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 lithium manganese iron phosphate having 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 an additive element is 0.7 or more; in the positive electrode active material, the atomic ratio of the additive element to the sum of the atomic ratios of manganese, iron, and the additive element is 0.02 to 0.2 (exclusive of 0.2); and the additive element has only an oxidation number of +2.

Description

Lithium-ion battery

[0001] One aspect 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 any one of semiconductor devices, display devices, light-emitting devices, energy storage devices, lighting devices, electronic devices, and vehicles can be listed as the technical field of the present invention. For example, the lithium-ion battery of the present invention can be applied as a necessary power source in semiconductor devices, display devices, light-emitting devices, lighting devices, electronic devices, and vehicles. Furthermore, methods for manufacturing the above-mentioned items can be listed as the technical field of the present invention. The above-mentioned electronic devices include information terminal devices equipped with lithium-ion batteries.

[0002] High-power, high-energy-density lithium-ion batteries have become indispensable to 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 = one of Fe, Mn, Ni, or Co). Among these, LiFePO ４ It has already been able to achieve a charge / discharge capacity close to the theoretical capacity (170 mAh / g) (for example, Non-Patent Document 1). However, LiFePO ４ As shown in Non-Patent Document 1 above, the operating voltage is approximately 3.4V (vs. Li / Li ＋ ) is low, and the operating voltage of lithium-ion batteries with other cathode active materials that are in practical use, such as lithium nickel manganese cobalt oxide (NMC), is about 4.2V (vs. Li / Li ＋ A challenge is that the energy density is lower compared to olivine-type crystal structure LiFePO ４ LiCoO has a layered rock salt-type crystalline structure. ２Since it is more stable and less likely to deteriorate, it has excellent charge-discharge cycle characteristics and good thermal stability. Also, since it does not use high-cost metals such as Co or Ni, it can be manufactured at a low cost. In view of such advantages, a lithium-ion battery having LiFePO ４ is being mounted as a power source in EVs and the like.

[0004] To improve the low energy density, materials such as a solid solution of LiFePO ４ and LiMnPO ４ LiMn ｘ Fe １−ｘ PO ４ (0 < x < 1) are being studied. The above solid solution is obtained by substituting Fe with Mn. Since Mn has a weaker ionic bond than Fe, an increase in the operating voltage is expected. However, increasing the proportion of Mn in the above solid solution increases the operating voltage, but the portion that cannot contribute to charge-discharge increases, and there is concern that the discharge capacity will be lower than that of LiFePO ４ . In LiMn ｘ Fe １−ｘ PO ４ (0 < x < 1), it is known that the lithium-ion insertion / desorption reaction is a two-phase coexistence reaction, and it is considered that the phase boundary moves rapidly and the entire crystal undergoes a phase change. At this phase boundary, strain occurs due to the volume difference between the crystal structures in the lithium-ion insertion state and the lithium-ion desorption state, and the activation barrier of the phase boundary becomes high, which raises concern about the deterioration of battery characteristics.

[0005] To improve the concerns of the above solid solution, materials such as LiFe ａ Mn ｂ M ｃ PO ４ (M represents Mg, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd or Gd) are being studied, and in Patent Document 1, LiFe ０．１ Mn ０．８ Mg ０．１ PO ４ carrying carbon is described.

[0006] WO2016 / 047491 Gazette

[0007] A. Yamada, S. C. Chung and K. Hinokuma, “Optimized LiFePO▲4▼ for Lithium Battery Cathodes”, J. Electrochem. Soc. , 148, A224-229 (2001).

[0008] LiFe having an olivine-type crystal structure ａ Mn ｂ M ｃ PO ４ While positive electrode active materials such as (where M represents Mg, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd) are disclosed in Patent Document 1, there is room for consideration regarding the optimal ratio of the element corresponding to M in order to achieve a higher energy density. Furthermore, there is room for consideration regarding the optimal ratio of the element corresponding to M in order to achieve an excellent discharge capacity.

[0009] Therefore, one aspect of the present invention aims to provide a lithium-ion battery using a positive electrode active material with high energy density. Another aspect of the present invention aims to provide a lithium-ion battery using a positive electrode active material that exhibits excellent discharge capacity.

[0010] Furthermore, the description of these problems does not preclude the existence of other problems. Moreover, one aspect of the present invention does not need to solve all of these problems. It is possible to extract other problems from the description, drawings, and claims.

[0011] To solve the above problems, one aspect of the present invention is a lithium-ion battery having a positive electrode, wherein the positive electrode has a positive electrode active material, the positive electrode active material has manganese iron lithium phosphate with an olivine-type crystal structure, the atomic ratio of manganese to the sum of the atomic ratios of manganese, iron, and additive elements in the positive electrode active material is 0.7 or more, the atomic ratio of the additive elements to the sum of the atomic ratios of manganese, iron, and additive elements in the positive electrode active material is 0.02 or more and less than 0.2, and the additive elements only have an oxidation state of +2.

[0012] In the present invention, it is preferable that the additive elements are two or more selected from Mg, Zn, Ca, Sr, Ba, Pb, and Eu.

[0013] In the present invention, the olivine-type crystal structure is preferably assigned to the space group Pnma.

[0014] In the present invention, when Rietveld analysis is performed on an XRD profile obtained by diffraction with the positive electrode active material placed at 23°C ± 5°C, it is preferable that the lattice constant of the a-axis of the olivine-type crystal structure is greater than 10.3729 Å and less than 10.4355 Å, the lattice constant of the b-axis is greater than 6.0564 Å and less than 6.0934 Å, and the lattice constant of the c-axis is greater than 4.7302 Å and less than 4.7387 Å.

[0015] In the present invention, the olivine-type crystal structure is preferably such that the crystallite size LVol-IB is 59.3 nm or more and less than 83.2 nm.

[0016] According to one aspect of the present invention, a lithium-ion battery can be provided using a positive electrode active material with high energy density. Furthermore, according to another aspect of the present invention, a lithium-ion battery can be provided using a positive electrode active material exhibiting excellent discharge capacity.

[0017] Furthermore, the description of these effects does not preclude the existence of other effects. Moreover, one aspect of the present invention does not necessarily have to possess all of these effects. It is possible to extract other effects from the description in the specification, drawings, claims, etc.

[0018] Figures 1A to 1D illustrate a positive electrode active material according to one embodiment of the present invention. Figure 2 illustrates an example of a method for producing a positive electrode active material according to one embodiment of the present invention. Figures 3A to 3C illustrate a lithium-ion battery according to one embodiment of the present invention. Figures 4A to 4C illustrate an electric vehicle according to one embodiment of the present invention. Figures 5A to 5E illustrate a vehicle, etc., according to one embodiment of the present invention. Figures 6A to 6D illustrate an electronic device, etc., according to one embodiment of the present invention. Figures 7A and 7B are graphs of lattice constant and additive element concentration. Figure 8 shows the charge-discharge cycle test results of the example.

[0019] Embodiments of the present invention will be described with appropriate use of the drawings. However, it will be readily apparent to those skilled in the art that the present invention is not limited to the following description, and that its form and details can be modified in various ways without departing from the spirit and scope of the present invention. Accordingly, in the embodiments of the present invention shown below, the same reference numerals will be common to different drawings.

[0020] LiMn （１−ｄ） Fe ｄ PO ４ (0 < d < 1) is generally referred to as LMFP, but can be referred to by changing the order, such as LFMP. In this specification, LiMn （１−ｄ−ｅ） Fe ｄ M ｅ PO ４ The function (0 < d < 1, 0 < e < 1) is called LMFMP when Mg is used for M, but it can also be called LFMMP, etc., by changing the order. Similarly, LiMn （１−ｄ−ｅ） Fe ｄ M ｅ PO ４ The compound (0 < d < 1, 0 < e < 1) is called LMFZP when Zn is used for M, but it can also be called LFMZP, etc., by changing the order. Similarly, when two elements, Mg and Zn, are used for M, it is called LMFMZP, but it can also be called LFMMZP, etc., by changing the order.

[0021] In this specification, the ordinal numbers "first," "second," etc., are used for convenience only and do not limit the number of components or the order of components. The order of components includes, for example, the order of processes or the order of stacking. That is, the ordinal numbers used in the embodiments of this specification may not match the ordinal numbers used in the claims. Also, the ordinal numbers used in the examples of this specification may not match the ordinal numbers used in the claims. Also, the ordinal numbers used in the embodiments of this specification may not match the ordinal numbers used in the examples of this specification.

[0022] 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 in this invention are not limited to lithium ions. For example, alkali metal ions or group 2 element ions can be used as carrier ions in this invention, and specifically, sodium ions, etc., can be applied. In this case, the present invention can be understood by substituting lithium ions with sodium ions, etc. Furthermore, when describing a configuration in which there are no limitations on the carrier ions, it may be written as a secondary battery or battery.

[0023] In this specification, the term "electrolyte" may be used interchangeably with "electrolyte." "Electrolyte" means that the solution is liquid at 25°C. Furthermore, "electrolyte" is not limited in any way to its state at 25°C.

[0024] In this specification, space groups are expressed using international notation (or Hermann-Mauguin notation) in short notation. Crystal planes and crystal directions are expressed using Miller indices. In crystallography, space groups, crystal planes, and crystal directions are expressed by superscripting numbers, but in this specification, due to formatting constraints, a minus sign (-) may be placed before the number instead of a superscript. Individual orientations indicating directions within a crystal are represented by [ ], collective orientations indicating all equivalent directions are represented by < >, individual crystal planes are represented by ( ), and collective planes with equivalent symmetry are represented by {}. Furthermore, for ease of understanding the structure, trigonal crystals represented by space group R-3m are generally represented as a composite hexagonal lattice, and in this specification, unless otherwise specified, space group R-3m will be represented as a composite hexagonal lattice. In addition, (hkl) as well as (hkil) may be used as Miller indices. Here, i is -(h+k).

[0025] In this specification, space groups are identified by XRD, electron diffraction, neutron diffraction, etc. Therefore, in this specification, "belonging to a space group," "being part of a space group," or "being a space group" can be rephrased as "being identified to a space group."

[0026] In this specification, the term "particle" is not limited to a so-called spherical shape with a circular cross-section. The cross-sectional shape of a particle may include an ellipse, rectangle, trapezoid, triangle, square with rounded corners, asymmetrical shapes, etc., and if there are multiple particles, their cross-sectional shapes may differ.

[0027] In this specification, the positive electrode active material particles have a surface layer and an interior (also called the bulk). The surface layer is, for example, the region from the surface up to 60 nm, and the interior is the region deeper than the surface layer.

[0028] In this specification, when describing the individual characteristics of positive electrode active material particles in embodiments, it is not necessarily required that all particles possess those characteristics. For example, if 50% or more, preferably 66% or more, and more preferably 90% or more of three or more randomly selected positive electrode active material particles possess those characteristics, it can be said that this is sufficient to improve the properties of the positive electrode active material particles and the secondary battery having them.

[0029] In this specification, particle size can be measured using a particle size analyzer (laser diffraction particle size distribution analyzer) or the like. In this specification, the median diameter (D50) can be used as the average particle size. D50 is the particle size at which its cumulative frequency accounts for 50% in the cumulative curve of the particle size distribution measurement results.

[0030] In this specification, particle size measurement is not limited to laser diffraction particle size distribution measurement, but may also be measured by measuring the major axis of the particle cross-section using analysis such as SEM (Scanning Electron Microscope) or TEM. In this specification, the maximum particle size can be defined as the particle size that can be confirmed in one cross-section of a 100 μm square positive electrode. Furthermore, as a method for measuring D50 from analysis such as SEM or TEM, for example, 20 or more particles can be measured, a cumulative curve can be created, and the particle size at which the cumulative frequency accounts for 50% can be defined as D50.

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

[0032] This section explains the flow of electrons and lithium ions during charging in a lithium-ion battery. When a charger is connected and charging of the secondary battery begins, electrons are released at the positive electrode, causing an oxidation reaction, and electrons are supplied at the negative electrode, causing a reduction reaction. Lithium ions are then released from the positive electrode into the electrolyte, and 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 and cathode are swapped during discharge and charging, and the oxidation and reduction reactions are swapped. Therefore, the electrode with the higher reaction potential is called the positive electrode, and the electrode with the lower reaction potential is called the negative electrode. Accordingly, in this specification, the positive electrode is referred to as the "positive electrode" and the negative electrode as the "negative electrode," regardless of whether it is charging or discharging. Using the terms anode and cathode in relation to oxidation or reduction reactions could lead to confusion, as they are reversed between charging and discharging. Therefore, the terms anode and cathode shall not be used in this specification or elsewhere.

[0033] In this specification, a full cell means a cell assembled so that different electrodes are located, such as a positive electrode / negative electrode unit cell. In this specification, a half cell means a cell assembled using lithium metal as the negative electrode (counter electrode).

[0034] In this specification, secondary particles refer to particles formed by the aggregation of primary particles. In particular, secondary particles refer to particles that are formed when primary particles aggregate, adhere to, or sinter so as to share a portion of the grain boundary (the outer circumference of the primary particle), and that do not separate easily. In this specification, primary particles may be referred to as single particles.

[0035] In this specification, the phrase "A and / or B" may be used, but this refers to "A," "B," or "A and B."

