Method for producing lithium manganese iron phosphate, and positive electrode

Abstract

Provided is lithium manganese iron phosphate that exhibits excellent charge / discharge characteristics and has a high manganese ratio. This positive electrode includes a positive electrode active material having an olivine-type crystal structure. The positive electrode active material includes lithium, manganese, iron, phosphorus, and oxygen. In the positive electrode active material, the atomic ratio (Mn / (Mn+Fe)) of manganese to the sum of manganese and iron is 0.80-0.95. When a powder X-ray diffraction pattern of the positive electrode active material as measured by using Cu Kα1 line is subjected to Rietveld analysis, the crystallite size (LVol-IB) of the olivine-type crystal structure is 25-50 nm.

Description

Method for producing lithium manganese iron phosphate and cathode

[0001] One aspect of the present invention relates to a product, method, or method of production; or to a process, machine, manufacture, or composition of matter. One aspect of the present invention relates to energy storage devices including secondary batteries, semiconductor devices, display devices, light-emitting devices, lighting devices, electronic devices, or methods for producing the same. Another aspect of the present invention relates to a secondary battery and a product that can be used as a material for the active material contained therein, or to a method for producing the same.

[0002] In this specification, "electronic equipment" refers to all devices that have an energy storage device, and all electro-optical devices with an energy storage device, information terminal devices with an energy storage device, etc., are considered electronic equipment.

[0003] In recent years, there has been a great deal of development on various energy storage devices, including lithium-ion secondary batteries, lithium-ion capacitors, and air batteries. In particular, lithium-ion secondary batteries, with their high output and high energy density, have seen a rapid increase in demand in portable information terminals such as mobile phones, smartphones, and notebook computers, as well as portable music players, digital cameras, medical equipment, and clean energy vehicles such as hybrid vehicles (HVs), electric vehicles (EVs), and plug-in hybrid vehicles (PHVs). Along with the development of the semiconductor industry, they have become an indispensable source of rechargeable energy for modern society.

[0004] LiMPO, which has an olivine-type crystal structure, is one of the materials that is expected to be used as a positive electrode active material for lithium-ion batteries and is being actively researched and developed. ４ (M = Fe, Mn, Ni, Co) Among these, LiFePO ４ It has already achieved charge / discharge capacities close to its theoretical capacity (168 mAh / g) (for example, Non-Patent Document 1), and secondary batteries using this have been installed in EVs, etc. LiFePO ４ It exhibits excellent charge-discharge cycle characteristics and good thermal stability.

[0005] Japanese Patent Publication No. 2011-222494

[0006] A. Yamada, S.C. Chung and K. Hinokuma, “Optimized LiFePO▲4▼ for Lithium Battery Cathodes”, J. Electrochem. Soc., 148, A224-229 (2001).

[0007] However, LiFePO ４ has a low energy density of 578 Wh / kg compared to other commercialized cathode active materials.

[0008] LiMnPO ４ is expected to be able to increase the energy density because it shows a higher voltage plateau than LiFePO ４ . Also, materials such as solid solutions of LiMnPO ４ and LiFePO ４ LiMn ｘ Fe （１−ｘ） PO ４ (0 < x < 1) (for example, LiMn ０．５ Fe ０．５ PO ４ ) have been studied (Patent Document 1).

[0009] However, LiMnPO ４ and LiMn ｘ Fe （１−ｘ） PO ４ (0 < x < 1) have problems that the conductivity becomes lower than that of LiFePO ４ when the manganese (Mn) ratio is high, that is, when x is large, and the solid-state lithium ion diffusion coefficient becomes small. Therefore, the charge-discharge capacity may be smaller than the theoretically expected value. Also, there is a problem that the charge-discharge capacity decreases at high rates or low temperatures (for example, 0 °C or lower). For example, when mounted on an EV, if the charge-discharge capacity is insufficient, the cruising range will be shortened. Also, if the discharge capacity at high rates is insufficient, there is a risk that the vehicle cannot be accelerated sufficiently, and if the charge-discharge capacity at low temperatures compared to room temperature is extremely low, the EV will become unusable due to a decrease in the outside air temperature.

[0010] Also, LiMn ｘ Fe （１−ｘ） PO ４(0 < x < 1) can be produced by liquid-phase methods such as hydrothermal methods and solvothermal methods, or by solid-phase methods in which powder materials are mixed and heated. The positive electrode active material used in secondary batteries is required to have a high energy density and high charge-discharge cycle characteristics, but at the same time, it is also required to be able to be manufactured at low cost. For this reason, LiMn ｘ Fe （１−ｘ） PO ４ (0 < x < 1) is preferably manufactured by a solid-phase method, which is easier to reduce manufacturing costs.

[0011] Therefore, one aspect of the present invention aims to provide a positive electrode active material or composite oxide with high energy density, or a secondary battery using the same. Alternatively, one aspect aims to provide a positive electrode active material or composite oxide with high discharge capacity, or a secondary battery using the same. Alternatively, one aspect aims to provide a positive electrode active material or composite oxide with a high voltage plateau, which maintains a high voltage plateau even after charge-discharge cycles, or a secondary battery using the same. Alternatively, one aspect aims to provide a positive electrode active material or composite oxide with suppressed reduction in charge-discharge capacity at low temperatures, or a secondary battery using the same. Alternatively, one aspect aims to provide a positive electrode active material or composite oxide with suppressed capacity reduction during high-rate charge-discharge, or a secondary battery using the same. Alternatively, one aspect aims to provide a positive electrode active material or composite oxide with suppressed reduction in energy density at high temperatures, or a secondary battery using the same. Alternatively, one aspect aims to provide a secondary battery that exhibits good electrical characteristics over a wide temperature range. Alternatively, one aspect aims to provide a secondary battery that is safe or highly reliable.

[0012] Furthermore, one aspect of the present invention aims to provide a novel positive electrode active material, composite oxide, secondary battery, energy storage device, or a method for producing the same. Alternatively, one aspect of the present invention aims to provide a novel positive electrode active material, composite oxide, secondary battery, energy storage device, or a method for producing the same at low cost.

[0013] Furthermore, the description of these problems does not preclude the existence of other problems. Moreover, one aspect of the present invention does not need to solve all of these problems. It is possible to extract other problems from the description, drawings, and claims.

[0014] To solve the above problems, in one aspect of the present invention, LiMn with a small crystallite size ｙ Fe （１−ｙ） PO ４ We decided to produce (y is between 0.80 and 0.95). Note that LiMn ｙ Fe （１−ｙ） PO ４ When y is between 0.80 and 0.95, it is called high-manganese lithium iron manganese phosphate.

[0015] One aspect of the present invention provides a positive electrode active material having an olivine-type crystal structure, wherein the positive electrode active material contains lithium, manganese, iron, phosphorus, and oxygen, and the atomic ratio of manganese to the sum of manganese and iron in the positive electrode active material (Mn / (Mn+Fe)) is 0.80 or more and 0.95 or less, and the positive electrode active material is CuKα １ When Rietveld analysis was performed on the powder X-ray diffraction pattern using a linear pattern, the cathode was found to have a crystallite size (LVol-IB) of olivine-type crystal structure between 25 nm and 50 nm.

[0016] One aspect of the present invention is LiMn ｙ Fe （１−ｙ） PO ４This is a method for producing lithium manganese iron phosphate, represented by (y being between 0.80 and 0.95). As a specific example of the said manufacturing method, in a first mixing process, a lithium source, a manganese source, an iron source, and a phosphoric acid source are mixed to produce a first mixture; in a first heat treatment, the first mixture is heated; in a second mixing process, the first mixture after the first heat treatment is mixed with glucose to produce a second mixture; in a second heat treatment, the second mixture is heated; the first and second mixing processes are performed using a ball mill device, the diameter of the balls used in the second mixing process is smaller than the diameter of the balls used in the first mixing process; the first heat treatment is performed in an inert atmosphere at a temperature of 300°C to 400°C for 1 hour to 20 hours; and the second heat treatment is performed in an inert atmosphere at a temperature of 500°C to 800°C for 1 hour to 20 hours, thereby producing lithium iron manganese phosphate.

[0017] In the above, the first mixing treatment and the second mixing treatment are wet mixing with acetone, the balls used in the second mixing treatment are zirconia balls, and the diameter of the zirconia balls used in the second mixing treatment is preferably 0.03 mm or more and 1.0 mm or less. Furthermore, the balls used in the first mixing treatment are zirconia balls, and the diameter of the zirconia balls used in the first mixing treatment is preferably 2.0 mm or more and 5.0 mm or less.

[0018] According to one aspect of the present invention, it is possible to provide a positive electrode active material or composite oxide with high energy density, or a secondary battery using the same. Alternatively, it is possible to provide a positive electrode active material or composite oxide with high discharge capacity, or a secondary battery using the same. Alternatively, it is possible to provide a positive electrode active material or composite oxide with a high voltage plateau, which is maintained even after charge-discharge cycles, or a secondary battery using the same. Alternatively, it is possible to provide a positive electrode active material or composite oxide with suppressed reduction in charge-discharge capacity at low temperatures, or a secondary battery using the same with suppressed reduction in capacity during high-rate charge-discharge. Alternatively, it is possible to provide a positive electrode active material or composite oxide with suppressed reduction in energy density at high temperatures, or a secondary battery using the same. Alternatively, it is possible to provide a secondary battery that exhibits good electrical characteristics over a wide temperature range. Alternatively, it is possible to provide a secondary battery that is safe or highly reliable.

[0019] Furthermore, according to one aspect of the present invention, a novel positive electrode active material, a composite oxide, a secondary battery, an energy storage device, or a method for producing the same can be provided. Alternatively, according to one aspect of the present invention, a novel positive electrode active material, a composite oxide, a secondary battery, an energy storage device, or a method for producing the same at low cost can be provided.

[0020] Furthermore, the description of these effects does not preclude the existence of other effects. Moreover, one aspect of the present invention does not necessarily have to possess all of these effects. Furthermore, those skilled in the art can naturally discover other effects from the description in the specification, drawings, and claims, and it is possible to extract other effects from the description in the specification, drawings, and claims.

[0021] Figures 1A, 1B, 1C, and 1D illustrate a positive electrode active material according to one embodiment of the present invention. Figure 2 illustrates an example of a method for producing a positive electrode active material according to one embodiment of the present invention. Figures 3A, 3B, and 3C illustrate a lithium-ion battery according to one embodiment of the present invention. Figures 4A, 4B, and 4C illustrate an electric vehicle according to one embodiment of the present invention. Figures 5A, 5B, 5C, 5D, and 5E illustrate a vehicle, etc., according to one embodiment of the present invention. Figures 6A, 6B, 6C, and 6D illustrate an electronic device, etc., according to one embodiment of the present invention. Figures 7A and 7B are XRD patterns of positive electrode active materials according to the embodiment. Figures 8A and 8B are SEM images of positive electrode active materials according to the embodiment. Figures 9A and 9B are SEM images of positive electrode active materials according to the embodiment. Figure 10A is a charge / discharge curve of a half-cell according to the embodiment, and Figure 10B is a charge / discharge cycle characteristic.

[0022] The following describes embodiments for carrying out the present invention with reference to drawings and other illustrations. However, the present invention is not limited to the following embodiments. It is possible to modify the embodiments for carrying out the invention without departing from the spirit of the present invention.

[0023] Furthermore, in drawings, size, layer thickness, or area may be exaggerated for clarity. Therefore, the scale is not necessarily limited.

[0024] Furthermore, ordinal numbers such as "first," "second," etc., in this specification are added to avoid confusion of constituent elements and do not indicate any order or rank, such as process order or layering order. Even if an ordinal number is not used for a term in this specification, an ordinal number may be used in the claims to avoid confusion of constituent elements. Even if an ordinal number is used for a term in this specification, a different ordinal number may be used in the claims. Even if an ordinal number is used for a term in this specification, the ordinal number may be omitted in the claims.

