is shown by a dashed line. From FIG. 24, the cycle characteristics obtained by measurement using this model are (solid line) was roughly reproduced.

[0251] As described above, by using a model that takes into account the diffusion of solvent molecules in the coating, the Therefore, it was concluded that one of the causes of the decrease in discharge capacity of the secondary battery is the solvent. It was found that this was caused by molecular decomposition and the resulting formation of a coating.

[0252] In addition, by applying this model, it is possible to measure the cycle characteristics at one environmental temperature. Therefore, it is possible to predict the cycle characteristics at other environmental temperatures. For example, when sampling to fabricate a secondary battery, the This allows the evaluation to be performed in a short time, thereby improving the productivity of secondary batteries. Cut.

[0253] Next, the vertical axis is the fitting coefficient (coefficients including the constant A and the diffusion coefficient D) and the horizontal axis is the temperature. An Arrhenius plot with a logarithmic vertical axis was then performed (see Figure 25). It was found that the Rhenius plot had an error with respect to the approximate straight line. This suggests that there are other factors that affect the decrease in discharge capacity besides the decomposition of solvent molecules as shown in the graph. However, as shown in Figure 24, the cycle characteristics were roughly reproducible. Therefore, it is believed to be a very useful model for understanding the degradation of secondary batteries. [Example]

[0254] In this example, cycle characteristics of a lithium-ion secondary battery using an electrode according to one embodiment of the present invention were evaluated. The results of the evaluation of the effectiveness are explained below.

[0255] First, a method for producing the electrode used as the negative electrode will be described.

[0256] First, graphite manufactured by JFE Chemical Corporation was used as the active material, and PVDF was used as the binder. A slurry of graphite and PVDF in a ratio of 90:10 was prepared. As the solvent, NMP was used.

[0257] Copper foil was used as the current collector, and a slurry containing graphite was applied to the current collector, which was then dried at 70°C. After drying, the mixture was dried in a vacuum atmosphere at 170°C for 10 hours. A material layer was formed.

[0258] Next, the current collector on which the active material layer was formed was punched out into a circular shape to form electrodes D1 and D2. Successful.

[0259] In addition, electrodes E1 to E4, electrodes F1 to F4, and electrodes G1 to G3 are created which are different from the electrodes D1 and D2. Made.

[0260] First, Si(OEt)4, ethyl acetoacetate, and toluene were added and stirred to obtain Si( A toluene solution of Si(OEt)4 was prepared. The compounding ratio of this solution was 3.14 x10 -4 mol, ethyl acetoacetate 6.28 x 10 -4 mol, toluene 2 mL The amount of Si(OEt)4 was determined by the ratio of silicon oxide generated later to graphite. There are three types, 1 weight%, 3 weight%, and 10 weight%. The conditions were met.

[0261] Next, graphite was added to the Si(OEt)4 toluene solution in a dry room and stirred. After this, the solution was kept at 70°C for 3 hours in a humid environment, and graphite was added. The hydrolysis and condensation reactions of Si(OEt)4 in toluene solution were carried out. That is, Si(OEt)4 in the solution is gradually hydrolyzed with moisture in the air, and the resulting In this way, a gel-like substance was formed on the surface of the graphite particles. Silicon was deposited to form a network of bonds consisting of CO—Si.

[0262] Then, it is baked at 500°C for 3 hours in a nitrogen atmosphere, and silicon oxide is coated. Three types of graphite were produced.

[0263] It is made by kneading graphite coated with 1 weight percent silicon oxide with PVDF. A slurry was formed, which was then applied to a current collector and dried to form an active material layer. The weight ratio of PVDF was 90:10. NMP was used as the solvent for the slurry. The current collector on which the active material layer is formed is punched into a circular shape to form electrodes E1, E2, and E3. , and electrode E4 were formed.

[0264] Also, it is made by kneading graphite coated with 3 weight percent silicon oxide with PVDF. The resulting slurry was applied to a current collector and dried to form an active material layer. The weight ratio of graphite to PVDF was 90:10. NMP was used as the solvent for the slurry. Next, the current collector on which the active material layer was formed was punched into a circle to form electrodes F1, F2, and F3. Electrode F3 and electrode F4 were formed.

[0265] In addition, graphite coated with 10% by weight of silicon oxide and PVDF were mixed and formed. The resulting slurry was applied to a current collector and dried to form an active material layer. The weight ratio of graphite to PVDF was 90:10. NMP was used as the solvent for the slurry. Next, the current collector on which the active material layer was formed was punched into a circle to obtain electrodes G1, G2, and G3. and electrode G3.

