Positive active material

Abstract

To provide a positive electrode active material for a secondary battery having high capacity and an excellent charging and discharging cycle characteristic, a positive electrode active material in which the decrease in capacity in the charging and discharging cycle is suppressed, a secondary battery with high capacity, a secondary battery with the excellent charging and discharging characteristic, and a secondary battery with high safety or reliability.SOLUTION: A positive electrode active material contains lithium, cobalt, oxygen, and aluminum. According to the Rietveld analysis about the pattern obtained by the powder X-ray diffraction, a crystal structure with a spatial group of R-3m is obtained. The atomic number of aluminum in the analysis of the X-ray photoelectron spectroscopy is 0.2 times or less the atomic number of cobalt.SELECTED DRAWING: Figure 1

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. Demand for high-power, high-energy-density lithium-ion secondary batteries, in particular, has rapidly expanded alongside the development of the semiconductor industry, and they are now essential to the modern information society as a rechargeable energy source, with applications including mobile phones, smartphones, tablets, and laptop computers, as well as portable music players, digital cameras, medical devices, and next-generation clean energy vehicles (hybrid electric vehicles (HEVs), electric vehicles (EVs), and plug-in hybrid electric vehicles (PHEVs)).

[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] Therefore, improvements to the positive electrode active material have been investigated with the aim of improving the cycle characteristics and increasing the capacity of lithium-ion secondary batteries (Patent Documents 1 and 2). Research is also being conducted on the crystal structure of the positive electrode active material (Non-Patent Documents 1 to 3).

[0007] 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.

[0008] 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.

[0009] Patent document 3 uses first-principles calculations to calculate LiNi 1-x M x An example of calculating the interatomic distance of O2 is shown. Patent Document 4 also describes the formation energy of silicon oxide compounds obtained by first-principles calculations. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-216760 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-261132 [Patent Document 3] Japanese Patent Application Laid-Open No. 2016-91633 [Patent Document 4] International Publication No. 2011 / 077654 [Non-patent literature]

[0011] [Non-Patent Document 1] Toyoki Okumura et al, “Correlation of lithium ion distribution and X-ray absorption near-edge structure in O3-and O2-lithium cobalt oxides from first-principle calculation”, Journal of Materials Chemistry, 2012, 22, p.17340-17348 [Non-patent document 2] Motohashi, T. et al, “Electronic phase diagram of the layered cobalt oxide system 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]

[0012] An object of one embodiment of the present invention is to provide a positive electrode active material for a secondary battery that has high capacity and excellent charge-discharge cycle characteristics. Another object is to provide a method for manufacturing the 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 that has excellent charge-discharge characteristics. Another object is to provide a secondary battery that is safe or highly reliable.

[0013] 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.

[0014] 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 of the specification, drawings, and claims. [Means for solving the problem]

[0015] One aspect of the present invention is a positive electrode active material that contains lithium, cobalt, oxygen, and aluminum, and that has a crystal structure with an R-3m space group when Rietveld analysis is performed on a pattern obtained by powder X-ray diffraction using CuKα1 radiation, and that, in X-ray photoelectron spectroscopy analysis, the number of aluminum atoms is 0.2 times or less the number of cobalt atoms.

[0016] In the above configuration, the take-off angle in X-ray photoelectron spectroscopy is preferably 40° or more and 50° or less.

[0017] Furthermore, in the above configuration, when the particle has a cross section that is analyzed by TEM-EDX, it is preferable that in a first region that is 20 nm or more and 200 nm or less away from the particle surface, the number of aluminum atoms is 0.04 times or more and less than 1.6 times the number of cobalt atoms in the TEM-EDX analysis, and in a second region that is 1 μm or more and 3 μm or less away from the particle surface, the number of aluminum atoms is less than 0.03 times the number of cobalt atoms in the TEM-EDX analysis.

[0018] In the above-described configuration, the cross section of the particle is preferably exposed by processing using a focused ion beam processing and observation device.

[0019] In the above-described structure, the positive electrode active material preferably has a coating in contact with the surface of the particle, the coating containing carbon, and the number of cobalt atoms contained in the coating being less than 0.05 times the number of carbon atoms contained in the coating.

[0020] In the above-described structure, it is preferable that the material contains magnesium, and that the number of magnesium atoms is 0.4 to 1.5 times the number of cobalt atoms in an X-ray photoelectron spectroscopy analysis.

[0021] Another embodiment of the present invention is a positive electrode active material containing lithium, cobalt, oxygen, nickel, and aluminum, which has a crystal structure with an R-3m space group when a Rietveld analysis is performed on a pattern obtained by powder X-ray diffraction using CuKα1 radiation, and in which the number of aluminum atoms is lower than that of cobalt and higher than that of nickel in X-ray photoelectron spectroscopy analysis.

[0022] In the above configuration, the take-off angle in X-ray photoelectron spectroscopy is preferably 40° or more and 50° or less.

[0023] Furthermore, in the above configuration, when the particle has a cross section that is analyzed by TEM-EDX, it is preferable that in a first region that is 20 nm or more and 200 nm or less away from the particle surface, the number of aluminum atoms is 0.04 times or more and less than 1.6 times the number of cobalt atoms in the TEM-EDX analysis, and in a second region that is 1 μm or more and 3 μm or less away from the particle surface, the number of aluminum atoms is less than 0.03 times the number of cobalt atoms in the TEM-EDX analysis.

[0024] In the above configuration, it is preferable that the number of nickel atoms in the first region is less than 0.5 times the number of aluminum atoms in TEM-EDX analysis.

[0025] In the above-described configuration, the cross section of the particle is preferably exposed by processing using a focused ion beam processing and observation device.

[0026] In the above-described structure, the positive electrode active material preferably has a coating in contact with the surface of the particle, the coating containing carbon, and the number of cobalt atoms contained in the coating being less than 0.05 times the number of carbon atoms contained in the coating.

[0027] In the above configuration, it is preferable that the sulfur concentration measured by glow discharge mass spectrometry is 150 ppm wt or more and 2000 ppm wt or less.

[0028] In the above-mentioned configuration, it is preferable that the titanium concentration measured by glow discharge mass spectrometry is 300 ppm wt or less.

[0029] Another embodiment of the present invention is a positive electrode active material that is an aggregate of particles, the positive electrode active material having a first particle group and a second particle group, lithium, cobalt, oxygen, and aluminum, and a crystal structure having an R-3m space group when Rietveld analysis is performed on a pattern obtained by powder X-ray diffraction using CuKα1 radiation, the number of magnesium atoms is Mg1 and the number of cobalt atoms is Co1 when measured by elemental analysis using ICP-MS, GD-MS, or atomic absorption spectrometry, and Mg1 / Co1 is 0.001 or more and 0.06 or less, the particle size distribution of the first particle group has a first maximum peak, and the particle size distribution of the second particle group has a second maximum peak, the first maximum peak having a maximum value between 9 μm and 25 μm, and the second maximum peak having a maximum value between 0.1 μm and less than 9 μm.

[0030] In the above configuration, it is preferable that the intensity of the maximum value of the first maximum peak is I1, the intensity of the maximum value of the second maximum peak is I2, and I1 / I2 is 0.01 or more and 0.6 or less.

[0031] In the above-described structure, the particle aggregate preferably contains magnesium, and the number of magnesium atoms is preferably 0.4 to 1.5 times the number of cobalt atoms as determined by X-ray photoelectron spectroscopy.

[0032] In the above configuration, the particle size distribution is preferably measured using a laser diffraction particle size distribution measuring device.

[0033] In the above configuration, the take-off angle in X-ray photoelectron spectroscopy is preferably 40° or more and 50° or less.

[0034] Another embodiment of the present invention is a secondary battery including a positive electrode having any one of the above positive electrode active materials, a negative electrode, and an electrolyte solution, wherein the secondary battery is charged and discharged once each to determine a first discharge capacity from the discharge, and then alternately charged and discharged 50 times each to determine a second discharge capacity from the final discharge, wherein the second discharge capacity is 90% or more of the first discharge capacity.

[0035] In the above configuration, charging is performed under CCCV conditions, the CC charging current is 0.01C or more and 1.0C or less, and the upper limit voltage of CC charging is Li / Li + The reference voltage is 4.55V or higher, the CV charge cut-off current is 0.001C or higher, discharge is carried out under CC conditions, the CC discharge current is 0.05C or higher and 2.0C or lower, and the measurement temperature is preferably 15°C or higher and 55°C or lower.

[0036] Alternatively, one embodiment of the present invention includes a positive electrode having any one of the positive electrode active materials described above, and metallic lithium is used as a counter electrode. The positive electrode is charged and discharged once each, a first discharge capacity is calculated from the discharge, and then the positive electrode and discharge are alternately performed 50 times, and a second discharge capacity is calculated from the final discharge, the second discharge capacity being 90% or more of the first discharge capacity, and the charge is performed under CCCV conditions, the CC charge current is 0.01 C or more and 1.0 C or less, and the upper limit voltage of the CC charge is Li / Li + This secondary battery has a reference voltage of 4.55V or higher, a CV charge cut-off current of 0.001C or higher, discharge is performed under CC conditions, the CC discharge current is 0.05C or higher and 2.0C or lower, and the measurement temperature is 15°C or higher and 55°C or lower.

[0037] Alternatively, one embodiment of the present invention is a method for producing a positive electrode active material, the method including: a first step of mixing aluminum with a composite oxide containing lithium and cobalt to prepare a first mixture; and a second step of heating the first mixture, wherein in the first step, the atomic ratio of aluminum in the first mixture to cobalt in the composite oxide is expressed as aluminum:cobalt=C_a:1, where C_a is 0.0005 or more and 0.02 or less.

[0038] In the above configuration, the heating temperature in the second step is preferably 700°C or higher and 920°C or lower.

[0039] Alternatively, one embodiment of the present invention is a method for producing a positive electrode active material, the method including: a first step of mixing a composite oxide containing lithium and cobalt with magnesium and fluorine to produce a first mixture; a second step of heating the first mixture to produce a second mixture; a third step of mixing the second mixture with aluminum to produce a third mixture; and a fourth step of heating the third mixture, wherein the atomic ratio of aluminum in the third mixture in the third step to cobalt in the composite oxide in the first step is expressed as aluminum:cobalt=C_a:1, where C_a is 0.0005 or greater and 0.02 or less.

[0040] In the above configuration, it is preferable that in the first step, the atomic ratio of magnesium contained in the first mixture to cobalt contained in the composite oxide is expressed as magnesium:cobalt=C_m:1, and C_m is 0.001 or more and 0.06 or less.

[0041] In the above configuration, the heating temperature in the fourth step is preferably 700°C or higher and 920°C or lower.

[0042] Alternatively, one embodiment of the present invention is a method for producing a positive electrode active material, the method including: a first step of mixing a composite oxide containing lithium and cobalt with magnesium and fluorine to produce a first mixture; a second step of heating the first mixture to produce a second mixture; a third step of mixing the second mixture with aluminum and nickel to produce a third mixture; and a fourth step of heating the third mixture, wherein an atomic ratio between aluminum in the third mixture in the third step and cobalt in the composite oxide in the first step is expressed as aluminum:cobalt=C_a:1, where C_a is 0.0005 or more and 0.02 or less; and an atomic ratio between nickel in the third mixture in the third step and cobalt in the composite oxide in the first step is expressed as nickel:cobalt=C_n:1, where C_n is 0.0005 or more and 0.02 or less.

[0043] In the above configuration, it is preferable that in the first step, the atomic ratio of magnesium contained in the first mixture to cobalt contained in the composite oxide is expressed as magnesium:cobalt=C_m:1, and C_m is 0.001 or more and 0.06 or less.

[0044] In the above configuration, the heating temperature in the fourth step is preferably 700°C or higher and 920°C or lower. [Effects of the Invention]

[0045] 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, and a manufacturing method thereof, can be provided. Furthermore, a manufacturing method for the positive electrode active material with high productivity can be provided. Furthermore, a positive electrode active material that, when used in a secondary battery, suppresses a decrease in capacity during charge / discharge cycles can be provided. Furthermore, a high-capacity secondary battery can be provided. Furthermore, a secondary battery with excellent charge / discharge characteristics can be provided. Furthermore, a secondary battery with high safety or reliability can be provided. Furthermore, a novel material, active material particles, a power storage device, or a manufacturing method thereof can be provided. [Brief explanation of the drawings]