[0025] In this specification, space groups are expressed using international notation (or Hermann-Mauguin notation) in short notation. In addition, a space group number may be added. Crystal planes and crystal directions are expressed using Miller indices. In crystallography, space groups, crystal planes, and crystal directions are expressed by adding a superscript bar to the number, but in this specification, due to formatting constraints, a minus sign (-) may be added before the number instead of adding a bar above it. Individual orientations indicating directions within a crystal are expressed with [ ], collective orientations indicating all equivalent directions are expressed with < >, individual crystal planes are expressed with ( ), and collective planes with equivalent symmetry are expressed with {}. Furthermore, even with the same space group number, the notation of the space group may differ depending on how the crystal axis is defined. For example, Pnm(a,b,c), Pmnb(a,b,-c), Pbnm(c,a,b), Pcmn(-c,b,a), Pmcn(b,c,a), and Pnam(a,-c,b), all belonging to space group number 62, represent the same unit cell, although they have different crystal axis settings.

[0026] In this specification, when the term "positive electrode active material" is used, depending on the analytical method, it may refer to multiple positive electrode active material particles or to a single positive electrode active material particle. For example, in descriptions of scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDX), STEM-electron energy loss spectroscopy (STEM-EELS), and electron diffraction, unless otherwise specified, the description refers to a single positive electrode active material particle. On the other hand, in the cases of X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and various mass spectrometry methods, unless otherwise specified, the description refers to multiple positive electrode active material particles.

[0027] In this specification, the term "particle" is not limited to spherical shapes (circular cross-sections), but includes individual particles with elliptical, rectangular, trapezoidal, triangular, rounded quadrilateral, asymmetrical shapes, and other cross-sectional shapes. Furthermore, individual particles may have irregular shapes. In addition, the term "particle" includes both primary and secondary particles.

[0028] Furthermore, when describing the characteristics of the positive electrode active material particles, it is not necessarily required that all particles possess those characteristics. For example, if 50% or more, preferably 70% or more, and more preferably 90% or more of three or more randomly selected positive electrode active material particles possess the desirable characteristics described later, it can be said that this sufficiently improves the characteristics of the positive electrode active material and the secondary battery having it.

[0029] Furthermore, the distribution of an element refers to the region in which that element is continuously detected within a non-noise range using a certain continuous analytical method. A region in which an element is continuously detected within a non-noise range can also be defined as a region in which the element is always detected when the analysis is performed multiple times.

[0030] Furthermore, the space group of a crystal structure is identified by XRD, electron diffraction, neutron diffraction, etc. Therefore, in this specification, the terms "belonging to a certain space group," "being part of a certain space group," or "being part of a certain space group" can be rephrased as "identified to a certain space group."

[0031] Unless otherwise specified, the materials of a secondary battery (positive electrode active material, negative electrode active material, electrolyte, separator, etc.) will be described in their state before degradation. A decrease in discharge capacity due to aging treatment during the secondary battery manufacturing process is not considered degradation. For example, a lithium-ion secondary single cell and lithium-ion secondary battery pack (hereinafter referred to as "lithium-ion secondary battery") can be considered to be in its pre-degradation state if it has a discharge capacity of 97% or more of its rated capacity. The rated capacity for lithium-ion secondary batteries for portable devices conforms to JIS C 8711:2019. For other lithium-ion secondary batteries, the rated capacity conforms to various JIS and IEC standards, including those for electric vehicle propulsion and industrial use, in addition to the above JIS standard.

[0032] In this specification, a high rate means that when 1C = 170 mA / g, the current per unit weight of positive electrode active material is 2C (340 mA / g) or more, typically 5C (850 mA / g). A low rate means that when 1C = 170 mA / g, the current per unit weight of positive electrode active material is less than 2C (340 mA / g), typically 0.2C (34 mA / g). Low temperature means 0°C or below, typically between -20°C and 0°C.

[0033] (Embodiment 1) In this embodiment, the features of the positive electrode active material 100 according to one aspect of the present invention will be described with reference to Figures 1A to 1D.

[0034] The positive electrode active material 100 shown in Figure 1A has manganese iron lithium phosphate. The manganese iron lithium phosphate in the positive electrode active material 100 of one aspect of the present invention is LiMn ｙ Fe （１−ｙ） PO ４ (where y is between 0.80 and 0.95) and has an olivine-type crystal structure. In other words, the positive electrode active material 100 contains lithium (Li), manganese (Mn), iron (Fe), phosphorus (P), and oxygen (O), and has an olivine-type crystal structure. Note that in this specification, LiMn ｙ Fe （１−ｙ） PO ４ When y is between 0.80 and 0.95, it is simply called lithium manganese iron phosphate, or sometimes called lithium manganese iron phosphate with a high manganese ratio.

[0035] In the manganese iron lithium phosphate contained in the positive electrode active material 100, the ratio of the number of manganese atoms to the sum of the number of iron atoms (Mn / (Mn+Fe)) is preferably a high manganese ratio of 0.80 or more, and more preferably 0.85 or more. The higher the ratio of the number of manganese atoms to the sum of the number of iron atoms contained in the positive electrode active material 100, the higher the energy density of the secondary battery can be. On the other hand, if the ratio of manganese atoms to the sum of iron atoms becomes too high, there is a concern that the conductivity will decrease and the lithium ion diffusion coefficient will decrease. For this reason, (Mn / (Mn+Fe)) is preferably 0.95 or less, and more preferably 0.92 or less. In summary, in the manganese iron lithium phosphate of the positive electrode active material 100 according to one aspect of the present invention, the ratio of the number of manganese atoms to the sum of the number of iron atoms (Mn / (Mn+Fe)) is preferably 0.80 or more and 0.95 or less, and more preferably 0.85 or more and 0.92 or less.

[0036] The olivine crystal structure is orthorhombic (also called orthorhombic) and belongs to space group Pnm (No. 62). LiMn ｙ Fe （１−ｙ） PO ４ In the case where y is between 0.80 and 0.95, oxygen has a hexagonal close-packed structure, lithium, manganese, and iron are present at octahedral sites, and phosphorus is present at tetrahedral sites. Although oxygen has a hexagonal close-packed structure, it has distortions compared to an ideal hexagonal close-packed structure. Furthermore, defects such as vacancies in cations or anions may be present. In addition, the composition of the positive electrode active material 100 is not strictly limited to Li:(Mn+Fe):P:O=1:1:1:4 (atomic ratio).

[0037] Also, LiMn ｙ Fe （１−ｙ） PO ４ In addition to lithium, manganese, iron, phosphorus, and oxygen, it may also contain additive elements. As additive elements, one or more can be selected from, for example, magnesium, zinc, calcium, aluminum, gallium, indium, scandium, yttrium, antimony, and bismuth.

[0038] The olivine-type crystal structure of the positive electrode active material 100 belongs to space group Pnm (No. 62). When Rietveld analysis is performed on the pattern obtained by diffraction, the lattice constant of the a-axis is preferably 10.430 Å or more and 10.440 Å or less. The lattice constant of the b-axis is more preferably 6.093 Å or more and 6.094 Å or less. The lattice constant of the c-axis is more preferably 4.738 Å or more and 4.739 Å or less.

[0039] <Shape> The positive electrode active material 100 is preferably a secondary particle having a plurality of primary particles 101, as shown in Figure 1A. In this specification, a secondary particle refers to a particle formed by the aggregation, fixation, and / or sintering of a plurality of primary particles.

[0040] Furthermore, it is preferable that the primary particles 101 of the positive electrode active material 100 are single crystals. For example, if the grain boundaries of the primary particles observable with a scanning electron microscope (SEM) coincide with the region of crystal orientation mapping captured by electron backscatter diffraction (EBSD), it can be determined that the primary particles 101 are single crystals. Alternatively, it can be determined that the primary particles 101 are single crystals by electron diffraction and high-resolution images using a transmission electron microscope (TEM) or scanning transmission electron microscope (STEM).

[0041] Furthermore, it is preferable that the positive electrode active material 100 is carbon-coated, and more preferably that each primary particle 101 is carbon-coated. The carbon coating enhances the conductivity of the positive electrode active material 100, thereby reducing the resistance of the secondary battery in which the positive electrode active material 100 is used as the positive electrode.

[0042] Figure 1A shows an example where the primary particles 101 are spherical or elongated spherical, but the present invention is not limited to these. For example, as shown in Figure 1B, the positive electrode active material 100 may have distorted spherical primary particles 101a. Also, as shown in Figure 1C, the positive electrode active material 100 may have flat or substantially plate-shaped primary particles 101b. Also, as shown in Figure 1D, the positive electrode active material 100 may have needle-shaped primary particles 101c.

[0043] Furthermore, the positive electrode active material 100 preferably has a small crystallite size in order to reduce the diffusion resistance of lithium. For example, when the olivine-type crystal structure of the positive electrode active material 100 is analyzed by Rietveld analysis or the like on a pattern obtained by a diffraction method such as X-ray diffraction (XRD), it is preferable that the crystallite size (LVol-IB) is between 25 nm and 50 nm.

[0044] <Charge / Discharge Capacity> When the crystallite size of the positive electrode active material 100 is within the above numerical range, the charge / discharge characteristics are improved, and the secondary battery having the positive electrode active material 100 has a larger charge / discharge capacity. In addition, the plateau derived from the oxidation-reduction of manganese is more easily maintained even after charge / discharge cycle testing.

[0045] As a charge-discharge cycle test, a coin-shaped half-cell can be fabricated using lithium metal as the negative electrode, and the properties of the positive electrode active material 100 can be evaluated. The electrolyte used in the half-cell can be, for example, a mixed solvent of ethylene carbonate (EC):diethyl carbonate (DEC) = 3:7 (volume ratio) with 1 M LiPF ６ In addition to the above, a mixture containing 2% by weight of vinylene carbonate (VC) can also be used.

[0046] In this specification, the number of cycles does not strictly represent the number of charge-discharge cycles since the secondary battery was manufactured. If the secondary battery is in a pre-degradation state, the counting of cycles can be started at any time. For example, after performing an aging process involving several charge-discharge cycles, a charge-discharge cycle test under the conditions described above can be started, and the first charge-discharge cycle test under the conditions described above can be counted as the first cycle.

[0047] <Analysis> <Composition> The composition of the positive electrode active material 100 in one embodiment of the present invention can be determined by, for example, ICP-MS (inductively coupled plasma mass spectrometry). If necessary, in addition to ICP-MS, multiple quantitative and semi-quantitative analyses such as X-ray fluorescence spectrometry, GD-MS (glow discharge mass spectrometry), EDX (energy dispersive X-ray spectroscopy), and EPMA (electron probe microanalyzer) can be combined for evaluation.

[0048] <Particle Size> The particle size of the positive electrode active material 100 can be measured, for example, by a laser diffraction particle size distribution analyzer. However, the size of fine particles of 1 μm or less, primary particles of particles that tend to aggregate, etc., may be determined by measuring the major axis of the particles by analysis such as SEM or TEM. For example, in analysis such as SEM or TEM, the size of 20 or more particles, preferably 100 or more particles, can be measured and the particle size distribution can be determined.

[0049] Furthermore, D50 refers to the particle size at which the cumulative amount accounts for 50% of the cumulative curve of the particle size distribution measurement results. Similarly, D10 refers to the particle size at which the cumulative amount accounts for 10% of the cumulative curve of the particle size distribution measurement results, and D90 refers to the particle size at which the cumulative amount accounts for 90% of the cumulative curve of the particle size distribution measurement results.

[0050] In one embodiment of the present invention, the particle diameter of the primary particles, D50, is preferably 30 nm to 70 nm, and more preferably 30 nm to 60 nm. Furthermore, the particle diameter of the primary particles, D90, is preferably 100 nm or less, and more preferably 80 nm or less.

