Secondary battery and method for manufacturing a secondary battery

Abstract

Provided is a novel positive electrode active material. Alternatively, provided is a secondary battery having a large charge / discharge capacity. Alternatively, provided is a secondary battery having a high charge / discharge voltage. Alternatively, provided is a secondary battery having high safety or reliability. By improving a positive electrode active material using lanthanum or yttrium, a highly reliable secondary battery having a large charge / discharge capacity can be obtained. An oxide is provided on the surface of positive electrode active material particles, and the oxide on the surface contains lanthanum, yttrium, or zirconium.

Description

Technical Field

[0001] The present invention relates to a secondary battery and a method for manufacturing the same. Alternatively, it relates to a portable information terminal, a vehicle, etc. having a secondary battery.

[0002] One aspect of the present invention relates to an object, a method, or a manufacturing method. Alternatively, the present invention relates to a process, a machine, a manufacture, or a composition of matter. One aspect of the present invention relates to a semiconductor device, a display device, a light-emitting device, a power storage device, a lighting device, an electronic device, or a method for manufacturing them.

[0003] In the present specification, the semiconductor device refers to all devices that can function by utilizing semiconductor characteristics, and electro-optical devices, semiconductor circuits, and electronic devices are all semiconductor devices.

[0004] In the present specification, the power storage device refers to all elements and devices having a power storage function. For example, it includes power storage devices (also referred to as secondary batteries) such as lithium-ion secondary batteries, lithium-ion capacitors, and electric double-layer capacitors.

Background Art

[0005] In recent years, the development of various power storage devices such as lithium-ion secondary batteries, lithium-ion capacitors, and air batteries has been actively carried out. In particular, lithium-ion secondary batteries with high output and high energy density have rapidly expanded their demand along with the development of the semiconductor industry, such as in portable information terminals such as mobile phones, smartphones, or notebook computers, portable music players, digital cameras, medical devices, or next-generation clean energy vehicles such as hybrid vehicles (HV), electric vehicles (EV), or plug-in hybrid vehicles (PHV), and have become indispensable in modern information society as a source of rechargeable energy.

[0006] Therefore, improvements to the positive electrode active material are being considered to improve the cycle characteristics and increase the capacity of lithium-ion secondary batteries (for example, Patent Document 1, Non-Patent Document 1).

[0007] Furthermore, the characteristics required of energy storage devices include safety in various operating environments and improved long-term reliability. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] WO2015-163356 [Non-patent literature]

[0009] [Non-Patent Document 1] Suppression of Cobalt Dissolution from the LiCoO▲2▼ Cathodes with Various Metal-Oxide Coatings, Yong Jeong Kim et.,al.,Journal of The Electrochemical Society,150(12)A1723-A1725(2003) [Overview of the project] [Problems that the invention aims to solve]

[0010] One aspect of the present invention aims to provide a positive electrode active material with a large charge / discharge capacity. Alternatively, it aims to provide a positive electrode active material with a high charge / discharge voltage. Alternatively, it aims to provide a positive electrode active material with minimal degradation. Alternatively, it aims to provide a novel positive electrode active material. Alternatively, it aims to provide a secondary battery with a large charge / discharge capacity. Alternatively, it aims to provide a secondary battery with a high charge / discharge voltage. Alternatively, it aims to provide a secondary battery with high safety or reliability. Alternatively, it aims to provide a secondary battery with minimal degradation. Alternatively, it aims to provide a secondary battery with a long lifespan. Alternatively, it aims to provide a novel secondary battery.

[0011] Furthermore, one aspect of the present invention aims to provide novel materials, active materials, energy storage devices, or methods for producing them.

[0012] Furthermore, the description of these problems does not preclude the existence of other problems. Moreover, one aspect of the present invention does not need to solve all of these problems. It is possible to extract other problems from the description, drawings, and claims. [Means for solving the problem]

[0013] When using lithium oxide, it is desirable to achieve two things simultaneously: that it is a positive electrode active material with a high charge / discharge voltage, and that it is a safe and reliable positive electrode active material. If there are areas on the particle surface where pure LiCoO2 is exposed, irregularities will occur, and during charging and discharging, cobalt or oxygen may be desorbed, causing the crystal structure to collapse and degradation to occur.

[0014] Materials with a layered rock salt crystal structure, such as lithium cobalt oxide (LiCoO2), are known to have high discharge capacity and are excellent as positive electrode active materials for secondary batteries. Examples of materials with a layered rock salt crystal structure include composite oxides represented by LiMO2. One or more elements selected from Co and Ni are examples of element M. In addition, one or more elements selected from Co and Ni, plus one or more elements selected from Al and Mg, are also examples of element M.

[0015] Lithium cobalt oxide (LiCoO2) can have different crystal structures depending on the Li occupancy rate x of the lithium sites. The extent to which insertion-deinsertable lithium remains in the positive electrode active material is determined by x in the composition formula, for example, Li x x in CoO2, or Li x Indicated by x in MO2. Li in this specification. x CoO2 contains Li as appropriate. x This can be interpreted as MO2. When properly synthesized lithium cobalt oxide, before being used as the positive electrode, approximately satisfies the stoichiometric ratio, it is LiCoO2 and x=1. Similarly, a secondary battery that has finished discharging can also be said to be LiCoO2 or x=1. Here, "finished discharging" refers to a state where, for example, the voltage is 3.0V or 2.5V or less at a current of 100mAh / g or less. Conventional LiCoO2 may degrade if its crystal structure collapses when repeatedly charged and discharged in a way that x is 0.24 or less.

[0016] Therefore, a metal oxide is provided as a modifier on part or all of the surface of the lithium cobalt oxide (LiCoO2) particles. Reliability is improved by providing the modifier on at least part of the particles. Preferably, the modifier is a material that is electrically or mechanically stronger than the lithium cobalt oxide (LiCoO2) particles.

[0017] Using a crystal model (layered crystal structure) of a typical LCO (LiCoO2) lithium cobalt oxide film, we will evaluate a model in which some of the cobalt is replaced with another metal and the surrounding oxygen is extracted, in order to search for materials for the modifier. The first energy at which the lithium cobalt oxide film becomes unstable when oxygen is removed was calculated to be 4.32 eV, and the second energy at which the metal (cobalt) becomes unstable when it is removed after the oxygen removal was found to be 7.46 eV.

[0018] Based on these calculation results, calculations were performed using various material compositions. In particular, the first energy at which instability occurs when oxygen is removed from lanthanum oxide is 6.68 eV, which is higher than the value for LCO, making it suitable as a modifier.

[0019] Furthermore, the first energy at which yttrium oxide becomes unstable when oxygen is removed is 6.63 eV, which is greater than the value for LCO, making it suitable as a modifier.

[0020] Furthermore, to reduce manufacturing costs, the oxide may contain lanthanum and zirconium as a modifier, or it may contain yttrium and zirconium as a modifier. The first energy at which the zirconium oxide becomes unstable when oxygen is removed is 6.07 eV, which is greater than the LCO value, making it suitable as a modifier.

[0021] Furthermore, it is preferable that the concentration of fluorine in the positive electrode active material containing the modifier is higher in the surface layer than in the center of the positive electrode active material. This fluorine concentration distribution is due to the two-step process in the manufacturing method of the positive electrode active material, namely, the addition of fluorine after the production of particles containing lithium and cobalt. To investigate the non-uniformity of fluorine concentration, XPS analysis, TOF-SIMS, or EDX analysis is used, and non-uniformity is defined as a difference of more than two times in the maximum concentration detected between a first region and a second region.

[0022] In this specification, the surface layer of particles such as active material refers to, for example, the region within 50 nm, more preferably within 35 nm, even more preferably within 20 nm, and most preferably within 10 nm from the surface inward. Surfaces formed by cracks or fissures may also be considered the surface. The region deeper than the surface layer is called the interior. In this specification, a grain boundary refers to, for example, a part where particles are stuck together, a part where the crystal orientation changes inside the particle (including the central part), a part containing many defects, or a part where the crystal structure is disordered. A grain boundary can be considered a type of surface defect. The vicinity of a grain boundary refers to the region within 10 nm from the grain boundary. In this specification, a particle is not limited to spherical (circular cross-section), but the cross-sectional shape of individual particles may be elliptical, rectangular, trapezoidal, conical, a square with rounded corners, asymmetrical, etc., and individual particles may also be irregular in shape.

[0023] Furthermore, if nickel, aluminum, or titanium is to be added to the positive electrode active material, it is preferable to obtain it by the sol-gel method.

[0024] Furthermore, when lanthanum or yttrium is used as a modifier, it is preferable to obtain it by the sol-gel method. The melting point of lanthanum is approximately 920°C. In the case of lanthanum, for example, if the number of cobalt atoms in lithium cobalt oxide is set to 1, the concentration of lanthanum in the metal source should be between 0.001 and 0.5 times. In the case of yttrium, for example, if the number of cobalt atoms in lithium cobalt oxide is set to 1, the concentration of yttrium in the metal source should be between 0.001 and 0.5 times. Furthermore, when zirconium is used, it is preferable to obtain it by the sol-gel method. In the case of zirconium, for example, if the number of cobalt atoms in lithium cobalt oxide is set to 1, the concentration of zirconium in the metal source should be between 0.001 and 0.5 times.

[0025] In this specification, the modifier refers to a plurality of materials attached to the positive electrode active material particles and has a function of suppressing deterioration of the positive electrode active material particles such as cobalt elution. Note that an alloy may be formed at the portion where the modifier contacts the positive electrode active material particles. Further, the modifier may or may not contribute to the movement of lithium ions during charge and discharge of the secondary battery. When it contributes, it can be called a positive electrode active material including the modifier. The modifier only needs to have at least a function of suppressing deterioration of the positive electrode active material particles, and can also be called a protective material that protects from a chemical reaction with an electrolytic solution. Further, the positive electrode active material disclosed in this specification may also be said to be a granular material in which child particles (lanthanum oxide or yttrium oxide or zirconium oxide) are coated on the surface of the mother particle in a non-uniform state.

[0026] Further, LiM represented by lithium cobalt oxide x O y (where x>0 and y > 0, more specifically, for example, y = 2 and 0.8 < x < 1.2) is not limited to the lithium composite oxide represented by, and one aspect of the present invention is LiNi x Co 1-x O2 (0 < x < 1) represented by the NiCo system, LiM x O y For example, as the lithium composite oxide represented by, LiNi x Mn 1-x O2 (0 < x < 1) represented by the NiMn system, etc. can also be applied. Also, LiNi x Co y Mn zIt can also be applied to NiCoMn-based (also referred to as NCM) represented by O2(x>0, y>0, 0.8<x + y + z<1.2). Specifically, for example, it is preferable to satisfy 0.1x<y<8x and 0.1x<z<8x. As an example, x, y, and z preferably satisfy x:y:z = 1:1:1 or values in the vicinity thereof. Or as an example, x, y, and z preferably satisfy x:y:z = 5:2:3 or values in the vicinity thereof. Or as an example, x, y, and z preferably satisfy x:y:z = 8:1:1 or values in the vicinity thereof. Or as an example, x, y, and z preferably satisfy x:y:z = 6:2:2 or values in the vicinity thereof. Or as an example, x, y, and z preferably satisfy x:y:z = 1:4:1 or values in the vicinity thereof.

[0027] In addition, as a lithium composite oxide having a layered rock salt-type crystal structure, for example, it can also be applied to Li2MnO3, Li2MnO3-LiMeO2 (Me is Co, Ni, Mn), etc.

Advantages of the Invention

[0028] According to one aspect of the present invention, cathode active material particles with less deterioration can be provided. In addition, one aspect of the present invention can provide a method for producing a cathode active material. Further, according to one aspect of the present invention, novel cathode active material particles can be provided. Also, according to one aspect of the present invention, a novel power storage device can be provided.

Brief Description of the Drawings

[0029] Figure 1A is a photographic view showing an electron beam image (SEM), and Figure 1B is a schematic diagram. Figure 2 is a diagram for explaining the crystal structure of the cathode active material (Configuration 1). Figure 3 is a diagram for explaining the crystal structure of the cathode active material (Configuration 2). Figure 4 is a graph showing the calculation results. Figure 5 is a diagram showing an example of a flow indicating one aspect of the present invention. Figure 6 is a diagram showing an example of a flow indicating one aspect of the present invention. Figures 7A to 7D are cross-sectional views illustrating examples of the positive electrode of a secondary battery. Figure 8A is an exploded perspective view of a coin-type rechargeable battery, Figure 8B is a perspective view of a coin-type rechargeable battery, and Figure 8C is a cross-sectional perspective view thereof. Figure 9A shows an example of a cylindrical secondary battery. Figure 9B shows an example of a cylindrical secondary battery. Figure 9C shows an example of multiple cylindrical secondary batteries. Figure 9D shows an example of an energy storage system with multiple cylindrical secondary batteries. Figures 10A and 10B illustrate examples of secondary batteries, while Figure 10C shows the inside of a secondary battery. Figures 11A to 11C illustrate an example of a secondary battery. Figures 12A and 12B show the external appearance of a secondary battery. Figures 13A to 13C illustrate the method for manufacturing a secondary battery. Figure 14A shows the external appearance of the battery pack, Figure 14B shows an example of the battery pack's configuration, and Figure 14C shows an example of the battery pack's configuration. Figures 15A and 15B illustrate examples of secondary batteries. Figures 16A to 16C illustrate an example of a secondary battery. Figures 17A and 17B illustrate an example of a secondary battery. Figure 18A is a perspective view of a battery pack showing one aspect of the present invention, Figure 18B is a block diagram of the battery pack, and Figure 18C is a block diagram of a vehicle having a motor. Figures 19A to 19D illustrate an example of a transport vehicle. Figures 20A and 20B illustrate an energy storage device according to one embodiment of the present invention. Figure 21A shows an electric bicycle, Figure 21B shows the secondary battery of an electric bicycle, and Figure 21C illustrates an electric motorcycle. Figures 22A to 22D illustrate an example of an electronic device. Figure 23A shows an example of a wearable device, Figure 23B shows a perspective view of a wristwatch-type device, and Figure 23C is a diagram illustrating the side view of a wristwatch-type device. Figure 24A is a graph showing the discharge capacity, and Figure 24B is a graph showing the discharge capacity retention rate. Figure 25A is a graph showing the discharge capacity, and Figure 25B is a graph showing the discharge capacity retention rate. Figure 26A is a graph showing the discharge capacity, and Figure 26B is a graph showing the discharge capacity retention rate. Figure 27 is a photograph showing an electron microscope (SEM) image. [Modes for carrying out the invention]

[0030] Embodiments of the present invention will be described in detail below with reference to the drawings. However, it will be readily apparent to those skilled in the art that the present invention is not limited to the following description, and its form and details can be modified in various ways. Furthermore, the present invention is not to be interpreted as being limited to the embodiments described below.

[0031] (Embodiment 1) In this embodiment, an example of the structure of a positive electrode active material produced by a manufacturing method according to one aspect of the present invention will be described.

[0032] <Configuration 1> A positive electrode active material according to one aspect of the present invention contains fluorine. Fluorine can improve the wettability of the positive electrode active material surface and homogenize it. The positive electrode active material thus obtained contains Li x In repeated charge-discharge cycles where x in CoO2 is 0.24 or less, the crystal structure is less likely to collapse, and secondary batteries using a positive electrode active material with such characteristics exhibit significantly improved cycle performance.

[0033] If areas of pure LiCoO2 are exposed on the surface of the positive electrode active material particles, irregularities will occur, and cobalt or oxygen will be desorbed during charging and discharging, causing the crystal structure to collapse and degradation to occur. To prevent these areas of pure LiCoO2 from being exposed on the surface, it is preferable to uniformly cover the surface with a magnesium-containing compound. Magnesium has the function of maintaining the crystal structure (layered rock salt type crystal structure) even if Li is desorbed during discharge. Another characteristic is the presence of magnesium (or fluorine) near the surface of the positive electrode active material particles.

[0034] By using the above configuration 1, cracks are less likely to occur when pressure is applied to the positive electrode containing the positive electrode active material during the manufacturing of secondary batteries, and the particle shape can be maintained. Since excess cracks can be reduced, the electrode density can be increased.

[0035] If the surface is rougher and has more irregularities than the range mentioned above, there is a risk of physical cracking or collapse of the crystal structure. If the crystal structure collapses, the areas where pure LiCoO2 is exposed may become exposed on the surface, potentially accelerating degradation.

[0036] As lithium oxide, materials having a layered rock salt type crystal structure are preferred, for example, composite oxides represented by LiMO2. As an example of element M, one or more selected from Co and Ni are given. In addition, as an example of element M, one or more selected from Al and Mg are given.

[0037] By incorporating fluorine near the surface, not only fluorine but also magnesium or aluminum can be distributed at high concentrations near the surface. By covering and heat-treating the material, the outward diffusion of fluorine as a gas is suppressed, while other elements such as aluminum diffuse into the solid material. Fluorine improves the wettability of the positive electrode active material surface, leading to homogenization.

[0038] Composite oxides containing lithium, transition metals, and oxygen preferably have a layered rock salt-type crystal structure with few defects and strains. Therefore, it is preferable that the composite oxide contains few impurities. If a composite oxide containing lithium, transition metals, and oxygen contains many impurities, it is highly likely to have a crystal structure with many defects or strains.

[0039] To prevent the inclusion of impurities, it is preferable to modify the surface of the positive electrode active material by heating it with a lid on after mixing in the fluoride. The timing of covering the container can be any of the following: covering the container with the lid before heating and then placing it in the heating furnace, covering the container with the lid after it has been placed in the heating furnace, or covering the container during heating before the fluoride melts.

[0040] Figure 2 shows the crystal structure of the positive electrode active material shown in configuration 1 above, before and after charging and discharging. The positive electrode active material shown in configuration 1 above is in the discharge state, i.e., Li x In the case of x=1 in CoO2, it is preferable to have a layered rock salt type crystal structure belonging to the space group R-3m. Layered rock salt type composite oxides have high discharge capacity, possess a two-dimensional lithium ion diffusion pathway, and are suitable for lithium ion insertion / desorption reactions, making them excellent as positive electrode active materials for secondary batteries. For this reason, it is particularly preferable that the interior, which occupies most of the volume of the positive electrode active material, has a layered rock salt type crystal structure. Figure 2 shows the layered rock salt type crystal structure with R-3m(O3) denoted.

[0041] On the other hand, it is preferable that the surface layer of the positive electrode active material 100 in one embodiment of the present invention shown in Figure 1B has a function to reinforce the layered structure consisting of an octahedron of the internal transition metal M and oxygen, so that it does not break down even if lithium is removed from the positive electrode active material 100 due to charging. Alternatively, it is preferable that the surface layer functions as a barrier film for the positive electrode active material 100. Alternatively, it is preferable that the surface layer of the positive electrode active material 100 reinforces the positive electrode active material 100. Reinforcement here means suppressing structural changes in the surface and internal parts of the positive electrode active material 100, including the removal of oxygen, and / or suppressing the oxidative decomposition of the electrolyte on the surface of the positive electrode active material 100.

[0042] Therefore, it is preferable that the surface layer has a different crystal structure from the interior. It is also preferable that the surface layer has a composition and crystal structure that is more stable at room temperature (25°C) than the interior. For example, it is preferable that at least a portion of the surface layer of the positive electrode active material 100 in one embodiment of the present invention has a rock salt type crystal structure. Alternatively, it is preferable that the surface layer has both layered rock salt type and rock salt type crystal structures. Alternatively, it is preferable that the surface layer has characteristics of both layered rock salt type and rock salt type crystal structures.

[0043] The surface layer is the region where lithium ions first detach during charging, and it is a region where the lithium concentration tends to be lower than in the interior. Furthermore, the atoms on the surface of the positive electrode active material 100 in the surface layer can be described as having some of their bonds broken. Therefore, the surface layer is prone to instability, and it is a region where degradation of the crystal structure is likely to begin. On the other hand, if the surface layer can be made sufficiently stable, Li x Even when x in CoO2 is small, for example, when x is 0.24 or less, the layered structure consisting of internal transition metal M and oxygen octahedra can be made less prone to breaking. Furthermore, the displacement of the layers consisting of internal transition metal M and oxygen octahedra can be suppressed.

[0044] To ensure a stable composition and crystal structure in the surface layer, it is preferable that the surface layer contains additive element A, and more preferably that it contains multiple additive element A. Furthermore, it is preferable that the surface layer has a higher concentration of one or more selected additive element A than the interior. It is also preferable that the one or more selected additive element A in the positive electrode active material 100 have a concentration gradient. Moreover, it is more preferable that the distribution of the positive electrode active material 100 differs depending on the additive element A. For example, it is more preferable that the depth of the concentration peak from the surface differs depending on the additive element A. Here, "concentration peak" refers to the maximum concentration value in the surface layer or at a depth of 50 nm or less from the surface.

[0045] For example, it is preferable that some of the additive elements A, such as magnesium, fluorine, titanium, silicon, phosphorus, boron, and calcium, have a concentration gradient that increases from the inside to the surface. Elements having such a concentration gradient will be called additive elements X.

[0046] Another additive element A, such as aluminum or manganese, preferably has a concentration gradient and a concentration peak in a deeper region. The concentration peak may be located at the surface or deeper than the surface. For example, it is preferable that the peak is in a region of 5 nm to 30 nm from the surface inward. An element having such a concentration gradient will be called additive element Y.

