Secondary battery

Abstract

To provide an electrolyte solution capable of suppressing ignition or the like, and a secondary battery having the electrolyte solution.SOLUTION: A secondary battery has a positive electrode, a negative electrode, a separator located between the positive electrode and the negative electrode, and an electrolyte solution. The electrolyte solution has a mixed solvent and a lithium salt. In the electrolyte solution, the concentration of the lithium salt is at least more than 1 mol per liter of the mixed solvent. The mixed solvent has a fluorinated chain carbonate and a fluorinate cyclic carbonate. In DSC measurement of the electrolyte solution, the peak of a heat flow rate in the exoergic reaction in a range of 180°C or more and 300°C or less is 200 mW / g or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a secondary battery. However, the technical field of the present invention is not limited to secondary batteries, and may also include semiconductors. device, display device, light-emitting device, power storage device, lighting device, electronic device, vehicle, and methods for manufacturing these devices For example, semiconductor devices, display devices, light-emitting devices, and power storage devices can be used. The secondary battery of the present invention is used as a necessary power source in devices, lighting devices, electronic devices, and vehicles. The electronic devices include information terminal devices equipped with secondary batteries. The electricity storage device includes a stationary electricity storage device. [Background technology]

[0002] In recent years, high-power, high-capacity lithium-ion secondary batteries have rapidly grown in popularity along with the development of the semiconductor industry. Demand for these batteries is expanding, and they are becoming an essential source of rechargeable energy in today's information society. It has become.

[0003] When a lithium-ion secondary battery is heated externally, the positive electrode, negative electrode, and electrolyte react independently. Or, the positive electrode, negative electrode, and electrolyte react with each other, causing an exothermic reaction. When the temperature of a lithium-ion secondary battery approaches 100°C, the negative electrode begins to break down, causing When heated above 100°C, a reduction reaction of the electrolyte occurs at the negative electrode, generating heat. After that, when the temperature of the lithium-ion secondary battery reaches nearly 180°C, thermal decomposition of the electrolyte occurs. It is known that oxygen release and thermal decomposition occur at the positive electrode, leading to thermal runaway. The resulting heat may cause the separator to melt. An internal short circuit occurs in the lithium-ion secondary battery, and the Joule heat generated by the internal short circuit causes the lithium ion This can cause the secondary battery to go into thermal runaway.

[0004] The heat generated by the lithium ion secondary battery causes hydrogen, carbon monoxide, carbon dioxide, or The gases include hydrocarbons and other gases that are generated by the organic solvents used in the electrolyte or the organic solvents. It is a thermal decomposition product and contains flammable gases, which may cause the lithium-ion secondary battery to ignite.

[0005] In order to suppress the thermal runaway reaction, Patent Document 1 describes a method of compounding a flame retardant into the positive electrode mixture or the negative electrode mixture. Furthermore, in Patent Document 2, positive and negative electrodes are alternately arranged with a separator interposed therebetween. A container for accommodating the stacked laminate, an electrolyte stored in the container, and a high-temperature electrolyte filled in the container. A configuration having a thermally conductive gas is proposed.

[0006] In addition, various research and development efforts are being conducted on the reliability and safety of lithium-ion secondary batteries. For example, Non-Patent Document 1 describes the thermal stability of positive electrode active materials and electrolyte solutions. . [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2009-16106 A [Patent Document 2] Patent Publication No. 2010-262792 [Non-patent literature]

[0008] [Non-Patent Document 1] Nobuo Eda 2-4 Heat Generation Mechanism Learning from Data Li-ion Battery Charging and Discharging Technology CQ Publishing April 4, 2020 pp. 68-72 Summary of the Invention [Problem to be solved by the invention]

[0009] To prevent thermal runaway or fire in secondary batteries, it is necessary to improve the electrolyte. Therefore, Patent Documents 1 and 2 do not consider the electrolyte solution. To provide an electrolyte solution with high thermal stability in order to at least suppress ignition or thermal runaway of a secondary battery. Another object of one embodiment of the present invention is to prevent at least the secondary battery from catching fire or overheating. To suppress running, an electrolyte that suppresses gas generation at temperatures above 25°C is provided. Another object of one embodiment of the present invention is to prevent at least fire or thermal runaway of a secondary battery. To suppress this, it is necessary to provide a separator that has high heat resistance and good wettability with respect to the electrolyte. Another object of one embodiment of the present invention is to provide a semiconductor device that can suppress at least fire or thermal runaway. One of the objectives is to provide a rechargeable battery.

[0010] The description of these problems does not preclude the existence of other problems. It is not necessary for the embodiments to solve all of these problems. It is also possible to extract other issues from the claims and other statements. [Means for solving the problem]

[0011] In view of the above-mentioned problems, one aspect of the present invention is a battery comprising a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. The electrolyte solution includes a mixed solvent and a lithium salt. In this case, the concentration of lithium salt is greater than 1 mole per liter of the mixed solvent, and the mixed solvent contains fluorine. Fluorinated linear carbonate and fluorinated cyclic carbonate, and Diffe In differential scanning calorimetry (DSC) measurements, The peak heat flow of the exothermic reaction in the range of 180°C to 300°C is 200mW / g or more. Below is a secondary battery.

[0012] Another aspect of the present invention is a battery comprising a positive electrode, a negative electrode, a separator positioned between the positive electrode and the negative electrode, and an electrode. The electrolyte solution includes a mixed solvent and a lithium salt. The concentration of the fluorinated chain carbonyl salt is greater than 1 mole per liter of the mixed solvent. and a fluorinated cyclic carbonate, and in DSC measurement of the electrolyte, The peak heat flow rate of the exothermic reaction in the range of 80°C to 300°C is 100mW / g or less That is, a secondary battery.

[0013] Another aspect of the present invention is a battery comprising a positive electrode, a negative electrode, a separator positioned between the positive electrode and the negative electrode, and an electrode. The electrolyte solution includes a mixed solvent and a lithium salt. The concentration of the fluorinated chain carbonyl salt is greater than 1 mole per liter of the mixed solvent. and a fluorinated cyclic carbonate, and in DSC measurement of the electrolyte, The peak heat flow rate of the exothermic reaction in the range of 80°C to 300°C is 200mW / g or less The separator has an imide compound in a region that comes into contact with the electrolyte solution.

[0014] Another aspect of the present invention is a battery comprising a positive electrode, a negative electrode, a separator positioned between the positive electrode and the negative electrode, and an electrode. The electrolyte solution includes a mixed solvent and a lithium salt. The concentration of the fluorinated chain carbonyl salt is greater than 1 mole per liter of the mixed solvent. and a fluorinated cyclic carbonate, and in DSC measurement of the electrolyte, The peak heat flow rate of the exothermic reaction in the range of 80°C to 300°C is 100mW / g or less The separator has an imide compound in a region that comes into contact with the electrolyte solution.

[0015] In the present invention, the lithium salt is LiPF6, LiClO4, LiAsF6, LiBF4 , LiAlCl4, LiSCN, LiBr, LiI, Li2SO4, Li2B 10 Cl1 0, Li2B 12 Cl 12 , LiCF3SO3, LiC4F9SO3, LiC(CF3S O2)3, LiC(C2F5SO2)3, LiN(CF3SO2)2, LiN(C4F9 SO2)(CF3SO2), LiN(C2F5SO2)2 It is preferable to have one.

[0016] In the present invention, the fluorinated chain carbonate is preferably FEC.

[0017] In the present invention, the fluorinated cyclic carbonate is preferably MTFP.

[0018] In the present invention, the imide compound is preferably a polyimide. [Effects of the Invention]

[0019] According to one embodiment of the present invention, an electrolyte solution with high thermal stability can be provided. According to one embodiment, an electrolyte solution is provided in which gas generation at temperatures higher than 50°C is suppressed. According to one embodiment of the present invention, a separator having high heat resistance and good wettability with respect to an electrolyte solution can be obtained. Furthermore, according to one aspect of the present invention, a heater that can suppress ignition or thermal runaway can be provided. It is possible to provide a secondary battery. [Brief explanation of the drawings]

[0020] [Figure 1] 1A to 1D illustrate a separator included in a secondary battery of one embodiment of the present invention. [Figure 2] 2A and 2B illustrate a secondary battery of one embodiment of the present invention. [Figure 3] FIG. 3A illustrates a secondary battery of one embodiment of the present invention, and FIG. 3B illustrates a positive electrode active material layer of one embodiment of the present invention. [Figure 4] FIG. 4 is a diagram illustrating an electrolyte injection device. [Figure 5] 5(A) and 5(B) are diagrams illustrating a bendable secondary battery according to one embodiment of the present invention. [Figure 6] FIG. 6 is a diagram illustrating a method for producing a positive electrode active material. [Figure 7] 7(A) to 7(C) are diagrams illustrating a method for producing a positive electrode active material. [Figure 8] 8(A) and 8(B) are diagrams illustrating the positive electrode active material. [Figure 9] 9A to 9F are cross-sectional views illustrating the positive electrode active material. [Figure 10] FIG. 10 is a diagram illustrating the crystal structure of the positive electrode active material. [Figure 11] FIG. 11 is a diagram illustrating the crystal structure of a conventional positive electrode active material. [Figure 12] FIG. 12 shows the XRD pattern calculated from the crystal structure. [Figure 13] FIG. 13 shows an XRD pattern calculated from the crystal structure. [Figure 14] 14(A) to 14(G) are diagrams for explaining the positional relationship of distribution in EDX line analysis. [Figure 15] FIG. 15 is a diagram illustrating a method for producing a negative electrode active material layer. [Figure 16] FIG. 16 is a diagram illustrating a TMA test device. [Figure 17] FIG. 17 is a diagram illustrating a tensile testing machine. [Figure 18] 18(A) and 18(B) are diagrams illustrating the nail penetration test. [Figure 19] FIG. 19 is a diagram illustrating the nail penetration operation. [Figure 20] FIG. 20 is a graph showing changes when the internal temperature rises in a secondary battery in which an internal short circuit has occurred. [Figure 21] FIG. 21 is a graph showing changes when the internal temperature of the secondary battery increases. [Figure 22] 22(A) is an exploded perspective view of a coin-type secondary battery, FIG. 22(B) is a perspective view of the coin-type secondary battery, and FIG. 22(C) is a cross-sectional perspective view thereof. [Figure 23] Fig. 23(A) shows an example of a cylindrical secondary battery. Fig. 23(B) shows an example of the internal structure of a cylindrical secondary battery. Fig. 23(C) shows an example of multiple cylindrical secondary batteries. Fig. 23(D) shows an example of a power storage system having multiple cylindrical secondary batteries. [Figure 24] 24(A) and 24(B) are diagrams for explaining an example of a secondary battery, and FIG. 24(C) is a diagram showing the internal structure of the secondary battery. [Figure 25] 25(A) to 25(C) are diagrams illustrating examples of secondary batteries. [Figure 26] 26(A) and 26(B) are diagrams showing examples of secondary batteries. [Figure 27] FIG. 27(A) shows an example of the configuration of an automobile, FIG. 27(B) shows a battery pack, and FIG. 27(C) shows an example of the configuration of an electric automobile and a battery pack. [Figure 28] 28(A) to 28(D) are diagrams showing an example of space equipment. [Figure 29] FIG. 29 shows the results of DSC measurement of the electrolyte solution. [Figure 30] FIG. 30 is a graph showing the vapor pressure of the electrolyte solution versus the temperature. [Figure 31] FIG. 31 shows the results of Raman spectroscopic analysis of the electrolyte solution. [Figure 32] FIG. 32 shows the results of DSC measurement of the separator. [Figure 33] Figures 33(A) and 33(B) show the results of TMA analysis of the separator. [Figure 34] 34(A) and 34(B) are images of the nail penetration test. DETAILED DESCRIPTION OF THE INVENTION

[0021] The present invention will be described with reference to the accompanying drawings. The present invention is not limited to the above embodiment, and various modifications and variations in form and detail may be made without departing from the spirit and scope of the present invention. It will be readily apparent to those skilled in the art that various modifications may be made to the present invention. In the embodiments, reference numerals indicating the same objects are common to different drawings.

[0022] In this specification, the ordinal numbers "first" and "second" are used for convenience and are not included in the structure. The number of components or the order of the components is not limited. The order of the components may be, for example, The ordinal numbers used in the embodiments of this specification include the order of processes and the order of stacking. The ordinal numbers used in the claims may not be consistent with those used in the embodiments of this specification. The ordinal numbers used in the examples do not match the ordinal numbers used in the claims. In addition, the ordinal numbers used in the embodiments of this specification are used in the examples of this specification. may not match the ordinal numbers used.

[0023] In this specification and the like, a lithium ion secondary battery may be referred to as a lithium ion battery. The term "carrier ion" refers to a secondary battery that uses lithium ions as carrier ions. The ions are not limited to lithium ions. For example, alkali metal ions can be used as carrier ions in the present invention. Metal ions or alkaline earth metal ions can be used, specifically sodium ions. In this case, lithium ions can be replaced with sodium ions, etc. The present invention can be understood by the above. When describing this, it may be referred to as a secondary battery or a battery.

[0024] In this specification and the like, the positive electrode active material may be referred to as a composite oxide, a positive electrode material, a positive electrode material for a secondary battery, It is sometimes referred to as a positive electrode material for lithium-ion secondary batteries.

[0025] In this specification, the electrolytic solution may be referred to as an electrolyte. The electrolytic solution is a liquid at 25°C. This also means that the electrolyte is not limited to the state at 25°C.

[0026] In this specification, the space group is expressed in international notation (or Hermann-Mauguin notation) as follows: Short notation is used to express the crystal planes and bonds. The notation of space groups, crystal planes, and crystal directions is given by the superscript However, due to formatting restrictions in this specification, instead of adding a bar above the number, It may be expressed by adding a minus sign (-). Also, individual orientations that indicate directions within a crystal is [ ], collective orientation indicating all equivalent directions is < >, individual faces indicating crystal faces are ( ) The set of planes with equivalent symmetry is expressed as {}. Also, it is expressed in the space group R-3m. The trigonal crystal is generally represented as a hexagonal composite hexagonal lattice for ease of understanding the structure. Unless otherwise specified, the space group R-3m is represented by a composite hexagonal lattice in this specification. The Miller indices are sometimes used as (hkil) instead of (hkl). Here, i is - (h+k).

[0027] In this specification, the space group of the positive electrode active material and the like is determined by XRD, electron beam diffraction, neutron beam diffraction, etc. Therefore, in this specification and the like, a certain molecule belonging to a certain space group is identified by Belonging to a space group or being a space group is another way of saying that a molecule is identified with a space group. can be done.

[0028] In this specification, a structure in which three layers of anions are stacked one on top of the other, such as ABCABC, is used. If the structure is such that it is a cubic close-packed structure, then the anions are strictly arranged in a cubic lattice. In addition, since real crystals always have defects, analytical results do not necessarily match the theory. For example, electron diffraction patterns or TEM (Transmission El FFT (Fast Fourier Transform) of electron microscope and transmission electron microscope images In the transformed pattern, spots may appear at positions slightly different from the theoretical positions. For example, if the deviation between the theoretical position and orientation is 5° or less, or 2.5° or less, it is a cubic close-packed structure. It can be said that this is a structure.

[0029] In this specification and the like, the (001) plane, the (003) plane, etc. are collectively referred to as the (001) plane. In this specification, the (001) plane is also called the C plane, the basal plane, etc. In addition, lithium in lithium cobalt oxide has two-dimensional diffusion paths. In other words, the diffusion path of lithium exists along the (001) plane. In the case of the surface where the diffusion path of lithium is exposed, that is, the surface where lithium is inserted and desorbed (specifically In practice, surfaces other than the (00l) surface are sometimes called edge surfaces.

[0030] In this specification and the like, the particle is not limited to a particle having a circular cross-sectional shape, that is, a so-called spherical shape. Particle cross-sectional shapes include oval, rectangular, trapezoidal, triangular, square with rounded corners, and asymmetrical shapes. When there are a plurality of particles, the cross-sectional shapes of the particles may be different from each other.

[0031] In this specification etc., when describing the characteristics of individual particles of the positive electrode active material in the embodiments etc. However, it is not necessary that all particles have this characteristic. For example, three or more particles are randomly selected. Of the particles of the selected positive electrode active material, 50% or more, preferably 70% or more, more preferably 90% or more, % or more of the characteristic, the characteristics of the positive electrode active material and the secondary battery containing the same are sufficiently improved. It can be said that it has an improving effect.

[0032] In this specification, particle size is measured using a particle size distribution analyzer (laser diffraction particle size analyzer) that uses a laser diffraction / scattering method. In this specification, the average particle size can be measured by a particle size distribution measuring device. The D50 is the cumulative curve of the particle size distribution measurement results. The particle size is the particle size when the cumulative amount accounts for 50%.

[0033] In this specification and the like, the measurement of particle size is not limited to laser diffraction particle size distribution measurement, SEM (Scanning Electron Microscope) The major axis of the particle cross section may be measured by analysis such as TEM or TEM. The maximum particle size that can be confirmed on a cross section of a positive electrode having a size of 100 μm square can be used. In addition, as a method for measuring D50 by SEM or TEM analysis, for example, 20 or more The particle size at which the cumulative amount accounts for 50% is called D50. It can be said that:

[0034] In this specification, the theoretical capacity of the positive electrode active material is the capacity of the positive electrode active material that can be inserted and removed. For example, the theoretical capacity of LiCoO2 is The theoretical capacity of LiNiO2 is 274mAh / g per weight, and that of LiMn The theoretical capacity of 2O4 is 148 mAh / g by weight.

[0035] In this specification, the amount of lithium remaining in the positive electrode active material that can be inserted or removed is referred to as the amount of lithium remaining in the positive electrode active material. , x in the composition formula, for example, Li x It is sometimes represented by x in MO2. Note that M represents a transition metal. In this specification and the like, unless otherwise specified, M is cobalt and / or nickel. In the case of the positive electrode active material in a lithium-ion secondary battery, x = (theoretical capacity - charging capacity) / theoretical capacity For example, a lithium-ion battery with a positive electrode active material comprising lithium cobalt oxide can be used. When a Li-ion secondary battery is charged at 219.2mAh / g, 0.2 CoO2 or x=0. 2. Li x For example, x in MO2 is small, for example, 0.1 <x≦0.24 This refers to

[0036] In this specification and the like, it is assumed that the lithium cobalt oxide properly synthesized before use in the positive electrode is stoichiometrically When the ratio is approximately satisfied, it is LiCoO2 and x = 1. The lithium cobalt oxide contained in lithium-ion secondary batteries is also LiCoO2, where x=1. The state where discharge is completed (discharged state) here means, for example, 100 mA / g or less. This refers to a state in which the voltage is 3.0V or less or 2.5V or less at a current of 1.

[0037] In this specification, Li x The charge capacity and / or discharge capacity used to calculate x in MO2 is It is preferable to measure under conditions where there is little or no influence of short circuit and / or thermal decomposition of the electrolyte. For example, data on a secondary battery that has experienced a sudden change in capacity that is thought to be due to a short circuit is used to calculate x. It should not be.

[0038] In this specification, the distribution of a certain element means the range in which the element is not noise in a certain analytical method. The term "area where the signal is detected continuously within the noise range" refers to the area where the signal is detected continuously within the noise range. The region can also be referred to as the region in which the element is detected above the lower detection limit.

[0039] In this specification and the like, unless otherwise specified, the materials (positive electrode, negative electrode, electrolyte) contained in the secondary battery The description of the state of the secondary battery (including the separator, etc.) before deterioration will be given. The decrease in discharge capacity due to aging and burn-in treatments in the first stage is considered to be degradation. For example, if the rated capacity of a secondary battery consisting of a single cell or a battery pack is 97% or more, If the battery has a discharge capacity, it can be said to be in a state before deterioration. For secondary batteries for instruments, the standard shall comply with JIS C 8711:2019. For other secondary batteries, the standard shall comply with JIS C 8711:2019. In this case, not only the above JIS standards but also other JIS and IEC standards for electric vehicle propulsion, industrial use, etc. Comply.

[0040] In this specification, etc., the term "secondary particles" refers to particles formed by aggregation of primary particles. In this specification, the term "primary particles" refers to particles that do not have grain boundaries visible on the surface. In this specification, a primary particle may be referred to as a single particle. It can be said to be the interface between two crystals that come into contact with each other.

[0041] Here, we will explain the flow of electrons and lithium ions in a secondary battery during charging. When a charger is connected and charging of the secondary battery begins, electrons are released from the positive electrode and an oxidation reaction occurs. At the negative electrode, electrons are supplied and a reduction reaction occurs. Then, lithium ions are released from the positive electrode. During discharge, a reduction reaction occurs at the positive electrode. In other words, in a secondary battery, the anode (positive electrode) ) and the cathode (negative electrode) are switched, and the oxidation reaction and reduction reaction are switched. The electrode with a high reaction potential is called the positive electrode, and the electrode with a low reaction potential is called the negative electrode. In the specification, the positive electrode is referred to as the "positive electrode" or "+ electrode" whether it is charging or discharging. The positive electrode is called the "positive electrode" and the negative electrode is called the "negative electrode" or "-electrode (minus electrode)."

[0042] In this specification, a full cell refers to a cell in which different electrodes are positioned, such as a positive electrode / negative electrode unit cell. In this specification, a half cell refers to a cell assembled to This refers to a cell assembled using aluminum metal as the negative electrode (counter electrode).

[0043] In this specification, unless otherwise specified, the charging voltage is based on the potential of lithium metal. In this specification, a high charging voltage refers to a charging voltage of, for example, 4.6 V or higher. The voltage is preferably 4.65 V or more, more preferably 4.7 V or more, and even more preferably Preferably, the voltage is 4.75 V or higher, and most preferably 4.8 V or higher. In the case of half cells using silicon metal, a charging voltage of 4.6V or more is called a high charging voltage. Let's say.

[0044] In this specification, the high charging voltage refers to the potential when the negative electrode is made of a carbon material (for example, graphite). In other words, the charging voltage should be 4.5V or higher. For full cells that use graphite, a charging voltage of 4.5V or higher is called a high charging voltage. It shall be.

[0045] In this specification, carbonate refers to a compound having at least one carbonate ester in its molecular structure. Unless otherwise specified, this refers to compounds containing cyclic carbonates and linear carbonates. Furthermore, the term "chain" includes both straight chain and branched chain.

[0046] In this specification and the like, a mixed solvent refers to a mixture of two or more solvents.

[0047] In this specification and the like, the porosity can be a value calculated from the volume, density, and mass. In this specification, the voids of an object having voids are filled with an organic material, and then processed into a thin film. The porosity can also be calculated based on the observed image of the object. Ion beam (Ion Beam) or ion milling can be used.

[0048] In this specification and the like, flexibility refers to the property that an object is soft and deformable. In the above, an object having flexibility means that at least a part of the object has flexibility. In other words, a flexible object has inflexible parts (also called hard parts). It may have.

[0049] In this specification, a secondary battery that can be transformed according to a transformable electronic device is referred to as a transformable These batteries are called shapable secondary batteries, flexible secondary batteries, or flexible batteries. In the above, deformability means that the shape of an object can change, and the object can respond to external forces acting on it. In this specification, the term "object" refers to an object whose shape changes in response to an external force. Shape means that it can be deformed by an average adult's hand without excessive force.

[0050] In this specification and the like, the shape of an object deformed in response to an external force includes the shape of an object bent in response to an external force. In this specification and the like, the shape of the electronic device that can be bent to follow the bendable electronic device is included. The secondary battery that can be bent is called a bendable secondary battery, a foldable battery or a battery Foldable batteries are also called foldable batteries. Includes folded shapes.

[0051] In this specification, etc., the bendable electronic device and the bendable secondary battery The present invention also includes a state in which the device is bent and fixed, and a state in which the device is repeatedly bent and stretched. In the detailed description, the form in which bending and stretching are repeated is shown with a bent state and a state before bending. In this specification, the state before bending includes a straight state, etc. Included.

[0052] In this specification, ignition in the nail penetration test means that a flame occurs within one minute after the nail is inserted into the cell. This refers to the occurrence of thermal runaway in a secondary battery, or the occurrence of a thermal runaway in a secondary battery. After the nail penetration test is completed, the positive and / or negative electrodes are Thermal runaway occurs when thermal decomposition products of the electrodes are observed. If a flame occurs but no flame is observed, it is considered non-ignition.

[0053] In this specification, "A and / or B" may be used, but this does not mean "A" and "B" " or "A and B."

[0054] (Embodiment 1) The secondary battery according to one embodiment of the present invention has an electrolyte solution, and the electrolyte solution contains at least a solvent and a lithium salt. Has.

[0055] [solvent] The solvent contained in the electrolytic solution according to one embodiment of the present invention will be described. It is preferable to have a solvent. Furthermore, as a mixed solvent, a fluorinated cyclic carbonate (fluorinated cyclic carbonate) Chain carbonates), and fluorinated chain carbonates (fluorinated chain carbonates) It is preferable to use a mixture of the above-mentioned compounds (sometimes referred to as "catenate"). A mixed solvent of fluorinated cyclic carbonate and fluorinated chain carbonate is called a fluoride mixed solvent. Both fluorinated cyclic carbonates and fluorinated linear carbonates have electron-withdrawing properties. The solvation energy with the lithium ion, which is the carrier ion, is However, it is possible to form a solvate in a secondary battery and use it as a mixed solvent. This is preferable.

[0056] The fluoride mixed solvent has a low viscosity at room temperature (for example, 25° C.), making it preferable as an electrolyte. In particular, fluorinated chain carbonates are expected to have low viscosity at low temperatures (e.g., 0°C). Therefore, the mixed solvent containing fluorinated chain carbonate is suitable for the secondary battery at low temperatures (including below freezing). It is suitable for use.

[0057] Furthermore, an electrolyte solution containing a fluoride mixed solvent is preferable because it can suppress exothermic reactions. The exothermic reaction was measured by differential scanning calorimetry (DSC). The heat flow rate obtained from the calorimeter measurement can be used as a reference. Suppressing the reaction includes keeping the peak of the heat release (heat flow) low. Suppressing the reaction means that the starting temperature of the exothermic reaction is set to a higher temperature. In the case of secondary batteries containing fluoride mixed solvents, the internal temperature of the secondary battery increases due to an internal short circuit. Even if the battery is heated, the exothermic reaction is suppressed, so that thermal runaway and / or fire of the secondary battery can be prevented. do.

[0058] In addition, the vapor pressure of the fluoride mixed solvent is low at temperatures above 50°C, so the vaporization at that temperature is Therefore, a secondary battery having a fluoride mixed solvent as an electrolyte solution can: Even if the internal temperature of the secondary battery rises due to an internal short circuit, the generation of flammable gas from the electrolyte is suppressed. This makes it possible to prevent thermal runaway and / or fire of the secondary battery.

[0059] Examples of fluorinated cyclic carbonates include fluoroethylene carbonate (fluorocarbonate) Ethylene, FEC, F1EC), difluoroethylene carbonate (DFEC, F2EC) ), trifluoroethylene carbonate (F3EC), or tetrafluoroethylene carbonate DFEC can be used with cis-4,5, tetracarbonate (F4EC), etc. There are isomers such as lance-4 and lance-5. All fluorinated cyclic carbonates exhibit electron-withdrawing properties. Because of the substituent, the solvation energy of lithium ions is low, making it a preferable solvent for the mixture. stomach.

[0060] The structural formula of FEC is as follows (H10). The substituent is an F group.

[0061] [ka]

[0062] An example of a fluorinated chain carbonate is methyl 3,3,3-trifluoropropionate. The abbreviation for methyl 3,3,3-trifluoropropionate is "MTFP." The structural formula of MTFP is as shown in the following structural formula (H22). The substituent is a CF3 group.

[0063] [ka]

[0064] As a fluorinated chain carbonate, trifluoromethyl 3,3,3-trifluoropropionate The structural formula of trifluoromethyl 3,3,3-trifluoropropionate is as follows: The structural formula is (H23). In chloromethyl, the electron-withdrawing substituent is a CF3 group.

[0065] [ka]

[0066] An example of a fluorinated chain carbonate is trifluoromethyl propionate. The structural formula of trifluoromethyl is as shown below: Propionic acid In trifluoromethyl, the electron-withdrawing substituent is a CF3 group.

[0067] [ka]

[0068] Fluorinated chain carbonates include methyl 2,2-difluoropropionate. The structural formula of methyl 1-difluoropropionate is shown below as structural formula (H25). In methyl 2,2-difluoropropionate, the electron-withdrawing substituent is the CF2 group .

[0069] [ka]

[0070] Fluorinated chain carbonates include 2,2,2-trifluoroethylmethyl carbonate. The structural formula of 2,2,2-trifluoroethylmethyl ester is as shown in the following structural formula (H26). In 2,2,2-trifluoroethylmethyl carbonate, the electron-withdrawing substituent is C It is an F3 group.

[0071] [ka]

[0072] The mixed solvent according to one embodiment of the present invention comprises one or more fluorinated cyclic carbonates selected from the above-mentioned fluorinated cyclic carbonates. and fluorinated chain carbonates. It is more preferable to include FEC and MTFP. The reason for this will be explained below.

[0073] [FEC and MTFP] FEC is a fluorinated cyclic carbonate with a high dielectric constant, making it suitable for use in electrolytes. When used, it has the effect of promoting the dissociation of lithium salts. FEC also exhibits electron-withdrawing properties. Since it has fluorine as a substituent, it is different from ethylene carbonate which does not have a substituent that exhibits electron-withdrawing properties. Compared to FEC, desolvation of lithium ions is more likely to proceed. The solvation energy of lithium ions is smaller than that of ethylene carbonate (EC). Therefore, lithium ions are easily released from the surfaces of the positive and negative electrode active materials, and secondary This is preferable because it can reduce the internal resistance of the battery.

[0074] Furthermore, FEC is the highest occupied molecular orbital (HOMO). It is difficult to oxidize due to its deep (orbital) level, and is favored for its high oxidation resistance. On the other hand, one concern with FEC is its high viscosity. It is preferable to use the mixed solvent containing MTFP as the electrolyte. Specifically, MTFP has the following properties: It is possible to maintain low viscosity even when the solvation energy is small. However, since the solvation energy of MTFP varies depending on the molecular configuration, When the energy is large, it may form a solvate with lithium ions. FEC and MTFP are preferred because they can both form solvates with lithium ions. stomach.