[0051] <Crystallite Size Determined by Diffraction Method> As described above, the olivine-type crystal structure of the positive electrode active material 100 is preferably such that the crystallite size is between 25 nm and 50 nm when Rietveld analysis is performed on the pattern obtained by diffraction. Among diffraction methods, CuKα １ X-ray diffraction by line, MoKα １ Linear X-ray diffraction, synchrotron X-ray diffraction, and neutron diffraction are preferred due to their high accuracy. Alternatively, the measurement target may be the powder of the positive electrode active material 100, or a positive electrode or secondary battery containing the positive electrode active material 100.

[0052] However, in the state of the positive electrode or secondary battery, the positive electrode active material 100 may be oriented due to the effects of pressurization during the manufacturing process. If the orientation is strong, it may be difficult to accurately calculate the crystallite size. Therefore, it is preferable to obtain the sample by removing the positive electrode active material layer from the positive electrode, removing some of the binder in the positive electrode active material layer using a solvent, etc., and then filling it into a sample holder. Alternatively, a method can be used in which grease is applied to a silicon anti-reflective plate and the sample is then attached to it.

[0053] For calculating crystallite size, for example, a Bruker D8 ADVANCE can be used, with CuKα as the X-ray source, 2θ between 15° and 120°, increase 0.005, 1 sec / step, and a LYNXEYE XE-T detector. The diffraction pattern obtained and the literature value for lithium iron phosphate (ICSD col. code. 193640) can be used. The crystal structure analysis can be performed using DIFFRAC. TOPAS ver. 6 as the crystal structure analysis software, and can be set as follows, for example: Emission Profile: CuKa5. lam Background: Chebychev polynomial, 5th Instrument Primary radius: 280mm Secondary radius: 280mm Linear PSD 2Th angular range: 2.9 FDS angle: 0.3 Full Axial Convolution Filament length: 12mm Sample length: 15mm Receiving Slit length: 12mm Primary Sollers: 2.5 Secondary Sollers: 2.5 Corrections Specimen displacement: Refine LP Factor: 0

[0054] It is preferable to use the LVol-IB value, which is the crystallite size corrected based on the integration width calculated using the above method, as the crystallite size. Note that if the calculated Preferred Orientation is less than 0.8, the sample orientation may be too strong, making it unsuitable for determining the crystallite size.

[0055] <Lattice Constant> The lattice constant of the olivine-type crystal structure of the positive electrode active material 100 can be determined by performing Rietveld analysis on the pattern obtained by diffraction. Rietveld analysis can be performed using the same method as for calculating the crystallite size described above.

[0056] This embodiment can be appropriately combined with the contents of other embodiments.

[0057] (Embodiment 2) In this embodiment, an example of a method for producing a positive electrode active material according to one aspect of the present invention will be described with reference to Figure 2.

[0058] <Step S11> First, as shown in Step S11 in Figure 2, a lithium source, manganese source, iron source, and phosphoric acid source are prepared. It is also preferable to prepare a grinding medium and solvent for mixing.

[0059] Lithium sources include, for example, lithium carbonate, lithium hydroxide, lithium oxide, and lithium phosphate (Li ３ PO ４ ), lithium acetate (CH ３ CO ２ Li, Li (CH ３ COO)・2H ２ O), Lithium oxalate (Li ２ C ２ O ４ ), lithium nitrate (LiNO) ３ ), lithium chloride (LiCl), lithium sulfate (Li ２ SO ４ Lithium compounds such as lithium fluoride (LiF) can be used.

[0060] Manganese sources include, for example, manganese carbonate and manganese oxide (MnO, Mn ３ O ４ Mn ２ O ３ MnO ２ MnO ３ (etc.), manganese hydroxide, manganese phosphate (MnPO ４ ), manganese acetate (Mn(OCOCH) ３ ) ２ , (CH ３ COO)３ Mn·2H ２ O, (CH ３ COO) ２ Mn·4H ２ O), manganese oxalate (MnC ２ O ４ ·2H ２ O), manganese nitrate (Mn(NO ３ ) ２ , Mn(NO ３ ) ２ ·4H ２ O, Mn(NO ３ ) ２ ·6H ２ O), manganese chloride (MnCl ２ ·4H ２ O), manganese sulfate (MnSO ４ , MnSO ４ ·H ２ O, MnSO ４ ·4H ２ O, MnSO ４ ·5H ２ O, MnSO ４ ·7H ２ O, ) manganese fluoride (MnF ２ , MnF[[ID=​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​２ O, Fe (NO ３ ) ３ 6H ２ O), iron chloride (FeCl ２ FeCl ２ 4H ２ O, FeCl ３ FeCl ３ 6H ２ O), iron sulfate (FeSO) ４ FeSO ４ ・H ２ O, FeSO ４ 4H ２ O, FeSO ４ ・5H ２ O, FeSO ４ 7H ２ O), iron fluoride (FeF ２ FeF ２ 4H ２ O, FeF ３ FeF ３ 3H ２ Iron compounds such as O) can be used.

[0062] For example, ammonium dihydrogen phosphate (NH₄) can be used as a source of phosphate. ４ H ２ PO ４ ), diammonium hydrogen phosphate ((NH ４ ) ２ HPO ４ ), lithium dihydrogen phosphate (LiH ２ PO ４ Phosphate compounds such as ) can be used.

[0063] It should be noted that the lithium, manganese, iron, and phosphate sources do not necessarily have to be separate; compounds that serve multiple purposes can be used. For example, lithium dihydrogen phosphate can serve as both a lithium and phosphate source.

[0064] In this embodiment, lithium carbonate is used as the lithium source, manganese carbonate as the manganese source, iron(II) oxalate dihydrate as the iron source, and ammonium dihydrogen phosphate as the phosphate source, Li:Mn:Fe:PO ４ The weighing should be done so that the molar ratio is 1:0.90:0.10:1.

[0065] In addition to the above, when using a planetary rotary mill device such as a ball mill for mixing, a grinding medium is prepared. For example, one or more of the following can be used as the grinding medium: zirconia (zirconium oxide) balls, agate balls, quartz balls, alumina (aluminum oxide) balls, silicon nitride balls, silicon carbide balls, tungsten carbide balls, hardened steel balls, stainless steel balls, polyamide balls, and Teflon balls. It is preferable to use zirconia balls or alumina balls as the mixing medium used in step S11. Furthermore, when using zirconia balls, it is preferable to use yttria-stabilized zirconia having yttria (yttrium oxide).

[0066] Furthermore, if wet mixing is used, a solvent is prepared. For example, one or more of the following solvents can be used: acetone, ethanol, methanol, isopropyl alcohol (IPA), hexane, cyclohexane, and N-methyl-2-pyrrolidone (NMP). It is preferable to use acetone as the solvent in step S11, and more preferable to use dehydrated acetone.

[0067] In this embodiment, in step S11, zirconia balls are used as the grinding medium, and dehydrated acetone is used as the solvent for wet mixing.

[0068] <Step S12> Next, in step S12, the lithium source, manganese source, iron source and phosphate source are mixed. The mixing can be done wet, for example, using a ball mill.

[0069] In the ball milling process of step S12, the diameter of the zirconia balls is preferably 2 mm to 10 mm, and more preferably 2 mm to 5 mm. The purpose of the ball milling process in step S12 is to mix and grind (also called grinding) the lithium source, manganese source, iron source, and phosphate source. However, if the material is ground too finely, there is a risk that excessive carbon dioxide will be generated from the contact between ammonium dihydrogen phosphate and carbonates (lithium carbonate and manganese carbonate). Therefore, by using zirconia balls of the above size, a mixture suitable for this process can be obtained.

[0070] In this embodiment, zirconia balls with a diameter of 3 mm are used as the grinding medium, dehydrated acetone is used as the solvent, and the mixture is mixed at 300 rpm for 2 hours while cooling using a planetary ball mill apparatus.

[0071] <Step S13> Next, in step S13, if wet mixing was performed, the solvent is dried, and if a grinding medium was used, the mixture is sieved to remove the grinding medium and obtain the mixture. To distinguish it from other processes, this is sometimes called the first mixture. In this embodiment, the mixture is dried using a ventilated drying oven and then recovered by sieving with a mesh size of 300 μm.

[0072] <Step S14> Next, in step S14, the first mixture is heated. The heating temperature is preferably 250°C to 450°C, more preferably 300°C to 400°C, and most preferably around 350°C. The heating time is preferably 1 hour to 60 hours, more preferably 2 hours to 20 hours, and most preferably around 10 hours. If the heating temperature is too low and / or the heating time is too short, the reaction may not be completed, such as the evaporation of the hydrate and / or carbon dioxide. On the other hand, if the heating temperature is too high and / or the heating time is too long, the fuel costs for heating will increase and productivity may decrease. Note that the heating in step S14 may be called calcination, and the mixing in step S12 may be called pre-calcination mixing.

[0073] During heating, it is preferable to use an inert or reducing atmosphere, such as a nitrogen or argon atmosphere. The reaction chamber may be depressurized and then filled (purged) with an inert atmosphere to prevent the atmosphere from entering or leaving the reaction chamber, or a constant flow of atmosphere may be maintained.

[0074] For the heating furnace, for example, a muffle furnace, roller hearth kiln, rotary kiln, etc., can be used. For the container that holds the material to be heated, an aluminum oxide crucible or an aluminum oxide setter (also called a sheath) can be used. It is preferable to cover the crucible or setter before heating to prevent the material from volatilizing. Mullite-cordierite may also be used as the material for the crucible and setter.

[0075] In this embodiment, the first mixture is placed in a crucible made of 99.9% pure aluminum oxide, covered, and heated in a muffle furnace under a nitrogen flow atmosphere at 350°C for 10 hours.

[0076] <Step S15, Step S16> Next, in step S15, the heated material is sieved. In this embodiment, a sieve with a mesh size of 300 μm is used. A composite oxide is obtained through the above steps (step S16).

[0077] <Step S17> Next, in step S17, a carbon source is prepared. In addition to the carbon source, it is preferable to prepare a grinding medium and a solvent for mixing.

[0078] As a carbon source, compounds containing carbon can be used, such as sugars including glucose and sucrose, polysaccharides including starch and cellulose, synthetic resins including polyvinyl alcohol (PVA) and polyacrylic acid. Carbon black including acetylene black, graphene, graphene oxide, and graphite can also be used. A combination of several of these can also be used.

[0079] For the grinding medium and solvent, refer to the description in step S11.

[0080] <Step S18> Next, in step S18, the composite oxide obtained in step S16 and the carbon source are mixed. The mixing can be done wet, for example, using a ball mill.

[0081] In the ball milling process of step S12, the diameter of the zirconia balls is preferably 0.03 mm or more and less than 2 mm, and more preferably 0.03 mm or more and 1.0 mm or less. By using zirconia balls of the above size, a finely ground mixture can be obtained.

[0082] In this embodiment, zirconia balls with a diameter of 1 mm are used as the grinding medium, dehydrated acetone is used as the solvent, and the mixture is mixed at 300 rpm for 2 hours while cooling using a planetary ball mill apparatus.

[0083] <Step S19> Next, in step S19, if wet mixing was performed, the solvent is dried, and if a grinding medium was used, the mixture is sieved to remove the grinding medium and obtain the mixture. To distinguish it from other steps, this is sometimes called the second mixture. For drying and sieving, refer to the description in step S13.

[0084] <Step S20> Next, in step S20, the second mixture is heated. The heating temperature is preferably 500°C to 900°C, more preferably 600°C to 700°C, and most preferably around 650°C. The heating time is preferably 1 hour to 60 hours, more preferably 2 hours to 20 hours, and most preferably around 10 hours. If the heating temperature is too low and / or the heating time is too short, there is a risk that an olivine-type crystal structure will not be formed, or that the carbon source will not be sufficiently carbonized. On the other hand, if the heating temperature is too high and / or the heating time is too long, there is a risk that sintering will proceed too much, the secondary particles will become too large, and productivity will decrease. Note that the heating in step S20 may be called the main firing, and the mixing in step S18 may be called the mixing before calcination.

