Lithium ion secondary battery

Abstract

To provide a positive electrode active material for a lithium ion secondary battery with high capacity and an excellent charging and discharging cycle characteristic.SOLUTION: A positive electrode whose crystal structure changes less in a charged state and a discharged state is provided. For example, the positive electrode active material having a crystal structure of a layered rock salt type in the discharged state and having a crystal structure of a pseudo-spinel type in a charged state with high voltage of about 4.6 V changes less in crystal structure and volume before and after the charging and discharging compared with the existing positive electrode active material. In order to manufacture the positive electrode active material with the pseudo-spinel type crystal structure in the charged state, it is preferable to synthesize lithium cobaltate, add and mix lithium fluoride and magnesium fluoride, and heat the mixture at proper temperature for proper time.SELECTED DRAWING: Figure 1

Description

Technical Field

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

[0002] Note that in this specification, the power storage device refers to all elements and devices having a power storage function. For example, it includes storage batteries (also referred to as secondary batteries) such as lithium ion secondary batteries, lithium ion capacitors, and electric double layer capacitors.

[0003] Also, in this specification, the electronic device refers to all devices having a power storage device. An electro-optical device having a power storage device, an information terminal device having a power storage device, etc. are all electronic devices.

Background Art

[0004] In recent years, various power storage devices such as lithium ion secondary batteries, lithium ion capacitors, and air batteries have been actively developed. In particular, lithium ion secondary batteries with high output and high energy density have rapidly expanded their demand along with the development of the semiconductor industry, for portable information terminals such as mobile phones, smartphones, tablets, or notebook computers, portable music players, digital cameras, medical devices, next-generation clean energy automobiles (hybrid electric vehicles (HEV), electric vehicles (EV), plug-in hybrid vehicles (PHEV), etc.), and are rechargeable. It has become indispensable in the modern information society as an energy source.

[0005] As characteristics required for lithium-ion secondary batteries, there are further increases in energy density, improvement of cycle characteristics, safety in various operating environments, and improvement of long-term reliability, etc.

[0006] Therefore, improvements in the cathode active material have been studied to improve the cycle characteristics and increase the capacity of lithium-ion secondary batteries (Patent Document 1 and Patent Document 2). In addition, research on the crystal structure of the cathode active material has also been conducted (Non-Patent Documents 1 to 3).

[0007] X-ray diffraction (XRD) is one of the methods used for analyzing the crystal structure of the cathode active material. By using the ICSD (Inorganic Crystal Stru cture Database) introduced in Non-Patent Document 5, the XRD data can be analyzed. cture Database) introduced in Non-Patent Document 5, the XRD data can be analyzed. can be performed.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0009]

Non-Patent Document 1

[0010] One aspect of the present invention is to provide a cathode active material for a lithium-ion secondary battery that has a high capacity and excellent charge-discharge cycle characteristics, and a method for producing the same as one of the problems. Or, one of the problems is to provide a method for producing a cathode active material with good productivity. Or, one aspect of the present invention is to provide a cathode active material that suppresses a decrease in capacity during charge-discharge cycles when used in a lithium-ion secondary battery. Or, one aspect of the present invention is to provide a high-capacity secondary battery as one of the problems. Or, one aspect of the present invention is to provide a secondary battery with excellent charge-discharge characteristics. Or, one aspect of the present invention is to provide a cathode active material in which elution of transition metals such as cobalt is suppressed even when a state of being charged at a high voltage is maintained for a long time. Or, one aspect of the present invention is to provide a secondary battery with high safety or reliability as one of the problems. Or, one aspect of the present invention is to provide a novel substance, active material particles, a power storage device, or a method for producing them as one of the problems. It should be noted that the description of these problems does not prevent the existence of other problems. It should be noted that one aspect of the present invention does not need to solve all of these problems. It is possible to extract other problems from the description of the specification, drawings, and claims.

Means for Solving the Problems

[0011] Or, one aspect of the present invention is to provide a novel substance, active material particles, a power storage device, or a method for producing them as one of the problems. It should be noted that the description of these problems does not prevent the existence of other problems. It should be noted that one aspect of the present invention does not need to solve all of these problems. It is possible to extract other problems from the description of the specification, drawings, and claims.

[0012] It should be noted that the description of these problems does not prevent the existence of other problems. It should be noted that one aspect of the present invention does not need to solve all of these problems. It is possible to extract other problems from the description of the specification, drawings, and claims. Or, one aspect of the present invention does not need to solve all of these problems. It is possible to extract other problems from the description of the specification, drawings, and claims. From the description of the specification, drawings, and claims, it is possible to extract other problems.

Means for Solving the Problems

[0013] To achieve the above problems, the cathode active material according to one aspect of the present invention is characterized in that there is little change in the crystal structure in the charged state and the discharged state. For example, in the discharged state, a layered rock salt type structure and in the charged state, the crystal structure change is small. For example, in the discharged state, a layered rock salt type structure It has a crystal structure and has a pseudo-spinel type crystal structure when charged at a high voltage of about 4.6 V. The positive electrode active material having this has less change in crystal structure and volume before and after charge and discharge than known positive electrode active materials. It is less.

[0014] In order to produce a positive electrode active material having a pseudo-spinel type crystal structure in the charged state, after synthesizing particles of a composite oxide having lithium, a transition metal, and oxygen, a halogen source such as a fluorine source or a chlorine source and a magnesium source are added and mixed, and then heated at an appropriate temperature and time. It is preferable. Halogen and magnesium are impurities for the layered rock salt type crystal structure. Therefore, first, by synthesizing composite oxide particles with less impurities, particles having a layered rock salt type crystal structure with few defects can be obtained. By adding a halogen source such as a fluorine source or a chlorine source and a magnesium source to the material and heating at an appropriate temperature and time, a positive electrode active material having few defects and having a pseudo-spinel type crystal structure in the charged state can be produced. It is preferable.

[0015] Halogen and magnesium are impurities for the layered rock salt type crystal structure. Therefore, first, by synthesizing composite oxide particles with less impurities, particles having a layered rock salt type crystal structure with few defects can be obtained. By adding a halogen source such as a fluorine source or a chlorine source and a magnesium source to the material and heating at an appropriate temperature and time, a positive electrode active material having few defects and having a pseudo-spinel type crystal structure in the charged state can be produced. First, by synthesizing composite oxide particles with less impurities, particles having a layered rock salt type crystal structure with few defects can be obtained. By adding a halogen source such as a fluorine source or a chlorine source and a magnesium source to the material and heating at an appropriate temperature and time, a positive electrode active material having few defects and having a pseudo-spinel type crystal structure in the charged state can be produced. By adding a halogen source such as a fluorine source or a chlorine source and a magnesium source to the material and heating at an appropriate temperature and time, a positive electrode active material having few defects and having a pseudo-spinel type crystal structure in the charged state can be produced. A method for producing a positive electrode active material having a pseudo-spinel type crystal structure in the charged state can be produced.

[0016] One aspect of the present invention is a method for producing a positive electrode active material, which includes a step of mixing a lithium source, a fluorine source, and a magnesium source to produce a first mixture, a step of mixing a composite oxide having lithium, a transition metal, and oxygen with the first mixture to produce a second mixture, and a step of heating the second mixture. In the above, when the composite oxide having lithium, a transition metal, and oxygen is analyzed by glow discharge mass spectrometry, the concentration of elements other than lithium, transition metal, and oxygen is preferably 5000 ppm wt or less. A method for producing a positive electrode active material having a pseudo-spinel type crystal structure in the charged state can be produced. It is a method for producing a positive electrode active material having the above.

[0017] Also, in the above, when the composite oxide having lithium, a transition metal, and oxygen is analyzed by glow discharge mass spectrometry, the concentration of elements other than lithium, transition metal, and oxygen is preferably 5000 ppm wt or less. It is preferably 5000 ppm wt or less. It is preferably 5000 ppm wt or less.

[0018] Also, in the above, the first mixture preferably has lithium fluoride LiF as a lithium source and a fluorine source. iF.

[0019] Also, in the above, it has magnesium fluoride MgF as a fluorine source and a magnesium source. 2 as and the molar ratio of lithium fluoride LiF to magnesium fluoride MgF 2 is preferably LiF:MgF 2 = x:1 (0.1 ≤ x ≤ 0.5).

[0020] Also, in the above, the transition metal TM contained in the composite oxide having lithium, a transition metal, and oxygen in the second mixture, and magnesium Mg contained in the first mixture Mix1 The atomic ratio of is preferably TM:Mg M ix1 = 1:y (0.001 ≤ y ≤ 0.01). Mix1 is preferable.

[0021] Also, in the above, the heating temperature in the step of heating the second mixture is preferably 600°C or higher and 95 0°C or lower.

[0022] Also, in the above, the heating time in the step of heating the second mixture is preferably 2 hours or longer. More preferably, it is 60 hours or longer.

[0023] Another aspect of the present invention is a secondary battery having a positive electrode having a positive electrode active material produced by the above method and a negative electrode.

Advantages of the Invention

[0024] According to one aspect of the present invention, a lithium-ion secondary battery having a high capacity and excellent charge-discharge cycle characteristics​ It is possible to provide a positive electrode active material and a method for producing the same. Further, a method for producing a positive electrode active material with good productivity can be provided. Further, a positive electrode active material that suppresses a decrease in capacity during charge and discharge cycles can be provided by using it in a lithium-ion secondary battery. Further, a secondary battery with a high capacity can be provided. Further, a secondary battery with excellent charge and discharge characteristics can be provided. Further, even when a state of being charged at a high voltage is maintained for a long time, a positive electrode active material in which elution of transition metals such as cobalt is suppressed can be provided. Further, a secondary battery with high safety or reliability can be provided. Further, a novel substance, active material particles, a power storage device, or a method for producing them can be provided.

Brief Description of the Drawings

[0025]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Figure 17

Figure 18

Figure 19

Figure 20

Figure 21

Figure 22

Figure 23

Figure 24

Figure 25

Figure 26

Figure 27

Figure 28

Figure 29

Figure 30

Figure 31

Figure 32

Figure 33

Figure 34

Figure 35

Figure 36

Figure 37

Figure 38

Figure 39

Figure 40

Figure 41

Figure 42

Figure 43

Figure 44

Figure 45

Figure 46

Figure 47

Figure 48

Figure 49

Figure 50

Figure 51

Figure 52

Figure 53

Figure 54

Figure 55

Figure 56

Figure 57

Figure 58

Mode for Carrying Out the Invention

[0026] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and those skilled in the art can easily understand that its form and details can be variously changed. Also, the present invention is not construed as being limited to the description of the embodiments shown below.

[0027] In addition, in this specification and the like, crystal planes and directions are indicated by Miller indices. In the description of crystal planes and directions, in crystallography, a bar is attached to the number, but in this specification and the like, due to the constraints of the application notation, instead of attaching a bar to the number, a -(minus sign) may be attached in front of the number to express it. Also, individual orientations indicating directions within a crystal are represented by [ ], collective orientations indicating all equivalent directions are represented by < >, individual planes indicating crystal planes are represented by ( ), and collective planes having equivalent symmetries are represented by {}, respectively.

[0028] In this specification and the like, segregation refers to a phenomenon in which, in a solid composed of a plurality of elements (for example, A, B, C), a certain element (for example, B) is spatially non-uniformly distributed.

[0029] In this specification and the like, the surface layer portion of particles such as active materials refers to a region up to about 10 nm from the surface. A surface generated by cracks may also be referred to as the surface. Also, a region deeper than the surface layer portion is ​ Internally.

[0030] In this specification and the like, the layered rock salt-type crystal structure of the composite oxide containing lithium and transition metal has a rock salt-type ion arrangement in which cations and anions are alternately arranged, and the transition metal and lithium are regularly arranged to form a two-dimensional plane, so that two-dimensional diffusion of lithium is possible. This refers to a crystal structure. Note that there may be defects such as cation or anion deficiencies. Also, strictly speaking, the layered rock salt-type crystal structure may be a structure in which the lattice of the rock salt-type crystal is distorted.

[0031] In this specification and the like, the rock salt-type crystal structure refers to a structure in which cations and anions are alternately arranged. Note that there may be cation or anion deficiencies.

[0032] In this specification and the like, the pseudo-spinel-type crystal structure of the composite oxide containing lithium and transition metal has a space group of R-3m and is not a spinel-type crystal structure. However, ions such as cobalt and magnesium occupy the oxygen six-coordination positions, and the cation arrangement has a symmetry similar to that of the spinel type. This refers to a crystal structure. Note that in the pseudo-spinel-type crystal structure, light elements such as lithium may occupy the oxygen four-coordination positions. In this case, the ion arrangement also has a symmetry similar to that of the spinel type.

[0033] The pseudo-spinel-type crystal structure can also be said to be a crystal structure similar to the CdCl 2 type, although it has Li randomly between layers. This crystal structure similar to the CdCl 2 type is obtained when lithium nickelate is charged to a charge depth of 0.94 (Li 0.06 NiO 2) crystal structure, but is similar to that of pure lithium cobalt oxide, or a layered rock rich in cobalt. It is known that salt-type positive electrode active materials do not usually have this crystal structure.

[0034] Layered rock salt crystals and the anions of rock salt crystals have a cubic close-packed structure (face-centered cubic lattice structure) It is assumed that the anions of pseudospinel crystals also have a cubic close-packed structure. When the anions are in contact with each other, there exists a crystal plane where the cubic close-packed structure formed by the anions is oriented in the same direction. However, the space group of the layered rock salt crystals and pseudospinel crystals is R-3m, and the space group of the rock salt crystals is R-3m. Crystal space groups Fm-3m (the common rock salt crystal space group) and Fd-3m (the simplest Since the space group of the crystal is different from that of the rock salt type crystals, the mirror of the crystal plane that satisfies the above conditions The -index is different between layered rock salt crystals and pseudospinel crystals and between rock salt crystals. In layered rock salt crystals, pseudospinel crystals, and rock salt crystals, the anions form When the orientation of the cubic close-packed structure is aligned, the crystal orientation is roughly the same. be.

[0035] The crystal orientation of the two regions roughly coincides, as can be seen from TEM (transmission electron microscope) and STEM images. (Scanning Transmission Electron Microscope) Image, HAADF-STEM (High Angle Scattering Annular Dark Field Scanning Transmission Electron Microscope) This can be judged from images such as ABF-STEM (annular bright-field scanning transmission electron microscope) images. X-ray diffraction (XRD), electron diffraction, neutron diffraction, etc. can also be used for judgment. In TEM images, the arrangement of cations and anions is observed as repeated bright and dark lines. When the orientation of the cubic close-packed structure in the layered rock salt crystal and the rock salt crystal is aligned, the intercrystalline The angle between the repeated bright and dark lines is 5 degrees or less, and preferably 2.5 degrees or less. The particles can be observed. In the case of a TEM image or the like, light elements such as oxygen and fluorine may not be clearly observable, but in such a case, the alignment can be determined by the arrangement of metal elements. .

[0036] In this specification and the like, the theoretical capacity of the positive electrode active material refers to the amount of electricity when all the insertable and removable lithium in the positive electrode active material has been removed. For example, the theoretical capacity of LiCoO is 274 2 mAh / g, the theoretical capacity of LiNiO is 274 mAh / g, and the theoretical capacity of LiMn 2 O 2 is 4 148 mAh / g.

[0037] In this specification and the like, the state of charge when all the insertable and removable lithium has been inserted is defined as 0, and the state of charge when all the insertable and removable lithium in the positive electrode active material has been removed is defined as 1. .

[0038] In this specification and the like, charging refers to moving lithium ions from the positive electrode to the negative electrode in the battery and moving electrons from the negative electrode to the positive electrode in the external circuit. For the positive electrode active material, removing lithium ions is defined as charging. Also, a positive electrode active material with a state of charge of 0.74 or more and 0 .9 or less, more specifically, a positive electrode active material with a state of charge of 0.8 or more and 0.83 or less, is defined as a positive electrode active material charged at a high voltage. Therefore, for example, if LiCoO is charged at 219. 2 mAh / g, it is a positive electrode active material charged at a high voltage. Also, in the case of LiCoO , at 25°C, when the charging voltage is 4.525 V or more and 4.65 V or less (versus the counter electrode lithium 2 . If it is charged at 2 mAh / g, it is a positive electrode active material charged at a high voltage. Also, in the case of LiCoO 2 , at 25°C, when the charging voltage is 4.525 V or more and 4.65 V or less (versus the counter electrode lithium In the case of a constant current charge and then a constant voltage charge until the current value becomes about 0.01C or 1 / 5 to 1 / 100 of the current value during the constant current charge, the positive electrode active material is also considered to be a positive electrode active material charged at a high voltage. Similarly, discharging means moving lithium ions from the negative electrode to the positive electrode in the battery and moving electrons from the positive electrode to the negative electrode in the external circuit. For the positive electrode active material, inserting lithium ions is called discharging. Also, a positive electrode active material with a state of charge (SOC) of 0.06 or less, or a positive electrode active material that has discharged 90% or more of its charge capacity from a state charged at a high voltage, is considered to be a positively electrode active material that has been fully discharged. For example, in the case of LiCoO if the charge capacity is 21

[0039] 9.2 mAh / g, it is in a state charged at a high voltage. After discharging 197.3 mAh / g or more, which is 90% of the charge capacity, the positive electrode active material is considered to be a fully discharged positive electrode active material. Also, in the case of LiCoO in a 25°C environment, when the battery voltage becomes 3V or less (in the case of a counter electrode lithium ion), the positive electrode active material after constant current discharge is also considered to be a fully discharged positive electrode active material. In addition, in this specification and the like, non-equilibrium phase change refers to a phenomenon that causes a non-linear change in physical quantities. For example, before and after the peak in the d Q / dV curve obtained by differentiating the capacitance (Q) with respect to the voltage (V) (dQ / dV), a non-equilibrium phase change occurs, and it is considered that the crystal structure changes significantly. 2 2

[0040] Also, in this specification and the like, non-equilibrium phase change refers to a phenomenon that causes a non-linear change in physical quantities. For example, non-equilibrium phase changes occur before and after the peak in the d Q / dV curve obtained by differentiating the capacitance (Q) with respect to the voltage (V) (dQ / dV), and it is considered that the crystal structure changes significantly.

[0041] (Embodiment 1) [Method for producing positive electrode active material] ​​​​​​​​First, with reference to FIG. 1, an example of a method for producing a positive electrode active material 100, which is one aspect of the present invention, will be described. Another example of a specific production method is shown in FIG. 2.

[0042] <Step S11> As shown in Step S11 of FIG. 1, first, as materials for the first mixture, a halogen source such as a fluorine source or a chlorine source and a magnesium source are prepared. It is also preferable to prepare a lithium source.

[0043] As the fluorine source, for example, lithium fluoride, magnesium fluoride, etc. can be used. Among them, lithium fluoride has a relatively low melting point of 848 °C and is easy to melt in the annealing process described later, so it is preferable. As the chlorine source, for example, lithium chloride, magnesium chloride, etc. can be used. As the magnesium source, for example, magnesium fluoride, magnesium oxide, magnesium hydroxide, magnesium carbonate, etc. can be used. As the lithium source, for example, lithium fluoride, lithium carbonate can be used. That is, lithium fluoride can be used as both a lithium source and a fluorine source. Also, magnesium fluoride can be used as both a fluorine source and a magnesium source.

[0044] In the present embodiment, lithium fluoride LiF is prepared as the fluorine source and the lithium source, and magnesium fluoride MgF is prepared as the fluorine source and the magnesium source ( 2 Step S11 of FIG. 2). Lithium fluoride LiF and magnesium fluoride MgF 2 2 When mixed at about Li ​​​​​​​​​​(Non-Patent Document 4). On the other hand, when the amount of lithium fluoride increases, there is a concern that lithium becomes excessively excessive and the cycle characteristics deteriorate. Therefore, the molar ratio of lithium fluoride LiF to magnesium fluoride is preferably LiF:MgF MgF 2 = x:1 (0 ≤ x ≤ 1.9), more preferably LiF:MgF 2 = x:1 (0.1 ≤ x ≤ 0.5), and even more preferably LiF:MgF = x:1 (x is around 0.33). In this specification, etc., "around" means a value greater than 0.9 times and less than 1.1 times that value. 2 = x:1 (0.1 ≤ x ≤ 0.5) is more preferable, and LiF:MgF 2 = x:1 (x = around 0.33) is even more preferable. In this specification, etc., "around" means a value greater than 0.9 times and less than 1.1 times that value. That is, it is a value greater than 0.9 times and less than 1.1 times that value.

[0045] Also, when the following mixing and pulverization steps are performed wet, a solvent is prepared. As the solvent, ketones such as acetone, alcohols such as ethanol and isopropanol, ethers, dioxane sane, acetonitrile, N-methyl-2-pyrrolidone (NMP), etc. can be used. It is more preferable to use an aprotic solvent that hardly reacts with lithium. In this embodiment, acetone is used (see step S11 in FIG. 2). can be used. It is more preferable to use an aprotic solvent that hardly reacts with lithium. In this embodiment, acetone is used (see step S11 in FIG. 2).

[0046] <Step S12> Next, the materials of the above first mixture are mixed and pulverized (step S1 2 in FIGS. 1 and 2). The mixing can be performed dry or wet, but wet is preferable because it can be pulverized smaller. For mixing, for example, a ball mill, a bead mill, etc. can be used. When using a ball mill, it is preferable to use zirconia balls as the media, for example. For example, when using a ball mill, it is preferable to use zirconia balls as the media. It is preferable to sufficiently perform this mixing and pulverization step to pulverize the first mixture into fine powder. For example, when using a ball mill, it is preferable to use zirconia balls as the media. It is preferable to sufficiently perform this mixing and pulverization step to pulverize the first mixture into fine powder.

[0047] <Step S13, Step S14> Recover the materials mixed and pulverized above (step S13 in FIGS. 1 and 2), and obtain a first mixture (step S14 in FIGS. 1 and 2).

[0048] The first mixture preferably has an average particle diameter (also referred to as D50: median diameter) of 600 nm or more and 20 μm or less, more preferably 1 μm or more and 10 μm or less. With the first mixture micronized in this way, when it is mixed with a composite oxide having lithium, a transition metal, and oxygen in a later step, the first mixture is likely to adhere uniformly to the surface of the composite oxide particles. When the first mixture adheres uniformly to the surface of the composite oxide particles, it is preferable because halogen and magnesium can be distributed uniformly in the surface layer portion of the composite oxide particles after heating. If there is a region in the surface layer portion that does not contain halogen and magnesium, there is a possibility that it is difficult to form a pseudo-spinel type crystal structure described later in the charged state.

[0049] <Step S21> Next, as shown in step S21 of FIG. 1, prepare a lithium source and a transition metal source as materials for a composite oxide having lithium, a transition metal, and oxygen.

[0050] As the lithium source, for example, lithium carbonate, lithium fluoride, etc. can be used.

[0051] As the transition metal, at least one of cobalt, manganese, and nickel can be used . Since the composite oxide having lithium, a transition metal, and oxygen preferably has a layered rock salt type crystal structure, it is preferable that the mixing ratio of cobalt, manganese, and nickel that can take the layered rock salt type. Also, within the range where the layered rock salt type crystal structure can be taken, to these transition metals an Lumminium may be added.

[0052] As the transition metal source, oxides, hydroxides, etc. of the above transition metals can be used. Cobalt As the cobalt source, for example, cobalt oxide, cobalt hydroxide, etc. can be used. Manganese As the source, manganese oxide, manganese hydroxide, etc. can be used. As the nickel source nickel oxide, nickel hydroxide, etc. can be used. As the aluminum source, aluminum oxide, aluminum hydroxide, etc. can be used.

[0053] <Step S22> Next, the above lithium source and transition metal source are mixed (Step S22 in FIG. 1). The mixing can be carried out dry or wet. For mixing, for example, a ball mill, a bead mill, etc. can be used When using a ball mill, it is preferable to use, for example, zirconia balls as the media for example.

[0054] <Step S23> Next, the material mixed above is heated. This step may be referred to as firing or the first heating for the purpose of distinction from the subsequent heating step. The heating is preferably carried out at 800 °C or higher and less than 1100 °C more preferably at 900 °C or higher and 1000 °C or lower, and even more preferably about 950 °C If the temperature is too low, there is a risk that the decomposition and melting of the starting materials will be insufficient. On the other hand, if the temperature is too high, defects may occur due to excessive reduction of the transition metal, evaporation of lithium, etc. For example, defects such as cobalt becoming divalent may occur.

[0055] The heating time is preferably 2 hours or more and 20 hours or less. The firing is carried out in dry air or the like where water is This can be done in an atmosphere with low dew point (for example, below -50°C, more preferably below -100°C). For example, heating is performed at 1000°C for 10 hours, the temperature is increased by 200°C / h, and the mixture is heated in a dry atmosphere. The flow rate of the ambient air is preferably 10 L / min. The heated material is then cooled to room temperature. For example, the time required for cooling from a specified temperature to room temperature can be set to 10 hours or more and 50 hours or less. It is preferable to set the above.

[0056] However, cooling to room temperature in step S23 is not essential. 4. There is no problem in carrying out the steps S25 and S31 to S34. If desired, cooling may be to a temperature above room temperature.

[0057] <Step S24, Step S25> The calcined material is collected (step S24 in FIG. 1), and lithium, transition metals, and oxygen are separated. A composite oxide having the following structure is obtained (Step S25 in FIG. 1). Specifically, lithium cobalt oxide , lithium manganese oxide, lithium nickel oxide, cobalt oxide in which some of the cobalt is replaced by manganese Lithium baltic oxide, or lithium nickel-manganese-cobalt oxide, is obtained.

[0058] In step S25, a catalyst having lithium, a transition metal, and oxygen that has been synthesized in advance is prepared. In this case, steps S21 to S22 may be used. 4 can be omitted.

[0059] When a composite oxide having lithium, a transition metal, and oxygen that has been synthesized in advance is used, It is preferable to use a material with few impurities. The composite oxide containing lithium and oxygen, and the positive electrode active material mainly composed of lithium, cobalt, and nickel Using nickel, manganese, aluminum and oxygen, with elements other than the above main components being regarded as impurities . For example, when analyzed by glow discharge mass spectrometry, the total impurity concentration is preferably 10,000 ppm wt or less, more preferably 5000 ppm wt or less. In particular, the total impurity concentration of transition metals such as titanium and arsenic is preferably 3000 ppm wt or less, more preferably 1500 ppm wt or less.

[0060] For example, as lithium cobaltate synthesized in advance, lithium cobaltate particles (trade name: Celsiode C-10N) manufactured by Nippon Chemical Industry Co., Ltd. can be used. This has an average particle size (D50) of about 12 μm, and in impurity analysis by glow discharge mass spectrometry (GD-MS), the magnesium concentration and fluorine concentration are 50 ppm wt or less, and the calcium concentration, aluminum concentration and silicon concentration are 100 ppm wt or less, the nickel concentration is 150 ppm wt or less, the sulfur concentration is 500 ppm wt or less, the arsenic concentration is 110 0 ppm wt or less, and the concentration of elements other than lithium, cobalt and oxygen is 150 p pm wt or less. It is lithium cobaltate.

[0061] Alternatively, lithium cobaltate particles (trade name: Celsiode C-5 H) manufactured by Nippon Chemical Industry Co., Ltd. can also be used. This has an average particle size (D50) of about 6.5 μm, and in impurity analysis by GD- MS, the concentration of elements other than lithium, cobalt and oxygen is about the same as or lower than that of C-1 0N. It is lithium cobaltate.

[0062] In this embodiment, cobalt is used as the transition metal, and lithium cobaltate synthesized in advance​​​​ Use thium particles (Celsseed C-10N manufactured by Nippon Chemical Industry Co., Ltd.) (Figure 2 reference).

[0063] The composite oxide having lithium, transition metal and oxygen in Step S25 preferably has a layered rock salt-type crystal structure with few defects and strains. Therefore, it is preferably a composite oxide with few impurities. If the composite oxide having lithium, transition metal and oxygen contains a large amount of impurities, it is highly likely to have a crystal structure with many defects or strains.

[0064] <Step S31> Next, mix the first mixture with the composite oxide having lithium, transition metal and oxygen (Step S31 in Figures 1 and 2). The atomic ratio of the transition metal TM in the composite oxide having lithium, transition metal and oxygen to magnesium Mg in the first mixture Mix1 is preferably TM:Mg Mix1 original = 1:y (0.0005 ≤ y ≤ 0.03), more preferably TM:Mg Mix1 = 1:y (0.001 ≤ y ≤ 0.01), and even more preferably about TM:Mg Mix1 = 1:0.005. Mix1

[0065] The mixing in Step S31 is preferably carried out under milder conditions than the mixing in Step S12 so as not to break the particles of the composite oxide. For example, it is preferable to use conditions with a lower rotation speed or a shorter time than the mixing in Step S12. Also, it can be said that the dry condition is milder than the wet condition. For mixing, for example, a ball mill, a bead mill, etc. can be used. When using a ball mill, for example, zirconia balls can be used as the media. Preferred.

