Rechargeable batteries, electronic equipment, and vehicles

Abstract

The present invention provides a lithium ion secondary battery which has high capacity and excellent charge and discharge cycle characteristics. The present invention provides a secondary battery which has high capacity. The present invention provides a secondary battery which has excellent charge and discharge characteristics. The present invention provides a secondary battery which is suppressed in decrease in the capacity even in cases where a state of charging at a high voltage is maintained for a long period of time. A secondary battery wherein: the surface layer part of each positive electrode active material particle is formed of lithium cobaltate which has an O3 structure after discharging after alternately repeating, in an environment at 60°C, a charging process, wherein constant current charging is performed to the voltage of 4.5 V at the current value of 0.5 C, and subsequently constant voltage charging is performed until the current value falls to 0.2 C, and a discharging process, wherein constant current discharging is performed to the voltage of 3 V at the current value of 0.5 C, 150 times or more; and the electrolyte comprises imidazolium cations.

Description

[Technical Field]

[0001] One aspect of the present invention relates to a product, a method, or a method of manufacture; or to a process, a machine, a manufacture, or a composition of matter. One aspect of the present invention relates to a semiconductor device, a display device, a light-emitting device, a power storage device, a lighting device, or an electronic device, or to a method of manufacturing the same. In particular, it relates to a positive electrode active material that can be used in a secondary battery, a secondary battery, an electronic device having a secondary battery, and a vehicle having a secondary battery.

[0002] Alternatively, one aspect of the present invention relates to an energy storage system having a secondary battery and a battery control circuit. Alternatively, one aspect of the present invention relates to an electronic device and a vehicle having an energy storage system.

[0003] In this specification, the term "energy storage device" refers to all elements and devices that have an energy storage function. For example, this includes rechargeable batteries (also called secondary batteries) such as lithium-ion secondary batteries, lithium-ion capacitors, and electric double-layer capacitors.

[0004] Furthermore, in this specification, "electronic equipment" refers to all devices that have an energy storage device, and electro-optical devices with an energy storage device, information terminal devices with an energy storage device, etc., are all considered electronic equipment. [Background technology]

[0005] In recent years, there has been a great deal of development on various energy storage devices, including lithium-ion secondary batteries, lithium-ion capacitors, and air batteries. In particular, lithium-ion secondary batteries, with their high output and high energy density, have seen a rapid increase in demand alongside the development of the semiconductor industry. They are used in mobile information terminals such as mobile phones, smartphones, tablets, and notebook computers, as well as portable music players, digital cameras, medical equipment, and next-generation clean energy vehicles (hybrid vehicles (HV), electric vehicles (EV), plug-in hybrid vehicles (PHV), etc.), and have become indispensable to today's information society as a source of rechargeable energy.

[0006] The characteristics required of lithium-ion secondary batteries include further increases in energy density, improved cycle characteristics, and enhanced safety and long-term reliability in various operating environments.

[0007] Therefore, improvements to the positive electrode active material are being considered to enhance the cycle characteristics and increase the capacity of lithium-ion secondary batteries (Patent Documents 1 and 2). Research is also being conducted on the crystal structure of the positive electrode active material (Non-Patent Documents 1 to 3).

[0008] Non-patent document 4 describes the physical properties of metal fluorides.

[0009] X-ray diffraction (XRD) is one of the techniques used to analyze the crystal structure of cathode active materials. By using ICSD (Inorganic Crystal Structure Database), which is introduced in Non-Patent Document 5, XRD data can be analyzed. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Japanese Patent Publication No. 2002-216760 [Patent Document 2] Japanese Patent Publication No. 2006-261132 [Non-patent literature]

[0011] [Non-Patent Document 1] Toyoki Okumura et al, “Correlation of lithium ion distribution and X-ray absorption near-edge structure in O3-and O2-lithium cobalt oxides from first-principle calculation”, Journal of Materials Chemistry, 2012, 22, p. 17340-17348 [Non-Patent Document 2] Motohashi, T. et al, “Electronic phase diagram of the layered cobalt oxide system LixCoO▲2▼(0.0≦x≦1.0)”, Physical Review B, 80(16);165114 [Non-Patent Document 3] Zhaohui Chen et al, “Staging Phase Transitions in LixCoO▲2▼,” Journal of The Electrochemical Society, 2002, 149(12)A1604-A1609 [Non-Patent Document 4] WECounts et al, “Fluoride Model Systems:II,The Binary Systems CaF▲2▼-BeF▲2▼,MgF▲2▼-BeF▲2▼,and LiF-MgF▲2▼,”Journal of the American Ceramic Society,(1953)36[1]12-17.Fig.01471 [Non-Patent Document 5] Belsky, A. et al., “New developments in the Inorganic Crystal Structure Database (ICSD): accessibility in support of materials research and design”, Acta Cryst., (2002) B58 364-369 [Overview of the project] [Problems that the invention aims to solve]

[0012] One aspect of the present invention aims to provide a lithium-ion secondary battery with high capacity and excellent charge-discharge cycle characteristics, and a method for manufacturing the same. Alternatively, one aspect of the present invention aims to provide a rapidly rechargeable secondary battery and a method for manufacturing the same. Alternatively, one aspect of the present invention aims to provide a high-capacity secondary battery and a method for manufacturing the same. Alternatively, one aspect of the present invention aims to provide a secondary battery with excellent charge-discharge characteristics and a method for manufacturing the same. Alternatively, one aspect of the present invention aims to provide a secondary battery in which capacity degradation is suppressed even when a high-voltage charge state is maintained for a long period of time, and a method for manufacturing the same. Alternatively, one aspect of the present invention aims to provide a safe or highly reliable secondary battery and a method for manufacturing the same. Alternatively, one aspect of the present invention aims to provide a secondary battery in which capacity degradation is suppressed even at high temperatures, and a method for manufacturing the same. Alternatively, one aspect of the present invention aims to provide a secondary battery with a long lifespan and a method for manufacturing the same.

[0013] One aspect of the present invention aims to provide an extremely excellent secondary battery that can be rapidly charged, used at high temperatures, has a high energy density achieved by increasing the charging voltage, and is safe and has a long lifespan.

[0014] One aspect of the present invention aims to provide a positive electrode active material for lithium-ion secondary batteries that has high capacity and excellent charge-discharge cycle characteristics, and a method for producing the same. Alternatively, one aspect of the present invention aims to provide a method for producing a positive electrode active material with good productivity. Alternatively, one aspect of the present invention aims to provide a positive electrode active material that, when used in a lithium-ion secondary battery, suppresses the decrease in capacity during charge-discharge cycles. Alternatively, one aspect of the present invention aims to provide a positive electrode active material in which the elution of transition metals such as cobalt is suppressed even when a high-voltage charged state is maintained for a long period of time.

[0015] Alternatively, one aspect of the present invention aims to provide a novel substance, active material particles, energy storage device, or method for producing the same.

[0016] Furthermore, the description of these problems does not preclude the existence of other problems. Moreover, one aspect of the present invention does not need to solve all of these problems. It is possible to extract other problems from the description, drawings, and claims. [Means for solving the problem]

[0017] One aspect of the present invention is a secondary battery comprising positive electrode active material particles and an electrolyte, wherein the surface layer of the positive electrode active material particles is lithium cobalt oxide having an O3 structure after being subjected to a charging process of a constant current value of 0.5C (where 1C = 210mA / g is satisfied) up to a voltage of 4.5V in a 60°C environment, followed by a constant voltage charging process of a constant current value of 0.2C, and a discharge process of a constant current value of 0.5C up to a voltage of 3V, repeated alternately 150 times or more, and the electrolyte is lithium cobalt oxide having an O3 structure, and the electrolyte is a secondary battery having imidazolium cations. Furthermore, in the above configuration, a negative electrode is also provided, and it is preferable that the negative electrode has graphite. Furthermore, in the above configuration, the negative electrode has a current collector and a negative electrode active material layer on the current collector, and it is preferable that the ratio of graphite to the total weight of the negative electrode active material layer is 50% by weight or more, or 70% by weight or more, or 80% by weight or more.

[0018] Alternatively, one aspect of the present invention is a secondary battery comprising positive electrode active material particles and an electrolyte, wherein a surface layer portion of the positive electrode active material particles is subjected to the following treatment in an environment of 20°C or higher and 60°C or lower, for example 25°C, 45°C, or 60°C: constant-current charging is performed at a current value of 0.5 C (provided that 1 C satisfies 210 mA / g) to a voltage of 4.55 V or more and 4.7 V or less, for example 4.6 V, based on lithium metal, followed by constant-voltage charging until the current value reaches 0.2 C; and constant-current discharging is performed at a current value of 0.5 C to a voltage of 2.5 V or more and 3.2 V or less, for example 3 V, based on lithium metal. After repeating the above charging and discharging processes alternately 10 times or more, more preferably 50 times or more, further preferably 100 times or more, the positive electrode active material after discharging is lithium cobalt oxide having an O3 structure, and the electrolyte contains an imidazolium cation.

[0019] Alternatively, one aspect of the present invention is a secondary battery comprising a positive electrode active material and an electrolyte, wherein after repeated charging and discharging, the positive electrode active material is lithium cobalt oxide having an O3 structure, and the electrolyte contains a compound represented by general formula (G1). In the following general formula (G1), R 1 is an alkyl group having 1 or more and 4 or less carbon atoms, and R 2 , R 3 and R 4 are each independently a hydrogen atom or an alkyl group having 1 or more and 4 or less carbon atoms, and R 5 represents an alkyl group or a main chain composed of two or more atoms selected from the group consisting of C, O, Si, N, S, and P atoms. Further, A - is (C n F 2n+1 SO2)2N - (n=0 or more and 3 or less) and is an amide-based anion represented thereby.

[0020]

Chemical Formula

[0021] Further, in the above configuration, R represented by general formula (G1) 1 is one selected from the group consisting of a methyl group, an ethyl group, and a propyl group, and R2 , R 3 and R 4 One of them is a hydrogen atom or a methyl group, and the other two are hydrogen atoms, R 5 The main chain is composed of two or more alkyl groups or atoms selected from C, O, Si, N, S, and P, and A - (FSO2)2N - and (CF3SO2)2N - It is preferable that it be one of these, or a mixture of the two.

[0022] Furthermore, in the above configuration, R shown in general formula (G1) 1 The number of carbon atoms it has and R 5 The number of carbon atoms it has and R 5 The number of oxygen atoms in and is preferably 7 or less.

[0023] Furthermore, in the above configuration, R shown in general formula (G1) 1 R is a methyl group, 2 R is a hydrogen atom, 5 Preferably, the sum of the number of carbon atoms and oxygen atoms in the atom is 6 or less.

[0024] Furthermore, in the above configuration, it is preferable that the electrolyte has one or more selected from 1-butyl-3-propylimidazolium cation, 1-ethyl-3-methylimidazolium cation, 1-butyl-3-methylimidazolium cation, 1-hexyl-3-methylimidazolium cation, and 1-methyl-3-(2-propoxyethyl)imidazolium cation.

[0025] Furthermore, in the above configuration, it is preferable that the electrolyte has a 1-ethyl-3-methylimidazolium cation.

[0026] Alternatively, one aspect of the present invention is an electronic device having a secondary battery as described above, a display unit, and a sensor.

[0027] Alternatively, one aspect of the present invention is a vehicle comprising a secondary battery as described above, an electric motor, and a control device, wherein the control device has the function of supplying power from the secondary battery to the electric motor. [Effects of the Invention]

[0028] According to one aspect of the present invention, a lithium-ion secondary battery with high capacity and excellent charge-discharge cycle characteristics, and a method for manufacturing the same can be provided. Furthermore, according to one aspect of the present invention, a rapidly rechargeable secondary battery and a method for manufacturing the same can be provided. Furthermore, according to one aspect of the present invention, a high-capacity secondary battery and a method for manufacturing the same can be provided. Furthermore, according to one aspect of the present invention, a secondary battery with excellent charge-discharge characteristics and a method for manufacturing the same can be provided. Furthermore, a secondary battery in which capacity degradation is suppressed even when a high-voltage charge state is maintained for a long period of time, and a method for manufacturing the same can be provided. Furthermore, according to one aspect of the present invention, a safe or highly reliable secondary battery and a method for manufacturing the same can be provided. Furthermore, according to one aspect of the present invention, a secondary battery in which capacity degradation is suppressed even at high temperatures, and a method for manufacturing the same can be provided. Furthermore, according to one aspect of the present invention, a long-life secondary battery and a method for manufacturing the same can be provided.

[0029] According to one aspect of the present invention, it is possible to provide an extremely excellent secondary battery that can be rapidly charged, used at high temperatures, has a high energy density achieved by increasing the charging voltage, and is safe and has a long lifespan.

[0030] According to one aspect of the present invention, a positive electrode active material for lithium-ion secondary batteries with high capacity and excellent charge-discharge cycle characteristics, and a method for producing the same can be provided. Furthermore, a method for producing a positive electrode active material with good productivity can be provided. In addition, according to one aspect of the present invention, a positive electrode active material can be provided that, when used in a lithium-ion secondary battery, suppresses the decrease in capacity during charge-discharge cycles. Furthermore, according to one aspect of the present invention, a positive electrode active material can be provided in which the elution of transition metals such as cobalt is suppressed even when a high-voltage charged state is maintained for a long period of time.

[0031] Alternatively, one aspect of the present invention can provide a novel substance, active material particles, energy storage device, or a method for producing the same.

[0032] Furthermore, the description of these effects does not preclude the existence of other effects. Moreover, one aspect of the present invention does not necessarily have to possess all of these effects. Other effects will become clear from the description in the specification, drawings, and claims, and it is possible to extract other effects from the description in the specification, drawings, and claims. [Brief explanation of the drawing]

[0033] Figure 1 illustrates the crystal structure of the positive electrode active material. Figure 2 illustrates the crystal structure of the positive electrode active material. Figure 3 is a schematic cross-sectional view of the positive electrode active material particles. Figures 4A and 4B illustrate an example of a method for producing a positive electrode active material according to one embodiment of the present invention. Figures 5A to 5C illustrate an example of a method for producing a positive electrode active material according to one embodiment of the present invention. Figure 6 illustrates an example of a method for producing a positive electrode active material according to one embodiment of the present invention. Figures 7A to 7C illustrate an example of a method for producing a positive electrode active material according to one embodiment of the present invention. Figures 8A, 8B, 8C, and 8D are schematic cross-sectional diagrams of the negative electrode active material particles. Figures 9A, 9B, 9C, and 9D are examples of cross-sectional views of a secondary battery. Figures 10A and 10B show examples of the external appearance of a secondary battery. Figures 11A and 11B illustrate the method for manufacturing a secondary battery. Figures 12A and 12B illustrate the method for manufacturing a secondary battery. Figure 13 shows an example of the appearance of a secondary battery. Figure 14 is a top view showing an example of a secondary battery manufacturing apparatus. Figure 15 is a cross-sectional view showing an example of a method for manufacturing a secondary battery. Figures 16A to 16C are perspective views showing an example of a method for manufacturing a secondary battery. Figure 16D is a cross-sectional view corresponding to Figure 16C. Figures 17A to 17F are perspective views showing an example of a method for manufacturing a secondary battery. Figure 18 is a cross-sectional view showing an example of a secondary battery. Figure 19A shows an example of a secondary battery. Figures 19B and 19C show an example of a method for fabricating a laminate. Figures 20A to 20C show an example of a method for manufacturing a secondary battery. Figures 21A and 21B are cross-sectional views showing an example of a laminate. Figure 21C is a cross-sectional view showing an example of a secondary battery. Figures 22A and 22B show an example of a secondary battery. Figure 22C shows the inside of a secondary battery. Figures 23A to 23C show examples of secondary batteries. Figure 24A is a perspective view showing an example of a battery pack. Figure 24B is a block diagram showing an example of a battery pack. Figure 24C is a block diagram showing an example of a vehicle with a motor. Figures 25A to 25E show examples of transport vehicles. Figure 26A shows an electric bicycle, Figure 26B shows the secondary battery of an electric bicycle, and Figure 26C illustrates an electric motorcycle. Figures 27A and 27B show an example of an energy storage device. Figures 28A to 28E show examples of electronic devices. Figures 29A to 29H illustrate an example of an electronic device. Figures 30A to 30C illustrate an example of an electronic device. Figure 31 illustrates an example of an electronic device. Figures 32A to 32C illustrate an example of an electronic device. Figures 33A to 33C show examples of electronic devices. Figures 34A and 34B show the cycle characteristics of a secondary battery. Figures 35A and 35B show the cycle characteristics of a secondary battery. Figure 36 shows the cycle characteristics of a secondary battery. Figures 37A to 37E show cross-sectional SEM images of the negative electrode. Figures 38A to 38E show cross-sectional SEM images of the negative electrode. Figure 39 shows the results of cobalt concentration measurements by EDX analysis and the film thickness of the negative electrode coating. Figures 40A to 40D show SEM images of the positive electrode. [Modes for carrying out the invention]

[0034] Embodiments of the present invention will be described in detail below with reference to the drawings. However, it will be readily apparent to those skilled in the art that the present invention is not limited to the following description, and its form and details can be modified in various ways. Furthermore, the present invention is not to be interpreted as being limited to the embodiments described below.

[0035] Furthermore, in this specification, crystal planes and directions are indicated by Miller indices. In crystallography, crystal planes and directions are indicated by a superscript bar above the number, but in this specification, due to limitations in patent application notation, a minus sign (-) may be placed before the number instead of a bar above it. In addition, individual orientations indicating directions within a crystal are indicated by [ ], collective orientations indicating all equivalent directions are indicated by < >, individual planes indicating crystal planes are indicated by ( ), and collective planes having equivalent symmetry are indicated by {}.

[0036] In this specification, segregation refers to the phenomenon in which a certain element (e.g., B) is spatially non-uniformly distributed in a solid composed of multiple elements (e.g., A, B, C).

[0037] In this specification, the surface layer of particles such as active material refers to the region from the surface down to approximately 10 nm. Surfaces formed by cracks or fissures may also be considered the surface. The region deeper than the surface layer is called the interior.

[0038] In this specification, the layered rock salt crystal structure of a composite oxide containing lithium and a transition metal refers to a crystal structure having a rock salt-type ionic arrangement in which cations and anions are arranged alternately, and in which the transition metal and lithium are regularly arranged to form a two-dimensional plane, thereby enabling two-dimensional diffusion of lithium. Defects such as vacancies in cations or anions may be present. Furthermore, strictly speaking, a layered rock salt crystal structure may have a distorted lattice structure of the rock salt crystal.

[0039] In this specification, a rock salt-type crystal structure refers to a structure in which cations and anions are arranged alternately. However, deficiencies in cations or anions are acceptable.

[0040] Furthermore, in this specification, the O3'-type crystal structure (also called a pseudo-spinel-type crystal structure) of a composite oxide containing lithium and a transition metal refers to a crystal structure with a space group R-3m, which is not a spinel-type crystal structure, but in which ions such as cobalt and magnesium occupy the oxygen 6-coordinate positions, and the arrangement of cations has a symmetry similar to that of the spinel type. Note that in the O3'-type crystal structure, light elements such as lithium may occupy the oxygen 4-coordinate positions, and in this case as well, the arrangement of ions has a symmetry similar to that of the spinel type.

[0041] Furthermore, the O3' type crystal structure can be described as a crystal structure similar to the CdCl2 type crystal structure, although it has Li randomly placed between layers. This crystal structure similar to the CdCl2 type is observed when lithium nickelate is charged to a depth of charge of 0.94 (Li 0.06 Although its crystal structure is similar to that of NiO2, it is known that pure lithium cobaltate or layered rock salt-type cathode active materials containing a large amount of cobalt do not usually adopt this crystal structure.

[0042] The anions in layered rock salt crystals and rock salt crystals adopt a cubic close-packed structure (face-centered cubic lattice structure). It is also presumed that the anions in O3'-type crystals adopt a cubic close-packed structure. When these are in contact, there exists a crystal plane in which the orientation of the cubic close-packed structure composed of anions is aligned. However, the space group of layered rock salt crystals and O3'-type crystals is R-3m, which is different from the space group of rock salt crystals Fm-3m (the space group of a typical rock salt crystal) and Fd-3m (the space group of a rock salt crystal with the simplest symmetry). Therefore, the Miller indices of the crystal planes that satisfy the above conditions are different for layered rock salt crystals and O3'-type crystals and for rock salt crystals. In this specification, when the orientation of the cubic close-packed structure composed of anions is aligned in layered rock salt crystals, O3'-type crystals, and rock salt crystals, it is sometimes said that the crystal orientation is approximately the same.

[0043] A secondary battery has, for example, a positive electrode and a negative electrode. The positive electrode is composed of a positive electrode active material. The positive electrode active material is, for example, a substance that performs a reaction that contributes to the charge and discharge capacity. However, the positive electrode active material may also contain a portion of substances that do not contribute to the charge and discharge capacity.

[0044] In this specification, the positive electrode active material of one aspect of the present invention may be expressed as a positive electrode material, a positive electrode material for secondary batteries, etc. In this specification, it is preferable that the positive electrode active material of one aspect of the present invention has a compound. In this specification, it is preferable that the positive electrode active material of one aspect of the present invention has a composition. In this specification, it is preferable that the positive electrode active material of one aspect of the present invention has a composite.

[0045] (Embodiment 1) This embodiment describes an example of a secondary battery according to one aspect of the present invention.

[0046] As shown in the embodiments described later, it has been found that a secondary battery according to one aspect of the present invention exhibits extremely stable characteristics even when charged at high voltages. In addition, a secondary battery according to one aspect of the present invention can operate stably over a wide temperature range. A secondary battery with remarkably superior characteristics can be realized by one aspect of one aspect of the present invention.

[0047] In one embodiment of the present invention, the positive electrode active material is an oxide having a metal that acts as a carrier ion (hereinafter referred to as element A) and a metal whose valency changes with charging and discharging of a secondary battery (hereinafter referred to as metal M).

[0048] As element A, one or more elements selected from alkali metals such as lithium, sodium, and potassium, as well as Group 2 elements such as calcium, beryllium, and magnesium, can be used. Preferably, element A is an element that functions as a metal that acts as a carrier ion.

[0049] For example, a transition metal can be used as metal M. A positive electrode active material in one aspect of the present invention has, for example, one or more of cobalt, nickel, and manganese as metal M, and in particular cobalt. Alternatively, metal M may be an element that does not change in valence and can take the same valence as metal M, such as aluminum, more specifically, a trivalent typical element.

[0050] A positive electrode active material according to one aspect of the present invention is chemical formula AM y O Z It can sometimes be represented as (y>0, z>0). Lithium cobalt oxide can sometimes be represented as LiCoO2. Also, lithium nickelate can sometimes be represented as LiNiO2.

[0051] In addition, the positive electrode active material according to one aspect of the present invention preferably contains the element X. As the element X, elements such as magnesium, calcium, zirconium, lanthanum, barium, titanium, and yttrium can be used. Further, as the element X, elements such as nickel, aluminum, cobalt, manganese, vanadium, iron, chromium, and niobium can be used. Further, for example, as the element X, elements such as copper, potassium, sodium, zinc, chlorine, fluorine, hafnium, silicon, sulfur, phosphorus, boron, and arsenic can be used. Further, two or more of the elements listed above may be used in combination as the element X.

[0052] For example, part of the element X may be substituted at the position of the element A. Alternatively, for example, part of the element X may be substituted at the position of the metal M.

[0053] The positive electrode active material according to one aspect of the present invention has the chemical formula A 1-w X w M y O Z (y>0, z>0, 0<w<1) in some cases. Further, the positive electrode active material according to one aspect of the present invention has the chemical formula AM yーj X j O Z (y>0, z>0, 0<j<y) in some cases. Further, the positive electrode active material according to one aspect of the present invention has the chemical formula A 1-w X w M yーj X j O Z (y>0, z>0, 0<w<1, 0<j<y) in some cases.

[0054] Further, the positive electrode active material according to one aspect of the present invention preferably contains halogen in addition to the element X. It is preferable to contain halogen such as fluorine and chlorine. When the positive electrode active material according to one aspect of the present invention contains the halogen, substitution of the element X at the position of the element A may be promoted in some cases.

[0055] As the charging voltage of a secondary battery increases, the crystal structure of the positive electrode active material may become unstable, potentially degrading the characteristics of the secondary battery. For example, consider the case where a material with a layered crystal structure, in which metal A is detached from between layers during the charging reaction, is used as the positive electrode active material. With such a positive electrode active material, the charging and discharging capacities can be increased by increasing the charging voltage. On the other hand, as the charging voltage increases, a large amount of metal A is detached from the positive electrode active material, and significant changes in the crystal structure may occur, such as changes in the interlayer distance and layer displacement. If the changes in the crystal structure due to the insertion and detachment of metal A are irreversible, the crystal structure may gradually collapse with repeated charging and discharging, resulting in a significant decrease in capacity with each charge-discharge cycle.

[0056] Furthermore, increasing the charging voltage may make it easier for metal M present in the positive electrode active material to dissolve into the electrolyte. When metal M dissolves from the positive electrode active material into the electrolyte, the amount of metal M in the positive electrode active material decreases, which may lead to a decrease in the capacity of the positive electrode.

[0057] In a positive electrode active material according to one aspect of the present invention, metal M is mainly bonded to oxygen. Desorption of oxygen from the positive electrode active material may significantly cause the dissolution of metal M.

[0058] As electrolytes, a salt of a metal that acts as a carrier ion and the following solvents, including carbonates, are used. For example, aprotic solvents such as 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), 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, and sultone are used.

[0059] During charging, when the oxidation state of metal M in the positive electrode active material increases, the reactivity of the positive electrode active material increases, making it more likely to react with organic solvents, more specifically carbonates with high polarity. For example, oxygen is desorbed from the positive electrode active material, and the organic solvent is oxidized. When oxygen is desorbed, the elution of metal M becomes more likely.

[0060] Charging and discharging under high voltage conditions of 4.5V or higher or high temperature (45°C or higher) may cause progressive defects (also called pits) to occur in the positive electrode active material particles. In addition, expansion and contraction of the positive electrode active material particles due to charging and discharging may cause defects such as cracks. Figure 3 shows a schematic cross-sectional view of the positive electrode active material particle 51. In the positive electrode active material particle 51, pits are shown as holes 54 and 58 in Figure 3, but the opening shape is not circular and has depth, and cracks are shown as crack 57 in Figure 3. Figure 3 also shows crystal planes 55, recesses 52, and barrier films 53 and 56.

[0061] Positive electrode active material particles may have defects, and these defects may change before and after charging and discharging. When used in secondary batteries, positive electrode active material particles may be chemically or electrochemically eroded by the surrounding environmental substances (such as electrolyte), or the material may deteriorate. This deterioration does not occur uniformly on the particle surface, but rather concentrates locally, and repeated charging and discharging of the secondary battery can cause defects to develop deeply from the surface into the interior.

[0062] The phenomenon in which defects progress in positive electrode active material particles to form holes can also be called pitting corrosion, and the holes generated by this phenomenon are referred to as pits in this specification.

[0063] In this specification, cracks and pits are distinct. Cracks may exist immediately after the fabrication of positive electrode active material particles, but pits do not. For example, in lithium cobalt oxide, pits can be described as holes where several layers of cobalt and oxygen have been removed due to charging and discharging under high voltage conditions of 4.5V or higher or high temperature (45°C or higher), and can also be described as areas where cobalt has leached out. Cracks refer to new surfaces created by the application of physical pressure, or cracks caused by grain boundaries. Cracks may also occur due to the expansion and contraction of particles due to charging and discharging. Furthermore, pits may occur from cracks or cavities within particles.

[0064] When lithium cobalt oxide is charged and discharged under high voltage or high temperature, cobalt may dissolve, leading to the formation of a crystalline phase different from lithium cobalt oxide on the surface. For example, one or more of the following may be formed: spinel-structured Co3O4, spinel-structured LiCo2O4, and rock salt-type CoO. These materials have, for example, lower discharge capacity compared to lithium cobalt oxide, or do not contribute to charging and discharging. Therefore, the formation of these materials on the surface may lead to a decrease in the discharge capacity of the secondary battery. It may also lead to a decrease in the output characteristics and low-temperature characteristics of the secondary battery. Furthermore, these materials may form near pits.

[0065] Furthermore, metal M may leach from the positive electrode active material, and the electrolyte may transport ions of metal M, leading to the deposition of metal M on the negative electrode surface. In addition, a film may form on the negative electrode surface from the decomposition products of metal M and the electrolyte. The formation of this film can make it difficult for carrier ions to be inserted into and removed from the negative electrode active material, potentially leading to a decrease in the rate characteristics, low-temperature characteristics, etc., of the secondary battery.

