Lithium-ion battery

Abstract

Provided is a lithium-ion battery having a positive electrode active material of an olivine-type crystal structure and exhibiting excellent battery characteristics. The lithium-ion battery has a positive electrode, wherein: the positive electrode has a positive electrode active material; the positive electrode active material has an olivine-type crystal structure; and in the positive electrode active material, the atomic number ratio of manganese to a total of atomic number ratios of manganese, iron, and an additive element is 0.7 or more, the atomic number ratio of the additive element to a total of atomic number ratios of manganese and the additive element is 0.02 to 0.1 (exclusive of 0,1), and the additive element is a divalent cation.

Description

Lithium-ion battery

[0001] One embodiment of the present invention relates to a lithium-ion battery. However, the technical field of the present invention is not limited to lithium-ion batteries, and the technical field of the present invention can include one or more of semiconductor devices, display devices, light-emitting devices, power storage devices, lighting devices, electronic devices, and vehicles. For example, the lithium-ion battery of the present invention can be applied as a power source required for semiconductor devices, display devices, light-emitting devices, lighting devices, electronic devices, and vehicles. Furthermore, the technical field of the present invention can include a manufacturing method for the above-mentioned devices. The electronic devices include information terminal devices equipped with a lithium-ion battery.

[0002] High-power, high-energy-density lithium-ion batteries have become essential in modern society as a rechargeable power source. Demand for lithium-ion batteries is rapidly expanding as they are installed as power sources in next-generation clean energy vehicles, such as hybrid vehicles (HVs), electric vehicles (EVs), and plug-in hybrid vehicles (PHVs).

[0003] One of the materials being actively researched and developed as a positive electrode active material for lithium-ion batteries is LiMePO, which has an olivine-type crystal structure. ４ (Me = any one of Fe, Mn, Ni, and Co). Among these, LiFePO ４ has already demonstrated a charge / discharge capacity close to the theoretical capacity (170 mAh / g) (see, for example, Non-Patent Document 1). ４ As shown in the above-mentioned Non-Patent Document 1, the operating voltage is about 3.4 V (vs. Li / Li ＋ ), which is lower than the operating voltage of other commercially available positive electrode active materials, such as lithium-ion batteries containing lithium nickel manganese cobalt oxide (NMC), at about 4.2 V (vs. Li / Li ＋ However, the energy density is lower than that of LiFePO4, which has an olivine crystal structure. ４ is LiCoO with a layered rock salt crystal structure ２Since it is more stable and less susceptible to deterioration, it has excellent charge-discharge cycle characteristics and good thermal stability. In addition, since it does not use expensive metals such as Co and Ni, it can be produced inexpensively. In view of these advantages, LiFePO ４ Lithium-ion batteries having the above characteristics are being installed in EVs and the like as power sources.

[0004] To improve the low energy density, LiFePO ４ and LiMnPO ４ A solid solution of LiMn ｘ Fe １−ｘ P.O. ４ Materials with a valence of 0<x<1 are being investigated. The above solid solution is a material in which Fe is substituted with Mn, and since Mn has a weaker ionic bond than Fe, it is expected that the operating voltage will be higher. However, although the operating voltage increases by increasing the proportion of Mn in the above solid solution, the portion that cannot contribute to charge and discharge increases, and the discharge capacity decreases to LiFePO ４ There are concerns that the price will fall further. ｘ Fe １−ｘ P.O. ４ In the range (0<x<1), the lithium ion insertion / extraction reaction is known to be a two-phase coexistence reaction, and it is believed that the phase boundary moves rapidly, causing the entire crystal to undergo a phase change. At this phase boundary, strain occurs due to the difference in volume between the crystalline structures in the lithium ion insertion state and the lithium ion desorption state, raising concerns about a rise in the activation barrier at the phase boundary and a deterioration in battery performance.

[0005] In order to alleviate the above-mentioned solid solution concerns, LiFe ａ Mn １−ａ−ｂ M ｂ P.O. ４ (M represents Mg, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd) have been investigated, and in Patent Document 1, a carbon-supported LiFe ０．１ Mn ０．８ Mg ０．１ P.O. ４ It describes:

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

[0007] WO2016 / 047491 publication

[0008] LiFe having an olivine-type crystal structure ａ Mn １−ａ−ｂ M ｂ P.O. ４ (M represents Mg, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd) In order to achieve a higher energy density, there is room for further study on the optimal ratio of the element corresponding to M. There is also room for further study on the optimal ratio of the element corresponding to M in order to achieve a superior discharge capacity.

[0009] In view of the above, an object of one embodiment of the present invention is to provide a lithium-ion battery using a positive electrode active material with high energy density, and an object of one embodiment of the present invention is to provide a lithium-ion battery using a positive electrode active material that exhibits excellent discharge capacity.

[0010] Note that the description of these problems does not preclude the existence of other problems. Note that one embodiment of the present invention does not necessarily solve all of these problems. Note that problems other than these can be extracted from the description of the specification, drawings, and claims.

[0011] In order to solve the above-described problems, one aspect of the present invention is a lithium-ion battery having a positive electrode, the positive electrode having a positive electrode active material, the positive electrode active material having an olivine-type crystal structure, in which the atomic ratio of manganese to the sum of the atomic ratios of manganese, iron, and the additional element in the positive electrode active material is 0.7 or more, the atomic ratio of the additional element to the sum of the atomic ratios of manganese and the additional element in the positive electrode active material is 0.02 or more and less than 0.1, and the additional element is a divalent cation.

[0012] Another embodiment of the present invention is a lithium-ion battery having a positive electrode, the positive electrode including a positive electrode active material having an olivine-type crystal structure, in which the atomic ratio of manganese to the sum of the atomic ratios of manganese, iron, and magnesium in the positive electrode active material is 0.7 or more, and the atomic ratio of magnesium to the sum of the atomic ratios of manganese and magnesium in the positive electrode active material is 0.02 or more and less than 0.1.

[0013] Another embodiment of the present invention is a lithium-ion battery having a positive electrode, the positive electrode including a positive electrode active material having an olivine crystal structure, in which the atomic ratio of manganese to the sum of the atomic ratios of manganese, iron, and zinc in the positive electrode active material is 0.7 or more, and the atomic ratio of zinc to the sum of the atomic ratios of manganese and zinc in the positive electrode active material is 0.02 or more and less than 0.08.

[0014] In the present invention, the olivine type crystal structure preferably belongs to the space group Pnma.

[0015] In the present invention, when the positive electrode active material is placed at 23°C ± 5°C and an XRD profile obtained by a diffraction method is subjected to Rietveld analysis, it is preferable that the lattice constant of the a-axis of the olivine-type crystal structure is greater than 10.4039 Å and not greater than 10.4319 Å, the lattice constant of the b-axis is greater than 6.0749 Å and not greater than 6.0911 Å, and the lattice constant of the c-axis is greater than 4.7346 Å and not greater than 4.7380 Å.

[0016] In the present invention, the olivine type crystal structure preferably has a crystallite size LVol-IB of 71.7 nm or more and 74.6 nm or less.

[0017] In the present invention, when the positive electrode active material is placed at 23°C ± 5°C and an XRD profile obtained by a diffraction method is subjected to Rietveld analysis, it is preferable that the lattice constant of the a-axis of the olivine-type crystal structure is 10.4087 Å or more and 10.4325 Å or less, the lattice constant of the b-axis is 6.0764 Å or more and 6.0915 Å or less, and the lattice constant of the c-axis is 4.7361 Å or more and 4.7385 Å or less.

[0018] In the present invention, the olivine type crystal structure preferably has a crystallite size LVol-IB of 68.5 nm or more and 71.8 nm or less.

[0019] According to one embodiment of the present invention, a lithium-ion battery using a positive electrode active material with high energy density can be provided. Also, according to one embodiment of the present invention, a lithium-ion battery using a positive electrode active material with excellent discharge capacity can be provided.

[0020] Note that the description of these effects does not preclude the existence of other effects. Note that one embodiment of the present invention does not necessarily have all of these effects. Note that it is possible to extract effects other than these from the description in the specification, drawings, claims, etc.

[0021] FIGS. 1A, 1B, 1C, and 1D are diagrams illustrating a cathode active material according to one embodiment of the present invention. FIG. 2 is a diagram illustrating an example of a method for manufacturing a cathode active material according to one embodiment of the present invention. FIGS. 3A, 3B, and 3C are diagrams illustrating a lithium ion battery according to one embodiment of the present invention. FIGS. 4A, 4B, and 4C are diagrams illustrating an electric vehicle according to one embodiment of the present invention. FIGS. 5A, 5B, 5C, 5D, and 5E are diagrams illustrating a vehicle according to one embodiment of the present invention. FIGS. 6A, 6B, 6C, and 6D are diagrams illustrating an electronic device according to one embodiment of the present invention. FIG. 7 is an XRD profile of a cathode active material according to an example. FIG. 8 is an XRD profile of a cathode active material according to an example. FIGS. 9A, 9B, and 9C are graphs illustrating lattice constants and Mg concentrations. FIGS. 10A, 10B, and 10C are graphs illustrating lattice constants and Zn concentrations. FIG. 11 shows LiFePO ４12A is a diagram illustrating a unit cell of the analytical sample. FIG. 12A is a cross-sectional STEM image of the analytical sample, and FIGS. 12B and 12C are graphs of the results of STEM-EDX ray analysis. FIGS. 13A and 13B are graphs of the results of STEM-EDX ray analysis. FIG. 14A is a cross-sectional STEM image of the analytical sample, and FIGS. 14B and 14C are graphs of the results of STEM-EDX ray analysis. FIGS. 15A and 15B are graphs of the results of STEM-EDX ray analysis. FIG. 16A is a cross-sectional STEM image of the analytical sample, and FIGS. 16B and 16C are graphs of the results of STEM-EDX ray analysis. FIGS. 17A and 17B are graphs of the results of STEM-EDX ray analysis. FIG. 18A is a cross-sectional STEM image of the analytical sample, and FIGS. 18B and 18C are graphs of the results of STEM-EDX ray analysis. FIGS. 19A and 19B are graphs of the results of STEM-EDX ray analysis. FIG. 20 is an observation image of the analytical sample. FIG. 21 is an observation image of the analytical sample. FIG. 22 is an observation image of the analytical sample. FIG. 23 is an observation image of the analytical sample. FIG. 24 is a graph of the results of the charge-discharge cycle test of the example. FIG. 25 is a graph of the results of the charge-discharge cycle test of the example. FIG. 26 is a graph of the results of the charge-discharge cycle test of the example. FIG. 27 is a graph of the results of the charge-discharge cycle test of the example. FIG. 28 is a graph of the results of the charge-discharge cycle test of the example. FIG. 29 is a graph of the results of the charge-discharge cycle test of the example. FIG. 30 is a graph of the results of the charge-discharge cycle test of the example. FIG. 31 is a graph of the results of the charge-discharge cycle test of the example.

[0022] The following description will explain the embodiments of the present invention with reference to the accompanying drawings. However, the present invention is not limited to the following description, and it will be readily understood by those skilled in the art that various changes can be made in form and detail without departing from the spirit and scope of the present invention. Therefore, in the embodiments described below, the same reference numerals are used in different drawings to indicate the same objects.

[0023] In this specification, ordinal numbers such as "first" and "second" are used for convenience and do not limit the number of components or the order of the components. The order of the components includes, for example, the order of processes or the order of stacking. In other words, the ordinal numbers used in the embodiments of this specification may not match the ordinal numbers used in the claims. Furthermore, the ordinal numbers used in the examples of this specification may not match the ordinal numbers used in the claims. Furthermore, the ordinal numbers used in the embodiments of this specification may not match the ordinal numbers used in the examples of this specification.

[0024] In this specification, a lithium ion battery may be referred to as a lithium ion secondary battery, and refers to a secondary battery that uses lithium ions as carrier ions. However, the carrier ions of the present invention are not limited to lithium ions. For example, alkali metal ions or Group 2 element ions may be used as carrier ions of the present invention, and specifically, sodium ions may be used. In this case, the present invention can be understood by replacing lithium ions with sodium ions. Furthermore, when describing a configuration in which there is no limitation on the carrier ions, the term "secondary battery" or "battery" may be used.

[0025] In this specification and the like, an electrolytic solution may be referred to as an electrolyte. The electrolytic solution means that the solution is liquid at 25°C. The electrolyte is not limited to a state at 25°C.

[0026] In this specification, space groups are expressed using short notation in international notation (or Hermann-Mauguin notation). Crystal planes and crystal directions are expressed using Miller indices. In crystallography, space groups, crystal planes, and crystal directions are expressed by placing a superscript bar above the number. However, due to formatting constraints, in this specification, instead of placing a bar above the number, a minus sign (-) may be placed before the number. Individual orientations indicating directions within a crystal are expressed using [ ], collective orientations indicating all equivalent directions are expressed using < >, individual planes indicating crystal planes are expressed using ( ), and collective planes with equivalent symmetry are expressed using {}. For ease of understanding the structure, trigonal crystals represented by the space group R-3m are generally expressed as a hexagonal composite hexagonal lattice. Unless otherwise specified, the space group R-3m will also be expressed as a composite hexagonal lattice in this specification. Miller indices may also be expressed as (hkil) rather than (hkl). Here, i is −(h+k).

[0027] In this specification, etc., the space group is identified by XRD, electron diffraction, neutron diffraction, etc. Therefore, in this specification, etc., "belonging to a certain space group," "belonging to a certain space group," or "being a certain space group" can be rephrased as "identified with a certain space group." In this specification, etc., the crystal structure is determined by XRD, electron diffraction, neutron diffraction, etc., and XRD can measure multiple particles, while electron diffraction or neutron diffraction can measure a single particle.

[0028] In this specification and the like, the cross-sectional shape of the positive electrode active material particles is not limited to a circle, so-called a sphere. The cross-sectional shape of the positive electrode active material particles includes an ellipse, a rectangle, a trapezoid, a triangle, a square with rounded corners, an asymmetric shape, etc., and when there are multiple particles, the cross-sectional shapes of the particles may be different from each other. Similarly, the cross-sectional shape of other particles is not limited to a circle, so-called a sphere.

[0029] In this specification, the positive electrode active material particles have a surface layer and an interior (also referred to as a bulk). The surface layer is, for example, a region up to 60 nm from the surface, and the interior is a region deeper than the surface layer.

[0030] In this specification, etc., when describing individual characteristics of the positive electrode active material particles in embodiments, etc., it is not necessary for all particles to have that characteristic. For example, if 50% or more, preferably 70% or more, and more preferably 90% or more of three or more randomly selected positive electrode active material particles have that characteristic, it can be said that there is a sufficient effect of improving the characteristics of the positive electrode active material particles and secondary batteries containing them.

[0031] In this specification, particle size can be measured using a particle size distribution analyzer (laser diffraction particle size distribution analyzer) using a laser diffraction / scattering method. In this specification, median diameter (D50) can be used as the average particle size. D50 is the particle size at which the cumulative frequency accounts for 50% in the cumulative curve of the particle size distribution measurement results.

[0032] In this specification, the measurement of particle size is not limited to laser diffraction particle size distribution measurement, and the major axis of the particle cross section may be measured by analysis such as SEM (Scanning Electron Microscope) or TEM. In this specification, the maximum particle size can be a particle size that can be confirmed on a cross section of a positive electrode measuring 100 μm square. Furthermore, as a method for measuring D50 by analysis such as SEM or TEM, for example, 20 or more particles are measured, a cumulative curve is created, and the particle diameter at which the cumulative frequency accounts for 50% can be taken as D50.

[0033] Unless otherwise specified, in this specification, the materials (positive electrode, negative electrode, electrolyte, separator, etc.) of a secondary battery are described in their pre-degradation state. Note that a decrease in discharge capacity due to pre-shipment inspection (sometimes referred to as aging treatment) during secondary battery manufacturing is not considered to be degradation. For example, a secondary battery consisting of a single cell or a battery pack can be said to be in its pre-degradation state if it has a discharge capacity of 97% or more of its rated capacity. For secondary batteries for portable devices, the rated capacity conforms to JIS C 8711:2019. For other secondary batteries, the rated capacity conforms to not only the above JIS standard but also various JIS and IEC standards for electric vehicle propulsion, industrial use, etc.

[0034] Here, we will explain the flow of electrons and lithium ions during charging in a lithium-ion battery. When a charger is connected and charging of a secondary battery begins, electrons are released from the positive electrode, causing an oxidation reaction, and electrons are supplied to the negative electrode, causing a reduction reaction. Lithium ions are then released from the positive electrode into the electrolyte, and the lithium ions move to the negative electrode. During discharge, a reduction reaction occurs at the positive electrode, and an oxidation reaction occurs at the negative electrode. In other words, in a secondary battery, the anode (positive electrode) and cathode (negative electrode) are interchanged during discharge and charging, and the oxidation reaction and reduction reaction alternate. Therefore, the electrode with a higher reaction potential is called the positive electrode, and the electrode with a lower reaction potential is called the negative electrode. Therefore, in this specification, the positive electrode is called the "positive electrode" and the negative electrode is called the "negative electrode" whether during charging or discharging.

[0035] In this specification, LiMnFePO ４ The abbreviation is LMFP, but Mn and Fe are sometimes swapped and the abbreviation is LFMP. When an additional element M is contained, LiMnFeMPO ４ The abbreviation is LMFMP, but Mn and Fe may be interchanged and the abbreviation may be LFMMP. When there are multiple additive elements M, LiMnFeM1M2PO ４ The abbreviation is LMFM1M2P, but Mn and Fe may be interchanged and the abbreviation may be LFMM1M2P.