[0047] For example, magnesium, one of the additive elements X, is divalent, and magnesium ions are more stable in lithium sites than in transition metal M sites in the layered rock salt crystal structure, so they readily enter the lithium sites. The presence of magnesium at an appropriate concentration in the surface lithium sites makes it easier to maintain the layered rock salt crystal structure. This is presumed to be because the magnesium present in the lithium sites functions as pillars that support the CoO2 layers. Furthermore, the presence of magnesium allows Li x When the occupancy rate x in CoO2 is, for example, 0.24 or less, the release of oxygen from around magnesium can be suppressed. Furthermore, the presence of magnesium is expected to increase the density of the positive electrode active material 100. In addition, a high magnesium concentration in the surface layer is expected to improve corrosion resistance to hydrofluoric acid produced by the decomposition of the electrolyte.

[0048] At appropriate concentrations, magnesium does not adversely affect lithium insertion and removal during charging and discharging, and the above benefits can be enjoyed. However, excessive magnesium may adversely affect lithium insertion and removal. Furthermore, its effect on stabilizing the crystal structure may be reduced. This is thought to be because magnesium enters not only lithium sites but also transition metal M sites. In addition, unwanted magnesium compounds (oxides, fluorides, etc.) that do not substitute for lithium sites or transition metal M sites may segregate on the surface of the positive electrode active material and become a resistive component of the secondary battery. Moreover, as the magnesium concentration of the positive electrode active material increases, the discharge capacity of the positive electrode active material may decrease. This is thought to be because too much magnesium enters the lithium sites, reducing the amount of lithium that contributes to charging and discharging.

[0049] Therefore, it is preferable that the total amount of magnesium in the positive electrode active material 100 is appropriate. For example, in one embodiment of the present invention, the ratio of magnesium to the sum of transition metals M (Mg / Co) in the positive electrode active material 100 is preferably 0.25% or more and 5% or less, more preferably 0.5% or more and 2% or less, and even more preferably about 1%. The amount of magnesium in the total positive electrode active material 100 referred to here may be the value obtained by performing an elemental analysis of the entire positive electrode active material 100 using, for example, GD-MS, ICP-MS, etc., or it may be based on the value of the raw material composition in the process of manufacturing the positive electrode active material 100.

[0050] Furthermore, fluorine, one of the additive elements X, is a monovalent anion, and if some of the oxygen in the surface layer is replaced by fluorine, the lithium detachment energy decreases. This is because the change in the valence of cobalt ions accompanying lithium detachment is from trivalent to tetravalent when fluorine is absent, and from divalent to trivalent when fluorine is present, resulting in different oxidation-reduction potentials. Therefore, if some of the oxygen in the surface layer of the positive electrode active material 100 is replaced by fluorine, the detachment and insertion of lithium ions near the fluorine can occur more smoothly. As a result, when used in a secondary battery, charge-discharge characteristics, high-current characteristics, etc., can be improved. In addition, the presence of fluorine in the surface layer, which is the part that comes into contact with the electrolyte, can effectively improve corrosion resistance to hydrofluoric acid. Furthermore, as will be described in later embodiments, if the melting point of fluorides, including lithium fluoride, is lower than the melting point of other additive element A sources, it can function as a flux (also called a fluxing agent) that lowers the melting point of other additive element A sources.

[0051] In this specification, the layered rock salt crystal structure belonging to space group R-3m, which is found in composite oxides containing lithium and transition metals M including cobalt, refers to a crystal structure that has a rock salt-type ionic arrangement in which cations and anions are arranged alternately, and in which the transition metal M and lithium are regularly arranged to form a two-dimensional plane, thereby enabling two-dimensional diffusion of lithium. Defects such as vacancies in cations or anions may be present. Furthermore, strictly speaking, the layered rock salt crystal structure may have a distorted lattice structure of the rock salt crystal.

[0052] Furthermore, a rock salt-type crystal structure refers to a cubic crystal structure, including the space group Fm-3m, in which cations and anions are arranged alternately. It is also acceptable for there to be vacancies in either the cations or anions.

[0053] Furthermore, the presence of characteristics of both layered rock salt and rock salt crystal structures can be determined by electron diffraction, TEM images, cross-sectional STEM images, etc.

[0054] In rock salt-type MgO, there is no distinction in the sites of cations, but in layered rock salt-type MgO, there are two types of cation sites in the crystal structure: one is mostly occupied by lithium, and the other by transition metal M. The layered structure, in which two-dimensional planes of cations and two-dimensional planes of anions are arranged alternately, is the same for both rock salt-type and layered rock salt-type MgO. Among the bright spots in the electron diffraction pattern corresponding to the crystal planes that form this two-dimensional plane, when the central spot (transmission spot) is taken as the origin 000, the bright spot closest to the central spot is, for example, the (111) plane in ideal rock salt-type MgO and the (003) plane in layered rock salt-type MgO. For example, when comparing the electron diffraction patterns of rock salt-type MgO and layered rock salt-type LiCoO2, the bright spot on the (003) plane of LiCoO2 is observed at approximately half the distance of the bright spot on the (111) plane of MgO. Therefore, when the analysis region contains two phases, for example, rock salt type MgO and layered rock salt type LiCoO2, the electron diffraction pattern will show plane orientations in which bright spots of high and low brightness are arranged alternately. Bright spots common to both rock salt type and layered rock salt type will have high brightness, while bright spots occurring only in the layered rock salt type will have low brightness.

[0055] Furthermore, in cross-sectional STEM images, when a layered rock salt crystal structure is observed from a direction perpendicular to the c-axis, layers with high brightness and layers with low brightness are observed alternately. This feature is not seen in rock salt crystals because there is no distinction in the sites of cations. In the case of a crystal structure that possesses characteristics of both rock salt and layered rock salt crystals, when observed from a specific crystal orientation, layers with high brightness and layers with low brightness are observed alternately in cross-sectional STEM images, and furthermore, a metal with an atomic number greater than lithium is present in a part of the low-brightness layer, i.e., the lithium layer.

[0056] Layered rock salt crystals and the anions in rock salt crystals adopt a cubic close-packed structure (face-centered cubic lattice structure). It is also presumed that the anions in the O3' type crystals, which will be discussed later, adopt a cubic close-packed structure. Therefore, when layered rock salt crystals and rock salt crystals are in contact, there exists a crystal plane in which the orientation of the cubic close-packed structure composed of anions is aligned.

[0057] Alternatively, it can be explained as follows: The anions in the {111} plane of the cubic crystal structure have a triangular lattice. The layered rock salt type has a space group R-3m and a rhombohedral structure, but to facilitate understanding of the structure, it is generally represented by a composite hexagonal lattice, and the (000l) plane of the layered rock salt type has a hexagonal lattice. The triangular lattice of the {111} plane of the cubic crystal has a similar atomic arrangement to the hexagonal lattice of the (000l) plane of the layered rock salt type. The consistency between the two lattices can be described as the orientation of the cubic close-packed structure being aligned.

[0058] However, the space group of layered rock salt crystals and O3'-type crystals is R-3m, which is different from the space group Fm-3m of rock salt crystals (the space group of typical rock salt crystals). Therefore, the Miller indices of crystal planes that satisfy the above conditions differ between layered rock salt crystals, O3'-type crystals, and rock salt crystals. In this specification, it is sometimes said that the crystal orientations are approximately the same when the orientations of the cubic close-packed structure composed of anions are aligned in layered rock salt crystals, O3'-type crystals, and rock salt crystals.

[0059] The approximate agreement of crystal orientation in two regions can be determined from TEM (Transmission Electron Microscope) images, STEM (Scanning Transmission Electron Microscope) images, HAADF-STEM (High-angle Annular Dark Field Scanning TEM) images, ABF-STEM (Annular Bright-Field Scanning Transmission Electron Microscopy) images, electron diffraction, FFT of TEM and STEM images, etc. XRD (X-ray Diffraction), electron diffraction, neutron diffraction, etc. can also be used as a basis for determination.

[0060] Li x The change in crystal structure associated with the change in x in CoO2 will be explained by comparing a conventional positive electrode active material with a positive electrode active material according to one embodiment of the present invention.

[0061] Figure 3 shows the changes in the crystal structure of a conventional positive electrode active material. The conventional positive electrode active material shown in Figure 3 is lithium cobalt oxide (LiCoO2) without additive element A. Changes in the crystal structure of lithium cobalt oxide without additive element A are described in Non-Patent Documents 1 to 3, etc.

[0062] Figure 3 shows R-3m(O3) and Li x This shows the crystal structure of lithium cobalt oxide with x=1 in CoO2. In this crystal structure, lithium occupies octahedral sites, and there are three CoO2 layers in the unit cell. For this reason, this crystal structure is sometimes called the O3 type crystal structure. The CoO2 layer is defined as a structure in which octahedral structures, in which oxygen is 6-coordinated to cobalt, are continuous in a plane with shared edges. This is sometimes referred to as a layer consisting of octahedra of cobalt and oxygen.

[0063] Furthermore, conventional lithium cobalt oxide is known to have a crystal structure that belongs to the monoclinic space group P2 / m when x = approximately 0.5, as the symmetry of lithium increases. This structure has one CoO2 layer in the unit cell. For this reason, it is sometimes called the O1 type or monoclinic O1 type.

[0064] Furthermore, the positive electrode active material at x=0 has a crystal structure of the trigonal space group P-3m1, and also has one CoO2 layer in the unit cell. For this reason, this crystal structure is sometimes called O1 type or trigonal O1 type. In addition, the trigonal structure is sometimes converted to a composite hexagonal lattice and called hexagonal O1 type.

[0065] Furthermore, conventional lithium cobalt oxide at x=0.24 has a crystal structure of space group R-3m. This structure can be described as a structure in which trigonal O1 type CoO2 structures and R-3m(O3) LiCoO2 structures are alternately stacked. For this reason, this crystal structure is sometimes called the H1-3 type crystal structure. In reality, the H1-3 type crystal structure has twice the number of cobalt atoms per unit cell compared to other structures. However, in this specification, including Figure 3, the c-axis of the H1-3 type crystal structure is shown as half the unit cell to facilitate comparison with other crystal structures.

[0066] As an example, in the H1-3 type crystal structure, as described in Non-Patent Literature 3, the coordinates of cobalt and oxygen in the unit cell can be represented 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 oxygen atoms, respectively. The unit cell that should be used to represent the crystal structure of the positive electrode active material can be determined, for example, by Rietveld analysis using XRD. In this case, the unit cell that yields the smallest GOF (goodness of fit) value should be adopted.

[0067] Li x When charging and discharging are repeatedly performed such that x in CoO2 becomes 0.24 or less, conventional lithium cobalt oxide undergoes repeated changes in its crystal structure (i.e., non-equilibrium phase transitions) between the H1-3 type crystal structure and the R-3m(O3) structure in the discharged state.

[0068] However, these two crystal structures exhibit a large displacement of the CoO2 layer. As shown by the dotted line and arrows in Figure 3, in the H1-3 type crystal structure, the CoO2 layer is significantly displaced from the R-3m(O3) layer in the discharge state. Such dynamic structural changes can negatively affect the stability of the crystal structure.

[0069] Furthermore, these two crystal structures also exhibit a significant volume difference. When comparing them per equal number of cobalt atoms, the volume difference between the H1-3 type crystal structure and the discharged R-3m(O3) type crystal structure exceeds 3.5%, and is typically 3.9% or more.

[0070] In addition, the H1-3 type crystal structure, which has a continuous CoO2 layer like the trigonal O1 type, is likely to be unstable.

[0071] Therefore, repeated charging and discharging cycles that result in x being 0.24 or less cause the conventional lithium cobalt oxide crystal structure to break down. This breakdown of the crystal structure leads to a deterioration of the cycle characteristics. This is because the breakdown of the crystal structure reduces the number of sites where lithium can exist stably, and also makes it more difficult for lithium to be inserted and removed.

[0072] On the other hand, in the positive electrode active material shown in the above configuration 1 in Figure 2, Li x The change in crystal structure between the discharge state where x is 1 and the state where x is 0.24 or less in CoO2 is less than that of conventional positive electrode active materials. More specifically, the displacement of the CoO2 layer between the state where x is 1 and the state where x is 0.24 or less can be reduced. In addition, the change in volume when compared per cobalt atom can be reduced. Therefore, the positive electrode active material shown in configuration 1 above is less prone to crystal structure collapse even when repeated charging and discharging where x is 0.24 or less, and can achieve excellent cycle characteristics. Furthermore, the positive electrode active material shown in configuration 1 above is Li x When x in CoO2 is 0.24 or less, it can adopt a more stable crystal structure than conventional positive electrode active materials. Therefore, the positive electrode active material shown in configuration 1 above is Li x When the value of x in CoO2 remains below 0.24, short circuits are less likely to occur. In such cases, the safety of the secondary battery is further improved, which is preferable.

[0073] Li xFigure 2 shows the crystal structure inside the positive electrode active material 100 when x in CoO2 is approximately 1 and 0.2. The interior occupies most of the volume of the positive electrode active material 100 and is the part that contributes greatly to charging and discharging, so it can be said that this is the part where shifting and volume changes of the CoO2 layer are most problematic.

[0074] When x=1, the positive electrode active material 100 has the same R-3m(O3) crystal structure as conventional lithium cobalt oxide.

[0075] However, when x is 0.24 or less, for example, around 0.2 and 0.15, the positive electrode active material 100 has a crystal structure different from that of conventional lithium cobalt oxide, which has an H1-3 type crystal structure.

[0076] When x = approximately 0.2, the positive electrode active material 100 of one embodiment of the present invention has a crystal structure that belongs to the trigonal space group R-3m. This is because the symmetry of the CoO2 layer is the same as that of O3. Therefore, this crystal structure will be called the O3' type crystal structure (pseudo-spinel type crystal structure). Figure 2 shows this crystal structure with R-3m(O3') labeled.

[0077] In the O3' type crystal structure, the coordinates of cobalt and oxygen in the unit cell can be expressed as Co(0,0,0.5), O(0,0,x), and 0.20≦x≦0.25. The lattice constant of the unit cell is preferably 2.797≦a≦2.837(Å) for the a-axis, more preferably 2.807≦a≦2.827(Å), and typically a=2.817(Å). For the c-axis, it is preferably 13.681≦c≦13.881(Å), more preferably 13.751≦c≦13.811, and typically c=13.781(Å).

[0078] In the O3' type crystal structure, ions such as cobalt, nickel, and magnesium occupy the six-coordinate positions of oxygen. Lighter elements such as lithium may occupy the four-coordinate positions of oxygen.

[0079] As shown by the dotted line in Figure 2, there is almost no displacement of the CoO2 layer between the R-3m(O3) in the discharged state and the O3'-type crystal structure.

[0080] Furthermore, the difference in volume per unit number of cobalt atoms between the discharged state R-3m(O3) and the O3'-type crystal structure is 2.5% or less, more specifically 2.2% or less, and typically 1.8%.

[0081] Thus, in the positive electrode active material 100 of one aspect of the present invention, Li x When the occupancy rate x in CoO2 is small, that is, when a large amount of lithium is released, the change in crystal structure is suppressed compared to conventional positive electrode active materials. Furthermore, the change in volume per unit of the same number of cobalt atoms is also suppressed. Therefore, the crystal structure of positive electrode active material 100 is less likely to collapse even when repeated charging and discharging cycles occur where the occupancy rate x is 0.24 or less. As a result, the decrease in charge / discharge capacity during charge / discharge cycles is suppressed in positive electrode active material 100. Also, because it can stably utilize more lithium than conventional positive electrode active materials, positive electrode active material 100 has a high discharge capacity per unit weight and per unit volume. Therefore, by using positive electrode active material 100, secondary batteries with high discharge capacity per unit weight and per unit volume can be manufactured.

[0082] The positive electrode active material 100 is Li x It has been confirmed that when the occupancy rate x in CoO2 is between 0.15 and 0.24, it may have an O3' type crystal structure, and it is estimated that it also has an O3' type crystal structure when the occupancy rate x is greater than 0.24 and less than or equal to 0.27. However, the crystal structure is Li x The occupancy rate x in CoO2 is affected not only by the number of charge / discharge cycles, charge / discharge current, temperature, electrolyte, etc., so it is not necessarily limited to the range of x mentioned above.

[0083] Therefore, the positive electrode active material 100 is Li x When the occupancy rate x in CoO2 is greater than 0.1 and less than or equal to 0.24, the entire interior of the positive electrode active material 100 does not have to be of the O3' type crystal structure. It may contain other crystal structures, or a portion may be amorphous.

[0084] Also Li xTo achieve a low occupancy rate x in CoO2, it is generally necessary to charge at a high charging voltage. Therefore, Li x A state in which the occupancy rate x in CoO2 is small can be rephrased as a state in which the device has been charged at a high charging voltage. For example, when CC / CV charging is performed at a voltage of 4.6V or higher relative to the potential of lithium metal in an environment of 25°C, the H1-3 type crystal structure appears in conventional positive electrode active materials. Therefore, a charging voltage of 4.6V or higher relative to the potential of lithium metal can be said to be a high charging voltage. Furthermore, unless otherwise specified in this specification, the charging voltage is expressed relative to the potential of lithium metal.

[0085] Therefore, the positive electrode active material 100 according to one aspect of the present invention is preferable because it can maintain a crystal structure with R-3m(O3) symmetry even when charged at a high charging voltage, for example, a voltage of 4.6V or higher at 25°C. It is also preferable because it can adopt an O3' type crystal structure when charged at a higher charging voltage, for example, a voltage of 4.65V or higher and 4.7V or lower at 25°C.

[0086] Even with the positive electrode active material 100, an H1-3 type crystal may only be observed when the charging voltage is further increased. Furthermore, as mentioned above, the crystal structure is affected by the number of charge / discharge cycles, charge / discharge current, electrolyte, etc., so even at lower charging voltages, for example, when the charging voltage is 4.5V or higher but less than 4.6V at 25°C, the positive electrode active material 100 according to one embodiment of the present invention may take on an O3' type crystal structure.

[0087] Furthermore, in the case of a secondary battery, if graphite is used as the negative electrode active material, for example, the voltage of the secondary battery will decrease by the amount of the graphite's potential compared to the above. The potential of graphite is approximately 0.05V to 0.2V relative to the potential of lithium metal. Therefore, in the case of a secondary battery using graphite as the negative electrode active material, the same crystal structure is observed when the voltage obtained by subtracting the graphite's potential from the above voltage is obtained.

[0088] Furthermore, while Figure 2 shows O3' with lithium present at all lithium sites with equal probability, this is not the only way. It may be concentrated at some lithium sites, or, for example, as shown in Figure 3, monoclinic O1(Li 0.5 It may have symmetry similar to that of CoO2. The distribution of lithium can be analyzed, for example, by neutron diffraction.

[0089] Furthermore, the O3' type crystal structure can be described as a crystal structure similar to the CdCl2 type crystal structure, although it has lithium randomly placed between the layers. This crystal structure similar to the CdCl2 type is formed when lithium nickelate is used. 0.06 Although the crystal structure is similar to that of NiO2 when charged to this level, it is known that pure lithium cobalt oxide, or layered rock salt-type cathode active materials containing a large amount of cobalt, do not usually adopt a CdCl2-type crystal structure.

[0090] Next, a modifying material is provided on the surface of the positive electrode active material having the above configurations 1 and 2.

[0091] The criteria for selecting the modifier are to calculate the energy value at which instability occurs, based on the procedure shown below. Based on the calculation results, in this embodiment, lanthanum oxide, yttrium oxide, and zirconium oxide are used as the modifier materials.

[0092] In order to select a material that is less prone to oxygen or metal deficiency compared to the above configurations 1 and 2, we first calculate the likelihood of oxygen or metal deficiency occurring for the standard LiCoO2 using first-principles calculations.

[0093] When the metallic element Co in LiCoO2 dissolves into the electrolyte, oxygen is released first, followed by the release of the oxygen-deficient Co. That is, it is assumed that after the Co-O bond is broken and oxygen is depleted, the Co adjacent to the depleted O is released from the LiCoO2 crystal, causing degradation. Therefore, a crystal structure in LiCoO2 that becomes unstable when oxygen adjacent to Co is extracted and oxygen is depleted has a lower energy threshold, which indicates that oxygen is more easily released from the crystal.

[0094] Therefore, we first used first-principles calculations to determine the amount of energy that destabilizes LiCoO2 when an oxygen vacancy occurs in its crystal structure.

[0095] Table 1 shows the specific calculation conditions for the quantum molecular dynamics calculations described above. The first-principles electronic state simulation package VASP (Vienna ab initio simulation package) was used for the calculations. The total number of atoms was set to 384 when there were no defects in the initial state, 383 when oxygen was missing from the crystal structure, and 382 when metallic elements were missing from the crystal structure.

[0096] The specific methods for calculating the first and second energies are shown below. First, we calculated the first energy ΔE1, which is the energy at which instability occurs when oxygen is deficient. ΔE is determined from the difference in formation energy that occurs when oxygen is extracted from the initial structure based on the LiCoO2 unit cell.

[0097] In this model, a LiCoO2 structure with 96 Li atoms, 96 Co atoms, and 192 O atoms was used as the initial structural model, and the lattice and atomic positions were optimized. This LiCoO2 was calculated using a layered rock salt crystal structure with a space group of R-3m.