[0066] <Steps S32 and S33> Recover the mixed material described above (Step S32 in FIGS. 1 and 2) to obtain a second mixture. (Step S33 in FIGS. 1 and 2).

[0067] In this embodiment, a method of adding a mixture of lithium fluoride and magnesium fluoride to cobalt lithium oxide with few impurities is described. However, one aspect of the present invention is not limited to this. Instead of the second mixture in Step S33, a material obtained by adding a magnesium source and a fluorine source to a starting material of cobalt lithium oxide and firing may be used. In this case, since it is not necessary to separate the steps of Steps S11 to S14 and the steps of Steps S21 to S25, it is simple and highly productive. Although a method of adding a mixture of lithium fluoride and magnesium fluoride to cobalt lithium oxide with few impurities is described in this embodiment, one aspect of the present invention is not limited to this. Instead of the second mixture in Step S33, a material obtained by adding a magnesium source and a fluorine source to a starting material of cobalt lithium oxide and firing may be used. In this case, since it is not necessary to separate the steps of Steps S11 to S14 and the steps of Steps S21 to S25, it is simple and highly productive. Instead of the second mixture in Step S33, a material obtained by adding a magnesium source and a fluorine source to a starting material of cobalt lithium oxide and firing may be used. In this case, since it is not necessary to separate the steps of Steps S11 to S14 and the steps of Steps S21 to S25, it is simple and highly productive. Steps S11 to S14 and Steps S21 to S25 Since it is not necessary to separate the steps of Steps S11 to S14 and the steps of Steps S21 to S25, it is simple and highly productive.

[0068] Alternatively, cobalt lithium oxide to which magnesium and fluorine have been added in advance may be used. If cobalt lithium oxide to which magnesium and fluorine have been added is used, the steps up to Step S32 can be omitted, which is more convenient. If cobalt lithium oxide to which magnesium and fluorine have been added is used, the steps up to Step S32 can be omitted, which is more convenient.

[0069] Furthermore, a magnesium source and a fluorine source may be further added to cobalt lithium oxide to which magnesium and fluorine have been added in advance. Furthermore, a magnesium source and a fluorine source may be further added to cobalt lithium oxide to which magnesium and fluorine have been added in advance.

[0070] <Step S34> Next, heat the second mixture. This step may be referred to as annealing or second heating for the purpose of distinguishing it from the previous heating step. This step may be referred to as annealing or second heating for the purpose of distinguishing it from the previous heating step.

[0071] Annealing is preferably performed at an appropriate temperature and time. The appropriate temperature and time are The size and composition, etc. of the composite oxide particles containing lithium, transition metal, and oxygen in step S25 vary depending on conditions. When the particles are small, a lower temperature or a shorter time may be more preferable than when they are large.

[0072] For example, when the average particle diameter (D50) of the particles in step S25 is about 12 μm, the annealing temperature is preferably, for example, 600°C or higher and 950°C or lower. The annealing time is preferably, for example, 3 hours or longer, more preferably 10 hours or longer, and even more preferably 60 hours or longer.

[0073] On the other hand, when the average particle diameter (D50) of the particles in step S25 is about 5 μm, the annealing temperature is preferably, for example, 600°C or higher and 950°C or lower. The annealing time is preferably, for example, 1 hour or longer and 10 hours or shorter, and more preferably about 2 hours.

[0074] The temperature drop time after annealing is preferably, for example, 10 hours or longer and 50 hours or shorter.

[0075] When annealing the second mixture, first, the material with a low melting point in the first mixture (for example, lithium fluoride, melting point 848°C) is considered to melt and distribute in the surface layer portion of the composite oxide particles. Next, due to the presence of this melted material, the melting point of other materials drops, and it is presumed that other materials melt. For example, magnesium fluoride (melting point 1263°C) is considered to melt and distribute in the surface layer portion of the composite oxide particles. And the elements contained in the first mixture distributed in the surface layer portion are considered to dissolve in the composite oxide containing lithium, transition metal, and oxygen.

[0076]

[0077] ​​The diffusion of the elements in this first mixture is faster in the surface layer and near the grain boundaries than inside the composite oxide particles. Therefore, magnesium and halogen are present in higher concentrations in the surface layer and near the grain boundaries than inside. As will be described later, when the magnesium concentration in the surface layer and near the grain boundaries is high, changes in the crystal structure can be more effectively suppressed. Therefore, magnesium and halogen are present in higher concentrations in the surface layer and near the grain boundaries than inside. As will be described later, when the magnesium concentration in the surface layer and near the grain boundaries is high, changes in the crystal structure can be more effectively suppressed.

[0078] <Step S35> Recover the material annealed above to obtain the positive electrode active material 100, which is one aspect of the present invention.

[0079] When produced by the methods shown in FIGS. 1 and 2, a positive electrode active material having a pseudo-spinel type crystal structure with few defects when charged at a high voltage can be produced. A positive electrode active material in which the pseudo-spinel type crystal structure is 50% or more when subjected to Rietveld analysis is a positive electrode active material excellent in cycle characteristics and rate characteristics. When subjected to Rietveld analysis, a positive electrode active material in which the pseudo-spinel type crystal structure is 50% or more is a positive electrode active material excellent in cycle characteristics and rate characteristics.

[0080] To produce a positive electrode active material having a pseudo-spinel type crystal structure after high voltage charging, it is effective for the positive electrode active material to contain magnesium and fluorine and to be annealed at an appropriate temperature and time. The magnesium source and the fluorine source may be added to the starting material of the composite oxide. However, when added to the starting material of the composite oxide, if the melting points of the magnesium source and the fluorine source are higher than the firing temperature, the magnesium source and the fluorine source will not melt, and diffusion may be insufficient. Then, there is a high possibility that many defects or strains will occur in the layered rock salt type crystal structure. Therefore, defects or strains may also occur in the pseudo-spinel type crystal structure after high voltage charging. To produce a positive electrode active material having a pseudo-spinel type crystal structure after high voltage charging, it is effective for the positive electrode active material to contain magnesium and fluorine and to be annealed at an appropriate temperature and time. The magnesium source and the fluorine source may be added to the starting material of the composite oxide. However, when added to the starting material of the composite oxide, if the melting points of the magnesium source and the fluorine source are higher than the firing temperature, the magnesium source and the fluorine source will not melt, and diffusion may be insufficient. Then, there is a high possibility that many defects or strains will occur in the layered rock salt type crystal structure. Therefore, defects or strains may also occur in the pseudo-spinel type crystal structure after high voltage charging.

[0081] Therefore, first, a layered rock salt type crystal structure with few impurities and few defects or strains is provided.​​​​​ It is preferable to obtain a composite oxide. Then, in a subsequent step, the composite oxide is mixed with a magnesium source and a fluorine source, and annealed to dissolve magnesium and fluorine in the surface layer portion of the composite oxide. It is preferable. By manufacturing in this way, a positive electrode active material having a pseudo-spinel structure with few defects or strains can be manufactured after high-voltage charging.

[0082] In addition, the positive electrode active material 100 manufactured in the above step may be further coated with another material. Further, heating may be performed.

[0083] For example, the positive electrode active material 100 and a compound having phosphoric acid can be mixed. Also after mixing, heating can be performed. By mixing a compound having phosphoric acid, even when the charged state at a high voltage is maintained for a long time, elution of transition metals such as cobalt is suppressed, and a positive electrode active material 100 can be obtained. Further, by heating after mixing, phosphoric acid can be more uniformly coated.

[0084] Examples of the compound having phosphoric acid include lithium phosphate and ammonium dihydrogen phosphate. Mixing can be performed, for example, by a solid phase method. Heating can be performed, for example, at 800 °C or higher for 2 hours.

[0085] [Structure of positive electrode active material] Next, using FIGS. 3 and 4, the positive electrode active material 100 which is one embodiment of the present invention that can be manufactured by the above method and a conventional positive electrode active material will be described, and the differences between them will be described. In FIGS. 3 and 4, the case where cobalt is used as the transition metal included in the positive electrode active material will be described. Further, the conventional positive electrode active material described in FIG. 4 includes elements other than lithium, cobalt, and oxygen.​​​ Simple cobalt that has not been processed such as being added to a part or coated on a surface layer lithium cobaltate (LiCoO 2 ).

[0086] <Conventional cathode active material> One lithium cobaltate LiCoO of the conventional cathode active material 2 As described in Non-Patent Document 1 and Non-Patent Document 2, etc., the crystal structure changes depending on the depth of charge. The typical crystal structure of lithium cobaltate is shown in Fig. 4.

[0087] As shown in Fig. 4, lithium cobaltate at a charge depth of 0 (discharged state) has a region with a crystal structure of space group R-3 m and there are 3 layers of CoO 2 layers in the unit cell. Therefore, this crystal structure may be called an O3-type crystal structure. Note that the CoO layer refers to a structure in which an octahedral structure with oxygen 6-coordinated to cobalt is continuous in a plane in a state of sharing edges. 2 layer

[0088] When the charge depth is 1, it has a crystal structure of space group P-3m1 and there is 1 layer of CoO 2 layer in the unit cell. Therefore, this crystal structure may be called an O1-type crystal structure.

[0089] Lithium cobaltate when the charge depth is about 0.88 has a crystal structure of space group R-3m This structure can also be said to be a structure in which structures such as P-3m1 (O1) of CoO 2 and structures such as R-3m (O3 ) of LiCoO 2 are alternately laminated. Therefore, this crystal structure may be called an H1-3 type crystal structure. Note that in actuality, the H1-3 type crystal structure ​​​, the number of cobalt atoms per unit cell is twice that of other structures. However, as shown in Fig. 4 At first, in this specification, for the sake of easy comparison with other structures, the c-axis of the H1-3 type crystal structure will be shown in a figure with the unit cell halved.

[0090] When high-voltage charging and discharging are repeated so that the depth of charge reaches about 0.88 or more, lithium cobaltate repeats a change in crystal structure (that is, a non-equilibrium phase change) between the H1-3 type crystal structure and the R-3m(O3) structure in the discharged state. However, the shift of the CoO

[0091] layers is large between these two crystal structures. As shown by the dotted line and the arrow in Fig. 4, in the H1-3 type crystal structure, the CoO 2 layer is greatly shifted from R-3m(O3). Such a dynamic structural change can have an adverse effect on the stability of the crystal structure. 2 layer is greatly shifted.

[0092] Furthermore, the volume difference is also large. When compared per the same number of cobalt atoms, the volume difference between the H1-3 type crystal structure and the O3 type crystal structure in the discharged state is 3.5% or more.

[0093] In addition, the structure in which the CoO 2 layers such as P-3m1(O1) in the H1-3 type crystal structure are continuous is likely to be unstable.

[0094] Therefore, when high-voltage charge and discharge are repeated, the crystal structure of lithium cobaltate will collapse. The collapse of the crystal structure causes deterioration of the cycle characteristics. This is considered to be because when the crystal structure collapses, the sites where lithium can stably exist decrease, and it becomes difficult for lithium to be inserted and extracted.

[0095] <The positive electrode active material of one aspect of the present invention> ≪Inside≫ On the other hand, in the positive electrode active material 100 of one aspect of the present invention, in a fully discharged state and a state charged at a high voltage the change in crystal structure and the volume difference per the same number of transition metal atoms are small when compared in the case.

[0096] The crystal structure of the positive electrode active material 100 before and after charge and discharge is shown in FIG. 3. The positive electrode active material 100 is a composite oxide having lithium, cobalt, and oxygen. In addition to the above, it preferably has magnesium and preferably has halogens such as fluorine and chlorine.

[0097] The crystal structure at a charge depth of 0 (discharged state) in FIG. 3 is the same R-3m (O3) as in FIG. 4. On the other hand the positive electrode active material 100 of one aspect of the present invention has crystals with a structure different from that of FIG. 4 when the charge depth is about 0.88 in a fully charged state This crystal structure of the space group R-3m will be referred to as a pseudo-spinel type crystal structure in this specification and the like In the figure of the pseudo-spinel type crystal structure shown in FIG. 3, the display of lithium is omitted in order to explain the symmetry of cobalt atoms and oxygen atoms, but actually CoO there is about 12 atomic% of lithium with respect to cobalt between the layers In addition, in both the O3 type crystal structure and the pseudo-spinel type crystal structure 2 it is preferable that magnesium is thinly present between the CoO layers, that is, in the lithium sites. Also, it is preferable that halogens such as fluorine are randomly and thinly present in the oxygen sites 2 In the positive electrode active material 100, when charging at a high voltage and many lithium atoms are detached, the change in crystal structure is small, and the volume difference per the same number of transition metal atoms is small. is preferable.

[0098] In the positive electrode active material 100, when charging at a high voltage and many lithium atoms are detached, the change in crystal structure The chemical change is more suppressed than that of the conventional LiCoO 2 For example, as shown by the dotted line in FIG. 3, in these crystal structures, there is almost no shift in the CoO 2 layers.

[0099] In addition, in the positive electrode active material 100, the difference in volume per unit cell between the O3-type crystal structure at a charge depth of 0 and the pseudo-spinel-type crystal structure at a charge depth of 0.88 is 2.5% or less, more specifically 2.2 % or less. Therefore, even when charging and discharging are repeated at a high voltage, the crystal structure is less likely to collapse.

[0100] The pseudo-spinel-type crystal structure can be represented by the coordinates of cobalt and oxygen in the unit cell within the range of Co(0

[0101] ,0,0.5), O(0,0,x), where 0.20 ≦ x ≦ 0.25 . It can be shown within the range of.

[0102] CoO 2 Magnesium, which is randomly and thinly present in the layer between the layers, that is, the lithium sites, has the effect of suppressing the shift of the C oO 2 layers. Therefore, when magnesium is present between the CoO 2 layers, it is likely to form a pseudo-spinel-type crystal structure. Therefore, it is preferable that magnesium is distributed throughout the particles of the positive electrode active material 100. In order to distribute magnesium throughout the particles , it is preferable to perform heat treatment in the manufacturing process of the positive electrode active material 100. However, if the temperature of the heat treatment is too high, cation mixing may occur and magnesium is more likely to enter the cobalt sites. When magnesium is present at the cobalt sites,

[0103] the effect of maintaining the R-3m structure is lost. Furthermore, if the temperature of the heat treatment is too high, it will result in. the effect of maintaining the R-3m structure is lost. Moreover, if the temperature of the heat treatment is too high, There are also concerns about adverse effects such as cobalt being reduced to divalent and lithium evaporating. This is the case.

[0104] Therefore, it is preferable to add a halogen compound such as a fluorine compound to lithium cobaltate before the heat treatment for distributing magnesium throughout the particles. Adding the halogen compound causes a decrease in the melting point of lithium cobaltate. By lowering the melting point, it becomes easier to distribute magnesium throughout the particles at a temperature where cation mixing is less likely to occur. Furthermore, if a fluorine compound is present, it can be expected that the corrosion resistance against hydrofluoric acid generated by the decomposition of the electrolytic solution will be improved. This is the case. This is the case. This is the case. This is the case. This is the case.

[0105] Incidentally, although the case where the positive electrode active material 100 is a composite oxide having lithium, cobalt, and oxygen has been described so far, nickel may also be included in addition to cobalt. In this case, the ratio Ni / (Co + Ni) of the number of nickel atoms (Ni) to the sum of the number of cobalt and nickel atoms (Co + Ni) is preferably less than 0.1, and more preferably 0.075 or less. This is the case. This is the case. This is the case. This is the case.

[0106] If the state of being charged at a high voltage is maintained for a long time, there is a risk that transition metals will elute from the positive electrode active material into the electrolytic solution and the crystal structure will collapse. However, by having nickel in the above ratio, it may be possible to suppress the elution of transition metals from the positive electrode active material 100. This is the case. This is the case.

[0107] By adding nickel, the charge and discharge voltage decreases. Therefore, in the case of the same capacity, since the voltage can be lowered to achieve it, as a result, there is a possibility of suppressing the elution of transition metals and the decomposition of the electrolytic solution. Here, the charge and discharge voltage refers to, for example, the voltage in the range from a state of zero charge depth to a predetermined charge depth. This is the case. This is the case.

[0108] ≪Surface layer≫ Magnesium is preferably distributed throughout the particles of the positive electrode active material 100, but in addition to this, it is more preferable that the magnesium concentration in the particle surface layer is higher than the average of the entire particles. That is, it is more preferable that the magnesium concentration in the particle surface layer measured by XPS or the like is higher than the average magnesium concentration of the entire particles measured by ICP-MS or the like. The particle surface is, so to speak, all crystal defects, and since lithium is removed from the surface during charging, it is a part where the lithium concentration is more likely to be lower than inside. Therefore, it is a part that is likely to become unstable and whose crystal structure is likely to collapse. If the magnesium concentration in the surface layer is high, changes in the crystal structure can be more effectively suppressed. Also, when the magnesium concentration in the surface layer is high, it can be expected that the corrosion resistance against hydrofluoric acid generated by the decomposition of the electrolytic solution will be improved. In addition, for halogens such as fluorine, it is preferable that the concentration in the surface layer of the positive electrode active material 100 is higher than the average of the entire particles. The presence of halogen in the surface layer, which is the region in contact with the electrolytic solution, can effectively improve the corrosion resistance against hydrofluoric acid.

[0109] Thus, it is preferable that the surface layer of the positive electrode active material 100 has a different composition with higher concentrations of magnesium and fluorine than the inside. Also, as the composition, it is preferable to have a crystal structure that is stable at room temperature. Therefore, the surface layer may have a crystal structure different from that of the inside. For example, at least a part of the surface layer of the positive electrode active material 100 may have a rock salt-type crystal structure. Also, when the surface layer and the inside have different crystal structures, it is preferable that the crystal orientations of the surface layer and the inside are substantially the same.

[0110] ​

[0111] However, if the surface layer is made of only MgO or a solid solution of MgO and CoO(II), Therefore, the surface layer must contain at least cobalt, In the discharged state, it must also contain lithium and have a path for lithium insertion and removal. Also, a higher concentration of cobalt than magnesium is preferred.

[0112] ≪Grain boundary≫ The magnesium or halogen contained in the positive electrode active material 100 is present randomly and dilutely inside. However, it is more preferable that a part of them is segregated at the grain boundaries.

[0113] In other words, the magnesium concentration at and near the grain boundaries of the positive electrode active material 100 is also It is preferable that the halogen concentration at the grain boundary and its vicinity is higher than that in other regions. It is preferable that the thickness of the slab is higher than that of other regions.

[0114] Like the particle surface, the grain boundary is also a planar defect. Therefore, it is prone to instability and changes in the crystal structure. Therefore, if the magnesium concentration is high at and near the grain boundaries, The change in the crystal structure can be more effectively suppressed.

[0115] In addition, when the magnesium and halogen concentrations at and near the grain boundaries are high, the positive electrode active material Even if a crack occurs along the grain boundary of a grain with a quality of 100, the surface area caused by the crack The magnesium and halogen concentrations are high near the surface. The corrosion resistance of the positive electrode active material to hydrofluoric acid can also be improved.

[0116] In the present specification and the like, the vicinity of the crystal grain boundary refers to a region up to about 10 nm from the grain boundary. It is assumed that.

[0117] ≪Particle size≫ If the particle size of the positive electrode active material 100 is too large, it becomes difficult for lithium to diffuse, and when coated on the current collector, there are problems such as the surface of the active material layer becoming too rough. On the other hand, if it is too small, it becomes difficult to support the active material layer during coating on the current collector, and problems such as an excessive reaction with the electrolyte also occur. Therefore, the D50 is preferably 1 μm or more and 100 μm or less, more preferably 2 μm or more and 40 μ m or less, and even more preferably 5 μm or more and 30 μm or less.

[0118] <Analysis method> Whether a certain positive electrode active material is the positive electrode active material 100 of an aspect of the present invention that exhibits a pseudo-spinel crystal structure when charged at a high voltage can be determined by analyzing the positive electrode charged at a high voltage using XRD, electron beam diffraction, neutron diffraction, electron spin resonance (ESR), nuclear magnetic resonance (NMR), etc. In particular, XRD can analyze the symmetry of transition metals such as cobalt in the positive electrode active material with high resolution, can compare the crystallinity and crystal orientation, can analyze the periodic strain of the lattice and the crystallite size, and sufficient accuracy can be obtained even by measuring the positive electrode obtained by disassembling the secondary battery as it is. Therefore, it is preferable in terms of the above points.

[0119] The positive electrode active material 100 of an aspect of the present invention is characterized in that there is little change in the crystal structure between the charged state at a high voltage and the discharged state as described above. A material in which a crystal structure with a large change between the charged state at a high voltage and the discharged state occupies 50 wt% or more is not preferable because it cannot withstand high-voltage charge and discharge. And simply adding impurity elements does not result in the desired crystal structure. ​ It is necessary to note that there may be cases. For example, cobalt lithium fluoride, even though they are common in that regard, when charged at a high voltage, the pseudo-spinel crystal structure becomes 60 wt% or more, and when the H1-3 crystal structure occupies 50 wt% or more. There are also cases where, at a predetermined voltage, the pseudo-spinel crystal structure becomes almost 100 wt%, and further when the predetermined voltage is increased, the H1-3 crystal structure may occur. Therefore, to determine whether the positive electrode active material 100 of one aspect of the present invention is present or not, analysis of the crystal structure including XRD is necessary.

[0120] However, the positive electrode active material in the charged state or discharged state at a high voltage may change its crystal structure when it comes into contact with the air. For example, it may change from the pseudo-spinel type crystal structure to the H1-3 type crystal structure. Therefore, it is preferable to handle all samples in an inert atmosphere such as an argon atmosphere.

[0121] ≪Charging method≫ To determine whether a certain composite oxide is the positive electrode active material 100 of one aspect of the present invention, high voltage charging can be performed, for example, by fabricating a coin cell (CR2032 type, diameter 20 mm, height 3.2 mm) with a lithium counter electrode and charging it.

[0122] More specifically, for the positive electrode, a slurry obtained by mixing a positive electrode active material, a conductive assistant, and a binder can be used, which is coated on a positive electrode current collector made of aluminum foil.

[0123] For the counter electrode, lithium metal can be used. When a material other than lithium metal is used for the counter electrode the potential of the secondary battery and the potential of the positive electrode are different. The voltage and potential in this specification and the like are​​ When not otherwise specified, it is the potential of the positive electrode.

[0124] The electrolyte in the electrolytic solution contains 1 mol / L of lithium hexafluorophosphate (LiPF 6 ). In addition, the electrolytic solution contains ethylene carbonate (EC) and diethyl carbonate (DEC) with an E C:DEC volume ratio of 3:7, and 2 wt% of vinylene carbonate (VC) mixed therein can be used.

[0125] A polypropylene with a thickness of 25 μm can be used for the separator.

[0126] For the positive electrode can and the negative electrode can, those made of stainless steel (SUS) can be used.

[0127] The coin cell fabricated under the above conditions is charged at a constant current of 4.6 V and 0.5 C, and then charged at a constant voltage until the current value reaches 0.01 C. Here, 1 C is defined as 137 mA / g. The temperature is 25°C. After charging in this way, if the coin cell is disassembled in a glove box under an argon atmosphere to take out the positive electrode, a positive electrode active material charged at a high voltage can be obtained. When performing various analyses thereafter, in order to suppress the reaction with external components, it is preferably sealed under an argon atmosphere. For example, XRD can be performed by enclosing it in a sealed container under an argon atmosphere.

[0128] ≪XRD≫ The ideal powder XRD patterns calculated from the models of the pseudo-spinel crystal structure and the H1-3 crystal structure for the CuKα1 line are shown in Fig. 5. For comparison, LiCoO with a charge depth of 0 and CoO with a charge depth of 1 are also shown. 2 (O3) and 2 ​​​​The ideal XRD calculated from the crystal structure of (O1) is also shown. Note that for LiCoO ... 2 (O3) and CoO 2 The patterns of (O1) were obtained from the crystal structure information in the IC SD (Inorganic Crystal Structure Database) (see Non-Patent Document 5) and created using the Reflex Powder Diffr action, which is one of the modules of Materials Studio (BIOVIA). The range of 2θ was set from 15° to 75°, Step size = 0.01, wavelength λ1 = 1.540562×10 -10 m, λ2 was not set, and the Mono chromator was set to single. The pattern of the H1-3 type crystal structure was created in the same manner from the crystal structure information described in Non-Patent Document 3. The pattern of the pseudo-spinel was estimated from the XRD pattern of the positive electrode active material of one aspect of the present invention, and fitted using TOPAS ver.3 (crystal structure analysis software manufactured by Bruk er), and the XRD pattern was created in the same manner as others. ... ...

[0129] As shown in Fig. 5, in the pseudo-spinel type crystal structure, diffraction peaks appear at 2θ = 19.30 ± 0.20° (19. 10° or more and 19.50° or less), and 2θ = 45.55 ± 0.10° (45.45° or more and 45.65° or less). More specifically, sharp diffraction peaks appear at 2θ = 19.30 ± 0.10° (19.20° or more and 19.40° or less), and 2θ = 45.55 ± 0.0 5° (45.50° or more and 45.60° or less). However, in the H1-3 type crystal structure and CoO 2 (P-3m1, O1), peaks do not appear at these positions Therefore, in the state charged at a high voltage, the peaks at 2θ = 19.30 ± 0.20° and 2θ = 4 5.55 ± 0.10° can be said to be the characteristics of the positive electrode active material 100 of one aspect of the present invention.

[0130] This can also mean that the crystal structures at a charge depth of 0 and when charged at a high voltage are such that the positions where the diffraction peaks of XRD appear are close. More specifically, in two or more, more preferably three or more of the main diffraction peaks of both, the difference in the positions where the peaks appear is 2θ = 0.7 or less, more preferably 2θ = 0.5 or less.

[0131] The positive electrode active material 100 of one aspect of the present invention has a pseudo-spinel type crystal structure when charged at a high voltage, but not all of the particles need to have a pseudo-spinel type crystal structure. It may contain other crystal structures or a part may be amorphous. However, when Rietveld analysis is performed on the XRD pattern, it is preferable that the pseudo-spinel type crystal structure is 50 wt% or more, more preferably 60 wt% or more, and even more preferably 66 wt% or more. If the pseudo-spinel type crystal structure is 50 wt% or more, more preferably 60 wt% or more, and even more preferably 66 wt% or more, a positive electrode active material with sufficiently excellent cycle characteristics can be obtained.

[0132] Also, even after 100 cycles or more of charge and discharge from the start of measurement, when Rietveld analysis is performed, it is preferable that the pseudo-spinel type crystal structure is 35 wt% or more, more preferably 40 wt% or more, and even more preferably 43 wt% or more.

[0133] ​​​​​​​​​​​In addition, the crystallite size of the pseudo-spinel structure of the particles of the positive electrode active material is reduced to only about 1 / 10 of that of LiCo O2 (O3) in the discharged state. Therefore, even under the measurement conditions of XRD identical to those before charge and discharge, a distinct peak of the pseudo-spinel type crystal structure can be confirmed after high-voltage charging. On the other hand, in the case of simple LiCoO2, even if a part has a structure similar to the pseudo-spinel type crystal structure, the crystallite size becomes small and the peak becomes broad and small. The crystallite size can be determined from the half-value width of the XRD peak.

[0134] In addition, in the layered rock salt type crystal structure of the particles of the positive electrode active material in the discharged state, which can be estimated from the XRD pattern, it is preferable that the lattice constant of the c-axis is small. The lattice constant of the c-axis increases when a foreign element substitutes at the lithium position or cobalt enters the oxygen four-coordinate position (A site). Therefore, first, a composite oxide having a layered rock salt type crystal structure with less substitution of foreign elements and less spinel type crystal structure Co 3 O 4 is made, and then a magnesium source and a fluorine source are mixed to insert magnesium into the lithium position, whereby a positive electrode active material showing good cycle characteristics can be produced.

[0135] The lattice constant of the c-axis in the crystal structure of the positive electrode active material in the discharged state is preferably 14.060 ×10 -10 m or less, more preferably 14.055 × 10 -10 m or less, and even more preferably 14 .051 × 10 -10 m or less. The lattice constant of the c-axis after annealing is preferably 14. 060 × 10 -10 m or less.

