Secondary battery

Abstract

Provided is a secondary battery in which internal short-circuits caused by dendrites are suppressed. The 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, dendrites between the negative electrode active material layer and the carbon sheet, and a positive electrode active material layer, the negative electrode active material layer including a negative electrode active material including at least one selected from the group consisting of graphite and silicon, the carbon sheet has a thickness of 25 nm or more and 50 [mu] m or less, and the dendrites have a portion along the surface of the carbon sheet. The carbon sheet includes carbon nanotubes.

Description

Technical Field

[0001] The present invention relates to a secondary battery. In addition, the present invention is not limited to the above field, and sometimes relates to a semiconductor device, a display device, a light-emitting device, a power storage device, a lighting device, an electronic device, a vehicle, and a method for manufacturing them. For example, the secondary battery of the present invention can be used as a required power source for a semiconductor device, a display device, a light-emitting device, a power storage device, a lighting device, an electronic device, and a vehicle. The above-mentioned electronic devices include an information terminal device equipped with a secondary battery, etc. And, the above-mentioned power storage device includes a stationary power storage device, etc. Background Art

[0002] In recent years, with the development of the semiconductor industry, the demand for high-output and high-capacity lithium-ion secondary batteries has increased dramatically, and as an energy supply source that can be charged, it has become a necessity in modern information society.

[0003] The lithium-ion secondary battery has the following problems: When charging and discharging are repeated, lithium dendrites precipitate on the negative electrode. Lithium dendrites are dendritic crystals of lithium metal that grow during the charging and discharging process. For example, they precipitate when the current concentrates on uneven parts of the negative electrode surface. When the lithium dendrites reach the positive electrode, sometimes internal short circuits occur in the lithium-ion secondary battery, resulting in a decrease in the reliability of the lithium-ion secondary battery.

[0004] In many cases, graphite is used as the negative electrode material. In addition, by using lithium metal instead of graphite, high-capacity lithium-ion secondary batteries are expected. In the case of using graphite, lithium dendrites are likely to precipitate when charging and discharging at low temperatures, while in the case of using lithium metal, lithium dendrites precipitate even when charging and discharging 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).

[0006] [Patent Document 1] Japanese PCT Patent Application Publication No. 2015-145288 Summary of the Invention

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

[0008] Note that the description of these objects does not prevent the existence of other objects. One aspect of the present invention does not need to solve all of the above objects. In addition, objects other than the above can be extracted from the descriptions in the present specification, drawings, claims, etc.

[0009] In view of the above problems, the present inventors have discovered a new structure to control the growth direction of dendrites precipitated in 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 precipitated and the separator. By adopting this structure, internal short circuits of the secondary battery can be suppressed, and thus the reliability of the secondary battery is improved.

[0010] One aspect of the present invention is a secondary battery including 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, and a positive electrode active material layer. The negative electrode active material layer contains a negative electrode active material, the negative electrode active material contains one or more selected from graphite and silicon, the thickness of the carbon sheet is 25 nm or more and 50 μm or less, and the dendrites have a portion along the surface of the carbon sheet.

[0011] In the present invention, preferably, the secondary battery further includes an electrolytic solution containing FEC and MTFP.

[0012] In the present invention, preferably, the secondary battery further includes an electrolytic solution containing ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate.

[0013] Another aspect of the present invention is a secondary battery including 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, and a positive electrode active material layer. The negative electrode active material layer contains a negative electrode active material, the negative electrode active material contains lithium metal, the thickness of the carbon sheet is 25 nm or more and 50 μm or less, and the dendrites have a portion along the surface of the carbon sheet.

[0014] In the present invention, preferably, the secondary battery further includes an electrolytic solution containing ethylene carbonate and diethyl carbonate.

[0015] In the present invention, the carbon sheet preferably contains carbon nanotubes.

[0016] According to one aspect of the present invention, a secondary battery with high reliability in which internal short circuits are suppressed can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1A and Figure 1B is a diagram illustrating a laminated secondary battery according to one aspect of the present invention, Figure 1C is a diagram illustrating the flow of electrons and the flow of lithium ions during charging of the secondary battery; Figure 2A is a diagram illustrating a negative electrode structure body and a separator according to one aspect of the present invention, Figures 2B to 2E is a diagram showing the growth direction of dendrites in an enlarged view of the negative electrode structure body; Figures 3A to 3F It is a diagram showing the growth direction of dendrites in an enlarged view of a negative electrode structure showing one aspect of the present invention; Figure 4 It is a diagram explaining a method for manufacturing a negative electrode structure showing one aspect of the present invention; Figure 5A and Figure 5B It is a diagram explaining a coating device for a negative electrode; Figures 6A to 6D It is a diagram explaining a positive electrode showing one aspect of the present invention; Figures 7A to 7C It is a diagram explaining a secondary battery showing one aspect of the present invention; Figures 8A to 8D It is a diagram explaining a secondary battery and a power storage system showing one aspect of the present invention; Figures 9A to 9C It is a diagram explaining a secondary battery showing one aspect of the present invention; Figures 10A to 10C It is a diagram explaining a secondary battery showing one aspect of the present invention; Figures 11A to 11C It is a diagram explaining an electric vehicle showing one aspect of the present invention; Figures 12A to 12D It is a diagram explaining a transportation vehicle showing one aspect of the present invention; Figures 13A to 13C It is a diagram explaining a two-wheeled vehicle or the like showing one aspect of the present invention; Figures 14A to 14D It is a diagram explaining an electronic device or the like showing one aspect of the present invention; Figures 15A to 15D It is a diagram showing an example of a space device. Detailed Embodiments

[0018] This embodiment will be described with appropriate reference to the accompanying drawings. Note that the present invention is not limited to the following description. It is easily understood by those skilled in the art that the modes and details of the present invention can be changed in various ways without departing from the spirit and scope of the present invention. Therefore, in the embodiments shown below, the reference numerals indicating the same components of the present invention are common to different drawings.

[0019] In this specification and the like, a full cell refers to a battery unit assembled in a manner including different electrodes, such as a unit cell of a positive electrode / negative electrode. In this specification and the like, a half cell refers to a battery unit assembled using lithium metal as the negative electrode (counter electrode).

[0020] In this specification and the like, the loading amount refers to the weight of the active material per unit area of the surface of the current collector. The loading amount of the negative electrode active material can be adjusted according to the capacity of the positive electrode. In double-sided coating in which a slurry containing an active material is coated on both surfaces of the current collector, the weight of one surface is regarded as the above-mentioned loading amount.

[0021] In this specification and the like, the slurry refers to a material liquid used to form an active material layer on a current collector, which contains an active material, a binder, and a solvent, and preferably also contains a conductive material mixed therein. Note that the slurry is sometimes also referred to as an electrode slurry or an active material slurry. The slurry used to form a positive electrode active material layer is sometimes referred to as a positive electrode slurry, and the slurry used to form a negative electrode active material layer is sometimes referred to as a negative electrode slurry.

[0022] In this specification and the like, the median diameter (D50) refers to the particle diameter at which the cumulative amount accounts for 50% on the cumulative curve of the particle size distribution measurement result. In addition, there is a method of measuring the median diameter (D50) using image analysis such as SEM or TEM. For example, more than 20 particles can be measured to form a cumulative particle amount curve, and the particle diameter at which the cumulative amount accounts for 50% is set as the median diameter (D50).

[0023] In this specification and the like, a lithium ion secondary battery is sometimes referred to as a lithium ion battery and refers to a battery that uses lithium ions as carrier ions. However, the carrier ions of the present invention are not limited to lithium ions. For example, alkali metal ions or alkaline earth metal ions can be used as the carrier ions of the present invention. Specifically, sodium ions and the like can be used. At this time, lithium ions can be referred to as sodium ions, etc. to understand the present invention. In addition, when there is no restriction on the carrier ions, it is sometimes denoted as a secondary battery.

[0024] In this specification and the like, dendrites include dendritic crystals of a metal that grow during charge and discharge, and the dendrites contain precipitates of the metal. During charge and discharge, sometimes a region with a large thickness or a high density is formed in the dendrites. The shapes of multiple dendrites can also be different from each other, and sometimes one of the multiple dendrites has a larger thickness or a higher density than another one of the multiple dendrites. Adjacent dendrites sometimes wind around each other and aggregate.

[0025] In this specification and the like, carbonate refers to a compound that contains at least one ester in its molecular structure. Without special instructions, it includes cyclic carbonates and chain carbonates. In the scope of the chain, it includes linear and branched chain forms.

[0026] In this specification and the like, the low-temperature environment refers to below 0°C, and sometimes below 0°C is denoted as sub-zero.

[0027] In this specification and the like, without special instructions, the charging voltage is expressed based on the potential of lithium metal. In this specification and the like, a high charging voltage is, for example, a charging voltage of 4.6V or more, preferably 4.65V or more, more preferably 4.7V or more, further preferably 4.75V or more, and most preferably 4.8V or more.

[0028] In this specification and the like, it is sometimes described as "including A and / or B", which means including A, including B, or including both A and B.

[0029] Embodiment 1 A secondary battery or the like according to one embodiment of the present invention will be described.

[0030] <Secondary battery> Refer to Figure 1A and Figure 1B A secondary battery according to one embodiment of the present invention will be described.

[0031] Figure 1A The laminated secondary battery 100 is shown, and in this drawing, each component is shown separately for easy understanding. The secondary battery 100 includes a plurality of positive electrodes. As the plurality of positive electrodes, the first positive electrode 103a and the second positive electrode 103b are shown. Note that in the secondary battery 100, the number of positive electrodes is not limited and may be one. The first positive electrode 103a and the second positive electrode 103b are collectively referred to as the positive electrode 103.

[0032] The secondary battery 100 includes a plurality of negative electrodes. As the plurality of negative electrodes, the first negative electrode 106a, the second negative electrode 106b, and the third negative electrode 106c are shown. Note that in the secondary battery 100, the number of negative electrodes is not limited and may be one. 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 includes a separator between the negative electrode and the positive electrode. For easy understanding, the separator is shown by a dashed line in Figure 1A In this drawing, the first separator 105a, the second separator 105b, the third separator 105c, and the fourth separator 105d are shown as the separator. Note that in the secondary battery 100, the number of separators is not limited and may be one. In addition, although the separators can be independent as shown in the drawing, a single continuous separator may also be used. By folding a single continuous separator, the separator can be disposed at positions corresponding to the first separator 105a to the fourth separator 105d.

[0034] The secondary battery 100 includes a first carbon sheet 115a between the first negative electrode 106a and the first separator 105a. Additionally, a second carbon sheet 115b is included between the second separator 105b and the second negative electrode 106b. Further, a third carbon sheet 115c is included between the second negative electrode 106b and the third separator 105c. Moreover, a fourth carbon sheet 115d is included 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. By using the carbon sheet 115, an internal short circuit of the secondary battery 100 can be suppressed, thereby improving the reliability of the secondary battery 100.

[0035] Figure 1B The state in which the components of the secondary battery 100 overlap each other is shown. The first positive electrode 103a and the second positive electrode 103b both include a positive electrode current collector, and a protruding portion 103t is included in each positive electrode current collector. The protruding portions 103t of the respective positive electrode current collectors overlap to form an aggregate. The aggregate of the protruding portions 103t is referred to as a positive electrode tab. The first negative electrode 106a, the second negative electrode 106b, and the third negative electrode 106c all include a negative electrode current collector, and a protruding portion 106t is included in each negative electrode current collector. The protruding portions 106t of the respective negative electrode current collectors overlap to form an aggregate. The aggregate of the protruding portions 106t is referred to as a negative electrode tab.

[0036] The positive electrode further includes a positive electrode active material layer. The positive electrode active material layer is a layer containing positive electrode active material particles and has a region in contact with the positive electrode current collector. In the manufacturing process of the positive electrode, there is a pressing process, and in the positive electrode after this pressing process, sometimes a concave portion is formed in which the positive electrode active material particles are pressed into a part of the positive electrode current collector. The positive electrode active material layer is preferably formed on both surfaces of the positive electrode current collector. This structure is referred to as a double-sided coating structure. The positive electrode active material layer may also be formed on one surface of the positive electrode current collector. This structure is referred to as a single-sided coating structure.

[0037] The negative electrode further includes a negative electrode active material layer. The negative electrode active material layer is a layer containing negative electrode active material particles and has a region in contact with the negative electrode current collector. In the manufacturing process of the negative electrode, there is a pressing process. In the negative electrode after this pressing process, sometimes a concave portion is formed in which the negative electrode active material particles are pressed into a part of the negative electrode current collector. The negative electrode active material layer can adopt a double-sided coating structure formed on both surfaces of the negative electrode current collector. However, the negative electrode disposed on the outermost layer preferably adopts a single-sided coating structure in which the negative electrode active material layer is formed only on one surface of the negative electrode current collector. In the negative electrode disposed on the outermost layer, in the negative electrode active material layer disposed so as not to face the positive electrode, the insertion and extraction of carrier ions do not occur or are not easily performed, so this negative electrode active material layer may not be formed. Since the productivity is high when all negative electrodes have a double-sided coating structure, it is preferable, and therefore a negative electrode with a double-sided coating structure may also be disposed in the outermost layer.

[0038] In addition, when the secondary battery 100 is bent and used, it is preferable to prepare a negative electrode with a single-sided coating structure. A structure in which a plurality of negative electrodes with a single-sided coating structure are stacked in such a way that the negative electrode current collectors are in contact with each other is called a back-to-back structure. By adopting the back-to-back structure, the negative electrode current collectors with low contact resistance are in contact with each other, so it is easy to bend the secondary battery 100.

[0039] As Figure 1B shown, 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 (protrusion 103t) is joined to the positive electrode lead 107a at the joining portion 109a. In the laminated electrode, the negative electrode tab (protrusion 106t) is joined to the negative electrode lead 107b at the joining portion 109b. In the joining, ultrasonic welding can be used. By joining, they are electrically connected to each other. The positive electrode lead 107a can use a material selected from aluminum, nickel, titanium, and their alloys. The negative electrode lead 107b can use a material selected from nickel, copper, titanium, and their alloys.