[0066] The positive electrode active material according to one aspect of the present invention can have the O3' structure described later during charging, allowing for charging to a deep depth of charge. By increasing the depth of charge, the capacity of the positive electrode can be increased, thereby increasing the energy density of the secondary battery. Furthermore, repeated charging and discharging can be performed even when using an extremely high charging voltage.

[0067] Incidentally, when charging is performed at a higher charging voltage, the oxidation state of metal M becomes higher. In this state, as mentioned above, the dissolution of metal M is more likely to occur.

[0068] In one embodiment of the present invention, although the extremely high charging voltage makes metal M more susceptible to dissolution, the presence of a desired ionic liquid electrolyte suppresses the dissolution of metal M. Therefore, it is possible to achieve both a high charging voltage and suppression of metal M dissolution. Furthermore, it is possible to realize high-rate charging and discharging. In addition, excellent charging and discharging characteristics at low temperatures can be achieved.

[0069] Furthermore, after forming a positive electrode active material layer on the current collector and then performing a press, steps may be observed on the particle surface perpendicular to the lattice fringes (c-axis direction) as seen in cross-sectional STEM images. Additionally, evidence of deformation along the lattice fringe direction (ab-plane direction) may be observed. This surface fringe pattern, observed due to the steps caused by the press, is called slippage. Such particle slippage indicates an unstable crystal structure, raising concerns about a decrease in the characteristics of the secondary battery. Therefore, it is desirable to minimize or eliminate particle slippage.

[0070] The present inventors have found that by using a positive electrode active material according to one aspect of the present invention and a desired ionic liquid having properties suitable for a secondary battery according to one aspect of the present invention, a secondary battery with extremely excellent properties can be realized.

[0071] Furthermore, the inventors have found that in a secondary battery according to one embodiment of the present invention, the generation of pits in the positive electrode active material is suppressed after repeated charging and discharging. In addition, in a secondary battery according to one embodiment of the present invention, they have found that after repeated charging and discharging, there are no or substantially no different phases in the surface layer of the positive electrode active material. More specifically, for example, when the positive electrode active material is lithium cobalt oxide, they have found that the surface layer of the positive electrode active material does not have or substantially does not have spinel-structured Co3O4, spinel-structured LiCo2O4, and rock salt-type structured CoO. Furthermore, in a secondary battery according to one embodiment of the present invention, they have found that after repeated charging and discharging, there are no or substantially no different phases in the vicinity of the pits in the positive electrode active material. More specifically, for example, when the positive electrode active material is lithium cobalt oxide, we found that the vicinity of the pits in the positive electrode active material does not contain, or substantially does not contain, spinel-structured Co3O4, spinel-structured LiCo2O4, or rock salt-type structured CoO. "Substantially absent" means that, for example, surface debris is not taken into consideration.

[0072] Furthermore, the inventors have found that in a secondary battery according to one embodiment of the present invention, after repeated charging and discharging, the coating on the surface of the negative electrode active material is thin, and the amount of metal M detected on the surface of the negative electrode active material or the coating formed on the surface of the negative electrode active material is extremely small.

[0073] In one embodiment of the present invention, the amount of metal M detected on the surface of the negative electrode active material, or on the coating formed on the surface of the negative electrode active material, is extremely small, suggesting that the coating is thin. For this reason, for example, carrier ions can easily enter and exit the negative electrode active material, resulting in a secondary battery with high output characteristics and easy charging and discharging even at low temperatures.

[0074] Furthermore, in a secondary battery according to one embodiment of the present invention, the dissolution of metal M can be suppressed, thereby suppressing a decrease in capacity and also suppressing the collapse of the crystal structure. Therefore, an excellent secondary battery can be realized in which a decrease in capacity is suppressed even during repeated charging and discharging, maintaining a charged state, and maintaining high temperatures.

[0075] Furthermore, in a secondary battery according to one aspect of the present invention, since no different phase is substantially formed on the positive electrode surface, capacity degradation is suppressed, and carrier ions can easily enter and exit the positive electrode active material. Therefore, a secondary battery with suppressed capacity degradation can be realized. In addition, a secondary battery with high output characteristics and easy charging and discharging even at low temperatures can be realized.

[0076] Ionic liquids have low volatility and flammability, and are stable over a wide temperature range. Because they do not easily volatilize even at high temperatures, they can suppress the expansion of secondary batteries caused by gas generation from the electrolyte. Therefore, secondary batteries operate stably even at high temperatures. Furthermore, they have low flammability and are flame-retardant.

[0077] For example, the organic solvents mentioned above have boiling points below 150°C and are highly volatile, so using them at high temperatures can generate gas, which may cause the casing of a secondary battery to expand. Furthermore, organic solvents may have flash points below 50°C. On the other hand, ionic liquids have low volatility and are extremely stable down to temperatures below those at which decomposition or other reactions occur, such as around 300°C.

[0078] Therefore, by using ionic liquids, it is possible to realize secondary batteries that can be used at high temperatures and have high safety. For example, by using ionic liquids, it is possible to realize secondary batteries that have stable characteristics even at temperatures above 50°C, 60°C, or even 80°C.

[0079] In other words, a secondary battery according to one aspect of the present invention can achieve good operation over a wide temperature range from low to high temperatures.

[0080] In one embodiment of the present invention, a secondary battery can be realized with a high energy density because the charging voltage can be increased by using a positive electrode active material in which irreversible changes in the crystal structure are suppressed at high charging voltages. In addition, in one embodiment of the present invention, the dissolution of metal M from the positive electrode active material can be suppressed by using an ionic liquid as the electrolyte, so that even when repeatedly charged at high charging voltages, the decrease in capacity associated with charge-discharge cycles can be suppressed.

[0081] Here, the surface layer is preferably a region within 50 nm from the surface, more preferably within 35 nm, and even more preferably within 20 nm. The region deeper than the surface layer is called the interior.

[0082] Ionic liquids are salts composed of combinations of cations and anions. Ionic liquids are sometimes called room-temperature molten salts.

[0083] By using a positive electrode active material according to one aspect of the present invention in combination with an ionic liquid, the elution of metal M from the positive electrode active material can be suppressed at deep charging depths. The positive electrode active material according to one aspect of the present invention contains element X. In the positive electrode active material according to one aspect of the present invention, it is preferable that element X has a concentration gradient. It is preferable that element X has a concentration gradient that increases from the interior to the surface. The concentration gradient of element X can be evaluated, for example, using energy dispersive X-ray spectroscopy (EDX).

[0084] As mentioned above, ionic liquids are stable even at high temperatures. On the other hand, if other components of a secondary battery, such as the positive electrode active material, negative electrode active material, or outer casing, change at high temperatures, especially if the change is irreversible, it can lead to a significant decrease in the capacity of the secondary battery.

[0085] For example, if charging at high temperatures causes irreversible changes in the crystal structure of the material constituting the positive electrode active material, significant degradation will occur in the secondary battery. For instance, a significant decrease in capacity may occur with each charge-discharge cycle. When the temperature is high and the charging voltage is also high, the crystal structure of the positive electrode may become even more unstable.

[0086] In a secondary battery according to one aspect of the present invention, by using a positive electrode active material whose crystal structure is extremely stable at high charging voltages and high temperatures, excellent performance can be achieved even at high temperatures and high charging voltages, thus allowing the effects of the ionic liquid to be fully utilized. In other words, the remarkable improvement in performance obtained by using the configuration of the secondary battery according to one aspect of the present invention is achieved through the combination with the positive electrode active material according to one aspect of the present invention.

[0087] Furthermore, the positive electrode active material of one aspect of the present invention preferably contains element X, and preferably contains a halogen in addition to element X, as described later. The presence of element X, or a halogen in addition to element X, in the positive electrode active material of one aspect of the present invention suggests the suppression of reactions with the ionic liquid on the surface of the positive electrode active material. As mentioned above, ionic liquids are extremely stable even at high temperatures. On the other hand, in the secondary battery of one aspect of the present invention, the reaction potential range is extremely wide. In such a wide reaction potential range, there may be concerns about reactions with the ionic liquid on the surface of the active material, and by using the positive electrode active material of one aspect of the present invention, it is suggested that reactions with the ionic liquid can be suppressed, leading to the realization of an even more stable secondary battery.

[0088] By using the configuration of a secondary battery according to one embodiment of the present invention, it is possible to realize a secondary battery that can be repeatedly charged at high temperatures of 42°C or higher and at high charging voltages. For example, when the ambient temperature is 42°C or higher and graphite is used as the negative electrode, it is possible to realize a secondary battery that can be repeatedly charged at a maximum charging voltage of preferably 4.37V or higher, more preferably 4.40V or higher, even more preferably 4.42V or higher, even more preferably 4.44V or higher, for example, around 4.45V.

[0089] Furthermore, it is possible to realize rechargeable batteries that perform well even at higher temperatures. For example, it may be possible to realize rechargeable batteries that operate stably at temperatures between 42°C and 200°C, or between 42°C and 180°C, or between 42°C and 150°C, or between 42°C and 120°C, or between 42°C and 100°C, or between 42°C and 90°C.

[0090] A secondary battery according to one aspect of the present invention has a discharge capacity of 160 mAh / g or more after discharging a cumulative charge of 57,000 mAh / g. Here, for example, it is preferable that the discharge capacity is measured at 0.2C. Furthermore, it is preferable that the cumulative charge and discharge capacity be calculated per unit weight of positive electrode active material.

[0091] Furthermore, in one embodiment of the present invention, when graphite is used as the negative electrode at 25°C, the discharge capacity after 300 charge cycles with a charging voltage of 4.5V is 160mAh / g or more. Here, for example, the discharge capacity is preferably measured at 0.2C. In addition, the cumulative charge amount and discharge capacity are preferably calculated per unit weight of the positive electrode active material.

[0092] Furthermore, a secondary battery according to one embodiment of the present invention is preferably used in combination with a battery control circuit. The battery control circuit preferably has a function for controlling charging, for example. Controlling charging refers to, for example, monitoring the parameters of the secondary battery and changing the charging conditions according to its state. Examples of secondary battery parameters to be monitored include the voltage, current, temperature, charge amount, impedance, etc.

[0093] Furthermore, a secondary battery according to one aspect of the present invention is preferably used in combination with a sensor. The sensor preferably has the ability to measure one or more of the following: displacement, position, velocity, acceleration, angular velocity, rotational speed, distance, light, liquid, magnetism, temperature, chemical substances, sound, time, hardness, electric field, current, voltage, power, radiation, flow rate, humidity, gradient, vibration, odor, and infrared radiation.

[0094] Furthermore, in one embodiment of the present invention, it is preferable that the charging of the secondary battery is controlled according to a value measured by a sensor. An example of controlling a secondary battery using a temperature sensor will be described later.

[0095] [Cathode active material] The following describes a positive electrode active material that is preferable for use in a secondary battery according to one embodiment of the present invention.

[0096] <Structure of the positive electrode active material> The positive electrode active material preferably contains element A. Element A can be one or more elements selected from alkali metals such as lithium, sodium, and potassium, as well as Group 2 elements such as calcium, beryllium, and magnesium.

[0097] In a positive electrode active material, carrier ions are detached from the positive electrode active material during charging. If a large amount of element A is detached, more ions contribute to the capacity of the secondary battery, increasing the capacity. On the other hand, if a large amount of element A is detached, the crystal structure of the compound contained in the positive electrode active material is more likely to collapse. Collapse of the crystal structure of the positive electrode active material may lead to a decrease in discharge capacity with charge-discharge cycles. In one embodiment of the present invention, the positive electrode active material contains element X, which may suppress the collapse of the crystal structure when carrier ions are detached during charging of the secondary battery. Element X is, for example, partially substituted for element A. Element X can be magnesium, calcium, zirconium, lanthanum, barium, etc. Alternatively, element X can be copper, potassium, sodium, zinc, etc. Furthermore, two or more of the above-mentioned elements may be used in combination as element X.

[0098] Furthermore, the positive electrode active material of one aspect of the present invention preferably contains a halogen in addition to element X. It is preferable that it contains a halogen such as fluorine or chlorine. The presence of such a halogen in the positive electrode active material of one aspect of the present invention may promote the substitution of element X to the position of element A.

[0099] In one embodiment of the present invention, if the positive electrode active material contains element X, or if it contains a halogen in addition to element X, the electrical conductivity on the surface of the positive electrode active material may be suppressed.

[0100] Furthermore, the positive electrode active material of one aspect of the present invention contains a metal M. The metal M is, for example, a transition metal. The positive electrode active material of one aspect of the present invention contains, for example, one or more of cobalt, nickel, and manganese as the metal M, and particularly contains cobalt. Alternatively, the position of metal M may contain an element that does not change in valence and can have the same valence as metal M, such as aluminum, more specifically, a trivalent typical element. The aforementioned element X may be substituted, for example, at the position of metal M. Also, if the positive electrode active material of one aspect of the present invention is an oxide, element X may be substituted at the position of oxygen.

[0101] In one embodiment of the present invention, it is preferable to use a lithium composite oxide having a layered rock salt crystal structure as the positive electrode active material. More specifically, examples of lithium composite oxides having a layered rock salt crystal structure include lithium cobaltate, lithium nickelate, lithium composite oxides having nickel, manganese, and cobalt, lithium composite oxides having nickel, cobalt, and aluminum, etc. Furthermore, it is preferable that these positive electrode active materials are represented by the space group R-3m.

[0102] In positive electrode active materials having a layered rock salt crystal structure, increasing the charging depth may cause a breakdown of the crystal structure. Here, a breakdown of the crystal structure refers to, for example, a shift in the layers. If the breakdown of the crystal structure is irreversible, the capacity of the secondary battery may decrease with repeated charging and discharging.

[0103] The positive electrode active material according to one embodiment of the present invention contains element X, which suppresses the shifting of the above-mentioned layers even when the charging depth increases. By suppressing the shifting, the change in volume during charging and discharging can be reduced. Therefore, the positive electrode active material according to one embodiment of the present invention can achieve excellent cycle characteristics. Furthermore, the positive electrode active material according to one embodiment of the present invention can adopt a stable crystal structure in a high-voltage charging state. Therefore, the positive electrode active material according to one embodiment of the present invention may be less prone to short circuits when a high-voltage charging state is maintained. In such cases, safety is further improved, which is preferable.

[0104] In one embodiment of the present invention, the positive electrode active material exhibits small changes in crystal structure and a small difference in volume per unit of the same number of transition metal atoms between a fully discharged state and a high-voltage charged state.

[0105] The positive electrode active material in one aspect of the present invention has the chemical formula AM y O Z It can sometimes be represented as (y>0, z>0). For example, lithium cobalt oxide can be represented as LiCoO2. Also, lithium nickelate can sometimes be represented as LiNiO2.

[0106] In a positive electrode active material according to one embodiment of the present invention, which contains element X, when the charging depth is 0.8 or greater, it is represented by the space group R-3m and is not a spinel-type crystal structure, but ions such as metal M (e.g., cobalt) and element X (e.g., magnesium) occupy the oxygen 6-coordinate position, and the arrangement of cations may have a symmetry similar to that of the spinel type. This structure is referred to as the O3'-type crystal structure in this specification. In the O3'-type crystal structure, light elements such as lithium may occupy the oxygen 4-coordinate position, and in this case as well, the arrangement of ions has a symmetry similar to that of the spinel type.

[0107] The desorption of carrier ions during charging destabilizes the structure of the positive electrode active material. The O3' type crystal structure can be said to be a structure that maintains high stability even after carrier ions have been desorbed.

[0108] Furthermore, the O3' type crystal structure can be described as a crystal structure similar to the CdCl2 type crystal structure, although it has Li randomly placed between layers. This crystal structure similar to the CdCl2 type is observed when lithium nickelate is charged to a depth of charge of 0.94 (Li 0.06 Although its crystal structure is similar to that of NiO2, it is known that pure lithium cobaltate or layered rock salt-type cathode active materials containing a large amount of cobalt do not usually adopt this crystal structure.

[0109] The anions in layered rock salt crystals and rock salt crystals adopt a cubic close-packed structure (face-centered cubic lattice structure). It is also presumed that the anions in O3'-type crystals adopt a cubic close-packed structure. When these are in contact, there exists a crystal plane in which the orientation of the cubic close-packed structure composed of anions is aligned. However, the space group of layered rock salt crystals and O3'-type crystals is R-3m, which is different from the space group of rock salt crystals Fm-3m (the space group of a typical rock salt crystal) and Fd-3m (the space group of a rock salt crystal with the simplest symmetry). Therefore, the Miller indices of the crystal planes that satisfy the above conditions are different for layered rock salt crystals and O3'-type crystals and for rock salt crystals. In this specification, when the orientation of the cubic close-packed structure composed of anions is aligned in layered rock salt crystals, O3'-type crystals, and rock salt crystals, it is sometimes said that the crystal orientation is approximately the same.

[0110] The crystal structure at charge depth 0 (discharge state) in Figure 1 is R-3m(O3), the same as in Figure 2. On the other hand, the positive electrode active material of one embodiment of the present invention shown in Figure 1 has a crystal structure different from the H1-3 type crystal structure (space group R-3m) shown in Figure 2 when it is fully charged. This structure has a space group R-3m and is not a spinel type crystal structure, but ions such as cobalt and magnesium occupy the oxygen 6-coordinate positions, and the arrangement of cations has a symmetry similar to that of the spinel type. Furthermore, the symmetry of the CoO2 layer in this structure is the same as that of the O3 type. Therefore, this structure is referred to as the O3' type crystal structure or pseudo-spinel type crystal structure in this specification. Note that in the diagram of the O3' type crystal structure shown in Figure 1, lithium may be present at any lithium site with a probability of about 20%, but this is not limited to this. It may be present only at certain lithium sites. Furthermore, in both the O3-type and O3'-type crystal structures, it is preferable that magnesium be present in a dilute manner between the CoO2 layers, i.e., at the lithium sites. It is also preferable that halogens such as fluorine be present randomly and dilutely at the oxygen sites.

[0111] In addition, in the O3' type crystal structure, light elements such as lithium may occupy the oxygen 4-coordinate position, and in this case as well, the arrangement of ions has a symmetry similar to that of the spinel type.

[0112] Furthermore, the O3' type crystal structure can be described as a crystal structure similar to the CdCl2 type crystal structure, although it has Li randomly placed between layers. This crystal structure similar to the CdCl2 type is observed when lithium nickelate is charged to a depth of charge of 0.94 (Li 0.06 Although its crystal structure is similar to that of NiO2, it is known that pure lithium cobaltate or layered rock salt-type cathode active materials containing a large amount of cobalt do not usually adopt this crystal structure.

[0113] The anions in layered rock salt crystals and rock salt crystals adopt a cubic close-packed structure (face-centered cubic lattice structure). It is also presumed that the anions in O3'-type crystals adopt a cubic close-packed structure. When these are in contact, there exists a crystal plane in which the orientation of the cubic close-packed structure composed of anions is aligned. However, the space group of layered rock salt crystals and O3'-type crystals is R-3m, which is different from the space group of rock salt crystals Fm-3m (the space group of a typical rock salt crystal) and Fd-3m (the space group of a rock salt crystal with the simplest symmetry). Therefore, the Miller indices of the crystal planes that satisfy the above conditions are different for layered rock salt crystals and O3'-type crystals and for rock salt crystals. In this specification, when the orientation of the cubic close-packed structure composed of anions is aligned in layered rock salt crystals, O3'-type crystals, and rock salt crystals, it is sometimes said that the crystal orientation is approximately the same.

[0114] In one embodiment of the present invention, the change in crystal structure when a large amount of lithium is released during high-voltage charging is suppressed compared to the comparative example described later. For example, as shown by the dotted line in Figure 1, there is almost no displacement of the CoO2 layer in these crystal structures.

[0115] More specifically, the positive electrode active material according to one embodiment of the present invention exhibits high structural stability even at high charging voltages. For example, in the positive electrode active material shown as an example in Figure 2, an H1-3 type crystal structure is formed at a voltage of approximately 4.6V relative to the potential of the lithium metal. However, the positive electrode active material according to one embodiment of the present invention can maintain an R-3m(O3) crystal structure even at the same charging voltage of approximately 4.6V. Furthermore, even at higher charging voltages, such as 4.65V to 4.7V relative to the potential of the lithium metal, the positive electrode active material according to one embodiment of the present invention can adopt an O3' type crystal structure. If the charging voltage is further increased above 4.7V, an H1-3 type crystal may finally be observed in the positive electrode active material according to one embodiment of the present invention. Moreover, even at lower charging voltages (for example, when the charging voltage is between 4.5V and 4.6V relative to the potential of the lithium metal), the positive electrode active material according to one embodiment of the present invention may adopt an O3' type crystal structure.

[0116] Furthermore, in the case of a secondary battery, if graphite is used as the negative electrode active material, for example, the voltage of the secondary battery will decrease by the amount of the graphite's potential compared to the above. The potential of graphite is approximately 0.05V to 0.2V, based on the potential of lithium metal. Therefore, for example, even when the voltage of a secondary battery using graphite as the negative electrode active material is between 4.3V and 4.5V, the positive electrode active material of one embodiment of the present invention can maintain the R-3m(O3) crystal structure, and can even adopt the O3' type crystal structure in a region with a higher charging voltage, for example, when the secondary battery voltage is above 4.5V and below 4.6V. Moreover, even at lower charging voltages, for example, when the secondary battery voltage is between 4.2V and 4.3V, the positive electrode active material of one embodiment of the present invention may adopt the O3' structure.

[0117] Therefore, in the positive electrode active material according to one aspect of the present invention, the crystal structure is less likely to collapse even when repeatedly charged and discharged at high voltage.

[0118] Furthermore, in one embodiment of the present invention, the difference in volume per unit cell between the O3-type crystal structure with a charging depth of 0 and the O3'-type crystal structure with a charging depth of 0.8 is 2.5% or less, more specifically 2.2% or less.

[0119] Furthermore, the O3' type crystal structure can be represented by showing the coordinates of cobalt and oxygen in the unit cell as follows: Co(0,0,0.5), O(0,0,x), within the range of 0.20≦x≦0.25.

[0120] Magnesium, randomly and dilutely present between CoO2 layers, i.e., at the lithium sites, has the effect of suppressing the displacement of the CoO2 layers when charged at high voltage. Therefore, the presence of magnesium between CoO2 layers makes it easier for an O3' type crystal structure to form.

[0121] However, if the heat treatment temperature is too high, cation mixing occurs, increasing the likelihood of magnesium entering the cobalt site. Magnesium present in the cobalt site may have little effect in maintaining the R-3m structure during high-voltage charging. Furthermore, if the heat treatment temperature is too high, there are concerns about adverse effects such as the reduction of cobalt to its divalent state and the evaporation of lithium.

[0122] Therefore, it is preferable to add a halogen compound such as a fluorine compound to lithium cobalt oxide before the heat treatment to distribute magnesium throughout the particles. Adding a halogen compound lowers the melting point of lithium cobalt oxide. Lowering the melting point makes it easier to distribute magnesium throughout the particles at a temperature where cation mixing is less likely to occur. Furthermore, if a fluorine compound is present, it can be expected that the corrosion resistance to hydrofluoric acid produced by the decomposition of the electrolyte will be improved.

[0123] Furthermore, if the magnesium concentration is increased beyond the desired value, the effect on stabilizing the crystal structure may decrease. This is thought to be because magnesium will enter not only the lithium sites but also the cobalt sites. The number of magnesium atoms in the positive electrode active material produced according to one aspect of the present invention is preferably 0.001 times or more and 0.1 times or less the number of cobalt atoms, more preferably greater than 0.01 times and less than 0.04 times, and even more preferably around 0.02. The magnesium concentration shown here may be, for example, a value obtained by elemental analysis of the entire particle of the positive electrode active material using ICP-MS, or it may be based on the value of the raw material composition during the process of producing the positive electrode active material.

[0124] The number of nickel atoms in the positive electrode active material according to one embodiment of the present invention is preferably 7.5% or less of the number of cobalt atoms, preferably 0.05% to 4%, and more preferably 0.1% to 2%. The nickel concentration shown herein may be, for example, a value obtained by elemental analysis of the entire particle of the positive electrode active material using ICP-MS, or it may be based on the value of the raw material composition during the manufacturing process of the positive electrode active material.

[0125] <Particle size> In one embodiment of the present invention, if the particle size of the positive electrode active material is too large, problems arise such as difficulty in lithium diffusion and excessive roughness of the surface of the active material layer when coated onto the current collector. On the other hand, if the particle size is too small, problems arise such as difficulty in supporting the active material layer when coating onto the current collector and excessive reaction with the electrolyte. Therefore, the average particle size (D50: also called the median diameter) is preferably 1 μm or more and 100 μm or less, more preferably 2 μm or more and 40 μm or less, and even more preferably 5 μm or more and 30 μm or less.

[0126] <Analysis method> Whether a positive electrode active material exhibits an O3'-type crystal structure when charged at high voltage can be determined by analyzing the high-voltage charged positive electrode using XRD, electron diffraction, neutron diffraction, electron spin resonance (ESR), nuclear magnetic resonance (NMR), etc. XRD is particularly preferable because it can analyze the symmetry of transition metals such as cobalt in the positive electrode active material with high resolution, compare the crystallinity and crystal orientation, analyze the periodic distortion of the lattice and crystallite size, and obtain sufficient accuracy even when measuring a positive electrode obtained by disassembling a secondary battery.

[0127] As described above, a positive electrode active material according to one aspect of the present invention is characterized by minimal change in crystal structure between a high-voltage charged state and a discharged state. Materials in which the crystal structure that changes significantly from the discharged state accounts for 50 wt% or more when charged at high voltage are undesirable because they cannot withstand high-voltage charging and discharging. It is important to note that simply adding impurity elements may not result in the desired crystal structure. For example, even if both materials are lithium cobalt oxide containing magnesium and fluorine, there are cases where the O3' type crystal structure accounts for 60 wt% or more when charged at high voltage, and cases where the H1-3 type crystal structure accounts for 50 wt% or more. Furthermore, at a predetermined voltage, the O3' type crystal structure may account for almost 100 wt%, and if the predetermined voltage is further increased, the H1-3 type crystal structure may be generated. Therefore, it is preferable that the crystal structure of the positive electrode active material according to one aspect of the present invention be analyzed by XRD or the like. By using it in combination with XRD or the like, more detailed analysis can be performed.

[0128] However, positive electrode active materials in a high-voltage charged or discharged state may undergo changes in their crystal structure when exposed to air. For example, they may change from an O3' type crystal structure to an H1-3 type crystal structure. Therefore, it is preferable to handle all samples in an inert atmosphere such as an argon-containing atmosphere.

[0129] <Comparative Example> The positive electrode active material shown in Figure 2 is lithium cobalt oxide (LiCoO2) without halogen and magnesium added, prepared using the method described later. The crystal structure of the lithium cobalt oxide shown in Figure 2 changes depending on the depth of charge.

[0130] As shown in Figure 2, lithium cobalt oxide at charge depth 0 (discharge state) has a region with a crystal structure of space group R-3m, and there are three CoO2 layers in the unit cell. For this reason, this crystal structure is sometimes called an O3 type crystal structure. The CoO2 layer refers to a structure in which octahedral structures, in which oxygen atoms are coordinated to cobalt in a 6-coordinate manner, are continuous in a plane with shared edges.

[0131] Furthermore, at a charge depth of 1, it has a crystal structure of space group P-3m1, with one CoO2 layer present in the unit cell. For this reason, this crystal structure is sometimes called an O1 type crystal structure.

[0132] Furthermore, lithium cobalt oxide at a charge depth of approximately 0.8 has a crystal structure with space group R-3m. This structure can be described as a structure in which CoO2 structures such as P-3m1(O1) and LiCoO2 structures such as R-3m(O3) are alternately stacked. For this reason, this crystal structure is sometimes called the H1-3 type crystal structure. In reality, the H1-3 type crystal structure has twice the number of cobalt atoms per unit cell compared to other structures. However, in this specification, including Figure 2, the c-axis of the H1-3 type crystal structure will be shown as half the unit cell for easier comparison with other structures.