[0136] ​​​​​​​​​In order to make the lattice constant of the c-axis within the above range, it is preferable that the impurity is less, especially cobalt. , it is preferable that the addition of transition metals other than manganese and nickel is less. Specifically, it is preferably 300 ppm wt or less, and more preferably 1500 ppm wt or less. Also, the cation mixing of lithium with cobalt, manganese, and nickel is less

[0137] Note that the characteristics revealed from the XRD pattern are the characteristics regarding the internal structure of the positive electrode active material. For a positive electrode active material with an average particle diameter (D50) of about 1 μm to 100 μm, since the volume of the surface layer part is extremely small compared to the inside, even if the surface layer part of the positive electrode active material 100 has a crystal structure different from that of the inside, it is highly likely not to appear in the XRD pattern.

[0138] ≪ESR≫ Here, using FIGS. 6 and 7, the difference between the pseudo-spinel type crystal structure and other crystal structures will be described for the case of judging using ESR. In the pseudo-spinel type crystal structure, as shown in FIGS. 3 and 6(A), cobalt exists at the oxygen 6-coordination site. As shown in FIG. 6(B), for cobalt with oxygen 6-coordination, the 3d orbitals are split into e g orbitals and t 2g orbitals, and the energy of the t orbital, which is the orbital avoiding the direction where oxygen exists, is low. A part of the cobalt existing at the oxygen 6-coordination site 2g is the diamagnetic Co in which the t 2g orbitals are all filled. However, another part of the cobalt existing at the oxygen 6-coordination site is the paramagnetic Co 3+ However, another part of the cobalt existing at the oxygen 6-coordination site is the paramagnetic Co or Co 2+ or Co 4 + This paramagnetic cobalt is Co2+ and Co 4+ In either case although the unpaired electron is one and they cannot be distinguished by ESR, depending on the valence of the elements present in the surroundings it can take either valence state

[0139] On the other hand, among conventional cathode active materials, there are those described as having a spinel-type crystal structure that does not contain lithium in the surface layer in the charged state In this case, it has the spinel-type crystal structure shown in Fig. 7(A), which is Co O 3 O 4 will have

[0140] When spinel is described by the general formula A[B 2 O 4 element A is coordinated to 4 oxygen atoms and element B is coordinated to 6 oxygen atoms Therefore, in this specification etc., the site coordinated to 4 oxygen atoms may be called the A site, and the site coordinated to 6 oxygen atoms may be called the B site

[0141] In the spinel-type crystal structure of Co 3 OO 4 not only the B site coordinated to 6 oxygen atoms but also the A site coordinated to 4 oxygen atoms contain cobalt As shown in Fig. 7(B), for cobalt coordinated to 4 oxygen atoms among the split e g orbitals and t 2g orbitals, the energy of the e g orbital is low Therefore, Co 2+ coordinated to 4 oxygen atoms, Co 3+ and Co 4+ all have unpaired electrons and are paramagnetic Therefore, if particles sufficiently containing spinel-type Co 3 O 4 are analyzed by ESR etc., peaks derived from paramagnetic cobalt of Co 2+ coordinated to 4 oxygen atoms, Co 3+ or Co 4+ should be detected ​

[0142] However, in the positive electrode active material 100 according to one embodiment of the present invention, the oxygen-coordinated paramagnetic cobalt is Therefore, the pseudospinel referred to in this specification and the like is Unlike spinel, it does not contain any ESR-detectable amounts of cobalt with four oxygen coordinates. Therefore, compared to the conventional example, the positive electrode active material of one embodiment of the present invention has a higher spin that can be detected by ESR or the like. Nel type Co 3 O 4 The peaks due to the saturation may be small or too few to be seen. Pinel type Co 3 O 4 does not contribute to the charge / discharge reaction, so spinel type Co 3 O 4 The less As seen from the ESR analysis, the positive electrode active material 100 is different from the conventional examples. It can be determined that:

[0143] <XPS> X-ray photoelectron spectroscopy (XPS) measures the surface to a depth of about 2 to 8 nm (usually about 5 nm). Since it is possible to analyze the area, the concentration of each element can be quantified for about half of the surface layer. In addition, 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 depends on the element. It depends on the material, but is about 1 atomic percent.

[0144] When XPS analysis was performed on 100% positive electrode active material, the cobalt concentration was set to 1. The relative value of the magnesium concentration is preferably 0.4 or more and 1.5 or less, and more preferably 0.45 or more and less than 1.00. The relative value of the concentration of halogen such as fluorine is preferably 0.05 or more and 1.5 or less. It is preferable that the ratio is 0.3 or more and 1.00 or less.

[0145] In addition, when the positive electrode active material 100 was analyzed by XPS, the bond energy between fluorine and other elements was The peak showing the ion exchange reaction is preferably 682 eV or more and less than 685 eV, and more preferably 684.3 eV. It is more preferable that the bond energy of the bond is about 68 5 eV, and the binding energy of magnesium fluoride, 686 eV. In other words, when the positive electrode active material 100 contains fluorine, lithium fluoride and Bonds other than magnesium fluoride are preferred.

[0146] Furthermore, when the positive electrode active material 100 was analyzed by XPS, the bonds between magnesium and other elements were The peak showing the energy is preferably 1302 eV or more and less than 1304 eV, It is more preferable that the bond energy of magnesium fluoride is about 1303 eV. This value is different from the 1305 eV, which is the energy of magnesium oxide. In other words, when the positive electrode active material 100 contains magnesium, magnesium fluoride A bond other than the following is preferred.

[0147] <EDX> Among EDX measurements, ED is a method of measuring an area while scanning it and evaluating the area in two dimensions. Also, data on linear areas is extracted from EDX area analysis, and the original Evaluation of the distribution of the molecular concentration within the positive electrode active material particles is sometimes called line analysis.

[0148] EDX surface analysis (e.g. elemental mapping) was used to identify the internal, surface and grain boundary regions. The concentrations of magnesium and fluorine can be quantitatively analyzed. Analysis can be used to analyze the peaks in the concentrations of magnesium and fluorine.

[0149] When EDX analysis is performed on the positive electrode active material 100, the peak in the magnesium concentration in the surface layer preferably exists from the surface of the positive electrode active material 100 to a depth of 3 nm towards the center, more preferably exists to a depth of 1 nm, and even more preferably exists to a depth of 0.5 nm.

[0150] Also, the distribution of fluorine in the positive electrode active material 100 preferably overlaps with the distribution of magnesium. Therefore, when EDX analysis is performed, the peak in the fluorine concentration in the surface layer preferably exists from the surface of the positive electrode active material 100 to a depth of 3 nm towards the center, more preferably exists to a depth of 1 nm, and even more preferably exists to a depth of 0.5 nm.

[0151] When line analysis or surface analysis is performed on the positive electrode active material 100, the ratio (Mg / Co) of the number of atoms of magnesium and cobalt near the grain boundaries is preferably 0.020 or more and 0.50 or less. More preferably, it is 0.025 or more and 0.30 or less. Even more preferably, it is 0.030 or more and 0. 20 or less.

[0152] ≪dQ / dV vs V curve≫ Also, when the positive electrode active material according to one aspect of the present invention is discharged at a low rate of, for example, 0.2C or less after being charged at a high voltage, a characteristic voltage change may appear near the end of discharge. This change can be clearly confirmed by the presence of at least one peak in the range of 3.5 V to 3.9 V in the dQ / dV vs V curve obtained from the discharge curve.

[0153] (Embodiment 2) In this embodiment, examples of materials that can be used for the secondary battery having the positive electrode active material 100 described in the previous embodiment will be described. In this embodiment, a secondary battery in which a positive electrode, a negative electrode, and an electrolytic solution are wrapped in an exterior body will be described as an example.

[0154] [Positive Electrode] The positive electrode has a positive electrode active material layer and a positive electrode current collector.

[0155] [Positive Electrode Active Material Layer] The positive electrode active material layer has at least a positive electrode active material. Further, the positive electrode active material layer may contain other substances such as a film on the surface of the active material, a conductive assistant, or a binder in addition to the positive electrode active material.

[0156] As the positive electrode active material, the positive electrode active material 100 described in the previous embodiment can be used. By using the positive electrode active material 100 described in the previous embodiment, a secondary battery with high capacity and excellent cycle characteristics can be obtained.

[0157] As the conductive assistant, a carbon material, a metal material, a conductive ceramic material, or the like can be used. Further, a fibrous material may be used as the conductive assistant. The content of the conductive assistant with respect to the total amount of the active material layer is preferably 1 wt% or more and 10 wt% or less, and more preferably 1 wt% or more and 5 wt% or less.

[0158] The conductive assistant can form an electric conduction network in the active material layer. The conductive assistant can maintain the electric conduction path between the positive electrode active materials. By adding the conductive assistant to the active material layer, an active material layer having high electric conductivity can be realized.

[0159] ​​​​​​​​​​​As the conductive aid, for example, natural graphite, artificial graphite such as mesocarbon microbeads, carbon fibers, etc. can be used. As the carbon fibers, for example, carbon fibers such as mesophase pitch-based carbon fibers, isotropic pitch-based carbon fibers, etc. can be used. Also, as the carbon fibers, carbon nanotubes, carbon nanofibers, etc. can be used. Carbon nanotubes can be produced, for example, by a vapor growth method. Further, as the conductive aid, for example, carbon materials such as carbon black (such as acetylene black (AB)), graphite (black lead) particles, graphene, fullerenes, etc. can be used. Also, for example, metal powders such as copper, nickel, aluminum, silver, gold, etc., metal fibers, conductive ceramic materials, etc. can be used.

[0160] Also, a graphene compound may be used as the conductive aid.

[0161] The graphene compound may have excellent electrical properties such as high conductivity, and excellent physical properties such as high flexibility and high mechanical strength. Also, the graphene compound has a planar shape. The graphene compound enables surface contact with low contact resistance. Also, it may have very high conductivity even when thin, and can efficiently form a conductive path in the active material layer in a small amount. Therefore, it is preferable to use a graphene compound as the conductive aid because the contact area between the active material and the conductive aid can be increased. By using a spray dryer, it is preferable to form a coating of the graphene compound, which is the conductive aid, covering the entire surface of the active material. Also, it may be possible to reduce the electrical resistance. Therefore, it is preferable. Here, as the graphene compound, for example, graphene, multi-graphene, or it is particularly preferable to use RGO. Here, RGO refers to, for example, a compound obtained by reducing graphene oxide (g raphene oxide: GO).

[0162] When using an active material with a small particle size, for example, an active material of 1 μm or less, the specific surface area of the active material is large, and more conductive paths connecting the active materials are required. Therefore, the amount of the conductive assistant tends to be large and the loading amount of the active material tends to relatively decrease. When the loading amount of the active material decreases, the capacity of the secondary battery decreases. In such a case, when using a graphene compound as the conductive assistant the graphene compound can efficiently form a conductive path even in a small amount, so it is not necessary to reduce the loading amount of the active material, which is particularly preferable.

[0163] Hereinafter, as an example, a cross-sectional configuration example in the case of using a graphene compound as a conductive assistant in the active material layer 200 will be described.

[0164] FIG. 8(A) shows a longitudinal sectional view of the active material layer 200. The active material layer 200 includes a granular positive electrode active material 100, a graphene compound 201 as a conductive assistant, and a binder (not shown). Here, for example, graphene or multi-graphene may be used as the graphene compound 201. Here, the graphene compound 201 preferably has a sheet-like shape. Also, the graphene compound 201 may be such that a plurality of multi-graphenes and / or a plurality of graphenes are partially overlapped to form a sheet shape.

[0165] In the longitudinal section of the active material layer 200, as shown in FIG. 8(B), inside the active material layer 200 In this case, the sheet-like graphene compound 201 is dispersed in a substantially uniform manner. In FIG. 8(B), the graphene compound 201 is schematically represented by a thick line, but in reality, it is a thin film having a thickness of a single layer or multiple layers of carbon molecules. The plurality of graphene compounds 201 are formed so as to partially cover the plurality of granular positive electrode active materials 100, or to adhere onto the surfaces of the plurality of granular positive electrode active materials 100, and thus are in surface contact with each other.

[0166] Here, by bonding the plurality of graphene compounds to each other, a network-like graphene compound sheet (hereinafter referred to as a graphene compound net or a graphene net) can be formed. When the active material is covered with the graphene net, the graphene net can also function as a binder that binds the active materials to each other. Therefore, the amount of the binder can be reduced or the binder can be not used, and thus the ratio of the active material in the electrode volume and the electrode weight can be improved. That is, the capacity of the secondary battery can be increased. Here, it is preferable to use graphene oxide as the graphene compound 201, mix it with the active material to form a layer that becomes the active material layer 200, and then reduce it. By using graphene oxide having extremely high dispersibility in a polar solvent for the formation of the graphene compound 201, the graphene compound 201 can be dispersed in a substantially uniform manner inside the active material layer 200. After volatilizing and removing the solvent from the dispersion medium containing uniformly dispersed graphene oxide and reducing the graphene oxide, the graphene compounds 201 remaining in the active material layer 200 partially overlap with each other and are dispersed to the extent of being in surface contact with each other, so that a three-dimensional conductive path can be formed.

[0167] Here, it is preferable to use graphene oxide as the graphene compound 201, mix it with the active material to form a layer that becomes the active material layer 200, and then reduce it. By using graphene oxide having extremely high dispersibility in a polar solvent for the formation of the graphene compound 201, the graphene compound 201 can be dispersed in a substantially uniform manner inside the active material layer 200. After volatilizing and removing the solvent from the dispersion medium containing uniformly dispersed graphene oxide and reducing the graphene oxide, the graphene compounds 201 remaining in the active material layer 200 partially overlap with each other and are dispersed to the extent of being in surface contact with each other, so that a three-dimensional conductive path can be formed. dispersed graphene oxide and reducing the graphene oxide, the graphene compounds 201 remaining in the active material layer 200 partially overlap with each other and are dispersed to the extent of being in surface contact with each other, so that a three-dimensional conductive path can be formed. Disperse the solvent from the dispersion medium containing uniformly dispersed graphene oxide and reduce the graphene oxide, so that the graphene compounds 201 remaining in the active material layer 200 partially overlap with each other and are dispersed to the extent of being in surface contact with each other, thereby forming a three-dimensional conductive path. By being dispersed to the extent of being in surface contact with each other, a three-dimensional conductive path can be formed. Note that the reduction of graphene oxide may be carried out, for example, by heat treatment or using a reducing agent. It may also be carried out.

[0168] Therefore, unlike granular conductive aids such as acetylene black that make point contact with the active material, the graphene compound 201 enables surface contact with low contact resistance. Thus, it can improve the electrical conductivity between the granular positive electrode active material 100 and the graphene compound 201 with a smaller amount than ordinary conductive aids. Therefore, the ratio in the active material layer 200 of the positive electrode active material 100 can be increased. As a result, the discharge capacity of the secondary battery can be increased.

[0169] Also, by using a spray dryer in advance, a graphene compound that covers the entire surface of the active material and serves as a conductive aid can be formed as a film, and an electrical conduction path can also be formed between the active materials with the graphene compound.

[0170] As the binder, for example, it is preferable to use rubber materials such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, and ethylene-propylene-diene copolymer. Also, fluororubber can be used as the binder.

[0171] Also, as the binder, it is preferable to use, for example, water-soluble polymers. As the water-soluble polymers, for example, polysaccharides can be used. As the polysaccharides, cellulose derivatives such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, and regenerated cellulose, or starch can be used. It can be used. Also, it is more preferable to use these water-soluble polymers in combination with the aforementioned rubber material. It is more preferable.

[0172] Alternatively, as the binder, polystyrene, polymethyl acrylate, polymethyl methacrylate (PMMA), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), ethylene propylene diene polymer, polyvinyl acetate, nitrocellulose and other materials are preferably used. (PVDF), polyacrylonitrile (PAN), ethylene propylene diene polymer, It is preferable to use materials such as polyvinyl acetate and nitrocellulose.

[0173] Multiple of the above binders may be used in combination.

[0174] For example, a material with particularly excellent viscosity adjustment effect may be used in combination with other materials. For example, rubber materials and the like are excellent in adhesive force and elastic force, but may be difficult to adjust viscosity when mixed with a solvent. In such a case, for example, it is preferable to mix with a material having a particularly excellent viscosity adjustment effect. As the material having a particularly excellent viscosity adjustment effect, for example, a water-soluble polymer may be used. Also, as the water-soluble polymer having a particularly excellent viscosity adjustment effect, the aforementioned polysaccharides, such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxy propyl cellulose and diacetyl cellulose, cellulose derivatives such as regenerated cellulose, or starch can be used. It can be used.

[0175] Note that cellulose derivatives such as carboxymethyl cellulose can be made more soluble, for example, by forming salts such as sodium salts or ammonium salts of carboxymethyl cellulose, and are more likely to exhibit their effects as viscosity modifiers. By increasing the solubility, the dispersibility with the active material and other components can also be enhanced when preparing the electrode slurry. In this specification, cellulose and cellulose derivatives used as electrode binders shall include those salts. Water-soluble polymers stabilize the viscosity by dissolving in water and can stably disperse the active material and other materials combined as binders, such as styrene-butadiene rubber, in an aqueous solution. Also, due to having functional groups, they are expected to be easily and stably adsorbed on the surface of the active material. Further, cellulose derivatives such as carboxymethyl cellulose have many materials having functional groups such as hydroxyl groups and carboxyl groups, and due to having functional groups, it is expected that the polymers interact with each other and widely cover the surface of the active material. When the binder covering or in contact with the surface of the active material forms a film, it is also expected to serve as a passivation film and suppress the decomposition of the electrolyte. Here, the passivation film is a film without electrical conductivity or with extremely low electrical conductivity. For example, when a passivation film is formed on the surface of the active material, the decomposition of the electrolyte can be suppressed at the battery reaction potential. Also, it is more desirable that the passivation film suppresses electrical conductivity while allowing lithium ions to conduct.

[0176] <Positive current collector>

[0177]

[0178] ​​​​​​​​​​​​As the positive electrode current collector, metals such as stainless steel, gold, platinum, aluminum, and titanium, and alloys thereof, etc., materials with high conductivity can be used. Also, the material used for the positive electrode current collector is preferably one that does not elute at the potential of the positive electrode. Further, an aluminum alloy added with elements for improving heat resistance such as silicon, titanium, neodymium, scandium, molybdenum, etc. can be used. Also, it may be formed of a metal element that reacts with silicon to form a silicide. As the metal element that reacts with silicon to form a silicide, there are zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, nickel, etc. The current collector can appropriately use shapes such as foil shape, plate shape (sheet shape), net shape, punching metal shape, expanded metal shape, etc. The current collector is preferably one having a thickness of 5 μm or more and 30 μm or less.

[0179] [Negative electrode] The negative electrode has a negative electrode active material layer and a negative electrode current collector. Also, the negative electrode active material layer may have a conductive assistant and a binder.

[0180] [Negative electrode active material] As the negative electrode active material, for example, alloy-based materials, carbon-based materials, etc. can be used.

[0181] As the negative electrode active material, elements capable of performing charge and discharge reactions by alloying and dealloying reactions with lithium can be used. For example, at least one of silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium, etc. can be used. Such elements have a larger capacity compared to carbon. ​​​​​​​​​​​Listen, especially silicon has a high theoretical capacity of 4200 mAh / g. Therefore, it is preferable to use silicon as the negative electrode active material. Also, compounds containing these elements may be used. For example, SiO, Mg 2 Si, Mg 2 Ge, SnO, SnO 2 , Mg 2 Sn, SnS 2 , V 2 Sn 3 , FeSn 2 , CoSn 2 , Ni 3 Sn 2 , Cu 6 Sn 5 , Ag 3 Sn, Ag 3 , Sb, Ni 2 , MnSb, CeSb 3 , LaSn 3 , La 3 , Co 2 Sn 7 , CoSb 3 , I nSb, SbSn, etc. Here, elements that can undergo charge-discharge reactions through alloying and dealloying reactions with lithium, and compounds containing such elements, etc., may be referred to as alloy-based materials in some cases.

[0182] In this specification, etc., SiO refers to, for example, silicon monoxide. Alternatively, SiO can be expressed as SiO x . Here, x preferably has a value near 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.

[0183] As the carbon-based material, graphite, graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), carbon nanotubes, graphene, carbon black, etc. may be used.

[0184] Examples of graphite include artificial graphite and natural graphite. Examples of artificial graphite include mesocarbon microbeads (MCMB), coke-based artificial graphite, pitch-based artificial graphite, and the like. Here, spherical graphite having a spherical shape can be used as the artificial graphite. For example, MCMB may have a spherical shape, which is preferable. In addition, it is relatively easy to reduce the surface area of MCMB, which may be preferable. Examples of natural graphite include scaly graphite, spheroidized natural graphite, and the like.

[0185] Graphite exhibits a potential as low as that of lithium metal (0.05 V or more and 0.3 V or less vs. Li / Li Li + ) when lithium ions are inserted into the graphite (when a lithium-graphite intercalation compound is formed). As a result, a lithium-ion secondary battery can exhibit a high operating voltage. Furthermore, graphite has advantages such as a relatively high capacity per unit volume, a relatively small volume expansion, low cost, and high safety compared to lithium metal,

[0186] so it is preferable. 2 In addition, oxides such as titanium dioxide (TiO 4 ), lithium titanate (Li T 5 O 12 ), lithium-graphite intercalation compound (Li x C 6 ), niobium pentoxide (Nb 2 O 5 ), tungsten oxide (WO 2 ), molybdenum oxide (MoO 2 ) can be used as the negative electrode active material.

[0187] In addition, Li 3Having an N-type structure Li 3-x M x N (M = Co, Ni, Cu) can be used. For example, Li 2.6 Co 0.4 N 3 shows a large charge-discharge capacity (900 mAh / g, 1890 mAh / cm 3 ) and is preferable. When using a lithium-transition metal double nitride, since the negative electrode active material contains lithium ions,

[0188] it is preferable to combine with materials such as V that do not contain lithium ions as the positive electrode active material, 2 O 5 、Cr 3 O 8 etc. Even when using a material containing lithium ions as the positive electrode active material, by previously desorbing the lithium ions contained in the positive electrode active material, a lithium-transition metal double nitride can be used as the negative electrode active material.

[0189] In addition, a material that undergoes a conversion reaction can also be used as the negative electrode active material. For example, transition metal oxides such as cobalt oxide (CoO), nickel oxide (NiO), iron oxide (FeO), etc., that do not form an alloy with lithium can be used as the negative electrode active material. Materials that undergo a conversion reaction further include oxides such as Fe 2 O 3 、CuO、Cu 2 O、RuO 2 、Cr 2 O 3 etc. sulfides such as CoS 0.89 、NiS、CuS, nitrides such as Zn 3 N 2 、Cu 3 N、Ge 3 N 4 etc., and phosphides such as NiP 2 、FeP2 , CoP 3 and other phosphides, FeF 3 , BiF 3 and others also occur with fluorides.

[0190] As the conductive assistant and binder that the negative electrode active material layer can have, materials similar to those that the positive electrode active material layer can have can be used.

[0191] [Negative current collector] For the negative current collector, the same materials as those for the positive current collector can be used. It is preferable to use a material that does not alloy with carrier ions such as lithium.

[0192] [Electrolyte] The electrolyte has a solvent and an electrolyte. As the solvent of the electrolyte, an aprotic organic solvent is preferable. For example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, chloroethylene carbonate, vinylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethoxyethane (DME), dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, sultone, etc. can be used alone, or two or more of these can be used in any combination and ratio. , 3-dioxane, 1,4-dioxane, dimethoxyethane (DME), dimethyl sulfoxide , diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran , sulfolane, sultone, etc. can be used alone, or two or more of these can be used in any combination and ratio.

[0193] Also, as the solvent of the electrolyte, an ionic liquid (room temperature molten salt) that is flame retardant and hardly volatile can be used alone. When used singly or in plurality, even if the internal temperature rises due to internal short circuit, overcharging, etc. of the secondary battery it is possible to prevent rupture, ignition, etc. of the secondary battery. The ionic liquid consists of a cation and an anion and contains an organic cation and an anion. Examples of the organic cation used in the electrolyte include quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, etc. of aliphatic onium cations, imidazolium cations, pyridinium cations, etc. Examples of the anion used in the electrolyte include monovalent amide-based anions, monovalent methide-based anions, fluorosulfonic acid anions, perfluoroalkyl sulfonic acid anions, tetrafluoroborate anions, perfluoroalkyl borate anions, hexafluorophosphate anions, or perfluoroalkyl phosphate anions, etc.

[0194] In addition, examples of the electrolyte dissolved in the above solvent include, for example, LiPF 6 , LiClO 4 , Li AsF 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 SO2 ) 3 , LiN(CF 3 SO 2 ) 2 , LiN(C 4 F 9 SO 2 )(CF 3 SO 2 ), LiN(C 2 F 5 SO 2 ) 2 and other lithium salts can be used singly or in any combination and ratio of two or more of these. This is possible.

[0195] It is preferable to use a highly purified electrolyte solution with a low content of particulate dust and elements other than the constituent elements of the electrolyte solution (hereinafter also simply referred to as "impurities"). Specifically, the weight ratio of impurities to the electrolyte solution is preferably 1% or less, more preferably 0.1% or less, and even more preferably 0.01% or less.

[0196]

[0197]

[0198] Additives such as vinylene carbonate, propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), lithium bis(oxalate) borate (LiBOB), and dinitrile compounds such as succinonitrile and adiponitrile may also be added. The concentration of the additive material may be, for example, 0.1 wt% or more and 5 wt% or less based on the total solvent.

[0197] A polymer gel electrolyte obtained by swelling a polymer with an electrolyte solution may also be used.

[0198] Using a polymer gel electrolyte enhances safety against leakage and the like. Also, the secondary battery can be made thinner and lighter. ​

[0199] As the polymer to be gelled, silicone gel, acrylic gel, acrylonitrile gel, polyethylene oxide-based gel, polypropylene oxide-based gel, fluorine-based polymer gels, etc. can be used.

[0200] As the polymer, for example, polymers having a polyalkylene oxide structure such as polyethylene oxide (PEO), PVDF, polyacrylonitrile, etc., and copolymers containing them can be used. For example, PVDF-HFP, which is a copolymer of PVDF and hexafluoropropylene (HFP), can be used. Further, the formed polymer may have a porous shape.

[0201] Further, instead of the electrolytic solution, a solid electrolyte having an inorganic material such as a sulfide-based or oxide-based material, or a solid electrolyte having a polymer material such as a PEO (polyethylene oxide)-based material can be used. When using a solid electrolyte, it is not necessary to install a separator or a spacer. Further, since the

[0202] [Separator] Moreover, the secondary battery preferably has a separator. As the separator, for example, paper, non-woven fabric, glass fiber, ceramics, or a synthetic fiber formed using nylon (polyamide), vinylon (polyvinyl alcohol-based fiber), polyester, acrylic, polyolefin, polyurethane, etc. can be used. The separator is preferably processed into an envelope shape and arranged so as to wrap either the positive electrode or the negative electrode.

[0203] The separator may have a multilayer structure. For example, an organic material film such as polypropylene or polyethylene can be coated with a ceramic-based material, a fluorine-based material, a polyamide-based material, or a mixture thereof. As the ceramic-based material, for example, aluminum oxide particles, silicon oxide particles, etc. can be used. As the fluorine-based material, for example, PVDF, polytetrafluoroethylene, etc. can be used. As the polyamide-based material, for example, nylon, aramid (meta-aramid, para-aramid), etc. can be used. Coating the organic material film with a ceramic-based material, a fluorine-based material, a polyamide-based material, or a mixture thereof can improve the oxidation resistance of the separator, suppress the deterioration of the separator during high-voltage charge and discharge, and improve the reliability of the secondary battery. Coating with a fluorine-based material can make the separator and the electrode adhere more easily, and improve the output characteristics. Coating with a polyamide-based material, especially aramid, can improve the heat resistance and thus improve the safety of the secondary battery. For example, both sides of a polypropylene film can be coated with a mixed material of aluminum oxide and aramid. Also, the side of the polypropylene film in contact with the positive electrode can be coated with a mixed material of aluminum oxide and aramid, and the side in contact with the negative electrode can be coated with a fluorine-based material. Using a separator with a multilayer structure can maintain the safety of the secondary battery even if the overall thickness of the separator is thin, so that the capacity per volume of the secondary battery can be increased. As the outer package of the secondary battery, for example, a metal material such as aluminum or a resin material can be used.