[0040] Moreover, the secondary battery 100 includes an outer packaging body (not shown), Figure 1B and the laminated electrode shown is accommodated in the outer packaging body. From the viewpoint of weight reduction, it is preferable to use a film as the outer packaging body. A secondary battery using a film as the outer packaging body is called a laminated secondary battery. Although not shown in this embodiment, a can case can also be used for the outer packaging body, and a secondary battery when using a circular can case is called a coin-type secondary battery.

[0041] Here, with reference to Figure 1C the flow of electrons and the flow of lithium ions (Li in the drawing + ) during charging of the secondary battery 100 will be described. Figure 1CThe two terminals shown are connected to a charger to charge the secondary battery 100. During charging, the positive electrode 103 releases electrons and undergoes an oxidation reaction. At this time, lithium ions (Li + ) in the positive electrode dissociate into the electrolyte 108. Additionally, during charging, electrons are supplied to the negative electrode 106, causing a reduction reaction. At this time, the lithium ions in the electrolyte 108 move to the negative electrode 106. When graphite is used as the negative electrode active material, the moved lithium is intercalated between the graphite layers. The potential of the negative electrode in the state where lithium is intercalated between the graphite layers is approximately equal to the potential when lithium metal is used as the negative electrode active material. Additionally, when silicon or its alloy is used as the negative electrode active material, its potential is also approximately equal to the potential when lithium metal is used as the negative electrode active material. When charging at a high rate or at a low temperature in this potential state, lithium metal precipitates. Note that when the secondary battery 100 is regarded as a closed circuit, current flows in the same direction as the migration direction of the lithium ions. Although not shown, during discharging, the negative electrode 106 releases electrons and lithium metal dissolves in the electrolyte 108. When charging and discharging are repeated, precipitation and dissolution of lithium metal repeatedly occur in the negative electrode. When this phenomenon repeatedly occurs, sometimes the surface of the negative electrode 106 becomes uneven due to the attachment of electrolyte decomposition products or defects in the electron conduction path, etc., and the lithium metal becomes dendrites, resulting in the growth of the dendrites progressing.

[0042] Note that in a secondary battery, since the anode and cathode, and the oxidation reaction and reduction reaction are switched according to discharging or charging, the electrode with a higher reaction potential is called the positive electrode, and the electrode with a lower reaction potential is called the negative electrode. Thus, in this specification, etc., even during charging and discharging, the positive electrode is called the "positive electrode" or the "+ electrode", and the negative electrode is called the "negative electrode" or the "- electrode".

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

[0044] <Structural Example 1> Figure 2A The negative electrode 106, carbon sheet 115, and separator 105 included in the secondary battery 100 are shown. 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 is preferably provided so as to overlap the negative electrode current collector 110 described later, and the carbon sheet 115 preferably exists at a position overlapping the negative electrode tab (protrusion 106t). In the negative electrode tab, the negative electrode current collector 110 and the carbon sheet 115 have the same potential. As 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 dendrites described later, it is important that the carbon sheet 115 overlaps the negative electrode active material layer 111.

[0045] <Negative electrode 106> The negative electrode 106 includes a negative electrode current collector 110 and a negative electrode active material layer 111. The negative electrode active material layer 111 is a layer containing negative electrode active material particles and may also contain a binder. The negative electrode active material layer 111 may also contain a conductive material. Of course, the negative electrode active material layer 111 may not contain a binder and a conductive material. The binder and the conductive material will be described later.

[0046] <Carbon sheet 115> The carbon sheet 115 only needs to contain carbon. For example, it may contain carbon fibers (also called carbon fibers, denoted as CF), and typically preferably contains carbon nanotubes (denoted as carbon nanotube: CNT). CNT refers to a substance composed of carbon. Specifically, it has a structure in which carbon atoms forming a hexagon are arranged in a planar shape and rolled into a cylindrical shape. The diameter of the cylindrical structure can satisfy 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 conductivity like a metal. Therefore, CNT is suitable for the carbon sheet 115, and the carbon sheet including CNT is called a CNT sheet.

[0047] CNT includes single-walled CNT. Single-walled CNT refers to CNT having a single cylindrical structure. Single-walled CNT is easily in a long and highly flexible state. Other CNT includes multi-walled CNT. Multi-walled CNT includes a first cylindrical structure (cylindrical structure) having a first diameter and a second cylindrical structure having a second diameter larger than the first diameter, and the first cylindrical structure is disposed in the second cylindrical structure. Multi-walled CNT may also have three or more cylindrical structures. Multi-walled CNT is easily in a short and hard state. The carbon sheet 115 can use single-walled CNT and / or multi-walled CNT. In addition, the carbon sheet can use a laminate of single-walled CNT and multi-walled CNT.

[0048] In the CNT sheet, the direction of the long axis (long axis direction) of CNT can be made consistent. In other words, in the CNT sheet, the long axes of CNT can be oriented in one direction or substantially one direction. Sometimes a group of CNTs whose long axes are oriented in one direction or substantially one direction is called a CNT bundle. Sometimes a thin sheet having a group of CNTs whose long axes are oriented in one direction or substantially one direction is called a unidirectionally aligned CNT sheet. The unidirectionally aligned CNT sheet has high strength when stretched in the long axis direction and is suitable for the carbon sheet 115.

[0049] In the drawings, the carbon sheet 115 is a single layer, but may also have a structure in which a plurality of carbon sheets are stacked (laminated structure). By adopting the laminated structure, the thickness of the carbon sheet 115 can be appropriately set. When stacking a plurality of CNT sheets, it is preferably stacked in such a way that their major axes cross each other. A plurality of CNT sheets whose major axes cross each other are suitable for the carbon sheet 115. When stacking, the CNTs at the interface can be aggregated by spraying an organic solvent. That is to say, an independent CNT sheet can be formed without using an adhesive.

[0050] The carbon sheet 115 may also have vapor-grown carbon fiber (VGCF: registered trademark). The diameter of the VGCF can be 90 nm or more and 200 nm or less, preferably 90 nm or more and 110 nm or less, and the fiber length can be 7 μm or more and 15 μm or less, so it is suitable for use in the carbon sheet 115.

[0051] The carbon sheet 115 may also contain graphene. A carbon sheet containing graphene is called a graphene sheet. In this specification and the like, graphene refers to a substance containing carbon and having a two-dimensional structure formed by a six-membered ring of carbon atoms, such as a flat plate shape or a sheet shape. Graphene may have defects in a part thereof. At this time, polycyclic rings such as seven-membered rings, eight-membered rings, nine-membered rings, and ten-membered rings are formed in the graphene. In addition, the polycyclic ring refers to a cyclic carbon skeleton in which a part of the carbon bonds of the six-membered ring composed of carbon are cut off and the cut carbon bonds are bonded to each other. The region surrounded by the carbon constituting the polycyclic ring becomes a gap. In this specification and the like, graphene includes multi-layer graphene. Since graphene exhibits excellent electrical properties with high conductivity, it is suitable for use in the carbon sheet 115.

[0052] The carbon sheet 115 may also contain a graphene compound. A carbon sheet containing a graphene compound is called a graphene compound sheet. In this specification and the like, graphene compounds include graphene oxide, multi-layer graphene oxide, reduced graphene oxide, reduced multi-layer graphene oxide, etc. In other words, the graphene compound may also have a functional group. Examples of the functional group include an epoxy group, a carboxyl group, or a hydroxyl group. The graphene compound exhibits excellent electrical properties of high flexibility and high conductivity, and thus is suitable for use in the carbon sheet 115. In addition, the graphene compound has defects or spaces that can allow lithium ions to pass through, so it is suitable for the carbon sheet 115.

[0053] In this specification and the like, reduced graphene oxide contains carbon and oxygen and has a two-dimensional structure formed by a six-membered ring composed of carbon atoms. The reduced graphene oxide preferably has a part with a carbon concentration greater than 80 atomic% and an oxygen concentration of 2 atomic% or more and 15 atomic% or less.

[0054] The carbon sheet 115 may also contain an adhesive to improve the adhesion to the negative electrode 106.

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

[0056] Figure 2B Shows an enlarged view of the region 116 surrounded by a dotted line in Figure 2A . As shown in Figure 2B , unevenness is confirmed on the surface or top surface of the negative electrode active material layer 111. This is the unevenness along the shape of the negative electrode active material particles. In addition, the electrolyte 108 is infiltrated between the carbon sheet 115 and the negative electrode active material layer 111, and regions separated or spaced apart from each other are confirmed. When the charge-discharge cycle test is repeatedly performed on the secondary battery 100, the current sometimes concentrates in the unevenness. At this time, since lithium is unevenly precipitated from the negative electrode active material layer 111, dendrites 118 are likely to be formed. Furthermore, by repeatedly performing the charge-discharge cycle test, the dendrites 118 grow.

[0057] In one aspect of the present invention, since the carbon sheet 115 is arranged as shown in Figure 2B , the dendrites 118 grow along the carbon sheet 115. When the surface of the carbon sheet 115 is confirmed, it can be said that the dendrites 118 have a portion along the surface of the carbon sheet 115. An arrow 119 is attached as an example of the growth direction of such dendrites 118. When the direction passing through the positive electrode and the negative electrode is determined as the normal direction of the secondary battery, the direction of the arrow 119 can be said to be a direction crossing the normal direction. In addition, when the normal direction is "vertical", the direction of the arrow 119 can be said to be "horizontal". The direction of the arrow 119 refers to the direction along the long axis of the CNT in the case where the CNT sheet is used for the carbon sheet 115. The direction of the arrow 119 can also be said to be the direction along the negative electrode. Note that the growth direction of the dendrites 118 may be different for each dendrite. That is, the growth direction of the dendrites 118 only needs to be the same as or substantially the same as the arrow 119, and furthermore, the dendrites 118 do not need to reach the positive electrode.

[0058] The reason for the growth of the dendrite 118 in the above direction can be considered that during the reduction reaction, the dendrite 118 grows while receiving electrons from the carbon sheet 115. Since the carbon sheet 115 has high conductivity, the reaction with the electrolyte 108 becomes active during the reduction reaction. Furthermore, it is preferable to set the carbon sheet 115 to the same potential as the negative electrode 106 during the reduction reaction. That is, in the negative electrode tab, the carbon sheet 115 preferably contacts the negative electrode current collector 110. Then, after the dendrite 118 reaches the carbon sheet 115, it may grow along the carbon sheet 115. As described above, the growth direction of the dendrite 118 varies depending on each dendrite. Due to this phenomenon, the dendrite 118 can be inhibited from reaching the positive electrode. Therefore, by the structure in which the carbon sheet 115 is arranged as shown in Figure 2B , the internal short circuit of the secondary battery 100 can be reduced. Figure 2C The figure showing Figure 2B the shape of the dendrite 118 is needle-shaped.

[0059] <Application Example 1> As Figure 2D shown, the dendrite 118b can also reach inside the carbon sheet 115. In other words, sometimes the dendrite 118b grows in the direction of the arrow 119 within the carbon sheet 115. Due to this phenomenon, the dendrite 118b can be inhibited from reaching the positive electrode. Therefore, by the structure in which the carbon sheet 115 is arranged as shown in Figure 2D , the internal short circuit of the secondary battery 100 can be reduced. Figure 2E The figure showing Figure 2D the shape of the dendrite 118b is needle-shaped.

[0060] <Application Example 2> As Figure 3A shown, when the dendrite 118c does not reach the positive electrode, the carbon sheet 115 can also be cut. The cutting of the carbon sheet 115 refers to the area of the carbon sheet 115 where cutting is confirmed in a top view. In addition, when viewed from the cross section, the cut area of the carbon sheet 115 is confirmed as a void 117. This is a void 117 through which lithium ions can enter and exit. The dendrite 118c can also grow in the direction of the arrow 119 without passing through the void 117. Furthermore, the dendrite 118c can also grow in the direction of the arrow 119 after passing through the void 117. Due to this phenomenon, the dendrite 118c can be inhibited from reaching the positive electrode. Therefore, by the structure in which the carbon sheet 115 is arranged as shown in Figure 3A , the internal short circuit of the secondary battery 100 can be reduced. Figure 3B The figure showing Figure 3A the shape of the dendrite 118c is needle-shaped.

[0061] <Application Example 3> As Figure 3CAs shown, when the dendrite 118d does not reach the positive electrode, it can pass through the carbon sheet 115. At this time, there is no area of the carbon sheet 115 that is cut. Furthermore, the dendrite 118d can also 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 does not pass through the separator 105. Due to this phenomenon, the dendrite 118d can be inhibited from reaching the positive electrode. Therefore, by the structure in which the carbon sheet 115 is arranged as shown in Figure 3C shown, the internal short circuit of the secondary battery 100 can be reduced. Figure 3D shows Figure 3C a diagram of the shape of the dendrite 118d shown in which is needle-like.

[0062] <Application Example 4> As Figure 3E shown, the carbon sheet 115 can also be arranged between the separator 105 and the positive electrode. The dendrite 118e can also pass through the separator 105. Furthermore, the dendrite 118e can also 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 does not pass through the carbon sheet 115. Due to this phenomenon, the dendrite 118e can be inhibited from reaching the positive electrode. Therefore, the internal short circuit of the secondary battery 100 can be reduced. Figure 3F shows Figure 3E a diagram of the shape of the dendrite 118e shown in which is needle-like.

[0063] <Application Example 5> Although not shown, the dendrite 118 can also wind around the carbon sheet 115. In other words, the carbon sheet 115 and the dendrite 118 can become integrated, and the dendrite 118 etc. can also be confirmed inside and outside the carbon sheet 115. Due to this phenomenon, the dendrite 118 can be inhibited from reaching the positive electrode. Therefore, the internal short circuit of the secondary battery 100 is reduced.

[0064] In view of the above Application Example 5, sometimes the growth direction of the dendrite 118 is not necessarily the arrow 119. That is, in one aspect of the present invention, the growth direction of the dendrite 118 is not important as long as the dendrite 118 can be inhibited from reaching the positive electrode by using the carbon sheet 115.

[0065] In Figures 2B to 3F the structure, the thickness of the carbon sheet 115 is 25 nm or more, preferably 25 nm or more and 50 μm or less, 25 nm or more and 10 μm or less, 25 nm or more and 1 μm or less, 25 nm or more and 500 nm or less. In order to satisfy this thickness, the carbon sheets 115 are sometimes laminated. In addition, the thickness of the above-mentioned carbon sheet 115 sometimes satisfies 0.5 times or more and 1.5 times or less of the thickness of the separator.