[0075] HOMO levels, solvation energies, and boiling points for FEC, MTFP, EC, and MP The HOMO level and solvation energy are calculated using quantum chemical calculations. In the table below, the larger the solvation energy value, the easier it is to solvate. Indicates that.

[0076] [Table 1]

[0077] The mixed solvent used for the electrolyte contains more fluorinated chain carbonate than fluorinated cyclic carbonate. For example, if the total content of the mixed solvent is 100 vol%, The fluorinated cyclic carbonate FEC and the fluorinated linear carbonate MTFP were The volume ratio (vol%) is x:100-x (where 5≦x≦30, preferably 10≦x≦ 20.) It is preferable to mix it so that MTFP is greater than FEC. When a large proportion of ZnO is mixed, the viscosity of the electrolyte can be reduced, which is preferable as an electrolyte. stomach.

[0078] Furthermore, each solvent in the mixed solvent is It is preferable that peaks due to impurities are hardly visible by measurement such as resonance. "Almost undetectable" means that the area of ​​the peak due to impurities is smaller than the integrated area of ​​the peak due to the main component. The ratio of the integrated areas of the peaks (simply referred to as the integral ratio) is 0.005 or less, preferably 0.002 This includes the following:

[0079] For example, in the case of MTFP, when 1H-NMR was measured using acetonitrile-d3 solvent, It is known that four peaks occur between 3.29 ppm and 3.43 ppm. However, if other peaks occur in this vicinity, for example, δ is 3.24 ppm or more and 3.29 ppm or more. If a peak appears below ppm, it is considered to be due to an impurity. The peak area between 29 ppm and 3.43 ppm is 3.24 ppm and 3.29 ppm. The ratio of peak areas below ppm (integral ratio) is 0.005 or less, preferably 0.002 or less In this case, it can be said that peaks due to impurities are almost impossible to detect.

[0080] The device used for NMR measurement is not particularly limited, but for example, Bruker's AVANCE In addition, in 1H-NMR measurement, The central peak of the five peaks of acetonitrile derived from acetonitrile-d3 used can be set to 1.94 ppm.

[0081] The mixed solvent preferably has a low content of water (H2O) or moisture and is highly purified. Specifically, the water (H2O) or moisture contained in the mixed solvent is 100 ppm or less. The moisture content is preferably 50 ppm or less, and more preferably less than 10 ppm. It can be measured by the Karl-Fischer titration method.

[0082] [Solvent that can be added] Another solvent may be added to the above-mentioned mixed solvent. For example, ethylene carbonate (EC), propylene carbonate (PC), butyl Carbonate, chloroethylene carbonate, vinylene carbonate, γ-butyrolactone ton, γ-valerolactone, dimethyl carbonate (DMC), diethyl carbonate ( DEC), ethyl methyl carbonate (EMC), methyl formate, methyl acetate, ethyl acetate , methyl propionate (MP), 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 two of these The above can be mentioned.

[0083] [Lithium salt] Next, lithium salts will be described. Examples of lithium salts include LiPF6 and LiClO 4, LiAsF6, LiBF4, LiAlCl4, LiSCN, LiBr, LiI, Li 2SO4, Li2B 10 Cl 10 , Li2B 12 Cl 12 , LiCF3SO3, LiC4 F9SO3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiN(CF3 SO2)2, LiN(C4F9SO2)(CF3SO2), LiN(C2F5SO2)2 One or more of these lithium salts may be used in any combination and ratio. For example, the fluorides LiPF6 and LiBF4 can be used to In order to improve the safety of the lithium secondary battery, LiPF6 and LiBF4 are used as lithium salts. The concentration of the lithium salt in the electrolyte is 1 liter of the mixed solvent. More than 1 mol and less than 3.0 mol per mole, preferably more than 1 mol and less than 2.0 mol per mole. 1 liter of mixed solvent means 1 liter of the total amount of mixed solvent. is.

[0084] For example, in a fluoride mixed solvent, the concentration is higher than 1 mol and 3 mol per liter of the fluoride mixed solvent. 0 mol or less, preferably greater than 1 mol and less than 2.0 mol of lithium salt If the electrolyte is made of a material that has been treated with a nitriding agent, even if the internal temperature of the secondary battery rises due to an internal short circuit, This can prevent thermal runaway and / or fire of the secondary battery. fluoride mixture solvent, more than 1 mol and not more than 3.0 mol, preferably 1 When a lithium salt with a concentration of more than 1.0 mol and less than 2.0 mol is dissolved, a highly thermally stable electrode is obtained. Furthermore, the fluoride mixed solvent contains 1 liter of More than 1 mol and less than 3.0 mol, preferably more than 1 mol and less than 2.0 mol Dissolving the following lithium salts will give 1 mol or less of lithium per liter of fluoride-mixed solvent. This electrolyte has a lower vapor pressure at temperatures above 50°C than an electrolyte containing a lithium salt. Therefore, if the internal temperature of the secondary battery rises due to an internal short circuit and exceeds 50°C, Even in this case, gas generation can be suppressed.

[0085] [DSC measurement] The electrolyte solution used in the secondary battery according to one embodiment of the present invention is resistant to oxidation at temperatures in the range of 180°C or higher and 300°C or lower. The peak heat flow (calorific value) is 200mW / g or less, preferably 100mW / g or less. If there are two or more peaks in the above temperature range, the maximum peak is 200mW. It is preferable that the peak power is 100mW / g or less, and preferably 100mW / g or less. If there are two or more peaks, all peaks should be 200mW / g or less, preferably 100mW / g or less. It is more preferable to satisfy the following: g or less. Surprisingly, the heat flow (calorific value) obtained from DSC measurement is independent of the concentration of the lithium salt, and there is no significant difference in the concentration of the lithium salt. By using a mixed solvent, the heat flow (heat generation amount) in the range of 180℃ to 300℃ The peak can be 200 mW / g or less, preferably 100 mW / g or less. For the value of the heat flow, please refer to the examples described later. In the secondary battery containing the mixed solvent, even if the internal temperature of the secondary battery rises due to an internal short circuit, the heat Since the reaction is suppressed, thermal runaway and / or fire of the secondary battery can be prevented.

[0086] The device and conditions for DSC measurement are not particularly limited, but in this embodiment, the following device and It is preferable to measure under these conditions. DSC equipment: Rigaku EVO2 DSC8271 Heating rate: 5℃ / min to 10℃ / min Temperature range: Room temperature (25°C) to 500°C The obtained measurement results were analyzed using the analysis software Thermo prus EVO. Background correction was performed. Heat flow was calculated as the heat flow per sample weight. It was decided.

[0087] [Combustion test] It is preferable to confirm non-flammability and thermal stability by a combustion test, which does not contradict the DSC measurement. The electrolyte solution used in the secondary battery according to one embodiment of the present invention is preferably non-flammable.

[0088] [Vapor pressure] The vapor pressure is a value that depends on the temperature, and surprisingly, the vapor pressure of the electrolyte also depends on the concentration of the lithium salt. The vapor pressure of the electrolyte solution used in the secondary battery according to one embodiment of the present invention is If the concentration of the electrolyte is higher than 1.0 mol per liter of the mixed solvent, the vapor pressure of the electrolyte at 50°C will be It is possible to satisfy the pressure of 0.03 MPa or less. If the temperature is higher than 1.0 mol per liter, the vapor pressure of the electrolyte at 75°C will be 0.08 MPa. It is possible to satisfy the following. In addition, the concentration of lithium salt per liter of fluoride mixed solvent is If the concentration is higher than 1.0 mol, the vapor pressure of the electrolyte at 100°C will be 0.2 MPa or less. It is also possible to obtain a lithium salt solution with a concentration of 1.0 per liter of the fluoride mixed solvent. If the temperature is higher than 1000 mol, the vapor pressure of the electrolyte at 125°C can be 0.3 MPa or less. In addition, the lithium salt concentration is less than 1.0 mol per liter of the fluoride mixed solvent. At the highest, the vapor pressure of the electrolyte at 150°C can be 0.4 MPa or less. For the value of the vapor pressure, reference can be made to the examples described later.

[0089] [Additives] The electrolyte solution contained in the secondary battery according to one embodiment of the present invention may be added as long as it has the above-described structure. The additives may be added. The additives are listed as the mixed solvents above. Other organic materials that can be used as additives include , vinylene carbonate (VC), propane sultone (PS), tert-butylbenzene (TBB), lithium bis(oxalato)borate (LiBOB), and succinyl It is preferable that the compound has one or more selected from dinitrile compounds such as tolyl or adiponitrile. The concentration of the additive must be 0.1 wt% or more of the total weight of the mixed solvent and lithium salt. 10 wt% or less is preferable. FEC, VC, or LiBOB tend to form a good coating. Therefore, it is preferable as an additive. When FEC is used as a fluoride mixed solvent, There is no need to have an FEC as the

[0090] Among the additives mentioned above, 1,3-propane sultone (PS) is a Because it has the same HOMO and LUMO levels as diethyl carbonate (DEC) and diethyl carbonate (DEC), Even when a high cutoff voltage is used as a charge / discharge condition, oxidation / reduction is unlikely to occur. When PS is decomposed on the surface of the positive electrode active material, it tends to become a polymer, and there is a possibility that it will gasify. The electrolyte has the advantage of being small in weight compared to the total weight of the mixed solvent and lithium salt. It is preferable that the electrolyte contains 0.25 wt % to 7.5 wt % of PS. By mixing additives, gas generation at temperatures above 25°C can be suppressed. Cut.

[0091] [Separator] The separator according to one embodiment of the present invention has a wettability with respect to the electrolyte solution containing the mixed solvent described above. Specific compounds having high wettability with the electrolyte solution containing the above-mentioned mixed solvent are is an imide compound, and typically polyimide is preferably used. It is preferable that the imide compound is present in the region in contact with the electrolyte. Because there is polarized oxygen, the polarized oxygen is hydrogen in the fluoride mixed solvent, typically water in FEC. It is believed that the wettability is high because of the interaction with hydrogen in the silicon dioxide and MTFP. In these cases, wettability can be evaluated by the contact angle. The contact angle is based on JISR3257. It is preferable to measure based on the above, for example, in a 25°C environment with an electric potential of 10 μL or more and 25 μL or less. Measurement can be performed after 30 to 60 seconds have elapsed since the solution was dropped onto the separator material. The contact angle can be measured from an image observed from the horizontal direction. It is preferable to use an average value of values ​​measured at multiple points. The term "good" means that the contact angle is less than 30 degrees, preferably less than 20 degrees, and more preferably less than 10 degrees. Less than.

[0092] Specific examples of the separator will be described with reference to FIGS. 1(A) to 1(D).

[0093] As shown in FIG. 1(A), the separator 105 can have a single layer structure having a member 15. The contact angle of the member 15 with respect to the electrolyte is less than 30 degrees, preferably less than 20 degrees, and more preferably Preferably, the angle is less than 10 degrees. High wettability with respect to the electrolyte improves the injection of the electrolyte into the exterior body. Furthermore, it is preferable that the member 15 located on the surface of the separator 105 has high wettability with respect to the electrolyte. This means that the electrolyte in the separator 105 remains constant even when the electrode expands and contracts during charging and discharging. It is preferable to use an imide compound as a material that satisfies the above contact angle. The imide compound is preferably a polyimide or a polyamic acid (a precursor of polyimide). When the above-mentioned DSC measurement is performed on the separator material, Below, preferably those that do not show a peak that is considered to be an endothermic reaction between 25°C and 350°C It has high heat resistance, and it can be said that secondary batteries using this separator material are highly safe. Imide compounds, specifically polyimides, are separator materials that do not exhibit endothermic reactions in this range. However, materials other than polyimide can be used as long as they do not show an endothermic reaction at the above temperatures. It's okay.

[0094] As shown in FIG. 1(B), the separator 105 is made up of the members 17, 16, and 15 in this order. The members 15 and 17 are each a layered structure. It is preferable that the antenna angle is less than 30 degrees, preferably less than 20 degrees, and more preferably less than 10 degrees. The members 15 and 17 located on the surface of the separator 105 are resistant to the electrolyte. In addition, high wettability is preferable because it allows the electrolyte to be easily injected into the exterior body. Furthermore, the members 15 and 17 located on the surface of the separator 105 are respectively The high wettability allows the separator 105 to remain wet even when the electrode expands and contracts during charging and discharging. As a material that satisfies the above contact angle, imidized It is preferable to use a compound of polyimide and polyamic acid (polyimide). precursors) etc.

[0095] It is preferable to use a porous substrate for the member 16. The material of the porous substrate is an insulating material. Preferably, the insulating material is one or more selected from organic materials and inorganic materials. The porous substrate can provide the separator 105 with a shutdown function. Therefore, it is preferable to use a thermoplastic resin as the organic material. This function is to close the pores of the separator 105 when the reservoir generates abnormal heat. The resin softens when heated, and the pores are closed by the softening. If a thermoplastic resin is used, a shutdown function can be imparted to the separator 105. It is preferable to use a material with a softening point or melting point of less than 200°C as the thermoplastic resin. Typically, polypropylene (PP), polyethylene (PE), acrylic and polyamide (P A) and A) can be used. Polypropylene has the heat resistance of polyethylene. Its softening point is 140°C or higher and its melting point is 164°C or higher and 170°C or lower. Since the softening point of propylene is close to the temperature at which abnormal heat occurs, polypropylene is When the separator material was subjected to the DSC measurement described above, The reaction temperature is 100°C or higher and 200°C or lower, preferably 160°C or higher and 180°C or lower. When a peak that corresponds to this is detected, it is considered that there is a good shutdown effect. Materials other than thermoplastic resins may be used for the separator as long as the peak can be detected from the materials.

[0096] The member 16 may be made of polypropylene (PP), polyethylene (PE), acrylic, or polyamide. Materials other than PA can also be used. The material may be a fiber having cellulose, a nonwoven fabric, a glass fiber, a ceramic, or a nylon. Polyamide, Vinylon (polyvinyl alcohol fiber), polyester, acrylic The material may be one or more selected from synthetic fibers using polyolefin and polyurethane. The above materials may have a lower shutdown function than polypropylene, etc. However, since the separator 105 has the members 15 and 17, it can be applied to the member 16. This allows for a wider range of material options.

[0097] Furthermore, in the separator 105, a fiber having cellulose is disposed between the member 16 and the member 15. Fiber, nonwoven fabric, glass fiber, ceramics, or nylon (polyamide), vinylon (polyamide) vinyl alcohol fiber), polyester, acrylic, polyolefin and polyurethane One or more selected from synthetic fibers using ethylene glycol may be provided.

[0098] Furthermore, in the separator 105, a cell such as paper is formed between the member 16 and the member 17. Fibers with low viscosity, nonwoven fabrics, glass fibers, ceramics, or nylon (polyamide ), Vinylon (polyvinyl alcohol fiber), polyester, acrylic, polyolefin The material may be one or more selected from synthetic fibers using polyester and polyurethane.

[0099] As shown in FIG. 1(C), the separator 105 is made up of the members 17, 16 and 15 in this order. The member 15 has a laminated structure, and the surface of the member 15 may have a coating layer 18. 8 is made of ceramic materials, fluorine-based materials, polyamide-based materials, or a mixture of these. As the ceramic material, for example, aluminum oxide particles can be used. Fluorine-based materials include, for example, PVDF, Polytetrafluoroethylene and the like can be used. Examples of polyamide-based materials include For example, nylon, aramid (meta-aramid, para-aramid), etc. can be used. In the plate 105, the member 17 can ensure high wettability with the electrolyte. In order to ensure high wettability with the electrolyte solution in the member 15, the coating layer 18 is selectively formed. In the separator 105, it is preferable that a part of the member 15 is exposed from the coating layer 18. stomach.

[0100] As shown in FIG. 1(D), the separator 105 is made up of the members 17, 16 and 15 in this order. The laminated structure includes a coating layer 18 on the surface of the member 15 and a coating layer 18 on the surface of the member 17. The coating layer 19 may be made of any of the materials mentioned for the coating layer 18. The material may be the same as that of the coating layer 18 or may be a material different from that of the coating layer 18. In the separator 105, the member 15 may have a material that has high wettability with the electrolyte. In order to ensure the high performance, the coating layer 18 is selectively formed to It is preferable that a part of the separator 105 is exposed from the coating layer 18. When the material 17 is to have high wettability with the electrolyte, the coating layer 19 is selectively formed. In the plater 105, it is preferable that a part of the member 17 is exposed from the coating layer 19.

[0101] Next, the thickness of the separator 105 will be described. The thickness is preferably 80 μm or less, and more preferably 20 μm or more and 60 μm or less. By applying a laminated structure to 5, it is possible to combine materials with different physical properties, It is possible to reduce the film thickness, typically between 20 μm and 40 μm. Therefore, the ratio of the positive electrode and the negative electrode is This allows the capacity per volume of the secondary battery to be increased. The thickness of the separator 105 is, for example, The length can be measured at the center of the observed image.

[0102] Next, the thicknesses of the members 15 to 17 will be described. It is a member that provides a drop-down function and is thicker than members 15 and 17. The polyimide used for each of the member 15 and the member 17 has a porosity of Since the ratio of the thickness of the material can be made smaller than that of the material 16, In addition, the members 15 and 17 are made of a material that ensures wettability with the electrolyte. Even if the thickness is thinner than that of the member 16, it still has sufficient function as the separator 105. The thickness of the members 15 to 17 can be, for example, In the cross-sectional observation image of the secondary battery including 17, the length can be measured at the center of the observation image. Cut.

[0103] Furthermore, when the member 15 is disposed close to the negative electrode side of the separator 105, The thickness of the member 15 is preferably greater than the thickness of the member 17. In addition, the coating layer of the separator 105 can prevent an internal short circuit of the secondary battery. Even when 18 is placed close to the negative electrode side, an internal short circuit of the secondary battery due to dendrites can be suppressed.

[0104] Furthermore, the member 15 may have a recess on the surface. The recess is a portion where the thickness is small in a cross-sectional observation image. It is possible to form a recess by removing a part of the member 15. The portions are preferably arranged in a stripe pattern. Similarly, the member 17 may have a recess on its surface. A recess is an area that is thinner than other areas in a cross-sectional observation image, and It is also possible to form recesses by removing the layer 17. The recesses are preferably arranged in a stripe pattern. It is preferable that the coating layer 18 and the coating layer 19 are formed easily when the recessed portion is provided. This makes it possible to selectively form the coating layer 18 and the coating layer 19.

[0105] The shape of the separator 105 is not limited, and it can be, for example, a sheet. The electrode 105 may be in the form of a bag, and the bag may contain either the positive electrode or the negative electrode. It is suitable as the separator 105.

[0106] [Thermomechanical analysis (TMA)] TMA is a method of applying non-oscillating loads such as compression, tension, or bending while changing the temperature of the sample. This is a method of measuring the degree of deformation of a sample when subjected to stress as a function of temperature or time.

[0107] Figure 16 shows a simplified diagram of the measuring device (TMA test device) used for thermomechanical analysis. The testing device has a load generating unit 701, a probe 702, and a heating furnace 705. While applying a constant tensile load to the sample 703 via the probe 702, the heating furnace 705 The temperature of the sample 703 can be changed by using the thermocouple 70 The temperature of the sample 703 can be obtained by detecting a temperature signal from the thermocouple 706. When deformation such as thermal expansion or softening occurs in the sample 703 in response to a temperature change, the resulting displacement The amount is measured by the position detector 707 as the amount of change in the position of the probe 702 and output as a signal. As described above, deformation with respect to temperature while applying a non-oscillating load (constant load) is measured. It becomes possible to measure.

[0108] When the separator material was subjected to thermomechanical analysis, it was found that the separator material It is preferable that the sample does not shrink or break, but rather stretches under the load. The graph shows the elongation rate (length of expansion or contraction [μm] / temperature [℃]) on the horizontal axis and the temperature [℃] on the horizontal axis. When created, the elongation rate is 0.2 μm / °C or more and 3.0 μm / °C or less between 150°C and 300°C. [μm / ℃] or less is preferable as a separator material. The elongation rate is in the range of 0.6 [μm / ℃] to 2.0 [μm / ℃] at temperatures below 300℃. This is more preferable as a separator material.

[0109] [Tensile test] In order to obtain the mechanical strength characteristics of the separator material, a tensile test was performed as a measurement different from TMA. A precision universal testing machine can be used for the tensile test, and the temperature is kept constant. The tensile strength is increased at a set rate, and the amount of change in the separator material is obtained. The difference from TMA is that the tensile test is performed at a constant temperature without temperature changes.

[0110] A simplified diagram of a tensile testing machine is shown in Figure 17. The first jig 711a and the second jig 711 The test sample 712 is attached to b, and the test is performed by pulling the sample 712 at a set speed. The test is completed when sample 712 breaks. However, for example, it is possible to set the temperature to 25°C, which is assumed to be room temperature, and 250°C, which is the temperature at which the secondary battery experiences thermal runaway. The specified pulling speed is typically 45 mm / min or more and 70 mm / min or more. The maximum test force [N] and the maximum stress [MPa] can be set to less than [min]. Evaluate the radiator materials.

[0111] For separator materials, the maximum test force in a tensile test at 25°C must be 0.2 [N] or less. Preferably, the strength is 1.0 [N] or more, and more preferably, 1.0 [N] or more. The maximum value of the stress is preferably 20 [MPa] or more, and more preferably 30 [MPa] or more. For separator materials, the maximum test force in a tensile test at 250°C is 0.1 N. In the same tensile test, the maximum stress is preferably 0.5 [N] or more, and more preferably 0.5 [N] or more. The maximum value is preferably 10 [MPa] or more, and more preferably 20 [MPa] or more. When evaluating a data material, a tensile tester and conditions other than those described in this embodiment may be used. stomach.

[0112] [Secondary battery] Next, the secondary battery having the above-mentioned electrolyte and separator 105 will be described with reference to FIGS. 2(A) to 3(C). 2(A) shows the state in which the components of the secondary battery 100 are stacked, 2(B) shows the components of the secondary battery 100 separated from each other. 3(B) shows a cross-sectional view of the positive electrode active material layer 22 of the secondary battery 100. FIG.

[0113] The secondary battery 100 has a plurality of positive electrodes. In FIG. 2(B), the plurality of positive electrodes includes a first positive electrode The first positive electrode 103a and the second positive electrode 103b are shown. b are collectively referred to as the positive electrode 103. However, in the secondary battery 100, the number of positive electrodes is limited to two layers. It may have a single layer or three or more layers.

[0114] The secondary battery 100 has a plurality of negative electrodes. In FIG. 2(B), the plurality of negative electrodes includes a first negative electrode The first negative electrode 106a, the second negative electrode 106b, and the third negative electrode 106c are shown. The second negative electrode 106b and the third negative electrode 106c are collectively referred to as negative electrode 106. In the battery 100, the number of negative electrodes is not limited to three layers, and may be one, two, or four. It may have more than one layer.

[0115] The secondary battery 100 has a separator between the negative electrode and the positive electrode. The separators are a first separator 105a, a second separator 105b, and a third separator 105c. The first separator 105a, the second separator 105c, and the fourth separator 105d are shown by dashed lines. The separator 105b, the third separator 105c and the fourth separator 105d are put together. The separator 105 is a separator layer. However, in the secondary battery 100, the number of separator layers is limited to four. The number of layers is not limited, and may be single, may have two or three layers, or may have five or more layers. As shown in Figure 2(B), multiple separators may be used, each of which is in the form of a separate sheet. Although it is possible to use a continuous separator, it is also possible to use a continuous separator. The separator is prepared with a larger area than the positive and negative electrodes, and the separator is folded appropriately. By bending the separator, the positions corresponding to the first separator 105a to the fourth separator 105d are set. The separator is placed in the positive electrode or negative electrode position. This reduces the overall thickness of the separator, thereby increasing the capacity per volume of the secondary battery. It is possible.

[0116] FIG. 3A is an example of a cross-sectional view of the secondary battery 100 taken along the dashed line AB in FIG. 2B. In FIG. 3(A), the positive electrode 103, the separator 105, the negative electrode 106, the protrusion 31t, etc. This will be used to explain.

[0117] The positive electrode 103 has a positive electrode current collector 21 and a positive electrode active material layer 22. The positive electrode active material layer 22 It is a layer having material particles and has an area in contact with the positive electrode current collector 21. In the positive electrode that has undergone the press processing, a part of the positive electrode current collector 21 has a positive electrode In some cases, depressions where active material particles are pressed into the surface are formed. The positive electrode active material layer 22 can be formed on both sides of the positive electrode current collector 21. This is called a double-sided coated structure. Although not shown, the positive electrode active material layer 22 is formed on only one surface of the positive electrode current collector 21. This is called a single-sided coated structure.

[0118] The protrusion 21t shown in FIG. 2(A) is a part of the positive electrode current collector 21. In other words, the protrusion 2 1t is a region of the positive electrode current collector 21 where the positive electrode active material layer 22 is not provided. As shown in Fig. 1, in the secondary battery 100, the plurality of protrusions 21t overlap each other, forming an assembly. The assembly of the protrusions 21t is called a positive electrode tab. The positive electrode tab is connected to the positive electrode lead at the joint 109a. The bonding can be performed by ultrasonic bonding. The positive electrode lead 107a is made of aluminum, nickel, titanium, Or, a material selected from these alloys can be used. An insulating seal may be disposed so as to surround the pole lead 107a. Ton tape can be used.

[0119] Furthermore, FIG. 3(B) shows an example of a cross-sectional view of the positive electrode active material layer 22. The positive electrode active material layer 22 has at least Both layers contain a positive electrode active material 10. The positive electrode active material layer 22 may contain a second positive electrode active material 20. The positive electrode active material layer 22 may contain a conductive material 41. The positive electrode active material layer 22 contains an electrolyte solution 108. Although not shown, the positive electrode active material layer 22 may contain a binder. The positive electrode active material layer 22 does not have to include the second positive electrode active material 20. The positive electrode active material layer 22 may not have a binder.

[0120] The positive electrode active material 10 is an active material having an average particle size of 9 μm or more and less than 20 μm, and a maximum particle size of less than 30 μm. It is preferable to use a material having a large diameter (also called a large particle size). Secondary particles may be used, and the secondary particles have an average particle size of 9 μm or more and less than 20 μm, and a maximum particle size The positive electrode active material 10 has a layered rock salt type crystal structure. M1O2 (M1 is one or more selected from Fe, Ni, Co, Mn, and Al) A composite oxide can be used, and typically lithium cobalt oxide can be used. . Lithium cobalt oxide with good high-voltage charging characteristics will be described after Embodiment 2. .

[0121] Furthermore, the positive electrode active material 10 preferably has an average particle diameter of 5 μm or less, more preferably 0.1 μm or more and 5 μm or less, and a maximum particle diameter of less than 9 μm, and it is also preferable to use an active material that satisfies a small diameter (also referred to as a small particle diameter). The positive electrode active material 10 can use LiM2PO4 (M2 is selected from one or more of Fe, Ni, Co, and Mn) having an olivine-type crystal structure. Li MPO4 examples include LiFePO4, LiNiPO4, LiCoPO4, LiMnPO 4, LiFe 4, LiFe a Ni b PO4, LiFe a Co b PO4, LiFe a Mn b PO4, Li Ni a Co b PO4, LiNi a Mn b PO4 (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 (c + d + e is 1 or less, 0 < c < 1, 0 < d < 1, 0 < e < 1), LiF e f Ni g Co h Mn i PO4 (f + g + h + i is 1 or less, 0 < f < 1, 0 < g < 1, 0 < h < 1, 0 < i < 1), etc., and typically lithium iron phosphate can be used. Further, it is preferable that the particle surface of the positive electrode active material 10 has a carbon layer.

[0122] As the second positive electrode active material 20 included in the positive electrode active material layer 22, it is preferable that the average particle diameter is 5 μm or less, more preferably 0.1 μm or more and 5 μm or less, and the maximum particle diameter is less than 9 μm, and it is preferable to use an active material satisfying a small diameter (also referred to as a small particle diameter). The second positive electrode active material 20 may be LiM2PO4 (M2 is one or more selected from Fe, Ni, Co, and Mn) having an olivine-type crystal structure. Examples of LiMPO4 include LiFePO4, LiNiPO4, LiCoPO4, LiMnPO4, LiFeNiPO4, LiFeCoPO4, LiFeMnPO4, LiNiCoPO4, LiNiMnPO4 (a + b ≤ 1, 0 < a < 1, 0 < b < 1), LiFeNiCoPO4, LiFeNiMnPO4, LiNiCoMnPO4 (c + d + e ≤ 1, 0 < c < 1, 0 < d < 1, 0 < e < 1), LiFeNiCoMnPO4 (f + g + h + i ≤ 1, 0 < f < 1, 0 < g < 1, 0 < h < 1, 0 < i < 1), etc. Typically, lithium iron phosphate can be used. Further, it is preferable that the particle surface of the second positive electrode active material 20 has a carbon layer. (also referred to as a small particle diameter). (M2 is one or more selected from Fe, Ni, Co, and Mn). can be used. O4, a Ni b PO4, a Co b P O4, a Mn b PO4, a Co b PO4, a Mn b PO4 (a + b ≤ 1, 0 < a < 1, 0 < b < 1), c Ni d Co e PO4, c Ni d Mn e PO4, c Co d Mn e PO4 (c + d + e ≤ 1, 0 < c < 1 , 0 < d < 1, 0 < e < 1), f Ni g Co h Mn i PO4 (f + g + h + i ≤ 1, 0 < f < 1, 0 < g < 1, 0 < h < 1, 0 < i < 1), etc. are available, and typically, lithium iron phosphate can be used. Further, it is preferable that the particle surface of the second positive electrode active material 20 has a carbon layer. is preferable.

