Positive electrode active material and method for manufacturing positive electrode active material

Abstract

To provide a positive electrode active material for a secondary battery having high capacity and excellent charge / discharge cycle characteristics.SOLUTION: A positive electrode active material includes an aggregate of particles including a first particle group and a second particle group, the aggregate of particles contains lithium, cobalt, nickel, aluminum, magnesium, oxygen, and fluorine, when the number of atoms of cobalt contained in the aggregate of particles is 100, the number of atoms of nickel is 0.05 or more and 2 or less, the number of atoms of aluminum is 0.05 or more and 2 or less, and the number of atoms of magnesium is 0.1 or more and 6 or less, and when the aggregate of particles is subjected to particle size distribution measurement by a laser diffraction / scattering method, the first particle group has a first peak. The second particle group has a second peak, the first peak has a maximum value in a range of 2 μm or more and 4 μm or less, and the second peak has a maximum value in a range of 9 μm or more and 25 μm or less.SELECTED DRAWING: Figure 26

Description

[Technical Field]

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

[0002] In this specification, the term "power storage device" refers to elements and devices in general that have a power storage function, including, for example, storage batteries (also called secondary batteries) such as lithium ion secondary batteries, lithium ion capacitors, and electric double layer capacitors.

[0003] In this specification, the term "electronic device" refers to any device having a power storage device, and includes electro-optical devices having a power storage device, information terminal devices having a power storage device, and the like. [Background technology]

[0004] In recent years, there has been active development of various types of electricity storage devices, such as lithium-ion secondary batteries, lithium-ion capacitors, and air batteries. In particular, demand for high-power, high-capacity lithium-ion secondary batteries has rapidly expanded in line with the development of the semiconductor industry, and they have become indispensable in today's information society as a rechargeable energy source.

[0005] The characteristics required of lithium ion secondary batteries include higher energy density, improved cycle characteristics, safety in various operating environments, and improved long-term reliability.

[0006] Increasing the amount of positive electrode active material carried in the positive electrode is an effective way to increase the energy density. Attempts to achieve this are described in, for example, Patent Document 1 and Patent Document 2.

[0007] Furthermore, research such as that in Non-Patent Documents 1 to 3 has been conducted on the crystal structure of positive electrode active materials.

[0008] In Non-Patent Document 3, LiNi 1-x M x An example of calculating the interatomic distance of O2 is shown. Non-Patent Document 4 also describes the formation energy of silicon oxide compounds obtained by first-principles calculations.

[0009] X-ray diffraction (XRD) is one of the techniques used to analyze the crystalline structure of positive electrode active materials. XRD data can be analyzed using the Inorganic Crystal Structure Database (ICSD) introduced in Non-Patent Document 5.

[0010] Furthermore, as shown in Non-Patent Documents 6 and 7, by using first-principles calculations, it is possible to calculate the energy according to the crystal structure, composition, etc. of a compound. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Application Publication No. 2019-021456 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-153197 [Non-patent literature]

[0012] [Non-Patent Document 1] Toyoki Okumura et al, “Correlation of lithium ion distribution and X-ray absorption near-edge structure in O3-and O2-lithium cobalt oxides from first-principle calculation”, Journal of Materials Chemistry, 2012, 22, p.17340-17348 [Non-patent document 2] Motohashi, T. et al, “Electronic phase diagram of the layered cobalt oxide system LixCoO2(0.0≦x≦1.0)”, Physical Review B, 80(16) ,2009, 165114 [Non-patent document 3] Zhaohui Chen et al, “Staging Phase Transitions in LixCoO2”, Journal of The Electrochemical Society, 2002, 149(12) A1604-A1609 [Non-patent document 4] WE Counts et al, Journal of the American Ceramic Society, 1953, 36[1] 12-17. Fig.01471 [Non-Patent Document 5] Belsky, A. et al., “New developments in the Inorganic Crystal Structure Database (ICSD): accessibility in support of materials research and design”, Acta Cryst., 2002, B58 364-369. [Non-patent document 6] Dudarev, SL et al, “Electron-energy-loss spectra and the structural stability of nickel oxide: An LSDA1U study”, Physical Review B, 1998, 57(3) 1505. [Non-Patent Document 7] Zhou, F. et al, “First-principles prediction of redox potentials in transition-metal compounds with LDA+U”, Physical Review B, 2004, 70 235121. Summary of the Invention [Problem to be solved by the invention]

[0013] An object of one embodiment of the present invention is to provide a positive electrode active material for a secondary battery having high capacity and excellent charge-discharge cycle characteristics. Another object is to provide a positive electrode active material having high powder packing density. Another object is to provide a positive electrode active material with a small particle size. Another object is to provide a positive electrode for a secondary battery having high capacity and excellent charge-discharge cycle characteristics. Another object is to provide a method for manufacturing a positive electrode active material with high productivity. Another object is to provide a positive electrode active material that, when used in a secondary battery, suppresses a decrease in capacity during charge-discharge cycles. Another object is to provide a high-capacity secondary battery. Another object is to provide a secondary battery having excellent charge-discharge characteristics. Another object is to provide a secondary battery with high safety or reliability.

[0014] Another object of one embodiment of the present invention is to provide a novel substance, active material particles, a power storage device, or a manufacturing method thereof.

[0015] Note that the description of these problems does not preclude the existence of other problems. Note that one embodiment of the present invention does not necessarily solve all of these problems. Note that problems other than these can be extracted from the description in the specification, drawings, and claims. [Means for solving the problem]

[0016] To achieve the above object, one aspect of the present invention is to prepare a cathode active material with a small particle size and excellent charge-discharge cycle characteristics. By mixing this cathode active material with a cathode active material with a large particle size and excellent charge-discharge cycle characteristics, the capacity per volume of a secondary battery can be improved.

[0017] One embodiment of the present invention is a positive electrode active material having a particle assembly, the particle assembly having a first particle group and a second particle group, the particle assembly including lithium, cobalt, nickel, aluminum, magnesium, oxygen, and fluorine, wherein, when the number of cobalt atoms in the particle assembly is taken as 100, the number of nickel atoms is 0.05 to 2, the number of aluminum atoms is 0.05 to 2, and the number of magnesium atoms is 0.1 to 6, and when particle size distribution of the particle assembly is measured by a laser diffraction / scattering method, the first particle group has a first peak, the second particle group has a second peak, the first peak has a maximum value between 2 μm and 4 μm, and the second peak has a maximum value between 9 μm and 25 μm.

[0018] In the above, the powder packing density of the positive electrode active material is preferably 4.30 g / cc or more and 4.60 g / cc or less.

[0019] Furthermore, in the above, when a lithium ion secondary battery using the particle aggregate as a positive electrode and metallic lithium as a negative electrode is charged at a constant current until the battery voltage reaches 4.6 V in an environment of 25°C, and then charged at a constant voltage until the current value reaches 0.02 C, and the positive electrode is analyzed by powder X-ray diffraction using CuKα1 radiation, it is preferable that the positive electrode has diffraction peaks at 2θ=19.30±0.20° and 2θ=45.55±0.10°.

[0020] Another aspect of the present invention is a positive electrode active material having a particle group containing lithium, cobalt, nickel, aluminum, magnesium, oxygen, and fluorine, wherein, when the number of cobalt atoms in the particle group is taken as 100, the number of nickel atoms is 0.05 to 2, the number of aluminum atoms is 0.05 to 2, and the number of magnesium atoms is 0.1 to 6, and when the particle group has a particle size distribution measured by a laser diffraction / scattering method, it has a maximum value of 2 μm to 4 μm. When a lithium-ion secondary battery using the particle group in a positive electrode and metallic lithium in a negative electrode is charged at a constant current until the battery voltage reaches 4.6 V in an environment of 25° C. and then charged at a constant voltage until the current value reaches 0.02 C, and then analyzed by powder X-ray diffraction using CuKα1 radiation, the positive electrode has diffraction peaks at 2θ=19.30±0.20° and 2θ=45.55±0.10°.

[0021] Another embodiment of the present invention is a particle size distribution measuring method for measuring a particle size distribution of a particle having lithium, cobalt, nickel, aluminum, magnesium, oxygen, and fluorine, the particle size distribution being D 50 a first step of preparing a first particle group having a particle size of 2 μm or more and 4 μm or less; and a second step of preparing a first particle group having lithium, cobalt, nickel, aluminum, magnesium, oxygen, and fluorine, the particle size distribution of which is measured by a laser diffraction / scattering method. 50 and a third step of mixing the first particle group and the second particle group to prepare a particle aggregate, wherein the proportion of the first particle group in the particle aggregate is 5 wt % or more and 20 wt % or less.

[0022] In the above, the first step preferably includes a step of disintegrating the material with a thin film swirl mixer. [Effects of the Invention]

[0023] According to one embodiment of the present invention, a positive electrode active material for a secondary battery having high capacity and excellent charge-discharge cycle characteristics can be provided. Alternatively, a positive electrode active material having high powder packing density can be provided. Alternatively, a positive electrode active material having a small particle size can be provided. Alternatively, a positive electrode for a secondary battery having high capacity and excellent charge-discharge cycle characteristics can be provided. Alternatively, a method for manufacturing a positive electrode active material with high productivity can be provided. Alternatively, one embodiment of the present invention can provide a positive electrode active material that, when used in a secondary battery, suppresses a decrease in capacity during charge-discharge cycles. Alternatively, one embodiment of the present invention can provide a high-capacity secondary battery. Alternatively, one embodiment of the present invention can provide a secondary battery having excellent charge-discharge characteristics. Alternatively, one embodiment of the present invention can provide a secondary battery with high safety or reliability. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 is a diagram illustrating the depth of charge and the crystal structure of the positive electrode active material. [Figure 2] FIG. 2 is a diagram illustrating the depth of charge and the crystal structure of the positive electrode active material. [Figure 3] Figure 3 shows the XRD pattern calculated from the crystal structure. [Figure 4] FIG. 4 is a diagram illustrating an example of a method for producing a positive electrode active material. [Figure 5] FIG. 5 is a diagram illustrating an example of a method for producing a positive electrode active material. [Figure 6] 6A and 6B are diagrams illustrating an example of a secondary battery. [Figure 7] FIG. 7 is a diagram illustrating an example of a secondary battery. [Figure 8] 8A and 8B are diagrams illustrating a coin-type secondary battery, and Fig. 8C is a diagram illustrating the current flow in the secondary battery. [Figure 9] Figures 9A and 9B are diagrams illustrating a cylindrical secondary battery, and Figures 9C and 9D are diagrams illustrating a module having a plurality of cylindrical secondary batteries. [Figure 10] 10A and 10B are diagrams illustrating an example of a secondary battery. [Figure 11] 11A to 11D are diagrams illustrating an example of a secondary battery. [Figure 12] 12A and 12B are diagrams illustrating an example of a secondary battery. [Figure 13] FIG. 13 is a diagram illustrating an example of a secondary battery. [Figure 14] 14A to 14C are diagrams illustrating a laminated secondary battery. [Figure 15] 15A and 15B are diagrams illustrating a laminated secondary battery. [Figure 16] FIG. 16 is a diagram showing the appearance of a secondary battery. [Figure 17] FIG. 17 is a diagram showing the appearance of a secondary battery. [Figure 18] 18A to 18C are diagrams illustrating a method for manufacturing a secondary battery. [Figure 19] 19A and 19B are diagrams illustrating an example of a secondary battery and a method for manufacturing the same. [Figure 20] 20A to 20C are diagrams illustrating an example of a secondary battery. [Figure 21] 21A and 21B are diagrams illustrating an example of a secondary battery. [Figure 22] 22A to 22H are diagrams illustrating examples of electronic devices. [Figure 23] 23A to 23C are diagrams illustrating examples of electronic devices. [Figure 24] FIG. 24 is a diagram illustrating an example of an electronic device. [Figure 25] 25A to 25C are diagrams illustrating an example of a vehicle. [Figure 26] FIG. 26 is a graph showing the particle size distribution of the positive electrode active material. [Figure 27] FIG. 27 is a graph showing the powder packing density of the positive electrode active material. [Figure 28] 28A and 28B are cross-sectional SEM images of the positive electrode. [Figure 29] FIG. 29 shows the XRD pattern of the positive electrode. [Figure 30] 30A and 30B are XRD patterns of the positive electrode. [Figure 31] 31A and 31B are graphs showing the cycle characteristics of a secondary battery. [Figure 32] 32A and 32B are graphs showing the cycle characteristics of the secondary battery. [Figure 33] 33A and 33B are graphs showing the cycle characteristics of the secondary battery. [Figure 34] 34A and 34B are graphs showing the cycle characteristics of the secondary battery. DETAILED DESCRIPTION OF THE INVENTION

[0025] Hereinafter, embodiments will be described with reference to the drawings. However, it will be readily understood by those skilled in the art that the embodiments can be implemented in many different ways and that various changes in form and details can be made without departing from the spirit and scope of the present invention. Therefore, the present invention should not be interpreted as being limited to the following description of the embodiments.

[0026] In this specification, the ordinal numbers "first," "second," and "third" are used to avoid confusion between components. Therefore, they do not limit the number of components. Furthermore, they do not limit the order of the components. For example, a component referred to as "first" in one embodiment of this specification may be a component referred to as "second" in another embodiment or in the claims. For example, a component referred to as "first" in one embodiment of this specification may be omitted in another embodiment or in the claims.

[0027] In the drawings, the same elements or elements having similar functions, elements made of the same material, or elements formed at the same time may be given the same reference numerals, and repeated explanations thereof may be omitted.

[0028] Furthermore, in this specification and the like, crystal planes and directions are indicated by Miller indices. In crystallography, crystal planes and directions are indicated by a superscript bar after the number, but in this specification and the like, due to restrictions on application notation, numbers may be expressed by a minus sign (-) before them instead of a bar above them. Furthermore, individual directions indicating directions within a crystal are expressed with [ ], collective directions indicating all equivalent directions are expressed with < >, individual planes indicating crystal planes are expressed with ( ), and collective planes with equivalent symmetry are expressed with {}.

[0029] In this specification, the surface layer of particles of active material or the like refers to the region from the surface to a depth of about 10 nm. Surfaces formed by cracks or fissures may also be considered the surface. The region deeper than the surface layer is called the interior.

[0030] In this specification, the layered rock-salt type crystal structure of a composite oxide containing lithium and a transition metal refers to a crystal structure having a rock-salt type ion arrangement in which cations and anions are alternately arranged, and in which the transition metal and lithium are regularly arranged to form a two-dimensional plane, allowing two-dimensional diffusion of lithium. Defects such as cation or anion deficiencies may also be present. Furthermore, strictly speaking, the layered rock-salt type crystal structure may have a distorted rock-salt type crystal lattice structure.

[0031] In this specification and the like, the rock salt type crystal structure refers to a structure in which cations and anions are arranged alternately, and it is also possible for there to be a deficiency of cations or anions.

[0032] In this specification and the like, the pseudospinel crystal structure of a composite oxide containing lithium and a transition metal refers to a crystal structure that has the space group R-3m and is not a spinel crystal structure, but in which ions of cobalt, magnesium, etc. occupy hexacoordinated oxygen positions and the arrangement of cations has a symmetry similar to that of a spinel structure. Note that in the pseudospinel crystal structure, light elements such as lithium may occupy tetracoordinated oxygen positions, and in this case, the arrangement of ions also has a symmetry similar to that of a spinel structure.

[0033] It can also be said that the pseudospinel crystal structure has random Li between the layers, but is similar to the CdCl2 crystal structure. This CdCl2-like crystal structure was observed when lithium nickel oxide was charged to a depth of charge of 0.94 (Li 0.06 The crystal structure is similar to that of lithium cobaltate (NiO2), but it is known that pure lithium cobaltate or layered rock salt-type positive electrode active materials containing a large amount of cobalt do not usually adopt this crystal structure.

[0034] The anions in layered rock salt crystals and rock salt crystals have a cubic close-packed structure (face-centered cubic lattice structure). It is presumed that the anions in pseudospinel crystals also have a cubic close-packed structure. When these crystals contact, there are crystal planes where the cubic close-packed structures formed by the anions are aligned. However, the space group of layered rock salt crystals and pseudospinel crystals is R-3m, which is different from the space groups of rock salt crystals, Fm-3m (the space group of general rock salt crystals) and Fd-3m (the space group of rock salt crystals with the simplest symmetry). Therefore, the Miller indices of the crystal planes that satisfy the above conditions are different between layered rock salt crystals and pseudospinel crystals and rock salt crystals. In this specification, when the cubic close-packed structures formed by the anions are aligned in layered rock salt crystals, pseudospinel crystals, and rock salt crystals, the crystal orientations may be said to be approximately aligned.

[0035] The general alignment of the crystal orientations of the two regions can be determined from TEM (transmission electron microscope), STEM (scanning transmission electron microscope), HAADF-STEM (high-angle annular dark-field scanning transmission electron microscope), and ABF-STEM (annular bright-field scanning transmission electron microscope) images. X-ray diffraction (XRD), electron diffraction, and neutron diffraction can also be used. In TEM images, the arrangement of cations and anions can be observed as repeated bright and dark lines. When the orientation of the cubic close-packed structure of the layered rock salt crystal and the rock salt crystal is aligned, the angle between the repeated bright and dark lines between the crystals can be observed to be less than 5 degrees, preferably less than 2.5 degrees. Light elements such as oxygen and fluorine may not provide sufficient contrast with the background in TEM images. In such cases, the alignment of the orientations can be determined from the arrangement of metal elements.