[0204] Coating with a ceramic-based material improves oxidation resistance, suppressing separator deterioration during high-voltage charge and discharge and enhancing secondary battery reliability. Coating with a fluorine-based material makes the separator and electrode adhere more easily, improving output characteristics. Coating with a polyamide-based material, especially aramid, improves heat resistance and thus secondary battery safety. For example, a mixed material of aluminum oxide and aramid can be coated on both sides of a polypropylene film. Or, the side of the polypropylene film in contact with the positive electrode can be coated with a mixed material of aluminum oxide and aramid, and the side in contact with the negative electrode can be coated with a fluorine-based material. Using a multilayer-structured separator can maintain secondary battery safety even with a thin overall thickness, enabling an increase in the volume-specific capacity of the secondary battery. As the outer package of the secondary battery, for example, a metal material such as aluminum or a resin material can be used.

[0205] Coating both sides of a polypropylene film with a mixed material of aluminum oxide and aramid is also acceptable. Additionally, the side of the polypropylene film in contact with the positive electrode can be coated with a mixed material of aluminum oxide and aramid, and the side in contact with the negative electrode can be coated with a fluorine-based material. Moreover, the side of the polypropylene film in contact with the positive electrode can be coated with a mixed material of aluminum oxide and aramid, and the side in contact with the negative electrode can be coated with a fluorine-based material.

[0206] Using a multilayer-structured separator can maintain secondary battery safety even with a thin overall thickness, allowing for an increase in the capacity per volume of the secondary battery.

[0207] [Outer package] As the outer package of the secondary battery, for example, a metal material such as aluminum or a resin material can be used. It is also possible to use a film-shaped exterior body. As the film, for example, polyethylene, polypropylene, polycarbonate, ionomer, polyamide, etc. On a film made of the above materials, a metal thin film with excellent flexibility such as aluminum, stainless steel, copper, nickel, etc. is provided, and further, a three-layer film in which an insulating synthetic resin film such as a polyamide-based resin or a polyester-based resin is provided as the outer surface of the exterior body on the metal thin film can be used.

[0208] [Charging and Discharging Method] The charging and discharging of the secondary battery can be performed, for example, as follows.

[0209] ≪CC Charging≫ First, CC charging will be described as one of the charging methods. CC charging is a charging method in which a constant current is passed through the secondary battery throughout the charging period and the charging is stopped when a predetermined voltage is reached. Assume that the secondary battery has an equivalent circuit of internal resistance R and secondary battery capacity C as shown in Fig. 9(A). In this case, the secondary battery voltage V B is the sum of the voltage V R across the internal resistance R and the voltage V across the secondary battery capacity C. C

[0210] During CC charging, as shown in Fig. 9(A), the switch is turned on and a constant current I flows through the secondary battery. During this period, since the current I is constant, according to Ohm's law V =R×I, the voltage V R across the internal resistance R is also constant. On the other hand, the voltage V across the secondary battery capacity C increases with time. Therefore, the secondary battery voltage V R increases with time. C B

[0211] ​​​​​​​ And when the secondary battery voltage V B reaches a predetermined voltage, for example, 4.3 V, charging is stopped. When CC charging is stopped, as shown in FIG. 9(B), the switch turns off and the current I = 0 results. Therefore, the voltage V R across the internal resistance R becomes 0 V. Therefore, the secondary battery voltage V B decreases.

[0212] Examples of the secondary battery voltage V B and the charging current during CC charging and after CC charging is stopped are shown in FIG. 9(C). The secondary battery voltage V that was rising during CC charging is shown to slightly decrease after CC charging is stopped. B C is shown to slightly decrease after CC charging is stopped.

[0213] ≪CCCV Charging≫ Next, CCCV charging, which is a charging method different from the above, will be described. CCCV charging first performs charging up to a predetermined voltage by CC charging, and then performs charging by CV (constant voltage) charging until the current flowing therein becomes less, specifically, until it reaches the termination current value.

[0214] During CC charging, as shown in FIG. 10(A), the switch of the constant current power supply is on, the switch of the constant voltage power supply is off, and a constant current I flows into the secondary battery. During this period, since the current I is constant, according to Ohm's law of V R = R×I, the voltage V R across the internal resistance R is also constant. On the other hand, the voltage V C across the secondary battery capacitance C rises with the passage of time. Therefore, the secondary battery voltage V B rises with the passage of time.

[0215] And the secondary battery voltage V BWhen it reaches a predetermined voltage, for example, 4.3V, it switches from CC charging to C V charging. While performing CV charging, as shown in Fig. 10(B), the switch of the constant-voltage power supply is turned on and the switch of the constant-current power supply is turned off, and the secondary battery voltage V becomes constant. On the other hand, the voltage V B across the secondary battery capacity C increases with the passage of time. Since V =V C +V B =V R +V C and V R across the internal resistance R decreases with the passage of time. As the voltage V R across the internal resistance R decreases, according to Ohm's law of V R =R×I, the current I flowing through the secondary battery also decreases. When the current I flowing through the secondary battery reaches a predetermined current, for example, a current equivalent to 0.01C

[0216] , the charging stops. When the CCCV charging stops, as shown in Fig. 10(C), all switches turn off and the current I = 0. Therefore, the voltage V across the internal resistance R becomes 0V R . However, since the voltage V across the internal resistance R due to CV charging is sufficiently small R , even when the voltage drop across the internal resistance R disappears, the secondary battery voltage V hardly drops. B An example of the secondary battery voltage V

[0217] and the charging current during CCCV charging and after stopping CCCV charging is shown in Fig. 10(D). It shows that even when the CCCV charging stops, the secondary battery voltage V B hardly drops. B

[0218] <<CC Discharge>>

[0218] Next, CC discharge, which is one of the discharge methods, will be described. CC discharge is a discharge method in which a constant current flows from the secondary battery throughout the discharge period and the discharge is stopped when the secondary battery voltage V B reaches a predetermined voltage, for example, 2.5 V. It is a discharge method that stops discharging when this occurs.

[0219] An example of the secondary battery voltage V and the discharge current while CC discharge is being performed is shown in FIG. 11. As the discharge progresses B , the state of the secondary battery voltage V decreasing is shown. B

[0220] Next, the discharge rate and the charge rate will be described. The discharge rate is the relative ratio of the current during discharge to the battery capacity and is expressed in units of C. In a battery with a rated capacity of X (Ah) , a current equivalent to 1 C is X (A). When discharging with a current of 2X (A), it is said to be discharging at 2 C , and when discharging with a current of X / 5 (A), it is said to be discharging at 0.2 C. Also, the charge rate is the same. When charging with a current of 2X (A), it is said to be charging at 2 C , and when charging with a current of X / 5 (A), it is said to be charging at 0.2 C. .

[0221] (Embodiment 3) In this embodiment, an example of the shape of the secondary battery having the positive electrode active material 100 described in the previous embodiment will be described. The materials used for the secondary battery described in this embodiment can refer to the description of the previous embodiment.

[0222] [Coin-type secondary battery] First, an example of a coin-type secondary battery will be described. FIG. 12(A) is an external view of a coin-type (single-layer flat-type ) secondary battery, and FIG. 12(B) is a cross-sectional view thereof.

[0223] The coin-shaped 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, which are insulated and sealed by a gasket 303 made of polypropylene or the like. The positive electrode 304 is formed by a positive electrode current collector 305 and a positive electrode active material layer 306 provided in contact therewith. Further, the negative electrode 307 is formed by a negative electrode current collector 308 and a negative electrode active material layer 309 provided in contact therewith. formed.

[0224] Note that for the positive electrode 304 and the negative electrode 307 used in the coin-shaped secondary battery 300, the active material layers may be formed only on one side. respectively.

[0225] For the positive electrode can 301 and the negative electrode can 302, metals such as nickel, aluminum, titanium, or alloys thereof, or alloys of these with other metals (e.g., stainless steel etc.) that are corrosion-resistant to the electrolyte can be used. Also, in order to prevent corrosion by the electrolyte, it is preferable to coat with nickel or aluminum etc. The positive electrode can 301 is electrically connected to the positive electrode 304, and the negative electrode can 302 is electrically connected to the negative electrode 30 7 respectively.

[0226] These negative electrode 307, positive electrode 304, and separator 310 are impregnated with an electrolyte, and as shown in Fig. 12(B ), with the positive electrode can 301 facing downwards, the positive electrode 304, separator 310, negative electrode 307, negative electrode can 302 are laminated in this order, and the positive electrode can 301 and the negative electrode can 302 are crimped via the gasket 303 to manufacture the coin-shaped secondary battery 300.

[0227] By using the positive electrode active material described in the previous embodiment for the positive electrode 304, a coin-shaped secondary battery 300 with high capacity and excellent cycle characteristics can be obtained.

[0228] ​Here, the flow of current during charging of the secondary battery will be described with reference to FIG. 12(C). When a secondary battery using lithium is regarded as a single closed circuit, the movement of lithium ions and the flow of current are in the same direction. Note that in a secondary battery using lithium, the anode (positive electrode) and the cathode (negative electrode) are switched during charging and discharging, and the oxidation reaction and the reduction reaction are switched. Therefore, the electrode with a higher reaction potential is called the positive electrode, and the electrode with a lower reaction potential is called the negative electrode. Thus, in this specification, regardless of whether it is during charging, discharging, or when a reverse pulse current is flowing, or when a charging current is flowing, the positive electrode is called the "positive electrode" or the "+ electrode (plus electrode)", and the negative electrode is called the "negative electrode" or the "- electrode (minus electrode)". When using terms such as anode (positive electrode) and cathode (negative electrode) related to oxidation reactions and reduction reactions, they will be reversed during charging and discharging, which may cause confusion. Therefore, the terms anode (positive electrode) and cathode (negative electrode) will not be used in this specification. If the terms anode (positive electrode ) and cathode (negative electrode) are used, it is necessary to specify whether it is during charging or discharging, and also indicate which one corresponds to the positive electrode ( plus electrode) and the negative electrode (minus electrode). ) and cathode (negative electrode) are used, it is necessary to specify whether it is during charging or discharging, and also indicate which one corresponds to the positive electrode ( plus electrode) and the negative electrode (minus electrode).

[0229] A charger is connected to the two terminals shown in FIG. 12(C), and the secondary battery 300 is charged. As the charging of the secondary battery 300 progresses, the potential difference between the electrodes increases.

[0230] [Cylindrical secondary battery] Next, an example of a cylindrical secondary battery will be described with reference to FIG. 13. The external view of the cylindrical secondary battery 600 is shown in FIG. 13(A). FIG. 13(B) is a diagram schematically showing the cross-section of the cylindrical secondary battery 600. As shown in FIG. 13(B), the cylindrical secondary battery 600 has on its upper surface, It has a positive electrode cap (battery cover) 601 and has a battery can (outer can) 602 on its side and bottom surface. These positive electrode cap and battery can (outer can) 602 are insulated by a gasket (insulating packing ) 610.

[0231] Inside the hollow cylindrical battery can 602, a battery element is provided in which a strip-shaped positive electrode 604 and a negative electrode 606 are wound with a separator 6 05 interposed therebetween. Although not shown, the battery element is wound around a center pin. The battery can 602 has one end closed and the other end open. The battery can 602 can be made of metals such as nickel, aluminum, titanium, etc. that are corrosion-resistant to the electrolytic solution, or alloys of these or alloys of these and other metals (for example, stainless steel, etc.). In addition, in order to prevent corrosion by the electrolytic solution, it is preferable to coat the battery can 602 with nickel, aluminum, etc. Inside the battery can 602, the battery element around which the positive electrode, negative electrode, and separator are wound is sandwiched between a pair of opposing insulating plates 608, 609. Also, a non-aqueous electrolytic solution (not shown) is injected into the inside of the battery can 602 where the battery element is provided. As the non-aqueous electrolytic solution, the same one as that used for a coin-type secondary battery can be used. Since the positive electrode and negative electrode used in the cylindrical storage battery are wound, it is preferable to form the active material on both sides of the current collector. A positive electrode terminal (positive electrode current collecting lead) 603 is connected to the positive electrode 604, and a negative electrode terminal (negative electrode current collecting lead) 607 is connected to the negative electrode 606. Both the positive electrode terminal 603 and the negative electrode terminal 607 can use a metal material such as aluminum. The positive electrode terminal 60

[0232] 3 is resistance welded to the safety valve mechanism 612, and the negative electrode terminal 607 is resistance welded to the bottom of the battery can 602 respectively. ​​​​​​ . The safety valve mechanism 612 is electrically connected to the positive electrode cap 601 via a PTC element (Positive Temperature Co efficient) 611. When the internal pressure of the battery rises beyond a predetermined threshold value, the safety valve mechanism 612 cuts off the electrical connection between the positive electrode cap 601 and the positive electrode 604. Also, the PTC element 611 is a thermosensitive resistance element whose resistance increases when the temperature rises. By increasing the resistance, the electric current is limited to prevent abnormal heat generation. For the PTC element, barium titanate (BaTiO )-based semi 3 conductive ceramics or the like can be used.

[0233] Also, as shown in Fig. 13(C), a module 615 may be formed by sandwiching a plurality of secondary batteries 600 between a conductive plate 613 and a conductive plate 614. The plurality of secondary batteries 600 may be connected in parallel, may be connected in series, or may be connected in parallel first and then further connected in series. By forming a module 615 having a plurality of secondary batteries 600, a large amount of power can be extracted.

[0234] Fig. 13(D) is a top view of the module 615. For clarity, the conductive plate 613 is shown by a dotted line. As shown in Fig. 13(D), the module 615 may have a conducting wire 616 for electrically connecting a plurality of secondary batteries 600. A conductive plate can be superimposed and provided on the conducting wire 616. Also, a temperature control device 617 may be provided between the plurality of secondary batteries 600. When the secondary battery 600 is overheated, it can be cooled by the temperature control device 617, and when the secondary battery 600 is too cold, it can be heated by the temperature control device 617. Therefore ​​The performance of module 615 is less affected by the outside air temperature. The heat medium of the temperature control device 617 preferably has insulation and incombustibility.

[0235] By using the positive electrode active material described in the previous embodiment for the positive electrode 604, a cylindrical secondary battery 600 with high capacity and excellent cycle characteristics can be obtained.

[0236] [Structural example of secondary battery] Another structural example of the secondary battery will be described with reference to FIGS. 14 to 18.

[0237] FIGS. 14(A) and 14(B) are views showing the external appearance of the secondary battery. The secondary battery 913 is connected to an antenna 914 and an antenna 915 via a circuit board 900. Also, a label 910 is attached to the secondary battery 913. Further, as shown in FIG. 14(B), the secondary battery 913 is connected to a terminal 951 and a terminal 952.

[0238] The circuit board 900 has a terminal 911 and a circuit 912. The terminal 911 is connected to the terminal 951, the terminal 952, the antenna 914, the antenna 915, and the circuit 912. Note that a plurality of terminals 911 may be provided, and each of the plurality of terminals 911 may be used as a control signal input terminal, a power supply terminal, etc.

[0239] The circuit 912 may be provided on the back surface of the circuit board 900. Note that the antenna 914 and the antenna 915 are not limited to a coil shape, and may be, for example, linear or plate-shaped. Also, a planar antenna, an aperture antenna, a traveling wave antenna, an EH antenna, a magnetic field antenna, a dielectric antenna, or other antennas may be used. Alternatively, the antenna 914 or the antenna 915 may be , it may be a flat conductor. This flat conductor functions as one of the conductors for electric field coupling. It can be. That is, as one of the two conductors of the capacitor, antenna 914 or antenna 915 may be made to function. Thereby, power can be exchanged not only by electromagnetic fields and magnetic fields but also by an electric field.

[0240] The line width of antenna 914 is preferably larger than the line width of antenna 915. Thereby, the amount of power received by antenna 914 can be increased.

[0241] The secondary battery has a layer 916 between antenna 914 and antenna 915 and the secondary battery 913. Layer 916 has a function of, for example, shielding the electromagnetic field generated by secondary battery 913. As layer 916, for example, a magnetic material can be used.

[0242] Note that the structure of the secondary battery is not limited to that shown in FIG. 14.

[0243] For example, as shown in FIGS. 15(A-1) and 15(A-2), antennas may be provided on each of a pair of opposing surfaces of the secondary battery 913 shown in FIGS. 14(A) and 14 (B). FIG. 15(A-1) is an external view showing one of the pair of surfaces, and FIG. 15(A-2 ) is an external view showing the other of the pair of surfaces. Note that, for the same parts as those of the secondary battery shown in FIGS. 14(A) and 14(B), the description of the secondary battery shown in FIGS. 14(A) and 14(B) can be appropriately incorporated. As shown in FIG. 15(A-1), antenna 914 is provided with layer 916 sandwiched between one of a pair of surfaces of secondary battery 913, and as shown in FIG. 15(A-2), one of a pair of surfaces of secondary battery 913

[0244] As shown in FIG. 15(A-1), antenna 914 is provided with layer 916 sandwiched between one of a pair of surfaces of secondary battery 913, and as shown in FIG. 15(A-2), one of a pair of surfaces of secondary battery 913 is provided with layer 916 sandwiched between and antenna 914 is provided. As shown in FIG. 15(A-2), one of a pair of surfaces of secondary battery 913 The antenna 918 is provided with the layer 917 interposed therebetween. The layer 917 has a function of being able to shield the electromagnetic field by, for example, the secondary battery 91 3. As the layer 917, for example, a magnetic material can be used.

[0245] By adopting the above structure, the sizes of both the antenna 914 and the antenna 918 can be increased . The antenna 918 has a function of, for example, performing data communication with an external device . As the antenna 918, for example, an antenna having a shape applicable to the antenna 914 can be applied . As the communication method between the secondary battery and another device via the antenna 918 , a response method such as NFC (Near Field Communication) that can be used between the secondary battery and another device can be applied .

[0246] Alternatively, as shown in FIG. 15(B-1), a display device 920 may be provided on the secondary battery 9 13 shown in FIGS. 14(A) and 14(B). The display device 920 is electrically connected to the terminal 911 . Note that a label 910 may not be provided at the portion where the display device 920 is provided. Note that, for the same portions as the secondary battery shown in FIGS. 14(A) and 14(B), the description of the secondary battery shown in FIGS. 14(A) and 14(B) can be appropriately incorporated.

[0247] The display device 920 may display, for example, an image indicating whether it is being charged, an image indicating the remaining battery level, etc . As the display device 920, for example, an electronic paper, a liquid crystal display device, an electroluminescence (also referred to as EL) display device, etc. can be used . For example, by using an electronic paper, the power consumption of the display device 920 can be reduced .

[0248] Alternatively, as shown in Fig. 15(B-2), a sensor 921 may be provided in the secondary battery 9 shown in Figs. 14(A) and 14(B). The sensor 921 is electrically connected to the terminal 911 via the terminal 922. Note that for the same parts as the secondary battery shown in Figs. 14(A) and 14(B), the description of the secondary battery shown in Figs. 14(A) and 14(B) can be appropriately incorporated by reference. For the same parts as the secondary battery shown in Figs. 14(A) and 14(B), the description of the secondary battery shown in Figs. 14(A) and 14(B) can be appropriately incorporated by reference. For the same parts as the secondary battery shown in Figs. 14(A) and 14(B), the description of the secondary battery shown in Figs. 14(A) and 14(B) can be appropriately incorporated by reference.

[0249] The sensor 921 may have a function of measuring, for example, displacement, position, velocity, acceleration, angular velocity, rotation speed, distance, light, liquid, magnetism, temperature, chemical substance, sound, time, hardness, electric field, current, voltage, power, radiation, flow rate, humidity, gradient, vibration, odor, or infrared rays. The sensor 921 may have a function of measuring, for example, displacement, position, velocity, acceleration, angular velocity, rotation speed, distance, light, liquid, magnetism, temperature, chemical substance, sound, time, hardness, electric field, current, voltage, power, radiation, flow rate, humidity, gradient, vibration, odor, or infrared rays. The sensor 921 may have a function of measuring, for example, displacement, position, velocity, acceleration, angular velocity, rotation speed, distance, light, liquid, magnetism, temperature, chemical substance, sound, time, hardness, electric field, current, voltage, power, radiation, flow rate, humidity, gradient, vibration, odor, or infrared rays. By providing the sensor 921, for example, data indicating the environment where the secondary battery is placed (such as temperature) can be detected and stored in the memory in the circuit 912. By providing the sensor 921, for example, data indicating the environment where the secondary battery is placed (such as temperature) can be detected and stored in the memory in the circuit 912.

[0250] Furthermore, a structural example of the secondary battery 913 will be described with reference to Figs. 16 and 17.

[0251] The secondary battery 913 shown in Fig. 16(A) has a wound body 950 in which a terminal 951 and a terminal 952 are provided inside a housing 930. The wound body 950 is impregnated with an electrolytic solution inside the housing 930. The terminal 952 is in contact with the housing 930, and the terminal 951 is not in contact with the housing 930 by using an insulating material or the like. In Fig. 16(A), for the sake of convenience, the housing 930 is shown separately, but actually, the wound body 950 is covered by the housing 930, and the terminals 951 and 952 extend outside the housing 930. As the housing 930, a metal material (such as aluminum) or a resin material can be used. The wound body 950 is impregnated with an electrolytic solution inside the housing 930. The terminal 952 is in contact with the housing 930, and the terminal 951 is not in contact with the housing 930 by using an insulating material or the like. In Fig. 16(A), for the sake of convenience, the housing 930 is shown separately, but actually, the wound body 950 is covered by the housing 930, and the terminals 951 and 952 extend outside the housing 930. As the housing 930, a metal material (such as aluminum) or a resin material can be used. The wound body 950 is impregnated with an electrolytic solution inside the housing 930. The terminal 952 is in contact with the housing 930, and the terminal 951 is not in contact with the housing 930 by using an insulating material or the like. In Fig. 16(A), for the sake of convenience, the housing 930 is shown separately, but actually, the wound body 950 is covered by the housing 930, and the terminals 951 and 952 extend outside the housing 930. As the housing 930, a metal material (such as aluminum) or a resin material can be used. The wound body 950 is impregnated with an electrolytic solution inside the housing 930. The terminal 952 is in contact with the housing 930, and the terminal 951 is not in contact with the housing 930 by using an insulating material or the like. In Fig. 16(A), for the sake of convenience, the housing 930 is shown separately, but actually, the wound body 950 is covered by the housing 930, and the terminals 951 and 952 extend outside the housing 930. As the housing 930, a metal material (such as aluminum) or a resin material can be used. The wound body 950 is impregnated with an electrolytic solution inside the housing 930. The terminal 952 is in contact with the housing 930, and the terminal 951 is not in contact with the housing 930 by using an insulating material or the like. In Fig. 16(A), for the sake of convenience, the housing 930 is shown separately, but actually, the wound body 950 is covered by the housing 930, and the terminals 951 and 952 extend outside the housing 930. As the housing 930, a metal material (such as aluminum) or a resin material can be used. The wound body 950 is impregnated with an electrolytic solution inside the housing 930. The terminal 952 is in contact with the housing 930, and the terminal 951 is not in contact with the housing 930 by using an insulating material or the like. In Fig. 16(A), for the sake of convenience, the housing 930 is shown separately, but actually, the wound body 950 is covered by the housing 930, and the terminals 951 and 952 extend outside the housing 930. As the housing 930, a metal material (such as aluminum) or a resin material can be used. The wound body 950 is impregnated with an electrolytic solution inside the housing 930. The terminal 952 is in contact with the housing 930, and the terminal 951 is not in contact with the housing 930 by using an insulating material or the like. In Fig. 16(A), for the sake of convenience, the housing 930 is shown separately, but actually, the wound body 950 is covered by the housing 930, and the terminals 951 and 952 extend outside the housing 930. As the housing 930, a metal material (such as aluminum) or a resin material can be used.

[0252] Note that, as shown in FIG. 16(B), the housing 930 shown in FIG. 16(A) may be formed of a plurality of materials. For example, in the secondary battery 913 shown in FIG. 16(B), a housing 930a and a housing 9 30b are bonded together, and a wound body 9 50 is provided in a region surrounded by the housing 930a and the housing 930b.

[0253] As the housing 930a, an insulating material such as an organic resin can be used. In particular, by using a material such as an organic resin on the surface where the antenna is formed, shielding of the electric field by the secondary battery 913 can be suppressed. If the shielding of the electric field by the housing 930a is small, an antenna such as an antenna 914 or an antenna 915 may be provided inside the housing 930a. As the housing 930b, for example, a metal material can be used. Furthermore, the structure of the wound body 950 is shown in FIG. 17. The wound body 950 has a negative electrode 931, a positive electrode 932, and a separator 933. The wound body 950 is a wound body in which the negative electrode 931 and the positive electrode 932 overlap and are laminated with the separator 933 interposed therebetween, and the laminated sheet is wound. Note that the lamination of the negative electrode 931, the positive electrode 932, and the separator 933 may be further laminated

[0254] in multiple layers. The negative electrode 931 is connected to the terminal 911 shown in FIG. 14 via one of the terminals 951 and 952. The positive electrode 932 is connected to the terminal 91 1 shown in FIG. 14 via the other of the terminals 951 and 952. By using the positive electrode active material described in the previous embodiment for the positive electrode 932, a secondary battery 913 with high capacity and excellent cycle characteristics can be obtained.

[0255] characteristics can be obtained. 1 shown in FIG. 14 via the other of the terminals 951 and 952. 1 shown in FIG. 14 via the other of the terminals 951 and 952.

[0256] By using the positive electrode active material described in the previous embodiment for the positive electrode 932, a secondary battery 913 with high capacity and excellent cycle characteristics can be obtained.

[0257] [Laminated secondary battery] Next, an example of a laminated secondary battery will be described with reference to FIGS. 18 to 24. La If the laminated secondary battery has a flexible configuration, when it is mounted on an electronic device that also has at least a part of a flexible portion, the secondary battery can also be bent in accordance with the deformation of the electronic device. It can be done.

[0258] The laminated secondary battery 980 will be described with reference to FIG. 18. The laminated secondary battery 980 has a wound body 993 shown in FIG. 18(A). The wound body 993 includes a negative electrode 994 , a positive electrode 995, and a separator 996. Similar to the wound body 950 described with reference to FIG. 17, the wound body 993 is formed by laminating the negative electrode 994 and the positive electrode 995 with the separator 996 interposed therebetween, and then winding the laminated sheet. It is.

[0259] Note that the number of laminations of the laminate composed of the negative electrode 994, the positive electrode 995, and the separator 996 may be appropriately designed according to the required capacity and the element volume. The negative electrode 994 is connected to a negative electrode current collector (not shown) through one of the lead electrodes 997 and the lead electrode 998, and the positive electrode 995 is connected to a positive electrode current collector (not shown) through the other of the lead electrode 997 and the lead electrode 998.

[0260] As shown in FIG. 18(B), the wound body 993 described above is housed in a space formed by thermocompression bonding or the like a film 981 serving as an exterior body and a film 98 2 having a concave portion, whereby the secondary battery 980 can be manufactured as shown in FIG. 18(C). The wound body 99 3 has lead electrodes 997 and 998 and is impregnated with an electrolytic solution inside the film 981 and the film 98 2 having a concave portion.

[0261] The film 981 and the film 982 having a concave portion can be made of a metal material such as aluminum or a resin material. If a resin material is used as the material of the film 981 and the film 982 having a concave portion, when a force is applied from the outside, the film 981 and the film 982 having a concave portion can be deformed, and a flexible storage battery can be manufactured .

[0262] In addition, FIGS. 18(B) and 18(C) show an example using two films, but a space may be formed by bending a single film, and the above-described winding body 99 3 may be housed in the space

[0263] By using the positive electrode active material described in the previous embodiment for the positive electrode 995, a secondary battery 980 with high capacity and excellent cycle characteristics can be obtained

[0264] In addition, in FIG. 18, an example of a secondary battery 9 80 having a winding body in a space formed by a film serving as an exterior body has been described. However, for example, as shown in FIG. 19, a secondary battery having a plurality of strip-shaped positive electrodes, separators, and negative electrodes in a space formed by a film serving as an exterior body may also be used

[0265] The laminated secondary battery 500 shown in FIG. 19(A) includes a positive electrode 503 having a positive electrode current collector 501 and a positive electrode active material layer 502, and a negative electrode having a negative electrode current collector 504 and a negative electrode active material layer 505 506, a separator 507, an electrolytic solution 508, and an exterior body 509. A separator 507 is installed between the positive electrode 503 and the negative electrode 506 provided in the exterior body 509 . Further, the interior of the exterior body 509 is filled with the electrolytic solution 508. The electrolytic solution 508 contains, for example ​​​​ The electrolytic solution shown in Embodiment 2 can be used.

[0266] In the laminated secondary battery 500 shown in Fig. 19(A), the positive electrode current collector 501 and the negative electrode current collector 504 also serve as terminals for obtaining electrical contact with the outside. Therefore, a part of the positive electrode current collector 501 and the negative electrode current collector 504 may be arranged to be exposed to the outside from the exterior body 509. Alternatively, the positive electrode current collector 501 and the negative electrode current collector 504 may not be exposed to the outside from the exterior body 509, and the lead electrode may be ultrasonically bonded to the lead electrode and the positive electrode current collector 501 or the negative electrode current collector 504 so that the lead electrode is exposed to the outside.