[0046] [Figure 1] 1A and 1B are diagrams illustrating an example of a cross section of a positive electrode active material according to one embodiment of the present invention. [Figure 2] 2A and 2B are diagrams illustrating an example of a cross section of a positive electrode active material according to one embodiment of the present invention. [Figure 3] FIG. 3 illustrates an example of a cross section of a positive electrode of one embodiment of the present invention. [Figure 4] FIG. 4 is a diagram illustrating the depth of charge and the crystal structure of a positive electrode active material according to one embodiment of the present invention. [Figure 5] FIG. 5 is a diagram illustrating the state of charge and the crystal structure of a conventional positive electrode active material. [Figure 6] Figure 6 shows the XRD pattern calculated from the crystal structure. [Figure 7] 7A and 7B show the calculation results of the relationship between the occupancy rate of lithium sites and energy. [Figure 8] Figure 8 shows the calculation results for the relationship between the occupancy rate of lithium sites and the c-axis. [Figure 9] FIG. 9 is a diagram showing the relationship between the occupancy rate of lithium sites and the c-axis. [Figure 10] 10A to 10C illustrate an example of a method for manufacturing a positive electrode active material of one embodiment of the present invention. [Figure 11] 11A and 11B are cross-sectional views of an active material layer in which a graphene compound is used as a conductive additive. [Figure 12] 12A and 12B illustrate an example of a secondary battery of one embodiment of the present invention. [Figure 13] 13A and 13B illustrate an example of a secondary battery of one embodiment of the present invention. [Figure 14] 14A to 14C illustrate an example of a secondary battery of one embodiment of the present invention. [Figure 15] 15A and 15B illustrate an example of a secondary battery of one embodiment of the present invention. [Figure 16]16A and 16B are diagrams illustrating a coin-type secondary battery, and Fig. 16C is a diagram illustrating the flow of electricity in the secondary battery. [Figure 17] Figures 17A and 17B are diagrams illustrating a cylindrical secondary battery, and Figures 17C and 17D are diagrams illustrating a module having a plurality of cylindrical secondary batteries. [Figure 18] 18A and 18B are diagrams illustrating an example of a secondary battery. [Figure 19] 19A to 19D are diagrams illustrating an example of a secondary battery. [Figure 20] 20A and 20B are diagrams illustrating an example of a secondary battery. [Figure 21] FIG. 21 is a diagram illustrating an example of a secondary battery. [Figure 22] 22A to 22C are diagrams illustrating a laminated secondary battery. [Figure 23] 23A and 23B are diagrams illustrating a laminated secondary battery. [Figure 24] FIG. 24 is a diagram showing the appearance of a secondary battery. [Figure 25] FIG. 25 is a diagram showing the appearance of a secondary battery. [Figure 26] 26A to 26C are diagrams for explaining a method for manufacturing a secondary battery. [Figure 27] 27A to 27E are diagrams illustrating a bendable secondary battery. [Figure 28] 28A and 28B are diagrams illustrating a bendable secondary battery. [Figure 29] 29A and 29B illustrate an example of a secondary battery and a manufacturing method thereof according to one embodiment of the present invention. [Figure 30] 30A to 30H are diagrams illustrating an example of an electronic device. [Figure 31] 31A to 31C are diagrams illustrating an example of an electronic device. [Figure 32] FIG. 32 is a diagram illustrating an example of an electronic device. [Figure 33]33A to 33C are diagrams illustrating an example of a vehicle. [Figure 34] FIG. 34 is a diagram showing the relationship between the discharge capacity retention rate and the discharge energy of a battery. [Figure 35] FIG. 35 is a diagram showing the relationship between the discharge capacity retention rate and the discharge energy of a battery. [Figure 36] FIG. 36 is a diagram showing the relationship between the discharge capacity retention rate and the discharge energy of a battery. [Figure 37] FIG. 37 is a diagram showing the relationship between the discharge capacity retention rate and the discharge energy of a battery. [Figure 38] 38A and 38B show the results of a continuous charging test of the battery. [Figure 39] FIG. 39 shows the results of XRD evaluation. [Figure 40] FIG. 40 shows the results of XRD evaluation. [Figure 41] FIG. 41 shows the evaluation results of particle size distribution. [Figure 42] FIG. 42 shows the cycle characteristics. [Figure 43] FIG. 43 shows the cycle characteristics results. [Figure 44] Figure 44 shows the evaluation results of particle size distribution. [Figure 45] FIG. 45 shows the cycle characteristics results. [Figure 46] FIG. 46 shows the evaluation results of particle size distribution. [Figure 47] FIG. 47 shows the evaluation results of particle size distribution. [Figure 48] FIG. 48 shows the cycle characteristics of the secondary battery. DETAILED DESCRIPTION OF THE INVENTION

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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 {}.

[0051] In this specification and the like, segregation refers to a phenomenon in which a certain element (for example, B) is spatially distributed non-uniformly in a solid composed of multiple elements (for example, A, B, and C).

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] It can also be said that the pseudospinel crystal structure is similar to the CdCl2 crystal structure, although it has random Li between the layers. 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.

[0057] 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.

[0058] 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, and more preferably less than 2.5 degrees. Light elements such as oxygen and fluorine may not be clearly visible in TEM images, but in such cases, the alignment of the orientations can be determined from the arrangement of metal elements.

[0059] 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.

[0060] 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.

[0061] 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 negative electrode to the positive 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 (in the case of a lithium counter electrode) at 25°C, followed by constant voltage charging at 0.01 C or until the current value drops to 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.

[0062] 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 positive electrode to the negative 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.

[0063] 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.

[0064] (Embodiment 1) In this embodiment, a positive electrode active material and the like according to one embodiment of the present invention will be described.

[0065] [Cathode active material] The discharge capacity can be increased by increasing the charging voltage of the secondary battery. Furthermore, if the positive electrode active material has a crystalline structure, increasing the charging voltage may change the crystalline structure.

[0066] If the change in crystal structure that occurs with charging is irreversible, repeated charge and discharge may cause the crystal structure of the positive electrode active material to collapse, resulting in a decrease in discharge capacity.

[0067] As the charging voltage of a secondary battery increases, the voltage of the positive electrode generally increases. The positive electrode active material of one embodiment of the present invention has a stable crystal structure even at high voltages. The stable crystal structure of the positive electrode active material during charging can suppress a decrease in capacity due to repeated charging and discharging.

[0068] Furthermore, a short circuit in a secondary battery not only causes problems in the charging and discharging operations of the secondary battery, but also may lead to heat generation and fire. In order to realize a safe secondary battery, it is preferable that the short circuit current be suppressed even at a high charging voltage. The positive electrode active material of one embodiment of the present invention suppresses the short circuit current even at a high charging voltage, thereby achieving both high capacity and safety.

[0069] A secondary battery using the positive electrode active material of one embodiment of the present invention preferably simultaneously satisfies high capacity, excellent charge / discharge cycle characteristics, and safety.

[0070] Positive electrode active materials with a layered structure, such as lithium cobalt oxide, lithium nickel-cobalt-manganese oxide, and lithium nickel-cobalt-aluminate, have an extremely high amount of lithium per volume and weight of the positive electrode active material that is inserted and removed during charging and discharging of secondary batteries. Therefore, secondary batteries using these positive electrode active materials have the advantage of high capacity.

[0071] On the other hand, as the charging voltage increases, a positive electrode active material having a layered structure may experience a change in lattice constant or a shift in layers due to the elimination of a metal that serves as a carrier ion, more specifically, lithium, which may lead to a collapse of the crystal structure. For example, when a metal that serves as a carrier ion is located between layers, the elimination of the metal may significantly change the lattice constant in the direction perpendicular to the layers.

[0072] The positive electrode active material of one embodiment of the present invention preferably contains magnesium in addition to a first metal (hereinafter, metal A), a second metal (hereinafter, metal M), and oxygen. Metal A is, for example, a metal that serves as a carrier ion. Metal M is one or more metals, and preferably contains a metal that is involved in a redox reaction. The inventors have also found that adding aluminum to the positive electrode active material containing magnesium suppresses short-circuiting of secondary batteries at high voltages compared to when other elements are added.

[0073] While suppressing short circuits is desirable from a safety perspective, suppressing short circuits can sometimes result in a decrease in discharge capacity. For example, while aluminum is effective in suppressing short circuit current, there is a concern that a high aluminum concentration may result in a decrease in capacity. Here, the inventors have discovered that adding nickel to the above-mentioned positive electrode active material containing magnesium and aluminum more effectively suppresses the decrease in discharge capacity of secondary batteries than when other elements are added.

[0074] When the positive electrode active material according to one embodiment of the present invention has particles, the particles preferably have a concentration gradient for each of magnesium, aluminum, and nickel, with the concentration preferably being higher near the surface. Meanwhile, nickel may be incorporated into the particles at a higher concentration than magnesium and aluminum. That is, the concentration gradients of magnesium and aluminum may be biased toward the surface, resulting in a steeper profile, compared with nickel.

[0075] Here, a high charging voltage is, for example, 4.55V (vs Li / Li + ) or more, preferably 4.6V (vs Li / Li + ) or more, more preferably 4.65V (vs Li / Li + )That's all.

[0076] The metal A can be, for example, an alkali metal such as lithium, sodium, or potassium, or a Group 2 element such as calcium, beryllium, or magnesium, with lithium being preferred as the metal A. The metal M can be, for example, one or more elements selected from cobalt, manganese, and iron, with cobalt being preferred as the metal M. In addition to these elements, the metal M may also be one or more elements selected from nickel and manganese.

[0077] Examples of the crystal structure of the positive electrode active material include a layered rock-salt crystal structure, a spinel crystal structure, and an olivine crystal structure. Among these, the positive electrode active material of one embodiment of the present invention preferably has a layered rock-salt crystal structure. The layered rock-salt crystal structure may be represented by the space group R-3m.

[0078] Consider a case where positive electrode active material 100 has particle 101. Particle 101 contains metal A, metal M, and oxygen. Particle 101 preferably contains magnesium and aluminum. In particle 101, magnesium and aluminum preferably have a concentration gradient, and for example, the concentration near the surface of particle 101 is preferably high. Alternatively, the concentration in the surface layer of particle 101 is preferably high.

[0079] For example, in the particles 101, the concentrations of magnesium and aluminum measured by XPS or the like are preferably higher than the concentrations measured by ICP-MS (inductively coupled plasma mass spectrometry) or GD-MS (glow discharge mass spectrometry).

[0080] Furthermore, for example, in particle 101, when a cross section is exposed by processing and the cross section is analyzed using TEM-EDX, it is preferable that the concentrations of magnesium and aluminum in the surface layer are higher than the concentrations in the region deeper than the surface layer. Processing can be performed, for example, by FIB.

[0081] The particles 101 preferably contain nickel. The particles 101 preferably have a concentration gradient of nickel, and for example, the concentration may be higher near the surface of the particles 101. Alternatively, the concentration may be higher in the surface layer of the particles 101.

[0082] For example, in the particle 101, the concentration of nickel measured by ICP-MS or GD-MS may be higher than the concentration measured by XPS or the like.

[0083] Furthermore, for example, when the cross section of the particle 101 is exposed by processing and analyzed using TEM-EDX, the concentration of nickel in the surface layer may be higher than the concentration in a region deeper than the surface layer.

[0084] For example, some of the magnesium, aluminum, and nickel contained in the positive electrode active material 100 may not be incorporated into the crystal structure. "Incorporated into the crystal structure" refers to, for example, the positive electrode active material 100 having a crystal structure containing metal A, metal M, and oxygen, and in the crystal structure, some of the elements contained in the crystal structure being substituted with one or more of magnesium, aluminum, and nickel. Alternatively, one or more of magnesium, aluminum, and nickel may be located in the interstitial spaces of the crystal structure.

[0085] A portion of the magnesium, aluminum, and nickel contained in the positive electrode active material 100 may not be incorporated into the crystal structure. Alternatively, the positive electrode active material 100 may have, for example, particles 102 containing one or more of magnesium, aluminum, and nickel as a main component. Alternatively, for example, the particles 102 may be in contact with the surface of the particles 101.

[0086] For example, the particles 102 have a higher concentration of at least one of magnesium, aluminum, and nickel than the concentration of the second metal.

[0087] 1A shows an example of a cross section of a particle 101 included in a positive electrode active material 100. The particle 101 has a region 111 and a region 112.

[0088] As shown in FIG. 1B, the distance x1 from the surface of the particle 101 to the region 111 is smaller than the distance x2 from the surface of the particle 101 to the region 112.

[0089] The distance from the particle surface can be, for example, the distance in a direction perpendicular to a tangent to the surface of the cross section of the particle, or the distance in a direction drawn from the surface of the cross section of the particle to the center of the cross section or the center of gravity of the particle.

[0090] FIG. 2A shows an example in which distances in a different direction from those in FIG. 1B are used.

[0091] When a secondary battery has a positive electrode, a negative electrode, and an electrolyte, the electrolyte decomposes during charging and discharging of the secondary battery, and the decomposition products may deposit a coating 103 on the surfaces of electrode components, such as particles 101 and 102 of the active material. Figure 2B shows an example in which a coating 103 is deposited on the surface of particle 101.

[0092] Fig. 3 shows an example of a cross section of a positive electrode. Fig. 3 shows an example in which a positive electrode active material layer 109 having particles 101 and 102 is formed on a current collector 108. The positive electrode active material layer and the current collector will be described in detail later.

[0093] When the number of cobalt atoms in the positive electrode active material 100 is taken as 1, the relative value of the number of magnesium atoms is, for example, preferably 0.001 to 0.06, more preferably 0.003 to 0.03. Furthermore, when the number of cobalt atoms is taken as 1, the relative value of the number of aluminum atoms is, for example, preferably 0.0005 to 0.02, more preferably 0.001 to 0.015, and more preferably 0.001 to 0.009. When the number of cobalt atoms is taken as 1, the relative value of the number of nickel atoms is, for example, preferably 0.0005 to 0.02, more preferably 0.001 to 0.015, and more preferably 0.001 to 0.009. The numbers of cobalt atoms, magnesium atoms, aluminum atoms, and nickel atoms can be evaluated, for example, by ICP-MS.

[0094] The particle size distribution of the positive electrode active material 100 preferably has a maximum peak in the range of 9 μm to 25 μm. Alternatively, the particle size distribution of the positive electrode active material according to one embodiment of the present invention preferably has an average particle diameter (D50) of 9 μm to 25 μm.

[0095] The particle size of the particles in the positive electrode active material 100 can be evaluated, for example, by surface observation using an SEM or cross-sectional observation using a TEM. The particle size of the particles in the positive electrode active material 100 can also be evaluated by particle size distribution. The particle size distribution of the positive electrode active material 100 can be measured, for example, using a laser diffraction particle size distribution measuring device.

[0096] Furthermore, when the particle size distribution maximum peak of the positive electrode active material 100 is 9 μm or more and 25 μm or less, the relative value of the number of magnesium atoms is, for example, preferably 0.001 or more and 0.06 or less, more preferably 0.003 or more and 0.03 or less, and even more preferably 0.007 or more and 0.025 or less, when the number of cobalt atoms in the positive electrode active material 100 is taken as 1. The numbers of cobalt atoms and magnesium atoms can be evaluated, for example, by ICP-MS.

[0097] The positive electrode active material 100 preferably contains a halogen such as fluorine.

[0098] In the positive electrode active material 100, the number of titanium atoms is, for example, 300 ppm wt or less.

[0099] The positive electrode active material 100 may have 150 ppm wt or more and 2000 ppm wt or less of sulfur.

[0100] The number of titanium atoms and the number of sulfur atoms in the positive electrode active material 100 can be measured by, for example, GD-MS.

[0101] The positive electrode active material 100 is preferably an aggregate of a plurality of particle groups having different particle size distributions. For details of each particle, the above descriptions of the particles 101 and 102 can be referred to.

[0102] When the positive electrode active material 100 is an aggregate of multiple particle groups with different particle size distributions, the particle size distribution preferably has a first maximum peak and a second maximum peak. The value of the first maximum peak is preferably, for example, 9 μm or more and 25 μm or less. The value of the second maximum peak is preferably, for example, 0.1 μm or more and less than 9 μm. Alternatively, the positive electrode active material 100 has a first particle group and a second particle group, and in the particle size distribution of the first particle group, the average particle diameter (D50) is preferably 9 μm or more and 25 μm or less, and in the particle size distribution of the second particle group, the average particle diameter (D50) is preferably 0.1 μm or more and less than 9 μm.

