Secondary battery

Abstract

To provide a secondary battery in which internal short-circuiting due to dendrite is suppressed.SOLUTION: A secondary battery includes a negative electrode active material layer, a separator, a carbon sheet disposed between the negative electrode active material layer and the separator, a dendrite between the negative electrode active material layer and the carbon sheet, and a positive electrode active material layer. The negative electrode active material layer includes a negative electrode active material. The negative electrode active material includes one or more selected from graphite and silicon. The thickness of the carbon sheet is 25 nm or more and 50 μm or less. The dendrite includes a part along a surface of the carbon sheet. The carbon sheet preferably has a carbon nanotube.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a secondary battery. However, the present invention is not limited to the above fields, and may also relate to semiconductor devices, display devices, light-emitting devices, power storage devices, lighting devices, electronic devices, vehicles, and manufacturing methods thereof. For example, the secondary battery of the present invention can be applied as a necessary power source in semiconductor devices, display devices, light-emitting devices, power storage devices, lighting devices, electronic devices, and vehicles. Electronic devices include information terminal devices equipped with a secondary battery. Power storage devices include stationary power storage devices. [Background technology]

[0002] In recent years, the demand for high-output, high-capacity lithium-ion secondary batteries has expanded rapidly in line with the development of the semiconductor industry, and they have become indispensable in the modern information society as a rechargeable energy source.

[0003] Lithium-ion secondary batteries have a problem in that lithium dendrites are precipitated on the negative electrode when they are repeatedly charged and discharged. Lithium dendrites are tree-like crystals of lithium metal that grow during the charging and discharging process, and precipitate when, for example, current concentrates on uneven areas on the surface of the negative electrode. If lithium dendrites reach the positive electrode, the lithium-ion secondary battery may experience an internal short circuit, reducing the reliability of the lithium-ion secondary battery.

[0004] Graphite is often used as the negative electrode material, and it is expected that the capacity of lithium-ion secondary batteries can be increased by replacing graphite with lithium metal. Graphite is prone to lithium dendrites when charged and discharged at low temperatures, while lithium metal will precipitate lithium dendrites even when charged and discharged at room temperature.

[0005] In order to suppress such lithium dendrites, a secondary battery using an inorganic salt containing fluorine in the electrolyte has been proposed (see Patent Document 1). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Republished Publication No. 2015 / 145288 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the configuration of Patent Document 1, since an inorganic salt containing fluorine must be used in the electrolyte, the electrolyte cannot be freely selected. For example, it becomes difficult to select an electrolyte suitable for operation in a low-temperature environment. Therefore, one of the objectives of the present invention is to provide a secondary battery having a new configuration that reduces the influence of dendrites.

[0008] Note that the description of these problems does not preclude the existence of other problems. In addition, it is not necessary for one embodiment of the present invention to solve all of these problems. In addition, it is possible to extract problems other than these from the description of this specification, drawings, claims, etc. [Means for solving the problem]

[0009] In view of the above problems, the present inventors have found a new structure for controlling the growth direction of dendrites deposited on the negative electrode. The new structure is a structure in which a carbon sheet is provided between the negative electrode on which the dendrites are deposited and the separator. This structure can suppress internal short circuits in the secondary battery, improving the reliability of the secondary battery.

[0010] One aspect of the present invention is a secondary battery having a negative electrode active material layer, a separator, a carbon sheet disposed between the negative electrode active material layer and the separator, a negative electrode active material layer, dendrites between the negative electrode active material layer and the carbon sheet, and a positive electrode active material layer, in which the negative electrode active material layer has a negative electrode active material, the negative electrode active material having one or more selected from graphite and silicon, the carbon sheet having a thickness of 25 nm or more and 50 μm or less, and the dendrites having a portion along the surface of the carbon sheet.

[0011] In the present invention, it is preferable that the battery further comprises an electrolyte, and the electrolyte contains FEC and MTFP.

[0012] In the present invention, it is preferable that the battery further includes an electrolytic solution, and the electrolytic solution contains ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate.

[0013] Another embodiment of the present invention is a secondary battery having a negative electrode active material layer, a separator, a carbon sheet disposed between the negative electrode active material layer and the separator, the negative electrode active material layer, dendrites between the carbon sheet, and a positive electrode active material layer, wherein the negative electrode active material layer has a negative electrode active material, and the negative electrode active material has lithium metal, the carbon sheet has a thickness of 25 nm or more and 50 μm or less, and the dendrites have portions along the surface of the carbon sheet.

[0014] In the present invention, it is preferable that the battery further includes an electrolytic solution, and the electrolytic solution contains ethylene carbonate and diethyl carbonate.

[0015] In the present invention, the carbon sheet preferably comprises carbon nanotubes. Effect of the Invention

[0016] According to one embodiment of the present invention, a highly reliable secondary battery in which internal short circuits are suppressed can be provided. [Brief description of the drawings]

[0017] [Figure 1] FIGS. 1A and 1B are diagrams illustrating a laminated secondary battery of one embodiment of the present invention, and FIG. 1C is a diagram illustrating the flow of electrons and the flow of lithium ions during charging of the secondary battery. [Diagram 2] FIG. 2A illustrates a negative electrode structure and a separator according to one embodiment of the present invention, and FIGS. 2B to 2E are enlarged views of the negative electrode structure illustrating the growth direction of a dendrite. [Diagram 3]3A to 3F are enlarged views of a negative electrode structure according to one embodiment of the present invention, each showing the growth direction of a dendrite. [Figure 4] FIG. 4 is a diagram illustrating a method for producing a negative electrode structure according to one embodiment of the present invention. [Diagram 5] 5(A) and 5(B) are diagrams illustrating a coating device for a negative electrode. [Figure 6] 6A to 6D illustrate a positive electrode of one embodiment of the present invention. [Figure 7] 7A to 7C illustrate a secondary battery of one embodiment of the present invention. [Figure 8] 8A to 8D are diagrams illustrating a secondary battery and a power storage system of one embodiment of the present invention. [Figure 9] 9A to 9C illustrate a secondary battery of one embodiment of the present invention. [Figure 10] 10A to 10C illustrate a secondary battery of one embodiment of the present invention. [Figure 11] 11A to 11C are diagrams illustrating an electric vehicle of one embodiment of the present invention. [Figure 12] 12A to 12D are diagrams illustrating a transportation vehicle according to one embodiment of the present invention. [Figure 13] 13A to 13C are diagrams illustrating a two-wheeled vehicle and the like according to one embodiment of the present invention. [Figure 14] 14A to 14D are diagrams illustrating electronic devices and the like according to one embodiment of the present invention. [Figure 15] 15(A) to 15(D) are diagrams showing an example of space equipment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] The embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to the following description, and it will be easily understood by those skilled in the art that the modes and details of the present invention can be modified in various ways without departing from the spirit and scope of the present invention. Therefore, in the embodiments of the present invention shown below, the same reference numerals are used in different drawings to indicate the same objects.

[0019] In this specification, a full cell refers to a battery cell assembled with different electrodes in place, such as a positive electrode / negative electrode unit cell, whereas a half cell refers to a battery cell assembled with lithium metal as the negative electrode (counter electrode).

[0020] In this specification, the amount of the supported active material is the weight of the active material per unit surface area of ​​the current collector. The amount of the negative electrode active material supported can be adjusted according to the capacity of the positive electrode. In the case of double-sided coating in which a slurry containing an active material is applied to both sides of the current collector, the above-mentioned amount of the supported active material is considered per side.

[0021] In this specification and the like, the slurry refers to a material liquid used for forming an active material layer on a current collector, containing an active material, a binder, and a solvent, and preferably further mixed with a conductive material. Note that the slurry is also called an electrode slurry or an active material slurry, and a slurry for forming a positive electrode active material layer is also called a positive electrode slurry, and a slurry for forming a negative electrode active material layer is also called a negative electrode slurry.

[0022] In this specification, the median diameter (D50) is the particle diameter when the cumulative amount in the cumulative curve of the particle size distribution measurement result is 50%. There is a method for measuring the median diameter (D50) by image analysis such as SEM or TEM. For example, 20 or more particles are measured, a cumulative particle amount curve is created, and the particle diameter when the cumulative amount is 50% can be regarded as the median diameter (D50).

[0023] In this specification and the like, a lithium ion secondary battery may be called a lithium ion battery, and refers to a battery using lithium ions as carrier ions, but the carrier ions of the present invention are not limited to lithium ions. For example, an alkali metal ion or an alkaline earth metal ion may be used as the carrier ion of the present invention, and specifically, sodium ions or the like may be applied. In this case, the present invention can be understood by reading lithium ions as sodium ions or the like. In addition, when describing a configuration in which there is no limitation on the carrier ions, it may be referred to as a secondary battery.

[0024] In this specification and the like, dendrites include dendritic crystals of metals that grow during charging and discharging, and also include deposits of the metal. During charging and discharging, dendrites may form regions of greater thickness or greater density. The shapes of multiple dendrites may differ, and one of the multiple dendrites may be thicker or denser than the other of the multiple dendrites. Adjacent dendrites may become entangled and aggregate.

[0025] In this specification and the like, carbonate refers to a compound having at least one ester in its molecular structure, and includes cyclic carbonates and chain carbonates unless otherwise specified. Furthermore, chain carbonate includes both linear and branched chain carbonates.

[0026] In this specification and the like, a low temperature environment refers to a temperature of 0° C. or lower, and a temperature of 0° C. or lower may be referred to as below freezing.

[0027] In this specification, unless otherwise specified, the charging voltage is expressed based on the potential of lithium metal. In addition, in this specification, a high charging voltage is, for example, a charging voltage of 4.6 V or more, preferably 4.65 V or more, more preferably 4.7 V or more, even more preferably 4.75 V or more, and most preferably 4.8 V or more.

[0028] In this specification and the like, the phrase "having A and / or B" may be used, which means having A, having B, or having both A and B.

[0029] (Embodiment 1) A secondary battery and the like which are one embodiment of the present invention will be described.

[0030] <Secondary battery> A secondary battery which is one embodiment of the present invention will be described with reference to FIGS.

[0031] FIG. 1(A) shows a laminated type secondary battery 100, in which each component is shown separated for ease of viewing. The secondary battery 100 has multiple positive electrodes. As the multiple positive electrodes, a first positive electrode 103a and a second positive electrode 103b are shown. However, in the secondary battery 100, there is no limitation on the number of positive electrodes, and a single positive electrode may be provided. The first positive electrode 103a and the second positive electrode 103b are collectively referred to as a positive electrode 103.

[0032] The secondary battery 100 has a plurality of negative electrodes. As the plurality of negative electrodes, a first negative electrode 106a, a second negative electrode 106b, and a third negative electrode 106c are illustrated. However, in the secondary battery 100, the number of negative electrodes is not limited in any way, and may be a single electrode. The first negative electrode 106a, the second negative electrode 106b, and the third negative electrode 106c are collectively referred to as the negative electrode 106.

[0033] The secondary battery 100 has a separator between the negative electrode and the positive electrode. For ease of viewing, the separator is shown by dotted lines in FIG. 1A. In the figure, the separators are a first separator 105a, a second separator 105b, a third separator 105c, and a fourth separator 105d. However, the number of separators in the secondary battery 100 is not limited, and a single separator may be used. The separator may be independent as shown in the figure, but a continuous separator can be used. By folding the continuous separator, the separator can be arranged at positions corresponding to the first separator 105a to the fourth separator 105d.

[0034] The secondary battery 100 has a first carbon sheet 115a between the first negative electrode 106a and the first separator 105a. Also, a second carbon sheet 115b between the second separator 105b and the second negative electrode 106b. Also, a third carbon sheet 115c between the second negative electrode 106b and the third separator 105c. Also, a fourth carbon sheet 115d between the fourth separator 105d and the third negative electrode 106c. The first carbon sheet 115a, the second carbon sheet 115b, the third carbon sheet 115c, and the fourth carbon sheet 115d are collectively referred to as the carbon sheet 115. The carbon sheet 115 can suppress an internal short circuit of the secondary battery 100, improving the reliability of the secondary battery 100.

[0035] FIG. 1(B) shows a state in which the components of the secondary battery 100 are overlapped. The first positive electrode 103a and the second positive electrode 103b each have a positive electrode current collector, and each positive electrode current collector has a protrusion 103t. The protrusions 103t of each positive electrode current collector overlap and form an assembly. The assembly of the protrusions 103t is called a positive electrode tab. The first negative electrode 106a, the second negative electrode 106b, and the third negative electrode 106c each have a negative electrode current collector, and each negative electrode current collector has a protrusion 106t. The protrusions 106t of each negative electrode current collector overlap and form an assembly. The assembly of the protrusions 106t is called a negative electrode tab.

[0036] The positive electrode further has a positive electrode active material layer. The positive electrode active material layer is a layer having positive electrode active material particles, and has an area in contact with the positive electrode current collector. The manufacturing process of the positive electrode includes a press process, and in a positive electrode that has been subjected to the press process, a recess in which the positive electrode active material particles are pressed may be formed in a part of the positive electrode current collector. The positive electrode active material layer is preferably formed on both sides of the positive electrode current collector. This is called a double-sided coated structure. The positive electrode active material layer may be formed on only one side of the positive electrode current collector. This is called a single-sided coated structure.

[0037] The negative electrode further has a negative electrode active material layer. The negative electrode active material layer is a layer having negative electrode active material particles, and has an area in contact with the negative electrode current collector. The manufacturing process of the negative electrode includes a press process, and in the negative electrode that has undergone the press process, a recess in which the negative electrode active material particles are pressed into a part of the negative electrode current collector may be formed. The negative electrode active material layer may be a double-sided coated structure formed on both sides of the negative electrode current collector. However, the negative electrode arranged in the outermost layer may use a single-sided coated structure in which the negative electrode active material layer is formed only on one side of the negative electrode current collector. In the negative electrode arranged in the outermost layer, the negative electrode active material layer that is not arranged to face the positive electrode does not insert and remove carrier ions, or is difficult to insert and remove, so the negative electrode active material layer may not be formed. It is preferable to prepare all negative electrodes as a double-sided coated structure because of high productivity, and therefore a negative electrode having a double-sided coated structure may be arranged in the outermost layer.

[0038] In addition, when the secondary battery 100 is used while being bent, it is preferable to prepare a negative electrode having a single-sided coating structure. A configuration in which multiple negative electrodes having a single-sided coating structure are stacked so that the negative electrode current collectors are in contact with each other is called a back-to-back configuration. When a back-to-back configuration is used, the negative electrode current collectors, which have low contact resistance, are in contact with each other, making it easier to bend the secondary battery 100.

[0039] As shown in FIG. 1(B), a plurality of positive electrodes, a plurality of negative electrodes, and a plurality of separators are collectively referred to as a laminated electrode. In the laminated electrode, the positive electrode tab (projection 103t) is joined to the positive electrode lead 107a at the joint 109a. In the laminated electrode, the negative electrode tab (projection 106t) is joined to the negative electrode lead 107b at the joint 109b. Ultrasonic bonding can be used for the bonding. As a result of the bonding, they are electrically connected to each other. The positive electrode lead 107a can be made of a material selected from aluminum, nickel, titanium, or an alloy thereof. The negative electrode lead 107b can be made of a material selected from nickel, copper, titanium, or an alloy thereof.

[0040] Furthermore, the secondary battery 100 has an exterior body (not shown), and the laminated electrode shown in FIG. 1(B) is housed in the exterior body. From the viewpoint of weight reduction, it is preferable to use a film for the exterior body. A secondary battery using a film for the exterior body is called a laminated type secondary battery. Although not shown in the present embodiment, a can case may be applied to the exterior body, and when a circular can case is used, the secondary battery is called a coin type secondary battery.