[0036] In this specification, the theoretical capacity of a positive electrode active material refers to the amount of electricity when all of the intercalable lithium contained in the positive electrode active material is deintercalated. For example, the theoretical capacity of LiCoO2 is 274 mAh / g, the theoretical capacity of LiNiO2 is 274 mAh / g, and the theoretical capacity of LiMn2O4 is 148 mAh / g.

[0037] In this specification and the like, the depth of charge when all intercalable and deintercalable lithium is intercalated is defined as 0, and the depth of charge when all intercalable and deintercalable lithium contained in the positive electrode active material is deintercalated is defined as 1.

[0038] In this specification, charging refers to the transfer of lithium ions from the positive electrode to the negative electrode within a battery and the transfer of electrons from the positive electrode to the negative electrode in an external circuit. Regarding positive electrode active materials, charging refers to the removal of lithium ions. A positive electrode active material with a charge depth of 0.74 to 0.9, more specifically, 0.8 to 0.83, is considered to be a positive electrode active material charged at a high voltage. For example, a LiCoO2 positive electrode active material charged at 219.2 mAh / g is considered to be a positive electrode active material charged at a high voltage. Furthermore, a positive electrode active material charged at a constant current of 4.525 V to 4.65 V (for a lithium counter electrode) at 25°C, followed by constant voltage charging at 0.02 C or approximately 1 / 5 to 1 / 100 of the current value during constant current charging, is also considered to be a positive electrode active material charged at a high voltage.

[0039] Similarly, discharging refers to the transfer of lithium ions from the negative electrode to the positive electrode within the battery and the transfer of electrons from the negative electrode to the positive electrode in an external circuit. For a positive electrode active material, discharging refers to the insertion of lithium ions. A fully discharged positive electrode active material is defined as a positive electrode active material with a charge depth of 0.06 or less, or a positive electrode active material that has been discharged from a high-voltage charged state to 90% or more of its charge capacity. For example, a LiCoO2 positive electrode active material with a charge capacity of 219.2 mAh / g is considered to be in a high-voltage charged state. A fully discharged positive electrode active material is defined as a positive electrode active material that has been discharged from this state to 90% of its charge capacity (197.3 mAh / g or more). Furthermore, a LiCoO2 positive electrode active material that has been discharged at a constant current until the battery voltage reaches 3 V or less (when using a lithium counter electrode) at 25°C is also defined as a fully discharged positive electrode active material.

[0040] In this specification, a non-equilibrium phase change refers to a phenomenon that causes a non-linear change in a physical quantity. For example, a non-equilibrium phase change occurs around the peak in the dQ / dV curve obtained by differentiating capacitance (Q) with voltage (V), and it is believed that the crystal structure changes significantly.

[0041] (Embodiment 1) In this embodiment, a positive electrode active material of one embodiment of the present invention, a positive electrode including the positive electrode active material, and a manufacturing method of the positive electrode active material will be described with reference to FIGS.

[0042] [Cathode active material 100] The positive electrode active material 100 of one embodiment of the present invention is a particle group of a composite oxide containing lithium, cobalt, nickel, aluminum, magnesium, oxygen, and fluorine.

[0043] When the particle size distribution of the positive electrode active material 100 is measured using a laser diffraction / scattering method, the maximum value is preferably in the range of 1 μm to 10 μm, more preferably 1 μm to 6 μm, and even more preferably 2 μm to 4 μm. 50 is preferably present in the range of 1 μm to 10 μm, more preferably 1 μm to 6 μm, and even more preferably 2 μm to 4 μm.

[0044] When such small particle size positive electrode active material 100 is used in a secondary battery, the contact area between the positive electrode active material and the electrolyte increases, and the distance that lithium ions and electrons travel within the particle is shortened, thereby reducing the internal resistance of the secondary battery. This is an advantage that arises not only in secondary batteries with liquid electrolytes but also in all-solid-state secondary batteries.

[0045] Furthermore, when the number of cobalt atoms in the positive electrode active material 100 is taken as 100, the relative value of the number of nickel atoms is preferably, for example, from 0.05 to 2, more preferably from 0.1 to 1.5, and even more preferably from 0.1 to 0.9.

[0046] When the number of cobalt atoms in the positive electrode active material 100 is taken as 100, the relative value of the number of aluminum atoms is, for example, preferably 0.05 to 2, more preferably 0.1 to 1.5, and even more preferably 0.1 to 0.9.

[0047] When the number of cobalt atoms in the positive electrode active material 100 is taken as 100, the relative value of the number of magnesium atoms is preferably, for example, 0.1 or more and 6 or less, and more preferably 0.3 or more and 3 or less.

[0048] By containing nickel, aluminum, and magnesium at the above concentrations, a stable crystal structure can be maintained even with small particle sizes, even after repeated charge and discharge at high voltages. This allows for a positive electrode active material 100 with high capacity and excellent charge and discharge cycle characteristics. The atomic ratio of cobalt, nickel, aluminum, and magnesium can be evaluated, for example, by inductively coupled plasma mass spectrometry (ICP-MS).

[0049] Furthermore, the relative value of the number of fluorine atoms in the positive electrode active material 100, where the number of magnesium atoms is 1, is preferably, for example, 2 or more and 3.9 or less. This range is effective in lowering the melting point when the magnesium source and the fluorine source are mixed in the production process, as described below, and does not result in an excessive amount of lithium. The fluorine atomic ratio can be evaluated, for example, by glow discharge mass spectrometry (GD-MS).

[0050] [Cathode active material 200] Furthermore, if an aggregate of particles in which the above-mentioned positive electrode active material 100 having a relatively small particle size and the positive electrode active material 200 having a larger particle size are mixed is used in a secondary battery, the capacity per volume can be improved, which is preferable.

[0051] When the particle size distribution of positive electrode active material 200 having a larger particle size is measured using, for example, a laser diffraction / scattering method, it is preferable that the maximum value is between 9 μm and 25 μm.

[0052] The positive electrode active material 200 is preferably a particle group of a composite oxide containing lithium, cobalt, nickel, aluminum, magnesium, oxygen, and fluorine, as in the positive electrode active material 100, because it has a high capacity and excellent charge / discharge cycle characteristics.

[0053] When the number of cobalt atoms in the positive electrode active material 200 is taken as 100, the relative value of the number of nickel atoms is, for example, preferably 0.05 to 2, more preferably 0.1 to 1.5, and even more preferably 0.1 to 0.9.

[0054] When the number of cobalt atoms in the positive electrode active material 200 is taken as 100, the relative value of the number of aluminum atoms is, for example, preferably 0.05 to 2, more preferably 0.1 to 1.5, and even more preferably 0.1 to 0.9.

[0055] When the number of cobalt atoms in the positive electrode active material 200 is taken as 100, the relative value of the number of magnesium atoms is preferably, for example, 0.1 or more and 6 or less, and more preferably 0.3 or more and 3 or less.

[0056] Furthermore, when the number of magnesium atoms contained in positive electrode active material 200 is taken as 1, the relative value of the number of fluorine atoms is preferably, for example, 2 or more and 3.9 or less.

[0057] [Mixing ratio] The mixing ratio of the positive electrode active material 100 and the positive electrode active material 200 is preferably set to a ratio that increases the powder packing density (hereinafter referred to as PPD), since this increases the capacity per volume of the secondary battery.

[0058] PPD is calculated by filling a pellet die with powder of weight W, gradually applying uniaxial pressure, and calculating the volume V when a predetermined pressure is reached (the following formula (1)).

[0059]

number

[0060] In this embodiment and example, 1.2 g (W) of powder is filled into a pellet die with a diameter of 10 mm, and the PPD is calculated from the volume (V) after uniaxial pressure of 50 kN for 30 seconds.

[0061] In the particle aggregate in which the positive electrode active material 100 and the positive electrode active material 200 are mixed, it is preferable that the proportion of the positive electrode active material 100 is 5% by weight or more and 30% by weight or less, since this improves the PPD, and it is more preferable that it is 10% by weight or more and 20% by weight or less.

[0062] [Crystal structure] Furthermore, it is preferable that the positive electrode active material 100 and the positive electrode active material 200 have a pseudo-spinel crystal structure when charged at a high voltage. The pseudo-spinel crystal structure will be described below.

[0063] The positive electrode active material shown in Fig. 2 is lithium cobalt oxide (LiCoO) to which magnesium, nickel, aluminum, etc. are not added. As described in Non-Patent Documents 1 and 2, the crystal structure of the lithium cobalt oxide shown in Fig. 2 changes depending on the depth of charge.

[0064] As shown in Figure 2, lithium cobalt oxide at a depth of charge of 0 (discharged state) has a region with a crystal structure of space group R-3m, with three CoO2 layers in the unit cell. For this reason, this crystal structure is sometimes called an O3-type crystal structure. Note that a CoO2 layer is an octahedral structure in which cobalt is six-coordinated with oxygen, and the layers are connected in a plane with edge sharing.

[0065] At a charge depth of 1, the crystal structure is of the space group P-3m1, with one CoO2 layer in the unit cell. Therefore, this crystal structure is sometimes called an O1-type crystal structure.

[0066] Furthermore, lithium cobalt oxide at a charge depth of approximately 0.88 has a crystal structure of the space group R-3m. This structure can be described as a structure in which a CoO2 structure such as P-3m1(O1) and a LiCoO2 structure such as R-3m(O3) are alternately stacked. Therefore, this crystal structure is sometimes referred to as the H1-3 crystal structure. In reality, the H1-3 crystal structure has twice the number of cobalt atoms per unit cell compared to other structures. However, in Figure 2 and other parts of this specification, for ease of comparison with other structures, the c-axis of the H1-3 crystal structure is shown as half the unit cell.

[0067] As an example, as described in Non-Patent Document 3, the coordinates of cobalt and oxygen in the unit cell of the H1-3 type crystal structure can be expressed as Co(0, 0, 0.42150±0.00016), O1(0, 0, 0.27671±0.00045), and O2(0, 0, 0.11535±0.00045). O1 and O2 are each an oxygen atom. Thus, the H1-3 type crystal structure is expressed by a unit cell using one cobalt and two oxygen atoms. On the other hand, as described below, the pseudospinel type crystal structure of one embodiment of the present invention is preferably expressed by a unit cell using one cobalt and one oxygen atom. This indicates that the symmetry between cobalt and oxygen differs between the pseudospinel structure and the H1-3 type structure, and that the pseudospinel structure changes less from the O3 structure than the H1-3 type structure. The unit cell that is more preferably used to represent the crystal structure of the positive electrode active material may be selected, for example, so that the GOF (good of fitness) value is smaller in Rietveld analysis of XRD.

[0068] When lithium cobalt oxide is repeatedly charged and discharged at a high voltage of 4.6 V or higher, based on the redox potential of lithium metal, or at a deep charge depth of 0.8 or higher, the crystal structure of the lithium cobalt oxide changes repeatedly (i.e., a non-equilibrium phase change) between the H1-3 crystal structure and the R-3m(O3) structure in the discharged state.

[0069] However, these two crystal structures have a large deviation in the CoO2 layers. As shown by the dotted lines and arrows in Figure 3, in the H1-3 type crystal structure, the CoO2 layers are significantly deviated from the R-3m(O3) structure. Such dynamic structural changes can adversely affect the stability of the crystal structure.

[0070] Furthermore, the difference in volume is large: when compared per the same number of cobalt atoms, the difference in volume between the H1-3 crystal structure and the O3 crystal structure in the discharged state is more than 3.0%.

[0071] In addition, the H1-3 type crystal structure, which has continuous CoO2 layers such as P-3m1(O1), is likely to be unstable.

[0072] Therefore, repeated high-voltage charging and discharging causes the crystalline structure of lithium cobalt oxide to collapse, which leads to a deterioration in cycle characteristics. This is thought to be because the collapse of the crystalline structure reduces the number of sites where lithium can exist stably and makes it difficult for lithium to be inserted and extracted.

[0073] Meanwhile, an example of the crystal structure of a positive electrode active material 100 and a positive electrode active material 200 according to one embodiment of the present invention before and after charge and discharge is shown in FIG.

[0074] The crystal structure at a charge depth of 0 (discharged state) in Figure 1 is the same as in Figure 2, R-3m(O3). However, when the cathode active material 100 and cathode active material 200 are fully charged, they preferably have a crystal structure different from the H1-3 crystal structure. This structure is in the space group R-3m and is not a spinel crystal structure. However, ions such as cobalt and magnesium occupy six oxygen coordination sites, and the cation arrangement has a symmetry similar to that of a spinel structure. Therefore, this structure is referred to as a pseudo-spinel crystal structure in this specification. Note that in the pseudo-spinel crystal structure shown in Figure 1, lithium is omitted to explain the symmetry of the cobalt atoms and the oxygen atoms. However, in reality, lithium is present between the CoO2 layers at, for example, 20 atomic % or less relative to cobalt. In both the O3 crystal structure and the pseudo-spinel crystal structure, it is preferable for magnesium to be present in a dilute amount between the CoO2 layers, i.e., at the lithium sites. It is also preferable that halogen such as fluorine is present randomly and dilutely at the oxygen sites.

[0075] In addition, in the pseudospinel crystal structure, light elements such as lithium may occupy the oxygen tetracoordination site, and in this case too, the arrangement of ions has a symmetry similar to that of the spinel structure.

[0076] It can also be said that the pseudospinel crystal structure has random Li between the layers, but is similar to the CdCl2 crystal structure. This CdCl2-like crystal structure was observed when lithium nickel oxide was charged to a depth of charge of 0.94 (Li 0.06 The crystal structure is similar to that of lithium cobaltate (NiO2), but it is known that pure lithium cobaltate or layered rock salt-type positive electrode active materials containing a large amount of cobalt do not usually adopt this crystal structure.

[0077] The anions in layered rock salt crystals and rock salt crystals have a cubic close-packed structure (face-centered cubic lattice structure). It is presumed that the anions in pseudospinel crystals also have a cubic close-packed structure. When these crystals contact, there are crystal planes where the cubic close-packed structures formed by the anions are aligned. However, the space group of layered rock salt crystals and pseudospinel crystals is R-3m, which is different from the space groups of rock salt crystals, Fm-3m (the space group of general rock salt crystals) and Fd-3m (the space group of rock salt crystals with the simplest symmetry). Therefore, the Miller indices of the crystal planes that satisfy the above conditions are different between layered rock salt crystals and pseudospinel crystals and rock salt crystals. In this specification, when the cubic close-packed structures formed by the anions are aligned in layered rock salt crystals, pseudospinel crystals, and rock salt crystals, the crystal orientations may be said to be approximately aligned.

[0078] When a large amount of lithium is released during high-voltage charging, the pseudo-spinel crystal structure suppresses changes in the crystal structure compared to conventional positive electrode active materials. For example, as shown by the dotted line in Figure 1, these crystal structures show almost no shifting of the CoO2 layers.

[0079] More specifically, when the cathode active material 100 and the cathode active material 200 have a pseudo-spinel crystal structure when charged at a high voltage, the structure is highly stable. For example, in the conventional cathode active material shown in FIG. 2, even at a charge voltage of approximately 4.6 V relative to the potential of lithium metal, where the H1-3 crystal structure is formed, there is a region of charge voltage where the R-3m(O3) crystal structure can be maintained. Furthermore, even at higher charge voltages, for example, at voltages of approximately 4.65 V to 4.7 V relative to the potential of lithium metal, there is also a region where the pseudo-spinel crystal structure can be formed. Furthermore, at higher charge voltages, for example, at voltages of 4.3 V to 4.5 V relative to the potential of lithium metal, there is also a region where the H1-3 crystal structure can be formed. Furthermore, when graphite is used as the anode active material in a secondary battery, there is a region of charge voltage where the R-3m(O3) crystal structure can be maintained even at a secondary battery voltage of 4.3 V to 4.5 V, and even at higher charge voltages, for example, at voltages of 4.35 V to 4.55 V relative to the potential of lithium metal, there is also a region where the pseudo-spinel crystal structure can be formed.

[0080] Therefore, the crystal structure of the positive electrode active material 100 and the positive electrode active material 200 is unlikely to be destroyed even when the material is repeatedly charged and discharged at a high voltage.

[0081] The pseudospinel crystal structure can be expressed by the coordinates of cobalt and oxygen in the unit cell being Co(0,0,0.5), O(0,0,x), with 0.20≦x≦0.25.

[0082] Additives such as magnesium, which are present randomly and dilutely between the CoO2 layers, i.e., at the lithium sites, have the effect of suppressing the displacement of the CoO2 layers during high-voltage charging. Therefore, the presence of magnesium between the CoO2 layers facilitates the formation of a pseudo-spinel crystal structure. Therefore, it is preferable that magnesium be distributed throughout the particles of the positive electrode active material 100. Furthermore, to distribute magnesium throughout the particles, it is preferable to perform a heat treatment during the manufacturing process of the positive electrode active material 100 and the positive electrode active material 200.

[0083] However, if the heat treatment temperature is too high, cation mixing occurs, increasing the possibility that magnesium will enter the cobalt site. Magnesium present in the cobalt site is ineffective in maintaining the R-3m structure during high-voltage charging. Furthermore, if the heat treatment temperature is too high, there are concerns that adverse effects such as cobalt being reduced to a divalent state and lithium evaporating may occur.

[0084] Therefore, it is preferable to add a halogen compound such as a fluorine compound to the lithium cobalt oxide before the heat treatment to distribute magnesium throughout the particles. The addition of the halogen compound lowers the melting point of the lithium cobalt oxide. Lowering the melting point makes it easier to distribute magnesium throughout the particles at a temperature where cation mixing is unlikely to occur. Furthermore, the presence of a fluorine compound is expected to improve corrosion resistance to hydrofluoric acid produced by decomposition of the electrolyte.