[0036] As used herein, a full cell refers to a cell assembled with different electrodes, such as a positive electrode / negative electrode unit cell, and a half cell refers to a cell assembled with lithium metal as the negative electrode (counter electrode).

[0037] In this specification, etc., primary particles may be referred to as single particles. In this specification, etc., secondary particles refer to particles formed by aggregation of primary particles. In particular, secondary particles refer to particles in which primary particles are aggregated, bonded, or sintered so as to share part of the grain boundary (the outer periphery of the primary particle), and are not easily separated. In this specification, etc., crystallite size refers to the size of the single crystal region observed by XRD.

[0038] In this specification and the like, the phrase "A and / or B" may be used, which means "A," "B," or "A and B."

[0039] Embodiment 1 In this embodiment, features of a positive electrode active material 100 of one embodiment of the present invention will be described with reference to FIGS. 1A to 1D. FIG.

[0040] The positive electrode active material 100 has an olivine-type crystal structure and contains lithium, manganese, iron, an additive element, phosphorus, and oxygen. The positive electrode active material 100 containing the additive element can exhibit superior energy density or superior discharge capacity compared to a positive electrode active material without the additive element. It is preferable to select an additive element that allows the positive electrode active material 100 to maintain an olivine-type crystal structure. Therefore, the additive element is preferably solid-dissolved in the manganese site or iron site, but may also be solid-dissolved in the lithium site. When the positive electrode active material 100 of the present invention is composed of secondary particles, the explanation regarding the crystal structure can be understood by replacing the positive electrode active material 100 with primary particles 101.

[0041] Typical examples of the additive element include those that become divalent cations or positive ions when dissolved in the positive electrode active material 100, in other words, elements that do not take on a valence other than divalent. For example, the additive element may be one or more selected from Mg, Zn, Ca, Sr, Ba, Pb, and Eu. As shown in the examples below, particularly preferred additive elements include Mg and Zn.

[0042] The olivine-type crystal structure is an orthorhombic crystal (also called an orthorhombic crystal) and belongs to the space group Pnma (No. 62). The positive electrode active material 100 preferably belongs to the space group Pnma (No. 62). In the positive electrode active material 100, lithium, manganese, iron, and the additive element are present in octahedral sites, and phosphorus is present in tetrahedral sites.

[0043] There may be defects such as a deficiency of cations or anions in the positive electrode active material 100. Furthermore, the composition of the positive electrode active material 100 is not strictly limited to Li:(Mn+Fe+additive element):P:O=1:1:1:4 (atomic ratio).

[0044] In the positive electrode active material 100, the atomic ratio of manganese to the sum of the atomic ratios of manganese, iron, and the additional element (Mn / (Mn+Fe+additive element)) is preferably 0.7 or more, more preferably 0.8 or more, even more preferably 0.85 or more, and even more preferably 0.9 or its vicinity. Note that "nearby" refers to 0.8 to 1.2 times that value. The atomic ratio of iron to the sum of the atomic ratios of manganese, iron, and the additional element (Mn / (Mn+Fe+additive element)) is not particularly limited, but is preferably 0.1 or its vicinity. By satisfying such an atomic ratio, the energy density of the secondary battery can be increased.

[0045] In the positive electrode active material 100, the atomic ratio of the additive element to the sum of the atomic ratios of manganese and the additive element (additive element / (Mn+additive element)) preferably satisfies 0.02 or more and less than 0.1, or 0.02 or more and less than 0.08. By satisfying such an atomic ratio, a decrease in discharge capacity can be suppressed.

[0046] When Mg is used as the additive element, the positive electrode active material 100 is LiMn （０．９−ｘ） Fe ０．１ Mg ｘ P.O. ４ (0.02≦x<0.1). When Zn is used as the additive element, the positive electrode active material 100 is LiMn （０．９−ｘ） Fe ０．１ Zn ｘ P.O. ４ (0.02≦x<0.08) A more preferable range for the value of x will be shown in the examples.

[0047] The additive element does not contribute to charge compensation during charge and discharge. This will be explained using Mg and Zn as an example. The oxidation number at which Mg and Zn can stably exist in the compound is +2, and charge compensation associated with the insertion and desorption of lithium, a monovalent cation, requires a change in valence difference of 1, for example, a change between divalent and trivalent. Therefore, it may be difficult for lithium around Mg and Zn to be inserted and desorbed. Therefore, it is preferable to set an upper limit as described above for the concentration of the additive element. On the other hand, it is possible for lithium to be inserted and desorbed by oxidizing manganese around Mg and Zn to a tetravalent state. In this case, since Mg and Zn are unlikely to adversely affect the lithium diffusion path, there is no upper limit on the concentration of the additive element. Alternatively, the upper limit of the concentration of the additive element can be the solid solubility limit.

[0048] The lattice constants (a, b, c) of the olivine-type crystal structure change depending on the proportion of the added element in solid solution, i.e., the concentration of the added element. Specifically, when Mg or Zn is used as the added element, the lattice constants (a, b, c) gradually decrease as the concentration of the added element increases.

[0049] When Rietveld analysis was performed on the XRD profile obtained by diffraction for the cathode active material 100 using magnesium as an additive element, the cathode active material 100 was assigned to an olivine-type crystal structure and space group Pnma (No. 62). Furthermore, the cathode active material 100 having Mg satisfying the above concentration ranges, according to the Rietveld analysis, satisfies the a-axis lattice constant of greater than 10.4039 Å and less than 10.4319 Å, the b-axis lattice constant of greater than 6.0749 Å and less than 6.0911 Å, and the c-axis lattice constant of greater than 4.7346 Å and less than 4.7380 Å. Taking into account the characteristics of a secondary battery containing the cathode active material 100, more preferred ranges for each lattice constant are shown in the examples.

[0050] When Rietveld analysis was performed on the XRD profile obtained by diffraction for the cathode active material 100 using zinc as an additive element, it was found to have an olivine-type crystal structure and the space group Pnma (No. 62). Furthermore, the cathode active material 100 having Mg satisfying the above concentration ranges, according to the Rietveld analysis, satisfies the a-axis lattice constant of 10.4087 Å to 10.4325 Å, the b-axis lattice constant of 6.0764 Å to 6.0915 Å, and the c-axis lattice constant of 4.7361 Å to 4.7385 Å. Taking into account the characteristics of a secondary battery containing the cathode active material 100, more preferred ranges for each lattice constant are shown in the examples.

[0051] The changes in the a-axis lattice constant, b-axis lattice constant and c-axis lattice constant with respect to the change in concentration of the added element follow Vegard's law, and this also indicates that magnesium or zinc is appropriately solid-dissolved.

[0052] Generally, LiMn ｘ Fe １−ｘ P.O. ４ Manganese and iron in (0<x<1) are Mn ２＋ and Fe ２＋ When lithium ions are released, Mn ｘ Fe １−ｘ P.O. ４ (0<x<1), and in this case, manganese and iron are Mn ３＋ and Fe ３＋ The lithium ion insertion / extraction reaction of olivine-type positive electrode active materials is known to be a two-phase coexistence reaction, and it is thought that the phase boundary moves rapidly, causing the entire crystal to undergo a phase change. At this phase boundary, strain occurs due to the volume difference between the crystalline structure in the lithium ion insertion state and the lithium ion desorption state.

[0053] This volume difference is due to the lithium ion intercalation state of Mn ２＋ and Fe ２＋ Therefore, Mn in the lithium ion desorption state ３＋ and Fe ３＋ This is caused by the smaller ionic radius of LiMn. In addition to the change in ionic radius, the strain due to the Jahn-Teller effect of manganese is also thought to be a factor.ｘ Fe １−ｘ P.O. ４ (0<x<1) has Fe and Mn in an octahedral configuration and high spin, and Fe ２＋ (3d ６ ), Fe ３＋ (3d ５ ) and Mn ２＋ (3d ５ ) have a weak or no Jahn-Teller effect. ３＋ (3d ４ ) has a strong Jahn-Teller effect, and the octahedron is greatly distorted. Therefore, the deformation of the octahedron in the change from divalent to trivalent manganese is greater than that of iron. Therefore, LiFePO ４ LiMnPO having manganese ４ and LiMn ｘ Fe １−ｘ P.O. ４ In the case of (0<x<1), the difference in volume before and after lithium intercalation and deintercalation is large, and the activation barrier at the phase boundary is likely to become a problem.

[0054] Therefore, the present invention is suitable for dissolving an additive element in the Mn and Fe sites so as to suppress the volume difference before and after lithium ion insertion and desorption. ２＋ (high spin) and Fe ２＋ (High spin) is smaller than Mn ３＋ (high spin) and Fe ３＋ In other words, Mg or Zn is preferable as an additive element. Furthermore, manganese and iron in the synthesis are preferably Mn ２＋ (high spin) and Fe ２＋ Since the dopant element has a high spin, it is preferable that the dopant element is a divalent cation when it is dissolved in a solid solution. In this respect, Mg or Zn is suitable as the dopant element.

[0055] As mentioned above, Mg satisfies all of these characteristics, and since it is not a transition metal, it does not exhibit the Jahn-Teller effect, making it a preferable additive element.As mentioned above, Zn satisfies all of these characteristics, and since it is not a transition metal, it does not exhibit the Jahn-Teller effect, making it a preferable additive element.

[0056] Furthermore, it is preferable that the additive element does not segregate in the surface layer portion of the positive electrode active material 100, but is uniformly distributed in the surface layer portion and the bulk. Specifically, it is preferable that Mg is uniformly distributed in the surface layer portion and the bulk, and it is also preferable that Zn is uniformly distributed in the surface layer portion and the bulk. When a plurality of positive electrode active material particles are observed using scanning transmission electron microscope-energy dispersive X-ray spectroscopy (STEM-EDX) line analysis or the like, it is possible to confirm that Mg or Zn is uniformly distributed in a cross section including the surface layer portion and the bulk. By uniformly distributing Mg or Zn in the surface layer portion and the bulk, it is possible to reduce the amount of Li during charge and discharge. ＋ The charge fluctuation in the bulk due to desorption / intercalation can be more uniformly distributed to Mn or Fe. In addition, Mg or Zn does not segregate in the surface layer, so that Li ＋ This has the effect of making it less likely that the diffusion pathway will be obstructed.

[0057] <Shape> As shown in FIG. 1A , the positive electrode active material 100 preferably includes secondary particles, and the secondary particles preferably include a plurality of primary particles 101 .

[0058] Furthermore, the primary particles 101 of the positive electrode active material 100 are preferably single crystals. For example, when the areas of the mapping of the crystal orientation captured by electron backscatter diffraction (EBSD) coincide with each other in the primary particles observable in an SEM image, the primary particles 101 can be determined to be single crystals.

[0059] Furthermore, the positive electrode active material 100 is preferably carbon coated, and it is more preferable that each of the primary particles 101 is carbon coated. By being carbon coated, the conductivity of the positive electrode active material 100 can be increased, and the resistance of the secondary battery can be suppressed. The carbon coating is a coating containing carbon, and the coating preferably has low crystallinity, specifically, is amorphous. The carbon coating is considered to be included in the positive electrode active material.

[0060] Although Fig. 1A shows an example in which the primary particles 101 are spherical or elongated spheroids, one embodiment of the present invention is not limited thereto. For example, as shown in Fig. 1B, the positive electrode active material 100 may have distorted spherical primary particles 101a. As shown in Fig. 1C, the positive electrode active material 100 may have flat plate-like or approximately plate-like primary particles 101b. As shown in Fig. 1D, the positive electrode active material 100 may have needle-like primary particles 101c.

[0061] Furthermore, the positive electrode active material 100 preferably has a small crystallite size to reduce the diffusion resistance of lithium ions. The crystallite size can be obtained by Rietveld analysis, and it is preferable to use the value of LVol-IB. For example, when Rietveld analysis is performed on an XRD profile obtained by diffraction, the olivine-type crystal structure of the positive electrode active material 100 preferably has a crystallite size of 10 nm to 90 nm. The powder to be measured by XRD may be either primary particles or secondary particles. The crystallite size can also be determined from an electrode sheet containing the powder to be measured by XRD.

[0062] <XRD conditions> XRD device: D8 ADVANCE manufactured by Bruker AXS Atmosphere: 24°C ± 10°C, atmospheric pressure X-ray: CuKα ray output: 40 kV, 40 mA Divergence slit: 0.6 mm Detector: LYNXEYE XE-T 2θ: 15° or more and 65° or less Scan speed: 1 second / step Increment: 0.005°

[0063] The obtained XRD profile was analyzed using the analysis software DIFFRAC.EVA. ２ Line peaks can be removed and background corrections can be performed.

[0064] <Crystal structure analysis software conditions> For calculating the crystallite size, for example, an XRD profile obtained using a Bruker D8 ADVANCE with a Cu X-ray source, 2θ of 15° to 120°, increment of 0.005, 1 sec / step, and a LYNXEYE XE-T detector, and ICSD Coll. Code. 193640 as the literature value for lithium iron phosphate can be used. Analysis can be performed using DIFFRAC. TOPAS ver. 6 as crystal structure analysis software, and can be set, for example, as follows: 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

[0065] It is preferable to use the value of LVol-IB, which is the crystallite size corrected by the integral width standard calculated by the above method, as the crystallite size. Note that if the calculated preferred orientation is less than 0.8, the orientation of the sample may be too strong and it may not be suitable for determining the crystallite size.

[0066] <Lattice Constant> The lattice constant of the olivine-type crystal structure of the positive electrode active material 100 can be determined by Rietveld analysis of an XRD profile obtained by a diffraction method. The Rietveld analysis can be performed by a method similar to the calculation of the crystallite size described above.

[0067] <Crystallite Size Determined by Diffraction Method> As described above, the olivine-type crystal structure of the positive electrode active material 100 preferably has a crystallite size of 10 nm or more and 90 nm or less when Rietveld analysis is performed on an XRD profile obtained by diffractometry. In addition, the measurement target may be a powder of the positive electrode active material, or a positive electrode or a secondary battery including the positive electrode active material.

[0068] However, in the state of a positive electrode or secondary battery, the positive electrode active material may be oriented due to the influence of pressure, etc., during the manufacturing process. Therefore, it is more preferable to obtain the sample by removing the positive electrode active material layer from the positive electrode, removing the binder, etc., in the positive electrode active material layer to some extent using a solvent, etc., and then filling the sample into a sample holder. Another method is to apply grease to a silicon non-reflective plate and then attach the powder sample.

[0069] Among the diffraction methods, CuKα １ X-ray diffraction by MoKα １ X-ray diffraction using radiation, synchrotron radiation X-ray diffraction, neutron diffraction, etc. are preferred because of their high accuracy. １ The conditions for X-ray diffraction using the beam are exemplified below.

[0070] <Analysis> <Composition> The composition of the positive electrode active material 100 of one embodiment of the present invention can be determined, for example, by X-ray photoelectron spectroscopy (XPS), inductively coupled plasma mass spectrometry (ICP-MS), etc. Furthermore, if necessary, evaluation can also be performed by combining multiple quantitative and semi-quantitative analyses, such as ICP-MS, X-ray fluorescence analysis, glow discharge mass spectrometry (GD-MS), energy dispersive X-ray spectroscopy (EDX), and electron probe microanalyzer (EPMA), in addition to ICP-MS.

[0071] <XPS Analysis> In XPS (X-ray Photoelectron Spectroscopy), in the case of inorganic oxides, elemental analysis of a region from the surface to a depth of about 2 to 8 nm (usually 5 nm or less) is possible when monochromatic aluminum Kα rays are used as X-rays. Furthermore, narrow scan analysis can be performed to analyze the bonding state of elements.

[0072] For example, monochromated aluminum Kα rays can be used as X-rays when performing XPS analysis. Furthermore, an XPS apparatus having an energy resolution such that the half-width of the Ag3d5 / 2 peak (112 eV) in the XPS spectrum of an Ag sample is 1.0 eV±0.1 eV can be used. The take-off angle can be, for example, 15° or 45°.

[0073] <ICP-MS Analysis> ICP-MS analysis can be used to measure the composition of elements contained in particles. First, 20 mg to 80 mg of a sample of positive electrode active material particles is prepared and dissolved using a decomposition reagent as a pretreatment. For example, nitric acid can be used as this decomposition reagent. The decomposed sample is then measured in quantitative analysis mode.

[0074] <EDX analysis, EPMA analysis> The main components and added elements of the positive electrode active material particles can be analyzed using EDX, EPMA (electron probe microanalysis), etc. EDX analysis and EPMA analysis are collectively referred to as elemental analysis. In elemental analysis, it is preferable to analyze a cut cross section in a thin slice state using a FIB (focused ion beam) or ion milling method, etc. Thinned samples are more preferable because elemental analysis can be performed without being affected by elements in the depth direction of the sample.

[0075] In EDX measurement, detecting characteristic X-rays while scanning an electron beam over a measurement area and evaluating the area in two dimensions is called EDX area analysis. Detecting characteristic X-rays while linearly scanning an electron beam over a measurement area and evaluating the distribution of elements in a cross section of a positive electrode active material particle is called line analysis. Extracting data from a linear area from EDX area analysis may also be called line analysis. Detecting characteristic X-rays without scanning an electron beam over a measurement area is called point analysis. Elemental analysis is possible based on characteristic X-rays in units of intensity (counts) or atomic concentration (atomic%).