[0041] Here, the flow of electrons and lithium ions (Li + The flow of the secondary battery 100 will be described. A charger is connected to the two terminals shown in FIG. 1(C), and the secondary battery 100 is charged. During charging, electrons are released from the positive electrode 103, and an oxidation reaction occurs. At this time, the positive electrode is charged with lithium ions (Li + ) is desorbed into the electrolyte 108. During charging, electrons are supplied to the negative electrode 106, and a reduction reaction occurs. At this time, lithium ions in the electrolyte 108 move to the negative electrode 106. When graphite is used as the negative electrode active material, the lithium that has moved is inserted between the graphite layers. The potential of the negative electrode in a state in which lithium is inserted between the graphite layers is almost equal to the potential when lithium metal is used as the negative electrode active material. Also, when silicon or its alloy is used as the negative electrode active material, the potential is almost equal to the potential when lithium metal is used as the negative electrode active material. When charging is performed at a high rate or at a low temperature in this potential state, lithium metal precipitates. When the secondary battery 100 is regarded as a closed circuit, the current flows in the same direction as the movement of the lithium ions. Although not shown, during discharge, the negative electrode 106 releases electrons, and lithium metal dissolves into the electrolyte 108. When charging and discharging are repeated, lithium metal is repeatedly precipitated and dissolved in the negative electrode. If such an event occurs repeatedly, the surface of the negative electrode 106 may become uneven due to adhesion of electrolyte decomposition products or loss of electronic conduction paths, causing the lithium metal to turn into dendrites, which may then continue to grow.

[0042] In a secondary battery, the anode (positive electrode) and the cathode (negative electrode) are switched during charging and discharging, and the oxidation reaction and the reduction reaction are switched, so the electrode with a high reaction potential is called the positive electrode, and the electrode with a low reaction potential is called the negative electrode. Therefore, in this specification, the positive electrode is called the "positive electrode" or "+ electrode (plus electrode)" and the negative electrode is called the "negative electrode" or "- electrode (minus electrode)" whether during charging or discharging.

[0043] Next, the negative electrode and the carbon sheet according to one embodiment of the present invention will be described.

[0044] <Configuration example 1> FIG. 2(A) shows the negative electrode 106, the carbon sheet 115, and the separator 105 of the secondary battery 100. The negative electrode 106 and the carbon sheet 115 are collectively referred to as the negative electrode structure 120. The carbon sheet 115 is disposed between the negative electrode 106 and the separator 105, and is provided so as to overlap the negative electrode 106. Specifically, the carbon sheet 115 may be provided so as to overlap the negative electrode collector 110 described later, and the carbon sheet 115 may be present up to a position where it overlaps with the negative electrode tab (protruding portion 106t). In the negative electrode tab, the negative electrode collector 110 and the carbon sheet 115 have the same potential. In another embodiment, the carbon sheet 115 may be provided so as to overlap the negative electrode active material layer 111 described later. In order to control the growth direction of the dendrite described later, it is important that the carbon sheet 115 overlaps with the negative electrode active material layer 111.

[0045] <Negative electrode 106> The negative electrode 106 has a negative electrode current collector 110 and a negative electrode active material layer 111. The negative electrode active material layer 111 is a layer having negative electrode active material particles, and may further have a binder. The negative electrode active material layer 111 may further have a conductive material. Of course, the negative electrode active material layer 111 does not have to have a binder or a conductive material. The binder and the conductive material will be described later.

[0046] <Carbon sheet 115> The carbon sheet 115 may contain carbon, and preferably contains, for example, carbon fibers (also called carbon fiber, denoted as CF), and typically contains carbon nanotubes (denoted as CNT). CNT is a substance made of carbon, and specifically has a structure in which a sheet of hexagonal carbon atoms arranged in a plane is rolled into a cylindrical shape. The diameter of the rolled structure can be 10 nm or more and 25 nm or less. CNT can be formed by an arc discharge method, a laser evaporation method (laser ablation method), or a chemical vapor deposition method (CVD method). CNT is chemically stable and thermally stable. Furthermore, CNT exhibits high electrical conductivity like metal. For this reason, CNT is suitable for the carbon sheet 115, and a carbon sheet having CNT is called a CNT sheet.

[0047] CNTs include single-walled CNTs, which refer to those with a cylindrical structure of one layer. Single-walled CNTs tend to be long and highly flexible. Other CNTs include multi-walled CNTs, which refer to those having a first cylindrical structure (cylindrical structure) with a first diameter and a second cylindrical structure with a second diameter larger than the first diameter, with the first cylindrical structure arranged within the second cylindrical structure. Multi-walled CNTs may have three or more cylindrical structures. Multi-walled CNTs tend to be short and rigid. Single-walled CNTs and / or multi-walled CNTs can be used for the carbon sheet 115. Also, a laminate of single-walled CNTs and multi-walled CNTs can be used for the carbon sheet.

[0048] In a CNT sheet, it is possible to align the direction of the long axes of the CNTs (long axis direction). In other words, in a CNT sheet, it is possible to orient the long axes of the CNTs in one direction or approximately one direction. A group of CNTs whose long axes are aligned in one direction or approximately one direction is sometimes called a CNT bundle. A sheet having a group of CNTs whose long axes are aligned in one direction or approximately one direction is sometimes called a unidirectionally aligned CNT sheet. A unidirectionally aligned CNT sheet has high tensile strength along the long axis and is suitable for the carbon sheet 115.

[0049] Although the carbon sheet 115 is illustrated as a single layer, it may have a structure in which multiple carbon sheets are laminated (laminated structure). The laminated structure allows the thickness of the carbon sheet 115 to be appropriate. When multiple CNT sheets are laminated, it is preferable to laminate them so that their long axes cross each other. Multiple CNT sheets whose long axes cross each other are suitable for the carbon sheet 115. When laminating, the CNTs at the interface can be agglomerated by spraying an organic solvent. In other words, a self-supporting CNT sheet can be obtained without using a binder.

[0050] Carbon sheet 115 may have vapor grown carbon fiber (VGCF: registered trademark). VGCF (registered trademark) has a diameter of 90 nm or more and 200 nm or less, preferably 90 nm or more and 110 nm or less, and a fiber length of 7 μm or more and 15 μm or less, and is therefore suitable for carbon sheet 115.

[0051] The carbon sheet 115 may have graphene. A carbon sheet having graphene is called a graphene sheet. In this specification, graphene refers to a material having carbon, a shape such as a plate or sheet, and a two-dimensional structure formed of six-membered carbon rings. Graphene may have defects in part, and in this case, a multi-membered ring such as a seven-membered ring, an eight-membered ring, a nine-membered ring, or a ten-membered ring is formed in the graphene. The multi-membered ring refers to a cyclic carbon skeleton in which some carbon bonds in a six-membered ring made of carbon are cut and the cut carbon bonds are bonded together. The area surrounded by the carbon constituting the multi-membered ring becomes a gap. In this specification, graphene includes multi-layer graphene. Graphene is suitable for the carbon sheet 115 because it exhibits excellent electrical properties such as high electrical conductivity.

[0052] The carbon sheet 115 may have a graphene compound. A carbon sheet having a graphene compound is called a graphene compound sheet. In this specification and the like, the graphene compound includes graphene oxide, multi-layer graphene oxide, reduced graphene oxide, reduced multi-layer graphene oxide, and the like. In other words, the graphene compound may have a functional group, and examples of the functional group include an epoxy group, a carboxy group, or a hydroxy group. The graphene compound is suitable for the carbon sheet 115 because it exhibits excellent electrical properties such as high flexibility and high conductivity. In addition, the graphene compound is suitable for the carbon sheet 115 because it has defects or spaces that can pass lithium ions.

[0053] In this specification and the like, reduced graphene oxide refers to a two-dimensional structure having carbon and oxygen and formed of six-membered carbon rings. Reduced graphene oxide preferably has a portion in which the carbon concentration is greater than 80 atomic % and the oxygen concentration is 2 atomic % or more and 15 atomic % or less.

[0054] The carbon sheet 115 may have a binder to enhance adhesion to the negative electrode 106 .

[0055] When the negative electrode structure 120 is applied to a negative electrode having a double-sided coated structure such as the second negative electrode 106b shown in Fig. 1, two carbon sheets 115 are prepared for the second negative electrode 106b. That is, a carbon sheet 115 is prepared between the second negative electrode 106b and the third separator 105c, and between the second negative electrode 106b and the second separator 105b.

[0056] FIG. 2(B) shows an enlarged view of the area 116 enclosed by the dashed line in FIG. 2(A). As shown in FIG. 2(B), irregularities are observed on the surface or upper surface of the negative electrode active material layer 111. These irregularities are along the shape of the negative electrode active material particles. Furthermore, the electrolyte 108 is impregnated between the carbon sheet 115 and the negative electrode active material layer 111, and an area in which they are separated or spaced apart is observed. When the charge-discharge cycle test is repeated on the secondary battery 100, current may concentrate on the irregularities. Then, lithium is non-uniformly precipitated from the negative electrode active material layer 111, and dendrites 118 are likely to be formed. Furthermore, when the charge-discharge cycle test is repeated, the dendrites 118 grow.

[0057] In one embodiment of the present invention, since the carbon sheet 115 is arranged as shown in FIG. 2(B), the dendrite 118 grows along the carbon sheet 115. When a surface is confirmed on the carbon sheet 115, it can be said that the dendrite 118 has a portion along the surface of the carbon sheet 115. An arrow 119 is attached as an example of the growth direction of such a dendrite 118. When a normal direction of the secondary battery penetrating the positive electrode and the negative electrode is determined, the direction of the arrow 119 can be said to be a direction intersecting the normal direction. Furthermore, when the normal direction is defined as "vertical", the direction of the arrow 119 can be said to be "horizontal". When a CNT sheet is used for the carbon sheet 115, the direction of the arrow 119 can be said to be a direction along the long axis of the CNT. The direction of the arrow 119 can also be said to be a direction along the negative electrode. The growth direction of the dendrite 118 may differ depending on each dendrite. In other words, it is sufficient that the growth direction of dendrite 118 coincides or approximately coincides with arrow 119, and more specifically, it is sufficient that dendrite 118 does not reach the positive electrode.

[0058] The reason why the dendrite 118 grows in such a direction is considered to be that the dendrite 118 grows while receiving electrons from the carbon sheet 115 during the reduction reaction. Since the carbon sheet 115 has high conductivity, the reaction with the electrolyte 108 becomes active during the reduction reaction. Furthermore, it is preferable that the carbon sheet 115 is set to have the same potential as the negative electrode 106 during the reduction reaction. In other words, it is preferable that the carbon sheet 115 and the negative electrode current collector 110 are in contact with each other at the negative electrode tab. Then, the dendrite 118 can grow along the carbon sheet 115 after reaching the carbon sheet 115. Again, the growth direction of the dendrite 118 differs depending on each dendrite. Due to such a phenomenon, the dendrite 118 is prevented from reaching the positive electrode. Therefore, the internal short circuit of the secondary battery 100 is reduced by the configuration in which the carbon sheet 115 is arranged as shown in FIG. 2(B). FIG. 2(C) shows the shape of the dendrite 118 in FIG. 2(B) made needle-like.

[0059] <Application Example 1> As shown in Fig. 2(D), dendrite 118b may reach inside carbon sheet 115. In other words, dendrite 118b may grow in the direction of arrow 119 inside carbon sheet 115. This phenomenon prevents dendrite 118b from reaching the positive electrode. Therefore, the configuration in which carbon sheet 115 is arranged as shown in Fig. 2(D) reduces internal short circuit in secondary battery 100. Fig. 2(E) shows the dendrite 118b of Fig. 2(D) in a needle-like shape.

[0060] <Application Example 2> As shown in FIG. 3(A), the carbon sheet 115 may be cracked as long as the dendrite 118c does not reach the positive electrode. The carbon sheet 115 is cracked when a cracked area is confirmed in the carbon sheet 115. In addition, in a cross-sectional view of the carbon sheet 115, the cracked area is confirmed as a gap 117. The gap 117 is a space through which lithium ions can enter and exit. The dendrite 118c may grow in the direction of the arrow 119 without passing through the gap 117. More specifically, the dendrite 118c may grow in the direction of the arrow 119 after passing through the gap 117. This phenomenon prevents the dendrite 118c from reaching the positive electrode. Therefore, the configuration in which the carbon sheet 115 is arranged as shown in FIG. 3(A) reduces internal short circuits in the secondary battery 100. FIG. 3(B) shows the dendrite 118c in FIG. 3(A) in a needle-like shape.

[0061] <Application example 3> As shown in FIG. 3(C), the dendrite 118d may penetrate the carbon sheet 115 as long as it does not reach the positive electrode. In this case, it is assumed that there is no split area in the carbon sheet 115. More specifically, the dendrite 118d may exist between the separator 105 and the carbon sheet 115 and grow in the direction of the arrow 119 between them. However, the dendrite 118d should not penetrate the separator 105. This prevents the dendrite 118d from reaching the positive electrode. Therefore, the configuration in which the carbon sheet 115 is arranged as shown in FIG. 3(C) reduces internal short circuits in the secondary battery 100. FIG. 3(D) shows the dendrite 118d in FIG. 3(C) in a needle-like shape.

[0062] <Application Example 4> As shown in FIG. 3(E), the carbon sheet 115 may be disposed between the separator 105 and the positive electrode. The dendrite 118e may penetrate the separator 105. More specifically, the dendrite 118e may exist between the carbon sheet 115 and the separator 105 and grow in the direction of the arrow 119 between them. However, the dendrite 118e should not penetrate the carbon sheet 115. This prevents the dendrite 118e from reaching the positive electrode. This reduces internal short circuits in the secondary battery 100. FIG. 3(F) shows the dendrite 118e of FIG. 3(E) in a needle-like shape.

[0063] <Application Example 5> Although not shown, the dendrites 118 may be entangled with the carbon sheet 115. In other words, the carbon sheet 115 and the dendrites 118 may be integrated, and the dendrites 118 may be visible inside and outside the carbon sheet 115. This prevents the dendrites 118 from reaching the positive electrode. This reduces internal short circuits in the secondary battery 100.

[0064] Considering the above Application Example 5, the growth direction of dendrite 118 may not necessarily be the direction of arrow 119. That is, in one embodiment of the present invention, the growth direction of dendrite 118 is not important, and it is sufficient that carbon sheet 115 can prevent dendrite 118 from reaching the positive electrode.

[0065] 2(B) to 3(F), the thickness of the carbon sheet 115 is set to 25 nm or more, preferably 25 nm to 50 μm, 25 nm to 10 μm, 25 nm to 1 μm, or 25 nm to 500 nm. To achieve this thickness, the carbon sheets 115 may be laminated. The thickness of the carbon sheet 115 may be 0.5 to 1.5 times the thickness of the separator.

[0066] With the above-mentioned configuration, the dendrites do not reach the positive electrode, and internal short circuits in the secondary battery can be suppressed.

[0067] <Manufacturing method example 1> An example of a method for manufacturing the above-mentioned negative electrode structure 120 will be described with reference to FIG.

[0068] <Step S10> In step S10 shown in FIG. 4, a negative electrode current collector 110 and a negative electrode active material layer 111 are prepared.

[0069] <Negative electrode current collector 110> The negative electrode current collector 110 will be described. As the negative electrode current collector, a material having high electrical conductivity, such as metals such as copper, stainless steel, gold, platinum, and titanium, and alloys thereof, can be used. In addition, an aluminum alloy to which an element that improves heat resistance, such as silicon, titanium, neodymium, scandium, and molybdenum, is added, can be used for the negative electrode current collector. In addition, it may be formed of a metal element that reacts with silicon to form a silicide. Examples of the metal element that reacts with silicon to form a silicide include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, and nickel. The negative electrode current collector can be appropriately shaped in a foil, plate, sheet, mesh, punched metal, expanded metal, or other shape. It is preferable to use a negative electrode current collector having a thickness of 5 μm to 30 μm.

