Method for manufacturing an electrode

Abstract

Provided is a method for producing a novel electrode. According to the present invention: a mixture that includes an active material, an electrically conductive auxiliary agent having a graphene compound, a binding agent, and a dispersion medium is applied to a current collector; a drying treatment is performed on the mixture; a heat treatment is performed on the mixture at a higher temperature than that in the drying treatment; the graphene compound in the mixture is reduced through a chemical reaction in which a reducing agent is used; and a heat reduction treatment is performed on the mixture at a temperature higher than that in the heat treatment.

Description

Technical Field

[0001] One aspect of the present invention relates to an electrode for a secondary battery, a positive electrode for a secondary battery, a secondary battery, and a method for manufacturing the same. Alternatively, the present invention relates to an article, a process, a machine, a manufacture, or a composition of matter. One aspect of the present invention relates to a semiconductor device, a display device, a light-emitting device, a power storage device, a lighting device, or an electronic device, or a method for manufacturing the same.

[0002] In the present specification, the power storage device refers to an element and a device having a power storage function in general. For example, it includes storage batteries (also referred to as secondary batteries) such as lithium-ion secondary batteries, lithium-ion capacitors, all-solid-state batteries, and electric double-layer capacitors.

[0003] In the present specification, the electronic device refers to a device having a power storage device in general, and an electro-optical device having a power storage device, an information terminal device having a power storage device, etc. are all electronic devices.

Background Art

[0004] In recent years, the development of various power storage devices such as lithium-ion secondary batteries, lithium-ion capacitors, air batteries, and all-solid-state batteries has been actively carried out. In particular, lithium-ion secondary batteries with high output and high capacity have rapidly expanded their demand along with the development of the semiconductor industry, such as portable information terminals such as mobile phones, smartphones, or notebook computers, portable music players, digital cameras, medical devices, or next-generation clean energy vehicles such as hybrid vehicles (HV), electric vehicles (EV), or plug-in hybrid vehicles (PHV), and have become indispensable in modern information society as a rechargeable energy supply source.

[0005] A lithium-ion secondary battery has at least a positive electrode and a negative electrode having an active material capable of reversibly inserting and extracting lithium ions, a separator positioned between the positive electrode and the negative electrode, and a non-aqueous electrolyte.

[0006] The positive electrode has a positive electrode active material and a positive electrode current collector, and is formed by applying a positive electrode slurry containing a conductive assistant, a binder, and a positive electrode active material to the positive electrode current collector. Similarly, the negative electrode has a negative electrode active material and a negative electrode current collector, and is formed by applying a negative electrode slurry containing a conductive assistant, a binder, and a negative electrode active material to the negative electrode current collector.

[0007] Here, the conductive assistant is added to efficiently obtain a conductive path from the active material to the current collector. However, if the content of the conductive assistant in the positive electrode or the negative electrode is large, the amount of the active material per unit electrode weight decreases, resulting in a decrease in the battery capacity. Therefore, there is a need for a highly conductive conductive assistant that can ensure an efficient conductive path with a small amount.

[0008] Therefore, in Patent Document 1, by mixing a conductive assistant such as acetylene black (AB) or graphite (carbon) particles, the electron conductivity between the active materials or between the active material and the current collector is improved. This enables the provision of a positive electrode active material with high electron conductivity.

[0009] However, generally used particulate conductive assistants such as acetylene black have a relatively large average particle size of several tens of nanometers to several hundreds of nanometers, making it difficult to achieve surface contact with the active material and prone to point contact. For this reason, the contact resistance between the active material and the conductive assistant is high. On the other hand, if the amount of the conductive assistant is increased to increase the contact points between the active material and the conductive assistant, the ratio of the amount of the active material in the electrode decreases, and the charge-discharge capacity of the battery decreases.

[0010] In contrast, Patent Document 2 discloses using a single layer or laminate of graphene (referred to as two-dimensional carbon in the document) as a conductive assistant instead of a particulate conductive assistant such as acetylene black. Since the single layer or laminate of graphene has a two-dimensional spread, it improves the adhesion between the active material and the conductive assistant, as well as between the conductive assistants, thereby improving the conductivity of the electrode.

[0011] Graphene is a carbon material that is expected to be applied in various fields such as field effect transistors and solar cells using graphene because it has electrically, mechanically, or chemically amazing properties. However, graphene is known to be difficult to disperse. In order to utilize graphene as a conductive aid, it is necessary to disperse graphene. Non-Patent Document 1 discloses an example of producing graphene by reducing graphene oxide (GO: Graphene Oxide) with thiourea. Note that the graphene obtained by reducing graphene oxide as described above is called RGO (Reduced Graphene Oxide).

Prior Art Documents

Patent Documents

[0012]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0013]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0014] As described above, since graphene has a high specific surface area, it is difficult to disperse, and graphene may aggregate. When aggregated graphene is used as a conductive aid, it is difficult to function sufficiently as a conductive aid. In addition, since RGO has many defect structures due to oxidation and reduction, its conductivity is a concern. Therefore, a method is required in which the active material and the conductive aid do not peel off even after the reduction treatment.

[0015] In view of the above, an aspect of the present invention aims to provide a novel method for manufacturing a positive electrode. Alternatively, an aspect of the present invention aims to provide a novel power storage device. Further, an aspect of the present invention aims to provide a novel positive electrode slurry. Additionally, an aspect of the present invention aims to provide a novel positive electrode.

[0016] Note that the description of these problems does not preclude the existence of other problems. It should be noted that an aspect of the present invention does not necessarily need to solve all of these problems. It is possible to extract other problems from the descriptions in the specification, drawings, and claims.

Means for Solving the Problems

[0017] In one aspect of the present invention, a mixture containing an active material, a conductive assistant having a graphene compound, a binder, and a dispersion medium is applied to a current collector, the mixture is subjected to a drying treatment, the mixture is subjected to a heat treatment at a temperature higher than that of the drying treatment, the graphene compound in the mixture is reduced by a chemical reaction using a reducing agent, and the mixture is subjected to a thermal reduction treatment at a temperature higher than that of the heat treatment.

[0018] In one aspect of the present invention, a mixture containing an active material, a conductive assistant having a graphene compound, a binder, and a dispersion medium is applied to a current collector, the mixture is subjected to a drying treatment, the mixture is subjected to a heat treatment at a temperature higher than that of the drying treatment and for a longer time than the drying treatment, the graphene compound in the mixture is reduced by a chemical reaction using a reducing agent, and the mixture is subjected to a thermal reduction treatment at a temperature higher than that of the heat treatment.

[0019] In the above configuration, the temperature of the drying treatment is from R.T. to 90°C.

[0020] In the above configuration, the temperature of the heat treatment is from 120°C to 140°C.

[0021] In the above configuration, the temperature of the thermal reduction treatment is from 120°C to 180°C.

[0022] In the above configuration, the temperature of the heat treatment is 120°C or higher and 140°C or lower, and the temperature of the thermal reduction treatment is 120°C or higher and 180°C or lower.

[0023] In the above configuration, the graphene compound is RGO.

Advantages of the Invention

[0024] According to one aspect of the present invention, a novel method for manufacturing a positive electrode can be provided. Further, according to one aspect of the present invention, a novel power storage device can be provided. Further, according to one aspect of the present invention, a novel positive electrode slurry can be provided. Further, according to one aspect of the present invention, a novel positive electrode can be provided.

Brief Description of the Drawings

[0025] FIG. 1 is a diagram for explaining an example of a method for manufacturing an electrode. FIG. 2 is a diagram for explaining an example of a method for manufacturing an electrode. FIG. 3A is a perspective view of a secondary battery, FIG. 3B is a cross-sectional perspective view thereof, and FIG. 3C is a schematic cross-sectional view during charging. FIG. 4A is a perspective view of a secondary battery, FIG. 4B is a cross-sectional perspective view thereof, FIG. 4C is a perspective view of a battery pack including a plurality of secondary batteries, and FIG. 4D is a top view thereof. FIGS. 5A and 5B are diagrams for explaining an example of a secondary battery. FIGS. 6A and 6B are diagrams for explaining a laminated secondary battery. FIGS. 7A and 7B are diagrams for explaining an example of a secondary battery. FIGS. 8A, 8B, 8C, 8D, and 8E are perspective views showing an electronic device. FIG. 9 is a charge-discharge curve of a sample manufactured in an example.

Modes for Carrying Out the Invention

[0026] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and those skilled in the art can easily understand that its form and details can be variously changed. Also, the present invention is not to be construed as being limited to the description of the embodiments shown below.

[0027] Graphene can be said to be a material having conductivity and a structure in which hexagons composed of six carbon atoms are formed in a two-dimensional sheet shape. Other such materials include carbon nanotubes and the like. Also, in this specification, there is no particular limitation on the number of layers of graphene, and it may be single-layer graphene, multi-layer graphene, thin-layer graphene, or few-layer graphene.