[0076] The measurement region can be a region including the inside, surface layer, grain boundary, or crystal defect of the positive electrode active material particle. Specifically, when the sample is sliced, it is preferable to process it so as to include the inside, surface layer, grain boundary, or crystal defect.

[0077] <STEM-EDX analysis> EDX analysis can be performed using a STEM device. An example of the analysis procedure will be described. First, a protective film can be vapor-deposited onto the surface of the positive electrode active material particles using an ion sputtering device or the like. Note that the protective film is not included in the positive electrode active material particles. The protective film may be a single-layer or multi-layer film of carbon, metal, oxide, resin, or the like. After the protective film is attached to the positive electrode active material particles, it is preferable to thin-section the sample. Furthermore, it is not necessary to distinguish between the carbon coat and the protective film for elemental analysis.

[0078] An Octane T Ultra W (manufactured by EDAX) can be used as the EDX detector. The EDX analysis conditions can be drift correction, a line width of 42 nm, a pitch of 0.2 nm, and six or more frames. Increasing the number of frames can suppress the influence of noise.

[0079] In order to increase the spatial resolution in STEM-EDX ray analysis, it is preferable that the beam diameter (also referred to as beam diameter, probe diameter, or probe diameter) of the electron beam (electron beam) is small. The beam diameter in STEM-EDX ray analysis is preferably 0.3 nm or less, more preferably 0.2 nm or less, and even more preferably 0.1 nm or less. Furthermore, in order to increase the analytical sensitivity in STEM-EDX ray analysis, it is preferable to increase the beam current (also referred to as probe current) of the electron beam. Therefore, it is preferable that the device used in STEM-EDX ray analysis is equipped with a spherical aberration corrector (Cs corrector) that can reduce the beam diameter and increase the beam current.

[0080] In STEM-EDX-ray analysis and the like, the graph of the detected amount of characteristic X-rays of an element may not show a sharp change, either in principle or due to measurement errors.

[0081] Furthermore, when referring to the depth direction in STEM-EDX-ray analysis or the like, it is preferable to determine a reference point. To calculate the reference point, oxygen can be used, taking into account that the positive electrode active material is a composite oxide, or the transition metal M, which is the main component, can be used. Furthermore, in the case of positive electrode active material particles containing multiple transition metals M, the reference point can be determined using the transition metal element that has the largest amount of characteristic X-rays detected inside.

[0082] <Calculation Example of Reference Point> A reference point may be used to explain the depth direction of a positive electrode active material particle. An example of calculating the reference point will be described. The average value M (AVE) of the detected amount of characteristic X-rays of the transition metal M inside the positive electrode active material particle is determined. The average value M (AVE) can be determined from the detected amount of any number of characteristic X-rays, but it is preferable to determine it inside where there is little change in the detected amount of characteristic X-rays of the transition metal M, and typically it is preferable to use an average value determined from a region of 10 nm or more inside. Then, the position of the distance [nm] that satisfies 50% of the average value M (AVE), or the position of the distance [nm] that satisfies the measurement value closest to that value, can be used as the reference point.

[0083] When oxygen is used, the same procedure as for the transition metal M can be used. The reference point can be the distance [nm] at which 50% of the average value O(AVE) is satisfied, or the distance [nm] at which the measured value of the detected amount is closest to that value. In the case of oxygen, when determining the 50% value, the reference point can be determined taking into account the characteristic X-rays of oxygen outside the positive electrode active material particles. Specifically, the reference point can be the distance [nm] at which 50% of the sum of the average value O(BG) of the detected amount of characteristic X-rays of oxygen outside (also referred to as the detected amount of characteristic X-rays of background oxygen) and the average value O(AVE) is satisfied, or the distance [nm] at which the measured value is closest to that value is satisfied. The average value O(BG) of the detected amount of characteristic X-rays of oxygen outside can be determined by averaging a range of 2 nm or more, preferably 3 nm or more, outside the positive electrode active material particles, avoiding the area where the detected amount begins to increase. The carbon coating can be located outside the reference point determined from the 50% value of the average value O(AVE) of oxygen.

[0084] In addition, if the reference point determined from the transition metal M differs from the reference point determined from oxygen, this is thought to be due to the influence of metal oxides, carbonates, etc. containing oxygen adhering to the surface, and therefore it is more preferable to adopt the reference point determined from the transition metal M.

[0085] <Charge-Discharge Cycle Test> To confirm the battery characteristics of the positive electrode active material 100, a coin cell (CR2032 type, diameter 20 mm, height 3.2 mm) can be prepared using a lithium counter electrode and a charge-discharge cycle test can be performed.

[0086] More specifically, the positive electrode may be prepared by coating a positive electrode current collector made of aluminum foil with a slurry containing a positive electrode active material, a conductive additive, and a binder.

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

[0088] The lithium salt was 1 mol / L lithium hexafluorophosphate (LiPF ６ ) can be used. As the mixed solvent, a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of EC:DEC = 3:7 can be used. A mixed solvent in which the lithium salt is dissolved and vinylene carbonate (VC) is added at 2 wt % as an additive can be used as the electrolyte.

[0089] The separator may be a porous polypropylene film having a thickness of 25 μm.

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

[0091] The coin cell fabricated under the above conditions is aged as necessary. It is then subjected to constant current charging (CC charging) at 4.5 V and 0.5 C, followed by constant voltage charging (CV charging) until the current reaches 0.05 C. 4.5 V is called the upper voltage limit, and is maintained at this upper voltage limit during CV charging. Voltages other than 4.5 V can also be used for the upper voltage limit. Note that the current reference value of 1 C is sometimes set to 170 mA / g per weight of positive electrode active material. This is an example value determined based on the theoretical capacity of lithium iron phosphate. If the cutoff current of the charging conditions is not reached, a time cutoff may be performed. The time cutoff time can be three hours. The discharge condition is constant current discharge (CC discharge) until the voltage reaches 2.5 V. 2.5 V is called the lower voltage limit. Voltages other than 2.5 V can also be used for the lower voltage limit. The temperature of the thermostatic chamber in which the coin cell is placed is set to 25°C or 45°C, for example. A charge-discharge cycle test can be performed in this manner.

[0092] After several cycles, the coin cell is disassembled in a glove box under an argon atmosphere and the positive electrode is removed to obtain a positive electrode active material charged at high voltage. When various analyses are performed after this, it is preferable to seal the cell in an argon atmosphere to prevent reactions with external components. For example, XRD can be performed by sealing the cell in a sealed container under an argon atmosphere. In this way, XRD data can be obtained during charging.

[0093] This embodiment mode can be combined with the contents of other embodiment modes as appropriate.

[0094] Embodiment 2 In this embodiment, an example of a method for manufacturing a positive electrode active material of one embodiment of the present invention will be described with reference to FIGS.

[0095] 2, an additive element source, a lithium source (Li source), a manganese source (Mn source), an iron source (Fe source), and a phosphate source are prepared. It is also preferable to prepare a grinding medium and a solvent for mixing.

[0096] When zinc is used as an additive element, examples of the zinc source include zinc oxide, zinc hydroxide, zinc carbonate, and zinc phosphate (Zn ３ (P.O. ４ )２ ・4H ２ O), zinc acetate (Zn(CH ３ COO) ２ , Zn(CH ３ COO) ２ ・2H ２ O), zinc oxalate (ZnC ２ O ４ ・2H ２ O), zinc nitrate (Zn(NO ３ ) ２ ・6H ２ O), zinc compounds such as zinc chloride, zinc sulfate, and zinc fluoride can be used.

[0097] When magnesium is used as an additive element, examples of the magnesium source include magnesium oxide, magnesium hydroxide, magnesium carbonate, and magnesium phosphate (Mg(H ２ P.O. ４ ) ２ ・4H ２ O, MgHPO ４ ・3H ２ O, Mg ３ (P.O. ４ ) ２ ・8H ２ O), magnesium acetate and its hydrate (Mg(CH ３ COO) ２ , Mg(CH ３ COO) ２ ・4H ２ O), magnesium oxalate hydrate (MgC ２ O ４ ・2H ２ O), magnesium nitrate hydrate (Mg(NO ３ ) ２ ・6H ２ O), magnesium chloride hydrate (MgCl ２ ・6H ２ O), magnesium sulfate and its hydrate (MgSO ４ , MgSO ４ ・7H ２ O), magnesium fluoride (MgF ２ ) and other magnesium compounds can be used.

[0098] Examples of the lithium source include lithium carbonate, lithium hydroxide, lithium oxide, and lithium phosphate (Li ３ P.O. ４ ), lithium acetate and its hydrate (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.

[0099] Examples of manganese sources include 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 and its hydrate (Mn(OCOCH ３ ) ２ , Mn(CH ３ COO) ３ ・2H ２ O, Mn(CH ３ COO) ２ ・4H ２ O), manganese oxalate (MnC ２ O ４ ・2H ２ O), manganese nitrate and its hydrate (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 and its hydrate (MnSO ４ ), MnSO ４ ・H ２ O, MnSO４ ・4H ２ O, MnSO ４ ・5H ２ O, MnSO ４ ・7H ２ O,) Manganese fluoride (MnF ２ , MnF ３ ) and other manganese compounds can be used.

[0100] The iron source may be, for example, iron carbonate (FeCO ３ ), iron oxide (FeO, Fe ３ O ４ , Fe ２ O ３ ), iron hydroxide, iron phosphate (FePO ４ ・2H ２ O, FePO ４ ・5H ２ O), iron acetate (Fe(CH ３ CO ２ ) ２ ), iron oxalate hydrate (Fe(C ２ O ４ ) 2H ２ O, Fe ２ (C ２ O ４ ) ３ ・6H ２ O), iron nitrate hydrate (Fe(NO ３ ) ３ ・9H ２ O, Fe(NO ３ ) ３ ・6H ２ O), iron chloride and its hydrate (FeCl ２ , FeCl ２ ・4H ２ OFeCl ３ , FeCl ３ ・6H ２ O), iron sulfate and its hydrate (FeSO ４ , FeSO ４ ・H ２ O, FeSO ４ ・4H ２ O, FeSO ４ ・5H ２ O, FeSO ４ ・7H ２ O), iron fluoride and its hydrate (FeF ２ , FeF ２・4H ２ O, FeF ３ , FeF ３ ・3H ２ Iron compounds such as CrO can be used.

[0101] The phosphate source may be, for example, ammonium dihydrogen phosphate (NH ４ H ２ P.O. ４ ), diammonium hydrogen phosphate ((NH ４ ) ２ HPO ４ ), lithium dihydrogen phosphate (LiH ２ P.O. ４ ) and other phosphate compounds can be used.

[0102] The additive element source, lithium source, manganese source, iron source, and phosphate source do not necessarily have to be separate sources, and a compound serving multiple purposes may be used. For example, using lithium hydroxide containing magnesium or lithium carbonate containing magnesium can serve as both a magnesium source and a lithium source, while reducing the cost of lithium purification. Furthermore, using lithium dihydrogen phosphate can serve as both a lithium source and a phosphate source.

[0103] In this embodiment, zinc oxide is used as the zinc source, lithium carbonate 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, and the resulting mixture is Li:Mn:Fe:Mg:PO ４ The components are weighed so that the molar ratio becomes 1:0.59:0.4:0.01:1.

[0104] In addition to the above, if a planetary mill such as a ball mill is used for mixing, grinding media must be prepared. Zirconia balls, for example, can be used as the grinding media. Furthermore, if wet mixing is used, a solvent must be prepared. Dehydrated acetone, for example, can be used as the solvent.

[0105] <Step S12> Next, in step S12, the zinc source, lithium source, manganese source, iron source, and phosphate source are mixed. Mixing can be performed wet using, for example, a ball mill. In this embodiment, zirconia balls with a diameter of 3 mm are used as the grinding medium, and dehydrated acetone is used as the solvent. Mixing is performed for 2 hours at 300 rpm while cooling using a planetary rotation ball mill.

[0106] <Step S13> Next, in step S13, if wet mixing was used, the solvent is dried, and if grinding media were used, the grinding media are removed by sieving to obtain a mixture. To distinguish this from other steps, this may be referred to as the first mixture. In this embodiment, the mixture is dried using a ventilated drying oven, and then sieved with a 300 μm mesh to recover the mixture.

[0107] <Step S14> Next, in step S14, the first mixture is heated. The heating temperature is preferably 250°C or higher and 450°C or lower, more preferably 300°C or higher and 400°C or lower, and most preferably around 350°C. The heating time is preferably 1 hour or higher and 60 hours or lower, more preferably 2 hours or higher and 20 hours or lower, 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 terminate, for example, the evaporation of the hydrate and / or carbon dioxide gas may not be completed. On the other hand, if the heating temperature is too high and / or the heating time is too long, the fuel cost for heating may increase, and productivity may decrease.

[0108] During heating, an inert or reducing atmosphere is preferably used, and examples of the inert atmosphere include a nitrogen atmosphere and an argon atmosphere. The reaction chamber may be evacuated and then purged with an inert gas (nitrogen or argon) to prevent the atmosphere from entering or leaving the reaction chamber, or a constant flow of the atmosphere may be maintained.

[0109] The heating furnace may be, for example, a muffle furnace, a roller hearth kiln, or a rotary kiln. The container for accommodating the object to be heated may be an aluminum oxide crucible or an aluminum oxide setter (also called a sheath). It is preferable to cover the crucible or setter before heating, as this prevents the material from volatilizing. Mullite-cordierite may also be used as the material for the crucible and setter.

[0110] In this embodiment, the first mixture is placed in a crucible made of aluminum oxide with a purity of 99.9%, and the crucible is covered with a lid. The crucible is heated in a muffle furnace in a nitrogen flow atmosphere at 350° C. for 10 hours.

[0111] <Steps S15 and S16> Next, in step S15, the heated material is sieved. In this embodiment, the heated material is sieved through a sieve with openings of 300 μm. Through these steps, a composite oxide is obtained (step S16).

[0112] <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.

[0113] Examples of carbon sources that can be used include compounds containing carbon, such as sugars including glucose and sucrose, polysaccharides including starch and cellulose, and synthetic resins including polyvinyl alcohol (PVA) and polyacrylic acid. Also usable are carbon blacks including acetylene black, graphene, graphene oxide, and graphite. A combination of these may also be used.

[0114] For details about the grinding medium and the solvent, please refer to the description of step S11.

[0115] <Step S18> Next, in step S18, the composite oxide obtained in step S16 is mixed with a carbon source. Mixing can be performed wet using, for example, a ball mill. In this embodiment, zirconia balls with a diameter of 3 mm are used as the grinding medium, and dehydrated acetone is used as the solvent. Mixing is performed for 2 hours at 300 rpm while cooling using a planetary rotation ball mill.

[0116] <Step S19> Next, in step S19, if wet mixing was performed, the solvent is dried, and if grinding media were used, the grinding media are removed by sieving to obtain a mixture. To distinguish this from other steps, this may be referred to as the second mixture. For details on drying and sieving, please refer to the description of step S13.

[0117] <Step S20> Next, in step S20, the second mixture is heated. The heating temperature is preferably 500°C or higher and 900°C or lower, more preferably 600°C or higher and 700°C or lower, and most preferably around 650°C. The heating time is preferably 1 hour or higher and 60 hours or lower, more preferably 2 hours or higher and 20 hours or lower, 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, secondary particles will become too large, productivity will decrease, etc.

[0118] For the atmosphere, heating furnace, and container during heating, the description of step S14 can be referred to.

[0119] In this embodiment, the second mixture is placed in a crucible made of aluminum oxide with a purity of 99.9%, and the crucible is covered with a lid. The second mixture is heated in a muffle furnace in a nitrogen flow atmosphere at 650° C. for 10 hours.

[0120] <Steps S21 and S22> Next, in step S21, the heated material is sieved. In this embodiment, the heated material is sieved through a sieve with openings of 53 μm. Through these steps, positive electrode active material 100 is obtained (step S22).

[0121] The positive electrode active material 100 can be produced through the above steps.

[0122] 2 illustrates an example in which a positive electrode active material is produced by a solid-phase method, but this is not a limitation of the present invention. Positive electrode active materials can be produced by methods other than the solid-phase method, such as a hydrothermal method, a coprecipitation method, a sol-gel method, or a spray-drying method. However, the solid-phase method is preferred because it has higher productivity than the hydrothermal method. Furthermore, the positive electrode active material can be produced by combining a plurality of methods selected from these methods.

[0123] This embodiment mode can be combined with the contents of other embodiment modes as appropriate.

[0124] Embodiment 3 In this embodiment, a structure of a lithium ion battery will be described.

[0125] [Positive Electrode] The positive electrode includes a positive electrode active material layer and a positive electrode current collector. The positive electrode active material layer includes a positive electrode active material and may further include at least one of a conductive additive and a binder. The positive electrode active material may be any of those described in the above embodiment.

[0126] <Positive Electrode Active Material> As the positive electrode active material, a mixture of the positive electrode active material 100 described in the above embodiment and another positive electrode active material may be used.

[0127] Other positive electrode active materials include composite oxides having an olivine-type crystal structure, a layered rock salt-type crystal structure, or a spinel-type crystal structure. 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 and the like compounds.

[0128] Other positive electrode active materials include LiMn ２O ４ Lithium-containing materials having a spinel-type crystal structure containing manganese, such as lithium nickel oxide (LiNiO ２ or LiNi １−ｘ M ｘ O ２ It is preferable to mix (0<x<1) (M=Co, Al, etc.) This configuration can improve the characteristics of the secondary battery.