[0266] Furthermore, electrodes H1 to H3 different from the above-mentioned electrodes were fabricated.

[0267] First, Si(OEt)4, ethyl acetoacetate, and toluene were added and stirred to obtain Si( A toluene solution of 4OEt was prepared. At this time, the proportion of silicon oxide generated later was black. The amount of Si(OEt)4 was determined to be 3 weight percent of lead. The compounding ratio is Si(OEt)4 3.14 × 10 -4 6.28 mol of ethyl acetoacetate x10 -4 mol, and toluene was 2 ml.

[0268] Next, graphite was added to the Si(OEt)4 toluene solution in a dry room and stirred. After this, the solution was kept at 70°C for 3 hours in a humid environment, and graphite was added. The hydrolysis and condensation reactions of Si(OEt)4 in toluene solution were carried out. That is, Si(OEt)4 in the solution is gradually hydrolyzed with moisture in the air, and the resulting The resulting condensation was followed by a dehydration reaction.

[0269] Then, it is baked at 500°C for 3 hours in a nitrogen atmosphere, and silicon oxide is coated. We produced graphite using this method.

[0270] Graphite coated with 3 weight percent silicon oxide, PVDF, and acetylene black (AB) and the mixture are mixed to form a slurry, which is then applied to a current collector and dried to form an active material. At this time, the weight ratio of graphite, PVDF, and AB was 88:10:2. NMP was used as the solvent for the slurry. Next, the current collector on which the active material layer was formed was By punching out circles, electrodes H1, H2, and H3 were formed.

[0271] Next, the electrode D1 prepared in the above process was used as a negative electrode, and a full-scale After assembling the cells, the cells were charged and discharged once to produce a secondary battery D1. The characteristics of the electrodes D2, E1 to E3, F1 to F3, and G1 to G3 were also measured. Similarly, for the electrodes H1 to H3, the secondary batteries D2, E1 to E3, F1 to F3, G1 to G 3, H1 to H3 were fabricated. Then, for each lithium-ion secondary battery, The cycle characteristics were also measured.

[0272] The characteristics were evaluated in the form of a coin cell. The positive electrode was an electrode with LiFePO4 as the active material. The electrolyte contains ethylene carbonate (EC) and diethyl carbonate (DEC). Add 1 part of lithium hexafluorophosphate (LiPF6) to the mixed solution in a volume ratio of 1:1. The separator was made of polypropylene (PP). The first cycle was charged and discharged at a rate of 0.2C (charging in 5 hours), and the second cycle was The charge and discharge rate after the first cycle was 1C (1 hour charge). Also, the charge and discharge rate was 0.2C every 200 cycles. The charge and discharge were performed at a rate of 1000 kJ / s (charged for 5 hours) and the discharge capacity was confirmed. The voltage range was 2 V to 4 V. The environmental temperature was set to 60° C. during the measurements.

[0273] Electrode D1, electrode D2, electrodes E1 to E3, electrodes F1 to F3, and electrodes G1 to G3 were used as negative electrodes. The measurement results of the cycle characteristics of the secondary battery are shown in FIG. 26. The horizontal axis indicates the number of cycles (times), and the vertical axis indicates the number of cycles (times). The axis indicates the discharge capacity (mAh / g) of the secondary battery.

[0274] As can be seen from Figure 26, the secondary battery using electrodes with a higher silicon oxide coverage shows a longer life with respect to the number of cycles. It was found that this resulted in a significant decrease in discharge capacity.

[0275] Next, the measurement results of the cycle characteristics of secondary batteries using electrodes F1 to F3 and electrodes H1 to H3 as negative electrodes were The results are shown in Figure 27. The horizontal axis shows the number of cycles (times), and the vertical axis shows the discharge capacity (mAh / g).

[0276] As can be seen from FIG. 27, the discharge capacity of electrodes F1 to F3 decreases with the number of cycles more than that of electrodes H1 to H3. This is because the electrode with a silicon oxide coverage of 3 weight percent F1 to F3 have poor current collection properties because the silicon oxide coating prevents the graphite particles from conducting. On the other hand, electrodes H1 to H3 containing acetylene black exhibited a decrease in the amount of silicon oxide. Even though the capacitor is coated, the conductivity to the graphite particles is ensured, and it is thought that the decrease in current collection performance is suppressed. can be done.

[0277] (Observation of electrodes E4 and F4 using an electron microscope) FIG. 28 shows SEM images of electrodes E4 and F4. 28(B) shows an SEM image of electrode E4, and FIG. 28(C) shows an SEM image of electrode F4. The SEM observation image shown in FIG. 28(A) and the SEM observation image shown in FIG. 28(B) are The images were observed at the same magnification.