[0085] However, if the magnesium concentration is increased beyond a desired value, the effect of stabilizing the crystal structure may be reduced, presumably because magnesium occupies the cobalt site in addition to the lithium site.

[0086] <Charging method and XRD measurement method> Whether a certain composite oxide has a pseudospinel crystal structure when charged at a high voltage can be determined, for example, by preparing a coin cell (CR2032 type, 20 mm diameter, 3.2 mm height) using lithium as the counter electrode, charging it, and estimating the crystal structure by XRD. 0112] More specifically, the positive electrode can be prepared by coating a positive electrode current collector made of aluminum foil with a slurry containing a positive electrode active material, a conductive additive, and a binder. If the positive electrode active material layer is too thin, the aluminum foil signal will be detected by XRD, so the positive electrode active material layer should preferably be thick enough. Furthermore, using a positive electrode that has not been pressed after coating is preferable because it is easier to observe peaks other than those derived from the (003) plane around 2θ = 18° to 20°.

[0087] Lithium metal can be used for the counter electrode. When a material other than lithium metal is used for the counter electrode, the voltage of the secondary battery and the potential of the positive electrode are different. Unless otherwise specified, the voltage and potential in this specification refer to the potential of the positive electrode.

[0088] The electrolyte in the electrolytic solution is 1 mol / L lithium hexafluorophosphate (LiPF6), and the solvent is a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of EC:DEC = 3:7.

[0089] The separator can be made of polypropylene with a thickness of 25 μm.

[0090] The positive electrode can and the negative electrode can may be made of stainless steel (SUS).

[0091] The coin cell fabricated under the above conditions was charged at a constant current of 4.6 V and 0.2 C, followed by a constant voltage charge until the current reached 0.02 C. It was then discharged at a constant current of 0.2 C to 2.5 V, after which it was again charged at a constant current of 4.6 V and 0.2 C, followed by a constant voltage charge until the current reached 0.02 C. Here, 1 C corresponds to 200 mA / g. The temperature was 25°C. After charging in this manner, the coin cell was disassembled in an argon-atmosphere glove box, washed with a solvent such as DMC to remove the electrolyte, and the positive electrode was removed to obtain a positive electrode active material charged at a high voltage. When performing various subsequent analyses, it is preferable to seal the cell in an argon atmosphere to prevent reactions with external components. For example, XRD can be performed in a sealed container under an argon atmosphere.

[0092] The XRD instrument should be set up for powder samples, and the sample height should be adjusted to fit the required measurement surface of the instrument. It is also preferable to set the positive electrode sample flat, without bending it. Specifically, the electrode can be attached to a glass plate with double-sided tape (the kind commonly used for stationery, made of nonwoven fabric coated with adhesive), and the sample can be sealed in an airtight cell for measurement.

[0093] <XRDパターン> Figure 3 shows an ideal powder XRD pattern calculated from the pseudospinel crystal structure and the H1-3 crystal structure model using CuKα1 radiation. For comparison, ideal XRD patterns calculated from the crystal structures of LiCoO2(O3) at a charge depth of 0 and CoO2(O1) at a charge depth of 1 are also shown. The LiCoO2(O3) and CoO2(O1) patterns were created using Reflex Powder Diffraction, a module of Materials Studio (BIOVIA), from crystal structure information obtained from the ICSD (Inorganic Crystal Structure Database) (see Non-Patent Document 5). The 2θ range was 15° to 75°, with a step size of 0.01 and a wavelength of λ1 of 1.540562×10. -10m and λ2 were not set, and Monochromator was set to single. A pattern of the H1-3 type crystal structure was similarly created from the crystal structure information described in Non-Patent Document 3. A pattern of the pseudospinel type crystal structure was created by estimating the crystal structure from the XRD pattern of a positive electrode active material according to one embodiment of the present invention, fitting the pattern using TOPAS ver. 3 (crystal structure analysis software manufactured by Bruker), and creating an XRD pattern in the same manner as the others.

[0094] As shown in Figure 3, the pseudospinel crystal structure exhibits diffraction peaks at 2θ = 19.30 ± 0.20° (19.10° to 19.50°) and 2θ = 45.55 ± 0.10° (45.45° to 45.65°). More specifically, sharp diffraction peaks appear at 2θ = 19.30 ± 0.10° (19.20° to 19.40°) and 2θ = 45.55 ± 0.05° (45.50° to 45.60°). However, peaks do not appear at these positions in the H1-3 crystal structure or CoO2(P-3m1, O1). Therefore, the appearance of peaks at 2θ = 19.30 ± 0.20° and 2θ = 45.55 ± 0.10° when charged at high voltage is characteristic of the pseudospinel crystal structure.

[0095] This can also be said to mean that the positions at which XRD diffraction peaks appear are close between the crystal structure at a charge depth of 0 and the crystal structure after high-voltage charging. More specifically, the difference in the positions at which two or more, preferably three or more, of the main diffraction peaks of both structures appear is 2θ=0.7 or less, more preferably 2θ=0.5 or less.

[0096] In addition, the cathode active materials 100 and 200 according to one aspect of the present invention preferably have a pseudo-spinel crystal structure when charged at a high voltage, but not all of the particles need to have a pseudo-spinel crystal structure. Other crystal structures may be included, or a part may be amorphous. However, when performing Rietveld analysis on the XRD pattern, the pseudo-spinel crystal structure is preferably 50 wt% or more, more preferably 60 wt% or more, and even more preferably 66 wt% or more. If the pseudo-spinel crystal structure is 50 wt% or more, more preferably 60 wt% or more, and even more preferably 66 wt% or more, a cathode active material with excellent cycle characteristics can be obtained sufficiently.

[0097] Further, even after 100 cycles or more of charge and discharge from the start of measurement, when performing Rietveld analysis, the pseudo-spinel crystal structure is preferably 35 wt% or more, more preferably 40 wt% or more, and even more preferably 43 wt% or more.

[0098] In addition, the crystallite size of the pseudo-spinel crystal structure possessed by the particles of the cathode active material only decreases to about 1 / 10 of that of LiCoO2 (O3) in the discharged state. Therefore, even under the same XRD measurement conditions as those of the cathode before charge and discharge, a clear peak of the pseudo-spinel 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 crystal structure, the crystallite size becomes small and the peak becomes broad and small. The crystallite size can be obtained from the half-width of the XRD peak.

[0099] <dQ / dV vs V curve> In addition, when the cathode active material according to one aspect of the present invention is discharged at a low rate of, for example, 0.2C or less after charging 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.

[0100] [Method for producing cathode active material 100] Next, an example of a method for producing the positive electrode active material 100 will be described with reference to Fig. 4. The positive electrode active material 100 is preferably produced by first synthesizing lithium cobalt oxide, then mixing a nickel source, an aluminum source, a magnesium source, and a fluorine source, and heating the mixture. After heating, it is also preferable to perform a crushing treatment.

[0101] <Step S11: Preparation of Li Source and Co Source> First, a lithium source and a cobalt source are prepared as starting materials. The lithium source can be, for example, lithium carbonate or lithium fluoride. The cobalt source can be, for example, cobalt oxide.

[0102] <Step S12: Crushing and Mixing of Li Source and Co Source> Next, the starting materials are mixed. For example, a ball mill, a bead mill, etc. can be used for mixing. When using a ball mill, zirconia balls can be used as the medium.

[0103] The particle size of the mixed materials affects the particle size of the lithium cobalt oxide after firing, so in this step, it is preferable to use a ball mill with an orbital radius of 75 mm and a rotational container radius of 20 mm, and to crush and mix the materials at 100 rpm to 300 rpm for about 12 hours.

[0104] <Step S13: Firing> Next, in step S12, the mixed materials are heated. This step is sometimes called firing or the first heating. Heating is preferably performed at a temperature of 800°C or higher but lower than 1100°C, more preferably 900°C or higher but lower than 1000°C, and even more preferably around 950°C. If the temperature is too low, the starting materials may not be sufficiently decomposed or melted. On the other hand, if the temperature is too high, defects such as divalent cobalt may occur due to factors such as cobalt reduction or lithium evaporation.

[0105] The heating time is preferably 2 hours or more and 20 hours or less. Firing is preferably carried out in an atmosphere such as dry air. For example, heating is preferably carried out at 950°C for 10 hours, with a temperature increase rate of 200°C / h and a dry atmosphere flow rate of 10 L / min. The heated material is then cooled to room temperature. For example, the cooling time from the holding temperature to room temperature is preferably 10 hours or more and 50 hours or less.

[0106] <Step S14: LiCoO2> In step S13, the heated material is recovered to obtain lithium cobalt oxide.

[0107] <Step S21: Preparation of Ni source> Next, a nickel source is prepared. As the nickel source, for example, nickel hydroxide or nickel fluoride can be used.

[0108] <Step S22: Preparation of Al source> Next, an aluminum source is prepared. As the aluminum source, for example, aluminum hydroxide, aluminum fluoride, etc. can be used.

[0109] <Step S31: Preparation of Mg Source and F Source> Next, a magnesium source and a fluorine source are prepared. Examples of magnesium sources that can be used include magnesium fluoride, magnesium hydroxide, and magnesium carbonate. Examples of fluorine sources that can be used include lithium fluoride and magnesium fluoride. That is, lithium fluoride can be used as both a lithium source and a fluorine source, and magnesium fluoride can be used as both a fluorine source and a magnesium source.

[0110] In this embodiment, lithium fluoride (LiF) is prepared as the fluorine source, and magnesium fluoride (MgF2) is prepared as both the fluorine source and the magnesium source. Mixing lithium fluoride (LiF) and magnesium fluoride (MgF2) at a molar ratio of approximately LiF:MgF2 = 1:3 effectively lowers the melting point. On the other hand, excessive lithium fluoride can lead to excessive lithium, potentially deteriorating cycle performance. Therefore, the molar ratio of lithium fluoride (LiF) to magnesium fluoride (MgF2) is preferably LiF:MgF2 = x:1 (0≦x≦1.9), more preferably LiF:MgF2 = x:1 (0.1≦x≦0.5), and even more preferably LiF:MgF2 = x:1 (near x = 0.33). In this specification, "near" refers to a value greater than 0.9 times but less than 1.1 times the value.

[0111] In this embodiment, the mixture is set to a molar ratio of LiF:MgF2=1:3 and a weight ratio of LiF:MgF2=12.19:87.81.

[0112] If the subsequent crushing and mixing steps are performed wet, a solvent is prepared. Examples of solvents that can be used include ketones such as acetone, alcohols such as ethanol and isopropanol, ether, dioxane, acetonitrile, and N-methyl-2-pyrrolidone (NMP). It is more preferable to use an aprotic solvent that is less likely to react with lithium. In this embodiment, acetone is used.

[0113] <Step S32: Crushing and Mixing of Mg Source and F Source> Next, the magnesium source and the fluorine source are crushed and mixed. Mixing can be performed by either a dry method or a wet method, but a wet method is preferred because it allows for finer grinding. For example, a ball mill, a bead mill, or the like can be used for mixing. When using a ball mill, it is preferable to use zirconia balls as the medium. It is preferable to perform this crushing and mixing process sufficiently to finely powder the mixture 902 of the magnesium source and the fluorine source.

[0114] In this embodiment, mixing and pulverization are performed using a ball mill. More specifically, the mixture is placed in a ball mill container (a zirconia pot manufactured by Ito Seisakusho, capacity 45 mL) together with zirconia balls (1 mm diameter), 20 mL of dehydrated acetone is added, and the mixture is pulverized and mixed at 400 rpm for 12 hours.

[0115] <Step S33: Mixture 902> In step S32, the crushed and mixed material is collected to obtain a mixture 902.

[0116] In this embodiment, after step S32 is completed, the zirconia balls are separated from the suspension using a sieve, and the suspension is dried on a hot plate at 50° C. for about 1 to 2 hours to obtain a mixture 902.

[0117] When the particle size distribution of the mixture 902 is measured by, for example, a laser diffraction / scattering method, D 50 Preferably, the particle size is 600 nm or more and 20 μm or less, more preferably 1 μm or more and 10 μm or less, and even more preferably around 3.5 μm. If the mixture 902 is finely powdered in this manner, when it is mixed with lithium cobalt oxide in a later process, the mixture 902 can be easily adhered uniformly to the surfaces of the lithium cobalt oxide particles. If the mixture 902 is evenly adhered to the surfaces of the lithium cobalt oxide particles, it is preferable because it is easy to distribute halogens such as fluorine and magnesium in the surface layer portion of the lithium cobalt oxide after heating.

[0118] <Step S41: Mixing> Next, lithium cobalt oxide, the nickel source, the aluminum source, and mixture 902 are mixed together. When the number of cobalt atoms in lithium cobalt oxide is taken as 100, the mixture is preferably mixed so that the relative value of the number of magnesium atoms in mixture 902 is 0.1 or more and 6 or less, and more preferably 0.3 or more and 3 or less.

[0119] The mixing conditions in step S41 are preferably milder than those in step S32 so as not to destroy the lithium cobalt oxide particles. For example, the mixing conditions are preferably lower in rotation speed or shorter in time than in step S32. Also, it can be said that dry mixing provides milder conditions than wet mixing. For example, a ball mill, bead mill, etc. can be used for mixing. When using a ball mill, it is preferable to use zirconia balls as the media.

[0120] <Step S42: Mixture 903> The mixed materials are collected to obtain a mixture 903.

[0121] <Step S43: Annealing> Next, the mixture 903 is heated. This step is sometimes called annealing or second heating to distinguish it from the previous heating step (step S13).

[0122] The annealing is preferably performed at an appropriate temperature and time. The appropriate temperature and time vary depending on conditions such as the size and composition of the lithium cobalt oxide particles in step S14. If the particles are small, a lower temperature or shorter time may be more preferable than if the particles are large. Also, if the annealing temperature is too high or too long, the particles may sinter.

[0123] The positive electrode active material 100 produced in this embodiment has a relatively small particle size, with a maximum particle size of 1 μm or more and 10 μm or less, when the particle size distribution is measured. Therefore, for example, the annealing temperature is preferably 600° C. or more and 950° C. or less. The annealing time is preferably 1 hour or more and 10 hours or less, and more preferably about 2 hours. In this embodiment, the annealing temperature is 800° C. and the annealing time is 2 hours.

[0124] The temperature drop time after annealing is preferably, for example, 10 hours or more and 50 hours or less.

[0125] When mixture 903 is annealed, it is believed that the material with a low melting point in mixture 903 (for example, lithium fluoride contained in mixture 902, melting point 848°C) melts first and distributes to the surface layer of the lithium cobalt oxide particles. Next, the presence of this molten material is thought to lower the melting points of other materials, causing them to melt. For example, magnesium fluoride (melting point 1263°C) is thought to melt and distribute to the surface layer of the lithium cobalt oxide particles. It can also be said that lithium fluoride acts as a flux.

[0126] It is believed that the elements contained in the mixture 902 distributed in the surface layer portion are dissolved in the lithium cobalt oxide.

[0127] The diffusion of elements contained in this mixture 902 is faster in the surface layer and near the grain boundaries than in the interior of the composite oxide particles, so that magnesium and fluorine are concentrated at higher concentrations in the surface layer and near the grain boundaries than in the interior.

[0128] <Step S44: Complex Oxide> In step S43, the heated material is recovered to obtain a composite oxide containing lithium, cobalt, nickel, aluminum, magnesium, oxygen, and fluorine.

[0129] <Step S45: Crushing> After annealing, the composite oxide may contain agglomerated primary particles that have formed secondary particles, so it is subjected to a crushing process. For example, a ball mill or a thin-film swirl high-speed mixer can be used for crushing. When using a ball mill for crushing, it is preferable to use a ball mill with an orbital radius of 75 mm and a rotational container radius of 20 mm, and crush and mix the mixture at 80 rpm to 150 rpm for 2 hours. Using a thin-film swirl high-speed mixer for crushing is preferable because it makes it more difficult to crush the primary particles. By performing this crushing process after annealing, the particle size can be reduced.

[0130] <Step S46: Positive Electrode Active Material 100> In step S45, the crushed material is collected to obtain the positive electrode active material 100.

[0131] [Method for producing positive electrode active material 200] Next, an example of a method for producing the positive electrode active material 200 will be described with reference to Fig. 5. The positive electrode active material 200 can be produced by mixing lithium cobalt oxide with a nickel source, an aluminum source, a magnesium source, and a fluorine source, and heating the mixture.

[0132] <Steps S11 to S14> 4, a lithium source and a cobalt source are mixed and fired to produce lithium cobalt oxide. In step S12, the particle size of the starting materials affects the particle size of the fired lithium cobalt oxide. Therefore, in this step, when a ball mill is used, it is preferable to use a ball mill having an orbital radius of 75 mm and a rotational container radius of 20 mm, and to perform crushing and mixing at 80 rpm or more and 300 rpm or less for about 2 hours.

[0133] Alternatively, pre-synthesized lithium cobalt oxide may be used, in which case steps S11 to S13 can be omitted.

[0134] For example, lithium cobalt oxide particles (product name: Cellseed C-10N) manufactured by Nippon Chemical Industry Co., Ltd. can be used as pre-synthesized lithium cobalt oxide. 50 ) is about 12 μm, and impurity analysis by glow discharge mass spectrometry (GD-MS) shows that the magnesium concentration and fluorine concentration are 50 ppm wt or less, 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 1100 ppm wt or less, and the concentration of other elements other than lithium, cobalt and oxygen is 150 ppm wt or less.