[0098] Atomic relaxation calculations were performed using the first-principles electronic state calculation package VASP. The calculation conditions used are shown in Table 1.

[0099] [Table 1]

[0100] The first energy at which Co becomes unstable when an oxygen atom adjacent to it is abstracted can be expressed by the following formula.

[0101]

number

[0102] Here Etotal(Li 96 Co 96 O 192 ) is the energy of 384 atoms in LiCoO2, and Etotal(Li 96 Co 96 O 191 ) represents the energy equivalent to 383 atoms of LiCoO2, where one oxygen atom has been removed. Etotal(O2) represents the energy of a single isolated oxygen molecule.

[0103] Furthermore, the second energy at which instability occurs when Co is deficient after oxygen is deficient can be expressed by the following formula.

[0104]

number

[0105] Here Etotal(Li 96 Co 95 O 191 ) represents the energy of 382 atoms in LiCoO2, where one adjacent oxygen and one adjacent coco atom are removed. Etotal(Co) represents the energy of a single isolated coco atom.

[0106] The first energy at which LiCoO2 becomes unstable when oxygen is deficient was calculated to be 4.32 eV.

[0107] Furthermore, based on the state of LiCoO2 after oxygen deficiency, the second energy at which Co becomes unstable when deficiency occurs was calculated to be 7.46 eV.

[0108] When a modifier is applied to the surface of LiCoO2, which serves as the positive electrode active material, if the first energy of the modifier is higher than the first energy of LiCoO2 before modification (4.32 eV), oxygen vacancies throughout the particles are less likely to occur, making the particles stronger. Furthermore, if the second energy of the modifier is higher, it can be said that the film is less prone to metal leaching after oxygen vacancies, so the film can be maintained for a longer period, and the effect of the modification on the positive electrode material is less likely to degrade due to charging and discharging. For this reason, modifiers that exhibit higher first and second energy values ​​are considered preferable.

[0109] Next, the specific methods for calculating the destabilization energy during oxygen deficiency in the modified material and during metal deficiency after oxygen deficiency are shown below.

[0110] For lanthanum oxide (La2O3), yttrium oxide (Y2O3: bixbyite), and zirconium oxide (ZrO2: baddeleyite), the first energy at which instability occurs when oxygen adjacent to the metal element is abstracted, and the second energy at which instability occurs when the metal element is missing after the oxygen has been removed, were calculated. Bulk cells containing 96 metal elements were prepared, and the instability energies were compared. Figure 4 shows the results.

[0111] Lanthanum oxide becomes unstable at a first energy level of 6.68 eV when oxygen adjacent to lanthanum is extracted, and at a second energy level of 11.32 eV when lanthanum is depleted after oxygen has been removed.

[0112] Yttrium oxide becomes unstable at a first energy of 6.63 eV when an oxygen atom adjacent to yttrium is extracted, and at a second energy of 18.83 eV when yttrium is depleted after the oxygen has been removed.

[0113] Zirconium oxide becomes unstable at a first energy of 6.07 eV when an oxygen atom adjacent to zirconium is abstracted, and at a second energy of 23.15 eV when zirconium is depleted after the oxygen has been removed.

[0114] The first energy of LiCoO2 is 4.32 eV, and the second energy is 7.46 eV. As shown in Figure 4, lanthanum oxide, yttrium oxide, and zirconium oxide all exceeded these values. Therefore, lanthanum oxide, yttrium oxide, and zirconium oxide are materials that release oxygen less easily and retain metal elements less easily than LiCoO2, making them suitable as modifiers. Furthermore, combinations of these materials, for example, both lanthanum oxide and zirconium oxide may be used as modifiers, or both yttrium oxide and zirconium oxide may be used as modifiers.

[0115] By fixing a modifier to particles of configuration 1 or configuration 2, a positive electrode resistant to degradation during charging and discharging can be realized. Figure 1A shows an electron microscope (SEM) image of the area around the obtained positive electrode active material 100. Figure 1B shows the positive electrode active material 100 and the modifiers 101a and 101b on its surface. Note that the modifier is small relative to the particles of configuration 1 or configuration 2, and is positioned at least in one place, scattered or dispersed on the surface of the particles.

[0116] Furthermore, if the particle size of the particles in Composition 1 or Composition 2 is too large, problems arise such as difficulty in lithium diffusion and excessive roughness of the surface of the active material layer when coated onto the current collector. On the other hand, if it is too small, problems arise such as difficulty in supporting the active material layer when coating onto the current collector and excessive reaction with the electrolyte. For this reason, the average particle diameter (D50: also called the median diameter) is preferably 1 μm or more and 100 μm or less, more preferably 2 μm or more and 40 μm or less, and even more preferably 5 μm or more and 30 μm or less.

[0117] (Embodiment 2) In this embodiment, an example of a method for producing the positive electrode active material 100 and modifiers 101a and 101b, which are particles of component 1 of Embodiment 1, is explained in Figure 5.

[0118] <Step S11> As step S11 in Figure 5, first, a lithium source and a transition metal M source are prepared as materials for a composite oxide (LiMO2) having lithium, a transition metal M, and oxygen. The composite oxide (LiMO2) may also be formed using a coprecipitation method.

[0119] For example, lithium carbonate, lithium fluoride, etc., can be used as lithium sources.

[0120] As the transition metal M, it is preferable to use a metal that can form a layered rock salt type composite oxide belonging to the space group R-3m together with lithium. For example, at least one of manganese, cobalt, and nickel can be used. In other words, as the transition metal M source, only cobalt may be used, only nickel may be used, two types of cobalt and manganese may be used, two types of cobalt and nickel may be used, or three types of cobalt, manganese, and nickel may be used.

[0121] When using metals capable of forming layered rock salt-type composite oxides, it is preferable to use a mixing ratio of cobalt, manganese, and nickel within a range that allows for a layered rock salt-type crystalline structure. Furthermore, aluminum may be added to these transition metals within a range that allows for a layered rock salt-type crystalline structure.

[0122] As the transition metal M source, oxides, hydroxides, etc. of the above-mentioned metals exemplified as transition 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.

[0123] <Step S12> Next, in step S12, the lithium source and the transition metal M source are mixed. The mixing can be done dry or wet. For example, a ball mill or a bead mill can be used for mixing. When using a ball mill, it is preferable to use zirconia balls as the grinding media.

[0124] <Step S13> Next, in step S13, the mixed material is heated. This step is sometimes referred to as the first heating or calcination to distinguish it from later heating steps. The first heating is performed by placing the material in an alumina crucible, covering it, and heating it in a muffle furnace. The heating is preferably performed at 800°C or higher but less than 1100°C, more preferably at 900°C or higher but less than 1000°C, and even more preferably at around 950°C. Alternatively, 800°C or higher but less than 1000°C is preferable. Alternatively, 900°C or higher but less than 1100°C is preferable. If the temperature is too low, the decomposition and melting of the lithium source and the transition metal M source may be insufficient. On the other hand, if the temperature is too high, defects may occur due to excessive reduction of the metal responsible for the oxidation-reduction reaction used as the transition metal M, or evaporation of lithium. For example, if cobalt is used as the transition metal M, a defect in which the cobalt becomes divalent may occur.

[0125] The heating time can be, for example, 1 hour to 100 hours, and preferably 2 hours to 20 hours. Alternatively, 1 hour to 20 hours is preferred. Alternatively, 2 hours to 100 hours is preferred. The firing is preferably carried out in an atmosphere with little water, such as dry air (for example, a dew point of -50°C or lower, more preferably -100°C or lower). For example, heating at 1000°C for 10 hours is preferred, with a heating rate of 200°C / h and a flow rate of 10 L / min of the dry atmosphere. The heated material can then be cooled to room temperature (25°C). For example, the cooling time from the specified temperature to room temperature is preferably 10 hours to 50 hours.

[0126] However, cooling to room temperature in step S13 is not mandatory. If there are no problems in carrying out the subsequent steps S31 to S33, or S41 to S43, the cooling may be extended to a temperature higher than room temperature.

[0127] The first heating may be carried out in a continuous or batch manner.

[0128] <Step S14> Next, in step S14, the material obtained in the first heating is recovered to obtain a composite oxide (LiMO2) having lithium, a transition metal M, and oxygen. Specifically, lithium cobaltate, lithium manganeseate, lithium nickelate, lithium cobaltate in which some of the cobalt is replaced by manganese, lithium cobaltate in which some of the cobalt is replaced by nickel, or nickel-manganese-cobaltate lithium are obtained.

[0129] Alternatively, a pre-synthesized composite oxide containing lithium, a transition metal M, and oxygen may be used as step S14. In this case, steps S11 to S13 can be omitted.

[0130] For example, lithium cobalt oxide particles (product name: Cellseed C-10N) manufactured by Nippon Chemical Industrial 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 elemental 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.

[0131] Alternatively, lithium cobalt oxide particles manufactured by Nippon Chemical Industrial Co., Ltd. (product name: Cellseed C-5H) can be used. These are lithium cobalt oxide particles with an average particle size (D50) of approximately 6.5 μm, and elemental analysis by GD-MS shows that the concentrations of elements other than lithium, cobalt, and oxygen are similar to or lower than those of C-10N.

[0132] In this embodiment, cobalt is used as the metal M, and pre-synthesized lithium cobalt oxide particles (Cellseed C-10N) are used. Assuming this lithium cobalt oxide is ideal LiCoO2, the amount of additive elements (nickel, aluminum, lanthanum, etc.) to be added in a later process is weighed based on the amount of cobalt calculated from the weight to be used.

[0133] <Step S21> Next, in step S21, a halogen source such as a fluorine source or a chlorine source and a magnesium source are prepared as materials for the mixture 902. It is also preferable to prepare a lithium source.

[0134] Examples of fluorine sources that can be used include lithium fluoride (LiF), magnesium fluoride (MgF2), aluminum fluoride (AlF3), titanium fluoride (TiF4), cobalt fluoride (CoF2, CoF3), nickel fluoride (NiF2), zirconium fluoride (ZrF4), vanadium fluoride (VF5), manganese fluoride, iron fluoride, chromium fluoride, niobium fluoride, zinc fluoride (ZnF2), calcium fluoride (CaF2), sodium fluoride (NaF), potassium fluoride (KF), barium fluoride (BaF2), cerium fluoride (CeF2), lanthanum fluoride (LaF3), and sodium aluminum hexafluoride (Na3AlF6). Furthermore, the fluorine source is not limited to a solid; for example, fluorine (F2), carbon fluoride, sulfur fluoride, oxygen fluoride (OF2, O2F2, O3F2, O4F2, O2F), etc., may be used and mixed in the atmosphere during the heating process described later. Multiple fluorine sources may also be used in combination. Among these, lithium fluoride is preferred because it has a relatively low melting point of 848°C and is easily melted during the heat treatment process described later.

[0135] For example, lithium chloride, magnesium chloride, etc., can be used as a chlorine source.

[0136] For example, magnesium fluoride, magnesium oxide, magnesium hydroxide, magnesium carbonate, etc., can be used as magnesium sources.

[0137] For example, lithium fluoride and lithium carbonate can be used as lithium sources. In other words, lithium fluoride can be used as both a lithium source and a fluorine source. Similarly, magnesium fluoride can be used as both a fluorine source and a magnesium source.

[0138] 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 effect of lowering the melting point is greatest when lithium fluoride (LiF) and magnesium fluoride (MgF2) are mixed in a molar ratio of approximately LiF:MgF2 = 65:35. On the other hand, if the amount of lithium fluoride is too high, there is a concern that the lithium will be in excess and the cycle characteristics will deteriorate. Therefore, the molar ratio of lithium fluoride (LiF) and magnesium fluoride (MgF2) is preferably LiF:MgF2 = x:1 (0 ≤ x ≤ 1.9), more preferably LiF:MgF2 = x:1 (0.1 ≤ x ≤ 0.5), and even more preferably LiF:MgF2 = x:1 (x = around 0.33). In this specification, "around" means a value greater than 0.9 times and less than 1.1 times the value.

[0139] Furthermore, if the following mixing and grinding steps are carried out wet, a solvent should be prepared. Suitable solvents include ketones such as acetone, alcohols such as ethanol and isopropanol, ethers such as diethyl ether, dioxane, acetonitrile, N-methyl-2-pyrrolidone (NMP), etc. It is more preferable to use an aprotic solvent that does not react easily with lithium. In this embodiment, acetone will be used.

[0140] <Step S22> Next, in step S22, the materials of the above mixture 902 are mixed and pulverized. Mixing can be done dry or wet, but wet mixing is preferred because it allows for finer pulverization. For example, a ball mill or a bead mill can be used for mixing. When using a ball mill, it is preferable to use zirconia balls as the pulverizing media. It is preferable to carry out this mixing and pulverization process thoroughly to finely pulverize the mixture 902.

[0141] <Step S23> Next, in step S23, the materials mixed and crushed above are recovered to obtain mixture 902.

[0142] The mixture 902 preferably has a median diameter (D50) of 600 nm to 20 μm, more preferably 1 μm to 10 μm, or 600 nm to 10 μm, or 1 μm to 20 μm. When the mixture 902 is finely powdered in this way, it is easier to uniformly adhere the mixture 902 to the surface of the composite oxide particles when it is mixed with lithium, a transition metal M, and oxygen in a later step. When the mixture 902 is uniformly adhered to the surface of the composite oxide particles, it is preferable because it is easier to distribute halogen and magnesium evenly in the near-surface region of the composite oxide particles after heating. If there are regions near the surface that do not contain halogen and magnesium, it may be difficult to form the O3' type crystal structure described later in the charged state.

[0143] <Step S31> Next, in step S31, the LiMO2 obtained in step S14 is mixed with the mixture 902. The ratio of the number of transition metal atoms M in the composite oxide having lithium, a transition metal, and oxygen to the number of magnesium atoms Mg in the mixture 902 is preferably X:Mg=100:y (0.1≦y≦6), and more preferably X:Mg=100:y (0.3≦y≦3).

[0144] The mixing in step S31 is preferably carried out under milder conditions than the mixing in step S12 in order to avoid destroying the particles of the composite oxide. For example, it is preferable to use conditions with a lower rotation speed or shorter mixing time than in step S12. Also, dry mixing is less likely to destroy particles than wet mixing. For mixing, for example, a ball mill or a bead mill can be used. When using a ball mill, it is preferable to use zirconia balls as the grinding medium.

[0145] <Step S32> Next, in step S32, the materials mixed above are recovered to obtain the first lithium mixture 903.

[0146] In this embodiment, a method of adding a mixture of lithium fluoride and magnesium fluoride to lithium cobalt oxide with few impurities (or added elements) is described, but the present invention is not limited to this. Instead of the first lithium mixture 903 in step S32, a starting material of lithium cobalt oxide to which a magnesium source and a fluorine source, etc., have been added and calcined may be used. In this case, it is not necessary to separate the processes in steps S11 to S14 and steps S21 to S23, making it simpler and more productive.

[0147] Alternatively, lithium cobalt oxide with magnesium and fluorine added beforehand may be used. Using lithium cobalt oxide with magnesium and fluorine added makes the process up to step S32 easier to perform.

[0148] Furthermore, magnesium sources and fluorine sources may be added to lithium cobalt oxide that has already been treated with magnesium and fluorine.

[0149] <Step S33> Next, in step S33, the first lithium mixture 903 is heated in an oxygen-containing atmosphere. It is more preferable that this heating is carried out in a way that inhibits adhesion so that the particles of the first lithium mixture 903 do not stick together. During this heating, some element sources, such as fluorine and lithium sources (LiF), are lighter than oxygen, so heating may cause LiF to volatilize and reduce the amount of LiF in the first lithium mixture 903. Therefore, when heating the first lithium mixture 903, it is preferable to control the partial pressure of fluorine or fluoride in the atmosphere to an appropriate range. For example, one method is to cover the heating crucible after placing the first lithium mixture 903 inside before and after this heating. This step is the second heating step and is sometimes called annealing to distinguish it from the previous heating step.

[0150] Examples of heating methods that have an anti-adhesion effect include heating the first lithium mixture 903 while stirring it, and heating the container containing the first lithium mixture 903 while vibrating it.

[0151] The temperature of the second heating in step S33 must be above the temperature at which the reaction between LiMO2 and mixture 902 proceeds. The temperature at which the reaction proceeds is simply the temperature at which the elemental interdiffusion between LiMO2 and mixture 902 occurs. Therefore, it may be lower than the melting temperature of these materials. For example, in oxides, the melting temperature T m 0.757 times (Tammann temperature T) d Solid-phase diffusion occurs from this point. Therefore, a temperature of, for example, 500°C or higher is sufficient.

[0152] However, it is preferable that the temperature is above the melting point of at least a portion of the first lithium mixture 903, as this facilitates the reaction. For this reason, it is preferable that the temperature of the second heating is above the eutectic point of the mixture 902. If the mixture 902 contains LiF and MgF2, the eutectic point of LiF and MgF2 is around 742°C, so it is preferable that the temperature in step S33 be 742°C or higher.

[0153] Furthermore, the first lithium mixture 903, which is mixed in a molar ratio of LiCoO2:LiF:MgF2 = 100:0.33:1, shows an endothermic peak around 830°C in differential scanning calorimetry (DSC measurement). Therefore, a temperature of 830°C or higher is more preferable for the second heating.

[0154] A higher second heating temperature is preferable because it facilitates the reaction, shortens the heating time, and increases productivity.

[0155] However, the temperature of the second heating must be below the decomposition temperature of LiMO2 (1130°C in the case of LiCoO2). Furthermore, at temperatures near the decomposition temperature, there is a concern that a small amount of LiMO2 may decompose. For this reason, the temperature of the second heating is preferably 1130°C or lower, more preferably 1000°C or lower, even more preferably 950°C or lower, and even more preferably 900°C or lower.

[0156] Therefore, the second heating temperature is preferably 500°C to 1130°C, more preferably 500°C to 1000°C, even more preferably 500°C to 950°C, and even more preferably 500°C to 900°C. Also, 742°C to 1130°C is preferred, more preferably 742°C to 1000°C, even more preferably 742°C to 950°C, and even more preferably 742°C to 900°C. Also, 830°C to 1130°C is preferred, more preferably 830°C to 1000°C, even more preferably 830°C to 950°C, and even more preferably 830°C to 900°C.

[0157] Furthermore, when heating the first lithium mixture 903, it is preferable to control the partial pressure of fluorine or fluoride in the atmosphere to an appropriate range.

[0158] In the manufacturing method described in this embodiment, some materials, such as LiF, which is a fluorine source, function as a flux. This function allows the second heating temperature to be lowered to below the decomposition temperature of LiMO2, for example, between 742°C and 950°C, enabling the distribution of additives, including magnesium, in the near-surface region and the production of a positive electrode active material with good properties.

[0159] However, since LiF is lighter than oxygen, heating causes LiF to volatilize, reducing the amount of LiF in the first lithium mixture 903. This weakens its function as a flux. Therefore, heating is necessary while suppressing the volatilization of LiF. Even if LiF is not used as a fluorine source, Li and F on the surface of LiMO2 may react to produce LiF, which may then volatilize. Therefore, even if a fluoride with a higher melting point than LiF is used, the same need to suppress volatilization is required.

[0160] Therefore, it is preferable to heat the first lithium mixture 903 in an atmosphere containing LiF, that is, to heat the first lithium mixture 903 while the partial pressure of LiF in the heating furnace is high. Such heating can suppress the volatilization of LiF in the first lithium mixture 903.

[0161] The second heating is preferably performed for an appropriate amount of time. The appropriate duration for the second heating varies depending on conditions such as the temperature of the second heating, the size and composition of the LiMO2 particles in step S14, and other factors. When the particles are small, a lower temperature or shorter duration may be preferable than when the particles are large.

[0162] For example, if the average particle size (D50) of the particles in step S14 is about 12 μm, the temperature of the second heating is preferably between 600°C and 950°C. The duration of the second heating is preferably 3 hours or more, more preferably 10 hours or more, and even more preferably 60 hours or more.

[0163] On the other hand, if the average particle size (D50) of the particles in step S24 is about 5 μm, the temperature of the second heating is preferably, for example, 600°C to 950°C. The duration of the second heating is preferably, for example, 1 hour to 10 hours, and more preferably about 2 hours.

[0164] The second cooling time after heating is preferably, for example, 10 hours or more and 50 hours or less.

[0165] The second heating process may be carried out in either a continuous or batch manner.

[0166] <Step S34> Step S34 involves crushing and mixing if necessary. After mixing, it is preferable to collect the powder and sift it.

[0167] <Step S35> Next, in step S35, the materials mixed above are recovered to obtain a second lithium mixture 904.

[0168] <Step S24> In step S24, an additive element source is prepared. The elements in the additive source can be selected from, for example, one or more of the following: lanthanum, aluminum, nickel, manganese, titanium, vanadium, iron, chromium, niobium, cobalt, arsenic, zinc, silicon, sulfur, phosphorus, and boron. Figure 5 illustrates an example using a nickel source as the additive source. Nickel can increase the capacity per unit weight and per unit volume. Nickel oxide, nickel hydroxide, etc., can be used as the nickel source.