[0070] <Negative electrode active material> The negative electrode active material of the negative electrode active material layer 111 will be described. The negative electrode active material may be a material that absorbs and releases lithium. The negative electrode active material may be a material that can undergo a charge / discharge reaction by alloying / dealloying reaction with lithium. The negative electrode active material may be, for example, one or a composite material of two or more selected from lithium metal, carbon, and silicon. Silicon is preferred because it has a high theoretical capacity of 4200 mAh / g per active material weight. When lithium metal is used as the negative electrode active material, the negative electrode current collector can be omitted.

[0071] As the carbon, graphite, graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), CNT, graphene, carbon black, etc. can be used. That is, when multi-layered CNT or multi-layered graphene is used for the carbon sheet 115, the carbon sheet 115 is capable of absorbing and releasing lithium.

[0072] When lithium ions are inserted into graphite (when lithium-graphite intercalation compounds are formed), the potential is as low as that of metallic lithium (0.05 V to 0.3 V vs. Li / Li + ) This allows the secondary battery to exhibit a high operating voltage. Furthermore, graphite is preferred because it has the advantages of a relatively high discharge capacity per unit volume, a relatively small volume expansion, low cost, and high safety compared to lithium metal.

[0073] If the negative electrode active material has a small median diameter (D50), it becomes bulky and may hinder the improvement of the electrode density. Therefore, the median diameter (D50) of the negative electrode active material is preferably 3 μm or more and 20 μm or less, and more preferably 7 μm or more and 12 μm or less. A representative example of a negative electrode active material that satisfies this range is graphite, and it is preferable that the median diameter (D50) of graphite satisfies the above range as a powder characteristic.

[0074] Examples of graphite include artificial graphite and natural graphite. Examples of artificial graphite that can be used include mesocarbon microbeads (MCMB), coke-based artificial graphite, and pitch-based artificial graphite. The artificial graphite may have a carbon coating layer, which is a low crystallinity layer. Since the shape of the artificial graphite is spherical, it is called spherical graphite. For example, MCMB is one of the preferred materials for spherical graphite. Furthermore, it is relatively easy to reduce the specific surface area of ​​MCMB. If the specific surface area is large, the decomposition reaction with the electrolyte on the surface of the negative electrode active material becomes large, and good cycle characteristics may not be obtained. In order to suppress the above decomposition reaction, the specific surface area of ​​the carbon is 0.8 m 2 / g or more 8m 2 / g or less, preferably 1m 2 / g or more 2m 2 / g or less. Typically, it is preferable for the spherical graphite to have the specific surface area described above as a powder characteristic. The specific surface area can be measured by the BET method (Brunauer Emmett Teller method). The BET method is an analytical method that extends the Langmuir theory to multilayer adsorption of adsorbed gas molecules, and is the most common method for calculating the specific surface area. The specific surface area by the BET method can be measured using an automatic specific surface area measuring device, Tristar 2 3020.

[0075] Examples of natural graphite include flake graphite, spheroidized natural graphite, etc. Natural graphite may have a carbon coating layer which is a low crystallinity layer.

[0076] The negative electrode active material may be a silicon carbon composite material having carbon and silicon. In the silicon carbon composite material, the carbon and silicon may be a mixture, and it is preferable that the sintered state can be confirmed through a heat treatment. In the silicon carbon composite material, it is preferable to use graphite particles as the carbon, and the median diameter (D50) of the graphite particles is 1 μm or more and 20 μm or less, preferably 3 μm or more and 20 μm or less, and more preferably 7 μm or more and 12 μm or less. The median diameter of the graphite particles can be determined based on the median diameter (D50) of silicon.

[0077] The specific surface area of ​​a graphite particle is 0.5 m 2 / g or more 3m 2 / g or less is preferable. The specific surface area can be measured by the BET method. The specific surface area by the BET method is a value measured by the nitrogen gas adsorption type BET single point method, and can be measured using an automatic specific surface area / pore distribution measuring device Tristar II3020 (manufactured by Micromeritics).

[0078] In the silicon carbon composite material, it is preferable to use silicon particles as the silicon. The silicon particles preferably have a silicon material, and specifically, preferably contain one selected from silicon, silicon oxide, and silicon alloy. Silicon oxide includes silicon monoxide (SiO). In this specification, SiO refers to, for example, silicon monoxide. Silicon monoxide is SiO x x is preferably 0.2 or more and 1.5 or less, and more preferably 0.3 or more and 1.2 or less.

[0079] The median diameter (D50) of silicon particles is preferably less than 1 μm, typically 50 nm to 800 nm, and preferably 100 nm to 500 nm. Silicon particles of this size are sometimes called nanosilicon particles. Silicon has problems with expansion and contraction during charging and discharging, but nanosilicon particles that have been refined to the above median diameter (D50) are suitable because they improve charge and discharge deterioration. It is preferable to make the silicon particles have a uniform median diameter (D50) by subjecting the silicon raw material to a crushing process.

[0080] The specific surface area of ​​a silicon particle is 10 m 2 / g or more 35m 2 / g or less, preferably 10m 2 / g or more 15m 2 / g or less is preferable. The specific surface area can be measured by the BET method. The specific surface area by the BET method is a value measured by the nitrogen gas adsorption type BET single point method, and can be measured using an automatic specific surface area / pore distribution measuring device Tristar II3020 (manufactured by Micromeritics).

[0081] A secondary battery with high discharge capacity can be realized by using a negative electrode active material containing both graphite particles and silicon particles. In addition, since the median diameter (D50) of graphite particles is different from the median diameter (D50) of silicon particles, specifically, it is larger, when these are mixed and used in the negative electrode, the amount of the negative electrode active material carried can be increased. If the amount carried is small, the output characteristics of the lithium ion secondary battery can be improved, but if the amount carried is large, the output characteristics are reduced. Therefore, the amount of the negative electrode active material carried is set to 3 mg / cm. 2 More than 10mg / cm 2 The following is preferred:

[0082] In the negative electrode active material layer 111, the weight of the graphite particles is preferably higher than the weight of the silicon particles, and typically, the weight ratio of the graphite particles in the negative electrode active material layer 111 is preferably 5 to 35 times the weight ratio of the silicon particles. In other words, the weight ratio of silicon to the total weight of the powder material constituting the negative electrode active material is preferably 2 wt% or more and 37.5 wt% or less.

[0083] As other negative electrode active materials, materials containing one or more elements selected from tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium, and the like can be used.

[0084] The negative electrode active material may be a compound containing one or more elements selected from tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium, etc. A compound containing two or more elements may be called an alloy material, and for example, magnesium silicide (Mg 2 Si).

[0085] Other alloy materials include magnesium-germanium alloys (Mg 2 Ge), stannous oxide (SnO), stannic oxide (SnO 2 ), magnesium tin compounds (Mg 2 Sn), tin disulfide (SnS) 2 ), other major binary alloys of tin (V 2 Sn 3 , FeSn2 , CoSn 2 , Ni 3 Sn 2 , Cu 6 Sn 5 , Ag 3 Sn, LaSn 3 , La 3 Co 2 Sn 7 , SbSn), binary alloys of antimony (Ag 3 Sb, Ni 2 MnSb, CeSb 3 , CoSb 3 , InSb), etc.

[0086] Titanium dioxide (TiO 2 ), lithium titanium oxide (Li 4 Ti 5 O 12 ), lithium graphite intercalation compound (Li x C 6 ), niobium pentoxide (Nb 2 O 5 ), tungsten dioxide (WO 2 ), molybdenum dioxide (MoO 2 ) and other oxides can be used.

[0087] In addition, the negative electrode active material is a nitride of lithium and a transition metal, Li 3 Li with N-type structure 3-x M x N (M=Co, Ni, Cu) can be used. For example, Li 2.6 Co 0.4 N has a large discharge capacity (900mAh / g, 1890mAh / cm per active material weight) 3 ) and is preferred.

[0088] When a nitride of lithium and a transition metal is used, the negative electrode active material contains lithium ions, so the positive electrode active material does not contain lithium ions. 2 O 5 , Cr 3 O 8It is preferable that the material can be combined with a material such as lithium ions. Even when a material containing lithium ions is used as the positive electrode active material, it is possible to use a nitride of lithium and a transition metal as the negative electrode active material by desorbing the lithium ions contained in the positive electrode active material in advance.

[0089] Another form of the negative electrode may be a negative electrode that does not have a negative electrode active material at the end of the battery production. For example, a negative electrode that does not have a negative electrode active material may be a negative electrode that has only a negative electrode current collector at the end of the battery production, in which lithium ions that are released from the positive electrode active material by charging the battery are deposited as lithium metal on the negative electrode current collector to form a negative electrode active material layer. A battery using such a negative electrode may be called a negative electrode-free battery (anode-free battery), a negative electrode-less battery (anode-less battery), etc.

[0090] When a negative electrode having no negative electrode active material is used, a film for uniforming the deposition of lithium may be provided on the negative electrode current collector. As the film for uniforming the deposition of lithium, for example, a solid electrolyte having lithium ion conductivity can be used. As the solid electrolyte, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a polymer-based solid electrolyte, and the like can be used. Among them, the polymer-based solid electrolyte is suitable as a film for uniforming the deposition of lithium, since it is relatively easy to form a uniform film on the negative electrode current collector. In addition, as the film for uniforming the deposition of lithium, for example, a metal film that forms an alloy with lithium can be used. As the metal film that forms an alloy with lithium, for example, a magnesium metal film can be used. Lithium and magnesium form a solid solution in a wide composition range, so that it is suitable as a film for uniforming the deposition of lithium.

[0091] In addition, when a negative electrode that does not have a negative electrode active material is used, a negative electrode current collector having projections and recesses can be used. When a negative electrode current collector having projections and recesses is used, the recesses of the negative electrode current collector become cavities into which lithium contained in the negative electrode current collector is likely to deposit, and therefore, when lithium is deposited, it is possible to suppress the lithium from forming a dendritic shape.

[0092] <Binder (binding agent)> The negative electrode active material layer 111 preferably has a binder. As the binder, it is preferable to use a polymer having a carboxy group. The carboxy group can be said to have two basic oxygens, one acidic hydrogen, and one electrophilic carbon. The carboxy group has a hydroxyl group OH and a carbonyl group C=O, and can be said to be a polar group. If the binder has a polar group such as a carboxy group, lithium ions are attracted by interaction with the lithium ions, and therefore there is a possibility that the binder will assist the insertion of lithium ions into the negative electrode active material. The carboxy group can be identified by Fourier Transform Infrared Spectroscopy (FT-IR) or the like.

[0093] Examples of polymers having carboxyl groups include polyglutamic acid (sometimes written as PGA), polyacrylic acid (sometimes written as PAA), and alginic acid (sometimes written as polysaccharide). Also, polyamino acids may be used as polymers having carboxyl groups, and specifically, polyornithine and polysarcosine may be applied as binders. Furthermore, polyaspartic acid may be applied as a binder as a polymer having carbonyl groups. Also, binary copolymers (copolymers) may be applied as polymers having ketone groups, and copolymers of acrylic acid and maleic acid, and copolymers of acrylic acid and sulfonic acid may be applied as binders. Using these as binders for the negative electrode also has the effect of reducing the amount of binder mixed in the negative electrode.

[0094] Among the above-mentioned polymers, polyglutamic acid or polyacrylic acid is particularly preferable as a binder for use in a negative electrode. The following structural formula (H2) is the structural formula of polyglutamic acid.

[0095] [ka]

[0096] As is clear from the structural formula (H2), polyglutamic acid has nitrogen in addition to the carboxyl group, and since the nitrogen has an unshared electron pair, it is expected to interact with lithium ions. For example, the unshared electron pair may attract lithium ions and assist their insertion into the negative electrode active material.

[0097] In addition, polyglutamic acid has a carbonyl group, C=O, as is clear from the structural formula. If the binder has a polar group such as a carbonyl group, it is expected to interact with lithium ions, which are carrier ions, and may assist in the insertion and desorption of lithium ions in the negative electrode active material, for example.

[0098] Either linear γ-polyglutamic acid or crosslinked γ-polyglutamic acid may be used as the binder, and these are collectively referred to as a structure mainly composed of γ-polyglutamic acid. Note that crosslinked γ-polyglutamic acid is more suitable for the binder in that it has a network structure. Furthermore, the molecular weight of polyglutamic acid is 1 million or more, preferably 3 million or more, and more preferably 10 million or more and 50 million or less.

[0099] Depending on the method for preparing polyglutamic acid, it may be said to have a structure mainly composed of γ-glutamic acid containing other elements (e.g., Ca, Al, Na, Mg, Fe, Si, S). That is, polyglutamic acid may be neutralized with an alkali metal ion, e.g., lithium ion or sodium ion.

[0100] Since such polyglutamic acid has hydrophilicity, deionized water can be used as a solvent, which is suitable for forming a slurry. Furthermore, polyglutamic acid can provide a secondary battery with good low-temperature characteristics.

[0101] The following structural formula (H1) is the structural formula of polyacrylic acid.

[0102] [ka]

[0103] As is clear from structural formula (H1), polyacrylic acid has a carboxy group.

[0104] A material made by cross-linking polyacrylic acid may be used. Since a cross-linked structure, i.e., a network structure, can be formed, it is preferable because it may enhance the function as a binder. Furthermore, polyacrylic acid can provide a secondary battery with good low-temperature characteristics.

[0105] As the binder other than the above, it is preferable to use a rubber material such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, ethylene-propylene-diene copolymer, etc. Also, fluororubber can be used as the binder.

[0106] As the binder, it is preferable to use materials such as polystyrene, polymethyl acrylate, 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, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), ethylene propylene diene polymer, polyvinyl acetate, and nitrocellulose.

[0107] <Thickener> It is also preferable to use a thickener in addition to the binder. As the thickener, it is preferable to use, for example, a water-soluble polymer. As the water-soluble polymer, for example, polysaccharides can be used. As the polysaccharide, cellulose derivatives such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, regenerated cellulose, etc., or starch can be used.

[0108] <Conductive material> The negative electrode active material layer 111 may have a conductive material. The conductive material functions to assist the current path between the active material and the current collector, or the current path between a plurality of active materials. In order to perform such a function, it is preferable that the conductive material has a material with a lower resistance than the active material. The conductive material is also called a conductive assistant or a conductive imparting agent because of its role. By attaching the conductive material between a plurality of active materials, the plurality of active materials are electrically connected to each other, and the conductivity is increased. In this specification, the term "attachment" does not only refer to the physical adhesion between the active material and the conductive material, but also includes the case where a covalent bond is formed, the case where the conductive material is bonded by van der Waals forces, the case where the conductive material covers a part of the surface of the active material, the case where the conductive material fits into the surface unevenness of the active material, and the case where the two materials are electrically connected even if they are not in contact with each other.

[0109] The conductive material is typically a carbon material or a metal material. The conductive material is particulate, and examples of the particulate conductive material include carbon black (furnace black, acetylene black, graphite, etc.). The conductive material may be fibrous, and examples of the fibrous conductive material include CNT and VGCF (registered trademark). The conductive material may be sheet-shaped, and an example of a sheet-shaped conductive material is multilayer graphene. The sheet-shaped conductive material may appear thread-like in the cross section of the positive electrode.

[0110] The particulate conductive material can enter the gaps between the negative electrode active material and the like, and is also prone to aggregation. Therefore, the particulate conductive material can assist the conductive path between the negative electrode active material arranged nearby. The fibrous conductive material also has a bent region, but is larger than the negative electrode active material. Therefore, the fibrous conductive material can assist the conductive path between the distant negative electrode active materials in addition to the adjacent negative electrode active materials. In this way, it is preferable to mix two or more shapes of conductive material.

[0111] When multilayer graphene is used as the sheet-like conductive material and carbon black is used as the particulate conductive material, the weight of the carbon black in a mixed slurry state is preferably 1.5 to 20 times, and more preferably 2 to 9.5 times, that of the multilayer graphene.