[0267] In the laminated secondary battery 500, the exterior body 509 may be provided with a flexible metal thin film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, polyamide, etc. on a film, and further, an insulating synthetic resin film such as a polyamide-based resin or a polyester-based resin may be provided as the outer surface of the exterior body on the metal thin film. A three-layer laminated film can be used.

[0268] Further, an example of the cross-sectional structure of the laminated secondary battery 500 is shown in Fig. 19(B). In Fig. 19( A), for simplicity, an example composed of two current collectors is shown, but actually, as shown in Fig. 19(B), it is composed of a plurality of electrode layers.

[0269] In Fig. 19(B), as an example, the number of electrode layers is 16. Even if the number of electrode layers is 16, the secondary battery 500 has flexibility. In Fig. 19(B), the negative electrode current collector 504 has 8 layers, and The positive current collector 501 has a structure of a total of 16 layers in 8 layers. Note that Fig. 19(B) shows the cross-section of the extraction part of the negative electrode, and the 8-layer negative current collector 504 is ultrasonically joined. Of course, the number of electrode layers is not limited to 16, and it may be more or less. When the number of electrode layers is large, a secondary battery with a larger capacity can be obtained. Also, when the number of electrode layers is small, a thin and highly flexible secondary battery can be obtained. Here, an example of the external view of the laminate type secondary battery 500 is shown in Figs. 20 and 21. Figs. 2

[0270] 0 and 21 have a positive electrode 503, a negative electrode 506, a separator 507, an exterior body 509, a positive electrode lead electrode 510, and a negative electrode lead electrode 511.

[0271] Fig. 22(A) shows the external views of the positive electrode 503 and the negative electrode 506. The positive electrode 503 has a positive current collector 50 1, and the positive electrode active material layer 502 is formed on the surface of the positive current collector 501. Also, the positive electrode 503 has a region where the positive current collector 501 is partially exposed (hereinafter referred to as the tab region). The negative electrode 506 has a negative current collector 504, and the negative electrode active material layer 505 is formed on the surface of the negative current collector 504 and the negative electrode 506 has a region where the negative current collector 504 is partially exposed, that is, the tab region . The area and shape of the tab regions of the positive and negative electrodes are not limited to the examples shown in Fig. 22(A).

[0272] [Manufacturing method of laminate type secondary battery] Here, an example of the manufacturing method of the laminate type secondary battery whose external view is shown in Fig. 20 will be described with reference to Figs. 22 (B) and (C).

[0273] First, the negative electrode 506, the separator 507, and the positive electrode 503 are laminated. Fig. 22(B) shows the laminated ​​The resulting negative electrode 506, separator 507, and positive electrode 503 are shown. Here, an example is shown in which five sets of negative electrodes and four sets of positive electrodes are used. Next, the tabs of the positive electrode 503 are joined together, and the positive electrode lead electrode 510 is joined to the tab region of the outermost positive electrode. For the joining, for example, ultrasonic welding or the like can be used. Similarly, the tabs of the negative electrode 506 are joined together, and the negative electrode lead electrode 511 is joined to the tab region of the outermost negative electrode.

[0274] Next, the negative electrode 506, separator 507, and positive electrode 503 are arranged on the exterior body 509.

[0275] Next, as shown in FIG. 22(C), the exterior body 509 is bent at the portion indicated by the dashed line. Then, the outer peripheral portion of the exterior body 509 is joined. For the joining, for example, thermocompression bonding or the like can be used. At this time, a region that is not joined (hereinafter referred to as an introduction port) is provided in a part (or one side) of the exterior body 509 so that the electrolytic solution 508 can be put in later.

[0276] Next, the electrolytic solution 508 (not shown) is introduced into the interior of the exterior body 509 through the introduction port provided in the exterior body 509. The introduction of the electrolytic solution 508 is preferably performed under a reduced-pressure atmosphere or an inert atmosphere. And finally, the introduction port is joined. In this way, the laminated-type secondary battery 500 can be manufactured. By using the positive electrode active material described in the previous embodiment for the positive electrode 503, a secondary battery 500 with high capacity and excellent cycle

[0277] characteristics can be obtained.

[0278] [Bendable Secondary Battery] Next, an example of a bendable secondary battery will be described with reference to FIGS. 23 and 24. ​​​​

[0279] Figure 23(A) shows a schematic top view of a bendable secondary battery 250. Figures 23(B1 ), (B2), and (C) are schematic cross-sectional views taken along the cut lines C1-C2, C3- C4, and A1-A2 in Figure 23(A), respectively. The secondary battery 250 includes an exterior body 251 and , and has a positive electrode 211a and a negative electrode 211b housed inside the exterior body 251. A lead 212a electrically connected to the positive electrode 21 1a and a lead 212b electrically connected to the negative electrode 211b extend outside the exterior body 251. Also, an electrolytic solution (not shown) is enclosed in the region surrounded by the exterior body 251 .

[0280] The positive electrode 211a and the negative electrode 211b of the secondary battery 250 will be described with reference to Figure 24 . Figure 24(A) is a perspective view for explaining the stacking order of the positive electrode 211a, the negative electrode 211b, and the separator 214 . Figure 24(B) is a perspective view showing the leads 212a and 212b in addition to the positive electrode 211a and the negative electrode 211b .

[0281] As shown in Figure 24(A), the secondary battery 250 has a plurality of strip-shaped positive electrodes 211a, a plurality of strip-shaped negative electrodes 211b, and a plurality of separators 214. The positive electrode 211a and the negative electrode 2 11b each have a protruding tab portion and a portion other than the tab. A positive electrode active material layer is formed on the portion other than the tab on one surface of the positive electrode 211a, and a negative electrode active material layer is formed on the portion other than the tab on one surface of the negative electrode 211b .

[0282] The surfaces of the positive electrode 211a where the positive electrode active material layer is not formed, and the negative electrode active materials of the negative electrode 211b ​​​The positive electrode 211a and the negative electrode 211b are stacked so that the unformed surfaces contact each other. are stacked.

[0283] Also, a separator 214 is provided between the surface on which the positive electrode active material of the positive electrode 211a is formed and the surface on which the negative electrode active material of the negative electrode 211b is formed. In FIG. 24, the separator 214 is shown by a dotted line for easy viewing. is shown by a dotted line for easy viewing.

[0284] Also, as shown in FIG. 24(B), the plurality of positive electrodes 211a and the lead 212a are electrically connected at the joint portion 215 a. Also, the plurality of negative electrodes 211b and the lead 212b are electrically connected at the joint portion 2 15b.

[0285] Next, the exterior body 251 will be described with reference to FIGS. 23(B1), (B2), (C), and (D). will be described.

[0286] The exterior body 251 has a film-like shape and is bent into two parts so as to sandwich the positive electrode 211a and the negative electrode 211b. The exterior body 251 has a bent portion 261, a pair of seal portions 2 62, and a seal portion 263. The pair of seal portions 262 are provided sandwiching the positive electrode 211a and the negative electrode 211b and can also be called side seals. Also, the seal portion 26 3 has a portion overlapping with the leads 212a and 212b and can also be called a top seal. 3 has a portion overlapping with the leads 212a and 212b and can also be called a top seal. can be called.

[0287] The exterior body 251 preferably has a wavy shape in which ridge lines 271 and valley lines 2 72 are alternately arranged in the portion overlapping with the positive electrode 211a and the negative electrode 211b. Also, the seal portions 26 2 and 263 of the exterior body 251 are preferably flat.

[0288] FIG. 23(B1) is a cross section taken along a portion overlapping the ridge line 271, and FIG. 23(B2) is a cross section taken along a portion overlapping the valley line 272. Both FIGS. 23(B1) and (B2) correspond to cross sections in the width direction of the secondary battery 250, the positive electrode 211a, and the negative electrode 211b.

[0289] Here, the distance between the end portions in the width direction of the positive electrode 211a and the negative electrode 211b, that is, the end portions of the positive electrode 211a and the negative electrode 211b, and the seal portion 262 is defined as distance La. When the secondary battery 250 is deformed such as being bent, as will be described later, the positive electrode 211a and the negative electrode 211b are deformed so as to shift from each other in the longitudinal direction. At this time, if the distance La is too short, the exterior body 251 and the positive electrode 211a and the negative electrode 211b may strongly rub against each other, and the exterior body 251 may be damaged. In particular, when the metal film of the exterior body 251 is exposed, the metal film may be corroded by the electrolytic solution. Therefore, it is preferable to set the distance La as long as possible. On the other hand, if the distance La is made too large, the volume of the secondary battery 250 will increase.

[0290] Also, the thicker the total thickness of the stacked positive electrode 211a and negative electrode 211b, the more preferably the distance La between the positive electrode 211 a and the negative electrode 211b and the seal portion 262 is increased.

[0291] More specifically, when the total thickness of the stacked positive electrode 211a, negative electrode 211b, and a separator 214 (not shown) is defined as t, the distance La is 0.8 times or more and 3.0 times or less, preferably 0.9 times or more and 2.5 times or less, more preferably 1.0 times or more and 2.0 times or less of the thickness t. By setting the distance La within this range, the battery is compact and resistant to bending. ​​A highly reliable battery can be realized.

[0292] Further, when the distance between the pair of seal portions 262 is defined as distance Lb, distance Lb is made sufficiently larger than the widths of the positive electrode 211a and the negative electrode 211b (here, the width Wb of the negative electrode 211b). This is preferable. Thereby, when the secondary battery 250 is repeatedly deformed such as being bent, even if the positive electrode 211a and the negative electrode 211b come into contact with the exterior body 251, a part of the positive electrode 211a and the negative electrode 211b can be displaced in the width direction, so that it is possible to effectively prevent the positive electrode 211a and the negative electrode 211b from rubbing against the exterior body 251.

[0293] For example, the difference between the distance Lb between the pair of seal portions 262 and the width Wb of the negative electrode 211b is 1.6 times or more and 6.0 times or less, preferably 1.8 times or more and 5.0 times or less, more preferably 2.0 times or more and 4.0 times or less of the thickness t of the positive electrode 211a and the negative electrode 211b. It is preferable that this is satisfied.

[0294] In other words, it is preferable that the distance Lb, the width Wb, and the thickness t satisfy the relationship of the following formula 1.

[0295]

Equation

[0296] Here, a satisfies 0.8 or more and 3.0 or less, preferably 0.9 or more and 2.5 or less, more preferably 1.0 or more and 2.0 or less.

[0297] Further, FIG. 23(C) is a cross section including the lead 212a and corresponds to a cross section in the longitudinal direction of the secondary battery 250, the positive electrode 211a and the negative electrode 211b. As shown in FIG. 23(C), when bent ​​In the portion 261, it is preferable to have a space 273 between the longitudinal end portions of the positive electrode 211a and the negative electrode 211b and the exterior body 251. Preferably, there is a space 273 between the longitudinal end portions of the positive electrode 211a and the negative electrode 211b and the exterior body 251.

[0298] FIG. 23(D) shows a schematic cross-sectional view when the secondary battery 250 is bent. FIG. 23(D) corresponds to the cross-section along the cutting line B1 - B2 in FIG. 23(A).

[0299] When the secondary battery 250 is bent, a part of the exterior body 251 located on the outer side of the bend extends, and another part located on the inner side is deformed so as to contract. More specifically, the part located on the outer side of the exterior body 251 is deformed such that the amplitude of the wave is small and the period of the wave is large. On the other hand, the part located on the inner side of the exterior body 2 51 is deformed such that the amplitude of the wave is large and the period of the wave is small. Thus, when the exterior body 251 is deformed, the stress applied to the exterior body 251 due to the bending is relaxed, so that the material itself constituting the exterior body 251 does not need to expand and contract. As a result, the secondary battery 250 can be bent with a small force without the exterior body 251 being damaged. As a result, the secondary battery 250 can be bent with a small force without the exterior body 251 being damaged.

[0300] Also, as shown in FIG. 23(D), when the secondary battery 250 is bent, the positive electrode 211a and the negative electrode 211b are relatively displaced from each other. At this time, since one end on the seal portion 263 side of the plurality of stacked positive electrodes 211a and negative electrodes 211b is fixed by the fixing member 217, they are displaced such that the amount of displacement increases as they get closer to the folding bending portion 261. As a result, the stress applied to the positive electrode 211a and the negative electrode 211b is relaxed, and the positive electrode 211a and the negative electrode 211b themselves do not need to expand and contract. As a result, the secondary battery 250 can be bent without the positive electrode 211a and the negative electrode 211b being damaged. ​​

[0301] Also, there is a space 273 between the positive electrode 211a, the negative electrode 211b, and the exterior body 251. As a result, the positive electrode 211a and the negative electrode 211b located on the inner side when bent can shift relative to each other without contacting the exterior body 251.

[0302] The secondary battery 250 illustrated in FIGS. 23 and 24 is a battery in which damage to the exterior body, damage to the positive electrode 211a and the negative electrode 211b, etc. are less likely to occur even when repeatedly bent and stretched, and the battery characteristics are also less likely to deteriorate. By using the positive electrode active material described in the previous embodiment for the positive electrode 211a included in the secondary battery 250, a battery with even better cycle characteristics can be obtained.

[0303] (Embodiment 4) In this embodiment, an example of mounting a secondary battery, which is one aspect of the present invention, on an electronic device will be described.

[0304] First, examples of mounting a bendable secondary battery, which was partially described in Embodiment 3, on an electronic device are shown in FIGS. 25(A) to 25(G). Examples of electronic devices to which a bendable secondary battery is applied include, for example, a television device (also referred to as a TV or a television receiver), a monitor for a computer, a digital camera, a digital video camera, a digital photo frame, a mobile phone (also referred to as a cellular phone or a mobile phone device), a portable game machine, a portable information terminal, an audio playback device, a large game machine such as a pachinko machine, and the like.

[0305] Also, it is possible to incorporate a secondary battery having a flexible shape along the inner wall or outer wall of a house or building, or along the curved surface of the interior or exterior of an automobile.

[0306] Figure 25(A) shows an example of a mobile phone. The mobile phone 7400 includes a housing 7401 In addition to the display unit 7402 incorporated therein, operation buttons 7403, an external connection port 7404, a speaker 7405, a microphone 7406, and the like. The mobile phone 7400 has a secondary battery 7407. By using the secondary battery of one aspect of the present invention for the above secondary battery 7407, a lightweight and long-life mobile phone can be provided.

[0307] Figure 25(B) shows a state in which the mobile phone 7400 is bent. When the mobile phone 740 0 is deformed by an external force and the whole is bent, the secondary battery 7407 provided inside thereof is also bent. Also, at that time, the state of the bent secondary battery 7407 is shown in Figure 25(C ). The secondary battery 7407 is a thin battery. The secondary battery 7407 is fixed in a bent state . The secondary battery 7407 has a lead electrode electrically connected to a current collector. For example, the current collector is a copper foil, which is alloyed with a part of gallium to improve the adhesion to the active material layer in contact with the current collector, and has a high reliability structure in a state where the secondary battery 7407 is bent. composition.

[0308] Figure 25(D) shows an example of a bangle-type display device. The portable display device 7100 includes a housing 7101, a display unit 7102, operation buttons 7103, and a secondary battery 7104. Also, Figure 25(E) shows the state of the bent secondary battery 7104. When the secondary battery 7104 is bent and worn on the user's arm, the housing deforms and part or all of the curvature of the secondary battery 7104 changes. Note that the degree of bending at an arbitrary point on the curve is represented by the value of the radius of the corresponding circle, which is called the radius of curvature, and the reciprocal of the radius of curvature is called the curvature. Specifically, the radius of curvature is as described above, and the curvature is the reciprocal of the radius of curvature. is called the curvature radius, and the reciprocal of the curvature radius is called the curvature. Specifically, the curvature radius is within the range of 40 mm or more and 150 mm or less, a part or all of the main surface of the housing or the secondary battery 7104 changes. If the radius of curvature on the main surface of the secondary battery 7104 is within the range of 40 mm or more and 150 mm or less, high reliability can be maintained. By using the secondary battery of one aspect of the present invention in the secondary battery 7104, a lightweight and long-life portable display device can be provided.

[0309] FIG. 25(F) shows an example of a wristwatch-type portable information terminal. The portable information terminal 7200 includes a housing 7201, a display unit 7202, a band 7203, a buckle 7204, operation buttons 72 05, input / output terminals 7206, and the like.

[0310] The portable information terminal 7200 can execute various applications such as mobile phones, e-mails, text viewing and creation, music playback, Internet communication, computer games, and the like.

[0311] The display surface of the display unit 7202 is provided in a curved shape, and display can be performed along the curved display surface. Further, the display unit 7202 includes a touch sensor and can be operated by touching the screen with a finger, a stylus, or the like. For example, an application can be launched by touching the icon 72 07 displayed on the display unit 7202.

[0312] In addition to time setting, the operation buttons 7205 can perform various functions such as power on / off operations, wireless communication on / off operations, execution and cancellation of the silent mode, and execution and cancellation of the power saving mode. For example, the functions of the operation buttons 7205 can be freely set by an operating system incorporated in the portable information terminal 7200.

[0313] ​​​​​​​ In addition, the mobile information terminal 7200 is capable of performing short-range wireless communication that complies with a communication standard. For example, it can communicate with a wireless headset to make a hands-free call.

[0314] The mobile information terminal 7200 is also provided with an input / output terminal 7206, and can directly exchange data with other information terminals via a connector. It can also be charged via the input / output terminal 7206. Note that the charging operation may also be performed by wireless power supply without going through the input / output terminal 7206.

[0315] The display unit 7202 of the mobile information terminal 7200 has a secondary battery according to one aspect of the present invention. By using the secondary battery according to one aspect of the present invention, a lightweight and long-life mobile information terminal can be provided. For example, the secondary battery 7104 shown in Fig. 25(E) can be incorporated inside the housing 7201 in a curved state or in a state where it can be curved inside the band 7203.

[0316] The mobile information terminal 7200 preferably has a sensor. Examples of the sensor include human body sensors such as a fingerprint sensor, a pulse sensor, and a body temperature sensor, and a touch sensor, a pressure sensor, an acceleration sensor, etc. It is preferable that these sensors are mounted.

[0317] Fig. 25(G) shows an example of a bracelet-type display device. The display device 7300 has a display unit 7304 and has a secondary battery according to one aspect of the present invention. In addition, the display device 7300 can also be provided with a touch sensor on the display unit 7304, and can also function as a mobile information terminal.

[0318] ​​​​​​​​​​The display unit 7304 has a curved display surface and can perform display along the curved display surface. In addition, the display device 7300 can change the display state by means of communication-standardized short-range wireless communication or the like.

[0319] Moreover, the display device 7300 is provided with input / output terminals and can directly perform data exchange with other information terminals via a connector. Charging can also be performed via the input / output terminals. Note that the charging operation may be performed by wireless power supply without passing through the input / output terminals.

[0320] By using the secondary battery of one aspect of the present invention as the secondary battery of the display device 7300, a lightweight and long-life display device can be provided.

[0321] In addition, an example of mounting the secondary battery with good cycle characteristics shown in the previous embodiment on an electronic device will be described with reference to FIGS. 25(H), 26, and 27.

[0322] By using the secondary battery of one aspect of the present invention as the secondary battery of a consumer electronic device, a lightweight and long-life product can be provided. For example, as consumer electronic devices, there are electric toothbrushes, electric shavers, electric beauty devices, etc. As the secondary batteries for these products, considering the ease of use by the user, a secondary battery with a stick shape, small size, light weight, and large capacity is desired.

[0323] FIG. 25(H) is a perspective view of a device also called a tobacco-containing smoking device (electronic cigarette). In FIG. 25(H), the electronic cigarette 7500 includes an atomizer 7501 including a heating element, a secondary battery 7504 that supplies power to the atomizer, and a cartridge 7502 including a liquid supply bottle, a sensor, etc. To enhance safety, overcharging and over-discharging of the secondary battery 7504 ​ A protection circuit for preventing discharge may be electrically connected to the secondary battery 7504. As shown in FIG. 25(H), the secondary battery 7504 has external terminals so that it can be connected to a charging device. Since the secondary battery 7 504 forms the tip portion when possessed, it is desirable that the total length is short and the weight is light. Since the secondary battery according to one aspect of the present invention has a high capacity and good cycle characteristics, it can provide a small and lightweight electronic cigarette 7500 that can be used for a long time over a long period.

[0324] Next, FIGS. 26(A) and 26(B) show an example of a foldable tablet terminal. The tablet terminal 9600 shown in FIGS. 26(A) and 26(B) includes a housing 9630 a, a housing 9630b, a movable part 9640 connecting the housing 9630a and the housing 9630b, a display unit 9631 having a display unit 9631a and a display unit 9631b, switches 9625 to 9627, a fastener 9629, and an operation switch 9628. By using a flexible panel for the display unit 9631, it is possible to obtain a tablet terminal having a wider display unit. FIG. 26(A) shows the tablet terminal 9600 in an open state, and FIG. 26( B) shows the tablet terminal 9600 in a closed state.

[0325] Further, the tablet terminal 9600 has a power storage body 9635 inside the housing 9630a and the housing 9630b. The power storage body 9635 is provided through the movable part 9640 across the housing 9630a and the housing 9630b.

[0326] The display unit 9631 can have all or part of the area as a touch panel area, and also when ​Data can be input by touching an icon, character, input form, etc. displayed in this area. For example, keyboard buttons can be displayed on the entire surface of the display unit 9631a on the housing 9630a side, and information such as characters and images can be displayed and used on the display unit 9631b on the housing 9630b side. This may be used.

[0327] Alternatively, a keyboard can be displayed on the display unit 9631b on the housing 9630b side, and information such as characters and images can be displayed and used on the display unit 9631a on the housing 9630a side. Also, a keyboard display switch button for the touch panel can be displayed on the display unit 9631, and by touching the button with a finger, a stylus, etc., a keyboard can be displayed on the display unit 9631. This may be done.

[0328] Also, touch input can be simultaneously performed on the touch panel area of the display unit 9631a on the housing 9630a side and the touch panel area of the display unit 9631b on the housing 9630b side.

[0329] Also, the switches 9625 to 9627 may be interfaces not only for operating the tablet terminal 9600 but also for switching various functions. For example, at least one of the switches 9625 to 9627 may function as a switch for turning on / off the power of the tablet terminal 9600. Also, for example, at least one of the switches 9625 to 9627 may have a function of switching the display orientation, such as vertical or horizontal display, or a function of switching between black and white display and color display. Also, for example, at least one of the switches 9625 to 9627 may have a function of switching the display orientation, such as vertical or horizontal display, or a function of switching between black and white display and color display. Also, for example, at least one of the switches 9625 to 9627 may have a function of switching the display At least one of them may have a function of adjusting the brightness of the display unit 9631. Also, the brightness of the display unit 963 1 can be made optimal according to the amount of external light detected by the optical sensor built into the tablet-type terminal 9600 during use. Note that the tablet-type terminal may incorporate not only an optical sensor but also other detection devices such as sensors for detecting inclination, such as a gyroscope and an acceleration sensor.

[0330] Also, in FIG. 26(A), an example is shown in which the display areas of the display unit 9631a on the housing 9630a side and the display unit 9631b on the housing 9630b side are substantially the same. However, the respective display areas of the display unit 9631a and the display unit 9 631b are not particularly limited, and the size of one may be different from that of the other, and the display quality may also be different. For example, one may be a display panel capable of performing higher-definition display than the other.

[0331] FIG. 26(B) shows a state in which the tablet-type terminal 9600 is closed in a two-fold manner. The tablet-type terminal 9600 includes a charging / discharging control circuit 9634 including a housing 9630, a solar cell 9633, and a DCDC converter 9636. Also, as the power storage body 9635, a power storage body according to one aspect of the present invention is used.

[0332] As described above, since the tablet-type terminal 9600 can be folded in two, the housing 9630a and the housing 9630b can be folded so as to overlap each other when not in use. By folding, the display unit 9631 can be protected, so the durability of the tablet-type terminal 9600 can be enhanced. Also, since the power storage body 9635 using the secondary battery according to one aspect of the present invention has a high capacity and good cycle characteristics, it can be used for a long time over a long period. ​​​​​​​​​​​​​The T-shaped terminal 9600 can be provided.

[0333] In addition, the tablet terminal 9600 shown in FIGS. 26(A) and 26(B) can have functions such as displaying various information (still images, moving images, text images, etc.), a calendar, a date or a time, etc. on a display unit, a touch input function for touching and inputting or editing the information displayed on the display unit, a function of controlling processing by various software (programs), etc.

[0334] Power can be supplied to a touch panel, a display unit, a video signal processing unit, etc. by a solar cell 9633 mounted on the surface of the tablet terminal 9600. Note that the solar cell 963 3 can be provided on one or both sides of the housing 9630, and can be configured to efficiently charge the power storage body 9635. As the power storage body 9635, using a lithium ion battery has advantages such as being able to achieve miniaturization.

[0335] Also, the configuration and operation of the charge / discharge control circuit 9634 shown in FIG. 26(B) will be described with reference to the block diagram in FIG. 26( C). FIG. 26(C) shows a solar cell 9633, a power storage body 963 5, a DCDC converter 9636, a converter 9637, switches SW1 to SW3, and a display unit 9631. The power storage body 9635, the DCDC converter 9636, the converter 9637, and the switches SW1 to SW3 correspond to the parts of the charge / discharge control circuit 96 34 shown in FIG. 26(B).

[0336] First, an example of the operation when power is generated by the solar cell 9633 by external light will be described. The power generated by the solar cell becomes a voltage for charging the power storage body 9635 by the DCDC co​​​​ Voltage boosting or bucking is performed by the converter 9636. When the operation of the display unit 9631 uses the power from the solar cell 9633, the switch SW1 is turned on, and the converter 9637 boosts or bucks the voltage to the voltage required for the display unit 9631. When the display unit 9631 is not displaying, SW1 can be turned off and SW2 can be turned on to charge the power storage body 9635. This is the configuration that should be adopted.

[0337] Note that the solar cell 9633 is shown as an example of the power generation means, but it is not particularly limited, and other power generation means such as piezoelectric elements (piezo elements) and thermoelectric conversion elements (Peltier elements) may be used to charge the power storage body 9635. For example, a contactless power transmission module that wirelessly (non-contact) transmits and receives power for charging, or a configuration that combines other charging means may be adopted. to charge, or a configuration that combines other charging means may be adopted. This is the configuration that should be adopted.

[0338] Fig. 27 shows an example of another electronic device. In Fig. 27, the display device 8000 is an example of an electronic device using the secondary battery 8004 according to one aspect of the present invention. Specifically, the display device 800 0 corresponds to a display device for receiving TV broadcasts, and includes a housing 8001, a display unit 8002, a speaker unit 8003, a secondary battery 8004, etc. The secondary battery 8004 according to one aspect of the present invention is provided inside the housing 8001. The display device 8000 can be supplied with power from a commercial power supply, or can use the power stored in the secondary battery 8004. Therefore even when power supply from a commercial power supply cannot be received due to a power outage or the like, the display device 8000 can be used by using the secondary battery 8004 according to one aspect of the present invention as an uninterruptible power supply. As a result, even when power supply from a commercial power supply cannot be received due to a power outage or the like, the display device 8000 can be used by using the secondary battery 8004 according to one aspect of the present invention as an uninterruptible power supply.

[0339] The display unit 8002 includes a light-emitting device such as a liquid crystal display device or an organic EL element provided in each pixel. Devices, electrophoretic display devices, DMD (Digital Micromirror Devi ce), PDP (Plasma Display Panel), FED (Field Emission Display), etc., and a semiconductor display device can be used.

[0340] In addition to being used for receiving TV broadcasts, the display device also includes display devices for personal computers, advertising displays, etc. All display devices for information display are included.

[0341] In FIG. 27, the installed lighting device 8100 is an example of an electronic device using the secondary battery 81 03 according to one aspect of the present invention. Specifically, the lighting device 8100 includes a housing 8101, a light source 8102, a secondary battery 8103, etc. In FIG. 27, the case where the secondary battery 8103 is provided inside the ceiling 81 01 and the light source 8102 are installed is illustrated However, the secondary battery 8103 may be provided inside the housing 8101. The lighting device 8100 can receive power supply from a commercial power source, or can use the power stored in the secondary battery 8103. Therefore, even when the power supply from the commercial power source cannot be received due to a power outage or the like, by using the secondary battery 8103 according to one aspect of the present invention as an uninterruptible power supply, the lighting device 8100 can be used. In FIG. 27, the installed lighting device 8100 provided on the ceiling 8104 is illustrated

[0342] However, the secondary battery according to one aspect of the present invention can also be used for installed lighting devices provided on walls other than the ceiling 8104, such as side walls 8105, floors 8 106, windows 8107, etc., or for desktop lighting devices. It can also be used for lighting devices of the like.