[0129] <Conductive additive> The conductive additive is also called a conductivity imparting agent or conductive material, and a carbon material can be used. By attaching the conductive additive between multiple active materials, the multiple active materials are electrically connected to each other, thereby increasing the conductivity. In this specification, the term "attachment" does not only refer to physical adhesion between the active material and the conductive additive, but also includes cases where a covalent bond is formed, bonding due to van der Waals forces, where the conductive additive covers part of the surface of the active material, where the conductive additive is embedded in the surface irregularities of the active material, and where the active material is electrically connected even when not in contact with each other.

[0130] Specific examples of carbon materials that can be used as the conductive additive include carbon black (furnace black, acetylene black, graphite, etc.), graphene, multi-graphene, graphene oxide, and / or reduced graphene oxide.

[0131] Furthermore, the use of a mixture of graphene and acetylene black is preferable because it allows for rapid charging, which is particularly effective when used in automotive lithium-ion batteries.

[0132] The content of the conductive additive in the positive electrode slurry is preferably 2 wt % or more and less than 15 wt %, and more preferably 3 wt % or more and 8 wt % or less. By keeping the content of the conductive additive low, the content of the positive electrode active material can be increased.

[0133] <Binder> Examples of the binder that can be used include rubber materials such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, and ethylene-propylene-diene copolymer. Fluorine rubber can also be used.

[0134] Furthermore, it is preferable to use, for example, a water-soluble polymer as the binder. Examples of the water-soluble polymer that can be used include polysaccharides. Examples of the polysaccharide that can be used include one or more of cellulose derivatives such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, and regenerated cellulose, and starch. It is even more preferable to use these water-soluble polymers in combination with the above-mentioned rubber material.

[0135] Alternatively, it is preferable to use, as the binder, materials such as polystyrene, polymethyl acrylate, polymethyl methacrylate (polymethyl methacrylate, PMMA), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), ethylene propylene diene polymer, polyvinyl acetate, and nitrocellulose.

[0136] Additionally, graphene, multi-graphene, graphene oxide, and / or reduced graphene oxide can function not only as a conductive additive but also as a binder.

[0137] The binder may be used in combination with two or more of the above.

[0138] The binder content of the positive electrode slurry is preferably 2 wt % to 10 wt %, more preferably 3 wt % to 7 wt %. By keeping the binder content low, the content of the positive electrode active material can be increased.

[0139] <Positive Electrode Current Collector> The current collector can be made of a highly conductive material, such as a metal such as stainless steel, gold, platinum, aluminum, or titanium, or an alloy thereof. It is preferable that the material used for the positive electrode current collector does not dissolve at the potential of the positive electrode. Aluminum alloys containing elements that improve heat resistance, such as silicon, titanium, neodymium, scandium, or molybdenum, can also be used. The current collector may also be made of a metal element that reacts with silicon to form a silicide. Examples of metal elements that react with silicon to form a silicide include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, and nickel. The current collector can be in the form of a foil, plate, sheet, mesh, punched metal, expanded metal, or the like. It is preferable that the current collector have a thickness of 5 μm to 30 μm.

[0140] [Negative Electrode] The negative electrode has a negative electrode active material layer and a negative electrode current collector. The negative electrode active material layer has a negative electrode active material, and may further have a conductive additive and a binder.

[0141] <Negative Electrode Active Material> As the negative electrode active material, for example, an alloy material and / or a carbon material can be used.

[0142] The carbon material used for the negative electrode active material may be one or more selected from graphite, easily graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), carbon fiber (carbon nanotube), graphene, graphene compounds, carbon black, and the like.

[0143] Examples of graphite include artificial graphite and natural graphite. Examples of artificial graphite that can be used include mesocarbon microbeads (MCMB), coke-based artificial graphite, and pitch-based artificial graphite. The artificial graphite may have a carbon coating layer, which is a low-crystalline layer. Since the shape of the artificial graphite is spherical, it is called spherical graphite. For example, MCMB is one of the preferred materials for spherical graphite. Furthermore, it is relatively easy to reduce the specific surface area of ​​MCMB. If the specific surface area is large, the decomposition reaction with the electrolyte on the surface of the negative electrode active material may become large, and good cycle characteristics may not be obtained. In order to suppress the decomposition reaction, the specific surface area of ​​the carbon is 0.8 m ２ / g or more 8m ２ / g or less, preferably 1m ２ / g or more 2m ２ / g or less. Typically, it is preferable that the spherical graphite has the specific surface area described above as a powder characteristic. The specific surface area can be measured by the BET method (Brunauer Emmett Teller method). The BET method is an analytical technique that extends the Langmuir theory to multilayer adsorption of adsorbed gas molecules, and is the most common method for calculating the specific surface area. The specific surface area by the BET method can be measured using an automatic specific surface area measuring device, Tristar 2 3020.

[0144] If the particle size or median diameter (D50) is small, the negative electrode active material becomes bulky and may inhibit improvement of electrode density. Therefore, the particle size or median diameter (D50) of the negative electrode active material should be 3 μm or more and 20 μm or less, preferably 7 μm or more and 12 μm or less. Typically, the median diameter (D50) should be in the above range as a powder characteristic of graphite.

[0145] When lithium ions are inserted into graphite (when a lithium-graphite intercalation compound is formed), graphite exhibits a potential as low as that of metallic lithium (0.05 V to 0.3 V vs. Li / Li ＋ This allows lithium-ion batteries using graphite to exhibit high operating voltages. Graphite is also preferred because it has advantages such as a relatively high capacity per unit volume, relatively small volume expansion, low cost, and greater safety compared to lithium metal.

[0146] The negative electrode active material may be an element capable of undergoing a charge-discharge reaction 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. may be used. These 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 , Cu ６ Sn ５ , Ag ３ Sn, Ag ３ Sb, Ni ２ MnSb, CeSb ３ , LaSn ３ , La ３ Co ２ Sn ７ , CoSb ３ , InSb, SbSn, etc. Here, elements capable of undergoing charge-discharge reactions by alloying / dealloying reactions with lithium, and compounds containing such elements, may be referred to as alloy-based materials. Compared to graphite, alloy-based materials such as silicon may be more suppressed in decreasing charge-discharge capacity at low temperatures, and are therefore preferred as negative electrode active materials for low-temperature secondary batteries.

[0147] In this specification, "SiO" refers to, for example, silicon monoxide. ｘ Here, x preferably has a value of 1 or close to 1. For example, x is preferably 0.2 or more and 1.5 or less, and more preferably 0.3 or more and 1.2 or less.

[0148] Furthermore, a material used in forming the graphene compound may be mixed with the graphene compound and used in the active material layer. For example, particles used as a catalyst in forming the graphene compound may be mixed with the graphene compound. Examples of catalysts used in forming the graphene compound include silicon oxide (SiO ２ , SiO ｘ (x<2)), aluminum oxide, iron, nickel, ruthenium, iridium, platinum, copper, germanium, etc. The particles preferably have a D50 of 1 μm or less, more preferably 100 nm or less.

[0149] Alternatively, silicon particles covered with a graphene compound may be used as the negative electrode active material. In this case, it is more preferable that there is a space between the graphene compound and the silicon particles that can buffer structural changes.

[0150] Titanium dioxide (TiO 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 ) and the like can be used.

[0151] In addition, as the negative electrode active material, a nitride of lithium and a transition metal, Li ３ Li with N-type structure ３−ｘ M ｘ N (M=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 / cm ３ ) and is preferred.

[0152] When a nitride of lithium and a transition metal is used, lithium ions are contained in the negative electrode active material, so V, which does not contain lithium ions, is used as the positive electrode active material. ２ O ５, Cr ３ O ８ It is preferable that the material can be combined with a material such as the above. Even when a material containing lithium ions is used as the positive electrode active material, it is possible to use a nitride of lithium and a transition metal as the negative electrode active material by first desorbing the lithium ions contained in the positive electrode active material.

[0153] Furthermore, a material that undergoes a conversion reaction can also be used as the negative electrode active material. For example, a transition metal oxide that does not form an alloy with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), or iron oxide (FeO), can be used as the negative electrode active material. Further examples of materials that undergo a conversion reaction include 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 , Cu ３ N, Ge ３ N ４ Nitrides such as NiP ２ , FeP ２ , CoP ３ Phosphides such as FeF ３ , BiF ３ This also occurs with fluorides such as

[0154] Furthermore, a combination of the above-mentioned negative electrode active materials may be used; for example, a negative electrode active material containing a mixture of graphite and silicon particles may be used. Silicon particles are silicon powders used as negative electrode active materials for lithium-ion batteries. These particles have an average particle size distribution, i.e., an average particle size of approximately 100 nm, and are sometimes referred to as nanosilicon particles. The silicon particles used are preferably prepared by pulverizing silicon raw materials to a uniform particle size. The silicon particles may include at least one of silicon, silicon oxide, and silicon alloy. While laser diffraction particle size distribution measurement is typically used to measure particle size, the measurement is not limited to laser diffraction particle size distribution measurement. The major axis of the particle cross section may also be measured by analysis using a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0155] Furthermore, as the conductive additive and binder that can be contained in the negative electrode active material layer, the same materials as the conductive additive and binder that can be contained in the positive electrode active material layer can be used.

[0156] <Negative electrode current collector> The negative electrode current collector may be made of the same material as the positive electrode current collector, or may be made of copper, etc. It is preferable that the negative electrode current collector be made of a material that does not alloy with carrier ions such as lithium.

[0157] [Electrolyte Solution] The electrolyte solution contains an organic solvent, but the organic solvent of the electrolyte according to one embodiment of the present invention is not limited to being liquid at 25°C, and may be solid at 25°C or semi-solid at room temperature. The organic solvent of the electrolyte according to one embodiment of the present invention is preferably liquid over a wide temperature range, including temperatures from below freezing to high temperatures, but is not limited thereto. The organic solvent may be liquid, solid, or semi-solid over a wide temperature range, including temperatures from below freezing to high temperatures.

[0158] The organic solvent is preferably an aprotic organic solvent, and examples thereof include 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-propane sultone (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, and sultones, and any combination and ratio of two or more of these may be used.

[0159] Because PS has HOMO and LUMO levels equivalent to those of EC and DEC, it is resistant to oxidation and reduction even at high cutoff voltages, and when decomposed on the surface of the positive electrode active material, it tends to form polymers. Therefore, it has the advantage of being less likely to gasify into small molecular weight decomposition products. Therefore, the electrolyte preferably contains 0.1 wt% to 10 wt%, more preferably 0.25 wt% to 7.5 wt% of PS.

[0160] FEC is a cyclic carbonate with a high dielectric constant, and when used in an organic solvent, it promotes the dissociation of lithium salts. On the other hand, FEC has electron-withdrawing substituents, making it easier to desolvate with lithium ions than EC. Specifically, the solvation energy of lithium ions in FEC is lower than that of EC without electron-withdrawing substituents. Therefore, FEC easily releases lithium ions from the surfaces of the positive and negative electrode active materials, thereby reducing the internal resistance of the secondary battery. Furthermore, FEC has a deep highest occupied molecular orbital (HOMO) level, making it less susceptible to oxidation and improving oxidation resistance. On the other hand, there are concerns about the high viscosity of FEC. Therefore, it is recommended to use a mixed organic solvent containing MTFP in addition to FEC alone in the electrolyte. MTFP is a type of chain carbonate, and can reduce the viscosity of the electrolyte solution 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 an electron-withdrawing substituent, it may form a solvation with lithium ions when used in an electrolyte solution. When a mixed organic solvent containing both FEC and MTFP is used, when the volume ratio is FEC:MTFP=1:y, y is preferably 2 or more and 20 or less, more preferably 4 or more and 9 or less.

[0161] The organic solvent described above is free from granular dust or molecules other than the constituent molecules of the organic solvent (hereinafter simply referred to as "impurities"), and oxygen (O ２ ), water (H ２ 0) or water. ) content is low and highly purified. Furthermore, it is preferable that reaction by-products during synthesis are suppressed through appropriate purification. Specifically, the impurities in the electrolyte are 100 ppm or less, preferably 50 ppm or less, and more preferably less than 10 ppm. The content of water among the impurities can be detected by Karl Fischer titration.

[0162] Furthermore, it is preferable that the above-mentioned organic solvent has almost no peaks due to impurities that can be confirmed by NMR measurement or the like. "Almost no peaks can be confirmed" means that the ratio of the integrated area of ​​the peak due to the impurity to the integrated area of ​​the peak due to the main component (simply referred to as "integral ratio") is 0.005 or less, preferably 0.002 or less. The device used for NMR measurement is not particularly limited, but for example, Bruker's "AVANCE III 400" can be used. Furthermore, among the five peaks of acetonitrile derived from acetonitrile-d3 used as a solvent in 1H-NMR measurement, the central peak can be located at 1.94 ppm.

[0163] For example, in the case of MTFP, it is known that when 1H-NMR is measured using acetonitrile-d3 solvent, four peaks appear at δ between 3.29 ppm and 3.43 ppm. However, if other peaks appear in this vicinity, for example, if a peak appears at δ between 3.24 ppm and 3.29 ppm, the peak is considered to be derived from 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 impossible to confirm.

[0164] 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 electricity storage device from exploding or catching fire even if the internal temperature of the electricity storage device rises due to an internal short circuit, overcharging, or the like. The ionic liquid is composed of a cation and an anion, and includes an organic cation and an anion. Examples of organic cations used in the electrolyte include aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, and aromatic cations such as imidazolium cations and pyridinium cations. Examples of anions used in the electrolyte include monovalent amide anions, monovalent methide anions, fluorosulfonate anions, perfluoroalkylsulfonate anions, tetrafluoroborate anions, perfluoroalkylborate anions, hexafluorophosphate anions, and perfluoroalkylphosphate anions.

[0165] The electrolyte to be dissolved in the 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 ３ SO２ ), LiN(C ２ F ５ SO ２ ) ２ , lithium bis(oxalato)borate (Li(C) ２ O ４ ) ２ , LiBOB), or two or more of these can be used in any combination and ratio.

[0166] The electrolyte solution may also contain additives. The additives can suppress reactive decomposition of the electrolyte that may occur on the positive electrode surface or the negative electrode surface when the secondary battery is operated at high voltage and / or high temperature. Examples of additives that can be used include propane sultone (PS), vinylene carbonate (VC), tert-butylbenzene (TBB), lithium bis(oxalato)borate (LiBOB), 1,3,6-hexanetricarbonitrile, ethyl 2-methylbutyrate, ethyl 2-methylvalerate, and propyl 2-methylbutyrate. PS is particularly preferred as an additive because it improves cycle characteristics.

[0167] The additive may be one or more dinitrile compounds, such as succinonitrile, glutaronitrile, adiponitrile (ADN), or ethylene glycol bis(propionitrile) ether (EGBE).

[0168] Fluorobenzene may also be added to the organic solvent. The concentration of the additive is, for example, 0.1 wt% to 5 wt% of the total electrolyte solution. PS or EGBE are preferred because they form a good coating on the positive electrode during charge and discharge, improving cycle characteristics. Fluorobenzene (FB) is preferred because it improves the wettability of the organic solvent to the positive and negative electrodes. Dinitrile compounds are preferred because their nitrile groups orient to the positive and negative electrodes, inhibiting oxidative decomposition of the organic solvent and improving voltage resistance. Furthermore, dinitrile compounds are preferred because they can prevent copper dissolution during overdischarge when a copper-containing current collector is used on the negative electrode. Considering the use of secondary batteries at high voltages, adding a nitrile compound is preferred.

[0169] The electrolyte used in the electricity storage device is preferably a highly purified electrolyte with a low content of granular waste or elements other than the constituent elements of the electrolyte (hereinafter simply referred to as "impurities"). Specifically, the weight ratio of impurities to the electrolyte is preferably 1% or less, preferably 0.1% or less, and more preferably 0.01% or less.

[0170] Alternatively, a polymer gel electrolyte may be used in which a polymer is swollen with an electrolytic solution.

[0171] The use of a polymer gel electrolyte improves safety against leakage, etc. It also enables the secondary battery to be made thinner and lighter.

[0172] Examples of polymers that can be gelled include silicone gel, acrylic gel, acrylonitrile gel, polyethylene oxide gel, polypropylene oxide gel, and fluorine-based polymer gel. For example, polymers having a polyalkylene oxide structure such as polyethylene oxide (PEO), PVDF, polyacrylonitrile, and copolymers containing these can be used. For example, PVDF-HFP, a copolymer of PVDF and hexafluoropropylene (HFP), can be used. The polymer formed may also have a porous shape.

[0173] In addition, the electrolyte can be a solid electrolyte containing an inorganic material such as a sulfide or oxide, or a polymer material such as a polyethylene oxide (PEO)-based solid electrolyte. When a solid electrolyte is used, the installation of a separator or spacer is unnecessary. Furthermore, since the entire battery can be solidified, the risk of leakage is eliminated, dramatically improving safety.

