Positive active material

Abstract

To improve the thermal safety of a lithium ion secondary battery for a stable power supply from the lithium ion secondary battery.SOLUTION: Ignition or overheating of a lithium-ion secondary battery is suppressed and thermal safety is improved by incorporating fluorine into the surface layer of a positive electrode active material or adsorbing fluorine onto the surface of the positive electrode active material. Since fluorine is adsorbed on the surface of the positive electrode active material, the fluorine can react with an electrolytic solution near the adsorbed fluorine, and thermal decomposition of the electrolytic solution can be suppressed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] One embodiment 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. Another embodiment of the present invention relates to a power storage device including a secondary battery, a semiconductor device, a display device, a light-emitting device, a lighting device, an electronic device, or a manufacturing method thereof.

[0002] In this specification, the term "electronic device" refers to any device having a power storage device, and includes electro-optical devices having a power storage device, information terminal devices having a power storage device, and the like. [Background technology]

[0003] In recent years, there has been active development of various types of energy storage devices, such as lithium-ion secondary batteries, lithium-ion capacitors, air batteries, and all-solid-state batteries. Demand for high-power, high-capacity lithium-ion secondary batteries has expanded rapidly in line with the development of the semiconductor industry, and they have become indispensable in today's information society as a rechargeable energy source.

[0004] In particular, there is a high demand for secondary batteries with large discharge capacity per weight and excellent cycle characteristics for mobile electronic devices, etc. To meet this demand, active improvements have been made to the positive electrode active materials of the positive electrodes of secondary batteries (for example, Patent Document 1).

[0005] It is known that lithium ion secondary batteries go through several states when the temperature rises, and then reach thermal runaway (Non-Patent Document 1). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2020-068210 [Non-patent literature]

[0007] [Non-Patent Document 1] Nobuo Eda 2-4 Heat Generation Mechanism Learning from Data Li-ion Battery Charging and Discharging Technology CQ Publishing April 4, 2020 pp. 68-72 Summary of the Invention [Problem to be solved by the invention]

[0008] Lithium-ion secondary batteries can be used in next-generation clean energy vehicles, such as hybrid vehicles (HVs), electric vehicles (EVs), and plug-in hybrid vehicles (PHVs). In addition to next-generation clean energy vehicles, secondary batteries can also be installed in transportation vehicles, such as agricultural machinery, mopeds including electrically assisted bicycles, motorcycles, electric wheelchairs, electric carts, small or large ships, submarines, aircraft, including fixed-wing and rotary-wing aircraft, rockets, satellites, space probes, planetary probes, and spacecraft.

[0009] Lithium-ion secondary batteries used for the above-mentioned various applications are subject to safety verification under various assumed conditions. For example, nail penetration tests are conducted to assume an internal short circuit in the secondary battery. If an internal short circuit occurs in the secondary battery, it may generate heat and ignite.

[0010] For stable power supply from lithium ion secondary batteries, it is necessary to further improve the thermal safety of lithium ion secondary batteries. [Means for solving the problem]

[0011] Therefore, by incorporating fluorine into the surface layer of the positive electrode active material or by having fluorine adsorbed onto the surface of the positive electrode active material, it is possible to suppress ignition or overheating of the lithium ion secondary battery and improve thermal safety.

[0012] The positive electrode active material contains a transition metal M and oxygen. The transition metal M is nickel, manganese, and cobalt, and such a positive electrode active material is called NCM. NCM has a layered rock-salt crystal structure. The energy density of NCM can be improved by increasing the nickel content.

[0013] The positive electrode active material may contain fluorine as a solid solution, for example, by substituting fluorine for some of the oxygen in the crystal structure that constitutes NCM. Fluorine is known to have a high electronegativity and to easily form stable compounds with many elements.

[0014] One embodiment of the invention disclosed herein is a cathode active material having fluorine adsorbed on its surface. Specifically, the fluoro groups adsorbed on the surface of the cathode active material can react with the electrolyte near the adsorbed fluoro groups, thereby suppressing thermal decomposition of the electrolyte. The fluorine adsorbed on the surface is considered to be fluorine contained in the cathode active material. If fluorine can be detected using a measuring device for measuring the element concentration in the cathode active material, such as X-ray photoelectron spectroscopy (XPS), the cathode active material can be said to contain fluorine. Furthermore, fluorine on the particle surface or inside the particle can be detected by using time-of-flight secondary ion mass spectroscopy (TOF-SIMS) instead of X-ray photoelectron spectroscopy (XPS). The presence or absence of fluorine may also be determined based on the results of analysis such as energy dispersive X-ray spectroscopy (EDX), gas chromatography mass spectrometry (GC / MS), pyrolysis gas chromatography mass spectrometry (Py-GC / MS), and liquid chromatography mass spectrometry (LC / MS).

[0015] Another embodiment of the invention disclosed in this specification is a positive electrode active material including a transition metal M, oxygen, and fluorine. The transition metal M includes nickel, manganese, and cobalt. The positive electrode active material has a surface layer portion and an interior portion, and the surface layer portion includes fluorine on the surface thereof, and the surface layer portion has a higher magnesium concentration than the interior portion.

[0016] Furthermore, a secondary battery using the above-described positive electrode active material is also one embodiment of the present invention. The secondary battery has a configuration including a positive electrode, a negative electrode, a separator between the positive electrode and the negative electrode, and an ionic liquid or an organic solvent between the positive electrode and the negative electrode. The positive electrode includes a positive electrode active material and a conductive material. The positive electrode active material includes a transition metal M, oxygen, and fluorine. The transition metal M includes nickel, manganese, and cobalt. The positive electrode active material has a surface layer portion and an interior portion, the surface layer portion has a higher magnesium concentration than the interior portion, and fluorine is present on the surface of the surface layer portion.

[0017] In the above configuration, fluorine may be adsorbed on the surface of the conductive material.

[0018] In the above configuration, the conductive material may be any carbon material, specifically, carbon nanotubes or acetylene black.

[0019] A method for producing a positive electrode active material is also one aspect of the present invention, and includes the steps of: forming a positive electrode active material containing nickel, manganese, and cobalt; mixing the positive electrode active material with a fluoride; placing the mixture in a container; and heating the container with a lid on to adsorb fluorine onto the surface of the positive electrode active material. Preferably, the container is pressurized during heating with the lid on.

[0020] Furthermore, in order to adsorb fluorine onto the surface of the positive electrode active material, a mixture of the positive electrode active material and the fluoride may be placed in a container and heated with the lid closed multiple times. By repeatedly adding fluorine, the fluorine concentration on the surface of the positive electrode active material can be increased. By increasing the fluorine concentration on the surface of the positive electrode active material, thermal decomposition of the electrolyte can be more effectively suppressed.

[0021] In the above structure, the surface layer of the positive electrode active material contains magnesium, and the magnesium concentration is higher in the surface layer than in the interior. The presence of magnesium at an appropriate concentration in the lithium sites in the surface layer makes it easier to maintain the layered rock-salt crystal structure in the interior. This is presumably because the magnesium present in the lithium sites functions as a pillar supporting the MO2 layers. Therefore, the inclusion of magnesium in the surface layer can improve the structural stability of the positive electrode active material.

[0022] At an appropriate concentration, magnesium does not adversely affect the intercalation and deintercalation of lithium during charging and discharging, providing the above benefits. However, excessive magnesium may adversely affect the intercalation and deintercalation of lithium. Furthermore, it may be less effective at stabilizing the crystal structure. In addition, unnecessary magnesium compounds (oxides, fluorides, etc.) that do not substitute for either the lithium site or the transition metal M site may segregate on the surface of the positive electrode active material and become a resistive component in the secondary battery. Furthermore, as the magnesium concentration in the positive electrode active material increases, the discharge capacity of the positive electrode active material may decrease. This is thought to be due to excessive magnesium entering the lithium site, reducing the amount of lithium contributing to charging and discharging.

[0023] Furthermore, by including fluorine and magnesium in the surface layer, it is possible to suppress ignition or overheating of the lithium ion secondary battery, and further improve thermal safety.

[0024] However, if the surface layer is occupied only by compounds of the added element (magnesium or aluminum) and oxygen, it is not desirable because it makes it difficult for lithium to be inserted and removed. For example, it is not desirable for the surface layer to be occupied only by magnesium oxide or a solid solution structure of magnesium oxide and an oxide of a divalent transition metal M. Therefore, the surface layer must contain at least the transition metal M, and in the discharged state, it must also contain cobalt or lithium, providing a path for lithium to be inserted and removed.

[0025] The region containing magnesium or fluorine may be in the form of islands. Even if the coverage is insufficient and a portion is exposed, the region functions as a positive electrode active material, and the island-shaped surface portion can have a higher energy density than the interior portion.

[0026] In order to ensure sufficient paths for lithium insertion and desorption, it is preferable that the total number of atoms of the transition metal M in the surface layer is greater than the total number of atoms of the additive elements, that is, the concentration of the transition metal M is high.

[0027] An additive element may be added to the positive electrode active material, and the additive element is one or more selected from aluminum, calcium, titanium, chromium, and zirconium.

[0028] Furthermore, titanium oxide, one of the additive elements, is known to have superhydrophilic properties. Therefore, by using a cathode active material with titanium oxide in the surface layer, it is possible that the cathode active material will have better wettability with highly polar solvents. When used in a secondary battery, this will improve the interface between the cathode active material and the highly polar electrolyte, potentially suppressing an increase in internal resistance.

[0029] Alternatively, a barrier film may be provided so as to cover the positive electrode active material, and the barrier film may also function as a part of the positive electrode active material.

[0030] The positive electrode active material contains a transition metal M and oxygen. The transition metal M is nickel, manganese, and cobalt, and such a positive electrode active material is called NCM. NCM has a layered rock-salt crystal structure. The energy density of NCM can be improved by increasing the nickel content.

[0031] The barrier film contains at least magnesium and cobalt. The barrier film has a layered rock salt crystal structure and functions as a part of the positive electrode active material, so it can also be called a surface layer portion.

[0032] Furthermore, by adsorbing fluorine onto the surface of the barrier film, the ignition or overheating of the lithium ion secondary battery is suppressed, improving thermal safety.

[0033] Fluorine may be dissolved in the barrier film, which is part of the positive electrode active material, for example, by substituting some of the oxygen in the crystal structure that makes up the NCM with fluorine. Fluorine is known to have a high electronegativity and to easily form stable compounds with many elements.

[0034] A manufacturing method of the present invention also includes the steps of: forming a cathode active material containing nickel, manganese, and cobalt; then, placing a mixture of the cathode active material, a cobalt compound, and a fluoride (magnesium fluoride) in a container; and heating the container with a lid on to adsorb fluorine onto the surface of the cathode active material. It is preferable to apply pressure during heating with the lid on. [Effects of the Invention]

[0035] According to one embodiment of the present invention, a positive electrode active material that is less likely to deteriorate can be provided. Alternatively, a novel positive electrode active material can be provided. Alternatively, a secondary battery with high safety or reliability can be provided. Alternatively, a lithium-ion secondary battery with a long life can be provided.

[0036] Furthermore, according to one embodiment of the present invention, ignition or overheating of a lithium ion secondary battery can be suppressed, and thermal safety can be improved.

[0037] Note that the description of these effects does not preclude the existence of other effects. Note that one embodiment of the present invention does not necessarily have all of these effects. Note that effects other than these will become apparent from the description in the specification, drawings, claims, etc., and it is possible to extract other effects from the description in the specification, drawings, claims, etc. [Brief explanation of the drawings]

[0038] [Figure 1] FIG. 1(A) is a cross-sectional schematic diagram of a positive electrode active material, FIG. 1(B) is a partially enlarged view thereof, and FIG. 1(C) is a cross-sectional schematic diagram of another example of a positive electrode active material. [Figure 2] 2(A) and 2(B) are diagrams illustrating a method for producing a positive electrode active material. [Figure 3] FIG. 3 is an example of a cross-sectional view showing a process of one embodiment of the present invention. [Figure 4] FIG. 4 is a diagram illustrating a method for producing a positive electrode active material. [Figure 5] FIG. 5 is a diagram illustrating a method for producing a positive electrode active material. [Figure 6] 6(A), 6(B), 6(C), and 6(D) are schematic cross-sectional views of the positive electrode. [Figure 7] 7(A) is an exploded perspective view of the coin-type secondary battery, FIG. 7(B) is a perspective view of the coin-type secondary battery, and FIG. 7(C) is a cross-sectional perspective view thereof. [Figure 8] Fig. 8(A) shows an example of a cylindrical secondary battery. Fig. 8(B) shows an example of a cylindrical secondary battery. Fig. 8(C) shows an example of multiple cylindrical secondary batteries. Fig. 8(D) shows an example of a power storage system having multiple cylindrical secondary batteries. [Figure 9] 9(A) and 9(B) are diagrams for explaining an example of a secondary battery, and FIG. 9(C) is a diagram showing the inside of the secondary battery. [Figure 10] 10A to 10C are diagrams illustrating examples of secondary batteries. [Figure 11] 11(A) and 11(B) are diagrams showing the external appearance of a secondary battery. [Figure 12] 12A to 12C are diagrams illustrating a method for manufacturing a secondary battery. [Figure 13] FIG. 13A is a perspective view of a battery pack illustrating one embodiment of the present invention, FIG. 13B is a block diagram of the battery pack, and FIG. 13C is a block diagram of a vehicle including the battery pack. [Figure 14] Figures 14(A) to 14(D) are diagrams illustrating an example of a transportation vehicle, and Figure 14(E) is a diagram illustrating an example of an artificial satellite. [Figure 15]FIG. 15(A) is a diagram showing an electric bicycle, FIG. 15(B) is a diagram showing a secondary battery of the electric bicycle, and FIG. 15(C) is a diagram explaining a scooter. [Figure 16] 16A to 16D are diagrams illustrating examples of electronic devices. [Figure 17] FIG. 17 is a graph showing the temperature rise of a secondary battery. [Figure 18] FIG. 18(A) is a diagram illustrating the nail penetration test, and FIG. 18(B) is an enlarged view of the positive electrode active material. [Figure 19] FIG. 19 is a graph showing the temperature rise of a secondary battery when an internal short circuit occurs. [Figure 20] FIG. 20 is a diagram illustrating the crystal plane of the positive electrode active material. [Figure 21] 21(A) and 21(B) are cross-sectional schematic diagrams of the positive electrode active material, and FIG. 21(C) is an enlarged view of FIG. 21(B). [Figure 22] 22(A) and 22(B) are diagrams illustrating a method for manufacturing a positive electrode active material. [Figure 23] FIG. 23 is a diagram illustrating a method for producing a positive electrode active material. [Figure 24] 24(A), 24(B), 24(C), and 24(D) are cross-sectional schematic diagrams of the positive electrode. DETAILED DESCRIPTION OF THE INVENTION

[0039] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and it will be readily understood by those skilled in the art that various modifications can be made to the embodiments and details. Furthermore, the present invention should not be interpreted as being limited to the description of the embodiments shown below.

[0040] In this specification and the like, the term "particle" is not limited to referring only to spherical particles (having a circular cross-sectional shape), and examples of the cross-sectional shape of individual particles include ellipsoids, rectangles, trapezoids, cones, squares with rounded corners, and asymmetric shapes, and further, individual particles may have an irregular shape.

[0041] Homogeneity refers to a state in which a certain element (e.g., A) is distributed with similar characteristics in a specific region of a solid composed of multiple elements (e.g., A, B, C). The concentration of the element in each specific region should be substantially the same. For example, the difference in the detected amount of a certain element (e.g., the number of counts in STEM-EDX) between specific regions should be within 10%. Examples of specific regions include the surface layer, surface, convex portions, concave portions, and interior.

[0042] A cathode active material to which an additive element is added may be referred to as a composite oxide, a cathode material, a cathode ingredient, a cathode material for a secondary battery, or the like. In this specification and the like, the cathode active material of one embodiment of the present invention preferably includes a compound. In this specification and the like, the cathode active material of one embodiment of the present invention preferably includes a composition. In this specification and the like, the cathode active material of one embodiment of the present invention preferably includes a composite.

[0043] Furthermore, when describing the characteristics of individual particles of the positive electrode active material in the following embodiments, etc., it is not necessary for all particles to have that characteristic. For example, if 50% or more, preferably 70% or more, and more preferably 90% or more of three or more randomly selected particles of the positive electrode active material have that characteristic, it can be said that there is a sufficient effect of improving the characteristics of the positive electrode active material and a secondary battery containing it.

[0044] Furthermore, a short circuit in a secondary battery not only causes problems in the charging and / or discharging operations of the secondary battery, but may also lead to heat generation and fire. To achieve a safe secondary battery, it is preferable that the short circuit current be suppressed even at a high charging voltage. The positive electrode active material of one embodiment of the present invention suppresses the short circuit current even at a high charging voltage. Therefore, a secondary battery that achieves both high discharge capacity and safety can be obtained.

[0045] Unless otherwise specified, the materials contained in secondary batteries (positive electrode active material, negative electrode active material, electrolyte, separator, etc.) are described in their pre-degraded state. Note that a decrease in discharge capacity due to aging treatment (which can also be called burn-in treatment) during secondary battery manufacturing is not considered degradation. For example, a lithium-ion secondary cell or lithium secondary battery pack (hereinafter referred to as a lithium-ion secondary battery) can be said to be in its pre-degraded state if it has a discharge capacity of 97% or more of its rated capacity. For lithium-ion secondary batteries for portable devices, the rated capacity conforms to JIS C 8711:2019. For other lithium-ion secondary batteries, the rated capacity conforms to not only the above JIS standard but also to various JIS and IEC standards for electric vehicle propulsion, industrial use, etc.

[0046] The state of the materials in a secondary battery before they deteriorate is sometimes called an initial product or initial state, and the state after deterioration (when the secondary battery has a discharge capacity of less than 97% of its rated capacity) is sometimes called a product in use or in use state, or a used product or used state.

[0047] (Embodiment 1) In this embodiment, a positive electrode active material 100 of one embodiment of the present invention will be described with reference to FIG.

[0048] The positive electrode active material 100 contains lithium, a transition metal M, oxygen, and fluorine. The transition metal M is one or more selected from nickel, manganese, and cobalt. The positive electrode active material 100 preferably contains an additive element in addition to the transition metal M. Alternatively, the positive electrode active material 100 may contain lithium nickel-manganese-cobalt oxide to which the additive element has been added.

[0049] The positive electrode active material of a lithium ion secondary battery must contain a transition metal capable of oxidation and reduction in order to maintain charge neutrality even when lithium ions are inserted or extracted. The positive electrode active material 100 of one embodiment of the present invention contains nickel, manganese, and cobalt as the transition metal M responsible for the oxidation and reduction reaction.

[0050] When nickel accounts for a large proportion of the transition metal M contained in the positive electrode active material 100, it is preferable that the charge / discharge capacity is easily increased even at a low charge voltage, compared to when cobalt accounts for the majority. Therefore, for example, nickel preferably accounts for 50% or more of the transition metal M contained in the positive electrode active material 100, more preferably 60% or more, and even more preferably 75% or more. The positive electrode active material 100 contains fluorine, but the composition of the positive electrode active material excluding fluorine is LiNi x Co y Mn z A NiCoMn-based alloy (also referred to as NCM) represented by O2 (x>0, y>0, z>0) is used. As an example, it is preferable that x, y, and z satisfy x:y:z=5:2:3 or a value close thereto, or x:y:z=6:2:2 or a value close thereto. Alternatively, it is preferable that x, y, and z satisfy x:y:z=8:1:1 or a value close thereto. Alternatively, it is preferable that x, y, and z satisfy x:y:z=9:0.5:0.5 or a value close thereto.

[0051] An additive element may also be added to the positive electrode active material 100, for example, one or more selected from magnesium, aluminum, calcium, titanium, zirconium, fluorine, vanadium, iron, manganese, chromium, niobium, arsenic, zinc, silicon, sulfur, phosphorus, boron, bromine, and beryllium. The ratio of the sum of the number of atoms of the transition metal M to the number of atoms of the additive element is preferably less than 25 atomic %, more preferably less than 10 atomic %, and even more preferably less than 5 atomic %. When a transition metal (e.g., titanium) is added as an additive element, the additive element is not included in the transition metal M.

[0052] As will be described later, these additive elements further stabilize the crystal structure of the positive electrode active material 100. In this specification and the like, the additive element has the same meaning as a mixture or a part of a raw material.

[0053] Furthermore, the surface layer portion 100b preferably has a higher fluorine concentration than the interior portion 100c. The interior portion 100c preferably has a higher nickel concentration than the surface layer portion. Furthermore, it is preferable that the fluorine has a concentration gradient that increases toward the surface. Furthermore, to allow the surface layer portion 100b to function as a barrier layer, an additional element may be added, such as magnesium. When magnesium is used, the magnesium concentration and fluorine concentration in the surface layer portion 100b can be made higher than those in the interior portion 100c by mixing magnesium fluoride and NCM and heating the mixture.