[0103] When the first maximum peak and the second maximum peak overlap, the peaks may be separated using a function, and the respective peak intensities, half-widths, etc. of the peaks may be analyzed.

[0104] The positive electrode active material 100 may have a plurality of particle groups with different particle size distributions, which may increase the density of the positive electrode active material layer using the positive electrode active material 100. Increasing the density of the positive electrode active material layer may increase the amount of active material per volume of the secondary battery. This may increase the capacity per volume of the secondary battery. On the other hand, if the density of the positive electrode active material is high, there is a concern that the electrolyte may have difficulty penetrating between the particles in the active material layer. In such a case, there is a concern that the output characteristics of the secondary battery may be reduced, for example.

[0105] The positive electrode active material according to one embodiment of the present invention is stable even at a high charging voltage, and therefore the charge capacity can be increased, and as a result, the discharge capacity of the secondary battery can be increased. Therefore, the capacity per volume of the secondary battery may be sufficiently high without excessively increasing the density of the positive electrode active material.

[0106] Furthermore, by reducing the proportion of materials other than the positive electrode active material, such as a conductive additive and a binder, in the positive electrode active material layer, the density of the positive electrode active material layer can be increased.

[0107] The thickness of the positive electrode active material layer is, for example, 10 μm or more and 200 μm or less, or 50 μm or more and 150 μm or less. For example, when the positive electrode active material has a material having a layered rock salt crystal structure containing cobalt, the amount of the positive electrode active material layer is 1 mg / cm. 2 More than 50mg / cm 2 or less than 5 mg / cm 2 More than 30mg / cm 2 For example, when the positive electrode active material has a material having a layered rock salt crystal structure containing cobalt, the density of the positive electrode active material layer is 2.2 g / cm 3 More than 4.9g / cm 3 or less. Or 3.8 g / cm 3 More than 4.5g / cm 3 Here, the amount of support is, for example, the value of the positive electrode active material layer on one side of the current collector.

[0108] <xps> X-ray photoelectron spectroscopy (XPS) can analyze regions from the surface to a depth of approximately 2 to 8 nm (usually about 5 nm), allowing quantitative analysis of the concentration of each element in approximately half of the surface layer. Narrow scan analysis also allows analysis of the bonding state of elements. The quantitative accuracy of XPS is often about ±1 atomic %, and the lower detection limit is approximately 1 atomic %, depending on the element. The unit of concentration in XPS is, for example, atomic %.

[0109] When the positive electrode active material 100 has a first particle group and a second particle group, the number of magnesium atoms in the first particle group may be higher than the number of magnesium atoms in the second particle group.

[0110] When the positive electrode active material 100 is subjected to elemental analysis by ICP-MS, GD-MS, or atomic absorption spectroscopy, the relative value of the number of magnesium atoms (Mg1) relative to the number of cobalt atoms (Co1) is preferably 0.4 or more and 1.5 or less, and more preferably 0.5 or more and 1.1 or less. In other words, the ratio Mg1 / Co1 is preferably 0.001 or more and 0.06 or less.

[0111] The relative value of the number of halogen atoms such as fluorine is preferably 0.05 or more and 1.5 or less, and more preferably 0.3 or more and 1.00 or less.

[0112] Furthermore, when the positive electrode active material 100 is subjected to XPS analysis, the peak showing the bond energy between fluorine and other elements is preferably 682 eV or more and less than 685 eV, and more preferably about 684.8 eV. This value is different from the 686 eV that is the bond energy of magnesium fluoride. In other words, when the positive electrode active material 100 contains fluorine, it is preferable that the bond is other than that of magnesium fluoride.

[0113] Furthermore, when the positive electrode active material 100 is subjected to XPS analysis, the peak showing the bond energy between magnesium and other elements is preferably 1302 eV or more and less than 1304 eV, and more preferably about 1303 eV. This value is different from the bond energy of magnesium fluoride, 1305 eV, and is closer to the bond energy of magnesium oxide. In other words, when the positive electrode active material 100 contains magnesium, the bond is preferably other than that of magnesium fluoride.

[0114] The number of aluminum atoms in the positive electrode active material 100 evaluated by XPS may be lower than that of magnesium and higher than that of nickel. Furthermore, when the number of cobalt atoms detected by XPS in the positive electrode active material 100 is taken as 1, the relative value of the number of aluminum atoms is, for example, 0.2 or less, or 0.15 or less. Nickel may not be detected by XPS after heat treatment in the production method described below.

[0115] In addition, when the positive electrode active material of one embodiment of the present invention is prepared by a manufacturing method described below, the number of bonds containing carbonate may be reduced compared to the composite oxide used in Step S24.

[0116] <edx> EDX measurement, in which an area is scanned and evaluated two-dimensionally, is sometimes called EDX area analysis. Extracting data from a linear area from EDX area analysis and evaluating the distribution of atomic concentrations within positive electrode active material particles is sometimes called line analysis.

[0117] EDX area analysis (e.g., elemental mapping) can quantitatively analyze the magnesium and fluorine concentrations in the interior, surface, and near grain boundaries. EDX line analysis can also analyze the magnesium and fluorine concentration peaks. The EDX concentration units are, for example, atomic percent.

[0118] When EDX analysis is performed on particle 101 of positive electrode active material 100, the number of aluminum atoms in the first region, which is 20 nm or more and 200 nm or less from the surface of particle 101, is preferably 0.04 times or more and less than 1.6 times the number of cobalt atoms in the EDX analysis. Furthermore, the number of aluminum atoms in the second region, which is 1 μm or more and 3 μm or less from the surface of particle 101, is preferably less than 0.03 times the number of cobalt atoms in the EDX analysis.

[0119] A more specific example of an EDX analysis method is to process the particles using an FIB to expose their cross sections, and then analyze them by TEM-EDX analysis.

[0120] [Example of the structure of the positive electrode active material] The positive electrode active material will be described with reference to Figures 4 and 5. Figures 4 and 5 describe the case where cobalt is used as the transition metal in the positive electrode active material.

[0121] The positive electrode active material shown in Fig. 5 is lithium cobalt oxide (LiCoO) to which no halogen or magnesium is added, prepared by the method described below. As described in Non-Patent Documents 1 and 2, the crystal structure of the lithium cobalt oxide shown in Fig. 5 changes depending on the depth of charge.

[0122] As shown in Figure 5, 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.

[0123] 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.

[0124] 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 an H1-3 crystal structure. In reality, the H1-3 crystal structure has twice the number of cobalt atoms per unit cell as other structures. However, in Figure 5 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.

[0125] 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.

[0126] 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.

[0127] However, these two crystal structures have a large deviation in the CoO2 layers. As shown by the dotted lines and arrows in Figure 5, in the H1-3 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.

[0128] 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%.

[0129] In addition, the H1-3 type crystal structure, which has continuous CoO2 layers such as P-3m1(O1), is likely to be unstable.

[0130] 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.

[0131] The positive electrode active material of one embodiment of the present invention can reduce the displacement of the CoO2 layer during repeated high-voltage charge and discharge. Furthermore, the volume change can be reduced. Therefore, the positive electrode active material of one embodiment of the present invention can achieve excellent cycle characteristics. Furthermore, the positive electrode active material of one embodiment of the present invention can have a stable crystal structure in a high-voltage charged state. Therefore, the positive electrode active material of one embodiment of the present invention may be less likely to cause a short circuit when maintained in a high-voltage charged state. In such cases, safety is further improved, which is preferable.

[0132] In the positive electrode active material of one embodiment of the present invention, the change in crystal structure and the difference in volume per the same number of transition metal atoms between a fully discharged state and a high-voltage charged state are small.

[0133] FIG. 4 shows an example of the crystal structure of the positive electrode active material 100 before and after charge and discharge.

[0134] The crystal structure at a charge depth of 0 (discharged state) in Figure 4 is the same as that in Figure 5, R-3m(O3). On the other hand, when the positive electrode active material 100 is fully charged, it has 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 the oxygen hexacoordination 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 4, lithium is omitted to explain the symmetry of the cobalt atoms and the oxygen atoms. In reality, however, 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, magnesium is preferably present in a dilute form between the CoO2 layers, i.e., at the lithium sites. Furthermore, it is preferable that halogens such as fluorine are present randomly and dilutely at the oxygen sites.

[0135] 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.

[0136] It can also be said that the pseudospinel crystal structure is similar to the CdCl2 crystal structure, although it has random Li between the layers. 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.

[0137] 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.

[0138] In the positive electrode active material 100, when a large amount of lithium is released during high-voltage charging, changes in the crystal structure are suppressed more than in conventional positive electrode active materials. For example, as shown by the dotted line in Figure 4, there is almost no displacement of the CoO2 layers in these crystal structures.

[0139] More specifically, the cathode active material 100 exhibits high structural stability even at high charging voltages. For example, in the conventional cathode active material shown in FIG. 5, even at charging voltages where the H1-3 crystal structure is formed, e.g., at a voltage of about 4.6 V relative to the potential of lithium metal, there exists a charging voltage region where the R-3m(O3) crystal structure can be maintained. Furthermore, even at higher charging voltages, e.g., at voltages of about 4.65 V to 4.7 V relative to the potential of lithium metal, there exists a region where the pseudo-spinel crystal structure can be formed. Furthermore, at higher charging voltages, e.g., at voltages of about 4.65 V to 4.7 V relative to the potential of lithium metal, there exists 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 exists a charging voltage region where the R-3m(O3) crystal structure can be maintained even at secondary battery voltages of 4.3 V to 4.5 V, and there exists a region where the pseudo-spinel crystal structure can be formed even at higher charging voltages, e.g., at voltages of 4.35 V to 4.55 V relative to the potential of lithium metal.

[0140] Therefore, the crystal structure of the positive electrode active material 100 is not easily broken even when it is repeatedly charged and discharged at a high voltage.

[0141] 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.

[0142] Magnesium, which is present randomly and dilutely between the CoO2 layers, i.e., at the lithium sites, has the effect of suppressing the displacement of the CoO2 layers. Therefore, the presence of magnesium between the CoO2 layers tends to form a pseudo-spinel crystal structure. Therefore, it is preferable that magnesium be distributed throughout the particles of the positive electrode active material 100. In addition, 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.

[0143] However, if the heat treatment temperature is too high, cation mixing occurs, increasing the possibility that magnesium will enter the cobalt site. If magnesium is present at the cobalt site, it will no longer be effective in maintaining the R-3m structure. 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.

[0144] 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.

[0145] 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.

[0146] <Charging method> High-voltage charging for determining whether a certain composite oxide is the positive electrode active material 100 of one embodiment of the present invention can be performed, for example, by preparing a coin cell (CR2032 type, diameter 20 mm, height 3.2 mm) with a lithium counter electrode and charging it.

[0147] More specifically, the positive electrode may 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.

[0148] Lithium metal can be used for the counter electrode. When a material other than lithium metal is used for the counter electrode, the potential of the secondary battery differs from the potential of the positive electrode. Unless otherwise specified, voltages and potentials in this specification refer to the potential of the positive electrode.

[0149] The electrolyte used in the electrolytic solution is 1 mol / L lithium hexafluorophosphate (LiPF6), and the electrolytic solution can be a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 3:7, with 2 wt% vinylene carbonate (VC).

[0150] The separator can be made of polypropylene with a thickness of 25 μm.

[0151] The positive electrode can and the negative electrode can may be made of stainless steel (SUS).

[0152] The coin cell fabricated under the above conditions was charged at a constant current of 4.6 V and 0.5 C, followed by constant voltage charging until the current reached 0.01 C. Here, 1 C corresponds to 137 mA / g. The temperature was 25°C. After charging in this manner, the coin cell was disassembled in an argon-filled glove box and the positive electrode was removed to obtain a positive electrode active material charged at high voltage. When various analyses were performed, it was preferable to seal the cell in an argon-filled container to prevent reactions with external components. For example, XRD could be performed by sealing the cell in an argon-filled container.

[0153] <xrd> Figure 6 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. -10 m 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.

[0154] As shown in Figure 6, 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, no peaks 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° in a state charged at a high voltage can be said to be a characteristic of the positive electrode active material 100 of one embodiment of the present invention.

[0155] It can also be said that the crystal structure at a state of charge (SOC) of 0% and the crystal structure when charged at a high voltage have similar positions where the diffraction peaks of XRD appear. More specifically, it can be said that for two or more, more preferably three or more of the main diffraction peaks of both, the difference in the positions where the peaks appear is 2θ = 0.7 or less, more preferably 2θ = 0.5 or less.

[0156] The positive electrode active material 100 of one embodiment of the present invention has a pseudo-spinel type crystal structure when charged at a high voltage, but not all of the particles need to have a pseudo-spinel type crystal structure. It may contain other crystal structures or a part thereof may be amorphous. However, when performing Rietveld analysis on the XRD pattern, the pseudo-spinel type 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 type crystal structure is 50 wt% or more, more preferably 60 wt% or more, and even more preferably 66 wt% or more, a positive electrode active material with excellent cycle characteristics can be obtained.

[0157] Also, even after 100 cycles or more of charge and discharge from the start of measurement, when performing Rietveld analysis, the pseudo-spinel type crystal structure is preferably 35 wt% or more, more preferably 40 wt% or more, and even more preferably 43 wt% or more.

[0158] In addition, the crystallite size of the pseudo-spinel type crystal structure possessed by the particles of the positive electrode 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 positive electrode before charge and discharge, a clear peak of the pseudo-spinel type crystal structure can be confirmed after high voltage charging. On the other hand, in the case of simple LiCoO2, even if a part has a structure similar to the pseudo-spinel type crystal structure, the crystallite size becomes small and the peak becomes broad and small. The crystallite size can be obtained from the half-width of the XRD peak.

[0159] <dQ / dV vs V curve> Furthermore, when the positive electrode active material of one embodiment of the present invention is charged at a high voltage and then discharged at a low rate of, for example, 0.2 C or less, a characteristic voltage change may occur 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.

[0160] [First principles calculation] Next, how the stability of the crystal structure and the like change due to the addition of magnesium to the positive electrode active material of one embodiment of the present invention was estimated by first-principles calculations.

[0161] The energy change when lithium is removed from the O3-type and H1-3-type crystal structures was calculated using first-principles calculations. Calculations were also performed for each crystal structure when 2% of lithium at the lithium site was replaced with magnesium.