[0085] The atmosphere during heating, the heating furnace, and the container can be described in step S14.

[0086] In this embodiment, the second mixture is placed in a crucible made of 99.9% pure aluminum oxide, covered, and heated in a muffle furnace under a nitrogen flow atmosphere at 650°C for 10 hours.

[0087] <Step S21, Step S22> Next, in step S21, the heated material is sieved. In this embodiment, a sieve with a mesh size of 53 μm is used. The positive electrode active material 100 is obtained through the above steps (step S22).

[0088] The positive electrode active material 100 can be produced through the above process.

[0089] To summarize the descriptions in steps S12 and S18, in the preparation of the positive electrode active material 100 according to one embodiment of the present invention, it is preferable that the size of the pulverized medium used in the mixing process before the main firing is smaller than the size of the pulverized medium used in the mixing process before calcination. More specifically, it is preferable that the diameter of the zirconia balls used in the mixing process before the main firing is smaller than the diameter of the zirconia balls used in the mixing process before calcination. For example, it is preferable that the diameter of the zirconia balls used in the mixing process before the main firing is 0.03 mm or more and 1.0 mm or less, and the diameter of the zirconia balls used in the mixing process before calcination is 2 mm or more and 5 mm or less. By going through such a process, it is possible to obtain a high manganese-ratio lithium manganese iron phosphate with a crystallite size (LVol-IB) of 25 nm or more and 50 nm or less, as described in Embodiment 1, and with good charge-discharge characteristics.

[0090] Although Figure 2 illustrates an example of producing a positive electrode active material by a solid-phase method, the present invention is not limited to this. Positive electrode active materials can be produced not only by solid-phase methods, but also by hydrothermal methods, coprecipitation methods, sol-gel methods, spray-drying methods, and other methods. Furthermore, multiple methods selected from these can be combined for production.

[0091] This embodiment can be appropriately combined with the contents of other embodiments.

[0092] (Embodiment 3) In this embodiment, the configuration of the lithium-ion battery will be described.

[0093] [Positive Electrode] The positive electrode comprises a positive electrode active material layer and a positive electrode current collector. The positive electrode active material layer contains a positive electrode active material and may further contain at least one of a conductive material and a binder. The positive electrode active material can be the one described in the previous embodiment.

[0094] <Positive electrode active material> As the positive electrode active material, the positive electrode active material 100 described in the previous embodiment may be used in combination with other positive electrode active materials.

[0095] Other positive electrode active materials include composite oxides having olivine-type crystal structures, layered rock salt-type crystal structures, or spinel-type crystal structures. For example, LiFePO ４ LiFeO ２ LiCoO ２ LiNiO ２ LiMnO ２ LiNi ａ Mn ｂ Co ｃ O ２ (a+b+c=1), LiMn ２ O ４ , V ２ O ５ , Cr ２ O ５ MnO ２ Examples of such compounds include:

[0096] In addition, LiMn is another positive electrode active material. ２ O ４ Lithium-containing materials having a spinel-type crystal structure containing manganese, etc., are treated with lithium nickelate (LiNiO2). ２ Or LiNi （１−ｘ） M1 ｘ O ２ It is preferable to mix (0 < x < 1) (M1 = Co, Al, etc.). By using this configuration, the characteristics of the secondary battery can be improved.

[0097] <Conductive Material> Conductive materials, also called conductivity imparters or conductivity enhancers, can be made of carbon. By attaching a conductive material between multiple active materials, the multiple active materials are electrically connected to each other, thereby increasing conductivity. In this specification, "attachment" does not only refer to physical contact between the active material and the conductive material, but also includes cases where covalent bonding occurs, bonding occurs due to van der Waals forces, the conductive material covers a portion of the surface of the active material, the conductive material fits into surface irregularities of the active material, or where they are electrically connected even if they are not in contact with each other.

[0098] Specific examples of carbon materials that can be used as conductive materials include carbon black (furnace black, acetylene black, graphite, etc.). Carbon nanotubes, graphene, multigraphene, graphene oxide, and / or reduced graphene oxide can also be used.

[0099] Furthermore, using a mixture of graphene and acetylene black is preferable as it enables rapid charging. Alternatively, using a mixture of carbon nanotubes and acetylene black is preferable as it enables rapid charging. Alternatively, using a mixture of carbon nanotubes, graphene, and acetylene black is preferable as it enables rapid charging. These are particularly effective when used as lithium-ion batteries for automobiles.

[0100] <Binder> As a binder, rubber materials such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, and ethylene-propylene-diene copolymer can be used. Fluororubber can also be used.

[0101] Furthermore, it is preferable to use a water-soluble polymer as the binder. Examples of water-soluble polymers include polysaccharides. One or more of the following polysaccharides can be used: carboxymethylcellulose (CMC), methylcellulose, ethylcellulose, hydroxypropylcellulose, diacetylcellulose, cellulose derivatives such as regenerated cellulose, and starch. It is even more preferable to use these water-soluble polymers in combination with the aforementioned rubber material.

[0102] Alternatively, it is preferable to use materials such as polystyrene, methyl polyacrylate, 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, or nitrocellulose as the binder.

[0103] Furthermore, graphene, multigraphene, graphene oxide, and / or reduced graphene oxide can function not only as conductive materials but also as binders.

[0104] You may use a combination of several of the binders mentioned above.

[0105] <Positive Electrode Current Collector> As the current collector, materials with high conductivity such as stainless steel, gold, platinum, aluminum, titanium, iron, and alloys thereof can be used. Furthermore, it is preferable that the material used for the positive electrode current collector does not dissolve at the potential of the positive electrode. In addition, aluminum alloys to which elements that improve physical properties such as iron, silicon, titanium, neodymium, scandium, and molybdenum have been added can be used. In addition, aluminum alloys to which iron has been added for improved strength can be used. Furthermore, it may be formed from a metallic element that reacts with silicon to form a silicide. Metallic elements that react with silicon to form a silicide include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, and nickel. The current collector can be in the shape of foil, plate, sheet, mesh, perforated metal, expanded metal, etc. as appropriate. The current collector should preferably have a thickness of 5 μm or more and 30 μm or less.

[0106] Furthermore, the positive electrode current collector may have a coating layer. Preferably, carbon can be used as the material for the coating layer. Preferably, the carbon used for the coating layer is amorphous or low-crystallinity carbon such as carbon black, carbon fibers such as carbon nanotubes, crystalline carbon such as graphite or graphene, or a combination thereof. Furthermore, the carbon used for the coating layer may contain metal fine powder. The coating layer may also contain a binder. The materials described in the <Binder> section above can be used as the binder. A coating layer using these materials is sometimes called an undercoat, anchor coat, or coating layer.

[0107] [Negative electrode] The negative electrode comprises a negative electrode active material layer and a negative electrode current collector. The negative electrode active material layer may also contain a negative electrode active material, a conductive material, and a binder.

[0108] <Negative electrode active material> As the negative electrode active material, for example, alloy materials and / or carbon materials can be used.

[0109] The carbon material used for the negative electrode active material may be one or more selected from graphite, easily graphitizable carbon (soft carbon), difficult-to-graphitize carbon (hard carbon), carbon fibers (carbon nanotubes), graphene, graphene compounds, carbon black, etc.

[0110] Examples of graphite include artificial graphite and natural graphite. Examples of artificial graphite include mesocarbon microbeads (MCMB), coke-based artificial graphite, and pitch-based artificial graphite. Here, spheroidal graphite having a spherical shape can be used as artificial graphite. For example, MCMB may have a spherical shape and is therefore preferable. Furthermore, it is relatively easy to reduce the surface area of ​​MCMB, which may also be preferable. Examples of natural graphite include flake graphite and spheroidized natural graphite.

[0111] Graphite exhibits a potential as low as lithium metal (0.05V to 0.3V vs. Li / Li) when lithium ions are inserted into it (during the formation of lithium-graphite intercalation compounds). ＋This allows lithium-ion batteries using graphite to exhibit a high operating voltage. Furthermore, graphite is preferable because it has advantages such as a relatively high capacity per unit volume, relatively small volume expansion, low cost, and higher safety compared to lithium metal.

[0112] Furthermore, the negative electrode active material can be an element capable of undergoing charge-discharge reactions through alloying and dealloying reactions with lithium. For example, one or more materials selected from silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium, etc., can be used. Such elements have a larger capacity than carbon, and silicon in particular has a high theoretical capacity of 4200 mAh / g. Compounds containing these elements may also be used. For example, SiO, Mg ２ Si, Mg ２ Ge, SnO, SnO ２ Mg ２ Sn, SnS ２ , V ２ Sn ３ FeSn ２ CoSn ２ Ni ３ Sn ２ ,Cd ６ Sn ５ Ag ３ Sn, Ag ３ Sb, Ni ２ MnSb, CeSb ３ LaSn ３ La ３ Co ２ Sn ７ CoSb ３ Examples include InSb and SbSn. For example, compounds of Si, SiO, or SiC with Ti may also be used. Here, elements capable of undergoing charge-discharge reactions through alloying and de-alloying reactions with lithium, and compounds containing such elements, are sometimes referred to as alloying materials. Alloying materials, including silicon, may exhibit a suppressed decrease in charge-discharge capacity at low temperatures compared to graphite, making them preferable as negative electrode active materials for low-temperature secondary batteries.

[0113] In this specification, "SiO" refers to silicon monoxide, for example. Alternatively, SiO refers to SiOｘ It can also be expressed as follows. Here, x preferably has a value of 1 or a value in the vicinity of 1. For example, x is preferably 0.2 or more and 1.5 or less, and more preferably 0.3 or more and 1.2 or less.

[0114] Alternatively, the active material layer may be made by mixing the graphene compound with the material used to form the graphene compound. For example, particles used as a catalyst when forming the graphene compound may be mixed together with the graphene compound. Examples of catalysts used when forming the graphene compound include silicon dioxide (SiO₂). ２ SiO ｘ Examples of particles include those having aluminum oxide, iron, nickel, ruthenium, iridium, platinum, copper, germanium, etc. (x < 2). Preferably, the D50 of the particles is 1 μm or less, and more preferably 100 nm or less.

[0115] Alternatively, silicon particles coated with a graphene compound may be used as the negative electrode active material. In this case, it is more preferable to have a space between the graphene compound and the silicon particles that can buffer structural changes.

[0116] Furthermore, titanium dioxide (TiO) is used as the negative electrode active material. ２ ), lithium titanium oxide (Li ４ Ti ５ O １２ ), lithium-graphite intercalation compound (Li ｘ C ６ ), niobium pentoxide (Nb ２ O ５ ), tungsten dioxide (WO ２ ), molybdenum dioxide (MoO ２ One or more oxides selected from the following can be used.

[0117] Furthermore, as the negative electrode active material, lithium and a nitride of a transition metal, Li ３ Li with an N-type structure ３−ｘ M2 ｘ N (M2 = Co, Ni, Cu) can be used. For example, Li ２．６ Co ０．４ N has a large discharge capacity (900 mAh / g, 1890 mAh / cm²). ３) indicates a preference.

[0118] When lithium and transition metal nitrides are used, lithium ions are contained in the negative electrode active material, so the positive electrode active material does not contain lithium ions. ２ O ５ , Cr ３ O ８ It is preferable that it be combined with materials such as the above. Furthermore, even when a material containing lithium ions is used as the positive electrode active material, lithium and a nitride of a transition metal can be used as the negative electrode active material by desorbing the lithium ions contained in the positive electrode active material in advance.