[0028] Methods for producing graphene include the method of reducing graphene oxide as described above to obtain RGO, and the method of physically exfoliating graphite. When reducing graphene oxide, it is difficult to desorb all the oxygen contained in graphene oxide, and a part of the oxygen remains on the RGO. On the other hand, when produced by the method of physically exfoliating graphene, the obtained graphene contains only a very small amount of oxygen. The oxygen content of graphene produced by the method of physically exfoliating graphite is preferably 0 atomic% or more and 4 atomic% or less, or greater than 0 atomic% and 4 atomic% or less, more preferably 0 atomic% or more and 2 atomic% or less, or greater than 0 atomic% and 2 atomic% or less.

[0029] In addition, in this specification and the like, graphene includes single-layer graphene or multi-layer graphene with 2 or more layers and 100 or fewer layers. Single-layer graphene refers to a sheet of a one-atom-thick carbon molecule having a π bond. Further, graphene oxide refers to a compound in which the above graphene is oxidized, and is a plurality of graphene with the distance between a plurality of single-layer graphenes being greater than 0.34 nm and 1.5 nm or less. In multi-layer graphene, strong interactions occur between single-layer graphenes, but since graphene oxide has polar functional groups such as epoxy groups, carbonyl groups, carboxyl groups, and hydroxyl groups, the interactions that occur between single-layer graphenes are reduced. Therefore, the distance between a plurality of single-layer graphenes in graphene oxide is larger than the distance between a plurality of single-layer graphenes in multi-layer graphene.

[0030] (Embodiment 1) In this embodiment, an electrode using graphene and a graphene compound as conductive aids will be described.

[0031] To obtain an electrode, first, an electrode binder composition is prepared. The electrode binder composition has an active material (hereinafter, a particulate active material is also referred to as an active material particle), and a conductive aid. Note that the electrode binder composition may contain a dispersion medium (also referred to as a solvent) and a binder, and may be in a slurry form or a paste form.

[0032] A compound having graphene as a basic skeleton that can be used as a conductive aid is referred to as a "graphene compound (Graphene Compound)". Graphene, graphene oxide, and RGO (Reduced Graphene Oxide) are each a type of graphene compound.

[0033] Graphene is a carbon material having a crystal structure in which hexagonal skeletons formed by carbon are arranged in a plane, and has amazing characteristics in electrical, mechanical, or chemical properties.

[0034] In addition, the graphene compound has excellent electrical properties such as high conductivity, and excellent physical properties such as high flexibility and high mechanical strength. The graphene compound is preferable because it enables surface contact with low contact resistance and may reduce electrical resistance. Further, the graphene compound has a planar shape, may have very high conductivity even when thin, and can efficiently form a conductive path in the active material layer in a small amount. Therefore, it is preferable to use the graphene compound as a conductive aid because it can increase the contact area between the active material and the conductive aid.

[0035] In particular, graphene oxide is preferable because it has extremely high dispersibility in a solvent. When graphene oxide is reduced to form graphene (RGO), not all of the oxygen etc. contained in the graphene oxide needs to be desorbed, and some oxygen may remain in the graphene, and it may have an alkyl group linked by an ether bond or an ester bond. Further, the alcohol intercalated in the graphene oxide may remain in the graphene without being completely desorbed.

[0036] In addition, a binder may be added to the mixture of graphene oxide and the active material. By adding the binder, the active material and the graphene oxide can be bound so as to maintain a state in which the graphene oxide is evenly mixed in the active material.

[0037] Here, the electrode using graphene oxide is subjected to a reduction treatment. Examples of the reduction method of graphene oxide include reduction by heating (hereinafter referred to as thermal reduction), electrochemical reduction (hereinafter referred to as electrochemical reduction) in which a potential for reducing graphene oxide is applied to the electrode in an electrolytic solution, and reduction by a chemical reaction using a reducing agent (hereinafter referred to as chemical reduction). The reduction treatment can apply at least one of chemical reduction and thermal reduction, but it is more preferable to perform both chemical reduction and thermal reduction.

[0038] In chemical reduction and thermal reduction, the functional groups that are easily reduced are different. Reducing agents have a great effect on reducing the carbonyl group (C=O) and carboxyl group (-COOH) in graphene oxide by proton addition. On the other hand, thermal reduction has a great effect on reducing the hydroxyl group (-OH) in graphene oxide by dehydration. Therefore, by performing both chemical reduction and thermal reduction, reduction can be carried out more efficiently, and the conductivity of the reduced graphene oxide can be increased.

[0039] In particular, it is preferable to further perform a thermal reduction treatment after the chemical reduction treatment, because the conductivity of the formed graphene can be further improved.

[0040] By the reduction treatment, oxygen contained in graphene oxide is desorbed, so that an active material layer containing graphene can be formed. Note that not all of the oxygen contained in graphene oxide needs to be desorbed, and some oxygen may remain in the graphene.

[0041] On the other hand, due to the influence of the chemical reduction treatment, the adhesion between the active material and graphene oxide in the electrode binder composition may decrease. For example, when the binder dissolves in the solvent used for the chemical reduction treatment, the adhesion between the active material and graphene oxide becomes weak, and the probability of the electrode collapsing in the subsequent process, such as the active material and graphene oxide peeling off from the current collector, increases.

[0042] Therefore, before performing the chemical reduction treatment, the electrode binder composition is heat-treated. By performing the heat treatment, the adhesion between the active material and graphene oxide in the electrode binder composition can be strengthened.

[0043] For example, it is preferable to perform the heat treatment under conditions where at least a part of the binder crystallizes. When the binder crystallizes, it becomes difficult for the binder to dissolve in the solvent used for the chemical reduction treatment, so that a decrease in the adhesion between the active material and graphene oxide can be suppressed. Therefore, the heat treatment may be performed at a temperature equal to or higher than the crystallization temperature of the binder and equal to or lower than the melting temperature of the binder.

[0044] In addition, when chemical reduction treatment is carried out after reduction treatment by heat, the reduction rate tends to decrease. Therefore, in the above heat treatment, conditions under which reduction by heat hardly occurs may be appropriately selected. Accordingly, when thermal reduction is carried out after chemical reduction treatment, the above heat treatment may be set at a temperature lower than the set temperature in the thermal reduction treatment and for a shorter time than the time in the thermal reduction treatment.

[0045] <Manufacturing method> Hereinafter, an electrode binder composition and a method for manufacturing an electrode according to one embodiment of the present invention will be described with reference to FIG. 1. Note that a mixture containing an active material and a conductive auxiliary may be referred to as an electrode binder composition.

[0046] First, a dispersion medium, a mixture 101 containing at least an active material, and a graphene compound serving as a conductive auxiliary are prepared (step S11 in FIG. 1). By mixing these (step S12 in FIG. 1), a mixture 102 is obtained (step S13 in FIG. 1). Note that as the graphene compound, any one or more of graphene, graphene oxide, and RGO may be used.

[0047] In step S11, the mixing ratio of the active material and the graphene compound is important. If the amount of the active material is large, the capacity of the positive electrode or negative electrode to be produced increases, while the content of the graphene compound as a conductive auxiliary relatively decreases. If the amount of the conductive auxiliary is too small, the conductivity decreases and the battery characteristics deteriorate. Therefore, the mixing ratio of the active material and the graphene compound preferably contains a graphene compound sufficient to ensure conductivity and has the maximum amount of the active material.

[0048] As the dispersion medium, a polar solvent is preferably used. As the polar solvent, N-methyl-2-pyrrolidone (abbreviation: NMP), N,N-dimethylformamide (abbreviation: DMF), dimethyl sulfoxide (abbreviation: DMSO), or the like can be used.

[0049] Next, a binder is prepared, and (step S21 in FIG. 1), and the mixture 102 and the binder are mixed (step S22 in FIG. 1) to obtain a mixture 103 (step S23 in FIG. 1).

[0050] The mixing amount of the binder may be appropriately set according to the amounts of the graphene compound and the active material. By mixing the binder in a state where the graphene compound is dispersed so as to be in surface contact with the particles of the plurality of active materials, the active material and the graphene compound can be bound while maintaining the dispersed state. Further, depending on the ratio of the active material and the graphene compound, it may not be necessary to add a binder, but when a binder is added, the strength of the electrode can be improved.

[0051] As the binder, polyvinylidene fluoride (PVDF), polyimide, polytetrafluoroethylene, polyvinyl chloride, ethylene propylene diene polymer, styrene-butadiene rubber, acrylonitrile-butadiene rubber, fluororubber, polyvinyl acetate, polymethyl methacrylate, polyethylene, nitrocellulose, etc. can be used.

