Manufacturing method for secondary battery

Abstract

To provide a manufacturing method for a secondary battery in which internal short-circuit due to dendrite is suppressed.SOLUTION: A manufacturing method for a secondary battery includes applying a slurry including carbon, a solvent, and a binder to a separator, forming a carbon layer including the binder by drying the slurry to remove the solvent, and performing a pressing process by making the carbon layer and a negative electrode face each other. In the pressing process, heating is preferably performed.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a secondary battery. However, the present invention is not limited to the above field, and may relate to semiconductor devices, display devices, light-emitting devices, power storage devices, lighting devices, electronic devices, vehicles, and manufacturing methods thereof. For example, in semiconductor devices, display devices, light-emitting devices, lighting devices, electronic devices, and vehicles, the secondary battery obtained by the present invention can be applied as a required power source. In addition, electronic devices include information terminal devices equipped with secondary batteries. In addition, power storage devices include stationary power storage devices.

Background Art

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

[0003] When a lithium-ion secondary battery repeats charge and discharge, there is a problem that lithium dendrites precipitate on the negative electrode. Lithium dendrites are dendritic crystals of lithium metal that grow during the charge and discharge process, and precipitate, for example, when current concentrates on uneven portions of the negative electrode surface. When lithium dendrites reach the positive electrode, the lithium-ion secondary battery may experience an internal short circuit, and the reliability of the lithium-ion secondary battery may decrease.

[0004] Graphite is often used as the negative electrode active material, and it is expected to increase the capacity of lithium-ion secondary batteries by using lithium metal instead of graphite. Graphite is likely to precipitate lithium dendrites when charging and discharging at a low temperature, and lithium metal will precipitate lithium dendrites even during charging and discharging at room temperature.

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

[0006] In addition, research and development on separators for lithium-ion secondary batteries have been actively conducted, and those provided with a porous substrate and an adhesive porous layer containing a polyvinylidene fluoride-based resin on one or both sides of the porous substrate have been proposed (see Patent Document 2).

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, in the configuration of Patent Document 1, an inorganic salt containing fluorine must be used in the electrolytic solution, so the choice of electrolytic solution is limited. For example, it becomes difficult to select an electrolytic solution suitable for operation in a low-temperature environment. Therefore, an object of the present invention is to provide a secondary battery having a new configuration for reducing the influence of dendrites and a method for manufacturing the same.

[0009] Note that the description of these problems does not prevent the existence of other problems. Also, one aspect of the present invention does not have to solve all of these problems. Further, it is possible to extract other problems from the description of this specification, drawings, claims, etc.

Means for Solving the Problems

[0010] In view of the above problems, the present inventors have found a new configuration and a method for manufacturing the same in order to control the growth direction of dendrites deposited on the negative electrode. The new configuration is a configuration having a carbon layer on one side of the separator, and by this configuration, internal short circuits of the secondary battery can be suppressed, and the reliability of the secondary battery is improved. In addition, in order to control the growth direction of dendrites deposited on the negative electrode, it is preferable that one side of the separator is the surface facing the negative electrode.

[0011] One aspect of the present invention is a method for manufacturing a secondary battery, which comprises coating a separator with a slurry containing carbon and a solvent, drying the slurry to remove the solvent, forming a carbon layer, opposing the carbon layer to a negative electrode, and performing a pressing treatment.

[0012] Another aspect of the present invention is a method for manufacturing a secondary battery, which comprises coating a separator with a slurry containing carbon, a solvent, and a binder, drying the slurry to remove the solvent, forming a carbon layer having a binder, opposing the carbon layer to a negative electrode, and performing a pressing treatment.

[0013] Another aspect of the present invention is a method for manufacturing a secondary battery, which comprises coating a separator with a slurry containing carbon, a solvent, and polyglutamic acid, drying the slurry to remove the solvent, forming a carbon layer having polyglutamic acid, opposing the carbon layer to a negative electrode, performing a pressing treatment, and the solvent has water.

[0014] In another aspect of the present invention, it is preferable to heat in the pressing treatment.

[0015] In another aspect of the present invention, it is preferable to perform linear pressing in the pressing treatment.

[0016] Another aspect of the present invention is a method for manufacturing a secondary battery, which comprises coating a separator with a slurry containing carbon and a solvent, drying the slurry to remove the solvent, forming a carbon layer, opposing the carbon layer to a negative electrode, performing a first pressing treatment, opposing the separator to a positive electrode, and performing a second pressing treatment.

[0017] Another aspect of the present invention is a method for manufacturing a secondary battery, which comprises coating a separator with a slurry containing carbon, a solvent, and a binder, drying the slurry to remove the solvent, forming a carbon layer having a binder, opposing the carbon layer to a negative electrode, performing a first pressing treatment, opposing the separator to a positive electrode, and performing a second pressing treatment.

[0018] Another aspect of the present invention is a method for manufacturing a secondary battery, comprising coating a separator with a slurry having carbon, a solvent, and polyglutamic acid, drying the slurry to remove the solvent, thereby forming a carbon layer having polyglutamic acid, opposing the carbon layer to a negative electrode, performing a first pressing process, opposing the separator to a positive electrode, performing a second pressing process, and the solvent having water.

[0019] In another aspect of the present invention, it is preferable to heat in the first pressing process or the second pressing process.

[0020] In another aspect of the present invention, it is preferable to perform linear pressing in the first pressing process and surface pressing in the second pressing process.

[0021] In another aspect of the present invention, it is preferable to perform the second pressing process after the positive electrode is cut.

Advantages of the Invention

[0022] According to one aspect of the present invention, it is possible to provide a method for manufacturing a highly reliable secondary battery with suppressed internal short circuit. According to one aspect of the present invention, the options for each member of the secondary battery can be expanded.

Brief Description of the Drawings

[0023]

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Embodiments for Carrying Out the Invention

[0024] Embodiments of the present invention will be described with appropriate reference to the drawings. However, the present invention is not limited to the following description, and it will be easily understood by those skilled in the art that the form and details thereof can be variously changed without departing from the spirit and scope of the present invention. Therefore, in the embodiments shown below, the same reference numerals denote the same objects in different drawings.

[0025] In this specification and the like, the slurry for a carbon layer is a material liquid containing materials necessary for forming a carbon layer on a separator, and refers to a material liquid containing at least carbon and a solvent. Further, the slurry for a carbon layer is preferably a material liquid containing a binder in addition to carbon and a solvent. Further, the slurry for a carbon layer is preferably a material liquid containing a dispersant in addition to carbon and a solvent. Further, the slurry for a carbon layer is preferably a material liquid containing a dispersant in addition to carbon, a solvent and a binder. Note that in this specification and the like, the viscosity of the material liquid is not limited at all.

[0026] In this specification and the like, the slurry for an electrode is a material liquid containing materials necessary for forming an active material layer on a current collector, and contains an active material, a binder and a solvent, and preferably further contains a conductive material mixed therein. Note that the slurry for forming a positive electrode active material layer may be referred to as a positive electrode slurry, and the slurry for forming a negative electrode active material layer may be referred to as a negative electrode slurry.

[0027] In this specification and the like, the loading amount refers to the weight of the active material per unit surface area 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 the case of double-sided coating where the slurry containing the active material is coated on both sides of the current collector, the above loading amount is considered per side.

[0028] In this specification and the like, a full cell means a battery cell assembled such that different electrodes are positioned, like a unit cell of a positive electrode / negative electrode. In this specification and the like, a half cell means a battery cell assembled using lithium metal as the negative electrode (counter electrode).

[0029] In this specification and the like, the median diameter (D50) is one of the powder characteristics, and is the particle diameter when the integrated amount occupies 50% in the cumulative curve of the particle size distribution measurement result. There is a method for measuring the median diameter (D50) from image analysis such as SEM or TEM. For example, when measuring 20 or more particles, creating an integrated particle amount curve, the particle diameter when the integrated amount occupies 50% can be defined as the median diameter (D50).

[0030] In this specification and the like, a lithium-ion secondary battery may be referred to as a lithium-ion battery, and refers to a battery using lithium ions as carrier ions, but in one aspect of the present invention, the carrier ions are not limited to lithium ions. For example, alkali metal ions or alkaline earth metal ions can be used as the carrier ions, and specifically, sodium ions and the like can be applied. In this case, by replacing lithium ions with sodium ions and the like, the present invention can be understood. Also, when explaining a configuration where there is no limitation on the carrier ions, it may be referred to as a secondary battery.

[0031] In this specification and the like, carbonate refers to a compound having at least one ester in its molecular structure, and includes cyclic carbonate and chain carbonate unless otherwise specified. Also, chain includes both linear and branched chains.

[0032] In this specification and the like, the low-temperature environment refers to 0°C or lower, and 0°C or lower may be referred to as below the freezing point.

[0033] In this specification and the like, the internal short circuit of a secondary battery includes the contact between the positive electrode and the negative electrode inside the secondary battery or the electrical conduction between the positive electrode and the negative electrode inside the secondary battery. The internal short circuit not only causes problems in the charging operation and / or discharging operation of the secondary battery but also may lead to heat generation and ignition. In order to realize a safe secondary battery, it is preferable that the internal short circuit is suppressed even at a high charging voltage. The positive electrode active material of one aspect of the present invention suppresses the internal short circuit even at a high charging voltage.

[0034] In this specification and the like, ignition in the nail penetration test means that a flame is observed outside the outer casing within 1 minute after the nail is penetrated or that thermal runaway of the secondary battery has occurred. For example, when pyrolysis products of the positive electrode and / or the negative electrode are observed at a location more than 2 cm away from the penetrated location after the nail penetration test, it is considered that thermal runaway has occurred. The pyrolysis products of the positive electrode and / or the negative electrode include, for example, aluminum oxide in which aluminum of the positive electrode current collector is oxidized and copper oxide in which copper of the negative electrode current collector is oxidized.

[0035] In this specification and the like, unless otherwise specified, the charging voltage is expressed based on the potential of lithium metal. Also, in this specification and the like, a high charging voltage is, for example, 4.6 V or higher, preferably 4.65 V or higher, more preferably 4.7 V or higher, even more preferably 4.75 V or higher, and most preferably 4.8 V or higher with respect to the lithium potential. Charging at the above voltage is called high-voltage charging.

[0036] In this specification and the like, there may be a description of "having A and / or B", which means "having A", "having B", or "having A and B".

[0037] In this specification and the like, the space group is represented using the Short notation of the international notation (or Hermann-Mauguin symbol). Also, crystal planes and crystal directions are represented using Miller indices. In crystallography, the notations for the space group, crystal planes, and crystal directions have a bar above the number, but in this specification and the like, due to formatting constraints, instead of putting a bar above the number, a - (minus sign) may be attached before the number for expression. Also, individual orientations indicating directions within the crystal are represented by [ ], set orientations indicating all equivalent directions are represented by < >, individual planes indicating crystal planes are represented by ( ), and set planes having equivalent symmetries are represented by {}.

[0038] (Embodiment 1) A secondary battery or the like, which is one aspect of the present invention, will be described.

[0039] <Secondary battery> A secondary battery, which is one aspect of the present invention, will be described with reference to FIGS. 1(A) and 1(B). FIG. 1(A) illustrates a conceptual diagram of the secondary battery 100, and in the figure, each component is separated for easy viewing. In this specification and the like, the term "component" refers to the components constituting the secondary battery, such as the positive electrode, negative electrode, separator, electrolyte, or outer package. FIG. 1(B) illustrates the cross-sectional structure of the secondary battery 100. It is an example of the cross-sectional structure corresponding to the X1 - X2 direction of the secondary battery 100 shown in FIG. 1(A), and is illustrated with each component in contact.

[0040] <Positive electrode> The secondary battery 100 has a plurality of positive electrodes 103. However, in the secondary battery 100, the number of positive electrodes 103 is not limited at all and may be a single one. The positive electrode 103 may form a wound body. The positive electrode 103 has a positive electrode current collector 101, and the positive electrode current collector 101 has a protruding portion 101t. The protruding portions 101t of each positive electrode current collector overlap to form an aggregate. The aggregate of the protruding portions 101t is called a positive electrode tab. Although the aggregate of the protruding portions 101t in the positive electrode is not shown in the figure, the aggregate of the protruding portions 101t, that is, the positive electrode tab, can be understood by referring to the description regarding the negative electrode tab described later.

[0041] The positive electrode 103 further has a positive electrode active material layer 102. The positive electrode active material layer 102 is a layer having positive electrode active material particles and can be obtained by coating a positive electrode collector 101 with a positive electrode slurry. The positive electrode active material layer 102 has a region in contact with the positive electrode collector 101. The manufacturing process of the positive electrode 103 includes a pressing process using a roll press machine. In the positive electrode 103 that has undergone the pressing process, there may be a recess formed by pressing positive electrode active material particles into a part of the positive electrode collector 101. That is, in the region where the positive electrode active material layer 102 is in contact with the positive electrode collector 101, the positive electrode active material particles are in contact with the positive electrode collector 101. The positive electrode collector 101 is not limited as long as it has a current collecting function, and a conductive material may be interposed between them in the region where the positive electrode active material particles are in contact with the positive electrode collector 101. Examples of the conductive material include a coating material for the positive electrode active material particles, a coating material for the positive electrode collector, or a conductive material included in the positive electrode 103. The conductive material will be described later. The coating material for the positive electrode active material particles has a material with lower resistance than the positive electrode active material particles, typically a carbon material or a metal material, etc., and coats all or part of the positive electrode active material particles. The state in which the above-described conductive material is interposed may be referred to as a state in which the positive electrode active material layer 102 is electrically connected to the positive electrode collector 101.

[0042] In addition to the positive electrode active material particles, the positive electrode active material layer 102 may have a binder. It is preferable that the binder can fix the position of the positive electrode active material particles in the positive electrode active material layer 102. Also, in addition to the positive electrode active material particles, the positive electrode active material layer 102 may have a conductive material. It is preferable that the conductive material can reduce the resistance of the positive electrode active material layer 102. By reducing the resistance, the voltage drop in the positive electrode active material layer 102 becomes smaller and can reach the same potential as the positive electrode collector 101. In addition to the positive electrode active material particles, the positive electrode active material layer 102 may have a binder and a conductive material. Of course, the positive electrode active material layer 102 does not necessarily have to have a binder and a conductive material. The binder will be described later.

[0043] The positive electrode active material layer 102 is preferably formed on both sides of the positive electrode collector 101. This is called a double-sided coating structure. The positive electrode active material layer 102 may be formed only on one side of the positive electrode collector 101. This is called a single-sided coating structure.

[0044] <Negative electrode> The secondary battery 100 has a plurality of negative electrodes 108. However, in the secondary battery 100, the number of negative electrodes is not limited at all and may be a single one. The negative electrode 108 may form a wound body. The negative electrode 108 has a negative electrode current collector 107, and the negative electrode current collector 107 has protruding portions 107t1 and 107t2. The protruding portions 107t1 and 107t2 of each negative electrode current collector overlap to form an aggregate. The aggregate 107t of the protruding portions is called a negative electrode tab. In addition, in the secondary battery 100, it is preferable that the area of the negative electrode is larger than the area of the positive electrode.

[0045] The negative electrode 108 further has a negative electrode active material layer 106. The negative electrode active material layer 106 is a layer having negative electrode active material particles and can be obtained by coating a negative electrode slurry on the negative electrode current collector 107. The negative electrode active material layer 106 has a region in contact with the negative electrode current collector 107. In the manufacturing process of the negative electrode 108, there is a pressing process using a roll press machine, and in the negative electrode 108 that has undergone the pressing process, recesses in which negative electrode active material particles are pressed into a part of the negative electrode current collector 107 may be formed. That is, in the region where the negative electrode active material layer 106 is in contact with the negative electrode current collector 107, the negative electrode active material particles are in contact with the negative electrode current collector 107. The negative electrode current collector 107 is not limited at all as long as it has a current collecting function, and a conductive material may be interposed in the region where the negative electrode active material particles are in contact with the negative electrode current collector 107. Examples of the conductive material include a coating material for the negative electrode active material particles, a coating material for the negative electrode current collector, or a conductive material included in the negative electrode 108. The coating material for the negative electrode active material particles has a material with lower resistance than the negative electrode active material particles, typically a carbon material or a metal material, etc., and coats all or part of the negative electrode active material particles. The state in which the conductive material is interposed may be called a state in which the negative electrode active material layer 106 is in electrical contact with the negative electrode current collector 107.

[0046] The negative electrode active material layer 106 may have a binder in addition to the negative electrode active material particles. It is preferable that the binder can fix the position of the negative electrode active material particles in the negative electrode active material layer 106. Further, the negative electrode active material layer 106 may have a conductive material in addition to the negative electrode active material particles. It is preferable that the conductive material can reduce the resistance of the negative electrode active material layer 106. By reducing the resistance, the voltage drop in the negative electrode active material layer 106 becomes smaller, and it can reach the same potential as the negative electrode current collector 107. The negative electrode active material layer 106 may have a binder and a conductive material in addition to the negative electrode active material particles. Of course, the negative electrode active material layer 106 may not have a binder and a conductive material.

[0047] A double-sided coating structure formed on both sides of the negative electrode current collector 107 can be used for the negative electrode active material layer 106. However, for the negative electrode 108 (the outermost negative electrode) disposed closest to the exterior body 109, it is preferable to use a single-sided coating structure in which the negative electrode active material layer 106 is formed on only one side of the negative electrode current collector 107. In the outermost negative electrode 108, since the insertion and extraction of carrier ions do not occur or are difficult to occur in the negative electrode active material layer not facing the positive electrode 103, it may not be necessary to form such a negative electrode active material layer. Note that since it may be more productive to prepare all the negative electrodes 108 with a double-sided coating structure, a negative electrode with a double-sided coating structure may also be disposed in the outermost layer.

[0048] When the secondary battery 100 is bent and used, it is preferable to use the negative electrode 108 with a single-sided coating structure. A configuration in which the negative electrode current collectors 107 are laminated so as to be in contact with each other for a plurality of negative electrodes with a single-sided coating structure is called a back-to-back configuration. When the back-to-back configuration is used, since the negative electrode current collectors 107 with low contact resistance are in contact with each other, the secondary battery 100 is easier to bend. Using the secondary battery 100 by bending includes mounting the secondary battery 100 on a movable electronic device and the secondary battery 100 bending following the electronic device. Also, using the secondary battery 100 by bending includes mounting the secondary battery 100 on a curved electronic device and bending the secondary battery 100 as well.

[0049] <Separator> The secondary battery 100 has a separator 104 between the positive electrode 103 and the negative electrode 108. However, in the secondary battery 100, the number of separators is not limited at all and may be a single one. Also, the separator may be in an independent state as shown in the figure, but it is also possible to use a continuous separator by bending it. The separator 104 may form a wound body.

[0050] The secondary battery 100 preferably has a carbon layer 105 on one side, one surface, or the surface facing the negative electrode of the separator 104. The separator 104 and the carbon layer 105 are collectively referred to as a separator laminate. The carbon layer 105 can suppress internal short circuits in the secondary battery 100 and improve the reliability of the secondary battery 100.

[0051] The separator 104 has at least a function of separating the positive electrode 103 and the negative electrode 108, and preferably, the separator 104 has an insulating region for electrical insulation. As the separator 104, for example, those formed of fibers having cellulose such as paper, non-woven fabrics, glass fibers, ceramics, or synthetic fibers using nylon (polyamide), vinylon (polyvinyl alcohol-based fibers), polypropylene (abbreviated as PP), polyimide (abbreviated as PI), polyester, acrylic, polyolefin, polyurethane, etc. can be used. These are materials having insulating properties.

[0052] The porosity of the separator 104 can be 35% or more and 90% or less, preferably 60% or more and 85% or less. The separator using polypropylene can have a porosity of 35% or more and 55% or less. The separator using polyimide can have a porosity of 75% or more and 85% or less. In this specification, etc., the porosity of the separator 104 can be calculated from the cross-sectional image of the separator 104. The cross-sectional image can have an arbitrary area, but it is preferable to satisfy an area of 2 10 μm or more and 200 μm 2 or less.

[0053] The thickness of the separator 104 is preferably 10 μm or more and 80 μm or less, more preferably 20 μm or more and 60 μm or less. In this specification and the like, the thickness of the separator 104 can be measured from a cross-sectional image of the separator 104. Since the separator 104 using polyimide has a high porosity, a typical thickness can be 50 μm or more and 80 μm or less, which is preferable.

[0054] The separator 104 may have a multilayer structure. A multilayer structure can be obtained by coating the above-described insulating material with a ceramic material, a fluorine-containing material, a polyamide-containing material, or a mixture thereof. The ceramic material can be referred to as an inorganic material. For example, one or more selected from aluminum oxide particles, silicon oxide particles, and magnesium oxide particles can be used, and it is preferable that at least one or more selected are present on the surface of the separator 104. Note that the separator 104 coated with the ceramic material is preferably in a form in which a layer having one or more selected from aluminum oxide particles, silicon oxide particles, and magnesium oxide particles is confirmed on the surface of the separator 104. As the fluorine-containing material, for example, one or more selected from PVDF and polytetrafluoroethylene can be used, and it is preferable that at least one or more selected are present on the surface of the separator 104. Note that the separator 104 coated with the fluorine-containing material is preferably in a form in which a layer having one or more selected from PVDF and polytetrafluoroethylene is confirmed on the surface of the separator 104. As the polyamide-containing material, for example, one or more selected from nylon and aramid (meta-aramid, para-aramid) can be used, and it is preferable that at least one or more selected are present on the surface of the separator 104. Note that the separator 104 coated with the polyamide-containing material is preferably in a form in which a layer having one or more selected from nylon and aramid (meta-aramid, para-aramid) is confirmed on the surface of the separator 104.

[0055] When using the separator 104 with a multilayer structure, even if the overall thickness of the separator is thin, the safety of the secondary battery 100 can be maintained, so the capacity per unit volume of the secondary battery 100 can be increased.

[0056] The separator 104 can also be processed into a bag shape and arranged to wrap either the positive electrode 103 or the negative electrode 108.

[0057] <Carbon layer 105> The carbon layer 105 is not limited as long as it contains carbon. Examples of carbon materials for the carbon layer 105 include carbon fibers (carbon fiber, CF), and typically carbon nanotubes (referred to as CNT) are preferred. CNT is a substance composed of carbon, specifically having a structure in which sheets of hexagonal carbon atoms arranged in a plane are rolled into a cylinder. The diameter of the rolled 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 also thermally stable. Furthermore, CNT exhibits high conductivity like a metal. Therefore, CNT is suitable for the carbon layer 105, and a carbon layer having CNT is called a CNT layer.

[0058] There is single-walled CNT in CNT, and single-walled CNT refers to a structure with a single layer of a cylindrical shape. Single-walled CNT tends to be long and highly flexible. Among other CNTs, there are multi-walled CNTs. Multi-walled CNTs have a first cylindrical structure (cylindrical structure) with a first diameter and a second cylindrical structure with a second diameter larger than the first diameter, and the first cylindrical structure is arranged inside the second cylindrical structure. Multi-walled CNTs may have three or more cylindrical structures. Multi-walled CNTs tend to be short and hard. Single-walled CNT and / or multi-walled CNT can be used for the carbon layer 105. Also, a laminate of single-walled CNT and multi-walled CNT can be used for the carbon layer.

[0059] In the CNT layer, it is possible to align the direction of the long axis (long axis direction) of the CNTs. In other words, in the CNT layer, the long axes of the CNTs can be oriented in one direction or approximately one direction. A group of CNTs with their long axes oriented in one direction or approximately one direction may be referred to as a bundle of CNTs. A sheet having a group of CNTs with their long axes oriented in one direction or approximately one direction may be referred to as a unidirectionally aligned CNT layer. The unidirectionally aligned CNT layer has high strength when pulled along the long axis direction and is suitable for the carbon layer 105.

[0060] Although the carbon layer 105 is illustrated as a single layer, it may have a structure in which a plurality of carbon layers are stacked (stacked structure). By adopting a stacked structure, the thickness of the carbon layer 105 can be made appropriate. When stacking a plurality of CNT layers, it is preferable to stack them such that their long axes intersect each other. A plurality of CNT layers with their long axes intersecting each other are suitable for the carbon layer 105. When stacking, the CNTs at the interface can be aggregated by spraying an organic solvent.

