Power storage device and electronic device

Abstract

One embodiment of the present invention provides an energy storage device with minimal degradation of charge and discharge characteristics due to heat treatment. Alternatively, it provides an energy storage device with high safety during heat treatment. One embodiment of the present invention is an energy storage device comprising: a positive electrode, a negative electrode, an insulator, an electrolyte, and an outer casing, wherein the insulator is located between the positive and negative electrodes, and the insulator comprises polyphenylene sulfide or cellulose fiber; the electrolyte comprises propylene carbonate, ethylene carbonate, ethylene carbonate, lithium hexafluorophosphate, and lithium bis(pentafluoroethanesulfonyl)amine, wherein the concentration weight ratio of lithium hexafluorophosphate to the electrolyte is 0.01 wt% or more and 1.9 wt% or less.

Description

Technical Field

[0001] One embodiment of the present invention relates to an energy storage device and an electronic device.

[0002] Note that one embodiment of the present invention is not limited to the above-described technical fields. One embodiment of the invention disclosed in this specification relates to an article, method, or manufacturing method. One embodiment of the present invention relates to a process, machine, manufacture, or composition of matter. Therefore, more specifically, examples of the technical fields of one embodiment of the invention disclosed in this specification include semiconductor devices, display devices, light-emitting devices, energy storage devices, memory devices, imaging devices, methods for driving these devices, and methods for manufacturing these devices.

[0003] In this specification, energy storage devices refer to all components and devices with energy storage functions. For example, energy storage devices such as lithium-ion secondary batteries (also known as secondary batteries), lithium-ion capacitors, and double-layer capacitors are all included in the scope of energy storage devices. Prior Technology

[0004] In recent years, various energy storage devices, such as lithium-ion rechargeable batteries, lithium-ion capacitors, and air batteries, have been actively developed. In particular, with the development of the semiconductor industry for portable information terminals such as mobile phones, smartphones, and laptops, portable music players, digital cameras, medical devices, and next-generation clean energy vehicles such as hybrid electric vehicles (HEVs), electric vehicles (EVs), and plug-in hybrid electric vehicles (PHEVs), the demand for high-output, high-energy-density lithium-ion rechargeable batteries has surged. As a rechargeable energy source, they have become a necessity in modern information society.

[0005] Thus, lithium-ion rechargeable batteries are used in various fields and applications. Among these, lithium-ion rechargeable batteries are required to possess characteristics such as high energy density, high cycle performance, and safety under various operating environments.

[0006] In addition, lithium-ion secondary batteries have at least a positive electrode, a negative electrode, and an electrolyte (Patent Document 1).

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2012-9418 Summary of the Invention

[0008] When energy storage devices are incorporated into electronic devices such as wearable devices and portable information terminals, they need to be able to withstand the heat treatment during the manufacturing of the electronic devices. In particular, when the casing of the electronic device is formed together with the lithium-ion battery, it needs to have heat resistance above the manufacturing temperature of the casing.

[0009] To improve the heat resistance of energy storage devices, electrolytes are required to have high heat resistance. To improve the heat resistance of electrolytes, it is considered effective to inhibit electrolyte decomposition due to heat or to inhibit decomposition due to reactions with other components. Reactions of the electrolyte with other components include, for example, reactions between the electrolyte and the positive electrode, negative electrode, insulator, or outer packaging.

[0010] In view of the above problems, one objective of one embodiment of the present invention is to provide an energy storage device with minimal degradation of charge and discharge characteristics due to heat treatment. Another objective of one embodiment of the present invention is to provide an energy storage device with high safety during heat treatment. Furthermore, one objective of one embodiment of the present invention is to provide an energy storage device with high flexibility. Moreover, one objective of one embodiment of the present invention is to provide a novel energy storage device or electronic device, etc.

[0011] Note that the description of these objectives does not preclude the existence of other objectives. One embodiment of the present invention does not need to achieve all of the above objectives. Objectives other than those described above can be obtained from the specification, drawings, claims, etc.

[0012] One embodiment of the present invention is an energy storage device, comprising: a positive electrode, a negative electrode, a first insulator, an electrolyte, and an outer packaging body, wherein the positive electrode comprises a positive electrode active material layer and a positive electrode current collector, the negative electrode comprises a negative electrode active material layer and a negative electrode current collector, the first insulator is located between the positive electrode and the negative electrode, the first insulator comprises polyphenylene sulfide or cellulose fiber, and the electrolyte comprises propylene carbonate, ethylene carbonate, ethylene carbonate, lithium hexafluorophosphate, and lithium salt represented by the following general formula (G1).

[0013]

[0014] In the above general formula (G1), R1 and R2 independently represent fluorine, or a fluoroalkyl group having 1 to 10 carbon atoms in a straight-chain, branched, or cyclic form.

[0015] In the above-mentioned energy storage device, it is preferable to further include a second insulator, wherein the second insulator is located between one or more of the positive and negative electrodes and the outer packaging body, and the second insulator comprises polyphenylene sulfide or cellulose fiber.

[0016] In the above-mentioned energy storage device, the concentration of lithium hexafluorophosphate relative to the electrolyte is preferably 0.01 wt% or more and 1.9 wt% or less.

[0017] In the above-mentioned energy storage device, the lithium salt represented by the general formula (G1) is preferably lithium bis(pentafluoroethanesulfonyl)amine.

[0018] In the above-mentioned energy storage device, the positive current collector is preferably made of aluminum or stainless steel.

[0019] One embodiment of the present invention is an electronic device comprising: the aforementioned energy storage device, a watch strap, a display panel, and a housing, wherein the energy storage device includes a positive lead and a negative lead, the positive lead being electrically connected to a positive terminal and the negative lead being electrically connected to a negative terminal, the energy storage device being embedded inside the watch strap, a portion of the positive lead and a portion of the negative lead protruding from the watch strap, the energy storage device being flexible, the energy storage device being electrically connected to the display panel, the display panel being included in the housing, the watch strap being connected to the housing, and the watch strap comprising a rubber material.

[0020] In the aforementioned electronic devices, the rubber material is preferably fluororubber or silicone rubber.

[0021] One embodiment of the present invention provides an energy storage device with minimal degradation of charge and discharge characteristics due to heat treatment. Furthermore, one embodiment of the present invention provides an energy storage device with high safety during heat treatment. Additionally, one embodiment of the present invention provides an energy storage device with high flexibility. Moreover, one embodiment of the present invention provides a novel energy storage device or electronic device, etc.

[0022] Note that the description of these effects does not preclude the existence of other effects. One embodiment of the present invention does not necessarily require all of the aforementioned effects. Furthermore, effects other than those described above are clearly present in the specification, drawings, and claims, and such effects can be derived from the description in the specification, drawings, and claims. Simple Explanation of the Diagram

[0023] In the diagram: Figures 1A to 1C are diagrams illustrating an example of an energy storage device and an example of an electrode; Figures 2A and 2B are diagrams illustrating an example of an energy storage device; Figures 3A and 3B are diagrams illustrating an example of an energy storage device; Figures 4A and 4B are diagrams illustrating an example of an energy storage device; Figures 5A and 5B are diagrams illustrating an example of an energy storage device; Figures 6A to 6F are diagrams illustrating an example of embossing; Figures 7A and 7B are diagrams illustrating an example of an energy storage device; Figure 8 is a diagram illustrating an example of an energy storage device; Figure 9 is a diagram illustrating an example of an energy storage device; Figures 10A to 10C are figures illustrating an example of a method for manufacturing an energy storage device; Figures 11A to 11C are figures illustrating an example of a method for manufacturing an energy storage device; Figures 12A to 12C are figures illustrating an example of a method for manufacturing an energy storage device; Figure 13 is a diagram illustrating an example of a method for manufacturing an energy storage device; Figures 14A to 14C are diagrams illustrating an example of an electronic device, a watchband, and a battery storage device; Figures 15A to 15C are diagrams illustrating an example of a watch strap and a battery storage device; Figures 16A and 16B are diagrams illustrating an example of an energy storage device; Figures 17A to 17C are diagrams illustrating an example of a liquid leak detection method; Figures 18A and 18B are diagrams illustrating an example of an energy storage device; Figures 19A and 19B are diagrams illustrating an example of an energy storage device; Figure 20 is a diagram illustrating an example of an energy storage device; Figures 21A to 21D are figures illustrating an example of a method for manufacturing an energy storage device; Figures 22A, 22B, 22C1 and 22C2 are diagrams illustrating an example of an energy storage device; Figure 23 is a diagram illustrating an example of an energy storage device; Figures 24A to 24D are figures illustrating an example of a method for manufacturing an energy storage device; Figure 25 is a diagram illustrating an example of an energy storage device; Figures 26A to 26F are diagrams illustrating an example of an electronic device; Figures 27A to 27D are diagrams illustrating an example of an electronic device; Figures 28A to 28C are diagrams illustrating an example of an electronic device; Figure 29 is a diagram illustrating an example of an electronic device; Figures 30A and 30B are diagrams illustrating an example of an electronic device; Figures 31A to 31D are graphs showing the charge-discharge curves according to Example 1; Figures 32A to 32D are graphs showing the charge-discharge curves according to Example 1; Figures 33A to 33D are graphs showing the charge-discharge curves according to Example 1; Figures 34A to 34D are graphs showing the charge-discharge curves according to Example 1; Figures 35A to 35D are diagrams illustrating the cyclic characteristics according to Example 1; Figures 36A to 36D are diagrams illustrating the cyclic characteristics according to Example 1; Figures 37A to 37D are diagrams illustrating the cyclic characteristics according to Example 1; Figures 38A to 38D are diagrams illustrating the cyclic characteristics according to Example 1; Figures 39A to 39D are diagrams illustrating the cyclic characteristics according to Example 1; Figures 40A to 40D are diagrams illustrating the cyclic characteristics according to Example 1; Figures 41A to 41D are diagrams illustrating the cyclic characteristics according to Example 1; Figures 42A to 42D are diagrams illustrating the cyclic characteristics according to Example 1; Figures 43A and 43B are graphs showing the relationship between lithium hexafluorophosphate concentration and cycling characteristics according to Example 1; Figures 44A to 44D are graphs showing the charge-discharge curves according to Example 2; Figures 45A and 45B are graphs showing the charge-discharge curves according to Example 2; Figures 46A to 46C are diagrams illustrating the cyclic characteristics according to Example 2; Figures 47A to 47C are diagrams illustrating the cyclic characteristics according to Example 2; Figures 48A to 48C are diagrams illustrating the cyclic characteristics according to Example 2; Figures 49A to 49C are diagrams illustrating the cyclic characteristics according to Example 2; Figures 50A and 50B are graphs showing the relationship between lithium hexafluorophosphate concentration and cycling characteristics according to Example 2; Figure 51 is a diagram showing the XPS measurement locations according to Example 3; Figures 52A to 52C are graphs showing the XPS spectra according to Example 3; Figures 53A to 53C are graphs showing the XPS spectra according to Example 3; Figures 54A to 54C are graphs showing the XPS spectra according to Example 3; Figures 55A and 55B are graphs showing the XPS spectra according to Example 3; Figures 56A and 56B are graphs showing the TG-DTA measurement results according to Example 4; Figure 57 is a graph showing the TG-DTA determination results according to Example 4. Implementation

[0024] The embodiments are described in detail below with reference to the drawings. Note that the present invention is not limited to the following description, and those skilled in the art will readily understand that its methods and details can be varied in many ways without departing from the spirit and scope of the invention. Therefore, the present invention should not be construed as being limited to the contents described in the embodiments shown below.

[0025] Note that in the structure of the invention described below, the same element symbols are used in different figures to represent the same parts or parts with the same function, and repeated descriptions are omitted. In addition, when parts with the same function are represented, the same shading lines are sometimes used without additional element symbols.

[0026] Furthermore, for ease of understanding, the positions, sizes, and extents of various components shown in drawings, etc., do not necessarily represent their actual positions, sizes, and extents. Therefore, the disclosed invention is not necessarily limited to the positions, sizes, and extents disclosed in the drawings, etc.

[0027] Furthermore, in this specification, flexibility refers to the property of a flexible and bendable object. Flexibility is the property of an object to deform according to an external force applied to it, without considering elasticity or the ability to recover its original shape. A flexible energy storage device can deform according to an external force. A flexible energy storage device can be used in a fixed deformed state, or in a repeatedly deformed state, or in a state without deformation. Furthermore, in this specification, the interior of the outer casing refers to the area within the energy storage device enclosed by the outer casing, which houses structures such as the positive electrode, negative electrode, active material layer, separator, and electrolyte.

[0028] Furthermore, depending on the circumstances or state, the "film" and "layer" can be interchanged. For example, sometimes a "conductive layer" can be replaced with a "conductive film." Additionally, sometimes an "insulating film" can be replaced with an "insulating layer."

[0029] Implementation Method 1 In this embodiment, an energy storage device according to one embodiment of the present invention will be described with reference to FIGS. 1A to 13.

[0030] An embodiment of the present invention provides an energy storage device comprising a positive electrode, a negative electrode, an insulator, an electrolyte, and an outer packaging.

[0031] To improve the heat resistance of energy storage devices, electrolytes are required to have high heat resistance. To improve the heat resistance of electrolytes, it is considered effective to inhibit electrolyte decomposition due to heat or to inhibit decomposition due to reactions with other components. Reactions of the electrolyte with other components include, for example, reactions between the electrolyte and the positive electrode, negative electrode, insulator, or outer packaging.

[0032] In this specification and other materials, an electrolyte refers to a substance that conducts electricity. Electrolytes are not limited to liquids; they can also be gels or solids. Liquid electrolytes are sometimes referred to as electrolyte solutions, and electrolyte solutions can be manufactured by dissolving a solute in a solvent. Furthermore, solid electrolytes are sometimes referred to as solid electrolytes.

[0033] For example, lithium hexafluorophosphate (LiPF6), represented by structural formula (100), is widely used as a solute in electrolytes. However, lithium hexafluorophosphate has low chemical and thermal stability. For instance, lithium hexafluorophosphate hydrolyzes with trace amounts of moisture to produce HF, which can cause degradation of energy storage devices. Furthermore, at high temperatures, lithium hexafluorophosphate decomposes into LiF and PF5, and PF5 causes solvent decomposition, resulting in low stability as a solute at high temperatures. The thermal decomposition temperature of lithium hexafluorophosphate is approximately 154°C. The thermal decomposition temperature refers to the temperature at which the weight of the powdered product decreases by 5% due to thermal decomposition. The weight change caused by thermal decomposition can be determined using methods such as thermogravimetry-differential thermal analysis (TG-DTA).

[0034]

[0035] The general formula (G1) represents the lithium salt used in one embodiment of the present invention.

[0036]

[0037] In general formula (G1), R1 and R2 independently represent fluorine, or a fluoroalkyl group having 1 to 10 carbon atoms in a straight-chain, branched, or cyclic form.

[0038] In this specification, etc., fluoroalkyl refers to a group in which some or all of the hydrogen atoms in an alkyl group are replaced by fluorine atoms. Preferably, more than 60% of the hydrogen atoms in the alkyl group are replaced by fluorine atoms. Fluoroalkyl may also contain atoms other than carbon, hydrogen, and fluorine, such as oxygen, sulfur, and nitrogen.

[0039] Lithium salts represented by the general formula (G1) exhibit high chemical and thermal stability. Due to their high decomposition temperature and heat resistance, their use as solutes can improve the heat resistance of energy storage devices. Furthermore, because lithium salts represented by the general formula (G1) contain highly electronegative fluorine, the fluoroalkyl sulfonic acid group exhibits strong electron-withdrawing properties and very high lithium-ion dissociation, making them suitable as solutes in electrolytes for energy storage devices such as lithium-ion secondary batteries. The more fluorine atoms contained in the fluoroalkyl group, the better.

[0040] In general formula (G1), R1 is preferably fluorine, or a linear, branched, or cyclic fluoroalkyl group having 1 to 7 carbon atoms. In general formula (G1), R2 is preferably fluorine, or a linear, branched, or cyclic fluoroalkyl group having 1 to 7 carbon atoms. By using this lithium salt as the solute in the electrolyte, the heat resistance of the energy storage device can be improved.

[0041] Furthermore, in general formula (G1), R1 is preferably fluorine, or a linear, branched, or cyclic fluoroalkyl group having 1 to 5 carbon atoms. In general formula (G1), R2 is preferably fluorine, or a linear, branched, or cyclic fluoroalkyl group having 1 to 5 carbon atoms. In this case, the dissociation of the lithium salt represented by general formula (G1) is improved, resulting in an electrolyte with high ionic conductivity. Furthermore, the molecular weight of the lithium salt represented by general formula (G1) is not increased, and the weight of the lithium salt dissolved in the solvent is very small. Therefore, the increase in electrolyte viscosity can be suppressed, and the degradation of battery characteristics can be prevented. In addition, cost can be reduced.

[0042] The specific structural formulas of lithium salts represented by general formula (G1) are shown below. Preferably, lithium bis(fluorosulfonyl)amine (Li(FSO₂)₂N, abbreviated as LiFSA, represented by structural formula (101), lithium bis(trifluoromethylsulfonyl)amine (Li(CF₃SO₂)₂N, abbreviated as LiTFSA, represented by structural formula (103), lithium bis(pentafluoroethanesulfonyl)amine (Li(C₂F₅SO₂)₂N, abbreviated as LiBETA, represented by structural formula (104), and lithium (perfluorobutylsulfonylfluoride)(trifluoromethylsulfonylfluoride)amine (LiN(C₄F₉SO₂)(CF₃SO₂)) are used as solutes. These materials have high thermal decomposition temperatures, thus using them as solutes can improve the heat resistance of the energy storage device. For example, lithium bis(fluorosulfonyl)amine has a melting point of 140°C and a thermal decomposition temperature of around 300°C. Lithium bis(trifluoromethylsulfonyl)amine has a melting point of 233°C and a thermal decomposition temperature of around 380°C. Lithium bis(pentafluoroethanesulfonyl)amine has a melting point of 328°C and a thermal decomposition temperature of around 350°C.

[0043]

[0044] However, lithium salts represented by the general formula (G1) sometimes react with the current collector, leading to corrosion of the current collector. Corrosion of the current collector can be a cause of reduced battery capacity.

[0045] Sometimes, the lithium hexafluorophosphate represented by the above structural formula (100) reacts with the current collector to form a transient film on the surface of the current collector, thereby inhibiting the corrosion of the current collector.

[0046] Therefore, in one embodiment of the present invention, the solute of the electrolyte preferably comprises a lithium salt represented by general formula (G1) and lithium hexafluorophosphate (LiPF6) represented by structural formula (100). Lithium hexafluorophosphate (LiPF6) forms a transient film on the surface of the current collector, thereby suppressing corrosion of the current collector. Preferably, an amount of lithium hexafluorophosphate (LiPF6) capable of forming a transient film on the surface of the current collector is used. Furthermore, the lithium salt represented by general formula (G1) primarily functions to supply lithium ions as carrier ions and has high heat resistance. Moreover, by using the lithium salt represented by general formula (G1) and lithium hexafluorophosphate (LiPF6) represented by structural formula (100), a high-heat-resistant energy storage device can be realized. Furthermore, an energy storage device whose capacity and energy density do not easily decrease after repeated charge-discharge cycles even after battery heating treatment can be realized.

[0047] Furthermore, to improve the heat resistance of the energy storage device, the solvent contained in the electrolyte is preferably a solvent with a high boiling point and low vapor pressure. It is also preferable to use a solvent with a high dielectric constant and a high solute dissolving capacity. Carbonates can be used as such solvents. Carbonates are compounds that contain at least one carbonate in their molecular structure, including cyclic carbonates and chain carbonates. The chain category includes linear and branched chains. Examples of cyclic carbonates include ethylene carbonate (EC) represented by structural formula (301), propylene carbonate (PC) represented by structural formula (302), and ethylene carbonate (VC) represented by structural formula (303). Ethylene carbonate (EC) has a boiling point of 243°C, propylene carbonate (PC) has a boiling point of 242°C, and ethylene carbonate (VC) has a boiling point of 162°C. These materials have high pressure resistance and low vapor pressure, making them preferable as solvents.

[0048]

[0049] When the negative electrode is graphite (layered graphite), propylene carbonate (PC) sometimes fails to form a passive film on the graphite surface and instead inserts into the spaces between the graphite layers along with lithium ions, causing a portion of the graphite layer to peel off from the graphite particles. Therefore, it is preferable to mix the electrolyte with a solvent that functions to form a passive film on the graphite surface. Examples of solvents that function to form a passive film on the graphite surface include ethylene carbonate (EC) and ethylene carbonate (VC). Thus, in one embodiment of the present invention, propylene carbonate (PC), ethylene carbonate (EC), and ethylene carbonate (VC) are used as the solvent for the electrolyte. This suppresses the peeling of a portion of the graphite layer from the graphite particles.

[0050] Therefore, in one embodiment of the present invention, the solvent as the electrolyte preferably comprises ethylene carbonate (EC), propylene carbonate (PC) and ethylene carbonate (VC), and the solute as the electrolyte preferably comprises a lithium salt represented by general formula (G1) and lithium hexafluorophosphate (LiPF6).

[0051] In one embodiment of the energy storage device of the present invention, the electrolyte is preferably prepared by mixing ethylene carbonate (VC) with a mixture of ethylene carbonate (EC) and propylene carbonate (PC) in a volume ratio of 1:1 and dissolving lithium bis(pentafluoroethanesulfonyl)amine (LiBETA) and lithium hexafluorophosphate.

[0052] Specifically, the dissolved ethylene carbonate (VC) has a weight ratio of 0.1 wt% to 5.0 wt% relative to the electrolyte, preferably 1.0 wt%. The dissolved lithium bis(pentafluoroethanesulfonyl)amine (LiBETA) has a molar concentration of 0.1 mol / L to 5.0 mol / L relative to the electrolyte, preferably 1 mol / L. Lithium hexafluorophosphate is preferably used with a weight ratio of 0.01 wt% to 1.9 wt% relative to the electrolyte. More preferably, lithium hexafluorophosphate has a weight ratio of 0.05 wt% to 1.2 wt% relative to the electrolyte. Even more preferably, lithium hexafluorophosphate has a weight ratio of 0.1 wt% to 0.8 wt% relative to the electrolyte.

[0053] The composition of electrolytes can be confirmed using the following methods: X-ray photoelectron spectroscopy (XPS), gas chromatography-mass spectrometry (GC-MS), liquid chromatography-mass spectrometry (LC-MS), ion chromatography (IC), inductively coupled plasma atomic emission spectrometry (ICP-AES), atomic absorption spectrometry (AAS), glow discharge mass spectrometry (GD-MS), nuclear magnetic resonance (NMR), and Fourier transform infrared spectroscopy (FT-IR).

[0054] Polyethylene, polypropylene, and other materials commonly used as separators have very low heat resistance. Sometimes, at high temperatures, the micropores of the separator become blocked, causing the energy storage device to malfunction.

[0055] Therefore, in an embodiment of the energy storage device of the present invention, it is preferred to use an insulator containing polyphenylene sulfide (PSS) or an insulator containing cellulose fibers.

[0056] Insulators containing polyphenylene sulfide and insulators containing cellulose fibers exhibit excellent heat resistance and drug resistance.

[0057] Insulators containing polyphenylene sulfide and insulators containing cellulose fibers exhibit very low reactivity with the electrolyte at high temperatures. Therefore, the degradation of output characteristics or charge-discharge cycle characteristics can be suppressed.

[0058] <Example of the structure of an energy storage device> The specific structure of an energy storage device according to one embodiment of the present invention will be described below.

[0059] Figure 1A shows a power storage device 500 according to one embodiment of the present invention. In Figure 1A, as an example of the power storage device 500, a thin power storage device is shown, but the power storage device according to one embodiment of the present invention is not limited thereto.

[0060] As shown in Figure 1A, the energy storage device 500 includes a positive electrode 503, a negative electrode 506, a first isolator 507, a second isolator 520, and an outer packaging 509. The energy storage device 500 may also include a positive lead 510 and a negative lead 511. In addition, the joint portion 518 is a portion that joins the outer periphery of the outer packaging 509 by heat pressing.

[0061] Figure 1B shows the appearance of the positive electrode 503. The positive electrode 503 includes a positive current collector 501 and a positive active material layer 502.