[0052] Next, a dispersion medium is prepared (step S31 in FIG. 1), the dispersion medium is added to and mixed with the mixture 103 until a predetermined viscosity is reached (step S32 in FIG. 1), and then kneaded (step S33 in FIG. 1). Through the above steps, the mixture 104 can be produced (step S34 in FIG. 1).

[0053] In addition, when the viscosity of the mixture 103 is about the predetermined viscosity, the mixture 104 may be produced by kneading the mixture 103 without adding the dispersion medium (without performing S31 and S32). Also, as the dispersion medium in this step, the above-mentioned polar solvent can be used. Further, it is preferable to use the same dispersion medium as the dispersion medium prepared in step S11.

[0054] Next, a current collector is prepared (step S41 in FIG. 1), and the mixture 104, which is the electrode binder composition produced in steps S11 to S34, is applied to one or both sides of the current collector by a coating method such as a roll coating method, a screen printing method, a doctor blade method, a spin coating method, a bar coating method, etc. using an applicator roll or the like (step S42 in FIG. 1).

[0055] The electrode mixture composition applied on the current collector is dried by a method such as ventilation drying or drying under reduced pressure (vacuum) (step S43 in FIG. 1). For example, heat treatment may be performed as the drying treatment. Note that the atmosphere for drying (heat treatment) is not particularly limited.

[0056] Here, the drying treatment is preferably performed at a relatively low temperature of room temperature (R.T.: Room Temperature) or higher and 120°C or lower, preferably room temperature or higher and 90°C or lower. In this specification, in the numerically defined ranges described step by step, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the upper limit value or the lower limit value of the numerical range described in other step-by-step descriptions.

[0057] In particular, when the drying treatment is performed at a high temperature, binder migration may occur. Specifically, the binder in the dispersion medium moves (also referred to as migration) in the dispersion medium, so that the binder is likely to be biased in the dispersion medium and the strength as an electrode is likely to decrease. In addition, the graphene compound and the active material in the dispersion medium may move in the dispersion medium, so that the graphene compound and the active material in the dispersion medium may be unevenly distributed. That is, by performing heat treatment abruptly, unevenness may occur in the electrode, and the active material and the graphene compound may be peeled off.

[0058] Subsequently, heat treatment is performed at a temperature higher than the drying treatment (step S44 in FIG. 1). Note that the atmosphere for heat treatment is not particularly limited. Preferably, it is performed under reduced pressure (vacuum).

[0059] For example, the heat treatment is preferably performed under conditions where at least a part of the binder is crystallized. Therefore, the heat treatment is preferably performed at a temperature equal to or higher than the temperature at which the binder crystallizes and equal to or lower than the temperature at which the binder melts.

[0060] In addition, for the heat treatment, conditions under which reduction by heat is less likely to occur are preferably selected as appropriate. When reduction by heat occurs, substituents that can be reduced by chemical reduction may change. Therefore, the reduction rate by chemical reduction may decrease.

[0061] Therefore, for example, the heat treatment is preferably carried out at 120°C or higher and 170°C or lower, more preferably 120°C or higher and 160°C or lower, and even more preferably 120°C or higher and 140°C or lower.

[0062] After the dispersion medium of the electrode binder composition is evaporated by the drying treatment, and then heat treatment is carried out at the temperature at which the binder crystallizes, the graphene compound and the active material in the electrode are evenly distributed, and the binding force between the active material and the graphene oxide in the electrode binder composition can be strengthened.

[0063] Therefore, the temperature of the heat treatment is preferably higher than that of the previous drying treatment (step S43) and lower than that of the subsequent thermal reduction treatment (step S45). Also, the time of the heat treatment is preferably longer than that of the previous drying treatment and shorter than that of the subsequent thermal reduction treatment.

[0064] From the above, the drying treatment and the heat treatment can be carried out, for example, using hot air at 40°C or higher and 170°C or lower for 1 minute or longer and 10 hours or shorter, preferably 1 minute or longer and 1 hour or shorter. By gradually increasing the temperature from the drying treatment to the heat treatment, an electrode without unevenness of the graphene compound and the active material in the electrode can be obtained.

[0065] Next, a reduction treatment is carried out on the electrode binder composition on the current collector that has been heat-treated (step S45 in FIG. 1). As the reduction method, it is preferable to use chemical reduction. In addition to chemical reduction, thermal reduction may also be applied.

[0066] As the reducing agent used for chemical reduction, organic acids such as ascorbic acid, hydrogen, sulfur dioxide, sulfurous acid, sodium sulfite, sodium bisulfite, ammonium sulfite, hydrazine, dimethylhydrazine, hydroquinone, or phosphorous acid can be used.

[0067] When using ascorbic acid as a reducing agent, first dissolve ascorbic acid in a solvent. As the solvent, any one of water, NMP, and ethanol, or a mixture of one or more thereof can be used. Then immerse the current collector and the electrode binder composition prepared in step S44 in the solution. This treatment can be carried out, for example, for 30 minutes or more and 10 hours or less, and about 1 hour is preferable. Also, heating can shorten the time of chemical reduction and is preferable. For example, it can be heated to a temperature of room temperature or higher and 100 ° C or lower, and about 60 ° C is preferable.

[0068] Also, after the chemical reduction treatment, a thermal reduction treatment may be performed. The thermal reduction treatment is preferably performed under reduced pressure. For heating, for example, a glass tube oven can be used. The glass tube oven can be heated under a reduced pressure of about 1 kPa.

[0069] The optimum heating temperature and heating time vary depending on the conductive aid and the binder material used as the material. For example, when using graphene oxide as the conductive aid and PVDF as the binder, it is preferable that the temperature is such that the graphene oxide is sufficiently reduced and the PVDF is crystallized without adversely affecting the PVDF. Specifically, it is preferably 125 ° C or higher and 200 ° C or lower, and preferably 125 ° C or higher and 180 ° C or lower.

[0070] Note that at 100 ° C or lower, the reduction of graphene oxide may not proceed sufficiently. Also, at 250 ° C or higher, there is a risk of adverse effects on PVDF and the electrode binder composition may easily peel off from the current collector.

[0071] The heating time is preferably 1 hour or more and 20 hours or less. If the heating time is less than 1 hour, there is a risk that the graphene oxide will not be sufficiently reduced. If the heating time exceeds 20 hours, the productivity will decrease.

[0072] By the above steps, a positive electrode or a negative electrode having a graphene compound as a conductive aid can be produced (step S46 in FIG. 1).

[0073] As described above, the electrode binder composition may have a binder and a dispersion medium in addition to the active material and the conductive assistant. When producing the electrode binder composition using acetylene black, which is often used as the conductive assistant, there are no particular restrictions on the procedure for mixing the dispersion medium, the active material, the conductive assistant, and the binder. However, when using a graphene compound, particularly a graphene compound with a low oxygen content produced by a method of physically (mechanically) exfoliating graphite, as the conductive assistant as in one aspect of the present invention, depending on the procedure for mixing the dispersion medium, the active material, the conductive assistant, and the binder, the graphene compound may aggregate, making it difficult to produce an electrode that exhibits good battery characteristics.

[0074] Also, as shown in FIG. 2, the mixture 101 may be adjusted by mixing the dispersion medium and the active material (steps S01 and S02). Performing steps S01 and S02 is preferable because the mixture 101 with an appropriate viscosity or concentration can be adjusted. In FIG. 2, for the same operations as in FIG. 1, since they are the same as in FIG. 1, detailed descriptions are omitted.

[0075] <Material> Here, the manufacturing method and the components of the electrode according to one aspect of the present invention will be described.

[0076] ≪Active Material≫ The material that can be used for the above-mentioned active material may be any material capable of inserting and removing carrier ions such as lithium ions, and a positive electrode active material or a negative electrode active material can be used.

[0077] <Positive Electrode Active Material> As the positive electrode active material, for example, compounds such as LiFeO2, LiCoO2, LiNiO2, LiMn2O4, V2O5, Cr2O5, and MnO2 can be used.

[0078] Alternatively, a lithium-containing composite phosphate (general formula LiMPO4 (M is one or more of Fe(II), Mn(II), Co(II), Ni(II))) can be used. Representative examples of the general formula LiMPO4 include LiFePO4, LiNiPO4, LiCoPO4, LiMnPO4, LiFe a Ni b PO4, LiFe a Co b PO4, LiFe a Mn b PO4, LiNi a Co b PO4, LiNi a Mn b PO4 (a + b is 1 or less, 0 < a < 1, 0 < b < 1), LiFe c Ni d Co e PO4, LiFe c Ni d Mn e PO4, LiNi c Co d Mn e PO4 (c + d + e is 1 or less, 0 < c < 1, 0 < d < 1, 0 < e < 1), LiFe f Ni g Co h Mn i 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.

[0079] In particular, LiFePO4 is preferable because it well balances 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).