[0133] As an example, the H1-3 type crystal structure can be represented by the coordinates of cobalt and oxygen in a unit cell as follows: Co(0,0,0.42150±0.00016), O1(0,0,0.27671±0.00045), and O2(0,0,0.11535±0.00045). O1 and O2 are oxygen atoms, respectively. Thus, the H1-3 type crystal structure is represented by a unit cell using one cobalt and two oxygen atoms. On the other hand, the O3' type crystal structure in one embodiment of the present invention is preferably represented by a unit cell using one cobalt and one oxygen atom. This indicates that the symmetry between cobalt and oxygen differs between the O3' type crystal structure and the H1-3 type structure, and that the O3' type crystal structure shows less variation from the O3 structure compared to the H1-3 type structure. The choice of which unit cell is preferable to represent the crystal structure of the positive electrode active material can be made, for example, in Rietveld analysis using XRD, by selecting the unit cell that results in a smaller GOF (good of fitness) value.

[0134] When high-voltage charging occurs, such as when the charging voltage is 4.6V or higher relative to the oxidation-reduction potential of lithium metal, or when deep charging occurs, such as when the charging depth is 0.8 or higher, and when this charging and discharging cycle is repeated, lithium cobalt oxide undergoes repeated changes in its crystal structure (i.e., non-equilibrium phase changes) between the H1-3 type crystal structure and the R-3m(O3) structure in the discharged state.

[0135] However, these two crystal structures exhibit a large displacement of the CoO2 layer. As shown by the dotted line and arrows in Figure 2, in the H1-3 type crystal structure, the CoO2 layer is significantly shifted from R-3m(O3). Such dynamic structural changes can negatively affect the stability of the crystal structure.

[0136] Furthermore, the volume difference is also significant. When comparing the same number of cobalt atoms, the volume difference between the H1-3 type crystal structure and the O3 type crystal structure in the discharged state is more than 3.0%.

[0137] In addition, the H1-3 type crystal structure, which consists of continuous CoO2 layers such as P-3m1(O1), is likely to be unstable.

[0138] Therefore, repeated high-voltage charging and discharging causes the crystal structure of lithium cobalt oxide to break down. This breakdown of the crystal structure leads to a deterioration of the cycle characteristics. This is thought to be because the breakdown of the crystal structure reduces the number of sites where lithium can exist stably, and also makes it more difficult for lithium to be inserted and removed.

[0139] An example of a method for producing a positive electrode active material according to one aspect of the present invention will be explained with reference to Figures 4 to 7. Here, as an example, a method for producing a positive electrode active material having lithium, a transition metal, and element X will be described.

[0140] [Method for preparing positive electrode active material 1] <Step S11> In step S11 of Figure 4A, a lithium source and a transition metal source are prepared as lithium and transition metal materials. In the drawing, the transition metal source is shown as the M source.

[0141] For example, lithium carbonate, lithium fluoride, etc., can be used as lithium sources.

[0142] As a transition metal source, at least one of manganese, cobalt, and nickel can be used. For example, as a transition metal source, only cobalt may be used, only nickel may be used, both cobalt and manganese may be used, both cobalt and nickel may be used, or all three may be used: cobalt, manganese, and nickel.

[0143] Furthermore, it is preferable to use a high-purity material as the transition metal source during synthesis. Specifically, the purity of the material should be 3N (99.9%) or higher, preferably 4N (99.99%) or higher, more preferably 4N5 (99.995%) or higher, and even more preferably 5N (99.999%) or higher. By using a high-purity material, the capacity of the secondary battery can be increased and / or the reliability of the secondary battery can be improved.

[0144] In addition, it is preferable that the transition metal source has high crystallinity. For example, it is preferable that the transition metal source has single crystal grains. The crystallinity of the transition metal source can be evaluated from, for example, TEM (transmission electron microscope) images, STEM (scanning transmission electron microscope) images, HAADF-STEM (high-angle scattering annular dark-field scanning transmission electron microscope) images, ABF-STEM (annular bright-field scanning transmission electron microscope) images, etc. Furthermore, the crystallinity of the transition metal source can also be evaluated using XRD, electron diffraction, neutron diffraction, etc. Note that the above evaluation of crystallinity can be applied not only to the transition metal source but also to the evaluation of the crystallinity of primary or secondary particles.

[0145] Furthermore, when using metals capable of forming layered rock salt-type composite oxides, it is preferable to use a mixing ratio of cobalt, manganese, and nickel within a range that allows for a layered rock salt-type crystal structure. Additionally, an additive element X may be added to these transition metals within a range that allows for a layered rock salt-type crystal structure. An example of the process of adding the additive element X is shown in Figure 4B. In step S11, a lithium source, a transition metal source, and an additive element X source are prepared, and then step S12 is carried out.

[0146] As the additive element X, one or more can be selected from magnesium, calcium, zirconium, lanthanum, barium, titanium, yttrium, nickel, aluminum, cobalt, manganese, vanadium, iron, chromium, niobium, copper, potassium, sodium, zinc, chlorine, fluorine, hafnium, silicon, sulfur, phosphorus, boron, and arsenic. In addition to the above elements, bromine and beryllium may also be used as additive element X. However, since bromine and beryllium are toxic to living organisms, it is preferable to use the additive element X described above.

[0147] Furthermore, as a transition metal source, oxides, hydroxides, etc., of the above-mentioned metals exemplified as transition metals can be used. As a cobalt source, for example, cobalt oxide, cobalt hydroxide, etc., can be used.

[0148] Furthermore, manganese oxide, manganese hydroxide, etc., can be used as manganese sources. Nickel oxide, nickel hydroxide, etc., can be used as nickel sources. Aluminum oxide, aluminum hydroxide, etc., can be used as aluminum sources.

[0149] <Step S12> Next, in step S12, the lithium source, transition metal source, and additive element X source are crushed and mixed. The crushing and mixing can be carried out dry or wet. It is particularly preferable to crush using dehydrated acetone with a purity of 99.5% or higher and a water content of 10 ppm or less. In this specification, the term "crushing" may be read as "grinding". For mixing, for example, a ball mill or a bead mill can be used. When using a ball mill, it is preferable to use zirconia balls as the media. When using a ball mill or a bead mill, it is preferable to set the peripheral speed to 100 mm / s or more and 2000 mm / s or less in order to suppress contamination from the media or material. For example, it may be carried out at a peripheral speed of 838 mm / s (rotation speed 400 rpm, ball mill diameter 40 mm). Furthermore, by using the above-mentioned dehydrated acetone in the crushing and mixing, it is possible to reduce impurities that may be mixed into the material.

[0150] <Step S13> Next, in step S13, the mixed materials are heated. The heating temperature in this step is preferably 800°C or higher and less than 1100°C, more preferably 900°C or higher and 1000°C or lower, and even more preferably around 950°C. If the temperature is too low, the decomposition and melting of the lithium source and the transition metal source may be insufficient. On the other hand, if the temperature is too high, defects may occur due to reasons such as lithium evaporating from the lithium source and / or the metal used as the transition metal source being excessively reduced. For example, if cobalt is used as the transition metal, a defect in which the cobalt becomes divalent may occur.

[0151] The heating time can be, for example, 1 hour to 100 hours, and preferably 2 hours to 20 hours. Heating is preferably carried out in an atmosphere with little water, such as dry air (for example, with a dew point of -50°C or lower, more preferably -80°C or lower). For example, heating may be carried out in an atmosphere with a dew point of -93°C. Furthermore, heating is preferable in an atmosphere where the impurity concentrations of CH4, CO, CO2, and H2 are each 5 ppb (parts per billion) or less, as this suppresses the incorporation of impurities into the material.

[0152] Furthermore, for example, when heating at 1000°C for 10 hours, it is preferable to raise the temperature at 200°C / h and the flow rate of dry air at 10 L / min. After that, the heated material can be cooled to room temperature. For example, it is preferable to set the cooling time from the specified temperature to room temperature to 10 hours or more and 50 hours or less. However, cooling to room temperature in step S13 is not essential.

[0153] Furthermore, the crucible used during heating in step S13 is preferably made of a material that does not allow impurities to enter. For example, a crucible made of alumina with a purity of 99.9% may be used.

[0154] Furthermore, when collecting the material after heating in step S13, it is preferable to transfer it from the crucible to a mortar before collection, as this prevents impurities from contaminating the material. It is also preferable that the mortar itself be made of a material that does not allow impurities to enter. Specifically, it is preferable to use a mortar made of alumina with a purity of 90% or higher, preferably 99% or higher. Note that the same conditions as in step S13 can be applied to the heating processes described later, other than step S13.

[0155] <Step S14> By the above steps, a positive electrode active material 100 according to one embodiment of the present invention can be produced (step S14). The positive electrode active material 100 may be represented as a composite oxide (LiMO2) having lithium, a transition metal, and oxygen. However, the positive electrode active material according to one embodiment of the present invention only needs to have the crystal structure of a lithium composite oxide represented as LiMO2, and its composition is not strictly limited to Li:M:O=1:1:2.

[0156] By using a high-purity material as the transition metal source during synthesis, and by producing the positive electrode active material in a process that minimizes the inclusion of impurities during synthesis, a material with a low impurity concentration, or in other words, a highly purified material, can be obtained. Furthermore, the positive electrode active material obtained by such a method of producing positive electrode active material is a material with high crystallinity. In addition, the positive electrode active material obtained by the method of producing positive electrode active material according to one aspect of the present invention can increase the capacity of a secondary battery and / or improve the reliability of a secondary battery.

[0157] [Method for preparing positive electrode active material 2] Next, another example of a method for producing a positive electrode active material according to one aspect of the present invention will be explained using Figures 5A, 5B, and 5C.

[0158] In Figure 5A, steps S11 to S14 are performed in the same manner as in Figure 4A to prepare a composite oxide (LiMO2) having lithium, a transition metal, and oxygen.

[0159] In addition, a pre-synthesized composite oxide may be used as step S14. In this case, steps S11 to S13 can be omitted. When preparing a pre-synthesized composite oxide, it is preferable to use a high-purity material. The purity of the material should be 99.5% or higher, preferably 99.9% or higher, and more preferably 99.99% or higher.

[0160] A heating step may be included between step S14 and the next step S20. This heating can, for example, smooth the surface of the composite oxide. For example, this heating can be carried out under the same conditions as the atmosphere and temperature in step S33 described later, but the processing time can be shorter than that of step S33. A smooth surface means that there are few irregularities, the surface is generally rounded, and the corners are also rounded. Furthermore, a state in which there are few foreign substances adhering to the surface is also called smooth. Foreign substances are thought to be a cause of irregularities, so it is preferable that they do not adhere to the surface.

[0161] <Step S20> As step S20 in Figure 5A, a source of additive element X is prepared. The materials described above can be used as the source of additive element X. In addition, multiple elements may be used as additive element X. The case in which multiple elements are used as additive element X will be explained using Figures 5B and 5C. Addition of additive element X can be carried out using methods such as solid-phase methods, liquid-phase methods including sol-gel methods, sputtering methods, vapor deposition methods, CVD (chemical vapor deposition), and PLD (pulsed laser deposition).

[0162] <Step S21> In step S21 of Figure 5B, a magnesium source (Mg source) and a fluorine source (F source) are prepared. Alternatively, a lithium source may be prepared in conjunction with the magnesium source and the fluorine source.

[0163] For example, magnesium fluoride, magnesium oxide, magnesium hydroxide, magnesium carbonate, etc., can be used as magnesium sources.

[0164] Examples of fluorine sources that can be used include lithium fluoride (LiF), magnesium fluoride (MgF2), aluminum fluoride (AlF3), titanium fluoride (TiF4), cobalt fluoride (CoF2, CoF3), nickel fluoride (NiF2), zirconium fluoride (ZrF4), vanadium fluoride (VF5), manganese fluoride, iron fluoride, chromium fluoride, niobium fluoride, zinc fluoride (ZnF2), calcium fluoride (CaF2), sodium fluoride (NaF), potassium fluoride (KF), barium fluoride (BaF2), cerium fluoride (CeF2), lanthanum fluoride (LaF3), and sodium aluminum hexafluoride (Na3AlF6). Furthermore, the fluorine source is not limited to a solid; for example, fluorine (F2), carbon fluoride, sulfur fluoride, oxygen fluoride (OF2, O2F2, O3F2, O4F2, O2F), etc., may be used and mixed in the atmosphere during the heating process described later. Multiple fluorine sources may also be used in combination. Among these, lithium fluoride is preferred because it has a relatively low melting point of 848°C and is easily melted during the heating process described later.

[0165] For example, lithium fluoride and lithium carbonate can be used as lithium sources. In other words, lithium fluoride can be used as both a lithium source and a fluorine source. Similarly, magnesium fluoride can be used as both a fluorine source and a magnesium source.

[0166] In this embodiment, lithium fluoride (LiF) is prepared as the fluorine source, and magnesium fluoride (MgF2) is prepared as both the fluorine source and the magnesium source. Mixing lithium fluoride (LiF) and magnesium fluoride (MgF2) in a molar ratio of approximately LiF:MgF2 = 65:35 yields the highest effect in lowering the melting point (Non-Patent Literature 4). On the other hand, if the amount of lithium fluoride is too high, there is a concern that the lithium will be in excess and the cycle characteristics will deteriorate. Therefore, the molar ratio of lithium fluoride (LiF) to magnesium fluoride (MgF2) is preferably LiF:MgF2 = x:1 (0 ≤ x ≤ 1.9), more preferably LiF:MgF2 = x:1 (0.1 ≤ x ≤ 0.5), and even more preferably LiF:MgF2 = x:1 (x = 0.33 or its vicinity). In this specification, "nearby" means a value greater than 0.9 times and less than 1.1 times the value.

[0167] Furthermore, if the following mixing and crushing steps are carried out wet, a solvent should be prepared. It is preferable to use a protic solvent that does not react easily with lithium, such as ketones like acetone, alcohols like ethanol and isopropanol, ethers, dioxane, acetonitrile, or N-methyl-2-pyrrolidone (NMP).

[0168] <Step S22> Next, in step S22 of Figure 5B, the above materials are mixed and crushed. Mixing can be done dry or wet, but wet mixing is preferred because it can crush the materials into smaller pieces. For mixing, for example, a ball mill or a bead mill can be used. When using a ball mill, it is preferable to use zirconia balls as the media. The conditions for the ball mill or bead mill can be the same as those in step S12.

[0169] <Step S23> Next, in step S23, the materials crushed and mixed above are recovered to obtain the additive element X source. Note that the additive element X source shown in step S23 is formed from multiple materials and may therefore be referred to as a mixture.

[0170] The above mixture preferably has a median diameter (D50) of 600 nm to 20 μm, and more preferably 1 μm to 10 μm. When the mixture is finely powdered in this way, it is easier to uniformly adhere the mixture to the surface of the composite oxide particles when it is mixed with lithium, a transition metal, and oxygen in a later process. When the mixture is uniformly adhered to the surface of the composite oxide particles, it is preferable because it is easier to distribute halogen and magnesium evenly near the surface of the composite oxide particles after heating. If there are regions near the surface that do not contain halogen and magnesium, it may be difficult to form the O3' type crystal structure described later in the charged state.

[0171] In step S21 of Figure 5B, a method for mixing two types of materials is illustrated, but the method is not limited to this. For example, as shown in Figure 5C, four types of materials (magnesium source (Mg source), fluorine source (F source), nickel source (Ni source), and aluminum source (Al source)) may be mixed to prepare the additive element X source. Alternatively, a single material, i.e., one type of material, may be used to prepare the additive element X source. Nickel oxide, nickel hydroxide, etc. can be used as the nickel source. Aluminum oxide, aluminum hydroxide, etc. can be used as the aluminum source.

[0172] <Step S31> Next, in step S31 of Figure 5A, the LiMO2 obtained in step S14 is mixed with the additive element X source. The ratio of the number of transition metal atoms M in the composite oxide having lithium, a transition metal, and oxygen to the number of magnesium atoms Mg in the additive element X source is preferably M:Mg=100:y (0.1≦y≦6), and more preferably M:Mg=100:y (0.3≦y≦3).

[0173] The mixing in step S31 is preferably carried out under milder conditions than the mixing in step S12 in order to avoid destroying the particles of the composite oxide. For example, it is preferable to use conditions with a lower rotation speed or a shorter time than the mixing in step S12. Also, dry mixing is generally milder than wet mixing. For mixing, for example, a ball mill or a bead mill can be used. When using a ball mill, it is preferable to use zirconia balls as the media.

[0174] In this embodiment, the mixing is performed dry using a ball mill with zirconia balls with a diameter of 1 mm at 150 rpm for 1 hour. The mixing is carried out in a dry room with a dew point of -100°C or higher and -10°C or lower.

[0175] <Step S32> Next, in step S32 of Figure 5A, the materials mixed above are collected to obtain mixture 903.

[0176] In this embodiment, a method of adding a mixture of lithium fluoride and magnesium fluoride to lithium cobalt oxide with few impurities is described, but the present invention is not limited to this. Instead of the mixture 903 in step S32, a starting material of lithium cobalt oxide to which a magnesium source and a fluorine source, etc., have been added and heated may be used. In this case, it is not necessary to separate the processes in steps S11 to S14 and steps S21 to S23, making it simpler and more productive.

[0177] Alternatively, lithium cobalt oxide with magnesium and fluorine added beforehand may be used. Using lithium cobalt oxide with magnesium and fluorine added makes the process up to step S32 easier to complete.

[0178] Alternatively, magnesium and fluorine sources may be added to lithium cobalt oxide that has already been treated with magnesium and fluorine.

[0179] <Step S33> Next, in step S33, the mixture 903 is heated in an oxygen-containing atmosphere. It is preferable to heat the mixture 903 in a way that prevents the particles from sticking together.

[0180] It is preferable that the additives be added uniformly and without bias across the entire surface of the particles. However, if the particles of mixture 903 stick together during heating, the additives may be added unevenly to only a part of the surface. Furthermore, even if the surface of the particles is preferably smooth with few irregularities, if the particles stick together, the irregularities will increase, and defects such as cracks and / or fissures may increase. This is thought to be due to the effect of the particles of mixture 903 sticking together, which reduces the contact area with oxygen in the atmosphere and obstructs the diffusion pathway of the additives.

[0181] Furthermore, heating in step S33 may be performed using a rotary kiln. Heating with a rotary kiln can be performed while stirring, whether in a continuous or batch system. Alternatively, heating in step S33 may be performed using a roller hearth kiln.

[0182] The heating temperature in step S33 must be above the temperature at which the reaction between LiMO2 and the additive element X source proceeds. The temperature at which the reaction proceeds is simply the temperature at which elemental interdiffusion occurs between LiMO2 and the additive element X source. Therefore, it may be possible to set the temperature lower than the melting temperature of these materials. For example, in oxides, the melting temperature T m 0.757 times (Tammann temperature T) d )Solid-phase diffusion occurs.Therefore, the heating temperature in step S33 should be, for example, 500°C or higher.

[0183] However, it is preferable that the heating temperature in step S33 be 742°C or higher, as this facilitates the reaction. For example, if LiF and MgF2 are used as the source of additive element X, the eutectic point of LiF and MgF2 is around 742°C, so it is preferable to set the heating temperature in step S33 to 742°C or higher.

[0184] Furthermore, when mixture 903 is prepared by mixing LiCoO2:LiF:MgF2 in a molar ratio of 100:0.33:1, an endothermic peak is observed around 830°C in differential scanning calorimetry (DSC measurement). Therefore, a heating temperature of 830°C or higher is more preferable.

[0185] A higher heating temperature is preferable because it facilitates the reaction, shortens the heating time, and increases productivity.

[0186] However, the heating temperature must be below the decomposition temperature of LiMO2 (1130°C in the case of LiCoO2). Furthermore, at temperatures near the decomposition temperature, there is a concern that a small amount of LiMO2 may decompose. For this reason, the heating temperature in step S33 is preferably less than 1130°C, more preferably 1000°C or less, even more preferably 950°C or less, and even more preferably 900°C or less.

[0187] Therefore, the heating temperature in step S33 is preferably 500°C or more and less than 1130°C, more preferably 500°C or more and 1000°C or less, even more preferably 500°C or more and 950°C or less, and even more preferably 500°C or more and 900°C or less. Also, it is preferably 742°C or more and less than 1130°C, more preferably 742°C or more and 1000°C or less, even more preferably 742°C or more and 950°C or less, and even more preferably 742°C or more and 900°C or less. Also, it is preferably 830°C or more and less than 1130°C, more preferably 830°C or more and 1000°C or less, even more preferably 830°C or more and 950°C or less, and even more preferably 830°C or more and 900°C or less.

[0188] Furthermore, when heating mixture 903, it is preferable to control the partial pressure of fluorine or fluoride in the atmosphere to an appropriate range.

[0189] In the manufacturing method described in this embodiment, some materials, such as LiF, which is a fluorine source, may function as a flux. This function allows the heating temperature to be lowered to below the decomposition temperature of LiMO2, for example, between 742°C and 950°C, enabling the distribution of additives such as magnesium near the surface and the production of a positive electrode active material with good properties.

[0190] However, since LiF is less dense than oxygen in its gaseous state, heating causes LiF to volatilize, reducing the amount of LiF in mixture 903. This weakens its function as a flux. Therefore, heating is necessary while suppressing the volatilization of LiF. Even if LiF is not used as a fluorine source, Li and F on the surface of LiMO2 may react to produce LiF, which may then volatilize. Therefore, even if a fluoride with a higher melting point than LiF is used, the same need to suppress volatilization is required.

[0191] Therefore, it is preferable to heat the mixture 903 in an atmosphere containing LiF, that is, to heat the mixture 903 while the partial pressure of LiF in the heating furnace is high. Such heating can suppress the volatilization of LiF in the mixture 903.

[0192] Furthermore, when heating with a rotary kiln, it is preferable to heat the mixture 903 by controlling the flow rate of the oxygen-containing atmosphere inside the kiln. For example, it is preferable to reduce the flow rate of the oxygen-containing atmosphere, or to purge the atmosphere first and then not allow oxygen gas to flow into the kiln.

[0193] When heating by roller hearth kiln, for example, the mixture 903 can be heated in an atmosphere containing LiF by placing a lid on the container containing the mixture 903.

[0194] Heating should preferably be carried out for an appropriate amount of time. The heating time varies depending on conditions such as the heating temperature, the size of the LiMO2 particles in step S14, and the composition. When the particles are small, a lower temperature or shorter time may be preferable than when the particles are large.

[0195] For example, when the average particle diameter (D50) of the composite oxide in step S14 of FIG. 5A is approximately 12 µm, the heating temperature is preferably, for example, 600°C to 950°C inclusive. The heating time is preferably, for example, 3 hours or more, more preferably 10 hours or more, and still more preferably 60 hours or more.

[0196] On the other hand, when the average particle diameter (D50) of the composite oxide in step S14 is approximately 5 µm, the heating temperature is preferably, for example, 600°C to 950°C inclusive. The heating time is preferably, for example, 1 hour to 10 hours inclusive, and more preferably approximately 2 hours. Note that the temperature reduction time after heating is preferably, for example, 10 hours to 50 hours inclusive.

[0197] <Step S34> Next, the heated material is collected to produce the positive electrode active material 100. At this time, it is preferable to further sieve the collected particles. Through the above steps, the positive electrode active material 100 according to one embodiment of the present invention can be produced (step S34).

[0198] [Production Method 3 of Positive Electrode Active Material] Next, another example of the method for producing a positive electrode active material according to one embodiment of the present invention will be described with reference to FIG. 6 and FIGS. 7A, 7B, and 7C.

[0199] In FIG. 6, steps S11 to S14 are performed in the same manner as in FIG. 4A to prepare a composite oxide (LiMO₂) containing lithium, a transition metal, and oxygen.

[0200] Note that a pre-synthesized composite oxide containing lithium, a transition metal, and oxygen may be used as step S14. In this case, steps S11 to S13 can be omitted.

[0201] As described in connection with FIG. 5, a heating step may be provided between step S14 and step S20. For this heating, for example, the same conditions of atmosphere and temperature as those in step S33 described later may be used, and the treatment time may be shorter than that in step S33.

[0202] <Step S20a> As step S20a in Figure 6, a source of additive element X1 is prepared. The additive element X1 source can be selected from the additive elements X described above. For example, one or more of magnesium, fluorine, and calcium can be suitably used as additive element X1. In this embodiment, a configuration using magnesium and fluorine as additive element X1 is illustrated in Figure 7A. Steps S21 and S22 included in step S20a shown in Figure 7A can be prepared in the same way as steps S21 and S22 shown in Figure 5B. Addition of additive element X1 can be carried out using methods such as solid-phase methods, liquid-phase methods including sol-gel methods, sputtering methods, vapor deposition methods, CVD (chemical vapor deposition), and PLD (pulsed laser deposition).

[0203] Step S23, shown in Figure 7A, is a process in which the material that has been crushed and mixed in step S22, also shown in Figure 7A, is recovered to be used as the source of additive element X1.

[0204] Furthermore, steps S31 to S33 shown in Figure 6 can be manufactured using the same process as steps S31 to S33 shown in Figure 5.

[0205] <Step S34a> Next, the material heated in step S33 is recovered to produce a composite oxide.

[0206] <Step S40> As step S40 in Figure 6, a source of additive element X2 is prepared. The additive element X2 source can be selected from the additive element X described above. For example, one or more of nickel, titanium, boron, zirconium, and aluminum can be suitably used as additive element X2. In this embodiment, a configuration using nickel and aluminum as additive element X2 is illustrated in Figure 7B. Steps S41 and S42 included in step S40 shown in Figure 7B can be manufactured in the same process as steps S21 and S22 shown in Figure 5B. Addition of additive element X2 can be performed using methods such as solid-phase methods, liquid-phase methods including sol-gel methods, sputtering methods, vapor deposition methods, CVD (chemical vapor deposition), and PLD (pulsed laser deposition).

[0207] Step S43, shown in Figure 7B, is a process in which the material crushed and mixed in step S42, also shown in Figure 7B, is recovered to serve as the source of additive element X2.

[0208] Furthermore, step S40 shown in Figure 7C is a modified example of step S40 shown in Figure 7B. In Figure 7C, a nickel source and an aluminum source are prepared (step S41), and each is crushed independently (step S42a) to prepare multiple additive element X2 sources (step S43).

[0209] Here, when using the sol-gel method for adding element X2, in addition to the element X2 source, a solvent for the sol-gel method is prepared. For example, a metal alkoxide can be used as the metal source for the sol-gel method, and an alcohol can be used as the solvent. For example, when adding aluminum, aluminum isopropoxide can be used as the metal source, and isopropanol (2-propanol) can be used as the solvent. For example, when adding zirconium, zirconium(IV) tetrapropoxide can be used as the metal source, and isopropanol can be used as the solvent.

[0210] <Steps S51 to S53> Next, step S51 in Figure 6 is a process of mixing the composite oxide prepared in step S34a with the additive element X2 source prepared in step S40. Step S51 in Figure 6 can be processed in the same way as step S31 shown in Figure 5A. Step S52 in Figure 6 can be processed in the same way as step S32 shown in Figure 5A. The material prepared in step S52 in Figure 6 is mixture 904. Mixture 904 is a material that contains the additive element X2 added in step S40 in addition to the material of mixture 903. Step S53 in Figure 6 can be processed in the same way as step S33 shown in Figure 5A.

[0211] <Step S54> Next, the heated material is recovered to produce the positive electrode active material 100. At this time, it is preferable to further sift the recovered particles. By the above steps, a positive electrode active material 100 according to one embodiment of the present invention can be produced (step S54).

[0212] As shown in Figures 6 and 7A to 7C, by separating the processes for introducing the transition metal, additive element X1, and additive element X2, it is sometimes possible to change the depth profile of each element. For example, the concentration of additives can be increased near the surface compared to the interior of the particles. Also, using the number of atoms of the transition metal as a reference, the ratio of the number of atoms of the additive elements to this reference can be made higher near the surface than in the interior.

[0213] Furthermore, by using high-purity materials as the transition metal source during synthesis, employing processes that minimize impurity contamination during synthesis, thoroughly eliminating impurity contamination during synthesis, and controlling the introduction of desired additive elements (additive element X, additive element X1, or additive element X2) into the positive electrode active material, it is possible to obtain a positive electrode active material in which regions with low impurity concentration and regions with introduced additive elements are controlled. In addition, a positive electrode active material with high crystallinity can be obtained. Moreover, a positive electrode active material obtained by the method for producing a positive electrode active material according to one aspect of the present invention can increase the capacity of a secondary battery and / or improve the reliability of a secondary battery.

[0214] [Cathode active material 2] The positive electrode active material according to one aspect of the present invention is not limited to the materials listed above. Alternatively, in addition to the materials listed above, other materials may be mixed and used as the positive electrode active material according to one aspect of the present invention.