[0036] (Embodiment 1) In this embodiment, the features of the positive electrode active material 100 according to one aspect of the present invention will be described with reference to Figures 1A to 1D.

[0037] One embodiment of the present invention is a positive electrode active material 100 which is manganese iron lithium phosphate having an olivine-type crystal structure and is characterized by having two or more additive elements in addition to lithium, manganese, iron, phosphorus, and oxygen. The presence of additive elements makes the positive electrode active material 100 preferable because it exhibits excellent energy density or excellent discharge capacity.

[0038] Examples of additive elements include those that become divalent cations or divalent ions when dissolved in the positive electrode active material 100, that is, elements that do not take on any valency other than divalent. In other words, examples of additive elements include those that only take on an oxidation state of +2. For example, two or more elements selected from Mg, Zn, Ca, Sr, Ba, Pb, and Eu can be used as additive elements. It is preferable that the additive elements are dissolved in the manganese sites and iron sites of the crystal structure of the positive electrode active material, and therefore, in this invention, it is particularly preferable to use Mg and Zn as additive elements. The additive elements may also be dissolved in the lithium sites.

[0039] The olivine-type crystal structure of the positive electrode active material 100 is orthorhombic (also called orthorhombic) and belongs to space group Pnm (No. 62). In the positive electrode active material 100 using two or more elements selected from Mg, Zn, Ca, Sr, Ba, Pb, and Eu as additive elements, lithium, manganese, iron, Mg, Zn, Ca, Sr, Ba, Pb, and Eu are present at octahedral sites, and phosphorus is present at tetrahedral sites. In the positive electrode active material 100 using Mg and Zn as particularly preferred additive elements, lithium, manganese, iron, magnesium, and zinc are present at octahedral sites, and phosphorus is present at tetrahedral sites.

[0040] The positive electrode active material 100 may have defects such as deficiencies in cations or anions. The composition of the positive electrode active material 100 is not strictly limited to Li:(Mn+Fe+Mg+Zn):P:O=1:1:1:4 (atomic ratio).

[0041] In the positive electrode active material 100, the atomic ratio of manganese (Mn / (Mn+Fe+Mg+Zn)) to the sum of the atomic ratios of manganese, iron, magnesium, and zinc is preferably 0.7 or higher, and more preferably 0.8 or higher.

[0042] In the positive electrode active material 100, if the atomic ratio of magnesium and zinc (Mg + Zn / (Mn + Fe + Mg + Zn)) in relation to the sum of the atomic ratios of manganese, iron, magnesium, and zinc satisfies the conditions of 0.02 or more and less than 0.2, or 0.02 or more and 0.1 or less, the discharge capacity of the secondary battery can be increased.

[0043] When Mg and Zn are used as additive elements, the positive electrode active material 100 is LiMn （０．９−ｘ） Fe ０．１ Mg ｙ Zn ｚ PO ４ (x = y + z) where x is between 0.02 and less than 0.2, for example, y is between 0.01 and less than 0.19, and z is between 0.01 and less than 0.19. Preferably, x is between 0.02 and 0.1, y is between 0.01 and 0.05, and z is between 0.01 and 0.05.

[0044] Furthermore, the added elements do not contribute to charge compensation during charging and discharging. While Mg and Zn are used as examples to explain why they do not contribute to charge compensation, the stable oxidation state of Mg and Zn in the compound is 2. Charge compensation associated with the insertion and removal of lithium, a monovalent cation, requires a change of 1 in valency, for example, between 2 and 3. Therefore, lithium around Mg and Zn may be difficult to insert and remove. For this reason, it is preferable to set an upper limit on the concentration of the added elements. However, there is a possibility that lithium can be inserted and removed by the oxidation of manganese around Mg and Zn to tetravalent, and in this case, the adverse effect on the lithium diffusion pathway is minimal, so the upper limit on the concentration of the added elements is not limited. Alternatively, the upper limit on the concentration of the added elements may be the solid solubility limit of the added element.

[0045] The lattice constants (a, b, c) of the olivine-type crystal structure change according to the proportion of the added element in solid solution, that is, 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.

[0046] When Rietveld analysis was performed on the XRD profile obtained by diffraction for the positive electrode active material 100 using Mg and Zn as additive elements, it was determined to have an olivine-type crystal structure and belong to space group Pnm (No. 62). Furthermore, the positive electrode active material 100 having Mg and Zn that satisfy the above concentration range satisfies the following conditions according to the Rietveld analysis: the lattice constant of the a-axis is greater than 10.3729 Å and less than 10.4355 Å; the lattice constant of the b-axis is greater than 6.0564 Å and less than 6.0934 Å; and the lattice constant of the c-axis is greater than 4.7302 Å and less than 4.7387 Å. Based on the characteristics of the secondary battery having the positive electrode active material 100, more preferable ranges for each lattice constant are shown in the examples.

[0047] Furthermore, since the changes in the lattice constants of the a-axis, b-axis, and c-axis in response to changes in the concentration of the added element follow Vegard's law, it can be said that magnesium or zinc is solid-dissolved in the positive electrode active material 100.

[0048] LiMn （１−ｄ） Fe ｄ PO４ Manganese and iron in (0 < d < 1) are Mn ２＋ and Fe ２＋ It exists as such. When lithium ions are released, Mn （１−ｄ） Fe ｄ PO ４ (0 < d < 1), and in this case, manganese and iron are Mn ３＋ and Fe ３＋ It exists as such. The lithium ion insertion and deinsertion reaction of olivine-type cathode active materials is known to be a two-phase coexistence reaction, and it is thought that the phase boundary rapidly shifts, causing a phase change throughout the entire crystal. At this phase boundary, strain occurs due to the volume difference between the crystal structure of the lithium ion insertion state and the lithium ion deinsertion state.

[0049] This volume difference is due to the lithium ion insertion state of Mn ２＋ and Fe ２＋ Therefore, Mn in the lithium-ion desorbed state ３＋ and Fe ３＋ This is due to the smaller ionic radius. Furthermore, it is thought that not only the change in ionic radius but also the strain due to the Jahn-Teller effect of manganese is influencing the result. Olivine-type LiMn （１−ｄ） Fe ｄ PO ４ The Fe and Mn present in (0 < d < 1) are arranged in an octahedral configuration and have high spin, and Fe ２＋ (3d ６ ), Fe ３＋ (3d ５ ) and Mn ２＋ (3d ５ ) The Jahn-Teller effect is weak or absent in all of these cases. However, Mn ３＋ (3d ４ ) has a strong Jahn-Teller effect and the octahedron is greatly distorted. Therefore, the deformation of the octahedron in manganese during the change from divalent to trivalent is greater than that of iron. Therefore LiFePO ４ LiMnPO, which contains manganese ４ and LiMn （１−ｄ） Fe ｄ PO ４ In the case of (0 < d < 1), the volume difference before and after lithium insertion / deinsertion is large, and the activation barrier at the phase boundary is likely to be a problem.

[0050] Therefore, it is preferable to solid-solve an additive element in the Mn and Fe sites that can suppress the volume difference before and after lithium ion insertion and deinsertion. For this reason, the ionic radius of the additive element is such that when solid-solved, it is Mn ２＋ (High spin) and Fe ２＋ Smaller than (high spin), Mn ３＋ (High spin) and Fe ３＋ (High spin) is preferable. Furthermore, manganese and iron during synthesis are Mn ２＋ (High spin) and Fe ２＋ Because it is (high spin), it is preferable that the added element is also a divalent cation when it is dissolved in solid solution.

[0051] Mg and Zn satisfy all of these characteristics and, furthermore, are not transition metals, do not produce the Jahn-Teller effect, making them preferable as additive elements.

[0052] Furthermore, it is preferable that Mg and Zn are homogeneously distributed in the bulk. When observing multiple particles using STEM-EDX analysis, it is possible to confirm that Mg and Zn are uniformly present in the cross-section of the bulk. The homogeneous distribution of Mg and Zn within the bulk ensures that Li during charging and discharging ＋ Charge fluctuations within the bulk due to desorption / insertion can be distributed more uniformly to Mn and Fe. In addition, since Mg and Zn do not segregate on the particle surface, Li ＋ This provides the benefit of being less likely to obstruct the diffusion pathway.

[0053] When two or more additive elements are present in the positive electrode active material 100, the reactivity improves and solid solution becomes easier. For this reason, the positive electrode active material 100 contains two or more additive elements.

[0054] <Shape> The positive electrode active material 100 is preferably a secondary particle having a plurality of primary particles 101, as shown in Figure 1A. In this specification, secondary particles refer to aggregates of a plurality of primary particles, fixed primary particles, sintered primary particles, or a collection of a plurality of these.

[0055] Furthermore, it is preferable that the primary particles 101 of the positive electrode active material 100 are single crystals. For example, if the grain boundaries of the primary particles that can be observed by SEM coincide with the region of the crystal orientation mapping that can be captured by electron backscatter diffraction (EBSD), it can be determined that the primary particles 101 are single crystals.

[0056] Furthermore, it is preferable that the positive electrode active material 100 is carbon-coated, and more preferably that each primary particle 101 is carbon-coated. The carbon coating enhances the conductivity of the positive electrode active material 100 and suppresses the resistance of the secondary battery. The carbon coating is a film containing carbon, and it is preferable that the film has low crystallinity, specifically amorphous. The carbon coating is included in the positive electrode active material.

[0057] Figure 1A shows an example where the primary particles 101 are spherical or elongated spheres, but the present invention is not limited to these. For example, as shown in Figure 1B, the positive electrode active material 100 may have distorted spherical primary particles 101a. Also, as shown in Figure 1C, the positive electrode active material 100 may have flat or substantially plate-shaped primary particles 101b. Also, as shown in Figure 1D, the positive electrode active material 100 may have needle-shaped primary particles 101c.

[0058] In order to reduce the diffusion resistance of lithium ions, it is preferable that the primary particle size and crystallite size of the positive electrode active material 100 be similarly small. The crystallite size can be obtained from Rietveld analysis, and the powder subject to XRD measurement may be either primary or secondary particles. Furthermore, the crystallite size can also be determined from an electrode sheet containing powder as the XRD measurement target. The crystallite size can be obtained from Rietveld analysis, and it is preferable to use the LVol-IB value. For example, when Rietveld analysis is performed on the XRD profile obtained by diffraction, the crystallite size of the olivine-type crystal structure of the positive electrode active material 100 is preferably between 10 nm and 90 nm.

[0059] <Analysis> <Composition> The composition of the positive electrode active material 100 according to one embodiment of the present invention can be determined by, for example, ICP-MS (Inductively Coupled Plasma Mass Spectrometry). If necessary, it is also possible to evaluate the composition by combining multiple quantitative and semi-quantitative analyses such as X-ray fluorescence spectroscopy, GD-MS (Glow Discharge Mass Spectrometry), EDX (Energy Dispersive X-ray Spectroscopy), and EPMA (Electron Probe Microanalyzer) in addition to ICP-MS.

[0060] <ICP-MS Analysis> For ICP-MS analysis, for example, an Agilent 8900 triple quadrupole ICP-MS from Agilent Technologies can be used. For example, ICP-MS can be performed as follows: First, prepare a sample of approximately 20 mg to 80 mg of positive electrode active material particles and dissolve it using a decomposition reagent as a pretreatment. For example, nitric acid can be used as this decomposition reagent. Measure the decomposed sample in quantitative analysis mode. This makes it possible to measure the elemental composition contained in the particles.

[0061] <STEM-EDX Radiation Analysis> STEM-EDX radiation analysis can be performed, for example, as follows: First, a protective film is deposited on the surface of the positive electrode active material particles. For example, carbon can be deposited using an ion sputtering apparatus (Hitachi High-Tech MC1000).

[0062] Next, the positive electrode active material particles are thinned to prepare a STEM cross-sectional sample. For example, thinning can be performed using a FIB-SEM device (Hitachi High-Tech XVision 200TBS). In this case, pickup is performed using an MPS (microprobing system), and the finishing conditions can be set to, for example, an acceleration voltage of 10kV.

[0063] STEM-EDX ray analysis can be performed using, for example, a STEM instrument (Hitachi High-Tech HD-2700) and an EDAX Octane T Ultra W EDX detector. An example of the conditions for EDX ray analysis using the Hitachi High-Tech HD-2700 is to set the emission current of the STEM instrument to 6 μA to 10 μA and measure areas of the thinned sample with little depth and unevenness. The magnification can be, for example, around 150,000x. The conditions for EDX ray analysis can be drift-corrected, with a line width of 42 nm, a pitch of 0.2 nm, and 6 or more frames.

[0064] To achieve high spatial resolution in STEM-EDX ray analysis, it is preferable to have a small electron beam diameter (also called beam diameter, probe diameter, or probe diameter). In STEM-EDX ray analysis, the beam diameter is preferably 0.3 nm or less, more preferably 0.2 nm or less, and even more preferably 0.1 nm or less. Furthermore, to increase the analytical sensitivity in STEM-EDX ray analysis, it is preferable to increase the electron beam current (also called probe current). Therefore, it is preferable that the apparatus used for STEM-EDX ray analysis be equipped with a spherical aberration correction device (Cs collector) that can reduce the beam diameter and increase the beam current.