[0066] By adopting the above structure and the like, dendrites do not reach the positive electrode, and internal short circuits of the secondary battery can be suppressed.

[0067] <Manufacturing Method Example 1> Refer to Figure 4 Describe an example of the manufacturing method of the negative electrode structure 120 described above.

[0068] <Step S10> In Figure 4 In the shown step S10, prepare the negative electrode current collector 110 and the negative electrode active material layer 111.

[0069] <Negative Electrode Current Collector 110> Describe the negative electrode current collector 110. As the negative electrode current collector, highly conductive materials such as metals and their alloys such as copper, stainless steel, gold, platinum, titanium, etc. can be used. In addition, as the negative electrode current collector, aluminum alloys added with heat resistance improving elements such as silicon, titanium, neodymium, scandium, molybdenum, etc. can be used. In addition, metal elements that react with silicon to form silicides can also be used. As the metal elements that react with silicon to form silicides, there are zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, nickel, etc. As the negative electrode current collector, shapes such as foil, plate, sheet, mesh, punched metal mesh, drawn metal mesh, etc. can be appropriately used. The thickness of the negative electrode current collector is preferably 5 μm or more and 30 μm or less.

[0070] <Negative Electrode Active Material> Describe the negative electrode active material contained in the negative electrode active material layer 111. As the negative electrode active material, materials that occlude and release lithium can be used. In addition, as the negative electrode active material, materials that can perform charge and discharge reactions through alloying / dealloying reactions with lithium can be used. As the negative electrode active material, for example, a composite material selected from one or more of lithium metal, carbon, and silicon can be used. Silicon has a high theoretical capacity, that is, the theoretical capacity per active material weight is 4200 mAh / g, so it is preferred. When using lithium metal as the negative electrode active material, the negative electrode current collector can be omitted.

[0071] As carbon, graphite, graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), CNT, graphene, carbon black, etc. can be used. That is, when using multi-layer CNT as the carbon sheet 115 or when using multi-layer graphene as the carbon sheet 115, the carbon sheet 115 can occlude and release lithium.

[0072] When lithium ions are intercalated in graphite (when forming a lithium-graphite intercalation compound), graphite shows a low potential similar to that of lithium metal (0.05 V or more and 0.3 V or less vs. Li / Li +) Thus, the secondary battery can exhibit a high working voltage. Graphite also has the following advantages: a relatively large discharge capacity per unit volume; a relatively small volume expansion; relatively low cost; high safety compared to lithium metal, etc., so it is preferred.

[0073] When the median particle diameter (D50) of the negative electrode active material is small, its thickness becomes large, which sometimes hinders the increase in electrode density. Thus, the median particle diameter (D50) of the negative electrode active material preferably satisfies 3 μm or more and 20 μm or less, more preferably satisfies 7 μm or more and 12 μm or less. Typically, as the negative electrode active material satisfying the above range, graphite can be cited, and the median particle diameter (D50) of the powder characteristics of graphite preferably satisfies the above range.

[0074] As the graphite, artificial graphite or natural graphite, etc. can be cited. As artificial graphite, mesocarbon microbeads (MCMB), coke-based artificial graphite, pitch-based artificial graphite, etc. can be used. Artificial graphite may also include a carbon coating with a low crystal layer. The shape of the artificial graphite is spherical, and this is called spherical graphite. For example, MCMB is one of the materials preferably used as spherical graphite. Furthermore, it is relatively easy to reduce the specific surface area of MCMB. When the specific surface area is large, the decomposition reaction between the surface of the negative electrode active material and the electrolyte sometimes becomes large, and good cycle characteristics cannot be obtained. In order to suppress the above decomposition reaction, the specific surface area of carbon preferably satisfies 0.8 m 2 / g or more and 8 m 2 / g or less, more preferably satisfies 1 m 2 / g or more and 2 m 2 / g or less. Typically, the powder characteristics of spherical graphite preferably have the above specific surface area. 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 the multilayer adsorption of adsorbed gas molecules and is the most commonly used method for calculating the specific surface area. The specific surface area using the BET method can be measured by an automatic specific surface area measuring device TriStar II 3020.

[0075] As the natural graphite, flake graphite or spheroidized natural graphite, etc. can be cited. Natural graphite may also include a carbon coating with a low crystal layer.

[0076] In addition, a silicon-carbon composite material containing carbon and silicon can be used as the negative electrode active material. In the silicon-carbon composite material, carbon and silicon may be a mixture, and it is preferable to confirm the sintering state by heat treatment. Further, in the silicon-carbon composite material, graphite particles are preferably used as the carbon, and the median particle 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, more preferably 7 μm or more and 12 μm or less. The median particle diameter of the graphite particles can be determined according to the median particle diameter (D50) of silicon.

[0077] The specific surface area of the graphite particles is preferably 0.5 m 2 / g or more and 3 m 2 / g or less. The specific surface area can be measured by the BET method. The specific surface area by the BET method is the value measured by the BET single-point method using nitrogen gas adsorption, and an automatic specific surface area / pore size distribution measuring device Tristar II 3020 (manufactured by Micromeritics) can be used as the measuring machine for measurement.

[0078] Further, in the silicon-carbon composite material, silicon particles are preferably used as the silicon. The silicon particles only need to contain a silicon material. Specifically, it preferably contains one selected from silicon, silicon oxide, and silicon alloy. As the silicon oxide, silicon monoxide (SiO) can be cited. In this specification, etc., SiO refers to silicon monoxide, for example. Silicon monoxide can also be expressed as SiO x . x is preferably 0.2 or more and 1.5 or less, more preferably 0.3 or more and 1.2 or less.

[0079] The median particle diameter (D50) of the silicon particles is preferably less than 1 μm, typically 50 nm or more and 800 nm or less, preferably 100 nm or more and 500 nm or less. Sometimes the silicon particles of this size are called nano-silicon particles. Although silicon has problems of expansion and contraction during charge and discharge, the charge and discharge deterioration of the nano-silicon particles miniaturized to the above median particle diameter (D50) is improved, so it is preferable. It is preferable that the median particle diameter (D50) of the silicon particles is made uniform through a pulverization process of the silicon raw material.

[0080] The specific surface area of the silicon particles is preferably 10 m 2 / g or more and 35 m 2 / g or less, more preferably 10 m 2 / g or more and 15 m 2 / g or less. The specific surface area can be measured by the BET method. The specific surface area by the BET method is the value measured by the BET single-point method using nitrogen gas adsorption, and an automatic specific surface area / pore size distribution measuring device Tristar II 3020 (manufactured by Micromeritics) can be used as the measuring machine for measurement.

[0081] By including both graphite particles and silicon particles in the negative electrode active material, a secondary battery with a high discharge capacity can be achieved. In addition, the median particle size (D50) of the graphite particles is different from that of the silicon particles. Specifically, the graphite particles are larger. Therefore, by mixing them and using them for the negative electrode, the loading amount of the negative electrode active material can be increased. When the loading amount is small, the output characteristics of the lithium-ion secondary battery can be improved, but when the loading amount is large, the above output characteristics decrease. Therefore, the loading amount of the negative electrode active material is preferably 3 mg / cm 2 or more and 10 mg / cm 2 or less.

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

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

[0084] In addition, the negative electrode active material can also use compounds containing one or more selected from tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, and indium, etc. Compounds containing two or more of the above can be called alloy materials. For example, magnesium silicide (Mg 2 Si) can be cited.

[0085] As other alloy materials, there are magnesium germanium alloy (Mg 2 Ge), tin monoxide (SnO), tin dioxide (SnO 2 ), magnesium tin compound (Mg 2 Sn), tin disulfide (SnS 2 ), other main binary alloys of tin (V 2 Sn 3 , FeSn 2 , 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, CeSb3 , CoSb 3 , InSb, etc.

[0086] In addition, as the negative electrode active material, oxides such as 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 ), etc. can be used.

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

[0088] When a nitride of lithium and a transition metal is used as the negative electrode active material, lithium ions are contained in the negative electrode active material. Therefore, the negative electrode active material can be combined with materials such as V 2 O 5 , Cr 3 O 8 that do not contain lithium ions and are used as the positive electrode active material. Therefore, it is preferred. Note that when a material containing lithium ions is used as the positive electrode active material, by previously removing the lithium ions contained in the positive electrode active material, a nitride of lithium and a transition metal can also be used as the negative electrode active material.

[0089] In addition, as another form of the negative electrode, it can also be a negative electrode that does not contain a negative electrode active material at the end of battery manufacturing. As a negative electrode that does not contain a negative electrode active material, for example, the following negative electrode can be used. This negative electrode only contains a negative electrode current collector at the end of battery formation. Lithium ions detached from the positive electrode active material during battery charging are deposited on the negative electrode current collector in the form of lithium metal, thereby forming a negative electrode active material layer. A battery using this negative electrode is sometimes called a non-negative electrode battery (non-anode battery), etc.

[0090] When using a negative electrode that does not contain a negative electrode active material, a film for making the precipitation of lithium uniform can also be included on the negative electrode current collector. As the film for making the precipitation of lithium uniform, for example, a solid electrolyte having lithium ion conductivity can be used. As the solid electrolyte, sulfide solid electrolytes, oxide solid electrolytes, polymer solid electrolytes, etc. can be used. Among them, the film of the polymer solid electrolyte is relatively easy to form uniformly on the negative electrode current collector, so it is suitable for the film for making the precipitation of lithium uniform. In addition, as the film for making the precipitation of lithium uniform, 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. Since lithium and magnesium form a solid solution in a wide composition range, it is suitable for the film for uniformly precipitating lithium.

[0091] In addition, when using a negative electrode that does not contain a negative electrode active material, a negative electrode current collector with unevenness can be used. When using a negative electrode current collector with unevenness, the concave portion of the negative electrode current collector is a cavity that easily precipitates the lithium contained in the negative electrode current collector, thereby suppressing the shape of the lithium from becoming dendritic during precipitation.

[0092] <Binder (adhesive)> The negative electrode active material layer 111 preferably contains a binder. As the binder, a polymer having a carboxyl group is preferably used. The carboxyl group can also be said to contain two basic oxygens, one acidic hydrogen, and one electrophilic carbon. The carboxyl group can also be said to be a group having a hydroxyl group OH and a carbonyl group C=O and having polarity. When the binder has a polar group such as a carboxyl group, the lithium ions are attracted due to the interaction with the lithium ions, so it may contribute to the insertion of lithium ions in the negative electrode active material. The carboxyl group can be specified by Fourier Transform Infrared Spectroscopy (FT-IR), etc.

[0093] As the polymer having a carboxyl group, there are polyglutamic acid (sometimes denoted as PGA), polyacrylic acid (sometimes denoted as PAA), and alginic acid (sometimes denoted as polysaccharide). In addition, as the polymer having a carboxyl group, polyamino acids can also be used. Specifically, polyornithine and poly(sarcosine) can also be used for the binder. Furthermore, as the polymer having a carbonyl group, polyaspartic acid can also be used for the binder. In addition, as the polymer having a keto group, a binary copolymer (copolymer) can also be used, and a copolymer of acrylic acid and maleic acid, a copolymer of acrylic acid and sulfonic acid can also be used for the binder. By using these materials as the binder of the negative electrode, there is also an effect of reducing the mixing amount of the binder in the negative electrode.

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

[0095] [Chemical Formula 1]

[0096] As can be seen from the structural formula (H2), polyglutamic acid contains nitrogen in addition to carboxyl groups, and this nitrogen has non-bonding electron pairs, so it is expected to interact with lithium ions. For example, it is also possible that the non-bonding electron pairs attract lithium ions and contribute to the insertion of lithium ions into the negative electrode active material.

[0097] In addition, as can be seen from the structural formula, polyglutamic acid has a C=O of a carbonyl group. When the binder has polar groups such as a carbonyl group, it is expected to interact with lithium ions as carrier ions. For example, it may contribute to the insertion and extraction of lithium ions in the negative electrode active material.

[0098] As polyglutamic acid, linear γ-polyglutamic acid or crosslinked γ-polyglutamic acid can be used as the binder, and they are collectively referred to as structures mainly composed of γ-polyglutamic acid. In addition, from the viewpoint of having a network structure, crosslinked γ-polyglutamic acid is suitable for the binder. Furthermore, the molecular weight of polyglutamic acid is preferably 1 million or more, more preferably 3 million or more, and further preferably 10 million or more and 50 million or less.

[0099] According to the manufacturing method of polyglutamic acid, polyglutamic acid can also be said to be a structure mainly composed of γ-glutamic acid containing other elements (for example, Ca, Al, Na, Mg, Fe, Si, S). That is to say, alkali metal ions, such as lithium ions or sodium ions, can also be used to neutralize polyglutamic acid.

[0100] This polyglutamic acid has hydrophilicity, so deionized water can be used as the solvent, which is very suitable for forming a slurry. In addition, 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] [Chemical Formula 2]

[0103] As can be seen from the structural formula (H1), polyacrylic acid has a carboxyl group.

[0104] In addition, a material that crosslinks polyacrylic acid can also be used. Since a crosslinked structure, that is, a mesh structure, can be formed, the function as a binder is likely to be improved, so it is preferred. In addition, polyacrylic acid can provide a secondary battery with good low-temperature characteristics.

[0105] As adhesives other than those described above, rubber materials such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, ethylene-propylene-diene copolymer, etc. are preferably used. In addition, fluororubber can also be used as an adhesive.

[0106] In addition, as adhesives, materials such as polystyrene, polymethyl acrylate, 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, nitrocellulose, etc. are preferably used.

[0107] <Thickening agent> In addition, it is preferable to use a thickening agent in addition to the adhesive. As the thickening agent, water-soluble polymers are preferably used. As water-soluble polymers, polysaccharides etc. can be used for example. As polysaccharides, cellulose derivatives such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, regenerated cellulose, starch, etc. can be used.

[0108] <Conductive material> The negative electrode active material layer 111 may also contain a conductive material. The conductive material serves to assist the current path between the active material and the current collector or the current path between multiple active materials. In order to serve such a function, the conductive material preferably contains a material with a lower resistance than the active material. The conductive material is sometimes referred to as a conductive aid or a conductivity imparting agent depending on its function. By attaching the conductive material between multiple active materials, the multiple active materials are electrically connected to each other and the conductivity is improved. Note that in this specification etc., "attachment" does not mean that the active material and the conductive material are physically in close contact but refers to a concept including the following cases: in the case of covalent bond formation; in the case of bonding by van der Waals forces; in the case where the conductive material covers a part of the surface of the active material; in the case where the conductive material is embedded in the surface irregularities of the active material; in the case of electrical connection without contact, etc.