[0061] As the carbon material for the carbon layer 105, vapor grown carbon fiber (VGCF: registered trademark) may be used. Since VGCF can satisfy a diameter of 90 nm or more and 200 nm or less, preferably 90 nm or more and 110 nm or less, and a fiber length of 7 μm or more and 15 μm or less, it is suitable for the carbon layer 105.

[0062] As the carbon material for the carbon layer 105, graphene may be used. A carbon layer having graphene is called a graphene sheet. In this specification and the like, graphene refers to a material having carbon, having a flat plate shape, a sheet shape, etc., and having a two-dimensional structure formed of carbon six-membered rings. Graphene may have defects in part, and in this case, graphene has polycyclic rings such as seven-membered rings, eight-membered rings, nine-membered rings, and ten-membered rings. Note that a polycyclic ring refers to a cyclic carbon skeleton in which some carbon bonds of a six-membered ring composed of carbon are broken and the broken carbon bonds are bonded to each other. A region surrounded by carbon constituting the polycyclic ring becomes a gap. In this specification and the like, graphene includes multilayer graphene. Since graphene exhibits excellent electrical properties of having high conductivity, it is suitable for the carbon layer 105.

[0063] As the carbon material for the carbon layer 105, it may have a graphene compound. A carbon layer having a graphene compound is called a graphene compound sheet. In this specification and the like, the graphene compound includes graphene oxide, multi-layer graphene oxide, reduced graphene oxide, reduced multi-layer graphene oxide, and the like. In other words, the graphene compound may have a functional group, and examples of the functional group include an epoxy group, a carboxy group, or a hydroxy group. Since the graphene compound exhibits excellent electrical properties such as high flexibility and high conductivity, it is suitable for the carbon layer 105.

[0064] In this specification and the like, reduced graphene oxide refers to a material having carbon and oxygen and having a two-dimensional structure formed by carbon six-membered rings. Reduced graphene oxide preferably has a portion where the carbon concentration is greater than 80 atomic% and the oxygen concentration is 2 atomic% or more and 15 atomic% or less.

[0065] <Slurry for carbon layer> The above-described carbon layer 105 can be obtained from a slurry for a carbon layer. Specifically, the carbon layer 105 can be obtained by coating the separator 104 with the slurry for a carbon layer. When the slurry for a carbon layer has a solvent, it is preferable to perform a drying process. After drying the slurry for a carbon layer, it is preferable to perform a pressing process using a roll press machine. When the separator 104 forms a wound body, the carbon layer 105 preferably also forms a wound body.

[0066] The slurry for a carbon layer is at least a material liquid having the above-described carbon material, and preferably further has a binder. The carbon layer 105 can be adhered to the separator 104 by the binder. The binder will be described later.

[0067] The solvent for the carbon layer slurry can be water or an organic solvent. Deionized water can be mentioned as water. As the organic solvent, one or more selected from ketones such as acetone, alcohols such as ethanol and isopropanol, ether, dioxane, acetonitrile, and NMP (N-methyl-2-pyrrolidone) can be mentioned.

[0068] Moreover, the carbon layer slurry may further have a dispersant. Typically, when using carbon fiber as the carbon material, it is advisable to disperse it in an organic solvent using a dispersant. When using NMP as the organic solvent, it is preferable to use polyvinylpyrrolidone (PVP) as the dispersant. PVP can adsorb on the surface of CNTs and can suppress the re-aggregation after the CNTs are dispersed.

[0069] The step of coating the carbon layer slurry onto the separator 104 is preferable as it can expand the options of materials that the carbon layer slurry has compared to the step of coating the carbon layer slurry onto the negative electrode 108. For example, it is not possible to coat a carbon layer slurry with water as the solvent onto the negative electrode 108 using lithium metal. However, in one aspect of the present invention, since the carbon layer slurry is coated onto the separator 104, it is possible to use water as the solvent, which is preferable.

[0070] Note that as long as the carbon layer slurry can be coated onto the separator 104, the viscosity is not limited in any way. It is also possible to make the separator 104 into a multilayer structure to facilitate the coating of the carbon layer slurry.

[0071] <Binder> Next, the binder will be described. The binder is a material contained in the positive electrode 103, negative electrode 108, or carbon layer 105. It is preferable to use a polymer having a carboxy group as the binder. The carboxy group can be said to have two basic oxygens, one acidic hydrogen, and one electrophilic carbon. The carboxy group also has an OH which is a hydroxy group and a C=O which is a carbonyl group, and can be said to be a polar group. The carboxy group can be specified by Fourier Transform Infrared Spectroscopy (FT-IR) or the like.

[0072] Examples of the polymer having a carboxy group include polyglutamic acid (sometimes abbreviated as PGA), polyacrylic acid (sometimes abbreviated as PAA), and alginic acid (sometimes referred to as a polysaccharide). A polyamino acid may also be used as the polymer having a carboxy group. Specifically, polyornithine or polysarcosine may be applied to the binder. Further, polyaspartic acid may be applied to the binder as the polymer having a carbonyl group. As the polymer having a ketone group, a binary copolymer (copolymer) may be applied, and a copolymer of acrylic acid and maleic acid or a copolymer of acrylic acid and sulfonic acid may be applied to the binder.

[0073] When a polymer having a carboxy group is used as the binder, there is also an effect of reducing the mixing amount of the binder in the positive electrode 103, negative electrode 108, or carbon layer 105. Among the above-described polymers, polyglutamic acid or polyacrylic acid is preferable as the binder used for the positive electrode 103, negative electrode 108, or carbon layer 105.

[0074] The following structural formula (H2) is the structural formula of polyglutamic acid.

[0075]

Chemical formula

[0076] As the polyglutamic acid, either linear γ-polyglutamic acid or crosslinked γ-polyglutamic acid may be applied as the binder, and these are collectively referred to as a structure mainly composed of γ-polyglutamic acid. Note that crosslinked γ-polyglutamic acid is more suitable as the binder in that it has a network structure. Furthermore, the molecular weight of the polyglutamic acid is preferably 1 million or more, more preferably 3 million or more, and even more preferably 10 million or more and 50 million or less.

[0077] Depending on the production method of the polyglutamic acid, it 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, the polyglutamic acid may be neutralized using an alkali metal ion, for example, a lithium ion or a sodium ion.

[0078] Since such polyglutamic acid has hydrophilicity, water, typically deionized water, can be used as the solvent. That is, when using polyglutamic acid as the binder, it is necessary to select water as the solvent for the positive electrode slurry, negative electrode slurry, or carbon layer slurry.

[0079] The following structural formula (H1) is the structural formula of polyacrylic acid.

[0080]

Chemical formula

[0081] Polyacrylic acid has a carboxy group as is clear from the structural formula (H1).

[0082] A material obtained by crosslinking polyacrylic acid may be used. Since a crosslinked structure, that is, a network structure can be formed, the function as a binder may be enhanced, which is preferable.

[0083] As binders other than those described above, it is preferable to use rubber materials such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, ethylene-propylene-diene copolymer, etc. Further, fluororubber can be used as the binder.

[0084] Also, as the binder, it is preferable to use materials such as polystyrene, methyl polyacrylate, 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.

[0085] <Outer package> Furthermore, the secondary battery 100 has an outer package 109, and the negative electrode 108, the separator 104, and the positive electrode 103 are housed in the outer package 109. An electrolytic solution 110 is injected into the outer package 109, and the separator 104 etc. are impregnated with the electrolytic solution 110. From the viewpoint of weight reduction, it is preferable to use a film for the outer package 109. A secondary battery 100 using a film for the outer package 109 is called a laminated secondary battery. Although not shown in this embodiment, a can case may be applied to the outer package 109. When a circular can case is used, the secondary battery is called a coin-type secondary battery.

[0086] As the exterior body used for the laminated secondary battery, for example, a metal material such as aluminum or a resin material can be used. As the resin material, for example, an organic material such as polyethylene, polypropylene, polycarbonate, ionomer, or polyamide can be used. As the exterior body having a three-layer structure, a metal thin film excellent in flexibility such as aluminum, stainless steel, copper, or nickel is provided on a film made of the above resin material, and further, an insulating synthetic resin film such as a polyamide-based resin or a polyester-based resin is provided on the metal thin film at a position corresponding to the outer surface of the exterior body.

[0087] The cross-sectional structure of FIG. 1(B) is a state in which the positive electrode 103, the separator laminate 120, and the negative electrode 108 are in contact. Next, FIGS. 2(A) and 2(B) are used to show the state in which the positive electrode 103, the separator laminate 120, and the negative electrode 108 are in contact. The contact state of FIGS. 2(A) and 2(B) can be obtained through a pressing process and may be referred to as a close contact state or an adhered state.

[0088] <Pressing process> After opposing the negative electrode 108 and the separator laminate 120, it is preferable to perform a pressing process using a roll press machine or the like as necessary. The negative electrode 108 and the separator laminate 120 can be brought into close contact with each other by a roll press machine. Further, when irregularities are formed on the surface of the negative electrode 108, the irregularities can be reduced. Since the distance between the flat-surfaced negative electrode 108 and the positive electrode 103 is constant, uneven reaction in the negative electrode 108 can be suppressed. By suppressing the uneven reaction, the generation and / or growth of dendrites can be suppressed, and the safety of the secondary battery 100 can be improved. The cross-sectional structure after opposing the negative electrode 108 and the separator laminate 120 and performing the pressing process will be described with reference to FIGS. 2(A) and 2(B).

[0089] In the secondary battery 100 shown in Fig. 2(A), the negative electrode 108 and the separator laminate 120 are in close contact. Fig. 2(A) is an example of a cross-sectional structure corresponding to the X1-X2 direction of the secondary battery shown in Fig. 1(A). Since the area of the separator laminate 120 is larger than the area of the negative electrode 108, the separator 104 is bent to the side surface side of the negative electrode 108. Similar to the separator 104, the carbon layer 105 is also bent to the side surface side of the negative electrode 108. Therefore, the carbon layer 105 can have a region in contact with the negative electrode current collector 107. Fig. 2(A) shows that the carbon layer 105 can be at the same potential as the negative electrode current collector 107, and it can be said that the carbon layer 105 has a region in electrical contact with the negative electrode current collector 107.

[0090] In the secondary battery 100 shown in Fig. 2(B) as well, the negative electrode 108 and the separator laminate 120 are in close contact, but the outer edge of the negative electrode 108 is different from that in Fig. 2(A). Fig. 2(B) is an example of a cross-sectional structure corresponding to the X1-X2 direction of the secondary battery shown in Fig. 1(A). In the negative electrode 108, since the negative electrode current collector 107 is larger than the area of the negative electrode active material layer 106, the negative electrode current collector 107 is bent to the side surface side of the negative electrode active material layer 106. Therefore, the carbon layer 105 can have a region in contact with the negative electrode current collector 107. Fig. 2(B) also shows that the carbon layer 105 can be at the same potential as the negative electrode current collector 107, and it can be said that the carbon layer 105 has a region in electrical contact with the negative electrode current collector 107.

[0091] In Fig. 2(A) and Fig. 2(B), pressing treatment is performed so that the negative electrode 108 and the separator laminate 120 are in close contact, but pressing treatment can be carried out so that the positive electrode 103 and the separator laminate 120 are in close contact. In this case, by replacing the negative electrode 108 in Fig. 2(A) and Fig. 2(B) with the positive electrode 103, a structure in which the positive electrode 103 and the separator laminate 120 are in close contact can be understood. In the separator laminate 120, it is preferable not to provide a carbon layer on the surface on the positive electrode 103 side. Of course, in the separator laminate 120, a carbon layer may be provided on the surface on the positive electrode 103 side.

[0092] <Roll press machine> FIG. 3(A) shows an example of a roll press machine that enables press processing. Although not shown, it is preferable that the roll press machine is provided with a dancer roll for controlling tension and an edge position control mechanism (EPC mechanism) for correcting the position. In the first unwinder 550, a sheet-like component is wound in a roll shape. It is preferable to use the negative electrode 108 for the sheet-like component. The roll-shaped negative electrode 108 is preferably wound so that the negative electrode active material layer 106 faces inward. Further, the roll-shaped negative electrode 108 is preferably wound in a state where the negative electrode current collector 107 is cut so as to have a protruding portion. Also, in the second unwinder 553, a sheet-like component is wound in a roll shape. It is preferable to use the separator laminate 120 for the sheet-like component. The roll-shaped separator laminate 120 is preferably wound so that the carbon layer 105 faces outward.

[0093] The negative electrode 108 changes its traveling direction by the rotating body 551a, and the separator laminate 120 changes its traveling direction by the rotating body 551b. The negative electrode 108 is pressed against the carbon layer 105 so as to be sandwiched between the rotating body 551c facing the rotating body 551b and the rotating body 551b. By being pressed, the negative electrode 108 comes into contact with the carbon layer 105. In the contacted state, it can be used as the secondary battery 100.

[0094] More preferably, as one aspect of the present invention, after opposing the negative electrode 108 and the separator laminate 120, it is preferable to bring them into close contact using the press mechanism 555. Since the press mechanism 555 enables linear pressing, it has an upper pressing roll 556 and a lower pressing roll 557, and the negative electrode 108 and the separator laminate 120 are fed between the upper pressing roll 556 and the lower pressing roll 557. The distance between the upper and lower pressing rolls can be changed, and FIG. 3(A) shows an example of a configuration in which the upper pressing roll 556 moves up and down. It is preferable to change the distance between the upper and lower pressing rolls according to the thicknesses of the negative electrode 108, the separator 104, and the carbon layer 105, so as to bring them into close contact using an appropriate pressure.

[0095] Furthermore, it is preferable that one or both of the upper pressing roll 556 and the lower pressing roll 557 be provided with a heating mechanism. It is also possible to make the binder in the carbon layer 105 function as an adhesion region by means of the heating mechanism. Of course, the adhesive force may be increased by providing a new adhesive layer at the interface between the negative electrode 108 and the separator laminate 120. After adhesion, the negative electrode 108 and the separator laminate 120 can be confirmed by the camera 559. Although not shown, a camera may be provided in the press mechanism 555.

[0096] After the negative electrode 108 and the separator laminate 120 are adhered, it is preferable to cut them to match the area of the secondary battery 100. Note that the negative electrode and the separator housed in the secondary battery 100 may form a wound body. Therefore, there may be cases where the negative electrode 108 and the separator laminate 120 are cut to a size intended for the wound body.

[0097] Regarding the roll press machine in Fig. 3(A), although the negative electrode 108 and the separator laminate 120 were used for the explanation, the roll press machine can also be applied to the lamination of the positive electrode 103 and the separator 104. After the positive electrode active material layer 102 and the separator 104 are opposed to each other, they may be heated by the heating mechanism of the roll press machine. It is also possible to make the binder in the positive electrode active material layer 102 function as an adhesion region. Of course, the adhesive force may be increased by providing a new adhesive layer at the interface between the positive electrode 103 and the separator laminate 120. For example, by making the separator 104 have a multilayer structure and providing an adhesive layer in the layer in contact with the positive electrode active material layer 102, the adhesive force can be increased, which is preferable.

[0098] Figure 3(B) also shows another example of a roll press machine that enables press processing. In addition to the roll press machine shown in Figure 3(A), the roll press machine in Figure 3(B) further has a third unwinder 563 next to the camera 559. In the third unwinder 563, a sheet-like part is wound in a roll shape. It is preferable to use the sheet-like part as the positive electrode 103. The roll-shaped positive electrode 103 is preferably wound so that the positive electrode active material layer 102 faces outward. Further, the roll-shaped positive electrode 103 is preferably wound in a state where the positive electrode current collector 101 is cut so as to have a protruding portion.

[0099] The positive electrode 103 changes its traveling direction by the rotating body 551d and is pressed against the separator 104 so as to be sandwiched between the rotating body 551e facing the rotating body 551d and the rotating body 551d. By being pressed, the positive electrode 103 comes into contact with the separator 104, and in this state, it can be used as the secondary battery 100.

[0100] More preferably, as one aspect of the present invention, after appropriately opposing the positive electrode 103, the negative electrode 108, and the separator laminate 120, it is preferable to bond them using the press mechanism 565. The press mechanism 565 has an upper pressure roll 566 and a lower pressure roll 567, and the positive electrode 103, the negative electrode 108, and the separator laminate 120 are fed between the upper pressure roll 566 and the lower pressure roll 567. The distance between the upper and lower pressure rolls can be varied, and Figure 3(B) shows an example of a configuration in which the upper pressure roll 566 moves up and down. Depending on the thicknesses of the positive electrode 103, the negative electrode 108, the separator 104, and the carbon layer 105, it is preferable to change the distance between the upper and lower pressure rolls to bond them using an appropriate pressure.

[0101] Furthermore, it is preferable that one or both of the upper pressing roll 566 and the lower pressing roll 567 be provided with a heating mechanism. The heating mechanism can also cause the binder possessed by each layer to function as an adhesion region. Of course, as a configuration in which a new adhesion layer is provided at the interface of each layer, the adhesive force may be increased. After adhesion, the state of the positive electrode 103, the negative electrode 108, and the separator laminate 120 can be confirmed by the camera 569. Although not shown, a camera may be provided in the pressing mechanism 565.

[0102] After adhering the positive electrode 103, the negative electrode 108, and the separator laminate 120, it is preferable to cut them to match the area of the secondary battery 100. Note that the positive electrode, negative electrode, and separator accommodated in the secondary battery 100 may form a wound body. Therefore, there are cases where the positive electrode 103, the negative electrode 108, and the separator laminate 120 are cut to the intended size for the wound body.

[0103] Also, FIG. 3(C) shows another example of a roll press machine that enables pressing. The roll press machine of FIG. 3(C) has a pressing mechanism 575 that enables surface pressing instead of the pressing mechanism 565 shown in FIG. 3(B). As a more preferable aspect of the present invention, after appropriately opposing the positive electrode 103, the negative electrode 108, and the separator laminate 120, it is preferable to bring them into close contact using the pressing mechanism 575. The pressing mechanism 575 has a pressing surface 576 and a pressing stage 577. It is preferable that the positive electrode 103, the negative electrode 108, and the separator laminate 120 fed between them can be bonded using the pressing surface 576. When using the pressing mechanism 575, it is preferable that at least the positive electrode 103 be fed into the pressing mechanism 575 in a state where it is cut to a size suitable for the area of the secondary battery 100. When pressing the cut positive electrode 103 with a pressing roll, there is a possibility of displacement with respect to the separator laminate 120 or the like, but using the pressing surface 576 and the pressing stage 577 can suppress the occurrence of such displacement, which is preferable.

[0104] It is preferable that the positive electrode 103, the negative electrode 108, and the separator laminate 120 be at least in a state of being in close contact with each other by such a roll press machine.

[0105] Note that by performing the assembly process of the positive electrode 103, the negative electrode 108, and the separator laminate 120 in a vacuum atmosphere, the positive electrode 103, the negative electrode 108, and the separator laminate 120 can be adhered to each other using atmospheric pressure. The vacuum atmosphere includes an atmosphere in which the differential pressure gauge provided in the chamber for the assembly work is depressurized so that the pressure is -0.1 MPa or more and less than -0.08 MPa.

[0106] Here, the flow of electrons during charging of the secondary battery 100 will be described with reference to FIG. 4. Chargers are connected to the two terminals shown in FIG. 4, and the secondary battery 100 is charged. During charging, electrons are released from the positive electrode 103 and an oxidation reaction occurs. At this time, lithium ions in the positive electrode 103 desorb into the electrolyte. Also during charging, electrons are supplied to the negative electrode 108 and a reduction reaction occurs. At this time, lithium ions in the electrolyte move to the negative electrode 108. When graphite is used as the negative electrode active material, the lithium ions that have migrated are inserted into the graphite interlayer. The potential of the negative electrode 108 in the state where lithium ions are inserted into the graphite interlayer is almost equal to the potential when lithium metal is used as the negative electrode active material. Also, when silicon or its alloy is used as the negative electrode active material, it is almost equal to the potential when lithium metal is used as the negative electrode active material. When charging at a high rate or at low temperature is performed in this potential state, lithium metal precipitates. When the secondary battery 100 is regarded as a single closed circuit, the current flows in the same direction as the movement of lithium ions. Although not shown, during discharging, the negative electrode 108 releases electrons and lithium metal dissolves into the electrolyte. When such charge and discharge are repeated, precipitation and dissolution of lithium metal are repeated at the negative electrode 108. When such events are repeated, the surface of the negative electrode 108 becomes non-uniform due to adhesion of electrolyte decomposition products or loss of the electron conduction path, and lithium metal becomes dendrites, and the growth of the dendrites may proceed.

[0107] In the secondary battery 100, the anode and the cathode are switched between during discharging and charging, and the oxidation reaction and the reduction reaction are switched. Therefore, the electrode with a higher reaction potential is called the positive electrode, and the electrode with a lower reaction potential is called the negative electrode. Thus, in this specification and the like, even during charging or discharging, the positive electrode is referred to as the "positive electrode" or the "+ electrode (plus electrode)", and the negative electrode is referred to as the "negative electrode" or the "- electrode (minus electrode)". Using the terms anode or cathode related to the oxidation reaction or the reduction reaction would result in the opposite during charging and discharging, which may cause confusion. Therefore, the terms anode and cathode are not used in this specification and the like.

[0108] Next, a configuration example of the separator 104, the carbon layer 105, and the negative electrode 108, which are one aspect of the present invention, will be described.

[0109] <Configuration Example 1> FIG. 5(A) shows the separator 104, the carbon layer 105, and the negative electrode 108. In this specification and the like, the separator 104 and the carbon layer 105 are collectively referred to as the separator laminate 120. When the separator 104 has a multilayer structure, the multilayer separator 104 and the carbon layer 105 are collectively referred to as the separator laminate 120. The carbon layer 105 is disposed between the negative electrode 108, specifically, between the negative electrode active material layer 106 and the separator 104. Further, the carbon layer 105 is provided so as to overlap the negative electrode active material layer 106, and with this configuration, the growth direction of dendrites can be controlled. Further, as shown in FIG. 2(B) and the like, it is preferable that the carbon layer 105 is provided so as to overlap, more preferably to be in contact with, the negative electrode current collector 107 at the peripheral portion of the carbon layer 105. That is, the negative electrode current collector 107 exists in a region beyond the outer edge of the negative electrode active material layer 106 and preferably overlaps the carbon layer 105. Further, in the secondary battery 100, it is preferable to have a configuration in which the peripheral portion of the negative electrode current collector 107 that has undergone pressing or the like extends along the negative electrode active material layer 106 to a region in contact with the carbon layer 105. This is because by maintaining the flat separator 104, defects in the separator 104 can be suppressed. Of course, as shown in FIG. 2(A), the peripheral portion of the flat separator 104 may be deformed so that the peripheral portion follows the negative electrode active material layer 106. With such a configuration, the negative electrode current collector 107 and the carbon layer 105 can have the same potential during charge and discharge of the secondary battery 100, which is preferable.

[0110] FIG. 5(B) shows an enlarged view corresponding to the region 116 surrounded by the dashed line in FIG. 5(A). As shown in FIG. 5(B), between the carbon layer 105 and the negative electrode active material layer 106, regions where they are separated or spaced apart from each other are confirmed. Also, irregularities are confirmed on the surface or upper surface of the negative electrode active material layer 106. These are irregularities along the shape of the negative electrode active material particles. When the charge-discharge cycle test is repeated for the secondary battery 100, the current may concentrate on the irregularities. Then, since lithium is unevenly deposited from the negative electrode active material layer 106, dendrite 118a is likely to be formed. Dendrite 118a is likely to be formed from the convex portion of the negative electrode active material layer 106. Further, by repeating the charge and discharge of the secondary battery 100, dendrite 118a grows.

[0111] In one aspect of the present invention, since the carbon layer 105 is arranged as shown in FIG. 5(B), after the dendrite 118a reaches the carbon layer 105, it grows in the lateral direction, that is, along the carbon layer 105. When a surface of the carbon layer 105 is confirmed, it can be said that the dendrite 118a has a portion along the surface of the carbon layer 105. An example of the growth direction of such a dendrite 118a is accompanied by an arrow 119. When the normal direction of the secondary battery passing through the positive electrode and the negative electrode is determined, the direction of the arrow 119 can be said to be a direction intersecting the normal direction. Also, when the above normal direction is defined as "vertical", the direction of the arrow 119 can be said to be "horizontal". The direction of the arrow 119 can be said to be the direction along the long axis of the CNT when a CNT layer is used for the carbon layer 105. The direction of the arrow 119 may also be said to be the direction along the negative electrode. When there are a plurality of dendrites, the growth direction of the dendrite 118a may vary depending on each dendrite. That is, the growth direction of the dendrite 118a only needs to coincide with or substantially coincide with the arrow 119, and further stated, the dendrite 118a only needs not to reach the positive electrode.