[0112] When the mixing ratio of the multilayer graphene and the carbon black is within the above range, the carbon black does not aggregate and is easily dispersed. Furthermore, when the mixing ratio of the multilayer graphene and the carbon black is within the above range, the electrode density can be made higher than when only carbon black is used as the conductive material. By increasing the electrode density, the capacity per unit weight can be increased.

[0113] Furthermore, by setting the mixing ratio of the multilayer graphene and the carbon black within the above range, rapid charging can be achieved.

[0114] In place of the multi-layer graphene described above, a graphene compound may be used in the conductive material. Fluorine-containing graphene may be used as the graphene compound. The fluorine in the graphene compound is preferably adsorbed on the surface. Fluorine-containing graphene can be produced by contacting graphene with a fluorine compound (called a fluorination process). The fluorination process uses fluorine (F 2 ) or fluorine compounds are preferably used. Fluorine compounds include hydrogen fluoride, halogen fluoride (ClF 3 , IF 5 etc.), gaseous fluorides (BF 3 , N.F. 3 , P.F. 5 , SiF 4 ,SCIENCE FICTION 6 etc.), metal fluorides (LiF, NiF 2 , AlF 3 , MgF 2 For the fluorination treatment, it is preferable to use a gaseous fluoride, which may be diluted with an inert gas. The temperature for the fluorination treatment is preferably room temperature, and is preferably 0°C or higher and 250°C or lower, which includes room temperature. When the fluorination treatment is performed at 0°C or higher, fluorine can be adsorbed on the surface of graphene.

[0115] Graphene or a graphene compound has excellent physical properties, such as high flexibility and high mechanical strength, and is therefore suitable as a conductive material. Graphene or a graphene compound may have a curved surface, enabling surface contact with low contact resistance. In addition, graphene or a graphene compound may have very high conductivity even when thin, and a conductive path can be efficiently formed in an active material layer with a small amount. Therefore, by using graphene or a graphene compound as a conductive material, the contact area between the active material and the conductive material can be increased. In addition, the graphene or graphene compound may have holes.

[0116] When using a negative electrode active material having a size of 1 μm or less, such as nanosilicon particles, more conductive paths connecting the active materials are required. In such a case, it is preferable to use graphene or a graphene compound, which can efficiently form conductive paths even in a small amount.

[0117] Because of the above-mentioned properties, it is particularly effective to use graphene or a graphene compound as a conductive material for secondary batteries that require rapid charging and rapid discharging. For example, secondary batteries for two-wheeled or four-wheeled vehicles and secondary batteries for drones may require rapid charging and rapid discharging. Furthermore, rapid charging characteristics may be required for mobile electronic devices. Rapid charging refers to, for example, charging at 400 mA / g or more, or charging at 1000 mA / g or more. Rapid discharging refers to, for example, discharging at 400 mA / g or more, or discharging at 1000 mA / g or more.

[0118] <Step S11> 4, a slurry 504 containing a negative electrode active material, a binder, and the like is prepared, and the slurry 504 is applied to the negative electrode current collector 110 to form the negative electrode 106. The viscosity of the slurry is adjusted using a thickener or the like to facilitate application to the negative electrode current collector 110.

[0119] 5(A) shows a coating device that coats a slurry 504 containing a negative electrode active material, a binder, and the like onto a negative electrode current collector 110. The coating device is called a comma coater. The slurry 504 may contain a solvent, and the solvent may be water, a ketone such as acetone, an alcohol such as ethanol or isopropanol, ether, dioxane, acetonitrile, or NMP (N-methyl-2-pyrrolidone), or the like.

[0120] The coating device has a back roll 521, a coating roll 522, a microbar 524, and the like. A roll-shaped negative electrode current collector (metal foil, typically copper foil) 110 serving as a negative electrode current collector is moved by the back roll 521. The back roll 521 can also rotate the coating roll 522. The slurry 504 is held by a dam bottom surface 523 and the coating roll 522, and the thickness of the slurry 504 is adjusted by the microbar 524, and the slurry is applied to the negative electrode current collector 110. Coating is also called application. In addition, when the thickness of the applied slurry 504 is monitored, the coating device preferably has a slurry thickness measurement sensor 505.

[0121] FIG. 5(B) shows another example of a coating device that applies the slurry 504 to the negative electrode current collector 110. The coating device is called a die coater. The coating device has a die 525, a back roll 521, and the like. The die 525 is an example of a coating nozzle, and has a manifold at the center of the die 525. The slurry 504 is supplied to the manifold by a pump, and is extruded from the manifold to the tip of the die. The extruded slurry 504 is coated onto the negative electrode current collector 110 that has been moved by the rotation of the back roll 521. In addition, when monitoring the thickness of the applied slurry 504, it is preferable that the coating device has a slurry thickness measurement sensor 505.

[0122] Using such a coating device, the negative electrode 106 is obtained. After coating, the negative electrode 106 may be pressed by a roll press as necessary. The linear pressure is 10 kN / m or more and 50 kN / m or less, preferably 15 kN / m or more and 25 kN / m or less. The upper and lower rolls are heated to 100°C or more, preferably 120°C or more. However, in the case of a slurry containing a binder, the upper and lower rolls are heated to the melting point of the binder or higher. In this manner, the negative electrode 106 is completed.

[0123] In the negative electrode 106, the thickness of the negative electrode active material layer 111 is set to 100 μm or more and 300 μm or less, preferably 110 μm or more and 150 μm or less. Furthermore, the amount of the negative electrode active material supported is 3 mg / cm 2 More than 20mg / cm 2 Less than 12 mg / cm, preferably 2 More than 18mg / cm 2 The following applies.

[0124] <Step S12> Next, in step S12 shown in FIG. 4, a carbon sheet 115 is prepared.

[0125] <Carbon sheet 115> The carbon sheet 115 is as described above, and a commercially available product may be used. Commercially available CNT sheets have a thickness of 400 nm or more and 500 nm or less per sheet. In order for the carbon sheet 115 to have a predetermined thickness, it is preferable to laminate commercially available sheets.

[0126] <Step S13> Next, in step S13 shown in FIG. 4, the negative electrode 106 and the carbon sheet 115 are laminated to obtain a negative electrode structure 120. The above-mentioned binder may be used to bond the negative electrode 106 and the carbon sheet 115. In this manner, the negative electrode structure 120 is obtained. After the negative electrode 106 and the carbon sheet 115 are laminated, they may be pressed by a roll press as necessary. The upper and lower rolls are heated to 100° C. or higher, preferably 120° C. or higher. However, when a binder is used, the upper and lower rolls are heated to the melting point of the binder or higher.

[0127] According to this example of the manufacturing method, it is possible to obtain the negative electrode structure 120 having the carbon sheet 115. The negative electrode structure 120 prevents dendrites from reaching the positive electrode.

[0128] The content of this embodiment mode can be appropriately combined with the content of other embodiment modes.

[0129] (Embodiment 2) In this embodiment, the configuration of a secondary battery will be described.

[0130] [Negative electrode] The negative electrode is as described in the above embodiment.

[0131] [Positive electrode] The positive electrode includes a positive electrode active material layer and a positive electrode current collector. The positive electrode active material layer includes a positive electrode active material, and may further include at least one of a conductive material and a binder. The positive electrode active material may be any of those described in the above embodiment.

[0132] FIG. 6(A) shows an example of a schematic cross-sectional view of a positive electrode.

[0133] The positive electrode current collector 550 can be, for example, a metal foil. The positive electrode can be formed by applying a slurry onto a metal foil and drying it. Note that pressing may be performed after drying. The positive electrode is formed by forming a positive electrode active material layer on the positive electrode current collector 550.

[0134] The positive electrode active material layer includes a positive electrode active material 561. The positive electrode active material may be called a positive electrode active material particle. The positive electrode active material 561 has a function of taking in and / or releasing lithium ions with charging and discharging. The positive electrode active material 561 used in one embodiment of the present invention may be a material that is less deteriorated with charging and discharging even at a high charging voltage. Note that the positive electrode active material 561 may be two or more materials with different particle sizes as long as the material is less deteriorated with charging and discharging even at a high charging voltage.

[0135] The conductive material can be selected from the conductive materials described in the above embodiment modes. Fig. 6(A) illustrates carbon black 553 as the conductive material.

[0136] A binder may be mixed to bond a positive electrode current collector 550 such as a metal foil to a positive electrode active material as the positive electrode of a secondary battery. The binder is a polymer material, and if a large amount of binder is included, the ratio of the active material in the positive electrode decreases, and the discharge capacity of the secondary battery decreases. Therefore, it is preferable to mix the binder in a minimum amount. In FIG. 6(A), the regions not filled with the positive electrode active material 561, the second positive electrode active material 562, and the carbon black 553 indicate voids or binders.

[0137] 6A shows an example in which the positive electrode active material 561 is illustrated as a sphere, but is not particularly limited thereto. For example, the cross-sectional shape of the positive electrode active material 561 may be an ellipse, a rectangle, a trapezoid, a pyramid, a polygon with rounded corners, or an asymmetric shape. For example, FIG. 6B shows an example in which the positive electrode active material 561 has a polygonal shape with rounded corners.

[0138] 6B, graphene 554 is used as a carbon material used as a conductive material. In FIG. 6B, a positive electrode active material layer including a positive electrode active material 561, graphene 554, and carbon black 553 is formed over a positive electrode current collector 550.

[0139] In the step of mixing the graphene 554 and the carbon black 553 to obtain an electrode slurry, the weight of the carbon black to be mixed is preferably 1.5 to 20 times, more preferably 2 to 9.5 times, that of the graphene.

[0140] In addition, when the mixture of graphene 554 and carbon black 553 is within the above range, the dispersion stability of carbon black 553 is excellent and agglomeration is unlikely to occur during slurry preparation. In addition, when the mixture of graphene 554 and carbon black 553 is within the above range, a higher electrode density can be achieved than a positive electrode using only carbon black 553 as a conductive material. By increasing the electrode density, the capacity per unit weight can be increased.

[0141] Although the electrode density is lower than that of a positive electrode using only graphene as a conductive material, by mixing the first carbon material (graphene) and the second carbon material (acetylene black) within the above range, it can be used for rapid charging. Therefore, it is particularly effective when used as an in-vehicle lithium-ion secondary battery.

[0142] Fig. 6C illustrates an example of a positive electrode using carbon fiber 555 instead of graphene. Fig. 6C illustrates an example different from Fig. 6B. When carbon fiber 555 is used, aggregation of carbon black 553 can be prevented and dispersibility can be improved.

[0143] In FIG. 6C, the regions not filled with the positive electrode active material 561, the carbon fibers 555, and the carbon black 553 indicate voids or binders.

[0144] In addition, as another example of the positive electrode, Fig. 6(D) is shown. Fig. 6(D) shows an example in which carbon fiber 555 is used in addition to graphene 554. When both graphene 554 and carbon fiber 555 are used, aggregation of carbon black such as carbon black 553 can be prevented and dispersibility can be further improved.

[0145] Note that in FIG. 6D, regions that are not filled with the positive electrode active material 561, the carbon fibers 555, the graphene 554, and the carbon black 553 indicate voids or binders.

[0146] A lithium ion secondary battery can be produced by using any one of the positive electrodes shown in Figures 6(A) to 6(D), stacking a separator on the positive electrode, placing the stack in which the negative electrode is stacked on the separator in a container (such as an outer casing or a metal can) that houses the stack, and filling the container with a liquid electrolyte.

[0147] [Electrolyte] The electrolytic solution has an organic solvent, but the organic solvent of the electrolyte according to one embodiment of the present invention is not limited to being liquid at 25° C., and may be solid at 25° C. or semi-solid at room temperature. The organic solvent of the electrolyte according to one embodiment of the present invention is preferably liquid in a wide temperature range including below freezing point to high temperature, but is not limited thereto. The organic solvent may be liquid, solid, or semi-solid in a wide temperature range including below freezing point to high temperature.

[0148] The organic solvent is preferably an aprotic organic solvent, for example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, chloroethylene carbonate, vinylene carbonate (VC), γ-butyrolactone, γ-valerolactone, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), 1,3-propane sultone (PS), fluoroethylene carbonate (FEC), methyl 3,3,3- One of trifluoropropionate (MTFP), methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethoxyethane (DME), dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, sultone, etc., or two or more of these can be used in any combination and ratio. An electrolyte solution containing vinylene carbonate (VC) or fluoroethylene carbonate (FEC) is preferred because it has a high tendency for dendrites to become thicker, thereby suppressing penetration of the separator. In this case, vinylene carbonate (VC) or fluoroethylene carbonate (FEC) is preferably used as an additive rather than as the main component of the electrolyte solution. Typically, ethylene carbonate (EC) and diethyl carbonate (DEC) are preferably used, and in this case, it is preferred to satisfy EC:DEC=3:7 (volume ratio).

[0149] Since PS has the same HOMO and LUMO levels as EC and DEC, it is not easily oxidized or reduced even at high cutoff voltages, and when it is decomposed on the surface of the positive electrode active material, it is likely to become a polymer. Therefore, it has the advantage that it is less likely to become a decomposition product with a small molecular weight and become gasified. Therefore, the electrolyte preferably contains PS at 0.1 wt% to 10 wt%, and more preferably at 0.25 wt% to 7.5 wt%.

[0150] FEC is one of the cyclic carbonates and has a high relative dielectric constant, so when used in an organic solvent, it has the effect of promoting the dissociation of lithium salts. On the other hand, FEC has a substituent that shows electron-withdrawing properties, so it is easier to desolvate with lithium ions than EC. Specifically, the solvation energy of lithium ions in FEC is smaller than that of EC that does not have a substituent that shows electron-withdrawing properties. Therefore, it is easier to separate lithium ions on the surface of the positive electrode active material and the surface of the negative electrode active material, and the internal resistance of the secondary battery can be reduced. Furthermore, since FEC has a deep highest occupied molecular orbital (HOMO: Highest Occupied Molecular Orbital) level, it is difficult to oxidize and the oxidation resistance is improved. On the other hand, there is a concern that FEC has a high viscosity. Therefore, it is recommended to use a mixed organic solvent containing not only FEC but also MTFP in the electrolyte. MTFP is one of the chain carbonates, and it is possible to have the effect of lowering the viscosity of the electrolyte, or maintaining the viscosity at room temperature (typically 25°C) even at low temperatures (typically 0°C). Furthermore, although MTFP has a smaller solvation energy than methyl propionate (abbreviated as "MP") that does not have a substituent that exhibits electron-withdrawing properties, it may form a solvation with lithium ions when used in an electrolyte. When using a mixed organic solvent containing both FEC and MTFP, the volume ratio of FEC:MTFP=1:y is preferably 2≦y≦20, and more preferably 4≦y≦9.

[0151] The organic solvents mentioned above are contaminated with particulate waste or molecules other than the constituent molecules of the organic solvent (hereinafter simply referred to as "impurities"), and oxygen (O 2 ), water (H 2 O) or water. It is preferable that the content of ) is low and highly purified. It is also preferable that reaction by-products during synthesis are suppressed through appropriate purification. Specifically, the impurities of the electrolyte are 100 ppm or less, preferably 50 ppm or less, and more preferably less than 10 ppm. The concentration of water among the impurities can be detected by Karl Fischer titration.

[0152] Furthermore, it is preferable that the above-mentioned organic solvents have almost no peaks due to impurities that can be confirmed by NMR measurement or the like. "Almost no peaks can be confirmed" includes that the ratio of the integrated area of ​​the peak due to the impurity to the integrated area of ​​the peak due to the main component (simply called integral ratio) is 0.005 or less, preferably 0.002 or less. There are no particular limitations on the device used for NMR measurement, but for example, Bruker's "AVANCE III 400" can be used. 1 Acetonitrile-d used as a solvent in H-NMR measurements 3 Of the five peaks of acetonitrile derived from the compound, the central peak can be located at 1.94 ppm.