[0109] Conductive materials typically use carbon materials or metal materials. The conductive materials are in particulate form, and examples of such particulate conductive materials include carbon black (furnace black, acetylene black, graphite, etc.). There are also fibrous conductive materials, and examples of such fibrous conductive materials include CNT and VGCF (registered trademark). There are also flaky conductive materials, and examples of such flaky conductive materials include multilayer graphene. In the cross-section of the positive electrode, the flaky conductive material may sometimes be observed as a line.

[0110] The particulate conductive material can enter the gaps between the negative electrode active material, etc., and is prone to aggregation. Therefore, the particulate conductive material can assist in the conduction path between the negative electrode active materials disposed in its vicinity. Although having a bent region, the fibrous conductive material is larger than the negative electrode active material. Therefore, the fibrous conductive material can assist in the conduction path between the separated negative electrode active materials in addition to between the adjacent negative electrode active materials. Thus, it is preferable to mix two or more materials having different shapes as the conductive material.

[0111] When using multilayer graphene as the flaky conductive material and carbon black as the particulate conductive auxiliary material, the weight of the carbon black in the state of the slurry in which they are mixed is preferably 1.5 times or more and 20 times or less, more preferably 2 times or more and 9.5 times or less, that of the multilayer graphene.

[0112] When the mixing ratio of the multilayer graphene and the carbon black is set within the above range, the carbon black does not aggregate and is easily dispersed. In addition, when the mixing ratio of the multilayer graphene and the carbon black is set within the above range, the electrode density can be increased compared with the case where only carbon black is used as the conductive material. By increasing the electrode density, the capacity per unit weight can be increased.

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

[0114] In the conductive material, a graphene compound can also be used instead of the above multilayer graphene. As the graphene compound, fluorinated graphene can also be used. Fluorine in the graphene compound is preferably adsorbed on the surface. Fluorinated graphene can be produced by bringing graphene into contact with a fluorine compound (referred to as fluorination treatment). In the fluorination treatment, fluorine (F 2 ) or a fluorine compound is preferably used. As the fluorine compound, hydrogen fluoride, halogen fluoride (ClF 3 , IF 5 , etc.), gaseous fluoride (BF 3 , NF 3 , PF 5 , SiF 4 , SF 6 , etc.), metal fluoride (LiF, NiF 2 , AlF 3 , MgF2 etc.). In the fluorination treatment, gaseous fluorides are preferably used, and gaseous fluorides can also be diluted with inert gases. The temperature of the fluorination treatment is preferably room temperature, and preferably 0 °C or higher and 250 °C or lower including this room temperature. By performing the fluorination treatment at a temperature of 0 °C or higher, fluorine can be adsorbed on the surface of graphene.

[0115] Graphene or a graphene compound has excellent physical properties of high flexibility and high mechanical strength, so it is suitable for conductive materials. Graphene or a graphene compound sometimes has a curved surface, and a surface contact with low contact resistance can be achieved. In addition, even when graphene or a graphene compound is thin, its conductivity is sometimes extremely high. Therefore, a conductive path can be efficiently formed in the active material layer using a small amount of graphene or a graphene compound. 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, graphene or a graphene compound can also have pores.

[0116] When using a negative electrode active material of 1 μm or less such as nano-silicon particles, more conductive paths connecting the active materials to each other are required. In this case, it is preferable to use graphene or a graphene compound that can efficiently form a conductive path even in a small amount.

[0117] Due to the above properties, it is particularly effective to use graphene or a graphene compound as a conductive material in a secondary battery that requires rapid charging and rapid discharging. For example, secondary batteries for two-wheeled or four-wheeled vehicles, secondary batteries for drones, etc. sometimes require rapid charging and rapid discharging. Mobile electronic devices, etc. sometimes also require rapid charging characteristics. Rapid charging, for example, refers to charging at 400 mA / g or more or 1000 mA / g or more. Rapid discharging, for example, refers to discharging at 400 mA / g or more or 1000 mA / g or more.

[0118] <Step S11> In Figure 4 In the step S11 shown, a slurry 504 containing a negative electrode active material and a binder, etc. is prepared, and the slurry 504 is applied to the negative electrode current collector 110 to form the negative electrode 106. In order to make the slurry easily applied to the negative electrode current collector 110, a thickener, etc. is used to adjust the viscosity.

[0119] Figure 5A A coating device for coating a slurry 504 containing a negative electrode active material and a binder, etc. on the negative electrode current collector 110 is shown. This coating device is called a comma coater. The slurry 504 sometimes contains a solvent, and as the solvent, water, ketones such as acetone, alcohols such as ethanol and isopropyl alcohol, diethyl ether, dioxane, acetonitrile, or NMP (N-methyl-2-pyrrolidone), etc. can be used.

[0120] The coating device includes a back roller 521, a coating roller 522, a micro rod 524, etc. The back roller 521 moves the roller-shaped negative electrode current collector (metal foil, typically copper foil) 110 that serves as the negative electrode current collector. Additionally, the back roller 521 can also rotate the coating roller 522. The slurry 504 is held by the dam bottom surface 523 and the coating roller 522, and the thickness of the slurry 504 is adjusted by the microspheres 524 and then coated on the negative electrode current collector 110. Coating is also referred to as spreading. Additionally, when monitoring the thickness of the coated slurry 504, the coating device preferably includes a slurry thickness measurement sensor 505.

[0121] Figure 5B Another example of a coating device for coating the slurry 504 on the negative electrode current collector 110 is shown. This coating device is called a die coater. The coating device includes a dye 525, a back roller 521, etc. The dye 525 is an example of a coating nozzle and has a manifold in the center. The slurry 504 is supplied to the manifold by a pump and extruded from the manifold to the front of the die. The extruded slurry 504 is coated on the negative electrode current collector 110 that moves due to the rotation of the back roller 521. Additionally, when monitoring the thickness of the coated slurry 504, the coating device preferably includes a slurry thickness measurement sensor 505.

[0122] By using such a coating device, the negative electrode 106 is obtained. Additionally, after coating, the negative electrode 106 can be pressed using a roller press as needed. The line 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 rollers are heated to 100 °C or more, preferably 120 °C or more. Note that when the slurry contains an adhesive, the upper and lower rollers are heated to the melting point of the adhesive or higher. Thus, the negative electrode 106 is completed.

[0123] In the negative electrode 106, the thickness of the negative electrode active material layer 111 is 100 μm or more and 300 μm or less, preferably 110 μm or more and 150 μm or less. And, the loading amount of the negative electrode active material is 3 mg / cm 2 or more and 20 mg / cm 2 or less, preferably 12 mg / cm 2 or more and 18 mg / cm 2 or less.

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

[0125] <Carbon sheet 115> As described above, commercially available carbon sheets 115 may also be used. Each of the commercially available CNT sheets has a thickness of 400 nm or more and 500 nm or less. In order to make the carbon sheet 115 satisfy the predetermined thickness, commercially available thin sheets may be laminated.

[0126] <Step S13> Next, in Figure 4 the step S13 shown, the negative electrode 106 and the carbon sheet 115 are laminated to obtain a negative electrode structure 120. In order to bond the negative electrode 106 and the carbon sheet 115, the above-mentioned adhesive may also be used. Thus, the negative electrode structure 120 is obtained. After overlapping the negative electrode 106 and the carbon sheet 115, pressing may be performed using a roll press as needed. The upper and lower rolls are heated to 100 °C or more, preferably 120 °C or more. Note that in the case of containing an adhesive, the upper and lower rolls are heated to the melting point of the adhesive or higher.

[0127] By this example of the manufacturing method, a negative electrode structure 120 having a carbon sheet 115 can be obtained. This negative electrode structure 120 inhibits dendrites from reaching the positive electrode.

[0128] The content of this embodiment may be appropriately combined with the content of other embodiments.

[0129] Embodiment 2 In this embodiment, the structure of the secondary battery will be described.

[0130] [Negative electrode] The negative electrode is as shown 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 contains a positive electrode active material, and may also contain at least one of a conductive material and an adhesive. As the positive electrode active material, the substances described in the above embodiment may be used.

[0132] Figure 6A An example of a cross-sectional schematic view of the positive electrode is shown.

[0133] The positive electrode current collector 550 may be made of a metal foil, for example. The positive electrode may be formed by coating a slurry on the metal foil and drying it. Alternatively, pressing may be performed after drying. In the positive electrode, a positive electrode active material layer is formed on the positive electrode current collector 550.

[0134] The positive electrode active material layer contains a positive electrode active material 561. Sometimes the positive electrode active material is referred to as positive electrode active material particles. The positive electrode active material 561 has the function of absorbing and / or releasing lithium ions during charge and discharge. As the positive electrode active material 561 for one embodiment of the present invention, a material with less deterioration during charge and discharge even when a high charging voltage is used. In addition, as long as the positive electrode active material 561 is a material with less deterioration during charge and discharge even when a high charging voltage is used, two or more materials with different particle sizes can be used.

[0135] The conductive material can be arbitrarily selected from the conductive materials described in the above embodiments. Figure 6A Carbon black 553 is shown as the conductive material therein.

[0136] In order to fix the positive electrode current collector 550 such as a metal foil and the positive electrode active material, the positive electrode of the secondary battery may also be mixed with an adhesive. The adhesive is a polymer material. When a large amount of adhesive is contained, 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 minimum amount of the adhesive. In Figure 6A The area not filled with the positive electrode active material 561, the second positive electrode active material 562, and carbon black 553 refers to voids or an adhesive.

[0137] Note that Figure 6A An example in which the shape of the positive electrode active material 561 is spherical is shown, but there is no particular limitation on this shape. The cross-sectional shape of the positive electrode active material 561 can also be, for example, elliptical, rectangular, trapezoidal, conical, a polygon with rounded corners, or an asymmetric shape. For example, Figure 6B An example in which the positive electrode active material 561 has a polygonal shape with rounded corners is shown.

[0138] In addition, in Figure 6B the positive electrode, graphene 554 is used as the carbon material serving as the conductive material. In Figure 6B a positive electrode active material layer containing the positive electrode active material 561, graphene 554, and carbon black 553 is formed on the positive electrode current collector 550.

[0139] Note that in the step of mixing graphene 554 and carbon black 553 to obtain an electrode paste, preferably, the weight of the mixed carbon black is 1.5 times or more and 20 times or less, preferably 2 times or more and 9.5 times or less, that of graphene.

[0140] When the mixing of graphene 554 and carbon black 553 is set within the above range, during the adjustment of the slurry, the dispersion stability of carbon black 553 is excellent and aggregation parts are not easily generated. In addition, when the mixing of graphene 554 and carbon black 553 is set within the above range, a higher electrode density can be achieved compared to a positive electrode using only carbon black 553 as the conductive material. By increasing the electrode density, the capacity per unit weight can be increased.

[0141] Compared with a positive electrode using only graphene as the conductive material, the electrode density is low, but when the mixture of the first carbon material (graphene) and the second carbon material (acetylene black) is within the above range, rapid charging can be achieved accordingly. Therefore, this is particularly effective when used in in-vehicle lithium-ion secondary batteries.

[0142] Figure 6C An example of a positive electrode using carbon fiber 555 instead of graphene is shown. Figure 6C Shows Figure 6B a different example. By using carbon fiber 555, the aggregation of carbon black 553 can be prevented, and the dispersibility can be improved.

[0143] Note that in Figure 6C , the regions not filled with the positive electrode active material 561, carbon fiber 555, and carbon black 553 refer to voids or binders.

[0144] Figure 6D Examples of other positive electrodes are shown. Figure 6D An example of using graphene 554 and carbon fiber 555 is shown. By using graphene 554 and carbon fiber 555, the aggregation of carbon black such as carbon black 553 can be prevented, and thus the dispersibility can be further improved.

[0145] Note that in Figure 6D , the regions not filled with the positive electrode active material 561, carbon fiber 555, graphene 554, and carbon black 553 refer to voids or binders.

[0146] A lithium-ion secondary battery can be manufactured by the following steps: using any one of the positive electrodes in Figures 6A to 6D , laminating a separator on the positive electrode, laminating a negative electrode on the separator to obtain a laminate, and placing the laminate in a container (such as an outer packaging body, a metal can, etc.) and filling the container with a liquid electrolyte.

[0147] [Electrolyte] The electrolyte contains an organic solvent. However, the organic solvent of the electrolyte in one embodiment of the present invention is not limited to being a liquid at 25°C, and can also be a solid at 25°C or a semi-solid at room temperature. Additionally, the organic solvent of the electrolyte in one embodiment of the present invention is preferably a liquid within a relatively wide temperature range from below the freezing point to a high temperature, but is not limited thereto. The organic solvent can be a liquid, a solid, or a semi-solid within a relatively wide temperature range from below the freezing point to a high temperature.

[0148] As the organic solvent, an aprotic organic solvent is preferably used. For example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, vinyl chloride 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-trifluoropropionate (MTFP), methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, 1,3-dioxane, 1,4-dioxane, ethylene glycol dimethyl ether (DME), dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, sultone, etc. can be used, or two or more of the above can be used in any combination and ratio. In an electrolyte containing vinylene carbonate (VC) or fluoroethylene carbonate (FEC), the thickness of dendrites tends to increase, so the penetration of the separator can be suppressed, which is preferred. At this time, vinylene carbonate (VC) or fluoroethylene carbonate (FEC) is preferably used as an additive rather than the main component of the electrolyte. Typically, ethylene carbonate (EC) and diethyl carbonate (DEC) can be used. At this time, it is preferably satisfied that EC:DEC = 3:7 (volume ratio).

[0149] PS has HOMO and LUMO energy levels equal to those of EC and DEC. Therefore, it is not easily oxidized or reduced even at a high cut-off voltage, and it easily becomes a polymer when decomposed on the surface of the positive electrode active material. Therefore, it has the advantage of having little possibility of gasifying as a decomposition product with a small molecular weight. Therefore, the electrolyte preferably contains 0.1 wt% or more and 10 wt% or less of PS, and more preferably contains 0.25 wt% or more and 7.5 wt% or less of PS.