[0162] The lattice and atomic positions were optimized using first-principles calculations, and the energy was calculated. The software used was VASP (The Vienna Ab initio simulation package). The functional used was LDA (Local density approximation) + U. The U potential of cobalt was set to 4.91. The electronic state pseudopotential used was a potential generated by the PAW (Projector Augmented Wave) method. The cutoff energy was set to 600 eV. The k-point was sampled using a 1 × 1 × 1 mesh. Non-patent literature 6 and non-patent literature 7 can be referenced for the U potential.

[0163] The number of atoms used in the calculations was (48-x) lithium, 48 cobalt, and 96 oxygen atoms when no magnesium was added, and (47-x) lithium, 1 magnesium, 48 cobalt, and 96 oxygen atoms when magnesium was added, where x is the number of lithium atoms removed.

[0164] In this specification and the like, the energy thus determined may be referred to as stabilization energy.

[0165] The energy difference ΔE between a crystal structure model in which one magnesium atom is substituted at the lithium site and a crystal structure model in which x lithium atoms are removed can be calculated using the following formula 1.

[0166]

number

[0167] Here, E total (Li 47 Mg1Co 48 O 96 ) is Li 48 Co 48 O 96 The energy of the structure in which one lithium atom is replaced by Mg is E total (Li 47-x Mg1Co 48 O 96 ) is Li 48 Co 48 O 96 The energy of the structure in which one lithium atom is replaced by Mg and x lithium atoms are removed is E atom (Li) is the energy of one lithium atom, E atom (Co) is the energy of one cobalt atom, E atom (Mg) is the energy of one magnesium atom. Furthermore, although the above formula 1 is a crystal structure model in which one lithium atom is replaced with a magnesium atom, calculations were also performed on a model in which no lithium atoms were replaced with magnesium atoms.

[0168] The calculation results are shown in Figures 7 and 8.

[0169] The horizontal axis of Figure 7A represents the occupancy rate of lithium sites, and the vertical axis represents the energy difference ΔE. Figure 7B is a graph plotting the difference between the calculated results and the straight line shown by the dashed line in Figure 7A, where the energy difference ΔE is 6 eV when the occupancy rate of lithium sites is 0%, on the vertical axis. Lithium is released from the positive electrode active material when the secondary battery is charged. Therefore, by calculating the energy when the occupancy rate of lithium sites decreases, it is possible to consider the state in which lithium is released during charging.

[0170] As shown in Figures 7A and 7B, as the occupancy rate of the lithium sites decreases, the energy difference ΔE increases, making the crystal structure unstable. Furthermore, as can be seen from Figure 7B, the energies of the O3-type crystal structure and the H1-3-type crystal structure intersect, suggesting that a phase change occurs at this intersection. In the structure with one magnesium atom substituted, the occupancy rate of the lithium sites where the intersection of the O3-type crystal structure and the H1-3-type crystal structure is observed is lower than in the structure without magnesium substitution. This suggests that more lithium can be desorbed without a phase change occurring.

[0171] From the calculation results shown in FIGS. 7A and 7B, it can be said that the addition of magnesium stabilizes the charging of the positive electrode active material at high charging voltages.

[0172] The horizontal axis of Figure 8 represents the occupancy rate of the lithium sites, and the vertical axis represents the lattice constant of the c-axis. As the occupancy rate of the lithium sites decreased, the lattice constant of the c-axis increased, and then decreased.

[0173] Figure 9 shows the relationship between the c-axis value calculated from the measured XRD values ​​and the lithium site occupancy rate for a positive electrode active material according to one embodiment of the present invention. The theoretical capacity of lithium cobalt oxide is assumed to be 274 mAh / g. Figure 9 shows that the phenomenon coincides with the calculated results.

[0174] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0175] (Embodiment 2) In this embodiment, an example of a method for manufacturing a positive electrode active material of one embodiment of the present invention will be described.

[0176] [Example of a method for producing a positive electrode active material] Next, an example of a method for manufacturing the positive electrode active material of one embodiment of the present invention will be described with reference to FIGS.

[0177] <Step S11> In step S11, first, a halogen source such as a fluorine source or a chlorine source and a magnesium source are prepared as materials for the mixture 902. In addition to these, a lithium source may also be prepared.

[0178] Examples of fluorine sources that can be used include lithium fluoride and magnesium fluoride. Among these, lithium fluoride is preferred because it has a relatively low melting point of 848°C and is easily melted in the annealing step described below. Examples of chlorine sources that can be used include lithium chloride and magnesium chloride. Examples of magnesium sources that can be used include magnesium fluoride, magnesium oxide, magnesium hydroxide, and magnesium carbonate. Examples of lithium sources that can be used include lithium fluoride and lithium carbonate. In other words, lithium fluoride can be used as both a lithium source and a fluorine source. Magnesium fluoride can be used as both a fluorine source and a magnesium source.

[0179] 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. The melting point is most effectively lowered when lithium fluoride (LiF) and magnesium fluoride (MgF2) are mixed in a molar ratio of approximately LiF:MgF2 = 65:35 (Non-Patent Document 4). On the other hand, if the amount of lithium fluoride is too high, there is a concern that the lithium content will be excessive, resulting in poor 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.

[0180] If the subsequent mixing and grinding 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.

[0181] <Step S12> Next, in step S12, the materials for the mixture 902 are mixed and pulverized. Mixing can be performed by either a dry or wet method, but a wet method is preferred because it allows for finer pulverization. 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 thoroughly perform this mixing and pulverization process to finely pulverize the mixture 902.

[0182] <Step S13> Next, in step S13, the mixed and crushed materials are collected to obtain a mixture 902.

[0183] The average particle size (D50) of the mixture 902 is preferably, for example, 600 nm or more and 20 μm or less, and more preferably 1 μm or more and 10 μm or less. Such a finely pulverized mixture 902 facilitates uniform adhesion of the mixture 902 to the surface of the composite oxide particles when mixed with a composite oxide containing lithium, transition metal, and oxygen in a subsequent process. Uniform adhesion of the mixture 902 to the surface of the composite oxide particles is preferable because it facilitates thorough distribution of halogen and magnesium throughout the surface layer of the composite oxide particles after heating. If there are regions in the surface layer that do not contain halogen and magnesium, it may be difficult to form the pseudospinel crystal structure described above in a charged state.

[0184] Next, steps S21 to S24 are carried out to obtain a composite oxide containing metal A, metal M, and oxygen.

[0185] <Step S21> First, in step S21, a metal A source and a metal M source are prepared as materials for a composite oxide having metal A, metal M, and oxygen.

[0186] An example will be described in which lithium is used as the metal A. As the lithium source, for example, lithium carbonate, lithium fluoride, etc. can be used.

[0187] As the metal M, for example, at least one of cobalt, manganese, and nickel can be used.

[0188] When a layered rock-salt type crystal structure is used as the positive electrode active material, the material ratio may be a mixture ratio of cobalt, manganese, and nickel that can form a layered rock-salt type. Aluminum may also be added to these transition metals to the extent that a layered rock-salt type crystal structure can be formed.

[0189] As the metal M source, oxides, hydroxides, etc. of the metals exemplified above as the metal M can be used. As the cobalt source, for example, cobalt oxide, cobalt hydroxide, etc. can be used. As the manganese source, manganese oxide, manganese hydroxide, etc. can be used. As the nickel source, nickel oxide, nickel hydroxide, etc. can be used. As the aluminum source, aluminum oxide, aluminum hydroxide, etc. can be used.

[0190] <Step S22> Next, in step S22, the metal A source and the metal M source are mixed. Mixing can be performed by a dry method or a wet method. 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.

[0191] <Step S23> Next, in step S23, the mixed materials are heated. This step is sometimes referred to as calcination or first heating to distinguish it from subsequent heating steps. 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 may occur due to excessive reduction of the metal used as metal M, which has a redox reaction, or evaporation of metal A. For example, if cobalt is used as metal M, defects may occur due to the cobalt becoming divalent.

[0192] The heating time is preferably 2 hours or more and 20 hours or less. Firing is preferably carried out in an atmosphere with little water, such as dry air (for example, a dew point of -50°C or less, more preferably -100°C or less). For example, heating is preferably carried out at 1000°C for 10 hours, with a temperature increase rate of 200°C / h and a flow rate of the dry atmosphere of 10 L / min. The heated material can then be cooled to room temperature. For example, the temperature decrease time from the specified temperature to room temperature is preferably 10 hours or more and 50 hours or less.

[0193] However, cooling to room temperature in step S23 is not essential, and cooling to a temperature higher than room temperature may be performed if there is no problem in carrying out the subsequent steps S24 and S31 to S33.

[0194] The metals contained in the positive electrode active material may be introduced in steps S22 and S23 described above, or some of the metals may be introduced in steps S41 to S44 described below. More specifically, metal M1 (M1 is one or more selected from cobalt, manganese, nickel, and aluminum) is introduced in steps S22 and S23, and metal M2 (M2 is, for example, one or more selected from manganese, nickel, and aluminum) is introduced in steps S41 to S44. By separating the steps of introducing metal M1 and metal M2 in this way, the depth profiles of the respective metals may be varied. For example, the concentration of metal M2 may be increased in the surface layer compared to the interior of the particles. Furthermore, the ratio of the number of atoms of metal M2 to the reference number of metal M1 may be higher in the surface layer than in the interior.

[0195] In the positive electrode active material of one embodiment of the present invention, preferably, cobalt is selected as the metal M1, and nickel and aluminum are selected as the metal M2.

[0196] <Step S24> Next, in step S24, the calcined material is recovered to obtain a composite oxide containing metal A, metal M, and oxygen. Specifically, lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium cobalt oxide in which some of the cobalt is substituted with manganese, or lithium nickel-manganese-cobalt oxide is obtained.

[0197] Alternatively, a composite oxide containing metal A, metal M, and oxygen that has been synthesized in advance may be used in step S24. In this case, steps S21 to S23 can be omitted.

[0198] For example, lithium cobalt oxide particles (product name: Cellseed C-10N) manufactured by Nippon Chemical Industry Co., Ltd. can be used as a pre-synthesized composite oxide. This lithium cobalt oxide has an average particle size (D50) of approximately 12 μm, and impurity analysis by glow discharge mass spectrometry (GD-MS) shows that the magnesium and fluorine concentrations are 50 ppm wt or less, the calcium, aluminum, and silicon concentrations 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 concentrations of other elements other than lithium, cobalt, and oxygen are 150 ppm wt or less.

[0199] Alternatively, lithium cobalt oxide particles (product name: Cellseed C-5H) manufactured by Nippon Chemical Industry Co., Ltd. can also be used. This is lithium cobalt oxide with an average particle size (D50) of approximately 6.5 μm, and in impurity analysis by GD-MS, the concentrations of elements other than lithium, cobalt, and oxygen are similar to or lower than those of C-10N.

[0200] In this embodiment, cobalt is used as the metal M, and pre-synthesized lithium cobalt oxide particles (Cellseed C-10N manufactured by Nippon Chemical Industry Co., Ltd.) are used.

[0201] <Step S31> Next, in step S31, mixture 902 is mixed with the composite oxide obtained in step S24. The ratio of the number of transition metal atoms TM in the composite oxide containing lithium, transition metal, and oxygen to the number of magnesium atoms MgMix1 in mixture 902 is preferably TM:MgMix1=1:y (0.001≦y≦0.06), and more preferably TM:MgMix1=1:y (0.003≦y≦0.03).

[0202] The mixing conditions in step S31 are preferably milder than those in step S12 so as not to destroy the composite oxide particles. For example, the mixing conditions are preferably lower in rotation speed or shorter in time than those in step S12. It can also be said that dry mixing conditions are milder 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.

[0203] <Step S32> Next, in step S32, the mixed materials are collected to obtain a mixture 903.

[0204] Although this embodiment describes a method of adding a mixture of lithium fluoride and magnesium fluoride to lithium cobalt oxide with few impurities, one embodiment of the present invention is not limited thereto. Instead of the mixture 903 in step S33, a lithium cobalt oxide starting material to which a magnesium source and a fluorine source have been added and then fired may be used. In this case, there is no need to separate steps S11 to S14 from steps S21 to S24, resulting in a simple and highly productive process.

[0205] Alternatively, lithium cobalt oxide to which magnesium and fluorine have been added in advance may be used. If lithium cobalt oxide to which magnesium and fluorine have been added is used, the steps up to step S32 can be omitted, which is simpler.

[0206] Furthermore, a magnesium source and a fluorine source may be further added to lithium cobalt oxide to which magnesium and fluorine have been added in advance.

[0207] <Step S33> Next, in step S33, the mixture 903 is heated. This step is sometimes called annealing or second heating to distinguish it from the previous heating step.

[0208] The annealing is preferably performed at an appropriate temperature and time, which vary depending on conditions such as the size and composition of the composite oxide particles containing lithium, transition metal, and oxygen in step S24. If the particles are small, a lower temperature or shorter time may be more preferable than if the particles are large.

[0209] For example, when the average particle size (D50) of the particles in step S24 is about 12 μm, the annealing temperature is preferably, for example, 600° C. or more and 950° C. or less. The annealing time is, for example, preferably 3 hours or more, more preferably 10 hours or more, and even more preferably 60 hours or more.

[0210] On the other hand, when the average particle size (D50) of the particles in step S24 is about 5 μm, the annealing temperature is preferably, for example, 600° C. to 950° C. The annealing time is preferably, for example, 1 hour to 10 hours, more preferably about 2 hours.

[0211] The temperature drop time after annealing is preferably, for example, 10 hours or more and 50 hours or less.

[0212] If the annealing temperature in step S33 is too high, the particles may sinter.

[0213] When mixture 903 is annealed, it is believed that the material with the lowest melting point in mixture 902 (e.g., lithium fluoride, melting point 848°C) melts first and distributes to the surface layer of the composite oxide particles. Next, the presence of this molten material lowers the melting points of other materials, which then melts them. For example, magnesium fluoride (melting point 1263°C) melts and distributes to the surface layer of the composite oxide particles.

[0214] It is believed that the elements contained in the mixture 902 distributed in the surface layer portion are dissolved in the composite oxide containing lithium, a transition metal, and oxygen.

[0215] The diffusion of elements contained in this mixture 902 is faster in the surface layer and near the grain boundaries than inside the composite oxide particles. Therefore, magnesium and halogens are concentrated at higher concentrations in the surface layer and near the grain boundaries than inside. As will be described later, a high magnesium concentration in the surface layer and near the grain boundaries can more effectively suppress changes in the crystal structure.

[0216] <Step S34> Next, in step S34, the annealed material is recovered to obtain a second composite oxide.