[0153] For example, in the case of MTFP, acetonitrile-d 3 Using a solvent 1 It is known that when H-NMR is measured, four peaks appear at δ between 3.29 ppm and 3.43 ppm. However, if other peaks appear in the vicinity, for example, if a peak appears at δ between 3.24 ppm and 3.29 ppm, the peak is considered to be due to impurities. Therefore, if the ratio (integral ratio) of the peak area between 3.24 ppm and 3.29 ppm to the peak area between 3.29 ppm and 3.43 ppm is 0.005 or less, preferably 0.002 or less, it can be said that the peaks due to impurities are almost not confirmed.

[0154] In addition, for the purpose of improving safety, etc., in order to form a coating (Solid Electrolyte Interphase Film) at the interface between the electrode (active material layer) and the electrolyte, an additive such as vinylene carbonate (VC), propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), lithium bis(oxalate)borate (LiBOB), or a dinitrile compound such as succinonitrile or adiponitrile may be added to the electrolyte. The concentration of the additive is preferably, for example, 0.1 wt% to 5 wt% relative to the solvent. When ethylene carbonate (EC) and diethyl carbonate (DEC) are used, it is preferable to mix 2 wt% of vinylene carbonate (VC) as an additive into a mixed organic solvent in which a lithium salt described below is dissolved, with EC:DEC=3:7 (volume ratio).

[0155] In addition, by using one or more ionic liquids (room-temperature molten salts) that are flame-retardant and non-volatile as a solvent for the electrolyte, even if the internal temperature of the electricity storage device rises due to an internal short circuit or overcharging, the electricity storage device can be prevented from bursting or catching fire. The ionic liquid is composed of a cation and an anion, and includes an organic cation and an anion. Examples of the organic cation used in the electrolyte include aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, and aromatic cations such as imidazolium cations and pyridinium cations. Examples of the anion used in the electrolyte include monovalent amide anions, monovalent methide anions, fluorosulfonic acid anions, perfluoroalkylsulfonic acid anions, tetrafluoroborate anions, perfluoroalkylborate anions, hexafluorophosphate anions, and perfluoroalkylphosphate anions.

[0156] The electrolyte (also called lithium salt) to be dissolved in the above-mentioned solvent is, for example, LiPF 6 , LiClO 4 , LiAsF 6 , LiBF 4 , LiAlCl 4, LiSCN, LiBr, LiI, Li 2 SO 4 , Li 2 B 10 Cl 10 , Li 2 B 12 Cl 12 , LiCF 3 SO 3 , LiC 4 F 9 SO 3 , LiC(CF 3 SO 2 ) 3 , LiC(C 2 F 5 SO 2 ) 3 , LiN(CF 3 SO 2 ) 2 , LiN(C 4 F 9 SO 2 )(CF 3 SO 2 ), LiN(C 2 F 5 SO 2 ) 2 , lithium bis(oxalato)borate (Li(C 2 O 4 ) 2 , LiBOB), etc., can be used alone or in any combination and ratio of two or more of these.

[0157] It is preferable to use a highly purified electrolyte with a small content of granular waste or elements other than the constituent elements of the electrolyte (hereinafter, simply referred to as "impurities"). Specifically, it is preferable to set the weight ratio of impurities to the electrolyte to 1% or less, preferably 0.1% or less, and more preferably 0.01% or less.

[0158] Alternatively, a polymer gel electrolyte may be used in which a polymer is swollen with an electrolytic solution.

[0159] By using a polymer gel electrolyte, safety against leakage etc. is improved, and the secondary battery can be made thinner and lighter.

[0160] Examples of the polymer to be gelled include silicon gel, acrylic gel, acrylonitrile gel, polyethylene oxide gel, polypropylene oxide gel, and fluorine-based polymer gel. For example, polymers having a polyalkylene oxide structure such as polyethylene oxide (PEO), PVDF, and polyacrylonitrile, and copolymers containing these can be used. For example, PVDF-HFP, which is a copolymer of PVDF and hexafluoropropylene (HFP), can be used. The polymer to be formed may also have a porous shape.

[0161] In addition, as the electrolyte, a solid electrolyte containing an inorganic material such as a sulfide or oxide, or a solid electrolyte containing a polymer material such as a PEO (polyethylene oxide) can be used. When a solid electrolyte is used, the installation of a separator or spacer becomes unnecessary. In addition, since the entire battery can be solidified, there is no risk of leakage, and safety is dramatically improved.

[0162] [Separator] The separator may be made of, for example, fibers containing cellulose such as paper, nonwoven fabric, glass fiber, ceramics, or synthetic fibers using nylon (polyamide), vinylon (polyvinyl alcohol fiber), polypropylene (referred to as PP), polyimide (referred to as PI), polyester, acrylic, polyolefin, or polyurethane. The porosity of the thickness of the separator may be 35% or more and 90% or less, preferably 60% or more and 85% or less. The porosity of the separator using polypropylene may be 35% or more and 45% or less. The porosity of the separator using polyimide may be 75% or more and 85% or less. The thickness of the separator is preferably 10 μm or more and 80 μm or less, more preferably 20 μm or more and 60 μm or less. The separator using polyimide can have a high porosity and can be made thick (typically, the thickness is 50 μm or more and 60 μm or less).

[0163] The separator is preferably processed into a bag shape and disposed so as to encase either the positive electrode or the negative electrode.

[0164] The separator may have a multi-layer structure. For example, an organic material film such as polypropylene or polyethylene may be coated with a ceramic material, a fluorine material, a polyamide material, or a mixture of these. As the ceramic material, for example, aluminum oxide particles or silicon oxide particles may be used. As the fluorine material, for example, PVDF or polytetrafluoroethylene may be used. As the polyamide material, for example, nylon or aramid (meta-aramid or para-aramid) may be used.

[0165] By using a separator with a multi-layer structure, the safety of the secondary battery can be maintained even if the overall thickness of the separator is thin, and therefore the capacity per volume of the secondary battery can be increased.

[0166] [Exterior body] The exterior body of the secondary battery can be made of a metal material such as aluminum or a resin material. A film-shaped exterior body can also be used. As the film, a three-layer structure film can be used in which a thin metal film having excellent flexibility such as aluminum, stainless steel, copper, nickel, etc. is provided on a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, polyamide, etc., and an insulating synthetic resin film such as a polyamide-based resin or polyester-based resin is further provided on the thin metal film as the outer surface of the exterior body.

[0167] This embodiment mode can be used in combination with other embodiment modes.

[0168] (Embodiment 3) In this embodiment, an electrolyte solution required for realizing a secondary battery having excellent discharge characteristics even in a low-temperature environment will be described.

[0169] A low-temperature environment typically refers to a temperature below freezing. In charging in a low-temperature environment, the energy barrier when lithium ions are desorbed from the positive electrode active material tends to be high. In other words, the lower the temperature of the charging environment, the higher the overvoltage required to desorb lithium ions from the positive electrode active material. In other words, the positive electrode active material may be exposed to a high voltage (high potential relative to the lithium potential) during charging in a low-temperature environment. In other words, if the positive electrode active material is not exposed to a high voltage during charging in a low-temperature environment, the charging capacity may be reduced.

[0170] Therefore, it is preferable to use a positive electrode active material that can withstand high voltage and obtain a high charge capacity during charging in a low-temperature environment as a positive electrode active material for a secondary battery having excellent charge and discharge characteristics even in a low-temperature environment.

[0171] In addition, it is preferable that the electrolyte of a secondary battery having excellent charging and discharging characteristics even in a low-temperature environment uses a material that has excellent lithium ion conductivity even when charging and / or discharging (charging and discharging) in a low-temperature environment.

[0172] An electrolyte solution that is preferable for a lithium ion secondary battery having excellent charge and discharge characteristics even in a low temperature environment will be described in detail below.

[0173] <Electrolyte suitable for low temperature environments 1> The mixed organic solvent used in the electrolyte can be a material that has excellent lithium ion conductivity even when charging and / or discharging (charging and discharging) in a low temperature environment (e.g., 0°C, -20°C, preferably -30°C, more preferably -40°C).

[0174] The mixed organic solvent may contain two or more selected from fluorinated cyclic carbonates (sometimes referred to as fluorinated cyclic carbonates) and fluorinated chain carbonates (sometimes referred to as fluorinated chain carbonates).

[0175] As the fluorinated cyclic carbonate, fluoroethylene carbonate (fluoroethylene carbonate, FEC, F1EC), difluoroethylene carbonate (DFEC, F2EC), trifluoroethylene carbonate (F3EC), tetrafluoroethylene carbonate (F4EC), etc. can be used. DFEC has isomers such as cis-4,5 and trans-4,5. Since all of the fluorinated cyclic carbonates have a substituent that exhibits electron-withdrawing properties, it is considered that the solvation energy of lithium ions is low.

[0176] The following structural formula (H10) is the structural formula of FEC, in which the electron-withdrawing substituent is an F group.

[0177] [ka]

[0178] Methyl 3,3,3-trifluoropropionate is an example of a fluorinated chain carbonate. The following structural formula (H22) is the structural formula of methyl 3,3,3-trifluoropropionate. The abbreviation for methyl 3,3,3-trifluoropropionate is "MTFP." In MTFP, the electron-withdrawing substituent is CF 3 It is based on

[0179] [ka]

[0180] An example of a fluorinated chain carbonate is trifluoromethyl 3,3,3-trifluoropropionate. The following structural formula (H23) is the structural formula of trifluoromethyl 3,3,3-trifluoropropionate. The electron-withdrawing substituent is CF 3 It is based on

[0181] [ka]

[0182] As a fluorinated chain carbonate, there is trifluoromethyl propionate. The following structural formula (H24) is the structural formula of trifluoromethyl propionate. The electron-withdrawing substituent is CF 3 group.

[0183]

Chemical formula

[0184] As a fluorinated chain carbonate, there is methyl 2,2-difluoropropionate. The following structural formula (H25) is the structural formula of methyl 2,2-difluoropropionate. The electron-withdrawing substituent is CF 2 group.

[0185]

Chemical formula

[0186] <FEC and MTFP> The mixed organic solvent described in this embodiment preferably contains FEC and MTFP. The reason will be explained.

[0187] FEC is a cyclic carbonate and has a high relative dielectric constant, so when used in an organic solvent, it has the effect of promoting the dissociation of lithium salts. On the other hand, FEC has a substituent that exhibits electron-withdrawing properties, so it is easier to desolvate with lithium ions than ethylene carbonate (EC). Specifically, the solvation energy of lithium ions in FEC is smaller than that of EC that does not have a substituent that exhibits electron-withdrawing properties. Therefore, it is easier to separate lithium ions on the surface of the positive electrode active material and the surface of the negative electrode active material, and the internal resistance of the secondary battery can be reduced. Furthermore, since FEC has a deep highest occupied molecular orbital (HOMO: Highest Occupied Molecular Orbital) level, it is less likely to be oxidized and its oxidation resistance is improved. On the other hand, there is a concern that FEC has a high viscosity. Therefore, it is recommended to use a mixed organic solvent containing not only FEC but also MTFP in the electrolyte. MTFP is a chain carbonate, and it is possible to have the effect of lowering the viscosity of the electrolyte, or maintaining the viscosity at room temperature (typically 25°C) even at low temperatures (typically 0°C). Furthermore, although MTFP has a smaller solvation energy than methyl propionate (abbreviated as "MP"), which does not have an electron-withdrawing substituent, it may form a solvate with lithium ions when used in an electrolyte.

[0188] The measured values ​​of the HOMO level, solvation energy, and melting point are summarized in the table below.

[0189] [Table 1]

[0190] It is preferable to use FEC and MTFP having such physical properties by mixing them so that the volume ratio is x:100-x (where 5≦x≦30, preferably 10≦x≦20) with the total content of these two mixed organic solvents being 100 vol%. In other words, it is preferable to mix them so that MTFP is greater than FEC in the mixed organic solvent. The above volume ratio may be the volume ratio measured before mixing the mixed organic solvent, and the outside air when mixing the mixed organic solvent may be room temperature (typically 25° C.). A mixed organic solvent in which FEC and MTFP are mixed is preferable because it exhibits a viscosity that allows it to operate as a secondary battery and maintains an appropriate viscosity even in a low-temperature environment.

[0191] Since typical solvents used in secondary batteries freeze at about -20°C, it is difficult to fabricate a secondary battery that can be charged and discharged at -30°C, preferably -40°C. However, the mixed organic solvent described as an example in this embodiment allows the freezing point to be -30°C or lower, preferably -40°C or lower, and a secondary battery that can be charged and discharged even in a low-temperature environment can be realized. As a result, a secondary battery that can be charged and discharged in a wide temperature range including at least a low-temperature environment can be realized.

[0192] Although FEC has been explained above as a representative example, all of the organic compounds mentioned as fluorinated cyclic carbonates have the following characteristics: they have the effect of promoting the dissociation of lithium salts, they have small solvation energies so that the bonds between lithium ions and the solvent are easily separated, and they have high viscosities, making them difficult to use below freezing points when used alone.

[0193] Although MTFP has been described as a representative example above, any of the organic compounds described as fluorinated chain carbonates can be said to have the effect of reducing or maintaining the viscosity of the electrolyte solution, which is one embodiment of the present invention. Therefore, if the mixed organic solvent, which is one embodiment of the present invention, contains a fluorinated cyclic carbonate and a fluorinated chain carbonate, it is possible to provide a lithium ion secondary battery that can be charged and discharged in a low temperature environment.

[0194] <Electrolyte suitable for low temperature environments 2> As a mixed organic solvent used in the electrolyte, it contains ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). When the total content of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate is 100 vol%, the volume ratio of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate is x:y:100 - x - y (where 5 ≤ x ≤ 35 and 0 < y < 65). Such a mixed organic solvent can be used. More specifically, a mixed organic solvent containing EC, EMC, and DMC in a volume ratio of EC:EMC:DMC = 30:35:35 can be used. The above volume ratio may be the volume ratio before mixing the mixed organic solvent, and the outside air temperature when mixing the mixed organic solvent may be room temperature (typically 25°C).

[0195] EC is a cyclic carbonate and has a high relative dielectric constant, so it has the effect of promoting the dissociation of lithium salts. On the other hand, EC has a high viscosity and a high freezing point (melting point) of 38°C. Therefore, when using EC alone as a solvent, it is difficult to use it in a low-temperature environment. Thus, the solvent specifically described as one aspect of the present invention is not EC alone but further contains EMC and DMC. EMC is a chain carbonate and has the effect of lowering the viscosity of the electrolyte, and its freezing point is -54°C. Also, DMC is a chain carbonate and has the effect of lowering the viscosity of the electrolyte, and its freezing point is -43°C. An electrolyte prepared using a mixed organic solvent obtained by mixing EC, EMC, and DMC having such physical properties with the total content of these three mixed organic solvents being 100 vol% and the volume ratio being x:y:100 - x - y (where 5 ≤ x ≤ 35 and 0 < y < 65) has the characteristic that its freezing point is -40°C or lower.

[0196] A typical electrolyte used in a secondary battery solidifies at a temperature of at least -20° C., making it difficult to fabricate a battery that can be charged and discharged at -40° C. The electrolyte described as an example in this embodiment has a freezing point of -40° C. or lower, making it possible to realize a secondary battery that can be charged and discharged even in an extremely low temperature environment of -40° C.