[0215] For example, a composite oxide having a spinel-type crystal structure can be used as the positive electrode active material. Alternatively, for example, a polyanionic material can be used as the positive electrode active material. Examples of polyanionic materials include materials having an olivine-type crystal structure, nasicone-type materials, and so on. Furthermore, for example, a material containing sulfur can be used as the positive electrode active material.

[0216] As a material having a spinel-type crystal structure, for example, a composite oxide represented by LiM2O4 can be used. It is preferable that the metal M contains Mn. For example, LiMn2O4 can be used. Furthermore, by having Ni in addition to Mn as the metal M, the discharge voltage of the secondary battery may be improved and the energy density may be improved, which is preferable. In addition, a small amount of lithium nickelate (LiNiO2 or LiNi) can be added to a lithium-containing material having a spinel-type crystal structure containing manganese, such as LiMn2O4. 1-x M x Mixing O2 (M=Co, Al, etc.) can improve the characteristics of the secondary battery, which is preferable.

[0217] As the polyanionic material, for example, a composite oxide comprising oxygen, a metal A, a metal M, and an element X can be used. The metal A is one or more of Li, Na, and Mg, the metal M is one or more of Fe, Mn, Co, Ni, Ti, V, and Nb, and the element X is one or more of S, P, Mo, W, As, and Si.

[0218] As a material having an olivine-type crystal structure, for example, a composite material represented by the general formula LiMPO₄ (wherein M is one or more of Fe(II), Mn(II), Co(II), and Ni(II)) can be used. Representative examples of the general formula LiMPO₄ include LiFePO₄, LiNiPO₄, LiCoPO₄, LiMnPO₄, LiFe a Ni b PO₄, LiFe a Co b PO₄, LiFe a Mn b PO₄, LiNi a Co b PO₄, LiNi a Mn b PO₄ (wherein a+b is 1 or less, 0<a<1, 0<b<1), LiFe c Ni d Co e PO₄, LiFe c Ni d Mn e PO₄, LiNi c Co d Mn e PO₄ (wherein c+d+e is 1 or less, 0<c<1, 0<d<1, 0<e<1), LiFe f Ni g Co h Mn i lithium compounds such as PO₄ (wherein f+g+h+i is 1 or less, 0<f<1, 0<g<1, 0<h<1, 0<i<1) can be used.

[0219] Further, a composite material represented by the general formula Li (2-j) MSiO₄ (wherein M is one or more of Fe(II), Mn(II), Co(II), and Ni(II), and 0≦j≦2) can be used. As representative examples of the general formula Li (2-j) MSiO₄ include Li (2-j)FeSiO₄, Li (2-j) NiSiO₄, Li (2-j) CoSiO₄, Li (2-j) MnSiO₄, Li (2-j) Fe k Ni l SiO₄, Li (2-j) Fe k Co l SiO₄, Li (2-j) Fe k Mn l SiO₄, Li (2-j) Ni k Co l SiO₄, Li (2-j) Ni k Mn l SiO₄ (k+l ≤ 1, 0<k<1, 0<l<1), Li (2-j) Fe m Ni n Co q SiO₄, Li (2-j) Fe m Ni n Mn q SiO₄, Li (2-j) Ni m Co n Mn q SiO₄ (m+n+q ≤ 1, 0<m<1, 0<n<1, 0<q<1), Li (2-j) Fe r Ni s Co t Mn u lithium compounds such as SiO₄ (r+s+t+u ≤ 1, 0<r<1, 0<s<1, 0<t<1, 0<u<1) can be used as a material.

[0220] Further, a NASICON-type compound represented by the general formula A x M₂(XO₄)₃ (A=Li, Na, Mg; M=Fe, Mn, Ti, V, Nb; X=S, P, Mo, W, As, Si) can be used. Examples of the NASICON-type compound include Fe₂(MnO₄)₃, Fe₂(SO₄)₃, Li₃Fe₂(PO₄)₃, etc. Further, as the positive electrode active material, a compound represented by the general formula Li₂MPO₄F, Li₂MP₂O₇, Li₅MO₄ (M=Fe, Mn) can be used.

[0221] Furthermore, as positive electrode active materials, perovskite-type fluorides such as NaFeF3 and FeF3, metal chalcogenides (sulfides, selenides, tellurides) such as TiS2 and MoS2, oxides having an inverse spinel crystal structure such as LiMVO4, and vanadium oxide systems (V2O5, V6O 13 Materials such as LiV3O8, manganese oxides, and organic sulfur compounds may also be used.

[0222] Furthermore, a borate-based material represented by the general formula LiMBO3 (where M is Fe(II), Mn(II), or Co(II)) may be used as the positive electrode active material.

[0223] Examples of materials containing sodium include NaFeO2, Na 2 / 3 [Fe 1 / 2 Mn 1 / 2 ]O2, Na 2 / 3 [Ni 1 / 3 Mn 2 / 3 Sodium-containing oxides such as O2, Na2Fe2(SO4)3, Na3V2(PO4)3, Na2FePO4F, NaVPO4F, NaMPO4 (where M is Fe(II), Mn(II), Co(II), Ni(II)), Na2FePO4F, and Na4Co3(PO4)2P2O7 may be used as positive electrode active materials.

[0224] Furthermore, lithium-containing metal sulfides may be used as the positive electrode active material. Examples include Li2TiS3 and Li3NbS4.

[0225] [Electrolyte] A secondary battery according to one aspect of the present invention preferably has an electrolyte. The electrolyte of a secondary battery according to one aspect of the present invention preferably comprises an ionic liquid and a salt containing a metal that acts as a carrier ion.

[0226] When the carrier ion metal is lithium, salts containing the carrier ion metal include, for example, LiN(FSO2)2, LiN(CF3SO2)2, LiN(C4F9SO2)(CF3SO2), LiN(C2F5SO2)2, LiC(FSO2)3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiCF3SO3, LiC4F9SO3, LiAsF6, LiBF4, LiAlCl4, LiSCN, LiBr, LiI, Li2SO4, and Li2B. 10 Cl 10 Li2B 12 Cl 12 Lithium salts such as LiPF6 and LiClO4 can be used individually, or two or more of these can be used in any combination and ratio.

[0227] In particular, metal salts of fluorosulfonic acid anions and metal salts of fluoroalkyl sulfonic acid anions may be preferred, and among them (C n F 2n+1 SO2)2N - Metal salts with amide anions represented by (n=0 to 3) are preferred because they have high stability at high temperatures and high resistance to oxidation and reduction.

[0228] Ionic liquids consist of cations and anions, and include organic cations and anions. Examples of organic cations used in electrolytes include aromatic cations such as imidazolium cations and pyridinium cations, quaternary ammonium cations, tertiary sulfonium cations, and aliphatic onium cations such as quaternary phosphonium cations. Examples of anions used in electrolytes include monovalent amide anions, monovalent methide anions, fluorosulfonic acid anions, perfluoroalkyl sulfonic acid anions, tetrafluoroborate anions, perfluoroalkyl borate anions, hexafluorophosphate anions, or perfluoroalkyl phosphate anions.

[0229] Furthermore, in addition to the ionic liquid, the electrolyte may also contain an aprotic solvent, such as one of the following: 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), 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, or a mixture of two or more of these in any combination and ratio.

[0230] Furthermore, additives such as vinylene carbonate (VC), propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), lithium bis(oxalate) borate (LiBOB), dinitrile compounds such as succinonitrile and adiponitrile, and fluorobenzene, cyclohexylbenzene, and biphenyl may be added to the electrolyte. The concentration of the added material should be, for example, 0.1 wt% to 5 wt% relative to the total solvent.

[0231] As an ionic liquid having an imidazolium cation, for example, an ionic liquid represented by the following general formula (G1) can be used. In general formula (G1), R 1 R represents an alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted aryl group having 6 to 13 carbon atoms, preferably an alkyl group having 1 to 4 carbon atoms. 2 ~R 4 Each independently represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 13 carbon atoms, preferably representing 1 to 4 alkyl groups, R 5 R represents an alkyl group or a main chain composed of two or more atoms selected from C, O, Si, N, S, and P.5 Substituents may be introduced into the main chain. Examples of substituents that can be introduced include alkyl groups and alkoxy groups. Also, R 5 The main chain may have a carboxyl group. Also, R 5 The main chain may have a carbonyl group.

[0232] [ka]

[0233] As an ionic liquid having a pyridinium cation, for example, an ionic liquid represented by the following general formula (G2) may be used. In general formula (G2), R 6 R represents an alkyl group or a main chain composed of two or more atoms selected from C, O, Si, N, S, and P. 7 ~R 11 Each of these independently represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. Also, R 6 Substituents may be introduced into the main chain. Examples of substituents that can be introduced include alkyl groups and alkoxy groups.

[0234] [ka]

[0235] As ionic liquids having quaternary ammonium cations, for example, ionic liquids represented by the following general formulas (G3), (G4), (G5), and (G6) can be used.

[0236] [ka]

[0237] In general formula (G3), R 28 ~R 31 Each of these independently represents an alkyl group having 1 to 20 carbon atoms, a methoxy group, a methoxymethyl group, a methoxyethyl group, or a hydrogen atom.

[0238] [ka]

[0239] In general formula (G4), R 12 ~R 17 Each of these independently represents an alkyl group having 1 to 20 carbon atoms, a methoxy group, a methoxymethyl group, a methoxyethyl group, or a hydrogen atom.

[0240] [ka]

[0241] In general formula (G5), R 18 ~R 24 Each of these independently represents an alkyl group having 1 to 20 carbon atoms, a methoxy group, a methoxymethyl group, a methoxyethyl group, or a hydrogen atom.

[0242] [ka]

[0243] In general formula (G6), n and m are between 1 and 3. α is between 0 and 6, where n is 1, α is between 0 and 4, n is 2, α is between 0 and 5, and n is 3, α is between 0 and 6. β is between 0 and 6, where m is 1, β is between 0 and 4, m is 2, β is between 0 and 5, and m is 3, β is between 0 and 6. Note that α or β being 0 means unsubstituted. Also, the case where both α and β are 0 is excluded. X or Y represents a linear or side-chain alkyl group having 1 to 4 carbon atoms, a linear or side-chain alkoxy group having 1 to 4 carbon atoms, or a linear or side-chain alkoxyalkyl group having 1 to 4 carbon atoms as a substituent.

[0244] As an ionic liquid having a tertiary sulfonium cation, for example, an ionic liquid represented by the following general formula (G7) can be used. In general formula (G7), R 25 ~R 27 Each of these independently represents a hydrogen atom, an alkyl group with 1 to 4 carbon atoms, or a phenyl group. Or, R 25 ~R 27 Alternatively, a main chain composed of two or more atoms selected from C, O, Si, N, S, and P may be used.

[0245] [ka]

[0246] As an ionic liquid having a quaternary phosphonium cation, for example, an ionic liquid represented by the following general formula (G8) can be used. In general formula (G8), R 32 ~R 35 Each of these independently represents a hydrogen atom, an alkyl group with 1 to 4 carbon atoms, or a phenyl group. Or, R 32 ~R 35 Alternatively, a main chain composed of two or more atoms selected from C, O, Si, N, S, and P may be used.

[0247] [ka]

[0248] A shown in general formulas (G1) to (G8) - One or more of the following can be used: monovalent amide anions, monovalent methide anions, fluorosulfonic acid anions, perfluoroalkyl sulfonic acid anions, tetrafluoroborate anions, perfluoroalkyl borate anions, hexafluorophosphate anions, and perfluoroalkyl phosphate anions.

[0249] As for monovalent amide anions, (C n F 2n+1 SO2)2N- (n=0 to 3), as a monovalent cyclic amide anion, (CF2SO2)2N - These can be used. As a monovalent methide anion, (C n F 2n+1 SO2)3C - (n=0 to 3), a monovalent cyclic methide anion is (CF2SO2)2C - (CF3SO2) and others can be used. As for fluoroalkyl sulfonate anions, (C m F 2m+1 SO3) - Examples include (m=0 or greater and 4 or less). Examples of fluoroalkylborate anions include {BF n (C m H k F 2m+1-k ) 4-n} - Examples include (n=0 to 3, m=1 to 4, k=0 to 2m). Examples of fluoroalkyl phosphate anions include {PF n (C m H k F 2m+1-k ) 6-n} - Examples include (n = 0 or greater and 5 or less, m = 1 or greater and 4 or less, k = 0 or greater and 2m or less).

[0250] Furthermore, as monovalent amide anions, one or more of the bis(fluorosulfonyl)amide anion and bis(trifluoromethanesulfonyl)amide anion can be used.

[0251] Furthermore, the ionic liquid may contain one or more hexafluorophosphate anions and tetrafluoroborate anions.

[0252] From here on, (FSO2)2N - The anion represented by (CF3SO2)2N is called the FSA anion. - The anion represented by is sometimes referred to as the TFSA anion.

[0253] Specific examples of the cation of the above general formula (G1) include, for example, structural formulas (111) to (174).

[0254] [ka]

[0255] [ka]

[0256] [ka]

[0257] [ka]

[0258] [ka]

[0259] [ka]

[0260] The ionic liquid shown in general formula (G1) is composed of an imidazolium cation and A - It has the anion shown by and . Ionic liquids having imidazolium cations have low viscosity and can be used over a wide temperature range. Furthermore, ionic liquids having imidazolium cations have high stability and a wide potential window, making them suitable for use as electrolytes in secondary batteries.

[0261] The ionic liquid shown in general formula (G1) can be mixed with a salt such as a lithium salt and used as an electrolyte for a secondary battery. The imidazolium cation shown in general formula (G1) has high oxidation and reduction resistance and a wide potential window, making it suitable as a solvent for use as an electrolyte. Here, the range of potentials in which the electrolyte does not undergo electrolysis is called the potential window. In particular, in a secondary battery according to one aspect of the present invention, a positive electrode active material that has excellent properties even at high charging voltages can be installed, thereby increasing the charging voltage. Therefore, by using an ionic liquid with a wide potential window and particularly outstanding oxidation resistance, a superior secondary battery can be realized.

[0262] Furthermore, in general formula (G1), R 1 R is a methyl group, an ethyl group, or a propyl group. 2 , R 3 and R 4 One of them is a hydrogen atom or a methyl group, and the other two are hydrogen atoms, and anion A - (FSO2)2N - The anions represented by (FSA anion) and (CF3SO2)2N - By using one or a mixture of the anions represented by (TFSA anions), it is possible to realize an electrolyte with a wide potential window, excellent oxidation resistance, and that does not solidify even at temperatures where viscosity decreases, allowing for use over a wide temperature range.

[0263] Furthermore, as salts used in electrolytes, metal salts of fluorosulfonate anions and metal salts of fluoroalkylsulfonate anions are particularly preferred, and among them (C n F 2n+1 SO2)2N - Metal salts with amide anions represented by (n=0 to 3) are preferred because they exhibit high stability at high temperatures and high oxidation-reduction resistance. In particular, by using either LiN(FSO2)2, LiN(CF3SO2)2, or a mixture of both, it is possible to realize a secondary battery that is highly stable and can operate over a wide temperature range.

[0264] In the general formula (G1), R1 R is a methyl group, an ethyl group, or a propyl group. 2 , R 3 and R 4 Examples of cations in which one of the atoms is a hydrogen atom or a methyl group and the other two atoms are hydrogen atoms include the cations represented by structural formulas (111) to (124), (131) to (136), (146) to (155), (156) to (166), and (170). It is preferable to use one selected from these cations. Alternatively, a combination of multiple selected from these cations may be used.

[0265] Furthermore, in the general formula (G1), R 1 and R 5 By reducing the sum of carbon and oxygen atoms in the ionic liquid to seven or less, the viscosity of the ionic liquid can be lowered, and a secondary battery with good output characteristics can be realized. For example, among the cations shown above, it is preferable to use the 1-butyl-3-propylimidazolium (BPI) cation represented by the above structural formula (131).

[0266] Also, for example, in general formula (G1), R 1 is a methyl group, R 2 is a hydrogen atom, and R 5It is preferable to use a cation in which the sum of carbon atoms and oxygen atoms is 6 or less. For example, it is preferable that the electrolyte of the secondary battery contains one or more cations selected from the above structural formulas (111) to (115) and structural formulas (156) to (162). In particular, it is preferable that the electrolyte of the secondary battery contains one or more cations selected from the above structural formula (111) 1-ethyl-3-methylimidazolium (EMI) cation, the above structural formula (113) 1-butyl-3-methylimidazolium (BMI) cation, the above structural formula (115) 1-hexyl-3-methylimidazolium (HMI) cation, and the above structural formula (157) 1-methyl-3-(2-propoxyethyl)imidazolium (poEMI) cation. Among these, ionic liquids using EMI cations are particularly preferable because they have low viscosity and extremely high stability.

[0267] For example, by mixing EMI cations and BMI cations, an ionic liquid with low viscosity and high stability can be realized. When mixing EMI cations and BMI cations, for example, the molar ratio of EMI cation:BMI cation = e:b should be set so that e > b, or e > 2b.

[0268] Furthermore, by mixing the ionic liquid shown in general formula (G1) with one or more ionic liquids selected from general formulas (G2) to (G8), a liquid with low viscosity and usable over a wide temperature range can be achieved. Thus, an ionic liquid with particularly high oxidation resistance and extremely high stability can be realized. In this case, for example, it is preferable that the volume of the ionic liquid shown in general formula (G1) is greater than the volume of one or more ionic liquids selected from general formulas (G2) to (G8), and it is more preferable that the volume of the ionic liquid shown in general formula (G1) is greater than twice the volume of one or more ionic liquids selected from general formulas (G2) to (G8).

[0269] Specific examples of the cation of the above general formula (G2) include, for example, structural formulas (701) to (719).

[0270] [ka]

[0271] [ka]

[0272] Specific examples of the cation of the above general formula (G4) include, for example, structural formulas (501) to (520).

[0273] [ka]

[0274] Specific examples of the cation of the above general formula (G5) include, for example, structural formulas (601) to (630).

[0275] [ka]

[0276] [ka]

[0277] Specific examples of the cation of the above general formula (G6) include, for example, structural formulas (301) to (309) and structural formulas (401) to (419).

[0278] [ka]

[0279] [ka]

[0280] Furthermore, structural formulas (301) to (309) and structural formulas (401) to (419) show examples where m is 1 in general formula (G6), but in structural formulas (301) to (309) and structural formulas (401) to (419), m may be replaced with 2 or 3.

[0281] Furthermore, specific examples of the cation of the general formula (G7) mentioned above include structural formulas (201) to (215).

[0282] [ka]

[0283] In a secondary battery according to one aspect of the present invention, by using a positive electrode active material according to one aspect of the present invention and having the ionic liquid described above as the electrolyte, it is possible to suppress the decrease in capacity and achieve remarkably superior characteristics even when the secondary battery is repeatedly used at a high charging voltage.

[0284] [Negative electrode active material]

[0285] A negative electrode according to one aspect of the present invention has a negative electrode active material. Furthermore, a negative electrode according to one aspect of the present invention preferably has a conductive agent. Furthermore, a negative electrode according to one aspect of the present invention preferably has a binder.

[0286] It is preferable to use materials as the negative electrode active material that can react with carrier ions in a secondary battery, materials that can insert and remove carrier ions, materials that can undergo alloying reactions with metals that become carrier ions, and materials that can dissolve and precipitate metals that become carrier ions.

[0287] As the negative electrode active material, carbon materials such as graphite, easily graphitizable carbon, poorly graphitizable carbon, carbon nanotubes, carbon black, and graphene can be used.

[0288] Furthermore, as the negative electrode active material, a material having one or more elements selected from silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, and indium can be used.

[0289] Furthermore, silicon may be made to have lower resistance by adding impurity elements such as phosphorus, arsenic, boron, aluminum, and gallium.

[0290] For example, a material containing silicon is SiO x A material represented by (where x is preferably less than 2, and more preferably between 0.5 and 1.6) can be used.

[0291] As a material containing silicon, for example, a form having multiple crystal grains within a single particle can be used. For example, a form having one or more silicon crystal grains within a single particle can be used. Furthermore, the single particle may have silicon oxide surrounding the silicon crystal grain. Furthermore, the silicon oxide may be amorphous.

[0292] Furthermore, as silicon-containing compounds, for example, Li2SiO3 and Li4SiO4 can be used. Li2SiO3 and Li4SiO4 may be crystalline or amorphous, respectively.

[0293] The analysis of silicon-containing compounds can be performed using methods such as NMR, XRD, and Raman spectroscopy.

[0294] Furthermore, examples of materials that can be used as negative electrode active materials include oxides having one or more elements selected from titanium, niobium, tungsten, and molybdenum.

[0295] Multiple metals, materials, compounds, etc., as described above can be used in combination as the negative electrode active material.

[0296] The negative electrode active material in one aspect of the present invention may have fluorine in its surface layer. Having a halogen in the surface layer of the negative electrode active material can suppress a decrease in charge-discharge efficiency. Furthermore, it is believed that the reaction with the electrolyte on the surface of the active material is suppressed. In addition, the negative electrode active material in one aspect of the present invention may have at least a portion of its surface covered by a halogen-containing region. This region may, for example, be in the form of a film. Fluorine is particularly preferred as the halogen.

[0297] <Example of manufacturing method> An example of a method for preparing a negative electrode active material having halogens in its surface layer will be described.

[0298] The material can be prepared by mixing the material described above as a negative electrode active material as the first material and a halogen-containing compound as the second material, and then performing a heat treatment.

[0299] In addition to the first and second materials, a third material may be mixed in which a eutectic reaction occurs with the second material. Furthermore, it is preferable that the eutectic point resulting from the eutectic reaction is lower than at least one of the melting points of the second material and the third material. By lowering the melting point due to the eutectic reaction, the second and third materials can more easily cover the surface of the first material during heat treatment, which may improve the coverage.

[0300] Furthermore, by using materials containing metals whose ions function as carrier ions in the reaction of a secondary battery as the second and third materials, if the negative electrode active material contains such metals, they may be able to contribute to charging and discharging as carrier ions.

[0301] As a third material, for example, a material having oxygen and carbon can be used. For example, a carbonate can be used as a material having oxygen and carbon. Alternatively, for example, an organic compound can be used as a material having oxygen and carbon.

[0302] Alternatively, hydroxides may be used as a third material.

[0303] Carbonates and hydroxides are preferred because many of them are inexpensive and highly safe materials. Furthermore, carbonates and hydroxides are also preferred because they may form eutectic points with materials containing halogens.

[0304] Let's look at some more specific examples of the second and third materials. When lithium fluoride is used as the second material, and it is mixed with the first material and heated, the lithium fluoride may not coat the surface of the first material, and may instead aggregate on its own. In such cases, using a third material that undergoes a eutectic reaction with lithium fluoride may improve the coating properties on the surface of the first material.

[0305] When the first material is heated, a reaction with oxygen in the atmosphere may occur during heating, and an oxide film may be formed on the surface. In the production of a negative electrode active material according to one aspect of the present invention, heating can be performed at a lower temperature by causing a eutectic reaction between the halogen-containing material and the oxygen and carbon-containing material in the annealing process described later, thereby suppressing oxidation reactions on the surface.

[0306] Furthermore, when a carbon material is used as the first material, there is a concern that carbon dioxide will be generated during heating due to the reaction between the carbon material and oxygen in the atmosphere, resulting in a decrease in the weight of the first material and damage to the surface of the first material. In the production of the negative electrode active material according to one aspect of the present invention, heating can be performed at a low temperature, so even when a carbon material is used as the first material, weight loss, surface damage, etc., can be suppressed.

[0307] Here, graphite is prepared as the first material. Flecked graphite, spheroidized natural graphite, MCMB, etc., can be used as the graphite. Furthermore, the graphite may be coated on its surface with a low-crystallinity carbon material.

[0308] As a second material, a material containing a halogen is prepared. As the material containing a halogen, a halogen compound containing metal A1 can be used. As metal A1, one or more selected from lithium, magnesium, aluminum, sodium, potassium, calcium, barium, lanthanum, cerium, chromium, manganese, iron, cobalt, nickel, zinc, zirconium, titanium, vanadium, and niobium can be used. As the halogen compound, for example, a fluoride or chloride can be used. The halogen contained in the material containing a halogen is represented by element Z.

[0309] Here, we will use lithium fluoride as an example.

[0310] As a third material, a material containing oxygen and carbon is prepared. As the material containing oxygen and carbon, for example, a carbonate containing metal A2 can be used. As metal A2, for example, one or more selected from lithium, magnesium, aluminum, sodium, potassium, calcium, barium, lanthanum, cerium, chromium, manganese, iron, cobalt, and nickel can be used.

[0311] For this example, we will use lithium carbonate.

[0312] The first material, the second material, and the third material are mixed to obtain a mixture.

[0313] The second material and the third material are preferably mixed in the ratio (second material):(third material)=a1:(1-a1)[unit is moles], where a1 is preferably greater than 0.2 and less than 0.9, and more preferably between 0.3 and 0.8.

[0314] Furthermore, it is preferable to mix the first material and the second material in a ratio of (first material):(second material)=1:b1 [unit is moles], where b1 is preferably 0.001 or more and 0.2 or less.

[0315] Next, an annealing process is performed to obtain a negative electrode active material according to one embodiment of the present invention.

[0316] Performing the annealing process under a reducing atmosphere is preferable because it suppresses oxidation of the surface of the first material and the reaction between the first material and oxygen. For example, the reducing atmosphere can be a nitrogen atmosphere or a noble gas atmosphere. Alternatively, a mixture of two or more gases from nitrogen and noble gases may be used. Furthermore, heating may be performed under reduced pressure.

[0317] When the melting point of the second material is expressed as M2[°C], the heating temperature is preferably higher than (M2-550)[K] and lower than (M2+50)[K], and more preferably between (M2-400)[°C] and (M2)[°C].

[0318] Furthermore, solid-phase diffusion is more likely to occur in compounds at temperatures above the Tammann temperature. For example, the Tammann temperature is 0.757 times the melting point for oxides. Therefore, for example, it is preferable that the heating temperature is 0.757 times or higher than the eutectic point, or a temperature near it.

[0319] Furthermore, as a typical example of a halogen-containing material, lithium fluoride shows a rapid increase in evaporation rate above its melting point. Therefore, for example, it is preferable that the heating temperature be below the melting point of the halogen-containing material.

[0320] The eutectic point of the second material and the third material is M. 23 When expressed as [K], the heating temperature is, for example, (M 23 It is preferable that it is higher than (M2+50)[K] and lower than (M 23 It is preferable that the temperature is between (M2 + 20) [K] and (M 23 It is preferable that the temperature is between (M2 + 20) [K] and M 23 It is preferable that it is higher than [K] and lower than (M2+10)[K], (M 23 It is more preferable that the temperature is between 0.8 [K] and M2 [K], (M 23 It is more preferable that the temperature is between [K] and M2[K].

[0321] When lithium fluoride is used as the second material and lithium carbonate as the third material, the heating temperature is preferably, for example, higher than 350°C and lower than 900°C, more preferably between 390°C and 850°C, even more preferably between 520°C and 910°C, even more preferably between 570°C and 860°C, and even more preferably between 610°C and 860°C.

[0322] The heating time is preferably between 1 hour and 60 hours, and more preferably between 3 hours and 20 hours.

[0323] Figures 8A, 8B, 8C, and 8D show examples of cross-sections of the negative electrode active material 400.

[0324] In the negative electrode active material 400, the cross-section can be exposed by processing, allowing for observation and analysis of the cross-section.

[0325] The negative electrode active material 400 shown in Figure 8A has region 401 and region 402. Region 402 is located outside region 401. It is also preferable that region 402 is in contact with the surface of region 401.

[0326] Preferably, at least a portion of region 402 includes the surface of the negative electrode active material 400.

[0327] Region 401 is, for example, a region that includes the interior of the negative electrode active material 400.

[0328] Region 401 contains the first material described above. Region 402 contains, for example, element Z, oxygen, carbon, metal A1, and metal A2. Element Z is, for example, fluorine, chlorine, etc. Note that region 402 may not contain some of the elements among element Z, oxygen, carbon, metal A1, and metal A2. Alternatively, the concentration of some of the elements among element Z, oxygen, carbon, metal A1, and metal A2 in region 402 may be low and undetectable by analysis.

[0329] Region 402 is sometimes referred to as the surface layer of the negative electrode active material 400.