[0217] Next, in step S34, the composite oxide obtained is further treated to add metal M2. By performing this treatment after step S24, the concentration of metal M2 in the surface layer of the positive electrode active material particles may be increased compared to the interior, which is preferable.

[0218] The metal M2 may be added by, for example, mixing a material containing the metal M2 with the mixture 902 in step S31. This is preferable because it reduces the number of steps and simplifies the process.

[0219] Alternatively, as will be described later, a step of adding the metal M2 may be performed after steps S31 to S33. In this case, for example, it may be possible to suppress the formation of a compound between magnesium and the metal M2.

[0220] The metal M2 is added to the positive electrode active material of one embodiment of the present invention through the following steps S41 to S43. The metal M2 can be added by a liquid phase method such as a sol-gel method, a solid phase method, a sputtering method, a vapor deposition method, a CVD (chemical vapor deposition) method, a PLD (pulsed laser deposition) method, or the like.

[0221] <Step S41> First, in step S41, a metal source is prepared. Furthermore, when a sol-gel method is employed, a solvent to be used in the sol-gel method is prepared. Examples of usable metal sources include metal alkoxides, metal hydroxides, and metal oxides. When the metal M2 is aluminum, for example, the number of cobalt atoms in the lithium cobalt oxide is set to 1, and the relative value of the number of aluminum atoms in the metal source is 0.005 or more and 0.02 or less. When the metal M2 contains nickel in addition to aluminum, for example, the number of cobalt atoms in the lithium cobalt oxide is set to 1, and the relative value of the number of nickel atoms in the metal source is 0.0005 or more and 0.02 or less.

[0222] Here, as an example, a sol-gel method is applied, and aluminum isopropoxide is used as the metal source and isopropanol is used as the solvent (step S41 in FIG. 10).

[0223] <Step S42> Next, in step S42, aluminum alkoxide is dissolved in alcohol, and lithium cobalt oxide particles are further mixed therein.

[0224] Next, the mixture of the alcohol solution of the metal alkoxide and the lithium cobalt oxide particles is stirred in an atmosphere containing water vapor. Stirring can be performed, for example, using a magnetic stirrer. The stirring time is sufficient to cause hydrolysis and polycondensation reactions between the water and metal alkoxide in the atmosphere, and can be performed, for example, for 4 hours at 25°C and 90% RH (relative humidity). Stirring can also be performed in an atmosphere without humidity or temperature control, such as in the air inside a draft chamber. In such cases, a longer stirring time is preferable, for example, 12 hours or more at room temperature.

[0225] By reacting water vapor in the atmosphere with metal alkoxide, the sol-gel reaction can proceed more slowly than when liquid water is added. Also, by reacting metal alkoxide with water at room temperature, the sol-gel reaction can proceed more slowly than when, for example, heating is performed at a temperature above the boiling point of the solvent alcohol. By proceeding with the sol-gel reaction slowly, a high-quality coating layer with a uniform thickness can be formed.

[0226] For example, when aluminum is added as metal M2, the relative value of the number of atoms of metal M2 to the sum of metal M1 and metal M2 is preferably 0.0005 to 0.02, more preferably 0.001 to 0.015, and more preferably 0.001 to 0.009. When nickel is added as metal M2, the relative value of the number of atoms of metal M2 to the sum of metal M1 and metal M2 is preferably 0.0005 to 0.02, more preferably 0.001 to 0.015, and more preferably 0.001 to 0.009.

[0227] <Step S43> Next, in step S43, the precipitate is collected from the mixture after the above treatment, and the collected residue is dried to obtain mixture 904. Methods for collecting the precipitate include filtration, centrifugation, and evaporation to dryness. The precipitate can be washed with the same alcohol as the solvent in which the metal alkoxide was dissolved. The drying process can be performed, for example, by vacuum or forced air drying at 80°C for 1 hour to 4 hours. Note that when evaporation to dryness is used, it is not necessary to separate the solvent and precipitate in this step; the precipitate can be collected, for example, in the next step (step S44), a baking process.

[0228] <Step S44> Next, in step S44, the resulting mixture 904 is fired.

[0229] The firing time is preferably 1 hour to 50 hours, more preferably 2 hours to 20 hours, within the specified temperature range. If the firing time is too short, the crystallinity of the compound containing metal M2 formed in the surface layer may be low. Alternatively, the diffusion of metal M2 may be insufficient. Alternatively, organic matter may remain on the surface. However, if the firing time is too long, the diffusion of metal M2 may proceed too far, resulting in a low concentration in the surface layer and near the grain boundaries. This also reduces productivity.

[0230] The specified temperature is preferably 500°C or higher and 1200°C or lower, more preferably 700°C or higher and 920°C or lower, and even more preferably 800°C or higher and 900°C or lower. If the specified temperature is too low, the crystallinity of the compound containing metal M2 formed in the surface layer portion may be low. Alternatively, the diffusion of metal M2 may be insufficient. Alternatively, organic matter may remain on the surface.

[0231] Furthermore, the firing is preferably carried out in an atmosphere containing oxygen. If the oxygen partial pressure is low, the firing temperature must be lowered to avoid the risk of Co being reduced.

[0232] In this embodiment, the specified temperature is set to 850° C. and is maintained for two hours, the temperature is increased at a rate of 200° C. / h, and the flow rate of oxygen is set to 10 L / min.

[0233] The cooling time after firing is preferably long, as this facilitates stabilization of the crystal structure. For example, the cooling time from the specified temperature to room temperature is preferably 10 hours or more and 50 hours or less. Here, the firing temperature in step S44 is preferably lower than the firing temperature in step S33.

[0234] <Step S45> Next, in step S45, the cooled particles are collected to produce the positive electrode active material 100 of one embodiment of the present invention. At this time, it is preferable to further sieve the collected particles.

[0235] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0236] (Embodiment 3) In this embodiment, examples of materials that can be used in a secondary battery including the positive electrode active material described in the previous embodiment will be described.

[0237] <Configuration example 1 of secondary battery> 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.

[0238] [Positive electrode] The positive electrode has a positive electrode active material layer and a positive electrode current collector.

[0239] <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.

[0240] The positive electrode active material can be the positive electrode active material 100 described in the previous embodiment. By using the positive electrode active material 100 described in the previous embodiment, a secondary battery with high capacity and excellent cycle characteristics can be obtained.

[0241] 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%.

[0242] 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.

[0243] 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, for example, vapor phase growth methods. Examples of the conductive additive include carbon materials such as carbon black (e.g., acetylene black (AB)), graphite particles, graphene, 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.

[0244] A graphene compound may also be used as the conductive additive.

[0245] Graphene compounds may have excellent electrical properties, such as high electrical conductivity, and excellent physical properties, such as high flexibility and high mechanical strength. Graphene compounds also have a planar shape. Graphene compounds enable surface contact with low contact resistance. Even thin graphene compounds can have very high electrical conductivity, allowing a small amount to efficiently form a conductive path within an active material layer. Therefore, using a graphene compound as a conductive additive is preferable because it increases the contact area between the active material and the conductive additive. Using a spray-drying device is preferable to form a coating of the graphene compound, which serves as a conductive additive, covering the entire surface of the active material. This is also preferable because it may reduce electrical resistance. Here, graphene, multigraphene, or RGO are particularly preferable as graphene compounds. Here, RGO refers to a compound obtained by reducing graphene oxide (GO), for example.

[0246] When using an active material with a small particle size, for example, an active material with a particle size of 1 μm or less, the specific surface area of ​​the active material is large, and more conductive paths connecting the active material particles are required. Therefore, the amount of conductive additive tends to be large, which tends to result in a relative decrease in the amount of active material supported. A decrease in the amount of active material supported results in a decrease in the capacity of the secondary battery. In such cases, using a graphene compound as a conductive additive is particularly preferable because even a small amount of the graphene compound can efficiently form conductive paths without reducing the amount of active material supported.

[0247] As an example, a cross-sectional configuration example in which a graphene compound is used as a conductive additive in the active material layer 200 will be described below.

[0248] FIG. 11A shows a longitudinal cross-sectional view of an active material layer 200. The active material layer 200 includes granular positive electrode active material 100, a graphene compound 201 as a conductive additive, and a binder (not shown). Here, graphene or multi-graphene may be used as the graphene compound 201, for example. Here, the graphene compound 201 preferably has a sheet-like shape. Alternatively, the graphene compound 201 may be a sheet-like shape formed by partially overlapping a plurality of multi-graphenes and / or a plurality of graphenes.

[0249] 11B, in a longitudinal cross section of the active material layer 200, sheet-like graphene compounds 201 are dispersed approximately uniformly within the active material layer 200. In FIG. 11B, the graphene compounds 201 are schematically represented by thick lines, but in reality, they are thin films having a thickness corresponding to a single layer or multiple layers of carbon molecules. The plurality of graphene compounds 201 are formed so as to partially cover the plurality of granular positive electrode active material 100 or to be attached to the surfaces of the plurality of granular positive electrode active material 100, and are therefore in surface contact with each other.

[0250] Here, a plurality of graphene compounds are bonded together to form a mesh-like graphene compound sheet (hereinafter referred to as a graphene compound net or graphene net). When an active material is covered with a graphene net, the graphene net can also function as a binder that binds the active materials together. Therefore, the amount of binder can be reduced or can be eliminated, thereby improving the ratio of the active material to the electrode volume or weight. In other words, the capacity of the secondary battery can be increased.

[0251] Here, it is preferable to use graphene oxide as the graphene compound 201, mix it with an active material to form a layer that will become the active material layer 200, and then reduce it. By using graphene oxide, which has extremely high dispersibility in a polar solvent, to form the graphene compound 201, it is possible to disperse the graphene compound 201 approximately uniformly inside the active material layer 200. Since the solvent is evaporated and removed from the dispersion medium containing the uniformly dispersed graphene oxide and the graphene oxide is reduced, the graphene compound 201 remaining in the active material layer 200 partially overlaps and is dispersed to such an extent that it is in surface contact with each other, thereby forming a three-dimensional conductive path. Note that the reduction of the graphene oxide may be performed by, for example, heat treatment or using a reducing agent.

[0252] Therefore, unlike a granular conductive additive such as acetylene black that makes point contact with the active material, the graphene compound 201 enables surface contact with low contact resistance, and therefore can improve the electrical conductivity between the granular positive electrode active material 100 and the graphene compound 201 with a smaller amount than that of a typical conductive additive. This makes it possible to increase the ratio of the positive electrode active material 100 in the active material layer 200. This allows the discharge capacity of the secondary battery to be increased.

[0253] Furthermore, by using a spray dryer in advance, a graphene compound serving as a conductive additive can be formed as a coating that covers the entire surface of the active material, and further a conductive path can be formed between the active material particles by the graphene compound.

[0254] 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.

[0255] 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.

[0256] 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.

[0257] The binder may be used in combination with two or more of the above.

[0258] 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.

[0259] 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.

[0260] 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.

[0261] 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.

[0262] <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.

[0263] [How to make the positive electrode] As an example of a method for manufacturing a positive electrode including the positive electrode active material of one embodiment of the present invention, a slurry is prepared and then coated to form an electrode. An example of a method for manufacturing a slurry used for manufacturing an electrode will be described.

[0264] The solvent used to prepare the slurry is preferably a polar solvent, such as water, methanol, ethanol, acetone, tetrahydrofuran (THF), dimethylformamide (DMF), N-methylpyrrolidone (NMP), and dimethyl sulfoxide (DMSO), or a mixture of two or more of these.

[0265] When the positive electrode active material of one embodiment of the present invention has a first particle group and a second particle group, the first particle group and the second particle group are mixed at a desired ratio of first particle group:second particle group=1:w (weight ratio), where w is preferably 0.01 to 0.6, more preferably 0.03 to 0.6, even more preferably 0.04 to 0.5, and even more preferably 0.09 to 0.3.

[0266] The positive electrode active material of one embodiment of the present invention may have a particle size distribution according to the mixing ratio of the first particle group and the second particle group. Furthermore, depending on the ratio of each particle group, the intensity or area of ​​the maximum peak corresponding to each particle group may have a value corresponding to the ratio of the respective particle groups. Furthermore, one particle group may have one maximum peak or two or more maximum peaks. In the case of two or more maximum peaks, the sum of the areas of the multiple maximum peaks may be used.

[0267] The positive electrode active material in which the first particle group and the second particle group are mixed is mixed with a conductive additive, a binder, and a solvent to prepare a mixture J. The mixing may be performed under normal pressure or under reduced pressure. For example, a kneader may be used in the mixing step.

[0268] Next, the viscosity of the mixture J is measured. Thereafter, a solvent is added as necessary to adjust the viscosity. Through the above steps, a slurry for coating the active material layer is obtained.

[0269] Here, for example, the higher the viscosity of the mixture J, the better the dispersibility of the active material, binder, and conductive additive within the mixture (they may be more easily mixed with each other). Therefore, for example, a higher viscosity of the mixture J is preferable. On the other hand, if the viscosity of the mixture J is too high, for example, the coating speed of the electrode may be reduced, which may be undesirable from the viewpoint of productivity.

[0270] Next, a method for forming an active material layer on a current collector using the prepared slurry will be described.

[0271] First, the slurry is applied onto the current collector. Here, before applying the slurry, the current collector may be subjected to a surface treatment. 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 the form of islands. Furthermore, the undercoat may also exhibit capacitance as an active material. For example, a carbon material can be used as the undercoat. Examples of carbon materials that can be used include graphite, carbon black such as acetylene black or Ketjen Black (registered trademark), and carbon nanotubes.

[0272] The slurry can be applied by a slot die method, a gravure method, a blade method, or a combination thereof. A continuous coater may also be used for application.

[0273] Next, the solvent of the slurry is evaporated to form the active material layer.

[0274] The evaporation process of the solvent in the slurry is preferably carried out at a temperature ranging from 50°C to 200°C, preferably from 60°C to 90°C. The evaporation may be carried out, for example, under atmospheric pressure or under reduced pressure. By carrying out the evaporation under a reduced pressure, the evaporation time may be shortened in some cases, or the evaporation temperature may be lowered in some cases.

[0275] The evaporation step can be carried out using a hot plate, a drying oven, or the like.

[0276] The active material layer may be formed on both sides of the current collector, or on only one side thereof, or both sides may have regions where the active material layer is partially formed.

[0277] After the solvent has evaporated from the active material layer, it is preferable to press the active material layer by a compression method such as a roll press method or a plate press method.

[0278] [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.