[0062] As shown in Figure 1B, the positive electrode 503 preferably has a tab region 281. A portion of the tab region 281 is preferably soldered to the positive electrode lead 510. The tab region 281 preferably has an area that exposes the positive current collector 501. By soldering the positive lead 510 to the area exposing the positive current collector 501, the contact resistance can be further reduced. In Figure 1B, an example is shown where the positive current collector 501 is exposed throughout the entire tab region 281, but the tab region 281 may also have a positive active material layer 502 in a portion thereof.

[0063] Figure 1C shows the appearance of the negative electrode 506. The negative electrode 506 includes a negative electrode current collector 504 and a negative electrode active material layer 505.

[0064] As shown in Figure 1C, the negative electrode 506 preferably has a tab region 282. A portion of the tab region 282 is preferably soldered to the negative electrode lead 511. The tab region 282 preferably has an area that exposes the negative electrode current collector 504. By soldering the negative electrode lead 511 to the area exposing the negative electrode current collector 504, the contact resistance can be further reduced. In Figure 1C, an example is shown where the negative electrode current collector 504 is exposed throughout the entire tab region 282, but the tab region 282 may also have a negative electrode active material layer 505 in a portion thereof.

[0065] As shown in Figure 1A, the first isolator 507 includes regions overlapping with the positive electrode 503 and the negative electrode 506. The second isolator 520 includes regions overlapping with the tab regions 281 and 282. Note that the second isolator 520 may also be omitted.

[0066] Figures 2A and 2B show examples of cross-sectional views along the dashed line A1-A2 in Figure 1A. Figures 2A and 2B show the cross-sectional structure of an energy storage device 500 manufactured using a set of positive electrodes 503 and negative electrodes 506.

[0067] As shown in Figures 2A and 2B, the energy storage device 500 includes a positive electrode 503, a negative electrode 506, a first insulator 507, a second insulator 520, an electrolyte 508, and an outer packaging 509. The first insulator 507 is located between the positive electrode 503 and the negative electrode 506. The second insulator 520 is located between the positive electrode 503 and the outer packaging 509, and between the negative electrode 506 and the outer packaging 509. The outer packaging 509 is filled with the electrolyte 508.

[0068] The positive electrode 503 includes a positive electrode active material layer 502 and a positive electrode current collector 501. The negative electrode 506 includes a negative electrode active material layer 505 and a negative electrode current collector 504. The active material layer can be formed on one or both surfaces of the current collector. A first separator 507 is located between the positive electrode current collector 501 and the negative electrode current collector 504.

[0069] An energy storage device may consist of one or more positive terminals and one or more negative terminals. For example, an energy storage device may have a stacked structure that includes multiple positive terminals and multiple negative terminals.

[0070] Here, the positive electrode 503 and the negative electrode 506 preferably include tab regions for electrically connecting the stacked plurality of positive electrodes to each other and the plurality of negative electrodes to each other. Additionally, the tab regions are preferably electrically connected with leads.

[0071] Figures 3A and 3B show examples of cross-sectional views along the dashed lines B3-B4 and B5-B6 in Figure 1A, respectively. The cross-sectional view along dashed line B3-B4 is a cross-sectional view of the region including the positive lead 510 and the positive electrode 503. The cross-sectional view along dashed line B5-B6 is a cross-sectional view of the region including the negative lead 511 and the negative electrode 506. Figures 3A and 3B show the cross-sectional structure of an energy storage device 500 manufactured using a set of positive electrodes 503 and negative electrodes 506, respectively.

[0072] As shown in Figure 3A, the second isolator 520 is disposed between the positive electrode 503 and the outer packaging 509. Preferably, the second isolator 520 has a region overlapping with the tab region 281 and the positive electrode lead 510 included in the positive electrode. As shown in Figure 3B, the second isolator 520 is disposed between the negative electrode 506 and the outer packaging 509. Preferably, the second isolator 520 has a region overlapping with the tab region 282 and the negative electrode lead 511 included in the negative electrode.

[0073] When a conductive material is used on the outside of the outer packaging 509 and an insulating resin is used on its inside (positive and negative electrode sides), the resin may sometimes melt due to heat treatment, exposing the conductive material on the outside. If the conductive material of the outer packaging comes into contact with the positive electrode lead 510, the negative electrode lead 511, the positive electrode current collector 501, or the negative electrode current collector 504, leakage may occur. By providing a second isolator 520 between the positive electrode 503 and the outer packaging 509, and between the negative electrode 506 and the outer packaging 509, the aforementioned leakage can be suppressed. Note that the second isolator 520 may also be omitted.

[0074] Figure 4A shows another example of a cross-sectional view along the dashed line A1-A2 in Figure 1A. Additionally, Figure 4B shows a cross-sectional view along the dashed line B1-B2 in Figure 1A.

[0075] Figures 4A and 4B show the cross-sectional structure of an energy storage device 500 manufactured using multiple sets of positive electrodes 503 and negative electrodes 506. There is no particular limitation on the number of electrode layers included in the energy storage device 500. A larger number of electrode layers allows for the realization of an energy storage device with a greater capacity. Conversely, a smaller number of electrode layers allows for the realization of a thinner and more flexible energy storage device.

[0076] Figures 4A and 4B show examples of using two positive electrodes 503 having a positive active material layer 502 on one surface of the positive current collector 501; two positive electrodes 503 having a positive active material layer 502 on both surfaces of the positive current collector 501; and three negative electrodes 506 having a negative active material layer 505 on both surfaces of the negative current collector 504. That is, the energy storage device 500 includes six positive active material layers 502 and six negative active material layers 505. Note that Figures 4A and 4B show an example where the first insulator 507 is bag-shaped, but it is not limited to this; the first insulator 507 can be rectangular or corrugated.

[0077] In Figures 4A and 4B, it is preferable to replace one positive electrode with a positive active material layer 502 on each of the two surfaces of the positive current collector 501 with two positive electrodes having a positive active material layer 502 on each of the two surfaces of the positive current collector 501. Similarly, it is preferable to replace one negative electrode with a negative active material layer 505 on each of the two surfaces of the negative current collector 504 with two negative electrodes having a negative active material layer 505 on each of the two surfaces of the negative current collector 504. In the energy storage device 500 shown in Figures 5A and 5B, the surfaces of the positive current collectors 501 without the positive active material layer 502 are in contact with each other, and the surfaces of the negative current collectors 504 without the negative active material layer 505 are in contact with each other. By adopting the above structure, when the energy storage device 500 is bent, the interfaces of the two positive current collectors 501 and the interfaces of the two negative current collectors 504 become sliding surfaces, thereby mitigating the stress generated inside the energy storage device 500.

[0078] Although Figure 1A shows an example where the end of the positive electrode 503 is roughly aligned with the end of the negative electrode 506, the positive electrode 503 may also have a portion located outside the end of the negative electrode 506.

[0079] In the energy storage device 500, the area of ​​the region of the negative electrode 506 that does not overlap with the positive electrode 503 should be as small as possible.

[0080] Figure 2A shows an example where the end of the negative electrode 506 is located inside the positive electrode 503. By adopting this structure, the entire negative electrode 506 can overlap with the positive electrode 503, or the area of ​​the negative electrode 506 that does not overlap with the positive electrode 503 can be reduced.

[0081] Alternatively, in the energy storage device 500, the areas of the positive electrode 503 and the negative electrode 506 are preferably approximately the same. For example, the areas of the positive electrode 503 and the negative electrode 506, which are separated by the first insulator 507, are preferably approximately the same. For example, the areas of the positive electrode active material layer 502 and the negative electrode active material layer 505, which are separated by the first insulator 507, are preferably approximately the same.

[0082] Figure 2B shows an example where the end of the positive electrode 503 is located inside the negative electrode 506. By employing this structure, the entire positive electrode 503 can overlap with the negative electrode 506, or the area of ​​the positive electrode 503 that does not overlap with the negative electrode 506 can be reduced. If the end of the negative electrode 506 is located inside the end of the positive electrode 503, current may sometimes concentrate at the end of the negative electrode 506. For example, if the current concentrates on a portion of the negative electrode 506, lithium may sometimes deposit on the negative electrode 506. By reducing the area of ​​the positive electrode 503 that does not overlap with the negative electrode 506, current concentration on a portion of the negative electrode 506 can be suppressed. Therefore, lithium deposition on the negative electrode 506 can be suppressed, which is preferable.

[0083] As shown in Figures 4A and 4B, even when using multiple sets of positive electrodes 503 and negative electrodes 506, the end of the positive electrode 503 can be located inside the negative electrode 506. Furthermore, the end of the positive electrode 503 can be approximately aligned with the end of the negative electrode 506. Additionally, the end of the negative electrode 506 can be located inside the positive electrode 503.

[0084] As shown in Figure 1A, the positive lead 510 is preferably electrically connected to the positive terminal 503. Similarly, the negative lead 511 is preferably electrically connected to the negative terminal 506. The positive lead 510 and the negative lead 511 are exposed on the outside of the outer casing 509 and serve as terminals for electrical contact with the outside.

[0085] Alternatively, the positive current collector 501 and the negative current collector 504 can also serve as terminals for external electrical contact. In this case, the positive current collector 501 and the negative current collector 504 can be configured with a portion of them exposed outside the outer casing 509 without the use of leads.

[0086] A portion of the surface of the outer packaging 509 is preferably uneven. By making the outer packaging 509 uneven, the stress applied to the outer packaging 509 can be mitigated when the energy storage device 500 is bent. Therefore, the flexibility of the energy storage device 500 can be improved. The aforementioned unevenness can be formed by embossing the outer packaging 509 before assembling the energy storage device 500.

[0087] Here, we will explain one of the pressing processes: embossing.

[0088] Figures 6A to 6F are cross-sectional views illustrating examples of embossing. Embossing refers to the process of pressing an embossing roller with an embossing surface onto a film, thereby forming a raised or recessed pattern on the film corresponding to the embossing roller. An embossing roller is a roller whose surface is engraved with a pattern.

[0089] Figure 6A shows an example of embossing one surface of the film 50 used for the outer packaging 509.

[0090] Figure 6A shows a film 50 sandwiched between an embossing roller 53 in contact with one surface of the film and a roller 54 in contact with the other surface, with the film 50 being conveyed in the forward direction 60. Patterns can be formed on the film surface by applying pressure or heating.

[0091] The process shown in Figure 6A is also known as one-side embossing, in which the embossing process is performed by combining embossing rollers 53 and 54 (metal rollers or elastic rollers (rubber rollers, etc.)).

[0092] Figure 6B shows a film 51, one surface of which has been embossed, sandwiched between embossing rollers 53 and 54, being conveyed in the travel direction 60. Embossing roller 53 rotates in contact with the unembossed surface of film 51, thereby embossing both surfaces of film 51. As shown in this example, a single film can also undergo multiple embossing processes.

[0093] Figure 6C shows an enlarged cross-sectional view of a membrane 52 with both surfaces embossed. H1 represents the thickness of the concave or convex portion of the membrane. H2 represents the thickness of the boundary portion between the concave portion and the adjacent convex portion, or the thickness of the boundary portion between the convex portion and the adjacent concave portion. The thickness of the membrane is not uniform with the cellulose fibers, and H2 is smaller than H1.

[0094] In addition, Figure 6D shows other examples of embossing on both surfaces of the film.

[0095] Figure 6D shows a film 50 sandwiched between an embossing roller 53 in contact with one surface of the film and an embossing roller 55 in contact with the other surface, with the film 50 being conveyed in the direction of travel 60.

[0096] Figure 6D shows the combination of embossing roller 53, which serves as the male embossing roller, and female embossing roller 55. In addition, a pattern is formed on the surface of the film 50 by a continuous embossing pattern that raises a portion of the surface and a debossing pattern that lowers the surface.

[0097] In Figure 6E, an embossing roller 56 is used, which changes the distance between the protrusions formed on an embossing roller 55 as shown in Figure 6D. Here, the distance between the protrusions or the embossing distance refers to the distance between the apexes of adjacent protrusions. For example, the distance P shown in Figure 6E is referred to as the distance between the protrusions or the embossing distance. Figure 6E shows a film 50 sandwiched between embossing rollers 53 and embossing roller 56, with the film 50 being conveyed in the travel direction 60. By changing the distance between the protrusions, the two surfaces of the film can be processed with different embossing distances.

[0098] Figure 6F shows a case where a film 50 is sandwiched between an embossing roller 57 that contacts one surface of the film and an embossing roller 58 that contacts the other surface, and the film 50 is being conveyed in the direction of travel 60 toward the film 50.

[0099] Figure 6F describes a tip-to-tip double-sided embossing process, where an embossing roller 57 and an embossing roller 58 with the same pattern as the embossing roller 57 are combined for embossing. By making the phases of the convex and concave portions of the same embossing roller the same, almost identical patterns can be formed on the front and back sides of the film 50. Alternatively, unlike Figure 6F, embossing can also be performed with the phases of the convex and concave portions of the same embossing roller different.

[0100] In addition, embossing plates can also be used instead of embossing rollers. Furthermore, embossing can also be formed in a portion of the film, not just in the embossing process.

[0101] Figure 7A shows an example of an energy storage device 500 using an outer packaging body 529 formed by the above-described embossing process. Figure 7B shows a cross-sectional view along the dashed line H1-H2 in Figure 7A. The structure of Figure 7B, except for the outer packaging body 529, is the same as that in Figure 4B.

[0102] The irregularities and protrusions included in the outer packaging 529 are formed in such a way that they include areas overlapping with the positive electrode 503 and the negative electrode 506. In FIG7A, the joint 518 has no irregularities and protrusions, but the joint 518 may also have irregularities and protrusions.

[0103] The protrusions and concavities included in the outer packaging 529 are periodically formed along the long axis direction (Y direction shown in FIG. 7A) of the energy storage device 500. In other words, a concave and a convex shape are formed in a manner that extends along the short axis direction (X direction shown in FIG. 7A) of the energy storage device 500. By having such protrusions and concavities, the stress caused by bending of the energy storage device 500 along the long axis direction can be mitigated.

[0104] The undulations included in the outer packaging 529 can also be a visible geometric pattern formed by the intersection of diagonal lines in two directions (see Figure 8). By adopting this structure, stress caused by bending of the energy storage device 500 in at least two directions can be mitigated.

[0105] In Figure 1A, the positive lead 510 and the negative lead 511 are arranged on the same side of the energy storage device 500. However, as shown in Figure 9, the positive lead 510 and the negative lead 511 can also be arranged on different sides of the energy storage device 500. Thus, in the energy storage device of one embodiment of the present invention, the leads can be freely arranged, resulting in high design flexibility. Therefore, the design flexibility of products using the energy storage device of one embodiment of the present invention can be improved. Furthermore, the productivity of products using the energy storage device of one embodiment of the present invention can be improved.

[0106] <Examples of manufacturing methods for energy storage devices> Hereinafter, an example of a method for manufacturing an energy storage device 500, which is an embodiment of the energy storage device of the present invention, will be described with reference to FIGS. 10A to 13.

[0107] First, a positive electrode 503, a negative electrode 506, and a first insulator 507 are stacked. Specifically, the first insulator 507 is disposed on the positive electrode 503. Then, the negative electrode 506 is disposed on the first insulator 507. When using two or more sets of positive and negative electrodes, the first insulator 507 is disposed again on the negative electrode 506, and then the positive electrode 503 is disposed. In this way, the positive electrode 503 and the negative electrode 506 are alternately stacked in such a way that the first insulator 507 is sandwiched between the positive electrode 503 and the negative electrode 506.

[0108] Alternatively, the first isolator 507 can also be bag-shaped. By using the first isolator 507 to surround the electrode, the electrode is less likely to be damaged during the process, which is therefore preferable.

[0109] First, a positive electrode 503 is disposed on the first insulator 507. Next, the first insulator 507 is folded in half along the dotted line shown in FIG10A, and the positive electrode 503 is clamped using the first insulator 507. In addition, the example of clamping the positive electrode 503 using the first insulator 507 has been described here, but the negative electrode 506 can also be clamped using the first insulator 507.

[0110] Here, it is preferable to form the outer periphery of the first insulator 507 on the outside of the positive electrode 503 into a bag shape (or envelope shape). The joining of the outer periphery of the first insulator 507 can be achieved by using an adhesive or the like, or by using ultrasonic welding or heating and melting.

[0111] Next, the outer periphery of the first insulator 507 is heated to form a bond. Figure 10A shows the bond portion 514. In this way, the positive electrode 503 can be covered by the first insulator 507.

[0112] When using adhesives or similar substances to join the outer periphery of the first insulator 507, the amount of adhesive used is preferably minimal. Since the outer periphery is joined in such a way that the electrode (positive electrode 503 in FIG. 10A) held by the first insulator 507 is not exposed from the first insulator 507, the amount of adhesive used can be reduced, for example, by forming the joining portion 514 as shown in FIG. 10B. In FIG. 10B, the joining portion 514 is formed near the crease of the two sides intersecting the crease-formed side and on a portion of the side opposite to the crease-formed side of the outer periphery of the first insulator 507.

[0113] Next, as shown in Figure 10C, the negative electrode 506 and the positive electrode 503, which is wrapped by an insulator, are alternately overlapped. Additionally, a positive electrode lead 510 and a negative electrode lead 511 with a sealing layer 115 are prepared. The sealing layer 115 can be a thermoplastic resin such as polypropylene.

[0114] Next, as shown in FIG11A, the positive electrode lead 510 with sealing layer 115 is connected to the tab region 281 of the positive electrode 503. FIG11B is an enlarged view of the connection. While applying pressure to the joint 512, ultrasonic waves are irradiated, thereby electrically connecting the tab region 281 of the positive electrode 503 and the positive electrode lead 510 (ultrasonic welding). At this time, it is preferable to provide a bend 513 in the tab region 281.

[0115] By providing the bending portion 513, the stress generated by external forces after the manufacture of the energy storage device 500 can be mitigated. Therefore, the reliability of the energy storage device 500 can be improved.

[0116] The tab region 282 of the negative electrode 506 can be electrically connected to the negative lead 511 in the same way.

[0117] Next, a positive electrode 503, a negative electrode 506, and a first isolation body 507 are configured on the second isolation body 520.

[0118] Next, the second insulator 520 is folded in half near the center of Figure 11C, as indicated by the dashed line, and the second insulator 520 is used to clamp the positive electrode 503, the negative electrode 506, and the first insulator 507. The second insulator 520 preferably covers the tab region 281 and the tab region 282.

[0119] Here, it is preferable to join the outer peripheral portion of the second separator 520 by forming the second separator 520 into a bag shape (or envelope shape). The joining of the outer peripheral portion of the second separator 520 can be achieved by using an adhesive or by using ultrasonic welding or heating and melting.

[0120] Next, the outer periphery of the second insulator 520 is heated to achieve bonding. Figure 12A shows the bonding portion 521. In this way, the second insulator 520 can be used to cover the positive electrode 503, the negative electrode 506, and the first insulator 507.

[0121] When using adhesives or similar substances to join the outer periphery of the second separator 520, the amount of adhesive used is preferably minimal. Since the outer periphery is joined in a manner that prevents the positive electrode 503, negative electrode 506, and first separator 507, which are clamped by the second separator 520, from being exposed from the second separator 520, the amount of adhesive used can be reduced, for example, by forming the joining portion 521 as shown in FIG. 12B. In FIG. 12B, the joining portion 521 is formed near the creases of the two sides intersecting the crease-formed sides in the outer periphery of the second separator 520, and near the tab regions 281 and 282.

[0122] Note that the second isolation body 520 may not be provided. If the second isolation body 520 is not provided, the processes related to the second isolation body 520 can be omitted.

[0123] Next, a positive electrode 503, a negative electrode 506, a first separator 507, and a second separator 520 are disposed on the outer packaging body 509.

[0124] Next, fold the outer packaging 509 along the dotted line near the center of the outer packaging 509 in Figure 12C.

[0125] In Figure 13, the joint 118 is the portion where the outer periphery of the outer packaging 509 is joined by heat pressing. Heat pressing is used to join the outer periphery of the outer packaging 509, excluding the inlet 119 for inserting the electrolyte 508. During heat pressing, the sealing layer on the lead wire also melts, thereby securing the lead wire to the outer packaging 509. Furthermore, this improves the tightness of the connection between the outer packaging 509 and the lead wire.

[0126] Furthermore, under reduced pressure or an inert gas atmosphere, the desired amount of electrolyte 508 is inserted into the inside of the outer packaging 509 through the inlet 119. Finally, the inlet 119 is joined by heat pressing. In this way, a battery storage device 500 as a thin battery storage device can be manufactured.

[0127] Furthermore, a curing process can be performed after manufacturing the energy storage device 500. An example of curing process conditions is described below. First, charging is performed at a rate of 0.001C or higher and 0.2C or lower. The temperature can be set to above room temperature and below 50°C. At this time, if electrolyte decomposition occurs and gas is generated, the space between the electrodes becomes filled with this gas, thus preventing the electrolyte from contacting the electrode surface in some areas. That is, the effective reaction area of ​​the electrodes decreases, and the effective resistance increases.

[0128] When the resistance is too high, the negative electrode potential decreases, causing lithium to embed in the graphite and precipitate on the graphite surface. This lithium precipitation sometimes leads to a decrease in capacity. For example, if a coating or similar material grows on the surface after lithium precipitation, the precipitated lithium cannot dissolve again, resulting in lithium that does not contribute to capacity. Similarly, when the precipitated lithium is physically damaged and no longer conducts to the electrode, lithium that does not contribute to capacity is also produced. Therefore, to prevent the negative electrode potential from reaching the lithium potential due to an increase in charging voltage, degassing is preferable.

[0129] When degassing is required, a portion of the outer packaging of the thin battery can be cut off and disassembled, for example. If the outer packaging expands due to gas, it is preferable to readjust its shape. Electrolyte can also be added as needed before resealing. When degassing is not possible, a space for degassing can be provided inside the battery to release the gas accumulated between the electrodes. The space formed by using the embossed laminated outer packaging described above can also be used as a degassing space.

[0130] After degassing, the charging state can be maintained at a temperature above room temperature, preferably 30°C to 60°C, and more preferably 35°C to 50°C, for example, for more than 1 hour and less than 100 hours. During the initial charging, the electrolyte decomposes on the surface to form a coating film. Therefore, by maintaining the charging state at a temperature above room temperature after degassing, it is possible to densify the formed coating film.

[0131] Here, we will explain the charging and discharging rates. The charging rate refers to the relative value of the current during constant current charging relative to the battery capacity, that is, the value of the charging current [A] ÷ the battery capacity [Ah], also known as the C-rate. Its unit is C. For example, when charging a 10Ah battery with a constant current of 2A, it can be said that the charging rate is 0.2C. A 1C charging rate means that the total battery capacity is charged in one hour. The higher the charging rate, the faster the charging speed. Similarly, the discharging rate refers to the relative value of the current during constant current discharging relative to the battery capacity, that is, the value of the discharging current [A] ÷ the battery capacity [Ah], also known as the C-rate. Its unit is C. For example, when discharging a 10Ah battery with a constant current of 2A, it can be said that the discharging rate is 0.2C. A 1C discharging rate means that the total battery capacity is discharged in one hour. The higher the discharging rate, the faster the discharging speed.

[0132] <Components of the energy storage device> The components of an energy storage device according to one embodiment of the present invention will be described in detail below. By selecting a flexible material from the materials of the components shown in this embodiment, a flexible energy storage device can be manufactured.

[0133] <<Electrolytes>> Electrolytes consist of a solute and a solvent.

[0134] As the solvent for the electrolyte, a material capable of carrying ion mobility is used. In particular, solvents with high heat resistance and low reactivity with the graphite anode are preferred. In an embodiment of the energy storage device of the present invention, a mixture of propylene carbonate, ethylene carbonate, and ethylene carbonate is used as the solvent.

[0135] As a solvent, it is preferred to use a non-protic organic solvent, in addition to propylene carbonate, ethylene carbonate and ethylene carbonate, one or more of butenyl carbonate, γ-butyrolactone, γ-valerolactone, dimethyl sulfoxide, methyl diglyme, benzonitrile and cyclobutane can be used in any combination and ratio.

[0136] By using gelled polymer materials as solvents for electrolytes, safety is improved, including protection against liquid leakage. Furthermore, it allows for the thinning and weight reduction of energy storage devices. Typical examples of gelled polymer materials include silicone gels, acrylic gels, acrylonitrile gels, polyethylene oxide gels, polypropylene oxide gels, and fluoropolymer gels.