[0174] [Separator] When the electrolyte contains a liquid electrolyte (also called an electrolyte solution), a separator is disposed between the positive electrode and the negative electrode. Examples of separators that can be used include cellulose-containing fibers such as paper, nonwoven fabrics, glass fibers, ceramics, or synthetic fibers such as nylon (polyamide), vinylon (polyvinyl alcohol-based fibers), polypropylene (referred to as PP), polyimide (referred to as PI), polyester, acrylic, polyolefin, and polyurethane. The porosity of the separator can be 35% to 90%, preferably 60% to 85%. Separators using polypropylene can have a porosity of 45% to 60%. Separators using polyimide can have a porosity of 75% to 85%. The separator thickness is preferably 10 μm to 80 μm, more preferably 20 μm to 60 μm. A separator using polyimide is preferable because it can have a high porosity and can be made thick (typically, the thickness is 50 μm or more and 60 μm or less).

[0175] The separator is preferably processed into a bag shape and disposed so as to encase either the positive electrode or the negative electrode.

[0176] The separator may have a multilayer structure. For example, an organic film such as polypropylene or polyethylene may be coated with a ceramic material, a fluorine-based material, a polyamide material, or a mixture of these. Examples of ceramic materials include aluminum oxide particles and silicon oxide particles. Examples of fluorine-based materials include PVDF and polytetrafluoroethylene. Examples of polyamide materials include nylon and aramid (meta-aramid, para-aramid).

[0177] 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, and the capacity per volume of the lithium-ion battery can be increased.

[0178] [Exterior Body] The exterior body of a lithium-ion battery can be made of a metal material such as aluminum or a resin material. Alternatively, a film-like exterior body can be used. Examples of the film include a three-layer structure film in which a thin, flexible metal film such as aluminum, stainless steel, copper, or nickel is provided on a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, or polyamide, and an insulating synthetic resin film such as a polyamide resin or polyester resin is further provided on the thin metal film as the outer surface of the exterior body.

[0179] This embodiment can be used in combination with other embodiments.

[0180] Embodiment 4 In this embodiment, an example of a lithium ion battery will be described with reference to FIGS. 3A to 3C.

[0181] Fig. 3A is a diagram illustrating a wound body 950a of a lithium ion battery 913, Fig. 3B is an exploded perspective view of the lithium ion battery 913, and Fig. 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, and 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 Fig. 3A.

[0182] The separator 933 has a width wider than the negative electrode active material layer 931 a and the positive electrode active material layer 932 a, and is wound so as to overlap the negative electrode active material layer 931 a and the positive electrode active material layer 932 a. From the standpoint of safety, it is preferable that the negative electrode active material layer 931 a be wider than the positive electrode active material layer 932 a. A wound body 950 a having such a shape is preferable due to its high safety and productivity.

[0183] 3B, the negative electrode 931 is electrically connected to a terminal 951. The terminal 951 is electrically connected to a terminal 911a. The positive electrode 932 is electrically connected to a terminal 952. The terminal 952 is electrically connected to a terminal 911b.

[0184] 3C , the wound body 950a is covered with a housing 930 to form 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 when the inside of the housing 930 reaches a predetermined internal pressure, and can prevent the battery from exploding.

[0185] 3B, the lithium ion battery 913 may have a plurality of wound bodies 950a. By using a plurality of wound bodies 950a, the lithium ion battery 913 can have a larger charge / discharge capacity.

[0186] By using the positive electrode active material of the present invention in the lithium ion battery 913 having a wound body, a secondary battery having high energy density and good electrical characteristics over a wide temperature range can be obtained.

[0187] The content of this embodiment mode can be combined with the content of other embodiment modes as appropriate.

[0188] Embodiment 5 In this embodiment, an example of application to an electric vehicle (EV) will be described with reference to FIGS. 4A to 4C.

[0189] 4A , the electric vehicle is equipped with first batteries 1301 a and 1301 b as main driving lithium ion batteries, and a second battery 1311 that supplies power to an inverter 1312 that starts a motor 1304. By using the positive electrode active material of the present invention for the first batteries 1301 a and 1301 b, a secondary battery that has high energy density and exhibits good electrical characteristics over a wide temperature range can be obtained.

[0190] The second battery 1311 is also called a cranking battery (also called a starter battery). The second battery 1311 only needs to have high output, and does not need to have a large capacity, and the capacity of the second battery 1311 is smaller than that of the first batteries 1301a and 1301b.

[0191] The internal structure of the first battery 1301a may be a wound type or a stacked type. The first battery 1301a may be a lithium-ion battery including the positive electrode active material of one embodiment of the present invention. By using the lithium-ion battery including the positive electrode active material of one embodiment of the present invention for the first battery 1301a, an electric vehicle with a long driving range and usable in a wide range of ambient temperatures can be obtained.

[0192] In this embodiment, an example is shown in which two first batteries 1301a and 1301b are connected in parallel, but three or more batteries may be connected in parallel. Furthermore, if the first battery 1301a can store sufficient power, the first battery 1301b may be omitted. By configuring a battery pack having multiple lithium ion batteries, it is possible to extract large amounts of power. The multiple lithium ion batteries may be connected in parallel, in series, or in series after being connected in parallel. A plurality of lithium ion batteries is also called a battery pack.

[0193] In addition, in an in-vehicle lithium-ion battery, in order to cut off power from multiple lithium-ion batteries, a service plug or circuit breaker that can cut off high voltage without using tools is provided in the first battery 1301a.

[0194] The power of the first batteries 1301a and 1301b is mainly used to rotate the motor 1304, but also supplies power to 42V in-vehicle components (such as an electric power steering 1307, a heater 1308, and a defogger 1309) via a DCDC circuit 1306. When a rear motor 1317 is provided for the rear wheels, the first battery 1301a is also used to rotate the rear motor 1317.

[0195] In addition, the second battery 1311 supplies power to 14V in-vehicle components (audio 1313, power windows 1314, lamps 1315, etc.) via the DCDC circuit 1310.

[0196] The first battery 1301a will be described with reference to FIG. 4B.

[0197] FIG. 4B shows an example in which nine prismatic lithium-ion batteries 1300 are combined into one battery pack 1415. Furthermore, nine prismatic lithium-ion batteries 1300 are connected in series, with one electrode fixed by a fixing portion 1413 made of an insulator and the other electrode fixed by a fixing portion 1414 made of an insulator. While this embodiment shows an example in which the batteries are fixed by the fixing portions 1413 and 1414, they may also be housed in a battery housing box (also referred to as a casing). Because it is expected that a vehicle will be subjected to external vibrations or shaking (e.g., from the road surface), it is preferable to fix multiple lithium-ion batteries using the fixing portions 1413 and 1414 and the battery housing box. Furthermore, one electrode is electrically connected to the control circuit unit 1320 by wiring 1421. The other electrode is electrically connected to the control circuit unit 1320 by wiring 1422.

[0198] A memory circuit including a transistor using an oxide semiconductor may be used for the control circuit portion 1320. A charge control circuit or a battery control system including a memory circuit including a transistor using an oxide semiconductor may be referred to as a battery operating system (BTOS) or a battery oxide semiconductor (BTOS).

[0199] It is preferable to use a metal oxide that functions as an oxide semiconductor. For example, a metal oxide such as In-M-Zn oxide (wherein 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, and magnesium) may be used as the oxide. In particular, the In-M-Zn oxide that can be used as the oxide is preferably a C-Axis Aligned Crystal Oxide Semiconductor (CAAC-OS) or a Cloud-Aligned Composite Oxide Semiconductor (CAC-OS). Alternatively, an In oxide, an In—Ga oxide, or an In—Zn oxide may be used as the oxide.

[0200] Furthermore, the control circuit unit 1320 preferably uses a transistor using an oxide semiconductor. To simplify the process, the control circuit unit 1320 may be formed using a unipolar transistor. A transistor using an oxide semiconductor for the semiconductor layer has a wider operating ambient temperature range than single-crystal Si, from −40° C. to 150° C., and its characteristics change less when the lithium-ion battery is heated than single-crystal Si. The off-current of a transistor using an oxide semiconductor is extremely small regardless of temperature, even at 150° C., whereas 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 unit 1320 can improve safety.

[0201] The control circuit unit 1320, which uses a memory circuit including transistors using oxide semiconductors, can also function as an automatic control device for lithium-ion batteries to address 10 causes of instability, such as micro-short circuits. The functions for addressing the 10 causes of instability include overcharging prevention, overcurrent prevention, overheating control during charging, cell balancing in the battery pack, over-discharging prevention, a fuel gauge, automatic control of charging voltage and current according to temperature, control of charging current 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, the automatic control device for lithium-ion batteries can be miniaturized.

[0202] Micro-short circuits are tiny short circuits that occur inside lithium-ion batteries. One of the causes of micro-short circuits is said to be local current concentration in parts of the positive electrode and negative electrode due to uneven distribution of the positive electrode active material caused by multiple charge and discharge cycles, or the generation of by-products due to side reactions, which causes micro-short circuits.

[0203] In addition to detecting micro-short circuits, the control circuit 1320 can also be said to detect the terminal voltage of the lithium-ion battery and manage the charge / discharge state of the lithium-ion battery. For example, to prevent overcharging, it can turn off both the output transistor and the cutoff switch of the charging circuit almost simultaneously.

[0204] FIG. 4C shows an example of a block diagram of the battery pack 1415 shown in FIG. 4B.

[0205] The control circuit 1320 includes a switch unit 1324 including at least a switch for preventing overcharging and a switch for preventing overdischarging, a control circuit 1322 for controlling the switch unit 1324, and a voltage measurement unit for the first battery 1301a. The control circuit 1320 sets upper and lower voltage limits for the lithium-ion battery used and limits the upper limit of the external current and the upper limit of the output current. The range between the lower and upper voltage limits for the lithium-ion battery is within the recommended voltage range. If the voltage falls outside this range, the switch unit 1324 activates and functions as a protection circuit. The control circuit 1320 can also be called a protection circuit because it controls the switch unit 1324 to prevent overcharging and overdischarging. For example, if the control circuit 1322 detects a voltage that could cause overcharging, it turns off the switch unit 1324 to cut off the current. Furthermore, a PTC element may be provided in the charge / discharge path to provide a function for cutting off the current in response to an increase in temperature. The control circuit section 1320 also has an external terminal 1325 (+IN) and an external terminal 1326 (-IN).

[0206] The switch unit 1324 can be configured 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, and may be, 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 portion 1324 may be formed using a power transistor having gallium oxide (x is a real number greater than 0). Furthermore, a memory element using an OS transistor can be freely arranged by stacking it on a circuit using a Si transistor, and thus integration can be easily achieved. By stacking the control circuit portion 1320 using an OS transistor on the switch portion 1324 and integrating them, it is possible to form it into a single chip, thereby enabling miniaturization.

[0207] The first batteries 1301a and 1301b primarily supply power to 42V (high-voltage) in-vehicle devices, while the second battery 1311 supplies power to 14V (low-voltage) in-vehicle devices. Lead-acid batteries are often used as the second battery 1311 due to their cost advantages. Using a lithium-ion battery as the second battery 1311 offers the advantage of being maintenance-free, but over extended use, e.g., three years or more, there is a risk of abnormalities occurring that cannot be detected 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 start even if the first batteries 1301a and 1301b have remaining capacity. If the second battery 1311 is a lead-acid battery, the first battery supplies power to the second battery, and the battery is charged to maintain a full charge state at all times, preventing the motor from being unable to operate as described above.

[0208] In this embodiment, an example in which lithium ion batteries are used for both the first battery 1301 a and the second battery 1311 is shown, but a lead-acid battery, an all-solid-state battery, or an electric double layer capacitor may be used for the second battery 1311. By using the positive electrode active material of the present invention in the above-described lithium ion battery, a secondary battery having high energy density and excellent electrical characteristics over a wide temperature range can be obtained.

[0209] Furthermore, regenerative energy generated by the rotation of the tire 1316 is sent to the motor 1304 via the gear 1305, and is then charged into the second battery 1311 from the motor controller 1303 and the battery controller 1302 via the control circuit unit 1321. Alternatively, the first battery 1301a is charged from the battery controller 1302 via the control circuit unit 1320. Alternatively, the first battery 1301b is charged from the battery controller 1302 via the control circuit unit 1320. In order to efficiently charge the regenerative energy, it is desirable that the first batteries 1301a and 1301b be capable of rapid charging.

[0210] The battery controller 1302 can set the charging voltage and charging current of the first batteries 1301a and 1301b. The battery controller 1302 can set charging conditions in accordance with the charging characteristics of the lithium ion batteries used, and can perform rapid charging.

[0211] Although not shown, when an external charger is connected, the charger's outlet or the charger's connection cable is electrically connected to the battery controller 1302. Power supplied from the external charger is charged to the first batteries 1301a and 1301b via the battery controller 1302. Some chargers are provided with a control circuit, and although the functions of the battery controller 1302 may not be used, it is preferable to charge the first batteries 1301a and 1301b via the control circuit unit 1320 to prevent overcharging. The control circuit unit 1320 may also be provided in the connection cable or the charger's connection cable. The control circuit unit 1320 is sometimes called an ECU (Electronic Control Unit). The ECU is connected to a CAN (Controller Area Network) provided in the electric vehicle. CAN is one of the serial communication standards used as an in-vehicle LAN. The ECU includes a microcomputer. The ECU uses a CPU or a GPU.

[0212] External chargers installed at charging stations and the like come in a variety of types, including 100V outlets, 200V outlets, and three-phase 200V and 50kW outlets. Charging can also be performed by receiving power from external charging equipment using a wireless power supply system or the like.

[0213] Next, an example in which a lithium-ion battery according to one embodiment of the present invention is mounted on a vehicle, typically a transportation vehicle, will be described.

[0214] Furthermore, installing lithium-ion batteries in vehicles will enable next-generation clean energy automobiles such as hybrid vehicles (HVs), electric vehicles (EVs), plug-in hybrid vehicles (PHVs), etc. Lithium-ion batteries can also be installed in transportation vehicles such as agricultural machinery, mopeds including electrically assisted bicycles, motorcycles, electric wheelchairs, electric carts, small or large ships, submarines, aircraft such as fixed-wing aircraft and rotary-wing aircraft, rockets, artificial satellites, space probes, planetary probes, and spacecraft.

[0215] 5A to 5E show examples of vehicles and the like using the lithium-ion battery of one embodiment of the present invention.

[0216] 5A illustrates an example of an electric bicycle using the lithium-ion battery of one embodiment of the present invention. The lithium-ion battery of one embodiment of the present invention can be applied to an electric bicycle 8700 illustrated in FIG. 5A. The lithium-ion battery of one embodiment of the present invention may include a protection circuit.

[0217] The electric bicycle 8700 includes a power storage device 8702. The power storage device 8702 can supply electricity to a motor that assists a rider. The power storage device 8702 can be detached from the main body of the electric bicycle 8700 and can be carried around. The power storage device 8702 includes a plurality of lithium-ion batteries of one embodiment of the present invention, and the remaining battery charge and the like can be displayed on a display unit. By using the positive electrode active material of the present invention for the lithium-ion battery, a secondary battery with high energy density and favorable electrical characteristics over a wide temperature range can be obtained.

[0218] FIG. 5B illustrates an example of a motorcycle using a lithium-ion battery of one embodiment of the present invention. A scooter 8600 illustrated in FIG. 5B includes a power storage device 8602, a side mirror 8601, and a turn signal light 8603. The scooter 8600 can store the power storage device 8602 in an under-seat storage compartment 8604. The power storage device 8602 can supply electricity to the turn signal light 8603. When 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 for the lithium-ion battery included in the power storage device 8602, a secondary battery with high energy density and favorable electrical characteristics over a wide temperature range can be obtained.

[0219] The automobile 2001 shown in FIG. 5C is an electric automobile that uses an electric motor as a power source for traveling. Alternatively, it is a hybrid automobile that can appropriately select and use an electric motor or an engine as a power source for traveling. When a lithium-ion battery is mounted on a vehicle, an example of the lithium-ion battery shown in the above embodiment is installed in one or more locations. By using the positive electrode active material of the present invention in the lithium-ion battery mounted on the vehicle, a secondary battery that has a high energy density and exhibits good electrical characteristics over a wide temperature range can be obtained.

[0220] 5C includes a battery pack 2200, which includes a battery module to which a plurality of lithium-ion batteries are connected. The battery pack 2200 further preferably includes a charge control device electrically connected to the battery module.

[0221] Furthermore, the automobile 2001 can charge its lithium-ion battery by receiving power supply from an external charging facility using a plug-in system, a contactless power supply system, or the like. The charging method and connector standards may be appropriately determined using a predetermined system such as CHAdeMO (registered trademark) or Combo. The external charging facility may be a charging station installed in a commercial facility, a household power source, or the like. For example, plug-in technology can be used to charge the power storage device installed in the automobile 2001 using an external power supply. Charging can be performed by converting AC power to DC power via a conversion device such as an AC-DC converter.

[0222] Furthermore, although not shown, a power receiving device can be mounted on a vehicle and power can be supplied contactlessly from a ground-based power transmitting device to charge the vehicle. In the case of this contactless power supply method, by incorporating a power transmitting device into a road or an exterior wall, charging can be performed not only while the vehicle is stopped but also while the vehicle is moving. This contactless power supply method can also be used to transmit and receive power between two vehicles. Furthermore, solar cells can be installed on the exterior of the vehicle to charge the lithium-ion battery while the vehicle is stopped and while moving. For such contactless power supply, an electromagnetic induction method or a magnetic field resonance method can be used.