[0197] The lithium salt to be dissolved in the solvent may be, for example, LiPF 6 , LiClO 4 , LiAsF 6 , LiBF 4 , LiAlCl 4 , LiSCN, LiBr, LiI, Li 2 SO 4 , Li 2 B 10 Cl 10 , Li 2 B 12 Cl 12 , LiCF 3 SO 3 , LiC 4 F 9 SO 3 , LiC(CF 3 SO 2 ) 3 , LiC(C 2 F 5 SO 2 ) 3 , LiN(CF 3 SO 2 ) 2 , LiN(C 4 F 9 SO 2 )(CF 3 SO 2 ), LiN(C 2 F 5 SO 2 ) 2At least one lithium salt selected from the group consisting of lithium bis(oxalate)borate (LiBOB) and lithium bis(oxalate)borate (LiBOB) can be used in any combination and ratio. The lithium salt dissolved in the solvent is preferably 0.5 mol / L or more and 1.5 mol / L or less, more preferably 0.7 mol / L or more and 1.3 mol / L or less, and even more preferably 0.8 mol / L or more and 1.2 mol / L or less, relative to the volume of the solvent. As a specific example of use, LiPF 6 is preferably 0.5 mol / L or more and 1.5 mol / L or less, more preferably 0.7 mol / L or more and 1.3 mol / L or less, and even more preferably 0.8 mol / L or more and 1.2 mol / L or less.

[0198] In addition, the mixed organic solvent is preferably highly purified with a low content of granular dust or elements other than the constituent elements of the electrolyte (hereinafter, simply referred to as "impurities"). Specifically, the weight ratio of impurities to the electrolyte is preferably 1% or less, more preferably 0.1% or less, and even more preferably 0.01% or less.

[0199] Furthermore, for the purpose of improving safety, etc., an additive such as vinylene carbonate (VC), propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), lithium bis(oxalate)borate (LiBOB), or a dinitrile compound such as succinonitrile or adiponitrile may be added to the electrolyte in order to form a coating (Solid Electrolyte Interphase Film) at the interface between the electrode (active material layer) and the electrolyte. The concentration of the additive is preferably, for example, 0.1 wt% to 5 wt% relative to the solvent.

[0200] In the electrolyte example 2, the lithium salt may be the same as that described in the electrolyte example 1. Also, as for the additive, the materials described in the electrolyte example 1 may be used.

[0201] As described above, examples of the electrolyte solution that can be used in the secondary battery of one embodiment of the present invention have been described, but the electrolyte solution that can be used in the secondary battery of one embodiment of the present invention is not limited to this example. Other materials can also be used as long as they have excellent lithium ion conductivity even in charge and discharge in a low-temperature environment.

[0202] The content of this embodiment mode can be appropriately combined with the content of other embodiment modes.

[0203] (Embodiment 4) In this embodiment, an example of a secondary battery will be described.

[0204] [Coin-type secondary battery] An example of a coin-type secondary battery will be described. Fig. 7(A) is an exploded perspective view of a coin-type (single-layer flat) secondary battery, Fig. 7(B) is an external view, and Fig. 7(C) is a cross-sectional view thereof. Coin-type secondary batteries are mainly used in small electronic devices. In this specification and the like, coin-type secondary batteries include button-type secondary batteries.

[0205] In order to make it easier to understand, Fig. 7(A) is a schematic diagram showing the overlapping of components (upper and lower relationships and positional relationships). Therefore, Fig. 7(A) and Fig. 7(B) are not completely corresponding views.

[0206] 7(A) shows a state in which the positive electrode 304, the negative electrode 307, the spacer 342, and the washer 332 are overlapped and sealed with the negative electrode can 302 and the positive electrode can 301. Note that the electrolyte and the separator described in the above embodiment are not shown in FIG. 7(A). The spacer 342 and the washer 332 are used to protect the inside or to fix the position inside the can when the positive electrode can 301 and the negative electrode can 302 are crimped together. The spacer 342 or the washer 332 is made of stainless steel or an insulating material.

[0207] A laminated structure in which a positive electrode active material layer 306 is formed on a positive electrode current collector 305 is used as a positive electrode 304 .

[0208] FIG. 7B is a perspective view of the completed coin-type secondary battery 300.

[0209] In the coin-type secondary battery 300, a positive electrode can 301 also serving as a positive electrode terminal and a negative electrode can 302 also serving as a negative electrode terminal may be insulated and sealed with a gasket 303 made of polypropylene or the like. The positive electrode 304 is formed of a positive electrode current collector 305 and a positive electrode active material layer 306 provided in contact with the positive electrode current collector. The negative electrode 307 is formed of a negative electrode current collector 308 and a negative electrode active material layer 309 provided in contact with the negative electrode current collector. The positive electrode can 301 is electrically connected to the positive electrode 304, and the negative electrode can 302 is electrically connected to the negative electrode 307.

[0210] In addition, the positive electrode 304 and the negative electrode 307 used in the coin-type secondary battery 300 may each have an active material layer formed on only one side.

[0211] As shown in FIG. 7(C), positive electrode can 301 is placed at the bottom, and positive electrode 304, negative electrode 307, and negative electrode can 302 are stacked in this order, and positive electrode can 301 and negative electrode can 302 are crimped together via gasket 303 to produce coin-type secondary battery 300.

[0212] By using the secondary battery of the present invention for the coin-type secondary battery 300, it is possible to obtain a highly reliable secondary battery. Furthermore, by using the secondary battery of the present invention for the coin-type secondary battery 300, it is possible to obtain a secondary battery that exhibits good low-temperature characteristics.

[0213] [Cylindrical secondary battery] An example of a cylindrical secondary battery will be described with reference to Fig. 8(A). As shown in Fig. 8(A), a cylindrical secondary battery 616 has a positive electrode cap (battery lid) 601 on the top surface, and a battery can (external can) 602 on the side and bottom surfaces. The positive electrode cap 601 and the battery can (external can) 602 are insulated by a gasket (insulating packing) 610.

[0214] Fig. 8(B) is a schematic diagram showing a cross section of a cylindrical secondary battery. The cylindrical secondary battery shown in Fig. 8(B) has a positive electrode cap (battery lid) 601 on the top surface, and a battery can (external can) 602 on the side and bottom surfaces. The positive electrode cap and the battery can (external can) 602 are insulated by a gasket (insulating packing) 610.

[0215] A battery element is provided inside a hollow cylindrical battery can 602, in which a strip-shaped positive electrode 604 and a negative electrode 606 are wound with an electrolyte layer 605 sandwiched therebetween. Although not shown, the battery element is wound around a central axis. One end of the battery can 602 is closed and the other end is open. Inside the battery can 602, the battery element in which the positive electrode, the negative electrode, and the separator are wound is sandwiched between a pair of opposing insulating plates 608 and 609. An electrolyte (not shown) according to one embodiment of the present invention is injected into the inside of the battery can 602 in which the battery element is provided.

[0216] Since the positive and negative electrodes used in a cylindrical storage battery are wound, it is preferable to form active materials on both sides of the current collector. Although the secondary battery 616 in which the height of the cylinder is greater than the diameter of the cylinder is illustrated in Figures 8(A) to 8(D), this is not limited thereto. A secondary battery in which the diameter of the cylinder is greater than the height of the cylinder may also be used. With such a configuration, for example, the secondary battery can be made smaller.

[0217] A positive electrode terminal (positive electrode current collector lead) 603 is connected to the positive electrode 604, and a negative electrode terminal (negative electrode current collector lead) 607 is connected to the negative electrode 606. The positive electrode terminal 603 can be made of a metal material such as aluminum. The negative electrode terminal 607 can be made of a metal material such as copper. The positive electrode terminal 603 is resistance-welded to a safety valve mechanism 613, and the negative electrode terminal 607 is resistance-welded to the bottom of the battery can 602. The safety valve mechanism 613 is electrically connected to the positive electrode cap 601 via a PTC (Positive Temperature Coefficient) element 611. The safety valve mechanism 613 cuts off the electrical connection between the positive electrode cap 601 and the positive electrode 604 when the increase in the internal pressure of the battery exceeds a predetermined threshold value. The PTC element 611 is a thermosensitive element whose resistance increases when the temperature increases, and the increase in resistance limits the amount of current to prevent abnormal heat generation. The PTC element is made of barium titanate (BaTiO 3 )-based ceramic materials, etc. can be used.

[0218] 8C shows an example of a power storage system 615. The power storage system 615 has a plurality of secondary batteries 616 and may be called a battery pack. A positive electrode of each secondary battery is in contact with and electrically connected to a conductor 624 separated by an insulator 625. The conductor 624 is electrically connected to a control circuit 620 via a wiring 623. In addition, a negative electrode of each secondary battery is electrically connected to the control circuit 620 via a wiring 626. A protection circuit that prevents overcharging or overdischarging, or the like, can be used as the control circuit 620.

[0219] 8(D) shows an example of a power storage system 615. The power storage system 615 has a plurality of secondary batteries 616, and the plurality of secondary batteries 616 are sandwiched between a conductive plate 628 and a conductive plate 614. The plurality of secondary batteries 616 are electrically connected to the conductive plate 628 and the conductive plate 614 by wiring 627. The plurality of secondary batteries 616 may be connected in parallel, may be connected in series, or may be connected in parallel and then further connected in series. By configuring the power storage system 615 having the plurality of secondary batteries 616, it is possible to extract a large amount of power.

[0220] A plurality of secondary batteries 616 may be connected in parallel and then further connected in series.

[0221] A temperature control device may be provided between the multiple secondary batteries 616. When the secondary batteries 616 are overheated, they can be cooled by the temperature control device, and when the secondary batteries 616 are too cold, they can be heated by the temperature control device. This makes the performance of the power storage system 615 less susceptible to the effect of the outside air temperature.

[0222] 8(D), the power storage system 615 is electrically connected to a control circuit 620 via wiring 621 and wiring 622. The wiring 621 is electrically connected to the positive electrodes of the multiple secondary batteries 616 via a conductive plate 628, and the wiring 622 is electrically connected to the negative electrodes of the multiple secondary batteries 616 via a conductive plate 614.

[0223] By using the secondary battery of the present invention for the cylindrical secondary battery 616, a highly reliable secondary battery can be obtained. Furthermore, by using the secondary battery of the present invention for the cylindrical secondary battery 616, a secondary battery exhibiting good low-temperature characteristics can be obtained.

[0224] [Other examples of secondary battery structures] An example of the structure of the secondary battery will be described with reference to FIGS.

[0225] A secondary battery 913 shown in FIG. 9A has a wound body 950 in which terminals 951 and 952 are provided inside a housing 930. The wound body 950 is impregnated with an electrolyte according to one embodiment of the present invention inside the housing 930. The terminal 952 contacts the housing 930, and the terminal 951 does not contact the housing 930 by using an insulating material or the like. Note that in FIG. 9A, the housing 930 is shown separated for convenience, but in reality, the wound body 950 is covered by the housing 930, and the terminals 951 and 952 extend outside the housing 930. The housing 930 can be made of a metal material (e.g., aluminum) or a laminate of a metal material and a resin material.

[0226] Note that, as shown in Fig. 9(B), the housing 930 shown in Fig. 9(A) may be formed using a plurality of materials. For example, a secondary battery 913 shown in Fig. 9(B) has a housing 930a and a housing 930b bonded together, and a wound body 950 is provided in a region surrounded by the housing 930a and the housing 930b.

[0227] The housing 930a may be made of a laminate of a metal material and a resin material. In particular, by forming an organic resin, which is a resin material, on the surface on which the antenna is formed, the electric field due to the secondary battery 913 can be suppressed. Note that if the electric field is not significantly blocked by the housing 930a, the antenna may be provided inside the housing 930a. The housing 930b may be made of, for example, a metal material or a laminate of a metal material and a resin material.

[0228] 9(C) shows the structure of the wound body 950. The wound body 950 has a negative electrode 931, a positive electrode 932, and an electrolyte layer 933. The wound body 950 is a wound body in which the negative electrode 931 and the positive electrode 932 are stacked on top of each other with the electrolyte layer 933 sandwiched therebetween, and the laminated sheet is wound. Note that the stack of the negative electrode 931, the positive electrode 932, and the electrolyte layer 933 may be stacked a plurality of times.

[0229] 10(A) to 10(C) may be used as a secondary battery 913 having a wound body 950a. The wound body 950a shown in Fig. 10(A) includes a negative electrode 931, a positive electrode 932, and an electrolyte layer 933. The negative electrode 931 includes a negative electrode active material layer 931a. The positive electrode 932 includes a positive electrode active material layer 932a.

[0230] The electrolyte layer 933 has a width wider than the negative electrode active material layer 931a and the positive electrode active material layer 932a, and is wound so as to overlap the negative electrode active material layer 931a and the positive electrode active material layer 932a. From the viewpoint of safety, it is preferable that the width of the negative electrode active material layer 931a is wider than that of the positive electrode active material layer 932a. Moreover, a wound body 950a having such a shape is preferable because of its high safety and productivity.

[0231] 10B, the negative electrode 931 is electrically connected to a terminal 951. The terminal 951 is electrically connected to a terminal 911a. The positive electrode 932 is electrically connected to a terminal 952. The terminal 952 is electrically connected to a terminal 911b.

[0232] 10C, the wound body 950a is covered with the housing 930 to form the secondary battery 913. It is preferable to provide a safety valve, an overcurrent protection element, and the like in the housing 930. The safety valve is a valve that opens when the inside of the housing 930 reaches a predetermined internal pressure, and can prevent the secondary battery 913 from bursting.

[0233] As shown in Fig. 10(B), the secondary battery 913 may have a plurality of wound bodies 950a. By using a plurality of wound bodies 950a, the secondary battery 913 can have a larger charge / discharge capacity. For other elements of the secondary battery 913 shown in Figs. 10(A) and (B), the description of the secondary battery 913 shown in Figs. 9(A) to 9(C) can be referred to.

[0234] By using the secondary battery of the present invention for the secondary battery 913 having a wound body, a highly reliable secondary battery can be obtained. Furthermore, by using the secondary battery of the present invention for the secondary battery 913 having a wound body, a secondary battery exhibiting good low-temperature characteristics can be obtained.

[0235] The content of this embodiment mode can be appropriately combined with the content of the other embodiment modes.

[0236] (Embodiment 5) In this embodiment, an example of application to an electric vehicle (EV) will be described with reference to FIG.

[0237] As shown in Fig. 11(A), an electric vehicle is equipped with first batteries 1301a and 1301b as main driving secondary batteries, and a second battery 1311 that supplies power to an inverter 1312 that starts a motor 1304. By using the secondary battery of the present invention for the first batteries 1301a and 1301b, it is possible to obtain a highly reliable secondary battery. Furthermore, by using the secondary battery of the present invention for the above-mentioned first batteries 1301a and 1301b, it is possible to obtain a secondary battery that exhibits good low-temperature characteristics.

[0238] The second battery 1311 is also called a cranking battery (also called a starter battery). The second battery 1311 only needs to have high output, and does not need to have a large capacity. The capacity of the second battery 1311 is smaller than that of the first batteries 1301a and 1301b.

[0239] The internal structure of the first battery 1301a may be a wound type or a laminated type. The first battery 1301a may use the all-solid-state battery of embodiment 6. By using the all-solid-state battery of embodiment 6 for the first battery 1301a, it is possible to achieve a high capacity, improve safety, and reduce the size and weight.

[0240] In this embodiment, an example is shown in which two first batteries 1301a and 1301b are connected in parallel, but three or more batteries may be connected in parallel. Also, if the first battery 1301a can store sufficient power, the first battery 1301b may not be necessary. By configuring a battery pack having multiple secondary batteries, it is possible to extract large power. The multiple secondary batteries may be connected in parallel, in series, or in series after being connected in parallel. A plurality of secondary batteries is also called a battery pack.

[0241] In addition, in a secondary battery for vehicle use, in order to cut off power from a plurality of secondary batteries, a service plug or circuit breaker capable of cutting off high voltage without using tools is provided in the first battery 1301a.

[0242] The power of the first batteries 1301a and 1301b is mainly used to rotate the motor 1304, but also supplies power to 42V in-vehicle components (such as an electric power steering 1307, a heater 1308, and a defogger 1309) via a DCDC circuit 1306. When a rear motor 1317 is provided for the rear wheels, the first battery 1301a is used to rotate the rear motor 1317.

[0243] In addition, the second battery 1311 supplies power to 14V in-vehicle components (such as an audio system 1313, a power window 1314, and lamps 1315) via the DCDC circuit 1310.