[0137] Furthermore, by using one or more flame-retardant and non-evaporable ionic liquids (also known as room-temperature molten salts) as the electrolyte solvent, even if the internal temperature of the storage device rises due to internal short circuits, overcharging, or other reasons, it can prevent the storage device from cracking or catching fire. This improves the safety of the storage device.

[0138] As a solute, a material capable of enabling the movement of carrier ions and possessing carrier ions can be used. When the carrier ion is a lithium ion, the solute is a lithium salt. Preferred lithium salts include those with high heat resistance such as LiBETA, lithium bis(trifluoromethylsulfonyl)amine (Li(CF3SO2)2N, abbreviated as LiTFSA), lithium bis(fluorosulfonyl)amine (Li(FSO2)2N, abbreviated as LiFSA), LiBF4, and lithium dioxoborate (LiB(C2O4)2, abbreviated as LiBOB).

[0139] In the battery reaction of an energy storage device, when the electrolyte reacts with the current collector at the positive electrode, causing the metal contained in the current collector to dissolve, the capacitance of the energy storage device decreases, leading to device degradation. In other words, during cycle characteristic testing of the energy storage device, the capacitance decreases significantly with increasing charge-discharge cycles, resulting in a shortened lifespan. Furthermore, when dissolution at the current collector at the connection point with the leads intensifies, it can sometimes even cause disconnection. To address this, in one embodiment of the present invention, the solute material contained in the electrolyte is a material that inhibits reaction with the current collector and inhibits the dissolution of metals from the current collector.

[0140] Metals used as current collector materials in the positive electrode can include, for example, aluminum or stainless steel. In one embodiment of the invention, a solute that inhibits the dissolution of these metals from the positive electrode current collector can also be used as a solute material for the electrolyte. Specifically, among the solutes that can be used in one embodiment of the invention, lithium salts represented by the above general formula (G1) and lithium hexafluorophosphate (LiPF6) can be cited as examples of lithium salts.

[0141] In one embodiment of the energy storage device of the present invention, the degradation of the positive current collector is suppressed by preventing metal from dissolving from the positive current collector into the electrolyte, and the deposition of metal onto the surface of the negative electrode is also suppressed. Therefore, an energy storage device with low capacitor degradation and long cycle life can be manufactured.

[0142] In addition to the solutes mentioned above, one or more of the following lithium salts can be used in any combination and ratio: LiPF6, LiClO4, LiAsF6, LiAlCl4, LiSCN, LiBr, LiI, Li2SO4, Li2B10Cl10, Li2B12Cl12, LiCF3SO3, LiC4F9SO3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiN(FSO2)2, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiN(C4F9SO2)(CF3SO2).

[0143] Note that this describes the case where the carrier ion in the solute is lithium ion, but carrier ions other than lithium ion can also be used. When the carrier ion is an alkali metal ion other than lithium ion or an alkaline earth metal ion, alkali metals (e.g., sodium, potassium, etc.) or alkaline earth metals (e.g., calcium, strontium, barium, beryllium, or magnesium, etc.) can be used as the solute instead of lithium in the lithium salt described above.

[0144] In addition, additives such as vinylene carbonate (VC), propanesulfonate lactone (PS), terebutylbenzene (TBB), fluoroethylene vinyl carbonate (FEC), lithium dioxoborate (LiBOB), or dinitrile compounds such as succinate and adiponitrile can be added to the electrolyte. The concentration of the additives can be set to, for example, 0.1 wt% or more and 5 wt% of the total solvent.

[0145] By using the above-mentioned solvent and solute, an electrolyte for an energy storage device according to one embodiment of the present invention can be prepared.

[0146] <<Current Discharge Machine>> As a current collector, there are no particular restrictions as long as the material exhibits high conductivity without causing significant chemical changes in the energy storage device. Materials used for both the positive and negative current collectors include, for example, stainless steel, gold, platinum, zinc, iron, nickel, copper, aluminum, titanium, tantalum, manganese, alloys of these metals, or sintered carbon. Furthermore, copper or stainless steel can be coated with carbon, nickel, or titanium. Additionally, aluminum alloys with added elements to improve heat resistance, such as silicon, titanium, neodymium, scandium, and molybdenum, can be used. Furthermore, metal elements that react with silicon to form silicates can be used to form current collectors. Examples of metal elements that react with silicon to form silicates include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, and nickel.

[0147] Irreversible reactions with the electrolyte sometimes occur on the surface of the positive or negative current collector. Therefore, it is preferable that the positive or negative current collector has low reactivity with the electrolyte.

[0148] Furthermore, both the positive and negative current collectors can be suitably shaped in various ways, including foil, plate (sheet), mesh, cylindrical, coil, perforated metal mesh, expanded metal mesh, porous, and non-woven fabric. Additionally, to improve adhesion to the active material layer, both the positive and negative current collectors may have minute irregularities on their surfaces. Preferably, both the positive and negative current collectors have a thickness of 5µm or more and 30µm or less.

[0149] Alternatively, a primer layer can be applied to a portion of the current collector's surface. Here, the primer layer refers to a covering layer used to reduce the contact resistance between the current collector and the active material layer, or to improve the tightness between them. Note that the primer layer does not necessarily have to be formed on the entire surface of the current collector; it can also be formed as an island (partially formed). Furthermore, the primer layer can also be used as the active material to form the capacity. For example, carbon materials can be used as the primer layer. Examples of carbon materials include graphite, carbon black such as acetylene black, and carbon nanotubes. Additionally, metal layers, layers containing carbon and polymers, and layers containing metals and polymers can also be used as the primer layer.

[0150] <<Active Substance Layer>> The active material layer contains active material. Active material refers only to substances related to the insertion and extraction of ions used as a carrier; in this specification, the layer containing active material is referred to as the active material layer. In addition to active material, the active material layer may also contain conductive additives and binders.

[0151] The positive electrode active material layer contains one or more positive electrode active materials. The negative electrode active material layer contains one or more negative electrode active materials.

[0152] The positive and negative electrode active materials play a central role in the battery reaction of the energy storage device, releasing and absorbing carrier ions. To extend the lifespan of the energy storage device, the active materials are preferably materials with small capacity involved in irreversible battery reactions, and preferably materials with high charge-discharge efficiency.

[0153] For example, composite oxides with layered rock salt-type or spinel-type crystal structures can be used as positive electrode active materials. For example, polyanionic positive electrode materials can be used. Examples of polyanionic positive electrode materials include materials with olivine-type crystal structures and sodium superionic conductors (NASICON). Furthermore, sulfur-containing positive electrode materials can be used as positive electrode active materials.

[0154] Various composite oxides can be used as positive electrode active materials. For example, compounds such as LiFeO 2, LiCoO 2, LiNiO 2, LiMn 2O 4, Li 2MnO 3, V 2O 5, Cr 2O 5, and MnO 2 can be used.

[0155] As a material with a layered rock salt-type crystalline structure, a composite oxide represented by LiMO₂ can be used, for example. Element M is preferably selected from one or more of Co and Ni. LiCoO₂ is preferred due to its advantages such as high capacity, atmospheric stability, and thermal stability. Furthermore, in addition to having one or more of Co and Ni, element M may also include one or more of Al and Mn.

[0156] For example, LiNixMnyCozOw can be used (e.g., x, y, z, and w are x=y=z=1 / 3 or nearby, w=2 or nearby). Alternatively, LiNixMnyCozOw can be used (e.g., x=0.8 or nearby, y=0.1 or nearby, z=0.1 or nearby, w=2 or nearby). Alternatively, LiNixMnyCozOw can be used (e.g., x=0.5 or nearby, y=0.3 or nearby, z=0.2 or nearby, w=2 or nearby). Alternatively, LiNixMnyCozOw can be used (e.g., x=0.6 or nearby, y=0.2 or nearby, z=0.2 or nearby, w=2 or nearby). In addition, for example, LiNi xMn yCo zO w can be used (for example, x, y, z and w are x=0.4 or nearby, y=0.4 or nearby, z=0.2 or nearby, w=2 or nearby, respectively).

[0157] "Nearby" refers to a range that is greater than 0.9 times a certain value and less than 1.1 times that value.

[0158] As a positive electrode active material, it can also be: a material in which one or more elements selected from Fe, Co, Ni, Cr, Al, Mg, etc. are replaced with a portion of the transition metal or lithium contained in the positive electrode active material; or a material in which one or more elements selected from Fe, Co, Ni, Cr, Al, Mg, etc. are doped into the positive electrode active material.

[0159] As a positive electrode active material, a solid solution combining multiple composite oxides can be used, for example. For example, a solid solution of LiNixMnyCozO2 (x, y, z>0, x+y+z=1) and Li2MnO3 can be used as a positive electrode active material.

[0160] As a material with a spinel-type crystalline structure, a composite oxide represented by LiM₂O₄ can be used, for example. Element M preferably includes Mn, such as LiMn₂O₄. Furthermore, by containing Ni in addition to Mn as element M, the discharge voltage and energy density of the secondary battery can sometimes be improved, which is therefore preferable. Moreover, it is preferable to mix a small amount of lithium nickel oxide (LiNiO₂ or LiNi₁⁻⁴M⁻¹⁴⁻O₂ (M = Co, Al, etc.)) into lithium-containing materials with a spinel-type crystalline structure containing manganese, such as LiMn₂O₄, thereby improving the characteristics of the secondary battery.

[0161] For example, preferably, the average particle size of the primary particles of the positive electrode active material is 1 nm or more and 100 µm or less, more preferably 50 nm or more and 50 µm or less, and even more preferably 1 µm or more and 30 µm or less. Preferably, the specific surface area is 1 m² / g or more and 20 m² / g or less. Preferably, the average particle size of the secondary particles is 5 µm or more and 50 µm or less. The average particle size can be measured by observation using SEM (scanning electron microscopy) or TEM, or by a particle size analyzer using laser diffraction and scattering methods. The specific surface area can be measured using gas adsorption methods.

[0162] A conductive material such as a carbon layer can also be deposited on the surface of the positive electrode active material. By depositing a conductive material such as a carbon layer, the conductivity of the electrode can be improved. For example, by mixing carbohydrates such as glucose during the calcination of the positive electrode active material, a carbon layer covering the positive electrode active material can be formed. Furthermore, graphene, multilayer graphene, graphene oxide (GO), or RGO (Reduced Graphene Oxide) can be used as conductive materials. Here, RGO, for example, refers to a compound obtained by reducing graphene oxide (GO).

[0163] A layer containing one or more oxides and fluorides can be formed on the surface of the positive electrode active material. The oxide can have a different composition from the positive electrode active material. Alternatively, the oxide can have the same composition as the positive electrode active material.

[0164] As a polyanion cathode material, a composite oxide containing oxygen, element X, metal A, and metal M can be used, for example. Metal M is one or more of Fe, Mn, Co, Ni, Ti, V, and Nb; metal A is one or more of Li, Na, and Mg; and element X is one or more of S, P, Mo, W, As, and Si.

[0165] As a material having an olivine-type crystal structure, a composite material (general formula: LiMPO4, where M is one or more of Fe(II), Mn(II), Co(II), Ni(II))) can be used, for example. As typical examples of LiMPO4, LiFePO4, LiNiPO4, LiCoPO4, LiMnPO4, LiFeaNibPO4, LiFeaCobPO4, LiFeaMnbPO4, LiNiaCobPO4, LiNiaMnbPO4 (a + b is 1 or less, 0 < a < 1, 0 < b < 1), LiFecNidCoePO4, LiFecNidMnePO4, LiNicCodMnePO4 (c + d + e is 1 or less, 0 < c < 1, 0 < d < 1, 0 < e < 1), LiFefNigCohMniPO4 (f + g + h + i is 1 or less, 0 < f < 1, 0 < g < 1, 0 < h < 1, 0 < i < 1), and other lithium compounds can be used.

[0166] In particular, LiFePO4 preferably satisfies the conditions required for a cathode active material, such as safety, stability, high capacity density, high potential, and the presence of lithium ions that can be intercalated and deintercalated during initial oxidation (charging), so it is preferred.

[0167] For example, the average particle diameter of the primary particles of the cathode active material having an olivine-type crystal structure is preferably 1 nm or more and 20 µm or less, more preferably 10 nm or more and 5 µm or less, and still more preferably 50 nm or more and 2 µm or less. The specific surface area is preferably 1 m2 / g or more and 20 m2 / g or less. The average particle diameter of the secondary particles is preferably 5 µm or more and 50 µm or less.

[0168] Alternatively, composite materials such as the general formula Li(2-j)MSiO4 (M is one or more of Fe(II), Mn(II), Co(II), Ni(II) and 0 ≤ j ≤ 2) can be used. As typical examples of the general formula Li(2-j)MSiO4, Li(2-j)FeSiO4, Li(2-j)NiSiO4, Li(2-j)CoSiO4, Li(2-j)MnSiO4, Li(2-j)Fe kNi lSiO4, Li(2-j)Fe kCo lSiO4, Li(2-j)Fe kMn lSiO4, Li(2-j)Ni kCo lSiO4, Li(2-j)Ni kMn lSiO4 (k + l is 1 or less, 0 < k < 1, 0 < l < 1), Li(2-j)Fe mNi nCo qSiO4, Li(2-j)Fe mNi nMn qSiO4, Li(2-j)Ni mCo nMn qSiO4 (m + n + q is 1 or less, 0 < m < 1, 0 < n < 1, 0 < q < 1), Li(2-j)Fe rNi sCo tMn uSiO4 (r + s + t + u is 1 or less, 0 < r < 1, 0 < s < 1, 0 < t < 1, 0 < u < 1) and other lithium compounds and materials can be used.

[0169] In addition, sodium superionic conductor type compounds represented by the general formula AxM2(XO4)3 (A = Li, Na, Mg, M = Fe, Mn, Ti, V, Nb, X = S, P, Mo, W, As, Si) can be used. As sodium superionic conductor type compounds, there are Fe2(MnO4)3, Fe2(SO4)3, Li3Fe2(PO4)3 and the like. As the positive electrode active material, compounds represented by the general formula Li2MPO4F, Li2MP2O7 or Li5MO4 (M = Fe, Mn) can be used.

[0170] In addition, polyanionic cathode materials containing V can be used. As typical examples thereof, α-LiVOPO4, β-LiVOPO4, α1-LiVOPO4, LiVPO4F, LiVPO4O, LiVP2O7, LiVOSO4, Li2VOSiO4, LiVMoO6 and the like can be cited.

[0171] In addition, perovskite-type fluorides such as NaFeF3 and FeF3, metal chalcogenides (sulfides, selenides, tellurides) such as TiS2 and MoS2, oxides with anti-spinel crystal structures such as LiMVO4, vanadium oxides (V2O5, V6O13, LiV3O8, etc.), manganese oxides, and organic sulfur compounds can also be used as positive electrode active materials.

[0172] In addition, borate-based cathode materials represented by LiMBO3 (where M represents Fe(II), Mn(II), or Co(II)) can also be used as positive electrode active materials.

[0173] Furthermore, as the positive electrode active material, a lithium-manganese composite oxide that can be represented by the formula LiaMnbMcOd can be used. Here, element M is preferably a metal element selected from lithium and manganese, or silicon and phosphorus, and more preferably nickel. In addition, when measuring the overall particle size of the lithium-manganese composite oxide, it is preferable that the particle size distribution satisfies 0 <a / (b+c)<2、c>0 and 0.26≤(b+c) / d<0.5 during discharge. In addition, in order to achieve a large capacity, the lithium-manganese composite oxide preferably includes regions with different crystal structures, crystal orientations, or oxygen contents in the surface and central parts. To form the above-mentioned lithium-manganese composite oxide, it is preferable, for example, to satisfy 1.6≤a≤1.848, 0.19≤c / b≤0.935, and 2.5≤d≤3. Furthermore, it is particularly preferable to use a lithium-manganese composite oxide represented by the formula Li1.68Mn0.8062Ni0.318O3. In this specification, the lithium manganese composite oxide represented by the composition Li 1.68Mn 0.8062Ni 0.318O 3 refers to a lithium manganese composite oxide formed by setting the molar ratio of the raw materials to Li 2CO 3:MnCO 3:NiO = 0.84:0.8062:0.318. Therefore, this lithium manganese composite oxide is represented by the composition Li 1.68Mn 0.8062Ni 0.318O 3, but sometimes the composition may differ slightly from this.

[0174] ​The composition of the metals, silicon, phosphorus, etc., of lithium manganese composite oxide particles can be measured, for example, using ICP-MS (Inductively Coupled Plasma Mass Spectrometry). Furthermore, the oxygen composition of the lithium manganese composite oxide particles can be measured, for example, using EDX (Energy Dispersive X-ray Spectroscopy). Additionally, the oxygen composition of the lithium manganese composite oxide particles can be calculated in conjunction with ICP-MS analysis using fusion gas analysis and XAFS (X-ray Absorption Fine Structure) analysis for valence evaluation. Moreover, lithium manganese composite oxides refer to oxides containing at least lithium and manganese, and may also contain at least one element selected from chromium, cobalt, aluminum, nickel, iron, magnesium, molybdenum, zinc, indium, gallium, copper, titanium, niobium, silicon, and phosphorus.

[0175] When the carrier ion is an alkali metal ion other than lithium ion or an alkaline earth metal ion, alkali metals (e.g., sodium, potassium, etc.) or alkaline earth metals (e.g., calcium, strontium, barium, beryllium, magnesium, etc.) can be used instead of lithium as the positive electrode active material. For example, layered oxides containing sodium can be used.

[0176] Sodium-containing materials include, for example, NaFeO 2, Na 2 / 3[Fe 1 / 2Mn 1 / 2]O 2, Na 2 / 3[Ni 1 / 3Mn 2 / 3]O 2, Na 2Fe 2(SO 4) 3, Na 3V 2(PO 4) 3, Na 2FePO 4F, NaVPO 4F, NaMPO 4 (M is Fe(II), Mn(II), Co(II), Ni(II)), Na 2FePO 4F, Na 4Co 3(PO 4) 2P 2O 7, etc., which are oxides containing sodium and can be used as positive electrode active materials.

[0177] In addition, lithium-containing metal sulfides can also be used as positive electrode active materials. Examples include Li₂TiS₃ and Li₃NbS₄.

[0178] As a negative electrode active material, carbon-based materials, alloy materials, etc. can be used.

[0179] As carbon-based materials, there are graphite, graphitizing carbon (soft carbon), non-graphitizing carbon (hard carbon), carbon nanotubes, graphene, carbon black, etc. As for graphite itself, there are mesophase carbon microspheres (MCMB), coke-based artificial graphite, pitch-based artificial graphite, and spherical natural graphite, among other artificial graphite. Furthermore, graphite can be shaped into flakes or spheres.

[0180] As graphite, when lithium ions are intercalated within it (during the formation of lithium-graphite intercalation compounds), it exhibits a low potential similar to that of lithium metal. Therefore, lithium-ion secondary batteries can exhibit high operating voltages. As mentioned above, graphite has the advantages of higher capacity per unit volume, less volume expansion, lower cost, and higher safety compared to lithium metal, making it a superior choice.

[0181] This section explains graphite materials. Graphite refers to a layered compound in which multiple graphene layers are stacked parallel to each other by van der Waals forces. The surface of a graphite material includes a surface parallel to the graphene layers (also called the substrate surface) and a surface formed by the ends of the multiple graphene layers (also called the end faces). The substrate surface exposes one surface of the outermost graphene layer that makes up the graphite, while the end faces expose the ends of the multiple graphene layers. During the charging and discharging of a secondary battery, the main entry and exit points for lithium insertion into and extraction from the graphite material are the end faces of the graphite material.

[0182] When graphite is used as the negative electrode active material, side reactions between graphite and PC may occur during charging and discharging when the exposed end face comes into contact with an electrolyte containing PC. In an embodiment of the energy storage device of the present invention, the negative electrode active material, spherical natural graphite, forms a layer with lower crystallinity than the graphite layer in contact with the aforementioned end face, thus sometimes suppressing the side reactions between graphite and PC.

[0183] When the carrier ion is lithium ion, alloy materials can be used, for example, materials containing at least one of Mg, Ca, Ga, Si, Al, Ge, Sn, Pb, As, Sb, Bi, Ag, Au, Zn, Cd, Hg, and In. These elements have a higher capacity than carbon, especially silicon, which has a theoretical capacity of 4200 mAh / g, thereby increasing the capacity of energy storage devices. Examples of alloy materials (compound-based materials) using these elements include Mg₂Si, Mg₂Ge, Mg₂Sn, SnS₂, V₂Sn₃, FeSn₂, CoSn₂, Ni₃Sn₂, Cu₆Sn₅, Ag₃Sn, Ag₃Sb, Ni₂MnSb, CeSb₃, LaSn₃, La₃Co₂Sn₇, CoSb₃, InSb, and SbSn.

[0184] Furthermore, oxides such as SiO, SnO, SnO₂, titanium dioxide (TiO₂), lithium titanium oxide (Li₄Ti₅O₁₂), lithium-graphite intercalation compound (LiₓC₆), niobium pentoxide (Nb₂O₅), tungsten oxide (WO₂), and molybdenum oxide (MoO₂) can be used as negative electrode active materials. Here, SiO is a compound containing silicon and oxygen, and when the atomic ratio of silicon to oxygen is silicon:oxygen = α:β, α is preferably close to a value close to β. Here, "close to a value" means, for example, that the absolute value of the difference between α and β is preferably less than 20% of the value of β, and more preferably less than 10%.

[0185] Furthermore, as the negative electrode active material, Li3-xMxN (where M is Co, Ni, or Cu) with a Li3N-type structure containing lithium and transition metal nitrides can be used. For example, Li2.6Co0.4N3 exhibits a large charge / discharge capacity (900 mAh / g, 1890 mAh / cm3) and is therefore preferred.

[0186] When lithium and transition metal nitrides are used as negative electrode active materials, lithium ions are contained in the negative electrode active material. Therefore, they can be combined with materials such as V₂O₅ and Cr₃O₈, which do not contain lithium ions, as positive electrode active materials. When lithium-ion-containing materials are used as positive electrode active materials, lithium ions can be pre-intercalated or deintercalated in the positive electrode active material. Nitrides containing lithium and transition metals can also be used as negative electrode active materials.

[0187] In addition, materials that induce the conversion reaction can also be used as negative electrode active materials. For example, transition metal oxides that do not alloy with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), and iron oxide (FeO), can be used as negative electrode active materials. Other materials that induce the conversion reaction include oxides such as Fe₂O₃, CuO, Cu₂O, RuO₂, and Cr₂O₃; sulfides such as CoS₀.₈, NiS, and CuS; nitrides such as Zn₃N₂, Cu₃N, and Ge₃N₄; phosphides such as NiP₂, FeP₂, and CoP₃; and fluorides such as FeF₃ and BiF₃.

[0188] The average particle size of the original particles of the negative electrode active material is preferably 5 nm or more and 100 µm or less.

[0189] The positive electrode active material layer and the negative electrode active material layer may also contain conductive additives.

[0190] For example, carbon materials, metallic materials, or conductive ceramic materials can be used as conductive additives. Furthermore, fibrous materials can also be used as conductive additives. The content of the conductive additive relative to the total weight of the active material layer is preferably 1 wt% or more and 10 wt% or less, more preferably 1 wt% or more and 5 wt% or less.

[0191] Conductive additives can be used to form conductive networks within the electrode. Conductive additives can also maintain conductive pathways between the negative electrode active materials. By adding conductive additives to the active material layer, an active material layer with high conductivity can be achieved.

[0192] As conductive additives, examples include natural graphite, artificial graphite such as mesophase carbon microspheres, and carbon fibers. For carbon fibers, examples include mesophase pitch-based carbon fibers and isotropic pitch-based carbon fibers. Carbon nanofibers or carbon nanotubes can also be used. For example, carbon nanotubes can be manufactured using methods such as vapor phase growth. As conductive additives, examples include carbon materials such as carbon black (acetylene black (AB), graphite (lead black) particles, graphene, graphene oxide, or fullerenes. For example, metal powders or fibers of copper, nickel, aluminum, silver, gold, etc., and conductive ceramic materials can also be used.

[0193] Thin-sheet graphene possesses excellent electrical properties, such as high conductivity, as well as good physical properties, such as flexibility and mechanical strength. Therefore, using graphene as a conductive additive can increase the contact points or contact area between active materials.

[0194] Graphene can achieve surface contact with low contact resistance, and it has very high conductivity even when it is thin. It can also form conductive pathways efficiently in active material layers even when the amount is small.