[0112] The reason why the dendrite 118a grows in such a direction is considered to be that during the reduction reaction, the carbon layer 105 has the same potential as the negative electrode 108, and the dendrite 118a grows while receiving electrons from the carbon layer 105. Since the carbon layer 105 has high conductivity, the reaction with the electrolyte 110 becomes active during the reduction reaction. After the dendrite 118a reaches the carbon layer 105, it can grow along the carbon layer 105. To repeat, the growth direction of the dendrite 118a varies depending on each dendrite. Due to such an event, the dendrite 118a is suppressed from reaching the positive electrode. Therefore, the internal short circuit of the secondary battery 100 is reduced by the configuration in which the carbon layer 105 is arranged as shown in FIG. 5(B).

[0113] <Application Example 1> As shown in FIG. 5(C), the dendrite 118b may reach into the carbon layer 105. In other words, the dendrite 118b may grow in the direction of arrow 119 within the carbon layer 105. Due to such an event, the dendrite 118b is suppressed from reaching the positive electrode. Therefore, the internal short circuit of the secondary battery 100 is reduced by the configuration in which the carbon layer 105 is arranged as shown in FIG. 5(C).

[0114] <Application Example 2> As shown in FIG. 6(A), as long as the dendrite 118c does not reach the positive electrode, the carbon layer 105 may be cracked. When the carbon layer 105 is cracked, a cracked region is confirmed in the carbon layer 105. Also, in a cross-sectional view of the carbon layer 105, the cracked region is confirmed as a void 117. The void 117 is one through which lithium ions can enter and exit. The dendrite 118c may grow in the direction of arrow 119 without passing through the void 117. Further stated, the dendrite 118c may grow in the direction of arrow 119 after passing through the void 117. Due to such an event, the dendrite 118c is suppressed from reaching the positive electrode. Therefore, the internal short circuit of the secondary battery 100 is reduced by the configuration in which the carbon layer 105 is arranged as shown in FIG. 6(A).

[0115] <Application Example 3> As shown in FIG. 6(B), as long as the dendrite 118d does not reach the positive electrode, it may penetrate the carbon layer 105. At this time, it is assumed that there is no cracked region in the carbon layer 105. Further stated, the dendrite 118d exists between the separator 104 and the carbon layer 105, and may grow in the direction of arrow 119 therebetween. However, the dendrite 118d is prevented from penetrating the separator 104. Due to such an event, the dendrite 118d is suppressed from reaching the positive electrode. Therefore, the internal short circuit of the secondary battery 100 is reduced by the configuration in which the carbon layer 105 is arranged as shown in FIG. 6(B).

[0116] <Application Example 4> As shown in FIG. 6(C), the carbon layer 105 may be disposed between the separator 104 and the positive electrode. The dendrite 118e may penetrate the separator 104. Further, the dendrite 118e may exist between the carbon layer 105 and the separator 104 and may grow in the direction of arrow 119 therebetween. However, the dendrite 118e is prevented from penetrating the carbon layer 105. Due to such an event, the dendrite 118e is suppressed from reaching the positive electrode. Thus, the internal short circuit of the secondary battery 100 is reduced.

[0117] <Application Example 5> Although not shown, dendrites may be entangled with the carbon layer 105. In other words, the carbon layer 105 and the dendrites may be integrated, and the dendrites etc. may be confirmed inside and outside the carbon layer 105. Due to such an event, the dendrites are suppressed from reaching the positive electrode. Thus, the internal short circuit of the secondary battery 100 is reduced.

[0118] Based on the above Application Example 5, the growth direction of the dendrite may not necessarily be the arrow 119. That is, in one aspect of the present invention, the growth direction of the dendrite is not important, and it is sufficient that the carbon layer 105 can suppress the dendrite from reaching the positive electrode.

[0119] In the structure of FIGS. 5(B) to 6(C), the thickness of the carbon layer 105 is made to satisfy 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 the thickness, the carbon layer 105 may be laminated. Further, the thickness of the carbon layer 105 may satisfy 0.5 times or more and 1.5 times or less the thickness of the separator.

[0120] Due to the above-described configuration etc., the dendrites do not reach the positive electrode, and the internal short circuit of the secondary battery can be suppressed.

[0121] <Manufacturing Method Example> An example of a method for manufacturing the separator laminate 120 and the like described above will be described with reference to FIG. 7(A).

[0122] <Step S10> In Step S10 shown in FIG. 7(A), the separator 104 and the carbon layer slurry 14 are prepared. In this manufacturing method, a carbon layer slurry 14 in which a carbon material, a solvent, and a binder are mixed is prepared. By using the carbon layer slurry 14 mixed with the binder, a carbon layer having the binder can be obtained. Note that the carbon layer slurry 14 may be mixed with a dispersant.

[0123] <Step S11> In Step S11 shown in FIG. 7(A), the carbon layer slurry 14 is applied to the separator 104. After the application, by drying, the separator 104 and the carbon layer 105 are bonded together. Then, the separator laminate 120 can be obtained.

[0124] <Coating device> FIG. 8(A) shows a coating device for applying the carbon layer slurry 504 to the separator 104. The coating device is called a comma coater. In the coating device, the viscosity of the carbon layer slurry 504 is not limited in any way, but can be adjusted using a thickener.

[0125] The coating device includes a back roll 521, a coating roll 522, a micro bar 524, etc. The roll-shaped separator serving as the separator 104 is moved by the back roll 521. Also, the back roll 521 can rotate the coating roll 522. The carbon layer slurry 504 is held by the dam bottom surface 523 and the coating roll 522, the thickness of the carbon layer slurry 504 is adjusted by the micro bar 524, and it is applied to the separator 104. The application is also called coating. Also, when monitoring the thickness of the applied carbon layer slurry 504, it is preferable for the coating device to have a thickness measurement sensor 505.

[0126] FIG. 8(B) shows another example of an application device for applying the carbon layer slurry 504 to the separator 104. This application device is called a die coater. In this application device, the viscosity of the carbon layer slurry 504 is not limited in any way, but it is preferably adjusted using a thickener.

[0127] The application device has a die 525, a back roll 521, etc. The die 525 is an example of an application nozzle and has a manifold at the center of the die 525. The carbon layer slurry 504 is supplied to the manifold by a pump and extruded from the manifold to the die tip. The extruded carbon layer slurry 504 is applied to the negative electrode current collector 107 that has moved by the rotation of the back roll 521. Also, when monitoring the thickness of the applied carbon layer slurry 504, it is preferable for the application device to have a thickness measurement sensor 505.

[0128] Using such an application device, a separator laminate 120 with a carbon layer laminated on the separator can be obtained. After application, the solvent and the like contained in the carbon layer slurry are removed by drying.

[0129] Furthermore, it is preferable to press the separator laminate 120 with a roll press as necessary. The upper and lower rolls of the roll press are heated to 100°C or higher, preferably 120°C or higher. However, in the case of a slurry having a binder, the upper and lower rolls are heated to the melting point of the binder or higher. If it is within the above temperature range, the temperatures of the upper and lower rolls may be different from each other. Going through the step of pressing with a roll press is preferable because the adhesion between the separator 104 and the carbon layer 105 is enhanced.

[0130] When manufacturing the separator laminate 120 in such a step, when using polyglutamic acid as the binder for the carbon layer, it is possible and preferable to select water, typically deionized water, as the solvent for the carbon layer slurry. Of course, it is also possible to use an organic solvent as the solvent for the carbon layer slurry.

[0131] <Step S12> In step S12 shown in FIG. 7(A), the negative electrode 108 is prepared. The negative electrode 108 is a component having a negative electrode current collector 107 and a negative electrode active material layer 106. Specifically, a negative electrode slurry having a negative electrode active material, a binder, etc. is applied to the negative electrode current collector 107, dried to remove the solvent, and if necessary, pressed by a roll press to obtain the negative electrode 108. The negative electrode slurry may have a conductive material. It is preferable to adjust the viscosity of the negative electrode slurry using a thickener or the like.

[0132] <Coating device> The coating device shown in FIGS. 8(A) and 8(B) is also applicable to the coating process of the negative electrode 108. By substituting the carbon layer slurry with the negative electrode slurry and the separator with the negative electrode current collector, the configuration of the coating device can be understood. After coating, the negative electrode 108 may be pressed by a roll press if necessary. 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. Both the upper and lower rolls of the roll press are heated to 100°C or more, preferably 120°C or more. However, in the case of a slurry having a binder, the upper and lower rolls are heated to the melting point of the binder or higher. Within the above temperature range, the temperatures of the upper and lower rolls may be different from each other. In this way, the negative electrode 108 is completed.

[0133] Water or an organic solvent can be used as the solvent of the negative electrode slurry. However, when lithium metal is used as the negative electrode active material, it is difficult to select water as the solvent of the negative electrode slurry. That is, when lithium metal is used, the solvent of the negative electrode slurry is selected as an organic solvent. When lithium metal is used, a binder can be used as long as it is dispersed in an organic solvent.

[0134] Using such a coating device, the negative electrode 108 is obtained. In the negative electrode 108, the thickness of the negative electrode active material layer 106 is 100 μm or more and 300 μm or less, preferably 110 μm or more and 150 μm or less. Furthermore, 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 / cm2 The following shall apply.

[0135] <Negative electrode current collector 107> The negative electrode current collector 107 will be described. As the negative electrode current collector, materials with high conductivity such as metals like copper, stainless steel, gold, platinum, titanium, and alloys thereof can be used. Also, an aluminum alloy added with elements that improve heat resistance such as silicon, titanium, neodymium, scandium, molybdenum, etc. can be used as the negative electrode current collector. Further, it may be formed of a metal element that reacts with silicon to form a silicide. Examples of the metal element that reacts with silicon to form a silicide include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, nickel, etc. The negative electrode current collector can appropriately use shapes such as foil, plate, sheet, net, punching metal, expanded metal, etc. The negative electrode current collector preferably has a thickness of 5 μm or more and 30 μm or less.

[0136] <Negative electrode active material> The negative electrode active material included in the negative electrode active material layer 106 will be described. As the negative electrode active material, a material that can occlude and release lithium can be used. Also, as the negative electrode active material, a material that can perform charge and discharge reactions through alloying and dealloying reactions with lithium can be used. For example, the negative electrode active material can use one or more composite materials selected from lithium metal, carbon, and silicon. Silicon has a high theoretical capacity of 4200 mAh / g per active material weight and is preferable. When lithium metal is used as the negative electrode active material, the negative electrode current collector can be omitted.

[0137] As the carbon, graphite, graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), CNT, graphene, carbon black, etc. can be used. That is, when multi-layer CNT or multi-layer graphene is used for the carbon layer 105, the carbon layer 105 can occlude and release lithium ions.

[0138] Graphite exhibits a potential as low as that of metallic lithium when lithium ions are inserted (when forming a lithium-graphite intercalation compound). The potential of graphite is typically 0.05 V or more and 0.3 V or less vs. Li / Li + Therefore, a secondary battery using graphite can exhibit a high operating voltage. Furthermore, graphite has advantages such as a relatively high discharge capacity per unit volume, relatively small volume expansion, low cost, and high safety compared to metallic lithium, and thus is preferable.

[0139] If the median diameter (D50) of the negative electrode active material is small, it may become bulky and hinder the improvement of the electrode density. Therefore, the median diameter (D50) of the negative electrode active material preferably satisfies 3 μm or more and 20 μm or less, more preferably 7 μm or more and 12 μm or less. Representative examples of the negative electrode active material satisfying this range include graphite, and it is preferable that the median diameter (D50) of the graphite powder characteristics satisfies the above range.

[0140] Examples of graphite include artificial graphite and natural graphite. As artificial graphite, mesocarbon microbeads (MCMB), coke-based artificial graphite, pitch-based artificial graphite, etc. can be used. Artificial graphite may have a carbon coating layer which is a low-crystalline layer. Since the shape of artificial graphite is spherical, it is called spherical graphite. For example, MCMB is one of the preferable materials 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 with the electrolyte becomes large on the surface of the negative electrode active material, and good cycle characteristics may not be obtained. In order to suppress the above decomposition reaction, the specific surface area of carbon is 0.8 m 2 / g or more and 8 m 2 / g or less, preferably 1 m 2 / g or more and 2 m 2It is preferable to satisfy the following. Typically, it preferably has the specific surface area described above as the powder characteristics of spherical graphite. 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 multi-layer adsorption of adsorbed gas molecules and is the most common method for calculating the specific surface area. The specific surface area by the BET method can be measured using an automatic specific surface area measuring device, TriStar 2 3020.

[0141] Examples of natural graphite include flake graphite or spheroidized natural graphite. Natural graphite may have a carbon coating layer that is a low crystal layer.

[0142] In addition, as the negative electrode active material, a silicon-carbon composite material having carbon and silicon can be used. In the silicon-carbon composite material, it is preferable that carbon and silicon are in a mixed state, and it is also preferable that a sintered state can be confirmed through heat treatment. In the silicon-carbon composite material, it is preferable to use graphite particles for carbon, and the median diameter (D50) of the graphite particles is 1 μm or more and 20 μm or less, preferably 3 μm or more and 20 μm or less, and more preferably 7 μm or more and 12 μm or less. The median diameter (D50) of the graphite particles can be determined based on the median diameter (D50) of silicon.

[0143] 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 a value measured by the BET single-point method using nitrogen gas adsorption, and as a measuring instrument, it can be measured using an automatic specific surface area / pore size distribution measuring device, TriStar II 3020 (manufactured by Micromeritics).

[0144] In the silicon-carbon composite material, it is preferable to use silicon particles for silicon. The silicon particles preferably have a silicon material, and specifically preferably contain one selected from silicon, silicon oxide, and silicon alloy. As the silicon oxide, silicon monoxide (SiO) can be mentioned. In this specification and the like, SiO refers to, for example, silicon monoxide. Silicon monoxide can also be expressed as SiO x It can also be represented as. x is preferably 0.2 or more and 1.5 or less, and more preferably 0.3 or more and 1.2 or less.

[0145] The median diameter (D50) of the silicon particles is preferably less than 1 μm, and typically 50 nm or more and 800 nm or less, preferably 100 nm or more and 500 nm or less. Silicon particles of this size may be called nanosilicon particles. Although silicon has problems with expansion and contraction during charge and discharge, nanosilicon particles refined to have the above median diameter (D50) are suitable because charge and discharge deterioration is improved. It is preferable that the silicon particles have a uniform median diameter (D50) through the pulverization process of the silicon raw material.

[0146] The specific surface area of the silicon particles is 10 m 2 / g or more and 35 m 2 / g or less, preferably 10 m 2 / g or more and 15 m 2 / g or less is good. The specific surface area can be measured by the BET method. The specific surface area by the BET method is a value measured by the BET single-point method using nitrogen gas adsorption, and as a measuring instrument, it can be measured using an automatic specific surface area / pore size distribution measuring device TriStar II 3020 (manufactured by Micromeritics).

[0147] A configuration in which the negative electrode active material contains both graphite particles and silicon particles can realize a secondary battery with a high discharge capacity. Also, since the median diameter (D50) of the graphite particles is different from, specifically larger than, the median diameter (D50) of the silicon particles, when these are mixed and used 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 enhanced, but when the loading amount is large, the above output characteristics deteriorate. 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.

[0148] In the negative electrode active material layer 106, it is preferable that the weight of the graphite particles is higher than the weight of the silicon particles. Typically, it is preferable that the weight ratio of the graphite particles in the negative electrode active material layer 106 satisfies 5 times or more and 35 times or less than the weight ratio of the silicon particles. In other words, it is preferable that the silicon weight ratio with respect to the total weight of the powder material constituting the negative electrode active material satisfies 2 wt% or more and 37.5 wt% or less.

[0149] As other negative electrode active materials, materials containing one or two or more selected from tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium, etc. can be used.

[0150] Also, as the negative electrode active material, a compound containing one or two or more selected from tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium, etc. may be used. A compound containing two or more can be called an alloy material, and for example, magnesium silicide (Mg2Si) can be mentioned.

[0151] As other alloy materials, there are magnesium-germanium alloy (Mg2Ge), stannous oxide (SnO), stannic oxide (SnO2), magnesium-tin compound (Mg2Sn), tin disulfide (SnS2), other main binary alloys of tin (V2Sn3, FeSn2, CoSn2, Ni3Sn2, Cu6Sn5, Ag3Sn, LaSn3, La3Co2Sn7, SbSn), binary alloys of antimony (Ag3Sb, Ni2MnSb, CeSb3, CoSb3, InSb), etc.

[0152] In addition, as the negative electrode active material, oxides such as titanium dioxide (TiO2), lithium titanate (Li4Ti5O 12 ), lithium graphite intercalation compound (Li x C6), niobium pentoxide (Nb2O5), tungsten dioxide (WO2), molybdenum dioxide (MoO2) can be used.

[0153] In addition, as the negative electrode active material, Li 3-x M x N (M = Co, Ni, Cu) having an Li3N type structure, which is a nitride of lithium and a transition metal, can be used. For example, Li 2.6 Co 0.4 N exhibits a large discharge capacity (900 mAh / g per active material weight, 1890 mAh / cm 3 ) and is preferable.

[0154] When using a nitride of lithium and a transition metal, since lithium ions are contained in the negative electrode active material, it can be preferably combined with materials such as V2O5 and Cr3O8 that do not contain lithium ions as the positive electrode active material. Even when using a material containing lithium ions for the positive electrode active material, by previously desorbing the lithium ions contained in the positive electrode active material, a nitride of lithium and a transition metal can be used as the negative electrode active material.

[0155] As another form of the negative electrode, it may be a negative electrode having no negative electrode active material at the end of the manufacture of the secondary battery. As a negative electrode having no negative electrode active material, for example, it is a negative electrode having only a negative electrode current collector at the end of the manufacture of the secondary battery, and lithium ions desorbed from the positive electrode active material by charging of the battery are deposited as lithium metal on the negative electrode current collector to form a negative electrode active material layer. A battery using such a negative electrode may be called a negative electrode-free (anode-free) battery, a negative electrode-less (anode-less) battery, or the like.

[0156] When using a negative electrode having no negative electrode active material, it may have a film for equalizing the precipitation of lithium on the negative electrode current collector. As a film for equalizing the precipitation of lithium, for example, a solid electrolyte having lithium ion conductivity can be used. As the solid electrolyte, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a polymer-based solid electrolyte, or the like can be used. Among them, the polymer-based solid electrolyte is relatively easy to form a uniform film on the negative electrode current collector, so it is suitable as a film for equalizing the precipitation of lithium. Also, as a film for equalizing the precipitation of lithium, for example, a metal film that forms an alloy with lithium can be used. As a 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 as a film for equalizing the precipitation of lithium.

[0157] Also, when using a negative electrode having no negative electrode active material, a negative electrode current collector having irregularities can be used. When using a negative electrode current collector having irregularities, the concave portion of the negative electrode current collector becomes a cavity where lithium possessed by the negative electrode current collector is likely to precipitate. Therefore, when lithium precipitates, it is possible to suppress the formation of a dendrite shape.

[0158] The negative electrode active material layer 106 can have the same binder as the binder of the carbon layer.

[0159] The polyglutamic acid described as a binder has nitrogen in addition to the carboxy group as is clear from the structural formula (H1). Since the nitrogen has a lone pair of electrons, interaction with lithium ions is expected. For example, the lone pair of electrons may attract lithium ions and assist in their insertion into the negative electrode active material.

[0160] Also, polyglutamic acid has C=O which is a carbonyl group as is clear from the structural formula. When the binder has a polar group such as a carbonyl group, interaction with lithium ions which are carrier ions is expected, and for example, it may assist in the insertion and desorption of lithium ions in the negative electrode active material.

[0161] Such polyglutamic acid can provide a secondary battery with good battery characteristics in a low temperature environment.

[0162] <Thickener> It is preferable to use a thickener in addition to the binder in the negative electrode active material layer 106. As the thickener, for example, it is preferable to use a water-soluble polymer. As the water-soluble polymer, for example, polysaccharides and the like can be used. As the polysaccharides, cellulose derivatives such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, regenerated cellulose, or starch and the like can be used.

[0163] <Conductive material> The negative electrode active material layer 106 preferably has a conductive material. The conductive material functions to assist the current path between the active material and the current collector, or the current path between a plurality of active materials. In order to perform such a function, it is preferable to use a material having a lower resistance than the active material for the conductive material. The conductive material is also called a conductive aid or a conductivity-imparting agent from its role. By adhering the conductive material between a plurality of active materials, the plurality of active materials are electrically connected to each other, and the conductivity is enhanced. Note that in this specification and the like, "adhesion" does not only refer to the physical close contact between the active material and the conductive material, but also includes cases where a covalent bond occurs, cases where they are bonded by van der Waals forces, cases where a part of the surface of the active material is covered by the conductive material, cases where the conductive material fits into the surface irregularities of the active material, and cases where they are electrically connected even if they are not in contact with each other.

[0164] Typically, a carbon material or a metal material is used for the conductive material. The conductive material is in a particulate form, and examples of the particulate conductive material include carbon black (furnace black, acetylene black, graphite, etc.). There is a fibrous conductive material, and examples of the fibrous conductive material include CNT and VGCF (registered trademark). There is a sheet-like conductive material, and for example, multilayer graphene is a sheet-like conductive material. The sheet-like conductive material may appear thread-like in the cross-section of the positive electrode.

[0165] The particulate conductive material can enter the gaps between the negative electrode active material and the like and is likely to aggregate. Therefore, the particulate conductive material can assist the conductive path between the negative electrode active materials arranged nearby. The fibrous conductive material has a bent region but is larger than the negative electrode active material. Therefore, the fibrous conductive material can also assist the conductive path between the separated negative electrode active materials in addition to the adjacent negative electrode active materials. Thus, it is preferable to use a mixture of two or more shapes of the conductive material.

[0166] When multilayer graphene is used as the sheet-like conductive material and carbon black is used as the particulate conductive material, in a slurry state in which they are mixed, the weight of the carbon black is preferably 1.5 times or more and 20 times or less, more preferably 2 times or more and 9.5 times or less the weight of the multilayer graphene.

[0167] When the mixing ratio of the multi-layer graphene and the carbon black is within the above range, the carbon black does not aggregate and is easily dispersed. Also, when the mixing ratio of the multi-layer graphene and the carbon black is within the above range, the electrode density can be made higher than when only carbon black is used as the conductive material. By increasing the electrode density, the capacity per unit weight can be increased.

[0168] Furthermore, by setting the mixing ratio of the multi-layer graphene and the carbon black within the above range, it is possible to cope with rapid charging.

[0169] In the conductive material, a graphene compound may be used instead of the above-mentioned multi-layer graphene. As the graphene compound, fluorine-containing graphene may be used. Fluorine in the graphene compound is preferably adsorbed on the surface. Also, the fluorine-containing graphene can be produced by bringing graphene into contact with a fluorine compound (referred to as fluorination treatment). For the fluorination treatment, fluorine (F2) or a fluorine compound may be used. As the fluorine compound, hydrogen fluoride, halogen fluoride (ClF3, IF5, etc.), gaseous fluoride (BF3, NF3, PF5, SiF4, SF6, etc.), metal fluoride (LiF, NiF2, AlF3, MgF2, etc.) and the like are preferable. For the fluorination treatment, it is preferable to use a gaseous fluoride, and the gaseous fluoride may be diluted with an inert gas. The temperature of the fluorination treatment is preferably room temperature, but 0°C or higher and 250°C or lower including the room temperature is preferable. When the fluorination treatment is carried out at 0°C or higher, fluorine can be adsorbed on the surface of the graphene.

[0170] Graphene or a graphene compound has excellent physical properties such as high flexibility and high mechanical strength, and is therefore suitable as a conductive material. Graphene or a graphene compound may have a curved surface, enabling surface contact with low contact resistance. Also, graphene or a graphene compound may have very high conductivity even when thin, and can efficiently form a conductive path in the active material layer in a small amount. Therefore, 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. Also, graphene or a graphene compound may have pores.