[0065] <XPS> In XPS (X-ray Photoelectron Spectroscopy), for inorganic oxides, using monochromatic aluminum Kα X-rays, elemental analysis is possible in regions from the surface to a depth of approximately 2 nm to 8 nm (usually less than 5 nm). Furthermore, narrow-scan analysis can be used to analyze the bonding state of elements.

[0066] When performing XPS analysis, for example, monochromatic aluminum Kα rays can be used as the X-rays. Furthermore, it is preferable to use an XPS instrument with an energy resolution such that the full width at half maximum of the Ag3d5 / 2 peak (112 eV) in the XPS spectrum of an Ag sample is 1.0 eV ± 0.1 eV. The extraction angle can be, for example, 15° or 45°. For example, the following XPS instrument and measurement conditions can be used: Measurement instrument: PHI Quantera II; X-ray: monochromatic Al Kα (1486.6 eV); Energy resolution: Full width at half maximum of the Ag3d5 / 2 peak is 1.0 eV ± 0.1 eV; Detection area: 100 μmφ; Detection depth: approximately 4-5 nm (extraction angle 45°), approximately 2-3 nm (extraction angle 15°); Measurement spectrum: wide scan, narrow scan of each detected element.

[0067] <Crystallite Size Determined by Diffraction Method> As described above, the olivine-type crystal structure of the positive electrode active material 100 is preferably such that the crystallite size is between 10 nm and 90 nm when Rietveld analysis is performed on the XRD profile obtained by diffraction. The measurement target may be the powder of the positive electrode active material, or a positive electrode or secondary battery containing the positive electrode active material.

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

[0069] Among diffraction methods, CuKα １ X-ray diffraction by line, MoKα １ Linear X-ray diffraction, synchrotron X-ray diffraction, and neutron diffraction are preferred due to their high accuracy. CuKα １ Examples of conditions for X-ray diffraction using lines are given.

[0070] <XRD Conditions> XRD device: Bruker D8 ADVANCE Atmosphere: 24°C ± 10°C, atmospheric pressure X-rays: CuKα rays Output: 40kV, 40mA Divergent slit: 0.6mm Detector: LYNXEYE XE-T 2θ: 15° to 65° Scan speed: 1 second / step Increase: 0.005°

[0071] The obtained XRD profiles were analyzed using the analysis software DIFFRAC.EVA to determine CuKα ２ It can remove peaks from lines and correct the background.

[0072] <Crystal Structure Analysis Software Conditions> For calculating crystallite size, for example, a Bruker D8 ADVANCE can be used, with a Cu source as the X-ray source, 2θ between 15° and 120°, increase 0.005, 1 sec / step, and a LYNXEYE XE-T detector. The acquired XRD profile and the literature value for lithium iron phosphate (ICSD col. code. 193640) can be used. The analysis can be performed using DIFFRAC. TOPAS ver. 6 as the crystal structure analysis software, and can be set as follows, for example: Emission Profile: CuKa5. lam Background: Chebychev polynomial, 5th Instrument Primary radius: 280mm Secondary radius: 280mm Linear PSD 2Th angular range: 2.9 FDS angle: 0.3 Full Axial Convolution Filament length: 12mm Sample length: 15mm Receiving Slit length: 12mm Primary Sollers: 2.5 Secondary Sollers: 2.5 Corrections Specimen displacement: Refine LP Factor: 0

[0073] It is preferable to use the LVol-IB value, which is the crystallite size corrected based on the integration width calculated using the above method, as the crystallite size. Note that if the calculated Preferred Orientation is less than 0.8, the sample orientation may be too strong, making it unsuitable for determining the crystallite size.

[0074] <Lattice Constant> The lattice constant of the olivine-type crystal structure of the positive electrode active material 100 can be determined by performing Rietveld analysis on the XRD profile obtained by diffraction. Rietveld analysis can be performed using the same method as for calculating the crystallite size described above.

[0075] <Charge-Discharge Cycle Test> To confirm the battery characteristics of the positive electrode active material 100, a coin cell (CR2032 type, 20 mm in diameter and 3.2 mm in height) can be fabricated using lithium as the counter electrode, and a charge-discharge cycle test can be performed.

[0076] More specifically, the positive electrode can be made by coating an aluminum foil positive electrode current collector with a slurry of a mixture of positive electrode active material, conductive additive, and binder.

[0077] Lithium metal can be used for the counter electrode. However, if a material other than lithium metal is used for the counter electrode, the voltage of the secondary battery and the potential of the positive electrode will differ. In this specification, unless otherwise specified, the voltage and potential refer to the potential of the positive electrode.

[0078] Lithium salts contain 1 mol / L lithium hexafluoride phosphate (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 solution in which the above lithium salt is dissolved in the mixed solvent and vinylene carbonate (VC) is added at a concentration of 2 wt% as an additive can be used as the electrolyte.

[0079] A porous polypropylene film with a thickness of 25 μm can be used as the separator.

[0080] The positive electrode and negative electrode cans can be made of stainless steel (SUS).

[0081] The coin cells manufactured under the above conditions are aged as needed. Then, they are charged with a constant current (CC charge) at 4.5V and 0.5C, followed by constant voltage (CV charge) charging until the current reaches 0.05C. 4.5V is called the upper voltage limit, and the voltage is maintained at this limit during CV charging. Voltages other than 4.5V are also applicable to the upper voltage limit. The reference current value of 1C is sometimes set to 170mA / g per weight of the positive electrode active material. This is an example of a value determined by referring to the theoretical capacity of lithium iron phosphate. If the charging condition does not reach the cutoff current, a time cut-off may be applied. The time cut-off can be 3 hours. For discharge, constant current discharge (CC discharge) is performed until the voltage reaches 2.5V. 2.5V is called the lower voltage limit. Voltages other than 2.5V are also applicable to the lower voltage limit. The temperature of the constant temperature bath in which the coin cells are placed is set to 25°C or 45°C, etc. In this way, the charge-discharge cycle test can be performed.

[0082] After several more cycles, the coin cell can be disassembled in a glove box under an argon atmosphere and the positive electrode removed to obtain a positive electrode active material charged at high voltage. When performing various analyses afterward, it is preferable to seal the material under an argon atmosphere to suppress reactions with external components. For example, XRD can be performed by sealing the material in a sealed container under an argon atmosphere. In this way, XRD can be obtained during charging.

[0083] This embodiment can be appropriately combined with the contents of other embodiments.

[0084] (Embodiment 2) In this embodiment, an example of a method for producing a positive electrode active material according to one aspect of the present invention will be described with reference to Figure 2.

[0085] <Step S11> First, as shown in Step S11 in Figure 2, a source of additive element A, a source of additive element B, a lithium source (Li source), a manganese source (Mn source), an iron source (Fe source), and a phosphoric acid source are prepared. It is also preferable to prepare a grinding medium and a solvent for mixing.

[0086] When zinc is used as the source of additive element A, suitable zinc sources include, for example, zinc oxide, zinc hydroxide, zinc carbonate, and zinc phosphate (Zn).３ (PO 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 chloride, zinc sulfate, zinc fluoride, and other zinc compounds can be used.

[0087] When magnesium is used as the additive element B source, examples of the magnesium source include magnesium oxide, magnesium hydroxide, magnesium carbonate, magnesium phosphate (Mg(H ２ PO ４ ) ２ ・4H ２ O, MgHPO ４ ・3H ２ O, Mg ３ (PO ４ ) ２ ・8H ２ O), magnesium acetate and its hydrates (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 hydrates (MgSO ４ , MgSO ４ ・7H ２ O), magnesium fluoride (MgF ２ ) and other magnesium compounds can be used.

[0088] Lithium sources include, for example, lithium carbonate, lithium hydroxide, lithium oxide, and lithium phosphate (Li ３ PO 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.

[0089] Manganese sources include, for example, manganese carbonate and manganese oxide (MnO, Mn ３ O ４ Mn ２ O ３ MnO ２ MnO ３ (etc.), manganese hydroxide, manganese phosphate (MnPO ４ ), manganese acetate 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 (MnSO4). 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 Manganese compounds such as ) can be used.

[0090] As an iron source, for example, iron carbonate (FeCO3) 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 (FeSO4) 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 ２4H ２ O, FeF ３ FeF ３ 3H ２ Iron compounds such as O) can be used.

[0091] For example, ammonium dihydrogen phosphate (NH₄) can be used as a source of phosphate. ４ H ２ PO ４ ), diammonium hydrogen phosphate ((NH ４ ) ２ HPO ４ ), lithium dihydrogen phosphate (LiH ２ PO ４ Phosphate compounds such as ) can be used.

[0092] Furthermore, the sources of additive elements A, B, lithium, manganese, iron, and phosphate do not necessarily have to be separate; compounds that serve multiple purposes may be used. For example, using lithium hydroxide containing magnesium, or lithium carbonate containing magnesium, can serve as both a magnesium and lithium source while reducing the cost of lithium purification. Alternatively, lithium dihydrogen phosphate can serve as both a lithium and phosphate source.

[0093] 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, with Li:Mn:Fe:Mg:PO ４ The weighing should be done so that the molar ratio is 1:0.59:0.4:0.01:1.

[0094] In addition to the above, when using a planetary rotary mill such as a ball mill for mixing, a grinding medium is prepared. For example, zirconia balls can be used as the grinding medium. Also, when wet mixing is used, a solvent is prepared. For example, dehydrated acetone can be used as the solvent.

[0095] <Step S12> Next, in step S12, the additive element A source, additive element B source, lithium source, manganese source, iron source, and phosphoric acid source are mixed. The mixing can be done wet, for example, using a ball mill. In this embodiment, zirconia balls with a diameter of 3 mm are used as the grinding medium, dehydrated acetone is used as the solvent, and the mixture is carried out at 300 rpm for 2 hours while cooling using a planetary ball mill apparatus.

[0096] <Step S13> Next, in step S13, if wet mixing was performed, the solvent is dried, and if a grinding medium was used, the mixture is sieved to remove the grinding medium and obtain the mixture. To distinguish it from other processes, this is sometimes called the first mixture. In this embodiment, the mixture is dried using a ventilated drying oven and then recovered by sieving with a mesh size of 300 μm.

[0097] <Step S14> Next, in step S14, the first mixture is heated. The heating temperature is preferably 250°C to 450°C, more preferably 300°C to 400°C, and most preferably around 350°C. The heating time is preferably 1 hour to 60 hours, more preferably 2 hours to 20 hours, and most preferably around 10 hours. If the heating temperature is too low and / or the heating time is too short, the reaction may not be completed, such as the evaporation of the hydrate and / or carbon dioxide. On the other hand, if the heating temperature is too high and / or the heating time is too long, fuel costs for heating will increase and productivity may decrease.

[0098] During heating, it is preferable to use an inert or reducing atmosphere, and as an inert atmosphere, for example, a nitrogen atmosphere or an argon atmosphere may be used. The reaction chamber may be depressurized and then filled (purged) with an inert gas (nitrogen or argon) to prevent the inert gas from entering or leaving the reaction chamber, or a constant flow of inert gas may be maintained.

[0099] For the heating furnace, for example, a muffle furnace, roller hearth kiln, rotary kiln, etc., can be used. For the container that holds the material to be heated, an aluminum oxide crucible or an aluminum oxide setter (also called a sheath) can be used. It is preferable to cover the crucible or setter before heating to prevent the material from volatilizing. Mullite-cordierite may also be used as the material for the crucible and setter.

[0100] In this embodiment, the first mixture is placed in a crucible made of 99.9% pure aluminum oxide, covered, and heated in a muffle furnace under a nitrogen flow atmosphere at 350°C for 10 hours.

[0101] <Step S15, Step S16> Next, in step S15, the heated material is sieved. In this embodiment, a sieve with a mesh size of 300 μm is used. A composite oxide is obtained through the above steps (step S16).

[0102] <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.

[0103] As a carbon source, compounds containing carbon can be used, such as sugars including glucose and sucrose, polysaccharides including starch and cellulose, synthetic resins including polyvinyl alcohol (PVA) and polyacrylic acid. Carbon black including acetylene black, graphene, graphene oxide, and graphite can also be used. A combination of several of these can also be used.

[0104] For the grinding medium and solvent, refer to the description in step S11.

[0105] <Step S18> Next, in step S18, the composite oxide obtained in step S16 and the carbon source are mixed. The mixing can be done wet, for example, using a ball mill. In this embodiment, zirconia balls with a diameter of 3 mm are used as the grinding medium, dehydrated acetone is used as the solvent, and the mixture is carried out at 300 rpm for 2 hours while cooling using a planetary ball mill apparatus.

[0106] <Step S19> Next, in step S19, if wet mixing was performed, the solvent is dried, and if a grinding medium was used, the mixture is sieved to remove the grinding medium and obtain the mixture. To distinguish it from other steps, this is sometimes called the second mixture. For drying and sieving, refer to the description in step S13.