[0080] Examples of the lithium-containing composite metal oxide having a layered rock salt-type crystal structure include lithium cobalt oxide (LiCoO2), LiNiO2, LiMnO2, Li2MnO3, LiNi 0.8 Co 0.2 O2 and other NiCo-based (general formula is LiNi x Co 1-x O2 (0 < x < 1)), LiNi 0.5 Mn 0.5O2 etc. NiMn system (general formula: LiNi x Mn 1-x O2(0 <x<1))、LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2, etc. NiMnCo system (also called NMC. The general formula is LiNi x Mn y Co 1-x-y O2(x>0, y>0, x+y<1)). 0.8 Co 0.15 Al 0.05 )O2, Li2MnO3-LiMO2 (M=Co, Ni, Mn), etc.

[0081] In particular, LiCoO2 is preferable because it has advantages such as a large capacity, being more stable in the air than LiNiO2, and being more thermally stable than LiNiO2.

[0082] Examples of lithium-containing composite manganese oxides having a spinel-type crystal structure include LiMn2O4, Li 1+x Mn 2-x O4(0 <x<2)、LiMn 2-x Al x O4(0 <x<2)、LiMn 1.5 Ni 0.5 There are O4 and so on.

[0083] Lithium-containing composite manganese oxides with a spinel-type crystal structure containing manganese, such as LiMn2O4, are mixed with a small amount of lithium nickel oxide (LiNi 1-x M x O2(0 <x<1))やLiNi 1-x M x O2(0 <x<1)(M=Co、Al等))を混合すると、マンガンの溶出を抑制する等の利点があり好ましい。

[0084] Or, the general formula Li (2-j) Lithium-containing composite silicates such as MSiO4 (where M is one or more of Fe(II), Mn(II), Co(II), and Ni(II), and 0≦j≦2) can be used. The general formula is Li (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 SiO4, Li (2-j) Ni k Mn l SiO4 (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 SiO4, Li (2-j) Ni m Co n Mn q SiO4 (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 (r + s + t + u is 1 or less, 0 < r < 1, 0 < s < 1, 0 < t < 1, 0 < u < 1), etc. can be mentioned.

[0085] Also, as the positive electrode active material, A xA NASICON-type compound represented by the general formula M2(XO4)3 (where A = Li, Na, Mg, M = Fe, Mn, Ti, V, Nb, Al, X = S, P, Mo, W, As, Si) can be used. Examples of NASICON-type compounds include Fe2(MnO4)3, Fe2(SO4)3, Li3Fe2(PO4)3, etc. Also, as the positive electrode active material, compounds represented by the general formula Li2MPO4F, Li2MP2O7, Li5MO4 (M = Fe, Mn), perovskite-type fluorides such as FeF3, metal chalcogenides (sulfides, selenides, tellurides) such as TiS2, MoS2, lithium-containing composite vanadium oxides having an inverse spinel-type crystal structure such as LiMVO4, vanadium oxide-based (V2O5, V6O 13 , LiV3O8, etc.), manganese oxides, organic sulfur compounds, and other materials can be used.

[0086] When the carrier ion is an alkali metal ion or an alkaline earth metal ion other than lithium ion, as the positive electrode active material, in the above lithium-containing substances, an alkali metal (e.g., sodium, potassium, etc.) or an alkaline earth metal (e.g., calcium, strontium, barium, beryllium, magnesium, etc.) can be used instead of lithium.

[0087] As the positive electrode active material, a granular active material composed of secondary particles having an average particle size and a particle size distribution, which is obtained by mixing and firing raw material compounds at a predetermined ratio and then pulverizing, granulating, and classifying them by appropriate means, can be used.

[0088] <Negative electrode active material> As the negative electrode active material, for example, alloy-based materials, carbon-based materials, etc. can be used.

[0089] As the negative electrode active material, an element capable of performing charge and discharge reactions through alloying and dealloying reactions with lithium can be used. For example, a material containing at least one of silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium, etc. can be used. Such elements have a larger capacity compared to carbon, and in particular, silicon has a high theoretical capacity of 4200 mAh / g. Therefore, it is preferable to use silicon as the negative electrode active material. Also, compounds containing these elements may be used. For example, there are SiO, Mg2Si, Mg2Ge, SnO, SnO2, Mg2Sn, SnS2, V2Sn3, FeSn2, CoSn2, Ni3Sn2, Cu6Sn5, Ag3Sn, Ag3Sb, Ni2MnSb, CeSb3, LaSn3, La3Co2Sn7, CoSb3, InSb, SbSn, etc. Here, an element capable of performing charge and discharge reactions through alloying and dealloying reactions with lithium, and compounds containing such an element, etc. may be referred to as alloy-based materials.

[0090] In this specification etc., SiO refers to, for example, silicon monoxide. Alternatively, SiO can also be expressed as SiO x Here, x preferably has a value near 1. For example, x is preferably 0.2 or more and 1.5 or less, and more preferably 0.3 or more and 1.2 or less.

[0091] As the carbon-based material, graphite, graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), carbon nanotubes, graphene, carbon black, etc. may be used.

[0092] Examples of graphite include artificial graphite and natural graphite. Examples of artificial graphite include mesocarbon microbeads (MCMB), coke-based artificial graphite, pitch-based artificial graphite, etc. Here, as artificial graphite, spherical graphite having a spherical shape can be used. For example, MCMB may have a spherical shape, which is preferable. Also, it is relatively easy to reduce the surface area of MCMB, which may be preferable. Examples of natural graphite include flaky graphite, spheroidized natural graphite, etc.

[0093] Graphite shows a potential as low as that of metallic lithium when lithium ions are inserted into it (when forming a lithium-graphite intercalation compound) (0.05 V or more and 0.3 V or less vs. Li / Li + ). As a result, lithium-ion secondary batteries can exhibit a high operating voltage. Furthermore, graphite has advantages such as a relatively high capacity per unit volume, relatively small volume expansion, low cost, and high safety compared to metallic lithium, so it is preferable.

[0094] In addition, oxides such as titanium dioxide (TiO2), lithium titanate (Li4Ti5O 12 ), lithium-graphite intercalation compound (Li x C6), niobium pentoxide (Nb2O5), tungsten oxide (WO2), molybdenum oxide (MoO2), etc. can be used as the negative electrode active material.

[0095] In addition, Li 3-x M x N (M = Co, Ni, Cu) having an Li3N-type structure, which is a complex nitride of lithium and a transition metal, can be used. For example, Li 2.6 Co 0.4 N3 shows a large charge-discharge capacity (900 mAh / g, 1890 mAh / cm 3 ) and is preferable.

[0096] When using a complex nitride of lithium and a transition metal, since lithium ions are contained in the negative electrode active material, it can be preferably combined with materials such as V2O5 and Cr3O8 that do not contain lithium ions as the positive electrode active material. Even when using a material containing lithium ions as the positive electrode active material, a complex nitride of lithium and a transition metal can be used as the negative electrode active material by previously desorbing the lithium ions contained in the positive electrode active material.

[0097] In addition, materials that undergo a conversion reaction can also be used as the negative electrode active material. For example, transition metal oxides that do not form alloys with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), iron oxide (FeO), etc., may be used as the negative electrode active material. As materials that undergo a conversion reaction, further, oxides such as Fe2O3, CuO, Cu2O, RuO2, Cr2O3, CoS 0.89 , sulfides such as NiS, CuS, nitrides such as Zn3N2, Cu3N, Ge3N4, phosphides such as NiP2, FeP2, CoP3, and fluorides such as FeF3, BiF3 also occur.

[0098] As the conductive assistant and binder that the negative electrode active material layer can have, the same materials as the conductive assistant and binder that the positive electrode active material layer can have can be used.

[0099] <<Current collector>> When manufacturing the positive electrode, the above-mentioned current collector uses a positive electrode current collector, and when manufacturing the negative electrode, a negative electrode current collector is used.

[0100] As the positive electrode current collector, materials with high conductivity, such as metals such as stainless steel, gold, platinum, aluminum, titanium, and alloys thereof, can be used. Also, the material used for the positive electrode current collector is preferably one that does not elute at the potential of the positive electrode. In addition, an aluminum alloy added with elements that improve heat resistance, such as silicon, titanium, neodymium, scandium, molybdenum, etc., can be used. Also, it may be formed of a metal element that reacts with silicon to form a silicide. Examples of metal elements that react with silicon to form a silicide include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, nickel, etc. The current collector can appropriately use shapes such as foil, plate (sheet), net, punched metal, expanded metal, etc. The current collector is preferably one with a thickness of 5 μm or more and 30 μm or less.

[0101] For the negative electrode current collector, the same material as that of the positive electrode current collector can be used. Note that it is preferable to use a material that does not alloy with carrier ions such as lithium for the negative electrode current collector.

[0102] (Embodiment 2) In this embodiment, an example of the shape of a secondary battery having a positive electrode active material manufactured by the manufacturing method described in the previous embodiment will be described. The materials used for the secondary battery described in this embodiment can refer to the description of the previous embodiment.