[0054] By including fluorine and magnesium in the surface layer portion 100b, it is possible to suppress ignition or overheating of the lithium ion secondary battery, and further improve thermal safety.

[0055] <Surface and surface layer> 1(A) is a cross-sectional view of a single particle of positive electrode active material 100. Positive electrode active material 100 preferably has a surface layer portion and an interior portion 100c.

[0056] The cathode active material 100 of one embodiment of the present invention preferably has a region capable of increasing resistance. This region is sometimes referred to as a "first region" to distinguish it from other regions. The region preferably has a narrow width of 2 nm to 20 nm, preferably 2 nm to 10 nm, and more preferably 2 nm to 5 nm in cross-sectional view. The narrow region is sometimes referred to as a "shell" in this specification. FIG. 1A shows an example in which the shells 100d are distributed at the ends of particles. The cathode active material 100 having such a shell 100d can slow the rate of current flowing into the cathode active material even when a nail penetration test is performed on a secondary battery, thereby preventing fire, smoke, and the like. To slow the rate of current flowing into the cathode active material, the shell 100d is preferably located outside the surface layer of the cathode active material 100.

[0057] The shell 100d may also contain cobalt, and the shell 100d may also contain lithium ions (Li +) can be inserted and removed, while slowing down the rate of current flow due to an internal short circuit. The positive electrode active material 100 has a first region and a second region deeper than the first region, and preferably contains magnesium in at least the first region, but the second region may not contain magnesium. Furthermore, by containing cobalt in the first region and the second region, it is possible to reduce the rate of current flow due to an internal short circuit. + ) is thought to be able to be inserted and removed.

[0058] 1(B) is an enlarged conceptual diagram of the boxed region B in FIG. 1(A). As shown in FIG. 1(B), it is preferable that fluorine, one of the additive elements, is adsorbed on the surface 100a of the positive electrode active material. Fluorine has a high electronegativity and easily forms stable compounds with many elements.

[0059] 1(B) shows a state in which at least fluorine is adsorbed to the shell 100d of the positive electrode active material 100. The surface 100a may coincide with the outline of a portion of the surface layer portion 100b, or may coincide with a portion of the shell 100d. As long as the adsorbed fluorine sufficiently contributes to suppressing ignition or overheating of the lithium ion secondary battery and further improving thermal safety, fluorine does not need to be present inside the shell 100d, and fluorine does not need to be present inside the surface layer portion 100b.

[0060] The presence of the shell 100d or the adsorbed fluorine makes it difficult for oxygen to be released from the positive electrode active material 100, thereby suppressing the thermal decomposition reaction. By using the positive electrode active material 100 having the shell 100d in the positive electrode, it is possible to suppress ignition or overheating of the lithium ion secondary battery and improve the thermal safety.

[0061] Adsorption includes chemical adsorption and physical adsorption. Chemical adsorption is the formation of a chemical bond through a chemical reaction between at least one of the added elements and the surface 100a of the positive electrode active material, while physical adsorption is adsorption due to an intermolecular force (van der Waals force) acting between at least one of the added elements and the surface of the positive electrode active material 100. As will be described later, fluorine may substitute for some of the oxygen in the positive electrode active material 100. If there is sufficient fluorine in the positive electrode active material 100, fluorine will be present adsorbed on the surface and fluorine will substitute for some of the oxygen.

[0062] Examples of fluorides used in lithium ion secondary batteries include lithium salts such as LiPF6 and LiBF4, and binders such as polyvinylidene fluoride (PVDF), which will be described later. Fluorine from such fluorides may be adsorbed onto the surface 100a of the positive electrode active material.

[0063] In FIG. 1(A), the surface layer 100b of the positive electrode active material 100 refers to, for example, a region extending from the surface where the surface layer is exposed to the interior within 50 nm, more preferably within 35 nm, even more preferably within 20 nm, and most preferably within 10 nm, perpendicular or approximately perpendicular to the surface where the surface layer is exposed to the interior. Note that "approximately perpendicular" refers to an angle of 80° to 100°. Surfaces resulting from cracks and / or fissures may also be considered to be the surface. The contour of the surface can be confirmed by cross-sectional observation.

[0064] FIG. 1(A) shows an example in which the shell 100d is provided so that a specific region is thicker. For example, if NCM is used for the positive electrode active material 100, the specific region may be a surface other than the (001) plane of the NCM. In other words, as long as the shell 100d does not ignite in a nail penetration test, the shell 100d may be positioned anywhere relative to the positive electrode active material 100, and the shell 100d may be positioned so that the shell 100d is thicker in a specific region than the (001) plane of the NCM. +If it is possible to slow down the rate of current flow due to an internal short circuit while allowing for the insertion and removal of magnesium, it is not impossible that magnesium exists throughout the entire surface layer.

[0065] The shell 100d preferably has a narrow width (short range). Furthermore, it is more preferable that the width of the shell 100d is thicker on the surface where lithium can be inserted and removed, i.e., other than the (001) surface, than on the (001) surface. Furthermore, it is preferable that the Mg-containing region and the Ni-containing region are overlapped, linked, or connected on the surface where lithium can be inserted and removed, i.e., other than the (001) surface. This configuration can suppress oxygen desorption from the positive electrode active material or suppress structural changes in the positive electrode active material. In other words, providing the shell 100d on a surface other than the (001) surface can sometimes suppress oxygen desorption from surfaces other than the (001) surface. The (001) surface and the (003) surface may also be collectively referred to as the (001) surface. The (001) surface may also be referred to as the C-plane, basal plane, or the like. Furthermore, lithium in NCM has a two-dimensional diffusion path. In other words, it can be said that the lithium diffusion path exists along the surface. In this specification, a surface where the lithium diffusion path is exposed, that is, a surface where lithium is inserted and extracted, that is, a surface other than the (001) surface, is sometimes referred to as an edge surface. Figure 1(A) shows a configuration in which a shell 100d is selectively provided on the edge surface and no shell 100d is provided on the basal surface.

[0066] The surface layer portion 100b has a LiMeO2 crystal structure of space group R-3m. Figure 20 shows the (003), (104), (012), (1-12), (101), (110), (2-10), (01-1), (10-2), and (01-4) planes in the LiMeO2 crystal structure. Examples of surfaces other than the (001) orientation include the (104), (012), (1-12), (101), (110), (2-10), (01-1), (10-2), and (01-4) planes, as well as planes parallel to these planes. The amount of added elements detected may be lower in surfaces other than the (001) orientation and their surface portion than in the (001) orientation.

[0067] In the surface layer 100b having a LiMeO2 crystal structure, lithium has a two-dimensional diffusion path. In other words, the lithium diffusion path can be said to exist along the surface. In this specification, a surface where the lithium diffusion path is exposed, that is, a surface where lithium is inserted and extracted, that is, a surface other than the (001) surface, may be referred to as an edge surface.

[0068] The positive electrode active material 100 contains at least nickel, manganese, and cobalt, and since it contains nickel, it is preferable that the region containing magnesium and the region containing nickel are overlapped, linked, or connected on a surface where lithium can be inserted and removed, that is, a surface other than the (001) orientation. By adopting such a configuration, it is possible to suppress the removal of oxygen from the positive electrode active material or to suppress structural changes in the positive electrode active material. As shown in FIG. 1(B), magnesium (Mg) is preferably bonded to oxygen in the shell 100d. Furthermore, the shell 100d preferably contains Co, and Co is preferably bonded to oxygen. The shell 100d is preferably a surface where lithium ions (Li + It is believed that this allows for the insertion and removal of the junction while slowing down the rate at which current flows in due to an internal short circuit.

[0069] The region of the positive electrode active material deeper than the surface layer 100b is referred to as the inner portion 100c, which is synonymous with the inner region or core.

[0070] The surface 100a of the positive electrode active material refers to the surface of the composite oxide including the surface layer 100b and the interior 100c. Therefore, the positive electrode active material 100 does not include metal oxides such as aluminum oxide (Al2O3) that do not have lithium sites that can contribute to charge and discharge, carbonates that are chemically adsorbed after the preparation of the positive electrode active material, or hydroxyl groups. Note that the attached metal oxide refers to, for example, a metal oxide whose crystal structure does not match that of the interior 100c and the surface layer 100b.

[0071] Since the positive electrode active material 100 is a compound containing oxygen and a transition metal capable of lithium insertion / extraction, the interface between the region where the transition metal M (e.g., Co, Ni, Mn, Fe, etc.) that is oxidized and reduced upon lithium insertion / extraction and the region where oxygen is present and the region where oxygen is not present is defined as the surface 100a of the positive electrode active material. When the positive electrode active material is subjected to analysis, a protective film may be attached to the surface, but the protective film is not included in the positive electrode active material. The protective film may be a single-layer or multi-layer film of carbon, metal, oxide, resin, etc.

[0072] Therefore, the position on the surface of the positive electrode active material in STEM-EDX ray analysis or the like is determined by the average M of the detected amount of characteristic X-rays of the transition metal M inside the positive electrode active material. AVE and the average amount of the characteristic X-rays of the transition metal M in the background, M BG The point where the detected amount of oxygen characteristic X-rays is 50% of the sum of the two, or the detected amount of oxygen characteristic X-rays is the average value O AVE and the average amount of background oxygen characteristic X-rays detected, O BGThe point where the detected amount of the characteristic X-rays of the transition metal M is 50% of the sum of the average value of the detected amount of the characteristic X-rays of the internal transition metal M and the average value of the detected amount of the characteristic X-rays of the background transition metal M is different from the point where the detected amount of the characteristic X-rays of oxygen is 50% of the sum of the average value of the detected amount of the characteristic X-rays of the internal oxygen and the average value of the detected amount of the characteristic X-rays of the background oxygen. This is considered to be due to the influence of metal oxides, carbonates, etc. containing oxygen adhering to the surface, so the detected amount of the characteristic X-rays of the transition metal M is set to be 50% of the sum of the average value of the detected amount of the characteristic X-rays of the internal transition metal M. AVE and the average amount of the characteristic X-rays of the transition metal M in the background, M BG The point where the sum of the transition metals M and M is 50% can be used as the surface position of the positive electrode active material. In the case of a positive electrode active material containing multiple transition metals M, the M of the element with the largest amount of characteristic X-rays detected inside can be used as the surface position of the positive electrode active material. AVE and M BG The position of the surface can be found using

[0073] The average amount of characteristic X-rays of the above transition metals M detected in the background is M BG can be obtained by averaging the range of 2 nm or more, preferably 3 nm or more, outside the area where the detected amount of characteristic X-rays of the transition metal M starts to increase, for example. AVE can be obtained by averaging a range of 2 nm or more, preferably 3 nm or more, at a depth of 30 nm or more, preferably more than 50 nm, from the region where the detected amount of characteristic X-rays of the transition metal M and oxygen saturates and stabilizes, for example, the region where the detected amount of characteristic X-rays of the transition metal M starts to increase. BG and the average value of the detected amount of characteristic X-rays of oxygen inside AVE can also be found in the same way.

[0074] The surface 100a of the positive electrode active material in a cross-sectional STEM (scanning transmission electron microscope) image or the like is the boundary between the region where an image derived from the crystalline structure of the positive electrode active material is observed and the region where it is not observed, and is the outermost region where atomic columns derived from the atomic nuclei of metal elements with atomic numbers larger than that of lithium among the metal elements constituting the positive electrode active material are observed. Alternatively, it is the intersection of the tangent line drawn to the brightness profile from the surface to the bulk in the STEM image and the depth axis. The surface in a STEM image or the like may also be determined in conjunction with analysis with higher spatial resolution.

[0075] Furthermore, the spatial resolution of STEM-EDX is approximately 1 nm. Therefore, the maximum value of the additive element profile may deviate by approximately 1 nm. For example, even if the maximum value of the additive element profile for magnesium or the like is outside the surface determined above, this can be considered an error as long as the difference between the maximum value and the surface is less than 1 nm.

[0076] In STEM-EDX analysis, a peak refers to the detected intensity in each element profile or the maximum value of the characteristic X-rays for each element. Note that noise in STEM-EDX analysis can be measured values ​​with a half-width less than the spatial resolution (R), for example, R / 2 or less.

[0077] The effects of noise can be reduced by scanning the same location multiple times under the same conditions. For example, the integrated values ​​measured over six scans can be used as the profile for each element. The number of scans is not limited to six; more scans can be performed and the average can be used as the profile for each element.

[0078] STEM-EDX line analysis can be performed, for example, as follows: First, a protective film is vapor-deposited on the surface of the positive electrode active material. For example, carbon can be vapor-deposited using an ion sputtering device (MC1000 manufactured by Hitachi High-Technologies).

[0079] Next, the positive electrode active material is sliced ​​to prepare a cross-sectional STEM sample. For example, the slice processing can be performed using a FIB-SEM device (Hitachi High-Tech XVision200TBS). The pickup is performed using an MPS (micro-probing system), and the finishing conditions can be, for example, an accelerating voltage of 10 kV.

[0080] STEM-EDX analysis can be performed using, for example, a STEM device (Hitachi High-Tech HD-2700) with an EDAX Octane T Ultra W (two-pole) EDX detector. During EDX analysis, the emission current of the STEM device is set to between 6 μA and 10 μA, and a portion of the thin-sectioned sample with minimal depth and unevenness is measured. The magnification is, for example, around 150,000 times. The conditions for EDX analysis can be drift correction, a line width of 42 nm, a pitch of 0.2 nm, and six or more frames.

[0081] <Concentration gradient> Furthermore, the concentration of at least one of the transition metals M, cobalt and manganese, is preferably higher in the surface layer portion 100b of the positive electrode active material than in the interior portion 100c. Similarly, the concentration of nickel is preferably higher in the interior portion 100c than in the surface layer portion. Furthermore, at least one of cobalt and manganese preferably has a concentration gradient that increases toward the surface of the positive electrode active material 100. Similarly, nickel preferably has a concentration gradient that increases toward the interior of the positive electrode active material 100.

[0082] It is more preferable that the distribution of the positive electrode active material 100 differs depending on the added element. For example, it is more preferable that the depth from the surface of the concentration peak differs depending on the added element. The concentration peak here refers to the maximum value of the concentration within 200 nm from the surface layer 100b or the surface 100a.

[0083] It is also preferable that the crystal structure changes continuously from the interior toward the surface due to the concentration gradient of the added element as described above, or that the crystal orientation of the surface layer portion and the interior 100c are roughly the same.

[0084] For example, it is preferable that the crystal structure continuously changes from the interior 100c of the layered rock salt type toward the surface and surface layer portion having characteristics of the rock salt type or both the rock salt type and the layered rock salt type.Alternatively, it is preferable that the orientation of the rock salt type or the surface layer portion having characteristics of both the rock salt type and the layered rock salt type and the interior 100c of the layered rock salt type are approximately the same.

[0085] In this specification, the layered rock-salt crystal structure of a composite oxide containing lithium and a transition metal M and belonging to the space group R-3m refers to a crystal structure having a rock-salt ion arrangement in which cations and anions are alternately arranged, and in which the transition metal and lithium are regularly arranged to form a two-dimensional plane, allowing two-dimensional diffusion of lithium. Defects such as vacancies of cations or anions may also be present. Strictly speaking, the layered rock-salt crystal structure may have a distorted rock-salt crystal lattice.

[0086] The rock salt crystal structure refers to a cubic crystal structure, such as that of the space group Fm-3m, in which cations and anions are arranged alternately. Note that cation or anion deficiencies are also acceptable.

[0087] Furthermore, the fact that it has both the characteristics of the layered rock salt type and the rock salt type crystal structure can be determined by electron diffraction, TEM images, cross-sectional STEM images, etc.

[0088] While the rock-salt structure has no distinction between cation sites, the layered rock-salt structure has two types of cation sites in its crystal structure: one is mostly occupied by lithium and the other by a transition metal. Both the rock-salt structure and the layered rock-salt structure share a layered structure, with alternating two-dimensional planes of cations and two-dimensional planes of anions. Among the bright spots in an electron diffraction pattern corresponding to the crystal planes that form these two-dimensional planes, if the central spot (transmitted spot) is taken as the origin (000), the bright spot closest to the central spot would be, for example, the (111) plane in an ideal rock-salt structure, and, for example, the (003) plane in a layered rock-salt structure. For example, when comparing the electron diffraction patterns of rock-salt MgO and layered rock-salt LiMO2, the bright spot on the (003) plane of LiMO2 is observed at a distance roughly half that of the bright spot on the (111) plane of MgO. Therefore, if the analyzed region contains two phases, for example, rock-salt MgO and layered rock-salt LiMO2, the electron diffraction image will show plane orientations in which bright spots with strong brightness and bright spots with weak brightness are arranged alternately. Bright spots common to both the rock-salt and layered rock-salt types will have strong brightness, while bright spots occurring only in the layered rock-salt type will have weak brightness.

[0089] Furthermore, when a layered rock-salt crystal structure is observed perpendicular to the c-axis in cross-sectional STEM images, layers observed with high brightness and layers observed with low brightness are observed alternating. This characteristic is not seen in the rock-salt structure, as there is no distinction in the cation sites. In the case of a crystal structure that has the characteristics of both the rock-salt and layered rock-salt structures, when observed from a specific crystal orientation, layers observed with high brightness and layers observed with low brightness are observed alternating in cross-sectional STEM images, and furthermore, metals with atomic numbers higher than that of lithium are present in part of the low-brightness layers, i.e., the lithium layers.

[0090] Layered rock salt crystals and the anions in rock salt crystals form a cubic close-packed structure (face-centered cubic lattice structure). Therefore, when layered rock salt crystals and rock salt crystals come into contact, there are crystal faces where the cubic close-packed structure composed of anions is oriented in the same direction.

[0091] Alternatively, it can be explained as follows: Anions on the {111} plane of the cubic crystal structure have a triangular lattice. Layered rocksalt has a space group of R-3m and a rhombohedral structure, but to make the structure easier to understand, it is generally expressed as a compound hexagonal lattice, and the (0001) plane of the layered rocksalt has a hexagonal lattice. The triangular lattice on the cubic {111} plane has the same atomic arrangement as the hexagonal lattice on the (0001) plane of the layered rocksalt. The compatibility of the two lattices can be said to be the alignment of the cubic close-packed structure.

[0092] However, since the space group of layered rock salt crystals is R-3m, which is different from the space group Fm-3m (the space group of general rock salt crystals) of rock salt crystals, the Miller indices of the crystal planes that satisfy the above conditions are different between layered rock salt crystals and rock salt crystals. In this specification, when the orientations of the cubic close-packed structures formed by anions in layered rock salt crystals and rock salt crystals are aligned, it may be said that the crystal orientations are approximately the same. In addition, the three-dimensional structural similarity in which the crystal orientations are approximately the same, or the same crystallographic orientation, is called topotaxis.

[0093] The general agreement of the crystal orientations of the 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 Microscope) images, electron diffraction patterns, FFT patterns of TEM and STEM images, etc. XRD (X-ray Diffraction), electron diffraction, neutron diffraction, etc. can also be used as materials for determination.

[0094] In addition, the positive electrode active material 100 according to one embodiment of the present invention is in a discharged state, i.e., Li x When x=1 in MO2 (where M is at least one of Ni, Co, and Mn), it preferably has a layered rock-salt type crystal structure belonging to the space group R-3m. Layered rock-salt type composite oxides have high discharge capacity, have two-dimensional lithium ion diffusion paths, and are suitable for lithium ion insertion and desorption reactions, making them excellent as positive electrode active materials for secondary batteries. Therefore, it is particularly preferable that the interior 100c, which occupies the majority of the volume of the positive electrode active material 100, has a layered rock-salt type crystal structure.

[0095] On the other hand, the surface layer portion 100b of the cathode active material according to one embodiment of the present invention preferably has a reinforcing function to prevent the layered structure of the interior portion 100c, which is composed of octahedra of the transition metal M and oxygen, from being destroyed even when a large amount of lithium is released from the cathode active material 100 upon charging. Alternatively, the surface layer portion 100b preferably functions as a barrier layer for the cathode active material 100. Alternatively, the surface layer portion, which is the outer periphery of the cathode active material 100, preferably reinforces the cathode active material 100. Here, "reinforcing" refers to suppressing structural changes in the surface layer portion 100b and interior portion 100c of the cathode active material, such as oxygen desorption, and / or suppressing oxidative decomposition of the electrolyte at the surface 100a of the cathode active material. In other words, "functioning as a barrier layer" refers to, for example, the surface layer portion suppressing structural changes in the cathode active material 100 and the oxidative decomposition of the electrolyte.

[0096] Furthermore, the particles of the positive electrode active material 100 are preferably single crystal or polycrystalline. Single crystal particles of the positive electrode active material 100 may be called single particles. Alternatively, the positive electrode active material 100 preferably has a large crystallite size.

[0097] Large primary particles suppress the formation of secondary particles due to aggregation and sintering of the primary particles. Furthermore, large primary particle sizes naturally result in larger crystallite sizes calculated from the half-width of the XRD diffraction pattern. Therefore, when the positive electrode active material 100 is a single particle, or when the crystallite size calculated from the XRD diffraction pattern is large, cracks that may occur between primary particles are absent or minimal compared to positive electrode active materials formed by sintering multiple primary particles. Therefore, even if the volume of the positive electrode active material 100 changes during charging and discharging, cracks can be expected to be suppressed.