[0123] The negative electrode 106 has a negative electrode current collector 31 and a negative electrode active material layer 32. The negative electrode active material layer 32 It is a layer having material particles and has an area in contact with the negative electrode current collector 31. In the negative electrode that has undergone the pressing process, a part of the negative electrode current collector 31 has a negative electrode As shown in Figure 3(A), depressions may be formed where the active material particles are pressed into the negative electrode. The active material layer 32 can be formed on only one surface of the negative electrode current collector 31. In the negative electrode arranged in the outer layer, the negative electrode active material layer that is not arranged facing the positive electrode is Since the insertion and desorption of ions does not occur or is difficult to occur, the negative electrode active material layer is not formed. In other words, the outermost negative electrode is often coated on one side. A double-sided coating structure in which the negative electrode active material layer 32 is formed on both sides of the negative electrode current collector 31 may also be used. It is preferable to prepare all negative electrodes as double-sided coated structures, as this increases productivity. In this case, a negative electrode having a double-sided coating structure can be disposed.

[0124] Furthermore, the negative electrode current collector 31 has a protruding portion 31t. The protruding portion 31t is provided with a negative electrode active material layer 32. In FIG. 2B, the plurality of protrusions are a first protrusion 31ta, The second protrusion 31tb and the third protrusion 31tc are shown. The first protrusion 31tb and the third protrusion 31tc are collectively referred to as protrusion 31t. The protrusions 31t are also shown in the figure. The protrusions 31t overlap each other to form an assembly. The aggregate of the protrusions 31t is called a negative electrode tab. In FIG. 3(A), the protrusions 31t are not connected to other protrusions. It is shown separated from the part.

[0125] As shown in FIG. 2(A), the negative electrode tab (protrusion 31t) is connected to the negative electrode lead 1 at the joint 109b. 07b. Ultrasonic welding can be used for the joining. The negative electrode lead 107b is electrically connected to a metal such as nickel, copper, titanium, or an alloy thereof. The material selected from the group consisting of gold and silver can be used. An insulating seal may be placed around b. Kapton tape is used as the insulating seal. You can be there.

[0126] The negative electrode active material layer 32 may further include a binder. Of course, the negative electrode active material layer 32 does not have to include a binder or a conductive material. The inductor and conductive material will be described later.

[0127] In this specification and the like, as shown in FIG. 2(B), a plurality of positive electrodes, a plurality of negative electrodes, and a plurality of separators The structure in which the electrodes are stacked is called a stacked electrode.

[0128] 4 shows a liquid injection device 280 for the electrolyte 180. The liquid injection device 280 includes a processing chamber 281 and a A liquid injection nozzle 282 is located on the upper surface of the electrode 281, and a port for supplying the electrolyte 180 to the liquid injection nozzle 282. The pump 283 has a pump speed of 1000 rpm and a tank 284 for storing the electrolyte 180. The processing chamber 281 is preferably provided with a function for adjusting the temperature. A fixing device 285 that fixes a stacked battery (a battery containing a stacked battery and a part of the outer casing that is thermocompressed) Although not shown, the processing chamber 281 has a vacuum pump and the like, and the liquid is injected in a vacuum atmosphere. The vacuum pump may be a dry pump, a turbo molecular pump, an oil rotary pump, or a cryogenic pump. A vacuum pump or a mechanical booster pump can be used. The differential pressure gauge of 81 was reduced to -0.1 MPa or more but less than -0.08 MPa. The liquid injection nozzle 282 is provided with a heating mechanism 2 at a portion close to the processing chamber 281. It is preferable to have a heating mechanism 286. The viscosity of the electrolyte 180 can be controlled by a heating mechanism 286. When the injection of the electrolyte 180 is completed, the injection nozzle 282 rises, and the processing chamber 281 The outer casing can be thermally compressed.

[0129] Since the separator 105 has a larger area than the positive electrode and the negative electrode, when the electrolyte is injected, the separator 105 Therefore, the separator 105, which has good wettability with the electrolyte, is used. The use of such a material is preferable because it makes it easier to inject the electrolyte.

[0130] In the separator 105, when stripe-shaped recesses are provided in the members 15 and 17, The stripe-shaped recesses start from the injection nozzle 282 side and extend toward the opposite side. It is preferable to do so.

[0131] [Exterior body] Although not shown, the secondary battery 100 has an exterior body, and the laminated electrodes are housed in the exterior body. The exterior of the battery 100 may be made of a material such as aluminum, stainless steel, or titanium. Metallic materials or resin materials can be used. Also, a film-like exterior body can be used. The film may be made of polyethylene, polypropylene, polycarbonate, Aluminum, stainless steel, titanium, etc. are applied to a membrane made of ionomer, polyamide, etc. A thin metal film or foil made of highly flexible material such as copper or nickel is provided on the thin metal film. The outer surface of the enclosure is provided with an insulating synthetic resin film such as polyamide resin or polyester resin. A three-layer film can be used. In this case, the name of the material of the metal layer of the laminate film is used. Aluminum (aluminum) laminate film, stainless steel laminate film, Also called tungsten laminate film, copper laminate film, nickel laminate film, etc. This sometimes happens.

[0132] The material or thickness of the metal layer of the laminate film is determined based on the flexibility of the secondary battery 100, i.e., This may affect the ease of bending. The outer casing used may have, for example, a polypropylene layer, an aluminum layer, and a nylon layer. It is preferable to use an aluminum laminate film. Here, the thickness of the aluminum layer is The thickness is preferably 50 μm or less, more preferably 40 μm or less, and even more preferably 30 μm or less. It is preferable that the thickness of the aluminum layer is less than 10 μm, and more preferably 20 μm or less. There is a concern that pinholes in the aluminum layer may reduce the gas barrier properties, so The thickness is preferably 10 μm or more.

[0133] For example, a polycarbonate exterior body is used for the secondary battery 100, which requires high physical strength or safety. A stainless steel laminate film having a propylene layer, a stainless steel layer, and a nylon layer. It is preferable to use a nylon film having a polyethylene terephthalate layer on the nylon layer. Here, the thickness of the stainless steel layer is preferably 50 μm or less, and more preferably 40 μm or less. More preferably, it is 30 μm or less, and even more preferably, it is 20 μm or less. If the stainless steel layer is thinner than 10 μm, pinholes in the stainless steel layer may cause a decrease in gas barrier properties. Therefore, it is desirable that the thickness of the stainless steel layer is 10 μm or more. In this specification, stainless steel refers to steel containing approximately 12% or more of chromium (iron and carbon). It refers to alloys of martensitic, ferritic or austenitic types. Stainless steel can be broadly divided into Ti, Nb, Mo, Cu, Ni, or Si. Also included are stainless steels to which one or more elements selected from the above have been added.

[0134] Also, for example, a titanium laminate film having a polypropylene layer, a titanium layer, and a nylon layer is It is preferable to use a polyethylene terephthalate film on the nylon layer. Here, the thickness of the titanium layer is preferably 50 μm or less, and more preferably 40 μm or less. More preferably, the thickness is 30 μm or less, and even more preferably, 20 μm or less. If the titanium layer is thinner than 10 μm, pinholes in the titanium layer will cause a decrease in gas barrier properties. Therefore, it is desirable that the thickness of the titanium layer is 10 μm or more.

[0135] A secondary battery that uses a film as an exterior body is called a laminated secondary battery. Although not shown, a can case may be used as the exterior body. A secondary battery that uses a cylindrical case is called a coin-type secondary battery. It's called a pond.

[0136] [Bendable secondary battery] Next, the bendable secondary battery 100x will be described with reference to FIGS. 5(A) and 5(B). FIG. 5(A) is a cross-sectional view of the secondary battery 100x, and FIG. 5(B) is a perspective view of the secondary battery 100x. The secondary battery 100x, like the secondary battery 100, includes a positive electrode 103, a separator 104, and a The positive electrode 103, the separator 105 and the negative electrode 106 are each It is preferable to use a flexible material. In this regard, the description of the same components as those of the secondary battery 100 will be omitted. As a different configuration, the bendable secondary battery 100x has two single-sided coated positive electrodes 103, A positive electrode in which the positive electrode current collectors are in contact with each other may be prepared. Similarly, two negative electrodes 106 with single-sided coating are prepared, and the negative electrode current collectors are placed in contact with each other. A negative electrode having a current collector overlapping structure may be prepared. When the battery is bent, the current collectors that are in contact with each other tend to come off. This is suitable for the secondary battery 100x that can

[0137] In the bendable secondary battery 100x, the protruding portion 31t is wrinkled, and the protruding portion In order to prevent the protrusion 31t from being wrinkled, In FIG. 5(A) and FIG. 5(B), the ends of the stacked battery on the protruding portion 31t side are bent to be aligned. In the secondary battery 100x, the side opposite to the protrusion 31t is In this case, a misalignment occurs in the stacked battery, and the misalignment increases toward the opposing side. When using a current collector alignment structure, the current collectors that are in contact with each other tend to slip out of alignment, so it is necessary to create an appropriate misalignment. The end of the stacked battery on the protruding portion 31t side is bent to be aligned. In Ike 100x, there is a possibility that separators other than the outermost layer may come into contact with the exterior body.

[0138] When the protrusion 31t is wrinkled and breaks, the secondary battery 100x is bent. The position where the external force is applied is a position farther from the center of the laminated electrode than the protruding portion 31t. Of course, it is preferable to bend the secondary battery 100x at a position where an external force is applied. The center position may be set to the center position of the

[0139] In this specification, the curved region (curved region) as shown in FIG. 5(A) and FIG. 5(B) The secondary battery 100x having the above structure is sometimes called a curved secondary battery. It is preferable to apply the laminate type secondary battery. Since it has flexibility, it is preferable because it can easily follow the deformation of the secondary battery, specifically the bending of the secondary battery. The secondary battery 100x is preferably bent and fixed as shown in Figs. 5(A) and 5(B) and is charged and discharged. It is possible to charge.

[0140] The bendable secondary battery 100x can be shown in a straight state as shown in FIG. 3(A) and in a state as shown in FIG. 5(A) and This also includes secondary batteries that can repeatedly change between the bent state shown in Figure 5(B) and the curved state shown in Figure 5(C). While changing from a straight to a bent state, or from a bent state to a straight The secondary battery 100x can be discharged while changing to a different state. It is also possible to do this.

[0141] The separator 105 of the bendable secondary battery 100x has the same structure as that shown in FIGS. It is preferable to use the separator 105 described using (D). In the secondary battery 100x, an adhesive layer is not provided on the outermost surface of the separator 105. The separator 105 preferably has an area in contact with the positive electrode 103. Similarly, the separator 105 is not provided with an adhesive layer, and the negative electrode 10 It is preferable that the separator 105 and the negative electrode 106 have an area in contact with each other. As a configuration in which no adhesive layer is provided, specifically, the outermost surface of the separator 105 is A member 15 is placed on one side, and a ceramic material, a fluorine material, a polyamide material, etc. It is preferable that the separator 1 is not coated with a material or a mixture thereof. In addition to the outermost surface of 05, a member 17 is positioned, and on the same surface, a ceramic material, a fluorine material, It is preferable that the material is not coated with a polyamide-based material or a mixture thereof. Ceramic materials, fluorine-based materials, polyamide-based materials, or mixtures of these That is, if the material does not exhibit adhesive properties, it may be coated on the members 15 and 17. .

[0142] The bendable secondary battery 100x has a separator that has good wettability with the electrolyte. Therefore, the electrolyte can be easily injected into the exterior body. Even if the electrode expands and contracts during charging and discharging, the amount of electrolyte held by the separator 105 is maintained. Furthermore, the separator with a multi-layer structure makes it possible to bend the battery. This allows the secondary battery 100x to have a large capacity per volume.

[0143] The content of this embodiment mode can be combined with the content of other embodiment modes as appropriate.

[0144] (Embodiment 2) A positive electrode active material according to one embodiment of the present invention will be described.

[0145] <<Method for producing positive electrode active material>> A method for manufacturing the positive electrode active material 10 will be described with reference to FIGS.

[0146] <Step S11> In step S11 shown in FIG. 6, the starting materials, lithium and transition metal, A lithium source (Li source) and a cobalt source (Co source) are prepared.

[0147] As the lithium source, it is preferable to use a compound containing lithium, such as lithium carbonate. Lithium hydroxide, lithium nitrate, lithium fluoride, etc. can be used. The hydrogen source preferably has a high purity, for example, a material with a purity of 99.99% or higher.

[0148] As the cobalt source, it is preferable to use a compound containing cobalt, for example, tricobalt tetroxide. Cobalt oxide such as cobalt hydroxide, etc. can be used.

[0149] The cobalt source preferably has a high purity, for example, a purity of 3N (99.9%) or more, preferably 4N (99.99%) or more, more preferably 4N5 (99.995%) or more, and even more preferably It is advisable to use materials with a purity of 5N (99.999%) or higher. As a result, the capacity of the secondary battery is increased, and the amount of impurities in the positive electrode active material can be controlled. and / or the reliability of the secondary battery is improved.

[0150] In addition, it is preferable that the cobalt source has high crystallinity, for example, single crystal grains. The crystallinity of the Baltic source was evaluated using TEM (transmission electron microscope) images and STEM (scanning transmission electron microscope) images. High-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) images, Evaluation by ABF-STEM (annular bright-field scanning transmission electron microscope) images, etc., or X-ray diffraction (X RD), electron diffraction, neutron diffraction, etc. The method can be applied to evaluate the crystallinity of not only cobalt sources but also other sources.

[0151] <Step S12> Next, in step S12 shown in FIG. 6, the lithium source and the cobalt source are crushed and mixed. The grinding and mixing can be carried out in a dry or wet manner. This is preferable because it can be crushed into small pieces. When using a wet method, a solvent is prepared. Examples include ketones such as acetone, alcohols such as ethanol and isopropanol, and ethers. , dioxane, acetonitrile, N-methyl-2-pyrrolidone (NMP), etc. It is more preferable to use an aprotic solvent that is less likely to react with lithium. In this embodiment, dehydrated acetone with a purity of 99.5% or more is used. The lithium source is added to dehydrated acetone with a purity of 99.5% or more, with the content reduced to 10 ppm or less. It is preferable to mix the cobalt source and the cobalt source together, and then grind and mix them. The use of acetone can reduce possible impurities.

[0152] A ball mill, a bead mill, or the like can be used as a means for pulverizing and mixing. When using balls, aluminum oxide balls or zirconium oxide balls are used as media. Zirconium oxide balls are preferable because they emit less impurities. When using a lubricant mill or bead mill, contamination from the media is suppressed. Therefore, it is preferable that the peripheral speed is set to 100 mm / s or more and 2000 mm / s or less. The shape is a peripheral speed of 838 mm / s (rotation speed 400 rpm, ball mill diameter 40 mm). This will be implemented.

[0153] <Step S13> Next, in step S13 shown in FIG. 6, the mixed material is heated to a temperature of 800° C. or higher. It is preferable to carry out the heating at a temperature of 900°C or higher and 1000°C or lower. If the temperature is too low, the lithium source and the cobalt On the other hand, if the temperature is too high, the lithium source may not be decomposed and melted sufficiently. Defects occur due to lithium evaporation and / or excessive reduction of cobalt. For example, cobalt may change from trivalent to divalent, which may induce oxygen defects. This may happen.

[0154] If the heating time is too short, lithium cobalt oxide will not be synthesized, but if it is too long, productivity will decrease. For example, the heating time is preferably 1 hour or more and 100 hours or less, and more preferably 2 hours or more and 20 hours or less. Even more preferable.

[0155] The temperature rise rate depends on the heating temperature reached, but is preferably between 80°C / h and 250°C / h. For example, when heating at 1000°C for 10 hours, it is preferable to set the temperature rising rate to 200°C / h. .

[0156] 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 less. An atmosphere with a dew point of -80°C or less is preferable. Heating is carried out in an atmosphere of -93°C. In addition, to suppress impurities that may be mixed into the material, In order to achieve this, the impurity concentrations of CH4, CO, CO2, and H2 in the heated atmosphere must be It is preferable to keep each below 5 ppb (parts per billion).

[0157] The heating atmosphere is preferably an oxygen-containing atmosphere. For example, dry air is continuously introduced into the reaction chamber. In this case, the flow rate of the dry air is preferably 10 L / min. is continuously introduced into the reaction chamber, and the way in which oxygen flows through the reaction chamber is called flow.

[0158] When the heating atmosphere is an atmosphere containing oxygen, it is preferable to use a method that does not allow the material to flow. For example, the reaction chamber is depressurized and then filled with oxygen (or purged), and the oxygen is then pumped into the reaction chamber. In some cases, it may be preferable to use a method that prevents the pressure from entering or exiting the reaction chamber. For example, It is preferable to reduce the pressure to 0 hPa and then fill with oxygen until the differential pressure gauge indicates 50 hPa. stomach.

[0159] After heating, the product can be cooled naturally, but the time required to cool the product from the specified temperature to room temperature must be 10 hours or more. However, it is not necessary to cool to room temperature, and the next step It is sufficient that the temperature is cooled to a temperature acceptable to the

[0160] The heating in this step may be performed using a rotary kiln or a roller hearth kiln. Heating in a rotary kiln involves stirring the material, whether it is a continuous or batch type. It is possible.

[0161] The container for containing the object to be heated during heating is an aluminum oxide crucible or Aluminum setters (also called sheaths) are preferred. Aluminum oxide crucibles are In this embodiment, aluminum oxide with a purity of 99.9% is used. Use a setter made of aluminum. If the crucible or setter is heated after the lid is attached, the material This is preferable because it can prevent the material from volatilizing. Mullite-cordierite may also be used.

[0162] It is also preferable to use a crucible that has been used multiple times rather than a new one. In the documents, a new crucible is a crucible containing lithium, a transition metal M and / or an additive element. This refers to a crucible that has been heated twice or less. and heating the material containing lithium, a transition metal M, and / or an additive element three or more times. This means that if a new crucible is used, lithium fluoride will be released during heating. There is a risk that some of the materials, including When a part of the material is lost due to these reasons, the distribution of elements in the surface layer of the positive electrode active material is affected. On the other hand, there is a growing concern that the temperature may not fall within the desired range. few.

[0163] After heating, the material may be crushed and sieved as necessary. When collecting the material, it may be transferred from the crucible to a mortar and then collected. It is preferable to use an aluminum oxide mortar. Aluminum oxide mortars release impurities. Specifically, the purity of the acid is 90% or more, preferably 99% or more. In the heating process described later except for step S13, The same heating conditions as in step S13 can be applied to this step.

[0164] <Step S14> By the above process, lithium cobalt oxide (LiCoO2 ) can be synthesized. The lithium cobalt oxide (LiCoO2) produced in this way can be used as a starting material.

[0165] An example of producing a composite oxide by the solid phase method as shown in steps S11 to S14 has been shown. The composite oxide may be prepared by a coprecipitation method or a hydrothermal method.

[0166] It is also possible to use lithium cobalt oxide synthesized in advance in step S14. In this case, steps S11 to S13 can be omitted. By heating the lithium cobalt oxide, a cobalt oxide with a smooth surface is obtained. Lithium can be obtained.

[0167] <Step S20> Next, as shown in step S20, it is preferable to add an additive element to the lithium cobalt oxide. In the method for manufacturing the positive electrode active material described in this embodiment, the additive element is added in a plurality of steps. In order to achieve this, the additive element added first in the flow shown in Figure 6 is A1, and the additive element added second is A2. The element A1 is added for the third time as A2, and the third added element is added as A3. The adding step will be described with reference to FIG.

[0168] <Step S21> In step S21 shown in FIG. 7(A), an additive element source (A1 A lithium source may be prepared in addition to the A1 source.

[0169] The additive element A1 can be any of the additive elements described in the previous embodiments. Typically, magnesium, fluorine, nickel, aluminum, titanium, zirconium, and vanadium from aluminum, iron, manganese, chromium, niobium, arsenic, zinc, silicon, sulfur, phosphorus and boron One or more selected ones can be used.

[0170] When magnesium is selected as the additive element, the additive element source can be called a magnesium source. The magnesium source may be magnesium fluoride, magnesium oxide, magnesium hydroxide, or the like. The magnesium source may be sodium carbonate or magnesium carbonate. Multiple units may be used.

[0171] When fluorine is selected as the additive element, the source of the additive element can be called a fluorine source. The sources include, for example, lithium fluoride (LiF), magnesium fluoride (MgF2), fluorine Aluminum fluoride (AlF3), titanium fluoride (TiF4), cobalt fluoride (CoF2, CoF3), Nickel Fluoride (NiF2), Zirconium Fluoride (ZrF4), Ba Fluoride Sodium (VF5), manganese fluoride, iron fluoride, chromium fluoride, niobium fluoride, fluoride Zinc (ZnF2), calcium fluoride (CaF2), sodium fluoride (NaF), fluoride Potassium fluoride (KF), barium fluoride (BaF2), cerium fluoride (CeF3, CeF 4), lanthanum fluoride (LaF3), or sodium aluminum hexafluoride (Na3Al Among them, lithium fluoride has a relatively low melting point of 848°C. This is preferable because it is easy to melt in the heating step described below.

[0172] Magnesium fluoride can be used as both a fluorine source and a magnesium source. The lithium fluoride used in step S21 can also be used as a lithium source. Another potential source of lithium is lithium carbonate.

[0173] The fluorine source is preferably a gas, such as fluorine (F2), fluorocarbon, or sulfur fluoride. , or oxygen fluoride (OF2, O2F2, O3F2, O4F2, O5F2, O6F2, O2 F), nitrogen trifluoride (NF3), etc. are mixed into the atmosphere during the heating process described below. In addition, a plurality of the above-mentioned fluorine sources may be used.

[0174] In the method for producing the positive electrode active material described with reference to FIGS. 6 and 7(A), magnesium is used as the additive element A1. Lithium fluoride (LiF) was prepared as the fluorine source. Magnesium fluoride (MgF2) is prepared as a fluorine source and a magnesium source. Lithium fluoride and magnesium fluoride are mixed in a molar ratio of LiF:MgF2 = 65:35. On the other hand, when the amount of lithium fluoride is large, the effect of lowering the melting point is greatest. There is a concern that the amount of fluoride will be too excessive and the cycle characteristics will deteriorate. The molar ratio of magnesium fluoride is LiF:MgF2=x:1 (0≦x≦1.9). is preferred, and LiF:MgF2=x:1 (0.1≦x≦0.5) is more preferred, and LiF It is more preferable that MgF2 = x: 1 (x = 0.33 or close thereto). In this case, "nearby" means a value greater than 0.9 times and less than 1.1 times that value.

[0175] <Step S22> Next, in step S22 shown in FIG. 7(A), the magnesium source and the fluorine source are crushed and mixed. This step is carried out under the conditions selected from the grinding and mixing conditions described in step S12. It is possible.

[0176] <Step S23> Next, in step S23 shown in FIG. 7(A), the crushed and mixed material is collected and It should be noted that the A1 source shown in step S23 has multiple starting materials. and can be called a mixture.

[0177] The particle size of the mixture is a median diameter (D50) of 600 nm or more and 200 μm or less. It is preferable that the thickness is 1 μm or more and 150 μm or less, and more preferable that the thickness is 1 μm or more and 150 μm or less. Even when using a single material, the median diameter (D50) is 600 nm or more. It is preferable that the thickness is 0 μm or less, and more preferable that the thickness is 1 μm or more and 150 μm or less. .

[0178] Such a finely powdered mixture (including the case where only one type of added element is added) can be easily processed in the subsequent process. When mixed with lithium cobalt oxide, the mixture is evenly distributed on the surface of the lithium cobalt oxide particles. If the mixture is evenly adhered to the surface of the lithium cobalt oxide particles, the This is preferable because it is easy to distribute or diffuse the additive elements uniformly in the surface layer 10a of the composite oxide after heating. stomach.

[0179] <Step S31> Next, in step S31 shown in FIG. 6, lithium cobalt oxide and an Al source are mixed. The number of cobalt atoms in lithium baltic oxide, Co, and the number of magnesium atoms in the Al source, M The ratio of Co to Mg is preferably Co:Mg=100:y (0.1≦y≦6), and Co: It is more preferable that Mg=100:y (0.3≦y≦3).

[0180] The mixing in step S31 is carried out in order not to destroy the shape of the lithium cobalt oxide particles. It is preferable to use milder conditions than those in step S12. For example, It is preferable to use conditions of a lower rotation speed or a shorter time than in the case of the wet method. It can be said that the mixing conditions are milder than those of the conventional method. For example, a ball mill or a bead mill is used for mixing. When using a ball mill, for example, zirconium oxide may be used as the media. Preferably, a ball is used.

[0181] In this embodiment, a ball mill using zirconium oxide balls with a diameter of 1 mm is used. Alternatively, the mixture may be mixed dry at 100°C for 1 hour at a dew point of -10°C or higher. This will be done in the following dry room.

[0182] In the step S31, the lithium cobalt oxide and the Al source are mixed together, and surface treatment, precision mixing, or A composite treatment such as spheroidization may also be used.

[0183] In the composite process, pressure and shear force are applied to a mixture of two or more raw materials. A composite in which one material is fused to the surface of another material, that is, a composite in which the materials are bonded together. can be generated.

[0184] A typical example of equipment for compound processing is the Picoline (Hoso) with a Nobilta rotor. (Kawamicron) can be used, and the rotation speed is between 2000 rpm and 4000 rpm. It is preferable to stir the mixture at a high temperature. The stirring time is preferably 5 minutes or more and 1 hour or less. During the compounding process, it is preferable to use cooling water to suppress heat generation in the stirring area. It is preferable to carry out the process in a dry room with a dew point of -100°C or higher and -10°C or lower.

[0185] <Step S32> Next, in step S32 of FIG. 6, the mixed materials are collected to obtain a mixture 901. When collecting the material, it may be crushed and then sieved if necessary.

[0186] <Step S33> Next, in step S33 shown in FIG. 6, the mixture 901 is heated. The heating conditions can be selected from the following. The heating time is preferably 2 hours or more. In this case, the pressure inside the furnace may be higher than atmospheric pressure in order to increase the oxygen partial pressure in the heating atmosphere. If the oxygen partial pressure in the heating atmosphere is insufficient, cobalt and other elements are reduced, and lithium cobalt oxide and other elements are formed. This is because there is a risk that the layered rock salt crystal structure will no longer be maintained.

[0187] Here, we will add a supplementary note about the heating temperature. The lower limit of the heating temperature in step S33 is The temperature must be higher than the temperature at which the reaction between the aluminum and the added element source proceeds. The temperature is preferably set at a temperature at which mutual diffusion of elements contained in the lithium phosphate and the additive element source occurs. The melting temperature T m 0 0.757 times (Tanman temperature T d ) solid-state diffusion occurs. The heating temperature in step S33 is preferably 650° C. or higher.

[0188] Of course, if the temperature is higher than the melting point of one or more of the materials contained in the mixture 901, For example, when LiF and MgF2 are used as additive element sources, Since the eutectic point of LiF and MgF2 is around 742°C, The limit is preferably 742°C or higher.

[0189] In addition, the molar ratio of LiCoO2:LiF:MgF2 was 100:0.33:1. The mixture 903 obtained by mixing had an initial melting temperature T im is 779℃, Melting peak temperature T pm is 815℃, and the melting end temperature T em The temperature was 826°C. The lower limit of the heat temperature is more preferably 826°C or higher.

[0190] A higher heating temperature is preferable because the reaction proceeds more easily, the heating time is shorter, and productivity is higher.

[0191] The upper limit of the heating temperature is below the melting point of lithium cobalt oxide (1130°C). At this temperature, there is concern that lithium cobalt oxide may decompose, even if only in small amounts. When heating, the partial pressure of fluorine or fluoride originating from the fluorine source, etc., should be controlled within an appropriate range. If the temperature is too high, the fluoride will be reduced by evaporation. The vapor pressure of the rubber rises sharply from 900°C onwards. Therefore, it is preferable that the temperature is 1000°C or less. It is preferable that the temperature is 950°C or lower, and more preferable that the temperature is 900°C or lower. It is more preferable that the temperature is 50°C or less. If the evaporation of lithium fluoride is suppressed, it is possible to obtain a high-concentration lithium fluoride. The surface layer 10a can be made to contain fluorine and lithium. If titanium is added in the later process, it is difficult to form a different phase (MgTiO3, etc.). There is also the advantage that

[0192] Considering these, the heating temperature in step S33 is set to 650°C or higher, 1130°C or higher. ° C. or less, more preferably 650° C. or more and 1000° C. or less, and more preferably 650° C. or more and 950° C. More preferably, the temperature is 650°C or higher and 900°C or lower, and even more preferably, the temperature is 742°C or higher. The temperature is preferably 1130°C or lower, more preferably 742°C or higher and 1000°C or lower, and more preferably 742°C or higher and 1000°C or lower. It is more preferable that the temperature is between 742°C and 900°C, and more preferably between 742°C and 900°C. 826°C or higher and 1100°C or lower, 826°C or higher and 1130°C or lower are preferred, and 826°C or higher and 1130°C or lower are preferred. 000℃ or less is more preferable, 826℃ or more and 950℃ or less is even more preferable, The heating temperature in step S33 is preferably 900° C. or less. Preferably lower than 13.

[0193] Furthermore, when the mixture 901 is heated, the partial pressure of fluorine or fluoride resulting from the fluorine source or the like is appropriately controlled. It is preferable to control the temperature within an appropriate range.

[0194] In the manufacturing method described in this embodiment, some materials, for example, LiF, which is a fluorine source, are used as a flux. This function can reduce the heating temperature below the melting point of lithium cobalt oxide, For example, the temperature can be lowered to between 742°C and 950°C, and the surface layer can contain magnesium and other materials. By distributing the additive elements, a positive electrode active material with good characteristics can be produced.

[0195] However, since LiF has a lower specific gravity in gaseous state than oxygen, LiF volatilizes or There is a possibility that the LiF in the mixture 903 will sublime, and if it volatilizes, the LiF in the mixture 903 will decrease. Therefore, it is necessary to heat the LiF while suppressing its volatilization. Even if LiF is not used as a fluorine source, the LiCoO2 surface There is also a possibility that LiF may react with the fluorine source F to produce LiF, which may then volatilize. Even if a fluoride with a higher melting point is used, it is still necessary to suppress volatilization.

[0196] Therefore, the mixture 901 is heated in an atmosphere containing LiF, that is, the Li It is preferable to heat the mixture 901 under a condition where the partial pressure of F is high. The volatilization of LiF in the compound 901 can be suppressed.