[0107] <Step S20> Next, in step S20, the second mixture is heated. The heating temperature is preferably 500°C to 900°C, more preferably 600°C to 700°C, and most preferably around 650°C. The heating time is preferably 1 hour to 60 hours, more preferably 2 hours to 20 hours, and most preferably around 10 hours. If the heating temperature is too low and / or the heating time is too short, there is a risk that an olivine-type crystal structure will not be formed, or that the carbon source will not be sufficiently carbonized. On the other hand, if the heating temperature is too high and / or the heating time is too long, there is a risk that sintering will proceed too much, the secondary particles will become too large, and productivity will decrease.

[0108] The atmosphere during heating, the heating furnace, and the container can be described in step S14.

[0109] In this embodiment, the second mixture is placed in a crucible made of 99.9% pure aluminum oxide, covered, and heated in a muffle furnace under a nitrogen flow atmosphere at 650°C for 10 hours.

[0110] <Step S21, Step S22> Next, in step S21, the heated material is sieved. In this embodiment, a sieve with a mesh size of 53 μm is used. The positive electrode active material 100 is obtained through the above steps (step S22).

[0111] The positive electrode active material 100 can be produced through the above process.

[0112] Although Figure 2 illustrates an example of producing a positive electrode active material by a solid-phase method, the present invention is not limited to this. Positive electrode active materials can be produced not only by solid-phase methods, but also by hydrothermal methods, coprecipitation methods, sol-gel methods, spray-drying methods, and other methods. However, solid-phase methods are preferred because they offer higher productivity compared to hydrothermal methods and the like. Furthermore, a combination of several of these methods can be used for production.

[0113] This embodiment can be appropriately combined with the contents of other embodiments.

[0114] (Embodiment 3) In this embodiment, the configuration of the lithium-ion battery will be described.

[0115] [Positive Electrode] The positive electrode comprises a positive electrode active material layer and a positive electrode current collector. The positive electrode active material layer contains a positive electrode active material and may further contain at least one of a conductive additive and a binder. The positive electrode active material can be the one described in the previous embodiment.

[0116] <Positive electrode active material> As the positive electrode active material, the positive electrode active material 100 described in the previous embodiment may be used in combination with other positive electrode active materials.

[0117] Other positive electrode active materials include composite oxides having olivine-type crystal structures, layered rock salt-type crystal structures, or spinel-type crystal structures. For example, LiFePO ４ LiFeO ２ LiCoO ２ LiNiO ２ LiMnO ２ LiNi ａ Mn ｂ Co ｃ O ２ (a+b+c=1), LiMn ２ O ４ , V ２ O ５ , Cr ２ O ５ MnO ２ Examples of such compounds include:

[0118] In addition, LiMn is another positive electrode active material. ２O ４ Lithium-containing materials having a spinel-type crystal structure containing manganese, etc., and lithium nickelate (LiNiO) ２ Or LiNi １−ｘ M ｘ O ２ It is preferable to mix (0 < x < 1) (M = Co, Al, etc.). By using this configuration, the characteristics of the secondary battery can be improved.

[0119] <Conductive Additives> Conductive additives, also called conductivity imparters or conductive materials, can be made of carbon material. By attaching conductive additives between multiple active materials, the multiple active materials are electrically connected to each other, increasing conductivity. In this specification, "attachment" does not only refer to physical contact between the active material and the conductive additive, but also includes cases where covalent bonding occurs, bonding occurs due to van der Waals forces, the conductive additive covers a part of the surface of the active material, the conductive additive fits into surface irregularities of the active material, or where they are electrically connected even if they are not in contact with each other.

[0120] Specific examples of carbon materials that can be used as conductive additives include carbon black (furnace black, acetylene black, graphite, etc.). Graphene, multigraphene, graphene oxide, and / or reduced graphene oxide can also be used.

[0121] Furthermore, using a mixture of graphene and acetylene black is preferable as it allows for rapid charging. This is particularly effective when used as a lithium-ion battery for automobiles.

[0122] The conductive additive is preferably present in an amount of 2 wt% or more and less than 15 wt%, more preferably 3 wt% or more and 8 wt%, relative to the positive electrode slurry. By keeping the proportion of the conductive additive low, the proportion of the positive electrode active material can be increased.

[0123] <Binder> As a binder, rubber materials such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, and ethylene-propylene-diene copolymer can be used. Fluororubber can also be used.

[0124] Furthermore, it is preferable to use a water-soluble polymer as the binder. Examples of water-soluble polymers include polysaccharides. One or more of the following polysaccharides can be used: carboxymethylcellulose (CMC), methylcellulose, ethylcellulose, hydroxypropylcellulose, diacetylcellulose, cellulose derivatives such as regenerated cellulose, and starch. It is even more preferable to use these water-soluble polymers in combination with the aforementioned rubber material.

[0125] Alternatively, it is preferable to use materials such as polystyrene, methyl polyacrylate, polymethyl methacrylate (polymethyl methacrylate, PMMA), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), ethylene propylene diene polymer, polyvinyl acetate, or nitrocellulose as the binder.

[0126] Furthermore, graphene, multigraphene, graphene oxide, and / or reduced graphene oxide can function not only as conductive additives but also as binders.

[0127] You may use a combination of several of the binders mentioned above.

[0128] The binder preferably makes up 2 wt% to 10 wt%, more preferably 3 wt% to 7 wt%, relative to the positive electrode slurry. By keeping the proportion of the binder low, the proportion of the positive electrode active material can be increased.

[0129] <Positive Electrode Current Collector> As the current collector, highly conductive materials such as stainless steel, gold, platinum, aluminum, titanium, and alloys thereof can be used. Furthermore, it is preferable that the material used for the positive electrode current collector does not dissolve at the potential of the positive electrode. In addition, aluminum alloys to which elements that improve heat resistance, such as silicon, titanium, neodymium, scandium, and molybdenum, have been added can be used. Alternatively, it may be formed from a metallic element that reacts with silicon to form a silicide. Metallic elements that react with silicon to form a silicide include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, and nickel. The current collector can be in various shapes such as foil, plate, sheet, mesh, perforated metal, or expanded metal as appropriate. The current collector should preferably have a thickness of 5 μm or more and 30 μm or less.

[0130] [Negative electrode] The negative electrode comprises a negative electrode active material layer and a negative electrode current collector. The negative electrode active material layer may also contain a negative electrode active material, a conductive additive, and a binder.

[0131] <Negative electrode active material> As the negative electrode active material, for example, alloy materials and / or carbon materials can be used.

[0132] The carbon material used for the negative electrode active material may be one or more selected from graphite, easily graphitizable carbon (soft carbon), difficult-to-graphitize carbon (hard carbon), carbon fibers (carbon nanotubes), graphene, graphene compounds, carbon black, etc.

[0133] Examples of graphite include artificial graphite and natural graphite. Examples of artificial graphite include mesocarbon microbeads (MCMB), coke-based artificial graphite, and pitch-based artificial graphite. Artificial graphite may have a carbon coating layer, which is a low-crystallinity layer. Since artificial graphite is spherical in shape, it is called spheroidal graphite. For example, MCMB is a preferred material for spheroidal 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 becomes large, and good cycle characteristics may not be obtained. To suppress the above decomposition reaction, the specific surface area of ​​carbon should be 0.8 m². ２ / g or more 8m ２ / g, preferably 1m ２ / g or more 2m ２ It is preferable that the value of / g is satisfied. Typically, it is preferable that the powder has the specific surface area described above as a characteristic of spheroidal graphite. The specific surface area can be measured by the BRENAUER-EMMETTT-TELLER method. The BRENAUER-TELLER method is an analytical technique that extends Langmuir theory to multilayer adsorption of adsorbed gas molecules, and is the most common method for calculating specific surface area. The specific surface area obtained by the BRENAUER method can be measured using the automatic specific surface area measuring device TriStar 23020.

[0134] If the particle size or median diameter (D50) is small, the bulkiness increases, which can hinder the improvement of electrode density. Therefore, the particle size or median diameter (D50) of the negative electrode active material should be between 3 μm and 20 μm, preferably between 7 μm and 12 μm. Typically, the median diameter (D50) of graphite powder is within the above range.

[0135] Graphite exhibits a potential as low as lithium metal (0.05V to 0.3V vs. Li / Li) when lithium ions are inserted into it (during the formation of lithium-graphite intercalation compounds). ＋ This allows lithium-ion batteries using graphite to exhibit a high operating voltage. Furthermore, graphite is preferable because it has advantages such as a relatively high capacity per unit volume, relatively small volume expansion, low cost, and higher safety compared to lithium metal.

[0136] Furthermore, the negative electrode active material can be an element capable of undergoing charge-discharge reactions through alloying and dealloying reactions with lithium. For example, one or more materials selected from silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium, etc., can be used. Such elements have a larger capacity than carbon, and silicon in particular has a high theoretical capacity of 4200 mAh / g. Compounds containing these elements may also be used. For example, SiO, Mg ２ Si, Mg ２ Ge, SnO, SnO ２ Mg ２ Sn, SnS ２ , V ２ Sn ３ FeSn ２ CoSn ２ Ni ３ Sn ２ ,Cd ６ Sn ５ Ag ３ Sn, Ag ３ Sb, Ni ２ MnSb, CeSb ３ LaSn ３ La ３ Co ２ Sn ７ CoSb ３ Examples include InSb and SbSn. Here, elements capable of undergoing charge-discharge reactions through alloying and de-alloying reactions with lithium, and compounds containing such elements, are sometimes referred to as alloying materials. Compared to graphite, alloying materials such as silicon may suppress the decrease in charge-discharge capacity at low temperatures, making them preferable as negative electrode active materials for low-temperature secondary batteries.

[0137] In this specification, "SiO" refers to silicon monoxide, for example. Alternatively, SiO refers to SiO ｘ It can also be expressed as follows. Here, x preferably has a value of 1 or a value in the vicinity of 1. For example, x is preferably 0.2 or more and 1.5 or less, and more preferably 0.3 or more and 1.2 or less.

[0138] Alternatively, the active material layer may be made by mixing the graphene compound with the material used to form the graphene compound. For example, particles used as a catalyst when forming the graphene compound may be mixed together with the graphene compound. Examples of catalysts used when forming the graphene compound include silicon oxide (SiO₂). ２ SiO ｘ Examples of particles include those having aluminum oxide, iron, nickel, ruthenium, iridium, platinum, copper, germanium, etc. (x < 2). Preferably, the D50 of the particles is 1 μm or less, and more preferably 100 nm or less.

[0139] Alternatively, silicon particles coated with a graphene compound may be used as the negative electrode active material. In this case, it is more preferable to have a space between the graphene compound and the silicon particles that can buffer structural changes.

[0140] Furthermore, titanium dioxide (TiO) is used as the negative electrode active material. ２ ), lithium titanium oxide (Li ４ Ti ５ O １２ ), lithium-graphite intercalation compound (Li ｘ C ６ ), niobium pentoxide (Nb ２ O ５ ), tungsten dioxide (WO ２ ), molybdenum dioxide (MoO ２ One or more oxides selected from the following can be used.

[0141] Furthermore, as the negative electrode active material, lithium and a nitride of a transition metal, Li ３ Li with an N-type structure ３−ｘ 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 / cm²). ３ ) indicates a preference.

[0142] When lithium and transition metal nitrides are used, lithium ions are contained in the negative electrode active material, so the positive electrode active material does not contain lithium ions. ２ O ５, Cr ３ O ８ It is preferable that it be combined with materials such as the above. Furthermore, even when a material containing lithium ions is used as the positive electrode active material, lithium and a nitride of a transition metal can be used as the negative electrode active material by desorbing the lithium ions contained in the positive electrode active material in advance.

[0143] Furthermore, materials that undergo a conversion reaction can also be used as the negative electrode active material. For example, transition metal oxides that do not form alloys with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), and iron oxide (FeO), may be used as the negative electrode active material. As for materials that undergo a conversion reaction, Fe ２ O ３ ,CuO,Cu ２ O, RuO ２ , Cr ２ O ３ Oxides such as CoS ０．８９ , sulfides such as NiS and CuS, Zn ３ N ２ ,Cd ３ N, Ge ３ N ４ Nitrides such as NiP ２ FeP ２ CoP ３ Phosphates such as FeF ３ BiF ３ Examples of fluorides include the following.

[0144] Furthermore, multiple negative electrode active materials may be used in combination; for example, a negative electrode active material mixed with graphite and silicon particles may be used. Silicon particles refer to silicon powder used as a material for the negative electrode active material of a lithium-ion battery, and the average particle size of the particle size distribution, i.e., the average particle diameter, is around 100 nm, and are sometimes called nanosilicon particles. It is preferable to grind the silicon raw material and adjust the particle size to a uniform particle size. The silicon particles may contain at least one of silicon, silicon oxide, or silicon alloy. While laser diffraction particle size distribution measurement is typically used to measure particle size, the method 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 (transmission electron microscope).

[0145] Furthermore, the same materials as those used for the conductive additive and binder in the positive electrode active material layer can be used for the conductive additive and binder in the negative electrode active material layer.

[0146] <Negative Electrode Current Collector> In addition to the same materials as the positive electrode current collector, copper and other materials can also be used for the negative electrode current collector. It is preferable to use a material for the negative electrode current collector that does not alloy with carrier ions such as lithium.