[0098] For example, the crystallite size calculated from the half-width of the XRD diffraction pattern is preferably 150 nm or more, more preferably 180 nm or more, and even more preferably 200 nm or more.

[0099] However, when attempting to increase the size of single crystals or crystallite size, prolonged heating or high-temperature heating, multiple heating processes, or a heating process after adding excessive lithium may be required. However, prolonged heating processes reduce productivity. Furthermore, high-temperature heating can cause cation mixing of nickel ions and lithium ions. Furthermore, excessive lithium can cause gelation of the binder. To avoid these disadvantages, it is preferable to maintain the size of the single crystal and the crystallite size at an appropriate level. For example, the crystallite size calculated from the XRD diffraction pattern is preferably 1000 nm or less, and more preferably 800 nm or less.

[0100] A positive electrode active material having a crystallite size calculated from the XRD diffraction pattern within the above range can be said to have a sufficiently large crystallite size and to have characteristics close to those of a single particle.

[0101] When calculating the crystallite size, the XRD diffraction pattern is preferably obtained from the positive electrode active material alone. However, it may also be obtained from the positive electrode, which includes the positive electrode active material, a current collector, a binder, a conductive material, and the like. However, in the positive electrode, the particles of the positive electrode active material may be oriented so that the crystal planes of the particles are aligned in one direction due to the influence of pressure and other factors during the fabrication process. Strong orientation can prevent accurate calculation of the crystallite size. Therefore, it is more preferable to obtain the XRD diffraction pattern by removing the positive electrode active material layer from the positive electrode, removing some of the binder and other materials in the positive electrode active material layer using a solvent, and then loading the sample into a sample holder. Another method involves applying grease to a silicon non-reflective plate and attaching a powder sample of the positive electrode active material or the like to the silicon non-reflective plate.

[0102] <XRD> The crystallite size can be calculated using, for example, a Bruker D8 ADVANCE with a CuKα X-ray source, a 2θ angle of 15° to 90° increments of 0.005, and a LYNXEYE XE-T detector, using a diffraction pattern acquired from the X-ray source and ICSD coll.code 172909 as the literature value for lithium cobalt oxide. Analysis can be performed using DIFFRAC.TOPAS ver.6 crystal structure analysis software, with the following settings, for example:

[0103] Emission Profile:CuKa5.lam Background:Chebychev polynomial, 5th order Instrument Primary radius: 280mm Secondary radius: 280 mm Linear PSD 2Th angular range:2.9 FDS angle: 0.3 Full Axial Convolution Filament length: 12mm Sample length: 15 mm Receiving Slit length: 12mm Primary Sollers: 2.5 Secondary Sollers: 2.5 Corrections Specimen displacement:Refine LP Factor:0

[0104] It is preferable to use the LVol-IB value, which is the crystallite size calculated by the above method, as the crystallite size. Note that if the calculated Preferred Orientation is less than 0.8, the sample may be unsuitable for determining the crystallite size because the orientation of the sample is too strong.

[0105] EDX The concentration gradient of fluorine and transition metal M in the positive electrode active material 100 can be evaluated, for example, by exposing a cross section of the positive electrode active material 100 using a focused ion beam (FIB) or the like, and analyzing the cross section using energy dispersive X-ray spectroscopy (EDX), electron probe microanalysis (EPMA), or the like.

[0106] Among EDX measurements, EDX area analysis is performed by scanning an area and evaluating the area in two dimensions. Linear analysis is performed by scanning a line to evaluate the distribution of atomic concentrations within the positive electrode active material. Linear analysis is also sometimes used to extract data from a linear area of ​​EDX area analysis. Point analysis is performed by measuring an area without scanning.

[0107] EDX area analysis (e.g., element mapping) can quantitatively analyze the concentrations of the additive element and the transition metal M in the surface layer portion and the interior portion 100c of the positive electrode active material 100. Furthermore, EDX line analysis can analyze the concentration distribution and maximum value of the additive element. Furthermore, analysis that thins the sample, such as STEM-EDX, is more suitable because it can analyze the concentration distribution in the depth direction from the surface to the center of the positive electrode active material in a specific region without being affected by the distribution in the depth direction.

[0108] Therefore, when EDX area analysis or EDX point analysis is performed on cathode active material 100 of one embodiment of the present invention, it is preferable that the fluorine concentration in surface layer portion 100b is higher than that in interior portion 100c. Increasing the fluorine concentration on the surface of the cathode active material can effectively suppress thermal decomposition of the electrolyte solution.

[0109] Furthermore, FIG. 1(A) shows an example in which island-shaped shells 100d are formed on the cathode active material 100 having an irregular shape, and fluorine adsorbed so as to cover the entire surface 100a of the cathode active material is shown by the dotted line portion, but this is not particularly limited, and the entire surface 100a does not have to be covered with fluorine.

[0110] Furthermore, the cathode active material 100 is not limited to having an island-shaped surface portion, and any configuration that allows fluorine to be adsorbed on the surface 100a may be used, such as the configuration shown in FIG. 1(C). FIG. 1(C) shows an example in which the surface portion 100b covers the interior 100c. FIG. 1(C) shows an example in which the particle shape is close to spherical. The configuration shown in FIG. 1(C) is an example in which a shell 100d uniformly covers the entire surface portion 100b of the cathode active material. Alternatively, the cathode active material shown in FIG. 1(A) and the cathode active material shown in FIG. 1(C) may be mixed to produce a cathode using multiple types of cathode active materials.

[0111] In FIG. 1(C) as well, the fluorine adsorbed so as to cover the entire surface 100a of the positive electrode active material is shown by the dotted line portion, but this is not particularly limited, and it is sufficient that the fluorine covers only a part of the surface 100a.

[0112] This embodiment can be used in combination with other embodiments.

[0113] (Embodiment 2) In this embodiment, an example of a method for manufacturing the positive electrode active material 100 described in Embodiment 1 is shown in FIG.

[0114] First, in step S11, a lithium source and a transition metal M for the inner portion 100c of the positive electrode active material 100 are mixed. 191 A source of transition metal M is prepared. 191 The source is NCM, which has nickel, manganese, and cobalt.

[0115] Next, in step S12, a lithium source and a transition metal M for the inner portion 100c of the positive electrode active material 100 are mixed. 191 The synthesis method includes, for example, a solid-phase method in which a lithium source and a transition metal source for the inner portion 100c of the positive electrode active material 100 are mixed together, followed by heating. By adding the lithium source and heating, the NCM, which was previously a secondary particle, becomes a single particle.

[0116] In this way, the composite oxide C contained in the interior 100c of the positive electrode active material 100 191 In this embodiment, an example of synthesis is shown, but the composite oxide C 191 A commercially available product equivalent to the above may also be used. 191 are called single-particle NCMs.

[0117] Next, in step S21, X for the surface layer portion 100b of the positive electrode active material 100 is 192 A fluorine source for the surface layer 100b of the positive electrode active material 100 is prepared. As the fluorine source, a fluorine compound, typically lithium fluoride (LiF), can be used. LiF is preferred because it has a relatively low melting point of 848°C and is easily melted in the annealing step described below. 192 Magnesium fluoride (MgF2) is used as the source. Magnesium fluoride is also a fluorine source, so 192When magnesium fluoride is used, magnesium can be distributed in the vicinity of the surface of the positive electrode active material at a high concentration, forming the surface layer portion 100b.

[0118] When lithium fluoride and magnesium fluoride are used, the eutectic point is around 742°C, which is useful for producing the positive electrode active material 100. A low eutectic point is preferable because it facilitates the reaction in the subsequent step S31. The ease of reaction shortens the annealing time, thereby increasing productivity.

[0119] Next, in step S31, the composite oxide C contained in the interior 100c of the positive electrode active material 100 is 191 and X for the surface layer portion 100b of the positive electrode active material 100. 192 The source and the halogen source for the surface layer portion 100b of the positive electrode active material 100 are synthesized. As a synthesis method, there is a method in which these are mixed by a solid phase method and then heated. Alternatively, a sol-gel method may be used as the synthesis method.

[0120] An example of the annealing method in step S31 is shown in FIG.

[0121] The heating furnace 220 shown in FIG. 3 includes a furnace space 202, a hot plate 204, a pressure gauge 221, a heater unit 206, and an insulating material 208. Annealing is preferably performed with a lid 218 attached to the container 216. This configuration allows the space 219 defined by the container 216 and the lid 218 to be filled with a fluoride-containing atmosphere. By maintaining the lid during annealing so that the concentration of gasified fluoride in the space 219 remains constant or does not decrease, fluorine and magnesium can be contained near the particle surfaces. Because the space 219 has a smaller volume than the furnace space 202, a small amount of fluoride volatilizes, creating a fluoride-containing atmosphere. In other words, the reaction system can be filled with a fluoride-containing atmosphere without significantly reducing the amount of fluoride contained in the mixture 903. Therefore, LiMO2 can be efficiently produced. Furthermore, the use of the lid 218 allows the mixture 903 to be annealed in a fluoride-containing atmosphere simply and inexpensively.

[0122] Furthermore, before heating in the heating furnace space 202, a step of creating an oxygen-containing atmosphere in the heating furnace space 202 and a step of placing the container 216 containing the mixture 903 in the heating furnace space 202 are performed. By performing these steps in this order, the mixture 903 can be annealed in an atmosphere containing oxygen and fluoride. For example, the annealing is performed while a gas is flowing. Furthermore, the heating furnace space 202 can be sealed during the annealing to form a closed space so that the gas is not transported to the outside.

[0123] There are no particular limitations on the method for creating an oxygen-containing atmosphere in the heating furnace space 202, but examples include a method of evacuating the heating furnace space 202 and then introducing an oxygen-containing gas such as oxygen gas or dry air, or a method of infusing an oxygen-containing gas such as oxygen gas or dry air for a certain period of time. Among these, the method of evacuating the heating furnace space 202 and then introducing oxygen gas (oxygen substitution) is preferred. Note that the air in the heating furnace space 202 may be considered to be an oxygen-containing atmosphere.

[0124] Furthermore, fluoride and the like adhering to the inner walls of the container 216 and the lid 218 can be re-emitted by heating and attached to the mixture 903 .

[0125] There is no particular limitation on the process for heating the heating furnace 220. Heating may be performed using a heating mechanism provided in the heating furnace 220.

[0126] Furthermore, there are no particular restrictions on how the mixture 903 is arranged when placed in the container 216, but it is preferable to arrange the mixture 903 so that the upper surface of the mixture 903 is flat with respect to the bottom surface of the container 216, in other words, so that the height of the upper surface of the mixture 903 is uniform, as shown in Figure 3.

[0127] The annealing in step S31 is preferably performed while controlling the pressure inside the furnace with a pressure gauge 221. The inside of the furnace is preferably atmospheric pressure or pressurized. When heated under pressure, the surface of the positive electrode active material 100 becomes smooth, and the positive electrode active material 100 may be more resistant to physical damage caused by pressure than a positive electrode active material that is not smooth. For example, the positive electrode active material 100 is less likely to be damaged in a test that involves pressure, such as a nail penetration test, and as a result, safety may be improved.

[0128] The annealing in step S31 is preferably performed at an appropriate temperature for an appropriate time. The temperature-lowering time after annealing is preferably, for example, 10 hours to 50 hours. The annealed material is then recovered to obtain the positive electrode active material 100.

[0129] In this manner, the positive electrode active material 100 shown in Fig. 1(A) is produced (step S32). After step S31, a process of contacting the surface 100a with a fluorine-containing solution may be performed to adsorb fluorine onto the surface 100a. In this case, fluorine or fluoride can be adsorbed onto the surface 100a.

[0130] When fluorine is added at a high concentration, the treatment of contacting the substrate with a solution containing fluorine may be repeated.

[0131] The positive electrode active material 101 shown in FIG. 1C can be produced, for example, according to the flow shown in FIG. 2B.

[0132] First, in step S11, a lithium source and a transition metal M for the inner 100c are 191 Prepare the source and.

[0133] Next, in step S12, a lithium source and a transition metal M for the inner portion 100c of the positive electrode active material 101 are mixed. 191 The synthesis method may be, for example, a method in which a lithium source and a transition metal source for inner portion 100c of positive electrode active material 101 are mixed by a solid phase method, and then heated.

[0134] In this way, the composite oxide C contained in the interior 100c of the positive electrode active material 101 191 In this embodiment, the composite oxide C 191 The synthesis of the composite oxide C 191 You can also purchase and use a commercially available product equivalent to the above.

[0135] Next, in step S41, a lithium source and a transition metal M for the surface layer portion 100b are mixed. 193 A source of transition metal M is prepared. 193 The source comprises cobalt.

[0136] Next, in step S51, the composite oxide C contained in the inside 100c of the positive electrode active material 101 is 191 a lithium source and a transition metal M 193 The source and are synthesized. One synthesis method is to mix them in a solid phase method and then heat them.

[0137] In this way, the composite oxide C having the inner portion 100c covered with the surface layer portion 100b is obtained. 191+193 (Step S52) Composite oxide C 191+193 has an area of ​​LCO outside the NCM.

[0138] Next, in step S61, X for shell 100d is 194Source and complex oxide C 191+193 A fluorine source for adsorbing fluorine onto the surface of the X is prepared. 194 Magnesium fluoride (MgF2) is used as the source.

[0139] Next, in step S71, a fluorine source (fluorine compound) and a composite oxide C 191+193 and X for Shell 100d 194 The source and the material are synthesized. For example, the synthesis method may be a method in which they are mixed by a solid phase method and then heated. Alternatively, a sol-gel method may be used as the synthesis method.

[0140] In this manner, the positive electrode active material 101 shown in FIG. 1(C) is produced (step S72). After step S71, a process of contacting the surface 100a with a solution containing fluorine may be performed to adsorb fluorine onto the surface 100a. In this case, fluorine or fluoride can be adsorbed onto the surface 100a.

[0141] This embodiment can be used in combination with other embodiments.

[0142] (Embodiment 3) In the second embodiment, an example is shown in which the inner portion 100c and the surface portion 100b of the positive electrode active material 100 are produced by a solid phase method, but the inner portion 100c of the positive electrode active material 100 can also be produced by a co-precipitation method.

[0143] In this embodiment, an example of a method for manufacturing the positive electrode active material 100 of one embodiment of the present invention will be described with reference to FIGS.

[0144] <Step S111> 4, a transition metal M source including a nickel source (Ni source), a cobalt source (Co source), and a manganese source (Mn source) is first prepared. The nickel, cobalt, and manganese are preferably mixed in a ratio that allows a layered rock-salt crystal structure to be formed.

[0145] In particular, a positive electrode active material 100 containing a large amount of nickel as the transition metal M may be cheaper than a positive electrode active material containing a large amount of cobalt, and may also have an increased charge / discharge capacity per weight, which is preferable. For example, the nickel content of the transition metal M is preferably greater than 25 atomic % of the total of nickel, manganese, and cobalt, more preferably 60 atomic % or more, and even more preferably 80 atomic % or more. However, if the proportion of nickel is too high, chemical stability and heat resistance may be reduced. Therefore, the nickel content of the transition metal M is preferably 95 atomic % or less of the total of nickel, manganese, and cobalt.

[0146] When cobalt is contained as the transition metal M, the average discharge voltage is high, and the cobalt contributes to stabilizing the layered rock salt structure, so that a highly reliable secondary battery can be obtained, which is preferable.

[0147] The inclusion of manganese as the transition metal M is preferable because it improves heat resistance and chemical stability. However, if the proportion of manganese is too high, the discharge voltage and discharge capacity tend to decrease. Therefore, for example, the manganese content of the transition metal M is preferably 2.5 atomic % to 34 atomic % of the total of nickel, manganese, and cobalt.

[0148] The transition metal M source is prepared as an aqueous solution containing the transition metal M. An aqueous solution of a nickel salt can be used as the nickel source. Examples of nickel salts that can be used include nickel sulfate, nickel chloride, nickel nitrate, and hydrates thereof. Organic acid salts of nickel, such as nickel acetate, and hydrates thereof can also be used. An aqueous solution of a nickel alkoxide or an organic nickel complex can also be used as the nickel source. In this specification and elsewhere, organic acid salts refer to compounds of metals and organic acids, such as acetic acid, citric acid, oxalic acid, formic acid, and butyric acid.

[0149] Similarly, an aqueous solution of a cobalt salt can be used as the cobalt source. Examples of the cobalt salt include cobalt sulfate, cobalt chloride, cobalt nitrate, and hydrates thereof. Organic acid salts of cobalt, such as cobalt acetate, and hydrates thereof can also be used. An aqueous solution of a cobalt alkoxide or an organic cobalt complex can also be used as the cobalt source.

[0150] Similarly, an aqueous solution of a manganese salt can be used as the manganese source. Examples of the manganese salt include manganese sulfate, manganese chloride, manganese nitrate, and hydrates thereof. Organic acid salts of manganese, such as manganese acetate, and hydrates thereof can also be used as the manganese salt. An aqueous solution of a manganese alkoxide or an organic manganese complex can also be used as the manganese source.

[0151] In this embodiment, an aqueous solution in which nickel sulfate, cobalt sulfate, and manganese sulfate are dissolved in pure water is prepared as a source of the transition metal M. The atomic ratio of nickel, cobalt, and manganese is Ni:Co:Mn=8:1:1 or approximately this ratio. The aqueous solution is acidic.

[0152] <Step S113> A chelating agent may also be prepared, as shown in step S113 of FIG. 4. Examples of chelating agents include glycine, oxine, 1-nitroso-2-naphthol, 2-mercaptobenzothiazole, and EDTA (ethylenediaminetetraacetic acid). Multiple agents selected from glycine, oxine, 1-nitroso-2-naphthol, and 2-mercaptobenzothiazole may also be used. At least one of these agents is dissolved in pure water to form a chelating aqueous solution. A chelating agent is a complexing agent that forms a chelate compound and is preferable to conventional complexing agents. Of course, a complexing agent may be used instead of a chelating agent, and ammonia water may be used as the complexing agent. Using a chelating aqueous solution is preferable because it suppresses the generation of unwanted crystal nuclei and promotes crystal growth. Suppressing the generation of unwanted nuclei suppresses the generation of fine particles, thereby producing composite hydroxide 98 with a good particle size distribution. Furthermore, using a chelating aqueous solution can slow the acid-base reaction, allowing the reaction to proceed gradually, resulting in the production of secondary particles that are nearly spherical. Glycine has the effect of maintaining a constant pH value at or near a pH of 9.0 or more and 10.0 or less, and using a glycine aqueous solution as the chelate aqueous solution makes it easier to control the pH in the reaction tank when obtaining the composite hydroxide 98, which is preferable.

[0153] <Step S114> Next, in step S114 of FIG. 4, a source of the transition metal M and a chelating agent are mixed to prepare an acid solution.

[0154] <Step S121> Next, in step S121 of Fig. 4, an alkaline solution is prepared. As the alkaline solution, for example, an aqueous solution containing sodium hydroxide, potassium hydroxide, lithium hydroxide, or ammonia can be used. An aqueous solution in which these are dissolved in pure water can also be used. Alternatively, an aqueous solution in which multiple types selected from sodium hydroxide, potassium hydroxide, lithium hydroxide, and ammonia are dissolved in pure water can also be used.

[0155] The pure water suitable for use in the transition metal M source and alkaline solution is water having a resistivity of 1 MΩ cm or more, more preferably 10 MΩ cm or more, and even more preferably 15 MΩ cm or more. Water satisfying this resistivity requirement has high purity and contains very few impurities.

[0156] <Step S122> As shown in step S122 of FIG. 4, it is preferable to prepare water in the reaction vessel. This water may be an aqueous solution of a chelating agent, but pure water is more preferable. The use of pure water promotes nucleation, allowing the production of a composite hydroxide with a small particle size. The small particle size of this composite hydroxide refers to an average particle size of less than 2 μm. The water prepared in this reaction vessel can be referred to as a filling liquid or an adjustment liquid for the reaction vessel. When using an aqueous chelating agent solution, the description of step S113 can be taken into consideration.

[0157] <Step S131> 4, the acid solution and the alkaline solution are mixed and reacted with each other, which can be called a co-precipitation reaction, a neutralization reaction, or an acid-base reaction.

[0158] During the coprecipitation reaction in step S131, it is preferable to keep the pH of the reaction system at 9.0 or higher and 11.5 or lower.

[0159] For example, when an alkaline solution is placed in a reaction tank and an acid solution is added dropwise to the reaction tank, it is advisable to maintain the pH of the aqueous solution in the reaction tank within the above range. The same applies when an acid solution is placed in a reaction tank and an alkaline solution is added dropwise. When the solution in the reaction tank is 200 mL or more and 350 mL or less, it is preferable to set the drop rate of the acid or alkaline solution to 0.01 mL / min or less, as this makes it easier to control the pH conditions. The reaction tank includes a reaction vessel, etc.