[0197] The heating in this step is preferably performed so that the particles of the mixture 901 do not stick together. When the particles of the mixture 901 adhere to each other, the contact area with the oxygen in the atmosphere decreases, and By blocking the route for the diffusion of elements (e.g. fluorine), the added elements (e.g. This may result in poor distribution of minerals (e.g. magnesium and fluorine).

[0198] In addition, if the additive element (e.g., fluorine) is uniformly distributed in the surface layer, the surface becomes smooth and has few irregularities. It is believed that the electrode active material can be obtained. Therefore, in this process, the surface is kept smooth. In order to make the mixture 901 smoother, it is better that the particles of the mixture 901 do not stick together. stomach.

[0199] In addition, when heating using a rotary kiln, the flow rate of the atmosphere containing oxygen in the kiln should be It is preferable to heat the material in a controlled manner. For example, the flow rate of the oxygen-containing atmosphere is reduced. It is preferable to purge the atmosphere and not allow the atmosphere to flow after introducing the oxygen atmosphere into the kiln. Flowing oxygen may evaporate the fluorine source, which may cause the surface to become smooth. It is not desirable for this purpose.

[0200] When heating by a roller hearth kiln, for example, cover the container containing the mixture 901. By disposing the mixture 901 in the atmosphere containing LiF, the mixture 901 can be heated in the atmosphere containing LiF.

[0201] The heating time depends on the heating temperature, the amount of lithium cobalt oxide in step S14, and the amount of the oxidized lithium cobalt oxide in step S14. The amount of lithium cobalt oxide varies depending on the size and composition of the material. A lower temperature or shorter time may be more preferable than a higher temperature or time.

[0202] In step S14 of FIG. 6, the median diameter (D50) of the lithium cobalt oxide is about 12 μm. In this case, the heating temperature is preferably, for example, 650° C. or more and 950° C. or less. The heating time is, for example, 3 hours. Preferably, the temperature is between 10 and 60 hours, more preferably between 10 and 30 hours, and more preferably about 20 hours. The temperature-lowering time after heating is, for example, 10 hours or more and 50 hours or less. It is preferable that

[0203] On the other hand, when the median diameter (D50) of the lithium cobalt oxide in step S14 is about 7 μm, In this case, the heating temperature is preferably, for example, 650° C. or higher and 950° C. or lower. The heating time is, for example, 1 hour or longer. The temperature is preferably lowered for 10 hours or less, and more preferably for about 5 hours. For example, it is preferable to set the time to 10 hours or more and 50 hours or less.

[0204] <Step S34> Next, in step S34 shown in FIG. 6, the heated material is collected and crushed as necessary. A composite oxide 902 is obtained.

[0205] <Step S40> Next, in step S40 shown in FIG. 6, an additive element source (A2 source) is prepared. The additive element described in step S21 can be used as the additive element. In the method for producing the positive electrode active material described in ), nickel and aluminum are used as the additive element A2. Nickel oxide, nickel hydroxide, etc. can be used as the nickel source. As the aluminum source, aluminum oxide, aluminum hydroxide, etc. can be used. As shown in steps S41 to S43 of FIG. The Kel source and the aluminum source can be crushed to obtain the A2 source. The crushing conditions are as follows: The conditions in step S22 can be referenced.

[0206] <Step S51> Next, in step S51 shown in Fig. 6, the composite oxide 902 and the A2 source are mixed. For details, please refer to the description of step S31.

[0207] <Step S52> Next, in step S52 shown in FIG. 6, the mixed materials are collected to obtain a mixture 903. When collecting the material, it may be crushed and then sieved if necessary.

[0208] <Step S53> Next, in step S53 shown in FIG. 6, the mixture 903 is heated. The heating conditions are as follows: Please refer to the description in 3.

[0209] <Step S54> Next, in step S54 shown in FIG. 6, the heated material is collected and crushed as necessary. A composite oxide 904 is obtained.

[0210] <Step S60> Next, in step S60 shown in FIG. 6, an additive element source (A3 source) is prepared. For this purpose, the additive elements described in step S21 can be used. In the method for producing a positive electrode active material described in , titanium is used as the additional element A3. As the titanium source, lithium titanate, titanium oxide, titanium hydroxide, etc. can be used. As shown in steps S61 to S63 of FIG. 7(C), the titanium source is pulverized. The grinding conditions can be referred to as the conditions in step S22.

[0211] <Step S71> In the next step S71 shown in FIG. 6, the composite oxide 904 and the A3 source are mixed. For details, please refer to the description of step S31.

[0212] <Step S72> Next, in step S72 shown in FIG. 6, the mixed materials are collected to obtain a mixture 905. When collecting the material, it may be crushed and then sieved if necessary.

[0213] <Step S73> Next, in step S73 shown in FIG. 6, the mixture 905 is heated. The heating conditions are as follows: Please refer to the description in 3.

[0214] <Step S74> Next, in step S74 shown in FIG. 6, the heated material is collected and crushed as necessary. The positive electrode active material 10 is obtained. At this time, it is preferable to further sieve the collected particles. Through the above steps, the positive electrode active material 10 of one embodiment of the present invention can be produced. The positive electrode active material of one embodiment has a smooth surface.

[0215] The positive electrode active material 10 having a smooth surface is more resistant to physical damage such as pressure than a positive electrode active material having a smooth surface. For example, in tests involving pressure such as nail penetration tests, the positive electrode active material Quality 10 may be less likely to be destroyed, resulting in increased safety.

[0216] [Initial heating] In the above-described manufacturing method, after lithium cobalt oxide is synthesized, an additive element is mixed. It may be more preferable to heat the material before heating. This heating is called initial heating.

[0217] The effect of lithium being released from a part of the surface layer 10a of the lithium cobalt oxide due to initial heating This results in a better distribution of the added elements.

[0218] More specifically, the initial heating makes it easier for the distribution to differ depending on the added elements through the following mechanism: First, lithium is released from a part of the surface layer portion 10a due to the initial heating. Next, the lithium cobalt oxide having the lithium-deficient surface layer portion 10a, a nickel source, Additive element sources, including an aluminum source and a magnesium source, are mixed and heated. Of these, magnesium is a divalent typical element, and nickel is a transition metal but a divalent ion. Therefore, Mg is easily formed in a part of the surface layer 10a. 2+ and Ni 2+ and lithium deficiency Co reduced by starvation 2+ A rock salt type phase having the following structure is formed. Since only a part of the surface layer 10a is formed, the electron microscope image such as STEM and the electron beam diffraction In some cases, the fold pattern may not be clearly visible.

[0219] Among the additive elements, nickel is used as the positive electrode active material 10, and cobalt has a layered rock salt type crystal structure. When lithium nitrate is used, it is easily dissolved and diffuses into the inside of the positive electrode active material 10. When a part of the surface layer of the electrode active material 10 has a rock salt type crystal structure, the surface layer 10a is Therefore, nickel and other divalent additive elements are added to the positive electrode active material. The concentration of divalent elements such as nickel is In particular, the surface of the positive electrode active material 10 other than the (001) orientation and the surface layer portion including the surface are It is preferable that the height is higher than the upper limit.

[0220] In addition, in these rock salt structures, the bond distance between metal Me and oxygen (Me-O distance) is longer than in the layered rock salt structure. also tends to be longer.

[0221] For example, rock salt Ni 0.5 Mg 0.5 The Me-O distance in O is 2.09 Å, and in rocksalt MgO In addition, if a part of the surface layer 10a has a spinel type Even if the phase is formed, the Me-O distance of the spinel-type NiAl2O4 is 2.0125 Å, The Me-O distance of spinel-type MgAl2O4 is 2.02 Å. More than 2Å. Note that 1Å=10 -10 m.

[0222] On the other hand, in the layered rock salt structure, the bond distance between metals other than lithium and oxygen is shorter than the above. The Al-O distance in the rocksalt LiAlO2 is 1.905 Å (the Li-O distance is 2.11 Å). ) and the Co-O distance in layered rock salt LiCoO2 is 1.9224 Å (Li- The O distance is 2.0916 Å.

[0223] According to Shannon's ionic radius, the ionic radius of hexacoordinated aluminum is 0.535 Å. The ionic radius of hexacoordinated oxygen is 1.4 Å, and the sum of these is 1.935 Å.

[0224] From the above, aluminum is more stable at the non-lithium sites in the layered rocksalt structure than in the rocksalt structure. Therefore, aluminum is considered to exist in the rock salt phase even in the surface layer 10a. the deeper regions and / or interior 10b having layered rock salt type than the regions closer to the surface having It is easily distributed in

[0225] In addition, the initial heating is expected to have the effect of enhancing the crystallinity of the layered rock salt crystal structure of the inner 10b. Cut.

[0226] However, initial heating is not necessarily required. By controlling the atmosphere, temperature, time, etc., x When x in CoO2 is small, O3' In some cases, it may be possible to prepare a positive electrode active material 10 having a mold.

[0227] The characteristics of the positive electrode active material 10 produced through the above-described process are shown in FIGS. 8(A) to 14(C). F) will be used to explain.

[0228] <Cathode active material 10> 8A and 8B are cross-sectional views of a positive electrode active material 10 according to one embodiment of the present invention. Enlarged views of the vicinity of AB in (B) are shown in Figs. 9(A) to 9(C). 9(D) to 9(F) are enlarged views of the CD area in the figure.

[0229] As shown in FIG. 8(A), the positive electrode active material 10 has a surface layer portion 10a and an inner portion 10b. In Fig. 8(A) and Fig. 8(B), a dashed line is drawn to indicate an example of the boundary between the surface layer portion 10a and the interior portion 10b.

[0230] The surface layer 10a of the positive electrode active material 10 is, for example, within 50 nm from the surface toward the inside, More preferably, the thickness is within 35 nm from the surface to the inside, and even more preferably, the thickness is within 35 nm from the surface to the inside. Within 20 nm, most preferably from the surface to the interior, perpendicular or nearly perpendicular from the surface The term "almost perpendicular" refers to an angle between 80° and 100°. The surface layer 10a includes the surface vicinity, the surface Synonymous with neighborhood or shell.

[0231] The region deeper than the surface layer 10a of the positive electrode active material is called the inner portion 10b. Synonymous with region or core.

[0232] In addition, when the positive electrode active material 10 has a layered rock salt type crystal structure of the space group R-3m, As shown in Fig. 1, the surface layer 10a includes an edge region 10a1 and a basal region 10a2. In addition, in FIG. 8(A) and FIG. 8(B), the line marked (001) is (00 Here, the edge region 10a1 is a region that intersects with the (00l) plane. The thickness of the edge region 10a1 is preferably within 50 nm from the surface toward the inside, and more preferably from the surface toward the inside. Within 35 nm from the surface to the interior, and more preferably within 20 nm from the surface to the interior Most preferably, the area extending from the surface to the interior is within 10 nm in a direction perpendicular or approximately perpendicular to the surface. The region that intersects with the (00l) plane is called an edge region 10a1. The angle formed by the line and the normal to the surface of the positive electrode active material 10 is preferably 10 degrees or more and 90 degrees or less. This means that the angle is between 30 degrees and 90 degrees.

[0233] The basal region 10a2 has a surface parallel to the (001) plane. Within 50 nm toward the inside, more preferably within 35 nm from the surface toward the inside, More preferably, it is within 20 nm from the surface toward the inside, and most preferably, it is within 20 nm from the surface toward the inside. The region within 10 nm perpendicular or approximately perpendicular from the surface is referred to as a basal region 10a2. The term "parallel to the (00l) plane" refers to the plane perpendicular to the (00l) plane and the plane normal to the surface of the positive electrode active material 10. The angle formed by these is 0 degrees or more and 5 degrees or less, more preferably 0 degrees or more and 2.5 degrees or less. say.

[0234] The surface of the positive electrode active material 10 refers to the surface of the composite oxide including the surface layer portion 10a and the inner portion 10b. Therefore, the positive electrode active material 10 does not have lithium sites that can contribute to charge and discharge. The metal oxides attached to the surface of aluminum oxide (Al2O3) and other positive electrode active materials This does not include carbonates, hydroxyl groups, etc. that are chemically adsorbed after the manufacturing process. This refers to, for example, a metal oxide whose crystal orientation does not match that of the interior 10b.

[0235] The crystalline orientation of the two regions roughly coincides with each other, as can be seen from TEM images, STEM images, and HAADF-S This can be determined from TEM images, ABF-STEM images, electron beam diffraction patterns, etc. Judgment should also be made based on the FFT patterns of TEM images and STEM images. Furthermore, XRD, neutron diffraction, etc. can also be used as materials for judgment.

[0236] In addition, the electrolyte solution, decomposition products of the electrolyte solution, organic solvent, binder, conductive material, etc., adhering to the positive electrode active material 10 Also, compounds derived from these substances are not included.

[0237] The positive electrode active material 10 is a compound containing a transition metal and oxygen that can insert and extract lithium. , transition metal M (e.g., Co, Ni, Mn, Fe, etc.) that is oxidized and reduced with lithium insertion and desorption The interface between the region where oxygen is present and the region where oxygen is not present is defined as the surface of the positive electrode active material. The surface of the positive electrode active material may also include cracks, chips, and / or fractures. When a substance is subjected to analysis, a protective film may be applied to the surface, but the protective film is not included in the positive electrode active material. The protective film is a single layer or multilayer film made of carbon, metal, oxide, resin, etc. This may be the case.

[0238] <Contained elements> The positive electrode active material 10 contains lithium, cobalt, oxygen, and an additive element A. The electrode active material 10 is made of lithium cobalt oxide (LiCoO2) to which an additive element A is added. However, the positive electrode active material 10 according to one embodiment of the present invention has a crystal structure described below. It is preferable that the composition of the lithium cobalt oxide is strictly limited to Li:Co:O=1:1:2. It is not something that can be done.

[0239] The positive electrode active material maintains charge neutrality even when lithium ions are inserted and removed, allowing oxidation and reduction The positive electrode active material 10 according to one embodiment of the present invention is required to contain a transition metal that is capable of carrying out an oxidation-reduction reaction. It is preferred to use mainly cobalt as the transition metal. In addition to cobalt, nickel and At least one or more selected from manganese may be used. Among the transition metals, cobalt is 75 atomic % or more, preferably 90 atomic % or more, and more preferably When the content is 95 atomic % or more, it is relatively easy to synthesize, easy to handle, and has excellent cycle characteristics. It has many advantages and is therefore preferable.

[0240] Cobalt is contained in the transition metals of the positive electrode active material 10 in an amount of 75 atomic % or more, preferably 90 atomic %. More preferably, 95 atomic % or more of lithium nickel oxide (LiNiO2) Compared with composite oxides in which nickel accounts for the majority of transition metals, such as Li x In CoO2 When x is small, the stability is better. This is because cobalt is more stable than nickel. This is thought to be because the influence of distortion due to the Teller effect is small. The strength of the Van Teller effect varies depending on the number of electrons in the d orbital of the transition metal. Octahedrally coordinated, low-spin nickel(III), such as lithium kelate, dominates the transition metals. The layered rock salt type composite oxides such as these are greatly affected by the Jahn-Teller effect, and nickel and oxygen This causes distortion in the octahedral layers, which can lead to breakdown of the crystal structure during charge / discharge cycles. In addition, nickel ions are larger than cobalt ions, and lithium ions The size of the nickel ion is close to that of the nickel ion, so that nickel is not a transition metal, as in lithium nickel oxide. In the layered rock salt type composite oxides that account for the majority, the cation mixing of nickel and lithium However, there is a problem that it is prone to problems.

[0241] The additive element A contained in the positive electrode active material 10 is magnesium, fluorine, nickel, aluminum, or the like. Aluminum, Zirconium, Titanium, Vanadium, Iron, Manganese, Chromium, Niobium, Arsenic, Zinc one or more elements selected from lead, silicon, sulfur, phosphorus, boron, barium, bromine, and beryllium; It is preferable to use two or more.

[0242] That is, the positive electrode active material 10 is composed of lithium cobalt oxide containing magnesium, magnesium and Lithium cobalt oxide with aluminum, cobalt oxide with magnesium, and nickel Lithium cobaltate with lithium tungstate, magnesium, aluminum, and nickel Lithium cobalt oxide with magnesium and fluorine, magnesium, fluorine and nickel Lithium cobalt oxide with fluorine, magnesium, nickel and aluminum Lithium cobalt oxide having the above structure, or lithium cobalt oxide having the above structure, may be used.

[0243] The positive electrode active material 10 is a positive electrode active material containing cobalt, oxygen, and magnesium. a positive electrode active material having cobalt, oxygen, magnesium, and aluminum; a positive electrode active material containing cobalt, oxygen, magnesium, and nickel; a positive electrode active material having magnesium, aluminum, and nickel; cobalt; a positive electrode active material containing oxygen, magnesium, and fluorine; a positive electrode active material containing sodium, fluorine, and aluminum; a positive electrode active material containing cobalt, oxygen, and magnesium; A positive electrode active material having sodium, fluorine, and nickel, and a positive electrode active material having cobalt, oxygen, and manganese A positive electrode active material containing magnesium, fluorine, nickel, and aluminum, etc. It can also be said that any one or more of them can be used in a lithium ion secondary battery.

[0244] The additive element A is preferably dissolved in the positive electrode active material 10. For example, STEM-ED When X-ray analysis was performed, the rising position where the added element A was detected in the depth direction was , the transition metal M is detected at a deeper position than the rising position, that is, at the position of the positive electrode active material 10. It is preferably located on the inner side.

[0245] These additive elements A further stabilize the crystal structure of the positive electrode active material 10, as will be described later. Can.

[0246] The additive element A does not necessarily include magnesium, fluorine, nickel, aluminum, or zinc. Cobalt, titanium, vanadium, iron, manganese, chromium, niobium, arsenic, zinc, silicon, It may be free of sulfur, phosphorus, boron, barium, bromine, or beryllium.

[0247] For example, if the positive electrode active material 10 does not substantially contain manganese, it is relatively easy to synthesize and handle. The advantages of the positive electrode active material, such as ease of use and excellent cycle characteristics, are further enhanced. The weight of manganese contained in the material 10 is, for example, 600 ppm or less, more preferably 100 ppm or less. It is preferable that the length is m or less.

[0248] The surface layer 10a is a region from which lithium ions are first desorbed during charging, and is more dense than the inner layer 10b. This is the region where the lithium concentration is likely to be low. The atoms on the surface are in a state where some of the bonds are broken. Therefore, the surface layer 10a is unstable. On the other hand, the surface layer 10a is easily deteriorated and the deterioration of the crystal structure is easily started. If it can be stabilized, Li x Even when x in CoO2 is small, for example, when x is 0.24 or less, This also makes the layered structure consisting of cobalt and oxygen octahedra in the inner 10b less likely to break. Furthermore, it is possible to suppress the displacement of the inner 10b layer consisting of cobalt and oxygen octahedra. Cut.

[0249] In order to make the surface layer 10a have a stable crystal structure, the surface layer 10a must contain an additive element A. It is preferable that the surface layer portion 10a has a plurality of additional elements A, and it is more preferable that the surface layer portion 10a has a plurality of additional elements A. It is preferable that the concentration of one or more selected from the additive elements A is higher than that of the positive electrode active material. It is preferable that one or more selected from the additive elements A contained in the substrate 10 have a concentration gradient. It is more preferable that the distribution of the positive electrode active material 10 varies depending on the additive element A. For example, it is more preferable that the depth of the concentration peak from the surface varies depending on the added element A. The concentration peak here refers to the concentration in the surface layer 10a or within 50 nm from the surface. This refers to the maximum value of

[0250] [distribution] The distribution of the additive element A will be described. FIGS. 9(A) to 9(C) show the distribution of the additive element A in the positive electrode active material 10. 9(D) to 9(F) are diagrams illustrating the edge region 10a1. 10 is a diagram illustrating the basal region 10a2 of the oscillating element 10.

[0251] For example, some of the additive elements A, magnesium, fluorine, silicon, phosphorus, titanium, boron, and calcium As shown by the gradation in Figures 9(A) and 9(D), sodium etc. It is preferable that the concentration gradient increases toward the surface. The additional element A will be called additional element X. Additional element X often corresponds to additional element A1. However, it does not necessarily have to correspond to the additive element A1. Accordingly, it is possible to have a concentration gradient as shown by the gradation in FIG. 9(A) and FIG. 9(D). can.

[0252] Other additive elements A, such as aluminum and manganese, are shown in hatched areas in Figures 9(B) and 9(E). As shown by the density of the additive element X in FIG. 9(A) and FIG. 9(D), the concentration gradient is It is preferable that the concentration peak is in a region deeper than the surface layer 10a. For example, the thickness of the pores 10a may be 5n from the surface to the inside. It is preferable that the peak is in the region of 100 nm or more and 30 nm or less. The additional element is called additional element Y. Additional element Y corresponds to additional element A2. It does not necessarily correspond to the additive element A2. The diffusion rate is not the timing of addition. As shown by the density of the hatching in Figs. 9(B) and 9(E), the surface layer 10a and the inner layer 10b are separated. The concentration gradient is such that the concentration at the 0b boundary is higher.

[0253] Other additive elements, such as nickel and barium, are shown in Figs. 9(C) and 9(F) with hatching. As shown by the density of the hatching, the edge region 10a1 is clearly present, but the background The negative region 10a2 may be substantially free of the negative region 10a1. The term "characteristic X" refers to the element in a cross-sectional STEM-EDX analysis of the positive electrode active material 10. The term "substantially free" refers to the case where a line energy spectrum is detected. In a cross-sectional STEM-EDX analysis of the material 10, the characteristic X-ray energy of the element is This refers to the case where the spectrum is not detected. In this case, the element is is below the detection limit. An added element with such a distribution is called added element Z. The additive element Z often corresponds to the additive element A2, but it does not necessarily correspond to the additive element A2. 9(B) and 9(C) are determined depending on the diffusion rate rather than the timing of addition. E) The concentration gradient is shown by the density of the hatch.

[0254] For example, magnesium ions, which are one of the additive elements X, are divalent and have a layered structure. It is more stable to exist at the lithium site than at the cobalt site in the rock salt crystal structure. Therefore, magnesium easily enters the lithium site. When present at an appropriate concentration, it is easier to maintain the layered rock salt crystal structure. This is because the magnesium present in the umsite acts as a pillar supporting the CoO2 layers. It is speculated that the presence of magnesium x For example, x in CoO2 is 0.2 In a state of 4 or less, the desorption of oxygen from the surroundings of magnesium can be suppressed. The presence of magnesium is expected to increase the density of the positive electrode active material 10. If the magnesium concentration in the layer 10a is high, the resistance to hydrogen fluoride generated by decomposition of the electrolyte is low. It is also expected that the food intake will improve.

[0255] At an appropriate concentration, magnesium does not adversely affect the intercalation and deintercalation of lithium during charging and discharging. However, if there is an excess of magnesium, lithium insertion becomes difficult. Furthermore, the effect on stabilizing the crystal structure may be reduced. This is because magnesium can occupy the cobalt site in addition to the lithium site. In addition, substitution occurs at both the lithium and cobalt sites. Excess magnesium compounds (oxides or fluorides, etc.) are concentrated on the surface of the positive electrode active material. In addition, the magnesium concentration in the positive electrode active material is high, which may lead to the formation of a resistance component in the secondary battery. As the charge on the lithium site increases, the discharge capacity of the positive electrode active material may decrease. This is thought to be because too much magnesium is added, reducing the amount of lithium that contributes to charging and discharging.

[0256] Therefore, it is preferable that the amount of magnesium contained in the entire positive electrode active material 10 is appropriate. For example, the number of magnesium atoms is preferably 0.001 to 0.1 times the number of cobalt atoms. Preferably, it is greater than 0.01 and less than 0.04, and more preferably about 0.02. The amount of magnesium contained in the entire positive electrode active material 10 is preferably, for example, Discharge Mass Spectrometry (GD-MS), Indu Actively Coupled Plasma Mass Spectrometry It may also be a value obtained by performing elemental analysis of the entire positive electrode active material 10 using ICP-MS or the like. Alternatively, it may be based on the values ​​of the blending of raw materials in the process of producing the positive electrode active material 10. .

[0257] In addition, aluminum, one of the added elements Y, acts as a cobalt ion sieve in the layered rock salt crystal structure. Aluminum is a trivalent element and its valence does not change, so it can be present in the Therefore, the lithium around the aluminum is difficult to move. The titanium acts as a pillar, preventing changes in the crystal structure. This has the effect of suppressing the dissolution of Co- Because it is stronger than the O bond, it can suppress the detachment of oxygen from the surrounding aluminum. These effects improve the thermal stability. This improves safety when the positive electrode active material 10 is used in a secondary battery. Therefore, the positive electrode active material 10 can have a crystal structure that is resistant to breakdown even if heated.

[0258] On the other hand, excessive aluminum may adversely affect lithium insertion and extraction. .

[0259] Therefore, it is preferable that the amount of aluminum contained in the entire positive electrode active material 10 is appropriate. For example, the number of aluminum atoms in the entire positive electrode active material 10 is 0.0 of the number of cobalt atoms. 5% or more and 4% or less is preferable, 0.1% or more and 2% or less is preferable, 0.3% or more and 1.5% The above numerical range is preferably 0.05% or more and 2% or less. The numerical range is preferably 0.1% or more and 4% or less. For example, elemental analysis of the entire positive electrode active material 10 is performed using GD-MS, ICP-MS, etc. The value may be a value determined by the formula or may be a value based on the blending of raw materials in the process of producing the positive electrode active material 10. That's fine.

[0260] In addition, nickel, one of the added elements Z, is present at both the cobalt site and the lithium site. If present at the cobalt site, it has a lower redox potential compared to cobalt. This leads to an increase in discharge capacity, which is preferable.

[0261] When nickel is present at the lithium site, a layer structure consisting of cobalt and oxygen octahedra is formed. The change in volume caused by charging and discharging can be suppressed. This is because the nickel present in the lithium site and the CoO2 layer It is thought that this is because the structure functions as a pillar supporting the building. This is preferable because it is expected that the crystal structure will be more stable in this charged state.

[0262] On the other hand, excessive nickel undesirably increases the influence of strain due to the Jahn-Teller effect. Moreover, an excess of nickel may adversely affect the insertion and extraction of lithium.

[0263] Therefore, it is preferable that the amount of nickel contained in the entire positive electrode active material 10 is appropriate. The number of nickel atoms in the positive electrode active material 10 is greater than 0% and less than 7% of the number of cobalt atoms. 0.5% or less is preferable, 0.05% or more and 4% or less is preferable, and 0.1% or more and 2% or less is preferable. It is preferable that the range is 0.2% or more and 1% or less, and more preferable that the range is 0% or more and 1% or less. Preferably, the range is greater than 0% and less than 2%. The above numerical range is preferably 0.05% or more and 7.5% or less. The above numerical range is preferably 0.1% or more and 7.5% or less. The above numerical range is preferably 0.1% or more and 4% or less. The amount of nickel shown here is, for example, Even if the value is obtained by performing elemental analysis of the entire positive electrode active material using GD-MS, ICP-MS, etc. Alternatively, it may be based on the values ​​of the blending of raw materials in the process of producing the positive electrode active material.

[0264] Fluorine, which is one of the added elements X, is a monovalent anion, and in the surface layer 10a, oxygen When part of the fluorine atoms is substituted, the lithium desorption energy decreases. The change in valence of the cobalt ion due to the elimination of thium is from trivalent to tetravalent in the absence of fluorine. However, when fluorine is present, the valence changes from divalent to trivalent, and the oxidation-reduction potential is different. Therefore, when part of the oxygen in the surface layer portion 10a of the positive electrode active material 10 is substituted with fluorine, It can be said that the desorption and insertion of lithium ions in the vicinity of the element occurs easily. When the electrode active material 10 is used in a secondary battery, it is possible to improve the charge / discharge characteristics, large current characteristics, etc. In addition, the presence of fluorine in the surface layer portion 10a, which has the surface that is in contact with the electrolyte, Therefore, the corrosion resistance against hydrogen fluoride can be effectively improved. As explained above, the melting points of fluorides, including lithium fluoride, are higher than those of other additive element sources. If the melting point is lower than this point, it acts as a flux (also called a fluxing agent) to lower the melting point of other added element sources. It can function as such.

[0265] As shown in FIGS. 9A and 9C, the surface layer 10a is made of magnesium and nickel. When divalent magnesium is present in the vicinity of divalent nickel, divalent nickel can exist more stably. Therefore, Li x Magnesium elution even when x in CoO2 is small This can contribute to the stabilization of the surface layer portion 10a.

[0266] In addition, additive elements with different distributions, such as additive element X, additive element Y, and additive element Z, can be used together. This is preferable because it is possible to stabilize the crystal structure in a wider region. Magnesium, one of the elements X, aluminum, one of the additive elements Y, and one of the additive elements Z. When a certain nickel is contained together with any one of the additional element X, the additional element Y, and the additional element Z, In this way, the crystal structure of the positive electrode active material can be stabilized in a wider area than when only two or more of the positive electrode active material are present. When the substrate 10 contains the additive element X, the additive element Y, and the additive element Z, the surface stabilization can be fully achieved by the addition of element X such as magnesium and element Z such as nickel, The additive element Y, such as aluminum, is not essential for the surface. Rather, aluminum is essential for the deeper regions. For example, it is preferable that the thickness of the nanoparticles is 1 nm or more and 25 nm or less from the surface in the depth direction. It is preferable that aluminum be detected continuously in the region. A wider distribution is preferred because it can stabilize the crystal structure over a wider area.

[0267] In addition, as shown in FIG. 9(C) and FIG. 9(F), the additional element Z is in the basal region 10a2. It is contained in a larger amount in the edge region 10a1 (preferentially contained, selectively contained, etc.) In the case of lithium ion secondary batteries, lithium ions are released from the positive electrode during charging and discharging. This is preferred because it improves the stability of the crystal structure of the edge region 10a1 that enters and exits from the active material 10. In addition, when the additive element Z has the above distribution, for example, the positive electrode active material 10 When the additive element Z is added to lithium phosphate, the discharge voltage is decreased or the discharge capacity is increased. This is preferable because it can minimize the effects of a decrease in the amount of the product.