[0278] In the electrode E4 shown in FIG. 28(A), a small amount of silicon oxide is formed on the surface graphite. It was confirmed that this was the case.

[0279] The electrode F4 shown in FIG. 28(B) has a larger area than the electrode E4 shown in FIG. 28(A). It was confirmed that silicon oxide was formed in the [Example]

[0280] In this embodiment, a laminated lithium ion battery (also called a laminated cell) and a We fabricated a coin-type lithium-ion battery (also called a coin cell) and evaluated its battery characteristics. Explain the results.

[0281] (Preparation of positive electrode) Lithium iron phosphate (LiFePO4) with a carbon layer on its surface was used as the positive electrode active material. First, lithium iron phosphate and glucose were mixed in acetone, and the mixture was dried. The mixture was then baked at 600°C to obtain a positive electrode active material.

[0282] Next, the positive electrode active material and NMP (N-methyl-pyrrolidone) as a polar solvent were mixed in a kneader. The mixture was stirred and mixed at 2000 rpm for 5 minutes, and then ultrasonic vibration was applied for 3 minutes. The mixture was stirred and mixed at 100 rpm for 1 minute and then subjected to ultrasonic vibration for 3 minutes twice. Next, graphene oxide was added to the mixture, and the mixture was kneaded at 2000 rpm for 5 minutes. After that, PVDF was added as a binder and the mixture was mixed in a kneader for 20 minutes. The mixture was stirred and mixed at 1000 rpm for 5 minutes, and then NMP was added to adjust the viscosity. The mixture was stirred and mixed at 1000 rpm for 1 minute. The resulting mixture was the same as that obtained by removing the polar solvent. The ratio of carbon-layered lithium iron phosphate, graphene oxide, and PVDF was 94.4:0. The ratio was adjusted by weighing to 6:5 (unit: weight %).

[0283] The mixture thus formed was applied to an aluminum foil serving as a current collector. After air drying to volatilize the polar solvent, the active material layer was compressed by a press.

[0284] Next, the electrode is dried by heating at 170°C for 10 hours under a reduced pressure atmosphere. Graphene oxide was reduced to form graphene that functions as a conductive additive.

[0285] Thereafter, the active material layer was compressed by pressing again so that the gap was the same as that of the previous press. This was punched out to prepare a positive electrode for a secondary battery.

[0286] (Preparation of negative electrode) As the negative electrode active material, graphite covered with a film made of silicon oxide was used. The graphite used was mesocarbon microspheres (MCMB) manufactured by JFE Chemical Corporation with an average particle size of 9 μm. First, Si(OEt)4 and hydrochloric acid, which acts as a catalyst, are mixed with water and ethanol. The mixture was stirred to prepare a Si(OEt)4 solution. OEt)4 to 1.8 × 10 -2 mol, hydrochloric acid 4.44 x 10 -4 mol, water 1.9ml Next, in a dry room environment, the Si(OEt)4 solution was dissolved in 6.3 ml of ethanol. Granular graphite, which is the negative electrode active material, was added to the solution and stirred. By keeping the solution at ℃ for 20 hours, the graphite-added Si(OEt)4 water and ethanol were The Si(OEt)4 in the mixed solution was subjected to hydrolysis and condensation reactions. The Si(OEt)4 reacts slowly with atmospheric moisture through hydrolysis, followed by dehydration. In this way, gel-like silicon oxide was attached to the surface of the granular graphite. After that, it was dried in air at 500°C for 3 hours, and the silicon oxide Granular graphite covered with a coating was prepared.

[0287] The negative electrode active material having the silicon oxide film thus prepared and PVDF as a binder were used. As a polar solvent, NMP (N-methyl-pyrrolidone) was prepared. The mixture was prepared by stirring and mixing three times at 2000 rpm for 10 minutes. The compounding ratio excluding the polar solvent was negative electrode active material: PVDF = 90:10 (unit: weight %) and adjusted accordingly.

[0288] The mixture thus formed was applied to a copper foil as a current collector. The polar solvent was evaporated.

[0289] Thereafter, the active material layer was compressed by a press and punched out to produce a negative electrode for a secondary battery. .

[0290] (Fabrication of laminated lithium-ion batteries) First, the positive electrode and the negative electrode were cut into rectangular shapes of 50 mm x 41 mm and 53 mm x 45 mm, respectively. The formed positive and negative electrodes had protrusions that functioned as terminals. The active material layer on the protruding portions was removed to expose the current collector.