[0195] When using active materials with small average particle sizes, such as those less than 1 µm, the specific surface area of ​​the active material is large, thus requiring more conductive pathways connecting the active materials to each other. In this case, graphene, which has very high conductivity and can efficiently form conductive pathways even in small quantities, is particularly preferred.

[0196] Both the positive electrode active material layer and the negative electrode active material layer may contain a binder.

[0197] In this specification, the binder has the function of bonding or adhering active materials to each other and / or bonding or adhering the active material layer to the current collector. Furthermore, the state of the binder sometimes changes during the manufacture of the electrode or battery. For example, the binder may sometimes be in at least one of the states of liquid, solid, and gel. Additionally, during the manufacture of the electrode or battery, the binder may sometimes change from a monomer to a polymer.

[0198] As a binder, water-soluble polymers can be used, for example. Polysaccharides can also be used as water-soluble polymers. Among polysaccharides, cellulose derivatives such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, and regenerated cellulose, as well as starch, can be used.

[0199] In addition, as a binder, rubber materials such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, fluororubber, and ethylene-propylene-diene copolymer can be used. These rubber materials can be combined with the aforementioned water-soluble polymers. Because these rubber materials possess rubber elasticity and are easily stretchable, electrodes with high reliability can be obtained that can withstand stresses caused by the expansion and contraction of the active material during charging and discharging, as well as electrode bending. On the other hand, these rubber materials sometimes have hydrophobic groups and are not easily soluble in water. In this case, because the particles are dispersed in the aqueous solution in an undissolved state, it is sometimes difficult to increase the viscosity of the composition containing the solvent used to form the active material layer (also called the electrode mixture composition) to a suitable level for coating. At this point, by using water-soluble polymers with high viscosity-regulating properties, such as polysaccharides, the viscosity of the solution can be appropriately increased, and the water-soluble polymers and rubber materials can be uniformly dispersed. This results in a highly uniform electrode (e.g., an electrode with high uniformity in electrode film thickness or electrode resistance).

[0200] As an adhesive, materials such as PVDF, polystyrene, polymethyl methacrylate, polymethyl methacrylate (PMMA), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, polyethylene terephthalate, nylon, polyacrylonitrile (PAN), ethylene propylene diene monomer (EPDM), polyvinyl acetate, and nitrocellulose can be used.

[0201] As an adhesive, two or more of these materials can also be used in combination.

[0202] The binder content in the total weight of the active material layer is preferably 1 wt% or more and 10 wt% or less, more preferably 2 wt% or more and 8 wt% or less, and even more preferably 2 wt% or more and 5 wt% or less.

[0203] <<Isolation>> In one embodiment of the energy storage device of the present invention, an insulator comprising polyphenylene sulfide (PPS) or cellulose fibers is used. The insulator may also have a single-layer structure or a multilayer structure. For example, it may also have a multilayer structure comprising an insulator containing cellulose fibers and other insulators.

[0204] In addition to polyphenylene sulfide or cellulose fibers, materials that can be used as separators may include one or more of the following: polypropylene sulfide, fluoropolymers, cellulose, paper, nonwoven fabric, glass fiber, ceramics, or synthetic fibers such as nylon (polyamide), vinylon (polyvinyl alcohol fiber), polyester, acrylic, polyolefin, polyurethane, etc.

[0205] <<Outer Packaging>> In the outer packaging 509, it is preferable that the surface in contact with the electrolyte 508, i.e., the inner surface, does not react significantly with the electrolyte 508. When moisture enters the energy storage device 500 from the outside, the components of the electrolyte 508 will react with the water. Therefore, the outer packaging 509 preferably has low moisture permeability.

[0206] As the outer packaging 509, for example, a three-layer film structure can be used: a highly flexible metal film such as aluminum, stainless steel, copper, or nickel is placed on a film made of polyethylene, polypropylene, polycarbonate, ionomer, polyamide, etc., and an insulating synthetic resin film such as polyamide resin or polyester resin is placed on the metal film as the outer surface of the outer packaging. By adopting the above three-layer structure, the permeation of electrolytes and gases can be blocked, while ensuring insulation and electrolyte resistance. A sealed structure can be formed by folding the outer packaging inward or by overlapping two outer packagings with their inner surfaces facing each other and heating them to melt the inner material and fuse the two outer packagings together.

[0207] When the portion of the outer packaging that has a sealing structure due to fusion bonding or the like is considered the sealing part, when the outer packaging is folded inward, the sealing part is formed in the portion outside the folded portion, forming a structure in which a first region of the outer packaging and a second region overlapping the first region are fused together. When two outer packagings are overlapped, the sealing part is formed along the entire outer perimeter by methods such as thermal fusion bonding.

[0208] The energy storage device 500 can be flexible by using a flexible outer casing 509. When the energy storage device is flexible, it can be installed on at least a portion of a flexible electronic device, and the energy storage device 500 can be bent as the electronic device deforms.

[0209] In one embodiment of the present invention, graphene compounds can be used to construct various components of an energy storage device. As described later, since graphene compounds can be modified to select a wider variety of structures and properties, better properties can be exhibited depending on the component using the graphene compound. Furthermore, due to the high mechanical strength of graphene compounds, they can be applied to construct various components of a flexible energy storage device. The graphene compounds will now be described.

[0210] Graphene is a material in which carbon atoms are arranged in a single atomic layer and are bonded together by π bonds. Sometimes, graphene stacked in two or more layers but less than one hundred layers is called multilayer graphene. For example, the long axis length of graphene and multilayer graphene is greater than 50 nm and less than 100 µm or greater than 800 nm and less than 50 µm along its long side or in its plane.

[0211] In this specification and other documents, compounds with graphene or multilayer graphene as their basic framework are referred to as graphene compounds. Graphene compounds include graphene and multilayer graphene.

[0212] The graphene compound will be explained in detail below.

[0213] Graphene compounds are, for example, compounds in which graphene or multilayer graphene is modified with atoms other than carbon or groups of atoms containing atoms other than carbon. Alternatively, they can be compounds in which graphene or multilayer graphene is modified with carbon-dominant groups such as alkyl groups or alkylene groups. Sometimes, the groups modifying graphene or multilayer graphene are referred to as substituents, functional groups, or characteristic groups. Here, in this specification, modification refers to the introduction of atoms other than carbon, groups of atoms including atoms other than carbon, or groups of atoms mainly composed of carbon into graphene, multilayer graphene, graphene compounds, or graphene oxide (described later) through substitution reactions, addition reactions, or other reactions.

[0214] The surface and back of graphene can also be modified with different atoms or groups of atoms. In addition, each layer of multilayer graphene can be modified with different atoms or groups of atoms.

[0215] As an example of graphene modified with atoms or groups of atoms as described above, graphene or multilayer graphene modified with oxygen or oxygen-containing functional groups can be used. Examples of oxygen-containing functional groups include carbonyl groups such as epoxy groups, carboxyl groups, or hydroxyl groups. Sometimes, graphene compounds modified with oxygen or oxygen-containing functional groups are referred to as graphene oxide. Furthermore, in this specification, graphene oxide also includes multilayer graphene oxide.

[0216] As an example of modification of graphene oxide, the silanization of graphene oxide is illustrated. First, graphene oxide is placed in a container under a nitrogen atmosphere, and n-butylamine (C₄H₁₉NH₂) is added to the container, maintaining a temperature of 60°C and stirring for 1 hour. Next, toluene is added to the container, along with an alkyltrichlorosilane as a silanizing agent, and the mixture is stirred at 60°C under a nitrogen atmosphere for 5 hours. Then, toluene is further added to the container, and the mixture is filtered through suction to obtain a solid powder. This solid powder is dispersed in ethanol. This is then filtered through suction again to obtain a solid powder, which is then dispersed in acetone. This is followed by suction filtration to obtain a solid powder, and the liquid components are vaporized to obtain silanized graphene oxide.

[0217] Note that modification is not limited to silanization, nor is silanization limited to the methods described above. Furthermore, it is possible to introduce not only one atom or group of atoms, but also multiple atoms or groups of atoms through various modifications. By introducing specific groups of atoms into a graphene compound, the physical properties of the graphene compound can be altered. Therefore, by appropriately modifying the graphene compound according to its intended use, it is possible to intentionally impart desired properties to the graphene compound.

[0218] Next, an example of a method for forming graphene oxide will be described. Graphene oxide can be obtained by oxidizing the above-mentioned graphene or multilayer graphene. Alternatively, graphene oxide can be obtained by separating graphene oxide. Graphene oxide can be obtained by oxidizing graphite. Here, graphene oxide can also be further modified by the above-mentioned atoms or groups.

[0219] The compound obtained by reducing graphene oxide is sometimes called RGO (Reduced Graphene Oxide). Furthermore, in RGO, not all the oxygen atoms in the graphene oxide are removed, and some oxygen atoms or oxygen-containing groups remain bonded to carbon. For example, RGO sometimes has functional groups such as carbonyl groups (e.g., epoxy groups, carboxyl groups), or hydroxyl groups.

[0220] Graphene compounds can also be formed by partially overlapping multiple graphene compounds to create a sheet. Such graphene compounds are sometimes referred to as graphene sheets. Graphene sheets typically have regions with a thickness of 0.33 nm or more and less than 10 mm, more preferably regions with a thickness greater than 0.34 nm and less than 10 µm. Graphene sheets can also be modified with atoms other than carbon, groups of atoms other than carbon, or carbon-dominant groups such as alkyl groups. Furthermore, each of the multiple layers comprising a graphene sheet can be modified with different atoms or groups of atoms.

[0221] In addition to six-membered rings composed of carbon, graphene compounds can also include five-membered rings or multi-membered rings of seven or more members composed of carbon. Here, regions capable of lithium ion penetration are sometimes generated near the multi-membered rings of seven or more members.

[0222] In addition, for example, multiple graphene compounds can also be aggregated to form sheets.

[0223] Because graphene compounds have a planar shape, they can form surface contacts.

[0224] Sometimes, even thin layers of graphene compounds exhibit high conductivity. Furthermore, forming surface contacts can increase the contact area between individual graphene compounds or between graphene compounds and active materials. Therefore, even with a small amount of graphene compound per unit volume, conductive pathways can be formed efficiently.

[0225] On the other hand, graphene compounds can be used as insulators. For example, graphene compound sheets can also be used as sheet-like insulators. Here, for example, graphene oxide sometimes has higher insulating properties than unoxidized graphene compounds. Furthermore, the insulating properties of graphene compounds modified with atomic groups can sometimes be improved depending on the type of atomic group being modified.

[0226] In this specification and the like, graphene compounds may also have graphene precursors. Graphene precursors refer to substances used to manufacture graphene, and graphene precursors may include, for example, the aforementioned graphene oxide or graphite oxide.

[0227] Graphene containing alkali metals or elements other than carbon, such as oxygen, is sometimes referred to as graphene analogues. In this specification and other documents, graphene compounds also include graphene analogues.

[0228] The graphene compounds described in this specification may also have atoms, atomic groups, and their ions in the interlayer. Because graphene compounds have atoms, atomic groups, and their ions in the interlayer, the physical properties of the graphene compounds, such as electrical conductivity or ionic conductivity, can sometimes change. Furthermore, the interlayer distance can sometimes increase.

[0229] Graphene compounds sometimes possess excellent electrical properties, such as high conductivity, and excellent physical properties, such as high flexibility and high mechanical strength. Furthermore, depending on the type of modification, graphene compounds can sometimes be made to have extremely low conductivity, thus becoming insulators. Additionally, graphene compounds have a planar shape. Graphene compounds can form surface contacts with low contact resistance.

[0230] This implementation method can be appropriately combined with other implementation methods.

[0231] Implementation Method 2 In this embodiment, an electronic device according to one embodiment of the present invention will be described with reference to FIGS. 14A to 17C.

[0232] <Example 1 of the structure of a smartwatch> Figure 14A shows a perspective view of a watch-type portable information terminal (also known as a smartwatch) 700. The portable information terminal 700 includes a housing 701, a display panel 702, a strap buckle 703, straps 705A and 705B, and operation buttons 711 and 712.

[0233] The display panel 702, mounted within the housing 701 which also serves as a bezel, has a rectangular display area. Furthermore, this display area is curved. Preferably, the display panel 702 is flexible. Alternatively, the display area may be non-rectangular.

[0234] Watch straps 705A and 705B are connected to the housing 701. The buckle 703 is connected to watch strap 705A. Watch strap 705A and housing 701 are connected at the connection point in a manner that allows rotation around a pin. The connection between watch strap 705B and housing 701, and between watch strap 705A and buckle 703, is the same.

[0235] Figures 14B and 14C show perspective views of the watch band 705A and the power storage device 750, respectively. The watch band 705A includes the power storage device 750. For example, the power storage device 500 described in Embodiment 1 can be used as the power storage device 750. The power storage device 750 is embedded inside the watch band 705A, with a portion of the positive lead 751 and a portion of the negative lead 752 protruding from the watch band 705A (see Figure 14B). The positive lead 751 and the negative lead 752 are electrically connected to the display panel 702. Furthermore, the surface of the power storage device 750 is covered by an outer casing 753 (see Figure 14C). Additionally, the aforementioned pin can also function as an electrode. Specifically, the positive lead 751 and the display panel 702, and the negative lead 752 and the display panel 702, are electrically connected to each other via pins connecting the watch band 705A and the housing 701. By adopting the above structure, the structure of the connection between the watch strap 705A and the case 701 can be simplified.

[0236] The energy storage device 750 is flexible. Specifically, the surface of the outer packaging 753 preferably has the irregularities formed by embossing as described in Embodiment 1. Furthermore, the energy storage device 750 preferably has the sliding surface of the energy storage device 500 shown in Figures 5A and 5B.

[0237] The watch band 705A can be formed together with the energy storage device 750. For example, the energy storage device 750 is placed in a mold corresponding to the shape of the watch band 705A, the material of the watch band 705A is poured into the mold, and the material is cured to form the watch band 705A shown in FIG14B.

[0238] When rubber is used as the material for the watchband 705A, it is cured by heat treatment. For example, when fluororubber is used, it is cured by heat treatment at 170°C for 10 minutes. Furthermore, when silicone rubber is used, it is cured by heat treatment at 150°C for 10 minutes. Because the energy storage device of one embodiment of the present invention has high heat resistance, damage or deterioration of charge / discharge characteristics caused by heat treatment during its formation with the rubber material can be suppressed.

[0239] Materials used for the 705A watch strap include fluororubber, silicone rubber, fluorosilicone rubber, and polyurethane rubber.

[0240] The energization of the energy storage device 750, including aging, is preferably performed after the energy storage device 750 and the watch strap 705A are formed together. In other words, the energy storage device 500 described in Embodiment 1 is preferably subjected to a heat treatment before the energy storage device 500 is energized. This heat treatment is preferably performed at a temperature of 110°C or higher and 190°C or lower, including an appropriate vulcanization time for the rubber material, for example, 10 minutes at 170°C. In this way, the deterioration of the charge and discharge characteristics of the energy storage device 500 caused by the heat treatment can be suppressed.

[0241] The portable information terminal 700 shown in Figure 14A can have various functions. For example, it can have the following functions: displaying various types of information (static images, moving images, text images, etc.) on the display area; touch panel function; displaying calendar, date, or time; control and processing with various software (programs); wireless communication function; connection to various computer networks using wireless communication function; sending and receiving various types of data using wireless communication function; and reading programs or data stored in the storage medium and displaying the programs or data on the display area, etc.

[0242] The interior of the housing 701 may include a speaker, sensors (including functions for measuring factors such as force, displacement, position, velocity, acceleration, angular velocity, rotational speed, distance, light, liquid, magnetism, temperature, chemical substances, sound, time, hardness, electric field, current, voltage, power, radiation, flow rate, humidity, slope, vibration, odor, or infrared radiation), a microphone, etc. The portable information terminal 700 can be manufactured by using light-emitting elements in the display panel 702.

[0243] Figures 14A to 14C show an example where the energy storage device 750 is built into the watch strap 705A. The energy storage device 750 can also be built into the watch strap 705B. The same material as the watch strap 705A can be used for the watch strap 705B.

[0244] The rubber material used for the watch strap 705A preferably has high chemical resistance. Specifically, it is preferably low in reactivity with the electrolyte contained in the energy storage device 750.

[0245] Even if the watchband 705A has high chemical resistance, if the watchband 705A cracks or peels off, the user of the portable information terminal 700 may come into contact with electrolyte leaking from the battery storage device 750. If the portable information terminal 700 has an electrolyte leakage detection function, the user can stop operating the portable information terminal 700 and remove it when an electrolyte leakage is detected. Therefore, a highly safe portable information terminal 700 can be achieved.

[0246] <Example 2 of Smartwatch Structure> Figure 15A is a perspective view of a watchband 735A, which has a different structure from the watchband 705A shown in Figure 14B. The housing 731 connected to the watchband 735A includes a liquid leak detection circuit (not shown) with an electrolyte leakage detection function for detecting the battery's electrolyte leakage (see Figure 14A). The perspective view of the portable information terminal 730, which includes the liquid leak detection circuit, is the same as that of the portable information terminal 700.

[0247] The watch band 735A includes a power storage device 760. The power storage device 760 is embedded inside the watch band 735A, and a positive lead 751, a negative lead 752, and terminals 761 and 762 protrude from the watch band 735A. The positive lead 751 and negative lead 752 are electrically connected to the display panel 702. Terminals 761 and 762 are, for example, electrically connected to the aforementioned liquid leak detection circuit.

[0248] Figure 15B shows a perspective view of the energy storage device 760. Figure 15B is an enlarged view of Figure 15A for clarity. The energy storage device 760 differs from the energy storage device 750 shown in Figure 14C in that it includes terminals 761 and 762, wiring 771 and wiring 772. Terminal 761 is electrically connected to wiring 771. In addition, terminal 762 is electrically connected to wiring 772.

[0249] For clarity, the shading pattern of wiring 771 in Figure 15B is different from that of wiring 772. However, by using the same material to form wiring 771 and wiring 772, manufacturing costs can be reduced, which is preferable. Furthermore, terminal 761 and wiring 771, as well as terminal 762 and wiring 772, are shown using the same shading pattern, but terminal 761 and wiring 771, as well as terminal 762 and wiring 772, can also be formed using different materials.

[0250] Wiring 771 and wiring 772 are arranged at a specified interval on the surface of the outer packaging 753 (see Figure 15B). When electrolyte leaks onto the surface of the outer packaging 753, wiring 771 and wiring 772 are connected by the electrolyte, thereby the liquid leakage detection circuit can detect the electrolyte leakage.

[0251] Figure 15B shows the wiring 771 and wiring 772 arranged in a straight line along the long axis of the energy storage device 760, but this is not a limitation. For example, as shown in Figure 15C, wiring 771 and wiring 772 can also be arranged in a comb-like, spaced-apart, interlocking manner.

[0252] Figure 15C shows an example where wiring 771 and 772 are only provided on the top surface of the outer packaging 753, but as shown in Figure 16A, it is preferable that wiring 771 and 772 are provided on the entire surface of the outer packaging 753. Figure 16B is a perspective view of the rear of the energy storage device 760 shown in Figure 16A.

[0253] It is preferable that the thickness and width of the wirings 771 and 772 are thin and narrow, thus maintaining the flexibility of the energy storage device 760. For example, the energy storage device 760 is preferably an area including the wirings 771 and 772 with a thickness of 5µm or more and 500µm or less. Furthermore, by making the spacing between the wirings 771 and 772 small and their width narrow, leakage can be detected even with minimal electrolyte leakage, which is also preferable. For example, the energy storage device 760 is preferably an area including the spacing between the wirings 771 and 772 with a spacing of 0.5mm or more and 20mm or less. Furthermore, the energy storage device 760 is preferably an area including the wirings 771 and 772 with a width of 0.5mm or more and 5mm or less. Furthermore, sometimes when the area occupied by the wiring 771, 772 on the surface of the outer packaging 753 is too small, electrolyte leakage cannot be detected on the entire surface of the outer packaging 753; conversely, when the area is too large, the flexibility of the energy storage device 760 decreases. In the energy storage device 760, it is preferable that the surface area excluding the sides of the wiring 771, 772 (the surfaces in contact with the outer packaging 753) accounts for 5% or more and 50% or less of the surface area of ​​the outer packaging 753.

[0254] Wiring 771 and 772 are preferably made of materials with high ductility or malleability. In particular, by using materials with both high ductility and malleability, breakage of wiring 771 and 772 due to bending of the energy storage device 760 can be suppressed. Materials with high ductility and malleability include, for example, metals such as gold, silver, platinum, iron, nickel, copper, aluminum, zinc, and tin, or alloys containing the above-mentioned metals.

[0255] <<Methods for Detecting Liquid Leaks>> Below, an example of a method for detecting electrolyte leakage in a portable information terminal 730 is described. Figure 17A shows a block diagram of the structure of the portable information terminal 730 in a state of electrolyte leakage 736. In Figure 17A, lines including arrows indicate the transmission direction of wired or wireless signals according to the direction of the arrows. Therefore, the components connected by these lines are sometimes electrically connected. Furthermore, lines without arrows represent wiring, and the components connected by these lines are electrically connected.

[0256] The portable information terminal 730 includes a liquid leak detection circuit 732, a power supply 733, a current meter 734, wiring 771, and wiring 772 (see Figure 17A). The liquid leak detection circuit 732, power supply 733, and current meter 734 are included in the housing 731. Alternatively, the power supply 733 and current meter 734 can be included in the liquid leak detection circuit 732. Furthermore, the portable information terminal 730 includes a functional circuit 739. The functional circuit 739 includes the aforementioned speaker, sensor, microphone, etc. The functional circuit 739 is included in the housing 731.

[0257] Wiring 771 and 772 are electrically connected to power supply 733, and an arbitrary voltage is applied between wiring 771 and wiring 772 (see Figure 17A). The switching of power supply 733 is controlled by liquid leak detection circuit 732.

[0258] Figure 17B is a flowchart illustrating the process of detecting electrolyte leakage in a portable information terminal 730. For example, the method for detecting electrolyte leakage in a portable information terminal 730 includes the following four steps.

[0259] When the electrolyte 736 of the energy storage device 760 leaks, the electrolyte 736 adheres to the surface of the outer packaging 753 (see S1 in Figures 17A and 17B). The electrolyte 736 adhering to the surface of the outer packaging 753 comes into contact with wiring 771 and wiring 772, thereby allowing current to flow through wiring 771 and wiring 772 (see S2 in Figure 17B). When the ammeter 734, connected in parallel with wiring 772, detects this current, the ammeter 734 outputs a detection signal to the liquid leakage detection circuit 732 (see S3 in Figure 17B). The liquid leakage detection circuit 732 stops the operation of the display panel 702 and / or the functional circuit 739 based on the detection signal (see S4 in Figure 17B).

[0260] Figure 17A shows an example of ammeter 734 connected to wiring 772, but ammeter 734 can also be connected to wiring 771. Furthermore, power supply 733 and ammeter 734 are included in liquid leak detection circuit 732, which can also be electrically connected to wirings 771 and 772 (see Figure 17C). In this case, liquid leak detection circuit 732 has the function of applying a specified voltage to wirings 771 and 772 and detecting the current flowing through wirings 771 and 772.

[0261] This implementation method can be appropriately combined with other implementation methods.

[0262] Implementation Method 3 In this embodiment, a flexible energy storage device according to one embodiment of the present invention will be described with reference to FIGS. 18A to 25. The energy storage device according to one embodiment of the present invention may also have a curved shape. Furthermore, the energy storage device according to one embodiment of the present invention is flexible and can be used in both a bent and non-bent state.

[0263] <Structure Example 1> Figure 18A shows a perspective view of the secondary battery 200, and Figure 18B shows a top view of the secondary battery 200.

[0264] Figure 19A shows a cross-sectional view along the dashed line C1-C2 in Figure 18B, and Figure 19B shows a cross-sectional view along the dashed line C3-C4 in Figure 18B. For clarity, Figures 19A and 19B abstractly show a portion of the components.

[0265] The secondary battery 200 includes a positive electrode 211, a negative electrode 215, and an insulator 203. The secondary battery 200 also includes a positive electrode lead 221, a negative electrode lead 225, and an outer casing 207.

[0266] Both the positive electrode 211 and the negative electrode 215 include a current collector and an active material layer. The positive electrode 211 and the negative electrode 215 are arranged such that the active material layers face each other with the separator 203 in between.