[0343] In addition, as the light source 8102, an artificial light source that artificially obtains light using electric power can be used. Specifically, incandescent bulbs, discharge lamps such as fluorescent lamps, and light-emitting elements such as LEDs and organic EL elements can be cited as examples of the above artificial light sources.

[0344] In FIG. 27, an air conditioner having an indoor unit 8200 and an outdoor unit 8204 is an example of an electronic device using a secondary battery 8203 according to an aspect of the present invention. Specifically, the indoor unit 8200 has a housing 8201, an air outlet 8202, a secondary battery 8203, etc. FIG. 27 illustrates the case where the secondary battery 8203 is provided in the indoor unit 8200, but the secondary battery 8203 may be provided in the outdoor unit 8204. Alternatively, the secondary battery 8203 may be provided in both the indoor unit 8200 and the outdoor unit 8204. The air conditioner can receive power supply from a commercial power source or use the power stored in the secondary battery 8203. In particular, when the secondary battery 8203 is provided in both the indoor unit 8200 and the outdoor unit 8204, even when power supply from the commercial power source cannot be received due to a power outage or the like, by using the secondary battery 8203 according to an aspect of the present invention as an uninterruptible power supply, the air conditioner can be used.

[0345] Note that in FIG. 27, a separate type of air conditioner composed of an indoor unit and an outdoor unit is illustrated, but a secondary battery according to an aspect of the present invention can also be used for an integrated type of air conditioner having the functions of the indoor unit and the outdoor unit in one housing.

[0346] ​​​​​​​​​​​​​In FIG. 27, an electric refrigerator-freezer 8300 includes a secondary battery 8304 according to one embodiment of the present invention. Specifically, an electric refrigerator-freezer 8300 includes a housing 8301, a refrigerator It has a storage compartment door 8302, a freezer compartment door 8303, a secondary battery 8304, etc. A secondary battery 8304 is provided inside the housing 8301. The electric refrigerator-freezer 8300 is It can receive power from a commercial power source, or use the power stored in the secondary battery 8304. Therefore, when power cannot be supplied from commercial power sources due to a power outage, etc. However, by using the secondary battery 8304 according to one embodiment of the present invention as an uninterruptible power supply, It will be possible to use the 8300 freezer refrigerator.

[0347] Among the above-mentioned electronic devices, high-frequency heating devices such as microwave ovens, electric rice cookers, etc. The equipment requires high power for a short period of time. Therefore, the equipment supplements the power that cannot be supplied by commercial power sources. By using a secondary battery according to one embodiment of the present invention as an auxiliary power source for It can prevent the commercial power breaker from tripping during use.

[0348] In addition, during periods when electronic devices are not in use, especially during periods when the total amount of power that can be supplied by commercial power suppliers is low, During times when the ratio of electricity actually used (called the electricity usage rate) is low, By storing power in the battery, it is possible to prevent high power usage outside of the above time periods. For example, in the case of the electric refrigerator-freezer 8300, when the temperature is low, the refrigerator compartment door 830 2. During the night when the freezer door 8303 is not opened or closed, the secondary battery 8304 stores electricity. Then, as the temperature rises, the refrigerator door 8302 and the freezer door 8303 are opened and closed. During the daytime, by using the secondary battery 8304 as an auxiliary power source, the daytime power utilization rate can be kept low.

[0349] According to one aspect of the present invention, the cycle characteristics of the secondary battery can be improved, and the reliability can be enhanced. Moreover, according to one aspect of the present invention, a high-capacity secondary battery can be achieved, thus the characteristics of the secondary battery can be improved, and therefore the secondary battery itself can be made smaller and lighter. Therefore, by mounting the secondary battery, which is one aspect of the present invention, on the electronic device described in this embodiment, an electronic device with a longer lifespan and lighter weight can be obtained. This embodiment can be implemented in appropriate combination with other embodiments.

[0350] (Embodiment 5) In this embodiment, an example of mounting the secondary battery, which is one aspect of the present invention, on a vehicle is shown.

[0351] When the secondary battery is mounted on a vehicle, next-generation clean energy vehicles such as hybrid electric vehicles (HEVs), electric vehicles (EVs), or plug-in hybrid electric vehicles (PHEVs) can be realized. .

[0352] In FIG. 28, a vehicle using the secondary battery, which is one aspect of the present invention, is illustrated. FIG. 28(A) shows an automobile 8400 that is an electric vehicle using an electric motor as a power source for driving. Alternatively, it is a hybrid vehicle that can appropriately select and use an electric motor and an engine as power sources for driving. By using one aspect of the present invention, a vehicle with a long cruising range can be realized. Moreover, the automobile 8400 has a secondary battery. The secondary battery is, with respect to the floor portion inside the vehicle, the module of the secondary battery shown in FIGS. 13(C) and 13(D). They may be arranged and used. Also, a battery pack obtained by combining a plurality of secondary batteries shown in FIG. 16 may be installed with respect to the floor portion inside the vehicle. The secondary battery not only drives the electric motor 8406 but can also supply power to a light-emitting device such as a headlight 8401 or a room light (not shown).

[0353] Also, the secondary battery can supply power to display devices such as a speedometer and a tachometer that the automobile 8400 has. Also, the secondary battery can supply power to semiconductor devices such as a navigation system that the automobile 8400 has.

[0354] The automobile 8500 shown in FIG. 28(B) can be charged by receiving power supply from an external charging facility by a plug-in method, a non-contact power supply method, or the like, to the secondary battery that the automobile 8500 has. FIG. 28(B) shows a state in which charging is being performed from a ground-installed charging device 8021 to a secondary battery 8024 mounted on an automobile 8500 via a cable 8022. When charging, the charging method, the connector specifications, etc. may be appropriately performed in a predetermined method such as CHAdeMO (registered trademark) or Combo. The charging device 8021 may be a charging station provided in a commercial facility or may also be a household power supply. For example, by plug-in technology, the secondary battery 8024 mounted on the automobile 8500 can be charged by external power supply. Charging can be performed by converting AC power into DC power via a conversion device such as an AC / DC converter.

[0355] Also, although not shown, a power receiving device may be mounted on the vehicle and charged by non-contact power supply from a power transmission device on the ground. In the case of this non-contact power supply method, a power transmission device is installed on a road or an outer wall.​​​​​​ By sucking in, charging can be performed not only while the vehicle is stationary but also while it is in motion. Also, using this non-contact power supply method, power can be transmitted and received between vehicles. Furthermore, a solar cell may be provided on the exterior of the vehicle to charge the secondary battery when the vehicle is stationary or in motion. For such non-contact power supply, an electromagnetic induction method or a magnetic field resonance method can be used.

[0356] Also, FIG. 28(C) is an example of a two-wheeled vehicle using the secondary battery of one aspect of the present invention. FIG. 28 (C) shows a scooter 8600 including a secondary battery 8602, a side mirror 8601, and a turn signal light 8603. The secondary battery 8602 can supply electricity to the turn signal light 8603.

[0357] Also, the scooter 8600 shown in FIG. 28(C) can store the secondary battery 860 2 in the under-seat storage 8604. The secondary battery 8602 can be stored in the under-seat storage 8604 even if the under-seat storage 8604 is small. The secondary battery 8602 is removable. When charging, the secondary battery 8602 can be carried indoors, charged, and stored before driving.

[0358] According to one aspect of the present invention, the cycle characteristics of the secondary battery are improved, and the capacity of the secondary battery can be increased. Therefore, the secondary battery itself can be made smaller and lighter. If the secondary battery itself can be made smaller and lighter, it contributes to the weight reduction of the vehicle, so the cruising range can be improved. Also, the secondary battery mounted on the vehicle can be used as a power supply other than the vehicle. In this case, for example, it is possible to avoid using a commercial power supply during peak power demand. If it is possible to avoid using commercial power during peak electricity demand, it can contribute to energy conservation and reduction of carbon dioxide emissions. Also, if the cycle characteristics are good, secondary batteries can be used over a long period, thus reducing the usage amount of rare metals such as cobalt.

[0359] This embodiment can be implemented in appropriate combination with other embodiments.

Example

[0360] In this example, a positive electrode active material which is one aspect of the present invention and a positive electrode active material of a comparative example were prepared, and their characteristics were analyzed using XPS, SEM, and XRD. Also, the cycle characteristics in high-voltage charging were evaluated.

[0361] [Preparation of Positive Electrode Active Material] ≪Sample 1≫ In Sample 1, a positive electrode active material having cobalt as a transition metal was prepared by the preparation method shown in FIG. 2 of Embodiment 1. First, LiF and MgF were weighed so that the molar ratio of LiF:MgF = 1:3, and acetone was added as a solvent, followed by wet mixing and pulverization. The mixing and pulverization were performed using a ball mill with zirconia balls at 150 rpm for 1 hour. The processed material was recovered to obtain a first mixture (Steps S11 to S14 in FIG. 2). 2 2

[0362] The particle size distributions of LiF and MgF before mixing and the first mixture after mixing are shown in FIG. 29. The measurement of the particle size distribution was performed using a laser diffraction particle size distribution measuring device SALD-2200 (Shimadzu Corporation). 2 It was carried out by (manufacturing). The D50 of the first mixture was 3.561 μm and the mode diameter was 4.008 μm From FIG. 29 and these results, it was confirmed that the first mixture was sufficiently pulverized to be.

[0363] In Sample 1, as the pre-synthesized lithium cobaltate, Celsid C-10N manufactured by Nippon Chemical Industry Co., Ltd. was used (Step S25 in FIG. 2). Celsid C-10N is lithium cobaltate with a D50 of about 12 μm and few impurities, as described in Embodiment 1 .

[0364] Next, with respect to the molecular weight of lithium cobaltate, the amount of magnesium atoms in the first mixture was weighed to be 0.5 atomic% and mixed dry. The mixing was carried out using a ball mill with zirconia balls at 150 rpm for 1 hour. The processed material was recovered to obtain a second mixture (Steps S31 to S33 in FIG. 2).

[0365] Next, the second mixture was placed in an alumina crucible and annealed in a muffle furnace in an oxygen atmosphere at 850 °C for 60 hours. During annealing, the alumina crucible was covered. The oxygen flow rate was 10 L / min. The temperature was raised at 200 °C / hr and the temperature was lowered over 10 hours or more. The heat-treated material was used as the positive electrode active material of Sample 1 (Steps S34 and S35 in FIG. 2 ).

[0366] ≪Sample 2≫ A product manufactured in the same manner as Sample 1 except that the annealing time was 2 hours in Step S34 of FIG. 2 was designated as Sample 2 (comparative example).

[0367] ≪Sample 3≫​​​ A sample was prepared in the same manner as Sample 1, except that annealing was not performed in step S34 of FIG. 2. This sample was designated as Sample 3 (comparative example).

[0368] ≪Sample 4≫ Cobalt lithium oxide (Cellseed C-10N) without any particular treatment (steps S31 to S35 in FIG. 2 are not performed) was designated as Sample 4 (comparative example).

[0369] ≪Sample 5≫ In Sample 5, Cellseed C-5H manufactured by Nippon Chemical Industry Co., Ltd. was used as the pre-synthesized cobalt lithium oxide (step S25 in FIG. 2). Also, annealing was performed at 900 °C for 2 hours in step S34 of FIG. 2. Other conditions were the same as those for Sample 1.

[0370] ≪Sample 6≫ Cobalt lithium oxide (Cellseed C-5H) without any particular treatment (steps S31 to S35 are not performed) was designated as Sample 6 (comparative example).

[0371] ≪Sample 7≫ In Sample 7, a magnesium source and a fluorine source were added to the starting materials of cobalt lithium oxide and fired to synthesize cobalt lithium oxide containing magnesium and fluorine. Then, annealing was performed.

[0372] Specifically, lithium carbonate was used as the lithium source, cobalt oxide as the cobalt source, magnesium oxide as the magnesium source, and lithium fluoride as the fluorine source, with an atomic ratio of Li Co 0.99 Mg 0.01 O 1.98 F0.02 Weighed so as to obtain the following, and mixed in a ball mill Thereafter.

[0373] Next, the mixture was put into an alumina crucible, covered, and fired in a muffle furnace in a dry air atmosphere at 95 0 °C for 10 hours. The flow rate of dry air was 10 L / min. The temperature was raised at 200 °C / h r, and the temperature was lowered over 10 hours or more. The material after the heat treatment was made into lithium cobaltate containing magnesium and fluorine Thereafter.

[0374] Next, the lithium cobaltate containing magnesium and fluorine was put into an alumina crucible, covered Thereafter, and annealed in a muffle furnace in an oxygen atmosphere at 800 °C for 2 hours. The flow rate of oxygen was 10 L / min. The temperature was raised at 200 °C / hr, and the temperature was lowered over 10 hours or more. The material after the heat treatment Thereafter was designated as Sample 7.

[0375] ≪Sample 8≫ Commercially available lithium cobaltate (Nippon Chemical Industry Co., Ltd.'s Celsiode C-20F) containing magnesium and fluorine in advance was put into an alumina crucible, covered, and annealed in a muffle furnace in an oxygen atmosphere at 800 °C for 2 hours. The flow rate of oxygen was 10 L / min. The temperature was raised at 2 00 °C / hr, and the temperature was lowered over 10 hours or more. The material after the heat treatment was designated as Sample 8 Thereafter. Thereafter. Thereafter.

[0376] ≪Sample 9≫ Lithium cobaltate (Nippon Chemical Industry Co., Ltd.'s Celsiode C-20F) containing magnesium and fluorine without any particular treatment (without performing Steps S31 to S35) was designated as Sample 9 (comparative example). Thereafter. Thereafter.

[0377] <Sample 10> In sample 10, the lithium cobalt oxide was synthesized using Aldrich Co. Lithium barium oxide (catalog No. 442704, D50 is about 11 μm) was used (Figure 2, step S25). Also, in step S34 of FIG. 2, annealing is performed at 850° C. for 20 The other conditions were the same as for Sample 1.

[0378] <<Sample 11>> Lithium cobalt oxide without any special treatment (without steps S31 to S35) The resulting mixture was used as Sample 11 (Comparative Example) (Aldrich Co., No. 442704).

[0379] <Sample 12> Sample 12 (comparison example) is a pre-synthesized lithium cobalt oxide (LiCO3) manufactured by Nippon Kayaku Co., Ltd. CellSeed C-5hV (D50 is about 6 μm) manufactured by Gakushu Kogyo Co., Ltd. was used (step S2 in FIG. 2). 5) This is lithium cobalt oxide containing about 5100 ppm wt of titanium as an impurity. In step S34 of FIG. 2, annealing was performed at 800° C. for 2 hours. The conditions for preparation were the same as for Sample 1.

[0380] <<Sample 13>> Sample 13 (comparative example) was annealed at 850° C. and 6 The sample was prepared in the same manner as Sample 12, except that the time was 0 hours.

[0381] <<Sample 14>> Lithium cobalt oxide without any special treatment (without steps S31 to S35) The sintered body (Cellseed C-5hV manufactured by Nippon Chemical Industry Co., Ltd.) was used as Sample 14 (Comparative Example).

[0382] ≪Sample 15≫ In Sample 15 (comparative example), a layer containing aluminum was formed on the surface of pre-synthesized lithium cobaltate (Cellseed C-5H manufactured by Nippon Chemical Industry Co., Ltd.) by the sol-gel method, and then annealed at 500 °C for 2 hours. Specifically, aluminum isopropoxide and 2-propanol were mixed, and lithium cobaltate (C-5H) was added thereto. At this time, the weight of aluminum isopropoxide relative to lithium cobaltate was set to be 0.0092 times. This mixture was stirred in a constant temperature bath with a relative humidity of 90% for 8 hours to react H₂O in the atmosphere with aluminum isopropoxide to form a layer containing aluminum on the surface of lithium cobaltate. Then, it was recovered by filtration and dried under reduced pressure at 70 °C for 1 hour. The lithium cobaltate with a layer of aluminum formed on its surface, which was dried above, was placed in an alumina crucible, covered, and annealed. The annealing was carried out at 500 °C (heating rate 200 °C / hour), holding time 2 hours, and oxygen flow rate 10 L / min. Then, it was cooled to room temperature over 10 hours or more and 15 hours or less, and the recovered product was designated as Sample 15.

[0383] Specifically, aluminum isopropoxide and 2-propanol were mixed, and lithium cobaltate (C-5H) was added thereto. At this time, the weight of aluminum isopropoxide relative to lithium cobaltate was set to be 0.0092 times. This mixture was stirred in a constant temperature bath with a relative humidity of 90% for 8 hours to react H₂O in the atmosphere with aluminum isopropoxide to form a layer containing aluminum on the surface of lithium cobaltate. Then, it was recovered by filtration and dried under reduced pressure at 70 °C for 1 hour. Specifically, aluminum isopropoxide and 2-propanol were mixed, and lithium cobaltate (C-5H) was added thereto. At this time, the weight of aluminum isopropoxide relative to lithium cobaltate was set to be 0.0092 times. This mixture was stirred in a constant temperature bath with a relative humidity of 90% for 8 hours to react H₂O in the atmosphere with aluminum isopropoxide to form a layer containing aluminum on the surface of lithium cobaltate. Then, it was recovered by filtration and dried under reduced pressure at 70 °C for 1 hour. Specifically, aluminum isopropoxide and 2-propanol were mixed, and lithium cobaltate (C-5H) was added thereto. At this time, the weight of aluminum isopropoxide relative to lithium cobaltate was set to be 0.0092 times. This mixture was stirred in a constant temperature bath with a relative humidity of 90% for 8 hours to react H₂O in the atmosphere with aluminum isopropoxide to form a layer containing aluminum on the surface of lithium cobaltate. Then, it was recovered by filtration and dried under reduced pressure at 70 °C for 1 hour. Specifically, aluminum isopropoxide and 2-propanol were mixed, and lithium cobaltate (C-5H) was added thereto. At this time, the weight of aluminum isopropoxide relative to lithium cobaltate was set to be 0.0092 times. This mixture was stirred in a constant temperature bath with a relative humidity of 90% for 8 hours to react H₂O in the atmosphere with aluminum isopropoxide to form a layer containing aluminum on the surface of lithium cobaltate. Then, it was recovered by filtration and dried under reduced pressure at 70 °C for 1 hour. 2 Specifically, aluminum isopropoxide and 2-propanol were mixed, and lithium cobaltate (C-5H) was added thereto. At this time, the weight of aluminum isopropoxide relative to lithium cobaltate was set to be 0.0092 times. This mixture was stirred in a constant temperature bath with a relative humidity of 90% for 8 hours to react H₂O in the atmosphere with aluminum isopropoxide to form a layer containing aluminum on the surface of lithium cobaltate. Then, it was recovered by filtration and dried under reduced pressure at 70 °C for 1 hour. Specifically, aluminum isopropoxide and 2-propanol were mixed, and lithium cobaltate (C-5H) was added thereto. At this time, the weight of aluminum isopropoxide relative to lithium cobaltate was set to be 0.0092 times. This mixture was stirred in a constant temperature bath with a relative humidity of 90% for 8 hours to react H₂O in the atmosphere with aluminum isopropoxide to form a layer containing aluminum on the surface of lithium cobaltate. Then, it was recovered by filtration and dried under reduced pressure at 70 °C for 1 hour. Specifically, aluminum isopropoxide and 2-propanol were mixed, and lithium cobaltate (C-5H) was added thereto. At this time, the weight of aluminum isopropoxide relative to lithium cobaltate was set to be 0.0092 times. This mixture was stirred in a constant temperature bath with a relative humidity of 90% for 8 hours to react H₂O in the atmosphere with aluminum isopropoxide to form a layer containing aluminum on the surface of lithium cobaltate. Then, it was recovered by filtration and dried under reduced pressure at 70 °C for 1 hour.

[0384] The lithium cobaltate with a layer of aluminum formed on its surface, which was dried above, was placed in an alumina crucible, covered, and annealed. The annealing was carried out at 500 °C (heating rate 200 °C / hour), holding time 2 hours, and oxygen flow rate 10 L / min. Then, it was cooled to room temperature over 10 hours or more and 15 hours or less, and the recovered product was designated as Sample 15. The lithium cobaltate with a layer of aluminum formed on its surface, which was dried above, was placed in an alumina crucible, covered, and annealed. The annealing was carried out at 500 °C (heating rate 200 °C / hour), holding time 2 hours, and oxygen flow rate 10 L / min. Then, it was cooled to room temperature over 10 hours or more and 15 hours or less, and the recovered product was designated as Sample 15. The lithium cobaltate with a layer of aluminum formed on its surface, which was dried above, was placed in an alumina crucible, covered, and annealed. The annealing was carried out at 500 °C (heating rate 200 °C / hour), holding time 2 hours, and oxygen flow rate 10 L / min. Then, it was cooled to room temperature over 10 hours or more and 15 hours or less, and the recovered product was designated as Sample 15. The lithium cobaltate with a layer of aluminum formed on its surface, which was dried above, was placed in an alumina crucible, covered, and annealed. The annealing was carried out at 500 °C (heating rate 200 °C / hour), holding time 2 hours, and oxygen flow rate 10 L / min. Then, it was cooled to room temperature over 10 hours or more and 15 hours or less, and the recovered product was designated as Sample 15.

[0385] The preparation conditions of Samples 1 to 15 are shown in Table 1.

[0386]

Table 1

[0387] [XPS] Surface XPS analysis was performed on Samples 1 to 4 prepared above. The main element concentrations (atomic %) are shown in Table 2.

[0388]

Table 2

[0389] A graph obtained by extracting data on magnesium and fluorine from Table 2 is shown in Fig. 30(A). In Sample 4 to which lithium fluoride and magnesium fluoride were not added, the concentrations of fluorine and magnesium were low. Also, in Sample 3 to which micronized lithium fluoride and magnesium fluoride were added but which was not annealed, the concentrations of fluorine and magnesium did not increase much. This is presumably because, due to the nature of surface XPS analysis, when fine particles 1002 containing a certain element adhere to particles 1001 not containing the certain element as shown in Fig. 30(B1), the certain element is less likely to be detected from the detection region 1010 than when there is a region 1003 containing the certain element with a large area as shown in Fig. 30(B2).

[0390] Also, in Sample 2 to which lithium fluoride and magnesium fluoride were added and annealed for 2 hours, the fluorine concentration increased significantly. Further, in Sample 1 to which lithium fluoride and magnesium fluoride were added and annealed

[0391] for 60 hours, the magnesium concentration also increased significantly. From a comparison between Sample 2 and Sample 1, it was speculated that when Furthermore, when the annealing time is prolonged, due to the presence of molten lithium fluoride, the melting point of magnesium fluoride (melting point: 1263 °C) decreases, and it is presumed that magnesium fluoride melts and distributes in the surface layer of lithium cobaltate particles.

[0392] Next, the region showing the bonding state of carbon in the narrow scan analysis of XPS is shown in Fig. 31. In sample 3 which was not annealed, the peak of CO 3 bonding was high. In contrast, in sample 2 annealed for 2 hours, the CO 3 bonding decreased, and in sample 1 annealed for 60 hours it further decreased. Since the CO 3 bonding in the surface layer of lithium cobaltate is likely lithium carbonate (Li 2 Co 3 ), it is considered that by performing annealing, the excess of lithium can be suppressed, and excellent lithium cobaltate can be produced.

[0393] [SEM] Next, the SEM images of samples 1 to 4 are shown in Fig. 32. Fig. 32(A1) is the SEM image of sample 1 , and Fig. 32(A2) is its enlarged view. Fig. 32(B1) is the SEM image of sample 2, and Fig. 32(B2) is its enlarged view. Fig. 32(C1) is the SEM image of sample 3, and Fig. 3 3(C2) is its enlarged view. Fig. 32(D1) is the SEM image of sample 4, and Fig. 32(D2 ) is its enlarged view.

[0394] Particularly, in sample 4 which is lithium cobaltate without any treatment, a large number of irregularities were observed on the surface. Also, in sample 3, it was observed that fine particles considered to be lithium fluoride and magnesium fluoride were attached.

[0395] ​​​​ On the other hand, the surfaces of the annealed Samples 2 and 1 were smooth and had less unevenness. Sample 1, which was annealed for a longer time than Sample 2, tended to have less unevenness.

[0396] [Fabrication of Secondary Battery] Next, using Samples 1, 2, 4 to 15 fabricated above, a coin-type secondary battery of CR2032 type (diameter 20 mm, height 3.2 mm) was fabricated.

[0397] As the positive electrode, a slurry obtained by mixing the positive electrode active material fabricated above, acetylene black (AB), and polyvinylidene fluoride (PVDF) at a weight ratio of positive electrode active material:AB:PVDF = 95:3:2 was applied to a current collector.

[0398] Lithium metal was used as the counter electrode.

[0399] As the electrolyte in the electrolytic solution, 1 mol / L lithium hexafluorophosphate (LiPF 6 ) was used. In the electrolytic solution, ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of EC:DEC = 3:7, and vinylene carbonate (VC) was mixed at 2 wt%.

[0400] Polypropylene with a thickness of 25 μm was used as the separator.

[0401] Stainless steel (SUS) was used for the positive electrode can and the negative electrode can.

[0402] The positive electrode of the secondary battery using Sample 7 was pressed at 210 kN. The positive electrodes of the secondary batteries using the other samples were not pressed.

[0403] [Calculating the lattice constant from the XRD before charging] For the positive electrodes of Samples 1, 4, 5 to 12, and 14 before charging, powder XRD analysis was performed using CuKα1 radiation. The XRD was measured in air, and the electrodes were attached to a glass plate to maintain flatness. The XRD apparatus was set up for powder samples, and the height of the samples was adjusted to the measurement surface required by the apparatus.

[0404] The obtained XRD patterns were subjected to background removal and Kα2 removal using DIFFRAC.EVA (XRD data analysis software manufactured by Bruker). As a result, signals derived from conductive aids, binders, and sealed containers were also removed. Thereafter, the lattice constant was calculated using TOPAS. At this time, optimization of atomic positions and the like was not performed, and only the lattice constant was fitted. The GOF (good of fitness), estimated

[0405] crystallite size, and the lattice constants of the a-axis and c-axis are shown in Table 3. The GOF (goodness of fit), estimated crystallite size, and the lattice constants of the a-axis and c-axis are shown in Table 3.

[0406]

Table 3

[0407] Samples 12 and 14 containing about 5100 ppm wt of titanium as an impurity tended to have a larger c-axis than the others.

[0408] [XRD after the first charge] The secondary batteries using Samples 1, 2, 7, and 9 were charged by CCCV at 4.6 V. Specifically, after constant current charging at 0.5 C up to 4.6 V, when the current value reached 0. It was charged at a constant voltage until it reached 01C. Here, 1C was taken as 137 mA / g. Then, the charged secondary battery was disassembled in a glove box under an argon atmosphere to take out the positive electrode, and it was washed with DMC (dimethyl carbonate) to remove the electrolyte. Then, it was sealed in a sealed container under an argon atmosphere, and XRD analysis was performed.

[0409] Figure 33 shows the XRD patterns of the positive electrodes of the secondary batteries using Sample 1, Sample 2, Sample 7, and Sample 9 after charging at 4.6 V. For comparison, the patterns of the pseudo-spinel crystal structure and the H1-3 type crystal structure are also shown together.

[0410] It was revealed that Samples 1 and 7 after charging at 4.6 V have a pseudo-spinel crystal structure. Also, compared to Sample 7 with a magnesium source and a fluorine source added as starting materials, Sample 1 with a magnesium source and a fluorine source mixed in lithium cobaltate has a sharper pattern and is presumed to have higher crystallinity.

[0411] On the other hand, it was revealed that Sample 2 with insufficient annealing and Sample 9 without annealing have an H1-3 type crystal structure after charging at 4.6 V. Also, the pattern of Sample 2 is clearly broader than that of Sample 1 and is presumed to have lower crystallinity.

[0412] [XRD after the first charge by depth of charge] Next, using the positive electrode active materials of Samples 1 and 2, XRD analysis of the charged state was performed on the secondary batteries charged with the charging voltage finely changed from 4.5 V to 4.65 V.

[0413] Figure 34 shows the positive electrode active material of Sample 1 at 4.5 V, 4.525 V, 4.55 V, 4. XRD patterns of the positive electrode after CCCV charging once at 575V, 4.6V, and 4.65V are shown. For comparison, the patterns of the spinel-like crystal structure, H1-3 type crystal structure, and Li 0.35 Co O 2 (charge depth 0.65) crystal structure (space group R-3m, O3) are shown together.