[0291] Next, a pouch-shaped separator was provided so as to enclose the positive electrode except for the protruding portion. Polypropylene (PP) was used for the separator. The active material layers are stacked so as to face each other, and a laminate in which eight pairs of electrodes are stacked is formed. Then, aluminum foil was used as the positive electrode terminal and nickel-plated aluminum foil was used as the negative electrode terminal. The copper foil was welded to the protrusions by ultrasonic welding. , in order to fill the gap between the laminate film and the electrode terminal, the laminate film is heated and pressed. Resin was previously applied to the area that would overlap the adhesive portion.

[0292] Next, the laminate is sandwiched between laminate films in which aluminum foil is sandwiched between resin films, The laminate film was heat-pressed to form a bag-like shape, except for one side. The sample was dried in this state under a reduced pressure atmosphere (differential pressure of approximately -100 kPa) at 70°C for 10 hours. After that, the electrolyte was injected into the laminate film in a dry atmosphere. Ethyl carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 3:7. Lithium hexafluorophosphate (LiPF6) was dissolved in the mixed solution at a concentration of 1 mol / L. After that, the laminate film was placed under a reduced pressure (differential pressure of about -60 kPa). By thermocompressing the one side of the battery that is not thermocompressed, a laminated lithium-ion battery was produced.

[0293] Figure 29(A) shows a photograph of the laminated lithium ion battery that was fabricated. FIG. 29B) shows a schematic diagram of the laminated lithium ion battery shown in FIG. 29A.

[0294] By this method, Samples 1, 3, 6, and 7 were prepared.

[0295] (Making a coin-type lithium-ion battery) First, the above-mentioned negative electrode was heated at a temperature of 170°C for 10 hours in a reduced pressure atmosphere to dry the electrode. Next, the positive electrode, negative electrode, and separator were cut into a circle. The CR2032 type (diameter 20 mm, height 3.2 mm) was used. The separator impregnated with cellulose and the negative electrode are stacked and placed in a stainless steel (SUS) positive electrode can and The negative electrode can and the negative electrode can are placed between them, and by crimping them together, a coin-type lithium-ion battery is produced. Ta.

[0296] In this way, Sample 2, Sample 4, Sample 5, Sample 8, Sample 9 , Sample 10 was prepared.

[0297] (Discharge characteristics) First, the discharge characteristics of laminated sample 1 and coin-shaped sample 2 were evaluated. The charge was CCCV charged at a rate of 0.2C, with the upper limit voltage set to 4.0V. The discharge was 0.2 CC discharge was performed at rates of C, 1C, 2C, and 5C, with the lower limit voltage being 2V. The measurement temperature was 25°C. The supported amount and volume ratio are shown in Table 1.

[0298] [Table 1]

[0299] The measurement results of the discharge characteristics are shown in Figure 30(A). The horizontal axis represents the discharge capacity per weight of active material (unit: The vertical axis indicates the capacity (mAh / g), and the vertical axis indicates the voltage (unit: V). The results for the coin-shaped sample 2 are shown by the solid line, and the results for the coin-shaped sample 2 are shown by the dashed line. 30(B) shows the discharge capacity and 1C discharge rate calculated from the results of FIG. 30(A). The capacity ratio is shown.

[0300] Both the laminated and coin-shaped samples showed an increase in capacity as the discharge rate increased. It was confirmed that the amount of cellulose decreased, and the same tendency was observed regardless of the shape of the sample.

[0301] (Discharge characteristics at low temperatures) Next, the discharge characteristics were evaluated under three conditions of temperature during discharge: -25°C, 0°C, and 25°C. The charging was carried out in the same manner as above, and the discharging was carried out at a rate of 0.2C. The experiment was carried out using the coin-shaped sample 3 and the coin-shaped sample 4 and sample 5. For the 25°C and 0°C samples, sample 4 was used for evaluation, and the -25°C The evaluation was carried out using Sample 5. The amount of the positive electrode, the amount of the negative electrode, and the amount of the positive electrode of each sample were The capacity ratio is shown in Table 2.

[0302] [Table 2]

[0303] The measurement results of the discharge characteristics are shown in Figure 31. As in Figure 30, the results for laminated sample 3 are shown in Figure 31. The solid line shows the results for coin-shaped Samples 4 and 5, and the dashed line shows the results for coin-shaped Samples 4 and 5.

[0304] For both the laminated and coin-shaped samples, the lower the evaluation temperature, the lower the capacity. It was confirmed that the same tendency was observed regardless of the shape of the sample.