[0147] [Electrolyte] The electrolyte contains an organic solvent, but the organic solvent of the electrolyte in one aspect of the present invention is not limited to being a liquid at 25°C, but may be a solid at 25°C or a semi-solid at room temperature. Furthermore, while it is preferable that the organic solvent of the electrolyte in one aspect of the present invention be a liquid over a wide temperature range including below freezing point and high temperatures, it is not limited to this. The organic solvent may be a liquid, a solid, or a semi-solid over a wide temperature range including below freezing point and high temperatures.

[0148] As the organic solvent, aprotic organic solvents are preferred, and for example, one of the following can be used, or two or more of these can be used in any combination and ratio: ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, chloroethylene carbonate, vinylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), 1,3-propanesultone (PS), fluoroethylene carbonate (FEC), methyl 3,3,3-trifluoropropionate (MTFP), methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethoxyethane (DME), dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, sultone, etc.

[0149] Because PS has HOMO and LUMO levels equivalent to EC and DEC, it is not easily oxidized or reduced even at high cutoff voltages, and when it decomposes on the surface of the positive electrode active material, it tends to form polymers. Therefore, it has the advantage of having a small molecular weight decomposition product that is less likely to gasify. For this reason, the electrolyte preferably contains 0.1 wt% to 10 wt% PS, and more preferably 0.25 wt% to 7.5 wt% PS.

[0150] FEC is a cyclic carbonate with a high dielectric constant, and when used in organic solvents, it promotes the dissociation of lithium salts. On the other hand, because FEC has electron-withdrawing substituents, desolvation with lithium ions proceeds more easily than with EC. Specifically, the solvation energy of lithium ions is lower for FEC than for EC, which does not have electron-withdrawing substituents. Therefore, lithium ions are more easily released from the positive electrode active material surface and the negative electrode active material surface, which can lower the internal resistance of the secondary battery. Furthermore, because FEC has a deep Highest Occupied Molecular Orbital (HOMO) level, it is less susceptible to oxidation, improving oxidation resistance. However, the high viscosity of FEC is a concern. Therefore, it is preferable to use a mixed organic solvent containing not only FEC but also MTFP as the electrolyte. MTFP is a type of linear carbonate that can lower the viscosity of the electrolyte or maintain the viscosity at room temperature (typically 25°C) even at low temperatures (typically 0°C). Furthermore, although MTFP has a lower solvation energy than methyl propionate (abbreviated as "MP") which does not have electron-withdrawing substituents, it may still generate solvation with lithium ions when used in an electrolyte. When using a mixed organic solvent containing both FEC and MTFP, the volume ratio is preferably y is 2 to 20, and more preferably 4 to 9, where FEC:MTFP = 1:y.

[0151] The organic solvents mentioned above contain particulate waste or molecules other than the constituent molecules of the organic solvent (hereinafter also simply referred to as "impurities"), and oxygen (O ２ ), water (H ２ It is preferable that the content of (O) or water is low and that the purity is high. It is also preferable that reaction by-products during synthesis are suppressed through appropriate purification. Specifically, the electrolyte impurities should be 100 ppm or less, preferably 50 ppm or less, and more preferably less than 10 ppm. The concentration of water among the impurities can be detected by Karl Fischer titration.

[0152] Furthermore, it is preferable that the above-mentioned organic solvent shows virtually no peaks attributable to impurities when measured by NMR or other methods. "Very virtually undetectable" means that the ratio of the integrated area of ​​the peaks attributable to impurities to the integrated area of ​​the peaks attributable to the main component (simply called the integral ratio) is 0.005 or less, preferably 0.002 or less. The apparatus used for NMR measurement is not particularly limited, but for example, Bruker's "AVANCE III 400" can be used. Also, in 1H-NMR measurement, the central peak among the five peaks of acetonitrile derived from acetonitrile-d3 used as the solvent can be set to 1.94 ppm.

[0153] For example, in the case of MTF, when 1H-NMR is measured using acetonitrile-d3 solvent, it is known that four peaks occur with δ between 3.29 ppm and 3.43 ppm. However, if other peaks occur in the vicinity of this, for example, if a peak occurs with δ between 3.24 ppm and 3.29 ppm, that peak is considered to be due to impurities. Therefore, if the ratio (integral ratio) of the peak area between 3.24 ppm and 3.29 ppm to the peak area between 3.29 ppm and 3.43 ppm is 0.005 or less, preferably 0.002 or less, it can be said that peaks due to impurities are almost not detectable.

[0154] Furthermore, by using one or more flame-retardant and non-volatile ionic liquids (room-temperature molten salts) as the solvent for the electrolyte, it is possible to prevent the energy storage device from rupturing or catching fire even if the internal temperature rises due to an internal short circuit or overcharging. Ionic liquids consist of cations and anions, and include organic cations and anions. Examples of organic cations used in the electrolyte include aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, as well as aromatic cations such as imidazolium cations and pyridinium cations. Examples of anions used in the electrolyte include monovalent amide anions, monovalent methide anions, fluorosulfonic acid anions, perfluoroalkyl sulfonate anions, tetrafluoroborate anions, perfluoroalkylborate anions, hexafluorophosphate anions, or perfluoroalkyl phosphate anions.

[0155] Furthermore, the electrolyte to be dissolved in the above solvent is, for example, LiPF ６ LiClO ４ LiAsF ６ LiBF ４ LiAlCl ４ , LiSCN, LiBr, LiI, Li ２ SO ４ Li ２ B １０ Cl １０ Li ２ B １２ Cl １２ LiCF ３ SO ３ LiC ４ F ９ SO ３ LiC (CF ３ SO ２ ) ３ LiC(C ２ F ５ SO ２ ) ３ ,LiN(CF ３ SO ２ ) ２ ,LiN(C ４ F ９ SO ２ ) (CF ３ SO２ ), LiN(C ２ F ５ SO ２ ) ２ Lithium bis(oxalate) borate (Li(C) ２ O ４ ) ２ Lithium salts such as LiBOB can be used individually, or two or more of these can be used in any combination and ratio.

[0156] Furthermore, the electrolyte can contain additives. Additives can suppress the reaction decomposition of the electrolyte that may occur on the positive or negative electrode surface when the secondary battery is operated at high voltage and / or high temperature. Suitable additives include, for example, propanesultone (PS), vinylene carbonate (VC), tert-butylbenzene (TBB), lithium bis(oxalate)borate (LiBOB), 1,3,6-hexanetricarbonitrate, ethyl 2-methylbutyrate, ethyl 2-methylvalerate, and propyl 2-methylbutyrate. PS is particularly preferred as an additive because it improves the cycle characteristics.

[0157] One or more dinitrile compounds can be used as additives. Specific examples of dinitrile compounds include succinonitrile, glutalonitrile, adiponitrile (ADN), or ethylene glycol bis(propionitrile) ether (EGBE).

[0158] Furthermore, fluorobenzene may be added to the above organic solvent. The concentration of the additive should be, for example, 0.1 wt% to 5 wt% relative to the total electrolyte. PS or EGBE is preferable because it can form a good film on the positive electrode during charging and discharging, thereby improving cycle characteristics. Fluorobenzene (FB) is preferable because it improves the wettability of the organic solvent to the positive and negative electrodes. Dinitrile compounds are preferable because the nitrile groups are oriented toward the positive and negative electrodes, inhibiting oxidative decomposition of the organic solvent, thereby improving voltage resistance. Furthermore, when a current collector having copper is used in the negative electrode, dinitrile compounds are preferable because they can prevent the dissolution of copper during over-discharge. Considering the use of secondary batteries at high voltages, it is preferable to add nitrile compounds.

[0159] It is preferable to use a highly purified electrolyte in which particulate matter or elements other than the constituent elements of the electrolyte (hereinafter simply referred to as "impurities") are present in small amounts. Specifically, it is preferable that the weight ratio of impurities to the electrolyte be 1% or less, preferably 0.1% or less, and more preferably 0.01% or less.

[0160] Alternatively, a polymer gel electrolyte, obtained by swelling a polymer with an electrolyte solution, may be used.

[0161] Using polymer gel electrolytes enhances safety against leakage and other issues. Furthermore, it enables the secondary battery to be made thinner and lighter.

[0162] As the polymer to be gelled, silicone gels, acrylic gels, acrylonitrile gels, polyethylene oxide gels, polypropylene oxide gels, fluorine-based polymer gels, etc., can be used. For example, polymers having a polyalkylene oxide structure such as polyethylene oxide (PEO), PVDF, polyacrylonitrile, and copolymers containing them can be used. For example, PVDF-HFP, which is a copolymer of PVDF and hexafluoropropylene (HFP), can be used. Furthermore, the formed polymer may have a porous structure.

[0163] Furthermore, as the electrolyte, a solid electrolyte containing inorganic materials such as sulfide-based or oxide-based materials, or a solid electrolyte containing polymeric materials such as PEO (polyethylene oxide)-based materials can be used. When a solid electrolyte is used, the installation of separators or spacers becomes unnecessary. In addition, since the entire battery can be solidified, the risk of leakage is eliminated, and safety is dramatically improved.

[0164] [Separator] When the electrolyte contains a liquid electrolyte (also called an electrolyte solution), a separator is placed between the positive electrode and the negative electrode. As a separator, for example, materials such as paper and other cellulose fibers, nonwoven fabrics, glass fibers, ceramics, or porous films made of nylon (polyamide), vinylon (polyvinyl alcohol-based fiber), polypropylene (PP), polyimide (PI), polyester, acrylic, polyolefin, polyimide, polyurethane can be used. The porosity of the separator film thickness can be 35% to 90%, preferably 60% to 85%. A separator made of polypropylene can have a porosity of 35% to 45%. A separator made of polyimide can have a porosity of 75% to 85%. The film thickness of the separator is preferably 10 μm to 80 μm, and more preferably 20 μm to 60 μm. Separators using polyimide can have a high porosity and can be made into thick films (typically with a film thickness of 50 μm to 60 μm), which is preferable.

[0165] It is preferable that the separator be processed into a bag shape and positioned to enclose either the positive or negative electrode.

[0166] The separator may have a multilayer structure. For example, an organic material film such as polypropylene or polyethylene can be coated with a ceramic material, a fluorine material, a polyamide material, or a mixture thereof. Examples of ceramic materials include aluminum oxide particles and silicon oxide particles. Examples of fluorine materials include PVDF and polytetrafluoroethylene. Examples of polyamide materials include nylon and aramid (meta-aramid, para-aramid).

[0167] By using a multilayer separator, the safety of the lithium-ion battery can be maintained even if the overall thickness of the separator is thin, thus increasing the capacity per unit volume of the lithium-ion battery.

[0168] [Outer Covering] For the outer covering of a lithium-ion battery, metal materials such as aluminum or resin materials can be used. Alternatively, a film-like outer covering can be used. As a film, for example, a three-layer film can be used, in which a highly flexible metal thin film such as aluminum, stainless steel, copper, or nickel is provided on a film made of materials such as polyethylene, polypropylene, polycarbonate, ionomer, or polyamide, and an insulating synthetic resin film such as a polyamide resin or polyester resin is provided on the metal thin film as the outer surface of the outer covering.

[0169] This embodiment can be used in combination with other embodiments.

[0170] (Embodiment 4) In this embodiment, examples of lithium-ion battery configurations will be described using Figures 3A to 3C.

[0171] Figure 3A is a diagram illustrating the wound body 950a of the lithium-ion battery 913, Figure 3B is an exploded perspective view of the lithium-ion battery 913, and Figure 3C is an external view of the lithium-ion battery 913. The lithium-ion battery 913 has a positive electrode 932 having the positive electrode active material described in the previous embodiment, a negative electrode 931, an electrolyte layer, and a separator 933. The negative electrode 931 has a negative electrode active material layer 931a. The positive electrode 932 has a positive electrode active material layer 932a. These are wound as shown in Figure 3A.

[0172] The separator 933 has a wider width than the negative electrode active material layer 931a and the positive electrode active material layer 932a, and is wound so as to overlap the negative electrode active material layer 931a and the positive electrode active material layer 932a. Furthermore, it is preferable from a safety standpoint that the negative electrode active material layer 931a is wider than the positive electrode active material layer 932a. A wound body 950a of this shape is also preferable due to its good safety and productivity.

[0173] As shown in Figure 3B, the negative electrode 931 is electrically connected to terminal 951. Terminal 951 is electrically connected to terminal 911a. The positive electrode 932 is electrically connected to terminal 952. Terminal 952 is electrically connected to terminal 911b.

[0174] As shown in Figure 3C, the coiled body 950a is covered by the housing 930, forming a lithium-ion battery 913. It is preferable to provide a safety valve, an overcurrent protection element, etc., in the housing 930. The safety valve is a valve that opens when the inside of the housing 930 reaches a predetermined internal pressure, thereby preventing the battery from rupturing.

[0175] As shown in Figure 3B, the lithium-ion battery 913 may have multiple windings 950a. By using multiple windings 950a, a lithium-ion battery 913 with a larger charge and discharge capacity can be made.

[0176] By using the positive electrode active material of the present invention in a lithium-ion battery 913 having a wound body, a secondary battery can be made that has a high energy density and exhibits good electrical characteristics over a wide temperature range.

[0177] The contents of this embodiment can be appropriately combined with the contents of other embodiments.