[0171] When using a negative electrode active material of 1 μm or less, such as nano silicon particles, more conductive paths for connecting the active materials are required. In such a case, it is preferable to use graphene or a graphene compound that can efficiently form a conductive path even in a small amount.

[0172] Due to having the above-mentioned properties, it is particularly effective to use graphene or a graphene compound as a conductive material in secondary batteries that require rapid charging and rapid discharging. For example, secondary batteries for two-wheeled or four-wheeled vehicles, secondary batteries for drones, etc. may require rapid charging and rapid discharging. Also, in mobile electronic devices, etc., rapid charging characteristics may be required. Rapid charging refers to charging at, for example, 400 mA / g or more, or 1000 mA / g or more. Rapid discharging refers to discharging at, for example, 400 mA / g or more, or 1000 mA / g or more.

[0173] <Step S15> Next, in Step S15 shown in FIG. 7(A), the separator laminate 120 and the negative electrode 108 can be bonded together to obtain a laminate 16 including the negative electrode. Since the step of bonding the carbon layer 105 to the separator 104 and the step of the negative electrode 108 are separated, the material options in the slurry for the carbon layer are wide and preferable. Also, the material options in the slurry for the negative electrode become wider.

[0174] When the carbon layer 105 has a binder, it may be pressed using a roll press and bonded to the separator 104. The upper and lower rolls of the roll press are heated to 100°C or higher, preferably 120°C or higher. However, in the case of a slurry having a binder, the upper and lower rolls are heated to the melting point of the binder or higher. Within the above temperature range, the temperatures of the upper and lower rolls may be different from each other.

[0175] By this manufacturing method example, a separator laminate 120 having a carbon layer 105 can be obtained. Then, a laminate including a negative electrode with the separator laminate 120 bonded to the negative electrode 108 can be obtained. Since the separator laminate 120 has the carbon layer 105, the dendrite reaching the positive electrode is suppressed.

[0176] After bonding the separator laminate 120 and the negative electrode 108, it is preferable to bond the positive electrode 103 so as to face the separator 104. Then, it is preferable to perform pressing using a roll press or the like as necessary. Of course, after bonding the positive electrode 103 to the separator 104, the negative electrode 108 may be bonded to the separator 104. In this way, the secondary battery 100 is completed.

[0177] FIG. 7(B) and FIG. 7(C) illustrate cross-sectional views of the secondary battery 100 that can be formed through the example of the present manufacturing method. In FIG. 7(B), the separator 104 is shown as a two-layer structure, and in FIG. 7(C), the separator is shown as a three-layer structure. As shown in FIG. 7(B), one surface of the separator 104 on the carbon layer 105 side may be provided with a layer having one or more selected from aluminum oxide particles, silicon oxide particles, and magnesium oxide particles. Also, as shown in FIG. 7(C), both surfaces of the separator 104 may be provided with a layer having one or more selected from aluminum oxide particles, silicon oxide particles, and magnesium oxide particles. After charging and discharging the secondary battery 100, one or more selected from aluminum oxide particles, silicon oxide particles, and magnesium oxide particles may elute into the negative electrode 108. Also, after charging and discharging the secondary battery 100, one or more selected from aluminum oxide particles, silicon oxide particles, and magnesium oxide particles may elute into the positive electrode 103.

[0178] Through a process of pressing with a roll press or the like, the respective materials of the secondary battery 100 can adhere to each other. Further, by impregnating the separator 104 mainly with the electrolytic solution 110, a sufficient amount of the electrolytic solution 110 can also be distributed to the positive electrode 103 and the negative electrode 108. By setting the appropriate amount of the electrolytic solution 110 of the secondary battery 100, the safety is improved, and the effect of preventing ignition of the secondary battery 100 is improved. That is, it is preferable that no ignition is confirmed even when a nail penetration test is performed on the secondary battery 100.

[0179] The content of the present embodiment can be appropriately combined with the content of other embodiments.

[0180] (Embodiment 2) In the present embodiment, the configuration of the secondary battery will be described.

[0181] [Negative electrode] The negative electrode is as described in the above embodiment.

[0182] [Positive electrode] The positive electrode has a positive electrode active material layer and a positive electrode current collector. The positive electrode active material layer has a positive electrode active material, and may further have at least one of a conductive material and a binder. As the positive electrode active material, those described in the previous embodiments can be used.

[0183] FIG. 9(A) shows an example of a schematic cross-sectional view of the positive electrode.

[0184] As the positive electrode current collector 580, for example, a metal foil can be used. The positive electrode can be formed by applying a slurry onto the metal foil and drying it. Note that pressing may be applied after drying. The positive electrode is formed by forming a positive electrode active material layer on the positive electrode current collector 580.

[0185] The positive electrode active material layer has a positive electrode active material 581. The positive electrode active material may be referred to as positive electrode active material particles. The positive electrode active material 581 has a function of taking in and / or releasing lithium ions during charge and discharge. As the positive electrode active material 581 used as one aspect of the present invention, a material with little deterioration during charge and discharge even at a high charging voltage can be used. Note that as long as the positive electrode active material 581 is a material with little deterioration during charge and discharge even at a high charging voltage, two or more types of materials with different particle sizes can be used.

[0186] The conductive material can be arbitrarily selected from the conductive materials described in the above embodiments. FIG. 9(A) shows carbon black 583 as the conductive material.

[0187] As the positive electrode of the secondary battery, a binder may be mixed in order to fix the positive electrode current collector 580 such as a metal foil and the positive electrode active material. The binder is a polymer material. If a large amount of the binder is included, the proportion of the active material in the positive electrode decreases, and the discharge capacity of the secondary battery becomes small. Therefore, it is preferable to mix the amount of the binder to a minimum. In FIG. 9(A), the regions not filled with the positive electrode active material 581, the second positive electrode active material 582, and the carbon black 583 indicate voids or the binder.

[0188] In FIG. 9(A), an example is shown in which the positive electrode active material 581 is illustrated as spherical, but it is not particularly limited. For example, the cross-sectional shape of the positive electrode active material 581 may be elliptical, rectangular, trapezoidal, conical, a rounded polygon, or an asymmetric shape. For example, FIG. 9(B) shows an example in which the positive electrode active material 581 has a shape of a rounded polygon.

[0189] In addition, in the positive electrode of FIG. 9(B), graphene 584 is used as the carbon material used as the conductive material. FIG. 9(B) shows a positive electrode active material layer having the positive electrode active material 581, graphene 584, and carbon black 583 formed on the positive electrode current collector 580.

[0190] In the step of mixing graphene 584 and carbon black 583 to obtain a positive electrode slurry, the weight of the carbon black to be mixed is preferably 1.5 times or more and 20 times or less, preferably 2 times or more and 9.5 times or less the weight of the graphene.

[0191] In addition, when the mixing of graphene 584 and carbon black 583 is within the above range, during the preparation of the positive electrode slurry, the carbon black 583 has excellent dispersion stability and is less likely to form agglomerated portions. Further, when the mixing of graphene 584 and carbon black 583 is within the above range, a higher electrode density can be achieved compared to a positive electrode using only carbon black 583 as the conductive material. By increasing the electrode density, the capacity per unit weight can be increased.

[0192] Also, compared to a positive electrode using only graphene as the conductive material, the electrode density is low, but by mixing the first carbon material (graphene) and the second carbon material (acetylene black) within the above range, rapid charging can be supported. Therefore, it is particularly effective when used as a vehicle-mounted lithium ion secondary battery.

[0193] FIG. 9(C) illustrates an example of a positive electrode using carbon fiber 585 instead of graphene. FIG. 9(C) shows an example different from FIG. 9(B). When using carbon fiber 585, agglomeration of carbon black 583 can be prevented and the dispersibility can be improved.

[0194] In addition, in FIG. 9(C), the region not filled with the positive electrode active material 581, carbon fiber 585, or carbon black 583 refers to voids or a binder.

[0195] Further, as an example of another positive electrode, FIG. 9(D) is illustrated. FIG. 9(C) shows an example in which carbon fiber 585 is used in addition to graphene 584. When both graphene 584 and carbon fiber 585 are used, aggregation of carbon black such as carbon black 583 can be prevented and the dispersibility can be further enhanced.

[0196] In addition, in FIG. 9(D), the region not filled with the positive electrode active material 581, carbon fiber 585, graphene 584, or carbon black 583 refers to voids or a binder.

[0197] A lithium-ion secondary battery can be manufactured by using any one of the positive electrodes of FIGS. 9(A) to 9(D), stacking a separator on the positive electrode, stacking a negative electrode on the separator, placing the stack in a container (such as an exterior body or a metal can) that houses the stack, and filling the container with a liquid electrolyte.

[0198] [Electrolyte solution] The electrolyte solution has an organic solvent. However, the organic solvent of the electrolyte which is one aspect of the present invention is not limited to being liquid at 25°C, and may be solid at 25°C or semi-solid at normal temperature. Note that the organic solvent of the electrolyte which is one aspect of the present invention is preferably liquid in a wide temperature range including below the freezing point to high temperature, but is not limited thereto. The organic solvent may be liquid, solid, or semi-solid in a wide temperature range including below the freezing point to high temperature.

[0199] As the organic solvent, an aprotic organic solvent is preferred. For example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, chloroethylene carbonate, vinylene carbonate, 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, dimethoxyethane (DME), dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, sultone, etc., one kind, or two or more of these can be used in any combination and ratio. Typically, it is preferable to use ethylene carbonate (EC) and diethyl carbonate (DEC). In this case, it is preferable to satisfy EC:DEC = 3:7 (volume ratio).

[0200] Since PS has HOMO and LUMO levels equivalent to those of EC and DEC, it is difficult to be oxidized or reduced even at a high cut-off voltage, and it is likely to become a polymer when decomposed on the surface of the positive electrode active material. Therefore, there is an advantage that it is less likely to gasify as a decomposition product with a small molecular weight. Therefore, the electrolytic solution preferably contains PS in an amount of 0.1 wt% or more and 10 wt% or less, and more preferably 0.25 wt% or more and 7.5 wt% or less.

[0201] FEC is one of the cyclic carbonates and has a high relative dielectric constant. When used in an organic solvent, it has the effect of promoting the dissociation of lithium salts. On the other hand, since FEC has a substituent showing electron-withdrawing property, the desolvation with lithium ions proceeds more easily than that of EC. Specifically, the solvation energy of lithium ions in FEC is smaller than that in EC which has no substituent showing electron-withdrawing property. Therefore, it is easy to release lithium ions on the surfaces of the positive electrode active material and the negative electrode active material, and the internal resistance of the secondary battery can be lowered. Furthermore, since FEC has a deep highest occupied molecular orbital (HOMO) level, it is difficult to be oxidized and its oxidation resistance is improved. On the other hand, there is a concern that FEC has a high viscosity. Therefore, it is preferable to use a mixed organic solvent containing not only FEC but also MTFP in the electrolyte. MTFP is one of the chain carbonates and has the effect of lowering the viscosity of the electrolyte or maintaining the viscosity at room temperature (typically 25 °C) even at a low temperature (typically 0 °C). Furthermore, although the solvation energy of MTFP is smaller than that of methyl propionate (abbreviation: "MP") which has no substituent showing electron-withdrawing property, it may form solvation with lithium ions when used in the electrolyte. When using a mixed organic solvent containing both FEC and MTFP, the volume ratio is preferably 2 ≤ y ≤ 20, more preferably 4 ≤ y ≤ 9 when FEC:MTFP = 1:y.

[0202] The above-mentioned organic solvent preferably has a low content of granular dust or molecules other than the constituent molecules of the organic solvent (hereinafter also simply referred to as "impurities", including oxygen (O2), water (H2O) or moisture) and is highly purified. Also, it is preferable that reaction by-products during synthesis are suppressed 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 water content among the impurities can be detected by the Karl Fischer titration method.

[0203] Furthermore, it is preferable that the above-mentioned organic solvent has substantially no peaks caused by impurities as confirmed by NMR measurement or the like. "Substantially no peaks" means that the ratio of the integrated area of peaks caused by impurities to the integrated area of peaks caused by the main component (simply referred to as the integration ratio) is 0.005 or less, preferably 0.002 or less. The apparatus used for NMR measurement is not particularly limited, but for example, "AVANCE III 400 type" manufactured by Bruker can be used. Also 1 In 1H-NMR measurement, the central peak of the five peaks of acetonitrile derived from acetonitrile-d3 used as the solvent can be set to 1.94 ppm.

[0204] For example, in the case of MTFP, when 1H-NMR is measured using an acetonitrile-d3 solvent 1 it is known that four peaks occur at δ of 3.29 ppm or more and 3.43 ppm or less. However, if other peaks occur in the vicinity, for example, if a peak occurs at δ of 3.24 ppm or more and 3.29 ppm or less, the peak is considered to be derived from impurities. Therefore, if the ratio (integration ratio) of the peak area at 3.24 ppm or more and 3.29 ppm or less to the peak area at 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 peaks caused by impurities are hardly detectable.

[0205] Also, for the purpose of improving safety, etc., in order to form a film (Solid Electrolyte Interphase Film) at the interface between the electrode (active material layer) and the electrolyte, it is preferable to add an additive such as vinylene carbonate (VC), propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), lithium bis(oxalate)borate (LiBOB), or a dinitrile compound such as succinonitrile or adiponitrile to the electrolyte. The concentration of the additive preferably satisfies, for example, 0.1 wt% or more and 5 wt% or less with respect to the solvent. When using ethylene carbonate (EC) and diethyl carbonate (DEC), it is preferable to mix 2 wt% of vinylene carbonate (VC) as an additive into the mixed organic solvent in which the lithium salt described below is dissolved with respect to EC:DEC = 3:7 (volume ratio).

[0206] Further, by using one or more ionic liquids (room temperature molten salts) that are flame-retardant and hardly volatile as the solvent of the electrolyte, even if the internal temperature of the power storage device rises due to an internal short circuit or overcharging of the power storage device, rupture and ignition of the power storage device can be prevented. An ionic liquid consists of a cation and an anion and contains an organic cation and an anion. Examples of the organic cation used in the electrolyte include aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, and aromatic cations such as imidazolium cations and pyridinium cations. Examples of the anion used in the electrolyte include monovalent amide-based anions, monovalent methide-based anions, fluorosulfonic acid anions, perfluoroalkylsulfonic acid anions, tetrafluoroborate anions, perfluoroalkylborate anions, hexafluorophosphate anions, or perfluoroalkylphosphate anions, etc.

[0207] Also, as the electrolyte (also called a lithium salt) dissolved in the above solvent, for example, LiPF6, LiClO4, LiAsF6, LiBF4, LiAlCl4, LiSCN, LiBr, LiI, Li2SO4, Li2B 10 Cl 10 、Li2B12 Cl 12 、 LiCF3SO3, LiC4F9SO3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiN(CF3SO2)2, LiN(C4F9SO2)(CF3SO2), LiN(C2F5SO2)2, lithium bis(oxalate) borate (Li(C2O4)2, LiBOB), etc. can be used alone or in any combination and ratio of two or more of these.

[0208] It is preferable to use a highly purified electrolytic solution with a low content of particulate dust or elements other than the constituent elements of the electrolytic solution (hereinafter also simply referred to as "impurities"). Specifically, it is preferable that the weight ratio of impurities to the electrolytic solution is 1% or less, preferably 0.1% or less, and more preferably 0.01% or less.

[0209] Also, a polymer gel electrolyte obtained by swelling a polymer with an electrolytic solution may be used.

[0210] By using a polymer gel electrolyte, the safety against liquid leakage and the like is enhanced. Also, the secondary battery can be made thinner and lighter.

[0211] As the polymer to be gelled, silicon gel, acrylic gel, acrylonitrile gel, polyethylene oxide-based gel, polypropylene oxide-based gel, fluorine-based polymer gel, etc. can be used. For example, polymers having a polyalkylene oxide structure such as polyethylene oxide (PEO), PVDF, polyacrylonitrile, and copolymers containing them can be used. For example, PVDF-HFP, which is a copolymer of PVDF and hexafluoropropylene (HFP), can be used. Also, the polymer formed may have a porous shape.

[0212] In addition, as the electrolyte, a solid electrolyte containing an inorganic material such as a sulfide-based or oxide-based material, or a solid electrolyte containing a polymer material such as a PEO (polyethylene oxide)-based material can be used. When using a solid electrolyte, it is not necessary to install a separator or a spacer. In addition, since the entire battery can be solidified, there is no risk of liquid leakage and the safety is dramatically improved.

[0213] [Separator] The separator is as described in the above embodiment.

[0214] [Outer casing] The outer casing is as described in the above embodiment.

[0215] This embodiment can be used in combination with other embodiments.

[0216] (Embodiment 3) In this embodiment, the positive electrode active material particles 20 of one aspect of the present invention will be described with reference to FIGS. 10 to 12. The positive electrode active material particles 20 can be applied to the positive electrode active material 581 and the like.

[0217] FIG. 10(A) is a cross-sectional view of the positive electrode active material particles 20 of one aspect of the present invention. The positive electrode active material particles 20 preferably have a surface layer portion 20a and an interior 20b. In FIG. 10(A), an example of the boundary between the surface layer portion 20a and the interior 20b is shown by a broken line.

[0218] In this specification and the like, the surface layer portion 20a can be referred to as a region within 20 nm in the depth direction from the particle surface, a region within 10 nm in the depth direction from the particle surface, a region within 5 nm in the depth direction from the particle surface, or a region within 3 nm in the depth direction from the particle surface. The depth direction is defined as the direction perpendicular or substantially perpendicular to the particle surface. Perpendicular or substantially perpendicular means a range of 80° or more and 100° or less with respect to the surface. A surface generated by a crack and / or a crack can also be referred to as the particle surface. The surface layer portion 20a is synonymous with the vicinity of the surface, the region near the surface, or the shell.

[0219] A region deeper than the surface layer portion 20a can be referred to as the interior 20b. The interior 20b is synonymous with the interior region or the core.

[0220] The positive electrode active material particles 20 preferably have lithium cobaltate as the main component and belong to the space group R-3m. The interior 20b preferably has a layered rock salt-type crystal structure. Also, the surface layer portion 20a preferably has a rock salt-type crystal structure whose crystal orientation coincides or approximately coincides with that of the layered rock salt type. Of course, since the surface layer portion 20a enables insertion and desorption of lithium ions, it is necessary for a part of it to have a layered rock salt-type crystal structure. Therefore, it is preferable that the surface layer portion 20a has both a layered rock salt-type crystal structure and a rock salt-type crystal structure.

[0221] (001) in FIG. 10(A) indicates the (001) plane of lithium cobaltate. The surface layer portion 20a includes a region having the (001) plane (a region oriented in (001), a region having a surface parallel to the (001) plane, referred to as the basal region). Also, the surface layer portion 20a includes an edge region. The edge region is a region having a surface exposed in a direction intersecting the (001) plane, or a region other than the (001) orientation. X1-X2 in FIG. 10(A) is a line along the cross section of the edge region, and Y1-Y2 is a line along the cross section of the basal region.

[0222] FIGS. 10(B) to 10(E) are schematic diagrams showing the distribution of additive elements in the edge region. In FIGS. 10(B) to 10(E), the horizontal axis indicates the distance from the measurement point, and the vertical axis indicates the element concentration. By defining the particle surface on the horizontal axis, the distance from the particle surface can be obtained. Schematic diagrams such as FIGS. 10(B) to 10(E) are obtained from the graph of the cross-sectional analysis result. The analysis direction of the cross-sectional analysis is from the particle surface toward the interior 20b, and this direction of analysis is called depth direction analysis. That is, the distance on the horizontal axis can also be said to be the depth of the particle. As the cross-sectional analysis, for example, line analysis of scanning transmission electron microscope-energy dispersive X-ray spectroscopy (STEM-EDX: Scanning Transmission Electron Microscope-Energy Dispersive X-ray Spectroscopy) can be used.

[0223] The positive electrode active material particles 20 are those to which a metal oxide having no lithium site capable of contributing to charge and discharge, such as aluminum oxide, is attached, and carbonates, hydroxy groups, etc. chemisorbed after the production of the positive electrode active material are not included in the positive electrode active material particles 20. Therefore, the surface of the positive electrode active material particles 20 is the surface of the particles including the surface layer portion 20a and the interior 20b. Note that the attached metal oxide refers to, for example, a metal oxide whose crystal orientation does not match that of the interior 20b.

[0224] Also, it is assumed that the electrolyte, organic solvent, binder, conductive material, or a compound derived therefrom attached to the positive electrode active material particles 20 is not included in the positive electrode active material particles 20. The attached electrolyte, organic solvent, binder, conductive material, or a compound derived therefrom, etc. can be removed by washing.

[0225] <Elements contained> The positive electrode active material particles 20 have lithium, transition metal M, oxygen, and an additive element. The transition metal M is one or more selected from cobalt, nickel, and manganese. When cobalt is selected as the transition metal M, it can be said that the positive electrode active material particles 20 have lithium cobaltate (LiCoO2) and an additive element. However, lithium cobaltate does not need to satisfy a strict composition like a chemical formula. That is, the composition of lithium cobaltate is not limited to Li:Co:O = 1:1:2 (atomic ratio).

[0226] The positive electrode active material particles 20 need to have a transition metal M capable of redox in order to maintain charge neutrality even when lithium ions are inserted and extracted. Among the transition metals contained in the positive electrode active material particles 20, when cobalt is 75 atomic% (sometimes denoted as atomic%) or more, preferably 90 atomic% or more, and more preferably 95 atomic% or more, there are many advantages such as relatively easy synthesis, easy handling, and excellent charge and discharge cycle characteristics, which are preferable.

[0227] <Additive element> As the additive element(s) included in the positive electrode active material particles 20, it is preferable to use one or more selected from magnesium, fluorine, nickel, aluminum, titanium, zirconium, vanadium, iron, manganese, chromium, niobium, arsenic, zinc, silicon, sulfur, phosphorus, and boron. Nickel may be used as a main component of the positive electrode active material particles 20, but nickel may be further added as an additive element to the positive electrode active material particles 20.

[0228] 〔Magnesium〕 When magnesium is present in the surface layer portion 20a, a layered rock salt-type crystal structure is likely to be retained. This phenomenon will be described. It is conceivable that the surface layer portion 20a is affected by magnesium eluted from the separator 104.

[0229] Magnesium ions are divalent cations, and magnesium ions are more stable in lithium sites than in cobalt sites in a layered rock salt-type crystal structure, so they tend to enter lithium sites. Magnesium present in lithium sites functions as a pillar supporting CoO2 layers, so a layered rock salt-type crystal structure is likely to be retained.

[0230] In addition, due to the presence of magnesium, Li x In a state where x in CoO2 is, for example, 0.24 or less, the desorption of oxygen around magnesium can be suppressed. Also, when the magnesium concentration in the surface layer portion 20a is high, an improvement in corrosion resistance against hydrofluoric acid generated by the decomposition of the electrolytic solution can be expected. In order to exhibit the effect of corrosion resistance against hydrofluoric acid, it is preferable that the magnesium concentration in the surface layer portion is high.

[0231] If the amount of magnesium is too small, the above-described effects cannot be fully exerted. On the other hand, if the amount of magnesium is too large, the capacity will decrease. Therefore, in the entire positive electrode active material particles 20, the number of magnesium atoms is preferably 0.002 times or more and 0.06 times or less, more preferably 0.005 times or more and 0.03 times or less, and even more preferably about 0.01 times the number of cobalt atoms. The amount of magnesium in the entire positive electrode active material particles 20 referred to here may be, for example, a value obtained by performing elemental analysis of the entire positive electrode active material particles 20 using GD-MS (glow discharge mass spectrometry), ICP-MS (inductively coupled plasma mass spectrometry), etc., or may be based on the value of the raw material formulation in the manufacturing process of the positive electrode active material particles 20.

[0232] [Aluminum] Aluminum can be present at the cobalt site in the layered rock salt-type crystal structure. That is, aluminum is present in the interior 20b. Since aluminum is a trivalent typical element and its valence does not change, lithium around aluminum is difficult to move even during charge and discharge. Therefore, aluminum and the lithium around it can function as pillars and suppress changes in the crystal structure. Therefore, even when a force that causes the positive electrode active material particles 20 to expand and contract in the c-axis direction due to the insertion and desorption of lithium ions acts, that is, even when a force that causes the positive electrode active material particles 20 to expand and contract in the c-axis direction by changing the depth of charge or the charge rate acts, deterioration of the positive electrode active material particles 20 can be suppressed.