[0103] [Coin-type secondary battery] First, an example of a coin-type secondary battery will be described. FIG. 3A is an external view of a coin-type (single-layer flat type) secondary battery, and FIG. 3B is a cross-sectional view thereof.

[0104] The coin-type secondary 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, which are insulated and sealed by a gasket 303 made of polypropylene or the like. The positive electrode 304 is formed by a positive electrode current collector 305 and a positive electrode active material layer 306 provided in contact therewith. The negative electrode 307 is formed by a negative electrode current collector 308 and a negative electrode active material layer 309 provided in contact therewith.

[0105] Note that for the positive electrode 304 and the negative electrode 307 used in the coin-type secondary battery 300, the active material layer may be formed only on one side.

[0106] For the positive electrode can 301 and the negative electrode can 302, metals such as nickel, aluminum, and titanium that are corrosion-resistant to the electrolytic solution, or alloys thereof or alloys of these with other metals (for example, stainless steel, etc.) can be used. Further, in order to prevent corrosion by the electrolytic solution, it is preferable to coat nickel, aluminum, or the like. The positive electrode can 301 is electrically connected to the positive electrode 304, and the negative electrode can 302 is electrically connected to the negative electrode 307.

[0107] These negative electrode 307, positive electrode 304, and separator 310 are impregnated with an electrolyte. As shown in FIG. 3(B), with the positive electrode can 301 facing downwards, the positive electrode 304, separator 310, negative electrode 307, and negative electrode can 302 are laminated in this order, and the positive electrode can 301 and the negative electrode can 302 are crimped via a gasket 303 to manufacture a coin-shaped secondary battery 300.

[0108] By using the active material layer described in the previous embodiment for the positive electrode 304, a coin-type secondary battery 300 with less deterioration and high safety can be obtained.

[0109] [Separator] Moreover, it is preferable for the secondary battery to have a separator. As the separator, for example, those formed of fibers having cellulose such as paper, non-woven fabric, glass fiber, ceramics, or synthetic fibers using nylon (polyamide), vinylon (polyvinyl alcohol-based fiber), polyester, acrylic, polyolefin, polyurethane, etc. can be used. The separator is preferably processed into a bag shape and arranged to wrap either the positive electrode or the negative electrode.

[0110] The separator may have a multilayer structure. For example, an organic material film such as polypropylene or polyethylene can be coated with a ceramic-based material, a fluorine-based material, a polyamide-based material, or a mixture thereof. As the ceramic-based material, for example, aluminum oxide particles, silicon oxide particles, etc. can be used. As the fluorine-based material, for example, PVDF, polytetrafluoroethylene, etc. can be used. As the polyamide-based material, for example, nylon, aramid (meta-aramid, para-aramid), etc. can be used.

[0111] Coating with a ceramic-based material can improve oxidation resistance, suppress the deterioration of the separator during high-voltage charge and discharge, and improve the reliability of the secondary battery. Also, coating with a fluorine-based material can make the separator and the electrode adhere more easily, improving the output characteristics. Coating with a polyamide-based material, especially aramid, can improve heat resistance, thus improving the safety of the secondary battery.

[0112] For example, a mixed material of aluminum oxide and aramid may be coated on both sides of a polypropylene film. Also, a mixed material of aluminum oxide and aramid may be coated on the surface of the polypropylene film that contacts the positive electrode, and a fluorine-based material may be coated on the surface that contacts the negative electrode.

[0113] Using a separator with a multilayer structure can maintain the safety of the secondary battery even when the overall thickness of the separator is thin, so the capacity per unit volume of the secondary battery can be increased.

[0114] Here, the flow of current during the charging of the secondary battery will be described with reference to Fig. 3C. When a secondary battery using lithium is regarded as a single closed circuit, the movement of lithium ions and the flow of current are in the same direction. In a secondary battery using lithium, the anode (positive electrode) and the cathode (negative electrode) are reversed during charging and discharging, and the oxidation reaction and the reduction reaction are also reversed. Therefore, the electrode with a higher reaction potential is called the positive electrode, and the electrode with a lower reaction potential is called the negative electrode. Thus, in this specification, whether during charging, discharging, when a reverse pulse current is flowing, or when a charging current is flowing, the positive electrode is referred to as the "positive electrode" or the "+ electrode (plus electrode)", and the negative electrode is referred to as the "negative electrode" or the "- electrode (minus electrode)". If terms such as anode (positive electrode) and cathode (negative electrode) related to oxidation and reduction reactions are used, they will be reversed during charging and discharging, which may cause confusion. Therefore, the terms anode (positive electrode) and cathode (negative electrode) will not be used in this specification. If the terms anode (positive electrode) and cathode (negative electrode) are used, it is necessary to specify whether it is during charging or discharging, and also to indicate which one corresponds to the positive electrode (plus electrode) and the negative electrode (minus electrode).

[0115] A charger is connected to the two terminals shown in Fig. 3C, and the secondary battery 300 is charged. As the charging of the secondary battery 300 progresses, the potential difference between the electrodes increases.

[0116] [Cylindrical secondary battery] An example of a cylindrical secondary battery will be described with reference to Figs. 4A to 4D. As shown in Fig. 4A, the cylindrical secondary battery 600 has a positive electrode cap (battery lid) 601 on the upper surface and a battery can (outer can) 602 on the side surface and the bottom surface. The positive electrode cap and the battery can (outer can) 602 are insulated by a gasket (insulating packing) 610.

[0117] FIG. 4B is a diagram schematically showing a cross section of a cylindrical secondary battery. Inside a hollow cylindrical battery can 602, a battery element is provided in which a strip-shaped positive electrode 604 and a negative electrode 606 are wound with a separator 605 interposed therebetween. Although not shown, the battery element is wound around a center pin. One end of the battery can 602 is closed and the other end is open. For the battery can 602, metals such as nickel, aluminum, and titanium that are corrosion-resistant to the electrolytic solution, or alloys thereof or alloys of these with other metals (for example, stainless steel, etc.) can be used. Further, in order to prevent corrosion by the electrolytic solution, it is preferable to coat nickel, aluminum, etc. Inside the battery can 602, the battery element in which the positive electrode, negative electrode, and separator are wound is sandwiched between a pair of opposing insulating plates 608 and 609. Further, a non-aqueous electrolytic solution (not shown) is injected into the inside of the battery can 602 in which the battery element is provided. As the non-aqueous electrolytic solution, the same one as that used for a coin-type secondary battery can be used.

[0118] For the positive electrode and negative electrode used in the cylindrical secondary battery to be wound, it is preferable to form the active material on both sides of the current collector. A positive electrode terminal (positive electrode current collecting lead) 603 is connected to the positive electrode 604, and a negative electrode terminal (negative electrode current collecting lead) 607 is connected to the negative electrode 606. Both the positive electrode terminal 603 and the negative electrode terminal 607 can use a metal material such as aluminum. The positive electrode terminal 603 is resistance-welded to the safety valve mechanism 612, and the negative electrode terminal 607 is resistance-welded to the bottom of the battery can 602, respectively. The safety valve mechanism 612 is electrically connected to the positive electrode cap 601 via a PTC element (Positive Temperature Coefficient) 611. The safety valve mechanism 612 disconnects the electrical connection between the positive electrode cap 601 and the positive electrode 604 when the internal pressure of the battery rises beyond a predetermined threshold value. Further, the PTC element 611 is a thermal sensing resistance element whose resistance increases when the temperature rises, and it limits the current amount due to the increase in resistance to prevent abnormal heat generation. For the PTC element, barium titanate (BaTiO3)-based semiconductor ceramics, etc. can be used.

[0119] Alternatively, as shown in FIG. 4C, a module 615 may be configured by sandwiching a plurality of secondary batteries 600 between a conductive plate 613 and a conductive plate 614. The plurality of secondary batteries 600 may be connected in parallel, in series, or in parallel and then further in series. By configuring a module 615 having a plurality of secondary batteries 600, a large amount of power can be extracted.

[0120] FIG. 4D is a top view of the module 615. The conductive plate 613 is shown by a dotted line for clarity. As shown in FIG. 4D, the module 615 may have a conductive wire 616 that electrically connects a plurality of secondary batteries 600. The conductive plate 613 can be provided so as to overlap the conductive wire 616. Further, a temperature control device 617 may be provided between the plurality of secondary batteries 600. When the secondary battery 600 is overheated, it can be cooled by the temperature control device 617, and when the secondary battery 600 is too cold, it can be heated by the temperature control device 617. Therefore, the performance of the module 615 is less likely to be affected by the outside air temperature.

[0121] By using the positive electrode active material produced by the production method described in the previous embodiment for the positive electrode 604, a cylindrical secondary battery 600 with less deterioration and high safety can be obtained.