[0305] (Cycle characteristics) Next, the discharge capacity cycles of the laminated sample and the coin-shaped sample were measured. The charging and discharging was performed at a rate of 1C, and the voltage range was 2V to 4V. The temperature was set to 60°C and the measurement was carried out. The evaluation was carried out on laminated sample 6, sample 7, and The in-type samples 8, 9, and 10 were used. The amounts of the supported metals on the positive and negative electrodes and the capacity ratios are shown in Table 3.

[0306] [Table 3]

[0307] The measurement results of the cycle characteristics are shown in Figure 32. The horizontal axis shows the number of cycles (times), and the vertical axis shows the secondary current. The discharge capacity (mAh / g) of the battery is shown.

[0308] From Figure 32, it can be seen that both the laminated sample and the coin-shaped sample The initial discharge capacity values ​​were similar for all samples. It was confirmed that the capacity decreased as the sample size increased, and the same tendency was observed regardless of the shape of the sample. In sample 10, the discharge capacity at 500 cycles was It was about 64%.

[0309] This embodiment may be implemented in appropriate combination with other embodiments and embodiments described in this specification. It is possible. [Explanation of symbols]

[0310] 101 Negative electrode active material 102 Coating 200 negative electrode 201 Negative electrode current collector 202 Negative electrode active material layer 203 Negative electrode active material 204 Conductive additives 205 Graphene 250 positive electrode 251 Positive electrode current collector 252 Cathode active material layer 253 Cathode active material 254 Graphene 300 Lithium-ion battery 301 Positive electrode can 302 Anode can 303 Gasket 304 Positive electrode 305 Positive electrode current collector 306 Positive electrode active material layer 307 Negative electrode 308 Negative electrode current collector 309 Negative electrode active material layer 310 Separator 400 Lithium-ion battery 401 Positive electrode current collector 402 Cathode active material layer 403 Positive electrode 404 Negative electrode current collector 405 Negative electrode active material layer 406 negative electrode 407 Separator 408 Electrolyte 409 Exterior body 500 Lithium-ion battery 501 Positive electrode cap 502 Battery can 503 Positive terminal 504 Positive electrode 505 Separator 506 negative electrode 507 Negative terminal 508 Insulating plate 509 Insulating board 510 Gasket (insulating packing) 511 PTC element 512 Safety valve mechanism 600 display device 601 Case 602 Display section 603 Speaker section 604 Electricity storage device 610 Lighting Equipment 611 Case 612 Light source 613 Energy storage device 614 Ceiling 615 Side wall 616 beds 617 Window 620 Indoor unit 621 Case 622 Ventilation vent 623 Energy storage device 624 Outdoor unit 630 Electric refrigerator-freezer 631 Case 632 Refrigerator door 633 Freezer door 634 Energy storage device 650 tablet devices 651 Case 652 Display section 652a Display section 652b Display section 653 Display mode switch 654 Power Switch 655 Power saving mode switch 656 Operation switch 657a area 657b area 658 Operation Key 659 Keyboard display switch button 660 solar cells 670 Charge / Discharge Control Circuit 671 Battery 672 DC-DC converter 673 Converter 680 Electric Vehicles 681 Battery 682 Control Circuit 683 Drive Unit 684 Processing equipment 700 Granular Graphite 701 Granular graphite 702 Niobium oxide film 703 Granular graphite 704 Carbon Film 705 Niobium oxide film 706 Tungsten film 780 Glass Substrate 781 Niobium oxide film 782 Carbon Film 783 Platinum film

Claims

1. a negative electrode current collector; a negative electrode active material layer on the negative electrode current collector, the negative electrode active material layer having a plurality of particles of negative electrode active material; a coating that covers a portion of the granular negative electrode active material, The negative electrode for an electricity storage device, wherein the coating is a film having insulating properties and lithium ion conductivity.

2. a negative electrode current collector; a negative electrode active material layer on the negative electrode current collector, the negative electrode active material layer including a plurality of granular graphite particles; a coating that covers a portion of the granular graphite, The negative electrode for an electricity storage device, wherein the coating is a film having insulating properties and lithium ion conductivity.

3. In claim 1 or 2, The coating is an oxide film of any one of niobium, titanium, vanadium, tantalum, tungsten, zirconium, molybdenum, hafnium, chromium, aluminum, and silicon, or an oxide film containing any one of these elements and lithium.

4. In claim 1 or 2, The coating is made of Nb having a hexagonal crystal structure. ２ O ５ The negative electrode for an electricity storage device is

5. In any one of claims 1 to 4, The negative electrode for an electricity storage device, wherein the coating has a thickness of 5 nm or more and 50 nm or less.

6. An electricity storage device using the electricity storage device negative electrode according to claim 1 .

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