[0268] When a plurality of additive elements are contained as described above, the effects of the respective additive elements are synergistically enhanced, and the surface layer 10 In particular, magnesium, nickel, and aluminum can contribute to further stabilization of the In particular, the surface of the positive electrode active material 10 is preferably The layer 10a has a region where magnesium is distributed closer to the surface than aluminum. In addition to the above-mentioned magnesium and aluminum distribution region, In the surface layer 10a of the positive electrode active material 10, the distribution of nickel in the edge region 10a1 It is most preferable that the distribution of magnesium and the distribution of sulphur dioxide overlap.

[0269] <Crystal structure> <Li x When x in CoO2 is 1> The positive electrode active material 10 according to one embodiment of the present invention is in a discharged state, i.e., Li x When x=1 in CoO2 It is preferable that the layered rock salt type crystal structure belongs to the space group R-3m. The composite oxide has a high discharge capacity and has two-dimensional lithium ion diffusion paths, It is suitable for ion insertion / extraction reactions and is an excellent positive electrode active material for secondary batteries. In particular, the inner portion 10b, which occupies most of the volume of the positive electrode active material 10, has a layered rock salt type crystal structure. It is preferable that:

[0270] On the other hand, the surface layer 10a of the positive electrode active material 10 according to one embodiment of the present invention is formed from the positive electrode active material 10 by charging. Even if lithium is removed from the 10b, the layer structure consisting of the transition metal M and oxygen octahedra in the inner 10b is not broken. It is preferable that the surface layer 10a has a reinforcing function to prevent the positive electrode active material 10 from being damaged. It is preferable that the surface layer 10a, which is the outer periphery of the positive electrode active material 10, functions as a rear film. It is preferable that the positive electrode active material 10 is reinforced. suppressing structural changes in the surface layer portion 10a and the interior portion 10b of the positive electrode active material 10; and / or Alternatively, it means that the oxidative decomposition of the electrolyte on the surface of the positive electrode active material 10 is suppressed.

[0271] Therefore, it is preferable that the surface layer 10a has a different crystal structure from that of the inner portion 10b. The surface layer 10a has a composition and a crystalline structure that are more stable at room temperature (25° C.) than the inner layer 10b. For example, at least one of the surface layer portions 10a of the positive electrode active material 10 according to one embodiment of the present invention is preferably The surface layer 10a preferably has a rock salt type crystal structure. It is preferable that the surface layer portion 10a has both a salt-type crystal structure and a crystalline structure of the crystalline structure of the crystalline structure of the salt-type. It is preferable that the crystalline structure of the crystalline salt be characterized by both the crystalline salt type and the rock salt type.

[0272] In addition, some of the additive elements A, especially magnesium, nickel and aluminum, are more resistant to oxidation than the inner 10b. Although it is preferable that the concentration of the surface layer 10a is higher than that of the inner layer 10b, the concentration of the surface layer 10a is also random and sparse. It is preferable that magnesium and aluminum are present in the lithium silicide layer 10b. When present in the solution at an appropriate concentration, it is possible to easily maintain the layered rock salt crystal structure as described above. In addition, if nickel exists in the inner part 10b at an appropriate concentration, the same effect as above can be obtained. This can suppress the deviation of the layer structure consisting of the transition metal M and oxygen octahedra. When divalent magnesium and nickel are present, the divalent magnesium is more likely to be present near divalent nickel. Since it may be possible for it to exist stably, a synergistic effect in suppressing the elution of magnesium can be expected. do.

[0273] Furthermore, due to the concentration gradient of the additive element A as described above, the crystals are condensed from the inside 10b toward the surface. It is preferable that the crystal structure changes continuously. It is preferable that these values ​​approximately match.

[0274] For example, from the inside 10b of the layered rock salt type, the rock salt type crystal structure, or the rock salt type crystal structure and the layered rock The crystal structure changes continuously toward the surface and the surface layer 10a, which have both a salt-type crystal structure. It is also preferable to use a rock salt type crystal structure, or a combination of a rock salt type crystal structure and a layered rock salt type crystal structure. The crystal orientation of the surface layer 10a having both the structure and the layered rock salt type inner portion 10b is approximately the same. It is preferable that

[0275] In this specification and the like, a composite oxide containing lithium and a transition metal M such as cobalt is The layered rock salt type crystal structure of the material, which belongs to the space group R-3m, is composed of cations and anions. The transition metal M and lithium are regularly arranged in a secondary This refers to a crystal structure that allows two-dimensional diffusion of lithium due to the formation of an original plane. The layered rock salt crystal structure may have defects such as ion or anion deficiencies. In other words, the lattice of the rock salt crystal may have a distorted structure, which is more difficult to achieve than the rock salt crystal structure. Symmetry may be reduced.

[0276] The rock salt crystal structure is a cubic crystal structure, including the crystal structure belonging to the space group Fm-3m. It has a crystal structure in which cations and anions are arranged alternately. Alternatively, there may be a deficiency of an anion.

[0277] The presence of both layered and rock salt crystal structures was also confirmed by electron diffraction and TE This can be determined by M images, cross-sectional STEM images, etc.

[0278] In the rock salt type, there is no distinction in the cation sites, but in the layered rock salt type, the cation sites in the crystal structure are There are two types, one dominated by lithium and the other by a transition metal M. The layered structure in which two-dimensional planes of ions and two-dimensional planes of anions are alternately arranged is called rock salt type and layered rock salt. The bright spots in the electron diffraction pattern correspond to the crystal planes that form this two-dimensional plane. Among them, when the central spot (transparent spot) is set as the origin 000, the point closest to the central spot is The bright spots are, for example, the (111) plane in the ideal rock salt type, and the bright spots are, for example, the (003 For example, comparing the electron diffraction patterns of rock-salt MgO and layered rock-salt LiCoO2 In this case, the distance between the bright spots on the (003) surface of LiCoO2 and the (111) surface of MgO is Therefore, if the analysis area is In the case of the layered rock salt LiCoO2 phase, the electron diffraction pattern shows a strong bright spot. There is a plane orientation where bright spots and weakly bright spots are arranged alternately. This is common to both rock salt and layered rock salt types. The bright spots that occur only in the layered rock salt type have a strong brightness, while the bright spots that occur only in the layered rock salt type have a weak brightness.

[0279] In cross-sectional STEM images, when the layered rock-salt crystal structure is observed from a direction perpendicular to the c-axis, Layers observed with strong brightness and layers observed with weak brightness are observed alternately. Since there is no distinction in the ion sites, such characteristics are not observed. In the case of a crystal structure with specific crystal orientations, when observed from a specific crystal orientation, cross-sectional STEM images etc. In the case of the luminance layer, layers observed with high brightness and layers observed with low brightness are observed alternately, and then layers observed with even lower brightness are observed. In the layer of the lithium, i.e., in part of the lithium layer, there is a metal with an atomic number higher than that of lithium.

[0280] Layered rock salt crystals and the anions of rock salt crystals form a cubic close-packed structure (face-centered cubic lattice structure). It is assumed that the anions in the O3' type crystal, which will be described later, also have a cubic close-packed structure. Therefore, when layered rock salt crystals come into contact with each other, the cubic closest packing composed of anions There are crystal planes along which the structure is oriented.

[0281] It can also be explained as follows: The negative polarity in the {111} plane of the cubic crystal structure The ions have a triangular lattice. The layered rock salt type has a space group of R-3m and a rhombohedral structure. To make the structure easier to understand, it is generally represented as a complex hexagonal lattice, and the layered rock salt type (0001 ) planes have a hexagonal lattice. The triangular lattice of the cubic {111} planes is similar to that of the layered rock salt type (0001) The atomic arrangement is similar to that of a hexagonal lattice on the surface. The compatibility of the two lattices is called cubic close-packed. This means that the orientation of the filling structure is aligned.

[0282] However, the space group of the layered rock salt crystal and the O3' type crystal is R-3m, and the space group of the rock salt type crystal is Since it is different from the group Fm-3m (the space group of general rock salt crystals), crystals that satisfy the above conditions The Miller indices of the planes are different between the layered rock salt crystal and the O3' type crystal and the rock salt type crystal. In the layered rock salt crystal, O3' type and rock salt type crystal, the When the orientation of the close-packed structure is aligned, it is sometimes said that the crystal orientation is roughly the same.

[0283] <Li x When x in CoO2 is small> The positive electrode active material 10 according to one embodiment of the present invention has the above-described distribution and and / or crystalline structure, x Crystals with small x in CoO2 The structure differs from conventional positive electrode active materials in that magnesium present at the lithium site is R-3m It is to be noted that the small value of x here means that the value is 0.1 <x≦ This will be referred to as 0.24.

[0284] 10 to 13, Li x Changes in the crystal structure of CoO2 with the change of x The description will be made by comparing a conventional positive electrode active material with the positive electrode active material 10 according to one embodiment of the present invention.

[0285] The change in the crystal structure of the conventional positive electrode active material is shown in Figure 11. The conventional positive electrode active material shown in Figure 11 has the following characteristics: In particular, lithium cobalt oxide (LiCoO2) without the added element A is used.

[0286] Figure 11 shows R-3m O3 and Li x Lithium cobalt oxide with x=1 in CoO2 has This crystal structure shows that lithium occupies octahedral sites. There are three CoO2 layers in the unit cell. The CoO2 layer is an octahedral structure in which cobalt is coordinated with six oxygen atoms. This is called the structure in which the cobalt and oxygen atoms are connected in a plane with the edges shared. It can also be called the layer made up of the body.

[0287] In addition, in conventional lithium cobalt oxide, the symmetry of lithium increases when x is about 0.5, and the It is known that the crystal structure belongs to the clinic space group P2 / m. There is one CoO2 layer in the knit cell. Therefore, it is sometimes called O1 type or monoclinic O1 type. There is a match.

[0288] When x = 0, the positive electrode active material has a crystal structure of the trigonal space group P-3m1. Therefore, this crystal structure is called O1 type, or It is sometimes called trigonal O1 type. Also, when the trigonal crystal is converted into a composite hexagonal lattice, it is called hexagonal O1 type. There are also cases where this happens.

[0289] In addition, when x is about 0.12, conventional lithium cobalt oxide has a crystal structure of the space group R-3m. This structure is different from the trigonal O1 type CoO2 structure and the R-3m O3 type The structure of LiCoO2 and the structure of LiCoO2 are stacked alternately. In reality, the H1-3 crystal structure is a unit The number of cobalt atoms per cell is twice that of other structures. In this specification, the c-axis of the H1-3 type crystal structure is used as a unit to facilitate comparison with other crystal structures. This will be shown in a diagram that is half the size of a tossel.

[0290] For example, the H1-3 type crystal structure has the coordinates of cobalt and oxygen in the unit cell as Co (0, 0, 0.42150±0.00016), O1(0, 0, 0.27671±0.0 0045), O2(0, 0, 0.11535±0.00045). 1 and O2 are oxygen atoms. Whether or not a cell should be used can be determined by, for example, Rietveld analysis of the XRD pattern. In this case, the value of GOF (goodness of fit) becomes smaller. Knit cells can be employed.

[0291] Li x When charging and discharging are repeated so that x in CoO2 becomes 0.24 or less, Lithium cobalt oxide has a crystal structure between H1-3 and R-3m O3 in the discharged state. This causes repeated changes in the crystal structure (i.e., non-equilibrium phase changes).

[0292] However, these two crystal structures have a large misalignment of the CoO2 layers. As shown by the arrows, in the H1-3 type crystal structure, the CoO2 layer is in the discharged state. Such dynamic structural changes have a negative effect on the stability of the crystal structure. It can have an impact.

[0293] Furthermore, there is a large difference in volume between these two crystal structures. In this case, the difference in volume between the H1-3 type crystal structure and the R-3m O3 type crystal structure in the discharged state is 3.5 %, typically 3.9% or more.

[0294] In addition, the H1-3 type crystal structure has a continuous CoO2 layer structure like the trigonal O1 type. is likely to be unstable.

[0295] Therefore, if charging and discharging are repeated so that x becomes 0.24 or less, the conventional lithium cobalt oxide The crystalline structure of lithium breaks down, which causes a deterioration in cycle characteristics. This is because the crystal structure collapses, reducing the number of sites where lithium can exist stably, and This is because it becomes difficult to insert and extract lithium.

[0296] On the other hand, in the positive electrode active material 10 according to one embodiment of the present invention shown in FIG. x x in CoO2 is 1 The change in the crystal structure during discharge and when x is 0.24 or less is greater than that of conventional positive electrode active materials. More specifically, the CoO2 layer in the state where x is 1 and the state where x is 0.24 or less The deviation of the volume per cobalt atom can be reduced. Therefore, in the positive electrode active material 10 of one embodiment of the present invention, x can be reduced to 0.24 Even if the charge and discharge are repeated as follows, the crystal structure is not easily broken, and it has excellent cycle characteristics. In addition, the positive electrode active material 10 according to one embodiment of the present invention can achieve the above-mentioned properties. x CoO2 When x is 0.24 or less, it can take on a more stable crystal structure than conventional positive electrode active materials. Therefore, the positive electrode active material 10 according to one embodiment of the present invention is Li x x in CoO2 is 0.24 or less When the state is maintained, the safety of the secondary battery is further improved, which is preferable.

[0297] Li x When x in CoO2 is about 1 or 0.2, the inner portion 10b of the positive electrode active material 10 The crystal structure is shown in Fig. 10. The inner portion 10b occupies most of the volume of the positive electrode active material 10 and is the major portion during charge and discharge. Since this is the part that contributes most to the formation of the CoO2 layer, the displacement and volume change of the CoO2 layer are the most problematic parts. I can say.

[0298] When x = 1, the positive electrode active material 10 has the same crystal structure as conventional lithium cobalt oxide, R-3m O3. It has a structure.

[0299] However, the positive electrode active material 10 is a material that has a H1-3 type crystal structure, unlike conventional lithium cobalt oxide. When x is 0.24 or less, for example, about 0.2 or 0.12, crystals with different structures It has.

[0300] When x=approximately 0.2, the positive electrode active material 10 according to one embodiment of the present invention is a trigonal space group R-3m This is because the symmetry of the CoO2 layer is the same as that of O3. This crystal structure is called the O3' type crystal structure. The crystal structure of this lever is shown.

[0301] The O3' type crystal structure has the coordinates of cobalt and oxygen in the unit cell as Co(0,0, 0.5), O(0,0,x), and can be shown in the range of 0.20≦x≦0.25. The lattice constant of the unit cell is 2.797≦a≦2.837(×10 -1 nm) Preferably, 2.807≦a≦2.827(×10 -1 nm) is more preferred, typically a = 2.817(×10 -1 nm). The c-axis is 13.681≦c≦13.881(× 10 -1 nm) is preferred, and 13.751≦c≦13.811 is more preferred, and typically is c=13.781(×10 -1 nm).

[0302] The O3' type crystal structure is characterized by the presence of ions such as cobalt, nickel, and magnesium ions occupying the 6-coordinate oxygen positions. Light elements such as lithium may occupy the oxygen tetracoordination position.

[0303] As shown by the dotted line in Figure 10, the R-3m(O3) in the discharged state and the O3'-type crystal structure There is almost no displacement of the CoO2 layer.

[0304] In addition, the R-3m(O3) in the discharged state and the O3'-type crystal structure have the same number of cobalt atoms. The difference in product is not more than 2.5%, more particularly not more than 2.2%, typically not more than 1.8%.

[0305] As described above, in the positive electrode active material 10 according to one embodiment of the present invention, Li x When x in CoO2 is small, In other words, the change in the crystal structure when a large amount of lithium is released is suppressed compared to conventional positive electrode active materials. In addition, the change in volume per the same number of cobalt atoms is also suppressed. Therefore, the positive electrode active material 10 is repeatedly charged and discharged so that x is 0.24 or less. Therefore, the positive electrode active material 10 is resistant to breakdown in the charge / discharge cycle. The capacity decrease is suppressed. In addition, more lithium can be used stably than with conventional positive electrode active materials. Therefore, the positive electrode active material 10 has a large discharge capacity per weight and per volume. By using the electrode active material 10, a secondary battery having a high discharge capacity per weight and per volume can be produced. It can be manufactured.

[0306] The positive electrode active material 10 is Li x When x in CoO2 is 0.15 or more and 0.24 or less, O3' It has been confirmed that the crystal structure may be of the type x, and x is greater than 0.24 and less than 0.27. The following is also assumed to have an O3' type crystal structure. However, the crystal structure is Li x CoO 2. It is affected not only by x but also by the number of charge / discharge cycles, charge / discharge current, temperature, electrolyte, etc. However, the range of x is not necessarily limited to the above range.

[0307] Therefore, the positive electrode active material 10 is Li x x in CoO2 is greater than 0.1 and less than or equal to 0.24 In this case, the entire inner portion 10b of the positive electrode active material 10 does not necessarily have to have the O3' type crystal structure. It may contain a crystalline structure or may be partially amorphous.

[0308] Also Li x To make the x in CoO2 small, charging is generally performed at a high charging voltage. Therefore, Li x When the x value in CoO2 is small, the charge voltage is high. For example, when the potential of lithium metal is 4.6 V or higher, When charged at constant current / constant voltage (CC / CV) at 25°C under high pressure, the conventional positive electrode active material Therefore, the H1-3 type crystal structure appears at potentials above 4.6 V based on the lithium metal potential. The upper charging voltage can be said to be a high charging voltage.

[0309] Therefore, the positive electrode active material 10 of one embodiment of the present invention can be used at a high charging voltage, for example, 4. Even when charged at a voltage of 6 V or higher, the crystal structure with the symmetry of R-3m O3 is maintained. In other words, it is preferable to use a higher charging voltage, for example, at 25°C. When charged at a voltage between 4.65V and 4.7V, the O3'-type crystal structure can be formed, which is preferable. This can be rephrased as desirable.

[0310] When the charging voltage was further increased in the positive electrode active material 10, the H1-3 type crystal structure was finally observed. As mentioned above, the crystal structure may change depending on the number of charge / discharge cycles, charge / discharge current, temperature, and voltage. Because it is affected by the solution, etc., when the charging voltage is lower, for example, at 25°C, Even at a voltage of 4.5 V or more and less than 4.6 V, the positive electrode active material 10 according to one embodiment of the present invention has the O3'-type crystal structure. There are cases where it is possible to get it.

[0311] In addition, when graphite is used as the negative electrode active material in a secondary battery, the electric conductivity of the graphite is higher than that of the negative electrode active material. The voltage of the secondary battery drops by the amount of the potential of the graphite. Therefore, in the case of secondary batteries using graphite as the negative electrode active material, In this case, the same crystal structure is obtained at a voltage obtained by subtracting the potential of graphite from the above voltage.

[0312] In addition, in the O3' type crystal structure shown in Figure 10, lithium exists at all lithium sites with equal probability. However, this is not limited to the case. For example, the monoclinic O1(Li 0.5 CoO2) The distribution of lithium can be analyzed by, for example, neutron diffraction.

[0313] The O3' type crystal structure has random lithium between layers, but the CdCl2 type crystal structure It can be said that this crystal structure is similar to the CdCl2 type. The structure is lithium nickel oxide, Li 0.06 The crystal structure is similar to that of NiO2 when charged However, pure lithium cobaltate or layered rock salt-type positive electrode active materials containing a large amount of cobalt are generally It is known that it does not normally take the CdCl2 type crystal structure.

[0314] The concentration gradient of the additive element A is the same at multiple locations on the surface layer 10a of the positive electrode active material 10. In other words, the reinforcement derived from the additive element A is uniformly distributed in the surface layer portion 10a. Even if a part of the surface layer portion 10a is reinforced, there is preferably no part without reinforcement. If there is a part of the positive electrode active material 10, stress may be concentrated in the part where there is no part. This can cause defects such as cracks, leading to breakage of the positive electrode active material and a decrease in discharge capacity. There is a risk of this happening.

[0315] However, it is not necessarily the case that the additive element A has a similar concentration throughout the entire surface layer portion 10a of the positive electrode active material 10. The additional element A does not have to have a gradient in the edge region 10a1 as shown in FIG. 9(E) in the basal region 10a2. It is preferable to have a distribution of element Y.

[0316] Here, the CD area has a layered rock-salt type crystal structure of R-3m, and the surface has a (00l) orientation. The distribution of the added element A on the (001) oriented surface is different from that on the other surfaces. For example, the (001) oriented surface and its surface layer 10a may be formed by adding an element selected from the additive element A. The distribution of one or more concentration peaks is different from the surface compared to surfaces other than the (001) orientation. The (001) oriented surface and its surface layer 10a may be limited to a shallow portion. However, the concentration of one or more selected from the additive elements A may be lower than that of the other orientations. The (001) oriented surface and its surface layer 10a are formed by adding one or two additional elements A. The above elements may be below the lower detection limit.

[0317] In the layered rock-salt crystal structure of R-3m, cations are arranged parallel to the (00l) plane. This is a structure in which CoO2 layers and lithium layers are alternately stacked parallel to the (00l) plane. Therefore, the diffusion path of lithium ions is parallel to the (00l) plane. do.

[0318] Since the CoO2 layer is relatively stable, it is preferable that the surface of the positive electrode active material 10 has a (001) orientation. The (001) plane is the main diffusion path for lithium ions during charging and discharging. not present.

[0319] On the other hand, the diffusion paths of lithium ions are exposed on surfaces other than the (00l) orientation. Therefore, the surface and the surface layer portion 10a other than the (001) orientation are required to maintain the diffusion path of lithium ions. This is an important region for the first time, but it is also unstable because it is the region where lithium ions are first desorbed. Therefore, it is preferable to reinforce the surface and the surface layer portion 10a other than the (001) orientation. This is extremely important for maintaining the crystal structure of the entire electrode active material 10 .

[0320] <Grain boundary> The additive element A contained in the positive electrode active material 10 of one embodiment of the present invention has the above distribution as well as a small amount of It is more preferable that at least a part of the particles be unevenly distributed in the grain boundaries and their vicinity, that is, be present in a high concentration. I wish.

[0321] In this specification, uneven distribution means that the concentration of an element in a certain region is different from that in other regions. Segregation, precipitation, unevenness, bias, or a mixture of high concentration and low concentration areas , is synonymous with.

[0322] For example, the magnesium concentration at the grain boundary and its vicinity of the positive electrode active material 10 is higher than that of the other portions in the interior 10b. It is preferable that the fluorine concentration at the grain boundary and its vicinity is higher than that in the inner portion 10b. It is preferable that the nickel concentration at the grain boundary and its vicinity is higher than that in the other regions. It is preferable that the aluminum concentration at the grain boundary and its vicinity is higher than that at the other regions of b. It is preferably higher than other areas of the interior 10b.

[0323] Grain boundaries are one type of planar defect. Therefore, just like surfaces, they are prone to instability and changes in the crystal structure. Therefore, if the concentration of the added element A at the grain boundary and its vicinity is high, the crystal structure This makes it possible to more effectively suppress changes in the structure.

[0324] Furthermore, when the magnesium concentration and fluorine concentration at the grain boundary and its vicinity are high, one of the advantages of the present invention is that the magnesium concentration and fluorine concentration are high. Even if cracks occur along the grain boundaries of the positive electrode active material 10 of this embodiment, the cracks The magnesium and fluorine concentrations are high near the cracked surface. The corrosion resistance of the positive electrode active material to hydrogen fluoride after heating can also be improved.

[0325] <Analysis method> A certain positive electrode active material is Li x When x in CoO2 is small, the present invention has an O3'-type crystal structure. Whether the positive electrode active material 10 is of the present embodiment or not can be determined by Li x Positive electrode active material with small x in CoO2 The positive electrode having the above structure was analyzed by XRD, electron diffraction, neutron diffraction, electron spin resonance (ESR), and nuclear magnetometry. This can be determined by analyzing using magnetic resonance (NMR) etc.

[0326] In particular, XRD can analyze the symmetry of transition metals such as cobalt contained in the positive electrode active material with high resolution. The degree of crystallinity and the orientation of the crystals can be compared. Analysis is possible, and sufficient accuracy can be obtained even when measuring the positive electrode obtained by disassembling the secondary battery. Among XRD methods, powder XRD is preferred in terms of the following points. Diffraction peaks reflecting the crystal structure of the interior 10b of the positive electrode active material 10 are obtained.

[0327] When analyzing the crystallite size by powder XRD, the influence of pressure on the orientation of the positive electrode active material particles can be considered. For example, the positive electrode active material is removed from the positive electrode obtained by disassembling the secondary battery. It is preferable to take out the powder sample and measure it.

[0328] As described above, the positive electrode active material 10 according to one embodiment of the present invention is Li x x in CoO2 is 1 The characteristic of this battery is that there is little change in the crystal structure when the voltage is 0.24 or less. When the crystal structure is changed significantly, the positive electrode active material with a crystal structure of 50 wt% or more exhibits high This is not preferable because the battery cannot withstand repeated charging and discharging of voltage.

[0329] Also, please note that adding only the additive element A may not result in an O3' type crystal structure. For example, lithium cobalt oxide with magnesium and fluorine, or magnesium Although they have in common the fact that they are lithium cobalt oxides containing sodium and aluminum, Depending on the concentration and distribution of element A, Li x CoO2 has an H1-3 type crystal structure when x is 0.24 or less. When the O3' type crystal structure is 60 wt% or more of the O3' type crystal structure and the O3' type crystal structure, The H1-3 type crystal structure is 50 wt% or more of the H1-3 type crystal structure and the O3' type crystal structure. Sometimes it occupies the top.

[0330] In addition, even in the positive electrode active material 10 of one embodiment of the present invention, when x is too small, such as 0.1 or less, or when charging Under conditions where the voltage exceeds 4.9 V, the H1-3 type or trigonal O1 type crystal structure is formed. Therefore, in order to determine whether or not the positive electrode active material 10 is one embodiment of the present invention, Analysis of the crystal structure, including XRD, and information such as charge capacity or charge voltage are required. It is essential.

[0331] However, when the positive electrode active material has a small x, the crystal structure may change when it is exposed to the air. For example, the O3' crystal structure may change to the H1-3 crystal structure. Therefore, all samples used for crystal structure analysis were handled in an inert atmosphere such as argon. Ringing is preferred.

[0332] In addition, whether the distribution of the additive element A in the positive electrode active material is in the state described above or not For example, XPS, EDX, EPMA (Electron Probe Micro A This can be determined by analyzing using a analyzer, electron probe microanalysis, etc.

[0333] The crystal structure, such as the grain boundaries, can be analyzed by electron beam diffraction of the cross section of the positive electrode active material 10. can.

[0334] <Charging method> The charging for determining whether the composite oxide is the positive electrode active material 10 of one embodiment of the present invention is performed as follows: For example, a coin cell (CR20) using this composite oxide as the positive electrode and lithium metal as the counter electrode 32 types, diameter 20mm height 3.2mm) can be made and charged. The battery includes an electrolyte, a separator, a positive electrode can, and a negative electrode can. The coin cell for determining the separator and electrolyte of one embodiment of the present invention is not required. do not have.

[0335] More specifically, a slurry containing a positive electrode active material, a conductive material, and a binder is mixed in the positive electrode. The slurry can be applied to a positive electrode current collector made of aluminum foil. is a material liquid used to form an active material layer on a positive electrode current collector, and is composed of an active material, a binder, and It refers to a material containing a solvent and preferably further mixed with a conductive material.

[0336] The counter electrode can be made of lithium metal. However, if a material other than lithium metal is used for the counter electrode, When the voltage of the secondary battery is low, the voltage of the secondary battery and the potential of the positive electrode are different. Unless otherwise specified, the potential is that of the positive electrode.

[0337] The electrolyte is a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DE C) Prepare EC:DEC = 3:7 (volume ratio) and add 2 wt% vinylene to the mixed solvent. The electrolyte solution can contain lithium salts such as VC. 1 mol of phosphoric acid hexafluoride per liter of the mixed solvent containing vinylene carbonate. Lithium (LiPF6) can be used.

[0338] The separator can be a 25 μm thick porous polypropylene film. The plate may be made of a material other than polypropylene.

[0339] The positive and negative electrode cans can be made of stainless steel (SUS). do.

[0340] The coin cell made under the above conditions was tested at an arbitrary voltage (e.g., 4.50V, 4.55V, 4.5 8V, 4.60V, 4.62V, 4.65V, 4.70V, 4.75V or 4.80V) There are no particular restrictions on the charging method as long as it is charged at the desired voltage for a sufficient amount of time. For example, when charging with CC / CV, the current in CC charging should be 20mA / g or more and 100 CV charging can be completed at 2mA / g or more and 10mA / g or less. To observe the phase change of the positive electrode active material, it is necessary to charge the positive electrode with such a small current value. It is recommended to charge the battery at a temperature of 25°C or 45°C. After charging in this way, If the coin cell is disassembled in an argon atmosphere glove box and the positive electrode is removed, This allows for the production of a positive electrode active material with a charging capacity of 1000 kJ / cm2. For example, XRD is performed in an argon atmosphere. After charging is complete, the positive electrode is quickly removed. It is preferable to analyze the battery within 1 hour after charging is completed, and within 30 minutes. is more preferred.

[0341] In addition, when analyzing the crystal structure in the charged state after multiple charge / discharge cycles, for example, charging can be performed at any voltage. (For example, 4.50V, 4.55V, 4.58V, 4.60V, 4.62V, 4.65V, 4.70V, 4.75V or 4.80V), current value 20mA / g or more 100mA / g Charge at a constant current of 2mA / g or less, and then charge at a constant voltage until the current value becomes 2mA / g or more and 10mA / g or less. Charge and discharge to 2.5V at a constant current of 20mA / g or more and 100mA / g or less. Discharge is possible up to 3.0V, and the current value is between 20mA / g and 200mA / g. The discharge current can be constant.

[0342] Furthermore, when analyzing the crystal structure in the discharged state after multiple charge / discharge cycles, for example, at 2.5 V, A constant current discharge can be achieved at a current value of 20 mA / g or more and 200 mA / g or less. At 0 V, constant current discharge can be performed at a current value of 20 mA / g or more and 200 mA / g or less.