[0169] Methods for mixing these additives include, for example, solid-phase methods, sol-gel methods, sputtering methods, mechanochemical methods, and CVD methods. Multiple methods may also be used in combination.

[0170] In step S41, the nickel source is mixed, and then in step S42, a third lithium mixture 905 is obtained. The mixing can be carried out dry or wet.

[0171] Next, in step S43, the third lithium mixture 905 is heated in an oxygen-containing atmosphere. The heating in step S43 is called the third heating. Preferably, the third heating temperature in step S43 is lower than the second heating temperature in step S33.

[0172] In step S51, an additive element source is prepared. The elements contained in the additive source may be one or more selected from, for example, lanthanum, zirconium, and yttrium.

[0173] In step S61, the third lithium mixture 905 is mixed with a lanthanum source, a zirconium source, or a yttrium source. The mixing can be done dry or wet. For example, step S61 can be performed by the sol-gel method. When using the sol-gel method, lanthanum alkoxide is used as the lanthanum source, and Zr(OC3H7)4 is used as the zirconium source.

[0174] In this embodiment, lanthanum oxide was fixed to a portion of the surface of the positive electrode active material 100 as a modifier using the sol-gel method.

[0175] The additive elements for forming the modifiers 101a and 101b are one or more selected from lanthanum, yttrium, and zirconium.

[0176] This embodiment shows an example of using lanthanum and applying the sol-gel method. When applying the sol-gel method, prepare the solvent to be used in the sol-gel method. In the case of lanthanum, for example, if the number of cobalt atoms in lithium cobalt oxide is set to 1, the concentration of lanthanum in the metal source should be between 0.001 and 0.5 times.

[0177] Here, as an example, we show an example of applying the sol-gel method, using lanthanum alkoxide as the metal source and 2-propanol as the solvent.

[0178] Next, lanthanum alkoxide (tri-i-propoxylanthanum manufactured by Kojunkagaku Co., Ltd.) is dissolved in 2-propanol, and then lithium cobaltate particles are mixed in (step S61 in Figure 5).

[0179] The required amount of metal alkoxide varies depending on the particle size of the lithium cobalt oxide.

[0180] 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 done, for example, with a magnetic stirrer. The stirring time should be sufficient to allow the water in the atmosphere and the metal alkoxide to undergo hydrolysis and polycondensation reactions, for example, 4 hours at 25°C and 90% RH (Relative Humidity). Alternatively, stirring may be performed in an atmosphere without humidity and temperature control, for example, in an air atmosphere in a fume hood. In such cases, it is preferable to extend the stirring time, for example, 12 hours or more at room temperature.

[0181] By gradually incorporating water vapor from the atmosphere and slowly evaporating the alcohol, the water and metal alkoxide react, allowing the sol-gel reaction to proceed gently. Furthermore, reacting the metal alkoxide with water at room temperature allows the sol-gel reaction to proceed more gently than, for example, heating at a temperature exceeding the boiling point of the solvent alcohol.

[0182] Water may also be added actively. If a gentler reaction is desired, the reaction time can be controlled by gradually adding water diluted with alcohol, reducing the amount of alcohol in the bath, or adding a stabilizer. By allowing the sol-gel reaction to proceed gently, a uniform and high-quality coating film can be formed. However, the resulting coating film may not be uniform and may be scattered. In this embodiment, the modifier material 101a and 101b are intentionally scattered to form convex portions on the surface of the positive electrode active material 100.

[0183] After the above processing is complete, the precipitate is recovered from the mixture. Methods of recovery include filtration, centrifugation, and evaporation to dryness. The precipitate can be washed with the same alcohol used to dissolve the metal alkoxide. Note that if evaporation to dryness is used, separation of the solvent and precipitate is not necessary in this step; the precipitate can be recovered, for example, in the drying step of the next procedure.

[0184] Next, the recovered residue is dried to obtain the fourth lithium mixture 906 (step S62 in Figure 5). The drying process can be carried out, for example, by vacuum or air drying at 80°C for 1 to 4 hours.

[0185] If the sol-gel method is not used, the first lithium mixture 903 may be subjected to film formation by sputtering or vapor deposition. In this case, the second lithium mixture 904 can be obtained after film formation. Other methods of heating include heating while stirring the stirring ball and the first lithium mixture 903, and heating while vibrating the container containing the stirring ball and the first lithium mixture 903. Zirconium oxide and titanium oxide are preferred materials for the stirring ball. Heating with a rotary kiln can be done while stirring in either a continuous or batch system, and is preferred as an annealing method to suppress adhesion. The continuous system is preferred because it is highly productive. The batch system is preferred because it is easy to control the atmosphere. When heating with a roller hearth kiln, it is preferable to vibrate the container containing the first lithium mixture 903 during heating. The roller hearth kiln is preferred because it is a continuous system and is highly productive. In this case, the second lithium mixture 904 can be obtained after stirring.

[0186] <Step S63> Next, the resulting mixture is heated (step S63 in Figure 5).

[0187] The fourth heating time is preferably such that the holding time within the heating temperature range is between 1 hour and 80 hours, and more preferably between 1 hour and 20 hours from a productivity standpoint.

[0188] The fourth heating temperature is less than 1000°C, preferably between 700°C and 950°C, and more preferably around 850°C.

[0189] Furthermore, the fourth heating step is preferably performed in an oxygen-containing atmosphere.

[0190] In this embodiment, the fourth heating temperature is set to 850°C and held for 2 hours, with a heating rate of 200°C / h and an oxygen flow rate of 10 L / min.

[0191] The fourth heating temperature in step S63 is preferably lower than the third heating temperature in step S43.

[0192] <Step S66> Next, the cooled particles are collected. Furthermore, it is preferable to sieve the particles. Through the above steps, a positive electrode active material 100 according to one embodiment of the present invention and modifiers 101a and 101b on its surface can be produced (step S66 in Figure 5).

[0193] Furthermore, the manufacturing flow shown in Figure 5 is merely an example and is not particularly limited. For example, when lanthanum and zirconium are used as modifiers, the manufacturing flow shown in Figure 6 may be used. Note that Figure 6 is identical to the manufacturing flow in Figure 5 except for some differences, so the same reference numerals are used for the same steps.

[0194] Figure 6 shows the fabrication flow in which nickel is used as the additive element source in S24, aluminum in S25, and lanthanum and zirconium are mixed in S51 using the sol-gel method.

[0195] (Embodiment 3) This embodiment describes a lithium-ion secondary battery containing a positive electrode active material according to one aspect of the present invention. The secondary battery comprises at least an outer casing, a current collector, an active material (positive electrode active material or negative electrode active material), a conductive additive, and a binder. It also has an electrolyte in which a lithium salt or the like is dissolved. In the case of a secondary battery using an electrolyte, a positive electrode, a negative electrode, and a separator between the positive and negative electrodes are provided.

[0196] [Positive electrode] The positive electrode comprises a positive electrode active material layer and a positive electrode current collector. The positive electrode active material layer preferably contains the positive electrode active material shown in Embodiment 1, and may further contain a binder, a conductive additive, etc.

[0197] Figure 7A shows an example of a schematic diagram of the cross-section of the positive electrode.

[0198] The current collector 550 is a metal foil, and the positive electrode is formed by applying a slurry to the metal foil and drying it. After drying, pressing may be applied further. The positive electrode is formed by creating an active material layer on the current collector 550.

[0199] A slurry is a liquid material used to form an active material layer on a current collector 550, and it contains at least an active material, a binder, and a solvent, preferably further mixed with a conductive additive. The slurry is sometimes called an electrode slurry or an active material slurry, and when forming a positive electrode active material layer, a positive electrode slurry is used, and when forming a negative electrode active material layer, it is sometimes called a negative electrode slurry.

[0200] Conductive additives, also called conductivity imparters or conductive materials, are typically made of carbon. By attaching a conductive additive between multiple active materials, the materials become electrically connected to each other, increasing their conductivity. Note that "attachment" does not only refer to physical contact between the active materials and the conductive additive, but also includes cases where covalent bonds are formed, bonds are formed by van der Waals forces, the conductive additive covers part of the surface of the active materials, the conductive additive fits into surface irregularities of the active materials, or where electrical connections are formed even without physical contact.

[0201] A typical example of a carbon material used as a conductive additive is carbon black (furnace black, acetylene black, graphite, etc.).

[0202] Figure 7A illustrates acetylene black 553 as a conductive additive. Figure 7A also shows an example where a second active material 562, with a smaller particle size than the positive electrode active material 100 shown in Embodiment 1, is mixed in. Mixing particles of different sizes allows for a high-density positive electrode active material layer, thereby increasing the charge and discharge capacity of the secondary battery. The particles of the positive electrode active material 100 shown in Embodiment 1 correspond to the active material 561 in Figure 7A.

[0203] As the positive electrode of a secondary battery, a binder (resin) is mixed with the active material to fix it to the current collector 550, such as metal foil. The binder is also called a binding agent. The binder is a polymer material, and if too much binder is included, the proportion of active material in the positive electrode decreases, reducing the discharge capacity of the secondary battery. Therefore, the amount of binder is mixed in to the minimum extent possible. In Figure 7A, the areas not filled with the active material 561, the second active material 562, and acetylene black 553 represent voids or binder.

[0204] Although Figure 7A shows an example where the active material 561 is depicted as spherical, it is not particularly limited and may have various shapes. The cross-sectional shape of the active material 561 may be elliptical, rectangular, trapezoidal, conical, a square with rounded corners, or asymmetrical.

[0205] Figure 7B shows examples of the active material 561 being illustrated in various shapes. Figure 7B shows examples different from those in Figure 7A.

[0206] Furthermore, in the positive electrode shown in Figure 7B, graphene 554 is used as the carbon material used as a conductive additive.

[0207] Graphene is a carbon material that possesses remarkable electrical, mechanical, and chemical properties, making it promising for applications in various fields, such as field-effect transistors and solar cells.

[0208] Figure 7B shows a positive electrode active material layer formed on the current collector 550, comprising an active material 561, graphene 554, and acetylene black 553.

[0209] In the step of mixing graphene 554 and acetylene black 553 to obtain an electrode slurry, it is preferable that the weight of the carbon black mixed is 1.5 to 20 times, preferably 2 to 9.5 times, the weight of the graphene.

[0210] Furthermore, when the mixture of graphene 554 and acetylene black 553 is within the above range, the dispersion stability of acetylene black 553 is excellent during slurry preparation, and aggregation is less likely to occur. Also, when the mixture of graphene 554 and acetylene black 553 is within the above range, a higher electrode density can be achieved compared to a positive electrode using only acetylene black 553 as a conductive additive. By increasing the electrode density, the capacity per unit weight can be increased. Specifically, the density of the positive electrode active material layer measured by weight can be higher than 3.5 g / cc. Moreover, when the positive electrode active material 100 shown in Embodiment 1 is used as the positive electrode, and the mixture of graphene 554 and acetylene black 553 is within the above range, a synergistic effect in achieving a higher capacity secondary battery can be expected, which is preferable.

[0211] Furthermore, although the electrode density is lower compared to a positive electrode using only graphene as a conductive additive, rapid charging can be achieved by setting the mixture of the first carbon material (graphene) and the second carbon material (acetylene black) within the above range. In addition, it is preferable to use the positive electrode active material 100 shown in Embodiment 1 as the positive electrode, and to set the mixture of graphene 554 and acetylene black 553 within the above range, as this is expected to have a synergistic effect in increasing the stability of the secondary battery and enabling even faster charging.

[0212] These features make it effective as a secondary battery for use in vehicles.

[0213] Increasing the number of rechargeable batteries increases the vehicle's weight, which in turn increases the energy required to move the batteries, thus shortening the driving range. By using high-density rechargeable batteries, the driving range can be maintained without significantly changing the total weight of a vehicle equipped with the same weight of batteries.

[0214] Furthermore, as the capacity of a vehicle's secondary battery increases, more power is required for charging, making it desirable to complete the charging process in a short time. In addition, regenerative charging, which involves temporarily generating electricity when the vehicle brakes are applied and then charging the battery, is performed under high-rate charging conditions, so good rate characteristics are required for vehicle secondary batteries.

[0215] By using the positive electrode active material 100 shown in Embodiment 1 as the positive electrode, and by setting the mixing ratio of acetylene black and graphene to an optimal range, it becomes possible to achieve both high electrode density and the creation of appropriate gaps necessary for ion conduction, thereby obtaining a secondary battery for automotive use with high energy density and good output characteristics.

[0216] Furthermore, this configuration is also effective for mobile information terminals. By using the positive electrode active material 100 shown in Embodiment 1 as the positive electrode and optimizing the mixing ratio of acetylene black and graphene, the secondary battery can be made smaller and have a higher capacity. In addition, optimizing the mixing ratio of acetylene black and graphene enables rapid charging of mobile information terminals.

[0217] In Figure 7B, the areas not filled with the active material 561, graphene 554, and acetylene black 553 represent voids or binders. While voids are necessary for electrolyte permeation, too many voids reduce electrode density, too few voids prevent electrolyte permeation, and if voids remain after the secondary battery is formed, the energy density decreases.

[0218] By using the positive electrode active material 100 obtained in Embodiment 1 as the positive electrode, and by setting the mixing ratio of acetylene black and graphene within an optimal range, it becomes possible to achieve both high electrode density and the creation of appropriate gaps necessary for ion conduction, thereby obtaining a secondary battery with high energy density and good output characteristics.

[0219] Figure 7C illustrates an example of a cathode using carbon nanotube 555 instead of graphene. Figure 7C shows a different example from Figure 7B. Using carbon nanotube 555 prevents aggregation of carbon black such as acetylene black 553 and improves dispersibility.

[0220] In Figure 7C, the areas not filled with active material 561, carbon nanotubes 555, and acetylene black 553 represent voids or binders.

[0221] Furthermore, Figure 7D illustrates an example of another cathode. Figure 7C shows an example in which carbon nanotubes 555 are used in addition to graphene 554. Using both graphene 554 and carbon nanotubes 555 can prevent aggregation of carbon black such as acetylene black 553 and further improve dispersibility.

[0222] In Figure 7D, the areas not filled with active material 561, carbon nanotube 555, graphene 554, and acetylene black 553 represent voids or binders.

[0223] A secondary battery can be manufactured by using one of the positive electrodes shown in Figures 7A to 7D, placing a separator on top of the positive electrode, and placing the resulting laminate on top of the separator, then placing it in a container (such as an outer casing or metal can), and filling the container with electrolyte.

[0224] Furthermore, the above configuration is an example of a secondary battery using an electrolyte, but it is not particularly limited.

[0225] For example, a semi-solid-state battery or a fully solid-state battery can be manufactured using the positive electrode active material 100 shown in Embodiment 1.

[0226] In this specification, a semi-solid battery refers to a battery having a semi-solid material in at least one of its components: the electrolyte layer, the positive electrode, or the negative electrode. Here, "semi-solid" does not mean that the solid material makes up 50% of the battery. A semi-solid material possesses solid properties, such as small volume change, while also having some liquid-like properties, such as flexibility. As long as these properties are met, the battery may consist of a single material or multiple materials. For example, a liquid material may be impregnated into a porous solid material.

[0227] Furthermore, in this specification, a polymer electrolyte secondary battery refers to a secondary battery having a polymer in the electrolyte layer between the positive and negative electrodes. Polymer electrolyte secondary batteries include dry (or intrinsic) polymer electrolyte batteries and polymer gel electrolyte batteries. Polymer electrolyte secondary batteries may also be called semi-solid batteries.

[0228] When a semi-solid battery is manufactured using the positive electrode active material 100 shown in Embodiment 1, the semi-solid battery becomes a secondary battery with a large charge / discharge capacity. Furthermore, it can be a semi-solid battery with a high charge / discharge voltage. Alternatively, a safe or highly reliable semi-solid battery can be realized.

[0229] Furthermore, the positive electrode active material described in Embodiment 1 may be mixed with other positive electrode active materials and used in combination.

[0230] Other positive electrode active materials include composite oxides having olivine-type crystal structures, layered rock salt-type crystal structures, or spinel-type crystal structures. Examples include compounds such as LiFePO4, LiFeO2, LiNiO2, LiMn2O4, V2O5, Cr2O5, and MnO2.

[0231] In addition, other positive electrode active materials include lithium-containing materials having a spinel-type crystal structure containing manganese, such as LiMn2O4, and lithium nickelate (LiNiO2 or LiNi 1-xM x It is preferable to mix O2(0 < x < 1) (M = Co, Al, etc.). By adopting such a configuration, the characteristics of the secondary battery can be improved.

[0232] Also, as another positive electrode active material, a lithium manganese composite oxide represented by the composition formula Li a Mn b M c O d can be used. Here, the element M is preferably a metal element selected from those other than lithium and manganese, or silicon or phosphorus, and more preferably nickel. Further, when measuring the entire particle of the lithium manganese composite oxide, it is preferable to satisfy 0 < a / (b + c) < 2, c > 0, and 0.26 ≤ (b + c) / d < 0.5 during discharge. The composition of metals, silicon, phosphorus, etc. in the entire particle of the lithium manganese composite oxide can be measured using, for example, ICP-MS (Inductively Coupled Plasma Mass Spectrometer). Also, the oxygen composition of the entire particle of the lithium manganese composite oxide can be measured using, for example, EDX (Energy Dispersive X-ray Analysis). Further, it can be obtained by using the valence evaluation of melting gas analysis and XAFS (X-ray Absorption Fine Structure) analysis in combination with ICPMS analysis. Note that the lithium manganese composite oxide refers to an oxide containing at least lithium and manganese, and may contain at least one element selected from the group consisting of chromium, cobalt, aluminum, nickel, iron, magnesium, molybdenum, zinc, indium, gallium, copper, titanium, niobium, silicon, and phosphorus.

[0233] <Binder> As the binder, it is preferable to use rubber materials such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, and ethylene-propylene-diene copolymer. Also, fluorine rubber can be used as the binder.

[0234] Furthermore, it is preferable to use a water-soluble polymer as the binder. Examples of water-soluble polymers include polysaccharides. Examples of polysaccharides include cellulose derivatives such as carboxymethylcellulose (CMC), methylcellulose, ethylcellulose, hydroxypropylcellulose, diacetylcellulose, and regenerated cellulose, or starch. It is even more preferable to use these water-soluble polymers in combination with the aforementioned rubber material.

[0235] Alternatively, it is preferable to use materials such as polystyrene, methyl polyacrylate, polymethyl methacrylate (PMMA), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), ethylene propylene diene polymer, polyvinyl acetate, or nitrocellulose as the binder.

[0236] You may use a combination of several of the binders mentioned above.

[0237] For example, a material with particularly excellent viscosity-modifying properties may be used in combination with other materials. For instance, rubber materials, while possessing excellent adhesive and elastic properties, can be difficult to adjust in viscosity when mixed with a solvent. In such cases, it is preferable to mix them with a material with particularly excellent viscosity-modifying properties. As a material with particularly excellent viscosity-modifying properties, a water-soluble polymer may be used. As a water-soluble polymer with particularly excellent viscosity-modifying properties, the aforementioned polysaccharides, such as carboxymethylcellulose (CMC), methylcellulose, ethylcellulose, hydroxypropylcellulose, and diacetylcellulose, cellulose derivatives such as regenerated cellulose, or starch can be used.

[0238] Cellulose derivatives such as carboxymethyl cellulose have increased solubility when made into salts such as the sodium salt or ammonium salt of carboxymethyl cellulose, for example, and are more likely to exhibit the effect as a viscosity modifier. By increasing the solubility, the dispersibility with the active material or other components can also be enhanced when preparing the electrode slurry. In this specification, the cellulose and cellulose derivatives used as the electrode binder shall include their salts.

[0239] Water-soluble polymers stabilize the viscosity by dissolving in water and can also stably disperse the active material or other materials combined as binders, such as styrene-butadiene rubber, etc., in an aqueous solution. Also, due to having functional groups, it is expected to be easily adsorbed stably on the surface of the active material. Moreover, cellulose derivatives such as carboxymethyl cellulose have many materials with functional groups such as hydroxyl groups or carboxyl groups, for example, and due to having functional groups, it is expected that the polymers interact with each other and exist covering the surface of the active material widely.

[0240] When the binder covering the surface of the active material or in contact with the surface forms a film, it is also expected to play a role as a passivation film and suppress the decomposition of the electrolyte. Here, the passivation film is a film having no electrical conductivity or having extremely low electrical conductivity. For example, when a passivation film is formed on the surface of the active material, the decomposition of the electrolyte can be suppressed at the battery reaction potential. Also, it is more desirable that the passivation film suppresses the electrical conductivity while allowing lithium ions to conduct.

[0241] <Positive electrode current collector> As the current collector, materials with high conductivity such as metals like stainless steel, gold, platinum, aluminum, titanium, and their alloys can be used. Also, the material used for the positive current collector preferably does not dissolve at the potential of the positive electrode. Further, an aluminum alloy added with elements for improving heat resistance such as silicon, titanium, neodymium, scandium, molybdenum, etc. can be used. Also, it may be formed of a metal element that reacts with silicon to form a silicide. Examples of the metal element that reacts with silicon to form a silicide include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, nickel, etc. The current collector can appropriately use shapes such as foil, plate, sheet, net, punching metal, expanded metal, etc. The current collector preferably has a thickness of 5 μm or more and 30 μm or less.