[0233] In addition, aluminum suppresses the elution of the surrounding cobalt and has the effect of improving the cycle characteristics. Also, since the Al-O bond is stronger than the Co-O bond, the desorption of oxygen around aluminum can be suppressed. Due to these effects, the thermal stability is improved. Therefore, having aluminum can improve the safety of the secondary battery.

[0234] If there is an excess of aluminum on one hand, it may have an adverse effect on the insertion and desorption of lithium. Therefore, it is preferable that the amount of aluminum contained in the entire positive electrode active material particles 20 is appropriate. For example, the number of aluminum atoms contained in the entire positive electrode active material particles 20 is preferably 0.05% or more and 4% or less, more preferably 0.1% or more and 2% or less, still more preferably 0.3% or more and 1.5% or less, even more preferably 0.05% or more and 2% or less, and yet more preferably 0.1% or more and 4% or less, based on the number of cobalt atoms. The amount of aluminum contained in the entire positive electrode active material particles 20 as referred to herein may be, for example, a value obtained by performing elemental analysis of the entire positive electrode active material particles 20 using GD-MS, ICP-MS, etc., or may be based on the value of the raw material formulation in the manufacturing process of the positive electrode active material particles 20.

[0235] [Fluorine] Fluorine is a monovalent anion. When a part of oxygen is replaced by fluorine in the surface layer portion 20a, the lithium desorption energy becomes smaller. This is because the redox potential of cobalt ions accompanying lithium desorption differs depending on the presence or absence of fluorine. That is, when there is no fluorine, cobalt ions change from trivalent to tetravalent as lithium desorbs. On the other hand, when there is fluorine, cobalt ions change from divalent to trivalent as lithium desorbs. The redox potential of cobalt ions is different between the two cases. Therefore, when a part of oxygen is replaced by fluorine in the surface layer portion 20a of the positive electrode active material particles 20, it can be said that the desorption and insertion of lithium ions in the vicinity of fluorine occur smoothly. Therefore, when the positive electrode active material particles 20 are used in a secondary battery, charge-discharge characteristics, high-current characteristics, etc. can be improved.

[0236] In addition, the presence of fluorine on the surface, which is the part in contact with the electrolytic solution, or the adhesion of a fluoride to the surface can suppress an excessive reaction between the positive electrode active material particles 20 and the electrolytic solution. Also, the corrosion resistance against hydrofluoric acid can be effectively improved.

[0237] [Nickel] Nickel can exist in either the cobalt site or the lithium site in lithium cobaltate having a layered rock salt crystal structure. That is, aluminum can be present in the surface layer portion 20a. When it exists in the cobalt site, since its redox potential is lower than that of cobalt, it can be said that it is easier to release lithium and electrons during charging. Therefore, it can be expected that the charge and discharge speed will increase.

[0238] Also, when nickel exists in the lithium site, the deviation of the layered structure composed of octahedrons of cobalt and oxygen can be suppressed. This is presumably because nickel present in the lithium site also functions as a pillar supporting the CoO2 layers. Furthermore, when nickel exists in the lithium site, it is expected that the crystal structure will become more stable in the charged state at high temperatures, for example, 45 °C or higher.

[0239] Also, the ionization tendency decreases in the order of magnesium, aluminum, cobalt, and nickel (Mg > Al > Co > Ni). Therefore, it is considered that nickel is less likely to elute into the electrolyte than the other above elements during charging. Therefore, it is considered that it has a high effect of stabilizing the crystal structure of the surface layer portion 20a in the charged state.

[0240] Furthermore, nickel is Ni 2+ 、Ni 3+ 、Ni 4+ Among them, Ni 2+ is the most stable, and nickel has a larger trivalent ionization energy compared to cobalt. Therefore, it is known that nickel and oxygen alone do not form a spinel-type crystal structure. Therefore, it is considered that nickel has an effect of suppressing the phase change from the layered rock salt type to the spinel type crystal structure.

[0241] On the other hand, if nickel is excessive, the influence of strain due to the Jahn-Teller effect is enhanced, which is not preferable. Also, if nickel is excessive, it may have an adverse effect on the insertion and desorption of lithium. Therefore, it is preferable that the amount of nickel in the entire positive electrode active material particles 20 is appropriate. Specifically, in the entire positive electrode active material particles 20, the atomic number of nickel preferably exceeds 0% and is 7.5% or less, more preferably 0.05% or more and 4% or less, still more preferably 0.1% or more and 2% or less, and even more preferably 0.2% or more and 1% or less of the atomic number of cobalt. The amount of nickel in the entire positive electrode active material particles 20 referred to here may be, for example, a value obtained by performing elemental analysis of the entire positive electrode active material particles 20 using GD-MS, ICP-MS, etc., or may be based on the value of the raw material formulation in the manufacturing process of the positive electrode active material.

[0242] 〔Titanium〕 The presence of titanium in the surface layer portion 20a can promote the insertion and desorption of lithium ions into and from the positive electrode active material particles 20. This phenomenon will be explained.

[0243] Although titanium stably exists at the oxygen 6-coordinate octahedral position in the oxide, titanium oxide and lithium titanate cannot form a stable layered rock salt-type crystal structure. For example, TiO2, which is a titanium oxide, has the most stable rutile-type crystal structure, and Li4Ti5O 12 which is lithium titanate has a spinel-type crystal structure. Therefore, when a small amount of titanium is dissolved in the surface layer portion 20a having a layered rock salt-type or rock salt-type crystal structure, defects occur in a part of the crystal structure of the surface layer portion 20a. Lithium cobalt oxide is known to have a large band gap and high resistance when in the discharged state (also referred to as when x in Li x CoO2 is 1). Therefore, by introducing defects due to titanium into a part of the surface layer portion 20a, the band gap can be reduced and the resistance can be decreased.

[0244] Also, cobalt is most stable as Co 3+ in the oxide, while titanium is Ti 4+is the most stable. Therefore, in the oxide, around cobalt, charge neutrality is maintained with oxygen, cobalt ions, and lithium ions, while around titanium, it is easier to maintain charge neutrality with oxygen even without lithium ions. Furthermore, Ti 4+ Defects may be induced in the cation sites near, and such defects reduce the diffusion resistance of cations, particularly lithium ions. Therefore, the diffusion resistance of lithium ions is reduced around titanium. Therefore, the presence of titanium in the surface layer portion 20a can lower the diffusion resistance of lithium ions at the interface between the electrolytic solution and the positive electrode active material particles 20.

[0245] If the amount of titanium is too small, the above-described effects cannot be fully exhibited. On the other hand, if there is too much titanium, there is a risk of forming a heterogeneous phase (such as MgTiO3 having an ilmenite-type crystal structure) with other additive elements such as magnesium. Furthermore, there is a risk that the concentration of magnesium in the surface layer portion 20a may decrease due to magnesium being taken away for heterogeneous phase formation. When charging at a high voltage exceeding 4.6V (vs. Li / Li + ), it is preferable for the surface layer portion 20a to have magnesium in order to suppress phase change. Therefore, the fact that magnesium is taken away due to heterogeneous phase formation is a major drawback. Also, if there are too many defects caused by titanium, there is a concern that oxygen may easily desorb from the surface. Therefore, it is preferable that titanium is present in the surface layer portion 20a together with magnesium, fluorine, etc., or that titanium is present in the surface layer portion 20a at a concentration lower than that of magnesium in the surface and the region near the surface.

[0246] Specifically, in the entire positive electrode active material particles 20, the number of Ti atoms is preferably 0.0001 times or more and 0.005 times (0.01% to 0.5%) or less of the number of Co atoms, and more preferably 0.0005 times or more and 0.0025 times (0.05% to 0.25%) or less. The amount of titanium in the entire positive electrode active material particles 20 referred to here may be a value obtained by performing elemental analysis of the entire positive electrode active material particles 20 using, for example, GD-MS, ICP-MS, etc., or may be based on the value of the raw material formulation in the manufacturing process of the positive electrode active material particles 20.

[0247] [Other Additive Elements] When the surface layer portion 20a has phosphorus, when the state where x in LiCoO2 is small is maintained, it may be possible to suppress a short circuit between the positive electrode and the negative electrode, which is preferable. For example, it is preferable to exist in the surface layer portion 20a as a compound containing phosphorus and oxygen. x When the positive electrode active material particles 20 have phosphorus, hydrogen fluoride generated by the decomposition of the electrolytic solution or electrolyte may react with phosphorus, and there is a possibility that the concentration of hydrogen fluoride in the electrolyte can be reduced, which is preferable. When the electrolyte has LiPF6, hydrogen fluoride may be generated by reacting with water. In addition, hydrogen fluoride may be generated by the reaction between polyvinylidene fluoride (PVDF) used as a component of the positive electrode and an alkali. When the concentration of hydrogen fluoride in the electrolyte decreases, corrosion of the current collector may be suppressed in some cases. Also, a decrease in adhesiveness due to gelation and / or insolubilization of PVDF may be suppressed in some cases.

[0248] When the positive electrode active material particles 20 have cracks or the like, if phosphorus, more specifically, a compound containing phosphorus and oxygen, exists inside the positive electrode active material particles having cracks or the like as the surface, such as the embedded portion, the progression of cracks or the like can be suppressed.

[0249]

[0250] [Synergistic Effect of Multiple Additive Elements] When the surface layer portion 20a has both magnesium and nickel, divalent nickel may be able to exist more stably near divalent magnesium. Therefore, even when x in LiCoO2 is small, the elution of magnesium can be suppressed. Therefore, it can contribute to the stabilization of the surface layer portion 20a. x

[0251] ​For the above reasons, in the manufacturing process, magnesium is preferably added to the positive electrode active material particles 20 in a step prior to nickel. Magnesium has a large ionic radius and tends to remain in the surface layer portion of lithium cobaltate regardless of the step of addition, while nickel can widely diffuse into the interior of lithium cobaltate in the absence of magnesium. Therefore, if nickel is added before magnesium, there is a concern that nickel will diffuse into the interior of lithium cobaltate and not remain in the surface layer portion in a preferable amount.

[0252] Furthermore, when the surface layer portion 20a contains magnesium, nickel, and titanium, the presence of nickel suppresses the formation of heterogeneous phases including MgTiO3 having an ilmenite-type crystal structure. The ilmenite-type crystal structure has anions in a hexagonal close-packed structure, which is different from the rock salt-type and layered rock salt-type crystal structures with a cubic close-packed structure, so a certain amount of activation energy is required for the phase transition. Since NiO(II) is a compound with low chemical activity, it has an effect of suppressing the formation of MgTiO3.

[0253] For the above reasons, in the manufacturing process, if titanium is added to the positive electrode active material particles 20 in a step after magnesium and nickel, the effect of suppressing the formation of heterogeneous phases by nickel can be strongly exerted.

[0254] As described above, when having a plurality of additive elements, the effects of the respective additive elements can be synergistic and contribute to further stabilization of the surface layer portion 20a. In particular, having magnesium, nickel, and aluminum is highly preferable as it has a high effect of achieving a stable composition and crystal structure.

[0255] However, if the surface layer portion 20a is occupied only by a compound of the additive element and oxygen, it becomes difficult for lithium to be inserted and removed, which is not preferable. For example, it is not preferable that the surface layer portion 20a is occupied only by a structure in which MgO or a solid solution of MgO and CoO(II) is present. Therefore, the surface layer portion 20a needs to have at least a transition metal M including cobalt, and also have lithium in the discharged state and a path for insertion and removal of lithium.

[0256] In order to sufficiently secure the path for insertion and extraction of lithium, it is preferable that the surface layer portion 20a has a higher cobalt concentration than magnesium. For example, when the surface of the positive electrode active material is measured by XPS, the ratio (Mg / Co) of the number of magnesium atoms Mg to the number of cobalt atoms Co is preferably 0.62 or less. Further, it is preferable that the surface layer portion 20a has a higher cobalt concentration than nickel. Further, it is preferable that the surface layer portion 20a has a higher cobalt concentration than aluminum. Further, it is preferable that the surface layer portion 20a has a higher cobalt concentration than fluorine.

[0257] Furthermore, if there is too much nickel, it may inhibit the diffusion of lithium. Therefore, it is preferable that the surface layer portion 20a has a higher magnesium concentration than nickel. For example, when measured from the surface of the positive electrode active material by XPS, the number of nickel atoms is preferably 1 / 6 or less of the number of magnesium atoms.

[0258] Although a part of the additive elements, particularly magnesium and nickel, preferably have a higher concentration in the surface layer portion 20a than in the interior 20b, it is preferable that they are also present randomly and thinly in the interior 20b. When magnesium and nickel are present in the lithium sites in the interior 20b at appropriate concentrations, there is an effect that it is easier to maintain the layered rock salt-type crystal structure as described above. Also, when nickel is present in the interior 20b at an appropriate concentration, the deviation of the layered structure composed of octahedra of cobalt and oxygen can be suppressed as described above. Also, when magnesium and nickel are combined, a synergistic effect of suppressing the elution of magnesium can be expected as described above.

[0259] The additive elements exhibit the detection amount of characteristic X-rays (which may be simply referred to as the detection amount) that can be determined not to be noise from the viewpoints of intensity and spatial resolution in the line analysis of STEM-EDX. Also, the state in which the detection amounts are continuously obtained is called the distribution of the additive elements. Further, it is preferable that a maximum value of the detection amount, that is, a peak of the detection amount, is confirmed in the distribution. There may be a plurality of the above peaks confirmed in the distribution.

[0260] When the added elements are magnesium, fluorine, nickel, and titanium, it is preferable that the peak of the detected amount is located in the surface layer portion 20a. In other words, it is preferable that the peak of the detected amount of any of magnesium, fluorine, nickel, and titanium is within 20 nm from the surface. The above-mentioned added elements may have a plurality of peaks of the detected amount, but it is preferable that any of magnesium, fluorine, nickel, and titanium has the maximum value (maximum peak) of the peak in the surface layer portion 20a or within 20 nm from the surface.

[0261] 〔Distribution〕 The desirable distributions of magnesium, aluminum, nickel, and titanium among the added elements are respectively illustrated in FIGS. 10(B) to 10(E). The distance on the horizontal axis in FIGS. 10(B) to 10(E) generally corresponds to X1 to X2 of the positive electrode active material particles 20 shown in FIG. 10(A).

[0262] As shown in FIGS. 10(B) to 10(E), magnesium is preferably distributed such that the concentration of the surface layer portion 20a is higher than the concentration of the interior 20b. As shown in FIGS. 10(C) and 10(E), titanium is preferably distributed such that the concentration of the surface layer portion 20a is higher than the concentration of the interior 20b. The fact that the concentration of the above-mentioned surface layer portion 20a is higher than the concentration of the interior 20b means that the detected amount of the surface layer portion 20a is larger than the detected amount of the interior 20b.

[0263] As shown in FIGS. 10(C) and 10(E), when the position where the distribution of magnesium starts (referred to as the rising position) overlaps with the position where the distribution of titanium starts, and the position where the distribution of magnesium ends (referred to as the falling position) overlaps with the falling position of the distribution of titanium, it is said that their distributions overlap with each other. That is, it is preferable that the distributions of magnesium and titanium overlap with each other. Further, when there are a position where the distribution of titanium starts and a position where the distribution of titanium ends between the position where the distribution of magnesium starts and the position where the distribution of magnesium ends, it is said that they have a region where their distributions overlap with each other. The configuration having a region where their distributions overlap with each other includes a case where the rising positions of their distributions are shifted and the falling positions of their distributions are also shifted, and a state where they have a region where their distributions overlap with each other.

[0264] Furthermore, as shown in FIGS. 10(B) to 10(E), the peak of magnesium, typically the maximum peak, preferably exists in the surface layer portion 20a, and more preferably exists in a region closer to the surface within the surface layer portion 20a. For example, the peak of the magnesium concentration preferably exists at the surface or within 3 nm from the reference point.

[0265] Also, as shown in FIGS. 10(C) and 10(E), the peak of titanium, typically the maximum peak, preferably exists in the surface layer portion 20a, and more preferably exists in a region closer to the surface within the surface layer portion 20a.

[0266] Also, as shown in FIGS. 10(C) and 10(E), the peak positions of magnesium and titanium may overlap with each other. When the peak positions of magnesium and titanium are different, the difference in peak positions is preferably within 3 nm, more preferably within 1 nm. When the full width at half maximum of the distribution based on the peak position can be obtained, the full width at half maximum of the titanium distribution is preferably narrower than that of the magnesium distribution.

[0267] Also, as shown in FIGS. 10(D) and 10(E), the nickel distribution preferably overlaps with the magnesium distribution and the titanium distribution. Or, it is preferable that there is a region where the nickel distribution overlaps with the magnesium distribution and the titanium distribution. The peak position of nickel preferably exists in the surface layer portion 20a, and more preferably exists in a region closer to the surface within the surface layer portion 20a. For example, the peak position of the nickel concentration preferably exists at the surface or within 3 nm from the reference point. Also, when the full width at half maximum based on the peak position can be obtained, the full width at half maximum of the nickel distribution is preferably narrower than that of the magnesium distribution.

[0268] As shown in FIG. 10(E), the distributions of magnesium, nickel, and titanium are preferably in the edge region within the surface layer portion 20a. On the other hand, within the surface layer portion 20a, in the basal region, the above distributions are not necessarily required.

[0269] Although it has been described that the detected amount of magnesium in the interior 20b is small compared to the surface layer portion 20a, it is preferable that magnesium is thinly present in the interior 20b. The detected amount of titanium in the interior 20b may be very small compared to the surface layer portion 20a, may not be detected, or may be 1 atomic % or less. Also, the detected amount of nickel in the interior 20b may be very small compared to the surface layer portion 20a, may not be detected, or may be 1 atomic % or less.

[0270] Although not shown, similar to magnesium, it is preferable that the detected amount of fluorine in the surface layer portion 20a is larger than that in the interior 20b. Also, it is preferable to have a peak in the detected amount in a region closer to the surface within the surface layer portion 20a. For example, it is preferable to have a peak in the detected amount at the surface or within 3 nm from the reference point. Similarly, for silicon, phosphorus, boron, and / or calcium, it is preferable that the detected amount in the surface layer portion 20a is larger than that in the interior 20b. Also, it is preferable to have a peak in the detected amount in a region closer to the surface within the surface layer portion 20a. For example, it is preferable to have a peak in the detected amount at the surface or within 3 nm from the reference point.

[0271] Also, the peak position of the detected amount of aluminum is preferably inside the distribution of magnesium or titanium as shown in FIGS. 10(B) to 10(E). That is, at least aluminum among the added elements preferably has a peak in the detected amount inside magnesium or titanium. The distribution of magnesium or titanium may have a region overlapping with the distribution of aluminum, but there may be almost no overlapping region. The peak of the detected amount of aluminum may be present in the surface layer portion 20a or may be deeper than the surface layer portion 20a. For example, it preferably has a peak position in a region of 5 nm or more and 30 nm or less from the surface or inward from the reference point.

[0272] It is considered that aluminum is distributed deeper than magnesium or titanium because the diffusion rate of aluminum is higher than that of magnesium or the like. On the other hand, it is presumed that the detected amount of aluminum is small in the region closest to the surface because aluminum can exist stably in a region where magnesium or the like is not present rather than in a region where magnesium or the like is present at a high concentration or intensity.

[0273] More specifically, in a region of a layered rock salt type or a cubic rock salt type of space group R-3m, in a region where magnesium is present at a high concentration or intensity, the distance between the cation and oxygen is longer than that in the layered rock salt type LiAlO2, so it is difficult for aluminum to exist stably. Also, around cobalt, the change in valence due to the substitution of Li + with Mg 2+ is compensated by the change from Co 3+ to Co 2+ to maintain the cation balance. However, since Al can only have a trivalent state, it is considered difficult for Al to exist stably in the vicinity of magnesium in the rock salt type or layered rock salt type structure.

[0274] The distribution of the additive elements in the basal region may be different from the distributions in FIGS. 10(B) to 10(E). For example, the basal region and the surface layer portion 20a having the same may have a lower detection amount of one or more selected from the additive elements as compared with the surface layer portion 20a having the edge region. Specifically, the detection amount of any one or more of magnesium, nickel, and titanium may be low. Or, in the basal region and the surface layer portion 20a having the same, one or more selected from the additive elements may not be detected, or the detection amount may be 1 atomic % or less. Specifically, the detection amount of nickel may not be detected or may be 1 atomic % or less. Particularly in the case of an analysis method for detecting characteristic X-rays such as EDX, since the energies of Co Kβ and Ni Kα are close, it is difficult to detect trace amounts of nickel in a material in which cobalt is the main element. Or, in the basal region and the surface layer portion 20a having the same, the peak of the detection amount of one or more selected from the additive elements may be shallower from the surface as compared with the surface layer portion 20a having the edge region. Specifically, the peaks of the detection amounts of magnesium and aluminum may be shallower as compared with the edge region and the surface layer portion 20a having the same.

[0275] In the R-3m layered rock salt-type crystal structure, cations are arranged in parallel to the (001) plane. This can be said to be a structure in which CoO2 layers and lithium layers are alternately stacked in parallel to the (001) plane. Therefore, the diffusion path of lithium ions also exists in parallel to the (001) plane. Since the CoO2 layer is relatively stable, the surface of the positive electrode active material particles 20 is more stable when it is (001) oriented. The main diffusion path of lithium ions during charge and discharge is not exposed on the (001) plane.

[0276] On one hand, on the surfaces other than the (001) orientation, the diffusion paths of lithium ions are exposed. Therefore, the surfaces other than the (001) orientation and the surface layer portion 20a are important regions for maintaining the diffusion paths of lithium ions. At the same time, since they are the regions where lithium ions first desorb, they tend to be unstable. Therefore, it is extremely important to reinforce the surfaces other than the (001) orientation and the surface layer portion 20a in order to maintain the crystal structure of the entire positive electrode active material particles 20. Thus, in the positive electrode active material particles 20, it is preferable that the distribution of the additive elements on the surfaces other than the (001) orientation and the surface layer portion 20a thereof is a distribution as shown in any of FIGS. 10(B) to 10(E).

[0277] In the manufacturing method of preparing high-purity LiCoO2 with a low impurity concentration and then mixing and heating the additive elements later, the additive elements mainly spread through the diffusion paths of lithium ions. Therefore, it is easy to make the distribution of the additive elements on the surfaces other than the (001) orientation and the surface layer portion 20a thereof fall within a preferable range.

[0278] Note that as the additive elements, it is not necessarily required to contain any one selected from magnesium, fluorine, nickel, aluminum, titanium, zirconium, vanadium, iron, manganese, chromium, niobium, arsenic, zinc, silicon, sulfur, phosphorus, and boron.

[0279] For example, if the positive electrode active material particles 20 substantially do not contain manganese, there are advantages such as relatively easy synthesis, easy handling, and excellent cycle characteristics. Therefore, it is preferable that the weight of manganese contained in the positive electrode active material particles 20 is, for example, 600 ppm or less, more preferably 100 ppm or less.

[0280] ≪Grain Boundaries≫ In addition to the above-described distribution, it is more preferable that at least a part of the additive elements contained in the positive electrode active material particles 20 are unevenly distributed at the grain boundaries and in the vicinity thereof. In this specification and the like, uneven distribution means that the concentration of an element in a certain region is different from that in other regions. It is synonymous with segregation, precipitation, non-uniformity, bias, or the coexistence of a portion with a high concentration and a portion with a low concentration.

[0281] For example, it is preferable that the magnesium concentration at the grain boundaries of the positive electrode active material particles 20 and in the vicinity thereof is higher than that in the interior 20b. Further, it is preferable that the fluorine concentration at the grain boundaries and in the vicinity thereof is also higher than that in the interior 20b. Also, it is preferable that the nickel concentration at the grain boundaries and in the vicinity thereof is higher than that in the interior 20b. Further, it is preferable that the aluminum concentration at the grain boundaries and in the vicinity thereof is higher than that in the interior 20b. Additionally, it is preferable that the titanium concentration at the grain boundaries and in the vicinity thereof is higher than that in the interior 20b.

[0282] Grain boundaries are one type of surface defect. Therefore, similar to the particle surface, they tend to become unstable and the change in the crystal structure is likely to start. Therefore, if the concentration of the additive element at the grain boundaries and in the vicinity thereof is high, the change in the crystal structure can be more effectively suppressed.