[0343] <xrd> The XRD measurement device and conditions are not particularly limited. For example, the measurement can be performed using the following device and conditions: XRD equipment: Bruker AXS, D8 ADVANCE, X Line: CuKα1, Output: 40KV, 40mA, Slit width: Div.Slit, 0 .5°, Detector: LynxEye, Scan method: 2θ / θ continuous scan, Measurement range ( 2θ): 15° to 90°, Step width (2θ): 0.01° Setting counting time: 1 second / step, sample stage rotation: 15 rpm.

[0344] If the sample to be measured is a powder, place it in a glass sample holder or apply grease. The sample can be set by sprinkling it on a silicon non-reflective plate. When the measurement sample is a positive electrode, attach the positive electrode to the substrate with double-sided tape and attach the positive electrode active material layer to the device. It can be set to suit the required measurement surface.

[0345] The crystal structure of the O3' type and the H1-3 type crystal structure model are calculated using CuKα1 radiation. The ideal powder XRD patterns are shown in Figures 12 and 13. For comparison, Li x CoO Calculated from the crystal structures of LiCoO2(O3) with x = 1 and trigonal O1 with x = 0 in The ideal XRD patterns of LiCoO2(O3) and CoO2(O1) are also shown. The pattern is based on the crystal structure information obtained from ICSD. Reflex Powder Dif, one of the modules of io (BIOVIA) The 2θ range was from 15° to 75°, and Step s ize=0.01, wavelength λ1=1.540562×10 -10 m, λ2 is not set, Mo The XRD pattern of the H1-3 type crystal structure is Based on the information on the H1-3 type crystal structure shown in Figure 11, it was prepared in the same manner as above. The XRD pattern of the '-type crystal structure was derived from the XRD pattern of the positive electrode active material of one embodiment of the present invention. The crystal structure was estimated and analyzed using TOPAS ver.3 (crystal structure analysis software manufactured by Bruker). ) was used to generate the XRD patterns as well as others.

[0346] As shown in Figure 12, in the O3' crystal structure, 2θ = 19.25 ± 0.12° (19. 13° or more and 19.37° or less), and 2θ=45.47±0.10° (45.37° or more) Diffraction peaks appear at angles below 45.57°.

[0347] However, as shown in Figure 13, in the H1-3 type crystal structure and trigonal O1, peaks do not appear at these positions. Therefore, Li x When x in CoO2 is small, 2θ=19.25±0 .12° (between 19.13° and 19.37°), and 2θ=45.47±0.10°( The appearance of a diffraction peak at an angle of 45.37° or more and 45.57° or less is one aspect of the present invention. This can be said to be a feature of the positive electrode active material 10.

[0348] As for the O3' type crystal structure, from the value of x in the XRD pattern shown in Figure 12, If it is slightly larger, for example, a voltage slightly lower than 4.60V (4.56V, 4.57V, 4. When charging with the upper limit of the charging voltage set to 5.58V or 4.59V, the above peak For example, when charging with the upper limit of the charging voltage set to 4.58V, In this case, the positive electrode active material 10 exhibits a diffraction peak at 2θ=18.5°C, which is attributable to the O3'-type crystal structure. It has diffraction peaks at 85±0.20° and 2θ=45.15±0.10°.

[0349] This is because the positions where the XRD diffraction peaks appear are close to each other in the crystal structures of x=1 and x≦0.24. More specifically, the main diffraction peaks of the crystal structure for x=1 and x≦0.24 are For peaks that appear with a 2θ between 42° and 46°, the difference in 2θ is 0. It can be said that the angle is 7° or less, and more preferably 0.5° or less.

[0350] The positive electrode active material 10 according to one embodiment of the present invention is Li x When x in CoO2 is small, O3' type Although the crystal structure of the positive electrode of one embodiment of the present invention is O3' type, it is not necessary that all of the positive electrode of the present invention is O3' type. The electrode active material 10 may contain other crystal structures, or may be partially amorphous. Among the plurality of positive electrode active materials 10, a positive electrode active material having a crystal structure other than the O3' type crystal structure However, Rietveld analysis of the XRD pattern is required. When the positive electrode active material 10 has the O3' type crystal structure, the ratio of the O3' type crystal structure to the crystal structures of the positive electrode active material 10 is 50% or more. Preferably, it is 60 wt% or more, more preferably 66 wt% or more. It is more preferable that the proportion of the O3' type crystal structure is 50 wt% or more, and more preferable that the proportion of the O3' type crystal structure is 50 wt% or more. If the content is preferably 60 wt% or more, and more preferably 66 wt% or more, excellent cycle characteristics can be obtained. It can show sexuality.

[0351] In addition, if the measurement is performed for 5 or more cycles, 30 or more cycles, 50 or more cycles, or 100 Even after more than 100 cycles of charge and discharge, when Rietveld analysis was performed on the XRD pattern, multiple The positive electrode active material 10 has a crystal structure in which the O3' type crystal structure accounts for 35 wt % or more. It is preferable that the content is 40 wt% or more, and more preferable that the content is 43 wt% or more. Even more preferable.

[0352] In addition, the sharpness of the diffraction peaks in the XRD pattern indicates high crystallinity. Each diffraction peak is preferably sharp, i.e., has a narrow half-width. The peaks that appear also vary depending on the XRD measurement conditions or 2θ values. In this case, the peak observed at 2θ = 43° or more and 46° or less has a half-width of, for example, 0 0.2° or less is preferred, 0.15° or less is more preferred, and 0.12° or less is even more preferred. It is not necessary for all peaks to meet this requirement. If the above requirements are met, the crystallinity of the crystalline phase can be said to be high. Such high crystallinity can be achieved by This contributes to stabilizing the crystal structure after sufficient charging.

[0353] The crystallite size of the O3' type crystal structure of the positive electrode active material 10 is Therefore, the same X as the positive electrode before charging and discharging is used. Even under the measurement conditions of RD, Li x When x in CoO2 is small, a clear O3'-type crystal structure is formed. On the other hand, in conventional LiCoO2, some of the peaks resemble the O3' type crystal structure. Even if a structure like this can be obtained, the crystallite size will be small and the peak will be broad and small. The crystallite size can be determined from the half-width of the XRD peak.

[0354] <xps> XPS (X-ray Photoelectron Spectroscopy, In electron spectroscopy, in the case of inorganic oxides, if monochromatic aluminum Kα rays are used as X-rays, It is possible to analyze the area from the surface to a depth of about 2 to 8 nm (usually 5 nm or less). Therefore, the concentration of each element is quantitatively analyzed in a region that is approximately half the depth of the surface layer 10a. Furthermore, narrow scan analysis can be used to analyze the bonding state of elements. The quantitative accuracy of XPS is usually about ±1 atomic %, and the detection limit varies depending on the element. The concentration is about 1 atomic %.

[0355] The positive electrode active material 10 according to one embodiment of the present invention has an internal concentration of one or more elements selected from the additive element A. It is preferable that the surface layer 10a has a higher temperature than the surface layer 10b. The concentration of one or more selected from the additive elements A is higher than the average of the entire positive electrode active material 10. Therefore, for example, the surface layer portion 10a measured by XPS or the like is selected. The concentration of one or more added elements A detected is measured by ICP-MS (inductively coupled plasma mass spectrometry). or the average of the entire positive electrode active material 10 measured by GD-MS (glow discharge mass spectrometry) or the like. It can be said that the concentration of the additive element A is preferably higher than the average concentration of the additive element A. For example, XPS, etc. The magnesium concentration in at least a part of the surface layer portion 10 a measured by It is preferable that the magnesium concentration in the surface layer 10a is higher than the average magnesium concentration in the body. It is preferable that the nickel concentration in a portion is higher than the average nickel concentration in the entire positive electrode active material 10. It is also preferable that the aluminum concentration in at least a part of the surface layer portion 10a is higher than that in the entire positive electrode active material 10. It is preferable that the aluminum concentration of the surface layer 10a is higher than the average aluminum concentration of the body. It is preferable that the fluorine concentration in a portion is higher than the average fluorine concentration in the entire positive electrode active material 10. stomach.

[0356] The surface and surface layer 10a of the positive electrode active material 10 according to one embodiment of the present invention are The surface of the positive electrode active material 10 does not include carbonates, hydroxyl groups, etc. that are subsequently chemically adsorbed. This does not include electrolyte, binder, conductive material, or compounds derived from these that are attached to the surface. Therefore, when quantifying the elements contained in the positive electrode active material, it is necessary to detect them using surface analysis such as XPS. Corrections may be made to remove carbon, hydrogen, excess oxygen, excess fluorine, etc. that may be present. For example, XPS can analyze and separate the types of bonds, and C—F bonds derived from binders Correction to exclude may be made.

[0357] Furthermore, before being subjected to various analyses, the electrolyte, binder, conductive material, and Or, to remove compounds derived from these, samples of the positive electrode active material and the positive electrode active material layer are washed. In this case, lithium may be dissolved in the solvent used for washing, Even in this case, the added element A is difficult to dissolve, so the atomic ratio of added element A is It's not something that has any impact.

[0358] The concentration of the added element A may be compared in terms of its ratio to cobalt. This allows comparison by reducing the influence of carbonates and other substances that are chemically adsorbed after the positive electrode active material is produced. For example, the ratio of the number of magnesium atoms to the number of cobalt atoms (Mg / Co) is preferably 0.400 or more and 1.20 or less, and more preferably 0.500 or more and 1.00 or less. It is more preferable that the ratio is 0.500 or more and 0.900 or less. , and more preferably 0.500 or more and 0.700 or less.

[0359] Also, for example, the ratio of the number of nickel and cobalt atoms (Ni / Co) according to XPS analysis is 0 It is preferably 0.050 or more and 0.200 or less, and more preferably 0.050 or more and 0.150 or less. It is more preferable that the ratio is 0.050 or more and 0.100 or less, and 0. It is more preferable that the ratio is 0.050 or more and 0.070 or less.

[0360] For example, the ratio of aluminum to cobalt atoms (Al / Co) determined by XPS analysis is , preferably 0.010 or more and 0.100 or less, and more preferably 0.010 or more and 0.050 or less It is more preferable that the ratio is 0.010 or more and 0.040 or less.

[0361] Also, for example, the ratio of the number of fluorine atoms to the number of magnesium atoms (F / Mg) according to XPS analysis is 0 Preferably, it is 0.100 or more and 1.00 or less, and more preferably 0.100 or more and 0.800 or less. It is more preferable that the ratio is 0.100 or more and 0.500 or less, and more preferable that the ratio is 0.1 It is more preferable that the ratio is 0.00 or more and 0.300 or less, and more preferably 0.100 or more and 0.200 or less. It is more preferable to do so.

[0362] The above range means that the additive element A is contained in a narrow area on the surface of the positive electrode active material 10. The positive electrode active material 10 is not adhered to the surface but is widely distributed in a desired concentration on the surface layer 10a of the positive electrode active material 10. In other words, as a result of the XPS analysis of the positive electrode active material 10, The reason is that the crystal structure is stable even if charging and discharging are repeated so that x is 0.24 or less. The positive electrode active material 10 is also excellent in terms of its structure and excellent cycle characteristics. This allows for good lithium insertion and desorption, resulting in excellent rate characteristics. do.

[0363] When performing XPS analysis, for example, monochromated aluminum Kα rays can be used as X-rays. In addition, the energy resolution of the XPS spectrum of the Ag sample is Energy resolution where the half-width of the d5 / 2 peak (112 eV) is 1.0 eV ± 0.1 eV It is advisable to use an XPS device having such a capability. The take-off angle can be set to, for example, 45°. For example, the measurement can be performed using the following XPS device and measurement conditions. Measurement equipment: PHI Quantera II X-ray: Monochromated Al Kα (1486.6 eV) Energy resolution: Half width of Ag3d5 / 2 peak is 1.0 eV ± 0.1 eV Detection area: 100 μmφ Detection depth: Approximately 4 to 5 nm (take-off angle 45°) Measurement spectrum: Wide scan, narrow scan for each detected element

[0364] When the positive electrode active material 10 according to one embodiment of the present invention was analyzed by XPS, magnesium and other elements The peak showing the binding energy (Mg1s peak) is between 1303.0 eV and 1305. It is preferably less than 0 eV, and more preferably about 1304.0 eV. This is a different value from the binding energy of magnesium fluoride, 1306.0 eV. , which is close to the bond energy of magnesium oxide.

[0365] In the XPS analysis of the positive electrode active material 10 according to one embodiment of the present invention, the measured XPS spectrum , correct the C1s peak to match the reference value (284.8 eV), that is, It is preferable to shift the entire column. This allows for the measurement of the XPS equipment and the measurement conditions. This can reduce the influence of differences in temperature, etc. on XPS measurements.

[0366] In addition, in the XPS analysis of the positive electrode active material 10 according to one embodiment of the present invention, the Mg1s peak was analyzed. By doing so, the peak components originating from the "O-Mg-O" bond and the peak components originating from the "O-Mg-F" bond were identified. The ratio of the peak component derived from the "F-Mg-F" bond to the peak component derived from the "F-Mg-F" bond was analyzed. It is preferable that the peak component derived from the O-Mg-O bond is present. The peak component derived from the bond may be included, but it must not exceed 30% of the total of the above three peak components. It is preferable that the ratio is 20% or less, more preferably 20% or less, and It is more preferable that the content is 10% or less. Although the peak component may be present, it is preferable that it accounts for 10% or less of the total.

[0367] That is, in the XPS analysis of the positive electrode active material 10 according to one embodiment of the present invention, the “O—Mg—O” bond The peak component originating from the "O-Mg-F" bond and the peak component originating from the "F-Mg- When analyzing the ratio of the peak components originating from the "F" bond and the "O-Mg-O" bond, The peak component is preferably 70% or more, more preferably 80% or more. It is more preferable that the ratio is 90% or more, and particularly preferable that the ratio is 100%.

[0368] This section explains how to analyze the Mg1s peak in the XPS spectrum during XPS analysis. In the analysis of the g1s peak, the peak component derived from the O-Mg-O bond was designated as fit peak 1. The peak component derived from the O-Mg-F bond is Fit Peak 2, and the peak derived from the F-Mg-F bond is Fit Peak 3. The component was designated as fit peak 3, and these three fit peaks were synthesized and analyzed in XPS. The synthesized peak was selected so that the difference with the Mg1s peak in the obtained XPS spectrum was minimized. Calculate the area ratio of fit peak 1, fit peak 2, and fit peak 3 in At this time, Fit Peak 1, Fit Peak 2, and Fit Peak The area ratio of the 3rd group is the ratio of O-Mg-O bond, O-Mg-F bond, and F-Mg-F bond. The analysis results can be output assuming that

[0369] In the above-mentioned XPS spectrum analysis method, the maximum value of fit peak 1 (peak The energy value (Ep1) at the top of the MgO-coated LiCoO2 Refer to the energy value at the maximum value of the Mg1s peak measured separately as a reference. In addition, the energy value (Ep3) at the maximum value of fit peak 3 is Magnesium chloride (MgF2, High Purity Chemical Laboratory MGH18XB, purity 99.9% (3N )up) as a standard sample, the energy at the maximum value of the Mg1s peak when measured separately The energy value at the maximum value of fit peak 2 ( Ep2) can be set to an intermediate value between Ep1 and Ep3. Also, EP1 can be set to an intermediate value between EP3 and EP4. The energy value at the maximum value of the peak is It is also called the position.

[0370] In the XPS analysis of the positive electrode active material 10 according to one embodiment of the present invention, the half width of the Mg1s peak is 1 Preferably, the voltage is 0.0 eV or more and 3.0 eV or less, and more preferably 1.0 eV or more and 2.8 eV or less. It is more preferable that the potential is 1.0 eV or more and particularly preferably 2.6 eV or less. In the above, the peak position of the Mg1s peak is calculated using magnesium fluoride as a standard sample. Lower energy side than the energy value at the maximum value of the Mg1s peak measured separately is located.

[0371] <edx> One or more selected from the additive elements A contained in the positive electrode active material 10 have a concentration gradient. In addition, when two or more additional elements A are used, the surface of the concentration peak of each additional element A is preferably It is more preferable that the depths from the FIB are different. The cross section of the positive electrode active material 10 is exposed by a holographic beam or the like, and the cross section is analyzed by EDX, EPMA, etc. (electron probe microanalysis) etc. to determine the concentration gradient and concentration peak of the added element A. It is possible to evaluate the quality, etc.

[0372] Among EDX measurements, ED is a method of measuring while scanning an area and evaluating the area two-dimensionally. This is called X-plane analysis. It is also measured by scanning linearly, and the distribution of atomic concentration within the positive electrode active material is Evaluating this is called line analysis. Furthermore, data on linear areas can be extracted from EDX area analysis. The measurement of an area without scanning is sometimes called a line analysis. It's called analysis.

[0373] By EDX surface analysis (for example, element mapping), it was found that the surface layer 10a and the inner layer 10b of the positive electrode active material 10 The concentration of the added element A in 0b and near the grain boundaries can be quantitatively analyzed. Furthermore, the concentration distribution and maximum value of the additional element A can be analyzed by EDX line analysis. In addition, analysis using thin-sectioned samples, such as STEM-EDX, requires careful observation of the depth of the sample. The positive electrode active material in a specific region moves from the surface to the center without being affected by elements in the opposite direction. This is more preferable because it allows the concentration distribution in the depth direction to be analyzed.

[0374] The positive electrode active material 10 is a compound containing a transition metal and oxygen that can insert and extract lithium. , transition metal M (e.g., Co, Ni, Mn, Fe, etc.) that is oxidized and reduced with lithium insertion and desorption ) and the interface between the region where oxygen is present and the region where oxygen is not present is the surface of the positive electrode active material. When an active material is subjected to analysis, a protective film may be applied to the surface. The protective film is a single layer or multilayer film made of carbon, metal, oxide, resin, etc. This may be the case.

[0375] The reference point in STEM-EDX line analysis is the characteristic of the transition metal M1 inside the positive electrode active material. The average value of the detected amount (including intensity) of X-rays M AVE The point where the reference point is 50% of the above. When the left side is the outside of the positive electrode active material and the right side of the reference point is the inside of the positive electrode active material, The quasi-point is sometimes called the surface position of the positive electrode active material. Therefore, if the detected amount of characteristic X-rays of transition metal M1 does not decrease sufficiently on the left side of the reference point, The amount of detected characteristic X-rays of the transition metal M1 on the left is called background. The average detected amount of characteristic X-rays of the transition metal M1 in the BG and the transition metal M1 Average detected amount M AVE The reference point is sometimes the point where the sum of the transition metals M1 is 50%. Instead of this, the amount of detected characteristic X-rays of oxygen inside the positive electrode active material may be used. The reference point can be found by replacing the group M1 with oxygen. However, oxygen is present in the outside of the positive electrode active material. Since the transition metal M1 is an element that is easily affected by the A VE It is preferable to calculate it from 50% of the average detected amount of characteristic X-rays of the transition metal M1. M AVE 50% of the detected amount of oxygen characteristic X-rays, M AVE The difference is that it is 50% of the If this occurs, it is thought to be due to the influence of metal oxides, carbonates, etc. containing oxygen that adhere to the surface of the positive electrode active material. Therefore, the average detected amount of characteristic X-rays of the transition metal M1 is AVE The point where it becomes 50% of In the case of a positive electrode active material having a plurality of transition metals M1, The average value M of the transition metal with the highest detected amount of characteristic X-rays AVE The reference point can be found using Cut.

[0376] The average detected amount of characteristic X-rays of the internal transition metal M1, M AVE is the characteristic X-ray of the transition metal M1 The region where the detected amount is saturated and stable, for example, the region where the detected amount of characteristic X-rays of transition metal M1 begins to increase. At a depth of 20 nm or more, preferably more than 30 nm, from the region, The above transition metal M1 in the background can be calculated by averaging the range of 3 nm or more. The average detected amount of characteristic X-rays M BG For example, the amount of detected characteristic X-rays of transition metal M1 increases. Avoid the area where the particle starts and take the average of the outermost 2 nm or more, preferably 3 nm or more. The average amount of characteristic X-rays of oxygen detected inside the sample is O AVE and background acid Average detected amount of characteristic X-rays of the element O BG can also be found in the same way.

[0377] The surface of the positive electrode active material 10 in the cross-sectional STEM image is a crystal structure of the positive electrode active material. The boundary between the area where the image is observed and the area where it is not observed is the metal constituting the positive electrode active material. Among the group elements, atomic columns originating from the nuclei of metallic elements with atomic numbers larger than that of lithium have been confirmed. The outermost area where the

[0378] In addition, peaks in STEM-EDX ray analysis are those that appear on the graph of the characteristic X-ray intensity of each element. The maximum value of the convex shape or the maximum value of the characteristic X-rays for each element. Noise in DX-ray analysis is less than the spatial resolution (R), for example, half-width less than R / 2. Measurement values ​​of

[0379] In addition, peaks in STEM-EDX ray analysis are those that appear on the graph of the characteristic X-ray intensity of each element. The maximum value of the convex shape or the maximum value of the characteristic X-rays for each element. Noise in DX-ray analysis is less than the spatial resolution (R), for example, half-width less than R / 2. Measurement values ​​of

[0380] The effect of noise can be reduced by scanning the same area multiple times under the same conditions. The integrated value of the scan measurement can be used as the detection value for each element. The number of scans is limited to 2. It is also possible to carry out the above steps and use the integrated value as the detection value for each element.

[0381] STEM-EDX analysis can be carried out, for example, as follows. First, the surface of the positive electrode active material is For example, a protective film is deposited on the surface of the ion sputtering device (Hitachi High-Tech MC1000). Carbon can be vapor deposited in a carbon coating unit.

[0382] Next, the cathode active material is sliced ​​into thin slices to prepare a STEM cross-section sample. Thinning can be done using a Tatehi-Tech XVision 200TBS. Pickup is performed using an MPS (micro-probing system), and the finishing conditions are as follows: For example, the acceleration voltage can be set to 10 kV.

[0383] STEM-EDX analysis is performed using a STEM device (Hitachi High-Tech HD-2700), for example. The EDX detector is the Octane T Ultra W (Dual ED) from EDAX. S) can be used. Conditions for EDX analysis using Hitachi High-Tech HD-2700 As an example of the conditions, the acceleration voltage of the STEM device is set to 200 kV and the emission current is set to 6 μA or less. The upper limit is set to 10 μA or less, and the thinned sample is placed in a location with minimal depth and unevenness. The EDX analysis conditions are as follows: Positive and negative, line width 42 nm, pitch 0.2 nm, number of frames 6 or more.

[0384] In order to increase the spatial resolution in STEM-EDX analysis, the beam diameter of the electron beam must be (also called beam diameter, probe diameter, or probe diameter) is preferably small. The beam diameter in EM-EDX ray analysis is preferably 0.3 nm or less, It is more preferably 0.2 nm or less, and even more preferably 0.1 nm or less. In addition, in order to increase the analytical sensitivity in STEM-EDX line analysis, the beam It is preferable to increase the beam current (also called the probe current). The equipment used for X-ray analysis can reduce the beam diameter and increase the beam current. It is preferable to provide a spherical aberration corrector (Cs corrector) capable of correcting spherical aberration.

[0385] In addition, in the positive electrode active material 10 containing magnesium and fluorine as the additive element A, the fluorine content The fabric preferably has an overlapping area with the magnesium distribution. The difference in the depth direction between the peak of the detected amount and the peak of the magnesium concentration or detected amount is 10 nm. It is preferably within 3 nm, more preferably within 3 nm, and even more preferably within 1 nm. It is preferable that the thickness is within 0.5 nm, and it is even more preferable that the thickness is within 0.5 nm.

[0386] In the positive electrode active material 10 containing nickel as the additional element A, the nickel in the surface layer portion 10a The peak of the concentration or detected amount is the depth from the surface or reference point of the positive electrode active material 10 toward the center. It is preferred that it be present up to 3 nm, and more preferred that it be present up to 1 nm deep. In the positive electrode active material 10 containing magnesium and nickel, the distribution of nickel is For example, the concentration or amount of nickel is preferably in the range of 0.1 to 1.0. The difference in depth between the peak and the peak of magnesium concentration or detection amount is within 3 nm. It is preferable that the thickness is within 1 nm, and more preferable that the thickness is within 1 nm.

[0387] In addition, when the positive electrode active material 10 contains aluminum as the added element A, EDX analysis is performed. When the concentration or detected amount of aluminum in the surface layer 10a is higher than that of magnesium, nickel, and the like, It is preferable that the peak of the concentration or detected amount of nickel or fluorine is close to the surface. The peak of the concentration or detected amount of aluminum in the surface layer portion 10a is It is preferable that the concentration or detected amount of fluorine is located on the inner side of the peak. The peak of the concentration or detected amount of ammonium ions is on the surface of the positive electrode active material 10 or at a depth from a reference point toward the center. Preferably, the thickness is 0.5 nm to 50 nm, and the depth is 5 nm to 50 nm. It is more preferred that the .alpha.-hydroxybenzoate be present in the .alpha.-hydroxybenzoate.

[0388] Here, how to express the positional relationship of the element distribution when EDX analysis is performed is shown in Figure 1. 14(A) to 14(G) are used for the following description. 1 is a schematic diagram showing the concentration distribution or the detected amount distribution of the first element e1 and the second element e2. 4(G) is the concentration distribution or detection amount distribution of the first element e1, the second element e2, and the third element e3. FIG.

[0389] For example, the concentration distribution or detected amount distribution of the first element e1 and the second element e2 is shown in FIG. In the case of the shape shown in FIG. 1, the position where the concentration or the detected amount of the second element e2 is maximum is It is said that the element e1 is located on the inner side of the position where the concentration or detected amount of the element e1 is maximum. The concentration distribution or detected amount distribution of the first element e1 and the second element e2 is shown in FIG. 14(B). In such a shape, the position where the concentration or the detected amount of the second element e2 is maximum is the position where the concentration or the detected amount of the first element e2 is maximum. It is said that the concentration or the detected amount of e1 is the maximum on the inner side. The concentration distribution or detected amount distribution of the first element e1 and the second element e2 has the shape shown in FIG. 14(C). In this case, the position where the concentration or the detected amount of the first element e1 is maximum is the position where the concentration or the detected amount of the second element e2 is maximum. It is said to be located inside the position where the concentration or the detected amount is maximum. The concentration distribution or detected amount distribution of e1 and the second element e2 has a shape as shown in FIG. 14(D). In this case, the position where the concentration or detected amount of the second element e2 is maximum is the position where the concentration or detected amount of the first element e1 is maximum. is located inside the position where the detected amount is maximum. When the concentration distribution or detected amount distribution of the second element e2 has a shape as shown in FIG. 14(E) The position where the concentration or detection amount of the first element e1 is maximum is the position where the concentration or detection amount of the second element e2 is maximum. For example, the first element e1 and the second element e2 are located inside the position where the amount is maximum. When the concentration distribution or detected amount distribution of element e2 has a shape as shown in FIG. 14(F), The position where the concentration or detected amount of the element e2 is maximum is the position where the concentration or detected amount of the first element e1 is minimum. It is said that it is located more inward than the point where it becomes largest.

[0390] The concentration distribution or detected amount distribution of the first element e1, the second element e2, and the third element e3 is shown in FIG. For example, in the case of the positional relationship shown in (G), the expression "has an area where the distributions overlap" is used. In this specification and the like, having a region where the distributions of two elements overlap means For example, the position at which the maximum value is reached in the concentration distribution or the detected amount distribution of at least one element is A concentration or detected amount that is 1 / 5 or more of the maximum value in the concentration distribution or detected amount distribution of the other element It means to be located within a range.

[0391] For example, in the case of the positional relationship shown in FIG. 14(G), the concentration distribution of the second element e2 or The position (P2) where the detected amount distribution has a maximum value is the concentration distribution or detection The range of the concentration or detectable amount in the distribution of the amount of a substance (Figure 1) is 1 / 5 of the maximum value (or the lower limit of detection). Since the first element e1 and the second element e2 are located in the region (the hatched area), In addition, the concentration distribution or detected amount distribution of the third element e3 The position (P3) where the concentration becomes maximum in the concentration distribution or the detected amount distribution of the first element e1 is The range where the concentration or detectable amount is 1 / 5 of the maximum value (or the lower limit of detection) or more (hatched area in the figure) Since the first element e1 and the third element e3 are not located in the region where the distributions overlap, It cannot be said that it has a territory.

[0392] In addition, in the case of the positional relationship shown in FIG. 14(G), the distribution of the second element e2 and the third element It can be said that the distribution of the element e3 is located more inward than the distribution of the first element e1. In addition, the distribution of the second element e2 and the distribution of the third element e3 are smaller than the distribution of the first element e1. It can be said that it exists biased towards the inside.

[0393] The content of this embodiment can be freely combined with the content of other embodiment modes.

[0394] (Embodiment 3) In this embodiment, each of the elements constituting the secondary battery will be described.

[0395] [Positive electrode] The secondary battery has a positive electrode, which is as described in the first and second embodiments.

[0396] <Positive electrode current collector> The positive electrode has a positive electrode current collector. The positive electrode current collector can be made of stainless steel, gold, platinum, or aluminum. Highly conductive materials such as metals such as titanium and alloys thereof can be used. A coating layer may be provided on the surface of the material. It is preferable that the material does not dissolve at the potential of the electrode. It is recommended to use an aluminum alloy containing elements such as aluminum and molybdenum that improve heat resistance. Alternatively, it may be formed from a metal element that reacts with silicon to form silicide. Metal elements that react with silicon to form silicides include zirconium, titanium, Hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, The positive electrode current collector is available in foil, plate, sheet, mesh, punched metal, etc. The positive electrode current collector may have a thickness of 1000 mm or less, and may have a shape such as a metal foil or an expanded metal. It is recommended to use a thickness of 5 μm or more and 30 μm or less.

[0397] <Binder> The positive electrode preferably contains a binder. Examples of the binder include styrene-butadiene. Rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene Uses rubber materials such as rubber, butadiene rubber, and ethylene-propylene-diene copolymer It is also preferable to use fluorine rubber as the binder.