[0150] FEC is one of the cyclic carbonates. Because of its high relative dielectric constant, when used as an organic solvent, it has the effect of promoting the dissociation of lithium salts. On the other hand, since FEC has a substituent with an electron-withdrawing property, it is easier to form desolvation with lithium ions compared to EC. Specifically, the solvation energy of lithium ions in FEC is smaller than that of EC which does not have a substituent with an electron-withdrawing property. Therefore, lithium ions are likely to leave the surfaces of the positive electrode active material and the negative electrode active material, thereby reducing the internal resistance of the secondary battery. And because the energy level of the highest occupied molecular orbital (HOMO) of FEC is deep, it is not easily oxidized and its antioxidant property is improved. On the other hand, there is a concern about the high viscosity of FEC. Thus, it is preferable to use a mixed organic solvent containing MTFP in addition to FEC for the electrolyte. MTFP is one of the chain carbonates and can have the effect of reducing the viscosity of the electrolyte or maintaining the viscosity at room temperature (typically 25 °C) even at low temperature (typically 0 °C). And the solvation energy of MTFP is smaller than that of methyl propionate (abbreviated as "MP") which does not have a substituent with an electron-withdrawing property. Therefore, it can also sometimes form solvation with lithium ions when used for the electrolyte. When using a mixed organic solvent containing FEC and MTFP, when the volume ratio is FEC:MTFP = 1:y, it is preferably 2 ≤ y ≤ 20, more preferably 4 ≤ y ≤ 9.

[0151] Preferably, the content of particulate dust or molecules other than the constituent molecules of the organic solvent (hereinafter simply referred to as "impurities", including oxygen (O 2 ) and water (H 2 O) or moisture) in the above-mentioned organic solvent is small and it is highly purified. In addition, it is preferable to suppress reaction by-products during synthesis through appropriate purification. Specifically, the impurities in the electrolyte are 100 ppm or less, preferably 50 ppm or less, more preferably less than 10 ppm. The concentration of moisture in the impurities can be detected by the Karl Fischer titration method.

[0152] And the above-mentioned organic solvent preferably has almost no peaks attributable to impurities confirmed by NMR measurement or the like. Almost no confirmation means that the ratio of the integral area of the peak attributable to the main component to the integral area of the peak attributable to the impurities (abbreviated as the integral ratio) is 0.005 or less, preferably 0.002 or less. There is no particular limitation on the device used for NMR measurement. For example, "AVANCE III 400 type" manufactured by Bruker Corporation can be used. In addition, in 1 H-NMR measurement, the central peak among the five acetonitrile peaks derived from acetonitrile-d 3 used as the solvent can be set to 1.94 ppm.

[0153] For example, it is known that in MTFP, when using acetonitrile-d 3 solvent measurement 1 in H-NMR, four peaks are generated at δ of 3.29 ppm or more and 3.43 ppm or less. However, when other peaks are generated in the vicinity, for example, when a peak is generated at δ of 3.24 ppm or more and 3.29 ppm or less, the peak is considered to originate from impurities. Therefore, when the ratio (integration ratio) of the peak area at δ of 3.24 ppm or more and 3.29 ppm or less to the peak area at δ of 3.29 ppm or more and 3.43 ppm or less is 0.005 or less, preferably 0.002 or less, it can be said that almost no peak due to impurities is confirmed.

[0154] In addition, for the purpose of improving safety, etc., a coating film (Solid Electrolyte Interphase Film) is formed at the interface between the electrode (active material layer) and the electrolyte solution, and additives such as vinylene carbonate (VC), propanesultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), lithium bis(oxalato)borate (LiBOB), or dinitrile compounds such as succinonitrile or adiponitrile can also be added to the electrolyte solution. The concentration of the additive can be set to, for example, 0.1 wt% or more and 5 wt% or less in the whole solvent. In the case of using ethylene carbonate (EC) and diethyl carbonate (DEC), preferably, 2 wt% of vinylene carbonate (VC) is mixed as an additive with the mixed organic solvent in which the following lithium salt is dissolved with respect to EC:DEC = 3:7 (volume ratio).

[0155] In addition, by using one or more flame-retardant and hardly volatile ionic liquids (room temperature molten salts) as the solvent of the electrolyte solution, even if the internal temperature of the power storage device rises due to internal short circuit or overcharging of the power storage device, etc., the rupture and fire of the power storage device can be prevented. Ionic liquids are composed of cations and anions and contain organic cations and anions. As the organic cations used for the electrolyte solution, aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, or aromatic cations such as imidazolium cations and pyridinium cations can be cited. In addition, as the anions used for the electrolyte solution, monovalent amide anions, monovalent methylide anions, fluorosulfonic acid anions, perfluoroalkylsulfonic acid anions, tetrafluoroboric acid anions, perfluoroalkylboric acid anions, hexafluorophosphoric acid anions, or perfluoroalkylphosphoric acid anions, etc. can be cited.

[0156] In addition, as the electrolyte (also called lithium salt) dissolved in the above solvent, for example, LiPF 6 、LiClO 4 、LiAsF 6 、LiBF 4 、LiAlCl4 , 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 , abbreviated as: LiBOB), etc., or two or more of the above can be used in any combination and ratio.

[0157] As the electrolyte, it is preferable to use a highly purified electrolyte with a low content of particulate dust or elements other than the constituent elements of the electrolyte (hereinafter simply referred to as "impurities"). Specifically, the ratio of impurities in the weight of the electrolyte is preferably 1% or less, more preferably 0.1% or less, and further preferably 0.01% or less.

[0158] In addition, a polymer gel electrolyte in which a polymer is swollen with an electrolyte can also be used.

[0159] In addition, by using a polymer gel electrolyte, the safety against leakage is improved. Moreover, the thinning and weight reduction of the secondary battery can be achieved.

[0160] As the polymer to be gelled, silicone gels, acrylic gels, acrylonitrile gels, polyethylene oxide gels, polypropylene oxide gels, fluoropolymer gels, etc. can be used. For example, polymers having a polyalkylene oxide structure such as polyethylene oxide (PEO), PVDF, polyacrylonitrile, and copolymers containing these can be used. For example, PVDF-HFP, which is a copolymer of PVDF and hexafluoropropylene (HFP), can be used. In addition, the formed polymer can also have a porous shape.

[0161] In addition, as the electrolyte, a solid electrolyte containing an inorganic material such as a sulfide or an oxide, or a solid electrolyte containing a polymer material such as a PEO (polyethylene oxide) type can be used. When using a solid electrolyte, there is no need to provide a separator or a spacer. In addition, since the entire battery can be solidified, there is no concern about liquid leakage, and the safety is significantly improved.

[0162] [Separator] As the separator, for example, the following materials can be used: fibers having cellulose such as paper, non-woven fabric, glass fiber, ceramics, or materials formed of synthetic fibers such as nylon (polyamide), vinylon (polyvinyl alcohol fiber), polypropylene (denoted as PP), polyimide (denoted as PI), polyester, acrylic resin, polyolefin, polyurethane. The porosity of the separator thickness can be 35% or more and 90% or less, preferably 60% or more and 85% or less. The porosity of the separator using polypropylene can be 35% or more and 45% or less. The porosity of the separator using polyimide can 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 thickened (typically, a thickness of 50 μm or more and 60 μm or less), so it is preferred.

[0163] Preferably, the separator is processed into a bag shape and arranged so as to surround either the positive electrode or the negative electrode.

[0164] The separator can also have a multilayer structure. For example, an organic material film such as polypropylene or polyethylene can be coated with a ceramic material, a fluorine material, a polyamide material, or a mixture thereof. As the ceramic material, for example, alumina particles, silica particles, etc. can be used. As the fluorine material, for example, PVDF, polytetrafluoroethylene, etc. can be used. As the polyamide material, for example, nylon, aromatic polyamide (meta-aramid, para-aramid), etc. can be used.

[0165] By adopting a separator with a multilayer structure, the safety of the secondary battery can be ensured even if the total thickness of the separator is small, so the capacity per unit volume of the secondary battery can be increased.

[0166] [Outer packaging body] As the outer packaging body included in the secondary battery, for example, a metal material such as aluminum or a resin material can be used. In addition, a film-shaped outer packaging body can also be used. As the film, for example, a film having the following three-layer structure can be used: a metal film with excellent flexibility such as aluminum, stainless steel, copper, nickel, etc. is provided on a film made of materials such as polyethylene, polypropylene, polycarbonate, ionomer, polyamide, etc., and an insulating synthetic resin film such as a polyamide resin or a polyester resin is provided on the outer surface of the metal film as the outer packaging body.

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

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

[0169] The low-temperature environment typically refers to below the freezing point. When charging in a low-temperature environment, the potential barrier for the lithium ions to detach from the positive electrode active material tends to become higher. In other words, it can be said that: the lower the temperature of the charging environment, the greater the overvoltage required for the lithium ions to detach from the positive electrode active material. That is, the positive electrode active material may be exposed to a high voltage (a high potential relative to the lithium potential) during charging in a low-temperature environment. In other words, during charging in a low-temperature environment, if the positive electrode active material is not exposed to a high voltage, the charging capacity may decrease.

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

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

[0172] Hereinafter, the electrolyte suitable for a lithium ion secondary battery having excellent charging characteristics and discharge characteristics even in a low-temperature environment will be described in detail.

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

[0174] The mixed organic solvent preferably contains 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, fluorinated ethylene carbonate (fluoroethylene carbonate FEC, F1EC), difluorinated ethylene carbonate (DFEC, F2EC), trifluorinated ethylene carbonate (F3EC) or tetrafluorinated ethylene carbonate (F4EC) etc. can be used. In addition, as DFEC, isomers such as cis-4,5 and trans-4,5 can be cited. Any fluorinated cyclic carbonate has a substituent with an electron-withdrawing property, so 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 FEC, the electron-withdrawing substituent is the F group.

[0177] [Chemical formula 3]

[0178] As the fluorinated chain carbonate, there is methyl 3,3,3-trifluoropropionate. The following structural formula (H22) is the structural formula of methyl 3,3,3-trifluoropropionate. The abbreviation of methyl 3,3,3-trifluoropropionate is "MTFP". In MTFP, the electron-withdrawing substituent is CF 3 group.

[0179] [Chemical formula 4]

[0180] As the fluorinated chain carbonate, there 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 group.

[0181] [Chemical formula 5]

[0182] As the 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 6]

[0184] As the 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 7]

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

[0187] FEC is one of the cyclic carbonates. Since it has a high relative dielectric constant, it has the effect of promoting the dissociation of lithium salts when used as an organic solvent. On the other hand, since FEC has a substituent that exhibits electron-withdrawing properties, it is easier to form desolvation with lithium ions than ethylene carbonate (EC). Specifically, the solvation energy of lithium ions in FEC is smaller than that of EC which does not have a substituent that exhibits electron-withdrawing properties. Therefore, lithium ions are likely to leave the surfaces of the positive electrode active material and the negative electrode active material, whereby the internal resistance of the secondary battery can be reduced. Also, since the highest occupied molecular orbital (HOMO) energy level of FEC is deep, it is not easily oxidized and its antioxidant property is improved. On the other hand, there is a concern that the viscosity of FEC is high. Then, it is preferable to use a mixed organic solvent containing MTFP in addition to FEC for the electrolyte. MTFP is one of the chain carbonates and can have the effect of reducing the viscosity of the electrolyte or maintaining the viscosity at room temperature (typically 25°C) even at low temperature (typically 0°C). Also, the solvation energy of MTFP is smaller than that of methyl propionate (abbreviated as "MP") which does not have a substituent that exhibits electron-withdrawing properties. Therefore, it can also form solvation with lithium ions sometimes when used for the electrolyte.

[0188] The following shows the measured values of the HOMO energy level, solvation energy, melting point, etc.

[0189] [Table 1]

[0190] It is preferable to mix and use the two mixed organic solvents of FEC and MTFP having the above physical properties such that the total content is 100 vol% and the volume ratio is x:100 - x (note that 5 ≤ x ≤ 30, preferably 10 ≤ x ≤ 20). That is to say, it is preferable to mix such that MTFP in the mixed organic solvent is more than FEC. Note that the above volume ratio may also be the volume ratio measured before mixing the mixed organic solvent, and the external air when mixing the mixed organic solvent may also be at room temperature (typically 25°C). The mixed organic solvent mixing FEC and MTFP exhibits viscosity capable of operating as a secondary battery and maintains appropriate viscosity even in a low-temperature environment, so it is preferable.

[0191] General solvents for secondary batteries solidify at around -20°C, so it is difficult to manufacture secondary batteries that can be charged and discharged at -30°C, preferably -40°C. However, in the present embodiment, as an example, the freezing point of the mixed organic solvent can be -30°C or lower, preferably -40°C or lower, whereby a secondary battery capable of being charged and discharged even in a low-temperature environment can be realized. As a result, a secondary battery capable of being charged and discharged in a relatively wide temperature range including at least a low-temperature environment can be realized.

[0192] In the above description, FEC is taken as an example for illustration. However, in any organic compound described as a fluorinated cyclic carbonate, it has the effect of promoting the dissociation of lithium salts, has a small solvation energy, and the bonding between lithium ions and the solvent is easily separated. And due to its high viscosity, it is difficult to be used alone at the freezing point.

[0193] In addition, although MTFP is taken as an example for illustration in the above description, it can be said that any organic compound described as a fluorinated linear carbonate has the effect of reducing or maintaining the viscosity of the electrolyte of one embodiment of the present invention. Therefore, as long as the mixed organic solvent of one embodiment of the present invention contains a fluorinated cyclic carbonate and a fluorinated linear carbonate, a lithium-ion secondary battery capable of being charged and discharged in a low-temperature environment can be provided.

[0194] <Electrolyte 2 suitable for low-temperature environment> When the mixed organic solvent used for the electrolyte contains ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC), in a state where the total content of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate is 100 vol%, a mixed organic solvent with a volume ratio of x:y:100 - x - y (note that 5 ≤ x ≤ 35 and 0 < y < 65) of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate 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 (volume ratio) can be used. Note that the above volume ratio can also be the volume ratio before mixing the mixed organic solvent, and the external air when mixing the mixed organic solvent can also be at room temperature (typically 25°C).