[0330] The negative electrode active material 400 can have various forms, such as a single particle, an aggregate of multiple particles, or a thin film.

[0331] Region 401 may consist of particles of the first material. Alternatively, region 401 may be an aggregate of multiple particles of the first material. Alternatively, region 401 may be a thin film of the first material.

[0332] Region 402 may be part of a particle. For example, region 402 may be the surface layer of a particle. Alternatively, region 402 may be part of a thin film. For example, region 402 may be the upper layer of a thin film.

[0333] Region 402 may be a coating layer formed on the surface of the particles.

[0334] Furthermore, region 402 may be a region having a bond between an element constituting the first material and element Z. For example, the surface of the first material may be modified with element Z or a functional group having element Z in region 402, or at the interface between region 401 and region 402. Therefore, in a negative electrode active material according to one aspect of the present invention, a bond between an element constituting the first material and element Z may be observed. For example, if the first material is graphite and element Z is fluorine, a CF bond may be observed. Also, as an example, if the first material has silicon and element Z is fluorine, a Si-F bond may be observed.

[0335] For example, when graphite is used as the first material, region 401 is the graphite particles and region 402 is the coating layer of the graphite particles. Alternatively, for example, when graphite is used as the first material, region 401 is the region including the interior of the graphite particles and region 402 is the surface layer of the graphite particles.

[0336] Region 402 may, for example, have a bond between element Z and carbon. It may also have a bond between element Z and metal A1. Furthermore, region 402 may, for example, have a carbonate group.

[0337] When analyzing the negative electrode active material 400 by X-ray photoelectron spectroscopy (XPS), it is preferable that element Z be detected, and preferably at a concentration of 1 atomic% or higher. In this case, the concentration of element Z can be calculated by taking the sum of the concentrations of carbon, oxygen, metal A1, metal A2, and element Z as 100%. Alternatively, the concentration of element Z may be calculated by adding the concentration of nitrogen to the concentrations of these elements as 100%. Furthermore, the concentration of element Z is, for example, 60 atomic% or less, or for example, 30 atomic% or less.

[0338] When analyzing the negative electrode active material 400 by XPS, it is preferable to detect a peak resulting from the bonding of element Z with carbon. Alternatively, a peak resulting from the bonding of element Z with metal A1 may also be detected.

[0339] When element Z is fluorine and metal A1 is lithium, in the XPS F1s spectrum, the peak suggesting carbon-fluorine bonding (hereinafter referred to as peak F2) is observed near 688 eV, for example, in an energy range higher than 686.5 eV and lower than 689.5 eV, while the peak suggesting lithium-fluorine bonding (hereinafter referred to as peak F1) is observed near 685 eV, for example, in an energy range higher than 683.5 eV and lower than 686.5 eV. Furthermore, the intensity of peak F2 is preferably greater than 0.1 times and less than 10 times the intensity of peak F1, for example, between 0.3 times and 3 times.

[0340] When analyzing the negative electrode active material 400 by XPS, it is preferable to observe peaks corresponding to carbonates or carbonate groups. In the XPS C1s spectrum, peaks corresponding to carbonates or carbonate groups are observed in the energy range around 290 eV, for example, higher than 288.5 eV and lower than 291.5 eV.

[0341] Furthermore, when analyzing the negative electrode active material 400 by XRD, spectra originating from Li2O with a space group represented as Fm-3m may be observed.

[0342] In the example shown in Figure 8B, region 401 has an area that is not covered by region 402. Also, in the example shown in Figure 8C, region 402 that covers the recessed area on the surface of region 401 is thicker.

[0343] In the negative electrode active material 400 shown in Figure 8D, region 401 has region 401a and region 401b. Region 401a is a region that includes the interior of region 401, and region 401b is located outside region 401a. It is also preferable that region 401b is in contact with region 402.

[0344] Region 401b is the surface layer of region 401.

[0345] Region 401b contains one or more elements present in region 402, such as element Z, oxygen, carbon, metal A1, and metal A2. Furthermore, in region 401b, the elements present in region 402, such as element Z, oxygen, carbon, metal A1, and metal A2, may have a concentration gradient in which the concentration gradually decreases from the surface or near the surface towards the interior.

[0346] The concentration of element Z in region 401b is higher than the concentration of element Z in region 401a. Furthermore, it is preferable that the concentration of element Z in region 401b is lower than the concentration of element Z in region 402.

[0347] The oxygen concentration in region 401b may be higher than that in region 401a. Conversely, the oxygen concentration in region 401b may be lower than that in region 402.

[0348] When measuring a negative electrode active material according to one embodiment of the present invention by energy-dispersive X-ray analysis using a scanning electron microscope, it is preferable that element Z is detected. Furthermore, it is preferable that the concentration of element Z is, for example, 10 atomic% to 70 atomic% when the sum of the concentrations of element Z and oxygen is 100 atomic%.

[0349] Region 402 has, for example, a thickness of 50 nm or less, more preferably 1 nm to 35 nm, and even more preferably 5 nm to 20 nm.

[0350] Region 401b has, for example, a thickness of 50 nm or less, more preferably 1 nm to 35 nm, and even more preferably 5 nm to 20 nm.

[0351] When fluorine is used as element Z and lithium as metals A1 and A2, region 402 may have a region covered by a region containing lithium fluoride and a region covered by a region containing lithium carbonate. Furthermore, since region 402 does not hinder the insertion and removal of lithium, an excellent secondary battery can be realized without reducing the output characteristics of the secondary battery.

[0352] This embodiment can be appropriately combined with descriptions of other embodiments.

[0353] (Embodiment 2) In this embodiment, an example of a secondary battery according to one aspect of the present invention will be described using Figure 9. The secondary battery has an outer casing (not shown), a positive electrode 503, a negative electrode 506, a separator 507, and an electrolyte 508 in which a lithium salt or the like is dissolved. The separator 507 is provided between the positive electrode 503 and the negative electrode 506.

[0354] A positive electrode according to one aspect of the present invention has a positive electrode active material layer. The positive electrode active material layer has a positive electrode active material. The positive electrode active material layer may also have a conductive agent, a binder, etc. Furthermore, a positive electrode according to one aspect of the present invention preferably has a current collector, and it is preferable that the positive electrode active material layer is provided on the current collector.

[0355] In Figure 9, the positive electrode 503 has a positive electrode active material layer 502 and a positive electrode current collector 501. The positive electrode active material layer 502 has a positive electrode active material 561, a conductive additive, and a binder. Figure 9B is an enlarged view of the region 502a shown in Figure 9A. Figure 9B shows an example in which acetylene black 553 and graphene 554 are used as conductive agents.

[0356] A negative electrode according to one aspect of the present invention has a negative electrode active material layer. The negative electrode active material layer has a negative electrode active material. The negative electrode active material layer may also have a conductive agent, a binder, etc. Furthermore, a negative electrode according to one aspect of the present invention preferably has a current collector, and it is preferable that the negative electrode active material layer is provided on the current collector.

[0357] The negative electrode 506 has a negative electrode active material layer 505 and a negative electrode current collector 504. The negative electrode active material layer 505 also has a negative electrode active material 563, a conductive agent, and a binder. Figure 9D is an enlarged view of the region 505a shown in Figure 9A. Figure 9D shows an example in which acetylene black 556 and graphene 557 are used as the conductive agent.

[0358] As the conductive agent, carbon materials, metal materials, or conductive ceramic materials can be used. Furthermore, fibrous materials may be used as the conductive agent. The content of the conductive agent relative to the total amount of the active material layer is preferably 1 wt% to 10 wt%, and more preferably 1 wt% to 5 wt%.

[0359] Conductive agents can form an electrical conduction network within the active material layer. Conductive agents can maintain electrical conduction paths between active materials. By adding conductive agents to the active material layer, an active material layer with high electrical conductivity can be realized.

[0360] Graphene compounds can be used as conductive agents. Alternatively, natural graphite, artificial graphite such as mesocarbon microbeads, and carbon fibers can also be used as conductive agents.

[0361] As carbon fibers, for example, mesophase pitch carbon fibers and isotropic pitch carbon fibers can be used. Carbon nanofibers and carbon nanotubes can also be used as carbon fibers. Carbon nanotubes can be fabricated, for example, by vapor deposition. As conductive agents, carbon materials such as carbon black (acetylene black (AB), etc.), graphite particles, graphene, and fullerene can be used. Furthermore, one or more materials selected from metal powders, metal fibers, and conductive ceramic materials such as copper, nickel, aluminum, silver, and gold can be used.

[0362] [Graphene compounds] In this specification, the term "graphene compound" includes multilayer graphene, multigraphene, graphene oxide, multilayer graphene oxide, multigraphene oxide, reduced graphene oxide, reduced multilayer graphene oxide, reduced multigraphene oxide, graphene quantum dots, etc. A graphene compound is defined as a material having carbon atoms, having a plate-like or sheet-like shape, and possessing a two-dimensional structure formed by a six-membered carbon ring. This two-dimensional structure formed by the six-membered carbon ring may also be called a carbon sheet. Graphene compounds may have functional groups. Furthermore, graphene compounds preferably have a bent shape. Graphene compounds may also be rolled up to resemble carbon nanofibers.

[0363] The materials described above can be used in combination as conductive agents.

[0364] In this specification, graphene oxide refers to a material having carbon and oxygen, having a sheet-like structure, and possessing functional groups, particularly epoxy groups, carboxyl groups, or hydroxyl groups.

[0365] In this specification, reduced graphene oxide refers to a material having carbon and oxygen, having a sheet-like shape, and possessing a two-dimensional structure formed by a six-membered carbon ring. It may also be called a carbon sheet. Reduced graphene oxide can function as a single sheet, but multiple sheets may be stacked. It is preferable that reduced graphene oxide has a portion where the carbon concentration is greater than 80 atomic%, and the oxygen concentration is between 2 atomic% and 15 atomic%. By having such carbon and oxygen concentrations, it can function as a highly conductive material even in small amounts. Furthermore, it is preferable that the intensity ratio of the G band to the D band in the Raman spectrum of reduced graphene oxide is 1 or greater. Reduced graphene oxide with such an intensity ratio can function as a highly conductive material even in small amounts.

[0366] In the longitudinal section of the active material layer, sheet-like graphene compounds are dispersed approximately uniformly within the internal region of the active material layer. Multiple graphene compounds are formed to partially cover multiple granular active materials or to adhere to the surfaces of multiple granular active materials, and thus are in surface contact with each other.

[0367] Here, multiple graphene compounds can bond together to form a mesh-like graphene compound sheet (hereinafter referred to as a graphene compound net or graphene net). When the active material is coated with the graphene net, the graphene net can also function as a binder that binds the active materials together. Therefore, the amount of binder can be reduced or eliminated, thereby improving the ratio of active material to electrode volume and electrode weight. In other words, the charge and discharge capacity of the secondary battery can be increased.

[0368] Here, it is preferable to use graphene oxide as the graphene compound, mix it with the active material to form an active material layer, and then reduce it. In other words, it is preferable that the completed active material layer has reduced graphene oxide. By using graphene oxide, which has extremely high dispersibility in polar solvents, for the formation of the graphene compound, the graphene compound can be dispersed approximately uniformly within the internal region of the active material layer. By volatilizing and removing the solvent from the dispersion medium containing the uniformly dispersed graphene oxide and reducing the graphene oxide, the graphene compounds remaining in the active material layer partially overlap and are dispersed to the extent that they are in surface contact with each other, thereby forming three-dimensional conductive paths. The reduction of graphene oxide may be carried out, for example, by heat treatment or by using a reducing agent. Unlike granular conductive agents such as acetylene black, which make point contact with the active material, the graphene compound enables surface contact with low contact resistance, so it is possible to improve electrical conductivity in the electrode with a smaller amount than ordinary conductive agents. Therefore, the ratio of the active material in the active material layer can be increased. This makes it possible to increase the discharge capacity of the secondary battery.

[0369] [Binder] As a binder, it is preferable to use rubber materials such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, or ethylene-propylene-diene copolymer. Fluororubber can also be used as a binder.

[0370] Furthermore, it is preferable to use a water-soluble polymer as the binder. Examples of water-soluble polymers include polysaccharides. One or more polysaccharides can be selected from cellulose derivatives such as carboxymethylcellulose (CMC), methylcellulose, ethylcellulose, hydroxypropylcellulose, diacetylcellulose, and regenerated cellulose, as well as starch. It is even more preferable to use these water-soluble polymers in combination with the aforementioned rubber material.

[0371] Alternatively, 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, or nitrocellulose as the binder.

[0372] You may use a combination of several of the binders mentioned above.

[0373] For example, a material with particularly excellent viscosity-modifying properties may be used in combination with other materials. For instance, rubber materials have excellent adhesive and elastic properties, but their viscosity can be difficult to adjust when mixed with a solvent. In such cases, it is preferable to mix them with a material with particularly excellent viscosity-modifying properties. As a material with particularly excellent viscosity-modifying properties, a water-soluble polymer may be used. As a water-soluble polymer with particularly excellent viscosity-modifying properties, one or more selected from the aforementioned polysaccharides, such as carboxymethylcellulose (CMC), methylcellulose, ethylcellulose, hydroxypropylcellulose, and diacetylcellulose, as well as cellulose derivatives such as regenerated cellulose, and starch can be used.

[0374] Furthermore, cellulose derivatives such as carboxymethylcellulose can be made more effective as viscosity modifiers by increasing their solubility, for example, by using salts such as sodium or ammonium salts of carboxymethylcellulose. Increased solubility also improves the dispersibility of the active material and other components when preparing electrode slurries. In this specification, cellulose and cellulose derivatives used as electrode binders include their salts.

[0375] Water-soluble polymers stabilize viscosity by dissolving in water and can stably disperse the active material and other materials used as binders, such as styrene-butadiene rubber, in aqueous solutions. Furthermore, because they possess functional groups, they are expected to be easily and stably adsorbed onto the surface of the active material. Additionally, cellulose derivatives such as carboxymethylcellulose often contain functional groups such as hydroxyl groups and carboxyl groups, and because of these functional groups, the polymers interact with each other, allowing them to broadly cover the surface of the active material.

[0376] When a binder covers or is in contact with the surface of the active material, it is expected to act as a passivation film, suppressing the decomposition of the electrolyte. Here, a passivation film is a film that does not conduct electricity, or has extremely low electrical conductivity. For example, when a passivation film is formed on the surface of the active material, the decomposition of the electrolyte can be suppressed at the battery reaction potential. Furthermore, it is even more desirable for the passivation film to suppress electrical conductivity while still allowing lithium ions to conduct.

[0377] The active material layer can be prepared by mixing the active material, binder, conductive agent, and solvent to create a slurry, forming the slurry on a current collector, and then volatilizing the solvent.

[0378] The solvent used in the slurry is preferably a polar solvent. For example, one or more of the following can be used: water, methanol, ethanol, acetone, tetrahydrofuran (THF), dimethylformamide (DMF), N-methylpyrrolidone (NMP), and dimethyl sulfoxide (DMSO).

[0379] [Current collector] As the positive electrode current collector and the negative electrode current collector, materials having high conductivity and not alloying with carrier ions such as lithium, including metals such as stainless steel, gold, platinum, zinc, iron, copper, aluminum and titanium, and alloys thereof can be used. Further, an aluminum alloy added with elements that improve heat resistance such as silicon, titanium, neodymium, scandium and molybdenum can be used. Alternatively, the current collector may be formed of a metal element that reacts with silicon to form silicide. Examples of metal elements that react with silicon to form silicide include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt and nickel. For the current collector, shapes such as a sheet shape, a mesh shape, a punched metal shape and an expanded metal shape can be appropriately used. The current collector preferably has a thickness of 10 μm or more and 30 μm or less.

[0380] Note that the negative electrode current collector is preferably made of a material that does not alloy with carrier ions such as lithium.

[0381] As the current collector, a titanium compound may be provided by being laminated on the above-mentioned metal element. Examples of the titanium compound include titanium nitride, titanium oxide, titanium nitride in which part of nitrogen is substituted with oxygen, titanium oxide in which part of oxygen is substituted with nitrogen, and titanium oxynitride (TiO x N y , 0<x<2, 0<y<1), or a mixture or laminate of two or more thereof can be used. Among them, titanium nitride is particularly preferable because it has high conductivity and a high function of suppressing oxidation. By providing the titanium compound on the surface of the current collector, for example, the reaction between the material contained in the active material layer formed on the current collector and the metal is suppressed. When the active material layer contains a compound having oxygen, the oxidation reaction between the metal element and oxygen can be suppressed. For example, when aluminum is used as the current collector and the active material layer is formed using graphene oxide described later, the oxidation reaction between oxygen contained in graphene oxide and aluminum may be a concern. In such a case, by providing the titanium compound on aluminum, the oxidation reaction between the current collector and graphene oxide can be suppressed.

[0382] Graphene or graphene compounds can be used as graphene 554 and graphene 557.

[0383] In this specification, the term "graphene compound" includes multilayer graphene, multigraphene, graphene oxide, multilayer graphene oxide, multigraphene oxide, reduced graphene oxide, reduced multilayer graphene oxide, reduced multigraphene oxide, graphene quantum dots, etc. A graphene compound is defined as a material having carbon atoms, having a plate-like or sheet-like shape, and possessing a two-dimensional structure formed by a six-membered carbon ring. This two-dimensional structure formed by the six-membered carbon ring may also be called a carbon sheet. Graphene compounds may have functional groups. Furthermore, graphene compounds preferably have a bent shape. Graphene compounds may also be rolled up to resemble carbon nanofibers.

[0384] In one embodiment of the present invention, graphene or a graphene compound can function as a conductive agent in the positive or negative electrode. Multiple graphene particles or graphene compounds can form three-dimensional conductive paths within the positive or negative electrode, thereby enhancing the conductivity of the positive or negative electrode. Furthermore, since graphene or a graphene compound can adhere to particles within the positive or negative electrode, it can suppress particle collapse within the positive or negative electrode, thereby increasing the strength of the positive or negative electrode. Because graphene or a graphene compound has a thin, sheet-like shape, it can form excellent conductive paths even with a small volume within the positive or negative electrode, thus increasing the volume of active material within the positive or negative electrode. Therefore, the capacity of the secondary battery can be increased.

[0385] [Separator] The separator 507 can be made of, for example, paper, nonwoven fabric, glass fiber, ceramics, etc. Alternatively, it can be made of nylon (polyamide), vinylon (polyvinyl alcohol-based fiber), polyester, acrylic, polyolefin, polyurethane, polypropylene, polyethylene, etc. It is preferable that the separator be processed into an envelope shape and arranged to enclose either the positive or negative electrode.

[0386] Furthermore, a polymer film made of, for example, polypropylene, polyethylene, or polyimide can be used for the separator 507. Polyimide has good wettability with ionic liquids and may be a more preferable material for the separator 507.

[0387] Polymer films containing polypropylene, polyethylene, etc., can be manufactured by dry or wet methods. The dry method involves stretching a polymer film containing polypropylene, polyethylene, polyimide, etc., while heating it, creating gaps between crystals and forming fine pores. The wet method involves mixing a solvent into the resin beforehand, forming it into a film, and then extracting the solvent to create pores.

[0388] Figure 9C (left) shows an enlarged view of region 507a, as an example of separator 507 (fabricated by a wet process), as shown in Figure 9A. In this example, a structure with multiple pores 582 is shown in the polymer film 581. Figure 9C (right) shows an enlarged view of region 507b, as another example of separator 507 (fabricated by a dry process). In this example, a structure with multiple pores 585 is shown in the polymer film 584.

[0389] The diameter of the pores in the separator may differ between the surface of the side facing the positive electrode and the surface of the side facing the negative electrode after charging and discharging. In this specification, the surface of the separator is preferably, for example, an area within 5 μm, more preferably within 3 μm, from the surface.

[0390] The separator may have a multilayer structure. For example, a structure in which two types of polymer materials are layered may be used.

[0391] Furthermore, structures can be used in which a ceramic material, fluorine material, polyamide material, or a mixture thereof is coated onto a polymer film, such as polypropylene, polyethylene, or polyimide. Alternatively, structures can be used in which a ceramic material, fluorine material, polyamide material, or a mixture thereof is coated onto a nonwoven fabric. Polyimide is preferable as a coating material because of its good wettability with ionic liquids.

[0392] Examples of fluorine-based materials that can be used include PVDF and polytetrafluoroethylene.

[0393] Examples of polyamide materials that can be used include nylon and aramid (meta-aramid, para-aramid).

[0394] [Exterior] The outer casing of the secondary battery can be made of one or more materials selected from metal materials such as aluminum and resin materials. A film-like outer casing can also be used. As a film, for example, a three-layer film can be used, in which a highly flexible metal thin film such as aluminum, stainless steel, copper, or nickel is provided on a film made of materials such as polyethylene, polypropylene, polycarbonate, ionomer, or polyamide, and an insulating synthetic resin film such as a polyamide resin or polyester resin is provided on the metal thin film as the outer surface of the outer casing.

[0395] This embodiment can be used in appropriate combination with other embodiments.

[0396] (Embodiment 3) This embodiment describes a method for manufacturing a secondary battery.

[0397] <Method 1 for manufacturing laminated rechargeable batteries> Here, an example of a method for manufacturing a laminate-type secondary battery, whose external view is shown in Figures 10A and 10B, will be explained using Figures 11A and 11B and Figures 12A and 12B. The secondary battery 500 shown in Figures 10A and 10B has a positive electrode 503, a negative electrode 506, a separator 507, an outer casing 509, a positive electrode lead electrode 510, and a negative electrode lead electrode 511. As for the cross-sectional structure of the laminate-type secondary battery shown in Figure 10A, etc., for example, a structure in which the positive electrode, separator, and negative electrode are stacked and enclosed by an outer casing can be used, as shown in Figure 15, which will be described later.

[0398] First, prepare the positive electrode 503, the negative electrode 506, and the separator 507. Figure 11A shows an example of the positive electrode 503 and the negative electrode 506. The positive electrode 503 has a positive electrode active material layer 502 on a positive electrode current collector 501. Preferably, the positive electrode 503 also has a tab region where the positive electrode current collector 501 is exposed. The negative electrode 506 has a negative electrode active material layer 505 on a negative electrode current collector 504. Preferably, the negative electrode 506 also has a tab region where the negative electrode current collector 504 is exposed.

[0399] Next, the negative electrode 506, separator 507, and positive electrode 503 are stacked. Figure 11B shows the stacked negative electrode 506, separator 507, and positive electrode 503. Here, an example using 5 sets of negative electrodes and 4 sets of positive electrodes is shown. This can also be called a laminate consisting of a negative electrode, separator, and positive electrode.

[0400] Next, the tab regions of the positive electrode 503 are joined together, and the positive electrode lead electrode 510 is joined to the tab region of the outermost positive electrode. For joining, ultrasonic welding, for example, may be used. Similarly, the tab regions of the negative electrode 506 are joined together, and the negative electrode lead electrode 511 is joined to the tab region of the outermost negative electrode.

[0401] Next, the negative electrode 506, separator 507, and positive electrode 503 are placed on the outer casing 509.

[0402] Next, as shown in Figure 12A, the outer casing 509 is bent at the portion indicated by the dashed line. Then, the outer periphery of the outer casing 509 is joined. For joining, for example, heat sealing can be used. At this time, a region that is not joined (hereinafter referred to as the inlet 516) is provided on a part (or one side) of the outer casing 509 so that the electrolyte 508 can be inserted later.

[0403] Next, as shown in Figure 12B, the electrolyte 508 is introduced into the inside of the outer casing 509 through the inlet 516 provided in the outer casing 509. It is preferable to introduce the electrolyte 508 under a reduced pressure atmosphere or an inert atmosphere. Finally, the inlet 516 is joined. In this way, a laminate-type secondary battery 500 can be manufactured.

[0404] In the above example, the positive lead electrode 510 and the negative lead electrode 511 were led out of the casing from the same side to create the secondary battery 500 shown in Figure 10A. Alternatively, the secondary battery 500 shown in Figure 10B can be created by leading the positive lead electrode 510 and the negative lead electrode 511 out of the casing from opposite sides.

[0405] <Method for manufacturing laminated rechargeable batteries, part 2> Next, an example of a method for manufacturing a laminate-type secondary battery 600, whose external view is shown in Figure 13, will be explained using Figures 14, 15, 16A to 16D, and 17A to 17F. The secondary battery 600 shown in Figure 13 has a positive electrode 503, a negative electrode 506, a separator 507, an outer casing 509, a positive electrode lead electrode 510, and a negative electrode lead electrode 511. The outer casing 509 is sealed in region 514.

[0406] A laminate-type secondary battery 600 can be manufactured, for example, using the manufacturing apparatus shown in Figure 14. The manufacturing apparatus 570 shown in Figure 14 has a component input chamber 571, a transport chamber 572, a processing chamber 573, and a component removal chamber 576. Each chamber can be configured to be connected to various exhaust mechanisms depending on the application. Each chamber can also be configured to be connected to various gas supply mechanisms depending on the application. To suppress the entry of impurities into the manufacturing apparatus 570, it is preferable to supply an inert gas into the manufacturing apparatus 570. It is preferable that the gas supplied to the inside of the manufacturing apparatus 570 is purified to a high degree by a gas purifier before being introduced into the manufacturing apparatus 570. The component input chamber 571 is a chamber for inputting positive electrodes, separators, negative electrodes, outer casings, etc. into the transport chamber 572, processing chamber 573, etc., within the manufacturing apparatus 570. The transport chamber 572 has a transport mechanism 580. The processing chamber 573 has a stage and an electrolyte dropping mechanism. The component removal room 576 is a room for removing the manufactured secondary batteries from the manufacturing apparatus 570.

[0407] The procedure for manufacturing the laminate-type rechargeable battery 600 is as follows:

[0408] First, the outer casing 509b is placed on the stage 591 of the processing chamber 573, a frame-shaped resin layer 513 is formed on the outer casing 509b, and then the positive electrode 503 is placed on the outer casing 509b (Figures 16A and 16B). Next, the electrolyte 515a is dropped onto the positive electrode 503 from the nozzle 594 (Figures 16C and 16D). Figure 16D is a cross-section corresponding to the dashed line AB in Figure 16C. Note that the stage 591 may be omitted in some cases to avoid making the drawings too complex. Any of the dropping methods can be used, for example, the dispensing method, the spray method, or the inkjet method. In addition, the ODF (One Drop Fill) method can be used for dropping the electrolyte.

[0409] By moving the nozzle 594, the electrolyte 515a can be dropped onto the entire surface of the positive electrode 503. Alternatively, the electrolyte 515a may be dropped onto the entire surface of the positive electrode 503 by moving the stage 591.

[0410] It is preferable that the electrolyte is dropped from a position where the shortest distance from the bottom surface to the droplet is greater than 0 mm and less than or equal to 1 mm.

[0411] Furthermore, it is preferable to adjust the viscosity of the electrolyte being dispensed from the nozzle as appropriate. If the total viscosity of the electrolyte is within the range of 0.3 mPa·s to 1000 mPa·s at room temperature (25°C), it can be dispensed from the nozzle.

[0412] Furthermore, since the viscosity of the electrolyte changes with its temperature, it is preferable to appropriately adjust the temperature of the electrolyte being added dropwise. The temperature of the electrolyte is preferably above its melting point, below its boiling point, or below its flash point.

[0413] Next, the separator 507 is placed on the positive electrode 503 so as to overlap the entire surface of the positive electrode 503 (Figure 17A). Then, the electrolyte 515b is dropped onto the separator 507 using the nozzle 594 (Figure 17B). After that, the negative electrode 506 is placed on the separator 507 (Figure 17C). The negative electrode 506 is placed so as to overlap the separator 507 so that it does not protrude when viewed from above. Then, the electrolyte 515c is dropped onto the negative electrode 506 using the nozzle 594 (Figure 17D). After that, the laminate 512 shown in Figure 15 can be fabricated by further stacking the laminate of the positive electrode 503, separator 507, and negative electrode 506. Next, the positive electrode 503, separator 507, and negative electrode 506 are sealed by the outer casings 509a and 509b (Figures 17E and 17F).

[0414] In Figure 15, the positive and negative electrodes are arranged such that the positive electrode active material layer and the negative electrode active material layer are sandwiched between a separator. In one embodiment of the present invention, it is preferable that the negative electrode active material layer has few or no regions that do not face the positive electrode active material layer. When the electrolyte is an ionic liquid and the negative electrode active material layer has regions that do not face the positive electrode active material layer, the charge and discharge efficiency of the secondary battery may decrease. Therefore, in one embodiment of the present invention, it is preferable that the edges of the positive electrode active material layer and the edges of the negative electrode active material layer are aligned as much as possible. Therefore, it is preferable that the areas of the positive electrode active material layer and the negative electrode active material layer are the same when viewed from above. Alternatively, it is preferable that the edges of the positive electrode active material layer are located inward from the edges of the negative electrode active material layer.