[0283] Moreover, when the magnesium concentration and the fluorine concentration at the grain boundaries and in the vicinity thereof are high, even when cracks occur along the grain boundaries of the positive electrode active material particles 20, due to subsequent heating or the like, the magnesium concentration and the fluorine concentration become high in the vicinity of the surface generated by the cracks. Therefore, the corrosion resistance against hydrofluoric acid can be enhanced even in the positive electrode active material after cracks occur. Also, the side reaction between the electrolytic solution and the positive electrode active material can be suppressed even in the positive electrode active material after cracks occur.

[0284] <Particle diameter> If the particle diameter of the positive electrode active material particles 20 is too large, there are problems such as difficulty in lithium diffusion and the surface of the active material layer becoming too rough when coated on the current collector. On the other hand, if it is too small, problems such as excessive progress of the reaction with the electrolytic solution also occur.

[0285] The particle diameter of the positive electrode active material particles 20 can be measured, for example, by a laser diffraction particle size distribution measuring device. As the particle diameter of the positive electrode active material measured by the laser diffraction particle size distribution measuring device, 1 μm or more and 100 μm or less is preferable, and a form in which those less than 10 μm and those of 10 μm or more and 50 μm or less are mixed is more preferable.

[0286] Also, as in Embodiment 1, when particles having different particle diameters or median diameters (D50) are mixed and used for the positive electrode, the electrode density can be increased, and a secondary battery with a high energy density can be obtained, which is preferable. The positive electrode active material particles 20 having a relatively small particle diameter or median diameter (D50) are expected to have high charge-discharge rate characteristics. The positive electrode active material particles 20 having a relatively large particle diameter or median diameter (D50) are expected to have high charge-discharge cycle characteristics and to be able to maintain a high discharge capacity.

[0287] It is preferable that the interior 20b has a low density of defects including dislocations. The dislocations in the interior 20b can be observed, for example, by TEM. When the density of defects including dislocations is sufficiently low, they may not be observed in a specific 1 μm square of the observation sample. Note that a dislocation is a type of crystal defect and is different from a vacancy defect.

[0288] Also, the positive electrode active material preferably has a large crystallite size measured by XRD. In other words, it is preferable that the interior 20b has high crystallinity. The larger the crystallite size, as will be described later, the more easily the O3'-type crystal structure is maintained in the state where x in Li x CoO2 is small, and the shrinkage of the c-axis length is more easily suppressed. Also, it is considered that the larger the crystallite size measured by XRD, the fewer the defects including dislocations observed by TEM.

[0289] For the calculation of the crystallite size, for example, Bruker D8 ADVANCE can be used. As the X-ray source, CuKα1 line, 2θ is 15° or more and 90° or less, increment 0.005, and the diffraction pattern obtained with the detector LYNXEYE XE-T and the ICSD coll.code.172909 as the literature value of lithium cobaltate can be used. The analysis can be performed using DIFFRAC.TOPAS ver.6 as the crystal structure analysis software, and it is preferable to adopt the value of LVol-IB as the crystallite size. Note that when the calculated Preferred Orientation is less than 0.8, the orientation of the sample may be too strong and not suitable for obtaining the crystallite size.

[0290] When performing XRD measurement to calculate the crystallite size, it is preferable to obtain the measurement in the state of only the positive electrode active material. However, it may also be obtained in the state of the positive electrode including a current collector, a binder, a conductive material, etc. in addition to the positive electrode active material. However, in the state of the positive electrode, there is a possibility that a plurality of positive electrode active material particles are oriented due to the influence of pressing or the like in the manufacturing process. Since there is a risk that the crystallite size cannot be accurately calculated when the orientation is strong, it is more preferable to obtain the measurement by a method such as taking out the positive electrode active material layer from the positive electrode, removing the binder, etc. in the positive electrode active material layer to some extent using a solvent or the like, and then filling the sample holder. Also, in the case of a powder sample, there is a method of applying grease on a silicon non-reflecting plate and attaching the sample.

[0291] <Crystal structure> Due to the distribution of the additive elements as described above, it is preferable that the crystal structure continuously changes from the inside 20b toward the surface. Or it is preferable that the crystal orientations of the surface layer portion 20a and the inside 20b are substantially the same.

[0292] It is preferable that the crystal structure continuously changes from the inside 20b of the layered rock salt type toward the surface and the surface layer portion 20a having a rock salt type crystal structure or both a rock salt type crystal structure and a layered rock salt type crystal structure. Or it is preferable that the crystal orientations of the surface layer portion 20a having a rock salt type crystal structure or both a rock salt type crystal structure and a layered rock salt type crystal structure and the inside 20b of the layered rock salt type are substantially the same.

[0293] In this specification etc., the layered rock salt type crystal structure belonging to the space group R-3m means a crystal structure having a rock salt type ion arrangement in which cations and anions are alternately arranged, and cobalt and lithium are regularly arranged to form a two-dimensional plane, so that two-dimensional diffusion of lithium is possible. Note that there may be defects such as deficiency of cations or anions. Also, strictly speaking, the layered rock salt type crystal structure may be a structure in which the lattice of the rock salt type crystal is distorted, and the symmetry may be lower than that of the rock salt type crystal structure.

[0294] The rock-salt type crystal structure refers to a cubic crystal structure including space group Fm-3m, in which cations and anions are arranged alternately. Note that there may be a deficiency of cations or anions.

[0295] Moreover, whether having both the layered rock-salt type crystal structure and the rock-salt type crystal structure can be determined by electron diffraction, TEM images, cross-sectional STEM images, etc.

[0296] There is no distinction in the cation sites in the rock-salt type crystal structure, while there are two types of cation sites in the layered rock-salt type crystal structure. One is mostly occupied by lithium, and the other is occupied by cobalt. The stacked structure in which the two-dimensional plane of cations and the two-dimensional plane of anions are arranged alternately is the same for both the rock-salt type crystal structure and the layered rock-salt type crystal structure. Among the bright spots in the electron diffraction pattern corresponding to the crystal plane forming this two-dimensional plane, when the central spot (transmission spot) is taken as the origin 000, the bright spot closest to the central spot is, for example, the (111) plane in the ideal rock-salt type crystal structure and the (003) plane in the layered rock-salt type crystal structure. For example, when comparing the electron diffraction patterns of MgO with a rock-salt type crystal structure and LiCoO2 with a layered rock-salt type crystal structure, the distance between the bright spots of the (003) plane of LiCoO2 is observed to be approximately half the distance between the bright spots of the (111) plane of MgO. Therefore, when the analysis region has two phases, such as MgO with a rock-salt type crystal structure and LiCoO2 with a layered rock-salt type crystal structure, in the electron diffraction pattern, there exists a plane orientation in which bright spots with strong luminance and bright spots with weak luminance are arranged alternately. The bright spots common to both the rock-salt type crystal structure and the layered rock-salt type crystal structure have strong luminance, and the bright spots that occur only in the layered rock-salt type crystal structure have weak luminance.

[0297] In a cross-sectional STEM image or the like, when observing the layered rock-salt type crystal structure from a direction perpendicular to the c-axis, layers observed with strong brightness and layers observed with weak brightness are alternately observed. Such a feature is not seen in the rock-salt type crystal structure because there is no distinction in the cation sites. When having both the rock-salt type crystal structure and the layered rock-salt type crystal structure, when observed from a specific crystal orientation, in a cross-sectional STEM image or the like, layers observed with strong brightness and layers observed with weak brightness are alternately observed, and furthermore, in a layer with even weaker brightness, that is, in a part of the lithium layer, a metal with an atomic number larger than that of lithium exists.

[0298] The anions of the layered rock-salt type crystal structure and the rock-salt type crystal structure adopt a cubic close-packed structure (face-centered cubic lattice structure). It is presumed that the anions of the O3’ type crystal structure and the monoclinic O1(15) type crystal structure described later also adopt a cubic close-packed structure. Therefore, when the layered rock-salt type crystal structure and the rock-salt type crystal structure are in contact, there is a crystal plane where the orientations of the cubic close-packed structures composed of anions are aligned.

[0299] Or, it can also be explained as follows. The anions on the {111} plane of the cubic crystal structure have a triangular lattice. The layered rock-salt type crystal structure has a space group of R-3m and is a rhombohedral structure, but is generally represented by a composite hexagonal lattice for easy understanding of the structure, and the (0001) plane of the layered rock-salt type crystal structure has a hexagonal lattice. The triangular lattice of the cubic {111} plane has the same atomic arrangement as the hexagonal lattice of the (0001) plane of the layered rock-salt type crystal structure. The fact that the lattices of both have consistency can be said that the orientations of the cubic close-packed structures are aligned.

[0300] However, since the space groups of the layered rock salt-type crystal structure and the O3'-type crystal structure are R-3m, which is different from the space group Fm-3m of the rock salt-type crystal structure (the space group of the general rock salt-type crystal structure), the Miller indices of the crystal planes that satisfy the above conditions are different between the layered rock salt-type crystal structure and the O3'-type crystal structure, and the rock salt-type crystal structure. In this specification, in the layered rock salt-type crystal structure, the O3'-type crystal structure, and the rock salt-type crystal structure, when the orientations of the cubic close-packed structures composed of anions are aligned, it may be said that the crystal orientations are approximately the same. Also, having a three-dimensional structural similarity such that the crystal orientations are approximately the same, or being crystallographically the same orientation, is called topotaxy.

[0301] The fact that the crystal orientations of two regions are approximately the same can be determined from a TEM image, STEM image, HAADF-STEM (High-angle Annular Dark Field Scanning TEM) image, ABF-STEM (Annular Bright-Field Scanning Transmission Electron Microscope) image, electron diffraction pattern, etc. It can also be determined by the fast Fourier transform (FFT) pattern of the TEM image and the FFT pattern of the STEM image, etc. Furthermore, XRD, neutron diffraction, etc. can also be used as materials for determination.

[0302] Fig. 11 shows an example of a TEM image in which the orientations of the layered rock salt-type crystal structure LRS and the rock salt-type crystal structure RS are approximately the same. In a TEM image, STEM image, HAADF-STEM image, ABF-STEM image, etc., an image reflecting the crystal structure can be obtained.

[0303] For example, in the high-resolution image of a TEM, contrast derived from crystal planes can be obtained. When an electron beam is incident perpendicular to the c-axis of a composite hexagonal lattice of a layered rock-salt-type crystal structure by electron beam diffraction and interference, for example, the contrast derived from the (0003) plane is obtained as a repetition of bright bands (bright strips) and dark bands (dark strips). Therefore, a repetition of bright and dark lines is observed in the TEM image. When the angle between bright lines (e.g., L RS and L LRS ) is 5 degrees or less, or 2.5 degrees or less, it can be determined that the crystal planes are approximately aligned, that is, the crystal orientations are approximately aligned. Similarly, when the angle between dark lines is 5 degrees or less, or 2.5 degrees or less, it can be determined that the crystal orientations are approximately aligned.

[0304] In addition, in the HAADF-STEM image, contrast proportional to the atomic number is obtained, and elements with a larger atomic number are observed brighter. For example, in the case of layered rock-salt-type lithium cobaltate belonging to the space group R-3m, since cobalt (atomic number 27) has the largest atomic number, the electron beam is strongly scattered at the position of cobalt atoms, and the arrangement of cobalt atoms is observed as an arrangement of bright lines or points with strong brightness. Therefore, when observing lithium cobaltate having a layered rock-salt-type crystal structure perpendicular to the c-axis, the arrangement of cobalt atoms perpendicular to the c-axis is observed as an arrangement of bright lines or points with strong brightness, and the arrangements of lithium atoms and oxygen atoms are observed as dark lines or regions with low brightness. The same applies when fluorine (atomic number 9) and magnesium (atomic number 12) are used as additive elements in lithium cobaltate.

[0305] Therefore, in the HAADF-STEM image, when a repetition of bright and dark lines is observed in two regions with different crystal structures and the angle between bright lines is 5 degrees or less, or 2.5 degrees or less, it can be determined that the atomic arrangements are approximately aligned, that is, the crystal orientations are approximately aligned. Similarly, when the angle between dark lines is 5 degrees or less, or 2.5 degrees or less, it can be determined that the crystal orientations are approximately aligned.

[0306] In ABF-STEM, elements with smaller atomic numbers are observed brighter. However, since it is similar to HAADF-STEM in that contrast according to the atomic number can be obtained, the crystal orientation can be determined in the same way as in the HAADF-STEM image.

[0307] Fig. 12(A) shows an example of a STEM image in which the orientations of the layered rock-salt type crystal structure LRS and the rock-salt type crystal structure RS are roughly consistent. The FFT pattern of the region of the rock-salt type crystal structure RS is shown in Fig. 12(B), and the FFT pattern of the region of the layered rock-salt type crystal structure LRS is shown in Fig. 12(C). On the left of Figs. 12(B) and 12(C), the composition, the JCPDS card number, and the d-values and angles calculated from the JCPDS card number are shown. The measured values are shown on the right. The spots marked with O are the zero-order diffractions.

[0308] The spot marked with A in Fig. 12(B) is derived from the 11-1 reflection of the cubic crystal. The spot marked with A in Fig. 12(C) is derived from the 0003 reflection of the layered rock-salt type. From Figs. 12(B) and 12(C), it can be seen that the orientation of the 11-1 reflection of the cubic crystal and the orientation of the 0003 reflection of the layered rock-salt type crystal structure are roughly consistent. That is, it can be seen that the straight line passing through AO in Fig. 12(B) and the straight line passing through AO in Fig. 12(C) are roughly parallel. Here, the so-called rough consistency and rough parallelism mean that the angle is 5 degrees or less, or 2.5 degrees or less.

[0309] Thus, in the FFT pattern and the electron diffraction pattern, when the orientations of the layered rock-salt type crystal structure and the rock-salt type crystal structure are roughly consistent, the <0003> orientation of the layered rock-salt type crystal structure and the <11-1> orientation of the rock-salt type crystal structure may be roughly consistent. At this time, it is preferable that these reciprocal lattice points are spot-shaped, that is, not continuous with other reciprocal lattice points. The fact that the reciprocal lattice points are spot-shaped and not continuous with other reciprocal lattice points means high crystallinity.

[0310] In addition, when the orientation of the 11-1 reflection of the cubic crystal and the orientation of the 0003 reflection of the layered rock salt-type crystal structure are approximately the same as described above, depending on the incident orientation of the electron beam, spots that do not originate from the 0003 reflection of the layered rock salt-type crystal structure may be observed in the reciprocal lattice space different from the orientation of the 0003 reflection of the layered rock salt-type crystal structure. For example, the spot marked B in Fig. 12(C) originates from the 10-14 reflection of the layered rock salt-type crystal structure. This is at an angle of 52° or more and 56° or less from the orientation of the reciprocal lattice point (A in Fig. 12(C)) originating from the 0003 reflection of the layered rock salt-type crystal structure (that is, ∠AOB is 52° or more and 56° or less), and may be observed at a location where the d value is 0.19 nm or more and 0.21 nm or less. Note that this index is an example and does not necessarily have to match this.

[0311] Similarly, spots that do not originate from the 11-1 reflection of the cubic crystal may be observed in a reciprocal lattice space different from the orientation where the 11-1 reflection of the cubic crystal is observed. For example, the spot marked B in Fig. 12(B) originates from the 200 reflection of the cubic crystal. This is at an angle of 54° or more and 56° or less from the orientation of the reflection originating from 11-1 of the cubic crystal (A in Fig. 12(B)) (that is, ∠AOB is 54° or more and 56° or less), and diffraction spots may be observed at this location. Note that this index is an example and does not necessarily have to match this.

[0312] Note that as for the cathode active material having a layered rock salt-type crystal structure such as lithium cobaltate, it is known that the (0003) plane and planes equivalent thereto, as well as the (10-14) plane and planes equivalent thereto, tend to appear as crystal planes. Therefore, for example, when observing the (0003) plane with a TEM or the like, first select cathode active material particles in which a crystal plane expected to be the (0003) plane is observed with an SEM or the like, and it is preferable to thin-process the cathode active material particles with an FIB (Focused Ion Beam) or the like so that the (0003) plane can be observed with an electron beam incident as [12-10] in a TEM or the like. When it is desired to judge the coincidence of the crystal orientation, it is preferable to thin the sample so that the (0003) plane of the layered rock salt-type crystal structure is easily observable.

[0313] <xps> In the case of inorganic oxides, when using the Kα line of monochromatic aluminum as the X-ray source in XPS analysis, it is possible to analyze the region from the surface to a depth of about 2 nm to 8 nm (usually 5 nm or less). Therefore, for a region about half the depth of the surface layer portion 20a, the concentration of each element can be quantitatively analyzed. Further, by performing narrow scan analysis, the bonding state of the elements can be analyzed. Note that the quantitative accuracy of XPS is often about ±1 atomic %, and the detection limit is about 1 atomic % depending on the element.

[0314] It is preferable that the concentration of one or more selected from the additive elements in the surface layer portion 20a of the positive electrode active material according to one aspect of the present invention is higher than that in the interior 20b. This is synonymous with the fact that it is preferable that the concentration of one or more selected from the additive elements in the surface layer portion 20a is higher than the average of the entire positive electrode active material. Therefore, for example, it can be said that it is preferable that the concentration of one or more additive elements selected from the surface layer portion 20a measured by XPS or the like is higher than the average concentration of the additive elements of the entire positive electrode active material measured by ICP-MS or GD-MS or the like. For example, it is preferable that the concentration of at least a part of magnesium in the surface layer portion 20a measured by XPS or the like is higher than the average magnesium concentration of the entire positive electrode active material. Also, it is preferable that the concentration of at least a part of nickel in the surface layer portion 20a is higher than the average nickel concentration of the entire positive electrode active material. Also, it is preferable that the concentration of at least a part of aluminum in the surface layer portion 20a is higher than the average aluminum concentration of the entire positive electrode active material. Also, it is preferable that the concentration of at least a part of fluorine in the surface layer portion 20a is higher than the average fluorine concentration of the entire positive electrode active material.

[0315] Also, in at least a part of the surface layer portion 20a measured by XPS, it is preferable that a bond between magnesium and fluorine exists. It is more preferable that a bond between magnesium, fluorine and oxygen (O-Mg-F bond) exists, rather than a bond between magnesium and fluorine (Mg-F bond). The bond between magnesium and fluorine in the surface layer portion 20a indicates that the flux effect by the fluoride has been sufficiently exerted, and the magnesium source and the surface of lithium cobaltate have melted, and as a result, magnesium has been sufficiently segregated.

[0316] The excitation X-ray used for XPS measurement can be monochromatic Al, and the detection region can be 100 μmφ. The take-off angle (the angle formed by the inclination of the sample stage and the detection direction of the detector) can be 45° or 15°. The detection depth when the take-off angle is 45° is approximately 4 to 5 nm, and the detection depth when the take-off angle is 15° is approximately 2 nm. In order to satisfy the above take-off angle values, the relative position between the X-ray source and the sample is changed. Typically, the X-ray source is fixed, and the take-off angle is changed by tilting the sample stage with respect to the X-ray source irradiation direction.

[0317] The existence of the O-Mg-F bond in the XPS spectrum of Mg1s, which is one of the magnesium bonding states, will be explained. When separating the waveform of the above XPS spectrum, prepare a fit peak 1 for the peak component derived from the O-Mg-O bond, a fit peak 2 for the peak component derived from the O-Mg-F bond, a fit peak 3 for the peak component derived from the F-Mg-F bond, and a composite peak obtained by synthesizing the three. Fit the composite peak so that the difference from the Mg1s peak of the above XPS spectrum becomes the smallest. Calculate the ratios of fit peak 1, fit peak 2, and fit peak 3 in the composite peak after fitting. Specifically, calculate each area corresponding to fit peak 1, fit peak 2, and fit peak 3 from the composite peak. The analysis results can be output assuming that each area is the abundance ratio of the O-Mg-O bond, the O-Mg-F bond, and the F-Mg-F bond. The existence of the O-Mg-F bond means that the abundance ratio of the O-Mg-F bond has been output.

[0318] It is preferable that the O-Mg-F bond can be confirmed at any of the extraction angles of 45° and 15°. Also, when there is a difference in the peak value of the O-Mg-F bond at the extraction angles of 45° and 15°, it can be said that the existence ratio of the O-Mg-F bond is different within the XPS detection region. For example, when the extraction angle of 15° is larger than 45°, it can be said that the O-Mg-F bond exists mainly in a very shallow region from the surface to 2 nm.

[0319] Since the positive electrode active material of the present embodiment can withstand high voltage charging, it is possible to provide a secondary battery having good cycle characteristics.

[0320] The present embodiment can be used in combination with other embodiments.

[0321] (Embodiment 4) In the present embodiment, an electrolyte required to realize a secondary battery having excellent discharge characteristics even in a low temperature environment will be described.

[0322] Typically, a low temperature environment means below freezing point. In charging in a low temperature environment, the energy barrier for desorbing lithium ions from the positive electrode active material tends to increase. That is, it can be said that the lower the temperature of the charging environment, the larger the overvoltage required to desorb lithium ions from the positive electrode active material. That is, the positive electrode active material may be exposed to a high voltage (a high potential with respect to the lithium potential) during charging in a low temperature environment. In other words, when the positive electrode active material is not exposed to a high voltage during charging in a low temperature environment, the charging capacity may decrease.

[0323] Therefore, as the positive electrode active material of 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 during charging in a low temperature environment.

[0324] In addition, for the electrolyte of a secondary battery having excellent charging characteristics and discharging characteristics even in a low-temperature environment, it is preferable to use a material excellent in lithium ion conductivity even in charging and / or discharging (charge and discharge) in a low-temperature environment.

[0325] The electrolyte preferably used for a lithium ion secondary battery having excellent charging characteristics and discharging characteristics even in a low-temperature environment will be described in detail below.

[0326] <Electrolyte 1 Suitable for Low-Temperature Environment> As the mixed organic solvent used in the electrolyte, a material excellent in lithium ion conductivity can be used even in 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).

[0327] The mixed organic solvent may contain two or more selected from fluorinated cyclic carbonates (sometimes referred to as fluorinated cyclic carbonates) and fluorinated chain carbonates (sometimes referred to as fluorinated chain carbonates).

[0328] As the fluorinated cyclic carbonate, fluoroethylene carbonate (fluoroethylene carbonate, FEC, F1EC), difluoroethylene carbonate (DFEC, F2EC), trifluoroethylene carbonate (F3EC), or tetrafluoroethylene carbonate (F4EC) can be used. Note that DFEC has isomers such as cis-4,5 and trans-4,5. Since any fluorinated cyclic carbonate has an electron-withdrawing substituent, it is considered that the solvation energy of lithium ions is low.

[0329] The following structural formula (H10) is the structural formula of FEC. In FEC, the electron-withdrawing substituent is the F group.

[0330]

Chemical formula

[0331] As a 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 the CF3 group.

[0332]

Chem.

[0333] As a 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 the CF3 group.

[0334]

Chem.

[0335] As a fluorinated chain carbonate, there is trifluoromethyl propionate. The following structural formula (H24) is the structural formula of trifluoromethyl propionate. The electron-withdrawing substituent is the CF3 group.

[0336]

Chem.

[0337] As a fluorinated chain carbonate, there is methyl 2,2-difluoropropionate. The following structural formula (H25) is the structural formula of methyl 2,2-difluoropropionate. The electron-withdrawing substituent is the CF2 group.

[0338]

Chem.

[0339] <FEC and MTFP> The mixed organic solvent described in this embodiment preferably contains FEC and MTFP. The reason will be explained below.

[0340] FEC is one of the cyclic carbonates and has a high relative dielectric constant. Therefore, 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 showing electron-withdrawing property, the desolvation with lithium ions proceeds more easily than that of ethylene carbonate (EC). Specifically, the solvation energy of lithium ions with FEC is smaller than that of EC having no substituent showing electron-withdrawing property. Therefore, it is easy to release lithium ions on the surfaces of the positive electrode active material and the negative electrode active material, and the internal resistance of the secondary battery can be lowered. Further, since FEC has a deep highest occupied molecular orbital (HOMO) level, it is difficult to be oxidized and its oxidation resistance is improved. On the other hand, there is a concern that FEC has a high viscosity. Therefore, it is preferable to use, as the electrolytic solution, a mixed organic solvent containing not only FEC but also MTFP. MTFP is one of the chain carbonates and has the effect of lowering the viscosity of the electrolytic solution or maintaining the viscosity at room temperature (typically 25°C) even at a low temperature (typically 0°C). Further, although the solvation energy of MTFP is smaller than that of methyl propionate (abbreviation: "MP") having no substituent showing electron-withdrawing property, it may form a solvation with lithium ions when used in the electrolytic solution.