[0119] Furthermore, materials that undergo a conversion reaction can also be used as the negative electrode active material. For example, transition metal oxides that do not form alloys with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), and iron oxide (FeO), may be used as the negative electrode active material. As for materials that undergo a conversion reaction, Fe ２ O ３ , CuO, Cu ２ O, RuO ２ , Cr ２ O ３ Oxides such as CoS ０．８９ , sulfides such as NiS and CuS, Zn ３ N ２ ,Cd ３ N, Ge ３ N ４ Nitrides such as NiP ２ FeP ２ CoP ３ Phosphates such as FeF ３ BiF ３ Examples of fluorides include the following.

[0120] Furthermore, multiple negative electrode active materials may be used in combination; for example, a negative electrode active material made by mixing graphite and silicon particles may be used. Silicon particles refer to silicon powder used as a material for the negative electrode active material of a lithium-ion secondary battery, and the average particle size of the particle size distribution, i.e., the average particle diameter, is around 100 nm, and are sometimes called nanosilicon particles. It is preferable to grind the silicon raw material and adjust the silicon particles to a uniform particle size. The silicon particles may include at least one of silicon, silicon oxide, and silicon alloy.

[0121] Furthermore, the conductive material and binder that the negative electrode active material layer may contain can be the same materials as those used for the positive electrode active material layer.

[0122] <Negative Electrode Current Collector> In addition to the same materials as the positive electrode current collector, copper and other materials can also be used for the negative electrode current collector. It is preferable that the negative electrode current collector be made of a material that does not alloy with carrier ions such as lithium. Furthermore, it is preferable that the negative electrode current collector has a coating layer, similar to the positive electrode current collector.

[0123] [Electrolyte] The electrolyte contains an organic solvent, but the organic solvent of the electrolyte in one aspect of the present invention is not limited to being a liquid at 25°C, but may be a solid at 25°C or a semi-solid at room temperature. Furthermore, while it is preferable that the organic solvent of the electrolyte in one aspect of the present invention be a liquid over a wide temperature range including below freezing point and high temperatures, it is not limited to this. The organic solvent may be a liquid, a solid, or a semi-solid over a wide temperature range including below freezing point and high temperatures.

[0124] As the organic solvent, aprotic organic solvents are preferred, and for example, one of the following can be used, or two or more of these can be used in any combination and ratio: ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, chloroethylene carbonate, vinylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), 1,3-propanesultone (PS), fluoroethylene carbonate (FEC), methyl 3,3,3-trifluoropropionate (MTFP), methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethoxyethane (DME), dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, sultone, etc.

[0125] Because PS has HOMO and LUMO levels equivalent to EC and DEC, it is not easily oxidized or reduced even at high cutoff voltages, and when it decomposes on the surface of the positive electrode active material, it tends to form polymers. Therefore, it has the advantage of having a small molecular weight decomposition product that is less likely to gasify. For this reason, the electrolyte preferably contains 0.1 wt% to 10 wt% PS, and more preferably 0.25 wt% to 7.5 wt% PS.

[0126] FEC is a cyclic carbonate with a high dielectric constant, and when used in organic solvents, it promotes the dissociation of lithium salts. On the other hand, because FEC has electron-withdrawing substituents, desolvation with lithium ions proceeds more easily than with EC. Specifically, the solvation energy of lithium ions is lower for FEC than for EC, which does not have electron-withdrawing substituents. Therefore, lithium ions are more easily released from the positive electrode active material surface and the negative electrode active material surface, which can lower the internal resistance of the secondary battery. Furthermore, because FEC has a deep Highest Occupied Molecular Orbital (HOMO) level, it is less susceptible to oxidation, improving oxidation resistance. However, the high viscosity of FEC is a concern. Therefore, it is preferable to use a mixed organic solvent containing not only FEC but also MTFP as the electrolyte. MTFP is a type of linear carbonate that can lower the viscosity of the electrolyte or maintain the viscosity at room temperature (typically 25°C) even at low temperatures (typically 0°C). Furthermore, although MTFP has a lower solvation energy than methyl propionate (abbreviated as "MP") which does not have electron-withdrawing substituents, it may still generate solvation with lithium ions when used in an electrolyte. When using a mixed organic solvent containing both FEC and MTFP, the volume ratio is preferably FEC:MTFP = 1:z, where z is between 2 and 20, and more preferably between 4 and 9.

[0127] The organic solvents mentioned above contain particulate debris or molecules other than the constituent molecules of the organic solvent (hereinafter also simply referred to as "impurities"), and oxygen (O ２ ), water (H ２ It contains O). It is preferable that the content of ) is low and that the purity is high. It is also preferable that reaction by-products during synthesis are suppressed through appropriate purification. Specifically, the electrolyte impurities should be 100 ppm or less, preferably 50 ppm or less, and more preferably less than 10 ppm. The concentration of water among the impurities can be detected by Karl Fischer titration.

[0128] Furthermore, it is preferable that the above-mentioned organic solvent shows virtually no peaks attributable to impurities when measured by NMR or other methods. "Very virtually undetectable" means that the ratio of the integrated area of ​​the peaks attributable to impurities to the integrated area of ​​the peaks attributable to the main component (simply called the integral ratio) is 0.005 or less, preferably 0.002 or less. The apparatus used for NMR measurement is not particularly limited, but for example, Bruker's "AVANCE III 400" can be used. Also, in 1H-NMR measurement, the central peak among the five peaks of acetonitrile derived from acetonitrile-d3 used as the solvent can be set to 1.94 ppm.

[0129] For example, in the case of MTF, when 1H-NMR is measured using acetonitrile-d3 solvent, it is known that four peaks occur with δ between 3.29 ppm and 3.43 ppm. However, if other peaks occur in the vicinity of this, for example, if a peak occurs with δ between 3.24 ppm and 3.29 ppm, that peak is considered to be due to impurities. Therefore, if the ratio (integral ratio) of the peak area between 3.24 ppm and 3.29 ppm to the peak area between 3.29 ppm and 3.43 ppm is 0.005 or less, preferably 0.002 or less, it can be said that peaks due to impurities are almost not detectable.

[0130] Furthermore, by using one or more flame-retardant and non-volatile ionic liquids (room-temperature molten salts) as the solvent for the electrolyte, it is possible to prevent the energy storage device from rupturing or catching fire even if the internal temperature rises due to an internal short circuit or overcharging. Ionic liquids consist of cations and anions, and include organic cations and anions. Examples of organic cations used in the electrolyte include aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, as well as aromatic cations such as imidazolium cations and pyridinium cations. Examples of anions used in the electrolyte include monovalent amide anions, monovalent methide anions, fluorosulfonic acid anions, perfluoroalkyl sulfonate anions, tetrafluoroborate anions, perfluoroalkylborate anions, hexafluorophosphate anions, or perfluoroalkyl phosphate anions.

[0131] Furthermore, the electrolyte to be dissolved in the above solvent is, for example, LiPF ６ LiClO ４ LiAsF ６ LiBF ４ LiAlCl ４ , LiSCN, LiBr, LiI, Li ２ SO ４ Li ２ B １０ Cl １０ Li ２ B １２ Cl １２ LiCF ３ SO ３ LiC ４ F ９ SO ３ LiC (CF ３ SO ２ ) ３ LiC(C ２ F ５ SO ２ ) ３ ,LiN(CF ３ SO ２ ) ２ ,LiN(C ４ F ９ SO ２ ) (CF ３SO ２ ), LiN(C ２ F ５ SO ２ ) ２ Lithium bis(oxalate) borate (Li(C) ２ O ４ ) ２ Lithium salts such as LiBOB can be used individually, or two or more of these can be used in any combination and ratio.

[0132] Furthermore, the electrolyte can contain additives. Additives can suppress the reaction decomposition of the electrolyte that may occur on the positive or negative electrode surface when the secondary battery is operated at high voltage and / or high temperature. Suitable additives include, for example, propanesultone (PS), vinylene carbonate (VC), tert-butylbenzene (TBB), lithium bis(oxalate)borate (LiBOB), 1,3,6-hexanetricarbonitrate, ethyl 2-methylbutyrate, ethyl 2-methylvalerate, and propyl 2-methylbutyrate. PS is particularly preferred as an additive because it improves the cycle characteristics.

[0133] One or more dinitrile compounds can be used as additives. Specific examples of dinitrile compounds include succinonitrile, glutalonitrile, adiponitrile (ADN), or ethylene glycol bis(propionitrile) ether (EGBE).

[0134] Furthermore, fluorobenzene may be added to the above organic solvent. The concentration of the additive should be, for example, 0.1 wt% to 5 wt% relative to the total electrolyte. PS or EGBE is preferable because it can form a good film on the positive electrode during charging and discharging, thereby improving cycle characteristics. Fluorobenzene (FB) is preferable because it improves the wettability of the organic solvent to the positive and negative electrodes. Dinitrile compounds are preferable because the nitrile groups are oriented toward the positive and negative electrodes, inhibiting oxidative decomposition of the organic solvent, thereby improving high-voltage resistance. Furthermore, when a current collector having copper is used in the negative electrode, dinitrile compounds are preferable because they can prevent the dissolution of copper during over-discharge. Considering the use of secondary batteries at high voltages, it is preferable to add nitrile compounds.

[0135] It is preferable to use a highly purified electrolyte in which particulate matter or elements other than the constituent elements of the electrolyte (hereinafter simply referred to as "impurities") are present in small amounts. Specifically, it is preferable that the weight ratio of impurities to the electrolyte be 1% or less, preferably 0.1% or less, and more preferably 0.01% or less.

[0136] Alternatively, a polymer gel electrolyte, obtained by swelling a polymer with an electrolyte solution, may be used.

[0137] Using polymer gel electrolytes enhances safety against leakage and other issues. Furthermore, it enables the secondary battery to be made thinner and lighter.

[0138] As the polymer to be gelled, silicone gels, acrylic gels, acrylonitrile gels, polyethylene oxide gels, polypropylene oxide gels, fluorine-based polymer gels, etc., can be used. For example, polymers having a polyalkylene oxide structure such as polyethylene oxide (PEO), PVDF, polyacrylonitrile, and copolymers containing them can be used. For example, PVDF-HFP, which is a copolymer of PVDF and hexafluoropropylene (HFP), can be used. Furthermore, the formed polymer may have a porous structure.

[0139] Furthermore, as the electrolyte, a solid electrolyte containing inorganic materials such as sulfide-based or oxide-based materials, or a solid electrolyte containing polymeric materials such as PEO (polyethylene oxide)-based materials can be used. When a solid electrolyte is used, the installation of separators or spacers becomes unnecessary. In addition, since the entire battery can be solidified, the risk of leakage is eliminated, and safety is dramatically improved.

[0140] [Separator] When the electrolyte contains a liquid electrolyte (also called an electrolyte solution), a separator is placed between the positive electrode and the negative electrode. As a separator, for example, materials such as paper and other cellulose fibers, nonwoven fabrics, glass fibers, ceramics, or porous films made of nylon (polyamide), vinylon (polyvinyl alcohol-based fiber), polypropylene (PP), polyimide (PI), polyester, acrylic, polyolefin, polyimide, polyurethane can be used. The porosity of the separator film thickness can be 35% to 90%, preferably 60% to 85%. A separator made of polypropylene can have a porosity of 35% to 45%. A separator made of polyimide can have a porosity of 75% to 85%. The film thickness of the separator is preferably 10 μm to 80 μm, and more preferably 20 μm to 60 μm. Separators using polyimide can have a high porosity and can be made into thick films (typically with a film thickness of 50 μm to 60 μm), which is preferable.

[0141] It is preferable that the separator be processed into a bag shape and positioned to enclose either the positive or negative electrode.

[0142] The separator may have a multilayer structure. For example, an organic material film such as polypropylene or polyethylene can be coated with a ceramic material, a fluorine material, a polyamide material, or a mixture thereof. Examples of ceramic materials include aluminum oxide particles and silicon oxide particles. Examples of fluorine materials include PVDF and polytetrafluoroethylene. Examples of polyamide materials include nylon and aramid (meta-aramid, para-aramid).