[0242] [Negative electrode] The negative electrode has a negative electrode active material layer and a negative electrode current collector. Also, the negative electrode active material layer has a negative electrode active material and may further have a conductive assistant and a binder.

[0243] <Negative electrode active material> As the negative electrode active material, for example, an alloy-based material or a carbon-based material can be used.

[0244] As the negative electrode active material, elements capable of undergoing charge-discharge reactions through alloying and dealloying reactions with lithium can be used. For example, materials containing at least one of silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium, etc., can be used. Such elements have a larger capacity than carbon, and silicon in particular has a high theoretical capacity of 4200 mAh / g. For this reason, it is preferable to use silicon as the negative electrode active material. Compounds containing these elements may 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, SbSn, etc. In this context, elements capable of undergoing charge-discharge reactions through alloying and de-alloying reactions with lithium, and compounds containing such elements, are sometimes referred to as alloying materials.

[0245] In this specification, SiO refers to silicon monoxide, for example. Alternatively, SiO refers to SiO x It can also be expressed as follows. Here, x is preferably 1 or a value in its immediate vicinity. For example, x is preferably between 0.2 and 1.5, and preferably between 0.3 and 1.2.

[0246] Suitable carbon-based materials include graphite, easily graphitizable carbon (soft carbon), difficult-to-graphitize carbon (hard carbon), carbon nanotubes, graphene, and carbon black.

[0247] 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, spheroidal graphite having a spherical shape can be used as artificial graphite. For example, MCMB may have a spherical shape and is therefore preferable. Furthermore, it is relatively easy to reduce the surface area of ​​MCMB, which may also be preferable. Examples of natural graphite include flake graphite and spheroidized natural graphite.

[0248] When lithium ions are inserted into graphite (during the formation of lithium-graphite intercalation compounds), graphite exhibits a potential as low as that of lithium metal (0.05V to 0.3V vs. Li / Li). + This allows lithium-ion secondary batteries using graphite to exhibit a high operating voltage. Furthermore, graphite is preferable because it has advantages such as a relatively high capacity per unit volume, relatively small volume expansion, low cost, and higher safety compared to lithium metal.

[0249] Furthermore, titanium dioxide (TiO2) and lithium titanium oxide (Li4Ti5O2) are used as negative electrode active materials. 12 ), lithium-graphite intercalation compound (Li x Oxides such as C6, niobium pentoxide (Nb2O5), tungsten oxide (WO2), and molybdenum oxide (MoO2) can be used.

[0250] Furthermore, as the negative electrode active material, a Li3N type structure is used, which is a lithium and transition metal binitride. 3-x M x N (M = Co, Ni, Cu) can be used. For example, Li 2.6 Co 0.4 The N3 has a large charge / discharge capacity (900mAh / g, 1890mAh / cm²). 3 ) indicates a preference.

[0251] Using a lithium-transition metal complex nitride is preferable because it contains lithium ions in the negative electrode active material, allowing it to be combined with lithium-ion-free materials such as V2O5 and Cr3O8 as the positive electrode active material. Even when using a lithium-ion-containing material as the positive electrode active material, the lithium-transition metal complex nitride can be used as the negative electrode active material by pre-desorbing the lithium ions contained in the positive electrode active material.

[0252] Furthermore, 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), may be used as the negative electrode active material. Other materials that undergo a conversion reaction include oxides such as Fe2O3, CuO, Cu2O, RuO2, Cr2O3, and CoS 0.89 This can also occur with sulfides such as NiS and CuS, nitrides such as Zn3N2, Cu3N, and Ge3N4, phosphides such as NiP2, FeP2, and CoP3, and fluorides such as FeF3 and BiF3.

[0253] The conductive additive and binder that the negative electrode active material layer may have can be the same materials as those used for the conductive additive and binder that the positive electrode active material layer may have.

[0254] <Negative electrode current collector> In addition to the same materials as the positive electrode current collector, copper and other materials can also be used for the negative electrode current collector. It is preferable to use a material for the negative electrode current collector that does not alloy with carrier ions such as lithium.

[0255] [Separator] A separator is placed between the positive and negative electrodes. The separator can be made from materials such as cellulose fibers including paper, nonwoven fabrics, glass fibers, ceramics, or synthetic fibers using nylon (polyamide), vinylon (polyvinyl alcohol-based fiber), polyester, acrylic, polyolefin, or polyurethane. It is preferable that the separator be processed into a bag shape and positioned to enclose either the positive or negative electrode.

[0256] 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 material, a polyamide material, or a mixture thereof. Examples of ceramic materials include aluminum oxide particles and silicon oxide particles. Examples of fluorine materials include PVDF and polytetrafluoroethylene. Examples of polyamide materials include nylon and aramid (meta-aramid, para-aramid).

[0257] Coating with ceramic materials improves oxidation resistance, Li x By suppressing the degradation of the separator during charging and discharging when the x value in CoO2 falls below 0.24, the reliability of the secondary battery can be improved. Furthermore, coating with a fluorine-based material improves the adhesion between the separator and the electrode, thereby improving the output characteristics. Coating with a polyamide-based material, especially aramid, improves heat resistance, thus improving the safety of the secondary battery.

[0258] For example, a polypropylene film may be coated on both sides with a mixture of aluminum oxide and aramid. Alternatively, the side of the polypropylene film in contact with the positive electrode may be coated with a mixture of aluminum oxide and aramid, and the side in contact with the negative electrode may be coated with a fluorine-based material.

[0259] By using a multi-layered separator, the safety of the secondary battery can be maintained even if the overall thickness of the separator is thin, thus increasing the capacity per unit volume of the secondary battery.

[0260] [Electrolyte] The electrolyte has a solvent and an electrolyte. As the solvent of the electrolyte, an aprotic organic solvent is preferred. For example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, chloroethylene carbonate, vinylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethoxyethane (DME), dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, sultone, etc. can be used singly, or two or more of these can be used in any combination and ratio.

[0261] In addition, by using one or more ionic liquids (room temperature molten salts) that are flame-retardant and hardly volatile as the solvent of the electrolyte, even if the internal temperature of the power storage device rises due to an internal short circuit or overcharging of the power storage device, rupture or ignition of the power storage device can be prevented. An ionic liquid consists of a cation and an anion and contains an organic cation and an anion. Examples of the organic cation used in the electrolyte include aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, or aromatic cations such as imidazolium cations and pyridinium cations. Examples of the anion used in the electrolyte include monovalent amide-based anions, monovalent methide-based anions, fluorosulfonic acid anions, perfluoroalkylsulfonic acid anions, tetrafluoroborate anions, perfluoroalkylborate anions, hexafluorophosphate anions, or perfluoroalkylphosphate anions.

[0262] In addition, as the electrolyte dissolved in the above solvent, for example, LiPF6, LiClO4, LiAsF6, LiBF4, LiAlCl4, LiSCN, LiBr, LiI, Li2SO4, Li2B 10 Cl 10 、Li2B12 Cl 12 Lithium salts such as LiCF3SO3, LiC4F9SO3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiN(CF3SO2)2, LiN(C4F9SO2)(CF3SO2), LiN(C2F5SO2)2, lithium bis(oxalate) borate (Li(C2O4)2, LiBOB) can be used individually or in any combination and ratio of two or more of these salts.

[0263] It is preferable to use a highly purified electrolyte in which particulate matter or elements other than the constituent elements of the electrolyte (hereinafter simply referred to as "impurities") are present in small amounts. Specifically, it is preferable that the weight ratio of impurities to the electrolyte be 1% or less, preferably 0.1% or less, and more preferably 0.01% or less.

[0264] Furthermore, additives such as vinylene carbonate, propanesultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), lithium bis(oxalate)borate (LiBOB), and dinitrile compounds such as succinonitrile and adiponitrile may be added to the electrolyte. The concentration of the additive should be, for example, 0.1 wt% to 5 wt% relative to the total solvent.

[0265] Alternatively, a polymer gel electrolyte, obtained by swelling a polymer with an electrolyte solution, may be used.

[0266] Using polymer gel electrolytes enhances safety against leakage and other issues. Furthermore, it enables the secondary battery to be made thinner and lighter.

[0267] As the polymer to be gelled, silicone gels, acrylic gels, acrylonitrile gels, polyethylene oxide gels, polypropylene oxide gels, fluorine-based polymer gels, etc., can be used. For example, polymers having a polyalkylene oxide structure such as polyethylene oxide (PEO), or PVDF and polyacrylonitrile, etc., and copolymers containing them can be used. For example, PVDF-HFP, which is a copolymer of PVDF and hexafluoropropylene (HFP), can be used. Furthermore, the polymer formed may have a porous structure.

[0268] Furthermore, instead of an electrolyte, a solid electrolyte containing inorganic materials such as sulfides or oxides, or a solid electrolyte containing polymeric materials such as PEO (polyethylene oxide), can be used. When a solid electrolyte is used, the installation of separators or spacers becomes unnecessary. In addition, since the entire battery can be solidified, the risk of leakage is eliminated, dramatically improving safety.

[0269] Therefore, the positive electrode active material 100 obtained in Embodiment 1 can also be applied to all-solid-state batteries. By applying the positive electrode slurry or electrode to an all-solid-state battery, an all-solid-state battery with high safety and good characteristics can be obtained.

[0270] [Exterior] The outer casing of a secondary battery can be made of a metal material such as aluminum or a resin material. Alternatively, a film-like outer casing can be used. As a film, for example, a three-layer film can be used, in which a highly flexible metal thin film such as aluminum, stainless steel, copper, or nickel is provided on a film made of 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 provided on the metal thin film as the outer surface of the outer casing.

[0271] This embodiment can be used in combination with other embodiments.

[0272] (Embodiment 4) This embodiment describes examples of multiple shapes of secondary batteries having a positive or negative electrode, manufactured by the manufacturing method described in the previous embodiment.

[0273] [Coin-type rechargeable battery] An example of a coin-type rechargeable battery is described below. Figure 8A is an exploded perspective view of a coin-type (single-layer flat type) rechargeable battery, Figure 8B is an external view, and Figure 8C is a cross-sectional view thereof. Coin-type rechargeable batteries are mainly used in small electronic devices.

[0274] Figure 8A is a schematic diagram to show the overlapping (upper and lower relationships and positional relationships) of the components for clarity. Therefore, Figures 8A and 8B are not perfectly identical corresponding diagrams.

[0275] In Figure 8A, the positive electrode 304, separator 310, negative electrode 307, spacer 322, and washer 312 are stacked. These are sealed with the negative electrode can 302 and the positive electrode can 301. Note that the gasket for sealing is not shown in Figure 11A. The spacer 322 and washer 312 are used to protect the inside or fix their position within the can when the positive electrode can 301 and the negative electrode can 302 are crimped together. The spacer 322 and washer 312 are made of stainless steel or insulating material.

[0276] The positive electrode 304 is a laminated structure in which a positive electrode active material layer 306 is formed on a positive electrode current collector 305.

[0277] To prevent a short circuit between the positive and negative electrodes, a separator 310 and a ring-shaped insulator 313 are arranged to cover the sides and top surfaces of the positive electrode 304, respectively. The separator 310 has a larger planar area than the positive electrode 304.

[0278] Figure 8B is a perspective view of the completed coin-type rechargeable battery.

[0279] The coin-type secondary battery 300 has a positive electrode casing 301, which also serves as the positive electrode terminal, and a negative electrode casing 302, which also serves as the negative electrode terminal, 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 it. 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 it. Furthermore, the negative electrode 307 is not limited to a laminated structure, and lithium metal foil or a lithium-aluminum alloy foil may be used.

[0280] Furthermore, for the positive electrode 304 and negative electrode 307 used in the coin-type secondary battery 300, the active material layer only needs to be formed on one side.

[0281] The positive electrode can 301 and the negative electrode can 302 can be made of metals such as nickel, aluminum, or titanium, which are corrosion-resistant to the electrolyte, or alloys thereof, or alloys of these with other metals (e.g., stainless steel). Furthermore, it is preferable to coat them with nickel or aluminum to prevent corrosion caused by the electrolyte. The positive electrode can 301 is electrically connected to the positive electrode 304, and the negative electrode can 302 is electrically connected to the negative electrode 307.

[0282] The negative electrode 307, positive electrode 304, and separator 310 are immersed in an electrolyte solution, and as shown in Figure 8C, the positive electrode 304, separator 310, negative electrode 307, and negative electrode 302 are stacked in this order with the positive electrode 301 at the bottom, and the positive electrode 301 and negative electrode 302 are crimped together via a gasket 303 to manufacture a coin-type secondary battery 300.

[0283] By using a rechargeable battery, a coin-type rechargeable battery 300 can be made with high capacity, high charge / discharge capacity, and excellent cycle characteristics. Furthermore, if a rechargeable battery is used between the negative electrode 307 and the positive electrode 304, the separator 310 can be omitted.

[0284] [Cylindrical rechargeable battery] An example of a cylindrical secondary battery will be explained with reference to Figure 9A. As shown in Figure 9A, the cylindrical secondary battery 616 has a positive electrode cap (battery cover) 601 on the top surface and a battery casing (outer casing) 602 on the sides and bottom. The positive electrode cap 601 and the battery casing (outer casing) 602 are insulated from each other by a gasket (insulating packing) 610.

[0285] Figure 9B is a schematic diagram showing a cross-section of a cylindrical secondary battery. The cylindrical secondary battery shown in Figure 9B has a positive electrode cap (battery cover) 601 on the top surface and a battery casing (outer casing) 602 on the sides and bottom. The positive electrode cap and the battery casing (outer casing) 602 are insulated from each other by a gasket (insulating packing) 610.

[0286] Inside the hollow cylindrical battery casing 602, a battery element is provided, in which a strip-shaped positive electrode 604 and a negative electrode 606 are wound with a separator 605 in between. Although not shown, the battery element is wound around a central axis. The battery casing 602 is closed at one end and open at the other. The battery casing 602 can be made of a metal such as nickel, aluminum, or titanium, or an alloy of these or an alloy of these with another metal (e.g., stainless steel), which is corrosion-resistant to the electrolyte. Furthermore, it is preferable to coat the battery casing 602 with nickel or aluminum to prevent corrosion by the electrolyte. Inside the battery casing 602, the 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. In addition, a non-aqueous electrolyte (not shown) is injected into the inside of the battery casing 602 in which the battery element is provided. The non-aqueous electrolyte can be the same as that used in coin-type secondary batteries.

[0287] Since the positive and negative electrodes used in cylindrical storage batteries are wound, it is preferable to form the active material on both sides of the current collector.

[0288] By using the positive electrode active material 100 obtained in Embodiment 1 as the positive electrode 604, a cylindrical secondary battery 616 with high capacity, high charge / discharge capacity, and excellent cycle characteristics can be obtained.

[0289] 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 metal materials such as aluminum. The positive electrode terminal 603 is resistance-welded to the safety valve mechanism 613, and the negative electrode terminal 607 is resistance-welded to the bottom of the battery can 602. The safety valve mechanism 613 is electrically connected to the positive electrode cap 601 via a PTC element (Positive Temperature Coefficient) 611. The safety valve mechanism 613 disconnects the electrical connection between the positive electrode cap 601 and the positive electrode 604 when the internal pressure of the battery rises above a predetermined threshold. The PTC element 611 is a thermal resistance element whose resistance increases when the temperature rises, and it prevents abnormal heat generation by limiting the amount of current through the increase in resistance. Barium titanate (BaTiO3) based semiconductor ceramics can be used for the PTC element.

[0290] Figure 9C shows an example of an energy storage system 615. The energy storage system 615 has multiple secondary batteries 616. The positive electrode of each secondary battery is in contact with a conductor 624 separated by an insulator 625 and is electrically connected. The conductor 624 is electrically connected to a control circuit 620 via wiring 623. The negative electrode of each secondary battery is also electrically connected to the control circuit 620 via wiring 626. The control circuit 620 can be a charge / discharge control circuit that performs charging and discharging, or a protection circuit that prevents overcharging or over-discharging.

[0291] Figure 9D shows an example of an energy storage system 615. The energy storage system 615 has multiple secondary batteries 616, which are sandwiched between conductive plates 628 and 614. The multiple secondary batteries 616 are electrically connected to conductive plates 628 and 614 by wiring 627. The multiple secondary batteries 616 may be connected in parallel, in series, or connected in parallel and then in series. By configuring an energy storage system 615 with multiple secondary batteries 616, a large amount of power can be extracted.

[0292] Multiple secondary batteries 616 may be connected in parallel and then further connected in series.

[0293] A temperature control device may be provided between the multiple secondary batteries 616. When a secondary battery 616 overheats, it can be cooled by the temperature control device, and when a secondary battery 616 becomes too cold, it can be heated by the temperature control device. This makes the performance of the energy storage system 615 less susceptible to the influence of ambient temperature.

[0294] Furthermore, in Figure 9D, the energy storage system 615 is electrically connected to the control circuit 620 via wiring 621 and wiring 622. Wiring 621 is electrically connected to the positive terminals of the multiple secondary batteries 616 via conductive plate 628, and wiring 622 is electrically connected to the negative terminals of the multiple secondary batteries 616 via conductive plate 614.

[0295] [Other structural examples of secondary batteries] Examples of secondary battery structures will be explained using Figures 10 and 11.

[0296] The secondary battery 913 shown in Figure 10A has a wound body 950 with terminals 951 and 952 inside a housing 930. The wound body 950 is immersed in an electrolyte inside the housing 930. Terminal 952 is in contact with the housing 930, while terminal 951 is not in contact with the housing 930 due to the use of an insulating material or the like. In Figure 10A, the housing 930 is shown separated for convenience, but in reality, the wound body 950 is covered by the housing 930, and terminals 951 and 952 extend outside the housing 930. The housing 930 can be made of a metal material (e.g., aluminum) or a resin material.

[0297] Furthermore, as shown in Figure 10B, the housing 930 shown in Figure 10A may be formed from multiple materials. For example, in the secondary battery 913 shown in Figure 10B, housing 930a and housing 930b are bonded together, and the winding body 950 is provided in the area surrounded by housing 930a and housing 930b.

[0298] For the housing 930a, an insulating material such as organic resin can be used. In particular, by using a material such as organic resin on the surface where the antenna is formed, shielding of the electric field by the secondary battery 913 can be suppressed. If the shielding of the electric field by housing 930a is small, the antenna may be placed inside housing 930a. For housing 930b, for example, a metal material can be used.

[0299] Furthermore, the structure of the wound body 950 is shown in Figure 10C. The wound body 950 has a negative electrode 931, a positive electrode 932, and a separator 933. The wound body 950 is a wound body in which the negative electrode 931 and the positive electrode 932 are stacked on top of each other with the separator 933 in between, and the stacked sheets are wound up. Note that multiple stacks of the negative electrode 931, positive electrode 932, and separator 933 may be stacked.

[0300] Alternatively, the secondary battery 913 may have a wound body 950a as shown in Figure 11. The wound body 950a shown in Figure 11A has a negative electrode 931, a positive electrode 932, and a separator 933. The negative electrode 931 has a negative electrode active material layer 931a. The positive electrode 932 has a positive electrode active material layer 932a.

[0301] By using the positive electrode active material 100 obtained in Embodiment 1 as the positive electrode 932, a secondary battery 913 with high capacity, high charge / discharge capacity, and excellent cycle characteristics can be obtained.

[0302] The separator 933 has a wider width than the negative electrode active material layer 931a and the positive electrode active material layer 932a, and is wound so as to overlap with the negative electrode active material layer 931a and the positive electrode active material layer 932a. Furthermore, it is preferable from a safety standpoint that the negative electrode active material layer 931a is wider than the positive electrode active material layer 932a. A wound body 950a of this shape is also preferable due to its good safety and productivity.

[0303] As shown in Figure 11B, the negative electrode 931 is electrically connected to terminal 951. Terminal 951 is electrically connected to terminal 911a. The positive electrode 932 is electrically connected to terminal 952. Terminal 952 is electrically connected to terminal 911b.

[0304] As shown in Figure 11C, the coiled body 950a and electrolyte are covered by the housing 930, forming a secondary battery 913. It is preferable to provide a safety valve, an overcurrent protection element, etc., in the housing 930. The safety valve is a valve that opens the inside of the housing 930 at a predetermined internal pressure to prevent the battery from rupturing.

[0305] As shown in Figure 11B, the secondary battery 913 may have multiple windings 950a. By using multiple windings 950a, a secondary battery 913 with a larger charge and discharge capacity can be made. Other elements of the secondary battery 913 shown in Figures 11A and 11B can be referenced from the description of the secondary battery 913 shown in Figures 10A to 10C.

[0306] <Laminated rechargeable battery> Next, an example of a laminate-type secondary battery is shown in Figures 12A and 12B, which show an example of its external appearance. Figures 12A and 12B show 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.

[0307] Figure 13A shows the external view of the positive electrode 503 and the negative electrode 506. The positive electrode 503 has a positive electrode current collector 501, and the 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 the tab region). The negative electrode 506 has a negative electrode current collector 504, and the 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., the tab region. The area or shape of the tab regions of the positive and negative electrodes are not limited to the example shown in Figure 13A.

[0308] <Method for manufacturing laminated rechargeable batteries> Here, an example of a method for manufacturing a laminate-type secondary battery, whose external view is shown in Figure 12A, will be explained using Figures 13B and 13C.