[0341] The actually measured values of the HOMO level, solvation energy, melting point, etc. are summarized in the following table.

[0342] [Table 1]

[0343] FEC and MTFP having such physical properties may be mixed and used such that the total content of these two mixed organic solvents is 100 vol%, and the volume ratio is x:100 - x (where 5 ≤ x ≤ 30, preferably 10 ≤ x ≤ 20). That is, it is preferable to mix the mixed organic solvents so that MTFP is more than FEC. Note that the above volume ratio may be the volume ratio measured before mixing the mixed organic solvents, and the outside air when mixing the mixed organic solvents may be at room temperature (typically 25°C). The mixed organic solvent in which FEC and MTFP are mixed exhibits a viscosity operable as a secondary battery and is preferable for maintaining an appropriate viscosity even in a low-temperature environment.

[0344] General solvents used in secondary batteries solidify at about -20°C, so it is difficult to manufacture a secondary battery that can be charged and discharged at -30°C, preferably -40°C. However, the mixed organic solvent described as an example in this embodiment enables the freezing point to be -30°C or lower, preferably -40°C or lower, and a secondary battery that can be charged and discharged even in a low-temperature environment can be realized. As a result, a secondary battery that can be charged and discharged in a wide temperature range including at least a low-temperature environment can be realized.

[0345] In the above, FEC was described as a representative, but any of the organic compounds described as fluorinated cyclic carbonates has the effect of promoting the dissociation of lithium salts, has a small solvation energy and the bond between lithium ions and the solvent is easily separated, and has a high viscosity and is difficult to use below the freezing point when used alone.

[0346] In the above, MTFP was described as a representative, but any of the organic compounds described as fluorinated chain carbonates can be said to have the effect of lowering or maintaining the viscosity of the electrolytic solution, which is one aspect of the present invention. Therefore, if the mixed organic solvent, which is one aspect of the present invention, contains a fluorinated cyclic carbonate and a fluorinated chain carbonate, a lithium-ion secondary battery that can be charged and discharged in a low-temperature environment can be provided.

[0347] <Electrolytic Solution Suitable for Low-Temperature Environment 2> As a mixed organic solvent used in the electrolyte, it contains ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). When the total content of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate is 100 vol%, a mixed organic solvent with a volume ratio of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate of x:y:100 - x - y (where 5 ≤ x ≤ 35 and 0 < y < 65) can be used. More specifically, a mixed organic solvent containing EC, EMC, and DMC in a volume ratio of EC:EMC:DMC = 30:35:35 can be used. Note that the above volume ratio may be the volume ratio before mixing the mixed organic solvent, and the outside air temperature when mixing the mixed organic solvent may be room temperature (typically 25°C).

[0348] EC is a cyclic carbonate and has a high relative dielectric constant, so it has the effect of promoting the dissociation of lithium salts. On the other hand, EC has a high viscosity and a high freezing point (melting point) of 38°C. Therefore, when using EC alone as a solvent, it is difficult to use it in a low-temperature environment. Thus, the solvent specifically described as one aspect of the present invention contains not only EC alone but also further contains EMC and DMC. EMC is a chain carbonate and has the effect of lowering the viscosity of the electrolyte, and its freezing point is -54°C. Also, DMC is also a chain carbonate and has the effect of lowering the viscosity of the electrolyte, and its freezing point is -43°C. An electrolyte prepared using a mixed organic solvent obtained by mixing EC, EMC, and DMC having such physical properties with the total content of these three mixed organic solvents being 100 vol% and a volume ratio of x:y:100 - x - y (where 5 ≤ x ≤ 35 and 0 < y < 65) has the characteristic that its freezing point is -40°C or lower.

[0349] A general electrolyte used in a secondary battery solidifies even at a temperature as low as about -20°C, so it is difficult to manufacture a secondary battery that can be charged and discharged at -40°C. The electrolyte described as an example in this embodiment has a freezing point of -40°C or lower, so a secondary battery that can be charged and discharged even in an extremely low temperature environment of -40°C can be realized.

[0350] In addition, as the lithium salt dissolved in the above solvent, it is possible to use a lithium salt. For example, at least one lithium salt of LiPF6, LiClO4, LiAsF6, LiBF4, LiAlCl4, LiSCN, LiBr, LiI, Li2SO4, Li2B 10 Cl 10 、Li2B 12 Cl 12 、LiCF3SO3, LiC4F9SO3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiN(CF3SO2)2, LiN(C4F9SO2)(CF3SO2), LiN(C2F5SO2)2, lithium bis(oxalate) borate (LiBOB) can be used in any combination and ratio. 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 even more preferably 0.8 mol / L or more and 1.2 mol / L or less, based on the volume of the above solvent. As a specific example of use, LiPF6 is preferably 0.5 mol / L or more and 1.5 mol / L or less, more preferably 0.7 mol / L or more and 1.3 mol / L or less, and even more preferably 0.8 mol / L or more and 1.2 mol / L or less, based on the volume of the above solvent.

[0351] In addition, the mixed organic solvent preferably has a high purity with a low content of particulate dust or elements other than the constituent elements of the electrolyte (hereinafter also simply referred to as "impurities"). Specifically, the weight ratio of impurities to the electrolyte is preferably 1% or less, more preferably 0.1% or less, and even more preferably 0.01% or less.

[0352] Also, for the purpose of improving safety, etc., in order to form a film (Solid Electrolyte Interphase Film) on the interface between the electrode (active material layer) and the electrolyte, additives such as vinylene carbonate (VC), propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), lithium bis(oxalate) borate (LiBOB), or dinitrile compounds such as succinonitrile or adiponitrile may be added to the electrolyte. The concentration of the additive preferably satisfies, for example, 0.1 wt% or more and 5 wt% or less with respect to the solvent.

[0353] In Example 2 of the electrolyte, the lithium salt can use the materials described in Example 1 of the electrolyte. Also, for the additives, the materials described in Example 1 of the electrolyte can be used.

[0354] As described above, examples of the electrolyte that can be used in the secondary battery of one aspect of the present invention have been described. However, the electrolyte that can be used in the secondary battery of one aspect of the present invention is not construed as being limited to this one example. Other materials can also be used as long as they are materials excellent in lithium ion conductivity even in charge and discharge under a low temperature environment.

[0355] The content of this embodiment can be appropriately combined with the content of other embodiments.

[0356] (Embodiment 5) In this embodiment, an example form of the secondary battery will be described.

[0357] [Coin-type secondary battery] An example of a coin-type secondary battery will be described. Fig. 13(A) is an exploded perspective view of a coin-type (single-layer flat-type) secondary battery, Fig. 13(B) is an external view, and Fig. 13(C) is a cross-sectional view thereof. Coin-type secondary batteries are mainly used in small electronic devices. In this specification, etc., coin-type secondary batteries include button-type secondary batteries.

[0358] In Fig. 13(A), it is a schematic diagram so that the overlap of the structures (vertical relationship and positional relationship) can be understood. Therefore, Fig. 13(A) and Fig. 13(B) are not considered to be completely corresponding diagrams that match exactly.

[0359] In Fig. 13(A), the positive electrode 304, the negative electrode 307, the spacer 342, and the washer 332 overlap, and the state of being sealed by the negative electrode can 302 and the positive electrode can 301 is shown. Note that in Fig. 13(A), the electrolyte and the separator described in the above embodiment are not shown. The spacer 342 and the washer 332 are 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 crimped. The spacer 342 or the washer 332 is made of stainless steel or an insulating material.

[0360] The positive electrode 304 has a laminated structure in which a positive electrode active material layer 306 is formed on the positive electrode current collector 305.

[0361] Fig. 13(B) is a perspective view of the completed coin-type secondary battery 300.

[0362] The coin-type secondary battery 300 may be insulated and sealed with a gasket 303 made of polypropylene or the like between the positive electrode can 301 that also serves as a positive electrode terminal and the negative electrode can 302 that also serves as a negative electrode terminal. The positive electrode 304 is formed by a positive electrode current collector 305 and a positive electrode active material layer 306 provided in contact therewith. The negative electrode 307 is formed by a negative electrode current collector 308 and a negative electrode active material layer 309 provided in contact therewith. 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.

[0363] Note that as the positive electrode 304 and the negative electrode 307 used for the coin-type secondary battery 300, a configuration in which the active material layer is formed only on one side of the current collector can be used.

[0364] As shown in Fig. 13(C), with the positive electrode can 301 at the bottom, the positive electrode 304, the negative electrode 307, and the negative electrode can 302 are laminated in this order, and the positive electrode can 301 and the negative electrode can 302 are crimped via the gasket 303 to manufacture the coin-type secondary battery 300.

[0365] By using the secondary battery of the present invention in the coin-shaped secondary battery 300, a highly reliable secondary battery can be obtained. Furthermore, by using the secondary battery of the present invention in the coin-shaped secondary battery 300, a secondary battery having good low-temperature characteristics can be obtained.

[0366] [Cylindrical secondary battery] An example of a cylindrical secondary battery will be described with reference to FIG. 14(A). As shown in FIG. 14(A), the cylindrical secondary battery 616 has a positive electrode cap (battery lid) 601 on the upper surface and a battery can (outer can) 602 on the side surface and the bottom surface. The positive electrode cap 601 and the battery can (outer can) 602 are insulated by a gasket (insulating packing) 610.

[0367] FIG. 14(B) is a diagram schematically showing a cross section of the cylindrical secondary battery. The cylindrical secondary battery shown in FIG. 14(B) has a positive electrode cap (battery lid) 601 on the upper surface and a battery can (outer can) 602 on the side surface and the bottom surface. The positive electrode cap 601 and the battery can (outer can) 602 are insulated by a gasket (insulating packing) 610.

[0368] Inside the hollow cylindrical battery can 602, a battery element is provided in which a strip-shaped positive electrode 604 and a negative electrode 606 are wound with 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 between a pair of opposing insulating plates 608 and 609. Further, the inside of the battery can 602 in which the battery element is provided is filled with an electrolyte (not shown) according to one embodiment of the present invention.

[0369] Since the positive and negative electrodes used in the cylindrical storage battery are wound, it is preferable to form the active material on both sides of the current collector. In FIGS. 14(A) to 14(D), although the secondary battery 616 in which the height of the cylinder is larger than the diameter of the cylinder is illustrated, the present invention is not limited thereto. A secondary battery in which the diameter of the cylinder is larger than the height of the cylinder may be used. With such a configuration, for example, miniaturization of the secondary battery can be achieved.

[0370] A positive electrode terminal (positive current collector lead) 603 is electrically connected to the positive electrode 604, and a negative electrode terminal (negative current collector lead) 607 is electrically connected to the negative electrode 606. As the positive electrode terminal 603, a metal material such as aluminum can be used. As the negative electrode terminal 607, a metal material such as copper can be used. The positive electrode terminal 603 is resistance-welded to the safety valve mechanism 613, and the negative electrode terminal 607 is resistance-welded to the bottom of the battery can 602, respectively. The safety valve mechanism 613 is electrically connected to the positive electrode cap 601 via a PTC (Positive Temperature Coefficient) element 611. The safety valve mechanism 613 cuts off the electrical connection between the positive electrode cap 601 and the positive electrode 604 when the internal pressure of the battery rises beyond a predetermined threshold value. Further, the PTC element 611 is a thermal resistance element whose resistance increases when the temperature rises, and restricts the current amount due to the increase in resistance to prevent abnormal heat generation. As the PTC element, a barium titanate (BaTiO3)-based ceramic material or the like can be used.

[0371] FIG. 14(C) shows an example of the power storage system 615. The power storage system 615 has a plurality of secondary batteries 616 and may also be called a battery pack. The positive electrodes of the respective secondary batteries are in contact with and electrically connected to a conductor 624 separated by an insulator 625. The conductor 624 is electrically connected to the control circuit 620 via a wiring 623. Further, the negative electrodes of the respective secondary batteries are electrically connected to the control circuit 620 via a wiring 626. As the control circuit 620, a protection circuit or the like for preventing overcharge or over-discharge can be applied.

[0372] FIG. 14(D) shows an example of the power storage system 615. The power storage system 615 has a plurality of secondary batteries 616, and the plurality of secondary batteries 616 are sandwiched between the conductive plate 628 and the conductive plate 614. The plurality of secondary batteries 616 are electrically connected to the conductive plate 628 and the conductive plate 614 by the wiring 627. The plurality of secondary batteries 616 may be connected in parallel, may be connected in series, or may be connected in series after being connected in parallel. By configuring the power storage system 615 having the plurality of secondary batteries 616, a large amount of power can be extracted.

[0373] The plurality of secondary batteries 616 may be further connected in series after being connected in parallel.

[0374] A temperature control device may be provided 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 too cold, it can be heated by the temperature control device. Therefore, the performance of the power storage system 615 is less affected by the outside air temperature.

[0375] Also, in FIG. 14(D), the power storage system 615 is electrically connected to the control circuit 620 via the wiring 621 and the wiring 622. The wiring 621 is electrically connected to the positive electrode of the plurality of secondary batteries 616 via the conductive plate 628, and the wiring 622 is electrically connected to the negative electrode of the plurality of secondary batteries 616 via the conductive plate 614.

[0376] By using the secondary battery of the present invention for the cylindrical secondary battery 616, a highly reliable secondary battery can be obtained. Further, by using the secondary battery of the present invention for the cylindrical secondary battery 616, a secondary battery having good low-temperature characteristics can be obtained.

[0377] [Other Structural Examples of Secondary Batteries] Structural examples of the secondary battery will be described with reference to FIGS. 15 and 16.

[0378] The secondary battery 913 shown in Fig. 15(A) has a wound body 950 provided with a terminal 951 and a terminal 952 inside a housing 930. The wound body 950 is impregnated with the electrolyte of one embodiment of the present invention inside the housing 930. The terminal 952 is in contact with the housing 930, and the terminal 951 is not in contact with the housing 930 by using an insulating material or the like. In Fig. 15(A), for the sake of convenience, the housing 930 is shown separately, but actually, the wound body 950 is covered by the housing 930, and the terminals 951 and 952 extend outside the housing 930. As the housing 930, a metal material (such as aluminum) or a laminate of a metal material and a resin material can be used.

[0379] Note that, as shown in Fig. 15(B), the housing 930 shown in Fig. 15(A) may be formed of a plurality of materials. For example, in the secondary battery 913 shown in Fig. 15(B), a housing 930a and a housing 930b are bonded together, and a wound body 950 is provided in the region surrounded by the housing 930a and the housing 930b.

[0380] As the housing 930a, a laminate of a metal material and a resin material or the like can be used. In particular, by forming an organic resin, which is a resin material, on the surface where the antenna is formed, the electric field by the secondary battery 913 can be suppressed. If the shielding of the electric field by the housing 930a is small, an antenna may be provided inside the housing 930a. As the housing 930b, for example, a metal material or a laminate of a metal material and a resin material can be used.

[0381] Furthermore, the structure of the wound body 950 is shown in Fig. 15(C). The wound body 950 has a negative electrode 931, a positive electrode 932, and an electrolyte layer 933. The wound body 950 is a wound body in which the negative electrode 931 and the positive electrode 932 overlap and are laminated with the electrolyte layer 933 interposed therebetween, and the laminated sheet is wound. Note that a plurality of laminations of the negative electrode 931, the positive electrode 932, and the electrolyte layer 933 may be further stacked.

[0382] Alternatively, a secondary battery 913 having a wound body 950a as shown in FIGS. 16(A) to 16(C) may be used. The wound body 950a shown in FIG. 16(A) has a negative electrode 931, a positive electrode 932, and an electrolyte layer 933. The negative electrode 931 has a negative electrode active material layer 931a. The positive electrode 932 has a positive electrode active material layer 932a.

[0383] The electrolyte layer 933 has a width wider than those of the negative electrode active material layer 931a and the positive electrode active material layer 932a, and is wound so as to overlap with the negative electrode active material layer 931a and the positive electrode active material layer 932a. Also, it is preferable from the viewpoint of safety that the width of the negative electrode active material layer 931a is wider than that of the positive electrode active material layer 932a. Further, the wound body 950a having such a shape is preferable in terms of safety and productivity.

[0384] As shown in FIG. 16(B), the negative electrode 931 is electrically connected to a terminal 951. The terminal 951 is electrically connected to a terminal 911a. Also, the positive electrode 932 is electrically connected to a terminal 952. The terminal 952 is electrically connected to a terminal 911b.

[0385] As shown in FIG. 16(C), the wound body 950a is covered with a housing 930 to form the secondary battery 913. It is preferable to provide a safety valve, an overcurrent protection element, etc. in the housing 930. The safety valve is a valve that opens when the inside of the housing 930 reaches a predetermined internal pressure, and can prevent the secondary battery from bursting.

[0386] As shown in FIG. 16(B), the secondary battery 913 may have a plurality of wound bodies 950a. By using a plurality of wound bodies 950a, a secondary battery 913 with a larger charge / discharge capacity can be obtained. For other elements of the secondary battery 913 shown in FIGS. 16(A) and (B), the description of the secondary battery 913 shown in FIGS. 15(A) to 15(C) can be referred to.

[0387] By using the secondary battery of the present invention in the secondary battery 913 having a wound body, a highly reliable secondary battery can be obtained. Further, by using the secondary battery of the present invention in the secondary battery 913 having a wound body, a secondary battery showing good low-temperature characteristics can be obtained.

[0388] The content of this embodiment can be appropriately combined with the content of other embodiments.

[0389] (Embodiment 6) In this embodiment, an example of applying to an electric vehicle (EV) is shown using FIG. 17.

[0390] As shown in FIG. 17(A), in the electric vehicle, first batteries 1301a and 1301b are provided as main driving secondary batteries, and a second battery 1311 that supplies power to an inverter 1312 for starting a motor 1304 is installed. By using the secondary battery of the present invention for the first batteries 1301a and 1301b, a highly reliable secondary battery can be obtained. Further, by using the secondary battery of the present invention for the first batteries 1301a and 1301b described above, a secondary battery having good low-temperature characteristics can be obtained.

[0391] The second battery 1311 is also called a cranking battery (also called a starter battery). The second battery 1311 only needs to be able to output high power, and a large capacity is not so necessary, and the capacity of the second battery 1311 is smaller compared to the first batteries 1301a and 1301b.

[0392] The internal structure of the first battery 1301a may be a wound type or a laminated type. Also, the first battery 1301a may use an all-solid-state battery. By using an all-solid-state battery for the first battery 1301a, a high capacity can be achieved, the safety can be improved, and miniaturization and weight reduction can be achieved.

[0393] In this embodiment, an example is shown in which the first batteries 1301a and 1301b are connected in parallel, but they may be connected in parallel in three or more. Also, if the first battery 1301a can store sufficient power, the first battery 1301b may not be necessary. By configuring a battery pack having a plurality of secondary batteries, a large amount of power can be extracted. The plurality of secondary batteries may be connected in parallel, may be connected in series, or may be further connected in series after being connected in parallel. The plurality of secondary batteries are also called a battery set.

[0394] Also, in an in-vehicle secondary battery, in order to cut off the power from a plurality of secondary batteries, it has a service plug or a circuit breaker that can cut off a high voltage without using tools, and is provided in the first battery 1301a.

[0395] Also, the power of the first batteries 1301a and 1301b is mainly used to rotate the motor 1304, but power is supplied to 42V in-vehicle components (electric power steering 1307, heater 1308, defogger 1309, etc.) via the DCDC circuit 1306. Even when the rear wheel has a rear motor 1317, the first battery 1301a is used to rotate the rear motor 1317.

[0396] Also, the second battery 1311 supplies power to 14V in-vehicle components (audio 1313, power window 1314, lamps 1315, etc.) via the DCDC circuit 1310.

[0397] Also, the first battery 1301a will be described with reference to FIG. 17(B).

[0398] FIG. 17(B) shows an example in which nine rectangular secondary batteries 1300 are used as one battery pack 1415. Also, the nine rectangular secondary batteries 1300 are connected in series, one electrode is fixed by a fixing portion 1413 made of an insulator, and the other electrode is fixed by a fixing portion 1414 made of an insulator. In the present embodiment, an example of fixing by the fixing portions 1413 and 1414 is shown, but a configuration in which they are housed in a battery housing box (also referred to as a casing) may be used. Since the vehicle is assumed to be subjected to vibration or shaking from the outside (such as a road surface), it is preferable to fix a plurality of secondary batteries by the fixing portions 1413 and 1414 and the battery housing box or the like. Also, one electrode is electrically connected to the control circuit portion 1320 by a wiring 1421. The other electrode is electrically connected to the control circuit portion 1320 by a wiring 1422.

[0399] Further, the control circuit portion 1320 may use a memory circuit including a transistor using an oxide semiconductor. A charge control circuit or a battery control system having a memory circuit including a transistor using an oxide semiconductor may be referred to as BTOS (Battery operating system, or Battery oxide semiconductor).

[0400] It is preferable to use a metal oxide that functions as an oxide semiconductor. For example, as the oxide, a metal oxide such as 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, or magnesium) may be used. In particular, the In-M-Zn oxide applicable as the oxide is preferably CAAC-OS (C-Axis Aligned Crystal Oxide Semiconductor) or CAC-OS (Cloud-Aligned Composite Oxide Semiconductor). Further, an In-Ga oxide or an In-Zn oxide may be used as the oxide. CAAC-OS is an oxide semiconductor having a plurality of crystal regions, and the plurality of crystal regions have their c-axes oriented in a specific direction. The specific direction is the thickness direction of the CAAC-OS film, the normal direction of the surface on which the CAAC-OS film is formed, or the normal direction of the surface of the CAAC-OS film. Further, the crystal region is a region having periodicity in the atomic arrangement. When the atomic arrangement is regarded as a lattice arrangement, the crystal region is also a region where the lattice arrangements are aligned. Furthermore, CAAC-OS has a region where a plurality of crystal regions are connected in the a-b plane direction, and this region may have strain. The strain refers to a portion where the orientation of the lattice arrangement changes between a region where the lattice arrangements are aligned and another region where the lattice arrangements are aligned in the region where the plurality of crystal regions are connected. That is, CAAC-OS is an oxide semiconductor in which the c-axis is oriented and there is no obvious orientation in the a-b plane direction.

[0401] In addition, since it can be used in a low-temperature environment, it is preferable that the control circuit unit 1320 uses a transistor using an oxide semiconductor. To simplify the process, the control circuit unit 1320 may be formed using a unipolar transistor. A transistor using an oxide semiconductor for the semiconductor layer has an operating ambient temperature range wider than that of single-crystalline Si, from -40°C to 150°C or less, and even when the secondary battery is heated, the characteristic change is smaller than that of single-crystalline Si. The off-current of a transistor using an oxide semiconductor is very low regardless of temperature even at 150°C, while the off-current characteristic of a single-crystalline Si transistor has a large temperature dependence. For example, at 150°C, the off-current of a single-crystalline Si transistor increases, and the current on / off ratio does not become sufficiently large. The control circuit unit 1320 can improve safety.

[0402] The control circuit unit 1320 using a memory circuit including a transistor using an oxide semiconductor can also function as an automatic control device for a secondary battery against the causes of 10 items of instability such as micro-shorts. The functions for eliminating the causes of the 10 items of instability include prevention of overcharging, prevention of overcurrent, overheat control during charging, cell balance in a battery pack, prevention of overdischarge, remaining amount measurement, automatic control of charging voltage and current according to temperature, control of charging current according to degree of deterioration, detection of abnormal behavior of micro-shorts, prediction of abnormalities related to micro-shorts, etc. The control circuit unit 1320 has at least one of these functions. In addition, miniaturization of the automatic control device for the secondary battery is possible.

[0403] Also, a micro-short is one type of internal short, referring to a minute short circuit inside the secondary battery. One of the causes of a micro-short is said to be that due to multiple charge and discharge cycles, due to the non-uniform distribution of the positive electrode active material, local current concentration occurs between a part of the positive electrode and a part of the negative electrode, or a microscopic short circuit occurs due to the generation of side reaction products due to side reactions.