[0135] Alternatively, lithium cobalt oxide particles (product name: Cellseed C-5H) manufactured by Nippon Chemical Industry Co., Ltd. can also be used. 50 ) is approximately 6.5 μm, and impurity analysis by GD-MS shows that the concentrations of elements other than lithium, cobalt, and oxygen are the same as or lower than those of C-10N.

[0136] In this embodiment, cobalt is used as the transition metal, and pre-synthesized lithium cobalt oxide particles (Cellseed C-10N manufactured by Nippon Chemical Industry Co., Ltd.) are used.

[0137] <Steps S21 and S22> Similar to FIG. 4, a nickel source and an aluminum source are prepared.

[0138] <Steps S31 to S33> As in FIG. 4, the magnesium source and fluorine are crushed and mixed to obtain a mixture 902 .

[0139] <Steps S41 and S42> As in FIG. 4, lithium cobalt oxide, a nickel source, an aluminum source, and a mixture 902 are mixed together to obtain a mixture 903 .

[0140] <Step S43: Annealing> Next, mixture 903 is heated. Since positive electrode active material 200 has a larger particle size than positive electrode active material 100, the appropriate annealing temperature and time are different from those for positive electrode active material 100.

[0141] 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. In this embodiment, the annealing temperature is 800° C. or higher and 850° C. or lower, and the annealing time is 2 hours or higher and 10 hours or lower.

[0142] <Step S44: Positive Electrode Active Material 200> In step S43, the annealed material is recovered to obtain positive electrode active material 200.

[0143] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0144] (Embodiment 2) In this embodiment, examples of materials and structures that can be used in a secondary battery including the positive electrode active material described in the previous embodiment will be described. Also, manufacturing methods for some of the structures will be described.

[0145] [Secondary battery configuration example 1] The following description will be given taking as an example a secondary battery in which a positive electrode, a negative electrode, and an electrolyte are enclosed in an exterior body.

[0146] [Positive electrode] The positive electrode has a positive electrode active material layer and a positive electrode current collector.

[0147] <Cathode active material layer> The positive electrode active material layer contains at least a positive electrode active material. In addition to the positive electrode active material, the positive electrode active material layer may contain other substances such as a coating on the surface of the active material, a conductive additive, or a binder.

[0148] As the positive electrode active material, the positive electrode active material 100 described in the previous embodiment or a mixture of the positive electrode active material 100 and the positive electrode active material 200 can be used.

[0149] When a mixture of the positive electrode active material 100 and the positive electrode active material 200 is used, the proportion of the positive electrode active material 100 in the sum is preferably 5% by weight or more and 30% by weight or less, and more preferably 10% by weight or more and 20% by weight or less. By using the positive electrode active material 100 described in the previous embodiment or a mixture of the positive electrode active material 100 and the positive electrode active material 200, a secondary battery with high capacity and excellent cycle characteristics can be obtained.

[0150] The conductive additive may be a carbon material, a metal material, a conductive ceramic material, or the like. Alternatively, a fibrous material may be used as the conductive additive. The content of the conductive additive relative to the total amount of the active material layer is preferably 1 wt% to 10 wt%, more preferably 1 wt% to 5 wt%.

[0151] The conductive additive can form an electrically conductive network in the active material layer. The conductive additive can maintain an electrical conduction path between the positive electrode active materials. By adding the conductive additive to the active material layer, an active material layer with high electrical conductivity can be realized.

[0152] Examples of the conductive additive include natural graphite, artificial graphite such as mesocarbon microbeads, and carbon fibers. Examples of the carbon fibers that can be used include mesophase pitch-based carbon fibers and isotropic pitch-based carbon fibers. Examples of the carbon fibers that can be used include carbon nanofibers and carbon nanotubes. Carbon nanotubes can be produced by vapor phase growth, for example. Examples of the conductive additive include carbon materials such as carbon black (e.g., acetylene black (AB)), graphite particles, graphene, multigraphene, reduced graphene oxide, and fullerene. Examples of the conductive additive include metal powders and metal fibers such as copper, nickel, aluminum, silver, and gold, and conductive ceramic materials.

[0153] The conductive additives may be used in combination of two or more of the above.

[0154] As the binder, it is preferable to use a rubber material such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, ethylene-propylene-diene copolymer, etc. Also, fluororubber can be used as the binder.

[0155] Furthermore, it is preferable to use, for example, a water-soluble polymer as the binder. Examples of water-soluble polymers that can be used include polysaccharides. Examples of polysaccharides that can be used include cellulose derivatives such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, and regenerated cellulose, as well as starch. It is even more preferable to use these water-soluble polymers in combination with the above-mentioned rubber material.

[0156] Alternatively, it is preferable to use materials such as polystyrene, polymethyl acrylate, polymethyl methacrylate (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, and nitrocellulose as the binder.

[0157] The binder may be used in combination with two or more of the above.

[0158] For example, a material with particularly excellent viscosity adjusting effect may be used in combination with other materials. For example, while rubber materials have excellent adhesive strength and elasticity, it may be difficult to adjust the viscosity when mixed with a solvent. In such cases, it is preferable to mix them with a material with particularly excellent viscosity adjusting effect. For example, a water-soluble polymer may be used as a material with particularly excellent viscosity adjusting effect. Furthermore, as water-soluble polymers with particularly excellent viscosity adjusting effect, the above-mentioned polysaccharides, for example, carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, cellulose derivatives such as regenerated cellulose, and starch may be used.

[0159] In addition, the solubility of cellulose derivatives such as carboxymethyl cellulose can be increased by converting them into salts such as sodium salts or ammonium salts of carboxymethyl cellulose, making them more effective as viscosity adjusters. Higher solubility can also improve dispersibility with active materials and other components when preparing electrode slurry. In this specification, the cellulose and cellulose derivatives used as electrode binders also include their salts.

[0160] Fluorine-based resins have advantages such as excellent mechanical strength, high chemical resistance, and high heat resistance. PVDF, one of the fluororesins, has extremely excellent properties among fluororesins, including mechanical strength, excellent processability, and high heat resistance.

[0161] On the other hand, PVDF may gel or become insolubilized if the slurry prepared when applying the active material layer becomes alkaline. The gelation or insolubilization of the binder may reduce the adhesion between the current collector and the active material layer. The use of a positive electrode active material according to one embodiment of the present invention is preferable because it may be possible to lower the pH of the slurry and inhibit gelation or insolubilization.

[0162] <Positive electrode current collector> The positive electrode current collector can be made of a highly conductive material, such as a metal such as stainless steel, gold, platinum, aluminum, or titanium, or an alloy thereof. It is preferable that the material used for the positive electrode current collector does not dissolve at the potential of the positive electrode. Aluminum alloys containing elements that improve heat resistance, such as silicon, titanium, neodymium, scandium, or molybdenum, can also be used. The positive electrode current collector may also be made of a metal element that reacts with silicon to form a silicide. Examples of metal elements that react with silicon to form a silicide include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, and nickel. The current collector can be in the form of a foil, plate (sheet), mesh, punched metal, or expanded metal, as appropriate. It is preferable to use a current collector with a thickness of 5 μm to 30 μm.

[0163] Surface-treated current collectors may also be used. Examples of surface treatments include corona discharge treatment, plasma treatment, and undercoat treatment. Here, the undercoat refers to a film formed on the current collector before applying the slurry to the current collector for the purpose of reducing the interfacial resistance between the active material layer and the current collector or for the purpose of increasing the adhesion between the active material layer and the current collector. The undercoat does not necessarily have to be in the form of a film, but may be formed in an island shape. Furthermore, the undercoat may also exhibit capacitance as an active material. For example, a carbon material can be used as the undercoat. For example, graphite, carbon black such as acetylene black or Ketjen Black (registered trademark), and carbon nanotubes can be used as the carbon material.

[0164] [How to make the positive electrode] An example of a method for producing a positive electrode including the positive electrode active material 100 of one embodiment of the present invention or a mixture of the positive electrode active material 100 and the positive electrode active material 200 is to prepare a slurry containing the positive electrode active material and apply the slurry to a positive electrode current collector. An example of a method for preparing the slurry and a method for applying the slurry will be described below.

[0165] The compounding ratio of the positive electrode active material, the conductive additive, and the binder may be, for example, positive electrode active material:conductive additive:binder=95:3:2 (weight ratio), or positive electrode active material:conductive additive:binder=97:1.5:1.5 (weight ratio), or another compounding ratio may be used.

[0166] The solvent used to prepare the slurry is preferably a polar solvent. For example, one or a mixture of two or more of water, methanol, ethanol, acetone, tetrahydrofuran (THF), dimethylformamide (DMF), N-methylpyrrolidone (NMP), and dimethyl sulfoxide (DMSO) can be used. In this embodiment, NMP is used.

[0167] It is preferable to use a mixer to prepare the slurry; for example, a rotation-revolution mixer called Awatori Rentaro (ARE-310, THINKY CORPORATION) can be used. However, if the entire amount of binder and solvent is put into the mixer from the beginning and mixed, clumps of particles will form, making uniform mixing difficult. For this reason, it is preferable to first perform a kneading process using a small amount of binder and solvent, and then mix the remaining binder and solvent.

[0168] Specifically, the process is preferably carried out as follows. First, the binder is dissolved in a solvent to prepare a 5 wt% binder solution. Next, the binder solution is measured out to contain approximately 35% to 50% of the final binder amount and added to a mixer. Next, the positive electrode active material and conductive additive are all added to the mixer, and the mixture is kneaded at 2000 rpm for 3 minutes. It is preferable that the amount of binder solution be such that the mixture becomes a clay-like mixture.

[0169] The mixture is then gathered with a spatula or the like, and then kneaded again in the mixer at 2000 rpm for 3 minutes. This process is repeated 8 times.

[0170] Next, the remaining binder solution and solvent are added to the mixer and mixed at 2000 rpm for 3 minutes.

[0171] By preparing the slurry in this manner, it is possible to obtain a smooth slurry with few particle agglomerates.

[0172] The current collector is an aluminum foil having a thickness of 20 μm, and the slurry is applied to the current collector, after which the solvent is evaporated and dried, for example, at 80° C. for 1 hour using a forced air dryer.

[0173] Thereafter, it is preferable to apply pressure at a press temperature of 120°C and a press linear pressure of 210 kN / m using a calender roll device (a test mini-calender (MSC-169), Yuri Roll Machinery Co., Ltd.), and then apply a further pressure of 1467 kN / m to form a positive electrode. This is because pressing at a low pressure followed by re-pressing at a high pressure can reduce damage to the positive electrode active material and facilitate higher density.

[0174] The positive electrode can also be dried again after pressing. The drying temperature is preferably 120°C in a vacuum for about 10 hours. In this case, the temperature must not exceed the melting point of PVDF. If the temperature is too high, the strength of the positive electrode may decrease.

[0175] [Negative electrode] The negative electrode includes a negative electrode active material layer and a negative electrode current collector. The negative electrode active material layer may also include a conductive additive and a binder.

[0176] <Negative electrode active material> As the negative electrode active material, for example, an alloy-based material or a carbon-based material can be used.

[0177] The negative electrode active material can be an element capable of undergoing charge-discharge reactions through alloying and dealloying reactions with lithium. For example, materials containing at least one of silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, and indium can be used. These elements have a larger capacity than carbon, and silicon, in particular, has a high theoretical capacity of 4200 mAh / g. For this reason, silicon is preferred as the negative electrode active material. Compounds containing these elements can also be used. Examples include SiO, Mg2Si, Mg2Ge, SnO, SnO2, Mg2Sn, SnS2, V2Sn3, FeSn2, CoSn2, Ni3Sn2, Cu6Sn5, Ag3Sn, Ag3Sb, Ni2MnSb, CeSb3, LaSn3, La3Co2Sn7, CoSb3, InSb, and SbSn. Here, elements that can undergo charge-discharge reactions by alloying / dealloying reactions with lithium, and compounds containing such elements, are sometimes called alloy-based materials.

[0178] In this specification and the like, SiO refers to, for example, silicon monoxide. Alternatively, SiO refers to SiO x Here, x preferably has a value close to 1. For example, x is preferably 0.2 or more and 1.5 or less, and more preferably 0.3 or more and 1.2 or less.

[0179] Examples of carbonaceous materials that can be used include graphite, easily graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), carbon nanotubes, graphene, and carbon black.

[0180] Examples of graphite include artificial graphite and natural graphite. Examples of artificial graphite include mesocarbon microbeads (MCMB), coke-based artificial graphite, and pitch-based artificial graphite. Here, spherical graphite having a spherical shape can be used as the artificial graphite. For example, MCMB may have a spherical shape and is preferred. Furthermore, it is relatively easy to reduce the surface area of ​​MCMB, and this may be preferred. Examples of natural graphite include flake graphite and spherical natural graphite.

[0181] When lithium ions are inserted into graphite (when lithium-graphite intercalation compounds are formed), graphite exhibits a low potential similar to that of metallic lithium (0.05 V to 0.3 V vs. Li / Li + ) This allows lithium-ion secondary batteries to exhibit high operating voltages. Furthermore, graphite is preferred because it has advantages such as a relatively high capacity per unit volume, a relatively small volume expansion, low cost, and a higher level of safety compared to lithium metal.

[0182] In addition, titanium dioxide (TiO2), lithium titanium oxide (Li4Ti5O 12 ), lithium-graphite intercalation compound (Li x C6), niobium pentoxide (Nb2O5), tungsten oxide (WO2), molybdenum oxide (MoO2), and other oxides can be used.

[0183] In addition, the negative electrode active material is a composite nitride of lithium and transition metals, Li3N-type 3-x M x N (M=Co, Ni, Cu) can be used. For example, Li 2.6 Co 0.4 N3 has a large charge / discharge capacity (900mAh / g, 1890mAh / cm 3 ) and is preferred.

[0184] When a composite nitride of lithium and a transition metal is used, lithium ions are contained in the negative electrode active material, and therefore it can be preferably combined with a material that does not contain lithium ions, such as V2O5 or Cr3O8, as the positive electrode active material. Even when a material containing lithium ions is used as the positive electrode active material, the composite nitride of lithium and a transition metal can be used as the negative electrode active material by first desorbing the lithium ions contained in the positive electrode active material.

[0185] In addition, materials that undergo a conversion reaction can also be used as the negative electrode active material. For example, transition metal oxides that do not form alloys with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), and iron oxide (FeO), can be used as the negative electrode active material. Materials that undergo a conversion reaction include oxides such as Fe2O3, CuO, Cu2O, RuO2, and Cr2O3, and CoS 0.89 It also occurs with sulfides such as NiS and CuS, nitrides such as Zn3N2, Cu3N and Ge3N4, phosphides such as NiP2, FeP2 and CoP3, and fluorides such as FeF3 and BiF3.

[0186] The conductive additive and binder that can be contained in the negative electrode active material layer can be the same materials as the conductive additive and binder that can be contained in the positive electrode active material layer.

[0187] <Negative electrode current collector> The negative electrode current collector may be made of the same material as the positive electrode current collector, in addition to copper, etc. It is preferable that the negative electrode current collector be made of a material that does not alloy with carrier ions such as lithium.

[0188] [Electrolyte] The electrolytic solution includes a solvent and an electrolyte. The solvent for the electrolytic solution is preferably an aprotic organic solvent, such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, chloroethylene carbonate, vinylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethoxyethane (DME), dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, or sultone, or any combination and ratio of two or more of these.

[0189] Furthermore, by using one or more flame-retardant and non-volatile ionic liquids (room-temperature molten salts) as the solvent for the electrolyte, it is possible to prevent the secondary battery from exploding or catching fire even if the internal temperature rises due to an internal short circuit or overcharging of the secondary battery. Ionic liquids are composed of cations and anions, including organic cations and anions. Examples of organic cations used in the electrolyte include aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, and aromatic cations such as imidazolium cations and pyridinium cations. Examples of anions used in the electrolyte include monovalent amide anions, monovalent methide anions, fluorosulfonate anions, perfluoroalkylsulfonate anions, tetrafluoroborate anions, perfluoroalkylborate anions, hexafluorophosphate anions, and perfluoroalkylphosphate anions.

[0190] Examples of the electrolyte to be dissolved in the solvent include LiPF6, LiClO4, LiAsF6, LiBF4, LiAlCl4, LiSCN, LiBr, LiI, Li2SO4, and Li2B 10 Cl 10 , Li2B 12 Cl 12 Lithium salts such as LiCF3SO3, LiC4F9SO3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiN(CF3SO2)2, LiN(C4F9SO2)(CF3SO2), LiN(C2F5SO2)2, and lithium bis(oxalato)borate (LiBOB) can be used alone or in any combination and ratio of two or more of these.

[0191] The electrolyte used in the secondary battery is preferably a highly purified electrolyte with a low content of granular dust and elements other than the constituent elements of the electrolyte (hereinafter simply referred to as "impurities"). Specifically, the weight ratio of impurities to the electrolyte is preferably 1% or less, preferably 0.1% or less, and more preferably 0.01% or less.

[0192] The electrolyte may also contain additives such as vinylene carbonate (VC), propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), lithium bis(oxalato)borate (LiBOB), or dinitrile compounds such as succinonitrile and adiponitrile. The concentration of the additive may be, for example, 0.1 wt % to 5 wt % of the total solvent.

[0193] Alternatively, a polymer gel electrolyte may be used in which a polymer is swollen with an electrolytic solution.