[0143] By using a multilayer separator, the safety of the lithium-ion battery can be maintained even if the overall thickness of the separator is thin, thus increasing the capacity per unit volume of the lithium-ion battery.

[0144] [Outer Covering] For the outer covering of a lithium-ion battery, metal materials such as aluminum or resin materials can be used. Alternatively, a film-like outer covering can be used. As a film, for example, a three-layer film can be used, in which a highly flexible metal thin film such as aluminum, stainless steel, copper, or nickel is provided on a film made of materials such as polyethylene, polypropylene, polycarbonate, ionomer, or polyamide, and an insulating synthetic resin film such as a polyamide resin or polyester resin is provided on the metal thin film as the outer surface of the outer covering.

[0145] This embodiment can be used in combination with other embodiments.

[0146] (Embodiment 4) In this embodiment, an example of the form of a lithium-ion battery will be described with reference to Figure 3.

[0147] Figure 3A is a diagram illustrating the wound body 950a of the lithium-ion battery 913, Figure 3B is an exploded perspective view of the lithium-ion battery 913, and Figure 3C is an external view of the lithium-ion battery 913. The lithium-ion battery 913 has a positive electrode 932 having the positive electrode active material described in the previous embodiment, a negative electrode 931, an electrolyte layer, and a separator 933. The negative electrode 931 has a negative electrode active material layer 931a. The positive electrode 932 has a positive electrode active material layer 932a. These are wound as shown in Figure 3A.

[0148] The separator 933 has a wider width than the negative electrode active material layer 931a and the positive electrode active material layer 932a, and is wound so as to overlap the negative electrode active material layer 931a and the positive electrode active material layer 932a. Furthermore, it is preferable from a safety standpoint that the negative electrode active material layer 931a is wider than the positive electrode active material layer 932a. A wound body 950a of this shape is also preferable due to its good safety and productivity.

[0149] As shown in Figure 3B, the negative electrode 931 is electrically connected to terminal 951. Terminal 951 is electrically connected to terminal 911a. The positive electrode 932 is electrically connected to terminal 952. Terminal 952 is electrically connected to terminal 911b.

[0150] As shown in Figure 3C, the coiled body 950a is covered by the housing 930, forming a lithium-ion battery 913. It is preferable to provide a safety valve, an overcurrent protection element, etc., in the housing 930. The safety valve is a valve that opens the inside of the housing 930 at a predetermined internal pressure in order to prevent the battery from rupturing.

[0151] As shown in Figure 3B, the lithium-ion battery 913 may have multiple windings 950a. By using multiple windings 950a, a lithium-ion battery 913 with a larger charge and discharge capacity can be made.

[0152] By using the positive electrode active material of the present invention in a lithium-ion battery 913 having a wound body, a secondary battery can be made that has a high energy density and exhibits good electrical characteristics over a wide temperature range.

[0153] The contents of this embodiment can be appropriately combined with the contents of other embodiments.

[0154] (Embodiment 5) In this embodiment, an example of application to an electric vehicle (EV) is shown using Figures 4A to 4C.

[0155] As shown in Figure 4A, the electric vehicle is equipped with a first battery 1301a, 1301b as the main lithium-ion battery for propulsion, and a second battery 1311 that supplies power to the inverter 1312 for starting the motor 1304. By using the positive electrode active material of the present invention in the first batteries 1301a, 1301b, it is possible to create a secondary battery with high energy density and good electrical characteristics over a wide temperature range.

[0156] The second battery 1311 is also called the cranking battery (or starter battery). The second battery 1311 only needs to be able to output high power, and does not require a large capacity, so the capacity of the second battery 1311 is smaller than that of the first batteries 1301a and 1301b.

[0157] The internal structure of the first battery 1301a may be wound or stacked. Furthermore, a lithium-ion battery having a positive electrode active material according to one embodiment of the present invention may be used in the first battery 1301a. By using a lithium-ion battery having a positive electrode active material according to one embodiment of the present invention in the first battery 1301a, an electric vehicle with a long driving range and usability in a wide range of ambient temperatures can be achieved.

[0158] 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 lithium-ion batteries, a large amount of power can be extracted. Multiple lithium-ion batteries may be connected in parallel, in series, or connected in parallel and then in series. Multiple lithium-ion batteries are also called a battery pack.

[0159] Furthermore, the lithium-ion battery for use in vehicles has a service plug or circuit breaker that can cut off high voltage without using tools in order to cut off power from multiple lithium-ion batteries, and this is provided on the first battery 1301a.

[0160] Furthermore, the power from the first batteries 1301a and 1301b is not only used to rotate the motor 1304, but can also be used to supply power to 42V onboard components (electric power steering 1307, heater 1308, defogger 1309, etc.) via the DC-DC circuit 1306. In the case of a rear motor 1317 on the rear wheels, the first battery 1301a is used to rotate the rear motor 1317.

[0161] Furthermore, the second battery 1311 supplies power to 14V automotive components (audio system 1313, power windows 1314, lights 1315, etc.) via the DC-DC circuit 1310.

[0162] Furthermore, the first battery 1301a will be explained using Figure 4B.

[0163] Figure 4B shows an example where nine rectangular lithium-ion batteries 1300 are arranged in a single battery pack 1415. In this example, nine rectangular lithium-ion batteries 1300 are connected in series, with one electrode fixed by an insulating fixing part 1413 and the other electrode fixed by an insulating fixing part 1414. While this embodiment shows an example of fixing with fixing parts 1413 and 1414, the batteries may also be housed in a battery housing box (also called a casing). Since vehicles are expected to be subjected to vibrations or shaking from external sources (such as the road surface), it is preferable to fix multiple lithium-ion batteries using fixing parts 1413, 1414 and a battery housing box. Furthermore, one electrode is electrically connected to the control circuit unit 1320 by wiring 1421, and the other electrode is electrically connected to the control circuit unit 1320 by wiring 1422.

[0164] Furthermore, the control circuit unit 1320 may also use a memory circuit that includes a transistor made of an oxide semiconductor. A charging control circuit or battery control system having a memory circuit that includes a transistor made of an oxide semiconductor may be referred to as BTOS (Battery operating system or Battery oxide semiconductor).

[0165] It is preferable to use a metal oxide that functions as an oxide semiconductor. For example, as the oxide, a metal oxide such as In-M-Zn oxide (where element M is one or more selected from aluminum, gallium, yttrium, copper, vanadium, beryllium, boron, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, or magnesium) is preferable. In particular, the In-M-Zn oxide that can be used as the oxide is preferably CAAC-OS (C-Axis Aligned Crystal Oxide Semiconductor) or CAC-OS (Cloud-Aligned Composite Oxide Semiconductor). Alternatively, In-Ga oxide or In-Zn oxide may be used as the oxide. CAAC-OS is an oxide semiconductor having multiple crystalline regions, the c-axis of which is oriented in a specific direction. This specific direction is the thickness direction of the CAAC-OS film, the normal direction to the surface on which the CAAC-OS film is formed, or the normal direction to the surface of the CAAC-OS film. A crystalline region is a region with periodic atomic arrangement. If the atomic arrangement is considered a lattice arrangement, then a crystalline region is also a region with a aligned lattice arrangement. Furthermore, CAAC-OS has regions where multiple crystalline regions are connected in the a-b plane direction, and these regions may exhibit distortion. Distortion refers to a point in the region where multiple crystalline regions are connected where the orientation of the lattice arrangement changes between a region with a aligned lattice arrangement and another region with a aligned lattice arrangement. In short, CAAC-OS is an oxide semiconductor that is c-axis oriented and does not exhibit clear orientation in the a-b plane direction.

[0166] Furthermore, since it can be used in low-temperature environments, it is preferable that the control circuit section 1320 uses a transistor made of an oxide semiconductor. To simplify the process, the control circuit section 1320 may also be formed using a unipolar transistor. Transistors using an oxide semiconductor in the semiconductor layer have a wider operating ambient temperature range than single-crystal Si transistors, from -40°C to 150°C, and even if the lithium-ion battery overheats, the change in characteristics is smaller compared to single-crystal Si transistors. The off-current of a transistor using an oxide semiconductor is below the lower limit of measurement regardless of temperature, even at 150°C, but the off-current characteristics of a single-crystal Si transistor are highly temperature-dependent. For example, at 150°C, the off-current of a single-crystal Si transistor increases, and the current on / off ratio does not become sufficiently large. The control circuit section 1320 can improve safety.

[0167] The control circuit unit 1320, which uses a memory circuit including an oxide semiconductor transistor, can also function as an automatic control device for lithium-ion batteries to address 10 causes of instability, such as micro-short circuits. Functions to eliminate the 10 causes of instability include overcharge prevention, overcurrent prevention, overheat control during charging, cell balancing in the battery pack, over-discharge prevention, remaining charge indicator, automatic control of charging voltage and current according to temperature, charging current control according to the degree of degradation, detection of abnormal behavior of micro-short circuits, and prediction of abnormalities related to micro-short circuits. The control circuit unit 1320 has at least one of these functions. Furthermore, it is possible to miniaturize the automatic control device for lithium-ion batteries.

[0168] Furthermore, a microshort refers to a tiny short circuit inside a lithium-ion battery. One of the causes of microshorts is said to be that, due to multiple charge-discharge cycles, the non-uniform distribution of the positive electrode active material causes localized current concentration in parts of the positive electrode and parts of the negative electrode, or that micro-short circuits occur due to the generation of by-reactants from side reactions.

[0169] Furthermore, in addition to detecting micro-shorts, the control circuit unit 1320 also detects the terminal voltage of the lithium-ion battery and manages the charging and discharging state of the lithium-ion battery. For example, to prevent overcharging, both the output transistor and the cutoff switch of the charging circuit can be turned off almost simultaneously.

[0170] Furthermore, an example of a block diagram of the battery pack 1415 shown in Figure 4B is shown in Figure 4C.

[0171] The control circuit unit 1320 includes at least a switch to prevent overcharging, a switch unit 1324 including a switch to prevent over-discharging, a control circuit 1322 that controls the switch unit 1324, and a voltage measurement unit for the first battery 1301a. The control circuit unit 1320 has upper and lower voltage limits set for the lithium-ion battery used, and limits the upper limit of external current and the upper limit of output current to the outside. Within the range between the lower voltage limit and the upper voltage limit of the lithium-ion battery, it is within the voltage range for which use is recommended, and if it goes outside this range, the switch unit 1324 activates and functions as a protection circuit. The control circuit unit 1320 can also be called a protection circuit because it controls the switch unit 1324 to prevent over-discharge and overcharge. For example, if the control circuit 1322 detects a voltage that is likely to cause overcharging, it cuts off the current by turning off the switch unit 1324. Furthermore, a PTC element may be provided in the charge / discharge path to provide a function to cut off the current in response to the rise in temperature. Furthermore, the control circuit unit 1320 has an external terminal 1325 (+IN) and an external terminal 1326 (-IN).

[0172] The switch unit 1324 can be constructed by combining an n-channel transistor and a p-channel transistor. The switch unit 1324 is not limited to a switch having a Si transistor using single-crystal silicon, but 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), GaO ｘThe switch section 1324 may be formed using a power transistor having (gallium oxide; x is a real number greater than 0), etc. Furthermore, since memory elements using OS transistors can be freely arranged by stacking them on circuits using Si transistors, integration can be easily achieved. By stacking a control circuit section 1320 using OS transistors on the switch section 1324 and integrating them, it is possible to create a single chip, enabling miniaturization.

[0173] The first batteries 1301a and 1301b primarily supply power to 42V (high-voltage HV) onboard equipment, while the second battery 1311 supplies power to 14V (low-voltage LV) onboard equipment. Lead-acid batteries are often used for the second battery 1311 due to cost advantages. While using a lithium-ion battery for the second battery 1311 offers the advantage of being maintenance-free, prolonged use, such as more than three years, may lead to malfunctions that were not detectable at the time of manufacture. In particular, if the second battery 1311, which starts the inverter, becomes inoperable, the motor may not be able to be started even if the first batteries 1301a and 1301b have remaining capacity. To prevent this, if the second battery 1311 is a lead-acid battery, power is supplied from the first battery to the second battery to keep it constantly fully charged.