[0267] In the electrodes (positive electrode 211 and negative electrode 215) included in the secondary battery 200, it is preferable that the electrode located on the outer diameter side of the bend is longer in the bending direction than the electrode located on the inner diameter side. By adopting the above structure, when the secondary battery 200 is bent at a certain curvature, the end of the positive electrode 211 can be aligned with the end of the negative electrode 215. That is, all regions of the positive electrode active material layer of the positive electrode 211 can be arranged opposite to the negative electrode active material layer of the negative electrode 215. As a result, the positive electrode active material of the positive electrode 211 can be effectively used for battery reaction. As a result, the capacity per unit volume of the secondary battery 200 can be increased. This structure is particularly effective when the curvature of the secondary battery 200 is fixed.

[0268] Positive lead 221 is electrically connected to multiple positive terminals 211. Negative lead 225 is electrically connected to multiple negative terminals 215. Both positive lead 221 and negative lead 225 include a sealing layer 220.

[0269] The outer packaging 207 covers multiple positive electrodes 211, multiple negative electrodes 215, and multiple separators 203. The secondary battery 200 contains an electrolyte (not shown) in the area covered by the outer packaging 207. The secondary battery 200 is sealed by adhesiveting the three sides of the outer packaging 207.

[0270] Figures 19A and 19B show an example using multiple rectangular insulators 203, with one insulator 203 sandwiched between each pair of positive electrodes 211 and negative electrodes 215; however, one embodiment of the invention is not limited to this. An insulator can also be positioned between the positive and negative electrodes by bending (or corrugating) or winding a thin sheet-like insulator.

[0271] For example, Figures 21A, 21B, 21C, and 21D illustrate a method for manufacturing a secondary battery 200. Figure 20 shows a cross-sectional view along the dashed line C1-C2 in Figure 18B when the above-described manufacturing method is used.

[0272] First, a negative electrode 215 (Fig. 21A) is disposed on the separator 203. At this time, the negative electrode active material layer included in the negative electrode 215 overlaps with the separator 203.

[0273] Next, the isolator 203 is folded and overlapped onto the negative electrode 215. Then, the positive electrode 211 is overlapped onto the isolator 203 (Fig. 21B). At this time, the positive electrode active material layer included in the positive electrode 211 overlaps with the isolator 203 and the negative electrode active material layer. When using an electrode with an active material layer formed on one surface of the current collector, the positive electrode 211 and the negative electrode 215 are configured such that the positive electrode active material layer of the positive electrode 211 and the negative electrode active material layer of the negative electrode 215 are opposite each other with the isolator 203 in between.

[0274] When a heat-welding material such as polypropylene is used for the insulator 203, electrode misalignment during manufacturing can be suppressed by heat-welding the overlapping areas of the insulators 203 and then overlapping another electrode onto the insulator 203. Specifically, it is preferable to heat-weld the areas of the insulators 203 that do not overlap with the negative electrode 215 or the positive electrode 211 but overlap with each other, such as the area 203a shown in FIG. 21B.

[0275] By repeating the above process, as shown in Figure 21C, the positive electrode 211 and the negative electrode 215 can be stacked with the separator 203 sandwiched between them.

[0276] Alternatively, multiple negative electrodes 215 and multiple positive electrodes 211 can be alternately sandwiched in the space between the pre-folded and repeatedly folded insulating body 203.

[0277] Next, as shown in Figure 21C, multiple positive electrodes 211 and multiple negative electrodes 215 are covered by an isolator 203.

[0278] As shown in Figure 21D, by thermally fusing the overlapping areas of the insulators 203, such as area 203b shown in Figure 21D, the insulators 203 cover and bind together multiple positive electrodes 211 and multiple negative electrodes 215.

[0279] Alternatively, multiple positive electrodes 211, multiple negative electrodes 215, and the isolator 203 can be bundled together using binding materials.

[0280] Because the positive electrode 211 and the negative electrode 215 are overlapped by the above steps, an insulator 203 includes a region sandwiched between the plurality of positive electrodes 211 and the plurality of negative electrodes 215 and a region configured to cover the plurality of positive electrodes 211 and the plurality of negative electrodes 215.

[0281] In other words, the separator 203 included in the secondary battery 200 shown in Figures 20 and 21D is a separator in which a portion of it is folded. Multiple positive electrodes 211 and multiple negative electrodes 215 are sandwiched in the folded area of ​​the separator 203.

[0282] <Structure Example 2> Figure 22A shows a perspective view of the secondary battery 250, and Figure 22B shows a top view of the secondary battery 250. In addition, Figure 22C1 shows a cross-sectional view of the first electrode assembly 230, and Figure 22C2 shows a cross-sectional view of the second electrode assembly 231.

[0283] The secondary battery 250 includes a first electrode assembly 230, a second electrode assembly 231, and an separator 203. The secondary battery 250 also includes a positive electrode lead 221, a negative electrode lead 225, and an outer packaging 207.

[0284] As shown in Figure 22C1, in the first electrode assembly 230, a positive electrode 211a, an insulator 203, a negative electrode 215a, an insulator 203, and a positive electrode 211a are stacked sequentially. Both the positive electrode 211a and the negative electrode 215a include active material layers on the two surfaces of the current collector.

[0285] As shown in Figure 22C2, in the second electrode assembly 231, a negative electrode 215a, an insulator 203, a positive electrode 211a, an insulator 203, and a negative electrode 215a are stacked sequentially. Both the positive electrode 211a and the negative electrode 215a include active material layers on the two surfaces of the current collector.

[0286] In other words, in the first electrode assembly 230 and the second electrode assembly 231, the positive electrode and the negative electrode are arranged opposite each other with an active material layer separated by an insulator 203.

[0287] Positive lead 221 is electrically connected to multiple positive terminals 211. Negative lead 225 is electrically connected to multiple negative terminals 215. Both positive lead 221 and negative lead 225 include a sealing layer 220.

[0288] Figure 23 shows an example of a cross-sectional view along the dashed line D1-D2 in Figure 22B. For clarity, Figure 23 abstractly shows a portion of the components.

[0289] As shown in Figure 23, the secondary battery 250 has a structure in which multiple first electrode assemblies 230 and multiple second electrode assemblies 231 are covered by a wound separator 203.

[0290] The outer packaging 207 covers a plurality of first electrode assemblies 230, a plurality of second electrode assemblies 231, and a separator 203. The secondary battery 200 has an electrolyte (not shown) in the area covered by the outer packaging 207. The secondary battery 200 is sealed by adhesiveting the three sides of the outer packaging 207.

[0291] Figures 24A, 24B, 24C and 24D show examples of manufacturing methods for secondary battery 250.

[0292] First, a first electrode assembly 230 is disposed on the isolator 203 (Fig. 24A).

[0293] Next, the isolator 203 is folded and overlapped on the first electrode assembly 230. Then, two second electrode assemblies 231 are overlapped on top of and below the first electrode assembly 230 through the isolator 203 (Fig. 24B).

[0294] Next, the isolator 203 is wound around the two second electrode assemblies 231. Then, the two first electrode assemblies 230 are overlapped on top of the two second electrode assemblies 231 through the isolator 203 (Fig. 24C).

[0295] Next, the isolator 203 is wound around the two first electrode assemblies 230 (Fig. 24D).

[0296] Because multiple first electrode assemblies 230 and multiple second electrode assemblies 231 are overlapped by the above process, these electrode assemblies are disposed between the spacers 203 which are wound into a spiral shape.

[0297] In addition, the outermost electrode is preferably one that does not include the active material layer on the outside.

[0298] Furthermore, although Figures 22C1 and 22C2 show a structure in which the electrode assembly includes three electrodes and two separators, one embodiment of the present invention is not limited to this and may include four or more electrodes and three or more separators. By increasing the number of electrodes, the capacity of the secondary battery 250 can be further increased. Alternatively, it may include two electrodes and one separator. When the number of electrodes is less, a secondary battery with higher resistance to bending can be manufactured. Furthermore, although Figure 23 shows a structure in which the secondary battery 250 includes three first electrode assemblies 230 and two second electrode assemblies 231, one embodiment of the present invention is not limited to this and may include more electrode assemblies. By increasing the number of electrode assemblies, the capacity of the secondary battery 250 can be further increased. Furthermore, the number of electrode assemblies included in the secondary battery 250 can also be less. When the number of electrode assemblies is less, a secondary battery with higher resistance to bending can be manufactured.

[0299] Additionally, Figure 25 shows another example of a cross-sectional view along the dashed line D1-D2 in Figure 22B. As shown in Figure 25, the insulator 203 can also be disposed between the first electrode assembly 230 and the second electrode assembly 231 by folding the insulator 203 into a corrugated tube shape.

[0300] This implementation method can be appropriately combined with other implementation methods.

[0301] Implementation Method 4 In this embodiment, an example of the use of an energy storage device according to an embodiment of the present invention will be described with reference to FIGS. 26A to 30B.

[0302] The energy storage device according to one embodiment of the present invention can be used, for example, in electronic devices or lighting equipment. The energy storage device according to one embodiment of the present invention has excellent charge-discharge characteristics. Therefore, long-term use can be achieved with only a single charge. Furthermore, because the capacity reduction associated with charge-discharge cycles is suppressed, the usable time is not easily shortened even with repeated charging. In addition, the energy storage device according to one embodiment of the present invention exhibits excellent charge-discharge characteristics over a wide temperature range, including high-temperature environments, and has high long-term reliability and safety, thus improving the safety and reliability of electronic devices or lighting equipment.

[0303] Examples of electronic devices include television sets (also known as televisions or television receivers), monitors for computers, digital cameras, digital camcorders, digital photo frames, mobile phones (also known as mobile phones or mobile phone devices), portable game consoles, portable information terminals, audio playback devices, pinball machines, and other large-scale game machines.

[0304] Because the energy storage device of one embodiment of the present invention is flexible, the energy storage device itself or the electronic device or lighting equipment using the energy storage device can also be assembled along the curved surface of the inner or outer wall of a house or high-rise building, or the interior or exterior decoration of a car.

[0305] Figure 26A shows an example of a mobile phone. In addition to the display unit 7402 assembled in the casing 7401, the mobile phone 7400 also includes operation buttons 7403, an external connection port 7404, a speaker 7405, a microphone 7406, etc. The mobile phone 7400 has a power storage device 7407.

[0306] Figure 26B shows the bent state of the mobile phone 7400. When the mobile phone 7400 is deformed by external force and bent as a whole, the energy storage device 7407 disposed inside it is also bent. The energy storage device 7407 is a thin energy storage device. The energy storage device 7407 is fixed in the bent state. Figure 26C shows the energy storage device 7407 in the bent state.

[0307] Figure 26D shows an example of a bracelet-type display device. The portable display device 7100 includes a housing 7101, a display unit 7102, operation buttons 7103, and a power storage device 7104. Figure 26E shows the bent power storage device 7104.

[0308] Figure 26F shows an example of a watch-type portable information terminal. The portable information terminal 7200 includes a housing 7201, a display unit 7202, a watch strap 7203, a buckle 7204, operation buttons 7205, input / output terminals 7206, etc.

[0309] The portable information terminal 7200 can run various applications such as mobile phone, email, article reading and writing, music playback, Internet communication, and computer games.

[0310] The display surface of the display unit 7202 is curved, allowing the display to follow the curve. Furthermore, the display unit 7202 is equipped with a touch sensor, allowing operation by touching the screen with a finger or stylus. For example, by touching the icon 7207 displayed on the display unit 7202, an application can be launched.

[0311] In addition to setting the time, the operation button 7205 can also have various functions such as power switch, wireless communication switch, setting and canceling silent mode, and setting and canceling power saving mode. For example, the functions of the operation button 7205 can be freely configured by using the operating system assembled in the portable information terminal 7200.

[0312] In addition, the portable information terminal 7200 can perform short-range wireless communication according to communication standards. For example, it can make hands-free calls by communicating with a wireless headset.

[0313] In addition, the portable information terminal 7200 has an input / output terminal 7206, which allows it to directly send data to or receive data from other information terminals via a connector. It can also be charged via the input / output terminal 7206. Charging can also be performed wirelessly without using the input / output terminal 7206.

[0314] The display unit 7202 of the portable information terminal 7200 includes a power storage device according to one embodiment of the present invention. For example, the power storage device 7104 shown in FIG26E in a bent state can be assembled inside the housing 7201, or the power storage device 7104 in a bent state can be assembled inside the watch strap 7203.

[0315] Figure 27A shows an example of a wrist-worn activity meter. The activity meter 7250 includes a housing 7251, a strap 7203, a buckle 7204, etc. Furthermore, the housing 7251 contains a wireless communicator, a pulse sensor, an accelerometer, a temperature sensor, etc. The activity meter 7250 functions by obtaining information such as the user's pulse changes and activity level from the pulse sensor and accelerometer, and transmitting this data to an external portable information terminal via the wireless communicator. In addition, the activity meter 7250 may also have functions such as measuring the user's calorie expenditure and intake, tracking steps, and detecting sleep patterns. The activity meter 7250 may also include a display unit, which can display the data obtained through the above functions.

[0316] The activity meter 7250 includes a power storage device according to one embodiment of the present invention. For example, the power storage device 7104 shown in FIG26E in a bent state can be assembled inside the housing 7201, or the power storage device 7104 in a bent state can be assembled inside the watch strap 7203.

[0317] Figure 27B shows an example of a sleeve-type display device. The display device 7300 includes a display unit 7304 and a power storage device according to one embodiment of the present invention. The display device 7300 may also include a touch sensor in the display unit 7304 and be used as a portable information terminal.

[0318] The display surface of the display unit 7304 is curved, allowing for display along the curved surface. Furthermore, the display device 7300 can change the display status using short-range wireless communication, which is standardized for communication.

[0319] The display device 7300 has input / output terminals, allowing it to directly send data to or receive data from other information terminals via connectors. It can also be charged via the input / output terminals. Charging can also be performed wirelessly without using the input / output terminals.

[0320] Figure 27C shows an example of an eyeglass-type display device. The display device 7350 includes a lens 7351, an eyeglass frame 7352, etc. It also includes a projection section (not shown) disposed inside the eyeglass frame 7352 or in contact with the eyeglass frame 7352, for projecting images or videos onto the lens 7351. The display device 7350 has the function of displaying an image 7351A on the entire lens 7351 in a direction visible to the user. Alternatively, it has the function of displaying an image 7351B on a portion of the lens 7351 in a direction visible to the user.

[0321] The display device 7350 includes a power storage device according to one embodiment of the present invention. FIG27D shows an enlarged view of the end portion 7355 of the eyeglass frame 7352. The end portion 7355 can be formed using a rubber material such as fluororubber or silicone rubber. A power storage device 7360 according to one embodiment of the present invention is embedded inside the end portion 7355, and a positive lead 7361 and a negative lead 7362 protrude from the end portion 7355. The positive lead 7361 and the negative lead 7362 are electrically connected to wiring connected to a projection portion or the like disposed inside the eyeglass frame 7352. The end portion 7355 can be formed together with the power storage device 7360 as described in Embodiment 2.

[0322] The end piece 7355 and the power storage device 7360 are flexible. Therefore, the display device 7350 can be worn in a close fit to the shape of the user's head.

[0323] Figures 28A and 28B show an example of a foldable tablet terminal. The tablet terminal 9600 shown in Figures 28A and 28B includes a pair of housings 9630, a movable part 9640 connecting the pair of housings 9630, a display unit 9631a, a display unit 9631b, a display mode switch 9626, a power switch 9627, a power-saving mode switch 9625, a fastener 9629, and an operation switch 9628. Figure 28A shows the tablet terminal 9600 in the open state, and Figure 28B shows the tablet terminal 9600 in the closed state.

[0324] The tablet terminal 9600 has a battery 9635 inside the housing 9630. The battery 9635 is disposed in the entire housing 9630 through the movable part 9640.

[0325] In the display unit 9631a, a portion of it can be used as a touch panel area 9632a, and data can be input by touching the displayed operation keys 9638. Figure 28A shows, as an example, a structure where one half of the display unit 9631a has only display functionality and the other half has touch panel functionality, but it is not limited to this structure. Furthermore, a structure where the entire area of ​​the display unit 9631a has touch panel functionality can also be used. For example, the entire surface of the display unit 9631a can be used as a touch panel by displaying keyboard buttons, and the display unit 9631b can be used to display a screen.

[0326] Furthermore, similar to display unit 9631a, a portion of display unit 9631b can also be used as a touch panel area 9632b. Additionally, by touching the location of the keyboard display switch button 9639 on the touch panel with a finger or stylus, keyboard buttons can be displayed on display unit 9631b.

[0327] In addition, touch input can be performed simultaneously on both area 9632a and area 9632b of the touch panel.

[0328] Additionally, the display mode switch 9626 can switch between portrait and landscape display orientations and select between monochrome and color display. Based on the amount of ambient light detected by the light sensor built into the tablet terminal 9600, the power-saving mode switch 9625 can set the display brightness to the most suitable level. Besides the built-in light sensor, the tablet terminal can also incorporate other detection devices such as a gyroscope and an accelerometer to detect tilt.

[0329] Furthermore, Figure 28A shows an example where the display area of ​​display unit 9631a is the same as that of display unit 9631b, but it is not limited to this. The size of one display unit can be different from that of the other, and their display quality can also be different. For example, one of the display units 9631a and 9631b can display a higher resolution than the other.

[0330] Figure 28B shows the closed state, and the tablet terminal includes a housing 9630, a solar cell 9633, and a charge / discharge control circuit 9634 with a DC-DC converter 9636. As the energy storage element 9635, an energy storage device according to one embodiment of the present invention is used.

[0331] Furthermore, the tablet terminal 9600 is foldable, so the pair of outer shells 9630 can be folded in an overlapping manner when not in use. By folding the outer shells 9630a and 9630b, the display units 9631a and 9631b can be protected, thereby improving the durability of the tablet terminal 9600. The energy storage element 9635 using an embodiment of the present invention is flexible, and its charging and discharging capacity is not easily reduced even when repeatedly bent. Therefore, a highly reliable tablet terminal can be provided.

[0332] In addition, the tablet terminals shown in Figures 28A and 28B can also have the following functions: displaying various types of information (static images, dynamic images, text images, etc.) on the display; displaying calendars, dates, or times on the display; touch input for touch input operations or editing of information displayed on the display; and control processing through various software (programs), etc.

[0333] By utilizing a solar cell 9633 mounted on the surface of a tablet terminal, power can be supplied to the touch panel, display unit, or image signal processing unit. The solar cell 9633 can be mounted on one or both surfaces of the casing 9630 and can efficiently charge the energy storage device 9635, making it preferable. Using a lithium-ion battery as the energy storage device 9635 offers advantages such as miniaturization.

[0334] Furthermore, the structure and operation of the charge / discharge control circuit 9634 shown in FIG28B will be explained with reference to the block diagram shown in FIG28C. FIG28C shows the solar cell 9633, the energy storage unit 9635, the DC-DC converter 9636, the converter 9637, the switches SW1 to SW3, and the display unit 9631. The energy storage unit 9635, the DC-DC converter 9636, the converter 9637, and the switches SW1 to SW3 correspond to the charge / discharge control circuit 9634 shown in FIG28B.

[0335] First, an example of operation when the solar cell 9633 generates electricity using external light will be explained. A DC-DC converter 9636 is used to boost or buck the power generated by the solar cell to provide a voltage for charging the energy storage unit 9635. Furthermore, when the display unit 9631 is operated using power from the solar cell 9633, switch SW1 is turned on, and converter 9637 boosts or bucks the voltage to the required voltage for the display unit 9631. Alternatively, when the display unit 9631 is not displaying, a structure can be adopted in which switch SW1 is turned off and switch SW2 is turned on to charge the energy storage unit 9635.

[0336] The solar cell 9633 is shown as an example of a power generation method, but it is not limited to this. Other power generation methods, such as piezoelectric elements or thermoelectric conversion elements, can also be used to charge the energy storage device 9635. For example, it can also be charged using a contactless power transmission module that can transmit and receive power wirelessly (without contact) or in combination with other charging methods.

[0337] Figure 29 shows examples of other electronic devices. In Figure 29, the display device 8000 is an example of an electronic device using a power storage device 8004 according to an embodiment of the present invention. Specifically, the display device 8000 is equivalent to a television broadcast receiving display device, including a housing 8001, a display section 8002, a speaker section 8003, and a power storage device 8004, etc. The power storage device 8004 according to an embodiment of the present invention is disposed inside the housing 8001. The display device 8000 can accept power supply from commercial power sources and can also use the power stored in the power storage device 8004. Therefore, even when power supply from commercial power sources cannot be received due to power outages, the display device 8000 can be used as an uninterruptible power supply system by using the power storage device 8004 according to an embodiment of the present invention.

[0338] As the display unit 8002, semiconductor display devices such as liquid crystal display devices, light-emitting devices having light-emitting elements such as organic EL elements in each pixel, electrophoretic display devices, DMD (Digital Micromirror Device), PDP (Plasma Display Panel), and FED (Field Emission Display) can be used.

[0339] In addition to display devices used for receiving television broadcasts, display devices also include all display devices used for displaying information, such as display devices for personal computers or display devices for advertising.

[0340] In Figure 29, the recessed lighting device 8100 is an example of an electronic device using an energy storage device 8103 according to an embodiment of the present invention. Specifically, the lighting device 8100 includes a housing 8101, a light source 8102, and an energy storage device 8103, etc. Although Figure 29 illustrates a case where the energy storage device 8103 is installed inside a ceiling 8104 containing the housing 8101 and the light source 8102, the energy storage device 8103 can also be installed inside the housing 8101. The lighting device 8100 can accept power from commercial power sources and also utilize the power stored in the energy storage device 8103. Therefore, even when power from commercial power sources is unavailable due to power outages, the lighting device 8100 can be used as an uninterruptible power supply system by employing the energy storage device 8103 according to an embodiment of the present invention.

[0341] Although Figure 29 illustrates an inlaid lighting device 8100 installed on the ceiling 8104, the energy storage device according to one embodiment of the present invention can be used for inlaid lighting devices installed outside the ceiling 8104, such as on a side wall 8105, floor 8106, or window 8107, as well as for tabletop lighting devices, etc.

[0342] Furthermore, as the light source 8102, an artificial light source that artificially generates light using electricity can be used. Specifically, examples of the aforementioned artificial light sources include incandescent bulbs, fluorescent lamps, and other discharge lamps, as well as light-emitting elements such as LEDs or organic EL elements.

[0343] In Figure 29, an air conditioner having an indoor unit 8200 and an outdoor unit 8204 is an example of an electronic device using an energy storage device 8203 according to an embodiment of the present invention. Specifically, the indoor unit 8200 includes a housing 8201, an air outlet 8202, and an energy storage device 8203, etc. Although Figure 29 illustrates the case where the energy storage device 8203 is provided in the indoor unit 8200, the energy storage device 8203 may also be provided in the outdoor unit 8204. Alternatively, the energy storage device 8203 may be provided in both the indoor unit 8200 and the outdoor unit 8204. The air conditioner can accept power from a commercial power source and also use the power stored in the energy storage device 8203. In particular, when an energy storage device 8203 is provided in both the indoor unit 8200 and the outdoor unit 8204, even when power supply from commercial power sources is unavailable due to power outages or other reasons, the air conditioner can be utilized by using the energy storage device 8203 according to an embodiment of the present invention as an uninterruptible power supply system.

[0344] Although a split-type air conditioner consisting of an indoor unit and an outdoor unit is illustrated in Figure 29, the energy storage device according to one embodiment of the present invention can also be used in an integrated air conditioner that has the functions of an indoor unit and an outdoor unit in one housing.

[0345] In Figure 29, the electric refrigerator / freezer 8300 is an example of an electronic device using an energy storage device 8304 according to an embodiment of the present invention. Specifically, the electric refrigerator / freezer 8300 includes a housing 8301, a refrigerator door 8302, a freezer door 8303, and an energy storage device 8304. In Figure 29, the energy storage device 8304 is disposed inside the housing 8301. The electric refrigerator / freezer 8300 can accept power from a commercial power source and also utilize the power stored in the energy storage device 8304. Therefore, even when power from a commercial power source is unavailable due to power outages, the electric refrigerator / freezer 8300 can be used as an uninterruptible power supply system by employing the energy storage device 8304 according to an embodiment of the present invention.

[0346] Microwave ovens and other high-frequency heating devices, as well as electric cookers and other electronic devices, require high power for short periods of time. Therefore, by using an energy storage device according to an embodiment of the present invention as an auxiliary power source to supplement the power supply when commercial power cannot provide sufficient power, the main power switch of the commercial power supply can be prevented from tripping when the electronic device is in use.