[0415] By arranging multiple laminates 512 on the outer casing 509b, multi-faceted processing can be achieved. After sealing the outer casings 509a and 509b with a region 514 so that each laminate 512 surrounds the active material layer, multiple secondary batteries can be individually separated by dividing them outside the region 514.

[0416] During sealing, first, a frame-shaped resin layer 513 is formed on the outer casing 509b. Next, at least a portion of the resin layer 513 is cured by irradiating it with light under reduced pressure. Then, sealing is performed in region 514 by thermocompression bonding or welding under atmospheric pressure. Alternatively, sealing may be performed only by thermocompression bonding or welding without the above-mentioned light irradiation sealing.

[0417] Although Figure 13 shows an example where the outer casing 509 is sealed on all four sides (sometimes called a four-sided seal), it may also be sealed on three sides (sometimes called a three-sided seal) as shown in Figures 10A and 10B.

[0418] Through the above process, a laminate-type secondary battery 600 can be manufactured.

[0419] <Other secondary batteries and their manufacturing methods 1> Figure 18 shows an example of a cross-sectional view of a laminate according to one aspect of the present invention. The laminate 550 shown in Figure 18 is manufactured by placing a single separator between the positive and negative electrodes while bending it.

[0420] In the laminate 550, a single separator 507 is folded multiple times so that it is sandwiched between the positive electrode active material layer 502 and the negative electrode active material layer 505. In Figure 18, since six layers each of positive electrodes 503 and negative electrodes 506 are laminated, the separator 507 is folded at least five times. In addition to being provided sandwiched between the positive electrode active material layer 502 and the negative electrode active material layer 505, the separator 507 may also be further folded so that multiple positive electrodes 503 and negative electrodes 506 are bundled together with tape or the like.

[0421] In one embodiment of the present invention, a method for manufacturing a secondary battery, the electrolyte can be dropped onto the positive electrode 503 after it has been placed. Similarly, the electrolyte can be dropped onto the negative electrode 506 after it has been placed. Furthermore, in one embodiment of the present invention, the electrolyte can be dropped onto the separator 507 before it has been folded, or after the separator 507 has been folded and placed on top of the negative electrode 506 or the positive electrode 503. By dropping the electrolyte onto at least one of the negative electrode 506, the separator 507, and the positive electrode 503, the electrolyte can be impregnated into the negative electrode 506, the separator 507, or the positive electrode 503.

[0422] The secondary battery 970 shown in Figure 19A has a laminate 972 inside the housing 971. Terminals 973b and 974b are electrically connected to the laminate 972. At least a portion of terminal 973b and at least a portion of terminal 974b are exposed to the outside of the housing 971.

[0423] As the laminate 972, a structure in which a positive electrode, a negative electrode, and a separator are laminated can be applied. Alternatively, as the laminate 972, a structure in which the positive electrode, negative electrode, and separator are wound can be applied, and so on.

[0424] For example, as the laminate 972, a laminate having a structure in which the separator is folded back, as shown in Figure 18, can be used.

[0425] An example of a method for fabricating the laminate 972 will be explained using Figures 19B and 19C.

[0426] First, as shown in Figure 19B, a strip-shaped separator 976 is placed on top of the positive electrode 975a, and the negative electrode 977a is placed on top of the positive electrode 975a with the separator 976 in between. Then, the separator 976 is folded back and placed on top of the negative electrode 977a. Next, as shown in Figure 19C, the positive electrode 975b is placed on top of the negative electrode 977a with the separator 976 in between. In this way, by folding back the separator and arranging the positive and negative electrodes in order, a laminate 972 can be manufactured. A structure including a laminate manufactured in this way is sometimes called a "zigzag structure".

[0427] Next, an example of a method for manufacturing the secondary battery 970 will be explained using Figures 20A to 20C.

[0428] First, as shown in Figure 20A, the positive lead electrode 973a is electrically connected to the positive electrode of the laminate 972. Specifically, for example, tab regions can be provided on each of the positive electrodes of the laminate 972, and each tab region and the positive lead electrode 973a can be electrically connected by welding or the like. In addition, the negative lead electrode 974a is electrically connected to the negative electrode of the laminate 972.

[0429] One laminate 972 may be placed inside the housing 971, or multiple laminates 972 may be placed inside. Figure 20B shows an example in which two sets of laminates 972 are prepared.

[0430] Next, as shown in Figure 20C, the prepared laminate 972 is placed inside the housing 971, terminals 973b and 974b are attached, and the housing 971 is sealed. It is preferable to electrically connect the conductor 973c to each positive lead electrode 973a of the multiple laminates 972. It is also preferable to electrically connect the conductor 974c to each negative lead electrode 974a of the multiple laminates 972. Terminal 973b is electrically connected to the conductor 973c, and terminal 974b is electrically connected to the conductor 974c. The conductor 973c may have a conductive region and an insulating region. Similarly, the conductor 974c may have a conductive region and an insulating region.

[0431] A metal material (such as aluminum) can be used for the housing 971. Furthermore, when a metal material is used for the housing 971, it is preferable to coat the surface with resin or the like. Alternatively, a resin material can be used for the housing 971.

[0432] It is preferable to provide a safety valve or overcurrent protection element in the housing 971. The safety valve is a valve that releases gas when the inside of the housing 971 reaches a predetermined pressure in order to prevent the battery from rupturing.

[0433] <Other secondary batteries and their manufacturing methods 2> Figure 21C shows an example of a cross-sectional view of a secondary battery according to another embodiment of the present invention. The secondary battery 560 shown in Figure 21C is manufactured using the laminate 130 shown in Figure 21A and the laminate 131 shown in Figure 21B. Note that in Figure 21C, the laminate 130, laminate 131, and separator 507 are shown in part for clarity.

[0434] As shown in Figure 21A, the laminate 130 is constructed by stacking a positive electrode 503 having positive electrode active material layers on both sides of a positive electrode current collector, a separator 507, a negative electrode 506 having negative electrode active material layers on both sides of a negative electrode current collector, a separator 507, and a positive electrode 503 having positive electrode active material layers on both sides of a positive electrode current collector in this order.

[0435] As shown in Figure 21B, the laminate 131 is constructed by stacking a negative electrode 506 having negative electrode active material layers on both sides of the negative electrode current collector, a separator 507, a positive electrode 503 having positive electrode active material layers on both sides of the positive electrode current collector, a separator 507, and a negative electrode 506 having negative electrode active material layers on both sides of the negative electrode current collector in this order.

[0436] A method for manufacturing a secondary battery according to one aspect of the present invention can be applied when manufacturing a laminate. Specifically, when stacking the negative electrode 506, separator 507, and positive electrode 503 to manufacture the laminate, an electrolyte is dropped onto at least one of the negative electrode 506, separator 507, and positive electrode 503. By dropping multiple drops of the electrolyte, the negative electrode 506, separator 507, or positive electrode 503 can be impregnated with the electrolyte.

[0437] As shown in Figure 21C, the multiple laminates 130 and the multiple laminates 131 are covered by a wound separator 507.

[0438] Furthermore, in a method for manufacturing a secondary battery according to one aspect of the present invention, the electrolyte can be dropped onto the laminate 130 after the laminate 130 has been placed. Similarly, the electrolyte can be dropped onto the laminate 131 after the laminate 131 has been placed. In addition, the electrolyte can be dropped onto the separator 507 before it is folded, or after the separator 507 has been folded and stacked with the laminate. By dropping multiple drops of the electrolyte, the laminate 130, laminate 131, or separator 507 can be impregnated with the electrolyte.

[0439] <Other secondary batteries and their manufacturing methods 3> Another embodiment of the present invention, a secondary battery, will be described with reference to Figures 22 and 23. The secondary battery shown here can be called a wound-type secondary battery, etc.

[0440] The secondary battery 913 shown in Figure 22A has a wound body 950 with terminals 951 and 952 inside a housing 930. The wound body 950 is immersed in an electrolyte inside the housing 930. Terminal 952 is in contact with the housing 930, while terminal 951 is not in contact with the housing 930 due to the use of an insulating material or the like. In Figure 22A, the housing 930 is shown separated for convenience, but in reality, the wound body 950 is covered by the housing 930, and terminals 951 and 952 extend outside the housing 930. The housing 930 can be made of a metal material (e.g., aluminum) or a resin material.

[0441] Furthermore, as shown in Figure 22B, the housing 930 shown in Figure 22A may be formed from multiple materials. For example, in the secondary battery 913 shown in Figure 22B, housing 930a and housing 930b are bonded together, and a winding body 950 is provided in the area surrounded by housing 930a and housing 930b.

[0442] For the housing 930a, an insulating material such as organic resin can be used. In particular, by using a material such as organic resin on the surface where the antenna is formed, shielding of the electric field by the secondary battery 913 can be suppressed. If the shielding of the electric field by housing 930a is small, the antenna may be placed inside housing 930a. For housing 930b, for example, a metal material can be used.

[0443] Furthermore, the structure of the wound body 950 is shown in Figure 22C. The wound body 950 has a negative electrode 931, a positive electrode 932, and a separator 933. The wound body 950 is a wound body in which the negative electrode 931 and the positive electrode 932 are stacked on top of each other with the separator 933 in between, and the stacked sheets are wound up. Note that multiple stacks of the negative electrode 931, positive electrode 932, and separator 933 may be stacked.

[0444] In a method for manufacturing a secondary battery according to one aspect of the present invention, when stacking the negative electrode 931, separator 933, and positive electrode 932, an electrolyte is dropped onto at least one of the negative electrode 931, separator 933, and positive electrode 932. In other words, it is preferable to drop the electrolyte before rolling up the stacked sheet. By dropping multiple drops of the electrolyte, the negative electrode 931, separator 933, or positive electrode 932 can be impregnated with the electrolyte.

[0445] Alternatively, the secondary battery 913 may have a wound body 950a as shown in Figure 23A. The wound body 950a shown in Figure 23A has a negative electrode 931, a positive electrode 932, and a separator 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.

[0446] The separator 933 has a wider width than 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. Furthermore, it is preferable from a safety standpoint that the negative electrode active material layer 931a is wider than the positive electrode active material layer 932a. In addition, a wound body 950a of this shape is preferable because it offers good safety and productivity.

[0447] As shown in Figure 23B, the negative terminal 931 is electrically connected to terminal 951. Terminal 951 is electrically connected to terminal 911a. The positive terminal 932 is electrically connected to terminal 952. Terminal 952 is electrically connected to terminal 911b.

[0448] As shown in Figure 23C, the coiled body 950a and electrolyte are covered by the housing 930, forming a secondary battery 913. It is preferable to provide a safety valve, an overcurrent protection element, etc., in the housing 930. The safety valve is temporarily opened only when the internal pressure inside the housing 930 exceeds a predetermined level in order to prevent the battery from rupturing.

[0449] As shown in Figure 23B, the secondary battery 913 may have multiple windings 950a. By using multiple windings 950a, a secondary battery 913 with a larger charge and discharge capacity can be made.

[0450] This embodiment can be combined with other embodiments as appropriate.

[0451] (Embodiment 4) In this embodiment, an example of the application of a secondary battery according to one aspect of the present invention will be explained with reference to Figures 24 to 33.

[0452] [vehicle] First, we will show an example of applying a secondary battery according to one aspect of the present invention to an electric vehicle (EV).

[0453] Figure 24C shows a block diagram of a vehicle with a motor. The electric vehicle is equipped with a first battery 1301a, 1301b as the main secondary battery for propulsion, and a second battery 1311 that supplies power to the inverter 1312 that starts the motor 1304. The second battery 1311 is also called the cranking battery or starter battery. The second battery 1311 only needs to have high output, and does not require a large capacity, so the capacity of the second battery 1311 is smaller than that of the first batteries 1301a, 1301b.

[0454] For example, one or both of the first batteries 1301a and 1301b can be a secondary battery manufactured using a secondary battery manufacturing method according to one aspect of the present invention.

[0455] In this embodiment, an example is shown in which two first batteries 1301a and 1301b are connected in parallel, but three or more may be connected in parallel. Also, if the first battery 1301a can store sufficient power, the first battery 1301b may not be necessary. By configuring a battery pack with multiple secondary batteries, a large amount of power can be extracted. Multiple secondary batteries may be connected in parallel, in series, or connected in parallel and then in series. Multiple secondary batteries are also called a battery pack.

[0456] Furthermore, the vehicle-mounted secondary battery has a service plug or circuit breaker that can cut off high voltage without using tools in order to interrupt power from multiple secondary batteries, and this is provided in the first battery 1301a.

[0457] Furthermore, the power from the first batteries 1301a and 1301b is mainly used to rotate the motor 1304, but also supplies power to 42V (high-voltage) onboard components (electric power steering 1307, heater 1308, defogger 1309, etc.) via the DC-DC circuit 1306. If a rear motor 1317 is located on the rear wheels, the first battery 1301a is also used to rotate the rear motor 1317.

[0458] Furthermore, the second battery 1311 supplies power to 14V (low-voltage) in-vehicle components (audio 1313, power windows 1314, lights 1315, etc.) via the DC-DC circuit 1310.

[0459] Furthermore, the first battery 1301a will be explained using Figure 24A.

[0460] Figure 24A shows an example of a large battery pack 1415. One electrode of the battery pack 1415 is electrically connected to the control circuit unit 1320 by wiring 1421. The other electrode is electrically connected to the control circuit unit 1320 by wiring 1422. The battery pack may also be configured by connecting multiple secondary batteries in series.

[0461] Furthermore, the control circuit section 1320 may also use a memory circuit that includes a transistor made of an oxide semiconductor. A charging control circuit or battery control system having a memory circuit that includes a transistor made of an oxide semiconductor may be referred to as a BTOS (Battery operating system or Battery oxide semiconductor).

[0462] The control circuit unit 1320 detects the terminal voltage of the secondary battery and manages the charging and discharging state of the secondary battery. For example, to prevent overcharging, both the output transistor of the charging circuit and the cutoff switch can be turned off almost simultaneously.

[0463] Furthermore, an example of a block diagram of the battery pack 1415 shown in Figure 24A is shown in Figure 24B.

[0464] The control circuit unit 1320 includes a switch unit 1324 that includes at least a switch to prevent overcharging and a switch to prevent over-discharging, a control circuit 1322 that controls the switch unit 1324, and a voltage measurement unit for the first battery 1301a. The control circuit unit 1320 sets the upper and lower voltage limits of the secondary battery used, and limits the upper limit of external current or the upper limit of output current to the outside. Within the range between the lower voltage limit and the upper voltage limit of the secondary battery, it is within the voltage range for which use is recommended, and if it goes outside this range, the switch unit 1324 activates and functions as a protection circuit. The control circuit unit 1320 can also be called a protection circuit because it controls the switch unit 1324 to prevent over-discharge or overcharge. For example, if the control circuit 1322 detects a voltage that is likely to cause overcharging, it cuts off the current by turning off the switch of the switch unit 1324. Furthermore, a PTC element may be provided in the charge / discharge path to provide a function to cut off the current in response to the rise in temperature. Furthermore, the control circuit unit 1320 has an external terminal 1325 (+IN) and an external terminal 1326 (-IN).

[0465] The switch section 1324 can be constructed using a combination of n-channel transistors and / or p-channel transistors. The switch section 1324 is not limited to switches using Si transistors made of single-crystal silicon; for example, the switch section 1324 may be formed using power transistors made of Ge (germanium), SiGe (silicon germanium), GaAs (gallium arsenide), GaAlAs (gallium aluminum arsenide), InP (indium phosphide), SiC (silicon carbide), ZnSe (zinc selenide), GaN (gallium nitride), GaOx (gallium oxide; x is a real number greater than 0), etc. Furthermore, since memory elements using OS transistors can be freely arranged by stacking them on circuits using Si transistors, integration can be easily achieved. Also, since OS transistors can be manufactured using the same manufacturing equipment as Si transistors, they can be manufactured at low cost. That is, a control circuit section 1320 using OS transistors can be stacked on the switch section 1324 and integrated into a single chip. Since the volume occupied by the control circuit unit 1320 can be reduced, miniaturization becomes possible.

[0466] The first batteries 1301a and 1301b primarily supply power to 42V (high-voltage) onboard equipment, while the second battery 1311 supplies power to 14V (low-voltage) onboard equipment. Lead-acid batteries are often used for the second battery 1311 due to their cost advantages.

[0467] This embodiment shows an example in which lithium-ion secondary batteries are used for both the first battery 1301a and the second battery 1311. The second battery 1311 may be a lead-acid battery, an all-solid-state battery, or an electric double-layer capacitor.

[0468] Furthermore, the regenerative energy generated by the rotation of the tire 1316 is sent to the motor 1304 via the gear 1305 and charged to the second battery 1311 via the control circuit unit 1321 from the motor controller 1303 or battery controller 1302. Alternatively, it is charged to the first battery 1301a via the control circuit unit 1320 from the battery controller 1302. Alternatively, 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.

[0469] The battery controller 1302 can set the charging voltage and charging current of the first batteries 1301a and 1301b. The battery controller 1302 can set the charging conditions according to the charging characteristics of the secondary battery being used and enable rapid charging.

[0470] Although not shown in the diagram, when connected to an external charger, the charger's outlet or connection cable is electrically connected to the battery controller 1302. Power supplied from the external charger charges the first batteries 1301a and 1301b via the battery controller 1302. In some chargers, a control circuit is provided, and 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. In some cases, the connection cable or the charger's connection cable may also have a control circuit. The control circuit unit 1320 is sometimes called an ECU (Electronic Control Unit). The ECU is connected to a CAN (Controller Area Network) installed in the electric vehicle. CAN is one of the serial communication standards used as an in-vehicle LAN. The ECU also includes a microcomputer. The ECU also uses a CPU or GPU.

[0471] Next, an example of implementing a secondary battery according to one aspect of the present invention in a vehicle, typically a transport vehicle, will be described.

[0472] By mounting a secondary battery according to one aspect of the present invention in a vehicle, next-generation clean energy vehicles such as hybrid vehicles (HV), electric vehicles (EV), or plug-in hybrid vehicles (PHV) can be realized. Furthermore, secondary batteries can also be mounted in agricultural machinery such as electric tractors, motorized bicycles including electric assist bicycles, motorcycles, electric wheelchairs, electric carts, small or large vessels, submarines, aircraft such as fixed-wing or rotary-wing aircraft, rockets, satellites, space probes or planetary probes, and other transport vehicles. By using the method for manufacturing a secondary battery according to one aspect of the present invention, large secondary batteries can be produced. Therefore, a secondary battery according to one aspect of the present invention is suitably used in transport vehicles.

[0473] Figures 25A to 25E show a transport vehicle using a secondary battery according to one embodiment of the present invention. The automobile 2001 shown in Figure 25A is an electric vehicle that uses an electric motor as a power source for driving. Alternatively, it is a hybrid vehicle that can appropriately select and use an electric motor and an engine as power sources for driving. When a secondary battery is mounted on a vehicle, the secondary battery is installed in one or more locations. The automobile 2001 shown in Figure 25A has the battery pack 1415 shown in Figure 24A. The battery pack 1415 has a secondary battery module. Preferably, the battery pack 1415 further has a charge control device that is electrically connected to the secondary battery module. The secondary battery module has one or more secondary batteries.

[0474] Furthermore, the automobile 2001 can be charged by receiving power from an external charging facility via a plug-in or contactless power supply method to the secondary battery it possesses. For charging, the charging method or connector specifications may be carried out appropriately using a prescribed method such as CHAdeMO® or Combo. The charging device may be a charging station installed in a commercial facility, or it may be a household power supply. For example, the secondary battery mounted on the automobile 2001 can be charged by an external power supply using plug-in technology. Charging can be performed by converting AC power to DC power via a conversion device such as an AC-DC converter.

[0475] Although not shown in the diagram, the vehicle can also be charged by mounting a power receiving device on the vehicle and receiving power wirelessly from a ground-based power transmission device. In this wireless power supply method, charging can be performed not only when the vehicle is stopped but also while it is in motion by incorporating the power transmission device into the road or exterior wall. Furthermore, this wireless power supply method can be used to transmit and receive power between two vehicles. In addition, solar panels can be installed on the exterior of the vehicle to charge the secondary battery when the vehicle is stopped or in motion. For such wireless power supply, electromagnetic induction or magnetic resonance methods can be used.

[0476] Figure 25B shows a large transport vehicle 2002 equipped with an electrically controlled motor as an example of a transport vehicle. The secondary battery module of the transport vehicle 2002 has a maximum voltage of 170V, achieved by connecting 48 cells in series, each consisting of four secondary batteries with a voltage of 3.5V to 4.7V. The secondary battery module of the battery pack 2201 has the same functions as Figure 25A, except for differences in the number of secondary batteries that make up the module, so the explanation is omitted.

[0477] Figure 25C shows, as an example, a large transport vehicle 2003 equipped with an electrically controlled motor. The secondary battery module of the transport vehicle 2003 has a maximum voltage of 600V, achieved by connecting more than 100 secondary batteries with voltages of 3.5V to 4.7V in series. Therefore, secondary batteries with small variation in characteristics are required. By using the secondary battery manufacturing method according to one aspect of the present invention, secondary batteries with stable battery characteristics can be manufactured, enabling low-cost mass production from a yield standpoint. Furthermore, since it has the same functions as Figure 25A except for differences in the number of secondary batteries constituting the secondary battery module of the battery pack 2202, a detailed explanation is omitted.

[0478] Figure 25D shows an example of an aircraft 2004 having a fuel-burning engine. The aircraft 2004 shown in Figure 25D has landing gear for takeoff and landing, and can therefore be considered part of a transport vehicle. It has a battery pack 2203 which includes a secondary battery module formed by connecting multiple secondary batteries and a charging control device.

[0479] The secondary battery module of aircraft 2004 has a maximum voltage of 32V, for example, by connecting eight 4V secondary batteries in series. The secondary battery module of battery pack 2203 has the same functionality as Figure 25A, except for differences in the number of secondary batteries that make up the module, so a detailed explanation is omitted.

[0480] Figure 25E shows a transport vehicle 2005 for transporting cargo as an example. It has an electrically controlled motor and performs various tasks by receiving power from a secondary battery that constitutes the secondary battery module of the battery pack 2204. Furthermore, the transport vehicle 2005 is not limited to being driven and operated by a human; it can also be operated unmanned via CAN communication or the like. Although Figure 25E illustrates a forklift, it is not particularly limited, and a battery pack having a secondary battery according to one aspect of the present invention can be mounted on industrial machinery that can be operated via CAN communication or the like, such as automated transport machines, work robots, or small construction machinery.

[0481] Furthermore, Figure 26A shows an example of an electric bicycle using a secondary battery according to one embodiment of the present invention. The secondary battery according to one embodiment of the present invention can be applied to the electric bicycle 2100 shown in Figure 26A. The energy storage device 2102 shown in Figure 26B includes, for example, a plurality of secondary batteries and a protection circuit.

[0482] The electric bicycle 2100 is equipped with a power storage device 2102. The power storage device 2102 can supply electricity to a motor that assists the rider. The power storage device 2102 is also portable, and Figure 26B shows it detached from the bicycle. The power storage device 2102 also has multiple secondary batteries 2101 according to one aspect of the present invention built in, and the remaining battery level can be displayed on a display unit 2103. The power storage device 2102 also has a control circuit 2104 capable of charging control or abnormality detection of the secondary batteries, as exemplified in one aspect of the present invention. The control circuit 2104 is electrically connected to the positive and negative electrodes of the secondary batteries 2101. A small solid-state secondary battery may also be provided in the control circuit 2104. By providing a small solid-state secondary battery in the control circuit 2104, power can be supplied to hold data in the memory circuit of the control circuit 2104 for a long period of time. Furthermore, a synergistic effect on safety can be obtained by combining it with a secondary battery that uses the positive electrode active material 100 according to one aspect of the present invention as the positive electrode. A secondary battery and control circuit 2104 using a positive electrode active material 100 according to one aspect of the present invention can greatly contribute to eliminating accidents such as fires caused by secondary batteries.

[0483] Figure 26C also shows an example of a motorcycle using a secondary battery according to one embodiment of the present invention. The scooter 2300 shown in Figure 26C is equipped with a power storage device 2302, side mirrors 2301, and turn signals 2303. The power storage device 2302 can supply electricity to the turn signals 2303. Furthermore, the power storage device 2302, which houses multiple secondary batteries using the positive electrode active material 100 according to one embodiment of the present invention as the positive electrode, can have a high capacity and contribute to miniaturization. To enhance safety, a protection circuit to prevent overcharging and / or over-discharging of the secondary battery may be electrically connected to the secondary battery.

[0484] Furthermore, the scooter 2300 shown in Figure 26C can accommodate the power storage device 2302 in the under-seat storage compartment 2304. The power storage device 2302 can be stored in the under-seat storage compartment 2304 even if the under-seat storage compartment 2304 is small.

[0485] [Buildings] Next, an example of implementing a secondary battery according to one aspect of the present invention in a building will be explained with reference to Figure 27.

[0486] The house shown in Figure 27A has a power storage device 2612 having a secondary battery with stable battery characteristics, and a solar panel 2610, using a secondary battery manufacturing method according to one aspect of the present invention. The power storage device 2612 is electrically connected to the solar panel 2610 via wiring 2611, etc. The power storage device 2612 may also be electrically connected to a ground-mounted charging device 2604. The power obtained from the solar panel 2610 can be used to charge the power storage device 2612. The power stored in the power storage device 2612 can be used to charge the secondary battery of the vehicle 2603 via the charging device 2604. The power storage device 2612 is preferably installed in the underfloor space. By installing it in the underfloor space, the space above the floor can be used effectively. Alternatively, the power storage device 2612 may be installed on the floor.

[0487] The electricity stored in the energy storage device 2612 can also be supplied to other electronic devices in the house. Therefore, even when power cannot be supplied from the commercial power source due to a power outage or other reasons, electronic devices can be used by using the energy storage device 2612 as an uninterruptible power supply.

[0488] Figure 27B shows an example of an energy storage device according to one aspect of the present invention. As shown in Figure 27B, a large energy storage device 791 having a secondary battery obtained by the secondary battery manufacturing method according to one aspect of the present invention is installed in the underfloor space 796 of the building 799.

[0489] The energy storage device 791 is equipped with a control device 790, which is electrically connected by wiring to the distribution board 703, the energy storage controller 705 (also called the control device), the display unit 706, and the router 709.

[0490] Power is supplied from the commercial power supply 701 to the distribution panel 703 via the service drop connection section 710. Power is also supplied to the distribution panel 703 from the energy storage device 791 and the commercial power supply 701, and the distribution panel 703 supplies the supplied power to the general load 707 and the energy storage system load 708 via outlets (not shown).

[0491] General load 707 is, for example, an electrical device such as a television or a personal computer, and energy storage load 708 is, for example, an electrical device such as a microwave oven, refrigerator, or air conditioner.

[0492] The energy storage controller 705 includes a measurement unit 711, a prediction unit 712, and a planning unit 713. The measurement unit 711 has the function of measuring the amount of electricity consumed by the general load 707 and the energy storage system load 708 during a day (for example, from 0:00 to 24:00). The measurement unit 711 may also have the function of measuring the amount of electricity consumed by the energy storage device 791 and the amount of electricity supplied from the commercial power supply 701. The prediction unit 712 has the function of predicting the amount of electricity demanded by the general load 707 and the energy storage system load 708 during the next day, based on the amount of electricity consumed by the general load 707 and the energy storage system load 708 during the day. The planning unit 713 has the function of planning the charging and discharging of the energy storage device 791 based on the amount of electricity demand predicted by the prediction unit 712.

[0493] The amount of electricity consumed by the general load 707 and the energy storage system load 708, as measured by the measurement unit 711, can be checked on the display unit 706. It can also be checked via the router 709 on electrical equipment such as televisions or personal computers. Furthermore, it can be checked via the router 709 on portable electronic devices such as smartphones or tablets. Additionally, the amount of electricity demand predicted by the forecasting unit 712 for each time period (or hourly) can be checked on the display unit 706, electrical equipment, and portable electronic devices.