[0398] As the binder, it is preferable to use, for example, a water-soluble polymer. For example, polysaccharides can be used. CMC, methylcellulose, ethylcellulose, hydroxypropylcellulose Cellulose derivatives such as cellulose, diacetyl cellulose, regenerated cellulose, or starch are used. These water-soluble polymers can be used in combination with the above-mentioned rubber materials. And even more preferable.

[0399] The binders include polystyrene, polymethyl acrylate, and polymethyl methacrylate (poly Poly(dimethyl methacrylate, PMMA), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide , polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, poly Isobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVD F), polyacrylonitrile (PAN), ethylene propylene diene polymer, polyacetic acid It is preferable to use materials such as vinyl and nitrocellulose.

[0400] The binder may be a combination of two or more of the above. For example, a binder having a particularly excellent viscosity adjusting effect may be used. The above materials may be used in combination with other materials. For example, rubber materials have good adhesive strength and Although it has excellent elasticity, it can be difficult to adjust the viscosity when mixed with a solvent. In this case, it is preferable to mix it with a material that has a particularly excellent viscosity adjusting effect. As a material having a particularly excellent viscosity adjusting effect, for example, a water-soluble polymer may be used. Particularly excellent water-soluble polymers include the aforementioned polysaccharides, such as carboxymethyl cellulose ( CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose and dicellulose Cellulose derivatives such as acetyl cellulose and regenerated cellulose, or starch can be used. can.

[0401] The cellulose derivatives such as carboxymethyl cellulose are, for example, The solubility increases by making cellulose into a salt such as sodium salt or ammonium salt. The increased solubility of the solubility of the electrode makes it easier to achieve the desired viscosity. This also helps to improve dispersion with the active material or other components when preparing a battery. In the above, cellulose and cellulose derivatives used as binders for electrodes include , and salts thereof.

[0402] Water-soluble polymers stabilize viscosity by dissolving in water, and are used as active materials and binders. Stable dispersion of other materials to be combined, such as styrene butadiene rubber, in an aqueous solution. In addition, since it has functional groups, it is expected to be easily and stably adsorbed onto the surface of the active material. In addition, cellulose derivatives such as carboxymethyl cellulose have a hydroxyl group or Many materials have functional groups such as carboxyl groups, and the polymers tend to intertwine due to the functional groups. It is expected that they interact with each other and cover the surface of the active material widely.

[0403] When the binder that covers or contacts the surface of the active material forms a film, it acts as a passive film. It is expected that the passive film will also have the effect of suppressing the decomposition of the electrolyte. A film with no electrical conductivity or extremely low electrical conductivity, e.g., an immobile film on the surface of an active material. When an electrolyte film is formed, decomposition of the electrolyte can be suppressed at the reaction potential of the secondary battery. In addition, the passive film suppresses electrical conductivity while allowing lithium ions to conduct. And even more desirable.

[0404] <Conductive material> The positive electrode preferably contains a conductive material. The conductive material is also called a conductive agent or a conductive assistant, and is a carbon material. By attaching a conductive material between multiple active materials, the multiple active materials can be electrically connected to each other. The active material and the conductive material are physically connected, which increases the conductivity. This does not only mean that when a covalent bond is formed, the van der Waals forces When bonding is performed by the conductive material, if a part of the surface of the active material is covered with the conductive material, the conductive material is formed on the surface irregularities of the active material. This concept includes cases where materials are fitted together, or when they are electrically connected even if they are not in contact with each other. do.

[0405] Examples of conductive materials include carbon such as acetylene black and furnace black. Graphite such as black, artificial graphite, and natural graphite, carbon nanofiber, and carbon One or more of carbon fibers such as nanotubes and graphene compounds can be used.

[0406] Examples of carbon fibers include mesophase pitch-based carbon fibers and isotropic pitch-based carbon fibers. Carbon fibers can be used. Carbon fibers can be carbon nanofibers or carbon fibers. Carbon nanotubes can be grown, for example, by vapor phase growth. It can be prepared by the method.

[0407] In this specification and the like, the graphene compound refers to graphene, multi-layer graphene, multi-graphene, graphene oxide, multi-layer graphene oxide, multi-graphene oxide, reduced graphene oxide graphene, reduced multilayer graphene oxide, reduced multi-graphene oxide, graphene Graphene compounds include graphene quantum dots and other compounds that contain carbon and have shapes such as flat plates and sheets. and has a two-dimensional structure formed by a six-membered carbon ring. The two-dimensional structure can be called a carbon sheet. It is also preferable that the graphene compound has a curved shape. The compound may be rolled into a shape similar to carbon nanofibers.

[0408] The content of the conductive material in the total amount of the active material layer is preferably 1 wt% or more and 10 wt% or less. More preferably, it is from 10 wt% to 5 wt%.

[0409] Unlike granular conductive materials such as carbon black, which make point contact with the active material, graphene compounds Since it allows for surface contact with low contact resistance, it requires less active material than ordinary conductive materials. Therefore, the electrical conductivity of the active material can be improved. This increases the ratio of the carbon nanotube in the porous layer, thereby increasing the discharge capacity of the secondary battery. It can be done.

[0410] Particulate carbon-containing compounds such as carbon black and graphite, or fibers such as carbon nanotubes Carbon-containing compounds with this structure tend to enter tiny spaces. For example, tiny spaces are spaces between multiple active materials. It refers to the area between particles. Carbon-containing compounds that easily enter tiny spaces and those that are conducted across multiple particles. It is used in combination with a sheet-like carbon-containing compound such as graphene, which can impart electrical conductivity. This increases the density of the electrodes and allows for the formation of excellent conductive paths. The secondary battery obtained by the manufacturing method of the embodiment has high capacity density and stability. This makes it effective as a secondary battery for vehicles.

[0411] [Negative electrode] The negative electrode has a negative electrode active material layer and a negative electrode current collector. The conductive material may further contain a conductive material and a binder.

[0412] <Negative electrode active material> As the negative electrode active material, for example, an alloy material or a carbon material can be used.

[0413] In addition, the negative electrode active material undergoes charge-discharge reactions through alloying and dealloying reactions with lithium. Any element can be used, such as silicon, tin, gallium, aluminum, Germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium, etc. Materials containing at least one of these elements can be used. These elements have a higher capacity than carbon. Silicon has a particularly high theoretical capacity of 4200mAh / g. Silicon is preferably used, and compounds containing these elements may also be used. For example, SiO, Mg2Si, Mg2Ge, SnO, SnO2, Mg2Sn, SnS2, V2Sn3, FeSn2, CoSn2, Ni3Sn2, Cu6Sn5, Ag3Sn, Ag 3Sb, Ni2MnSb, CeSb3, LaSn3, La3Co2Sn7, CoSb3, Examples include InSb and SbSn. Here, charging and discharging occurs through alloying and dealloying reactions with lithium. Elements that can undergo a reaction and compounds containing such elements are sometimes called alloy materials. do.

[0414] In this specification, "SiO" refers to, for example, silicon monoxide. Alternatively, SiO can refer to S iO x Here, x preferably has a value of 1 or close to 1. For example, x is preferably 0.2 or more and 1.5 or less, and more preferably 0.3 or more and 1.2 or less.

[0415] Carbon materials include graphite, easily graphitizable carbon (soft carbon), and non-graphitizable carbon (hard carbon). carbon fiber (carbon nanotube), graphene, carbon black, etc. good.

[0416] Examples of graphite include artificial graphite and natural graphite. Examples include carbon microbeads (MCMB), coke-based artificial graphite, and pitch-based artificial graphite. Here, as the artificial graphite, spherical graphite having a spherical shape can be used. For example, the MCMB may have a spherical shape, which is preferable. It is relatively easy to reduce the particle size, which is sometimes preferable. , flake graphite, and spherical natural graphite.

[0417] Graphite is formed when lithium ions are inserted into graphite (forming a lithium-graphite intercalation compound) It shows a low potential similar to that of lithium metal (0.05V to 0.3V vs. Li / Li + ) This allows lithium-ion secondary batteries using graphite to exhibit high operating voltages. Furthermore, graphite has a relatively high capacity per unit volume and a relatively small volume expansion. It is preferable because it has the advantages of being inexpensive, safe, and more reliable than metallic lithium.

[0418] In addition, titanium dioxide (TiO2) and lithium titanium oxide (Li4T i5O 12 ), lithium-graphite intercalation compound (Li x C6), niobium pentoxide (Nb2O5) The oxides used are tungsten dioxide (WO2), molybdenum dioxide (MoO2), etc. This can be done.

[0419] In addition, the negative electrode active material is a nitride of lithium and transition metals, which has a Li3N structure. i 3-x M x N (M=Co, Ni, Cu) can be used. For example, Li 2.6 C o 0.4 N has a large discharge capacity (900mAh / g, 1890mAh / cm 3 ) indicates preference It's nice.

[0420] When a nitride of lithium and a transition metal is used, the negative electrode active material contains lithium ions, so the positive electrode Combine with materials such as V2O5 and Cr3O8 that do not contain lithium ions as electrode active materials Even when a material containing lithium ions is used as the positive electrode active material, By first removing the lithium ions contained in the positive electrode active material, lithium is released as the negative electrode active material. Nitrides of metals and transition metals can be used.

[0421] In addition, a material that undergoes a conversion reaction can also be used as the negative electrode active material. , cobalt oxide (CoO), nickel oxide (NiO), iron oxide (FeO), etc. A transition metal oxide that does not form an alloy with the metal may be used as the negative electrode active material. Further materials that can be produced include Fe2O3, CuO, Cu2O, RuO2, Cr2O3, etc. oxide, CoS 0.89 , NiS, CuS and other sulfides, Zn3N2, Cu3N, Ge3 Nitrides such as N4, phosphides such as NiP2, FeP2, CoP3, FeF3, BiF3, etc. Fluoride is one example.

[0422] As another form of the negative electrode, a negative electrode that does not have a negative electrode active material at the time of completing the production of the secondary battery can be used. As a negative electrode having no negative electrode active material, for example, at the end of the production of a secondary battery, In the negative electrode, the negative electrode has only a negative electrode current collector, and the positive electrode active material is separated from the negative electrode current collector by charging the secondary battery. The released lithium ions are deposited as lithium metal on the negative electrode current collector, forming a negative electrode active material layer. A secondary battery using such an anode can be called an anode-free (an anode-free) secondary battery. These batteries are sometimes called negative electrode-free secondary batteries, negative electrode-less (anode-less) secondary batteries, etc.

[0423] When using a negative electrode that does not have a negative electrode active material, in order to uniformly deposit lithium on the negative electrode current collector, As a film for uniformly depositing lithium, for example, a lithium ion film may be provided. A solid electrolyte having ionic conductivity can be used. As the solid electrolyte, a sulfide-based solid Electrolytes, oxide-based solid electrolytes, polymer-based solid electrolytes, etc. can be used. However, it is relatively easy to form a uniform film of polymer solid electrolyte on the negative electrode current collector. Therefore, it is suitable as a film for uniformly depositing lithium. As the film for unification, for example, a metal film that forms an alloy with lithium can be used. As a metal film that forms an alloy with lithium, for example, a magnesium metal film can be used. Lithium and magnesium form a solid solution over a wide range of compositions. It is suitable as a film for making the deposition of rubber uniform.

[0424] When a negative electrode having no negative electrode active material is used, a negative electrode current collector having irregularities may be used. When a negative electrode current collector having irregularities is used, the concave portions of the negative electrode current collector are formed by the This creates cavities in which lithium can easily deposit, and when lithium deposits, it forms a dendrite-like shape. This can prevent the above from happening.

[0425] The conductive material and binder that can be contained in the negative electrode active material layer are the same as those contained in the positive electrode active material layer. The same materials as the conductive material and binder can be used.

[0426] <Negative electrode current collector> The negative electrode current collector is preferably made of a material that does not alloy with carrier ions such as lithium. Specifically, the negative electrode current collector may be made of the same material as the positive electrode current collector, or may be made of copper in addition to the same material. Alternatively, a configuration in which a coating layer is provided on the surface of the above-mentioned material may be used.

[0427] <Method of manufacturing the negative electrode> The method for producing the negative electrode will be described with reference to FIG.

[0428] <Step S160> As shown in step S160, a negative electrode active material is prepared. The binder, thickener, conductive material, and solvent were prepared. There were no limitations on the binder, thickener, and conductive material. The proportion of the negative electrode active material in the negative electrode active material layer is not limited. The content of the solvent should be between 95 wt% and 99 wt%. Water can be used as the solvent.

[0429] <Steps S161 and S162> As shown in step S161, the prepared materials are mixed in a solvent, and then in step S162 The slurry is formed as shown in the figure. The slurry here refers to a slurry in which an active material is deposited on a negative electrode current collector, which will be described later. It is a material liquid used to form a layer, and contains an active material, a binder, and a solvent. Furthermore, in step S162, the negative electrode current collector Prepare your body.

[0430] <Steps S165 and S166> As shown in step S165, the slurry is applied to the negative electrode current collector, and as shown in step S166, As shown, the slurry is dried to remove the solvent.

[0431] <Step S167, Step S169> As shown in step S167, the negative electrode active material layer is pressed together with the negative electrode current collector, and step S The negative electrode is completed as shown at 169.

[0432] [Separator] The secondary battery has a separator. As described in the first embodiment, etc. is.

[0433] [Exterior body] The secondary battery has an exterior body, which is as described in the first embodiment and the like.

[0434] [Electrolyte] The secondary battery has an electrolyte solution containing carrier ions. As explained in.

[0435] [Nail penetration test] The nail penetration test is one of the tests to check the safety of secondary batteries. Then, nails with a specified diameter selected from 2 mm to 10 mm are inserted at a specified speed. This is a test in which the battery is inserted.

[0436] <Nail penetration test device> First, the nail penetration test device will be described. Fig. 18(A) shows the side view of the nail penetration test device 1000. 18(A) and 18(B) show a perspective view of the stage of the nail penetration test device 1000. The nail penetration test device 1000 shown in A) comprises a stage 1001, a driving unit 1002, and a nail 10 03, a voltage measuring device 1015, a temperature measuring device 1016, and a control unit 1018. The drive unit 1002 has a drive mechanism 1012 that moves the nail 1003 in the direction of the arrow in the figure. The nail 1003 is placed on the stage 1001 by the moving mechanism 1012. At this time, the secondary battery 1004 is in a fully charged state (State Of Charge: SOC 100% (equivalent to the state) and this action is a nail piercing action. The broken line in FIG. 18(A) indicates the length of the nail 1003 after penetration during the nail insertion operation. 10 shows a recess in the stage 1001 provided to accommodate the

[0437] The voltage measuring device 1015 sends information about the voltage of the secondary battery during the nail penetration operation to the control unit 1018. Specifically, the amount of voltage change and the like are transmitted to the control unit 1018. Information about the temperature during the nail penetration operation is sent from the control unit 1016 to the control unit 1018. 18 transmits a control signal to the driving unit 1002 when controlling the operating conditions of the nail 1003. This can be done.

[0438] FIG. 18(B) is a perspective view illustrating the vicinity of the upper part of the stage 1001 of the nail penetration test device 1000. The secondary battery 1004 placed on the stage 1001 is connected to the wiring 1005a and The wiring 1005a and the wiring 1005b are electrically connected to each other. The pressure measuring device 1015 has the wiring 1005a and the wiring 1005b. The secondary battery 1004 is electrically connected to the positive electrode tab and the negative electrode tab of the secondary battery 1004. The voltage of the secondary battery 1004 can be measured simply by measuring the voltage between the positive and negative electrodes. It is called voltage value, battery voltage, cell voltage, or open voltage. When a temperature sensor is used, the temperature sensor is provided so as to be in contact with the surface of the exterior body of the secondary battery 1004. do.

[0439] In FIG. 18(B), a first temperature sensor 1006a and a second temperature sensor 1006b are arranged. In FIG. 18(B), one temperature sensor or three or more temperature sensors may be arranged. A first temperature sensor 1006a is provided on the side where the wire 1005a and the wiring 1005b are not arranged. The second temperature sensor 1006b is located on the side where the wiring 1005a and the wiring 1005b are arranged. If two or more temperature sensors are installed, the expansion of the exterior body may cause one of the temperature sensors to This is preferred because even if the temperature sensor becomes unavailable, other temperature sensors can be used. It's nice.

[0440] Furthermore, there is a welding area on the side where the wiring 1005a and the wiring 1005b are arranged, but The exterior body is folded back on the side where the wiring 1005a and the wiring 1005b are not arranged. Therefore, even if the exterior body expands, the wiring 1005a and the wiring 1005b are The expansion of the side where the first temperature sensor 1006a is not arranged is suppressed, and the first temperature sensor 1006b detects the second temperature It is more difficult to peel off than sensor 1006b and is therefore preferable.

[0441] The broken ellipse shown in FIG. 18B indicates the area where the nail 1003 penetrates the secondary battery 100 4. The first temperature sensor 1006a and the second temperature sensor 1006b It is preferable to provide the area equidistant from the area through which the nail 1003 penetrates. The first temperature sensor 10 is located within 5 cm, preferably within 2 cm, of the area penetrated by the 003. A second temperature sensor 1006a and a second temperature sensor 1006b are preferably provided near the area where the nail 1003 penetrates. When two or more temperature sensors are installed, it is preferable to be able to grasp the temperature change. Check that the temperature difference indicated by the temperature sensor is within ±5°C, preferably ±2°C. It is preferable to start the nailing operation from the

[0442] <Secondary battery in nail penetration test> Next, the state of the secondary battery in the nail penetration test will be explained again with reference to FIG. 19 etc. The test was carried out with the secondary battery 1004 in a fully charged state, and the battery was placed in a predetermined position selected from 2 mm to 10 mm. This test involves inserting a nail 1003 with a diameter of 100 mm into a secondary battery 1004 at a predetermined speed. 19 shows a cross-sectional view of a secondary battery 1004 with a nail 1003 stuck in it. The positive electrode 503, the separator 508, the negative electrode 506, and the electrolyte 530 are housed in an exterior body 541. The positive electrode 503 has a structure in which a positive electrode current collector 501 and positive electrode active materials formed on both sides of the positive electrode current collector 501 are stacked. The positive electrode active material layer has a layer 502. The structure described in the above embodiment is preferably applied to the positive electrode active material layer. The negative electrode 506 has a negative electrode current collector 521 and a negative electrode active material layer 512 formed on both sides of the negative electrode current collector 521. .

[0443] As shown in FIG. 19, when a nail 1003 is stuck into a secondary battery 1004, specifically, When the nail 1003 penetrates the positive electrode 503 and the negative electrode 506, an internal short circuit occurs. The potential of 003 becomes equal to the potential of the negative electrode 506, and the potential of the negative electrode 506 is changed via the nail 1003 etc. So electrons (e - ) flows to the positive electrode 503, and Joule heat is generated at the internal short circuit point and its vicinity. In addition, due to an internal short circuit, carrier ions, typically lithium ions, are released from the negative electrode 506. Umium ion (Li + ) is released into the electrolyte as shown by the white arrow. Before all the lithium ions are released, the battery temperature rises rapidly due to Joule heat generated by an internal short circuit. As the temperature rises, the electrolyte begins to reduce and decompose on the surface of the negative electrode. This is an electrochemical reaction. This is called the reduction reaction of the electrolyte by the negative electrode.

[0444] In addition, when the temperature of the secondary battery 1004 rises due to Joule heat, the positive electrode active material contains cobalt oxide. When lithium is used, lithium cobalt oxide has a H1-3 type crystal structure and an O1 type crystal structure. This can cause a phase change (i.e., structural change) to the structure, which can also generate heat.

[0445] The electrons (e - ) in the charged lithium cobalt oxide The tetravalent Co in the reaction is reduced to trivalent or divalent, and this reduction reaction results in the formation of cobalt oxide. Oxygen is released from the lithium, and the electrolyte 530 is decomposed by an oxidation reaction caused by the oxygen. This is an electrochemical reaction, and is called the oxidation reaction of the electrolyte by the positive electrode. The rate at which current flows into the positive electrode active material, such as lithium nitrate, depends on the insulating properties of the positive electrode active material. Alternatively, the rate at which the current flows may also affect the electrochemical reaction.

[0446] As mentioned above, when an internal short circuit occurs in a secondary battery, the temperature changes as shown in the graph in Figure 20. Figure 20 shows the graph shown on page 70 [Figure 2-12] of Non-Patent Document 1. This is a partially revised figure, showing the temperature (specifically the internal temperature) of the secondary battery over time. This is a graph. When an internal short circuit occurs at (P0), the temperature of the secondary battery rises over time. As shown in (P1), the temperature of the secondary battery increases due to Joule heat generated by an internal short circuit. When the temperature rises to around 100°C, it is the limit temperature at which the secondary battery will not go into thermal runaway. In this case, the negative electrode (graphite) In (P3), the electrolyte is reduced and heat is generated by the positive electrode. Oxidation of the electrolyte occurs and heat is generated, and in (P4), heat is generated due to thermal decomposition of the electrolyte. The secondary battery may go into thermal runaway and catch fire.

[0447] At this time, the electrons that suddenly flow into the positive electrode active material convert cobalt into Co4 valence This reaction occurs when the positive electrode active material is reduced to divalent Co, and oxygen is released from the positive electrode active material. Since this is an exothermic reaction, it accelerates thermal runaway. This makes it possible to provide a safe secondary battery that is less prone to runaway.

[0448] In order to suppress the above reaction, for example, the surface layer of the positive electrode active material is made of an additive that does not easily release oxygen. It is preferable that the positive electrode active material contains the element X, and that the concentration of the added element X is higher than that of the interior. If oxygen is not released from the substrate, the above reduction reaction (e.g., the reaction from tetravalent Co to divalent Co) will not occur. The additive element X that does not easily release oxygen is, for example, magnesium, aluminum, etc. The closer the oxygen is to the magnesium, the more easily it will be released. Therefore, it is suitable as an additive element X that does not easily release oxygen. Nickel is also thought to have the effect of suppressing oxygen release when present at the lithium site. can be obtained.

[0449] In addition, even if cobalt or other substances are reduced, lithium ions are inserted into the positive electrode active material before oxygen is released. If oxygen can be absorbed into the positive electrode active material, electrical neutrality is maintained and oxygen release does not occur. Even if electrons suddenly flow in, lithium ions are inserted into the positive electrode active material through the electrolyte from the negative electrode. It is sufficient if the crystal structure of the positive electrode active material is kept stable during this period.

[0450] In addition, in order to prevent smoking, heat generation, etc. from occurring during the nail penetration test, the temperature rise of the secondary battery must be suppressed. It is considered desirable that the negative electrode, positive electrode and / or electrolyte have stable properties at high temperatures. Specifically, the first positive electrode active material 10x does not release oxygen, and in particular, does not release oxygen even when exposed to high temperatures. It is preferable that the positive electrode active material has a stable structure that does not release the charge. It is preferable that the first positive electrode active material 10x has a structure in which the temperature gradient is gentle. As will be described later, one aspect of the present invention is The first positive electrode active material 10x has both the above-mentioned stable structure and a structure that slows down the current flow rate. You can have it.

[0451] <Thermal runaway of secondary batteries> Regarding the principle of thermal runaway in secondary batteries, the graph shown on page 69 [Figure 2-11] of Non-Patent Document 1 is A partially revised version of the rough draft is shown in Figure 21. For example, when charging the secondary battery described above, As the temperature (specifically the internal temperature) rises, it goes through several stages and eventually reaches thermal runaway. 1 is a graph of the temperature of the secondary battery against time, for example, when the temperature of the secondary battery is 100°C or In the vicinity of that point, (1) the SEI (Solid Electrolyte Intermetallic Compound) of the negative electrode When the temperature of the secondary battery exceeds 100°C, the 2) The negative electrode (when graphite is used, the negative electrode becomes C6Li) reduces the electrolyte and generates heat. (3) At or near 150°C, oxidation of the electrolyte by the positive electrode and heat generation occur. When the temperature of the battery reaches or approaches 180°C, (4) thermal decomposition of the electrolyte occurs, and (5) the positive The oxygen release from the electrode and the thermal decomposition of the positive electrode (which involves structural changes in the positive electrode active material) Then, when the temperature of the secondary battery exceeds 200°C, (6) decomposition of the negative electrode occurs, and finally In this state, especially in the state of (5) and (6), the positive and negative electrodes come into direct contact. After passing through state (7) or state (8), the secondary battery goes into thermal runaway.

[0452] To prevent thermal runaway, it is necessary to suppress the temperature rise of the secondary battery, It is considered desirable that the electrode, positive electrode and / or electrolyte have stable properties at high temperatures.

[0453] <Characteristics of secondary batteries in nail penetration tests> In the secondary battery including the positive electrode having the positive electrode active material and the separator described in the above embodiment, The characteristics of the secondary battery when subjected to a nail penetration test will be described below.

[0454] Temperature rise of the secondary battery when a nail penetration test is performed, i.e., temperature before and after the nail penetration test The difference in the maximum temperature reached (also called the temperature rise ΔT) is preferably 100°C or less, and 70°C The temperature is preferably within 5 cm from the nail hole, and more preferably below 50°C. The temperature should be within 2 cm of the nail hole, specifically within 5 cm, preferably within 2 cm. The temperature sensor is placed in contact with the exterior body of the secondary battery. It is advisable to set it up so that

[0455] The maximum temperature during the nail penetration test is preferably 250°C or less, more preferably 200°C or less. More preferably, the temperature is 180° C. or lower. It is preferable that the temperature is lower than the temperature at which the reaction occurs.

[0456] Furthermore, the maximum temperature during the nail penetration test is preferably 150°C or less, and more preferably 100°C or less. More preferably, the temperature is a temperature at which oxidation of the electrolyte occurs by the positive electrode. It is more preferable that the maximum temperature is lower than the flammability of the mixed solvent used in the electrolyte. If the flash point of the mixed solvent is unknown, the flash point of each solvent can be used as a reference. More preferably, the temperature is lower than the softening point of the separator. The softening point of polypropylene applicable to this application is about 155°C.

[0457] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0458] (Fourth embodiment) In this embodiment, a secondary battery including an electrolyte solution and a separator according to one embodiment of the present invention will be described. Secondary batteries that have an electrolyte and a separator can prevent thermal runaway and / or fire. Furthermore, when the secondary battery is charged and discharged, the separator can be used even when the electrodes expand and contract. This is preferable because it ensures the retention of the electrolyte in the battery.

[0459] [Coin-type secondary battery] An example of a coin-type secondary battery will be described. FIG. 22(A) shows a coin-type (single-layer flat type) 22(B) is an external view, and FIG. 22(C) is a cross-sectional view of the secondary battery. Coin-type secondary batteries are mainly used in small electronic devices.

[0460] In FIG. 22(A), for ease of understanding, the overlapping of the components (vertical relationship and positional relationship) is not shown. Therefore, Figure 22(A) and Figure 22(B) are completely identical. This is not a corresponding diagram.

[0461] In FIG. 22(A), a positive electrode 304, a separator 310, a negative electrode 307, a spacer 322, a wafer The separator 310 is a separator according to one embodiment of the present invention. These are sealed with a negative electrode can 302 and a positive electrode can 301 by a gasket. In addition, the gasket for sealing is not shown in FIG. 22(A). 22, the washer 312 is used to protect the inside when the positive electrode can 301 and the negative electrode can 302 are crimped together. The spacer 322 and washer 312 are used to fix the position inside the can. Use stainless steel or insulating material.

[0462] The positive electrode 304 has a laminated structure in which a positive electrode active material layer 306 is formed on a positive electrode current collector 305. The positive electrode active material of the positive electrode active material layer 306 is lithium cobalt oxide, which is one embodiment of the present invention. It is possible.

[0463] FIG. 22(B) is a perspective view of the completed coin-type secondary battery.

[0464] The coin-type secondary battery 300 has a positive electrode can 301 that also serves as a positive electrode terminal and a negative electrode can 302 that also serves as a negative electrode terminal. 302 is insulated and sealed by a gasket 303 made of polypropylene or the like. The positive electrode 304 is composed of a positive electrode current collector 305 and a positive electrode active material layer 306 provided in contact with the positive electrode current collector 305. The negative electrode 307 is formed by a negative electrode current collector 308 and a The negative electrode 307 is formed by a negative electrode active material layer 309 formed by stacking the negative electrode active material layer 309. Alternatively, a lithium metal foil or a lithium-aluminum alloy foil may be used.

[0465] The positive electrode 304 and the negative electrode 307 used in the coin-type secondary battery 300 are each made of an active material The layer can be formed on only one side.

[0466] The positive electrode can 301 and the negative electrode can 302 are made of nickel and aluminum, which are corrosion-resistant to the electrolyte. Metals such as titanium, or alloys of these or alloys of these with other metals (e.g. stainless steel) In addition, nickel or The positive electrode can 301 is preferably covered with aluminum or the like. 2 are electrically connected to the negative electrode 307.

[0467] The negative electrode 307, the positive electrode 304 and the separator 310 are immersed in an electrolyte solution, and the .... As shown in the figure, the positive electrode can 301 is placed downward, the positive electrode 304, the separator 310, the negative electrode 307, and the negative electrode can The positive electrode can 301 and the negative electrode can 302 are stacked in this order, and the positive electrode can 301 and the negative electrode can 302 are pressed together with a gasket 303 interposed therebetween. The electrolytic solution is then coated with a solvent, to manufacture a coin-type secondary battery 300. Preferably, a mixture of solvents is applied.

[0468] [Cylindrical secondary battery] An example of a cylindrical secondary battery will be described with reference to FIG. 23(A). Cylindrical secondary battery 61 As shown in FIG. 23(A), the battery 6 has a positive electrode cap (secondary battery cover) 601 on the top surface and a side The positive electrode cap 601 and the secondary battery can (external can) 602 are provided on the top and bottom surfaces. The secondary battery can (external can) 602 is insulated by a gasket (insulating packing) 610. There are.

[0469] FIG. 23(B) is a schematic diagram showing a cross section of a cylindrical secondary battery. The cylindrical secondary battery has a positive electrode cap (secondary battery lid) 601 on the top surface, and The positive electrode cap and the secondary battery can (external can) 602 are disposed in the positive electrode cap and the secondary battery can (external can) 603. ) 602 is insulated by a gasket (insulating packing) 610.