[0160] The aqueous solution in the reaction vessel is preferably stirred using a stirring means. The stirring means may have a stirrer or stirring blades. Between two and six stirring blades may be provided. For example, if four stirring blades are used, they may be arranged in a cross shape when viewed from above. The rotation speed of the stirring means is preferably between 800 rpm and 1200 rpm. Baffle plates may also be provided in the reaction vessel to change the stirring direction and flow rate. The provision of baffle plates improves mixing efficiency, allowing for the synthesis of more uniform composite hydroxide particles.

[0161] The temperature of the reaction vessel is preferably adjusted to be 50° C. or higher and 90° C. or lower. The dropwise addition of the alkaline solution or acid solution should be started after the reaction vessel has reached the appropriate temperature.

[0162] The inside of the reaction vessel should preferably be in an inert atmosphere. In this case, nitrogen or argon can be used as the inert atmosphere. When using a nitrogen atmosphere, nitrogen gas should be introduced at a flow rate of 0.5 L / min to 2 L / min.

[0163] The reactor may also be equipped with a reflux condenser, which allows nitrogen gas to be released from the reactor and water vapor to be returned to the reactor.

[0164] By the above coprecipitation reaction, a composite hydroxide 98 containing the transition metal M is precipitated.

[0165] <Step S132> To recover the composite hydroxide 98, filtration is preferably performed as shown in step S132 of Fig. 4. The filtration is preferably suction filtration. During filtration, the reaction product precipitated in the reaction tank may be washed with pure water, and then an organic solvent (e.g., acetone) may be used.

[0166] <Step S133> As shown in step S133 of Fig. 4, the composite hydroxide 98 after filtration may be dried. For example, it may be dried under vacuum at a temperature of 60°C to 200°C for 0.5 hours to 20 hours. For example, it may be dried for 12 hours.

[0167] In this manner, a composite hydroxide 98 containing a transition metal M can be obtained. In this specification and the like, the composite hydroxide 98 refers to a hydroxide of multiple metals. The composite hydroxide 98 can be said to be a precursor of the interior 100c of the positive electrode active material 100.

[0168] <Step S141> Next, in step S141 of Fig. 5, a lithium source is prepared. At this time, because the process of adding the lithium source and heating is performed multiple times, an amount of lithium prepared in step S141 that is less than the final amount is used. For example, when the sum of the atoms of nickel, cobalt, and manganese is 1, the lithium can be 0.5 to 0.9 (atomic ratio), and more preferably 0.7 (atomic ratio).

[0169] Examples of lithium sources that can be used include lithium hydroxide, lithium carbonate, and lithium nitrate. It is particularly preferable to use a material with a low melting point among lithium compounds, such as lithium hydroxide (melting point 462°C). Positive electrode active materials with a high nickel content are more susceptible to cation mixing than lithium cobalt oxide, etc., so heating, such as in step S143, must be performed at a low temperature. Therefore, it is preferable to use a material with a low melting point.

[0170] Furthermore, a smaller particle size of the lithium source is preferable because it facilitates the reaction. For example, a lithium source micronized using a fluidized-bed jet mill can be used. The particle size here refers to the particle size at 50% of the cumulative value in the particle size distribution measured by laser diffraction / scattering (also referred to as the average particle size). The average particle size refers to D50, assuming a symmetrical particle size distribution. D50 refers to the particle size at 50% of the cumulative distribution calculated using a particle size distribution analyzer (Shimadzu SALD-2200) using laser diffraction / scattering. Particle size measurement is not limited to laser diffraction particle size distribution measurement; it can also be performed by measuring the major axis of the particle cross section using SEM or TEM (Transmission Electron Microscope). For example, to measure D50 using SEM or TEM analysis, 20 or more particles can be measured, an accumulated particle amount curve can be created, and the particle size at 50% of the accumulated amount can be used as D50.

[0171] <Step S142> Next, in step S142 of FIG. 5, the composite hydroxide and the lithium source are mixed. Mixing can be performed by a dry method or a wet method. For example, a ball mill, a bead mill, or the like can be used for mixing. When using a ball mill, it is preferable to use zirconia balls as the media. Furthermore, when using a ball mill, a bead mill, or the like, it is preferable to set the peripheral speed to 100 mm / sec or more and 2000 mm / sec or less in order to suppress contamination from the media or materials. The lithium compound may be pulverized simultaneously with mixing.

[0172] <Step S143> Next, the mixture of composite hydroxide 98 and the lithium source is heated (step S143). To distinguish from other heating steps, in Fig. 5, step S143 may be referred to as the first heating, step S153 as the second heating, and step S155 as the third heating.

[0173] The firing equipment used for these heating processes can be an electric furnace or a rotary kiln. The crucibles, saggers, setters, and containers used during heating should preferably be made of materials that do not easily release impurities. For example, a crucible made of aluminum oxide with a purity of 99.9% is recommended. For mass production, a sagger made of mullite-cordierite (Al2O3·SiO2·MgO) is recommended. It is also preferable to heat these containers with their lids on.

[0174] The heating temperature in step S143 is preferably 400° C. to 750° C., more preferably 650° C. to 750° C. The heating time in step S143 is preferably 1 hour to 30 hours, more preferably 2 hours to 20 hours.

[0175] The heating atmosphere is preferably an oxygen-containing atmosphere or a so-called dry air atmosphere containing oxygen with little water (for example, a dew point of -50°C or less, more preferably a dew point of -80°C or less).

[0176] Furthermore, it is preferable to have a crushing step after heating as step S144. Crushing can be performed, for example, in a mortar. Furthermore, classification can be performed using a sieve. Through the above steps, a composite oxide 99 is obtained as step S145. The composite oxide 99 is a material that can be called NCM.

[0177] <Step S151> Next, in step S151, a fluorine source (fluorine compound) is prepared. Examples of fluorine compounds include hydrogen fluoride, halogen fluorides (ClF3, IF5, etc.), gaseous fluorides (BF3, NF3, PF5, SiF4, SF6, etc.), and metal fluorides (LiF, NiF2, AlF3, MgF2, etc.). In this embodiment, magnesium fluoride or lithium fluoride is used as the fluorine source. When the positive electrode active material 100 is formed into single particles, it is preferable to use lithium fluoride and heat it to grow crystals. When lithium fluoride is used, the amount of lithium in step S151 is adjusted so that the final amount of lithium is achieved in combination with step S141. For example, when the sum of the atoms of nickel, cobalt, and manganese is 1, the final amount of lithium is preferably 0.95 to 1.25, and more preferably 1.00 to 1.05 (atomic ratio). Although the method of adding lithium in two separate steps, step S141 and step S151, and heating each step will be described, one embodiment of the present invention is not limited to this. Lithium may also be added in three or more separate steps, with heating performed after each addition.

[0178] <Step S152> Next, the composite oxide 99 obtained in step S145 is mixed with the above-mentioned fluorine source (fluorine compound).

[0179] <Step S153> Next, the mixture of composite oxide 99 and fluorine source is heated. The heating in step S153 is preferably performed at a sufficiently high temperature to increase the crystallite size of positive electrode active material 100, but the range may vary depending on the composition of transition metal M.

[0180] When the proportion of nickel in the transition metal M is high, for example, 70% or more, the temperature is preferably, for example, 750°C or higher, more preferably 800°C or higher, and even more preferably 850°C or higher. On the other hand, if the temperature is too high, there is a risk that the transition metal M, such as nickel, may be reduced to a divalent state. Therefore, for example, the temperature is preferably 950°C or lower, more preferably 920°C or lower, and even more preferably 900°C or lower.

[0181] When the proportion of nickel in the transition metal M is 40% or more and 60% or less, for example, a temperature of 900°C or more is preferable, more preferably 950°C or more, and more preferably around 970°C. On the other hand, if the temperature is too high, the same disadvantages as those described above may occur, so a temperature of 1020°C or less is preferable, and more preferably 990°C or less. For other heating conditions, refer to the description of step S143.

[0182] It is also preferable to have a crushing step after heating as step S154. The description of step S144 can be referred to for the crushing step.

[0183] <Step S155> Furthermore, it is more preferable to perform heating in step S155. By performing this heating, residues of the lithium source and the like can be reduced. The heating temperature in step S155 is preferably 400°C or higher and 900°C or lower, more preferably 750°C or higher and 850°C or lower. The heating time in step S155 is preferably 1 hour or higher and 30 hours or lower, more preferably 2 hours or higher and 20 hours or lower. However, the heating in step S155 does not necessarily have to be performed.

[0184] It is also preferable to have a crushing step after heating as step S156. The description of step S144 can be referred to for the crushing step.

[0185] 5, a method is described in which the fluorine source is mixed in step S152 and then heated twice in steps S153 and S155, but this is not a limitation of one embodiment of the present invention. Three or more heating steps may also be performed.

[0186] The above steps produce the positive electrode active material 100 (Step S175). The size of each particle of the positive electrode active material 100 is preferably such that the average particle diameter measured by a laser diffraction / scattering method is in the range of 2 μm to 20 μm.

[0187] This embodiment mode can be freely combined with other embodiment modes.

[0188] (Fourth embodiment) To fabricate a secondary battery using the positive electrode active material described in any one of Embodiments 1 to 3, an example of a positive electrode to be fabricated is shown below. The secondary battery includes at least an outer casing, a current collector, an active material (positive electrode active material or negative electrode active material), a conductive material, and a binder. It also includes an electrolyte solution in which a lithium salt or the like is dissolved. In the case of a secondary battery using an electrolyte solution, a positive electrode, a negative electrode, and a separator are provided between the positive electrode and the negative electrode. It is also preferable to include fluorine in the electrolyte solution. By including fluorine in the electrolyte solution, fluorine can be adsorbed onto the surface of the positive electrode active material. Furthermore, by including a fluoro group in the electrolyte solution, the fluorine adsorbed onto the surface of the positive electrode active material can be stably maintained.

[0189] First, the positive electrode will be described. Figure 6(A) shows an example of a schematic cross-sectional view of the positive electrode.

[0190] The current collector 400 is a metal foil, and the positive electrode is formed by applying a slurry onto the metal foil and drying it. After drying, a pressing process may be further performed. The positive electrode is formed by forming an active material layer on the current collector 400.

[0191] The slurry is a material liquid used to form an active material layer on the current collector 400, and refers to a material containing at least an active material, a binder, and a solvent, and preferably further mixed with a conductive material. The slurry is also called an electrode slurry or an active material slurry, and is also called a positive electrode slurry when forming a positive electrode active material layer, and a negative electrode slurry when forming a negative electrode active material layer.

[0192] The conductive material, also called a conductivity imparting agent or a conductivity aid, is made of a carbon material. By attaching the conductive material between multiple active materials, the active materials are electrically connected to each other, thereby increasing their conductivity. Note that "attachment" does not only refer to physical adhesion between the active material and the conductive material, but also encompasses cases where a covalent bond is formed, bonding due to van der Waals forces, the conductive material covering part of the surface of the active material, the conductive material fitting into the surface irregularities of the active material, and electrical connection even when not in contact with each other.

[0193] Typical carbon materials used as conductive materials include carbon black (particulate carbon such as furnace black and acetylene black, graphite, etc.).

[0194] 6A illustrates acetylene black 403 as the conductive material. Also, FIG. 6A illustrates an example in which a second active material 402 having a particle size smaller than that of the positive electrode active material 100 described in any of Embodiments 1 to 3 is mixed. By mixing particles of different sizes, a high-density positive electrode can be obtained.

[0195] A binder (resin) is mixed to bond the active material to a current collector 400, such as a metal foil, in the positive electrode of a secondary battery. The binder is also called a binding agent. The binder is a polymer material, and if a large amount of binder is added, the proportion of active material in the positive electrode decreases, resulting in a smaller discharge capacity of the secondary battery. Therefore, the amount of binder mixed is kept to a minimum. In Figure 6(A), the areas not filled with the active material 401, second active material 402, and acetylene black 403 indicate voids or binder.

[0196] In addition, in Figure 6(A), the boundary between the interior and shell of active material 401 is indicated by a dotted line. Also, active material 401 in Figure 6(A) shows an example of a spherical shape, which corresponds to positive electrode active material 101 in Figure 1(C). The shell contains magnesium at a higher concentration than the interior, which can suppress ignition or overheating of the lithium ion secondary battery and improve thermal safety.

[0197] 6A shows an example in which the active material 401 is spherical, but the shape is not particularly limited and various shapes are possible. The cross-sectional shape of the active material 401 may be elliptical, rectangular, trapezoidal, conical, quadrangular with rounded corners, or asymmetrical.

[0198] Figure 6(B) shows an example different from Figure 6(A). Active material 401 in Figure 6(B) shows an example of an irregular shape, which corresponds to positive electrode active material 100 in Figure 1(A). In Figure 6(B), the boundary between the interior and shell of active material 401 is indicated by a dotted line. The shell contains magnesium at a higher concentration than the interior, which can suppress ignition or overheating of the lithium-ion secondary battery and improve thermal safety.

[0199] In addition, in the positive electrode in FIG. 6B, graphene 404 is used as a carbon material used as a conductive material.

[0200] Graphene is a carbon material that has amazing electrical, mechanical, and chemical properties and is expected to be applied in various fields, such as field-effect transistors and solar cells.

[0201] In this specification, graphene includes multilayer graphene and multigraphene. In other words, graphene refers to a substance containing carbon, having a shape such as a plate or sheet, and having a two-dimensional structure formed by six-membered carbon rings. The two-dimensional structure formed by six-membered carbon rings is sometimes called a carbon sheet. The carbon material used as the conductive material for the positive electrode is not limited to graphene, and graphene compounds can also be used. Graphene compounds include graphene oxide, multilayer graphene oxide, multi-graphene oxide, reduced graphene oxide, reduced multilayer graphene oxide, reduced multi-graphene oxide, graphene quantum dots, and the like. In other words, graphene compounds may have functional groups. Graphene or graphene compounds preferably have a curved shape. Graphene or graphene compounds may be rolled, and rolled graphene is sometimes called carbon nanofiber.

[0202] In this specification and the like, graphene oxide refers to a material that contains carbon and oxygen, has a sheet shape, and has a functional group, in particular, an epoxy group, a carboxy group, or a hydroxy group.

[0203] In this specification and the like, reduced graphene oxide refers to a material containing carbon and oxygen, having a sheet-like shape, and having a two-dimensional structure formed by six-membered carbon rings. A single sheet of reduced graphene oxide can function, but multiple sheets may also be stacked. Reduced graphene oxide preferably has a portion where the carbon concentration is greater than 80 atomic % and the oxygen concentration is between 2 atomic % and 15 atomic %. By achieving these carbon and oxygen concentrations, reduced graphene oxide can function as a highly conductive material even in small amounts. Furthermore, reduced graphene oxide preferably has an intensity ratio G / D between the G band and the D band in a Raman spectrum of 1 or greater. Reduced graphene oxide with such an intensity ratio can function as a highly conductive material even in small amounts.

[0204] Fluorine-containing graphene may be used as the graphene compound. Fluorine-containing graphene can be produced by contacting graphene with a fluorine compound (called fluorination treatment). Fluorine (F2) or a fluorine compound may be used for the fluorination treatment. Preferred fluorine compounds include hydrogen fluoride, halogen fluorides (ClF3, IF5, etc.), gaseous fluorides (BF3, NF3, PF5, SiF4, SF6, etc.), and metal fluorides (LiF, NiF2, AlF3, MgF2, etc.). Gaseous fluorides are preferably used for the fluorination treatment, and the gaseous fluorides may be diluted with an inert gas. The fluorination treatment temperature is preferably room temperature, but is preferably between 0°C and 250°C, including room temperature. When the fluorination treatment is performed at 0°C or higher, fluorine can be adsorbed onto the surface of graphene.

[0205] Graphene compounds may have excellent electrical properties, such as high conductivity, and excellent physical properties, such as high flexibility and high mechanical strength. Graphene compounds may also have a sheet-like shape. Graphene compounds may have curved surfaces, enabling surface contact with low contact resistance. Even when thin, they may have very high conductivity, allowing a small amount of material to efficiently form a conductive path within an active material layer. Therefore, using a graphene compound as a conductive material can increase the contact area between the active material and the conductive material. The graphene compound preferably covers 80% or more of the active material. It is preferable that the graphene compound clings to at least a portion of the active material particles. It is also preferable that the graphene compound overlaps at least a portion of the active material particles. It is also preferable that the shape of the graphene compound matches at least a portion of the shape of the active material particles. The shape of the active material particles refers, for example, to the unevenness of a single active material particle or the unevenness formed by multiple active material particles. It is also preferable that the graphene compound surrounds at least a portion of the active material particles. The graphene compound may also have holes.

[0206] In FIG. 6B, a positive electrode active material layer including an active material 401, graphene 404, and acetylene black 403 is formed on a current collector 400. The graphene 404 is formed so as to partially cover a plurality of active material particles 401 or to be attached to the surfaces of the plurality of active material particles 401, and thus the particles are in surface contact with each other. Note that the graphene 404 preferably wraps around at least a portion of the active material 401. It is also preferable that the graphene 404 overlaps at least a portion of the active material 401. It is also preferable that the shape of the graphene 404 matches at least a portion of the shape of the active material 401. The shape of the active material refers to, for example, the unevenness of a single active material particle or the unevenness formed by a plurality of active material particles. It is also preferable that the graphene 404 surrounds at least a portion of the active material 401. The graphene 404 may have holes.

[0207] In the step of mixing graphene 404 and acetylene black 403 to obtain electrode slurry, the weight of acetylene black to be mixed is preferably 1.5 to 20 times, more preferably 2 to 9.5 times, that of graphene.

[0208] Furthermore, when the mixture of graphene 404 and acetylene black 403 is within the above range, the dispersion stability of acetylene black 403 is excellent and aggregation is unlikely to occur during slurry preparation. Furthermore, when the mixture of graphene 404 and acetylene black 403 is within the above range, a higher electrode density can be achieved than a positive electrode using only acetylene black 403 as a conductive material. Increasing the electrode density can increase the capacity per unit volume. Specifically, the density of the positive electrode active material layer measured by weight can be increased to more than 3.5 g / cc. Furthermore, when the positive electrode active material described in any of Embodiments 1 to 3 is used for the positive electrode and the mixture of graphene 404 and acetylene black 403 is within the above range, a synergistic effect can be expected in terms of increasing the capacity of the secondary battery, which is preferable.

[0209] Although the electrode density is lower than that of a positive electrode using only graphene as a conductive material, rapid charging can be achieved by mixing the first carbon material (graphene) and the second carbon material (acetylene black) in the above range. Furthermore, when the positive electrode active material described in any of Embodiments 1 to 3 is used for the positive electrode and the mixture of graphene 404 and acetylene black 403 is in the above range, the secondary battery is more stable and a synergistic effect of enabling further rapid charging can be expected, which is preferable.

[0210] These features are effective for use as a secondary battery for vehicles.

[0211] Increasing the number of secondary batteries and increasing the vehicle's weight reduces the driving range because the energy required to move increases. By using high-density secondary batteries, the driving range can be maintained with almost no change in the total weight of the vehicle equipped with the same weight of secondary batteries.

[0212] Furthermore, as vehicle secondary batteries reach high capacity, they require more power for charging, so it is desirable to complete charging in a short time.Furthermore, charging is performed under high-rate charging conditions during so-called regenerative charging, in which temporary power is generated when the vehicle brakes are applied and the power is charged, so good rate characteristics are required for vehicle secondary batteries.

[0213] By using the positive electrode active material described in any of the first to third embodiments for the positive electrode and setting the mixture ratio of acetylene black and graphene in an optimal range, it is possible to achieve both high electrode density and creation of appropriate gaps necessary for ion conduction, and a secondary battery for vehicle use having high energy density and favorable output characteristics can be obtained.

[0214] This configuration is also effective for a portable information terminal, and the secondary battery can be miniaturized and have a high capacity by using the positive electrode active material described in any of Embodiments 1 to 3 for the positive electrode and by setting the mixture ratio of acetylene black and graphene in an optimal range. In addition, by setting the mixture ratio of acetylene black and graphene in an optimal range, the portable information terminal can be rapidly charged.

[0215] In addition, in Figure 6(B), the boundary between the interior and surface of the active material 401 is indicated by a dotted line inside the active material 401. In Figure 6(B), the areas not filled with the active material 401, graphene 404, and acetylene black 403 indicate voids or binder. The voids are necessary for the electrolyte to penetrate, but if there are too many voids, the electrode density decreases, and if there are too few voids, the electrolyte cannot penetrate, and if they remain as voids even after the secondary battery is fabricated, the efficiency decreases.

[0216] By using the positive electrode active material described in any of Embodiments 1 to 3 for the positive electrode and setting the mixture ratio of acetylene black and graphene in an optimal range, it is possible to achieve both high electrode density and creation of appropriate gaps necessary for ion conduction, and a secondary battery with high energy density and favorable output characteristics can be obtained.