[0309] First, the negative electrode 506, separator 507, and positive electrode 503 are stacked. Figure 13B shows the stacked negative electrode 506, separator 507, and positive electrode 503. Here, an example using 5 sets of negative electrodes and 4 sets of positive electrodes is shown. This can also be called a laminate consisting of negative electrodes, separators, and positive electrodes. Next, the tab regions of the positive electrode 503 are joined together, and the positive electrode lead electrode 510 is joined to the tab region of the outermost positive electrode. For joining, ultrasonic welding, for example, can be used. Similarly, the tab regions of the negative electrode 506 are joined together, and the negative electrode lead electrode 511 is joined to the tab region of the outermost negative electrode.

[0310] Next, the negative electrode 506, separator 507, and positive electrode 503 are placed on the outer casing 509.

[0311] Next, as shown in Figure 13C, the outer casing 509 is bent at the portion indicated by the dashed line. Then, the outer periphery of the outer casing 509 is joined. For joining, for example, heat compression bonding may be used. At this time, a region that is not joined (hereinafter referred to as the inlet) is provided on a part (or one side) of the outer casing 509 so that the electrolyte 508 can be added later.

[0312] Next, the electrolyte 508 (not shown) is introduced into the inside of the outer casing 509 through an inlet provided in the outer casing 509. It is preferable to introduce the electrolyte 508 under a reduced pressure atmosphere or an inert atmosphere. Finally, the inlet is sealed. In this way, a laminate-type secondary battery 500 can be manufactured.

[0313] By using the positive electrode active material 100 obtained in Embodiment 1 as the positive electrode 503, a secondary battery 500 can be made that has high capacity, high charge / discharge capacity, and excellent cycle characteristics.

[0314] [Example of a battery pack] An example of a secondary battery pack according to one embodiment of the present invention, which is capable of wireless charging using an antenna, will be explained with reference to Figure 14.

[0315] Figure 14A shows the external appearance of the secondary battery pack 531, which has a thin rectangular parallelepiped shape (it can also be called a thick flat plate shape). Figure 14B is a diagram illustrating the configuration of the secondary battery pack 531. The secondary battery pack 531 has a circuit board 540 and a secondary battery 513. A label 529 is attached to the secondary battery 513. The circuit board 540 is fixed by a seal 515. The secondary battery pack 531 also has an antenna 517.

[0316] The internal structure of the secondary battery 513 may have a wound structure or a laminated structure.

[0317] In the secondary battery pack 531, for example, as shown in Figure 14B, a control circuit 590 is located on the circuit board 540. The circuit board 540 is electrically connected to terminal 514. The circuit board 540 is also electrically connected to the antenna 517, one of the positive and negative leads 551 of the secondary battery 513, and the other of the positive and negative leads 552.

[0318] Alternatively, as shown in Figure 14C, the system may have a circuit system 590a provided on the circuit board 540 and a circuit system 590b electrically connected to the circuit board 540 via terminals 514.

[0319] The antenna 517 is not limited to a coil shape; for example, it may be linear or plate-shaped. Alternatively, antennas such as planar antennas, aperture antennas, traveling wave antennas, EH antennas, magnetic field antennas, and dielectric antennas may be used. Alternatively, the antenna 517 may be a flat conductor. This flat conductor can function as one of the conductors for electric field coupling. In other words, the antenna 517 may function as one of the two conductors of the capacitor. This allows for power exchange not only through electromagnetic and magnetic fields, but also through electric fields.

[0320] The secondary battery pack 531 has a layer 519 between the antenna 517 and the secondary battery 513. The layer 519 has the function of shielding, for example, the electromagnetic field from the secondary battery 513. For the layer 519, a magnetic material can be used, for example.

[0321] This embodiment can be freely combined with other embodiments.

[0322] (Embodiment 5) This embodiment shows an example of fabricating an all-solid-state battery using the positive electrode active material 100 obtained in Embodiment 1.

[0323] As shown in Figure 15A, a secondary battery 400 according to one embodiment of the present invention has a positive electrode 410, a solid electrolyte layer 420, and a negative electrode 430.

[0324] The positive electrode 410 has a positive electrode current collector 413 and a positive electrode active material layer 414. The positive electrode active material layer 414 has a positive electrode active material 411 and a solid electrolyte 421. The positive electrode active material 411 is the positive electrode active material 100 obtained in Embodiment 1, and the positive electrode active material layer 414 may also have a conductive additive and a binder.

[0325] The solid electrolyte layer 420 has a solid electrolyte 421. The solid electrolyte layer 420 is located between the positive electrode 410 and the negative electrode 430 and is a region that does not contain either the positive electrode active material 411 or the negative electrode active material 431.

[0326] The negative electrode 430 has a negative electrode current collector 433 and a negative electrode active material layer 434. The negative electrode active material layer 434 has a negative electrode active material 431 and a solid electrolyte 421. The negative electrode active material layer 434 may also have a conductive additive and a binder. When metallic lithium is used for the negative electrode 430, the negative electrode 430 can be made without the solid electrolyte 421, as shown in Figure 15B. Using metallic lithium for the negative electrode 430 is preferable because it can improve the energy density of the secondary battery 400.

[0327] As the solid electrolyte 421 in the solid electrolyte layer 420, for example, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a halogen-based solid electrolyte, etc., can be used.

[0328] Sulfide-based solid electrolytes include thiolysicone-based (Li 10 GeP2S 12 Li 3.25 Ge 0.25 P 0.75 S4, etc.), sulfide glass (70Li2S·30P2S5, 30Li2S·26B2S3·44LiI, 63Li2S·36SiS2·1Li3PO4, 57Li2S·38SiS2·5Li4SiO4, 50Li2S·50GeS2, etc.), sulfide crystallized glass (Li7P3S 11 Li 3.25 P 0.95 It contains S4, etc. Sulfide-based solid electrolytes have advantages such as the availability of materials with high conductivity, the ability to be synthesized at low temperatures, and their relatively soft nature which helps maintain conductive paths even after charging and discharging.

[0329] Oxide-based solid electrolytes include materials having a perovskite-type crystal structure (La 2 / 3-x Li 3x Materials having a NASICON-type crystal structure (Li 1-Y Al Y Ti 2-Y (PO4)3 etc.) Materials having a garnet-type crystal structure (Li7La3Zr2O 12 Materials having a LISICON-type crystal structure (Li 14 ZnGe4O 16 etc.), LLZO(Li7La3Zr2O 12 ), oxide glass (Li3PO4-Li4SiO4, 50Li4SiO4·50Li3BO3, etc.), oxide crystallized glass (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.

[0330] Halide-based solid electrolytes include LiAlCl4, Li3InBr6, LiF, LiCl, LiBr, LiI, etc. In addition, composite materials in which these halide-based solid electrolytes are filled in the pores of porous aluminum oxide or porous silica can also be used as solid electrolytes.

[0331] Also, different solid electrolytes may be mixed and used.

[0332] Among them, Li 1+x Al x Ti 2-x (PO4)3 (0 〔x 〔1) (hereinafter referred to as LATP) contains aluminum and titanium, which are elements that the positive electrode active material used in the secondary battery 400 of one aspect of the present invention may have. Therefore, a synergistic effect can be expected for improving the cycle characteristics, which is preferable. In addition, an improvement in productivity due to a reduction in processes can also be expected. In this specification, etc., the NASICON type crystal structure refers to a compound represented by M2(XO4)3 (M: transition metal, X: S, P, As, Mo, W, etc.), and has a structure in which MO6 octahedra and XO4 tetrahedra share vertices and are three-dimensionally arranged.

[0333] 〔Shape of the exterior body and the secondary battery〕 For the exterior body of the secondary battery 400 of one aspect of the present invention, various materials and shapes can be used, but it is preferable to have a function of pressing the positive electrode, the solid electrolyte layer, and the negative electrode.

[0334] For example, FIG. 16 is an example of a cell for evaluating the materials of an all-solid-state battery.

[0335] Figure 16A is a schematic cross-sectional view of the evaluation cell, which has a lower member 761, an upper member 762, and fixing screws or wing nuts 764 that secure them together. The evaluation material is fixed by pressing the electrode plate 753 by rotating the retaining screw 763. An insulator 766 is provided between the lower member 761 and the upper member 762, which are made of stainless steel. An O-ring 765 for sealing is provided between the upper member 762 and the retaining screw 763.

[0336] The evaluation material is placed on an electrode plate 751, surrounded by an insulating tube 752, and pressed from above by an electrode plate 753. Figure 16B is a magnified perspective view of the area around this evaluation material.

[0337] As an example of the evaluated material, an example of a stacked structure consisting of a positive electrode 750a, a solid electrolyte layer 750b, and a negative electrode 750c is shown, and a cross-sectional view is shown in Figure 16C. Note that the same parts are referred to in Figures 16A to 16C.

[0338] The electrode plate 751 and lower member 761, which are electrically connected to the positive electrode 750a, can be considered to correspond to the positive electrode terminal. The electrode plate 753 and upper member 762, which are electrically connected to the negative electrode 750c, can be considered to correspond to the negative electrode terminal. Electrical resistance and other parameters can be measured while applying pressure to the evaluation material via the electrode plates 751 and 753.

[0339] Furthermore, it is preferable to use a package with excellent airtightness for the outer casing of a secondary battery according to one embodiment of the present invention. For example, a ceramic package or a resin package can be used. Also, when sealing the outer casing, it is preferable to block out the outside air and perform the sealing in a sealed atmosphere, for example, inside a glove box.

[0340] Figure 17A shows a perspective view of a secondary battery according to one embodiment of the present invention, having a different exterior and shape from that of Figure 16. The secondary battery in Figure 17A has external electrodes 771 and 772 and is sealed with an exterior having a plurality of package members.

[0341] Figure 17B shows an example of a cross-section cut by the dashed line in Figure 17A. The laminate having a positive electrode 750a, a solid electrolyte layer 750b, and a negative electrode 750c is enclosed and sealed by a package member 770a having an electrode layer 773a on a flat plate, a frame-shaped package member 770b, and a package member 770c having an electrode layer 773b on a flat plate. Insulating materials, such as resin materials or ceramics, can be used for the package members 770a, 770b, and 770c.

[0342] The external electrode 771 is electrically connected to the positive electrode 750a via the electrode layer 773a and functions as a positive electrode terminal. The external electrode 772 is electrically connected to the negative electrode 750c via the electrode layer 773b and functions as a negative electrode terminal.

[0343] By using the positive electrode active material 100 obtained in Embodiments 1 and 2, an all-solid-state secondary battery with high energy density and good output characteristics can be realized.

[0344] This embodiment can be used in appropriate combination with other embodiments.

[0345] (Embodiment 6) This embodiment is a different example from Figure 9D, which is a cylindrical secondary battery. Figures 18A, 18B, and 18C illustrate an example of its application to an electric vehicle (EV).

[0346] Electric vehicles are equipped with a first battery 1301a and 1301b as the main secondary battery for propulsion, and a second battery 1311 that supplies power to the inverter 1312 that starts the motor 1304. The second battery 1311 is also called the cranking battery (or starter battery). The second battery 1311 only needs to be able to output power, and does not require a large capacity, so its capacity is smaller than that of the first batteries 1301a and 1301b.

[0347] The internal structure of the first battery 1301a may be a wound type as shown in Figure 10A or Figure 11C, or a stacked type as shown in Figure 12A or Figure 12B. Furthermore, the first battery 1301a may use the all-solid-state battery of Embodiment 5. Using the all-solid-state battery of Embodiment 5 for the first battery 1301a allows for higher capacity, improved safety, and miniaturization and weight reduction.

[0348] In this embodiment, an example is shown in which two first batteries 1301a and 1301b are connected in parallel, but three or more may be connected in parallel. Also, if the first battery 1301a can store sufficient power, the first battery 1301b may not be necessary. By configuring a battery pack with multiple secondary batteries, a large amount of power can be extracted. Multiple secondary batteries may be connected in parallel, in series, or connected in parallel and then in series. Multiple secondary batteries are also called a battery pack.

[0349] Furthermore, the vehicle-mounted secondary battery has a service plug or circuit breaker that can cut off high voltage without using tools in order to interrupt power from multiple secondary batteries, and this is provided in the first battery 1301a.

[0350] Furthermore, the power from the first batteries 1301a and 1301b is mainly used to rotate the motor 1304, but also supplies power to 42V onboard components (electric power steering 1307, heater 1308, defogger 1309, etc.) via the DC-DC circuit 1306. If a rear motor 1317 is located on the rear wheels, the first battery 1301a is used to rotate the rear motor 1317.

[0351] Furthermore, the second battery 1311 supplies power to 14V automotive components (audio 1313, power windows 1314, lights 1315, etc.) via the DC-DC circuit 1310.

[0352] Furthermore, the first battery 1301a will be explained using Figure 18A.

[0353] Figure 18A shows an example where nine rectangular secondary batteries 1300 are arranged in a single battery pack 1415. In this example, nine rectangular secondary batteries 1300 are connected in series, with one electrode fixed by an insulating fixing part 1413 and the other electrode fixed by an insulating fixing part 1414. While this embodiment shows an example of fixing with fixing parts 1413 and 1414, the batteries may also be housed in a battery housing box (also called a casing). Since vehicles are expected to be subjected to vibrations or shaking from external sources (such as the road surface), it is preferable to fix multiple secondary batteries in a battery housing box or similar structure using fixing parts 1413 and 1414. Furthermore, one electrode is electrically connected to the control circuit unit 1320 by wiring 1421, and the other electrode is electrically connected to the control circuit unit 1320 by wiring 1422.

[0354] Furthermore, the control circuit unit 1320 may also use a memory circuit that includes a transistor made of an oxide semiconductor. A charging control circuit or battery control system having a memory circuit that includes a transistor made of an oxide semiconductor may be referred to as a BTOS (Battery operating system or Battery oxide semiconductor).

[0355] It is preferable to use a metal oxide that functions as an oxide semiconductor. For example, as the oxide, a metal oxide such as In-M-Zn oxide (where element M is one or more selected from aluminum, gallium, yttrium, copper, vanadium, beryllium, boron, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, or magnesium, etc.) is preferable. In particular, the In-M-Zn oxide that can be applied as the oxide is preferably CAAC-OS (C-Axis Aligned Crystal Oxide Semiconductor) or CAC-OS (Cloud-Aligned Composite Oxide Semiconductor). Alternatively, In-Ga oxide or In-Zn oxide may be used as the oxide. CAAC-OS is an oxide semiconductor having multiple crystalline regions, the c-axis of which is oriented in a specific direction. The specific direction is the thickness direction of the CAAC-OS film, the normal direction to the surface on which the CAAC-OS film is formed, or the normal direction to the surface of the CAAC-OS film. Furthermore, a crystalline region is a region in which the atomic arrangement has periodicity. If the atomic arrangement is considered as a lattice arrangement, then a crystalline region is also a region in which the lattice arrangement is aligned. In addition, CAAC-OS has regions in which multiple crystalline regions are connected in the ab-plane direction, and these regions may have distortion. Distortion refers to a point in a region in which multiple crystalline regions are connected where the orientation of the lattice arrangement changes between a region in which the lattice arrangement is aligned and another region in which the lattice arrangement is aligned. In other words, CAAC-OS is an oxide semiconductor that is c-axis oriented and does not have a clear orientation in the ab-plane direction. Furthermore, CAC-OS is a material composition in which, for example, elements constituting a metal oxide are unevenly distributed in sizes of 0.5 nm to 10 nm, preferably 1 nm to 3 nm, or close to that size. In the following, in a metal oxide, a state in which one or more metal elements are unevenly distributed, and regions containing these metal elements are mixed in sizes of 0.5 nm to 10 nm, preferably 1 nm to 3 nm, or close to that size, is also referred to as a mosaic or patchy state.

[0356] Furthermore, CAC-OS is a composite metal oxide having a mosaic-like structure formed by the separation of the material into a first region and a second region, with the first region distributed within the film (hereinafter also referred to as a cloud-like structure). In other words, CAC-OS is a composite metal oxide having a structure in which the first region and the second region are mixed.

[0357] Here, the atomic ratios of In, Ga, and Zn to the metal elements constituting the CAC-OS in In-Ga-Zn oxide are denoted as [In], [Ga], and [Zn], respectively. For example, in the CAC-OS of In-Ga-Zn oxide, the first region is the region where [In] is greater than the [In] in the composition of the CAC-OS film. The second region is the region where [Ga] is greater than the [Ga] in the composition of the CAC-OS film. Alternatively, for example, the first region is the region where [In] is greater than the [In] in the second region, and [Ga] is smaller than the [Ga] in the second region. The second region is the region where [Ga] is greater than the [Ga] in the first region, and [In] is smaller than the [In] in the first region.

[0358] Specifically, the first region described above is a region whose main components are indium oxide, indium zinc oxide, etc. The second region described above is a region whose main components are gallium oxide, gallium zinc oxide, etc. In other words, the first region can be rephrased as a region whose main component is In. Similarly, the second region can be rephrased as a region whose main component is Ga.

[0359] Furthermore, a clear boundary may not be observed between the first region and the second region described above.

[0360] For example, in the case of CAC-OS in In-Ga-Zn oxide, EDX mapping obtained using energy dispersive X-ray spectroscopy (EDX) confirms that it has a structure in which regions mainly composed of In (first region) and regions mainly composed of Ga (second region) are unevenly distributed and mixed.

[0361] When CAC-OS is used in a transistor, the conductivity due to the first region and the insulation due to the second region work complementaryly to give CAC-OS a switching function (on / off function). In other words, CAC-OS has conductive function in part of the material, insulating function in part of the material, and semiconductor function as a whole. By separating the conductive function and the insulating function, both functions can be maximized. Therefore, by using CAC-OS in a transistor, a high on-current (I) can be achieved. on This enables high field-effect mobility (μ) and good switching operation.

[0362] Oxide semiconductors can take on diverse structures, each possessing different properties. One embodiment of the present invention may include two or more of the following: amorphous oxide semiconductors, polycrystalline oxide semiconductors, a-like OS, CAC-OS, nc-OS, and CAAC-OS.

[0363] Furthermore, since it can be used in high-temperature environments, it is preferable that the control circuit section 1320 uses a transistor made of an oxide semiconductor. To simplify the process, the control circuit section 1320 may be formed using a unipolar transistor. Transistors using an oxide semiconductor in the semiconductor layer have an operating ambient temperature range of -40°C to 150°C, which is wider than that of single-crystal Si, and the change in characteristics is smaller than that of single crystal even when the secondary battery is heated. The off-current of a transistor using an oxide semiconductor is below the lower limit of measurement regardless of temperature, even at 150°C, but the off-current characteristics of a single-crystal Si transistor are highly temperature-dependent. For example, at 150°C, the off-current of a single-crystal Si transistor increases, and the current on / off ratio does not become sufficiently large. The control circuit section 1320 can improve safety. In addition, a synergistic effect on safety can be obtained by combining it with a secondary battery that uses the positive electrode active material 100 obtained in Embodiments 1 and 2 as the positive electrode. The secondary battery and control circuit unit 1320 using the positive electrode active material 100 obtained in Embodiments 1 and 2 as the positive electrode can greatly contribute to eliminating accidents such as fires caused by secondary batteries.

[0364] The control circuit unit 1320, which uses a memory circuit including an oxide semiconductor transistor, can also function as an automatic control device for secondary batteries to address 10 causes of instability, such as micro-short circuits. Functions to eliminate the 10 causes of instability include overcharge prevention, overcurrent prevention, overheat control during charging, cell balancing in the battery pack, over-discharge prevention, remaining charge indicator, automatic control of charging voltage and current according to temperature, charging current control according to the degree of degradation, detection of abnormal behavior of micro-short circuits, and prediction of abnormalities related to micro-short circuits. The control circuit unit 1320 has at least one of these functions. Furthermore, it is possible to miniaturize the automatic control device for secondary batteries.

[0365] Furthermore, a micro-short refers to a tiny short circuit inside a secondary battery. It does not mean that the positive and negative electrodes of the secondary battery are short-circuited, making charging and discharging impossible. Rather, it refers to a phenomenon where a small short-circuit current flows through a tiny short circuit. Because even a relatively short-circuit in a small area can cause a large voltage change, the abnormal voltage value may affect subsequent estimations.

[0366] One of the causes of micro-short circuits is said to be that multiple charge-discharge cycles result in an uneven distribution of the positive electrode active material, causing localized current concentration in parts of the positive and negative electrodes, leading to areas where the separator malfunctions, or causing micro-short circuits due to the generation of by-reactants from side reactions.

[0367] Furthermore, in addition to detecting micro-shorts, the control circuit unit 1320 also detects the terminal voltage of the secondary battery and manages the charging and discharging state of the secondary battery. For example, to prevent overcharging, both the output transistor and the cutoff switch of the charging circuit can be turned off almost simultaneously.

[0368] Furthermore, an example of a block diagram of the battery pack 1415 shown in Figure 18A is shown in Figure 18B.