[0122] [Structure Example of Secondary Battery] Another structural example of the power storage device will be described with reference to FIGS. 5 and 6.

[0123] FIG. 5A shows the structure of the wound body 950. The wound body 950 has a negative electrode 931, a positive electrode 932, and a separator 933. The wound body 950 is a wound body in which the negative electrode 931 and the positive electrode 932 overlap and are laminated with the separator 933 interposed therebetween, and the laminated sheet is wound. Note that a plurality of laminations of the negative electrode 931, the positive electrode 932, and the separator 933 may be further stacked.

[0124] The secondary battery 913 shown in FIG. 5B has a wound body 950 in which a terminal 951 and a terminal 952 are provided inside a housing 930. The wound body 950 is impregnated with an electrolytic solution inside the housing 930. The terminal 952 is in contact with the housing 930, and the terminal 951 is not in contact with the housing 930 by using an insulating material or the like. In FIG. 5B, for convenience, the housing 930 is shown separately, but actually, the wound body 950 is covered by the housing 930, and the terminals 951 and 952 extend outside the housing 930. As the housing 930, a metal material (such as aluminum) or a resin material can be used.

[0125] [Laminated secondary battery] Next, an example of a laminated secondary battery will be described with reference to FIGS. 6A and 6B.

[0126] FIG. 6A shows an example of an external view of a laminated secondary battery 500. Further, FIG. 6B shows another example of an external view of the laminated secondary battery 500.

[0127] FIGS. 6A and 6B include a positive electrode 503, a negative electrode 506, a separator 507, an exterior body 509, a positive electrode lead electrode 510, and a negative electrode lead electrode 511.

[0128] The laminated secondary battery 500 has a plurality of positive electrodes 503, a separator 507, and a negative electrode 506 in a wound body or strip shape.

[0129] The wound body has a negative electrode 506, a positive electrode 503, and a separator 507. The wound body is formed by winding a laminated sheet in which the negative electrode 506 and the positive electrode 503 overlap with each other with the separator 507 interposed therebetween, similar to the wound body described in FIG. 5A.

[0130] A secondary battery having a plurality of strip-shaped positive electrodes 503, a separator 507, and a negative electrode 506 may be provided in a space formed by a film serving as the exterior body 509.

[0131] A method for manufacturing a secondary battery having a plurality of strip-shaped positive electrodes 503, separators 507, and negative electrodes 506 is shown below.

[0132] First, the negative electrode 506, the separator 507, and the positive electrode 503 are laminated. In this embodiment, an example of using 5 sets of negative electrodes and 4 sets of positive electrodes is shown. Next, the tabs of the positive electrodes 503 are joined together, and the positive electrode lead electrode 510 is joined to the tab area of the outermost positive electrode. For the joining, for example, ultrasonic welding or the like may be used. Similarly, the tabs of the negative electrodes 506 are joined together, and the negative electrode lead electrode 511 is joined to the tab area of the outermost negative electrode.

[0133] Next, the negative electrode 506, the separator 507, and the positive electrode 503 are arranged on the exterior body 509.

[0134] For the exterior body 509, for example, a flexible metal thin film such as aluminum, stainless steel, copper, nickel, etc. is provided on a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, polyamide, etc., and further an insulating synthetic resin film such as a polyamide-based resin or a polyester-based resin is provided as the outer surface of the exterior body on the metal thin film. A three-layer laminated film can be used.

[0135] The exterior body 509 is bent to sandwich the lamination therein. Then, the outer peripheral portion of the exterior body 509 is joined. For the joining, for example, thermocompression bonding or the like may be used. At this time of joining, a region that is not joined (hereinafter referred to as an inlet) is provided in a part (or one side) of the exterior body 509 so that an electrolytic solution can be put in later.

[0136] Next, the electrolytic solution is introduced into the interior of the exterior body 509 from the inlet provided in the exterior body 509. The introduction of the electrolytic solution is preferably performed under a reduced-pressure atmosphere or an inert atmosphere. And finally, the inlet is joined. In this way, the secondary battery 500, which is a laminated type secondary battery, can be manufactured.

[0137] By using the active material layer described in the previous embodiment for the positive electrode 503, a secondary battery 500 with less deterioration and high safety can be obtained.

[0138] This embodiment can be freely combined with other embodiments.

[0139] (Embodiment 3) In this embodiment, the configuration of the solid secondary battery will be described. In this specification, not only secondary batteries using only solid electrolytes, but also cases where polymer gel electrolytes, trace amounts of electrolytes, or combinations thereof are used will be referred to as solid batteries.

[0140] As shown in FIG. 7A, the secondary battery 400, which is a solid battery according to one aspect of the present invention, includes a positive electrode 410, a solid electrolyte layer 420, and a negative electrode 430. FIG. 7A shows the case where a solid electrolyte is used. When a solid electrolyte is used, it is not necessary to provide a separator or a spacer. In addition, since the entire battery can be solidified, there is no risk of liquid leakage and the safety is significantly improved.

[0141] The positive electrode 410 has a positive electrode current collector 413 and a positive electrode active material layer 414. The positive electrode active material layer 414 has a positive electrode active material 411 and a solid electrolyte 421. As the positive electrode active material 411, the positive electrode active material described in the previous embodiment can be used. Further, the positive electrode active material layer 414 may have a conductive material and a binder. As the conductive material, carbon materials such as carbon black (such as acetylene black (AB)), graphite (graphite) particles, carbon nanotubes (CNT), and fullerenes can be used. Also, for example, metal powders such as copper, nickel, aluminum, silver, and gold, metal fibers, and conductive ceramic materials can be used. Further, a graphene compound may be used as the conductive material. The graphene compound may have excellent electrical properties such as high conductivity, and excellent physical properties such as high flexibility and high mechanical strength. Also, the graphene compound has a planar shape. The graphene compound enables surface contact with low contact resistance. Also, it may have very high conductivity even when thin, and can efficiently form a conductive path in the active material layer in a small amount. Therefore, it is preferable to use a graphene compound as a conductive aid because it can increase the contact area between the active material and the conductive aid. Also, it is preferable because it may be able to reduce the electrical resistance. Here, examples of the graphene compound include graphene, multilayer graphene, multi-graphene, graphene oxide, multilayer graphene oxide, multi-graphene oxide, reduced graphene oxide, reduced multilayer graphene oxide, reduced multi-graphene oxide, graphene quantum dots, etc. Reduced graphene oxide is also called Reduced Graphene Oxide (hereinafter, RGO). Here, RGO refers to a compound obtained by reducing, for example, graphene oxide (GO: Graphene Oxide). When using active material particles with a small particle size, for example, active material particles of 1 μm or less, the specific surface area of the active material particles is large, and more conductive paths connecting the active material particles are required. In such a case, it is particularly preferable to use a graphene compound that can efficiently form a conductive path even in a small amount.In addition, in this specification and the like, graphene oxide refers to a material that contains carbon and oxygen, has a sheet-like shape, and has functional groups, particularly epoxy groups, carboxyl groups, or hydroxy groups. Further, when a plurality of graphene compounds are bonded to each other, a network-like graphene compound sheet (hereinafter referred to as a graphene compound net or a graphene net) can be formed. When the active material is coated with the graphene net, the graphene net can also function as a binder that binds the active materials together. Therefore, the amount of the binder can be reduced or the binder can be dispensed with, so that the ratio of the active material in the electrode volume and the electrode weight can be improved. That is, the capacity of the secondary battery can be increased.

[0142] The solid electrolyte layer 420 has a solid electrolyte 421. The solid electrolyte layer 420 is located between the positive electrode 410 and the negative electrode 430 and is a region that does not have either the positive electrode active material 411 or the negative electrode active material 431.

[0143] The negative electrode 430 has a negative electrode current collector 433 and a negative electrode active material layer 434. The negative electrode active material layer 434 has a negative electrode active material 431 and a solid electrolyte 421. The negative electrode active material layer 434 may also have a conductive material and a binder. When metallic lithium is used for the negative electrode 430, as shown in FIG. 7B, the negative electrode 430 that does not have the solid electrolyte 421 can be used. When metallic lithium is used for the negative electrode 430, the energy density of the secondary battery 400 can be improved, which is preferable. In FIGS. 7A and 7B, the solid electrolyte 421, the positive electrode active material 411, and the negative electrode active material 431 are shown as spherical shapes as ideal particle shapes, but in reality, they have various shapes and are schematically illustrated for convenience.

[0144] Examples of the solid electrolyte 421 included in the solid electrolyte layer 420 and the material used for the solid electrolyte layer 420 include sulfide-based solid electrolytes, oxide-based solid electrolytes, halide-based solid electrolytes, and the like.