[0223] 5D shows, as an example, a large transport vehicle 2003 having an electrically controlled motor. The battery module of the transport vehicle 2003 has, for example, one hundred or more lithium ion batteries with a nominal voltage of 3.0 V to 5.0 V connected in series to produce a maximum voltage of 600 V. Furthermore, except for the number of lithium ion batteries constituting the battery module of the battery pack 2202, the battery module has the same functions as that shown in FIG. 5C , and therefore a description thereof will be omitted. By using the positive electrode active material of the present invention in the lithium ion batteries of the module, a secondary battery having a high energy density and good electrical characteristics over a wide temperature range can be obtained.

[0224] 5E shows, as an example, an aircraft 2004 having an engine that burns fuel. The aircraft 2004 has wheels for takeoff and landing, and can therefore be considered a part of a transportation vehicle. The aircraft 2004 has a battery pack 2203 including a battery module formed by connecting multiple lithium-ion batteries and including the battery module and a charge control device.

[0225] The battery module of the aircraft 2004 is, for example, eight 4 V lithium ion batteries connected in series, with a maximum voltage of 32 V. Other than the number of lithium ion batteries constituting the battery module of the battery pack 2203, the battery module has the same functions as those shown in FIG. 5C , and therefore a description thereof will be omitted.

[0226] The content of this embodiment mode can be combined with the content of other embodiment modes as appropriate.

[0227] (Embodiment 6) In this embodiment, an example of mounting a lithium-ion battery according to one embodiment of the present invention in an electronic device will be described. Examples of electronic devices mounting a lithium-ion battery include television sets (also referred to as televisions or television receivers), computer monitors, digital cameras, digital video cameras, digital photo frames, mobile phones (also referred to as mobile phones or mobile phone devices), portable game consoles, personal digital assistants, sound players, and large game consoles such as pachinko machines. Examples of personal digital assistants include notebook personal computers, tablet devices, e-book readers, and mobile phones.

[0228] 6A shows an example of a mobile phone. The mobile phone 2100 includes a display portion 2102 built into a housing 2101, operation buttons 2103, an external connection port 2104, a speaker 2105, a microphone 2106, and the like. The mobile phone 2100 also includes a lithium ion battery 2107. By using the positive electrode active material of the present invention in the lithium ion battery, a secondary battery having high energy density and excellent electrical characteristics over a wide temperature range can be obtained.

[0229] The mobile phone 2100 can execute various applications such as mobile phone calls, e-mail, document browsing and creation, music playback, internet communication, and computer games.

[0230] The operation button 2103 can be provided with various functions such as time setting, power on / off operation, wireless communication on / off operation, silent mode activation / deactivation, power saving mode activation / deactivation, etc. For example, the functions of the operation button 2103 can be freely set by an operating system incorporated in the mobile phone 2100.

[0231] The mobile phone 2100 is also capable of performing standardized short-range wireless communication, and can also make hands-free calls by communicating with a wirelessly enabled headset, for example.

[0232] The mobile phone 2100 also includes an external connection port 2104, which allows direct data exchange with other information terminals via a connector. Charging can also be performed via the external connection port 2104. Note that charging may be performed by wireless power supply without using the external connection port 2104.

[0233] The mobile phone 2100 preferably has a sensor, such as a fingerprint sensor, a pulse sensor, a body temperature sensor, a touch sensor, a pressure sensor, an acceleration sensor, or the like.

[0234] 6B shows an unmanned aerial vehicle 2300 having a plurality of rotors 2302. The unmanned aerial vehicle 2300 is sometimes called a drone. The unmanned aerial vehicle 2300 includes a lithium-ion battery 2301 according to one embodiment of the present invention, a camera 2303, and an antenna (not shown). The unmanned aerial vehicle 2300 can be remotely controlled via the antenna. By using the positive electrode active material of the present invention in a lithium-ion battery, a secondary battery having high energy density and favorable electrical characteristics over a wide temperature range can be obtained.

[0235] Fig. 6C shows an example of a robot. The robot 6400 shown in Fig. 6C includes 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, etc.

[0236] The microphone 6402 has a function of detecting the user's speaking voice, environmental sounds, etc. The speaker 6404 has a function of emitting sound. The robot 6400 can communicate with the user using the microphone 6402 and the speaker 6404.

[0237] The display unit 6405 has a function of displaying various information. The robot 6400 can display information desired by the user on the display unit 6405. The display unit 6405 may be equipped with a touch panel. The display unit 6405 may also be a detachable information terminal, which can be installed in a fixed position on the robot 6400 to enable charging and data transfer.

[0238] The upper camera 6403 and the lower camera 6406 have the function of capturing images of the surroundings of the robot 6400. In addition, the obstacle sensor 6407 can detect the presence or absence of obstacles in the direction of travel when the robot 6400 moves forward using the movement mechanism 6408. The robot 6400 can recognize the surrounding environment and move safely using the upper camera 6403, the lower camera 6406, and the obstacle sensor 6407.

[0239] The robot 6400 includes a lithium-ion battery 6409 according to one embodiment of the present invention and a semiconductor device or an electronic component in its internal region. By using the positive electrode active material of the present invention for the lithium-ion battery, the secondary battery can have high energy density and good electrical characteristics over a wide temperature range.

[0240] 6D shows an example of a cleaning robot. The cleaning robot 6300 includes a display unit 6302 arranged on the top surface of a housing 6301, a plurality of cameras 6303 arranged on the side surfaces, a brush 6304, an operation button 6305, a lithium-ion battery 6306, various sensors, and the like. Although not shown, the cleaning robot 6300 is provided with tires, a suction port, and the like. The cleaning robot 6300 can move by itself, detect dust 6310, and suck up the dust from a suction port arranged on the bottom surface.

[0241] For example, the cleaning robot 6300 can analyze an image captured by the camera 6303 and determine whether or not there is an obstacle such as a wall, furniture, or a step. Furthermore, when an object that may become entangled in the brush 6304, such as a wire, is detected through image analysis, the cleaning robot 6300 can stop the rotation of the brush 6304. The cleaning robot 6300 includes a lithium-ion battery 6306 according to one embodiment of the present invention and a semiconductor device or electronic component in 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 favorable electrical characteristics can be obtained.

[0242] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0243] In this example, LiMn ｘ Fe １−ｘ P.O. ４ Positive electrode active materials were prepared by dissolving Mg or Zn as an additive element in (0<x<1), and their properties were evaluated.

[0244] First, the ionic radii proposed by Shannon for each element are shown in Table 1. All ionic radii are shown for the 6-coordinated state, and for transition metal elements, the ionic radii are shown for the high-spin state.

[0245]

[0246] The ionic radius of divalent Mg is smaller than the ionic radius of divalent Mn and Fe, but larger than the ionic radius of trivalent Mn and Fe. ｘ Fe １−ｘ P.O. ４ (0<x<1). The ionic radius of divalent Zn is smaller than the ionic radius of Mn and the ionic radius of Fe, but larger than the ionic radius of trivalent Mn and the ionic radius of Fe. ｘ Fe １−ｘ P.O. ４ It is an element that easily dissolves in (0<x<1).

[0247] <Preparation of Positive Electrode Active Material> Next, a method for preparing the positive electrode active material in this example will be described with reference to FIG.

[0248] <Positive electrode active material A> MgO as an Mg source, Li as a Li source ２ CO ３ , MnCO as a Mn source ３ , FeC as an Fe source ２ O ４ ・2H ２ O, NH as a phosphate source ４ H ２ P.O. ４ The composition is LiMn （０．９−ｘ） Fe ０．１ Mg ｘ P.O. ４ The starting material was weighed so that (x = 0.01). The weighed value is called the added amount of starting material. The raw materials, grinding media, and solvent were placed in a mill container and sealed. Zirconia balls with a diameter of 3 mm were used as the grinding media, and dehydrated acetone was used as the solvent.

[0249] While the mill container was cooled, mixing was performed using a planetary ball mill at 300 rpm for 2 hours. By maintaining the temperature of the mill container at 50°C or less, evaporation of the solvent can be suppressed. The mixture was recovered from the mill container, dried in a ventilation drying oven, and then sieved with a 300 μm mesh to obtain a first mixture.

[0250] The first mixture was placed in an aluminum oxide crucible, which was then covered with a lid, and heated in a muffle furnace at 350°C for 10 hours in a nitrogen flow atmosphere. Nitrogen was supplied into the muffle furnace at a rate of 5 L / min to create the nitrogen flow atmosphere. The heated mixture was recovered and passed through a sieve with 300 µm openings to obtain a first composite oxide.

[0251] Glucose was used as the carbon source, and the first composite oxide and the carbon source were weighed out so that the weight ratio of the first composite oxide to the carbon source was 10:1. The raw materials, grinding media, and a solvent were placed in a mill container and sealed. Zirconia balls with a diameter of 3 mm were used as the grinding media, and dehydrated acetone was used as the solvent.

[0252] The mill container was mixed using a planetary ball mill at 300 rpm for 2 hours. The mixture was recovered from the mill container, dried in a ventilation drying oven, and then passed through a sieve with 300 μm openings to recover a second mixture.

[0253] The second mixture was placed in an aluminum oxide crucible, covered, and heated in a muffle furnace at 650°C for 10 hours in a nitrogen flow atmosphere. Nitrogen was supplied into the muffle furnace at a rate of 5 L / min to create the nitrogen flow atmosphere. The heated mixture was recovered and sieved through a 53 μm mesh sieve to obtain a carbon-coated positive electrode active material. The carbon-coated positive electrode active material prepared in the above process was referred to as positive electrode active material A and C / LiMn. （０．９−ｘ） Fe ０．１ Mg ｘ P.O. ４ (x=0.01), C / LiMn ０．８９ Fe ０．１ Mg ０．０１ P.O. ４、 Alternatively, it will be referred to as Mg 1%.

[0254] <Positive electrode active material B> Composition: LiMn （０．９−ｘ） Fe ０．１ Mg ｘ P.O. ４ (x=0.02) ２ CO ３ , MnCO ３ , FeC ２ O ４ ・2H ２ O, N.H. ４ H ２ P.O. ４ The other conditions were the same as for Mg 1%. The carbon-coated positive electrode active materials prepared in the above steps were used as positive electrode active materials B and C / LiMn （０．９−ｘ） Fe ０．１ Mg ｘ P.O. ４ (x=0.02), C / LiMn ０．８８ Fe ０．１ Mg ０．０２ P.O. ４、 Alternatively, it will be referred to as Mg2%.

[0255] <Positive electrode active material C> Composition: LiMn （０．９−ｘ） Fe ０．１ Mg ｘ P.O. ４ (x=0.03) ２ CO ３ , MnCO ３ , FeC ２ O４ ・2H ２ O, N.H. ４ H ２ P.O. ４ The other conditions were the same as for Mg 1%. The carbon-coated positive electrode active material prepared in the above process was used as positive electrode active material C, C / LiMn （０．９−ｘ） Fe ０．１ Mg ｘ P.O. ４ (x=0.03), C / LiMn ０．８７ Fe ０．１ Mg ０．０３ P.O. ４、 Alternatively, it will be referred to as Mg3%.

[0256] <Positive electrode active material D> Composition: LiMn （０．９−ｘ） Fe ０．１ Mg ｘ P.O. ４ (x=0.05) ２ CO ３ , MnCO ３ , FeC ２ O ４ ・2H ２ O, N.H. ４ H ２ P.O. ４ The other conditions were the same as for Mg 1%. The carbon-coated positive electrode active material prepared in the above process was used as positive electrode active material D, C / LiMn （０．９−ｘ） Fe ０．１ Mg ｘ P.O. ４ (x=0.05), C / LiMn ０．８５ Fe ０．１ Mg ０．０５ P.O. ４、 Alternatively, it will be called Mg5%.

[0257] <Positive electrode active material E> Composition: LiMn （０．９−ｘ） Fe ０．１ Mg ｘ P.O. ４ (x=0.1) ２ CO ３ , MnCO ３ , FeC ２ O ４ ・2H ２ O, N.H. ４ H ２P.O. ４ The other conditions were the same as for Mg 1%. The carbon-coated positive electrode active material prepared in the above process was used as positive electrode active material E, C / LiMn （０．９−ｘ） Fe ０．１ Mg ｘ P.O. ４ (x=0.1), C / LiMn ０．８ Fe ０．１ Mg ０．１ P.O. ４、 Alternatively, it may be referred to as Mg 10%. Positive electrode active material E can be said to be a positive electrode active material similar to Examples 1-4 of Patent Document 1.

[0258] <Positive electrode active material F> The Mg source was changed to a Zn source, and ZnO was prepared as the Zn source. （０．９−ｘ） Fe ０．１ Zn ｘ P.O. ４ (x=0.01) ２ CO ３ , MnCO ３ , FeC ２ O ４ ・2H ２ O, N.H. ４ H ２ P.O. ４ The other conditions were the same as for Mg 1%. The carbon-coated positive electrode active material prepared in the above process was used as positive electrode active material F, C / LiMn （０．９−ｘ） Fe ０．１ Zn ｘ P.O. ４ (x=0.01), C / LiMn ０．８９ Fe ０．１ Zn ０．０１ P.O. ４、 Or, it will be called Zn 1%.

[0259] <Positive electrode active material G> Composition: LiMn （０．９−ｘ） Fe ０．１ Zn ｘ P.O. ４ (x=0.02) ２ CO ３ , MnCO ３ , FeC ２ O ４ ・2H ２ O, N.H. ４ H２ P.O. ４ The other conditions were the same as those for Zn 1%. The carbon-coated positive electrode active material prepared in the above process was used as positive electrode active material G, C / LiMn （０．９−ｘ） Fe ０．１ Zn ｘ P.O. ４ (x=0.02), C / LiMn ０．８８ Fe ０．１ Zn ０．０２ P.O. ４、 Or, it will be called Zn2%.

[0260] <Positive electrode active material H> Composition: LiMn （０．９−ｘ） Fe ０．１ Zn ｘ P.O. ４ (x=0.03) ２ CO ３ , MnCO ３ , FeC ２ O ４ ・2H ２ O, N.H. ４ H ２ P.O. ４ The other conditions were the same as those for Zn 1%. The carbon-coated positive electrode active material prepared in the above process was used as the positive electrode active material H, C / LiMn （０．９−ｘ） Fe ０．１ Zn ｘ P.O. ４ (x=0.03), C / LiMn ０．８７ Fe ０．１ Zn ０．０３ P.O. ４、 Or, it will be called Zn3%.

[0261] <Positive electrode active material I> Composition: LiMn （０．９−ｘ） Fe ０．１ Zn ｘ P.O. ４ (x=0.05) ２ CO ３ , MnCO ３ , FeC ２ O ４ ・2H ２ O, N.H. ４ H ２ P.O. ４The other conditions were the same as those for Zn 1%. The carbon-coated positive electrode active material prepared in the above process was called positive electrode active material I, C / LiMn （０．９−ｘ） Fe ０．１ Zn ｘ P.O. ４ (x=0.05), C / LiMn ０．８５ Fe ０．１ Zn ０．０５ P.O. ４、 Or, it will be called Zn5%.

[0262] <Positive electrode active material J> Composition: LiMn （０．９−ｘ） Fe ０．１ Zn ｘ P.O. ４ (x=0.1) ２ CO ３ , MnCO ３ , FeC ２ O ４ ・2H ２ O, N.H. ４ H ２ P.O. ４ The other conditions were the same as those for Zn 1%. The carbon-coated positive electrode active material prepared in the above process was called positive electrode active material J, C / LiMn （０．９−ｘ） Fe ０．１ Zn ｘ P.O. ４ (x=0.1), C / LiMn ０．８ Fe ０．１ Zn ０．１ P.O. ４、 Or, it will be called Zn10%.

[0263] <Positive electrode active material ref> Composition is LiMn ０．９ Fe ０．１ P.O. ４ So that Li ２ CO ３ , MnCO ３ , FeC ２ O ４ ・2H ２ O, N.H. ４ H ２ P.O. ４ The other conditions were the same as for Mg 1%. The carbon-coated positive electrode active material prepared in the above process was used as the positive electrode active material ref, C / LiMn ０．９ Fe０．１ P.O. ４、 Alternatively, they will be referred to as comparative examples.

[0264] Table 2 shows the compositions of the positive electrode active materials prepared.

[0265]

[0266] Tables 3 and 4 also show the atomic ratio of manganese to the sum of the atomic ratios of manganese, iron, and magnesium, and the atomic ratio of magnesium to the sum of the atomic ratios of manganese and magnesium, for positive electrode active material C and positive electrode active material E.

[0267]

[0268]

[0269] Tables 5 and 6 also show the atomic ratio of manganese to the sum of the atomic ratios of manganese, iron, and zinc, and the atomic ratio of magnesium to the sum of the atomic ratios of manganese and zinc, for positive electrode active material H and positive electrode active material J.

[0270]

[0271]

[0272] <XRD> Of the samples prepared above, XRD measurements and Rietveld analysis were performed on cathode active materials A to J. The XRD apparatus and measurement and analysis conditions were as described in embodiment 1. The samples were placed at room temperature (23°C ± 5°C). Figure 7 shows the XRD profiles of cathode active materials A to E, with reference, Mg 10%, Mg 5%, Mg 3%, Mg 2%, and Mg 1% added. Figure 8 shows the XRD profiles of cathode active materials F to J, with reference, Zn 10%, Zn 5%, Zn 3%, Zn 2%, and Zn 1% added. No particular heterogeneous phases were observed in any of the samples.