[0217] FIG. 6(C) illustrates an example of a positive electrode in which carbon nanotubes 405 are used as an example of fibrous carbon instead of graphene. FIG. 6(C) shows an example different from FIG. 6(B). The use of carbon nanotubes 405 can prevent aggregation of carbon black such as acetylene black 403 and improve dispersibility. The carbon nanotubes 405 have a fiber length of 1 μm or more and 20 μm or less and a fiber diameter of 10 nm or more and 100 nm or less.

[0218] Fluorine-containing carbon nanotubes may also be used. Fluorine-containing carbon nanotubes can be produced by contacting carbon nanotubes with a fluorine compound (called fluorination treatment). The same fluorination treatment as described for graphene can be applied to carbon nanotubes.

[0219] In FIG. 6(C), the regions not filled with the active material 401, the carbon nanotubes 405, and the acetylene black 403 indicate voids or binders.

[0220] Another example of a positive electrode is shown in Fig. 6(D). Fig. 6(C) shows an example in which carbon nanotubes 405 are used in addition to graphene 404. Using both graphene 404 and carbon nanotubes 405 can prevent aggregation of carbon black such as acetylene black 403 and further improve dispersibility.

[0221] Fluorine-containing acetylene black may also be used. Fluorine-containing acetylene black can be produced by contacting acetylene black with a fluorine compound (called fluorination treatment). The same fluorination treatment as described for graphene can be applied to acetylene black.

[0222] In FIG. 6(D), the regions that are not filled with the active material 401, the carbon nanotubes 405, the graphene 404, and the acetylene black 403 indicate voids or binders.

[0223] A secondary battery can be produced by using any one of the positive electrodes shown in Figures 6(A), 6(B), 6(C), and 6(D), placing a separator on the positive electrode, placing the laminate in which the negative electrode is placed on the separator, in a container (exterior body, metal can, etc.) that contains the laminate, and filling the container with an electrolyte.

[0224] As the binder, it is preferable to use a rubber material such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, ethylene-propylene-diene copolymer, etc. Also, as the binder, fluororubber can be used.

[0225] Furthermore, it is preferable to use, for example, a water-soluble polymer as the binder. Examples of the water-soluble polymer that can be used include polysaccharides. Examples of the polysaccharide that can be used include cellulose derivatives such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, and regenerated cellulose, as well as starch. It is even more preferable to use these water-soluble polymers in combination with the aforementioned rubber material.

[0226] Alternatively, it is preferable to use materials such as polystyrene, polymethyl acrylate, polymethyl methacrylate (polymethyl methacrylate, PMMA), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), ethylene propylene diene polymer, polyvinyl acetate, and nitrocellulose as the binder.

[0227] The binder may be used in combination with two or more of the above.

[0228] For example, a material with particularly excellent viscosity adjusting effect may be used in combination with other materials. For example, while rubber materials have excellent adhesive strength or elasticity, it may be difficult to adjust the viscosity when mixed with a solvent. In such cases, it is preferable to mix them with a material with particularly excellent viscosity adjusting effect. As a material with particularly excellent viscosity adjusting effect, for example, a water-soluble polymer may be used. Furthermore, as a water-soluble polymer with particularly excellent viscosity adjusting effect, the above-mentioned polysaccharides, for example, carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, cellulose derivatives such as regenerated cellulose, or starch may be used.

[0229] In addition, the solubility of cellulose derivatives such as carboxymethyl cellulose can be increased by converting them into salts such as sodium or ammonium salts of carboxymethyl cellulose, making them more effective as viscosity adjusters. Higher solubility can also improve dispersibility with active materials or other components when preparing electrode slurries. In this specification, the cellulose and cellulose derivatives used as electrode binders also include their salts.

[0230] Water-soluble polymers stabilize viscosity by dissolving in water, and can stably disperse active materials or other materials combined as binders, such as styrene-butadiene rubber, in aqueous solutions. Furthermore, their functional groups are expected to facilitate stable adsorption to the surface of active materials. Furthermore, many cellulose derivatives, such as carboxymethyl cellulose, contain functional groups, such as hydroxyl or carboxyl groups, and the functional groups are expected to allow interactions between polymers, resulting in widespread coverage of the active material surface.

[0231] When the binder covering or contacting the surface of the active material forms a film, it is expected to function as a passive film and suppress the decomposition of the electrolyte. Here, the passive film is a film with no electrical conductivity or a film with extremely low electrical conductivity. For example, when a passive film is formed on the surface of the active material, it can suppress the decomposition of the electrolyte at the battery reaction potential. Furthermore, it is more desirable that the passive film suppresses electrical conductivity while still allowing lithium ions to conduct.

[0232] Although the above configuration shows an example of a secondary battery using an electrolytic solution, the present invention is not particularly limited.

[0233] For example, a semi-solid battery can be fabricated using the positive electrode active material 100 described in the first to third embodiments.

[0234] In this specification, a semi-solid battery refers to a battery that has a semi-solid material in at least one of the electrolyte layer, positive electrode, and negative electrode. The term "semi-solid" does not mean that the ratio of solid material is 50%. Semi-solid means that the battery has solid properties, such as small volume change, while also possessing some liquid-like properties, such as flexibility. As long as these properties are met, the battery may be made of a single material or multiple materials. For example, the battery may be made by infiltrating a porous solid material with a liquid material.

[0235] In this specification, a polymer electrolyte secondary battery refers to a secondary battery having a polymer in the electrolyte layer between a positive electrode and a negative electrode. 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.

[0236] When a semi-solid battery is fabricated using the positive electrode active material 100 described in any of the first to third embodiments, the semi-solid battery becomes a secondary battery with a large charge / discharge capacity. Furthermore, the semi-solid battery can be a semi-solid battery with a high charge / discharge voltage. Alternatively, a semi-solid battery with high safety and reliability can be realized.

[0237] This embodiment mode can be freely combined with other embodiment modes.

[0238] (Embodiment 5) In this embodiment mode, examples of shapes of a secondary battery having a positive electrode manufactured by the manufacturing method described in the previous embodiment mode will be described.

[0239] [Coin-type secondary battery] An example of a coin-type secondary battery will be described. Fig. 7(A) is an exploded perspective view of a coin-type (single-layer flat) secondary battery, Fig. 7(B) is an external view, and Fig. 7(C) is a cross-sectional view thereof. Coin-type secondary batteries are mainly used in small electronic devices.

[0240] In addition, in order to make it easier to understand, Fig. 7(A) is a schematic diagram that shows the overlapping of components (upper and lower relationships and positional relationships), and therefore Fig. 7(A) and Fig. 7(B) are not completely corresponding drawings.

[0241] In Fig. 7(A), a positive electrode 304, a separator 310, a negative electrode 307, a spacer 322, and a washer 312 are stacked. These are sealed with a negative electrode can 302, a positive electrode can 301, and a gasket. Note that the gasket for sealing is not shown in Fig. 7(A). The spacer 322 and the washer 312 are used to protect the inside or to fix the position inside the can when the positive electrode can 301 and the negative electrode can 302 are crimped together. The spacer 322 and the washer 312 are made of stainless steel or an insulating material.

[0242] A positive electrode 304 has a laminated structure in which a positive electrode active material layer 306 is formed on a positive electrode current collector 305 .

[0243] FIG. 7(B) is a perspective view of the completed coin-type secondary battery.

[0244] In the coin-type secondary battery 300, a positive electrode can 301, which also serves as a positive electrode terminal, and a negative electrode can 302, which also serves as a negative electrode terminal, are insulated and sealed by a gasket 303 made of polypropylene or the like. The positive electrode 304 is formed by a positive electrode current collector 305 and a positive electrode active material layer 306 provided in contact with the positive electrode current collector. The negative electrode 307 is formed by a negative electrode current collector 308 and a negative electrode active material layer 309 provided in contact with the negative electrode current collector. The negative electrode 307 is not limited to a laminated structure, and may be made of lithium metal foil or a lithium-aluminum alloy foil.

[0245] It is to be noted that the positive electrode 304 and the negative electrode 307 used in the coin-type secondary battery 300 each only need to have an active material layer formed on one side.

[0246] Positive electrode can 301 and negative electrode can 302 can be made of a metal such as nickel, aluminum, or titanium that is corrosion-resistant to the electrolyte, or an alloy of these metals or an alloy of these metals with other metals (e.g., stainless steel). Furthermore, to prevent corrosion by the electrolyte, etc., they are preferably coated with nickel, aluminum, or the like. Positive electrode can 301 is electrically connected to positive electrode 304, and negative electrode can 302 is electrically connected to negative electrode 307.

[0247] These negative electrode 307, positive electrode 304, and separator 310 are immersed in an electrolyte solution, and as shown in FIG. 7(C), the positive electrode 304, separator 310, negative electrode 307, and negative electrode can 302 are stacked in this order with the positive electrode can 301 facing downwards, and the positive electrode can 301 and the negative electrode can 302 are crimped together via a gasket 303, thereby producing a coin-type secondary battery 300.

[0248] With the above configuration, the coin-type secondary battery 300 can be made to be highly safe.

[0249] [Cylindrical secondary battery] An example of a cylindrical secondary battery will be described with reference to Fig. 8(A). As shown in Fig. 8(A), a cylindrical secondary battery 616 has a positive electrode cap (battery lid) 601 on the top surface and a battery can (external can) 602 on the side and bottom surfaces. The positive electrode cap 601 and the battery can (external can) 602 are insulated by a gasket (insulating packing) 610.

[0250] Fig. 8(B) is a diagram showing a schematic cross section of a cylindrical secondary battery. The cylindrical secondary battery shown in Fig. 8(B) has a positive electrode cap (battery lid) 601 on the top surface, and a battery can (external can) 602 on the side and bottom surfaces. The positive electrode cap and battery can (external can) 602 are insulated by a gasket (insulating packing) 610.

[0251] A wound body is provided inside a hollow cylindrical battery can 602. The wound body is formed by winding a strip-shaped positive electrode 604 and a negative electrode 606 with a separator 605 sandwiched therebetween. Although not shown, the wound body is wound around a central axis. One end of the battery can 602 is closed and the other end is open. The battery can 602 can be made of a metal such as nickel, aluminum, or titanium that is corrosion-resistant to the electrolyte, or an alloy of these metals or an alloy of these metals with other metals (e.g., stainless steel). Furthermore, to prevent corrosion by the electrolyte, the battery can 602 is preferably coated with nickel, aluminum, or the like. Inside the battery can 602, the wound body formed by winding the positive electrode, the negative electrode, and the separator is sandwiched between a pair of opposing insulating plates 608 and 609. A nonaqueous electrolyte (not shown) is poured into the battery can 602, where the wound body is provided. The non-aqueous electrolyte may be the same as that used in coin-type secondary batteries.

[0252] Since the positive and negative electrodes used in a cylindrical storage battery are wound, it is preferable to form active materials on both sides of the current collector.

[0253] By using the positive electrode active material 100 obtained in any of Embodiments 1 to 3 for the positive electrode 604, a cylindrical secondary battery 616 with excellent safety can be obtained.

[0254] A positive electrode terminal (positive electrode current collector lead) 603 is connected to the positive electrode 604, and a negative electrode terminal (negative electrode current collector lead) 607 is connected to the negative electrode 606. Both the positive electrode terminal 603 and the negative electrode terminal 607 can be made of a metal material such as aluminum. The positive electrode terminal 603 is resistance-welded to a safety valve mechanism 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 (Positive Temperature Coefficient) element 611. The safety valve mechanism 613 cuts off the electrical connection between the positive electrode cap 601 and the positive electrode 604 when the increase in internal pressure of the battery exceeds a predetermined threshold. The PTC element 611 is a thermosensitive resistor whose resistance increases with an increase in temperature. This increase in resistance limits the amount of current and prevents abnormal heat generation. The PTC element can be made of barium titanate (BaTiO3)-based semiconductor ceramics or the like.

[0255] 8C shows an example of a power storage system 615. The power storage system 615 has a plurality of secondary batteries 616. A positive electrode of each secondary battery is in contact with and electrically connected to a conductor 624 separated by an insulator 625. The conductor 624 is electrically connected to a control circuit 620 via a wiring 623. A negative electrode of each secondary battery is electrically connected to the control circuit 620 via a 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 and / or overdischarging.

[0256] 8(D) shows an example of a power storage system 615. The power storage system 615 has a plurality of secondary batteries 616, and the plurality of secondary batteries 616 are sandwiched between a conductive plate 628 and a conductive plate 614. The plurality of secondary batteries 616 are electrically connected to the conductive plate 628 and the conductive plate 614 by wiring 627. The plurality of secondary batteries 616 may be connected in parallel or in series. By configuring the power storage system 615 to have a plurality of secondary batteries 616, a large amount of power can be extracted.

[0257] A plurality of secondary batteries 616 may be connected in parallel and then further connected in series.

[0258] Furthermore, a temperature control device may be provided between the multiple secondary batteries 616. When the secondary batteries 616 are overheated, they can be cooled by the temperature control device, and when the secondary batteries 616 are too cold, they can be heated by the temperature control device. This makes it difficult for the performance of the power storage system 615 to be affected by the outside temperature.

[0259] 8(D), the power storage system 615 is electrically connected to a control circuit 620 via wiring 621 and wiring 622. The wiring 621 is electrically connected to the positive electrodes of the plurality of secondary batteries 616 via a conductive plate 628, and the wiring 622 is electrically connected to the negative electrodes of the plurality of secondary batteries 616 via a conductive plate 614.

[0260] [Other examples of secondary battery structures] An example of the structure of the secondary battery will be described with reference to FIGS.

[0261] A secondary battery 913 shown in FIG. 9(A) has a wound body 950 provided with terminals 951 and 952 inside a housing 930. The wound body 950 is immersed in an electrolyte inside the housing 930. The terminal 952 contacts the housing 930, and the terminal 951 is not in contact with the housing 930 by using an insulating material or the like. Note that in FIG. 9(A), the housing 930 is shown separated for convenience, but in reality, the wound body 950 is covered by the housing 930, and the terminals 951 and 952 extend outside the housing 930. The housing 930 can be made of a metal material (e.g., aluminum) or a resin material.

[0262] 9(B), the housing 930 shown in FIG. 9(A) may be formed using a plurality of materials. For example, a secondary battery 913 shown in FIG. 9(B) has a housing 930a and a housing 930b bonded together, and a wound body 950 is provided in a region surrounded by the housing 930a and the housing 930b.

[0263] The housing 930a can be made of an insulating material such as organic resin. In particular, by using a material such as organic resin on the surface on which the antenna is formed, it is possible to prevent the secondary battery 913 from blocking the electric field. Note that if the electric field blocking effect of the housing 930a is small, the antenna may be provided inside the housing 930a. The housing 930b can be made of, for example, a metal material.

[0264] 9(C) shows the structure of the wound body 950. The wound body 950 has a negative electrode 931, a positive electrode 932, and a separator 933. The wound body 950 is a wound body in which the negative electrode 931 and the positive electrode 932 are stacked on top of each other with the separator 933 sandwiched therebetween, and the laminated sheet is wound. Note that a plurality of layers of the negative electrode 931, the positive electrode 932, and the separator 933 may be stacked.

[0265] 10A may be a secondary battery 913 having a wound body 950a. The wound body 950a shown in FIG. 10A includes a negative electrode 931, a positive electrode 932, and a separator 933. The negative electrode 931 includes a negative electrode active material layer 931a. The positive electrode 932 includes a positive electrode active material layer 932a.

[0266] By using the positive electrode active material 100 obtained in any of Embodiments 1 to 3 for the positive electrode 932, the secondary battery 913 can be highly safe.

[0267] The separator 933 has a width wider than the negative electrode active material layer 931a and the positive electrode active material layer 932a, and is wound so as to overlap the negative electrode active material layer 931a and the positive electrode active material layer 932a. From the standpoint of safety, it is preferable that the negative electrode active material layer 931a be wider than the positive electrode active material layer 932a. A wound body 950a having such a shape is preferable because of its high safety and productivity.

[0268] 10(B), the negative electrode 931 is electrically connected to a terminal 951 by ultrasonic bonding, welding, or crimping. The terminal 951 is electrically connected to a terminal 911a. The positive electrode 932 is electrically connected to a terminal 952 by ultrasonic bonding, welding, or crimping. The terminal 952 is electrically connected to a terminal 911b.

[0269] 10(C), the wound body 950a and the electrolyte are covered with a housing 930 to form a secondary battery 913. It is preferable that a safety valve, an overcurrent protection element, etc. be provided in the housing 930. The safety valve is a valve that opens when the inside of the housing 930 reaches a predetermined internal pressure to prevent the battery from exploding.

[0270] 10(B), the secondary battery 913 may have a plurality of wound bodies 950a. By using a plurality of wound bodies 950a, the secondary battery 913 can have a larger discharge capacity. For other elements of the secondary battery 913 shown in FIGS. 10(A) and 10(B), the descriptions of the secondary battery 913 shown in FIGS. 9(A) to 9(C) can be referred to.

[0271] <Laminated secondary battery> Next, an example of an external view of a laminated secondary battery is shown in Figures 11(A) and 11(B), which include 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.

[0272] FIG. 12(A) shows an external view of a positive electrode 503 and a negative electrode 506. The positive electrode 503 has a positive electrode current collector 501, and a positive electrode active material layer 502 is formed on the surface of the positive electrode current collector 501. The positive electrode 503 also has a region where the positive electrode current collector 501 is partially exposed (hereinafter referred to as a tab region). The negative electrode 506 has a negative electrode current collector 504, and a negative electrode active material layer 505 is formed on the surface of the negative electrode current collector 504. The negative electrode 506 also has a region where the negative electrode current collector 504 is partially exposed, i.e., a tab region. Note that the area or shape of the tab regions of the positive electrode and negative electrode are not limited to the example shown in FIG. 12(A).

[0273] <Method for manufacturing laminated secondary batteries> An example of a method for manufacturing the laminated secondary battery whose external view is shown in FIG. 11(A) will be described with reference to FIGS. 12(B) and 12(C).

[0274] First, the negative electrode 506, separator 507, and positive electrode 503 are stacked. FIG. 12(B) shows the stacked negative electrode 506, separator 507, and positive electrode 503. Here, an example is shown in which five pairs of negative electrodes and four pairs of positive electrodes are used. This can also be called a laminate consisting of a negative electrode, a separator, and a positive electrode. Next, the tab regions of the positive electrodes 503 are joined together, and a positive electrode lead electrode 510 is joined to the tab region of the outermost positive electrode. For example, ultrasonic welding or the like may be used for joining. Similarly, the tab regions of the negative electrodes 506 are joined together, and a negative electrode lead electrode 511 is joined to the tab region of the outermost negative electrode.

[0275] Next, the negative electrode 506 , the separator 507 , and the positive electrode 503 are placed on the exterior body 509 .

[0276] Next, as shown in Fig. 12(C), the exterior body 509 is folded at the portion indicated by the dashed line. Thereafter, the outer periphery of the exterior body 509 is joined. For example, thermocompression bonding may be used for joining. At this time, an area (hereinafter referred to as an inlet) that is not joined is provided in a part (or one side) of the exterior body 509 so that an electrolyte can be introduced later.

[0277] Next, the electrolyte solution is introduced into the inside of the exterior body 509 through an inlet provided in the exterior body 509. The introduction of the electrolyte solution is preferably carried out under a reduced pressure atmosphere or an inert atmosphere. Finally, the inlet is joined. In this manner, the laminated secondary battery 500 can be produced.

[0278] By using the positive electrode active material 100 obtained in any of the first to third embodiments for the positive electrode 503, the secondary battery 500 can be made to be excellent in safety.

[0279] (Sixth embodiment) In this embodiment, an example of a vehicle including a secondary battery of one embodiment of the present invention will be described.

[0280] The secondary battery can be applied to a typical example of a vehicle, such as an automobile. Examples of the automobile include next-generation clean energy automobiles, such as hybrid vehicles (HVs), electric vehicles (EVs), and plug-in hybrid vehicles (PHEVs or PHVs), and the secondary battery can be used as one of the power sources mounted on the automobile. The vehicle is not limited to an automobile. Examples of the vehicle include trains, monorails, ships, submersibles (deep-sea exploration vessels, unmanned submersibles), aircraft (helicopters, unmanned aerial vehicles (drones), airplanes, rockets, and artificial satellites), electric bicycles, and electric motorcycles. The secondary battery of one embodiment of the present invention can be applied to these vehicles.

[0281] The electric vehicle is equipped with first batteries 1301a and 1301b as main driving secondary batteries, and a second battery 1311 that supplies power to an inverter 1312 that starts a motor 1304. The second battery 1311 is also called a cranking battery (also called a starter battery). The second battery 1311 only needs to have high output, and does not need to have a large capacity, and the capacity of the second battery 1311 is smaller than that of the first batteries 1301a and 1301b.

[0282] The internal structure of the first battery 1301a may be a wound type shown in FIG. 9(C) or FIG. 10(A), or may be a stacked type shown in FIG. 11(A) or FIG. 11(B).