[0494] [Electronic equipment] A secondary battery according to one aspect of the present invention can be used, for example, in either or both electronic devices and lighting devices. Examples of electronic devices include mobile phones, smartphones, or notebook computers, portable game consoles, portable music players, digital cameras, and digital video cameras.

[0495] The personal computer 2800 shown in Figure 28A includes a casing 2801, a casing 2802, a display unit 2803, a keyboard 2804, and a pointing device 2805, etc. A secondary battery 2807 is provided inside casing 2801, and a secondary battery 2806 is provided inside casing 2802. To enhance safety, protection circuits to prevent overcharging and / or over-discharging of secondary batteries 2807 and 2806 may be electrically connected to secondary batteries 2807 and 2806. A touch panel is also applied to the display unit 2803. As shown in Figure 28B, the personal computer 2800 can be used as a tablet terminal by removing casings 2801 and 2802, and using only casing 2802.

[0496] A large secondary battery obtained by the secondary battery manufacturing method according to one aspect of the present invention can be applied to either or both of secondary batteries 2806 and 2807. The shape of the secondary battery obtained by the secondary battery manufacturing method according to one aspect of the present invention can be freely changed by changing the shape of the casing. By shaping secondary batteries 2806 and 2807 to match the shape of the casings 2801 and 2802, for example, the capacity of the secondary battery can be increased, and the operating time of the personal computer 2800 can be extended. In addition, the personal computer 2800 can be made lighter.

[0497] Furthermore, a flexible display is applied to the display unit 2803 of the housing 2802. The secondary battery 2806 is a large secondary battery obtained by the secondary battery manufacturing method according to one aspect of the present invention. In the large secondary battery obtained by the secondary battery manufacturing method according to one aspect of the present invention, by using a flexible film for the outer casing, a bendable secondary battery can be made. As a result, as shown in Figure 28C, the housing 2802 can be folded for use. At this time, as shown in Figure 28C, a part of the display unit 2803 can also be used as a keyboard.

[0498] Furthermore, the housing 2802 can be folded so that the display unit 2803 faces inward, as shown in Figure 28D, or so that the display unit 2803 faces outward, as shown in Figure 28E.

[0499] One embodiment of the present invention is applicable to a bendable secondary battery, which can be mounted in electronic devices and incorporated along curved surfaces of interior or exterior walls of houses, buildings, or the interior or exterior of automobiles.

[0500] Figure 29A shows an example of a mobile phone. The mobile phone 7400 includes a display unit 7402 built into the housing 7401, as well as operation buttons 7403, an external connection port 7404, a speaker 7405, a microphone 7406, and the like. The mobile phone 7400 also has a secondary battery 7407. By using a secondary battery according to one embodiment of the present invention for the secondary battery 7407, a lightweight and long-life mobile phone can be provided. To enhance safety, a protection circuit to prevent overcharging and / or over-discharging of the secondary battery 7407 may be electrically connected to the secondary battery 7407.

[0501] Figure 29B shows the mobile phone 7400 in a bent state. When the mobile phone 7400 is deformed by an external force and the entire device is bent, the secondary battery 7407 located inside is also bent. Figure 29C shows the state of the bent secondary battery 7407 at that time. The secondary battery 7407 is a thin storage battery. The secondary battery 7407 is fixed in the bent state. The secondary battery 7407 has lead electrodes that are electrically connected to a current collector. For example, the current collector is made of copper foil, and a portion of it is alloyed with gallium to improve the adhesion with the active material layer that is in contact with the current collector, resulting in a configuration that ensures high reliability of the secondary battery 7407 when it is bent.

[0502] Figure 29D shows an example of a bangle-type display device. The portable display device 7100 comprises a housing 7101, a display unit 7102, operation buttons 7103, and a secondary battery 7104. To enhance safety, a protection circuit to prevent overcharging and / or over-discharging of the secondary battery 7104 may be electrically connected to the secondary battery 7104. Figure 29E shows the state of the bent secondary battery 7104. When the secondary battery 7104 is worn on the user's arm in a bent state, the housing deforms, and the curvature of part or all of the secondary battery 7104 changes. The degree of curvature at any point in the curve is expressed as the radius of the corresponding circle, and the reciprocal of the radius of curvature is called the curvature. Specifically, part or all of the main surface of the housing or secondary battery 7104 changes within the range of radius of curvature of 40 mm to 150 mm. High reliability can be maintained if the radius of curvature on the main surface of the secondary battery 7104 is within the range of 40 mm to 150 mm. By using a secondary battery according to one aspect of the present invention in the secondary battery 7104 described above, a lightweight and long-lasting portable display device can be provided.

[0503] Figure 29F shows an example of a wristwatch-type personal information terminal. The personal information terminal 7200 includes a housing 7201, a display unit 7202, a band 7203, a buckle 7204, operation buttons 7205, input / output terminals 7206, and the like.

[0504] The 7200 personal digital assistant (PDCA) can run various applications such as mobile phone calls, email, document viewing and creation, music playback, internet communication, and computer games.

[0505] The display unit 7202 has a curved display surface, allowing it to display information along the curved surface. The display unit 7202 also features a touch sensor, allowing it to be operated by touching the screen with a finger or stylus. For example, touching the icon 7207 displayed on the display unit 7202 can launch an application.

[0506] The operation button 7205 can be assigned various functions, including time setting, power on / off, wireless communication on / off, silent mode activation / deactivation, and power saving mode activation / deactivation. For example, the functions of the operation button 7205 can be freely configured by the operating system built into the personal digital assistant 7200.

[0507] Furthermore, the 7200 portable information terminal is capable of performing standardized short-range wireless communication. For example, it can communicate with a wireless-enabled headset to enable hands-free calling.

[0508] Furthermore, the portable information terminal 7200 is equipped with an input / output terminal 7206, allowing it to directly exchange data with other information terminals via a connector. It can also be charged via the input / output terminal 7206. Note that charging may also be performed wirelessly without using the input / output terminal 7206.

[0509] The display unit 7202 of the portable information terminal 7200 has a secondary battery according to one aspect of the present invention. By using a secondary battery according to one aspect of the present invention, a lightweight and long-lasting portable information terminal can be provided. To enhance safety, a protection circuit to prevent overcharging and / or over-discharging of the secondary battery may be electrically connected to the secondary battery. For example, the secondary battery 7104 shown in Figure 29E can be incorporated inside the housing 7201 in a curved state, or inside the band 7203 in a bendable state.

[0510] The portable information terminal 7200 preferably has sensors. Preferably, the sensors include, for example, a fingerprint sensor, a pulse sensor, a body temperature sensor, a touch sensor, a pressure sensor, or an acceleration sensor.

[0511] Figure 29G shows an example of an armband-type display device. The display device 7300 has a display unit 7304 and a secondary battery according to one embodiment of the present invention. To enhance safety, a protection circuit to prevent overcharging and / or over-discharging of the secondary battery may be electrically connected to the secondary battery. The display device 7300 may also be equipped with a touch sensor on the display unit 7304 and may also function as a portable information terminal.

[0512] The display unit 7304 has a curved display surface, allowing it to display information along the curved surface. Furthermore, the display device 7300 can change its display status via standardized short-range wireless communication.

[0513] Furthermore, the display device 7300 is equipped with input / output terminals, allowing it to directly exchange data with other information terminals via connectors. It can also be charged via the input / output terminals. Note that charging may also be performed wirelessly without using the input / output terminals.

[0514] By using a secondary battery according to one aspect of the present invention as the secondary battery of the display device 7300, a lightweight and long-life display device can be provided.

[0515] Furthermore, an example of mounting a secondary battery with good cycle characteristics in an electronic device, according to one aspect of the present invention, will be explained using Figures 29H, 30, and 31.

[0516] By using a secondary battery according to one embodiment of the present invention as a secondary battery in electronic devices, it is possible to provide lightweight and long-lasting products. Examples of everyday electronic devices include electric toothbrushes, electric shavers, and electric beauty devices. For the secondary batteries in these products, there is a demand for a stick-shaped, small, lightweight, and high-capacity secondary battery that is easy for the user to hold.

[0517] Figure 29H is a perspective view of a device also known as a tobacco-containing smoking device (electronic cigarette). In Figure 29H, the electronic cigarette 7500 consists of an atomizer 7501 including a heating element, a secondary battery 7504 that supplies power to the atomizer, and a cartridge 7502 including a liquid supply bottle or a sensor. To enhance safety, a protection circuit to prevent overcharging and / or over-discharging of the secondary battery 7504 may be electrically connected to the secondary battery 7504. The secondary battery 7504 shown in Figure 29H has external terminals so that it can be connected to a charging device. Since the secondary battery 7504 is the tip when held, it is desirable that its total length be short and its weight be light. A secondary battery according to one aspect of the present invention has high capacity and good cycle characteristics, so it is possible to provide a small and lightweight electronic cigarette 7500 that can be used for a long time over a long period of time.

[0518] Next, Figures 30A and 30B show an example of a foldable tablet terminal. The tablet terminal 7600 shown in Figures 30A and 30B includes a housing 7630a, a housing 7630b, a movable part 7640 connecting housings 7630a and 7630b, a display unit 7631 having display units 7631a and 7631b, switches 7625 to 7627, a fastener 7629, and an operation switch 7628. By using a flexible panel for the display unit 7631, a tablet terminal with a larger display area can be created. Figure 30A shows the tablet terminal 7600 in an open state, and Figure 30B shows the tablet terminal 7600 in a closed state.

[0519] Furthermore, the tablet terminal 7600 has a power storage unit 7635 inside the housings 7630a and 7630b. The power storage unit 7635 is provided across the housings 7630a and 7630b, passing through the movable part 7640.

[0520] The display unit 7631 can have all or part of its area designated as a touch panel area, and data can be entered by touching images, characters, input forms, etc., including icons, displayed in that area. For example, keyboard buttons may be displayed on the entire surface of the display unit 7631a on the housing 7630a side, and information such as characters and images may be displayed on the display unit 7631b on the housing 7630b side.

[0521] Alternatively, the display unit 7631b on the housing 7630b may be used to display a keyboard, while the display unit 7631a on the housing 7630a may be used to display information such as characters and images. Alternatively, the display unit 7631 may be used to display a touch panel keyboard display switching button, so that the keyboard is displayed on the display unit 7631 when the button is touched with a finger or stylus.

[0522] Furthermore, it is possible to simultaneously input touch input to the touch panel area of ​​the display unit 7631a on the housing 7630a and the touch panel area of ​​the display unit 7631b on the housing 7630b.

[0523] Furthermore, switches 7625 to 7627 may not only serve as an interface for operating the tablet terminal 7600, but also as an interface for switching various functions. For example, at least one of switches 7625 to 7627 may function as a switch to turn the tablet terminal 7600 on and off. Also, for example, at least one of switches 7625 to 7627 may have a function to switch the display orientation, such as portrait or landscape, or a function to switch between monochrome or color display. Also, for example, at least one of switches 7625 to 7627 may have a function to adjust the brightness of the display unit 7631. The brightness of the display unit 7631 can be optimized according to the amount of ambient light during use, as detected by the light sensor built into the tablet terminal 7600. Note that the tablet terminal 7600 may incorporate other detection devices in addition to the light sensor, such as a gyroscope, an accelerometer, or other sensors that detect tilt.

[0524] Furthermore, while Figure 30A shows an example where the display area of ​​the display unit 7631a on the housing 7630a side and the display unit 7631b on the housing 7630b side are approximately the same, the display areas of the display units 7631a and 7631b are not particularly limited, and the size of one may differ from the other, and the display quality may also differ. For example, one display panel may be capable of displaying a higher resolution than the other.

[0525] Figure 30B shows the tablet terminal 7600 in a folded state. The tablet terminal 7600 includes a housing 7630, a solar cell 7633, and a charge / discharge control circuit 7634 including a DC-DC converter 7636. Furthermore, a secondary battery according to one embodiment of the present invention is used as the energy storage body 7635.

[0526] As mentioned above, the tablet terminal 7600 is foldable, so when not in use, the casings 7630a and 7630b can be folded together. Folding protects the display unit 7631, thereby increasing the durability of the tablet terminal 7600. Furthermore, since the energy storage unit 7635 using a secondary battery according to one embodiment of the present invention has high capacity and good cycle characteristics, it is possible to provide a tablet terminal 7600 that can be used for a long period of time over a long period of time. To enhance safety, a protection circuit to prevent overcharging and / or over-discharging of the secondary battery in the energy storage unit 7635 may be electrically connected to the secondary battery.

[0527] Furthermore, the tablet terminal 7600 shown in Figures 30A and 30B may also have functions such as displaying various information (still images, videos, text images, etc.), displaying a calendar, date, or time on the display unit, a touch input function for touch input operation or editing of information displayed on the display unit, and a function for controlling processing by various software (programs).

[0528] The solar cell 7633 mounted on the surface of the tablet terminal 7600 can supply power to the touch panel, display unit, or video signal processing unit, etc. The solar cell 7633 can be installed on one or both sides of the housing 7630, allowing for an efficient configuration of charging the energy storage unit 7635. Using a lithium-ion battery as the energy storage unit 7635 offers advantages such as miniaturization.

[0529] Furthermore, the configuration and operation of the charge / discharge control circuit 7634 shown in Figure 30B will be explained with a block diagram in Figure 30C. Figure 30C shows the solar cell 7633, energy storage unit 7635, DC-DC converter 7636, converter 7637, switches SW1 to SW3, and display unit 7631. The energy storage unit 7635, DC-DC converter 7636, converter 7637, and switches SW1 to SW3 correspond to the charge / discharge control circuit 7634 shown in Figure 30B.

[0530] First, let's explain an example of operation when electricity is generated by the solar cell 7633 using ambient light. The power generated by the solar cell is boosted or stepped down by the DC-DC converter 7636 to obtain a voltage suitable for charging the energy storage unit 7635. When power from the solar cell 7633 is used to operate the display unit 7631, switch SW1 is turned on, and the converter 7637 boosts or steps down the voltage to the voltage required by the display unit 7631. When the display unit 7631 is not being used, switch SW1 is turned off, and switch SW2 is turned on to charge the energy storage unit 7635.

[0531] The solar cell 7633 is shown as an example of a power generation method, but it is not particularly limited, and the storage unit 7635 may be charged by other power generation methods such as piezoelectric elements or thermoelectric elements (Peltier elements). For example, a contactless power transmission module that transmits and receives power wirelessly (non-contact) to charge the storage unit, or a combination of other charging methods may be used.

[0532] Figure 31 shows an example of another electronic device. In Figure 31, the display device 8000 is an example of an electronic device using a secondary battery 8004 according to one aspect of the present invention. Specifically, the display device 8000 corresponds to a display device for receiving TV broadcasts and has a housing 8001, a display unit 8002, a speaker unit 8003, a secondary battery 8004, etc. To enhance safety, a protection circuit to prevent overcharging and / or over-discharging of the secondary battery 8004 may be electrically connected to the secondary battery 8004. The secondary battery 8004 according to one aspect of the present invention is provided inside the housing 8001. The display device 8000 can receive power from a commercial power source or use power stored in the secondary battery 8004. Therefore, even when power cannot be supplied from a commercial power source due to a power outage or the like, the display device 8000 can be used by using the secondary battery 8004 according to one aspect of the present invention as an uninterruptible power supply.

[0533] The display unit 8002 can use semiconductor display devices such as liquid crystal displays, light-emitting devices equipped with light-emitting elements such as organic EL elements in each pixel, electrophoretic displays, DMDs (Digital Micromirror Devices), PDPs (Plasma Display Panels), and FEDs (Field Emission Displays).

[0534] Furthermore, the term "display device" includes all information display devices, such as those for receiving TV broadcasts, personal computers, and advertising displays.

[0535] In Figure 31, the fixed-type lighting device 8100 is an example of an electronic device using a secondary battery 8103 according to one aspect of the present invention. Specifically, the lighting device 8100 includes a housing 8101, a light source 8102, a secondary battery 8103, etc. To enhance safety, a protection circuit to prevent overcharging and / or over-discharging of the secondary battery 8103 may be electrically connected to the secondary battery 8103. In Figure 31, the case in which the secondary battery 8103 is installed inside the ceiling 8104 on which the housing 8101 and light source 8102 are installed is illustrated, but the secondary battery 8103 may also be installed inside the housing 8101. The lighting device 8100 can receive power from a commercial power source or use power stored in the secondary battery 8103. Therefore, even when power cannot be supplied from a commercial power source due to a power outage or the like, the lighting device 8100 can be used by using the secondary battery 8103 according to one aspect of the present invention as an uninterruptible power source.

[0536] Although Figure 31 illustrates a fixed lighting device 8100 installed on the ceiling 8104, the secondary battery according to one aspect of the present invention can also be used in fixed lighting devices installed on surfaces other than the ceiling 8104, such as the side wall 8105, floor 8106, window 8107, etc., or in tabletop lighting devices, etc.

[0537] Furthermore, the light source 8102 can be an artificial light source that artificially generates light using electricity. Specifically, examples of the above artificial light sources include incandescent light bulbs, discharge lamps such as fluorescent lamps, LEDs, and / or light-emitting elements such as organic EL elements.

[0538] In Figure 31, an air conditioner having an indoor unit 8200 and an outdoor unit 8204 is an example of an electronic device using a secondary battery 8203 according to one aspect of the present invention. Specifically, the indoor unit 8200 has a housing 8201, an air outlet 8202, a secondary battery 8203, etc. To enhance safety, a protection circuit to prevent overcharging and / or over-discharging of the secondary battery 8203 may be electrically connected to the secondary battery 8203. In Figure 31, the case in which the secondary battery 8203 is provided in the indoor unit 8200 is illustrated, but the secondary battery 8203 may also be provided in the outdoor unit 8204. Alternatively, the secondary battery 8203 may be provided in both the indoor unit 8200 and the outdoor unit 8204. The air conditioner can receive power from a commercial power source or it can use power stored in the secondary battery 8203. In particular, when both the indoor unit 8200 and the outdoor unit 8204 are equipped with secondary batteries 8203, even when power cannot be supplied from the commercial power source due to a power outage or the like, the air conditioner can be used by using the secondary battery 8203 according to one aspect of the present invention as an uninterruptible power supply.

[0539] Although Figure 31 illustrates a separate-type air conditioner consisting of an indoor unit and an outdoor unit, the secondary battery according to one aspect of the present invention can also be used in an integrated-type air conditioner that has the functions of both the indoor and outdoor units in a single housing.

[0540] In Figure 31, the electric refrigerator-freezer 8300 is an example of an electronic device using a secondary battery 8304 according to one aspect of the present invention. Specifically, the electric refrigerator-freezer 8300 includes a housing 8301, a refrigerator door 8302, a freezer door 8303, a secondary battery 8304, etc. To enhance safety, a protection circuit to prevent overcharging and / or over-discharging of the secondary battery 8304 may be electrically connected to the secondary battery 8304. In Figure 31, the secondary battery 8304 is provided inside the housing 8301. The electric refrigerator-freezer 8300 can receive power from a commercial power source or use power stored in the secondary battery 8304. Therefore, even when power cannot be supplied from a commercial power source due to a power outage or the like, the electric refrigerator-freezer 8300 can be used by using the secondary battery 8304 according to one aspect of the present invention as an uninterruptible power source.

[0541] Furthermore, among the electronic devices mentioned above, high-frequency heating devices such as microwave ovens and electric rice cookers require high power in a short period of time. Therefore, by using a secondary battery according to one aspect of the present invention as an auxiliary power source to supplement the power that cannot be supplied by the commercial power supply, it is possible to prevent the commercial power supply circuit breaker from tripping when the electronic device is in use.

[0542] Furthermore, by storing power in the secondary battery during periods when electronic devices are not in use, particularly during periods when the proportion of the total amount of power supplied by the commercial power source that is actually used (referred to as the power usage rate) is low, it is possible to suppress the increase in the power usage rate outside of these periods. For example, in the case of the electric refrigerator-freezer 8300, power is stored in the secondary battery 8304 at night when the temperature is low and the refrigerator door 8302 and freezer door 8303 are not opened or closed. Then, during the daytime when the temperature is high and the refrigerator door 8302 and freezer door 8303 are opened and closed, the secondary battery 8304 can be used as an auxiliary power source, thereby keeping the daytime power usage rate low.

[0543] According to one aspect of the present invention, the cycle characteristics of a secondary battery can be improved, thereby enhancing its reliability. Furthermore, according to one aspect of the present invention, a high-capacity secondary battery can be created, thereby improving the characteristics of the secondary battery and thus making the secondary battery itself smaller and lighter. Therefore, by incorporating a secondary battery according to one aspect of the present invention into the electronic device described in this embodiment, it is possible to create an electronic device that has a longer lifespan and is lighter.

[0544] Figure 32A shows an example of a wearable device. Wearable devices use rechargeable batteries as a power source. Furthermore, in order to enhance splash resistance, water resistance, or dust resistance when used by users in daily life or outdoors, there is a demand for wearable devices that can be charged wirelessly in addition to wired charging with exposed connectors.

[0545] For example, a secondary battery according to one aspect of the present invention can be mounted in a spectacle-type device 9000 as shown in Figure 32A. The spectacle-type device 9000 has a frame 9000a and a display unit 9000b. By mounting the secondary battery in the temple portion of the curved frame 9000a, a lightweight spectacle-type device 9000 can be made with good weight balance and a long continuous usage time. To enhance safety, a protection circuit to prevent overcharging and / or over-discharging of the secondary battery may be electrically connected to the secondary battery. By incorporating a secondary battery according to one aspect of the present invention, a configuration that can accommodate space saving due to miniaturization of the housing can be realized.

[0546] Furthermore, a secondary battery according to one aspect of the present invention can be mounted in the headset-type device 9001. The headset-type device 9001 has at least a microphone section 9001a, a flexible pipe 9001b, and an earphone section 9001c. The secondary battery can be provided in the flexible pipe 9001b or in the earphone section 9001c. To enhance safety, a protection circuit to prevent overcharging and / or over-discharging of the secondary battery may be electrically connected to the secondary battery. By incorporating a secondary battery according to one aspect of the present invention, a configuration that can accommodate space saving due to miniaturization of the housing can be realized.

[0547] Furthermore, a secondary battery according to one aspect of the present invention can be mounted in a device 9002 that can be directly attached to the body. The secondary battery 9002b can be provided within the thin housing 9002a of the device 9002. To enhance safety, a protection circuit to prevent overcharging and / or over-discharging of the secondary battery 9002b may be electrically connected to the secondary battery 9002b. By incorporating a secondary battery according to one aspect of the present invention, a configuration that can accommodate space saving due to the miniaturization of the housing can be realized.

[0548] Furthermore, a secondary battery according to one aspect of the present invention can be mounted on a device 9003 that can be attached to clothing. The secondary battery 9003b can be provided within the thin housing 9003a of the device 9003. To enhance safety, a protection circuit to prevent overcharging and / or over-discharging of the secondary battery 9003b may be electrically connected to the secondary battery 9003b. By incorporating a secondary battery according to one aspect of the present invention, a configuration that can accommodate space saving due to the miniaturization of the housing can be realized.

[0549] Furthermore, a secondary battery according to one aspect of the present invention can be mounted in the belt-type device 9006. The belt-type device 9006 has a belt portion 9006a and a wireless power supply / receiving portion 9006b, and a secondary battery can be mounted inside the belt portion 9006a. To enhance safety, a protection circuit to prevent overcharging and / or over-discharging of the secondary battery may be electrically connected to the secondary battery. By incorporating a secondary battery according to one aspect of the present invention, a configuration that can accommodate space saving due to the miniaturization of the housing can be realized.

[0550] Furthermore, a secondary battery according to one aspect of the present invention can be mounted in the wristwatch-type device 9005. The wristwatch-type device 9005 has a display unit 9005a and a belt unit 9005b, and the secondary battery can be provided in either the display unit 9005a or the belt unit 9005b. To enhance safety, a protection circuit to prevent overcharging and / or over-discharging of the secondary battery may be electrically connected to the secondary battery. By incorporating a secondary battery according to one aspect of the present invention, a configuration that can accommodate space saving due to miniaturization of the housing can be realized.

[0551] The display unit 9005a can display not only the time, but also various other information such as incoming emails and / or phone calls.

[0552] Furthermore, since the wristwatch-type device 9005 is a wearable device that is worn directly on the wrist, it may be equipped with sensors to measure the user's pulse, blood pressure, etc. It can accumulate data on the user's exercise level and health, and manage their health.

[0553] Figure 32B shows a perspective view of the wristwatch-type device 9005 after it has been removed from the arm.

[0554] A side view is also shown in Figure 32C. Figure 32C shows a secondary battery 913 according to one embodiment of the present invention built inside. The secondary battery 913 is located in a position overlapping with the display unit 9005a, and is small and lightweight.

[0555] Figure 33A shows an example of a cleaning robot. The cleaning robot 9300 has a display unit 9302 located on the top surface of the housing 9301, multiple cameras 9303 located on the sides, a brush 9304, operation buttons 9305, a secondary battery 9306, and various sensors. To enhance safety, a protection circuit to prevent overcharging and / or over-discharging of the secondary battery 9306 may be electrically connected to the secondary battery 9306. Although not shown, the cleaning robot 9300 is equipped with wheels, a suction port, etc. The cleaning robot 9300 is self-propelled, can detect dirt 9310, and can suck up the dirt from a suction port located on the bottom surface.

[0556] For example, the cleaning robot 9300 can analyze images captured by the camera 9303 to determine the presence or absence of obstacles such as walls, furniture, or steps. Furthermore, if the image analysis detects an object that could become entangled in the brush 9304, such as wiring, the rotation of the brush 9304 can be stopped. The cleaning robot 9300 is equipped with a secondary battery 9306 according to one aspect of the present invention and a semiconductor device or electronic component. By using the secondary battery 9306 according to one aspect of the present invention in the cleaning robot 9300, the cleaning robot 9300 can be made into a highly reliable electronic device with a long operating time.

[0557] Figure 33B shows an example of a robot. The robot 9400 shown in Figure 33B is equipped with a secondary battery 9409, an illuminance sensor 9401, a microphone 9402, an upper camera 9403, a speaker 9404, a display unit 9405, a lower camera 9406 and an obstacle sensor 9407, a movement mechanism 9408, a computing device, etc. To enhance safety, a protection circuit to prevent overcharging and / or over-discharging of the secondary battery 9409 may be electrically connected to the secondary battery 9409.

[0558] Microphone 9402 has the function of detecting the user's voice and ambient sounds. Speaker 9404 has the function of emitting sound. Robot 9400 can communicate with the user using microphone 9402 and speaker 9404.

[0559] The display unit 9405 has the function of displaying various types of information. The robot 9400 can display the user's desired information on the display unit 9405. The display unit 9405 may be equipped with a touch panel. The display unit 9405 may also be a detachable information terminal, and by installing it in a fixed position on the robot 9400, charging and data transfer can be made possible.

[0560] The upper camera 9403 and lower camera 9406 have the function of imaging the area around the robot 9400. In addition, the obstacle sensor 9407 can detect the presence or absence of obstacles in the direction of travel when the robot 9400 moves forward using the movement mechanism 9408. The robot 9400 can recognize its surrounding environment and move safely using the upper camera 9403, lower camera 9406 and obstacle sensor 9407.

[0561] The robot 9400 is equipped with a secondary battery 9409 according to one aspect of the present invention and a semiconductor device or electronic components inside. By using the secondary battery according to one aspect of the present invention in the robot 9400, the robot 9400 can be made into an electronic device with a long operating time and high reliability.

[0562] Figure 33C shows an example of an aircraft. The aircraft 9500 shown in Figure 33C has a propeller 9501, a camera 9502, and a secondary battery 9503, and has the capability to fly autonomously. To enhance safety, a protection circuit to prevent overcharging and / or over-discharging of the secondary battery 9503 may be electrically connected to the secondary battery 9503.

[0563] For example, image data captured by camera 9502 is stored in electronic component 9504. Electronic component 9504 can analyze the image data and detect the presence or absence of obstacles during movement. Furthermore, electronic component 9504 can estimate the remaining battery level from the change in the storage capacity of secondary battery 9503. The aircraft 9500 is equipped with a secondary battery 9503 according to one aspect of the present invention. By using a secondary battery according to one aspect of the present invention in the aircraft 9500, the aircraft 9500 can be made into an electronic device with a long operating time and high reliability.

[0564] This embodiment can be implemented in appropriate combination with other embodiments.

[0565] (Notes regarding the descriptions in this specification, etc.) The above embodiments and a description of each component in those embodiments are provided below.