[0195] EC is a cyclic carbonate. Because of its high relative dielectric constant, 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), namely 38 °C. Therefore, when only EC is used as a solvent, it is difficult to use it in a low-temperature environment. Thus, the solvent specifically described as one mode of the present invention contains not only EC, but also EMC and DMC. EMC is a chain carbonate and has the effect of reducing the viscosity of the electrolyte, and its freezing point is -54 °C. In addition, DMC is also a chain carbonate, has the effect of reducing the viscosity of the electrolyte, and the freezing point is -43 °C. The three mixed organic solvents of EC, EMC, and DMC with the above physical properties are mixed in such a way that the total content is 100 vol% and the volume ratio is x:y:100 - x - y (note that 5 ≤ x ≤ 35 and 0 < y < 65), and the electrolyte manufactured using this mixed organic solvent has a freezing point of -40 °C or lower.

[0196] The lowest freezing point of a general electrolyte for secondary batteries is about -20 °C. Therefore, it is difficult to manufacture a battery that can be charged and discharged at -40 °C. The freezing point of the electrolyte described as an example in this embodiment is -40 °C or lower. Thus, a secondary battery that can be charged and discharged even in an extremely low-temperature environment of -40 °C can be realized.

[0197] In addition, as the lithium salt dissolved in the above solvent, the following lithium salts can be used. For example, LiPF can be used in any combination and ratio 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 and at least one lithium salt selected from lithium bis(oxalato)borate (LiBOB). The volume of the lithium salt dissolved in the above 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 still more preferably 0.8 mol / L or more and 1.2 mol / L or less. 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 still more preferably 0.8 mol / L or more and 1.2 mol / L or less.

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

[0199] Furthermore, in order to improve safety and other purposes, a coating film (Solid Electrolyte Interphase Film) is formed at the interface between the electrode (active material layer) and the electrolyte, and additives such as vinylene carbonate (VC), propanesultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), lithium bis(oxalato)borate (LiBOB), or dinitrile compounds such as succinonitrile or adiponitrile can also be added to the electrolyte. The concentration of the additive can be set to, for example, 0.1 wt% or more and 5 wt% or less in the whole solvent.

[0200] In Example 2 of the electrolyte, the lithium salt can use the materials described in Example 1 of the electrolyte. In addition, the materials described in Example 1 of the electrolyte can also be used as additives.

[0201] An example of the electrolyte of the secondary battery applicable to one embodiment of the present invention has been described above, but the electrolyte of the secondary battery applicable to one embodiment of the present invention is not limited to this example. As long as it is a material with excellent lithium ion conductivity during charge and discharge in a low temperature environment, other materials can also be used.

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

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

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

[0205] To easily understand the overlapping relationship (vertical relationship and positional relationship) of components, Figure 7A schematic diagrams are used. Therefore, Figure 7A is not a diagram that is Figure 7B completely identical.

[0206] In Figure 7A , the stacked positive electrode 304, negative electrode 307, spacer 342, and gasket 332 are shown, and the above components are sealed with a negative electrode can 302 and a positive electrode can 301. Note that the electrolyte and separator described in the above embodiment are not shown in Figure 7A . The spacer 342 or the gasket 332 is used to protect the inside or fix the position inside the can when the positive electrode can 301 and the negative electrode can 302 are pressed together. The spacer 342 or the gasket 332 is made of stainless steel or an insulating material.

[0207] The stacked structure in which the positive electrode active material layer 306 is formed on the positive electrode current collector 305 is denoted as the positive electrode 304.

[0208] Figure 7B is a perspective view of the manufactured coin-shaped secondary battery 300.

[0209] In the coin-shaped secondary battery 300, the positive electrode can 301 that also serves as the positive terminal and the negative electrode can 302 that also serves as the negative terminal can also be insulated and sealed by a gasket 303 made of polypropylene or the like. The positive electrode 304 is formed by a positive electrode current collector 305 and a positive electrode active material layer 306 provided in contact therewith. In addition, the negative electrode 307 is formed by a negative electrode current collector 308 and a negative electrode active material layer 309 provided in contact therewith. 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 the positive electrode 304 and the negative electrode 307 for the coin-shaped secondary battery 300, the active material layers can be formed on one surface, respectively.

[0211] As shown Figure 7C shown in FIG. 1, the positive electrode can 301 is disposed below, and the positive electrode 304, the negative electrode 307, and the negative electrode can 302 are stacked in order, and the positive electrode can 301 and the negative electrode can 302 are pressed together with the gasket 303 interposed therebetween to manufacture the coin-type secondary battery 300.

[0212] By using the secondary battery of the present invention as the coin-type secondary battery 300, a secondary battery with high reliability can be realized. Further, by using the secondary battery of the present invention as the coin-type secondary battery 300, a secondary battery with good low-temperature characteristics can be realized.

[0213] [Cylindrical secondary battery] Next, an example of a cylindrical secondary battery will be described with reference to Figure 8A FIG. 2. As shown Figure 8A in FIG. 2, the top surface of the cylindrical secondary battery 616 includes a positive electrode cap (battery cap) 601, and its side surface and bottom surface include a battery can (outer can) 602. The positive electrode cap 601 and the battery can (outer can) 602 are insulated by a gasket (insulating gasket) 610.

[0214] Figure 8B FIG. 2 is a diagram schematically showing a cross section of the cylindrical secondary battery. Figure 8B The cylindrical secondary battery shown in FIG. 2 has a positive electrode cap (battery cap) 601 on its top surface, and a battery can (outer can) 602 on its side surface and bottom surface. The positive electrode cap and the battery can (outer can) 602 are insulated by a gasket (insulating gasket) 610.

[0215] A battery element is provided inside the hollow cylindrical battery can 602. In this battery element, a strip-shaped positive electrode 604 and a strip-shaped negative electrode 606 are wound with an electrolyte layer 605 interposed 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 by a pair of opposed insulating plates 608 and insulating plate 609. Further, an electrolyte (not shown) of 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 electrode and the negative electrode for the cylindrical storage battery are wound, it is preferable that the active material is formed on both surfaces of the current collector. Note that Figures 8A to 8D FIG. 2 shows a secondary battery 616 in which the height of the cylinder is greater than the diameter of the cylinder, but it is not limited thereto. Further, a secondary battery in which the diameter of the cylinder is greater than the height of the cylinder can also be used. By adopting the above structure, for example, miniaturization of the secondary battery can be achieved.

[0217] The positive electrode 604 is connected to the positive terminal (positive electrode current collector wire) 603, and the negative electrode 606 is connected to the negative terminal (negative electrode current collector wire) 607. The positive terminal 603 can be made of a metal material such as aluminum. The negative terminal 607 can be made of a metal material such as copper. The positive terminal 603 is resistance-welded to the safety valve mechanism 613, and the negative terminal 607 is resistance-welded to the bottom of the battery can 602. The safety valve mechanism 613 and the positive electrode cover 601 are electrically connected through a PTC (Positive Temperature Coefficient) element 611. When the internal pressure of the battery rises above a specified threshold value, the safety valve mechanism 613 cuts off the electrical connection between the positive electrode cover 601 and the positive electrode 604. In addition, the PTC element 611 is a thermosensitive resistance element whose resistance increases when the temperature rises, and limits the current flow through the increase in resistance to prevent abnormal heating. As the PTC element, a barium titanate (BaTiO 3 )-type ceramic material or the like can be used.

[0218] Figure 8C An example of the power storage system 615 is shown. The power storage system 615 includes a plurality of secondary batteries 616, sometimes referred to as a battery pack. The positive electrode of each secondary battery contacts a conductor 624 separated by an insulator 625, and the positive electrodes are electrically connected to each other. The conductor 624 is electrically connected to the control circuit 620 through a wiring 623. In addition, the negative electrode of each secondary battery is electrically connected to the control circuit 620 through a wiring 626. As the control circuit 620, a protection circuit that prevents overcharging or over-discharging or the like can be used.

[0219] Figure 8D An example of the power storage system 615 is shown. The power storage system 615 includes 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 through a wiring 627. The plurality of secondary batteries 616 can be connected in parallel, connected in series, or connected in parallel and then in series. By constructing the power storage system 615 including a plurality of secondary batteries 616, a large amount of power can be obtained.

[0220] In addition, the plurality of secondary batteries 616 can also be connected in parallel and then in series.

[0221] In addition, a temperature control device can also be included between the plurality of secondary batteries 616. When the secondary battery 616 is overheated, it can be cooled by the temperature control device, and when the secondary battery 616 is overcooled, it can be heated by the temperature control device. Therefore, the performance of the power storage system 615 is not easily affected by the external air temperature.

[0222] In addition, in Figure 8DIn this case, the power storage system 615 is electrically connected to the control circuit 620 through the wiring 621 and the wiring 622. The wiring 621 is electrically connected to the positive electrodes of the plurality of secondary batteries 616 through the conductive plate 628, and the wiring 622 is electrically connected to the negative electrodes of the plurality of secondary batteries 616 through the conductive plate 614.

[0223] By using the secondary battery of the present invention as the cylindrical secondary battery 616, a secondary battery with high reliability can be realized. Further, by using the secondary battery of the present invention as the cylindrical secondary battery 616, a secondary battery with good low-temperature characteristics can be realized.

[0224] [Other structural examples of secondary batteries] Structural examples of secondary batteries will be described with reference to FIGS. 9 and 10.

[0225] Figure 9A The secondary battery 913 shown includes a wound body 950 provided with a terminal 951 and a terminal 952 inside a casing 930. The wound body 950 is immersed in the electrolyte of one embodiment of the present invention inside the casing 930. The terminal 952 is in contact with the casing 930, and an insulating material prevents the terminal 951 from coming into contact with the casing 930. Note that, for convenience, although the casing 930 is separately illustrated in Figure 9A in fact, the wound body 950 is covered with the casing 930, and the terminals 951 and 952 extend outside the casing 930. As the casing 930, a metal material (such as aluminum or the like) or a laminate of a metal material and a resin material can be used.

[0226] In addition, as Figure 9B shown, the casing 930 can also be formed using a plurality of materials. Figure 9A For example, in the secondary battery 913 shown in Figure 9B the casings 930a and 930b are joined, and the wound body 950 is provided in the region surrounded by the casings 930a and 930b.

[0227] As the casing 930a, a laminate of a metal material and a resin material or the like can be used. In particular, by using a material such as an organic resin of the resin material to form the surface of the antenna, shielding of the electric field of the secondary battery 913 can be suppressed. Further, if the electric field shielding caused by the casing 930a is small, an antenna can also be provided inside the casing 930a. As the casing 930b, for example, a metal material or a laminate of a metal material and a resin material can be used.

[0228] Furthermore, Figure 9CThe structure of the wound body 950 is shown. The wound body 950 includes a negative electrode 931, a positive electrode 932, and an electrolyte layer 933. The wound body 950 is formed by overlapping the negative electrode 931 and the positive electrode 932 with the electrolyte layer 933 interposed therebetween to form a laminated sheet, and winding the laminated sheet. Additionally, a stack of multiple negative electrodes 931, positive electrodes 932, and electrolyte layers 933 may also be laminated.

[0229] Additionally, a secondary battery 913 including a wound body 950a as shown Figures 10A to 10C may also be used. Figure 10A The wound body 950a shown 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 width of the electrolyte layer 933 is greater than that of the negative electrode active material layer 931a and the positive electrode active material layer 932a, and the electrolyte layer 933 is wound in a manner overlapping the negative electrode active material layer 931a and the positive electrode active material layer 932a. Additionally, from the perspective of safety, it is preferable that the width of the negative electrode active material layer 931a is greater than that of the positive electrode active material layer 932a. Additionally, the wound body 950a having the above shape has good safety and productivity, so it is preferable.

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

[0232] As Figure 10C shown, the wound body 950a is covered by a housing 930 to form a secondary battery 913. The housing 930 preferably is provided with a safety valve, an overcurrent protection element, etc. The safety valve is a valve that is opened when the internal pressure of the housing 930 reaches a specified internal pressure, and can prevent the secondary battery 913 from bursting.

[0233] As Figure 10B shown, the secondary battery 913 may also include multiple wound bodies 950a. By using multiple wound bodies 950a, a secondary battery 913 with a larger charge-discharge capacity can be achieved. Regarding Figure 10A and Figure 10B the other components of the secondary battery 913 shown, reference may be made to Figures 9A to 9C the description of the secondary battery 913 shown.

[0234] By using the secondary battery of the present invention as the secondary battery 913 including a wound body, a secondary battery with high reliability can be achieved. And, by using the secondary battery of the present invention as the secondary battery 913 including a wound body, a secondary battery with good low-temperature characteristics can be achieved.

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

[0236] Embodiment 5 In this embodiment, an example applicable to an electric vehicle (EV) will be described with reference to FIG. 11.

[0237] As Figure 11A shown, in an electric vehicle, as secondary batteries for main driving, first batteries 1301a and 1301b are provided, and a second battery 1311 that supplies power to an inverter 1312 for starting an engine 1304. By using the secondary battery of the present invention as the first batteries 1301a and 1301b, a secondary battery with high reliability can be achieved. Also, by using the secondary battery of the present invention as the above-mentioned first batteries 1301a and 1301b, a secondary battery with good low-temperature characteristics can be achieved.

[0238] The second battery 1311 is also referred to as a cranking battery (also known as a starting battery). The second battery 1311 only needs to have a high output and does not necessarily need to have a high capacity. In addition, 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 can be either a wound type or a stacked type. In addition, the all-solid-state battery of Embodiment 6 can also be used as the first battery 1301a. By using the all-solid-state battery of Embodiment 6 as the first battery 1301a, a high capacity can be achieved, and miniaturization and weight reduction can be achieved due to improved safety.

[0240] In this embodiment, an example of parallel connection of the first batteries 1301a and 1301b is shown, but three or more batteries can also be connected in parallel. In addition, as long as sufficient power can be stored in the first battery 1301a, the first battery 1301b can be omitted. By forming a battery pack from a plurality of secondary batteries, a larger amount of power can be taken out. The plurality of secondary batteries can be connected in parallel, in series, or in series after parallel connection. Sometimes a plurality of secondary batteries are referred to as a battery pack.