[0194] The use of a polymer gel electrolyte improves safety against leakage, etc. It also enables the secondary battery to be made thinner and lighter.

[0195] Examples of polymers that can be gelled include silicone gel, acrylic gel, acrylonitrile gel, polyethylene oxide gel, polypropylene oxide gel, and fluorine-based polymer gel.

[0196] Examples of polymers that can be used include polymers having a polyalkylene oxide structure, such as polyethylene oxide (PEO), PVDF, polyacrylonitrile, and copolymers containing these. For example, PVDF-HFP, a copolymer of PVDF and hexafluoropropylene (HFP), can be used. The polymer formed may also have a porous shape.

[0197] In addition, instead of an electrolyte solution, a solid electrolyte containing inorganic materials such as sulfides or oxides, or a solid electrolyte containing polymer materials such as polyethylene oxide (PEO) can be used. When a solid electrolyte is used, the installation of a separator or spacer is unnecessary. Furthermore, since the entire battery can be solidified, there is no risk of leakage, dramatically improving safety.

[0198] [Separator] The secondary battery preferably has a separator. Examples of the separator include paper, nonwoven fabric, glass fiber, ceramics, and synthetic fibers such as nylon (polyamide), vinylon (polyvinyl alcohol fiber), polyester, acrylic, polyolefin, and polyurethane. The separator is preferably envelope-shaped and disposed so as to encase either the positive electrode or the negative electrode.

[0199] The separator may have a multilayer structure. For example, an organic material film such as polypropylene or polyethylene can be coated with a ceramic material, a fluorine-based material, a polyamide material, or a mixture of these. Examples of ceramic materials that can be used include aluminum oxide particles and silicon oxide particles. Examples of fluorine-based materials that can be used include PVDF and polytetrafluoroethylene. Examples of polyamide materials that can be used include nylon and aramid (meta-aramid, para-aramid).

[0200] Coating with ceramic materials improves oxidation resistance, suppressing separator degradation during high-voltage charging and discharging and improving the reliability of secondary batteries. Coating with fluorine-based materials also improves adhesion between the separator and electrodes, improving output characteristics. Coating with polyamide materials, especially aramid, improves heat resistance, improving the safety of secondary batteries.

[0201] For example, both sides of a polypropylene film may be coated with a mixed material of aluminum oxide and aramid, or the surface of the polypropylene film that contacts the positive electrode may be coated with a mixed material of aluminum oxide and aramid, and the surface that contacts the negative electrode may be coated with a fluorine-based material.

[0202] When a separator with a multilayer structure is used, the safety of the secondary battery can be maintained even if the overall thickness of the separator is thin, and therefore the capacity per volume of the secondary battery can be increased.

[0203] [Exterior body] The exterior body of the secondary battery can be made of a metal material such as aluminum or a resin material. Alternatively, a film-like exterior body can be used. Examples of the film include a three-layer structure film in which a thin, flexible metal film such as aluminum, stainless steel, copper, or nickel is provided on a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, or polyamide, and an insulating synthetic resin film such as a polyamide resin or polyester resin is further provided on the thin metal film as the outer surface of the exterior body.

[0204] [Secondary battery configuration example 2] As an example of the configuration of a secondary battery, the configuration of a secondary battery using a solid electrolyte will be described below.

[0205] As shown in FIG. 6A, a secondary battery 400 according to one embodiment of the present invention includes a positive electrode 410, a solid electrolyte layer 420, and a negative electrode 430.

[0206] Positive electrode 410 includes positive electrode current collector 413 and positive electrode active material layer 414. Positive electrode active material layer 414 includes positive electrode active material 411 and solid electrolyte 421. Positive electrode active material 411 can be positive electrode active material 100 described in the previous embodiment or a mixture of positive electrode active material 100 and positive electrode active material 200. Positive electrode active material layer 414 may also include a conductive additive and a binder.

[0207] Solid electrolyte layer 420 has solid electrolyte 421. Solid electrolyte layer 420 is located between positive electrode 410 and negative electrode 430, and is a region that has neither positive electrode active material 411 nor negative electrode active material 431.

[0208] The negative electrode 430 includes a negative electrode current collector 433 and a negative electrode active material layer 434. The negative electrode active material layer 434 includes a negative electrode active material 431 and a solid electrolyte 421. The negative electrode active material layer 434 may also include a conductive additive and a binder. When metallic lithium is used for the negative electrode 430, the negative electrode 430 may not include the solid electrolyte 421, as shown in FIG. 6B . Using metallic lithium for the negative electrode 430 is preferable because it can improve the energy density of the secondary battery 400.

[0209] 7A, a secondary battery may be formed by stacking combinations of positive electrodes 410, solid electrolyte layers 420, and negative electrodes 430. By stacking a plurality of positive electrodes 410, solid electrolyte layers 420, and negative electrodes 430, the output voltage of the secondary battery can be increased. Fig. 7A is a schematic diagram of a case where four combinations of positive electrodes 410, solid electrolyte layers 420, and negative electrodes 430 are stacked.

[0210] The solid electrolyte 421 included in the solid electrolyte layer 420 and the material used for the solid electrolyte layer 420 may be, for example, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a halide-based solid electrolyte, or the like.

[0211] Sulfide-based solid electrolytes include thiosilicon-based (Li 10 GeP2S 12 , Li 3.25 Ge 0.25 P 0.75 S4, etc.), sulfide glasses (70Li2S·30P2S5, 30Li2S·26B2S3·44LiI, 63Li2S·38SiS2·1Li3PO4, 57Li2S·38SiS2·5Li4SiO4, 50Li2S·50GeS2, etc.), sulfide crystallized glasses (Li7P3S 11 , Li 3.25 P 0.95 Sulfide-based solid electrolytes have the advantages of being highly conductive, being able to be synthesized at low temperatures, and being relatively soft, which makes it easy to maintain conductive paths even after charging and discharging.

[0212] Oxide-based solid electrolytes include materials with a perovskite crystal structure (La2 / 3-x Li 3x materials having a NASICON-type crystal structure (such as Li 1-X Al X Ti 2-X (PO4)3, etc.), materials having a garnet-type crystal structure (Li7La3Zr2O 12 , etc.), materials having a LISICON-type crystal structure (Li 14 ZnGe4O 16 , etc.), LLZO (Li7La3Zr2O 12 ), oxide glasses (such as Li3PO4-Li4SiO4, 50Li4SiO4·50Li3BO3, etc.), oxide crystallized glasses (Li 1.07 Al 0.69 Ti 1.46 (PO4)3, Li 1.5 Al 0.5 Ge 1.5 (PO4)3, etc.) are included. Oxide-based solid electrolytes have the advantage of being stable in the atmosphere.

[0213] Halide-based solid electrolytes include LiAlCl4, Li3InBr6, LiF, LiCl, LiBr, LiI, etc. Also, composite materials in which these halide-based solid electrolytes are filled in the pores of porous alumina or porous silica can be used as solid electrolytes.

[0214] Also, different solid electrolytes may be mixed and used.

[0215] Among them, Li 1+x Al x Ti 2-x (PO4)3 (0 < x < 1) (hereinafter referred to as LATP) contains aluminum, an element that the positive electrode active material 100 of one aspect of the present invention has. Therefore, a synergistic effect can be expected for improving the cycle characteristics, which is preferable. Also, an improvement in productivity due to reduction of processes can be expected. In this specification, etc., the NASICON-type crystal structure refers to a compound represented by M2(XO4)3 (M: transition metal, X: S, P, As, Mo, W, etc.), which has a structure in which MO6 octahedra and XO4 tetrahedra share vertices and are three-dimensionally arranged.

[0216] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0217] (Embodiment 3) In this embodiment, an example of the shape of a secondary battery including the positive electrode active material 100 described in the previous embodiment or a mixture of the positive electrode active material 100 and the positive electrode active material 200 will be described. The description of the previous embodiment can be referred to for the materials used in the secondary battery described in this embodiment.

[0218] [Coin-type secondary battery] First, an example of a coin-type secondary battery will be described. Fig. 8A is an external view of a coin-type (single-layer flat) secondary battery, and Fig. 8B is a cross-sectional view thereof.

[0219] In a coin-type secondary battery 300, a positive electrode can 301, which also serves as a positive electrode terminal, and a negative electrode can 302, which also serves as a negative electrode terminal, 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 with the positive electrode current collector. The negative electrode 307 is formed by a negative electrode current collector 308 and a negative electrode active material layer 309 provided in contact with the negative electrode current collector.

[0220] It is to be noted that the positive electrode 304 and the negative electrode 307 used in the coin-type secondary battery 300 each only need to have an active material layer formed on one side.

[0221] Positive electrode can 301 and negative electrode can 302 can be made of a metal such as nickel, aluminum, or titanium that is corrosion-resistant to the electrolyte, or an alloy of these metals or an alloy of these metals with other metals (e.g., stainless steel). Furthermore, to prevent corrosion by the electrolyte, it is preferable to coat them with nickel, aluminum, or the like. Positive electrode can 301 is electrically connected to positive electrode 304, and negative electrode can 302 is electrically connected to negative electrode 307.

[0222] These negative electrode 307, positive electrode 304, and separator 310 are impregnated with an electrolyte, and as shown in FIG. 8B, the positive electrode 304, separator 310, negative electrode 307, and negative electrode can 302 are stacked in this order with the positive electrode can 301 facing downwards, and the positive electrode can 301 and the negative electrode can 302 are crimped together via a gasket 303 to produce a coin-type secondary battery 300.

[0223] By using the positive electrode active material described in the above embodiment for the positive electrode 304, the coin-type secondary battery 300 can have a high capacity and excellent cycle characteristics.

[0224] Here, we will use Figure 8C to explain the flow of current during charging of a secondary battery. When a lithium-based secondary battery is considered as a closed circuit, the movement of lithium ions and the flow of current are in the same direction. In lithium-based secondary batteries, the anode (positive electrode) and cathode (negative electrode) are interchanged during charging and discharging, and the oxidation and reduction reactions are alternated. Therefore, the electrode with the higher reaction potential is called the positive electrode, and the electrode with the lower reaction potential is called the negative electrode. Therefore, in this specification, the positive electrode will be called the "positive electrode" or "+ electrode (plus electrode)," and the negative electrode will be called the "negative electrode" or "- electrode (minus electrode)," regardless of whether the battery is being charged or discharged, whether a reverse pulse current is being applied, or whether a charging current is being applied. Using the terms anode (positive electrode) and cathode (negative electrode), which are related to oxidation and reduction reactions, could lead to confusion because their meanings are reversed during charging and discharging. Therefore, the terms anode (positive electrode) and cathode (negative electrode) will not be used in this specification. If the terms anode and cathode are used, it should be clearly stated whether they are used during charging or discharging, and whether they correspond to the positive or negative pole.

[0225] A charger is connected to the two terminals shown in Fig. 8C to charge the secondary battery 300. As the charging of the secondary battery 300 progresses, the potential difference between the electrodes increases.

[0226] [Cylindrical secondary battery] Next, an example of a cylindrical secondary battery will be described with reference to Fig. 9. Fig. 9A shows an external view of a cylindrical secondary battery 600. Fig. 9B is a schematic diagram showing a cross section of the cylindrical secondary battery 600. As shown in Fig. 9B, the cylindrical secondary battery 600 has a positive electrode cap (battery lid) 601 on the top surface, and a battery can (external can) 602 on the side and bottom surfaces. The positive electrode cap and battery can (external can) 602 are insulated by a gasket (insulating packing) 610.

[0227] A battery element is provided inside a hollow cylindrical battery can 602, in which a strip-shaped positive electrode 604 and a negative electrode 606 are wound with a separator 605 sandwiched between them. Although not shown, the battery element is wound around a center pin. One end of the battery can 602 is closed and the other end is open. The battery can 602 can be made of a metal that is corrosion-resistant to the electrolyte, such as nickel, aluminum, or titanium, or an alloy of these or an alloy of these with another metal (e.g., stainless steel). To prevent corrosion by the electrolyte, the battery can 602 is preferably coated with nickel, aluminum, or the like. Inside the battery can 602, the wound battery element, in which the positive electrode, negative electrode, and separator are wound, is sandwiched between a pair of opposing insulating plates 608 and 609. A nonaqueous electrolyte (not shown) is poured into the battery can 602, in which the battery element is provided. The nonaqueous electrolyte may be the same as that used in coin-type secondary batteries.

[0228] Because the positive and negative electrodes used in cylindrical storage batteries are wound, it is preferable to form active materials on both sides of the current collector. A positive electrode terminal (positive electrode current collector lead) 603 is connected to the positive electrode 604, and a negative electrode terminal (negative electrode current collector lead) 607 is connected to the negative electrode 606. Both the positive electrode terminal 603 and the negative electrode terminal 607 can be made of a metal material such as aluminum. The positive electrode terminal 603 is resistance-welded to a safety valve mechanism 612, and the negative electrode terminal 607 is resistance-welded to the bottom of the battery can 602. The safety valve mechanism 612 is electrically connected to the positive electrode cap 601 via a PTC (Positive Temperature Coefficient) element 611. The safety valve mechanism 612 cuts off the electrical connection between the positive electrode cap 601 and the positive electrode 604 when the internal pressure of the battery exceeds a predetermined threshold. The PTC element 611 is a thermosensitive resistor whose resistance increases as the temperature rises, and the increased resistance limits the amount of current to prevent abnormal heat generation. Barium titanate (BaTiO3) based semiconductor ceramics or the like can be used for the PTC element.

[0229] 9C , a module 615 may be configured by sandwiching a plurality of secondary batteries 600 between conductive plates 613 and 614. The plurality of secondary batteries 600 may be connected in parallel, in series, or in series after being connected in parallel. By configuring a module 615 having a plurality of secondary batteries 600, a large amount of power can be extracted.

[0230] FIG. 9D is a top view of the module 615. For clarity, the conductive plate 613 is shown with a dotted line. As shown in FIG. 9D, the module 615 may have conductive wires 616 that electrically connect the multiple secondary batteries 600. A conductive plate can be superimposed on the conductive wires 616. A temperature control device 617 may also be provided between the multiple secondary batteries 600. When the secondary batteries 600 overheat, they can be cooled by the temperature control device 617, and when the secondary batteries 600 are too cold, they can be heated by the temperature control device 617. This makes the performance of the module 615 less susceptible to the influence of the outside air temperature. The heat medium in the temperature control device 617 is preferably insulating and non-flammable.

[0231] By using the positive electrode active material described in the above embodiment for the positive electrode 604, the cylindrical secondary battery 600 can have high capacity and excellent cycle characteristics.

[0232] [Example of secondary battery structure] Another structural example of the secondary battery will be described with reference to FIGS.

[0233] 10A and 10B are diagrams showing the external appearance of a secondary battery. Secondary battery 913 is connected to antennas 914 and 915 via circuit board 900. A label 910 is attached to secondary battery 913. Furthermore, as shown in FIG. 10B, secondary battery 913 is connected to terminals 951 and 952.

[0234] The circuit board 900 has a terminal 911 and a circuit 912. The terminal 911 is connected to a terminal 951, a terminal 952, an antenna 914, an 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, or the like.

[0235] The circuit 912 may be provided on the back surface of the circuit board 900. The antennas 914 and 915 are not limited to being coil-shaped, and may be, for example, wire-shaped or plate-shaped. Also, antennas such as a planar antenna, an aperture antenna, a traveling-wave antenna, an EH antenna, a magnetic field antenna, and a dielectric antenna may be used. Alternatively, the antenna 914 or 915 may be a flat-plate conductor. This flat-plate conductor can function as one of the conductors for electric field coupling. In other words, the antenna 914 or 915 may function as one of the two conductors of a capacitor. This allows power to be exchanged not only by electromagnetic fields and magnetic fields, but also by electric fields.

[0236] The line width of the antenna 914 is preferably larger than the line width of the antenna 915. This allows the amount of power received by the antenna 914 to be increased.

[0237] The secondary battery has a layer 916 between the antenna 914 and the antenna 915 and the secondary battery 913. The layer 916 has a function of, for example, shielding an electromagnetic field caused by the secondary battery 913. The layer 916 can be made of, for example, a magnetic material.

[0238] The structure of the secondary battery is not limited to that shown in FIG.

[0239] For example, as shown in Figures 11A and 11B, an antenna may be provided on each of a pair of opposing surfaces of secondary battery 913 shown in Figures 10A and 10B. Figure 11A is an external view showing one of the pair of surfaces, and Figure 11B is an external view showing the other of the pair of surfaces. Note that the description of the secondary battery shown in Figures 10A and 10B can be used as appropriate for the same parts as those of the secondary battery shown in Figures 10A and 10B.

[0240] 11A, an antenna 914 is provided on one of a pair of surfaces of a secondary battery 913 with a layer 916 sandwiched therebetween, and as shown in Fig. 11B, an antenna 918 is provided on the other of the pair of surfaces of the secondary battery 913 with a layer 917 sandwiched therebetween. The layer 917 has a function of, for example, shielding an electromagnetic field caused by the secondary battery 913. The layer 917 can be made of, for example, a magnetic material.

[0241] The above structure allows the sizes of both the antenna 914 and the antenna 918 to be increased. The antenna 918 has a function of, for example, performing data communication with an external device. For example, an antenna having a shape applicable to the antenna 914 can be used as the antenna 918. As a communication method between the secondary battery and other devices via the antenna 918, a response method that can be used between the secondary battery and other devices, such as NFC (near field wireless communication), can be used.