[0273] These XRD profiles were obtained from LiFePO ４(ICSD coll.code.193640) The results of refined Rietveld analysis assuming a single phase are shown in Tables 7 to 10. In the tables, Mg 10%, Mg 5%, Mg 3%, Mg 2%, Mg 1%, Zn 10%, Zn 5%, Zn 3%, Zn 2%, and Zn 1% are added. By using the numerical values, space groups, etc. in Tables 7 to 10, it is possible to identify positive electrode active materials A to J.

[0274]

[0275]

[0276]

[0277]

[0278] 9A to 9C are graphs showing the relationship between the Mg concentration of Samples A to E and the change in the lattice constant of the unit cell obtained from the above analysis. Fig. 9A is a graph of the a-axis lattice constant (Lattice constant (a axis)) and Mg concentration, Fig. 9B is a graph of the b-axis lattice constant (Lattice constant (b axis)) and Mg concentration, and Fig. 9C is a graph of the c-axis lattice constant (Lattice constant (c axis)) and Mg concentration.

[0279] As shown in Figures 9A to 9C, the higher the Mg concentration, the smaller both the lattice constants and the unit cell size. Furthermore, the contraction of both lattice constants could be linearly approximated and followed Vegard's law. Approximation formulas are shown in the figures. This suggests that Mg is dissolved in the positive electrode active material having an olivine-type crystal structure. Furthermore, it was found that the higher the Mg concentration, the smaller both the lattice constants. Specifically, the positive electrode active material 100, which has an olivine-type crystal structure and contains lithium, manganese, iron, magnesium, phosphorus, and oxygen, has an a-axis lattice constant greater than 10.4039 Å and less than 10.4319 Å, a b-axis lattice constant greater than 6.0749 Å and less than 6.0911 Å, and a c-axis lattice constant greater than 4.7346 Å and less than 4.7380 Å. Considering the charge-discharge characteristics of the examples described later, the a-axis lattice constant satisfied by the positive electrode active material 100 is preferably 10.4203 Å or more and 10.4294 Å or less, the b-axis lattice constant is preferably 6.0844 Å or more and 6.0896 Å or less, and the c-axis lattice constant is preferably 4.7369 Å or more and 4.7379 Å or less.

[0280] 10A to 10C are graphs showing the relationship between the Zn concentration of Samples A to E and the change in the lattice constant of the unit cell obtained from the above analysis. Fig. 10A is a graph of the a-axis lattice constant (Lattice constant (a axis)) and Zn concentration, Fig. 10B is a graph of the b-axis lattice constant (Lattice constant (b axis)) and Zn concentration, and Fig. 10C is a graph of the c-axis lattice constant (Lattice constant (c axis)) and Zn concentration. It was found that the a-axis lattice constant and the b-axis lattice constant each shrink as the Zn concentration increases.

[0281] As shown in Figures 10A to 10C, the higher the Zn concentration, the smaller both the lattice constants and the unit cell size. Furthermore, the contraction of both lattice constants could be linearly approximated and followed Vegard's law. Approximation formulas are shown in the figures. This suggests that Zn is dissolved in a positive electrode active material having an olivine-type crystal structure. Furthermore, it was found that the higher the Zn concentration, the smaller both the lattice constants. Specifically, the positive electrode active material 100, which has an olivine-type crystal structure and contains lithium, manganese, iron, zinc, phosphorus, and oxygen, has an a-axis lattice constant of 10.4087 Å or more and 10.4325 Å or less, a b-axis lattice constant of 6.0764 Å or more and 6.0901 Å or less, and a c-axis lattice constant of 4.7361 Å or more and 4.7385 Å or less. Considering the charge-discharge characteristics of the examples described later, the a-axis lattice constant satisfied by the positive electrode active material 100 is preferably 10.4225 Å or more and 10.4303 Å or less, the b-axis lattice constant is preferably 6.0851 Å or more and 6.0901 Å or less, and the c-axis lattice constant is preferably 4.7374 Å or more and 4.7382 Å or less.

[0282] FIG. 11 shows LiFePO having an olivine-type crystal structure of the space group Pnma. ４ It can be seen that the lithium diffusion path exists in the b-axis direction in the unit cell.

[0283] Furthermore, as shown in Table 7, the sample containing 3% Mg had a crystallite size LVol-IB of 71.7 nm or more and 74.6 nm or less, specifically 72.0 nm.

[0284] Furthermore, as shown in Table 9, the crystallite size LVol-IB of the sample containing 3% Zn was 68.5 nm or more and 71.8 nm or less, specifically 68.9 nm.

[0285] <XPS> Of the samples prepared above, XPS analysis was performed on the Mg 3%, Mg 10%, Zn 3%, Zn 10% and comparative example. Measurements were performed using the following XPS device and measurement conditions. Furthermore, the atomic ratio of elements below the detection limit was not determined. The atomic ratio was determined as the concentration of each element relative to the sum of the atomic ratios of each element shown in the table below. Measurement device: PHI Quantera II X-ray: Monochromated Al Kα (1486.6 eV) Energy resolution: Half-width of Ag3d5 / 2 peak is 1.0 eV±0.1 eV Detection area: 100 μmφ Detection depth: Approximately 4-5 nm (take-off angle 45°), approximately 2-3 nm (take-off angle 15°) Measurement spectrum: Wide scan, narrow scan of each detected element

[0286] The results of the XPS analysis are shown in Tables 11 to 15.

[0287]

[0288] Table 11 shows that when the measurement condition is 45°, that is, in the region from the surface of the positive electrode active material C to a depth of about 5 nm, the atomic ratio of Mn to the sum of the atomic ratio of Mn, the atomic ratio of Fe, the atomic ratio of O, the atomic ratio of C, and the atomic ratio of P is 7.3 atomic %. The atomic ratios of the other elements can be determined in the same manner. The atomic ratios can also be determined when the measurement condition is 15°.

[0289]

[0290] Table 12 shows that when the measurement condition is 45°, that is, in the region from the surface of the positive electrode active material E to a depth of about 5 nm, the atomic ratio of Mn to the sum of the atomic ratios of Mn, Fe, O, C, and P is 6.5 atomic %. The atomic ratios of the other elements can be determined in the same manner. The atomic ratios can also be determined when the measurement condition is 15°.

[0291]

[0292] From Table 13, it can be seen that when the measurement condition is 45°, that is, in the region from the surface of the positive electrode active material H to a depth of about 5 nm, the atomic ratio of Mn to the sum of the atomic ratio of Mn, the atomic ratio of Fe, the atomic ratio of O, the atomic ratio of C, and the atomic ratio of P is 7.3 atomic %. The atomic ratios of the other elements can be similarly determined. The atomic ratios can also be similarly determined when the measurement condition is 15°.

[0293]

[0294] Table 14 shows that when the measurement condition is 45°, that is, in the region from the surface of positive electrode active material J to a depth of about 5 nm, the atomic ratio of Mn to the sum of the atomic ratios of Mn, Fe, O, C, and P is 6.0 atomic %. The atomic ratios of the other elements can be determined in a similar manner. The atomic ratios can also be determined when the measurement condition is 15°.

[0295]

[0296] Table 15 shows that when the measurement condition was 45°, that is, in the region from the surface of the positive electrode active material ref to a depth of about 5 nm, the atomic ratio of Mn to the sum of the atomic ratio of Mn, the atomic ratio of Fe, the atomic ratio of O, the atomic ratio of C, and the atomic ratio of P was 7.4 atomic%. The atomic ratios of the other elements were also found in the same way. The atomic ratios were also found when the measurement condition was 15°.

[0297] It was found that the C atomic ratio was 30 atomic% or more and 40 atomic% or less, preferably 35 atomic% or more and 38 atomic% or less, in positive electrode active materials A to J. The amount of glucose added as the C source was the same in positive electrode active materials A to J, and it is considered that the C atomic ratio was 30 atomic% or more and 40 atomic% or less, preferably 35 atomic% or more and 38 atomic% or less, even in samples not subjected to XPS. These results and others indicate that carbon coating was sufficiently performed in at least the region up to 5 nm from the surface of the positive electrode active material particles.

[0298] Furthermore, the 15° and 45° XPS measurement results for the 3% Mg cathode active material C and the 15° XPS result for the 10% Mg cathode active material E revealed that Mg was not present in the region up to 5 nm from the surface. In other words, it was inferred that Mg was present inside the cathode active material. The 15° and 45° XPS measurement results for the 3% Zn cathode active material H and the 15° and 45° XPS result for the 10% Zn cathode active material J revealed that Zn was present in the region up to 5 nm from the surface.

[0299] <STEM-EDX Analysis> Of the samples prepared above, STEM-EDX analysis was carried out on the positive electrode active material C, the positive electrode active material E, the positive electrode active material H, and the positive electrode active material J. The analysis procedure will be described.

[0300] First, a protective film was deposited on each positive electrode active material particle using a carbon coating unit of an ion sputtering apparatus (Hitachi High-Tech MC1000). Fig. 12A shows a cross-sectional STEM image of positive electrode active material C (Mg 3%) with a carbon protective film attached, Fig. 14A shows a cross-sectional STEM image of positive electrode active material E (Mg 10%) with carbon attached, Fig. 16A shows a cross-sectional STEM image of positive electrode active material H (Zn 3%) with carbon attached, and Fig. 18A shows a cross-sectional STEM image of positive electrode active material J (Zn 10%) with carbon attached.

[0301] Each cathode active material was then thinned using a FIB-SEM (Hitachi High-Tech's XVision 200TBS) to include the analysis area. In Figures 12A, 14A, 16A, and 18A, the area remaining after thinning, i.e., the analysis area, is indicated by an arrow. STEM-EDX analysis was performed using a JEM-ARM200F NEOARM (JEOL Ltd.) at an accelerating voltage of 80 kV.

[0302] [Positive Electrode Active Material C (Mg3%)] The results of STEM-EDX analysis of the Mg3% sample are shown in FIG. 12B , and an enlarged view of the vertical axis of FIG. 12B is shown in FIG. 12C . Because the vertical axis represents atomic concentration (atomic %), the values ​​on the horizontal axis can be read as the atomic concentration of each element. The concentration of each element was determined so that the sum of the Mn concentration, Fe concentration, Mg concentration, P concentration, and O concentration equaled 100%. The vertical axis can also be used to represent intensity (counts). The results of STEM-EDX analysis of the Mg3% sample with the vertical axis representing intensity (counts) are shown in FIG. 13A , and an enlarged view of the vertical axis of FIG. 13B is shown. No peaks in the concentration or intensity of the added element Mg were observed, and no segregation or uneven distribution of Mg was confirmed. That is, Mg is thought to be uniformly distributed in the positive electrode active material particles, especially inside, and such Mg is ＋ This is preferable because it does not block the diffusion path.

[0303] [Positive Electrode Active Material E (Mg10%)] The results of STEM-EDX analysis of a 10% Mg sample are shown in FIG. 14B , and an enlarged view of the vertical axis of FIG. 14B is shown in FIG. 14C . Because the vertical axis represents atomic concentration (atomic %), the values ​​on the horizontal axis can be interpreted as the atomic concentration of each element. The concentration of each element was determined so that the sum of the Mn, Fe, Mg, P, and O concentrations equaled 100%. The vertical axis can also be used to represent intensity (counts). The results of STEM-EDX analysis of a 3% Mg sample with intensity (counts) on the vertical axis are shown in FIG. 15A , and an enlarged view of the vertical axis of FIG. 15A is shown in FIG. 15B . No peaks in the concentration or intensity of the added element Mg were observed, and no segregation or uneven distribution of Mg was confirmed. That is, Mg is thought to be uniformly distributed in the positive electrode active material particles, especially inside, and such Mg is ＋ This is preferable because it is unlikely to obstruct the diffusion pathway.

[0304] [Positive Electrode Active Material H (Zn3%)] The results of STEM-EDX analysis of a Zn3% sample are shown in FIG. 16B, and an enlarged view of the vertical axis of FIG. 16B is shown in FIG. 16C. Since the vertical axis represents atomic concentration (atomic%), the values ​​on the horizontal axis can be read as the atomic concentration of each element. The concentration of each element was determined so that the sum of the Mn concentration, Fe concentration, Zn concentration, P concentration, and O concentration equaled 100%. The vertical axis can also be expressed as intensity (counts). The results of STEM-EDX analysis of a Mg3% sample with the vertical axis representing intensity (counts) are shown in FIG. 17A, and an enlarged view of the vertical axis of FIG. 17B is shown. No peaks in the concentration of the added element Zn or the intensity peaks of Zn were observed, and no segregation or uneven distribution of Zn was confirmed. In other words, Zn is thought to be uniformly distributed in the positive electrode active material particles, especially inside, and such Zn is ＋ This is preferable because it is unlikely to obstruct the diffusion pathway.

[0305] [Positive Electrode Active Material J (Zn10%)] The results of STEM-EDX analysis of a Zn10% sample are shown in FIG. 18B, and an enlarged view of the vertical axis of FIG. 18B is shown in FIG. 18C. Since the vertical axis represents atomic concentration (atomic%), the values ​​on the horizontal axis can be read as the atomic concentration of each element. The concentration of each element was determined so that the sum of the Mn concentration, Fe concentration, Zn concentration, P concentration, and O concentration equaled 100%. The vertical axis can also be expressed as intensity (counts). The results of STEM-EDX analysis of a Mg3% sample with intensity (counts) on the vertical axis are shown in FIG. 19A, and an enlarged view of the vertical axis of FIG. 19B is shown. No peaks in the concentration of the added element Zn or Zn intensity were observed, and no segregation or uneven distribution of Zn was confirmed. In other words, Zn is thought to be uniformly distributed in the positive electrode active material particles, especially inside, and such Zn is ＋ This is preferable because it is unlikely to obstruct the diffusion pathway.

[0306] [Increasing the Number of Positive Electrode Active Material C (Mg 3%)] The number of measurement regions for positive electrode active material C was increased to five, and the concentration of each element was determined using similar STEM-EDX-ray analysis. Figure 20 shows the five measurement locations. Because positive electrode active material C was broken down into secondary particles, primary particles existed corresponding to each measurement location. Therefore, each measurement location is sometimes referred to as an individual primary particle. Table 16 shows the concentration of each element. The lower detection limit for Mg concentration is 0.3 atomic %. Table 16 also shows the atomic ratio of manganese to the sum of the atomic ratios of manganese, iron, and magnesium. Table 16 also shows the atomic ratio of magnesium to the sum of the atomic ratios of manganese and magnesium.

[0307]

[0308] In the positive electrode active material C, the atomic ratio of manganese to the sum of the atomic ratios of manganese, iron, and magnesium was 0.7 or more. In addition, in the positive electrode active material C, the atomic ratio of the additional element to the sum of the atomic ratios of manganese and the additional element was 0.02 or more and less than 0.1.

[0309] [Increasing the Number of Cathode Active Material E (Mg 10%)] The number of measurement regions for cathode active material E was increased to five, and the concentration of each element was determined using similar STEM-EDX-ray analysis. Figure 21 shows the five measurement locations. Because cathode active material E was divided into secondary particles, primary particles existed corresponding to each measurement location. Therefore, each measurement location is sometimes referred to as an individual primary particle. Table 17 shows the concentration of each element. The lower detection limit for Mg concentration is 0.3 atomic %. Table 17 also shows the atomic ratio of manganese to the sum of the atomic ratios of manganese, iron, and magnesium. Table 17 also shows the atomic ratio of magnesium to the sum of the atomic ratios of manganese and magnesium.

[0310]

[0311] In positive electrode active material E, the atomic ratio of manganese to the sum of the atomic ratios of manganese, iron, and magnesium was 0.7 or more, but the atomic ratio of the additional element to the sum of the atomic ratios of manganese and the additional element did not satisfy the requirement of 0.02 or more and less than 0.1.

[0312] [Increasing the Number of Positive Electrode Active Material H (Zn 3%)] The number of measurement regions for positive electrode active material H was increased to five, and the concentration of each element was determined using similar STEM-EDX-ray analysis. Figure 22 shows the five measurement locations. Because positive electrode active material H was divided into secondary particles, primary particles existed corresponding to each measurement location. Therefore, each measurement location is sometimes referred to as an individual primary particle. Table 18 shows the concentration of each element. The lower detection limit for Zn concentration is 0.1 atomic %. Table 18 also shows the atomic ratio of manganese to the sum of the atomic ratios of manganese, iron, and zinc. Table 18 also shows the atomic ratio of zinc to the sum of the atomic ratios of manganese and zinc.

[0313]

[0314] In positive electrode active material H, the atomic ratio of manganese to the sum of the atomic ratios of manganese, iron, and zinc was 0.7 or more. In positive electrode active material H, the atomic ratio of zinc to the sum of the atomic ratios of manganese and zinc was 0.02 or more and less than 0.1.

[0315] [Increasing the Number of Positive Electrode Active Material J (Zn 10%)] The number of measurement regions for positive electrode active material J was increased to five, and the concentration of each element was determined using similar STEM-EDX-ray analysis. Figure 23 shows the five measurement locations. Because positive electrode active material J was divided into secondary particles, primary particles existed corresponding to each measurement location. Therefore, each measurement location is sometimes referred to as an individual primary particle. Table 19 shows the concentration of each element. The lower detection limit for Zn concentration is 0.1 atomic %. Table 19 also shows the atomic ratio of manganese to the sum of the atomic ratios of manganese, iron, and zinc. Table 19 also shows the atomic ratio of zinc to the sum of the atomic ratios of manganese and zinc.