[0347] Furthermore, during periods when electronic devices are not used, especially when the actual percentage of electricity used out of the total electricity available from commercial power sources (referred to as electricity usage rate) is low, electricity is stored in energy storage devices, thereby suppressing increased electricity usage during periods outside of these periods. For example, in the electric refrigerator / freezer 8300, electricity is stored in energy storage device 8304 at night when the temperature is low and the refrigerator door 8302 or freezer door 8303 is not opened or closed. During the day when the temperature is high and the refrigerator door 8302 or freezer door 8303 is opened or closed, energy storage device 8304 is used as an auxiliary power source, thereby suppressing daytime electricity usage.

[0348] Alternatively, the energy storage device according to one embodiment of the present invention can be installed in a vehicle.

[0349] When energy storage devices are integrated into vehicles, a new generation of clean energy vehicles, such as hybrid electric vehicles (HEVs), electric vehicles (EVs), or plug-in hybrid electric vehicles (PHEVs), can be realized.

[0350] Figures 30A and 30B illustrate a vehicle using an energy storage device according to one embodiment of the present invention. The vehicle 8400 shown in Figure 30A is an electric vehicle that uses an electric motor as its driving power source. Alternatively, vehicle 8400 is a hybrid vehicle capable of appropriately selecting both an electric motor and an engine as driving power sources. By using one embodiment of the present invention, a high-range vehicle can be achieved. Furthermore, vehicle 8400 is equipped with an energy storage device. The energy storage device can not only drive the electric motor but also supply electricity to lighting devices such as headlights 8401 or interior lights (not shown).

[0351] In addition, the energy storage device can supply power to display devices such as the speedometer and tachometer in the car 8400. Furthermore, the energy storage device can supply power to semiconductor devices such as the navigation system in the car 8400.

[0352] In the vehicle 8500 shown in Figure 30B, the energy storage device in the vehicle 8500 can be charged by receiving power from an external charging device using a plug-in method or a contactless power supply method. Figure 30B shows the charging of the energy storage device installed in the vehicle 8500 from a ground-mounted charging device 8021 via a cable 8022. When charging, the charging method and connector specifications should be appropriately followed according to the specifications of CHAdeMO (registered trademark) or the "Combined Charging System". The charging device 8021 can also use power from charging stations installed in commercial facilities or from home. For example, the energy storage device 8024 installed in the vehicle 8500 can be charged by receiving power from an external source using plug-in technology. The AC power can be converted to DC power using a conversion device such as an AC / DC converter for charging.

[0353] Alternatively, although not illustrated, the receiving device can be installed in the vehicle and charged by receiving power from a ground-based power supply device without contact. When using a contactless power supply method, by assembling the power supply device in the road or exterior wall, charging can be performed both while the vehicle is parked and while it is in motion. Furthermore, this contactless power supply method can also be used for power transmission and reception between vehicles. Moreover, solar cells can be installed on the exterior of the vehicle to charge the energy storage device when parked or in motion. Such contactless power supply can be achieved using electromagnetic induction or magnetic field resonance.

[0354] According to one embodiment of the present invention, the cycle characteristics and reliability of the energy storage device can be improved. Furthermore, according to one embodiment of the present invention, the characteristics of the energy storage device can be improved, allowing the energy storage device itself to be smaller and lighter. Additionally, if the energy storage device itself can be smaller and lighter, it contributes to the lightweighting of the vehicle, thereby extending the driving range. Furthermore, the energy storage device installed in the vehicle can be used as a power supply source outside the vehicle. In this case, the use of commercial power sources can be avoided during peak electricity demand periods.

[0355] This implementation method can be appropriately combined with other implementation methods. Example 1

[0356] In this embodiment, an energy storage device according to an embodiment of the present invention was manufactured with reference to Embodiment 1, and a cycle life test was conducted at 25°C together with a comparative energy storage device.

[0357] <Sample Manufacturing Method> In this embodiment, the energy storage device 500 shown in FIG1A is manufactured. The manufacturing method of the sample is described below.

[0358] There are 14 types of samples for applying one embodiment of the present invention, namely sample A1, sample A2, sample B1, sample B2, sample C1, sample C2, sample D1, sample D2, sample E1, sample E2, sample F1, sample F2, sample B3, and sample B4. There are 2 types of comparison samples, namely comparison sample a1 and comparison sample a2.

[0359] In samples A1, A2, B1, B2, C1, C2, D1, D2, E1, E2, F1, F2, B3, and B4, lithium bis(pentafluoroethanesulfonyl)amine lithium (LiBETA) and lithium hexafluorophosphate were used as solutes. The concentration of lithium hexafluorophosphate varied among samples A1, A2, B1, B2, C1, C2, D1, D2, E1, E2, F1, F2, B3, and B4. However, in comparative samples a1 and a2, lithium bis(pentafluoroethanesulfonyl)amine lithium (LiBETA) was used as a solute instead of lithium hexafluorophosphate.

[0360] Cellulose fibers were used as the separator in samples A1, A2, B1, B2, C1, C2, D1, D2, E1, E2, F1, F2, and comparative samples a1 and a2. Polyphenylene sulfide (PPS) was used in samples B3 and B4.

[0361] Furthermore, after manufacturing the energy storage device 500, samples A2, B2, C2, D2, E2, F2, B4, and comparative sample a2 were subjected to a heat treatment at 170°C for 15 minutes. This heat treatment is assumed to be performed together with fluororubber as described in Embodiment 2. Samples A1, B1, C1, D1, E1, F1, B3, and comparative sample a1 were not subjected to heat treatment.

[0362] Table 1 shows the electrolytes, separators, and heat treatment conditions for each sample.

[0363] Table 1 sample electrolytes Insulator Heat treatment condition LiPF6 [wt%] Comparison sample a1 Electrolyte a 0.0 Cellulose fiber - Compare sample a2 170°C for 15 minutes Sample A1 Electrolyte A 0.18 Cellulose fiber - Sample A2 170°C for 15 minutes Sample B1 Electrolyte B 0.27 Cellulose fiber - Sample B2 170°C for 15 minutes Sample C1 Electrolyte C 0.51 Cellulose fiber - Sample C2 170°C for 15 minutes Sample D1 Electrolyte D 1.1 Cellulose fiber - Sample D2 170°C for 15 minutes Sample E1 Electrolyte E 2.0 Cellulose fiber - Sample E2 170°C for 15 minutes Sample F1 Electrolyte F 3.0 Cellulose fiber - Sample F2 170°C for 15 minutes Sample B3 Electrolyte B 0.27 polyphenylene sulfide - Sample B4 170°C for 15 minutes

[0364] The manufacturing method of the electrolyte is explained.

[0365] Electrolyte a, used for comparative samples a1 and a2, is described below. Electrolyte a was prepared by mixing ethylene carbonate (VC) with a 1:1 volume ratio of ethylene carbonate (EC) and propylene carbonate (PC), and dissolving lithium bis(pentafluoroethanesulfonyl)amine (LiBETA). The amount of ethylene carbonate (VC) dissolved relative to the weight of electrolyte a was 1 wt%. The amount of lithium bis(pentafluoroethanesulfonyl)amine (LiBETA) dissolved relative to the molar concentration of electrolyte a was 1 mol / L.

[0366] Electrolyte A, used in samples A1 and A2, is described below. Electrolyte A was prepared by mixing ethylene carbonate (VC) and propylene carbonate (PC) in a 1:1 volume ratio, dissolving lithium bis(pentafluoroethanesulfonyl)amine (LiBETA) and lithium hexafluorophosphate. The dissolved amount of ethylene carbonate (VC) relative to the weight of electrolyte A was 1 wt%. The dissolved amount of lithium bis(pentafluoroethanesulfonyl)amine (LiBETA) relative to the molar concentration of electrolyte A was 1 mol / L. The dissolved amount of lithium hexafluorophosphate relative to the weight of electrolyte A was 0.18 wt%.

[0367] Electrolyte B, used in samples B1, B2, B3, and B4, is described below. Electrolyte B was prepared by mixing ethylene carbonate (VC) with a 1:1 volume ratio of ethylene carbonate (EC) and propylene carbonate (PC), dissolving lithium bis(pentafluoroethanesulfonyl)amine (LiBETA) and lithium hexafluorophosphate. The dissolved amount of ethylene carbonate (VC) relative to the weight of electrolyte B was 1 wt%. The dissolved amount of lithium bis(pentafluoroethanesulfonyl)amine (LiBETA) relative to the molar concentration of electrolyte B was 1 mol / L. The dissolved amount of lithium hexafluorophosphate relative to the weight of electrolyte B was 0.27 wt%.

[0368] Electrolyte C, used in samples C1 and C2, is described below. Electrolyte C was prepared by mixing ethylene carbonate (VC) with a 1:1 volume ratio of ethylene carbonate (EC) and propylene carbonate (PC), dissolving lithium bis(pentafluoroethanesulfonyl)amine (LiBETA) and lithium hexafluorophosphate. The dissolved amount of ethylene carbonate (VC) relative to the weight of electrolyte C was 1 wt%. The dissolved amount of lithium bis(pentafluoroethanesulfonyl)amine (LiBETA) relative to the molar concentration of electrolyte C was 1 mol / L. The dissolved amount of lithium hexafluorophosphate relative to the weight of electrolyte C was 0.51 wt%.

[0369] Electrolyte D, used in samples D1 and D2, is described below. Electrolyte D was prepared by mixing ethylene carbonate (VC) with a 1:1 volume ratio of ethylene carbonate (EC) and propylene carbonate (PC), dissolving lithium bis(pentafluoroethanesulfonyl)amine (LiBETA) and lithium hexafluorophosphate. The dissolved amount of ethylene carbonate (VC) relative to the weight of electrolyte D was 1 wt%. The dissolved amount of lithium bis(pentafluoroethanesulfonyl)amine (LiBETA) relative to the molar concentration of electrolyte D was 1 mol / L. The dissolved amount of lithium hexafluorophosphate relative to the weight of electrolyte D was 1.1 wt%.

[0370] Electrolyte E, used in samples E1 and E2, is described below. Electrolyte E was prepared by mixing ethylene carbonate (VC) with a 1:1 volume ratio of ethylene carbonate (EC) and propylene carbonate (PC), dissolving lithium bis(pentafluoroethanesulfonyl)amine (LiBETA) and lithium hexafluorophosphate. The amount of ethylene carbonate (VC) dissolved relative to the weight of electrolyte E was 1 wt%. The amount of lithium bis(pentafluoroethanesulfonyl)amine (LiBETA) dissolved relative to the molar concentration of electrolyte E was 1 mol / L. The amount of lithium hexafluorophosphate dissolved relative to the weight of electrolyte E was 2.0 wt%.

[0371] Electrolyte F, used in samples F1 and F2, is described below. Electrolyte F was prepared by mixing ethylene carbonate (VC) with a 1:1 volume ratio of ethylene carbonate (EC) and propylene carbonate (PC), dissolving lithium bis(pentafluoroethanesulfonyl)amine (LiBETA) and lithium hexafluorophosphate. The dissolved amount of ethylene carbonate (VC) relative to the weight of electrolyte F was 1 wt%. The dissolved amount of lithium bis(pentafluoroethanesulfonyl)amine (LiBETA) relative to the molar concentration of electrolyte F was 1 mol / L. The dissolved amount of lithium hexafluorophosphate relative to the weight of electrolyte F was 3.0 wt%.

[0372] As a mixture of ethylene carbonate (EC) and propylene carbonate (PC) in a 1:1 volume ratio, lithium battery grade (product number: LBG-00798) manufactured by KISHIDA Chemical Co., Ltd., Japan, was used. As ethylene carbonate (VC), lithium battery grade (product number: LBG-84923) manufactured by KISHIDA Chemical Co., Ltd., Japan, was used. As lithium bis(pentafluoroethanesulfonyl)amine (LiBETA), a product manufactured by IoLiTec (Ionic Liquids Technologies Inc.) (product number: KI-0016-HP) was used. As lithium hexafluorophosphate, lithium battery grade (product number: LBG-45860) manufactured by KISHIDA Chemical Co., Ltd., Japan, was used.

[0373] The manufacturing method of the negative electrode is described. The manufacturing method of the negative electrode is common to samples A1, A2, B1, B2, C1, C2, D1, D2, E1, E2, F1, F2, B3, B4, comparison sample a1, and comparison sample a2.

[0374] Spherical natural graphite (manufactured by Japan Black Lead Industry Co., Ltd., CGB-15) with a specific surface area of ​​6.3 m² / g and an average particle size of 15 µm was used as the negative electrode active material. Sodium carboxymethyl cellulose (CMC-Na) and SBR were used as binders. The degree of polymerization of the CMC-Na used was 600 or higher and 800 or lower, and the viscosity of the 1 wt% aqueous solution was in the range of 300 mPa·s or higher and 500 mPa·s or lower. The mixing ratio of graphite, CMC-Na, and SBR was graphite:CMC-Na:SBR = 97:1.5:1.5 (wt%).

[0375] First, CMC-Na powder and active substances are mixed and kneaded using a mixer to obtain a first mixture.

[0376] Next, a small amount of water is added to the first mixture, and a dry-thickening process is performed to obtain the second mixture. Here, dry-thickening refers to high-viscosity mixing.

[0377] Next, water is added and the mixture is kneaded using a mixer to obtain a third mixture.

[0378] Next, 50 wt% aqueous dispersion of SBR was added and the mixture was kneaded using a mixer. Then, degassing was performed under reduced pressure to obtain a slurry.

[0379] Next, the slurry was coated onto the negative electrode current collector using a continuous coating machine. A rolled copper foil with a thickness of 18µm was used as the negative electrode current collector. The coating speed was 0.75m / min.

[0380] Next, the solvent of the slurry coated on the negative electrode current collector was vaporized using a drying oven. First, it was treated at 50°C for 120 seconds under atmospheric conditions, then at 80°C for 120 seconds. Following this, it was treated at 100°C for 10 hours under reduced pressure (gauge pressure -100 kPa).

[0381] The negative electrode is manufactured by forming a layer of negative active material on one surface of the negative current collector through the above process.

[0382] The manufacturing method of the positive electrode is described. The manufacturing method of the positive electrode is the same in samples A1, A2, B1, B2, C1, C2, D1, D2, E1, E2, F1, F2, B3, B4, comparative sample a1 and comparative sample a2.

[0383] LiCoO2 was used as the positive electrode active material, polyvinylidene fluoride (PVDF) as the binder, and acetylene black as the conductive additive. The LiCoO2 used was a product manufactured by Nippon Chemical Industries, Ltd. (C-5hV) with a specific surface area of ​​0.55 m² / g and an average particle size of 6.3 µm. The mixing ratio of LiCoO2, PVDF, and acetylene black was LiCoO2:acetylene black:PVDF = 95:3:2 (wt%).

[0384] In this specification, the average particle size refers to the cumulative 50% value based on volume (D50).

[0385] First, acetylene black and PVDF are mixed and kneaded using a mixer to obtain a third mixture.

[0386] Next, an active substance was added to the third mixture to obtain the fourth mixture.

[0387] Next, N-methyl-2-pyrrolidone (NMP) as a solvent is added to the fourth mixture, and the mixture is then kneaded using a mixer. A slurry is produced through the above process.

[0388] Next, the mixture is mixed using a large mixing machine.

[0389] Next, the slurry was coated onto the positive current collector using a continuous coating machine. An aluminum current collector (20µm thick) was used as the positive current collector. The coating speed was 0.2m / min.

[0390] Next, the solvent of the slurry coated on the positive current collector is vaporized using a drying oven. The solvent is vaporized by treating at 70°C for 7.5 minutes in an atmospheric atmosphere, followed by treating at 90°C for 7.5 minutes.

[0391] Next, the material was heated at 170°C for 10 hours under reduced pressure (gauge pressure -100 kPa). Then, the positive electrode active material layer was pressed using a rolling method to achieve compaction.

[0392] The positive electrode is manufactured by forming a layer of positive active material on one surface of the positive current collector using the above process.

[0393] Tables 2 and 3 show the average values ​​of the active material loading, thickness, and density of the formed positive and negative electrode active material layers, respectively. Note that these values ​​shown in this specification are averages of measurements taken from the electrodes used in manufacturing the samples. In the case where active material layers are present on both surfaces of the current collector, these values ​​correspond to the average values ​​of the active material loading, thickness, and density of the active material layer on one surface.

[0394] The load capacity is calculated based on the electrode area and the weight measured using an electronic balance. Furthermore, the density is calculated based on the thickness measured using a micrometer.

[0395] Table 2 sample positive electrode Load capacity [mg / cm²] thickness [mm] density [g / cm 3] Comparison sample a1 21.1 66 3.20 Compare sample a2 21.2 67 3.16 Sample A1 21.4 66 3.25 Sample A2 21.5 66 3.25 Sample B1 21.3 70 3.05 Sample B2 21.3 67 3.18 Sample C1 21.3 66 3.22 Sample C2 21.3 66 3.22 Sample D1 21.3 66 3.23 Sample D2 21.3 66 3.23 Sample E1 21.6 67 3.23 Sample E2 21.6 68 3.18 Sample F1 21.3 65 3.28 Sample F2 21.4 67 3.19 Sample B3 24.4 72 3.39 Sample B4 24.4 71 3.44

[0396] Table 3 sample negative electrode Load capacity [mg / cm²] thickness [mm] density [g / cm 3] Comparison sample a1 9.5 107 0.89 Compare sample a2 9.7 101 0.96 Sample A1 10.2 106 0.96 Sample A2 10.2 103 0.99 Sample B1 9.7 99 0.98 Sample B2 9.8 105 0.93 Sample C1 10.1 103 0.98 Sample C2 10.1 102 0.99 Sample D1 10.1 107 0.95 Sample D2 10.2 102 1.00 Sample E1 10.3 109 0.95 Sample E2 10.4 103 1.01 Sample F1 10.2 106 0.96 Sample F2 10.2 108 0.94 Sample B3 9.7 101 0.96 Sample B4 9.7 103 0.95

[0397] Next, the manufacturing method of the energy storage device will be described. In each sample manufactured in this embodiment, a positive electrode having a positive active material layer on one surface of the positive current collector and a negative electrode having a negative active material layer on one surface of the negative current collector are used. That is, each sample in this embodiment includes a positive active material layer and a negative active material layer.

[0398] First, disconnect the positive electrode, negative electrode, and first insulator. The dimensions of the positive electrode are 20.49 cm², the dimensions of the negative electrode are 23.84 cm², and the dimensions of the first insulator are 24.75 cm².

[0399] In samples A1, A2, B1, B2, C1, C2, D1, D2, E1, E2, F1, F2, and comparative samples a1 and a2, cellulose fibers were used as the separator. Specifically, solvent-spun regenerated cellulose fibers (product number: TF40) manufactured by Kōkō Paper Industries, Ltd. of Japan, with a thickness of 30µm were used. In samples B3 and B4, polyphenylene sulfide was used. Specifically, two sheets of polyphenylene sulfide paper (product number: PS0020) manufactured by Toray Industries, Ltd., with a thickness of 46µm, were overlapped.

[0400] Next, the positive and negative active materials on the tab area are stripped to expose the current collector.

[0401] Next, the positive and negative electrodes are stacked with the first separator sandwiched between them. At this point, the positive and negative electrodes are stacked with the positive active material layer and the negative active material layer facing each other.

[0402] Next, ultrasonic welding is used to connect the leads to the positive and negative terminals.

[0403] Next, a second isolator is used to encapsulate the stacked electrodes and the areas where the leads are joined. This prevents the aluminum contained in the outer packaging from contacting the electrodes due to the melting of the resin layer within the outer packaging during subsequent heat treatment. The second isolator has a dimension of 104 cm².

[0404] Next, two of the four sides of the outer packaging are joined together by heating.

[0405] As the outer packaging, a thin film consisting of a resin layer covering both surfaces of aluminum is used.

[0406] Next, the sealing layer on the lead wire is arranged so that it overlaps with the sealing layer of the outer packaging, and then joined by heating. At this time, the edges other than the edge used for injecting electrolyte are joined.

[0407] Next, a heat treatment is performed to dry the outer packaging and the positive electrode, separator, and negative electrode enclosed by the outer packaging. The heating conditions are: reduced pressure atmosphere (gauge pressure -100 kPa), 80°C, 10 hours.

[0408] Next, under an argon atmosphere, approximately 600 µL of electrolyte was injected from the unsealed side. Electrolyte a was injected into comparative samples a1 and a2. Electrolyte A was injected into samples A1 and A2. Electrolyte B was injected into samples B1, B2, B3, and B4. Electrolyte C was injected into samples C1 and C2. Electrolyte D was injected into samples D1 and D2. Electrolyte E was injected into samples E1 and E2. Electrolyte F was injected into samples F1 and F2.

[0409] Then, one side of the outer packaging is sealed by heating under reduced pressure (gauge pressure -100 kPa). This process manufactures a thin energy storage device.

[0410] Next, samples A2, B2, C2, D2, E2, F2, B4, and comparative sample a2 were subjected to heat treatment. Assuming they were formed with fluororubber as described in Embodiment 2, the heating conditions were atmospheric pressure, 170°C, and 15 minutes. Specifically, after heating the thermostat to approximately 170°C, each sample was placed in the thermostat and removed after 15 minutes. No expansion of the outer packaging of any sample was observed during this heat treatment.

[0411] Samples A1, A2, B1, B2, C1, C2, D1, D2, E1, E2, F1, F2, B3, B4, comparison sample a1, and comparison sample a2 are manufactured using the above process.

[0412] Measurement of charge and discharge characteristics Next, the charge-discharge characteristics of each sample in this embodiment at 25°C were evaluated. This measurement was performed using a charge-discharge measuring instrument (manufactured by Toyo Systems, Inc., Japan). Constant current-constant voltage charging was performed with an upper limit of 4.3V, and constant current discharging was performed with a lower limit of 2.5V. Three charge-discharge cycles were performed at a rate of 0.1C, followed by a long-term cycle test at a rate of 0.3C. A 10-minute rest period was set after each charge and discharge cycle.

[0413] Here, the rate is calculated based on the capacity of 170 mAh / g obtained when the upper limit charging voltage of LiCoO2, the positive electrode active material, is 4.3V.

[0414] Figures 31A, 31B, 31C, 31D, 32A, 32B, 32C, 32D, 33A, 33B, 33C, 33D, 34A, 34B, 34C, and 34D respectively show the charging and discharging curves of comparison samples a1, a2, A1, A2, B1, B2, C1, C2, D1, D2, E1, E2, F1, F2, B3, and B4. In Figures 31A, 31B, 31C, 31D, 32A, 32B, 32C, 32D, 33A, 33B, 33C, 33D, 34A, 34B, 34C, and 34D, the horizontal axis represents capacity [mAh / g], and the vertical axis represents voltage [V]. Furthermore, the charge and discharge characteristics of each sample at the 1st and 300th cycles are shown. Capacity is expressed as the capacity per weight of the positive electrode active material.

[0415] It was confirmed that the capacity decreased after repeated charge-discharge cycles on samples heated to 170°C for 15 minutes. It was also confirmed that the capacity decrease of samples A2, B2, C2, D2, and B4 of one embodiment of the present invention containing lithium hexafluorophosphate was suppressed after repeated charge-discharge cycles, compared to a comparative sample a2 that did not contain lithium hexafluorophosphate.

[0416] Figure 35A shows the cycle characteristics of discharge capacity for comparative samples a1 and a2; Figure 35B shows the cycle characteristics of discharge capacity for samples A1 and A2; Figure 35C shows the cycle characteristics of discharge capacity for samples B1 and B2; Figure 35D shows the cycle characteristics of discharge capacity for samples C1 and C2; Figure 36A shows the cycle characteristics of discharge capacity for samples D1 and D2; Figure 36B shows the cycle characteristics of discharge capacity for samples E1 and E2; Figure 36C shows the cycle characteristics of discharge capacity for samples F1 and F2; and Figure 36D shows the cycle characteristics of discharge capacity for samples B3 and B4. In Figures 35A, 35B, 35C, 35D, 36A, 36B, 36C, and 36D, the horizontal axis represents cycles (times), and the vertical axis represents capacity (mAh / g).