[0241] In order to cut off the power from the plurality of secondary batteries, the in-vehicle secondary battery includes a charging plug or a circuit breaker that can cut off high voltage without using tools, and it is provided in the first battery 1301a.

[0242] In addition, the power of the first batteries 1301a and 1301b is mainly used to rotate the engine 1304, and power is also supplied to 42V series vehicle components (such as the electric power steering system 1307, the heater 1308, the defroster 1309, etc.) through the DCDC circuit 1306. When the rear wheels include the rear-mounted engine 1317, the first battery 1301a is used to rotate the rear-mounted engine 1317.

[0243] In addition, the second battery 1311 supplies power to 14V series vehicle components (such as the audio 1313, the power window 1314, the lamps 1315, etc.) through the DCDC circuit 1310.

[0244] In addition, Figure 11B the first battery 1301a will be described.

[0245] Figure 11B An example is shown in which nine square secondary batteries 1300 are used as one battery pack 1415. In addition, the nine square secondary batteries 1300 are connected in series, and one electrode is fixed using the fixing portion 1413 made of an insulator, and the other electrode is fixed using the fixing portion 1414 made of an insulator. In the present embodiment, an example of fixing using the fixing portions 1413 and 1414 is shown, but they may also be housed in a battery housing (also referred to as a casing). Assuming that the vehicle is subjected to vibrations or shakes from the outside (such as the road surface, etc.), it is preferable to fix a plurality of secondary batteries using the fixing portions 1413 and 1414 and the battery housing. In addition, one electrode is electrically connected to the control circuit unit 1320 through the wiring 1421. The other electrode is electrically connected to the control circuit unit 1320 through the wiring 1422.

[0246] In addition, the control circuit unit 1320 may also use a memory circuit including a transistor using an oxide semiconductor. Sometimes, a charge control circuit or a battery control system including a memory circuit using a transistor using an oxide semiconductor is referred to as BTOS (Battery operating system or Battery oxide semiconductor).

[0247] Preferably, a metal oxide used as an oxide semiconductor is employed. For example, as the oxide, an In-M-Zn oxide (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, magnesium, etc.) and other metal oxides are preferably used. In particular, the In-M-Zn oxide that can be applied to the oxide is preferably CAAC-OS (C-Axis Aligned Crystal Oxide Semiconductor) or CAC-OS (Cloud-Aligned Composite Oxide Semiconductor). Additionally, an In-Ga oxide or an In-Zn oxide can also be used as the oxide. CAAC-OS is an oxide semiconductor including a plurality of crystal regions, and the c-axis of the plurality of crystal regions is oriented in a specific direction. Moreover, the specific direction refers to 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. Additionally, the crystal region is a region having periodicity in the atomic arrangement. Note that when the atomic arrangement is regarded as a lattice arrangement, the crystal region is also a region where the lattice arrangements are consistent. Furthermore, CAAC-OS has a region where a plurality of crystal regions are connected in the a-b plane direction, and sometimes this region has distortion. Additionally, the distortion refers to the portion where the direction of the lattice arrangement changes between the region where the lattice arrangements are consistent and other regions where the lattice arrangements are consistent in the region where a plurality of crystal regions are connected. In other words, CAAC-OS refers to an oxide semiconductor in which the c-axis is oriented and there is no obvious orientation in the a-b plane direction.

[0248] In addition, the control circuit unit 1320 preferably uses a transistor including an oxide semiconductor because this transistor can be used in a low-temperature environment. To simplify the process, the control circuit unit 1320 can also be formed using a unipolar transistor. The operating ambient temperature range of the transistor including an oxide semiconductor in the semiconductor layer is larger than that of a single-crystal Si transistor, that is, it is above -40°C and below 150°C, and the characteristic change during secondary battery heating is smaller than that of a single-crystal Si transistor. The off-state current of the transistor including an oxide semiconductor does not depend on temperature and is extremely low even at 150°C, but the temperature dependence of the off-state current characteristic of a single-crystal Si transistor is large. For example, at 150°C, the off-state 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 utilizing an oxide semiconductor can also be used as an automatic control device for a secondary battery that is the cause of instability due to ten conditions such as a micro short circuit. As functions for solving the cause of instability due to the ten conditions, examples include prevention of overcharging, prevention of overcurrent, control of overheating during charging, cell balance in a battery pack, prevention of overdischarge, a capacity meter, automatic control of charging voltage and current amount according to temperature, control of charging current amount according to the degree of deterioration, detection of abnormal behavior of a micro short circuit, prediction of abnormality regarding a micro short circuit, etc. The control circuit unit 1320 has at least one of the above functions. In addition, miniaturization of the automatic control device for a secondary battery can be achieved.

[0250] In addition, a micro short circuit is one of internal short circuits and refers to a very small short circuit inside a secondary battery. One of the causes of a micro short circuit is considered to be due to repeated charge and discharge, resulting in uneven distribution of the positive electrode active material, local current concentration occurring between a part of the positive electrode and a part of the negative electrode, or side reactants being generated due to side reactions, leading to the occurrence of a micro short circuit.

[0251] In addition, the control circuit unit 1320 detects the terminal voltage of the secondary battery in addition to the micro short circuit and manages the charge and discharge state of the secondary battery. For example, in order to prevent overcharging, both the output transistor of the charging circuit and the cutoff switch can be turned off almost simultaneously.

[0252] In addition, Figure 11C shows Figure 11B An example of a block diagram of the battery pack 1415 shown.

[0253] The control circuit unit 1320 includes: a switch unit 1324 including at least 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. In the control circuit unit 1320, the upper limit voltage and lower limit voltage of the secondary battery used are set to control the upper limit of the current flowing from the outside and the upper limit of the output current flowing to the outside, etc. The range between the lower limit voltage and the upper limit voltage of the secondary battery is the recommended voltage range. When the voltage is outside this range, the switch unit 1324 operates as a protection circuit. In addition, since the control circuit unit 1320 controls the switch unit 1324 to prevent overdischarge and overcharging, it can also be called a protection circuit. For example, when the control circuit 1322 detects a voltage that will cause overcharging, the current is blocked by turning the switch of the switch unit 1324 to the off state. In addition, a function of blocking the current according to the rise in temperature can be set by providing a PTC element in the charge and discharge path. In addition, the control circuit unit 1320 includes an external terminal 1325 (+IN) and an external terminal 1326 (-IN).

[0254] The switching section 1324 can be constituted by combining an n-channel transistor and a p-channel transistor. In addition to the switches including Si transistors using single crystal silicon, for example, power transistors such as 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 x (gallium oxide; x is a real number greater than 0), etc. can be used to constitute the switching section 1324. In addition, the memory element using an OS transistor can be freely arranged by being stacked on a circuit using an Si transistor, etc., so integration is easily achieved. By integrating by stacking the control circuit section 1320 using an OS transistor on the switching section 1324, the switching section 1324 and the control circuit section 1320 can be integrated in one chip, so miniaturization can be achieved.

[0255] The first batteries 1301a and 1301b mainly supply power to 42V series (high voltage series) in-vehicle devices, while the second battery 1311 supplies power to 14V series (low voltage series) in-vehicle devices. The second battery 1311 often uses a lead-acid battery because of cost advantages. Although there is an advantage of no need for maintenance when using a secondary battery as the second battery 1311, abnormalities that cannot be identified during manufacturing may occur during long-term use, for example, use for more than three years. In particular, when the second battery 1311 for starting the inverter cannot operate, the engine sometimes cannot be started even if the first batteries 1301a and 1301b have remaining capacity. When the second battery 1311 is a lead-acid battery, power is supplied from the first battery to the second battery to charge it in a way that always maintains a fully charged state, so the situation where the engine cannot operate as described above does not occur.

[0256] This embodiment shows an example in which both the first battery 1301a and the second battery 1311 use secondary batteries, but the second battery 1311 can also use a lead-acid battery, a 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 achieved. And, by using the secondary battery of the present invention as the above-mentioned secondary battery, a secondary battery with good low-temperature characteristics can be achieved.

[0257] In addition, the regenerative energy generated by the rotation of the tire 1316 is sent to the engine 1304 through the transmission 1305, and is charged from the engine controller 1303 and the battery controller 1302 to the second battery 1311 through the control circuit unit 1321. Additionally, it is charged from the battery controller 1302 to the first battery 1301a through the control circuit unit 1320. Additionally, it is charged from the battery controller 1302 to the first battery 1301b through the control circuit unit 1320. To efficiently charge the regenerative energy, it is preferable that the first batteries 1301a and 1301b can be charged at high speed.

[0258] The battery controller 1302 can set the charging voltage, charging current, etc. of the first batteries 1301a and 1301b. The battery controller 1302 sets the charging conditions according to the charging characteristics of the secondary battery used for high-speed charging.

[0259] In addition, although not shown in the figure, when connected to an external charger, the socket of the charger or the connection cable of the charger is electrically connected to the battery controller 1302. The electric power supplied from the external charger is charged to the first batteries 1301a and 1301b through the battery controller 1302. Additionally, some chargers are provided with a control circuit and do not use the functions of the battery controller 1302, but to prevent overcharging, it is preferable to charge the first batteries 1301a and 1301b through the control circuit unit 1320. In addition, sometimes the connection cable or the connection cable of the charger is provided with a control circuit. The control circuit unit 1320 is sometimes referred to as an ECU (Electronic Control Unit). The ECU is connected to the CAN (Controller Area Network) provided in the electric vehicle. CAN is one of the serial communication standards used as an in-vehicle LAN. In addition, the ECU includes a microcomputer. In addition, the ECU uses a CPU or a GPU.

[0260] As external chargers provided in charging stations, etc., there are 100V sockets, 200V sockets, three-phase 200V and 50kW sockets, etc. Additionally, charging can also be performed by being supplied with electric power from an external charging device through a non-contact power supply method, etc.

[0261] Next, an example of installing a secondary battery as one aspect of the present invention in a vehicle, typically a transport vehicle, will be described.

[0262] In addition, secondary batteries can be installed in next-generation clean energy vehicles such as hybrid vehicles (HV), electric vehicles (EV), or plug-in hybrid vehicles (PHV) in which the secondary batteries are installed in vehicles. In addition, secondary batteries can also be installed in transportation vehicles such as agricultural machinery, electric bicycles including electric assist bicycles, motorcycles, electric wheelchairs, electric go-karts, small or large ships, submarines, airplanes such as fixed-wing aircraft and rotary-wing aircraft, rockets, artificial satellites, space probes, planetary probes, and spacecraft.

[0263] Figures 12A to 12D A transportation vehicle using one mode of the present invention is shown. Figure 12A The shown vehicle 2001 is an electric vehicle that uses an electric motor as a power source for driving. Alternatively, the vehicle 2001 is a hybrid vehicle that can appropriately select an electric motor and an engine as power sources for driving. When installing a secondary battery in a vehicle, examples of the secondary battery shown in the above-described embodiments can be provided in one or more parts. By using the secondary battery of the present invention as the secondary battery installed in the vehicle, a highly reliable secondary battery can be realized. And, by using the secondary battery of the present invention as the above-described secondary battery, a secondary battery having good low-temperature characteristics can be realized.

[0264] Figure 12A The shown vehicle 2001 includes a battery pack 2200, and the battery pack includes battery modules that connect a plurality of secondary batteries. In addition, the battery pack 2200 preferably further includes a charge control device electrically connected to the battery modules.

[0265] In addition, in the vehicle 2001, the secondary battery included in the vehicle 2001 can be charged by supplying power from an external charging device using a plug-in method, a non-contact power supply method, or the like. When charging, as the charging method, the specifications of the connector, etc., can be appropriately carried out according to a prescribed method such as CHAdeMO (registered trademark) or the Combined Charging System. As the charging device, a charging station installed in a commercial facility or a power source at home can also be used. For example, by supplying power from the outside using plug-in technology, the power storage device installed in the vehicle 2001 can be charged. The alternating current power can be converted into direct current power by a conversion device such as an AC-DC converter for charging.

[0266] In addition, although not shown, the power receiving device can also be installed in a vehicle and charged by non-contact power supply from a power transmitting device on the ground. When using the non-contact power supply method, by assembling the power transmitting device in a road or an outer wall, charging can be performed not only while the vehicle is parked but also while it is in motion. In addition, using this non-contact power supply method, power can be transmitted and received between two vehicles. Furthermore, a solar cell can be provided outside the vehicle to charge the secondary battery while the vehicle is parked or in motion. Such non-contact power supply can be achieved by means of electromagnetic induction or magnetic field resonance.

[0267] In Figure 12B as an example of a transport vehicle, a large transport vehicle 2002 including an electrically controlled engine is shown. The battery module of the transport vehicle 2002 is, for example, a battery module with a maximum voltage of 170V in which 48 units are connected in series with four secondary batteries having a nominal voltage of 3.0V or more and 5.0V or less as battery cells. Except for differences such as the number of secondary batteries, the battery pack 2201 has the same functions as Figure 11B so the description thereof is 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 realized. And, by using the secondary battery of the present invention as the secondary battery of the above-mentioned battery pack 2201, a secondary battery with good low-temperature characteristics can be realized.

[0268] In Figure 12C as an example, a large transport vehicle 2003 including an electrically controlled engine is shown. The battery module of the transport vehicle 2003 is, for example, a battery module with a maximum voltage of 600V in which 100 or more secondary batteries having a nominal voltage of 3.0V or more and 5.0V or less are connected in series. In addition, except for differences such as the number of secondary batteries constituting the battery module, the battery pack 2202 has the same functions as Figure 11B so the description thereof is omitted. By using the secondary battery of the present invention as the secondary battery in the module, a highly reliable secondary battery can be realized. And, by using the secondary battery of the present invention as the secondary battery in the above-mentioned module, a secondary battery with good low-temperature characteristics can be realized.

[0269] In Figure 12D as an example, an aircraft 2004 equipped with an engine that burns fuel is shown. Figure 12D The aircraft 2004 shown includes landing and takeoff wheels, so it can be said that the aircraft 2004 is part of a transport vehicle. In the aircraft 2004, a plurality of secondary batteries are connected to form a battery module, and a battery pack 2203 including the battery module and a charge control device is included.

[0270] The battery module of the aircraft 2004, for example, has eight 4V secondary batteries connected in series, and its maximum voltage is 32V. In addition to the number of secondary batteries of the battery module constituting the battery pack 2203, etc., it has the same function as Figure 11B and thus the description thereof is omitted.