[0242] 11C, a display device 920 may be provided on the secondary battery 913 shown in FIGS. 10A and 10B. The display device 920 is electrically connected to the terminal 911. Note that the label 910 does not need to be provided on the portion where the display device 920 is provided. Note that the description of the secondary battery shown in FIGS. 10A and 10B can be used as appropriate for the same portions as those of the secondary battery shown in FIGS. 10A and 10B.

[0243] The display device 920 may display, for example, an image indicating whether charging is in progress or an image indicating the amount of stored power. For example, electronic paper, a liquid crystal display device, an electroluminescence (EL) display device, or the like can be used as the display device 920. For example, by using electronic paper, the power consumption of the display device 920 can be reduced.

[0244] 11D, a sensor 921 may be provided in the secondary battery 913 shown in Figures 10A and 10B. The sensor 921 is electrically connected to the terminal 911 via a terminal 922. Note that the description of the secondary battery shown in Figures 10A and 10B can be used as appropriate for the same parts as those in the secondary battery shown in Figures 10A and 10B.

[0245] The sensor 921 may have a function of measuring, for example, displacement, position, speed, 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 ray. By providing the sensor 921, for example, data indicating the environment in which the secondary battery is placed (such as temperature) can be detected and stored in the memory in the circuit 912.

[0246] Furthermore, an example of the structure of the secondary battery 913 will be described with reference to FIGS.

[0247] A secondary battery 913 shown in Fig. 12A has a wound body 950 in which terminals 951 and 952 are provided inside a housing 930. The wound body 950 is impregnated with an electrolyte inside the housing 930. The terminal 952 contacts the housing 930, and the terminal 951 is not in contact with the housing 930 by using an insulating material or the like. Note that in Fig. 12A, for convenience, the housing 930 is shown separated, but in reality, the wound body 950 is covered by the housing 930, and the terminals 951 and 952 extend outside the housing 930. The housing 930 can be made of a metal material (such as aluminum) or a resin material.

[0248] 12B, the housing 930 shown in Fig. 12A may be formed from a plurality of materials. For example, the secondary battery 913 shown in Fig. 12B has housings 930a and 930b bonded together, and a wound body 950 is provided in the area surrounded by the housings 930a and 930b.

[0249] The housing 930a can be made of an insulating material such as organic resin. In particular, by using a material such as organic resin on the surface on which the antenna is formed, it is possible to prevent the secondary battery 913 from blocking the electric field. Note that if the electric field blocking by the housing 930a is small, antennas such as the antenna 914 and the antenna 915 may be provided inside the housing 930a. The housing 930b can be made of, for example, a metal material.

[0250] 13 shows the structure of the wound body 950. The wound body 950 has a negative electrode 931, a positive electrode 932, and a separator 933. The wound body 950 is a wound body in which the negative electrode 931 and the positive electrode 932 are stacked on top of each other with the separator 933 sandwiched therebetween, and the laminated sheet is wound. Note that a plurality of layers of the negative electrode 931, the positive electrode 932, and the separator 933 may be stacked.

[0251] 10 via one of the terminal 951 and the terminal 952. The positive electrode 932 is connected to the terminal 911 shown in FIG.

[0252] By using the positive electrode active material described in the above embodiment for the positive electrode 932, the secondary battery 913 can have high capacity and excellent cycle characteristics.

[0253] [Laminated secondary battery] Next, examples of laminated secondary batteries will be described with reference to Figures 14 to 19. If a laminated secondary battery has a flexible configuration, and is mounted in an electronic device having at least a flexible portion, the secondary battery can also be bent in accordance with deformation of the electronic device.

[0254] A laminated secondary battery 980 will be described using Fig. 14. The laminated secondary battery 980 has a wound body 993 shown in Fig. 14A. The wound body 993 has a negative electrode 994, a positive electrode 995, and a separator 996. The wound body 993 is formed by stacking the negative electrode 994 and the positive electrode 995 on top of each other with the separator 996 sandwiched therebetween, similar to the wound body 950 described in Fig. 13, and winding the laminated sheet.

[0255] The number of layers of the negative electrode 994, the positive electrode 995, and the separator 996 may be appropriately designed depending on the required capacity and element volume. The negative electrode 994 is connected to a negative electrode current collector (not shown) via one of the lead electrodes 997 and 998, and the positive electrode 995 is connected to a positive electrode current collector (not shown) via the other of the lead electrodes 997 and 998.

[0256] 14B, a film 981 serving as an exterior body and a film 982 having a recess are bonded together by thermocompression or the like to form a space, and the above-described wound body 993 is stored in the space, thereby producing a secondary battery 980 as shown in Fig. 14C. The wound body 993 has lead electrodes 997 and 998, and is impregnated with an electrolyte solution between the film 981 and the film 982 having a recess.

[0257] For example, a metal material such as aluminum or a resin material can be used for film 981 and film 982 having recesses. If a resin material is used as the material for film 981 and film 982 having recesses, film 981 and film 982 having recesses can be deformed when an external force is applied, and a flexible storage battery can be produced.

[0258] Although FIGS. 14B and 14C show an example in which two films are used, a space may be formed by folding one film, and the wound body 993 described above may be housed in that space.

[0259] By using the positive electrode active material described in the above embodiment for the positive electrode 995, the secondary battery 980 can have a high capacity and excellent cycle characteristics.

[0260] Furthermore, although Figure 14 describes an example of a secondary battery 980 having a wound body in a space formed by a film that serves as an outer casing, it may also be a secondary battery having multiple rectangular positive electrodes, separators, and negative electrodes in a space formed by a film that serves as an outer casing, as shown in Figure 15, for example.

[0261] 15A includes a positive electrode 503 having a positive electrode current collector 501 and a positive electrode active material layer 502, a negative electrode 506 having a negative electrode current collector 504 and a negative electrode active material layer 505, a separator 507, an electrolyte solution 508, and an exterior body 509. The separator 507 is disposed between the positive electrode 503 and the negative electrode 506 provided in the exterior body 509. The exterior body 509 is filled with the electrolyte solution 508. The electrolyte solution described in Embodiment 2 can be used as the electrolyte solution 508.

[0262] 15A, the positive electrode current collector 501 and the negative electrode current collector 504 also serve as terminals for electrical contact with the outside. Therefore, the positive electrode current collector 501 and the negative electrode current collector 504 may be arranged so as to be partially 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 a lead electrode may be used and ultrasonically bonded to the positive electrode current collector 501 or the negative electrode current collector 504 so as to expose the lead electrode to the outside.

[0263] In the laminated secondary battery 500, the exterior body 509 can be a three-layer laminate film having a highly flexible metal thin film made of aluminum, stainless steel, copper, nickel, or the like provided on a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, or polyamide, and further having an insulating synthetic resin film made of polyamide-based resin, polyester-based resin, or the like provided on the metal thin film as the outer surface of the exterior body.

[0264] 15B shows an example of the cross-sectional structure of laminated secondary battery 500. For simplicity, Fig. 15A shows an example configured with two current collectors, but in reality, as shown in Fig. 15B, it is configured with multiple electrode layers.

[0265] In FIG. 15B, the number of electrode layers is 16 as an example. Note that even if the number of electrode layers is 16, the secondary battery 500 remains flexible. FIG. 15B shows a structure with a total of 16 layers, including eight layers of negative electrode current collectors 504 and eight layers of positive electrode current collectors 501. Note that FIG. 15B also shows a cross section of the negative electrode lead-out portion, in which eight layers of negative electrode current collectors 504 are ultrasonically bonded. Of course, the number of electrode layers is not limited to 16 and may be more or less. When the number of electrode layers is large, a secondary battery with a larger capacity can be obtained. Furthermore, when the number of electrode layers is small, a secondary battery can be made thinner and have excellent flexibility.

[0266] 16 and 17 show examples of the external appearance of a laminated secondary battery 500. The battery 500 includes a positive electrode 503, a negative electrode 506, a separator 507, an outer casing 509, a positive electrode lead electrode 510, and a negative electrode lead electrode 511.

[0267] FIG. 18A shows the appearance of a positive electrode 503 and a negative electrode 506. The positive electrode 503 has a positive electrode current collector 501, and a positive electrode active material layer 502 is formed on the surface of the positive electrode current collector 501. The positive electrode 503 also has a region where the positive electrode current collector 501 is partially exposed (hereinafter referred to as a tab region). The negative electrode 506 has a negative electrode current collector 504, and a negative electrode active material layer 505 is formed on the surface of the negative electrode current collector 504. The negative electrode 506 also has a region where the negative electrode current collector 504 is partially exposed, i.e., a tab region. The areas and shapes of the tab regions of the positive electrode and negative electrode are not limited to the example shown in FIG. 18A.

[0268] [Method for manufacturing laminated secondary batteries] Here, an example of a method for manufacturing the laminated secondary battery whose external view is shown in FIG. 16 will be described with reference to FIGS. 18B and 18C.

[0269] First, the negative electrode 506, the separator 507, and the positive electrode 503 are stacked. FIG. 18B shows the stacked negative electrode 506, the separator 507, and the positive electrode 503. Here, an example is shown in which five pairs of negative electrodes and four pairs of positive electrodes are used. Next, the tab regions of the positive electrodes 503 are joined together, and the positive electrode lead electrode 510 is joined to the tab region of the outermost positive electrode. For example, ultrasonic welding or the like may be used for joining. Similarly, the tab regions of the negative electrode 506 are joined together, and the negative electrode lead electrode 511 is joined to the tab region of the outermost negative electrode.

[0270] Next, the negative electrode 506 , the separator 507 and the positive electrode 503 are placed on the exterior body 509 .

[0271] Next, as shown in Fig. 18C, exterior body 509 is folded at the portion indicated by the dashed line. Thereafter, the outer periphery of exterior body 509 is joined. For the joining, for example, thermocompression bonding or the like may be used. At this time, an area (hereinafter referred to as an inlet) that is not joined is provided in a part (or one side) of exterior body 509 so that electrolyte 508 can be introduced later.

[0272] Next, electrolyte solution 508 (not shown) is introduced into the inside of exterior body 509 through an inlet provided in exterior body 509. The introduction of electrolyte solution 508 is preferably carried out under a reduced pressure atmosphere or an inert atmosphere. Finally, the inlet is joined. In this manner, laminated secondary battery 500 can be produced.

[0273] By using the positive electrode active material described in the above embodiment for the positive electrode 503, the secondary battery 500 can have a high capacity and excellent cycle characteristics.

[0274] 19A is a perspective view showing how three laminated secondary batteries 500 are sandwiched and fixed between a first plate 521 and a second plate 524. As shown in FIG. 19B, by using fixing fixtures 525a and 525b to fix the distance between first plate 521 and second plate 524, the three secondary batteries 500 can be pressurized.

[0275] 19A and 19B show an example in which three laminated secondary batteries 500 are used, but this is not particularly limited, and four or more secondary batteries 500 can be used, and if ten or more batteries are used, it can be used as a power source for a small vehicle, and if 100 or more batteries are used, it can be used as a large in-vehicle power source. Furthermore, the laminated secondary battery 500 may be provided with a protection circuit to prevent overcharging and a temperature sensor to monitor temperature rise.

[0276] [Exterior and shape of all-solid-state batteries] Various materials and shapes can be used for the exterior of a secondary battery having a solid electrolyte, but it is preferable that the exterior have the function of applying pressure to the positive electrode, solid electrolyte layer, and negative electrode.

[0277] For example, Figure 20 shows an example of a cell for evaluating materials for all-solid-state batteries.

[0278] 20A is a cross-sectional schematic diagram of the evaluation cell, which has a lower member 761, an upper member 762, an insulator 766 that electrically insulates the lower member 761 and the upper member 762, and a fixing screw and a wing nut 764 that fix these together, and the electrode plate 753 is pressed and fixed in place by rotating a holding screw 763. An insulator 766 is provided between the lower member 761 and the upper member 762, both made of stainless steel. An O-ring 765 is provided between the upper member 762 and the holding screw 763 to provide a tight seal.

[0279] The evaluation material is placed on electrode plate 751, surrounded by insulating tube 752, and pressed from above by electrode plate 753. An enlarged perspective view of the evaluation material and its surroundings is shown in FIG. 20B.

[0280] The evaluation material is an example of a laminate of a positive electrode 750a, a solid electrolyte layer 750b, and a negative electrode 750c, and its cross-sectional view is shown in Fig. 20C. Note that the same reference numerals are used for the same parts in Fig. 20A, Fig. 20B, and Fig. 20C.

[0281] The electrode plate 751 and lower member 761 electrically connected to the positive electrode 750a can be said to correspond to a positive electrode terminal. The electrode plate 753 and upper member 762 electrically connected to the negative electrode 750c can be said to correspond to a negative electrode terminal. Electrical resistance and the like can be measured by applying pressure to the evaluation material via the electrode plate 751 and the electrode plate 753.

[0282] The secondary battery of one embodiment of the present invention preferably uses an airtight package for its exterior. For example, a ceramic package or a resin package can be used. Furthermore, the exterior is preferably sealed in a sealed atmosphere, such as in a glove box, while blocking external air.

[0283] Fig. 21A shows a perspective view of a secondary battery of one embodiment of the present invention, which has an exterior body and a shape different from those in Fig. 20. The secondary battery in Fig. 21A has external electrodes 771 and 772 and is sealed in an exterior body having multiple package members.

[0284] An example of a cross section taken along the dashed line in Figure 21A is shown in Figure 21B. A laminate including positive electrode 750a, solid electrolyte layer 750b, and negative electrode 750c is enclosed and sealed within package member 770a, which is a flat plate with electrode layer 773a provided thereon, frame-shaped package member 770b, and package member 770c, which is a flat plate with electrode layer 773b provided thereon. Package members 770a, 770b, and 770c can be made of an insulating material, such as a resin material or ceramic.

[0285] The external electrode 771 is electrically connected to the positive electrode 750a via the electrode layer 773a and functions as a positive electrode terminal, while the external electrode 772 is electrically connected to the negative electrode 750c via the electrode layer 773b and functions as a negative electrode terminal.

[0286] In an all-solid-state battery, applying a predetermined pressure in the stacking direction of the stacked positive and negative electrodes can maintain good contact at the internal interfaces. Applying a predetermined pressure in the stacking direction of the positive and negative electrodes can suppress expansion in the stacking direction due to charging and discharging of the all-solid-state battery, thereby improving the reliability of the all-solid-state battery.

[0287] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0288] (Fourth embodiment) In this embodiment, an example in which a secondary battery according to one embodiment of the present invention is mounted on an electronic device will be described.

[0289] 22A to 22G show examples of electronic devices incorporating the secondary battery described in part of Embodiment 3. Examples of electronic devices to which the secondary battery of one embodiment of the present invention is applied include television sets (also referred to as televisions or television receivers), computer monitors, digital cameras, digital video cameras, digital photo frames, mobile phones (also referred to as mobile phones or mobile phone devices), portable game machines, personal digital assistants, sound players, and large game machines such as pachinko machines.

[0290] Furthermore, a secondary battery having a flexible shape can be incorporated into the inner or outer wall of a house or building, or along the curved surface of the interior or exterior of an automobile.

[0291] 22A illustrates an example of a mobile phone. The mobile phone 7400 includes a display portion 7402 built into a housing 7401, operation buttons 7403, an external connection port 7404, a speaker 7405, a microphone 7406, and the like. Note that the mobile phone 7400 includes a secondary battery 7407. By using the secondary battery of one embodiment of the present invention as the secondary battery 7407, a lightweight mobile phone with a long lifetime can be provided.

[0292] FIG. 22B shows the mobile phone 7400 in a bent state. When the mobile phone 7400 is deformed by an external force and bent as a whole, the secondary battery 7407 installed inside is also bent. FIG. 22C shows the state of the bent secondary battery 7407 at that time. The secondary battery 7407 is a thin storage battery. The secondary battery 7407 is fixed in a bent state. The secondary battery 7407 has a lead electrode electrically connected to the current collector. For example, the current collector is copper foil, and a portion of the current collector is alloyed with gallium to improve adhesion with the active material layer in contact with the current collector, resulting in a configuration with high reliability when the secondary battery 7407 is bent.

[0293] FIG. 22D 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. FIG. 22E shows a bent secondary battery 7104. When the secondary battery 7104 is worn on a user's arm in a bent state, the housing deforms, causing a change in the curvature of part or the entire secondary battery 7104. Note that the degree of curvature at any point on the curve, expressed as the radius of the corresponding circle, is called the radius of curvature, and the reciprocal of the radius of curvature is called the curvature. Specifically, part or the entire main surface of the housing or the secondary battery 7104 changes when the radius of curvature is in the range of 40 mm to 150 mm. High reliability can be maintained when the radius of curvature of the main surface of the secondary battery 7104 is in the range of 40 mm to 150 mm. By using a secondary battery of one embodiment of the present invention as the secondary battery 7104, a lightweight and long-life portable display device can be provided.

[0294] 22F shows an example of a wristwatch-type portable information terminal 7200. The portable information terminal 7200 includes a housing 7201, a display portion 7202, a band 7203, a buckle 7204, operation buttons 7205, an input / output terminal 7206, and the like.

[0295] The portable information terminal 7200 can execute various applications such as mobile phone calls, e-mail, document browsing and creation, music playback, internet communication, and computer games.

[0296] The display surface of the display portion 7202 is curved, and a display can be performed along the curved display surface. The display portion 7202 is also provided with 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 started by touching an icon 7207 displayed on the display portion 7202.

[0297] The operation button 7205 can be provided with various functions, such as time setting, power on / off operation, wireless communication on / off operation, silent mode activation / deactivation, power saving mode activation / deactivation, etc. For example, the functions of the operation button 7205 can be freely set by an operating system incorporated in the mobile information terminal 7200.