[0414] From Figure 34, it was revealed that the positive electrode active material of Sample 1 had the crystal structure of Li i 0.35 CoO 2 (O3) when charged at 4.5V and 4.525V.

[0415] Also, when charged at 4.55V, peaks of both the crystal structure of Li 0.35 CoO 2 (O3) and the spinel-like type crystal structure were observed, so it was speculated that these two crystal structures coexisted.

[0416] Also, when charged at 4.575V, peaks of the spinel-like crystal structure were observed.

[0417] Furthermore, when charged at 4.6V, in addition to the peaks of the spinel-like crystal structure, peaks of the slightly H 1-3 type crystal structure were observed, so it was speculated that these two crystal structures coexisted.

[0418] When charged at 4.65V, mainly peaks of the H1-3 type crystal structure were observed. Also, it was speculated that it became the main peak and the crystallinity decreased.

[0419] Thus, in the sufficiently annealed Sample 1, around the charging voltage of 4.55V, Li 0 .35 CoO 2 ​​​​The phase changes from the crystal structure of (O3) to a pseudo-spinel type crystal structure, and it was found that the pseudo-spinel type crystal structure was maintained up to a charging voltage of about 4 .6 V. The change to the H1-3 type crystal structure occurred at a charging voltage of about 4.65 V.

[0420] Fig. 35 shows the XRD patterns of the positive electrode after one CCCV charge at 4.5 V, 4.55 V, 4.6 V, or 4 .65 V using the positive electrode active material of Sample 2. For comparison, the crystal structure patterns of the pseudo-spinel type, H1-3 type, Li 0.35 CoO 2 (O3) when the crystal structure, and the pattern of the CoO (O1) type crystal structure are shown together. 2

[0421] From Fig. 35, it was revealed that the positive electrode active material of Sample 2 has the crystal structure of Li CoO 0.35 (O3) when charged at 4.5 V, similar to Sample 1. 2

[0422] However, when charged at 4.55 V, different from Sample 1, peaks of both the crystal structure of Li 0.35 CoO 2 (O3) and the H1-3 type crystal structure were observed.

[0423] Furthermore, when charged at 4.6 V, also different from Sample 1, mainly peaks of the H1-3 type crystal structure were observed.

[0424] Also, when charged at 4.65 V, peaks of the CoO 2 (O1) type crystal structure were observed together with the H1-3 type crystal structure. Also, it was speculated that the peaks became quite broad and the crystallinity decreased significantly.

[0425] Thus, in Sample 2 where annealing was insufficient, at around a charging voltage of 4.55 V, early also Li 0.35 CoO 2 (O3) crystal structure changed to the H1-3 type crystal structure.

[0426] As described in Embodiment 1, the H1-3 type crystal structure is a structure in which the CoO 2 layer is greatly displaced, and since the volume difference is also large, it is considered that the crystal structure collapses by repeating the change to the H1-3 type crystal structure. Therefore, when used in an actual product, it is necessary to determine the upper limit of the charging voltage so as not to change to the H1-3 type crystal structure. Therefore, for a positive electrode active material that changes to the H1-3 type crystal structure at around a charging voltage of 4.55 V like Sample 2,

[0427] the upper limit of the charging voltage is 4.55 V or less, for example, 4.5 V. On the other hand, for a positive electrode active material like Sample 1 that maintains the pseudo-spinel type crystal structure even at a charging voltage of 4.6 V,

[0428] the upper limit of the charging voltage can be set to 4.6 V. If the charging voltage can be increased, then the capacity per unit weight of the positive electrode active material can be increased, and a high-capacity secondary battery can be obtained.

[0429] [XRD after 10 charge-discharge cycles (discharged state)] Next, secondary batteries using Sample 1 and Sample 2 were charged and discharged 10 times at a high voltage. Specifically, charge and discharge in which CC discharge (2.5 V) is performed after CCCV charging (4.6 V) was repeated 10 times, and then the secondary battery in the discharged state was disassembled to take out the positive electrode, and XRD analysis was performed.

[0430] Fig. 36 shows the positive electrodes of the secondary batteries using Sample 1 and Sample 2 after being charged and discharged 10 times. The XRD patterns are shown. For comparison, the pattern of the ideal crystal structure of lithium cobaltate is also shown. It is also shown together.

[0431] The pattern of Sample 2, which has an insufficient annealing and takes on an H1-3 type crystal structure during high-voltage charging, is clearly broader and less crystalline than that of Sample 1, which is sufficiently annealed and takes on a spinel-like crystal structure during high-voltage charging. It was presumed that the crystallinity was low.

[0432] [XRD after 100 charge-discharge cycles (charged state)] Next, after the secondary batteries using Sample 1 and Sample 2 were subjected to CCCV charging (4.45 V) and then CC discharging (2.5 V) 100 times in repetition, they were charged at 4.6 V, and the secondary batteries in the charged state were disassembled to take out the positive electrodes and subjected to XRD analysis.

[0433] Fig. 37 shows the XRD patterns of the positive electrodes of the secondary batteries using Sample 1 and Sample 2 after 100 charge-discharge cycles and then charged at a high voltage. For comparison, the patterns of the spinel-like crystal structure and the H1-3 type crystal structure are also shown together.

[0434] As shown in Fig. 37, even after 100 cycles, the positive electrode active material of Sample 1 had a spinel-like crystal structure. When Rietveld analysis was performed, the proportion of the spinel-like crystal structure was 43.6 wt% and the proportion of the H1-3 type crystal structure was 56.4 wt%.

[0435] On the other hand, almost all of the positive electrode active material of Sample 2 had an H1-3 type crystal structure. Moreover, it was presumed that the peaks were quite broad and the crystallinity had significantly decreased.

[0436] [Cycle characteristics] ​​​​​Next, for the secondary batteries using Sample 1, Sample 2, Sample 4, Sample 5, Sample 7, Sample 10, the results of evaluating the cycle characteristics of Sample 12 and Sample 13 are shown in FIGS. 38 and 39. The secondary batteries evaluated here have a loading amount of the positive electrode active material layer of 7 mg / cm 2 or more and 8 mg / cm 2 or less.

[0437] FIG. 38 shows the results of measuring 50 cycles at 25°C for Sample 1, Sample 2, Sample 4, Sample 10, Sample 12 and Sa mple 13 with charging being CCCV (0.5C, 4.6V, termination current 0.0 1C) and discharging being CC (0.5C, 2.5V). FIG. 38(A) shows the discharge capacity and FIG. 38(B) shows the discharge capacity retention rate. In FIG. 38, 1C is the current value per unit weight of the positive electrode active material and is 137 mA / g.

[0438] Sample 1, which was annealed for 60 hours and had a pseudo-spinel crystal structure after high-voltage charging, showed extremely good cycle characteristics. The discharge capacity retention rate after 50 cycles was 96.1%.

[0439] On the other hand, Sample 4, which was not particularly treated, and Sample 2, which was annealed for 2 hours and had an H 1-3 type crystal structure after high-voltage charging, were significantly deteriorated. The discharge capacity retention rates after 50 cycles were both 60% or less.

[0440] Sample 10, which used lithium cobaltate synthesized in advance as Aldrich No. 442704 and was annealed after mixing with a magnesium source and a fluorine source, showed good cycle characteristics. The discharge capacity retention rate after 50 cycles was 79.8%.

[0441] On one hand, lithium cobaltate containing about 5100 ppm wt of titanium as an impurity was used. In the cases of Sample 12 and Sample 13, even though they were annealed after being mixed with a magnesium source and a fluorine source, the deterioration was significant. This was the same for both the short-annealing-time Sample 12 and the long-annealing-time Sample 13.

[0442] Fig. 39 shows the results of measurements at 45 °C for 100 cycles for Sample 1, Sample 5, and Sample 7. Fig. 39(A) shows the discharge capacity, and Fig. 39(B) shows the discharge capacity retention rate. In Fig. 39, 1C was set to 160 mA / g, which is the current value per unit weight of the positive electrode active material. The measurement conditions were as follows: charging was CCCV (1.0C, 4.55V, termination current 0.05C), and discharging was CC (1.0C, 3.0V).

[0443] When measured at 45 °C, Sample 1 also showed extremely good cycle characteristics. The discharge capacity retention rate after 100 cycles was 93.3%. Also, Sample 5, which was prepared in the same manner as Sample 1 except that lithium cobaltate with a small particle size was used and the annealing time was 2 hours, also showed extremely good cycle characteristics.

[0444] Furthermore, Sample 7, which was annealed after adding a magnesium source and a fluorine source to the starting material and firing, also showed good cycle characteristics.

[0445] Also, regarding Sample 1 and Sample 4, the results of evaluating the cycle characteristics by changing the loading amount of the positive electrode active material layer, the electrolyte, and the charging voltage are shown in Fig. 40 and Fig. 41.

[0446] All of the secondary batteries used for evaluation here had a loading of the positive electrode active material layer of 20 mg / cm 2 or more . Further, as the electrolytic solution, a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC ) in a volume ratio of EC:DEC = 3:7 and a mixture in which vinylene carbonate (VC) was further added at 2 wt% were used. The charging voltage was 4.5 V or 4.6 V

[0447] Fig. 40 shows the cycle characteristics of Sample 1 and Sample 4 using a mixture of EC:DEC = 3:7 (volume ratio) as the electrolytic solution. Fig. 40(A) shows the cycle characteristics when the charging voltage was 4.5 V , and Fig. 40(B) shows the cycle characteristics when the charging voltage was 4.6 V .

[0448] Fig. 41 also shows the cycle characteristics of Sample 1 and Sample 4 using a mixture in which vinylene carbonate (VC) was further added at 2 wt% to EC:DEC = 3:7 (volume ratio) as the electrolytic solution. Fig. 41(A) shows the cycle characteristics when the charging voltage was 4.5 V, and Fig. 41(B) shows the cycle characteristics when the charging voltage was 4. 6 V .

[0449] As is clear from Figs. 40 and 41, even when the loading of the positive electrode active material layer, the electrolytic solution, and the charging voltage were changed, Sample 1 showed extremely good cycle characteristics

[0450] From the above various analysis results, it became clear that the positive electrode active material having a pseudo-spinel type crystal structure when charged at a high voltage of 4.6 V showed extremely good cycle characteristics. Also , in order to take on a pseudo-spinel type crystal structure after high voltage charging, it was found to be effective to have magnesium and fluorine and to anneal at an appropriate temperature and time . It was also found that the appropriate annealing time varies depending on the particle size or composition of lithium cobaltate. It was speculated that they were different.

[0451] In addition, lithium cobaltate obtained by adding magnesium and fluorine to the starting material and firing it may be annealed, but it was found that it is more effective to mix magnesium and fluorine into lithium cobaltate with less impurities and then anneal. When annealed, it was found that it is more effective to mix magnesium and fluorine into lithium cobaltate with less impurities and then anneal. It was also found that when a magnesium source and a fluorine source are mixed and annealed using lithium cobaltate with a lattice constant of 14.060×10

[0452] m or less, a positive electrode active material showing good cycle characteristics tends to be obtained. From this, it was also considered that first, a composite oxide having a layered rock salt-type crystal structure with less substitution of different elements and spinel-type crystal structure Co -10 m O is produced, and then a magnesium source and a fluorine source are mixed to insert magnesium into the lithium position, whereby a positive electrode active material showing good cycle characteristics can be produced. It was also considered that a positive electrode active material showing good cycle characteristics can be produced. Therefore, first, a composite oxide having a layered rock salt-type crystal structure with less substitution of different elements and spinel-type crystal structure Co 3 O 4 is produced, and then a magnesium source and a fluorine source are mixed to insert magnesium into the lithium position, whereby a positive electrode active material showing good cycle characteristics can be produced. Next, regarding the rate characteristics of a secondary battery using Sample 1, which shows extremely good cycle characteristics as described above, and Sample 4, which is a comparative example in which a magnesium source and a fluorine source are not mixed, the results of the evaluation are shown in FIGS. 42 and 43. The coin cell for rate characteristic evaluation was prepared in the same manner as the coin cell for XRD measurement described above, except that the loading amount of the positive electrode active material layer was 20.8 mg / cm or more and 2

[0453] [Rate characteristics] Next, regarding the rate characteristics of a secondary battery using Sample 1, which shows extremely good cycle characteristics as described above, and Sample 4, which is a comparative example in which a magnesium source and a fluorine source are not mixed, the results of the evaluation are shown in FIGS. 42 and 43. Next, regarding the rate characteristics of a secondary battery using Sample 1, which shows extremely good cycle characteristics as described above, and Sample 4, which is a comparative example in which a magnesium source and a fluorine source are not mixed, the results of the evaluation are shown in FIGS. 42 and 43. The results of the evaluation of the rate characteristics are shown in FIGS. 42 and 43.

[0454] The coin cell for rate characteristic evaluation was prepared in the same manner as the coin cell for XRD measurement described above, except that the loading amount of the positive electrode active material layer was 20.8 mg / cm 2 or more and 2 1.0 mg / cm 2 or less. The initial charge was set to a maximum of 4.5 V or 4.6 V, and was performed with CCCV, 0.2C, 4.6 V, and a cut-off current of 0.05C. The initial discharge was performed with CC, 0.2C, and a cut-off voltage of 3.0 V. Here, 1C was defined as a current value of 200 mA / g per unit weight of the positive electrode active material. For subsequent charge and discharge cycles, only the discharge rate was changed, and measurements were taken in the order of 0.2C charge / 0.2C discharge, 0.2C charge / 0.5C discharge, 0.2C charge / 1.0C discharge, and 0.2C charge / 2.0C discharge. The measurement temperature was set to 25°C. Note that 1C here is defined as a current value of 200 mA / g per unit weight of the positive electrode active material. In the charge and discharge cycles after the first cycle, only the discharge rate was changed, and measurements were taken in the order of 0.2C charge / 0.2C discharge, 0.2C charge / 0.5C discharge, 0.2C charge / 1.0C discharge, and 0.2C charge / 2.0C discharge. The measurement temperature was 25°C. Figure 42(A) shows the discharge curves of Sample 1 at each rate when the charging voltage is 4.5 V, and Figure 42(B) shows the discharge curves of Sample 1 at each rate when the charging voltage is 4.6 V. Figure 43(A) shows the discharge curves of Sample 4 at each rate when the charging voltage is 4.5 V, and Figure 43(B) shows the discharge curves of Sample 4 at each rate when the charging voltage is 4.6 V.

[0455] As is clear from Figures 42 and 43, the secondary battery using Sample 1 showed better rate characteristics when charged at a high voltage compared to Sample 4, and this tendency became more prominent at higher rates. Also, in the secondary battery using Sample 1, it was revealed that there is a characteristic voltage change near the end of discharge during low-rate discharges such as 0.2C. Figure 42(A) shows the discharge curves of Sample 1 at each rate when the charging voltage is 4.5 V, and Figure 42(B) shows the discharge curves of Sample 1 at each rate when the charging voltage is 4.6 V. Figure 43(A) shows the discharge curves of Sample 4 at each rate when the charging voltage is 4.5 V, and Figure 43(B) shows the discharge curves of Sample 4 at each rate when the charging voltage is 4.6 V. As is clear from Figures 42 and 43, the secondary battery using Sample 1 showed better rate characteristics when charged at a high voltage compared to Sample 4, and this tendency became more prominent at higher rates.

[0456] Also, in the secondary battery using Sample 1, it was revealed that there is a characteristic voltage change near the end of discharge during low-rate discharges such as 0.2C. As is clear from Figures 42 and 43, the secondary battery using Sample 1 showed better rate characteristics when charged at a high voltage compared to Sample 4, and this tendency became more prominent at higher rates. Also, in the secondary battery using Sample 1, it was revealed that there is a characteristic voltage change near the end of discharge during low-rate discharges such as 0.2C.

[0457] As is clear from Figures 42 and 43, the secondary battery using Sample 1 showed better rate characteristics when charged at a high voltage compared to Sample 4, and this tendency became more prominent at higher rates. Also, in the secondary battery using Sample 1, it was revealed that there is a characteristic voltage change near the end of discharge during low-rate discharges such as 0.2C.

[0458] [Charge Curve and dQ / dV vs V Curve] Next, for the secondary battery using Sample 1, which is one aspect of the present invention, and Sample 15, which had an aluminum-containing layer formed on its surface and was annealed at 500°C for 2 hours, the results of comparing the charge curve and the dQ / dV vs V curve are shown. The measurement temperature was 25°C. The results of comparing the charge curve and the dQ / dV vs V curve are shown.

[0459] Secondary batteries using Sample 1 and Sample 15 were charged at 10 mAh / g up to 4.9 V at 25°C. The charging curves are shown in Figure 44. The solid line is sample 1 and the dashed line is sample 15. Two secondary batteries using each sample were measured.

[0460] The dQ / dV vs V curve, which shows the change in voltage relative to the charge capacity, was obtained from the data in Figure 44. The results are shown in Fig. 45. Fig. 45(A) shows the d for sample 1, and Fig. 45(B) shows the d for sample 15. This is the Q / dV vs V curve.

[0461] As is clear from Fig. 45(A) and Fig. 45(B), either Sample 1 or Sample 15 Even in this case, peaks were observed at voltages of approximately 4.06 V and 4.18 V. The change in capacity was nonlinear with the charge depth of 0.5. The space group P2 / m at a charge depth of 0.5 is shown in Figure 1. As shown in Figure 4, the lithium atoms are aligned. Energy is used to align the lithium atoms. It is believed that this causes the change in capacitance to become nonlinear with respect to voltage.

[0462] In addition, in the comparative sample 15, a large peak was observed at approximately 4.54V and 4.61V. Between these two peaks is the H1-3 phase type crystal structure. .

[0463] On the other hand, sample 1, which shows extremely good cycle characteristics, has a small peak at about 4.55 V. However, it was not clear. Therefore, dQ / d was obtained from more detailed measurement results. The VvsV curves are shown in Figures 46 and 47. Figure 47 is an expanded view of Figure 46.

[0464] As shown in Fig. 47, when measured in detail, peaks are observed at about 4.55 V and about 4.63 V. It is considered that the region between these two peaks has a pseudo-spinel crystal structure. Also, it is considered that the region between the peaks at about 4.63 V and about 4.64 V has an H1-3 crystal structure.

[0465] Thus, in the dQ / dV vs V curve of Sample 1, some peaks may be extremely broad or small. In such cases, it is possible that two crystal structures coexist. For example, it may be a two-phase coexistence of O3 and pseudo-spinel, or a two-phase coexistence of pseudo-spinel and H1-3, etc.

[0466] [Discharge curve and dQ / dV vs V curve] Next, the results of comparing the discharge curve and the dQ / dV vs V curve for the secondary battery using Sample 1, which is one aspect of the present invention, and Sample 4, which is a comparative example, are shown.

[0467] The discharge curve of Sample 1 is shown in Fig. 48(A), and the discharge curve of Sample 4 is shown in Fig. 48(B). In both cases, the discharge is after CCCV charging at 4.6 V. The discharge is performed by CC discharge until 2.5 V. The discharge rate is 0.05 C (1 C = 200 mA / g).

[0468] As shown in Fig. 48(A), in Sample 1, a characteristic voltage change was confirmed near the end of discharge (the portion surrounded by the broken line in the figure). This is the same as the voltage change observed in the low-rate discharge of Fig. 40.

[0469] The dQ / dV vs V curve representing the change amount of voltage with respect to the discharge capacity, obtained from the data of Fig. 48 is shown in FIG. 49. FIG. 49(A) is for Sample 1, and FIG. 49(B) is the dQ / dVv sV curve. To clearly draw the peaks, the graph in the region where the voltage is 3.5 V or higher was used.

[0470] As shown in FIG. 49(B), in Sample 4 where the magnesium source and the fluorine source were not mixed two large downward convex peaks were observed at about 4.37 V and about 3.87 V, and it became clear that there were two inflection points in the discharge curve of Sample 4.

[0471] On the other hand, as is clear from FIG. 49(A), more downward convex peaks were observed in Sample 1. The largest peak existed at about 3.9 V. Also, as indicated by the arrow in the figure at least one peak existed in the range from 3.5 V to 3.9 V. This arrow peak indicates the change in voltage of the portion surrounded by the broken line in FIG. 48(A).

[0472] Thus, as described with reference to FIGS. 40, 48, and 49, the positive electrode active material of Sample 1, which is one aspect of the present invention, after being charged at a high voltage and then discharged at a low rate of, for example, 0.2 C or less it became clear that a characteristic voltage change appears near the end of discharge. This change in the dQ / dV vs V curve can be clearly confirmed by the presence of at least one peak in the range from 3.5 V to 3.9 V.

Example

[0473] In this example, a positive electrode active material having cobalt and nickel as transition metals was prepared and analyzed for its characteristics using X RD.

[0474] [Preparation of Positive Electrode Active Material] ≪Sample 21 (Sample 21)≫​ As Sample 21, using the production method shown in FIG. 1 of Embodiment 1, the proportion of the number of nickel atoms (Ni) in the sum of the number of cobalt and nickel atoms (Co + Ni), Ni / (Co + Ni ) was 0.01, and a positive electrode active material was produced. )

[0475] First, in the same manner as Steps S11 to S14 of Embodiment 1 and Example 1, a first mixture with a molar ratio of LiF to MgF of LiF:MgF of 1:3 was prepared. 2 2 = 1:3 was prepared.

[0476] Next, as in Steps S21 and S22 of Embodiment 1, the raw materials were weighed and mixed so that the atomic ratio became Li:Ni:Co = 1:0.01:0.99 (Ni / (Co + Ni) = 0.01). Lithium carbonate was used as the lithium source, cobalt oxide was used as the cobalt source, and nickel hydroxide was used as the nickel source. The mixing was carried out wetly with acetone added at 300 rpm for 20 hours.

[0477] Next, as in Steps S23 to S25 of Embodiment 1, it was calcined in a muffle furnace in a dry air atmosphere at 900°C for 10 hours and then recovered to obtain a composite oxide having lithium, cobalt, nickel, and oxygen. The flow rate of dry air was 10 L / min. The temperature increase was set at 20 0°C / hr, and the temperature decrease was carried out over 10 hours or more.

[0478] Next, as in Steps S31 to S33 of Embodiment 1, the first mixture was mixed with the composite oxide having lithium, cobalt, nickel, and oxygen to prepare a second mixture. The mixing was carried out so that the atomic weight of magnesium in the first mixture was 0.5 atomic% with respect to the sum of the number of cobalt and nickel atoms. ​​​​​​​​​

[0479] Next, like in steps S34 and S35 of Embodiment 1, the second mixture was annealed in a muffle furnace in an oxygen atmosphere at 850°C for 2 hours and then recovered to obtain a positive electrode active material. . The oxygen flow rate was set to 10 L / min. The temperature increase was set to 200°C / hr, and the temperature decrease was carried out over 10 hours or more . The positive electrode active material thus obtained was designated as Sample 21.

[0480] ≪Sample 22≫ In step S11, LiF and MgF 2 were not added, and except that annealing was not performed in step S34, a positive electrode active material prepared in the same manner as Sample 21 was designated as Sample 22 (comparative example).

[0481] ≪Sample 23≫ In step S21, the raw materials were weighed so that Ni / (Co + Ni) = 0.075, and otherwise a positive electrode active material prepared in the same manner as Sample 21 was designated as Sample 23.

[0482] ≪Sample 24≫ In step S11, LiF and MgF 2 were not added, and except that annealing was not performed in step S34, a positive electrode active material prepared in the same manner as Sample 23 was designated as Sample 24 (comparative example).

[0483] ≪Sample 25≫ In step S21, the raw materials were weighed so that Ni / (Co + Ni) = 0.1, and otherwise a positive electrode active material prepared in the same manner as Sample 21 was designated as Sample 25.

[0484] ≪Sample 26≫ In step S11, LiF and MgF 2 were not added, and in step S34, except that annealing was not performed, the positive electrode active material produced in the same manner as in sample 25 was used as sample 26 (comparative example). (Comparative example).

[0485] The production conditions of samples 21 to 26 are shown in Table 4.

[0486] [Table 4]

[0487] [Production of secondary battery] Next, using samples 21 to 26 produced above, a coin-type secondary battery was produced in the same manner as in Example 1. [Production of coin-type secondary battery]

[0488] [XRD after first charge] The secondary batteries using samples 21 to 26 were charged by CC-CV at 4.6 V in the same manner as in Example 1, and then the positive electrode was taken out and subjected to XRD analysis. [XRD analysis after charging at 4.6 V]

[0489] Figs. 50 and 51 show the XRD patterns of the positive electrodes of the secondary batteries using samples 21 and 22 after charging at 4.6 V. Fig. 51(A) shows an enlarged view of the portion from 2θ = 18° to 2θ = 20° in Fig. 50. Fig. 51(B) shows an enlarged view of the portion from 2θ = 43° to 2θ = 46° in Fig. 50. For comparison, the crystal structure patterns of the pseudo-spinel type crystal structure, H1-3 type crystal structure, and LiCoO (at a charge depth of 0.65) are also shown. The pseudo-spinel type crystal structure, H1-3 type crystal structure, and LiCoO shown in this example [XRD pattern of positive electrode after charging at 4.6 V] In Fig. 51(A), an enlarged view of the portion from 2θ = 18° to 2θ = 20° in Fig. 50 is shown. In Fig. 51(B), an enlarged view of the portion from 2θ = 43° to 2θ = 46° in Fig. 50 is shown. For comparison, the crystal structure patterns of the pseudo-spinel type crystal structure, H1-3 type crystal structure, and LiCoO (at a charge depth of 0.65) are also shown. [XRD pattern of positive electrode after charging at 4.6 V] [XRD pattern of positive electrode after charging at 4.6 V] 0.35 CoO 2 (when the charge depth is 0.65) are also shown together. The pseudo-spinel type crystal structure, H1-3 type crystal structure, and LiCoO shown in this example [XRD pattern of positive electrode after charging at 4.6 V] [XRD pattern of positive electrode after charging at 4.6 V] 0.35 CoO 2All comparison patterns of the crystal structures at [conditions] are calculated for structures that have only cobalt as the transition metal and do not contain nickel. In sample 21, where Mg source and F source were added and annealing was performed, peaks of a pseudo-spinel type crystal structure

[0490] were observed. Also, peaks of the H1-3 type crystal structure and the crystal structure at [conditions] of Li 0.35 CoO 2 were also observed. Also, the fact that some peaks are shifted from the comparison pattern is considered to be the influence of having nickel.

[0491] On the other hand, in sample 22, where Mg source and F source were not added and annealing was not performed, peaks of a pseudo-spinel type crystal structure were not observed. However, peaks of the H1-3 type crystal structure and the crystal 0.35 structure at [conditions] of Li 2 CoO

[0492] Figure 52 shows the XRD patterns of the positive electrodes of secondary batteries using sample 23 and sample 24 after charging at 4.6V. For comparison, the patterns of the pseudo-spinel type crystal structure, the H1-3 type crystal structure and the crystal structure at [conditions] of Li 0.35 CoO 2 (at a depth of charge of 0.65) are also shown together.

[0493] In sample 23, where Mg source and F source were added and annealing was performed, peaks of the pseudo-spinel type crystal structure and the H1-3 type crystal structure were observed, but the peaks of the pseudo-spinel type crystal structure were more dominant.

[0494] On the other hand, in sample 24, where Mg source and F source were not added and annealing was not performed, the H1-3 type crystal structure and the crystal 0.35 structure of Li 2 ​​​Peaks of the crystal structure were observed at this time. Also, it was speculated that there was a lot of noise and the peaks became broad, indicating a decrease in crystallinity.

[0495] Figure 53 shows the XRD patterns of the positive electrode after charging the secondary battery using Sample 25 and Sample 26 at 4.6 V. For comparison, the patterns of the crystal structures of the pseudo-spinel type, H1-3 type and Li 0.35 CoO 2 (at a depth of charge of 0.65) are also shown together.

[0496] For Samples 25 and 26 with Ni / (Co + Ni) = 0.1, no significant difference was observed in the crystal structure. Also, this crystal structure was speculated to be neither the pseudo-spinel type crystal structure, H1-3 type crystal structure nor Li 0.35 CoO 2 .

[0497] From Figures 50 to 53, it became clear that the positive electrode active material containing lithium, transition metals, and oxygen preferably has less than 0.1, more specifically 0.075 or less, of Ni / (Co + Ni) when cobalt and nickel are included as the main component transition metals. When Ni / ( Co + Ni) is within the above range, by adding the Mg source and F source and annealing, it has a pseudo-spinel type crystal structure in the 4.6 V charged state. The positive electrode active material having a pseudo-spinel type crystal structure in the 4.6 V charged state exhibits good cycle characteristics as described in the previous examples.