[0244] The first battery 1301a will be described with reference to FIG.

[0245] FIG. 11B shows an example in which nine rectangular secondary batteries 1300 are used as one battery pack 1415. Nine rectangular secondary batteries 1300 are connected in series, one electrode is fixed by a fixing part 1413 made of an insulator, and the other electrode is fixed by a fixing part 1414 made of an insulator. In this embodiment, an example in which the batteries are fixed by the fixing parts 1413 and 1414 is shown, but the batteries may be stored in a battery storage box (also called a housing). Since it is assumed that the vehicle is subjected to vibration or shaking from the outside (such as a road surface), it is preferable to fix a plurality of secondary batteries by the fixing parts 1413 and 1414 and the battery storage box. One electrode is electrically connected to the control circuit part 1320 by a wiring 1421. The other electrode is electrically connected to the control circuit part 1320 by a wiring 1422.

[0246] A memory circuit including a transistor using an oxide semiconductor may be used for the control circuit unit 1320. A charge control circuit or a battery control system having a memory circuit including a transistor using an oxide semiconductor may be referred to as a Battery operating system (BTOS) or a Battery oxide semiconductor.

[0247] It is preferable to use a metal oxide that functions as an oxide semiconductor. For example, a metal oxide such as In-M-Zn oxide (wherein element M is one or more selected from aluminum, gallium, yttrium, copper, vanadium, beryllium, boron, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, and magnesium) may be used as the oxide. In particular, the In-M-Zn oxide that can be used as the oxide is preferably CAAC-OS (C-Axis Aligned Crystal Oxide Semiconductor) or CAC-OS (Cloud-Aligned Composite Oxide Semiconductor). In-Ga oxide or In-Zn oxide may be used as the oxide. CAAC-OS is an oxide semiconductor that has a plurality of crystal regions, and the plurality of crystal regions have c-axes oriented in a specific direction. The specific direction is the thickness direction of the CAAC-OS film, the normal direction of the surface on which the CAAC-OS film is formed, or the normal direction of the surface of the CAAC-OS film. The crystalline region is a region in which the atomic arrangement has periodicity. If the atomic arrangement is regarded as a lattice arrangement, the crystalline region is also a region in which the lattice arrangement is uniform. Furthermore, the CAAC-OS has a region in which a plurality of crystalline regions are connected in the ab-plane direction, and the region may have distortion. Note that the distortion refers to a portion in which the direction of the lattice arrangement changes between a region in which the lattice arrangement is uniform and another region in which the lattice arrangement is uniform in a region in which a plurality of crystalline regions are connected. In other words, the CAAC-OS is an oxide semiconductor that is c-axis oriented and does not have a clear orientation in the ab-plane direction.

[0248] In addition, since the control circuit unit 1320 can be used in a low-temperature environment, it is preferable that the control circuit unit 1320 uses a transistor using an oxide semiconductor. In order to simplify the process, the control circuit unit 1320 may be formed using a unipolar transistor. The operating ambient temperature of a transistor using an oxide semiconductor is wider than that of a single-crystal Si transistor, that is, from -40°C to 150°C, and the characteristic change is smaller than that of a single-crystal Si transistor even when the secondary battery is heated. The off-current of a transistor using an oxide semiconductor is extremely low regardless of temperature even at 150°C, but the off-current characteristic of a single-crystal Si transistor is highly temperature-dependent. For example, at 150°C, the off-current of a single-crystal Si transistor increases, and the current on / off ratio does not become sufficiently large. The control circuit unit 1320 can improve safety.

[0249] The control circuit unit 1320 using a memory circuit including a transistor using an oxide semiconductor can also function as an automatic control device for a secondary battery against ten causes of instability such as micro-short circuit. Functions for eliminating the ten causes of instability include overcharging prevention, overcurrent prevention, overheating control during charging, cell balancing in a battery pack, over-discharging prevention, a remaining capacity meter, automatic control of charging voltage and current amount according to temperature, control of charging current amount according to deterioration degree, detection of abnormal behavior of micro-short circuit, and prediction of abnormality related to micro-short circuit, and the control circuit unit 1320 has at least one of these functions. In addition, the automatic control device for a secondary battery can be made ultra-compact.

[0250] A micro-short circuit is a type of internal short circuit, and refers to a very small short circuit inside a secondary battery. One of the causes of a micro-short circuit is said to be localized current concentration in a part of the positive electrode and a part of the negative electrode due to uneven distribution of the positive electrode active material caused by multiple charge and discharge cycles, or the generation of by-products due to side reactions, which causes a micro-short circuit.

[0251] In addition to detecting micro-shorts, the control circuit 1320 can also be said to detect the terminal voltage of the secondary battery and manage the charge / discharge state of the secondary battery. For example, to prevent overcharging, it can turn off both the output transistor and the cutoff switch of the charging circuit almost simultaneously.

[0252] FIG. 11C shows an example of a block diagram of the battery pack 1415 shown in FIG.

[0253] The control circuit unit 1320 has at least a switch unit 1324 including a switch for preventing overcharging and a switch for preventing overdischarging, a control circuit 1322 for controlling the switch unit 1324, and a voltage measurement unit for the first battery 1301a. The control circuit unit 1320 is set with an upper limit voltage and a lower limit voltage for the secondary battery to be used, and limits the upper limit of the current from the outside and the upper limit of the output current to the outside. The range between the lower limit voltage and the upper limit voltage of the secondary battery is within the voltage range recommended for use, and when it is outside this range, the switch unit 1324 operates and functions as a protection circuit. In addition, the control circuit unit 1320 can also be called a protection circuit because it controls the switch unit 1324 to prevent overcharging and overdischarging. For example, when the control circuit 1322 detects a voltage that is likely to cause overcharging, the switch unit 1324 is turned off to cut off the current. Furthermore, a PTC element may be provided in the charge / discharge path to provide a function of cutting off the current in response to an increase in temperature. In addition, the control circuit section 1320 has an external terminal 1325 (+IN) and an external terminal 1326 (-IN).

[0254] The switch unit 1324 can be configured by combining n-channel transistors and p-channel transistors. The switch unit 1324 is not limited to a switch having a Si transistor using single crystal silicon, and may be, for example, Ge (germanium), SiGe (silicon germanium), GaAs (gallium arsenide), GaAlAs (gallium aluminum arsenide), InP (indium phosphide), SiC (silicon carbide), ZnSe (zinc selenide), GaN (gallium nitride), GaO xThe switch unit 1324 may be formed of a power transistor having an OS transistor (gallium oxide; x is a real number greater than 0). Memory elements using OS transistors can be freely arranged by stacking them on a circuit using Si transistors, and therefore integration can be easily achieved. A control circuit unit 1320 using an OS transistor can be stacked on the switch unit 1324 and integrated into a single chip, enabling miniaturization.

[0255] The first batteries 1301a and 1301b mainly supply power to 42V (high voltage) in-vehicle devices, and the second battery 1311 supplies power to 14V (low voltage) in-vehicle devices. Lead-acid batteries are often used as the second battery 1311 because they are cost-effective. The advantage of using the second battery 1311 as a secondary battery is that it is maintenance-free, but after a long period of use, for example, more than three years, there is a risk of abnormalities occurring that cannot be identified at the time of manufacture. In particular, if the second battery 1311 that starts the inverter becomes inoperable, the motor may not be able to start even if the first batteries 1301a and 1301b have remaining capacity. If the second battery 1311 is a lead-acid battery, the first battery supplies power to the second battery, and the battery is charged to always maintain a fully charged state, so the motor will not be unable to operate as described above.

[0256] In this embodiment, an example in which secondary batteries are used for both the first battery 1301a and the second battery 1311 is shown, but the second battery 1311 may be a lead storage battery, an all-solid-state battery, or an electric double layer capacitor. By using the secondary battery of the present invention as the above-mentioned secondary battery, a highly reliable secondary battery can be obtained. Furthermore, by using the secondary battery of the present invention as the above-mentioned secondary battery, a secondary battery exhibiting good low-temperature characteristics can be obtained.

[0257] Moreover, regenerative energy due to the rotation of the tire 1316 is sent to the motor 1304 via the gear 1305, and is charged into the second battery 1311 from the motor controller 1303 and the battery controller 1302 via the control circuit unit 1321. Alternatively, the first battery 1301a is charged from the battery controller 1302 via the control circuit unit 1320. Alternatively, the first battery 1301b is charged from the battery controller 1302 via the control circuit unit 1320. In order to efficiently charge the regenerative energy, it is desirable that the first batteries 1301a and 1301b are capable of being quickly charged.

[0258] The battery controller 1302 can set the charging voltage and charging current of the first batteries 1301a and 1301b. The battery controller 1302 can set charging conditions in accordance with the charging characteristics of the secondary battery used, and can perform rapid charging.

[0259] Although not shown, when connecting to an external charger, the charger outlet or the connection cable of the charger is electrically connected to the battery controller 1302. The power supplied from the external charger is charged to the first batteries 1301a and 1301b via the battery controller 1302. Some chargers are provided with a control circuit and may not use the function of the battery controller 1302, but it is preferable to charge the first batteries 1301a and 1301b via the control circuit unit 1320 to prevent overcharging. In some cases, the connection cable or the connection cable of the charger is provided with a control circuit. The control circuit unit 1320 is also called an ECU (Electronic Control Unit). The ECU is connected to a CAN (Controller Area Network) provided in the electric vehicle. The CAN is one of the serial communication standards used as an in-vehicle LAN. The ECU includes a microcomputer. The ECU uses a CPU or a GPU.

[0260] External chargers installed at charging stations and the like come in a variety of types, including 100V outlets, 200V outlets, and three-phase 200V and 50kW outlets. In addition, charging can also be achieved by receiving power from external charging equipment using a contactless power supply system or the like.

[0261] Next, an example in which the secondary battery according to one embodiment of the present invention is mounted on a vehicle, typically a transportation vehicle, will be described.

[0262] Furthermore, by installing secondary batteries in vehicles, next-generation clean energy automobiles such as hybrid vehicles (HVs), electric vehicles (EVs), plug-in hybrid vehicles (PHVs), etc. Secondary batteries can also be installed in transportation vehicles such as agricultural machinery, motorized bicycles including electrically assisted bicycles, motorcycles, electric wheelchairs, electric carts, small or large ships, submarines, aircraft such as fixed-wing aircraft and rotary-wing aircraft, rockets, artificial satellites, space probes, planetary probes, and spacecraft.

[0263] 12A to 12D show an example of a transportation vehicle using one embodiment of the present invention. An automobile 2001 shown in FIG. 12A is an electric automobile that uses an electric motor as a power source for running. Or, it is a hybrid automobile that can appropriately select and use an electric motor and an engine as a power source for running. When a secondary battery is mounted on a vehicle, an example of the secondary battery described in the above embodiment is installed in one or more locations. By using the secondary battery of the present invention as the secondary battery mounted on the vehicle, the secondary battery can have high reliability. Furthermore, by using the secondary battery of the present invention as the above-mentioned secondary battery, the secondary battery can have good low-temperature characteristics.

[0264] 12A includes a battery pack 2200, which includes a battery module to which a plurality of secondary batteries are connected. The battery pack 2200 preferably further includes a charge control device electrically connected to the battery module.

[0265] Moreover, the automobile 2001 can charge the secondary battery of the automobile 2001 by receiving power supply from an external charging facility by a plug-in method, a contactless power supply method, or the like. Charging can be performed appropriately using a predetermined method such as CHAdeMO (registered trademark) or a combo as the charging method and connector standard. The charging facility may be a charging station provided in a commercial facility, or a home power source. For example, a power storage device mounted on the automobile 2001 can be charged by an external power supply using plug-in technology. Charging can be performed by converting AC power to DC power via a conversion device such as an ACDC converter.

[0266] Although not shown, a power receiving device may be mounted on a vehicle, and charging may be performed by supplying power contactlessly from a ground power transmitting device. In the case of this contactless power supply method, by incorporating a power transmitting device in a road or an exterior wall, charging may be performed not only while the vehicle is stopped but also while it is moving. This contactless power supply method may also be used to transmit and receive power between two vehicles. Furthermore, a solar cell may be provided on the exterior of the vehicle, and a secondary battery may be charged while the vehicle is stopped and while it is moving. An electromagnetic induction method or a magnetic resonance method may be used for such contactless power supply.

[0267] FIG. 12(B) shows a large transport vehicle 2002 having an electrically controlled motor as an example of a transport vehicle. The battery module of the transport vehicle 2002 is, for example, a four-cell unit of secondary batteries with a nominal voltage of 3.0 V to 5.0 V, with 48 cells connected in series to achieve a maximum voltage of 170 V. Other than the number of secondary batteries in the battery pack 2201, the battery pack 2202 has the same functions as those in FIG. 11(B), and therefore a description thereof will be omitted. By using the secondary battery of the present invention as the secondary battery of the battery pack 2201, a highly reliable secondary battery can be obtained. Furthermore, by using the secondary battery of the present invention as the secondary battery of the above-mentioned battery pack 2201, a secondary battery exhibiting good low-temperature characteristics can be obtained.

[0268] FIG. 12(C) shows, as an example, a large transport vehicle 2003 having an electrically controlled motor. The battery module of the transport vehicle 2003 has, for example, a maximum voltage of 600V, in which more than 100 secondary batteries with a nominal voltage of 3.0V to 5.0V are connected in series. In addition, except for the number of secondary batteries constituting the battery module of the battery pack 2202, the battery module has the same functions as those of FIG. 11(B), so a description thereof will be omitted. By using the secondary battery of the present invention as the secondary battery of the module, a highly reliable secondary battery can be obtained. Furthermore, by using the secondary battery of the present invention as the secondary battery of the above-mentioned module, a secondary battery exhibiting good low-temperature characteristics can be obtained.

[0269] Fig. 12(D) shows, as an example, an aircraft 2004 having an engine that burns fuel. The aircraft 2004 shown in Fig. 12(D) has wheels for takeoff and landing, and therefore can be said to be a part of a transportation vehicle, and has a battery pack 2203 including a battery module formed by connecting multiple secondary batteries and including a battery module and a charge control device.

[0270] The battery module of the aircraft 2004 has, for example, eight 4 V secondary batteries connected in series to produce a maximum voltage of 32 V. Other than the number of secondary batteries constituting the battery module of the battery pack 2203, it has the same functions as those in FIG. 11(B), and therefore a description thereof will be omitted.

[0271] The content of this embodiment mode can be appropriately combined with the content of the other embodiment modes.

[0272] (Embodiment 6) In this embodiment, an example will be described in which a secondary battery according to one embodiment of the present invention is mounted on a vehicle such as a motorcycle or a bicycle.

[0273] 13A is an example of an electric bicycle using a secondary battery of one embodiment of the present invention. The secondary battery of one embodiment of the present invention can be applied to an electric bicycle 8700 shown in FIG 13A. The secondary battery of one embodiment of the present invention may include a protection circuit.

[0274] The electric bicycle 8700 includes a power storage device 8702. The power storage device 8702 can supply electricity to a motor that assists a rider. The power storage device 8702 is portable, and is shown in a state removed from the bicycle in FIG. 13B. The power storage device 8702 includes a plurality of secondary batteries 8701 of one embodiment of the present invention, and the remaining battery charge and the like can be displayed on a display unit 8703. By using the secondary battery of the present invention for the secondary battery 8701, the secondary battery can have high reliability. Furthermore, by using the secondary battery of the present invention for the secondary battery 8701, the secondary battery can have good low-temperature characteristics.

[0275] The power storage device 8702 also includes a control circuit 8704 capable of controlling charging or detecting an abnormality of the secondary battery. The control circuit 8704 is electrically connected to the positive and negative electrodes of the secondary battery 8701. This can greatly contribute to preventing accidents such as fires caused by secondary batteries.