[0178] (Embodiment 5) In this embodiment, an example of application to an electric vehicle (EV) is shown using Figures 4A to 4C.

[0179] As shown in Figure 4A, the electric vehicle is equipped with a first battery 1301a, 1301b as the main lithium-ion battery for propulsion, and a second battery 1311 that supplies power to the inverter 1312 for starting the motor 1304. By using the positive electrode active material of the present invention in the first batteries 1301a, 1301b, it is possible to create a secondary battery with high energy density and good electrical characteristics over a wide temperature range.

[0180] The second battery 1311 is also called the cranking battery (or starter battery). The second battery 1311 only needs to be able to output high power, and does not require a large capacity, so the capacity of the second battery 1311 is smaller than that of the first batteries 1301a and 1301b.

[0181] The internal structure of the first battery 1301a may be wound or stacked. Furthermore, a lithium-ion battery having a positive electrode active material according to one embodiment of the present invention may be used in the first battery 1301a. By using a lithium-ion battery having a positive electrode active material according to one embodiment of the present invention in the first battery 1301a, an electric vehicle with a long driving range and usability in a wide range of ambient temperatures can be achieved.

[0182] In this embodiment, an example is shown in which two first batteries 1301a and 1301b are connected in parallel, but three or more may be connected in parallel. Also, if the first battery 1301a can store sufficient power, the first battery 1301b may not be necessary. By configuring a battery pack having multiple lithium-ion batteries, a large amount of power can be extracted. Multiple lithium-ion batteries may be connected in parallel, in series, or connected in parallel and then in series. Multiple lithium-ion batteries are also called a battery pack.

[0183] Furthermore, the lithium-ion battery for use in vehicles has a service plug or circuit breaker that can cut off high voltage without using tools in order to cut off power from multiple lithium-ion batteries, and this is provided on the first battery 1301a.

[0184] Furthermore, the power from the first batteries 1301a and 1301b is mainly used to rotate the motor 1304, but also supplies power to 42V onboard components (electric power steering 1307, heater 1308, defogger 1309, etc.) via the DC-DC circuit 1306. Even when there is a rear motor 1317 on the rear wheels, the first battery 1301a is used to rotate the rear motor 1317.

[0185] Furthermore, the second battery 1311 supplies power to 14V automotive components (audio system 1313, power windows 1314, lights 1315, etc.) via the DC-DC circuit 1310.

[0186] Furthermore, the first battery 1301a will be explained using Figure 4B.

[0187] Figure 4B shows an example where nine rectangular lithium-ion batteries 1300 are arranged in a single battery pack 1415. In this example, nine rectangular lithium-ion batteries 1300 are connected in series, with one electrode fixed by an insulating fixing part 1413 and the other electrode fixed by an insulating fixing part 1414. While this embodiment shows an example of fixing with fixing parts 1413 and 1414, the batteries may also be housed in a battery housing box (also called a casing). Since vehicles are expected to be subjected to vibrations or shaking from external sources (such as the road surface), it is preferable to fix multiple lithium-ion batteries using fixing parts 1413, 1414 and a battery housing box. Furthermore, one electrode is electrically connected to the control circuit unit 1320 by wiring 1421, and the other electrode is electrically connected to the control circuit unit 1320 by wiring 1422.

[0188] Furthermore, the control circuit unit 1320 may also use a memory circuit that includes a transistor made of an oxide semiconductor. A charging control circuit or battery control system having a memory circuit that includes a transistor made of an oxide semiconductor may be referred to as BTOS (Battery operating system or Battery oxide semiconductor).

[0189] It is preferable to use a metal oxide that functions as an oxide semiconductor. For example, as the oxide, a metal oxide such as In-M-Zn oxide (where element M is one or more selected from aluminum, gallium, yttrium, copper, vanadium, beryllium, boron, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, or magnesium) is preferable. In particular, the In-M-Zn oxide that can be applied as the oxide is preferably CAAC-OS (C-Axis Aligned Crystal Oxide Semiconductor) or CAC-OS (Cloud-Aligned Composite Oxide Semiconductor). Alternatively, In oxide, In-Ga oxide, or In-Zn oxide may be used as the oxide.

[0190] In addition, it is preferable that the control circuit unit 1320 uses a transistor using an oxide semiconductor. In order to simplify the process, the control circuit unit 1320 may be formed using unipolar transistors. A transistor using an oxide semiconductor for the semiconductor layer has an operating ambient temperature range wider than that of a single-crystalline Si transistor, from -40°C to 150°C or less. Even when the lithium-ion battery is heated, the characteristic change is smaller than that of a single-crystalline transistor. The off-current of a transistor using an oxide semiconductor is less than the measurement lower limit regardless of temperature even at 150°C, while the off-current characteristics of a single-crystalline Si transistor have a large temperature dependence. For example, at 150°C, the off-current of a single-crystalline Si transistor increases, and the current on / off ratio does not become sufficiently large. The control circuit unit 1320 can improve safety.

[0191] A control circuit unit 1320 using a memory circuit including a transistor using an oxide semiconductor can also function as an automatic control device for a lithium-ion battery against the causes of 10 items of instability such as micro-shorts. The functions for eliminating the causes of the 10 items of instability include prevention of overcharging, prevention of overcurrent, overheat control during charging, cell balance in a battery pack, prevention of over-discharge, remaining capacity meter, automatic control of charging voltage and current according to temperature, control of charging current according to degree of deterioration, detection of abnormal behavior of micro-shorts, prediction of abnormality related to micro-shorts, etc. The control circuit unit 1320 has at least one of these functions. In addition, the automatic control device for a lithium-ion battery can be miniaturized.

[0192] Also, a micro-short refers to a minute short circuit inside a lithium-ion battery. One of the causes of a micro-short is said to be that due to multiple charge / discharge cycles, the uneven distribution of the positive electrode active material causes local current concentration between a part of the positive electrode and a part of the negative electrode, or a micro-short occurs due to the generation of side reaction products by side reactions.

[0193] Further, not only detecting a micro short, the control circuit unit 1320 can also be said to detect the terminal voltage of the lithium-ion battery and manage the charge and discharge state of the lithium-ion battery. For example, in order to prevent overcharging, both the output transistor of the charging circuit and the cutoff switch can be turned off almost simultaneously.

[0194] Further, an example of the block diagram of the battery pack 1415 shown in FIG. 4B is shown in FIG. 4C.

[0195] The control circuit unit 1320 includes a switch unit 1324 including at least a switch for preventing overcharging and a switch for preventing overdischarging, a control circuit 1322 for controlling the switch unit 1324, and a voltage measurement unit for the first battery 1301a. The control circuit unit 1320 has the upper limit voltage and the lower limit voltage of the lithium-ion battery to be used set, and restricts the current upper limit from the outside and the upper limit of the output current to the outside. The range within the lower limit voltage and the upper limit voltage of the lithium-ion battery is the voltage range in which use is recommended. When it is outside that range, the switch unit 1324 operates and functions as a protection circuit. Further, since the control circuit unit 1320 controls the switch unit 1324 to prevent overdischarging and overcharging, it can also be called a protection circuit. For example, when a voltage that is likely to cause overcharging is detected by the control circuit 1322, the current is cut off by turning off the switch of the switch unit 1324. Further, a PTC element may be provided in the charge and discharge path to provide a function of cutting off the current according to the rise in temperature. The control circuit unit 1320 also has an external terminal 1325 (+IN) and an external terminal 1326 (-IN).

[0196] The switch unit 1324 can be configured by combining an n-channel type transistor and a p-channel type transistor. The switch unit 1324 is not limited to a switch having an Si transistor using single crystal silicon. For example, Ge (germanium), SiGe (silicon germanium), GaAs (gallium arsenide), GaAlAs (gallium aluminum arsenide), InP (indium phosphide), SiC (silicon carbide), ZnSe (zinc selenide), GaN (gallium nitride), GaO ｘThe switch section 1324 may be formed using a power transistor having (gallium oxide; x is a real number greater than 0), etc. Furthermore, since memory elements using OS transistors can be freely arranged by stacking them on circuits using Si transistors, integration can be easily achieved. By stacking a control circuit section 1320 using OS transistors on the switch section 1324 and integrating them, it is possible to create a single chip, enabling miniaturization.

[0197] The first batteries 1301a and 1301b primarily supply power to 42V (high-voltage) onboard equipment, while the second battery 1311 supplies power to 14V (low-voltage) onboard equipment. Lead-acid batteries are often used for the second battery 1311 due to cost advantages. Using a lithium-ion battery for the second battery 1311 offers the advantage of being maintenance-free, but after long-term use, for example more than three years, there is a risk of malfunctions occurring that could not be detected at the time of manufacture. In particular, if the second battery 1311, which starts the inverter, becomes inoperable, the motor may not start even if the first batteries 1301a and 1301b have remaining capacity. If the second battery 1311 is a lead-acid battery, power is supplied from the first battery to the second battery, and it is charged to always be in a fully charged state, so the motor will not become inoperable as described above.

[0198] In this embodiment, an example is shown in which lithium-ion batteries are used for both the first battery 1301a and the second battery 1311. However, the second battery 1311 may be a lead-acid battery, an all-solid-state battery, or an electric double-layer capacitor. By using the positive electrode active material of the present invention in the lithium-ion battery described above, a secondary battery with high energy density and good electrical characteristics over a wide temperature range can be obtained.

[0199] Furthermore, the regenerative energy generated by the rotation of the tire 1316 is sent to the motor 1304 via the gear 1305 and charged to the second battery 1311 via the control circuit unit 1321 from the motor controller 1303 and battery controller 1302. Alternatively, it is charged to the first battery 1301a via the control circuit unit 1320 from the battery controller 1302. Alternatively, it is charged to the first battery 1301b via the control circuit unit 1320 from the battery controller 1302. In order to efficiently charge the regenerative energy, it is desirable that the first batteries 1301a and 1301b are capable of rapid charging.

[0200] The battery controller 1302 can set the charging voltage and charging current of the first batteries 1301a and 1301b. The battery controller 1302 can set the charging conditions according to the charging characteristics of the lithium-ion battery being used and enable rapid charging.

[0201] Although not shown in the diagram, when connected to an external charger, the charger's outlet or connection cable is electrically connected to the battery controller 1302. Power supplied from the external charger charges the first batteries 1301a and 1301b via the battery controller 1302. In some cases, the charger may have a control circuit and may not use the functions of the battery controller 1302, but it is preferable to charge the first batteries 1301a and 1301b via the control circuit unit 1320 to prevent overcharging. In some cases, the connection cable or the charger's connection cable may also have a control circuit. The control circuit unit 1320 is sometimes called an ECU (Electronic Control Unit). The ECU is connected to a CAN (Controller Area Network) installed in the electric vehicle. CAN is one of the serial communication standards used as an in-vehicle LAN. The ECU also includes a microcomputer. The ECU uses a CPU or GPU.

[0202] External chargers installed at charging stations and other locations include 100V outlets, 200V outlets, and 3-phase 200V with 50kW output. Additionally, it is possible to charge by receiving power from external charging equipment using contactless power supply methods.

[0203] Next, we will describe an example in which a lithium-ion battery, which is one aspect of the present invention, is implemented in a vehicle, typically a transport vehicle.

[0204] Furthermore, equipping vehicles with lithium-ion batteries can enable the creation of next-generation clean energy vehicles such as hybrid vehicles (HVs), electric vehicles (EVs), or plug-in hybrid vehicles (PHVs). Lithium-ion batteries can also be installed in agricultural machinery, motorized bicycles including electric-assist bicycles, motorcycles, electric wheelchairs, electric carts, small or large vessels, submarines, aircraft such as fixed-wing and rotary-wing aircraft, rockets, satellites, space probes, planetary probes, and spacecraft.

[0205] Figures 5A to 5E show examples of vehicles and the like using a lithium-ion battery according to one embodiment of the present invention.

[0206] Figure 5A shows an example of an electric bicycle using a lithium-ion battery according to one embodiment of the present invention. The lithium-ion battery according to one embodiment of the present invention can be applied to the electric bicycle 8700 shown in Figure 5A. The lithium-ion battery according to one embodiment of the present invention may have a protection circuit.

[0207] The electric bicycle 8700 is equipped with a power storage device 8702. The power storage device 8702 can supply electricity to a motor that assists the rider. The power storage device 8702 can also be detached from the electric bicycle 8700 and carried separately. The power storage device 8702 also contains multiple lithium-ion batteries according to one embodiment of the present invention, and the remaining battery level and other information can be displayed on a display unit. By using the positive electrode active material of the present invention in the lithium-ion battery, it is possible to create a secondary battery with high energy density and good electrical characteristics over a wide temperature range.

[0208] Figure 5B shows an example of a two-wheeled vehicle using a lithium-ion battery according to one embodiment of the present invention. The scooter 8600 shown in Figure 5B is equipped with a power storage device 8602, side mirrors 8601, and turn signals 8603. The power storage device 8602 can be stored in the under-seat storage compartment 8604 of the scooter 8600. The power storage device 8602 can supply electricity to the turn signals 8603. If the scooter has a motor, the power storage device 8602 can also supply electricity to the motor. By using the positive electrode active material of the present invention in the lithium-ion battery of the power storage device 8602, a secondary battery with high energy density and good electrical characteristics over a wide temperature range can be obtained.