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

[0272] Embodiment 6 In this embodiment, an example of installing a secondary battery of one aspect of the present invention in a vehicle such as a two-wheeler or a bicycle is shown.

[0273] Figure 13A An example of an electric bicycle using a secondary battery of one aspect of the present invention is shown. Figure 13A The shown electric bicycle 8700 can use a secondary battery of one aspect of the present invention. A secondary battery of one aspect of the present invention may also include a protection circuit.

[0274] The electric bicycle 8700 includes a power storage device 8702. The power storage device 8702 supplies power to an engine that assists the rider. In addition, the power storage device 8702 is portable. Figure 13B The power storage device 8702 taken out from the bicycle is shown. The power storage device 8702 incorporates a plurality of secondary batteries 8701 of one aspect of the present invention, and the remaining battery level, etc., can be displayed by a display unit 8703. By using the secondary battery of the present invention as the secondary battery 8701, a highly reliable secondary battery can be realized. Also, by using the secondary battery of the present invention as the secondary battery 8701, a secondary battery having good low-temperature characteristics can be realized.

[0275] In addition, the power storage device 8702 includes a control circuit 8704 capable of performing charge control or abnormality detection of the secondary battery. The control circuit 8704 is electrically connected to the positive and negative electrodes of the secondary battery 8701. It contributes greatly to reducing accidents such as fires caused by secondary batteries.

[0276] Figure 13C It is an example of a two-wheeler using a secondary battery of one aspect of the present invention. Figure 13C The shown scooter 8600 includes a power storage device 8602, side mirrors 8601, and direction indicators 8603. The power storage device 8602 can supply power to the direction indicators 8603. By using the secondary battery of the present invention as the secondary battery, a highly reliable secondary battery can be realized. Also, by using the secondary battery of the present invention as the secondary battery, a secondary battery having good low-temperature characteristics can be realized.

[0277] In addition, in Figure 13CIn the scooter 8600 shown, the power storage device 8602 can be accommodated in the under-seat storage portion 8604. Even if the under-seat storage portion 8604 is small, the power storage device 8602 can be stored in the under-seat storage portion 8604.

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

[0279] Embodiment 7 In this embodiment, an example of mounting a secondary battery of one aspect of the present invention in an electronic device will be described. As the electronic device equipped with the secondary battery, for example, a television device (also referred to as a television or a television receiver), a display for a computer or the like, a digital camera, a digital video camera, a digital photo frame, a mobile phone (also referred to as a mobile telephone, a mobile phone device), a portable game machine, a portable information terminal, a sound reproduction device, a large game machine such as a pachinko machine, etc. can be cited. As the portable information terminal, a notebook personal computer, a tablet terminal, an e-book terminal, a mobile phone, etc. can be cited.

[0280] Figure 14A An example of a mobile phone is shown. The mobile phone 2100 includes operation buttons 2103, an external connection port 2104, a speaker 2105, a microphone 2106, etc. in addition to a display portion 2102 mounted in a housing 2101. Further, 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 realized. And, by using the secondary battery of the present invention as the secondary battery, a secondary battery having good low-temperature characteristics can be realized.

[0281] The mobile phone 2100 can execute various application programs such as mobile phone calls, e-mails, reading and writing of texts, music playback, network communication, computer games, etc.

[0282] In addition to time setting, the operation buttons 2103 can have various functions such as a power switch, a switch for wireless communication, setting and canceling of a silent mode, setting and canceling of a power saving mode, etc. For example, by using the operating system assembled in the mobile phone 2100, the functions of the operation buttons 2103 can be freely set.

[0283] In addition, the mobile phone 2100 can execute short-range wireless communication standardized for communication. For example, by communicating with a wirelessly communicable headset, hands-free calling can be performed.

[0284] In addition, the mobile phone 2100 is provided with an external connection port 2104, through which data can be directly sent to other information terminals or received from other information terminals via a connector. In addition, charging can also be performed through the external connection port 2104. Furthermore, the charging operation can also be carried out by wireless power supply instead of using the external connection port 2104.

[0285] The mobile phone 2100 preferably includes sensors. As sensors, for example, it is preferably equipped with human body sensors such as fingerprint sensors, pulse sensors, and body temperature sensors, touch sensors, pressure sensors, acceleration sensors, etc.

[0286] Figure 14B An unmanned aerial vehicle 2300 including a plurality of rotors 2302 is shown. The unmanned aerial vehicle 2300 is also referred to as a drone. The unmanned aerial vehicle 2300 includes a secondary battery 2301, a camera 2303, and an antenna (not shown) according to one embodiment of the present invention. The unmanned aerial vehicle 2300 can be remotely operated via the antenna. By using the secondary battery of the present invention as the secondary battery, a highly reliable secondary battery can be realized. Moreover, by using the secondary battery of the present invention as the secondary battery, a secondary battery with good low-temperature characteristics can be realized.

[0287] Figure 14C An example of a robot is shown. Figure 14C The shown robot 6400 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, an arithmetic unit, etc.

[0288] The microphone 6402 has the function of detecting the user's voice and surrounding sounds, etc. In addition, the speaker 6404 has the function of emitting sounds. The robot 6400 can communicate with the user through the microphone 6402 and the speaker 6404.

[0289] The display unit 6405 has the function of displaying various information. The robot 6400 can display the information required by the user on the display unit 6405. The display unit 6405 may also be equipped with a touch panel. In addition, the display unit 6405 can be a detachable information terminal, and by setting it at a fixed position of the robot 6400, charging and data transmission and reception can be carried out.

[0290] The upper camera 6403 and the lower camera 6406 have the function of photographing the surrounding environment of the robot 6400. In addition, the obstacle sensor 6407 can use the moving mechanism 6408 to detect whether there are obstacles in the forward direction when the robot 6400 moves forward. The robot 6400 can confirm the surrounding environment by using the upper camera 6403, the lower camera 6406 and the obstacle sensor 6407 and move safely.

[0291] The internal area of the robot 6400 is provided with a secondary battery 6409 and semiconductor devices or electronic components according to one aspect of the present invention. By using the secondary battery of the present invention as a secondary battery, a highly reliable secondary battery can be realized. And, by using the secondary battery of the present invention as a secondary battery, a secondary battery having good low-temperature characteristics can be realized.

[0292] Figure 14D An example of a floor cleaning robot is shown. The floor cleaning robot 6300 includes a display unit 6302 disposed on the top surface of the housing 6301, a plurality of cameras 6303 disposed on the side surface, a brush 6304, operation buttons 6305, a secondary battery 6306, various sensors, etc. Although not shown, the floor cleaning robot 6300 also has wheels, a suction port, etc. The floor cleaning robot 6300 can move autonomously and can detect garbage 6310 and suck the garbage from the suction port provided below.

[0293] For example, the floor cleaning robot 6300 can determine whether there are obstacles such as walls, furniture, or steps by analyzing the images captured by the camera 6303. In addition, when an object such as a wire that may get entangled with the brush 6304 is found through image analysis, the rotation of the brush 6304 can be stopped. The internal area of the floor cleaning robot 6300 is provided with a secondary battery 6306 and semiconductor devices or electronic components according to one aspect of the present invention. By using the secondary battery of the present invention as a secondary battery, a highly reliable secondary battery can be realized. And, by using the secondary battery of the present invention as a secondary battery, a secondary battery having good low-temperature characteristics can be realized.

[0294] This embodiment can be implemented by appropriately combining with other embodiments.

[0295] Embodiment 8 In this embodiment, an example of installing a secondary battery according to one aspect of the present invention in a space device is described.

[0296] In Figure 15A as an example of a space device, a satellite 6800 is shown. The satellite 6800 includes a main body 6801, a solar panel 6802, an antenna 6803, and a secondary battery 6805. Sometimes the solar panel is called a solar cell module.

[0297] When sunlight shines on the solar panel 6802, electricity required for the operation of the satellite 6800 is generated. However, for example, when sunlight does not shine on the solar panel or when the amount of sunlight shining on the solar panel is small, the amount of generated electricity decreases. Therefore, it is possible that the electricity required for the operation of the satellite 6800 is not generated. In order to operate the satellite 6800 even when the generated electricity is small, it is preferable to provide a secondary battery 6805 in the satellite 6800. By using the secondary battery of the present invention as the secondary battery, a highly reliable secondary battery can be realized. Also, by using the secondary battery of the present invention as the secondary battery, a secondary battery having good low-temperature characteristics can be realized.

[0298] The satellite 6800 can generate a signal. This signal is transmitted through the antenna 6803 and can be received by, for example, a receiver on the ground or another satellite. By receiving the signal transmitted by the satellite 6800, for example, the position of the receiver that receives the signal can be measured. Thus, the satellite 6800 can constitute, for example, a satellite positioning system.

[0299] Alternatively, the satellite 6800 may include a sensor. For example, by including a visible light sensor, the satellite 6800 can have a function of detecting sunlight reflected by an object on the ground. Or, by including a thermal infrared sensor, the satellite 6800 can have a function of detecting thermal infrared rays released from the earth's surface. Thus, the satellite 6800 can be used as, for example, an earth observation satellite.

[0300] Figure 15B As an example of a space device, a probe 6900 including a solar sail (also called a light sail) is shown. The probe 6900 includes a main body 6901, a solar sail 6902, and a secondary battery 6905. By using the secondary battery of the present invention as the secondary battery, a highly reliable secondary battery can be realized. Also, by using the secondary battery of the present invention as the secondary battery, a secondary battery having good low-temperature characteristics can be realized. When photons emitted by the sun irradiate the surface of the solar sail 6902, momentum is transferred to the solar sail 6902. Therefore, preferably, the surface of the solar sail 6902 has a high-reflectivity film and faces the direction of the sun.

[0301] In addition, the solar sail 6902 can also be designed to be in a folded state of a smaller size before leaving the atmosphere and to be unfolded into a large thin sheet as Figure 15B shown outside the atmosphere (outer space).

[0302] In Figure 15CAmong them, as an example of a space device, a spacecraft 6910 is shown. The spacecraft 6910 includes a main body 6911, solar panels 6912, and a secondary battery 6913. By using the secondary battery of the present invention as the secondary battery, a secondary battery with high reliability can be achieved. Also, by using the secondary battery of the present invention as the secondary battery, a secondary battery with good low-temperature characteristics can be achieved. The main body 6911 can include, for example, a pressurized cabin and a non-pressurized cabin. The pressurized cabin can also be of a specification that allows crew members to enter. The electricity generated by sunlight irradiating the solar panels 6912 can be charged to the secondary battery 6913.

[0303] In Figure 15D Among them, as an example of a space device, a rover 6920 is shown. The rover 6920 includes a main body 6921 and a secondary battery 6923. By using the secondary battery of the present invention as the secondary battery, a secondary battery with high reliability can be achieved. Also, by using the secondary battery of the present invention as the secondary battery, a secondary battery with good low-temperature characteristics can be achieved. The rover 6920 can also include solar panels 6922.

[0304] The rover 6920 can also be of a specification that allows crew members to enter. Additionally, the electricity generated by sunlight irradiating the solar panels 6912 can be charged to the secondary battery 6923, and the electricity generated by other power sources such as fuel cells and radioisotope thermoelectric generators can also be charged to the secondary battery 6923.

[0305] The content of this embodiment can be appropriately combined with the content of other embodiments.

Claims

1. A secondary battery comprising: A negative electrode active material layer; Isolate body; A carbon sheet between the negative electrode active material layer and the separator; Dendrites between the negative electrode active material layer and the carbon sheet; and positive electrode active material layer, Wherein, the negative electrode active material layer comprises a negative electrode active material, The negative electrode active material comprises at least one selected from graphite and silicon, The thickness of the carbon sheet is greater than or equal to 25 nm and less than or equal to 50 μm. Also, the dendrite has a portion along a surface of the carbon sheet.

2. The secondary battery according to claim 1, further comprising: Electrolyte, The electrolyte contains FEC and MTFP.

3. The secondary battery according to claim 1, further comprising: Electrolyte, The electrolyte comprises ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate.

4. The secondary battery according to claim 1, further comprising: Electrolyte, The electrolyte comprises ethylene carbonate and diethyl carbonate.

5. The secondary battery according to claim 1, The carbon sheet comprises carbon nanotubes.

6. A secondary battery comprising: A negative electrode active material layer; Isolate body; A carbon sheet between the negative electrode active material layer and the separator; a dendrite between the negative electrode active material layer and the carbon sheet; and positive electrode active material layer, Wherein, the negative electrode active material layer comprises a negative electrode active material, The negative electrode active material comprises lithium metal, The thickness of the carbon sheet is greater than or equal to 25 nm and less than or equal to 50 μm. Also, the dendrite has a portion along a surface of the carbon sheet.

7. The secondary battery according to claim 6, further comprising: Electrolyte, The electrolyte comprises ethylene carbonate and diethyl carbonate.

8. The secondary battery according to claim 6, The carbon sheet comprises carbon nanotubes.

9. The secondary battery according to claim 6, further comprising: Electrolyte, The electrolyte contains FEC and MTFP.

10. The secondary battery according to claim 6, further comprising: Electrolyte, The electrolyte comprises ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate.

11. A secondary battery comprising: A negative electrode active material layer; Carbon sheet; A separator between the negative electrode active material layer and the carbon sheet; Dendrites between the negative electrode active material layer and the separator; and positive electrode active material layer, Wherein, the negative electrode active material layer comprises a negative electrode active material, The thickness of the carbon sheet is greater than or equal to 25 nm and less than or equal to 50 μm. Also, the dendrite has a portion along a surface of the carbon sheet.

12. The secondary battery according to claim 11, The negative electrode active material includes at least one selected from graphite and silicon.

13. The secondary battery according to claim 11, The negative electrode active material comprises lithium metal.

14. The secondary battery according to claim 11, further comprising: Electrolyte, The electrolyte contains FEC and MTFP.

15. The secondary battery according to claim 11, further comprising: Electrolyte, The electrolyte comprises ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate.

16. The secondary battery according to claim 11, further comprising: Electrolyte, The electrolyte comprises ethylene carbonate and diethyl carbonate.

17. The secondary battery according to claim 11, The carbon sheet comprises carbon nanotubes.

Images