[0417] Figure 37A shows the cyclic characteristics of discharge capacity retention for comparative samples a1 and a2; Figure 37B shows the cyclic characteristics of discharge capacity retention for samples A1 and A2; Figure 37C shows the cyclic characteristics of discharge capacity retention for samples B1 and B2; Figure 37D shows the cyclic characteristics of discharge capacity retention for samples C1 and C2; Figure 38A shows the cyclic characteristics of discharge capacity retention for samples D1 and D2; Figure 38B shows the cyclic characteristics of discharge capacity retention for samples E1 and E2; Figure 38C shows the cyclic characteristics of discharge capacity retention for samples F1 and F2; and Figure 38D shows the cyclic characteristics of discharge capacity retention for samples B3 and B4. In Figures 37A, 37B, 37C, 37D, 38A, 38B, 38C, and 38D, the horizontal axis represents cycles [times], and the vertical axis represents capacity retention [%]. Capacity retention rate refers to the ratio of the discharge capacity at each cycle in each sample to the maximum discharge capacity.

[0418] It was confirmed that the capacity decreased after repeated charge-discharge cycles on samples heated to 170°C for 15 minutes. It was also confirmed that the capacity decrease of samples A2, B2, C2, D2, and B4 of one embodiment of the present invention containing lithium hexafluorophosphate was suppressed after repeated charge-discharge cycles, compared to a comparative sample a2 that did not contain lithium hexafluorophosphate.

[0419] It is understood that, in one embodiment of the present invention, lithium bis(pentafluoroethanesulfonyl)amine (LiBETA), which has high heat resistance, primarily functions to supply lithium ions as carrier ions. Therefore, even after heat treatment, capacity reduction after repeated discharge can be suppressed. Furthermore, it is considered that, due to the presence of lithium hexafluorophosphate, a passivation film forms on the surface of the aluminum used as the positive electrode current collector during heat treatment at 170°C or charge-discharge, thus maintaining good cycle characteristics. Additionally, compared to comparative sample a2, samples E2 and F2 show a greater capacity reduction. This can be attributed to the high concentration of lithium hexafluorophosphate in samples E2 and F2, causing lithium hexafluorophosphate to decompose into LiF and PF5 during heat treatment at 170°C. PF5 decomposes the solvent, leading to capacity reduction and other battery characteristic degradation. In other words, it is understood that it is preferable to use an amount of lithium hexafluorophosphate (LiPF6) capable of forming a passivation film on the current collector surface.

[0420] It is understood that in one embodiment of the present invention, by using lithium bis(pentafluoroethanesulfonyl)amine (LiBETA) and lithium hexafluorophosphate (LiPF6) as solutes, the capacity of the battery is not easily reduced even after repeated charging and discharging, even after heating treatment.

[0421] Figure 39A shows the cycling characteristics of energy density for comparative samples a1 and a2; Figure 39B shows the cycling characteristics of energy density for samples A1 and A2; Figure 39C shows the cycling characteristics of energy density for samples B1 and B2; Figure 39D shows the cycling characteristics of energy density for samples C1 and C2; Figure 40A shows the cycling characteristics of energy density for samples D1 and D2; Figure 40B shows the cycling characteristics of energy density for samples E1 and E2; Figure 40C shows the cycling characteristics of energy density for samples F1 and F2; and Figure 40D shows the cycling characteristics of energy density for samples B3 and B4. In Figures 39A, 39B, 39C, 39D, 40A, 40B, 40C, and 40D, the horizontal axis represents cycles [times], and the vertical axis represents energy density [mWh / g]. Energy density refers to the product of discharge capacity and voltage as shown in the discharge curves of Figures 31A, 31B, 31C, 31D, 32A, 32B, 32C, 32D, 33A, 33B, 33C, 33D, 34A, 34B, 34C, and 34D.

[0422] Figure 41A shows the cyclic characteristics of energy density retention for comparative samples a1 and a2; Figure 41B shows the cyclic characteristics of energy density retention for samples A1 and A2; Figure 41C shows the cyclic characteristics of energy density retention for samples B1 and B2; Figure 41D shows the cyclic characteristics of energy density retention for samples C1 and C2; Figure 42A shows the cyclic characteristics of energy density retention for samples D1 and D2; Figure 42B shows the cyclic characteristics of energy density retention for samples E1 and E2; Figure 42C shows the cyclic characteristics of energy density retention for samples F1 and F2; and Figure 42D shows the cyclic characteristics of energy density retention for samples B3 and B4. In Figures 41A, 41B, 41C, 41D, 42A, 42B, 42C, and 42D, the horizontal axis represents cycles [times], and the vertical axis represents energy density retention [%]. Energy density retention rate refers to the ratio of the energy density at each cycle in each sample to the maximum energy density.

[0423] It was confirmed that the energy density decreased after repeated charge-discharge cycles on samples heated to 170°C for 15 minutes. It was also confirmed that the energy density decrease after repeated charge-discharge cycles on samples A2, B2, C2, D2, and B4 of one embodiment of the present invention, which contain lithium hexafluorophosphate, was suppressed compared to a comparative sample a2 that does not contain lithium hexafluorophosphate.

[0424] It is understood that, in one embodiment of the present invention, lithium bis(pentafluoroethanesulfonyl)amine (LiBETA), which has high heat resistance, primarily functions to supply lithium ions as carrier ions. Therefore, even after heat treatment, the energy density reduction after repeated discharge can be suppressed. Furthermore, it is considered that, due to the presence of lithium hexafluorophosphate, a passivation film forms on the surface of the aluminum used as the positive electrode current collector during heat treatment at 170°C or charge / discharge, thus maintaining good cycle characteristics. Additionally, compared to comparative sample a2, samples E2 and F2 show a significant decrease in energy density. This can be attributed to the high concentration of lithium hexafluorophosphate in samples E2 and F2, causing lithium hexafluorophosphate to decompose into LiF and PF5 during heat treatment at 170°C. PF5 decomposes the solvent, leading to a decrease in energy density and other degradation of battery characteristics. In other words, it is understood that it is preferable to use an amount of lithium hexafluorophosphate (LiPF6) capable of forming a passivation film on the current collector surface.

[0425] It is understood that in one embodiment of the present invention, by using lithium bis(pentafluoroethanesulfonyl)amine (LiBETA) and lithium hexafluorophosphate (LiPF6) as solutes, the energy density is not easily reduced even after repeated charging and discharging of the battery under heat treatment.

[0426] Table 3 and Figure 43A show the relationship between the concentration of lithium hexafluorophosphate (LiPF6) relative to the electrolyte and the capacity retention rate of comparative samples a2, A2, B2, C2, D2, E2, F2, and B4 after heat treatment at 170°C. In Figure 43A, the horizontal axis represents the concentration of LiPF6 [wt%], and the vertical axis represents the capacity retention rate [%]. In Figure 43A, black dots represent data for comparative samples a2, A2, B2, C2, D2, E2, and F2 using cellulose fibers as the insulator, and crosses represent data for sample B4 using polyphenylene sulfide as the insulator. The capacity retention rate refers to the value at the 300th cycle for each sample shown in Figures 37A, 37B, 37C, 37D, 38A, 38B, 38C, and 38D.

[0427] Table 4 and Figure 43B show the relationship between the concentration of lithium hexafluorophosphate (LiPF6) relative to the electrolyte and the energy density retention rate for comparative samples a2, A2, B2, C2, D2, E2, F2, and B4 after heat treatment at 170°C for 15 minutes. In Figure 43B, the horizontal axis represents the concentration of LiPF6 [wt%], and the vertical axis represents the energy density retention rate [%]. In Figure 43B, black dots represent data for comparative samples a2, A2, B2, C2, D2, E2, and F2 using cellulose fibers as the insulator, and crosses represent data for sample B4 using polyphenylene sulfide as the insulator. The energy density retention rate refers to the value at the 300th cycle for each sample shown in Figures 41A, 41B, 41C, 41D, 42A, 42B, 42C, and 42D.

[0428] Table 4 sample electrolytes Insulator Capacity retention rate [%] Energy retention rate [%] condition LiPF6 [wt%] Comparison sample a1 Electrolyte a 0.0 Cellulose fiber 89.8 87.9 Compare sample a2 84.3 81.8 Sample A1 Electrolyte A 0.18 Cellulose fiber 87.9 86.6 Sample A2 89.0 88.3 Sample B1 Electrolyte B 0.27 Cellulose fiber 88.7 87.3 Sample B2 88.9 88.0 Sample C1 Electrolyte C 0.51 Cellulose fiber 89.3 88.6 Sample C2 85.8 84.1 Sample D1 Electrolyte D 1.1 Cellulose fiber 89.4 88.8 Sample D2 84.9 82.3 Sample E1 Electrolyte E 2.0 Cellulose fiber 89.6 89.0 Sample E2 79.0 73.8 Sample F1 Electrolyte F 3.0 Cellulose fiber 88.5 87.9 Sample F2 71.4 59.9 Sample B3 Electrolyte B 0.27 polyphenylene sulfide 85.0 82.7 Sample B4 86.0 84.7

[0429] As shown in Table 4, Figures 43A and 43B, compared with the comparative sample a2 that does not use lithium hexafluorophosphate, samples A2, B2, C2, D2, and B4 of one embodiment of the present invention exhibit higher capacity retention and energy retention after repeated charge-discharge cycles. On the other hand, samples E2 and F2, which have high lithium hexafluorophosphate concentrations, exhibit lower capacity retention and energy retention.

[0430] Based on the above results, it is preferable that the electrolyte comprises ethylene carbonate (EC), propylene carbonate (PC), ethylene carbonate (VC), lithium bis(pentafluoroethanesulfonyl)amine (LiBETA), and lithium hexafluorophosphate, and the weight ratio of lithium hexafluorophosphate relative to the electrolyte is preferably 0.01 wt% or more and 1.9 wt% or less. More preferably, the weight ratio of lithium hexafluorophosphate relative to the electrolyte is 0.05 wt% or more and 1.2 wt% or less. Further preferably, the weight ratio of lithium hexafluorophosphate relative to the electrolyte is 0.1 wt% or more and 0.8 wt% or less.

[0431] It is known that by using lithium bis(pentafluoroethanesulfonyl)amine (LiBETA) and lithium hexafluorophosphate as solutes for electrolytes, a battery with high heat resistance can be obtained. Example 2

[0432] In this embodiment, an energy storage device according to an embodiment of the present invention was manufactured with reference to Embodiment 1, and a cycle life test was conducted at 45°C together with a comparative energy storage device.

[0433] <Sample Manufacturing Method> In this embodiment, the energy storage device 500 shown in FIG1A is manufactured. The manufacturing method of the sample is described below.

[0434] There are four types of samples used in one embodiment of the present invention, namely sample G1, sample G2, sample H1, and sample H2. There are two types of comparison samples, namely comparison sample a3 and comparison sample a4.

[0435] In samples G1, G2, H1, and H2, lithium bis(pentafluoroethanesulfonyl)amine lithium (LiBETA) and lithium hexafluorophosphate were used as solutes. The concentration of lithium hexafluorophosphate differed among samples G1, G2, H1, and H2. However, in comparative samples a3 and a4, lithium bis(pentafluoroethanesulfonyl)amine lithium (LiBETA) was used as a solute instead of lithium hexafluorophosphate.

[0436] Cellulose fibers were used as separators in samples G1, G2, H1, H2, comparison sample a3, and comparison sample a4.

[0437] Furthermore, after manufacturing the energy storage device 500, samples G2, H2, and comparative sample a4 were subjected to a heat treatment at 170°C for 15 minutes. This heat treatment is assumed to be performed together with fluororubber as described in Embodiment 2. Samples G1, H1, and comparative sample a3 were not subjected to a heat treatment.

[0438] Table 5 shows the electrolyte, separator, and heat treatment conditions for each sample.

[0439] Table 5 sample electrolytes Insulator Heat treatment condition LiPF6 [wt%] Comparison sample a3 Electrolyte a 0.0 Cellulose fiber - Comparison sample a4 170°C for 15 minutes Sample G1 Electrolyte G 0.26 Cellulose fiber - Sample G2 170°C for 15 minutes Sample H1 Electrolyte H 0.51 Cellulose fiber - Sample H2 170°C for 15 minutes

[0440] The manufacturing method of the electrolyte is explained.

[0441] Electrolyte a was used as the electrolyte for comparative samples a3 and a4. For details regarding electrolyte a, please refer to Example 1 above; therefore, its description is omitted.

[0442] Electrolyte G, used in samples G1 and G2, is described below. Electrolyte G was prepared by mixing ethylene carbonate (VC) with a 1:1 volume ratio of ethylene carbonate (EC) and propylene carbonate (PC), dissolving lithium bis(pentafluoroethanesulfonyl)amine (LiBETA) and lithium hexafluorophosphate. The dissolved amount of ethylene carbonate (VC) relative to the weight of electrolyte G was 1 wt%. The dissolved amount of lithium bis(pentafluoroethanesulfonyl)amine (LiBETA) relative to the molar concentration of electrolyte G was 1 mol / L. The dissolved amount of lithium hexafluorophosphate relative to the weight of electrolyte G was 0.26 wt%.

[0443] Electrolyte H, used for samples H1 and H2, is described below. Electrolyte H was prepared by mixing ethylene carbonate (VC) with a 1:1 volume ratio of ethylene carbonate (EC) and propylene carbonate (PC), dissolving lithium bis(pentafluoroethanesulfonyl)amine (LiBETA) and lithium hexafluorophosphate. The dissolved amount of ethylene carbonate (VC) relative to the weight of electrolyte H was 1 wt%. The dissolved amount of lithium bis(pentafluoroethanesulfonyl)amine (LiBETA) relative to the molar concentration of electrolyte H was 1 mol / L. The dissolved amount of lithium hexafluorophosphate relative to the weight of electrolyte H was 0.51 wt%.

[0444] As a mixture of ethylene carbonate (EC) and propylene carbonate (PC) in a 1:1 volume ratio, lithium-ion battery grade (product number: LBG-00798) manufactured by KISHIDA Chemical Co., Ltd., Japan was used. As ethylene carbonate (VC), lithium-ion battery grade (product number: LBG-84923) manufactured by KISHIDA Chemical Co., Ltd., Japan was used. As lithium bis(pentafluoroethanesulfonyl)amine (LiBETA), a product manufactured by IoLiTec (Ionic Liquids Technologies Inc.) (product number: KI-0016-HP) was used. As lithium hexafluorophosphate, lithium-ion battery grade (product number: LBG-45860) manufactured by KISHIDA Chemical Co., Ltd., Japan was used.

[0445] Next, the negative electrode is manufactured. The method for manufacturing the negative electrode can be referred to in Example 1 above, so its description is omitted.

[0446] Next, the positive electrode is manufactured. The manufacturing method of the positive electrode can be referred to in Example 1 above, so its description is omitted.

[0447] Tables 6 and 7 show the average values ​​of the active material loading, thickness, and density of the formed positive and negative electrode active material layers, respectively.

[0448] Table 6 sample positive electrode Load capacity [mg / cm²] thickness [mm] density [g / cm 3] Comparison sample a3 21.2 67 3.16 Comparison sample a4 21.2 66 3.21 Sample G1 21.3 66 3.23 Sample G2 21.3 66 3.23 Sample H1 21.5 67 3.20 Sample H2 21.5 66 3.26

[0449] Table 7 sample negative electrode Load capacity [mg / cm²] thickness [mm] density [g / cm 3] Comparison sample a3 9.7 106 0.91 Comparison sample a4 9.7 99 0.98 Sample G1 9.9 101 0.98 Sample G2 9.9 105 0.95 Sample H1 10.3 106 0.97 Sample H2 10.3 110 0.93

[0450] Next, the manufacturing method of the energy storage device will be described. In each sample manufactured in this embodiment, a positive electrode having a positive active material layer on one surface of the positive current collector and a negative electrode having a negative active material layer on one surface of the negative current collector are used. That is, each sample in this embodiment includes a positive active material layer and a negative active material layer.

[0451] First, disconnect the positive electrode, negative electrode, and first insulator. The dimensions of the positive electrode are 20.49 cm², the dimensions of the negative electrode are 23.84 cm², and the dimensions of the first insulator are 24.75 cm².

[0452] Cellulose fibers were used as separators in samples G1, G2, H1, H2, comparative sample a3, and comparative sample a4. Specifically, solvent-spun regenerated cellulose fibers (product number: TF40) manufactured by Kotaka Paper Industries, Ltd. of Japan, with a thickness of 30 µm were used.

[0453] Next, the positive and negative active materials on the tab area are stripped to expose the current collector.

[0454] Next, the positive and negative electrodes are stacked with the first separator sandwiched between them. At this point, the positive and negative electrodes are stacked with the positive active material layer and the negative active material layer facing each other.

[0455] Next, ultrasonic welding is used to connect the leads to the positive and negative terminals.

[0456] Next, a second isolator is used to encapsulate the stacked electrodes and the areas where the leads are joined. This prevents the aluminum contained in the outer packaging from contacting the electrodes due to the melting of the resin layer within the outer packaging during subsequent heat treatment. The second isolator has a dimension of 104 cm².

[0457] Next, two of the four sides of the outer packaging are joined together by heating.

[0458] As the outer packaging, a thin film consisting of a resin layer covering both surfaces of aluminum is used.

[0459] Next, the sealing layer on the lead wire is arranged so that it overlaps with the sealing layer of the outer packaging, and then joined by heating. At this time, the edges other than the edge used for injecting electrolyte are joined.

[0460] Next, a heat treatment is performed to dry the outer packaging and the positive electrode, separator, and negative electrode enclosed by the outer packaging. The heating conditions are: reduced pressure atmosphere (gauge pressure -100 kPa), 80°C, 10 hours.

[0461] Next, under an argon atmosphere, approximately 600 µL of electrolyte was injected from the unsealed side. Electrolyte a was injected into comparative samples a3 and a4. Electrolyte G was injected into samples G1 and G2. Electrolyte H was injected into samples H1 and H2.

[0462] Then, one side of the outer packaging is sealed by heating under reduced pressure (gauge pressure -100 kPa). This process manufactures a thin energy storage device.

[0463] Next, samples G2, H2, and comparative sample a4 were subjected to heat treatment. Assuming they were formed with fluororubber as described in Embodiment 2, the heating conditions were atmospheric pressure, 170°C, and 15 minutes. Specifically, after heating the thermostat to approximately 170°C, each sample was placed in the thermostat and removed after 15 minutes. No expansion of the outer packaging of any sample was observed during this heat treatment.

[0464] Samples G1, G2, H1, H2, comparison sample a3, and comparison sample a4 are manufactured using the above process.

[0465] Measurement of charge and discharge characteristics Next, the charge-discharge characteristics of each sample in this embodiment at 45°C were evaluated. This measurement was performed using a charge-discharge measuring instrument (manufactured by Toyo Systems, Inc., Japan). Constant current-constant voltage charging was performed with an upper limit of 4.3V, and constant voltage discharging was performed with a lower limit of 2.5V. Charge and discharge were performed at a rate of 0.1C, with a 10-minute rest period after charging. The charge-discharge cycle was repeated twice.

[0466] Here, the rate is calculated based on the capacity of 170 mAh / g obtained when the upper limit charging voltage of LiCoO2, the positive electrode active material, is 4.3V.

[0467] Figures 44A, 44B, 44C, 44D, 45A, and 45B show the charging and discharging curves of comparative samples a3, a4, G1, G2, H1, and H2, respectively. In Figures 44A, 44B, 44C, 44D, 45A, and 45B, the horizontal axis represents capacity [mAh / g], and the vertical axis represents voltage [V]. Furthermore, the charging and discharging characteristics of each sample at the 1st and 300th cycles are shown. Capacity is shown as the capacity per weight of the positive electrode active material.

[0468] In comparative samples a3 and a4, which do not contain lithium hexafluorophosphate, the capacity is almost zero at 300 cycles.

[0469] Figure 46A shows the cycle characteristics of discharge capacity for comparative samples a3 and a4, Figure 46B shows the cycle characteristics of discharge capacity for samples G1 and G2, and Figure 46C shows the cycle characteristics of discharge capacity for samples H1 and H2. In Figures 46A, 46B, and 46C, the horizontal axis represents cycles [times], and the vertical axis represents capacity [mAh / g].

[0470] Figure 47A shows the cycle characteristics of discharge capacity retention for comparative samples a3 and a4; Figure 47B shows the cycle characteristics of discharge capacity retention for samples G1 and G2; and Figure 47C shows the cycle characteristics of discharge capacity retention for samples H1 and H2. In Figures 47A, 47B, and 47C, the horizontal axis represents cycles [times], and the vertical axis represents capacity retention [%]. Capacity retention refers to the ratio of discharge capacity at each cycle to the maximum discharge capacity for each sample.

[0471] In comparative samples a3 and a4, which do not contain lithium hexafluorophosphate, the capacity is almost zero after approximately 150 cycles. It can be assumed that lithium bis(pentafluoroethanesulfonyl)amine (LiBETA) corrodes the aluminum used as the positive current collector through repeated charge-discharge cycles at 45°C. Compared to comparative samples a3 and a4, samples G1, G2, H1, and H2 of one embodiment of the present invention show very little capacity reduction even after repeated charge-discharge cycles. In particular, sample H2 exhibits high capacity retention even after heat treatment at 170°C for 15 minutes. It can be assumed that the passivation film formed by lithium hexafluorophosphate on the aluminum surface inhibits aluminum corrosion even after heat treatment.

[0472] Figure 48A shows the cycling characteristics of energy density for comparative samples a3 and a4; Figure 48B shows the cycling characteristics of energy density for samples G1 and G2; and Figure 48C shows the cycling characteristics of energy density for samples H1 and H2. In Figures 48A, 48B, and 48C, the horizontal axis represents cycles [times], and the vertical axis represents energy density [mWh / g]. Energy density refers to the product of discharge capacity and voltage as shown in the discharge curves of Figures 44A, 44B, 44C, 44D, 45A, and 45B.

[0473] Figure 49A shows the cyclic characteristics of energy density retention for comparative samples a3 and a4; Figure 49B shows the cyclic characteristics of energy density retention for samples G1 and G2; and Figure 49C shows the cyclic characteristics of energy density retention for samples H1 and H2. In Figures 49A, 49B, and 49C, the horizontal axis represents cycles [times], and the vertical axis represents energy density retention [%]. Energy density retention refers to the ratio of energy density at each cycle in each sample to the maximum energy density.

[0474] In comparative samples a3 and a4, which do not contain lithium hexafluorophosphate, the energy density is almost zero after approximately 150 cycles. Compared to comparative samples a3 and a4, samples G1, G2, H1, and H2 of one embodiment of the present invention exhibit very little capacity reduction after repeated charge-discharge cycles. In particular, sample H2 maintains a high energy density retention even after heat treatment at 170°C for 15 minutes.

[0475] Table 5 and Figure 50A show the relationship between the lithium hexafluorophosphate (LiPF6) concentration relative to the electrolyte and the capacity retention for comparative samples a3, G2, and H2 after heat treatment at 170°C. In Figure 50A, the horizontal axis represents the LiPF6 concentration [wt%], and the vertical axis represents the capacity retention [%]. The capacity retention is the value at the 300th cycle for each sample shown in Figures 47A, 47B, and 47C.

[0476] Table 8 and Figure 50B show the relationship between the lithium hexafluorophosphate (LiPF6) concentration relative to the electrolyte and the energy density retention rate for comparative samples a4, G2, and H2 after heat treatment at 170°C for 15 minutes. In Figure 50B, the horizontal axis represents the LiPF6 concentration [wt%], and the vertical axis represents the energy density retention rate [%]. The energy density retention rate refers to the value at the 300th cycle for each sample shown in Figures 49A, 49B, and 49C.

[0477] Table 8 sample electrolytes Insulator Capacity retention rate [%] Energy retention rate [%] condition LiPF6 [wt%] Comparison sample a3 Electrolyte a 0.0 Cellulose fiber 0.105 0.081 Comparison sample a4 0.051 0.041 Sample G1 Electrolyte G 0.26 Cellulose fiber 87.0 85.7 Sample G2 76.0 67.3 Sample H1 Electrolyte H 0.51 Cellulose fiber 88.1 87.5 Sample H2 87.6 85.2

[0478] As shown in Table 8, Figures 50A and 50B, compared with the comparative sample a4 which does not use lithium hexafluorophosphate, samples G2 and H2 of one embodiment of the present invention have high capacity retention and energy retention after repeated charge and discharge cycles.