[0283] 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 having multiple secondary batteries, it is possible to extract large amounts of power. The multiple secondary batteries may be connected in parallel, in series, or in series after being connected in parallel. A plurality of secondary batteries is also called a battery pack.

[0284] In addition, in order to cut off power from a plurality of secondary batteries in a vehicle, a service plug or circuit breaker that can cut off high voltage without using tools is provided in the first battery 1301a.

[0285] The power of the first batteries 1301a and 1301b is mainly used to rotate the motor 1304, but also supplies power to 42V in-vehicle components (such as an electric power steering 1307, a heater 1308, and a defogger 1309) via a DC-DC circuit 1306. When a rear motor 1317 is provided on the rear wheels, the first battery 1301a is also used to rotate the rear motor 1317.

[0286] Furthermore, the second battery 1311 supplies power to 14V in-vehicle components (audio 1313, power windows 1314, lamps 1315, etc.) via the DCDC circuit 1310.

[0287] Next, the first battery 1301a will be described with reference to FIG.

[0288] FIG. 13A shows an example in which nine prismatic secondary batteries 1300 are used as one battery pack 1415. The nine prismatic secondary batteries 1300 are connected in series, with one electrode fixed by a fixing portion 1413 made of an insulator and the other electrode fixed by a fixing portion 1414 made of an insulator. While this embodiment shows an example in which the batteries are fixed by the fixing portions 1413 and 1414, they may also be housed in a battery housing box (also called a casing). Because it is expected that a vehicle will be subjected to external vibrations or shaking (such as from the road surface), it is preferable to fix multiple secondary batteries by the fixing portions 1413 and 1414, a battery housing box, or the like. One electrode is electrically connected to a control circuit unit 1320 by a wiring 1421. The other electrode is electrically connected to the control circuit unit 1320 by a wiring 1422.

[0289] Next, an example of a block diagram of the battery pack 1415 shown in FIG. 13(A) is shown in FIG. 13(B).

[0290] The control circuit unit 1320 includes a switch unit 1324 including at least a switch for preventing overcharging and a switch for preventing overdischarging, a control circuit 1322 for controlling the switch unit 1324, and a voltage measurement unit for the first battery 1301a. The control circuit unit 1320 sets upper and lower voltage limits for the secondary battery used and limits the upper limit of the current from the outside or the upper limit of the output current to the outside. The range between the lower limit and the upper limit of the secondary battery's voltage is within the recommended voltage range. If the voltage falls 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 overcharging and / or overdischarging. For example, if the control circuit 1322 detects a voltage that could cause overcharging, it turns off the switch unit 1324 to cut off the current. A PTC element may also be provided in the charge / discharge path to cut off the current in response to a rise in temperature. The control circuit section 1320 also has an external terminal 1325 (+IN) and an external terminal 1326 (-IN).

[0291] The switch unit 1324 can be configured by combining n-channel transistors or p-channel transistors. The switch unit 1324 is not limited to a switch having a Si transistor using single crystal silicon, and may be formed of a power transistor having, 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), or the like.

[0292] The first batteries 1301a and 1301b mainly supply power to 42V (high voltage) in-vehicle devices, and the second battery 1311 supplies power to 14V (low voltage) in-vehicle devices. A lead-acid battery is often used as the second battery 1311 because of its cost advantage.

[0293] In this embodiment, an example is shown in which lithium ion batteries are used for both the first battery 1301a and the second battery 1311. The second battery 1311 may be a lead storage battery, an all-solid-state battery, or an electric double layer capacitor.

[0294] Furthermore, regenerated energy generated by the rotation of the tire 1316 is sent to the motor 1304 via the gear 1305, and is then sent from the motor controller 1303 or the battery controller 1302 via the control circuit unit 1321 to charge the second battery 1311. Alternatively, the first battery 1301a is charged from the battery controller 1302 via the control circuit unit 1320. Alternatively, the first battery 1301b is charged from the battery controller 1302 via the control circuit unit 1320. In order to efficiently charge the regenerated energy, it is desirable that the first batteries 1301a and 1301b be capable of being rapidly charged.

[0295] 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 charging conditions according to the charging characteristics of the secondary battery used, and can perform rapid charging.

[0296] Although not shown, when an external charger is connected, the charger's outlet or the charger's connection cable is electrically connected to the battery controller 1302. The power supplied from the external charger is charged to the first batteries 1301a, 1301b via the battery controller 1302. Some chargers are provided with a control circuit, and although the function of the battery controller 1302 may not be used, it is preferable to charge the first batteries 1301a, 1301b via a control circuit unit 1320 to prevent overcharging. In some cases, the charger's outlet or the charger's connection cable is provided with a control circuit. The control circuit unit 1320 is also called an ECU (Electronic Control Unit). The ECU is connected to a CAN (Controller Area Network) provided in the electric vehicle. CAN is one of the serial communication standards used as an in-vehicle LAN. The ECU includes a microcomputer. The ECU uses a CPU or a GPU.

[0297] External chargers installed at charging stations and the like are available in 100V-200V outlets, or three-phase 200V and 50kW. Charging is also possible by receiving power from external charging equipment using a wireless power supply system, etc.

[0298] When rapid charging is performed, a secondary battery that can withstand high voltage charging is desired in order to charge in a short time.

[0299] Furthermore, by using graphene as a conductive material, it is possible to suppress capacity loss even when the electrode layer is thickened and the amount of graphene supported is increased, and this synergistic effect of maintaining high capacity allows for the realization of a secondary battery with significantly improved electrical properties. This is particularly effective for secondary batteries used in vehicles, and it is possible to provide vehicles with a long driving range, specifically a driving distance of 500 km or more per charge, without increasing the weight ratio of the secondary battery to the total vehicle weight.

[0300] In particular, the secondary battery of the present embodiment described above can increase the operating voltage of the secondary battery by using the positive electrode active material 100 described in any of the first to third embodiments, and the usable capacity can be increased as the charging voltage increases. Furthermore, by using the positive electrode active material 100 described in any of the first to third embodiments in the positive electrode, a secondary battery for vehicles with excellent safety can be provided.

[0301] Next, an example in which a secondary battery according to one embodiment of the present invention is mounted on a vehicle, typically a transportation vehicle, will be described.

[0302] When the secondary battery shown in any one of FIGS. 8(D), 10(C), and 13(A) is installed in a vehicle, next-generation clean energy automobiles such as hybrid vehicles (HVs), electric vehicles (EVs), and plug-in hybrid vehicles (PHVs) can be realized. Furthermore, the secondary battery can also be installed in agricultural machinery, motorized bicycles including electrically assisted bicycles, motorcycles, electric wheelchairs, electric carts, ships, submarines, aircraft, rockets, artificial satellites, space probes, planetary probes, or spacecraft. The secondary battery of one embodiment of the present invention can be a high-capacity secondary battery. Therefore, the secondary battery of one embodiment of the present invention is suitable for miniaturization and weight reduction and can be suitably used in transportation vehicles.

[0303] 14A to 14D illustrate examples of transportation vehicles using one embodiment of the present invention. An automobile 2001 shown in FIG. 14A is an electric automobile using an electric motor as a power source for traveling. Alternatively, it is a hybrid automobile that can appropriately select and use an electric motor or an engine as a power source for traveling. When a secondary battery is installed in a vehicle, an example of the secondary battery described in Embodiment 5 is installed in one or more locations. The automobile 2001 shown in FIG. 14A includes a battery pack 2200, which includes a secondary battery module to which multiple secondary batteries are connected. It is preferable that the automobile further includes a charge control device electrically connected to the secondary battery module.

[0304] Furthermore, automobile 2001 can charge its secondary battery by receiving power supply from an external charging facility using a plug-in system, a contactless power supply system, or the like. Charging can be performed using a predetermined charging method or connector standard, such as CHAdeMO (registered trademark) or Combo, as appropriate. The charging facility may be a charging station installed in a commercial facility or a household power source. For example, plug-in technology can be used to charge an electricity storage device installed in automobile 2001 using an external power supply. Charging can be performed by converting AC power to DC power via a conversion device such as an AC-DC converter.

[0305] Although not shown, a power receiving device can be mounted on a vehicle and power can be supplied contactlessly from a ground-based power transmitting device for charging. In the case of this contactless power supply method, by incorporating a power transmitting device into the road or an exterior wall, charging can be performed not only while the vehicle is stopped but also while the vehicle is moving. This contactless power supply method can also be used to transmit and receive power between two vehicles. Furthermore, solar cells can be installed on the exterior of the vehicle, and the secondary battery can be charged while the vehicle is stopped or moving. For such contactless power supply, an electromagnetic induction method or a magnetic field resonance method can be used.

[0306] Figure 14(B) shows a large transport vehicle 2002 having an electrically controlled motor as an example of a transport vehicle. The secondary battery module of the transport vehicle 2002 is, for example, a four-cell unit of secondary batteries with a nominal voltage of 3.0V to 5.0V, with 48 cells connected in series to achieve a maximum voltage of 170V. Apart from the number of secondary batteries constituting the secondary battery module of the battery pack 2201, it has the same functions as Figure 14(A), and therefore a description thereof will be omitted.

[0307] FIG. 14(C) shows, as an example, a large transport vehicle 2003 having an electrically controlled motor. The secondary battery module of the transport vehicle 2003 has, for example, a maximum voltage of 600 V, in which one hundred or more secondary batteries with a nominal voltage of 3.0 V or more and 5.0 V or less are connected in series. Therefore, a secondary battery with little variation in characteristics is required. By using a secondary battery using the positive electrode active material 100 described in any of the first to third embodiments as a positive electrode, a secondary battery with stable battery characteristics can be manufactured, and mass production at low cost is possible from the viewpoint of yield. Furthermore, except for the number of secondary batteries constituting the secondary battery module of the battery pack 2202, the same functions as those of FIG. 14(A) are provided, and therefore a description thereof will be omitted.

[0308] 14(D) shows, as an example, an aircraft 2004 having an engine that burns fuel. The aircraft 2004 shown in Fig. 14(D) has wheels for takeoff and landing, and can therefore be considered a type of transport vehicle, and has a battery pack 2203 that includes a secondary battery module formed by connecting multiple secondary batteries, and includes the secondary battery module and a charge control device.

[0309] The secondary battery module of the aircraft 2004 has a maximum voltage of 32 V, for example, when eight 4 V secondary batteries are connected in series. Except for the number of secondary batteries constituting the secondary battery module of the battery pack 2203, it has the same functions as those in Fig. 14(A), and therefore a description thereof will be omitted.

[0310] 14(E) shows an example of an artificial satellite 2005 equipped with a secondary battery 2204. Since the artificial satellite 2005 is used in outer space, it is desirable that the artificial satellite 2005 does not suffer from failure due to ignition, and it is preferable that the artificial satellite 2005 be equipped with the secondary battery 2204, which is an embodiment of the present invention and has excellent safety. It is further preferable that the secondary battery 2204 be mounted inside the artificial satellite 2005 while being covered with a heat-insulating member.

[0311] (Embodiment 7) In this embodiment, an example in which a lithium-ion battery according to one embodiment of the present invention is mounted on a motorcycle or a bicycle will be described as an example in which a secondary battery is mounted on a vehicle.

[0312] 15A illustrates an example of an electric bicycle using a power storage device of one embodiment of the present invention. The power storage device of one embodiment of the present invention can be applied to an electric bicycle 8700 illustrated in FIG. 15A. The power storage device of one embodiment of the present invention includes, for example, a plurality of storage batteries and a protection circuit.

[0313] The electric bicycle 8700 includes a power storage device 8702. The power storage device 8702 can supply electricity to a motor that assists a rider. The power storage device 8702 is portable and is shown in a state removed from the bicycle in FIG. 15B . The power storage device 8702 includes a plurality of built-in storage batteries 8701, which are included in the power storage device of one embodiment of the present invention, and a display unit 8703 can display the remaining battery charge and other information. The power storage device 8702 also includes a control circuit 8704 that can control charging or detect an abnormality of the secondary battery. The control circuit 8704 is electrically connected to the positive electrode and the negative electrode of the storage battery 8701. Combining the power storage device 8702 with a secondary battery using the positive electrode active material 100 obtained in any of Embodiments 1 to 3 for its positive electrode provides a synergistic effect in terms of safety. The secondary battery using the positive electrode active material 100 obtained in any of Embodiments 1 to 3 for its positive electrode and the control circuit 8704 are highly safe and can significantly contribute to preventing accidents such as fires caused by secondary batteries.

[0314] 15C illustrates an example of a two-wheeled vehicle using the power storage device of one embodiment of the present invention. A scooter 8600 illustrated in FIG. 15C includes a power storage device 8602, a side mirror 8601, and a turn signal light 8603. The power storage device 8602 can supply electricity to the turn signal light 8603. The power storage device 8602 includes a plurality of secondary batteries each using the positive electrode active material 100 obtained in any of Embodiments 1 to 3 for its positive electrode. This power storage device 8602 can have a high capacity, which can contribute to miniaturization.

[0315] 15C, a scooter 8600 can store a power storage device 8602 in an 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.

[0316] (Embodiment 8) In this embodiment, an example in which a secondary battery according to one embodiment of the present invention is mounted in an electronic device will be described. Examples of electronic devices in which a secondary battery is mounted include television sets (also referred to as televisions or television receivers), computer monitors, digital cameras, digital video cameras, digital photo frames, mobile phones (also referred to as mobile phones or mobile phone devices), portable game consoles, personal digital assistants, sound players, and large game consoles such as pachinko machines. Examples of personal digital assistants include notebook personal computers, tablet devices, e-book readers, and mobile phones.

[0317] 16A shows an example of a mobile phone. The mobile phone 2100 includes a display portion 2102 built into a housing 2101, an operation button 2103, an external connection port 2104, a speaker 2105, a microphone 2106, and the like. The mobile phone 2100 also includes a secondary battery 2107. By including the secondary battery 2107 using the positive electrode active material 100 described in any of Embodiments 1 to 3 as a positive electrode, a high capacity can be achieved, and a configuration that can accommodate space saving due to miniaturization of the housing can be realized.

[0318] The mobile phone 2100 can execute various applications such as mobile phone calls, e-mail, document browsing and creation, music playback, internet communication, and computer games.

[0319] The operation button 2103 can be provided with various functions, such as time setting, power on / off operation, wireless communication on / off operation, silent mode activation / deactivation, power saving mode activation / deactivation, etc. For example, the functions of the operation button 2103 can be freely set by an operating system built into the mobile phone 2100.

[0320] The mobile phone 2100 is also capable of performing standardized short-range wireless communication, and can also make hands-free calls by communicating with a wirelessly enabled headset, for example.

[0321] The mobile phone 2100 also has an external connection port 2104, and can directly exchange data with other information terminals via a connector. Charging can also be performed via the external connection port 2104. Charging may also be performed by wireless power supply without using the external connection port 2104.

[0322] Furthermore, the mobile phone 2100 preferably has a sensor. As the sensor, for example, a fingerprint sensor, a pulse sensor, a human body sensor such as a body temperature sensor, a touch sensor, a pressure sensor, an acceleration sensor, or the like is preferably installed.

[0323] FIG. 16B illustrates an unmanned aerial vehicle 2300 having a plurality of rotors 2302. The unmanned aerial vehicle 2300 is sometimes called a drone. The unmanned aerial vehicle 2300 includes a secondary battery 2301 according to one embodiment of the present invention, a camera 2303, and an antenna (not shown). The unmanned aerial vehicle 2300 can be remotely controlled via the antenna. A secondary battery using the positive electrode active material 100 obtained in any of Embodiments 1 to 3 for its positive electrode has high energy density and high safety; therefore, it can be used safely for a long period of time and is suitable as a secondary battery to be installed in the unmanned aerial vehicle 2300.

[0324] Fig. 16(C) shows an example of a robot. The robot 6400 shown in Fig. 16(C) includes 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, an obstacle sensor 6407, a moving mechanism 6408, a computing device, etc.

[0325] The microphone 6402 has a function of detecting the user's speaking voice, environmental sounds, etc. The speaker 6404 has a function of emitting sound. The robot 6400 can communicate with the user using the microphone 6402 and the speaker 6404.

[0326] The display unit 6405 has a function of displaying various information. The robot 6400 can display 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, which can be installed in a fixed position on the robot 6400 to enable charging and data transfer.

[0327] The upper camera 6403 and the lower camera 6406 have the function of capturing images of the surroundings of 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 the surrounding environment and move safely using the upper camera 6403, the lower camera 6406, and the obstacle sensor 6407.

[0328] The robot 6400 includes a secondary battery 6409 according to one embodiment of the present invention and a semiconductor device or an electronic component in its internal region. The secondary battery using the positive electrode active material 100 obtained in any of Embodiments 1 to 3 for its positive electrode has high energy density and high safety, and therefore can be used safely for a long period of time. Therefore, the secondary battery 6409 is suitable for the robot 6400.

[0329] 16(D) shows an example of a cleaning robot. The cleaning robot 6300 includes a display unit 6302 arranged on the top surface of a housing 6301, a plurality of cameras 6303 arranged on the side surfaces, a brush 6304, an operation button 6305, a secondary battery 6306, various sensors, and the like. Although not shown, the cleaning robot 6300 is provided with tires, a suction port, and the like. The cleaning robot 6300 can move by itself, detect dust 6310, and suck up the dust from a suction port arranged on the bottom surface.

[0330] The cleaning robot 6300 can analyze an image captured by the camera 6303 and determine whether or not there is an obstacle such as a wall, furniture, or a step. Furthermore, when an object that may become entangled in the brush 6304, such as a wire, is detected by image analysis, the cleaning robot 6300 can stop rotation of the brush 6304. The cleaning robot 6300 includes a secondary battery 6306 according to one embodiment of the present invention and a semiconductor device or an electronic component in its internal region. The secondary battery using the positive electrode active material 100 obtained in any of Embodiments 1 to 3 for its positive electrode has high energy density and high safety, and therefore can be used safely for a long period of time. Therefore, the secondary battery 6306 is suitable for use in the cleaning robot 6300.

[0331] (Embodiment 9) In this embodiment, thermal runaway and nail penetration tests of secondary batteries will be described, and the principles behind why secondary batteries using one or more of the positive electrode active materials 100 and 101 according to one embodiment of the present invention are less likely to catch fire when subjected to a nail penetration test will be described.

[0332] <Thermal runaway of secondary batteries> The graph shown on page 69 [Figure 2-11] of Non-Patent Document 1 is quoted and partially modified in Figure 17. Figure 17 is a graph of the internal temperature (hereinafter simply referred to as temperature) of a secondary battery versus time, and shows that as the temperature rises, it passes through several states before reaching thermal runaway.

[0333] Generally, when the temperature of a secondary battery reaches or approaches 100°C, (1) the SEI (Solid Electrolyte Interphase) of the negative electrode collapses and heat is generated. Furthermore, when the temperature of the secondary battery exceeds 100°C, (2) the negative electrode (when graphite is used, the negative electrode becomes C6Li) reduces the electrolyte and generates heat, and (3) the positive electrode oxidizes the electrolyte and generates heat. When the temperature of the secondary battery reaches or approaches 180°C, (4) the electrolyte thermally decomposes, and (5) oxygen is released from the positive electrode and thermal decomposition occurs (this thermal decomposition includes a structural change in the positive electrode active material). When the temperature of the secondary battery exceeds 200°C, (6) the negative electrode decomposes, and finally (7) the positive and negative electrodes come into direct contact. After experiencing the above-mentioned states (5), (6), or (7), the secondary battery reaches thermal runaway. That is, to prevent thermal runaway, it is advisable to suppress the temperature rise of the secondary battery and to keep the negative electrode, positive electrode and / or electrolyte in a stable state even at high temperatures exceeding 100°C.

[0334] The cathode active materials 100 and 101 according to the first to third embodiments of the present invention have a stable crystal structure and exhibit the effect of suppressing oxygen desorption. Therefore, a secondary battery using the cathode active material 100 or the cathode active material 101 is considered to at least prevent the state (5) and subsequent states from occurring, thereby suppressing the temperature rise of the secondary battery, and exhibiting the remarkable effect of preventing thermal runaway.

[0335] <Nail penetration test> Next, the nail penetration test will be described using Figures 18(A) and 18(B), etc. The nail penetration test is a test in which a secondary battery 1500 is fully charged (a state equivalent to a 100% SOC state), and a nail 1603 having a predetermined diameter selected from 2 mm to 10 mm is inserted into the battery at a predetermined speed selected from 1 mm / s to 20 mm / s, etc. Figure 18(A) shows a cross-sectional view of the secondary battery 1500 with the nail 1603 inserted. The secondary battery 1500 has a structure in which a positive electrode 1503, a separator 1508, a negative electrode 1506, and an electrolyte 1530 are housed in an exterior body 1531. The positive electrode 1503 has a positive electrode current collector 1501 and positive electrode active material layers 1502 formed on both sides thereof, and the negative electrode 1506 has a negative electrode current collector 1511 and negative electrode active material layers 1512 formed on both sides thereof. 18(B) shows an enlarged view of the nail 1603 and the positive electrode current collector 1501, and clearly shows the positive electrode active material 101 of Embodiment 1 and the conductive material 1553 contained in the positive electrode active material layer 1502.