[0145] Among the sulfide-based solid electrolytes, there are thiobased silicon systems (Li 10 GeP2S12 , Li 3.25 Ge 0.25 P 0.75 S4, etc.), sulfide glasses (70Li2S·30P2S5, 30Li2S·26B2S3·44LiI, 63Li2S·38SiS2·1Li3PO4, 57Li2S·38SiS2·5Li4SiO4, 50Li2S·50GeS2, etc.), sulfide crystallized glasses (Li7P3S 11 , Li 3.25 P 0.95 S4, etc.) are included. Sulfide-based solid electrolytes have advantages such as having materials with high conductivity, being synthesizable at low temperatures, and being relatively soft, so the conduction path is likely to be maintained even after charge and discharge.

[0146] Oxide-based solid electrolytes include materials having a perovskite crystal structure (La 2 / 3-x Li 3x TiO3, etc.), materials having a NASICON crystal structure (Li 1-X Al X Ti 2-X (PO4)3, etc.), materials having a garnet crystal structure (Li7La3Zr2O 12 , etc.), materials having a LISICON crystal structure (Li 14 ZnGe4O 16 , etc.), LLZO (Li7La3Zr2O 12 ), oxide glasses (Li3PO4-Li4SiO4, 50Li4SiO4·50Li3BO3, etc.), oxide crystallized glasses (Li 1.07 Al 0.69 Ti 1.46 (PO4)3, Li 1.5 Al 0.5 Ge 1.5 (PO4)3, etc.) are included. Oxide-based solid electrolytes have the advantage of being stable in the air.

[0147] In this specification, etc., the NASICON crystal structure refers to a compound represented by M2(XO4)3 (M: transition metal, X: S, P, As, Mo, W, etc.), which has a structure in which MO6 octahedra and XO4 tetrahedra share vertices and are three-dimensionally arranged.

[0148] Halide-based solid electrolytes include LiAlCl4, Li3InBr6, LiF, LiCl, LiBr, LiI, etc. In addition, composite materials in which these halide-based solid electrolytes are filled in the pores of porous alumina or porous silica can also be used as solid electrolytes.

[0149] Also, different types of solid electrolytes may be mixed and used.

[0150] Also, an electrolytic solution may be mixed with the solid electrolyte and used.

[0151] As the electrolytic solution to be mixed with the solid electrolyte, it is preferable to use a highly purified electrolytic solution with a low content of particulate dust and elements other than the constituent elements of the electrolytic solution (hereinafter also simply referred to as "impurities"). Specifically, it is preferable that the weight ratio of impurities to the electrolytic solution is 1% or less, preferably 0.1% or less, and more preferably 0.01% or less.

[0152] Also, additives such as vinylene carbonate, propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), lithium bis(oxalate) borate (LiBOB), and dinitrile compounds such as succinonitrile and adiponitrile may be added to the electrolytic solution to be mixed with the solid electrolyte. The concentration of the additive material may be, for example, 0.1 wt% or more and 5 wt% or less based on the whole solvent.

[0153] Also, as a material to be mixed with the solid electrolyte, a polymer gel electrolyte in which a polymer is swollen with an electrolytic solution may be used.

[0154] By using the polymer gel electrolyte, the safety against liquid leakage and the like is enhanced. Also, the secondary battery can be made thinner and lighter.

[0155] As the polymer to be gelled, silicone gel, acrylic gel, acrylonitrile gel, polyethylene oxide-based gel, polypropylene oxide-based gel, fluorine-based polymer gel, etc. can be used.

[0156] As the polymer, for example, a polymer having a polyalkylene oxide structure such as polyethylene oxide (PEO), PVDF, polyacrylonitrile, etc., and copolymers containing them can be used. For example, PVDF-HFP, which is a copolymer of PVDF and hexafluoropropylene (HFP), can be used. Further, the formed polymer may have a porous shape.

[0157] Also, this embodiment can be freely combined with other embodiments.

[0158] (Embodiment 4) In this embodiment, an example of mounting a secondary battery, which is one aspect of the present invention, on an electronic device or a moving body will be described.

[0159] First, examples of mounting a secondary battery on an electronic device, which were partly described in Embodiment 2, are shown in FIGS. 8A to 8E. As an electronic device to which a bendable secondary battery is applied, for example, a television device (also referred to as a TV or a television receiver), a monitor for a computer, a digital camera, a digital video camera, a digital photo frame, a mobile phone (also referred to as a mobile phone or a mobile phone device), a portable game machine, a portable information terminal, an audio playback device, a large game machine such as a pachinko machine, etc. can be mentioned.

[0160] Also, a secondary battery can be applied to a moving body, typically an automobile. Examples of automobiles include next-generation clean energy vehicles such as hybrid vehicles (HEV), electric vehicles (EV), or plug-in hybrid vehicles (PHEV), and a secondary battery can be applied as one of the power sources mounted on the automobile. The moving body is not limited to an automobile. For example, as the moving body, trains, monorails, ships, flying bodies (helicopters, unmanned aerial vehicles (drones), airplanes, rockets), electric bicycles, electric motorcycles, etc. can also be mentioned, and a secondary battery of one aspect of the present invention can be applied to these moving bodies.

[0161] In addition, the secondary battery of the present embodiment may be applied to a ground-mounted charging device provided in a house or a charging station provided in a commercial facility.

[0162] FIG. 8A shows an example of a mobile phone. The mobile phone 2100 includes, in addition to a display unit 2102 incorporated in a housing 2101, operation buttons 2103, an external connection port 2104, a speaker 2105, a microphone 2106, and the like. Note that the mobile phone 2100 has a secondary battery 2107.

[0163] The mobile phone 2100 can execute various applications such as mobile phone calls, e-mails, text viewing and creation, music playback, Internet communication, and computer games.

[0164] In addition to time setting, the operation buttons 2103 can have various functions such as turning on and off the power, turning on and off wireless communication, executing and canceling the silent mode, and executing and canceling the power-saving mode. For example, the functions of the operation buttons 2103 can be freely set by an operating system incorporated in the mobile phone 2100.

[0165] In addition, the mobile phone 2100 can execute short-range wireless communication conforming to a communication standard. For example, it can communicate with a wireless headset to make hands-free calls.

[0166] The mobile phone 2100 is provided with an external connection port 2104 and can directly exchange data with other information terminals via a connector. Charging can also be performed via the external connection port 2104. Note that the charging operation may be performed by wireless power supply without using the external connection port 2104.

[0167] The mobile phone 2100 preferably has a sensor. As the sensor, for example, a human body sensor such as a fingerprint sensor, a pulse sensor, or a body temperature sensor, or a touch sensor, a pressure sensor, an acceleration sensor, etc. are preferably mounted.

[0168] Figure 8B shows a drone 2300 having a plurality of rotors 2302. The drone 2300 may also be called an unmanned aerial vehicle. The drone 2300 has a secondary battery 2301, a camera 2303, and an antenna (not shown), which is an aspect of the present invention. The drone 2300 can be remotely operated via the antenna. Since the secondary battery of an aspect of the present invention has high safety, it can be safely used for a long time over a long period, and is suitable as a secondary battery mounted on the drone 2300.

[0169] Also, as shown in Figure 8C, a secondary battery 2602 having a plurality of secondary batteries 2601 of an aspect of the present invention may be mounted on a hybrid electric vehicle (HEV), an electric vehicle (EV), a plug-in hybrid electric vehicle (PHEV), or other electronic devices.

[0170] Figure 8D shows an example of a vehicle equipped with the secondary battery 2602. The vehicle 2603 is an electric vehicle that uses an electric motor as a power source for driving. Alternatively, it is a hybrid vehicle that can appropriately select and use an electric motor and an engine as a power source for driving.

[0171] Here, a lithium-ion battery mounted on an automobile is mounted after passing performance tests, reliability tests, abuse tests, etc. In particular, in the reliability test, it is confirmed whether battery damage or electrical contact failure occurs due to random waves caused by vibrations during vehicle running or vibrations of the drive system.

[0172] For example, due to the drop collision of a lithium-ion battery, the structure inside the battery moves downward, and the separator is sandwiched between the positive electrode current collector and the negative electrode plate and damaged, which may cause a short circuit during charging. Therefore, by using the secondary battery of an aspect of the present invention with high electrode strength, a lithium-ion battery capable of withstanding the reliability test can be provided.

[0173] A vehicle 2603 using an electric motor has a plurality of ECUs (Electronic Control Units), and the ECUs perform engine control and the like. The ECU includes a microcomputer. The ECU is connected to a CAN (Controller Area Network) provided in the electric vehicle. CAN is one of the serial communication standards used as an in-vehicle LAN. By using the secondary battery according to one aspect of the present invention, it can function as a power source for the ECU, and a vehicle with high safety and a long cruising range can be realized.

[0174] The secondary battery can not only drive an electric motor (not shown), but also supply power to a light-emitting device such as a headlight and a room light. Further, the secondary battery can supply power to a display device and a semiconductor device such as a speedometer, a tachometer, and a navigation system that the vehicle 2603 has.