[0276] 13C is an example of a two-wheeled vehicle using a secondary battery of one embodiment of the present invention. A scooter 8600 shown in FIG. 13C includes a power storage device 8602, a side mirror 8601, and a turn signal light 8603. The power storage device 8602 can supply electricity to the turn signal light 8603. By using the secondary battery of the present invention as the secondary battery, the secondary battery can have high reliability. Furthermore, by using the secondary battery of the present invention as the secondary battery, the secondary battery can have good low-temperature characteristics.

[0277] 13C, a power storage device 8602 can be stored in an under-seat storage compartment 8604. The power storage device 8602 can be stored in the under-seat storage compartment 8604 even if the under-seat storage compartment 8604 is small in size.

[0278] The content of this embodiment mode can be appropriately combined with the content of other embodiment modes.

[0279] (Embodiment 7) In this embodiment, an example of mounting a secondary battery according to one embodiment of the present invention in an electronic device will be described. Examples of electronic devices mounting a secondary battery include television devices (also called televisions or television receivers), monitors for computers, digital cameras, digital video cameras, digital photo frames, mobile phones (also called mobile phones or mobile phone devices), portable game machines, portable information terminals, audio playback devices, and large game machines such as pachinko machines. Examples of portable information terminals include notebook personal computers, tablet terminals, e-book terminals, and mobile phones.

[0280] 14A shows an example of a mobile phone. The mobile phone 2100 includes a display unit 2102 built into a housing 2101, an operation button 2103, an external connection port 2104, a speaker 2105, a microphone 2106, and the like. The mobile phone 2100 includes a secondary battery 2107. By using the secondary battery of the present invention as the secondary battery, a highly reliable secondary battery can be obtained. Furthermore, by using the secondary battery of the present invention as the secondary battery, a secondary battery exhibiting good low-temperature characteristics can be obtained.

[0281] The mobile phone 2100 is capable of executing a variety of applications, such as mobile phone calls, e-mail, document browsing and creation, music playback, Internet communications, and computer games.

[0282] The operation button 2103 can have various functions, such as time setting, power on / off operation, wireless communication on / off operation, silent mode activation / cancellation, power saving mode activation / cancellation, etc. For example, the function of the operation button 2103 can be freely set by an operating system built into the mobile phone 2100.

[0283] The mobile phone 2100 is also capable of performing short-range wireless communication according to a communication standard. For example, the mobile phone 2100 can communicate with a wireless headset to enable hands-free calling.

[0284] The mobile phone 2100 also includes an external connection port 2104, and can directly exchange data with other information terminals via a connector. Charging can also be performed via the external connection port 2104. Note that charging may be performed by wireless power supply without using the external connection port 2104.

[0285] It is preferable that the mobile phone 2100 has a sensor. For example, it is preferable that a fingerprint sensor, a pulse sensor, a human body sensor such as a body temperature sensor, a touch sensor, a pressure sensor, an acceleration sensor, or the like is mounted as the sensor.

[0286] FIG. 14B shows an unmanned aerial vehicle 2300 having a plurality of rotors 2302. The unmanned aerial vehicle 2300 is sometimes called a drone. The unmanned aerial vehicle 2300 includes a secondary battery 2301 which is one embodiment of the present invention, a camera 2303, and an antenna (not shown). The unmanned aerial vehicle 2300 can be remotely controlled via the antenna. By using the secondary battery of the present invention as the secondary battery, a highly reliable secondary battery can be obtained. Furthermore, by using the secondary battery of the present invention as the secondary battery, a secondary battery exhibiting good low-temperature characteristics can be obtained.

[0287] Fig. 14C shows an example of a robot. The robot 6400 shown in Fig. 14C includes a secondary battery 6409, an illuminance sensor 6401, a microphone 6402, an upper camera 6403, a speaker 6404, a display unit 6405, a lower camera 6406, an obstacle sensor 6407, a moving mechanism 6408, a computing device, and the like.

[0288] The microphone 6402 has a function of detecting the user's voice, environmental sounds, etc. The speaker 6404 has a function of emitting sound. The robot 6400 can communicate with the user using the microphone 6402 and the speaker 6404.

[0289] The display unit 6405 has a function of displaying various information. The robot 6400 can display information desired by the user on the display unit 6405. The display unit 6405 may be equipped with a touch panel. The display unit 6405 may be a removable information terminal, and by installing it at a fixed position on the robot 6400, charging and data transfer are possible.

[0290] The upper camera 6403 and the lower camera 6406 have a function of capturing images of the surroundings of the robot 6400. In addition, the obstacle sensor 6407 can detect the presence or absence of an obstacle in the moving direction when the robot 6400 moves forward using the moving mechanism 6408. The robot 6400 can recognize the surrounding environment and move safely using the upper camera 6403, the lower camera 6406, and the obstacle sensor 6407.

[0291] The robot 6400 includes a secondary battery 6409 according to one embodiment of the present invention and a semiconductor device or electronic component in its internal area. By using the secondary battery of the present invention as the secondary battery, the secondary battery can have high reliability. Furthermore, by using the secondary battery of the present invention as the secondary battery, the secondary battery can have good low-temperature characteristics.

[0292] 14(D) shows an example of a cleaning robot. The cleaning robot 6300 has a display unit 6302 arranged on the top surface of a housing 6301, a plurality of cameras 6303 arranged on the side surface, a brush 6304, an operation button 6305, a secondary battery 6306, various sensors, and the like. Although not shown, the cleaning robot 6300 is provided with tires, a suction port, and the like. The cleaning robot 6300 can move by itself, detect dust 6310, and suck up the dust from a suction port arranged on the bottom surface.

[0293] For example, the cleaning robot 6300 can analyze an image captured by the camera 6303 and determine the presence or absence of an obstacle such as a wall, furniture, or a step. When an object that may become entangled in the brush 6304, such as a wire, is detected by image analysis, the rotation of the brush 6304 can be stopped. The cleaning robot 6300 includes a secondary battery 6306 according to one embodiment of the present invention and a semiconductor device or electronic component in its internal area. By using the secondary battery of the present invention as the secondary battery, a highly reliable secondary battery can be obtained. Furthermore, by using the secondary battery of the present invention as the secondary battery, a secondary battery exhibiting good low-temperature characteristics can be obtained.

[0294] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0295] (Embodiment 8) In this embodiment, an example in which a secondary battery which is one embodiment of the present invention is mounted in space equipment will be described.

[0296] 15A shows an artificial satellite 6800 as an example of space equipment. The artificial satellite 6800 has a body 6801, a solar panel 6802, an antenna 6803, and a secondary battery 6805. The solar panel may be called a solar cell module.

[0297] When sunlight is irradiated onto the solar panel 6802, power required for the operation of the artificial satellite 6800 is generated. However, for example, in a situation where the solar panel is not irradiated with sunlight or in a situation where the amount of sunlight irradiated onto the solar panel is small, the generated power is small. Therefore, there is a possibility that the power required for the operation of the artificial satellite 6800 is not generated. In order to operate the artificial satellite 6800 even under a situation where the generated power is small, it is preferable to provide a secondary battery 6805 in the artificial satellite 6800. By using the secondary battery of the present invention as the secondary battery, it is possible to obtain a secondary battery with high reliability. Furthermore, by using the secondary battery of the present invention as the secondary battery, it is possible to obtain a secondary battery that exhibits good low-temperature characteristics.

[0298] The artificial satellite 6800 can generate a signal. The signal is transmitted via an antenna 6803, and can be received by, for example, a receiver installed on the ground or another artificial satellite. By receiving the signal transmitted by the artificial satellite 6800, for example, the position of the receiver that received the signal can be measured. As described above, the artificial satellite 6800 can constitute, for example, a satellite positioning system.

[0299] Alternatively, the artificial satellite 6800 may be configured to have a sensor. For example, by configuring the artificial satellite 6800 to have a visible light sensor, the artificial satellite 6800 may have a function of detecting sunlight reflected by an object on the ground. Alternatively, by configuring the artificial satellite 6800 to have a thermal infrared sensor, the artificial satellite 6800 may have a function of detecting thermal infrared rays emitted from the earth's surface. As described above, the artificial satellite 6800 may have a function as, for example, an earth observation satellite.

[0300] FIG. 15(B) shows a probe 6900 having a solar sail (also called a sun sail) as an example of space equipment. The probe 6900 has a body 6901, a solar sail 6902, and a secondary battery 6905. By using the secondary battery of the present invention as the secondary battery, it is possible to obtain a highly reliable secondary battery. Furthermore, by using the secondary battery of the present invention as the secondary battery, it is possible to obtain a secondary battery that exhibits good low-temperature characteristics. When photons emitted from the sun hit the surface of the solar sail 6902, momentum is transferred to the solar sail 6902. Therefore, it is preferable that the surface of the solar sail 6902 has a thin film with high reflectivity, and further preferably faces the sun.

[0301] The solar sail 6902 may also be designed to be folded up small until it leaves the atmosphere, and then deployed into a large sheet outside the Earth's atmosphere (in outer space) as shown in Figure 15(B).

[0302] FIG. 15(C) shows a spacecraft 6910 as an example of space equipment. The spacecraft 6910 has an aircraft 6911, a solar panel 6912, and a secondary battery 6913. By using the secondary battery of the present invention as the secondary battery, a highly reliable secondary battery can be obtained. Furthermore, by using the secondary battery of the present invention as the secondary battery, a secondary battery exhibiting good low-temperature characteristics can be obtained. The aircraft 6911 can have, for example, a pressurized compartment and a non-pressurized compartment. The pressurized compartment may be designed to accommodate a crew member. Electricity generated by irradiating the solar panel 6912 with sunlight can be charged into the secondary battery 6913.

[0303] 15D shows a rover 6920 as an example of space equipment. The rover 6920 has a body 6921 and a secondary battery 6923. By using the secondary battery of the present invention as the secondary battery, the secondary battery can have high reliability. Furthermore, by using the secondary battery of the present invention as the secondary battery, the secondary battery can have good low-temperature characteristics. The rover 6920 may have a solar panel 6922.

[0304] The exploration vehicle 6920 may be designed to accommodate a crew member. The secondary battery 6923 may be charged with electricity generated by irradiating the solar panel 6912 with sunlight, or may be charged with electricity generated by other power sources, such as a fuel cell, a radioisotope thermoelectric converter, or the like.

[0305] The content of this embodiment mode can be appropriately combined with the content of other embodiment modes. [Explanation of symbols]

[0306] 100 Secondary battery 103 Positive electrode 103a first positive electrode 103b Second positive electrode 103t protrusion 105 Separator 105a first separator 105b Second separator 105c Third separator 105d Fourth separator 106 negative electrode 106a first negative electrode 106b second negative electrode 106c Third negative electrode 106t protrusion 107a Positive lead 107b Negative lead 108 Electrolyte 109a Joint 109b Joint 110 Negative electrode current collector 111 Negative electrode active material layer 115 Carbon Sheet 115a first carbon sheet 115b Second carbon sheet 115c 3rd carbon sheet 115d 4th carbon sheet 116 areas 117 void 118 Dendrite 118b Dendrite 118c Dendrite 118d Dendrite 118e Dendrite 119 Arrow 120 Negative electrode structure 300 Coin-type secondary battery 301 Positive electrode can 302 Anode can 303 Gasket 304 Positive electrode 305 Positive electrode current collector 306 Positive electrode active material layer 307 Negative electrode 308 Negative electrode current collector 309 Negative electrode active material layer 332 Washer 342 Spacer 504 Slurry 505 Slurry thickness measurement sensor 521 Back Roll 522 Coating roll 523 Dam Bottom 524 Microbar 525 Die 550 Positive electrode current collector 553 Carbon Black 554 Graphene 555 Carbon Fiber 561 Cathode active material 562 Second positive electrode active material 601 Positive electrode cap 602 Battery Can 603 Positive terminal 604 Positive electrode 605 Electrolyte layer 606 negative electrode 607 Negative terminal 608 Insulating plate 609 Insulating plate 611 PTC element 613 Safety valve mechanism 614 Conductive plate 615 Energy Storage System 616 Secondary battery 620 Control circuit 621 Wiring 622 Wiring 623 Wiring 624 Conductors 625 Insulators 626 Wiring 627 Wiring 628 Conductive plate 911a Terminal 911b Terminal 913 Secondary battery 930 Case 930a Case 930b Case 931 negative electrode 931a Negative electrode active material layer 932 Positive electrode 932a Cathode active material layer 933 Electrolyte layer 950 Wound body 950a Wound body 951 Terminal 952 Terminal 1300 Square rechargeable battery 1301a First Battery 1301b 1st Battery 1302 Battery Controller 1303 Motor Controller 1304 Motor 1305 Gear 1306 DC-DC circuit 1307 Electric power steering 1308 Heater 1309 Defogger 1310 DC-DC circuit 1311 Second Battery 1312 Inverter 1313 Audio 1314 Power window 1315 Lamps 1316 Tires 1317 Rear motor 1320 Control circuit section 1321 Control circuit section 1322 Control circuit 1324 Switch section 1413 Fixed part 1414 Fixed part 1415 Battery Pack 1421 Wiring 1422 Wiring 2001 Automobiles 2002 Transport vehicle 2003 Transport Vehicles 2004 aircraft 2100 Mobile phone 2101 Case 2102 Display section 2103 Operation button 2104 External connection port 2105 Speaker 2106 Mike 2107 Secondary battery 2200 Battery Pack 2201 Battery Pack 2202 Battery Pack 2203 Battery Pack 2300 Unmanned Aircraft 2301 Secondary battery 2302 Rotor 2303 Camera 6300 Cleaning robot 6301 Case 6302 Display section 6303 Camera 6304 Brush 6305 Operation button 6306 Secondary battery 6310 Garbage 6400 Robot 6401 Light Sensor 6402 Microphone 6403 Upper Camera 6404 Speaker 6405 Display section 6406 Lower Camera 6407 Obstacle Sensor 6408 Moving mechanism 6409 Secondary battery 6800 satellite 6801 Aircraft 6802 Solar Panel 6803 Antenna 6805 Secondary battery 6900 Probe 6901 Aircraft 6902 Solar Sail 6905 Secondary battery 6910 Spaceship 6911 Aircraft 6912 Solar Panel 6913 Secondary battery 6920 Rover 6921 Aircraft 6922 Solar Panel 6923 Secondary battery 8600 Scooter 8601 Side mirror 8602 Energy storage devices 8603 Turn signal light 8604 Under-seat storage 8700 Electric Bike 8701 Secondary battery 8702 Energy storage devices 8703 Display section 8704 Control circuit

Claims

1. A negative electrode active material layer; A separator; a carbon sheet disposed between the negative electrode active material layer and the separator; dendrites between the negative electrode active material layer and the carbon sheet; A secondary battery having a positive electrode active material layer, The negative electrode active material layer has a negative electrode active material, The negative electrode active material includes at least one selected from graphite and silicon, The thickness of the carbon sheet is 25 nm or more and 50 μm or less, The dendrite has a portion along a surface of the carbon sheet. Secondary battery.

2. The method according to claim 1, further comprising the steps of: The secondary battery, wherein the electrolyte contains FEC and MTFP.

3. The method according to claim 1, further comprising the steps of: The secondary battery, wherein the electrolyte contains ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate.

4. A negative electrode active material layer; A separator; a carbon sheet disposed between the negative electrode active material layer and the separator; dendrites between the negative electrode active material layer and the carbon sheet; A secondary battery having a positive electrode active material layer, The negative electrode active material layer has a negative electrode active material, The negative electrode active material comprises lithium metal, The thickness of the carbon sheet is 25 nm or more and 50 μm or less, The dendrite has a portion along a surface of the carbon sheet. Secondary battery.

5. The method according to claim 4, further comprising the steps of: The secondary battery, wherein the electrolyte contains ethylene carbonate and diethyl carbonate.

6. In claim 1 or claim 4, The carbon sheet comprises carbon nanotubes.

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