[0279] <Negative electrode active material> As the negative electrode active material, for example, an alloy-based material or a carbon-based material can be used.

[0280] 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.

[0281] 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.

[0282] 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.

[0283] 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.

[0284] 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.

[0285] 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.

[0286] 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.

[0287] 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.

[0288] 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 in 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.

[0289] 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.

[0290] <Negative electrode current collector> The negative electrode current collector may be made of the same material as the positive electrode current collector, but it is preferable that the negative electrode current collector be made of a material that does not alloy with carrier ions such as lithium.

[0291] [Electrolyte] The electrolytic solution contains 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.

[0292] 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.

[0293] 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, etc. can be used alone or in any combination and ratio of two or more of these.

[0294] 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.

[0295] The electrolyte may also contain additives such as vinylene carbonate, 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.

[0296] Alternatively, a polymer gel electrolyte may be used in which a polymer is swollen with an electrolytic solution.

[0297] The use of a polymer gel electrolyte improves safety against leakage, etc. It also enables the secondary battery to be made thinner and lighter.

[0298] 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.

[0299] 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.

[0300] 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.

[0301] [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.

[0302] 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).

[0303] 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.

[0304] 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.

[0305] 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.

[0306] [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.

[0307] <Configuration example 2 of secondary battery> As an example of the configuration of a secondary battery, the configuration of a secondary battery using a solid electrolyte layer will be described below.

[0308] As shown in FIG. 12A, 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.

[0309] Positive electrode 410 has positive electrode current collector 413 and positive electrode active material layer 414. Positive electrode active material layer 414 has positive electrode active material 411 and solid electrolyte 421. Positive electrode active material layer 414 may also have a conductive additive and a binder.

[0310] 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.

[0311] 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. 12B . Using metallic lithium for the negative electrode 430 is preferable because it can improve the energy density of the secondary battery 400.

[0312] 13A, 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 voltage of the secondary battery can be increased. Fig. 13A is a schematic diagram of a four-layer stack of combinations of positive electrodes 410, solid electrolyte layers 420, and negative electrodes 430.

[0313] The secondary battery of one embodiment of the present invention may be a thin-film all-solid-state battery. A thin-film all-solid-state battery can be manufactured by forming a positive electrode, a solid electrolyte, a negative electrode, a wiring electrode, and the like using a gas-phase method (vacuum evaporation, pulsed laser deposition, aerosol deposition, sputtering). For example, FIG. 13B shows an example of a thin-film all-solid-state battery 450. As shown in FIG. 13B, after forming a wiring electrode 441 and a wiring electrode 442 on a substrate 440, a positive electrode 410 is formed on the wiring electrode 441, a solid electrolyte layer 420 is formed on the positive electrode 410, and a negative electrode 430 is formed on the solid electrolyte layer 420 and the wiring electrode 442, thereby manufacturing the thin-film all-solid-state battery 450. The substrate 440 can be made of a ceramic substrate, a glass substrate, a plastic substrate, a metal substrate, or the like.

[0314] As the solid electrolyte 421 of the solid electrolyte layer 420, for example, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a halide-based solid electrolyte, or the like can be used.

[0315] 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.

[0316] Oxide-based solid electrolytes include materials with a perovskite crystal structure (La 2 / 3-x Li 3x TiO3, etc.), materials with NASICON-type crystal structure (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 (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.

[0317] 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. <00012​​​​​​​​​​​​​​​​​The exterior of the secondary battery 400 of one embodiment of the present invention can be made of various materials and in various shapes, but preferably has a function of applying pressure to the positive electrode, the solid electrolyte layer, and the negative electrode.

[0321] For example, Figure 14 shows an example of a cell for evaluating materials for all-solid-state batteries.

[0322] 14A is a cross-sectional schematic diagram of the evaluation cell, which has a lower member 761, an upper member 762, and a fixing screw and wing nut 764 that fix them in place, and electrode plate 753 is pressed by rotating a holding screw 763 to fix the evaluation material. An insulator 766 is provided between lower member 761 and upper member 762, both made of stainless steel. An O-ring 765 is provided between upper member 762 and holding screw 763 to provide a tight seal.

[0323] 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. 14B.

[0324] 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. 14C. Note that the same reference numerals are used for the same parts in Fig. 14A, Fig. 14B, and Fig. 14C.

[0325] 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.

[0326] 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.

[0327] Fig. 15A 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. 14. The secondary battery in Fig. 15A has external electrodes 771 and 772 and is sealed in an exterior body having multiple package members.

[0328] An example of a cross section taken along the dashed line in Figure 15A is shown in Figure 15B. 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.

[0329] 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.

[0330] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0331] (Fourth embodiment) In this embodiment, an example of the shape of a secondary battery including the positive electrode active material 100 described in the previous embodiment will be described. The description in the previous embodiment can be referred to for materials used in the secondary battery described in this embodiment.

[0332] [Coin-type secondary battery] First, an example of a coin-type secondary battery will be described. Fig. 16A is an external view of a coin-type (single-layer flat) secondary battery, and Fig. 16B is a cross-sectional view thereof.

[0333] 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.

[0334] 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.

[0335] 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.

[0336] These negative electrode 307, positive electrode 304, and separator 310 are impregnated with an electrolyte, and as shown in FIG. 16B, the positive electrode can 301 is placed downward, and the positive electrode 304, separator 310, negative electrode 307, and negative electrode can 302 are stacked in this order, 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.

[0337] 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.

[0338] Here, we will explain the current flow during charging of a secondary battery using Figure 16C. 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, may 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.

[0339] 16C is connected to a charger to charge the secondary battery 300. As the charging of the secondary battery 300 progresses, the potential difference between the electrodes increases.

[0340] [Cylindrical secondary battery] Next, an example of a cylindrical secondary battery will be described with reference to FIG. 17. FIG. 17A shows an external view of a cylindrical secondary battery 600. FIG. 17B is a schematic diagram showing a cross section of the cylindrical secondary battery 600. As shown in FIG. 17B, 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 the battery can (external can) 602 are insulated by a gasket (insulating packing) 610.

[0341] 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.

[0342] 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.

[0343] 17C, 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.

[0344] FIG. 17D is a top view of module 615. For clarity, conductive plate 613 is shown with dotted lines. As shown in FIG. 17D, module 615 may have conductors 616 that electrically connect multiple secondary batteries 600. A conductive plate can be superimposed on the conductors 616. Furthermore, a temperature control device 617 may be provided between multiple secondary batteries 600. When a secondary battery 600 overheats, it can be cooled by the temperature control device 617, and when a secondary battery 600 is too cold, it can be heated by the temperature control device 617. This makes the performance of module 615 less susceptible to the influence of the outside air temperature. It is preferable that the heat medium in temperature control device 617 is insulating and non-flammable.

[0345] 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.

[0346] [Example of secondary battery structure] Another structural example of the secondary battery will be described with reference to FIGS.

[0347] 18A and 18B are diagrams showing the external appearance of a secondary battery. A secondary battery 913 is connected to antennas 914 and 915 via a circuit board 900. A label 910 is attached to the secondary battery 913. Furthermore, as shown in FIG. 18B, the secondary battery 913 is connected to terminals 951 and 952.

[0348] 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.

[0349] 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.

[0350] 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.

[0351] 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.

[0352] The structure of the secondary battery is not limited to that shown in FIG.

[0353] For example, as shown in Figures 19A and 19B, an antenna may be provided on each of a pair of opposing surfaces of secondary battery 913 shown in Figures 18A and 18B. Figure 19A is an external view showing one of the pair of surfaces, and Figure 19B is an external view showing the other of the pair of surfaces. Note that the description of the secondary battery shown in Figures 18A and 18B can be used as appropriate for the same parts as those of the secondary battery shown in Figures 18A and 18B.

[0354] 19A, 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. 19B, 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, being able to shield an electromagnetic field caused by the secondary battery 913. The layer 917 can be made of, for example, a magnetic material.

[0355] 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.

[0356] Alternatively, as shown in Fig. 19C, a display device 920 may be provided on the secondary battery 913 shown in Figs. 18A and 18B. 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. 18A and 18B can be used as appropriate for the same portions as those of the secondary battery shown in Figs. 18A and 18B.

[0357] 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.

[0358] 19D, a sensor 921 may be provided in the secondary battery 913 shown in Figures 18A and 18B. 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 18A and 18B can be used as appropriate for the same parts as those in the secondary battery shown in Figures 18A and 18B.

[0359] 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.

[0360] Furthermore, an example of the structure of the secondary battery 913 will be described with reference to FIG.

[0361] A secondary battery 913 shown in Fig. 20A 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. 20A, 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.

[0362] 20B, the housing 930 shown in Fig. 20A may be formed from a plurality of materials. For example, the secondary battery 913 shown in Fig. 20B has housings 930a and 930b bonded together, and a wound body 950 is provided in the area surrounded by the housings 930a and 930b.

[0363] 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.

[0364] 21 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 formed by stacking the negative electrode 931 and the positive electrode 932 on top of each other with the separator 933 sandwiched therebetween, and winding the laminated sheet. Note that a plurality of layers of the negative electrode 931, the positive electrode 932, and the separator 933 may be stacked.

[0365] 18 via one of the terminal 951 and the terminal 952. The positive electrode 932 is connected to the terminal 911 shown in FIG.

[0366] 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.

[0367] [Laminated secondary battery] Next, examples of laminated secondary batteries will be described with reference to Figures 22 to 26. 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.

[0368] A laminated secondary battery 980 will be described using Fig. 22. The laminated secondary battery 980 has a wound body 993 shown in Fig. 22A. The wound body 993 has a negative electrode 994, a positive electrode 995, and a separator 996. Similar to the wound body 950 described in Fig. 21, 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, and winding the laminated sheet.

[0369] 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.

[0370] 22B, 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. 22C. 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.

[0371] 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.

[0372] Although an example using two films is shown in FIGS. 22B and 22C, a space may be formed by folding one film, and the wound body 993 described above may be housed in that space.

[0373] 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.

[0374] Furthermore, although Figure 22 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 23, for example.

[0375] 23A 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 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 508. The electrolyte solution described in Embodiment 2 can be used as the electrolyte solution 508.

[0376] 23A , positive electrode current collector 501 and negative electrode current collector 504 also serve as terminals for electrical contact with the outside. Therefore, positive electrode current collector 501 and negative electrode current collector 504 may be arranged so as to be partially exposed to the outside from outer casing 509. Alternatively, positive electrode current collector 501 and negative electrode current collector 504 may not be exposed to the outside from outer casing 509, and lead electrodes may be used to ultrasonically bond positive electrode current collector 501 or negative electrode current collector 504 to the lead electrodes so as to be exposed to the outside.

[0377] 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.

[0378] 23B shows an example of the cross-sectional structure of laminated secondary battery 500. For simplicity, Fig. 23A shows an example configured with two current collectors, but in reality, as shown in Fig. 23B, it is configured with multiple electrode layers.

[0379] In FIG. 23B, 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. 23B 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. 23B 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.

[0380] 24 and 25 show an example of an external view 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.

[0381] FIG. 26A shows an external view 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. 26A.

[0382] [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. 24 will be described with reference to FIGS. 26B and 26C.

[0383] First, the negative electrode 506, the separator 507, and the positive electrode 503 are stacked. FIG. 26B 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.

[0384] Next, the negative electrode 506 , the separator 507 and the positive electrode 503 are placed on the exterior body 509 .

[0385] Next, as shown in Fig. 26C, 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.

[0386] Next, electrolyte 508 (not shown) is introduced into the inside of exterior body 509 through an inlet provided in exterior body 509. The introduction of electrolyte 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.

[0387] 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.

[0388] [Bendable secondary battery] Next, an example of a bendable secondary battery will be described with reference to FIGS. 27 and 28. FIG.

[0389] FIG. 27A shows a schematic top view of a bendable secondary battery 250. FIGS. 27B, 27C, and 27D are schematic cross-sectional views taken along the cutting lines C1-C2, C3-C4, and A1-A2 in FIG. 27A, respectively. The secondary battery 250 has an exterior body 251 and a positive electrode 211a and a negative electrode 211b housed inside the exterior body 251. A lead 212a electrically connected to the positive electrode 211a and a lead 212b electrically connected to the negative electrode 211b extend outside the exterior body 251. In addition to the positive electrode 211a and the negative electrode 211b, an electrolyte (not shown) is enclosed in the area surrounded by the exterior body 251.

[0390] The positive electrode 211a and the negative electrode 211b of the secondary battery 250 will be described with reference to Fig. 28. Fig. 28A is a perspective view illustrating the stacking order of the positive electrode 211a, the negative electrode 211b, and the separator 214. Fig. 28B is a perspective view showing the lead 212a and the lead 212b in addition to the positive electrode 211a and the negative electrode 211b.

[0391] 28A, secondary battery 250 has a plurality of strip-shaped positive electrodes 211a, a plurality of strip-shaped negative electrodes 211b, and a plurality of separators 214. Positive electrode 211a and negative electrode 211b each have a protruding tab portion and a portion other than the tab. A positive electrode active material layer is formed on one surface of positive electrode 211a in the portion other than the tab, and a negative electrode active material layer is formed on one surface of negative electrode 211b in the portion other than the tab.

[0392] The positive electrode 211a and the negative electrode 211b are stacked so that the surfaces of the positive electrode 211a on which the positive electrode active material layer is not formed and the surfaces of the negative electrode 211b on which the negative electrode active material layer is not formed are in contact with each other.

[0393] Furthermore, a separator 214 is provided between the surface of the positive electrode 211a on which the positive electrode active material is formed and the surface of the negative electrode 211b on which the negative electrode active material is formed. In Fig. 28, the separator 214 is indicated by a dotted line for ease of viewing.

[0394] 28B, the positive electrodes 211a and the lead 212a are electrically connected at a joint 215a, and the negative electrodes 211b and the lead 212b are electrically connected at a joint 215b.

[0395] Next, exterior body 251 will be described with reference to FIGS. 27B, 27C, 27D, and 27E.

[0396] The exterior body 251 has a film-like shape and is folded in two to sandwich the positive electrode 211a and the negative electrode 211b. The exterior body 251 has a folded portion 261, a pair of sealing portions 262, and a sealing portion 263. The pair of sealing portions 262 are provided to sandwich the positive electrode 211a and the negative electrode 211b, and can also be called side seals. The sealing portion 263 has a portion that overlaps with the lead 212a and the lead 212b, and can also be called a top seal.