[0369] The control circuit unit 1320 includes at least a switch to prevent overcharging, a switch unit 1324 including a switch to prevent over-discharging, a control circuit 1322 that controls the switch unit 1324, and a voltage measurement unit for the first battery 1301a. The control circuit unit 1320 has upper and lower voltage limits set for the secondary battery used, and limits the upper limit of external current or the upper limit of output current to the outside. Within the range between the lower voltage and upper voltage of the secondary battery, it is within the recommended voltage range for use, and if it goes outside this range, the switch unit 1324 activates and functions as a protection circuit. The control circuit unit 1320 can also be called a protection circuit because it controls the switch unit 1324 to prevent over-discharge or overcharge. For example, if the control circuit 1322 detects a voltage that is likely to cause overcharging, it cuts off the current by turning off the switch in the switch unit 1324. Furthermore, a PTC element may be provided in the charge / discharge path to provide a function to cut off the current in response to the rise in temperature. Furthermore, the control circuit unit 1320 has an external terminal 1325 (+IN) and an external terminal 1326 (-IN).

[0370] The switch section 1324 can be constructed by combining n-channel or p-channel transistors. The switch section 1324 is not limited to switches using Si transistors made of single-crystal silicon, but may also be formed using power transistors made of, for example, Ge (germanium), SiGe (silicon germanium), GaAs (gallium arsenide), GaAlAs (gallium aluminum arsenide), InP (indium phosphide), SiC (silicon carbide), ZnSe (zinc selenide), GaN (gallium nitride), GaOx (gallium oxide; x is a real number greater than 0), etc. Furthermore, since memory elements using OS transistors can be freely arranged by stacking them on circuits using Si transistors, integration can be easily achieved. Also, since OS transistors can be manufactured using the same manufacturing equipment as Si transistors, they can be manufactured at low cost. That is, by stacking a control circuit section 1320 using OS transistors on the switch section 1324 and integrating them, it is possible to create a single chip. This makes it possible to reduce the occupied volume of the control circuit section 1320, thus enabling miniaturization.

[0371] The first batteries 1301a and 1301b primarily supply power to 42V (high-voltage) onboard equipment, while the second battery 1311 supplies power to 14V (low-voltage) onboard equipment. Lead-acid batteries are often used for the second battery 1311 due to their cost advantages. Lead-acid batteries have the disadvantage of higher self-discharge and are prone to degradation due to a phenomenon called sulfation compared to lithium-ion secondary batteries. Using a lithium-ion secondary battery for the second battery 1311 offers the advantage of being maintenance-free, but after long-term use, for example more than three years, there is a risk of malfunctions occurring that could not be detected at the time of manufacture. In particular, if the second battery 1311, which starts the inverter, becomes inoperable, it will be impossible to start the motor even if the first batteries 1301a and 1301b have remaining capacity. To prevent this, if the second battery 1311 is a lead-acid battery, power is supplied from the first battery to the second battery to keep it constantly charged to a full state.

[0372] This embodiment shows an example in which lithium-ion secondary batteries are used for both the first battery 1301a and the second battery 1311. The second battery 1311 may be a lead-acid battery, an all-solid-state battery, or an electric double-layer capacitor. For example, the all-solid-state battery of Embodiment 5 may be used. By using the all-solid-state battery of Embodiment 5 for the second battery 1311, high capacity can be achieved, and the device can be made smaller and lighter.

[0373] Furthermore, the regenerative energy generated by the rotation of the tire 1316 is sent to the motor 1304 via the gear 1305 and charged to the second battery 1311 via the control circuit unit 1321 from the motor controller 1303 or battery controller 1302. Alternatively, it is charged to the first battery 1301a via the control circuit unit 1320 from the battery controller 1302. Alternatively, it is charged to the first battery 1301b via the control circuit unit 1320 from the battery controller 1302. In order to efficiently charge the regenerative energy, it is desirable that the first batteries 1301a and 1301b are capable of rapid charging.

[0374] The battery controller 1302 can set the charging voltage and charging current of the first batteries 1301a and 1301b. The battery controller 1302 can set the charging conditions according to the charging characteristics of the secondary battery being used and enable rapid charging.

[0375] Although not shown in the diagram, when connected to an external charger, the charger's outlet or connection cable is electrically connected to the battery controller 1302. Power supplied from the external charger charges the first batteries 1301a and 1301b via the battery controller 1302. In some chargers, a control circuit is provided, and the functions of the battery controller 1302 may not be used, but it is preferable to charge the first batteries 1301a and 1301b via the control circuit unit 1320 to prevent overcharging. In some cases, the connection cable or the charger's connection cable may also have a control circuit. The control circuit unit 1320 is sometimes called an ECU (Electronic Control Unit). The ECU is connected to a CAN (Controller Area Network) installed in the electric vehicle. CAN is one of the serial communication standards used as an in-vehicle LAN. The ECU also includes a microcomputer. The ECU also uses a CPU or GPU.

[0376] External chargers installed at charging stations and other locations may have 100V outlets, 200V outlets, or 3-phase 200V and 50kW outputs. Additionally, it is possible to charge by receiving power from external charging equipment using contactless power supply methods.

[0377] For fast charging, to charge in a short time, Li x A secondary battery capable of withstanding charging such that x in CoO2 becomes 0.24 or less is desired.

[0378] Furthermore, the secondary battery of this embodiment described above has a high-density positive electrode by using the positive electrode active material 100 obtained in Embodiments 1 and 2. In addition, by using graphene as a conductive additive, the capacity reduction is suppressed even when the electrode layer is thickened and the load is increased, and high capacity is maintained. As a synergistic effect, a secondary battery with significantly improved electrical characteristics can be realized. This is particularly effective for secondary batteries used in vehicles, and it is possible to provide a vehicle with a long driving range, specifically a driving range of 500 km or more on a single charge, without increasing the ratio of the weight of the secondary battery to the total weight of the vehicle.

[0379] In particular, the secondary battery of this embodiment described above can achieve a higher operating voltage by using the positive electrode active material 100 described in Embodiment 1, and the usable capacity can be increased with increasing charging voltage. Furthermore, by using the positive electrode active material 100 described in Embodiment 1 as the positive electrode, a secondary battery for vehicles with excellent cycle characteristics can be provided.

[0380] Next, we will describe an example in which a secondary battery, which is one aspect of the present invention, is implemented in a vehicle, typically a transport vehicle.

[0381] Furthermore, by mounting a secondary battery shown in any one of Figures 9D, 11C, or 18A onto a vehicle, next-generation clean energy vehicles such as hybrid vehicles (HV), electric vehicles (EV), or plug-in hybrid vehicles (PHV) can be realized. Secondary batteries can also be mounted on agricultural machinery, motorized bicycles including electric-assist bicycles, motorcycles, electric wheelchairs, electric carts, small or large vessels, submarines, aircraft such as fixed-wing or rotary-wing aircraft, rockets, satellites, space probes or planetary probes, and other transport vehicles. A secondary battery according to one embodiment of the present invention can be a high-capacity secondary battery. Therefore, a secondary battery according to one embodiment of the present invention is suitable for miniaturization and weight reduction, and can be suitably used in transport vehicles.

[0382] Figures 19A to 19D illustrate a transport vehicle using one embodiment of the present invention. The automobile 2001 shown in Figure 19A is an electric vehicle that uses an electric motor as a power source for driving. Alternatively, it is a hybrid vehicle that can appropriately select and use an electric motor and an engine as power sources for driving. When a secondary battery is mounted on the vehicle, one or more examples of the secondary battery shown in Embodiment 4 are installed in one location. The automobile 2001 shown in Figure 19A has a battery pack 2200, and the battery pack has a secondary battery module in which multiple secondary batteries are connected. Furthermore, it is preferable to have a charging control device electrically connected to the secondary battery module.

[0383] Furthermore, the automobile 2001 can be charged by receiving power from an external charging facility via a plug-in or contactless power supply method to the secondary battery it possesses. For charging, the charging method or connector specifications may be carried out appropriately using a prescribed method such as CHAdeMO® or Combo. The secondary battery may be a charging station installed in a commercial facility, or it may be a household power supply. For example, the energy storage device mounted on the automobile 2001 can be charged by an external power supply using plug-in technology. Charging can be performed by converting AC power to DC power via a conversion device such as an AC / DC converter.

[0384] Although not shown in the diagram, the vehicle can also be charged by mounting a power receiving device on the vehicle and receiving power wirelessly from a ground-based power transmission device. In this wireless power supply method, charging can be performed not only when the vehicle is stopped but also while it is in motion by incorporating the power transmission device into the road or exterior wall. Furthermore, this wireless power supply method can be used to transmit and receive power between two vehicles. In addition, solar panels can be installed on the exterior of the vehicle to charge the secondary battery when the vehicle is stopped or in motion. For such wireless power supply, electromagnetic induction or magnetic resonance methods can be used.

[0385] Figure 19B shows a large transport vehicle 2002 equipped with an electrically controlled motor as an example of a transport vehicle. The secondary battery module of the transport vehicle 2002 has a maximum voltage of 170V, achieved by connecting 48 cells in series, each consisting of four secondary batteries with a nominal voltage of 3.0V to 5.0V. The secondary battery module of the battery pack 2201 has the same functions as Figure 19A, except for differences in the number of secondary batteries that make up the module, so the explanation is omitted.

[0386] Figure 19C shows, as an example, a large transport vehicle 2003 equipped with an electrically controlled motor. The secondary battery module of the transport vehicle 2003 has a maximum voltage of 600V, achieved by connecting more than 100 secondary batteries with a nominal voltage of 3.0V to 5.0V in series. Therefore, secondary batteries with small variation in characteristics are required. By using a secondary battery that uses the positive electrode active material 100 described in Embodiment 1 as the positive electrode, it is possible to manufacture a secondary battery with stable battery characteristics, enabling low-cost mass production from a yield standpoint. Furthermore, since it has the same functions as Figure 19A except for differences in the number of secondary batteries constituting the secondary battery module of the battery pack 2202, the explanation is omitted.

[0387] Figure 19D shows an aircraft 2004 having a fuel-burning engine as an example. The aircraft 2004 shown in Figure 19D has landing gear for takeoff and landing, and can therefore be considered part of a transport vehicle. It has a battery pack 2203 which includes a secondary battery module formed by connecting multiple secondary batteries and a charging control device.

[0388] The secondary battery module of aircraft 2004 has a maximum voltage of 32V, for example, by connecting eight 4V secondary batteries in series. The secondary battery module of battery pack 2203 has the same functionality as Figure 19A, except for differences in the number of secondary batteries that make up the module, so the explanation is omitted.

[0389] This embodiment can be used in appropriate combination with other embodiments.

[0390] (Embodiment 7) In this embodiment, an example of implementing a secondary battery, which is one aspect of the present invention, in a building will be explained using Figures 20A and 20B.

[0391] The house shown in Figure 20A has a power storage device 2612 having a secondary battery, which is one embodiment of the present invention, and a solar panel 2610. The power storage device 2612 is electrically connected to the solar panel 2610 via wiring 2611, etc. The power storage device 2612 may also be electrically connected to a ground-mounted charging device 2604. The electricity obtained from the solar panel 2610 can be used to charge the power storage device 2612. The electricity stored in the power storage device 2612 can be used to charge the secondary battery of the vehicle 2603 via the charging device 2604. The power storage device 2612 is preferably installed in the underfloor space. By installing it in the underfloor space, the space above the floor can be used effectively. Alternatively, the power storage device 2612 may be installed on the floor.

[0392] The electricity stored in the energy storage device 2612 can also supply power to other electronic devices in the house. Therefore, even when power cannot be supplied from the commercial power source due to a power outage or the like, electronic devices can be used by using the energy storage device 2612 according to one aspect of the present invention as an uninterruptible power supply.

[0393] Figure 20B shows an example of an energy storage device 700 according to one aspect of the present invention. As shown in Figure 20B, an energy storage device 791 according to one aspect of the present invention is installed in the underfloor space 796 of the building 799. Furthermore, the control circuit described in Embodiment 6 may be provided in the energy storage device 791, and a synergistic effect on safety can be obtained by using a secondary battery with the positive electrode active material 100 obtained in Embodiments 1 and 2 as the positive electrode in the energy storage device 791. The control circuit described in Embodiment 6 and the secondary battery with the positive electrode active material 100 described in Embodiment 1 as the positive electrode can greatly contribute to eliminating accidents such as fires caused by the energy storage device 791 having a secondary battery.

[0394] The energy storage device 791 is equipped with a control device 790, which is electrically connected by wiring to the distribution board 703, the energy storage controller 705 (also called the control device), the display unit 706, and the router 709.

[0395] Power is supplied from the commercial power supply 701 to the distribution panel 703 via the service drop connection section 710. Power is also supplied to the distribution panel 703 from the energy storage device 791 and the commercial power supply 701, and the distribution panel 703 supplies the supplied power to the general load 707 and the energy storage system load 708 via outlets (not shown).

[0396] General load 707 is, for example, an electrical device such as a television or a personal computer, and energy storage load 708 is, for example, an electrical device such as a microwave oven, refrigerator, or air conditioner.

[0397] The energy storage controller 705 includes a measurement unit 711, a prediction unit 712, and a planning unit 713. The measurement unit 711 has the function of measuring the amount of electricity consumed by the general load 707 and the energy storage system load 708 during a day (for example, from 0:00 to 24:00). The measurement unit 711 may also have the function of measuring the amount of electricity consumed by the energy storage device 791 and the amount of electricity supplied from the commercial power supply 701. The prediction unit 712 has the function of predicting the amount of electricity demanded by the general load 707 and the energy storage system load 708 during the next day, based on the amount of electricity consumed by the general load 707 and the energy storage system load 708 during the day. The planning unit 713 has the function of planning the charging and discharging of the energy storage device 791 based on the amount of electricity demand predicted by the prediction unit 712.

[0398] The amount of electricity consumed by the general load 707 and the energy storage system load 708, as measured by the measurement unit 711, can be checked on the display unit 706. It can also be checked via the router 709 on electrical equipment such as televisions or personal computers. Furthermore, it can be checked via the router 709 on portable electronic devices such as smartphones or tablets. Additionally, the amount of electricity demand predicted by the forecasting unit 712 for each time period (or hourly) can be checked on the display unit 706, electrical equipment, and portable electronic devices.

[0399] This embodiment can be used in appropriate combination with other embodiments.

[0400] (Embodiment 8) This embodiment shows an example of mounting an energy storage device according to one aspect of the present invention on a motorcycle or bicycle.

[0401] Furthermore, Figure 21A shows an example of an electric bicycle using a power storage device according to one embodiment of the present invention. The power storage device according to one embodiment of the present invention can be applied to the electric bicycle 8700 shown in Figure 21A. The power storage device according to one embodiment of the present invention includes, for example, a plurality of storage batteries and a protection circuit.

[0402] The electric bicycle 8700 is equipped with a power storage device 8702. The power storage device 8702 can supply electricity to a motor that assists the rider. The power storage device 8702 is also portable, and Figure 21B shows it detached from the bicycle. The power storage device 8702 also has multiple built-in batteries 8701, which are part of a power storage device according to one embodiment of the present invention, and the remaining battery level can be displayed on a display unit 8703. The power storage device 8702 also has a control circuit 8704 capable of controlling the charging of a secondary battery or detecting abnormalities, as exemplified in Embodiment 6. The control circuit 8704 is electrically connected to the positive and negative electrodes of the batteries 8701. A small solid-state secondary battery, as shown in Figures 17A and 17B, may also be provided in the control circuit 8704. By providing the small solid-state secondary battery shown in Figures 17A and 17B in the control circuit 8704, power can also be supplied to hold data in the memory circuit of the control circuit 8704 for a long period of time. Furthermore, a synergistic effect on safety can be obtained by combining the positive electrode active material 100 obtained in Embodiments 1 and 2 with a secondary battery that uses the positive electrode as the positive electrode. The secondary battery and control circuit 8704 that use the positive electrode active material 100 obtained in Embodiments 1 and 2 as the positive electrode can greatly contribute to eliminating accidents such as fires caused by secondary batteries.

[0403] Furthermore, Figure 21C shows an example of a two-wheeled vehicle using a power storage device according to one embodiment of the present invention. The scooter 8600 shown in Figure 21C is equipped with a power storage device 8602, side mirrors 8601, and turn signals 8603. The power storage device 8602 can supply electricity to the turn signals 8603. In addition, the power storage device 8602, which houses multiple secondary batteries using the positive electrode active material 100 obtained in Embodiments 1 and 2 as the positive electrode, can have a high capacity and contribute to miniaturization.

[0404] Furthermore, the scooter 8600 shown in Figure 21C can accommodate the power storage device 8602 in the under-seat storage compartment 8604. The power storage device 8602 can be stored in the under-seat storage compartment 8604 even if the under-seat storage compartment 8604 is small.

[0405] (Embodiment 9) This embodiment describes an example of mounting a secondary battery, which is one aspect of the present invention, in an electronic device. Examples of electronic devices on which a secondary battery is mounted include television equipment (also called televisions or television receivers), monitors for computers, digital cameras, digital video cameras, digital photo frames, mobile phones (also called mobile phones or mobile phone devices), portable game consoles, personal information terminals, sound playback devices, and large game machines such as pachinko machines. Personal information terminals include notebook personal computers, tablet terminals, e-book readers, and mobile phones.

[0406] Figure 22A shows an example of a mobile phone. The mobile phone 2100 includes a display unit 2102 built into the housing 2101, as well as operation buttons 2103, an external connection port 2104, a speaker 2105, a microphone 2106, and the like. The mobile phone 2100 also has a secondary battery 2107. By providing a secondary battery 2107 that uses the positive electrode active material 100 described in Embodiment 1 as the positive electrode, a high capacity can be achieved, and a configuration that can accommodate space saving due to the miniaturization of the housing can be realized.

[0407] The mobile phone 2100 can run various applications such as making phone calls, sending emails, reading and creating documents, playing music, communicating on the internet, and playing computer games.

[0408] The operation button 2103 can be assigned various functions, including time setting, power on / off operation, wireless communication on / off operation, silent mode activation / deactivation, and power saving mode activation / deactivation. For example, the function of the operation button 2103 can be freely configured by the operating system built into the mobile phone 2100.

[0409] Furthermore, the 2100 mobile phone is capable of performing standardized short-range wireless communication. For example, it can communicate with a wireless headset to enable hands-free calling.

[0410] Furthermore, the mobile phone 2100 is equipped with an external connection port 2104, which allows for direct data exchange with other information terminals via a connector. It can also be charged via the external connection port 2104. Note that charging may also be performed wirelessly without using the external connection port 2104.

[0411] The mobile phone 2100 preferably has sensors. Preferably, the sensors include, for example, human body sensors such as fingerprint sensors, pulse sensors, and body temperature sensors, or touch sensors, pressure sensors, acceleration sensors, etc.

[0412] Figure 22B shows an unmanned aerial vehicle 2300 having multiple rotors 2302. The unmanned aerial vehicle 2300 is sometimes called a drone. The unmanned aerial vehicle 2300 has a secondary battery 2301, a camera 2303, and an antenna (not shown), which are embodiments of the present invention. The unmanned aerial vehicle 2300 can be remotely controlled via the antenna. The secondary battery using the positive electrode active material 100 obtained in Embodiments 1 and 2 as the positive electrode has a high energy density and high safety, so it can be used safely for a long period of time over a long period of time and is suitable as a secondary battery to be mounted on an unmanned aerial vehicle 2300.

[0413] Figure 22C shows an example of a robot. The robot 6400 shown in Figure 22C is equipped with a secondary battery 6409, an illuminance sensor 6401, a microphone 6402, an upper camera 6403, a speaker 6404, a display unit 6405, a lower camera 6406 and an obstacle sensor 6407, a movement mechanism 6408, a computing device, and the like.

[0414] Microphone 6402 has the function of detecting the user's voice and ambient sounds. Speaker 6404 has the function of emitting sound. Robot 6400 can communicate with the user using microphone 6402 and speaker 6404.

[0415] The display unit 6405 has the function of displaying various types of information. The robot 6400 can display the information desired by the user on the display unit 6405. The display unit 6405 may be equipped with a touch panel. The display unit 6405 may also be a detachable information terminal, and by installing it in a fixed position on the robot 6400, charging and data transfer can be made possible.

[0416] The upper camera 6403 and lower camera 6406 have the function of imaging the area around the robot 6400. In addition, the obstacle sensor 6407 can detect the presence or absence of obstacles in the direction of travel when the robot 6400 moves forward using the movement mechanism 6408. The robot 6400 can recognize its surrounding environment and move safely using the upper camera 6403, lower camera 6406 and obstacle sensor 6407.

[0417] The robot 6400 is equipped with a secondary battery 6409 according to one aspect of the present invention and a semiconductor device or electronic components in its internal region. The secondary battery using the positive electrode active material 100 obtained in Embodiments 1 and 2 as the positive electrode has a high energy density and high safety, so it can be used safely for a long period of time over a long period of time and is suitable as a secondary battery 6409 to be mounted on the robot 6400.

[0418] Figure 22D shows an example of a cleaning robot. The cleaning robot 6300 has a display unit 6302 located on the top surface of the housing 6301, multiple cameras 6303 located on the sides, a brush 6304, operation buttons 6305, a secondary battery 6306, and various sensors. Although not shown, the cleaning robot 6300 is equipped with wheels, a suction port, etc. The cleaning robot 6300 is self-propelled, can detect dirt 6310, and can suck up the dirt from a suction port located on the bottom surface.