[0175] The vehicle 2603 can be charged by receiving power supply from an external charging facility by a plug-in method, a non-contact power supply method, or the like to the secondary battery included in the secondary battery 2602.

[0176] FIG. 8E shows a state in which the vehicle 2603 is being charged from a ground-installed charging device 2604 via a cable. When charging, the charging method, the connector standard, and the like may be appropriately performed in a predetermined manner such as CHAdeMO (registered trademark) or Combo. For example, by the plug-in technology, the secondary battery 2602 mounted on the vehicle 2603 can be charged by external power supply. The charging can be performed by converting AC power into DC power via a conversion device such as an AC-DC converter. The charging device 2604 may be provided in a house as shown in FIG. 8E, or may be a charging station provided in a commercial facility.

[0177] Further, although not shown, a power receiving device can be mounted on a vehicle and charged by non - contact power supply from a power transmission device on the ground. In the case of this non - contact power supply method, by incorporating the power transmission device into a road or an outer wall, charging can be performed not only while the vehicle is parked but also while it is running. Also, using this non - contact power supply method, power can be transmitted and received between vehicles. Furthermore, a solar cell can be provided on the exterior of the vehicle to charge the secondary battery when the vehicle is parked or running. For such non - contact power supply, an electromagnetic induction method or a magnetic field resonance method can be used.

[0178] Also, the house shown in Fig. 8E has a power storage system 2612 having a secondary battery, which is one aspect of the present invention, and a solar panel 2610. The power storage system 2612 is electrically connected via the solar panel 2610, wiring 2611, etc. Also, the power storage system 2612 and a ground - mounted charging device 2604 may be electrically connected. The power obtained by the solar panel 2610 can be charged into the power storage system 2612. Also, the power stored in the power storage system 2612 can be charged into the secondary battery 2602 of the vehicle 2603 via the charging device 2604.

[0179] The power stored in the power storage system 2612 can also supply power to other electronic devices in the house. Therefore, even when power supply from the commercial power source cannot be received due to a power outage or the like, by using the power storage system 2612 according to one aspect of the present invention as an uninterruptible power supply, the use of electronic devices becomes possible.

[0180] This embodiment can be used in appropriate combination with other embodiments.

Example

[0181] In this example, a secondary battery (Sample 1A) having a positive electrode with reduced graphene as a conductive material was fabricated and its characteristics were evaluated.

[0182] <Fabrication of secondary battery> For evaluation, a coin-type secondary battery of the CR2032 type (diameter 20 mm, height 3.2 mm) was fabricated.

[0183] Commercially available LCO (C-10N manufactured by Nippon Chemical Industry Co., Ltd.) was used as the positive electrode active material of the secondary battery. Graphene oxide (manufactured by Nisenco Materials Co., Ltd., using the Modified Hummers method in the oxidation process) was used as the conductive material. This is reduced in a later process. PVDF (TA5130 manufactured by Solvay) was used as the binder. The positive electrode active material, conductive material, and binder were mixed so that the ratio was 95:3:2 (weight %), and a slurry was prepared. NMP was used as the solvent. The slurry was coated on the current collector. Aluminum foil was used as the current collector.

[0184] Next, a drying treatment was performed. The drying treatment was carried out in a ventilation drying oven. In a ventilated state, after heat treatment at a set temperature of 50 °C for 1 hour, the set temperature was raised to 80 °C, and heat treatment at 80 °C for 30 minutes was performed.

[0185] Subsequently, heat treatment was performed. The heat treatment was carried out under vacuum at a set temperature of 130 °C for 10 hours.

[0186] Next, the graphene oxide in the positive electrode active material layer was reduced.

[0187] First, chemical reduction was performed. L-ascorbic acid was used as the reducing agent for chemical reduction. The solvent was water:NMP = 1:9 (volume ratio), and a 0.078 mol / L L-ascorbic acid solution was prepared. The electrode coated with the positive electrode active material layer was immersed in the ascorbic acid solution and reacted at 60 °C for 1 hour.

[0188] Subsequently, thermal reduction was performed at a heating temperature of 170 °C and a heating time of 10 hours.

[0189] After the reduction treatment, it was pressed at a linear pressure of 210 kN / m, and then pressed again at a linear pressure of 1467 kN / m to obtain the positive electrode.

[0190] Lithium metal was used as the counter electrode.

[0191] As the electrolyte in the electrolytic solution, lithium hexafluorophosphate (LiPF6) at 1 mol / L was used. As the electrolytic solution, a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) with EC:DEC = 3:7 (volume ratio) was used, and furthermore, vinylene carbonate (VC) was added at 2 wt% as an additive.

[0192] For the separator, polypropylene with a thickness of 25 μm was used.

[0193] For the positive electrode can and the negative electrode can, those made of stainless steel (SUS) were used.

[0194] <Battery Characteristics and Cycle Characteristics> Next, a charge-discharge test was conducted on Sample 1A. Charging was performed by CCCV (0.5C, 4.2V, termination current 0.05C), and discharging was performed by CC (0.5C, termination voltage 2.5V), and the measurements were taken at 25°C. In this example, 1C was defined as 137 mA / g.

[0195] The charge-discharge curve of Sample 1A is shown in Figure 9. Sample 1A was capable of sufficient charge and discharge. Also, the strength of the positive electrode active material layer of Sample 1A was good.

[0196] Thus, the secondary battery using graphene oxide as the conductive material was good in terms of the strength of the positive electrode active material layer, discharge characteristics, etc.

Explanation of Reference Signs

[0197] 101 mixture, 102 mixture, 103 mixture, 104 mixture, 300 secondary battery, 301 positive electrode can, 302 negative electrode 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 secondary battery, 410 positive electrode, 411 positive electrode active material, 413 positive electrode current collector, 414 positive electrode active material layer, 420 solid electrolyte layer, 421 solid electrolyte, 430 negative electrode, 431 negative electrode active material, 433 negative electrode current collector, 434 negative electrode active material layer, 500 secondary battery, 503 positive electrode, 506 negative electrode, 507 separator, 508 electrolyte solution, 509 exterior body, 510 positive electrode lead electrode, 511 negative electrode lead electrode, 520 solid electrolyte layer, 600 secondary battery, 601 positive electrode cap, 602 battery can, 603 positive electrode terminal, 604 positive electrode, 605 separator, 606 negative electrode, 607 negative electrode terminal, 608 insulating plate, 609 insulating plate, 611 PTC element, 612 safety valve mechanism, 613 conductive plate, 614 conductive plate, 615 module, 616 conducting wire, 617 temperature control device, 904 positive electrode active material, 913 secondary battery, 930 housing, 931 negative electrode, 932 positive electrode, 933 separator, 950 wound body, 951 terminal, 952 terminal, 2100 mobile phone, 2101 housing, 2102 display unit, 2103 operation button, 2104 external connection port, 2105 speaker, 2106 microphone, 2107 secondary battery, 2300 unmanned aerial vehicle, 2301 secondary battery, 2302 rotor, 2303 camera, 2601 secondary battery, 2602 secondary battery, 2603 vehicle, 2604 charging device, 2610 solar panel, 2611 wiring, 2612 energy storage system

Claims

1. A first step of applying a mixture comprising an active material, a conductive aid having a graphene compound, a binder having polyvinylidene fluoride, and a dispersion medium to a current collector; A second step of drying the mixture at a temperature of room temperature or higher and 90°C or lower; A third step of heat-treating the mixture at a temperature of 120°C or higher and 140°C or lower; A fourth step of reducing the graphene compound in the mixture by a chemical reaction using a reducing agent; A fifth step of performing a thermal reduction treatment on the mixture at a temperature higher than the temperature of the third step and 125°C or higher and 180°C or lower, and The temperature of the third step is equal to or higher than the temperature at which at least a part of the binder crystallizes and equal to or lower than the temperature at which the binder melts. A method for manufacturing an electrode.

2. A first step of applying a mixture comprising an active material, a conductive aid having a graphene compound, a binder having polyvinylidene fluoride, and a dispersion medium to a current collector; A second step of drying the mixture at a temperature of room temperature or higher and 90°C or lower; A third step of heat-treating the mixture at a temperature of 120°C or higher and 140°C or lower and for a longer time than the time of the second step; A fourth step of reducing the graphene compound in the mixture by a chemical reaction using a reducing agent; A fifth step of performing a thermal reduction treatment on the mixture at a temperature higher than the temperature of the third step and 125°C or higher and 180°C or lower, and The temperature of the third step is equal to or higher than the temperature at which at least a part of the binder crystallizes and equal to or lower than the temperature at which the binder melts. A method for manufacturing an electrode.

3. In Claim 1 or Claim 2, The method for manufacturing an electrode, wherein the graphene compound is graphene oxide.

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