[0566] The configurations shown in each embodiment can be appropriately combined with the configurations shown in other embodiments to form one aspect of the present invention. Furthermore, if multiple configuration examples are shown within a single embodiment, these configuration examples can be appropriately combined.

[0567] Furthermore, the content described in one embodiment (even if only a part of it) can be applied to, combined with, or substituted for other content described in the same embodiment (even if only a part of it), and / or content described in one or more other embodiments (even if only a part of it).

[0568] The content described in the embodiments refers to the content described using various figures or the content described using text in the specification in each embodiment.

[0569] Furthermore, a diagram (even a part of it) described in one embodiment can be combined with another part of that diagram, another diagram (even a part of it) described in that embodiment, and / or a diagram (even a part of it) described in one or more other embodiments to form even more diagrams.

[0570] Furthermore, in this specification, block diagrams classify components by function and show them as independent blocks. However, in actual circuits, it is difficult to separate components by function, and there may be cases where multiple functions are involved in a single circuit, or where a single function is involved across multiple circuits. Therefore, the blocks in the block diagrams are not limited to the components described in the specification, and can be appropriately rephrased depending on the situation.

[0571] Furthermore, in the drawings, the size, layer thickness, or area are shown at arbitrary sizes for the sake of explanation. Therefore, they are not necessarily limited to that scale. Also, the drawings are schematic for clarity and are not limited to the shapes or values ​​shown in the drawings. For example, they may include variations in signals, voltages, or currents due to noise, or variations in signals, voltages, or currents due to timing differences.

[0572] In this specification and other documents, when describing the connection relationships of a transistor, the terms "one of the source or drain" (or first electrode or first terminal) and "the other of the source or drain" (or second electrode or second terminal) are used to refer to the other of the source and drain. This is because the source and drain of a transistor vary depending on the transistor's structure or operating conditions. The terms "source" and "drain" of a transistor can be appropriately rephrased as "source (drain) terminal" or "source (drain) electrode" depending on the context.

[0573] Furthermore, the terms "electrode" and "wiring" in this specification do not functionally limit these components. For example, "electrode" may be used as part of "wiring," and vice versa. Moreover, the terms "electrode" and "wiring" also include cases where multiple "electrodes," multiple "wirings," or multiple "electrodes" and multiple "wirings" are formed as a single unit.

[0574] Furthermore, in this specification, voltage and potential may be used interchangeably as appropriate. Voltage is the potential difference from a reference potential; for example, if the reference potential is the ground voltage, then voltage can be replaced with potential. Ground potential does not necessarily mean 0V. Note that potential is relative, and depending on the reference potential, it may change the potential applied to wiring, etc.

[0575] In this specification, terms such as "film" and "layer" may be interchanged depending on the context or situation. For example, the term "conductive layer" may be changed to "conductive film." Or, for example, the term "insulating film" may be changed to "insulating layer."

[0576] In this specification, a switch refers to a device that has the function of controlling whether or not to allow current to flow by being in a conductive state (on state) or a non-conductive state (off state). Alternatively, a switch refers to a device that has the function of selecting and switching the path through which current flows.

[0577] In this specification, channel length refers, for example, to the distance between the source and drain in the region where the semiconductor (or the part of the semiconductor through which current flows when the transistor is ON) and the gate overlap in a top view of a transistor, or in the region where the channel is formed.

[0578] In this specification, channel width refers, for example, to the length of the region where the semiconductor (or the part of the semiconductor through which current flows when the transistor is ON) and the gate electrode overlap, or the region in which the channel is formed, where the source and drain face each other.

[0579] In this specification, "A and B are connected" includes not only those that are directly connected, but also those that are electrically connected. Here, "electrically connected" means that when there is an object between A and B that has some kind of electrical effect, it enables the exchange of electrical signals between A and B. [Examples]

[0580] In this embodiment, a secondary battery according to one aspect of the present invention was fabricated and evaluated.

[0581] [Fabrication of positive electrode active material] The positive electrode active material was prepared according to the manufacturing method shown in Figure 6.

[0582] For step S14, a commercially available lithium cobalt oxide (Cellseed C-10N, manufactured by Nippon Chemical Industrial Co., Ltd.) containing cobalt as the transition metal M and no particular additives was prepared as LiMO2. Similar to step S20a, lithium fluoride and magnesium fluoride were prepared as the X1 source, and the lithium fluoride and magnesium fluoride were mixed by the solid-phase method, similar to step S31. The mixture was prepared such that, with 100 cobalt atoms, the number of lithium fluoride molecules was 0.33 and the number of magnesium fluoride molecules was 1. Similar to step S32, this was designated as mixture 903.

[0583] Next, the mixture was annealed in the same manner as in step S33. 30g of mixture 903 was placed in a rectangular alumina container, a lid was placed on, and it was heated in a muffle furnace. The furnace was purged and oxygen gas was introduced, and there was no flow during heating. The annealing temperature was 900°C for 20 hours.

[0584] Nickel hydroxide and aluminum hydroxide were added to the heated composite oxide as step S51 and dry-mixed. The nickel and aluminum atoms were added so that, with a cobalt atom count of 100, the nickel atoms and aluminum atoms each amounted to 0.5. This mixture was designated as mixture 904.

[0585] Next, the mixture was annealed in the same manner as in step S33. 30g of mixture 903 was placed in a rectangular alumina container, a lid was placed on, and it was heated in a muffle furnace. The furnace was purged and oxygen gas was introduced, and flow was performed during heating. The annealing temperature was 850°C for 10 hours.

[0586] The powder was then collected by sieving it through a 53 μm diameter sieve to obtain the positive electrode active material.

[0587] [Fabrication of the positive electrode] Next, a positive electrode was fabricated using the positive electrode active material prepared above. The positive electrode active material prepared above, acetylene black (AB), and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of positive electrode active material:AB:PVDF = 95:3:2, and a slurry was prepared using NMP as the solvent. The prepared slurry was coated onto a current collector, and the solvent was evaporated. Then, a press of 120 kN / m was performed at 120°C to form a positive electrode active material layer on the current collector, thereby fabricating the positive electrode. A 20 μm thick aluminum foil was used as the current collector. The positive electrode active material layer was provided on one side of the current collector. The loading amount was approximately 10 mg / cm³. 2 That was the case.

[0588] [Fabrication of the negative electrode] A negative electrode was fabricated using graphite as the negative electrode active material.

[0589] As graphite, it has a specific surface area of ​​1.5 m². 2 Using MCMB graphite (at a weight ratio of 1 / g), a slurry was prepared by mixing it with a conductive agent, CMC-Na, and SBR in a ratio of graphite:conductive agent:CMC-Na:SBR = 96:1:1:2, and using water as the solvent.

[0590] The degree of polymerization of the CMC-Na used ranged from 600 to 800, and the viscosity of the aqueous solution when used as a 1-weight% aqueous solution ranged from 300 mPa·s to 500 mPa·s. Furthermore, VGCF(registered trademark)-H (manufactured by Showa Denko K.K., fiber diameter 150 nm, specific surface area 13 m²), a vapor-grown carbon fiber, was used as the conductive agent. 2 / g) was used.

[0591] Each prepared slurry was coated onto a current collector and dried to create a negative electrode active material layer on the current collector. 18 μm thick copper foil was used as the current collector. The negative electrode active material layer was applied to either one or both sides of the current collector. The loading amount was approximately 9 mg / cm³. 2 That was the case.

[0592] [Manufacturing of secondary batteries] Using the positive and negative electrodes prepared as described above, a secondary battery with a film casing was fabricated.

[0593] A 23 μm thick polyimide was used as the separator.

[0594] In the secondary battery using electrolyte A described later, one negative electrode with negative electrode active material layers formed on both sides and two positive electrodes with positive electrode active material layers formed on one side were prepared. The positive electrode active material layers were placed facing each other on the negative electrode active material layers formed on both sides of the negative electrode, with a separator in between.

[0595] In the secondary battery using electrolyte B described later, one negative electrode with a negative electrode active material layer formed on one side and one positive electrode with a positive electrode active material layer formed on one side were prepared. The negative electrode active material layer and the positive electrode active material layer were arranged facing each other with a separator in between.

[0596] Leads were attached to the positive and negative electrodes, respectively.

[0597] A laminate consisting of a positive electrode, a negative electrode, and a separator was sandwiched between two halves of a folded outer casing, with the laminate positioned so that one end of the lead protruded outside the outer casing. Next, one side of the outer casing was left open, while the other sides were sealed.

[0598] A film consisting of a polypropylene layer, an acid-modified polypropylene layer, an aluminum layer, and a nylon layer was used as the outer casing. The thickness of the film was approximately 110 nm. The outer casing film was folded so that the nylon layer was on the outer side and the polypropylene layer was on the inner side. The thickness of the aluminum layer was approximately 40 μm, the thickness of the nylon layer was approximately 25 μm, and the combined thickness of the polypropylene layer and the acid-modified polypropylene layer was approximately 45 μm.

[0599] Next, under an argon gas atmosphere, electrolyte was injected through the side that remained open. Two types of electrolyte (hereinafter referred to as electrolyte A and electrolyte B) were prepared.

[0600] Electrolyte A was prepared. EMI-FSA, shown in structural formula (G11), was used as the solvent for the electrolyte. LiFSA (lithium bis(fluorosulfonyl)amide) was used as the lithium salt, and the concentration of the lithium salt relative to the electrolyte was 2.15 mol / L.

[0601] [ka]

[0602] As a comparative example, electrolyte B was prepared, which contained a cyclic carbonate. Specifically, a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of EC:DEC = 3:7 was used as the solvent. Lithium hexafluoride phosphate (LiPF6) was used as the lithium salt. The concentration of the lithium salt in the electrolyte was 1.00 mol / L.

[0603] Next, under reduced pressure, one side of the outer casing that had been left open was sealed.

[0604] The secondary battery was manufactured using the above process.

[0605] [aging] Next, we performed aging on the secondary battery.

[0606] The secondary battery was sandwiched between two plates and charged at 0.01C with a CC charge of 15mAh / g. After a 10-minute rest period, it was charged again at 0.1C with a CC charge of 105mAh / g. The two plates were then removed, and the battery was kept at 0°C for 24 hours. Finally, one side of the casing was cut open under an argon atmosphere to release the gas, and the casing was resealed.

[0607] [Cycle Characteristics Evaluation 1] The cycle characteristics of a secondary battery were evaluated by sandwiching it between two plates.

[0608] The area of ​​the positive electrode active material layer at the positive electrode is 20.493 cm². 2 That's what I decided.

[0609] The amount of negative electrode active material in the negative electrode of each battery cell was adjusted so that the capacity ratio was approximately 75% to 85%. Here, the capacity ratio is the value expressed as a percentage of the positive electrode capacity to the negative electrode capacity. In calculating the capacity ratio, the negative electrode capacity was set to 330 mAh / g, based on the weight of the negative electrode active material. When negative electrode active material layers were provided on both sides of the current collector, the amount of negative electrode active material provided was divided in half to calculate the amount of negative electrode active material.

[0610] In the secondary battery using electrolyte A, the areas of the positive electrode and the negative electrode were made equal.

[0611] Cycle tests were conducted under environmental conditions of 0°C, 25°C, 45°C, 60°C, and -20°C.

[0612] Charging was performed at 0°C using CCCV (0.2C, termination current 0.1C, 4.5V), and discharging was performed using CC (0.2C, 3.0V). The capacity of the secondary battery was calculated based on the weight of the positive electrode active material. For secondary batteries using electrolyte A, the C rate was calculated using 210 mA / g (per positive electrode active material weight) for 1C. For secondary batteries using electrolyte B, the C rate was calculated using 210 mA / g (per positive electrode active material weight) for 1C. The cycle characteristics are shown in Figure 34A. The initial discharge capacity was 161.3 mAh / g for electrolyte A and 145.5 mAh / g for electrolyte B.

[0613] Charging was performed at 25°C using CCCV (0.2C, termination current 0.1C, 4.5V), and discharging was performed using CC (0.2C, 3.0V). The capacity of the secondary battery was calculated based on the weight of the positive electrode active material. For secondary batteries using electrolyte A, the C rate was calculated using 210 mA / g (per positive electrode active material weight) for 1C. For secondary batteries using electrolyte B, the C rate was calculated using 210 mA / g (per positive electrode active material weight) for 1C. The cycle characteristics are shown in Figure 34B. The maximum discharge capacity in the cycle test was 205.1 mAh / g for electrolyte A and 195.0 mAh / g for electrolyte B.

[0614] Charging was performed at 45°C using CCCV (0.5C, termination current 0.2C, 4.5V), and discharging was performed using CC (0.5C, 3.0V). The capacity of the secondary battery was calculated based on the weight of the positive electrode active material. For secondary batteries using electrolyte A, the C rate was calculated using 210mA / g (per positive electrode active material weight) for 1C. For secondary batteries using electrolyte B, the C rate was calculated using 210mA / g (per positive electrode active material weight) for 1C. The cycle characteristics are shown in Figure 35A. The maximum discharge capacity in the cycle test was 201.8mAh / g for electrolyte A and 201.0mAh / g for electrolyte B.

[0615] Charging was performed at 60°C using CCCV (0.5C, termination current 0.2C, 4.5V), and discharging was performed using CC (0.5C, 3.0V). The capacity of the secondary battery was calculated based on the weight of the positive electrode active material. For secondary batteries using electrolyte A, the C rate was calculated using 210 mA / g (per positive electrode active material weight) for 1C. For secondary batteries using electrolyte B, the C rate was calculated using 210 mA / g (per positive electrode active material weight) for 1C. The cycle characteristics are shown in Figure 35B. The maximum discharge capacity in the cycle test was 197.2 mAh / g for electrolyte A and 213.9 mAh / g for electrolyte B.

[0616] Charging was performed at -20°C using CCCV (0.1C, termination current 0.05C, 4.5V), and discharging was performed using CC (0.1C, 3.0V). The capacity of the secondary battery was calculated based on the weight of the positive electrode active material. For secondary batteries using electrolyte A, the C rate was calculated using 210mA / g (per positive electrode active material weight) for 1C. For secondary batteries using electrolyte B, the C rate was calculated using 210mA / g (per positive electrode active material weight) for 1C. The cycle characteristics are shown in Figure 36. The maximum discharge capacity in the cycle test was 112.0mAh / g for electrolyte A and 87.2mAh / g for electrolyte B. [Examples]

[0617] In this example, a secondary battery prepared in Example 1 and subjected to more than 150 charge-discharge cycles at 60°C was disassembled, and the positive and negative electrodes were observed.

[0618] The negative electrodes of a secondary battery using electrolyte A (2.15M LiFSA EMI-FSA) and a secondary battery using electrolyte B (1M LiPF6 EC:DEC=3:7) were observed using a scanning electron microscope (SEM). A Hitachi High-Tech SU8030 was used, with an acceleration voltage of 1kV. The cross-sections were exposed and observed using ion milling.

[0619] Figure 37A shows a cross-sectional SEM image of the negative electrode of a secondary battery using electrolyte A. As shown in Figure 37A, it was observed that a negative electrode active material layer 905a containing graphite 991a is provided on the current collector 904a. Figure 37B shows an enlarged view of the square frame 992a shown in Figure 37A, Figure 37C shows an enlarged view of the frame 993a, Figure 37D shows an enlarged view of the frame 994a, and Figure 37E shows an enlarged view of the frame 995a.

[0620] Figure 38A shows a cross-sectional SEM image of the negative electrode of a secondary battery using electrolyte B. As shown in Figure 38A, it was observed that a negative electrode active material layer 905b containing graphite 991b is provided on the current collector 904b. Figure 38B shows an enlarged view of the square frame 992b shown in Figure 38A, Figure 38C shows an enlarged view of the frame 993b, Figure 38D shows an enlarged view of the frame 994b, and Figure 38E shows an enlarged view of the frame 995b.

[0621] Furthermore, EDX analysis was performed at point a1 in Figure 37B, point b1 in Figure 37C, point c1 in Figure 37D, point d1 in Figure 37E, point a2 in Figure 38B, point b2 in Figure 38C, point c2 in Figure 38D, and point d2 in Figure 38E. EDX analysis was also performed at the points indicated in the figures. The acceleration voltage used for the analysis was 5kV.

[0622] EDX analysis at points a1, b1, c1, and d1 detected carbon, nitrogen, oxygen, fluorine, and sulfur. Magnesium, aluminum, and cobalt were below detection limits in the EDX analysis at points a1, b1, c1, and d1. Copper was detected in the EDX analysis at points b1, c1, and d1, although below detection limits at point a1. The presence of copper may be due to the current collector.

[0623] EDX analysis at points a2, b2, c2, and d2 detected carbon, oxygen, fluorine, and phosphorus. Nitrogen, magnesium, and aluminum were below detection limits in the EDX analysis at points a2, b2, c2, and d2. Copper was detected in the EDX analysis at point d2, while it was below detection limits at points a2, b2, and c2. The presence of copper may be due to the current collector.

[0624] Furthermore, cobalt was detected in EDX analysis at points a2, b2, and c2. At point d2, the cobalt level was below the detection limit. The cobalt detected at points a2, b2, and c2 is suggested to be due to cobalt leaching from the positive electrode active material.

[0625] As shown in Figures 37A to 37E and Figures 38A to 38E, a film was observed on the graphite surface. Furthermore, the negative electrode of the secondary battery using electrolyte A showed a thinner film compared to the negative electrode of the secondary battery using electrolyte B, and the amount of cobalt detected by EDX analysis was also lower. In both electrolytes, carbon and oxygen were detected by EDX. In addition, nitrogen, fluorine, and sulfur were detected when electrolyte A was used. On the other hand, fluorine and phosphorus were detected when electrolyte B was used.

[0626] Furthermore, the film on the graphite surface appeared to be thicker the closer it was to the surface of the negative electrode active material layer, i.e., the further it was from the current collector. Similarly, the amount of cobalt detected by EDX also increased the closer it was to the surface of the negative electrode active material layer, i.e., the further it was from the current collector. Figure 39 shows the film thickness and the cobalt concentration detected by EDX in each measurement region. The film thickness was measured at five locations, and the average value was calculated.

[0627] Next, the positive electrodes of a secondary battery using electrolyte A and a secondary battery using electrolyte B were observed using a scanning electron microscope (SEM). A Hitachi High-Tech SU8030 was used, with an acceleration voltage of 1.0 kV. Figure 40 shows the SEM images. Figure 40A shows the SEM image of the positive electrode of the secondary battery using electrolyte A, and Figure 40B shows the SEM image of the positive electrode of the secondary battery using electrolyte B. Figure 40C shows a magnified view of the area indicated by the square frame in Figure 40A, and Figure 40D shows a magnified view of the area indicated by the square frame in Figure 40B.

[0628] Pits were observed at the locations indicated by arrows in Figures 40C and 40D. As shown in Figures 40C and 40D, it was found that there were fewer pits in the positive electrode of the secondary battery using electrolyte A. This suggests that in the configuration of a secondary battery according to one embodiment of the present invention, in which an ionic liquid is used as the electrolyte, the elution of cobalt was suppressed, and the generation of pits was suppressed. [Explanation of Symbols]

[0629] 51: Positive electrode active material particles, 52: Recess, 53: Barrier film, 54: Pit, 55: Crystal plane, 56: Barrier film, 57: Crack, 58: Pit, 100: Positive electrode active material, 130: Laminate, 131: Laminate, 400: Negative electrode active material, 401: Region, 401a: Region, 401b: Region, 402: Region, 500: Secondary battery, 501: Positive electrode current collector, 502: Positive electrode active material layer, 503: Positive electrode, 504: Negative electrode current collector, 505: Negative electrode active material layer, 506: Negative electrode, 507: Separator, 507a: Region, 507b: Region, 508: Electrolyte, 509: Outer casing, 509a: Outer casing, 509b: Outer casing, 510: positive lead electrode, 511: negative lead electrode, 512: laminate, 513: resin layer, 514: region, 515a: electrolyte, 515b: electrolyte, 515c: electrolyte, 516: inlet, 550: laminate, 553: acetylene black, 554: graphene, 556: acetylene black, 557: graphene, 560: secondary battery, 561: positive electrode active material, 563: negative electrode active material, 570: manufacturing equipment, 571: material input chamber, 572: transport chamber, 573: processing chamber, 576: material removal chamber, 580: transport mechanism, 581: polymer film, 582: pore, 584: poly Mar film, 585: Hole, 591: Stage, 594: Nozzle, 600: Secondary battery, 701: Commercial power supply, 703: Distribution board, 705: Energy storage controller, 706: Display unit, 707: General load, 708: Energy storage system load, 709: Router, 710: Service drop mounting section, 711: Measurement section, 712: Prediction section, 713: Planning section, 790: Control device, 791: Energy storage device, 796: Underfloor space section, 799: Building, 903: Mixture, 904: Mixture, 904a: Current collector, 904b: Current collector, 905a: Negative electrode active material layer, 905b: Negative electrode active material layer, 911a: Terminal, 911b: Terminal, 913 : Secondary battery, 930: Housing, 930a: Housing, 930b: Housing, 931: Negative electrode, 931a: Negative electrode active material layer, 932: Positive electrode, 932a: Positive electrode active material layer, 933: Separator, 950: Winding body, 950a: Winding body, 951: Terminal, 952: Terminal, 970: Secondary battery, 971: Housing, 972: Laminate, 973a: Positive electrode lead electrode, 973b: Terminal, 973c: Conductor, 974a: Negative electrode lead electrode, 974b: Terminal, 974c: Conductor, 975a: Positive electrode, 975b: Positive electrode, 976: Separator, 977a: Negative electrode, 991a: Graphite, 991b: Graphite, 992a: Frame,992b: Frame, 993a: Frame, 993b: Frame, 994a: Frame, 994b: Frame, 995a: Frame, 995b: Frame, 1301a: First battery, 1301b: First battery, 1302: Battery controller, 1303: Motor controller, 1304: Motor, 1305: Gear, 1306: DC-DC circuit, 1307: Electric power steering, 1308: Heater, 1309: Defogger, 1310: DC-DC circuit, 1311: Second battery, 1312: Inverter, 1313: Audio, 1314: Power windows, 1315: Lights, 1316: Tie Ya, 1317: Rear motor, 1320: Control circuit unit, 1321: Control circuit unit, 1322: Control circuit, 1324: Switch unit, 1325: External terminal, 1326: External terminal, 1415: Battery pack, 1421: Wiring, 1422: Wiring, 2001: Automobile, 2002: Transport vehicle, 2003: Transport vehicle, 2004: Aircraft, 2005: Transport vehicle, 2100: Electric bicycle, 2101: Secondary battery, 2102: Energy storage device, 2103: Display unit, 2104: Control circuit, 2201: Battery pack, 2202: Battery pack, 2203: Battery pack, 2204: Battery pack, 2300 :Scooter, 2301:Side mirror, 2302:Power storage device, 2303:Turn signal light, 2304:Under-seat storage, 2603:Vehicle, 2604:Charging device, 2610:Solar panel, 2611:Wiring, 2612:Power storage device, 2800:Personal computer, 2801:Casing, 2802:Casing, 2803:Display unit, 2804:Keyboard, 2805:Pointing device, 2806:Rechargeable battery, 2807:Rechargeable battery, 7100:Portable display device, 7101:Casing, 7102:Display unit, 7103:Operation buttons, 7104:Rechargeable battery, 7200:Portable information Terminal, 7201: Housing, 7202: Display unit, 7203: Band, 7204: Buckle, 7205: Operation buttons, 7206: Input / Output terminals, 7207: Icons, 7300: Display device, 7304: Display unit, 7400: Mobile phone, 7401: Housing, 7402: Display unit, 7403: Operation buttons, 7404: External connection port, 7405: Speaker, 7406: Microphone, 7407: Rechargeable battery, 7500: Electronic cigarette, 7501: Atomizer, 7502: Cartridge, 7504: Rechargeable battery, 7600: Tablet terminal, 7625: Switch, 7627: Switch,7628: Operation switch, 7629: Fastener, 7630: Housing, 7630a: Housing, 7630b: Housing, 7631: Display unit, 7631a: Display unit, 7631b: Display unit, 7633: Solar cell, 7634: Charge / discharge control circuit, 7635: Energy storage unit, 7636: DC-DC converter, 7637: Converter, 7640: Movable part, 8000: Display device, 8001: Housing, 8002: Display unit, 8003: Speaker unit, 8004: Secondary battery, 8030: SU, 8100: Illumination Lighting device, 8101: housing, 8102: light source, 8103: secondary battery, 8104: ceiling, 8105: side wall, 8106: floor, 8107: window, 8200: indoor unit, 8201: housing, 8202: air outlet, 8203: secondary battery, 8204: outdoor unit, 8300: electric refrigerator / freezer, 8301: housing, 8302: refrigerator door, 8303: freezer door, 8304: secondary battery, 9000: glasses-type device, 9000a: frame, 9000b: display unit, 9001: headset-type device Chair, 9001a: Microphone unit, 9001b: Flexible pipe, 9001c: Earphone unit, 9002: Device, 9002a: Housing, 9002b: Rechargeable battery, 9003: Device, 9003a: Housing, 9003b: Rechargeable battery, 9005: Wristwatch-type device, 9005a: Display unit, 9005b: Belt unit, 9006: Belt-type device, 9006a: Belt unit, 9006b: Wireless power supply / receiving unit, 9300: Cleaning robot, 9301: Housing, 9302: Display unit, 9303: Camera, 9304: Brush, 9305: Operation button, 9306: Rechargeable battery, 9310: Dust, 9400: Robot, 9401: Illuminance sensor, 9402: Microphone, 9403: Upper camera, 9404: Speaker, 9405: Display unit, 9406: Lower camera, 9407: Obstacle sensor, 9408: Movement mechanism, 9409: Rechargeable battery, 9500: Aircraft, 9501: Propeller, 9502: Camera, 9503: Rechargeable battery, 9504: Electronic component,

Claims

1. A secondary battery comprising a positive electrode, an electrolyte, and a negative electrode, The positive electrode has a positive electrode active material containing lithium cobalt oxide, The positive electrode active material comprises magnesium, nickel, and aluminum. The surface layer of the positive electrode active material has an O3 structure after more than 150 charge-discharge cycles, where charging is performed at CCCV (0.5C, termination current 0.2C, 4.5V) and discharging is performed at CC (0.5C, 3.0V) in a 60°C environment with 1C = 210mA / g (per weight of positive electrode active material). In the EDX analysis of the negative electrode, after the charge-discharge procedure, magnesium, aluminum, and cobalt were below the detection limit. The electrolyte is a secondary battery having a compound represented by general formula (G1). 【Chemistry 1】 (wherein R １ is an alkyl group having 1 to 4 carbon atoms, and R ２ , R ３ and R ４ are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and R ５ represents an alkyl group or a main chain composed of two or more atoms selected from the group consisting of C, O, Si, N, S and P. Further, A － is (C ｎ F ２ｎ＋１ SO ２ ) ２ N － amide-based anion represented by (n=0 to 3).

2. In claim 1, R shown in general formula (G1) １ It is one selected from a methyl group, an ethyl group, and a propyl group. R ２ , R ３ and R ４ One of them is a hydrogen atom or a methyl group, and the other two are hydrogen atoms. R ５ The main chain is composed of two or more alkyl groups or atoms selected from C, O, Si, N, S, and P. A － (FSO ２ ) ２ N － and (CF ３ SO ２ ) ２ N － A secondary battery that is one of the following, or a combination of the two.

3. In claim 1 or claim 2, R shown in general formula (G1) １ The number of carbon atoms it has and R ５ The number of carbon atoms it has and R ５ A secondary battery in which the number of oxygen atoms in and the sum of are 7 or less.

4. In claim 1 or claim 2, R shown in general formula (G1) １ R is a methyl group, ２ is a hydrogen atom, R ５ A secondary battery in which the sum of the number of carbon atoms and oxygen atoms is 6 or less.

5. In claim 1, The electrolyte is a secondary battery having one or more selected from 1-butyl-3-propylimidazolium cation, 1-ethyl-3-methylimidazolium cation, 1-butyl-3-methylimidazolium cation, 1-hexyl-3-methylimidazolium cation, and 1-methyl-3-(2-propoxyethyl)imidazolium cation.

6. In claim 1, The electrolyte is a secondary battery having a 1-ethyl-3-methylimidazolium cation.

7. An electronic device having a secondary battery according to any one of claims 1 to 6, a display unit, and a sensor.

8. A secondary battery according to any one of claims 1 to 7, an electric motor, and a control device, The control device is a vehicle having the function of supplying power from the secondary battery to the electric motor.

Images