[0397] The exterior body 251 preferably has a wave shape in which ridge lines 271 and valley lines 272 are alternately arranged in the portions overlapping the positive electrode 211a and the negative electrode 211b. Furthermore, the seal portions 262 and 263 of the exterior body 251 are preferably flat.

[0398] Fig. 27B is a cross section taken at a portion overlapping with ridge line 271, and Fig. 27C is a cross section taken at a portion overlapping with valley line 272. Fig. 27B and Fig. 27C both correspond to widthwise cross sections of secondary battery 250 and positive electrode 211a and negative electrode 211b.

[0399] Here, the distance La is defined as the distance between the widthwise ends of the positive electrode 211a and the negative electrode 211b, i.e., the ends of the positive electrode 211a and the negative electrode 211b, and the seal portion 262. When the secondary battery 250 is deformed, such as by bending, the positive electrode 211a and the negative electrode 211b deform so as to be displaced from each other in the longitudinal direction, as described below. In this case, if the distance La is too short, the exterior body 251 may rub strongly against the positive electrode 211a and the negative electrode 211b, resulting in damage to the exterior body 251. In particular, if the metal film of the exterior body 251 is exposed, the metal film may be corroded by the electrolyte. Therefore, it is preferable to set the distance La as long as possible. On the other hand, if the distance La is made too large, the volume of the secondary battery 250 increases.

[0400] Furthermore, it is preferable that the distance La between the positive electrode 211a and the negative electrode 211b and the seal portion 262 is increased as the total thickness of the stacked positive electrode 211a and the negative electrode 211b increases.

[0401] More specifically, when the total thickness of the stacked positive electrode 211a, negative electrode 211b, and separator 214 (not shown) is t, the distance La is preferably 0.8 to 3.0 times, more preferably 0.9 to 2.5 times, and even more preferably 1.0 to 2.0 times the thickness t. By setting the distance La in this range, a compact battery with high reliability against bending can be realized.

[0402] Furthermore, when the distance between the pair of seal portions 262 is distance Lb, it is preferable to make distance Lb sufficiently larger than the width of the positive electrode 211a and the negative electrode 211b (here, width Wb of the negative electrode 211b). This allows parts of the positive electrode 211a and the negative electrode 211b to shift in the width direction even if the positive electrode 211a and the negative electrode 211b come into contact with the exterior body 251 when deformation such as repeated bending is applied to the secondary battery 250, thereby effectively preventing the positive electrode 211a and the negative electrode 211b from rubbing against the exterior body 251.

[0403] For example, it is preferable that the difference between the distance Lb between the pair of seal portions 262 and the width Wb of the negative electrode 211b is 1.6 to 6.0 times, preferably 1.8 to 5.0 times, and more preferably 2.0 to 4.0 times the thickness t of the positive electrode 211a and the negative electrode 211b.

[0404] In other words, it is preferable that the distance Lb, the width Wb, and the thickness t satisfy the relationship of the following formula 2.

[0405]

number

[0406] Here, a satisfies the range of 0.8 to 3.0, preferably 0.9 to 2.5, and more preferably 1.0 to 2.0.

[0407] 27D is a cross section including lead 212a, and corresponds to a cross section in the longitudinal direction of secondary battery 250, positive electrode 211a, and negative electrode 211b. As shown in FIG. 27D, it is preferable that a space 273 be formed between exterior body 251 and the ends of positive electrode 211a and negative electrode 211b in the longitudinal direction at bent portion 261.

[0408] Fig. 27E shows a schematic cross-sectional view of the bent secondary battery 250. Fig. 27E corresponds to the cross section taken along the cutting line B1-B2 in Fig. 27A.

[0409] When the secondary battery 250 is bent, a portion of the exterior body 251 located on the outside of the bend expands, and another portion located on the inside contracts. More specifically, the portion located on the outside of the exterior body 251 deforms so that the wave amplitude becomes smaller and the wave period becomes larger. On the other hand, the portion located on the inside of the exterior body 251 deforms so that the wave amplitude becomes larger and the wave period becomes smaller. In this way, the deformation of the exterior body 251 relieves the stress applied to the exterior body 251 due to bending, so the material that constitutes the exterior body 251 itself does not need to expand or contract. As a result, the exterior body 251 does not break, and the secondary battery 250 can be bent with a small force.

[0410] 27E, when the secondary battery 250 is bent, the positive electrodes 211a and the negative electrodes 211b are displaced relative to each other. At this time, because one end of each of the stacked positive electrodes 211a and negative electrodes 211b on the sealing portion 263 side is fixed by the fixing member 217, the amount of displacement increases toward the bending portion 261. This relieves stress on the positive electrodes 211a and negative electrodes 211b, and the positive electrodes 211a and negative electrodes 211b themselves do not need to expand or contract. As a result, the secondary battery 250 can be bent without damaging the positive electrodes 211a and negative electrodes 211b.

[0411] Furthermore, by providing space 273 between positive electrode 211a and negative electrode 211b and exterior body 251, positive electrode 211a and negative electrode 211b located on the inner side when bent can be relatively displaced without coming into contact with exterior body 251.

[0412] 27 and 28 is a battery that is resistant to damage to the exterior body, the positive electrode 211a, and the negative electrode 211b, etc., even when repeatedly bent and stretched, and the battery characteristics are also resistant to deterioration. By using the positive electrode active material described in the previous embodiment for the positive electrode 211a of the secondary battery 250, it is possible to obtain a battery with even better cycle characteristics.

[0413] 29A is a perspective view showing how three laminated secondary batteries 500 are sandwiched and fixed between first plate 521 and second plate 524. As shown in FIG. 29B, by using fixing fixture 525a and fixing fixture 525b to fix the distance between first plate 521 and second plate 524, the three secondary batteries 500 can be pressurized.

[0414] 29A and 29B 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.

[0415] 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.

[0416] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0417] (Embodiment 5) 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.

[0418] 30A to 30G show examples of electronic devices incorporating the bendable secondary battery described in part of Embodiment 3. Examples of electronic devices that use the bendable secondary battery include television devices (also called televisions or television receivers), computer monitors, digital cameras, digital video cameras, digital photo frames, mobile phones (also called mobile phones or mobile phone devices), portable game machines, personal digital assistants, audio playback devices, and large game machines such as pachinko machines.

[0419] 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.

[0420] 30A 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 life can be provided.

[0421] FIG. 30B 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. 30C 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.

[0422] FIG. 30D 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. 30E 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 the 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.

[0423] 30F 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.

[0424] 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.

[0425] 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.

[0426] 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.

[0427] 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.

[0428] 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.

[0429] 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. 30E can be installed in a curved state inside the housing 7201 or in a bendable state inside the band 7203.

[0430] 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.

[0431] 30G 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.

[0432] 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.

[0433] 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.

[0434] 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.

[0435] 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. 30H, 31 and 32. FIG.

[0436] By using the secondary battery of one embodiment of the present invention as a secondary battery for 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 for these products, a stick-shaped secondary battery that is small, lightweight, and has a large capacity is desired in consideration of ease of holding by users.

[0437] FIG. 30H is a perspective view of a device also known as a tobacco-containing smoking device (electronic cigarette). In FIG. 30H, electronic cigarette 7500 includes atomizer 7501 including a heating element, secondary battery 7504 that supplies power to the atomizer, and cartridge 7502 including 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. 30H 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.

[0438] Next, an example of a foldable tablet terminal is shown in FIGS. 31A and 31B. The tablet terminal 9600 shown in FIGS. 31A and 31B 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. 31A shows the tablet terminal 9600 in an open state, and FIG. 31B shows the tablet terminal 9600 in a closed state.

[0439] 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.

[0440] 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.

[0441] 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.

[0442] 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.

[0443] 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.

[0444] 31A 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, but 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.

[0445] 31B 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 according to one embodiment of the present invention.

[0446] 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.

[0447] In addition, the tablet terminal 9600 shown in Figures 31A and 31B 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).

[0448] 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.

[0449] The configuration and operation of the charge / discharge control circuit 9634 shown in Fig. 31B will be described with reference to a block diagram in Fig. 31C. Fig. 31C 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. 31B.

[0450] 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.

[0451] 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.

[0452] FIG. 32 illustrates an example of another electronic device. In FIG. 32, 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.

[0453] 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).

[0454] 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.

[0455] 32 , 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. 32 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.

[0456] Note that although Figure 32 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.

[0457] 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.

[0458] 32, 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. 32 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.

[0459] Note that although FIG. 32 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.

[0460] 32 , 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. 32 , 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.

[0461] 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.

[0462] 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.

[0463] 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.

[0464] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0465] (Embodiment 6) 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.

[0466] By installing a secondary battery in a vehicle, next-generation clean energy vehicles such as hybrid electric vehicles (HEV), electric vehicles (EV), and plug-in hybrid electric vehicles (PHEV) can be realized.

[0467] FIG. 33 illustrates an example of a vehicle using a secondary battery according to one embodiment of the present invention. An automobile 8400 illustrated in FIG. 33A 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. 17C and 17D on the floor of the vehicle interior. Alternatively, a battery pack including a combination of a plurality of secondary batteries as shown in FIG. 20 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).

[0468] 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.

[0469] The automobile 8500 shown in FIG. 33B 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. 33B 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.

[0470] 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.

[0471] 33C 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. 33C 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.

[0472] 33C, the secondary battery 8602 can be stored in the under-seat storage 8604. Even if the under-seat storage 8604 is small, the secondary battery 8602 can be stored in the under-seat storage 8604. The secondary battery 8602 is removable, and when charging, the secondary battery 8602 can be carried indoors, charged, and stored before riding.

[0473] 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.

[0474] This embodiment mode can be implemented in appropriate combination with other embodiment modes. [Example]

[0475] <Preparation of positive electrode active material> Referring to the flow chart of FIG. 10, positive electrode active materials were prepared so that the number of atoms of magnesium, nickel, and aluminum would be as shown in Table 1, assuming that the number of atoms of cobalt was 100.

[0476] [Table 1]

[0477] First, a mixture 902 containing magnesium and fluorine was prepared by steps S11 to S13. LiF and MgF2 were weighed so that the molar ratio of LiF:MgF2 was 1:3, and then dry mixed and pulverized. Mixing and pulverization were performed in a ball mill using zirconia balls at 150 rpm for 1 hour. The processed material was collected and designated mixture 902.

[0478] Next, Cellseed C-10N manufactured by Nippon Chemical Industry Co., Ltd. was prepared as a composite oxide (step S24).

[0479] Next, the mixture 902 and the composite oxide were mixed (step S31). The mixture was weighed so that the number of magnesium atoms in the mixture 902 would be the value shown in Table 1, assuming that the number of cobalt atoms in the composite oxide was 100. The mixing was performed by a dry method. The mixing was performed in a ball mill using zirconia balls at 150 rpm for 1 hour.

[0480] Next, the treated material was collected to obtain a mixture 903 (step S32).

[0481] Next, the mixture 903 was placed in an alumina crucible and annealed in a muffle furnace in an oxygen atmosphere at 850°C for 60 hours (step S33). During the annealing, the alumina crucible was covered with a lid. The oxygen flow rate was 10 L / min. The temperature was increased at a rate of 200°C / hr and decreased over 10 hours or more. The material after the heat treatment was recovered and sieved to obtain a second composite oxide (step S34).

[0482] Next, nickel was added in step S41, and aluminum was added by repeating steps S41 to S44. Note that a sample was also prepared under conditions in which steps S41 to S44 were not performed.

[0483] First, nickel hydroxide, the metal source, and the second composite oxide were mixed in a ball mill. They were mixed so that the number of nickel atoms, assuming the number of cobalt atoms to be 100, would be the value shown in Table 1. Mixing was carried out in a ball mill using zirconia balls at 150 rpm for 1 hour. After mixing, the mixture was passed through a 300 μm diameter sieve. The resulting mixture was then placed in an alumina crucible, covered, and annealed in an oxygen atmosphere at 850°C for 2 hours.

[0484] Next, an aluminum-containing coating layer was formed by the sol-gel method. Al isopropoxide was used as the metal source, and 2-propanol was used as the solvent. The materials were mixed so that the aluminum atomic number was the value shown in Table 1, assuming the cobalt atomic number to be 100. The resulting mixture was then placed in an alumina crucible, capped, and annealed in an oxygen atmosphere at 850°C for 2 hours. The powder was then sieved through a 53 μm diameter sieve to recover the powder, yielding the cathode active materials with the respective conditions shown in Table 1. The particle size distributions of the resulting cathode active materials were measured for conditions in which the magnesium, nickel, and aluminum atomic numbers were 1, 0.5, and 0.5, respectively. The results are shown in Figure 46.

[0485] <Preparation of secondary battery> Each positive electrode was fabricated using the positive electrode active material obtained above. The positive electrode active material, AB, and PVDF were mixed in a weight ratio of active material:AB:PVDF = 95:3:2, and the slurry was coated onto a current collector. NMP was used as the solvent for the slurry.

[0486] After the slurry was applied to the current collector, the solvent was evaporated. Then, a pressure of 210 kN / m was applied, followed by a further pressure of 1467 kN / m. A positive electrode was obtained through these steps. The loading on the positive electrode was approximately 7 mg / cm. 2 It was decided.

[0487] Using the prepared positive electrode, a coin-type secondary battery of CR2032 type (diameter 20 mm, height 3.2 mm) was prepared.

[0488] The counter electrode was made of lithium metal.

[0489] The electrolyte used in the electrolytic solution was 1 mol / L lithium hexafluorophosphate (LiPF6), and the electrolytic solution was a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of EC:DEC = 3:7. For the secondary batteries used to evaluate the cycle characteristics, 2 wt% vinylene carbonate (VC) was added to the electrolytic solution.

[0490] The separator was made of polypropylene with a thickness of 25 μm.

[0491] The positive electrode can and the negative electrode can were made of stainless steel (SUS).

[0492] <Cycle characteristics> Next, the cycle characteristics of the fabricated secondary battery were evaluated by repeatedly charging and discharging at 25°C using CCCV (0.5C, 4.6V, cut-off current 0.05C) charging and CC (0.5C, 2.5V) discharging.

[0493] The results of the cycle characteristics after 50 cycles are shown in Figures 34 to 36. The horizontal axis represents the discharge capacity retention rate, and the vertical axis represents the discharge energy. Figures 34, 35, and 36 summarize the values ​​when the magnesium content is 0.5, 1.0, and 2.0, respectively, relative to the cobalt content of 100. Table 2 shows the discharge capacity retention rate after 50 cycles when the magnesium content is 2.0, and Table 3 shows the discharge energy.