[0298] The mobile information terminal 7200 is also capable of performing standardized short-range wireless communication. For example, hands-free conversation is also possible by communicating with a wirelessly enabled headset.

[0299] The portable information terminal 7200 also includes an input / output terminal 7206, and can directly exchange data with other information terminals via a connector. Charging can also be performed via the input / output terminal 7206. Note that charging may be performed by wireless power supply without using the input / output terminal 7206.

[0300] The display portion 7202 of the mobile information terminal 7200 includes the secondary battery of one embodiment of the present invention. By using the secondary battery of one embodiment of the present invention, a lightweight mobile information terminal with a long life can be provided. For example, the secondary battery 7104 shown in FIG. 22E can be installed in a curved state inside the housing 7201 or in a bendable state inside the band 7203.

[0301] The portable information terminal 7200 preferably has a sensor, such as a fingerprint sensor, a pulse sensor, a body temperature sensor, or other human body sensor, a touch sensor, a pressure sensor, or an acceleration sensor.

[0302] 22G illustrates an example of an armband-type display device. The display device 7300 includes a display portion 7304 and the secondary battery of one embodiment of the present invention. The display device 7300 can also be provided with a touch sensor in the display portion 7304 and can function as a portable information terminal.

[0303] The display surface of the display portion 7304 is curved, and display can be performed along the curved display surface. The display state of the display device 7300 can be changed by short-range wireless communication according to a communication standard.

[0304] The display device 7300 also has an input / output terminal, allowing direct data exchange with other information terminals via a connector. Charging can also be performed via the input / output terminal. Note that charging may also be performed by wireless power supply without using the input / output terminal.

[0305] By using the secondary battery of one embodiment of the present invention as the secondary battery included in the display device 7300, a lightweight display device with a long lifetime can be provided.

[0306] An example in which the secondary battery having good cycle characteristics shown in the above embodiment is mounted in an electronic device will be described with reference to FIGS. 22H, 23, and 24. FIG.

[0307] By using a secondary battery of one embodiment of the present invention as a secondary battery in daily electronic devices, products that are lightweight and have a long life can be provided. For example, daily electronic devices include electric toothbrushes, electric shavers, and electric beauty devices. For secondary batteries in these products, a small, lightweight, and large-capacity secondary battery with a stick shape is desired, taking into account ease of holding by users.

[0308] FIG. 22H is a perspective view of a device also known as a tobacco-containing smoking device (electronic cigarette). In FIG. 22H, electronic cigarette 7500 includes atomizer 7501 including a heating element, secondary battery 7504 that supplies power to the atomizer, and cartridge 7502 that includes a liquid supply bottle, a sensor, and the like. To enhance safety, a protection circuit that prevents overcharging and overdischarging of secondary battery 7504 may be electrically connected to secondary battery 7504. Secondary battery 7504 shown in FIG. 22H has external terminals so that it can be connected to a charging device. Because secondary battery 7504 is the tip portion when held, it is desirable that its total length be short and its weight be light. The secondary battery of one embodiment of the present invention has high capacity and favorable cycle characteristics, making it possible to provide a compact and lightweight electronic cigarette 7500 that can be used for a long period of time.

[0309] Next, an example of a foldable tablet terminal is shown in FIGS. 23A and 23B. The tablet terminal 9600 shown in FIGS. 23A and 23B includes a housing 9630a, a housing 9630b, a movable portion 9640 connecting the housings 9630a and 9630b, a display portion 9631 having display portions 9631a and 9631b, switches 9625 to 9627, a fastener 9629, and an operation switch 9628. A flexible panel can be used for the display portion 9631 to provide a tablet terminal with a larger display area. FIG. 23A shows the tablet terminal 9600 in an open state, and FIG. 23B shows the tablet terminal 9600 in a closed state.

[0310] The tablet terminal 9600 also includes a power storage unit 9635 inside the housing 9630a and the housing 9630b. The power storage unit 9635 passes through the movable portion 9640 and is provided across the housing 9630a and the housing 9630b.

[0311] The entire or part of the display portion 9631 can be a touch panel area, and data can be input by touching an image including an icon, text, an input form, etc. displayed in the area. For example, keyboard buttons may be displayed on the entire surface of the display portion 9631a on the housing 9630a side, and information such as text and images may be displayed on the display portion 9631b on the housing 9630b side.

[0312] A keyboard may be displayed on the display portion 9631b of the housing 9630b, and information such as text and images may be displayed on the display portion 9631a of the housing 9630a. A keyboard display switch button of a touch panel may be displayed on the display portion 9631, and the keyboard may be displayed on the display portion 9631 by touching the button with a finger, a stylus, or the like.

[0313] In addition, touch input can be simultaneously performed on the touch panel area of ​​the display portion 9631a on the housing 9630a side and the touch panel area of ​​the display portion 9631b on the housing 9630b side.

[0314] The switches 9625 to 9627 may be interfaces capable of switching various functions in addition to interfaces for operating the tablet terminal 9600. For example, at least one of the switches 9625 to 9627 may function as a switch for turning the tablet terminal 9600 on and off. For example, at least one of the switches 9625 to 9627 may have a function for switching the display orientation, such as portrait or landscape, or a function for switching between monochrome and color display. For example, at least one of the switches 9625 to 9627 may have a function for adjusting the brightness of the display unit 9631. The brightness of the display unit 9631 can be optimized depending on the amount of external light detected by an optical sensor built into the tablet terminal 9600 during use. The tablet terminal may also have built-in not only an optical sensor but also other detection devices, such as a gyroscope, an acceleration sensor, or other sensors for detecting tilt.

[0315] 23A shows an example in which the display area of ​​the display portion 9631a on the housing 9630a side and the display portion 9631b on the housing 9630b side are substantially the same, the display areas of the display portion 9631a and the display portion 9631b are not particularly limited, and one size and the other size may be different, and the display quality may also be different. For example, one may be a display panel that can display at a higher resolution than the other.

[0316] 23B shows a tablet terminal 9600 folded in half, and the tablet terminal 9600 includes a housing 9630, a solar cell 9633, and a charge / discharge control circuit 9634 including a DC-DC converter 9636. The power storage unit 9635 is a power storage unit of one embodiment of the present invention.

[0317] As described above, the tablet terminal 9600 can be folded in half, and therefore, the housing 9630a and the housing 9630b can be folded together when not in use. By folding, the display portion 9631 can be protected, thereby improving durability of the tablet terminal 9600. Furthermore, the power storage unit 9635 using the secondary battery of one embodiment of the present invention has high capacity and favorable cycle characteristics, and therefore, the tablet terminal 9600 can be used for a long period of time.

[0318] In addition, the tablet terminal 9600 shown in Figures 23A and 23B can have functions such as displaying various information (still images, videos, text images, etc.), displaying a calendar, date or time on the display unit, a touch input function for touch input operations or editing information displayed on the display unit, and controlling processing using various software (programs).

[0319] A solar cell 9633 attached to the surface of the tablet terminal 9600 can supply power to a touch panel, a display unit, a video signal processor, or the like. The solar cell 9633 can be provided on one or both sides of the housing 9630, and can be configured to efficiently charge the power storage unit 9635. Use of a lithium-ion battery as the power storage unit 9635 has the advantage of enabling miniaturization.

[0320] The configuration and operation of the charge / discharge control circuit 9634 shown in Fig. 23B will be described with reference to a block diagram in Fig. 23C. Fig. 23C shows a solar cell 9633, a power storage unit 9635, a DC-DC converter 9636, a converter 9637, switches SW1 to SW3, and a display unit 9631. The power storage unit 9635, the DC-DC converter 9636, the converter 9637, and the switches SW1 to SW3 correspond to the charge / discharge control circuit 9634 shown in Fig. 23B.

[0321] First, an example of operation when power is generated by the solar cell 9633 using external light will be described. The power generated by the solar cell is stepped up or down by a DC-DC converter 9636 to a voltage for charging a power storage unit 9635. When power from the solar cell 9633 is used to operate the display unit 9631, a switch SW1 is turned on, and the converter 9637 steps up or steps down the voltage to a voltage required for the display unit 9631. When no display is to be performed on the display unit 9631, SW1 is turned off and SW2 is turned on to charge the power storage unit 9635.

[0322] Note that the solar cell 9633 is shown as an example of a power generating means, but is not particularly limited thereto, and the power storage unit 9635 may be charged by other power generating means such as a piezoelectric element (piezo element) or a thermoelectric conversion element (Peltier element). For example, a contactless power transmission module that transmits and receives power wirelessly (contactlessly) for charging, or a combination of other charging means may be used.

[0323] FIG. 24 illustrates an example of another electronic device. In FIG. 24, a display device 8000 is an example of an electronic device using a secondary battery 8004 according to one embodiment of the present invention. Specifically, the display device 8000 corresponds to a display device for receiving TV broadcasts and includes a housing 8001, a display portion 8002, a speaker portion 8003, a secondary battery 8004, and the like. The secondary battery 8004 according to one embodiment of the present invention is provided inside the housing 8001. The display device 8000 can receive power from a commercial power source or can use power stored in the secondary battery 8004. Therefore, even when power cannot be supplied from the commercial power source due to a power outage or the like, the display device 8000 can be used by using the secondary battery 8004 according to one embodiment of the present invention as an uninterruptible power source.

[0324] The display unit 8002 can be a liquid crystal display device, a light-emitting device having a light-emitting element such as an organic EL element in each pixel, an electrophoretic display device, a semiconductor display device such as a DMD (Digital Micromirror Device), a PDP (Plasma Display Panel), or an FED (Field Emission Display).

[0325] The display device includes all display devices for displaying information, such as those for receiving TV broadcasts, those for personal computers, and those for displaying advertisements.

[0326] 24 , a stationary lighting device 8100 is an example of an electronic device using a secondary battery 8103 according to one embodiment of the present invention. Specifically, the lighting device 8100 includes a housing 8101, a light source 8102, a secondary battery 8103, and the like. Although FIG. 24 illustrates the case where the secondary battery 8103 is provided inside a ceiling 8104 on which the housing 8101 and the light source 8102 are installed, the secondary battery 8103 may be provided inside the housing 8101. The lighting device 8100 can receive power from a commercial power source or can use power stored in the secondary battery 8103. Therefore, even when power cannot be supplied from the commercial power source due to a power outage or the like, the lighting device 8100 can be used by using the secondary battery 8103 according to one embodiment of the present invention as an uninterruptible power supply.

[0327] Note that although Figure 24 illustrates an example of a stationary lighting device 8100 provided on the ceiling 8104, the secondary battery of one embodiment of the present invention can also be used in a stationary lighting device provided in places other than the ceiling 8104, such as a side wall 8105, a floor 8106, or a window 8107, or can also be used in a tabletop lighting device.

[0328] Furthermore, an artificial light source that artificially obtains light using electric power can be used as the light source 8102. Specifically, examples of the artificial light source include discharge lamps such as incandescent lamps and fluorescent lamps, and light-emitting elements such as LEDs and organic EL elements.

[0329] 24, an air conditioner including an indoor unit 8200 and an outdoor unit 8204 is an example of an electronic device using a secondary battery 8203 of one embodiment of the present invention. Specifically, the indoor unit 8200 includes a housing 8201, an air outlet 8202, a secondary battery 8203, and the like. Although FIG. 24 illustrates the case where the secondary battery 8203 is provided in the indoor unit 8200, 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 from a commercial power source or can use 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, the air conditioner can be used by using the secondary battery 8203 of one embodiment of the present invention as an uninterruptible power supply even when power cannot be supplied from a commercial power source due to a power outage or the like.

[0330] Note that although FIG. 24 illustrates an example of a separate-type air conditioner including an indoor unit and an outdoor unit, a secondary battery according to one embodiment of the present invention can also be used in an integrated air conditioner that has the functions of both the indoor unit and the outdoor unit in a single housing.

[0331] 24 , an electric refrigerator-freezer 8300 is an example of an electronic device using a secondary battery 8304 of one embodiment of the present invention. Specifically, the electric refrigerator-freezer 8300 includes a housing 8301, a refrigerator door 8302, a freezer door 8303, a secondary battery 8304, and the like. In FIG. 24 , the secondary battery 8304 is provided inside the housing 8301. The electric refrigerator-freezer 8300 can receive power from a commercial power source or can use power stored in the secondary battery 8304. Therefore, even when power cannot be supplied from the commercial power source due to a power outage or the like, the electric refrigerator-freezer 8300 can be used by using the secondary battery 8304 of one embodiment of the present invention as an uninterruptible power source.

[0332] Among the electronic devices described above, electronic devices such as microwave ovens and other high-frequency heating devices and electric rice cookers require a large amount of power for a short period of time. Therefore, by using a secondary battery according to one embodiment of the present invention as an auxiliary power source for supplementing the power that cannot be supplied by the commercial power source, it is possible to prevent the breaker of the commercial power source from tripping when the electronic device is in use.

[0333] Furthermore, by storing power in the secondary battery during time periods when electronic devices are not in use, particularly during time periods when the ratio of the amount of power actually used to the total amount of power that can be supplied by the commercial power supplier (referred to as the power usage rate) is low, it is possible to prevent the power usage rate from increasing outside of these time periods. For example, in the case of electric refrigerator-freezer 8300, power is stored in secondary battery 8304 during the night when the temperature is low and refrigerator door 8302 and freezer door 8303 are not opened or closed. Then, during the daytime when the temperature rises and refrigerator door 8302 and freezer door 8303 are opened and closed, secondary battery 8304 is used as an auxiliary power source, thereby making it possible to keep the daytime power usage rate low.

[0334] According to one embodiment of the present invention, the cycle characteristics of the secondary battery can be improved, and the reliability can be improved. Furthermore, according to one embodiment of the present invention, a high-capacity secondary battery can be obtained, and therefore the characteristics of the secondary battery can be improved, and therefore the secondary battery itself can be made smaller and lighter. Therefore, by incorporating the secondary battery according to one embodiment of the present invention in the electronic device described in this embodiment, the electronic device can have a longer life and be lighter.

[0335] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0336] (Embodiment 5) In this embodiment, an example in which a secondary battery according to one embodiment of the present invention is mounted on a vehicle will be described.

[0337] By installing secondary batteries in vehicles, next-generation clean energy vehicles such as hybrid vehicles (HVs), electric vehicles (EVs), and plug-in hybrid vehicles (PHVs) can be realized.

[0338] FIG. 25 illustrates an example of a vehicle using a secondary battery according to one embodiment of the present invention. An automobile 8400 illustrated in FIG. 25A is an electric automobile using an electric motor as a power source for traveling. Alternatively, it is a hybrid automobile that can appropriately select and use an electric motor or an engine as a power source for traveling. By using one embodiment of the present invention, a vehicle with a long cruising distance can be realized. Furthermore, the automobile 8400 includes a secondary battery. The secondary battery may be arranged in the form of secondary battery modules shown in FIGS. 9C and 9D on the floor of the vehicle interior. Alternatively, a battery pack including a combination of a plurality of secondary batteries as shown in FIG. 12 may be installed on the floor of the vehicle interior. The secondary battery not only drives the electric motor 8406 but also supplies power to light-emitting devices such as a headlight 8401 and a room light (not shown).

[0339] The secondary battery can also supply power to display devices such as a speedometer and a tachometer included in the automobile 8400. The secondary battery can also supply power to semiconductor devices such as a navigation system included in the automobile 8400.

[0340] The automobile 8500 shown in FIG. 25B can charge its secondary battery by receiving power from an external charging facility using a plug-in system, a wireless power supply system, or the like. FIG. 25B shows a state in which a secondary battery 8024 mounted on the automobile 8500 is being charged via a cable 8022 from a ground-mounted charging device 8021. The charging method and connector specifications may be determined appropriately using a predetermined system such as CHAdeMO (registered trademark) or Combo. The charging device 8021 may be a charging station installed in a commercial facility or a household power source. For example, plug-in technology can be used to charge the secondary battery 8024 mounted on the automobile 8500 using external power supply. Charging can be performed by converting AC power to DC power using a conversion device such as an AC-DC converter.

[0341] Although not shown, a power receiving device can be mounted on a vehicle and power can be supplied contactlessly from a ground power transmitting device to charge the vehicle. In the case of this contactless power supply method, by incorporating a power transmitting device into a road or an exterior wall, charging can be performed not only while the vehicle is stopped but also while the vehicle is moving. This contactless power supply method can also be used to transmit and receive power between vehicles. Furthermore, a solar cell can be installed on the exterior of the vehicle to charge the secondary battery while the vehicle is stopped or moving. For such contactless power supply, an electromagnetic induction method or a magnetic field resonance method can be used.

[0342] 25C shows an example of a two-wheeled vehicle using the secondary battery of one embodiment of the present invention. A scooter 8600 shown in FIG. 25C includes 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.

[0343] 25C can store a secondary battery 8602 in under-seat storage 8604. Even if under-seat storage 8604 is small, secondary battery 8602 can be stored in under-seat storage 8604. Secondary battery 8602 is removable, and when charging, secondary battery 8602 can be carried indoors, charged, and stored before riding.

[0344] 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 will contribute to reducing the weight of the vehicle, thereby improving the cruising range. Furthermore, the secondary battery installed in the vehicle can also be used as a power supply source for purposes other than the vehicle. In this case, for example, it is possible to avoid using a commercial power source during peak power demand. Avoiding the use of a commercial power source during peak power demand can contribute to energy conservation and reduction of carbon dioxide emissions. Furthermore, if the cycle characteristics are good, the secondary battery can be used for a long period of time, and the amount of rare metals used, such as cobalt, can be reduced.