[0470] Inside a hollow cylindrical secondary battery can 602, a strip-shaped positive electrode 604 and a strip-shaped negative electrode 606 are separated. The secondary battery element is wound with a separator 605 sandwiched between them. The separator according to one embodiment of the present invention can be applied to a secondary battery element. The secondary battery can 602 is wound around the central axis. One end is closed and the other end is open. The secondary battery can 602 is made of nickel, aluminum, or Metals such as titanium, or their alloys, or alloys of these with other metals (e.g., stainless steel In addition, nickel and aluminum can be used to prevent corrosion by the electrolyte. It is preferable to coat the secondary battery can 602 with aluminum or the like. The secondary battery element, in which the positive electrode, negative electrode and separator are wound, is sandwiched between a pair of opposing insulating plates 608. , and is sandwiched between insulating plates 609. In addition, a secondary battery can 602 in which a secondary battery element is provided The inside of the battery is filled with an electrolyte (not shown). can be used.

[0471] The positive and negative electrodes used in cylindrical secondary batteries are wound up, so active materials are formed on both sides of the current collector. It is preferable that

[0472] The positive electrode active material of the positive electrode 604 can be lithium cobalt oxide, which is one embodiment of the present invention. This allows the cylindrical secondary battery 616 to have good high-voltage charging characteristics.

[0473] A positive electrode terminal (positive electrode current collecting lead) 603 is connected to the positive electrode 604, and a negative electrode terminal The positive electrode terminal 603 is made of a metal material such as aluminum. The negative electrode terminal 607 can be made of a metal material such as copper. The positive terminal 603 is connected to a safety valve mechanism 613, and the negative terminal 607 is connected to the bottom of the secondary battery can 602. The safety valve mechanism 613 is a PTC (Positive Temperature Control) It is electrically connected to the positive electrode cap 601 through a (Cure Coefficient) element 611. The safety valve mechanism 613 is connected to the secondary battery when the internal pressure of the secondary battery exceeds a predetermined threshold. It cuts off the electrical connection between the positive electrode cap 601 and the positive electrode 604. The element 611 is a thermosensitive resistor whose resistance increases when the temperature rises. The PTC element is made of barium titanate. (BaTiO3) based semiconductor ceramics and the like can be used.

[0474] 23C shows an example of a power storage system 615. The power storage system 615 includes a plurality of secondary batteries. The positive electrode of each secondary battery has a conductor 624 separated by an insulator 625. The conductor 624 is in contact with and electrically connected to the control circuit 62 via the wiring 623. 0. The negative electrodes of the secondary batteries are electrically connected to the The control circuit 620 is electrically connected to a charger that performs charging and discharging. A discharge control circuit or a protection circuit to prevent overcharging and / or over-discharging can be applied. Cut.

[0475] FIG. 23D shows an example of a power storage system 615. The power storage system 615 includes a plurality of secondary batteries. The plurality of secondary batteries 616 are sandwiched between the conductive plate 628 and the conductive plate 614. The plurality of secondary batteries 616 are electrically connected to the conductive plate 628 and the conductive plate 614 by wiring 627. The plurality of secondary batteries 616 may be connected in parallel or in series. They may be connected in parallel and then in series. By configuring a power storage system 615 having a battery 616, it is possible to extract a large amount of power. can.

[0476] A plurality of secondary batteries 616 may be connected in parallel and then further connected in series.

[0477] Furthermore, a temperature control device may be provided between the plurality of secondary batteries 616. When the secondary battery 616 is overheated, it is cooled by the temperature control device. The temperature can be controlled by a temperature control device. It becomes less susceptible to

[0478] 23D, the power storage system 615 is connected to a control circuit 620 via a wiring 621 and a wiring The wiring 621 is electrically connected to the plurality of two electrodes via a conductive plate 628. The wiring 622 is connected to the positive electrode of the secondary battery 616 via the conductive plate 614. are electrically connected to the respective

[0479] [Other examples of secondary battery structures] An example of the structure of the secondary battery will be described with reference to FIGS. 24 and 25. FIG.

[0480] The secondary battery 913 shown in FIG. 24(A) has a terminal 951 and a terminal 952 provided inside a housing 930. The winding 950 is immersed in an electrolyte solution inside the housing 930. It is preferable to use the mixed solvent according to one aspect of the present invention as the solvent for the electrolyte. 2 is in contact with the housing 930, and the terminal 951 is in contact with the housing 930 by using an insulating material or the like. In FIG. 24(A), for convenience, the housing 930 is shown separated. However, in reality, the winding body 950 is covered by the housing 930, and the terminals 951 and 952 are enclosed by the housing 930. The housing 930 may be made of a metal material (for example, aluminum) or A laminate of a metal material and a resin material can be used.

[0481] As shown in FIG. 24(B), the housing 930 shown in FIG. 24(A) is made of a plurality of materials. For example, the secondary battery 913 shown in FIG. 24(B) may be formed by a housing 930a and a housing 930b. The wound body 930 is located in the area surrounded by the housing 930a and the housing 930b. 50 are provided.

[0482] The housing 930a is made of a metal material (for example, aluminum) or a metal material and a resin material. The resin material may be an organic resin or the like. By using a material such as organic resin on the surface where the antenna is formed, the secondary battery 913 If the shielding of the electric field by the housing 930a is small, the housing The antenna may be provided inside the body 930a. The housing 930b may be made of a metal material (e.g., Aluminum or a laminate of a metal material and a resin material can be used.

[0483] The structure of the wound body 950 is shown in FIG. The separator 933 includes a positive electrode 932 and a separator 933. The winding body 950 is made up of a plurality of separators sandwiched between the separator 933. The negative electrode 931 and the positive electrode 932 are stacked one on top of the other, and the laminated sheet is wound to form a wound body. The negative electrode 931, the positive electrode 932, and the separator 933 may be stacked in multiple layers. May be layered.

[0484] Also, a secondary battery 913 having a wound body 950a as shown in FIG. The wound body 950a shown in (A) includes 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 932b. It has a.

[0485] The positive electrode active material of the positive electrode active material layer 932a is lithium cobalt oxide, which is one embodiment of the present invention. It is possible.

[0486] The separator 933 has a width greater than that of the negative electrode active material layer 931a and the positive electrode active material layer 932a. The negative electrode active material layer 931a and the positive electrode active material layer 932a are wound so as to overlap with each other. In addition, it is preferable from the viewpoint of safety that the width of the negative electrode active material layer 931a is wider than that of the positive electrode active material layer 932a. Furthermore, the wound body 950a having such a shape is preferable in terms of safety and productivity.

[0487] As shown in FIG. 25(B), the negative electrode 931 is connected to the terminal 95 by ultrasonic bonding, welding, or crimping. The terminal 951 is electrically connected to the terminal 911a. 32 is electrically connected to terminal 952 by ultrasonic bonding, welding, or crimping. 2 is electrically connected to terminal 911b.

[0488] As shown in FIG. 25(C), the wound body 950a and the electrolyte are covered by the housing 930, and the secondary This becomes the battery 913. The housing 930 is preferably provided with a safety valve, an overcurrent protection element, and the like. The safety valve is a valve that opens when the inside of the housing 930 reaches a predetermined internal pressure, and prevents the secondary battery from exploding. It is possible.

[0489] As shown in FIG. 25(B), the secondary battery 913 may have a plurality of wound bodies 950a. By using a plurality of wound bodies 950a, the secondary battery 913 can have a larger discharge capacity. Other elements of the secondary battery 913 shown in FIG. 25(A) and FIG. 25(B) are the same as those shown in FIG. The description of the secondary battery 913 shown in FIGS. 24A to 24C can be referred to.

[0490] <Laminated secondary battery> Next, an example of an external view of a laminated secondary battery is shown in FIG. 26(A) and FIG. 26(B). 26(A) and 26(B) show a positive electrode 503, a negative electrode 506, a separator 507, and a 07, an outer casing 509, a positive electrode lead electrode 510, and a negative electrode lead electrode 511. A separator according to one aspect of the present invention can be applied to the separator 507. However, it is preferable to use the electrolyte according to one embodiment of the present invention, particularly a mixed solvent, as the electrolyte.

[0491] 26(A) shows an external view of the positive electrode 103 and the negative electrode 106. The positive electrode 103 is connected to the positive electrode current collector 21. The positive electrode active material layer 22 is formed on the surface of the positive electrode current collector 21. The lithium cobalt oxide according to one embodiment of the present invention can be used as the positive electrode active material. In addition, the positive electrode 103 has a region where the positive electrode current collector 21 is partially exposed (hereinafter referred to as a tab region). The negative electrode 106 has a negative electrode current collector 31, and the negative electrode active material layer 32 is formed on the surface of the negative electrode current collector 31. The negative electrode 106 has a region where the negative electrode current collector 31 is partially exposed, i.e., a tab region. The area or shape of the tab regions of the positive electrode and the negative electrode is as shown in FIG. Examples are not limited to:

[0492] The content of this embodiment can be freely combined with the content of other embodiment modes.

[0493] (Embodiment 5) In this embodiment, a secondary battery having an electrolyte solution and a separator according to one embodiment of the present invention is mounted. Examples of vehicles include automobiles, trains, airplanes, and buses. A secondary battery having a regulator is preferable because it can prevent thermal runaway and / or fire. Even if the electrodes expand and contract during charging and discharging of the battery, the amount of electrolyte retained in the separator can be ensured. This is preferable because it can be done easily.

[0494] The automobile 2001 shown in FIG. 27(A) is an electric vehicle that uses an electric motor as a power source for running. In addition, the electric motor and the engine are selected as the power source for driving. The vehicle 2001 is a hybrid vehicle that can be used with a secondary battery pack 22. 00, and the secondary battery pack includes a secondary battery module in which a plurality of secondary batteries are connected, and It is preferred to have a charge controller electrically connected to the secondary battery module.

[0495] Next, the secondary battery pack 2200 will be described with reference to FIG. 1 shows an example in which one secondary battery pack 2200 has nine prismatic secondary batteries 1300. In addition, nine square secondary batteries 1300 are connected in series, and one electrode group is fixed to an insulating material. The other electrode group is fixed by a fixing part 1414 made of an insulating material. Instead of the fixing portion 1413 and the fixing portion 1414, a secondary battery is housed in a housing (also called a case). The electrode group may be fixed by using a structure in which the electrode group is housed. Since it is assumed that shaking will be applied, the fixing parts 1413 and 1414 and the secondary battery housing It is preferable to fix a plurality of square secondary batteries 1300 in a container box or the like. The electrode group is electrically connected to the control circuit section 1320 by wiring 1421. The electrodes are electrically connected to the control circuit section 1320 by wiring 1422 .

[0496] The control circuit 1320 uses a memory circuit including a transistor using an oxide semiconductor. A charge control circuit having a memory circuit including a transistor using an oxide semiconductor may be provided. or secondary battery control system, BTOS (Battery operating system) stem, or Battery oxide semiconductor) There are cases where this happens.

[0497] It is preferable to use a metal oxide that functions as an oxide semiconductor. In-M-Zn oxide (element M is aluminum, gallium, yttrium, copper, Vanadium, beryllium, boron, titanium, iron, nickel, germanium, zirconium , molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, It is preferable to use a metal oxide such as one or more selected from the group consisting of titanium dioxide, magnesium, etc. In-M-Zn oxides that can be used as metal oxides are CAAC-OS (C-Axi s Aligned Crystal Oxide Semiconductor), C AC-OS(Cloud-Aligned Composite Oxide Semi In addition, the metal oxide is preferably an In-Ga oxide. In-Zn oxides and other In-Zn oxides may also be used. The multiple crystalline regions are oxide semiconductors in which the c-axes are oriented in a specific direction. The direction is the thickness direction of the CAAC-OS film, the normal direction to the surface on which the CAAC-OS film is formed, or the C The direction of the normal to the surface of the AAC-OS film is the direction of the crystal. If the atomic arrangement is considered as a lattice arrangement, the crystalline region is a region where the lattice arrangement is uniform. It is also an area.

[0498] "CAC-OS" is a mosaic material that is separated into a first region and a second region. The first region is in a cloud-like shape, and the first region is distributed throughout the film (hereinafter also referred to as a cloud-like shape). In other words, the CAC-OS is a mixture of the first and second regions. However, the first and second regions do not have a clear boundary. However, it may be difficult to observe.

[0499] Oxide semiconductors have a variety of structures, each of which has different characteristics. Oxide semiconductors include amorphous oxide semiconductors, polycrystalline oxide semiconductors, a-like OS, and CA Two or more of C-OS, nc-OS, and CAAC-OS may be included.

[0500] In addition, transistors that use oxide semiconductors for the semiconductor layer are also susceptible to the ambient operating temperature of single-crystal silicon transistors. The temperature range is wider than that of a secondary battery, from -40℃ to 150℃, and even if the secondary battery is overheated, the characteristics do not change easily. The off-state current of a transistor using an oxide semiconductor was 150°C. The off-current characteristics of single-crystal Si transistors are below the lower limit of measurement regardless of temperature. For example, at 150°C, the off-current of a single-crystal Si transistor increases. However, the current on / off ratio is not large enough. The control circuit unit 1320 can improve safety. 20 can make a significant contribution to eliminating accidents such as fires caused by secondary batteries.

[0501] Next, a car 2001 shown in FIG. 27(A) and a secondary battery pack 220 shown in FIG. 27(B) An example of a block diagram for 0 is shown in FIG.

[0502] As shown in FIG. 27(C), the electric vehicle has a first battery as a main driving secondary battery. The inverter 1312 supplies power to the batteries 1301a and 1301b and starts the motor 1304. A second battery 1311 is installed to provide power to the Also called a starting battery (also called a second battery) The second battery 1311 only needs to have a high output, and does not need to have a large capacity. The capacity of the first battery 1301a is smaller than that of the second battery 1301b.

[0503] The internal structure of the first battery 1301a is the wound type shown in FIG. 24(C) or FIG. 25(A). Alternatively, it may be a laminated type shown in FIG. 26(A) or FIG. 26(B).

[0504] In this embodiment, two first batteries 1301a and 1301b are connected in parallel. Although an example is shown, three or more batteries may be connected in parallel. If sufficient power can be stored, the first battery 1301b may be omitted. By configuring a secondary battery pack with a secondary battery, it is possible to extract large amounts of power. The plurality of secondary batteries may be connected in parallel, in series, or in parallel. After being connected in series, the secondary batteries may be further connected in series. Call.

[0505] In addition, in the case of secondary batteries for vehicles, tools are used to cut off power from multiple secondary batteries. The first one has a service plug or circuit breaker that can cut off high voltage without It is provided in the battery 1301a.

[0506] The power of the first batteries 1301a and 1301b is mainly used to rotate the motor 1304. It is used to power 42V automotive components (electric power supplies) via the DCDC circuit 1306. 1307, heater 1308, defogger 1309, etc.) to supply power to the rear wheels. Even when the rear motor 1317 is provided, the first battery 1301a is connected to the rear motor 131 Used to rotate the number 7.

[0507] The second battery 1311 also supplies power to 14V-based in-vehicle components ( Powers the audio 1313, power windows 1314, lamps 1315, etc. do.

[0508] The first batteries 1301a and 1301b are mainly used for 42V (high voltage HV) in-vehicle equipment. The second battery 1311 supplies power to the 14V system (low voltage system LV) in-vehicle equipment. The second battery 1311 is often a lead battery because of its cost advantage. Lead-acid batteries have a higher self-discharge rate than lithium-ion secondary batteries, and a problem called sulfation occurs. The second battery 1311 is a lithium ion secondary battery. The advantage of using batteries is that they are maintenance-free, but for long-term use, e.g. 3 If the inverter is more than 1 year old, there is a risk of abnormalities occurring that are difficult to identify during manufacturing. If the second battery 1311 that powers the system becomes inoperable, the first battery 1301a, To prevent the motor from being unable to start even if there is remaining capacity in 301b, If the second battery 1311 is a lead battery, power is supplied from the first battery to the second battery. The battery is supplied with electricity and charged to keep it fully charged at all times.

[0509] In this embodiment, both the first battery 1301a and the second battery 1311 are lithium. The second battery 1311 is a lead-acid battery, an all-solid-state secondary battery, or the like. A battery or an electric double layer capacitor may also be used.

[0510] The regenerative energy generated by the rotation of the tire 1316 is transmitted to the motor 13 via the gear 1305. 04, and is controlled by the motor controller 1303 or the battery controller 1302. The second battery 1311 is charged via the battery control circuit 1321. The first battery 1301 a is charged from the controller 1302 via the control circuit unit 1320 . The battery controller 1302 also supplies the first battery 13 via the control circuit unit 1320. In order to efficiently charge the regenerative energy, the first battery 13 It is desirable that the O1a and 1301b are capable of rapid charging.

[0511] The battery controller 1302 controls the charging voltage and The battery controller 1302 can set the charging current, etc. Charging conditions can be set according to the battery's charging characteristics, allowing for rapid charging.

[0512] Although not shown, when connecting the electric vehicle to an external charger, the charger plug Alternatively, the connection cable of the charger is electrically connected to the battery controller 1302. The power supplied from the external charger is transferred to the first battery via the battery controller 1302. 1301a and 1301b. In addition, some chargers are equipped with a control circuit. Therefore, the functions of the battery controller 1302 may not be used, but they are restricted to prevent overcharging. It is preferable to charge the first batteries 1301a and 1301b via the control circuit unit 1320. In addition, the charger plug or the charger connection cable may be equipped with a control circuit. The control circuit section 1320 is an ECU (Electronic Control Unit The ECU is also called a CAN (Controller CAN is used as an in-vehicle LAN. It is one of the serial communication standards. The ECU includes a microcomputer. The ECU uses a CPU or a GPU.

[0513] External chargers installed at charging stations, etc., are connected to 100V outlets and 200V outlets. There are also other types, such as 3-phase 200V and 50kW. It can also be charged by receiving power from charging equipment.

[0514] When performing rapid charging, a secondary battery that can withstand high voltage charging is required in order to charge in a short time. A pond is desired.

[0515] The content of this embodiment can be freely combined with the content of other embodiment modes.

[0516] (Embodiment 6) In this embodiment, a secondary battery having an electrolyte solution and a separator according to one embodiment of the present invention is mounted. Secondary batteries, which have an electrolyte and a separator, are designed to prevent thermal runaway and In addition, the electrodes expand and contract during charging and discharging of the secondary battery. This is also preferable because it ensures the amount of electrolyte retained by the separator.

[0517] FIG. 28(A) shows an artificial satellite 6800 as an example of space equipment. 6800 includes a body 6801, a solar panel 6802, an antenna 6803, and a secondary battery. Pond 6805.

[0518] The satellite 6800 operates when sunlight hits the solar panel 6802. However, for example, when sunlight hits a solar panel, the electricity required for In situations where there is little sunlight or when the amount of sunlight irradiating the solar panel is low, This reduces the amount of power required to operate the satellite 6800. It may not be possible to operate the satellite 6800 even under conditions where the generated power is low. In order to achieve this, it is advisable to provide a secondary battery 6805 in the satellite 6800. By using this secondary battery, a highly reliable secondary battery can be obtained. In addition, by using the secondary battery of the present invention, it is possible to obtain a secondary battery that exhibits good low-temperature characteristics. do.

[0519] The satellite 6800 can generate a signal, which is transmitted via an antenna 6803. The signal is then transmitted to a receiver, for example, on the ground or another satellite. By receiving the signal transmitted by the artificial satellite 6800, for example, Therefore, the satellite 6800 can measure the position of the receiver that received the signal. A star positioning system can be configured.

[0520] The satellite 6800 may also be configured to include a sensor. For example, a visible light sensor By configuring the satellite 6800 with a sensor, the satellite 6800 can detect objects on the ground. The infrared sensor can detect the reflected sunlight. By adopting this configuration, the satellite 6800 can detect thermal infrared rays emitted from the earth's surface. As a result, the artificial satellite 6800 can be used as an Earth observation satellite, for example. It can have the function of

[0521] FIG. 28(B) shows a solar sail (also called a sun sail) as an example of space equipment. The figure shows the spacecraft 6900. The spacecraft 6900 consists of a spacecraft 6901 and a solar sail 6 902 and a secondary battery 6905. The secondary battery of the present invention is used as the secondary battery. Furthermore, the secondary battery of the present invention can be used as a secondary battery with high reliability. By using this, it is possible to make a secondary battery that exhibits good low-temperature characteristics. When a photon hits the surface of Solar Sail 6902, it gains momentum. Therefore, the surface of the solar sail 6902 is preferably provided with a thin film with high reflectivity. Preferably, it faces the sun.

[0522] Solar Sail 6902 will remain folded up until it leaves the atmosphere, Outside the atmosphere (outer space), the sphere will unfold into a large sheet as shown in Figure 28(B). It may be designed as follows.

[0523] FIG. 28(C) shows a spacecraft 6910 as an example of space equipment. 10 has a body 6911 , a solar panel 6912 , and a secondary battery 6913 . By using the secondary battery of the present invention as a secondary battery, a highly reliable secondary battery can be obtained. Furthermore, by using the secondary battery of the present invention as a secondary battery, it is possible to obtain a secondary battery that exhibits good low-temperature characteristics. The vehicle 6911 may have, for example, a pressurized compartment and an unpressurized compartment. The pressurized cabin may be designed to accommodate crew members. The power generated by this can be charged into the secondary battery 6913.

[0524] FIG. 28(D) shows a rover 6920 as an example of space equipment. 20 has a body 6921 and a secondary battery 6923. The secondary battery is a secondary battery of the present invention. By using a battery, a highly reliable secondary battery can be obtained. By using such a secondary battery, it is possible to obtain a secondary battery that exhibits good low-temperature characteristics. The vehicle 6920 may have a solar panel 6922 .

[0525] Rover 6920 may be designed to accommodate a crew member. Solar panel 6912 The power generated by irradiation may be charged into the secondary battery 6923, or other power sources may be used. For example, electricity generated by a fuel cell, a radioisotope thermoelectric converter, etc. can be converted into a secondary battery 6923 You can charge it.

[0526] The content of this embodiment mode can be combined with the content of other embodiment modes as appropriate. [Example]

[0527] In this example, DSC measurements, combustion tests, vapor pressure calculations, and Raman spectroscopy analysis was performed. Electrolyte A and B contain lithium salt LiFP6. The electrolyte C is a lithium salt. The electrolyte D is a solution containing 1 mole or less of LiFP6 per liter of the fluoride mixed solvent. The electrolyte E does not use lithium salts, and the lithium salt LiFP6 is mixed with the solvent It was less than 1 mole per liter.

[0528] [Table 2]

[0529] <DSC measurement of electrolyte> DSC measurements were carried out to confirm the thermal stability of the electrolytes. First, electrolytes B, C, and 15 mL of electrolyte E was prepared. Each electrolyte was placed in a SUS container in an Ar-filled glove box. The measurement equipment and conditions for the DSC measurement were as follows: did. DSC equipment: Rigaku EVO2 DSC8271 Heating rate: 5℃ / min Temperature range: Room temperature (25°C) to 350°C The obtained measurement results were analyzed using the analysis software Thermo prus EVO. Background correction was performed.

[0530] The results of the DSC measurement are shown in Figure 29. In Figure 29, the horizontal axis represents temperature. The vertical axis indicates the heat flow [mW / g]. The heat flow rate per unit volume is equivalent to the heat flow rate per unit volume. Electrolytes B and C have smaller heat flows than electrolyte E. That is, electrolytes B and C, which contain fluoride mixed solvents, are thermally more stable than electrolyte E. It was confirmed that electrolyte B and electrolyte C are stable in the temperature range of 180℃ to 300℃. The peak of the heat flow (calorific value) in the range is 200mW / g or less, preferably 100mW / g It was found that the following was satisfied. There was no significant difference in the thermal stability between electrolyte B and electrolyte C. It was found that there was no significant ...

Claims

1. a positive electrode, a negative electrode, a separator located between the positive electrode and the negative electrode, and an electrolyte; the positive electrode has a positive electrode active material including lithium cobalt oxide, the positive electrode active material contains magnesium, aluminum, nickel, and fluorine, In the positive electrode active material, a surface layer portion has a rock salt type crystal structure, and an inner portion has a layered rock salt type crystal structure, The electrolyte solution includes a fluoride mixed solvent and a lithium salt, In the electrolyte solution, the concentration of the lithium salt is greater than 1 mole per liter of the fluoride mixed solvent; In a DSC measurement of the electrolyte solution, the peak of the heat flow rate of the exothermic reaction in the range of 180°C to 300°C is 200 mW / g or less. Secondary battery.

2. a positive electrode, a negative electrode, a separator located between the positive electrode and the negative electrode, and an electrolyte; the positive electrode has a positive electrode active material including lithium cobalt oxide, the positive electrode active material contains magnesium, aluminum, nickel, and fluorine, In the positive electrode active material, a surface layer portion has a rock salt type crystal structure, and an inner portion has a layered rock salt type crystal structure, The electrolyte solution includes a fluoride mixed solvent and a lithium salt, In the electrolyte solution, the concentration of the lithium salt is greater than 1 mole per liter of the fluoride mixed solvent; In a DSC measurement of the electrolyte solution, the peak of the heat flow rate of an exothermic reaction in the range of 180°C or higher and 300°C or lower is 200 mW / g or lower; the separator has an imide compound in a region that comes into contact with the electrolyte solution; Secondary battery.

3. a positive electrode, a negative electrode, a separator located between the positive electrode and the negative electrode, and an electrolyte; the positive electrode has a positive electrode active material containing lithium cobalt oxide and a conductive material, the positive electrode active material contains magnesium, aluminum, nickel, and fluorine, In the positive electrode active material, a surface layer portion has a rock salt type crystal structure, and an inner portion has a layered rock salt type crystal structure, the conductive material covers a part of the surface of the positive electrode active material, the conductive material includes a graphene compound, The electrolyte solution includes a fluoride mixed solvent and a lithium salt, In the electrolyte solution, the concentration of the lithium salt is greater than 1 mole per liter of the fluoride mixed solvent; In a DSC measurement of the electrolyte solution, the peak of the heat flow rate of an exothermic reaction in the range of 180°C or higher and 300°C or lower is 200 mW / g or lower; the separator has an imide compound in a region that comes into contact with the electrolyte solution; Secondary battery.

4. a positive electrode, a negative electrode, a separator located between the positive electrode and the negative electrode, and an electrolyte; the positive electrode has a positive electrode active material containing lithium cobalt oxide and a conductive material, the positive electrode active material contains magnesium, aluminum, nickel, and fluorine, In the positive electrode active material, a surface layer portion has a rock salt type crystal structure, and an inner portion has a layered rock salt type crystal structure, the conductive material includes a graphene compound, the graphene compound has a region in surface contact with the positive electrode active material, The electrolyte solution includes a fluoride mixed solvent and a lithium salt, In the electrolyte solution, the concentration of the lithium salt is greater than 1 mole per liter of the fluoride mixed solvent; In a DSC measurement of the electrolyte solution, the peak of the heat flow rate of an exothermic reaction in the range of 180°C or higher and 300°C or lower is 200 mW / g or lower; the separator has an imide compound in a region that comes into contact with the electrolyte solution; Secondary battery.

5. a positive electrode, a negative electrode, a separator located between the positive electrode and the negative electrode, and an electrolyte; the positive electrode has a positive electrode active material containing lithium cobalt oxide and a conductive material, the positive electrode active material contains magnesium, aluminum, nickel, and fluorine, In the positive electrode active material, a surface layer portion has a rock salt type crystal structure, and an inner portion has a layered rock salt type crystal structure, the conductive material covers a part of the surface of the positive electrode active material, the conductive material includes a graphene compound, the negative electrode has a negative electrode active material containing silicon or silicon oxide, The electrolyte solution includes a fluoride mixed solvent and a lithium salt, In the electrolyte solution, the concentration of the lithium salt is greater than 1 mole per liter of the fluoride mixed solvent; In a DSC measurement of the electrolyte solution, the peak of the heat flow rate of an exothermic reaction in the range of 180°C or higher and 300°C or lower is 200 mW / g or lower; the separator has an imide compound in a region that comes into contact with the electrolyte solution; Secondary battery.

6. a positive electrode, a negative electrode, a separator located between the positive electrode and the negative electrode, and an electrolyte; the positive electrode has a positive electrode active material including lithium cobalt oxide and a first conductive material, the positive electrode active material contains magnesium, aluminum, nickel, and fluorine, In the positive electrode active material, a surface layer portion has a rock salt type crystal structure, and an inner portion has a layered rock salt type crystal structure, the first conductive material covers a portion of the surface of the positive electrode active material, the first conductive material includes a graphene compound; the negative electrode has a negative electrode active material containing silicon or silicon oxide and a second conductive material, the second conductive material covers a portion of the surface of the negative electrode active material, the second conductive material includes a graphene compound; The electrolyte solution includes a fluoride mixed solvent and a lithium salt, In the electrolyte solution, the concentration of the lithium salt is greater than 1 mole per liter of the fluoride mixed solvent; In a DSC measurement of the electrolyte solution, the peak of the heat flow rate of an exothermic reaction in the range of 180°C or higher and 300°C or lower is 200 mW / g or lower; the separator has an imide compound in a region that comes into contact with the electrolyte solution; Secondary battery.

7. In any one of claims 1 to 6, The lithium salt is LiPF ６ , LiClO ４ , LiAsF ６ , LiBF ４ , LiAlCl ４ , LiSCN, LiBr, LiI, Li ２ SO ４ , Li ２ B １０ Cl １０ , Li ２ B １２ Cl １２ , LiCF ３ SO ３ , LiC ４ F ９ SO ３ , LiC(CF ３ SO ２ ) ３ , LiC(C ２ F ５ SO ２ ) ３ , LiN(CF ３ SO ２ ) ２ , LiN(C ４ F ９ SO ２ ) (CF ３ SO ２ ), LiN(C ２ F ５ SO ２ ) ２ One or more selected from Secondary battery.

8. In any one of claims 1 to 6, The secondary battery, wherein the fluoride mixed solvent has FEC.

9. In any one of claims 1 to 6, The secondary battery, wherein the fluoride mixed solvent has MTFP.

10. In any one of claims 2 to 6, The secondary battery, wherein the imide compound is a polyimide.

Images