Example

[0498] In this example, a secondary battery using the positive electrode active material which is one aspect of the present invention was fabricated, and differential scanning calorimetry Differential scanning calorimetry (DSC) measurements and a charge resistance test were performed.

[0499] ≪Sample 27≫ Lithium phosphate was pulverized in a zirconia mortar.

[0500] The lithium phosphate pulverized in a mortar was mixed with Sample 1 prepared in the previous example. The amount of the mixed lithium phosphate corresponded to 0.04 mol per 1 mol of Sample 1. The mixing was carried out using a ball mill with zirconia balls at 150 rpm for 1 hour. After mixing, it was sieved through a 300 μm sieve. Then, the obtained mixture was placed in an aluminum crucible, covered, and annealed at 850 °C for 2 hours in an oxygen atmosphere. Then, it was sieved through a 5 3 μm sieve to obtain Sample 27.

[0501] ≪Sample 28≫ Lithium phosphate was pulverized. The pulverization was carried out using a ball mill with zirconia balls at 4 00 rpm for 60 hours. After pulverization, it was sieved through a 300 μm sieve.

[0502] The pulverized lithium phosphate was mixed with Sample 1 prepared in the previous example. The amount of the mixed lithium phosphate corresponded to 0.06 mol per 1 mol of Sample 1. The mixing was carried out using a ball mill with zirconia balls at 150 rpm for 1 hour. After mixing, it was sieved through a 300 μm sieve. Then, the obtained mixture was placed in an alumina crucible, covered, and annealed at 750 °C for 20 hours in an oxygen atmosphere. Then, it was sieved through a 53 μm sieve to obtain Sample 28.

[0503] [Fabrication of Secondary Battery] Next, using the samples 27 and 28 fabricated above and the sample 1 shown in the previous example a coin-type secondary battery of CR2032 type was fabricated.

[0504] As the positive electrode, sample 1, sample 27, or sample 28 was used as the active material, and a slurry obtained by mixing AB and PVDF in a ratio of active material:AB:PVDF = 95:3:2 (weight ratio) was applied to a current collector. was used.

[0505] Lithium metal was used as the counter electrode.

[0506] As the electrolyte in the electrolytic solution, 1 mol / L lithium hexafluorophosphate (LiPF6) was used For the electrolytic solution, ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of EC:DEC = 3:7 for the secondary battery whose charge-discharge characteristics were evaluated later For the secondary battery whose cycle characteristics were evaluated later, ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of EC:DEC = 3:7, and vinylene carbonate (VC) was mixed at 2 wt%.

[0507] Polypropylene with a thickness of 25 μm was used as the separator.

[0508] Stainless steel (SUS) was used for the positive electrode can and the negative electrode can.

[0509] The positive electrode of the secondary battery was pressurized at 210 kN / m and then further pressurized at 1467 kN / m The loading amount of the positive electrode using sample 1 was approximately 21 mg / cm 2 and the electrode density was approximately 3.9 g / cm 3It was. The loading amount of the positive electrode using Sample 28 was approximately 20 mg / c m 2 and the electrode density was approximately 3.7 g / cm 3 .

[0510] [Charge-discharge characteristics] The secondary batteries using Sample 1 and Sample 28 were charged by CCCV (0.05C, 4. 5V or 4.6V, termination current 0.005C), and discharged by CC (0.5C, 2.5V). The initial charge capacity, discharge capacity, and Coulomb efficiency are shown in Table 5. The Coulomb efficiency is the value obtained by normalizing the discharge capacity by the charge capacity and expressing it as a percentage. As shown in Table 5, excellent Coulomb efficiency was obtained.

[0511]

Table 5

[0512] [Cycle characteristics] The secondary batteries using Sample 1 and Sample 28 were charged by CCCV (0.05C, 4. 5V or 4.6V, termination current 0.005C), and discharged by CC (0.05C, 2.5V) and measured for 2 cycles at 25°C.

[0513] Thereafter, the secondary batteries using Sample 1 and Sample 28 were charged by CCCV (0.2C, 4.5V or 4.6V, termination current 0.02C) at 25°C, and discharged by CC (0. 2C, 2.5V) and repeatedly charged and discharged to evaluate the cycle characteristics. The capacity retention rate after 25 cycles was 99.0% for Sample 1 under the condition of a charging voltage of 4.5V, 96.1% under the condition of a charging voltage of 4.6 V, 99.0% for Sample 28 under the condition of a charging voltage of 4.5V, and 97.8% under the condition of a charging voltage of 4.6 V. The capacity retention rate after 50 cycles was 99.0% for Sample 1 V, 96.1% for Sample 28 under the condition of a charging voltage of 4.6 V, and 97.8% for Sample 28 under the condition of a charging voltage of 4.6V. The capacity retention rate after 50 cycles for Sample 1 In the case of [sample name], the capacity retention was 97.3% under the condition of a charging voltage of 4.5 V and 80.0% under the condition of a charging voltage of 4.6 V. In sample 28, the capacity retention was 96.6% under the condition of a charging voltage of 4.5 V and 93 .5% under the condition of a charging voltage of 4.6 V. Fig. 54(A) shows the change in discharge capacity with respect to a charging voltage of 4.5 V, and Fig. 5 4(B) shows the change in discharge capacity with respect to the condition of a charging voltage of 4.6 V. The horizontal axis of each graph represents the number of cycles, and the vertical axis represents the discharge capacity. In the case of sample 28 coated with lithium phosphate, although the charge-discharge capacity decreases with the weight fraction of lithium phosphate, the cycle characteristics are further improved. This is considered to be the result of suppressing the elution of metal ions such as cobalt from the positive electrode active material and suppressing the decomposition of the electrolyte due to the coating of lithium phosphate. Each horizontal axis of the graphs represents the number of cycles, and the vertical axis represents the discharge capacity. In sample 28 coated with lithium phosphate, although the charge-discharge capacity decreases with the weight fraction of lithium phosphate, the cycle characteristics are further improved. This is considered to be the result of suppressing the elution of metal ions such as cobalt from the positive electrode active material and suppressing the decomposition of the electrolyte due to the coating of lithium phosphate. In sample 28 coated with lithium phosphate, although the charge-discharge capacity decreases with the weight fraction of lithium phosphate, the cycle characteristics are further improved. This is considered to be the result of suppressing the elution of metal ions such as cobalt from the positive electrode active material and suppressing the decomposition of the electrolyte due to the coating of lithium phosphate. In sample 28 coated with lithium phosphate, although the charge-discharge capacity decreases with the weight fraction of lithium phosphate, the cycle characteristics are further improved. This is considered to be the result of suppressing the elution of metal ions such as cobalt from the positive electrode active material and suppressing the decomposition of the electrolyte due to the coating of lithium phosphate. In sample 28 coated with lithium phosphate, although the charge-discharge capacity decreases with the weight fraction of lithium phosphate, the cycle characteristics are further improved. This is considered to be the result of suppressing the elution of metal ions such as cobalt from the positive electrode active material and suppressing the decomposition of the electrolyte due to the coating of lithium phosphate.

[0514] [Differential Scanning Calorimetry] The secondary batteries using sample 1, sample 27, and sample 28 were measured for 2 cycles at 25 °C with charging performed in CCCV mode (0 .05C, 4.5 V or 4.6 V, termination current 0.005C) and discharging performed in CC mode (0.05C , 2.5V).

[0515] Thereafter, the secondary batteries using sample 1, sample 27, and sample 28 were charged in CCCV mode (0.05C, 4.5 V or 4.6 V, termination current 0.005C). Thereafter , the charged secondary batteries were disassembled in a glove box under an argon atmosphere to remove the positive electrodes, which were then washed with DMC to remove the electrolyte. Then, they were punched out to a diameter of 3 mm. Thereafter, the charged secondary batteries were disassembled in a glove box under an argon atmosphere to remove the positive electrodes, which were then washed with DMC to remove the electrolyte. Then, they were punched out to a diameter of 3 mm. Thereafter, the charged secondary batteries were disassembled in a glove box under an argon atmosphere to remove the positive electrodes, which were then washed with DMC to remove the electrolyte. Then, they were punched out to a diameter of 3 mm.

[0516] 1 μL of the electrolyte was dropped onto the punched-out positive electrode and placed in a sealed container made of SUS. The electrolyte used contained 1 mol / L of lithium hexafluorophosphate (LiPF ) and the electrolyte used was 6 ) and the electrolyte used was , ethylene carbonate (EC) and diethyl carbonate (DEC) with EC:DEC = 3 :7 (volume ratio) were used as the mixture.

[0517] Evaluation was performed by DSC. For the measurement, a Rigaku high-sensitivity differential scanning calorimeter Thermo p lus EV02 DSC8231 was used. The measurement conditions were in the temperature range from room temperature to 400 °C, and the heating rate was set at 5 °C / min.

[0518] The results of the DSC measurement are shown in Fig. 55. The horizontal axis represents Temperature (temperature), and the vertical axis represents Heat Flow (heat flow). Fig. 55(A) shows the comparison between Sample 1 and Sample 27, and Fig. 55(B) shows the comparison between Sample 1 and Sample 28, respectively.

[0519] From Fig. 55(A), in Sample 1, the peaks observed near 171 °C and near 251 °C rose to near 188 °C and near 252 °C, respectively, in Sample 27, and the area intensity representing the heat quantity decreased. Also, from Fig. 55(B), in Sample 28, an increase in the peak and a decrease in the area intensity were observed, and particularly in the range from 150 °C to 200 °C, a significant decrease in the area intensity was seen. From the above, it was suggested that the thermal stability was improved by mixing with a compound containing phosphoric acid in the process of preparing the positive electrode active material.

[0520] [Charge resistance test] Secondary batteries using Sample 1 and Sample 28 were charged by CCCV (0.05C, 4. 5V or 4.6V, termination current 0.005C), and discharged by CC (0.05C, 2.5V) and measured at 25 °C for 2 cycles.

[0521] After that, the battery was charged at 60°C with CCCV (0.05C). The upper limit voltage was 4.55V. or 4.65V, and the termination condition is when the secondary battery voltage is 0.01V below the upper limit voltage ( The time until the voltage of the secondary battery dropped below 4.55V was measured. If the voltage falls below the upper limit voltage, a phenomenon such as a short circuit may have occurred. 1C was set to 200mA / g.

[0522] The times measured for each secondary battery are shown in Table 6.

[0523] [Table 6]

[0524] In sample 28, it took a long time for the voltage of the secondary battery to decrease, and the positive electrode active material was It was suggested that mixing the compound with phosphoric acid in the electrolyte improves charging durability. EXAMPLES

[0525] In this example, a secondary battery using the positive electrode active material of one embodiment of the present invention was manufactured, and the battery was subjected to atomic absorption spectrometry. Metal elution was evaluated by measurement.

[0526] [Preparation of secondary battery] First, the above-prepared sample 27 and the sample 1 shown in the previous example were used to perform lamination. A laminate-type secondary battery was fabricated.

[0527] For the positive electrode, sample 1 or sample 27 was used as the active material, and the mixture of AB and PVDF was used. The slurry was mixed with the active material, AB, and PVDF in a ratio of 95:3:2 (by weight) and applied to one side of the current collector. The material used was coated with

[0528] For the negative electrode, graphite was used as the active material, and a mixture of VGCF (registered trademark), CMC-Na, and SBR was prepared with the active material:VGCF (registered trademark):CMC-Na:SBR = 96:1:1:2 (by weight). The slurry was adjusted in viscosity with pure water and then coated on one side of the current collector, followed by drying to volatilize the pure water. A 18-μm-thick copper foil was used as the current collector. The loading amount was approximately 14 mg / cm². The mixture was prepared with the active material:VGCF (registered trademark):CMC-Na:SBR = 96:1:1:2 (by weight). The slurry was adjusted in viscosity with pure water and then coated on one side of the current collector, followed by drying to volatilize the pure water. A 18-μm-thick copper foil was used as the current collector. The loading amount was approximately 14 mg / cm². mg / cm 2 ².

[0529] As the electrolyte in the electrolyte solution, 1 mol / L lithium hexafluorophosphate (LiPF6) was used. In the electrolyte solution, ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of EC:DEC = 3:7, and vinylene carbonate (VC) was mixed at 2 wt%. As the electrolyte in the electrolyte solution, 1 mol / L lithium hexafluorophosphate (LiPF6) was used. In the electrolyte solution, ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of EC:DEC = 3:7, and vinylene carbonate (VC) was mixed at 2 wt%. The mixture was used. The mixture was used.

[0530] A 25-μm-thick polypropylene was used as the separator.

[0531] The fabricated secondary battery was subjected to a process of discharging and degassing at a low rate several times for the purpose of aging. The process was carried out several times.

[0532] After aging, the secondary battery fabricated by combining the positive electrode with Sample 1 or Sample 27 and the negative electrode with graphite was charged at 25°C under CCCV (0.05C, 4.4 V, cut-off current 0.005C) and discharged under CC (0.05C, 2.5 V). 1C was approximately 200 mA / g. After aging, the secondary battery fabricated by combining the positive electrode with Sample 1 or Sample 27 and the negative electrode with graphite was charged at 25°C under CCCV (0.05C, 4.4 V, cut-off current 0.005C) and discharged under CC (0.05C, 2.5 V). 1C was approximately 200 mA / g. After aging, the secondary battery fabricated by combining the positive electrode with Sample 1 or Sample 27 and the negative electrode with graphite was charged at 25°C under CCCV (0.05C, 4.4 V, cut-off current 0.005C) and discharged under CC (0.05C, 2.5 V). 1C was approximately 200 mA / g. 1C was approximately 200 mA / g.

[0533] After that, the charging was carried out under CCCV (0.05C, 4.45 V, cut-off current 0.005C). After that, the secondary battery was stored at 60°C for 14 days.

[0534] Thereafter, at 25°C, discharge was performed under CC (0.05C, 2.5V). 1C was defined as 200 mA / g.

[0535] [Atomic absorption measurement] Next, the secondary battery was disassembled in a glove box under an argon atmosphere to remove the negative electrode, and it was washed with DM C to remove the electrolyte. Thereafter, the current collector was removed. The powder of the active material layer was mixed and about 0.1 mg was taken out for atomic absorption measurement.

[0536] Using a furnace atomic absorption, the amount of cobalt was measured. For the measurement, a ContrAA 600 continuous light source atomic absorption analysis device from Analytik J ena (Analytik Jena) was used. In the measurement, cobalt was atomized at 2500°C and irradiated with light of wavelength 235.8183 nm For Sample 1 and Sample 27, two secondary batteries were fabricated for each, and the average value was calculated. The measurement was performed 20 times for each cell, and the average value was calculated. The amount of cobalt obtained was 9722 ppm for Sample 1 and 597

[0537] 1 ppm for Sample 27. The amount of cobalt is a value normalized by the amount of cobalt in the positive electrode active material layer. Specifically, the amount of cobalt contained in the entire negative electrode of the secondary battery was calculated from the obtained measurement values and normalized using the amount of cobalt contained in the entire positive electrode of the secondary battery. The amount of cobalt decreased in Sample 27. By mixing with a compound having phosphoric acid in the production process of the positive electrode active material, the elution of cobalt from the positive electrode active material was suppressed, and the amount deposited on the negative electrode also decreased which is suggested.

[0538]

Example

[0538] In this example, a positive electrode active material, which is one aspect of the present invention, was fabricated, and its characteristics were analyzed using XRD. Also, the cycle characteristics during high-voltage charging were evaluated.

[0539] ≪Sample 51≫ A sample fabricated in the same manner as Sample 1 shown in Example 1 was designated as Sample 51, except that the annealing time was set to 8 hours in step S34 of FIG. 2.

[0540] ≪Sample 52≫ A sample fabricated in the same manner as Sample 1 shown in Example 1 was designated as Sample 52, except that the annealing time was set to 30 hours in step S34 of FIG. 2.

[0541] [XRD after First Charge] Similar to Example 1, secondary batteries were fabricated using Sample 51 and Sample 52, and the first charge was performed, followed by evaluation of the XRD after the first charge.

[0542] FIG. 56 shows the XRD patterns of the positive electrodes of the secondary batteries using Sample 51 and Sample 52 after charging at 4.6V.

[0543] It was revealed that Sample 52 after charging at 4.6V has a pseudo-spinel type crystal structure. On the other hand, an H1-3 type crystal structure was suggested for Sample 51. From this, it was suggested that an excellent positive electrode active material can be obtained at 30 hours compared to the case where the annealing time is 8 hours, indicating that the annealing time is preferably longer than 8 hours.

[0544] [Cycle Characteristics] Similar to Example 1, the cycle characteristics of the secondary batteries using Sample 51 and Sample 52 were evaluated.

[0545] At 25°C, charging was performed in a CCCV mode (1C, 4.6V, termination current 0.01C), and discharging was performed in a CC mode (0. 5C, 2.5V) to evaluate the cycle characteristics. 1C was approximately 137 mA / g . After performing 40 charge-discharge cycles, the discharge capacity retention rate was 47.8 % for Sample 28, 98.4% for Sample 29, and 97.6% for Sample 1 prepared in Example 1 .

[0546] At 45°C, charging was performed in a CCCV mode (1C, 4.55V, termination current 0.05C), and discharging was performed in a CC mode (1 C, 3.0V) to evaluate the cycle characteristics. 1C was approximately 160 mA / g . After performing 100 charge-discharge cycles, the discharge capacity retention rate was 39. 4% for Sample 51 and 78.4% for Sample 52

[0547] For Sample 52, excellent cycle characteristics were obtained at both 25°C and 45°C . From this, it was suggested that excellent positive electrode active materials can be obtained by annealing for 30 hours .

Example

[0548] In this example, a positive electrode active material, which is one aspect of the present invention, was fabricated, and its characteristics were analyzed using XRD . Also, the cycle characteristics under high voltage charging were evaluated

[0549] ≪Sample 61≫ In step S11 of FIG. 2, without adding MgF 2 , and with other conditions the same as those shown in Sample 1 of Example 1 , the resulting product was designated as Sample 61. Lithium cobaltate was weighed such that the atomic weight of lithium in the first mixture was 1.17 atomic% relative to the molecular weight of lithium cobaltate , and dry-mixed .

[0550] ≪Sample 62≫ In step S11 of FIG. 2, LiF and MgF 2 were not added. Instead, Mg(OH) 2 was added, and the other conditions were the same as those of Sample 1 shown in Example 1, and the product was made into Sample 62. With respect to the molecular weight of lithium cobaltate, magnesium having an atomic weight of 0.5 atomic% in the first mixture was weighed and mixed dry.

[0551] [XRD after the first charge] Similar to Example 1, a secondary battery was fabricated using Samples 61 and 62, and the first charge was performed, and the XRD after the first charge was evaluated.

[0552] FIG. 57 shows the XRD patterns of the positive electrodes of the secondary batteries using Samples 61 and 62 after charging at 4.6 V.

[0553] For both Sample 61 and Sample 62 after charging at 4.6 V, a crystal structure of the H1- 3 type was suggested rather than a spinel-like crystal structure. From this, it was suggested that when using a compound having lithium and a compound having fluorine in the process of step S11, a more excellent positive electrode active material can be obtained.

[0554] [Cycle characteristics] Similar to Example 1, the cycle characteristics of the secondary batteries using Samples 61 and 62 were evaluated. FIG. 58(A) shows the results of cycle measurements at 25 °C with a charging voltage of 4.6 V, and FIG. 58(B) shows the results of charging at 45 °C with a charging voltage of 4.55 V. For both Sample 61 and Sample 62, compared with Sample 1 shown in Example 1, the cycle​​​​ The decrease in capacity associated therewith was more significant. It is considered that this is because the pseudo-spinel type crystal structure was not significantly observed after high voltage charging.

Explanation of symbols

[0555] 100 Positive electrode active material 1001 Particle 1002 Fine particle 1003 Region 1010 Detection region​

Claims

1. A lithium ion secondary battery having a positive electrode, the positive electrode has a positive electrode active material including lithium cobalt oxide, The positive electrode active material of the lithium ion secondary battery contains magnesium. However, the positive electrode is A plurality of coin-type batteries each having the positive electrode, a counter electrode using lithium metal, an electrolytic solution, and a separator using polypropylene were fabricated (here, the electrolyte in the electrolytic solution was 1 mol / L lithium hexafluorophosphate, and the electrolytic solution was a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of EC:DEC = 3:7). Thereafter, a first battery among the plurality of batteries was charged at a constant current of 0.5 C to 4.525 V in a 25° C. environment (where 1 C is the current value per weight of the positive electrode active material, which is 137 mA / g). Thereafter, the first battery that had been subjected to the constant current charging was subjected to constant voltage charging at 4.525 V in an environment of 25° C. until the current value reached 0.01 C. Thereafter, the positive electrode was taken out from the first battery that had been subjected to the constant voltage charging in a glove box under an argon atmosphere, and the positive electrode was sealed in a first sealed container, Thereafter, the positive electrode sealed in the first sealed container was subjected to powder XRD analysis using CuKα1 radiation, and the XRD pattern showed a diffraction peak of an O3-type crystal structure of space group R-3m, Furthermore, a second battery among the plurality of batteries was charged at a constant current of 0.5 C up to 4.55 V in a 25° C. environment (where 1 C is the current value per weight of the positive electrode active material, which is 137 mA / g), Thereafter, the second battery that had been subjected to the constant current charging was subjected to constant voltage charging at 4.55 V in an environment of 25° C. until the current value reached 0.01 C. Thereafter, the positive electrode was taken out from the second battery that had been subjected to the constant voltage charging in a glove box under an argon atmosphere, and the positive electrode was sealed in a second sealed container, Thereafter, the positive electrode sealed in the second sealed container was subjected to powder XRD analysis using CuKα1 radiation, and the XRD pattern showed diffraction peaks at 2θ=19.30±0.20° and 2θ=45.55±0.10°.

2. A lithium ion secondary battery having a positive electrode, the positive electrode has a positive electrode active material including lithium cobalt oxide, The positive electrode active material of the lithium ion secondary battery contains magnesium. However, the positive electrode is A plurality of coin-type batteries each having the positive electrode, a counter electrode using lithium metal, an electrolytic solution, and a separator using polypropylene were fabricated (here, the electrolyte in the electrolytic solution was 1 mol / L lithium hexafluorophosphate, and the electrolytic solution was a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of EC:DEC = 3:7). Thereafter, a first battery among the plurality of batteries was charged at a constant current of 0.5 C to 4.525 V in a 25° C. environment (where 1 C is the current value per weight of the positive electrode active material, which is 137 mA / g). Thereafter, the first battery that had been subjected to the constant current charging was subjected to constant voltage charging at 4.525 V in an environment of 25° C. until the current value reached 0.01 C. Thereafter, the positive electrode was taken out from the first battery that had been subjected to the constant voltage charging in a glove box under an argon atmosphere, and the positive electrode was sealed in a first sealed container, Thereafter, the positive electrode sealed in the first sealed container was subjected to powder XRD analysis using CuKα1 radiation, and the XRD pattern showed a diffraction peak of an O3-type crystal structure of space group R-3m, Furthermore, a second battery among the plurality of batteries was charged at a constant current of 0.5 C up to 4.55 V in a 25° C. environment (where 1 C is the current value per weight of the positive electrode active material, which is 137 mA / g), Thereafter, the second battery that had been subjected to the constant current charging was subjected to constant voltage charging at 4.55 V in an environment of 25° C. until the current value reached 0.01 C. Thereafter, the positive electrode was taken out from the second battery that had been subjected to the constant voltage charging in a glove box under an argon atmosphere, and the positive electrode was sealed in a second sealed container, Thereafter, the positive electrode sealed in the second sealed container was subjected to powder XRD analysis using CuKα1 radiation, and the XRD pattern showed diffraction peaks at 2θ=19.30±0.20° and 2θ=45.55±0.10°, Furthermore, a third battery among the plurality of batteries was charged at a constant current of 0.5 C up to 4.6 V in a 25° C. environment (where 1 C is the current value per weight of the positive electrode active material, which is 137 mA / g), Thereafter, the third battery that had been subjected to the constant current charging was subjected to constant voltage charging at 4.6 V in an environment of 25° C. until the current value reached 0.01 C. Thereafter, the positive electrode was taken out from the third battery that had been subjected to the constant voltage charging in a glove box under an argon atmosphere, and the positive electrode was sealed in a third sealed container, Thereafter, the positive electrode sealed in the third sealed container was subjected to powder XRD analysis using CuKα1 radiation, and the XRD pattern showed diffraction peaks at 2θ=19.30±0.20° and 2θ=45.55±0.10° as well as diffraction peaks corresponding to an H1-3 type crystal structure.

3. A lithium ion secondary battery having a positive electrode, the positive electrode has a positive electrode active material including lithium cobalt oxide, The positive electrode active material of the lithium ion secondary battery contains magnesium. However, the positive electrode is A plurality of coin-type batteries each having the positive electrode, a counter electrode using lithium metal, an electrolytic solution, and a separator using polypropylene were fabricated (here, the electrolyte in the electrolytic solution was 1 mol / L lithium hexafluorophosphate, and the electrolytic solution was a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of EC:DEC = 3:7). Thereafter, a first battery among the plurality of batteries was charged at a constant current of 0.5 C to 4.525 V in a 25° C. environment (where 1 C is the current value per weight of the positive electrode active material, which is 137 mA / g). Thereafter, the first battery that had been subjected to the constant current charging was subjected to constant voltage charging at 4.525 V in an environment of 25° C. until the current value reached 0.01 C. Thereafter, the positive electrode was taken out from the first battery that had been subjected to the constant voltage charging in a glove box under an argon atmosphere, and the positive electrode was sealed in a first sealed container, Thereafter, the positive electrode sealed in the first sealed container was subjected to powder XRD analysis using CuKα1 radiation, and the XRD pattern showed a diffraction peak of an O3-type crystal structure of space group R-3m, Furthermore, a second battery among the plurality of batteries was charged at a constant current of 0.5 C up to 4.55 V in a 25° C. environment (where 1 C is the current value per weight of the positive electrode active material, which is 137 mA / g), Thereafter, the second battery that had been subjected to the constant current charging was subjected to constant voltage charging at 4.55 V in an environment of 25° C. until the current value reached 0.01 C. Thereafter, the positive electrode was taken out from the second battery that had been subjected to the constant voltage charging in a glove box under an argon atmosphere, and the positive electrode was sealed in a second sealed container, Thereafter, the positive electrode sealed in the second sealed container was subjected to powder XRD analysis using CuKα1 radiation, and the XRD pattern showed diffraction peaks at 2θ=19.30±0.20° and 2θ=45.55±0.10°, Furthermore, a third battery among the plurality of batteries was charged at a constant current of 0.5 C up to 4.6 V in a 25° C. environment (where 1 C is the current value per weight of the positive electrode active material, which is 137 mA / g), Thereafter, the third battery that had been subjected to the constant current charging was subjected to constant voltage charging at 4.6 V in an environment of 25° C. until the current value reached 0.01 C. Thereafter, the positive electrode was taken out from the third battery that had been subjected to the constant voltage charging in a glove box under an argon atmosphere, and the positive electrode was sealed in a third sealed container, Thereafter, the positive electrode sealed in the third sealed container was subjected to powder XRD analysis using CuKα1 radiation, and the XRD pattern showed diffraction peaks at 2θ=19.30±0.20° and 2θ=45.55±0.10° as well as diffraction peaks of an H1-3 type crystal structure, Furthermore, a fourth battery among the plurality of batteries was charged at a constant current of 0.5 C up to 4.65 V in a 25° C. environment (where 1 C is the current value per weight of the positive electrode active material, which is 137 mA / g), Thereafter, the fourth battery that had been subjected to the constant current charging was subjected to constant voltage charging at 4.65 V in an environment of 25° C. until the current value reached 0.01 C. Thereafter, the positive electrode was taken out from the fourth battery that had been subjected to the constant voltage charging in a glove box under an argon atmosphere, and the positive electrode was sealed in a fourth sealed container, Thereafter, the positive electrode sealed in the fourth sealed container is subjected to powder XRD analysis using CuKα1 radiation, and the XRD pattern has a diffraction peak of an H1-3 type crystal structure.

4. In any one of claims 1 to 3, The lithium ion secondary battery has magnesium at the lithium site of the positive electrode active material.

5. In any one of claims 1 to 3, CoO of the positive electrode active material ２ A lithium-ion secondary battery with magnesium between the layers.

6. In any one of claims 1 to 5, The positive electrode active material further contains fluorine.

7. In claim 6, The lithium ion secondary battery has fluorine at the oxygen site of the positive electrode active material.

Images