[0174] 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. However, the second battery 1311 may be a lead-acid battery, an all-solid-state battery, or an electric double-layer capacitor. By using the positive electrode active material of the present invention in the lithium-ion battery described above, a secondary battery with high energy density and good electrical characteristics over a wide temperature range can be obtained.

[0175] Furthermore, the regenerative energy generated by the rotation of the tire 1316 is sent to the motor 1304 via the gear 1305 and charged to the second battery 1311 via the control circuit unit 1321 from the motor controller 1303 and battery controller 1302. Alternatively, it is charged to the first battery 1301a via the control circuit unit 1320 from the battery controller 1302. Alternatively, it is charged to the first battery 1301b via the control circuit unit 1320 from the battery controller 1302. In order to efficiently charge the regenerative energy, it is desirable that the first batteries 1301a and 1301b are capable of rapid charging.

[0176] The battery controller 1302 can set the charging voltage and charging current of the first batteries 1301a and 1301b. The battery controller 1302 can set the charging conditions according to the charging characteristics of the lithium-ion battery being used and enable rapid charging.

[0177] Although not shown in the diagram, when connected to an external charger, the charger's outlet or connection cable is electrically connected to the battery controller 1302. Power supplied from the external charger charges the first batteries 1301a and 1301b via the battery controller 1302. In some cases, the charger may have a control circuit and may not use the functions of the battery controller 1302, but it is preferable to charge the first batteries 1301a and 1301b via the control circuit unit 1320 to prevent overcharging. In some cases, the connection cable or the charger's connection cable may also have a control circuit. The control circuit unit 1320 is sometimes called an ECU (Electronic Control Unit). The ECU is connected to a CAN (Controller Area Network) installed in the electric vehicle. CAN is one of the serial communication standards used as an in-vehicle LAN. The ECU also includes a microcomputer. The ECU uses a CPU or GPU.

[0178] External chargers installed at charging stations and other locations include 100V outlets, 200V outlets, and 3-phase 200V with 50kW output. Additionally, it is possible to charge by receiving power from external charging equipment using contactless power supply methods.

[0179] Next, we will describe an example in which a lithium-ion battery, which is one aspect of the present invention, is implemented in a vehicle, typically a transport vehicle.

[0180] Furthermore, equipping vehicles with lithium-ion batteries can enable the creation of next-generation clean energy vehicles such as hybrid vehicles (HVs), electric vehicles (EVs), or plug-in hybrid vehicles (PHVs). Lithium-ion batteries can also be installed in agricultural machinery, motorized bicycles including electric-assist bicycles, motorcycles, electric wheelchairs, electric carts, small or large vessels, submarines, aircraft such as fixed-wing and rotary-wing aircraft, rockets, satellites, space probes, planetary probes, and spacecraft.

[0181] Figures 5A to 5E show examples of vehicles and the like using a lithium-ion battery according to one embodiment of the present invention.

[0182] Figure 5A shows an example of an electric bicycle using a lithium-ion battery according to one embodiment of the present invention. The lithium-ion battery according to one embodiment of the present invention can be applied to the electric bicycle 8700 shown in Figure 5A. The lithium-ion battery according to one embodiment of the present invention may have a protection circuit.

[0183] The electric bicycle 8700 is equipped with a power storage device 8702. The power storage device 8702 can supply electricity to a motor that assists the rider. The power storage device 8702 can also be detached from the electric bicycle 8700 and carried separately. The power storage device 8702 also contains multiple lithium-ion batteries according to one embodiment of the present invention, and the remaining battery level and other information can be displayed on a display unit. By using the positive electrode active material of the present invention in the lithium-ion battery, it is possible to create a secondary battery with high energy density and good electrical characteristics over a wide temperature range.

[0184] Figure 5B shows an example of a two-wheeled vehicle using a lithium-ion battery according to one embodiment of the present invention. The scooter 8600 shown in Figure 5B is equipped with a power storage device 8602, side mirrors 8601, and turn signals 8603. The power storage device 8602 can be stored in the under-seat storage compartment 8604 of the scooter 8600. The power storage device 8602 can supply electricity to the turn signals 8603. If the scooter has a motor, the power storage device 8602 can also supply electricity to the motor. By using the positive electrode active material of the present invention in the lithium-ion battery of the power storage device 8602, a secondary battery with high energy density and good electrical characteristics over a wide temperature range can be obtained.

[0185] The automobile 2001 shown in Figure 5C is an electric vehicle that uses an electric motor as a power source for driving. Alternatively, it is a hybrid vehicle that can appropriately select and use an electric motor and an engine as power sources for driving. When a lithium-ion battery is installed in the vehicle, one or more examples of the lithium-ion battery shown in the above embodiment are installed in one location. By using the positive electrode active material of the present invention in the lithium-ion battery installed in the vehicle, a secondary battery with high energy density and good electrical characteristics over a wide temperature range can be obtained.

[0186] The automobile 2001 shown in Figure 5C has a battery pack 2200, which has a battery module to which a plurality of lithium-ion batteries are connected. Furthermore, it is preferable that the battery pack 2200 has a charge control device electrically connected to the battery module.

[0187] Furthermore, the automobile 2001 can be charged by receiving power from an external charging facility via a plug-in method or a contactless power supply method to the lithium-ion battery it possesses. When charging, the charging method and connector specifications may be carried out as appropriate in accordance with the prescribed methods of CHAdeMO (registered trademark) or Combo. External charging facilities can include charging stations installed in commercial facilities, household power supplies, etc. For example, the battery storage device mounted on the automobile 2001 can be charged by supplying power from an external source using plug-in technology. Charging can be performed by converting AC power to DC power via a conversion device such as an ADC converter.

[0188] Although not shown in the diagram, the vehicle can also be charged by mounting a power receiving device on the vehicle and receiving power wirelessly from a ground-based power transmission device. In this wireless power supply method, charging can be performed not only when the vehicle is stopped but also while it is in motion by incorporating the power transmission device into the road or exterior wall. Furthermore, this wireless power supply method can be used to transmit and receive power between two vehicles. In addition, solar panels can be installed on the exterior of the vehicle to charge the lithium-ion battery when the vehicle is stopped and when it is in motion. For such wireless power supply, an electromagnetic induction method or a magnetic resonance method can be used.

[0189] Figure 5D shows, as an example, a large transport vehicle 2003 equipped with an electrically controlled motor. The battery module of the transport vehicle 2003 has a maximum voltage of 600V, achieved by connecting more than 100 lithium-ion batteries with a nominal voltage of 3.0V to 5.0V in series. The battery pack 2202 has the same functions as Figure 5C, except for differences in the number of lithium-ion batteries constituting the battery module, so the explanation is omitted. By using the positive electrode active material of the present invention in the lithium-ion batteries of the module, it is possible to create a secondary battery with high energy density and good electrical characteristics over a wide temperature range.

[0190] Figure 5E shows an example of an aircraft 2004 having a fuel-burning engine. The aircraft 2004 can be considered a type of transport vehicle because it has wheels for takeoff and landing, and it has a battery pack 2203 which includes a battery module formed by connecting multiple lithium-ion batteries and a charge control device.

[0191] The battery module of aircraft 2004 has a maximum voltage of 32V, for example, by connecting eight 4V lithium-ion batteries in series. The battery module of battery pack 2203 has the same functions as Figure 5C, except for the number of lithium-ion batteries that make up the module, so the explanation will be omitted.

[0192] The contents of this embodiment can be appropriately combined with the contents of other embodiments.

[0193] (Embodiment 6) This embodiment describes an example of mounting a lithium-ion battery, which is one aspect of the present invention, in an electronic device. Examples of electronic devices on which a lithium-ion battery is mounted include television equipment (also called televisions or television receivers), monitors for computers, digital cameras, digital video cameras, digital photo frames, mobile phones (also called mobile phones or mobile phone devices), portable game consoles, personal information terminals, sound playback devices, and large game machines such as pachinko machines. Personal information terminals include notebook personal computers, tablet terminals, e-book readers, and mobile phones.

[0194] Figure 6A shows an example of a mobile phone. The mobile phone 2100 includes a display unit 2102 built into the housing 2101, as well as operation buttons 2103, an external connection port 2104, a speaker 2105, a microphone 2106, and the like. The mobile phone 2100 also has a lithium-ion battery 2107. By using the positive electrode active material of the present invention in the lithium-ion battery, it is possible to create a secondary battery with high energy density and good electrical characteristics over a wide temperature range.

[0195] The mobile phone 2100 can run various applications such as making phone calls, sending emails, reading and creating documents, playing music, communicating on the internet, and playing computer games.

[0196] The operation button 2103 can be assigned various functions, including time setting, power on / off operation, wireless communication on / off operation, silent mode activation / deactivation, and power saving mode activation / deactivation. For example, the function of the operation button 2103 can be freely configured by the operating system built into the mobile phone 2100.

[0197] Furthermore, the mobile phone 2100 is capable of performing standardized short-range wireless communication. For example, it can communicate with a wireless communication-enabled headset to enable hands-free calling.

[0198] Furthermore, the mobile phone 2100 is equipped with an external connection port 2104, which allows for direct data exchange with other information terminals via a connector. It can also be charged via the external connection port 2104. Note that charging may also be performed wirelessly without using the external connection port 2104.

[0199] The mobile phone 2100 preferably has sensors. For example, it is preferable that the mobile phone be equipped with human body sensors such as a fingerprint sensor, pulse sensor, and body temperature sensor, as well as touch sensors, pressure sensors, acceleration sensors, etc.

[0200] Figure 6B shows an unmanned aerial vehicle 2300 having multiple rotors 2302. The unmanned aerial vehicle 2300 is sometimes called a drone. The unmanned aerial vehicle 2300 has a lithium-ion battery 2301, a camera 2303, and an antenna (not shown), which are embodiments of the present invention. The unmanned aerial vehicle 2300 can be remotely controlled via the antenna. By using the positive electrode active material of the present invention in the lithium-ion battery, a secondary battery can be made that has a high energy density and exhibits good electrical characteristics over a wide temperature range.

[0201] Figure 6C shows an example of a robot. The robot 6400 shown in Figure 6C is equipped with a lithium-ion 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 movement mechanism 6408, a computing device, and the like.

[0202] Microphone 6402 has the function of detecting the user's voice and ambient sounds. Speaker 6404 has the function of emitting sound. Robot 6400 can communicate with the user using microphone 6402 and speaker 6404.

[0203] The display unit 6405 has the function of displaying various types of information. The robot 6400 can display the information desired by the user on the display unit 6405. The display unit 6405 may be equipped with a touch panel. The display unit 6405 may also be a detachable information terminal, and by installing it in a fixed position on the robot 6400, charging and data transfer can be made possible.

[0204] The upper camera 6403 and the lower camera 6406 have the function of imaging the area around the robot 6400. In addition, the obstacle sensor 6407 can detect the presence or absence of obstacles in the direction of travel when the robot 6400 moves forward using the movement mechanism 6408. The robot 6400 can recognize its surrounding environment and move safely using the upper camera 6403, the lower camera 6406 and the obstacle sensor 6407.

[0205] The robot 6400 is equipped with a lithium-ion battery 6409 according to one aspect of the present invention and a semiconductor device or electronic components in its internal region. By using the positive electrode active material of the present invention in the lithium-ion battery, a secondary battery can be made that has a high energy density and exhibits good electrical characteristics over a wide temperature range.