[0494] [Table 2]

[0495] [Table 3]

[0496] FIG. 37 shows excerpts of the discharge capacity retention rate and discharge energy under two conditions in which both nickel and aluminum were set to 0.25 or 0.5, and under a condition in which steps S41 to S44 were not performed and nickel and aluminum were not added (the figure legend states "Ni: -, Al: -").

[0497] Better properties were obtained under conditions where the nickel content was greater than 0.1 and less than 1, and the aluminum content was 0.1 or greater and less than 1. Particularly better properties were obtained under conditions where the magnesium content was 1.

[0498] <Continuous charging durability> Next, positive electrode active materials were prepared in which the number of magnesium atoms was 1.0 or 1.5, and the number of nickel and aluminum atoms was either not added or 0.25, assuming that the number of cobalt atoms was 100. Secondary batteries were prepared according to the method described above, and their continuous charge durability was evaluated.

[0499] The secondary batteries using each of the prepared positive electrode active materials were charged and discharged once at 25°C. Charging was performed using CCCV (0.2C, 4.5V, cut-off current 0.02C) with a 2-minute rest period after charging. Discharging was performed using CC (0.2C, 3.0V) with a 2-minute rest period after discharging.

[0500] Thereafter, continuous charging was performed at 60° C. using CCCV (0.5 C). The upper limit voltage was set to 4.6 V. 1 C was set to 191.7 mA / g.

[0501] FIG. 38A shows the results when the number of magnesium atoms is 1.0 relative to the number of cobalt atoms, which is 100, and FIG. 38B shows the results when it is 1.5.

[0502] Excellent continuous durability was obtained under the condition where nickel and aluminum were added.

[0503] <xps> Positive electrode active materials were prepared with reference to the above method so that the amounts of magnesium, nickel, and aluminum, assuming the number of cobalt atoms to be 100, met the four conditions (XPS-1 to XPS-4) shown in Table 4, and XPS analysis was performed.

[0504] [Table 4]

[0505] The concentrations of each element obtained by XPS are shown in Table 5.

[0506] [Table 5]

[0507] Even when nickel was added, XPS analysis showed that the amount was below the detection limit. When aluminum was added, aluminum was also detected. The amount of aluminum was also less than one-quarter of the amount of magnesium. This suggests that aluminum may diffuse more easily within particles than magnesium, and that nickel may diffuse more easily within particles than aluminum.

[0508] <XRD of positive electrode> Of the obtained positive electrode active materials, positive electrode active materials in which the number of magnesium, nickel, and aluminum atoms was 1, 0.5, and 0.5, respectively, were used to fabricate positive electrodes.

[0509] This positive electrode was charged and discharged once to confirm the capacity, and then charged at 4.5 V, 4.55 V, or 4.6 V, and subjected to XRD analysis.

[0510] To check the capacity, the charge was CCCV (0.2C, 4.5V, final current 0.05C) with a 20-minute rest period after charging. The discharge was CC (0.2C, 3V) with a 20-minute rest period after discharging. The temperature was 25°C, and 1C = 191mA / g.

[0511] Subsequent charging at 4.5 V, 4.55 V, or 4.6 V was performed using CCCV (0.2 C, each voltage, final current 0.02 C). After charging, the secondary battery was disassembled in a glove box under an argon atmosphere, and the positive electrode was removed and washed with DMC. It was then sealed in an airtight container under an argon atmosphere and subjected to XRD analysis. Figures 39 and 40 show the XRD results. Figures 39 and 40 each have different 2θ ranges on the horizontal axis.

[0512] The lattice constants were calculated from the XRD results, and the a-axis was 2.812, 2.814, and 2.818[×10] at charging voltages of 4.5 V, 4.55 V, and 4.6 V, respectively. -10 m], and the c-axis is 14.28, 14.04, and 13.79 [× 10 -10 m]. [Example]

[0513] Next, a secondary battery was fabricated using a composite oxide material different from that in Example 1.

[0514] <Secondary battery production 2> As the composite oxide used in step S24, EQ-Lib-LCO manufactured by MTI was used to prepare a positive electrode active material.

[0515] The following five fabrication conditions were used. The first was a condition in which steps S11 to S13 and steps S21 to S24 were not performed and magnesium, nickel, and aluminum were not added (shown as "Mg:-, Ni:-, Al:-" in Figure 42). The second was a condition in which the number of magnesium atoms was 1.0 when the number of cobalt atoms was 100, and nickel and aluminum were not added (Mg:1, Ni:-, Al:-). The third was a condition in which the number of magnesium atoms was 1.0 when the number of cobalt atoms was 100, and the numbers of nickel and aluminum atoms were both 0.25 (Mg:1, Ni:0.25, Al:0.25). The fourth was a condition in which the number of magnesium atoms was 1.0 when the number of cobalt atoms was 100, and the numbers of nickel and aluminum atoms were both 0.5 (Mg:1, Ni:0.5, Al:0.5). The fifth condition is a condition where the number of atoms of magnesium, nickel, and aluminum is all 1.0 when the number of atoms of cobalt is 100 (Mg:1, Ni:1, Al:1). A secondary battery was fabricated using the positive electrode active material prepared under the above conditions, with reference to the method of Example 1, and the cycle characteristics were evaluated. The loading amount was approximately 7 mg / cm. 2 The positive electrode was approximately 20 mg / cm 2 The temperature for the cycle test was 45°C, and the upper limit voltage for charging was 4.6V.

[0516] <Cycle characteristics> The particle size distribution of the MTI composite oxide used is shown in Figure 41. The loading amount was approximately 7 mg / cm. 2 The results of the cycle characteristics of the positive electrode with a loading of approximately 20 mg / cm are shown in Figure 42. 2 The cycle characteristics of the positive electrode are shown in Figure 43. The addition of magnesium improved the cycle characteristics, and the addition of nickel and aluminum further improved them.

[0517] <Secondary battery production 3> A positive electrode active material was prepared using lithium cobalt oxide manufactured by Aldrich as the composite oxide used in step S24. The following two preparation conditions were used. The first was a condition in which steps S11 to S13 and steps S21 to S24 were not performed, and magnesium, nickel, and aluminum were not added. The second was a condition in which the number of magnesium atoms was 0.5 relative to the number of cobalt atoms of 100, and nickel and aluminum were not added. A secondary battery was prepared using the positive electrode active material prepared under these conditions, following the method of Example 1, and its cycle characteristics were evaluated. The cycle test temperature was 45°C, and the upper limit charge voltage was 4.55V.

[0518] <Cycle characteristics> The particle size distribution of the Aldrich composite oxide used is shown in Figure 44. The results of the cycle characteristics are shown in Figure 45. The addition of magnesium improved the cycle characteristics. [Example]

[0519] In this example, characteristics of a secondary battery including a positive electrode active material of one embodiment of the present invention were evaluated.

[0520] <Preparation of positive electrode active material> A positive electrode active material was produced with reference to the flow chart in FIG.

[0521] First, a mixture 902 containing magnesium and fluorine was prepared by steps S11 to S13. LiF and MgF2 were weighed so that the molar ratio of LiF:MgF2 was 1:3. The weighed LiF and MgF2 were dry-ground and mixed. The grinding and mixing were performed in a ball mill using zirconia balls at 150 rpm for 1 hour. The processed material was collected and designated mixture 902.

[0522] Next, CellSeed 5H manufactured by Nippon Chemical Industry Co., Ltd. was prepared as a composite oxide (step S24). The particle size distribution of 5H is shown in FIG.

[0523] Next, the mixture 902 and the composite oxide were mixed (step S31). The mixture was weighed so that the number of magnesium atoms in the mixture 902 was 0.5 or 2, assuming that the number of cobalt atoms in the composite oxide was 100. The mixing was performed by dry mixing. The mixing was performed in a ball mill using zirconia balls at 150 rpm for 1 hour. As a comparative example, a condition in which no magnesium was added was also prepared.

[0524] Next, the treated material was collected to obtain a mixture 903 (step S32).

[0525] Next, the mixture 903 was placed in an alumina crucible and annealed in a muffle furnace in an oxygen atmosphere at 850°C for 60 hours (step S33). During the annealing, the alumina crucible was covered with a lid. The oxygen flow rate was 10 L / min. The temperature was increased at a rate of 200°C / hr and decreased over 10 hours or more. The material after the heat treatment was recovered and sieved to obtain a second composite oxide (step S34).

[0526] Next, nickel hydroxide, the metal source, and the second composite oxide were mixed in a ball mill. They were mixed so that the number of nickel atoms was 0.5 when the number of cobalt atoms was 100. Mixing was carried out in a ball mill using zirconia balls at 150 rpm for 1 hour. After mixing, the mixture was passed through a 300 μm diameter sieve. The resulting mixture was then placed in an alumina crucible, covered, and annealed in an oxygen atmosphere at 850°C for 2 hours.

[0527] Next, an aluminum-containing coating layer was formed using a sol-gel method. Al isopropoxide was used as the metal source, and 2-propanol was used as the solvent. The materials were mixed so that the aluminum atomic ratio was 0.5 per 100 cobalt atoms. The resulting mixture was then placed in an alumina crucible, capped, and annealed at 850°C for 2 hours in an oxygen atmosphere. The powder was then passed through a 53 μm diameter sieve to recover the positive electrode active material.

[0528] <Preparation of secondary battery> Each positive electrode was fabricated using the positive electrode active material obtained above. As a comparative example, a positive electrode (shown as Mg:-, Ni:-, Al:- in FIG. 48) using CellSeed 5H as the positive electrode active material was also fabricated. A slurry of the positive electrode active material, AB, and PVDF mixed in a weight ratio of active material:AB:PVDF = 95:3:2 was applied to a current collector. NMP was used as the solvent for the slurry.

[0529] After the slurry was applied to the current collector, the solvent was evaporated. Then, a pressure of 210 kN / m was applied, followed by a further pressure of 1467 kN / m. A positive electrode was obtained through these steps. The loading on the positive electrode was approximately 7 mg / cm. 2 It was decided.

[0530] Using the prepared positive electrode, a coin-type secondary battery of CR2032 type (diameter 20 mm, height 3.2 mm) was prepared.

[0531] The counter electrode was made of lithium metal.

[0532] The electrolyte used in the electrolytic solution was 1 mol / L lithium hexafluorophosphate (LiPF6), and the electrolytic solution was a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of EC:DEC = 3:7. For the secondary batteries used to evaluate the cycle characteristics, 2 wt% vinylene carbonate (VC) was added to the electrolytic solution.

[0533] The separator was made of polypropylene with a thickness of 25 μm.

[0534] The positive electrode can and the negative electrode can were made of stainless steel (SUS).

[0535] <Cycle characteristics> Next, the cycle characteristics of the fabricated secondary battery were evaluated at 45° C. First, the battery was charged and discharged three times to confirm the capacity, and then charged and discharged 50 times for a cycle test.

[0536] To check the capacity, charging was performed using CCCV (0.2C, 4.5V, final current 0.02C) with a 20-minute rest period after charging. Discharging was performed using CV (0.2C, 3V) with a 20-minute rest period after discharging.

[0537] The charging cycle was CCCV (0.76C, 4.6V, final current 0.02C) with a 20-minute rest period after charging. The discharging cycle was CV (0.76C, 3V) with a 20-minute rest period after discharging. 1C = 177.5mA / g.

[0538] The results of the cycle characteristics are shown in Figure 48. The addition of nickel and aluminum significantly improved the cycle characteristics. The amount of magnesium added also affected the discharge capacity, with a higher discharge capacity being obtained when the magnesium content was 0.5. [Explanation of symbols]

[0539] 100: Positive electrode active material, 101: Particles, 102: Particles, 103: Film, 108: Current collector, 109: Positive electrode active material layer, 111: Region, 112: Region< / xps> < / xrd> < / edx> < / xps>

Claims

1. A positive electrode active material having particles containing lithium, cobalt, oxygen, and aluminum, the positive electrode active material has a crystal structure with a space group of R-3m, The crystal structure is estimated by Rietveld analysis of a pattern obtained by powder X-ray diffraction using CuKα1 radiation, When EDX ray analysis was performed on the cross section of the particle, the particle has a first region at a distance of 20 nm or more and 200 nm or less from the surface thereof, and in the first region, the number of aluminum atoms is 0.04 to 1.6 times the number of cobalt atoms as determined by the EDX ray analysis; a positive electrode active material having a second region at a distance of 1 μm or more and 3 μm or less from the surface of the particle, wherein the number of aluminum atoms in the second region is less than 0.03 times the number of cobalt atoms as determined by EDX ray analysis.

2. In claim 1, The cross section of the particle is exposed by processing using a focused ion beam processing and observation device.

3. In claim 1 or claim 2, the positive electrode active material has a coating in contact with the surface of the particle, the coating comprises carbon; The number of cobalt atoms in the coating is less than 0.05 times the number of carbon atoms in the coating.

4. A positive electrode active material having particles containing lithium, cobalt, oxygen, nickel, and aluminum, The positive electrode active material has a crystalline structure having an R-3m space group when a Rietveld analysis is performed on a pattern obtained by powder X-ray diffraction using CuKα1 radiation, When EDX ray analysis was performed on the cross section of the particle, the particle has a first region at a distance of 20 nm or more and 200 nm or less from the surface thereof, and in the first region, the number of aluminum atoms is 0.04 to 1.6 times the number of cobalt atoms as determined by the EDX ray analysis; a positive electrode active material having a second region at a distance of 1 μm or more and 3 μm or less from the surface of the particle, wherein the number of aluminum atoms in the second region is less than 0.03 times the number of cobalt atoms as determined by EDX ray analysis.

5. In claim 4, In the positive electrode active material, the number of nickel atoms in the first region is less than 0.5 times the number of aluminum atoms as determined by the EDX ray analysis.

6. In claim 4 or claim 5, The cross section of the particle is exposed by processing using a focused ion beam processing and observation device.

7. In any one of claims 4 to 6, the positive electrode active material has a coating in contact with the surface of the particle, the coating comprises carbon; The number of cobalt atoms in the coating is less than 0.05 times the number of carbon atoms in the coating.

8. In any one of claims 1 to 7, A positive electrode active material having a number of sulfur atoms of 150 ppm wt or more and 2000 ppm wt or less as measured by glow discharge mass spectrometry.

9. In any one of claims 1 to 8, A positive electrode active material having a titanium atomic number of 300 ppm wt or less as measured by glow discharge mass spectrometry.

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