[0209] The automobile 2001 shown in Figure 5C is an electric vehicle that uses an electric motor as a power source for driving. Alternatively, it is a hybrid vehicle that can appropriately select and use an electric motor and an engine as power sources for driving. When a lithium-ion battery is installed in the vehicle, one or more examples of the lithium-ion battery shown in the above embodiment are installed in one location. By using the positive electrode active material of the present invention in the lithium-ion battery installed in the vehicle, a secondary battery with high energy density and good electrical characteristics over a wide temperature range can be obtained.

[0210] The automobile 2001 shown in Figure 5C has a battery pack 2200, which has a battery module to which a plurality of lithium-ion batteries are connected. Furthermore, it is preferable that the battery pack 2200 has a charge control device electrically connected to the battery module.

[0211] Furthermore, the automobile 2001 can be charged by receiving power from an external charging facility via a plug-in method or a contactless power supply method to the lithium-ion battery it possesses. When charging, the charging method and connector specifications may be carried out as appropriate in accordance with the prescribed methods of CHAdeMO (registered trademark) or Combo. External charging facilities can include charging stations installed in commercial facilities, household power supplies, etc. For example, the battery storage device mounted on the automobile 2001 can be charged by supplying power from an external source using plug-in technology. Charging can be performed by converting AC power to DC power via a conversion device such as an ADC converter.

[0212] Although not shown in the diagram, the vehicle can also be charged by mounting a power receiving device on the vehicle and receiving power wirelessly from a ground-based power transmission device. In this wireless power supply method, charging can be performed not only when the vehicle is stopped but also while it is in motion by incorporating the power transmission device into the road or exterior wall. Furthermore, this wireless power supply method can be used to transmit and receive power between two vehicles. In addition, solar panels can be installed on the exterior of the vehicle to charge the lithium-ion battery when the vehicle is stopped and when it is in motion. For such wireless power supply, an electromagnetic induction method or a magnetic resonance method can be used.

[0213] Figure 5D shows, as an example, a large transport vehicle 2003 equipped with an electrically controlled motor. The battery module of the transport vehicle 2003 has the same functions as in Figure 5C, except that it has a maximum voltage of 600V, achieved by connecting more than 100 lithium-ion batteries with a nominal voltage of 3.0V to 5.0V in series, and the number of lithium-ion batteries constituting the battery module of the battery pack 2202 is different, so the explanation is omitted. By using the positive electrode active material of the present invention in the lithium-ion batteries of the module, it is possible to create a secondary battery with high energy density and good electrical characteristics over a wide temperature range.

[0214] Figure 5E shows an example of an aircraft 2004 having a fuel-burning engine. The aircraft 2004 can be considered a type of transport vehicle because it has wheels for takeoff and landing, and it has a battery pack 2203 which includes a battery module formed by connecting multiple lithium-ion batteries and a charge control device.

[0215] The battery module of aircraft 2004 has a maximum voltage of 32V, for example, by connecting eight 4V lithium-ion batteries in series. The battery module of battery pack 2203 has the same functions as Figure 5C, except for the number of lithium-ion batteries that make up the module, so the explanation will be omitted.

[0216] The contents of this embodiment can be appropriately combined with the contents of other embodiments.

[0217] (Embodiment 6) This embodiment describes an example of mounting a lithium-ion battery, which is one aspect of the present invention, in an electronic device. Examples of electronic devices on which a lithium-ion battery is mounted include television equipment (also called televisions or television receivers), monitors for computers, digital cameras, digital video cameras, digital photo frames, mobile phones (also called mobile phones or mobile phone devices), portable game consoles, personal information terminals, sound playback devices, and large game machines such as pachinko machines. Personal information terminals include notebook personal computers, tablet terminals, e-book readers, and mobile phones.

[0218] Figure 6A shows an example of a mobile phone. The mobile phone 2100 includes a display unit 2102 built into the housing 2101, as well as operation buttons 2103, an external connection port 2104, a speaker 2105, a microphone 2106, and the like. The mobile phone 2100 also has a lithium-ion battery 2107. By using the positive electrode active material of the present invention in the lithium-ion battery, it is possible to create a secondary battery with high energy density and good electrical characteristics over a wide temperature range.

[0219] The mobile phone 2100 can run various applications such as making mobile phone calls, sending emails, reading and creating documents, playing music, communicating on the internet, and playing computer games.

[0220] The operation button 2103 can be assigned various functions, including time setting, power on / off operation, wireless communication on / off operation, silent mode activation / deactivation, and power saving mode activation / deactivation. For example, the function of the operation button 2103 can be freely configured by the operating system built into the mobile phone 2100.

[0221] Furthermore, the mobile phone 2100 is capable of performing standardized short-range wireless communication. For example, it can communicate with a wireless communication-enabled headset to enable hands-free calling.

[0222] Furthermore, the mobile phone 2100 is equipped with an external connection port 2104, which allows for direct data exchange with other information terminals via a connector. It can also be charged via the external connection port 2104. Note that charging may also be performed wirelessly without using the external connection port 2104.

[0223] The mobile phone 2100 preferably has sensors. For example, it is preferable that the mobile phone be equipped with human body sensors such as a fingerprint sensor, pulse sensor, and body temperature sensor, as well as touch sensors, pressure sensors, acceleration sensors, etc.

[0224] Figure 6B shows an unmanned aerial vehicle 2300 having multiple rotors 2302. The unmanned aerial vehicle 2300 is sometimes called a drone. The unmanned aerial vehicle 2300 has a lithium-ion battery 2301, a camera 2303, and an antenna (not shown), which are embodiments of the present invention. The unmanned aerial vehicle 2300 can be remotely controlled via the antenna. By using the positive electrode active material of the present invention in the lithium-ion battery, a secondary battery can be made that has a high energy density and exhibits good electrical characteristics over a wide temperature range.

[0225] Figure 6C shows an example of a robot. The robot 6400 shown in Figure 6C is equipped with a lithium-ion battery 6409, an illuminance sensor 6401, a microphone 6402, an upper camera 6403, a speaker 6404, a display unit 6405, a lower camera 6406, an obstacle sensor 6407, a movement mechanism 6408, a computing device, and the like.

[0226] The microphone 6402 has a function of detecting the user's voice, environmental sounds, etc. Also, the speaker 6404 has a function of emitting sound. The robot 6400 can communicate with the user by using the microphone 6402 and the speaker 6404.

[0227] The display unit 6405 has a function of displaying various information. The robot 6400 can display the information desired by the user on the display unit 6405. The display unit 6405 may be equipped with a touch panel. Also, the display unit 6405 may be a removable information terminal, and by installing it at a fixed position of the robot 6400, charging and data transfer are made possible.

[0228] The upper camera 6403 and the lower camera 6406 have a function of imaging the surroundings of the robot 6400. Also, the obstacle sensor 6407 can detect the presence or absence of obstacles in the traveling direction when the robot 6400 moves forward by using the moving mechanism 6408. The robot 6400 can recognize the surrounding environment and move safely by using the upper camera 6403, the lower camera 6406, and the obstacle sensor 6407.

[0229] The robot 6400 includes a lithium-ion battery 6409 according to one aspect of the present invention and semiconductor devices or electronic components in its internal area. By using the positive electrode active material of the present invention for the lithium-ion battery, a secondary battery with a high energy density and good electrical characteristics in a wide temperature range can be obtained.

[0230] FIG. 6D shows an example of a cleaning robot. The cleaning robot 6300 has a display unit 6302 arranged on the upper surface of the housing 6301, a plurality of cameras 6303 arranged on the side surface, a brush 6304, an operation button 6305, a lithium-ion battery 6306, various sensors, etc. Although not shown, the cleaning robot 6300 is equipped with tires, a suction port, etc. The cleaning robot 6300 can move autonomously, detect dust 6310, and suck the dust from the suction port provided on the lower surface.

[0231] For example, the cleaning robot 6300 can analyze images captured by the camera 6303 to determine the presence or absence of obstacles such as walls, furniture, or steps. Furthermore, if the image analysis detects an object that might become entangled in the brush 6304, such as wiring, the rotation of the brush 6304 can be stopped. The cleaning robot 6300 is equipped with a lithium-ion battery 6306 according to one aspect of the present invention and a semiconductor device or electronic components within its internal region. By using the positive electrode active material of the present invention in the lithium-ion battery, a secondary battery with high energy density and good electrical characteristics can be obtained.

[0232] This embodiment can be implemented in appropriate combination with other embodiments.

[0233] In this embodiment, LiMn （１−ｄ） Fe ｄ PO ４ A positive electrode active material was prepared by solid-solving Mg and Zn in a solution of (0 < d < 1), and its properties were evaluated.

[0234] First, the ionic radii proposed by Shannon for each element are shown. All ionic radii are shown for the 6-coordinate state, and for transition metal elements, they are also shown for the high-spin state.

[0235]

[0236] The ionic radius of divalent Mg is smaller than that of divalent Mn and Fe, and larger than that of trivalent Mn and Fe, therefore LiMn （１−ｄ） Fe ｄ PO ４ It is an element that readily dissolves in solid solutions where (0 < d < 1). Also, the ionic radius of divalent Zn is smaller than that of Mn and Fe, and larger than that of trivalent Mn and Fe, therefore LiMn （１−ｄ） Fe ｄ PO ４ It is an element that readily dissolves in solid solutions where (0 < d < 1).

[0237] <Preparation of positive electrode active material> Next, the preparation of the positive electrode active material in this embodiment will be explained with reference to the preparation method shown in Figure 2.

[0238] <Positive electrode active material A> Mg source: MgO, Zn source: ZnO, Li source: Li ２ CO ３ , MnCO as the Mn source ３ FeC as the Fe source ２ O ４ ・2H ２ O, NH as a phosphate source ４ H ２ PO ４ Prepare a LiMn （０．９−ｘ） Fe ０．１ Mg ｙ Zn ｚ PO ４ The mixture was weighed so that (x = y + z, y = 0.02, z = 0.01). The raw material, grinding medium, and solvent were placed in a mill container and sealed. A 3 mm diameter zirconia ball was used as the grinding medium, and dehydrated acetone was used as the solvent.

[0239] The mixture was mixed using a planetary ball mill at 300 rpm for 2 hours while cooling the mill container. Maintaining the mill container temperature below 50°C suppressed the evaporation of the solvent. The mixture was collected from the mill container, dried in a draft drying oven, and then passed through a sieve with a mesh size of 300 μm to obtain the first mixture.

[0240] The first mixture was placed in an aluminum oxide crucible, covered, and heated in a muffle furnace under a nitrogen flow atmosphere at 350°C for 10 hours. Nitrogen was supplied to the muffle furnace at a rate of 5 L / min to create the nitrogen flow atmosphere. The heated mixture was collected and passed through a sieve with a mesh size of 300 μm to obtain the first composite oxide.

[0241] Glucose was used as the carbon source, and the first complex oxide and the carbon source were weighed so that the ratio of the first complex oxide to the carbon source was 10:1 (by weight). The raw materials, grinding medium, and solvent were placed in a mill container and sealed. Zirconia balls with a diameter of 3 mm were prepared as the grinding medium, and dehydrated acetone was prepared as the solvent.

[0242] The mixture in the mill container was mixed using a planetary ball mill at 300 rpm for 2 hours. The mixture was collected from the mill container, dried in a ventilated drying oven, and then passed through a sieve with a mesh size of 300 μm to collect a second mixture.

[0243] The second mixture was placed in an aluminum oxide crucible, covered, and heated in a muffle furnace under a nitrogen flow atmosphere at 650°C for 10 hours. Nitrogen was supplied to the muffle furnace at a rate of 5 L / min to create the nitrogen flow atmosphere. The heated mixture was collected and passed through a sieve with a mesh size of 53 μm to obtain a carbon-coated cathode active material. The carbon-coated cathode active material produced in the above process is called cathode active material A.

[0244] <Positive electrode active material B> Composition is LiMn （０．９−ｘ） Fe ０．１ Mg ｙ Zn ｚ PO ４ (x = y + z, y = 0.03, z = 0.03) MgO, ZnO, Li ２ CO ３ MnCO ３ FeC ２ O ４ ・2H ２ O, NH ４ H ２ PO ４ The material was weighed. Other conditions were the same as for positive electrode active material A. The carbon-coated positive electrode active material produced in the above process is called positive electrode active material B.

[0245] <Positive electrode active material C> Composition is LiMn （０．９−ｘ） Fe ０．１ Mg ｙ Zn ｚ PO ４ (x = y + z, y = 0.05, z = 0.05) MgO, ZnO, Li ２ CO ３ MnCO ３ FeC ２ O ４ ・2H ２ O, NH ４ H ２ PO ４ The amount was weighed. Other conditions were the same as for positive electrode active material A. The carbon-coated positive electrode active material produced in the above process is called positive electrode active material C.

[0246] <Positive electrode active material D> Composition is LiMn （０．９−ｙ） Fe ０．１ Mgｙ PO ４ (y = 0.03) MgO, Li ２ CO ３ MnCO ３ FeC ２ O ４ ・2H ２ O, NH ４ H ２ PO ４ The material was weighed. Other conditions were the same as for positive electrode active material A. The carbon-coated positive electrode active material produced in the above process is called positive electrode active material D.