[0206] Figure 6D shows an example of a cleaning robot. The cleaning robot 6300 has a display unit 6302 located on the top surface of the housing 6301, multiple cameras 6303 located on the sides, a brush 6304, operation buttons 6305, a lithium-ion battery 6306, and various sensors. Although not shown, the cleaning robot 6300 is equipped with wheels, a suction port, etc. The cleaning robot 6300 is self-propelled, can detect dirt 6310, and can suck up the dirt from a suction port located on the bottom surface.

[0207] For example, the cleaning robot 6300 can analyze images captured by the camera 6303 to determine the presence or absence of obstacles such as walls, furniture, or steps. Furthermore, if the image analysis detects an object that might become entangled in the brush 6304, such as wiring, the rotation of the brush 6304 can be stopped. The cleaning robot 6300 is equipped with a lithium-ion battery 6306 according to one embodiment of the present invention and a semiconductor device or electronic components within its internal region. By using the positive electrode active material of the present invention in the lithium-ion battery, a secondary battery with high energy density and good electrical characteristics over a wide temperature range can be obtained.

[0208] This embodiment can be implemented in appropriate combination with other embodiments.

[0209] In this embodiment, LiMn ｙ Fe （１−ｙ） PO ４ A positive electrode active material with a composition (y being between 0.80 and 0.95) was prepared, and its properties were evaluated.

[0210] <Preparation of positive electrode active material> The preparation of the positive electrode active material in this embodiment will be explained with reference to the preparation method shown in Figure 2.

[0211] [Positive electrode active material sample 1] Li as lithium source ２ CO ３ , as a manganese source, MnCO ３ FeC as an iron source ２ O ４ ・2H ２ O, NH as a phosphate source ４ H ２ PO ４ Prepare a LiMn０．９０ Fe ０．１０ PO ４ The material was weighed to achieve the following result. Zirconia balls with a diameter of 3 mm (manufactured by Nikkatoh, yttria-stabilized zirconia balls YTZ) were used as the grinding medium, and dehydrated acetone was used as the solvent.

[0212] These were mixed at 300 rpm for 2 hours while cooling using a planetary ball mill (LP-4, manufactured by Ito Seisakusho) (first ball milling process). After drying in a ventilated drying oven, the first mixture was recovered by sieving it through a 300 μm sieve.

[0213] The first mixture was placed in a crucible made of 99.9% pure aluminum oxide, covered, and heated in a muffle furnace under a nitrogen flow atmosphere at 350°C for 10 hours. The heated mixture was then passed through a sieve with a mesh size of 300 μm to obtain the composite oxide.

[0214] Glucose was used as the carbon source, and the complex oxide and glucose were weighed so that the ratio of complex oxide to glucose was 10:1 (by weight). Zirconia balls with a diameter of 1 mm (manufactured by Nikkatoh, yttria-stabilized zirconia balls YTZ) were prepared as the grinding medium, and dehydrated acetone was prepared as the solvent.

[0215] These were mixed using a planetary ball mill (LP-4, manufactured by Ito Seisakusho) at 300 rpm for 2 hours (second ball milling treatment). After drying in a ventilated drying oven, the second mixture was recovered by sieving it through a 300 μm sieve.

[0216] The second mixture was placed in a crucible made of 99.9% pure aluminum oxide, covered, and heated in a muffle furnace under a nitrogen flow atmosphere at 650°C for 10 hours. The heated mixture was passed through a sieve with a mesh size of 53 μm to obtain cathode active material sample 1. The cathode active material sample 1 prepared in the above process was then mixed with carbon-coated cathode active material in a C / LiMn ratio. ０．９０ Fe ０．１０ PO ４ It is sometimes called that.

[0217] [Comparative Sample 1] Next, the preparation of comparative sample 1 will be explained. Comparative sample 1 was prepared in the same manner as positive electrode active material sample 1, except that 3 mm diameter zirconia balls were used as the grinding medium in the second ball milling process.

[0218] In other words, in the preparation of positive electrode active material sample 1, the size of the zirconia balls used in the second ball milling process was smaller than the size of the zirconia balls used in the first ball milling process. On the other hand, in the preparation of comparative sample 1, the size of the zirconia balls used in the first ball milling process and the zirconia balls used in the second ball milling process were the same.

[0219] <XRD> XRD measurements were performed on the positive electrode active material sample 1 and comparative sample 1 prepared above, and Rietveld analysis was conducted. The XRD apparatus and measurement conditions were as described in Embodiment 1. Figures 7A and 7B show the XRD patterns. In Figures 7A and 7B, the vertical axis represents the X-ray detection intensity [a.u.], and the horizontal axis represents 2θ (diffraction angle) [°]. Figure 7B is an enlarged graph of a part of Figure 7A.

[0220] In both positive electrode active material sample 1 and comparative sample 1, LiMn was found at the position indicated by the black inverted triangle in Figure 7B. ０．９０ Fe ０．１０ PO ４ Peaks originating from [the specified phase] were observed. In comparison sample 1, as shown by the white inverted triangles in Figure 7B, peaks originating from a different phase, which is thought to be reaction residue, were observed at diffraction angles of 28.8°, 29.0°, and 30.4°. In contrast, no peaks originating from a different phase were observed in positive electrode active material sample 1.

[0221] Also, these patterns are LiFePO ４ Table 1 shows the results of the Rietveld analysis performed using the single-phase model (ICSD col.code.193640).

[0222]

[0223] As shown in Table 1, the crystallite size (LVol-IB) of positive electrode active material sample 1 was in the range of 25 nm to 50 nm, specifically 45.7 nm. On the other hand, the crystallite size (LVol-IB) of comparative sample 1 was 70.4 nm.

[0224] <SEM Observation> Figures 8A and 8B show SEM images of positive electrode active material sample 1. Figures 9A and 9B show SEM images of comparison sample 1. Figure 8B is an enlarged view of a portion of Figure 8A, and Figure 9B is an enlarged view of a portion of Figure 9A.

[0225] In the positive electrode active material sample 1 shown in Figure 8B, many primary particles with a particle diameter of 100 nm or less were observed. On the other hand, in the comparative sample 1 shown in Figure 9B, many primary particles with a particle diameter of 100 nm or more were observed. The results of measuring the size of the primary particles in Figures 8B and 9B are shown in Table 2.

[0226]

[0227] As shown in Table 2, in positive electrode active material sample 1, the D50 value measured in the primary particle diameter in the SEM image was 60 nm or less, specifically 52.5 nm. On the other hand, in comparison sample 1, the D50 value was larger at 83.3 nm. Furthermore, in positive electrode active material sample 1, the D50 value measured in the primary particle diameter in the SEM image was 100 nm or less, specifically 74.4 nm. On the other hand, in comparison sample 1, the D90 value was 140.4 nm, significantly exceeding 100 nm.

[0228] <Half-cell fabrication> Using the positive electrode active material sample 1 and comparative sample 1 prepared above as the positive electrode, a coin-shaped (CR2032 type, 20 mm in diameter, 3.2 mm in height) half-cell was fabricated and its characteristics were evaluated. A lithium metal foil was used as the negative electrode.

[0229] The electrolyte consists of a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of EC:DEC = 3:7, to which 1 mol / L of lithium hexafluoride phosphate (LiPF) is added. ６A solution containing the dissolved substance was used, to which 2 wt% vinylene carbonate (VC) was added as an additive. A porous polypropylene film was used as the separator.

[0230] Acetylene black was used as the conductive material, and PVDF was used as the binder. A slurry was prepared by mixing the positive electrode active material, acetylene black, binder, and NMP as the solvent. At this time, the ratio of positive electrode active material:conductive material:PVDF was 90:5:5 (by weight).

[0231] Carbon-coated aluminum foil was used as the positive electrode current collector, and the slurry described above was applied to the positive electrode current collector. The amount of positive electrode active material supported was 5 mg / cm³. ２ After drying, it was pressed at 210 kN / m and 120°C.

[0232] <Charge / Discharge Characteristics> The charge / discharge cycle test consisted of charging at CCCV (4.5V, 85mA / g, cutoff current 8.5mA / g) and discharging at CC (85mA / g, cutoff voltage 2.5V), with a 10-minute pause between charging and discharging. The measurement environment was 25°C.

[0233] The results of the charge-discharge cycle test at a measurement environment of 25°C are shown in Figures 10A and 10B. Figure 10A is a graph showing the charge curve and discharge curve at the 20th cycle of the charge-discharge cycle test of a coin cell using positive electrode active material sample 1 and a coin cell using comparative sample 1. In the graph of Figure 10A, the vertical axis represents voltage and the horizontal axis represents capacity. The capacity is the value per unit weight of positive electrode active material possessed by the positive electrode.

[0234] Figure 10B is a graph showing the cycle characteristics of a coin cell using positive electrode active material sample 1 and a coin cell using comparative sample 1 during charge-discharge cycle tests. In the graph of Figure 10B, the vertical axis represents the discharge capacity, and the horizontal axis represents the number of charge-discharge cycles. The results of the charge-discharge cycle tests shown in Figure 10B are shown in Table 3.

[0235]

[0236] As shown in Figure 10B and Table 3, while comparative sample 1 has a high discharge capacity of 111.7 mAh / g in the first cycle, it decreases to 98.4 mAh / g by the tenth cycle, which is lower than the discharge capacity of positive electrode active material sample 1, which is 102.9 mAh / g, in the same cycle. Even in the progression of discharge capacity from the tenth cycle onward, positive electrode active material sample 1 has a higher discharge capacity than comparative sample 1, indicating that positive electrode active material sample 1, which is an example of positive electrode active material 100 according to one embodiment of the present invention, has excellent cycle characteristics.

[0237] Furthermore, comparing the discharge curves in Figure 10A, the voltage of positive electrode active material sample 1 is higher than that of comparison sample 1, and comparing the charge curves, the voltage of positive electrode active material sample 1 is lower than that of comparison sample 1. This indicates that positive electrode active material sample 1 has lower reaction resistance and superior charge / discharge characteristics.

[0238] 100: positive electrode active material, 101: primary particles, 101a: primary particles, 101b: primary particles, 101c: primary particles,

Claims

The positive electrode active material has an olivine-type crystal structure, The positive electrode active material comprises lithium, manganese, iron, phosphorus, and oxygen. The atomic ratio of manganese to iron in the positive electrode active material (Mn / (Mn+Fe)) is 0.80 or more and 0.95 or less. The positive electrode active material is CuKα １ When Rietveld analysis was performed on the powder X-ray diffraction pattern using a linear method, the crystallite size (LVol-IB) of the olivine-type crystal structure was found to be between 25 nm and 50 nm. Positive electrode. LiMn ｙ Fe （１−ｙ） PO ４ A method for producing lithium iron manganese phosphate represented by (y being 0.80 or more and 0.95 or less), In the first mixing process, a lithium source, a manganese source, an iron source, and a phosphoric acid source are mixed to produce a first mixture. In the first heat treatment, the first mixture is heated, In the second mixing process, the first mixture after the first heat treatment and glucose are mixed to produce a second mixture. In the second heat treatment, the second mixture is heated, The first mixing process and the second mixing process are carried out using a ball mill device. The diameter of the ball used in the second mixing process is smaller than the diameter of the ball used in the first mixing process. The first heat treatment is carried out in an inert atmosphere at a temperature of 300°C to 400°C for 1 hour to 20 hours. The second heat treatment is carried out in an inert atmosphere at a temperature of 500°C to 800°C for 1 hour to 20 hours. Method for producing lithium iron manganese phosphate. 　 In claim 2, The first mixing process and the second mixing process are wet mixing processes using acetone. The ball used in the second mixing process has a zirconia ball. The diameter of the zirconia balls used in the second mixing process is 0.03 mm or more and 1.0 mm or less. Method for producing lithium iron manganese phosphate. 　 In claim 3, The ball used in the first mixing process has a zirconia ball. The diameter of the zirconia balls used in the first mixing process is 2.0 mm or more and 5.0 mm or less. Method for producing lithium iron manganese phosphate.

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