[0345] This embodiment mode can be implemented in appropriate combination with other embodiment modes. [Example]

[0346] In this example, a positive electrode active material according to one embodiment of the present invention was prepared, and the particle size distribution and powder packing density (PPD) were evaluated.

[0347] First, a small particle size positive electrode active material was produced by the method for producing the positive electrode active material 100 shown in the first embodiment and FIG.

[0348] First, lithium carbonate was prepared as a lithium source and tetracobalt trioxide was prepared as a cobalt source (step S11), which were then crushed and mixed in a ball mill at 200 rpm for 12 hours (step S12), and then fired at 950°C for 10 hours (step S13) to obtain lithium cobalt oxide (step S14).

[0349] Next, nickel hydroxide was prepared as a nickel source (step S21), and aluminum hydroxide was prepared as an aluminum source (step S22).

[0350] In addition, magnesium fluoride (MGH18XB, Kojundo Chemical Laboratory) was prepared as a magnesium source and a fluorine source, and lithium fluoride (LIH10XB, Kojundo Chemical Laboratory) was prepared as a fluorine source (step S31). LiF:MgF2 was weighed out to a molar ratio of 1:3, and crushed and mixed in a ball mill (step S32), to obtain a mixture 902 (step S33). The mixture 902 had a median diameter D 50 was about 3.5 μm.

[0351] Next, the lithium cobalt oxide, nickel hydroxide, aluminum hydroxide, and mixture 902 prepared above were mixed in a ball mill (step S41) to obtain mixture 903 (step S42). The mixing ratio was such that, when the number of cobalt atoms was 100, the number of nickel atoms was 0.5, the number of aluminum atoms was 0.5, and the number of magnesium atoms was 1.

[0352] The mixture 903 was annealed in an oxygen atmosphere at 800° C. for 2 hours (step S43), to obtain a composite oxide (step S44). This composite oxide after annealing and before crushing was designated as sample 99.

[0353] Next, the composite oxide was crushed using a thin-film swirl high-speed mixer (Filmix 30-L model, Primix Corporation) or a ball mill (step S45). The crushed composite oxide was collected to obtain a positive electrode active material (step S46). The positive electrode active material produced using the thin-film swirl high-speed mixer for crushing was designated Sample 100, and the positive electrode active material produced using the ball mill for crushing was designated Sample 101.

[0354] Next, a large particle size positive electrode active material was produced by the method for producing positive electrode active material 200 shown in Embodiment 1 and FIG.

[0355] As the lithium cobalt oxide, a pre-synthesized lithium cobalt oxide (C-10N, Nippon Chemical Industry) was prepared (step S14). Nickel hydroxide was prepared as the nickel source (step S21), and aluminum hydroxide was prepared as the aluminum source (step S22). As in FIG. 4, a mixture 902 was produced (steps S31 to S33).

[0356] Next, lithium cobalt oxide, nickel hydroxide, aluminum hydroxide, and mixture 902 were mixed in a ball mill (step S41) to obtain mixture 903 (step S42). The mixing ratio was such that, when the number of cobalt atoms was 100, the number of nickel atoms was 0.5, the number of aluminum atoms was 0.5, and the number of magnesium atoms was 1.

[0357] Mixture 903 was heated at 850° C. for 10 hours in an oxygen atmosphere (step S43), to obtain positive electrode active material 200 (step S44).

[0358] Next, as a comparative example, a small particle size positive electrode active material containing no nickel, aluminum, magnesium, or fluorine was prepared.

[0359] Lithium cobalt oxide particles (product name: CellSeed C-5H) manufactured by Nippon Chemical Industry Co., Ltd. were crushed in a ball mill at 200 rpm for 12 hours to prepare Sample 300. CellSeed C-5H is a lithium cobalt oxide in which, in impurity analysis by glow discharge mass spectrometry (GD-MS), the magnesium and fluorine concentrations were 50 ppm wt or less, the calcium, aluminum, and silicon concentrations were 100 ppm wt or less, the nickel concentration was 150 ppm wt or less, the sulfur concentration was 500 ppm wt or less, the arsenic concentration was 1100 ppm wt or less, and the concentrations of other elements other than lithium, cobalt, and oxygen were 150 ppm wt or less.

[0360] The preparation conditions for Samples 99, 100, 101, 200 and 300 are shown in Table 1.

[0361] [Table 1]

[0362] <Particle size distribution> The particle size distribution of the samples shown in Table 1 was measured by the laser diffraction / scattering method. The particle size distribution is shown in Figure 26. 50 , D 10 , D 90 The mean values ​​and standard deviations (SD) are shown in Table 2.

[0363] [Table 2]

[0364] 26, Sample 100 and Sample 101 with relatively small particle sizes, and Sample 200 with relatively large particle sizes, were able to be produced by the method described in the first embodiment. It was found that the use of a thin film rotary high-speed mixer rather than a ball mill was more preferable as a method for crushing Sample 99, as the particles did not become too fine.

[0365] <ppd> Next, a sample was prepared by mixing the small particle size sample 100 and the large particle size sample 200, and the PPD was measured. The mixing ratio and PPD of Sample 100 and Sample 200 are shown in Table 3. Figure 27 shows a graph of the relationship between the mixing ratio and PPD.

[0366] [Table 3]

[0367] Mixing Sample 100 and Sample 200 allowed for a larger PPD than when they were not mixed. Samples 5:95 to 30:70 showed good results with a PPD of 4.3 g / cc or more, with Sample 20:80 showing the best PPD. [Example]

[0368] In this example, positive electrodes were fabricated using positive electrode active material 100' and positive electrode active material 100", which were fabricated in the same manner as in Example 1 except for slight changes in the annealing conditions. The cross sections were observed by SEM, and the crystal structures were estimated by XRD. Secondary batteries were also fabricated, and their charge-discharge cycle characteristics were evaluated.

[0369] <Cross-sectional SEM> Positive electrodes for cross-sectional SEM observation were prepared as follows. Sample 100" and Sample 200 were prepared in the same manner as in Example 1, except that the annealing conditions were 850°C and 10 hours, respectively. The positive electrode active materials used were Sample 100", which was prepared in the same manner as in Example 1, and Sample 200", which was prepared in the same manner as in Example 1. Carbon black (TIMCAL SUPER C65, Imerys) was used as the conductive additive, and PVDF (Solef 5130, SOLVEY) was used as the binder. Aluminum foil with a thickness of 20 μm was used as the current collector. NMP was used as the solvent.

[0370] The mixing ratio of the positive electrode active material, conductive additive, and binder was positive electrode active material:conductive additive:binder=97:1.5:1.5 (weight ratio). Using the method for producing the positive electrode described in the second embodiment, a slurry was prepared, applied to a current collector, dried, and pressed. The pressure was applied at 210 kN / m and then at 1467 kN / m. The amount of the positive electrode active material layer carried on the current collector was 10 mg / cm. 2 It became about that level.

[0371] FIG. 28A shows a cross-sectional SEM image of a positive electrode fabricated using Sample 15:85 (Sample 100":Sample 200 = 15:85 (weight ratio)) as the positive electrode active material. FIG. 28B shows a cross-sectional SEM image of a positive electrode fabricated using only Sample 200 as the positive electrode active material.

[0372] In FIG. 28A, in which small particle size positive electrode active material 100'' and large particle size positive electrode active material 200 were mixed, there were few voids where particles of the positive electrode active material did not exist. However, in FIG. 28B, which was made using only large particle size positive electrode active material 200, many voids were observed.

[0373] <xrd> Positive electrodes for XRD were prepared as follows: Sample 100', which was prepared in the same manner as in Example 1 except that the annealing conditions were 800°C for 10 hours, Sample 100'(2), which was prepared in the same manner as in Example 1 except that the amounts of nickel, aluminum, magnesium, and fluorine mixed were changed, and Sample 200, which was prepared in the same manner as in Example 1, were used as the positive electrode active material.

[0374] The conductive additive and binder were the same as those used for cross-sectional SEM observation. The mixing ratio of the positive electrode active material, conductive additive, and binder was positive electrode active material:conductive additive:binder = 95:3:2. Then, as with the cross-sectional SEM observation, a slurry was prepared, applied to the current collector, and dried. However, no pressure was applied.

[0375] Using the charging method and XRD measurement method described in embodiment 1, the coin cell having the positive electrode prepared above was charged and discharged for one cycle at 4.6 V, and then charged again at 4.6 V, and the crystal structure was estimated by XRD.

[0376] Table 4 shows the preparation conditions of Sample 100', Sample 100'(2), and Sample 200 prepared for XRD measurement, and the charge capacities after one charge-discharge cycle before XRD measurement.

[0377] [Table 4]

[0378] As shown in Table 4, all of Sample 100', Sample 100'(2) and Sample 200 exhibited high charge capacities.

[0379] Figure 29 shows the XRD patterns of the positive electrodes using Sample 100', Sample 100'(2), and Sample 200. For comparison, pseudospinel, H1-3, and Li 0.35 The patterns for CoO2 are also shown side by side. Also, Fig. 30A shows an enlarged pattern of the region in Fig. 29 where 2θ is 18 or more and 21 or less, and Fig. 30B shows an enlarged pattern of the region in 2θ is 43 or more and 46 or less.

[0380] 29, 30A, and 30B, diffraction peaks at 2θ=19.30±0.20° and 2θ=45.55±0.10° were observed in Sample 100', Sample 100'(2), and Sample 200 charged at 4.6 V, demonstrating that they all have a pseudospinel crystal structure. Furthermore, none of the samples exhibited any characteristics of the H1-3 crystal structure.

[0381] The pattern of sample 200 has sharp peaks, suggesting high crystallinity. Sample 100' also shows broad peaks at around 18.9° and 45.2°, which are likely due to Li 0.35 This was thought to be due to a slight influence from the crystal structure of CoO2.

[0382] <Cycle characteristics of positive electrode active material 100'> The positive electrode active material 100' having small particle diameter was prepared by varying the amounts of nickel, aluminum, magnesium, and fluorine, and the secondary batteries were used to evaluate the cycle characteristics. The cells for evaluating the cycle characteristics were prepared as follows.

[0383] Sample 100' (1.5) was used as the positive electrode active material, which was prepared in the same manner as Sample 100', except that in step S41 described in the embodiment, the number of nickel atoms was 0.75, the number of aluminum atoms was 0.75, and the number of magnesium atoms was 1.5, assuming that the number of cobalt atoms was 100. Similarly, Sample 100' (2) was used as a positive electrode active material prepared in the same manner as Sample 100', except that the number of nickel atoms was 1, the number of aluminum atoms was 1, and the number of magnesium atoms was 2, assuming that the number of cobalt atoms was 100. As a comparative example, Sample 300, which is a small particle size positive electrode active material free of nickel, aluminum, magnesium, and fluorine, prepared in Example 1, was used.

[0384] The preparation conditions for Sample 100′, Sample 100′(1.5), Sample 100′(2), and Sample 300 are shown in Table 5.

[0385] [Table 5]

[0386] The conductive additive, binder, and mixing ratio of the conductive additive, binder, and positive electrode active material, as well as the coating and pressing on the current collector, were prepared in the same manner as for the positive electrode used for cross-sectional SEM observation. The electrolyte used was 1 mol / L LiPF6, and the electrolyte was a mixture of EC:DEC = 3:7 (volume ratio) with 2 wt% VC. The separator was made of polypropylene (Celgard 2400, Celgard) with a thickness of 25 μm and a porosity of 41%. Lithium metal was used for the negative electrode. The exterior was a coin cell (CR2032 type, 20 mm diameter, 3.2 mm height) made of stainless steel (SUS).

[0387] The secondary battery fabricated under the above conditions was repeatedly charged and discharged. Charging was performed at a constant current of 100 mA / g until the voltage reached 4.6 V, and then at a constant voltage until the current reached 10 mA / g. Discharging was performed at a constant current of 100 mA / g until the voltage reached 2.5 V. After discharging, a 10-minute wait was allowed before the next charge. The temperature was 25°C or 45°C.

[0388] Graphs of the cycle characteristics measured under the above conditions are shown in Figures 31 and 32. Figure 31A is a graph of the discharge capacity measured at 25°C, and Figure 31B is a graph of the discharge capacity retention rate measured at 25°C. Figure 32A is a graph of the discharge capacity measured at 45°C, and Figure 32B is a graph of the discharge capacity retention rate measured at 45°C.

[0389] As is clear from Figures 31 and 32, the cycle characteristics of all the positive electrode active materials, Sample 100', Sample 100'(1.5), and Sample 100'(2), were good compared to Sample 300, which is a small particle size positive electrode active material that does not contain nickel, aluminum, magnesium, or fluorine.

[0390] <Cycle characteristics of an aggregate of particles made by mixing positive electrode active material 100' and positive electrode active material 200> Next, an aggregate of particles, in which the small particle size positive electrode active material 100' and the larger particle size positive electrode active material 200 were mixed, was used in a secondary battery to evaluate cycle characteristics.

[0391] The positive electrode active materials used were Sample 200, Sample 5:95, Sample 10:90, Sample 15:85, Sample 20:80, and Sample 100′ prepared in Example 1. Other conditions were the same as those for evaluating the cycle characteristics of Positive Electrode Active Material 100′.

[0392] Graphs of the cycle characteristics measured under the above conditions are shown in Figures 33 and 34. Figure 33A is a graph of the discharge capacity measured at 25°C, and Figure 33B is a graph of the discharge capacity retention rate measured at 25°C. Figure 34A is a graph of the discharge capacity measured at 45°C, and Figure 34B is a graph of the discharge capacity retention rate measured at 45°C.

[0393] As is clear from Figures 33 and 34, Sample 200, Sample 5:95, Sample 10:90, Sample 15:85, Sample 20:80, and Sample 100' exhibited good cycle characteristics. The cycle characteristics of Sample 200, Sample 5:95, Sample 10:90, Sample 15:85, and Sample 20:80 were extremely good. In particular, Sample 10:90 and Sample 20:80 maintained high discharge capacities at 25°C.

[0394] The above examples demonstrate that the PPD can be increased by mixing a small particle size positive electrode active material with a large particle size positive electrode active material. Furthermore, the positive electrode active material according to one embodiment of the present invention has a pseudospinel crystal structure during high-voltage charging and exhibits good cycle characteristics. [Explanation of symbols]

[0395] 100: Positive electrode active material, 200: Positive electrode active material< / xrd> < / ppd>

Claims

1. A positive electrode active material having an aggregate of particles, the particle aggregate has a first particle group and a second particle group, The particle aggregate is containing lithium, cobalt, nickel, aluminum, magnesium, oxygen, and fluorine; When the number of cobalt atoms contained in the particle aggregate is 100, The number of nickel atoms is 0.05 or more and 2 or less, The number of aluminum atoms is 0.05 or more and 2 or less, The number of magnesium atoms is 0.1 or more and 6 or less, When the particle size distribution of the particle aggregate is measured by a laser diffraction / scattering method, the first particle group has a first peak, the second particle group has a second peak, the first peak has a maximum value between 2 μm and 4 μm, The positive electrode active material, wherein the second peak has a maximum value in a range of 9 μm or more and 25 μm or less.

2. In claim 1, The positive electrode active material has a powder packing density of 4.30 g / cc or more and 4.60 g / cc or less.

3. In claim 1 and claim 2, A lithium ion secondary battery using the aggregate of particles as a positive electrode and metallic lithium as a negative electrode was charged at a constant current in a 25° C. environment until the battery voltage reached 4.6 V, and then charged at a constant voltage until the current value reached 0.02 C. When the positive electrode was analyzed by powder X-ray diffraction using CuKα1 radiation, Diffraction peaks at 2θ=19.30±0.20° and 2θ=45.55±0.10° Cathode active material.

4. A positive electrode active material having a particle group containing lithium, cobalt, nickel, aluminum, magnesium, oxygen, and fluorine, When the number of cobalt atoms contained in the particle group is 100, The number of nickel atoms is 0.05 or more and 2 or less, The number of aluminum atoms is 0.05 or more and 2 or less, The number of magnesium atoms is 0.1 or more and 6 or less, When the particle size distribution is measured by a laser diffraction / scattering method, the maximum value is between 2 μm and 4 μm, A lithium ion secondary battery using the particle group in a positive electrode and metallic lithium in a negative electrode was charged at a constant current in a 25° C. environment until the battery voltage reached 4.6 V, and then charged at a constant voltage until the current value reached 0.02 C. When the positive electrode was analyzed by powder X-ray diffraction using CuKα1 radiation, Diffraction peaks at 2θ=19.30±0.20° and 2θ=45.55±0.10° Cathode active material.

5. Contains lithium, cobalt, nickel, aluminum, magnesium, oxygen, and fluorine, and has a particle size distribution of D when measured by a laser diffraction / scattering method. ５０ a first step of preparing a first particle group having a particle size of 2 μm or more and 4 μm or less; Contains lithium, cobalt, nickel, aluminum, magnesium, oxygen, and fluorine, and has a particle size distribution of D when measured by a laser diffraction / scattering method. ５０ a second step of preparing a second particle group having a particle size of 16 μm or more and 22 μm or less; a third step of mixing the first particle group and the second particle group to prepare a particle aggregate, a ratio of the first particle group to the particle aggregate is 5% by weight or more and 20% by weight or less.

6. 6. The method according to claim 5, wherein the first step comprises: A method for producing a positive electrode active material, comprising a step of crushing the material using a thin film swirling mixer.

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