[0479] Based on the above results, it is preferable that the electrolyte comprises ethylene carbonate (EC), propylene carbonate (PC), ethylene carbonate (VC), lithium bis(pentafluoroethanesulfonyl)amine (LiBETA), and lithium hexafluorophosphate, and the weight ratio of lithium hexafluorophosphate relative to the electrolyte is preferably 0.01 wt% or more and 1.9 wt% or less. More preferably, the weight ratio of lithium hexafluorophosphate relative to the electrolyte is 0.05 wt% or more and 1.2 wt% or less. Further preferably, the weight ratio of lithium hexafluorophosphate relative to the electrolyte is 0.1 wt% or more and 0.8 wt% or less.

[0480] It is known that by using lithium bis(pentafluoroethanesulfonyl)amine (LiBETA) and lithium hexafluorophosphate as solutes for electrolytes, a high-heat-resistant battery with good charge-discharge characteristics can be obtained even in a high-temperature environment of 45°C. Example 3

[0481] In this embodiment, the results confirming the reaction between aluminum, used as the positive electrode current collector, and the electrolyte are explained.

[0482] <Sample Manufacturing Method> In this embodiment, a battery according to one embodiment of the present invention was manufactured. After undergoing a heat treatment at 170°C for 15 minutes, the positive electrode was removed from the battery, and the composition of the aluminum surface of the positive electrode was analyzed using XPS. The battery that underwent the heat treatment at 170°C for 15 minutes is battery 1, and the positive electrode removed from battery 1 is positive electrode 1. Furthermore, as a comparative example, XPS analysis was also performed on a sample (comparative positive electrode 1) that was not assembled into a battery after manufacturing the positive electrode.

[0483] The manufacturing method of the positive electrode is described. The same manufacturing method is used for both the comparative positive electrode 1 and the storage battery 1 (positive electrode 1).

[0484] LiCoO2, with a specific surface area of ​​0.21 m² / g and an average particle size of 10 µm, is used as the positive electrode active material; polyvinylidene fluoride (PVDF) is used as the binder; and acetylene black is used as the conductive additive. The mixing ratio of LiCoO2, PVDF, and acetylene black is LiCoO2:acetylene black:PVDF = 95:3:2 (wt%).

[0485] First, acetylene black and PVDF are mixed and kneaded using a mixer to obtain a fifth mixture.

[0486] Next, an active substance was added to the fifth mixture to obtain the sixth mixture.

[0487] Next, N-methyl-2-pyrrolidone (NMP) as a solvent is added to the fourth mixture, and the mixture is then kneaded using a mixer. A slurry is produced through the above process.

[0488] Next, the mixture is mixed using a large mixing machine.

[0489] Next, the slurry was coated onto the positive current collector using a continuous coating machine. An aluminum current collector (20µm thick) was used as the positive current collector. The coating speed was 0.2m / min.

[0490] Next, the solvent of the slurry coated on the positive current collector is vaporized using a drying oven. The solvent is vaporized by treating at 70°C for 7.5 minutes in an atmospheric atmosphere, followed by treating at 90°C for 7.5 minutes.

[0491] Next, the material was heated at 170°C for 10 hours under reduced pressure (gauge pressure -100 kPa). Then, the positive electrode active material layer was pressed using a rolling method to achieve compaction.

[0492] Through the above process, a layer of positive electrode active material is formed on one surface of the positive current collector.

[0493] The sample obtained through this process is the comparative positive electrode 1.

[0494] Furthermore, the manufacturing method of battery 1 will be explained.

[0495] The manufacturing method of the negative electrode is explained.

[0496] Spherical natural graphite (manufactured by Japan Black Lead Industry Co., Ltd., CGB-15) with a specific surface area of ​​6.3 m² / g and an average particle size of 15 µm was used as the negative electrode active material. Sodium carboxymethyl cellulose (CMC-Na) and SBR were used as binders. The degree of polymerization of the CMC-Na used was 600 or higher and 800 or lower, and the viscosity of the 1 wt% aqueous solution was in the range of 300 mPa·s or higher and 500 mPa·s or lower. The mixing ratio of graphite, CMC-Na, and SBR was graphite:CMC-Na:SBR = 97:1.5:1.5 (wt%).

[0497] First, CMC-Na powder and active substances are mixed and kneaded using a mixer to obtain the seventh mixture.

[0498] Next, a small amount of water is added to the seventh mixture, and a dry-thickening process is performed to obtain the eighth mixture. Here, dry-thickening refers to high-viscosity mixing.

[0499] Next, water is added and the mixture is kneaded using a mixer to obtain the ninth mixture.

[0500] Next, 50 wt% aqueous dispersion of SBR was added and the mixture was kneaded using a mixer. Then, degassing was performed under reduced pressure to obtain a slurry.

[0501] Next, the slurry was coated onto the negative electrode current collector using a continuous coating machine. A rolled copper foil with a thickness of 18µm was used as the negative electrode current collector. The coating speed was 0.75m / min.

[0502] Next, the solvent of the slurry coated on the negative electrode current collector was vaporized using a drying oven. First, it was treated at 50°C for 120 seconds under atmospheric conditions, then at 80°C for 120 seconds. Following this, it was treated at 100°C for 10 hours under reduced pressure (gauge pressure -100 kPa).

[0503] The negative electrode is manufactured by forming a layer of negative active material on one surface of the negative current collector through the above process.

[0504] The manufacturing method of the electrolyte of battery 1 is described.

[0505] Electrolyte B2 was prepared by mixing ethylene carbonate (EC) and propylene carbonate (PC) in a 1:1 volume ratio with ethylene carbonate (VC), dissolving lithium bis(pentafluoroethanesulfonyl)amine (LiBETA) and lithium hexafluorophosphate. The dissolved amount of ethylene carbonate (VC) relative to electrolyte A was 1 wt%. The dissolved amount of lithium bis(pentafluoroethanesulfonyl)amine (LiBETA) relative to the molar concentration of electrolyte B2 was 1 mol / L. The dissolved amount of lithium hexafluorophosphate relative to the weight of electrolyte B2 was 0.27 wt%. The method for preparing electrolyte B2 in this example is the same as that for electrolyte B shown in Example 1 above.

[0506] Next, the positive electrode, negative electrode, and first insulator are disconnected. The dimensions of the positive electrode are 20.49 cm², the dimensions of the negative electrode are 23.84 cm², and the dimensions of the first insulator are 24.75 cm².

[0507] Cellulose fibers are used as the separator. Specifically, solvent-spun regenerated cellulose fibers (product number: TF40) manufactured by Kōkō Paper Industries, Ltd. of Japan, with a thickness of 30µm are used.

[0508] Next, the positive and negative active materials on the tab area are stripped to expose the current collector.

[0509] Next, the positive and negative electrodes are stacked with the separator sandwiched between them. At this point, the positive and negative electrodes are stacked with the positive active material layer and the negative active material layer facing each other.

[0510] Next, ultrasonic welding is used to connect the leads to the positive and negative terminals.

[0511] Next, an insulator is used to encapsulate the stacked electrodes and the areas where the leads are joined. This prevents the aluminum contained in the outer packaging from contacting the electrodes due to the melting of the resin layer within the outer packaging during subsequent heat treatment. The second insulator has a dimension of 104 cm².

[0512] Next, two of the four sides of the outer packaging are joined together by heating.

[0513] As the outer packaging, a thin film consisting of a resin layer covering both surfaces of aluminum is used.

[0514] Next, it is arranged such that the sealing layer provided on the lead wire overlaps with the sealing layer of the outer package, and they are joined by heating. At this time, joining is performed on the sides other than the side used for injecting the electrolyte.

[0515] Next, a heat treatment for drying the outer package and the positive electrode, separator, and negative electrode wrapped by the outer package is performed. The heating conditions are a reduced-pressure atmosphere (gauge pressure of -100 kPa), 80 °C, and 10 hours.

[0516] Next, approximately 600 μL of electrolyte B2 is injected from the unsealed side in an argon atmosphere.

[0517] Then, one side of the outer package is sealed by heating in a reduced-pressure atmosphere (gauge pressure of -100 kPa).

[0518] The storage battery 1 is manufactured by the above process.

[0519] Next, a heat treatment is performed on the storage battery 1. Assuming it is formed together with fluororubber as described in Embodiment 2, the heating conditions are an atmospheric pressure atmosphere, 170 °C, and 15 minutes. Specifically, after raising the temperature of the constant temperature bath to approximately 170 °C, each sample is placed in the constant temperature bath, and the storage battery 1 is taken out after 15 minutes.

[0520] Next, the storage battery 1 is disassembled inside a glove box in a nitrogen atmosphere, and the positive electrode 1 of the positive electrode of the storage battery 1 is taken out. The positive electrode 1 is washed with dimethyl carbonate (DMC: DimethylCarbonate) and dried.

[0521] The positive electrode 1 is manufactured by the above process.

[0522] <X-ray Photoelectron Spectroscopy> Next, the comparative positive electrode 1 and the positive electrode 1 are measured using X-ray photoelectron spectroscopy (XPS: X-ray Photoelectron Spectroscopy). X-rays are irradiated onto the surface of the aluminum where the positive electrode active material is not coated. FIG. 51 shows the position where the XPS measurement is performed. In FIG. 51, the arrow indicates the irradiation direction of the X-rays.

[0523] In XPS measurements, a Quantera SXM manufactured by Physical Electronics was used. Monochromatic Al Kα line (1486.6 eV) was used as the X-ray source. The detection area was 100 µm Φ. The extraction angle was 45°. The detection depth was estimated to be approximately 4 nm to 5 nm.

[0524] Figures 52A, 52B, 52C, 53A, 53B, 53C, 54A, 54B, 54C, 55A, and 55B show the spectra of Al2p, C1s, O1s, S2p, Li1s, F1s, P2s, N1s, Si2s, Na1s, and Ca2p obtained by XPS measurement, respectively. In Figures 52A, 52B, 52C, 53A, 53B, 53C, 54A, 54B, 54C, 55A, and 55B, the horizontal axis represents the bond energy [eV], and the vertical axis represents the photoelectron intensity (in arbitrary units).

[0525] Al, O, C, and trace amounts of F and Si were detected in the untreated cathode 1. Al, F, O, Li, C, and trace amounts of P, N, Na, and Ca were detected in the treated cathode 1.

[0526] Table 9 shows the quantitative values ​​of each element obtained from XPS spectra. The quantitative accuracy is approximately ±1 atomic%. The detection limit is approximately 1 atomic%, but there are slight differences for individual elements.

[0527] Table 9 Quantitative value [atomic%] Compare positive electrode 1 Positive electrode 1 Al 26.8 17.9 C 25.5 15.7 O 40.4 9.3 S Detection limit below Detection limit below Li Detection limit below 5.3 F 3.3 48.3 P Detection limit below 1.9 N Detection limit below 0.5 Si 4.0 Detection limit below Na Detection limit below 0.6 Ca Detection limit below 0.5

[0528] Compared to the comparative cathode 1, cathode 1 has less O and more F. It can be seen that the Al in the comparative cathode 1 is in an oxidized and metallic state, while the Al in the cathode 1 is in a fluorinated and metallic state. Furthermore, the Li detected in cathode 1 is mainly in the LiPFx and LiF states. Additionally, the Si detected in cathode 1 can be considered to be mainly in the oxidized state. The C can be considered to be mainly in the CC and CHC states.

[0529] As can be seen from the above results, an aluminum surface heated together with the electrolyte of one embodiment of the present invention forms a coating containing aluminum fluoride. In other words, it can be seen that when a secondary battery containing lithium hexafluorophosphate as the electrolyte undergoes a heating process during manufacturing, a coating is formed on the positive electrode current collector, and this coating helps to suppress degradation during charge-discharge cycles. Example 4

[0530] In this embodiment, the results confirming the heat resistance of lithium bis(pentafluoroethanesulfonyl)amine (LiBETA) are explained.

[0531] <Sample Manufacturing Method> In this embodiment, there are three types of samples used, namely sample 1, sample 2 and sample 3.

[0532] Sample 1 is described below. Lithium bis(pentafluoroethanesulfonyl)amine (LiBETA) was used as Sample 1. As lithium bis(pentafluoroethanesulfonyl)amine (LiBETA), the product manufactured by IoLiTec (Ionic Liquids Technologies Inc.) (product number: KI-0016-HP) was used, and the determination was performed in powder form.

[0533] Sample 2 is described below. A mixture of ethylene carbonate (EC) and propylene carbonate (PC) in a volume ratio of 1:1 was used as Sample 2. As the mixture of ethylene carbonate (EC) and propylene carbonate (PC) in a volume ratio of 1:1, lithium battery grade (product number: LBG-00798) manufactured by KISHIDA Chemical Co., Ltd. of Japan was used.

[0534] Sample 3 is described below. Sample 3 was prepared by dissolving lithium bis(pentafluoroethanesulfonyl)amine (LiBETA) in a mixture of ethylene carbonate (EC) and propylene carbonate (PC) at a volume ratio of 1:1. The amount of lithium bis(pentafluoroethanesulfonyl)amine (LiBETA) dissolved relative to the molar concentration of Sample 3 was 1 mol / L. Sample 3 was prepared using the above process. The mixture of ethylene carbonate (EC) and propylene carbonate (PC) at a volume ratio of 1:1 was a lithium battery grade product (product number: LBG-00798) manufactured by KISHIDA Chemical Co., Ltd., Japan. The lithium bis(pentafluoroethanesulfonyl)amine (LiBETA) was a product (product number: KI-0016-HP) manufactured by IoLiTec (Ionic Liquids Technologies Inc.).

[0535] <Thermogravimetric Analysis - Differential Thermal Analysis> Next, thermogravimetry-differential thermal analysis (TG-DTA) was performed. In the TG-DTA determination, a Thermo Mass Photograph manufactured by Rigaku Corporation was used, and the measurement was carried out under a helium flow (flow rate: 300 ml / min) at a heating rate of 10 °C / min from room temperature to 600 °C.

[0536] Figures 56A, 56B, and 57 show the TG-DTA measurement results for Sample 1, Sample 2, and Sample 3, respectively. In Figures 56A, 56B, and 57, the horizontal axis represents temperature [°C], the left vertical axis represents the rate of weight change ΔW [%], and the right vertical axis represents heat flow [µV]. The rate of weight change ΔW refers to the rate of change of weight during heating relative to the initial (before heating) weight; a negative value indicates a decrease in weight due to heating.

[0537] The weight of Sample 1 began to decrease around 330°C, reaching approximately -95% of its initial weight around 420°C. Furthermore, endothermic reactions were observed around 327.4°C and 416.7°C. The endothermic reaction around 327.4°C can be attributed to lithium bis(pentafluoroethanesulfonyl)amine (LiBETA). Therefore, lithium bis(pentafluoroethanesulfonyl)amine (LiBETA) is considered stable from room temperature to around 300°C.

[0538] The weight of Sample 2 began to decrease around 150°C, reaching approximately -96% of its initial weight around 235°C. Furthermore, an endothermic reaction was observed around 232.5°C. This endothermic reaction around 232.5°C can be attributed to the evaporation of ethylene carbonate (EC) and propylene carbonate (PC).

[0539] The weight of Sample 3 begins to decrease around 150°C, reaching approximately -78% of its initial weight around 300°C, and approximately -100% around 450°C. The weight change from room temperature to around 300°C is largely consistent with the trend of Sample 2, suggesting that the change within this temperature range is almost entirely due to ethylene carbonate (EC) and propylene carbonate (PC). Therefore, it can be concluded that lithium bis(pentafluoroethanesulfonyl)amine (LiBETA) exhibits thermal stability even in solvents below 300°C.

[0540] 50: Membrane 51: Membrane 52: Membrane 53: Embossing roller 54: Roller 55: Embossing roller 56: Embossing roller 57: Embossing roller 58: Embossing roller 60: Direction of movement 115: Sealing layer 118: Joint 119: Inlet Port 200: Secondary battery 203: Isolation 203a: Area 203b: Area 207: Outer packaging 211: Positive electrode 211a: Positive electrode 215: Negative electrode 215a: Negative electrode 220: Sealing layer 221: Positive lead 225: Negative lead 230: Electrode assembly 231: Electrode Assembly 250: Secondary battery 281: Electrode Region 282: Electrode region 500: Energy storage device 501: Positive Current Collector 502: Positive electrode active material layer 503: Positive electrode 504: Negative current collector 505: Negative electrode active material layer 506: Negative electrode 507: Isolation 508: Electrolyte 509: Outer Packaging 510: Positive lead 511: Negative lead 512: Joint 513: Bending section 514: Joint 518: Joint 520: Isolation Body 521: Joint 529: Outer Packaging 700: Portable Information Terminal 701: Outer shell 702: Display Panel 703: Watch strap buckle 705A: Watch Strap 705B: Watch Strap 711: Operation Button 712: Operation Button 730: Portable Information Terminal 731: Outer shell 732: Liquid Leakage Detection Circuit 733: Power Supply 734: Ammeter 735A: Watch Strap 736: Electrolyte 739: Functional Circuit 750: Energy storage device 751: Positive lead 752: Negative lead 753: Outer Packaging 760: Energy storage device 761:Terminal 762:Terminal 771: Wiring 772: Wiring 7100: Portable display device 7101: Outer casing 7102: Display Unit 7103: Operation Button 7104: Energy storage device 7200: Portable Information Terminal 7201: Outer casing 7202: Display Unit 7203: Watch Strap 7204: Buckle 7205: Operation Button 7206: Input / output terminals 7207: Illustration 7250: Activity meter 7251: Outer casing 7300: Display device 7304: Display Unit 7350: Display device 7351: Eyeglass lenses 7351A: Image 7351B: Image 7352: Eyeglass frames 7355:End 7360: Energy Storage Device 7361: Positive lead 7362: Negative lead 7400: Mobile Phone 7401: Outer casing 7402: Display Unit 7403: Operation button 7404: External connection port 7405: Speaker 7406: Microphone 7407: Energy Storage Device 8000: Display device 8001: Casing 8002: Display Unit 8003: Speaker Section 8004: Energy Storage Device 8021: Charging device 8022: Cable 8024: Energy Storage Device 8100: Lighting equipment 8101: Outer casing 8102: Light source 8103: Energy storage device 8104: Ceiling 8105: Sidewall 8106: Floor 8107: Window 8200: Indoor unit 8201: Outer casing 8202: Air vent 8203: Energy storage device 8204: Outdoor unit 8300: Electric Refrigeration and Freezing Box 8301: Outer casing 8302: Refrigerator door 8303: Freezer door 8304: Energy storage device 8400: Car 8401: Headlights 8500: Car 9600: Tablet Terminal 9625: Switch 9626: Switch 9627: Power switch 9628: Operation switch 9629: Fasteners 9630: Outer casing 9631: Display Unit 9631a: Display Unit 9631b: Display Unit 9632a: Area 9632b: Area 9633: Solar Cell 9634: Charge / Discharge Control Circuit 9635: Storage element 9636: DC-DC converter 9637: Converter 9638: Operation Key 9639: Button 9640: Movable Part

[0541] none

Claims

1. A method for manufacturing an electronic device including a power storage device and a watchband, the method comprising: A layered structure is formed, comprising a positive electrode, a negative electrode, and a first separator located between the positive electrode and the negative electrode; The stacked structure is wrapped in an outer packaging body; an electrolyte is injected into the stacked structure wrapped in the outer packaging body; the outer packaging body is sealed to form the energy storage device; the energy storage device is placed in a mold corresponding to the shape of the watch strap, and the material of the watch strap is poured into the mold; and the energy storage device and the material are heat-treated, wherein the electrolyte comprises propylene carbonate, ethylene carbonate, ethylene carbonate, lithium hexafluorophosphate and a lithium salt represented by the following general formula (G1), where R1 and R2 independently represent fluorine, or a linear fluoroalkyl group having 2 to 10 carbon atoms, a branched fluoroalkyl group having 2 to 10 carbon atoms, or a cyclic fluoroalkyl group having 3 to 10 carbon atoms, the heat treatment is carried out at a temperature of 110°C or higher and 190°C or lower, and the concentration weight ratio of the lithium hexafluorophosphate relative to the electrolyte is 0.01 wt% or higher and 1.9 wt% or lower.

2. A method for manufacturing an electronic device including a power storage device and a watchband, the method comprising: A layered structure is formed, comprising a positive electrode, a negative electrode, and a first separator located between the positive electrode and the negative electrode; The stacked structure is enclosed by a second insulator; The stacked structure, which is wrapped by the second isolator, is encased in an outer packaging body; an electrolyte is injected into the stacked structure encased in the outer packaging body; the outer packaging body is sealed to form the energy storage device; the energy storage device is placed in a mold corresponding to the shape of the watch strap, and the material of the watch strap is poured into the mold; and the energy storage device and the material are heat-treated, wherein the electrolyte comprises propylene carbonate, ethylene carbonate, ethylene carbonate, lithium hexafluorophosphate, and a lithium salt represented by the following general formula (G1), where R1 and R2 independently represent fluorine, or a linear fluoroalkyl group having 2 to 10 carbon atoms, a branched fluoroalkyl group having 2 to 10 carbon atoms, or a cyclic fluoroalkyl group having 3 to 10 carbon atoms, the heat treatment is performed at a temperature of 110°C or higher and 190°C or lower, and the concentration weight ratio of the lithium hexafluorophosphate relative to the electrolyte is 0.01 wt% or higher and 1.9 wt% or lower.

3. A method of manufacturing an electronic device as described in claim 1 or 2, wherein the first insulator comprises one or both of polyphenylene sulfide and cellulose fibers.

4. A method of manufacturing an electronic device as described in claim 1 or 2, wherein the material comprises rubber.

5. The method of manufacturing an electronic device as described in claim 4, wherein the material comprises fluororubber or silicone rubber.

6. A method of manufacturing an electronic device as described in claim 1 or 2, wherein the heating treatment is performed before the energy storage device is energized.

7. An energy storage device, comprising: The structure includes the positive electrode active material layer and the positive electrode current collector; the negative electrode; and the first insulator. The electrolyte; the first separator is located between the positive electrode and the negative electrode, the electrolyte comprising propylene carbonate, ethylene carbonate, ethylene carbonate, lithium hexafluorophosphate and a lithium salt represented by the following general formula (G1), where R1 and R2 independently represent fluorine, or a linear fluoroalkyl group having 2 to 10 carbon atoms, a branched fluoroalkyl group having 2 to 10 carbon atoms, or a cyclic fluoroalkyl group having 3 to 10 carbon atoms, and the lithium hexafluorophosphate has a concentration weight ratio of 0.01 wt% or more and 1.9 wt% or less relative to the electrolyte.

8. An energy storage device, comprising: Including the positive electrode active material layer and the positive electrode current collector; Negative electrode; First isolator; Second separator; Electrolyte; And the outer packaging; The first isolator is located between the positive electrode and the negative electrode, and the second isolator is located between the outer packaging and one of the positive electrode and the negative electrode. The second isolator includes a region that overlaps with the tab region included in one of the positive electrode and the negative electrode. The electrolyte contains propylene carbonate, ethylene carbonate, ethylene carbonate, lithium hexafluorophosphate, and a lithium salt represented by the following general formula (G1), where R1 and R2 independently represent fluorine, or a linear fluoroalkyl group having 2 to 10 carbon atoms, a branched fluoroalkyl group having 2 to 10 carbon atoms, or a cyclic fluoroalkyl group having 3 to 10 carbon atoms. The lithium hexafluorophosphate has a concentration weight ratio of 0.01 wt% or more and 1.9 wt% or less relative to the electrolyte.

9. An energy storage device, comprising: Including the first positive electrode of the first positive current collector; The second positive electrode includes a positive active material layer and a second positive current collector; Includes the first negative electrode of the first negative current collector; the second negative electrode of the second negative current collector, including the negative electrode active material layer and the second negative current collector; and a first insulator; The first positive current collector and the second positive current collector are in contact with each other in a manner opposite to each other, the first negative current collector and the second negative current collector are in contact with each other in a manner opposite to each other, the first separator is located between the positive active material layer and the negative active material layer, the electrolyte comprises propylene carbonate, ethylene carbonate, ethylene carbonate, lithium hexafluorophosphate and a lithium salt represented by the following general formula (G1), where R1 and R2 independently represent fluorine, or a linear fluoroalkyl group having 2 to 10 carbon atoms, a branched fluoroalkyl group having 2 to 10 carbon atoms, or a cyclic fluoroalkyl group having 3 to 10 carbon atoms, and the concentration weight ratio of the lithium hexafluorophosphate relative to the electrolyte is 0.01 wt% or more and 1.9 wt% or less.

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