[0336] Generally, as shown in Figures 18(A) and 18(B), when a nail 1603 penetrates the positive electrode 1503 and the negative electrode 1506, an internal short circuit occurs. Then, the potential of the nail 1603 becomes equal to the potential of the negative electrode, and electrons (e - ) flows to the positive electrode 1503, and Joule heat is generated at the internal short circuit point and its vicinity. In addition, due to the internal short circuit, carrier ions, typically lithium ions (Li + ) are released into the electrolyte as shown by the white arrow. If there are insufficient anions in the electrolyte 1530 at this time, the electrolyte 1530 cannot absorb all the lithium ions released from the negative electrode 1506, and the electrolyte 1530 begins to decompose. This is an electrochemical reaction, and is called a reduction reaction of the electrolyte by the negative electrode. Then, the electrons (e -), the tetravalent cobalt in the charged lithium cobalt oxide (also called LCO) is reduced to trivalent or divalent, and this reduction reaction causes oxygen to be released from the lithium cobalt oxide, which then decomposes the electrolyte 1530. This is an electrochemical reaction, and is called the oxidation reaction of the electrolyte by the positive electrode. The same reaction occurs in NCM.

[0337] Generally, when an internal short circuit occurs in a secondary battery, the temperature changes as shown in the graph in Figure 19. Figure 19 is a partially modified version of the graph shown on page 70 (Figures 2-12) of Non-Patent Document 1. It is a graph of the temperature of a secondary battery over time, showing that when an internal short circuit occurs at (P0), the temperature of the secondary battery rises over time. Specifically, as shown in (P1), heat generation due to Joule heat continues, and when the temperature of the secondary battery reaches or near 100°C, it exceeds the reference temperature (Ts) of the secondary battery. Then, at (P2), the negative electrode (if graphite is used, the negative electrode becomes C6Li) reduces the electrolyte and generates heat. At (P3), the positive electrode oxidizes the electrolyte and generates heat. At (P4), heat is generated due to thermal decomposition of the electrolyte. The secondary battery then experiences thermal runaway and may catch fire.

[0338] When a nail penetration test is performed on a secondary battery using one or more of the positive electrode active materials 100 and 101 according to the present invention described in the first to third embodiments, it is believed that the rate at which current flows into the positive electrode in the event of an internal short circuit is slowed down because the positive electrode active materials 100 and 101 have the above-described shell. This is expected to have significant effects, such as reducing the likelihood of thermal runaway and catching fire.

[0339] (Embodiment 10) In this embodiment, a positive electrode active material 1201 of one embodiment of the present invention will be described with reference to FIG.

[0340] The positive electrode active material 1201 contains lithium, a transition metal M, and oxygen. The transition metal M is one or more selected from nickel, manganese, and cobalt. It is preferable that the positive electrode active material 1201 further contains an additive element. Alternatively, the positive electrode active material 1201 may contain lithium nickel-manganese-cobalt oxide to which the additive element has been added.

[0341] A positive electrode active material of a lithium-ion secondary battery needs to contain a transition metal capable of oxidation and reduction in order to maintain charge neutrality even when lithium ions are inserted or extracted. The positive electrode active material 1201 of one embodiment of the present invention contains nickel, manganese, and cobalt as the transition metal M responsible for the oxidation and reduction reaction.

[0342] When the proportion of nickel in the transition metal M contained in the positive electrode active material 1201 is large, it is preferable that the charge / discharge capacity is easily increased even at a low charge voltage, compared to when cobalt is the majority. Therefore, for example, nickel preferably accounts for 50% or more of the transition metal M, more preferably 60% or more, and even more preferably 75% or more. The positive electrode active material 1201 contains fluorine, but the positive electrode active material excluding fluorine is LiNi x Co y Mn z A NiCoMn-based alloy (also called NCM) represented by O2 (x>0, y>0, z>0) is used. As an example, it is preferable that x, y, and z satisfy the following relationship: x:y:z=5:2:3 or a value close thereto. Alternatively, it is preferable that x, y, and z satisfy the following relationship: x:y:z=8:1:1 or a value close thereto. Alternatively, it is preferable that x, y, and z satisfy the following relationship: x:y:z=9:0.5:0.5 or a value close thereto.

[0343] An additive element may be added to the positive electrode active material 1201, for example, one or more selected from magnesium, aluminum, calcium, titanium, zirconium, fluorine, vanadium, iron, manganese, chromium, niobium, arsenic, zinc, silicon, sulfur, phosphorus, boron, bromine, and beryllium. The ratio of the number of atoms of the additive element to the sum of the number of atoms of the transition metal M (M is nickel, cobalt, and manganese) is preferably less than 25 atomic %, more preferably less than 10 atomic %, and still more preferably less than 5 atomic %.

[0344] These added elements further stabilize the crystal structure of the positive electrode active material 1201, as will be described later.

[0345] Furthermore, the surface layer 1204 preferably has a higher fluorine concentration than the interior 1200c. The interior 1200c preferably has a higher nickel concentration than the surface layer. Furthermore, to allow the surface layer 1204 to function as a barrier film, LCO with an additive element added thereto may be used, such as magnesium. When magnesium is used, the interior 1200c can be made into NCM by mixing a cobalt compound, magnesium fluoride, and NCM and heating the mixture, and the magnesium concentration and fluorine concentration of the surface layer 1204 can be made higher than those of the interior 1200c.

[0346] Stability is improved by including magnesium in the LCO surface layer 1204. Furthermore, fluorine is included in the surface layer 1204, which can suppress ignition or overheating of the lithium-ion secondary battery, further improving thermal safety.

[0347] <Surface and surface layer> 21A is a cross-sectional view of a single particle of positive electrode active material 1201. Positive electrode active material 1201 preferably has a shell 1200d, a surface layer 1204, and an inner portion 1200c.

[0348] The positive electrode active material 1201 of one embodiment of the present invention preferably has a region capable of increasing resistance. This region is sometimes referred to as a "first region" to distinguish it from other regions. The region preferably has a narrow (short) width of 2 nm to 20 nm, preferably 2 nm to 10 nm, and more preferably 2 nm to 5 nm in cross-sectional view. The narrow region is sometimes referred to as a "shell" in this specification and elsewhere. FIG. 21A shows an example in which the shell 1200d covers the surface layer 1204 of the particle. The positive electrode active material 1201 having such a shell 1200d is preferable because it can slow down the rate of current flowing into the positive electrode active material and prevent fire, smoke, or the like even when a nail penetration test is performed on a secondary battery.

[0349] The Shell 1200d may also contain cobalt, and the Shell 1200d may also contain lithium ions (Li + ) can be inserted and removed, and the rate of current flow due to an internal short circuit can be slowed down. The positive electrode active material 1201 has a first region and a second region deeper than the first region. At least the first region may contain magnesium, but the second region may not contain magnesium. When the first region and the second region contain cobalt, lithium ions (Li + ) is thought to be able to be inserted and removed.

[0350] When EDX analysis is performed on the positive electrode active material 1201, the peak of the magnesium concentration in the surface layer 1204 is preferably present at a depth of 3 nm from the boundary between the shell and the surface layer of the positive electrode active material 1201 toward the center, more preferably at a depth of 1 nm, and even more preferably at a depth of 0.5 nm. The magnesium concentration preferably decays to 60% or less of the peak at a depth of 1 nm from the peak top. It is also preferable that the magnesium concentration decays to 30% or less of the peak at a depth of 2 nm from the peak top. The "peak concentration" referred to here refers to the maximum concentration value.

[0351] Furthermore, when EDX analysis is performed, the fluorine distribution in surface layer 1204 of positive electrode active material 1201 preferably overlaps with the magnesium distribution. For example, the difference in depth between the peak of the fluorine concentration and the peak of the magnesium concentration is preferably within 10 nm, more preferably within 3 nm, and even more preferably within 1 nm.

[0352] Furthermore, when EDX analysis is performed, the nickel concentration peak in the surface layer 1204 preferably exists within a depth of 3 nm from the boundary between the shell and the surface layer toward the center, more preferably within a depth of 1 nm, and even more preferably within a depth of 0.5 nm. Furthermore, in the surface layer 1204 containing magnesium and nickel, the nickel distribution preferably overlaps with the magnesium distribution. For example, the difference in depth between the nickel concentration peak and the magnesium concentration peak is preferably within 10 nm, more preferably within 3 nm, and even more preferably within 1 nm.

[0353] Furthermore, when EDX line analysis, area analysis, or point analysis is performed on the positive electrode active material 1201, the ratio of the number of atoms of magnesium (Mg) to cobalt (Co) (Mg / Co) at the peak of the magnesium concentration is preferably 0.05 or more and 0.6 or less, and more preferably 0.1 or more and 0.4 or less. The ratio of the number of atoms of nickel (Ni) to cobalt (Co) (Ni / Co) at the peak of the nickel concentration is preferably 0 or more and 0.2 or less, and more preferably 0.01 or more and 0.1 or less. The ratio of the number of atoms of fluorine (F) to cobalt (Co) (F / Co) at the peak of the fluorine concentration is preferably 0 or more and 1.6 or less, and more preferably 0.1 or more and 1.4 or less.

[0354] FIG. 21(B) shows a schematic cross-sectional view of the positive electrode active material 1211, and FIG. 21(C) shows an enlarged conceptual diagram of the boxed region B in FIG. 21(B). As shown in FIG. 21(C), it is preferable that fluorine, one of the additive elements, is adsorbed onto the surface 1200a of the positive electrode active material. Fluorine has a high electronegativity and easily forms stable compounds with many elements. When the adsorbed fluorine chemically reacts with and bonds to the surface elements, the surface can be said to have fluoro groups.

[0355] 21(C) shows a state in which at least fluorine is adsorbed to shell 1200d of positive electrode active material 1201. Furthermore, as long as the adsorbed fluorine sufficiently contributes to suppressing ignition or overheating of the lithium ion secondary battery and further improving thermal safety, fluorine does not need to be present inside shell 1200d, and fluorine does not need to be present inside surface layer 1204 either.

[0356] The presence of shell 1200d or adsorbed fluorine makes it difficult for oxygen to be released from positive electrode active material 1201, thereby suppressing thermal decomposition reactions. By using positive electrode active material 1201 having shell 1200d in the positive electrode, it is possible to suppress ignition or overheating of the lithium ion secondary battery and improve thermal safety.

[0357] Note that adsorption includes chemical adsorption and physical adsorption. Chemical adsorption is the formation of a chemical bond through a chemical reaction between at least one of the added elements and the surface 1200a of the positive electrode active material, while physical adsorption is adsorption due to an intermolecular force (van der Waals force) acting between at least one of the added elements and the surface of the positive electrode active material 1201. As will be described later, fluorine may substitute for some of the oxygen in the positive electrode active material 1201. If there is sufficient fluorine in the positive electrode active material 1201, fluorine will be present adsorbed on the surface and fluorine will substitute for some of the oxygen.

[0358] Examples of fluorides used in lithium ion secondary batteries include lithium salts such as LiPF6 and LiBF4, and binders such as polyvinylidene fluoride (PVDF). Fluorine from such fluorides may be adsorbed onto the surface 1200a of the positive electrode active material.

[0359] In FIG. 21(A), the surface layer 1204 of the positive electrode active material 1201 refers to, for example, a region extending from the interface between the shell 1200d and the surface layer to the interior within 50 nm, more preferably within 35 nm, even more preferably within 20 nm, and most preferably within 10 nm, perpendicular or approximately perpendicular to the surface from the interface between the shell 1200d and the surface layer to the interior. Note that "approximately perpendicular" refers to an angle between 80° and 100°. Surfaces resulting from cracks and / or fissures may also be referred to as the surface 1200a. The contour of the surface 1200a of the positive electrode active material 1201 can be confirmed by cross-sectional observation. The surface layer 1204 can also be referred to as a barrier film, which is synonymous with the near-surface or near-surface region.

[0360] In FIG. 21(A), an example in which the shell 1200d is provided so as to have a uniform thickness is shown, but this is not particularly limited.

[0361] The region deeper than the surface layer 1204 of the positive electrode active material is referred to as the interior 1200c. The interior 1200c is synonymous with the internal region or core. The surface layer 1204 can also be referred to as the first shell, and the shell 1200d can also be referred to as the second shell. The interior 1200c has a different composition from the surface layer 1204, which is LCO, and is NCM. Therefore, the interior 1200c and the surface layer 1204 have a boundary, but the boundary may not be clear depending on the heating conditions.

[0362] The surface 1200a of the positive electrode active material refers to the surface of the shell 1200d. Therefore, the positive electrode active material 1201 does not include metal oxides, such as aluminum oxide, that do not have lithium sites that can contribute to charge and discharge and are attached to the surface 1200a, carbonates that are chemically adsorbed after the preparation of the positive electrode active material, or hydroxyl groups. The attached metal oxides refer to metal oxides whose crystal structure does not match that of the interior 1200c and the surface layer 1204, for example.

[0363] The positive electrode active material 1201 is a compound containing oxygen and a transition metal capable of inserting and extracting lithium ions. Therefore, the interface between the region where the transition metal M (e.g., Co, Ni, Mn, Fe, etc.) that is oxidized and reduced upon insertion and extraction of lithium ions and oxygen is present and the region where they are not present is defined as the surface 1200a of the positive electrode active material. When analyzing the positive electrode active material, a protective film may be attached to the surface, but the protective film is not included in the positive electrode active material. The protective film may be a single-layer or multilayer film of carbon, metal, oxide, resin, or the like.

[0364] This embodiment can be used in combination with other embodiments.

[0365] (Embodiment 11) In this embodiment, an example of a method for manufacturing the positive electrode active material 1201 described in Embodiment 10 is shown in FIG.

[0366] First, in step S11, a lithium source and a transition metal M for the inside 1200c of the positive electrode active material 1201 are mixed. 191 A source of transition metal M is prepared. 191 Sources include cobalt, nickel, and manganese.

[0367] Next, in step S12, a lithium source and a transition metal M for the inside 1200c of the positive electrode active material 1201 are 191 As a synthesis method, for example, a method in which a lithium source and a transition metal source for the inner portion 1200c of the positive electrode active material 1201 are mixed by a solid phase method, and then heated is used.

[0368] In this way, the composite oxide C contained in the interior 1200c of the positive electrode active material 1201 191 In this embodiment, an example of synthesis is shown, but the composite oxide C 191 A commercially available product equivalent to the above may also be used.

[0369] Next, in step S121, a cobalt source, a lithium source, and a fluorine source for the surface layer 1204 of the positive electrode active material 1201 are prepared. Cobalt fluoride can be used as the cobalt source, lithium fluoride (LiF) can be used as the lithium source, and magnesium fluoride can be used as the fluorine source. LiF is preferable because it has a relatively low melting point of 848°C and is easily melted in the annealing step described below. Using magnesium fluoride allows magnesium to be concentrated near the surface of the positive electrode active material.

[0370] Next, in step S131, a fluorine source and a composite oxide C contained in the inside 1200c of the positive electrode active material 1201 are mixed. 191 The cathode active material 1201 is synthesized with a cobalt source and a lithium source for the surface layer 1204 of the cathode active material 1201. This synthesis converts the interior 1200c of the cathode active material 1201 into an NCM, and the interior 1200c is covered with the surface layer 1204. The surface layer 1204 is a barrier film containing at least cobalt, magnesium, and lithium, and has a layered rock salt crystal structure. The synthesis method includes mixing these materials using a solid-phase method and then heating. Alternatively, a sol-gel method may be used as the synthesis method.

[0371] The annealing method in step S131 is the same as that in step S31 in the first embodiment, and therefore will not be described here.

[0372] The annealing in step S131 is preferably performed at an appropriate temperature for an appropriate time. If the annealing temperature is too high, the materials melt and mix with each other, making it impossible to obtain the positive electrode active material 1201 having a barrier layer. The temperature-reducing time after annealing is preferably, for example, 10 hours to 50 hours. The annealed material is then recovered to obtain the positive electrode active material 1201.

[0373] In this manner, the positive electrode active material 1201 shown in Fig. 21(A) is produced (step S132). After step S131, a process of contacting the surface 1200a with a solution containing fluorine may be performed to adsorb fluorine onto the surface 1200a. In this case, fluorine or fluoride can be adsorbed onto the surface 1200a.

[0374] When fluorine is added at a high concentration, the treatment of contacting the substrate with a solution containing fluorine may be repeated.

[0375] The positive electrode active material 1211 shown in FIG. 21B can be manufactured according to the flow shown in FIG. 22B, for example.

[0376] First, in step S11, a lithium source and a transition metal M for the internal 1200c are 191 Prepare the source and.

[0377] Next, in step S12, a lithium source and a transition metal M for the inside 1200c of the positive electrode active material 1211 are mixed. 191 As a synthesis method, for example, a method of mixing a lithium source and a transition metal source for the inner portion 1200c of the positive electrode active material 1211 by a solid phase method, and then heating the mixture is used.

[0378] In this way, the composite oxide C contained in the inside 1200c of the positive electrode active material 1211 191 In this embodiment, an example of synthesis is shown, but the composite oxide C 191 A commercially available product equivalent to the above may also be used.

[0379] Next, in step S42, a lithium source and a cobalt source for the surface layer portion 1204 are prepared.

[0380] Next, in step S53, the composite oxide C contained in the inside 1200c of the positive electrode active material 1211 is 191 The lithium source and the cobalt source are mixed together by a solid phase method, followed by heating.

[0381] In this way, a composite oxide C having an inner portion 1200c covered with a surface layer portion 1204 is formed. 194At this stage, it is possible to obtain particles in which the interior 1200c of the positive electrode active material 1211, that is, the surface of the NCM, is coated with LCO (lithium cobalt oxide) (step S54).

[0382] Next, in step S62, a magnesium source for the surface layer 1204 and a fluorine source for adsorbing fluorine onto the surface are prepared.

[0383] Next, in step S73, the composite oxide C 194 , and a magnesium source and a fluorine source for the surface layer portion 1204 are synthesized. Through this synthesis, the surface layer portion 1204, which is made of LCO (lithium cobalt oxide), is doped with magnesium or fluorine. As a synthesis method, for example, a method in which these are mixed by a solid phase method and then heated may be used. Alternatively, a sol-gel method may be used as the synthesis method.

[0384] In this way, the positive electrode active material 1211 shown in Fig. 21(C) is produced (step S74). After step S73, a process of contacting the surface 1200a with a solution containing fluorine may be performed to adsorb fluorine onto the surface 1200a. In this case, fluorine or fluoride can be adsorbed onto the surface 1200a.

[0385] This embodiment can be used in combination with other embodiments.

[0386] (Embodiment 12) In the eleventh embodiment, an example is shown in which the inner portion 1200c and the surface portion 1204 of the positive electrode active material 1201 are produced by the solid phase method, but the inner portion 1200c of the positive electrode active material 1201 can also be produced by the coprecipitation method.

[0387] In this embodiment, an example of a method for manufacturing a positive electrode active material 1200f of one embodiment of the present invention will be described with reference to Fig. 4, Fig. 5, and Fig. 23. The steps up to the middle of the manufacturing process are the same as those for the positive electrode active material 100 of Embodiment 3, that is, the steps up to the manufacturing process of the composite oxide 99, and therefore detailed description thereof will be omitted here.

[0388] According to the third embodiment, in step S111 of FIG. 4, first, a transition metal M source including a nickel source (Ni source), a cobalt source (Co source), and a manganese source (Mn source) is prepared.

[0389] Next, as shown in step S113 of FIG. 4, a chelating agent is prepared.

[0390] Next, in step S114 of FIG. 4, a source of the transition metal M and a chelating agent are mixed to prepare an acid solution.

[0391] Next, in step S121 of FIG. 4, an alkaline solution is prepared.

[0392] Next, as shown in step S122 of FIG. 4, water is prepared in the reaction vessel.

[0393] 4, the acid solution and the alkaline solution are mixed and reacted with each other, which can be called a co-precipitation reaction, a neutralization reaction, or an acid-base reaction.

[0394] During the coprecipitation reaction in step S131, it is preferable to keep the pH of the reaction system at 9.0 or higher and 11.5 or lower.

[0395] By the above coprecipitation reaction, a composite hydroxide 98 containing the transition metal M is precipitated.

[0396] Next, in order to recover the composite hydroxide 98, it is preferable to carry out filtration as shown in step S132 of FIG.

[0397] Next, as shown in step S133 of FIG. 4, the composite hydroxide 98 after filtration may be dried.

[0398] In this way, a composite hydroxide 98 containing a transition metal M can be obtained.

[0399] Next, as in the third embodiment, a lithium source is prepared in step S141 of Fig. 23. Note that step S141 of Fig. 23 is the same as step S141 of Fig. 5. At this time, because the process of adding the lithium source and heating is performed multiple times, an amount of lithium prepared in step S141 that is less than the final amount is used. For example, when the sum of the atoms of nickel, cobalt, and manganese is 1, the amount of lithium can be 0.5 to 0.9 (atomic ratio), and more preferably 0.7 (atomic ratio).