[0404] In addition to detecting micro-shorts, it can also be said that the control circuit unit 1320 detects the terminal voltage of the secondary battery 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.

[0405] Further, an example of the block diagram of the battery pack 1415 shown in FIG. 17(B) is shown in FIG. 17(C).

[0406] The control circuit unit 1320 includes at least a switch for preventing overcharging, a switch unit 1324 including a switch for preventing over-discharging, a control circuit 1322 for controlling the switch unit 1324, and a voltage measurement unit for the first battery 1301a. The control circuit unit 1320 has the upper limit voltage and the lower limit voltage of the secondary battery to be used set, and limits the external current upper limit, the upper limit of the output current to the outside, etc. The range within the lower limit voltage and the upper limit voltage of the secondary battery is the voltage range in which use is recommended. When outside this range, the switch unit 1324 operates and functions as a protection circuit. Further, since the control circuit unit 1320 controls the switch unit 1324 to prevent over-discharging and overcharging, it can also be called a protection circuit. For example, when the control circuit 1322 detects a voltage that is likely to cause overcharging, the current is cut off by turning off the switch of the switch unit 1324. Further, a PTC element may be provided in the charge and discharge path to provide a function of cutting off the current in response to an increase in temperature. The control circuit unit 1320 also has an external terminal 1325(+IN) and an external terminal 1326(-IN).

[0407] The switch unit 1324 can be configured by combining an n-channel type transistor and a p-channel type transistor. The switch unit 1324 is not limited to a switch having an Si transistor using single crystal silicon. For example, Ge (germanium), SiGe (silicon germanium), GaAs (gallium arsenide), GaAlAs (gallium aluminum arsenide), InP (indium phosphide), SiC (silicon carbide), ZnSe (zinc selenide), GaN (gallium nitride), GaO x The switching section 1324 may be formed by a power transistor having (gallium oxide; x is a real number greater than 0), etc. Further, since the memory element using an OS transistor can be freely arranged by laminating it on a circuit using an Si transistor or the like, integration can be easily performed. By laminating and integrating the control circuit section 1320 using an OS transistor on the switching section 1324, it can be made into one chip, and miniaturization is possible.

[0408] The first batteries 1301a and 1301b mainly supply power to in-vehicle devices of the 42V system (high voltage system), and the second battery 1311 supplies power to in-vehicle devices of the 14V system (low voltage system). The second battery 1311 is often adopted because a lead-acid battery is advantageous in terms of cost. There is an advantage of being maintenance-free by using the second battery 1311 as a secondary battery, but when used for a long period, for example, for three years or more, abnormal occurrences that cannot be discriminated during manufacturing may occur. In particular, when the second battery 1311 that starts the inverter becomes inoperable, the motor may not be able to start even if the first batteries 1301a and 1301b have remaining capacity. When the second battery 1311 is a lead-acid battery, power is supplied from the first battery to the second battery and it is charged so as to always maintain a fully charged state, so the motor does not become inoperable as described above.

[0409] In the present embodiment, an example is shown in which secondary batteries are used for both the first battery 1301a and the second battery 1311, but the second battery 1311 may use a lead-acid battery, an all-solid-state battery, or an electric double layer capacitor. By using the secondary battery of the present invention for the above-described secondary battery, a highly reliable secondary battery can be obtained. Further, by using the secondary battery of the present invention for the above-described secondary battery, a secondary battery having good low-temperature characteristics can be obtained.

[0410] In addition, the regenerative energy generated by the rotation of the tire 1316 is sent to the motor 1304 via the gear 1305, and is charged to the second battery 1311 via the motor controller 1303 and the control circuit unit 1321 from the battery controller 1302. Or it is charged to the first battery 1301a via the control circuit unit 1320 from the battery controller 1302. Or it is charged to the first battery 1301b via the control circuit unit 1320 from the battery controller 1302. In order to efficiently charge the regenerative energy, it is desirable that the first batteries 1301a and 1301b are capable of rapid charging.

[0411] The battery controller 1302 can set the charging voltage, charging current, etc. of the first batteries 1301a and 1301b. The battery controller 1302 can set the charging conditions according to the charging characteristics of the secondary battery to be used and perform rapid charging.

[0412] Also, although not shown, when connecting to an external charger, the charger's socket or the charger's connection cable is electrically connected to the battery controller 1302. The power supplied from the external charger is used to charge the first batteries 1301a and 1301b via the battery controller 1302. Also, depending on the charger, a control circuit may be provided and in some cases the functions of the battery controller 1302 may not be used, but it is preferable to charge the first batteries 1301a and 1301b via the control circuit unit 1320 to prevent overcharging. Also, in some cases, the connection cable or the charger's connection cable may be equipped with a control circuit. The control circuit unit 1320 may also be called an ECU (Electronic Control Unit). The ECU is connected to a CAN (Controller Area Network) provided in the electric vehicle. CAN is one of the serial communication standards used as an in-vehicle LAN. Also, the ECU includes a microcomputer. Also, the ECU uses a CPU or a GPU.

[0413] External chargers installed in charging stands, etc., include 100V outlets, 200V outlets, three-phase 200V and 50kW, etc. In addition, it is also possible to charge by receiving power supply from external charging facilities by means of non-contact power supply methods, etc.

[0414] Next, an example of mounting a secondary battery, which is one aspect of the present invention, on a vehicle, typically a transport vehicle, will be described.

[0415] In addition, when a secondary battery is mounted on a vehicle, next-generation clean energy vehicles such as hybrid vehicles (HV), electric vehicles (EV), or plug-in hybrid vehicles (PHV) can be realized. Further, secondary batteries can also be mounted on transport vehicles such as agricultural machinery, motorized bicycles including electric assist bicycles, motorcycles, electric wheelchairs, electric carts, small or large ships, submarines, aircraft such as fixed-wing aircraft and rotary-wing aircraft, rockets, artificial satellites, space exploration vehicles, planetary exploration vehicles, and spacecraft.

[0416] In FIGS. 18(A) to 18(D), a transport vehicle using one aspect of the present invention is illustrated. The automobile 2001 shown in FIG. 18(A) is an electric vehicle that uses an electric motor as a power source for running. Or, it is a hybrid vehicle that can appropriately select and use an electric motor and an engine as power sources for running. When a secondary battery is mounted on a vehicle, an example of the secondary battery shown in the above embodiment is installed at one location or a plurality of locations. By using the secondary battery of the present invention for the secondary battery mounted on the vehicle, a highly reliable secondary battery can be obtained. Furthermore, by using the secondary battery of the present invention for the above-described secondary battery, a secondary battery having good low-temperature characteristics can be obtained.

[0417] The automobile 2001 shown in FIG. 18(A) has a battery pack 2200, and the battery pack has a battery module to which a plurality of secondary batteries are connected. Furthermore, it is preferable that the battery pack 2200 has a charge control device electrically connected to the battery module.

[0418] In addition, the vehicle 2001 can be charged by receiving power supply from an external charging facility by means of a plug-in method, a non-contact power supply method, etc. to the secondary battery of the vehicle 2001. When charging, the charging method, the specifications of the connector, etc. may be appropriately carried out in a predetermined method such as CHAdeMO (registered trademark) or Combo. As the charging facility, a charging station provided in a commercial facility can be used, or the power supply of a household can be used. For example, by plug-in technology, the power storage device mounted on the vehicle 2001 can be charged by external power supply. Charging can be carried out by converting AC power into DC power via a conversion device such as an AC-DC converter.

[0419] Also, although not shown, a power receiving device can be mounted on the vehicle, and power can be supplied non-contact from a power transmitting device on the ground for charging. In the case of this non-contact power supply method, by incorporating the power transmitting device into a road or an outer wall, charging can be carried out not only while the vehicle is stopped but also while it is running. Further, using this non-contact power supply method, power transmission and reception may be performed between two vehicles. Furthermore, a solar cell may be provided on the exterior of the vehicle to charge the secondary battery when the vehicle is stopped and when it is running. For such non-contact power supply, an electromagnetic induction method or a magnetic field resonance method can be used.

[0420] FIG. 18(B) shows a large transport vehicle 2002 having a motor controlled by electricity as an example of a transport vehicle. The battery module of the transport vehicle 2002 has, for example, four secondary batteries with a nominal voltage of 3.0 V or more and 5.0 V or less as a cell unit, and has a maximum voltage of 170 V with 48 cells connected in series. Since it has the same functions as FIG. 17(B) except for the number of secondary batteries of the battery pack 2201 and the like, the description is omitted. By using the secondary battery of the present invention for the secondary battery of the battery pack 2201, a highly reliable secondary battery can be obtained. Further, by using the secondary battery of the present invention for the secondary battery of the battery pack 2201 described above, a secondary battery showing good low-temperature characteristics can be obtained.

[0421] FIG. 18(C) shows a large transport vehicle 2003 having a motor controlled by electricity as an example. The battery module of the transport vehicle 2003 has a maximum voltage of 600V by connecting more than a hundred secondary batteries with a nominal voltage of, for example, 3.0V or more and 5.0V or less in series. Also, since it has the same functions as FIG. 17(B) except for the number of secondary batteries constituting the battery module of the battery pack 2202, the description thereof is omitted. By using the secondary battery of the present invention for the secondary battery included in the module, a highly reliable secondary battery can be obtained. Furthermore, by using the secondary battery of the present invention for the secondary battery included in the above-described module, a secondary battery exhibiting good low-temperature characteristics can be obtained.

[0422] FIG. 18(D) shows an aircraft 2004 having an engine that burns fuel as an example. Since the aircraft 2004 shown in FIG. 18(D) has wheels for takeoff and landing, it can be said to be a part of a transport vehicle. It has a battery pack 2203 including a plurality of secondary batteries connected to form a battery module and a charge control device.

[0423] The battery module of the aircraft 2004 has a maximum voltage of 32V by connecting eight 4V secondary batteries in series. Since it has the same functions as FIG. 17(B) except for the number of secondary batteries constituting the battery module of the battery pack 2203, the description thereof is omitted.

[0424] The content of the present embodiment can be appropriately combined with the content of other embodiments.

[0425] (Embodiment 7) In the present embodiment, an example in which a secondary battery, which is an aspect of the present invention, is mounted on a vehicle such as a two-wheeled vehicle or a bicycle is shown.

[0426] FIG. 19(A) is an example of an electric bicycle using a secondary battery according to an aspect of the present invention. The secondary battery according to an aspect of the present invention can be applied to the electric bicycle 8700 shown in FIG. 19(A). The secondary battery according to an aspect of the present invention may have a protection circuit.

[0427] The electric bicycle 8700 is equipped with a power storage device 8702. The power storage device 8702 can supply electricity to a motor that assists the driver. Also, the power storage device 8702 is portable and is shown in the state of being removed from the bicycle in Fig. 19(B). Further, the power storage device 8702 incorporates a plurality of secondary batteries 8701 according to an aspect of the present invention, and can display the remaining battery level and the like on a display unit 8703. By using the secondary battery of the present invention for the secondary battery 8701, a highly reliable secondary battery can be obtained. Furthermore, by using the secondary battery of the present invention for the secondary battery 8701, a secondary battery with good low-temperature characteristics can be obtained.

[0428] Also, the power storage device 8702 has a control circuit 8704 capable of controlling the charging of the secondary battery or detecting abnormalities. The control circuit 8704 is electrically connected to the positive and negative electrodes of the secondary battery 8701. It can greatly contribute to extinguishing accidents such as fires caused by secondary batteries.

[0429] Fig. 19(C) shows an example of a two-wheeled vehicle using the secondary battery according to an aspect of the present invention. The scooter 8600 shown in Fig. 19(C) includes a power storage device 8602, side mirrors 8601, and direction indicator lights 8603. The power storage device 8602 can supply electricity to the direction indicator lights 8603. By using the secondary battery of the present invention for the secondary battery of the power storage device 8602, a highly reliable secondary battery can be obtained. Furthermore, by using the secondary battery of the present invention for the secondary battery of the power storage device 8602, a secondary battery with good low-temperature characteristics can be obtained.

[0430] The scooter 8600 shown in Fig. 19(C) can store the power storage device 8602 in an under-seat storage 8604. The power storage device 8602 can be stored in the under-seat storage 8604 even if the under-seat storage 8604 is small.

[0431] The content of this embodiment can be appropriately combined with the content of other embodiments.

[0432] (Embodiment 8) In this embodiment, an example of mounting a secondary battery, which is one aspect of the present invention, on an electronic device will be described. Examples of the electronic device on which the secondary battery is mounted include, for example, a television device (also referred to as a TV or a television receiver), a monitor for a computer, a digital camera, a digital video camera, a digital photo frame, a mobile phone (also referred to as a cellular phone or a mobile phone device), a portable game machine, a portable information terminal, an audio reproduction device, and a large game machine such as a pachinko machine. Examples of the portable information terminal include a notebook personal computer, a tablet terminal, an e-book terminal, and a mobile phone.

[0433] FIG. 20(A) shows an example of a mobile phone. The mobile phone 2100 includes, in addition to a display unit 2102 incorporated in a housing 2101, operation buttons 2103, an external connection port 2104, a speaker 2105, a microphone 2106, and the like. Note that the mobile phone 2100 has a secondary battery 2107. By using the secondary battery of the present invention for the secondary battery 2107, a highly reliable secondary battery can be obtained. Furthermore, by using the secondary battery of the present invention for the secondary battery 2107, a secondary battery having good low-temperature characteristics can be obtained.

[0434] The mobile phone 2100 can execute various applications such as mobile phone calls, e-mail, text viewing and creation, music reproduction, Internet communication, and computer games.

[0435] In addition to time setting, the operation buttons 2103 can have various functions such as power on / off operations, wireless communication on / off operations, execution and cancellation of a manner mode, and execution and cancellation of a power saving mode. For example, the functions of the operation buttons 2103 can be freely set by an operating system incorporated in the mobile phone 2100.

[0436] In addition, the mobile phone 2100 can execute communication-standardized short-range wireless communication. For example, it can communicate with a wireless headset to make hands-free calls.

[0437] In addition, the mobile phone 2100 is provided with an external connection port 2104 and can directly exchange data with other information terminals via a connector. Charging can also be performed via the external connection port 2104. Note that the charging operation may also be performed by wireless power supply without using the external connection port 2104.

[0438] The mobile phone 2100 preferably has a sensor. As the sensor, for example, a fingerprint sensor, a pulse sensor, a body temperature sensor and other human body sensors, a touch sensor, a press sensor, an acceleration sensor, etc. are preferably mounted.

[0439] FIG. 20(B) shows an unmanned aerial vehicle 2300 having a plurality of rotors 2302. The unmanned aerial vehicle 2300 is sometimes called a drone. The unmanned aerial vehicle 2300 has a secondary battery 2301, a camera 2303, and an antenna (not shown), which are aspects 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 for the secondary battery 2301, a highly reliable secondary battery can be obtained. Furthermore, by using the secondary battery of the present invention for the secondary battery 2301, a secondary battery showing good low-temperature characteristics can be obtained.

[0440] FIG. 20(C) shows an example of a robot. The robot 6400 shown in FIG. 20(C) 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.

[0441] The microphone 6402 has a function of detecting the user's voice, environmental sounds, etc. Also, the speaker 6404 has a function of emitting sound. The robot 6400 can communicate with the user by using the microphone 6402 and the speaker 6404.

[0442] The display unit 6405 has the function of displaying various information. The robot 6400 can display the information desired by the user on the display unit 6405. The display unit 6405 may be equipped with a touch panel. Also, the display unit 6405 may be a removable information terminal, and by installing it at a fixed position of the robot 6400, charging and data transfer are made possible.

[0443] The upper camera 6403 and the lower camera 6406 have the function of imaging the surroundings of the robot 6400. Also, the obstacle sensor 6407 can detect the presence or absence of obstacles in the traveling direction when the robot 6400 moves forward using the movement mechanism 6408. The robot 6400 can recognize the surrounding environment and move safely using the upper camera 6403, the lower camera 6406, and the obstacle sensor 6407.

[0444] The robot 6400 includes a secondary battery 6409 according to one aspect of the present invention and a semiconductor device or electronic components in its internal area. By using the secondary battery of the present invention for the secondary battery 6409, a highly reliable secondary battery can be obtained. Furthermore, by using the secondary battery of the present invention for the secondary battery 6409, a secondary battery with good low-temperature characteristics can be obtained.

[0445] Figure 20(D) shows an example of a cleaning robot. The cleaning robot 6300 has a display unit 6302 arranged on the upper surface of the housing 6301, a plurality of cameras 6303 arranged on the side surface, a brush 6304, an operation button 6305, a secondary battery 6306, various sensors, etc. Although not shown, the cleaning robot 6300 is equipped with tires, a suction port, etc. The cleaning robot 6300 can move autonomously, detect dust 6310, and suck the dust from the suction port provided on the lower surface.

[0446] For example, the cleaning robot 6300 can analyze the images captured by the camera 6303 and determine the presence or absence of obstacles such as walls, furniture, or steps. Also, when an object that is likely to get caught in the brush 6304, such as wiring, is detected by image analysis, the rotation of the brush 6304 can be stopped. The cleaning robot 6300 includes a secondary battery 6306 according to one aspect of the present invention and a semiconductor device or electronic components in its internal area. By using the secondary battery of the present invention for the secondary battery 6306, a highly reliable secondary battery can be obtained. Furthermore, by using the secondary battery of the present invention for the secondary battery 6306, a secondary battery having good low-temperature characteristics can be obtained.

[0447] This embodiment can be implemented in appropriate combination with other embodiments.

[0448] (Embodiment 9) In this embodiment, an example of mounting a secondary battery, which is one aspect of the present invention, on a space device will be described.

[0449] FIG. 21(A) shows an artificial satellite 6800 as an example of a space device. The artificial satellite 6800 includes a body 6801, a solar panel 6802, an antenna 6803, and a secondary battery 6805. The solar panel may sometimes be called a solar cell module.

[0450] When the solar panel 6802 is irradiated with sunlight, the electric power necessary for the operation of the artificial satellite 6800 is generated. However, for example, in a situation where the solar panel is not irradiated with sunlight or in a situation where the amount of sunlight irradiated on the solar panel is small, the generated electric power decreases. Therefore, there is a possibility that the electric power necessary for the operation of the artificial satellite 6800 is not generated. In order to operate the artificial satellite 6800 even in a situation where the generated electric power is small, it is advisable to provide the artificial satellite 6800 with a secondary battery 6805. By using the secondary battery of the present invention for the secondary battery 6805, a highly reliable secondary battery can be obtained. Furthermore, by using the secondary battery of the present invention for the secondary battery 6805, a secondary battery having good low-temperature characteristics can be obtained.

[0451] The artificial satellite 6800 can generate signals. These signals can be transmitted via the antenna 6803 and received, for example, by a receiver installed on the ground or by other artificial satellites. By receiving the signals transmitted by the artificial satellite 6800, for example, the position of the receiver that received the signals can be measured. From the above, the artificial satellite 6800 can, for example, constitute a satellite positioning system.

[0452] Alternatively, the artificial satellite 6800 can be configured to have sensors. For example, by being configured to have a visible light sensor, the artificial satellite 6800 can have the function of detecting sunlight reflected by an object provided on the ground. Or, by being configured to have a thermal infrared sensor, the artificial satellite 6800 can have the function of detecting thermal infrared rays emitted from the earth's surface. From the above, the artificial satellite 6800 can, for example, have the function as an earth observation satellite.

[0453] Figure 21(B) shows an exploration vehicle 6900 having a solar sail (also called a solar sail) as an example of space equipment. The exploration vehicle 6900 has a fuselage 6901, a solar sail 6902, and a secondary battery 6905. By using the secondary battery of the present invention for the secondary battery 6905, a highly reliable secondary battery can be obtained. Furthermore, by using the secondary battery of the present invention for the secondary battery 6905, a secondary battery with good low-temperature characteristics can be obtained. When photons emitted from the sun hit the surface of the solar sail 6902, momentum is transferred to the solar sail 6902. Therefore, it is preferable to use a thin film with a high reflectivity for the surface of the solar sail 6902, and it is more preferable that the surface faces the sun.

[0454] Also, the solar sail 6902 can be designed to be in a small folded state until it exits the atmosphere and to be deployed in a large sheet shape as shown in Figure 21(B) in outer space (space) of the earth.

[0455] FIG. 21(C) shows a spacecraft 6910 as an example of space equipment. The spacecraft 6910 includes a body 6911, a solar panel 6912, and a secondary battery 6913. By using the secondary battery of the present invention for the secondary battery 6913, a highly reliable secondary battery can be obtained. Furthermore, by using the secondary battery of the present invention for the secondary battery 6913, a secondary battery with good low-temperature characteristics can be obtained. The body 6911 can have, for example, a pressurized chamber and a non-pressurized chamber. The pressurized chamber may be designed such that crew members can enter. The electric power generated by irradiating the solar panel 6912 with sunlight can be used to charge the secondary battery 6913.

[0456] FIG. 21(D) shows a rover 6920 as an example of space equipment. The rover 6920 includes a body 6921 and a secondary battery 6923. By using the secondary battery of the present invention for the secondary battery 6923, a highly reliable secondary battery can be obtained. Furthermore, by using the secondary battery of the present invention for the secondary battery 6923, a secondary battery with good low-temperature characteristics can be obtained. The rover 6920 may have a solar panel 6922.

[0457] The rover 6920 may be designed such that crew members can enter. The electric power generated by irradiating the solar panel 6912 with sunlight may be used to charge the secondary battery 6923, or the electric power generated by other power sources, such as fuel cells, radioisotope thermoelectric generators, etc., may be used to charge the secondary battery 6923.

[0458] The content of this embodiment can be appropriately combined with the content of other embodiments.

Explanation of Reference Numerals

[0459] 20 Positive electrode active material particles 20a Surface layer portion 20b Interior 100 Secondary battery 101 Positive electrode current collector 101t Protrusion 102 Positive electrode active material layer 103 Positive electrode 104 Separator 105 Carbon layer 106 Anode active material layer 107 Anode current collector 107t Aggregate 108 Anode 109 Outer package 110 Electrolyte 116 Region 117 Void 118a Dendrite 118b Dendrite 118c Dendrite 118d Dendrite 118e Dendrite 119 Arrow 120 Separator laminate< / xps>

Claims

1. Applying a slurry having carbon and a solvent to the separator; drying the slurry to remove the solvent to form a carbon layer; the carbon layer and the negative electrode are placed opposite each other and subjected to a press treatment.

2. Applying a slurry having carbon, a solvent and a binder to the separator; drying the slurry to remove the solvent to form a carbon layer having the binder; the carbon layer and the negative electrode are placed opposite each other and subjected to a press treatment.

3. Coating the separator with a slurry having carbon, a solvent, and polyglutamic acid; drying the slurry to remove the solvent to form a carbon layer having the polyglutamic acid; The carbon layer and the negative electrode are placed opposite each other and subjected to a press treatment; The method for producing a secondary battery, wherein the solvent comprises water.

4. 4. The method for producing a secondary battery according to claim 1, wherein heating is performed in the pressing process.

5. 4. The method for producing a secondary battery according to claim 1, wherein the pressing step comprises performing linear pressure.

6. Applying a slurry having carbon and a solvent to the separator; drying the slurry to remove the solvent to form a carbon layer; a first pressing process is performed with the carbon layer and a negative electrode facing each other; and performing a second press treatment while the separator and the positive electrode are opposed to each other.

7. Applying a slurry having carbon, a solvent and a binder to the separator; drying the slurry to remove the solvent to form a carbon layer having the binder; a first pressing process is performed with the carbon layer and a negative electrode facing each other; and performing a second press treatment while the separator and the positive electrode are opposed to each other.

8. Coating the separator with a slurry having carbon, a solvent, and polyglutamic acid; drying the slurry to remove the solvent to form a carbon layer having the polyglutamic acid; a first pressing process is performed with the carbon layer and a negative electrode facing each other; The separator and the positive electrode are placed opposite each other, and a second press treatment is performed; The method for producing a secondary battery, wherein the solvent comprises water.

9. 9. The method for manufacturing a secondary battery according to claim 6, wherein heating is performed in the first press treatment or the second press treatment.

10. 9. The method for manufacturing a secondary battery according to claim 6, wherein the first pressing process is a linear pressing process, and the second pressing process is a surface pressing process.

11. 9. The method for manufacturing a secondary battery according to claim 6, wherein the second pressing process is performed after the positive electrode is cut.

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