[0247] <Positive electrode active material E> Composition is LiMn （０．９−ｚ） Fe ０．１ Zn ｚ PO ４ (z = 0.03) ZnO, Li ２ CO ３ MnCO ３ FeC ２ O ４ ・2H ２ O, NH ４ H ２ PO ４ The material was weighed. Other conditions were the same as for positive electrode active material A. The carbon-coated positive electrode active material produced in the above process is called positive electrode active material E.

[0248] <Positive electrode active material ref1> Composition is LiMn ０．９ Fe ０．１ PO ４ Li ２ CO ３ MnCO ３ FeC ２ O ４ ・2H ２ O, NH ４ H ２ PO ４ The amount was weighed. Other conditions were the same as for positive electrode active material A. The carbon-coated positive electrode active material prepared in the above process is called positive electrode active material ref1 or comparative example. <Positive electrode active material ref2> Composition is LiMn （０．９−ｘ） Fe ０．１ Mg ｙ Zn ｚ PO ４(x = y + z, y = 0.1, z = 0.1) MgO, ZnO, Li ２ CO ３ MnCO ３ FeC ２ O ４ ・2H ２ O, NH ４ H ２ PO ４ The amount was weighed. Other conditions were the same as for positive electrode active material A. The carbon-coated positive electrode active material produced in the above process is called positive electrode active material ref2.

[0249] The table below summarizes the compositions of the prepared positive electrode active materials.

[0250]

[0251] <ICP-MS Analysis> The atomic ratio of transition metals in the positive electrode active material can sometimes be measured using methods such as ICP-MS analysis. In this example, ICP-MS analysis was performed on positive electrode active material A and positive electrode active material B under the following conditions. First, approximately 100 mg each of positive electrode active material A and positive electrode active material B were prepared as samples and microwave-decomposed with nitric acid. Next, using an Agilent 8900 triple quadrupole ICP-MS manufactured by Agilent Technologies, the dissolved samples were analyzed in quantitative analysis mode, according to the instrument operation manual. The results of this ICP-MS analysis are shown in Table 3. In Table 3, the values ​​of the atomic ratio of each element are rounded, so the sum may deviate from 1.00.

[0252] Furthermore, based on the results shown in Table 3, the calculated charging ratios for each sample of positive electrode active material A and positive electrode active material B are shown in Table 4. Note that Table 4 shows the atomic ratio to P for each element, with P set to 1.00.

[0253]

[0254] As shown in Table 4, there is no significant difference in the atomic ratio values ​​of each element between the charge ratio and the ICP-MS analysis results. From this, it can be seen that the composition ratio of the positive electrode active material is almost the same as that of the charge ratio. This makes it possible to more accurately determine the composition of the positive electrode active material by using ICP-MS analysis in this embodiment. Note that the charge ratio is the elemental abundance ratio in the raw materials at the raw material weighing stage during synthesis.

[0255] <XRD> Of the samples prepared as described above, XRD measurements were performed on positive electrode active materials A to E, and positive electrode active material ref2, and Rietveld analysis was conducted. The XRD apparatus, measurement, and analysis conditions were as described in Embodiment 1. The samples were placed at room temperature (23°C ± 5°C).

[0256] These XRD profiles are LiFePO ４ (ICSD col.code.193640) The table below shows the results of a refined Rietveld analysis assuming a single phase. In addition to the results for positive electrode active materials A to E and positive electrode active material ref2, the table also includes the results for other samples prepared with Mg and / or Zn addition amounts of Mg 20%, Mg 10%, Mg 5%, Mg 2%, Mg 1%, Zn 20%, Zn 10%, Zn 5%, Zn 2%, and Zn 1%. By using the values ​​and space groups in the table below, it is possible to identify positive electrode active materials A to E and positive electrode active material ref2.

[0257] Table 5 shows the results of Rietveld analysis for positive electrode active materials A through C and positive electrode active material ref2. Tables 6 and 7 show the results of Rietveld analysis for samples in which the amount of Mg added to the positive electrode active material was varied at concentrations of 20%, 10%, 5%, 3%, 2%, and 1%. In these results, Mg 3% corresponds to positive electrode active material D. Tables 8 and 9 show the results of Rietveld analysis for samples in which the amount of Zn added to the positive electrode active material was varied at concentrations of 20%, 10%, 5%, 3%, 2%, and 1%. In these results, Zn 3% corresponds to positive electrode active material E.

[0258] Furthermore, the results for positive electrode active material B, positive electrode active material C, and positive electrode active material ref2 shown in Table 5 are collectively referred to as "Mg + Zn addition amount variation (1:1)". The results shown in Tables 6 and 7 are collectively referred to as "Mg addition amount variation". The results shown in Tables 8 and 9 are collectively referred to as "Zn addition amount variation".

[0259]

[0260]

[0261]

[0262]

[0263]

[0264] Figures 7A and 7B are graphs showing the relationship between the concentration of added elements in each sample and the change in the lattice constant of the unit cell obtained from the above analysis. Figure 7A is a graph of the lattice constant (a) on the a-axis and the concentration of added elements, and Figure 7B is an enlarged view of a part of Figure 7A. Note that the concentration of added elements referred to here is LiMn ０．９ Fe ０．１ PO ４ The Mg concentration when Mg is added (plotted as white squares), LiMn ０．９ Fe ０．１ PO ４ Zn concentration when Zn is added (plotted as black squares), LiMn ０．９ Fe ０．１ PO ４ This refers to the Mg+Zn concentration (plotted by white triangles) when 2% Mg and 1% Zn are added. In this case, the value for 3% added element concentration is the value for positive electrode active material A. Furthermore, LiMn ０．９ Fe ０．１ PO ４ This refers to the Mg+Zn concentration (plotted with white circles) when Mg and Zn are added in a 1:1 ratio. In this case, the value at a 6% added element concentration is the value for positive electrode active material B, the value at a 10% added element concentration is the value for positive electrode active material C, and the value at a 20% added element concentration is the value for positive electrode active material ref2.

[0265] As shown in Figures 7A and 7B, both lattice constants tended to decrease as the Mg and Zn concentrations increased, and the unit cells also tended to decrease. Furthermore, the contraction of both lattice constants could be approximated linearly and followed Vegard's law. This suggests that both added elements are solid-solved in an olivine-type crystal structure. In particular, the fact that the linear approximation line for the Mg + Zn addition ratio (1:1) falls between the linear approximation line for Mg concentration and the linear approximation line for Zn concentration suggests that Mg and Zn are uniformly solid-solved in the samples to which Mg and Zn were added.

[0266] Figure 7B shows the graph in Figure 7A with the horizontal axis representing the concentration of added elements magnified up to 6%. Figure 7B shows LiMn, which is represented by a white triangle in Figure 7A. ０．９ Fe ０．１ PO ４ This is a straight line connecting (no added elements) and positive electrode active material A. Also, in Figure 7B, LiMn ０．９ Fe ０．１ PO ４ Figure 7B shows excerpts of linear approximation lines for samples with no added elements and samples with varying Mg + Zn addition ratios (1:1), represented by white circles. In Figure 7B, as in Figure 7A, the line connecting the white triangles shows a slope similar to the linear approximation line for the samples with varying Mg + Zn addition ratios (1:1). This also indicates that both elements are uniformly dissolved in the olivine-type crystal structure.

[0267] <Lattice Constants> According to Rietveld analysis, positive electrode active materials A to C satisfy a-axis lattice constant of 10.3779 Å or more and 10.4272 Å or less, b-axis lattice constant of 6.0581 Å or more and 6.0887 Å or less, and c-axis lattice constant of 4.7319 Å or more and 4.7383 Å or less.

[0268] <Crystallite size determined by diffraction method> The crystallite size LVol-IB of positive electrode active materials A to C, determined by Rietveld analysis, was between 59.3 nm and less than 83.2 nm.

[0269] <Charge and Discharge Characteristics> Using the five positive electrode active materials prepared above, coin cells (CR2032 type, 20 mm in diameter, 3.2 mm in height) (hereinafter also referred to as half cells) with lithium metal as the negative electrode were fabricated, and their characteristics were evaluated.

[0270] Acetylene black (AB) was used as the conductive additive, and polyvinylidene fluoride (PVDF) was used as the binder. A slurry was prepared by mixing the positive electrode active material, acetylene black, binder, and NMP as the solvent. At this time, the weight ratio of positive electrode active material:AB:PVDF was 90:5:5.

[0271] The conditions for each sample are summarized in the table below.

[0272]

[0273] Polypropylene was used as the separator. For the lithium salt, 1 mol of LiPF per liter of the mixed solvent was used. ６ Using this method, a mixed solvent with EC:DEC = 3:7 (volume ratio) was used, and 2 wt% VC was added as an additive to the mixed solvent containing the dissolved lithium salt, which was then used as the electrolyte.

[0274] Carbon-coated aluminum foil was used as the positive electrode current collector, and the slurry described above was applied to the positive electrode current collector. The amount of positive electrode active material supported was 5 mg / cm³. ２ After removing the solvent by drying, the material was pressed at 210 kN / m and 120°C.

[0275] The conditions for the charge-discharge cycle test are described below. Each sample was placed in a constant temperature bath maintained at 25°C, and the following charge-discharge cycle was repeated 200 times. Charging 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 equivalent to 1C was set to 170mA / g per weight of positive electrode active material. After the completion of charging, a 10-minute rest period was observed before the next discharge.

[0276] <Charge-discharge cycle test of cells A to E, cell ref1, and cell ref2> Cell A was fabricated using positive electrode active material A, cell B was fabricated using positive electrode active material B, cell C was fabricated using positive electrode active material C, cell D was fabricated using positive electrode active material D, cell E was fabricated using positive electrode active material E, cell ref1 was fabricated using positive electrode active material ref1, and cell ref2 was fabricated using positive electrode active material ref2. Figure 8 shows the results of the charge-discharge cycle test of coin cells fabricated using positive electrode active materials A to E, positive electrode active material ref1, and positive electrode active material ref2. Figure 8 is a graph with the number of cycles (times) on the horizontal axis and the discharge capacity (mAh / g) on ​​the vertical axis.

[0277] As shown in Figure 8, all samples from cells A through E exhibited superior battery characteristics compared to cells ref1 and ref2. In particular, cells A and B showed superior battery characteristics compared to cells D, E, ref1, and ref2. Furthermore, cell C showed superior battery characteristics compared to cells ref1 and ref2.

[0278] From the above, LiMn （０．９−ｘ） Fe ０．１ M ｘ PO ４ When M is used as Mg or Zn, LiMn ０．９ Fe ０．１ PO ４ It exhibits superior discharge characteristics. Also, as shown in Figure 8, LiMn （０．９−ｘ） Fe ０．１ Mg ｙ Zn ｚ PO ４ It was found that when M is used in the form (x = y + z), Mg and Zn are used, superior discharge characteristics are observed compared to when only Mg or Zn is used for M. Furthermore, y + z is preferably less than 0.2. Specifically, as shown in Figure 8, the one that shows superior discharge characteristics compared to cell ref1 and cell ref2 is the one with the composition LiMn （０．９−ｘ） Fe ０．１ Mg ｘ PO ４ (x = 0.03 and its vicinity, where the vicinity refers to a value of x that is 0.8 times or more and 1.2 times or less), preferably LiMn （０．９−ｘ） Fe ０．１ Znｘ PO ４ (x = 0.03 and its vicinity, where the vicinity refers to a value of x that is 0.8 times or more and 1.2 times or less), and more preferably LiMn （０．９−ｘ） Fe ０．１ Mg ｙ Zn ｚ PO ４ It was found that (x = y + z, where y is between 0.01 and 0.05, and z is between 0.01 and 0.05).

[0279] 100: positive electrode active material, 101: primary particles, 101a: primary particles, 101b: primary particles, 101c: primary particles

Claims

A lithium-ion battery having a positive electrode, The positive electrode has a positive electrode active material, The positive electrode active material has manganese iron lithium phosphate with 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 additive elements is 0.7 or more. In the positive electrode active material, the sum of the atomic ratios of the additive elements to the sum of the atomic ratios of manganese, iron, and the additive elements is 0.02 or more and less than 0.

2. The aforementioned additive element is a lithium-ion battery that takes only an oxidation state of +2. 　 In claim 1, A lithium-ion battery in which the aforementioned additive elements are two or more selected from Mg, Zn, Ca, Sr, Ba, Pb, and Eu. 　 In claim 1, The olivine-type crystal structure is attributed to the space group Pnma, and the lithium-ion battery. 　 In claim 1, When the XRD profile obtained by diffraction with the positive electrode active material placed at 23°C ± 5°C was subjected to Rietveld analysis, The olivine-type crystal structure, The lattice constant of the a-axis is greater than 10.3729 Å and less than 10.4355 Å. The lattice constant of the b-axis is greater than 6.0564 Å and less than 6.0934 Å. A lithium-ion battery in which the lattice constant of the c-axis is greater than 4.7302 Å and less than 4.7387 Å. 　 In claim 1, The olivine-type crystal structure is a lithium-ion battery in which the crystallite size LVol-IB is 59.3 nm or more and less than 83.2 nm.

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