[0419] For example, the cleaning robot 6300 can analyze images captured by the camera 6303 to determine the presence or absence of obstacles such as walls, furniture, or steps. Furthermore, if the image analysis detects an object that could become entangled in the brush 6304, such as wiring, the rotation of the brush 6304 can be stopped. The cleaning robot 6300 is equipped with a secondary battery 6306 according to one embodiment of the present invention and a semiconductor device or electronic component within its internal region. The secondary battery using the positive electrode active material 100 obtained in Embodiments 1 and 2 as the positive electrode has high energy density and high safety, allowing for safe use over long periods, making it suitable as a secondary battery 6306 for the cleaning robot 6300.

[0420] Figure 23A shows an example of a wearable device. Wearable devices use rechargeable batteries as a power source. Furthermore, in order to enhance splash resistance, water resistance, or dust resistance when used by users in daily life or outdoors, there is a demand for wearable devices that can be charged wirelessly in addition to wired charging with exposed connectors.

[0421] For example, a secondary battery according to one embodiment of the present invention can be mounted in a spectacle-type device 4000 as shown in Figure 23A. The spectacle-type device 4000 has a frame 4000a and a display unit 4000b. By mounting the secondary battery in the temple portion of the curved frame 4000a, a lightweight spectacle-type device 4000 can be made with good weight balance and a long continuous usage time. The secondary battery using the positive electrode active material 100 obtained in Embodiment 1 and Embodiment 2 as the positive electrode has a high energy density and can realize a configuration that can accommodate space saving due to the miniaturization of the housing.

[0422] Furthermore, a secondary battery according to one aspect of the present invention can be mounted in the headset-type device 4001. The headset-type device 4001 has at least a microphone section 4001a, a flexible pipe 4001b, and an earphone section 4001c. The secondary battery can be provided in the flexible pipe 4001b or in the earphone section 4001c. The secondary battery using the positive electrode active material 100 obtained in Embodiments 1 and 2 as the positive electrode has a high energy density and can realize a configuration that can accommodate space saving due to the miniaturization of the housing.

[0423] Furthermore, a secondary battery according to one embodiment of the present invention can be mounted on a device 4002 that can be directly attached to the body. The secondary battery 4002b can be provided inside the thin housing 4002a of the device 4002. The secondary battery using the positive electrode active material 100 obtained in Embodiment 1 and Embodiment 2 as the positive electrode has a high energy density and can realize a configuration that can accommodate space saving due to the miniaturization of the housing.

[0424] Furthermore, a secondary battery according to one embodiment of the present invention can be mounted on a device 4003 that can be attached to clothing. The secondary battery 4003b can be provided inside the thin housing 4003a of the device 4003. The secondary battery using the positive electrode active material 100 obtained in Embodiment 1 and Embodiment 2 as the positive electrode has a high energy density and can realize a configuration that can accommodate space saving due to the miniaturization of the housing.

[0425] Furthermore, a secondary battery according to one embodiment of the present invention can be mounted on the belt-type device 4006. The belt-type device 4006 has a belt portion 4006a and a wireless power supply and receiving portion 4006b, and a secondary battery can be mounted in the internal region of the belt portion 4006a. The secondary battery using the positive electrode active material 100 obtained in Embodiment 1 and Embodiment 2 as the positive electrode has a high energy density and can realize a configuration that can accommodate space saving due to the miniaturization of the housing.

[0426] Furthermore, a secondary battery according to one embodiment of the present invention can be mounted in the wristwatch-type device 4005. The wristwatch-type device 4005 has a display unit 4005a and a belt unit 4005b, and the secondary battery can be provided in either the display unit 4005a or the belt unit 4005b. The secondary battery using the positive electrode active material 100 obtained in Embodiments 1 and 2 as the positive electrode has a high energy density and can realize a configuration that can accommodate space saving due to the miniaturization of the housing.

[0427] The display unit 4005a can display not only the time, but also various other information such as incoming emails or phone calls.

[0428] Furthermore, since the wristwatch-type device 4005 is a wearable device that is worn directly on the wrist, it may be equipped with sensors to measure the user's pulse, blood pressure, etc. It can accumulate data on the user's exercise level and health, and manage their health.

[0429] Figure 23B shows a perspective view of the wristwatch-type device 4005 after it has been removed from the arm.

[0430] A side view is also shown in Figure 23C. Figure 23C shows how the secondary battery 913 is built into the internal region. The secondary battery 913 is the secondary battery shown in Embodiment 4. The secondary battery 913 is located in a position that overlaps with the display unit 4005a, allowing for high density and high capacity, as well as being small and lightweight.

[0431] Since the wristwatch-type device 4005 is required to be small and lightweight, using the positive electrode active material 100 obtained in Embodiments 1 and 2 as the positive electrode of the secondary battery 913 makes it possible to create a secondary battery 913 that is both high in energy density and compact.

[0432] This embodiment can be implemented in appropriate combination with other embodiments. [Examples]

[0433] In this example, after fabricating a positive electrode active material according to one aspect of the present invention, multiple coin-shaped battery cells were manufactured, and their cycle characteristics were evaluated.

[0434] The samples prepared in this embodiment will now be described. For each sample, the positive electrode active material used was the positive electrode active material obtained by the method shown in Embodiment 1. As a pre-synthesized composite oxide, lithium cobalt oxide particles (product name: Cellseed C-10N) manufactured by Nippon Chemical Industrial Co., Ltd. were used as the positive electrode active material. Lithium fluoride (LiF) was prepared as the fluorine source, and magnesium fluoride (MgF2) was used as both the fluorine source and the magnesium source. The first heat treatment was performed at 850°C for 60 hours under an oxygen atmosphere.

[0435] Following the flow chart shown in Figure 5, a cathode active material was prepared by the sol-gel method using LiCoO2 in S14, nickel hydroxide (0.5 at%) as the additive element source in S24, and aluminum alkoxide (0.5 at%) and lanthanum as the additive element sources in S51, and a sample was prepared.

[0436] When lanthanum was used as the additive element source, high-purity tri-i-propoxylanthanum from a chemical company was used in the sol-gel method. For aluminum, aluminum isopropoxide and other aluminum alkoxides can be used. Five types of samples were prepared under the same conditions and procedures except for the amount of lanthanum oxide. The amounts of lanthanum used in the sol-gel method were 0.05 at%, 0.125 at%, 0.25 at%, 0.375 at%, and 0.5 at%. Figure 1A shows electron beam cross-sectional images of the prepared particles.

[0437] In the sol-gel method, 10 ml of 2-propanol was used as the solvent. The heat treatment conditions for the sol-gel method were heating at 850°C for 2 hours.

[0438] Acetylene black was used as a conductive additive during sample preparation. A slurry was prepared by mixing the materials, and this slurry was applied to an aluminum current collector.

[0439] After coating the current collector with slurry, the solvent was evaporated. Then, pressurization was applied at 210 kN / m, followed by further pressurization at 1467 kN / m. The positive electrode was obtained through these steps. The loading weight of the positive electrode was approximately 7 mg / cm³. 2 That's what I decided.

[0440] Using the fabricated positive electrode, a coin-shaped battery cell of the CR2032 type (20 mm in diameter, 3.2 mm in height) was created.

[0441] Lithium metal was used for the counter electrode.

[0442] For the sample electrolyte, 1 mol / L lithium hexafluoride phosphate (LiPF6) was used, and ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a volume ratio of EC:DEC = 3:7. In addition, vinylene carbonate (VC) was added as an additive at a concentration of 2 wt% relative to the total solvent.

[0443] A 25 μm thick polypropylene was used for the separator.

[0444] The positive electrode and negative electrode cans were made of stainless steel (SUS).

[0445] In evaluating the cycle characteristics, the charging voltage was set to 4.7V. The measurement temperature was 25°C. Charging was performed using CC / CV (0.5C, 0.05C cut), and discharging was performed using CC (0.5C, 2.5V cut), with a 10-minute rest period between each charge. In this embodiment, 1C was defined as 200mA / g.

[0446] The discharge rate is the relative ratio of the discharge current to the battery capacity, and is expressed in units of C. For a battery with a rated capacity of X (Ah), the current equivalent to 1C is X (A). If the battery is discharged with a current of 2X (A), it is said to have been discharged at 2C, and if it is discharged with a current of X / 5 (A), it is said to have been discharged at 0.2C. Similarly, the charge rate is also expressed in the same way: if the battery is charged with a current of 2X (A), it is said to have been charged at 2C, and if it is charged with a current of X / 5 (A), it is said to have been charged at 0.2C.

[0447] Constant current charging refers to a method of charging while maintaining a constant charging rate. Constant voltage charging refers to a method of charging while maintaining a constant voltage once the upper voltage limit is reached. Constant current discharging refers to a method of discharging while maintaining a constant discharge rate.

[0448] When the cycle characteristics of five different samples were measured, the 0.25 at% sample showed the best results. The 0.25 at% sample demonstrated that the degradation of charge / discharge capacity was suppressed even when repeatedly charging and discharging at high voltages such as 4.7V, indicating it was a superior cathode active material. Furthermore, the 0.5 at% sample showed the most degraded characteristics. Based on these results, it is preferable to adjust the lanthanum concentration to less than 0.5 at%.

[0449] Furthermore, samples were prepared using yttrium (Y) instead of lanthanum, and the cycle characteristics were measured, as shown in Figures 24A and 24B. The sol-gel method was used, and yttrium alkoxide (tri-i-propoxyyttrium manufactured by Kojunkagaku Co., Ltd.) was used. Both samples were at 0.25 at%. In Figure 24A, the vertical axis represents discharge capacity and the horizontal axis represents the number of cycles. Comparing the two conditions, lanthanum showed superior values ​​compared to yttrium.

[0450] Furthermore, samples were prepared under even more conditions. Figures 25A and 25B show the results of performing similar cycle characteristics after adding zirconium (0.25 at%, 0.125 at%, and 0.05 at%), respectively. Nickel was set to 0.5 at%, and aluminum to 0.5 at%. When using zirconium as an additive element source, zirconium alkoxides, including zirconium isopropoxide, can be used. In Figure 25A, the vertical axis represents discharge capacity, and the horizontal axis represents the number of cycles. The second heat treatment after the sol-gel method was performed at 850°C for 2 hours. In Figure 25B, the vertical axis represents the maintenance rate with the maximum discharge capacity set to 100%, and the horizontal axis represents the number of cycles.

[0451] Figures 25A and 25B show that the sample with 0.25 at% zirconium and 0.125 at% lanthanum exhibited the best characteristics. Figure 27 shows an SEM image of the positive electrode active material of this sample. Analysis of the small particles on the particle surface in Figure 27 detected lanthanum and zirconium. The discharge capacity retention rate after 50 cycles was a good 82.4%. The maximum discharge capacity was 219.6 mAh / g.

[0452] Furthermore, the characteristics of the other samples, each containing 0.05 at% zirconium and 0.125 at% lanthanum, 0.25 at% zirconium and 0.5 at% lanthanum, 0.25 at% zirconium and 0.375 at% lanthanum, 0.125 at% zirconium and 0.125 at% lanthanum, 0.25 at% zirconium and 0.25 at% lanthanum, and 0.25 at% zirconium and 0.05 at% lanthanum, are shown in Figures 25A and 25B. Note that although these samples contain lanthanum and zirconium, they do not form the LLZ known for garnet-type lithium-ion conductors. These positive electrode active material particles have an appearance with zirconium or lanthanum oxides attached to the particle surface. Also, the amount of lanthanum in the positive electrode active material of these samples is less than the amount of aluminum. Furthermore, the amount of lanthanum in the positive electrode active material of these samples is less than the amount of nickel. These concentrations can be determined using XRD, TOF-SIMS, or EDX methods. Additionally, lanthanum is not detected within the particles themselves, but rather on the convex portions of the particle surface.

[0453] Furthermore, multiple samples were prepared under different conditions, and their cycle characteristics were measured in the same manner. The results are shown in Figures 26A and 26B. In Figure 26A, the vertical axis represents the discharge capacity, and in Figure 26B, the vertical axis represents the discharge capacity retention rate.

[0454] In Figure 26A, the sample with 0.25 at% zirconium and 0.025 at% yttrium exhibits a maximum discharge capacity exceeding 230 mAh / g. Figures 24A and 24B also show the values ​​for the same sample, lanthanum at 0.25 at%, as an example.

[0455] Furthermore, samples containing 0.125 at% zirconium and 0.125 at% yttrium, and samples containing 0.25 at% zirconium and 0.25 at% yttrium are shown in Figures 26A and 26B.

[0456] Furthermore, in the samples shown in Figures 26A and 26B, the nickel content is set to 0.5 at%, and the aluminum content is also set to 0.5 at%. In addition, the amount of lanthanum or yttrium contained in these samples is less than the amount of aluminum.

[0457] Thus, it has been shown that, with the positive electrode active material according to one aspect of the present invention, even when repeatedly charging and discharging at a high voltage of 4.7V with each of the lanthanum sample, yttrium sample, lanthanum and zirconium sample, and yttrium and zirconium sample, the decrease in charge / discharge capacity can be suppressed by adjusting the respective amounts.

[0458] The implementer can adjust the amounts of lanthanum, yttrium, and zirconium as needed to create the desired positive electrode active material.

[0459] Furthermore, unless otherwise specified in this specification, the charging and discharging voltages refer to the voltages when the counter electrode is lithium. However, even with the same positive electrode, the charging and discharging voltages of a secondary battery change depending on the material used for the negative electrode. For example, the potential of graphite is approximately 0.1V (vs Li / Li + Therefore, in the case of a graphite negative electrode, the charge and discharge voltage will be approximately 0.1V lower than in the case of a lithium counter electrode. Furthermore, even if the charging voltage of a secondary battery is, for example, 4.7V or higher in this specification, it is not necessary for it to have only a discharge voltage of 4.7V or higher as a plateau region. [Explanation of Symbols]

[0460] 100: Positive electrode active material, 101a: Modifier, 101b: Modifier, 300: Secondary battery, 301: Positive electrode can, 302: Negative electrode can, 303: Gasket, 304: Positive electrode, 305: Positive electrode current collector, 306: Positive electrode active material layer, 307: Negative electrode, 308: Negative electrode current collector, 309: Negative electrode active material layer, 310: Separator, 312: Washer, 313: Ring-shaped insulator, 322: Spacer, 400: Secondary battery, 410: Positive electrode, 411: Positive electrode active material, 413: Positive electrode current collector, 414: Positive electrode active material layer, 420: Solid electrolyte layer, 421: Solid electrolyte, 430: Negative electrode, 431: Negative electrode active material, 433: Negative 434: Negative electrode active material layer, 500: Secondary battery, 501: Positive electrode current collector, 502: Positive electrode active material layer, 503: Positive electrode, 504: Negative electrode current collector, 505: Negative electrode active material layer, 506: Negative electrode, 507: Separator, 508: Electrolyte, 509: Outer casing, 510: Positive electrode lead electrode, 511: Negative electrode lead electrode, 513: Secondary battery, 514: Terminal, 515: Seal, 517: Antenna, 519: Layer, 529: Label, 531: Secondary battery pack, 540: Circuit board, 550: Current collector, 551: One side, 552: The other side, 553: Acetylene black, 554: Graphene, 555: -carbon nanotube, 561:active material, 562:active material, 590:control circuit, 590a:circuit system, 590b:circuit system, 600:secondary battery, 601:positive electrode cap, 602:battery can, 603:positive electrode terminal, 604:positive electrode, 605:separator, 606:negative electrode, 607:negative electrode terminal, 608:insulating plate, 609:insulating plate, 611:PTC element, 613:safety valve mechanism, 614:conducting plate, 615:energy storage system, 616:secondary battery, 620:control circuit, 621:wiring, 622:wiring, 623:wiring, 624:conductor, 625:insulator, 626:wiring, 627: Wiring, 628: Conductive plate, 700: Energy storage device, 701: Commercial power supply, 703: Distribution board, 705: Energy storage controller, 706: Display unit, 707: General load, 708: Energy storage system load, 709: Router, 710: Service drop mounting section, 711: Measurement section, 712: Prediction section, 713: Planning section, 750a: Positive electrode, 750b: Solid electrolyte layer, 750c: Negative electrode, 751: Electrode plate, 752: Insulating tube, 753: Electrode plate, 761: Lower component, 762: Upper component, 764: Wing nut, 765: O-ring, 766: Insulator, 770a: Package component, 770b: Package component770c: Package component, 771: External electrode, 772: External electrode, 773a: Electrode layer, 773b: Electrode layer, 790: Control device, 791: Energy storage device, 796: Underfloor space, 799: Building, 902: Mixture, 903: First lithium mixture, 904: Second lithium mixture, 911a: Terminal, 911b: Terminal, 913: Secondary battery, 930: Housing, 930a: Housing, 930b: Housing, 931: Negative electrode, 931a: Negative electrode active material layer, 932: Positive electrode, 932a: Positive electrode active material layer, 933: Separator, 950: Winding body, 950a: Winding body, 951: Terminal, 952: Terminal, 1300: Rectangular rechargeable battery, 1301a: Battery, 1301b: Battery, 1302: Battery controller, 1303: Motor controller, 1304: Motor, 1305: Gear, 1306: DC-DC circuit, 1307: Electric power steering, 1308: Heater, 1309: Defogger, 1310: DC-DC circuit, 1311: Battery, 1312: Inverter, 1313: Audio, 1314: Power windows, 1315: Lights, 1316: Tires, 1317: Rear motor, 1320: Control circuit section, 1321: Control circuit section, 1322: Control circuit, 13 24: Switch section, 1325: External terminal, 1326: External terminal, 1413: Fixing section, 1414: Fixing section, 1415: Battery pack, 1421: Wiring, 1422: Wiring, 2001: Automobile, 2002: Transport vehicle, 2003: Transport vehicle, 2004: Aircraft, 2100: Mobile phone, 2101: Housing, 2102: Display section, 2103: Operation buttons, 2104: External connection port, 2105: Speaker, 2106: Microphone, 2107: Rechargeable battery, 2200: Battery pack, 2201: Battery pack, 2202: Battery pack, 2203: Battery pack, 2300: Unmanned aerial vehicle, 230 1: Rechargeable battery, 2302: Rotor, 2303: Camera, 2603: Vehicle, 2604: Charging device, 2610: Solar panel, 2611: Wiring, 2612: Energy storage device, 4000: Glasses-type device, 4000a: Frame, 4000b: Display unit, 4001: Headset-type device, 4001a: Microphone unit, 4001b: Flexible pipe, 4001c: Earphone unit, 4002: Device, 4002a: Housing, 4002b: Rechargeable battery, 4003: Device, 4003a: Housing, 4003b: Rechargeable battery, 4005: Wristwatch-type device, 4005a: Display unit,4005b: Belt section, 4006: Belt-type device, 4006a: Belt section, 4006b: Wireless power supply / receiving section, 6300: Cleaning robot, 6301: Housing, 6302: Display section, 6303: Camera, 6304: Brush, 6305: Operation buttons, 6306: Rechargeable battery, 6310: Dust, 6400: Robot, 6401: Illuminance sensor, 6402: Microphone, 6403: Top 6404: Camera, Speaker, 6405: Display Unit, 6406: Lower Camera, 6407: Obstacle Sensor, 6408: Movement Mechanism, 6409: Secondary Battery, 8600: Scooter, 8601: Side Mirror, 8602: Energy Storage Unit, 8603: Turn Signal Light, 8604: Under-seat Storage, 8700: Electric Bicycle, 8701: Battery, 8702: Energy Storage Unit, 8703: Display Unit, 8704: Control Circuit,

Claims

1. It has a layered rock salt-type crystalline structure and a positive electrode active material containing lithium cobalt oxide, The positive electrode active material has magnesium, fluorine, nickel, and aluminum as additive elements. The positive electrode active material has an oxide containing lanthanum and zirconium on at least a portion of its surface. The lanthanum content in the positive electrode active material is less than the aluminum content in the positive electrode active material. The zirconium content in the positive electrode active material is less than the aluminum content in the positive electrode active material. The lanthanum content in the positive electrode active material is less than the nickel content in the positive electrode active material. The zirconium content in the positive electrode active material is less than the nickel content in the positive electrode active material. A secondary battery in which the lanthanum content in the positive electrode active material is less than the zirconium content in the positive electrode active material.

2. A positive electrode active material having a layered rock salt type crystalline structure and lithium cobalt oxide, The positive electrode active material has magnesium, fluorine, nickel, and aluminum as additive elements. The method for manufacturing a secondary battery is as follows: The positive electrode active material has an oxide containing lanthanum and zirconium on at least a portion of its surface. The positive electrode active material is prepared by mixing lithium cobalt oxide, a fluorine source, and a magnesium source to obtain a first lithium mixture. The first lithium mixture and a nickel source are mixed to obtain a second lithium mixture. It is produced by the step of mixing the second lithium mixture, an aluminum source, a lanthanum source, and a zirconium source to obtain a third lithium mixture. The lanthanum content in the positive electrode active material is less than the aluminum content in the positive electrode active material. The zirconium content in the positive electrode active material is less than the aluminum content in the positive electrode active material. The lanthanum content in the positive electrode active material is less than the nickel content in the positive electrode active material. The zirconium content in the positive electrode active material is less than the nickel content in the positive electrode active material. A method for manufacturing a secondary battery, wherein the lanthanum content in the positive electrode active material is less than the zirconium content in the positive electrode active material.

Images