[0400] Next, in step S142 of Fig. 23, composite hydroxide 98 and a lithium source are mixed together. Note that step S142 of Fig. 23 is the same as step S142 of Fig. 5.

[0401] Next, the mixture of composite hydroxide 98 and the lithium source is heated (step S143). To distinguish from other heating steps, in Fig. 23, step S143 may be referred to as the first heating, step S253 as the second heating, and step S255 as the third heating.

[0402] The firing equipment used for these heating processes can be an electric furnace or a rotary kiln. The crucibles, saggers, setters, and containers used during heating should preferably be made of materials that do not easily release impurities. For example, a crucible made of aluminum oxide with a purity of 99.9% is recommended. For mass production, a sagger made of mullite-cordierite (Al2O3·SiO2·MgO) is recommended. It is also preferable to heat these containers with their lids on.

[0403] The heating temperature in step S143 is preferably 400° C. to 750° C., more preferably 650° C. to 750° C. The heating time in step S143 is preferably 1 hour to 30 hours, more preferably 2 hours to 20 hours.

[0404] The heating is preferably carried out in an oxygen-containing atmosphere or a so-called dry air atmosphere containing little water (for example, a dew point of -50°C or less, more preferably a dew point of -80°C or less).

[0405] Next, in step S144, it is preferable to have a crushing step after heating. Through the above steps, in step S145, a composite oxide 99 is obtained. The composite oxide 99 is a material that can be called NCM.

[0406] <Step S181> Next, in step S181, a lithium source is prepared. Lithium fluoride is used as the lithium source. When lithium fluoride is used, the amount of lithium in step S181 is adjusted so that the final amount of lithium is achieved in combination with step S141.

[0407] <Step S252> Next, the composite oxide 99 obtained in step S145 is mixed with the lithium source (lithium fluoride).

[0408] <Step S253> Next, the mixture of composite oxide 99 and fluorine source is heated. The heating in step S253 is preferably performed at a sufficiently high temperature to increase the crystallite size of positive electrode active material 1200f, but the range may vary depending on the composition of transition metal M.

[0409] When the proportion of nickel in the transition metal M is high, for example, 70% or more, the temperature is preferably, for example, 750°C or higher, more preferably 800°C or higher, and even more preferably 850°C or higher. On the other hand, if the temperature is too high, there is a risk that the transition metal M, such as nickel, may be reduced to a divalent state. Therefore, for example, the temperature is preferably 950°C or lower, more preferably 920°C or lower, and even more preferably 900°C or lower.

[0410] When the proportion of nickel in the transition metal M is 40% or more and 60% or less, for example, a temperature of 900°C or more is preferable, more preferably 950°C or more, and more preferably around 970°C. On the other hand, if the temperature is too high, the same disadvantages as those described above may occur, so a temperature of 1020°C or less is preferable, and more preferably 990°C or less. For other heating conditions, refer to the description of step S143.

[0411] It is also preferable to have a crushing step after heating as step S254. The description of step S144 can be referred to for the crushing step.

[0412] <Step S255> Furthermore, it is more preferable to perform heating in step S255. By performing this heating, residues of the lithium source and the like can be reduced. The heating temperature in step S255 is preferably 400°C or higher and 900°C or lower, more preferably 750°C or higher and 850°C or lower. Furthermore, the heating time in step S255 is preferably 1 hour or higher and 30 hours or lower, more preferably 2 hours or higher and 20 hours or lower. However, the heating in step S255 does not necessarily have to be performed.

[0413] It is also preferable to have a crushing step after heating as step S256. The crushing can be carried out in accordance with the description of step S144. After crushing, the mixture is collected.

[0414] Through the above process, in step S257, a composite oxide 199 is obtained. The composite oxide 199 is a material that can be called NCM.

[0415] <Step S258> Next, a lithium source and a cobalt source are prepared.

[0416] Next, in step S260, the composite oxide 199, the lithium source, and the cobalt source are synthesized. The synthesis in step S260 may involve mixing these materials by a solid phase method and then heating them.

[0417] In this way, composite oxide 299 having an interior (composite oxide 199) covered with a surface layer is produced (step S262). At this stage, particles in which the interior of positive electrode active material 1200f, i.e., NCM, is covered with LCO (lithium cobalt oxide), can be obtained.

[0418] Next, in step S263, a magnesium source and a fluorine source to be adsorbed onto the surface of the composite oxide 299 are prepared.

[0419] Next, in step S271, composite oxide 299, a magnesium source, and a fluorine source are synthesized. This synthesis results in magnesium or fluorine being doped into the surface layer of LCO (lithium cobalt oxide). For example, the synthesis method may involve mixing these materials using a solid-phase method and then heating. Alternatively, a sol-gel method may be used as the synthesis method.

[0420] Through the above steps, positive electrode active material 1200f can be produced (step S275). Note that, since the steps from step S257 onwards are the same as the steps from step S12 onwards shown in embodiment 2, they are shown here in a simplified manner. Furthermore, in order to shorten the process, the steps from step S257 onwards may be the steps from step S121 onwards shown in FIG. 22(A).

[0421] This embodiment mode can be freely combined with other embodiment modes.

[0422] (Embodiment 13) To fabricate a secondary battery using the positive electrode active materials 1201, 1211, and 1200f described in any one of Embodiments 10 to 12, an example of a positive electrode to be fabricated is shown below. The secondary battery includes at least an outer casing, a current collector, an active material (positive electrode active material or negative electrode active material), a conductive material, and a binder. It also includes an electrolyte solution containing a lithium salt or the like. A secondary battery using an electrolyte solution includes a positive electrode, a negative electrode, and a separator between the positive electrode and the negative electrode. It is preferable to use a material having a fluoro group in the electrolyte solution. Using a material having a fluoro group in the electrolyte solution also allows fluorine to be adsorbed on the surface of the positive electrode active materials 1201, 1211, and 1200f. Furthermore, using a material having a fluoro group in the electrolyte solution allows fluorine adsorbed on the surface of the positive electrode active materials 1201, 1211, and 1200f to be stably maintained.

[0423] First, the positive electrode will be described. Figure 24(A) shows an example of a schematic cross-sectional view of a positive electrode. Figure 24(A) is the same as Figure 6(A) except for the active material, so the same parts are designated by the same reference numerals and detailed descriptions of the same parts will be omitted.

[0424] The current collector 400 is a metal foil, and the positive electrode is formed by applying a slurry onto the metal foil and drying it. After drying, a pressing process may be further performed. The positive electrode is formed by forming an active material layer on the current collector 400.

[0425] 24A illustrates acetylene black 403 as the conductive material. Also, FIG. 24A illustrates an example in which a second active material 402 having a particle size smaller than that of the positive electrode active materials 1201, 1211, and 1200f described in any one of Embodiments 10 to 12 is mixed. Mixing particles of different sizes allows a high-density positive electrode to be obtained.

[0426] A binder (resin) is mixed to bond the current collector 400, such as a metal foil, and the active material to form the positive electrode of the secondary battery. The binder is also called a binding agent. The binder is a polymer material, and if a large amount of binder is added, the proportion of active material in the positive electrode decreases, resulting in a smaller discharge capacity of the secondary battery. Therefore, the amount of binder mixed is kept to a minimum. In Figure 24(A), the areas not filled with the active material 701, second active material 402, and acetylene black 403 indicate voids or binder.

[0427] In addition, in Figure 24(A), the boundary between the interior and surface layer of active material 701 is indicated by a solid line. Note that the shell corresponding to the outer shell of the surface layer of active material 701 is thin and is not shown in Figure 24(A). Also, active material 701 in Figure 24(A) shows an example in which the cross-sectional shape is nearly circular, and is an example equivalent to positive electrode active material 1201 in Figure 21(A). The surface layer contains magnesium at a higher concentration than the interior, which can suppress ignition or overheating of the lithium-ion secondary battery and improve thermal safety.

[0428] 24A shows an example in which the active material 701 is spherical, but the shape is not particularly limited and various shapes are possible. The cross-sectional shape of the active material 701 may be elliptical, rectangular, trapezoidal, conical, quadrangular with rounded corners, or asymmetrical.

[0429] FIG. 24(B) shows an example different from FIG. 24(A). Also, FIG. 24(B) shows an example of an active material 701 having an irregular shape. Also, in FIG. 24(B), the boundary between the interior and surface layer of active material 701 is indicated by a solid line. Note that the shell corresponding to the outer shell of the surface layer of active material 701 is thin and is not shown in FIG. 24(B). The surface layer of active material 701 contains magnesium at a higher concentration than the interior, which can suppress ignition or overheating of the lithium-ion secondary battery and improve thermal safety.

[0430] In addition, in the positive electrode in FIG. 24B, graphene 404 is used as a carbon material used as a conductive material.

[0431] In FIG. 24B, a positive electrode active material layer including an active material 701, graphene 404, and acetylene black 403 is formed on a current collector 400. The graphene 404 is formed so as to partially cover a plurality of active material particles 701 or to be attached to the surfaces of the plurality of active material particles 701, and thus the particles are in surface contact with each other. Note that the graphene 404 preferably wraps around at least a portion of the active material 701. It is also preferable that the graphene 404 overlaps at least a portion of the active material 701. It is also preferable that the shape of the graphene 404 matches at least a portion of the shape of the active material 701. The shape of the active material refers to, for example, the unevenness of a single active material particle or the unevenness formed by a plurality of active material particles. It is also preferable that the graphene 404 surrounds at least a portion of the active material 701. The graphene 404 may have holes.

[0432] In the step of mixing graphene 404 and acetylene black 403 to obtain electrode slurry, the weight of acetylene black to be mixed is preferably 1.5 to 20 times, more preferably 2 to 9.5 times, that of graphene.

[0433] Furthermore, when the mixture of graphene 404 and acetylene black 403 is within the above range, the dispersion stability of acetylene black 403 is excellent and agglomerations are less likely to occur during slurry preparation. Furthermore, when the mixture of graphene 404 and acetylene black 403 is within the above range, a higher electrode density can be achieved than a positive electrode using only acetylene black 403 as a conductive material. Increasing the electrode density increases the capacity per unit volume. Specifically, the density of the positive electrode active material layer measured gravimetrically can be increased to more than 3.5 g / cc. Furthermore, when one or more of 1201, 1211, and 1200f described in Embodiments 10 to 12 are used as the positive electrode active material 701 and the mixture of graphene 404 and acetylene black 403 is within the above range, a synergistic effect can be expected to increase the capacity of the secondary battery, which is preferable.

[0434] Although the electrode density is lower than that of a positive electrode using only graphene as a conductive material, rapid charging can be achieved by mixing the first carbon material (graphene) and the second carbon material (acetylene black) in the above range. Furthermore, using one or more of the positive electrode active materials 1201, 1211, and 1200f described in any of Embodiments 10 to 12 as the positive electrode active material 701 and mixing the graphene 404 and the acetylene black 403 in the above range is expected to produce a synergistic effect of further increasing the stability of the secondary battery and enabling it to be further rapidly charged, which is preferable.

[0435] These features are effective for use as a secondary battery for vehicles.

[0436] Increasing the number of secondary batteries and increasing the vehicle's weight reduces the driving range because the energy required to move increases. By using high-density secondary batteries, the driving range can be maintained with almost no change in the total weight of the vehicle equipped with the same weight of secondary batteries.

[0437] Furthermore, as vehicle secondary batteries reach high capacity, they require more power for charging, so it is desirable to complete charging in a short time.Furthermore, charging is performed under high-rate charging conditions during so-called regenerative charging, in which temporary power is generated when the vehicle brakes are applied and the power is charged, so good rate characteristics are required for vehicle secondary batteries.

[0438] By using one or more of the positive electrode active materials 1201, 1211, and 1200f described in any of Embodiments 10 to 12 as the positive electrode active material 701 and by adjusting the mixing ratio of acetylene black to graphene within an optimal range, it is possible to achieve both high electrode density and creation of appropriate gaps necessary for ion conduction, and a secondary battery for automotive use having high energy density and favorable output characteristics can be obtained.

[0439] This configuration is also effective in a portable information terminal, and by using one or more of the positive electrode active materials 1201, 1211, and 1200f described in any of Embodiments 10 to 12 as the positive electrode active material 701 and by adjusting the mixture ratio of acetylene black to graphene in an optimal range, the secondary battery can be miniaturized and have a high capacity. In addition, by adjusting the mixture ratio of acetylene black to graphene in an optimal range, the portable information terminal can be rapidly charged.

[0440] 24(B), the boundary between the interior and surface of the active material 701 is indicated by a solid line inside the active material 701. In FIG. 24(B), the areas not filled with the active material 701, graphene 404, and acetylene black 403 indicate voids or binders. The voids are necessary for the electrolyte to penetrate, but if there are too many voids, the electrode density decreases, and if there are too few voids, the electrolyte cannot penetrate, and if they remain as voids even after the secondary battery is fabricated, the efficiency decreases.

[0441] By using one or more of the positive electrode active materials 1201, 1211, and 1200f described in any of embodiments 10 to 12 as the positive electrode active material 701 and by adjusting the mixing ratio of acetylene black to graphene within an optimal range, it is possible to achieve both high electrode density and creation of appropriate gaps necessary for ion conduction, and a secondary battery with high energy density and favorable output characteristics can be obtained.

[0442] Fig. 24(C) shows an example of a positive electrode in which carbon nanotubes 405 are used as an example of fibrous carbon instead of graphene. Fig. 24(C) shows an example different from Fig. 24(B). The use of carbon nanotubes 405 can prevent aggregation of carbon black such as acetylene black 403 and improve dispersibility.

[0443] Fluorine-containing carbon nanotubes may also be used. Fluorine-containing carbon nanotubes can be produced by contacting carbon nanotubes with a fluorine compound (called fluorination treatment). The same fluorination treatment as described for graphene can be applied to carbon nanotubes.

[0444] In FIG. 24(C), the regions not filled with the active material 701, the carbon nanotubes 405, and the acetylene black 403 indicate voids or binders.

[0445] Another example of a positive electrode is shown in Fig. 24(D). Fig. 24(C) shows an example in which carbon nanotubes 405 are used in addition to graphene 404. Using both graphene 404 and carbon nanotubes 405 can prevent aggregation of carbon black such as acetylene black 403 and further improve dispersibility.

[0446] Fluorine-containing acetylene black may also be used. Fluorine-containing acetylene black can be produced by contacting acetylene black with a fluorine compound (called fluorination treatment). The same fluorination treatment as described for graphene can be applied to acetylene black.

[0447] In FIG. 24(D), the regions that are not filled with the active material 701, the carbon nanotubes 405, the graphene 404, and the acetylene black 403 indicate voids or binders.

[0448] A secondary battery can be produced by using any one of the positive electrodes shown in Figures 24(A), 24(B), 24(C), and 24(D), stacking a separator on the positive electrode, placing the stacked negative electrode on the separator in a container (exterior body, metal can, etc.) that contains the stacked body, and filling the container with an electrolyte.

[0449] Although the above configuration shows an example of a secondary battery using an electrolytic solution, the present invention is not particularly limited.

[0450] For example, a semi-solid battery can be fabricated using one or more of the positive electrode active materials 1201, 1211, and 1200f described in the tenth to twelfth embodiments as the positive electrode active material.

[0451] When a semi-solid battery is fabricated using one or more of the positive electrode active materials 1201, 1211, and 1200f described in Embodiments 10 to 12, the semi-solid battery becomes a secondary battery with a large charge / discharge capacity. Furthermore, the semi-solid battery can be a semi-solid battery with a high charge / discharge voltage. Alternatively, a semi-solid battery with high safety and reliability can be realized.

[0452] This embodiment mode can be freely combined with other embodiment modes. [Explanation of symbols]

[0453] 98 Complex hydroxides 99 Complex oxides 100a surface 100b Surface layer 100c internal 100d shell 100f positive electrode active material 100 Cathode active material 101 Cathode active material 104 Surface layer 111 Cathode active material 199 Complex Oxides 202 Space inside heating furnace 204 Hot plate 206 Heater section 208 Insulation 216 Container 218 Lid 219 Space 220 Heating Furnace 299 Complex Oxides 300 Secondary battery 301 Positive electrode can 302 Anode 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 322 Spacer 400 current collector 401 Active material 402 Second active material 403 Acetylene Black 404 Graphene 405 Carbon nanotubes 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 509 Exterior body 510 Positive lead electrode 511 Negative lead electrode 601 Positive electrode cap 602 Battery can 603 Positive terminal 604 Positive electrode 605 Separator 606 negative electrode 607 Negative terminal 608 Insulating plate 609 Insulating board 611 PTC element 613 Safety valve mechanism 614 Conductive Plate 615 Energy Storage System 616 Secondary battery 620 Control Circuit 621 Wiring 622 Wiring 623 Wiring 624 Conductors 625 Insulator 626 Wiring 627 Wiring 628 Conductive Plate 701 Active material 903 mixture 911a terminal 911b terminal 913 Secondary battery 930a housing 930b housing 930 chassis 931a Negative electrode active material layer 931 negative electrode 932a Cathode active material layer 932 Positive electrode 933 Separator 950a Wound body 950 Wound body 951 terminal 952 terminals 1200a surface 1200c internal 1200d shell 1200f positive electrode active material 1201c internal 1201 Cathode active material 1204 Surface layer 1211 Cathode active material 1300 Prismatic secondary battery 1301a First Battery 1301b First 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 Second Battery 1312 inverter 1313 Audio 1314 Power window 1315 Lamps 1316 Tires 1317 Rear motor 1320 Control circuit section 1321 Control circuit section 1322 control circuit 1324 Switch section 1413 Fixed part 1414 Fixed part 1415 Battery Pack 1421 Wiring 1422 Wiring 1500 secondary battery 1501 Positive electrode current collector 1502 Cathode active material layer 1503 Positive electrode 1506 negative electrode 1508 Separator 1511 Negative electrode current collector 1512 Negative electrode active material layer 1530 Electrolyte 1531 Exterior body 1553 Conductive materials 1603 Nail 2001 Automobile 2002 Transport Vehicle 2003 Transport Vehicle 2004 aircraft 2005 Satellite 2100 mobile phone 2101 Housing 2102 Display section 2103 Operation button 2104 External connection port 2105 Speaker 2106 Mike 2107 Secondary battery 2200 battery pack 2201 Battery pack 2202 Battery Pack 2203 Battery Pack 2204 Secondary battery 2300 Unmanned Aircraft 2301 Secondary battery 2302 rotor 2303 Camera 6300 Cleaning Robot 6301 Housing 6302 Display section 6303 Camera 6304 Brush 6305 Operation button 6306 Secondary battery 6310 Garbage 6400 Robot 6401 Illuminance Sensor 6402 Microphone 6403 Upper Camera 6404 Speaker 6405 Display section 6406 Lower Camera 6407 Obstacle Sensor 6408 Moving mechanism 6409 Secondary battery 8600 Scooter 8601 Side mirror 8602 Energy storage devices 8603 Turn signal light 8604 Under-seat storage 8700 Electric Bicycle 8701 Storage battery 8702 Energy storage devices 8703 Display section 8704 Control circuit

Claims

1. A positive electrode active material having a transition metal M, oxygen, fluorine, and magnesium, The transition metal M comprises nickel, manganese, and cobalt. The positive electrode active material has a surface layer and an interior, The surface of the positive electrode active material contains fluorine, The surface layer has a higher magnesium concentration than the interior. A positive electrode active material having magnesium bonded with oxygen in its surface layer, wherein some of the oxygen in the oxygen-bonded magnesium is replaced with fluorine.

2. A positive electrode active material having a transition metal M, oxygen, fluorine, and magnesium, The transition metal M comprises nickel, manganese, and cobalt. The positive electrode active material has a surface layer and an interior, The surface of the positive electrode active material contains fluorine, The surface layer has a higher magnesium concentration than the interior. A positive electrode active material having magnesium bonded with oxygen and fluorine in the surface layer.

3. A positive electrode active material having a transition metal M, oxygen, fluorine, and magnesium, The transition metal M comprises nickel, manganese, and cobalt. The positive electrode active material has a surface layer and an interior, The surface of the positive electrode active material contains fluorine, The surface layer has a higher magnesium concentration than the interior. In the aforementioned surface layer, magnesium bonded with oxygen is present, and a portion of the oxygen in the oxygen-bonded magnesium is replaced by fluorine. A positive electrode active material in which, in the surface layer, some of the oxygen contained in the positive electrode active material is replaced with fluorine.

4. A positive electrode active material having a transition metal M, oxygen, fluorine, and magnesium, The transition metal M comprises nickel, manganese, and cobalt. The positive electrode active material has a surface layer and an interior, The surface of the positive electrode active material contains fluorine, The surface layer has a higher magnesium concentration than the interior. The surface layer contains magnesium bonded with oxygen and fluorine, A positive electrode active material having cobalt bonded with fluorine in the surface layer.

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