[0316]

[0317] In positive electrode active material J, the atomic ratio of manganese to the sum of the atomic ratios of manganese, iron, and zinc was 0.7 or more, and the atomic ratio of zinc to the sum of the atomic ratios of manganese and zinc was 0.02 or more and less than 0.08.

[0318] <Elemental analysis by ICP-MS> Elemental analysis by ICP-MS was carried out on the positive electrode active materials C, E, H, and J. First, as a pretreatment, the positive electrode active material C and nitric acid were mixed in a quartz container and dissolved under microwave irradiation. This is called a sample solution. Sample solutions were prepared for the positive electrode active materials E, H, and J in the same manner as for the positive electrode active material C. Note that organic matter and the like attached to each positive electrode active material was removed by microwave irradiation. ２ and gaseous CO ２ By such pretreatment, it is possible to prepare a sample solution from which unnecessary organic matter has been removed.

[0319] After the pretreatment, elemental analysis by ICP-MS was carried out under the following conditions: Measurement device: Agilent 8900 Triple Quadrupole ICP-MS (manufactured by Agilent Technologies) Measurement conditions: according to the Agilent Technologies instrument operation manual Measurement mode: quantitative analysis

[0320] The results are shown in Tables 20 to 23. Tables 20 to 23 show values ​​normalized so that the atomic ratio of P is 1.

[0321]

[0322] In the positive electrode active material C, the atomic ratio of manganese to the sum of the atomic ratios of manganese, iron, and magnesium was 0.7 or more. In addition, in the positive electrode active material C, the atomic ratio of the additional element to the sum of the atomic ratios of manganese and the additional element was 0.02 or more and less than 0.1.

[0323] Comparing Table 3 above with Table 20, it can be seen that the elemental analysis by ICP-MS is in close agreement with the amount of starting material added.

[0324]

[0325] In positive electrode active material E, the atomic ratio of manganese to the sum of the atomic ratios of manganese, iron, and magnesium was 0.7 or more, but the atomic ratio of the additional element to the sum of the atomic ratios of manganese and the additional element did not satisfy the requirement of 0.02 or more and less than 0.1.

[0326] Comparing Table 4 above with Table 21, it can be seen that the elemental analysis by ICP-MS is in close agreement with the amount of starting material added.

[0327]

[0328] In positive electrode active material H, the atomic ratio of manganese to the sum of the atomic ratios of manganese, iron, and zinc was 0.7 or more. In positive electrode active material H, the atomic ratio of zinc to the sum of the atomic ratios of manganese and zinc was 0.02 or more and less than 0.1.

[0329] Comparing Table 5 above with Table 22, it can be seen that the elemental analysis by ICP-MS is in close agreement with the amount of starting material added.

[0330]

[0331] In positive electrode active material J, the atomic ratio of manganese to the sum of the atomic ratios of manganese, iron, and zinc was 0.7 or more, and the atomic ratio of zinc to the sum of the atomic ratios of manganese and zinc was 0.02 or more and less than 0.08.

[0332] Comparing Table 6 above with Table 23, it can be seen that the elemental analysis by ICP-MS is in close agreement with the amount of starting material added.

[0333] <Charge-Discharge Characteristics> Coin cells (CR2032 type, 20 mm diameter, 3.2 mm height) (hereinafter also referred to as half cells) were fabricated using each of the positive electrode active materials prepared above and lithium metal as the negative electrode (counter electrode), and their characteristics were evaluated. The coin cell containing positive electrode active material A is referred to as sample A, and similarly, the coin cells containing positive electrode active materials B to J and the positive electrode active material ref are referred to as samples B to J and the sample ref, respectively.

[0334] Acetylene black (AB) was used as the conductive additive, and polyvinylidene fluoride (PVDF) was used as the binder. The positive electrode active material, acetylene black, binder, and NMP as the solvent were mixed to prepare a slurry. The weight ratio of the positive electrode active material:AB:PVDF was 90:5:5.

[0337] The separator used was a porous polypropylene film with a thickness of 25 μm, a Gurley value of 200 seconds based on JIS, and a porosity (calculated value) of 55%. The lithium salt was 1 mol of LiPF per 1 liter of the mixed solvent. ６ The mixed solvent used was EC:DEC=3:7 (volume ratio), and 2 wt % of VC was added as an additive to the mixed solvent in which the lithium salt was dissolved, to prepare an electrolyte solution.

[0338] A carbon-coated aluminum foil was used as a positive electrode current collector, and the slurry was applied to the positive electrode current collector. The amount of the positive electrode active material supported was 5 mg / cm. ２ After the solvent was removed by drying, the mixture was pressed at 210 kN / m and 120°C.

[0335] Table 24 summarizes the conditions of the positive electrode for each sample.

[0336]

[0339] The conditions for the charge-discharge cycle test will be described below. Each sample was placed in a thermostatic chamber maintained at 25°C, and a cycle under the following charge-discharge conditions was repeated 100 times. Charge conditions: CCCV charge, 0.5C rate, 4.5V, 0.05C cutoff. Discharge conditions: CC discharge, 0.5C rate, 2.5V cutoff. In this charge-discharge cycle test, the current value corresponding to 1C was 170mA / g per weight of positive electrode active material. After charging, a 10-minute rest period was provided before the next discharge.

[0340] <Charge-Discharge Cycle Test of Samples A to E, and Sample ref> Figure 24 shows the results of the charge-discharge cycle test of Samples A to E, and Sample ref, with the horizontal axis representing the number of cycles (times) and the vertical axis representing the discharge capacity (mAh / g). Figure 25 shows the results of the charge-discharge cycle test of Samples A to E, and Sample ref, with the horizontal axis representing the number of cycles (times) and the vertical axis representing the discharge energy density (mWh / g). The discharge energy density corresponds to the discharge capacity multiplied by the discharge voltage. Figure 26 shows the results of the charge-discharge cycle test of Samples A to E, and Sample ref, with the horizontal axis representing the number of cycles (times) and the vertical axis representing the coulombic efficiency (% g).

[0341] All the samples exhibited better battery characteristics than the comparative example. Specifically, as shown in FIG. 24, the samples exhibiting better discharge characteristics than the comparative example were those with a composition of LiMn （０．９−ｘ） Fe ０．１ Mg ｘ P.O. ４ (0.02≦x<0.1), preferably LiMn （０．９−ｘ） Fe ０．１ Mg ｘ P.O. ４ (0.02≦x≦0.05), preferably LiMn （０．９−ｘ） Fe ０．１ Mg ｘ P.O. ４ (x=0.03 or its vicinity, "nearby" means 0.8 times or more and 1.2 times or less). Also, from FIG. 25, it was found that the composition of LiMn （０．９−ｘ） Fe ０．１ Mg ｘ P.O. ４ (0.02≦x<0.1), preferably LiMn （０．９−ｘ） Fe ０．１ Mg ｘ P.O. ４ (0.02≦x≦0.05), preferably LiMn （０．９−ｘ） Fe ０．１ Mg ｘ P.O. ４ (x=0.03 or its vicinity, "nearby" refers to 0.8 times or more and 1.2 times or less). Also, from FIG. 26, it was found that the composition of LiMn （０．９−ｘ） Fe ０．１ Mg ｘ P.O. ４ (0.02≦x<0.1), preferably LiMn （０．９−ｘ） Fe ０．１ Mg ｘ P.O. ４ (x=0.1 or its vicinity, "nearby" means 0.8 times or more and 1.2 times or less), or LiMn （０．９−ｘ） Fe ０．１ Mg ｘ P.O. ４ (x=0.03 or its vicinity, "nearby" refers to 0.8 times or more and 1.2 times or less).

[0342] FIG. 27 shows the charge / discharge curves of Sample C, with the horizontal axis representing capacity (mAh / g) and the vertical axis representing voltage (V). FIG. 27 shows charge and discharge curves corresponding to the first cycle (1st), the 50th cycle (50th), and the 100th cycle (100th). No plateau voltage was observed in the discharge curve of Sample C at any of the cycles. The absence of a plateau voltage is desirable because it facilitates circuit design, such as a protection circuit, for controlling a lithium-ion battery containing Sample C.

[0343] <Charge-Discharge Cycle Test of Samples F to J, and Sample ref> Figure 28 shows the results of the charge-discharge cycle test of Samples F to J, and Sample ref, with the horizontal axis representing the number of cycles (times) and the vertical axis representing the discharge capacity (mAh / g). Figure 29 shows the results of the charge-discharge cycle test of Samples F to J, and Sample ref, with the horizontal axis representing the number of cycles (times) and the vertical axis representing the discharge energy density (mWh / g). The discharge energy density corresponds to the discharge capacity multiplied by the discharge voltage. Figure 30 shows the results of the charge-discharge cycle test of Samples F to J, and Sample ref, with the horizontal axis representing the number of cycles (times) and the vertical axis representing the Coulomb efficiency (% g).

[0344] All the samples exhibited better battery characteristics than the comparative example. Specifically, as shown in FIG. 28, the samples exhibiting better discharge characteristics than the comparative example were those with a composition of LiMn （０．９−ｘ） Fe ０．１ Zn ｘ P.O. ４ (0.02≦x<0.1), preferably LiMn （０．９−ｘ） Fe ０．１ Zn ｘ P.O. ４ (0.02≦x≦0.05), preferably LiMn （０．９−ｘ） Fe ０．１ Zn ｘ P.O. ４ (x=0.03 or its vicinity, "nearby" means 0.8 times or more and 1.2 times or less). Also, from FIG. 29, it was found that the material having a composition of LiMn （０．９−ｘ） Fe ０．１ Zn ｘ P.O.４ (0.02≦x<0.1), preferably LiMn （０．９−ｘ） Fe ０．１ Zn ｘ P.O. ４ (0.02≦x≦0.05), preferably LiMn （０．９−ｘ） Fe ０．１ Zn ｘ P.O. ４ (x=0.03 or its vicinity, "nearby" means 0.8 times or more and 1.2 times or less). Also, from FIG. 30, the material showing a superior coulomb efficiency to the comparative example is a material having a composition of LiMn （０．９−ｘ） Fe ０．１ Zn ｘ P.O. ４ (0.02≦x≦0.1), preferably LiMn （０．９−ｘ） Fe ０．１ Zn ｘ P.O. ４ (x=0.1 or its vicinity, "nearby" means 0.8 times or more and 1.2 times or less), or LiMn （０．９−ｘ） Fe ０．１ Zn ｘ P.O. ４ (x=0.03 or its vicinity, "nearby" refers to 0.8 times or more and 1.2 times or less).

[0345] FIG. 31 shows the charge / discharge curves of Sample H, with the horizontal axis representing capacity (mAh / g) and the vertical axis representing voltage (V). FIG. 31 shows charge and discharge curves corresponding to the first cycle (1st), the 50th cycle (50th), and the 100th cycle (100th). No plateau voltage was observed in the discharge curve of Sample H at any of the cycles. The absence of a plateau voltage is desirable because it facilitates circuit design, such as a protection circuit, for controlling a lithium-ion battery containing Sample H.

[0346] <XRD during charging> A new sample C was prepared, and a coin cell C equivalent to sample C was prepared. A new sample H was prepared, and a coin cell H equivalent to sample H was prepared. A new sample ref was prepared, and a coin cell ref equivalent to sample ref was prepared. The coin cell conditions were the same as those used to measure the charge-discharge characteristics. The XRD test during charging will be explained using coin cell C, coin cell H, and coin cell ref.

[0347] For each coin cell, XRD measurements were performed during discharge and during charge. XRD measurements during discharge were performed on the coin cell in a discharged state at the end of aging, and XRD measurements during charge were performed on the coin cell in a charged state after aging.

[0348] The aging conditions and the charging conditions after aging were as follows: Charging conditions for aging: CCCV charging, 0.1C rate, 4.5V, 0.01C cutoff Discharging conditions for aging: CC discharge, 0.1C rate, 2.5V cutoff Charging conditions after aging: CCCV charging, 0.1C rate, 4.5V, 0.01C cutoff Under these conditions, the current value corresponding to 1C was 170mA / g per weight of positive electrode active material. During aging, a 10-minute rest period was provided after charging before the next discharge, and charging and discharging were repeated twice.

[0349] The XRD conditions were as follows: XRD device: D8 ADVANCE manufactured by Bruker AXS X-ray: CuKα ray output: 40 kV, 40 mA Detector: LYNXEYE XE-T Scan method: 2θ / θ continuous scan Measurement range (2θ): 15° to 75° increment: 0.01° Counting time: 1 sec / step Sample stage rotation: 15 rpm Sample setting: Measurement was performed by placing a charged or discharged coin cell in a ufocell. 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

[0350] Each coin cell in the discharged state was disassembled, the positive electrode was removed, and the removed positive electrode was placed in a Ufosell. Similarly, each coin cell in the charged state was disassembled, the positive electrode was removed, and the removed positive electrode was placed in a Ufosell. In both states, the coin cells were disassembled in a glove box with an argon atmosphere, and the positive electrode was placed in a Ufosell within the glove box. The Ufosell was thoroughly dried. The time from placing the positive electrode to XRD measurement was within 30 minutes.

[0351] The obtained XRD profile was analyzed using CuKα ２The line peaks were removed and background correction was performed. For the XRD profile after charging, literature values ​​for iron phosphate ICSD Coll. Code. 92199 and aluminum ICSD Coll. Code. 18839 were used, and the XRD profile after charging was fitted with two phases of iron phosphate and aluminum. For the XRD profile after discharge, literature values ​​for lithium iron phosphate ICSD Coll. Code. 72545 and aluminum ICSD Coll. Code. 18839 were used, and the XRD profile after discharge was fitted with two phases of lithium iron phosphate and aluminum. Aluminum is a component of the current collector. The XRD profile was subjected to Rietveld analysis using the analysis software DIFFRAC. TOPAS ver. 6 to determine the lattice constant.

[0352] The lattice constants in the charged state and in the discharged state after aging were measured. The results are shown in the table below. In coin cell C and coin cell H, the a-axis length [Å], b-axis length [Å], and c-axis length [Å] were approximately the same as those of coin cell ref. In other words, the addition of Mg and Zn did not change the lattice constants in the charged state or the discharged state.

[0353]

[0354] Next, the ratios of the lattice constant in the discharged state to the lattice constant in the charged state were calculated, and these values ​​were designated as the a-axis change percentage [%], b-axis change percentage [%], and c-axis change percentage [%], respectively. The results are shown in the table below. In coin cell C and coin cell H, the a-axis change percentage [%], b-axis change percentage [%], and c-axis change percentage [%] were approximately the same as those in coin cell ref. In other words, the addition of Mg and Zn did not change the a-axis change percentage [%], b-axis change percentage [%], and c-axis change percentage [%].

[0355]

[0356] 100: positive electrode active material, 101: primary particles, 101a: primary particles, 101b: primary particles, 101c: primary particles

Claims

1. A lithium ion battery having a positive electrode, the positive electrode has a positive electrode active material, the positive electrode active material has an olivine-type crystal structure, In the positive electrode active material, the atomic ratio of manganese to the sum of the atomic ratios of manganese, iron, and the additive element is 0.7 or more, In the positive electrode active material, the atomic ratio of the additional element to the sum of the atomic ratios of manganese and the additional element is 0.02 or more and less than 0.1, A lithium ion battery, wherein the additive element is a divalent cation.

1. A lithium ion battery having a positive electrode, the positive electrode has a positive electrode active material, the positive electrode active material has an olivine-type crystal structure, In the positive electrode active material, the atomic ratio of manganese to the sum of the atomic ratios of manganese, iron, and magnesium is 0.7 or more, a ratio of the number of atoms of magnesium to the sum of the number of atoms of manganese and magnesium in the positive electrode active material is 0.02 or more and less than 0.1; 　 1. A lithium ion battery having a positive electrode, the positive electrode has a positive electrode active material, the positive electrode active material has an olivine-type crystal structure, In the positive electrode active material, the atomic ratio of manganese to the sum of the atomic ratios of manganese, iron, and zinc is 0.7 or more, a ratio of the number of atoms of zinc to the sum of the number of atoms of manganese and zinc in the positive electrode active material of the lithium ion battery, the ratio being 0.02 or more and less than 0.

08. In any one of claims 1 to 3, The olivine-type crystal structure belongs to the space group Pnma. 　 In claim 2, When the positive electrode active material was placed at 23°C ± 5°C and an XRD profile obtained by a diffraction method was subjected to Rietveld analysis, The olivine-type crystal structure, the lattice constant of the a-axis is greater than 10.4039 Å and less than or equal to 10.4319 Å; the b-axis lattice constant is greater than 6.0749 Å and less than or equal to 6.0911 Å; A lithium-ion battery having a c-axis lattice constant greater than 4.7346 Å and less than or equal to 4.7380 Å. 　 In claim 2, The lithium ion battery, wherein the olivine-type crystal structure has a crystallite size L Vol -IB of 71.7 nm or more and 74.6 nm or less. 　 In claim 3, When the positive electrode active material was placed at 23°C ± 5°C and an XRD profile obtained by a diffraction method was subjected to Rietveld analysis, The olivine-type crystal structure, the lattice constant of the a-axis is 10.4087 Å or more and 10.4325 Å or less, the lattice constant of the b axis is 6.0764 Å or more and 6.0915 Å or less; A lithium-ion battery having a c-axis lattice constant of 4.7361 Å or more and 4.7385 Å or less. 　 In claim 3, The lithium ion battery, wherein the olivine-type crystal structure has a crystallite size L Vol -IB of 68.5 nm or more and 71.8 nm or less.

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